Thermomechanical analysis of the effects of homogeneous thermal field induced in the sensing coil of a fiber-optic gyroscope

Abstract

A thermal field in the sensing coil of fiber-optic gyroscope gives rise to bias drift. The transient effect and the quasi-static effect are distinguished. The equations of this phenomenon developed in this article highlight the importance of knowing the strain field versus temperature along the optical fiber in the sensing coil. The influence of winding patterns on thermal bias is discussed using an analytical approach. To determine the strain field, a parameterized approach is proposed. An axisymmetric finite element model describing a double coated optical fiber is implemented. Thanks to this model, the thermo-mechanical behavior of the optical fiber coil is computed and explained in detail. Then, the computed strain field is validated with strain measurements by Rayleigh Optical Frequency Domain Reflectometry (Rayleigh-OFDR) for two different coils using two different optical fibers. The thermal bias drift for a spatial homogeneous thermal loading, referred to as Mohr effect in this paper, is computed. Finally, we point out that the contribution of radial and axial strains in the reference frame formed by the optical fiber coil is negligible compared to orthoradial strain on Mohr effect.