Mid-spatial frequency surface errors (MSFSE) can cause small angle scattering in optical systems. In order to determine a reasonable tolerance for MSFSE in optical design and processing, this paper conducts a quantitative study on the impact of MSFSE on the modulation transfer function (MTF) of optical systems. Under diffraction-limited conditions, we derived an expression for the influence of MSFSE on the MTF of optical systems and analyzed it. Then, we verified the theoretical derivation results through optical design software simulation. Assuming that the optical system has a sinusoidal MSFSE on the pupil, we performed the Fourier transform on the pupil function and squared it to obtain the point spread function (PSF), and then performed the Fourier transform on the PSF to obtain the optical transfer function (OTF) of the optical system. By taking the OTF mode, the expression of MTF under the influence of MSFSE can be obtained. By comparing this expression of MTF with the MTF of an optical system without MSFSE under diffraction-limited conditions, the quantitative impact of MSFSE on the MTF of the optical system can be obtained. Theoretical calculation results indicate that sinusoidal MSFSE can lead to different losses of MTF at different spatial frequencies and that the changes in MTF losses are periodic. The maximum loss ratios of MTF in optical systems caused by sinusoidal MSFSE with peak-to-valley (PV) of 0.030 μm, 0.095 μm, 0.159 μm and 0.223 μm are 0.89 %, 8.80 %, 23.48 % and 43.31 %, respectively. The loss of MTF will increase nonlinearly with the increase of PV of MSFSE. The theoretical calculation results are consistent with the software simulation results.

For the first time, Tb³⁺ and Dy³⁺ co-doped AlN films were prepared using ion implantation, and their crystal structure, cathodoluminescence properties and energy transfer mechanism were investigated. Raman scattering and X-ray diffraction results indicate that ion implantation of Dy³⁺ has caused increased compressive stress within the internal lattice when the dosage of Tb³⁺ remains constant. Continuous implantation led to the recombination of some point defects, resulting in a partial release of internal compressive stress. Cathodoluminescence spectra demonstrated that with high-dose Tb³⁺ implantation, the emission intensities of Tb³⁺ and Dy³⁺ exhibited different trends with increasing Dy³⁺ dosage. We propose the existence of a resonance energy transfer from Tb³⁺ ions ⁵D₄→⁷F₆ to Dy³⁺ ions ⁶H_15/2→⁴F_9/2 in AlN films. Finally, we observe that under different implantation dose of Dy³⁺ ions to Tb³⁺ ions, the emission color of the sample shifts between yellow-green and orange-yellow, with color temperatures ranging from 4042 to 5119K. Adjusting the dose ratio of Dy³⁺ to Tb³⁺ enables effective control of chromaticity coordinates and color temperatures.

Focusing on the influence of the matrix lattice anisotropy on the polarization luminescence of rare earth ions, ZnO microrods and europium-doped ZnO microrods were prepared using a hydrothermal method. Comparative studies have found that the length-to-diameter ratio of doped samples increases, and the morphology of the microrod changes from dumbbell-like to straight. Analysis of the optical properties shows that the bound exciton luminescence at 385-nm makes the UV luminescence of ZnO microrods appear asymmetrical, and a weak luminescence in visible region is observed at 550 nm. After europium ion doping, the luminescence in the visible region is enhanced. For Eu³⁺ doped ZnO microrods, Eu³⁺ ion characteristic luminescence peaks with narrow half width can be observed under 532-nm excitation. When the polarization direction of the incident excitation light is adjusted, the emission of Eu³⁺ ions changes periodically with the angle of the polarized light. The polarization degree increases as the doping concentration increases. These results show that the luminescence of the europium ions in the ZnO microrod matrix lattice is sensitive to the polarization of excited light. Doped ZnO microrods can integrate the ultraviolet absorption properties of low-dimensional ZnO materials with the excellent visible luminescence properties of rare earth ions, meaning they have significant application value in fields such as polarization detection.

