A novel distributed sensor using long-distance Mach-Zehnder interferometer

This paper demonstrates the recent achievements in the field of distributed optical fiber sensor (DOFS). A novel type of distributed optic fiber vibration sensor is presented to detect and locate a time-varying disturbance along the whole fiber length. It measures the first simultaneous information by using Mach-Zehnder Interferometer(MZI). The sensor consists of a MZI where two directional optical signals are simultaneously traveling. We discuss the principles of distributed optic fiber vibration sensor based on long-length MZI, and present the preliminary results on the application of distributed optic fiber sensor for the measurements of distributed signals in long-distance region. The sensor is illuminated by one continuous-wave laser, which is different from the conventional scheme. The phase shift caused by any disturbance around the fiber is detected and converted to the information on the perturbation position and amplitude, which can be determined by combining two phase signals from the above device. In addition, we adopt a new technique by using optical delay effect to improve the spatial resolution of distributed optic fiber sensor. It is completely different from the spatial-resolution technique of optical time-domain reflectometry (OTDR). The system has capability for cross-correlation algorithm and fast Fourier transform (FFT) analysis of the detected disturbance signals. For the sake of determining the disturbance position and type, high speed digital processing (DSP) technology is used in the sensor system, which can carry out all operations in real time and promote the resolution of localization. The hardware design of the sensor is completed and the experimental results are obtained. This type of optic fiber sensor has better sensitivity and resolution than the others. It achieves a 100Hz-20KHz frequency of vibration resolution, with 100-m practical spatial resolution, over a sensing length of 8 km. At the time of writing, the system is only partially completed; therefore the content of this paper will focus on the principle of distributed optical fiber sensor. The results mainly are presented in laboratory.