Most optical information processors deal with text or image data, and it is very difficult to deal experimentally with acoustic data. Therefore, optical advances that deal with acoustic data are highly desirable in this area. In particular, the development of a voice or acoustic-signal authentication technique using optical correlation can open a new line of research in the field of optical security and could also provide a tool for other applications where comparison of acoustic signals is required. Here, we report holographic acoustic-signal authentication by integrating the holographic microphone recording with optical correlation to meet some of the above requirements. The reported method avails the flexibility of 3D visualization of acoustic signals at sensitive locations and parallelism offered by an optical correlator/processor. We demonstrate text-dependent optical voice correlation that can determine the authenticity of acoustic signal by discarding or accepting it in accordance with the reference signal. The developed method has applications in security screening and industrial quality control.

Metasurfaces have prompted the transformation from the investigation of scalar holography to vectorial holography and led various applications in vectorial optical field manipulation. However, the majority of previously demonstrated methods focused on the reconstruction of a vectorial holographic image located at a predefined individual image plane. The evolution of polarization transformation during propagation can provide more design freedoms for realizing three-dimensional holography with complicated polarization feature. Here, we demonstrated a Jones matrix framework to generate vectorial holographic images with continuously varied polarization distributions at multiple different image planes based on a height tunable metasurface. The proposed metasurface is composed of IP-L (a type of photoresist) nanofins with different lengths, widths, heights, as well as orientation angles fabricated by femtosecond laser direct writing. Such a fabrication method is in favor of 3D arbitrary structure processing, large area fabrication, as well as fabrication on curved substrates. Meanwhile, it is easy to fabricate structures that can be integrated with other devices, including optical fibers, photodetectors, and complementary metal–oxide semiconductors. Our demonstrated method provides a feasible way to generate high-dimensional vectorial fields with longitudinally varied features from the perspective of holography and can be used in the related areas including optical trapping, sensing, and imaging.

The utilization of multimode fibers (MMFs) displays significant potential for advancing the miniaturization of optical endoscopes. However, the imaging quality is constrained by the physical conditions of MMF, which is particularly serious in small-core MMFs because of the limited mode quantity. To break this limitation and enhance the imaging ability of MMF to the maximum, we propose a mode modulation method based on the singular value decomposition (SVD) of MMF’s transmission matrix (TM). Before injection into the MMF, a light beam is modulated by the singular vectors obtained by SVD. Because the singular vectors couple the light field into eigenchannels during transmission and selectively excite the modes of different orders, the optimal distribution of the excited modes in MMF can be achieved, thereby improving the imaging quality of the MMF imaging system to the greatest extent. We conducted experiments on the MMF system with 40 μm and 105 μm cores to verify this method. Deep learning is utilized for image reconstruction. The experimental results demonstrate that the properties of the output speckle pattern were customized through the selective excitation of optical modes in the MMF. By applying singular vectors for mode modulation, the imaging quality can be effectively improved across four different types of scenes. Especially in the ultrafine 40 μm core MMF, the peak signal-to-noise ratio can be increased by up to 7.32 dB, and the structural similarity can be increased by up to 0.103, indicating a qualitative performance improvement of MMF imaging in minimally invasive medicine.

Arrays of optically levitated nanoparticles with fully tunable light-induced dipole–dipole interactions have emerged as a platform for fundamental research and sensing applications. However, previous experiments utilized two optical traps with identical polarization, leading to an interference effect. Here, we demonstrate light-induced dipole–dipole interactions using two orthogonally polarized optical traps. Furthermore, we achieve control over the strength and polarity of the optical coupling by adjusting the polarization and propose a method to simultaneously and stably measure conservative and non-conservative coupling rates. Our results provide a new scheme for exploring entanglement and topological phases in arrays of levitated nanoparticles.

Synchronously pumped optical parametric oscillators (OPOs) provide uniquely versatile platforms to generate ultrafast mid-infrared pulses within a spectral range beyond the access of conventional mode-locked lasers. However, conventional OPO sources based on bulk crystals have been plagued by complex optical alignment and large physical footprint. Here, we devise and implement two OPO variants based on a polarization-maintaining fiber-feedback cavity, which allow to robustly deliver sub-picosecond MIR pulses without the need of active stabilization. The first one integrates an erbium-doped fiber into the OPO cavity as the additional gain medium, which significantly reduces the pump threshold and allows stable optical pulse formation within a spectral range of 1553–1586 nm. The second one adopts a chirped poling nonlinear crystal in a passive-fiber cavity to further extend the operation spectral coverage, which facilitates broad tuning ranges of 1350–1768 nm and 2450–4450 nm for the signal and idler bands, respectively. Therefore, the presented mid-infrared OPO source is featured with high compactness, robust operation, and wide tunability, which would be attractive for subsequent applications such as infrared photonics, biomedical examination, and molecular spectroscopy.

Topological insulators are most frequently constructed using lattices with specific degeneracies in their linear spectra, such as Dirac points. For a broad class of lattices, such as honeycomb ones, these points and associated Dirac cones generally appear in non-equivalent pairs. Simultaneous breakup of the time-reversal and inversion symmetry in systems based on such lattices may result in the formation of the unpaired Dirac cones in bulk spectrum, but the existence of topologically protected edge states in such structures remains an open problem. Here a photonic Floquet insulator on a honeycomb lattice with unpaired Dirac cones in its spectrum is introduced that can support unidirectional edge states appearing at the edge between two regions with opposite sublattice detuning. Topological properties of this system are characterized by the nonzero valley Chern number. Remarkably, edge states in this system can circumvent sharp corners without inter-valley scattering even though there is no total forbidden gap in the spectrum. Our results reveal unusual interplay between two different physical mechanisms of creation of topological edge states based on simultaneous breakup of different symmetries of the system.

Responsivity is a critical parameter for sensors utilized in industrial miniaturized sensors and biomedical implants, which is typically constrained by the size and the coupling with external reader, hindering their widespread applications in our daily life. Here, we propose a highly-responsive sensing method based on Hamiltonian hopping, achieving the responsivity enhancement by 40 folds in microscale sensor detection compared to the standard method. We implement this sensing method in a nonlinear system with a pair of coupled resonators, one of which has a nonlinear gain. Surprisingly, our method surpasses the sensing performance at an exceptional point (EP)—simultaneous coalescence of both eigenvalues and eigenvectors. The responsivity of our method is notably enhanced thanks to the large frequency response at a Hamiltonian hopping point (HHP) in the strong coupling, far from the EP. Our study also reveals a linear HHP shift under different perturbations and demonstrates the detection capabilities down to sub-picofarad (<1 pF) of the microscale pressure sensors, highlighting their potential applications in biomedical implants.

Quasi-bound states in the continuum (quasi-BICs) offer an excellent platform for the flexible and efficient control of light-matter interactions by breaking the structural symmetry. The active quasi-BIC device has great application potential in fields such as optical sensing, nonlinear optics, and filters. Herein, we experimentally demonstrate an active terahertz (THz) quasi-BIC device induced by the polarization conversion in a liquid crystal (LC)-integrated metasurface, which consists of a symmetrically broken double-gap split ring resonator (DSRR), an LC layer, and double graphite electrodes. In the process of LC orientation control under the external field, the device realizes the active control from the OFF state to the ON state. In the OFF state, the LC has no polarization conversion effect, and the device behaves in a non-resonant state; but for the ON state, the device exhibits obvious quasi-BIC resonance. Furthermore, we achieve asymmetric transmission based on polarization-induced quasi-BIC modulation precisely at the quasi-BIC resonance position, and its isolation can be controlled by the external field. The study on dynamic quasi-BIC by the LC-integrated metasurface introduces a very promising route for active THz devices, which guarantees potential applications for THz communications, switching, and sensing systems.

Optical manipulation of objects at the nanometer-to-micrometer scale relies on the precise shaping of a focused laser beam to control the optical forces acting on them. Here, we introduce and experimentally demonstrate surface-shaped laser traps with conformable phase-gradient force field enabling multifunctional optical manipulation of nanoparticles in two dimensions. For instance, we show how this optical force field can be designed to capture and move multiple particles to set them into an autonomous sophisticated optical transport across any flat surface, regardless of the shape of its boundary. Unlike conventional laser traps, the extended optical field of the surface laser trap makes it easier for the particles to interact among themselves and with their environment. It allowed us to optically transport multiple plasmonic nanoparticles (gold nanospheres) while simultaneously enabling their electromagnetic interaction to form spinning optically bound (OB) dimers, which is the smallest case of optical matter system. We have experimentally demonstrated, for the first time, the creation of stable spinning OB dimers with control of their rotational and translational motion across the entire surface. These traveling OB dimers guided by the phase-gradient force work as switchable miniature motor rotors, whose rotation is caused by the combined effects of optical binding forces and optical torque induced by a circularly polarized surface laser trap. The degree of customization of the surface laser traps provides a versatility that can boost the study and control of complex systems of interacting particles, including plasmonic structures as the optical matter ones of high interest in optics and photonics.

