基于模拟外差解调的光纤分布式振动传感系统的设计与实现
发布时间：2018-08-27 09:05
【摘要】：基于相位敏感型光时域反射(φ-OTDR)原理的分布式光纤振动传感系统利用光纤中背向瑞利散射光受振动信号调制的原理对光纤沿线的振动信号进行探测。由于光纤本身既是传输介质也是φ-OTDR系统的传感介质,因此它可以实现长距离分布式的振动传感,这在长距离轨道安全监测、长距离管道安全监测方面具有无可比拟的优势和广泛的应用前景。目前φ-OTDR系统的研究方向主要集中于对背向瑞利散射光的数字信号采集和相位信息解调与处理的算法研究,但实时数字信号的采集和处理需要高性能的采集板卡和计算设备。因此本文提出了一种基于模拟外差鉴相电路对φ-OTDR系统的背向瑞利散射光的相位信息进行解调的方法,其主要的工作内容和创新点集中在以下几点:首先,根据φ-OTDR理论结构搭建了模拟外差解调型φ-OTDR系统。在搭建过程中,主要对数据采集、光脉冲调制、耦合器分光比等一些系统参数进行了设计,使其达到各项探测性能的要求。随后对φ-OTDR系统中光功率和光源线宽对系统性能的影响进行了分析和验证,经过功率优化找到最佳的脉冲探测光功率,优化了系统的信噪比。在模拟外差鉴相部分,在AD8302模拟鉴相芯片的基础鉴相功能之上设计了双路AD8302参考鉴相电路,并进行了PCB板的设计与制作。经过实测,将鉴相范围由0°到180°扩展到了0°到360°,并且通过鉴相解调程序对鉴相特征曲线的非线性区域进行修正,大大的降低了AD8302的鉴相误差,鉴相特征曲线的鉴相最大误差由7°左右下降至1.1795°。随后,将鉴相电路模块加入了φ-OTDR系统进行了外差解调实验,并成功实现了对5.09km处的振源进行定位。通过模拟外差解调与数字外差解调方案的比较,模拟外差解调的解调精度低于数字外差解调的精度,这主要是因为外差型φ-OTDR系统的混频信号具有一定的边频带,且信号幅值受偏振衰落和相位衰落等因素的影响,其解调幅值存在一定的波动,这两种因素导致了AD8302模拟鉴相电路出现较大的误差。但是应当看到的是,通过模拟鉴相实现了对混频信号的模拟下变频处理,使得数据采样率由数字外差解调方案的1GSa/s降低到了模拟外差解调方案的10MSa/s,可以极大的降低外差式φ-OTDR系统的成本。最后,针对上述问题提出将AOM反馈控制和模拟方波鉴相技术引入φ-OTDR系统,以提高模拟鉴相的精度。
[Abstract]:A distributed optical fiber vibration sensing system based on phase-sensitive optical time domain reflection (蠁 -OTDR) detects the vibration signals along the fiber by using the principle that the Rayleigh backscattering light in the optical fiber is modulated by the vibration signal. Since optical fiber itself is both a transmission medium and a sensing medium for 蠁 -OTDR system, it can realize long distance distributed vibration sensing, which can be monitored safely in long distance orbit. Long-distance pipeline safety monitoring has unparalleled advantages and wide application prospects. At present, the research direction of 蠁 -OTDR system is mainly focused on the algorithms of digital signal acquisition and phase information demodulation and processing of backscatter light. However, the acquisition and processing of real-time digital signals require high performance acquisition boards and computing equipment. Therefore, this paper presents a demodulation method based on analogue heterodyne phase discriminant circuit to demodulate the phase information of backscattered Rayleigh light in 蠁 -OTDR system. Its main work and innovation are as follows: first, According to the 蠁 -OTDR theory structure, the simulated heterodyne demodulation 蠁 -OTDR system is built. In the process of building, some system parameters, such as data acquisition, optical pulse modulation, coupler split-light ratio and so on, are designed to meet the requirements of the detection performance. Then the influence of optical power and light source linewidth on system performance in 蠁 -OTDR system is analyzed and verified. Through power optimization, the optimal pulse detection optical power is found and the signal-to-noise ratio of the system is optimized. In the part of analogue heterodyne phase detection, the dual AD8302 reference circuit is designed based on the function of AD8302 analog phase detector, and the PCB board is designed and fabricated. The range of phase detection is extended from 0 掳to 180 掳to 0 掳to 360 掳, and the nonlinear region of the phase characteristic curve is corrected by the phase demodulation program, which greatly reduces the phase discrimination error of AD8302. The maximum error of the phase discrimination curve decreased from about 7 掳to 1.1795 掳. Then, the phase detection circuit module is added to 蠁 -OTDR system for heterodyne demodulation experiment, and the location of vibration source at 5.09km is realized successfully. Through the comparison between analog heterodyne demodulation and digital heterodyne demodulation, the demodulation accuracy of analog heterodyne demodulation is lower than that of digital heterodyne demodulation, which is mainly due to the fact that the mixing signal of heterodyne 蠁 -OTDR system has a certain side band. The amplitude of the signal is affected by polarization fading and phase fading, and the demodulation amplitude fluctuates to a certain extent. These two factors lead to large errors in the AD8302 analog phase discriminator circuit. However, it should be noted that the analog downconversion processing of mixing signals is realized through analog phase discrimination. The data sampling rate is reduced from the digital heterodyne demodulation scheme (1GSa/s) to the analog heterodyne demodulation scheme (10msa-s), which can greatly reduce the cost of the heterodyne 蠁 -OTDR system. Finally, AOM feedback control and simulated square wave phase detection technique are introduced into 蠁 -OTDR system to improve the accuracy of simulation phase detection.
