This study aims to enhance the understanding of broadband background light radiation and fulfill the requirements for the real-time measurement of sky background radiation for scientific research and experiments. A broadband sky background light radiometer was developed that is capable of full sky scanning and fixed-point observation, thereby broadening the measurable wavelength range. The radiometer successfully measured integrated radiance across the 200?2500 nm band. This paper presents the equipment's overall structural schematic and details the development plans for each subsystem component along with comprehensive technical specifications, calibration principles, and experimental procedures. An analysis of the equipment's uncertainty confirmed its reliability by meeting the predefined uncertainty requirements. The radiometer was employed for field measurements in the Changchun area, and the data underwent preliminary analysis. The findings were consistent with the expected radiation variation laws, offering a novel and efficient method for scientific research and practical applications.

With the characteristics self-focusing, the partially coherent Airy beam can efficiently limit the adverse effects of ocean turbulence, which negatively affects the coupling performance of space light and fiber. In this paper, the generalized Huygens-Fresnel principle and the partial coherent optical cross-spectral density function are used to derive the analytical expression of the coupling efficiency of partially coherent Airy beam-few-mode (four-mode) fiber through ocean turbulence. The effects of light source parameters, coupling parameters and ocean turbulence intensity on coupling efficiency are numerically analyzed. The results show that the coupling efficiency gradually decreases with the increase of wavelength, initial radius, truncation factor and coherence length, and gradually decreases with the enhancement of ocean turbulence. At different transmission distances, the best coupling parameters are given, so that the coupling of partially coherent Airy beams and four-mode fibers achieves the best effect.

In this study, the subwavelength grating multilayer structure with asymmetric boundary conditions is investigated using scattering matrix theory. A formal expression linking the reflection phase to the dielectric constant of the grating boundary medium is derived. Based on this expression, simulation experiments are conducted using the time-domain finite difference method to validate the pre designed silicon-based liquid crystal structure embedded with subwavelength gold gratings(G-LCoS). Through continuous optimization of the asymmetric boundary conditions of the subwavelength gold gratings, nearly 2π phase modulation across multiple wavelengths in the visible spectrum is realized via the G-LCoS. The formal expression and optimization process detailed in this paper offer reference for the design of devices with dynamic asymmetric boundary conditions, particularly complex amplitude modulation devices featuring nano/micro-scale structures. Additionally, this study contributes to a deeper understanding of these devices in terms of their physical mechanisms to a certain extent.

Herein, we propose an algorithm to address the issue of communication resource limitations in vertical federated learning. The vertical federated learning algorithm is designed to simultaneously optimize transmission power, user selection, and channel estimation with a hybrid system combining visible light communication (VLC) and radio-frequency (RF) communication. The first step involves constructing a VLC/RF hybrid system by introducing a VLC link in a traditional RF link. Following this, we introduce a channel estimation algorithm based on multilayer perceptron to improve the accuracy of transmitted data. The final step involves establishing an optimization problem to minimize the longitudinal federated learning loss function. This problem is then solved by co-optimizing transmission power and user selection. The simulation results show that the accuracy of the proposed algorithm is improved by 7.2% and 18.2%, respectively, compared with the existing method.

This study proposes a D-shaped photonic crystal-fiber sensing structure for exploring the physical mechanisms of sensitivity improvement. The structure is based on surface plasmon resonance enhanced using gold nanoparticles. The gold particles are modified on the surface of a gold film coated on the D-shaped polished surface. The free charge on the gold nanoparticles interacts with the induced charge in the metal film, improving the intensity and sensitivity of surface plasmon resonance. The effects of the structural parameters on the sensing performance are investigated numerically using the finite element method assuming an anisotropically perfect matching layer. The D-shaped photonic crystal fiber/Au film/gold nanoparticle sensor with a gold nanoparticle diameter of 12 nm, a relative spacing between the gold nanoparticles of 3.2× the nanoparticle diameter, a gold film thickness of 45 nm, a distance between the fiber core and polishing surface of 3.0 μm, an air hole spacing of 2.0 μm, a large air hole diameter in the outer layer of 0.75× the air hole spacing, and a small air hole diameter in the inner layer of 0.80× the large air hole diameter, the linearity is 0.97 and the refractive index sensitivity is 6240 nm/RIU in the refractive index range 1.370?1.385. The linearity is 0.99 and the refractive index sensitivity is 13640 nm/RIU in the refractive index range 1.385?1.400. In the refractive index range 1.370?1.400, the average refractive index sensitivity reaches 9940 nm/RIU, 1.27× that of a D-shaped photonic crystal fiber/Au film sensor. The proposed sensing mechanism and structure are expected to assist research and applications in areas such as biomolecular detection.

In this paper, a highly sensitive fiber optic strain sensor based on the Fabry-Perot interferometer vernier effect is proposed and prepared. The sensor consists of two parallel Fabry-Perot interferometers, where the sensing interferometer consists of a single-mode fiber and a short segment of capillary quartz tube fused together, and the reference interferometer is aligned by a single-mode fiber placed in a fiber fusion machine. When the two interferometers have similar free spectral ranges, the strain sensitivity of the sensing interferometer is further amplified by using the vernier effect. Based on this, the parallel structure can be selected with different magnifications to obtain different sensitivities by simply adjusting the fusion splicer to change the reference interferometer cavity length. The experimental results showed that the strain sensitivity of the parallel structures in the strain range of 0~250 με with the assistance of the fusion splicer reached 22.16 pm/με and 32.88 pm/με, which were 3.84 and 5.70 times higher than the sensitivity of the single structure (5.76 pm/με), respectively.The sensor has the advantages of simple fabrication, high sensitivity, good repeatability, easy operation, and low cost, which provides a new idea for strain detection.

