Raman Distributed Feedback Fiber Laser and High Power Laser System Using the Same

• US 20140112357A1
• Filed: 04/25/2012
• Published: 04/24/2014
• Est. Priority Date: 04/25/2011
• Status: Active Grant

• Current Assignee: OFS Fitel LLC (Furukawa Electric Company Limited)
• Original Assignee: OFS Fitel LLC (Furukawa Electric Company Limited)
• Inventors: Abedin, Kazi S., Westbrook, Paul S., Kremp, Tristan, Nicholson, Jeffrey W., Porque, Jerom C.
• Granted Patent: US 9,325,152 B2
• Time in Patent Office: Days
• US Class Current: 372/3
• CPC Class Codes: H01S 3/0014 Monitoring arrangements not otherwise provided for photometry G01J1/00, e.g. G01J1/4257; radiation pyrometry G01J5/00; measuring coherence of light G01J9/00; measuring wavelength of light G01J9/00, e.g. G01J9/0246; measuring optical pulses G01J11/00; calorimetrically measuring power of laser beams G01K17/003
• CPC Class Codes: H01S 3/06712 Polarising fibre; Polariser
• CPC Class Codes: H01S 3/0675 Resonators including a grating structure, e.g. distributed Bragg reflectors [DBR] or distributed feedback [DFB] fibre lasers
• CPC Class Codes: H01S 3/07 consisting of a plurality of parts, e.g. segments H01S3/067 takes precedence
• CPC Class Codes: H01S 3/08022 Longitudinal modes mode suppression using a plurality of resonators H01S3/082
• CPC Class Codes: H01S 3/0826 using a diffraction grating
• CPC Class Codes: H01S 3/094003 the pumped medium being a fibre
• CPC Class Codes: H01S 3/094042 of a fibre laser
• CPC Class Codes: H01S 3/094046 of a Raman fibre laser
• CPC Class Codes: H01S 3/1086 using scattering effects, e.g. Raman or Brillouin effect
• CPC Class Codes: H01S 3/302 in an optical fibre

Abstract

A Raman distributed feedback (DFB) fiber laser is disclosed. It includes a pump source and a Raman gain fiber of a length smaller than 20 cm containing a distributed feedback (DFB) grating with a discrete phase structure located within no more than 10% off the center of the grating and wherein the Raman DFB fiber laser generates a laser signal with an optical spectrum, which has an optical bandwidth at half maximum optical intensity of less than 1 gigahertz (GHz) (wherein a maximum intensity frequency is different from the frequency of the pump laser). The Raman laser includes compensation for the nonlinear phase change due to Kerr effect and thermal effect resulting from absorption of the optical field, thus enhancing the conversion efficiency.

Claims

1. A Raman laser, comprising:

an optical input enabled to receive radiation from a pump source; and

a Raman gain fiber less than 20 cm in length, comprising at least one Bragg grating enabled to provide Raman radiation on an optical output.

2. The Raman laser of claim 1, wherein the at least one Bragg grating has a phase shift.

3. The Raman laser of claim 1, wherein the at least one Bragg grating has a longitudinally nonuniform profile in refractive index modulation in strength

4. The Raman laser of claim 1, wherein the at least one Bragg grating has a longitudinally nonuniform profile in phase.

5. The Raman laser of claim 1, wherein the Raman laser generates Raman radiation on the optical output with an optical spectrum having an optical bandwidth at half maximum optical intensity of about or less than 1 gigahertz (GHz).

6. The Raman laser of claim 5, wherein the optical bandwidth is about or less than 100 MHz.

7. The Raman laser of claim 5, wherein the optical bandwidth is between about 6 MHz and 10 MHz.

8. The Raman laser of claim 1, wherein the Raman laser has a threshold power within a range of 0.08-10 W.

9. The Raman laser of claim 1, wherein the Raman laser has a threshold power within a range of 1.28-4.4 W.

10. The Raman laser of claim 1, further comprising at least one external Raman gain fiber, wherein the external gain fiber utilizes unabsorbed pump radiation to amplify the Raman radiation output.

11. The Raman laser of claim 10, further comprising an isolation element between the at least one Bragg grating and the at least one Raman gain fiber.

12. The Raman laser of claim 1, wherein the Raman laser is placed within a laser resonator and input radiation is generated by a resonant field of the laser resonator.

