Based on the resonant coupling principle between the photonic crystal ring cavity and the waveguide,a dual-function device of a six-port two-dimensional photonic crystal circular lattice with square arrangement composed of ring defects and line defects was designed.The transmission characteristics of the two-dimensional photonic crystal device were analyzed using the plane wave expansion method (PWEM) and finite-difference time-domain method (FDTD),and the transmission characteristics curve and light field distribution were obtained.Then,the influence of the inner diameter of the central column of the ring cavity and the radius of the dielectric column in the coupling region on the filtering efficiency and transmission rate of the output port was discussed.The results show that by adjusting the parameters of the center columns of the ring cavity and the dielectric columns in the coupling region,the device can simultaneously achieve good filtering and beam splitting functions.For input light waves with wavelengths of 1.510 μm and 1.515 μm,the device mainly has a filtering function,with filtering efficiencies of close to 99.95% and 93.27%,respectively.For input light waves with a wavelength of 1.490 μm,the device mainly has a beam splitting function,with a maximum transmission rate of 99.74%.

The micro-dsplacement sensor based on double-layer grating Talbot effect has the advantages of high resolution and anti-electromagnetic interference,however,its accuracy is affected by the fabrication and assembly errors of gratings. In this paper,COMSOL software is employed to simulate and analyze the influence of the fabrication errors (including the line width,thickness and duty cycle of the grating) and assembly errors (including the included angle of layers,included angle of grid lines and grating spacing of double-layer grating) of the gratings.The final results shows that the allowable error of the grating period is less than ±0.1 μm,the influence of the thickness of the grating on the diffraction efficiency is negligible,and the optimal value of the duty cycle is 0.5.In addition,the included angle of layers,included angle of grid lines of double-layer grating also have a significant impact on the diffraction efficiency,the allowable errors of included angle of layers,included angle of grid lines and grating spacing of double-layer grating are less than 1°,0.1° and ±0.1 μm,respectively.The analysis will be helpful to compensate for various types of errors in the future,thereby ensuring high-precision micro-displacement detection system based on grating Talbot effect.

Aiming at the current limitation that most terahertz (THz) absorbers can only possess a single narrow absorption peak and are unable to achieve dynamically tunable absorption to meet practical demands,a dynamic tunable absorber based on vanadium dioxide (VO2) and photoconductive silicon (PSi) metasurface in THz regime is proposed in this paper.The proposed design consists of five layers,namely the PSi patterned layer,two layers of silicon dioxide (SiO2) dielectric layers,the VO2 modulation layer and the gold (Au) metal substrate.The simulation results show that the designed absorber has the dual-band absorptive characteristic with a conductivity of 10 S/m for VO2 (σvo2) and 1.5×105 S/m for PSi (σPSi).The absorptivity (A(ω)) in the dual-band of 0.50—0.79 THz and 1.93—2.25 THz is over 90%,and the corresponding relative bandwidths are 44.96% and 15.31%,respectively.For σvo2=2×105 S/m and σPSi=1.5×105 S/m, the designed absorber exhibits a single-band absorptive characteristic in 0.96—1.63 THz with a relative bandwidth of 51.74% (A(ω)>90%).The proposed design in this paper has the characteristics of wide-angle stability (60°),polarization insensitivity and dynamic tunable wave-absorption,which has potential application value in multifunctional devices such as modulation,sensing and electromagnetic stealth.

Aiming at the problems of large waveguide loss and low optical confinement factor of long-wavelength infrared quantum cascade laser (QCL),this paper studies in detail the effects of the three-dimensional optical structure of 8.3 μm long-wavelength infrared QCL chip on the optical waveguide and the electrical performance.In the direction of epitaxial growth,the effects of material thickness,doping concentration and other factors on the optical waveguide performance of "InP+InGaAs" and "All-InP" waveguide structures are investigated and compared.The results confirm that the "All-InP" waveguide structure can achieve lower waveguide loss and mode overlap coefficient.In the direction of ridge waveguide sides,the effect of ridge width on the optical waveguide performance is investigated.It is found that the mode overlap coefficient of the chip with ridge width less than 10 μm can be reduced by using InP∶Fe buried heterostructure (BH) on both sides of the ridge.In the direction of the cavity surface film,the optimization of the mirror loss is accomplished by studying the relationship between the film thickness and reflectivity.The results show that when the thickness of the Y2O3 antireflection (AR) coating is 990 nm,the reflectivity of the antireflection and the mirror loss are 3.43% and 3.37 cm-1,respectively,and which then lead to the maximum wall plug efficiency (WPE) of 12.91%.