There is a significant narrowing of the lateral radiation spectrum of the substrate of organic light-emitting diodes as compared to the forward radiation spectrum. Studying the factors that affect the lateral radiation spectrum narrowing of the device and further reducing the spectral linewidth can provide a foundation for the study of the electrically pumped organic light-emitting diode laser radiation. We study the full width at half maximum, peak wavelength, and polarization characteristics of lateral radiation spectrum in organic light-emitting diode substrate, with the thickness changes of hole transport layer NPB. The lateral radiation spectra of organic light-emitting diode with Ag film evaporated on both sides of the substrate edge are compared with those of organic light-emitting diode without Ag film. The full width at half maximum of the lateral radiation spectrum with Ag film is narrower. When the NPB thickness is 130 nm, the full width at half maximum of the lateral radiation spectrum in the device substrate reaches its narrowest, which is 14 nm. This shows that the optical resonator will affect the light propagating laterally in an organic light-emitting diode substrate when mirrors are provided on both edge sides of the substrate. The results indicate new approaches to narrowing the radiation spectrum and amplifying the light of organic light-emitting diodes.

In this paper, a terahertz band-stop filter based on a symmetrical H-type structure was designed, the continuous metal arms of which can flow current. By using electromagnetic simulation software CST Microwave Studio 2021, the filtering characteristics of the filter were studied, and the geometric parameters of the filter were determined by changing the arm length, period length and gap of double H. The results show that the filter can realize the tunable polarization properties. Under the y-polarization condition, the transmission spectrum has no obvious resonance peak in the range of 0.2−2.3 THz, but the intensity ranges from −15 dB to −3 dB. Under the x-polarization condition, a remarkably sharp dipole resonance valley occurs at 1.34 THz in the transmission spectrum, and the bandwidth and intensity are 0.15 THz and −30 dB, respectively. In order to verify the simulation results, the designed metamaterial filter was fabricated using micromachining technology, and the sample was tested by transmissed-terahertz time-domain spectroscopy (THz-TDS) system. The experiment results are in good agreement with the simulation results, which verifies the feasibility of this method.

Passively Q-switched mode-locked operation was realized for the first time by inserting a semiconductor saturable absorption mirror (SESAM) as a mode-locking element into a Tm:CaYALO₄(Tm:CYA) laser using tandem-pumping technology. The laser cavity adopted an X-type four-mirror cavity structure, and the pumping source was an Er:Y₃Al₅O₁₂(Er:YAG) solid-state laser with a central wavelength of 1650 nm. Output coupling mirrors with transmittances of 0.5%, 1.5%, 3%, and 5% were used to study the laser’s continuous wave (CW) output and mode-locking output characteristics. The experimental results show that the laser has the best output characteristics when an output coupling mirror with a transmittance of 5% is used. The maximum power of 894 mW and the maximum slope efficiency of 16% were obtained when the laser operated in the CW regime. After the CW power was optimized to the highest, the mode-locked element SESAM was added to the optical path. When the absorbed pump power became greater than 1.86 W, the laser operation entered an unstable Q-switched state; when the absorbed pump power increased to 5.7 W, a stable passively Q-switched mode-locked operation was achieved; when the absorbed pump power reached 6.99 W, a mode-locked pulse laser with a maximum output power of 399 mW was obtained by using the output coupling mirror with transmittance of 5%. At that time, the repetition frequency under the Q-switched envelope was 98.11 MHz, the pulse width was 619.4 ps, and the corresponding maximum single pulse energy was 4.07 nJ. The mode-locked pulse modulation depth in a Q-switched envelope was observed to be close to 100%. The above results show that tandem-pumping technology can be used in lasers to generate Q-switched mode-locked pulses, which provides a new pumping method for generating ultrashort pulse lasers.

We investigate a silicon-glass fiber-optic Fabry-Perot (FP) pressure sensor based on Micro-Electro-Mechanical Systems (MEMS) technology for high-pressure measurements. Silicon material was used as the sensitive element, and the Inductively Coupled Plasma (ICP) dry-etched monocrystalline silicon diaphragm was anode bonded with a high borosilicate glass to form the FP cavity. The sensor head was manufactured in batches utilizing MEMS technology, which is structurally stable, strongly resistant to overload, and not prone to fail in high-pressure environments. The experimental results show that the sensor can acheive high-pressure measurements up to 30 MPa with a sensitivity of 46.94 nm/MPa and a linearity of 0.99897, with high consistency and reliable measurement results. The designed pressure sensor has strong application prospects in high-pressure sensing.

