Technique to reduce signal crosstalk between cores in a multi-core optical fiber transmission

1 . An optical transmission system that transmits signal light by using a multi-core optical fiber having two or more cores as transmission paths, the optical transmission system comprising:

two or more transmitters that transmit signal light to adjacent cores, in opposite directions; and

two or more pump light oscillators that inject pump light into the same cores as transmission cores to which the signal light is transmitted of the adjacent cores such that the pump light propagates in the same directions as or directions reverse to the directions of the signal light, and perform distributed Raman amplification of the signal light by using the pump light,

wherein a signal light gain of the signal light transmitted from the transmitters is set such that a ratio of signal intensity to a crosstalk noise intensity leaked from the adjacent transmission cores is maximized,

wherein a signal light gain G s of the signal light satisfies the following formula with respect to a transmission distance L of the adjacent transmission cores:

G

s

≤

1

⁢

2

.

1

-

1

⁢

8

.

1

×

1

⁢

0

3

⁢

L

-

1.9

.

2 . An optical transmission system that transmits signal light by using a multi-core optical fiber having two or more cores as transmission paths, the optical transmission system comprising:

two or more transmitters that transmit signal light to adjacent cores, in opposite directions; and

two or more pump light oscillators that inject pump light into the same cores as transmission cores to which the signal light is transmitted of the adjacent cores such that the pump light propagates in the same directions as or directions reverse to the directions of the signal light, and perform distributed Raman amplification of the signal light by using the pump light,

wherein a signal light gain of the signal light transmitted from the transmitters is set such that a ratio of signal intensity to a crosstalk noise intensity leaked from the adjacent transmission cores is maximized,

wherein signal light gains of the signal light in the adjacent transmission cores are G 1 and G 2 , and

the signal light gain G 1 satisfies the following formula with respect to a signal light gain difference ΔG, which is a difference of G 1 to G 2 , and the transmission distance L:

G

1

≤

-

2

.

0

+

0

.2

L

+

(

-

0.4

-

140.5

L

-

1.27

)

⁢

Δ

⁢

G

+

(

-

0

.

0

⁢

4

+

1

.

1

×

1

⁢

0

-

4

)

⁢

Δ

⁢

G

2

and

G

1

≥

(

-

0

.40

-

44

⁢

3

.

8

⁢

L

-

1.54

)

⁢

Δ

⁢

G

+

(

-

0

.10

-

8.

×

1

⁢

0

6

⁢

L

-

4

)

⁢

Δ

⁢

G

2

⁢

provided

⁢

ΔG

≥

0

.

3 . An optical transmission method of transmitting signal light by using a multi-core optical fiber having two or more cores as transmission paths, the optical transmission method comprising:

transmitting, by means of two or more transmitters, signal light to adjacent cores, in opposite directions; and

injecting, by means of two or more pump light oscillators, pump light into the same cores as transmission cores to which the signal light is transmitted of the adjacent cores such that the pump light propagates in the same directions as or directions reverse to the directions of the signal light, and performing distributed Raman amplification of the signal light by using the pump light,

wherein a signal light gain of the signal light transmitted from the transmitters is set such that a ratio of signal intensity to a crosstalk noise intensity leaked from the adjacent transmission cores is maximized high,

wherein a signal light gain G s of the signal light satisfies the following formula with respect to a transmission distance L of the adjacent transmission cores:

G

s

≤

1

2.1

-

18.

1

×

1

⁢

0

3

⁢

L

-

1

⁢

9

.