System and method for aligning wavelength beam combining resonators

文档序号：1821803 发布日期：2021-11-09 浏览：20次中文

阅读说明：本技术 用于对准波长光束组合谐振器的系统和方法 (System and method for aligning wavelength beam combining resonators ) 是由 B·查恩 K·M·诺瓦克周望龙 F·比利亚雷亚尔苏塞多于 2020-01-24 设计创作，主要内容包括：在各种实施例中,用于激光谐振器的对准系统生成由激光谐振器产生的输入光束的近场和/或远场图像以实现输入光束的对准。(In various embodiments, an alignment system for a laser resonator generates near-field and/or far-field images of an input beam produced by the laser resonator to achieve alignment of the input beam.)

1. An alignment system for use with a laser resonator that spatially overlaps multiple input beams along a Wavelength Beam Combining (WBC) dimension and outputs a resulting output beam from a beam output, the alignment system comprising:

a dispersive element for receiving the output beam and dispersing the output beam to generate a plurality of dispersed beams in the WBC dimension;

a beam analyzer for receiving the plurality of dispersed beams and generating an image of the relative positions of the dispersed beams received by the beam analyzer;

a first lens having an optical power in a non-WBC dimension perpendicular to the WBC dimension disposed optically downstream of the beam output end and optically upstream of the beam analyzer; and

a second lens having an optical power in the WBC dimension for focusing the dispersed beam on the beam analyzer, disposed optically downstream of the dispersive element and optically upstream of the beam analyzer.

2. The alignment system of claim 1, wherein the dispersive element comprises a diffraction grating.

3. The alignment system of claim 1, wherein the first lens is disposed optically upstream of the dispersive element.

4. The alignment system of claim 1, wherein the first lens has optical power only in non-WBC dimensions.

5. The alignment system of claim 1, wherein a focal length of the first lens is greater than a focal length of the second lens.

6. The alignment system of claim 1, wherein at least one of the first or second lenses comprises a cylindrical lens.

7. The alignment system of claim 1, wherein an optical distance between the first lens and the beam analyzer is approximately equal to a focal length of the first lens.

8. The alignment system of claim 1, wherein an optical distance between the first lens and the beam analyzer is greater than a focal length of the first lens.

9. The alignment system of claim 1, wherein an optical distance between the first lens and the beam output end is approximately equal to a focal length of the first lens.

10. The alignment system of claim 1, wherein an optical distance between the second lens and the beam analyzer is approximately equal to a focal length of the second lens.

11. The alignment system of claim 1, wherein an optical distance between the second lens and the dispersive element is approximately equal to a focal length of the second lens.

12. The alignment system of claim 1, wherein the second lens has optical power only in the WBC dimension.

13. The alignment system of claim 1, wherein the first lens is movable between (i) a first position within a path of the output beam to generate a far-field image by the beam analyzer and (ii) a second position outside the path of the output beam to generate a near-field image by the beam analyzer.

14. The alignment system of claim 1, further comprising a third lens, wherein:

the focal length of the third lens is smaller than that of the first lens; and is

The first lens and the third lens are interchangeable within the path of the output beam such that (i) a far-field image is generated by the beam analyzer when the first lens is within the path of the output beam, and (ii) a near-field image is generated by the beam analyzer when the third lens is within the path of the output beam.

15. The alignment system of claim 1, further comprising a third lens disposed optically downstream of the beam output end and optically upstream of the first lens.

16. The alignment system of claim 15, wherein the third lens has optical power in non-WBC dimensions.

17. The alignment system of claim 15, wherein the third lens has optical power only in non-WBC dimensions.

18. The alignment system of claim 15, wherein a focal length of the third lens is less than a focal length of the first lens.

19. The alignment system of claim 15, wherein an optical distance between the third lens and the beam output end is approximately equal to a focal length of the third lens.

20. The alignment system of claim 15, wherein an optical distance between the third lens and the beam analyzer is greater than a focal length of the third lens.

21. The alignment system of claim 15, wherein the third lens is movable between (i) a first position within the path of the output beam to generate the near-field image by the beam analyzer and (ii) a second position outside the path of the output beam to generate the far-field image by the beam analyzer.

22. The alignment system of claim 1, further comprising a beam rotator disposed optically downstream of the beam output end.

23. The alignment system of claim 22, wherein the beam rotator is configured to rotate the output beam by approximately 90 °.

24. The alignment system of claim 22, wherein the beam rotator comprises (i) two confocal cylindrical lenses, (ii) a dove prism, or (iii) two reflectors.

25. The alignment system of claim 1, wherein the beam output end comprises a partially reflective output coupler.

26. An alignable laser system comprising:

a laser resonator comprising (i) a plurality of beam emitters for emitting a plurality of input beams, (ii) a plurality of optical elements for manipulating the input beams, and (iii) a beam output end, wherein the laser resonator is configured to spatially overlap the input beams along a Wavelength Beam Combining (WBC) dimension and output a resulting output beam from the beam output end; and

an alignment system includes a beam analyzer for generating an image of the input beam emitted by the beam emitter.

27. The laser system of claim 26, further comprising a controller configured to adjust the optical element to align the input beam based at least on the image generated by the beam analyzer.

28. The laser system of claim 27, wherein the optical element comprises one or more interleaving mirrors and/or one or more collimating lenses.

29. The laser system of claim 28, wherein the controller is configured to adjust the optical element by tilting one or more of the interlacing mirrors and/or translating one or more of the collimating lenses.

30. The laser system of claim 28, wherein at least one of the collimating lenses is a slow-axis collimating lens.

31. The laser system of claim 26, wherein the laser resonator comprises:

a dispersive element for receiving and wavelength dispersing an input light beam to form a multi-wavelength light beam; and

a partially reflective output coupler for (i) transmitting a first portion of the multi-wavelength optical beam as an output optical beam, and (ii) reflecting a second portion of the multi-wavelength optical beam back to the dispersive element.

32. The laser system of claim 31, wherein the laser resonator comprises: associated with each beam emitter

A fast axis collimator; and

an optical rotator for causing a rotation of the light beam by about 90 °.

33. The laser system of claim 31, wherein the dispersive element comprises a diffraction grating.

34. The laser system of claim 31, wherein the laser resonator comprises:

a plurality of first collimators, each first collimator receiving and collimating one or more beams from one of the beam emitters;

a plurality of interleavers, each interleaver receiving the one or more light beams from one of the first collimators; and

a second collimator for receiving all the light beams from the plurality of interleavers, collimating the light beams, and transmitting the light beams to a dispersive element.

35. The laser system of claim 34, wherein each first collimator comprises a slow-axis collimating lens.

36. The laser system of claim 31, wherein the laser resonator comprises a fold mirror disposed optically downstream of the dispersive element and optically upstream of the partially reflective output coupler.

37. The laser system of claim 31, wherein the partially reflective output coupler is a beam output.

38. The laser system of claim 26, wherein the beam analyzer is disposed optically downstream of the beam output end.

39. The laser system of claim 26, wherein the alignment system comprises:

a dispersive element for receiving the output beam and dispersing the output beam to generate a plurality of dispersed beams in the WBC dimension;

a first lens having an optical power in a non-WBC dimension perpendicular to the WBC dimension disposed optically downstream of the beam output end and optically upstream of the beam analyzer; and

wherein the beam analyzer is configured to receive the plurality of dispersed light beams and to generate an image of the relative positions of the dispersed light beams received by the beam analyzer.

40. The laser system of claim 39, wherein the first lens is movable between (i) a first position within the path of the output beam to generate a far-field image by the beam analyzer and (ii) a second position outside the path of the output beam to generate a near-field image by the beam analyzer.

41. The laser system of claim 39, wherein:

the alignment system includes a third lens;

the focal length of the third lens is smaller than that of the first lens; and is

42. The laser system of claim 39, wherein the alignment system comprises a third lens disposed optically downstream of the beam output end and optically upstream of the first lens.

43. The laser system of claim 42, wherein a focal length of the third lens is less than a focal length of the first lens.

44. The laser system of claim 42, wherein the third lens is movable between (i) a first position within the path of the output beam to generate the near-field image by the beam analyzer and (ii) a second position outside the path of the output beam to generate the far-field image by the beam analyzer.

45. The laser system of claim 39, wherein the alignment system comprises a beam rotator disposed optically downstream of the beam output end.

46. The laser system of claim 45, wherein the beam rotator is configured to rotate the output beam by approximately 90 °.

47. The laser system of claim 45, wherein said beam rotator comprises (i) two confocal cylindrical lenses, (ii) a dove prism, or (iii) two reflectors.

48. An alignment system for use with a laser resonator that spatially overlaps multiple input beams along a Wavelength Beam Combining (WBC) dimension and outputs a resulting output beam from a beam output, the alignment system comprising:

a dispersive element configured to disperse a beam of WBC dimensions;

a beam analyzer for receiving the light beam and generating an image of its relative position;

a first lens having an optical power in a non-WBC dimension perpendicular to the WBC dimension disposed optically downstream of the beam output end and optically upstream of the beam analyzer;

a third lens having optical power in the non-WBC dimension disposed optically downstream of the beam output end and optically upstream of the beam analyzer; and

a plurality of optical elements configured to (i) receive the output light beam, (ii) direct a first portion of the output light beam to the third lens, and (iii) direct a second portion of the output light beam to the first lens.

49. The alignment system of claim 48, wherein the second portion of the output beam is not directed to the third lens.

50. The alignment system of claim 48, wherein the first lens is positioned to receive the first portion of the output beam and the second portion of the output beam.

51. The alignment system of claim 50, wherein the optical element is configured to direct the first and second portions of the output beam at different angles to the first lens.

52. The alignment system of claim 48, wherein the dispersive element is positioned to receive and disperse the first portion of the output beam, thereby generating a near-field image of the input beam via the beam analyzer.

53. The alignment system of claim 48, wherein the dispersive element is positioned to receive and disperse the second portion of the output beam, thereby generating a far field image of the input beam via the beam analyzer.

54. The alignment system of claim 48, wherein the dispersive element comprises a diffraction grating.

55. The alignment system of claim 48, wherein the first lens is disposed optically upstream of the dispersive element.

56. The alignment system of claim 48, wherein the third lens is disposed optically upstream of the first lens.

57. The alignment system of claim 48, wherein a focal length of the first lens is greater than a focal length of the second lens.

