Optical fiber structures and methods for varying laser beam profile

1. A laser system comprising:

a beam source for emission of an input laser beam;

a step-clad optical fiber having an input end and an output end opposite the input end, the step-clad optical fiber comprising (i) a central core having a first refractive index, (ii) surrounding the central core, a first cladding having a second refractive index, (iii) surrounding the first cladding, an annular core having a third refractive index, and (iv) surrounding the annular core, a second cladding having a fourth refractive index, wherein (i) the first refractive index is larger than the fourth refractive index, (ii) the third refractive index is larger than the fourth refractive index, and (iii) the second refractive index is smaller than the first refractive index and larger than the fourth refractive index;

an in-coupling mechanism for receiving the input laser beam and directing the input laser beam toward the input end of the step-clad optical fiber, whereby the input laser beam is in-coupled into the step-clad optical fiber and emitted from the output end of the step-clad optical fiber as an output beam; and

a controller for controlling the in-coupling mechanism to direct the input laser beam onto one or more in-coupling locations on the input end of the step-clad optical fiber, whereby at least one of a beam parameter product or a numerical aperture of the output beam is determined at least in part by the one or more in-coupling locations.

2. The laser system of claim 1 , wherein the in-coupling mechanism comprises an optical element for focusing the input laser beam toward the input end of the step-clad optical fiber, the optical element being movable, in response to the controller, along at least one of (i) an axis substantially parallel to a propagation direction of the input laser beam or (ii) one or more axes substantially perpendicular to the propagation direction of the input laser beam.

3. The laser system of claim 2 , wherein the in-coupling mechanism comprises a reflector for receiving the input laser beam and reflecting the input laser beam toward the step-clad optical fiber.

4. The laser system of claim 2 , wherein the optical element comprises one or more lenses, one or more mirrors, and/or one or more prisms.

5. The laser system of claim 1 , wherein the in-coupling mechanism comprises a reflector for receiving the input laser beam and reflecting the input laser beam toward the step-clad optical fiber, the reflector being rotatable in response to the controller.

6. The laser system of claim 5 , wherein the in-coupling mechanism comprises an optical element for receiving the input laser beam from the reflector and focusing the input laser beam toward the step-clad optical fiber.

7. The laser system of claim 6 , wherein the optical element is movable, in response to the controller, along at least one of (i) an axis substantially parallel to a propagation direction of the input laser beam or (ii) one or more axes substantially perpendicular to the propagation direction of the input laser beam.

8. The laser system of claim 6 , wherein the optical element comprises one or more lenses, one or more mirrors, and/or one or more prisms.

9. The laser system of claim 1 , wherein:

the beam source is responsive to the controller; and

the controller is configured to direct the input laser beam onto a plurality of different in-coupling locations without modulating an output power of the input laser beam as the input laser beam is directed between the different in-coupling locations.

10. The laser system of claim 1 , wherein the controller is configured to direct the input laser beam onto at least one in-coupling location at least partially overlapping the first cladding, whereby beam energy in-coupled into the first cladding forms at least a portion of the output beam.

11. The laser system of claim 1 , wherein the second refractive index is smaller than the third refractive index.

12. The laser system of claim 1 , wherein the second refractive index is equal to the third refractive index.

13. The laser system of claim 1 , wherein the third refractive index is smaller than the first refractive index.

14. The laser system of claim 1 , wherein the third refractive index is greater than the first refractive index.

15. The laser system of claim 1 , wherein the beam source comprises:

one or more beam emitters emitting a plurality of discrete beams;

focusing optics for focusing the plurality of beams onto a dispersive element;

a dispersive element for receiving and dispersing the received focused beams; and

a partially reflective output coupler positioned to receive the dispersed beams, transmit a portion of the dispersed beams therethrough as the input laser beam, and reflect a second portion of the dispersed beams back toward the dispersive element,

wherein the input laser beam is composed of multiple wavelengths.

