Phase error bounds of fibre gyro with imperfect polariser/depolariser

In fibre-optic gyroscopes a drifting zero-offset due to changing fibre birefringence may be reduced by inserting a single-mode polarising filter and a depolariser. For a real gyro, in which these components and their alignment are imperfect, bounds are derived for the remaining zero-offset. A simple experimental procedure permits the measurement of that offset.