Based On Potdr Distributed Optical Fiber Sensing Technology And Its Applications

With the development of modern measurement technology, more and more research interests are focused to optical fiber sensors in the past two decades. Compared to conventional electrical sensors, optical fiber sensors offer several outstanding advantages, including immunity to electromagnetic interference, capability of responding to a wide variety of measurands, high resolution, capability of multiplexing, small size and light weight, and resistance to harsh environments. Distributed optical fiber sensor (DOFS) is one of the most successful optical fiber sensors in practice, such as polarization optical time domain reflectometry (POTDR), in this technique, pulse from narrow linewidth laser is coupled into the optical fiber which severed as a sensor, at the emitting end, a detector is used to explore the State of Polarization (SOP) by using Rayleigh backscattering. POTDR is a kind of distributed sensor which makes use of inspecting the state of polarization (SOP) in fiber for sensing. As we known,the change of SOP in fiber is actually aroused by the change of phase,consequently,this sensing methed is very sensitive and it can feel very little influence.After described the research history and current status of DOFS, it can be seen that POTDR exist some limitations, such as, POTDR can only measure one parameter along the fiber link, signal is week, and the sensors are not practically etc. Hence, we would find some ways to overcome these limitations.The main work completed is summarized as follows:(1)The principle, structure, typical test curve and main parrneters of OTDR are studied, and its application and limitation are indicated. On this base, the polarization optical time domain reflectometry is proposed. The SOP, birefringence and Rayleigh backscattering in the sigle mode fiber is described, and the principle of POTDR is explained too.(2)The backscatter data has much noise in the system, which has bad effect on the subsequent analysis. Wavelet transform has a good performance in both time and frequency field. A denoising analysis to the data using wavelet transform is given with better precision. (3)After designed and selected the device and system, we built an experiment equipment of POTDR for optical fiber link surveillance. Experimental results show that a high SNR of the sensor signal at 2km and 14km along the fiber link was achieved, and it's also indicated that POTDR could only detected one perturbation.(4) The principle and application in the intrusion-sensor system is described, On this base, A distributed optical fiber perturbation sensing system, based on the combination of polarization optical time domain reflectometry (POTDR) and phase-sensitive optical time-domain reflectometry (φ-OTDR), is demonstrated and bulit for optical fiber link surveillance. Experimental results show that a high SNR of the sensor signal at 14km along the fiber link with a spatial resolution of 50m was achieved. POTDR andφ-OTDR work together to detect the phase and polarization perturbations of the returned light pulses, such an approach can keep the system cost low and enhance the detection accuracy of perturbations and hence reduce the error rate simultaneously.(5) The data acquisition and analysis technology is described, and the testing software of POTDR is developed on the basis of personal computer with the tool of Visual C++. The function of the testing software contains panel controlling, time-domain wave display, data analysis and processing, I/0 interface etc, and a lot of tests are completed by means of the mutual way realized by the software.