FIBER BRAGG GRATING DEVICES UTILIZING SLOW LIGHT

• US 20110001981A1
• Filed: 06/02/2010
• Published: 01/06/2011
• Est. Priority Date: 06/05/2009
• 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., Wen, He
• Granted Patent: US 9,019,482 B2
• Time in Patent Office: Days
• US Class Current: 356/477
• CPC Class Codes: G01D 5/35316 using a Bragg gratings
• CPC Class Codes: G01J 9/0246 Measuring optical wavelength
• CPC Class Codes: G01K 11/3206 at discrete locations in the fibre, e.g. using Bragg scattering
• CPC Class Codes: G01L 1/246 using integrated gratings, e.g. Bragg gratings
• CPC Class Codes: G02B 6/02076 Refractive index modulation gratings, e.g. Bragg gratings
• CPC Class Codes: G02B 6/0208 characterised by their structure, wavelength response G02B6/02114, G02B6/02171, G02B6/02195 take precedence; multiple layer cores or claddings G02B6/036, protective coverings G02B6/4429

Abstract

In certain embodiments, an optical device and a method of use is provided. The optical device includes a fiber Bragg grating having a substantially periodic refractive index modulation along a length of the fiber Bragg grating. The fiber Bragg grating has a power transmission spectrum with a plurality of local transmission minima, wherein each pair of neighboring local transmission minima has a local transmission maximum therebetween. The local transmission maximum has a maximum power at a transmission peak wavelength. The optical device further includes a narrowband optical source in optical communication with a first optical path and a second optical path. The narrowband optical source is configured to generate light having a wavelength at or in the vicinity of a local transmission maximum or at or in the vicinity of a wavelength at which the power transmission spectrum has a maximum slope between a local transmission maximum and either one of two local transmission minima neighboring the local transmission maximum.

Claims

1. An optical device comprising:

a fiber Bragg grating comprising a substantially periodic refractive index modulation along a length of the fiber Bragg grating, wherein the fiber Bragg grating has a power transmission spectrum comprising a plurality of local transmission minima, wherein each pair of neighboring local transmission minima has a local transmission maximum therebetween, the local transmission maximum having a maximum power at a transmission peak wavelength; and

a narrowband optical source in optical communication with a first optical path and a second optical path, the narrowband optical source configured to generate light having a wavelength at or in the vicinity of a local transmission maximum or at or in the vicinity of a wavelength at which the power transmission spectrum has a maximum slope between a local transmission maximum and either one of two local transmission minima neighboring the local transmission maximum.

2. The optical device of claim 1, wherein the substantially periodic refractive index modulation has a constant period along the length of the fiber Bragg grating.

3. The optical device of claim 1, wherein the substantially periodic refractive index modulation has a period that varies along the length of the fiber Bragg grating such that the fiber Bragg grating is a chirped grating.

4. The optical device of claim 1, wherein the substantially periodic refractive index modulation has an amplitude which varies along the length of the fiber Bragg grating such that the fiber Bragg grating is an apodized grating.

5. The optical device of claim 1, further comprising:

at least one optical detector in optical communication with the fiber Bragg grating, wherein the light generated by the narrowband optical source is split into a first portion and a second portion, the first portion transmitted along the first optical path extending along and through the length of the fiber Bragg grating, the at least one optical detector configured to receive the first portion, the second portion, or both the first and second portions;

a second optical path not extending along and through the fiber Bragg grating, wherein the second portion is transmitted along the second optical path;

a first fiber coupler in optical communication with the narrowband light source, the first optical path, and the second optical path, wherein the light generated by the narrowband optical source is split by the first fiber coupler into the first portion and the second portion; and

a second fiber coupler in optical communication with the first optical path and the second optical path, wherein the first portion and the second portion are recombined by the second fiber coupler and transmitted to the at least one optical detector, wherein the at least one optical detector is configured to detect a change in power resulting from a phase difference between the first portion and the second portion.

6. The optical device of claim 5, wherein the phase difference is indicative of an amount of strain applied to the fiber Bragg grating.

