Closed-loop, low-noise fiber-optic rotation sensor.

A closed-loop, multiturn fiber-optic rotation sensor has been developed that exhibits low noise of the order of 0.1 masculine/h for an averaging time of 30 sec. This performance is consistent with the photon-noise limit for our setup. The length of the fiber is 200 m, and the coil diameter is 19 cm. Nonreciprocal phase modulation is accomplished with an electro-optic crystal driven at 470 kHz, and closed-loop operation is achieved by means of acousto-optic frequency shifters.