Patent ID: 8786941

Claim:
A semiconductor optical amplifier comprising: a laminated structure including (i) a first compound semiconductor layer that has a first conductivity type and is composed of GaN compound semiconductor, (ii) a second compound semiconductor layer that has a second conductivity type different from the first conductivity type and is composed of GaN compound semiconductor, and (iii) a third compound semiconductor layer that has a light amplification region composed of GaN compound semiconductor, the first compound semiconductor layer, the third compound semiconductor layer, and the second compound semiconductor layer being sequentially layered; a second electrode on the second compound semiconductor layer; and a first electrode electrically connected to the first compound semiconductor layer, wherein, the laminated structure has a ridge stripe structure, when a width of the ridge stripe structure in a light output end face is W out , and a width of the ridge stripe structure in a light incident end face is W in , W out >W in is satisfied, and a carrier non-injection region is provided in the laminated structure, the carrier non-injection region extending from the light output end face of the ridge stripe structure and towards the light incident end face of the ridge stripe structure along an axis line of the semiconductor optical amplifier, the first, second, and third compound semiconductor layers being present in the carrier non-injection region, and the second electrode not being present in the carrier non-injection region.