Distributed Optical Fiber Sensing System Based On LabVIEW

When light transmits in optical fiber,it can be affected by surroundings such as stress,temperature etc..Correspondingly,the intensity,wavelength,phase,and polarization of the light will be changed.The distributed optical fiber sensing system is a system that can infer the change of external environment by measuring and analyzing these characteristic parameters.The ?-OTDR optical fiber sensing system based on Rayleigh scattering makes use of the property that the high coherent laser can respond to phase modulation.The change of external factors could be actively detected through the analysis of the signal generated by mutually coherent between the Rayleigh back scatterings.Just as other optical fiber sensing technologies based on OTDR,the ?-OTDR has high detection sensitivity,high-accurate positioning and good concealment.But it is easier in signal processing than others,so the cp-OTDR technology is very suitable for the disturbance monitoring field with high real-time requirement.Therefore,the ?-OTDR optical fiber sensing system is a research of great value.This thesis focuses on the research of the principle and characteristic of(p-OTDR optical fiber sensing system.A new method combining the traditional(p-OTDR and the coherence technique has been proposed.It solved the problem that the backscatter-light detected in long-distance optical fiber sensing system will be too weak.Then,a series of experiments were conducted on the basis of modified system.The main research and innovations are listed as followings:(1)A distributed sensing system based on the coherent principle and?-OTDR technology was designed.And the performance requirements of the hardware devices in the system were elaborated.In order to process low SNR signal,which was seriously affected by the environmental noise,a denoise method combining the data averaging algorithm with wavelet technology was proposed.Then,a disturbance feature extraction method was designed,according to the frequency feature of the disturbance.(2)A signal processing and alarm software system was developed,taking the advantages of Lab VIEW in the aspects of data collection and processing,instrument measurement and control.In order to control the devices and monitor the operation of the system conveniently,a control software based on laser and EDFA was designed,which are integrated with the signal processing and alarm system.This can provide a great convenience for researchers and users.(3)The distributed fiber sensing system designed before was constructed and experiments have been done to test the performance.Experimental results showed that alarm system could effectively monitor the specified disturbance events within 25km.When multiple point disturbances occur simultaneously in the system,different events could be identified clearly,in this case,the actual positioning accuracy could be up to 100m.Meanwhile,the disturbance information would be presented accurately on the alarm interface.