Herein, a phase-sensitive optical time domain reflectometer (φ-OTDR) pattern recognition method based on cross-model knowledge distillation is introduced to meet the demands for high precision and efficiency in distributed fiber optic pattern recognition. This method employed hierarchical token-semantic audio transformer as the teacher model and broadcasting-residual network as the student model. This setup enables the student model to achieve recognition performance comparable to transformer-like networks with disparate architectures using less parameters. For practical engineering experiments, a φ-OTDR was used as the signal acquisition device. The dataset used in practical engineering scenarios included signals from four categories, such as climbing nets, background noises, striking nets, and wind noises. Compared to typical deep learning algorithms, this improved algorithm demonstrates superior accuracy and faster convergence, resulting in higher recognition efficiency and offering considerable potential for engineering applications.

In order to solve the problem that the original signal collected by Φ-OTDR optical fiber sensor contains a lot of noise and low signal-to-noise ratio, a denoising algorithm based on empirical mode decomposition and interval iterative invariant threshold is proposed. In this method, the signal is decomposed based on the time scale features,without setting the basis function in advance. And then a standard Butterworth filter is used to eliminate the noise in the intrinsic model components. Simulation experiments are designed, and the results show that the signal-to-noise ratio of humman beating signal and mechanical excavation signal is improved by 3.01 dB and 5.12 dB respectively, which can effectively restrain the noise of original signal data, thus improving the sensitivity of Φ-OTDR system.

L-band extended erbium-doped fiber amplifiers (LE-EDFA) have been studied in recent years for their extended gain bandwidths. However, the pump conversion efficiency and gain level are generally low due to the relatively long gain fiber required for this amplifier. In this paper, we improve the gain level of LE-EDFA by employing the backward amplified spontaneous emission (ASE) co-pumping technique. It is found that gain level improvement up to 5.1 dB?16.7 dB can be achieved in the wavelength range of 1570?1620 nm when the pump power is relatedly low or the Er/Yb co-doped fiber (EYDF) is relatively long. We then use the backward ASE co-pumping technique in a pre-amplified LE-EDFA and achieve a 20 dB gain bandwidth covering 1570?1610 nm and noise figure less than 6.0 dB at a relatively low pump power of 550 mW. And the gain at 1620 nm is 13.7 dB. Compared with other reported LE-EDFAs, the L-band extended EDFA co-pumped by backward ASE achieves the same high gain level at the lowest pump power. The extended gain bandwidth, high pump conversion efficiency and low cost make it very prospective in high-capacity optical transmission systems.

Cassegrain antennas, as crucial optical antennas, find widespread application in space laser communication. With the increasing demands of communication, there is a continuous rise in the requirements for antenna transmission efficiency. However, the unavoidable secondary mirror obstruction issue significantly hampers transmission efficiency and complicates communication. In order to address this problem and eliminate the adverse effects of secondary mirror obstruction, this paper proposes a novel method to enhance Cassegrain antenna transmission efficiency based on multi-plane light converter (MPLC) technology. MPLC is utilized to transform communication Gaussian beams into hollow Gaussian beams that matches the Cassegrain antenna's obscuration ratio, ensuring that the outgoing beam fills the effective range of the Cassegrain antenna while avoiding secondary mirror obstruction. This method is applicable to Cassegrain antennas with varying obscuration ratios and can substantially improve transmission efficiency, reducing communication complexity. It holds significance for research in long-distance space laser communication.

This study discusses the spatial resolution of a forward stimulated Brillouin scattering (F-SBS) sensing system based on phase demodulation. A theoretical analysis of this resolution is conducted, and numerical simulations confirm that inadequate signal-to-noise ratios in the original data lead to a noticeable degradation of the system's spatial resolution. To mitigate the impact of an insufficient signal-to-noise ratio, this study proposes the utilization of an attention-guided denoising convolutional neural network algorithm for data post-processing. The signal-to-noise ratio of the zero-order sideband of the reading pulse increases from 47.05 dB to 64.23 dB when this algorithm is applied. As a result, the system's spatial resolution is restored from 15 m to its theoretical value of 3 m. This approach effectively enhances the spatial resolution without introducing additional complexity to the measurement apparatus, thereby contributing to the practical implementation of phase-demodulated F-SBS sensors.

In this paper, we report on a single-modulator electro-optic frequency comb whose repetition frequency can be modulated at high speed with a modulation rate of 1 MHz. With spectral broadening in a nonlinear fiber, a comb spectrum spanning 1.25 THz (10 nm, the central wavelength is 1550 nm) with 4800 narrow-linewidth combs separated by 260 MHz is achieved. The optical comb pulse width is compressed to 260 fs by dispersion compensation in a single-mode fiber. Also, the impacts of optical fiber amplification and nonlinear spectral broadening on the comb coherence are studied, and the common-mode phase noise of the comb is suppressed by a feedforward method based on the acousto-optic modulator. The developed electro-optic comb has promising applications for molecular spectroscopy and interferometric ranging.

In this study, the specific reasons for pincushion distortion during the scanning process of galvanometers are analyzed. A complete mathematical model of the galvanometer-scanning system is established based on theory and principle, and an algorithm for reverse compensation of the driving voltage is proposed to solve the pincushion distortion problem. The proposed algorithm expresses the relationship between the scanning path and the deflection angle of the galvanometer, presents simulation results of the intermediate voltage compensation process, and derives the correction formula of the galvanometer-driving reverse voltage compensation algorithm. The correction amount of pincushion distortion is presented in a simulation form. The simulation and experimental results demonstrate that the proposed algorithm can effectively correct pincushion distortion, thereby improving the accuracy of the galvanometer scanning system and satisfying the requirements for practical applications.