Cascaded Microring Resonators (CMRR), a new type of optical sensor, are widely used in biology, medicine, and other fields because of their high sensitivity, easy integration, and low power consumption. In this paper, we propose a Python-based envelope fitting method for real-time CMRR sensor’s output spectrum to achieve real-time data analysis and processing of the CMRR sensor’s output spectrum. First, different fitting models were used to fit the output spectrum of the CMRR sensor. Then, the fitting errors of different fitting models were compared by sensitivity error percentage, and it was concluded that the smooth spline fitting method performed best in real-time processing of the output spectrum of the CMRR sensor. Finally, NaCl solution with different concentrations was used for real-time acquisition and processing of the output spectrum. The reliability of the real-time acquisition and processing program for the CMRR sensor’s output spectrum is verified. The experimental results show that the wavelength drift of the CMRR sensor is linearly related to the concentration of the solution. It can be seen from the calculation that the sensitivity of the CMRR sensor for brine is about 671.03529 nm/RIU.

In this paper, we developed a dual-sideband beat-suppressed heterodyne phase-sensitive dispersion spectroscopy (HPSDS) for sensitive detection of trace gases across a wide dynamic range and explored the operational characteristics of the electro-optic modulator (EOM) and bias voltage control methods under sideband suppression mode. The dispersion phase spectral profiles and the corresponding signal-to-noise ratios in both suppression and non-suppression modes were compared before a comprehensive evaluation of the detection performance. A HPSDS-based detection system was developed based on a near-infrared distributed feedback laser and an EOM. The suppression of the dual-sideband beat was achieved by exploring and analyzing the optimal operational range of the EOM, leading to the optimization of dispersion phase signals with increased amplitude and high signal-to-noise ratio. The dispersion phase signals under typical high-frequency (1.2 GHz) intensity modulation were recorded for different standard methane/nitrogen mixtures. The relationship between the peak-to-peak values of the dispersion phase signals and the varied gas concentrations was then summarized. Meanwhile, wavelength modulation spectroscopy (WMS) experiments were conducted; subsequently, the HPSDS and WMS techniques’ performances were compared in terms of linearity, dynamic detection range, and immunity to optical power fluctuations. Finally, the HPSDS-based system's performance under a wide dynamic range and rapid time response was verified by measuring different concentrations of standard gases. Experimental results indicate that the HPSDS technique exhibits high linearity (R² = 0.9999), a wide dynamic range (38.5 ppm to 40%), and remarkable immunity to optical power fluctuations. The dual-sideband-beat-suppression-HPSDS-based methane sensor developed in this paper shows great potential for applications involving wide dynamic range detection and on-site practical trace gas detection.

We use an electro-optical potential phase modulator to modulate the pump light to obtain radio frequency modulation transfer spectroscopy (MTS), and study the optimization problem of the zero-crossing slope of the center of the dispersive signal of the MTS spectrum. By changing the modulation frequency of the pump light, the spot size of the pump light and the probe light, we study the parameter dependence between the zero-crossing slope of the MTS spectral signal and the modulation frequency, and spot size. The optimal MTS spectral signal is obtained when the pump light modulation frequency is −3.6 MHz (about 0.69 times the natural linewidth). Finally, by using the optimal MTS spectrum, the DL Pro @ 852 nm laser frequency is locked to the cesium atom D2 line (F = 4) - (F = 5') cycle transition, and the laser frequency fluctuation is about 170 kHz in the 60 minutes sampling time, which is significantly improved compared with the frequency fluctuation of the laser −11 MHz during free running.

