A Potpourri of Comments about the Fiber Optic Gyro for Its Fortieth Anniversary: How Fascinating It Was and Still Is!

Forty years after its first experimental demonstration by Vali and Shorthill in 1976, the fiber optic gyro (FOG) remains a fascinating device. Reciprocity and serendipity have allowed it to reach a unique performance of long-term bias stability: pure, unaided strapdown inertial navigation with a drift of less than one nautical mile in a month, which corresponds to a rate bias stability of 10 μdeg/h, i.e., 0.3 nanoradian in terms of interferometer phase stability. This chapter begins with the historical context of the Sagnac effect and proposes that it be renamed, as we shall see, as the Sagnac–Laue effect. It then recalls the various points that make the FOG potentially perfect and finishes with a potpourri of comments that should be outlined.