Collagen characterization is crucial for disease diagnostics, prevention, and understanding, with growing focus on quantitative analysis at tissue and fibril levels. Numerous models have been developed to quantify structural changes in collagen linked to various pathologies. However, many approaches remain limited to conceptual descriptions or rely on custom software, often requiring programming skills, which restricts their clinical application and potential impact. We introduce CollagenFitJ, a plugin for the open-source software platform ImageJ/FIJI, which represents a widely used microscopy image analysis tool. CollagenFitJ makes use of the cylindrical symmetry model for collagen to enable facile quantitative assessment of polarization-resolved second harmonic generation microscopy image stacks. The plugin’s main outputs are collagen structure-related maps (e.g., orientation and anisotropy of collagen fibrils within the focal volume), which can be accompanied by distribution and randomness maps for a series of structure-related parameters. We describe and validate the use of CollagenFitJ on images acquired on rat-tail tendons, collagen capsules surrounding human thyroid nodules, and mouse colon tumors, using both scanning and widefield second harmonic generation microscopy datasets. The plugin was designed to be user-friendly, requiring little to no experience in image processing and coding to facilitate access for life scientists, medical staff, and microscopy practitioners with limited coding skills or time availability required for coding.

In recent years, artificial intelligence (AI) has demonstrated immense potential in driving breakthroughs in the semiconductor industry, particularly in full-color display technologies. Benefiting from the deep integration of AI, these technologies are experiencing unprecedented innovation and industrial transformation, garnering significant attention. These advancements provide a solid foundation for displays with higher color gamut and resolution. In addition, the integration of deep learning with dimming technologies has enabled new display systems to deliver superior viewing experiences with reduced energy consumption. This review highlights recent progress in four key areas of AI application in full-color display technologies: epitaxial structure design, defect detection and repair, perovskite synthesis, and dynamic dimming. AI-driven advancements in these domains are paving the way for smarter, more efficient display technologies. By leveraging AI’s powerful data processing and optimization capabilities, full-color display systems are poised to achieve enhanced performance, energy efficiency, and user satisfaction, marking a significant step toward a more intelligent and innovative future.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.

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.