OPTICAL SEMICONDUCTOR DEVICE AND METHOD OF MANUFACTURING OPTICAL SEMICONDUCTOR DEVICE

There is provided a configuration which includes: a burying layer which has a current narrowing window where portions protruding onto a top part of a ridge stripe are opposed to each other with an interval therebetween narrower than a width of the top part; and a diffraction grating in which a λ/4 phase shifter is placed at an intermediate portion in a light traveling direction; wherein a sectional shape of the current narrowing window varies depending on a position in the light traveling direction so that, at a region where the λ/4 phase shifter is placed, a resistance of a current path from a second cladding layer to a first cladding layer through the current narrowing window is minimum.