The degradation of image quality in space-based remote sensing is a critical challenge due to atmospheric disturbances. In this paper, we propose a new model to simulate image blur effects caused by turbulence and aerosol scattering. It also analyzes a distortion vector field to simulate the distortion effects from atmospheric turbulence. Using this time-varying physical model, we present a generative adversarial network called MSFFA-GAN. It uses a multi-scale feature fusion and attention mechanism to analyze and apply optimal constraints on deep neural networks for atmospheric impact parameters. This helps our network handle complex atmospheric conditions that cause image degradation. Experimental results show that MSFFA-GAN improves the peak signal-to-noise ratio (PSNR) by 5.05 dB and the structural similarity index (SSIM) by 4.43%. It effectively restores degraded images and enhances the image quality of remote sensing systems.

Photon-level single-pixel imaging overcomes the reliance of traditional imaging techniques on large-scale array detectors, offering the advantages such as high sensitivity, high resolution, and efficient photon utilization. In this paper, we propose a photon-level dynamic feature single-pixel imaging method, leveraging the frequency domain sparsity of the object’s dynamic features to construct a compressed measurement system through discrete random photon detection. In the experiments, we successfully captured 167 and 200 Hz featured frequencies and achieved high-quality image reconstruction with a data compression ratio of 20%. Our approach introduces a new detection dimension, significantly expanding the applications of photon-level single-pixel imaging in practical scenarios.

This study proposes compact Alvarez varifocal lenses with a wide varifocal range, which consist of a set of Alvarez lenses and three sets of ordinary lenses. The Alvarez lenses have a double freeform surface and are driven by a cam-driven structure. The axial size of the proposed varifocal Alvarez lenses is only 30.50 mm. The experimental results show that the proposed varifocal lens can achieve a focal length range from 15 to 75 mm, and the imaging quality is still in an acceptable range for optical lens requirements. The compact varifocal Alvarez lenses are expected to be used in surveillance systems, industrial inspection, and machine vision.

Deep learning-assisted facial expression recognition has been extensively investigated in sentiment analysis, human-computer interaction, and security surveillance. Generally, the recognition accuracy in previous reports requires high-quality images and powerful computational resources. In this work, we quantitatively investigate the impacts of frequency-domain filtering on spatial-domain facial expression recognition. Based on the Fer2013 dataset, we filter out 82.64% of high-frequency components, resulting in a decrease of 3.85% in recognition accuracy. Our findings well demonstrate the essential role of low-frequency components in facial expression recognition, which helps reduce the reliance on high-resolution images and improve the efficiency of neural networks.

Non-line-of-sight (NLOS) imaging enables the detection and reconstruction of hidden objects around corners, offering promising applications in autonomous driving, remote sensing, and medical diagnosis. However, existing steady-state NLOS imaging methods face challenges in achieving high efficiency and precision due to the need for multiple diffuse reflections and incomplete Fourier amplitude sampling. This study proposes, to our knowledge, a novel steady-state NLOS imaging technique via polarization differential correlography (PDC-NLOS). By employing the polarization difference of the laser speckle, the method designs a single-shot polarized speckle illumination strategy. The fast and stable real-time encoding for hidden objects ensures stable imaging quality of the PDC-NLOS system. The proposed method demonstrates millimeter-level imaging resolution when imaging horizontally and vertically striped objects.