Combining resonant excitation with Purcell-enhanced single quantum dots (QDs) stands out as a prominent strategy for realizing high-performance solid-state single-photon sources. However, optimizing photon extraction efficiency requires addressing the challenge of effectively separating the excitation laser from the QDs’ emission. Traditionally, this involves polarization filtering, limiting the achievable polarization directions and the scalability of polarized photonic states. In this study, we have successfully tackled this challenge by employing spatially orthogonal resonant excitation of QDs, deterministically coupled to monolithic Fabry–Perot microcavities. Leveraging the planar microcavity structure, we have achieved spectral filter-free single-photon resonant fluorescence. The resulting source produces single photons with a high extraction efficiency of 0.87 and an indistinguishability of 0.963(4).

The orbital angular momentum (OAM) of photons provides a pivotal resource for carrying out high-dimensional classical and quantum information processing due to its unique discrete high-dimensional nature. The cyclic transformation of a set of orthogonal OAM modes is an essential building block for universal high-dimensional information processing. Its realization in the quantum domain is the universal quantum Pauli-X gate. In this work, we experimentally demonstrate a cyclic transformation of six OAM modes with an averaged efficiency higher than 96% by exploiting a nonreciprocal Mach–Zehnder interferometer. Our system is simple and can, in principle, be scaled to more modes. By improving phase stabilization and inputting quantum photonic states, this method can perform universal single-photon quantum Pauli-X gate, thus paving the way for scalable high-dimensional quantum computation.

Phase change materials (PCMs), characterized by high optical contrast (Δn>1), nonvolatility (zero static power consumption), and quick phase change speed (∼ns), provide new opportunities for building low-power and highly integrated photonic tunable devices. Optical integrated devices based on PCMs, such as optical switches and optical routers, have demonstrated significant advantages in terms of modulation energy consumption and integration. In this paper, we theoretically verify the solution for a highly integrated nonvolatile optical switch based on the modulation of the topological interface state (TIS) in the quasi-one-dimensional photonic crystal (quasi-1D PC). The TIS exciting wavelength changes with the crystalline level of the PCM. The extinction ratio (ER) of the topological optical switch is over 18 dB with a modulation length of 9 μm. Meanwhile, the insertion loss (IL) can be controlled within 2 dB. Furthermore, we have analyzed the impact of fabrication errors on the device’s performance. The obtained results show that, the topological optical switch, which changes its “on/off” state by modulating TIS, exhibits enhanced robustness to the fabrication process. We provide an interesting and highly integrated scheme for designing the on-chip nonvolatile optical switch. It offers great potential for designing highly integrated on-chip optical switch arrays and nonvolatile optical neural networks.

In the field of quantum metrology, transition matrix elements are crucial for accurately evaluating the black-body radiation shift of the clock transition and the amplitude of the related parity-violating transition, and can be used as probes to test quantum electrodynamic effects, especially at the 10-3–10-4 level. We developed a universal experimental approach to precisely determine the dipole transition matrix elements by using the shelving technique, for the species where two transition channels are involved, in which the excitation pulses with increasing duration were utilized to induce shelving, and the resulting shelving probabilities were determined by counting the scattered photons from the excited P1/22 state to the S1/22 ground state. Using the scattered photons offers several advantages, including insensitivity to fluctuations in magnetic field, laser intensity, and frequency detuning. An intensity-alternating sequence to minimize detection noise and a real-time approach for background photon correction were implemented in parallel. We applied this technique to a single Yb+ ion, and determined the 6p P1/22-5d D23/2 transition matrix element 2.9979(20) ea0, which indicates an order of magnitude improvement over existing reports. By combining our result with the 6p P1/22 lifetime of 8.12(2) ns, we extracted the 6s S1/22-6p P1/22 transition matrix element to be 2.4703(31) ea0. The accurately determined dipole transition matrix elements can serve as a benchmark for the development of high-precision atomic many-body theoretical methods.

Surface plasmons have been given high expectations in terahertz (THz) on-chip photonics with highly bound integrated transmission and on-chip wavefront engineering. However, most surface plasmonic coupling strategies with tailorable polarization-dependent features are challenged in broadband propagation and dynamic manipulation. In this work, a liquid crystal (LC)-integrated surface plasmonic metadevice based on arc-arrayed pair-slit resonators (APSRs) is demonstrated. The mirror-symmetry structures of this metadevice achieve the spin-selective unidirectional achromatic focusing, of which the broadband characteristic is supported by containing multiple APSRs with slits of different sizes corresponding to different excitation frequencies. Moreover, arc radii are precisely designed to meet the phase matching condition of constructive interference, so that the operating frequency of this on-chip metadevice is broadened to 0.33–0.60 THz. Furthermore, the LC integration provides the active energy distribution between the left and right focal spots, and the actual modulation depth reaches up to 73%. These THz active, wideband, on-chip manipulation mechanisms and their devices are of great significance for THz-integrated photonic communication, information processing, and highly sensitive sensing.

Nanoparticle-based plasmonic optical fiber sensors can exhibit high sensing performance, in terms of refractive index sensitivities (RISs). However, a comprehensive understanding of the factors governing the RIS in this type of sensor remains limited, with existing reports often overlooking the presence of surface plasmon resonance (SPR) phenomena in nanoparticle (NP) assemblies and attributing high RIS to plasmonic coupling or waveguiding effects. Herein, using plasmonic optical fiber sensors based on spherical Au nanoparticles, we investigate the basis of their enhanced RIS, both experimentally and theoretically. The bulk behavior of assembled Au NPs on the optical fiber was investigated using an effective medium approximation (EMA), specifically the gradient effective medium approximation (GEMA). Our findings demonstrate that the Au-coated optical fibers can support the localized surface plasmon resonance (LSPR) as well as SPR in particular scenarios. Interestingly, we found that the nanoparticle sizes and surface coverage dictate which effect takes precedence in determining the RIS of the fiber. Experimental data, in line with numerical simulations, revealed that increasing the Au NP diameter from 20 to 90 nm (15% surface coverage) led to an RIS increase from 135 to 6998 nm/RIU due to a transition from LSPR to SPR behavior. Likewise, increasing the surface coverage of the fiber from 9% to 15% with 90 nm Au nanoparticles resulted in an increase in RIS from 1297 (LSPR) to 6998 nm/RIU (SPR). Hence, we ascribe the exceptional performance of these plasmonic optical fibers primary to SPR effects, as evidenced by the nonlinear RIS behavior. The outstanding RIS of these plasmonic optical fibers was further demonstrated in the detection of thrombin protein, achieving very low limits of detection. These findings support broader applications of high-performance NP-based plasmonic optical fiber sensors in areas such as biomedical diagnostics, environmental monitoring, and chemical analysis.

In this paper, the concept of anisotropic impedance holographic metasurface is proposed and validated by realizing holographic imaging with multipoint focusing techniques in near-field areas at the radio frequency domain. Combining the microwave holographic leaky-wave theory and near-field focusing principle, the mapped geometrical patterns can be constructed based on the correspondence between meta-atom structural parameters and equivalent scalar impedances in this modulated metasurface. Different from conventional space-wave modulated holographic imaging metasurfaces, this surface-wave-based holographic metasurface fed by monopole antenna embedded back on metal ground enables elimination of the misalignment error between the air feeding and space-wave-based metasurface and increase of the integration performance, which characterizes ultra-low profile, low cost, and easy integration. The core innovation of this paper is to use the classical anisotropic equivalent surface impedance method to achieve the near-field imaging effect for the first time. Based on this emerging technique, a surface-wave meta-hologram is designed and verified through simulations and experimental measurements, which offers a promising choice for microwave imaging, information processing, and holographic data storage.

Mid-infrared frequency-comb spectroscopy enables measurement of molecules at megahertz spectral resolution, sub-hertz frequency accuracy, and microsecond acquisition speed. However, the widespread adoption of this technique has been hindered by the complexity and alignment sensitivity of mid-infrared frequency-comb sources. Leveraging the underexplored mid-infrared window of silica fibers presents a promising approach to address these challenges. In this study, we present the first, to the best of our knowledge, experimental demonstration and quantitative numerical description of mid-infrared frequency-comb generation in silica fibers. Our all-silica-fiber frequency comb spans over two octaves (0.8 μm to 3.4 μm) with a power output of 100 mW in the mid-infrared region. The amplified quantum noise is suppressed using four-cycle (25 fs) driving pulses, with the carrier-envelope offset frequency exhibiting a signal-to-noise ratio of 40 dB and a free-running bandwidth of 90 kHz. Our developed model provides quantitative guidelines for mid-infrared frequency-comb generation in silica fibers, enabling all-fiber frequency-comb spectroscopy in diverse fields such as organic synthesis, pharmacokinetics processes, and environmental monitoring.

Self-assembly of dissipative solitons arouses versatile configurations of molecular complexes, enriching intriguing dynamics in mode-locked lasers. The ongoing studies fuel the analogy between matter physics and optical solitons, and stimulate frontier developments of ultrafast optics. However, the behaviors of multiple constituents within soliton molecules still remain challenging to be precisely unveiled, regarding both the intramolecular and intermolecular motions. Here, we introduce the concept of “soliton isomer” to elucidate the molecular dynamics of multisoliton complexes. The time-lens and time-stretch techniques assisted temporal-spectral analysis reveals the diversity of assembly patterns, reminiscent of the “isomeric molecule”. Particularly, we study the fine energy exchange during the intramolecular motions, therefore gaining insights into the degrees of freedom of isomeric dynamics beyond temporal molecular patterns. All these findings further answer the question of how far the matter-soliton analogy reaches and pave an efficient route for assisting the artificial manipulation of multisoliton structures.

