Obtaining the ground truth for imaging through the scattering objects is always a challenging task. Furthermore, the scattering process caused by complex media is too intricate to be accurately modeled by either traditional physical models or neural networks. To address this issue, we present a learning from better simulation (LBS) method. Utilizing the physical information from a single experimentally captured image through an optimization-based approach, the LBS method bypasses the multiple-scattering process and directly creates highly realistic synthetic data. The data can then be used to train downstream models. As a proof of concept, we train a simple U-Net solely on the synthetic data and demonstrate that it generalizes well to experimental data without requiring any manual labeling. 3D holographic particle field monitoring is chosen as the testing bed, and simulation and experimental results are presented to demonstrate the effectiveness and robustness of the proposed technique for imaging of complex scattering media. The proposed method lays the groundwork for reliable particle field imaging in high concentration. The concept of utilizing realistic synthetic data for training can be significantly beneficial in various deep learning-based imaging tasks, especially those involving complex scattering media.

Silicon carbide (core third-generation wide-bandgap semiconductor) nanowires have superior characteristics and vital engineering potential in microelectric and photonic devices operating in harsh high-temperature and strong-irradiation environments. Herein, the dense monocrystalline forest-like 4H- and 6H-SiC nanowires (intrinsically bound as a single crystal) are fabricated using the top–down peeling method. They exhibit broadband light emissions spanning the red–green–blue spectral region. The naturally formed microcavity encapsulating the SiC nanowires yields discrete and multimodal emission lines; the luminescence lifetimes decrease to the order of picoseconds owing to improved photon density of states in the microcavity by the quantum electrodynamic Purcell effect. The measured Purcell factor of 8.35 agrees well with the theoretical value of 8.6. The low-temperature luminescence and work functions show significant dependence on the nanowire polytype. The luminescence exhibits peculiar staircase-function enhancement when the temperature is elevated to 200 K, owing to suppression of nonradiative transition channels.

Ising problems are critical for a wide range of applications. Solving these problems on a photonic platform takes advantage of the unique properties of photons, such as high speed, low power consumption, and large bandwidth. Recently, there has been growing interest in using photonic platforms to accelerate the optimization of Ising models, paving the way for the development of ultrafast hardware in machine learning. However, these proposed systems face challenges in simultaneously achieving high spin scalability, encoding flexibility, and low system complexity. We propose a wavelength-domain optical Ising machine that utilizes optical signals at different wavelengths to represent distinct Ising spins for Ising simulation. We design and experimentally validate a chip-scale Ising machine capable of solving classical non-deterministic polynomial-time problems. The proposed Ising machine supports 32 spins and features 2 distinct coupling encoding schemes. Furthermore, we demonstrate the feasibility of scaling the system to 256 spins. This approach verifies the viability of performing Ising simulations in the wavelength dimension, offering substantial advantages in scalability. These advancements lay the groundwork for future large-scale expansion and practical applications in cloud computing.

Passive imaging through intense atmospheric scattering is a critical yet formidable challenge in optical imaging, with profound implications across various applications. Conventional cameras struggle under severe scattering conditions, fundamentally limiting their effectiveness. We propose a groundbreaking directional atmospheric scattering model that revolutionizes passive imaging capabilities, converting a conventional camera to a super-camera. The model precisely characterizes directional photon propagation through scattering media, transforming this historically ill-posed problem into a well-posed solution, based on which a 4D spatial-angular scattering reconstruction method is proposed, which leverages both ballistic photons and directionally resolved scattered light, without relying on any scene-specific priors, to achieve unprecedented passive imaging performance enabling color imaging through over 12 transport mean free paths at distances up to 1.76 km. Our system recovers targets contributing as little as 0.00016% of the total detected signal, enhancing a standard camera’s signal recovery capacity by nearly 200×. To validate our approach, we introduce the first-ever real-world multiperspective scattering dataset, providing a critical benchmark for future research. We mark a paradigm shift in passive imaging, offering transformative potential for real-world applications under extreme atmospheric scattering conditions.

Mid-infrared (MIR) spectral imaging enables precise target identification and analysis by capturing rich chemical fingerprints, which calls for high-sensitivity broadband MIR imagers at room temperature. Here, we devise and implement a continuous-wave pumping MIR upconversion imaging system based on external-cavity enhancement, which favors a large field of view, a low cavity loss, and a high spectral resolution. The involved optical cavity is constructed in an integrated fashion by utilizing one crystal facet as a cavity mirror, which allows a 43-fold power enhancement for the single-longitudinal-mode pump at 1064 nm. In combination with the chirped-poling crystal design, high-fidelity and wide-field spectral imaging mapping is permitted to facilitate an acceptance angle of up to 28.5 deg over a spectral coverage of 2.5 to 5 μm. Moreover, a thermal locking approach is used to stabilize the cavity at high-power operation, eliminating active feedback and ensuring long-term stability. A proof-of-principle demonstration is presented to showcase real-time observation of CO2 gas injection dynamics. The implemented MIR upconversion imager features wide-field operation, high detection sensitivity, and compact footprint, which would benefit subsequent applications, including environment monitoring, gas leakage inspection, and medical diagnostics.

Multispectral imaging, which simultaneously captures the spatial and spectral information of a scene, is widely used across diverse fields, including remote sensing, biomedical imaging, and agricultural monitoring. We introduce a snapshot multispectral imaging approach employing a standard monochrome image sensor with no additional spectral filters or customized components. Our system leverages the inherent chromatic aberration of wavelength-dependent defocusing as a natural source of physical encoding of multispectral information; this encoded image information is rapidly decoded via a deep learning-based multispectral Fourier imager network (mFIN). We experimentally tested our method with six illumination bands and demonstrated an overall accuracy of 98.25% for predicting the illumination channels at the input and achieved a robust multispectral image reconstruction on various test objects. This deep learning-powered framework achieves high-quality multispectral image reconstruction using snapshot image acquisition with a monochrome image sensor and could be useful for applications in biomedicine, industrial quality control, and agriculture, among others.

Thin-film lithium niobate (TFLN) possesses great potential because it enables high-speed modulation by voltage, which allows higher resolution and lower power consumption for laser beam scanning than direct laser modulation. To achieve these functions, a red, green, and blue (RGB) multiplexer using TFLN is required as an important building block for photonic integrated circuits. We fabricated an RGB multiplexer using TFLN and experimentally confirmed its operation. Three different laser lights of red (λ = 638 nm), green (λ = 520 nm), and blue (λ = 473 nm) were successfully coupled as a single laser beam by an RGB multiplexer composed of multimode interferometers. Furthermore, the TFLN was fabricated by sputter deposition, whereas conventionally, it is fabricated via bulk-lithium niobate adhesion to the substrate. The sputter-deposited TFLN is advantageous for large-volume mass production.

High-speed imaging is crucial for understanding the transient dynamics of the world, but conventional frame-by-frame video acquisition is limited by specialized hardware and substantial data storage requirements. We introduce “SpeedShot,” a computational imaging framework for efficient high-speed video imaging. SpeedShot features a low-speed dual-camera setup, which simultaneously captures two temporally coded snapshots. Cross-referencing these two snapshots extracts a multiplexed temporal gradient image, producing a compact and multiframe motion representation for video reconstruction. Recognizing the unique temporal-only modulation model, we propose an explicable motion-guided scale-recurrent transformer for video decoding. It exploits cross-scale error maps to bolster the cycle consistency between predicted and observed data. Evaluations on both simulated datasets and real imaging setups demonstrate SpeedShot’s effectiveness in video-rate up-conversion, with pronounced improvement over video frame interpolation and deblurring methods. The proposed framework is compatible with commercial low-speed cameras, offering a versatile low-bandwidth alternative for video-related applications, such as video surveillance and sports analysis.

To capture the nonlinear dynamics and gain evolution in chirped pulse amplification (CPA) systems, the split-step Fourier method and the fourth-order Runge–Kutta method are integrated to iteratively address the generalized nonlinear Schrödinger equation and the rate equations. However, this approach is burdened by substantial computational demands, resulting in significant time expenditures. In the context of intelligent laser optimization and inverse design, the necessity for numerous simulations further exacerbates this issue, highlighting the need for fast and accurate simulation methodologies. Here, we introduce an end-to-end model augmented with active learning (E2E-AL) with decent generalization through different dedicated embedding methods over various parameters. On an identical computational platform, the artificial intelligence–driven model is 2000 times faster than the conventional simulation method. Benefiting from the active learning strategy, the E2E-AL model achieves decent precision with only two-thirds of the training samples compared with the case without such a strategy. Furthermore, we demonstrate a multi-objective inverse design of the CPA systems enabled by the E2E-AL model. The E2E-AL framework manifests the potential of becoming a standard approach for the rapid and accurate modeling of ultrafast lasers and is readily extended to simulate other complex systems.

Three-dimensional (3D) nanoprinting via two-photon polymerization offers unparalleled design flexibility and precision, thereby enabling rapid prototyping of advanced micro-optical elements and systems that have found important applications in endomicroscopy and biomedical imaging. The potential of this versatile tool for monolithic manufacturing of dynamic micro-opto-electro-mechanical systems (MOEMSs), however, has not yet been sufficiently explored. This work introduces a 3D-nanoprinted lens actuator with a large optical aperture, optimized for remote focusing in miniaturized imaging systems. The device integrates orthoplanar linear motion springs, a self-aligned sintered micro-magnet, and a monolithic lens, actuated by dual microcoils for uniaxial motion. The use of 3D nanoprinting allows complete design freedom for the integrated optical lens, whereas the monolithic fabrication ensures inherent alignment of the lens with the mechanical elements. With a lens diameter of 1.4 mm and a compact footprint of 5.74 mm, it achieves high mechanical robustness at resonant frequencies exceeding 300 Hz while still providing a large displacement range of 200 μm (±100 μm). A comprehensive analysis of optical and mechanical performance, including the effects of coil temperature and polymer viscoelasticity, demonstrates its advantages over conventional micro-electro-mechanical system actuators, showcasing its potential for next-generation imaging applications.

Manufacturing-robust imaging systems leveraging computational optics hold immense potential for easing manufacturing constraints and enabling the development of cost-effective, high-quality imaging solutions. However, conventional approaches, which typically rely on data-driven neural networks to correct optical aberrations caused by manufacturing errors, are constrained by the lack of effective tolerance analysis methods for quantitatively evaluating manufacturing error boundaries. This limitation is crucial for further relaxing manufacturing constraints and providing practical guidance for fabrication. We propose a physics-informed design paradigm for manufacturing-robust imaging systems with computational optics, integrating a physics-informed tolerance analysis methodology for evaluating manufacturing error boundaries and a physics-informed neural network for image reconstruction. With this approach, we achieve a manufacturing-robust imaging system based on an off-axis three-mirror freeform all-aluminum design, delivering a modulation transfer function exceeding 0.34 at the Nyquist frequency (72 lp / mm) in simulation. Notably, this system requires a manufacturing precision of only 0.5λ in root mean square (RMS), representing a remarkable 25-fold relaxation compared with the conventional requirement of 0.02λ in RMS. Experimental validation further confirmed that the manufacturing-robust imaging system maintains excellent performance in diverse indoor and outdoor environments. Our proposed method paves the way for achieving high-quality imaging without the necessity of high manufacturing precision, enabling practical solutions that are more cost-effective and time-efficient.

Single-wavelength interferometry achieves high resolution for smooth surfaces but struggles with rough industrially relevant ones due to limited unambiguous measuring range and speckle effects. Multiwavelength interferometry addresses these challenges using synthetic wavelengths, enabling a balance between extended measurement range and resolution by combining several synthetic wavelengths. This approach holds immense potential for diverse industrial applications, yet it remains largely untapped due to the lack of suitable light sources. Existing solutions are constrained by limited flexibility in synthetic-wavelength generation and slow switching speeds. We demonstrate a light source for multiwavelength interferometry based on electro-optic single-sideband modulation. It reliably generates synthetic wavelengths with arbitrary values from centimeters to meters and switching time below 30 ms. This breakthrough paves the way for dynamic reconfigurable multiwavelength interferometry capable of adapting to complex surfaces and operating efficiently even outside laboratory settings. These capabilities unlock the full potential of multiwavelength interferometry, offering unprecedented flexibility and speed for industrial and technological applications.

Due to its broken out-of-plane symmetry, z-cut periodically poled lithium niobate (PPLN) has exhibited ultrahigh second-order optical nonlinearity. Precise quantification of the domain structure of z-cut PPLN plays a critical role during poling fabrication. To enhance the imaging detection efficiency of the domain structure in z-cut PPLN, we have developed a second-harmonic generation microscope system specifically designed to produce a longitudinal electric field in foci for the imaging domain inversion. We demonstrated that imaging using a longitudinal electric field can achieve a contrast ratio enhancement by a factor of 1.77, showing high imaging efficiency and making the proposed method suitable for in situ monitoring of the z-cut PPLN poling process.

The principle of optical time-domain reflection localization limits the sensing spatial resolution of Raman distributed optical fiber sensing. We provide a solution for a Raman distributed optical fiber sensing system with kilometer-level sensing distance and submeter spatial resolution. Based on this, we propose a Raman distributed optical fiber sensing scheme based on chaotic pulse cluster demodulation. Chaotic pulse clusters are used as the probe signal, in preference to conventional pulsed or chaotic single-pulse lasers. Furthermore, the accurate positioning of the temperature variety region along the sensing fiber can be realized using chaotic pulse clusters. The proposed demodulation scheme can enhance the signal-to-noise ratio by improving the correlation between the chaotic reference and the chaotic Raman anti-Stokes scattering signals. The experiment achieved a sensing spatial resolution of 30 cm at a distributed temperature-sensing distance of ∼6.0 km. Furthermore, we explored the influence of chaotic pulse width and detector bandwidth on the sensing spatial resolution. In addition, the theoretical experiments proved that the sensing spatial resolution in the proposed scheme was independent of the pulse width and sensing distance.

Analog neural networks, which mimic numerical computations through energy-efficient physical transformations in hardware architectures, typically achieve lower accuracies than digital neural networks. We explore the potential of photonic neural networks to outperform digital counterparts. Unlike traditional analog computing, our extreme learning machine (ELM)-based photonic neural network operates with physical synaptic connections without relying on mathematical descriptions. Noteworthy accuracy enhancements are achieved through photonic multi-synaptic connections, going beyond conventional notions of network depth or nonlinearity. Experimental results on MNIST, Fashion-MNIST, and CIFAR-10 datasets demonstrate classification accuracies up to 99.79%, 98.26%, and 90.29%, respectively, outperforming digital counterparts and most reported hardware architectures. This underscores the transformative impact of photonic neural networks, especially with the pivotal role of photonic multi-synapses, in advancing intelligent devices and signal processing.

Based on the first-order correlation function of light, we propose analogous optical coherent states (AOCSs) sourced by partially coherent beams, which can nondiffractively propagate with sinusoidal oscillation in the harmonic potential when the nondiffraction propagation matching condition (NPMC) is met. Unlike the traditional quantum coherent state, the minimum uncertainty of AOCS is related to the coherence of light, and only when the NPMC is met, its uncertainty is the least. Furthermore, based on the mathematical similarity between the Schrödinger and the Helmholtz equations, we find that our proposed AOCSs correspond to the partially coherent steady states of the harmonic oscillator. Our research not only increases the understanding of the coherence of light and enriches the types of nondiffraction beams but also increases the understanding of the quantum coherence regulating the evolution of probability waves.

We present the Fourier lightfield multiview stereoscope (FiLM-Scope). This imaging device combines concepts from Fourier lightfield microscopy and multiview stereo imaging to capture high-resolution 3D videos over large fields of view. The FiLM-Scope optical hardware consists of a multicamera array, with 48 individual microcameras, placed behind a high-throughput primary lens. This allows the FiLM-Scope to simultaneously capture 48 unique 12.8 megapixel images of a 28 × 37 mm field-of-view, from unique angular perspectives over a 21 deg × 29 deg range, with down to 22 μm lateral resolution. We also describe a self-supervised algorithm to reconstruct 3D height maps from these images. Our approach demonstrates height accuracy down to 11 μm. To showcase the utility of our system, we perform tool tracking over the surface of an ex vivo rat skull and visualize the 3D deformation in stretching human skin, with videos captured at up to 100 frames per second. The FiLM-Scope has the potential to improve 3D visualization in a range of microsurgical settings.

The investigation of topological transitions has opened up unprecedented avenues for scientific exploration in photonic metamaterials. However, previous studies mainly focused on exploring different types of three-dimensional (3D) equifrequency surfaces and their topological transition processes in magnetic topological systems. In this work, we study the multiple photonic topological transitions and dual-frequency photonic Weyl points in the topological chiral metamaterials. Through effective medium theory and topological band theory, we systematically characterize and draw comprehensive topological phase diagrams associated with diverse 3D equifrequency surface configurations in nonmagnetic photonic systems. We further demonstrate that the resonance frequency ω0 and dual-frequency Weyl points are the critical points of these topological transitions. Notably, when the vacuum state is in contact with the phases I or III chiral metamaterials, the high-local and frequency chirality-dependent topological Fermi arc surface states arise. We reveal that the parameter ω can be used as a degree of freedom to regulate the bandwidth of such topological surface states. Moreover, different types of multichannel and directional topological photonic routings are achieved using the chirality-dependent Fermi arc surface states. We theoretically show that the physical mechanism of achieving these multichannel topological photonic routings is caused by the different interface properties. We could offer promising perspectives on 3D topological semimetal systems and provide more adaptability for multichannel devices in the nonmagnetic continuous media.

Acoustic detection has many applications across science and technology from medicine to imaging and communications. However, most acoustic sensors have a common limitation in that the detection must be near the acoustic source. Alternatively, laser interferometry with picometer-scale motional displacement detection can rapidly and precisely measure sound-induced minute vibrations on remote surfaces. Here, we demonstrate the feasibility of sound detection up to 100 kHz at remote sites with ≈60 m optical path length via laser homodyne interferometry. Based on our ultrastable hertz linewidth laser with 10 - 15 fractional stability, our laser interferometer achieves 0.5 pm / Hz1/2 displacement sensitivity near 10 kHz, bounded only by laser frequency noise over 10 kHz. Between 140 Hz and 15 kHz, we achieve a homodyne acoustic sensing sensitivity of subnanometer/Pascal across our conversational frequency overtones. The minimal sound pressure detectable over 60 m optical path length is ≈2 mPa, with dynamic ranges over 100 dB. With the demonstrated standoff picometric distance metrology, we successfully detected and reconstructed musical scores of normal conversational volumes with high fidelity. The acoustic detection via this precision laser interferometer could be applied to selective area sound sensing for remote acoustic metrology, optomechanical vibrational motion sensing, and ultrasensitive optical microphones at the laser frequency noise limits.

Chronic diabetic wounds, a common and severe complication of diabetes, are characterized by their inability to heal due to impaired blood and oxygen supply. In addition to glycemic control, various clinical treatments such as wound dressings, hyperbaric oxygen therapy, and phototherapy have been employed to manage these wounds. Low-level light therapy has emerged as an effective, noninvasive, and painless therapeutic approach for wound management. However, the bulkiness of traditional light sources and the need for frequent clinic visits have limited its widespread adoption. We have developed a wearable, flexible light-emitting bandage with cyanobacterial impregnation (LEB@Cyan). The bioactive bandage is designed to provide sustained oxygen generation and robust photobiomodulation, promoting keratinocyte migration, fibroblast proliferation, and angiogenesis. This addresses the hypoxic conditions and enhances bioenergetic supply to accelerate the healing process of diabetic wounds. In detail, the wound area of diabetic rats treated with LEB@Cyan showed significant reductions of 74.76% and 96.32% compared with that of LEB-treated diabetic rats and untreated diabetic rats, respectively. Such self-oxygenated wearable light-emitting fabric holds great promise for future clinical and commercial applications, potentially revolutionizing the management of chronic diabetic wounds.

We propose a high-refractive-index (RI) sensor based on a no-core fiber (NCF) with a waist-enlarged fusion-taper (WEFT) structure, achieving high measurement accuracy with the assistance of the gated recurrent unit (GRU) neural network. This sensor integrates the NCF in series with single-mode fibers, forming the WEFT structure through arc discharge using a fiber fusion splicer to construct a modal interferometer. In the experiment, the proposed sensor has been used for high RI (ranging from 1.4330 to 1.4505) measurement. Due to the high RI being close to that of the optical fiber, traditional spectral interference dip demodulation produces nonlinear responses, increasing the measurement error in sensing. The GRU neural network algorithm is employed to train and test the recorded spectral samples, and the experimental results indicate that the coefficient of determination for this neural network model reaches 99.93%, with a mean squared error of 2.24 × 10 - 8 ( RIU ) . This deep learning model can be widely applied to similar fiber sensing applications and demonstrates significant potential for intelligent sensing within optical networks.

Microsphere and microcylinder-assisted microscopy (MAM) has grown steadily over the last decade and is still an intensively studied optical far-field imaging technique that promises to overcome the fundamental lateral resolution limit of microscopy. However, the physical effects leading to resolution enhancement are still frequently debated. In addition, various configurations of MAM operating in transmission mode as well as reflection mode are examined, and the results are sometimes generalized. We present a rigorous simulation model of MAM and introduce a way to quantify the resolution enhancement. The lateral resolution is compared for microscope arrangements in reflection and transmission modes. Furthermore, we discuss different physical effects with respect to their contribution to resolution enhancement. The results indicate that the effects impacting the resolution in MAM strongly depend on the arrangement of the microscope and the measurement object. As a highlight, we outline that evanescent waves in combination with whispering gallery modes also improve the imaging capabilities, enabling super-resolution under certain circumstances. This result is contrary to the conclusions drawn from previous studies, where phase objects have been analyzed, and thus further emphasizes the complexity of the physical mechanisms underlying MAM.

Laser interferometry with higher resolution, faster update rate, and larger dynamic range is highly anticipated in the exploration of physics frontiers, advanced manufacturing, and precision sensing. Real-time dispersive spectral interferometry (DSI) shows promise for high-speed precision measurements, whereas the resolution of subnanometers has not yet been achieved. We present a comprehensive theoretical framework to analyze the limitations of real-time DSI based on the signal-to-noise ratio and data volume. A real-time orthogonal polarization spectral interferometry technique is proposed, which utilizes a pair of interferograms with the pi-phase shift to effectively mitigate the phase noise embedded in real-time spectral envelopes, thereby enabling the precise measurements with subnanometer resolution at megahertz frame rates. The recorded time series data are processed through interpolation, segmentation, time–frequency mapping, and de-enveloping to regain the typical cosine-shaped spectral evolution, followed by a fitting-based phase retrieval method to extract the interference phase. The phase resolution of 1.1 mrad (0.91 as for time delay and 0.3 nm for distance) is obtained at the update rate of 22.2 MHz even under the detection bandwidth of 500 MHz, and can be further enhanced to 0.29 mrad (0.24 as for time delay) after 500 times averaging (∼0.5 MHz). Our approach is validated through periodic phase modulations and applied to measure the rapid damped oscillations of a piezo stage, yielding results consistent with those obtained from a commercial picometer interferometer.

Fourier ptychographic microscopy (FPM) is an innovative computational microscopy approach that enables high-throughput imaging with high resolution, wide field of view, and quantitative phase imaging (QPI) by simultaneously capturing bright-field and dark-field images. However, effectively utilizing dark-field intensity images, including both normally exposed and overexposed data, which contain valuable high-angle illumination information, remains a complex challenge. Successfully extracting and applying this information could significantly enhance phase reconstruction, benefiting processes such as virtual staining and QPI imaging. To address this, we introduce a multi-exposure image fusion (MEIF) framework that optimizes dark-field information by incorporating it into the FPM preprocessing workflow. MEIF increases the data available for reconstruction without requiring changes to the optical setup. We evaluate the framework using both feature-domain and traditional FPM, demonstrating that it achieves substantial improvements in intensity resolution and phase information for biological samples that exceed the performance of conventional high dynamic range (HDR) methods. This image preprocessing-based information-maximization strategy fully leverages existing datasets and offers promising potential to drive advancements in fields such as microscopy, remote sensing, and crystallography.

Ultra-narrow bandwidth mode-locked lasers with tunable pulse duration can be versatile light sources for diverse applications. However, the spectral-temporal control of a narrow bandwidth mode-locked laser is challenging due to limited gain and nonlinearity, hindering practical applications of such lasers. We demonstrate a pulse duration widely tunable mode-locked ultra-narrow bandwidth laser using a composite filtering mechanism and a single-wall carbon nanotube. The laser pulse duration can be adjusted from 481 ps to 1.38 ns, which is the widest tuning range achieved in narrow-bandwidth passively mode-locked lasers. When the pulse duration is 1.38 ns, the corresponding spectral width reaches 4 pm (502 MHz). Numerical simulations support the experimental results and show that the evolution of long pulses in the laser cavity behaves similarly to a quasi-continuous wave with a low breathing ratio. We have not only designed a simple and flexible tunable scheme for the dilemma of spectral-temporal control in narrow-bandwidth mode-locked fiber lasers but also provided a unique and idealized light source for various applications that takes into account robust output.

Recent progress in the design and fabrication of thermal metasurfaces allows a broad control of the properties of light emission, including its polarization state. Stokes polarimetry is a key approach to accurately characterize partially polarized light. The quality of a Stokes polarimeter made of retarders and polarizers can be evaluated by use of metrics such as the equally weighted variance or the condition number of the matrix representing the polarimeter. Although specific instrument configurations are used to maximize polarimeter performance at a given wavelength, such optimal solutions are not spectrally robust because of the wavelength dependence of retardance. This becomes an issue in characterizing broadband thermal sources in the infrared. We report a Stokes polarimeter making use of five polarization analysis states and consisting of two simple and common optical elements—a crystalline waveplate and a linear polarizer. We combine this setup with a Fourier transform infrared spectrometer to measure accurately in a single set of acquisitions without requiring any spectral filtering, and to measure the polarization state with accuracy over a broad range of wavelengths. Such a Stokes polarimeter allows for close to optimal noise in the data reduction process in the mid-wave infrared spectral range from 2.5 to 5 μm.

With the urgently increasing demand for high-speed and large-capacity communication transmission, there remains a critical need for tunable terahertz (THz) devices with multi-channel in 5G/6G communication systems. A magnetic phase-coding meta-atom (MPM) is formed by the heterogeneous integration of La:YIG magneto-optical (MO) materials and Si microstructures. The MPM couples the magnetic induction phase of spin states with the propagation phase and can simultaneously satisfy the required output phase for dual frequencies under various external magnetic fields to realize the dynamic beam steering among multiple channels at 0.25 and 0.5 THz. The energy ratio of the target direction can reach 96.5%, and the nonreciprocal one-way transmission with a max isolation of 29.8 dB is realized due to the nonreciprocal phase shift of the MO layer. This nonreciprocal mechanism of magnetic induction reshaping of wavefront significantly holds promise for advancing integrated multi-functional THz devices with the characteristics of low-crosstalk, multi-channel, and multi-frequency, and has great potential to promote the development of THz large-capacity and high-speed communication.

Propelled by the rise of artificial intelligence, cloud services, and data center applications, next-generation, low-power, local-oscillator-less, digital signal processing (DSP)-free, and short-reach coherent optical communication has evolved into an increasingly prominent area of research in recent years. Here, we demonstrate DSP-free coherent optical transmission by analog signal processing in frequency synchronous optical network (FSON) architecture, which supports polarization multiplexing and higher-order modulation formats. The FSON architecture that allows the numerous laser sources of optical transceivers within a data center can be quasi-synchronized by means of a tree-distributed homology architecture. In conjunction with our proposed pilot-tone assisted Costas loop for an analog coherent receiver, we achieve a record dual-polarization 224-Gb/s 16-QAM 5-km mismatch transmission with reset-free carrier phase recovery in the optical domain. Our proposed DSP-free analog coherent detection system based on the FSON makes it a promising solution for next-generation, low-power, and high-capacity coherent data center interconnects.