For multi-node optical signal monitoring based on traditional deep learning techniques in dynamic optical networks, many labeled samples and unlabeled samples are not fully used, and sample labeling is difficult. This paper introduces an optical performance monitoring method based on semi-supervised deep learning. The proposed method uses a substantial amount of unlabeled asynchronous delay-tap photographs as input features for the FixMatch model to monitor optical signal-to-noise ratio. The results show that compared to traditional methods, such as semi-supervised learning Mean Teacher and convolutional neural networks, FixMatch achieves classification accuracies of 100.00%, 98.67%, and 98.44% for different modulation formats, such as 16-quadrature amplitude modulation (16QAM), 32QAM, and 64QAM, respectively, at a transmission speed of 40 Gbit/s using only 10% labeled data. When the labeling rate is reduced to 5%, FixMatch still maintains good results with accuracies of 99.33%, 96.00%, and 97.67%. Dispersion experiments demonstrate the clear advantage of FixMatch compared to other methods. Furthermore, considering it as both a classification and regression task yields a classification accuracy and mean absolute error of 99.33% and 0.095 dB, respectively. This study demonstrates the effectiveness of using unlabeled data to improve the performance and generalization capability of optical performance monitoring models. In addition, the effect of a lower labeled data rate on the method is discussed.

In this paper, a non-contact vibration detection method for gas insulated line (GIL) based on laser Doppler vi-brometer (LDV) technology is proposed. First, vibration frequency and amplitude distribution under normal and defect conditions are obtained by transient electromagnetic-structural coupled field finite element modeling and physical experiments. Besides measuring points on GIL surface and parameters of LDV system are also con-firmed. The 1550 nm fiber optical path component including narrow linewidth laser, optical transceiver, acous-to-optic modulator (AOM) and balanced detector is designed, and the optical beat signal which contains object movement information is successfully obtained. Vibration signal demodulation scheme based on digital orthog-onal and differential cross multiplication algorithm is developed. The mechanical vibration signals within frequency range 50 Hz?20 kHz between 0.5?20 m distance are acquired by proposed system. The developed system has been successfully applied to GIL prototype platform testing and on-site GIL inspections, effectively overcoming the shortcomings of contact-based accelerometers, such as installation difficulties, low detection efficiency, and poor accuracy. This has enabled non-contact vibration measurement for long-distance GIL equipment.

Because the existing ellipse fitting methods have problems such as poor anti-interference ability and poor extraction accuracy when extracting the spot centroid under atmospheric turbulence disturbance, it is difficult to improve the servo tracking accuracy of the laser communication system. To this end, this paper proposes a fast spot centroid extraction method based on ellipse fitting. First, according to the degree of turbulence, a genetic algorithm is used to optimize the variable threshold segmentation and combine it with morphological processing, edge detection and other operations to extract the spot edges. Then, the set of edge feature points is divided into subsets of different sizes and the scatter matrices of different subsets are superimposed to obtain the scatter matrix of the entire set. Finally, the direct least squares method is used to calculate the fitting ellipse parameters and complete the spot centroid extraction. Experimental results show that when there is strong turbulence and the mask radius is 120 pixel, the mean gray intensity within the mask of this method is 1.32 pixel higher than that of the ellipse fitting method, and the horizontal center of mass offset is reduced by 4.59 pixel. This method can effectively achieve spot centroid extraction under varying degrees of turbulence disturbance, and can still maintain high accuracy when the spot is broken, providing technical support for spot centroid extraction in capture, pointing, and tracking systems for space laser communications.

In some cold-atom experiments, it is necessary to measure the density distribution of cold atoms in advance and provide data support for subsequent experiments. The previously established manual method is no longer suitable for such experiments. In this study, we propose a new method for measuring the density distribution of cold atoms during a single preparation period of cold atoms. The proposed method uses a pair of anti-Helmholtz coils and a pair of Helmholtz coils to generate gradient and bias magnetic fields, respectively. By adjusting the Helmholtz coil current, the position of zero point of the total magnetic field can be changed, the contribution of atoms at different positions to the probe light absorption can be affected, and finally, the atomic density distribution can be measured. The feasibility of this method is analyzed theoretically, and an experimental scheme for fast cold atom density measurements is proposed.

Given that plant leaves correspond to strong scattering media, a self-built Stokes polarization imaging system is used in this study to accurately describe the scattering characteristics of leaves. By further calculation of Stokes vector of plant leaves, the polarization uniformity of the physical quantity is used to systematically examine their polarization characteristics: 1) the polarization characteristics of circularly polarized light and linearly polarized light on plant leaves are investigated, and it is determined that the polarization uniformity of leaves is higher under the incidence of linearly polarized light when compared to circularly polarized light; 2) the dependence between the angle of leaf vein and direction of polarized light is examined, and it is determined that when the direction of linear polarized light is perpendicular to the angle direction of leaf vein, the polarization uniformity of leaf vein is the highest; 3) the relationship between depolarization parameters and leaf water content is obtained. It is observed that as the leaf water content gradually decreases, the polarization uniformity of the leaf correspondingly increases. By examining the interaction between polarized light and plant leaves, this study demonstrates that polarization uniformity is a significant descriptor of leaf depolarization characteristics in response to polarized light. This insight lays a foundation for subsequent research into plant microstructure and growth state.