58. The alignment system of claim 48, wherein at least one of the first, second, or third lenses comprises a cylindrical lens.

59. The alignment system of claim 48, wherein an optical distance between the first lens and the beam analyzer is approximately equal to a focal length of the first lens.

60. The alignment system of claim 48, wherein an optical distance between the first lens and the beam output end is approximately equal to a focal length of the first lens.

61. The alignment system of claim 48, wherein an optical distance between the second lens and the beam analyzer is approximately equal to a focal length of the second lens.

62. The alignment system of claim 48, wherein an optical distance between the second lens and the dispersive element is approximately equal to a focal length of the second lens.

63. The alignment system of claim 48, wherein a focal length of the third lens is less than a focal length of the first lens.

64. The alignment system of claim 48, wherein an optical distance between the third lens and the beam output end is approximately equal to a focal length of the third lens.

65. The alignment system of claim 48, wherein an optical distance between the third lens and the beam analyzer is greater than a focal length of the third lens.

66. The alignment system of claim 48, further comprising a beam rotator disposed optically downstream of the beam output end.

67. The alignment system of claim 66, wherein the beam rotator is configured to rotate the output beam by approximately 90 °.

68. The alignment system of claim 66, wherein the beam rotator comprises, consists essentially of, or consists of (i) two confocal cylindrical lenses, (ii) a dove prism, or (iii) two reflectors.

69. The alignment system of claim 48, wherein the first lens has optical power only in non-WBC dimensions.

70. The alignment system of claim 48, wherein the second lens has only optical power in the WBC dimension.

71. The alignment system of claim 48, wherein the third lens has optical power only in non-WBC dimensions.

72. The alignment system of claim 48, wherein the plurality of optical elements includes at least one beam splitter and/or at least one reflector.

73. The alignment system of claim 48, wherein the beam output end comprises a partially reflective output coupler.

74. An alignable laser system comprising:

a laser resonator comprising (i) a plurality of beam emitters for emitting a plurality of input beams, (ii) a beam output end, and (iii) a plurality of first optical elements disposed optically upstream of the beam output end for manipulating the input beams, wherein the laser resonator is configured to spatially overlap the input beams along a Wavelength Beam Combining (WBC) dimension and output a resulting output beam from the beam output end; and

an alignment system comprising a plurality of second optical elements disposed optically downstream of the beam output end, the alignment system configured to simultaneously generate near-field and far-field images of the input beam without physical movement of the plurality of second optical elements.

75. The laser system of claim 74, wherein the alignment system comprises a beam analyzer for generating near and far field images.

76. The laser system of claim 75, wherein said beam analyzer is disposed optically downstream of the beam output end.

77. The laser system of claim 74, further comprising a controller configured to adjust the first optical element to align the input beam based at least on the near-field and/or far-field images.

78. The laser system of claim 77, wherein said first optical element comprises one or more interleaving mirrors and/or one or more collimating lenses.

79. The laser system of claim 78, wherein the controller is configured to adjust the first optical element by tilting one or more of the interlacing mirrors and/or translating one or more of the collimating lenses.

80. The laser system of claim 78, wherein at least one of the collimating lenses is a slow-axis collimating lens.

81. The laser system of claim 74, wherein the laser resonator comprises:

a dispersive element for receiving and wavelength dispersing an input light beam to form a multi-wavelength light beam; and

82. The laser system of claim 81, wherein the laser resonator comprises: associated with each beam emitter

A fast axis collimator; and

an optical rotator for causing a rotation of the light beam by about 90 °.

83. The laser system of claim 81, wherein said dispersive element comprises a diffraction grating.

84. The laser system of claim 81, wherein the laser resonator comprises:

a plurality of first collimators, each first collimator receiving and collimating one or more beams from one of the beam emitters;

a plurality of interleavers, each interleaver receiving the one or more light beams from one of the first collimators; and

a second collimator for receiving all the light beams from the plurality of interleavers, collimating the light beams, and transmitting the light beams to a dispersive element.

85. The laser system of claim 84, wherein each first collimator comprises a slow-axis collimating lens.

86. The laser system of claim 81, wherein the laser resonator comprises a fold mirror disposed optically downstream of the dispersive element and optically upstream of the partially reflective output coupler.

87. The laser system of claim 81, wherein said partially reflective output coupler is a beam output.

88. The laser system of claim 74, wherein the alignment system includes (i) a dispersive element configured to disperse the beam in the WBC dimension, and (ii) a beam analyzer for receiving the beam and generating an image of its relative position.

89. The laser system of claim 88, wherein said plurality of second optical elements comprises:

a first lens having an optical power in a non-WBC dimension perpendicular to the WBC dimension disposed optically downstream of the beam output end and optically upstream of the beam analyzer;

a third lens having optical power in the non-WBC dimension disposed optically downstream of the beam output end and optically upstream of the beam analyzer; and

a plurality of third optical elements configured to (i) receive the output light beam, (ii) direct a first portion of the output light beam to the third lens, and (iii) direct a second portion of the output light beam to the first lens.

90. The laser system of claim 89, wherein the second portion of the output beam is not directed to the third lens.

91. The laser system of claim 89, wherein the first lens is positioned to receive the first portion of the output beam and the second portion of the output beam.

92. The laser system of claim 91, wherein the third optical element is configured to direct the first and second portions of the output beam at different angles to the first lens.

93. The laser system of claim 89, wherein the dispersive element is positioned to receive and disperse the first portion of the output beam, thereby generating a near-field image of the input beam via the beam analyzer.

94. The laser system of claim 89, wherein the dispersive element is positioned to receive and disperse the second portion of the output beam, thereby generating a far field image of the input beam via the beam analyzer.

95. The laser system of claim 89, wherein said plurality of third optical elements comprises at least one beam splitter and/or at least one reflector.

96. The laser system of claim 88, wherein said dispersive element comprises a diffraction grating.

97. The laser system of claim 74, wherein the alignment system comprises a beam rotator disposed optically downstream of the beam output end.

98. The laser system of claim 97, wherein the beam rotator is configured to rotate the output beam by approximately 90 °.

99. The laser system of claim 97, wherein the beam rotator comprises (i) two confocal cylindrical lenses, (ii) a dove prism, or (iii) two reflectors.

100. An alignment method for use with a laser resonator that spatially overlaps multiple input beams along a Wavelength Beam Combining (WBC) dimension and outputs a resulting output beam from a beam output end, the laser resonator including a plurality of optical elements for manipulating the input beams, the method comprising:

generating at least one of (i) a near-field image of the input beam or (ii) a far-field image of the input beam with a beam analyzer; and

when one of the input beams is misaligned in at least one of the near-field image or the far-field image, one or more of the optical elements are adjusted to align the input beams.

101. The method of claim 100, wherein both near field images and far field images are generated.

102. The method of claim 101, wherein the near field image and the far field image are generated sequentially.

103. The method of claim 101, wherein the near field image and the far field image are generated simultaneously.

104. The method of claim 100, further comprising, prior to generating at least one of the near-field image or the far-field image, (i) wavelength dispersing the output beam to generate a plurality of dispersed beams in the WBC dimension, and (ii) focusing the dispersed beams toward the beam analyzer.

105. The method of claim 100, wherein the optical element comprises one or more interlacing mirrors and/or one or more collimating lenses.

106. The method of claim 105, wherein adjusting one or more of the optical elements comprises tilting one or more of the interlacing mirrors and/or translating one or more of the collimating lenses.

107. The method of claim 105, wherein at least one of the collimating lenses is a slow-axis collimating lens.

108. The method of claim 100, wherein:

generating the far-field image includes positioning a first lens in a path of the output beam; and

generating the near-field image includes removing the first lens from a path of the output beam.

109. The method of claim 100, wherein:

generating the far-field image includes positioning a first lens in a path of the output beam; and

generating the near-field image includes replacing the first lens with a second lens having a focal length less than a focal length of the first lens.

110. The method of claim 100, wherein:

generating the near-field image includes positioning first and second lenses within a path of the output beam;

generating the far-field image includes removing the second lens from the path of the output beam.

111. The method of claim 110, wherein the focal length of the second lens is less than the focal length of the first lens.

112. The method of claim 100, wherein:

generating the far-field image includes directing a first portion of the output beam to a first lens;

generating the near-field image includes directing a second portion of the output beam to a second lens.

113. The method of claim 100, further comprising rotating the output beam prior to generating at least one of the near field image or the far field image.

114. The method of claim 100, wherein the laser resonator comprises:

a dispersive element for receiving and wavelength dispersing an input light beam to form a multi-wavelength light beam; and

115. The method of claim 114 wherein the laser resonator comprises (i) a plurality of beam emitters configured to emit an input beam and (ii) associated with each of the beam emitters

A fast axis collimator; and

an optical rotator for causing a rotation of the light beam by about 90 °.

116. The method of claim 114, wherein the dispersive element comprises a diffraction grating.

117. The method of claim 114, wherein the plurality of optical elements comprises:

a plurality of first collimators, each first collimator receiving and collimating one or more input beams;

a plurality of interleavers, each interleaver receiving the one or more input beams from one of the first collimators; and

a second collimator for receiving all of the input beams from the plurality of interleavers, collimating the beams, and transmitting the beams to a dispersive element.

118. The method of claim 117, wherein each first collimator comprises a slow-axis collimating lens.

119. The method of claim 114 wherein the laser resonator comprises a fold mirror disposed optically downstream of the dispersive element and optically upstream of the partially reflective output coupler.

120. The method of claim 114, wherein the partially reflective output coupler is a beam output.

121. The method of claim 100, wherein the beam analyzer is disposed optically downstream of the beam output end.

Technical Field

In various embodiments, the present invention relates to laser systems, and in particular to methods and systems for aligning a laser system with a plurality of beam emitters.

Background

High power laser systems are used in many different applications such as welding, cutting, drilling and material processing. Such laser systems typically include a laser emitter from which laser light is coupled into an optical fiber (or simply "fiber") and an optical system that focuses the laser light from the fiber onto a workpiece to be machined. The optical systems used in laser systems are typically designed to produce the highest quality laser beam or equivalently, a beam with the smallest Beam Parameter Product (BPP). BPP is the product of the laser beam divergence angle (half angle) and the radius of the beam at its narrowest point (i.e., beam waist, minimum spot size). That is, BPP ═ NA × D/2, where D is the focal point (waist) diameter and NA is the numerical aperture; thus, the BPP can be changed by changing NA and/or D. BPP quantifies the quality of a laser beam and the extent to which it can be focused to a small spot and is typically expressed in units of millimeters-milliradians (mm-mrad). The gaussian beam has as small a BPP as possible, resulting from dividing the wavelength of the laser by pi. The ratio of the actual beam BPP to the ideal Gaussian beam BPP at the same wavelength is M²Which is a measure of the wavelength-independent beam quality.

