A space laser interferometric gravitational wave observatory requires spaceborne clocks with ultralow phase noise in the millihertz frequency band. Such noise can be suppressed using a sideband multiplication transfer scheme and pilot tone techniques. To meet the requirements of the clock noise suppression technique, ultralow residual phase noise synthesizers are required to generate the microwave (2.4 GHz) for electro-optic modulator modulation and the pilot tone signal (75 MHz). To this end, two different structures of microwave chains have been designed, implemented and compared. The application of low phase noise phase-locked dielectric resonator oscillators (PDROs) and frequency division techniques enabled the development of a frequency synthesis chain with ultralow residual phase noise. The residual phase noise of the 75 MHz pilot signal is measured to be \begin{document}$ 1.06\times {10}^{-3}\;\mathrm{r}\mathrm{a}\mathrm{d}/\sqrt{\mathrm{H}\mathrm{z}} $\end{document}, \begin{document}$ 8.18\times {10}^{-5}\;\mathrm{r}\mathrm{a}\mathrm{d}/\sqrt{\mathrm{H}\mathrm{z}} $\end{document}, \begin{document}$ 7.63\times {10}^{-6}\;\mathrm{r}\mathrm{a}\mathrm{d}/\sqrt{\mathrm{H}\mathrm{z}} $\end{document}, \begin{document}$ 1.30\times {10}^{-6}\;\mathrm{r}\mathrm{a}\mathrm{d}/\sqrt{\mathrm{H}\mathrm{z}} $\end{document} and \begin{document}$ 1.53\times {10}^{-7}\;\mathrm{r}\mathrm{a}\mathrm{d}/\sqrt{\mathrm{H}\mathrm{z}} $\end{document} at Fourier frequencies of 0.1 mHz, 1 mHz, 10 mHz, 100 mHz, and 1 Hz, respectively. The pilot signal is generated by frequency division of a 2.4 GHz microwave signal, and the residual phase noise of the latter is lower. As a result, the residual phase noise levels of both signals meet the requirements of the "Taiji Program" in the range of 20 mHz to 1 Hz. By further reducing the residual phase noise of power dividers, frequency dividers and other devices, reducing the temperature sensitivity of key devices, and adding temperature control and pilot tone correction technologies, the noise floor of the frequency synthesizer can be further reduced to meet the requirements of the Taiji Project in the entire frequency range (0.1 mHz−1 Hz). The development of this frequency synthesizer lays a solid foundation for the time-frequency system required for China's space gravitational wave detection.

Deep Frequency Modulation (DFM) interferometry is an effective approach for simplifying laser interferometry systems in space gravitational wave detection. However, the conventional use of kHz-level modulation frequencies in current DFM techniques introduces coupling of laser power noise into the system, which increases background noise and limits the ability to meet the stringent requirements of high-precision space measurements. This paper proposes to increase the DFM modulation frequency to the MHz range to mitigate the effects of laser power noise. Through an in-depth analysis of the DFM technique, we developed a phase signal extraction method for DFM interferometry using Bessel function expansion, orthogonal demodulation, and promotion of J1···J4 method. Based on the signal processing requirements at the MHz-level, the hardware and software architecture of a phase measurement system was developed, followed by extensive testing and evaluation under various operating conditions. The results demonstrate that the phase measurement system exhibits excellent linearity and accuracy, with phase noise in the frequency band from 2 mHz to 1 Hz consistently below 2π µrad/√Hz, thus meeting the phase measurement requirements for space-based gravitational wave detection.

The traditional Pound-Drever-Hall (PDH) technique utilizes analog devices to actively stabilize the frequency of lasers. However, this results in a bulky system and a rigid control process, making it difficult to meet the requirements of miniaturization and automation of the frequency stabilization system for new applications such as space gravitational wave detection. In this paper, an automatic peak-finding algorithm based on backward difference is specifically designed for frequency discrimination signal peak search, which effectively reduces human intervention in the frequency stabilization process. This method identifies the main signal peak and controls state switching by comparing the time width of consecutive signal peaks. Moreover, it avoids the inherent drawbacks of the conventional thresholding method. We have also designed and built a digital frequency stabilization system based on a field-programmable gate array (FPGA). This system digitizes and integrates the discrete components of the stabilization servo feedback control into a single FPGA, forming a fast servo feedback loop with a piezoelectric actuator. The digital frequency stabilization system first obtains the frequency discrimination signal locally through an amplitude demodulation, and then achieves automatic peak-finding through the designed backward difference algorithm. Finally, the servo controller is activated at the lock-in point, and an incremental digital PID algorithm is used to successfully lock the frequency of a commercial Nd:YAG laser to a resonance of a 10 cm Fabry-Pérot cavity with a finesse of 350000. During functional testing, the system maintained frequency lock for half an hour, with a wavelength meter measurement showing a relative frequency drift of less than 2 MHz. This result validates the effectiveness of the designed automatic peak-finding algorithm and underscores the merits of FPGA as an effective approach for achieving comprehensive digital laser frequency stabilization control.

Addressing the issue of beam alignment with Fabry-Pérot cavities, this paper employs an adaptive step adjustment method of dual mirrors based on the gradient ascent of resonant mode energy, achieving mode coupling of the cavity and incident beam. By cavity mode image recognition and incident beam pointing adjustment, fundamental and higher-order modes can be excited. By utilizing the relationship between the angles of the dual mirrors and the beam pointing, it enables separate adjustment of the incident position and angle of the beam entering the cavity. Classification of different mode images using the EfficientNet neural network facilitates the recognition of fundamental and higher-order modes. Based on the energy gradient of the cavity mode, this approach adaptively adjusts the step values of the dual mirrors, enabling low-cost and efficient coupling of both fundamental and higher-order modes into the cavity. The beam pointing adjustment method proposed will offer a novel option for coupling lasers with Fabry-Pérot cavities.

To address the high sensitivity measurement requirement of the test mass’s displacement in spaceborne gravitational wave detection, a ground-based simulation system using laser heterodyne interferometry has been established, initiating research into picometer-level displacement measurement techniques. Initially, the translational sensitivity of the designed laser heterodyne interferometer is tested under vacuum conditions. Subsequently, based on the sensitivity outcomes, noise source tracing research for the laser heterodyne interferometric system is conducted, including the development of a system noise model, analysis of various noise source mechanisms, and investigation of strategies to reduce the predominant noise sources. Ultimately, upon completion of the noise source tracing, the interferometric system is optimized, with tests indicating a displacement measurement sensitivity better than 1 pm/Hz^1/2 in the range of 30 mHz to 1 Hz. This paper is expected to provide a reliable ground-based test platform for noise source tracing, facilitating the advancement of picometer-level laser interferometry technologies for spaceborne gravitational wave detection.

To meet the picometer-level ranging accuracy requirements for space-based gravitational wave detection, this paper proposes an optimization method for the inter-spacecraft optical metrology noise link metrics. The method optimizes the design parameter to ensure the inter-spacecraft ranging accuracy while improving the technical feasibility of the spacecraft design. Firstly, the design parameters and objective functions of the optimization problem are clearly defined, and Sobol sensitivity analysis is used to effectively identify the key parameters. Subsequently, the optimization problem is solved using the Non-dominated Sorting Genetic Algorithm II (NSGA-II), from which the optimal solution is selected from the Pareto front based on the requirements. On this basis, the design metrics for each parameter are determined, and an initial metric tree is constructed. Simulation experiments verify the feasibility of the method. The results show that by optimizing the noise link metrics in accordance with the proposed approach, it is possible to achieve an optical metrology noise level of 8 pm/\begin{document}$\sqrt{{\mathrm{Hz}}} $\end{document} while obtaining the most technically feasible design solution. This study provides a valuable reference framework and approach for the construction of the metric system in the subsequent spacecraft design phase, demonstrating strong applicability and laying the foundation for future gravitational wave detection missions.

