Phase bias in dual-axis optical gyroscope based on a double-ring structure

A two axes fiber optical gyroscope comprising a two loops structure (TLS) using a 3 × 3 coupler is presented. The length of the two loops is 2 m and 1.8 m. When one of the two axes is vertical to another, a dual-axis gyroscope comes into being. The phase difference between the counter-propagating waves in TLS is calculated and discussed. The sensitivity can be improved by adding a bias phase, but only if the phase difference is a monotonic function of the angular rate, with the best sensitivity obtained by adding a phase bias of ±3π/2.