| Sagnac interferometer is a typical two-beam interferometer, whose primary application area is the interferometric fiber-optic gyroscope(IFOG). Based on Sagnac effect, IFOG is able to measure an object’s rotation rate relative to the inertial frame. The focus of this dissertation is open-loop IFOG’s digital signal processing method.The hardware of an IFOG consists of optical part and signal processing circuit. In this dissertation, typical optical parts of open-loop IFOG are described, with analysis on the main optical components’ erformance. The design of signal processing circuirts is also introduced, and the focus is on individual electronic components selection and operational principles. A number of demodulation schemes have been proposed for open-loop IFOG, and this dissertation summarizes the ideas of several schemes.The central part of this dissertation is multi-harmonic based digital signal processing scheme for open-loop IFOG, which is realized on Field Programmable Gate Array(FPGA). Digital lock-in amplifier(LIA) is used to detect the weak signals generated by the IFOG’s photo detector. One innovation of this diseration is the adoption of high efficient, resource-saving CORDIC algorithm to accomplish important signal processing steps including modulation sine wave generation, phase-sensitive detector of the LIA and Sagnac phase demodulation. Moreover, engineering problems like modulation depth control and demodulation of critical phase points are also discussed in detail. Major error sources of the digital signal processing are analyzed, with a focus on the bias caused by phase modulator nonlinearity. The other innovation is the proposal of a demodulation scheme based on digital phase tracking.The proposed open-loop IFOG has the following performance under normal temperature condition:scale factor nonlinearity is 818ppm over ±200°/ s rotation rate range, zero bias is - 10.60°/h, bias instability is 0.046°/h and random walk coefficient is 0.008°/√h. |
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