This PDF file contains the front matter associated with SPIE Proceedings Volume 13153, including the Title Page, Copyright information, Table of Contents, and Conference Committee information.

As the special type optical glass materials, the optical and chemical durability of SiO₂-B₂O₃-BaO-TiO₂ glass doped with TiO₂ is important. In this paper, the optical and chemistry stability was studied on SiO₂-B₂O₃-BaO-TiO₂ glass doped with 4%, 6%, 8%, 10%, and 12% TiO₂. The results showed that TiO₂ content had influence on the density、 the hardness、the thermal expansion coefficient、the refractive index and the water resistance of SiO₂-B₂O₃-BaO-TiO₂ glass. With the increase of B₂O₃ content, the density, the hardness, the refractive index, the water resistance of SiO₂-B₂O₃-BaO-TiO₂ glass increase. The thermal expansion coefficient of SiO₂-B₂O₃-BaO-TiO₂ glass decreases firstly, and then increases with increasing the TiO₂ content.

A 360° continuous detection system based on visual elimination of image rotation was designed to meet the requirement of high precision and full working interval continuous detection of the image tile index of a vehicle's commander panoramic sight. The system will drive the rotation value and visual measurement value for comparison measurement. The high precision motor and encoder output the angle and the PID algorithm is used to control the motor rotation speed to ensure the accurate positioning of the detected angle; Combined with sub-image processing and visual measurement , 360° continuous detection of image elimination rotation is realized. The experimental results show that the system can satisfy the 360° continuous detection of the image tile index of a vehicle's commander panoramic sight, eliminate the problem of extreme value out-of-tolerance, and improve the image stabilization accuracy of the sight system of a vehicle's commander panoramic sight.

Rotating Doppler velocimetry of a target has gained huge development in decade, from the initially required alignment between optical and rotary axes to lateral and angular deviations of them. However, signal-to-noise ratio (SNR) and measured error are still salient for rotating velocimetry of an arbitrary pose-varied target, especially when the deviations (including lateral or/and angular conditions) inevitably exist. Here, we proposed and demonstrate a feed-back compensation scheme for overcoming these difficulties, based upon measuring and manipulating orbital-angular-momentum (OAM) phase spectrum. The conjugate OAM superposed states are firstly launched to a rotating surface with lateral or/and angular deviations and then we measure the OAM complex spectrum and rotating Doppler spectrum of the echo photons, respectively. We further modulate the measured specific OAM phase spectrum components and combine the original OAM amplitude spectrum to reconstruct the updated emitted light on a diffractive phase element. In doing so, the measured SNR and the accuracy of the rotating Doppler velocimetry are gradually improved. As a consequence, we thus develop a high-sensitive and high-accuracy rotating Doppler velocimeter This laboratory-constructed prototype might be additionally pushed for applications in astrophysics, industrial manufacturing and meteorological monitoring, etc.

Spectral Confocal Displacement Sensor is a new type of displacement sensor that can meet the requirements of high precision, high speed and non-destructive testing, and can be applied in aerospace, medical and industrial testing fields. The traditional point-scan spectral confocal displacement sensor only collects depth information of one point at a time, which is slow and has a large amount of back-end data. In order to improve the scanning speed of the point-scan spectral confocal displacement sensor and reduce the workload of data processing, it is proposed to extend the point-scan type to line-scan type, which can obtain the depth information of thousands of points at one time, improve the scanning speed and reduce the workload of data processing by processing all the points on the scanning line at one time. Aiming at the dispersive objective lens design in the line-scan spectral confocal displacement sensor, a dispersive lens with a large linear dispersion range is designed based on the principle of linear axial chromatic aberration design. The lens consists of four single lenses and two double-glued lenses and a beam-splitting prism, in order to solve the problem of energy uniformity into the spectrometer and the problem of uniformity of illumination on the image surface, the double telecentric optical path design is adopted, and the size of the detector element selected is 5.5 um, and the Nyquist cutoff frequency is 91 Lp/mm. The design results show that: the dispersive range of the lens reaches 3 mm, and the length of the scanning line reaches 10 mm. At the Nyquist cutoff frequency, the MTF value of the whole field of view is greater than 0.6, which indicates that the system has good imaging quality.

AlGaN/GaN heterostructures is a promising wide-bandwidth semiconductor material for underwater blue light detection due to their unique physical properties. Nevertheless, due to the thin two-dimensional electron gas (2DEG) at the heterostructure interface, the contact resistance remains relatively high. To reduce the contact resistance and improve the potential of AlGaN/GaN heterostructures in high-power and high-frequency electronic devices, multi-channel AlGaN/GaN heterostructures were designed and manufactured in this research. The carrier distribution and distribution of Al, Ga and N elements in the multi-channel AlGaN/GaN heterostructures were characterized. Moreover, the effect of polarization charge on carrier distribution was analysed using energy band theory. The results indicate that multi-channel AlGaN/GaN heterostructures can effectively reduce the contact resistance of devices and that several parallel 2DEGs are present inside the device. The polarisation charge at the heterostructure interface results in an uneven carrier distribution in each channel region. This work is helpful for the application of AlGaN/GaN to underwater blue light detectors.

High Dynamic Range Imaging Based on Attenuation Microarray Mask has broad application prospects due to its good real-time performance and small size. But at the current level of craftsmanship, it is hard to fabricate a microattenuation array mask whose attenuation rate is adjustable. This leads to the fact that the imaging dynamic range cannot adapt to changes in scene brightness in most cases. To this end, this paper proposes a novel imaging system whose dynamic range can adaptively change according to the brightness of the scene. The core components are the micro polarization array mask mounted on the CMOS surface and the on-sensor rotatable linear polarizer in front of the lens. By controlling the rotation angle of the polarizer placed before the lens, the CMOS pixel exposure can be precisely controlled. Therefore, the imaging system dynamic range can be adjusted adaptively according to the scene brightness. Through horizontal comparison with Sony’s multi-quadrant polarization chip, we determined the optimal parameters of the multi-quadrant micro-polarization array mask for extending the dynamic range. The experimental results show that the imaging performance remains consistently good even when the dynamic range of the photographed scene is large, and the dynamic range of the device can be adapted to the dynamic range of the shooting scene, so that the image after shooting and processing can always show sufficient details. By rotating the polarizer in front of the lens to a specific angle, the high dynamic imaging of the scene can be significantly improved.

The spectral shifts and spectral switches of partially coherent electromagnetic Gaussian Schell-model (PCEGSM) vortex beam in atmospheric turbulence have been investigated. It can be found that the on-axis spectral peak and the off-axis spectral peak of PCEGSM vortex beam will shift rapidly in turbulence with the increase of propagation distance in comparison with PCEGSM non-vortex beam. We find also that the two spectral peaks and three spectral peaks of PCEGSM vortex beam appear in atmospheric turbulence. It is shown that the spectrum of PCEGSM vortex beam in turbulence alternates between redshift and blueshift with increasing propagation distance, the phenomenon is defined as the spectral switches. And it indicates that the spectral shift of PCEGSM vortex beam will be extremely small at a large propagation distance, meaning that the PCEGSM vortex beam has a strong anti-turbulence ability. Our results can provide the theoretical reference for the detection of Doppler lidar.