Aiming at the loss of target point information caused by the degradation of underwater calibration images collected by camera calibration in underwater visual measurement, an underwater calibration image enhancement algorithm based on image block decomposition and fusion is proposed. First, given the difficulty of image dehazing caused by uneven illumination of underwater calibration images, image segmentation is implemented based on homomorphic filtering to calculate the global background light intensity and to achieve image dehazing. Then, given the problems such as noise, blur, and uneven illumination that still exist after the underwater image is dehazed, contrast enhancement and detail information enhancement are performed to obtain two complementary enhanced images. The complementary images are divided into multiple image blocks, and the image blocks are decomposed into three independent components, each of which is average intensity, signal intensity, and signal structure. The three components are separately fused and solved for the final enhanced image. Finally, subjective and objective evaluation and target point detection experiments are used to evaluate the enhanced quality of the underwater calibration image. Experimental results indicate that the visual effects and evaluation scores of the proposed method are higher than those of UDCP, MSR, and ACDC methods. When the turbidity is 7.6 NTU, 11.4 NTU, 15.7 NTU, and 18.4 NTU, the number of detected target points increases by 2.0%, 2.3%, 9.3%, and 21.2%. Therefore, we present a reliable and effective method to improve the quality of underwater calibration images and provides a stable and reliable underwater calibration image enhancement method for underwater visual measurement.

This paper focuses on the comprehensive detection of defects in cold rolled steel through examination for surface and internal defects. Regarding surface defect detection, a bilateral line light illumination scheme is proposed and a comparison with line light illumination scheme is carried out. As for internal defect detection, the applicability of various metal internal inspection technologies such as X-ray, ultrasound, and infrared thermography is analyzed from the perspectives of detection resolution and defect edge characteristics. The results show that bilateral line light illumination not only increases the overall average precision of the YOLOv5 object detection algorithm model to 90.16% (an increase of 15.46% compared to the line light illumination) but also improves model classification and training efficiency. X-ray and ultrasound inspection technologies can detect blind holes with a diameter of 0.25 mm, while infrared thermography can detect blind holes with a diameter of 1 mm. In evaluating defect edge characteristics, X-ray inspection technology exhibits a minimum blind hole edge grayscale difference of 145, ultrasound of 89, and infrared thermography of 30. This study proposes an improved scheme for the detection of surface defects in cold rolled steel and offers insights for the research on internal defect detection.

Linear optical processors based on the cascaded topology of Mach-Zehnder Interferometer (MZI) have been demonstrated to be an important way of implementing Optical Neural Networks (ONN), but several practical challenges still need resolution. Concerning issues arising from chip manufacturing and testing processes that could lead to phase errors and insertion losses, we conducted experiments and theoretical simulations for various reconfigurable optical processors. We found that the weights of any arbitrary unitary matrix can be realized through some single N×N Clements units, that can substantially reduce the optical depth and enhance robustness against insertion losses. This approach allows for the construction of fully complex optical neural networks. Additionally, In multi-layer ONN, due to the limited degrees of freedom in constructing this arbitrary matrix, we introduced a phase-shift layer before each layer of the Clements unit. This design aids in mapping classification data to higher-dimensional spaces, facilitating faster neural network convergence.

Strain reconstruction is a vital component in the characterization of mechanical properties of phase-contrast optical coherence tomography (PC-OCT). It requires an accurate calculation for gradient distributions on the differential wrapped phase map. In order to address the challenge of low signal-to-noise ratio (SNR) in phase gradient calculation under severe noise interference, a Bayesian-neural-network-based phase gradient calculation is presented. Initially, wrapped phase maps with varying levels of speckle noise and their corresponding ideal phase gradient distributions are generated through a computer simulation. These wrapped phase maps and phase gradient distributions serve as the training datasets. Subsequently, the network learns the “end-to-end” relationship between the wrapped phase maps and phase gradient distributions in a noisy environment by utilizing a Bayesian inference theory. Finally, the wrapped phase measured by PC-OCT is processed by Bayesian neural network (BNN), and the high-quality distribution of phase gradients is accurately predicted by inputting the measured wrapped phase-difference maps into the network. Additionally, the statistical process introduced by BNN allows for the utilization of model uncertainty in the quantitative assessment of the network predictions’ reliability. Computer simulation and three-point bending mechanical loading experiment compare the performance of the BNN and the popular vector method. The results indicate that the BNN can enhance the SNR of estimated phase gradients by 8% in the presence of low noise levels. Importantly, the BNN successfully recovers the phase gradients that the vector method is unable to calculate due to the unresolved phase fringes in the presence of strong noise. Moreover, the BNN model uncertainty can be used to quantitatively analyze the prediction errors. It is expected that the contribution of this work can offer effective strain estimation for PC-OCT, enabling the internal mechanical property characterization to become high-quality and high-reliability.

