NARROW LINEWIDTH BRILLOUIN LASER

• US 20110134940A1
• Filed: 12/08/2009
• Published: 06/09/2011
• Est. Priority Date: 12/08/2009
• Status: Abandoned Application

• Current Assignee: Schlumberger Technology Corporation (SLB)
• Original Assignee: Schlumberger Technology Corporation (SLB)
• Inventors: Hartog, Arthur H.
• Application Number:
  US12/633,162
• Publication Number:
  US 20110134940A1
• Time in Patent Office: Days
• US Class Current: 372/6
• CPC Class Codes: G01D 5/35335 Aspects of emitters or receivers used by an interferometer in an optical fibre sensor arrangement using multiple sensor devices using multiplexing techniques G01D5/35383
• CPC Class Codes: H01S 3/06791 Fibre ring lasers fibre laser gyrometers G01C19/72
• CPC Class Codes: H01S 3/08031 Single-mode emission
• CPC Class Codes: H01S 3/094038 End pumping
• CPC Class Codes: H01S 3/1392 by using a passive reference, e.g. absorption cell H01S3/1396, H01S3/1398 take precedence
• CPC Class Codes: H01S 3/1398 by using a supplementary modulation of the output
• CPC Class Codes: H01S 3/302 in an optical fibre

Abstract

A Brillouin laser having a narrowed linewidth, reduced relative intensity noise, and increased output power includes a pump laser that provides pump energy to an optical fiber resonant cavity to stimulate Brillouin emission. The output of pump laser is stabilized and its linewidth is narrowed by locking the frequency and phase of the optical signal generated by the pump laser to a longitudinal mode of the optical fiber resonant cavity. In addition, the resonant cavity is temperature and/or strain-tuned so that the Brillouin gain is substantially centered on a longitudinal mode of the cavity, thereby ensuring that the Brillouin frequency shift is substantially equal to an integer number of the free spectral range of the cavity.

Claims

1. A method of providing a narrow linewidth optical signal comprising:

providing an optical source to launch a frequency-stabilized optical signal at a first frequency into an optical fiber resonant cavity, wherein the first frequency corresponds to a longitudinal mode of the optical fiber resonant cavity;

pumping the optical fiber resonant cavity to stimulate a Brillouin emission; and

controlling a Brillouin frequency shift of the optical fiber resonant cavity so that a gain of the Brillouin emission is substantially centered on a longitudinal mode of the optical fiber resonant cavity.

2. The method as recited in claim 1, wherein a free spectral range of the optical fiber resonant cavity is at least the same value as the bandwidth of the gain of the Brillouin emission.

3. The method as recited in claim 1, wherein pumping the optical fiber resonant cavity comprises launching an optical signal at a second frequency into the optical fiber resonant cavity, wherein the second frequency is different than the first frequency.

4. The method as recited in claim 3, wherein the optical source outputs the optical signal at the second frequency, and the method further comprises shifting a portion of the optical signal at the second frequency by an integer multiple of a free spectral range of the optical fiber resonant cavity to produce the frequency-stabilized optical signal at the first frequency.

5. The method as recited in claim 1, wherein controlling the Brillouin frequency shift comprises straining at least a portion of the optical fiber forming the optical fiber resonant cavity.

6. The method as recited in claim 1, wherein controlling the Brillouin frequency shift comprises adjusting a temperature of the optical fiber resonant cavity.

7. The method as recited in claim 1, wherein the provided narrow linewidth optical signal is at a first-order Stokes wavelength of the Brillouin emission, and the method further comprises suppressing second-order Stokes Brillouin emissions produced by the optical fiber resonant cavity in response to the pumping.

8. The method as recited in claim 7 wherein suppressing second-order Stokes Brillouin emissions comprises launching an optical signal at the third-order Stokes wavelength into the optical fiber resonant cavity to convert second-order Stokes Brillouin emissions to third-order Stokes Brillouin emissions.

9. The method as recited in claim 7, wherein suppressing second-order Stokes Brillouin emissions comprises inducing a loss in the resonant cavity at the second Stokes Brillouin wavelength.

10. The method as recited in claim 9, wherein inducing the loss comprises providing a fiber Bragg grating in the resonant cavity having a higher loss at the second Stokes Brillouin wavelength than at the first Stokes Brillouin wavelength.

