RARE-EARTH DOPED FIBER, OPTICAL AMPLIFIER, AND METHOD FOR CONTROLLING OPTICAL AMPLIFIER
An optical amplifier of the present disclosure includes a rare-earth doped fiber including a plurality of cores, in which a v value of the plurality of cores of the rare-earth doped fiber is less than 2.405, the plurality of cores has a core pitch of a normalized coupling coefficient of 1.0×10 −3 or more, and on injection of excitation light into a clad part of the rare-earth doped fiber in a state of being bent at a predetermined bending radius, propagating light in the rare-earth doped fiber is amplified with mode-dependent gain characteristics dependent on the bending radius.
1 . A rare-earth doped fiber including a plurality of cores,
wherein
a v value of the plurality of cores is less than 2.405, and
the plurality of cores has a core pitch of a normalized coupling coefficient of 1.0×10 −3 or more.
2 . An optical amplifier comprising the rare-earth doped fiber according to claim 1 ,
wherein the optical amplifier amplifies propagating light in the rare-earth doped fiber, with mode-dependent gain characteristics dependent on a predetermined bending radius, on injection of excitation light into a clad part of the rare-earth doped fiber in a state of being bent at the bending radius.
3 . A method of controlling the optical amplifier according to claim 2 , the method comprising reducing the mode-dependent gain characteristics by bending at the predetermined bending radius.
4 . The method according to claim 3 , wherein the rare-earth doped fiber is a two-core erbium doped fiber having a core pitch ∧,
the method comprising controlling a bending radius R based on the following expression to keep the mode-dependent gain characteristics 0.1 dB or less:
R
=
a
Λ
+
b
a
=
-
3
2
.
7
3
7
v
2
+
145.97
v
-
154.36
b
=
474
.
1
9
v
2
-
2
0
6
7
.
2
v
+
2169.4
where v is the v value of the plurality of cores.
5 . The method according to claim 3 , wherein the rare-earth doped fiber is a two-core erbium doped fiber having a core pitch ∧,
the method comprising controlling a bending radius R based on the following expression to keep the mode-dependent gain characteristics 0.5 dB or less:
R
=
a
Λ
+
b
a
=
165
.
9
v
2
+
673.92
v
-
693.54
b
=
-
1
9
1
5
.
4
v
2
-
7935.6
v
+
8233.2
where v is the v value of the plurality of cores.