This paper analyzes the basic theory of rapid rotating scanning scheme for the off-axis 45° parallel two-mirror system, and constructs the transformation action matrix of optical vector in the rotating scanning process. Based on simulation with MATLAB, the relationship between the four control parameters of rotating scanning scheme for the off-axis 45° parallel two-mirror system and the scanning trajectories is analyzed in-depth, and the basic conditions of the control parameters are determined to achieve various scanning strategies. The performances of two scanning strategies (Linear scanning in any direction and Elliptical scanning in different ranges) are analyzed in detail. The scanning scheme discussed in this paper has the advantages of simple control, high scanning efficiency (100%), and flexible scanning strategy and so on by scanning with mirror rotating. It can realize the functions of rapid scanning for imaging with high linearity, region ergodic searching, random or complex path for searching and so on.

In this paper, an absorber based on split square graphene is designed, which produces double absorption peaks at different polarization incidence. The absorption rates of x-polarized waves at 7.86 THz and 12.63THz are 97.9% and 91.2% respectively. The absorption rates of y-polarized waves at 6.30 THz and 10.52 THz are 94.1% and 93.2%. In this paper, an absorber based on split square graphene is designed, which produces double absorption peaks at different polarization incidence. The absorption rates of x-polarized waves at 7.86 THz and 12.63THz are 97.9% and 91.2% respectively. The absorption rates of y-polarized waves at 6.30 THz and 10.52 THz are 94.1% and 93.2%. The effect of Fermi level on the dual polarization absorptivity of graphene is discussed. Therefore, this work may have great reference value for terahertz sensing, selective spectral detection and other fields. The effect of Fermi level on the dual polarization absorptivity of graphene is discussed. Therefore, this work may have great reference value for terahertz sensing, selective spectral detection and other fields.

This paper presents a hybrid phase retrieval algorithm that combines deep learning and traditional algorithms. During the process of detecting large dynamic range, the problem of phase wrapping arises, which cannot be solved by traditional iterative algorithms. Firstly, Zernike polynomials are used to represent the low-frequency component of mirror errors, and a CNN neural network model is trained to predict the coefficients of Zernike polynomials. Then, the high-frequency component of the error is retrieved using the GS algorithm. In the simulation, the tested spherical mirror is set with PV 3.87λ, RMS 0.267λ. The recovered phase wavefront error is 4.098λ, with RMS 0.258λ, and the RMS relative error is 3.21%.

With the growth of military demand for multi-spectrum, high-resolution, long-range photoelectric reconnaissance and surveillance, large-aperture multispectral optical system with common aperture is widely used in airborne optoelectronic mission payloads. At the flight altitude of 10000 meters, the optical system actually works at -30℃ ambient temperature, while it is assembled and tested at room temperature. Therefore, the airborne optical system should ensure excellent image performance in the wide temperature range, such as from -50℃ to +70℃. A large aperture catadioptric optical system with long focal length is designed. The optical model with zoom multi-configuration structures at room temperature, high temperature and low temperature is established, and it is based on the linear thermal expansion thermal-structural-optical integrated model. Optical focusing variables are introduced at high temperature and low temperature to optimize the image quality at the respective temperature. The optical system has excellent image performance at both high temperature and low temperature. The design results show that the waveband is 0.7μm～0.9μm. The MTF of the catadioptric optics with relative aperture F/3.6 and focal length 900mm is close to the optical diffraction limit at +20℃, -50℃ and +70℃, which ensures good image quality from -50℃ to +70℃.

As an important optical component, the mirror is an important part of the tracking camera. The rapid prototyping technology of 3D printing is becoming more and more mature, and its application scope is more and more extensive. Silicon carbide material has excellent physical properties such as high elastic modulus, specific stiffness and thermal stability. To meet the practical requirements of high stiffness, light weight of a special-shaped mirror, topology optimization was adopted to design the mirror structure. The objective is maximizing the weighted superposition of the structural stiffness and the first-order natural frequency；the constraint function is an upper bound on the volume fraction. After optimized design, the mirror with a special shape back was obtained. A feasible CAD model was formed by adjusting the position and thickness of the stiffener. The self-weight deformation and natural frequency of the model were analyzed by commercial finite element analysis software and the results show that the maximum RMS value of the mirror under 1g gravity condition is 14.6nm, and the first-order natural frequency is 2037Hz. Then the 3D printing additive manufacturing technology was used to fabricate the special-shaped mirror. After adjusting ,when the optical axis of the mirror and the ground into an Angle of -40°, 0°, 40°and 80°, the mirror surface accuracy meets the requirements.

Based on the polarization splitting principle of the only-phase liquid crystal device, a common path phase-shifting interferometry is built to measure the whole and local phase modulation characteristics of a liquid-crystal spatial light modulator (LC-SLM) with high spatial resolution and high gray level. In this technique, the SLM is not only a device to be measured but also an optical component that is used to splitting the incident linearly polarized light. A specially designed control grayscale image is loaded into the SLM, and then several frames of phase-shifted interferograms are recorded. The wavefront phase can be calculated by using the phase-shifting algorithm. Through changing the loaded images, the phase modulation curve is obtained. The experimental steps and results are presented in the paper, and the uniformity of local phase modulation is also evaluated. The proposed method has stable measuring results and has the advantage of simple principle and convenient operation.

In response to the requirements for small size, low-power, and high-precision target recognition and ranging systems for platforms such as unmanned vehicles and drones, research has been conducted on a multi-camera array bionic compound eye system and its accompanying target recognition ranging algorithm. In this paper, we have designed a multi-camera array compound eye by combining multiple focal length lenses with a CMOS array. This compound eye system boasts a compact size and low power consumption. Integrated with an RV1126 core processing board for image processing, it is capable of independent target recognition and ranging within the system without the need for an external computer. Additionally, it provides real-time streaming of video and target distance information. Furthermore, this paper introduces a multi-focal length ranging algorithm based on the improved YOLOv5. By enhancing the small object recognition capability of the YOLOv5 and effectively utilizing the multi-scale target information obtained from multiple focal length lenses, the system achieves improved ranging accuracy, especially for distant small targets. The proposed multi-camera array compound eye system has dimensions of 80mm×80mm×80mm, weight of 460g, power consumption of 6.5W, and a single-frame image ranging speed of 60ms. Experimental results demonstrate that it successfully measures the distance to human targets within the range of 30m-120m, with an average ranging accuracy error of less than 1%. This bionic compound eye system holds significant potential for a wide range of applications, including emergency obstacle avoidance for drones, munition-borne reconnaissance, and navigation for underwater unmanned submersibles.