In order to achieve real-time 3D measurement of dynamic objects and to overcome the measurement accuracy limitations caused by spectral aliasing of different carrier frequencies in traditional Fourier demodulation methods, as well as the color coupling problem in color composite stripe projection techniques, this paper proposes a three-frequency color stripe projection profilometry method based on fast iterative filtering. The method first captures a color image using a CCD camera, where the red, green, and blue channels carry gray stripe images with different carrier frequencies. Background interference is then reduced by component subtraction, followed by carrier frequency separation and color decoupling using fast iterative filtering. The subsequent application of the Fourier transform is applied to the carrier-frequency stripe images in the red, green, and blue channels enables the extraction of wrapped phase information. To achieve accurate phase unwrapping, a spatial domain unwrapping algorithm is employed. The low-frequency phase is first unwrapped, followed by the middle and high-frequency phases, which are unwrapped sequentially to complete the entire phase unwrapping process. The simulation and experimental results demonstrates that the proposed method exhibits a phase unwrapping accuracy that is 7 times higher than that of traditional Fourier methods. In comparison with other single-frame demodulation methods, the proposed method demonstrates superior accuracy and robust noise resistance, thus providing an effective technical solution for high-precision, dynamic real-time 3D measurement.

The purpose of this study is to solve the problem of optical waveguide shape defects. These defects occur during the process of vertical end face waveguide bridging in photonic chips. The obstruction of the laser beam by the surface of the chip is the root cause of these defects. The present study investigates the light intensity distribution based on the focusing light field of high numerical aperture (NA) lenses. The study focuses on the laser focus at different x-direction offsets on the vertical end-face of the chip. First, we give the analytical expressions of the light field near the focus. These are in the focusing system of high NA lenses. In addition, we give the expressions for the focused light field components. This analysis is conducted under the assumption of linearly polarized light incident. We then conduct numerical simulations with the given expressions. We study the focal light intensity distribution at different offsets in the x-direction. These offsets are measured from the vertical end face of the photonic chip. The intensity changes resulting from the disturbance of the focal light field are presented. The focal light field intensity changes are drawn. These curves are then compared with the trend of the waveguide shape changes in the experiments. Finally, based on the focal light intensity distribution curves, the reverse curves of the laser power compensation coefficients are derived. These are then applied to the optical waveguide compensation processing experiments. After power compensation processing, the parts with waveguide width less than 4 μm. Following this compensation, these components are successfully adjusted to a width of 4 μm, resulting in a straighter shape. The defects are effectively repaired. This finding is corroborated by both numerical simulations and experimental results. This method has been demonstrated to be an effective means of compensating for defects in waveguide shape. These defects are attributed to insufficient laser power. This method provides an effective solution for waveguide processing in photonic chip integration.

Quantum noise is one of the main noises affecting the detection of laser interference gravitational waves. To cope with quantum noise and further improve detection sensitivity, this paper applies the quantum transfer function method to rederive the source attribution of quantum noise in convention Michelson interferometers. The findings reveal that for two types of quantum noise-radiation pressure noise and shot noise-radiation pressure noise can be directly attributed to the amplitude quadrature fluctuations of vacuum fluctuations at the unused port of the interferometer, while shot noise can be completely attributed to the phase quadrature fluctuations at the unused port only under certain conditions. Provided that the source attribution of the quantum noise is clearly known, the squeezed light technique can improve the sensitivity of detectors. However, when adopting unequal arm interference detection schemes, attention must be paid to the length difference between the two unequal arm lengths. Finally, this article also mentions the issues that may need to be considered when promoting the application of squeezed light technology in space gravitational wave detection, including the impact of weak light lock-in amplification technology, the relationship between different interferometers, the impact of data post-processing, and the generation of squeezed light.

To precisely evaluate the noise induced by magnetic field and magnetic field gradient fluctuations acting on the test masses in space gravitational wave detection missions, a Multi-stage Bias Correction Model (MSBCM) is proposed for the accurate reconstruction of the magnetic fields at the test mass. Based on the ensemble learning method, the standard fully connected neural network modules and residual fully connected neural network modules are constructed as weak predictors for the MSBCM. Each weak predictor sequentially corrects the prediction biases from the preceding model, cumulatively forming a robust predictive model to realize precise magnetic field reconstruction at test mass locations. Magnetic field reconstruction experiments conducts on the LISA Pathfinder, eLISA, and Taiji-2 space gravitational wave detection spacecraft, and the proposed MSBCM method demonstrates the lowest mean relative errors along sensitive axes in comparison with other interpolation or estimation methods. In simulating on-orbit experiments, the MSBCM method achieves the root mean square error of magnetic field fluctuations and gradient fluctuations in acceleration noise on the sensitive axis of test mass 1 of 1.68×10⁻¹⁷ (m/s²/Hz^1/2) and 4.00×10⁻¹⁷ (m/s²/Hz^1/2), respectively. Additionally, MSBCM closely only to the distance weighted method in minimizing the root mean square error for magnetic field fluctuations and gradient acceleration noise on the sensitive axis of test mass 2, records at 1.72×10⁻¹⁶ (m/s²/Hz^1/2) and 2.93×10⁻¹⁶ (m/s²/Hz^1/2), further validating the advantages of the proposed method in assessing magnetic fields around test masses in space-based gravitational wave detection missions.

Objective: Aiming at the problem that the diffraction phenomenon generated in the Long-Wave Infrared (LWIR) polarized optics system containing Digital Micro-mirror Device (DMD) will lead to the change of the polarization aberration in the system, which will cause a decrease in the accuracy of the polarization measurement of the LWIR polarized optics system, we propose a method for analyzing and compensating for the polarization aberration of the LWIR secondary imaging optical system containing DMD. Method: Firstly, a diffraction and polarization aberration characteristic transmission model is constructed for the relationship between wavelength and DMD size in the LWIR polarized optics system, and a polarization aberration analysis method based on the Jones vector theory of vector diffraction-polarized light is proposed. Secondly, the polarization aberration and polarizability of DMD are deduced to determine the optimal diffraction order, incidence angle and diffraction efficiency of DMD, and then the secondary imaging LWIR polarized optics system containing DMD is designed to obtain the influence of DMD diffraction characteristics on polarization aberration. Finally, the polarization aberration of the optical system is compensated by tilting the projection objective, coating the lens and reducing the surface incidence angle, so as to solve the influence of diffraction phenomenon on the polarization aberration of the LWIR polarized optical system. Result: Simulation results show that the full-field-of-view modulation transfer function of the system is close to the diffraction limit at the cut-off frequency, the maximum aberration is less than 0.2%, the imaging quality is good, and the two-way attenuation of the whole system is reduced to 1/12 of the original one after compensation. Conclusion: This analytical model can reveal the relationship between diffraction and polarization aberration, and the compensation method can effectively reduce the polarization aberration.

In order to quantitatively assess the solar stray light suppression capability of the heliospheric imager, a testing approach and experimental validation of the solar stray light suppression capability of the heliospheric imager were investigated. In this paper, we propose a method to test the solar stray light suppression capability of the heliospheric imager under laboratory circumstances by conducting segmented tests of the front-end baffle and the camera. This approach circumvented the issue that the structural scattering caused by the test under vacuum conditions would be overly large and influence the accuracy of the test results. The proposed method was then employed to assess the effectiveness of a heliospheric imager in suppressing solar stray light under laboratory conditions. The experimental results indicated that the PST of the heliospheric imager was 1.4×10⁻⁸ at WACH1 and 4.3×10⁻⁹ at WACH2. The error analysis of the test results revealed that the random error was 21.6%, and the PST resulting from the sum of system errors was 1.1×10⁻⁸ at WACH1 and 4.2×10⁻⁹ at WACH2. The test accuracy met the requirements, demonstrating the feasibility and accuracy of the test method. The study presented in this paper offers a novel means to test the solar stray light suppression capability of heliospheric imager.

