SEMICONDUCTOR LASER

PURPOSE:To radiate a high output laser beam of basic mode and to obtain a semiconductor laser having a low threshold value by providing an active region having a refractive index distribution of small refractive index difference near the end face of a laser beam radiating side and a refractive index distribution of large refractive index difference in other region. CONSTITUTION:A thickness t2 is reduced and an equivalent refractive index difference N2 is increased in a region except the vicinity of a resonator end face 4, while a thickness t1 is increased and an equivalent refractive index difference N1 is decreased near the end face 4. Accordingly, a light enclosure to an active region 1 is improved in the region except the end face 4 of the laser light radiating side, a laser light containing a high order mode excited by the region except the vicinity of the end face having large refractive index difference near the end face 4 of the laser beam radiating side is converted to a basic mode, and then irradiated. Thus, the invasion of the laser beam to a low refractive index region 3 is increased and its optical density is decreased, and its output can be enhanced.