The semiconductor optical amplifier

In the present invention, an InP substrate (11) as a semiconductor substrate, presents a SOA polarization-independent made using GaInNAs introduced with tensile strain as the active layer (14). According to this configuration, to realize a polarization-independent through the introduction of tensile strain, also to achieve a high saturation optical output power by reducing the thickness of the active layer (14), nitrogen GaInAs (N) the active layer in use that the material of the active layer (14) is smaller to the gain peak wavelength band gap (14) is long wave of the GaInNAs with added, band filling at the time of high current injection into the active layer (14) there also exists, in particular to achieve the high gain in the C band and L band.