Cross-domain communication between sea and air plays a vital role in cross-domain collaborative operations and the establishment of cross-domain heterogeneous marine unmanned systems. Based on the different deployment methods of cross-domain communication systems between sea and air, this work introduces direct, relay, and conversion cross-domain communication technologies. The characteristics and limitations of various cross-domain communication technologies, both domestic and international, are summarized in terms of communication rate, communication distance, and deployment flexibility. Finally, the future research direction of this field is prospected.

Quantum cascade laser (QCL) exhibit considerable potential for applications in diverse fields including chemical sensing, free-space optical communications, and infrared countermeasure systems, owing to their distinctive characteristics of broad spectral coverage, compact size, and manufacturability at scale. Nevertheless, the performance of current mid-infrared QCL devices is fundamentally limited by existing material systems and fabrication technologies, resulting in wall-plug efficiencies that remain substantially inferior to those of near-infrared semiconductor lasers. Furthermore, the constrained output power from individual devices presents a significant barrier to their practical implementation in these application areas. Beam combining methodologies have consequently emerged as a promising approach for power scaling of QCL systems. This review comprehensively examines contemporary advancements in beam combining techniques specifically developed for QCLs, providing a systematic evaluation of their respective merits and prevailing technical limitations.

As an important branch of the optical fiber sensing field, optical fiber magnetic field sensors have demonstrated significant application value in various fields owing to their advantages such as small size, remote measurement capability, and easy integration. Their development is closely related to magneto-optical materials. This study focuses on two types of typical magneto-optical materials in recent years: magnetic fluids in the classical field and nitrogen-vacancy centers in diamond in the quantum field. It reviews their research progress in optical fiber magnetic field sensors from the aspects of sensing principles, demodulation methods, structural design, and sensing applications. Finally, the current key challenges are analyzed, and the future research directions and application prospects are prospected.

Underwater laser ranging technology is a crucial approach for ocean exploration and underwater sensing, with broad applications in marine engineering, environmental monitoring, and resource development. Owing to its advantages of rapid and accurate measurement, this technology demonstrates highly efficient detection capabilities in complex aquatic environments, providing strong support for acquiring high-resolution underwater information. This study first introduces the principles and recent technological advancements of four commonly used underwater laser ranging methods, including time-of-flight, phase detection, triangulation, and photon counting. It then reviews the typical application progress of this technology, followed by a comparative analysis of the advantages and limitations of each method in underwater detection. Finally, future development trends and potential applications of underwater laser ranging are discussed.

For the calibration of line structured light sensors in small fields of view, this paper proposes a light plane parameter calibration method based on unified homography estimation. By intersecting the light stripe with non-chessboard regions of the target plane to form calibration feature points for the light plane, a high-precision one-dimensional displacement device and a two-dimensional target movement are used to establish an affine coordinate system. The introduction of spatial unit vectors and movement step constraints extends the two-dimensional target feature points into three-dimensional space, fully leveraging the noise resistant advantages of three-dimensional feature points. A unified homography estimation is performed on all spatial feature points, achieving high-precision calibration of the line structured light sensor in small fields of view. Experimental results show that, compared with traditional methods, the proposed method reduces the distance measurement error by approximately 60%, and improves the calibration repeatability by about 93%.

The nonlinear compression technique reduces the time-domain pulse width while simultaneously broadening the spectrum. This study employs multilayer thin plate for spectrum broadening. Through theoretical simulations, the spatial propagation of light, spectrum broadening upon traversing fused silica plates, and the optimal placement of these plates to achieve maximum spectral broadening without material damage are determined. Experimental results demonstrate that pulse width of a ytterbium-doped laser with a single pulse energy of 250 μJ and a repetition rate range of 20?200 kHz is compressed from 570 fs to 107 fs. After compression, the lateral beam quality factor is 1.384, the longitudinal beam quality factor is 1.413, the spot ellipticity is 0.978, and the compression efficiency is about 78.5%. By analyzing variations in beam waist at different power levels and their effects on beam quality, this work investigates methods to enhance beam quality while achieving narrower pulses and proposes corresponding optimization strategies.

