Research On All-fiber Current Sensor Based On Cycle Structure And Polarization Detection

With the promotion of the power capacity,the traditional operation of the current sensor has been unable to meet the requirement of the clients.All-fiber current sensor has shown enormous development potential with the advantages of anti-electromagnetic interference,flexible assembly,high security,easy maintenance and low cost.However,it also has two bottlenecks with low current sensitivity and low SNR.This paper focuses on the two bottlenecks in research work: improves current sensitivity by amplification of Faraday rotation effect based on the loop structure and tries to add the reflection structure with single-polarization detection in order to reduce environmental disturbance.Furthermore,a multi-channels fiber current sensor,which can detect currents at different points,is designed based on the loop fiber current sensor.This paper is mainly composed of the following points:Firstly,the fiber current sensor has one bottleneck with low current sensitivity,so the sensing head based on the fiber loop architecture using the common single mode fiber is traversed by the optical signal repeatedly.Therefore,the Faraday effect can be increased to improve the sensitivity of current measurement.On this basis a multichannel fiber current sensor which can detect multichannel current is designed based on pulse time division multiplexing.The feasibility of real-time measured and non-crosstalk for the multichannel fiber current sensor is proved by theory and experiment.Secondly,the fiber current sensor has another bottleneck with low SNR and weak anti-interference capability,so a fiber current sensor which consists of Faraday rotator mirror and single-polarization detection is designed based on the loop fiber current sensor.The signal instability caused by random birefringence of optical fiber is effectively suppressed.The feasibility of this method is proved by theory and experiment.Finally,for the random birefringence of ordinary single-mode fiber,the differential group delay of polarization mode dispersion is derived by using vector analysis and Fourier analysis.The general formula of polarization decorrelation may be derived by using gaussian statistics and linear phase approximation under the condition of weak random birefringence.This simple approximation method avoids the complexities of mathematical processing without the need for Stratonovich integration.At the same time this theory deduces the correction of optical fiber sensor signal measurement and the qualitative analysis of optical fiber sensor signal instability.