Based on the generalized Huygens-Fresnel principle, the spectral density, degree of coherence, and the coherent vortex of partially coherent elliptical vortex beam propagation through anisotropic non-Kolmogorov turbulence are studied. Among them, we focus on the important properties of coherent vortex beams as partially coherent vortex beams. It is found that the elliptic rate, coherence length, and turbulence parameters all have influences on the conservation distance. Moreover, it is easier to separate the newly generated coherent vortex points of partially coherent elliptical vortex beams than that of partially coherent circular vortex beams.

This study retrieves the aerosol extinction coefficient, the height of the boundary layer, and the mass concentration of ozone based on differential absorption lidar. Through the atmospheric temperature profile, ground meteorological elements, and air quality data, backward trajectory and naval aerosol analysis and prediction system, a heavy pollution process in Wangdu County is analyzed. Experiment results show that during the observation period, Wangdu County is under the control of the East Asian trough system, and there is always a temperature inversion layer within 100?200 m of the surface layer. When particulate pollution is severe, the relative humidity on the ground is high, the wind speed is low, and there is a weak downdraft at high altitude, which is conducive to the moisture absorption growth and long-term accumulation of particles. The boundary layer height is always low, which is not conducive to the diffusion of pollutants. In addition, the boundary layer height has no obvious correlation with the particle mass concentration, but it is negatively correlated with visibility, and the correlation coefficient is -0.344. The mass concentration of ozone is positively correlated with temperature and visibility and negatively correlated with relative humidity, boundary layer height, and wind speed. The local quiet and stable weather and the transmission of pollution sources from other places are the major causes of air pollution in Wangdu County.

In this paper, a plasmonic color filter based on a rectangular metal block array structure is designed. The device combines the surface plasmon resonance effect with the guided wave characteristics of planar waveguides, and realizes the dynamic control of transmission spectra in the visible light band by using the polarization sensitivity of the asymmetric rectangular metal block periodic array structure for the incident light. The effects of the array period, filling factor, thickness of dielectric and metal layers, and polarization angle of incident light on transmission spectra and color filtering characteristics are studied by using the finite difference time domain method. The results show that the transmission spectra can be adjusted statically by changing the period parameters of the rectangular metal block array and can be controlled by dynamically changing the polarization angle of the incident light when the period of the rectangular metal block array is asymmetric. By adjusting the structural parameters, the transmittance of the filter can be as high as 75% in the visible light range, and the static and dynamic control of the filtered color can be realized simultaneously. This research provides a theoretical basis for the design of next-generation color-tunable plasmonic color filters.

By using two phase modulators, two circulators, one electro-optic modulator, etc., stimulated Brillouin scattering can be generated in the upper and lower highly nonlinear optical fibers, forming an instantaneous microwave frequency measurement system for the bisymmetric stimulated Brillouin scattering effect. Using the one-to-one correspondence between the output optical power ratio of the system and the microwave signal to be measured, the amplitude comparison function is established to realize the microwave frequency measurement. Theoretical analysis results show that by adjusting the line center gain coefficient difference and the Brillouin frequency shift difference of the highly nonlinear fibers, the measurement range and measurement error of the microwave frequency can be changed. When the line center gain coefficient difference is 30 and the Brillouin frequency shift difference is 2 GHz, the frequency measurement range is 0?18 GHz, and the measurement error is less than 52 MHz. When the line center gain coefficient difference is 30, the Brillouin frequency shift difference is 0.4 GHz, the frequency measurement range is 0?21 GHz, and the measurement error is less than 148 MHz.

Three-dimensional (3D) tension sensor based on fiber Bragg grating (FBG) is used to test the installation state of high-voltage bushing in substations, and the stress state of the bushing end is continuously monitored for 1500 h. By measuring the stress at the end of the bushing under different kinds of installation, the arrangement of the down line and fittings installation type are optimized. By monitoring the stress at the end of the bushing for a long time, the 3D tension and the thermal stress due to temperature changing at the end of the bushing are measured. Low-frequency signals (0.18 and 0.22 Hz) are obtained from the 3D tension, which are due to substation shaking resulting from the wind load on the cross line. The health monitoring of the substation is preliminarily realized by the 3D tension sensor based on FBG, which can further facilitate the development of the smart grid.