Wavelength Beam Combining (WBC) is a technique for scaling the output power and brightness from laser diodes, laser diode bars, diode bar stacks, or other lasers arranged in one-or two-dimensional arrays. WBC methods have been developed that combine beams along one or two dimensions of an emitter array. A typical WBC system includes multiple emitters, such as one or more diode bars, which are combined with dispersive elements to form a multi-wavelength beam. Each emitter in a WBC system resonates individually and is stabilized by wavelength specific feedback from a common partially reflective output coupler that is filtered along the beam combining dimension by a dispersive element. Exemplary WBC systems are described in detail in U.S. patent No.6,192,062, filed on 4/2/2000, U.S. patent No.6,208,679, filed on 8/9/1998, U.S. patent No.8,670,180, filed on 25/8/2011, U.S. patent No.8,670,180, filed on 7/3/2011, and U.S. patent application 8,559,107, filed on 7/3/2011, each in its entirety by 8,559,107, the entire disclosure of each application being incorporated herein by reference.

Various WBC laser systems combine beams emitted by beam emitters in a single direction or dimension (referred to as the "WBC dimension"). Thus, a WBC system, or "resonator," typically has the feature that its various components lie in the same plane in the WBC dimension. The dimension perpendicular to the WBC dimension, in which the beams are not combined, is commonly referred to as the "non-WBC dimension".

As disclosed in some of the references mentioned above, WBC laser systems typically have diode bars or other multi-beam emitters whose outputs are combined into a single output beam. A typical WBC resonator includes a dispersive element and a downstream feedback surface that provides (e.g., by reflecting) a feedback beam to each respective emitter to stabilize the resonator by locking each emitter to its respective laser wavelength. To optimize the WBC resonator, the combined beam in the resonator is typically aligned perpendicular to the feedback surface in both the WBC and non-WBC dimensions.

Advantageously, the WBC resonator is generally adaptive to a degree of misalignment in the WBC dimension, as the resonator will simply lock to different wavelengths propagating in the normal direction of the feedback surface in the WBC dimension. If the new lasing wavelength is within the substantially flat region of the transmitter gain curve and the misalignment does not cause significant power clipping (power clipping) on the optics in the resonator, the misalignment in the WBC dimension will generally not affect the resonator power and stability.

However, the alignment of WBC resonators in non-WBC dimensions is more challenging. Since the WBC resonator is actually a combination of many independent single beam resonators, each single beam resonator would ideally be aligned independently. Especially in systems where the emitters are diode bars or other multi-emitter sources, the performance of the WBC resonator depends on the alignment of the individual sub-resonators corresponding to the individual diode bars. Accordingly, there is a need for systems and methods that enable optimized alignment of WBC resonators and their beam sources, particularly in the non-WBC dimension.

Disclosure of Invention

Systems and techniques in accordance with embodiments of the present invention detect and are capable of mitigating emitter misalignment in a laser resonator (e.g., a WBC resonator) where beams from multiple beam emitters spatially overlap. According to various embodiments, the resonator beams (e.g., WBC resonator beams) are demultiplexed and near-field and far-field images of the resulting sub-beams are generated (sequentially or simultaneously) via a beam analysis system. The resulting image reveals beam eccentricity and pointing errors that can be reduced or substantially eliminated by adjusting one or more optical elements in the laser system. For example, the interlacing mirrors may be tilted, and/or lenses (e.g., SAC lenses or other lenses that adjust the beams in the slow axis and/or non-WBC dimensions) may be translated to adjust the alignment of the individual beams.

As used herein, a "near-field image" corresponds to an image of a beam or sub-beam at the output end of the beam (e.g., the output end of a laser resonator). Generally, in the near field, the optical beam is relatively collimated and has a relatively large beam size. In various embodiments, near field images may be produced via projection of beams or sub-beams onto a beam analysis system without passing through a lens having optical power in the WBC dimension (or another dimension of interest for imaging). (in various embodiments, such beams or sub-beams may still propagate through a lens having no optical power in the WBC dimension to produce a near-field image.) in other embodiments, a near-field image may be produced by imaging the beams or sub-beams onto a beam analysis system at a beam output end with an imaging lens (i.e., a lens having optical power in the WBC dimension and which may be located at an optical distance from the beam output end corresponding to its focal length). The near field image can be used to monitor and determine the shape and size of the beam or sub-beam at the beam output.

In contrast, a "far field image" corresponds to an image of a beam or sub-beam at the focal plane of a lens (e.g., a lens optically downstream of the beam output end). In various embodiments, the far field image may be produced by focusing the beams or sub-beams onto a beam analysis system using a lens, which may be located at an optical distance from the beam analysis system corresponding to the focal length of the lens. The far field image can be used to monitor and determine beam pointing (corresponding to beam position at the beam analysis system) and divergence (corresponding to beam size at the beam analysis system) of the beams or sub-beams.

Alignment systems according to various embodiments of the present invention have optical elements (e.g., lenses, beam splitters, reflectors, and/or beam rotators) that may, but need not, be capable of moving in and out of the path of the output beam of the resonator. The optical elements and their positioning and/or movement enable far-field and near-field images to be generated with a beam analysis system. This also enables detection and correction of misalignment of WBC and non-WBC dimensions, as the output beam can be rotated by the beam rotator moving into the beam path. That is, demultiplexing of the non-rotated beams may be used to detect, for example, misalignment of the non-WBC dimensions, and demultiplexing of the rotated beams may be used to detect, for example, misalignment of the WBC dimensions. The optical element may be moved (e.g., translatable and/or tiltable) using a mechanical stage, gimbal, platform, and/or support, as is known in the art; thus, providing a movable optical element can be accomplished by one skilled in the art without undue experimentation.

Since many laser resonators utilize individual beams that overlap spatially at the resonator output, alignment of such systems typically requires powering up only a single emitter (e.g., diode bar) at a time, and adjusting only the resulting beam (or set of beams) to optimize the resulting sub-resonator created by the beam. In contrast, embodiments of the present invention advantageously demultiplex spatially overlapping light beams so that one or more, or even all, of the light beams can be aligned simultaneously. In this manner, embodiments of the present invention are able to more efficiently align a multi-emitter laser resonator. Furthermore, the laser resonator power supply and power supply switching configuration may be simplified because embodiments of the present invention do not require separate powering of a single transmitter for alignment.

Systems and techniques according to embodiments of the present invention may be used with WBC resonators that include multiple diode bars as beam emitters. Each beam emitter may have a respective staggered mirror and a Slow Axis Collimating (SAC) lens, and the beams from all emitters may be combined optically downstream into a multi-wavelength output beam. Each diode bar may be coupled to a fast axis collimator and an optical rotator (or "optical twister") that rotates the fast and slow axes of the beam by 90 ° in a plane perpendicular to the direction of propagation of the beam. In such WBC systems, the slow axis of the beam is in the non-WBC dimension or in a direction optically downstream of the optical rotator. Thus, the emitters of a single diode bar can all be collimated in the slow axis by a single SAC lens (or "slow axis collimator").

Embodiments of the present invention may be used to detect and compensate for slow axis pointing errors caused by, for example, tilting of a dispersive element in a WBC system in a non-WBC direction, as detailed in U.S. patent application No. 16/598,001 (' 001 application) filed on 10.10.2019, the entire disclosure of which is incorporated herein by reference. Furthermore, embodiments of the present invention may be used to detect and then reduce or substantially eliminate beam blur (beam blur) using "stepped" (i.e., SAC lens arrays that vary in height and/or position relative to each other), as detailed in the' 001 application.

In embodiments of the present invention, the beam emitters (or simply "emitters") may comprise, consist essentially of, or consist of diode lasers, fiber pigtail diode lasers, and the like, and may be packaged individually or in groups in one-or two-dimensional arrays. In various embodiments, the emitter or emitter array is a high power diode bar, each bar having a plurality (e.g., tens) of emitters. The emitter may have a microlens attached to it for emitter collimation and beam shaping. The transformation optics, which are typically confocal and located between the emitters and the dispersive element (e.g., diffraction grating), collimate the individual beams from the different emitters and converge all of the chief rays of the beams to the grating center, particularly in the WBC dimension (i.e., the dimension or direction in which the beams are combined). The main beam diffracted by the dispersive element propagates to a partially reflective output coupler which provides feedback to the individual emitters and defines the wavelength of the individual emitters through the dispersive element. That is, the couplers reflect a portion of the various beams back to their respective emitters, thereby forming an external lasing cavity (cavity), and transmit the combined multi-wavelength beam for use in applications such as welding, cutting, machining, and/or for coupling into one or more optical fibers.

Various embodiments of the present invention may be used with laser systems having techniques for varying the BPP of their output laser beams, such as those described in U.S. patent application serial No. 14/632,283 filed on 26/2/2015 and U.S. patent application No. 15/188,076 filed on 21/6/2016, the entire disclosure of each being incorporated herein by reference. Laser systems according to embodiments of the present invention may also include power and/or spectral monitoring functionality, as described in detail in U.S. patent application serial No. 16/417,861 filed on 2019, 5, 21, the entire disclosure of which is incorporated herein by reference.

Herein, "optical element" may refer to any one of a lens, mirror, prism, grating, beam splitter, or the like, which redirects, reflects, bends, or otherwise optically manipulates electromagnetic radiation unless otherwise indicated. In this application, a beam transmitter, transmitter or laser includes any electromagnetic beam generating device, such as a semiconductor element, that generates an electromagnetic beam, but may or may not be self-resonant. These also include fiber lasers, slab lasers, non-solid state lasers, and the like. Typically, each emitter includes a rear reflective surface, at least one optical gain medium, and a front reflective surface. The optical gain medium increases the gain of electromagnetic radiation, which is not limited to any particular portion of the electromagnetic spectrum, but may be visible, infrared, and/or ultraviolet light. The emitter may comprise, consist essentially of, or consist of a plurality of beam emitters, such as diode bars or the like configured to emit a plurality of beams. The input beam received in embodiments of the present application may be a single or multiple wavelength beam combined using various techniques known in the art.