Non-destructive, non-contact phase-shifting digital holography technology has distinct advantages in identifying micro-optical components. As traditional phase-shifting digital holography technology requires fine control and cumbersome calibration of the phase shifter, furthermore, its optical path is susceptible to mechanical vibration interference, which reduces the quality of the holographically reproduced image. To solve the above problems, we propose a vortex phase-shifting digital holography for the micro-optical element surface measurement with the help of the special phase distribution of vortex light. The method utilizes a helical phase plate to modulate the vortex phase and introduce a high-precision phase shift. Based on the constructed vortex phase-shifting digital holographic microscopy experimental setup, the actual phase shifts between phase-shift interferograms were determined using the interferometric polarity method, the relationship between the rotation angle of the helical phase plate and the phase shift was calibrated, and the feasibility of the vortex phase shift was experimentally verified. Repeated measurement experiments were carried out on the micro-lens arrays, and the measurement results were compared with those of the ZYGO white light interferometer. The results indicate that a single micro-lens's average longitudinal vector height is 12.897 μm with an average relative error of 0.155%. The proposed method enables highly precise measurement of the surface topography of micro-optical elements. It offers the advantages of easy operation, high stability, and high accuracy.

The reconstruction of the three-dimensional surface morphology of objects based on binocular stereo matching is constrained by physical conditions such as sensor size, lens focal length, and environmental light. A binocular surface three-dimensional reconstruction method based on interpolation super-resolution is proposed in response to this issue. First, at the image preprocessing stage, an image enhancement method based on wavelet transform and dual histogram equalization fusion is established to overcome the problems of traditional binocular vision limited by complex environmental light interference. Second, a super-resolution algorithm based on Lagrange and cubic polynomial interpolation is constructed to increase the image’s pixel density and add image details to the binocular matching cost calculation stage, thereby improving the matching accuracy. Finally, a simple linear iterative clustering (SLIC) method is used to segment the target image, and a secondary surface fitting is performed for each segmented area to obtain a height curve that is more closely aligned with the actual surface of the object, which can reduce the reconstruction error and improve the reconstruction accuracy. The experimental results show that the average relative error of the global height measurement of 5 sets of measurement samples is ±2.3%, the average measurement time of the experiment is 1.8828 s, and the maximum time is 1.9362 s. This is a significant improvement over traditional methods. Experimental analysis results verify the effectiveness of the proposed algorithm.

We propose an improved point cloud registration method based on point-by-point forward feature point extraction to improve the efficiency and accuracy of point cloud registration. Firstly, the point-by-point forward method was used to quickly extract the point cloud feature points, significantly reducing the number of point clouds while retaining the characteristics of the point cloud model. Then, the improved KN-4PCS algorithm using normal vector constraints was coarsely registered to achieve the preliminary registration of the source point cloud and the target point cloud. Finally, the two-way Kd-tree optimized LM-ICP algorithm was used to complete the fine registration. In this paper, registration experiments were conducted on different point cloud data. In the registration experiment on Stanford University open point cloud data, the average error was reduced by about 70.2% compared with the SAC-IA+ICP algorithm, about 49.6% compared with the NDT+ICP algorithm, and the registration time was reduced by about 86.2% and 81.9%, respectively, while maintaining high accuracy and lower time consumption after introducing different degrees of Gaussian noise. In the point cloud registration experiment on real indoor objects, the average registration error was 0.0742 mm, and the average algorithm time was 0.572 s. The experimental results show that the proposed method can effectively improve the point cloud registration’s efficiency, accuracy, and robustness, thereby providing a solid foundation for indoor target recognition and pose estimation based on the point cloud.