7. The optical device of claim 5, wherein the phase difference is indicative of a temperature of the fiber Bragg grating.

8. The optical device of claim 5, wherein the first fiber coupler, second fiber coupler, first optical path, and second optical path form a nominally balanced Mach-Zehnder interferometer.

9. The optical device of claim 1, wherein the power transmission spectrum has a first local transmission maximum between a first local transmission minimum comprising the Bragg wavelength and a second local transmission minimum on a short wavelength side of the Bragg wavelength, and a second local transmission maximum between the second local transmission minimum and a third local transmission minimum on the short wavelength side of the Bragg wavelength, wherein the wavelength of the light generated by the narrowband optical source is between the first local transmission minimum and the second local transmission minimum, wherein the wavelength of the light generated by the narrowband optical source is at or in the vicinity of the first local transmission maximum or at or in the vicinity of a wavelength at which the power transmission spectrum has a maximum slope between the first local transmission maximum and either one of the first local transmission minimum or the second local transmission minimum.

10. The optical device of claim 1, wherein the power transmission spectrum has a first local transmission maximum between a first local transmission minimum comprising the Bragg wavelength and a second local transmission minimum on a short wavelength side of the Bragg wavelength, and a second local transmission maximum between the second local transmission minimum and a third local transmission minimum on the short wavelength side of the Bragg wavelength, wherein the wavelength of the light generated by the narrowband optical source is between the second local transmission minimum and the third local transmission minimum, wherein the wavelength of the light generated by the narrowband optical source is at or in the vicinity of the second local transmission maximum or at or in the vicinity of a wavelength at which the power transmission spectrum has a maximum slope between the second local transmission maximum and either one of the second local transmission minimum or the third local transmission minimum.

11. The optical device of claim 1, wherein the power transmission spectrum has a first local transmission maximum between a first local transmission minimum comprising the Bragg wavelength and a second local transmission minimum on a long wavelength side of the Bragg wavelength, and a second local transmission maximum between the second local transmission minimum and a third local transmission minimum on the long wavelength side of the Bragg wavelength, wherein the wavelength of the light generated by the narrowband optical source is between the first local transmission minimum and the second local transmission minimum, wherein the wavelength of the light generated by the narrowband optical source is at or in the vicinity of the first local transmission maximum or at or in the vicinity of a wavelength at which the power transmission spectrum has a maximum slope between the first local transmission maximum and either one of the first local transmission minimum or the second local transmission minimum.

12. The optical device of claim 1, wherein the power transmission spectrum has a first local transmission maximum between a first local transmission minimum comprising the Bragg wavelength and a second local transmission minimum on a long wavelength side of the Bragg wavelength, and a second local transmission maximum between the second local transmission minimum and a third local transmission minimum on the long wavelength side of the Bragg wavelength, wherein the wavelength of the light generated by the narrowband optical source is between the second local transmission minimum and the third local transmission minimum, wherein the wavelength of the light generated by the narrowband optical source is at or in the vicinity of the second local transmission maximum or at or in the vicinity of a wavelength at which the power transmission spectrum has a maximum slope between the second local transmission maximum and either one of the second local transmission minimum or the third local transmission minimum.

13. The optical device of claim 1, further comprising:

at least one optical detector in optical communication with the fiber Bragg grating, wherein the light generated by the narrowband optical source is split into a first portion and a second portion, the first portion transmitted along the first optical path extending along and through the length of the fiber Bragg grating, the at least one optical detector configured to receive the first portion, the second portion, or both the first and second portions;

a fiber loop, wherein at least a portion of the fiber loop comprises the fiber Bragg grating, wherein the first optical path extends in a first direction along the fiber loop;

a second optical path, wherein the second optical path extends in a second direction along the fiber loop, the second direction opposite to the first direction; and

at least one fiber coupler optically coupled to the narrowband optical source and the fiber loop, wherein the light generated by the narrowband optical source is split by the at least one fiber coupler into the first portion and the second portion such that the first portion propagates along the first optical path and the second portion propagates along the second optical path, wherein the first portion and the second portion are recombined by the at least one fiber coupler after propagating along and through the length of the fiber Bragg grating, wherein the at least one optical detector comprises an optical phase detector configured to receive the recombined first and second portions and to detect the phase difference between the first portion and the second portion.