Although diffraction gratings are used as exemplary dispersive elements in the present application, embodiments of the present invention may utilize other dispersive elements, such as dispersive prisms, transmission gratings, or Echelle gratings. Embodiments of the present invention may utilize one or more prisms in addition to one or more diffraction gratings, for example, as described in U.S. patent application serial No. 15/410,277 filed on 2017, 1, 19, the entire disclosure of which is incorporated herein by reference.

Embodiments of the present invention may couple a multi-wavelength output beam into an optical fiber. In various embodiments, the optical fiber has multiple claddings surrounding a single core, multiple discrete core regions (or "cores") within a single cladding, or multiple cores surrounded by multiple claddings. In various embodiments, the output beam may be delivered to a workpiece for applications such as cutting, welding, and the like.

Laser diode arrays, bars, and/or stacks, such as those described in the general description below, may be used in association with the inventive embodiments described herein. The laser diodes may be packaged individually or in groups, typically in one-dimensional rows/arrays (diode bars) or two-dimensional arrays (diode bar stacks). The diode array stack is typically a vertical stack of diode bars. Laser diode bars or arrays are typically more power and cost effective than an equivalent single large area diode (broad area diode). High power diode bars typically contain large area emitter arrays, producing tens of watts with relatively poor beam quality; despite the higher power, the brightness is generally lower than for large area laser diodes. High power diode bars may be stacked to produce high power stacked diode bars to produce very high power of hundreds or thousands of watts. The laser diode array may be configured to emit light beams into free space or into an optical fiber. Fiber coupled diode laser arrays can be conveniently used as pump sources for fiber lasers and fiber amplifiers.

The diode laser bar is a type of semiconductor laser comprising a one-dimensional array of large area emitters, or alternatively a sub-array comprising, for example, 10-20 narrow strip-shaped emitters. A wide emission area diode bar typically contains, for example, 19-49 emitters, each having dimensions of, for example, about 1 μm x 100 μm. The beam quality along the 1 μm dimension or fast axis is typically diffraction limited. The beam quality along the 100 μm dimension or slow axis or array size is typically limited by many times diffraction. Typically, the laser resonator for a diode bar for commercial applications is about 1 to 4 millimeters in length, about 10 millimeters wide, and produces tens of watts of output power. Most diode bars operate in the wavelength range 780 to 1070nm, with wavelengths 808nm (for pumping neodymium lasers) and 940nm (for pumping Yb: YAG) being most prominent. The 915-976nm wavelength range is used to pump erbium-doped or ytterbium-doped high power fiber lasers and amplifiers.

Diode stacks are merely arrangements of multiple diode bars capable of providing very high output power. Also known as a diode laser stack, a multi-strip module or a two-dimensional laser array, the most common diode stacks are arranged as vertical stacks, which are in fact two-dimensional arrays of edge emitters. Such a stack may be manufactured by connecting the diode bars to a thin heat sink and stacking the assemblies so as to obtain a periodic array of diode bars and heat sinks. There are also horizontal diode stacks and two-dimensional stacks. To obtain a high beam quality, the diode bars should generally be as close to each other as possible. On the other hand, efficient cooling requires a minimum thickness of the heat sink mounted between the bars. This tradeoff in diode bar spacing makes the beam quality (and consequently the brightness) of the diode stack in the vertical direction much lower than that of a single diode bar. However, there are several techniques to significantly alleviate this problem, e.g. by spatial interleaving of the outputs of different diode stacks, by polarization coupling or by wavelength multiplexing. Various types of high power beam shapers and related devices have been developed for this purpose. The diode stack may provide extremely high output power (e.g., hundreds or thousands of watts).

In contrast to optical techniques that merely probe a surface with light (e.g., reflectance measurements), output beams generated according to embodiments of the present invention may be used to machine a workpiece such that the surface of the workpiece is physically altered and/or such that features are formed on or in the surface. Exemplary processes according to embodiments of the present invention include cutting, welding, drilling, and welding. Various embodiments of the present invention may also machine the workpiece at one or more points or along a one-dimensional linear or curvilinear machining path, rather than flood all or substantially all of the workpiece surface with radiation from the laser beam. Such a one-dimensional path may be composed of a plurality of segments, each of which may be linear or curvilinear.

In one aspect, embodiments of the invention feature an alignment system for use with a laser resonator that spatially overlaps multiple input beams along a Wavelength Beam Combining (WBC) dimension and outputs a resulting output beam from a beam output end. The alignment system comprises, consists essentially of, or consists of a dispersive element, a beam analyzer, a first lens and a second lens. The dispersive element receives the output beam and disperses the output beam to generate a plurality of dispersed beams in the WBC dimension. A beam analyzer receives the plurality of dispersed light beams and generates an image of the relative positions of the dispersed light beams received by the beam analyzer. The first lens has optical power in a non-WBC dimension perpendicular to the WBC dimension. The first lens is disposed optically downstream of the beam output end and optically upstream of the beam analyzer. The second lens focuses the dispersed beam on or towards the beam analyzer. The second lens has optical power in the WBC dimension. The second lens is disposed optically downstream of the beam output end (e.g., optically downstream of the dispersive element) and optically upstream of the beam analyzer.

Embodiments of the invention may include one or more of any of the following various combinations. The dispersive element may comprise, consist essentially of, or consist of a diffraction grating. The first lens may be disposed optically upstream of the dispersive element. The first lens may have only optical power in the non-WBC dimension. The focal length of the first lens may be greater than the focal length of the second lens. The first lens and/or the second lens may comprise, consist essentially of, or consist of one or more cylindrical lenses. The optical distance between the first lens and the beam analyzer may be approximately equal to the focal length of the first lens. The optical distance between the first lens and the beam analyzer may be greater than the focal length of the first lens. The optical distance between the first lens and the beam output end may be approximately equal to the focal length of the first lens. The optical distance between the second lens and the beam analyzer may be approximately equal to the focal length of the second lens. The optical distance between the second lens and the dispersive element may be approximately equal to the focal length of the second lens. The second lens may have only optical power in the WBC dimension.

The first lens may be movable between (i) a first position within the path of the output beam to generate a far-field image by the beam analyzer and (ii) a second position outside the path of the output beam to generate a near-field image by the beam analyzer. The alignment system may include a third lens. The focal length of the third lens may be less than the focal length of the first lens. The first lens and the third lens are interchangeable within the path of the output beam such that (i) a far-field image is generated by the beam analyzer when the first lens is within the path of the output beam, and (ii) a near-field image is generated by the beam analyzer when the third lens is within the path of the output beam.

The alignment system may include a third lens disposed optically downstream of the beam output end and optically upstream of the first lens. The third lens may have an optical power of non-WBC dimensions. The third lens may have only optical power in the non-WBC dimension. The focal length of the third lens may be less than the focal length of the first lens. The optical distance between the third lens and the beam output end may be approximately equal to the focal length of the third lens. The optical distance between the third lens and the beam analyzer may be greater than the focal length of the third lens. The third lens may be movable between (i) a first position within the path of the output beam to generate a near-field image by the beam analyzer and (ii) a second position outside the path of the output beam to generate a far-field image by the beam analyzer.

In another aspect, embodiments of the invention feature a laser system capable of alignment that includes, consists essentially of, or consists of a laser resonator and an alignment system. The laser resonator comprises, consists essentially of, or consists of, (i) a plurality of beam emitters for emitting a plurality of input beams, (ii) a plurality of optical elements for manipulating the input beams, and (iii) a beam output. The laser resonator is configured to spatially overlap an input beam along a Wavelength Beam Combining (WBC) dimension and output a generated output beam from a beam output end. The alignment system comprises a beam analyzer for generating, consisting essentially of, or consisting of an image of the input beam emitted by the beam emitter.

Embodiments of the invention may include one or more of any of the following various combinations. The laser system may include a controller configured to adjust an optical element to align the input beam based at least on the image generated by the beam analyzer. The optical element may comprise, consist essentially of, or consist of one or more interlacing mirrors and/or one or more collimating lenses. The controller may be configured to adjust the optical element by tilting one or more of the interlacing mirrors and/or translating one or more of the collimating lenses. At least one or even each of the collimating lenses may be a slow axis collimating lens. At least one or even each of the collimating lenses may be a fast axis collimating lens. The laser resonator may comprise, consist essentially of, or consist of: (a) a dispersive element for receiving and wavelength dispersing an input optical beam to form a multi-wavelength optical beam, and (b) a partially reflective output coupler for (i) transmitting a first portion of the multi-wavelength optical beam as an output optical beam and (ii) reflecting a second portion of the multi-wavelength optical beam back to the dispersive element (and then to the beam emitters to form external laser cavities and to stabilize the beam emitters to their emission wavelengths, each of which may be different). The laser resonator may include a fast axis collimator associated with each beam emitter and an optical rotator for causing a beam rotation of approximately 90 °. The dispersive element may comprise, consist essentially of, or consist of a diffraction grating. The laser resonator may include (a) a plurality of first collimators, each of which receives and collimates one or more beams from one of the beam emitters, (b) a plurality of interleavers, each of which receives one or more beams from one of the first collimators, and (c) a second collimator for receiving all of the beams from the plurality of interleavers, collimating the beams, and transmitting the beams to the dispersive element. At least one or even each first collimator may comprise, consist essentially of, or consist of a slow-axis collimating lens. At least one or even each first collimator may comprise, consist essentially of, or consist of a fast axis collimating lens. The laser resonator may comprise a fold mirror disposed optically downstream of the dispersive element and optically upstream of the partially reflective output coupler. The partially reflective output coupler may be the beam output. The beam analyser may be arranged optically downstream of the beam output end.