Accurate droplet edge extraction is crucial for measuring water contact angle. To address issues like poor noise robustness, incomplete edge extraction, and low precision in conventional methods, we propose an improved model for droplet edge detection based on Richer Convolutional Feature (RCF) algorithm. Firstly, a feature fusion module is introduced in the deep feature extraction stage to enhance model robustness and reduce overfitting risks. Secondly, a multi-receptive field module replaces the contact layer after RCF to extract more semantic information and enrich edge details. Thirdly, an efficient channel attention mechanism is introduced before each layer of the models to enhance focus on important features of the image. Lastly, the MaxBlurPool downsampling technique is designed and incorporated to reduce computation and parameter requirements while improving translation invariance. Experimental results on a self-made droplet dataset demonstrate that the proposed model achieves an ODS value of 0.816, an OIS value of 0.829, and a detection accuracy of up to 90.17%, which is an improvement of 1.85 percentage points compared to the original model. It can improve accuracy in droplet edge features detections.

Space-borne two-dimensional turntables are the main bearing mechanism of space cameras and other optoelectronic equipment, and the U-frame is the key supporting part of these turntables. In order to optimize the structure and lightweight design of the U-frame of the two-dimensional turntable and to develop a lightweight two-dimensional turntable with a high load-bearing ratio, we design a U-frame for the space two-dimensional turntable based on Carbon Fiber Reinforce Plastics (CFRP). First, a variable cross-section tubular structure U-frame was designed using carbon fiber composites instead of titanium alloy material considering the manufacturability. Then, according to the finite element modeling method based on the lay-up process, the carbon fiber U-frame was subjected to finite element modeling and simulation analysis. Then, a prototype U-frame was fabricated, and modal tests verified the accuracy of the finite element model. Finally, a three-level optimization method combining theoretical analysis, genetic algorithm, and the finite element method was proposed to optimize the design of carbon fiber U-frame ply angle, ply thickness, and ply sequence. The results indicate that the vibration patterns of the U-frame obtained from the modal test and simulation are identical and that the frequency difference is less than 5%. The initial design of the carbon fiber U-frame is 45.7% lighter than the titanium U-frame. Through the secondary optimization of the composite layup, the U-frame is further reduced in weight by 13.8%. Additionally, the intrinsic frequency of the U-frame is improved by 10.14%. It can be concluded that the composite modeling and optimization methods used in this paper are correct, and the designed carbon fiber U-frame meets the lightweight design requirements of space-born two-dimensional turntable.

The alignment accuracy of the emitting and receiving optical axes of laser communication equipment in the satellite ground field is crucial. Temperature fluctuation can cause deformations of optical components and mechanical structures, affecting the optical axis’ alignment and reducing the system’s detection accuracy. We design a high-precision optical axis stability system for detection. First, according to the technical requirements of broadband and conjugate imaging, an off-axis reflective Keplerian telescope system with image transfer was applied to compress the beam. After passing through a beam splitter, the beams entered the detection subunit separately. A long focal length optical axis stability detection system was designed to improve detection accuracy. To correct the thermal difference of the reflective system, an optical passive non-thermalization technique was employed using a refractive mirror group to compensate for the thermal-induced aberration of the reflective mirror group. The mechanical structure was designed and subjected to finite element analysis. Finite element data were processed and fed into optical software to simulate the optical axis deviation angle caused by temperature fluctuation. Finally, experiments were conducted for validation. The results show that the optical axis stability detection system has an optical axis deviation angle of 3.90" at −10 °C and 4.23" at 45 °C, reducing the impact of temperature fluctuation on optical axis deviation.

