Spectral beam combination of broad-stripe laser diodes
View Patent ↗A method and apparatus for improving the beam quality of the emissions from a multimode gain medium such as a broad-stripe laser through the use of SBC techniques is provided. In order to achieve the desired beam quality without a significant reduction in output power, discrete lasing regions are formed across the gain medium using an etalon or similar device located within the SBC cavity.
1. A spectral beam combining (SBC) optical system comprising:
a broad-stripe laser diode;
an external resonator cavity comprising:
a mirror located adjacent to a first facet of said broad-stripe laser diode; and
an output coupler, wherein emissions from a second facet of said broad-stripe laser diode are incident on said output coupler, said output coupler outputting a single output beam;
a dispersive element interposed between said broad-stripe laser diode and said output coupler, said dispersive element reflecting a portion of said emissions back into said broad-stripe laser diode;
a collimating optical system interposed between said broad-stripe laser diode and said dispersive element, said collimating optical system spatially overlapping emissions from said broad-stripe laser diode onto said dispersive element;
a spatial filter interposed between said dispersive element and said output coupler, wherein said spatial filter comprises an aperture; and
means for creating a plurality of pseudo emitters across said second facet of said broad-stripe laser diode with a corresponding lateral spacing between adjacent pseudo emitters, said means located within said external cavity, wherein said means generates wavelength-periodic variations in transmission or reflectivity, and wherein an aperture width associated with said aperture forms an image at said second facet of said broad-stripe laser diode less than twice said lateral spacing of adjacent pseudo emitters multiplied by a factor by which the output beam divergence exceeds the diffraction limit.
2. The SBC optical system of claim 1 , wherein said mirror further comprises a reflective coating applied to said first facet of said broad-stripe laser diode.
3. The SBC optical system of claim 1 , wherein said collimating optical system is located a distance from said second facet of said broad-stripe laser diode substantially equivalent to a collimating optical system focal length.
4. The SBC optical system of claim 1 , wherein said collimating optical system is located a distance from said dispersive element substantially equivalent to a collimating optical system focal length.
5. The SBC optical system of claim 1 , further comprising a divergence reducing optical system adjacent to second facet of said broad-stripe laser diode, said divergence reducing optical system reducing divergence in the emissions corresponding to a fast axis of said broad-stripe laser diode.
6. The SBC optical system of claim 1 , wherein said pseudo emitter creating means is comprised of a birefringent material.
7. The SBC optical system of claim 1 , wherein said pseudo emitter creating means is comprised of an etalon.
8. The SBC optical system of claim 7 , wherein said etalon is located between said broad-stripe laser diode and said dispersive element.
9. The SBC optical system of claim 2 , wherein said pseudo emitter creating means is comprised of an etalon, said etalon comprising said broad-stripe laser diode, said reflective coating applied to said first facet of said broad-stripe laser diode and a second reflective coating applied to said second facet of said broad-stripe laser diode.
10. The SBC optical system of claim 9 , wherein a maximum gain corresponding to said plurality of pseudo emitters is at least 1.5 times higher than a minimum gain corresponding to said plurality of pseudo emitters.
11. The SBC optical system of claim 10 , wherein said maximum gain is between 2 and 4 times higher than said minimum gain.
12. The SBC optical system of claim 1 , wherein a maximum gain corresponding to said plurality of pseudo emitters is at least 1.5 times higher than a minimum gain corresponding to said plurality of pseudo emitters.
13. The SBC optical system of claim 12 , wherein said maximum gain is between 2 and 4 times higher than said minimum gain.
14. The SBC optical system of claim 9 , wherein lasing is suppressed at a plurality of minimum gain locations associated with said plurality of pseudo emitters.
15. The SBC optical system of claim 14 , wherein said plurality of minimum gain locations correspond to a plurality of wavelengths.
16. The SBC optical system of claim 1 , wherein lasing is suppressed at a plurality of minimum gain locations associated with said plurality of pseudo emitters.
17. The SBC optical system of claim 16 , wherein said plurality of minimum gain locations correspond to a plurality of wavelengths.
18. The SBC optical system of claim 1 , wherein said lateral spacing is at least equivalent to one half of a fundamental mode diameter associated with said external resonator cavity.
19. The SBC optical system of claim 1 , wherein said lateral spacing is at least equivalent to a fundamental mode diameter associated with said external resonator cavity.
20. A spectral beam combining (SBC) optical system comprising:
a broad-stripe laser diode;
an external resonator cavity comprising:
a mirror located adjacent to a first facet of said broad-stripe laser diode; and
an output coupler, wherein emissions from a second facet of said broad-stripe laser diode are incident on said output coupler, said output coupler outputting a single output beam;
a dispersive element interposed between said broad-stripe laser diode and said output coupler, said dispersive element reflecting a portion of said emissions back into said broad-stripe laser diode;
a collimating optical system interposed between said broad-stripe laser diode and said dispersive element, said collimating optical system spatially overlapping emissions from said broad-stripe laser diode onto said dispersive element;
a spatial filter interposed between said dispersive element and said output coupler; and
means for creating a plurality of pseudo emitters across said second facet of said broad-stripe laser diode with a corresponding lateral spacing between adjacent pseudo emitters, said means located within said external cavity, wherein said means generates wavelength-periodic variations in transmission or reflectivity, and wherein said lateral spacing is equivalent to at least one half of a fundamental mode diameter associated with said external resonator cavity multiplied by a factor by which the output beam divergence exceeds the diffraction limit.
