A full theoretical analysis of the performance of passive inline Sagnac interferometric optical current sensor with component errors has been completed. A mathematical model was developed to show how nonideal components affect the overall performance of the sensor. The Faraday rotator element is a critical component in this passively biased optical current sensor. The analysis indicates that errors in the rotation element in the assembly can cause a ∼10  %    /  deg nonlinear error with current. Another source of nonlinearity in the response of the sensor is the 45-deg splices to the polarization maintaining fiber (PMF) link between the rotator element and the sensing head assembly. The analysis indicates a ∼0.2  %    /  deg error for the splice between the rotator and PMF link to the sensing head and a ∼0.1  %    /  deg error for the splice between the PMF and the quarter waveplate fiber at the sensing head. All quarter waveplate errors in the rotator assembly have linear effects to the sensor response function which can be calibrated out of the final sensor assembly. Temperature response data are presented for an uncompensated sensor over the +40  °  C to −30  °  C temperature range and the sensor shows a ±1.5  %   accuracy.