Coupled-waveguide devices are essential in photonic integrated circuits for coupling, polarization handling, and mode manipulation. However, the performance of these devices usually suffers from high wavelength and structure sensitivity, which makes it challenging to realize broadband and reliable on-chip optical functions. Recently, topological pumping of edge states has emerged as a promising solution for implementing robust optical couplings. In this paper, we propose and experimentally demonstrate broadband on-chip mode manipulation with very large fabrication tolerance based on the Rice–Mele modeled silicon waveguide arrays. The Thouless pumping mechanism is employed in the design to implement broadband and robust mode conversion and multiplexing. The experimental results prove that various mode-order conversions with low insertion losses and intermodal crosstalk can be achieved over a broad bandwidth of 80 nm ranging from 1500 to 1580 nm. Thanks to such a topological design, the device has a remarkable fabrication tolerance of ±70 nm for the structural deviations in waveguide width and gap distance, which is, to the best of our knowledge, the highest among the coupled-waveguide mode-handling devices reported so far. As a proof-of-concept experiment, we cascade the topological mode-order converters to form a four-channel mode-division multiplexer and demonstrate the transmission of a 200-Gb/s 16-quadrature amplitude modulation signal for each mode channel, with the bit error rates below the 7% forward error correction threshold of 3.8 × 10 - 3. We reveal the possibility of developing new classes of broadband and fabrication-tolerant coupled-waveguide devices with topological photonic approaches, which may find applications in many fields, including optical interconnects, quantum communications, and optical computing.

Laser frequency microcombs provide a series of equidistant, coherent frequency markers across a broad spectrum, enabling advancements in laser spectroscopy, dense optical communications, precision distance metrology, and astronomy. Here, we design and fabricate silicon nitride, dispersion-managed microresonators that effectively suppress avoided-mode crossings and achieve close-to-zero averaged dispersion. Both the stochastic noise and mode-locking dynamics of the resonator are numerically and experimentally investigated. First, we experimentally demonstrate thermally stabilized microcomb formation in the microresonator across different mode-locked states, showing negligible center frequency shifts and a broad frequency bandwidth. Next, we characterize the femtosecond timing jitter of the microcombs, supported by precise metrology of the timing phase and relative intensity noise. For the single-soliton state, we report a relative intensity noise of -153.2 dB / Hz, close to the shot-noise limit, and a quantum-noise–limited timing jitter power spectral density of 0.4 as2 / Hz at a 100 kHz offset frequency, measured using a self-heterodyne linear interferometer. In addition, we achieve an integrated timing jitter of 1.7 fs ± 0.07 fs, measured from 10 kHz to 1 MHz. Measuring and understanding these fundamental noise parameters in high clock rate frequency microcombs is critical for advancing soliton physics and enabling new applications in precision metrology.

The vectorial evolution of light polarization can reveal the microstructure and anisotropy of a medium beyond what can be obtained from measuring light intensity alone. However, polarization imaging in reflection geometry, which is ubiquitous and often preferred in diverse applications, has often suffered from poor and even incorrect characterization of anisotropic media. We present reciprocal polarization imaging of complex media in reflection geometry with the reciprocal polar decomposition of backscattering Mueller matrices enforcing reciprocity. We demonstrate that reciprocal polarization imaging of complex chiral and anisotropic media accurately quantifies their anisotropic properties in reflection geometry, whereas traditional approaches encounter difficulties and produce inferior and often erroneous results from the violation of reciprocity. In particular, reciprocal polarization imaging provides a consistent characterization of complex media of different thicknesses, accurately measures the optical activity and glucose concentration of turbid media in reflection, and discriminates between cancerous and normal tissue with even stronger contrast than forward measurement. Reciprocal polarization imaging promises broad applications of polarization optics ranging from remote sensing to biomedicine in reflection geometries, especially in in vivo biomedical imaging, where reflection is the only feasible geometry.

Almost half of the solar energy that reaches a silicon solar cell is lost due to the reflection at the silicon–air interface. Antireflective coatings aim to suppress the reflection and thereby to increase the photogenerated current. The conventional few-layer dielectric antireflective coatings may significantly boost the transmission of solar light, but only in a narrow wavelength range. Using forward and inverse design optimization algorithms, we develop the designs of antireflective coatings for silicon solar cells based on single-layer silicon metasurfaces (periodic subwavelength nanostructure arrays), leading to a broadband reflection suppression in the wavelength range from 500 to 1200 nm for the incidence angles up to 60 deg. The reflection averaged over the visible and near-infrared spectra is at the record-low level of approximately 2 % and 4.4% for the normal and oblique incidence, respectively. The obtained results demonstrate the potential of machine learning–enhanced photonic nanostructures to outperform the classical antireflective coatings.

Tunable mid-infrared lasers are essential for optical sensing and imaging. Existing technologies, however, face challenges in simultaneously achieving broadband spectral tunability and ultra-rapid scan rates, limiting their utility in dynamic scenarios such as real-time characterization of multiple molecular absorption bands. We present a high-speed approach for broadband wavelength sweeping in the mid-infrared region, leveraging spectral focusing via difference-frequency generation between a chirped fiber laser and an asynchronous, frequency-modulated electro-optic comb. This method enables pulse-to-pulse spectral tuning at a speed of 5.6 THz / μs with 380 elements. Applied to spectroscopic sensing, our technique achieves broad spectral coverage (2600 to 3780 cm - 1) with moderate spectral resolution (8 cm - 1) and rapid acquisition time (∼6.3 μs). Notably, the controllable electro-optic comb facilitates high scan rates of up to 2 Mscans / s across the full spectral range (corresponding to a speed of 60 THz / μs), with trade-offs in number of elements (∼30) and spectral point spacing or resolution (33 cm - 1). Nevertheless, these capabilities make our platform highly promising for applications such as flow cytometry, chemical reaction monitoring, and mid-infrared ranging and imaging.

Neural organoids and confocal microscopy have the potential to play an important role in microconnectome research to understand neural patterns. We present PLayer, a plug-and-play embedded neural system, which demonstrates the utilization of sparse confocal microscopy layers to interpolate continuous axial resolution. With an embedded system focused on neural network pruning, image scaling, and post-processing, PLayer achieves high-performance metrics with an average structural similarity index of 0.9217 and a peak signal-to-noise ratio of 27.75 dB, all within 20 s. This represents a significant time saving of 85.71% with simplified image processing. By harnessing statistical map estimation in interpolation and incorporating the Vision Transformer–based Restorer, PLayer ensures 2D layer consistency while mitigating heavy computational dependence. As such, PLayer can reconstruct 3D neural organoid confocal data continuously under limited computational power for the wide acceptance of fundamental connectomics and pattern-related research with embedded devices.

We propose a method of full-color, scan-free, and natural-light motion-picture holography for full-color 4D (3D + time) imaging and develop a portable natural-light motion-picture holographic camera that can be set on a movable table without any antivibration structure. Full-color motion-picture holograms of objects illuminated by natural light are obtained at the frame rate of an image sensor. We perform the single-shot natural-light full-color 3D imaging of objects illuminated by sunlight and the full-color 4D imaging of a moving object. This holographic camera is capable of full-color 4D imaging of objects ranging in size from the centimeter order to the 10-m order. This opens up a new stage in holographic imaging, overcoming the limitations of conventional holographic imaging despite the portability of this camera.

Single-pixel imaging (SPI) enables efficient sensing in challenging conditions. However, the requirement for numerous samplings constrains its practicality. We address the challenge of high-quality SPI reconstruction at ultra-low sampling rates. We develop an alternative optimization with physics and a data-driven diffusion network (APD-Net). It features alternative optimization driven by the learned task-agnostic natural image prior and the task-specific physics prior. During the training stage, APD-Net harnesses the power of diffusion models to capture data-driven statistics of natural signals. In the inference stage, the physics prior is introduced as corrective guidance to ensure consistency between the physics imaging model and the natural image probability distribution. Through alternative optimization, APD-Net reconstructs data-efficient, high-fidelity images that are statistically and physically compliant. To accelerate reconstruction, initializing images with the inverse SPI physical model reduces the need for reconstruction inference from 100 to 30 steps. Through both numerical simulations and real prototype experiments, APD-Net achieves high-quality, full-color reconstructions of complex natural images at a low sampling rate of 1%. In addition, APD-Net’s tuning-free nature ensures robustness across various imaging setups and sampling rates. Our research offers a broadly applicable approach for various applications, including but not limited to medical imaging and industrial inspection.

Fractional optical vortices in the terahertz (THz) regime are supposed to have unique applications in various areas, i.e., THz communications, optical manipulations, and THz imaging. However, it is still challenging to generate and manipulate high-power THz vortices. Here, we present a way to generate intense THz vortex beams with a continuously tunable topological charge by injecting a weakly relativistic ultrashort laser pulse into a parabolic plasma channel. By adjusting the injection conditions of the laser pulse, the trajectory of the laser centroid can be twisted into a cylindrical spiral, along which laser wakefields are also excited. Due to the inhomogeneous transverse density profile of the plasma channel and laser wakefield excitation, intense THz radiation carrying orbital angular momentum is produced with field strength reaching sub-GV/m, even though the drive laser energy is at a few tens of mJ. The topological charge of such a radiation is determined by the laser trajectories, which are continuously tunable as demonstrated by theoretical analysis as well as three-dimensional particle-in-cell simulations. Such THz vortices with unique properties may find applications in broad areas.

Spatiotemporal optical vortices (STOVs) have attracted significant attention for their unique properties. Recently, the second harmonic generation (SHG) of STOV pulses has been experimentally demonstrated, but the phase singularity dynamics during this process remain elusive. Here, we theoretically investigate the separation and tilting of the phase singularities in STOVs during the SHG. Using the nonlinear Maxwell equation, we show that singularity separation is governed by group velocity mismatch, with accurate predictions provided by a Simpson-type integral under weak spatiotemporal walk-off conditions. In addition, paraxial wave equation analysis reveals that propagation induces singularity tilting, driven by spatial phase shifts. Our results not only offer deeper insights into the spatiotemporal coupling induced by complex nonlinear interactions but also reveal the underlying physical mechanisms in frequency up-conversion of space–time light pulses.

A new on-chip light source configuration has been proposed, which utilizes the interaction between a microwave or laser and a dielectric nanopillar array to generate a periodic electromagnetic near-field and applies periodic transverse acceleration to relativistic electrons to generate high-energy photon radiation. The dielectric nanopillar array interacting with the driving field acts as an electron undulator, in which the near-field drives electrons to oscillate. When an electron beam propagates through this nanopillar array in this light source configuration, it is subjected to a periodic transverse near-field force and will radiate X-ray or even γ-ray high-energy photons after a relativistic frequency up-conversion. Compared with the undulator which is based on the interaction between strong lasers and nanostructures to generate a plasmonic near-field, this configuration is less prone to damage during operation.

Metal micro-nano grating has received much attention due to its ability to provide high-efficiency light absorption. However, the current research scales of these metal gratings are focused on subwavelengths, and little attention has been paid to the absorption properties of metal gratings at other scales. We investigate the absorption properties of metal gratings based on surface plasmon resonance (SPR) across the scales from superwavelength to subwavelength. Under grazing incidence, we observe continuous strong absorption phenomena from superwavelength to subwavelength Al triangle-groove gratings (TGGs). Perfect absorption is realized at the subwavelength scale, whereas the maximum absorption at all other scales exceeds 74%. The electric field distribution gives the mechanism of the strong absorption phenomenon attributed to SPR on the surface of Al TGGs at different scales. In particular, subwavelength Al TGGs have perfectly symmetric absorption properties for different blaze angles, and the symmetry is gradually broken as the grating period’s scale increases. Furthermore, taking Al gratings with varying groove shapes for example, we extend the equivalence rule of grating grooves to subwavelength from near-wavelength and explain the symmetric absorption properties in Al TGGs. We unify the research of metal grating absorbers outside the subwavelength scale to a certain extent, and these findings also open new perspectives for the design of metal gratings in the future.

The spectral memory effect in scattering media is crucial for applications that employ broadband illumination, as it dictates the available spectral range from independent scattering responses. Previous studies mainly considered a passive result with the average impact of the scattering medium, whereas it is vital to actively enhance or suppress this effect for applications concerned with large spectral range or fine resolution. We construct an analytical model by integrating the concepts of wave-based interference and photon-based propagation, which manifests a potential physical image for active manipulation by utilizing scattering eigenchannels. Our theoretical predictions indicate that the spectral memory effect is enhanced using high-transmission eigenchannels while it is suppressed using low-transmission eigenchannels. These predictions are supported by finite-difference time-domain simulations and experiments, demonstrating that the spectral memory effect’s range can be actively manipulated. Quantitatively, the experiments achieved variations in enhancement and suppression that exceeded threefold (∼3.27). We clarify the underlying principles of the spectral memory effect in scattering media and demonstrate active manipulation of multispectral scattering processes.

Laser frequency combs, which are composed of a series of equally spaced coherent frequency components, have triggered revolutionary progress in precision spectroscopy and optical metrology. Length/distance is of fundamental importance in both science and technology. We describe a ranging scheme based on chirped pulse interferometry. In contrast to the traditional spectral interferometry, the local oscillator is strongly chirped which is able to meet the measurement pulses at arbitrary distances, and therefore, the dead zones can be removed. The distances can be precisely determined via two measurement steps based on the time-of-flight method and synthetic wavelength interferometry, respectively. To overcome the speed limitation of the optical spectrum analyzer, the spectrograms are stretched and detected by a fast photodetector and oscilloscope and consequently mapped into the time domain in real time. The experimental results indicate that the measurement uncertainty can be well within ±2 μm, compared with the reference distance meter. The Allan deviation can reach 0.4 μm at 4 ns averaging time and 25 nm at 1 μs and can achieve 2 nm at 100 μs averaging time. We also measured a spinning disk with grooves of different depths to verify the measurement speed, and the results show that the grooves with about 150 m / s line speed can be clearly captured. Our method provides a unique combination of non-dead zones, ultrafast measurement speed, high precision and accuracy, large ambiguity range, and only one single comb source. This system could offer a powerful solution for field measurements in practical applications in the future.

Deep ultraviolet coherent light, particularly at the wavelength of 193 nm, has become indispensable for semiconductor lithography. We present a compact solid-state nanosecond pulsed laser system capable of generating 193-nm coherent light at the repetition rate of 6 kHz. One part of the 1030-nm laser from the home-made Yb:YAG crystal amplifier is divided to generate 258 nm laser (1.2 W) by fourth-harmonic generation, and the rest is used to pump an optical parametric amplifier producing 1553 nm laser (700 mW). Frequency mixing of these beams in cascaded LiB3O5 crystals yields a 193-nm laser with 70-mW average power and a linewidth of less than 880 MHz. By introducing a spiral phase plate to the 1553-nm beam before frequency mixing, we generate a vortex beam carrying orbital angular momentum. This is, to our knowledge, the first demonstration of a 193-nm vortex beam generated from a solid-state laser. Such a beam could be valuable for seeding hybrid ArF excimer lasers and has potential applications in wafer processing and defect inspection.

Existing single-pixel imaging (SPI) and sensing techniques suffer from poor reconstruction quality and heavy computation cost, limiting their widespread application. To tackle these challenges, we propose a large-scale single-pixel imaging and sensing (SPIS) technique that enables high-quality megapixel SPI and highly efficient image-free sensing with a low sampling rate. Specifically, we first scan and sample the entire scene using small-size optimized patterns to obtain information-coupled measurements. Compared with the conventional full-sized patterns, small-sized optimized patterns achieve higher imaging fidelity and sensing accuracy with 1 order of magnitude fewer pattern parameters. Next, the coupled measurements are processed through a transformer-based encoder to extract high-dimensional features, followed by a task-specific plug-and-play decoder for imaging or image-free sensing. Considering that the regions with rich textures and edges are more difficult to reconstruct, we use an uncertainty-driven self-adaptive loss function to reinforce the network’s attention to these regions, thereby improving the imaging and sensing performance. Extensive experiments demonstrate that the reported technique achieves 24.13 dB megapixel SPI at a sampling rate of 3% within 1 s. In terms of sensing, it outperforms existing methods by 12% on image-free segmentation accuracy and achieves state-of-the-art image-free object detection accuracy with an order of magnitude less data bandwidth.

Optical and hybrid convolutional neural networks (CNNs) recently have become of increasing interest to achieve low-latency, low-power image classification, and computer-vision tasks. However, implementing optical nonlinearity is challenging, and omitting the nonlinear layers in a standard CNN comes with a significant reduction in accuracy. We use knowledge distillation to compress modified AlexNet to a single linear convolutional layer and an electronic backend (two fully connected layers). We obtain comparable performance with a purely electronic CNN with five convolutional layers and three fully connected layers. We implement the convolution optically via engineering the point spread function of an inverse-designed meta-optic. Using this hybrid approach, we estimate a reduction in multiply-accumulate operations from 17M in a conventional electronic modified AlexNet to only 86 K in the hybrid compressed network enabled by the optical front end. This constitutes over 2 orders of magnitude of reduction in latency and power consumption. Furthermore, we experimentally demonstrate that the classification accuracy of the system exceeds 93% on the MNIST dataset of handwritten digits.

A microwave photonic prototype for concurrent radar detection and spectrum sensing is proposed. A direct digital synthesizer and an analog electronic circuit are integrated to generate an intermediate frequency (IF) linearly frequency-modulated (LFM) signal ranging from 2.5 to 9.5 GHz, with an instantaneous bandwidth of 1 GHz. The IF LFM signal is converted to the optical domain via an intensity modulator and filtered by a fiber Bragg grating to generate two second-order sidebands. The two sidebands beat each other to generate a frequency-and-bandwidth-quadrupled LFM signal. By changing the center frequency of the IF LFM signal, the radar function can be operated within 8 to 40 GHz. One second-order sideband works in conjunction with the stimulated Brillouin scattering gain spectrum for microwave frequency measurement, providing an instantaneous measurement bandwidth of 2 GHz and a frequency measurement range from 0 to 40 GHz. The prototype is demonstrated to be capable of achieving a range resolution of 3.75 cm, a range error of less than ±2 cm, a radial velocity error within ±1 cm / s, delivering clear imaging of multiple small targets, and maintaining a frequency measurement error of less than ±7 MHz and a frequency resolution of better than 20 MHz.

In traditional sensing, each parameter is treated as a real number in the signal demodulation, whereas the electric field of light is a complex number. The real and imaginary parts obey the Kramers–Kronig relationship, which is expected to help further enhance sensing precision. We propose a self-Bayesian estimate of the method, aiming at reducing measurement variance. This method utilizes the intensity and phase of the parameter to be measured, achieving statistical optimization of the estimated value through Bayesian inference, effectively reducing the measurement variance. To demonstrate the effectiveness of this method, we adopted an optical fiber heterodyne interference sensing vibration measurement system. The experimental results show that the signal-to-noise ratio is effectively improved within the frequency range of 200 to 500 kHz. Moreover, it is believed that the self-Bayesian estimation method holds broad application prospects in various types of optical sensing.

We demonstrate an effective and optimal strategy for generating spatially resolved longitudinal spin angular momentum (LSAM) in optical tweezers by tightly focusing the first-order spirally polarized vector (SPV) beams with zero intrinsic angular momentum into a refractive index stratified medium. The stratified medium gives rise to a spherically aberrated intensity profile near the focal region of the optical tweezers, with off-axis intensity lobes in the radial direction possessing opposite LSAM (helicities corresponding to σ = + 1 and -1) compared to the beam center. We trap mesoscopic birefringent particles in an off-axis intensity lobe as well as at the beam center by modifying the trapping plane and observe particles spinning in opposite directions depending on their location. The direction of rotation depends on the particle size with larger particles spinning either clockwise or anticlockwise depending on the direction of spirality of the polarization of the SPV beam after tight focusing, while smaller particles spin in both directions depending on their spatial locations. Numerical simulations support our experimental observations. Our results introduce new avenues in spin–orbit optomechanics to facilitate novel yet straightforward avenues for exotic and complex particle manipulation in optical tweezers.

Holographic microscopy has emerged as a vital tool in biomedicine, enabling visualization of microscopic morphological features of tissues and cells in a label-free manner. Recently, deep learning (DL)-based image reconstruction models have demonstrated state-of-the-art performance in holographic image reconstruction. However, their utility in practice is still severely limited, as conventional training schemes could not properly handle out-of-distribution data. Here, we leverage backpropagation operation and reparameterization of the forward propagator to enable an adaptable image reconstruction model for histopathologic inspection. Only given with a training dataset of rectum tissue images captured from a single imaging configuration, our scheme consistently shows high reconstruction performance even with the input hologram of diverse tissue types at different pathological states captured under various imaging configurations. Using the proposed adaptation technique, we show that the diagnostic features of cancerous colorectal tissues, such as dirty necrosis, captured with 5× magnification and a numerical aperture (NA) of 0.1, can be reconstructed with high accuracy, whereas a given training dataset is strictly confined to normal rectum tissues acquired under the imaging configuration of 20× magnification and an NA of 0.4. Our results suggest that the DL-based image reconstruction approaches, with sophisticated adaptation techniques, could offer an extensively generalizable solution for inverse mapping problems in imaging.

Edge couplers, widely recognized for their efficiency and broad bandwidth, have gained significant attention as optical fiber-to-chip couplers. Silicon waveguides exhibit strong birefringence properties, resulting in substantial polarization-dependent loss for edge couplers in the O-band. We introduce a bilayer and double-tip edge coupler designed to efficiently couple both transverse electric (TE) and transverse magnetic (TM) modes while maintaining compatibility with standard manufacturing processes used in commercial silicon photonics foundries. We have successfully designed and fabricated this edge coupler, achieving coupling losses of <1.52 dB / facet for TE mode and 2 dB / facet for TM mode when coupled with a lensed optical fiber [4-μm mode field diameter (MFD)] within the wavelength range of 1260 to 1360 nm.

Conventional superconducting nanowire single-photon detectors (SNSPDs) have been typically limited in their applications due to their size, weight, and power consumption, which confine their use to laboratory settings. However, with the rapid development of remote imaging, sensing technologies, and long-range quantum communication with fewer topographical constraints, the demand for high-efficiency single-photon detectors integrated with avionic platforms is rapidly growing. We herein designed and manufactured the first drone-based SNSPD system with a system detection efficiency (SDE) as high as 91.8%. This drone-based system incorporates high-performance NbTiN SNSPDs, a self-developed miniature liquid helium dewar, and custom-built integrated electrical setups, making it capable of being launched in complex topographical conditions. Such a drone-based SNSPD system may open the use of SNSPDs for applications that demand high SDE in complex environments.

Multiphoton entanglement with high information capacity plays an essential role in quantum information processing. The appearance of parallel beam splitting (BS) in a gradient metasurface provides the chance to prepare the multiphoton entanglement in one step. Here, we use a single metasurface to construct multiphoton path-polarization entanglement. Based on the parallel BS property, entanglement among N unentangled photons is created after they pass through a gradient metasurface. Also, with this ability, entanglement fusion among several pairs of entangled photons is set up, which can greatly enlarge the entanglement dimension. These theoretical results pave the way for manipulating metasurface-based multiphoton entanglement, which holds great promise for ultracompact on-chip quantum information processing.

Full-color imaging is essential in digital pathology for accurate tissue analysis. Utilizing advanced optical modulation and phase retrieval algorithms, Fourier ptychographic microscopy (FPM) offers a powerful solution for high-throughput digital pathology, combining high resolution, large field of view, and extended depth of field (DOF). However, the full-color capabilities of FPM are hindered by coherent color artifacts and reduced computational efficiency, which significantly limits its practical applications. Color-transfer-based FPM (CFPM) has emerged as a potential solution, theoretically reducing both acquisition and reconstruction threefold time. Yet, existing methods fall short of achieving the desired reconstruction speed and colorization quality. In this study, we report a generalized dual-color-space constrained model for FPM colorization. This model provides a mathematical framework for model-based FPM colorization, enabling a closed-form solution without the need for redundant iterative calculations. Our approach, termed generalized CFPM (gCFPM), achieves colorization within seconds for megapixel-scale images, delivering superior colorization quality in terms of both colorfulness and sharpness, along with an extended DOF. Both simulations and experiments demonstrate that gCFPM surpasses state-of-the-art methods across all evaluated criteria. Our work offers a robust and comprehensive workflow for high-throughput full-color pathological imaging using FPM platforms, laying a solid foundation for future advancements in methodology and engineering.

The unique phase profile and polarization distribution of the vector vortex beam (VVB) have been a subject of increasing interest in classical and quantum optics. The development of higher-order Poincaré sphere (HOPS) and hybrid-order Poincaré sphere (HyOPS) has provided a systematic description of VVB. However, the generation of arbitrary VVBs on a HOPS and a HyOPS via a metasurface lacks a unified design framework, despite numerous reported approaches. We present a unified design framework incorporating all design parameters (e.g., focal lengths and orders) of arbitrary HOPS and HyOPS beams into a single equation. In proof-of-concept experiments, we experimentally demonstrated four metasurfaces to generate arbitrary beams on the fifth-order HOPS (nonfocused and tightly focused, NA 0.89), 0-2 order, and 0-1 order HyOPS. We showed HOPS beams’ propagation and focusing properties, the superresolution focusing characteristics of the first-order cylindrical VVBs, and the different focusing properties of integer-order and fractional-order cylindrical VVBs. The simplicity and feasibility of the proposed design framework make it a potential catalyst for arbitrary VVBs using metasurfaces in applications of optical imaging, communication, and optical trapping.

Research on supercontinuum sources on silicon has made significant progress in the past few decades. However, conventional approaches to broaden the spectral bandwidth often rely on complex and critical dispersion engineering by optimizing the core thickness or introducing the cladding with special materials and structures. We propose and demonstrate supercontinuum generation using long-period-grating (LPG) waveguides on silicon with a C-band pump. The LPG waveguide is introduced for quasi-phase matching, and the generated supercontinuum spectrum is improved greatly with grating-induced dispersive waves. In addition, the demonstrated LPG waveguide shows a low propagation loss comparable with regular silicon photonic waveguides without gratings. In experiments, when using a 1550-nm 75-fs pulse pump with a pulse energy of 200 pJ, the supercontinuum spectrum generated with the present LPG waveguide shows an ultrabroad extent from 1150 to 2300 nm, which is much wider by 200 nm than that achieved by dispersion-engineered uniform silicon photonic waveguides on the same chip. This provides a promising option for on-chip broadband light source for silicon photonic systems.

High-resolution seeing through complex scattering media such as turbid water, biological tissues, and mist is a significant challenge because the strong scattering scrambles the light paths and forms the scattering wall. We propose an active polarized iterative optimization approach for high-resolution imaging through complex scattering media. By acquiring a series of sub-polarized images, we can capture the diverse pattern-illuminated images with various high-frequency component information caused by the Brownian motion of complex scattering materials, which are processed using the common-mode rejection of polarization characteristics to extract target information from scattering medium information. Following that, our computational reconstruction technique employs an iterative optimization algorithm that commences with pattern-illuminated Fourier ptychography for reconstructing the high-resolution scene. It is extremely important that our approach for high-resolution imaging through complex scattering media is not limited by priori information and optical memory effect. The proposed approach is suitable for not only dynamic but also static scattering media, which may find applications in the biomedicine field, such as skin abnormalities, non-invasive blood flow, and superficial tumors.

