The fiber-optic gyroscope, a century after Sagnacʹs experiment: The ultimate rotation-sensing technology?

Taking advantage of the development of optical-fiber communication technologies, the fiber-optic gyroscope (often abbreviated FOG) started to be investigated in the mid-1970s, opening the way for a fully solid-state rotation sensor. It was firstly seen as dedicated to medium-grade applications ( 1 ° / h range), but today, it reaches strategic-grade performance ( 10 − 4 ° / h range) and surpasses its well-established competitor, the ring-laser gyroscope, in terms of bias noise and long-term stability. Further progresses remain possible, the challenge being the ultimate inertial navigation performance of one nautical mile per month corresponding to a long-term bias stability of 10 − 5 ° / h . This paper is also the opportunity to recall the historical context of Sagnacʹs experiment, the origin of all optical gyros.