High power fiber lasers can be incoherently combined to form the basis for high energy laser applications. Incoherent combining of fiber lasers has a number of advantages over other laser beam combining methods. However, the far-field beam quality of the incoherently combined laser array can still be significantly degraded by atmospheric optical turbulence. In this article, a general scaling law for propagation of incoherently combined laser array through atmosphere is developed by employing theoretical analysis and the common stochastic wave optics technique, and mainly focus on the effects of diffraction and atmospheric optical turbulence. The scaling law developed in the present work differs from standard scaling laws in its definition of irradiance. We show that the far-field irradiance and beam dispersion of any incoherently combined laser array, regardless of near-field beamlets geometry, can be obtained in terms of four basic parameters: laser power, field effective area, pupil field factor, and the Fried parameter.The results show that the formula is simple but predicts peak irradiance and beam dispersion accurately in the far field with varying levels of atmospheric turbulence, regardless of the near-field beamlets geometry.

Sounding data can be said to be the most important data source for numerical weather prediction models, and the sounding instrument can obtain sounding data with different resolutions according to different data acquisition frequencies. In this paper, to investigate the effects of different spatial vertical resolutions on meteorological parameters, we first compare the conventional meteorological parameters with the different resolutions of the sounding data obtained from the sounding experiments in the Lhasa area of Tibet (with resolutions of 5m and 25m, respectively) and the ERA5 data. Comparisons were also made between the calculated vertical gradient quantities and the atmospheric refractive index structure constants (C²_n ) estimated using three different methods. The result shows that the conventional meteorological parameters show good agreement in magnitude, trend, and detail variation in both 5m and 25m resolution data. The conventional meteorological parameters under ERA5 data are relatively consistent except for relative humidity. Vertical gradient quantities calculated using different resolution data have essentially the same trend at 5m and 25m data resolution, but the high-resolution data are larger than those for the low-resolution data. The trend and magnitude of the Thorpe method over the entire altitude range are more consistent with the measured values. The resolution of the data affects the amount of vertical gradient, leading to differences in the final estimates. HMNSP99 is more sensitive to data resolution.

Laser scanners could reflect the surface topography of the measured object through the measurement of massive point cloud data, possessing the characteristics of high accuracy and high efficiency, which are currently widely used in the measurement of parts and components of aircrafts, aero-engines, ships, and other machineries. The accuracy and reliability of data from laser scanners under site conditions for engineering applications has been an urgent problem to be solved. This paper proposes the design method of the standardizer based on the analysis of the error influencing elements of the laser scanner, which is able to meet the on-site verification requirements of the laser scanner. Considering the size detection error, shape detection error, sphere space error, length measurement error, plane space error five error parameters, and resolution performance parameters of the laser scanner, the standardizer needs to be composed of several concave-convex surfaces, steps, standard spheres, cylindrical tables, square tables, and multi-sized sawtooth surfaces. In order to ensure the accuracy of the standard, a precise assignment method of the standard parameters is proposed to achieve the ultimate traceability of the measurement value of the laser scanner.

Due to its non-invasive nature, high sensitivity and selectivity, the laser-induced fluorescence (LIF) spectroscopy has become an essential tool for the qualitative and quantitative diagnosing of plasma parameters. To obtain the distribution of plasma parameters, deconvolution technique must be used to separate the pure Doppler effect from the raw LIF spectrum. However, the presence of inherent noise in the received signal can result in the amplification of high-frequency noise, thereby causing deviations from accurate solutions. To solve this problem, we propose an enhanced deconvolution algorithm based on Richardson-Lucy (R-L) method with the adaptive gain coefficient, which effectively mitigates the ringing artifacts and noise amplification existing in the conventional R-L algorithm, and discuss the influence of parameter selection of gain coefficient. We use the numerical reconstructed LIF spectra at different noise levels as well as the measured LIF spectra of Xe to test the effectiveness of the proposed algorithm. The results show that the enhanced algorithm can significantly suppress the ringing effect and noise, and at the same time recover the Doppler lineshape well. Moreover, this approach presents a novel perspective for spectrum deconvolution algorithms such as infrared spectrum, Raman spectrum X-ray spectrum, etc.

Aiming at the problem of moving targets by the laser active imaging system, a laser active imaging technology based on random coding is proposed. The laser pulse coding is used to replace the shuttle coding exposure, combining the random coding exposure imaging technique with the active range-gated laser imaging technique. In the coded exposure mode, when imaging a moving target, the pulsed laser and ICCD image intensifier are synchronously gated based on FPGA, to obtain the encoded exposure image. And the blurred images are recovered based on LO regularization, which improves the laser active imaging quality. According to the laser active imaging theory, the image signal-to-noise ratio in pulse code modulation mode is analyzed, which shows that the pulse random coding technology can effectively improve the brightness of the imaging image, improve the image signal-to-noise ratio, and have a certain inhibitory effect on motion blur. The blurred image restoration effect under the 31-bit coding length was simulated and analyzed, and the imaging effect and applicability conditions of the typical parameter laser imaging system on moving targets under the coding pulse system were analyzed. Compared with other deblurring methods, under the condition of pulse coding accuracy of 5ns, the 31-bit coding length can achieve better blurred image restoration for the target of relative speed of 10m/s.

Scintillation is a highly discussed problem in laser atmospheric transmission, which plays an important role in improving the reliability and performance of laser communication systems. In this study, numerical simulations are conducted using a computational model to investigate the variation of the on-axis scintillation index of the focused platform beam during horizontal atmospheric propagation, considering different transmitter aperture sizes. The simulation results indicate that the aperture size significantly affects the scintillation index. Under the same Rytov variance conditions, larger aperture sizes lead to stronger scintillation effects. For smaller aperture sizes, the scintillation index maintains a relatively linear relationship with the Rytov variance. The findings of this study provide further insights into the factors influencing the scintillation characteristics in laser atmospheric transmission and offer valuable references for the design and engineering applications of laser communication systems.