13. The Raman laser of claim 1, further comprising:

at least one additional instance of the Raman laser as claimed in claim 1 which is placed in series with the Raman laser of claim 1.

14. The Raman laser of claim 13, wherein the pump source is common to the Raman lasers placed in series.

15. The Raman laser of claim 2, wherein the Bragg grating is chirped to cause a Bragg wavelength excursion along at least a part of a length of the Bragg grating, wherein an intensity of the an associated optical field is large in relation to a different part of the length of the Bragg grating, wherein a location of a largest negative Bragg wavelength excursion is coincident with a location of the phase-shift of the at least one Bragg grating.

16. The Raman laser of claim 2, further comprising:

a temperature control element to control a temperature excursion along at least a part of a length of the Bragg grating wherein an intensity of an associated optical field is large in relation to a different part of the length of the Bragg grating, wherein a location of a largest temperature excursion is coincident with a location of the phase-shift.

17. The Raman laser of claim 2, further comprising:

a strain control element to control a strain excursion along at least a part of a length of the Bragg grating wherein an intensity of changes to an associated optical field is large in relation to a different part of the length of the Bragg grating, wherein a location of a largest strain excursion is coincident with a location of the phase-shift.

18. A fiber Raman laser cavity, comprising:

a pump laser;

an optical input enabled to receive radiation from the pump laser;

a Raman gain fiber comprising at least one Bragg grating enabled to provide Raman radiation;

the fiber Bragg grating having a phase shift, wherein the Bragg grating is chirped to cause a Bragg wavelength excursion along at least a part of a length of the Bragg grating, wherein an intensity of an associated optical field is large in relation to a different part of the length of the Bragg grating, wherein a location of a largest negative Bragg wavelength excursion is coincident with a location of the phase-shift of the at least one Bragg grating; and

an output to provide Raman radiation.

19. The fiber Raman laser cavity of claim 18, wherein the phase shift is about π

radians.

20. The fiber Raman laser cavity of claim 18, wherein the wavelength excursion is approximately proportional to an intensity of an associated optical field.

21. A fiber Raman laser cavity, comprising:

a pump laser;

an optical input enabled to receive radiation from the pump laser;

a Raman gain fiber comprising at least one Bragg grating enabled to provide Raman radiation;

a temperature control element to control a temperature excursion along at least a part of a length of the Bragg grating wherein an intensity of an associated optical field is large in relation to a different part of the length of the Bragg grating, wherein a location of a largest temperature excursion is coincident with a location of the phase-shift; and

an output to provide Raman radiation.

22. The fiber Raman laser cavity of claim 21, wherein the temperature control element is a heating device.

23. The fiber Raman laser cavity of claim 21, wherein the temperature control element is a cooling device.

24. The fiber Raman laser cavity of claim 21, wherein the phase shift is about π

radians.

25. The fiber Raman laser cavity of claim 21, wherein the Bragg grating is chirped to cause a Bragg wavelength excursion along at least a part of a length of the Bragg grating, wherein an intensity of an associated optical field is large in relation to a different part of the length of the Bragg grating, wherein a location of a largest negative Bragg wavelength excursion is coincident with a location of the phase-shift of the at least one Bragg grating.

26. A Raman laser, comprising:

an optical input enabled to receive radiation from a pump laser; and

a first Raman gain fiber less than 20 cm in length connected to the optical input and comprising at least one Bragg grating enabled to provide Raman radiation on a first optical output;

a second Raman gain fiber less than 20 cm in length connected in series with the first Raman gain fiber to the first optical output, the second Raman gain fiber comprising at least one Bragg grating enabled to provide Raman radiation on a second optical output;

wherein the second Raman gain fiber is amplified by unabsorbed output from the pump laser.

27. The Raman laser of claim 26, further comprising:

one or more additional Raman gain fibers, each less than 20 cm in length, connected in series to the second optical output, each of the additional Raman gain fibers comprising at least one Bragg grating enabled to provide Raman radiation.

28. A laser, comprising:

a laser pump;

a laser resonator connected to the laser pump, wherein the laser resonator is pumped by the laser pump;

a Raman gain fiber located within the laser resonator, wherein the Raman gain fiber is less than 20 cm in length, and comprises at least one Bragg grating.