Techniques and devices for low-loss coupling to a multicore fiber

Patent metadata

Field	Value
Publication number	US-9946014-B2
Application number	US-201214126564-A
Country	US
Kind code	B2
Filing date	Jun 20, 2012
Priority date	Mar 16, 2010
Publication date	Apr 17, 2018
Grant date	Apr 17, 2018

Abstract

An optical pedestal fiber is configured to be taperable to form a tapered fiber having a mode field diameter at the tapered end that differs from the mode field diameter at the untapered end in correspondence with the difference between the cladding diameter at the tapered end and the cladding diameter at the untapered end. A plurality of such pedestal fibers can be used to construct a tapered fiber bundle coupler that provides matching of both core pitch and mode field diameter between a plurality of input fibers and individual cores of a multicore fiber. Further, the tapered fiber bundle coupler can be constructed using a plurality of fibers, in which individual fibers are configured to have different effective refractive indices, thereby suppressing crosstalk therebetween.

First claim

The invention claimed is:

1. An optical fiber coupler for providing an interface between a plurality of input fibers and a plurality of individual cores of a multicore fiber, wherein the input fibers and the multicore fiber have respective outer diameters that are equal in size, comprising:
a plurality of coupler fibers, each having a respective input core, that are bundled together at one end, fused, and tapered to form a tapered fiber bundle (TFB) having a multicore output endface, wherein each coupler fiber has an untapered end forming a respective TFB input and a tapered end terminating at the multicore output endface,
wherein the plurality of coupler fibers and the multicore output endface have respective outer diameters that are equal in size to each other and to the respective outer diameters of the input fibers and the multicore fiber for which an interface is being provided,
wherein each of the plurality of TFB inputs has a respective geometry and mode field diameter configured for a low-loss connection to a respective input fiber,
wherein each of the plurality of coupler fibers has a respective pedestal refractive index profile that is configured such that the tapering of the plurality of coupler fibers to a predetermined taper ratio results in a multicore TFB output endface having a geometry and individual cores with respective mode field diameters that are configured for low-loss connection to respective cores of a multicore fiber, and
wherein each of the plurality of coupler fibers has a respective pedestal refractive index profile that is configured such that, throughout each coupler fiber's untapered and tapered ends, each of the input cores has a respective mode field diameter that is equal to that of the other input cores, and each of the input cores has a respective effective index that is different from that of neighboring input cores, and
wherein the TFB has a core-to-core pitch that avoids spatial overlap between neighboring mode fields,
such that crosstalk between neighboring cores is suppressed at each position within the TFB.

2. The optical fiber coupler of claim 1 , wherein each of the plurality of coupler fibers comprises:
a central core region having a first refractive index, a pedestal region surrounding the core region and having a second refractive index lower than the first refractive index, and a cladding region surrounding the pedestal region and having a third refractive index lower than the second refractive index,
wherein the core region, pedestal region, and cladding region are configured such that the fiber is taperable to form a tapered fiber having an untapered outer cladding diameter at a first end and a tapered outer cladding diameter at a second end, and
wherein the tapered fiber has a first mode field diameter at the untapered end and a second, different mode field diameter at the tapered end, wherein the second mode field diameter differs from the first mode field diameter in correspondence with the difference between the tapered outer cladding diameter and the untapered outer cladding diameter.

3. The optical fiber coupler of claim 2 ,
wherein for each of the plurality of coupler fibers the tapered outer cladding diameter is smaller than the untapered outer cladding diameter.

4. The optical fiber coupler of claim 3 ,
wherein the first mode field diameter corresponds to a mode field diameter of a pigtail optical fiber, and wherein the second mode field diameter corresponds to a mode field diameter of a core of an optical gain fiber.

5. The optical fiber coupler of claim 4 ,
wherein the second mode field diameter corresponds to a mode field diameter of a selected individual core of a multicore optical gain fiber.

6. The optical fiber coupler of claim 2 ,
wherein the tapered outer cladding diameter is larger than the untapered outer cladding diameter, and the second mode field diameter is larger than the first mode field diameter, so that the tapered fiber can be utilized to increase mode field diameter from individual input fibers to multicore output fibers.

7. The optical fiber coupler of claim 1 ,
wherein the tapered fiber bundle coupler is adapted for use in launching signal and pump radiation from individual fibers into a multicore gain fiber such that the core to core pitch and respective mode field diameters of the individual fibers is converted to respective core-to-core pitch and mode field diameters of respective cores of the multicore gain fiber.

8. The optical fiber coupler of claim 1 ,
wherein the optical fiber coupler is adapted for connection to passive optical components.

9. The optical fiber coupler of claim 8 ,
wherein the passive optical components include any of isolators, filters, and couplers.

10. The optical fiber coupler of claim 1 ,
wherein the tapered fiber bundle coupler is adapted for connection to active optical components.

11. The optical fiber coupler of claim 1 ,
including one or more active optical components,
wherein the one or more active optical components include any of transmitters, receivers, modulators.

12. The optical fiber coupler of claim 11 ,
wherein the plurality of coupler fibers is configured to have modes matching modes of respective component cores to which individual fibers are coupled.

13. The optical fiber coupler of claim 12 ,
wherein modes of a multicore fiber section of a tapered fiber bundle coupler optimize propagation in a multicore fiber connected to the coupler.

Assignees

• Abedin Kazi S
• Taunay Thierry F
• Yan Man F
• Zhu Benyuan
• Ofs Fitel Llc

Inventors

• Abedin Kazi S
• Taunay Thierry F
• Yan Man F
• Zhu Benyuan

Classifications

• H01S3/094003

  the pumped medium being a fibre · CPC title

• G02B6/2552

  reshaping or reforming of light guides for coupling using thermal heating, e.g. tapering, forming of a lens on light guide ends · CPC title

• H01S3/06754

  Fibre amplifiers (H01S3/06708 takes precedence) · CPC title

• G02B6/03633

  arranged - - · CPC title

• G02B6/262

  Optical details of coupling light into, or out of, or between fibre ends, e.g. special fibre end shapes or associated optical elements · CPC title