Numerical analysis of second order polarization effects in a Sagnac current sensor

A Sagnac optical-fiber current sensor that allows the compensation of all effects modifying the intensity of the interfering beams, such as source variations, losses, or mode coupling, is presented. Particular attention is given to the numerical analysis of the polarization effects in a fiber showing both linear and circular birefringence in order to demonstrate the efficiency of the compensation scheme and to determine the theoretical accuracy and the actual limits of the sensor configuration. The efficiency is self-evident, keeping in mind that all the amplitude variations are fully compensated. The limits of the system depend on the phase variations, which can be divided into a steady component and a random component. The theoretical limits are set by the random component because the steady component can be compensated like a sensor nonlinearity, provided that the mean linear birefringence is known