Noise Mechanism Analysis And Performance Optimization Of Optical Pulse Compression Reflectometry

Optical reflectometry has been widely used in many fields such as optical fiber communication networks,sea monitoring,petrochemical industry,health examination of building,electric power system and aerospace,etc.This technology is effectively used in measuring the energy loss,temperature fluctuation,stress change of the fiber.For optical reflectometry,the working principal and experimental structure of optical time domain reflection technology(OTDR)is understandable,but it has the tradeoff between spatial resolution and measurement range;while optical frequency domain reflection technology(OFDR)uses wide band frequency modulation to improve spatial resolution,but the measurement range is still limited by the coherent length of the laser.The proposition of optical pulse compression reflectometry(OPCR)by us in recent years successfully overcome the restriction between the spatial resolution and measurement range of OTDR,the measurement range limited by the coherence length of laser was tackled as well.This paper theoretically analyzed and simulated the influence of phase noise to different coherence length of optical source and measurement range in OPCR.Through digital simulation,this thesis reveals the influence of photoelectric device used in OPCR to system performance.On the basis of digital simulation,we used narrow linewidth laser as optical source,introduced optical amplifier to compensate the transmission loss of the fiber under test and added optical filter to block noise outside the band of interests in experiment to optimize system.The optimized system can be used to the measurement of long-distance fiber.Basically,this thesis is consist of three parts:(1)Theoretical analysisFirst,we analyzed the noise generation mechanism in the OPCR photon link including thermal noise,shot noise and relative intensity noise(RIN).Then the working mechanism of photoelectric devices which are used in the OPCR system such as single sideband modulator(SSBM),balance photodetector(BPD)and erbium-doped fiber amplifier(EDFA)were analyzed,to reveal the influence of photoelectric devices to long-distance fiber measurement.(2)Simulation analysisFirstly,this paper theoretically analyzed and simulated the influence of phase noise to different coherence length of optical source and measurement range in OPCR.Secondly,through digital simulation,this thesis analyzed the performance of photoelectric device used in OPCR system.Lastly,we applied related photoelectric device parameters to OPCR simulation to study how photoelectric devices in OPCR photon link affect the dynamic range.(3)Experimental resultBased on the optimized OPCR system,the experiment setup is built to verify the effectiveness of theoretical analysis and numerical simulation.The linewidth of narrow linewidth laser(NLL)and semiconductor laser using in experiment setup were measured by using of the traditional heterodyne method.With centimeter-level spatial resolution,NLL is used to measure the longdistance fiber in optimized OPCR system,as a comparison,the NLL was replaced by semiconductor laser as optical source in the original configuration.Finally,under optimized structure we achieved 58 km measurement range with centimeter-level spatial resolution.