The alignment system may further comprise, consist essentially of, or consist of a dispersive element, a first lens, and a second lens. The dispersive element can receive the output beam and disperse the output beam to generate a plurality of dispersed beams in the WBC dimension. The first lens may have an optical power in a non-WBC dimension perpendicular to the WBC dimension. The first lens may be disposed optically downstream of the beam output end and optically upstream of the beam analyzer. The second lens may have an optical power in the WBC dimension. The second lens may focus the dispersed beam on or towards the beam analyzer. The second lens may be disposed optically downstream of the beam output end (e.g., optically downstream of the dispersive element) and optically upstream of the beam analyzer. The beam analyzer may be configured to receive the plurality of dispersed light beams and generate an image of the relative positions of the dispersed light beams received by the beam analyzer. The first lens may be movable between (i) a first position within the path of the output beam to generate a far-field image by the beam analyzer and (ii) a second position outside the path of the output beam to generate a near-field image by the beam analyzer. The alignment system may include a third lens. The focal length of the third lens may be less than the focal length of the first lens. The first lens and the third lens are interchangeable within the path of the output beam such that (i) a far-field image is generated by the beam analyzer when the first lens is within the path of the output beam, and (ii) a near-field image is generated by the beam analyzer when the third lens is within the path of the output beam.

The alignment system may include a third lens disposed optically downstream of the beam output end and optically upstream of the first lens. The focal length of the third lens may be less than the focal length of the first lens. The third lens may be movable between (i) a first position within the path of the output beam to generate a near-field image by the beam analyzer and (ii) a second position outside the path of the output beam to generate a far-field image by the beam analyzer. The alignment system may include a beam rotator disposed optically downstream of the beam output end. The beam rotator may be configured to rotate the output beam by about 90 °. The beam rotator may comprise, consist essentially of, or consist of (i) two confocal cylindrical lenses, (ii) a dove prism, or (iii) two reflectors.

In yet another aspect, embodiments of the invention feature an alignment system for use with a laser resonator that spatially overlaps multiple input beams along a Wavelength Beam Combining (WBC) dimension and outputs a resulting output beam from a beam output end. The alignment system comprises, consists essentially of, or consists of a dispersive element, a beam analyzer, a first lens, a second lens, a third lens, and a plurality of optical elements. The dispersive element is configured to disperse the WBC dimension beam. The beam analyzer receives the light beam and generates an image of its relative position. The first lens has optical power in a non-WBC dimension perpendicular to the WBC dimension. The first lens is disposed optically downstream of the beam output end and optically upstream of the beam analyzer. The second lens has optical power in the WBC dimension. The second lens focuses the dispersed beam on or towards the beam analyzer. The second lens is disposed optically downstream of the beam output end (e.g., optically downstream of the dispersive element) and optically upstream of the beam analyzer. The third lens has an optical power in the non-WBC dimension. A third lens is disposed optically downstream of the beam output end and optically upstream of the beam analyzer. The optical element is configured to (i) receive the output beam, (ii) direct a first portion of the output beam to the third lens, and (iii) direct a second portion of the output beam to the first lens.

Embodiments of the invention may include one or more of any of the following various combinations. The second portion of the output beam may not be directed to the third lens. The first lens may be positioned to receive a first portion of the output beam and a second portion of the output beam. The optical element may be configured to direct the first and second portions of the output beam at different angles to the first lens. The dispersive element may be positioned to receive and disperse a first portion of the output beam, thereby generating a near-field image of the input beam via the beam analyzer. The dispersive element may be positioned to receive and disperse the second portion of the output beam, thereby generating a far field image of the input beam via the beam analyzer. The dispersive element may comprise, consist essentially of, or consist of a diffraction grating.

The first lens may be disposed optically upstream of the dispersive element. The third lens may be disposed optically upstream of the first lens. The focal length of the first lens may be greater than the focal length of the second lens. The first lens, the second lens, and/or the third lens may comprise, consist essentially of, or consist of one or more cylindrical lenses. The optical distance between the first lens and the beam analyzer may be approximately equal to the focal length of the first lens. The optical distance between the first lens and the beam output end may be approximately equal to the focal length of the first lens. The optical distance between the second lens and the beam analyzer may be approximately equal to the focal length of the second lens. The optical distance between the second lens and the dispersive element may be approximately equal to the focal length of the second lens. The focal length of the third lens may be less than the focal length of the first lens. The optical distance between the third lens and the beam output end may be approximately equal to the focal length of the third lens. The optical distance between the third lens and the beam analyzer may be greater than the focal length of the third lens.

The alignment system may include a beam rotator disposed optically downstream of the beam output end. The beam rotator may be configured to rotate the output beam by about 90 °. The beam rotator may comprise, consist essentially of, or consist of (i) two confocal cylindrical lenses, (ii) a dove prism, or (iii) two reflectors. The first lens may have only optical power in the non-WBC dimension. The second lens may have only optical power in the WBC dimension. The third lens may have only optical power in the non-WBC dimension. At least one of the optical elements, or even each, may comprise, consist essentially of, or consist of a beam splitter and/or a reflector. The beam output end may comprise, consist essentially of, or consist of a partially reflective output coupler.

In another aspect, embodiments of the invention feature a laser system capable of alignment that includes, consists essentially of, or consists of a laser resonator and an alignment system. The laser resonator comprises, consists essentially of, or consists of: (i) a plurality of beam emitters for emitting a plurality of input beams, (ii) a beam output, and (iii) a plurality of first optical elements disposed optically upstream of the beam output for manipulating the input beams. The laser resonator is configured to spatially overlap an input beam along a Wavelength Beam Combining (WBC) dimension and output a generated output beam from a beam output end. The alignment system comprises, consists essentially of, or consists of a plurality of second optical elements disposed optically downstream of the beam output end. The alignment system is configured to simultaneously generate near-field and far-field images of the input optical beam without physical movement of the plurality of second optical elements.

Embodiments of the invention may include one or more of any of the following various combinations. The alignment system may include a beam analyzer for generating near-field and far-field images (e.g., of the input beam of the laser resonator). The beam analyser may be arranged optically downstream of the beam output end. The laser system may include a controller configured to adjust the first optical element to align the input beam based at least in part on the near-field and/or far-field images. One or more, or even each, of the first optical elements may comprise, consist essentially of, or consist of one or more interlacing mirrors and/or one or more collimating lenses. The controller may be configured to adjust the first optical element by tilting one or more of the interlacing mirrors and/or translating one or more of the collimating lenses. At least one or even each of the collimating lenses may be a slow axis collimating lens. At least one or even each of the collimating lenses may be a fast axis collimating lens. The laser resonator may include (a) a dispersive element for receiving and wavelength dispersing an input optical beam to form a multi-wavelength optical beam, and (b) a partially reflective output coupler for (i) transmitting a first portion of the multi-wavelength optical beam as an output optical beam and (ii) reflecting a second portion of the multi-wavelength optical beam back to the dispersive element. The laser resonator may include a fast axis collimator associated with each beam emitter and an optical rotator for causing a beam rotation of approximately 90 °. The dispersive element may comprise, consist essentially of, or consist of a diffraction grating. The laser resonator may include (a) a plurality of first collimators, each of which receives and collimates one or more beams from one of the beam emitters, (b) a plurality of interleavers, each of which receives one or more beams from one of the first collimators, and (c) a second collimator for receiving all of the beams from the plurality of interleavers, collimating the beams, and transmitting the beams to the dispersive element. At least one or even each first collimator may comprise, consist essentially of, or consist of a slow-axis collimating lens. At least one or even each first collimator may comprise, consist essentially of, or consist of a fast axis collimating lens. The laser resonator may comprise a fold mirror disposed optically downstream of the dispersive element and optically upstream of the partially reflective output coupler. The partially reflective output coupler may be the beam output.

The alignment system may include (i) a dispersive element configured to disperse the light beam in the WBC dimension, and (ii) a beam analyzer for receiving the light beam and generating an image of its relative position. The plurality of second optical elements may include, consist essentially of, or consist of the first lens, the second lens, the third lens, and a plurality of third optical elements. The first lens may have an optical power in a non-WBC dimension perpendicular to the WBC dimension. The first lens may be disposed optically downstream of the beam output end and optically upstream of the beam analyzer. The second lens may have an optical power in the WBC dimension. The second lens may focus the dispersed beam on or towards the beam analyzer. The second lens may be disposed optically downstream of the beam output end (e.g., optically downstream of the dispersive element) and optically upstream of the beam analyzer. The third lens may have an optical power of non-WBC dimensions. The third lens may be disposed optically downstream of the beam output end and optically upstream of the beam analyzer. The third optical element may be configured to (i) receive the output light beam, (ii) direct a first portion of the output light beam to the third lens, and (iii) direct a second portion of the output light beam to the first lens.

The second portion of the output beam may not be directed to the third lens. The first lens may be positioned to receive a first portion of the output beam and a second portion of the output beam. The third optical element may be configured to direct the first and second portions of the output beam at different angles to the first lens. The dispersive element may be positioned to receive and disperse a first portion of the output beam, thereby generating a near-field image of the input beam via the beam analyzer. The dispersive element may be positioned to receive and disperse the second portion of the output beam, thereby generating a far field image of the input beam via the beam analyzer. At least one or even each of the third optical elements may comprise, consist essentially of, or consist of a beam splitter and/or a reflector. The dispersive element may comprise, consist essentially of, or consist of a diffraction grating. The alignment system may include a beam rotator disposed optically downstream of the beam output end. The beam rotator may be configured to rotate the output beam by about 90 °. The beam rotator may comprise, consist essentially of, or consist of (i) two confocal cylindrical lenses, (ii) a dove prism, or (iii) two reflectors.

In yet another aspect, embodiments of the invention feature an alignment method for use with a laser resonator that spatially overlaps multiple input beams along a Wavelength Beam Combining (WBC) dimension and outputs a resulting output beam from a beam output end. The laser resonator includes a plurality of optical elements for manipulating an input beam. The method comprises the following steps: (a) generating, with a beam analyzer, at least one of (i) a near-field image of the input beam or (ii) a far-field image of the input beam; (b) adjusting one or more of the optical elements to align one of the input beams when the input beam is misaligned in at least one of the near-field image or the far-field image, consisting essentially of, or consisting of, the input beam.

