Stabilized fiber optic sensor
First Claim
1. A fiber optic sensor, comprising:
- a single uninterrupted strand of optical fiber having first and second end portions and a loop portion therebetween;
fiber optic coupling means for optically closing said fiber loop;
means for applying a lightwave to said first end portion for propagation through said fiber to said second end portion to provide an optical output signal, the intensity of said optical output signal dependent upon the length of said loop;
means for controlling the roundtrip phase delay of light circulating through said fiber loop to provide a resonant cavity for said circulating light;
said fiber loop length sensitive to first and second ambient effects, said first ambient effect varying in a first frequency range, said second ambient effect varying in a second frequency range;
means for compensating for fiber loop length changes caused by said first ambient effect to stabilize said output signal against said first ambient effect, said output signal remaining sensitive to said second ambient effect; and
means for detecting intensity variations in said output signal to detect said second ambient effect.
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Accused Products
Abstract
A fiber optic sensor comprises a length of optical fiber, forming a loop, and a fiber optic directional coupler for optically closing the loop. The loop and coupler form a resonant cavity for light circulating therethrough. A PZT cylinder, about which the fiber loop is wrapped, is utilized to control the total round trip phase delay of the circulating light, and thus, control the intensity of the optical output signal. The phase delay is adjusted to a point where the optical output signal is at maximum sensitivity to changes in phase. When the fiber loop is exposed to, e.g., acoustic waves, the loop length changes correspondingly, thereby causing the phase delay, and thus, the optical output signal to vary. By detecting variations in output signal intensity, the frequency and intensity of the acoustic waves may be determined. The sensor also includes a feedback system for stabilizing the fiber loop against low frequency thermal drift.
59 Citations
21 Claims
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1. A fiber optic sensor, comprising:
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a single uninterrupted strand of optical fiber having first and second end portions and a loop portion therebetween; fiber optic coupling means for optically closing said fiber loop; means for applying a lightwave to said first end portion for propagation through said fiber to said second end portion to provide an optical output signal, the intensity of said optical output signal dependent upon the length of said loop; means for controlling the roundtrip phase delay of light circulating through said fiber loop to provide a resonant cavity for said circulating light; said fiber loop length sensitive to first and second ambient effects, said first ambient effect varying in a first frequency range, said second ambient effect varying in a second frequency range; means for compensating for fiber loop length changes caused by said first ambient effect to stabilize said output signal against said first ambient effect, said output signal remaining sensitive to said second ambient effect; and means for detecting intensity variations in said output signal to detect said second ambient effect. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10)
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11. A method of sensing acoustic waves utilizing an optical fiber, said method comprising:
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forming a loop in said fiber; applying input light for propagation through said loop to provide an optical output signal; using a fiber optic coupler to optically close said loop; selecting the length of said loop to provide a resonant cavity, said loop length affecting the intensity of said output signal; compensating for thermally induced loop length changes to stabilize said output signal intensity against said thermally induced changes; and detecting said output signal to sense the presence of said acoustic waves. - View Dependent Claims (12, 13)
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14. A method of sensing an ambient effect utilizing an optical fiber, having first and second end portions, said method comprising:
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forming a loop in said fiber, between said first and second end portions; optically closing said loop to provide a resonant cavity for light circulating in said loop; applying input light to said first end portion, for propagation through said fiber loop to provide an optical output signal at said second end portion, said output signal sensitive to the total roundtrip phase delay of light circulating in said fiber loop; controlling the roundtrip phase delay of light circulating through said fiber loop to adjust said optical output signal to a selected value, between a minimum value, corresponding to full resonance of said light circulating in said loop, and a maximum value corresponding to non-resonance of said light circulating in said loop; exposing said loop to said ambient effect to cause variations in said roundtrip phase delay; and detecting said ambient effect by observing variations from said selected value. - View Dependent Claims (15, 16, 17)
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18. A fiber optic sensor for sensing an ambient effect, comprising:
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an optical fiber having first and second end portions and a loop portion therebetween; means for optically closing said loop to provide a resonant cavity; means for applying a lightwave to said first end portion for propagation through said loop to said second end portion to provide an optical output signal; means for controlling the total roundtrip phase delay for light in said loop to adjust said output signal to a selected value, between a minimum value, corresponding to full resonance of said lightwave in said loop, and a maximum value, corresponding to nonresonance of said lightwave in said loop; and means for detecting variations in said output signal from said selected value to sense said ambient effect. - View Dependent Claims (19, 20, 21)
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Specification