External-cavity one-dimensional multi-wavelength beam combining of two-dimensional laser elements

• US 8,049,966 B2
• Filed: 11/03/2009
• Issued: 11/01/2011
• Est. Priority Date: 11/04/2008
• Status: Active Grant

• Current Assignee: Massachusetts Institute of Technology
• Original Assignee: Massachusetts Institute of Technology
• Inventors: Sanchez-Rubio, Antonio, Chann, Bien, Fan, Tso Yee
• Primary Examiner(s): Spector; David N
• Application Number:
  US12/611,514
• Publication Number:
  US 20100110556A1
• Time in Patent Office: 728 Days
• Field of Search: 359/341.3, 359/341.33, 359/337.21, 359/624, 372/25, 372/92, 372/98, 372/102
• US Class Current: 359/624
• CPC Class Codes: H01S 5/4012 Beam combining, e.g. by the use of fibres, gratings, polarisers, prisms
• CPC Class Codes: H01S 5/405 Two-dimensional arrays
• CPC Class Codes: H01S 5/4062 with an external cavity or using internal filters, e.g. Talbot filters
• CPC Class Codes: H01S 5/4087 emitting more than one wavelength

Abstract

An external-cavity one-dimensional multi-wavelength beam combiner that performs wavelength beam combining along a stacking dimension of a laser stack formed of a plurality of laser arrays, each laser array configured to generate optical radiation having a unique wavelength, and each of the plurality of laser arrays including a plurality of laser emitters arranged along an array dimension of the laser stack. The multi-wavelength beam combiner includes a cylindrical telescope configured to image each of the laser emitters along a slow axis of the laser emitters, a transform lens arranged to intercept the optical radiation from each of the plurality of laser arrays and combine the optical radiation along a stacking dimension of the laser stack to form a multi-wavelength optical beam, and a diffraction element positioned at a region of overlap of the optical radiation to receive and transmit the multi-wavelength optical beam.

Claims

1. A multi-wavelength beam combiner comprising:

a laser stack comprising a plurality of laser arrays arranged along a stacking dimension of the laser stack, each laser array configured to generate optical radiation having a unique wavelength, and each of the plurality of laser arrays comprising a plurality of optical gain elements arranged along an array dimension of the laser stack;

a cylindrical telescope configured to image each of the plurality of optical gain elements along a slow axis of the optical gain elements;

a transform lens arranged to intercept the optical radiation from each of the plurality of laser arrays and combine the optical radiation along the stacking dimension of the laser stack to form a multi-wavelength optical beam; and

a diffraction element positioned at a region of overlap of the optical radiation to receive and transmit the multi-wavelength optical beam;

wherein the cylindrical telescope is configured to image each of the plurality of optical gain elements onto the diffraction element.

2. The multi-wavelength beam combiner as claimed in claim 1, further comprising a volume Bragg grating positioned between the laser stack and the cylindrical telescope and configured to form a free-space cavity with the laser stack to generate the plurality of unique wavelengths;

wherein the volume Bragg grating is a wavelength-chirped volume Bragg grating; and

wherein the wavelength is chirped along the stacking dimension.

3. The multi-wavelength beam combiner as claimed in claim 1, wherein the transform lens is positioned a focal length away from the laser stack.

4. The multi-wavelength beam combiner as claimed in claim 1, wherein the stacking dimension is substantially perpendicular to the array dimension.

5. The multi-wavelength beam combiner as claimed in claim 1, wherein the diffraction element is a diffraction grating.

6. The multi-wavelength beam combiner as claimed in claim 1, wherein the transform lens is a cylindrical transform lens;

wherein the cylindrical telescope comprises a first lens element and a second lens element; and

wherein the cylindrical transform lens is positioned between the first and second lens elements.

7. The multi-wavelength beam combiner as claimed in claim 1, wherein the plurality of laser arrays comprises a plurality of laser diode bars;

and

wherein the plurality of optical gain elements comprises a plurality of laser diode emitters.

8. The multi-wavelength beam combiner as claimed in claim 1, wherein the plurality of laser arrays comprises a plurality of fiber laser arrays;

and

wherein the plurality of optical gain elements comprises a plurality of fiber laser emitters.

9. The multi-wavelength beam combiner as claimed in claim 1, wherein the laser stack comprises a stack of discrete semiconductor laser emitters arranged in rows along the array dimension;

and wherein the each laser array of the plurality of laser arrays comprises a row of the discrete semiconductor laser emitters.

10. The multi-wavelength beam combiner as claimed in claim 1, further comprising a plurality of collimating micro-lenses coupled to the laser stack.

11. The multi-wavelength beam combiner as claimed in claim 1, further comprising a passive fiber output coupler arranged to receive the multi-wavelength optical beam from the diffraction element, to reflect a portion of the multi-wavelength optical beam back to the region of overlap, and to transmit the multi-wavelength optical beam comprising optical radiation having the plurality of unique wavelengths;

wherein the diffraction element, the passive fiber output coupler and the laser stack together form a free space cavity that produces the plurality of unique wavelengths.

