Multi-channels Fiber Current Sensor Based On Series Structure

All fiber current sensor(AFCS) is one of branches in the field of optical fiber sensing, which can be used for the measurement of current and voltage in power station, converting station, power transmission. Its advantages include electrical isolation, immunity against electromagnetic, withstand high temperature and chemical etching, safer and so on. In this paper, it focuses on elaborating AFCS based on fiber loop structure and series structure.In order to improve current sensitivity of AFCS, the fiber loop structure is adopted. This structure can make signal traverse fiber solenoid repeatedly to enlarge Faraday rotation, which greatly make up defect of low Verdet constant. Starting from Faraday effect, we present the theoretical model of loop structure's AFCS based on the Jones Vectors and principle of fiber transmission matrix. Mathematical expressions of current sensitivity and degree of polarization can be derived from this theoretical model. The necessary numerical calculation and experiments are made and their results show that degree of polarization is linear with current to some extent and the current sensitivity increases periodically with the number of trips K. Therefore, it is vital to choose an appropriate K for the system's sensitivity.Moreover, this paper describes a quasi-distributed all-fiber current sensor based on series structure to meet demand in measurement current. Compared with one channel measured and parallel structure, this structure can detect many conducts at the same time and has higher usage light intensity. We establish multi-channels serial structure experiment to prove our thought. The result shows that signal of two fiber solenoid can varies with current and the variation of polarization changes with K. It's well verified that serial structure's fiber current sensor is viable. Besides, the paper detailed describes the formula derivation of light intensity of each channel. comparing the utility rate of light between parallel and serial structure, result highlights that serial structure has unique advantage.