Chirality,which generally manifests itself as the inability to coincide with its mirror image structure by translation or rotation.In optics,the interaction between chiral structures and circularly polarized light produces circular dichroism (CD),which has great applications in polarization switching,filtering,and sensing.Here,a design strategy is proposed for a single-layer all-dielectric diatomic metasurface working in the near-infrared (NIR) band,where the interference effect generated between neighboring nanoscale silicon pillars is capable of inducing spin-selective transmission of circularly polarized light,producing up to 95.33% of the CD amplitude at 292.33 THz.The metaface unit can be reconfigured by varying the relative rotation angle of the right cross elliptical silicon pillars,further providing a flexible way to switch the type of response for CD spectrum.The proposed design can also be employed as a polarization converter from linearly to circularly polarized light and still have reconfigurable properties.Therefore,the designed diatomic chiral metasurfaces can be generally applied to dynamic multifunctional devices,which provides a new idea for the design and development of integrated photonic devices.

A fiber Bragg grating (FBG) acceleration sensor with an increased sensitivity symmetric simply supported beam structure is proposed to meet the requirements of high sensitivity vibration detection at medium and low frequencies.Firstly,theoretical analysis is conducted on the sensor model,followed by numerical optimization of the sensor structural parameters.In order to meet the requirements of high sensitivity,the thickness of the simply supported beam is only 0.5 mm.Then,finite element method is used to simulate and analyze the sensor.Finally,the actual sensor is processed and experimentally tested.The experiment shows that the resonant frequency of the sensor is 294.6 Hz,The sensitivity is 307 pm/g,and the lateral anti-interference degree is less than 2.7%.It can be used for measuring vibration signals in the frequency range of 30—130 Hz.

Aiming at the low accuracy of existing nighttime image visibility detection algorithms,this paper proposes a nighttime visibility classification algorithm based on stable light sources.Firstly,all stable light source street lights in the image are detected by the target detection network,and all light source blocks in the image are obtained.Secondly,the light source blocks are fog classified by the classification network.At the same time,all the light source blocks are sorted by size and average size and the corresponding weights are obtained.Finally,the visibility levels of nighttime images are classified after combining the classification results of light source blocks with their weights to conduct statistical analysis.The experimental results show that the accuracy of the nighttime visibility classification algorithm in this paper reaches 77.6% in the real social dataset,and the classification results are more accurate than the existing methods,and have good generalization in different scenarios.

In order to achieve accurate subpixel mapping (SPM) results,this paper proposes a dual path subpixel mapping method for hyperspectral images (HSIs) using super-resolution fusion (SRF) technology.In this method,two paths are used to process hyperspectral images.In one path,the abundance image of the original hyperspectral image is interpolated to obtain a high resolution abundance image.In the other path,the super-resolution fusion technology is used to process the original image using multispectral images (MSIs) to obtain a new high resolution abundance image,and the results of the two paths are fused.Because the abundance images under the interpolation path and the super-resolution path are combined,the predicted values with rich spatial-spectral information are obtained.Finally,the final sub-pixel mapping results are obtained according to the predicted values.Experimental analysis on two real datasets shows that this method can further improve the accuracy.

The propagation of a femtosecond laser pulse as a filament in a medium is subject to complex linear and nonlinear effects and it is significant to study the filamentation characteristics of femtosecond lasers in a medium.Since the beam propagation is highly sensitive to the shape and wavelength of the input beam,the distribution of energy and intensity in the medium can be controlled by modifying both the shape and wavelength of the beam.In this paper,we investigate the propagation characteristics of super-Gaussian and wrapped beams at varying wavelengths and shapes,based on the nonlinear Schrdinger equation.Our results show that super-Gaussian beams can facilitate faster beam focusing and induce changes in the intensity and plasma density values in the medium.Furthermore,we find that using wrapped beams composed of super-Gaussian beams and surrounding annular beams,which form an “energy reservoir”,is more favorable for promoting and sustaining beam propagation.Moreover,we observe that decreasing the wavelength of the beam leads to higher confinement intensity and faster beam focusing with better intensity preservation.