Resonant metasurfaces provide a promising solution to overcome the limitations of nonlinear materials in nature by enhancing the interaction between light and matter and amplifying optical nonlinearity. In this paper, we design an aluminum (Al) metasurface that supports surface lattice resonance (SLR) with less nanoparticle filling density but more prominent saturable absorption effects, in comparison to a counterpart that supports localized surface plasmon resonance (LSPR). In detail, the SLR metasurface exhibits a narrower resonance linewidth and a greater near-field enhancement, leading to a more significant modulation depth (9.6%) at a low incident fluence of 25 μJ/cm2. As an application example, we have further achieved wavelength-tunable Q-switched pulse generation from 1020 to 1048 nm by incorporating the SLR-based Al metasurface as a passive saturable absorber (SA) in a polarization-maintaining ytterbium-doped fiber laser. Typically, the Q-switched pulse with a repetition rate of 33.7 kHz, pulse width of 2.1 μs, pulse energy of 141.7 nJ, and signal-to-noise ratio (SNR) of greater than 40 dB at the fundamental frequency can be obtained. In addition, we have investigated the effects of pump power and central wavelength of the filter on the repetition rate and pulse width of output pulses, respectively. In spite of demonstration of only using the Al metasurface to achieve a passive Q-switched fiber laser, our work offers an alternative scheme to build planar, lightweight, and broadband SA devices that could find emerging applications from ultrafast optics to neuromorphic photonics, considering the fast dynamics, CMOS-compatible fabrication, and decent nonlinear optical response of Al-material-based nanoplasmonics.

The fast algorithms in Fourier optics have invigorated multifunctional device design and advanced imaging technologies. However, the necessity for fast computations limits the widely used conventional Fourier methods, where the image plane has a fixed size at certain diffraction distances. These limitations pose challenges in intricate scaling transformations, 3D reconstructions, and full-color displays. Currently, the lack of effective solutions makes people often resort to pre-processing that compromises fidelity. In this paper, leveraging a higher-dimensional phase space method, a universal framework is proposed for customized diffraction calculation methods. Within this framework, a variable-scale diffraction computation model is established for adjusting the size of the image plane and can be operated by fast algorithms. The model’s robust variable-scale capabilities and its aberration automatic correction capability are validated for full-color holography, and high fidelity is achieved. The tomography experiments demonstrate that this model provides a superior solution for holographic 3D reconstruction. In addition, this model is applied to achieve full-color metasurface holography with near-zero crosstalk, showcasing its versatile applicability at nanoscale. Our model presents significant prospects for applications in the optics community, such as beam shaping, computer-generated holograms (CGHs), augmented reality (AR), metasurface optical elements (MOEs), and advanced holographic head-up display (HUD) systems.

Ultrafast imaging simultaneously pursuing high temporal and spatial resolution is a key technique to study the dynamics in the microscopic world. However, the broadband spectra of ultra-short pulses bring a major challenge to traditional coherent diffraction imaging (CDI), as they result in an indistinct diffraction pattern, thereby complicating image reconstruction. To address this, we introduce, to our knowledge, a new ultra-broadband coherent imaging method, and empirically demonstrate its efficacy in facilitating high-resolution and rapid image reconstruction of achromatic objects. The existing full bandwidth limitation for snapshot CDI is enhanced to ∼60% experimentally, restricted solely by our laser bandwidth. Simulations indicate the applicability of our method for CDI operations with a bandwidth as high as ∼140%, potentially supporting ultrafast imaging with temporal resolution into ∼50-attosecond scale. Even deployed with a comb-like harmonic spectrum encompassing multiple octaves, our method remains effective. Furthermore, we establish the capability of our approach in reconstructing a super-broadband spectrum for CDI applications with high fidelity. Given these advancements, we anticipate that our method will contribute significantly to attosecond imaging, thereby advancing cutting-edge applications in material science, quantum physics, and biological research.

The embedded ultra-precision displacement measurement is of great interest in developing high-end equipment as well as precision metrology. However, conventional interferometers only focus on measurement accuracy neglecting the sensor volume and requirement of embedded measurement, thus hindering their broad applications. Here we present a new sensing method for realizing large-range displacement measurement in narrow space scenarios based on the combination of a fiber microprobe interference-sensing model and precision phase-generated carrier. This is achieved by microprobe tilted-axis Gaussian optical field diffraction and high-order carrier demodulation to realize large-range displacement sensing. It is uncovered that the microprobe element misalignment and phase demodulation means play pivotal roles in the interference signal and the accuracy of large-range displacement sensing. The analysis shows that the proposed interference-sensing method can effectively reduce the nonlinearities. Experimental results illustrate that the measurement range extends from 0 to 700 mm. Furthermore, the maximum nonlinear error is reduced from tens of nanometers to 0.82 nm over the full range, allowing subnanometer accuracy for embedded measurements in the hundreds of millimeters range.

In two-dimensional (2D) material studies, tracking the anisotropic ultrafast carrier dynamics is essential for the development of optoelectronic nano-devices. Conventionally, the anisotropic optical and electronic properties are investigated via either polarization-dependent Raman spectroscopy or field-effect transistors measurements. However, study of the anisotropic transient carrier behaviors is still challenging, due largely to the lack of picosecond-resolved acquisition or programmable scanning capabilities in the current characterization systems. In this work, we select Ta2NiSe5 as a model system to investigate the ultrafast anisotropic transportation properties of photo-excited carriers and transient polarized responses via a digital micromirror device (DMD)-based pump-probe microscope, where the probe beam scans along the armchair and zigzag directions of a crystal structure via binary holography to obtain distinct carrier diffusion coefficients, respectively. The results reveal the nonlinear diffusion behaviors of Ta2NiSe5 in tens of picoseconds, which are attributed to the interplay between excited electrons and phonons. The trend of the measured local polarization-dependent transient reflectivity is consistent with the polarized Raman spectra results. These results show that the DMD-based pump-probe microscope is an effective and versatile tool to study the optoelectronic properties of 2D materials.

Optical frequency combs (OFCs) have enabled significant opportunities for high-precision frequency metrology and high-resolution broadband spectroscopy. Although nonlinear photonics chips have the capacity of frequency expansion for OFCs, most of them can only access the limited bandwidths in the partial infrared region, and it is still hard to satisfy many measurement applications in the ultraviolet-to-visible region. Here, we demonstrate a compact broadband OFC scheme via the combination of three χ(2) nonlinearities in a three-stage periodically poled lithium niobate (PPLN) chain. With a supercontinuum spectrum OFC delivered into the PPLN chain, the intra-pulse diffidence frequency generation, optical parametric amplification, and high-order harmonic generation were carried out in sequence. It is crucial that the harmonics of the 1st–10th orders are simultaneously obtained with an offset-free OFC spectrum from 0.35 to 4.0 μm. In view of the great potential for integration and spectral expansion, this wideband frequency comb source will open a new insight for the valuable applications of two-dimensional material analysis, biofluorescence microscopy, and nonlinear amplitude-phase metrology.

Ultra-high-quality-factor (Q) resonators are a critical component for visible to near-infrared (NIR) applications, including quantum sensing and computation, atomic timekeeping and navigation, precision metrology, microwave photonics, and fiber optic sensing and communications. Implementing such resonators in an ultra-low-loss CMOS foundry compatible photonic integration platform can enable the transitioning of critical components from the lab- to the chip-scale, such as ultra-low-linewidth lasers, optical reference cavities, scanning spectroscopy, and precision filtering. The optimal operation of these resonators must preserve the ultra-low losses and simultaneously support the desired variations in coupling over a wide range of visible and NIR wavelengths as well as provide tolerance to fabrication imperfections. We report a significant advancement in high-performance integrated resonators based on a two-point-coupling design that achieves critical coupling simultaneously at multiple wavelengths across wide wavebands and tuning of the coupling condition at any wavelength, from under-, through critically, to over-coupled. We demonstrate critical coupling at 698 nm and 780 nm in one visible-wavelength resonator and critical coupling over a wavelength range from 1550 nm to 1630 nm in a 340-million intrinsic Q 10-meter-coil waveguide resonator. Using the 340-million intrinsic Q coil resonator, we demonstrate laser stabilization that achieves six orders of magnitude reduction in the semiconductor laser frequency noise. We also report that this design can be used as a characterization technique to measure the intrinsic waveguide losses from 1300 nm to 1650 nm, resolving hydrogen-related absorption peaks at 1380 nm and 1520 nm in the resonator, giving insight to further reduce waveguide loss. The CMOS foundry compatibility of this resonator design will provide a path towards scalable system-on-chip integration for high-performance precision experiments and applications, improving reliability, and reducing size and cost.