A temperature sensor based on orbital angular momentum (OAM) modal interference is proposed, which demodulates the information using the image detection method. The sensing mechanism and demodulation principle of the sensor are studied, and the sensing performance and immunity to light-noise are analyzed. The simulation results show that the temperature can be demodulated by a single image using the phase information carried by the OAM modes. Moreover, the demodulated result is linearly dependent on the modal phase difference. The temperature sensitivity of the sensor is immune to the fluctuation of the modal intensity and external light-noise. The proposed OAM modal interference sensor has better stability and reliability than conventional modal interference sensor based on LP modes.

Aiming at the impact of multiple environmental factors on atmospheric visibility, this study proposes an entangled wave division access strategy of quantum satellite communication under the background of multiple factors in a natural environment. When each pair of ground stations distributes quantum keys, they can form entanglement pairs of different wavelengths through the quantum satellite. According to quantum entanglement of different wavelengths, many ground stations can connect to the same satellite. The simulation results show that under the same atmospheric humidity and haze particle concentration, the system’s channel capacity increases, and the bit error rate decreases from 3.3415×10-3 to 2.243×10-3. The increase in the bit error rate caused by atmospheric visibility factors will also decrease. Thus, in the environmental multifactorial context, the entangled wave-split access strategy can improve the quantum satellite communication performance.

Additive manufacturing technology can prepare highly flexible inclinometer sensors, i.e., the sensitivity, resolution, and range of the sensor can be designed and manufactured according to requirements. Therefore, this study develops a new type of inclinometer sensor based on fiber Bragg grating and the additive manufacturing technology. In order to verify the performance of the sensor, the measurement principle of the sensor is deduced, and the calibration and slope-model loading experiments are conducted. The experimental results show that the sensor's inclinometer sensitivity is 0.0824 (°)/pm, resolution is 12.14 pm/(°), and range is greater than 60°. The sensor is consistent with the slope test results of the linear variable differential transformer sensor, and the displacement difference is less than 0.08 mm.

A temperature and humidity sensor based on cascaded fiber Bragg gratings comprising tapered coreless fibers is designed. A composite nanofiber membrane is prepared for this sensor comprising a layer of polyvinyl alcohol/carboxymethyl cellulose nanofibers, each containing a biconical connector prepared by electrospinning in the cone area. Changes in humidity change the effective refractive index and thickness of the nanofiber film, thereby affecting the transmission loss of light through the fiber, and then changing the output spectral power. In addition, temperature fluctuations cause the center wavelength of the fiber grating to shift. Monitoring the peak power and peak wavelength of the output spectrum (changes in the center wavelength) enables temperature and humidity sensing. Temperature and humidity response tests are performed on the designed sensor. The relative humidity sensitivity of the sensor is 0.0198 dB/%, and the relative temperature sensitivity is 11.730 pm/℃. Results show that electrospinning is an effective method for preparing moisture-sensitive coatings on the surface of optical fiber sensors.

Aiming at the problems of high dynamic topology nodes and difficult communication link construction in space laser communication networking, based on the existing "one point to many points" networking optical principle, the servo performance of its mirror optical antenna is studied. Two different optical closed-loop control strategies based on the position loop and speed loop are compared through experiments. The results show that the optical closed-loop control strategy based on the speed loop will have large instantaneous jitter of tracking and reversing errors, while the optical closed-loop control strategy based on the position loop is more stable and has small error when reversing. The optical closed-loop tracking simulation based on the speed loop is carried out by using the Matlab platform. The tracking error obtained by the simulation is basically consistent with the actual tracking error, but there is no large reversing error. By combining with the low-speed start-up experiment, we concluded that the error comes from the poor low-speed start-up performance of the speed loop, and the scheme of reducing the reversing and tracking errors by adding the position loop is suitable for the optical mechanical system with high resonance frequency of the shafting. The experiment also studied the velocity feedforward of position loop tracking. The results show that when the feedforward gain increases from 0 to 2, the position tracking error first decreases and then increases, and the minimum tracking error appears near the gain value of 0.95?1.05.

