⊗Figure 1. System structure of digital closed-loop FOG. Study on the Drift of Modulated Phase in Interference Fiber Optic Gyroscope

Abstract—Integrated optical chip (IOC) is an essential component in the closed-loop interference fiber optic gyroscope(IFOG) system. One of the main functions of IOC in IFOG is to modulate the phase, which includes the π/2 phase biased by square waves and Sagnac phase biased by ladder waves. In fact, both square waves and ladder waves have high frequency, including multiple harmonic waves and being disturbed easily, which induce the drift of modulated phase in IOC, and has great effect on IFOG performance, such as zero bias and drift. This paper analyzes theoretically the relationship between two kinds of modulated phases and the performance of IFOG drift, and searches for the error information in two kinds of modulated phases. Focusing on different error factors in IOC, the system is optimized in aspects of power source, clock, electromagnetic compatibility (EMC), signal processing and so on, to restrain phase drift error of 2π, then to improve the bias stability of IFOG. Signals of the power source, clock, EMC, and signal processing and so on are tested, the test results show that all these methods are effective to restrain the drift of modulated phase in IOC, the system is stable and reliable. The static testing data of FOG is obtained in Three-axis Turntable, and the static testing data is analyzed quantitatively by using the method of Allan variance to identify random errors related to the drift of modulated phase from all kinds of error sources in the FOG system. The result is shown that the bias stability of the FOG system is better than 0.03°/hr. We also obtained the dynamic testing data of FOG in Three-axis Turntable, the result is shown that scale factor stability of the FOG system is better than 25ppm. To sum up, the whole performance of the IFOG system can meet the requirements of inertial navigation system (INS) with high precision. Index Terms—Interference fiber optic gyroscope (IFOG)