The Sagnac phase shift between two counterpropagating beams is the basis for all optical gyroscopes [11, although it is detected in a variety of ways. In the ring laser gyro and various "closed loop" optical gyroscopes, the scale factor (e.g. counts per unit rotation rate) is fixed by the area of the optical medium whereas the phase reading fiber optic gyroscope (FOG) has a scale factor which increases with increasing length of optical fiber. Thus development of low-loss fibers holds the possibility of extremely sensitive gyroscope operation, and has made the FOG a competitive optical gyroscope. Although most of the first decade of FOG development has concentrated on improving sensitivity, attention is now turning to other aspects of performance.
N. J. Frigo, N. J. Frigo,
"A Constant Accuracy, High Dynamic Range Fiber Optic Gyroscope", Proc. SPIE 0719, Fiber Optic Gyros: 10th Anniversary Conf, (11 March 1987); doi: 10.1117/12.937552; https://doi.org/10.1117/12.937552