Optical transmission apparatus

A semiconductor laser device comprising:

• a striped optical waveguide structure composed of an active layer acting as a light-emitting layer, a diffraction grating acting as feedback means of a laser resonator provided in a waveguide of the laser light generated in the active layer, and a first barrier layer for adding sufficient energy to the carriers injected into said active layer to cause a voltage drop of 0.3 to 1.0 volts;
• a first and second cladding layer for sandwiching the optical waveguide structure;
• and
• a plurality of current injection regions arranged in the direction in which said laser light travels.

A semiconductor laser device comprising:

• a substrate;
• a first cladding layer in a projected shape provided on the substrate whose thermal conductivity is lower than that of the substrate;
• an active layer formed on the projected portion of the first cladding layer and acting as both a light-emitting layer and an optical waveguide layer;
• means for injecting current into said active layer;
• a second cladding layer provided on the active layer and, together with said first cladding layer, sandwiching said active layer;
• and
• a diffraction grating provided in a waveguide of the laser light generated in said active layer and acting as a distributed feedback resonator;
• wherein, when a thermal conductivity of the substrate is K.sub.s (w/(m.multidot.K)), a thermal conductivity of the first cladding layer is K.sub.1 (W/(m.multidot.K)), a thickness of the first cladding layer is d.sub.1 (m), a width of the second cladding layer is w (m), and a height of a part above the first clad layer is h (m), the following inequality is satisfied:
• C.multidot.h<K.sub.1 /d.sub.1 <K.sub.s /(2w) (I)
• where C=1.5.times.10.sup.11 (W/m.sup.3 K).

A semiconductor laser device comprising:

• a substrate;
• a heat flow delay layer provided on the substrate whose thermal conductivity is lower than that of the substrate;
• a first cladding layer provided on the heat flow delay layer which has a higher thermal conductivity than the heat flow delay layer and a narrower width than the substrate;
• an active layer formed on the first cladding layer and acting as both a light-emitting layer and an optical waveguide layer;
• a second cladding layer provided on the active layer and, together with said first cladding layer, sandwiching said active layer;
• and
• a diffraction grating provided in a waveguide of the laser light generated in said active layer and acting as a distributed feedback resonator.