Patent ID: 8824842

Claim:
An optical semiconductor device fabrication method, comprising: forming a first semiconductor layer and a first diffraction grating layer above a substrate; forming a grating pattern mask above the first diffraction grating layer, the mask including a plurality of stripes spaced from each other along a first direction; etching the first diffraction grating layer exposed in the grating pattern mask; etching the first semiconductor layer exposed in the grating pattern mask to form a plurality of ridges in the first semiconductor layer along the first direction; forming a second semiconductor layer on a bottom surface of one of a plurality of first grooves formed between adjacent ones of the plurality of ridges in the first semiconductor layer; removing the grating pattern mask before or after the step of forming the second semiconductor layer; selectively forming a second diffraction grating layer dominantly in second grooves in the second semiconductor layer, the second grooves in the second semiconductor layer being above the first grooves between the ridges, the second diffraction grating layer having a refractive index different from a refractive index of the second semiconductor layer; and forming a third semiconductor layer on diffraction gratings included in the first and the second diffraction grating layers and on the second semiconductor layer.