Patent ID: 8811784

Claim:
An optical fiber that propagates light over a use wavelength bandwidth of 100 nm or wider in a plurality of propagation modes, comprising: a core portion including a center core portion and an outer core portion that is formed around the center core portion and has a refractive index lower than a maximum refractive index of the center core portion; and a cladding portion that is formed around the core portion and has a refractive index lower than the maximum refractive index of the center core portion and higher than the refractive index of the outer core portion, wherein a confinement loss is equal to or less than 1 dB/km in three or fewer of propagation modes over the use wavelength bandwidth, a bending loss is equal to or less than 100 dB/m in each of the plurality of propagation modes over the use wavelength bandwidth when the optical fiber is bent at a diameter of 20 mm, a relative refractive-index difference Δ1 of the center core portion to the cladding portion is 0.33% to 0.46%, a relative refractive-index difference Δ2 of the outer core portion to the cladding portion is equal to or greater than −0.1% and less than 0%, a diameter of the center core portion is 11.8 μm to 17.2 μm, and a ratio of an outer diameter of the outer core portion to a diameter of the center core portion is equal to or greater than 2.0 and equal to or less than 3.0.