To achieve efficient denoising of polarization images without losing their original polarization characteristics, this paper proposes a polarization image denoising algorithm based on masked pre-training. The algorithm first performs pre-training on a clear polarization image dataset by applying masks, using the parameters obtained from the pre-trained model as initial parameters for self-supervised masked training. Noisy polarization images are then input for iterative training. During each iteration, predictions for the masked pixels are extracted, and an exponential moving average strategy is employed to generate the final prediction of the clean image. Experimental results demonstrate that the proposed algorithm not only achieves direct denoising of polarization images but also delivers superior visual performance in restoring polarization information. Additionally, its robustness is validated across different noise patterns and noise levels.

A calibration method for strain based on microwave true time delay is proposed for distributed optical fiber strain sensors. When a segment of the sensing fiber is subjected to strain, causing a change in the fiber's time delay, the phase of the microwave signal transmitted through the sensing fiber will correspondingly change. Based on this principle, a microwave signal is confined to propagate within the sensing fiber using a microwave photonic link. The phase change of this microwave signal is measured using a vector network analyzer, and the strain applied to the sensing fiber is derived, thereby enabling the calibration of the strain coefficient for the distributed optical fiber strain sensor. This method directly measures the change in fiber time delay to determine the strain value and achieves a measurement time as low as ms level. Experimental results demonstrate that the calibration accuracy of this method is 0.18 (°)/(km·με).

A distributed phase-stabilized frequency transmission system implemented over a ring fiber-optic link is proposed. Through phase self-sensing and optoelectronic cooperative compensation, frequency signals precisely twice the central station's reference is recovered at remote stations, achieving multi-node distributed phase-stabilized frequency transmission. The system architecture employs a ring topology with replicable receiver modules, enabling phase self-sensing and real-time synchronization at remote stations. By implementing optoelectronic cooperative compensation at the central station, the system demonstrates significant improvement in phase stability across distributed nodes. An experimental setup of a 40 km fiber-optic link is constructed to perform multi-node phase-stabilized transmission, and it is compared and evaluated against traditional compensation methods. With measured results indicating less than 1 ps peak-to-peak timing jitter and optimal frequency stability of 9.762×10?1?@1000 s. The cooperative compensation scheme achieves a remarkable root mean square (RMS) of timing jitter of about 0.11 ps, outperforming both optical delay line (0.1742 ps RMS) and electronic phase shifter (0.2128 ps RMS) approaches, confirming its enhanced capability for precision frequency signal distribution in ring-based fiber networks.

Conventional Brillouin optical time-domain reflectometer (BOTDR) system faces challenges in accurately measuring temperature or strain variations in sub-pulse event zones. To address this technical challenge, a joint demodulation scheme based on Brillouin frequency shift (BFS) and power is proposed to achieve length, temperature, and strain measurements in sub-pulse event zone. By utilizing the principle of pulse superposition, a linear relationship has been established between BFS, scattered light power, event zone length, and temperature. Both numerical simulation and experimental validation have confirmed the validity of this linear relationship. Ultimately, with a pulse width of 100 ns, in the measurement experiment where the actual length of the event zone is 3 m and the temperature is 52 ℃, measurements of 2.91 m for length and 51.68 ℃ for temperature of event zone are achieved at the end of a 10 km fiber, resulting in a significant improvement in measurement accuracy compared to the 32.63 ℃ measured using traditional BOTDR demodulation scheme. The proposed scheme overcomes the limitations of pulse width, enabling the measurement of sub-pulse length event zones and providing a novel approach for enhancing the spatial resolution of BOTDR systems.