Most of the current visual training products available on the market use electronic screens to display objects of varying dimensions and distances, thereby stimulating the ciliary muscle through looking at the screen for visual function training. However, this method involves blue light radiation, which poses a potential hazard to the human eye. To address this issue, a visual optical system based on a Varifocal zoom structure has been designed. The system achieves continuous magnification of optical power by manipulating the lateral movement of two sets of lenses perpendicular to the optical axis. This simulates changes in object distance and stimulating ciliary muscle regulation training. This paper first derives the surface shape limits of variable focal length lenses, incorporates the variable focal length spherical effect equation to optimize the basic surface shape of Alvarez lenses, and uses Zemax software for design. The designed lens surface is characterized by a third-order XY polynomial free-form surface, with a maximum relative vertical axis offset of 5.6 mm between the two groups of lenses, achieving continuous magnification of refractive power between +4D and −8D. The design results indicate that the full-field modulation transfer function exceeds 0.3 at a Nyquist frequency of 30lp/mm, with root mean square (RMS) radius values approaching the Airy spot radius value and distortion below 2%. The imaging quality of this optical system is satisfactory.

In this paper, a method for vortex beam OAM detection using crosshair diffraction is proposed. The OAM-related main bright spot in the far-field distribution contains most of the energy of the incident beam (50%~84%) and there is no secondary bright spot that interferes with the detection. In contrast, the energy proportion of the main bright spot in the conventional small-hole diffraction method is extremely low, particularly in the far-field main bright spot above the 7th-order topological charge, which contains less than 1% of the energy of the incident beam. Furthermore, as the topological charge level increases, the secondary bright spot becomes more intrusive. Consequently, crosshair measurements are particularly applicable to the detection of weak vortex beams, which has potentially important implications for the development of long-range free-space optical communications.

To address measurement inaccuracies in traditional swept-frequency methods caused by laser linewidth effects, this study proposes a convolution-based signal analysis approach that accounts for the convolutional relationship between Gaussian-shaped laser spectra and Lorentzian-type Fabry-Perot (F-P) resonator responses. An experimental platform employing two F-P cavities (one custom-built and one commercial) demonstrated three key advancements: 1) Quantitative simulations established laser linewidth impacts on signal profiles, coupled with a dedicated fitting algorithm; 2) Beat-frequency characterization revealed a Gaussian laser lineshape with 11.59 ± 1.23 kHz linewidth; 3) Comparative analysis of Lorentzian versus convolutional fitting across different linewidth regimes showed critical performance differences. For Cavity 1 (204.1 kHz nominal), both methods yielded comparable results (Lorentzian: 204.1 ± 11.2 kHz; Convolutional: 203.9 ± 11.2 kHz), while for Cavity 2 (4.17 kHz reference), convolutional fitting achieved superior accuracy (4.42 ± 0.50 kHz vs. Lorentzian's 8.97 ± 0.42 kHz). The methodology effectively recovers true linewidths when laser and cavity linewidths are spectrally comparable, and converges with Lorentzian fitting when laser linewidth (11.59 kHz) \begin{document}$\ll $\end{document} cavity linewidth (204.1 kHz). This approach significantly expands the applicability range of narrow-linewidth F-P cavity measurement systems by relaxing laser source requirements.

A new type of 785 nm semiconductor laser device has been proposed. The thin cladding and mode expansion layer structure incorporated into the epitaxy on the p-side significantly impacts the regulation of grating etching depth. Thinning of the P-side waveguide layer makes the light field bias to the N-side cladding layer. By coordinating the confinement effect of the cladding layer, the light confinement factor on the p-side is regulated. On the other hand, the introduction of a mode expansion layer facilitates the expansion of the mode profile on the P side cladding layer. Both these factors contribute positively to reducing the grating etching depth. Compared to the reported epitaxial structures of symmetric waveguides, the new structure significantly reduces the etching depth of the grating while ensuring adequate reflection intensity and maintaining resonance. Moreover, to improve the output performance of the device, a new epitaxial structure has been optimized. Based on the traditional epitaxial structure, an energy release layer and an electron blocking layer are added to improve the electronic recombination efficiency. This improved structure has an output performance comparable to that of a symmetric waveguide, despite being able to have a smaller gain area.

The Taiji space gravitational wave detection mission employs laser interferometry to measure picometer-level distance variations induced by gravitational waves. Attitude jitter in both satellites and movable optical subassemblies (MOSA) generates tilt-to-length (TTL) coupling noise that critically degrades detection sensitivity. Therefore, it is necessary to fit and subtract TTL noise during the data processing stage. To address this challenge, we propose an iterative TTL noise suppression algorithm for post-processing. First, a first-order linear approximation model of TTL noise is established and incorporated into the time-delay interferometry (TDI) combinations to derive its expression in TDI outputs. We subsequently perform initial maximum likelihood estimation of the TTL coupling coefficients, subtract the preliminary TTL noise estimate from the TDI data to characterize the residual baseline noise statistics, and reincorporate these statistics into the updated likelihood function for subsequent TTL coefficient estimation. Through ten iterative cycles, we achieve a refined baseline noise model. Finally, The posterior distribution of the TTL coefficients is obtained via the Markov Chain Monte Carlo (MCMC) method, thereby accomplishing the precise fitting of the TTL noise and consequently achieving effective noise suppression. Results demonstrate that over 80% of estimated coefficients fall within three standard deviations, and more than 80% of the coefficient estimates deviate from the true values by less than 0.1 mm/rad. For various levels of TTL coefficients, the residual TTL noise after suppression is one order of magnitude lower than the secondary noise, demonstrating a certain degree of robustness. This is particularly applicable to real detection scenarios where the noise floor model is unknown, meeting the requirements for space-based gravitational wave detection.

As a follow-on mission to the GRACE low-low satellite-to-satellite tracking gravity mission, one of the twin satellites of laser ranging interferometer gravity mission GRACE Follow-On experienced an anomaly in its accelerometer payload after one month of operation. This anomaly resulted in the loss of scientific measurement data, a situation similar to the final phase of the GRACE. Therefore, research on accelerometer data recovery is important to achieve the detection objectives of both GRACE and GRACE Follow-On. This paper proposes a novel method for accelerometer data recovery and reconstruction based on the Echo State Network in machine learning. By constructing a mapping relationship of accelerometer data between the twin satellites using the Echo State Network and improving the network performance through Bayesian optimization, this method can achieve high-precision and high-efficiency reconstruction of missing accelerometer data. Through experimental comparison with measured data, in the frequency band of gravity field detection, the prediction results in the along-track and radial directions have been shown to reach the level of \begin{document}$ {10}^{-8} $\end{document} m∙s⁻²/\begin{document}$ \sqrt{H\textit{z}} $\end{document}. In the cross-track direction, the results reach levels between \begin{document}$ {10}^{-8}$\end{document} m∙s⁻²/\begin{document}$ \sqrt{H\textit{z}} $\end{document}~\begin{document}${10}^{-7} $\end{document} m∙s⁻²/\begin{document}$\sqrt{H\textit{z}} $\end{document}. This reconstruction accuracy is comparable to, or even partially superior to, the official GRACE data transplant accuracy, making it preliminarily applicable to gravity field inversion. This research achieves high-precision accelerometer data recovery for low-low satellite-to-satellite tracking missions using machine learning methods.

The optical frequency standard based on two-photon transition is expected to become a practical miniaturized optical frequency standard due to its significant advantages such as high stability, good reproducibility and easy miniaturization. In this paper, the basic principle of two-photon transition is briefly described, and the research status and progress of rubidium atomic optical frequency standards based on two-photon transition at home and abroad are introduced. Finally, it is concluded that the future development trends of rubidium atomic optical frequency standards based on two-photon transition are system miniaturization, performance improvement, integrated application and engineering.