In order to achieve a large image plane and large zoom ratio in microscopic imaging and solve the problem of the high integration of coaxial Kohler illumination, we propose a design method for a compact optical system with a large zoom ratio based on coaxial Kohler illumination. First, the imaging principle of the continuous zoom optical system of telescopes and microscopes is analyzed, and the design principle of the positive group compensation zoom microscope is analyzed theoretically. Then, the front fixed group is divided into a collimation group and a convergence group, and a beam splitter prism is designed between the two lens groups to achieve a compact coaxial Kohler illumination optical system by sharing lens groups. Finally, the continuous zoom microscope with a large image plane and the matched coaxial Kohler illumination optical system are designed. The design results show that the zoom ratio of the microscope optical system is 10×, the working distance is 60 mm, the highest resolution of the object side is 1.75 µm, and the coaxial illumination uniformity is 94.3%. The designed microscope has excellent imaging quality, minimal distortion, a smooth zoom curve, and a compact size, verifying the feasibility of the design method.

Spectral synthesis technology is an important technical approach to achieving high-energy laser output. Ensuring high-quality laser output under the premise of high-power output has become the most urgent goal in further developing spectral synthesis technology. Aiming at the challenge of parameter detection for 155 mm × 140 mm rectangular aperture, (1064 ± 3) nm, (1030 ± 3) nm, and (635 ± 5) nm band beams, we design a large-aperture multi-band multi-parameter detection system. The wavefront detection unit is based on Kepler’s telescopic structure, the conjugate relationship between the deformable mirror and the microlens is constructed, at the same time, the compressed beam matches the detector size. The front group objective lenses adopt a Cassegrain structure to solve the problem of color difference correction in large-aperture and multi-band. The rear group of mirrors adopts a three-piece apochromatic refractor group, which compensates for the color difference while accounting for the non-thermal design. It can be used for compensation to the residual thermal difference of the front group of objectives and the thermal difference of the rear group of mirrors. After passing through the wavefront detection unit, the beam quality and beam uniformity can be measured. In order to improve the environmental adaptability of the system, it was designed through an optical passive anthermic method at 20 °C±10 °C. Finally, the system was installed and tested, and the wavefront spot image collected by the wavefront detection camera was restored using the Zernike wavefront restoration method. The measured RMS value of the wavefront of the system is better than 0.0524λ (λ=632.8 nm), the beam uniformity is better than 0.893, and the beam quality β factor is better than 1.26 times the diffraction limit at 10 °C−30 °C.

Noise Figure (NF) is an important parameter in evaluating the performance of transmitting a signal from a high-frequency electronic device. As the operating frequency increases, the NF of high-frequency electronic devices usually increases, and the Excess Noise Ratio (ENR) of existing noise sources cannot meet the associated measurement requirements. Therefore, to meet the measurement requirements for the NF of high-frequency electronic devices, we propose combining three incoherent optical beams into an unitraveling carrier photodiode (UTC-PD) based on incoherent optical mixing technology. A tunable terahertz (THz) photonics noise source with a high ENR in the 220−325 GHz frequency range is developed. The ENR can be tuned up to 45 dB. By using the Y-factor method, the proposed THz photonics noise source is applied to measure a THz mixer with large NF and negative conversion gain. The measured NF of the THz mixer ranges from 16 to 32 dB, the conversion gain is about −13 dB, and the uncertainty is 0.43 dB. The tunable THz photonics noise source with high ENR can meet the measurement requirements of THz electronic devices with high NF. It will play an important role in the measurement of NF of THz electronic devices and in guiding further optimization.

A phase noise suppression algorithm based on real-imaginary-alternate pilots was proposed for a coherent optical orthogonal frequency division multiplexing communication system with offset quadrature amplitude modulation (CO-OFDM-OQAM). The algorithm uses the properties of laser phase noise and the intrinsic imaginary interference (IMI) symmetry law to design real-imaginary-alternate pilots. In combination with a linear fitting, it can accurately estimate the common phase error (CPE) for CO-OFDM-OQAM. As the compensation was performed in the frequency domain, the computational complexity was significantly reduced compared to the time-domain phase noise suppression algorithms. A numerical simulation platform was built for a polarization multiplexed CO-OFDM-OQAM system with an effective bit rate of 65 GBits/s. Through it, the transmission performance of the system with different laser linewidths and numbers of subcarriers was studied, and the suppression effect of the proposed method on phase noise was examined. The results obtained confirm that the linewidths required to reach the FEC limit for BER are equal to 801.1, 349, and 138.4 kHz for a fixed OSNR of 25 dB and a total number of subcarriers of 256, 512, and 1024, respectively. For the system using a 16-QAM modulation format with 256 or 512 subcarriers, it compensates well for the laser phase noise without affecting the power peak-to-average ratio.

