Patent ID: 8837884

Claim:
An optical semiconductor device comprising: a spot-size converter formed on a semiconductor substrate, wherein the spot-size converter has a multilayer structure including a light transition region, wherein the multilayer structure comprises a lower core layer and an upper core layer having a refractive index higher than that of the lower core layer, wherein the width of the upper core layer is gradually decreased in the light transition region, wherein the width of the lower core layer is gradually increased in the light transition region, wherein both sides and an upper side of the multilayer structure are buried by a semi-insulating semiconductor layer in the light transition region, wherein light incident from one end section of the spot-size converter is propagated to the upper core layer, wherein the light transits from the upper core layer to the lower core layer in the light transition region, is propagated to the lower core layer, and is output from the other end section thereof, wherein the semiconductor substrate is n-type, and wherein the multilayer structure further comprises a first p-type semiconductor clad layer which is formed on an upper side of the upper core layer and a second p-type semiconductor clad layer which is formed on an upper side of the semi-insulating semiconductor layer in the light transition region.