Ytterbium-doped fiber amplifiers (YDFAs) are widely applied in the fields of industrial processing, radar detection, medical treatment, and communications due to its simple energy level structure and high conversion efficiency. However, the performance of a YDFA is affected by many factors. Particularly under the influence of reabsorption effect, the signal power will increase first and then decrease as the length of the gain fiber increases. In this work, a simulation model of a YDFA is established, and the amplification processes of the signal light, pump light, and amplified spontaneous emission in Yb-doped fiber are simulated and calculated. In addition, the influencing factors affecting the performance of the YDFA are analyzed. The internal relationships between the pump method, pump power, peak wavelength of the signal light, type of gain fiber, and amplification performance are discussed herein. This study can provide theoretical support for the optimal design of YDFAs and further power scaling.

We characterized and studied tunable narrow-linewidth semiconductor lasers based on external cavity feedback and silicon-nitride micro-rings. Tuning of the driving current of the gain chip, voltages of the two micro ring thermoelectric electrodes, voltage of the phase saving thermoelectric electrodes, and temperature control of the semiconductor cooler, the C-band tunable output has been achieved in a side mode suppression ratio and output power larger than 52 dB and larger than 10 dBm, respectively. Further, white noise measurements of the narrow-linewidth semiconductor laser indicate a laser linewidth of 0.84 kHz, and the phase noise values at 0.01, 0.1 and 1 kHz are 581.04, 60.47 and 6.70 μrad/Hz1/2, respectively. In the 1?20 GHz range, the relative intensity noise (RIN) of the laser is less than -156 dB/Hz. These excellent performance parameters of tunable narrow-linewidth semiconductor lasers suggest their application potential in optical fiber sensing, microwave photonics, coherent communication, and Doppler LiDAR.

The frequency response of electro-optic sampling with a β-barium metaborate (β-BaB2O4, BBO) crystal in the near-infrared band was investigated based on numerical calculations. The detection performance of the electro-optic sampling in the measurement of a near-infrared few-cycle laser pulse was also analyzed. The study then examined the pulse distortion of a few-cycle laser pulse resulting from detection under different thicknesses of BBO crystals, while also considering the central frequency shift and change in bandwidth. The changes in bandwidth and central wavelength based on the BBO thickness levels were given with laser wavelengths in the range of 0.9 μm to 2.1 μm. The results show that these changes are less than 0.1% when the BBO is 10 μm. They then increase when the BBO thickens. When the BBO is 200 μm, the observed change in bandwidth is 20%, and the shift in the central wavelength is 6%. This study provides a theoretical reference for extending electro-optical sampling detection technology to the near-infrared band and provides guidelines in detecting and calibrating few-cycle laser pulses in the area of high-field physics.

To enhance the beam quality, reduce manufacturing costs, and prevent overheating during cladding power stripping, this study utilizes a domestic 20/400 μm energy transmitting fiber. A cost-effective glass etching cream (TMS-307) serves as the etching agent. By applying segmented etching, a cladding power stripper with five symmetrically structured sections, each 5 cm long, is developed. Tests of the cladding power stripper, both in forward and reverse configurations, reveal that with an input power of 488 W, the output power is approximately 15.3 W, and the power stripping efficiency reaches 15 dB. Notably, without water-cooling, the peak operating temperature at the laser input terminal of the stripper remains stable around 120 ℃. The temperature distribution is relatively uniform, with no significant hot spots detected. These results indicate that the cladding power stripper successfully meets the demands of high-power fiber lasers, offering cost reduction, improved beam quality, and enhanced stability.

We report high-energy tunable 6.5‒12 μm ps mid-infrared radiation generation based on OPA pumped using 1064 nm laser in LISe crystal. We simulated the relationship between the idler energy and crystal length. An optimum LISe length of 4 mm was used to enhance the idler energy experimentally. At a pump energy of ~9.4 mJ, energy levels of ~146 and of ~27 μJ are generated at 6.5 μm and 12 μm, respectively. The highest energy of ~205 μJ is achieved at 8.1 μm at a pump energy of ~19 mJ. Finally, the angular and spectral width acceptance are measured.

To extend the theory related to new composite materials that can enhance the performance of optical modulators, the modulation mechanism of the optoelectronic properties of B-doped and P-doped MoS2/Gr heterojunctions is investigated. The results show that after the formation of the heterojunction, there is an electron transfer from the graphene layer to the surface of the MoS2 layer between the heterojunction layers; after the doping of atoms, the electrons transferred between the graphene and molybdenum disulfide layers of the heterojunction are redistributed, and the electron transfer from the B atom to the C atom, the P atom to the S atom, and between the B atom and the P atom mainly occurs, leading to the phenomenon of electron aggregation between the layers near the doped P atom. Near the Fermi energy level, orbital hybridization between the dopant atoms and graphene and molybdenum disulfide occurs, resulting in a narrower energy gap for carrier jumps, leading to enhanced interaction with light in the low energy region in the near-infrared and even below, and some optical absorption peaks move towards the low energy region, the modulation of the optical properties in the low-energy region of the heterojunction can be achieved to some extent by changing the concentration and ratio of doped atoms.

This study constructed an ultrathin photovoltaic cell model with an inverted pyramid velvet surface front structure, double-layer anti-reflection film, 3 μm thick single-crystal silicon absorption layer, finger-crossed back contact electrode, and oxide passivation layer. The study first used the finite-difference time-domain (FDTD) method to solve the Maxwell equations of electromagnetic wave propagation in semiconductors, and it then obtained the field distribution. Next, the inclination of the inverted pyramid velvet surface was optimized and an optimal short-circuit current density of 44.65 mA?cm-2 was achieved. The study used small-signal alternating current scanning to solve the drift-diffusion and Poisson equations describing the carrier motion law and electrostatic potential, respectively. A particle swarm optimization algorithm was then employed to optimize the position and doping concentration of the finger-crossed back contact electrode. The model's volt-ampere characteristic curve was obtained, and its photoelectric conversion efficiency was calculated to be 23.03%.