This paper aims to improve the control performance of the precision tracking system for laser communication by studying the control method of Fast Steering Mirrors (FSM) driven by a voice coil motor. FSM often face the problems of strong cross-coupling characteristics and external disturbances. To overcome these challenges, we propose a composite fast nonsingular terminal sliding mode control strategy integrating feedforward decoupling compensation and fixed-time extended state observer. First, the FSM’s coupling transfer function matrix model with double inputs and double outputs is established by using the system identification method, and the feedforward decoupling compensator is designed to compensate for the coupling components and achieve motion decoupling between the X-axis and Y-axis. Second, the fixed-time extended state observer is designed for each decoupled single-axis model to achieve a fixed-time estimation of angular velocity and external disturbances simultaneously. Then, the fast nonsingular terminal sliding mode surface is constructed, and the exponential power function is adopted to replace the sign function in control law design, so as to improve the system’s convergence speed and suppress the chattering of the sliding mode. The proposed control system’s stability and the tracking error finite-time convergence are proved based on the Lyapunov stability analysis method. Finally, the effectiveness of the proposed composite control strategy is verified by comparative experiments. The experimental results show that under the 100 Hz strong disturbances, for the FSM tracking 60 Hz and 120 Hz circular trajectories, the average absolute values of its trajectory tracking error are 0.0036° and 0.0131°, respectively, indicating that the system can maintain good tracking performance. The proposed composite control strategy is validated as effectively meeting the FSM’s high-precision and strong anti-disturbance requirements for laser communication.

To address issues such as uneven illumination in coronary angiography images, low contrast between vascular structures and background regions, and the complexity of coronary vascular topology, we establish a coronary angiography vascular segmentation annotation dataset. Additionally, we propose a coronary angiography image vascular segmentation model based on the feature map pyramid. On the basis of the U-Net architecture, this model was improved and optimized. First, the first convolutional layer in the U-Net encoding part was replaced with a 7×7 convolutional layer to increase the receptive field of each layer. Modified ConvNeXt blocks were added to the encoding and decoding layers to enhance the network's ability to extract deeper-level features. Second, a Group Attention (GA) mechanism module was designed and incorporated at the U-Net skip connection to strengthen the features extracted from the encoding part, addressing semantic gaps between the encoder and decoder. Finally, a Pyramid Feature Concatenation (PFC) module was designed at the U-Net decoder, which fused features from different scales. Squeeze-and-Excitaton (SE) attention mechanisms were added to each layer of the PFC to filter out effective information from the feature maps. The loss function of the network is weighted based on the outputs of the PFC module at each layer, serving to supervise the feature extraction process across different layers of the network. The test results of this model on the test set are as follows: the Dice coefficient is 0.8843 and the Jaccard coefficient is 0.7926. Experimental results indicate that this model is highly robust in coronary vascular segmentation, more effectively suppressing noise under low contrast and achieving better segmentation results for coronary vessels when compared to other methods.

Magnification endoscopy with narrow-band imaging (ME-NBI) has been widely used for cancer diagnosis. However, some microstructures are rendered invisible by a white opaque substance (WOS) composed mainly of lipids. In such lesions, the morphological structure of lipids becomes another marker of tumor grade. We propose a lipid segmentation method. First, the lipid image enhancement algorithm and the specular reflection correction algorithm are introduced. Then, in the framework of the active contour model, the proposed segmentation method extracts local information from modified hue value and global information from intensity value and adaptively obtains the weight factor to segment the lipid region based on the initial contour. This method’s effectiveness is verified by a phantom experiment, which shows that it attained higher than 90% in several key measures: pixel accuracy, sensitivity, and Dice coefficient. The proposed method can accurately reflect the shape of lipids to provide available information for doctors.