To achieve high-precision residual stress detection in key components in precision manufacturing, an electro-optic modulatied ellipsometric stress sensing stress has been established. This study focused on the ellipsometric signal response of common 304 stainless-steel materials in engineering under uniaxial tensile stress conditions. Firstly, based on the fundamental principles of reflection ellipsometry, the relationship between the ellipsometric signal and the ordinary and extraordinary refractive indices was established for different optical axis directions. Secondly, the working point of ellipsometric stress sensing was optimized for stainless steel materials. By comparing the ellipsometric signals at the extinction point and the non-zero linear working point, it was demonstrated that the non-zero linear condition is suitable for stress signal sensing. Finally, the stress-induced ellipsometric signals were measured under different optical axis directions. The experimental results indicate that for 304 stainless steel, the system's minimum stress detection limit is 7.84 kPa, and the stress detection accuracy of the system is better than 7.84 kPa. This system can be utilized for high-precision stress detection requirements in metal workpieces in precision manufacturing.

In this paper, a conventional soliton (CS) mode-locked erbium-doped fiber (EDF) laser was realized using MAX phase material (MAX-PM) Nb₄AlC₃ as a saturable absorber (SA). First, the liquid phase exfoliation (LPE) method was utilized to prepare Nb₄AlC₃ nanosheets, and then a piece of tapered fiber was adopted to fabricate Nb₄AlC₃-SA. It was found that the saturation intensity and modulation depth of the Nb₄AlC₃-SA are 2.02 MW/cm² and 1.88 %. Based on the Nb₄AlC₃-SA, a conventional soliton (CS) mode-locked EDF laser was achieved. The central wavelength, pulse duration, and pulse repetition rate were found to be 1565.65 nm, 615.37 fs, and 24.63 MHz, respectively. The performance is competitive and particularly superior in terms of pulse duration. To the researchers’ knowledge, this is the first report of Nb₄AlC₃ material used as a modulator for ultrafast pulse generation. This study fully confirms that Nb₄AlC₃ possesses marvellous nonlinear saturable absorption properties and opens new possibilities for further research on air-stable ultrafast photonic devices.

To improve the processing efficiency of large-aperture optical components, a multi-robot, multi-tool collaborative processing method was proposed. A collaborative layout that has been tailored to the optical components was designed, and three feasible trajectories were simulated for analysis. The discrete simulation results were then used to establish principles for selecting trajectory parameters. To address the limitation of discrete simulation in capturing the influence of trajectory continuity on the surface map, an integral removal function model adapted to the motion mode was introduced. Furthermore, a collaborative machining obstacle avoidance strategy was developed. The experimental results obtained using the optimal trajectory demonstrated that with an initial surface shape of PV=18.310λ (λ=632.8 nm) and RMS=1.788λ, the final surface achieved PV=4.873λ and RMS=1.113λ. In addition, within the effective range of 120 mm diameter, PV=4.661 λ, RMS=0.857λ, converged to PV=2.465λ and RMS=0.622λ after processing. The total execution time was 3.943 hours, with the maximum execution time for a single processing unit being 2.041 hours, representing a 1.93-fold improvement over single-tool processing. This method significantly enhances processing efficiency, ensures surface shape accuracy, and holds great potential for the manufacturing of large-aperture optical components.

The Bi₂O₃/Bi₂S₃ heterojunction composite was prepared by thermal polymerization combined with room temperature solution method, and its micromorphology, crystal structure and elemental composition were characterized. The results demonstrate that the Bi₂O₃/Bi₂S₃ heterojunction composite exhibits a bulk morphology, accompanied by the presence of pores and a relatively rough surface. Based on the Bi₂O₃/Bi₂S₃ heterojunction composite, the photodetector was fabricated and its photodetection performance was measured under zero bias voltage. When exposed to ultraviolet (UV) light, the maximum photocurrent (0.32 μA) and response speed (65.65/80.56 ms) of the Bi₂O₃/Bi₂S₃ photodetector are significantly enhanced compared to those of the Bi₂O₃ photodetector. In addition, the device exhibits a wide photodetection band from the ultraviolet (UV) to the visible (Vis) spectrum, as well as fast and stable self-driven photodetection capability. This is mainly attributed the successful coupling of Bi₂O₃ and Bi₂S₃ with a narrow band gap, resulting in the formation of a heterojunction composite that exhibits a type II band structure. It is noteworthy that the photodetection performance of the device was measured by continuously alternating between blue light on and off for 100 times. This indicates that the Bi₂O₃/Bi₂S₃ photodetector exhibits excellent cycle stability.

During the propagation of high-power lasers within internal channels, the laser beam heats the propagation medium, causing the thermal blooming effect that degrades the beam quality at the output. The intricate configuration of the optical path within the internal channel necessitates complex and time-consuming efforts to assess the impact of thermal blooming effect on the optical path. To meet the engineering need for rapid evaluation of thermal blooming effect in optical paths, this study proposes a rapid simulation method for the thermal blooming effect in internal optical paths based on the finite element method. This method discretizes the fluid region into infinitesimal elements and employs finite element analysis for flow field analysis. A simplified analytical model of the flow field region in complex internal channels is established, and regions with similar thermal blooming effect are divided within this model.Based on the calculated optical path differences within these regions, numerical simulations of phase distortion caused by thermal blooming were conducted.The calculated result were compared with those obtained using existing methods. The findings reveal that for complex optical paths, the discrepancy between the two approaches is less than 3.6%, with similar phase distortion patterns observed. For L-type units,this method and existing methods identify the same primary factors influencing aberrations and exhibited consistent trends in their variation.This method was used to analyze the impact of thermal blooming effect in a straight channel under different gravity directions. The results show that phase distortion varies with changes in the direction of gravity, and the magnitude of the phase difference is strongly correlated with the component of gravity perpendicular to the optical axis. Compared to existing methods, this approach offers greater flexibility, obviates the need for complex custom analysis programming.The analytical results of this method enable a rapid assessment of the thermal blooming effect in optical paths within the internal channel. This is especially useful during the engineering design phase. These results also provide crucial references for developing strategies to suppress thermal blooming effect.

A folding off-axis three mirror telescope has been used as the common optical path component in the design of an optical system suitable for a new airborne multispectral common aperture targeting pod. The optical system is characterized by miniaturization, high transmittance, multispectral, long focal length, and low difficulty of installation and adjustment. The designed multispectral common aperture optical system has an effective optical aperture of 220 mm, a near-infrared focal length of 1100 mm, a short-wave infrared focal length of 1200 mm, and a medium-wave infrared focal length of 880 mm. It can be integrated as a transmitting and receiving antenna with a laser sensor, which shares the same aperture and fast steering mirror with other imaging sensors. The system is mounted on a typical airborne spherical electro-optical pod platform with a diameter of 500 mm. The optical design analysis and results indicate that the image quality of the optical design has reached the diffraction limit. All indicators and parameters meet the technical requirements.

The coupling noise between test mass stiffness and displacement, as a significant component of the residual acceleration noise, critically impacts the performance of space gravitational wave detection, making stiffness identification essential for validating and optimizing control strategies and meeting the noise suppression requirements. For non-coaxial test mass configurations, this paper proposes a novel identification method based on dual sensitive axis decomposition. First, a relative dynamic model between the test mass and the spacecraft is constructed, and the model parameters are decomposed along the dual sensitive axis to isolate the influence of spacecraft acceleration disturbances and predominant angular acceleration disturbances on the on-orbit identification. Second, utilizing on-board laser interferometers, inertial sensors, and associated control loops, an on-orbit identification scheme is designed and a stiffness identification method using recursive least squares is proposed. Finally, numerical simulations are performed to verify the performance of the method. The experimental results demonstrate that the proposed stiffness identification method can effectively identify the stiffness of the test mass on the sensitive axis. Under the given simulation conditions, the mean absolute error is less than 5×10⁻⁹ s⁻², the root mean square error is less than 1.5×10⁻⁸ s⁻², and the maximum steady-state error is less than 2×10⁻⁹ s⁻². These findings suggest that the method can be applied to future gravitational wave science missions.

