Interface configuration for rate sensor apparatus

An optical rate sensor apparatus (300) measures rates of angular rotation along a plurality of orthogonal axes. The apparatus (300) comprises a passive ring Sagnac interferometric arrangement having a light source circuit (308) and a series of multi-turn fiber optic rings (302, 304, 306). An optics/modulator circuit (312) selectively switches optical waves emitted from the light source circuit (308) into gyroscope channels and transmits the signals through fiber optic rings as counter-propagating optical waves. The optics/modulator circuit (312) also recombines the optical waves after they emerge from the corresponding rings. The optics/modulator circuit (312) includes optical components integrated onto an integrated optics chip (IOC) consisting substantially of lithium niobate. Optical fibers (606, 608) are coupled from the rings (302, 304, 306) to the integrated optics chip. To reduce bias error effects of reflections, the interface (610) between the optical fibers and the integrated optics chip is angled in the plane of the interferometer. Also, the angled interface (610) creates a path length difference greater than the coherence length of the reflections traversing the IOC optical paths between the interface (610) and circuitry which recombines optical waves on the IOC paths.