Single mode propagation in fibers and rods with large leakage channels
Various embodiments include large cores fibers that can propagate few modes or a single mode while introducing loss to higher order modes. Some of these fibers are holey fibers that comprise cladding features such as air-holes. Additional embodiments described herein include holey rods. The rods and fibers may be used in many optical systems including optical amplification systems, lasers, short pulse generators, Q-switched lasers, etc. and may be used for example for micromachining.
1. An optical fiber for propagating at least one lower order mode having a wavelength λ, while limiting propagation of higher order modes having a wavelength λ by providing said higher order modes with a higher loss than said at least one lower order mode at said wavelength λ, said optical fiber comprising:
a first cladding region comprising a plurality of holes having a diameter, d, and a center-to-center spacing, Λ, wherein the ratio d/Λ is larger than 0.4 and less than 0.95; and
a core region surrounded by said first cladding region, said plurality of holes of the first cladding region providing confinement of said at least one lower order mode to the core region,
wherein said core region has a width of at least 20 micrometers,
wherein the ratio Λ/λ is greater than 15 and less than 500, and
wherein said optical fiber is configured such that said at least one lower order mode has no more than 1.0 dB/m of loss at a bending radius of 30 centimeters.
2. The optical fiber of claim 1 , wherein said core and cladding regions are in a optically transmissive main body of said optical fiber, said main body comprising material optically transmissive of said wavelength λ, said main body having a width and thickness of at least 250 μm so as to reduce mode coupling of said lower order modes to said higher order modes.
3. The optical fiber of claim 2 , said main body having a width and thickness of at least 500 μm − .
4. The optical fiber of claim 1 , wherein said core region is configured to provide a loss for said higher order modes of at least 1 dB/m.
5. The optical fiber of claim 1 , wherein said width of said core region is at least about 40 micrometers and less than about 300 micrometers.
6. The optical fiber of claim 1 , wherein said holes have a minimum size, d, yielding a ratio of d/λ that is at least 10 and less than about 100.
7. The optical fiber of claim 6 , wherein said ratio of d/λ is at least 20.
8. The optical fiber of claim 1 , wherein said cladding holes are arranged in a single row.
9. The optical fiber of claim 1 , wherein said optical fiber is spliced to a length of a second non-waveguiding fiber.
10. The optical fiber of claim 1 , wherein said optical fiber is configured such that said higher order modes have a loss of at least 0.5 dB/m.
11. The optical fiber of claim 10 , wherein the number of said at least one lower order mode is no more than 5.
12. The optical fiber of claim 1 , wherein the at least one lower order mode has no more than 0.5 dB/m of loss at a bending radius of 10 centimeters.
13. The optical fiber according to claim 1 , wherein said core region is doped to provide optical gain.
14. The optical fiber according to claim 1 , wherein the core region and the first cladding region comprise polymer materials.
15. The optical fiber of claim 1 , wherein said plurality of holes of the first cladding region are separated by bridges having a bridge width a, and wherein a ratio of a/λ is at least 10 and less than about 100.
16. The optical fiber of claim 1 , wherein said plurality of holes are arranged in a circle.
17. The optical fiber of claim 1 , wherein said plurality of holes is arranged in no more than two rings around said core region.
18. The optical fiber of claim 1 , wherein said optical fiber comprises stress elements that are incorporated into at least some of the plurality of holes of the first cladding region, and which generate two-dimensional asymmetries and provide birefringence so that a polarization-maintaining effect for the optical fiber is obtained.
19. The optical fiber of claim 1 , wherein said first cladding region is surrounded by a second cladding region.
20. The optical fiber of claim 19 , wherein said second cladding region comprises a polymer with a refractive index lower than said core region.
21. The optical fiber of claim 19 , wherein said second cladding region comprises at least one cladding hole and a bridge.
22. The optical fiber of claim 19 , wherein said optical fiber is spliced to a length of a second fiber with a single cladding matched in dimension to the second cladding of said optical fiber.
23. The optical fiber of claim 1 , further comprising a tapered end.
24. The optical fiber of claim 23 , wherein said tapered end is spliced and mode matched to a single or few mode fiber.
25. The optical fiber of claim 1 , wherein said plurality of holes comprise air holes, and said air-holes are collapsed at each end, thereby sealing said air holes and producing air-hole free ends.
26. The optical fiber of claim 1 , wherein said plurality of holes is arranged in no more than two layers, and d/Λ is larger than 0.6.
27. An optical fiber for propagating at least one lower order mode having a wavelength λ, while limiting propagation of higher order modes having a wavelength λ by providing said higher order modes with a higher loss than said at least one lower order mode at said wavelength λ, said optical fiber comprising:
a first cladding region comprising a plurality of holes having a diameter, d, and a center-to-center spacing, Λ, wherein the ratio d/Λ is larger than 0.4 and less than 0.95; and
a core region surrounded by said first cladding region, said plurality of holes of the first cladding region providing confinement of said at least one lower order mode to the core region,
wherein said core region has a width greater than about 20 micrometers and less than about 300 micrometers,
wherein said plurality of holes are configured to form a partially enclosed region, said partially enclosed region having at least one opening therein formed by one or more spaces in said partially enclosed region, said plurality of holes having a maximum bridge width, a, said maximum bridge width in part determining the size of said one or more spaces in said partially enclosed region,
wherein said maximum bridge width, a, and said diameter, d, have respective values that yield a ratio of a/λ that is at least about 5 and less than about 100, and a ratio of d/λ, that is at least about 10 and less than about 100.
28. The optical fiber of claim 27 , wherein said core region is configured to provide a loss for said higher order modes of at least 1 dB/m.
29. The optical fiber of claim 27 , wherein said plurality of holes is arranged in no more than two rings around said core region.
30. The optical fiber of claim 27 , wherein the number of said at least one lower order mode is no more than 5.
31. The optical fiber of claim 27 , wherein said plurality of holes is arranged in no more than two layers, and d/Λ is larger than 0.6.