Tissue oximetry parameter detection based on near-infrared spectroscopy has the advantages of being rapid, real-time, and non-invasive, and has been widely used in clinics with important application values. Near-infrared spectroscopic tissue oximetry requires a combination of different wavelengths of near-infrared light to calculate the concentration of oxyhaemoglobin and reduced haemoglobin, but the combination of wavelengths currently used to detect oximetry information is not uniform. The wavelength selection of the light source is directly related to the accuracy of the extraction of tissue blood oxygenation parameters. In order to improve the measurement accuracy, a wavelength selection method based on condition number was established in this study and experimentally verified by tissue mimicry and in vivo experiments. The experimental results show that when the absorption and scattering coefficients of tissue mimics are changed, the error of total haemoglobin concentration calculated by the smallest conditioned number group is the smallest, and the error calculated by the largest conditioned number group is the largest. In the in vivo experiment, when the collected spectral signals were denoised, the smallest conditioned number group calculated oxygen saturation with small error and the largest conditioned number group inverted oxygen saturation with the largest error, which is in accordance with the underlying theory of conditioned numbers. Therefore, it is feasible to optimize and select the wavelength using the conditional number method, which improves the tolerance of error in the calculation of optical parameters into physiological parameters, and provides a methodological basis for the rational selection of wavelength for tissue blood oxygen detection.

Diffractive lenses are lightweight and exhibit loose surface tolerance, rendering them a competitive option for lightweight lidar optical receiving systems. To address the challenge of low transmittance in single diffractive lenses when the F-number of the receiving system is small, this study introduces a hybrid structure comprising a diffractive lens, collimating group, and converging group. Based on this structure, a receiving optical system with a 50-mm aperture, a full angle of view of 0.9 mrad, an F-number of 1.78, and a wavelength band of (1064±0.1) nm is designed. The analysis results of the system indicate that the root-mean-square radius of the diffuse spot is significantly smaller than the Airy spot radius, and the imaging quality is approached to the diffraction limit. Considering the diffraction efficiency of the diffractive lens and the absorption and reflection of the glass material, the transmittance of the system is calculated to be 78.2%, meeting the practical application requirements of LiDAR for optical receiving systems. Therefore, a reference for the design of diffractive LiDAR optical receiving systems is provided by this system, offering a solution to enhance transmittance and overall performance.

Simulated annealing algorithm combined with illuminance superposition theory model is used to describe the design method of LED arrays scheme for large area high uniform lighting from two aspects of light source luminous angle and arrangement mode in this paper, and the accuracy of the algorithm and conclusion is verified by experiments,in order to solve the problem that the ambient light simulation system in the aircraft cockpit ergonomics experimental verification platform can achieve high uniform illumination distribution on a large area target surface. The results show that the illuminance of the light source arrays arranged according to the modularization of 363 LED light sources can reach 5×104 lx in the range of 4 m×4 m target plane at the distance of 1.5 m, and the uniformity of illuminance is 98.17%. It meets the design requirements of large-area, high-intensity, and high-uniformity high-altitude ambient light simula-tion systems, and can provide a reference for the design of lighting systems that achieve high-uniform illuminance distribution on large-area target surfaces.

Before the infrared dual-field lens is put into use, it is necessary to carry out impact, vibration, and high and low temperature tests. Sometimes, various problems will appear in the test, such as lens damage, unstable lens imaging, lens motion jamming and so on. In order to solve the above problems, this paper analyzes the impact and vibration of an infrared dual-field lens with a focal length of 25?75 mm and F-number of 1.0?1.2. On the basis of previous work, the corresponding impact vibration model is established, and the corresponding simulation analysis of the infrared dual-view lens is carried out based on the established impact vibration model. Then, the force of the transmission part of the lens is analyzed, and a method of designing the cam curve is put forward to reduce the movement force and reduce the probability of the cam barrel being stuck at low temperature. Combined with the above work, the corresponding impact vibration and high and low temperature tests of the lens are carried out, and the test results are satisfactory. From the above, it provides reference for the simulation analysis and structural design of infrared dual-field lens, and avoids the economic and time losses caused by defects in the design stage.

To enable a spectrophotometer to achieve high resolution across a broad spectral range, an optical system utilizing an asymmetric Czerny-Turner configuration is developed, featuring a rotating grating. This system's design adheres to the working principle of the spectrophotometer and the theory of geometric aberration while accounting for the effects on central and edge wavelengths. The characteristic and structural parameters of each optical component in the spectroscopic system are accurately determined. Focusing on spectral resolution, the optical system is simulated and optimized using Zemax software to determine the optimal optical path structure. The multi-configuration is used to simulate the grating rotation, thereby allowing for the scanning of wide wavelength bands. The simulations indicate that the system's resolution consistently surpasses 0.1 nm within the 300?1000 nm spectral range. The experimental setup confirms that the spectrophotometer's spectral resolution attains a technical specification of 0.1 nm. Consequently, The designed spectrophotometer optical system serves as a valuable reference for the development of high-resolution spectroscopic instruments capable of operating across a broad spectrum.

For terahertz communication, a beam reconfigurable reflector array antenna based on graphene material is designed, combining the unique advantages of impedance matching and electrical controllability of graphene material compared with metal in terahertz band and the advantages of high radiation efficiency of reconfigurable reflector array antenna. The graphene patch is embedded in the gap of the antenna phase-shifting unit radiation patch, and the surface resistance value can be changed by adjusting the chemical potential of the graphene patch in the software simulation to realize the purpose of dynamically adjusting the antenna unit compensation phase. The simulation results show that when the center frequency is 3.6976 THz, the phase shifter unit has a phase difference of 180° at 0.1 and 4.0 eV. When the chemical potential of the graphene patch is adjusted within 0.1?4.0 eV, the chemical potential is proportional to the phase of the antenna unit. A 4×4 array antenna is designed, and the simulation results show that the array antenna can achieve beam scanning in the range of (-30°, +30°), and the maximum gain is 20.9 dBi. This paper provides a new idea for the study of terahertz reflector array antenna and the application of graphene materials in reconfigurable communication devices.

