Patent ID: 7787732

Claim:
An optical fiber, made of silica-based glass, comprising: a core including a first core having a diameter “a” of 5.3 μm to 9.4 μm and a second core that surrounds the first core, the second core having a diameter “b” of 13.0 μm to 21.9 μm; and a cladding, the optical fiber having a mode field diameter of 5.5 μm or larger at a wavelength of 1100 nm, transmitting light with a wavelength of 1100 nm in a single mode, and having a bending loss of 1 dB/turn or smaller at a wavelength of 1100 nm when the optical fiber is bent with a curvature radius of 2 mm, wherein the core has a refractive index profile with a relative refractive index difference (Δ1) of the first core with respect to the cladding being 0.6% or larger, and a relative refractive index difference (Δ2) of the second core with respect to the cladding being −0.02% or smaller.