Optical fiber modal distribution conditioner

Patent metadata

Field	Value
Publication number	US-10018785-B2
Application number	US-201414301646-A
Country	US
Kind code	B2
Filing date	Jun 11, 2014
Priority date	Jun 14, 2013
Publication date	Jul 10, 2018
Grant date	Jul 10, 2018

Abstract

There is provided a modal distribution conditioner comprising the combination of a mandrel-wrapped optical fiber and an adjustable and fixable loop of optical fiber. It is noted that light entering the modal distribution conditioner is to be generally overfilled compared with the target encircled flux function (as defined by the Standard). The mandrel wrapping introduces macrobends to the optical fiber, inducing modal pre-filtering that roughly transforms the initially overfilled modal distribution to be close to compliance with the appropriate Standard. However, the modal distribution of light having traversed the fixed mandrel typically remains somewhat overfilled. The adjustable loop provides for the fine-tuning of the modal distribution, in conformity with the Standard. Once the requirements defined by the Standard are met, the adjustable loop may be secured in place such that modal distribution becomes fixed and remain stable.

First claim

What is claimed is:

1. An apparatus for adjusting the modal distribution of light propagating in a multimode optical fiber, the apparatus comprising:
a first portion of multimode optical fiber wrapped about a mandrel having a first radius of curvature adapted for inducing preferential attenuation of high-order optical fiber modes of said light in said first portion of multimode optical fiber, wherein the mandrel has a shape that is non-adjustable;
an adjustable loop of a second portion of multimode optical fiber optically coupled to said first portion, said adjustable loop having a curvature being adjusted to a second radius of curvature being smaller than said first radius of curvature of said mandrel, for adjusting the modal distribution of said light propagated in the multimode optical fiber; and
a first fiber positioning feature for receiving an adjustable end of said adjustable loop of multimode optical fiber, said first fiber positioning feature determining an orientation of said multimode optical fiber at said adjustable end, said loop being adjustable by sliding the adjustable end within the first fiber positioning feature.

2. The apparatus as claimed in claim 1 , wherein said mandrel comprises a cylindrical surface and an end surface, said first portion of multimode optical fiber being wrapped about said cylindrical surface, and said first fiber positioning feature being disposed on said end surface of said mandrel.

3. The apparatus as claimed in claim 2 , further comprising a second fiber positioning feature determining an orientation of the other end of said adjustable loop.

4. The apparatus as claimed in claim 1 , wherein said apparatus comprises a plurality of first fiber positioning features into which the adjustable end may be inserted, wherein said curvature of said adjustable loop is also adjustable by selecting one of said first positioning features into which to insert the adjustable end.

5. The apparatus as claimed in claim 2 , wherein the first fiber positioning feature comprises a groove on said end surface.

6. The apparatus as claimed in claim 1 , wherein said adjustable loop is fixable after adjustment by affixing at least the adjustable end in place.

7. The apparatus as claimed in claim 6 , wherein said apparatus further comprises an adhesive at the adjustable end of said adjustable loop for fixing said adjustable loop after adjustment.

8. The apparatus as claimed in claim 1 , wherein said light propagating in the multimode optical fiber traverses said first portion before traversing said adjustable loop.

9. The apparatus as claimed in claim 1 , wherein said first portion and said second portion of said multimode optical fiber are continuous lengths of a same optical fiber.

10. A method for adjusting the modal distribution of light propagating in a multimode optical fiber, the method comprising:
wrapping a first portion of multimode optical fiber about a mandrel having a first radius of curvature adapted for inducing preferential attenuation of high-order optical fiber modes of said light in said first portion of multimode optical fiber, wherein the mandrel has a shape that is non-adjustable;
forming a loop of a second portion of multimode optical fiber optically coupled to said first portion; and
adjusting a curvature of said loop of said second portion of multimode optical fiber to one of a plurality of second radiuses of curvature, the second radiuses of curvature being smaller than said first radius of curvature of said mandrel, for adjusting the modal distribution of said light propagated in the multimode optical fiber, said loop comprising a first end and being adjusted at least by sliding said first end within a first fiber positioning feature.

11. The method as claimed in claim 10 , further comprising monitoring said modal distribution of light while adjusting said curvature of said loop.

12. The method as claimed in claim 11 , further comprising fixing said loop after adjustment by affixing at least said first end within the fiber positioning feature.

13. The method as claimed in claim 10 , wherein said curvature of said loop is adjusted such that said modal distribution complies with a modal distribution requirement defined by a target distribution and a predetermined tolerance.

14. The method as claimed in claim 13 , further comprising measuring encircled-flux values, said target distribution being defined as target values of encircled-flux measurements.

15. The method as claimed in claim 10 , wherein said curvature of said loop is further adjusted by inserting said first end into one of a plurality of positioning features.

16. A device to be used in adjusting the modal distribution of light propagating in a multimode optical fiber, the device comprising:
a mandrel adapted for wrapping a first portion of said multimode optical fiber thereabout, having a first radius of curvature adapted for inducing preferential attenuation of high-order optical fiber modes of light in the multimode optical fiber, wherein the mandrel has a shape that is non-adjustable; and
at least a first fiber positioning feature on said mandrel for receiving one end of an adjustable loop of a second portion of said multimode optical fiber and determining an orientation of the multimode optical fiber at said one end, said first fiber positioning feature allowing said one end of said loop to be slid therein in order to adjust a curvature of said loop to a second radius of curvature being smaller than said first radius of curvature of said mandrel.

17. The device as claimed in claim 16 , wherein said mandrel comprises a cylindrical surface, about which said first portion of multimode optical fiber is wrapped, and an end surface, said first fiber positioning feature protruding from said end surface along an axis of said cylindrical surface, and said end surface comprising a flat portion adjacent which said adjustable loop is to be disposed.

18. The device as claimed in claim 16 , wherein said device comprises a second positioning feature on said mandrel for receiving the other end of said adjustable loop and for determining an orientation thereof.

19. The device as claimed in claim 16 , wherein said device comprises a plurality of first fiber positioning features into which the one end may be inserted, wherein said curvature of said loop is also adjustable by selecting one of said first fiber positioning features into which to insert the one end.

20. The device as claimed in claim 16 , wherein the positioning feature comprises a groove on said end surface.

Assignees

• Exfo Inc

Inventors

• Fortin Remi
• He Gang

Classifications

• G02B6/0288

  Multimode fibre, e.g. graded index core for compensating modal dispersion · CPC title

• G02B6/14

  Mode converters · CPC title

• G02B6/0281 Primary

  Graded index region forming part of the central core segment, e.g. alpha profile, triangular, trapezoidal core (G02B6/0288, G02B6/0286 take precedence) · CPC title

• G02B6/268 Primary

  for modal dispersion control, e.g. concatenation of light guides having different modal dispersion properties (graded index multimode fibres G02B6/0288; multimodal transmission systems H04B10/2581) · CPC title