【学位授予单位】：电子科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TP212;TN253
本文编号：2206773
[Abstract]:A distributed optical fiber vibration sensing system based on phase-sensitive optical time domain reflection (蠁 -OTDR) detects the vibration signals along the fiber by using the principle that the Rayleigh backscattering light in the optical fiber is modulated by the vibration signal. Since optical fiber itself is both a transmission medium and a sensing medium for 蠁 -OTDR system, it can realize long distance distributed vibration sensing, which can be monitored safely in long distance orbit. Long-distance pipeline safety monitoring has unparalleled advantages and wide application prospects. At present, the research direction of 蠁 -OTDR system is mainly focused on the algorithms of digital signal acquisition and phase information demodulation and processing of backscatter light. However, the acquisition and processing of real-time digital signals require high performance acquisition boards and computing equipment. Therefore, this paper presents a demodulation method based on analogue heterodyne phase discriminant circuit to demodulate the phase information of backscattered Rayleigh light in 蠁 -OTDR system. Its main work and innovation are as follows: first, According to the 蠁 -OTDR theory structure, the simulated heterodyne demodulation 蠁 -OTDR system is built. In the process of building, some system parameters, such as data acquisition, optical pulse modulation, coupler split-light ratio and so on, are designed to meet the requirements of the detection performance. Then the influence of optical power and light source linewidth on system performance in 蠁 -OTDR system is analyzed and verified. Through power optimization, the optimal pulse detection optical power is found and the signal-to-noise ratio of the system is optimized. In the part of analogue heterodyne phase detection, the dual AD8302 reference circuit is designed based on the function of AD8302 analog phase detector, and the PCB board is designed and fabricated. The range of phase detection is extended from 0 掳to 180 掳to 0 掳to 360 掳, and the nonlinear region of the phase characteristic curve is corrected by the phase demodulation program, which greatly reduces the phase discrimination error of AD8302. The maximum error of the phase discrimination curve decreased from about 7 掳to 1.1795 掳. Then, the phase detection circuit module is added to 蠁 -OTDR system for heterodyne demodulation experiment, and the location of vibration source at 5.09km is realized successfully. Through the comparison between analog heterodyne demodulation and digital heterodyne demodulation, the demodulation accuracy of analog heterodyne demodulation is lower than that of digital heterodyne demodulation, which is mainly due to the fact that the mixing signal of heterodyne 蠁 -OTDR system has a certain side band. The amplitude of the signal is affected by polarization fading and phase fading, and the demodulation amplitude fluctuates to a certain extent. These two factors lead to large errors in the AD8302 analog phase discriminator circuit. However, it should be noted that the analog downconversion processing of mixing signals is realized through analog phase discrimination. The data sampling rate is reduced from the digital heterodyne demodulation scheme (1GSa/s) to the analog heterodyne demodulation scheme (10msa-s), which can greatly reduce the cost of the heterodyne 蠁 -OTDR system. Finally, AOM feedback control and simulated square wave phase detection technique are introduced into 蠁 -OTDR system to improve the accuracy of simulation phase detection.
【学位授予单位】：电子科技大学
【学位级别】：硕士
【学位授予年份】：2017
【分类号】：TP212;TN253
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