Optical fiber

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 a1 (μm) for a master channel, a low refractive index layer surrounding a periphery of the core and having a relative refractive index difference Δ1 (%) with respect to the core, and a clad having a relative refractive index difference Δ2 (%) 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(μ2/Δ1)<a1<0.13(Δ2/Δ1)+(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
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• Expression
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• C2
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• Δ
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• τ
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• L
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• 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.