Soliton molecules (SMs), bounded and self-assembled of particle-like dissipative solitons, exist with versatile mutual interactions and manifest substantial potential in soliton communication and optical data storage. However, controllable manipulation of the bounded molecular patterns remains challenging, as reaching a specific operation regime in lasers generally involves adjusting multiple control parameters in connection with a wide range of accessible pulse dynamics. An evolutionary algorithm is implemented for intelligent control of SMs in a 2 μm ultrafast fiber laser mode locked through nonlinear polarization rotation. Depending on the specifications of the merit function used for the optimization procedure, various SM operations are obtained, including spectra shape programming and controllable deterministic switching of doublet and triplet SMs operating in stationary or pulsation states with reconfigurable temporal separations, frequency locking of pulsation SMs, doublet and SM complexes with controllable pulsation ratio, etc. Digital encoding is further demonstrated in this platform by employing the self-assembled characteristics of SMs. Our work opens up an avenue for active SM control beyond conventional telecom bands and brings useful insights into nonlinear science and applications.

Quantum photonic processors are emerging as promising platforms to prove preliminary evidence of quantum computational advantage toward the realization of universal quantum computers. In the context of nonuniversal noisy intermediate quantum devices, photonic-based sampling machines solving the Gaussian boson sampling (GBS) problem currently play a central role in the experimental demonstration of quantum computational advantage. A relevant issue is the validation of the sampling process in the presence of experimental noise, such as photon losses, which could undermine the hardness of simulating the experiment. We test the capability of a validation protocol that exploits the connection between GBS and graph perfect match counting to perform such an assessment in a noisy scenario. In particular, we use as a test bench the recently developed machine Borealis, a large-scale sampling machine that has been made available online for external users, and address its operation in the presence of noise. The employed approach to validation is also shown to provide connections with the open question on the effective advantage of using noisy GBS devices for graph similarity and isomorphism problems and thus provides an effective method for certification of quantum hardware.

Diffractive optical neural networks (DONNs) have exhibited the advantages of parallelization, high speed, and low consumption. However, the existing DONNs based on free-space diffractive optical elements are bulky and unsteady. In this study, we propose a planar-waveguide integrated diffractive neural network chip architecture. The three diffractive layers are engraved on the same side of a quartz wafer. The three-layer chip is designed with 32-mm3 processing space and enables a computing speed of 3.1 × 109 Tera operations per second. The results show that the proposed chip achieves 73.4% experimental accuracy for the Modified National Institute of Standards and Technology database while showing the system’s robustness in a cycle test. The consistency of experiments is 88.6%, and the arithmetic mean standard deviation of the results is ~4.7%. The proposed chip architecture can potentially revolutionize high-resolution optical processing tasks with high robustness.

Depolarizing behavior is commonly observed in most natural samples. For this reason, optical tools measuring the differences in depolarization response among spatially separated structures are highly useful in a wide range of imaging applications for enhanced visualization of structures, target identification, etc. One commonly used tool for depolarizing discrimination is the so-called depolarizing spaces. In this article, we exploit the combined use of two depolarizing spaces, the indices of polarization purity (IPP) and polarizance–reflection–transformation (PRT) spaces, to improve the capability of optical systems to identify polarization–anisotropy depolarizers. The potential of these spaces to discriminate among different depolarizers is first studied from a series of simulations by incoherently adding diattenuations or retarders, with some control parameters emulating samples in nature. The simulated results demonstrate that the proposed methods are capable of increasing differences among depolarizers beyond other well-known techniques. Experimentally, validation is provided by conducting diverse phantom experiments of easy interpretation and mimicking the stated simulations. As a useful application of our approach, we developed a model able to retrieve intrinsic microscopic information of samples from macroscopic polarimetric measurements. The proposed methods enable non-invasive, straightforward, macroscopic characterization of depolarizing samples, and may be of interest for enhanced visualization of samples in multiple imaging scenarios.

Mid-infrared (MIR)-polarized thermal emission has broad applications in areas such as molecular sensing, information encryption, target detection, and optical communication. However, it is difficult for objects in nature to produce polarized thermal emission. Moreover, simultaneously generating and modulating broadband MIR thermal emission with both circular and linear polarization is even more difficult. We present a chiral plasmonic metasurface emitter (CPME) composed of asymmetric L-shaped and I-shaped antennas. The CPME consists of In3SbTe2 (IST) phase-change material (PCM) antennas, an Al2O3 dielectric layer, and an Au substrate. It is demonstrated that the CPME can selectively emit polarized light with different polarization states. Numerical simulations show that the CPME can achieve full Stokes parameter control of MIR thermal emission. By changing the state of the PCM IST, the spectral emissivity of 0 deg, 45 deg, 90 deg, and 135 deg linearly polarized (LP) lights and left-handed/right-handed circularly polarized (LCP/RCP) lights can be adjusted. In the crystalline state, the CPME exhibits the total degree of polarization (DoP) greater than 0.5 in the wavelength range of 3.4 to 5.3 μm, the degree of linear polarization (DoLP) greater than 0.4 in the range of 3.0 to 5.1 μm, and the degree of circular polarization (DoCP) greater than 0.4 in the range of 4.5 to 5.6 μm. The physical mechanism of polarized emission has been investigated fully based on the near-field intensity distribution and power loss distribution. Finally, the potential applications of the designed CPME in infrared polarization detection and antidetection are verified through numerical calculations.

In a few-mode erbium-doped fiber (FM-EDF), which is a key section in a space-division multiplexing (SDM) communication system, linearly polarized (LP) and orbital angular momentum (OAM) modes, as two-mode bases with different phase profiles, can be transformed into each other. In principle, the LP and OAM modes have a different mode spatial intensity distribution and a gain difference for FM-EDF amplifiers. How to analyze and characterize the differential mode-bases gain (DMBG) is important, but still an issue. We build, for the first time to our knowledge, a local analysis model composed of discrete elements of the FM-EDF cross section in areas of mode spatial intensity distribution azimuthal variation. Using the model of the two mode bases, analysis of local particle number distribution and detailed description of the local gain difference are realized, and the overall gain difference between the two mode bases is obtained. By building an amplifier system based on mode phase profile controlling, the gain of two mode bases is characterized experimentally. The measured DMBG is ∼0.8 dB in the second-order mode, which is consistent with the simulation result. This result provides a potential way to reduce the mode gain difference in the FM-EDF, which is important in improving the performance of the SDM communication system.

Plasmonic colors are attracting attention for their subwavelength small size, vibrant hues, and environmental sustainability beyond traditional pigments while suffering from angular and/or polarization dependency due to distinct excitations of lattice resonances and/or surface plasmon polaritons (SPPs). Here, we demonstrate the sodium metasurface-based plasmonic color palettes with polarization-independent wide-view angle (approximately >±60 deg in experiment and up to ±90 deg in theory) and single-particle-level pixel size (down to ∼60 nm) that integrate both pigment-like and structure coloring advantages, fabricated by the templated nanorod-pixelated solidification of wetted liquid metals. Such intriguing performances are mainly attributed to the particle plasmon dominant spectral response by steering the filling profile and thus the interplay between localized surface plasmons and SPPs. Combining low material cost, potentially scalable manufacturing process, and pronounced optical performance, the proposed sodium-based metasurfaces will provide a promising route for advanced color information technology.

Optical phased arrays (OPAs) are crucial in beam-steering applications, particularly as transmitters in light detection and ranging and free-space communication systems. In this paper, we demonstrate a on-chip OPA that emits multiple orbital angular momentum (OAM) beams in different directions, each carrying unique topological charges. By superimposing a forked 1 × 3 Dammann grating on the grating array, six OAM beams with topological charges of ±3, ±4, and ±5 can be radiated from the OPA region. The OPA chip was fabricated on a silicon-on-insulator platform, and the simultaneous generation of multiple OAM beams was realized experimentally. The directions of these vortices can be steered by adjusting the wavelength of the input light and the bias voltages of the phase shifters, enabling a remarkable field of view (FOV) of 140 deg × 40 deg within a 120-nm wavelength range. We pave the way for developing systems with ultrawide FOVs, improving the resolution of remote sensing and broadening the possibilities of free-space communications.

In recent years, many phase space distributions have been proposed, and one of the more independently interesting is the Bai distribution function (BDF). The BDF has been shown to interpolate between the instantaneous auto-correlation function and the Wigner distribution function, and be applied in linear frequency modulated signal parameter estimation and optical partial coherence areas. Currently, the BDF is only defined for continuous signals. However, for both simulation and experimental purposes, the signals must be discrete. This necessitates the development of a BDF analysis workflow for discrete signals. In this work, we analyze the sampling requirements imposed by the BDF and demonstrate their correctness by comparing the continuous BDFs of continuous test signals with their numerically approximated counterparts. Our results permit more accurate simulations using BDFs, which will be useful in applying them to problems such as partial coherence.

Confronting the escalating global challenge of counterfeit products, developing advanced anticounterfeiting materials and structures with physical unclonable functions (PUFs) has become imperative. All-optical PUFs, distinguished by their high output complexity and expansive response space, offer a promising alternative to conventional electronic counterparts. For practical authentications, the expansion of optical PUF keys usually involves intricate spatial or spectral shaping of excitation light using bulky external apparatus, which largely hinders the applications of optical PUFs. Here, we report a plasmonic PUF system based on heterogeneous nanostructures. The template-assisted shadow deposition technique was employed to adjust the morphological diversity of densely packed metal nanoparticles in individual PUFs. Transmission images were processed via a hash algorithm, and the generated PUF keys with a scalable capacity from 2875 to 243401 exhibit excellent uniqueness, randomness, and reproducibility. Furthermore, the wavelength and the polarization state of the excitation light are harnessed as two distinct expanding strategies, offering the potential for multiscenario applications via a single PUF. Overall, our reported plasmonic PUFs operated with the multidimensional expanding strategy are envisaged to serve as easy-to-integrate, easy-to-use systems and promise efficacy across a broad spectrum of applications, from anticounterfeiting to data encryption and authentication.

Microcirculation imaging is crucial in understanding the function and health of various tissues and organs. However, conventional imaging methods suffer from fluorescence label dependency, lack of depth resolution, and quantification inaccuracy. Here, we report a light-sheet dynamic light-scattering imaging (LSH-DSI) system to overcome these shortcomings. LSH-DSI utilizes selected plane illumination for an optical sectioning, while a time-frequency analysis method retrieves blood flow velocity estimates from dynamic changes in the detected light intensity. We have performed imaging experiments with zebrafish embryos to obtain angiographs from the trunk and head regions. The results show that LSH-DSI can capture label-free tomographic images of microvasculature and three-dimensional quantitative maps of local blood flow velocities.

A power splitter with a wideband arbitrary splitting ratio, which provides flexibility and adaptability in forming photonic devices such as microring resonators and Mach–Zehnder interferometers, proves to be essential in photonic integrated circuits (PICs). We designed and fabricated a directional coupler-based power splitter with a wideband arbitrary splitting ratio and a microring resonator with a wideband uniform extinction ratio (ER) based on artificial gauge field (AGF) optimization. The neural network-aided inverse design method is applied to complete the target. Less than 0.9 dB power splitting variation and 1.6 dB ER variation have been achieved experimentally over a 100-nm bandwidth. Wideband performance, design efficiency, and device compactness are obtained by utilizing this optimization, which indicates great potential and universality in PIC applications.

Spectroscopy, especially for plasma spectroscopy, provides a powerful platform for biological and material analysis with its elemental and molecular fingerprinting capability. Artificial intelligence (AI) has the tremendous potential to build a universal quantitative framework covering all branches of plasma spectroscopy based on its unmatched representation and generalization ability. Herein, we introduce an AI-based unified method called self-supervised image-spectrum twin information fusion detection (SISTIFD) to collect twin co-occurrence signals of the plasma and to intelligently predict the physical parameters for improving the performances of all plasma spectroscopic techniques. It can fuse the spectra and plasma images in synchronization, derive the plasma parameters (total number density, plasma temperature, electron density, and other implicit factors), and provide accurate results. The experimental data demonstrate their excellent utility and capacity, with a reduction of 98% in evaluation indices (root mean square error, relative standard deviation, etc.) and an analysis frequency of 143 Hz (much faster than the mainstream detection frame rate of 1 Hz). In addition, as a completely end-to-end and self-supervised framework, the SISTIFD enables automatic detection without manual preprocessing or intervention. With these advantages, it has remarkably enhanced various plasma spectroscopic techniques with state-of-the-art performance and unsealed their possibility in industry, especially in the regions that require both capability and efficiency. This scheme brings new inspiration to the whole field of plasma spectroscopy and enables in situ analysis with a real-world scenario of high throughput, cross-interference, various analyte complexity, and diverse applications.

In the field of short-range optical interconnects, the development of low-power-consumption, ultrawideband on-chip optical waveguide amplifiers is of critical importance. Central to this advancement is the creation of host materials that require low pump power and provide ultrabroadband emission capabilities. We introduce a tri-doped lanthanum aluminate glass (composition: 5Er2O3-5Yb2O3-0.2Tm2O3-43.8La2O3-46Al2O3), which exhibits exceptional near-infrared (NIR) luminescence intensity, significantly outperforming other bands by 3 orders of magnitude. This glass can achieve an ultrawideband NIR gain spanning 478 nm, from 1510 to 1988 nm. Notably, the glass achieves positive optical gain with a low population inversion threshold (P > 0.2), highlighting its efficiency and low-power consumption. The high glass transition temperature (Tg &sim; 842&deg;C) and large temperature difference (&Delta;T &sim; 120&deg;C) between Tg and the onset of crystallization (Tx) indicate excellent thermal stability, which is crucial for producing high-quality amorphous films for on-chip amplifiers. This research examines the unique energy levels and spectral properties of the Er3 + -Yb3 + -Tm3 + tri-doped glass, assessing its potential for use in ultrawideband on-chip optical waveguide amplifiers. This work lays the groundwork for low-power, ultrabroadband on-chip waveguide amplifiers, offering new avenues for short-range optical interconnect systems.

The physical mechanism of gain motivation is the main theoretical bottleneck that restricts the signal-to-noise ratio (SNR) and results in a mono-merit implementation for the existing stimulated Brillouin scattering-based fiber sensors. A phase-chaos laser (PCL) is proposed and introduced in the Brillouin optical correlation domain analysis (BOCDA) scheme to promote the SNR and achieve a high-accuracy measurement. The PCL characteristics are presented, and a theoretical model of chaos gain accumulation and extraction is perfected. Then, the simulation results reveal that the SNR is improved by 5.56 dB, and the signal-to-background noise ratio (SBR) of the Brillouin gain spectrum (BGS) is promoted by 8.28 dB with a 100-km sensing distance. Further, the PCL is experimentally generated. In the proof-of-concept experiment, the accuracy of the Brillouin frequency shift is upgraded to ±0.64 MHz, and the SBR of BGS is improved by 10.77 dB. The PCL provides a new research direction for optical chaos, and the PCL-BOCDA showcases a promising future for optimal-merit-coupling sensing and its application.

The microring resonator (MRR) plays an important role in signal processing because high-quality bandpass filtering can be obtained at its drop port. To promote the signal-to-noise ratio, a high rejection ratio is significantly demanded. However, it is still challenging to promote the rejection ratio of the MRR-based bandpass filter. To solve this problem, we propose to use an all-pass filter to enhance the rejection ratio of the MRR-based bandpass filter. Experimental results show that the improved rejection ratio is as high as 47.7 dB, which is improved by 23.6 dB compared with that of the MRR. Meanwhile, the bandwidth of the MRR-based bandpass filter is reduced from 2.61 to 1.14 GHz due to the constructive interference in the passband. In addition, the center frequency of this ultrahigh rejection MRR can be continuously tuned from 6.26 to 46.25 GHz. The quality factor (Q) of the MRR is improved from 7.4 × 104 to 1.7 × 105. During the adjustment, the rejection ratio of the bandpass filter exceeds 40 dB. The proposed approach can be used to achieve optical bandpass filters with high performance.

Efficiently tracking and imaging interested moving targets is crucial across various applications, from autonomous systems to surveillance. However, persistent challenges remain in various fields, including environmental intricacies, limitations in perceptual technologies, and privacy considerations. We present a teacher-student learning model, the generative adversarial network (GAN)-guided diffractive neural network (DNN), which performs visual tracking and imaging of the interested moving target. The GAN, as a teacher model, empowers efficient acquisition of the skill to differentiate the specific target of interest in the domains of visual tracking and imaging. The DNN-based student model learns to master the skill to differentiate the interested target from the GAN. The process of obtaining a GAN-guided DNN starts with capturing moving objects effectively using an event camera with high temporal resolution and low latency. Then, the generative power of GAN is utilized to generate data with position-tracking capability for the interested moving target, subsequently serving as labels to the training of the DNN. The DNN learns to image the target during training while retaining the target’s positional information. Our experimental demonstration highlights the efficacy of the GAN-guided DNN in visual tracking and imaging of the interested moving target. We expect the GAN-guided DNN can significantly enhance autonomous systems and surveillance.

Thin-film lithium niobate (LN) has emerged as an ideal platform for efficient nonlinear wave-mixing processes due to its strong quadratic nonlinearity and high optical confinement. We demonstrate unprecedentedly efficient second-harmonic generation (SHG) in a double-layer thin-film LN waveguide. The modal overlap between fundamental and second-harmonic waves is significantly enhanced by the polarization-reversed double layers, leading to a normalized conversion efficiency higher than 10,000 % W - 1 cm - 2 in theory. Under the low- and high-power pumping conditions, the measured normalized and absolute conversion efficiencies are 9600 % W - 1 cm - 2 and 85 % , respectively, substantially higher than state-of-the-art values among the reported SHGs in thin-film LN waveguides. Our results hold great promise for the development of efficient and scalable nonlinear photonic devices, with applications including metrology and quantum information processing.

Unidirectional imagers form images of input objects only in one direction, e.g., from field-of-view (FOV) A to FOV B, while blocking the image formation in the reverse direction, from FOV B to FOV A. Here, we report unidirectional imaging under spatially partially coherent light and demonstrate high-quality imaging only in the forward direction (A → B) with high power efficiency while distorting the image formation in the backward direction (B → A) along with low power efficiency. Our reciprocal design features a set of spatially engineered linear diffractive layers that are statistically optimized for partially coherent illumination with a given phase correlation length. Our analyses reveal that when illuminated by a partially coherent beam with a correlation length of ≥ ∼ 1.5λ, where λ is the wavelength of light, diffractive unidirectional imagers achieve robust performance, exhibiting asymmetric imaging performance between the forward and backward directions—as desired. A partially coherent unidirectional imager designed with a smaller correlation length of <1.5λ still supports unidirectional image transmission but with a reduced figure of merit. These partially coherent diffractive unidirectional imagers are compact (axially spanning <75λ), polarization-independent, and compatible with various types of illumination sources, making them well-suited for applications in asymmetric visual information processing and communication.

Distributed fiber-optic sensing (DFOS) can turn the worldwide fiber network into a sensing array, which may immensely extend the sensing range and approaches for hazard assessment, earth observation, and human activity measurement. However, most existing DFOS schemes cannot simultaneously give dual attention to the detection ability (for example, sensing distance) and multipoint localizing function. A mirror-image correlation method is proposed and can precisely extract the time delay between two original signals from their composite detected signal. This method enables the distributed vibration sensing function of the laser interferometer and maintains its high detection ability. We demonstrate its feasibility by simultaneously localizing multiple knocking vibrations on a 250-km round-trip fiber and distinguishing traffic vibrations at two urban positions in a field test. The localizing precision is analyzed and satisfies the requirements for fiber network sensing.

Optical reservoir computing (ORC) offers advantages, such as high computational speed, low power consumption, and high training speed, so it has become a competitive candidate for time series analysis in recent years. The current ORC employs single-dimensional encoding for computation, which limits input resolution and introduces extraneous information due to interactions between optical dimensions during propagation, thus constraining performance. Here, we propose complex-value encoding-based optoelectronic reservoir computing (CE-ORC), in which the amplitude and phase of the input optical field are both modulated to improve the input resolution and prevent the influence of extraneous information on computation. In addition, scale factors in the amplitude encoding can fine-tune the optical reservoir dynamics for better performance. We built a CE-ORC processing unit with an iteration rate of up to ∼1.2 kHz using high-speed communication interfaces and field programmable gate arrays (FPGAs) and demonstrated the excellent performance of CE-ORC in two time series prediction tasks. In comparison with the conventional ORC for the Mackey–Glass task, CE-ORC showed a decrease in normalized mean square error by ∼75 % . Furthermore, we applied this method in a weather time series analysis and effectively predicted the temperature and humidity within a range of 24 h.

Integrated electro-optic tuning devices are essential parts of optical communication, sensors, and optical machine learning. Among the available materials, silicon is the most promising for on-chip signal processing and networks. However, silicon is limited owing to the absence of efficient Pockels electro-optic tuning. Herein, we propose a new hybrid silicon-barium-titanate (Si-BTO) integrated photonic platform, in which the BTO thin film is deposited by the chemical solution deposition (CSD) method. A tunable racetrack resonator is demonstrated to confirm the Pockels electro-optic tuning potential of the BTO thin film. The hybrid racetrack resonator has a tuning efficiency of 6.5 pm / V and a high-power efficiency of 2.16 pm / nW. Moreover, the intrinsic quality factor of the fabricated racetrack resonator is 48,000, which is the highest in hybrid Si-BTO platforms, to the best of our knowledge. The high-speed test verifies the stability of the racetrack resonator. The hybrid Si-BTO technology based on the CSD method has the advantages of low equipment cost and simple fabrication process, which holds promise for low-power electro-optic tuning devices.

Recording and identifying faint objects through atmospheric scattering media by an optical system are fundamentally interesting and technologically important. We introduce a comprehensive model that incorporates contributions from target characteristics, atmospheric effects, imaging systems, digital processing, and visual perception to assess the ultimate perceptible limit of geometrical imaging, specifically the angular resolution at the boundary of visible distance. The model allows us to reevaluate the effectiveness of conventional imaging recording, processing, and perception and to analyze the limiting factors that constrain image recognition capabilities in atmospheric media. The simulations were compared with the experimental results measured in a fog chamber and outdoor settings. The results reveal good general agreement between analysis and experiment, pointing out the way to harnessing the physical limit for optical imaging in scattering media. An immediate application of the study is the extension of the image range by an amount of 1.2 times with noise reduction via multiframe averaging, hence greatly enhancing the capability of optical imaging in the atmosphere.

Frequency-modulated continuous-wave light detection and ranging (FMCW lidar) is a powerful high-precision ranging and three-dimensional (3D) imaging technology with inherent immunity to ambient light and the ability to simultaneously yield distance and velocity information. However, the current withdraws of the traditional FMCW lidar systems are the poor resistance to environmental disturbance and high requirements for echo power, which greatly restrict their applications for high-precision ranging of noncooperative targets in dynamic measurement scenes. Here, we report an all-fiber anti-interference FMCW lidar system with high sensitivity and precision, employing a unique self-mixing stimulation radiation process for signal amplification, a special reversely chirped dual laser structure, and a common-path design for disturbance compensation. We evaluate the ranging accuracy, precision, and stability of the system completely. Finally, we demonstrate an ultralow echo detection limit of subpicowatts with a probe power of below 0.1 mW, a state-of-art localization accuracy of better than 50 μm, high stability with a standard deviation of 6.51 μm over 3 h, and high-quality 3D imaging of noncooperative objects in a fluctuating environment. With the advantages of high precision and stability, weak signal detection capability, and anti-interference ability, the proposed system has potential applications in space exploration, autodriving, and high-precision manufacturing.

Many technologies, including dot projectors and lidar systems, benefit greatly from using polarized illumination. However, conventional polarizers and polarizing beam splitters have a fundamental limit of 50% efficiency when converting unpolarized light into one specific polarization. Here, we overcome this restriction and achieve near-complete conversion of unpolarized light to a spatially uniform polarization state over several output directions with our topology-optimized metasurfaces. Our results provide a path toward greatly improving the efficiency of common unpolarized light sources, such as LEDs, for a variety of applications requiring uniformly polarized illumination. Our fabricated metasurface realizes a 70% conversion efficiency, surpassing the aforementioned limit, and achieves a polarization extinction ratio exceeding 20, when characterized with laboratory measurements. We further demonstrate that arbitrary power splitting can be achieved between three or more polarized outputs, offering flexibility in target illumination.

The mode sorter is the crucial component of the communication systems based on orbital angular momentum (OAM). However, schemes proposed so far can only effectively sort integer OAM (IOAM) modes. Here, we demonstrate the effective sorting of fractional OAM (FOAM) modes by utilizing the coordinate transformation method, which can convert FOAM modes to IOAM modes. The transformed IOAM modes are subsequently sorted using a mode conversion method called topological charge matching. The validation of our scheme is verified by implementing two FOAM sorting processes and corresponding mode purity analyses, both theoretically and experimentally. This new sorting method exhibits great potential for implementing a highly confidential and high-capacity FOAM-based communication and data storage system, which may inspire further applications in both classical and quantum regimes.

We present what we believe is the first conjugate adaptive optics (AO) extension that can be retrofitted into a commercial microscope by being positioned between the camera port and the image sensor. The extension features a deformable phase plate (DPP), a refractive wavefront modulator, and indirect wavefront sensing to form a completely in-line architecture. This allows the axial position of the DPP to be optimized by maximizing an image quality metric, which is a cumbersome task with deformable mirrors as the correction element. We demonstrate the performance of the system on a Zeiss AxioVert 200M microscope equipped with a 20 × 0.75 NA air objective. To simulate sample-induced complex aberrations, transparent custom-made arbitrary phase plates were introduced between the sample and the objective. We demonstrate that the extension can provide high-quality full-field correction even for large aberrations, when the DPP is placed at the conjugate plane of the phase plates. We also demonstrate that both the DPP position and its surface profile can be optimized blindly, which can pave the way for plug-and-play conjugate-AO systems.

Structurally anisotropic materials are ubiquitous in several application fields, yet their accurate optical characterization remains challenging due to the lack of general models linking their scattering coefficients to the macroscopic transport observables and the need to combine multiple measurements to retrieve their direction-dependent values. Here, we present an improved method for the experimental determination of light-transport tensor coefficients from the diffusive rates measured along all three directions, based on transient transmittance measurements and a generalized Monte Carlo model. We apply our method to the characterization of light-transport properties in two common anisotropic materials—polytetrafluoroethylene tape and paper—highlighting the magnitude of systematic deviations that are typically incurred when neglecting anisotropy.

Single-pixel imaging (SPI) enables an invisible target to be imaged onto a photosensitive surface without a lens, emerging as a promising way for indirect optical encryption. However, due to its linear and broadcast imaging principles, SPI encryption has been confined to a single-user framework for the long term. We propose a multi-image SPI encryption method and combine it with orthogonal frequency division multiplexing-assisted key management, to achieve a multiuser SPI encryption and authentication framework. Multiple images are first encrypted as a composite intensity sequence containing the plaintexts and authentication information, simultaneously generating different sets of keys for users. Then, the SPI keys for encryption and authentication are asymmetrically isolated into independent frequency carriers and encapsulated into a Malus metasurface, so as to establish an individually private and content-independent channel for each user. Users can receive different plaintexts privately and verify the authenticity, eliminating the broadcast transparency of SPI encryption. The improved linear security is also verified by simulating attacks. By the combination of direct key management and indirect image encryption, our work achieves the encryption and authentication functionality under a multiuser computational imaging framework, facilitating its application in optical communication, imaging, and security.

