Fiber optic gyroscope refractive index induced error compensation

An error compensator for providing compensation of rotation rate errors arising because of an optical Kerr effect in a coiled optical fiber in a rotation sensor capable of sensing rotation about an axis of said coiled optical fiber formed in a closed optical path in conjunction with at least a first coil coupler which is connected therewith such that electromagnetic waves can be coupled between said coiled optical fiber and a first external optical fiber, said rotation sensing based on having opposing electromagnetic waves propagating through said coiled optical fiber in opposing directions so as to result in each said opposing optical fiber electromagnetic wave impinging at least in part on a corresponding one of first and second photodetectors in a plurality of photodetectors each coupled to a selected one of said coiled optical fiber and said external optical fiber with at least one of said opposing coiled optical fiber electromagnetic waves propagating in one of said opposing directions being subject to having the phasing thereof varied by selected signals supplied to a first input of a first phase modulator, said first photodetector providing an output signal in response to such impingement thereon of a corresponding said opposing coiled optical fiber electromagnetic wave which is representative of that wave, said error compensator comprising:

• a controlled frequency adjustment signal generator means having a frequency adjustment input and having an output electrically connected to said first phase modulator first input, said first controlled frequency adjustment signal generator means being capable of providing an output signal at said output thereof having a basic waveform repeated at a selected first shift operation frequency of a value selected based on signals appearing on said frequency adjustment input;
• a signal component selection means having an input electrically connected to said first photodetector to receive said first photodetector output signal, and an output electrically connected to said first controlled frequency adjustment signal generator means frequency adjustment input, said first signal component selection means being capable of extracting a desired signal component from said photodetector output signal and providing an output signal based thereon at said output thereof;
• an amplitude modulation signal generator means capable of providing amplitude modulation component in said opposing coiled optical fiber electromagnetic waves;
• and
• a compensation means having a first input electrically connected to at least one of said plurality of photodetectors to receive a corresponding photodetector output signal, said compensation means being capable of extracting a plurality of differing characteristics from said corresponding photodetector signal and combining them so as to result in a determination of substantially that rotation rate error due to said optical Kerr effect in said coiled optical fiber.