Jingyuan Liang

In adaptive optics systems, most methods rely on reconstruction techniques centered on regional or global orthogonal bases, which struggle to accommodate the multi-scale characteristics of atmospheric turbulence wavefronts. This paper adopts a hybrid basis wavefront reconstruction method based on mutual information sorting, combining Zernike modes with Daubechies wavelet modes for mutual information calculation and sorting. The modes with the highest correlation are selected for reconstruction, effectively reducing the scale of the reconstruction matrix while considering both global and local features. The reconstruction results show that when the number of modes is 20, the root mean square (RMS) of the wavefront residual error of the hybrid basis reconstruction drops to 0.14 rad, outperforming 0.19 rad of the Zernike mutual information method and 0.33 rad of the Zernike expansion method. The peak-to-valley (PV) value after wavefront correction converges to 0.057 μm at the 39th iteration, demonstrating a faster convergence speed and smaller residual error; the RMS value converges to 0.027 μm at the 77th iteration after correction.

When optical signals are transmitted in the atmosphere, they will be affected by atmospheric turbulence, causing phenomena such as light intensity flickering and light spot drift, resulting in signal intensity attenuation. In this paper, a 0.8 km and a 4 km corner reflector array experimental return link were built. Under different weather conditions, the experiment obtained light intensity data samples and echo spot video data. It analyzed the light intensity flicker and spot drift characteristics and laws of Gaussian beams under different weather conditions. The results show that the turbulence intensity increases with an increase in link distance. At the same time, the atmospheric refractive index structure constant gradually decreases in the order of sunny, light rain, moderate rain, heavy rain, and cloudy. The light intensity distribution of the 0.8 km link is weakly undulating, and the light intensity distribution of the 4 km link is moderately undulating. The distribution of the centroid range of the light spot also decreases in the order of sunny days, light rain days, moderate rain days, heavy rain days, and cloudy days, and as the link distance increases, the distribution range of the centroid of the light spot under the same weather conditions also increases. Studying the reflection characteristics of laser echoes is of great significance to wireless optical communication systems. It brings important technological breakthroughs to large-scale, high-speed wireless optical communication technology and plays an important role in the development of wireless optical communication technology.

In indoor visible light communication, a rational layout of light sources is required to ensure that multiple users at different locations in the room can obtain better communication quality and achieve uniform coverage of optical power on the receiving surface. The article investigates the performance of an indoor visible light communication system when the random layout of the Matern hardcore point process is used and compares it with the communication performance under the Poisson point process and the binomial point process. A particle swarm optimization algorithm is introduced based on the Matern hardcore point process, where the points generated under the Matern hardcore point process are used as the initial positions of the particles, and optimization adjustments are made according to the objective function to find the optimal layout. The results show that compared with the Poisson point process and the binomial point process, the use of the Matern hardcore point process to randomly lay out the LEDs makes the light intensity in the system more uniform and the numerical fluctuation of the received power is smaller. The uniformity of the indoor illumination after the combination of the Matern hardcore point process and the particle swarm optimization algorithm reaches 0.84, the deviation of the peak power is reduced by 20%, and the average signal-to-noise ratio value is 0.86, which is an increase in the average signal-to-noise ratio compared to the average signal-to-noise ratio before optimization.

In order to satisfy the large-scale access of visible light communication (VLC) users, as well as the demand for user request rate, the resource allocation problem of visible light communication with drone-assisted non-orthogonal multiple access (NOMA) technique is investigated. An efficient scheme for joint optimization of power allocation and access point (AP) location is proposed. According to the state of user channel information, a user pairing strategy with uniform channel gain difference for any number of users is designed, and an objective function of maximizing the average user data rate with constraints is constructed. For this non-convex NP-hard problem, the optimization problem with constraints is transformed into an optimization problem without constraints by introducing the idea of a penalty function and then solved by the Harris Hawk Optimization (HHO) algorithm based on the nonlinear energy convergence factor, and ultimately, the optimal user power allocation factor, as well as the location of the AP, are found. The simulation results show that the scheme in this paper can improve the average user data rate better compared to other classical schemes. The system performance of the HHO algorithm is improved by about 20.31% compared to the Particle Swarm Optimization (PSO) algorithm. The HHO algorithm based on the nonlinear energy convergence factor improves the convergence speed by about 50% compared to the classical HHO algorithm.

