Modulation frequency control in a fiber optic rotation sensor
First Claim
1. Apparatus for controlling the frequency of a modulation signal applied to a pair of counter-propagating light waves in an optical waveguide loop, comprising:
- signal generator means, for generating the modulation signal having a certain frequency;
phase modulator means, for phase modulating said light waves in response to said modulation signal;
means for combining said light waves to form an optical output signal; and
detection means, for detecting said optical output signal, and for providing a feedback signal proportional to the magnitude of a component of said optical output signal, said magnitude of said component being proportional to any deviation in the frequency of the modulation signal from said certain frequency, said signal generator means being responsive to said feedback signal in generating the modulation signal at a frequency equal to said certain frequency, said magnitude of said component being driven to zero when the frequency of the modulation signal equals said certain frequency.
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Abstract
In a fiber optic rotation sensor having a pair of light waves counter-propagating in an optical waveguide loop, a phase modulator is driven by a modulating signal at the loop eigenfrequency. Upon exiting the loop the waves are combined into a light intensity signal which is sensed, the sensed signal including a component in quadrature with a desired rotation rate component, the magnitude of the quadrature component being proportional to any deviations in the frequency of the modulating signal from the loop eigenfrequency. The phase modulator is servo-controlled so as to drive the quadrature component to zero, thereby compensating for any deviations in the modulator frequency from the loop eigenfrequency.
56 Citations
23 Claims
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1. Apparatus for controlling the frequency of a modulation signal applied to a pair of counter-propagating light waves in an optical waveguide loop, comprising:
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signal generator means, for generating the modulation signal having a certain frequency; phase modulator means, for phase modulating said light waves in response to said modulation signal; means for combining said light waves to form an optical output signal; and detection means, for detecting said optical output signal, and for providing a feedback signal proportional to the magnitude of a component of said optical output signal, said magnitude of said component being proportional to any deviation in the frequency of the modulation signal from said certain frequency, said signal generator means being responsive to said feedback signal in generating the modulation signal at a frequency equal to said certain frequency, said magnitude of said component being driven to zero when the frequency of the modulation signal equals said certain frequency. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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12. A fiber optic rotation sensor, comprising:
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an optical waveguide loop; means for providing a pair of light waves counter-propagating in said loop; signal generator means, for generating a modulation signal having a certain frequency; phase modulator means, for phase modulating said light waves in response to said modulation signal; means for combining said light waves after counter-propagating in said loop, and for providing an optical output signal indicative thereof, said combined light waves having a phase difference therebetween proportional to any rotation of said loop; detection means, for detecting said optical output signal, and for providing a feedback signal proportional to the magnitude of a component of said optical output signal, said magnitude of said component being proportional to any deviation in the frequency of said modulation signal from said certain frequency, said signal generator means being responsive to said feedback signal in generating the modulation signal at a frequency equal to said certain frequency, said magnitude of said component being driven to zero when the frequency of said modulation signal equals said certain frequency. - View Dependent Claims (13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23)
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Specification