A polarization-independent metasurface optical switch based on electrochemical metallization working at 1.55 μm is proposed. The unit cell of the device comprises a silicon substrate, silica dielectric layer, and silver cross structure embedded in silica. The formation and rupture of conductive filaments between sub-units can alter the resonant wavelength of the cross structure, which triggers the state of the optical switch on or off. Numerical results demonstrate that the extinction ratio of the metasurface optical switch can exceed 14 dB at 1.55 μm, and it is insensitive to the transverse electric (TE) mode and transverse magnetic (TM) mode of light. The proposed device is expected to address the problems of high-power consumption, enabling the adoption of large-scale optical switches in optical switches, optical modulation, optical storage and computing, and large-scale photonic integrated devices.

In recent years, bound states in the continuum (BIC) in optical metasurfaces have garnered significant attention owing to their unique properties. Because of the interaction of two accidental quasi-bound states in the continuum (A-QBIC) modes, we explore the related novel optical phenomena in an all-dielectric metasurface that comprises a square nano-aperture array. It is shown that the A-BIC phenomenon can occur under x- and y-polarized normal incidences but exhibits the interaction of the two A-QBIC modes under 45° polarized incidence. The A-QBIC modes, which are analyzed using band and multipole expansion theories, are primarily governed by the toroidal dipole. Notably, the high Q-factor of the A-QBIC modes not only allows for the implementation of highly sensitive refractive index sensing but also facilitates the realization of flexible tunability of the interaction between the two A-QBIC modes, thereby achieving an analogue of electromagnetically induced transparency and tunable slow-light. Our results provide a feasible strategy to develop a high Q-factor meta-device based on A-QBIC in highly sensitive refractive index sensing and slow-light applications.

Raman scattering measurement technology based on plasmon enhancement mechanism can improve the Raman scattering cross-sections of molecules by several orders of magnitude. Accordingly, they have a wide range of application prospects for trace substance identification and tracking. Many previous studies have reported identification of single-molecules when the enhancement factor reaches ~1010. Measuring physical and chemical behaviors at the single-molecule level is expected to provide richer and more accurate results compared to measuring the statistical behavior of an ensemble of many molecules. This study uses a radially polarized laser to excite a picocavity hotspot in a longitudinally polarized plasmonic antenna. We achieve an accurate observation of the chemical processes of individual molecules using their vibrational spectra. In particular, we observe that 4-nitrobenzenethiol dimerized into 4,4'-dimercaptoazobenzene and that a single-molecule of the latter briefly switched from trans- to cis-conformation; it then desorbs from the gold atom and reverts to trans-conformation. This study preliminarily shows the power of picocavity plasmon-enhanced vibrational spectroscopy in investigating single-molecule chemical kinetics.

In this study, a method based on the convolutional neural network is developed to estimate the topological charge of vortex beams affected by astigmatic lenses. Vortex beams with different topological charges are incident on lenses with different astigmatism coefficients. The generated diffraction intensity images are input into six classical neural network models, which are VGG, AlexNet, ResNet-18, ResNet-34, ResNet-50, and Xception. Specificity, precision, recall, F1-score, and accuracy are used as evaluation functions to measure the topological charge estimated by the network model. The network models are used to estimate the topological charge of the entire and part intensity images. The results show that the proposed method is effective for estimating the topological charge. The VGG model exhibits the best performance in this task, and the accuracy of topological charge estimation is more than 99%. Therefore, it is feasible to use neural network to estimate the different topological charges carried by the vortex beams after passing through the lens with astigmatism. This method can be further applied in the feature recognition of beam transmission through optical systems.

Quantum key distribution (QKD) is an absolutely secure key distribution guaranteed by quantum physics and has attracted significant attention. Among existing quantum key distribution protocols, the round-robin differential phase shift quantum key distribution protocol (RRDPS-QKD) has significant advantages in practical applications because of its large error tolerance. In this study, a novel round-robin differential phase shift quantum key distribution protocol is proposed. The received pulse trains are divided into odd and even branches using a switch. A random delay device, followed by a delay device, are added to each branch so that all the pulses from the source can participate in the interference at the receiver, and thus, improve the utilization rate of the pulse trains. The proposed protocol also ensures that the source can transmit the pulse trains continuously. The simulation analysis results and simulation quantum key distribution experimental results show that the proposed protocol can considerably increase the interference probability of the pulse trains and effectively improve the security key rate of the round-robin differential phase shift quantum key distribution protocol.

To investigate the impact of haze particles on quantum interferometric radar, we examine the correlation between the polarization characteristics of photons detected by quantum interferometric radar and the extinction features of haze particles in a hazy environment, by integrating the Mie scattering theory with the standard gamma distribution. For varying mass concentrations of haze particles, we establish and simulate relationship models between quantum link attenuation and the transmission distance of quantum interferometric radar detection photons. Similarly, for different quantities of photons in the transmitted beam, we develope and simulate relationship models between mass concentration of haze particles and the resolution and sensitivity of quantum interferometric radar. The experimental results reveal that, under a constant mass concentration of haze particles, the resolution of quantum interferometric radar increases with the augmentation of the number of photons in the emitted beam, while its sensitivity decreases with the rise in photon count. Hence, haze particles exert a substantial influence on the detection performance of quantum interferometric radar. These simulation outcomes provide certain reference basis for investigating the detection efficiency of quantum interferometric radar in hazy weather conditions.

