Patent ID: 7239784

Claim:
An optical fiber comprising: a center core provided in a center of the optical fiber, having a refractive index difference Δ 1 relative to a refractive index n 0 of silica and an outer diameter of A; a side core formed around said center core, having a refractive index difference Δ 2 relative to the refractive index n 0 of silica and an outer diameter of B; a first cladding formed around said side core, having a refractive index difference Δ 3 relative to the refractive index n 0 of silica; and a second cladding formed around said first cladding, and in which the refractive index differences Δ 1 through Δ 3 satisfy a relationship as follows: Δ 1 >Δ 2 >Δ 3 , where, −0.20%<Δ 1 <0.20%, −0.45%<Δ 2 <−0.05%, and −0.50% <Δ 3 <−0.20%, and wherein an absolute value of a dispersion value at 1,550 nm falls within a range of between 4 ps/nm 2 −km and 20 ps/nm 2 −inclusive, a dispersion slope at 1,550 nm falls within a range of between 0.05 ps/nm 2 −km and 0.08 ps/nm 2 −km inclusive, transmission loss at 1,550 nm is equal to or less than 0.2 dB/km, and an effective area A eff at 1,550 nm is equal to or more than 80 μm 2 .