Patent ID: 7859746

Claim:
A semiconductor optical amplifier, comprising: a semiconductor substrate; and an active layer formed over said semiconductor substrate, wherein said semiconductor substrate includes InP, and said active layer includes GaInNAs having a tensile strain introduced thereinto, wherein resonance of light due to reflection of an incident signal light incident on a light incident end surface and on a light emission end surface of said active layer is suppressed, and amplified light emitted as an emission signal light from the light emission end surface exhibits a gain that is constant independent of a polarization state of the incident signal light, and wherein said active layer has a composition ratio of N to GaInNAs as a whole has a value ranging from not less than about 0.1% to not more than about 0.8%; and wherein an amount of the tensile strain of said active layer has a value ranging from not less than about 0.1% to not more than about 1.5%.