High-power, high-efficiency single-mode vertical-cavity surface-emitting lasers (VCSELs) are crucial in the realm of green photonics for high-speed optical communication. However, in recent years, the power and efficiency of single-mode VCSELs have remained relatively low and have been progressing slowly. This study combines theoretical models with experiments to show that multi-junction cascaded 940 nm VCSELs based on surface microstructures can achieve high power, high efficiency, and low divergence in single-mode laser output. Simulations show multi-junction VCSELs with surface microstructures can boost mode modulation capabilities, power, and efficiency, potentially allowing high-power single-mode VCSELs to surpass 60% efficiency. Using this technique, the 6 μm oxide aperture VCSELs with surface relief of different diameters were fabricated. The single-mode VCSELs with the output power of 20.2 mW, side-mode suppression ratios greater than 35 dB, 42% electro-optical efficiency, and a 9.8° divergence angle (at 1/e2) under continuous-wave operation were demonstrated. Near-field images verified its fundamental mode operation. To the best of the authors’ knowledge, this is the highest single-mode power recorded for a single-unit VCSEL to date, almost twice the currently known record, while still maintaining a very high electro-optical conversion efficiency. This research will provide valuable references for the further development and application of high-power, high-efficiency single-mode semiconductor lasers.

Cylindrical vector beams (CVBs) with special polarization distribution have been extensively investigated due to the unique ways of interacting with matter. Although several configurations have been developed to generate CVBs, such as Q-plates and subwavelength gratings, the bandwidth of a single CVB is inherently narrow due to the phase geometry, which would limit its application for femtosecond lasers. Here, a broadband CVB mode converter based on an acoustically induced fiber grating (AIFG) and a tuning method of dispersion turning point (DTP) is demonstrated both theoretically and experimentally with the 3-dB bandwidth of 125 nm, which is more than 10 times that of conventional AIFGs. Not only can the DTP wavelength be tuned from the original 1500 nm to 1650 nm by thinning the fiber, but also the stable generation of a single broadband HE21odd/even mode can be controllably implemented by adjusting the polarization state of the incident light, owing to the larger beat length difference between HE21 and other CV modes. Additionally, the femtosecond CVBs and orbital angular momentum (OAM) modes are successfully generated and amplified by combining the broadband AIFG with a figure-9 mode-locked fiber laser. Meanwhile, it is verified by simulation that the choice of broadband CV mode and the tunability of DTP wavelength can be realized by designing ring-core fibers with different structures, which can furthermore improve the flexibility of generating high purity CVBs. This study provides a highly controllable technique for the generation of broadband CVBs and OAMs paving the way for high-capacity CVBs communication.

Sensitive detection of remote vibrations at nanometer scale owns promising potential applications such as geological exploration, architecture, and public security. Nevertheless, how to detect remote vibration information with high sensitivity and anti-disturbance has become a major challenge. Reported current non-contact measurement methods are difficult to simultaneously possess characteristics of high light intensity sensitivity, long working distance, high vibration response sensitivity, and anti-disturbance of ambient light. Here, we propose a polarization-modulated laser frequency-shifted feedback interferometry method with the above characteristics, to obtain remote vibration information. The method can directly measure non-cooperative targets without the need for any cooperative markers. In each interference cycle, the energy as low as 2.3 photons can be effectively responded to, and the vibration amplitude sensitivity at 300 m can reach 0.72 nm/Hz1/2 at 1 kHz. This approach provides a strategy for the ultrasensitive detection of remote vibration that is immune to electromagnetic interference.

133Cs, the only stable cesium (Cs) isotope, is one of the most investigated elements in atomic spectroscopy and was used to realize the atomic clock in 1955. Among all atomic clocks, the cesium atomic clock has a special place, since the current unit of time is based on a microwave transition in the Cs atom. In addition, the long lifetime of the 6P3/2 state and simple preparation technique of Cs vapor cells have great relevance to quantum and atom optics experiments, which suggests the use of the 6S-6P D2 transition as an optical frequency standard. In this work, using one laser as the local oscillator and Cs atoms as the quantum reference, we realize two atomic clocks at the optical and microwave frequencies. Both clocks can be freely switched or simultaneously output. The optical clock, based on the vapor cell, continuously operated with a frequency stability of 3.9×10-13 at 1 s, decreasing to 2.2×10-13 at 32 s, which was frequency-stabilized by modulation transfer spectroscopy and estimated by an optical comb. Then, applying this stabilized laser to an optically pumped Cs beam atomic clock to reduce the laser frequency noise, we obtained a microwave clock with a frequency stability of 1.8×10-12/τ, reaching 6×10-15 at 105 s. This study demonstrates an attractive feature for the commercialization and deployment of optical and microwave clocks, and will guide the further development of integrated atomic clocks with better stability. Therefore, this study holds significant practical implications for future applications in satellite navigation, communication, and timing.

Quantum-dot mode-locked lasers have advantages such as high temperature stability, large optical bandwidth, and low power consumption, which make them ideal optical comb sources, especially for wavelength-division multiplexing (WDM) telecommunications, and optical I/O applications. In this work, we demonstrate an O-band quantum dot colliding pulse mode-locked laser (QD-CPML) to generate optical frequency combs with 200 GHz spacing with maximum channels of 12 within 3 dB optical bandwidth. To achieve the high output power of individual comb lines, four channel conditions are implemented at central wavelength of 1310 nm for WDM transmission experiments. Each channel exhibits more than 10 dBm output power with 200 Gb/s PAM-4 and 270 Gb/s PAM-8 modulation capability via thin-film LiNbO3 Mach–Zehnder interferometer modulator without the requirement of any optical amplifications. This high-order QD-CPML is an ideal comb source for power-efficient optical interconnects and large bandwidth optical data transmission.

The fiber single-cavity dual-comb laser (SCDCL) is an emerging light-source architecture that opens up the possibility for low-complexity dual-comb pump-probe measurements. However, the fundamental trade-off between measurement speed and time resolution remains a hurdle for the widespread use of fiber SCDCLs in dual-comb pump-probe measurements. In this paper, we break this fundamental trade-off by devising an all-optical dynamic repetition rate difference (Δfrep) modulation technique. We demonstrate the dynamic Δfrep modulation in a modified version of the recently developed counterpropagating all-normal dispersion (CANDi) fiber laser. We verify that our all-optical dynamic Δfrep modulation technique does not introduce excessive relative timing jitter. In addition, the dynamic modulation mechanism is studied and validated both theoretically and experimentally. As a proof-of-principle experiment, we apply this so-called dynamic CANDi (DCANDi) fiber laser to measure the relaxation time of a semiconductor saturable absorber mirror, achieving a measurement speed and duty cycle enhancement factor of 143. DCANDi fiber laser is a promising light source for low-complexity, high-speed, high-sensitivity ultrafast dual-comb pump-probe measurements.

Image reconstruction through the opaque medium has great significance in fields of biophotonics, optical imaging, mesoscopic physics, and optical communications. Previous researches are limited in the simple linear scattering process. Here, we develop a nonlinear speckle decoder network, which can reconstruct the phase information of the fundamental frequency wave via the nonlinear scattering signal. Further, we validate the ability of our model to recover simple and complex structures by using MNIST and CIFAR data sets, respectively. We then show that the model is able to restore the image information through different sets of nonlinear diffusers and reconstruct the image of a kind of completely unseen object category. The proposed method paves the way to nonlinear scattering imaging and information encryption.

Achieving ultra-precise wide-range terahertz (THz) phase modulation has been a long-standing challenge due to the short wavelength and sensitive phase of THz waves. This paper proposes a new ultra-high precision phase control method employing a digitally coding needle meta-chip embedded in a waveguide. The needle tips can effectively couple THz waves via the charge aggregation effect. By controlling the Schottky diodes with coding voltages, the charge on each meta-structure part can be tuned to form strong or weak resonances, producing phase shifts. Crucially, the massive charge accumulation and the sub-λ/10 distance between needle tips lead to near-field coupling among multiple tips. Therefore, modulation of the charge at each tip by multichannel coding voltages enables combined resonance tuning of THz waves, yielding a nonlinear phase superposition. Here, a meta-chip containing 8 needle meta-structure units is demonstrated, which breaks through the precision limitation of independent units and realizes super-resolution precision phase modulation similar to super-resolution imaging. In the 213–227 GHz band, we achieve a phase shift exceeding 180° with 11.25° accuracy, and a phase shift of over 170° with an accuracy of 3°. This super-resolution phase modulation strategy provides a new idea for future high-precision applications of THz integrated systems.

An optical frequency comb, as a spectrum made of discrete and equally spaced spectral lines, is a light source with essential applications in modern technology. Cavity optomechanical systems were found to be a feasible candidate for realizing an on-chip frequency comb with low repetition rate. However, it was difficult to increase the comb line numbers of this type of frequency combs because the mechanical oscillation amplitude of such a system, which determines the frequency comb bandwidth, cannot quickly increase with pump laser power. Here, we develop a new approach to generate a broadband optomechanical frequency comb by employing a different mechanism to enhance the mechanical oscillation. Two pump tones with their frequency difference matching the mechanical frequency will drive the system into a self-organized nonlinear resonance and thus tremendously transfer the energy to the mechanical resonator. As a result, more than 10,000 or even more comb lines become available under the pump laser power of the order of milliwatts. A unique feature of the self-organized resonance is the mechanical frequency locking so that, within a certain range of the frequency difference between two drive tones, the distance between comb teeth can be locked by the two drive tones and becomes independent of any change of pump power. This property guarantees a stable repetition rate of the generated frequency comb.

