Research Of Distributed Optical Fiber Vibration Sensor Based On OFDR

As a branch of in optical engineering, distributed optical fiber sensing technology has drawn plenty of attentions in recent years. Because of the outstanding advantages of electrical insulation, adaptability, small size, high sensitivity, it has widespread applications in civil and military areas such as monitoring optical communications, aerospace, medical diagnostics and security systems. In these significant applications, the research of distributed optical fiber sensing system based on OFDR(Optical Frequency Domain Reflectometer) becomes remarkable popular in recent years. This thesis aims to extract and demodulation vibration signal based on optical frequency domain reflectometry(OFDR). The key issues(nonlinear phase noise, polarization fading effects, etc.) in OFDR are researched and the detailed vibration signal demodulation scheme is proposed. The main contents are exhibited as follows:1 The principle of OFDR system is studied. A physical model of OFDR is created. The influence on the system performance caused by the optical source parameters is analyzed in detail. A mathematical model of nonlinear phase noise source is created. The effect of cubic spline interpolation method for phase error correction is simulated. This thesis confirmed the correctness of spline interpolation method for phase error compensation. The method of suppression for polarization fading phenomenon in experiment is discussed using polarization diversity can achieve the expected effect.2 The affection of vibration and spectral broadening to the light phase is studied according to its physical mechanism. This thesis also gives mathematical deducing and simulation results of the influence of spectral broadening. The phase demodulation methods based on the 3?3 coupler, Hilbert Thansform and phase discriminator are studied.3 We carried out experiments of distributed vibration sensing system based on OFDR and built experiment platform. Data acquisition is completed. High-precision positioning of the vibration signal is realized. The spatial resolution is up to 0.04 m. The vibration frequency is measured successfully by cross-correlation. Measurement range is 100Hz-1000 Hz. On the other hand, we have extracted the time domain of vibration signal by the phase demodulation method. By dividing the time-domain data, rehabilitation of small frequency vibration signal is realized(below 10Hz). The vibration without rules is analyzed and research too.4 Vibration signal demodulation based Φ-OTDR is completed. By comparison and analyzing with OFDR, we found that OFDR has advantages in the fine structure of the detector(cm degree). In terms of signal to noise ratio, OFDR still has good performance of about 15 dB. The test distance of Φ-OTDR is longer than OFDR and it is more suitable for long-distance line monitoring.The innovation of this thesis is to realize a high-precision positioning of the vibration singal by cross-correlation and frequency measurement. The vibration signal in time domain is demodulated by dividing the time-domain data and phase demodulation.