The stability of linear frequency modulated signals generated by optical fiber structure is easily affected by experimental devices and environmental factors, which leads to the change of amplitude and phase characteristics of the generated signal, and then affects the detection performance of photonic time-stretched coherent radar system. This paper mainly analyzes the impacts of experimental devices and environmental factors on detection performance of linear frequency modulated signals, including splitting ratio of optical couplers, center wavelength shift of the filter and delay perturbation of the interference arm. By simulating peak power and range resolution of signals after pulse compression under different conditions, comparing them with the results after pulse compression under the ideal condition, the influence of every factor and the parameter range to ensure the detection performance are obtained, which can provides a reference for design and implementation of photonic time-stretched coherent radar.

IEEE 1588v2 protocol is mainly used in carrier level ground time service, which can meet the requirements in 4G phase, but can not meet the requirements of some applications of 5G communication. In order to further improve the accuracy, this paper uses time synchronization technology based on white rabbit precision time protocol(WR-PTP) to achieve sub nanosecond synchronization. In this paper, after deeply studying the technical characteristics of WR-PTP, the WR-PTP clock module with long-distance transmission capability is developed based on WRPC-v4.2 kernel. By correcting the asymmetry of the transmission link, an experiment was carried out on a 100 km long-distance point-to-point optical fiber link. The measured time synchronization deviation was 41.5 ps and the time synchronization accuracy was -9.5 ps.

For a coherent optical fiber transmission system that fully compensates for the signal-signal nonlinear interaction, the communication performance of the system is mainly limited by the nonlinear signal-noise interaction (NSNI). The theoretical mod-el of the full-order NSNI is proposed, and the full-order NSNI model is verified by taking a Nyquist optical transmission system with a rate of 256 Gb/s and a 16-order quadrature amplitude modulation(16QAM) signal based on polarization multiplexing as an example. The experimental results show that only considering the first-order and second-order NSNI effects will overestimate the communication performance of the system, while the full-order NSNI model can more accurately reflect the influence of the NSNI effect on the system.

Nonlinear effect seriously affects the signal transmission in optical fiber communication, resulting in signal distortion in waveform or spectrum. In order to overcome the nonlinear effect, Darboux transform is used to synthesize the information of the soliton signal at the transmitter, and the nonlinear Fourier transform is used to demodulate the eigenvalue recovery signal at the receiver. Through the improvement of the algorithm, the computational complexity of the nonlinear frequency division multiplexing (NFDM) communication system is reduced. The simulation results show that the NFDM communication system can effectively suppress the nonlinear effect.

In order to improve the channel capacity of short code transmission in the visible light channel, a polarization-coded carrierless amplitude-phase (CAP) modulation transmission scheme for indoor visible light communication (VLC) is proposed. This solution introduces 5G-Polar code coding technology based on visible light CAP modulation, and uses a distributed cyclic redundancy check bit assisted serial cancellation list decoding algorithm. The simulation results show that low code rate and modulation order, repetitive patterns, and more candidate paths can improve system reliability. In addition, when the block error rate is 10-3, compared with the (2, 1, 7) convolutional code, the polar code can obtain a gain of about 6.3 dB.

In the real-time transmission of audio and video in visible light, the system requires high speed. In order to reduce the transmission rate, video data and audio data are collected by field programmable gate array(FPGA) modulation module at the transmitting end, and then loaded into the corresponding light emitting diode(LED) driver circuit, the light from two LEDs is projected to the photodetector at the same time, and the receiving end separates the audio data and video data according to the intensity of the voltage signal after the photoelectricity conversion, and transmits them to the corresponding terminal. Experimental results show that the system can transmit real-time audio and video at a relatively low transmission rate.

In order to realize high-speed communication between two rotating parts, a free space optical communication system suitable for double-end rotation is designed. By designing an aspheric collimator and selecting proper two-way color splitter, the optical signal can pass through the center of rotation axis, and the laser signal emitted from one rotating part can be transmitted to the light detection module in another rotating part. When the distance between the two rotating ends changes from 10 mm to 550 mm, and the relative speed changes from 10 r/min to 120 r/min, the minimum received power of the system can still meet the communication requirements, and the bit error rate is 0.

In order to monitor the bending deformation of buried pipelines due to geological instability, a method of polyethylene(PE) pipeline microbending detection based on Brillouin optical frequency domain analysis(BOFDA) technology is proposed in this paper. The fiberglass substrate strain cable is laid along the wall of the pipe to make the fiber and the pipe deform together. The Brillouin frequency shift is used to calculate the stress variation of the fiber, and conjugate beam reconstruction algorithm is used to invert the bending disturbance of the pipe. The experiment resulshows that this method can distinguish and measure the direction and displacement of pipe bending very well, and the error is less than 0.4 cm, which improves the digital safety monitoring and early warning level of pipe.

With the continuous development and progress of optical fiber specklegram detection technology and image processing technology, the sensing technology based on multi-mode fiber specklegram is becoming more and more mature. Using the optical fiber space status information carried by the multi-mode fiber output specklegram, the interference information and the degree of interference of the fiber can be obtained, which has important application value. Starting from various application fields, the application and development of the multimode fiber specklegram are introduced in detail. The endless research results and rich application scenarios show that the fiber speckle pattern sensing technique has strong vitality. Finally, the paper looks forward to the future research directions of multimode fiber speckle patterns in the field of sensing.

In the laser communication system, the detection accuracy of the laser light spot is of great significance to the communication system. In order to improve the accuracy of light spot positioning, a laser nutation positioning algorithm based on photodetector is proposed, the basic principle of space light to single mode fiber coupling is analyzed, and the effect of lateral offset on coupling efficiency is studied, and the expression of the nutation positioning algorithm is derived. In this paper, the positioning accuracy of nutation algorithm and the parameters affecting nutation scanning are analyzed by Matlab simulation. The simulation results show that the positioning accuracy of the nutation positioning algorithm is 0.04 μm, which meets the requirements of the communication system for light spot detection.

In order to compensate for the coupling efficiency loss of space optical-single mode fiber caused by random vibration of satellite platform, the influence of parameter selection based on nutation algorithm and random parallel gradient descent (SPGD) algorithm on the stability and convergence speed of the two algorithms is compared and analyzed. The compensation effects of the two algorithms are evaluated under typical satellite vibration spectrum conditions. The simulation results show that the average coupling efficiency of nutation algorithm is 81.26%, and the root mean square error is 7.2×10-4; the average coupling efficiency of SPGD algorithm is 80.72%, and the root mean square error is 1.9×10-3. Compared with SPGD algorithm, the root mean square error of nutation algorithm is reduced by 62.1% in the optimal case, and its stability is better.

The optical signal to noise ratio(OSNR) is one of the key indexes for health assessment and performance prediction of optical network. However, traditional methods face great challenges for computing accusation and system robustness. Based on the recurrent neural network and attention mechanism, this paper presents an OSNR calculation method based on attention mechanism. This method directly captures the logical relationship between the timing input and the OSNR, and improves the calculation accuracy of OSNR. According to different fiber input power, transmission distance and demodulation methods, a variety of experiments are designed. The results show that the proposed method can reduce the calculation error of OSNR to less than 0.360 dB.

In order to further guarantee the information security of power communication network and improve the level of network security, the influence of high electromagnetic radiation on quantum light is analyzed, and the security key encoding of two kinds of quantum key distribution (QKD) devices of phase type and polarization type in high electromagnetic radiation environment is measured. The measured results show that the phase QKD device is more suitable for the power communication network under high electromagnetic radiation environment.nication network