In optical wireless communication,undesirable channel is the main factor affecting system reliability,and placing an equalizer with opposite channel characteristics at the receiving end can offset the negative impact of the channel on the signal,so as to correct the inter-code crosstalk problem caused by multipath delay and other factors,and enable the signal to be recovered and reconstructed at the receiving end.On the basis of summarizing the research progress of equalization techniques both domestically and internationally,the article compares and summarizes various typical channel equalization techniques for reference,including zero forcing equalization,minimum-mean-square-error equalization,decision feedback equalization,Volterra equalization,etc.In practical applications,appropriate equalizers can be selected based on specific requirements and equalization algorithm characteristics to achieve channel equalization.Finally,the development prospects of channel equalization technology in optical wireless communication are prospected,providing new ideas and reference value for future researchers to explore in this field.

In polarization imaging detection,polarization multi-channel video sequence brings challenges to data transmission and processing,while detection accuracy depends on high-resolution images.Therefore,super resolution computing imaging becomes the key technology of polarization imaging detection system.A polarization video super-resolution reconstruction method is proposed based on enhanced alignment and multi-attention fusion.A three-level cascade structure is adopted to achieve feature alignment.Each level of features is obtained by twice downsampling of the upper level features,and feature alignment is performed by using deformable convolution guided by optical flow; In the fusion stage,multiple attention mechanisms,including temporal attention,spatial attention and channel attention,are combined to make full use of inter channel dependency and spatiotemporal correlation to improve the effect of super-resolution reconstruction.qualitative and quantitative comparative experiments were conducted between the method proposed and other video super-resolution methods,such as VSR-DUF,RBPN,EDVR,RLSP,RSDN,RRN,DARN,MSAWN,on 0°,45°,90°,135°polarized videos.Experiments show that the method outperforms other algorithms in terms of peak signal-to-noise ratio and structural similarity metrics,and that the high-frequency texture detail restoration of video frames is richer and closer to the original HD image frames from the polarization imaging system.

In off-axis digital holography and non-coherent light imaging research,spatial frequency domain filtering plays a crucial role in reconstructing both the amplitude and phase information of the target object.The selection and precise localization of the signal spectrum have a profound impact on the quality of the phase reconstruction after filtering.Even minute pixel-level differences can lead to severe distortions in the reconstructed phase.To address this challenge,a method for signal spectrum localization and interference suppression in digital holographic microscopy is introduced.The approach adapts the filtering shape and size based on the histogram distribution characteristics of the holographic spectrum.Additionally,it employs the centroid method for rapid and accurate localization of the signal spectrum's center and employs morphological processing in the frequency domain to eliminate interference in the vicinity of the signal spectrum.:This method achieves adaptive filtering of the signal spectrum,thereby improving the quality of phase reconstruction.The phase simulation in this study was conducted using a two-dimensional mountain-shaped graph,and experimental validations were performed by setting up the optical path to capture the digital area on the USAF 1951 resolution test chart as well as onion epidermal cells.Simulation and experimental results demonstrate that this algorithm can achieve high-quality phase reconstruction while effectively suppressing interference,enhancing the imaging quality of off-axis digital holography systems.

Using lensless imaging based on Fresnel aperture coding,low-cost and lightweight incoherent optical imaging systems are constructed,which improves the possibility of becoming an everyday application.However,it still suffers from poor image reconstruction quality due to the difference in gradient domain sparsity between the twin image and the original image in the reconstructed imageIn order to improve the imaging quality,this paper proposes to use the augmented Lagrangian function method and the alternating direction method based on total variational regularization to realize the reconstruction of Fresnel aperture-coded lensless imaging.The experimental results show that the algorithm we use improves the quality of the reconstructed image and also recovers more sharp details of the image compared to the two-step iterative shrinkage/thresholding algorithm (TwIST).

A measurement method that combines parallel compressed sensing and temporal ghost imaging for the high-speed detection of non-periodic time-varying light signals is proposed.With the help of the high-speed modulation ability of the spatial light modulator DMD,the fast time-varying signal can be recovered within a single exposure time of the detector,with good recovery effect for non-periodic fast time-varying signals.Through experimental verification,this method can recover time-varying signals with a frequency of 1kHz and has a high signal-to-noise ratio.

