A semiconductor laser basically includes a first cladding layer; an active layer; a second cladding layer; and a current constriction means for defining a current injection region in the active layer. The active layer has a gain region which acquires an optical gain by current injection thereto; a saturable absorption region in which current injection thereto little occurs and light effusion thereto occurs; and an outside region, being in contact with the saturable absorption region, in which current injection thereto little occurs and light effusion thereto little occurs. In this semiconductor laser, an effective band gap of the saturable absorption region is set to be larger than that of the outside region. With this configuration, carriers in the saturable absorption region are efficiently migrated to the outside region, so that the carrier lifetime in the saturable absorption region is actually shortened. As a result, the semiconductor laser can sustain the self pulsation at a high light output and a high operational temperature, and further can be produced with a good production yield.
A buried heterostructure quantum cascade laser structure uses reverse biased junction to achieve current blocking. Doping and ridge width of the structure may be adjusted to provide effective mode discrimination.
A Fabry-Perot laser generates a mode-locked channel having the same wavelength as that of light injected into the laser. The laser includes a semiconductor substrate and a lower cladding layer formed on the substrate. An active layer is formed on the lower cladding layer and has a band gap distribution that continuously varies in a longitudinal direction of the substrate. The laser further includes an upper cladding layer formed on the active layer and the lower cladding layer.
A digital optical communication method transmits an optical signal over a long distance with a reduced power penalty. The method has the step of shaping the waveform of the optical signal to be transmitted through the optical fiber to increase the frequency thereof before the waveform is stabilized when the optical signal starts increasing in level at the time the optical signal is applied to the optical fiber.
In a monolithic dual-laser semiconductor laser device capable of high power output, a window structure for each of laser elements is formed through a common step, thereby improving the device reliability. The semiconductor laser device has an infrared laser element li0 and a red laser element 120 monolithically integrated on an n-type semiconductor substrate i01. Each of the infrared and red laser elements 110 and 120 has a ridged waveguide and a window structure formed by Zn diffusion at each resonator facet. The infrared and red laser elements ii0 and 120 include p-type contact layers 109 and 119 on the ridges of the respective waveguides. The p-type contact layer 109 is thinner than the p-type contact layer 119.
There is provided a semiconductor laser device which is generally uniform in carrier concentration of a clad layer, almost free from strain, and less demanding for time and labor in its manufacturing, and which has stable characteristics. On an n-GaAs substrate, an n-type clad layer, an active layer, a p-type clad layer, and a cap layer are stacked one on another at a temperature of 700-750.degree. C. Widthwise both side portions of the cap layer as well as widthwise both side specified-depth portions of the p-type clad layer are removed by etching to form a ridge portion, and a current constriction layer is formed on widthwise both sides of the ridge portion. A flattening layer having a planar surface is formed on the current constriction layer and the cap layer by slow cooling LPE process at a temperature of 700.degree. C. or lower. On the flattening layer, a contact layer is formed by MOCVD process at a temperature of about 650.degree. C.
