Generation of high-power, high brightness optical beams by optical cutting and beam-shaping of diode lasers

• US 6,778,732 B1
• Filed: 06/07/2002
• Issued: 08/17/2004
• Est. Priority Date: 06/07/2002
• Status: Expired due to Fees

• Current Assignee: Boston Laser, Inc.
• Original Assignee: Boston Laser, Inc.
• Inventors: Fermann, Martin E.
• Primary Examiner(s): Lee, John D.
• Assistant Examiner(s): WONG, TINA MEI SENG
• Application Number:
  US10/163,999
• Time in Patent Office: 802 Days
• Field of Search: 385/31, 385/33, 359/642-830
• US Class Current: 385/31
• CPC Class Codes: G02B 19/0014 at least one surface having optical power
• CPC Class Codes: G02B 19/0028 refractive and reflective surfaces, e.g. non-imaging catadioptric systems
• CPC Class Codes: G02B 19/0057 in the form of a laser diode array, e.g. laser diode bar semiconductor laser arrays with beam combining arrangement H01S5/4012
• CPC Class Codes: G02B 27/09 Beam shaping, e.g. changing the cross-sectional area, not otherwise provided for adapting the beam shape of a laser diode G02B19/0052; adapting the beam shape of an LED G02B19/0061; coupling into light guides using intermediate optical elements G02B6/4204; beam shaping specially adapted for lasers H01S3/005
• CPC Class Codes: G02B 27/0961 Lens arrays lens arrays per se G02B3/0006
• CPC Class Codes: G02B 6/4206 Optical features G02B6/4207, G02B6/421 take precedence
• CPC Class Codes: H01S 3/005 Optical devices external to the laser cavity, specially adapted for lasers, e.g. for homogenisation of the beam or for manipulating laser pulses, e.g. pulse shaping shaping laser beam for working metal or other materials B23K26/06; optical elements, systems or apparatus in general G02B
• CPC Class Codes: H01S 5/005 Optical components external to the laser cavity, specially adapted therefor, e.g. for homogenisation or merging of the beams or for manipulating laser pulses, e.g. pulse shaping H01S5/026, H01S5/18388 take precedence
• CPC Class Codes: H01S 5/0071 for beam steering, e.g. using a mirror outside the cavity to change the beam direction

Abstract

An optical beam-shaping element is used to produce a high brightness laser beam from a diode bar or a single emitter diode, allowing for efficient coupling of the beam into an optical fiber. An embodiment of the beam-shaping element allows the construction of a quasi-monolithic beam shaper incorporating both fast axis collimation as well as beam rotation. Additional slow axis collimation of the individual emitting elements of the diode bar is also possible in one quasi-monolithic design. The beam rotation element may comprise an array of beam-inverting planar grin lenses aligned with their axes of equal refractive index at an angle of ±45° with respect to the slow axes of the emitters. Alternative embodiments comprise beam rotation elements based on Fresnel lens arrays or aspheric cylindrical lens arrays. The beam-shaping element can be used in conjunction with stacks of diode bars, where optical cutting of the diode bar beams in a parallelepiped coated with multiple reflective stripes can be further implemented to symmetrize the resulting optical beam. Alternatively optical beams of ultra-high power can be generated by combining multiple fiber coupled diode bars in a fiber bundle incorporating rectangular fiber cores, metallization and a heat sink.

Claims

1. An optical system, comprising:

a diode laser having an active area substantially elongated along and parallel to a slow axis of said diode laser, said active area configured to emit an optical beam;

a fast axis collimation lens configured to collimate a fast axis of said optical beam; and

an optical beam inverting array comprising a planar grin lens array and including a plurality of individual array elements aligned such that said optical beam is cut into more than two individual beam sections, said optical beam inverting array configured such that said beam sections propagate through said individual array elements, each of said individual array elements imaging said individual optical beam sections with a magnification M of substantially M=−

1,

wherein planes of equal refractive index in said planar grin lens array are aligned at an angle of substantially ±

45°

with respect to a plane defined by a propagation direction of said optical beam and said slow axis of the diode laser.

2. The planar grin lens array according to claim 1, wherein a pitch of said planar grin lens array is equal to approximately 0.5.

9. The optical system according to claim 1, further comprising a coupling element configured to couple said optical beam of the diode laser beam into an optical fiber.

10. The optical system according to claim 9, wherein said coupling element comprises optical elements selected from the group consisting of cylindrical, spherical and aspherical optical elements.

11. The optical system according to claims 9, wherein a core of said optical fiber is shaped substantially in the form of a rectangle.

12. The optical system according to claim 1, comprising:

a plurality of said laser diode each emitting a respective optical beam, said laser diodes arranged in a two-dimensional array;

a plurality of said fast axis collimation lens and a corresponding plurality of said beam inverting array comprising individual array elements aligned such that said optical beams are cut into individual beam sections; and

said individual array elements arranged to propagate said beam sections, each of said individual array elements imaging said individual optical beam sections with a magnification M of substantially M=−

1.

