Patent ID: 7095940

Claim:
An optical fiber comprising: a first region provided in a center of the optical fiber, having a refractive index difference Δn 1 relative to a refractive index n 0 of silica and an outer diameter of a; a second region formed around said first region, having a refractive index difference Δn 2 relative to the refractive index n 0 of silica and an outer diameter of b; a third region formed around said second region, having a refractive index difference Δn 3 relative to the refractive index n 0 of silica and an outer diameter of c; a fourth region formed around said third region, having a refractive index difference Δn 4 relative to the refractive index n 0 of silica and an outer diameter of d; and a fifth region formed around said fourth region, having a refractive index difference Δn 5 relative to the refractive index n 0 of silica and an outer diameter of e, in which the refractive index differences Δn 1 through Δn 5 satisfy a relationship as follows: Δn 2 <Δn 4 <Δn 3 <Δn 1 Δn 1 , Δn 2 , Δn 3 , Δn 4 <0 Δn 5 >0.