In free-space optical communication, the transmission of signal light and beacon light of differing wavelengths through the same atmospheric channel encounters variations in how the atmospheric refractive index absorbs and scatters light. This leads to distinct degrees of wavefront aberrations between the signal and beacon lights. In this study, we employed statistical optics to derive wavefront phase structure functions for both signal and beacon lights under conditions of strong turbulence. We explored how wavefront distortion varies among beams of different wavelengths after propagation through such turbulent conditions. Our findings revealed that as the turbulence outer scale escalates, the difference in wavefront distortion between signal and beacon lights stabilizes after an initial increase, assuming constant wavelengths. Furthermore, we observed significant changes in the relative wavefront aberrations when the inner scale of turbulence surpasses the separation between two points on the receiving apertures. As the disparity in wavelength decreases, so does the difference in wavefront aberrations. Finally, we propose a method for correcting wavefront aberrations based on coefficients of Zernike polynomials corresponding to beams with different wavelengths. This approach is validated through simulation and experimentation, demonstrating an 11% enhancement in the signal-to-optical Strehl ratio and a 0.072 increase in spot energy after the addition of correction coefficients compared with before their inclusion. These results solidify the efficacy of our method in improving adaptive optics correction accuracy.

Four-level pulse amplitude modulation (PAM4) can transmit more information in the same symbol interval, effectively improving the information transmission rate and frequency band utilization of visible light communication (VLC). This paper proposes a method for encoding and decoding the PAM4 signal based on FPGA. The PAM4 signal is studied and analyzed under different channel noise models. The research results show that the bit error rate (BER) performance of the PAM4 signal is the best under the additive noise model. The influence of the multiplicative noise on the BER of the PAM4 signal is much greater than that of the additive noise. The BER performance of the PAM4 signal depends on the variance of the noise data. The greater the variance, the worse the BER performance. At the same time, an indoor VLC system based on PAM4 is designed. The simulation results verify that the system scheme is feasible and provides a way to further realize high-speed signal transmission.

When coherent detection occurs, the polarization mismatch between signal light and local oscillator light can reduce the efficiency of coherent detection. This article combines the principle of optical mixers to derive the relationship between the polarization state and mixing efficiency of signal light and local oscillator light, and builds an experimental platform for the coherent detection of a partially coherent electromagnetic Gaussian Schell beam (EGSM). Polarization devices are used to regulate the polarization state of the signal EGSM light and local oscillator EGSM light, and different polarization states of the EGSM beams are generated. When the output power of the signal light is constant, the mixing efficiency is measured according to the output amplitude of the intermediate frequency signal. This experiment found that when the signal light is in a linearly polarized state and the local oscillator light is in a linearly polarized state, a circularly polarized state, or an elliptically polarized state, the amplitude of the intermediate frequency signal is 369.6 mv, 146.6 mv, or 92.1 mv, respectively. When the signal light is in a circularly polarized state, the amplitude of the intermediate frequency signal is 446.4 mv, 504.0 mv, or 159.2 mv, respectively. When the signal light is in an elliptical polarization state, the amplitude of the intermediate frequency signal is 94.4 mv, 124.0 mv, or 254.8 mv, respectively.

Aiming at the problem of resource allocation strategies limiting the system transmission rate in indoor visible light communication and radio frequency (VLC/RF) systems, a new resource allocation method is proposed, and orthogonal frequency-division multiple access (OFDMA) technology is introduced. The capacity of the communication system is effectively increased. In the VLC/RF system model based on OFDMA, the Lyapunov optimization method is used to transform the time averaging problem into a series of single-slot online problems to reduce its computational complexity, the optimization problem is decomposed into three independent subproblems, and the Lagrange relaxation method and convex optimization theory are used to solve the subproblems to maximize the average transmission rate of the system, and the Lyapunov drift is used to ensure the stability of the system. Simulation verifies that the Lyapunov optimization algorithm does not require iteration, which improves the optimization speed to a high extent. The simulation results show that the proposed resource allocation strategy effectively balances the system queue length and transmission rate, improves the average transmission rate of the system to the greatest extent under the premise of ensuring the stability of the system, and compares with other algorithms from the aspects of system stability and transmission rate, which proves the effectiveness of the Lyapunov optimization algorithm.