Patent ID: 7859745

Claim:
A semiconductor optical amplifying device, comprising: a semiconductor substrate; and an active layer provided over said semiconductor substrate, wherein an incident signal light being incident from a light incident end surface of said active layer is amplified to be radiated as a radiation signal light from a light radiation end surface of said active layer while suppressing resonances of the light caused by reflections at the light incident end surface and the light radiation end surface, and a gain that the radiation signal light achieves is kept constant without depending on a polarization state of the incident signal light; said semiconductor substrate is made of InP; and said active layer takes a multiple quantum well structure formed of a barrier layer made of GaInAs with tensile strain applied thereto and a well layer made of GaInNAs alternately laminated in one or a plurality of layers, wherein a range of the amount of compressive strain applied to the well layer is not less than 0.1% nor more than 0.3% and a range of the amount of tensile strain applied to the barrier layer is not less than 0.5% nor more than 1.2%.