Spun round core fiber
Optical waveguide cores having refractive index profiles that vary angularly about a propagation axis of the core can provide single-mode operation with larger core diameters than conventional waveguides. In one representative embodiment, an optical waveguide comprises a core that extends along a propagation axis and has a refractive index profile that varies angularly about the propagation axis. The optical waveguide can also comprise a cladding disposed about the core and extending along the propagation axis. The refractive index profile of the core can vary angularly along a length of the propagation axis.
1. An optical waveguide, comprising:
a core that extends along a propagation axis, the core comprising a mode-discriminating region comprising a material having a first index of refraction, the mode-discriminating region being surrounded by a material having a second index of refraction different from the first index of refraction and configured such that the core has a refractive index profile that varies angularly about the propagation axis; and
a cladding disposed about the core and extending along the propagation axis;
wherein the refractive index profile of the core varies angularly along a length of the propagation axis.
2. The optical waveguide of claim 1 , wherein the refractive index profile of the core varies radially about the propagation axis.
3. The optical waveguide of claim 1 , wherein the refractive index profile of the core is periodic along the propagation axis.
4. The optical waveguide of claim 1 , wherein the refractive index profile of the core is aperiodic along the propagation axis.
5. The optical waveguide of claim 1 , wherein the refractive index profile of the core is configured to attenuate one or more higher order modes.
6. The optical waveguide of claim 1 , wherein the refractive index profile of the core is radially asymmetric about the propagation axis.
7. The optical waveguide of claim 1 , wherein the refractive index profile of the core is angularly asymmetric about the propagation axis.
8. The optical waveguide of claim 1 , wherein the core has a round cross-section.
9. The optical waveguide of claim 1 , wherein the core comprises a plurality of mode-discriminating regions.
10. The optical waveguide of claim 9 , wherein each of the mode-discriminating regions is radially offset from the propagation axis.
11. The optical waveguide of claim 9 , wherein:
the material of the core comprises a first material having the second index of refraction; and
the material of each of the mode-discriminating regions comprises a second material having the first index of refraction.
12. The optical waveguide of claim 9 , wherein the plurality of mode-discriminating regions are arranged symmetrically about the propagation axis.
13. The optical waveguide of claim 9 , wherein each of the mode-discriminating regions has a round cross-section.
14. The optical waveguide of claim 1 , wherein the core is doped with one or more rare-earth metals.
15. The optical waveguide of claim 1 , wherein the diameter of the core is from about 10 micrometers to about 250 micrometers.
16. The optical waveguide of claim 1 , wherein the optical waveguide is configured to exhibit losses of from about 0.01 decibel per meter to about 1 decibel per meter for an LP 01 mode.
17. The optical waveguide of claim 1 , wherein the optical waveguide is configured to exhibit losses of from about 10 decibels per meter to about 100 decibels per meter for an LP 11 mode.
18. A method of discriminating against a higher order mode in an optical waveguide, comprising:
directing optical radiation into a core of an optical waveguide, the core extending along a propagation axis, the core comprising a mode-discriminating region comprising a material having a first index of refraction, the mode-discriminating region being surrounded by a material having a second index of refraction different from the first index of refraction and configured such that the core has a refractive index profile that varies angularly about the propagation axis and varies angularly along a length of the propagation axis, the optical waveguide further comprising a cladding disposed about the core and extending along the propagation axis; and
receiving the optical radiation after propagation in the optical waveguide.
19. The method of claim 18 , wherein the higher order mode is an LP 11 mode.
20. An optical system, comprising:
a seed optical source configured to provide a seed optical beam;
one or more optical amplifiers configured to receive and amplify the seed optical beam;
at least one optical pump source configured to provide at least one pump optical beam to a combiner, the combiner being configured to couple pump optical radiation from the pump optical beam into a cladding of a passive optical fiber; and
an active optical fiber in communication with the passive optical fiber;
wherein the active optical fiber comprises a core that extends along a propagation axis, the core comprising a mode-discriminating region comprising a material having a first index of refraction, the mode-discriminating region being surrounded by a material having a second index of refraction different from the first index of refraction and configured such that the core has a refractive index profile that varies angularly about the propagation axis;
wherein the active optical fiber further comprises a cladding disposed about the core and extending along the propagation axis;
wherein the refractive index profile of the core varies angularly along a length of the propagation axis; and
wherein the active optical fiber is configured to discriminate against higher order modes.
21. The optical system of claim 20 , wherein the core of the active optical fiber has a round cross-section.
22. The optical waveguide of claim 1 , wherein the refractive index profile of the core is configured to discriminate against a fundamental mode.