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

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. • Theory of thermal bias drift in a Fiber-Optic Gyroscope (FOG) is proposed. • An analytical approach to evaluate the influence of winding pattern on the Mohr coefficient is discussed. • A finite element axisymmetric model is presented to compute the strain field into the optical fiber coil. • Computed orthoradial strain is correlated with Rayleigh-OFDR strain measurements. • A procedure to compute Mohr coefficient, thanks to results of finite elements model is presented.