To enhance the hardness and wear resistance of tin-nickel bronze (CuSn12Ni2) for high-load and high-friction applications, this study proposes a CuSn12Ni2 alloy reinforced with tungsten carbide (WC) ceramic particles by a circular oscillating dual-laser technique. Taking the merits of the high absorption rate of blue laser and high power of infrared laser, the melt of WC/CuSn12Ni2 composite powder can be sufficiently promoted by a dual-laser with a grain-refining effect. WC particles underwent slight melting during the cladding process, some decomposed into tungsten (W) and carbon (C) elements. During the solidification process, a series of phases are formed, including CuZn, W2C, WC, and MC carbide. The increase mass fraction of WC particles lead to an increase in carbide content while simultaneously reducing grain size. The combined effects of grain refinement and solution strengthening result in the enhanced hardness of the deposited composites. Compared to the CuSn12Ni2 alloy, the hardness of the CuSn12Ni2 deposition layer with WC mass fraction of 24% reinforcement exhibited a remarkable 66.26% improvement. Based on ring-on-block friction experiments, the wear rate of the WC/CuSn12Ni2 composite deposition layer can be reduced to 0.637×10-4 mg/mm. The WC particles are functioning as a supporting skeleton within the composite and can inhibit the increase of wear parameter, indicating a significant enhancement in wear resistance. These findings offer a reliable insight for the application of CuSn12Ni2 in complex industrial environments.

To address ssues such as low real-time performance and high resource consumption in existing grayscale image algorithms for airborne target feature analysis on strongly physically constrained platforms, this study proposes a multivariate statistical parameter representation approach based on mean, variance, entropy, and energy. The feasibility and data validation of this method for characterizing feature changes in continuous grayscale images of airborne targets are conducted. Experimental results demonstrate that the set of multivariate statistical parameters can effectively characterize the process of imaging field of view approaching the target aircraft, the process of AIM-9X hitting the target aircraft with flashes and smoke, and the process of target aircraft exploding and disintegrating in continuous grayscale images. The analysis confirms the feasibility of using these multivariate statistical parameters to characterize the feature changes of airborne targets in continuous grayscale images. The analytical process provides new insights for trend judgment and predictive analysis of continuous airborne target changes under stringent platform constraints.

To address the problems such as small measurement area, low damage threshold, and easy saturation of existing measurement methods in laser wireless power transfer technology, this paper proposes a photovoltaic array measurement method based on current inversion, which uses the photovoltaic array composed of discrete photovoltaic cells to receive laser, and inverts the incident light intensity of the photovoltaic cell based on the mathematical model of the photovoltaic cell and the output current. Based on the output characteristic of the photovoltaic cell and the five-parameter model, the correlation model between light intensity and output current is constructed, and the accuracy of the inversion method is verified through simulation calculations under different light intensities. Light intensities obtained from the inversion are processed using cubic spline interpolation to recover the incident spot, and the total power and uniformity of the large spot are obtained based on the light intensity distribution of the light spot. The theoretical calculations and simulation results show that this method can achieve effective measurement of high-energy large spot. This method is helpful for the optimal design of the laser transmitter and receiver, and also provides a theoretical basis for the development of high-energy large spot measurement instruments.

In this paper, the picosecond ultrasonic metal film thickness measurement based on asynchronous optical sampling with dual-comb is carried out to address the problems of the traditional picosecond ultrasonic technology based on mechanical delay lines, such as limited range and slow measurement speed. Based on two passively mode-locked ytterbium-doped fiber lasers working at 1030 nm waveband, a dual-comb picosecond ultrasonic measurement system is constructed. Based on asynchronous optical sampling, a time delay of 4 ns is generated, which is equivalent to a 0.6 m long mechanical delay line. Thickness measurement experiments are carried out on Au films with thickness of 43.67?165.33 nm, and the ultrasonic flight time is extracted by combining Gaussian filtering and multimodal Gaussian fitting to obtain a measurement resolution of ~2 nm. This device has potential application value for improving the film thickness detection process in chip, semiconductor, and micro-nano manufacturing.

With the continuous expansion of laser application fields and ongoing advancements in the development of ultra-high-power laser sources, megawatt-level semiconductor laser sources have been playing an increasingly important role in driving technological innovation and industry upgrades. Owing to their high-energy density, compactness, and multifunctionality, megawatt-level semiconductor laser sources are gradually becoming core technologies in several key areas. To meet the demand for ultra-high-power laser output, laser beam combining technology is widely used. This technology combines multiple laser beams in a space or frequency, effectively increasing the overall laser output power and overcoming the limitations of single laser sources. Currently, megawatt-level semiconductor laser sources are extensively applied in fields such as defense and military, industrial manufacturing, aerospace, telecommunications, and high-energy physics. In this article, the development status, implementation methods, technical challenges, and applications of megawatt-level semiconductor laser sources are explored, the challenges they face are analyzed, and the vast prospects of megawatt-level laser sources are forecasted.