16. The laser system of claim 15 , wherein the dispersive element comprises a diffraction grating.

17. A method of adjusting at least one of a beam parameter product or a numerical aperture of a laser beam, the method comprising:

providing a step-clad optical fiber having an input end and an output end opposite the input end, the step-clad optical fiber comprising (i) a central core having a first refractive index, (ii) surrounding the central core, a first cladding having a second refractive index, (iii) surrounding the first cladding, an annular core having a third refractive index, and (iv) surrounding the annular core, a second cladding having a fourth refractive index, wherein (i) the first refractive index is larger than the fourth refractive index, (ii) the third refractive index is larger than the fourth refractive index, and (iii) the second refractive index is smaller than the first refractive index and larger than the fourth refractive index; and

directing an input laser beam onto one or more in-coupling locations on the input end of the step-clad optical fiber, whereby (i) the input laser beam is in-coupled into the step-clad optical fiber and emitted from the output end of the step-clad optical fiber as an output beam, and (ii) at least one of a beam parameter product or a numerical aperture of the output beam is determined at least in part by the one or more in-coupling locations.

18. The method of claim 17 , wherein the input laser beam is directed onto a plurality of different in-coupling locations.

19. The method of claim 18 , wherein an output power of the input laser beam is not modulated as the input laser beam is directed between the different in-coupling locations.

20. The method of claim 17 , wherein at least one of the in-coupling locations at least partially overlaps the first cladding, whereby beam energy in-coupled into the first cladding forms at least a portion of the output beam.

21. The method of claim 17 , wherein the second refractive index is smaller than the third refractive index.

22. The method of claim 17 , wherein the second refractive index is approximately equal to the third refractive index.

23. The method of claim 17 , wherein the third refractive index is smaller than the first refractive index.

24. The method of claim 17 , wherein the third refractive index is greater than the first refractive index.

25. The method of claim 17 , wherein the input laser beam is emitted by a beam source comprising:

one or more beam emitters emitting a plurality of discrete beams;

focusing optics for focusing the plurality of beams onto a dispersive element;

a dispersive element for receiving and dispersing the received focused beams; and

a partially reflective output coupler positioned to receive the dispersed beams, transmit a portion of the dispersed beams therethrough as the input laser beam, and reflect a second portion of the dispersed beams back toward the dispersive element,

wherein the input laser beam is composed of multiple wavelengths.

26. The method of claim 25 , wherein the dispersive element comprises a diffraction grating.

27. A method of adjusting at least one of a beam parameter product or a numerical aperture of a laser beam, the method comprising:

providing a step-clad optical fiber having an input end and an output end opposite the input end, the step-clad optical fiber comprising (i) a central core having a first refractive index, (ii) surrounding the central core, a first cladding having a second refractive index, (iii) surrounding the first cladding, an annular core having a third refractive index, and (iv) surrounding the annular core, a second cladding having a fourth refractive index, wherein (i) the third refractive index is larger than the fourth refractive index, (ii) the third refractive index is larger than the second refractive index, and (iii) the second refractive index is larger than the fourth refractive index; and

directing an input laser beam onto one or more in-coupling locations on the input end of the step-clad optical fiber, whereby (i) the input laser beam is in-coupled into the step-clad optical fiber and emitted from the output end of the step-clad optical fiber as an output beam, and (ii) at least one of a beam parameter product or a numerical aperture of the output beam is determined at least in part by the one or more in-coupling locations,

wherein at least one of the in-coupling locations at least partially overlaps the first cladding, whereby beam energy in-coupled into the first cladding forms at least a portion of the output beam.

28. The method of claim 27 , wherein the input laser beam is directed onto a plurality of different in-coupling locations.

29. The method of claim 28 , wherein an output power of the input laser beam is not modulated as the input laser beam is directed between the different in-coupling locations.

30. The method of claim 27 , wherein the input laser beam is emitted by a beam source comprising:

one or more beam emitters emitting a plurality of discrete beams;

focusing optics for focusing the plurality of beams onto a dispersive element;

a dispersive element for receiving and dispersing the received focused beams; and

a partially reflective output coupler positioned to receive the dispersed beams, transmit a portion of the dispersed beams therethrough as the input laser beam, and reflect a second portion of the dispersed beams back toward the dispersive element,

wherein the input laser beam is composed of multiple wavelengths.

31. The method of claim 30 , wherein the dispersive element comprises a diffraction grating.