Underwater cracks are a common problem in buildings and infrastructure, and their presence can have a significant impact on the stability and safety of the structure. Therefore, early detection and repair of cracks is very important. However, traditional underwater crack detection methods usually require manual involvement, which is time-consuming and dangerous. Therefore, it is of great significance to develop an automated crack identification and detection system that can be mounted on an underwater robot. For traditional underwater crack detection, the obtained underwater video is usually segmented and preprocessed, and the obtained data is input into a computer vision-based system for crack recognition and detection, which is much less efficient than the current deep learning methods. In this paper, two kinds of underwater building crack recognition network and detection network based on convolutional neural network are proposed respectively, by collecting different light, depth, turbidity and other multi-waters video materials, after a series of computer vision processing, it will be input into the neural network for the expansion of the data set, and the obtained data set is divided into test set, training set and validation set, and the training set will be input into the neural network used for the target recognition to be trained, to get the comprehensive recognition model of cracks in underwater complex environment. The size and shape of the cracks are manually depicted using the training set, and inputted into the neural network for crack detection to obtain the complex background underwater crack detection model. Using the complex background underwater crack detection model to detect the underwater environment through the neural network for target recognition, the underwater robot equipped with a waterproof and anti-shaking camera communicates with the shore and moves, follows the recognition results of the neural network for target recognition to lock the crack location, and then manipulates the underwater robot to approach the target crack, and then uses the neural network for target recognition to detect the underwater crack with a complex background using the complex background underwater crack detection model. The neural network for target recognition uses a complex background underwater crack detection model to segment the scaled underwater video captured by the camera and process it in high-definition to map the length and width of the cracks with pixel-level accuracy, and then transmits the data to the shore in real time to complete the identification and detection of cracks in underwater buildings.

As a common dynamic phenomenon in seawater, turbulence can affect the performance of underwater light transmission. Monte Carlo turbulence model is used in this paper, and this model is based on the Monte Carlo method to simulate the transmission of photons in turbulence with changing refractive index. The results show that the received light intensity probability density distribution is lognormal under weak, moderate and strong turbulence. With the increase of the variations of temperature and salinity, the intensity of turbulence is enhanced, and the effect on the received light intensity is increased, which is manifested by the gradual increase of the scintillation index as well as the asymmetry of the probability density distribution of the received light intensity. In addition, it is found that the asymmetry of the probability density distribution of the received light intensity is affected by the field angle of the receiving end and the divergence angle of the transmitting end.

With continuous development, the hyperspectral imaging has become a hot topic in the field of remote sensing, since its enormous advantage in obtaining the material composition of atmosphere, land resources, battlefield environment and marine resources while observing the Earth in space. However, some challenges have hindered the application of space-based hyperspectral imaging system. To fulfill the requirements of the spectral imager especially for space use, the lightweight and stable structure is especially important. Here the implementation of a Large Aperture Hyperspectral Imaging Optical System is presented. The optical system achieves hyperspectral imaging from ultraviolet to infrared spectral bands. The different spectral bands share a large common aperture of Ø1.8m. A lightweight primary mirror is designed and supported by bipod structure. To keep the large distance between the primary mirror and second mirror, a Lightweight and high-strength truss has been applied. A hierarchical structure is adopt as the main structure of the whole system. With the diffraction gratings and optical slits, the image information of different spectral bands are detected by the different lines of pixels in a focal plane of planar array. By the creative works of the optical and mechanical design, a hyperspectral imaging optical system is implemented and shows the extensive application potential in space remote sensing.

Visible light communication (VLC) emerging as an essential technology in the 6G era has expanded its application from indoor to outdoor scenarios. Underwater optical wireless communication (UOWC) technology is presented aiming to provide high-speed and safe communication service for complex underwater scenarios. The blue-green band exists as a transmission window in seawater with less transmission loss than other visible light counterparts. In this paper, a self-designed full-duplex UOWC transceiver is demonstrated. A green laser and an avalanche photodiode (APD) are used as core devices of the transmitter and receiver, respectively. We use a field programmable gate array (FPGA) as the main processing unit where an on-off-key (OOK) modem and reed-solomon (RS) coder are adopted which can correct up to 8-bit errors at a correction efficiency of 94%. A bias-tee module is used as the emitting driver of the modulated signals for the green laser diode (LD) and a receiving circuit is self-designed realizing photoelectric conversion and signal processing, in which the transceiver could simultaneously emit and receive light. We conducted an experiment using a water flume to simulate underwater communication channels and realize full-duplex communication. The transmission rate of the transceiver is 5 Mbps. The photoelectric properties of the LD are characterized in this paper. Eye patterns and flowing signals are analyzed for the communication performance of the transceiver. This work provides a feasible method for advanced UOWC technology.

Using the continuous observation data of wind profiler radar, the temporal and spatial variation characteristics of wind direction and wind speed in the summer Boundary layer atmosphere wind field in the southern foot of Tianshan Mountains in Xinjiang are analyzed. The preliminary exploration of the impact of low-level jet streams on near surface atmospheric turbulence activity is of great significance for studying laser atmospheric transport, triggering convective weather, and atmospheric pollution and diffusion. Experimental area is located in a valley, and the circulation characteristics dominated by Mountain breeze and valley breeze are the basic characteristics of the daily variation of the wind field in the region, and also the main reason for the occurrence of low-level jet. Through statistics and analysis, it was found that the summer turbulent activity near the surface in this area is strong, which is caused by thermal stress on the underlying surface. During the day, the surface temperature is high, and there is a strong exchange of air flow near the surface with the upper layer, resulting in strong turbulent activity. In the evening, it may be the low-level jet that brings the horizontal wind shear near the ground, which intensifies the turbulence vortex activity and leads to the occurrence of turbulence.

In this paper, the transport properties of the autofocusing Airy vortex beams are investigated in the case of coexistence of positive and negative topological charges in the cross-section of the optical field. It is found that, unlike homogeneous vortex pairs, vortex pairs with opposite sign do not rotate the optical field during the transmission process, and that the autofocusing properties of the optical field can be modulated by a simple algebraic addition and subtraction operation of the topological charges. This study provides an important reference for the application of OAM-based communication systems and imaging systems in the atmosphere.

In optical systems, the accuracy of the lens is the basis for system performance. To ensure the accuracy of the lens, high-precision detection methods are crucial in lens processing. Commonly used phase-shifting interferometers are susceptible to environmental influences, while the quadriwave lateral shearing interferometer (QWLSI) can solve this problem. QWLSI reconstructs the wavefront from just one interferogram and is becoming increasingly popular owing to its compactness and portability. The most commonly used method to analyze interferograms in QWLSI is the Fourier transform method (FTM), which requires more sophisticated processing and computing time and is erroneous at the edge of the aperture. This study deduces that the spatial carrier phase-shifting (SCPS) algorithm should replace the FTM in QWLSI. Theoretical derivations and simulation results showed that QWLSI works faster and more accurately when the SCPS replaces the FTM.

The continuous zoom optical system has the ability to continuously observe and lock targets during the field of view conversion process, which can be used for target search, tracking, reconnaissance, and early warning. In order to ensure clear imaging of targets at different distances, in addition to controlling the change in magnification, it is also necessary to fine tune the zoom position. This fine-tuning requires precise positioning of the zoom motor, frequent step changes, and start-stop commutation. Therefore, the motor is greatly affected by interference such as friction and torque fluctuations. In addition, oscillations and crawling may occur at low speeds. In response to the above issues, this paper proposes an improved MPC control strategy, adding PID inner loop to the traditional MPC to improve the anti-interference ability of the system. Moreover, this algorithm can effectively handle multivariable problems with constraints, using rolling optimization to determine the current optimal control strategy, thereby improving the position tracking accuracy, antiinterference, and response speed of the DC zoom motor.

