Multi-clad optical fiber with delocalization of pedestal modes

Patent metadata

Field	Value
Publication number	US-11309677-B2
Application number	US-202117162852-A
Country	US
Kind code	B2
Filing date	Jan 29, 2021
Priority date	Jan 31, 2020
Publication date	Apr 19, 2022
Grant date	Apr 19, 2022

Abstract

A multi-clad optical fiber is provided. The fiber includes, concentrically and radially outwards from the center of the optical fiber, a core doped with at least one rare-earth dopant material, a pedestal cladding structure, an inner cladding and an outer cladding. The pedestal cladding structure includes a pedestal layer having a refractive index smaller than a refractive index of the core, and a raised index layer having a refractive index larger than the refractive index of the pedestal layer. The raised index layer has a thickness and a refractive index which preserve the confinement of the core mode in the core and minimize the overlap of one or more pedestal modes with the core.

First claim

The invention claimed is:

1. A cladding-pumped multi-clad optical fiber comprising, concentrically and radially outwards from a center axis of the optical fiber:
a core configured to guide a light signal in a core mode, said core having a core diameter d core smaller than about 30 μm, the core being doped with at least one rare-earth dopant material providing amplification of the light signal, the core having a refractive index n core ;
a pedestal cladding structure supporting light propagation in a plurality of pedestal modes, the pedestal cladding structure having a pedestal cladding structure diameter d pcs , the pedestal cladding structure comprising:
a pedestal layer contiguously surrounding the core and configured to confine the light signal in said core mode, the pedestal layer having a refractive index n ped smaller than the refractive index of the core n core ; and
a raised index layer contiguously surrounding the pedestal layer and having a thickness Δw, the raised index layer having a refractive index n ril larger than the refractive index of the pedestal layer n ped and smaller than the refractive index of the core n core , the thickness Δw and the refractive index n ril of the raised index layer preserving a confinement of the core mode in the core;

an inner cladding having a refractive index n icl smaller than the refractive index n ril of the raised index layer; and
an outer cladding having a refractive index n ocl smaller than the refractive index n icl of the inner cladding;

wherein the pedestal cladding structure is a thin pedestal cladding structure characterized by a ratio of the pedestal cladding structure diameter d pcs to the core diameter d core smaller than about 3, and the thickness Δw and the refractive index n ril of the raised index layer minimize an overlap of one or more modes of the plurality of pedestal modes with the core to reduce a probability of amplification of the pedestal modes without requiring extraction of said pedestal modes.

2. The multi-clad optical fiber according to claim 1 , wherein the diameter of the core is between about 10 μm and about 25 μm.

3. The multi-clad optical fiber according to claim 1 , wherein the diameter of the core is smaller than about 10 μm.

4. The multi-clad optical fiber according to claim 1 , wherein the core is made of silica and the at least one dopant material comprises ytterbium, erbium, thulium or a combination thereof.

5. The multi-clad optical fiber according to claim 4 , wherein the core is co-doped with at least one of aluminum oxide, phosphorus oxide, cerium oxide and fluorine.

6. The multi-clad optical fiber according to claim 1 , wherein the pedestal layer is made of silica doped with at least one index-raising dopant.

7. The multi-clad optical fiber of claim 6 , wherein the at least one index-raising dopant of the pedestal layer comprises germanium oxide, phosphorus oxide, aluminum oxide, titanium oxide or a combination thereof.

8. The multi-clad optical fiber according claim 1 , wherein the raised index layer is made of silica doped with at least one index-raising dopant.

9. The multi-clad optical fiber of claim 8 , wherein the at least one index-raising dopant of the raised index layer comprises germanium oxide, phosphorus oxide, aluminum oxide, titanium oxide or a combination thereof.

10. The multi-clad optical fiber according to claim 1 , wherein at least one of the core, the pedestal layer, the raised index layer, the inner cladding and the outer cladding has a non-uniform refractive index profile.

11. The multi-clad optical fiber according to claim 1 , having a V parameter of less than about 4.

12. The multi-clad optical fiber according to claim 1 , comprising a pair of stress-applying parts extending parallel to the core.

13. The multi-clad optical fiber according to claim 12 , wherein the stress-applying parts are enclosed within the inner cladding.

14. The multi-clad optical fiber according to claim 12 , wherein the stress-applying parts extend within the inner cladding and partially into the pedestal cladding structure.

15. The multi-clad optical fiber according to claim 1 , wherein the one or more modes of the plurality of pedestal modes having a minimized overlap with the core is an LP 11 -like mode.

Assignees

• Institut Nat Doptique

Inventors

• Proulx Antoine
• Roy Vincent
• Boivin Mathieu
• Taillon Yves

Classifications

• H01S3/06716

  Fibre compositions (per se C03C13/04)or doping with active elements (lasing materials in general H01S3/14) · CPC title

• H01S3/06754

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

• H01S3/06733 Primary

  Fibre having more than one cladding · CPC title

• H01S3/06712

  Polarising fibre; Polariser · CPC title

• G02B6/03627

  arranged - + · CPC title