Fiber optic sensor for detecting very small displacements of a surface
First Claim
1. An apparatus for detecting small displacements of a surface comprising:
- a first directional coupler for dividing a single coherent light signal into first and second coherent light signals;
a first delay line for delaying said first coherent signal relative to said second coherent light signal by a first delay period to provide a delayed first light signal;
a waveguide for directing each of said delayed first and said second light signals onto said surface to produce a first reflected light signal corresponding to said delayed first light signal and a second reflected light signal corresponding to said second light signal;
a second delay line for delaying said second reflected light signal by said first delay period to produce a second delayed reflected light signal; and
a detector for measuring the phase difference between said first reflected light signal and said second delayed reflected light signal to measure variations in the geometric path length between said waveguide and said surface.
1 Assignment
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Accused Products
Abstract
A light source (10) coupled to a first fiber optic waveguide (14) which is coupled by a first directional coupler (22) and a second directional coupler (24) to a second waveguide (20). The first waveguide (14) has a phase modulator (60), a delay loop (62) and a polarization controller (68) therein to cause a differential delay time T on counterpropagating coherent light waves phase modulated at a frequency 1M. The first directional coupler (22) has one part connected to a photodector (28) and the second directional coupler (24) has a probe (20D) coupled to the first fiber (14) and the second fiber (20). The probe directs light toward a surface (18) whereupon the counterpropagating waves are shifted in phase by an amount proportional to the amplitude of displacement of the surface 18.
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Citations
36 Claims
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1. An apparatus for detecting small displacements of a surface comprising:
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a first directional coupler for dividing a single coherent light signal into first and second coherent light signals; a first delay line for delaying said first coherent signal relative to said second coherent light signal by a first delay period to provide a delayed first light signal; a waveguide for directing each of said delayed first and said second light signals onto said surface to produce a first reflected light signal corresponding to said delayed first light signal and a second reflected light signal corresponding to said second light signal; a second delay line for delaying said second reflected light signal by said first delay period to produce a second delayed reflected light signal; and a detector for measuring the phase difference between said first reflected light signal and said second delayed reflected light signal to measure variations in the geometric path length between said waveguide and said surface. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17)
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18. A method of sensing small movements of a surface comprising the steps of:
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directing first and second optical signals to a surface, said first signal preceding said second signal by a time T; receiving third and fourth optical signals reflected from said surface in response to said first and second optical signals, said third signal preceding said fourth signal; delaying said third optical signal by a time T, thereby providing a delayed third optical signal; and causing interference between said delayed third optical signal and said fourth optical signal to determine the relative phase shift therebetween. - View Dependent Claims (19, 20, 21, 22, 23, 24)
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25. A surface acoustic wave sensor comprising:
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a light source; a first optical fiber connected to receive light from said light source; light detector means; a second optical fiber connected to transmit light to said light detector means; a first directional coupler through which said first and second optical fibers pass; a second directional coupler through which said first and second optical fibers pass; and a segment of optical fiber extending from said second directional coupler for directing light from said second directional coupler to a sample and for returning reflected light from said sample to said second directional coupler. - View Dependent Claims (26, 27, 28, 29, 30)
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31. A method of sensing a surface acoustic wave comprising the steps of:
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directing first and second optical signals to a surface, said first signal preceding said second signal by a time, T; receiving third and fourth optical signals reflected from said surface in response to said first and second optical signals, respectively; delaying said third optical signal by a time, T, thereby providing a delayed third optical signal; and combining said delayed third optical signal and said fourth optical signal thereby providing a combined signal. - View Dependent Claims (32, 33, 34, 35, 36)
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Specification