SEMICONDUCTOR LASER

PURPOSE:To increase the intensity at a resonance frequency fr further, increase the limit frequency and realize a high speed operation by a method wherein an active layer is divided into a plurality of sections along the lateral direction perpendicular to the direction of a resonator and the lateral width including divided sections of the active layer is selected to be smaller than the oscillation wavelength. CONSTITUTION:If an InGaAsP active layer 10 is divided into a plurality of layers, movement of carriers toward the center part is suppressed and the lateral direction movement of the carriers is not induced even if the carrier concentration of the center part is reduced. Therefore, the limitation against the output increase at a resonance frequency is relieved and the light intensity at the resonance frequency can be further increased. Although the carrier concentration shows a distribution which is low at the center part, as the distribution of the light intensity is determined by a waveguide mode, a status wherein the light intensity is high at the center like with the conventional constitution is maintained and the lateral diffusion of the carriers is avoided. Therefore, the responsiveness at a relaxation frequency is improved accordingly and the light intensity at the relaxation frequency is increased so that a -3dB band can be extended to the higher frequency accordingly.