Semiconductor laser device, chip on submount, and semiconductor laser module

A semiconductor laser device of an edge emission type, where a waveguide mode is multi-mode, the semiconductor laser device comprising:

• a first facet of the waveguide on an emission direction front side, the first facet having a first width in a horizontal direction perpendicular to a longitudinal direction of the waveguide;
• and
• a second facet of the waveguide on an emission direction rear side, the second facet having the first width;
• and
• a current injection region from which current is injected into the waveguide, the current injection region having a width, in the horizontal direction, that is at least partially narrower, between the first facet on an emission direction front side and the second facet on an emission direction rear side, than a width, in the horizontal direction, of another region of the current injection region.