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US RE34,604 EGranted
Sensor using fiber interferometer
AssigneeStanford University
InventorHerbert J. Shaw
Life of this patent
Estimating the term…
Abstract
A closed loop optical fiber interferometer is used in sensing a quantity, Q, by applying a time varying or modulated measure of, Q, asymmetrically to the closed loop (24) and detecting phase shift between two counterpropagating optical signals in the closed loop. The closed loop (24) can be used in the sensing element or a separate sensor (68, 70) can develop a time varying signal which is then applied to the closed loop interferometer.
Claims26
An apparatus for sensing, comprising:
- an interferometer having a [coil of] loop comprising an optical [fiber] waveguide for propagating light, a light source for producing said light, and a coupling device for coupling said light to said [coil] loop to provide first and second counterpropagating light signals which propagate in opposite directions through said [coil] loop along an optical path formed by said [coil] loop ;
- a detector for detecting the phase difference between said light signals after propagating through said [coil] loop , said detector providing an output signal;
- a modulator for sensing a time varying quantity, Q, independently of said output signal, said modulator adapted to generate a carrier signal and modulate said carrier signal with said quantity Q, said modulator thereby transforming Q into a time varying signal q(t);
- and
- a transducer for receiving said time varying signal q(t) from said modulator and modulating the light propagating through said [coil] loop in accordance with the signal q(t), said transducer located at a location on said [coil] loop which causes said quantity Q to be applied asymmetrically to said loop such that the detected phase difference between said signals varies in response to the quantity Q.
2 more elements
An apparatus as defined in claim [1] 23 , wherein said transducer changes the birefringence of said fiber in response to q(t).
An apparatus for sensing, comprising:
- an interferometer having a coil of optical fiber for propagating light and a detector for detecting said light to provide an output signal;
- a modulator for sensing a time varying quantity, Q, independently of said output signal, said modulator adapted to generate a carrier signal and modulate said carrier signal with said quantity Q, said modulator thereby transforming said quantity Q into a time varying signal q(t);
- and
- a transducer for receiving said time varying signal q(t) from said modulator and modulating the light propagating through said coil in accordance with the signal q(t), said signal q(t) varying in amplitude.
1 more element
An apparatus for sensing, comprising:
- an interferometer having a coil of optical fiber for propagating light, a light source for producing said light, and a coupling device for coupling said light to said coil to provide first and second counterpropagating light signals which propagate in opposite directions through said coil along an optical path formed by said coil;
- a detector for detecting the phase difference between said light signals after propagating through said coil, said detector providing an output signal;
- a modulator for sensing a time varying quantity, Q, independently of said output signal, said modulator adapted to generate a carrier signal and modulate said carrier signal with said quantity Q, said modulator thereby transforming Q into a time varying signal q(t);
- and
- a transducer for receiving said time varying signal q(t) from said modulator and modulating the light propagating through said coil] in accordance with the signal q(t), wherein said transducer comprises a phase modulator which causes phase modulation by stretching the optical fiber such that each of said first and second light signals travels a different optical path around said coil than each would travel in the absence of said signal q(t), said transducer located at a location on said coil which causes said quantity Q to be applied asymmetrically to said loop such that the detected phase difference between said signals varies in response to the quantity Q.
2 more elements
An apparatus for sensing, comprising:
- an interferometer having a [coil of] loop comprising an optical [fiber] waveguide for propagating first and second light signals in opposite directions through said [coil] loop along an optical path formed by said light to provide an output signal;
- a modulator for sensing a time varying quantity, Q, independently of said output signal, said modulator adapted to generate a carrier signal and modulate said carrier signal with said quantity Q, said modulator thereby transforming Q into a time varying signal q(t);
- and
- a transducer for receiving said time varying signal q(t) from said modulator and modulating the light propagating through said [coil] loop in accordance with the signal q(t), said transducer changing the velocity of propagation of said first and second light signals in response to q(t).
1 more element
An apparatus for sensing, comprising:
- an interferometer having a [coil of] loop comprising an optical [fiber] waveguide for propagating first and second light signals in opposite directions through said [coil] loop along an optical path formed by said [coil] loop and a detector for detecting said light to provide an output signal;
- a modulator for sensing a time varying quantity, Q, independently of said output signal, said modulator adapted to generate a carrier signal and modulate said carrier signal with said quantity Q, said modulator thereby transforming Q into a time varying signal q(t);
- and
- a transducer for receiving said time varying signal q(t) from said modulator and modulating the light propagating through said [coil] loop in accordance with the signal q(t), said transducer shifting the relative phase of said first and second light signals in response to q(t).
1 more element
A method of sensing a time varying quantity, Q, utilizing an [optical fiber] interferometer having, [comprised of] a loop [of] comprising an optical waveguide [fiber] which forms an optical path having an optical path length, a light source for producing light, a coupling device for splitting the light into two counterpropagating light signals which traverse said optical path in opposite directions, and a detector for detecting the phase difference between the signals after traversing the optical path length, said method comprising the steps of:
- generating a signal q(t) in response to the time varying quantity Q by superimposing said quantity Q on a bias signal;
- converting the signal q(t) to a corresponding change in the optical properties of the optical path at a location on said loop which is offset from the midpoint of said optical path length such that said phase difference varies in response to the quantity Q;
- detecting said phase difference;
- and
- producing a signal indicative of said phase difference to sense a quantity Q.
2 more elements
An apparatus for sensing a time varying signal, Q, comprising:
- [a fiber optic] an interferometer having a [closed] loop [of] comprising an optical waveguide [fiber] for propagating first and second light waves in opposite directions about said loop;
- means for receiving said time varying signal, Q, and for modulating a bias signal in accordance with said signal, Q, to transform the signal Q into a time varying signal q(t);
- means for altering optical transmission of said lightwaves propagating in said [fiber optic] loop in response to said signal q(t) to produce a phase difference between said first and second light waves;
- and
- means for detecting said phase difference between said first and second light waves caused by said altering means, said phase difference being indicative of said quantity Q.
2 more elements
An apparatus for sensing a time varying quantity Q, comprising:
- an interferometer having an optical fiber for forming an optical path for two counterpropagating light waves;
- and
- a modulator responsive to said quantity Q for modulating a bias signal in accordance with the same time varying quantity Q, said modulator connected to drive a transducer disposed at a location on said optical fiber which is offset from the center of said optical path, for locally altering the propagation characteristics in said optical path at said location to cause a phase shift between said waves, said phase shift being indicative of said quantity Q.
An apparatus for sensing, comprising:
- an interferometer having a loop comprising an optical waveguide for propagating light and a detector for detecting said light to provide an output signal;
- a modulator for sensing a time varying quantity, Q, independently of said output signal, said modulator adapted to generate a carrier signal and modulate said carrier signal with said quantity Q, said modulator thereby transforming said quantity Q into a time varying signal q(t);
- and
- a transducer for receiving said time varying signal 20 q(t) from said modulator and modulating the light propagating through said loop in accordance with the signal q(t), said signal q(t) varying in amplitude.
1 more element
An apparatus for sensing a time varying quantity comprising:
- an interferometer having an optical waveguide for forming an optical path for two counterpropagating light waves;
- and
- a modulator responsive to said quantity for modulating a bias signal in accordance with the same time varying quantity, said modulator connected to drive a transducer disposed at a location on said optical waveguide which is offset from the center of said optical path, for locally altering the propagation characteristics in said optical path at said location to cause a phase shift between said waves, said phase shift being indicative of said quantity Q.
Dependencies are inferred from the claim text.