Integrated photonics have attracted considerable attention and have been applied in both classical and quantum optics, thus fulfilling the requirements for modern optical communication experiments. Due to the remarkable flexibility in the design of optical properties, glass materials are a current focus of extensive research for their potential in integrated photonic devices. In the field of glass materials, the diverse functional micro/nanostructures directly written inside glass by ultrafast lasers have received widespread attention from researchers. In this review, the research progress in ultrafast laser-induced controllable structures in glass is briefly described with an emphasis on the transition from controllable complex physical fields to materials chemistry. The future trends of research are also prospected.

The optical clock based on ultracold neutral atoms has seen rapid development in recent years, pushing humanity's horizontal capability for time and frequency measurements to unprecedented heights. Among them, the performance of the optical clock with ultracold neutral atoms is significantly dependent on the trapping scheme of its quantum reference system. This article will introduce the principles and performance evaluation of the optical clock with ultracold neutral atoms, and provide a detailed exploration of how different trapping schemes for the quantum reference system impact the system's uncertainty and stability.

It is very important in the detection of gas isotope abundance for numerous fields including industrial production, biomedicine, and geological surveys, as it facilitates applications such as online safety monitoring in industries and real-time non-invasive clinical diagnoses derived from the analysis of human exhaled gases. This paper first underscores the extensive application potential of isotopic gas detection technology, highlighting its value and utilization. It then delineates five pivotal isotope abundance detection methodologies encompassing mass spectrometry and spectroscopy-namely, mass spectrometry, photoacoustic spectroscopy, tunable semiconductor laser absorption spectroscopy, cavity ring-down spectroscopy, and cavity-enhanced absorption spectroscopy. This paper elucidates the underlying principles of these techniques and sheds light on the recent advancements in isotope gas detection research. Subsequently, a comparative analysis of the performance of the five isotopic gas detection techniques is undertaken to discern their respective merits, limitations, and optimal application environments. Lastly, this paper offers insights into the prospective avenues for future research in isotopic gas signature analysis.

Spatial resolution is a crucial index to measure Brillouin optical time domain reflectometry. The spatial resolution of traditional Brillouin optical time domain reflectometer is restricted to 1 m, which cannot fully meet the demand for high spatial resolution in the engineering field. To improve the spatial resolution of the system, researchers have generally used two methods: optical pulse modulation at the optical path end and signal processing at the circuit end. However, the method of back-end signal processing has certain advantages in simplifying the system structure, reducing the hardware cost, and realizing the iterative upgrade. Furthermore, it can meet the requirements of the instrument's cost-effective and batch industrial applications in the engineering field. This study introduces comprehensive signal processing methods based on pulse segmentation and Brillouin spectrum analysis to improve spatial resolution. The principle and experimental scheme of these methods are analyzed and discussed, and the results obtained by each method are summarized and compared. Finally, the development prospect of Brillouin optical time domain reflectometry is prospected.

Recently, significant progress has been made in the organic thin film transistor field, which has prompted the development and application of microelectronic circuits, organic light-emitting displays, organic bioelectronics, and organic optoelectronic detectors. However, polycrystalline or amorphous organic semiconductors are prone to many defects, and the device fabrication process introduces defects, resulting in localized trap states in the band gap to trap charge carriers. Consequently, the trap states affect the carrier transport in organic thin film transistors considerably. Thus, in this study, several methods to detect and characterize the trap density of the states in organic semiconductor devices are reviewed. Different methods utilize different approximations and assumptions, employ different measurement principles, and cover different energy ranges. Therefore, the advantages and limitations of several detection methods are compared and analyzed, and guiding opinions are presented to facilitate effective measurement of the trap states in organic thin films.

The transverse mode of a radially polarized beam has a hollow ring distribution, with a special polarization form along the polarization direction. Specifically, the polarization is always along the radial direction and is axisymmetric with the optical axis. Radially polarized beams, with better focusing and particle manipulation than spatially uniform polarized beams, have shown high application value in industrial processing, space communication, and microscopy. This study briefly introduces the electric field characteristics of radially polarized beams, summarizes the research progress and principles of generation methods for radially polarized beams in the last decade, discusses the problems that need to be solved for the further development of radially polarized beams and proposes possible solutions to these problems. Finally, it suggests the future development trend of radially polarized beam-related research.

The aero-optical (AO) effects generated by the unsteady flow field around a hemisphere-on-cylinder turret can cause deflection, jitter, and defocus of a laser beam, consequently degrading the optical performance of an airborne laser communication system. These negative effects have multi-frequency, multi-mode, and space-distributed characteristics, posing significant challenges to research in this area. To mitigate the AO effects around the turret, previous studies have investigated the generation mechanisms of AO effects and the corresponding flow controls and optical corrections. This paper reviews the engineering background and research framework for AO effects around a turret, summarizing the research progress of the flow/optical simulation methods, experimental measurement systems, and post-processing algorithms for the aberrated wavefront data. Additionally, this paper discusses the major progress and current understanding on the AO effects in terms of numerical simulations, experimental measurements, flow controls, and adaptive optics. Finally, the research progress on the AO effects around the turret is summarized, and some research references are provided for future outlook.

Mach-Zehnder-Sagnac (MZ-Sagnac) interferometric distributed optical fiber vibration sensing technique is a widely used interferometric distributed optical fiber sensing technique, which has the advantages of high stability, good versatility, simple structure, and easy to deploy. This paper summarizes the research progress on MZ-Sagnac interferometric distributed optical fiber vibration sensing technology in recent years, systematically describes the basic principles and practical applications of MZ-Sagnac interferometric distributed optical fiber sensing technology, compares the performance of relevant works, and looks forward to the future development of MZ-Sagnac interferometric distributed optical fiber vibration sensing technology.

