Aiming at the problem of free-space optical（FSO） link line-of-sight constraint, this paper proposes an optical intelligent reflective surface（OIRS）-assisted hybrid FSO/radio frequency（RF） system, introduces the system model. OIRS is used to solve the obstacle occlusion problem, its auxiliary FSO link obeying the Malaga distribution under geometric and jitter errors, the RF link obeying the Nakagami-m distribution with arbitrary correlation and using equal-gain combined reception technique at the destination node. The closed-form expressions for the outage probability and average bit error rate of the hybrid FSO/RF system are derived, and asymptotic analysis of the outage probability is performed. The simulation results show that the interrupt and bit error performance of the OIRS-assisted hybrid FSO/RF system depends on the one channel with worse quality, and the bit error performance of the binary phase-shift keying modulation is better than the binary frequency-shift keying modulation.

In order to overcome the influence of atmospheric turbulence effect on the performance of wireless optical communication system, it is necessary to establish a turbulence model which can accurately describe the fluctuations of atmospheric refractive index. This paper summarizes the research progress of atmospheric turbulence models at home and abroad, analyzes the theoretical establishment of different atmospheric turbulence models in depth and compares their application ranges. At the same time, the channel model of atmospheric established in the actual atmospheric turbulence measurement is introduced. Finally, the development trend of atmospheric turbulence model is forecasted.

Aiming at the problem that the research scene of multi Bessel Gaussian beam distorted wavefront correction under atmospheric turbulence interference is single, a multi Bessel Gaussian beam distorted wavefront correction method based on Gasberg Sexton（GS） algorithm is proposed, and the anisotropic turbulence phase screen is obtained by using the power spectrum inversion method. The distorted wavefront correction of two kinds of multi Bessel Gaussian beam with different sign topology and the same sign topology under the influence of three different atmospheric turbulence refractive index structure constants is simulated and analyzed. The simulation results show that the purity of the target orbital angular momentum（OAM） mode of the two kinds of multi Bessel Gaussian beam after correction can be improved by more than 12%, and the dispersion of OAM spectrum can also be effectively suppressed.

In order to improve the spectral efficiency of existing optical spatial modulation systems, an optical generalized quadrature spatial modulation（OGQSM） technology is proposed, in which multiple transmitting optical antennas are simultaneously activated in the in-phase and quadrature domains to transmit the real and imaginary parts of the modulated signals respectively. This technology extends the modulation symbols to the in-phase and quadrature domains, so that the system can carry more bits in the spatial domain, thus improving the spectral efficiency and bit error performance of the system. The Malaga turbulent channel which is suitable for all turbulent states is used to analyze the OGQSM system bit error performance of the proposed technology under the combined action of atmospheric turbulence, pointing error and path loss. Monte Carlo simulation results show that, compared with the existing optical spatial modulation technology, the proposed OGQSM technology can obtain better spectral efficiency and error performance, and the number of receiving optical antennas is positively correlated with the bit error performance of the system, the pointing error and the atmospheric turbulence intensity are negative correlated with the bit error performance of the system.

In order to study the average bit error rate performance of satellite-ground laser communication system under the combined influence of atmospheric turbulence, pointing error and various noises. In this paper, a combined attenuation model of atmospheric turbulence and pointing error is established using the Gamma-Gamma channel model, and a closed expression for the average bit error rate of the satellite-ground laser communication system with respect to the combined attenuation model is derived by combining various noises. The research results show that when the satellite orbit altitude is 400 km, zenith angle is 45 °, wavelength is 1550 nm and the normalized ratio of equivalent beam and the pointing error displacement standard deviation（jitter） is 4, the average bit error rates corresponding to total noise, thermal noise and background noise are 1.519×10-7、6.907×10-8、1.357×10-8 respectively.

In order to further improve the information transmission quality and network performance of the wireless ultraviolet optical communication network, this paper proposes a novel wireless ultraviolet light cooperative communication network. The network nodes adopt the decoding and forwarding mode, and set the priority of each node, so as to realize the real-time forwarding cooperation strategy of network nodes. The paper simulates and analyzes the normalized throughput, average latency of each node of the new wireless ultraviolet light communication network with or without cache setting, and with or without cooperation. The simulation results show that when there is no cache setting, with the increase of the success rate of data frame transmission, the high-priority nodes always have higher normalized throughput, while the low-priority nodes lose data frames and the normalized throughput decreases. When cache is set, the normalized throughput of each node increases with the increase of cache. Compared with non-cooperation, cooperative ultraviolet light communication network has higher node normalized throughput and average latency.

In response to the problem of existing traditional wave division multiplex（WDM） cannot simultaneously meet the needs of operators for large-scale deployment and cost reduction and efficiency improvement. This paper analyzes the advantages of metro box WDM devices over traditional WDM devices in terms of open decoupling, low energy consumption, and low cost. Combining demand scenarios such as internet data center（IDC） and metropolitan area cloud networks, the paper proposes the network deployment and application suggestion of metro box WDM devices, which has strong feasibility.

To explore the impact of source coding on light fidelity（Li-Fi） technology, this paper studies four different source codes methods: non return zero（NRZ） code, return-to-zero（RZ） code, carrier suppressed return-to-zero（CSRZ） code and double binary code, and builds the Li-Fi system based on wave division multiplexing（WDM） by using OptiSystem software to discuss the performance influence of the four codes on the Li-Fi system based on WDM. The simulation results show that the NRZ code type performs well in transmission distance at 10 Gb/s transmission rate and CSRZ code type shows strong anti nonlinear performance and advantages in transmission distance at 40 Gb/s transmission rate.

