Study On The Optical Current Sensor With Polarization-Preserving Films

Optical current sensors (OCSs) are the kind of devices that directly or indirectly realizethe transformer measurement of current in order to achieve the sensing of the current. The substitution of OCS for the current-transforming techniques based on electromagnetic induction is a revolutionary evolution in the techniques of current measurement and power line protection in the industry of power transfer. This paper focuses on the study of Bulk Glass Optical Current Sensor (BGOCS). The work is significant in both theory and engineering application.The mathematic model of BGOCS is established in the paper. Measuring methods of two optical parameters (Reflection-lnduced-Retardance: RIR and linear birefringence: LB) of BGOCS with polarization-preserving total reflection layers and of relative phase angle of quarter wave plate were put forward and realized, which established the foundation for the experimental investigation of optical performance of the sensing head. The effects of RIR, LB and parameters of the polarizing elements (polarizing angle and extinction ratio) on the performance of the BGOCT system at constant temperature are analyzed. The effects of central wavelength variation of the optical source due to temperature fluctuation upon the output of the system through the dispersions of the RIR, LB and Verdet constant are studied. The temperature features of the RIR, LB and Verdet constant and their effect on the scale factor of the output of the BGOCT system are presented. The temperature characteristics of the BGOCT system through the combination of the temperature features of the optical source with that of the RIR, LB and Verdet constant are summarized. All of these are on the purpose of providing theory basis for improving the performance of the sensing head and its temperature stability.The results show that the RIR and LB can clearly degrade the sensitivity of thesystem at constant temperature; the joint effect of central wavelength variation of the optical source due to temperature variation from 10℃ to 30℃ through the dispersions of the RIR, LB and Verdet constant and the temperature features of the RIR, LB and Verdet constant upon the output scale factor of the system reaches 1.38% relative to its value at20℃. Therefore, effective temperature-controlling measures to the optical source and the sensing head or other measures like signal processing method have to be taken in the design of the optical current sensors to stabilizing the sensitivity of the measuring system.