To reduce the system bit error rate and increase the system rate of the radio of fiber (RoF) system without increasing the average optical power, this study proposes a W-band orthogonal frequency division multiplexing-radio of fiber (OFDM-RoF) system based on probability shaping (PS). The theory and operating rules of PS are analyzed theoretically. The OFDM-RoF system is developed on the simulation platform. In this system, the PS is used to adjust the transmission probability of each constellation point of 16 quadrature amplitude modulation (16QAM), and the 80 GHz PS-16QAM-OFDM millimeter-wave signal is generated jointly with the OFDM-RoF system. Results after the signals are transmitted 0, 10, and 20 km through an optical fiber show that when the symbol rate is 2.5 GBaud and lg RBE= -9(RBE is bit error tate), compared with the traditional 16QAM/OFDM-RoF system, the transmitting optical power of the PS-16QAM/OFDM-RoF system is reduced by 1 dBm, and its system performance is better. However, when the symbol rate is 10 GBaud, the constellation diagram of the 16QAM/OFDM-RoF system using PS diverges in the outer circle, but the constellation points in the inner circle are concentrated; its system performance is good.

Sampling noise affects each frequency of white light interference signal Fourier frequency spectrum. Selecting an appropriate filter method will help improve the signal-to-noise ratio of a white light interference signal and obtain highly accurate solution results. In this study, an energy concentration constraint under a certain energy ratio is constructed, and a cost function for selecting the bandpass filter is established. The part calculation process and results of the cost equation under white light LED illumination are given in the experiment. When the cost function reaches its minimum value, the standard deviation of surface roughness is only 0.02 nm. Finally, a silver mirror and a step structure are measured under the selected parameters. The results show that the proposed method has good performances with respect to repeatability and resolution.

In order to solve the problem of low radiation uniformity of a solar simulator, a variable coefficient ellipsoid condenser system was established according to the working principle of solar simulators. Firstly, the high-order equation is obtained by Taylor expansion of the traditional ellipsoid equation, and an ellipsoid equation with variable coefficients is obtained by evolution. Then, the optimal variable coefficient ellipsoid equation is obtained by adjusting the coefficients of the variable coefficient ellipsoid equation. Then, MATLAB is used to simulate the energy at the second focal planes of the variable coefficient ellipsoid and the traditional ellipsoid, and the two are compared. The LIGHTTOOLS software is used to simulate the optical systems of the traditional ellipsoid and the variable coefficient ellipsoidal condenser. The simulation results show that the uniformity of the second focal plane of the variable coefficient ellipsoid is higher than that of the traditional ellipsoid. The radiation uniformity of the variable coefficient ellipsoid is 3.91% higher than that of the traditional ellipsoid, which basically meets the requirements of high radiation uniformity of solar simulators.

To improve the anti-interference ability of the laser interferometry acoustic measurement method, the amplitude modulated laser interferometry is proposed. Using the high-frequency tuning characteristics of a tunable semiconductor laser to modulate the laser signal amplitude, the underwater sound field information is obtained from the interference of the reflected light on the water surface and the reference light. In addition, the phase-locked amplification and demodulation method is used to obtain the laser interferometry underwater sound signal with accurate inversion. The characteristics of the amplitude-modulated signal are simulated, and a fiber-coupled laser interferometry underwater acoustic test system is built. A modulation frequency of 10 kHz is used to drive a pigtail with a center wavelength of 1405 nm to output a tunable semiconductor laser, and the sound signal is tuned down for measurement. Results show that the proposed method can effectively extract the vibration characteristics of underwater acoustic signals with different frequencies and intensities. Under the interference of pulse noise with a frequency of 2 Hz, the proposed method can be used to measure the signal noise better than the traditional measurement method. The ratio is increased by more than 10 dB, which enhances the anti-interference ability of the underwater acoustic measurement.

This paper proposes a scheme which uses a single Mach-Zehnder modulator (MZM) to generate a flat and wide optical comb based on the double-sideband modulation method. The frequency difference between two lasers directly determines the spectral width and quality of this comb after double-sideband modulation. Through the theoretical analysis of the standard deviation between the sidebands of different orders under different modulation coefficients and the Bessel value of each order sideband, we find sidebands above the fifth order have a negligible effect on the wide comb. The lower-power fifth-order sidebands are superimposed on the sidebands of different orders, so that the powers of the sidebands of different orders can be compensated or cancelled, thereby reducing the influence of the higher-order sidebands on the optical frequency comb and improving the flatness. The flatness of the wide optical comb obtained by simulation reaches 3.7 dB, and the effective spectral width is 700 GHz. After the non-return to zero data with transmission rate of 5 Gbit·s-1 is modulated on this optical comb and transmitted through an optical fiber, the eye diagram is still clearly visible, and the power penalty is less than 1.8 dB at the bit error rate level of 10-9. Such an optical comb can transmit more data information in optical communications, realize high-speed data transmission and maintain the flatness of the optical comb with good stability and low cost.