With the wide application of holographic head-up display system and virtual reality augmented display technology, holographic reproduced images are required to be virtual images with higher quality, more realistic reproduction image size and more in line with human visual characteristics. Based on the principle of computer-generated holograms reproduction imaging, this paper used the Gerchberg-Saxton (GS) algorithm to iteratively solve the phase distribution of the original simulation images under different characteristic parameters (line width, ring diameter) and different calculated sampling intervals by performing direct and inverse Fourier transforms on the optical field distributions of the input and output planes, and the corresponding reproduced images were obtained by simulation calculation. The optical path of the holographic reproduction experiment was constructed by using the liquid crystal spatial light modulator, and the reproduction experiment was carried out by loading the phase distribution maps of different original simulation images, the holographic reproduction images of far-field diffraction were taken by the camera, and the actual feature size of the reproduced images was obtained by image processing. The experimental results show that the feature size of the reproduced images is basically linear with the characteristic size of the original simulation images. Furthermore, the reproduction image size shows a non-linear change relationship with the sampling intervals of the simulation calculation, which is consistent with the derived theoretical calculation relationship curve. In order to further verify the correctness of the conclusion, when the size of the expected reproduced image is designed as the ring diameter of 0.943mm and the line width of the central cross of 0.015mm. The characteristic size and sampling interval of the original simulation image of the expected target are obtained by the simulation calculation as the line width of 3pixel, the ring diameter of 594pixel and the sampling interval of 25μm, respectively. The ring diameter and line width of the holographic reproduction image, as measured by the reproduction experiment, are 0.93mm and 0.017mm, respectively. The error accuracy is within 0.02mm. The findings of this study provide an effective reference for application scenarios such as holographic display and AR/VR display to improve the authenticity of virtual display image size.

The mirror is one of the most important components of ground-based telescopes: its surface accuracy affects the imaging quality, and the stability of the visual axis affects the telescope’s measurement accuracy. It often requires a complex supporting structure to ensure that both indicators are met simultaneously. In order to simplify the support method of the mirror of a ground-based telescope and ensure the imaging quality and accuracy of the telescope, the optimization design of a 460 mm aperture uniaxial supported SIC mirror was studied. First, a uniaxial support scheme for materials with similar linear expansion coefficients and a fan-shaped mirror back structure was determined. Advanced SIC sintering technology was used to prepare anisotropic structures based on the characteristics of the support structure and materials. Combined with optimization design theory, the mirror was designed to be lightweight while meeting the required accuracy. The optimized mirror weighs only 4.82 kg, and the RMS of the horizontal simulation analysis of the mirror is λ/51.4. After actual engineering verification, the accuracy detection results of the horizontal state under the mirror support were found to be better than λ/42. The lightweight effect is significant and meets the requirements of practical use. This research provides a theoretical foundation and technical reserve for engineering projects.

Diffractive waveguide, known for their lightweight, wide field of view, and large eyebox, have emerged as one of the most promising solutions for augmented reality (AR) near-eye display technologies. However, most commercially available AR waveguide simulation software is developed by foreign companies, and domestic advancements in 3D visualization software for optical waveguide design and simulation remain notably absent. To our knowledge, this work introduces the first domestically developed 3D visualization module for optical waveguide design and simulation based on ray-field tracing. Using this module, we engineered a two-dimensional exit-pupil-expansion diffractive waveguide, demonstrating a systematic design workflow. The workflow integrates k-domain analysis, automated layout generation of grating regions within the optical waveguide, waveguide optimization, and ray-field tracing simulations, establishing a cohesive methodology for device development. The module extends beyond single-waveguide simulations to system-level analyses of near-eye displays, incorporating micro-dislplays, micro-projectors, and human eye models. By bridging microscopic and macroscopic scales, it enables holistic performance evaluation of AR optical systems, highlighting its capabilities and technical advantages. This module provides a robust and efficient platform for domestic optical engineers to advance optical waveguide design and simulation, thereby accelerating the industrialization and technological progression of AR optics in our country.

The space-based gravitational wave detection need to use laser acquisition technique to construct the inter-satellite laser link, and the spot center positioning is the core technique for measurement in the laser acquisition phase. Taking the Taiji program for example, the spot center positioning precision should be less than 0.1 pixel, and the receiving laser intensity is nearly 100 pW at the detector surface due to the long-distance propagation, significantly degrading the precision of most of the conventional positioning methods under low signal-to-noise ratio conditions, so it is crucial to study how detector noise affects the spot center positioning precision. To address these challenges, this study first elucidates the operational principles of laser acquisition and pointing technique, then theoretically analyze the mechanism by which the background noise of CMOS affects the spot center positioning precision and introduce an improved spot center positioning algorithm. Finally, the coupling relationship between different system parameters and the background noise of CMOS is measured through the experiment. The experimental results agree with the theoretical analysis, validating the correctness of the noise model and proving that this algorithm can achieve the measurement precision of 0.018 pixel under weak light conditions.

High-precision inertial sensors have broad application prospects in fields such as aerospace, navigation, and precision measurement. However, the accurate evaluation of noise in these sensors is imperative for optimal performance, with residual gas noise being a significant source of noise in inertial sensors. The current methods for calculating the level of residual gas noise lack numerical simulations based on the actual structure of inertial sensors, which hinders the ability to meet the demands of high-precision noise analysis. This paper proposes a novel residual gas noise simulation method based on ray tracing technology. Firstly, the method simulates the trajectories of residual gas inside the electrode cage of the inertial sensor under orbital conditions using a real inertial sensor model to obtain the statistical characteristics of the residual gas acceleration noise. Secondly, the influence of different pressures and temperatures on the residual gas noise is investigated. Finally, the dependence of the residual gas noise on the gap size of the non-sensitive axis is analyzed. The simulation results demonstrate the efficacy of Ray Tracing technology in simulating and tracking the interaction between the residual gas and the sensitive structures, achieving a high-precision simulation of residual gas acceleration noise at the level of 10⁻¹⁵. Temperature and pressure have been shown to significantly affect the level of residual gas acceleration noise, and reducing the gap between the electrode cage and the test mass will increase the power spectrum of the residual gas noise in the inertial sensor.

For space-borne gravitational wave detection missions based on the heterodyne interferometry principle, tilt-to-length (TTL) coupling noise is an important optical noise source, significantly influencing the accuracy of the measurement system. This paper presents a method for analyzing TTL coupling noise under the joint influence of multiple factors. An equivalent simulated optical bench for the test mass interferometer was designed, and Gaussian beam tracing was adopted to simulate beam propagation. By simulating the interference signal, it can analyze the impact of various factors on the TTL coupling noise, including positional, beam parameters, detector parameters, and signal definition factors. On this basis, a random parameter space composed of multiple influential factors was constructed within a range satisfying the analysis requirement, and the corresponding simulation results from random sampling were evaluated via variance-based global sensitivity analysis. The calculated results of the main and total effect indexes show that the test mass rotation angle and the piston effect -lateral significantly influence the TTL coupling noise in the test mass interferometer. The analysis provides a qualitative reference for designing and optimizing space-borne laser interferometry systems.

The Taiji program aims to achieve inter-satellite laser communication and absolute distance measurement using spread spectrum phase modulation technology based on the interferometric laser link. The selection of pseudo-random codes is the initial step in the design and implementation of the ranging and communication system, which requires comprehensive research and comparison of various aspects, including the implementation principles, correlation properties, and ranging error functions associated with different pseudo-random codes. This paper first elucidates the generation principles of m-sequences, Gold sequences, and Weil sequences. Pseudo-random sequences are generated using different hardware structures such as Fibonacci, Galois, and register addressing. The hardware circuits for Gold and Weil sequence generation are implemented on an FPGA development platform. The GPS C/A code is used as the Gold sequence, which facilitates its comparison and analysis with the Weil sequence. An analysis of the resource consumption and complexity of different hardware implementation methods is performed. Then, correlation values and root mean square errors are calculated to compare the pseudorandom noise performance of the Gold and Weil sequences. Finally, an error function for ranging is constructed based on the ranging principles and the intersymbol interference phenomenon after laser interference. This function is then compared with the ideal error function to evaluate the advantages and disadvantages of using different pseudorandom codes for ranging. The analysis reveals that Weil sequences demonstrate superior performance, exhibiting a sidelobe range of −60.27 dB to −24.01 dB, an autocorrelation rms of 0.303, and a cross-correlation rms of 0.307, outperforming Gold sequences in all metrics. Additionally, Weil sequences require only 30% of the hardware resources of Gold sequences and have a smaller error function deviation. Weil sequences are better suited to the laser ranging and data communication requirements of the Taiji program.

