Optical fiber
An object of the present invention is to achieve a low delay core applicable to a Master channel of a Master-Slave CPE (MS-CPE) transmission method with a general-purpose refractive index distribution structure. An optical fiber according to the present invention is a single-mode optical fiber, and has an SI-type refractive index distribution structure, in which a clad region relative refractive index difference Δ (%) with respect to a core region refractive index, a radius a (μm) of the core region, and a group delay time difference Δ τ between the Master channel and the Slave channel satisfy “Mathematical Expression 19” and “Mathematical Expression 20”, or has a W-type refractive index distribution structure, in which a mode field diameter MFD is 9.5 to 10.1 μm, and a relative refractive index difference Δ 1 (%) of a low refractive index layer with respect to a core, a relative refractive index difference Δ 2 (%) of the clad region with respect to the core, the core radius a 1 , and the group delay time difference Δ τ between the Master channel and the Slave channel satisfy “Mathematical Expression 41”.
1 . An optical fiber provided in an optical communication system of a master-slave carrier-phase-estimation transmission method, the optical fiber comprising
a core having a radius a (μm) for a master channel and a clad having a relative refractive index difference Δ (%) with respect to the core, the core and the clad having a step index (SI) type refractive index distribution structure and satisfying Mathematical Expression C1,
[Mathematical Expression C1]
−1.05+0.37 a− 0.05 a 2 <Δ<−1.02+0.26 a− 0.02 a 2
and
Δ>4.23+7.37Δτ+3.81Δτ 2 −(3.15+4.77Δτ+2.47Δτ 2 ) a +(0.52+0.77Δτ+0.40Δτ 2 ) a 2 (C1)
where Δτ (ns/km) is a group delay time difference between the master channel and a slave channel, and is a value that satisfies Mathematical Expression C2,
[
Mathematical
Expression
C2
]
Δ
τ
≤
-
s
L
×
10
3
(
C2
)
where s (μs) is a signal arrival time difference when an optical signal is transmitted through the master channel and the slave channel of the optical communication system, and L (km) is a transmission distance of the optical signal.
2 . The optical fiber according to claim 1 , wherein a refractive index of the core is lower than a refractive index of pure silica glass.
3 . The optical fiber according to claim 1 , wherein
a refractive index of the core is lower than a refractive index of pure silica glass,
the radius a (μm) satisfies Mathematical Expression C4,
the group delay time difference Δτ min (nm/km) that is minimum satisfies Mathematical Expression C5, and
a relative refractive index difference Δ F (%) of the core with respect to the pure silica glass satisfies Mathematical Expression C6,
[Mathematical Expression C4]
−4.4+0.8MFD< a <−1.2+0.6MFD (C4)
[Mathematical Expression C5]
Δτ min =−18.93+7.00×10 3 MFD −3.30 (C5)
[Mathematical Expression C6]
0.98−0.06MFD−(0.42+0.03MFD) a −(0.04+0.002MFD) a 2 <Δ F <0.03+1.16×10 3 MFD −3.47 +0.02Δτ−(0.01+1.88×10 5 MFD −5.09 ) a +(0.64×10 −3 +1.89×10 4 MFD −7.16 ) a 2 (C6)
where MFD is a mode field diameter (μm) of the core.
4 . The optical fiber according to claim 1 , further comprising
a plurality of cores, wherein
one of the plurality of cores is the core for the master channel.
5 . An optical fiber provided in an optical communication system of a master-slave carrier-phase-estimation transmission method, the optical fiber comprising
a core having a radius a 1 (μm) for a master channel, a low refractive index layer surrounding a periphery of the core and having a relative refractive index difference Δ 1 (%) with respect to the core, and a clad having a relative refractive index difference Δ 2 (%) with respect to the core, wherein the core, the low refractive index layer, and the clad have a W-type refractive index distribution structure and satisfy Mathematical Expression C3,
[Mathematical Expression C3]
0.23+0.66MFD−3.33(μ 2 /Δ 1 )< a 1 <0.13(Δ 2 /Δ 1 )+(1.11−0.14MFD)Δτ+0.10−0.41MFD (C3)
where MFD is a mode field diameter (μm) of the core, and Δτ (ns/km) is a group delay time difference between the master channel and the slave channel and is a value that satisfies Mathematical Expression C2,
[
Mathematical
Expression
C2
]
Δ
τ
≤
-
s
L
×
10
3
(
C2
)
where s (μs) is a signal arrival time difference when an optical signal is transmitted through the master channel and the slave channel of the optical communication system, and L (km) is a transmission distance of the optical signal.
6 . The optical fiber according to claim 5 , wherein a refractive index of the core is lower than a refractive index of pure silica glass.