Optical cross-coupling mitigation systems for wavelength beam combining laser systems

• US 10,168,517 B2
• Filed: 08/31/2017
• Issued: 01/01/2019
• Est. Priority Date: 03/05/2010
• Status: Active Grant

• Current Assignee: Panasonic Corporation Of North America (Panasonic Holdings Corporation)
• Original Assignee: TeraDiode, Inc. (Panasonic Holdings Corporation)
• Inventors: Chann, Bien
• Primary Examiner(s): Pinkney, Dawayne A
• Application Number:
  US15/692,046
• Publication Number:
  US 20170363847A1
• Time in Patent Office: 488 Days
• Field of Search: 359618, 359299, 359624, 359245, 359241, 359244, 359288, 359305, 359285, 359308, 359311-312, 359290-292, 359872, 359263, 359223-224, 359318, 359649, 359846, 359129, 359496, 359631, 359629, 359634, 359636, 359638-640, 359831, 359833-834, 359630, 3593413, 35934133, 35933721, 353 31, 353 34, 353 81, 451 28, 451 41, 372 25, 372 92, 372 98, 372102
• CPC Class Codes: G02B 19/0014 at least one surface having optical power
• CPC Class Codes: G02B 19/0028 refractive and reflective surfaces, e.g. non-imaging catadioptric systems
• CPC Class Codes: G02B 19/0057 in the form of a laser diode array, e.g. laser diode bar semiconductor laser arrays with beam combining arrangement H01S5/4012
• CPC Class Codes: G02B 2005/1804 Transmission gratings
• CPC Class Codes: G02B 27/0905 Dividing and/or superposing multiple light beams
• CPC Class Codes: G02B 27/1006 for splitting or combining different wavelengths G02B27/1086, G02B27/141 take precedence
• CPC Class Codes: G02B 27/4244 in wavelength selecting devices spectrometry G01J
• CPC Class Codes: G02B 6/0208 characterised by their structure, wavelength response G02B6/02114, G02B6/02171, G02B6/02195 take precedence; multiple layer cores or claddings G02B6/036, protective coverings G02B6/4429
• CPC Class Codes: G02B 6/14 Mode converters
• CPC Class Codes: G02B 6/262 Optical details of coupling light into, or out of, or between fibre ends, e.g. special fibre end shapes or associated optical elements
• CPC Class Codes: G02B 6/29317 Light guides of the optical fibre type
• CPC Class Codes: G02B 6/32 having lens focusing means positioned between opposed fibre ends with lens being an integral part of the single fibre end G02B6/262
• CPC Class Codes: H01S 3/08063 Graded reflectivity, e.g. variable reflectivity mirror
• CPC Class Codes: H01S 5/141 using a wavelength selective device, e.g. a grating or etalon H01S5/146 takes precedence
• CPC Class Codes: H01S 5/4062 with an external cavity or using internal filters, e.g. Talbot filters
• CPC Class Codes: H01S 5/4068 with lateral coupling by axially offset or by merging waveguides, e.g. Y-couplers
• CPC Class Codes: H01S 5/4087 emitting more than one wavelength

Abstract

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.

Claims

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%.