Laser processing techniques play a crucial role in precision manufacturing; however, laser microhole fabrication still faces several challenges, such as the impact of plasma shielding effects on processing efficiency and quality. Magnetic field-assisted laser processing has attracted significant attention in recent years. The principle behind this technique is the use of magnetic fields to constrain the expansion of plasma, thereby enhancing processing efficiency and quality. Previous studies have shown that static magnetic fields can significantly increase processing depth, whereas dynamic magnetic fields can improve the circularity of hole entrances. Additionally, the combination of magnetic fields with other techniques, such as ultrasonic waves, has demonstrated positive effects. In the future, this technique is expected to be further developed through in-depth studies of its micromechanisms and integration with artificial intelligence, thereby expanding its application areas and driving the advancement of precision manufacturing.

Extreme ultraviolet lithography (EUVL) has received significant attention for the mass production of chips at the 7 nm technology node and below. Although the lithographic resolution is constrained by the wavelength of the light source and the numerical aperture (NA) of the projection optics system, the actual resolution depends on the contrast and dose limitations. Achieving good contrast in aerial images is essential for controlling the distribution of critical dimensions across fields, wafers, and batches. One of the primary reasons for the reduced contrast of aerial images is the mask three-dimensional (M3D) effect. Unlike conventional lithography, EUVL is characterized by the M3D effect. Therefore, understanding and mitigating the M3D effect are particularly important for EUVL imaging at the resolution limit. This paper first reviews EUV masks, including their structures, fabrication processes, and defects, followed by an introduction to the M3D effect and the mitigation strategies. The technical challenges associated with high-NA EUVL are investigated. Finally, a summary and some perspectives are provided.

Micro-light-emitting diode (Micro-LED) has attracted widespread attention in academia and the display industry due to its outstanding performance characteristics, such as high contrast, fast response time, and low power consumption. Angular color shift, which refers to the color differences presented by display devices from different viewing angles, can alter the color gamut and contrast of Micro-LED displays, thereby affecting the user's visual experience. This article aims to analyze the causes and main influencing factors of the angular color shift phenomenon, and comprehensively review the current solutions for alleviating angular color shift, including optimizing device structural parameters, adding black matrix structure, designing reflective structure, and using optical thin film structure. Based on various solutions to alleviate angular color shift, this article looks forward to possible research directions. Further optimization design of black matrix and reflective structure, as well as exploration of optical thin film structure with superior performance, may have higher efficiency and potential in suppressing the angular color shift phenomenon of Micro-LED, and may be a more worthwhile direction for further research.

Spectroscopic instruments are essential scientific tools used to analyze and measure the properties and characteristics of light, are widely applied in fields such as national defense, biomedicine, food safety, and product quality inspection. To meet the evolving challenges of scientific research and market demands, the design and application of spectrometers have seen significant advancements in recent years. This research analyzes the research progress of typical grating-based spectrometers, Fourier transform spectrometers, and microspectrometers, with a focus on optimization strategies for achieving high resolution, wide broadband, real-time performance, and convenience. With breakthroughs in artificial intelligence, micro-electro-mechanical systems, and nanotechnology, modern spectrometer development is moving toward greater intelligence, integration, and portability to meet the diverse demands of emerging applications, contributing significantly to scientific research and industrial development.

Burst-mode fiber laser has the advantages of rich and adjustable time-domain parameters, and has unique advantages and wide applications in the fields such as material processing, LiDAR, high-speed detection imaging, and microwave photonics. Since the concept of burst-mode fiber laser is proposed, some methods for generating burst-mode fiber laser have emerged, which have promoted the development of burst-mode fiber laser technology. In this paper, the concept of burst-mode fiber laser is first introduced. Second, starts from the method principle of burst-mode fiber laser generation, the generation methods of 1 μm band burst-mode fiber laser, such as combination of high frequency pulse and active modulation, direct generation, and pulse stacking are introduced, and the advantages, disadvantages, and research status of different methods are emphasize summarized. Then, the typical applications of burst-mode fiber laser are introduced. Finally, the future development trend of burst-mode fiber laser technology is comprehensive analyzed.