12. The multi-wavelength beam combiner as claimed in claim 1, further comprising a plurality of mirrors configured to optically arrange the optical radiation from the plurality of laser arrays so as to form the laser stack with the plurality of laser arrays optically arranged along the stacking dimension of the laser stack.

13. The multi-wavelength beam combiner as claimed in claim 1, where the plurality of laser arrays are physically arranged along the stacking dimension of the laser stack.

14. The multi-wavelength beam combiner as claimed in claim 1, further comprising a partially reflecting output coupler arranged to receive the multi-wavelength optical beam from the diffraction element, to reflect a portion of the multi-wavelength optical beam back to the region of overlap, and to transmit the multi-wavelength optical beam comprising optical radiation having the plurality of unique wavelengths;

wherein the diffraction element, the partially reflecting output coupler and the laser stack together form a free space cavity that produces the plurality of unique wavelengths.

15. The multi-wavelength beam combiner as claimed in claim 14, further comprising an anamorphic beam expander positioned between the laser stack and the cylindrical telescope.

16. The multi-wavelength beam combiner as claimed in claim 14, further comprising an additional cylindrical telescope positioned between the diffraction element and the partially reflecting output coupler;

wherein the additional cylindrical telescope is configured to image the plurality of optical gain elements along the array dimension onto the partially reflecting output coupler.

17. A multi-wavelength beam combiner comprising:

a laser stack comprising a first laser array configured to generate a first optical beam having a first wavelength, and a second laser array configured to generate a second optical beam having a second wavelength, each of the first and second laser arrays comprising a plurality of optical gain elements arranged along an array dimension of the laser stack and configured to produce optical radiation to generate the first and second optical beams;

a cylindrical telescope arranged to intercept the optical radiation and to image each of the plurality of optical gain elements along the array dimension;

a transform lens arranged to intercept the first and second optical beams and to spatially overlap in a stacking dimension of the laser stack the first and second optical beams to form a multi-wavelength optical beam;

a diffraction element positioned at a region of overlap of the first and second optical beams; and

a partially reflecting output coupler arranged to receive the multi-wavelength optical beam from the diffraction element, to reflect a portion of the multi-wavelength optical beam back to the region of overlap, and to transmit the multi-wavelength optical beam comprising optical radiation having the first and second wavelengths;

wherein the diffraction element, the partially reflecting output coupler and the laser stack together form a free space cavity that produces the first and second wavelengths; and

wherein the stacking dimension is substantially perpendicular to the array dimension.

18. The multi-wavelength beam combiner as claimed in claim 17, wherein the partially reflecting output coupler is a passive fiber output coupler.

19. The multi-wavelength beam combiner as claimed in claim 17, further comprising an anamorphic beam expander positioned between the laser stack and the cylindrical telescope.

20. The multi-wavelength beam combiner as claimed in claim 17, further comprising an additional cylindrical telescope positioned between the diffraction element and the partially reflecting output coupled and configured to image in the array dimension an image on the diffraction element onto the partially reflecting output coupler.

21. The multi-wavelength beam combiner as claimed in claim 17, further comprising an imaging telescope positioned between the laser stack and the cylindrical telescope and configured to reduce a beam size of the first and second optical beams in the stacking dimension;

wherein the imaging telescope comprises a first lens and a second lens; and

wherein at least one of the first and second lenses is a spherical lens.

22. The multi-wavelength beam combiner as claimed in claim 17, wherein the first and second laser arrays are laser diode bars, each laser diode bar comprising a plurality of laser diode emitters.

23. The multi-wavelength beam combiner as claimed in claim 17, wherein the laser stack comprises a stack of discrete semiconductor laser emitters arranged in rows along the array dimension;

and wherein the first and second laser arrays each comprises a row of the discrete semiconductor laser emitters.

24. The multi-wavelength beam combiner as claimed in claim 17, wherein the first and second laser arrays are fiber laser arrays;

and

wherein the plurality of optical gain elements comprises a plurality of fiber laser emitters.

25. The multi-wavelength beam combiner as claimed in claim 17, further comprising a plurality of minors configured to optically arrange the first and second optical beams along the stacking dimension of the laser stack so as to form the laser stack.

26. A method of wavelength beam combining comprising:

generating with a plurality of laser arrays a plurality of optical beams each having a unique wavelength;

imaging the plurality of optical beams along a first dimension with a cylindrical telescope; and

spatially overlapping the plurality of optical beams in a second dimension at a region of overlap using a cylindrical transform lens to produce a multi-wavelength optical beam comprising the plurality of unique wavelengths.

27. The method as claimed in claim 26, wherein spatially overlapping the plurality of optical beams includes propagating the plurality of optical beams to a diffractive element positioned at the region of overlap.

28. The method as claimed in claim 26, further comprising:

propagating the multi-wavelength optical beam to a partially reflecting element positioned to receive radiation from the diffractive element, the partially reflecting element and the plurality of laser arrays together forming a free space laser cavity that produces the plurality of unique wavelengths; and

transmitting the multi-wavelength beam comprising radiation having the plurality of unique wavelengths through the partially reflecting element.

29. The method as claimed in claim 26, further comprising stabilizing the plurality of unique wavelengths with a wavelength-chirped volume Bragg grating.