Neural networks have provided faster and more straightforward solutions for laser modulation. However, their effectiveness when facing diverse structured lights and various output resolutions remains vulnerable because of the specialized end-to-end training and static model. Here, we propose a redefinable neural network (RediNet), realizing customized modulation on diverse structured light arrays through a single general approach. The network input format features a redefinable dimension designation, which ensures RediNet wide applicability and removes the burden of processing pixel-wise light distributions. The prowess of originally generating arbitrary-resolution holograms with a fixed network is first demonstrated. The versatility is showcased in the generation of 2D/3D foci arrays, Bessel and Airy beam arrays, (perfect) vortex beam arrays, and even snowflake-intensity arrays with arbitrarily built phase functions. A standout application is producing multichannel compound vortex beams, where RediNet empowers a spatial light modulator (SLM) to offer comprehensive multiplexing functionalities for free-space optical communication. Moreover, RediNet has the hitherto highest efficiency, only consuming 12 ms (faster than the mainstream SLM framerate of 60 Hz) for a 10002-resolution holograph, which is critical in real-time required scenarios. Considering the fine resolution, high speed, and unprecedented universality, RediNet can serve extensive applications, such as next-generation optical communication, parallel laser direct writing, and optical traps.

Dual-comb interferometric systems with high time accuracy have been realized for various applications. The flourishing ultralow noise dual-comb system promotes the measurement and characterization of relative timing jitter, thus improving time accuracy. With optical solutions, introducing an optical reference enables 105 harmonics measurements, thereby breaking the limit set by electrical methods; nonlinear processes or spectral interference schemes were also employed to track the relative timing jitter. However, such approaches operating in the time domain either require additional continuous references or impose stringent requirements on the amount of timing jitter. We propose a scheme to correct the relative timing jitter of a free-running dual-comb interferometry assisted by a Fabry–Pérot (F–P) cavity in the frequency domain. With high wavelength thermal stability provided by the F–P cavity, the absolute wavelength deviation in the operating bandwidth is compressed to <0.4 pm, corresponding to a subpicosecond sensitivity of pulse-to-pulse relative timing jitter. Also, Allan deviation of 10 - 10 is obtained under multiple coherent averaging, which lays the foundation for mode-resolved molecular spectroscopic applications. The spectral absorption features of hydrogen cyanide gas molecules at ambient temperature were measured and matched to the HITRAN database. Our scheme promises to provide new ideas on sensitive measurements of relative timing jitter.

Quantum microwave photonics (QMWP) is an innovative approach that combines energy–time entangled biphoton sources as the optical carrier with time-correlated single-photon detection for high-speed radio frequency (RF) signal recovery. This groundbreaking method offers unique advantages, such as nonlocal RF signal encoding and robust resistance to dispersion-induced frequency fading. We explore the versatility of processing the quantum microwave photonic signal by utilizing coincidence window selection on the biphoton coincidence distribution. The demonstration includes finely tunable RF phase shifting, flexible multitap transversal filtering (with up to 14 taps), and photonically implemented RF mixing, leveraging the nonlocal RF mapping characteristic of QMWP. These accomplishments significantly enhance the capability of microwave photonic systems in processing ultraweak signals, opening up new possibilities for various applications.

Dynamically tunable metasurfaces employing chalcogenide phase-change materials (PCMs) such as Ge2Sb2Te5 alloys have garnered significant attention and research efforts. However, the utilization of chalcogenide PCMs in dynamic metasurface devices necessitates protection, owing to their susceptibility to volatilization and oxidation. Conventional protective layer materials such as Al2O3, TiO2, and SiO2 present potential drawbacks including diffusion, oxidation, or thermal expansion coefficient mismatch with chalcogenide PCMs during high-temperature phase transition, severely limiting the durability of chalcogenide PCM-based devices. In this paper, we propose, for the first time to our knowledge, the utilization of chalcogenide glass characterized by high thermal stability as a protective material for chalcogenide PCM. This approach addresses the durability challenge of current dynamic photonic devices based on chalcogenide PCM by virtue of their closely matched optical and thermal properties. Building upon this innovation, we introduce an all-chalcogenide dynamic tunable metasurface filter and comprehensively simulate and analyze its characteristics. This pioneering work paves the way for the design and practical implementation of optically dynamically tunable metasurface devices leveraging chalcogenide PCMs, ushering in new opportunities in the field.

Fiber sensors are commonly used to detect environmental, physiological, optical, chemical, and biological factors. Thermally drawn fibers offer numerous advantages over other commercial products, including enhanced sensitivity, accuracy, improved functionality, and ease of manufacturing. Multimaterial, multifunctional fibers encapsulate essential internal structures within a microscale fiber, unlike macroscale sensors requiring separate electronic components. The compact size of fiber sensors enables seamless integration into existing systems, providing the desired functionality. We present a multimodal fiber antenna monitoring, in real time, both the local deformation of the fiber and environmental changes caused by foreign objects in proximity to the fiber. Time domain reflectometry propagates an electromagnetic wave through the fiber, allowing precise determination of spatial changes along the fiber with exceptional resolution and sensitivity. Local changes in impedance reflect fiber deformation, whereas proximity is detected through alterations in the evanescent field surrounding the fiber. The fiber antenna operates as a waveguide to detect local deformation through the antisymmetric mode and environmental changes through the symmetric mode. This multifunctionality broadens its application areas from biomedical engineering to cyber&ndash;physical interfacing. In antisymmetric mode, the device can sense local changes in pressure, and, potentially, temperature, pH, and other physiological conditions. In symmetric mode, it can be used in touch screens, environmental detection for security, cyber&ndash;physical interfacing, and human&ndash;robot interactions.

We propose pattern self-referenced single-pixel common-path holography (PSSCH), which can be realized using either the digital-micromirror-device (DMD) based off-axis scheme or the DMD-based phase-shifting approach, sharing the same experimental setup, to do wavefront reconstructions. In this method, each modulation pattern is elaborately encoded to be utilized to not only sample the target wavefront but also to dynamically introduce the reference light for single-pixel common-path holographic detection. As such, it does not need to intentionally introduce a static reference light, resulting in it making full use of the pixel resolution of the modulation patterns and suppressing dynamically varying noises. Experimental demonstrations show that the proposed method can not only obtain a larger field of view than the peripheral-referenced approach but also achieve a higher imaging resolution than the checkerboard-referenced approach. The phase-shifting-based PSSCH performs better than the off-axis-based PSSCH on imaging fidelity, while the imaging speed of the latter is several times faster. Further, we demonstrate our method to do wavefront imaging of a biological sample as well as to do phase detection of a physical lens. The experimental results suggest its effectiveness in applications.

Photonic computing has recently become an interesting paradigm for high-speed calculation of computing processes using light&ndash;matter interactions. Here, we propose and study an electromagnetic wave-based structure with the ability to calculate the solution of partial differential equations (PDEs) in the form of the Helmholtz wave equation, &nabla; 2f ( x , y ) + k2f ( x , y ) = 0, with k as the wavenumber. To do this, we make use of a network of interconnected waveguides filled with dielectric inserts. In so doing, it is shown how the proposed network can mimic the response of a network of T-circuit elements formed by two series and a parallel impedances, i.e., the waveguide network effectively behaves as a metatronic network. An in-depth theoretical analysis of the proposed metatronic structure is presented, showing how the governing equation for the currents and impedances of the metatronic network resembles that of the finite difference representation of the Helmholtz wave equation. Different studies are then discussed including the solution of PDEs for Dirichlet and open boundary value problems, demonstrating how the proposed metatronic-based structure has the ability to calculate their solutions.

Phase recovery, calculating the phase of a light wave from its intensity measurements, is essential for various applications, such as coherent diffraction imaging, adaptive optics, and biomedical imaging. It enables the reconstruction of an object&rsquo;s refractive index distribution or topography as well as the correction of imaging system aberrations. In recent years, deep learning has been proven to be highly effective in addressing phase recovery problems. The two most direct deep learning phase recovery strategies are data-driven (DD) with supervised learning mode and physics-driven (PD) with self-supervised learning mode. DD and PD achieve the same goal in different ways yet there is a lack of necessary research to reveal similarities and differences. Therefore, we comprehensively compare these two deep learning phase recovery strategies in terms of time consumption, accuracy, generalization ability, ill-posedness adaptability, and prior capacity. What is more, we propose a co-driven strategy of combining datasets and physics for the balance of high- and low-frequency information.

Deep learning has transformed computational imaging, but traditional pixel-based representations limit their ability to capture continuous multiscale object features. Addressing this gap, we introduce a local conditional neural field (LCNF) framework, which leverages a continuous neural representation to provide flexible object representations. LCNF&rsquo;s unique capabilities are demonstrated in solving the highly ill-posed phase retrieval problem of multiplexed Fourier ptychographic microscopy. Our network, termed neural phase retrieval (NeuPh), enables continuous-domain resolution-enhanced phase reconstruction, offering scalability, robustness, accuracy, and generalizability that outperform existing methods. NeuPh integrates a local conditional neural representation and a coordinate-based training strategy. We show that NeuPh can accurately reconstruct high-resolution phase images from low-resolution intensity measurements. Furthermore, NeuPh consistently applies continuous object priors and effectively eliminates various phase artifacts, demonstrating robustness even when trained on imperfect datasets. Moreover, NeuPh improves accuracy and generalization compared with existing deep learning models. We further investigate a hybrid training strategy combining both experimental and simulated datasets, elucidating the impact of domain shift between experiment and simulation. Our work underscores the potential of the LCNF framework in solving complex large-scale inverse problems, opening up new possibilities for deep-learning-based imaging techniques.

Recent breakthroughs in the field of non-Hermitian physics present unprecedented opportunities, from fundamental theories to cutting-edge applications such as multimode lasers, unconventional wave transport, and high-performance sensors. The exceptional point, a spectral singularity widely existing in non-Hermitian systems, provides an indispensable route to enhance the sensitivity of optical detection. However, the exceptional point of the forementioned systems is set once the system is built or fabricated, and machining errors make it hard to reach such a state precisely. To this end, we develop a highly tunable and reconfigurable exceptional point system, i.e., a single spoof plasmonic resonator suspended above a substrate and coupled with two freestanding Rayleigh scatterers. Our design offers great flexibility to control exceptional point states, enabling us to dynamically reconfigure the exceptional point formed by various multipolar modes across a broadband frequency range. Specifically, we experimentally implement five distinct exceptional points by precisely manipulating the positions of two movable Rayleigh scatterers. In addition, the enhanced perturbation strength offers remarkable sensitivity enhancement for detecting deep-subwavelength particles with the minimum dimension down to 0.001λ (with λ to be the free-space wavelength).

Two mainstream approaches for solving inverse sample reconstruction problems in programmable illumination computational microscopy rely on either deep models or physical models. Solutions based on physical models possess strong generalization capabilities while struggling with global optimization of inverse problems due to a lack of sufficient physical constraints. In contrast, deep-learning methods have strong problem-solving abilities, but their generalization ability is often questioned because of the unclear physical principles. In addition, conventional deep models are difficult to apply to some specific scenes because of the difficulty in acquiring high-quality training data and their limited capacity to generalize across different scenarios. To combine the advantages of deep models and physical models together, we propose a hybrid framework consisting of three subneural networks (two deep-learning networks and one physics-based network). We first obtain a result with rich semantic information through a light deep-learning neural network and then use it as the initial value of the physical network to make its output comply with physical process constraints. These two results are then used as the input of a fusion deep-learning neural work that utilizes the paired features between the reconstruction results of two different models to further enhance imaging quality. The proposed hybrid framework integrates the advantages of both deep models and physical models and can quickly solve the computational reconstruction inverse problem in programmable illumination computational microscopy and achieve better results. We verified the feasibility and effectiveness of the proposed hybrid framework with theoretical analysis and actual experiments on resolution targets and biological samples.

Leveraging an optical system for image encryption is a promising approach to information security since one can enjoy parallel, high-speed transmission, and low-power consumption encryption features. However, most existing optical encryption systems involve a critical issue that the dimension of the ciphertexts is the same as the plaintexts, which may result in a cracking process with identical plaintext-ciphertext forms. Inspired by recent advances in computational neuromorphic imaging (CNI) and speckle correlography, a neuromorphic encryption technique is proposed and demonstrated through proof-of-principle experiments. The original images can be optically encrypted into event-stream ciphertext with a high-level information conversion form. To the best of our knowledge, the proposed method is the first implementation for event-driven optical image encryption. Due to the high level of encryption data with the CNI paradigm and the simple optical setup with a complex inverse scattering process, our solution has great potential for practical security applications. This method gives impetus to the image encryption of the visual information and paves the way for the CNI-informed applications of speckle correlography.

We propose an approach for recognizing the pose and surface material of diverse objects, leveraging diffuse reflection principles and data fusion. Through theoretical analysis and the derivation of factors influencing diffuse reflection on objects, the method concentrates on and exploits surface information. To validate the feasibility of our theoretical research, the depth and active infrared intensity data obtained from a single time-of-flight camera are initially combined. Subsequently, these data undergo processing using feature extraction and lightweight machine-learning techniques. In addition, an optimization method is introduced to enhance the fitting of intensity. The experimental results not only visually showcase the effectiveness of our proposed method in accurately detecting the positions and surface materials of targets with varying sizes and spatial locations but also reveal that the vast majority of the sample data can achieve a recognition accuracy of 94.8% or higher.

Terahertz (THz) radiation finds important applications in various fields, making the study of THz sources significant. Among different approaches, electron accelerator-based THz sources hold notable advantages in generating THz radiation with narrow bandwidth, high brightness, high peak power, and high repetition rate. To further improve the THz radiation energy, the bunching factor of the free electron bunch train needs to be increased. We propose and numerically reveal that, by adding an additional short-pulse drive beam before the main beam as the excitation source of nonlinear plasma wake, the bunching factor of the main beam can be further increased to ∼0.94, even though with a relatively low charge, low current, and relatively diffused electron beam. Two such electron beams with loose requirements can be easily generated using typical photoinjectors. Our work provides a way for a new THz source with enhanced radiation energy.

Water photoacoustic microscopy (PAM) enables water absorption contrast mapping in deep biological tissue, which further allows a more detailed architecture analysis and facilitates a better understanding of metabolic and pathophysiological pathways. The strongest absorption peak of water in the near-infrared region occurs at 1930 nm, where the first overtone of the O-H bond lies. However, general light sources operating in this band hitherto still suffer from low optical signal-to-noise ratio and suboptimal pulse widths for photoacoustic signal generation. These lead to not only PAM contrast deterioration but also a high risk of sample photodamage. Consequently, we developed a hybrid optical parametrically-oscillating emitter (HOPE) source for an improved water PAM image contrast, leading to noninvasive and safer bioimaging applications. Our proposed source generates 1930 nm laser pulses with high spectral purity at a repetition rate of 187.5 kHz. The pulse width is flexibly tunable from 4 to 15 ns, and the maximum pulse energy is 700 nJ with a power stability of 1.79%. Leveraging these advancements, we also demonstrated high-contrast water PAM in multifaceted application scenarios, including tracking the dynamic of water distribution in a zebrafish embryo, visualizing the water content of a murine tumor xenograft, and mapping the fluid distribution in an edema mouse ear model. Finally, we showcased 1750-nm/1930-nm dual-color PAM for quantitative imaging of lipid and water distributions with reduced cross talk and imaging artifacts. Given all these results, we believe that our HOPE source can heighten water PAM’s relevance in both biological research and clinical diagnostics.

Broad and safe access to ultrafast laser technology has been hindered by the absence of optical fiber-delivered pulses with tunable central wavelength, pulse repetition rate, and pulse width in the picosecond–femtosecond regime. To address this long-standing obstacle, we developed a reliable accessory for femtosecond ytterbium fiber chirped pulse amplifiers, termed a fiber-optic nonlinear wavelength converter (FNWC), as an adaptive optical source for the emergent field of femtosecond biophotonics. This accessory empowers the fixed-wavelength laser to produce fiber-delivered ∼ 20 nJ pulses with central wavelength across 950 to 1150 nm, repetition rate across 1 to 10 MHz, and pulse width across 40 to 400 fs, with a long-term stability of >2000 h. As a prototypical label-free application in biology and medicine, we demonstrate the utility of FNWC in real-time intravital imaging synergistically integrated with modern machine learning and large-scale fluorescence lifetime imaging microscopy.

A compact and high-resolution fiber-optic refractive index (RI) sensor based on a microwave photonic filter (MPF) is proposed and experimentally validated. The sensing head utilizes a cascaded in-line interferometer fabricated by an input single-mode fiber (SMF) tapered fusion with no-core fiber-thin-core fiber (TCF)-SMF. The surrounding RI (SRI) can be demodulated by tracing the passband’s central frequency of the MPF, which is constructed by the cascaded in-line interferometer, electro-optic modulator, and a section of dispersion compensation fiber. The sensitivity of the sensor is tailorable through the use of different lengths of TCF. Experimental results reveal that with a 30 mm length of TCF, the sensor achieves a maximum theoretical sensitivity and resolution of -1.403 GHz / refractive index unit (RIU ) and 1.425 × 10 - 7 RIU, respectively, which is at least 6.3 times higher than what has been reported previously. Furthermore, the sensor exhibits temperature-insensitive characteristics within the range of 25 ° C - 75 ° C, with a temperature-induced frequency change of only ±1.5 MHz. This value is significantly lower than the frequency change induced by changes in the SRI. The proposed MPF-based cascaded in-line interferometer RI sensor possesses benefits such as easy manufacture, low cost, high resolution, and temperature insensitivity.

The detection of the state of polarization (SOP) of light is essential for many optical applications. However, cost-effective SOP measurement is a challenge due to the complexity of conventional methods and the poor transferability of new methods. We propose a straightforward, low-cost, and portable SOP measurement system based on the multimode fiber speckle. A convolutional neural network is utilized to establish the mapping relationship between speckle and Stokes parameters. The lowest root-mean-square error of the estimated SOP on the Poincaré sphere can be 0.0042. This method is distinguished by its low cost, clear structure, and applicability to different wavelengths with high precision. The proposed method is of great value in polarization-related applications.

Since the concept of computational spectroscopy was introduced, numerous computational spectrometers have emerged. While most of the work focuses on materials, optical structures, and devices, little attention is paid to the reconstruction algorithm, thus resulting in a common issue: the effectiveness of spectral reconstruction is limited under high-level noise originating from the data acquisition process. Here, we fabricate a computational spectrometer based on a quantum dot (QD) filter array and propose what we believe is a novel algorithm, TKVA (algorithm with Tikhonov and total variation regularization, and the alternating direction method of multipliers), to suppress the impact of noise on spectral recovery. Surprisingly, the new TKVA algorithm gives rise to another advantage, i.e., the spectral accuracy can be enhanced through interpolation of the precalibration data, providing a convenient solution for performance improvement. In addition, the accuracy of spectral recovery is also enhanced via the interpolation, highlighting its superiority in spectral reconstruction. As a result, the QD spectrometer using the TKVA algorithm shows supreme spectral recovery accuracy compared to the traditional algorithms for complex and broad spectra, a spectral accuracy as low as 0.1 nm, and a spectral resolution of 2 nm in the range of 400 to 800 nm. The new reconstruction algorithm can be applied in various computational spectrometers, facilitating the development of this kind of equipment.

Secure and high-speed optical communications are of primary focus in information transmission. Although it is widely accepted that chaotic secure communication can provide superior physical layer security, it is challenging to meet the demand for high-speed increasing communication rate. We theoretically propose and experimentally demonstrate a conceptual paradigm for orbital angular momentum (OAM) configured chaotic laser (OAM-CCL) that allows access to high-security and massive-capacity optical communications. Combining 11 OAM modes and an all-optical feedback chaotic laser, we are able to theoretically empower a well-defined optical communication system with a total transmission capacity of 100 Gb / s and a bit error rate below the forward error correction threshold 3.8 × 10 - 3. Furthermore, the OAM-CCL-based communication system is robust to 3D misalignment by resorting to appropriate mode spacing and beam waist. Finally, the conceptual paradigm of the OAM-CCL-based communication system is verified. In contrast to existing systems (traditional free-space optical communication or chaotic optical communication), the OAM-CCL-based communication system has three-in-one characteristics of high security, massive capacity, and robustness. The findings demonstrate that this will promote the applicable settings of chaotic laser and provide an alternative promising route to guide high-security and massive-capacity optical communications.

Achieving efficient and intense second-harmonic generation (SHG) in the terahertz (THz) spectrum holds great potential for a wide range of technical applications, including THz nonlinear functional devices, wireless communications, and data processing and storage. However, the current research on THz harmonic emission primarily focuses on inorganic materials, which often offers challenges in achieving both efficient and broadband SHG. Herein, the remarkable efficiency of organic materials in producing THz harmonics is studied and demonstrated, thereby opening up a new avenue for searching candidates for frequency-doubling devices in the THz band. By utilizing DAST, DSTMS, and OH1 crystals, we showcase their superior frequency conversion capabilities when pumped by the narrowband THz pulses centered at 2.4, 1.6, and 0.8 THz. The SHG spans a high-frequency THz domain of 4.8 THz, achieving an unprecedented conversion efficiency of ∼1.21 % while maintaining a perturbative nonlinear response. The highly efficient SHG of these materials is theoretically analyzed by considering the combined effects of dispersion, phonon absorption, polarization, and the nonlinear susceptibility of organic crystals. This work presents a promising platform for efficient THz frequency conversion and generation across a wide range of frequencies, offering new opportunities for novel nonlinear THz applications in next-generation electronics and optics.

Dual-comb ranging allows rapid and precise distance measurement and can be universally implemented on different comb platforms, e.g., fiber combs and microcombs. To date, dual-fiber-comb ranging has become a mature and powerful tool for metrology and industry, but the measurement speed is often at a kilohertz level due to the lower repetition rates. Recently, dual-microcomb ranging has given rise to a new opportunity for distance measurement, in consequence of its small footprint and high repetition rates, but full-comb stabilization is challenging. Here, we report a dual-hybrid-comb distance meter capable of ultrarapid and submicrometer precision distance measurement, which can not only leverage the advantage of easy locking inherited from the fiber comb but also sustain ultrarapid measurement speed due to the microcomb. The experimental results show that the measurement precision can reach 3.572 μm at 4.136 μs and 432 nm at 827.2 μs averaging time. Benefiting from the large difference between the repetition rates of the hybrid combs, the measurement speed can be enhanced by 196 folds, in contrast to the dual-fiber-comb system with about a 250 MHz repetition rate. Our work can offer a solution for the fields of rapid dimensional measurement and spectroscopy.

The optoelectronic oscillator (OEO) is a typical time-delay system with rich nonlinear dynamical characteristics. Most of the previous research on OEOs has been focused on analyzing the properties of OEOs with a long time delay, which makes it difficult to realize mode locking without additional phase-locking mechanisms. We have achieved, for the first time to our knowledge, a self-mode-locking OEO and generated stable microwave frequency combs by analyzing the characteristics of OEOs with an ultrashort time scale. In the experiment, the self-mode-locking OEOs with fundamental mode, second-order harmonic, and sixth-order harmonic were realized by adjusting the system parameters, all of which produced uniform square wave signals with tunable duty cycles, steep rising and falling edges, and periods of less than 20 ns. The self-fundamental-mode-locking OEOs with different time delays were also implemented and experimentally realized. Furthermore, the experiment revealed the self-hybrid mode-locking OEO, which is the coexistence and synchronization of the three measured self-locking modes in one OEO cavity, demonstrating the complex nonlinear dynamical behaviors of the OEO system and enabling the generation of periodic nonuniform hybrid square wave signals. The realization of the self-mode-locking OEO and the generation of flexible and stable square wave signals at ultrashort time scales enrich the study of OEO nonlinear dynamics in the realm of complex microwave waveform generation, offering promising applications in areas such as atomic clocks, radars, communications, and optoelectronic neural networks.

Fluorescent nanothermometers for remote temperature measurement at the micro/nanoscale have stimulated growing efforts in developing efficient temperature-responsive materials and detection procedures. However, the efficient collection and transmission of optical signals have been a tremendous challenge for practical applications of these nanothermometers. Herein, we design an all-fiberized thermometry based on a fiber-coupled microsphere cavity coated with thermo-sensitive NaYF4 : 20 % Yb3 + , 2 % Er3 + @ NaYF4 nanocrystals (NCs), allowing for spatial temperature sensing with resolution down to the few-micrometer scale. In our design, the microsphere efficiently excites the NCs and collects their upconversion emissions, and the use of a fiber splitter coupled with the microsphere allows for lossless routing of excitation and emitted light. We demonstrate the use of this all-fiber temperature sensor in diverse environments, especially in strongly acidic and alkaline conditions. Leveraging the high flexibility of commercial silica fiber, this all-fiber temperature sensor was employed for stable fixed-point real-time temperature measurement and multipurpose temperature recording/mapping in opaque environments, microscale areas, various solutions, and complicated bent structures. Thus, the demonstrated design could have strong implications for the practical use of nanothermometers in various possible scenarios, especially monitoring temperatures in diverse physiological settings.

The ultimate goal of artificial intelligence (AI) is to mimic the human brain to perform decision-making and control directly from high-dimensional sensory input. Diffractive optical networks (DONs) provide a promising solution for implementing AI with high speed and low power-consumption. Most reported DONs focus on tasks that do not involve environmental interaction, such as object recognition and image classification. By contrast, the networks capable of decision-making and control have not been developed. Here, we propose using deep reinforcement learning to implement DONs that imitate human-level decision-making and control capability. Such networks, which take advantage of a residual architecture, allow finding optimal control policies through interaction with the environment and can be readily implemented with existing optical devices. The superior performance is verified using three types of classic games: tic-tac-toe, Super Mario Bros., and Car Racing. Finally, we present an experimental demonstration of playing tic-tac-toe using the network based on a spatial light modulator. Our work represents a solid step forward in advancing DONs, which promises a fundamental shift from simple recognition or classification tasks to the high-level sensory capability of AI. It may find exciting applications in autonomous driving, intelligent robots, and intelligent manufacturing.

Sensitive mid-infrared (MIR) detection is in high demand in various applications, ranging from remote sensing, infrared surveillance, and environmental monitoring to industrial inspection. Among others, upconversion infrared detectors have recently attracted increasing attention due to their advantageous features of high sensitivity, fast response, and room-temperature operation. However, it remains challenging to realize high-performance passive MIR sensing due to the stringent requirement of high-power continuous-wave pumping. Here, we propose and implement a high-efficiency and low-noise MIR upconversion detection system based on pumping enhancement via a low-loss optical cavity. Specifically, a single-longitudinal-mode pump at 1064 nm is significantly enhanced by a factor of 36, thus allowing for a peak conversion efficiency of up to 22% at an intracavity average power of 55 W. The corresponding noise equivalent power is achieved as low as 0.3 fW / Hz1/2, which indicates at least a 10-fold improvement over previous results. Notably, the involved single-frequency pumping would facilitate high-fidelity spectral mapping, which is particularly attractive for high-precision MIR upconversion spectroscopy in photon-starved scenarios.

