Reduction of demodulator offset errors in fibre-optic gyroscopes
First Claim
1. A fibre-optic gyroscope comprising:
- a light source;
a coil of optical fibre, connected to the light source for receiving light therefrom;
beam splitting/combining means for splitting light from the light source and directing it in opposite directions around the coil and then combining said light;
phase modulation means for modulating the phase of the light in the coil in accordance with a combined signal produced by combining a first signal at a first frequency with a second chopper signal at a frequency lower than the first frequency so as to produce a phase shift in the light passing through the coil;
a light detector for detecting the combined light passing from said coil and for producing an output signal;
a first rate demodulator for demodulating the output from the light detector so as to produce an output signal whose amplitude is a measure of the non-reciprocity occurring in the gyro as well as a dc signal of which part will be due to the offsets in the first rate demodulator;
second demodulation means for demodulating the output signal from the first demodulator at a frequency lower than the frequency at which the first demodulator operates so as to produce a signal whose amplitude is substantially unaffected by any dc signal due to the offsets in the second demodulator and is substantially a measure of the non-reciprocity occurring in the gyro.
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Accused Products
Abstract
A fibre optic gyroscope which reduces the sensitivity of the gyroscope to offsets in the demodulator, the reduction in sensitivity being achieved by modulating the radiation passing through the gyroscope by a first waveform which is derived from second and third periodic waveforms, the third waveform having a frequency substantially less than that of the second waveform in use and the second waveform having a frequency of about 1/2T where T is the time taken for the radiation to travel through the gyroscope, and detecting said radiation which is subsequently demodulated with respect to both second and third waveforms in order to minimize any offset introduced by the demodulation with respect to the second waveform.
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Citations
11 Claims
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1. A fibre-optic gyroscope comprising:
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a light source; a coil of optical fibre, connected to the light source for receiving light therefrom; beam splitting/combining means for splitting light from the light source and directing it in opposite directions around the coil and then combining said light; phase modulation means for modulating the phase of the light in the coil in accordance with a combined signal produced by combining a first signal at a first frequency with a second chopper signal at a frequency lower than the first frequency so as to produce a phase shift in the light passing through the coil; a light detector for detecting the combined light passing from said coil and for producing an output signal; a first rate demodulator for demodulating the output from the light detector so as to produce an output signal whose amplitude is a measure of the non-reciprocity occurring in the gyro as well as a dc signal of which part will be due to the offsets in the first rate demodulator; second demodulation means for demodulating the output signal from the first demodulator at a frequency lower than the frequency at which the first demodulator operates so as to produce a signal whose amplitude is substantially unaffected by any dc signal due to the offsets in the second demodulator and is substantially a measure of the non-reciprocity occurring in the gyro. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11)
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Specification