Abstract: A rotary motion sensor which employs a fiber interferometer more particularly comprises a system for driving a laser interferometer and electronically detecting the fringe shifts caused by rotation. In the preferred embodiment, a light emitting diode pumps a fiber laser which, in turn, drives a distribution waveguide. Coherent radiation from the distribution waveguide is partly backward-coupled by means of an acousto-optic grating into a reference optical waveguide. The acousto-optic grating also serves to offset the laser frequency by the acoustic drive frequency. Coherent radiation from the distribution waveguide is also coupled into each end of a multiple turn optical waveguide which serves as a fiber interferometer. A pair of directional couplers, one for the clockwise radiation and one for the counter-clockwise radiation, extract the coherent radiation from the fiber interferometer after the radiation has made at least one transversal of the multiple turn optical waveguide.