Optical-resolution photoacoustic microscopy (OR-PAM) has rapidly developed and is capable of characterizing optical absorption properties of biological tissue with high contrast and high resolution (micrometer-scale lateral resolution). However, the conventional excitation source of rapidly diverging Gaussian beam imposes limitations on the depth of focus (DOF) in OR-PAM, which in turn affects the depth-resolving ability and detection sensitivity. Here, we proposed a flexible DOF, depth-invariant resolution photoacoustic microscopy (FDIR-PAM) with nondiffraction of Airy beams. The spatial light modulator was incorporated into the optical pathway of the excitation source with matched switching phase patterns, achieving the flexibly adjustable modulation parameters of the Airy beam. We conducted experiments on phantoms and intravital tissue to validate the effectiveness of the proposed approach for high sensitivity and high-resolution characterization of variable topology of tissue, offering a promising DOF of 926 μm with an invariant lateral resolution of 3.2 μm, which is more than 17-fold larger compared to the Gaussian beam. In addition, FDIR-PAM successfully revealed clear individual zebrafish larvae and the pigment pattern of adult zebrafishes, as well as fine morphology of cerebral vasculature in a large depth range with high resolution, which has reached an evident resolving capability improvement of 62% mean value compared with the Gaussian beam.

High-order Laguerre–Gaussian (LG) petal-like beams have become a topic of significant interest due to their potential application in next-generation optical trapping, quantum optics, and materials processing technologies. In this work, we demonstrate the generation of high-order LG beams with petal-like spatial profiles and tunable orbital angular momentum (OAM) in the mid-infrared wavelength region. These beams are generated using idler-resonant optical parametric oscillation (OPO) in a KTiOAsO4 (KTA) crystal. By adjusting the length of the resonant cavity, the OAM of the mid-infrared idler field can be tuned and we demonstrate tuning in the range of 0 to ± 10. When using a maximum pump energy of 20.2 mJ, the maximum output energy of high-order modes LG0 , ± 5, LG0 , ± 8, and LG0 , ± 10 were 0.8, 0.53, and 0.46 mJ, respectively. The means by which high-order LG modes with petal-like spatial profiles and tunable OAM were generated from the OPO is theoretically modeled by examining the spatial overlap efficiency of the beam waists of the pump and resonant idler fields within the center of the KTA crystal. The methodology presented in this work offers a simple and flexible method to wavelength-convert laser emission and generate high-order LG modes.

A high-performance silicon arrayed-waveguide grating (AWG) with 0.4-nm channel spacing for dense wavelength-division multiplexing systems is designed and realized successfully. The device design involves broadening the arrayed waveguides far beyond the single-mode regime, which minimizes random phase errors and propagation loss without requiring any additional fabrication steps. To further enhance performance, Euler bends have been incorporated into the arrayed waveguides to reduce the device’s physical footprint and suppress the excitation of higher modes. In addition, shallowly etched transition regions are introduced at the junctions between the free-propagation regions and the arrayed waveguides to minimize mode mismatch losses. As an example, a 32 × 32 AWG (de)multiplexer with a compact size of 900 μm × 2200 μm is designed and demonstrated with a narrow channel spacing of 0.4 nm by utilizing 220-nm-thick silicon photonic waveguides. The measured excess loss for the central channel is ∼0.65 dB, the channel nonuniformity is around 2.5 dB, while the adjacent-channel crosstalk of the central output port is -21.4 dB. To the best of our knowledge, this AWG (de)multiplexer is the best one among silicon-based implementations currently available, offering both dense channel spacing and a large number of channels.

Detecting gravity-mediated entanglement can provide evidence that the gravitational field obeys quantum mechanics. We report the result of a simulation of the phenomenon using a photonic platform. The simulation tests the idea of probing the quantum nature of a variable by using it to mediate entanglement and yields theoretical and experimental insights, clarifying the operational tools needed for future gravitational experiments. We employ three methods to test the presence of entanglement: the Bell test, entanglement witness, and quantum state tomography. We also simulate the alternative scenario predicted by gravitational collapse models or due to imperfections in the experimental setup and use quantum state tomography to certify the absence of entanglement. The simulation reinforces two main lessons: (1) which path information must be first encoded and subsequently coherently erased from the gravitational field and (2) performing a Bell test leads to stronger conclusions, certifying the existence of gravity-mediated nonlocality.

Vector structured beams (VSBs) offer infinite eigenstates and open up new possibilities for high-capacity optical and quantum communications by the multiplexing of the states. Therefore, the sorting and measuring of VSBs are extremely important. However, the efficient manipulations of a large number of VSBs have simultaneously remained challenging up to now, especially in integrated optical systems. Here, we propose a compact spin-multiplexed diffractive metasurface capable of continuously sorting and detecting arbitrary VSBs through spatial intensity separation. By introducing a diffractive optical neural network with cascaded metasurface systems, we demonstrate arbitrary VSBs sorters that can simultaneously identify Laguerre–Gaussian modes (l = - 4 to 4, p = 1 to 4), Hermitian–Gaussian modes (m = 1 to 4, n = 1 to 3), and Bessel–Gaussian modes (l = 1 to 12). Such a sorter for arbitrary VSBs could revolutionize applications in integrated and high-dimensional optical communication systems.

Random fiber lasers (RFLs) have attracted extensive attention due to their rich physical properties and wide applications. Here, a RFL using a cascaded fiber loop mirror (CFLM) is proposed and presented. A CFLM with 10 fiber loop mirrors (FLMs) is simulated by the transfer matrix method and used to provide random feedback. Multiple spikes are observed in both the simulated and measured reflection spectra. The RFL operates in a single longitudinal mode near the threshold and a time-varying multilongitudinal mode at higher pump powers. The RFL exhibits a time-varying radio-frequency spectrum. The Lévy–Gaussian distribution transition is observed, as in many RFLs. The operation mechanism of the lasing longitudinal modes and the impact of complex mode competition and mode hopping on the output characteristics are discussed through experimental and theoretical results. In this study, we unveil an artificial random feedback structure and pave another way for the realization of RFLs, which should be a platform for multidisciplinary studies in complex systems.

Neurodegenerative diseases, such as Parkinson&rsquo;s and Alzheimer&rsquo;s diseases, affect the elderly worldwide and will become more prevalent as the global population ages. Neuroinflammation is a common characteristic of neurodegenerative diseases. By regulating the phenotypes of microglia, it is possible to suppress neuroinflammation and, in turn, help prevent neurodegenerative diseases. We report a noninvasive photonic approach to regulating microglia from overexcited M1/M2 to the resting M0 phenotype using a special near-infrared (NIR) light emitted by the SrGa12O19 : Cr3 + phosphor. The absorbance and internal and external quantum efficiencies of the optimal Sr ( Ga0.99Cr0.01)12O19 phosphor synthesized at 1400&deg;C for 8 h using 1 % H3BO3 + 1 % AlF3 as flux are 53.9 % , 99.2 % , and 53.5 % ; the output power and energy-conversion efficiency of the LED device packaged using the optimal SrGa12O19 : Cr3 + phosphor driven at 20 mA reach unprecedentedly 19.69 mW and 37.58 % , respectively. The broadband emission of the NIR LED device covers the absorption peaks of cytochrome c oxidase well, and the NIR light can efficiently promote the proliferation of microglia, produce adenosine triphosphate (ATP), reverse overexcitation, alleviate and inhibit inflammation, and improve cell survival rate and activity, showing great prospects for photomedicine application.

We propose a joint look-up-table (LUT)-based nonlinear predistortion and digital resolution enhancement scheme to achieve high-speed and low-cost optical interconnects using low-resolution digital-to-analog converters (DACs). The LUT-based predistortion is employed to mitigate the pattern-dependent effect (PDE) of a semiconductor optical amplifier (SOA), while the digital resolution enhancer (DRE) is utilized to shape the quantization noise, lowering the requirement for the resolution of DAC. We experimentally demonstrate O-band intensity modulation and direct detection (IM/DD) transmission of 124-GBd 4 / 6-level pulse-amplitude modulation ( PAM ) -4 / 6 and 112-GBd PAM-8 signals over a 2-km standard single-mode fiber (SSMF) with 3 / 3.5 / 4-bit DACs. In the case of 40-km SSMF transmission with an SOA-based preamplifier, 124-GBd on-off-keying (OOK)/PAM-3/PAM-4 signals are successfully transmitted with 1.5 / 2 / 3-bit DACs. To the best of our knowledge, we have achieved the highest net data rates of 235.3-Gb / s PAM-4, 289.7-Gb / s PAM-6, and 294.7 Gb / s PAM-8 signals over 2-km SSMF, as well as 117.6-Gb / s OOK, 173.8-Gb / s PAM-3, and -231.8 Gb / s PAM-4 signals over 40-km SSMF, employing low-resolution DACs. The experimental results reveal that the joint LUT-based predistortion and DRE effectively mitigate the PDE and improve the signal-to-quantization noise ratio by shaping the noise. The proposed scheme can provide a powerful solution for low-cost IM/DD optical interconnects beyond 200 Gb / s.

Moiré superlattices, a twisted functional structure crossing the periodic and nonperiodic potentials, have recently attracted great interest in multidisciplinary fields, including optics and ultracold atoms, because of their unique band structures, physical properties, and potential implications. Driven by recent experiments on quantum phenomena of bosonic gases, the atomic Bose–Einstein condensates in moiré optical lattices, by which other quantum gases such as ultracold fermionic atoms are trapped, could be readily achieved in ultracold atom laboratories, whereas the associated nonlinear localization mechanism remains unexploited. Here, we report the nonlinear localization theory of ultracold atomic Fermi gases in two-dimensional moiré optical lattices. The linear Bloch-wave spectrum of such a twisted structure exhibits rich nontrivial flat bands, which are separated by different finite bandgaps wherein the existence, properties, and dynamics of localized superfluid Fermi gas structures of two types, gap solitons and gap vortices (topological modes) with vortex charge S = 1, are studied numerically. Our results demonstrate the wide stability regions and robustness of these localized structures, opening up a new avenue for studying soliton physics and moiré physics in ultracold atoms beyond bosonic gases.

Light-field fluorescence microscopy (LFM) is a powerful elegant compact method for long-term high-speed imaging of complex biological systems, such as neuron activities and rapid movements of organelles. LFM experiments typically generate terabytes of image data and require a substantial amount of storage space. Some lossy compression algorithms have been proposed recently with good compression performance. However, since the specimen usually only tolerates low-power density illumination for long-term imaging with low phototoxicity, the image signal-to-noise ratio (SNR) is relatively low, which will cause the loss of some efficient position or intensity information using such lossy compression algorithms. Here, we propose a phase-space continuity-enhanced bzip2 (PC-bzip2) lossless compression method for LFM data as a high-efficiency and open-source tool that combines graphics processing unit-based fast entropy judgment and multicore-CPU-based high-speed lossless compression. Our proposed method achieves almost 10% compression ratio improvement while keeping the capability of high-speed compression, compared with the original bzip2. We evaluated our method on fluorescence beads data and fluorescence staining cells data with different SNRs. Moreover, by introducing temporal continuity, our method shows the superior compression ratio on time series data of zebrafish blood vessels.

Valley topological photonic crystals (TPCs), which are robust against local disorders and structural defects, have attracted great research interest, from theoretical verification to technical applications. However, previous works mostly focused on the robustness of topologically protected edge states and little attention was paid to the importance of the photonic bandgaps (PBGs), which hinders the implementation of various multifrequency functional topological photonic devices. Here, by systematically studying the relationship between the degree of symmetry breaking and the working bandwidth of the edge states, we present spoof surface plasmon polariton valley TPCs with broadband edge states and engineered PBGs, where the operation frequency is easy to adjust. Furthermore, by connecting valley TPCs operating at different frequencies, a broadband multifunctional frequency-dependent topological photonic device with selectively directional light transmission is fabricated and experimentally demonstrated, achieving the functions of wavelength division multiplexing and add–drop multiplexing. We provide an effective and insightful method for building multi-frequency topological photonic devices.

Orbital-angular-momentum (OAM) multiplexing technology offers a significant dimension to enlarge communication capacity in free-space optical links. The coherent beam combining (CBC) system can simultaneously realize OAM multiplexing and achieve high-power laser output, providing substantial advantages for long-distance communication. Herein, we present an integrated CBC system for free-space optical links based on OAM multiplexing and demultiplexing technologies for the first time, to the best of our knowledge. A method to achieve flexible OAM multiplexing and efficient demultiplexing based on the CBC system is proposed and demonstrated both theoretically and experimentally. The experimental results exhibit a low bit error rate of 0.47% and a high recognition precision of 98.58% throughout the entire data transmission process. By employing such an ingenious strategy, this work holds promising prospects for enriching ultra-long-distance structured light communication in the future.

Compressing all the energy of a laser pulse into a spatiotemporal focal cube edged by the laser center wavelength will realize the highest intensity of an ultra-intense ultrashort laser, which is called the λ3 regime or the λ3 laser. Herein, we introduced a rotational hyperbolic mirror—an important rotational conic section mirror with two foci—that is used as a secondary focusing mirror after a rotational parabolic mirror to reduce the focal spot size from several wavelengths to a single wavelength by significantly increasing the focusing angular aperture. Compared with the rotational ellipsoidal mirror, the first focal spot with a high intensity, as well as some unwanted strong-field effects, is avoided. The optimal focusing condition of this method is presented and the enhanced tight focusing for a femtosecond petawatt laser and the λ3 laser is numerically simulated, which can enhance the focused intensities of ultra-intense ultrashort lasers for laser physics.

Holographic display stands as a prominent approach for achieving lifelike three-dimensional (3D) reproductions with continuous depth sensation. However, the generation of a computer-generated hologram (CGH) always relies on the repetitive computation of diffraction propagation from point-cloud or multiple depth-sliced planar images, which inevitably leads to an increase in computational complexity, making real-time CGH generation impractical. Here, we report a new CGH generation algorithm capable of rapidly synthesizing a 3D hologram in only one-step backward propagation calculation in a novel split Lohmann lens-based diffraction model. By introducing an extra predesigned virtual digital phase modulation of multifocal split Lohmann lens in such a diffraction model, the generated CGH appears to reconstruct 3D scenes with accurate accommodation abilities across the display contents. Compared with the conventional layer-based method, the computation speed of the proposed method is independent of the quantized layer numbers, and therefore can achieve real-time computation speed with a very dense of depth sampling. Both simulation and experimental results validate the proposed method.

A 60-mW solid-state deep ultraviolet (DUV) laser at 193 nm with narrow linewidth is obtained with two stages of sum frequency generation in LBO crystals. The pump lasers, at 258 and 1553 nm, are derived from a homemade Yb-hybrid laser employing fourth-harmonic generation and Er-doped fiber laser, respectively. The Yb-hybrid laser, finally, is power scaling by a 2 mm × 2 mm × 30 mm Yb:YAG bulk crystal. Accompanied by the generated 220-mW DUV laser at 221 nm, the 193-nm laser delivers an average power of 60 mW with a pulse duration of 4.6 ns, a repetition rate of 6 kHz, and a linewidth of ∼640 MHz. To the best of our knowledge, this is the highest power of 193- and 221-nm laser generated by an LBO crystal ever reported as well as the narrowest linewidth of 193-nm laser by it. Remarkably, the conversion efficiency reaches 27% for 221 to 193 nm and 3% for 258 to 193 nm, which are the highest efficiency values reported to date. We demonstrate the huge potential of LBO crystals for producing hundreds of milliwatt or even watt level 193-nm laser, which also paves a brand-new way to generate other DUV laser wavelengths.

The pseudo-magnetic field, an artificial synthetic gauge field, has attracted intense research interest in the classical wave system. The strong pseudo-magnetic field is realized in a two-dimensional photonic crystal (PhC) by introducing the uniaxial linear gradient deformation. The emergence of the pseudo-magnetic field leads to the quantization of Landau levels. The quantum-Hall-like edge states between adjacent Landau levels are observed in our designed experimental implementation. The combination of two reversed gradient PhCs gives rise to the spatially nonuniform pseudo-magnetic field. The propagation of the large-area edge state and the interesting phenomenon of the snake state induced by the nonuniform pseudo-magnetic field is experimentally demonstrated in a PhC heterostructure. This provides a good platform to manipulate the transport of electromagnetic waves and to design useful devices for information processing.

Non-line-of-sight (NLOS) imaging has emerged as a prominent technique for reconstructing obscured objects from images that undergo multiple diffuse reflections. This imaging method has garnered significant attention in diverse domains, including remote sensing, rescue operations, and intelligent driving, due to its wide-ranging potential applications. Nevertheless, accurately modeling the incident light direction, which carries energy and is captured by the detector amidst random diffuse reflection directions, poses a considerable challenge. This challenge hinders the acquisition of precise forward and inverse physical models for NLOS imaging, which are crucial for achieving high-quality reconstructions. In this study, we propose a point spread function (PSF) model for the NLOS imaging system utilizing ray tracing with random angles. Furthermore, we introduce a reconstruction method, termed the physics-constrained inverse network (PCIN), which establishes an accurate PSF model and inverse physical model by leveraging the interplay between PSF constraints and the optimization of a convolutional neural network. The PCIN approach initializes the parameters randomly, guided by the constraints of the forward PSF model, thereby obviating the need for extensive training data sets, as required by traditional deep-learning methods. Through alternating iteration and gradient descent algorithms, we iteratively optimize the diffuse reflection angles in the PSF model and the neural network parameters. The results demonstrate that PCIN achieves efficient data utilization by not necessitating a large number of actual ground data groups. Moreover, the experimental findings confirm that the proposed method effectively restores the hidden object features with high accuracy.

A designed visual geometry group (VGG)-based convolutional neural network (CNN) model with small computational cost and high accuracy is utilized to monitor pulse amplitude modulation-based intensity modulation and direct detection channel performance using eye diagram measurements. Experimental results show that the proposed technique can achieve a high accuracy in jointly monitoring modulation format, probabilistic shaping, roll-off factor, baud rate, optical signal-to-noise ratio, and chromatic dispersion. The designed VGG-based CNN model outperforms the other four traditional machine-learning methods in different scenarios. Furthermore, the multitask learning model combined with MobileNet CNN is designed to improve the flexibility of the network. Compared with the designed VGG-based CNN, the MobileNet-based MTL does not need to train all the classes, and it can simultaneously monitor single parameter or multiple parameters without sacrificing accuracy, indicating great potential in various monitoring scenarios.

The optical rogue wave (RW), known as a short-lived extraordinarily high amplitude dynamics phenomenon with small appearing probabilities, plays an important role in revealing and understanding the fundamental physics of nonlinear wave propagations in optical systems. The random fiber laser (RFL), featured with cavity-free and “modeless” structure, has opened up new avenues for fundamental physics research and potential practical applications combining nonlinear optics and laser physics. Here, the extreme event of optical RW induced by noise-driven modulation instability that interacts with the cascaded stimulated Brillouin scattering, the quasi-phase-matched four-wave mixing as well as the random mode resonance process is observed in a Brillouin random fiber laser comb (BRFLC). Temporal and statistical characteristics of the RWs concerning their emergence and evolution are experimentally explored and analyzed. Specifically, temporally localized structures with high intensities including chair-like pulses with a sharp leading edge followed by a trailing plateau appear frequently in the BRFLC output, which can evolve to chair-like RW pulses with adjustable pulse duration and amplitude under controlled conditions. This investigation provides a deep insight into the extreme event of RWs and paves the way for RW manipulation for its generation and elimination in RFLs through adapted laser configuration.

On-chip diffractive optical neural networks (DONNs) bring the advantages of parallel processing and low energy consumption. However, an accurate representation of the optical field’s evolution in the structure cannot be provided using the previous diffraction-based analysis method. Moreover, the loss caused by the open boundaries poses challenges to applications. A multimode DONN architecture based on a more precise eigenmode analysis method is proposed. We have constructed a universal library of input, output, and metaline structures utilizing this method, and realized a multimode DONN composed of the structures from the library. On the designed multimode DONNs with only one layer of the metaline, the classification task of an Iris plants dataset is verified with an accuracy of 90% on the blind test dataset, and the performance of the one-bit binary adder task is also validated. Compared to the previous architectures, the multimode DONN exhibits a more compact design and higher energy efficiency.

Chiral sum-frequency generation (SFG) has proven to be a versatile spectroscopic and imaging tool for probing chirality. However, due to polarization restriction, the conventional chiral SFG microscopes have mostly adopted noncollinear beam configurations, which only partially cover the aperture of microscope and strongly spoil the spatial resolution. In this study, we report the first experimental demonstration of collinear chiral SFG microscopy, which fundamentally supports diffraction-limited resolution. This advancement is attributed to the collinear focus of a radially polarized vectorial beam and a linearly polarized (LP) beam. The tightly focused vectorial beam has a very strong longitudinal component, which interacts with the LP beam and produces the chiral SFG. The collinear configuration can utilize the full aperture and thus push the spatial resolution close to the diffraction limit. This technique can potentially boost the understanding of chiral systems.

Optical metasurfaces, which consist of subwavelength scale meta-atoms, represent a novel platform to manipulate the polarization and phase of light. The optical performance of metasurfaces heavily relies on the quality of nanofabrication. Retrieving the Jones matrix of an imperfect metasurface optical element is highly desirable. We show that this can be realized by decomposing the generalized Jones matrix of a meta-atom into two parallel ones, which correspond to the ideal matrix and a phase retardation. To experimentally verify this concept, we designed and fabricated metasurface polarizers, which consist of geometric phase-controlled dielectric meta-atoms. By scanning the polarization states of the incident and transmitted light, we are able to extract the coefficients of the two parallel matrices of a metasurface polarizer. Based on the results of the Jones matrix decomposition, we also demonstrated polarization image encryption and spin-selective optical holography. The proposed Jones matrix retrieval protocol may have important applications in computational imaging, optical computing, optical communications, and so on.

Although visible femtosecond lasers based on nonlinear frequency conversion of Ti:sapphire femtosecond oscillators or near-infrared ultrafast lasers have been well developed, limitations in terms of footprint, cost, and efficiency have called for alternative laser solutions. The fiber femtosecond mode-locked oscillator as an ideal solution has achieved great success in the 0.9 to 3.5 μm infrared wavelengths, but remains an outstanding challenge in the visible spectrum (390 to 780 nm). Here, we tackle this challenge by introducing a visible-wavelength mode-locked femtosecond fiber oscillator along with an amplifier. This fiber femtosecond oscillator emits red light at 635 nm, employs a figure-nine cavity configuration, applies a double-clad Pr3 + -doped fluoride fiber as the visible gain medium, incorporates a visible-wavelength phase-biased nonlinear amplifying loop mirror (PB-NALM) for mode locking, and utilizes a pair of customized high-efficiency and high-groove-density diffraction gratings for dispersion management. Visible self-starting mode locking established by the PB-NALM directly yields red laser pulses with a minimum pulse duration of 196 fs and a repetition rate of 53.957 MHz from the oscillator. Precise control of the grating pair spacing can switch the pulse state from a dissipative soliton or a stretched-pulse soliton to a conventional soliton. In addition, a chirped-pulse amplification system built alongside the oscillator immensely boosts the laser performance, resulting in an average output power over 1 W, a pulse energy of 19.55 nJ, and a dechirped pulse duration of 230 fs. Our result represents a concrete step toward high-power femtosecond fiber lasers covering the visible spectral region and could have important applications in industrial processing, biomedicine, and scientific research.

A pin-like beam is a kind of structured light with a special intensity distribution that can be against diffraction, which can be seen as a kind of quasi-nondiffracting beam (Q-NDB). Due to its wide applications, recently, numerous researchers have used optical lenses or on-chip integrated optical diffractive elements to generate this kind of beam. We theoretically verify and experimentally demonstrate an all-fiber solution to generate a subwavelength inverted pin beam by integrating a simple plasma structure on the fiber end surface. The output beams generated by two kinds of plasma structures, i.e., nanoring slot and nanopetal structure, are investigated and measured experimentally. The results show that both the structures are capable of generating subwavelength beams, and the beam generated using the nanopetal structure has the sidelobe suppression ability along the x-axis direction. Our all-fiber device can be flexibly inserted into liquid environments such as cell cultures, blood, and biological tissue fluids to illuminate or stimulate biological cells and molecules in them. It provides a promising fiber-integrated solution for exploring light–matter interaction with subwavelength resolution in the field of biological research.

Recently, deep learning has been used to establish the nonlinear and nonintuitive mapping between physical structures and electromagnetic responses of meta-atoms for higher computational efficiency. However, to obtain sufficiently accurate predictions, the conventional deep-learning-based method consumes excessive time to collect the data set, thus hindering its wide application in this interdisciplinary field. We introduce a spectral transfer-learning-based metasurface design method to achieve excellent performance on a small data set with only 1000 samples in the target waveband by utilizing open-source data from another spectral range. We demonstrate three transfer strategies and experimentally quantify their performance, among which the “frozen-none” robustly improves the prediction accuracy by ∼26 % compared to direct learning. We propose to use a complex-valued deep neural network during the training process to further improve the spectral predicting precision by ∼30 % compared to its real-valued counterparts. We design several typical teraherz metadevices by employing a hybrid inverse model consolidating this trained target network and a global optimization algorithm. The simulated results successfully validate the capability of our approach. Our work provides a universal methodology for efficient and accurate metasurface design in arbitrary wavebands, which will pave the way toward the automated and mass production of metasurfaces.

Shaping the light beam is always essential for laser technology and its applications. Among the shaping technologies, shaping the laser in its Fourier domain is a widely used and effective method, such as a pulse shaper, or a 4f system with a phase mask or an iris in between. Orbital angular momentum (OAM) modes spectrum, the Fourier transform of the light field in azimuth, provides a perspective for shaping the light. Here, we propose and experimentally demonstrate a shaping strategy for the azimuthal field by modulating the complex amplitude of the OAM mode spectrum. The scheme utilizes multi-plane light conversion technology and consists only of a spatial light modulator and a mirror. Multiple functions, including beam rotating, beam splitting/combining in azimuth, and OAM mode filtering, are demonstrated. Our work provides a compact and programmable solution for modulating the OAM mode spectrum and shaping beams in azimuth.

We present a unified electromagnetic modeling of coherence scanning interferometry, confocal microscopy, and focus variation microscopy as the most common techniques for surface topography inspection with micro- and nanometer resolution. The model aims at analyzing the instrument response and predicting systematic deviations. Since the main focus lies on the modeling of the microscopes, the light–surface interaction is considered, based on the Kirchhoff approximation extended to vectorial imaging theory. However, it can be replaced by rigorous methods without changing the microscope model. We demonstrate that all of the measuring instruments mentioned above can be modeled using the same theory with some adaption to the respective instrument. For validation, simulated results are confirmed by comparison with measurement results.

This study introduces a handheld terahertz (THz) scanner designed to quantitatively evaluate human skin hydration levels and thickness. This device, through the incorporation of force sensors, demonstrates enhanced repeatability and accuracy over traditional fixed THz systems. The scanner was evaluated in the largest THz skin study to date, assessing 314 volunteers, successfully differentiating between individuals with dry skin and hydrated skin using a numerical stratified skin model. The scanner measures and displays skin hydration dynamics within a quarter of a second, indicating its potential for real-time, noninvasive examinations, opening up opportunities for in vivo and ex vivo diagnosis during patient consultations. Furthermore, the portability and ease of use of our scanner enable its widespread application for in vivo and ex vivo diagnosis during patient consultations, potentially allowing in situ biopsy evaluation and elimination of histopathology processing wait times, thereby improving patient outcomes by facilitating simultaneous tumor diagnosis and removal.

