Combined Multi-ring Cavity Rayleigh Backscattering Fiber Optic Rotation Sensor

Optical fiber rotation sensor is used to monitor the angle velocity of an objectrelative to some rotation axis,which is useful to industrial manufacture andscientific experiments.Rayleigh backscattering optical fiber rotation sensor(RBFORS) based on the backward scattering characteristic of a single-modeoptical fiber ring resonator,was firstly proposed by A.Kung at el in 1997,whichbelongs to an non-interference optical fiber rotation sensor.This type of ringstructure enables the optical pulse signal to circulate a while in the ring resonant.The optical pulse from the optical time domain reflectometer(OTDR),and theRayleigh backscattering signal returned to the OTDR is the sum of interferenceoverlap of scattering signals at the same point and the non-interference overlap ofthe scattering signals at different points.After a mount of investigation to the current Rayleigh backscattering opticalfiber rotation sensor proposed by other researchers,a multi-ring-resonatorsRayleigh backscattering is constructed by using multi fiber ring-resonatorslooking for a combination structure with much higher rotation velocity accuracythan that of the single-ring measurement.The output characteristic,feasibility and the superiority of the presented newstructure with multi-combination is in-depth investigated.The testing system isalso constructed by selecting the lengths of three rings at 1500m,1078m and680m,the four 2×2 couplers have keen used in our experiments with couplingratios 95.23%,94.88%,95.26%,95.01% respectively.The main work of thisthesis includes:(1) The principle of the Rayleigh backscattering rotation sensor is illustratedand the output signal intensity of the sensor is calculated.(2) The theoretical model of Rayleigh backscattering rotation sensor isestablished with multi-ring resonators structure and the output signal expression of the multi-resonators is deduced based on the principle of single-ring resonatorRayleigh backscattering rotation sensor.(3) The characteristic of output signal is simulated in Rayleigh backscatteringrotation sensor with various combination structures by using the theoreticalsimulation model and find the optimized structure by analyzing the output signalin the structures with different cavity lengths and splitting ratios.(4) The test system of Rayleigh backscattering optical fiber rotation sensorwith two-ring-parallel,two-ring-combination,three-ring series-parallel andthree-ring combination structures is constructed,and the system is calibrated andtested,then the metrical results are analyzed and disposed,the feasibility of thesystem is verified.By comparing the result with that of single-ring system,thesuperiority is found.Compared with the single-ring Rayleigh backscattering optical fiber rotationsensor,the multi-ring resonators combination system increases the valid test data,which makes it much more helpful to be identified.The combination structure ofthe two-ring and the three-ring rotation sensor also enhanced the intensity of themeasurement signal,which improved the accuracy of rotation velocitymeasurement.