Patent ID: 7474817

Claim:
An integrated optical waveguide comprising: a first optical waveguide formed on a semiconductor substrate; a second optical waveguide formed on said semiconductor substrate, and having a refractive index different from that of said first optical waveguide; and a semiconductor board disposed between said first optical waveguide and said second optical waveguide, and formed on said semiconductor substrate perpendicularly to the waveguide direction and separately from said first optical waveguide via a groove, wherein said groove is filled with a material whose refractive index differs from the refractive index of said first optical waveguide, said first optical waveguide and said semiconductor board have a same refractive index, and said second optical waveguide and said material filling said groove have a same refractive index, and wherein either of the following expressions holds, N 1 d 1 >λ/2 n, N 2 d 2 >λ/2 m, N 1 d 1 +N 2 d 2 <λ/4(2 l+ 1) (l, m and n are integers satisfying the relation n+m=l) or N 1 d 1 <λ/2 n, N 2 d 2 <λ/2 m, N 1 d 1 +N 2 d 2 >λ/4(2 l+ 1) (l, m and n are integers satisfying a relation of n+m=l−1) or where N 1 and d 1 are a refractive index and width of said groove respectively, N 2 and d 2 are a refractive index and thickness of said semiconductor board respectively, and λ is a wavelength of the waveguide light.