Embodiments of the invention may include one or more of any of the following various combinations. Both near field images and far field images may be generated. The near field image and the far field image may be generated sequentially or simultaneously. The method may include, prior to generating at least one of the near-field image or the far-field image, (i) wavelength dispersing the output beam to generate a plurality of dispersed beams in the WBC dimension, and (ii) focusing the dispersed beams toward a beam analyzer. The optical element may comprise, consist essentially of, or consist of one or more interlacing mirrors and/or one or more collimating lenses. Adjusting one or more of the optical elements may comprise, consist essentially of, or consist of tilting one or more of the interlacing mirrors and/or translating one or more of the collimating lenses. At least one or even each of the collimating lenses may be a slow axis collimating lens. At least one or even each of the collimating lenses may be a fast axis collimating lens. Generating the far-field image may include, consist essentially of, or consist of positioning the first lens within the path of the output beam. Generating the near field image may comprise, consist essentially of, or consist of removing the first lens from the path of the output beam. Generating the far-field image may include, consist essentially of, or consist of positioning the first lens within the path of the output beam. Generating the near-field image may include, consist essentially of, or consist of replacing the first lens with a second lens having a focal length that is less than the focal length of the first lens. Generating the near-field image may include, consist essentially of, or consist of positioning the first and second lenses within the path of the output beam. Generating the far-field image may include, consist essentially of, or consist of removing the second lens from the path of the output beam. The focal length of the second lens may be less than the focal length of the first lens. Generating the far-field image may include, consist essentially of, or consist of directing a first portion of the output beam to the first lens. Generating the near-field image may comprise, consist essentially of, or consist of directing the second portion of the output beam to a second lens. The method may include rotating the output beam prior to generating at least one of the near field image or the far field image.

The laser resonator may include (a) a dispersive element for receiving and wavelength dispersing an input optical beam to form a multi-wavelength optical beam, and (b) a partially reflective output coupler for (i) transmitting a first portion of the multi-wavelength optical beam as an output optical beam and (ii) reflecting a second portion of the multi-wavelength optical beam back to the dispersive element. The laser resonator may include a plurality of beam emitters configured to emit an input beam. The laser resonator may include a fast axis collimator associated with each beam emitter and an optical rotator for causing a beam rotation of approximately 90 °. The dispersive element may comprise, consist essentially of, or consist of a diffraction grating. The plurality of optical elements may include: (a) a plurality of first collimators, each first collimator receiving and collimating one or more light beams, (b) a plurality of interleavers, each interleaver receiving the one or more input light beams from one of the first collimators, and (c) a second collimator for receiving all input light beams from the plurality of interleavers, collimating the light beams and transmitting the light beams to a dispersive element, consisting essentially of, or consisting of, the above. At least one or even each first collimator may comprise, consist essentially of, or consist of a slow-axis collimating lens. At least one or even each first collimator may comprise, consist essentially of, or consist of a fast axis collimating lens. The laser resonator may comprise a fold mirror disposed optically downstream of the dispersive element and optically upstream of the partially reflective output coupler. The partially reflective output coupler may be the beam output. The beam analyser may be arranged optically downstream of the beam output end.

These and other objects, as well as advantages and features of the present invention disclosed herein, will become more apparent by reference to the following description, drawings and claims. Furthermore, it is to be understood that the features of the various embodiments described herein are not mutually exclusive and can exist in various combinations and permutations. As used herein, the term "substantially" means ± 10%, and in some embodiments, ± 5%. Unless otherwise defined herein, the term "consisting essentially of … …" is meant to exclude other materials that contribute to function. However, these other materials may be present together or individually in trace amounts. Herein, the terms "radiation" and "light" are used interchangeably unless otherwise indicated. As used herein, "downstream" or "optically downstream" is used to indicate the relative position of a second element that a beam of light impinges upon after encountering a first element that is "upstream" or "optically upstream" of the second element. In this context, the "optical distance" between two components is the distance that the light beam actually travels between the two components; the optical distance may be equal to, but not necessarily equal to, the physical distance between the two components due to, for example, reflections from mirrors or other changes in the direction of propagation experienced by light traveling from one component to the other. As used herein, unless otherwise noted, "distance" may be considered "optical distance".

Drawings

In the drawings, like reference numerals generally refer to like parts throughout the different views. Moreover, the drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the invention. In the following description, various embodiments of the present invention are described with reference to the following drawings, in which:

FIG. 1 is a schematic diagram of a Wavelength Beam Combining (WBC) resonator in the WBC dimension, according to an embodiment of the present invention;

fig. 2 is a schematic diagram of a portion of a WBC resonator in the WBC dimension, according to an embodiment of the invention;

fig. 3 is a schematic diagram of portions of a WBC resonator in a non-WBC dimension, in accordance with an embodiment of the present invention;

FIG. 4A is a schematic diagram of an alignment system in the dimension of a WBC, according to an embodiment of the present invention;

FIG. 4B is a schematic diagram of an alignment system in the non-WBC dimension, according to an embodiment of the present invention;

FIGS. 5A and 5B are exemplary far field and near field images, respectively, illustrating a beam misaligned in a non-WBC dimension;

FIGS. 5C and 5D are exemplary far-field and near-field images, respectively, showing light beams aligned in a non-WBC dimension;

FIG. 6A is a schematic diagram of an alignment system in the non-WBC dimension, according to an embodiment of the present invention;

FIG. 6B is a schematic diagram of an alignment system in the non-WBC dimension, in accordance with an embodiment of the present invention;

FIG. 7A is a schematic view of an alignment system according to an embodiment of the present invention;

FIGS. 7B-7D are schematic diagrams of exemplary beam rotators according to embodiments of the present invention; and

FIG. 8 is a schematic diagram of an alignment system according to an embodiment of the present invention.

Detailed Description

Fig. 1 schematically illustrates various components of a WBC resonator 100. in the illustrated embodiment, the WBC resonator 100 combines beams emitted by eleven different diode bars (as used herein, "diode bar" refers to any multi-beam emitter, i.e., an emitter from which multiple beams are emitted from a single package). Embodiments of the present invention may be used with fewer or more than eleven emitters. According to embodiments of the present invention, each emitter may emit a single light beam, or each of the emitters may emit multiple light beams. The view of fig. 1 is along the WBC dimension, i.e., the beams from the bars are combined in this dimension. The resonator 100 has eleven diode bars 110 (110-1-110-11), and each diode bar 110 includes, consists essentially of, or consists of an array of emitters along the WBC dimension (e.g., a one-dimensional array). Each emitter of diode bar 110 emits an asymmetric beam having a large divergence in one direction (referred to as the "fast axis", here oriented vertically with respect to the WBC dimension) and a small divergence in the vertical direction (referred to as the "slow axis", here along the WBC dimension).

In various embodiments, each of the diode bars 110 is associated with (e.g., attached to or otherwise optically coupled with) a Fast Axis Collimator (FAC)/optically twisted micro-lens assembly that collimates the fast axis of the emitted light beams when the fast and slow axes of the light beams are rotated 90 ° such that the slow axis of each emitted light beam is perpendicular to the WBC dimension downstream of the micro-lens assembly. The micro-lens assembly also converges the chief rays from the emitters of each diode bar 110 towards the dispersive element 120. Suitable microlens assemblies are described in U.S. patent No.8,553,327, filed 3/7/2011 and U.S. patent No.9,746,679, filed 6/8/2015, the entire disclosures of each of which are incorporated herein by reference.

Embodiments of the invention presented herein associate a FAC lens and an optical twister (e.g., as a micro-lens assembly) with each emitted beam, and thus a SAC lens (as described in detail below) affects beams in non-WBC dimensions. In other embodiments, the emitted light beam does not rotate, and a FAC lens may be used to change the pointing angle of the non-WBC dimensions. Accordingly, it should be understood that references to SAC lenses in this application generally refer to lenses having power in the non-WBC dimension (power), and that in various embodiments, such lenses may be or include FAC lenses.

As shown in fig. 1, the resonator 100 also has a set of SAC lenses 130, one SAC lens 130 associated with and receiving a light beam from one of the diode bars 110. Each SAC lens 130 collimates the slow axis (i.e., in the non-WBC dimension) of the beam emitted from a single diode bar 110. After being collimated in the slow axis by SAC lens 130, the beam propagates to a set of interleaving mirrors 140, redirecting beam 150 towards dispersive element 120. (in fig. 1, beam 150 is the central chief ray representing eleven combined beams from eleven diode bars 110.) in various embodiments, the arrangement of the staggered mirrors 140 enables the free space between diode bars 110 to be minimized. The dispersion element 120 multiplexes the spatially separated individual light beams into a single light beam having a plurality of wavelengths (i.e., the wavelengths of the individual light beams). Upstream of the dispersive element 120 (which may comprise, consist essentially of, or consist of, for example, a diffraction grating, such as the transmission diffraction grating shown in fig. 1, or a reflection diffraction grating), a lens 160 collimates the individual beams (e.g., sub-beams, rather than primary rays) from the diode bars 110. In various embodiments, the lens 160 is disposed an optical distance from the diode bar 110 that is substantially equal to the focal length of the lens 160. Note that the overlap of the chief rays at the dispersive element 120 is primarily due to the redirection of the interleaving mirror 140, and not due to the focusing power of the lens 160.

Also shown in fig. 1 are lenses 170, 175, which form an optical telescope for mitigating optical crosstalk, as disclosed in U.S. patent No.9,256,073 filed 3, 15, 2013 and U.S. patent No.9,268,142 filed 6, 23, 2015, the entire disclosure of each of which is incorporated herein by reference. The resonator 100 may also include one or more optional fold mirrors 180 for redirection of the optical beam so that the resonator 100 may fit within a smaller physical footprint. The dispersive element 120 combines the beams from the diode bars 110 into a single multi-wavelength beam that propagates to the partially reflective output coupler 190. Coupler 190 transmits a portion of the beam as the output beam of resonator 100 while reflecting another portion of the beam back to dispersive element 120 and thus to diode bar 110 as feedback to stabilize the emitted wavelength of each beam (which is typically different from one another).

As shown in fig. 1, each diode bar 110 has a respective SAC 130 and a respective interleaving mirror 140, and all optics optically downstream of the interleaving mirror 140 are shared by all diode bars 110.

In general, WBC resonators are ideally aligned in the WBC and non-WBC dimensions. That is, the beams from the different diodes (i.e., the individual emitters in the diode bar) are ideally tailored to overlap in the WBC and non-WBC dimensions at the dispersive element 120 (e.g., approximately at its center) and generally perpendicular to the output coupler 190 for stable lasing.

