采用APD检测的编码瑞利BOTDA系统性能

瑞利布里渊光时域分析系统具有单光源、单端工作、非破坏的优点，为了解决系统信噪比与空间分辨率之间的矛盾，将编码技术应用到瑞利布里渊光时域分析系统中，可以在保持空间分辨率不变的前提下提高系统信噪比。提出了基于雪崩光电二极管检测和Simplex编码的瑞利布里渊光时域分析系统，系统中的随机散粒噪声功率和信号功率有关，而热噪声功率主要取决于雪崩光电二极管光电检测器的性能、与信号功率无关。由系统中与两种噪声相关的电流波动的方差和Simplex码的编解码规则可得编码系统的均方误差，由此推导了系统信噪比和编码增益公式。随着编码长度的增加，编码增益会逐渐增大并在某一编码长度后趋于稳定，因此系统存在最佳编码长度，最终推导了最佳编码长度公式，并对信噪比和最佳编码长度进行了MATLAB仿真。仿真结果表明，在基于Simplex码的瑞利布里渊光时域分析系统中，当脉冲基底1阶边带产生的瑞利散射光功率为0.5 mW时，随编码长度的增加，编码增益逐渐增大并趋于稳定值6.69 dB，系统的最佳编码长度为63 bit。

Performance of coding Rayleigh Brillouin Optical Time Domain Analysis system with APD detector

The Rayleigh Brillouin Optical Time Domain Analysis system has the advantages of single source, single ended operation and non destruction. In order to solve the contradiction between the system signal-to-noise ratio and the spatial resolution, the coding technique was applied to the Rayleigh Brillouin Optical Time Domain Analysis system and a simplex code Rayleigh Brillouin Optical Time Domain Analysis sensing system based on the Avalanche Photo Diode detector was presented. The Rayleigh Brillouin Optical Time Domain Analysis system applied coding technology can improve the signal to noise ratio while maintaining the same spatial resolution. In the system, the random shot noise power was related to signal power, and the thermal noise power that was irrelevant to signal power mainly depended on the performance of the Avalanche Photo Diode detector. By analyzing the variance of current volatility which was relevant to two kinds of noise and Simplex code encoding and decoding rules, the mean square error of coding system was obtained, then the signal-to-noise ratio and coding gain formula were deduced. With the increase of coding length, the coding gain was also increased, then stabilized at a stable value, so the system had the optimal coding length. Finally, the optimal coding length formula was deduced. By using MATLAB it is verified that as the coding length increases, the coding gain tends to a stable value of 6.69 dB when the first-order Rayleigh scattering light power is 0.5 mW in the Rayleigh Brillouin Optical Time Domain Analysis system based on Simplex code, and the optimal code length was 63 bit.