Patent ID: 8228966

Claim:
A semiconductor laser comprising: a substrate; and an active layer that is provided over said substrate, said active layer in a region near at least one end surface is alloyed by the diffusion of impurities, the band gap of said active layer in said region near said end surface is wider than that of said active layer in a region other than said region near said end surface, and wherein (λa−λw)>15 (nm) and Lt is less than 25 (μm), where “λw (nm)” is the wavelength of light corresponding to the band gap of said active layer disposed at a position within a distance of 2 μm from one end surface in a resonator direction, “λa” (nm) is the wavelength of light corresponding to the band gap of said active layer disposed at a position that is spaced a distance of equal to or more than ( 3/10)L and equal to or less than ( 7/10)L from said one end surface in a resonator direction, “L” is said resonator length, and “Lt” is the length of a transition region provided between the position of said active layer with a band gap corresponding to a light wavelength of λw+2 (nm) and the position of said active layer with a band gap corresponding to a light wavelength of λa−2 (nm) in said resonator direction.