Programmable photonic integrated circuits (PPICs) emerge as a novel technology with an enormous potential for ground-breaking innovation. Different architectures are currently being considered that dictate how waveguides should be connected to realize a broadly usable circuit. We focus on the effect of varying connectivity architectures on the routing of light. Three types of uniform meshes are studied, and we introduce a newly developed mesh that is called ring-connected straight lines. We provide an analytical formula to calculate exact distances in these meshes and introduce several metrics relating to routing to compare these meshes. We show that hexagonal tiles are the most promising, but the ring-connected straight lines architecture has a use case as well. Besides this, the effect of defect couplers is also studied. We find that the effects of these failures vary greatly by type and severity on the routability of the mesh.

Improving the functionality of an optical sensor on a prefabricated platform relies heavily on an optical signal conditioning method that actively modulates optical signals. In this work, we present a method for active modulation of an optical sensor response that uses fiber modal interferometers integrated in parallel. Over a broad frequency range of 1 Hz to 1 kHz, the interferometers’ technology allows for adjustable amplification, attenuation, and filtering of dynamic signals. The suggested method is also used to enhance the real-time response of an optical fluid flowmeter. In order to keep tabs on different physical fields, the suggested approach promotes the creation of self-conditioning sensing systems.

The layered two-dimensional material tungsten diselenide (WSe2) has triggered tremendous interests in the field of optoelectronic devices due to its exceptional carrier transport property. Nevertheless, the limited absorption of WSe2 in the near infrared (NIR) band poses a challenge for the application of WSe2 photodetectors in night vision, telecommunication, etc. Herein, the enhanced performance of the WSe2 photodetector is demonstrated through the incorporation of titanium nitride nanoparticles (TiN NPs), complemented by an atomically-thick Al2O3 layer that aids in suppressing the dark current. It is demonstrated that TiN NPs can dramatically enhance the absorption of light in the proposed WSe2 photodetector in the NIR regime. This enhancement boosts photocurrent responses through the generation of plasmonic hot electrons, leading to external quantum efficiency (EQE) enhancement factors of 379.66% at 850 nm and 178.47% at 1550 nm. This work presents, for the first time, to our knowledge, that the WSe2 photodetector is capable of detecting broadband light spanning from ultraviolet to the telecommunication range, all achieved without the reliance on additional semiconductor materials. This achievement opens avenues for the advancement of cost-effective NIR photodetectors.

Two-dimensional (2D) graphene has emerged as an excellent partner for solving the scarcity of ultraviolet photodetectors based on three-dimensional (3D) AlGaN, in which the design of a 2D graphene/3D AlGaN junction becomes crucial. This study investigates the response mechanisms of two distinct graphene/AlGaN (Gr-AlGaN) photodetectors in the lateral and vertical configurations. For the lateral Gr-AlGaN photodetector, photogenerated electrons drifting into p-type graphene channel induce negative photoconductivity and a persistent photoconductive effect, resulting in a high responsivity of 1.27×104 A/W and detectivity of 3.88×1012 Jones. Although the response capability of a vertical Gr-AlGaN device is inferior to the lateral one, it shows significantly reduced dark current and self-powered detection. The photogenerated electron-hole pair can be spontaneously separated by the junction electric field and generate a photocurrent at zero bias. Hence, the vertical Gr-AlGaN photodetector array is satisfied for passive driving imaging like deep space detection. Conversely, the exceptional response of the lateral Gr-AlGaN device emphasizes its prospects for steady object recognition with low-light emission. Moreover, the improved imaging sharpness with light illumination duration makes it suitable for biomimetic visual learning, which follows a recognition to memory process. This study elucidates an efficient approach for diverse photodetection applications through the configuration design of Gr-AlGaN junctions.

Flexible quantum dot light-emitting diodes (QLEDs) show great promise for the next generation of flexible, wearable, and artificial intelligence display applications. However, the performance of flexible QLEDs still lags behind that of rigid substrate devices, hindering their commercialization for display applications. Here we report the superior performance of flexible QLEDs based on efficient red ZnCdSe/ZnS/ZnSe QDs (A-QDs) with anti-type-I nanostructures. We reveal that using ZnS as an intermediate shell can effectively confine the exciton wavefunction to the inner core, reducing the surface sensitivity of the QDs and maintaining its excellent emission properties. These flexible QLEDs exhibit a peak external quantum efficiency of 23.0% and a long lifetime of 63,050 h, respectively. The anti-type-I nanostructure of A-QDs in the device simultaneously suppresses defect-induced nonradiative recombination and balances carrier injection, achieving the most excellent performance of flexible QLEDs ever reported. This study provides new insights into achieving superior performance in flexible QD-based electroluminescent devices.

The dynamics of wave packets carrying a spatiotemporal vortex in the spatial fractional system is still an open problem. The difficulty stems from the fact that the fractional Laplacian derivative is essentially a nonlocal operator, and the vortex is space-time coupled. Here, we investigate the transmission of spatiotemporal vortices in the spatial fractional wave equation (FWE) and demonstrate the effects of linewidth, vortex topological charge, and linear chirp modulation on the transmission of Bessel-type spatiotemporal vortex pulses (BSTVPs). Under narrowband conditions, we find that the propagation of BSTVP in the FWE can be seen as the coherent superposition of two linearly shifted half-BSTVPs and can reveal orbital angular momentum backflow for the half-BSTVP. Our analysis can be extended to other spatiotemporal vortex pulses.

Optical antennas play a pivotal role in interfacing integrated photonic circuits with free-space systems. Designing antennas for optical phased arrays ideally requires achieving compact antenna apertures, wide radiation angles, and high radiation efficiency all at once, which presents a significant challenge. Here, we experimentally demonstrate a novel ultra-compact silicon grating antenna, utilizing subwavelength grating nanostructures arranged in a transversally interleaved topology to control the antenna radiation pattern. Through near-field phase engineering, we increase the antenna’s far-field beam width beyond the Fraunhofer limit for a given aperture size. The antenna incorporates a single-etch grating and a Bragg reflector implemented on a 300-nm-thick silicon-on-insulator (SOI) platform. Experimental characterizations demonstrate a beam width of 44°×52° with -3.22 dB diffraction efficiency, for an aperture size of 3.4 μm×1.78 μm. Furthermore, to the best of our knowledge, a novel topology of a 2D antenna array is demonstrated for the first time, leveraging evanescently coupled architecture to yield a very compact antenna array. We validated the functionality of our antenna design through its integration into this new 2D array topology. Specifically, we demonstrate a small proof-of-concept two-dimensional optical phased array with 2×4 elements and a wide beam steering range of 19.3º × 39.7º. A path towards scalability and larger-scale integration is also demonstrated on the antenna array of 8×20 elements with a transverse beam steering of 31.4º.

Optical trapping has revolutionized various scientific disciplines with its non-invasive, high-resolution manipulation capabilities. However, conventional optical tweezers face limitations in effectively manipulating metallic particles due to their high reflectivity and associated scattering forces. Plasmonic tweezers, harnessing surface plasmons in metallic nanostructures, offer a promising solution by confining light to deep subwavelength scales and enhancing optical forces. However, dynamically manipulating metallic particles with plasmonic tweezers without mechanical adjustments remains a significant challenge. In this paper, we propose a novel approach utilizing dynamic optical tweezers with tunable plasmonic fields for metallic particle manipulation. By dynamically tailoring plasmonic fields with holograms, metallic particles can be manipulated without mechanical adjustments. Finite-difference time-domain simulations and Maxwell stress tensor calculations demonstrate the effectiveness of this technique, which offers simplicity, precision, and motionlessness in metallic particle manipulation. This advancement holds promise for applications in surface-enhanced Raman scattering, biosensing, super-resolved detection, and nanoparticle assembly, opening new avenues in plasmonic tweezers technology.

The dynamic and integrated control of near- and far-field electromagnetic waves is essential for advancing emerging intelligent information technology. Metasurfaces, distinguished by their low-profile design, cost-effectiveness, and ease of fabrication, have successfully revolutionized various electromagnetic functions. However, current research on the dynamic integrated manipulation of near-field and far-field electromagnetic waves using a single metasurface remains relatively constrained, due to the complexity of element-level control, restricted dynamic tuning range, and tuning speed. Herein, we propose an element-level controlled, versatile, compact, and broadband platform allowing for the real-time electronic reconstruction of desired near/far-field electromagnetic wavefronts. This concept is achieved by precisely regulating the 1-bit amplitude coding pattern across a guided-wave-excited metasurface aperture loaded with PIN diodes, following our binary-amplitude holographic theory and modified Gerchberg–Saxton (G–S) algorithm. Consistent findings across calculations, simulations, and experiments highlight the metasurface’s robust performance in 2D beam scanning, frequency scanning, dynamic focusing lens, dynamic holography display, and 3D multiplexing holography, even under 1-bit control. This simplified and innovative metasurface architecture holds the promise of substantially propelling forthcoming investigations and applications of highly integrated, multifunctional, and intelligent platforms.