Fiber-optic frequency transfer systems enable high-precision transmission of frequency signals.However,in long-distance frequency transmission,the signal optical power is constantly lost,which needs to be compensated by using an optical amplifier.Based on the good performance of two-stage amplifier,a two-stage bidirectional erbium-doped fiber amplifier (Dual-stage Bi-EDFA) that can be used for fiber-optic frequency transfer is designed,and the scheme is experimented and analysed.The results show that the measured gain of the scheme is up to 27.5dB,the noise figure is 3.56dB,and the gain flatness is less than 0.3dB.The scheme is applied to a 160km frequency transfer system with 1.09×10-14@1s and 2.36×10-17@10000s frequency transmission stability.

The BBO crystal is a non-linear frequency conversion crystal that is widely used in optical fields such as laser frequency doubling,frequency mixing and optical parametric oscillation.However,due to the large departure angle of the crystal during the quadrupling process,the resulting frequency doubled light is gradually separated from the fundamental frequency light,which reduces the quadrupling efficiency.The effect of the incident spot shape on the quadrupling efficiency of the BBO crystal is simulated for both circular and rectangular shapes during the 532~266 nm frequency doubling process.The results show that the use of a rectangular spot incident on the surface of the BBO crystal can extend the effective doubling aperture length,reduce the effect of the walk-off effect on the doubling light and significantly improve the quadrupling efficiency.

Due to the limitation of the number of pixel,the wide band and high resolution are difficult to meet at the same time.Raman spectrometer with wide band and high resolution is designed for 532nm excitation wavelength.The whole spectral range is divided into four bands according to the limiting resolution requirement of first band,and the integrated design of switching between different bands is completed by using rotating grating and rotating focusing mirror,and the spectral range of Raman spectrometer is 80~4000cm-1 and the resolution is 1.2cm-1.Taking into account the large size of the detector,in order to avoid interference of the components,the components in the system have enough distance between them.Compared with similar products in the market,the spectrometer has a wide band and high resolution without replacing other components inside the structure,which saves the cost to a certain extent.

Studies have shown that the photonic nanojet produced by spherical microparticle has an extremely narrow half-height width and can greatly improve the lens resolution.Microparticle preparation may result in a nonstandard microsphere,which may affect the characteristic parameters of the photonic nanojets.The characteristics of photonic nanojet (PNJ) generated by egg-shaped microcolumn are calculated by the (2D) finite difference time domain (FDTD) method.The results show that the incident and outgoing surface curvature can regulate photonic nanojet generated by egg-shaped microcolumn,the effect of the incident light wavelength and refractive index on the photonic nanojet produced by the egg shape is further investigated.This work provides the characteristic parameters of the photonic nanojet generated by egg-shaped microcolumn,which provides a reference for the future work.

Weyl semimetals (WSMs) have unique bulk energy band structures and non-trivial surface states.The revelation and study of their optical properties are of great significance for understanding this kind of materials and expanding related applications.In order to explore the interaction between light and WSM,an attenuated total internal reflection structure is proposed to study the dispersion and coupling properties of WSM.Starting from the dielectric function tensor,the anisotropic transmission matrix is used to solve Maxwell′s equations,and the Fresnel reflection coefficient is obtained to study the dispersion properties of WSM.On this basis,a polar crystal film with a subwavelength thickness is introduced,and the hybrid dispersion curve is obtained through the co-excitation of the dielectric function epsilon-near-zero (ENZ) mode and the surface plasmon polaritons.The findings show that both high-frequency and low-frequency branches of the dispersion relation exhibit strong coupling at the anti-crossing point.The WSM-based coupled hybrid mode has the characteristics of high propagation characteristics and subwavelength light confinement,which can provide a theoretical basis for the preparation and application of future infrared optoelectronic devices.