The integration of mid-wave infrared (MWIR) and long-wave infrared (LWIR) imaging into a compact high-performance system remains a significant challenge in infrared optics. In this work, we present a dual-band infrared imaging system based on hybrid refractive-diffractive-metasurface optics. The system integrates a silicon-based metalens for the MWIR channel and a hybrid refractive-diffractive lens made of high-refractive-index chalcogenide glass for the LWIR channel. It achieves a compact total track length (TTL) of 11.31 mm. The MWIR channel features a 1.0 mm entrance pupil diameter, a 10° field of view (FOV), and achromatic imaging across the 3–4 µm spectral range with a focal length of 1.5 mm. The LWIR channel provides an 8.7 mm entrance pupil diameter, a 30° FOV, and broadband achromatic correction over the 8–12 µm spectral range with a focal length of 13 mm. To further enhance spatial resolution and recover fine image details, we employ low-rank adaptation (LoRA) fine-tuning within a physics-informed StableSR framework. This hybrid optical approach establishes, to our knowledge, a new paradigm in dual-band imaging systems by leveraging the complementary advantages of metalens dispersion engineering, diffractive phase modulation, and conventional refractive optics, delivering a lightweight, multispectral imaging solution with superior spectral discrimination and system compactness.

Terahertz (THz) radiation, with unique properties and wide-ranging applications, hinges on efficient sources and detectors for further development. Research on THz array detectors for low-repetition-frequency, high-pulse-energy sources is in its infancy. This study presents a THz optoacoustic array detector. It has high response speed and sensitivity, enabling 3D THz spot scanning and imaging. Size reduction of the piezoelectric probe crystal improves resolution, parallel scanning boosts efficiency, and it is highly scalable for real-time imaging.

Optical diagnostics are essential in monitoring the progression of plasma in high-energy-density physics research. The abrupt transitions in plasma evolution, whether caused by laser irradiation or hydrodynamic instabilities, cannot be accurately distinguished using only two-dimensional (2D) gated detectors or a streak camera individually. In this paper, we introduce a hybrid diagnostic system that combines a streak camera and gated detectors. This innovative approach enables us to measure both the plasma density evolution and 2D morphology simultaneously. These advanced diagnostics have been utilized in recent laboratory astrophysics experiments, effectively capturing the plasma flow density distribution and flow velocity.

The growing demand for broadband near-infrared (NIR) irradiation in security, biomedicine, and food science is driving the development of new NIR light sources. Herein, a series of Cr3+/Ni2+ co-doped transparent glass ceramics containing octahedrally coordinated KCdF3 nanocrystals have been successfully prepared. Under 450 nm blue light excitation, the combination of Cr3+ and Ni2+ results in an ultra-broadband NIR emission band ranging from 700 to 1800 nm. Based on the excitation and emission spectra and the decay lifetime curves, the energy transfer (ET) efficiency from Cr3+ to Ni2+ is confirmed to be 50.2%. A glass ceramic-converted NIR-LED was fabricated by integrating a commercial blue LED chip with a representative Cr3+/Ni2+ co-doped glass ceramic and has demonstrated potential applications in the areas of covert information recognition and night vision illumination. Our investigation provides new insights into the development of ultra-broadband NIR light sources that are both cost-effective and efficient.

A hydrogen peroxide (H2O2) detection system is demonstrated with multi-pass tunable diode laser absorption spectroscopy using a 75 m Herriott absorption cell. The system utilizes an ∼8 µm continuous wave distributed feedback quantum cascade laser (CW DFB-QCL) targeting a prominent H2O2 line at 1253.1 cm-1 within the fundamental absorption band. A wavelength modulation spectroscopy with the first harmonic normalized second harmonic (WMS-2f/1f) detection method is employed to eliminate laser light intensity fluctuations. Calibration of the system is conducted by means of chemical titration to establish the correlation between the peak value of the 2f/1f signal and H2O2 concentration. An Allan–Werle deviation analysis shows that a minimum detection limit (MDL) of 2.9 ppb (1 ppb = 10-9) for H2O2 is achieved with an average time of 147 s. To the best of our knowledge, this is the lowest detection limit for H2O2 at the wavenumber of 1253.1 cm-1. The system exhibits robust resistance to interference from other gases, especially water vapor (H2O), making it suitable for measuring the residual concentration of H2O2 post-sterilization and the concentration of H2O2 in the atmosphere.