Laser communication utilizes light waves as the transmission medium. It offers many advantages, including high data rates, expansive bandwidth, compactness, robust interference resistance, and superior confidentiality. It has the critical capability to enable high-speed transmission and secure operation of space information networks. Prominent research institutions have committed to studying a series of challenges that need to be solved in the process of networking laser communication technology, including point-to-multipoint simultaneous laser communication, all-optical switching and forwarding of multi-channel signals within nodes, node dynamic random access, and network topology design. Numerous demonstration and verification experiments have been conducted, with a subset of these research results finding practical applications. Based on the analysis and discussion of space laser communication networking technology, this paper summarizes the development of laser communication networking technology both domestically and internationally, focusing on the application of laser communication networking technology in the fields of satellite constellations, satellite relays, and aviation networks. Furthermore, it presents a review of pertinent domestic research methodologies, experimental validations, and technical solutions. Finally, it predicts the development trend of laser communication networking technology and applications.

This paper investigates optical transport in metamaterial waveguide arrays (MMWAs) exhibiting Bloch-like oscillations (BLOs). The MMWAs is fabricated by laterally combining metal and dielectric layers in a Fibonacci sequence. By mapping the field distribution of Gaussian wave packets in these arrays, we directly visualize the mechanical evolution in a classical wave environment. Three distinct oscillation modes are observed at different incident positions in the ninth-generation Fibonacci structure, without introducing thickness or refractive index gradient in any layer. Additionally, the propagation period of BLOs increases with a redshift of the incident wavelength for both ninth- and tenth-generation Fibonacci MMWAs. These findings provide a valuable method for manipulating BLOs and offer new insights into optical transport in metamaterials, with potential applications in optical device and wave control technologies.

Owing to the low p-type doping efficiency of GaN-based ultraviolet (UV) vertical-cavity surface-emitting laser (VCSEL) hole injection layers (HILs), effective hole injection in multi-quantum wells (MQW) is not achieved, significantly limiting the photoelectric performance of UV VCSELs. By improving hole injection efficiency, the hole concentration in the HIL is increased, and the hole barrier at the electron barrier layer (EBL)/HIL interface is decreased. This minimises the hindering effect of hole injection. In this study, we developed a slope-shaped HIL and an EBL structure in AlGaN-based UV VCSELs. A mathematical model of this structure was established using a commercial software, photonic integrated circuit simulator in three-dimension (PICS3D). We conducted simulations and theoretical analyses of the band structure and carrier concentration. Introducing polarisation doping through the Al composition gradient in the HIL enhanced the hole concentration, thereby improving the hole injection efficiency. Furthermore, modifying the EBL eliminated the abrupt potential barrier for holes at the HIL/EBL interface, smoothing the valence band. This improved the stimulated radiative recombination rate in the MQW, increasing the laser power. Therefore, the sloped p-type layer can enhance the optoelectronic performance of UV VCSELs.

Atmospheric coherence length is a critical indicator of the impact of atmospheric turbulence on free-space optical communication links. This paper proposes a novel strategy for measuring atmospheric coherence length by utilizing extended targets as the information source. Specifically, the method integrates the wavefront structure function approach with the extended target offset algorithm to directly estimate the atmospheric coherence length. Traditional methods, such as the Differential Image Motion Monitor (DIMM), typically rely on guide star targets, which are difficult to set appropriately in horizontal communication links, thereby limiting their effectiveness in practical applications. In contrast, employing extended targets as direct detection targets provides a feasible solution for measuring atmospheric coherence length. The paper first reviews the principles and current research status of mainstream algorithms, emphasizing the reliance of existing algorithms on guide star targets and their limitations in horizontal links. Subsequently, we propose a new measurement scheme that combines the improved normalized cross-correlation algorithm with the wavefront structure function method to estimate atmospheric coherence length under extended targets scenarios. In comparison to traditional measurement methods, our approach enables coherence length measurement based on extended targets in horizontal links, thereby significantly reducing system complexity and equipment costs. To validate the effectiveness and measurement accuracy of the proposed method, both simulations and experiments were designed and conducted. The results demonstrate that the coherence length values measured by this method are highly consistent with those obtained using the DIMM method and the wavefront phase variance method, with a measurement accuracy error of approximately 4%. This indicates that the proposed method can effectively assess atmospheric coherence length, thereby providing a valuable reference for enhancing the reliability of free-space laser communication systems.

A fiber-optic Fabry-Perot pressure sensor based on microelectromechanical systems (MEMS) technology is proposed for transient pressure measurements such as shock waves. The sensitive unit is made of etched silicon wafers and BF33 glass wafers through anodic bonding, and the adhesive-free integration of the optical fiber and the sensitive unit is realized by laser fusion bonding technology. A signal demodulation experiment platform was built to comprehensively evaluate the pressure sensing characteristics of sensors in static and dynamic pressure environments. The test results show that the sensor has a good linear response over the pressure range of 0-10 MPa, with a full-scale nonlinear error of 0.41% and a hysteresis of 0.37%. In dynamic pressure measurement, the sensor has a rise time of 8.5μs. The sensor has the advantages of anti-electromagnetic interference, high consistency, low cost, and has a theoretical resonant frequency of 1.39 MHz, demonstrating the prospect of its wide application for dynamic pressure measurements in harsh environments such as explosion fields.

Division of Focal Plane (DoFP) polarization camera is a widely used integrated polarization imaging system. Crosstalk between pixels of Micro-Polarizer Arrays (MPAs) is a unique interference factor in such system, and its intensity varies with the polarization characteristics of incident light, thereby introducing errors into the measurement of the target's polarization information. This paper reviews the development of polarization crosstalk models and summarizes the factors affecting crosstalk identified in relevant research. Focusing on sensor parameters and optical system parameters as key factors, this study discusses the cause-effect model of crosstalk in cameras and its relation to temporal noise. It analyzes the results of the parameter changes caused by crosstalk, primarily summarizing the crosstalk's factor correlation, experimental repeatability, error randomness, and parameter calibration. Finally, this study prospects the future development trends of crosstalk models.

To achieve wide-area detection of space targets, this study designs an optical system design with a broad spectrum range (400 nm−1000 nm), a large field of view (61°), a small F-number (1.38), and low distortion. This optical system is capable of detecting space targets with a magnitude of 6, enabling wide-area detection. Initially, a mapping between the radiation model of space target detection and the optical system parameters is established. The optical design is then theoretically analyzed using a reverse telephoto layout as the starting point. The design is optimized to balance and correct severe chromatic aberration resulting from the large field of view and wide spectral range, while improving enclosed energy and considering the roundness of scattered spots. The detection capability is verified through space optical simulation experiments. Results show that the optical system meets the wide-area detection requirements for space targets with a magnitude of 6. Finally, the physical detection capability of the optical system is experimentally verified. The results indicate that the optical system is capable of wide-area detection of space targets with a magnitude of 6. The overall design of the optical system is reasonable and compact, meeting the requirements of wide-area detection of space targets.