In the field of aperture coding super-resolution imaging, an important reason limiting the image super-resolution effect is that aperture coding greatly reduces the incident light flux of the system. Phase wavefront encoding modulation technology can effectively increase the system light flux and improve image super-resolution results. However, using phase wavefront coding instead of aperture coding will cause complex frequency domain calculations. In this paper, the feasibility of the single-seam phase encoding pattern is proved through the mathematical calculation of phase wavefront coding modulation. In the subsequent reconstruction process, the Fourier ptychographic (FP) imaging algorithm is used for verification. The resolvable line pairs of the USAF are increased from Group0 Number2 to Group1 Number3, means the image resolution is approximately doubled. The optical system built based on this phase mask prove the luminous flux of the acquired down-sampled image is increased about more than 5 times, and the image signal-to-noise ratio (SNR) is increased about more than 7 times. This makes it possible for higher super-resolution computational imaging.

In this paper, a radio frequency-underwater wireless optical communication (RF-UWOC) dual-hop decode-and forward (DF) relaying link for Satellite-Underwater communication is proposed to extend the communication distance based on RF and underwater optical wireless communication technology. The communication system consists of satellite, surface relay platform and underwater destination node, where the RF communication technology is adopted for satellite surface relay link, which is modeled as Rician fading distributions considering rain and snow attenuation. Surface relay platform and underwater destination node adopt underwater wireless optical communication (UWOC, and the link is modeled as Gamma-Gamma fading distributions considering sea water absorption and scattering. The closed-form mathematical expression of the RF link channel models and the UWOC link channel models is derived and analyzed, the outage probability (OP) and average bit error rate (ABER) performance of the satellite-underwater (RF-UWOC) dual-hop decode-and-forward (DF) relaying communication link is investigated and simulated.

As one of the most promising schemes to address the bottleneck confronted by conventional optical devices (e.g., bulky sizes, high cost, and complex geometrical structure), metalens have drawn great attentions in the recent years. In this work, a metalens operating in mid-wave infrared (MW-IR) range is proposed, which can accomplish broadband achromatic under both x- and y-polarization incidence. In order to satisfy the strict phase requirements with relatively high transmission, three types of architectures composed of silicon symmetrical structures on a hexagonal magnesium fluoride substrate are delicately designed. In specific, these meta-atoms are supposed to simultaneously realize MW-IR waves focusing at 4.2 μm, and they can also compensate the phase differences between 3.7 to 4.2 μm. The numerical results indicate that the chromatic aberration in the concerned wavelength range can be well corrected for both x- and y-polarized incidence, and the corresponding maximum deviation values of focal length are only 3.10% and 3.09%, respectively. Moreover, the average focusing efficiencies of two different incidences are 51.15% and 49.01%, respectively. This work may have great potential to promote the integration of broadband MW-IR devices.

Antimonide high-power semiconductor laser diodes emitting at 2μm have broad prospects in many fields, such as tunable diode laser absorption spectroscopy. However, power is an important indicator for the application of antimonide semiconductor laser diodes. In this paper, we reported the high-power antimony laser diodes emitting around 2μm achieved in our group. The maximum optical power is 1.001W with injected current 3.04A at working temperature 20℃.

The heated air formed inside a solar telescope due to solar radiation will warm up the mirror surface, and local atmospheric turbulence will be generated above the mirror surface, which will cause the mirror seeing and thus the serious attenuation of image quality. In this paper, based on the theory of atmospheric turbulence, we analyze the physical process of mirror seeing produced by turbulent shear airflow, and use the experimental data of 1550mm large diameter hyperboloid mirror to derive and verify the theoretical model of mirror seeing. The effect of the change of temperature difference between the mirror and the surrounding air on the mirror seeing was experimented under two conditions of free convection and forced convection, respectively, at different mirror wind speeds. The results show that it is clear that the temperature difference between the mirror surface and the surrounding air is strongly correlated with the seeing, and the mirror seeing can be reduced by increasing the active ventilation. The mirror seeing is 0.98" at free convection of 4°C, 0.20" at forced convection with low wind speed, and 0.12" at forced convection with high wind speed under a mirror-air temperature difference of 3°C. The research results aim to reveal the formation mechanism and propagation law of air turbulence and its influence on the image quality degradation of the telescope, and lay the foundation for improving the working resolution of the large solar telescope.

As an important detecting, perception and monitoring equipment, the optoelectronic platform is always equipped with a series of optoelectronic devices such as optical imaging device, photoelectric encoder and fiber optic gyroscope. These devices all require high-precision data acquisition systems. As the basic method of sensing a variety of mass physical changes, data acquisition systems have been increasingly used in optical sensing, photoelectric platform control and many other fields. The traditional optoelectronic platform design method uses distributed device for assembly, which occupies a large volume. In this paper, we take the multi-channel acquisition system in consideration, instead of the acquisition circuit scattered in each device, during the optoelectronic platform design process, which can effectively improve the system integration. The characteristics of multi-channel and high-precision data acquisition system are studied, and a multi-channel, high-precision AD data acquisition system is designed and verified. The system provides 16 parallel channels, each channel supports 32-bit sampling accuracy, we adopts FPGA as the core processing device, with gigabit network port for data reporting, this scheme has been applied in gyro test systems and weak signal acquisition systems.

We proposed a method of optimizing random illumination pattern, to solve the problem that data acquisition is excessive when random pattern is used in computational ghost imaging. By introducing a transverse and longitudinal cyclic shift with a random number of moving pixels on the original random pattern, the illumination of light field is more uniform, which can further accelerate the convergence of reconstructing image quality and sampling data quantity relationship curve meanwhile reduce the system sample rate. In this paper, the peak signal to noise ratio is taken as the evaluation metric, and the effectiveness of the optimization method is verified by three sets of simulation experiments using different objects. The results show that the scheme has a certain universality, and has a certain guiding role for the experimental research of computational ghost imaging and the subsequent engineering application.

Underwater wireless optical communication (UWOC) with blue-green light is a useful way to transmit data in ocean for short distance application, because it has high speed. In application, the transmitter should have larger divergence angle to make it easier to establish communication link, besides high modulated rate. Laser diode (LD) is suitable to design such transmitter, thanks to its simpler structure and much faster switching speed. However, it is difficult to be widespread used in ocean engineering because of its quite small divergence angle. For this, we present a transmitter based on blue LD and engineered diffuser. It has 100Mbps modulation rate, 80° divergence angle, and 18mW optical power. It could be used to transmit large volume data in short distance underwater communication.

