Optical cross-coupling mitigation systems for wavelength beam combining laser systems
In various embodiments, wavelength beam combining laser systems incorporate optical cross-coupling mitigation systems and/or engineered partially reflective output couplers in order to reduce or substantially eliminate unwanted back-reflection of stray light.
1. A laser system comprising:
an array of beam emitters each emitting a beam having a different wavelength;
focusing optics for focusing the beams toward a dispersive element;
a dispersive element for receiving and dispersing the focused beams, thereby forming a multi-wavelength beam;
a cross-coupling mitigation system for receiving and transmitting the multi-wavelength beam while reducing cross-coupling thereof;
disposed optically downstream of the cross-coupling mitigation system, an optical fiber for receiving the multi-wavelength beam; and
disposed within the optical fiber, a fiber Bragg grating for (i) receiving the multi-wavelength beam, reflecting a first portion thereof back to the array of beam emitters via the cross-coupling mitigation system, wherein the first portion stabilizes each of the beams to its wavelength, and (ii) transmitting a second portion thereof as an output beam composed of multiple wavelengths.
2. The laser system of claim 1 , further comprising an end cap attached to the optical fiber and disposed optically upstream of the fiber Bragg grating.
3. The laser system of claim 1 , further comprising a mode stripper disposed around at least a portion of the optical fiber.
4. The laser system of claim 1 , wherein the fiber Bragg grating is disposed within a Rayleigh range of the multi-wavelength beam transmitted by the cross-coupling mitigation system.
5. The laser system of claim 1 , wherein at least a portion of the cross-coupling mitigation system is disposed within a Rayleigh range of the multi-wavelength beam transmitted by the dispersive element.
6. The laser system of claim 1 , wherein the cross-coupling mitigation system comprises an afocal telescope.
7. The laser system of claim 1 , wherein the cross-coupling mitigation system comprises a first optical element having a first focal length and a second optical element having a second focal length, the first optical element being disposed optically upstream of the second optical element.
8. The laser system of claim 7 , wherein the first focal length is at least two times greater than the second focal length.
9. The laser system of claim 7 , wherein the first focal length is at least seven times greater than the second focal length.
10. The laser system of claim 7 , wherein each of the first and second optical elements comprises a lens.
11. The laser system of claim 7 , wherein the first optical element is disposed within a Rayleigh range of the multi-wavelength beam transmitted by the dispersive element.
12. The laser system of claim 7 , wherein the fiber Bragg grating is disposed within a Rayleigh range of the multi-wavelength beam transmitted by the second optical element.
13. The laser system of claim 7 , wherein an optical distance between the first and second optical elements is approximately equal to a sum of the first and second focal lengths.
14. The laser system of claim 1 , wherein (i) the fiber Bragg grating is disposed within a core of the optical fiber, (ii) the optical fiber comprises a cladding surrounding the core, the cladding having an outer surface (a) partially defining an end surface of the optical fiber along a diameter of the optical fiber and (b) having a reflectivity to the multi-wavelength beam of less than 1%.
15. The laser system of claim 14 , wherein a portion of the core protrudes from the cladding.
16. The laser system of claim 14 , further comprising an anti-reflective coating disposed over the cladding of the optical fiber.
17. The laser system of claim 1 , wherein the optical fiber is positioned such that, at an end surface of a core of the optical fiber, a diameter of the core is no smaller than a diameter of the multi-wavelength beam.
18. The method of claim 7 , wherein the optical fiber is positioned such that, at an end surface of the core of the optical fiber, a diameter of the core is no smaller than a diameter of the multi-wavelength beam.
19. A method of coupling a laser beam to an optical fiber having (i) a core and (ii) a cladding surrounding the core, the method comprising:
emitting a plurality of beams each having a different wavelength from a plurality of beam emitters;
wavelength-dispersing the plurality of beams to form a multi-wavelength beam;
reflecting a first portion of the multi-wavelength beam back to the plurality of beam emitters with the core of an optical fiber, the first portion of the multi-wavelength beam stabilizing each of the beams to its wavelength; and
transmitting a second portion of the multi-wavelength beam through the core of the optical fiber as an output beam composed of multiple wavelengths.
20. The method of claim 19 , wherein the core of the optical fiber comprises therewithin a fiber Bragg grating.
21. The method of claim 19 , wherein an outer surface of the core of the optical fiber is partially reflective to the multi-wavelength beam.
22. The method of claim 19 , wherein the cladding has an outer surface (a) partially defining an end surface of the optical fiber along a diameter of the optical fiber and (b) has a reflectivity to the multi-wavelength beam of less than 1%.
23. The method of claim 19 , further comprising reducing or preventing cross-coupling of the beams and/or the multi-wavelength beam.
24. The method of claim 23 , wherein the cross-coupling is reduced or prevented by a cross-coupling mitigation system disposed within a Rayleigh range of the multi-wavelength beam.
25. The method of claim 23 , wherein the cross-coupling is reduced or prevented by a cross-coupling mitigation system comprising an afocal telescope.
26. The method of claim 23 , wherein the cross-coupling is reduced or prevented by a cross-coupling mitigation system comprising a first optical element having a first focal length and a second optical element having a second focal length, the first optical element being disposed optically upstream of the second optical element.
27. The method of claim 26 , wherein the first focal length is at least two times greater than the second focal length.
28. The method of claim 26 , wherein the first focal length is at least seven times greater than the second focal length.
29. The method of claim 26 , wherein each of the first and second optical elements comprises a lens.
30. The method of claim 26 , wherein the first optical element is disposed within a Rayleigh range of the multi-wavelength beam.
31. The method of claim 26 , wherein an optical distance between the first and second optical elements is approximately equal to a sum of the first and second focal lengths.
32. The method of claim 19 , wherein a portion of the core protrudes from the cladding.
33. The method of claim 19 , wherein the cladding has an anti-reflective coating disposed thereover.
34. The method of claim 20 , wherein the fiber Bragg grating is disposed within a Rayleigh range of the multi-wavelength beam.
35. The method of claim 21 , wherein the partially reflective outer surface of the core has a reflectivity to the multi-wavelength beam of less than approximately 15%.
36. The method of claim 21 , wherein the partially reflective outer surface of the core has a reflectivity to the multi-wavelength beam ranging from approximately 2% to approximately 10%.
37. The method of claim 21 , wherein the partially reflective outer surface of the core has a reflectivity to the multi-wavelength beam ranging from approximately 4% to approximately 10%.