If the resonators are misaligned, especially if misaligned in the non-WBC dimension or severely misaligned in the WBC dimension, the individual emitters may emit at a free-running (i.e., unlocked) wavelength. For example, if misalignment of the transmitter shifts the emission to a non-lasing region (i.e., beyond the transmitter effective gain bandwidth), or if the transmitter output is heavily clipped, e.g., 20% power and/or beam size reduction, e.g., due to decentration at one or more optics, at the optics. For example, assuming that the resonator dispersive elements are aligned at littrow angle (i.e., diffraction angle equal to incident angle), the linear density is 1.6/μm for an emitter wavelength of 975nm, and regardless of power clipping, a misalignment of 20mrad with respect to the direction of the dispersive element in the WBC dimension will result in a wavelength shift of about 8nm, which may be large enough to shift the "lasing wavelength" out of the diode emitter bandwidth (typically ranging from 14nm to 20nm), especially considering that the gain curve of a diode emitter is associated with variations in emitter temperature from room temperature (or coolant temperature) to typical operating temperatures (e.g., ranging from about 60 ℃ to about 70 ℃ or even higher), typically with an inherent shift of over 10 nanometers.

Typically, once aligned in the non-WBC dimension, the emitter will be locked at a resonator wavelength that satisfies the grating diffraction equation (i.e., sin (Ai)) + sin (B) ═ p λ i, where Ai is the angle of incidence on the dispersive element 120 of the ith emitter, λ i is the lasing wavelength of the ith emitter, and B and p are the diffraction angle and grating line density, respectively.

Since the emitters are typically locked at wavelengths having diffraction angles perpendicular to the output coupler 190 in the WBC dimension, any alignment variation in the WBC dimension will result in a wavelength shift, but will typically not cause other serious problems such as significant power drop, as long as the shifted wavelength remains within the operating band of the individual emitters. (for example, diode emitters emitting at the 975nm region typically have a gain bandwidth ranging from 14nm to 20nm (full width at 90%). if temperature variations are not accounted for, the operating band of the emitter is equal to its gain bandwidth.

Fig. 2 shows the result of the WBC resonators 200 being misaligned in the WBC dimension. For illustrative purposes and clarity, the resonator 200 is shown with only a single diode bar 110, but it is understood that the principles shown can be applied to resonators with multiple diode bars 110. Furthermore, for clarity, only the light beam from a single emitter (the ith emitter) is shown. In the aligned state, the emitter is locked at wavelength λ i, and its chief ray 210 propagates along direction 210u, through the center of each optical element and perpendicular to coupler 190 in both the WBC and non-WBC directions.

In an exemplary embodiment, the misalignment in the WBC dimension is caused by small angular variations (e.g., rotations) of the interleaver 140 corresponding to the emitter, which causes the emitter chief ray 210 to propagate in direction 210 v. This direction 210v is offset from the original direction 210u by an angle a in the WBC dimension. Further, a change in the angle of incidence on the dispersive element 120 from Ai to the approximate angle (Ai + α) results in a wavelength shift from λ i to (λ i + Δ λ), as determined by the grating equation: sin (Ai + α) + sin (b) ≈ p × (λ i + Δ λ).

As shown in the enlarged portion of fig. 2, misalignment in the WBC dimension will also result in an eccentricity distance δ at the output coupler 190, which may degrade the beam quality in the WBC dimension by a factor of 1+ δ/S, where S is the beam size in the WBC dimension at the output coupler 190. Since the lenses 170 and 175 are typically in a confocal arrangement (i.e., forming an optical telescope), the decentration distance δ can be estimated by δ ≈ α × D/R × cos (b)/cos (ai), where D is the distance from the interleaver 140 to the dispersive element 120 and R is the focal length ratio of the lenses 170, 175, which in various embodiments is in the range of about 3 to about 20. If the dispersive element 120 is configured at littrow angle, i.e., cos (B)/cos (ai) ≈ 1, δ ≈ α × D/R.

In an exemplary embodiment, it may be assumed that D is 1000mm, R is 10, λ i is 0.975 μm, and the dispersive element 120 is oriented at littrow angle, and the linear density p is 1.6/μm. The wavelength shift and the eccentricity distance due to the misalignment of the angle α can be estimated by Δ λ (μm) ≈ 0.4 × α and δ (mm) ≈ 100 × α. If α ≈ 1mrad, Δ λ ≈ 0.4nm, δ ≈ 100 μm. In such an example, misalignment in the WBC dimension may not significantly affect emitter lasing and may not cause stability issues for the WBC resonator. The wavelength shift of about 0.4nm is small compared to the gain width of a diode laser exceeding 15nm in the 1 μm emission range. Furthermore, an off-center distance of 100 μm may correspond to about 5-10% of the beam size in the WBC dimension, which corresponds to a 5-10% degradation of the beam quality in the WBC dimension. The severity of this degradation may depend on the particular resonator and the application in which it is deployed.

Fig. 3 shows portions of a resonator 300 similar to the resonator 200 of fig. 2, but in a non-WBC dimension, to illustrate an exemplary misalignment in the non-WBC dimension. For simplicity, only interleaver 140, dispersive element 120, and output coupler 190 are shown. It is assumed that lenses 150, 170, and 175 shown in fig. 2 lack optical power in the non-WBC dimension, although this need not be the case in other embodiments of the invention. The chief ray 310 of the ith transmitter (not shown) is perfectly aligned in direction 310u, perpendicular to coupler 190 and passing through the center of coupler 190. The coupler is a partial reflector that splits the resonator beam into an output beam 320 and a feedback beam 330. The feedback beam 330 is perpendicular to the coupler 190 and will therefore propagate back to the dispersive element 120 and thus to the respective emitter, thereby forming a stable resonator between the emitter and the coupler 190.

In an exemplary embodiment, the misalignment in the non-WBC dimension is caused by a slight tilt of the interleaving mirror 140 in the non-WBC dimension, which causes the chief ray 310 to propagate along the misalignment direction 310v, offset from the direction 310u by an angle β. In contrast to the case of the WBC dimension shown in fig. 2, in the non-WBC dimension, the laser beam 310 (wavelength locked or free running) from the example i-th emitter will propagate all the way to the coupler 190 in the misalignment direction 310v, as shown in fig. 3. As shown, exemplary misalignment results in misaligned output beam 340 having a relatively large eccentricity distance (Δ) and a non-zero pointing error (β), resulting in less efficient resonator feedback because feedback beam 350 differs by 2 β from the ideal perpendicular direction along which feedback beam 330 propagates.

For purposes of illustration, it may be assumed that the emitter slow axis is in the non-WBC dimension and is collimated by a SAC lens (e.g., SAC lens 130 in FIGS. 1 and 2) having a focal length of 50mm, such that the slow axis beam size at coupler 190 is about 6 mm. Further assuming a maximum acceptable slow axis decentration distance of 0.6mm (corresponding to a 10% beam quality degradation) and an optical distance of 1.5m from the interleaver 140 to the coupler 190, the maximum acceptable misalignment angle β is calculated to be 0.4mrad from a beam decentration perspective. However, a misalignment of 0.4mrad from the resonator feedback point of view will result in a displacement of the feedback beam of the emitting surface by 40 μm on the slow axis; thus, the efficiency of the feedback will be reduced by 40% (e.g., emitter size 100 μm). The displacement of the feedback beam relative to the corresponding transmitter beam not only results in a power reduction, but may also result in unstable wavelength locking (i.e., unstable resonator power) and beam shape distortion at the output. Thus, in general, WBC resonators are much more sensitive to misalignment of the non-WBC dimensions than the WBC dimensions. In various embodiments, for a WBC resonator similar to fig. 1, the misalignment of the slow axis (i.e., the non-WBC dimension) is desirably controlled to be less than or equal to about 0.1 mrad.

Fig. 4A and 4B illustrate portions of an alignment system 400 according to various embodiments of the invention. As shown, alignment system 400 includes a first cylindrical lens 410, a dispersive element 420, a second cylindrical lens 430, and a beam analyzer 440. Fig. 4A and 4B illustrate an alignment system 400 in the WBC dimension and the non-WBC dimension, respectively. Lens 410 has optical power and focal length f1 in the non-WBC dimension, and lens 430 has optical power and focal length f2 in the WBC dimension. The dispersive element 420 may comprise, consist essentially of, or consist of, for example, a diffraction grating, such as a transmissive diffraction grating or a reflective diffraction grating.

The beam analyzer 440 may comprise, consist essentially of, or consist of, for example, a camera or other image sensor (e.g., a CCD sensor, CMOS sensor, or other light responsive sensor), and may include or be operatively connected to a display. For example, the beam incident of the beam analyzer 440 may be displayed on a display to determine their alignment with each other. The beam analyzer 440 is commercially available and can be provided and used without undue experimentation. For example, the beam analyzer 440 may comprise, consist essentially of, or consist of one of the WinCamD family of beam analyzers available, for example, from DataRay corporation of Redin, Calif. In various embodiments, beam analyzer 440 may be or include a physical screen (e.g., a near-infrared sensor board for emitters emitting in the near-infrared region, a white or other board for emitters emitting in the visible region, or a UV-sensitive board for emitters emitting in the UV range), or a collection of conventional cameras or other image sensors (e.g., two-dimensional sensors).

Alignment system 400 accepts WBC resonator beam 450, which includes, consists essentially of, or consists of n wavelength subbands (Δ λ i, i ═ 1: n). The beam 450 is dispersed in the WBC dimension by the dispersive element 420 and the chief ray of the dispersed beam is collimated by the lens 430. In general, collimation of the chief rays of the divergent beams produces a well-defined overall image size and beam separation at the beam analyzer 440. In various embodiments, lens 430 is located one focal length downstream of dispersive element 420 (i.e., the focal length of lens 430). Lens 430 also focuses the individual beams on beam analyzer 440, and in various embodiments, beam analyzer 440 is located one focal length downstream of lens 430 (i.e., the focal length of lens 430). In various embodiments, the resonator beam 450 is an output beam produced by the WBC resonator 100 or similar resonators.

Although in the embodiment of the alignment system 400 shown in fig. 4A and 4B, the lens 430 is located optically downstream of the dispersive element 420, in other embodiments, the lens 430 may be located optically upstream of the dispersive element 420. In such an embodiment, lens 430 would still focus the individual beams on beam analyzer 440, but would typically not collimate the chief rays of the beams. Furthermore, such an embodiment may not be preferred from a distortion point of view, as the dispersive element 420 may cause more distortion to a highly focused or divergent beam.

