Design, Production, and Analysis of A Low Noise Navigation Grade Fiber Opticgyroscope

Abstract

Inertial Navigation Systems (INS) use an independent navigation technique for tracking the position and direction of an object relative to a known starting point, orientation or velocity. INSs are used in a wide variety of applications such as aircraft, tactical and strategic missiles, spacecraft, submarines and ships. Interferometric fiber-optic gyroscopes (IFOGs) are widely used in military and industrial applications due to their high sensitivity and stability for the INS. Within the scope of this doctoral thesis, extensive research and development studies have been caried out for the improvement of the noise performance of an IFOG. The reduction of the bias errors caused by environmental changes in IFOG systems is one of the important hot topics in this area. As such, in this study, improvements and alternative structures have been proposed for the reduction of the systematic errors in the critical components of the IFOG to eventually obtain a low-noise IFOG configuration that is critical for high sensitivity. In addition to that, an alternative IFOG configuration minimizing the bias errors caused by environmental changes such as temperature and magnetic field, has been proposed. ii For a better performing FOG, it is preferred that the light source, on the main unit, has low noise, high stability, and a wide spectral band. The commonly utilized light sources for FOGs are a fiber-based Amplified Spontaneous Emission (ASE) source and a super-luminescent diode (SLD). Therefore, an optical algorithm has been specifically developed in this study so as to perform optimum spectral measurements of the ASE light source and SLD. The examined optical spectra have clearly revealed that the experimental results are in good agreement with the simulation results. The spectral width of the ASE light source has been improved by 62% from 14.5 nm to 23.5 nm, the temperature dependence of the wavelength has been improved fourfold, and the spectral width has been improved fivefold compared to the minimum configuration of the ASE light source, and thereby the noise of the light source has been minimized. The crystal polarization feature of the multifunctional integrated optical chip (MIOC) has been increased and with this feature the phase noise due to polarization non-reciprocity of the MIOC has been decreased. The system performances of MIOCs fabricated by Annealing Proton Exchange (APE) and Titanium diffusion (Ti-diffusion) methods have been examined and characterized, and the optimum configuration in terms of noise performance has been obtained by performance tests in IFOG. The system performance of the MIOC fabricated by the APE method and Ti-diffusion method without polarizer have been analyzed and the bias error is reduced more than 20 times by using MIOC fabricated by the APE method. The fiber optic coil is the heart of the IFOG and it has been designed to minimize the environmental changes that are critical for the IFOG. These parameters, which are optimized to reduce the system noise that directly affects the IFOG performance, are calculated with different variables and their effect on the noise performance is observed. In the scope of this thesis, it is clearly observed that the new adhesive composition is proposed and this composition has improved Young Modulus more than 3 times the basic adhesive formula. With the experimental application of these parameters, low-noise IFOG is obtained. The temperature-dependent bias sensitivity of the fiber optic coil containing adhesive material with high mechanical strength is calculated as 0.16 (°/h)/(°C/min), and by the adhesive composition developed within the scope of this thesis provides an at least 18 times improvement compared to other designs. In this way, solutions are provided for critical points in system installation and contributed to the iii development of high-precision IFOG production and precision position determination systems. The Faraday effect is a nonreciprocal error source that affects the performance of IFOG, especially the precision of IFOG. In this thesis, a literature search has been made for a more detailed examination of the Faraday effect on the IFOG, and a new and unique method has been developed to suppress this effect in the fiber optic coil. Our theoretical analysis has shown that two orthogonal polarities caused by the Faraday Effect are effectively suppressed by the proposed method and the experimental results are in good agreement with the expectations of our theoretical analysis. According to the experimental results, the bias error is reduced approximately 20 times from ±9.6 °/h/mT to ±0.5 °/h/mT without any additional part. In summary, a low-noise and high-sensitivity IFOG has been developed as the output of this study. During this development, many innovative studies have been carried out and these studies have made significant contributions to the relevant literature. The acquisition of this important technology will take Türkiye one step forward in the production of IFOG and will make it one of the world’s leading countries in this field.