13. The optical system according to claim 12, further comprising coupling elements for coupling the plurality of diode laser beams into an optical fiber.

14. The optical system according to claim 13, further comprising a plurality of said optical fibers each associated with a respective one of said coupling element for receiving a respective one of said diode laser beams.

15. The optical system according to claim 14 wherein each of said plurality of optical fibers is formed to have a cross-section substantially in the form of a rectangle.

16. The optical system according to claim 1, comprising a plurality of subsystems of said diode laser, fast axis collimation lens, an optical beam inverting array, said diode lasers coupled into a plurality of optical fibers, said optical fibers aligned to form at least one optical fiber bundle so as to provide at least one beam of ultra-high optical power.

3. An optical system comprising:

a diode laser having an active area substantially elongated along and parallel to a slow axis of said diode laser, said active area configured to emit an optical beam;

a fast axis collimation lens configured to collimate a fast axis of said optical beam; and

an optical beam inverting array comprising two sets of cylidrical Fresnel lens arrays with their optical axes oriented at an angle of substantially ±

45°

with respect to said slow axis of said diode laser, said optical beam inverting array including a plurality of individual array elements aligned such that said optical beam is cut into more than two individual beam sections, said optical beam inverting array configured such that said beam sections propagate through said individual array elements, each of said individual array elements imaging said individual optical beam sections with a magnification M of substantially M=−

1.

4. The optical system according to claim 3, wherein said Fresnel lens arrays are separated by approximately twice their focal lengths.

21. The optical system according to claim 3, further comprising a coupling element configured to couple said optical beam of the diode laser beam into an optical fiber.

22. The optical system according to claim 21, wherein said coupling element comprises optical elements selected from the group consisting of cylindrical, spherical and aspherical optical elements.

23. The optical system according to claims 21, wherein a core of said optical fiber is shaped substantially in the form of a rectangle.

24. The optical system according to claim 3, comprising:

a plurality of said laser diode each emitting a respective optical beam, said laser diodes arranged in a two-dimensional array;

a plurality of said fast axis collimation lens and a corresponding plurality of said beam inverting array comprising individual array elements aligned such that said optical beams are cut into individual beam sections; and

said individual array elements arranged to propagate said beam sections, each of said individual array elements imaging said individual optical beam sections with a magnification M of substantially M=−

1.

25. The optical system according to claim 24, further comprising coupling elements for coupling the plurality of diode laser beams into an optical fiber.

26. The optical system according to claim 25, further comprising a plurality of said optical fibers each associated with a respective one of said coupling element for receiving a respective one of said diode laser beams.

27. The optical system according to claim 26 wherein each of said plurality of optical fibers is formed to have a cross-section substantially in the form of a rectangle.

28. The optical system according to claim 3, comprising a plurality of subsystems of said diode laser, fast axis collimation lens, an optical beam inverting array, said diode lasers coupled into a plurality of optical fibers, said optical fibers aligned to form at least one optical fiber bundle so as to provide at least one beam of ultra-high optical power.

5. An optical system comprising:

a diode laser having an active area substantially elongated along and parallel to a slow axis of said diode laser, said active area configured to emit an optical beam;

a fast axis collimation lens configured to collimate a fast axis of said optical beam; and

an optical beam inverting array comprising two sets of aspheric cylindrical lens arrays with their optical axes oriented at an angle of substantially ±

45°

with respect to said slow axis of said diode laser, said optical beam inverting array including a plurality of individual array elements aligned such that said optical beam is cut into more than two individual beam sections, said otical beam inverting array configured such that said beam sections propagate through said individual array elements, each of said individual array elements imaging said individual optical beam sections with a magnification M of substantially M=−

1.

6. The optical system according to claim 5, wherein said aspheric cylindrical lens arrays are separated by twice their focal lengths.

29. The optical system according to claim 5, further comprising a coupling element configured to couple said optical beam of the diode laser beam into an optical fiber.

30. The optical system according to claim 29, wherein said coupling element comprises optical elements selected from the group consisting of cylindrical, spherical and aspherical optical elements.

31. The optical system according to claims 29, wherein a core of said optical fiber is shaped substantially in the form of a rectangle.

32. The optical system according to claim 5, comprising:

a plurality of said laser diode each emitting a respective optical beam, said laser diodes arranged in a two-dimensional array;

a plurality of said fast axis collimation lens and a corresponding plurality of said beam inverting array comprising individual array elements aligned such that said optical beams are cut into individual beam sections; and

said individual array elements arranged to propagate said beam sections, each of said individual array elements imaging said individual optical beam sections with a magnification M of substantially M=−

1.