Quantum technologies rely on creating and manipulating entangled sources, which are essential for quantum information, communication, and imaging. By integrating quantum technologies and all-dielectric metasurfaces, the performance of miniature display devices can be enhanced to a higher level. Miniature display technology, such as virtual reality display, has achieved original commercial success, and was initially applied to immersive games and interactive scenes. While the consumer market has quickly adopted this technology, several areas remain for improvement, including concerns around bulkiness, dual-channel display, and noise reduction. Here, we experimentally realize a quantum meta-hologram concept demonstration of a miniature display. We fabricate an ultracompact meta-hologram based on 1 μm thick titanium dioxide (TiO2). The meta-hologram can be remotely switched with heralding technique and is robust against noise with the quantum entangled source. The platform can alter the miniature display channel by manipulating heralding photons’ polarization, removing speckles and multiple reflective light noise, improving imaging contrast, and potentially decreasing device weight. Imaging contrast increases from 0.36 dB under speckle noise influences to 6.8 dB in quantum correlation imaging. This approach has the potential to miniaturize quantum displays and quantum communication devices.

As an optical processor, a diffractive deep neural network (D2NN) utilizes engineered diffractive surfaces designed through machine learning to perform all-optical information processing, completing its tasks at the speed of light propagation through thin optical layers. With sufficient degrees of freedom, D2NNs can perform arbitrary complex-valued linear transformations using spatially coherent light. Similarly, D2NNs can also perform arbitrary linear intensity transformations with spatially incoherent illumination; however, under spatially incoherent light, these transformations are nonnegative, acting on diffraction-limited optical intensity patterns at the input field of view. Here, we expand the use of spatially incoherent D2NNs to complex-valued information processing for executing arbitrary complex-valued linear transformations using spatially incoherent light. Through simulations, we show that as the number of optimized diffractive features increases beyond a threshold dictated by the multiplication of the input and output space-bandwidth products, a spatially incoherent diffractive visual processor can approximate any complex-valued linear transformation and be used for all-optical image encryption using incoherent illumination. The findings are important for the all-optical processing of information under natural light using various forms of diffractive surface-based optical processors.

Unlike conventional topological edge states confined at a domain wall between two topologically distinct media, the recently proposed large-area topological waveguide states in three-layer heterostructures, which consist of a domain featuring Dirac points sandwiched between two domains of different topologies, have introduced the mode width degree of freedom for more flexible manipulation of electromagnetic waves. Until now, the experimental realizations of photonic large-area topological waveguide states have been exclusively based on quantum Hall and quantum valley-Hall systems. We propose a new way to create large-area topological waveguide states based on the photonic quantum spin-Hall system and observe their unique feature of pseudo-spin-momentum-locking unidirectional propagation for the first time in experiments. Moreover, due to the new effect provided by the mode width degree of freedom, the propagation of these large-area quantum spin-Hall waveguide states exhibits unusually strong robustness against defects, e.g., large voids with size reaching several unit cells, which has not been reported previously. Finally, practical applications, such as topological channel intersection and topological energy concentrator, are further demonstrated based on these novel states. Our work not only completes the last member of such states in the photonic quantum Hall, quantum valley-Hall, and quantum spin-Hall family, but also provides further opportunities for high-capacity energy transport with tunable mode width and exceptional robustness in integrated photonic devices and on-chip communications.

A supercontinuum white laser with ultrabroad bandwidth, intense pulse energy, and high spectral flatness can be accomplished via synergic action of third-order nonlinearity (3rd-NL) and second-order nonlinearity. In this work, we employ an intense Ti:sapphire femtosecond laser with a pulse duration of 50 fs and pulse energy up to 4 mJ to ignite the supercontinuum white laser. Remarkably, we use water instead of the usual solid materials as the 3rd-NL medium exhibiting both strong self-phase modulation and stimulated Raman scattering effect to create a supercontinuum laser with significantly broadened bandwidth and avoid laser damage and destruction. Then the supercontinuum laser is injected into a water-embedded chirped periodically poled lithium niobate crystal that enables broadband and high-efficiency second-harmonic generation. The output white laser has a 10 dB bandwidth encompassing 413 to 907 nm, more than one octave, and a pulse energy of 0.6 mJ. This methodology would open up an efficient route to creating a long-lived, high-stability, and inexpensive white laser with intense pulse energy, high spectral flatness, and ultrabroad bandwidth for application to various areas of basic science and high technology.

Carbon-based materials, such as graphene and carbon nanotubes, have emerged as a transformative class of building blocks for state-of-the-art metamaterial devices due to their excellent flexibility, light weight, and tunability. In this work, a tunable carbon-based metal-free terahertz (THz) metasurface with ultrabroadband absorption is proposed, composed of alternating graphite and graphene patterns, where the Fermi level of graphene is adjusted by varying the applied voltage bias to achieve the tunable ultrabroadband absorption characteristics. In particular, when the Fermi level of graphene is 1 eV, the absorption coefficient exceeds 90% from 7.24 through 16.23 THz, and importantly, the absorption bandwidth reaches as much as 8.99 THz. In addition, it is polarization-insensitive to incident waves and maintains a high absorption rate at an incident angle of up to 50 deg. This carbon-based device enjoys higher absorption bandwidth, rates, and performance compared to conventional absorbers in the THz regime and can be potentially applied in various fields, including THz wave sensing, modulation, as well as wearable health care devices, and biomedicine detection.

Mode-division multiplexers (MDMUXs) play a pivotal role in enabling the manipulation of an arbitrary optical state within few-mode fibers, offering extensive utility in the fields of mode-division multiplexing and structured optical field engineering. The exploration of MDMUXs employing cascaded resonant couplers has garnered significant attention owing to their scalability, exceptional integration capabilities, and the anticipated low insertion loss. In this work, we present the successful realization of high-quality orbital angular momentum MDMUX corresponding to topological charges 0, ±1, and ±2, achieved through the utilization of cascaded fused-biconical tapered couplers. Notably, the measured insertion losses at 1550 nm exhibit remarkable minimal values: 0.31, 0.10, and 0.64 dB, respectively. Furthermore, the 80% efficiency bandwidths exceed 106, 174, and 174 nm for these respective modes. The MDMUX is composed of precision-manufactured high-quality mode selective couplers (MSCs). Utilizing a proposed supermode propagation method based on mode composition analysis, we precisely describe the operational characteristics of MSCs. Building upon this comprehensive understanding, we embark on a pioneering analysis elucidating the influence of MSC cascading order on the performance of MDMUXs. Our theoretical investigation substantiates that when constructing MDMUXs, MSCs should adhere to a specific cascading sequence.

The use of orbital angular momentum (OAM) as an independent dimension for information encryption has garnered considerable attention. However, the multiplexing capacity of OAM is limited, and there is a need for additional dimensions to enhance storage capabilities. We propose and implement orbital angular momentum lattice (OAML) multiplexed holography. The vortex lattice (VL) beam comprises three adjustable parameters: the rotation angle of the VL, the angle between the wave normal and the z axis, which determines the VL’s dimensions, and the topological charge. Both the rotation angle and the VL’s dimensions serve as supplementary encrypted dimensions, contributing azimuthally and radially, respectively. We investigate the mode selectivity of OAML and focus on the aforementioned parameters. Through experimental validation, we demonstrate the practical feasibility of OAML multiplexed holography across multiple dimensions. This groundbreaking development reveals new possibilities for the advancement of practical information encryption systems.

Orbital angular momentum (OAM), described by an azimuthal phase term exp ( jlθ ) , has unbound orthogonal states with different topological charges l. Therefore, with the explosive growth of global communication capacity, especially for short-distance optical interconnects, light-carrying OAM has proved its great potential to improve transmission capacity and spectral efficiency in the space-division multiplexing system due to its orthogonality, security, and compatibility with other techniques. Meanwhile, 100-m free-space optical interconnects become an alternative solution for the “last mile” problem and provide interbuilding communication. We experimentally demonstrate a 260-m secure optical interconnect using OAM multiplexing and 16-ary quadrature amplitude modulation (16-QAM) signals. We study the beam wandering, power fluctuation, channel cross talk, bit-error-rate performance, and link security. Additionally, we also investigate the link performance for 1-to-9 multicasting at the range of 260 m. Considering that the power distribution may be affected by atmospheric turbulence, we introduce an offline feedback process to make it flexibly controllable.

Chaotic optical communication has shown large potential as a hardware encryption method in the physical layer. As an important figure of merit, the bit rate–distance product of chaotic optical communication has been continually improved to 30 Gb/s × 340 km, but it is still far from the requirement for a deployed optical fiber communication system, which is beyond 100 Gb/s × 1000 km. A chaotic carrier can be considered as an analog signal and suffers from fiber channel impairments, limiting the transmission distance of high-speed chaotic optical communications. To break the limit, we propose and experimentally demonstrate a pilot-based digital signal processing scheme for coherent chaotic optical communication combined with deep-learning-based chaotic synchronization. Both transmission impairment recovery and chaotic synchronization are realized in the digital domain. The frequency offset of the lasers is accurately estimated and compensated by determining the location of the pilot tone in the frequency domain, and the equalization and phase noise compensation are jointly performed by the least mean square algorithm through the time domain pilot symbols. Using the proposed method, 100 Gb / s chaotically encrypted quadrature phase-shift keying (QPSK) signal over 800 km single-mode fiber (SMF) transmission is experimentally demonstrated. In order to enhance security, 40 Gb / s real-time chaotically encrypted QPSK signal over 800 km SMF transmission is realized by inserting pilot symbols and tone in a field-programmable gate array. This method provides a feasible approach to promote the practical application of chaotic optical communications and guarantees the high security of chaotic encryption.

Spatiotemporal shaping of ultrashort pulses is pivotal for various technologies, such as burst laser ablation and ultrafast imaging. However, the difficulty of pulse stretching to subnanosecond intervals and independent control of the spatial profile for each pulse limit their advancement. We present a pulse manipulation technique for producing spectrally separated GHz burst pulses from a single ultrashort pulse, where each pulse is spatially shapable. We demonstrated the production of pulse trains at intervals of 0.1 to 3 ns in the 800- and 400-nm wavelength bands and applied them to ultrafast single-shot transmission spectroscopic imaging (4 Gfps) of laser ablation dynamics with two-color sequentially timed all-optical mapping photography. Furthermore, we demonstrated the production of pulse trains containing a shifted or dual-peak pulse as examples of individual spatial shaping of GHz burst pulses. Our proposed technique brings unprecedented spatiotemporal manipulation of GHz burst pulses, which can be useful for a wide range of laser applications.

In recent years, notable progress has been achieved in both the hardware and algorithms of structured illumination microscopy (SIM). Nevertheless, the advancement of three-dimensional structured illumination microscopy (3DSIM) has been impeded by challenges arising from the speed and intricacy of polarization modulation. We introduce a high-speed modulation 3DSIM system, leveraging the polarization-maintaining and modulation capabilities of a digital micromirror device (DMD) in conjunction with an electro-optic modulator. The DMD-3DSIM system yields a twofold enhancement in both lateral (133 nm) and axial (300 nm) resolution compared to wide-field imaging and can acquire a data set comprising 29 sections of 1024 pixels × 1024 pixels, with 15 ms exposure time and 6.75 s per volume. The versatility of the DMD-3DSIM approach was exemplified through the imaging of various specimens, including fluorescent beads, nuclear pores, microtubules, actin filaments, and mitochondria within cells, as well as plant and animal tissues. Notably, polarized 3DSIM elucidated the orientation of actin filaments. Furthermore, the implementation of diverse deconvolution algorithms further enhances 3D resolution. The DMD-based 3DSIM system presents a rapid and reliable methodology for investigating biomedical phenomena, boasting capabilities encompassing 3D superresolution, fast temporal resolution, and polarization imaging.

After reaching a world record of 10 PW, the peak power development of the titanium-sapphire (Ti:sapphire) PW ultraintense lasers has hit a bottleneck, and it seems to be difficult to continue increasing due to the difficulty of manufacturing larger Ti:sapphire crystals and the limitation of parasitic lasing that can consume stored pump energy. Unlike coherent beam combining, coherent Ti:sapphire tiling is a viable solution for expanding Ti:sapphire crystal sizes, truncating transverse amplified spontaneous emission, suppressing parasitic lasing, and, importantly, not requiring complex space-time tiling control. A theoretical analysis of the above features and an experimental demonstration of high-quality laser amplification are reported. The results show that the addition of a 2 × 2 tiled Ti:sapphire amplifier to today’s 10 PW ultraintense laser is a viable technique to break the 10 PW limit and directly increase the highest peak power recorded by a factor of 4, further approaching the exawatt class.

Space–time metasurfaces are promising candidates for breaking Lorentz reciprocity, which constrains light propagation in numerous practical applications. There is a substantial difference between carrier and modulation frequencies in space–time photonic metasurfaces that leads to negligible spatial pathway variation of light and weak nonreciprocal response. To surmount this obstacle, herein, the design principle of a high-quality-factor space–time gradient metasurface is demonstrated at the near-infrared regime that increases the lifetime of photons and allows for strong power isolation by lifting the adiabaticity of modulation. The all-dielectric metasurface consists of an array of silicon subwavelength gratings (SWGs) that are separated from distributed Bragg reflectors by a silica buffer. The resonant mode with ultrahigh quality-factor exceeding 104 is excited within the SWG, which is characterized as magnetic octupole and features strong field localization. The SWGs are configured as multijunction p–n layers, whose multigate biasing with time-varying waveforms enables modulation of carriers in space and time. The proposed nonreciprocal metasurface is exploited for free-space optical power isolation by virtue of modulation-induced phase shift. It is shown that under time reversal and by interchanging the directions of incident and observation ports, power isolation of ≈35 dB can be maintained between the two ports in free space.

Breathing solitons, i.e., dynamic dissipative solitons with oscillating pulse shape and energy caused by different mechanisms of spatiotemporal instabilities, have received considerable interest from the aspects of nonlinear science and potential applications. However, by far, the study of breathing solitons is still limited within the time scale of hundreds of cavity round trips, which ignores the slow dynamics. To fill this lacuna, we theoretically investigate a new type of vector dissipative soliton breathing regime and experimentally demonstrate this concept using mode-locked fiber lasers, which arise from the desynchronization of orthogonal states of polarization (SOPs) in the form of complex oscillations of the phase difference between the states. The dynamic evolution of polarization states of the vector breathings solitons takes the form of a trajectory connecting two quasi-equilibrium orthogonal SOPs on the surface of the Poincaré sphere. The dwelling time near each state is on the scale of a tenth of a thousand cavity round trip times that equals the breathing period, which is up to 2 orders of magnitude longer than that for common breathers. The obtained results can reveal concepts in nonlinear science and may unlock approaches to the flexible manipulation of laser waveforms toward various applications in spectroscopy and metrology.

As a successful case of combining deep learning with photonics, the research on optical machine learning has recently undergone rapid development. Among various optical classification frameworks, diffractive networks have been shown to have unique advantages in all-optical reasoning. As an important property of light, the orbital angular momentum (OAM) of light shows orthogonality and mode-infinity, which can enhance the ability of parallel classification in information processing. However, there have been few all-optical diffractive networks under the OAM mode encoding. Here, we report a strategy of OAM-encoded diffractive deep neural network (OAM-encoded D2NN) that encodes the spatial information of objects into the OAM spectrum of the diffracted light to perform all-optical object classification. We demonstrated three different OAM-encoded D2NNs to realize (1) single detector OAM-encoded D2NN for single task classification, (2) single detector OAM-encoded D2NN for multitask classification, and (3) multidetector OAM-encoded D2NN for repeatable multitask classification. We provide a feasible way to improve the performance of all-optical object classification and open up promising research directions for D2NN by proposing OAM-encoded D2NN.

Transmission matrix (TM) allows light control through complex media, such as multimode fibers (MMFs), gaining great attention in areas, such as biophotonics, over the past decade. Efforts have been taken to retrieve a complex-valued TM directly from intensity measurements with several representative phase-retrieval algorithms, which still see limitations of slow or suboptimum recovery, especially under noisy environments. Here, we propose a modified nonconvex optimization approach. Through numerical evaluations, it shows that the optimum focusing efficiency is approached with less running time or sampling ratio. The comparative tests under different signal-to-noise levels further indicate its improved robustness. Experimentally, the superior focusing performance of our algorithm is collectively validated by single- and multispot focusing; especially with a sampling ratio of 8, it achieves a 93.6% efficiency of the gold-standard holography method. Based on the recovered TM, image transmission through an MMF is realized with high fidelity. Due to parallel operation and GPU acceleration, our nonconvex approach retrieves a 8685 × 1024 TM (sampling ratio is 8) with 42.3 s on average on a regular computer. The proposed method provides optimum efficiency and fast execution for TM retrieval that avoids the need for an external reference beam, which will facilitate applications of deep-tissue optical imaging, manipulation, and treatment.

Dealing with the increase in data workloads and network complexity requires efficient selective manipulation of any channels in hybrid mode-/wavelength-division multiplexing (MDM/WDM) systems. A reconfigurable optical add-drop multiplexer (ROADM) using special modal field redistribution is proposed and demonstrated to enable the selective access of any mode-/wavelength-channels. With the assistance of the subwavelength grating structures, the launched modes are redistributed to be the supermodes localized at different regions of the multimode bus waveguide. Microring resonators are placed at the corresponding side of the bus waveguide to have specific evanescent coupling of the redistributed supermodes, so that any mode-/wavelength-channel can be added/dropped by thermally tuning the resonant wavelength. As an example, a ROADM for the case with three mode-channels is designed with low excess losses of <0.6, 0.7, and 1.3 dB as well as low cross talks of < - 26.3, -28.5, and -39.3 dB for the TE0, TE1, and TE2 modes, respectively, around the central wavelength of 1550 nm. The data transmission of 30 Gbps / channel is also demonstrated successfully. The present ROADM provides a promising route for data switching/routing in hybrid MDM/WDM systems.

A miniaturized short-wavelength infrared spectrometer for use with diffuse light was created by combining a thin form factor carbon nanotube composite collimator, a linear variable filter, and an InGaAs photodiode array. The resulting spectrometer measures 3 mm × 4 mm × 14 mm and shows a significant improvement in resolution over a spectrometer without the collimator when used with diffuse light. Its small size and high throughput make it ideal for applications such as wearable optical sensing, where light from highly scattering tissue is measured. Plethysmographic measurements on the wrist were demonstrated, showing rapid data collection with diffuse light.

Ultrashort pulses at 920 nm are a highly desired light source in two-photon microscopy for the efficient excitation of green fluorescence protein. Although Nd3 + -doped fibers have been utilized for 920-nm ultrashort pulse generation, the competitive amplified spontaneous emission (ASE) at 1.06 μm remains a significant challenge in improving their performance. Here, we demonstrate a coordination engineering strategy to tailor the properties of Nd3 + -doped silica glass and fiber. By elevating the covalency between Nd3 + and bonded anions via sulfur incorporation, the fiber gain performance at 920 nm is enhanced, and 1.06-μm ASE intensity is suppressed simultaneously. As a result, the continuous-wave laser efficiencies and signal-to-noise ratio at 920 nm by this fiber are significantly enhanced. Importantly, the stable picosecond pulses at 920 nm are produced by a passive mode-locking technique with a fundamental repetition rate up to 207 MHz, which, to the best of our knowledge, is the highest reported repetition rate realized by Nd3 + -doped silica fibers. The presented strategy enriches the capacity of Nd3 + -doped silica fiber in generating 920-nm ultrashort pulses for application in biophotonics, and it also provides a promising way to tune the properties of rare-earth ion-doped silica glasses and fibers toward ultrafast lasers.

Photonic analogs of the moiré superlattices mediated by interlayer electromagnetic coupling are expected to give rise to rich phenomena, such as nontrivial flatband topology. Here, we propose and demonstrate a scheme to tune the flatbands in a bilayer moiré superlattice by employing a band offset. The band offset is changed by fixing the bands of one slab while shifting those of the other slab, which is accomplished by modifying the thickness of the latter slab. Our results show that the band-offset tuning not only makes some flatbands emerge and disappear but also leads to two sets of flatbands that are robustly formed even with the change of band offset over a broad range. These robust flatbands form either at the AA-stack site or at the AB-stack site, and as a result, a single-cell superlattice can support a pair of high-quality localized modes with tunable frequencies. Moreover, we develop a diagrammatic model to provide an intuitive insight into the formation of the robust flatbands. Our work demonstrates a simple yet efficient way to design and control complex moiré flatbands, providing new opportunities to utilize photonic moiré superlattices for advanced light–matter interaction, including lasing and nonlinear harmonic generation.

Laser processing with high-power ultrashort pulses, which promises high precision and efficiency, is an emerging new tool for material structuring. High repetition rate ultrafast laser highlighting with a higher degree of freedom in its burst mode is believed to be able to create micro/nanostructures with even more variety, which is promising for electrochemical applications. We employ a homemade high repetition rate ultrafast fiber laser for structuring metal nickel (Ni) and thus preparing electrocatalysts for hydrogen evolution reaction (HER) for the first time, we believe. Different processing parameters are designed to create three groups of samples with different micro/nanostructures. The various micro/nanostructures not only increase the surface area of the Ni electrode but also regulate local electric field and help discharge hydrogen bubbles, which offer more favorable conditions for HER. All groups of the laser-structured Ni exhibit enhanced electrocatalytic activity for HER in the alkaline solution. Electrochemical measurements demonstrate that the overpotential at 10 mA cm - 2 can be decreased as much as 182 mV compared with the overpotential of the untreated Ni (-457 mV versus RHE).

Structured illumination-based super-resolution Förster resonance energy transfer microscopy (SIM-FRET) provides an approach to resolving molecular behavior localized in intricate biological structures in living cells. However, SIM reconstruction artifacts will decrease the quantitative analysis fidelity of SIM-FRET signals. To address these issues, we have developed a method called HiFi spectrum optimization SIM-FRET (HiFi-SO-SIM-FRET), which uses optimized Wiener parameters in the two-step spectrum optimization to suppress sidelobe artifacts and achieve super-resolution quantitative SIM-FRET. We validated our method by demonstrating its ability to reduce reconstruction artifacts while maintaining the accuracy of FRET signals in both simulated FRET models and live-cell FRET-standard construct samples. In summary, HiFi-SO-SIM-FRET provides a promising solution for achieving high spatial resolution and reducing SIM reconstruction artifacts in quantitative FRET imaging.

Imaging through multimode fiber (MMF) provides high-resolution imaging through a fiber with cross section down to tens of micrometers. It requires interferometry to measure the full transmission matrix (TM), leading to the drawbacks of complicated experimental setup and phase instability. Reference-less TM retrieval is a promising robust solution that avoids interferometry, since it recovers the TM from intensity-only measurements. However, the long computational time and failure of 3D focusing still limit its application in MMF imaging. We propose an efficient reference-less TM retrieval method by developing a nonlinear optimization algorithm based on fast Fourier transform (FFT). Furthermore, we develop an algorithm to correct the phase offset error of retrieved TM using defocused intensity images and hence achieve 3D focusing. The proposed method is validated by both simulations and experiments. The FFT-based TM retrieval algorithm achieves orders of magnitude of speedup in computational time and recovers 2286 × 8192 TM of a 0.22 NA and 50 μm diameter MMF with 112.9 s by a computer of 32 CPU cores. With the advantages of efficiency and correction of phase offset, our method paves the way for the application of reference-less TM retrieval in not only MMF imaging but also broader applications requiring TM calibration.

A wideband sensitive needle ultrasound sensor based on a polarized PVDF-TrFE copolymer piezoelectric film has been developed, which is capable of providing a noise equivalent pressure of 14 Pa and a uniform frequency response ranging from 1 to 25 MHz. Its high sensitivity (1.6 μV / Pa) and compact size were achieved by capitalizing on the large electromechanical coupling coefficient of PVDF-TrFE and minimizing parasitic capacitance in a two-stage amplifier structure. The detection sensitivity of the newly designed sensor outperformed commercially available hydrophones with an equivalent sensing element area by a factor of 9. The sensor has been successfully integrated into a light scanning optoacoustic microscopy (OAM) system with a limited working space. Submicrometer resolution images were subsequently attained from living mice without employing signal averaging. The miniature sensor design can readily be integrated into various OAM systems and further facilitate multimodal imaging system implementations.

One-dimensional Airy beams allow the generation of thin light-sheets without scanning, simplifying the complex optical arrangements of light-sheet microscopes (LSMs) with an extended field of view (FOV). However, their uniaxial acceleration limits the maximum numerical aperture of the detection objective in order to keep both the active and inactive axes within the depth of field. This problem is particularly pronounced in miniaturized LSM implementations, such as those for endomicroscopy or multi-photon neural imaging in freely moving animals using head-mounted miniscopes. We propose a new method to generate a static Airy light-sheet with biaxial acceleration, based on a novel phase profile. This light-sheet has the geometry of a spherical shell whose radius of curvature can be designed to match the field curvature of the micro-objective. We present an analytical model for the analysis of the light-sheet parameters and verify it by numerical simulations in the paraxial regime. We also discuss a micro-optical experimental implementation combining gradient-index optics with a 3D-nanoprinted, fully refractive phase plate. The results confirm that we are able to match detection curvatures with radii in the range of 1.5 to 2 mm.

Electron–phonon coupling can tailor electronic transition processes and result in direct lasing far beyond the fluorescence spectrum. The applicable time scales of these kinds of multiphonon-assisted lasers determine their scientific boundaries and further developments, since the response speed of lattice vibrations is much slower than that of electrons. At present, the temporal dynamic behavior of multiphonon-assisted lasers has not yet been explored. Herein, we investigate the Q-switched laser performance of ytterbium-doped YCa4O(BO3)3 (Yb:YCOB) crystal with phonon-assisted emission in nanosecond scales. Using different Q-switchers, the three-phonon-assisted lasers around 1130 nm were realized, and a stable Q-switching was realized in the time domain from submicroseconds to tens of nanoseconds. To the best of our knowledge, this is the longest laser wavelength in all pulse Yb lasers. The minimum pulse width and maximum pulse energy are 29 ns and 204 μJ, respectively. These results identify that the electron–phonon coupling is a fast physical process, at least much faster than the present nanosecond pulse width, which supports the operation of multiphonon-assisted lasers in the nanosecond range. In addition, we also provide a simple setup to create pulse lasers at those wavelengths with weak spontaneous emission.

On-chip focusing of plasmons in graded-index lenses is important for imaging, lithography, signal processing, and optical interconnects at the deep subwavelength nanoscale. However, owing to the inherent strong wavelength dispersion of plasmonic materials, the on-chip focusing of plasmons suffers from severe chromatic aberrations. With the well-established planar dielectric grating, a graded-index waveguide array lens (GIWAL) is proposed to support the excitation and propagation of acoustic graphene plasmon polaritons (AGPPs) and to achieve the achromatic on-chip focusing of the AGPPs with a focus as small as about 2% of the operating wavelength in the frequency band from 10 to 20 THz, benefiting from the wavelength-independent index profile of the GIWAL. An analytical theory is provided to understand the on-chip focusing of the AGPPs and other beam evolution behaviors, such as self-focusing, self-collimation, and pendulum effects of Gaussian beams as well as spatial inversions of digital optical signals. Furthermore, the possibility of the GIWAL to invert spatially broadband digital optical signals is demonstrated, indicating the potential value of the GIWAL in broadband digital communication and signal processing.