Femtosecond laser micro-ablation is a new high-precision processing method. In this study, the ablation characteristics of a face gear material (18Cr2Ni4WA steel) were studied. The energy coupling effect of the electronic and lattice subsystems of the ablated 18Cr2Ni4WA steel was investigated. In addition, a two-temperature model was established, and the effects of pulse width and average power on electron and lattice temperature were simulated using the finite difference method. Results reveal that when thermal equilibrium between electron and lattice is reached and the electron and lattice temperatures exceed the melting point of the material, the tooth surface is ablated; furthermore, when the electron and lattice temperatures are higher than the material boiling and phase explosion temperature, the material removal is mainly achieved by phase explosion. The material ablation depth is generally taken as ~40 nm to prevent the thermal effects on surface quality. The single-pulse ablation threshold of the 18Cr2Ni4WA steel ablated by a Gaussian distributed femtosecond laser using the femtosecond laser microprocessing system was 0.29 J/cm2. The effects of average power and pulse number on the ablative morphology of the material were analyzed. The ablation characteristics of the 18Cr2Ni4WA steel microprocessed by a femtosecond laser in this study provide a technical basis for improving the processing quality of face gears.

To study the effect of laser processing parameters on the surface texture morphology of Ni-Co-Si3N4 composite coating, we used an electrodeposition technique to prepare the Ni-Co-Si3N4 composite coating on the 45 steel surfaces and then processed the coating by optical fiber laser with 1070-nm wavelength. We studied the influence of pulse energy density, pulse width, and pulse number of laser on microstructure by single-factor method, obtaining the evolution law of characteristic parameters such as inside diameter, outside diameter, center point height, edge height, and nadir height of microstructure. The results showed that the laser interacts with the Ni-Co-Si3N4 composite coating, forming four typical morphologies: spherical-cap-shaped bump, W-shaped pit, crater pit, and pit with double concentric holes. The surface microstructure changed from spherical-cap-shaped bump to pit with double concentric holes because of the increased pulse energy density and changed from crater pit to spherical-cap-shaped bump because of the increased pulse width. Besides, the depth and edge height of the surface microstructure increased because of the increased pulse number.

To gain an in-depth understanding of the thermal effect of the excimer laser on the linewidth narrowing module (LNM), we investigated the influence of the internal heat accumulated in the module on the output spectrum of the system. Through theoretical analysis and experimental verification, we consider the uneven distribution of the refractive index caused by the temperature change of the prism and the influence of different inert gases on the long-term stability of the output laser spectrum. The results show that the laser interacts with the internal components in the LNM to increase the temperature of the optical components and broaden the output spectrum. The inert gas protection system reduces the accumulation of heat inside the LNM through gas flow and maintains the long-term stability of the output spectrum. The accumulation of heat inside the module has a great influence on the spectral purity value, and has little influence on the full width at half maximum. Compared with N2, the refractive index of He has a smaller change with temperature, which can keep the spectral purity of the output laser spectrum stable for a long time.

We use nonlinear polarization rotation mode-locked mechanism and high-gain-coefficient Ytterbium-doped fiber to design two new devices (polarization splitter + Faraday rotator and wave plate axis) and build a set of ultra-short cavity length mode-locked fiber lasers. And finally, the mode-locked pulse output with repetition rate of 706 MHz is realized. At the pump power of 1.5 W, the mode-locked laser can achieve laser pulse with average output power of 260 mW and pulse duration of 158 fs. The laser can operate stably for 72 h under mode-locked condition, and its structure is more conducive to miniaturization and portability for high repetition frequency systems.

Herein, the effects of phenolic resin addition amount, graphite powder with different particle sizes, and coating pretreatment time on the bending strength and forming accuracy of graphite parts were investigated. The variation law was obtained, and the formation mechanism of graphite additives was revealed. Results show that the bending strength and forming error of graphite parts increase with an increase in the phenolic resin addition amount. Compared with -325, -200, and -150 mesh, when the mass ratio of -100 mesh natural flake graphite powder to phenolic resin powder is 6∶?4, the bending strength of the formed parts is optimal, reaching 1.93 MPa. The coating pretreatment of graphite powder not only helps to improve the mechanical properties of the graphite molded parts, but also reduces the thermal conductivity of the powder, thereby improving the forming accuracy of the molded parts. When the coating time is doubled, the bending strength of the formed parts reaches 2.976 MPa and the relative dimension errors of the X, Y, and Z axes are 8.42%, 8.45%, and 13.05%, respectively. In addition, a porous graphite skeleton with a diamond-like carbon structure can be quickly manufactured, realizing the synergy of strength and precision.

