Optical fiber with micro-structured cladding

1. An optical fiber having a length, comprising:

a core; and

at least one cladding disposed about the core, said one cladding comprising at least first volumetric regions having a first refractive index n 1 and second volumetric regions having a second refractive index n 2 , different from n 1 ,

said first and second volumetric regions in any cross-section taken through said fiber being randomly intermingled with one another, the random intermingling of the first and second volumetric regions changing with changes in the location of the cross-section along the length of the fiber.

2. An optical fiber as defined in claim 1 , wherein:

for substantially any line extending parallel to said core and in said one cladding, the line will pass at least once from one of the volumetric regions to a volumetric region having a different index.

3. An optical fiber as defined in claim 2 , wherein:

said first volumetric regions of silica-based material are fused to one another to form a sintered body defining said hollows.

4. An optical fiber as defined in claim 3 , wherein:

said hollows contain air.

5. An optical fiber as defined in claim 3 , wherein:

said hollows are empty.

6. An optical fiber as defined in claim 3 , wherein:

said hollows contain a gas.

7. An optical fiber as defined in claim 1 , wherein:

said fiber has an inner cladding disposed about the core and an outer cladding disposed about the inner cladding,

said inner cladding being comprised of a silica-based material, and

said one cladding is said outer cladding.

8. An optical fiber as defined in claim 7 , wherein:

said outer cladding is surrounded by a sheath made of a silica-based material.

9. An optical fiber as defined in claim 8 , wherein:

at least said first volumetric regions of said outer cladding are made of a silica-based material.

10. An optical fiber as defined in claim 9 wherein:

said first volumetric regions of said outer cladding are fused to one another to form a sintered body and said second volumetric regions are hollows in said sintered body.

11. An optical fiber as defined in claim 8 , wherein:

both said first and second volumetric regions are made of silica-based materials.

12. An optical fiber as defined in claim 11 , wherein:

said first and second volumetric regions are fused to one another.

13. An optical fiber defined in claim 1 , wherein:

said one cladding contains essentially no volumetric regions other than said first and second volumetric regions.

14. An optical fiber as defined in claim 1 , wherein:

said first volumetric regions are comprised of a first silica-based material of refractive index n 1 ,

said second volumetric regions are comprised of a second silica-based material of refractive index n 2 , and

said first and second volumetric regions are fused to one another to form a rigid body.

15. An optical fiber as defined in claim 1 , wherein:

said one cladding is located immediately adjacent to said core.

16. An optical fiber as defined in claim 1 , wherein:

said fiber has an inner cladding disposed about the core and an outer cladding disposed about the inner cladding, and

said one cladding is said inner cladding.

17. An optical fiber as defined in claim 1 , wherein:

said fiber has an inner cladding disposed about the core and an outer cladding disposed about the inner cladding, and

said one cladding is said outer cladding.

18. An optical fiber having a length, said fiber comprising:

a core;

a first cladding disposed about the core;

a second cladding disposed about the first cladding, said second cladding including first volumetric regions having a first refractive index and second volumetric regions having a second index of refraction that is different than said first index of refraction, said second cladding having an effective index of refraction that is less than one of said indices of refraction, and wherein said at least some of said first volumetric regions are truncated such that they do not extend within said fiber for the entire length.

19. An optical fiber as defined in claim 18 wherein one of said first and second volumetric regions comprises empty hollows.

20. An optical fiber as defined in claim 18 wherein one of said first and second volumetric regions comprises hollows containing a gas.

21. An optical fiber as defined in claim 18 wherein one of said first and second volumetric regions comprises hollows containing air.

22. A method of making an optical fiber having a length and having at least one cladding, the method comprising the steps of:

making an early stage preform having an elongate core made of a first silica-based material, an outer region disposed about the core, and an intermediate region located radially inwardly of the outer region, improving the early stage preform to a later stage preform by at least disposing first particles in the intermediate region so that the later stage preform includes in the intermediate region first volumetric regions constituted by the first particles intermingled with the second volumetric regions constituted by something other than the particles of the first volumetric regions; and

drawing an optical fiber from a preform that includes at least the later stage preform.

23. The method defined in claim 22 , wherein:

disposing particles in the intermediate region includes selecting the particles to be of such sizes and shapes, and selecting the conditions attending the disposing of the particles into the intermediate region so that after the intermediate region includes the particles hollows are intermixed with the particles in the intermediate region.

24. The method defined in claim 23 , wherein:

selecting the conditions includes mixing a gas with the particles as they are disposed in the intermediate region so that the hollows include the gas.

25. The method defined in claim 24 , wherein:

the gas is air.

26. The method defined in claim 22 , comprising:

disposing second particles with the first particles, the second particles having an different index of refraction than the first particles, the second volumetric regions being constituted by the second particles.