Light detection and ranging (LiDAR), as a hot imaging technology in both industry and academia, has undergone rapid innovation and evolution. The current mainstream direction is towards system miniaturization and integration. There are many metrics that can be used to evaluate the performance of a LiDAR system, such as lateral resolution, ranging accuracy, stability, size, and price. Until recently, with the continuous enrichment of LiDAR application scenarios, the pursuit of imaging speed has attracted tremendous research interest. Particularly, for autonomous vehicles running on motorways or industrial automation applications, the imaging speed of LiDAR systems is a critical bottleneck. In this review, we will focus on discussing the upper speed limit of the LiDAR system. Based on the working mechanism, the limitation of optical parts on the maximum imaging speed is analyzed. The beam scanner has the greatest impact on imaging speed. We provide the working principle of current popular beam scanners used in LiDAR systems and summarize the main constraints on the scanning speed. Especially, we highlight the spectral scanning LiDAR as a new paradigm of ultrafast LiDAR. Additionally, to further improve the imaging speed, we then review the parallel detection methods, which include multiple-detector schemes and multiplexing technologies. Furthermore, we summarize the LiDAR systems with the fastest point acquisition rate reported nowadays. In the outlook, we address the current technical challenges for ultrafast LiDAR systems from different aspects and give a brief analysis of the feasibility of different approaches.

Independent light propagation through one or multiple modes is commonly considered as a basic demand for mode manipulation in few-mode fiber (FMF)- or multimode fiber (MMF)-based optical systems such as transmission links, optical fiber lasers, or distributed optical fiber sensors. However, the insertion of doped-fiber amplifiers always kills the entire effort by inducing significant modal crosstalk. In this paper, we propose the design of doped-fiber amplifiers in FMF-based systems adopting identical multiple-ring-core (MRC) index profiles for both passive and doped fibers to achieve low modal crosstalk. We develop the direct-glass-transition (DGT) modified chemical vapor deposition (MCVD) processing for precise fabrication of few-mode erbium-doped fibers (FM-EDFs) with MRC profiles of both refractive index and erbium-ion doping distribution. Then, a few-mode erbium-doped-fiber amplifier (FM-EDFA) with a maximum gain of 26.08 dB and differential modal gain (DMG) of 2.3 dB is realized based on fabricated FM-EDF matched with a transmission FMF supporting four linearly polarized (LP) modes. With the insertion of the FM-EDFA, 60 + 60 km simultaneous LP01/LP11/LP21/LP02 transmission without inter-modal multiple-input multiple-output digital signal processing (MIMO-DSP) is successfully demonstrated. The proposed design of low-modal-crosstalk doped-fiber amplifiers provides, to our knowledge, new insights into mode manipulation methods in various applications.

Rayleigh backscattering enhancement (RSE) of optical fibers is an effective means to improve the performance of distributed optical fiber sensing. Femtosecond laser direct-writing techniques have been used to modulate the fiber core for RSE. However, in-core modulation loses more transmission light, thus limiting the sensing distance. In this work, a cladding-type RSE (cl-RSE) structure is proposed, where the femtosecond laser is focused in the fiber cladding and an array of scatterers is written parallel to the core. The refractive-index modulation structure redistributes the light in the cladding, and the backward scattered light is recovered, which enhances the Rayleigh backscattered signal with almost no effect on the core light. Experimentally, it was demonstrated that in an effectual cl-RSE structure, the insertion loss was reduced to 0.00001 dB per scatterer, corresponding to the lowest value for a point scatterer to date. The cl-RSE structure accomplished measurements up to 800°C. In particular, the temperature measurement fluctuation of the cl-RSE fiber portion is only 0.00273°C after annealing. These results show that the cl-RSE structure has effective scattering enhancement, ultra-low loss, and excellent high-temperature characteristics, and has great potential for application in Rayleigh scattering-enhanced distributed fiber sensing.

Polarimetric dehazing is an effective way to enhance the quality of images captured in foggy weather. However, images of essential polarization parameters are vulnerable to noise, and the brightness of dehazed images is usually unstable due to different environmental illuminations. These two weaknesses reveal that current polarimetric dehazing algorithms are not robust enough to deal with different scenarios. This paper proposes a novel, to our knowledge, and robust polarimetric dehazing algorithm to enhance the quality of hazy images, where a low-rank approximation method is used to obtain low-noise polarization parameter images. Besides, in order to improve the brightness stability of the dehazed image and thus keep the image have more details within the standard dynamic range, this study proposes a multiple virtual-exposure fusion (MVEF) scheme to process the dehazed image (usually having a high dynamic range) obtained through polarimetric dehazing. Comparative experiments show that the proposed dehazing algorithm is robust and effective, which can significantly improve overall quality of hazy images captured under different environments.

Various neuromodulation techniques have been developed to modulate the peak activity of neurons, thereby regulating brain function and alleviating neurological disorders. Additionally, neuronal stimulation and imaging have significantly contributed to the understanding and treatment of these diseases. Here, we propose utilizing photonic nanojets for optical stimulation and imaging of neural cells. The application of resin microspheres as microlenses enhances fluorescence imaging of neural lysosomes, mitochondria, and actin filaments by generating photonic nanojets. Moreover, optical tweezers can precisely manipulate the microlenses to locate specific targets within the cell for real-time stimulation and imaging. The focusing capabilities of these microlenses enable subcellular-level spatial precision in stimulation, allowing highly accurate targeting of neural cells while minimizing off-target effects. Furthermore, fluorescent signals during neural cell stimulation can be detected in real-time using these microlenses. The proposed method facilitates investigation into intercellular signal transmission among neural cells, providing new insights into the underlying mechanisms of neuronal cell activities at a subcellular level.

Optical time-stretch (OTS) imaging flow cytometry offers a promising solution for high-throughput and high-precision cell analysis due to its capabilities of high-speed, high-quality, and continuous imaging. Compressed sensing (CS) makes it practically applicable by significantly reducing the data volume while maintaining its high-speed and high-quality imaging properties. To enrich the information of the images acquired with CS-equipped OTS imaging flow cytometry, in this work we propose and experimentally demonstrate Fourier-domain-compressed OTS quantitative phase imaging flow cytometry. It is capable of acquiring intensity and quantitative phase images of cells simultaneously from the compressed data. To evaluate the performance of our method, static microparticles and a corn root cross section are experimentally measured under various compression ratios. Furthermore, to show how our method can be applied in practice, we utilize it in the drug response analysis of breast cancer cells. Experimental results show that our method can acquire high-quality intensity and quantitative phase images of flowing cells at a flowing speed of 1 m/s and a compression ratio of 30%. Combined with machine-learning-based image analysis, it can distinguish drug-treated and drug-untreated cells with an accuracy of over 95%. We believe our method can facilitate cell analysis in both scientific research and clinical settings where both high-throughput and high-content cell analysis is required.

Whispering gallery mode (WGM) microlasers are highly sensitive to localized refractive index changes allowing to link their emission spectrum to various chemical, mechanical, or physical stimuli. Microlasers recently found applications in biological studies within single cells, in three-dimensional samples such as multicellular spheroids, or in vivo. However, detailed studies of biological samples also need to account for the structural heterogeneity of tissues and live animals, therefore requiring a combination of high-resolution microscopy and laser spectroscopy. Here, we design and construct a light sheet fluorescence microscope with a coupled spectrometer for use in microlaser studies for combined high-resolution, high-speed imaging and WGM spectral analysis. The light sheet illumination profile and the decoupled geometry of excitation and emission hereby directly affect the lasing and sensing properties, mainly through geometric constraints and by light coupling effects. We demonstrate the basic working principle of microlaser spectroscopy under light sheet excitation and measure the absolute refractive index within agarose and in zebrafish tail muscle tissue. We further analyze the light coupling conditions that lead to the occurrence of two separate oscillation planes. These so-called cross modes can be scanned around the entire microlaser surface, which allows to estimate a surface-averaged refractive index profile of the microlaser environment.

Non-destructive and accurate inspection of gallium nitride light-emitting diode (GaN-LED) epitaxial wafers is important to GaN-LED technology. However, the conventional electroluminescence inspection, the photoluminescence inspection, and the automated optical inspection cannot fulfill the complex technical requirements. In this work, an inspection method and an operation system based on soft single-contact operation, namely, single-contact electroluminescence (SC-EL) inspection, are proposed. The key component of the SC-EL inspection system is a soft conductive probe with an optical fiber inside, and an AC voltage (70Vpp, 100 kHz) is applied between the probe and the ITO electrode under the LED epitaxial wafer. The proposed SC-EL inspection can measure both the electrical and optical parameters of the LED epitaxial wafer at the same time, while not causing mechanical damage to the LED epitaxial wafer. Moreover, it is demonstrated that the SC-EL inspection has a higher electroluminescence wavelength accuracy than photoluminescence inspection. The results show that the non-uniformity of SC-EL inspection is 444.64%, which is much lower than that of photoluminescence inspection. In addition, the obtained electrical parameters from SC-EL can reflect the reverse leakage current (Is) level of the LED epitaxial wafer. The proposed SC-EL inspection can ensure high inspection accuracy without causing damage to the LED epitaxial wafer, which holds promising application in LED technology.

A spectral programmable, continuous-wave mid-infrared (MIR) optical parametric oscillator (OPO), enabled by a self-developed high-power spectral tailorable fiber laser, was proposed and realized. While operating at a single-wavelength, the maximum idler power reached 5.53 W at 3028 nm, with a corresponding pump-to-idler conversion efficiency of 14.7%. The wavelength number switchable output was available from one to three. The single idler was tunable in a range of 528 nm (2852–3380 nm). In a dual-wavelength operation, the interval between two idlers could be flexibly tuned for 470 nm (53–523 nm), and the intensity of each channel was controllable. Triple-wavelength idler emission was realized, meanwhile exhibiting spectral custom-tailored characteristics. Furthermore, we balanced the parametric gain through the pre-modulating broadband multi-peak pump spectra, enabling a 10 dB bandwidth adjustment of the idler emission from 20 to 125 nm. This versatile mid-infrared laser, simultaneously featuring wide tuning, multi-wavelength operation, and broad bandwidth manipulation, has great application potential in composition detection, terahertz generation, and speckle-free imaging.