The article is based on the Two Photon Polymerization (TPP) effect,namely the Two Photon Lithography (TPL) 3D printing technology,which achieves the fabrication of ultra diffraction limits and highly complex structures.It also achieves the processing of large aspect ratio nanopillars and metasurfaces composed of these nanopillars.The effects of different TPP process parameters on the nanopillars size of IP-Dip photoresist are studied,and the parameters are optimized.The innovation of this paper is in the following two points:(1)Analyzed the size changes of nanopillars under different laser parameters,and identified the threshold parameter corresponding to the minimum linewidth to prepare nanopillars with high aspect ratios.(2)For the optimization of fabrication steps,steps such as UV curing and supercritical carbon dioxide drying were added after the development step,are used to ensure that the nanopillars does not collapse and has good stability.The rectangular nanopillars with a maximum aspect ratio of nearly 15∶1 and a minimum line width of 214.80nm are prepared stably,and the circular nanopillars with a maximum aspect ratio of nearly 20∶1 and a minimum diameter of 145.44nm are prepared stably,and the prepared large aspect ratio nanopillars are applied in the fabrication of metasurfaces.

Based on the sinusoidal phase-modulation laser self-mixing interference technique,the precision measurement of the small vibration on the rough surface is realized,such as speaker surface or white paper.The 532nm solid-state laser is selected as the laser light source.And the sinusoidal phase-modulation of the laser is achieved based on the electro-optical modulator,with a corresponding modulation frequency of 251kHz.By using the mixer/filter circuits,the high signal- to-noise ratio sinusoidal and cosine function laser power oscillation signals caused by displacement change are extracted from the self-mixing interference optical fringes modulated by sinusoidal phase-modulation,further obtaining the phase change of the laser caused by displacement change.Therefore,the vibration and displacement of external targets can be efficiently calculated from the phase change of the laser.By comparing the measurement results with a precision displacement platform with an accuracy of 50nm,the two instruments showed good agreement,and the performance of the laser self-mixing interferometer was experimentally verified.The new technology can provide reliable technical support for high-precision low-frequency micro-vibration and micro-displacement measurement.

Turbidity measurement has important applications in water quality monitoring and other fields.Aiming at the problem of large-scale turbidity measurement,a turbidity measurement method based on equivalent minimum optical path is proposed.Using the 90 ° scattering method,the light intensity intercept is calculated by linear fitting of multiple groups of light paths and scattered light intensity measurements,and the mathematical relationship between the light intensity intercept and the turbidity to be measured is established.The light intensity intercept represents the equivalent scattered light intensity under the condition of minimum optical path,so as to reduce the influence of optical path under high turbidity,and ensure the high measurement accuracy in the low turbidity and high turbidity range.An experimental device for turbidity measurement with 13-path combination was built.The experimental results show that the maximum relative error of this method is 2.818% in the range of 250~2000 NTU.Compared with the direct measurement of scattering method,the average relative error is reduced by about 71%,which expands the measurement range of scattering method on the premise of ensuring the measurement accuracy.

Aiming at the problems of low calibration accuracy and large depth direction error of traditional calibration methods based on BP neural network,a monocular camera calibration method based on phase target and Radial basis function(RBF)neural network is proposed.The feature extraction method adopts a three-step phase shift method,and the multi frequency method is used to calculate the absolute phase.The absolute phase carried by the phase target feature points is converted into three-dimensional space,and the corresponding relationship between the feature point image coordinates and world coordinates is established.Finally,the RBF neural network is used to directly map the two-dimensional image coordinates to the three-dimensional space coordinates.The experimental results show that compared with the traditional use of BP neural network for calibration and the calibration results of checkerboard and circular calibration targets,the average calibration error of this method is 0.0980mm,At the same time,under a focal length of 1.4mm and a 220 ° field of view fisheye lens,high accuracy can still be maintained,proving the feasibility and effectiveness of the proposed method.

