Patent ID: 6931189

Claim:
An optical waveguide, comprising: a core; and a clad provided with a photonic crystal structure, wherein the photonic crystal structure of the clad is formed by a two-dimensional photonic crystal provided with a plurality of circular holes in which (r) denotes a radius of the circular hole and (a) denotes a distance between centers of the circular holes, and the effective refractive index of the clad is spatially varied by one of (A) changing the distance (a) from a region having a large mode field diameter to a region having a small mode field diameter when (r/a) is fixed, and (B) changing the radius (r) of the circular hole or the (r/a) from the region having the large mode field diameter to the region having the small mode field diameter, and by thickening the core from the region having the large mode field diameter to the region having the small mode field diameter.