Compact three-frequency resonant optical gyroscope

A passive resonant optical gyroscope operating with three frequencies, the gyroscope comprising:

• a cavity;
• a first injecting laser configured to inject a first optical beam into the cavity in a first direction;
• a second injecting laser configured to inject a second optical beam into the cavity in a direction opposite the first direction;
• a third injecting laser configured to inject a third optical beam into the cavity in one of the two aforementioned directions, one laser amongst one of the injecting lasers, which is selected as master laser, having a master frequency, the two other injecting lasers, which are respectively denoted the first and second slave lasers, respectively having a first slave frequency and a second slave frequency;
• a master servocontrol device configured to directly servocontrol the master frequency to an eigenfrequency corresponding to a resonant mode of the cavity or to servocontrol an eigenfrequency corresponding to a resonant mode of the cavity to the master frequency of the master laser;
• a first servocontrol stage comprising a first slave device and a second slave device that are configured to respectively generate a first frequency error signal and a second frequency error signal having a minimum absolute value when the first and second slave frequencies each correspond to a resonant mode of the cavity, respectively;
• and
• a second servocontrol stage comprising a first optical phase-locking device and a second optical phase-locking device respectively comprising a first slave oscillator and a second slave oscillator that are configured to generate a first radiofrequency offset signal and a second radiofrequency offset signal, wherein
• said first and second optical phase-locking devices being configured to respectively make the first slave laser coherent with the master laser and the second slave laser coherent with the master laser and to servocontrol the first and second slave frequencies to resonant modes of the cavity that are different from the resonant mode corresponding to the master frequency,
• each radiofrequency offset signal of the second servocontrol stage being determined from the corresponding frequency error signal of the first servocontrol stage,
• the first and second optical phase-locking devices respectively comprise a first optical phase-locking device photodetector and a second optical phase-locking device photodetector that are configured to respectively generate a first and a second beat signal, respectively from an optical beam output by the master laser and an optical beam output by the first slave laser, and from an optical beam output by the master laser and an optical beam output by the second slave laser,
• each radiofrequency offset signal has a tunable reference frequency and a reference phase, and wherein each optical phase-locking device is configured to control the frequency of the corresponding slave laser so as to servocontrol the beat signal to the radiofrequency offset signal, the reference frequency being made equal to an integer number of free spectral ranges of the cavity using a correction signal obtained from the corresponding frequency error signal, each slave frequency then respectively being offset from the master frequency by a value corresponding to the corresponding reference frequency, and
• each optical phase-locking device comprises, to achieve the servocontrol of the beat signal to the radiofrequency offset signal:
• a phase comparator configured to compare respectively a phase of the beat signal or of the converted signal and the phase of the radiofrequency offset signal, the comparator being configured to generate a phase error signal;
• and
• control electronics configured to generate a correction signal and to control the slave frequency of the slave laser on the basis of the phase error signal.