Underwater wireless optical communication (UWOC) is an useful way to transmit date in ocean with short distance, because it has high speed. In application, the first challenge for this technology is establishing optical link underwater. There are two schemes to deal with this issue. The first one is enlarging the angle of divergence of the transmitter, and the field of view of receiver, which reduces the requirement to align the UWOC transmitter and receiver. However, the energy loss is increased in the transmission link. The other method needs a pointing, acquisition, and tracking (PAT) system to establish optical link. The angle of divergence of the transmitter is quite small in this way, which is helpful to reduce energy loss in the transmission link. However, in order to make the optical link stable, the receiver should measure the angle of incident of communication light all the time to provide feedback parameters to PAT system. In this work, a method is presented and demonstrated based on four-quadrant detector (QD) for such issue. It shows that the tested error for pitch angle and azimuth angle is less than 1°, as the communication system could still work with 50Kbps communication rate and 2m distance. It has demonstrated the feasibility of the method.

A real-time straightness measurement method for two-dimensional long guide rails is introduced based on the current measurement principle and status, combined with the requirements of existing work and the characteristics and performance of laser geometry measurement systems. The system uses a collimated laser beam as a reference line and outputs displacement values instead of angle values using coordinate data obtained from a dual two-dimensional PSD. Therefore, real-time measurement of intermittent guide rail straightness can be achieved. In addition, the system only has an output optical path and no return optical path, making the adjustment of the optical path much easier than that of a laser interferometer. When the 2D PSD fixed on the rail slider moves along the rail, the position data of the light spot will be transmitted to the terminal through the Bluetooth module. After inputting the position information, the software will automatically draw the 2D straightness curve of the rail. The reliability of this method was verified through experiments on a high-precision displacement platform. At the same time, while meeting the accuracy requirements, it is simple and practical, improving measurement efficiency, and providing a new way to improve measurement accuracy.

Oceans cover approximately 71% of the Earth’s surface and contain 97% of the planet’s total water resources. However, over 80% of the ocean remains unexplored and unmapped. Thus, the research of underwater detection technology and the development of underwater detection equipment are crucial to marine scientific research and development. Underwater Lidar detection technology has the advantages of high ranging accuracy, high spatial resolution and strong anti-interference ability compared with traditional sonar and other technologies. It is an important underwater information acquisition method and has been widely concerned by researchers. This technology is used in submarine topographic mapping, marine rights and interests maintenance, marine resources development and other fields. In this article, firstly, the detection principles of various underwater detection Lidar systems are described, including the time-of-flight detection principle based on the linear detection regime and the photon counting detection regime, and the laser line scanning detection principle, as well as the laser line scanning detection principle. Additionally, the development history of various underwater detection Lidar systems is summarized and sorted out, including Spaceborne Lidar, Airborne Lidar and Underwater Vehicle Mounted Lidar. In addition, the technical characteristics, advantages and disadvantages of the Lidar underwater detection systems under different mounted platforms are compared and analyzed. Generally speaking, Lidar underwater detection system has been fully developed and tends to be mature, and has been widely used in many fields of underwater detection, making up for the gaps in many fields of marine information detection, and gradually forming commercialized products and entering into operational observation. With the continuous progress of laser technology, detection technology, information processing technology and the development of artificial intelligence, deep learning and other high-end fields, the development of Lidar underwater detection system also tends to be intelligent, automated and miniaturized.

Traditional mid-infrared optical devices are characterized by complex structures, large volumes, and high prices, which impede the advancement of future multidimensional, multifunctional, and miniaturized integration. However, metasurfaces comprising planar and ultra-thin nanostructures have emerged as a promising alternative. By manipulating the interaction between light and materials at subwavelength scales, metasurfaces exhibit remarkable control over optical fields and offer multifunctional capabilities. Consequently, they provide new avenues for integrating infrared systems in a miniaturized form. In this paper, an efficient metalens based on Pancharatnam-Berry (PB) phase working in the mid-infrared range(3.7μm-4.8μm) is proposed and numerically demonstrated. The proposed metalens enables precise control of incident light phase, thereby converge the incident light into two focal spots within spectral-band ranges: 3.7μm-4.0μm (with a focal length of 150μm) and 4.5μm-4.8μm (with a focal length of 250μm). The bifocal metalens is space division multiplexing designed using alternately arranged a-Si nanobricks, facilitating a high polarization conversion efficiency exceeding 80% and achieving achromatic behavior within the two spectral-band ranges. This work demonstrates the potential application of metalens for addressing complex tasks in infrared optical detection.

Metal isotope abundance detection is significant in earth science, environmental monitoring and industrial applications. A new technique for the detection of metal isotopes was developed by wavelength modulation spectroscopy technology in this work. The measurements were made for the rubidium transition at 795 nm using four kinds of rubidium compound samples (RbCl, Rb₂CO₃, Rb₂SO₄, and RbI). Based on the redox reaction, the solid rubidium compound was mixed with the reducing agent. The micro-channel array structure of the atomic generator can produce highly collimated atomic vapor. The ability of high-order harmonics (2nd, 4th, and 6th) to suppress system noise was compared, and the result showed that the fourth-harmonic signal not only enhanced signal-to-noise ratio but also ensured effective spectral resolution. Compared with direct absorption, the signal-to-noise ratio of the 4th harmonic was enhanced by approximately 3.3 times. In addition, wavelet denoising further suppressed the baseline standard deviation of the system by about a factor of 1.

Atmospheric optical turbulence significantly impacts the efficacy of adaptive optics and various laser systems. The parameter known as the atmospheric refractive index structure constant, or C²_n, is crucial for characterizing this turbulence. In response to this challenge, we have developed a model utilizing the Whale Optimization Algorithm combined with a Support Vector Machine (WOA-SVM) designed to estimate atmospheric optical turbulence profiles along Eastern China’s coast. The WOA-SVM model uses standard atmospheric sounding data from the region to forecast turbulence profiles at different times, subsequently comparing these estimates with actual observations. Our error analysis indicates that the model’s estimates have root mean square errors (RMSE) of 0.4441, 0.3012, 0.4734, and 0.4904 for the respective times, while correlation coefficients range from 85.10% to 93.66%. The research shows that despite minor discrepancies in atmospheric optical turbulence profiles estimated by the WOA-SVM model using standard atmospheric sounding data and those measured directly, the general trend is consistent. This consistency confirms the WOA-SVM model’s practicality for estimating atmospheric optical turbulence in coastal areas. Therefore, the study made an attempt for direct estimation of turbulence profiles using routine meteorological data and paves the way for future model development in this domain.

