Patent ID: 6970633

Claim:
A semiconductor optical device comprising: a waveguide layer including two cladding layers and an active layer sandwiched between the two cladding layers; and a reflecting multi-layer film including a plurality of layers and disposed on at least one of a pair of opposing end faces of the waveguide layer, wherein a summation Î£n i d i of products n i d i of refractive indexes n i and thicknesses d i for each of i layers of the reflecting multi-layer film, and wavelength Î» 0 of light guided through the waveguide layer satisfies Î£ n i d i >Î» 0 /4, and a first wavelength bandwidth Î”Î» is wider than a second wavelength bandwidth Î”Î›, the first wavelength bandwidth Î”Î» being a wavelength range including the wavelength Î» 0 in which a reflectance R of the reflecting multi-layer film is not higher than +2.0% of reflectance R at the wavelength Î» 0 , the second wavelength bandwidth Î”Î› being a wavelength range including the wavelength Î» 0 in which a reflectance Râ€² of a hypothetical layer is not higher than +2.0% from reflectance Râ€² at the wavelength Î» 0 of a hypothetical layer having a thickness 5Î» 0 /(4n f ), a refractive index n f , disposed on the at least one of opposing end faces, and satisfying R â€²=(( n c âˆ’n f 2 )/( n c +n f 2 )) 2 , where n c denotes an effective refractive index of the waveguide layer.