In order to apply laser layering cleaning for aircraft structure and paint repair purposes, the effects of laser thermal ablation and thermal expansion on residual primer paint were analyzed, and a laser layering cleaning test on aluminum alloy skin was designed and carried out to reveal adhesion change of the residual primer paint after laser cleaning. The results show that the residual primer paint surface obtained by laser layering cleaning is smooth and easy to clean. The ablation "keyhole" can increase the contact surface, which can improve the adhesion of the paint film when recoating the new paint. When the thickness of the residual primer paint is over 24.8 μm, the thermal ablation effect of the laser will not affect the adhesion of the residual primer paint; and when the thickness of the primer is small, the adhesion will be reduced due to the thermal expansion effect of the residual primer paint.

To improve the service life of a mining hydraulic column, an Fe35A alloy layer was prepared on the surface of 45 steel material by laser cladding technology. The cladding layer, which was prepared using different laser powers, scanning speeds, and powder feeding rates, was tested using digital testing equipment to study the surface hardness, geometric size, microstructure, and sectional microhardness of the sample, and the optimal process parameters for laser cladding were obtained. Results show that under the optimal laser cladding parameters of 2100 W laser power, scanning speed of 5 mm/s, and powder feeding rate of 15 g/min, the quality of the cladding layer is the best, the microstructure of the cladding layer are good, the grain size is fine and uniform, and the fusion between the matrix structure and the cladding layer is satisfactory, the hardness of the cladding layer surface is 42 HRC, and the average microhardness of the cross-section of the cladding layer is 643 HV. The comprehensive mechanical properties of the laser cladding layer are higher than those of the matrix structure. The preparation of Fe35A alloy coating with high-quality on 45 steel substrate is realized.

High Q-factor Fano resonances were proposed and realized using toroidal dipoles in planar metamaterials composed of asymmetric split ring resonators at 9.1 GHz. Owing to the rapidly increased toroidal dipole, the presented subwavelength structure exhibits a remarkable characteristic, which is demonstrated using simulation and experiment. The toroidal excitation of the Fano resonances were verified using the conduction current, vortex H-field distribution, and scattered power in the far field. The relation between the Fano resonances and the scattered power of multipoles of the normal incident wave at different polarization angles was analyzed. The proposed toroidal metamaterial has application potentials in the wavelength bands of microwave, terahertz, and optical band, including ultrasensitive sensors and optical switches.

A simple one-pot solvothermal procedure was employed to synthesize N/Al co-doped carbon dots(CDs) with a red emission photoluminescence quantum yield up to 30% in aqueous solution. The particle size, surface functional groups and fluorescent properties of the as-prepared CDs were characterized by atomic force microscopy (AFM), dynamic light scattering (DLS) granulometer, fluorescence spectrometer, X-ray photoelectron spectroscopy (XPS), and Fourier transform infrared spectroscopy (FTIR). The average diameter of the as-prepared N/Al co-doped carbon point particles is 6.5 nm, and CD particles have strong anti-bleaching ability under the influences of high concentration salt ion solution, UV irradiation and temperature change. Meanwhile, these CDs can be developed as a novel fluorescence probe for the detection of H2O2 with a detection limit of 1.3 μmol/L. Moreover, there exists a linear correlation between the quenching efficiency of CD fluorescence and the concentration of H2O2 within 0.12?1 mmol/L.