Circularly polarized lasers play a pivotal role in classical optics, nanophotonics, and quantum optical information processing, while their fabrication remains complex. This article begins with examining the interactions between stimulated emission and chiral matter, outlining a simple strategy for producing circularly polarized lasing from chiral metal-organic frameworks (MOFs), such as the zeolitic imidazolate framework (ZIF), embedded with achiral laser dyes (L/D-ZIF⊃dyes). It is found that the stimulated emission threshold and intensity are influenced by the interplay between the chiral polarization of the pump light and the inherent chirality of the MOF nanoparticles. We further present the design of a chiral vertical-cavity surface-emitting laser (VCSEL), comprising an L/D-ZIF⊃dyes solid-state film sandwiched between a high-reflectivity distributed Bragg reflector (DBR) mirror and a silver film. The cavity-based lasing exhibits higher asymmetry between emitting left-handed and right-handed polarized light compared to chiral spontaneous emission (SE) and amplified spontaneous emission (ASE), with an asymmetry value glum of approximately ±0.31. This value is nearly four-fold greater than that of SE and twice that of ASE. Our findings reveal a new approach to amplify chiral signals, promoting the comprehension and application of chiral–matter interactions, and offering a simple yet effective strategy to fabricate chiral lasers.

Thin-film periodically poled lithium niobate (TF-PPLN) devices have recently gained prominence for efficient wavelength conversion processes in both classical and quantum applications. However, the patterning and poling of TF-PPLN devices today are mostly performed at chip scales, presenting a significant bottleneck for future large-scale nonlinear photonic systems that require the integration of multiple nonlinear components with consistent performance and low cost. Here, we take a pivotal step towards this goal by developing a wafer-scale TF-PPLN nonlinear photonic platform, leveraging ultraviolet stepper lithography and an automated poling process. To address the inhomogeneous broadening of the quasi-phase matching (QPM) spectrum induced by film thickness variations across the wafer, we propose and demonstrate segmented thermal optic tuning modules that can precisely adjust and align the QPM peak wavelengths in each section. Using the segmented micro-heaters, we show the successful realignment of inhomogeneously broadened multi-peak QPM spectra with up to 57% enhancement of conversion efficiency. We achieve a high normalized conversion efficiency of 3802% W-1 cm-2 in a 6 mm long PPLN waveguide, recovering 84% of the theoretically predicted efficiency in this device. The advanced fabrication techniques and segmented tuning architectures presented herein pave the way for wafer-scale integration of complex functional nonlinear photonic circuits with applications in quantum information processing, precision sensing and metrology, and low-noise-figure optical signal amplification.

Standing-wave supermode microresonators that are created through the strong coupling between counter-propagating modes have emerged as versatile platforms for sensing and nonlinear optics. For example, these microresonators have shown potential in nanoparticle sizing and counting, as well as enhancing the single-photon optomechanical coupling rate of stimulated Brillouin scattering. However, it has been observed that the relation between the mode linewidth and on-resonance transmission of the split supermodes differs obviously from that of the non-split modes. This behavior is typically quantified by the coupling ideality (I), which remains inadequately explored for the standing-wave supermodes. In this study, we theoretically and experimentally investigate the coupling ideality of standing-wave supermodes in a commonly employed configuration involving a SiO2 microresonator side-coupled to a tapered fiber. Our findings demonstrate that, even with a single-mode tapered fiber, the coupling ideality of the standing-wave supermodes is limited to 0.5, due to the strong backscattering-induced energy loss into the counter-propagating direction, resulting in an additional equivalent parasitic loss. While achieving a coupling ideality of 0.5 presents challenges for reaching over-coupled regimes, it offers a convenient approach for adjusting the total linewidth of the modes while maintaining critically-coupled conditions.

Advancements in microwave photonics have yielded novel approaches for generating high-purity microwave sources. Among these, optoelectronic oscillators (OEOs) and coupled optoelectronic oscillators (COEOs) have demonstrated the capability to generate frequency-independent microwaves with exceptionally low phase noise. Nonetheless, the tunability of the oscillators is rather limited due to the necessity for narrowband electronic bandpass filters, presenting challenges in achieving both wide and rapid tuning capabilities. Here, we present a COEO featuring ultralow phase noise, flexible tuning capability, and high robustness. This is achieved through a quiet point (QP)-operated harmonic mode-locked fiber laser, which effectively mitigates optical amplifier noise and supermode competition, thus significantly diminishing the necessity for ultra-narrow electronic filters. Due to the liberated tuning ability, we present an oscillator that can be tuned from 2 GHz to 18 GHz, with phase noise as low as -140 dBc/Hz at 10 kHz under the QP operation. We then illustrate the practical application of the proposed oscillator in generating frequency-hopping signals with consistent spurious modes less than -85 dBc, absolute phase noise below -135 dBc/Hz at 10 kHz, hopping resolution of 1.25 MHz, and fractional frequency stability below 6.1×10-12 at 1 s averaging time when locked to a reference. The presented COEO structure emerges as a compelling solution for agile and low-noise microwave sources in advanced wireless communication and radar systems.

Neuromorphic applications have shown great promise not only for efficient parallel computing mode to hold certain computational tasks, such as perception and recognition, but also as key biomimetic elements for the intelligent sensory system of next-generation robotics. However, achieving such a biomimetic nociceptor that can adaptively switch operation mode with a stimulation threshold remains a challenge. Through rational design of material properties and device structures, we realized an easily-fabricated, low-energy, and reconfigurable nociceptor. It is capable of threshold-triggered adaptive bi-mode jump that resembles the biological alarm system. With a tunnel silicon nitride (Si3N4) we mimicked the intensity- and rehearsal-triggered jump by means of the tunneling mode transition of Si3N4 dielectric. Under threshold signals the device can also express some common synaptic functions with an extremely low energy density of 33.5 fJ/μm2. In addition, through the modulation of Si3N4 thickness it is relatively easy to fabricate the device with differing pain degree. Our nociceptor analog based on a tunneling layer provides an opportunity for the analog pain alarm system and opens up a new path toward threshold-related novel applications.

There recently has been increasing interest in the research and application of the rotational Doppler effect (RDE), which paves a promising way to detect rotating objects remotely. In order to obtain more information about the rotating object from the rotational Doppler signal, composite vortex beams by coaxial superposition of orbital angular momentum (OAM) modes are often used as the probe beam. However, to the best of our knowledge, the RDE of composite vortex beams with arbitrary OAM spectra has not yet been comprehensively studied. In this paper, the correspondence between the OAM spectrum of a probe beam and the frequency spectrum of a rotational Doppler signal is theoretically analyzed. It is explicitly revealed that the RDE frequency spectrum of scattered light is related to the product of two autocorrelation functions: one from the OAM spectrum of probe beam and the other from the spiral spectrum of rotating object. On the basis of this relation, one can regulate the RDE frequency spectrum on demand via tailoring the OAM spectrum of the probe beam. As a proof of concept we design a special composite vortex beam to eliminate the broadening of the RDE spectrum induced by misalignment. These findings are of practical value in applications such as remote sensing and optical metrology.

Optical singularity states, which significantly affect propagation properties of light in free space or optical medium, can be geometrically classified into screw and edge types. These different types of singularity states do not exhibit direct connection, being decoupled from each other in the absence of external perturbations. Here we demonstrate a novel optical process in which a higher-order edge singularity state initially nested in the propagating Gaussian light field gradually involves into a screw singularity with a new-born topological charge determined by order of the edge state. The considered edge state comprises an equal superposition of oppositely charged vortex and antivortex modes. We theoretically and experimentally realize this edge-to-screw conversion process by introducing intrinsic vortex–antivortex interaction. We also present a geometrical representation for mapping this dynamical process, based on the higher-order orbital Poincaré sphere. Within this framework, the edge-to-screw conversion is explained by a mapping of state evolution from the equator to the north or south pole of the Poincaré sphere. Our demonstration provides a novel approach for manipulating singularity state by the intrinsic vortex–antivortex interactions. The presented phenomenon can be also generalized to other wave systems such as matter wave, water wave, and acoustic wave.

All-optical thermometry plays a crucial role in precision temperature measurement across diverse fields. Quantum defects in solids are one of the most promising sensors due to their excellent sensitivity, stability, and biocompatibility. Yet, it faces limitations, such as the microwave heating effect and the complexity of spectral analysis. Addressing these challenges, we introduce a novel approach to nanoscale optical thermometry using quantum defects in silicon carbide (SiC), a material compatible with complementary metal-oxide-semiconductor (CMOS) processes. This method leverages the intensity ratio between anti-Stokes and Stokes emissions from SiC color centers, overcoming the drawbacks of traditional techniques such as optically detected magnetic resonance (ODMR) and zero-phonon line (ZPL) analysis. Our technique provides a real-time, highly sensitive (1.06%K-1), and diffraction-limited temperature sensing protocol, which potentially helps enhance thermal management in the future miniaturization of electronic components.

