Semiconductor laser device

A semiconductor laser device comprising:

• a compound semiconductor layer including an active layer emitting laser light, the compound semiconductor layer having a first mesa structure;
• and
• a silicon layer bonded with the compound semiconductor layer, a diffraction grating being provided on a surface of the silicon layer facing the compound semiconductor layer, the diffraction grating including a main diffraction grating and two sub-diffraction gratings, the main diffraction grating extending in a longitudinal direction of the first mesa structure, the sub-diffraction gratings being disposed on both sides of the main diffraction grating,
• wherein
• each of the main diffraction grating and the two sub-diffraction gratings is entirely disposed directly under the first mesa structure
• the main diffraction grating is disposed at a region containing a node of a first higher-order transverse mode of the laser light,
• each of the sub-diffraction gratings is disposed at a region containing a node of a second higher-order transverse mode of the laser light,
• and
• each of the sub-diffraction gratings is disposed with its period and phase substantially equal to those of the main diffraction grating.