Online Evaluation Technology for Fiber-Optic Coil Assembly in Depolarized Fiber-Optic Gyroscope

The depolarized fiber optic gyroscope (DFOG) uses single-mode fibers (SMFs) to fabricate a depolarized fiber optic coil, which has obvious cost advantages in high sensitivity and precision rotation measurement applications, such as fiber optic rotary seismometers, etc. The depolarized fiber coil assembly (DFCA) is the key component of DFOG, consisting of a SMF coil and at least two polarization maintaining fibers (PMFs) depolarizers. To control the quality of the DFCA, this paper proposes an online evaluation technology for it. A more accurate broad-spectrum light source spectral modulation model is established based on polarization mode interference in the DFCA. The model simulation and experimental testing indicate that the modulated spectrum is a multi-period deep modulated spectrum, and the envelope is the same as the input spectrum. Moreover, the self-coherence curve of the modulated spectrum was calculated, and it contains multiple coherent peaks. It was found that the position and amplitude of self-coherence peaks are determined by the length of PMFs and polarization angular deviation at joint points, respectively. A spectrometer was used to replace the detector of the DFOG and an online testing system for the quality of the DFCA was built and an online evaluation process and algorithm is developed. The exact length of PMFs and angular deviation of depolarizers are obtained. The proposed technology has the advantages of easy implementation and high sensitivity, making it well-suited for monitoring and evaluating the quality of DFCA for an assembled high-precision depolarized FOG.