In order to solve the problem of poor vibrational localization of phase-sensitive optical time-domain reflectometer (Φ-OTDR) system caused by random coding method,a cascade modulation method of random code fused with long pulse is proposed.The acousto-optic modulator and semiconductor optical amplifier are used to realize the fusion modulation of random code and the long pulse,respectively,to improve the extinction ratio.The autocorrelation random code is used to generate the pulse train,and the digital quadrature demodulation algorithm is designed to obtain the beat frequency signal amplitude and phase information.The experimental results show that the scheme can improve the extinction ratio by 13.7dB with 40 ns-width pulse and 4 km-length sensing fiber.When the vibration signal frequency is 200Hz,the root-mean-square error of the vibration signal localization is 2.1m,and the maximal absolute error is 3.8m,which improves the vibration signal localization accuracy.The research provides a new method for the localization performance enhancement of the coded Φ-OTDR system.

To improve the accuracy and stability of the visible light indoors three dimensional positioning,a visible light indoors positioning method based on deep learning and received signal strength indication filtering is proposed.Firstly,all received signal strength indication samples acquired on each reference point are collected,a clustering algorithm is used to filter the received signal strength indication samples,the received signal strength indication samples with significant deviation in the low value cluster and high value cluster are eliminated; then,the deep neural networks regression model is trained on the high accuracy radio map,so as to learn the statistical relationship between the receiver position and the receive signal strength.Simulation results show that the average positioning error of the proposed method is lower than 4cm in a 6m×6m×3m room,it also has the ability of LED scalability.

To improve the fluorescence detection sensitivity of multi-core fiber,based on the spatial conduction theory model of multi-core fiber,the effects of the number of multi-core fiber,the core radius of excitation fiber,the core radius of receiving fiber and their numerical aperture on the coupling efficiency of multi-core fiber are analyzed.To improve the coupling efficiency,the curvature radius and spacing between non-spherical lenses in the coupling system are designed and optimized.Based on the analysis and optimization of the parameters,a multi-core optical fiber fluorescence quantitative detection system is constructed.Quantitative tests are conducted on different concentration gradients of Rhodamine 6G solution.Compared with direct coupling,the designed multi-core optical fiber coupling system shows an increase of 80.171% and 95.314% in excitation and emission light coupling efficiency,respectively,starting from below 10%.The lowest detection concentration is reduced to 2.08759551×10-9nM/L,and the fluorescence intensity at this concentration is increased by 4.5 times compared to direct coupling.The feasibility of the multi-core optical fiber coupling system is further validated,demonstrating that increasing the optical coupling system can effectively improve the sensitivity of fiber-optic fluorescence quantitative detection and meet application requirements.

Electron microscope and other instruments are important tools to study the microstructure of materials,often working in a vacuum environment.In order to quickly target the target area measured by the electron microscope,it is necessary to introduce an auxiliary optical microscope to provide a spatial image of the sample area directly.This paper introduces the design of an ultra-high vacuum optical microscope system for direct observation in ultra-high vacuum environment.The optical microscope objective lens has a long working distance of 21.8mm,achieving 40X optical magnification and transverse 1.28μm,longitudinal 1.59μm actually measured high resolution imaging effect,which can assist many kinds of electron microscopy instruments to search the target area.The objective is divided into two groups,the front group is in ultra-high vacuum,the rear group is outside ultra-high vacuum.The distance between two groups is 680mm.And the whole microscopic objective is controlled by the vacuum six-dimensional adjustment frame to scan the target sample,which has a very obvious effect on improving the detection efficiency of the electron microscope.In addition,the microscope can also be used in vacuum mechanical stripping and other systems requiring optical assistance.

The rapid implementation of national major projects such as space remote sensing,deep space exploration,space strategic equipment in China,requests the highly productive manufacture of large-aperture complex optical components.A flexible grinding technique based on industrial robots is suggested to increase the processing effectiveness of the grinding stage in the optical processing process.The differences between flexible grinding technology,class rigid grinding,and conventional grinding technology are compared.And a const-volume removal characteristic model for flexible grinding is presented and proven.Investigation is done into the connections between dwell time,pressure,and rotational speed and grinding removal volume.In the experiment,the grinding removal efficiency of flexible grinding was 0.59mm3/s which was higher than that of conventional small tool grinding which was 8.4×10-2mm3/s.For the effective grinding of large diameter SiC space mirrors,the flexible grinding method put forward in this study offers a novel technological solution.