Self-Compensative Fiber Optic Current Sensor

The measurement accuracy of fiber optic current sensors (FOCS) is closely related to the stability of Verdet constant and the polarization characteristic of the sensing coils, which are easily influenced by environmental disturbance. In this article, a self-compensative fiber optic current sensor (SFOCS) with two sensing heads made of single mode fibers is designed and demonstrated. Utilizing sensing and compensative unit as well as a close-loop system, variation of Verdet constant and birefringence is compensated. We numerically calculate the output signal of SFOCS with temperature varying from $-\text{30}^{\circ }$C to 75 $^{\circ }$C and simulate the situation where SFOCS is affected by the circular and linear birefringence from the environment, and the results confirm that well designed SFOCS is completely temperature- and vibration-independent. Additionally, in order to achieve the ideal compensation, $\mathcal {H}$ function of SFOCS related to birefringence and the current to be measured is introduced and deeply studied. Moreover, we discuss the measurement errors of SFOCS caused by the difference between two sensing heads such as the coupling ratio, the linear and circular birefringence, and we calculate the acceptable error range, within which SFOCS can meet the class 0.2 standard.