Metasurfaces have emerged as a flexible platform for shaping the electromagnetic field via the tailoring phase, amplitude, and polarization at will. However, the chromatic aberration inherited from building blocks’ diffractive nature plagues them when used in many practical applications. Current solutions for eliminating chromatic aberration usually rely on searching through many meta-atoms to seek designs that satisfy both phase and phase dispersion preconditions, inevitably leading to intensive design efforts. Moreover, most schemes are commonly valid for incidence with a specific spin state. Here, inspired by the Rayleigh criterion for spot resolution, we present a design principle for broadband achromatic and polarization-insensitive metalenses using two sets of anisotropic nanofins based on phase change material Ge2Sb2Se4Te1. By limiting the rotation angles of all nanofins to either 0 deg or 90 deg, the metalens with a suitable numerical aperture constructed by this fashion allows for achromatic and polarization-insensitive performance across the wavelength range of 4–5 μm, while maintaining high focusing efficiency and diffraction-limited performance. We also demonstrate the versatility of our approach by successfully implementing the generation of broadband achromatic and polarization-insensitive focusing optical vortex. This work represents a major advance in achromatic metalenses and may find more applications in compact and chip-scale devices.

The photosensitivity of silicon is inherently very low in the visible electromagnetic spectrum, and it drops rapidly beyond 800 nm in near-infrared wavelengths. We have experimentally demonstrated a technique utilizing photon-trapping surface structures to show a prodigious improvement of photoabsorption in 1-&mu;m-thin silicon, surpassing the inherent absorption efficiency of gallium arsenide for a broad spectrum. The photon-trapping structures allow the bending of normally incident light by almost 90 deg to transform into laterally propagating modes along the silicon plane. Consequently, the propagation length of light increases, contributing to more than one order of magnitude improvement in absorption efficiency in photodetectors. This high-absorption phenomenon is explained by finite-difference time-domain analysis, where we show an enhanced photon density of states while substantially reducing the optical group velocity of light compared to silicon without photon-trapping structures, leading to significantly enhanced light&ndash;matter interactions. Our simulations also predict an enhanced absorption efficiency of photodetectors designed using 30- and 100-nm silicon thin films that are compatible with CMOS electronics. Despite a very thin absorption layer, such photon-trapping structures can enable high-efficiency and high-speed photodetectors needed in ultrafast computer networks, data communication, and imaging systems, with the potential to revolutionize on-chip logic and optoelectronic integration.

Optical skyrmion serves as a crucial interface between optics and topology. Recently, it has attracted great interest in linear optics. Here, we theoretically introduce a framework for the all-optical generation and control of free-space optical skyrmions in extreme ultraviolet regions via high harmonic generation (HHG). We show that by employing full Poincaré beams, the created extreme ultraviolet fields manifest as skyrmionic structures in Stokes vector fields, whose skyrmion number is relevant to harmonic orders. We reveal that the generation of the skyrmionics structure is attributed to spatial-resolved spin constraint of HHG. Through qualifying the geometrical parameters of full Poincaré beams, the topological texture of extreme ultraviolet fields can be completely manipulated, generating the Bloch-type, Néel-type, anti-type, and higher-order skyrmions. We promote the investigation of topological optics in optical highly nonlinear processes, with potential applications toward ultrafast spintronics with structured light fields.

Orbital angular momentum (OAM), emerging as an inherently high-dimensional property of photons, has boosted information capacity in optical communications. However, the potential of OAM in optical computing remains almost unexplored. Here, we present a highly efficient optical computing protocol for complex vector convolution with the superposition of high-dimensional OAM eigenmodes. We used two cascaded spatial light modulators to prepare suitable OAM superpositions to encode two complex vectors. Then, a deep-learning strategy is devised to decode the complex OAM spectrum, thus accomplishing the optical convolution task. In our experiment, we succeed in demonstrating 7-, 9-, and 11-dimensional complex vector convolutions, in which an average proximity better than 95% and a mean relative error <6 % are achieved. Our present scheme can be extended to incorporate other degrees of freedom for a more versatile optical computing in the high-dimensional Hilbert space.

Silicon nitride (Si3N4) waveguides with high confinement and low loss have been widely used in integrated nonlinear photonics. Indeed, state-of-the-art ultralow-loss Si3N4 waveguides are all fabricated using complex fabrication processes, and all of those reported that high Q microring resonators (MRRs) are fabricated in laboratories. We propose and demonstrate an ultralow-loss Si3N4 racetrack MRR by shaping the mode using a uniform multimode structure to reduce its overlap with the waveguide. The MRR is fabricated by the standard multi project wafer (MPW) foundry process. It consists of two multimode straight waveguides (MSWs) connected by two multimode waveguide bends (MWBs). In particular, the MWBs are based on modified Euler bends, and an MSW directional coupler is used to avoid higher-order mode excitation. In this way, although a multimode waveguide is used in the MRR, only the fundamental mode is excited and transmitted with ultralow loss. Meanwhile, thanks to the 180 deg Euler bend, a compact chip footprint of 2.226 mm perimeter with an effective radius as small as 195 μm and a waveguide width of 3 μm is achieved. Results show that based on the widely used MPW process, a propagation loss of only 3.3 dB / m and a mean intrinsic Q of around 10.8 million are achieved for the first time.

Large-scale computational imaging can provide remarkable space-bandwidth product that is beyond the limit of optical systems. In coherent imaging (CI), the joint reconstruction of amplitude and phase further expands the information throughput and sheds light on label-free observation of biological samples at micro- or even nano-levels. The existing large-scale CI techniques usually require scanning/modulation multiple times to guarantee measurement diversity and long exposure time to achieve a high signal-to-noise ratio. Such cumbersome procedures restrict clinical applications for rapid and low-phototoxicity cell imaging. In this work, a complex-domain-enhancing neural network for large-scale CI termed CI-CDNet is proposed for various large-scale CI modalities with satisfactory reconstruction quality and efficiency. CI-CDNet is able to exploit the latent coupling information between amplitude and phase (such as their same features), realizing multidimensional representations of the complex wavefront. The cross-field characterization framework empowers strong generalization and robustness for various coherent modalities, allowing high-quality and efficient imaging under extremely low exposure time and few data volume. We apply CI-CDNet in various large-scale CI modalities including Kramers–Kronig-relations holography, Fourier ptychographic microscopy, and lensless coded ptychography. A series of simulations and experiments validate that CI-CDNet can reduce exposure time and data volume by more than 1 order of magnitude. We further demonstrate that the high-quality reconstruction of CI-CDNet benefits the subsequent high-level semantic analysis.

Structured illumination microscopy (SIM) has been widely applied in the superresolution imaging of subcellular dynamics in live cells. Higher spatial resolution is expected for the observation of finer structures. However, further increasing spatial resolution in SIM under the condition of strong background and noise levels remains challenging. Here, we report a method to achieve deep resolution enhancement of SIM by combining an untrained neural network with an alternating direction method of multipliers (ADMM) framework, i.e., ADMM-DRE-SIM. By exploiting the implicit image priors in the neural network and the Hessian prior in the ADMM framework associated with the optical transfer model of SIM, ADMM-DRE-SIM can further realize the spatial frequency extension without the requirement of training datasets. Moreover, an image degradation model containing the convolution with equivalent point spread function of SIM and additional background map is utilized to suppress the strong background while keeping the structure fidelity. Experimental results by imaging tubulins and actins show that ADMM-DRE-SIM can obtain the resolution enhancement by a factor of ∼1.6 compared to conventional SIM, evidencing the promising applications of ADMM-DRE-SIM in superresolution biomedical imaging.

The carrier-free phase-retrieval (CF-PR) receiver can reconstruct the optical field information only from two de-correlated intensity measurements without the involvement of a continuous-wave optical carrier. Here, we propose a digital subcarrier multiplexing (DSM)-enabled CF-PR receiver with hardware-efficient and modulation format-transparent merits. By numerically retrieving the optical field information of 56 GBaud DSM signals with QPSK/16QAM/32QAM modulation after 80-km standard single-mode fiber (SSMF) transmission, we identify that the DSM enabled CF-PR receiver is beneficial in reducing the implementation complexity of the CF-PR process, in comparison with the traditional single-carrier counterpart, because the lower symbol rate of each subcarrier is helpful in reducing the implementation complexity of multiple chromatic dispersion compensations and emulations during the PR iteration. Moreover, the DSM-enabled CF-PR receiver is verified to be robust toward various transmission imperfections, including transmitter-side laser linewidth and its wavelength drift, receiver-side time skew, and amplitude imbalance between two intensity tributaries. Finally, the superiority of the DSM-enabled CF-PR receiver is experimentally verified by recovering the optical field information of 25 GBaud 16QAM signals, after 40-km SSMF transmission for the first time. Thus, the DSM-enabled CF-PR receiver is promising for high-capacity photonic interconnection with direct detection.

Suitable optoelectronic integration platforms enable the realization of numerous application systems at the chip scale and are highly anticipated in the rapidly growing market. We report a GaN-on-silicon-based photonic integration platform and demonstrate a photonic integrated chip comprising a light source, modulator, photodiode (PD), waveguide, and Y-branch splitter based on this platform. The light source, modulator, and PD adopt the same multiple quantum wells (MQWs) diode structure without encountering incompatibility problems faced in other photonic integration approaches. The waveguide-structure MQW electro-absorption modulator has obvious indirect light modulation capability, and its absorption coefficient changes with the applied bias voltage. The results successfully validate the data transmission and processing using near-ultraviolet light with peak emission wavelength of 386 nm. The proposed complete active–passive approach that has simple fabrication and low cost provides new prospects for next-generation photonic integration.

We present a scheme for estimating the noise-equivalent temperature difference (NETD) of frequency upconversion detectors (UCDs) that detect mid-infrared (MIR) light. In particular, we investigate the frequency upconversion of a periodically poled crystal based on lithium niobate, where an MIR conversion bandwidth of 220 nm can be achieved in a single-poled period by a special design. Experimentally, for an MIR radiating target at a temperature of 95°C, the NETD of the device was estimated to be 56 mK with an exposure time of 1 s. Meanwhile, a direct measurement of the NETD was performed utilizing conventional methods, which resulted in 48 mK. We also compared the NETD of our UCD with commercially available direct MIR detectors. We show that the limiting factor for further NETD reduction of our device is not primarily from the upconversion process and camera noise but from the limitations of the heat source and laser performance. Our detectors have good temperature measurement performance and can be used for a variety of applications involving temperature object identification and material structure detection.

Accurate localization of blood vessels with image navigation is a key element in vascular-related medical research and vascular surgery. However, current vascular navigation techniques cannot provide naked-eye visualization of deep vascular information noninvasively and with high resolution, resulting in inaccurate vascular anatomy and diminished surgical success rates. Here, we introduce a photoacoustic-enabled automatic vascular navigation method combining photoacoustic computed tomography with augmented and mixed reality, for the first time, to our knowledge, enabling accurate and noninvasive visualization of the deep microvascular network within the tissues in real time on a real surgical surface. This approach achieves precise vascular localization accuracy (<0.89 mm) and tiny vascular relocation latency (<1 s) through a zero-mean normalization idea-based visual tracking algorithm and a curved surface-fitting algorithm. Further, the subcutaneous vessels of minimum diameter (∼0.15 mm) in rabbit thigh and the maximum depth (∼7 mm) in human arm can be vividly projected on the skin surface with a computer vision-based projection tracking system to simulate preoperative and intraoperative vascular localization. Thereby, this strategy provides a way to visualize deep vessels without damage on the surgical surface and with precise image navigation, opening an avenue for the application of photoacoustic imaging in surgical operations.

Recently, structured light beams have attracted substantial attention in many applications, including optical communications, imaging, optical tweezers, and quantum optics. We propose and experimentally demonstrate a reconfigurable structured light beam generator in order to generate diverse structured light beams with adjustable beam types, beam orders, and beam sizes. By controlling the sizes of generated free-space structured light beams, free-space orbital angular momentum (OAM) beams and vector beams are coupled into an air–core fiber. To verify that our structured light generator enables generating structured light with high beam quality, polarization distributions and mode purity of generated OAM beams and vector beams in both free space and air–core fiber are characterized. Such a structured light generator may pave the way for future applications based on higher-order structured light beams.

The photonic neural processing unit (PNPU) demonstrates ultrahigh inference speed with low energy consumption, and it has become a promising hardware artificial intelligence (AI) accelerator. However, the nonidealities of the photonic device and the peripheral circuit make the practical application much more complex. Rather than optimizing the photonic device, the architecture, and the algorithm individually, a joint device-architecture-algorithm codesign method is proposed to improve the accuracy, efficiency and robustness of the PNPU. First, a full-flow simulator for the PNPU is developed from the back end simulator to the high-level training framework; Second, the full system architecture and the complete photonic chip design enable the simulator to closely model the real system; Third, the nonidealities of the photonic chip are evaluated for the PNPU design. The average test accuracy exceeds 98%, and the computing power exceeds 100TOPS.

Optical orbital angular momentum (OAM) multiplexed holography has been implemented as an effective method for information encryption and storage. Multiramp helicoconical-OAM multiplexed holography is proposed and experimentally implemented. The mode selectivity of the multiramp mixed screw-edge dislocations, constant parameter K, and normalized factor are investigated, respectively, which demonstrates that those parameters can be used as additional coding degrees of freedom for holographic multiplexing. The combination of the topological charge and the other three parameters can provide a four-dimensional multiplexed holography and can enhance information capacity.

The combination of photonic integrated circuits and free-space metaoptics has the ability to untie technological knots that require advanced light manipulation due to their conjoined ability to achieve strong light–matter interaction via wave-guiding light over a long distance and shape them via large space-bandwidth product. Rapid prototyping of such a compound system requires component interchangeability. This represents a functional challenge in terms of fabrication and alignment of high-performance optical systems. Here, we report a flexible and interchangeable interface between a photonic integrated circuit and the free space using an array of low-loss metaoptics and demonstrate multifunctional beam shaping at a wavelength of 780 nm. We show that robust and high-fidelity operation of the designed optical functions can be achieved without prior precise characterization of the free-space input nor stringent alignment between the photonic integrated chip and the metaoptics chip. A diffraction limited spot of ∼3 μm for a hyperboloid metalens of numerical aperture 0.15 is achieved despite an input Gaussian elliptical deformation of up to 35% and misalignments of the components of up to 20 μm. A holographic image with a peak signal-to-noise ratio of >10 dB is also reported.

We propose and experimentally demonstrate a long-range chaotic Brillouin optical correlation domain analysis by employing an optimized time-gated scheme and differential denoising configuration, where the number of effective resolving points largely increases to more than one million. The deterioration of the chaotic Brillouin gain spectrum (BGS) and limitation of sensing range owing to the intrinsic noise structure, resulting from the time delay signature (TDS) and nonzero background of chaotic laser, is theoretically analyzed. The optimized time-gated scheme with a higher extinction ratio is used to eliminate the TDS-induced impact. The signal-to-background ratio of the measured BGS is enhanced by the differential denoising scheme to furthest remove the accumulated nonzero noise floor along the fiber, and the pure chaotic BGS is ulteriorly obtained by the Lorentz fit. Ultimately, distributed strain sensing along a 27.54-km fiber with a 2.69-cm spatial resolution is experimentally demonstrated, and the number of effective resolving points is more than 1,020,000.

In recent years, there has been tremendous progress in the development of deep-learning-based approaches for optical metrology, which introduce various deep neural networks (DNNs) for many optical metrology tasks, such as fringe analysis, phase unwrapping, and digital image correlation. However, since different DNN models have their own strengths and limitations, it is difficult for a single DNN to make reliable predictions under all possible scenarios. In this work, we introduce ensemble learning into optical metrology, which combines the predictions of multiple DNNs to significantly enhance the accuracy and reduce the generalization error for the task of fringe-pattern analysis. First, several state-of-the-art base models of different architectures are selected. A K-fold average ensemble strategy is developed to train each base model multiple times with different data and calculate the mean prediction within each base model. Next, an adaptive ensemble strategy is presented to further combine the base models by building an extra DNN to fuse the features extracted from these mean predictions in an adaptive and fully automatic way. Experimental results demonstrate that ensemble learning could attain superior performance over state-of-the-art solutions, including both classic and conventional single-DNN-based methods. Our work suggests that by resorting to collective wisdom, ensemble learning offers a simple and effective solution for overcoming generalization challenges and boosts the performance of data-driven optical metrology methods.

Compressive full-Stokes spectropolarimetric imaging (SPI), integrating passive polarization modulator (PM) into general imaging spectrometer, is powerful enough to capture high-dimensional information via incomplete measurement; a reconstruction algorithm is needed to recover 3D data cube (x, y, and λ) for each Stokes parameter. However, existing PMs usually consist of complex elements and enslave to accurate polarization calibration, current algorithms suffer from poor imaging quality and are subject to noise perturbation. In this work, we present a single multiple-order retarder followed a polarizer to implement passive spectropolarimetric modulation. After building a unified forward imaging model for SPI, we propose a deep image prior plus sparsity prior algorithm for high-quality reconstruction. The method based on untrained network does not need training data or accurate polarization calibration and can simultaneously reconstruct the 3D data cube and achieve self-calibration. Furthermore, we integrate the simplest PM into our miniature snapshot imaging spectrometer to form a single-shot SPI prototype. Both simulations and experiments verify the feasibility and outperformance of our SPI scheme. It provides a paradigm that allows general spectral imaging systems to become passive full-Stokes SPI systems by integrating the simplest PM without changing their intrinsic mechanism.

A phase-only method is proposed to transform an optical vortex field into desired spiral diffraction–interference patterns. Double-ring phase apertures are designed to produce a concentric high-order vortex beam and a zeroth-order vortex beam, and the diffracted intensity ratio of two beams is adjustable between 0 and 1. The coherent superposition of the two diffracted beams generates a brighter Airy spot (or Poisson spot) in the middle of the spiral pattern, where the singularity for typical vortex beam is located. Experiments employing circular, triangular, and rectangular phase apertures with topological charges from 3 to 16 demonstrate a stable, compact, and flexible apparatus for vortex beam conversion. By adjusting the parameters of the phase aperture, the proposed method can realize the optical Gaussian tweezer function and the optical vortex tweezer function simultaneously along the same axis or switch the experimental setup between the two functions. It also has potential applications in light communication through turbulent air by transmitting an orbital angular momentum-coded signal with a concentric beacon laser.

Laguerre-Gaussian (LG) modes, carrying the orbital angular momentum of light, are critical for important applications, such as high-capacity optical communications, superresolution imaging, and multidimensional quantum entanglement. Advanced developments in these applications demand reliable and tunable LG mode laser sources, which, however, do not yet exist. Here, we experimentally demonstrate highly efficient, highly pure, broadly tunable, and topological-charge-controllable LG modes from a Janus optical parametric oscillator (OPO). The Janus OPO featuring a two-faced cavity mode is designed to guarantee an efficient evolution from a Gaussian-shaped fundamental pump mode to a desired LG parametric mode. The output LG mode has a tunable wavelength between 1.5 and 1.6 μm with a conversion efficiency >15 % , a controllable topological charge up to 4, and a mode purity as high as 97%, which provides a high-performance solid-state light source for high-end demands in multidimensional multiplexing/demultiplexing, control of spin-orbital coupling between light and atoms, and so on.

Light plays a central role in many applications. The key to unlocking its versatility lies in shaping it into the most appropriate form for the task at hand. Specifically tailored refractive index modifications, directly manufactured inside glass using a short pulsed laser, enable an almost arbitrary control of the light flow. However, the stringent requirements for quantitative knowledge of these modifications, as well as for fabrication precision, have so far prevented the fabrication of light-efficient aperiodic photonic volume elements (APVEs). Here, we present a powerful approach to the design and manufacturing of light-efficient APVEs. We optimize application-specific three-dimensional arrangements of hundreds of thousands of microscopic voxels and manufacture them using femtosecond direct laser writing inside millimeter-sized glass volumes. We experimentally achieve unprecedented diffraction efficiencies up to 80%, which is enabled by precise voxel characterization and adaptive optics during fabrication. We demonstrate APVEs with various functionalities, including a spatial mode converter and combined intensity shaping and wavelength multiplexing. Our elements can be freely designed and are efficient, compact, and robust. Our approach is not limited to borosilicate glass but is potentially extendable to other substrates, including birefringent and nonlinear materials, giving a preview of even broader functionalities, including polarization modulation and dynamic elements.

The statistical dynamics of partially incoherent ultrafast lasers are complex and chaotic, which is significant for fundamental research and practical applications. We experimentally and theoretically reveal the statistical dynamics of the spectral evolutions and correlations in an incoherent noise-like rectangle pulse laser (NLRPL). Based on statistical histogram analysis, the probability distribution asymmetry of the spectral intensity fluctuation is decayed with the wavelength far away from the spectral peak due to the detection noise. The full-spectral correlation values indicate that the spectral similarity between two round trips is exponentially weakened as the round-trip offset increases. By studying the correlation map of spectral components, we find that the area of the high-correlation region is relevant to the pump power, which is reduced by increasing the pump power. The mutual information of the spectra demonstrates that two spectral components with symmetry about the spectral peak have a statistical dependence. Experimental observations and statistical properties can coincide well with theoretical numerical simulations. We reveal the pump-dependent spectral correlation of the NLRPL and provide multiple statistical methods for the characterizations of chaotic dynamics in incoherent light sources.

The spectroscopic methods for the ultrafast electronic and structural dynamics of materials require fully coherent extreme ultraviolet and soft X-ray radiation with high-average brightness. Seeded free-electron lasers (FELs) are ideal sources for delivering fully coherent soft X-ray pulses. However, due to state-of-the-art laser system limitations, it is challenging to meet the ultraviolet seed laser’s requirements of sufficient energy modulation and high repetition rates simultaneously. The self-modulation scheme has been proposed and recently demonstrated in a seeded FEL to relax the seed laser requirements. Using numerical simulations, we show that the required seed laser intensity in the self-modulation is ~3 orders of magnitude lower than that in the standard high-gain harmonic generation (HGHG). The harmonic self-modulation can launch a single-stage HGHG FEL lasing at the 30th harmonic of the seed laser. Moreover, the proof-of-principle experimental results confirm that the harmonic self-modulation can still amplify the laser-induced energy modulation. These achievements reveal that the self-modulation can not only remarkably reduce the requirements of the seed laser but also improve the harmonic upconversion efficiency, which paves the way for realizing high-repetition-rate and fully coherent soft X-ray FELs.

The AlGaN/GaN p–n junction has received extensive attention due to its capability of rapid photogenerated carrier separation in photodetection devices. The AlGaN/GaN heterojunction nanowires (NWs) have been especially endowed with new life for distinctive transport characteristics in the photoelectrochemical (PEC) detection field. A self-powered PEC ultraviolet photodetector (PEC UV PD) based on the p-AlGaN/n-GaN heterojunction NW is reported in this work. The n-GaN NW layer plays a crucial role as a current flow hub to regulate carrier transport, which mainly acts as a light absorber under 365 nm and carrier recombination layer under 255 nm illumination, which can effectively modulate photoresponsivity at different wavelengths. Furthermore, by designing the thicknesses of the NW layer, the photocurrent polarity reversal was successfully achieved in the constructed AlGaN/GaN NW PEC UV PD at two different light wavelengths. In addition, by combining with platinum decoration, the photoresponse performance could be further enhanced. Our work provides insight into transport mechanisms in the AlGaN/GaN NW PEC system, and offers a feasible and comprehensive strategy for further exploration of multifunctional optoelectronic devices.

Recently, transmitting diverse signals in different cores of a multicore fiber (MCF) has greatly improved the communication capacity of a single fiber. In such an MCF-based communication system, mux/demux devices with broad bandwidth are of great significance. In this work, we design and fabricate a 19-channel mux/demux device based on femtosecond laser direct writing. The fabricated mux/demux device possesses an average insertion loss of 0.88 dB and intercore crosstalk of no more than - 29.1 dB. Moreover, the fabricated mux/demux device features a broad bandwidth across the C+L band. Such a mux/demux device enables low-loss 19-core fiber (de)multiplexing over the whole C+L band, showing a convincing potential value in wavelength-space division multiplexing applications. In addition, a 19-core fiber fan-in/fan-out system is also established based on a pair of mux/demux devices in this work.

X-ray beams carrying orbital angular momentum (OAM) are an emerging tool for probing matter. Optical elements, such as spiral phase plates and zone plates, have been widely used to generate OAM light. However, due to the high impinging intensities, these optics are challenging to use at X-ray free-electron lasers (XFELs). Here, we propose a self-seeded free-electron laser (FEL) method to produce intense X-ray vortices. Unlike passive filtering after amplification, an optical element will be used to introduce the helical phase to the radiation pulse in the linear regime, significantly reducing thermal load on the optical element. The generated OAM pulse is then used as a seed and significantly amplified. Theoretical analysis and numerical simulations demonstrate that the power of the OAM seed pulse can be amplified by more than two orders of magnitude, reaching peak powers of several tens of gigawatts. The proposed method paves the way for high-power and high-repetition-rate OAM pulses of XFEL light.

Lipid imaging by conventional photoacoustic microscopy subjects to direct contact sensing with relatively low detection bandwidth and sensitivity, which induces superficial imaging depth and low signal-to-noise ratio (SNR) in practical imaging scenarios. Herein, we present a photoacoustic remote sensing microscopy for lipid distribution mapping in bio-tissue, featuring noncontact implementation, broad detection bandwidth, deep penetration depth, and high SNR. A tailored high-energy pulsed laser source with a spectrum centered at 1750 nm is used as the excitation beam, while a cofocused 1550 nm continuous-wave beam is used as the probe signal. The pump wavelength is selected to overlap the first overtone of the C-H bond in response to the intensive absorption of lipid molecules, which introduces a much-enhanced SNR (55 dB) onto photoacoustic remote sensing (PARS) signals. Meanwhile, the optical sensing scheme of the photoacoustic signals provides broadband detection compared to the acoustic transducer and refrains the bio-samples from direct contact operations by eliminating the ultrasonic coupling medium. Taking merits of the high detection sensitivity, deep penetration depth, broadband detection, and high resolution of the PARS system, high-quality tissue scale lipid imaging is demonstrated in a model organism and brain slice.

Scattered light imaging through complex turbid media has significant applications in biomedical and optical research. For the past decade, various approaches have been proposed for rapidly reconstructing full-color, depth-extended images by introducing point spread functions (PSFs). However, because most of these methods consider memory effects (MEs), the PSFs have angular shift invariance over certain ranges of angles. This assumption is valid for only thin turbid media and hinders broader applications of these technologies in thick media. Furthermore, the time-variant characteristics of scattering media determine that the PSF acquisition and image reconstruction times must be less than the speckle decorrelation time, which is usually difficult to achieve. We demonstrate that image reconstruction methods can be applied to time-variant thick turbid media. Using the time-variant characteristics, the PSFs in dynamic turbid media within certain time intervals are recorded, and ergodic scattering regimes are achieved and combined as ensemble point spread functions (ePSFs). The ePSF traverses shift-invariant regions in the turbid media and retrieves objects beyond the ME. Furthermore, our theory and experimental results verify that our approach is applicable to thick turbid media with thickness of 1 cm at visible incident wavelengths.

The explosive growth of information urgently requires extending the capacity of optical communication and information processing. Orbital-angular-momentum-based mode division multiplexing (MDM) is recognized as the most promising technique to improve the bandwidth of a single fiber. To make it compatible with the dominant wavelength division multiplexing (WDM), broadband equal high-efficient phase encoding is highly pursued. Here, we propose a twisted-liquid-crystal and rear-mirror-based design for ultrabroadband reflective planar optics. The backtracking of the light inside the twisted birefringent medium leads to an achromatic phase modulation. With this design, a single-twisted reflective q-plate is demonstrated to convert a white beam to a polychromatic optical vortex. Jones calculus and vector beam characterization are carried out to analyze the broadband phase compensation. A dual-twisted configuration further extends the working band to over 600 nm. It supplies an ultrabroadband and reflective solution for the WDM/MDM-compatible elements and may significantly promote advances in ultrabroadband planar optics.

