Raman gain efficiency distribution testing method, and Raman gain efficiency distribution testing device

Patent metadata

Field	Value
Publication number	US-11519817-B2
Application number	US-201917268113-A
Country	US
Kind code	B2
Filing date	Aug 16, 2019
Priority date	Aug 16, 2018
Publication date	Dec 6, 2022
Grant date	Dec 6, 2022

Abstract

An object of the present invention is to provide a Raman gain efficiency distribution testing method and a Raman gain efficiency distribution testing apparatus for measuring a Raman gain efficiency distribution of a fundamental mode and a first high-order mode in a few-mode fiber. The Raman gain efficiency distribution testing method and the Raman gain efficiency distribution testing apparatus according to the present invention compute a Raman gain coefficient of a tested optical fiber from a Raman gain coefficient of a pure quartz core optical fiber at an excitation wavelength of 1 μm, a wavelength of excitation light, and a relative refractive index difference between a core and a clad at an arbitrary position z, compute electric field distribution overlap integrals at an arbitrary position z, between modes, of a mode field diameter of each mode at a wavelength of signal light, and a mode field diameter of each mode at a wavelength of excitation light; and compute the product of the Raman gain coefficient and the electric field distribution overlap integrals, and acquire Raman gain efficiencies, between modes, of the signal light and the excitation light at the arbitrary position z.

First claim

The invention claimed is:

1. A Raman gain efficiency distribution testing method, comprising using a computing processor to perform: on the basis of information of return light resulting from a test optical pulse being incident on a tested optical fiber and having a wavelength of signal light and a wavelength of excitation light that are shorter than an effective cutoff wavelength of the tested optical fiber,
a relative refractive index difference calculation procedure of acquiring a relative refractive index difference between a core and a clad at an arbitrary position z in a longitudinal direction of the tested optical fiber;
a mode field diameter calculation procedure of acquiring a mode field diameter of a fundamental mode and a mode field diameter of a first high-order mode at the arbitrary position z in the longitudinal direction of the tested optical fiber for each of the wavelength of the signal light and the wavelength of the excitation light;
a Raman gain coefficient computation procedure of computing a Raman gain coefficient of the tested optical fiber from a Raman gain coefficient of a pure quartz core optical fiber at an excitation wavelength of 1 μm, the wavelength of the excitation light, and the relative refractive index difference between the core and the clad at the arbitrary position z acquired in the relative refractive index difference calculation procedure;
an electric field distribution overlap integral computation procedure of computing an electric field distribution overlap integral at the arbitrary position z, between a set of modes and another set of modes, of the mode field diameter of a mode of the set of modes at the wavelength of the signal light and the mode field diameter of a mode of the other set of modes at the wavelength of the excitation light which are acquired in the mode field diameter calculation procedure, the set of modes and the other set of modes each including the fundamental mode and a plurality of the first high-order modes; and
a Raman gain efficiency computation procedure of computing a product of the Raman gain coefficient and the electric field distribution overlap integral to acquire a Raman gain efficiency, between a mode of the set of modes and a mode of the other set of modes, of the signal light and the excitation light at the arbitrary position z.

2. The Raman gain efficiency distribution testing method according to claim 1 , wherein the tested optical fiber is a quartz optical fiber in which GeO 2 is added to a core, and a Raman gain coefficient is computed according to equation C1 in the Raman gain coefficient computation procedure:

[

Math
.

C1

]



g
g

=

g
0

(

1
+

80
⁢
Δ

)

λ
P

(
C1
)

where g 0 is a Raman gain coefficient of a pure quartz core optical fiber at an excitation wavelength of 1 μm, Δ is a relative refractive index difference between a core and a clad, and λ p is a wavelength of excitation light.

3. The Raman gain efficiency distribution testing method according to claim 1 , wherein in the electric field distribution overlap integral computation procedure, the electric field distribution overlap integrals are computed according to equation C2 to equation C6:

[

Math
.

C2

]



F
11

=

2

π
[

w
1
2

(

λ
S

)

+

w
1
2

(

λ
P

)

]

(
C2
)

[

Math
.

C3

]



F
12

=

F
13

=

2
⁢

w
1
2

(

λ
S

)

π

Assignees

• Nippon Telegraph & Telephone

Inventors

• Nakamura Atsushi
• Okamoto Keiji
• Manabe Tetsuya

Classifications

• G01M11/319 Primary

  Reflectometers using stimulated back-scatter, e.g. Raman or fibre amplifiers · CPC title