Few mode optical fibers for space division multiplexing

Patent metadata

Field	Value
Publication number	US-9638856-B2
Application number	US-201315023028-A
Country	US
Kind code	B2
Filing date	Sep 20, 2013
Priority date	Sep 20, 2013
Publication date	May 2, 2017
Grant date	May 2, 2017

Abstract

The invention relates to an optical fiber comprising an optical core and an optical cladding surrounding the optical core, the optical core having a single α graded-index profile with α≧1, and the optical core having a radius R1 and a maximal refractive index n 0 , said optical cladding having a refractive index n Cl . Said optical cladding comprises a region of depressed refractive index n trench , having an inner radius R 2 , with R 2 ≧R 1 , and an outer radius R3, with R3>R2. According to embodiments of the invention, the α-value of said graded index profile and the optical core radius R 1 are chosen such that R 1 ≧13.5 μm and so as to satisfy a criterion C of quality. Thus, the invention provides a few-mode optical fiber, which allow guiding an increased number of LP modes as compared to prior art FMFs, while reaching the lowest Differential Mode Group Delay. The system reach is thus increased over prior art.

First claim

The invention claimed is:

1. An optical fiber comprising
an optical core and
an optical cladding surrounding the optical core, the optical core having a single α graded-index profile with α≧1, α being a non-dimensional parameter defining an index profile shape of the optical core, and the optical core having a radius R 1 and a maximal refractive index n 0 ,

wherein the optical cladding having a refractive index n Cl at an outer edge of the optical cladding,
wherein the optical cladding comprises a region of depressed refractive index, n trench being a trench, surrounding the optical core, said trench having an inner radius R 2 , with R 2 ≧R 1 , and an outer radius R 3 , with R 3 >R 2 ,
wherein the optical core radius R 1 , expressed in microns, of the optical fiber satisfies a criterion C of quality of optical communications defined by the following equation:

C
=

10
·

Max
⁢


DMGDs


(

R
1
2

·

Dn
1

)

3

where DMGD is the Differential Mode Group Delay between two guided modes in the optical fiber, where Max|DMGDs| is an absolute maximum value of DMGD between any combination of guided modes, expressed in ps/km, and where Dn 1 =n 0 −n Cl is a core-cladding index difference at λ=λ C , where λ c is a central transmission wavelength of an operating band of the optical fiber, in that the α-value of the graded index profile and the optical core radius R 1 such that R 1 ≧13.5 μm and C≦18, and
that the optical fiber guides at least 4 LP modes.

2. The optical fiber according to claim 1 , wherein said optical core radius R 1 is R 1 ≦20 μm.

3. The optical fiber according to claim 1 , wherein said trench satisfies the following: 55≦1000·|(R 3 −R 2 )·Dn 3 ·(R 1 2 ·Dn 1 )|≦150 where Dn 3 =n trench −n Cl is the trench-cladding index difference at λ=λ C , and wherein the radii R 1 , R 2 , and R 3 are expressed in microns.

4. The optical fiber according to claim 3 , wherein Dn 3 ≦−3.10 −3 .

5. The optical fiber according to claim 1 , wherein the fiber guides 4 to 16 LP modes.

6. The optical fiber according to claim 1 , wherein the fiber guides 6 to 16 LP modes.

7. The optical fiber according to claim 1 , wherein said optical core has a minimal refractive index n 1 =n Cl , and wherein said optical cladding also comprises an inner cladding layer directly surrounding said optical core, with an inner radius R 1 and an outer radius R 2 ≧R 1 , said inner cladding layer having a constant refractive index n 2 , such that n 2 ≠n Cl and n 2 >n trench .

8. The optical fiber according to claim 1 , wherein said optical core has a minimal refractive index n 1 ≠n Cl , and wherein said optical cladding further comprises an inner cladding layer directly surrounding said optical core, with an inner radius R 1 and an outer radius R 2 ≧R 1 , said inner cladding layer having a constant refractive index n 2 , such that n 2 =n 1 and n 2 >n trench .

9. The optical fiber according to claim 1 , wherein said optical core has a minimal refractive index that equals n Cl , and wherein said optical cladding further comprises an inner cladding layer directly surrounding said optical core, with an inner radius R 1 and an outer radius R 2 ≧R 1 , said inner cladding layer being an extension of said single α graded-index profile of said optical core, and wherein said inner layer has a minimal refractive index n 1 =n trench .

10. The optical fiber according to claim 1 , wherein the fiber supports four LP guided modes, and wherein Max|DMGDs|<10 ps/km at λ=λ C , and wherein Max|DMGDs|<20 ps/km for λε[λ C −δλ; λ C +δλ], where λ c is a central transmission wavelength of an operating band for which said optical fiber is intended and where 2δλ is a width of said operating band.

11. The optical fiber according to claim 1 , wherein the fiber supports six LP guided modes, and wherein Max|DMGDs|<15 ps/km at λ=λ C , and wherein Max|DMGDs|<30 ps/km for λε[λ C −δλ; λ C +δλ], where λ c is a central transmission wavelength of an operating band for which said optical fiber is intended and where 2δλ is a width of said operating band.

12. The optical fiber according to claim 1 , wherein the fiber supports nine LP guided modes, and wherein Max|DMGDs|<60 ps/km at λ=λ C , and wherein Max|DMGDs|<120 ps/km for λε[λ C −δλ; λ C +δλ], where λ c is a central transmission wavelength of an operating band for which said optical fiber is intended and where 2δλ is a width of said operating band.

13. The optical fiber according to claim 1 , wherein the fiber supports twelve LP guided modes, and wherein Max|DMGDs|<120 ps/km at λ=λ C , and wherein Max|DMGDs|<250 ps/km for λε[λ C −δλ; λ C +δλ], where λ c is a central transmission wavelength of an operating band for which said optical fiber is intended and where 2δλ is a width of said operating band.

14. The optical fiber according to claim 1 , wherein the fiber supports sixteen LP guided modes, and wherein Max|DMGDs|<250 ps/km at λ=λ C , and wherein Max|DMGDs|<500 ps/km for λε[λ C −δλ; λ C +δλ], where λ c is a central transmission wavelength of an operating band for which said optical fiber is intended and where 2δλ is a width of said operating band.

15. The optical fiber according to claim 14 , wherein λ c =1550 nm and δλ=20 nm.

16. The optical fiber according to claim 15 , wherein LP modes guided by said optical fiber have effective areas, A eff <350 μm 2 , and bend losses <50 dB/turn, at 10 mm bend radius at 1550 nm, and wherein LP leakage modes have leakage losses >0.5 dB/m, at λ=λ C .

17. An optical link comprising at least one optical fiber of claim 1 .

18. An optical system comprising at least one optical fiber of claim 1 .

Assignees

• Draka Comteq Bv

Inventors

• Sillard Pierre
• Molin Denis
• Bigot-Astruc Marianne

Classifications

• H04J14/00

  Optical multiplex systems · CPC title

• H04B10/2504

  Electricity · mapped topic

• G02B6/03627

  arranged - + · CPC title

• G02B6/0365

  arranged - - + · CPC title

• G02B6/0288 Primary

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