Fiber-Optic Gyros and MEMS Accelerometers

Abstract

Fiber-optic gyros (FOGs) and micro-electro-mechanical-systems (MEMS) accelerometers are used today in inertial strapdown systems for medium accuracy and expanding into high-performance strapdown navigation systems in competition with ring laser gyros (RLGs), whereas from the low-accuracy side, MEMS gyros are used for expanding to the medium accuracy ranges. The FOG principle is based on constant light velocity. This results in a phase difference of lights which are propagating through a fiber coil in clockwise (cw) or counterclockwise (ccw) directions if a rate is applied. The phase difference is proportional to the rate. The FOG technology has been developed from an open-loop design — still used in some market niches — to closed-loop design with high bandwidth and random phase modulation technique. The first generation of FOG systems uses one light source split by a 3×3 coupler to three fiber coils. More than 15.000 FOGs for such triad systems have been produced and delivered. Typical applications are Attitude and Heading Reference Systems or Land Navigators, which are described. The second generation of FOG systems uses single-axis FOGs with internal processors. A large quantity of these fiber-optic rate sensors (µ-FORS) can be easily calibrated separately and later assembled to modular systems. The features of the µ-FORS family for bias values from 6°/h down to 0.05°/h are given. The different bias values are realized by adapting the fiber length on the coil. The other optical parts and the electronics are unchanged. One main feature for the common electronics is the tracking of the modulation frequency to the actual fiber length.