Delayed wound healing is one of the most challenging clinical complications of diabetes mellitus (DM) and is related to the excessive production of reactive oxygen species (ROS). Photobiomodulation (PBM) can promote the healing of delayed wounds in DM patients. We studied the effect of PBM on the active oxygen homeostasis of human embryonic skin fibroblasts (CCC-ESFs) that were cultured in a high glucose environment, and explored the effect of PBM on improving oxidative stress injuries. CCC-ESFs were cultured in vitro, and the cells were randomly divided into control group (normal glucose group and high glucose group) and 808 nm laser irradiation group (power density: 10, 20, and 40 mW/cm2; energy density: 1.5, 3, 6, and 12 J/cm2). After 48 hours of high glucose modeling, the experimental group was irradiated with a laser and we measured the cell proliferation, ROS content, total superoxide dismutase, total antioxidant capacity, mitochondrial membrane potential and the expression level of the related cytokines. The results show that cell proliferation activity was reduced, ROS content was significantly increased, antioxidant capacity was decreased and cell apoptosis was increased in the high glucose environment; however, the proliferation effect of the cells was not significantly improved after 808 nm laser irradiation, but ROS content of the cells decreased, the expression of antioxidant enzymes showed an upward trend, and the expression of pro-inflammatory cytokines decreased. These results show that PBM can repair oxidative stress damage, regulate inflammatory responses, and promote wound healing under a high glucose environment.

In optical design, to provide more design freedom for optical system design and optimization, a rotationally symmetric aspheric surface is often used. The standard expression for a rotationally symmetric aspheric surface is usually a combination of a base quadric surface and an additional polynomial, which can be an even-power-series polynomial, Zernike polynomial, or Q-type polynomial, among others. Hence, the expressions for the base quadric surface and aspheric surface based on different additional polynomials are derived, the aspheric coefficient and the slope of the aspheric surface of various rotationally symmetric aspheric surfaces are compared, and the application of an aspheric surface based on different additional polynomials in optical design is compared with design examples, and the characteristics of each aspheric surface are identified. The results show that, compared with other aspheric surfaces, the aspheric surface based on a Q-type polynomial can better control the surface shape of the aspheric surface, and the optimization efficiency is higher.

In this study, a comparative investigation of the subwavelength transmission properties of graphene- and metal-coated nanowires is conducted. By using the finite element method, the modal field distribution and transmission properties of the lowest-order modes are investigated based on the frequency and structural dimensions for single nanowires and nanowire dimers. The results showed that when the thickness of the metal layer is larger than the skin-depth, graphene-coated nanowires exhibit better fundamental modal field confinement. However, when the thickness of the metal layer is far smaller than the skin-depth, the subwavelength transmission properties of the metal-coated nanowires are comparable to those of graphene-coated nanowires. These results will provide a reference for choosing plasmonic materials and have potential applications in subwavelength photonic devices.

We theoretically analyze influence of the crosstalk, insertion loss, and bandwidth of the arrayed waveguide grating on the dynamic range, wavelength resolution, and demodulation accuracy of the demodulation system. The results show that the larger the bandwidth, the larger is the dynamic range of the demodulation system; however, the wavelength resolution will decrease. It also shows that the smaller the crosstalk, the higher is the demodulation accuracy. Then, we theoretically investigate the factors affecting the output spectral bandwidth of the arrayed waveguide grating, such as the number of diffraction orders of the arrayed waveguide grating, the number of arrayed waveguides, and the width of the horn. The results show that the passband bandwidth of the arrayed waveguide grating is larger when the number of waveguides is smaller and the width of the tapered waveguide opening is larger. Finally, we design an arrayed waveguide grating based on a 2% refractive index difference silica material system, which has the characteristics of wide bandwidth, low loss, and low crosstalk. It provides theoretical guidance for research on fiber-grafting demodulation systems based on arrayed waveguide grating. We then specify the optimization direction of the device and system.

A sub-wavelength periodic composite structure with square frame and hollow cylinder nested by Au is proposed. The finite difference time domain algorithm is used to simulate the composite structure. It is found that the minimum transmittance can reach 7.46%, the minimum full width at half maxima can reach 7.25 nm, the maximum reflectivity is 87.61%, and the maximum absorptivity is 38.00%, when the wavelength is 400?900 nm. It is found that the resonant mode of the composite structure is coupled by the resonant mode of the two basic structures, and the nested mode can further reduce the transmission of single structure and increase the interaction between light and composite structure. By changing the parameters of the composite structure, a wide and efficient control range of plasmon and a narrow transmission spectrum are obtained. This provides theoretical guidance for the design of artificial subwavelength periodic composite structures.

The identification and secure transmission of the station phase codes in the Loran C system are the premise of judging chains and receiving signals for hyperbolic positioning. Aiming at the problem that the Loran C system cannot achieve high security transmission by classical means, we propose a phase code transmission scheme based on EPR state quantum signals and analyse the security of this scheme under the entanglement attack and spectroscopic attack. The relationship between the information transmission efficiency and the transmission coefficient of the spectroscope as well as that between the information transmission efficiency and the compression degree of the spectroscope is obtained, which verifies that the proposed scheme can effectively improve the security of phase code transmission between the main station and the secondary station in the Loran C system.

