Study On Polarization Errors In The Sagnac Nterferometer Fiber-Optic Current Transducer

With the enhancing level of the voltage, the capacity of power network isincreasing year by year, and the information, digitization, automation need for smartgrid, as a result, the traditional electromagnetic current transducer has graduallyexposed serious flaws. Because of the fiber optic current transducer (FOCT) has theadvantages of small volume, light weight, large range of measurement and frequencyresponse, good at resisting electromagnetic interference, etc. It is the trend of currenttransformer.In this paper, it is aimed that the application of Sagnac interferometer fiber-opticcurrent transducer and the impact of the system factors of measurement accuracy arecalculated and simulated. Optimal performance parameters of the influential factorsare acquired. The experiment of optical path has been set up，and part of thetheoretical simulation results were verified.First, theoretic calculating the errors which are caused by the incompleteness ofoptical devices(polarizer, polarization-maintaining fiber coupler,90degree splice,quarter-wave plate and sensor fiber,etc.) of the in-line Sagnac interferometerfiber-optic current transducer, using the method of Jones matrix, draws up thecorresponding additional error curves. The simulation result shows that the linearbirefringence could be restrained by adding a larger amount of circular birefringencein the sensing fiber. The factors such as the ratio of polarization maintaining coupler,the delay error of the quarter-wave plate and the birefringence error of sensor fiberetc., which would affect the measuring precision and reduce the sensitivity of thesystem. The birefringence error of sensor fiber is the main polarization error source,and the effect of90degree splice can be neglected.Second, theoretic calculating the errors which are caused by the incompletenessof optical devices (polarizer, quarter-wave plate and sensor fiber,etc.) of the loopSagnac interferometer fiber-optic current transducer, using the method of Jonesmatrix, draws up the corresponding additional error curves. According to the simulation results, the factors such as the splicing error of fiber polarizer, the twoquarter-wave plate’s axes coincidence error, the delay error of the quarter-wave platesand the birefringence error of sensor fiber etc., which would affect the measuringprecision and reduce the sensitivity of the system. The linear birefringence can’texceed, which is a characteristic value of the sensing fiber linear birefringence. Thebirefringence error of sensor fiber is the main polarization error source, and thepolarization of the other error sources will be easy to process if the system canelimination the linear birefringence.At last, the experiment system of optical path of the in-line Sagnacinterferometer fiber-optic current transducer has been established. The experimentalresult shows that when the optical fiber polarizer and polarization maintaining opticalfiber fusion angle of45degrees, the experimentally obtained numerical processingamount is the largest, the sensitivity of the system the best. The quarter-wave plate isalso with polarization-maintaining optical fiber fusion angle of45degrees, thesensitivity of the system the best. The measurement results show that the error ofpolarizer and the error of the quarter-wave plate would affect the measuring precisionand reduce the sensitivity of the system.The study is expected to provide theoretical basis of the development on Sagnacfiber-optic current sensor and to help for optical device selection and practical systemdesign.