11. A narrow linewidth optical source, comprising:

an optical fiber resonant cavity to produce a Brillouin emission in response to receipt of optical power;

an optical source to launch an optical signal at a first frequency into the optical fiber resonant cavity; and

a frequency stabilization circuit to lock the first frequency to a longitudinal mode of the optical fiber resonant cavity,

wherein a Brillouin frequency shift of the optical fiber resonant cavity is stabilized so that a gain of the Brillouin emission is substantially centered on a longitudinal mode of the optical fiber resonant cavity.

12. The narrow linewidth optical source as recited in claim 11, wherein the launched optical signal at the first frequency provides the optical power to stimulate the Brillouin emission.

13. The narrow linewidth optical source as recited in claim 11, wherein the optical source is further configured to launch a pump optical signal into the optical fiber resonant cavity to stimulate the Brillouin emission, wherein the pump optical signal has a second frequency that is different than the first frequency.

14. The narrow linewidth optical source as recited in claim 13, further comprising a frequency-shifting circuit coupled to the optical source to frequency-shift a portion of the second frequency optical signal by an integer multiple of a free spectral range of the optical fiber resonant cavity to generate the first frequency optical signal.

15. The narrow linewidth optical source as recited in claim 11, further comprising a thermal element to adjust a temperature of the optical fiber resonant cavity to stabilize the Brillouin frequency shift.

16. The narrow linewidth optical source as recited in claim 11, further comprising a strain element to impart a strain on at least a portion of the optical fiber forming the optical fiber resonant cavity to stabilize the Brillouin frequency shift.

17. The narrow linewidth optical source as recited in claim 11, further comprising:

an output circuit to output a narrow linewidth optical output at a first-order Stokes frequency of the Brillouin emission; and

means for suppressing second-order Stokes Brillouin emissions that are produced by the optical fiber resonant cavity in response to the receipt of optical power.

18. The narrow linewidth optical source as recited in claim 17, wherein the means for suppressing comprises an optical source to launch an optical signal at a third-order Stokes frequency into the optical fiber resonant cavity at a power sufficient to transfer any Brillouin emissions at a second-order Stokes frequency to a third-order Stokes frequency.

19. The narrow linewidth optical source as recited in claim 18, further comprising a pump optical source to provide the optical power to produce the Brillouin emission, wherein the optical source to launch the third-order Stokes optical signal is different than the pump optical source.

20. The narrow linewidth optical source as recited in claim 17, wherein the means for suppressing comprises a fiber Bragg grating provided in the fiber optic resonant cavity, the fiber Bragg grating having a higher loss at the second-order Stokes frequency than at the first-order Stokes frequency.

21. The narrow linewidth optical source as recited in claim 11, wherein the optical fiber resonator cavity comprises a polarization-maintaining optical fiber.

22. A method of producing a narrow linewidth optical signal, comprising:

providing a pumping optical signal at a first frequency to launch into a first end of an optical fiber resonant cavity;

providing a locking optical signal at a second frequency to launch into a second end of an optical fiber resonant cavity; and

locking the second frequency of the locking optical signal to a longitudinal mode of the optical fiber resonant cavity to narrow the linewidth of Brillouin emission emerging from the first end of the optical fiber resonant cavity in response to the pumping optical signal.

23. The method as recited in claim 22, wherein providing the locking optical signal comprises frequency-shifting a portion of the pumping optical signal by an integer multiple of a free spectral range of the resonant cavity to generate the locking optical signal at the second frequency

24. The method as recited in claim 22, further comprising adjusting a temperature of the optical fiber resonant cavity to substantially center a gain of the Brillouin emission on a longitudinal mode of the optical fiber resonant cavity.

25. The method as recited in claim 22, further comprising straining at least a portion of the optical fiber forming the optical fiber resonant cavity to substantially center a gain of the Brillouin emission on a longitudinal mode of the optical fiber resonant cavity.

26. The method as recited in claim 22, further comprising;

outputting the first-order Stokes portion of the Brillouin emission as the narrow linewidth optical signal; and

suppressing second-order Stokes Brillouin emissions produced by the optical fiber resonant cavity in response to the pumping optical signal.

27. The method as recited in claim 26, wherein suppressing the second-order Stokes comprises launching an optical signal at the third-order Stokes frequency into the second end of the optical fiber resonant cavity to transfer second-order Stokes Brillouin emissions to third-order Stokes Brillouin emissions.

28. The method as recited in claim 26, wherein suppressing the second-order Stokes comprises inducing a loss in the optical fiber resonant cavity at the second-order Stokes Brillouin wavelength.