The balanced homodyne detection technique is the one of the main methods for the detection of squeezed state quantum noise in the low frequency range, in which the signal-noise ratio and saturation power are the important parameters limiting balanced homodyne detection. Based on the characteristic of inductance impedance changing with frequency, a current-voltage-conversion frequency function is adopted to make the conversion impedance corresponding to the low-frequency (or direct current) component of photocurrent is lower than that corresponding to the high-frequency part, and thus the saturation power and signal-noise ratio of the photodetector are both enhanced. By combining the instrument amplifier and trans-resistance operational amplifier circuit, a kHz balanced homodyne detector with high signal-noise ratio and high common-mode rejection ratio for direct current and alternating current output is obtained, whose measured common-mode rejection ratio is 54 dB. When the input power is 14.4 mW, the shot noise at 50‒100 kHz is 31 dB higher than the electronic noise and the saturation power of the detector is 17 mW.

To solve the problem that radar emitter signal feature evaluation is not objective and lacks an evaluation basis, a group evaluation method based on interval fuzzy principle, cross-entropy, and multi-criterion compromise method is proposed. First, establish a signal noise rate (SNR) evaluation model, then combine the triangular fuzzy number cut set and interval approximation ideas to convert the evaluation system of radar emitter signal features into interval-valued intuitionistic fuzzy numbers. Next, optimize the SNR weight based on Hamming distance, and use interval-valued intuitionistic fuzzy weighted average operator-integrated group decision matrix based on the maximum entropy method to calculate the attribute weights. Finally, the multi-criteria compromise method and fuzzy cross-entropy are used to achieve the feature scheme ranking. Simulation results show that the proposed method can provide a consistent feature evaluation-ranking scheme with the actual situation and is consistent with the analysis results of the approach to the ideal point method and projection model method, verifying the feasibility and effectiveness of the proposed method.

In view of cross sensitivity of the high-precision frequency-modulated continuous-wave fiber optic pressure sensor to temperature and pressure, the temperature characteristics of the pressure sensor are analyzed theoretically and experimentally. The structure of the pressure sensor is optimized, the effect of temperature on Fabry-Perot (F-P) cavity can be reduced to 50 μm. After theoretical calculations, it can be known when the temperature changes from 25 ℃ to 65 ℃, the deformation of the F-P cavity by the temperature is 1000 μm. By optimizing the F-P cavity design, the influence of temperature on the length of the F-P cavity can be effectively reduced. The relationship between the deformation of the cavity length of the optimized F-P cavity and the temperature is tested through experiments. The least-squares method is used for temperature compensation in real-time. After the temperature compensation, the deformation of the F-P cavity length is directly reduced from 50 to 4.5 μm, which reduces temperature cross-sensitivity, improves the reliability and practicability of high-precision frequency-modulated continuous-wave fiber optic pressure sensing measurement.

A dynamic metasurface is a metasurface in which adjustable elements are integrated into static metaatoms and whose functions are controlled by different external excitation methods. Various adjustable devices have been realized based on dynamic metasurfaces, including frequency conversion filters or absorbers, zoom lenses, dynamic beam controllers, dynamic holographic elements, etc. In this review, first, the modulation method of dynamic metasurfaces is summarized systematically, and then the related research work is reviewed. Dynamic metasurfaces can be divided into two categories: one is a uniformly regulated dynamic metasurface that controls all metaatoms uniformly, and is used to achieve dynamic conversion of spectrum, polarization, and wavefront; the other is a dynamically reconfigurable/programmable metasurface with individually controlled metaatoms, and is used to realize flexible control of the wavefront. Dynamic devices with flexible and controllable functions are the main direction of future research on metasurfaces. The existing dynamic devices are summarized, and the development direction and challenges of dynamic metasurfaces are further discussed and prospected.

The research background, design scheme, and structure characteristics of a convex grating imaging spectrometer based on a concentric structure are introduced. Five main configuration types of concentric imaging spectrometers with a convex grating at home and abroad are reviewed, including Offner type, off-plane type, catadioptric type, +1st order diffraction type, and freeform surface type. The advantages and disadvantages of these five configuration types are summarized. It has important guiding significance for the research and development of a new generation of light and small imaging spectrometers with high imaging quality, high resolution, high diffraction efficiency, large relative aperture, long slit, and wide wavelength range.

