Technology Research Of Digital Closed-loop Solution Of Sagnac Fiber Interferometer

Sagnac fiber interferometer, also called interferometric fiber optic gyroscope (IFOG) is a device based on Sagnac effect and is used to measure the rotation velocity. The digital closed-loop FOG detection solution has a wide range of applications in the industrial field with its wide dynamic range and high precision characters.IFOG technology of digital closed-loop detection solution is proposed here. Firstly, analysed the optical structure, device, noise and error mechanism of the system. Secondly, systematic analyed closed-loop detection solution and came to a steady-state angular velocity error is zero and zero angle error conditions. Designed and analyzed a second close loop in order to improve the stability of the system linearity. Thirdly, analyzed the various components of the signal processing circuitry. Then, several major technologies which can improve the performance of IFOG are showed. A new double-sensitivity structure of IFOG is proposed, dead zone is eliminated and the maximum detection range is extended. Finally, two prototypes of IFOG are developed and tested their performances.The results of experiments are listed as follows. Under normal temperature condition, the scale factor stability of IFOG is6.38ppm, the bias is-7.72°/h (Containing the projection of the Earth’s rotation in Hangzhou which is-7.56°/h), the bias stability is0.01°/h, and the random walk coefficience is0.002°/(?)h. Under the full temperature range of-40℃C伍～60℃conditon, when temperature is constant, the bias repeatability is about l°/h, the bias stability is0.01°/h, the random walk coefficience is0.005°/(?)h. when temperature is varying at the speed of1℃/min, the performance is poor and both PCB and optical fiber coil will induce zero bias error. The double-sensitivity IFOG prototype is only tested at room temperature, and its scale factor stability is60.2ppm (discrete devices impacts its performance), the bias is-7.45°/h (Containing the projection of the Earth’s rotation which is-7.56°/h), the bias stability is0.006°/h, and the random walk coefficient is0.002°/(?)h, which means the performance of this kind of IFOG is improved.