Patent ID: 6490045
Filing Date: 2002-12-03
Classification: G01D

Abstract:
A Sagnac interferometer for sensing a disturbance, the interferometer comprising:a light source arranged to generate a light signal over a range of wavelengths &lgr;s; an optical receiver arranged to receive light signals generated by the light source; a fibre optic loop sensor in optical communication with both the light source and the optical receiver; first optical splitter means, in optical communication with the said source, for spectrally slicing the light signal received from the source into first and second split signal channels, the first split signal channel having a range of wavelengths centred at &lgr;1, and the second split signal channel having a range of wavelengths centred at &lgr;2. wherein both &lgr;1 and &lgr;2 are subsets of &lgr;s and wherein the electromagnetic energy contained within the range of wavelengths centred at &lgr;1 substantially does not overlap with the electromagnetic energy contained within the range of wavelengths centred at X2; first optical combiner means, in optical communication with the optical receiver; the first split signal channel being defined along a first optical path between the optical splitter means and the optical combiner means via the loop sensor and the second split signal channel being defined along a second optical path, different from the first optical path, between the optical splitter means and the optical combiner means via the loop sensor; the first optical path including a first optical phase angle modulating means arranged to modulate the phase angle of light in the first split signal channel at a first frequency, the first optical path having a total optical path length whose centre lies at a first non-central location around the loop sensor; the second optical path including a second optical phase angle modulating means arranged to modulate the phase angle of light in the second split signal channel at a second frequency different from the said first frequency, the second optical path having a total optical path length whose centre lies at a second non-central location different from the said first location around the loop sensor; the first optical combiner means being arranged to combine the phase modulated light in first and second split signal channels into a composite light signal; the optical receiver being arranged to receive the composite light signal and to extract therefrom signal variations arising from light traversing the said first and second optical paths, whereby the distance of the disturbance around the loop sensor may be determined on the basis of the said signal variations.