Patent ID: 6907057

Claim:
A semiconductor optical device, comprising: a semiconductor optical element; and a nonreflective film receiving light emitted from said semiconductor optical element and in which incident light interferes with reflected light of a certain wavelength bringing reflectance of the light to substantially zero, wherein said nonreflective film includes a plurality of films, each film having a refractive index higher than 1, said plurality of films include a high-refractive index film having a refractive index higher than a square root of an effective refractive index of said semiconductor optical element, and a low-refractive index film having a refractive index lower than the square root of the effective refractive index of said semiconductor optical element, each of said plurality of films includes a single composition, said plurality of films including at least three different compositions, and a real part and an imaginary part of an amplitude reflectance of said nonreflective film are respectively zero, as a whole.