Abstract: An interferometric fiber-optic gyro system includes a light source and a plurality of optical fiber rings employed to measure angular displacement along three axes. Optical circuit elements interposed between the source and the rings include an optical switch for periodically applying the optical signal to each of the rings individually along three separate optical transmission paths. Included in each of the optical transmission paths is a modal filter, including a polarizer, and a beam splitter which provides two separate beams to the optical ring for counter-propagation through the ring. Compensating birefringent devices are added in the optical circuits to compensate for a residual birefringence introduced by the various optical elements in the circuits. The characteristics of the compensating devices consist of predetermined lengths of polarization preserving, single-mode optical fiber. The birefringence of each of the optical devices is characterized in terms of a total number of beat lengths.