Accurate Prediction of Thermal Bias Drift of km-Level FOG Coil Using High-Performance OFDR

The degradation of optical symmetry caused by the thermal strain of the fiber coil results in the thermal bias drift of fiber optic gyro (FOG). This paper presents a method for quantitative analysis of the optical symmetry of the fiber coil and accurate prediction of thermal bias drift in FOG. Firstly, a thermal strain model is established to illustrate the strain characteristics of the layer structure in the fiber coil under temperature fields, emphasizing the importance of thermal strain on optical symmetry. Then, an equivalent asymmetric index (<italic xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">α_Tk</i>) is introduced to quantitatively evaluate the optical symmetry of the fiber coil. By deriving equations for optical symmetry and thermal bias drift caused by thermal strain, a novel method is proposed to predict and optimize the thermal bias drift. This method utilizes high-performance OFDR to measure temperature and strain in a 3 km fiber coil to predict thermal bias drift. It also discusses the relationship between the length of the tail fiber and optical symmetry, predicting the precise length required to optimize thermal bias drift. Subsequently, the same fiber coil is placed in the FOG to verify the accuracy of the thermal bias drift prediction. Adjusting the length of the tail fiber reduces the thermal bias drift from 0.33 °/h to 0.13 °/h.