Simulating the dynamic evolution of physical and molecular systems in a quantum computer is of fundamental interest in many applications. The implementation of dynamics simulation requires efficient quantum algorithms. The Lie-Trotter-Suzuki approximation algorithm, also known as the Trotterization, is basic in Hamiltonian dynamics simulation. A multi-product algorithm that is a linear combination of multiple Trotterizations has been proposed to improve the approximation accuracy. However, implementing such multi-product Trotterization in quantum computers remains challenging due to the requirements of highly controllable and precise quantum entangling operations with high success probability. Here, we report a programmable integrated-photonic quantum simulator based on a linear combination of unitaries, which can be tailored for implementing the linearly combined multiple Trotterizations, and on the simulator we benchmark quantum simulation of Hamiltonian dynamics. We modify the multi-product algorithm by integrating it with oblivious amplitude amplification to simultaneously reach high simulation precision and high success probability. The quantum simulator is devised and fabricated on a large-scale silicon-photonic quantum chip, which allows the initialization, manipulation, and measurement of arbitrary four-qubit states and linearly combined unitary gates. As an example, the quantum simulator is reprogrammed to emulate the dynamics of an electron spin and nuclear spin coupled system. This work promises the practical dynamics simulations of real-world physical and molecular systems in future large-scale quantum computers.

Integrated semiconductor lasers represent essential building blocks for integrated optical components and circuits and their stability in frequency is fundamental for the development of numerous frontier applications and engineering tasks. When dense optical circuits are considered, the stability of integrated laser sources can be impaired by the thermal cross-talk generated by the action of neighboring components, leading to a deterioration of the long-term system performance (on the scale of seconds). In this work we show the design and the experimental characterization of a silicon nitride photonic integrated circuit (PIC) that is able to frequency stabilize 16 semiconductor lasers, simultaneously. A stabilized 50 GHz-spaced two-channel system is demonstrated through the detection of the related beating note and the stability of the resulting waveform is characterized via the use of artificially induced thermal cross-talk stimuli.

Photonic integrated circuits are emerging as a promising platform for accelerating matrix multiplications in deep learning, leveraging the inherent parallel nature of light. Although various schemes have been proposed and demonstrated to realize such photonic matrix accelerators, the in situ training of artificial neural networks using photonic accelerators remains challenging due to the difficulty of direct on-chip backpropagation on a photonic chip. In this work, we propose a silicon microring resonator (MRR) optical crossbar array with a symmetric structure that allows for simple on-chip backpropagation, potentially enabling the acceleration of both the inference and training phases of deep learning. We demonstrate a 4×4 circuit on a Si-on-insulator platform and use it to perform inference tasks of a simple neural network for classifying iris flowers, achieving a classification accuracy of 93.3%. Subsequently, we train the neural network using simulated on-chip backpropagation and achieve an accuracy of 91.1% in the same inference task after training. Furthermore, we simulate a convolutional neural network for handwritten digit recognition, using a 9×9 MRR crossbar array to perform the convolution operations. This work contributes to the realization of compact and energy-efficient photonic accelerators for deep learning.

On-chip spectrometers with high compactness and portability enable new applications in scientific research and industrial development. Fourier transform (FT) spectrometers have the potential to realize a high signal-to-noise ratio. Here we propose and demonstrate a generalized design for high-performance on-chip FT spectrometers. The spectrometer is based on the dynamic in-plane reconfiguration of a waveguide coupler enabled by an integrated comb-drive actuator array. The electrostatic actuation intrinsically features ultra-low power consumption. The coupling gap is crucial to the spectral resolution. The in-plane reconfiguration surmounts the lithography accuracy limitation of the coupling gap, boosting the resolution to 0.2 nm for dual spectral spikes over a large bandwidth of 100 nm (1.5–1.6 μm) within a compact footprint of 75 μm×1000 μm. Meanwhile, the in-plane tuning range can be large enough for arbitrary wavelengths to ensure the effectiveness of spectrum reconstruction. As a result, the proposed spectrometer can be easily transplanted to other operation bands by simply scaling the structural parameters. As a proof-of-concept, a mid-infrared spectrometer is further demonstrated with a dual-spike reconstruction resolution of 1.5 nm and a bandwidth of 300 nm (4–4.3 μm).

Whispering gallery mode optical microresonators represent a promising avenue for realizing optical analogs of coherent light–atom interactions, circumventing experimental complexities. All-optical analogs of Autler–Townes splitting have been widely demonstrated, harnessing coupled optical microresonators, also known as photonic molecules, wherein the strong coupling between resonant fields enables energy level splitting. Here, we report the characterizations of Autler–Townes splitting in waveguide-coupled microring dimers featuring mismatched sizes. By exploiting backscattering-induced coupling via Rayleigh and Mie scatterers in individual rings, high-order Autler–Townes splitting has been realized, yielding supermode hybridization in a multi-level system. Upon resonance detuning using an integrated phase shifter, intra-cavity coupling-induced splitting becomes almost indistinguishable at the zero-detuning point where the strong inter-cavity coupling counteracts the imbalance of backscattering strengths in individual rings. Through demonstrations on the maturing silicon photonics platform, our findings establish a framework of electrically tunable photonic molecules for coupling-mediated Autler–Townes splitting, offering promising prospects for on-chip signal generation and processing across classical and quantum regimes.

The progress of on-chip optical communication relies on integrated multi-dimensional mode (de)multiplexers to enhance communication capacity and establish comprehensive networks. However, existing multi-dimensional (de)multiplexers, involving modes and wavelengths, face limitations due to their reliance on single-directional total internal reflection and multi-level mode conversion based on directional coupling principles. These constraints restrict their potential for full-duplex functionality and highly integrated communication. We solve these problems by introducing a photonic-like crystal-connected bidirectional micro-ring resonator array (PBMRA) and apply it to duplex mode-wavelength multiplexing communication. The directional independence of total internal reflection and the cumulative effect of the subwavelength-scale pillar within the single-level photonic crystal enable bidirectional mode and wavelength multiplexed signals to transmit among multi-pair nodes without interference, improving on-chip integration in single-level mode conversion. As a proof of concept, we fabricated a nine-channel bidirectional multi-dimensional (de)multiplexer, featuring three wavelengths and three TE modes, compactly housed within a footprint of 80 μm×80 μm, which efficiently transmits QPSK-OFDM signals at a rate of 216 Gbit/s, achieving a bit error rate lower than 10-4. Leveraging the co-ring transmission characteristic and the orthogonality of the mode-wavelength channel, this (de)multiplexer also enables a doubling of communication capacity using two physical transmission channels.

An integrated photonic circuit architecture to perform a modified-convolution operation based on the discrete fractional Fourier transform (DFrFT) is introduced. This is accomplished by utilizing two nonuniformly coupled waveguide lattices with equally spaced eigenmode spectra, the lengths of which are chosen so that the DFrFT and its inverse operations are achieved. A programmable modulator array is interlaced so that the required fractional convolution operation is performed. Numerical simulations demonstrate that the proposed architecture can effectively perform smoothing and edge detection tasks even for noisy input signals, which is further verified by electromagnetic wave simulations. Notably, mild lattice defects do not jeopardize the architecture performance, showing its resilience to manufacturing errors.

Optical tweezers (OTs) can immobilize and manipulate objects with sizes that span between nano- and micro-meter scales. The manipulating ability of OTs is traditionally characterized by stability factor (S), which can only indicate an empirical “hit-or-miss” process. Additionally, the current quantitative models for trapping stability rarely consider the influence of external flow. In this paper, a comprehensive analysis to quantify the optical trapping stability in a perturbed asymmetric potential well is presented from the perspective of statistics, especially for weak trapping scenarios. Our analytical formulation takes experimentally measurable parameters including particle size, optical power, and spot width as inputs and precisely outputs a statistically relevant mean trapping time. Importantly, this formulation takes into account general and realistic cases including fluidic flow velocity and other perturbations. To verify the model, a back-focal-plane-interferometer-monitored trapping experiment in a flow is set up and the statistical characteristics of trapping time demonstrate good agreement with theoretical predictions. In total, the model quantitatively reveals the effects of external disturbance on trapping time, which will find applications where optical trapping stability is challenged by external perturbations in weak trapping conditions.

Ultrathin plasmonic nanostructures offer an unparalleled opportunity for the study of light–matter interactions at the nanoscale and realization of compact nanophotonic devices. In this study, we introduce an ultrathin gold nanoribbon array and demonstrate an electric approach to actively tuning its plasmonic resonance, which leveraging the extreme light confinement capability in the ultrathin plasmonic nanostructure and a robust nanoscale electro-optical effect in indium tin oxide. Optimizing the design (to a total thickness as small as 12 nm for a 2-nm-thick gold nanoribbon array), we numerically demonstrate a spectral shift in the plasmonic resonance up to 36 nm along with an approximately 16% change in the transmission at a gate voltage below 1.7 V at the wavelength of 1.47 μm. This work presents progress towards electric tuning of plasmonic resonances in ultrathin metallic nanostructures for various applications including surface-enhanced spectroscopy, spontaneous emission enhancement, and optical modulation.