The strong-field processes, including preferential ionization and immediate electronic couplings, can result in a certain permanent alignment of cations. Utilizing the permanent alignment together with molecular alignment to control the polarization of follow-up coherent emissions from ions remains unexplored to date. In the present work, we first demonstrate the permanent alignment effect on N2+ lasing by examining its polarization, which is based on a polarization perpendicular configuration with a pump-seed scheme. It is found that the output polarization of N2+ lasing can incline toward the pump polarization direction under a weak seed triggering, which is in contrast to the previous polarization measurement and manifests the crucial role of permanent alignment. In addition, at the alignment delay, the polarization of N2+ lasing can be varied from linear polarization to elliptical polarization by adjusting the seed intensity. Our analysis indicates that the permanent alignment in essence arises from the anisotropic distribution of magnetic quantum number M, i.e., the projection of rotational number J on the fixed z-axis. These findings shed light on the physics of N2+ lasing and offer various approaches to manipulate the polarization of ionic coherent radiations.

Small-angle X-ray scattering (SAXS) is a promising metrology technology for complex nanostructures in semiconductor manufacturing. However, parameter reconstruction based on SAXS measurement often faces challenges in achieving high precision and repeatability due to the increasing complexity of structures and the demands for precise measurement. To address these challenges, a correlation learning-based method is proposed to enhance the accuracy and reduce the uncertainty of the profile reconstruction in SAXS measurement. This method leverages the long short-term memory (LSTM) mechanism to capture and learn inherent parameter correlation effectively. The precision and reliability of the proposed method are demonstrated through the simulations of synthetic Si gratings. Our method exhibits remarkable measurement accuracy with an improvement of at least 13.9%, and the measurement repeatability is nearly 1.4 times higher compared to the previous learning-based methods. We expect that our approach will provide a novel solution for SAXS measurement, enabling accurate and reliable profile reconstruction of nanostructures.

Tail artifacts are a significant issue in optical coherence tomography angiography (OCTA), as they cast shadows over underlying signals and interfere with the reconstruction of 3D vessel images. While many methods have been developed to reduce these artifacts, most only shorten the tails and fail to clearly distinguish between vessels and artifacts. In this Letter, we present an image processing technique designed to reduce artifacts. By combining structural images with OCTA images, we can more effectively distinguish between vessels and artifacts, leading to shorter and less pronounced tail artifacts. This method is integrated with other tail artifact removal techniques to further enhance image quality. The vessels of the palm are used as samples to experimentally demonstrate the effectiveness of our technique.

In this work, we achieve a fourfold enhancement in thermo-optic coefficient measurement resolution for KTiOPO4 crystal using a self-stabilized birefringence interferometer integrated with cascaded second-harmonic generation. We observe the tunable interference beating phenomenon by rotating a birefringent crystal versus the temperature of the crystal. Furthermore, the fourth-harmonic interference fringes beat 4 times faster than the fundamental wave interference fringes. This beating effect is used to determine the thermo-optic coefficients of the two principal refractive axes with a single measurement. This work provides a feasible, real-time, and robust method for superresolution measurements based on birefringence interferometry.

Hybrid integrated external cavity lasers (ECLs) using cascaded micro-rings with the advantages of a wide tunable range and a narrow linewidth have rich applications. However, due to the limited bandwidth of the reflector, continuous correction of the reflectivity is required to sustain the optimal performance of the ECLs when spanning large wavelength ranges. Here, by introducing bent direction couplers in a Mach–Zehnder interferometer (MZI)-based reflector, we have designed a wide-bandwidth adjustable Sagnac-loop reflector (WASR) with a bandwidth over 100 nm. Moreover, the proposed external cavity was fabricated on the 800-nm-thick low-loss Si3N4 waveguides. In the experiment, we have measured a tuning range of over 81 and 90 nm for butt-coupling with two reflective semiconductor optical amplifiers (RSOAs) with different wavelength bands. An intrinsic linewidth of < 23.8 kHz and a side-mode suppression ratio (SMSR) of > 50 dB across the entire tuning range were also obtained.