Hyperspectral imaging (HSI) is a powerful tool widely used for various scientific and industrial applications due to its ability to provide rich spatiospectral information. However, in exchange for multiplex spectral information, its image acquisition rate is lower than that of conventional imaging, with up to a few colors. In particular, HSI in the infrared region and using nonlinear optical processes is impractically slow because the three-dimensional (3D) data cube must be scanned in a point-by-point manner. In this study, we demonstrate a framework to improve the spectral image acquisition rate of HSI by integrating time-domain HSI and compressed sensing. Specifically, we simulated broadband coherent Raman imaging at a record high frame rate of 25 frames per second (fps) with 100 pixels × 100 pixels, which is 10 × faster than that of previous work, based on an experimentally feasible sampling scheme utilizing 3D Lissajous scanning.

Achieving valley pseudospin with large polarization is crucial in the implementation of quantum information applications. Transition metal dichalcogenides (TMDC) with different phase structures provide an ideal platform for valley modulation. The valley splitting has been achieved in hybrid phase WSe2, while its valley polarization remains unstudied. Magnetic field controllable valley polarization is explored in WSe2 with coexistence of H and T phases by an all-optical route. A record high valley polarization of 58.3% is acquired with a 19.9% T phase concentration under a 4-T magnetic field and nonresonant excitation. The enhanced valley polarization is dependent on the phase component and shows various increasing slopes, owing to the synergy between the T phase WSe2 and the magnetic field. The magnetic field controlled local magnetic momentums are revealed as the mechanism for the large valley polarization in H / T-WSe2. This speculation is also verified by theoretical simulations of the nonequilibrium spin density. These results display a considerable valley magnetic response in phase-engineered TMDC and provide a large-scale scheme for valley polarization applications.

Stable operation is one of the most important requirements for a laser source for high-precision applications. Many efforts have been made to improve the stability of lasers by employing various techniques, e.g., electrical and/or optical injection and phase locking. However, these techniques normally involve complex experimental facilities. Therefore, an easy implementation of the stability evaluation of a laser is still challenging, especially for lasers emitting in the terahertz (THz) frequency range because the broadband photodetectors and mature locking techniques are limited. In this work, we propose a simple method, i.e., relative phase locking, to quickly evaluate the stability of THz lasers without a need of a THz local oscillator. The THz laser system consists of a THz quantum cascade laser (QCL) frequency comb and a single-mode QCL. Using the single-mode laser as a fast detector, heterodyne signals resulting from the beating between the single-mode laser and the comb laser are obtained. One of the heterodyne beating signals is selected and sent to a phase-locked loop (PLL) for implementing the relative phase locking. Two kinds of locks are performed by feeding the output error signal of the PLL, either to the comb laser or to the single-mode laser. By analyzing the current change and the corresponding frequency change of the PLL-controlled QCL in each phase-locking condition, we, in principle, are able to experimentally compare the stability of the emission frequency of the single-mode QCL (fs) and the carrier envelope offset frequency (fCEO) of the QCL comb. The experimental results reveal that the QCL comb with the repetition frequency injection locked demonstrates much higher stability than the single-mode laser. The work provides a simple heterodyne scheme for understanding the stability of THz lasers, which paves the way for the further locking of the lasers and their high-precision applications in the THz frequency range.

Compact passive silicon photonic devices with high performance are always desired for future large-scale photonic integration. Inverse design provides a promising approach to realize new-generation photonic devices, while it is still very challenging to realize complex photonic devices for most inverse designs reported previously due to the limits of computational resources. Here, we present the realization of several representative advanced passive silicon photonic devices with complex optimization, including a six-channel mode (de)multiplexer, a broadband 90 deg hybrid, and a flat-top wavelength demultiplexer. These devices are designed inversely by optimizing a subwavelength grating (SWG) region and the multimode excitation and the multimode interference are manipulated. Particularly, such SWG structures are more fabrication-friendly than those random nanostructures introduced in previous inverse designs. The realized photonic devices have decent performances in a broad bandwidth with a low excess loss of <1 dB, which is much lower than that of previous inverse-designed devices. The present inverse design strategy shows great effectiveness for designing advanced photonic devices with complex requirements (which is beyond the capability of previous inverse designs) by using affordable computational resources.

The blue phase, which emerges between cholesteric and isotropic phases within a three-dimensional periodical superstructure, is of great significance in display and photonic applications. The crystalline orientation plays an important role in the macroscopic performance of the blue phase, where the single crystal shows higher uniformity over the polydomain and monodomain, resulting in higher Bragg reflection intensity, lower hysteresis, and lower driving voltage. However, currently reported methods of forming a single-crystal blue phase based on thermal controlling or e-beam lithography are quite time-consuming or expensive for large-scale fabrication, especially in the centimeter range, thus hindering the broad practical applications of single-crystal blue-phase-based photonic devices. Herein, a strategy to fabricate a large scale single crystalline blue-phase domain using holography lithography is proposed. Defect-free single-crystal domains both in blue phase I and blue phase II with a desired orientation of over 1 cm2 are fabricated based on a nanopatterned grating with periodic homeotropic and degenerate parallel anchoring, with colors from red and green to blue. This holography lithography-assisted strategy for fabrication of a large-scale single-crystal blue phase provides a time-saving and low-cost method for a defect-free single crystalline structure, leading to broad applications in liquid crystal displays, laser devices, adaptive optics elements, and electro-optical devices.

We propose and experimentally demonstrate a dielectric metasurface that allows monitoring of polarization deviations from an arbitrary elliptical input anchor state simply by tracking in real-time the output ratio between the powers of horizontal and vertical components after the metasurface. Importantly, this ratio can be enhanced corresponding to increased responsivity. Such nontrivial functionality is achieved by designing binary metasurfaces that realize tailored nonunitary and chiral polarization transformation. We experimentally demonstrate the operation at telecommunication wavelengths with enhanced responsivity up to 25 for various anchor states, including the strongly elliptical and circular. We also achieve the uncertainty of deviation measurement that is significantly better than the fundamental limit for nonchiral metasurfaces.

A thorough understanding of biological species and emerging nanomaterials requires, among other efforts, their in-depth characterization through optical techniques capable of nanoresolution. Nanoscopy techniques based on tip-enhanced optical effects have gained tremendous interest over the past years, given their potential to obtain optical information with resolutions limited only by the size of a sharp probe interacting with focused light, irrespective of the illumination wavelength. Although their popularity and number of applications is rising, tip-enhanced nanoscopy (TEN) techniques still largely rely on probes that are not specifically developed for such applications, but for atomic force microscopy. This limits their potential in many regards, e.g., in terms of signal-to-noise ratio, attainable image quality, or extent of applications. We take the first steps toward next-generation TEN by demonstrating the fabrication and modeling of specialized TEN probes with known optical properties. The proposed framework is highly flexible and can be easily adjusted to be used with diverse TEN techniques, building on various concepts and phenomena, significantly augmenting their function. Probes with known optical properties could potentially enable faster and more accurate imaging via different routes, such as direct signal enhancement or facile and ultrafast optical signal modulation. We consider that the reported development can pave the way for a vast number of novel TEN imaging protocols and applications, given the many advantages that it offers.

Vector optical vortices exhibit complex polarization patterns due to the interplay between spin and orbital angular momenta. Here we demonstrate, both analytically and with simulations, that certain polarization features of optical vortex beams maintain constant transverse spatial dimensions independently of beam divergence due to diffraction. These polarization features appear in the vicinity of the phase singularity and are associated with the presence of longitudinal electric fields. The predicted effect may prove important in metrology and high-resolution imaging applications.

Structured illumination microscopy (SIM) has been widely used in live-cell superresolution (SR) imaging. However, conventional physical model-based SIM SR reconstruction algorithms are prone to artifacts in handling raw images with low signal-to-noise ratios (SNRs). Deep-learning (DL)-based methods can address this challenge but may lead to degradation and hallucinations. By combining the physical inversion model with a total deep variation (TDV) regularization, we propose a hybrid restoration method (TDV-SIM) that outperforms conventional or DL methods in suppressing artifacts and hallucinations while maintaining resolutions. We demonstrate the performance superiority of TDV-SIM in restoring actin filaments, endoplasmic reticulum, and mitochondrial cristae from extremely low SNR raw images. Thus TDV-SIM represents the ideal method for prolonged live-cell SR imaging with minimal exposure and photodamage. Overall, TDV-SIM proves the power of integrating model-based reconstruction methods with DL ones, possibly leading to the rapid exploration of similar strategies in high-fidelity reconstructions of other microscopy methods.

The Mathieu beam is a typical nondiffracting beam characterized by its propagation invariance and self-reconstruction. These extraordinary properties have given rise to potentialities for applications such as optical communications, optical trapping, and material processing. However, the experimental generation of Mathieu–Gauss beams possessing high quality and compactness is still challenging. In this work, even and helical Mathieu phase plates with different orders m and ellipticity parameters q are fabricated by femtosecond laser two-photon polymerization. The experimentally generated nondiffracting beams are propagation-invariant in several hundred millimeters, which agree with numerical simulations. This work may promote the miniaturization of the application of nondiffracting beams in micronanooptics.

Recently, the metasurfaces for independently controlling the wavefront and amplitude of two orthogonal circularly polarized electromagnetic (EM) waves have been demonstrated to open a way toward spin-multiplexing compact metadevices. However, these metasurfaces are mostly restricted to a single operation frequency band. The main challenge to achieving multiple frequency manipulations stems from the complicated and time-consuming design caused by multifrequency cross talk. To solve this problem, we propose a deep-learning-assisted inverse design method for designing a dual-spin/frequency metasurface with flexible multiplexing of off-axis vortices. By analyzing the cross talk between different spin/frequency channels based on the deep-learning method, we established the internal mapping relationship between the physical parameters of a meta-atom and its phase responses in multichannels, realizing the rapid inverse design of the spin/frequency multiplexing EM device. As a proof of concept, we demonstrated in the microwave region a dual-frequency arbitrary spin-to-orbit angular momentum converter, a dual-frequency off-axis vector vortex multiplexer, and a large-capacity (16-channel) vortex beam generator. The proposed method may provide a compact and efficient platform for the multiplexing of vortices, which may further stimulate their applications in wireless communication and quantum information science.

Structured illumination microscopy (SIM) is an established optical superresolution imaging technique. However, conventional SIM based on wide-field image acquisition is generally limited to visualizing thin cellular samples. We propose combining one-dimensional image rescan and structured illumination in the orthogonal direction to achieve superresolution without the need to rotate the illumination pattern. The image acquisition speed is consequently improved threefold, which is also beneficial for minimizing photobleaching and phototoxicity. Optical sectioning in thick biological tissue is enhanced by including a confocal slit in the system to significantly suppress the out-of-focus background and the associated noise. With all the technical improvements, our method captures three-dimensional superresolved image stacks of neuronal structures in mouse brain tissue samples for a depth range of more than 200 μm.

Filament- and plasma-grating-induced breakdown spectroscopy (F-GIBS) was demonstrated as an efficient technique for sensitive detection of metals in water, where plasma gratings were established through synchronized nonlinear interaction of two noncollinear filaments and an additional filament was generated with another fs laser beam propagating along their bisector. A water jet was constructed vertically to the three co-planar filaments, overcoming side effects from violent plasma explosion and bubble generation. Three distinct regimes of different mechanisms were validated for nonlinear couplings of the third filament with plasma gratings. As the third filament was temporally overlapped with the two noncollinear filaments in the interaction zone, all the three filaments participated in synchronous nonlinear interaction and plasma grating structures were altered by the addition of the third filament. As the third filament was positively or negatively delayed, the as-formed plasma gratings were elongated by the delayed third filament, or plasma gratings were formed in the presence of plasma expansion of the ahead third filament, respectively. Using F-GIBS for trace metal detection in water, significant spectral line enhancements were observed.

Multimode optical interferometers represent the most viable platforms for the successful implementation of several quantum information schemes that take advantage of optical processing. Examples range from quantum communication and sensing, to computation, including optical neural networks, optical reservoir computing, or simulation of complex physical systems. The realization of such routines requires high levels of control and tunability of the parameters that define the operations carried out by the device. This requirement becomes particularly crucial in light of recent technological improvements in integrated photonic technologies, which enable the implementation of progressively larger circuits embedding a considerable amount of tunable parameters. We formulate efficient procedures for the characterization of optical circuits in the presence of imperfections that typically occur in physical experiments, such as unbalanced losses and phase instabilities in the input and output collection stages. The algorithm aims at reconstructing the transfer matrix that represents the optical interferometer without making any strong assumptions about its internal structure and encoding. We show the viability of this approach in an experimentally relevant scenario, defined by a tunable integrated photonic circuit, and we demonstrate the effectiveness and robustness of our method. Our findings can find application in a wide range of optical setups, based on both bulk and integrated configurations.

Photonic and acoustic topological insulators exhibiting one-way transportation that is robust against defects and impurities are typically realized in coupled arrays of two-dimensional ring resonators. These systems have produced a series of applications, including optical isolators, delay lines, and lasers. However, the structures are complicated because an additional coupler ring between neighboring rings is needed to construct photonic pseudospin. A photonic anomalous Floquet topological insulator is proposed and experimentally demonstrated in the microwave regime. This improved design takes advantage of the efficient and backward coupling of negative-index media. The results contribute to the understanding of topological structures in metamaterials and point toward a unique direction for constructing useful topological photonic devices.

Electrically connected optical metasurfaces with high efficiencies are crucial for developing spatiotemporal metadevices with ultrahigh spatial and ultrafast temporal resolutions. While efficient metal–insulator–metal (MIM) metasurfaces containing discretized meta-atoms require additional electrodes, Babinet-inspired slot-antenna-based plasmonic metasurfaces suffer from low efficiencies and limited phase coverage for copolarized optical fields. Capitalizing on the concepts of conventional MIM and slot-antenna metasurfaces, we design and experimentally demonstrate a new type of optical reflective metasurfaces consisting of mirror-coupled slot antennas (MCSAs). By tuning the dimensions of rectangular-shaped nanoapertures atop a dielectric-coated gold mirror, we achieve efficient phase modulation within a sufficiently large range of 320 deg and realize functional phase-gradient metadevices for beam steering and beam splitting in the near-infrared range. The fabricated samples show (22 % ± 2 % ) diffraction efficiency for beam steering and (17 % ± 1 % ) for beam splitting at the wavelength of 790 nm. The considered MCSA configuration, dispensing with auxiliary electrodes, offers an alternative and promising platform for electrically controlled reflective spatiotemporal metasurfaces.

Parity‐time (PT) symmetry breaking offers mode selection capability for facilitating single‐mode oscillation in the optoelectronic oscillator (OEO) loop. However, most OEO implementations depend on discrete devices, which impedes proliferation due to size, weight, power consumption, and cost. In this work, we propose and experimentally demonstrate an on-chip tunable PT‐symmetric OEO. A tunable microwave photonic filter, a PT‐symmetric mode‐selective architecture, and two photodetectors are integrated on a silicon‐on‐insulator chip. By exploiting an on‐chip Mach–Zehnder interferometer to match the gain and loss of two mutually coupled optoelectronic loops, single‐mode oscillation can be obtained. In the experiment, the oscillation frequency of the on-chip tunable PT‐symmetric OEO can be tuned from 0 to 20 GHz. To emulate the integrated case, the OEO loop length is minimized, and no extra-long fiber is used in the experiment. When the oscillation frequency is 13.67 GHz, the single‐sideband phase noise at 10-kHz offset frequency is -80.96 dBc / Hz and the side mode suppression ratio is 46 dB. The proposed on-chip tunable PT‐symmetric OEO significantly reduces the footprint of the system and enhances mode selection.

The large-photon-number quantum state is a fundamental but nonresolved request for practical quantum information applications. We propose an N-photon state generation scheme that is feasible and scalable, using lithium niobate on insulator circuits. Such a scheme is based on the integration of a common building block called photon-number doubling unit (PDU) for deterministic single-photon parametric downconversion and upconversion. The PDU relies on a 107-optical-quality-factor resonator and mW-level on-chip power, which is within the current fabrication and experimental limits. N-photon state generation schemes, with cluster and Greenberger&ndash;Horne&ndash;Zeilinger state as examples, are shown for different quantum tasks.

Highly sensitive and broadband ultrasound detection is important for photoacoustic imaging, biomedical ultrasound, and ultrasonic nondestructive testing. The elasto-optical refractive index modulation induced by ultrasound arouses a transient phase shift of a probe beam. Highly sensitive phase detection with a high Q factor resonator is desirable to visualize the ultraweak transient ultrasonic field. However, current phase-sensitive ultrasonic detectors suffer from limited bandwidth, mutual interference between intensity and phase, and significant phase noise, which become key to limiting further improvement of detection performance. We report a phase-sensitive detector with a bandwidth of up to 100 MHz based on dual-comb multiheterodyne interferometry (DCMHI). By sensing the phase shift induced by the ultrasound without any resonators in the medium, the DCMHI boosted the phase sensitivity by coherent accumulation without any magnitude averaging and extra radio frequency amplification. DCMHI offers high sensitivity and broad bandwidth as the noise-equivalent pressure reaches 31 mPa / √Hz under 70 MHz acoustic responses. With a large repetition rate difference of up to 200 MHz of dual comb, DCMHI can achieve broadband acoustic responses up to 100 MHz and a maximum possible imaging acquisition rate of 200 MHz. It is expected that DCMHI can offer a new perspective on the new generation of optical ultrasound detectors.

In light-sheet fluorescence microscopy, the axial resolution and field of view are mutually constrained. Axially swept light-sheet microscopy (ASLM) can decouple the trade-off, but the confocal detection scheme using a rolling shutter also rejects fluorescence signals from the specimen in the field of interest, which sacrifices the photon efficiency. Here, we report a laterally swept light-sheet microscopy (LSLM) scheme in which the focused beam is first scanned along the axial direction and subsequently laterally swept with the rolling shutter. We show that LSLM can obtain a higher photon efficiency when similar axial resolution and field of view can be achieved. Moreover, based on the principle of image scanning microscopy, applying the pixel reassignment to the LSLM images, hereby named iLSLM, improves the optical sectioning. Both simulation and experimental results demonstrate the higher photon efficiency with similar axial resolution and optical sectioning. Our proposed scheme is suitable for volumetric imaging of specimens that are susceptible to photobleaching or phototoxicity.

Manipulating motion of microobjects with light is indispensable in various technologies. On solid interfaces, its realizations, however, are hampered by surface friction. To resolve this difficulty, light-induced elastic waves have been recently proposed to drive microobjects against friction. Despite its expected applicability for arbitrary optical-absorptive objects, the new principle has only been tested with microsized gold plates. Herein, we validate this principle using a new material and report directional and continuous movements of a two-dimensional topological insulator (Sb2Te3) plate on an untreated microfiber surface driven by nanosecond laser pulses. The motion performance of the Sb2Te3 plate is characterized by a scanning electron microscope. We observe that the motion velocity can be controlled by tuning the average power of laser pulses. Further, by intentionally increasing the pulse repetition rate and exploiting the low thermal conductivity of Sb2Te3, we examine the thermal effects on actuation and reveal the motion instability induced by formations of microbumps on Sb2Te3 surfaces due to the Marangoni effects. Moreover, as the formed microbumps are heated to viscoelasticity states, liquid-like motion featuring asymmetry in contact angles is observed and characterized, which expands the scope of light-induced actuation of microobjects.

Nanochannel structures with a feature size deeply under the diffraction limit and a high aspect ratio hold huge biomedical significance, which is especially challenging to be realized on hard and brittle materials, such as silica, diamond, and sapphire. By simultaneously depositing the pulse energy on the surface and inside the sample, nanochannels with the smallest feature size of 18 nm (∼1 / 30λ) and more than 200 aspect ratios are achieved inside silica, the mechanism of which can be concluded as the surface assisting material ejection effect. Both the experimental and theoretical results prove that the coaction of the superficial “hot domain” and internal hot domain dominates the generation of the nanochannels, which gives new insights into the laser-material interacting mechanisms and potentially promotes the corresponding application fields.

Emerging as a family of waves, Janus waves are known to have “real” and “virtual” components under inversion of the propagation direction. Although tremendous interest has been evoked in vortex beams featuring spiral wavefronts, little research has been devoted to the vortex beam embedded Janus waves, i.e., Janus vortex beams. We propose a liquid crystal (LC) Pancharatnam–Berry (PB) phase element to demonstrate the realization of the Janus vortex beams and the modulation of the associated orbit angular momentum (OAM) and spin angular momentum (SAM). The generated Janus vortex beams show opposite OAM and SAM states at two distinct foci, revealing a spin-orbit interaction during propagation enabled by the LC PB phase element, which may play special roles in applications such as optical encryption and decryption. Other merits like reconfigurability and flexible switching between Janus vortex beams and autofocusing or autodefocusing vortex beams additionally increase the degree of freedom of manipulating vortex beams. This work provides a platform for tailoring complex structured light and may enrich the applications of vortex beams in classical and quantum optics.

Structural color from artificial structures, due to its environmental friendliness and excellent durability, represents a route for color printing applications. Among various physical mechanisms, the Fabry–Perot (F–P) cavity effect provides a powerful way to generate vivid colors in either the reflection or transmission direction. Most of the previous F–P type color printing works rely on electron beam grayscale lithography, however, with this technique it is challenging to make large-area and low-cost devices. To circumvent this constraint, we propose to fabricate the F–P type color printing device by the laser grayscale lithography process. The F–P cavity consists of two thin silver films as mirrors and a photoresist film with a spatially variant thickness as the spacer layer. By controlling the laser exposure dose pixel by pixel, a centimeter-scale full-color printing device with a spatial resolution up to 5 μm × 5 μm is demonstrated. The proposed large area color printing device may have great potential in practical application areas such as color displays, hyperspectral imaging, advanced painting, and so on.

In two-photon microscopy, low illumination powers on samples and a high signal-to-noise ratio (SNR) of the excitation laser are highly desired for alleviating the problems of photobleaching and phototoxicity, as well as providing clean backgrounds for images. However, the high-repetition-rate Ti:sapphire laser and the low-SNR Raman-shift lasers fall short of meeting these demands, especially when used for deep penetrations. Here, we demonstrate a 937-nm laser frequency-doubled from an all-fiber mode-locked laser at 1.8 μm with a low repetition rate of ∼9 MHz and a high SNR of 74 dB. We showcase two-photon excitations with low illumination powers on multiple types of biological tissues, including fluorescence imaging of mouse brain neurons labeled with green and yellow fluorescence proteins (GFP and YFP), DiI-stained and GFP-labeled blood vessels, Alexa Fluor 488/568-stained mouse kidney, and second-harmonic-generation imaging of the mouse skull, leg, and tail. We achieve a penetration depth in mouse brain tissues up to 620 μm with an illumination power as low as ∼10 mW, and, even for the DiI dye with an extremely low excitation efficiency of 3.3%, the penetration depth is still up to 530 μm, indicating that the low-repetition-rate source works efficiently for a wide range of dyes with a fixed excitation wavelength. The low-repetition-rate and high-SNR excitation source holds great potential for biological investigations, such as in vivo deep-tissue imaging.

Orbital angular momentum (OAM) of an optical vortex has attracted great interest from the scientific community due to its significant values in high-capacity optical communications such as mode or wavelength division multiplexer/demultiplexer. Although several configurations have been developed to demultiplex an optical vortex, the multiwavelength high-order optical vortex (HOOV) demultiplexer remains elusive due to lack of effective control technologies. In this study, we present the design, fabrication, and test of metasurface optical elements for multiwavelength HOOV demultiplexing based on optical gyrator transformation transformations in the visible light range. Its realization in a metasurface form enables the combined measurement of OAM, the radial index p, and wavelength using a single optical component. Each wavelength channel HOOV can be independently converted to a high-order Hermitian–Gaussian beam mode, and each of the OAM beams is demultiplexed at the converter output. Furthermore, we extend the scheme to realize encoding of the three-digit gray code by controlling the wavelength or polarization state. Experimental results obtained at three wavelengths in the visible band exhibit good agreement with the numerical modeling. With the merits of ultracompact device size, simple optical configuration, and HOOV recognition ability, our approach may provide great potential applications in photonic integrated devices and systems for high-capacity and demultiplex-channel OAM communication.

We introduce a formalism, inspired on the perturbation theory for nearly free electrons in a solid-state crystal, to describe the resonances in optical ring resonators subjected to a perturbation in their dielectric profile. We find that, for small perturbations, degenerate resonant modes are split with the splitting proportional to one specific coefficient of the Fourier expansion of the perturbation. We also find an expected asymmetry in the linewidths (and Q factors) of the split modes. Experimental transmission spectra from rings with specially designed perturbations show a qualitative match with the formalism predictions.

Since Allen et al. demonstrated 30 years ago that beams with helical wavefronts carry orbital angular momentum (OAM), the OAM of beams has attracted extensive attention and stimulated lots of applications in both classical and quantum physics. Akin to an optical frequency comb, a beam can carry multiple various OAM components simultaneously. A series of discrete, equally spaced, and equally weighted OAM modes comprise an OAM comb. Inspired by the spatially extended laser lattice, we demonstrate both theoretically and experimentally an approach to producing OAM combs through azimuthal binary phases. Our study shows that transition points in the azimuth determine the OAM distributions of diffracted beams. Multiple azimuthal transition points lead to a wide OAM spectrum. Moreover, an OAM comb with any mode spacing is achievable through reasonably setting the position and number of azimuthal transition points. The experimental results fit well with theory. This work presents a simple approach that opens new prospects for OAM spectrum manipulation and paves the way for many applications including OAM-based high-security encryption and optical data transmission, and other advanced applications.

Entanglement serves as a fundamental resource for quantum information protocols, and hyperentanglement has received an increasing amount of attention for its high-capacity characteristic. Increasing the scale of hyperentanglement, i.e., the number of modes in a hyperentangled system, is crucial for enhancing its capability in quantum information processing. Here, we demonstrate the generation of large-scale continuous-variable (CV) hyperentanglement in three degrees of freedom (DOFs), including azimuthal and radial indices of Laguerre–Gaussian (LG) modes and frequency. In our experiment, 216 pairs of hyperentangled modes are deterministically generated from the four-wave mixing process in an atomic vapor. In addition, we show that the entanglement between coherent LG superposition modes denoted by both azimuthal and radial quantum numbers can also be generated from this system. Such large-scale CV hyperentanglement in three DOFs presents an efficient scheme to significantly increase the information capacity of the CV system. Our results provide a new platform for studying CV quantum information and open the avenue for constructing high-capacity parallel and multiple-DOF CV quantum information protocols.

Thin-film lithium niobate is a promising material platform for integrated nonlinear photonics, due to its high refractive index contrast with the excellent optical properties. However, the high refractive index contrast and correspondingly small mode field diameter limit the attainable coupling between the waveguide and fiber. In second harmonic generation processes, lack of efficient fiber-chip coupling schemes covering both the fundamental and second harmonic wavelengths has greatly limited the overall efficiency. We design and fabricate an ultra-broadband tri-layer edge coupler with a high coupling efficiency. The coupler allows efficient coupling of 1 dB / facet at 1550 nm and 3 dB / facet at 775 nm. This enables us to achieve an ultrahigh overall second harmonic generation normalized efficiency (fiber-to-fiber) of 1027 % W - 1 cm - 2 (on-chip second harmonic efficiency &sim;3256 % W - 1 cm - 2) in a 5-mm-long periodically-poled lithium niobate waveguide, which is two to three orders of magnitude higher than that in state-of-the-art devices.