The 2-D galvo scanners refer to motorized mirror mounts and systems specifically designed for applications involving laser-beam steering or scanning. They excel in swiftly manipulating small laser beams, offering exceptional levels of accuracy and precision. Functioning as dynamic electro-optical components, galvo scanners employ a rotatable mirror with low inertia to accurately position a laser beam with a high degree of precision and repeatability. In a series of applications, achieving a repeatability of less than 2 μrad is critical for galvo scanner. However, the galvo scanner system could suffer from optical and control errors because of lacking researchers’ intervention. These errors may give rise to deviations between the actual motion of the galvo scanner and the desired motion, then impede the precise positioning and control of the beam. Hence, an exceedingly precise and accurate calibration of the galvo scanner is imperative to attain high-precision control. To realize the standard accuracy of 0.3 mm in applications, current methods still keep imperfections. To evaluate the accuracy of the galvanometer's scanning beam location across a specified voltage range and the variations in its scanning capabilities with signal frequency, this research introduces a high-precision calibration measurement method for the 2-D galvo scanner. This method serves as a valuable resource for future studies on galvanometer scanner calibration and trajectory matching algorithms, establishing a research foundation for the eventual implementation of uniform light field illumination by galvanometers.

Adaptive optics (AO) systems are trending towards miniaturization and cost reduction, with wavefront sensorless adaptive optics systems (WFSless AOSs) emerging as a field of interest due to their simple structure and application versatility. The advent of deep learning has propelled the use of convolutional neural networks (CNNs) to extract aberration information from CCD images. Nevertheless, CNNs often fail to focus on the regions of images where effective information is concentrated, which limits the accuracy in aberration extraction. This paper introduces a novel Swin-UNet-based model for WFSless AOSs based on point source that employs an attention mechanism to target relevant areas within CCD light intensity images, thus addressing CNN shortcomings. Furthermore, the proposed model fuses in-focus and out-of- focus image information to directly output the reconstructed wavefront image, enhancing the overall wavefront reconstruction process. Our simulations across various D/r0 ratios reveal significant improvements with the Swin-UNet-based model: a reduction in rms wavefront error from 0.0219 to 0.0061 wavelengths at D/r0=1, from 0.0806 to 0.03825 at D/r0=6, and from 0.1241 to 0.0991 at D/r0=11. Correspondingly, the Strehl ratio improved from 0.9950 to 0.9988, from 0.8380 to 0.9567, and from 0.6814 to 0.7522, indicating enhanced image quality post-correction. Compared with existing CNN-based technology, our Swin-UNet approach can more effectively concentrate on the relevant areas of the image and mitigate the influence of invalid regions on the analysis, thereby substantially improving the effectiveness and robustness of the correction performance in WFSless AOSs.

The Solar Upper Transition Region Imager (SUTRI) was proposed to observe for the first time the Ne VII line at 46.5nm emitted from the upper solar transition region. As the key optical elements of the SUTRI, Sc/Si multilayer reflective mirrors are developed to offer high spectral selectivity and high reflectivity at 46.5nm with a normal-incidence angle. To avoid spectral contamination, the reflective bandwidth of the multilayer is required less than 4nm, which is achieved when the Sc layer thickness ratio is tuned to above 0.65. Meanwhile, the mechanical property, resistivity to thermal cycling, and temporal stability of the Sc/Si multilayer are characterized. The addition of an ultrathin Si layer (thickness of 0.6nm) in each Sc layer decreased the crystallization of Sc and flatted the interface, resulting in the enhancement of the mechanical property of the Sc/Si multilayer with new structure. After three times of thermal cycling, the temperature from 5°C to 40°C, the surface morphology of the new Sc/Si multilayer remained unchanged. The grazing incidence reflectometer test results showed that the periodic structure and thickness of the new multilayer were still similar after 2 years of storage. The optimized Sc/Si multilayer has a d-spacing of 24.55nm and a Sc thickness ratio of 0.72, achieving the extreme ultraviolet reflectivity of 28% at 46.1nm obtained from the laboratory-based reflectometer. The optimized Sc/Si multilayer mirrors have been applied in the SUTRI and received bright solar images at 46.5nm.

In the adaptive optics system of large-aperture ground-based telescopes, the wavefront sensor plays a crucial role. Pyramid wavefront sensors are increasingly favored by an expanding number of world-class telescopes. However, traditional wavefront reconstruction algorithms with pyramid wavefront sensors have limited ability to fit nonlinearity, resulting in restricted improvement in reconstruction accuracy. The kernel of deep learning lies in the ability of artificial neural networks to approximate nonlinear functions with arbitrary precision, which is well-suited for solving the nonlinear wavefront reconstruction problem of pyramid wavefront sensors and achieving more accurate wavefront sensing. This paper introduces the application of deep learning in pyramid wavefront sensors and Shack-Hartmann wavefront sensors, conducts a comparative analysis between them, and discusses potential future research directions.

This research focuses on atmospheric aerosols in China's maritime regions, utilizing aerosol data from the next-generation geostationary meteorological satellite Himawari-8 (H8) and the spaceborne lidar CALIPSO (Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations). It examines the distribution and variation of typical aerosols across different time and space scales and explores the optical properties of aerosols in the eastern maritime regions. The findings indicate: 1. Aerosol optical properties in coastal regions are predominantly influenced by anthropogenic aerosols from land, signifying a dominance of fine-mode aerosols in these areas, with the central and eastern parts primarily characterized by larger sea salt aerosol particles. 2. Outside of summer, irregular, larger aerosol particles are mainly found at lower altitudes. 3. Further examination of meteorological factors influencing aerosol optical properties reveals a notable correlation between sea surface temperature, wind speed, relative humidity, and aerosol optical thickness.

Deformable mirrors are key active components in adaptive optics systems that enable real-time correction of wavefronts. When using lightweight high-coupling deformable mirrors to fit large RMS wavefronts, the best-fitting voltage often exceeds the maximum deformation voltage of the deformable mirror. In such a case, cropping the voltage directly will greatly destroy the wavefront. This will affect the closed-loop effect. In response to the above issues, we propose using the interior point method to fit the wavefront. This method can directly solve the problem in the voltage range allowed by the deformable mirror, which not only simplifies the steps of the original method, but also greatly improves the fitting capability of the deformable mirror. We used the traditional least-squares method and the interior-point method to fit the static aberrations separately in the simulations. Results show that for the original wavefront (RMS = 2059.70 nm), the least squares algorithm can correct the aberrations to 425.35 nm, while the interior point method can correct the aberrations to 248.10 nm. In the experiments, we used a deformable mirror with 294 actuators for closed-loop testing. The experiment results show that for the original wavefront (RMS = 808.53 nm), the least squares algorithm can correct the aberrations to 182.39 nm, while the interior point method can correct the aberrations to 100.95 nm. This method has great significance for giving full exploit to the performance of the deformable mirror and improving the wavefront correction capability of the AO system.

