针对传统单脉冲布里渊光时域反射系统信号微弱、性能提升受限的问题, 提出了一种雪崩光电二极管(APD)检测器本地外差检测的格雷(Golay)编码布里渊光时域反射系统。分析了Golay码应用于该系统的编解码原理及系统外差检测原理, 讨论了光纤受激布里渊散射阈值对编码系统平均入纤功率的限制, 推导了系统信噪比的数学表达式, 研究系统信噪比与APD倍增因子、编码长度的关系, 分别得到了APD最佳倍增因子和系统最佳编码长度的表达式。MATLAB仿真结果表明, 选用带宽为500 MHz的APD光电检测器和峰值功率50 mW、脉冲宽度100 ns的入纤脉冲时, 系统APD倍增因子和编码长度均存在最佳值, 系统最佳编码长度的确定不仅依赖于系统的散粒噪声和热噪声功率, 还由光纤受激布里渊散射阈值共同决定。经优化计算得, 该系统的APD最佳倍增因子为5, 最佳编码长度为128位时, 在25 km光纤末端的系统信噪比比传统单脉冲系统提高了26.42 dB, 温度和应变分辨率分别达到了1.60 ℃和35.48。

Considering that for traditional single-pulse Brillouin Optical Time Domain Reflectometer(BOTDR) system, Brillouin signal is weak and the performance improvement is limited, a Golay pulse coding BOTDR system with Avalanche Photo Diode(APD) detector and local-heterodyne detection was proposed. The coding and decoding principle of Golay code in applying to the system and the principle of local-heterodyne detection were analyzed. The restriction of Stimulated Brillouin Scattering threshold in optical fiber on the coding length of the system was discussed. The mathematical expression of signal-to-noise ratio was deduced and the relationship of signal-to-noise ratio with APD multiplication factor and coding length was studied. The expressions of the optimal multiplication factor of APD and the optimal coding length were obtained, respectively. The MATLAB simulation results show that the optimal value of APD multiplication factor and the optimum coding length exist for this specific system with a bandwidth of the APD detector of 500 MHz, and the peak power and pulse width of 50 mW and 100 ns. The determination of optimum coding length of the system depends on not only the shot noise and thermal noise power, but also the Stimulated Brillouin Scattering threshold of optical fiber. With the APD optimal multiplication factor of 5 and the optimal coding length of 128 bits, the signal-to-noise ratio at the end of 25 km ending fiber increased by 26.42 dB compared to that of traditional single-pulse system, and temperature and strain resolution of 1.60 ℃ and 35.48 are achieved, respectively.