Laser power meter is widely used in measuring the power of continuous laser and average power of pulsed laser. Fast and accurate measurement of laser power is of great significance in scientific research and industrial development. In this paper, the working principle of various laser power meters is introduced systematically. The advantages and disadvantages of various measurement methods, and the wavelength, measurement range and uncertainty of power measurement, are analyzed. The laser power measurement method based on photodynamics and its development potential are discussed. Furthermore, the future development and application of laser power measurement are prospected.

Spectral combining technologies of fiber laser can overcome the limitation of the output power limit of a single-fiber laser, which is an effective technical means to obtain laser output with high power and perfect beam quality. The basic combining principles and research progress of the four spectral combining technologies are introduced. The structure, limiting factors, and characteristics of various synthetic components are analyzed separately. The key technologies of spectral combining based on dichromatic mirrors and their domestic and foreign research progress are introduced. The development prospects of spectral combining technologies are introduced.

This paper reviews and summarizes various methods for linewidth measurement, introduces their development process, principles, and the required experimental equipment. According to the difference in principle, the methods for linewidth measurement are divided into two categories based on signal power spectra or phase noises. The limiting factors of linewidth measurement accuracy for these methods are analyzed and the precautions for the operation of these methods are summarized. In addition, the advantages and disadvantages of these methods as well as the corresponding detection ranges are comprehensively listed. According to the performance parameters and experimental conditions for different lasers, suitable linewidth detection methods are recommended. Finally, as for their practical applications, the methods for linewidth measurement of narrow-linewidth tunable lasers (widely used for coherent communications) are analyzed and discussed in detail.

Landslides occur frequently in China, often causing serious property losses and casualties. Therefore, scientific and effective landslide monitoring is of great significance for disaster prevention and mitigation. In recent decades, with the continuous development of monitoring technology, the level of landslide monitoring has been observably developed and improved in recent decades. It has gradually transferred from the past low-precision, point-type and manual monitoring to high-precision, distributed, and automated monitoring, which strongly supports the ability of governments at all levels from the national to the local level to cope with landslide disasters. In this paper, the current landslide monitoring methods and techniques are summarized and evaluated from four aspects: space (space satellite remote sensing), air (low altitude unmanned aerial vehicle remote sensing), ground (surface), and interior (inside the landslide body). The application method and effect of distributed optical fiber sensing technology in landslide monitoring are described, emphatically. The results show that the multi-source and multi-field monitoring inside the landslide body can obtain the multi-field information of the landslide, and the correlation model of the multi-field information can be established through further analysis, which can provide reliable data support for the evaluation and management of the landslide stability and has good research potential and application prospect. Finally, a new thinking of accurate and reliable monitoring, prediction and early warning of landslide deformation is proposed in this paper.

Nanomaterials are emerging materials developed at the end of the 20th century that have attracted wide attention owing to their excellent and unique properties. Moreover, nanomaterial preparation is a key field in nanotechnology. In this paper, two important methods to prepare nanomaterials using pulsed laser ablation(pulsed laser deposition and pulsed laser liquid-phase ablation) are introduced, including their principles, characteristics, applications, and research progress at home and abroad. Finally, the challenges and development trends of pulsed laser deposition and pulsed laser liquid-phase ablation in terms of the preparation process and properties of nanomaterials are discussed.

Trapiche structure refers to a special structure comprising arms, core, and main body. In this study, the spectroscopic characteristics and element, structure are investigated using various modern testing methods. The results showed that the infrared spectrum of beryl agrees with the characteristics of water-type beryl of alkali-deficient structure. The Raman spectra show that the components of the core and arms are consistent with that of the main body, which belongs to beryl. The UV-Vis absorption spectra showed that Fe2+ exists in octahedron and tunnel, confirming the reason for the blue color of the sample. The composition analysis shows that high content of Fe2+ exists in the periphery and arms of hexagonal, with deeper blue color. The Trapiche arms' position of the aquamarine agrees with the hexagonal columnar plane, which belongs to the Trapiche-like gem. The microscopic characteristics show that the "arm" comprises a large number of directionally arranged flocculent inclusions, which are jointly caused by defects formed in the process of crystal-layered outward growth and parallel concatenation according to the theory of crystal-layered growth.