Optical fiber structures and methods for varying laser beam profile

1. A step-clad optical fiber for use in a laser system comprising (i) a beam source for emission of an input laser beam and (ii) an in-coupling mechanism for receiving the input laser beam and directing the input laser beam toward an input end of the step-clad optical fiber for emission as an output beam from an output end of the step-clad optical fiber opposite the input end, the step-clad optical fiber consisting of:

a central core having a first refractive index, the central core being composed of fused silica or fused silica doped with fluorine, titanium, germanium, and/or boron;

surrounding the central core, a first cladding having a second refractive index;

surrounding the first cladding, an annular core having a third refractive index; and

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, (iii) the second refractive index is smaller than the first refractive index and larger than the fourth refractive index, and (iv) the second refractive index is smaller than the third refractive index, and

wherein (i) the third refractive index is greater than or approximately equal to the first refractive index, (ii) a thickness of the first cladding ranges from approximately 40 μm to approximately 100 μm, (iii) a thickness of the annular core ranges from approximately 60 μm to approximately 150 μm, and/or (iv) a thickness of the central core is at least approximately 100 μm.

2. The step-clad optical fiber of claim 1 , wherein the third refractive index is smaller than the first refractive index.

3. The step-clad optical fiber of claim 1 , wherein the third refractive index is larger than the first refractive index.

4. The step-clad optical fiber of claim 1 , wherein a numerical aperture of the first cladding is larger than 0.12.

5. The step-clad optical fiber of claim 1 , wherein a thickness of the first cladding ranges from approximately 40 μm to approximately 100 μm.

6. The step-clad optical fiber of claim 1 , wherein a thickness of the annular core ranges from approximately 60 μm to approximately 150 μm.

7. The step-clad optical fiber of claim 1 , wherein a ratio of a diameter of the first cladding to a diameter of the central core ranges between 1.2 and 3.

8. The step-clad optical fiber of claim 1 , wherein a ratio of a diameter of the annular core to a diameter of the central core ranges between 1.5 and 6.5.

9. A step-clad optical fiber for use in a laser system comprising (i) a beam source for emission of an input laser beam and (ii) an in-coupling mechanism for receiving the input laser beam and directing the input laser beam toward an input end of the step-clad optical fiber for emission as an output beam from an output end of the step-clad optical fiber opposite the input end, the step-clad optical fiber comprising:

a central core having a first refractive index;

surrounding the central core, a first cladding having a second refractive index;

surrounding the first cladding, an annular core having a third refractive index; and

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, (iii) the second refractive index is smaller than the first refractive index and larger than the fourth refractive index, (iv) the second refractive index is approximately equal to the third refractive index, and (v) a thickness of the annular core ranges from approximately 60 μm to approximately 150 μm.

10. The step-clad optical fiber of claim 9 , wherein a thickness of the first cladding ranges from approximately 40 μm to approximately 100 μm.

11. The step-clad optical fiber of claim 9 , wherein a thickness of the annular core ranges from approximately 80 μm to approximately 120 μm.

12. The step-clad optical fiber of claim 9 , wherein a ratio of a diameter of the first cladding to a diameter of the central core ranges between 1.2 and 3.

13. The step-clad optical fiber of claim 9 , wherein a ratio of a diameter of the annular core to a diameter of the central core ranges between 1.5 and 6.5.

14. A step-clad optical fiber for use in a laser system comprising (i) a beam source for emission of an input laser beam and (ii) an in-coupling mechanism for receiving the input laser beam and directing the input laser beam toward an input end of the step-clad optical fiber for emission as an output beam from an output end of the step-clad optical fiber opposite the input end, the step-clad optical fiber comprising:

a central core having a first refractive index, the central core being composed of fused silica or fused silica doped with fluorine, titanium, germanium, and/or boron;

surrounding the central core, a first cladding having a second refractive index;

surrounding the first cladding, an annular core having a third refractive index; and

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, (iii) the second refractive index is smaller than the first refractive index and larger than the fourth refractive index, and (iv) the third refractive index is larger than the first refractive index.

15. The step-clad optical fiber of claim 14 , wherein a thickness of the first cladding ranges from approximately 40 μm to approximately 100 μm.

16. The step-clad optical fiber of claim 14 , wherein a thickness of the annular core ranges from approximately 60 μm to approximately 150 μm.

17. The step-clad optical fiber of claim 14 , wherein a ratio of a diameter of the first cladding to a diameter of the central core ranges between 1.2 and 3.

18. The step-clad optical fiber of claim 14 , wherein a ratio of a diameter of the annular core to a diameter of the central core ranges between 1.5 and 6.5.

19. The step-clad optical fiber of claim 1 , wherein a thickness of the central core is at least approximately 100 μm.

20. The step-clad optical fiber of claim 9 , wherein a thickness of the central core is at least approximately 100 μm.

21. The step-clad optical fiber of claim 14 , wherein a thickness of the central core is at least approximately 100 μm.

22. The step-clad optical fiber of claim 1 , wherein a thickness of the annular core is at least approximately 80 μm.

23. The step-clad optical fiber of claim 14 , wherein a thickness of the annular core is at least approximately 80 μm.

24. The step-clad optical fiber of claim 1 , wherein the central core is composed of fused silica.

25. The step-clad optical fiber of claim 14 , wherein the central core is composed of fused silica.

26. The step-clad optical fiber of claim 1 , wherein the third refractive index is approximately equal to the first refractive index.