Aiming at the problems that there are the insufficient estimation performance and the inadequate channel feature extraction when the existing channel estimation algorithms based on the deep learning (DL) for OFDM systems generate the mismatch of the signal-to-noise ratio (SNR),a channel estimation scheme based on the noise estimation and multiscale channel reconstruction neural network (NE-MCRNNet) is proposed.Firstly,the noise estimation network (NENet) is designed to estimate the SNR of the current transmission environment,and then the multiscale channel reconstruction network (MCRNet) is constructed and the network is selected according to the estimated SNR value,the channel matrix at the pilot frequency is reconstructed by using the multiscale feature extraction for channel reconstruction,the ability of extracting the channel information at different scales is enhanced,finally,the channel estimation is accomplished by using the residual structure to focus on learning the high-frequency differences.The simulation result shows that the proposed channel estimation scheme can obtain the better estimation results than the traditional channel estimation,and can better adapt to the case of the SNR mismatch,so the proposed channel estimation scheme can better meet the channel estimation requirements of OFDM systems.

In this paper,COMSOL Multiphysics finite element simulation software was used to numerically simulate the paint removal depth and temperature field distribution under different laser powers and scanning speeds,and the reliability of the simulation results was verified by experiments.The results show that the higher the laser power,the deeper the cleaning depth and the higher the surface temperature of the paint layer.The slower the scanning speed,the deeper the cleaning depth,and the flatter the cleaned surface.When the scanning speed is too fast,the cleaning depth remains unchanged,and the flatness of the cleaned surface decreases.In addition,when the scanning speed is slow,the maximum temperature of the paint layer increases with the increase of the number of pulses until it stabilizes;when the scanning speed is too fast,the maximum temperature of the paint layer no longer changes with the increase of the number of pulses.The experimental results show that when the laser power is 20 W and the scanning speed is 1 250 mm/s,there is no paint residue on the surface of the cleaned substrate,the surface quality is optimal,and it meets the requirements of the coating process.

In the context of long-distance communication in atmospheric channels,the Gaussian light beam is impacted by atmospheric turbulence,leading to the problem of low energy coupling at the receiver.In order to solve this problem,a highly efficient coupling method for Gaussian spot spatial transmission in turbulent atmospheric channels is proposed.This method takes into account the distribution characteristics of Gaussian spot intensity and scintillation index (SI).By monitoring statistical values of intensity and scintillation index as feedback,the emission end is controlled to suppress turbulence-induced intensity scintillation,achieving efficient coupling of the light beam and enhancing communication system performance.Validation is conducted through a 1 km laser communication experiment.The results indicate that after adjusting the terminal based on scintillation monitoring,the average optical power increases from 19.63 μW to 24.91 μW.The scintillation index decreases from 0.140 to 0.088,and the communication bit error rate (BER) drops from 1.27×10-6 to 1.07×10-10.Under weak turbulence conditions,the communication BER decreases by four orders of magnitude.This way effectively enhances the performance of atmospheric laser communication systems,laying the foundation for the widespread adoption and application of atmospheric laser communication systems.

In order to overcome the shortcomings of stannic oxide (SnO2) film material with low conductivity and limited transmittance,SnO2 film with better photoelectric properties was obtained by doping modification.SnO2 films doped with Ti were prepared by soliquid-gelatum（sol-gel） spin coating method using anhydrous ethanol as solvent,which were 0 at%,3 at%,5 at%,7 at% and 9 at%,respectively.The structure,morphology and photoelectric properties of Ti doped SnO2 thin films were systematically analyzed by X-ray diffractometer (XRD),X-ray photoelectron spectroscopy (XPS),scanning electron microscope (SEM),atomic force microscope (AFM),ultraviolet-visible (UV-Vis) spectrophotometer and Hall effect tester.The results show that the transmittance of the samples is above 90% except for Ti doping of 9 at%.The optical band gap values first decrease and then increase with the increase of doping concentration.In addition,Ti doping reduces the resistivity of SnO2 films,and the highest figure of merit (FOM) of the samples can reach 14.45×10-3 Ω-1 when the Ti doping amount is 3 at%.