| 摘要 |
A semiconductor optical device includes a waveguide layer and a reflecting multi-layer film. The waveguide layer includes two cladding layers and an active layer sandwiched between the two cladding layers. The reflecting multi-layer film including multiple layers is on at least one of a pair of opposing end faces of the waveguide layer. A summation Sigman<SUB>i</SUB>d<SUB>i </SUB>of products n<SUB>i</SUB>d<SUB>i </SUB>of refractive indexes n<SUB>i </SUB>and thicknesses d<SUB>i </SUB>of the layers denoted i in the reflecting multi-layer film, and a wavelength lambda<SUB>0 </SUB>of light guided through the waveguide layer satisfies a relationship, Sigman<SUB>i</SUB>d<SUB>i</SUB>>lambda<SUB>0</SUB>/4. A first wavelength bandwidth Deltalambda is wider than a second wavelength bandwidth DeltaLambda. Deltalambda is a wavelength range including the wavelength lambda<SUB>0 </SUB>in which a reflectance R of the reflecting multi-layer film is not higher than +2.0% from reflectance R at the wavelength lambda<SUB>0</SUB>. DeltaLambda is a wavelength range including the wavelength lambda<SUB>0 </SUB>in which a reflectance R' of a hypothetical layer is not higher than +2.0% from a hypothetical reflectance R' at the wavelength lambda<SUB>0 </SUB>of a hypothetical layer having a thickness of 5lambda<SUB>0</SUB>/(4n<SUB>f</SUB>), a refractive index n<SUB>f</SUB>, on the at least one of opposing end faces, and satisfying a relationship, R'=((n<SUB>c</SUB>-n<SUB>f</SUB><SUP>2</SUP>)/(n<SUB>c</SUB>+n<SUB>f</SUB><SUP>2</SUP>))<SUP>2</SUP>, where n<SUB>c </SUB>denotes an effective refractive index of the waveguide layer. |