We propose and demonstrate experimentally a tunable filter based on a Mach-Zehnder interferometer (MZI)-assisted micro-ring resonator (MRR) formed on the lithium niobate on insulator (LNOI) platform. Our proposed filter can achieve electro-optic (EO) and thermo-optic (TO) tuning for the bandwidth and the dip wavelength simultaneously. Our typically fabricated filter shows that the minimum and maximum 3 dB bandwidths at the through port are 27.86 and 31.74 GHz, respectively, while at the drop port, these values are 14.68 and 30.69 GHz. Meanwhile, the TO and EO tuning rates of the dip wavelength are approximately -6.5 pm/mW and -65.09 pm/V, respectively. Our proposed filter has the potential to be used in optical communication and optical information processing systems to achieve multifunctional filtering characteristics.

A high-power single-mode semiconductor laser with a photonic crystal structure is demonstrated. The high-order surface gratings are designed as longitudinal photonic crystals to introduce distributed reflection defects. A broad ridge is employed to enhance output power, accompanied by two sets of transverse photonic crystals on either side to filter out high-order lateral modes. At an injection current of 700 mA, the output power of the laser reaches 120 mW, featuring a single-flap horizontal far-field (HFF) distribution with a full width at half-maximum (FWHM) of only 8.8°. The lasing wavelength is 1.3 µm with a side-mode suppression ratio (SMSR) of up to 41.74 dB. The fabrication process is based on standard lithography, and it avoids the need for high-precision lithography and regrowth techniques and provides a cost-effective and simple-process solution for single-mode lasers.

Photonic crystal (PC) laser diodes (LDs) exhibit high power and narrow divergence angle output. Enhancing their thermal characteristics is critical for improving device performance and reliability. In this study, we develop a 3D heat dissipation model for 976 nm PC LDs packaged in conduction-cooled heat sink mounts (CS-mounts). The steady-state thermal characteristics are simulated using the finite element method (FEM) to optimize heat sink dimensions and transition heat sink design. Through optimization, the heat sink volume is reduced by 83.3%, while heat dissipation efficiency is improved by 18.2%. Under 60 A continuous-wave operation, the PC LD with the optimized heat dissipation structure achieves an output power of 48.2 W at 20°C with the thermal resistance of 1.17 K/W, and an output power of 54.5 W at 5°C with the maximum power conversion efficiency of 62.4%.

Metasurfaces have revolutionized planar optics due to their prominent ability in light field manipulation. Recently, the incorporation of machine learning has further improved computational efficiency and reduced the reliance on professionals in designing various metasurfaces. However, the prevalent methods still suffer from configuration complexity and expensive training costs due to more than one model or a combination of rule-driven algorithms. This study proposes a deep learning-based paradigm using only one deep learning model for the end-to-end design of versatile metasurfaces. The adopted deep-enhanced RseNet acts both as the surrogate of the electromagnetic simulator in forward spectrum prediction and as the path for backward gradient descent optimization of the meta-atom structures in the paralleled calculation. Without loss of generality, a polarization-multiplexing holographic and a polarization-independent vortex metasurface were designed by this paradigm and successfully demonstrated in the terahertz range. The extremely simplified framework presented here will not only propel the design and application of metasurfaces in terahertz communication and imaging fields, but its universality will also accelerate the research and development of subwavelength planar optics across various wavelengths through artificial intelligence (AI)-enhanced design for optical devices.

