Method and system for detecting optical ring resonator resonance frequencies and free spectral range to reduce the number of lasers in a resonator fiber optic gyroscope

A method of measuring a free spectral range (FSR) of a gyroscope resonator in a resonator fiber optic gyroscope, the method comprising:

• modulating a laser to emit a clockwise optical beam with sidebands at up-shifted and down-shifted frequencies, wherein a laser modulation frequency is one of a first multiple integral of a FSR or the first multiple integral of the FSR plus a delta;
• and
• coupling the clockwise optical beam into a clockwise input port of the gyroscope resonator;
• coupling a counter-clockwise optical beam into a counter-clockwise input port of the gyroscope resonator;
• periodically switching the modulation frequency of the laser between fmod+ and fmod− to cancel out errors due to imperfection in the modulation;
• and
• measuring the FSR of the gyroscope resonator based on the switching.

A resonator fiber optic gyroscope, comprising:

• a gyroscope resonator having a clockwise input port and a counter-clockwise input port and a free spectral range (FSR);
• a first laser configured to couple a clockwise optical beam into to the clockwise input port;
• a clockwise Pound-Drever-Hall modulation generator;
• a clockwise phase modulator communicatively coupled to the clockwise Pound-Drever-Hall modulation generator, the clockwise phase modulator operable to modulate the clockwise optical beam;
• a clockwise transmission photodetector positioned to detect the optical beam output from the counter-clockwise input port of the gyroscope resonator;
• first bias correction electronics to input signals from the clockwise transmission photodetector;
• first free spectral range (FSR)-detection-and-servo electronics to input signals from the clockwise transmission photodetector, wherein the first FSR-detection-and-servo electronics include a first switch;
• clockwise Pound-Drever-Hall servo electronics to input signals from the first bias correction electronics and to output signals to the clockwise phase modulator and to the first laser;
• a second laser configured to couple a counter-clockwise optical beam into to the clockwise input port;
• a counter-clockwise Pound-Drever-Hall modulation generator;
• a counter-clockwise phase modulator communicatively coupled to the counter-clockwise Pound-Drever-Hall modulation generator, the counter-clockwise phase modulator operable to modulate the counter-clockwise optical beam;
• a counter-clockwise transmission photodetector positioned to detect the optical beam output from the counter-clockwise input port of the gyroscope resonator;
• second bias correction electronics to input signals from the counter-clockwise transmission photodetector;
• second FSR-detection-and-servo electronics to input signals from the counter-clockwise transmission photodetector, the second FSR-detection-and-servo electronics including a second switch, wherein the first switch and second switch are operable to periodically switch a modulation frequency of the respective first and second laser between a first modulation frequency and a second modulation frequency.