21. The SBC optical system of claim 20 , wherein said mirror further comprises a reflective coating applied to said first facet of said broad-stripe laser diode.
22. The SBC optical system of claim 20 , wherein said collimating optical system is located a distance from said second facet of said broad-stripe laser diode substantially equivalent to a collimating optical system focal length.
23. The SBC optical system of claim 20 , wherein said collimating optical system is located a distance from said dispersive element substantially equivalent to a collimating optical system focal length.
24. The SBC optical system of claim 20 , wherein said spatial filter comprises an aperture.
25. The SBC optical system of claim 24 , wherein said aperture is selected from the group consisting of slits, circular apertures and oblong apertures.
26. The SBC optical system of claim 24 , wherein an aperture width associated with said aperture forms an image at said second facet of said broad-stripe laser diode less than twice said lateral spacing of adjacent pseudo emitters.
27. The SBC optical system of claim 24 , wherein said aperture comprises a slit, and wherein a slit width associated with said slit forms an image at said second facet of said broad-stripe laser diode less than twice said lateral spacing of adjacent pseudo emitters.
28. The SBC optical system of claim 20 , further comprising a divergence reducing optical system adjacent to second facet of said broad-stripe laser diode, said divergence reducing optical system reducing divergence in the emissions corresponding to a fast axis of said broad-stripe laser diode.
29. The SBC optical system of claim 20 , wherein said pseudo emitter creating means is comprised of a birefringent material.
30. The SBC optical system of claim 20 , wherein said pseudo emitter creating means is comprised of an etalon.
31. The SBC optical system of claim 30 , wherein said etalon is located between said broad-stripe laser diode and said dispersive element.
32. The SBC optical system of claim 21 , wherein said pseudo emitter creating means is comprised of an etalon, said etalon comprising said broad-stripe laser diode, said reflective coating applied to said first facet of said broad-stripe laser diode and a second reflective coating applied to said second facet of said broad-stripe laser diode.
33. The SBC optical system of claim 32 , wherein a maximum gain corresponding to said plurality of pseudo emitters is at least 1.5 times higher than a minimum gain corresponding to said plurality of pseudo emitters.
34. The SBC optical system of claim 33 , wherein said maximum gain is between 2 and 4 times higher than said minimum gain.
35. The SBC optical system of claim 20 , wherein a maximum gain corresponding to said plurality of pseudo emitters is at least 1.5 times higher than a minimum gain corresponding to said plurality of pseudo emitters.
36. The SBC optical system of claim 35 , wherein said maximum gain is between 2 and 4 times higher than said minimum gain.
37. The SBC optical system of claim 32 , wherein lasing is suppressed at a plurality of minimum gain locations associated with said plurality of pseudo emitters.
38. The SBC optical system of claim 37 , wherein said plurality of minimum gain locations correspond to a plurality of wavelengths.
39. The SBC optical system of claim 20 , wherein lasing is suppressed at a plurality of minimum gain locations associated with said plurality of pseudo emitters.
40. The SBC optical system of claim 39 , wherein said plurality of minimum gain locations correspond to a plurality of wavelengths.
41. The SBC optical system of claim 20 , wherein said lateral spacing is at least equivalent to a fundamental mode diameter associated with said external resonator cavity.
42. A method for improving the beam quality of a broad-stripe laser diode, the method comprising the steps of:
forming a plurality of pseudo emitters from an output of the broad-stripe laser diode;
laterally spacing said pseudo emitters by at least one half of a fundamental cavity mode diameter multiplied by a factor corresponding to an amount by which an output beam divergence exceeds a system diffraction limit; and
passing a plurality of emissions corresponding to said plurality of pseudo emitters through an SBC optical system.
43. The method of claim 42 , wherein said forming step comprises the step of transmitting the output of the broad-stripe laser diode through an etalon.
44. The method of claim 42 , further comprising the step of suppressing lasing at a plurality of wavelengths corresponding to pseudo emitter minimums.
45. A method for improving the beam quality of a broad-stripe laser diode, the method comprising the steps of:
forming a plurality of pseudo emitters from an output of the broad-stripe laser diode;
passing a plurality of emissions corresponding to said plurality of pseudo emitters through an SBC optical system; and
selecting a slit width for a slit associated with a spatial filter of said SBC optical system so that an image of said slit projected onto a front facet of the broad-strip laser diode is less than twice a lateral spacing of adjacent pseudo emitters multiplied by a factor corresponding to an amount by which an output beam divergence exceeds a system diffraction limit.
46. The method of claim 45 , wherein said forming step further comprises the step of laterally spacing said pseudo emitters by at least one half of a fundamental cavity mode diameter.
47. The method of claim 45 , wherein said forming step further comprises the step of laterally spacing said pseudo emitters by at least a fundamental cavity mode diameter.
48. The method of claim 45 , wherein said forming step comprises the step of transmitting the output of the broad-stripe laser diode through an etalon.
49. The method of claim 45 , further comprising the step of suppressing lasing at a plurality of wavelengths corresponding to pseudo emitter minimums.
50. The SBC optical system of claim 1 , wherein said aperture is selected from the group consisting of slits, circular apertures and oblong apertures.