This paper explores a hierarchical shape control method for large, lightweight polymer mirrors with unimorph actuation. Two methods of generating strain-driven forces are discussed. The initial focus is on the study of linear interaction matrices for various actuation configurations. Subsequently, control algorithms are designed for a large active optics aperture. The controlled degrees of freedom for the injection spots of electron flux are estimated, and criteria for examining iteration convergence are proposed.

The composite photovoltaic anode, leveraging the unique characteristics of a composite structure and high thermal conductivity materials, is progressively replacing traditional sample anodes in X-ray sources. This paper elucidates the structure of the diamond-based X-ray source anode (referred to as the “composite anode”). By incorporating a diamond layer, the composite anode aims to achieve rapid heat conduction and high-temperature durability. The characteristics and thermal conductivity weight of the diamond layer are explored. Furthermore, finite element analysis (FEA) methodology is employed to simulate and compare different thicknesses of the diamond layer. The findings illustrate that the diamond layer in the composite anode structure exhibits a high thermal conductivity rate and high melting point characteristics. Additionally, the thickness variation of the diamond layer directly impacts the overall heat conduction capacity of the composite anode. Consequently, the relationship between the thermal conductivity coefficient of the composite anode and the thickness of the diamond layer is ascertained, provided that the experimental conditions allow for reproducibility.

Structured illumination microscopy (SIM) is more applicable to the super-resolution imaging of living cells by virtue of its wide field of view, fast imaging and low phototoxicity. However, a high-quality super-resolution image requires accurate parameter estimation. Recently, we have proposed an efficient and robust SIM algorithm based on principal component analysis (PCA-SIM) that integrates iteration-free reconstruction, noise robustness, and limited computational complexity. Nevertheless, as with many parameter estimation algorithms, the performance of PCA-SIM may be affected when using high-frequency sinusoidal illumination and total internal reflection fluorescence (TIRF) objective. In this work, we present a parameter estimation method of combining cross-correlation and principal component analysis, capable of accurate sub-pixel precision estimation when the 1-order spectral information is lacking without iteration, promising to achieve high-speed, long-term, artifact-free super-resolution imaging of live cells.

The distribution of optical turbulence with height over the plateau is one of the most important points for laser propagation in the atmosphere. The simultaneous measurement of optical turbulence at three layers (2m, 5m and 10m) was carried out on Plateau with sand-grass underlying surface. The measured refraction index structure constant at 2m and local sunrise and sunset times were used to verify the applicability of the HAP model. The index of the HAP model and its diurnal variation are re-fitted by the measured refraction index structure constant. Compared with the traditional model, the average correlation coefficient and root mean square error are increased from 0.893, 0.796, 0.263 and 0.286 to 0.899, 0.816, 0.158 and 0.243, respectively. It is improved that the applicability of the new HAP model to plateau atmosphere. The new HAP model provides a new reference for the evaluation of the turbulence effect for plateau laser atmospheric transmission.

In response to the problem of common mode noise in transmission optical cables caused by external environmental factors during the long-term operation of underwater autonomous fiber optic hydrophone systems. This paper proposes a single-element fiber optic hydrophone based on a symmetrical structure for common mode noise suppression. The proposed symmetrical structure utilizes the characteristics of fiber optic couplers, where the output phase difference of the two interference lights is fixed, and then the two interference lights are output separately through an optical circulator. Subsequently, the detected two interference signals are used to noise cancellation processing, followed by phase demodulation, in order to suppress common mode noise and improve detection performance. A corresponding testing system was built, and the experimental results indicate that this measurement system has a simple optical circuit and does not require additional optical paths and time division channels compared with traditional structures. In addition, this measurement system can effectively reduce common mode noise. The actual test results of common mode intensity noise suppression are in good agreement with theoretical results. The symmetric system structure and common mode noise suppression method and theories reported in this article can also be extended to other interference systems, and hence have important value for large-scale multiplexing of hydrophone arrays.

Underwater in-situ darkfield microscopy can achieve high-resolution high-contrast plankton images for plankton species identification, size measurement and abundance estimation. However, light is scattered and absorbed by water, and this will blur plankton images and reduce signal-to-noise ratio, especially for turbid water conditions. Different wavelength light has different optical scatter and absorption characteristics. Therefore, we investigate effect of light wavelength on underwater in-situ darkfield microscopy in different water optical attenuation coefficients. An underwater darkfield microscopy system with the spatial resolution of 10 μm has been established. The illuminators at blue, green, red and white bands are designed to generate sheet light, and then underwater darkfield images were grasped from 0.7/m to 7.04/m optical attenuation coefficients. The target-to-background contrast and intensity attenuation characteristics show that the red light has the better contrast and weaker attenuation performance than the green and blue light in turbid water environments.

Spectral responsivity is a key parameter for imaging sensors and systems. Traditionally, the spectral responsivity is measured in darkroom with no ambient light. However, the dark condition is not similar to most application science where ambient light generally exist. To investigate the ambient light bias effect on the detection performance, we introduce a differential approach to measure the spectral responsivity of the imaging sensors and systems under the biased lighting condition. The differential spectral responsivity (DSR) can reflect the target-environment interaction in complex scenes such as object detection in very bright/weak lighting environment or with very low image contrast. In this paper, a measurement facility for the differential spectral responsivity in irradiance mode in the waveband (300~1100)nm is established and described. The factors affecting the measurement are analyzed. As a case study, a standard relative uncertainty of 2.35% (k=1) is obtained for a CMOS sensor system in the waveband (400~800)nm.

This paper presents a method for optimizing spectral imaging based on incoherent correlation holography. By adjusting the axial position of the PZT, a series of interference patterns with varying optical path differences (OPD) is captured. Due to the limited precision of the PZT, we propose an optimization algorithm capable of accurately retrieving the intensity variation. Following the Fourier transform to the image stack, the spatial wavefront corresponding to different wavelengths can be reconstructed. We demonstrate the effectiveness of our approach through spectral reconstruction under quasimonochromatic illumination, while also highlighting the potential for multi-spectral imaging applications.

In order to measure fiber strain using distributed fiber strain sensing technology, the strain of three composite submarine cables is reflected. The on-line stress monitoring and intelligent early warning technology of long-distance and highprecision distributed fiber optic sensing submarine cable are studied, and the stress decoupling method of Brillouin distributed fiber based on fiber Brillouin scattering model is realized. Finite element simulation method is used to calculate conductor core strain through optical fiber strain. Combined with finite element simulation analysis, stress distribution characteristics of different stress damage modes of submarine cable such as anchor breakage, anchor hook and hanging are obtained, the alarm threshold of submarine cable stress anomaly is proposed to complete intelligent early warning of submarine cable stress anomaly. It also provides a theoretical basis for submarine cable routing and topographic information anomaly location and typical submarine cable fault diagnosis.