Modeling and reduction of thermally induced non-reciprocal error in differential interference fiber optic gyroscope sensing coil

In this paper, thermally induced non-reciprocity in differential interference fiber optic gyroscope (DIFOG) sensing coil is investigated. Model of thermally induced error is developed with an integral, which is similar to that used by Shupe and others. Thermal error in DIFOG is a sum of Shupe error and inherent error. The Shupe error is caused by temporary phase imbalance in the counter-propagating optical paths and the inherent error is caused by thermal induced inherent non-reciprocity phase variation. In magnitude, the Shupe error is four orders smaller than the inherent error and therefore can be negligible in practice. Theory analysis shows that inherent error is a function of birefringence temperature sensitivity and position of 90° splice in fiber coil. It can be reduced significantly by using a mid-point 90° spliced photonic crystal fiber (PCF) coil which has lower birefringence temperature sensitivity than that of conventional polarization maintained fiber. An experiment setup was built and experimental results verified the theoretical analysis. By using a PCF coil, a total of ∼6400 times reduction in thermal error is realized which makes DIFOG possible for application.