Theory And Methods Of Characterizing Temperature Transient Effects In FOG Fiber Coils

Fiber coil is the most important component in a fiber optic gyro (FOG) because its winding quality directly reflects the performance of the gyro. Traditional methods (for example, evaluating polarization-maintaining fiber coil by the extinction ratio) only characterize the static properties of a FOG fiber coil and therefore are insufficient for obtaining its complete quality information. To overcome the limitations of the traditional methods, we establish a new method, with supporting theory, for characterizing the performance of a FOG fiber coil under the influence of different temperature transients. With this method, one can obtain the complete information on the winding quality of a fiber coil without the need of integrating the coil into a final gyro. Specifically, the major accomplishments of this thesis are as follows:1. A three-dimensional (3-D) mathematical model of a fiber coil in response to different temperature transients is established to fully describe the dependence of the nonreciprocity in a fiber coil caused by temperature gradient along the radial, axial, and circumferential directions respectively. This is the theoretical basis for the new testing method. In addition, a software package is developed to describe different winding patterns of the fiber coil under the 3-D mathematical model.2. A 3-D finite element model of the fiber coil is developed to simulate heat transfer induced by different temperature excitations by using the finite element analysis techniques. Using the information on the thermal fields, we are able to quantitatively analyze the 3-D responses of the fiber coil to different temperature transients. We then validate the 3-D model by comparing numerical and experimental results. Finally, the feasibility of the new method of using different temperature excitations to test fiber coil's transient temperature responses is confirmed theoretically.3. A test system is developed for the complete characterization of a FOG fiber coil's temperature transient characteristics. The system includes a measurement platform, an algorithm for the quick and accurate determination of fiber coil's eigen frequency, an FOG calibration platform, and different temperature excitation sources.4. With the temperature transient characterization system for FOG fiber coils, experiments are conducted to see how a FOG coil responds to different temperature excitations when its symmetry properties are purposely changed. The effectiveness of the temperature transient characterization method in obtaining the complete quality information of a fiber coil is successfully verified. Finally, the Effective Degrees of Asymmetry in radial and axial directions are introduced respectively to quantify asymmetric properties of the fiber coil caused by imperfect fiber winding.5. The method of periodic temperature excitation is introduced to compensate for the shortcomings of constant temperature excitation, and its feasibility is experimentally and theoretically demonstrated. The experimental results indicate that the periodic temperature excitation method is more superior in repeatability, accuracy and efficiency than the constant temperature excitation method.