Sensor using fiber interferometer

Claim 2

A sensor comprising: a medium for carrying a quantity to be sensed; a coil (24) of fiber optic waveguide arranged such that a light signal travelling in one direction in said waveguide is non-reciprocally affected by said quantity; and a detector (40) for sensing the difference between said first light signal when affected by said quantity.

Claim 3

A sensor apparatus as defined in Claim 1 wherein said coil (24) of fiber optic waveguide comprises: a fiber optic waveguide (24) coiled into a number of turns where the diameter of the turns and spacing thereof are such that a wave to be sensed (26) travels down the longitudinal axis (X) of said coil at the same axial rate that an optical signal propagating in said waveguide (24) around said longitudinal axis (X) moves down said axis (X).

Claim 4

An apparatus as defined in Claim 1 further comprising: a source (32, 34, 36) of light of a selected polarization; a splitter (38) for splitting said polarized light into first and second light signals counterpropagating through said coil (24) of fiber optic waveguide.

Claim 5

An apparatus as defined in Claim 3 wherein said coil (24) of fiber optic waveguide is arranged in said medium such that said first and second light signals are affected unequally by said wave (26).

Claim 6

An apparatus as defined in Claim 3 further comprising a detector (40) to detect the phase shift between said counterpropagating first and second light waves.

Claim 7

An apparatus as defined in Claim 2 wherein the axial length of said coil (24) is a predetermined fraction of the wavelength of the wave to be sensed (26).

Claim 8

An apparatus as defined in Claim 5 wherein said detector (40) is coupled to said coil (24) through a polarizer (36) which is set to pass only light from said coil (24) in the selected polarization of said source (32, 34, 36,) and said coil (24) includes a polarization controller to control the polarization mode of propagation of said first and second light signals.

Claim 9

An apparatus as defined in Claim 1 further comprising: a light source (32); a fiber optic waveguide (34) to guide light from said light source (32) to said coil (24) and from said coil (24) to said detector (40) for sensing; a first directional coupler (42) in said fiber optic waveguide (34) to couple light signals from said coil (24) into said detector (40); a polarizer (36) in said waveguide (34) to block light signals from travelling in said waveguide (34) which are not of a selected polarization; and a second directional coupler (38) coupling said waveguide (34) to said coil (24).

Claim 10

A sensor as defined in Claim 1 further including: a source (32, 34, 36) of light of a selected polarization; and a beam divider (38) for splitting light from said source (32, 34, 36) into a co-propagating first light signal and a counterpropagating second light signal.

Claim 11

An apparatus as defined in Claim 9 wherein said source (32, 34, 36) included a light,source (32) coupled to a polarizer (38) for preventing substantially all light of other than a selected polarization from passing in either direction.

Claim 12

A sensor as detined in Claim 9 wherein said coil (24) of fiber optic waveguide is coiled into a plurality of delay coils (Cl and C2) for delaying light signals travelling therein for a predetermined period, said coils (Cl and C2) separated by a link of transfer waveguide (62) of a predetermined length.

Claim 13

An apparatus as defined in Claim 11 wherein each said delay coil (Cl and C2) consists of a number of turns of a predetermined diameter about a longitudinal axis (X) said turns spaced along said axis such that light signals propagating in said delay coils (Cl and C2) travel in planes substantially parallel to the planes (60) of the subject wave (47) and the optical transit time is approximately 1/4 of the period of said subject wave (26).

Claim 14

An apparatus as defined in Claim 11 wherein said transfer waveguide (62) is arranged between said delay coils (Cl and C2) such that the optical transit time of said first and second counterpropagating light signals is substantially faster than the transit time of said subject wave (47) between said delay coils (Cl and C2) and wherein said delay coils (Cl and C2) are sized and spaced such that said co-propagating first light signal arrives at each lat.er delay coil (C2) at a time when the subject wave (47) has an effect on the optical properties of the coil which is approximately the same as the subject wave (47) affect on the optical properties in the next preceding delay coil (Cl) when said co-propagating light signal was propagating therethrough.

