Patent ID: 9267799
Filing Date: 2016-02-23
CPC Classification: G01C,G02F

Claim Text:
1. A resonator fiber optic gyroscope comprising: a first light source configured to produce a first laser beam having a first carrier frequency; a second light source configured to produce a second laser beam having a second carrier frequency; a first modulator coupled to the first light source and configured to modulate the first laser beam, the modulated first laser beam comprising the first carrier frequency and a first plurality of sideband frequencies; a second modulator coupled to the second light source and configured to modulate the second laser beam, the modulated second laser beam comprising the second carrier frequency and a second plurality of sideband frequencies; a first optical coupler coupled to an output of the first modulator and configured to split off a portion of the modulated first laser beam; a second optical coupler coupled to an output of the second modulator and configured to split off a portion of the modulated second laser beam; a beam combiner coupled to the first optical coupler and the second optical coupler; the beam combiner configured to combine the portion split off the modulated first laser beam with the portion split off the modulated second laser beam to produce a combined signal containing a carrier beat frequency between the first carrier frequency and the second carrier frequency; a filter configured to select a range of frequencies in the combined signal; a photodetector configured to convert the combined signal to an electrical signal; and a processor configured to perform a fast Fourier transform (FFT) on the filtered electrical signal, to track the carrier beat frequency based on the FFT, and to output a rate signal based on the carrier beat frequency which indicates a rotation rate of the resonator fiber optic gyroscopes; wherein the processor is further configured to identify the carrier beat frequency by outputting a command to the first modulator and to the second modulator to turn off modulation of the first laser beam and the second laser beam such that the first laser beam and the second laser beam are unmodulated; wherein the beam combiner combines a portion of the unmodulated first laser beam with a portion of the unmodulated second laser beam to produce a combined signal containing the carrier beat frequency without sideband beat frequencies; and wherein the processor is further configured to perform the FFT on the combined signal containing the carrier beat frequency without sideband beat frequencies, to identify the carrier beat frequency based on the FFT of the combined signal containing the carrier beat frequency without sideband beat frequencies, and to output a command to the first modulator and to the second modulator to turn on modulation of the first laser beam and the second laser beam after identifying the carrier beat frequency.