脉冲编码多模激光器BOTDR系统建模分析与优化设计

发布时间：2019-07-08 11:01

【摘要】：本文在阐述布里渊光时域反射(BOTDR)技术研究现状的基础上,对光纤布里渊散射理论,包括自发布里渊散射和受激布里渊散射机理进行了分析,同时介绍了利用布里渊频移和强度实现温度和应变同时测量的原理。研究了外差检测脉冲编码BOTDR系统,分别介绍了Golay码、Simplex码和CCPONS码应用于移频外差检测BOTDR系统的编解码原理及编码增益,用MATLAB对三种不同码型编码系统时域输出信号进行仿真对比,并对比分析了编码长度和叠加平均次数增加时的信噪比改善效果。分别提出了基于窄谱DFB激光器单波长、三波长和多模FP激光器的APD外差检测Golay编码BOTDR系统,分析了三种系统编解码原理及外差检测原理,讨论了光纤受激布里渊散射阈值对编码长度的限制问题,并推导了系统信噪比的数学表达式;研究了系统信噪比与APD倍增因子、编码长度和纵模数之间的相互制约关系,分别得到了APD最佳倍增因子、最佳编码长度和最佳纵模数的表达式,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,分别对提出的三种系统进行建模分析和优化设计并用MATLAB对系统性能进行仿真验证。结果表明,为了实现高精度传感,除了要考虑光纤受激布里渊散射对编码长度的限制问题、信号功率过大造成的APD光电检测器饱和的问题,还需根据实际系统考虑激光器类型、接收机带宽等其他因素,权衡各个参数来确定最佳APD倍增因子、最佳编码长度和最佳纵模数。对于单频编码BOTDR系统,选取APD倍增因子为5,编码长度128位时可获得最佳的温度和应变分辨率1.60℃和35.48??;对于三波长编码系统,APD倍增因子为5,编码长度64位时可获得最佳的温度和应变分辨率1.33℃和29.49??;对于多模编码系统,APD倍增因子为5,编码长度32位,纵模数为7时可获得最佳的温度和应变分辨率1.29℃和29.16??。
文内图片：
图片说明：自发布里渊散射过程示意图
[Abstract]:On the basis of expounding the research status of Brillouin optical time domain reflection (BOTDR) technology, this paper analyzes the Brillouin scattering theory of optical fiber, including the mechanism of self-published Brillouin scattering and stimulated Brillouin scattering, and introduces the principle of simultaneous measurement of temperature and strain by Brillouin frequency shift and intensity. The pulse coding BOTDR system of heterodyne detection is studied. The coding and decoding principle and coding gain of Golay code, Simplex code and CCPONS code applied to frequency shift heterodyne detection BOTDR system are introduced respectively. The time domain output signals of three different code coding systems are simulated and compared with MATLAB, and the signal to noise ratio (SNR) improvement effect with the increase of coding length and superposition average number is compared and analyzed. The APD heterodyne detection Golay encoded BOTDR system based on narrow spectrum DFB laser single wavelength, three wavelength and multimode FP laser is proposed respectively. the coding and decoding principles and heterodyne detection principles of the three systems are analyzed. The limitation of fiber stimulated Brillouin scattering threshold to the coding length is discussed, and the mathematical expression of the signal to noise ratio of the system is derived. The relationship between signal-to-noise ratio (SNR) and APD multiplication factor, coding length and longitudinal modulus is studied. The expressions of optimal multiplication factor, optimal coding length and optimal longitudinal modulus of APD are obtained respectively. The APD photodetector with bandwidth of 500 MHz and the input pulse with peak power of 50 mW, pulse width of 100 ns are selected. The three proposed systems are modeled, analyzed and optimized, and the performance of the system is verified by MATLAB simulation. The results show that in order to realize high precision sensing, in addition to the limitation of fiber stimulated Brillouin scattering to coding length and the saturation of APD photodetector caused by excessive signal power, it is necessary to weigh the parameters to determine the optimal APD multiplication factor, optimal coding length and optimal longitudinal modulus according to other factors such as laser type, receiver bandwidth and so on. For single-frequency coding BOTDR system, the best temperature and strain resolution can be obtained when the APD multiplication factor is 5, and the best temperature and strain resolution can be obtained when the coding length is 128 bits, and the best temperature and strain resolution can be obtained when the APD multiplication factor is 5 and the coding length is 64 bits for the three-wavelength coding system, and the best temperature and strain resolution can be obtained when the coding length is 128 bits, and the best temperature and strain resolution can be obtained at 1.60 鈩，

本文编号：2511540