Few-mode optical fiber

Patent metadata

Field	Value
Publication number	US-10459158-B2
Application number	US-201716072864-A
Country	US
Kind code	B2
Filing date	Jan 19, 2017
Priority date	Jan 28, 2016
Publication date	Oct 29, 2019
Grant date	Oct 29, 2019

Abstract

The refractive index of a fiber core of a few mode optical fiber is n1. A cladding layer surrounding the fiber core includes: a downward-concave cladding layer surrounding the fiber core, the refractive index thereof is n2; a first upward-convex cladding layer surrounding the downward-concave cladding layer, the refractive index thereof is n3; a second upward-convex cladding layer surrounding the first upward-convex cladding layer, the refractive index thereof is n4; an outer layer surrounding the second upward-convex cladding layer, the refractive index thereof is n5. The refractive indexes of the fiber core, the downward-concave cladding layer, the first upward-convex cladding layer, the second upward-convex cladding layer, the outer layer satisfy: n1>n3>n4>n5>n2. The fiber is a non-single mode in a direct waveguide state, and equivalent single-mode transmission can be achieved when the optical fiber is bent at a specific bending radius.

First claim

What is claimed is:

1. A few-mode optical fiber comprising:
a fiber core and a cladding layer surrounding the fiber core, wherein the refractive index of the fiber core is n 1 ;
the cladding layer comprising: a downward-concave cladding layer with a refractive index of n 2 surrounding the fiber core; a first upward-convex cladding layer with a refractive index of n 3 surrounding the downward-concave cladding layer, a second upward-convex cladding layer with a refractive index of n 4 surrounding the first upward-convex cladding layer, an outer layer with a refractive index of n 5 surrounding the second upward-convex cladding layer;
wherein the refractive indexes of the fiber core, the downward-concave cladding layer, the first upward-convex cladding layer, the second upward-convex cladding layer, and the outer layer satisfy: n 1 >n3>n 4 >n 5 >n 2 , the parameter between the fiber core and the downward-concave cladding layer is defined by F, with F=8.0 μm˜10.0 μm, where F=2(0.65+1.62V −3/2 +2.88V −6 )a 1 , and

V
=

2
⁢

⁢
π
⁢

⁢

a
1

λ
0

⁢

(

n
1
2

-

n
2
2

)

1
/
2

,

 where V denotes the normalized frequency, a 1 denotes the core radius, and λ 0 =1310 nm and 2.9<V<5.

2. The few-mode optical fiber according to claim 1 , wherein the optical fiber has a cutoff wavelength of more than 1.625 μm.

3. The few-mode optical fiber according to claim 1 , wherein the refractive index of the first upward-convex cladding layer meet the condition of n 3 <n 01 /(1+0.78d c /R b ), where n 01 =n 2 (1+(1.1428−0.9960/V) 2 (n 1 −n 2 )/n 1 )) and the normalized frequency:

V
=

2
⁢

⁢
π
⁢

⁢

a
1

λ
0

⁢

(

n
1
2

-

n
2
2

)

1
/
2

;

where d c is defined as the center distance between the fiber core and the first upward-convex cladding layer with d c =a 1 +a 2 +a 3 /2, and R b =7.5 mm; where a 2 , a 3 are the radial width of the downward-concave cladding layer and the first upward-convex cladding layer, respectively.

4. The few-mode optical fiber according to claim 1 , wherein the index difference between the fiber core and the downward-concave cladding layer in the optical fiber falls within the following ranges: 0.015≥n 1 −n 2 ≥0.0051; the index difference between the downward-concave cladding layer and the first upward-convex cladding layer falls within the following ranges: 0.006≥n 3 −n 2 ≥0.0015; the index difference between the first and second upward-convex cladding layers falls within the following ranges: 0.002≥n 3 −n 4 >0; and the index difference between the downward-concave cladding layer and the outer cladding layer falls within the following ranges: 0.004≥n 5 −n 2 ≥0.001.

5. The few-mode optical fiber according to claim 1 , wherein core radius a 1 , width of the downward-concave cladding layer a 2 and radial thickness of first upward-convex cladding layer a 3 fall within the following ranges: 7.5 μm≥a 1 ≥4 μm, 8.5 μm≥a 2 ≥3.6 μm, and 15 μm≥a 3 ≥5.5 μm.

6. The few-mode optical fiber according to claim 1 , wherein radial widths of the first upward-convex cladding layer and the second upward-convex cladding layer should meet the condition of 4≥a 3 /a 4 ≥2, where a 4 is the radial width of the second upward-convex cladding layer.

7. The few-mode optical fiber according to claim 1 , wherein the second upward-convex cladding layer has a parabolic structure, the refractive index distribution of the second upward-convex cladding layer at the radius r of the optical fiber satisfies:
n ( r )=√{square root over ( n 4 2 −( n 4 2 −n 5 2 )(( r−a 1 −a 2 −a 3 )/ a 4 ) 2 )}, where a 1 +a 2 +a 3 +a 4 ≥r≥a 1 +a 2 −a 3 .

8. The few-mode optical fiber according to claim 1 , wherein the bending loss of the LP 01 mode in the optical fiber at a wavelength of 1550 nm is less than 0.01 dB/turn for bending radius R b ≥7.5 mm, and the bending loss of the LP 11 mode in the optical fiber is larger than 1 dB/turn for bending radius R b <10 mm.

9. The few-mode optical fiber according to claim 1 , wherein the mode field diameter F of the optical fiber at a wavelength of 1310 nm is 8.6 μm˜9.5 μm.

Assignees

• State Grid Jiangxi Electric Power Company Information & Telecommunication Branch
• State Grid Corp China
• Univ Jiangsu

Inventors

• Wang Hua
• Chen Mingyang
• Yin Ping
• Li Luming
• Wei Jin
• Yang Jihai
• Cai Zhimin
• Zhu Yuanfeng
• Tian Hui

Classifications

• G02B6/03661 Primary

  having 4 layers only · CPC title

• G02B6/02047

  Dual mode fibre (G02B6/105 takes precedence) · CPC title

• G02B6/02009 Primary

  Large effective area or mode field radius, e.g. to reduce nonlinear effects in single mode fibres · CPC title

• G02B6/028

  with core or cladding having graded refractive index {(G02B6/02033, G02B6/02295 take precedence)} · CPC title

• G02B6/036

  core or cladding comprising multiple layers {(multicore optical fibres G02B6/02042; microstructured properties G02B6/02295; omniguide fibres G02B6/023)} · CPC title