Patent ID: 7809227

Claim:
An optical fiber whose core diameter is 10 μm˜40 μm, wherein the optical fiber has at least two propagation modes in a wavelength over 1200 nm, and the optical fiber has a refractive index which is described below: n ( r )= n 1 [1-2Δ( r/a ) g ] 1/2 , 0≦ r≦a n ( r )= n 1 [1-2Δ] 1/2 , r≧a where, n 1 denotes a maximum refractive index at the core center, r denotes a radial distance from the core center to any point in the fiber, and g denotes a parameter showing a refractive index profile of a core, a denotes a core radius, and Δ denotes a parameter showing a difference between the maximum refractive index n 1 at the core center and a refractive index n 2 in a cladding, in which Δ is (n l -n 2 )/n l .