Brillouin distributed fiber sensing technology can realize distributed, long-distance, high precision temperature, or strain sensing and has a wide range of applications in large-scale infrastructure security monitoring. Traditional Brillouin optical time domain analysis and reflectometry (BOTDA/R) must measure Brillouin's gain spectrum by sweeping frequency to obtain Brillouin's frequency shift. The measurement process is time-consuming, and it is difficult to measure the dynamic strain. To solve this problem, researchers have proposed various technical schemes and made significant progress. This paper summarizes the recent progress of the time-domain Brillouin optical distributed fiber dynamic strain sensing system, including the BOTDA/R dynamic sensing system based on the slope-assisted method as well as the frequency-agile, optical chirp chain, and optical frequency comb techniques.

Hypersonic wind tunnels play a crucial role in aerospace research, and tunable diode laser absorption spectroscopy (TDLAS) serves as an invaluable diagnostic method in this field. TDLAS offers no-contact, highly sensitive, and multiparameter measurement capabilities coupled with a simple structure, cost-effectiveness, and high spatiotemporal resolution. This study introduces the measurement principle and typical optical design of TDLAS, highlighting its widespread use for measuring parameters such as temperature, component concentration, and airflow velocity in extreme environments such as hypersonic wind tunnels. Furthermore, this study provides an overview of recent applications of TDLAS in hypersonic wind tunnel flow field diagnosis globally. Additionally, it summarizes the current development status and challenges of TDLAS in hypersonic wind tunnel flow field diagnosis in China. It concludes with a brief outlook on the prospective development of TDLAS flow field diagnosis technology in hypersonic wind tunnels, offering valuable insights for future advancements and related experiments in this domain.

The thermal emission spectrum has found widespread applications in environmental monitoring, astrophysics, medical diagnosis, and drug development. Despite the effectiveness of micro-electro-mechanical system (MEMS)-based infrared emitters in reducing device size, they exhibit drawbacks like a broad spectral distribution range and low emissivity. This paper explores the enhancement of thermal emission characteristics by integrating nanostructures, allowing precise control over spectral features, and effectively improving narrowband emission. The discussion begins with an elucidation of the fundamental principles governing MEMS infrared thermal emission emitters. Subsequently, we delve into the advancements in MEMS infrared narrowband thermal emitters featuring nanostructures such as gratings, photonic crystals, and metasurface structures. The paper further provides a brief overview of the applications of infrared narrowband thermal emitters in gas sensing, thermophotovoltaic power generation, biomedical, and other fields. Finally, a comparative analysis and summary of the performance of nanostructure-based narrowband emitters are presented.

This study explored the quantitative detection of hazelnut oil adulteration. A portable laser Raman spectrometer was used on 180 adulterated samples of hazelnut oil mixed with corn oil, walnut oil, and flaxseed oil. The acquired spectra were divided into calibration and validation sets in a 3∶1 ratio. Qualitative analysis was performed using principal component analysis and quantitative detection of adulterated samples was achieved by establishing a partial least-squares regression. The experiment yielded three binary pseudo samples of hazelnut oil mixed with flaxseed oil, walnut oil, and corn oil, respectively. The corresponding correlation coefficients were 0.9894, 0.9872, and 0.9688; the root mean square errors on calibration were 0.0037, 0.0098, and 0.0121; the root mean square errors on prediction were 0.0114, 0.0126, and 0.0190; and the relative analysis errors were 9.707, 8.848, and 5.662. The difference in the model parameters of the three kinds of adulterated samples was reasonably explained. The results show that the proposed system has excellent predictive performance for quantitative detection of hazelnut oil adulteration. The system can be used for simple, rapid, and nondestructive quantitative detection of hazelnut oil adulteration.

A segmented Transformer feature extraction network is proposed to address the challenges posed by near infrared spectroscopy, including high dimensionality, susceptibility to noise interference, and high spectral similarity among samples from different provinces. This network is applied to tobacco leaf origin identification to enhance classification accuracy. First, based on the one-dimensional structure of near infrared spectroscopy, an embedding layer is designed to compress features using one-dimensional convolution. Second, the data is divided into three parts along the spectral dimension using sliding windows. The Transformer architecture is improved to extract spectral features, addressing the issue of computational inefficiency caused by a large number of spectral bands. Last, to adapt to the characteristics of spectral data, a regression head with multiple layers of one-dimensional convolution is designed to predict the origin of the samples. To validate the effectiveness of the proposed algorithm, several comparative experiments are conducted, comparing classification accuracy, precision, recall, and other metrics with other algorithms. The superiority of each structure in the model is verified. The experimental results demonstrate that the proposed model effectively utilizes the spectral structure for feature extraction and noise suppression, successfully accomplishing the task of tobacco leaf origin identification.

With the development of laser technology, lasers has become a powerful tool for the cutting of glass due to its high precision, high speed, high quality, and high efficiency. In this paper, a method of cutting medical glass tubes by using picosecond Bessel laser beam is proposed. In our experiment, the cutting of glass tubes is induced by Friedrich Bessel beam, which is a spatial beam pattern suitable for cutting transparent material with a large thickness. The changes of cold storm surface and roughness under different pulse energy and pulse distance are analyzed and compared. According to our measurement, the amount of insoluble particles (debris) in the glass tube after cutting can meet the medical requirements. Compared to traditional cutting methods, the proposed method greatly improves cutting efficiency and quality.