Claim 15

An apparatus as defined in Claim 1 or 9 or 10 or 11 or 12 or 13 wherein said detector (40) detects the phase difference between said first co-propagating light signal and said second counterpropagating light signal by detecting the amplitude of the combined signal resulting form interference of the two light signals.

Claim 16

An apparatus as defined in Claim 11 wherein each said delay coil (Cl and C2) is sized such that the transit time of the first and second light signals through each is approximately 1/4 the period of said subject wave (47) and the spacing between said delay coils (Cl and C2) is 1/4 of the wavelength of the subject wave (47).

Claim 17

An apparatus as defined in Claim 11 wherein each said delay coils (Cl and C2) is sized such that the transit time therethrough for the first and second light signals is equal to some predetermined fraction of the period of the subject wave (47) and wherein the delay coils (Cl and C2) are separated by a distance approximately equal to the same fraction of the wavelength that the transit time in each delay coil (Cl and C2) is of the period of the subject wave (47).

Claim 18

An apparatus as defined in Claim 9 or 10 or 11 or 12 or 13 or 15 or 16 further comprising a polarization controller to control the polarization of said first and second light signals.

Claim 20

An apparatus as defined in Claim 18, further comprising a light source (32, 34, 38) for causing counter propagating first and second light signals to propagate in said coil (24) and wherein said transducer (70) is located at a location on said coil (24) which is offset from the geometric center on the optical path formed by said coil (24).

Claim 21

An apparatus as defined in Claim 19, further comprising a polarizer (36) for causing said light source to couple light of a selected polarization into said coil (24).

Claim 22

An apparatus as defined in Claim 20 wherein said signal q(t) is the quantity Q modulated onto a bias signal having a predetermined relationship with the optical transit time of said counterpropagating light signals around said coil (24).

Claim 23

An apparatus as defined in Claim 21 wherein said predetermined relationship is such that said signal q(t) has a different amplitude at the different times when said first and second light signals arrive at said transducer (70) location.

Claim 24

An apparatus as defined in Claim 21 wherein said transducer (70) is a phase modulator which stretches the fiber optic waveguide in the coil (24) at the location of the transducer (70) such that each of said first and second light signals travels a different optical path around said coil (24) than each would travel in the absence of said signal q(t).

Claim 25

An apparatus as defined in Claim 23 wherein said predetermined relationship is such that said phase modulator stretches said fiber by different amounts at the different times when said first and second light signals arrive at said transducer, thereby causing a phase shift of said first light signal relative to said second light signal.

Claim 26

An apparatus as defined in Claim 24 wherein said detector (40) senses said relative phase shift.

Claim 27

An apparatus as defined in Claim 21 wherein Q is rapidly time varying and q(t) is directly proportional to Q such that q(t) has a different amplitude at the different times said first and second light signals arrive at said transducer.

Claim 28

An apparatus as defined in Claim 21 or 26 wherein said transducer (70) is for changing the birefringence of said fiber in response to q(t).

Claim 29

An apparatus as defined in Claim 21 or 26 wherein said transducer (70) is for changing the velocity of propagation or said first and second light signals in response to q(t).

Claim 30

An apparatus as defined in Claim 21 or 26 wherein said transducer is for shifting the relative phase of said first and second light signals in response to q(t).

Claim 33

The method as defined by Claim 30 wherein said quantity, Q, is modulated to obtain a signal q(t), and q(t) is applied non-reciprocally to said closed loop.

Claim 34

The method as defined by Claim 31 wherein said quantity, q(t), is applied to at least one point of said closed loop optical fiber interferometer which is offset from the geometric center on the optical path formed by said loop.

Claim 35

A method as defined in Claim 30 wherein the step of applying the quantity Q comprises the steps of: applying the quantity Q to the loop such that a first light signal travelling in said loop is uniformly affected by said quantity Q as said first light signal moves through said loop but so that a second counterpropagating light signal is non-uniformly affected by said quantity Q as said second light signal moves through said loop.

Claim 36

A method as defined in Claim 33 wherein said second light signal is first affected by a change having a first arithmetic sign and later is affected by a change having the opposite arithmetic sign.

Claim 37

A method as defined in Claim 34 wherein the magnitudes of the oppositely signed changes to said second light signal are equal, thereby resulting in no net change.