We make a comparison study of linear and nonlinear diffraction by a periodically poled lithium niobate (PPLN) dual linear–nonlinear thin-plate grating with weak surface corrugation against four types of white light sources. They are the ordinary halogen lamp thermal radiation source (WL1), the silica photonic crystal fiber supercontinuum nanosecond laser source (WL2), and two femtosecond white lasers made by a Ti:sapphire pump laser beam passing through a fused silica plate with significant spectrum broadening (WL3) and through a cascaded silica plate and a chirped PPLN crystal with ultrabroadband second-harmonic generation (WL4). The experiments show that the coherence, peak power, spectral bandwidth, profile, and flatness of the pump white light all contribute to shaping the characteristics of linear and nonlinear optical diffraction patterns. In particular, for WL1, WL2, and WL4, the peak power is not sufficiently large; thus, only linear diffraction occurs. For incoherent WL1, the interference is absent. Remarkably, when a femtosecond white laser with sufficiently large peak power (WL3) shines upon the PPLN grating, bright and sharp linear Bragg scattering spots, dispersive colored linear diffraction patterns, and nonlinear Cherenkov radiation nonlinear diffraction patterns are observed simultaneously by naked eyes. The experiments would enrich the basic physical and optical understanding of linear and nonlinear optical diffraction characteristics of ultrabroadband white laser sources.

Nonlinear photonic crystals (NPCs) with modulated second-order nonlinear coefficients (χ(2)) enable quasi-phase-matching (QPM) for efficient frequency conversion. Traditional electric-field poling is limited to two-dimensional domain engineering and cannot achieve three-dimensional (3D) χ(2) distributions, while femtosecond laser writing (FLW) offers greater control but introduces crystal damage. In this work, we use the pyroelectric-based fabrication process by performing the cooling step in a vacuum after FLW, suppressing thermal fluctuations, and maximizing the pyroelectric field. Vacuum cooling significantly improves domain inversion probability and uniformity compared to air cooling, making the periodicity close to electrical poling. Real-time polarized microscopy reveals improved domain growth, while nonlinear diffraction analysis confirms negligible refractive index changes. We demonstrate domain-inverted NPCs with a periodicity of 4 µm, achieving QPM at near-infrared wavelengths. This method provides a scalable and efficient pathway for advanced nonlinear photonic devices.

A novel fabrication method for a 32-channel image slicer within the China Space Station Telescope (CSST) integral field spectrograph (IFS) is proposed, addressing challenges in multi-channel micro-slicer manufacturing. Our approach employs ladder stacking, polishing, and reverse stacking, combined with the Ritz method and blade crack propagation theory, to optimize molecular bonding and minimize deformation. This approach simplifies fabrication while ensuring high imaging quality, thereby meeting the requirements of CSST-IFS. This study advances precision optical instrument manufacturing and provides valuable insights for its future developments.

Micro-light-emitting diode (micro-LED) has been widely concerned in the field of display and wireless optical communication due to its excellent optoelectronic characteristics, but the reduction of the pixel size has a significant impact on the performance of GaN-based micro-LEDs, which then affects the display and wireless optical communication applications. In this work, different sizes of violet and blue GaN-based micro-LEDs have been successfully fabricated, and the size-dependent characteristics of micro-LEDs in display and communication applications have been systematically studied. It can be found that the pixel size reduction of the micro-LEDs from 80 to 10 µm leads to an obvious decrease in light output power (LOP) by 88.30 % and 44.10 % for blue and violet micro-LEDs, respectively, and a decrease in peak external quantum efficiency (EQE) by 55.14 % and 46.25 % for blue and violet micro-LEDs, respectively. Additionally, micro-LEDs with smaller sizes tend to exhibit a less obvious shift of peak wavelength and smaller broadening of full-width at half-maximum (FWHM) with the increases of current density, showing the potential to achieve a stable display with high quality. Also, the influence of current density on chrominance coordinate migration is determined, which shows that the driving current density corresponding to the maximum EQE can promote display efficiency and color gamut. In addition, the violet and blue micro-LEDs with a diameter of 20 µm show potential in balancing between the LOP and the modulation bandwidth to achieve the highest data rates of 1.347 and 1.032 Gbps, respectively, in wireless optical communication applications. The results of this study are of great significance for optimizing the pixel size of the micro-LED to improve the performance in display and wireless optical communication applications in the future.