In the non-WBC dimension, as shown in fig. 4B, the lens 410 may be located at one focal length upstream of the beam analyzer 440 (i.e., the focal length of the lens 410). In various embodiments, focal length f1 of lens 410 is longer than focal length f2 of lens 430, and lens 410 is disposed at a position upstream of dispersive element 420.

As shown in fig. 4B, lens 410 may be disposed at a location 460 in the path of resonator beam 450 (e.g., such that the beam is approximately centered on lens 410) or at a location 465 outside the beam path. This produces a far field image 470 or a near field image 475, respectively, on the beam analyzer 440. Assuming that the centerline of the beam analyzer 440 in the WBC dimension corresponds to zero offset distance and zero pointing error at the output coupler (e.g., coupler 190 in fig. 1) in the non-WBC dimension for all of the sub-beams in the output beam 450, the amount of off-center distance of the sub-beams in the far field 470 or near field 475 may be scaled to represent the amount of pointing error or off-center distance of the respective sub-beam at the resonator output in the non-WBC dimension. In this manner, the alignment system 400 shown in fig. 4A and 4B may be an effective tool for optimizing the alignment of multi-wavelength resonators (e.g., WBC resonators).

Fig. 5A and 5B show example far and near field images in which some of the sub-beams (beams #3, #7, and #10 from the left side of the image) are misaligned in the non-WBC dimension in a WBC resonator similar to the resonator 100 shown in fig. 1. Each image includes 11 sub-beam images corresponding to 11 diode bars (e.g., diode bar 110 in fig. 1) or 11 wavelength sub-bands (Δ λ i, i ═ 1:11) as shown in fig. 4A and 4B. Each sub-band may comprise, consist essentially of, or consist of a plurality of different wavelengths, as each diode bar may comprise, consist essentially of, or consist of an array of emitters. The spectral gaps (or "dead zones") between adjacent diode bars allow the sub-beam images to be separated without overlapping on the beam analyzer 440. In various embodiments, the sub-beam images are easily recognizable even when partially overlapped on the beam analyzer 440. Thus, even if full sub-image separation on the beam analyzer 440 requires, for example, a spectral gap of at least 20%, embodiments of the present invention may facilitate identification and mitigation of misalignment, even for spectral gaps between at least 10% of the emitters, or even at least 5%.

The resulting image from the beam analyzer 440 effectively indicates whether and which individual beam emitters (e.g., diode bars) are misaligned. In various embodiments, misalignment (e.g., decentration) in the far field image may be adjusted or mitigated by tilt adjustment of the corresponding mirror of the emitter (e.g., interleaver 140 in fig. 1) in the non-WBC dimension, as described in the' 001 application. In various embodiments, the tilt adjustment of the interlacing mirrors may also reduce or minimize misalignment (e.g., decentration) in the near-field image. In other embodiments, for example, the optical beam in the far field but not in the near field may be aligned by iteratively translating the position of the respective SAC lens (e.g., in the slow axis, the non-WBC dimension) and adjusting the tilt of the interleaved reflector 130 in the non-WBC dimension, as described in the' 001 application.

As described above, misalignment in the non-WBC dimension may significantly reduce the resonator power, even causing the corresponding emitter to emit at an unlocked wavelength. However, unlike conventional lasers (e.g., solid-state lasers and gas lasers), using output power as an indicator of the alignment of the WBC resonator may be largely ineffective because the diodes or emitters in a typical WBC resonator operate independently and may each contribute only a small fraction of the power to the total output of the resonator. Thus, misalignment of the individual diodes may be difficult to detect based on the total output power. In contrast, optical techniques according to embodiments of the present invention effectively reveal misalignment of the individual emitters. Fig. 5C and 5D show example far-field and near-field images, respectively, with all sub-beams well aligned in the non-WBC dimension.

Various embodiments of the present invention may automatically align the emitter in the non-WBC dimension in response to the image acquired by the beam analyzer 440. For example, a system according to an embodiment of the invention may include a controller 195 (see fig. 1) that adjusts the tilt of the interleaving mirror 140 and/or the position (i.e., translation) of the SAC lens 130 in at least the non-WBC dimension to reduce or substantially eliminate the misalignment shown in the image acquired by the beam analyzer 440. According to various embodiments, the controller 195 may utilize conventional image processing software or algorithms to measure the alignment or misalignment of the emitters shown in the near and far field images produced by the beam analyzer 440 and to adjust (e.g., via computer control of a tip/tilt stage, stepper motor, etc.) the tilt of the interlacing mirror 140 and/or the position (i.e., translation) of the SAC lens 130 to mitigate the misalignment, as described above.

The controller 195 may be provided as software, hardware, or some combination thereof. For example, the system may be implemented on one or more conventional server-level computers, such as a PC with a CPU board containing one or more processors, such as Pentium or Sayan series processors manufactured by Intel corporation of Santa Clara, Calif., 680x0 and POWER PC series processors manufactured by Motorola, Inc. of Sharey, Illinois, and/or ATHLON series processors manufactured by Advanced Micro Devices, Inc. of Santa Clavia, Calif. The processor may also include a main memory unit for storing programs and/or data related to the methods described herein. The memory may include Random Access Memory (RAM), Read Only Memory (ROM), and/or FLASH memory, residing on commonly available hardware, such as one or more Application Specific Integrated Circuits (ASICs), Field Programmable Gate Arrays (FPGAs), Electrically Erasable Programmable Read Only Memory (EEPROM), Programmable Read Only Memory (PROM), Programmable Logic Device (PLD), or read only memory device (ROM). In some embodiments, the program may be provided using external RAM and/or ROM (such as optical disks, magnetic disks, and other common storage devices). For embodiments in which functionality is provided as one or more software programs, the programs may be written in any of a number of high-level languages, such as PYTHON, FORTRAN, PASCAL, JAVA, C + +, C #, BASIC, various scripting languages, and/or HTML. Additionally, the software may be implemented in assembly language directed to a microprocessor residing on the target computer; for example, if the software is configured to run on an IBM PC or PC clone, it may be implemented in Intel 80x86 assembly language. The software may be embodied on an article of manufacture including, but not limited to, a floppy disk, a flash disk, a hard disk, an optical disk, magnetic tape, a PROM, an EPROM, an EEPROM, a field programmable gate array or a CD-ROM.

In various embodiments, the near-field image 475 produced by the beam analyzer 440 in fig. 4B is an orthographic projection of the beam 450. Thus, the de-center distance of the sub-beam image on the near-field image (e.g., as shown in fig. 5B) may not directly reflect the actual de-center distance of the corresponding sub-beam on the output coupler of the WBC resonator. This may be addressed by an alignment system 600 according to various embodiments of the present invention as shown in fig. 6A and 6B. In fig. 6A, a near-field image 610 is obtained by replacing the first lens 410 with a third lens 620 having a focal length f3 shorter than f1, satisfying the lens imaging equation 1/S1+ 1/S2-1/f 3, where S1 and S2 are the distances from the lens 620 to the coupler 190 and to the beam analyzer 440, respectively. Since S2 is f1, S1 is f1 × f3/(f1-f 3).

In a similar embodiment shown in fig. 6B, the near-field image 630 is obtained by adding a third lens 640 having a focal length f3, where S1 ═ f 3. In various embodiments, as shown in fig. 6B, third lens 640 is disposed optically downstream of the beam output end (e.g., coupler 190) and optically upstream of lens 410. In either of the alignment systems 600 shown in fig. 6A and 6B, a far-field image can be obtained by merely placing the first lens (or lens group) 410 in place and holding S2 ═ f 1. Since the near field image 610 or 630 is an image of the beam 450 at the coupler 190, the off-center distance of the sub-beam image on the near field image will directly and proportionally reflect the off-center distance of those sub-beams at the coupler 190.

Fig. 7A shows an alignment system 700 according to various embodiments of the invention that is similar to alignment system 600 of fig. 6B, but with the addition of a beam rotator 710 disposed optically downstream of output coupler 190. In various embodiments, beam rotator 710 rotates output beam 450 by approximately 90 °, and thus alignment system 700 will now show sub-beam misalignment and pointing errors in the WBC direction. In various embodiments, beam rotator 710 can move in and out of the path of beam 450, thereby enabling selective detection (and resulting mitigation) of misalignment along a non-WBC dimension or a WBC dimension.

An exemplary beam rotator 710 according to an embodiment of the present invention is shown in fig. 7B-7D. For example, fig. 7B shows beam rotator 710 as a pair of confocal cylindrical lenses oriented at 45 ° with respect to the vertical and horizontal dimensions of the beam. Fig. 7C shows beam rotator 710 as a dove prism (dove prism) oriented at 45 ° with respect to the vertical and horizontal dimensions of the beam. Fig. 7D shows beam rotator 710 as a pair of mirrors, where a first mirror reflects the beam 90 ° in a first plane and a second mirror reflects the beam 90 ° in a second plane orthogonal to the first plane.

FIG. 8 illustrates an alignment system 800 according to an embodiment of the present invention. In various embodiments, the alignment system 800 obtains the far field image 810 and the near field image 820 simultaneously without physical movement of lenses or other optical elements. In the illustrated example alignment system 800, the light beam 450 is received at a beam splitter 830, where it is split such that a portion of the light beam propagates through both lenses 640, 410, while another portion of the light beam propagates only through the lens 410 (after being redirected around the lens 640). Both beam portions then propagate to the beam analyzer 440 to display the near field and far field images. As shown in the exemplary embodiment of fig. 8, a portion of the beam is redirected around lens 640 by reflectors (e.g., mirrors) 840, 850, and then the beam portion is redirected to beam splitter 860, where the primary beam path is rejoined. Although fig. 8 shows two reflectors 840, 850 for redirecting beam portions around the lens 640, various embodiments may use only one reflector or more than two reflectors to redirect beam portions.

As shown in fig. 8, the angle of one or more of the beam splitters and/or reflectors may be adjusted so that the near field and far field images do not overlap each other. In this manner, near and far field images of the beam 450 may be monitored simultaneously while reducing or substantially eliminating misalignment of the transmitter.

The terms and expressions which have been employed herein are used as terms of description and not of limitation, and there is no intention, in the use of such terms and expressions, of excluding any equivalents of the features shown and described or portions thereof, but it is recognized that various modifications are possible within the scope of the invention claimed.

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