Patent ID: 7038783
Filing Date: 2006-05-02
Classification: G01C

Abstract:
1. A system for detecting the eigen frequency of a sensing coil in a fiber optic gyro (FOG), the FOG comprising a light source, a fiber coupler connected to the light source, an integrated optics chip (IOC) capable of modulating light received from the light source via the fiber coupler, a sensing coil in communication with the IOC, a first modulation generator for imparting a first modulation signal to the light, and a photodetector for receiving light returning from the sensing coil that is representative of a rotation rate of the sensing coil, the system comprising: a second modulation generator for imparting a second modulation signal to the light; a high-frequency demodulator in communication with a signal produced, at least indirectly, by the photodector; and a low-frequency demodulator in communication with the high-frequency demodulator, wherein the high-frequency demodulator receives the second modulation signal as a reference frequency and the low-frequency demodulator receives the first modulation signal as a reference frequency, and wherein an output of the low-frequency demodulator represents a magnitude and sign of a frequency difference between a frequency of the second modulation signal and an even-harmonic of the eigen frequency of the sensing coil.