SYSTEM AND METHOD FOR USING SLOW LIGHT IN OPTICAL SENSORS

• US 20090059238A1
• Filed: 06/13/2008
• Published: 03/05/2009
• Est. Priority Date: 06/15/2007
• Status: Active Grant

• Current Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford Management Co.)
• Original Assignee: Board of Trustees of the Leland Stanford Junior University (Stanford Management Co.)
• Inventors: Fan, Shanhui, Terrel, Matthew A., Digonnet, Michel J.F.
• Granted Patent: US 7,911,622 B2
• Time in Patent Office: Days
• US Class Current: 356/465
• CPC Class Codes: G01C 19/721 Details
• CPC Class Codes: G01D 5/35303 using a reference fibre, e.g. interferometric devices
• CPC Class Codes: Y10T 29/49826 Assembling or joining

Abstract

An optical sensor includes at least one optical coupler and an optical waveguide in optical communication with the at least one optical coupler. The optical waveguide is configured to receive a first optical signal from the at least one optical coupler. The first optical signal has a group velocity and a phase velocity while propagating through at least a portion of the optical waveguide, the group velocity less than the phase velocity. An interference between the first optical signal and a second optical signal is affected by perturbations to at least a portion of the optical sensor.

Claims

1. An optical sensor comprising:

at least one optical coupler; and

an optical waveguide in optical communication with the at least one optical coupler, the optical waveguide configured to receive a first optical signal from the at least one optical coupler, wherein the first optical signal has a group velocity and a phase velocity while propagating through at least a portion of the optical waveguide, the group velocity less than the phase velocity, wherein an interference between the first optical signal and a second optical signal is affected by perturbations to at least a portion of the optical sensor.

2. The optical sensor of claim 1, wherein the interference has a sensitivity to the perturbations which is dependent on the group velocity.

3. The optical sensor of claim 1, wherein the optical waveguide comprises a Bragg fiber.

4. The optical sensor of claim 1, wherein the optical waveguide comprises a photonic-bandgap fiber.

5. The optical sensor of claim 1, wherein the optical waveguide comprises a hollow-core optical fiber.

6. The optical sensor of claim 1, wherein the group velocity is less than 50% of the speed of light in vacuum.

7. The optical sensor of claim 1, wherein the group velocity is less than 20% of the speed of light in vacuum.

8. The optical sensor of claim 1, wherein the perturbations comprise a movement of the optical waveguide relative to another portion of the optical sensor.

9. The optical sensor of claim 8, wherein the movement comprises a rotation of the optical waveguide and the interference is indicative of a rate of rotation of the optical waveguide.

10. The optical sensor of claim 8, wherein the movement comprises a translation of the optical waveguide and the interference is indicative of a velocity of the optical waveguide.

11. The optical sensor of claim 1, wherein the perturbations comprise a change of strain of the at least a portion of the optical waveguide and the interference is indicative of the change of strain.

12. The optical sensor of claim 1, wherein the perturbations comprise a change of temperature of the at least a portion of the optical waveguide and the interference is indicative of the change of temperature.

13. An optical sensor comprising:

at least one optical coupler; and

an optical waveguide configured to receive a first optical signal and a second optical signal from the at least one optical coupler, wherein light propagates through at least a portion of the optical waveguide with a group velocity and a phase velocity, the group velocity less than the phase velocity, wherein the optical waveguide is configured to move along a first direction while the first optical signal propagates through the optical waveguide in the first direction and the second optical signal propagates through the optical waveguide in a second direction generally opposite to the first direction, wherein an interference between the first optical signal and the second optical signal is affected by perturbations to at least a portion of the optical sensor.

14. The optical sensor of claim 13, wherein the group velocity is less than 50% of the speed of light in vacuum.

15. The optical sensor of claim 13, wherein the interference has a sensitivity to the perturbations which is inversely proportional to the group velocity.

16. An optical sensor comprising:

a fiber coupler configured to receive light from a light source and to transmit light to a light detector; and

a fiber coil optically coupled to the fiber coupler, at least a portion of the fiber coil comprising an optical fiber through which light propagates with a group velocity and a phase velocity, the group velocity less than the phase velocity, at least one of the fiber coil and the fiber coupler configured to move relative to the other such that a first optical pathlength between a first portion of the fiber coil and the fiber coupler increases and a second optical pathlength between a second portion of the fiber coil and the fiber coupler decreases, wherein a first portion of the light received by the fiber coupler from the light source propagates from the fiber coupler, through the fiber coil in a first direction, and back to the fiber coupler and a second portion of the light received by the fiber coupler from the light source propagates from the fiber coupler, through the fiber coil in a second direction opposite to the first direction, and back to the fiber coupler, the first portion of the light and the second portion of the light propagating to the light detector and interfering with one another, wherein the interference between the first portion of the light and the second portion of the light is indicative of the movement of the fiber coil relative to the fiber coupler.

17. The optical sensor of claim 16, wherein the fiber coil is configured to rotate about a direction generally perpendicular to the fiber coil with a rotation rate, the interference indicative of the rotation rate.

18. The optical sensor of claim 17, wherein the fiber coupler comprises a prism coupler.

19. The optical sensor of claim 17, wherein the rotation of the fiber coil is less than 20 degrees.

20. The optical sensor of claim 16, wherein the first portion of the fiber coil comprises a first end of the fiber coil and the second portion of the fiber coil comprises a second end of the fiber coil.

21. The optical sensor of claim 20, wherein the fiber coupler comprises a first port and a second port, the first port optically coupled to the first end of the fiber coil and the second port optically coupled to the second end of the fiber coil.

22. The optical sensor of claim 21, further comprising a first gap between the first port and the first end such that optical signals traveling between the first port and the first end propagate in free space.

23. The optical sensor of claim 22, further comprising a second gap between the second port and the second end such that optical signals traveling between the second port and the second end propagate in free space.

24. The optical sensor of claim 21, further comprising a first lengthwise stretchable optical waveguide between the first port and the first end.

25. The optical sensor of claim 24, further comprising a second lengthwise stretchable optical waveguide between the second port and the second end.

26. The optical sensor of claim 16, wherein the optical fiber comprises a Bragg fiber.

27. The optical sensor of claim 16, wherein the optical fiber comprises a photonic-bandgap fiber.

28. The optical sensor of claim 16, wherein the group velocity is less than 50% of the speed of light in vacuum.

29. The optical sensor of claim 16, wherein the interference has a sensitivity to the movement of the fiber coil relative to the fiber coupler which is dependent on the group velocity.

30. A method of fabricating an optical sensor having a first sensitivity to changes of a first measurand and a second sensitivity to changes of a second measurand, the method comprising:

providing an optical waveguide through which light is configured to propagate with a group velocity and a phase velocity, the group velocity less than the phase velocity, wherein a first enhancement of the first sensitivity is dependent on a group index of the optical waveguide and a second enhancement of the second sensitivity is dependent on the group index;

selecting the group index such that the first enhancement is greater than the second enhancement.

31. The method of claim 30, wherein the first measurand is strain and the second measurand is temperature.