33. The optical system according to claim 32, further comprising coupling elements for coupling the plurality of diode laser beams into an optical fiber.

34. The optical system according to claim 33, further comprising a plurality of said optical fibers each associated with a respective one of said coupling element for receiving a respective one of said diode laser beams.

35. The optical system according to claim 34 wherein each of said plurality of optical fibers is formed to have a cross-section substantially in the form of a rectangle.

36. The optical system according to claim 5, comprising a plurality of subsystems of said diode laser, fast axis collimation lens, an optical beam inverting array, said diode lasers coupled into a plurality of optical fibers, said optical fibers aligned to form at least one optical fiber bundle so as to provide at least one beam of ultra-high optical power.

7. An optical system comprising:

a diode laser having an active area substantially elongated along and parallel to a slow axis of said diode laser, said active area configured to emit an optical beam;

a fast axis collimation lens configured to collimate a fast axis of said optical beam; and

an optical beam inverting array comprising two sets of toroidal aspheric cylindrical lens arrays with their optical axes oriented at an angle of substantially ±

45°

with respect to said slow axis of said diode laser, at least one of said toroidal aspheric cylindrical lens array with non-zero curvatures along two orthogonal axes, said optical beam inverting array including a plurality of individual array elements aligned such that said optical beam is cut into more than two individual beam sections, said optical beam inverting array configured such that said beam sections propagate through said individual array elements, each of said individual array elements imaging said individual optical beam sections with a magnification M of substantially M=−

1.

8. The optical system according to claim 7, wherein said toroidal aspheric cylindrical lens arrays are separated by approximately twice the focal length of a surface thereof having a largest curvature.

37. The optical system according to claim 7, further comprising a coupling element configured to couple said optical beam of the diode laser beam into an optical fiber.

38. The optical system according to claim 37, wherein said coupling element comprises optical elements selected from the group consisting of cylindrical, spherical and aspherical optical elements.

39. The optical system according to claims 37, wherein a core of said optical fiber is shaped substantially in the form of a rectangle.

40. The optical system according to claim 7, comprising:

a plurality of said laser diode each emitting a respective optical beam, said laser diodes arranged in a two-dimensional array;

a plurality of said fast axis collimation lens and a corresponding plurality of said beam inverting array comprising individual array elements aligned such that said optical beams are cut into individual beam sections; and

said individual array elements arranged to propagate said beam sections, each of said individual array elements imaging said individual optical beam sections with a magnification M of substantially M=−

1.

41. The optical system according to claim 40, further comprising coupling elements for coupling the plurality of diode laser beams into an optical fiber.

42. The optical system according to claim 41, further comprising a plurality of said optical fibers each associated with a respective one of said coupling element for receiving a respective one of said diode laser beams.

43. The optical system according to claim 41 wherein each of said plurality of optical fibers is formed to have a cross-section substantially in the form of a rectangle.

44. The optical system according to claim 7, comprising a plurality of subsystems of said diode laser, fast axis collimation lens, an optical beam inverting array, said diode lasers coupled into a plurality of optical fibers, said optical fibers aligned to form at least one optical fiber bundle so as to provide at least one beam of ultra-high optical power.

17. An optical system, comprising:

a diode laser, including an array of active areas substantially elongated along and parallel to slow axes of said active areas, said active areas further arranged to be separated by substantially equal distances along an axis orthogonal to said slow axes, said array of active areas emitting a plurality of optical beams;

an array of fast axis collimation lenses for fast axis collimation of said plurality of optical beams; and

a monolithic optical element arranged such that said optical beams are cut into at least two individual beam sections, each of said beam sections propagating through said monolithic optical element, thereby defining an input optical beam and an output optical beam,

said monolithic optical element characterized in that the Lagrange invariant of the output beam is reduced by substantially a factor of two along a first axis and increased by less than a factor of two along a second axis orthogonal to said first axis.

18. An optical system according to claim 17, where said monolithic optical element is characterized in that the Lagrange invariant of the output beam is reduced by substantially a factor of 1/x along said first axis and increased by less than a factor of x along said second axis.

19. An optical system according to claim 17, comprising a plurality of said monolithic optical elements arranged such that said optical beams pass through the optical elements successively characterized in that the Lagrange invariant of the output beam of the optical system is reduced by substantially a factor of¹/_x along a first axis and increased by less than a factor of x along a second axis orthogonal to said first axis.

20. An optical system according to claim 17, where the monolithic optical element comprises:

an optically transmissive substrate;

a substantially planar first surface formed on said substrate, said first surface vertically partitioned to form inwardly facing mirror portions and optically clear portions; and

a substantially planar second, surface formed on said substrate substantially parallel to said first surface, said second surface horizontally partitioned to form an inwardly facing mirrored portion and an optically clear portion.