With the rapid development of bioluminescence technology, the demand for high-precision signal transmission has increased significantly. The spectral characteristic of the filter film, as the core component of the system, directly affects the accuracy of signal transmission. In this study, Nb₂O₅ and SiO₂ were selected as high and low refractive index materials, respectively. A multi-channel negative filter was optimized using the Gaussian apodization function and Optilayer software. The filter film was deposited on a D263T substrate using an inductively coupled magnetron sputtering technique. The effect of thickness control errors on spectral shift and passband transmittance was addressed through inverse film sensitivity analysis. The effect of process parameters on film roughness was investigated, and it was found that adjusting the ICP power could effectively improve film roughness. When the developed multi-channel negative filter was tested at a 45° angle of incidence, the reflectance half-bandwidths of the center wavelengths of 576 nm, 639 nm, and 690 nm were 5 nm, 6 nm and 7 nm, respectively, with an average reflectance of about 98%. The average transmittance in the transmission ranges of 545−562 nm, 597−624 nm, 655−675 nm, and 708−755 nm was 92%. The multi-channel negative filter successfully passed both the environmental resistance test and the spectral stability test, thus meeting the application requirements of the multi-channel negative filter in the bioluminescence system.

Compared to traditional single-frequency bound states in the continuum (BIC), dual-band BIC offers higher degrees of freedom and functionality. Therefore, implementing independent control of dual-band BICs can further enhance their advantages and maximize their performance. This study presents a design for a dielectric metasurface that achieves dual-band BICs in the terahertz (THz) range. By adjusting two asymmetry parameters of the structure, independent control of the two symmetry-protected BICs is achieved. Furthermore, by varying the shape of the silicon holes, the design's robustness to geometric variations is demonstrated. Finally, the test results show that the figures of merit (FOMs) for both BICs reach 10⁹. This work provides a new approach for realizing and tuning dual-frequency BICs, offering expanded possibilities for applications in multimode lasers, nonlinear optics, multi-channel filtering, and optical sensing.

To address issues related to the accurate control of infrared band film thickness and precise wavelength positioning, this study employs the LabVIEW programming language to develop a dynamic monitoring and compensation technology for optical film thickness, based on an optical film thickness monitoring system. Based on the principles of light interference and optical thin film design, a mathematical model is constructed using the photoelectric polarimetric method. This study focuses on resolving stopping errors and filtering noise at extremum points, thereby accurately restoring the real-time monitoring data of light intensity. The system achieves real-time and synchronous fitting of the film’s transmittance curve, calculates and fits the stopping point corresponding to the extremum of the film thickness. To validate the reliability and stability of the optical control system, a 1064 nm narrow-band filter film was fabricated. The results indicate that the peak transmittance of the 1064 nm narrow-band filter film reached 91.5%, with a pass-band half-width of 5 nm. The error of the monitoring system was calculated to be less than 0.01%.

Organic-inorganic hybrid lead-free perovskites have garnered significant attention due to their non-biotoxicity and environmental sustainability. Among these materials, MA₃Sb₂I₉, with its stable zero-dimensional (0D) structure and lead-free nature, shows great promise for stable and efficient photodetection applications. In this study, we employ a MACl post-treatment to enhance the quality of MA₃Sb₂I₉ perovskite thin films fabricated through antisolvent processing. This treatment facilitated the formation of Cl-Sb bond interactions between MACl and the perovskite thin films, effectively passivating the I⁻ vacancies and grain boundary defects on the MA₃Sb₂I₉ thin-film surface. This process not only improve the surface morphology and crystallinity of the thin film but also reduced the defect states density of the surface, thereby enhancing carrier extraction and transport efficiency. Consequently, the sensitivity of self-powered photodetectors based on the optimized thin-film preparation increased from 3.89 × 10⁷ Jones to 5.72 × 10⁸ Jones, representing an improvement by one order of magnitude. Furthermore, the rise and fall times were shortened from 37/76 ms to 31/37 ms, respectively, indicating an enhancement in the response speed of the devices.

Accurate hypothesis evaluation metrics are crucial for point cloud registration, as they facilitate the identification of correct hypotheses during the evaluation process. However, existing metrics often short in this regard. Traditional metrics, such as inlier count, are highly sensitive to parameter changes and vary significantly across different application scenarios. Recent correspondence-based metrics perform inadequately under low-parameter settings, while point-cloud-based metrics are computationally expensive. To address these limitations, this paper proposes a novel metric that integrates confidence scores of correspondences, obtained through a Triangle Voting (TV) method, with correspondence-based metrics. The proposed metric assumes that a good hypothesis aligns correspondences with high-confidence scores very closely, thereby yielding higher score contributions. We further introduce two enhancement to improve the effectiveness of inlier-based metrics with confidence scores: (1) ignoring the distance of inliers with minor transformation errors, and (2) suppressing the erroneous high-score contributions caused by numerous low-confidence correspondences. Comparative experiments conducted on three datasets demonstrate the superiority of the proposed metric over all previously known correspondence-based metrics. The proposed metric achieves registration performance enhancements ranging from 1% to 16.95% and time savings ranging from 1.67% to 10.79% under default parameter settings. Moreover, it strikes a better balance among time consumption, robustness, and registration performance. Specifically, the improved inlier count metric exhibits highly robust and accurate performance. In conclusion, the proposed metric can accurately identify the more correct hypothesis during the hypothesis evaluation stage of RANSAC, thereby enabling precise point cloud registration.

The counter-rotating prisms Atmospheric Dispersion Corrector (ADC) has been widely used for the calibration of large-aperture astronomical telescopes. To achieve an optimal design method for the counter-rotating prism ADC, effectively compensate for dispersion, and suppress optical axis drift introduced by the ADC, this study establishes a vector model for ray tracing of the counter-rotating prism ADC based on traditional atmospheric dispersion compensation theory. The vector models of dispersion compensation and optical axis drift are then derived. Using this mathematical model, the impacts of ADCs with different parameters on the dispersion compensation, prism rotation angle, and optical axis drift are simulated and analyzed. The simulation results show that when compensating for the same atmospheric dispersion with different material combinations and bonding types, the rotation angle of the prism group remains relatively consistent, with differences increasing as the zenith angle increases. Choosing materials with similar refractive indices near the central wavelength reduces chromatic aberration in the ADC output light and improves dispersion compensation. When compensating for large dispersions at different zenith angles, the optical axis offset angle of the system decreases as the number of bonded surfaces increases. Specifically, each additional bonded surface can reduce the optical axis drift angle by one order of magnitude. In practical ADC design, dispersion can be effectively compensated, and optical axis drift can be suppressed by controlling the number of bonded surfaces and material selection.

Stripe projection technology is widely used in 3D measurement and surface morphology reconstruction, where phase quality is a critical determinant of measurement accuracy. However, the nonlinear relationship between input and output light intensity is a major source of phase error. To address this issue, this paper introduces a novel system nonlinear active correction method. This method captures the variation pattern between input and output light intensity by projecting a small number of uniform gray-scale images onto a standard plane. This pattern is then integrated with active system nonlinear correction to construct a system nonlinear model based on the input-output light intensity variation. Genetic algorithms are used to optimize the coding values, which are then used to actively correct the projected fringes via fringe coding. The corrected fringes effectively reduce the influence of nonlinear effects, thereby significantly improving the quality of phase acquisition. To validate the proposed method, computer simulations were performed using three-step phase shifting. The results showed an 88% reduction in the standard error and an 85.5% reduction in the maximum error. In actual standard plane experiments, the corrected standard phase error decreased from 0.0706 rad to 0.0168 rad, and the maximum phase error decreased from 0.4129 rad to 0.0960 rad. In the face plaster model experiments, the corrected standard phase error decreased from 0.0472 rad to 0.0102 rad, and the maximum phase error decreased from 0.2990 rad to 0.2408 rad. In 3D reconstruction of complex morphology plaster models of human faces, the surface quality was significantly improved, and the water ripple effect, which affects the phase quality, was significantly reduced. Compared with existing large-step phase-shifting methods, the proposed method not only achieves high-quality phase acquisition accuracy, but also offers clear advantages in terms of required data volume and operational convenience, demonstrating broad application potential.