14. The optical device of claim 1, wherein the second portion is reflected from the fiber Bragg grating, and wherein the at least one optical detector comprises at least one optical power detector configured to receive and to detect an optical power of the first portion, the second portion, or both the first and second portions.

15. The optical device of claim 14, wherein the at least one optical power detector comprises a photodiode configured to receive and to detect the optical power of the first portion.

16. The optical device of claim 14, wherein the at least one optical power detector comprises a photodiode configured to receive and to detect the optical power of the second portion.

17. The optical device of claim 14, wherein the detected optical power is indicative of an amount of strain applied to the fiber Bragg grating.

18. The optical device of claim 14, wherein the detected optical power is indicative of a temperature of the fiber Bragg grating.

19. The optical device of claim 1, wherein the first portion transmitted along the fiber Bragg grating has a group velocity such that a ratio of the speed of light in vacuum to the group velocity is greater than 5.

20. The optical device of claim 19, wherein the ratio is greater than 100.

21. The optical device of claim 19, wherein the ratio is greater than 1000.

22. The optical device of claim 1, wherein the narrowband optical source has a linewidth less than or equal to 10⁻

13 meters.

23. An optical device comprising:

a fiber Bragg grating comprising a substantially periodic refractive index modulation along a length of the fiber Bragg grating; and

a narrowband optical source in optical communication with the fiber Bragg grating, the narrowband optical source configured to generate light having a wavelength such that the light is transmitted along the fiber Bragg grating with a group velocity such that a ratio of the speed of light in vacuum to the group velocity is greater than 5.

24. The optical device of claim 23, further comprising at least one optical detector in optical communication with the fiber Bragg grating, wherein the light generated by the narrowband optical source is split into a first portion and a second portion, the first portion transmitted along a first optical path extending along and through the length of the fiber Bragg grating, the at least one optical detector configured to receive the first portion, the second portion, or both the first and second portions.

25. A method of using a fiber Bragg grating comprising:

providing a fiber Bragg grating comprising a substantially periodic refractive index modulation along a length of the fiber Bragg grating;

wherein the fiber Bragg grating has a power transmission spectrum comprising a plurality of local transmission minima, wherein each pair of neighboring local transmission minima has a local transmission maximum therebetween, the local transmission maximum having a maximum power at a transmission peak wavelength;

generating light having a wavelength between two neighboring local transmission minima from a narrowband optical source, wherein the wavelength of the light generated by the narrowband optical source is at or in the vicinity of a first local transmission maximum or at or in the vicinity of a wavelength at which the power transmission spectrum has a maximum slope between a local transmission maximum and either one of two local transmission minima neighboring the local transmission maximum;

transmitting a first portion of light along a first optical path extending along and through the length of the fiber Bragg grating.

26. The method of claim 25, further comprising detecting the first portion, the second portion, or both the first and second portions with an optical detector.

27. The method of claim 26, wherein detecting comprises detecting a phase difference between the first portion and the second portion.

28. The method of claim 25, further comprising transmitting the second portion of light along a second optical path by reflecting the second portion from the fiber Bragg grating.

29. The method of claim 27, further comprising detecting an optical power of the first portion, the second portion, or both the first and second portions.

30. The method of claim 25, wherein the first portion transmitted along the fiber Bragg grating has a group velocity such that a ratio of the speed of light in vacuum to the group velocity is greater than 5.

31. A method of using a fiber Bragg grating comprising:

providing a fiber Bragg grating comprising a substantially periodic refractive index modulation along a length of the fiber Bragg grating;

generating light having a wavelength from a narrowband optical source;

transmitting a first portion of light along a first optical path extending along and through the fiber Bragg grating with a group velocity such that a ratio of the speed of light in vacuum to the group velocity is greater than 5;

transmitting a second portion of light along a second optical path.

32. The method of claim 31, further comprising detecting the first portion, the second portion, or both the first and second portions with an optical detector.