Quarter Wave Plate for Fiber Optic Current Sensor: Comparison of Modeling and Experimental Study

Abstract

Fiber optic current sensor is the high-precision device for measuring large current values in high-voltage grids. A quarter wave plate is an important part of this sensor, as its quality affects the accuracy of the entire system. Firstly, this plate must be fiber so as not to violate the integrity of the device. Secondly, its length must be equal to the quarter of fiber beat length. It is just a few millimeters. Finally, the optical length of quarter wave plate depends on its temperature. Due to all this facts, a perfect quarter wave plate preparation is a very difficult task, and it is often not ideal in a real device. In this paper, we studied the plate imperfections effect on the performance of the fiber optic current sensor. The mathematical model of the sensor was developed using the Jones matrices formalism. The non-ideality of a quarter-wave plate was considered by introducing a small phase shift between two orthogonal linear modes, which led to the formation of an elliptical polarization mode instead of a circular one at the plate output. The similar experimental study was conducted for the real prototype of a fiber optic current sensor and compared with the modeling results. Thus, it was found that the quarter wave plate affects not only the sensor measurement error, but also the contrast of the interference signal.KeywordsFiber optic current sensorCurrent measuringQuarter wave plateJones matrices formalism