This study investigates the transmission loss characteristics of gallium nitride (GaN) planar optical waveguides using a finite element simulation model based on the Beam Propagation Method (BPM). To address the high transmission loss in conventional GaN waveguides, we propose process optimization solutions and develop a comprehensive transmission loss model for systematic analysis. Our investigation focuses on comparing the effects of top etching and back thinning processes on waveguide optimization. Both processes significantly reduce the waveguide transmission loss, with the top etching process reducing loss from 2.29 dB/mm to 0.19 dB/mm and the back thinning process reducing it to 0.24 dB/mm. Additionally, we analyze the impact of manufacturing defects, such as sidewall angles and surface roughness, on transmission loss. Through parameter optimization, we identify the key dimensions necessary for single mode light transmission. This study provides a theoretical basis and process guidance for the development of low-loss GaN waveguides.

In comparison with traditional photoelectric displacement measurement technologies, displacement measurement methods based on digital image processing methods exhibit superior fault tolerance and flexibility, making them a current research hotspot. To achieve high-precision and high-reliability angular displacement measurement, an image-based angular displacement measurement system based on Manchester coding is proposed. First, a single code-channel raster code disc was designed using Manchester coding based on M-sequence pseudo-random coding. A digital image sensor was then used to construct an optical path for capturing patterns on the raster code disc. Subsequently, a decoding recognition algorithm tailored to the coded patterns was developed. Additionally, edge positioning and sub-pixel subdivision algorithms for coded marker edge pattern fitting were proposed to further enhance the system’s resolution. The proposed method was then experimentally validated. The experimental results demonstrated that the system achieved a resolving power of 21 bits and an accuracy of 1.73 arcseconds with a 100 mm grating code disc. This research provides a foundation for the development of highly reliable and high-performance photoelectric angular displacement measurement technologies. Image-based angular displacement measurement system based on Manchester coding

Terahertz molecular fingerprinting is a promising method for label-free detection, particularly for micro or trace amount samples in practical applications. However, the wavelength of terahertz waves is much larger than the size of the molecules to be tested, resulting in a weak interaction between the waves and the matter. To address this challenge, additional structures are needed to enhance the absorption of electromagnetic waves by trace amount samples. In this study, we constructed an inverted asymmetric dielectric grating structure on a metal substrate. By utilizing guided-mode resonance (GMR) and a bound state in the continuum (BIC) effect, the terahertz absorption spectrum of thin film samples was significantly enhanced. The enhanced absorption spectra can be easily obtained by measuring the reflected absorption signal. The samples are coated on the flat back of the inverted dielectric grating, which simplifies the preparation process. For instance, when the thickness of an α-lactose film is 0.2 μm, the absorption enhancement factor reaches 236. This study provides a new method for detecting trace analytes in the terahertz band.

Multiple functional metasurfaces with high information capacity have attracted considerable attention from researchers. This study proposes a 2-bit tunable decoupled coded metasurface designed for the terahertz band, which utilizes the tunable properties of Dirac semimetals (DSM) to create a novel multilayer structure. By incorporating both geometric and propagating phases into the metasurface design, we can effectively control the electromagnetic wave. When the Fermi energy level of the DSM is set at 6 meV with 80 meV, the electromagnetic wave is manipulated by the DSM patch with the gold patch embedded in the DSM film, operating at a frequency of 1.3 THz and 1.4 THz. Both modes enable independent control of beam splitting under left-rotating circularly polarized (LCP) and right-rotating circularly polarized (RCP) wave excitation, resulting in the generation of vortex beams with distinct orbital angular momentum (OAM) modes. The findings of this study hold significant potential for enhancing information capacity and polarization multiplexing techniques in wireless communications.

In order to solve the problem of RF discharge impedance matching of high-power fast axial flow CO₂ lasers, an impedance matching network with low reflectivity and high dynamic matching range was designed to realize the efficient utilization of RF excited fast axial flow CO₂ lasers under different discharge structures. Based on the impedance matching theory of RF circuits, a multi-electrode equivalent circuit model was constructed, a method of introducing tunable high-voltage ceramic capacitors into the matching network was proposed, and a dynamic L-type matching network suitable for high-power RF excited fast axial flow CO₂ lasers was designed. The simulated dynamic L-type matching network can inject 60 kW RF power into 16 discharge tubes and achieve a reflectivity of less than 1% in the range of total load impedance of 12.81 Ω~49.94 Ω. A single-tube RF discharge experimental device was built, and the reflectivity of the dynamic L-type matching network was measured as less than 1% at 4 kW injection power, which was consistent with the simulation results. It is proved that the dynamic L-type matching network with adjustable high-voltage ceramic capacitors can achieve impedance matching in the high dynamic range, which meets the design requirements of high-power RF excited fast axial flow CO₂ laser matching circuits.

Microdefects in cavity mirrors utilized in cavity ring-down spectroscopy (CRDS) adversely affect measurement accuracy. This paper establishes a microdefect scattering model grounded in Bobbert and Vlieger's Bidirectional Reflectance Distribution Function (BRDF) theory to analyze the characteristics of scattered light from microdefects under varying wavelengths, incident angles, defect sizes, types, densities, and substrate coatings. Studying the cavity mirror microdefect scattering model shows that defects in the micrometer to submicron range (100 um to 0.1 um) affect the ring-down absorption accuracy. Aiming at detecting microdefects of this order, this paper’s authors constructed analytical models of microdefect scattering and dark field detection of microdefects in cavity mirrors. Establishing and analyzing the scattering light model of CRDS mirror microdefects is critical to realizing the high-precision detection of CRDS mirror microdefects and recovering CRDS measurement accuracy.

For segmented detectors, surface flatness is critical as it directly influences both energy resolution and image clarity. Additionally, the limited adjustment range of the segmented detectors necessitates precise benchmark construction. This paper proposes an architecture for detecting detector flatness based on optical fiber interconnection. By measuring the dispersion fringes for coplanar adjustment, the final adjustment residual is improved to better than 300 nm. This result validates the feasibility of the proposed technology and provides significant technical support for the development of next-generation large-aperture sky survey equipment.

To detect gravitational waves in space, the telescope and optical platform require high stability and reliability. However, the cantilevered design presents challenges, especially in the glass-metal hetero-bonding process. This study focuses on the analysis and experimental research of the bonding layer in the integrated structure. By optimizing the structural configuration and selecting suitable bonding processes, the reliability of the telescope system is enhanced. The research indicates that the use of J-133 adhesive achieves the best performance, with a bonding layer thickness of 0.30 mm and a metal substrate surface roughness of Ra 0.8. These findings significantly enhance the reliability of the optical system while minimizing potential risks.

The Terahertz wave possesses characteristics of high penetration, low energy, and fingerprint spectrum, etc., making it widely used in the detection field. Therefore, developing a Terahertz wave detection optical imaging system holds substantial significance and wide application prospects. Firstly, we refer to the structure of Tessar objective lens, which consists four lenses. The balance equations of aberration for the system were established through the application of the aberration theory of the paraxial optical system. Subsequently, we provide a solution function and method of the initial structure parameters of the system. Then, we combine it with optical design software to further correct the aberration of the system. Finally, we design a Terahertz wave detection optical imaging system with a large aperture. The optical system consists of four coaxial refractive lenses with a total focal length of 70 mm, an F-number of 1.4, and a full field of view angle of 8°. The value of modulation transfer function (MTF) in the range of full field of view angle is greater than 0.32 at the Nyquist frequency of 10 lp/mm, and the root mean square (RMS) radius of the diffused spot in each field of view is less than the airy disk radius. Finally, the paper analyzes and discusses the various tolerance types of the system. The results indicate that the Terahertz wave detection optical imaging system, designed in this paper, has a large aperture, a simple, compact form, a lightweight structure, excellent imaging performance and simple processing, which meets the design requirements, and it has important applications in the field of high-resolution detection and other fields within the Terahertz wave band.