System for Cancelling Phase Noise in an Interferometric Fiber Optic Sensor Arrangement.
Patent, Filed 24 Apr 91, patented 13 Jul 93,
DEPARTMENT OF THE NAVY WASHINGTON DC
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A fiber optic sensor system for canceling phase noise while it senses a measurand field is disclosed. The system includes circuitry for developing a light beam that is frequency modulated at a fundamental frequency. First and second unbalanced interferometers, having equal path imbalances, are responsive to the frequency modulated light beam for producing respective first and second optical outputs. Detection circuitry is responsive to the fundamental frequency, the second harmonic of the fundamental frequency, and the first and second optical outputs for producing a plurality of sine and cosine signals containing phase difference and phase noise components. A signal processor is responsive to the plurality of sine and cosine signals for cancelling the phase noise components and only producing output sine and cosine components of the difference in the phase shift between the first and second unbalanced interferometers. The system can further include a demodulator for demodulating the sine and cosine components to produce an output signal proportional to the phase shift difference between the first and second unbalanced interferometers.
- Fiber Optics and Integrated Optics