Research On Distributed Optic Fiber Sensor Based On P-OTDR

Polarization sensitive optical time-domain reflectometer (P-OTDR) 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 method is very sensitive and it can feel very little influence. It is very difficult to obtain the polarization detection of Rayleigh backscattering along the fiber. Firstly, the intensity of the input light must be strong enough, but it can not be too strong, or it will bring the brillouin backscattering. secondly, the fresnel reflection should be avoided which is brought by the linkers in the system . In addition, all kinds of noise in system such as hot noise of laser, ASE noise of EDFA or some noise coming from optical receiver etc deteriorate the Signal Noise Ratio(SNR) of the signals and space resolution of the system. Improving the SNR and space resolution and extracting the SOP information are the main problems we have to face.Focus on improving stability of SOP in fiber, SNR of signal, enhancing space resolution of the system and extracting SOP information from data, the dissertation does some work as follows:1. The principle, structure, purpose and main parameters of OTDR are studied. On this base, the experiment equipment, the principle of P-OTDR are introduced, and the SOP distribution of fiber is deduced.2. We built an experiment equipment of P-OTDR independently. the optical equipments were modulated, the influence of the fresnel reflection was dealt with, the influence of the parameter of parts of the apparatus were studied experimently, and the Rayleigh Polarization backscattering was successfully observed.3. Summed up the reasons of why the obvious Rayleigh backscatter signal can not be observed and the main solution.4. The signal data were dealt with to improve the SNR and space resolution of the system.