The Research Of De-noising Method And Application In Quasi-distributed Vibration Fiber Sensing System

Distributed optical fiber sensing system based on Optical Time Domain Reflectometry(OTDR)has many advantages,such as resistance to electromagnetic interference,a lot sensing channels,which can be widely used in engineering structure health monitoring system,underground geological exploration,security alert system etc.However,the sensing system is influenced by weak reflected light and polarization fading,which lead to the problem of high background noise and demodulation signal fluctuates greatly,seriously limits the popularization and application of the system.In order to reduce the system noise,we have further research in noise suppression of the distributed optical fiber sensing system,and take the methods of increasing reflected light power and restraining polarization decline.In this paper,main work and innovation points are as follows:1.We study the de-noising method of the reflection grating or Fresnel reflex to increasing reflected light power.By fiber grating or Fresnel reflection point in the optical fiber,we can acquire reflected light power higher than local backward Rayleigh scattering the light power,thus reducing the noise of the system.2.We study the polarization diversity reception technology which can suppress polarization decline phenomenon.Analyzes the principle of double and three states of polarization diversity reception to suppress polarization decline.By improving the coherence degree of the interference signal,it can reduce background noise of the system.3.Built a distributed sensing system based on Rayleigh scattering and quasi distributed sensing system based on fiber grating and Fresnel reflection point,take a test experiment of noise comparison,which obtain the best background noise of-80 d B for quasi distributed sensing system.4.As for actual application demand,we optimize the system with a continuous acquisition and real-time demodulation system.The vibration test and sound sensing experiment are taken,the good application result is obtained.