Aiming at the problem of harsh information synchronization conditions in optical chaotic confidential communication, a bidirectional communication system based on optical chaos is proposed. First, two laser beams emitted by a semiconductor laser（SL） are coupled with a partially translucent optical mirror to generate chaotic power, and the internal parameters of two SLs are set to generate synchronous chaotic carriers according to the delay rate equation of SL. Then, the decryption signal is obtained by monitoring the synchronization error of the signals at both ends and comparing with the signals at the receiving end. The synchronization, signal decryption process and robustness of the system are simulated and analyzed. The simulation results show that the system can realize synchronous communication, recover the secret signal and has good robustness.

In order to overcome the problems of transmission capacity and Doppler frequency shift in high-speed environments, a novel high-speed railway mobile communication two-layer link structure based on radio over fiber（RoF） and orthogonal time frequency space（OTFS） modulation technology is proposed. In the high-speed railway communication environment, wired part uses RoF technology as a solution for distributing high-frequency broadband wireless signals along the railway. The wireless part uses OTFS modulation to solve the problem of Doppler frequency shift （DFS） destroying the orthogonality between subcarriers of existing wideband orthogonal frequency division multiplexing（OFDM） signals by converting time-frequency domain signals into relatively stable time-delay Doppler domain signals. The simulation results show that under the same transmission conditions, when the bit error rate of OFDM modulation drops below 10-1, the bit error rate of OTFS modulation has dropped to the order of 10-4, and the transmission performance is better.

In order to overcome the influence of phase and noise on the current angle of arrival（AOA） measurement in the microwave photon field, and to achieve a wide range of AOA measurement in a two-dimensional plane, a two-dimension AOA estimation scheme based on microwave photonic de-chirping reception is proposed and experimentally demonstrated in this paper. At the receiver of this scheme, an L-shaped antenna with a fixed delay time method is used to estimate the one-dimensional AOA. The elevation angle and azimuth angle of two-dimension AOA can be obtained by using the one-dimensional AOA. The experimental results show that when the antenna spacing is 5 m and the signal-to-noise ratio of the input linear frequency modulation continuous signal is 10 dB or -7.8 dB, the estimation results of one-dimensional AOA of the proposed scheme have a wide range of characteristics, and the estimation error is less than 2° in the range of -79°~74°, at the same time, the calculated elevation angle and azimuth angle have high accuracy in a large range.

In order to improve the information transmission density and capacity of fiber Bragg grating sensing networks, a fiber Bragg grating multiplexing technology based on ultrasonic pulse excitation is proposed and experimental analysis is conducted. By introducing ultrasonic pulse excitation into a single grating and a grating string respectively, chirping occurs in the single grating and grating string. The experimental results indicate that in the single grating experiment, ultrasonic pulses reduce the relative reflectivity of the grating. In the grating string experiment, when the ultrasonic pulse causes the relative reflectance of one grating to decrease, the relative reflectance of the other gratings increases, which can effectively separate three gratings with similar spectra.

Optical fiber is more and more widely used in low temperature environment, and the research and exploration of more excellent low temperature coatings and optical fiber low temperature performance are gradually deepened. G.652 single-mode fiber with three different coatings is used for fiber pressure resistance test. The surface morphology of the fiber after pressure resistance test is analyzed. At the same time, the anti-pressure and additional attenuation properties of the fiber coating after low temperature test are tested and characterized. The experimental results show that the higher the pressure resistance value of the fiber, the smaller the low temperature additional attenuation value, the better the low temperature resistance performance, and the difference between the pressure resistance value of the fiber before and after the low temperature test is small.

In order to solve the problems of difficulty and high cost in installing and maintaining sensors in water injection well, a target type fiber Bragg grating（FBG） flow sensor based on lever-hinge structure is designed and theoretically analyzed. FBG1 and FBG3 in the sensor structure are pasted on the two ends of lever-hinge respectively to form a differential structure, which makes the sensor have the characteristics of low start-up and large range. Temperature compensation grating FBG2 is used to measure the temperature and flow simultaneously. The structure of the sensor is simulated and optimized, and the optimization parameters of the sensor are obtained. Based on these parameters, flow measurement, repeatability, temperature measurement, temperature compensation and stability experiment are carried out. The experimental results show that the sensor can simultaneously measure the fluid flow and temperature, its temperature sensitivity is 17.94 pm/℃ and the flow resolution is 0.039 L/s.

In view of the design requirements of the characteristic frequency of the photoacoustic cell in the photoacoustic spectroscopy gas detection system in specific occasions, the first eight acoustic modes are obtained by using the finite element analysis method and taking the first order cylindrical resonant photoacoustic cell as the research object. This paper simulates and analyzes the influence of the radius and length of the resonant cavity and buffer chamber on the characteristic frequency and photoacoustic signal strength of the photoacoustic cell. The simulation results show that when the radius of the resonant cavity is 3 mm, the length of the resonant cavity is 120 mm, and the radius and length of the buffer chamber are 14.7 mm and 60 mm respectively, which are the optimal dimensions for the characteristic frequency of the photoacoustic cell around 1 400 Hz.