Fiber bundles and methods of making fiber bundles

1. A fused fiber bundle having a terminal section ending with an endface, the fused fiber bundle comprising:

a glass tube;

at least one spacer member having a selected shape inserted in the glass tube; and

a plurality of optical fibers, each of the optical fibers having a terminal segment ending with a proximal end, and a distal end, said terminal segments being arranged between the glass tube and the at least one spacer member;

wherein the glass tube surrounds the terminal segments of the optical fibers,

wherein the terminal segments of the optical fibers are arranged substantially in parallel,

wherein the terminal segment of each of the optical fibers is substantially fused to any adjacent optical fibers and the terminal segment of each optical fiber adjacent to the glass tube is substantially fused thereto, thereby forming the terminal section of the fused fiber bundle, and

wherein the glass tube is a thick-walled tube, such that at the endface of the fused fiber bundle, the ratio of the cross-sectional area of the endface to the cross sectional area of the plurality of optical fibers is at least about 2.5.

2. The fused fiber bundle of claim 1 , wherein the ratio of the cross-sectional area of the endface to the cross sectional area of the plurality of optical fibers is at least about 4.

3. The fused fiber bundle of claim 1 , wherein the plurality of optical fibers comprises at least 4 optical fibers.

4. The fused fiber bundle of claim 1 , wherein the plurality of optical fibers is in a triangular lattice.

5. The fused fiber bundle of claim 1 , wherein the plurality of optical fibers is arranged in a geometry selected from the group consisting of diamond-shaped, triangular, hexagonal, trapezoidal and rectangular.

6. The fused fiber bundle of claim 1 , wherein the terminal section of the fused fiber bundle has substantially no organic material between neighboring optical fibers and between the optical fibers and the thick-walled tube.

7. The fused fiber bundle of claim 1 , wherein the optical fibers each include a core and a cladding, and wherein the refractive index of the glass tube is less than the refractive index of the claddings of the optical fibers.

8. The fused fiber bundle of claim 6 , wherein the difference between the refractive index of the glass tube and the refractive index of the claddings of the optical fibers is at least 0.005.

9. The fused fiber bundle of claim 1 , wherein the terminal section of the fused fiber bundle is collapsed so that substantially no airspace remains between neighboring optical fibers and between the optical fibers and the glass tube.

10. The fused fiber bundle of claim 1 , wherein the distal ends of at least one of the optical fibers are lensed.

11. The fused fiber bundle of claim 1 , wherein the optical fibers have rectangular cross-sections.

12. The fused fiber bundle of claim 1 , wherein the terminal section of the fused fiber bundle ends in a taper.

13. The fused fiber bundle of claim 1 , wherein the endface of the fused fiber bundle is polished.

14. The fused fiber bundle of claim 1 , wherein the endface of the fused fiber bundle is greater than 0.78 mm 2 in cross-sectional area.

15. An optical device comprising the fused fiber bundle of claim 1 operatively coupled to an optical system.

16. A cladding-pumped fiber device, comprising the fused fiber bundle of claim 1 operatively coupled to a cladding-pumped fiber.

17. A fused fiber bundle having a terminal section ending with an endface, the fused fiber bundle comprising:

a glass tube;

at least one spacer member having a selected shape inserted in the glass tube; and

a plurality of optical fibers, each of the optical fibers having a terminal segment ending with a proximal end, and a distal end, said terminal segments being arranged between the glass tube and the at least one spacer member;

wherein the glass tube surrounds the terminal segments of the optical fibers,

wherein the terminal segments of the optical fibers are arranged substantially in parallel, and are substantially fused to one another and to the glass tube to form the terminal section of the fused fiber bundle, and

wherein the refractive index of the glass tube is less than the refractive index of the claddings of the optical fibers.

18. The fused fiber bundle of claim 17 , wherein the difference between the refractive index of the claddings of the optical fibers and the refractive index of the glass tube is at least 0.005.

19. The fused fiber bundle of claim 17 , wherein the terminal section of the fused fiber bundle is tapered.

20. The fused fiber bundle of claim 17 , wherein the terminal section of the fused fiber bundle has substantially no organic adhesive between neighboring optical fibers and between the optical fibers and the glass tube.

21. The fused fiber bundle of claim 17 , wherein the endface of the fused fiber bundle is greater than 0.78 mm 2 in diameter.

22. An optical device comprising the fused fiber bundle of claim 17 operatively coupled to an optical system.

23. A cladding-pumped fiber device, comprising the fused fiber bundle of claim 17 operatively coupled to a cladding-pumped fiber.