Fiber optic mode scrambler and a method of manufacturing thereof
A fiber optic mode scrambler includes a multi-mode optical fiber formed with a core and a cladding around the core and a non-adiabatic cross-sectional shape change zone in the optical fiber. The fiber further has a bending region extending over a length of the optical fiber. The optical fiber has a non-zero curvature at the bending region and a device for maintaining the curvature of the optical fiber at the bending region. Mode scramblers can be provided that are accurately adjusted to match with different desired optical characteristics. A well-controlled manufacturing method for the mode scrambler is also described.
1. A fiber optic mode scrambler, comprising:
a multi-mode optical fiber formed of a core and a cladding around said core;
a non-adiabatic cross-sectional shape change zone in said optical fiber;
a bending region extending over a length of said optical fiber, said optical fiber having a non-zero curvature at said bending region; and
a device for maintaining said curvature of said optical fiber at said bending region.
2. The mode scrambler according to claim 1 , wherein said shape change zone is at least partially located within said bending region.
3. The mode scrambler according to claim 1 , wherein said shape change zone is entirely located within said bending region.
4. The mode scrambler according to claim 1 , wherein said non-adiabatic shape change zone comprises at least one narrowing of optical fiber.
5. The mode scrambler according to claim 4 , wherein said at least one narrowing of optical fiber is one of a plurality of successive narrowings.
6. The mode scrambler according to claim 1 , wherein a radius of curvature (r) of said optical fiber at each point within said bending region is more than 50 times a diameter (D) of said optical fiber.
7. The mode scrambler according to claim 1 , wherein a radius of curvature (r) of said optical fiber is constant over an entire said bending region.
8. The mode scrambler according to claim 1 , wherein said device for maintaining the curvature comprises a rigid coating or sleeve on said optical fiber at said bending region.
9. The mode scrambler according to claim 1 , wherein said device for maintaining the curvature comprises an assembly element having a shape-maintaining means adapted to receive and immobilize the bending region of the optical fiber.
10. The mode scrambler according to claim 1 , wherein said device for maintaining the curvature comprises a rigid base member to which said optical fiber is potted or glued.
11. The mod scrambler according to claim 9 , wherein said optical fiber is potted or glued to said rigid base member with a material selected from the group consisting of epoxy, urethane, silicone and acrylate.
12. The mode scrambler according to claim 1 , wherein said shape change zone comprises a plurality of narrowings having a modulation depth of 5-30% and a total angle of curvature of said bending region is between 10 and 90 degrees.
13. A method of manufacturing an optical mode scrambler, comprising:
providing an optical fiber having a core and cladding around the core;
providing at least one zone capable of causing non-adiabatic optical mode mixing of multi-mode light travelling in the optical fiber;
bending the optical fiber on at least one bending region;
simultaneously with the bending, injecting laser light into the optical fiber and measuring characteristics of the light passing the at least one bending region; and
when a predefined light characteristic has been achieved, immobilizing the optical fiber at the bending region so as to form a tuned optical mode scrambler.
14. The method according to claim 13 , wherein the light characteristic is one or more criteria selected from the group consisting of mode-scrambling efficiency and brilliance.
15. The method according to claim 13 , wherein the immobilizing step comprises adding a rigid coating or sleeve around the optical fiber at the bending zone or mounting the optical fiber to an assembly element capable of maintaining the shape of the optical fiber at the bending region.
16. The method according to claim 13 , which comprises injecting the laser light into the optical fiber from a laser light source connected to or integral with said optical fiber.
17. The method according to claim 16 , wherein the laser source is a fiber laser source.
18. The method according to claim 13 , wherein the at least one zone and the at least one bending region are formed to at least partially overlap.
19. The method according to claim 13 , wherein the immobilizing step comprises one or more of the following:
providing the optical fiber with a rigid sleeve capable of maintaining the shape of the fiber;
mounting the optical fiber to an assembly element having a shape-maintaining device for the optical fiber; and
gluing or potting the optical fiber to a base member with a glue or potting material.