Because of extensive potential applications in health fields, wearable self-driven sensors are indispensable for next-generation medical systems. In this paper, a wearable self-driven sensor utilizing a lift-off (In,Ga)N film is proposed and demonstrated successfully. (In,Ga)N film is separated from an epitaxial silicon substrate through an economical and fast electrochemical etching procedure. With good flexibility, the self-driven sensor can continuously monitor localized sweat and sweat electrolyte concentrations. Hence, it can monitor the electrolyte loss in the human body, which is crucial to facilitate proper fluid replenishment for people during exercise. Furthermore, the sensor maintains stable detection performance under different bending conditions, indicating good stability. Therefore, this study holds great potential for the advancement of wearable devices for personalized health management requiring ultra-low energy consumption.

Propagation-invariant beams have attracted major attention and presented applications in research areas such as particle acceleration, optical tweezers, and optical coherence tomography. On the basis of the introduced radial cosine phase gratings with high diffraction efficiency, this study observes a kind of novel shape-invariant radial lattice by assessing its Fresnel diffraction. Then, on the stationary phase principle, we originally construct and experimentally generate a family of new propagation-invariant (non-diffracting) radial lattices with polar symmetry. Their optical structures, propagation characteristics, and distinctive phase characteristics are studied. This study has important value for applying it in scientific fields in the future given that lattices have offered many applications, including optical communication in free space, quantum computation, quantum phase transition, spin–exchange interaction, and realization of magnetic fields.

We report a broadband energy-time entangled photon-pair source based on a fiber-pigtailed periodically poled lithium niobate (PPLN) waveguide, designed for applications in the quantum secure network. Utilizing the spontaneous parametric down-conversion nonlinear optical process, the source generates entangled photon pairs within a wavelength range of 64 nm in the telecom band at a pump wavelength of 770.3 nm. Photon pairs from eight paired International Telecommunication Union (ITU) channels are selected, and their correlation and entanglement properties are characterized. The measured coincidence counts of photon pairs from eight paired ITU channels are larger than 152.9 kHz when the coincidence-to-accidental ratios are greater than 260. Entanglement properties are measured through two-photon interference in the Franson interferometer, with all visibilities of interference curves exceeding 98.13%. Our demonstration provides a broadband energy-time entangled photon-pair source, contributing to the development of a large-scale quantum secure network.

Quantum correlation imaging plays an important role in quantum information processing. The existing quantum correlation imaging schemes mostly use the Gaussian beam as the pump source, resulting in the entangled two photons exhibiting a Gaussian distribution. In this Letter, we report the experimental demonstration of quantum correlation imaging using a flat-top beam as the pump source, which can effectively solve the problem of imaging distortion. The sampling time for each point is 5 s, and the imaging similarity is 93.4%. The principle of this scheme is reliable, the device is simple, and it can achieve high-similarity quantum correlation imaging at room temperature.

Large Purcell enhancement, requiring high-quality factors and small mode volumes, is essential to single-photon sources. Whispering gallery microcavities possessing a high-quality factor are limited by a large mode volume, while dielectric nanoantennas with an ultra-small mode volume suffer from significant scattering loss. Here, by combining the advantages of the microtoroids and the nanoantennas, we achieve large Purcell enhancement with a narrow linewidth in all-dielectric nanoantenna-microtoroid hybrid structures. The scattering loss of the nanoantenna is suppressed by the high-Q microtoroids; meanwhile, its ultra-small mode volume remains almost unchanged. As a result, the Purcell factor of the emitter located at the gap of the nanoantenna reaches as high as 1000–1700, while its linewidth is kept at the order of hundreds of picometers. The proposed mechanism holds promise for applications in on-chip single-photon sources and low-threshold nanolasers.