Phase Demodulation Technology Of Quantitative Detection Phase-sensitive Optical Time Domain Reflectometer

Distributed optical fiber sensor can obtain sensing signal along long-distance measured field with the advantages of high pressure,corrosion resistance and high sensitivity.With the development of sensing technology,researchers focus on not only the qualitative detection but also the restoration and quantitative determination of sensing signal.Phase-sensitive Optical Time Domain Reflectometer(?-OTDR)is remarkable on the detection of invasion and vibration with high sensitivity.But traditional ?-OTDR is based on amplitude detection and can hardly conduct quantitive detection.Phase demodulation system based on ?-OTDR can restore the signal quantitatively by detecting the phase change of Rayleigh backscattering and is promising in the application field.In this paper,theoretical analysis of phase demodulation ?-OTDR based on heterodyne,phase-generated carrier and 3×3 Michelson interferometer are studied,the demodulation systems based on these methods are constructed and elementary experiments are carried out.By synthetical comparison of these three systems,the paper chooses the phase demodulation O-OTDR based on 3 X 3 Michelson interferometer which is relatively stable,convenient and better.A modified four-channel detecting system is proposed to conquer the disadvantage of low spatial resolution then verified.Sensing signals are restored and quantitatively detected along 5.15km-long fiber.The repeat-ability and linearity of the system are tested by experiments.Proposed four-channel phase demodulation system based on 3 X 3 Michelson interferometer can restore sensing signal quantitatively and preserve the spatial resolution of traditional ?-OTDR.Follow-up work is focused on improvement of algorithm and performance of the system.