Semiconductor laser

A semiconductor laser comprising:

• a multi-quantum well layer included in a mesa structure;
• a buried layer comprising a semi-insulating semiconductor,
• wherein the buried layer is in contact with a first side and a second side of the mesa structure;
• a first cladding layer with a first conductivity type, under the mesa structure and the buried layer, wherein
• the first cladding layer has a lower refractive index than the multi-quantum well layer,
• the first cladding layer is one of a pair of first cladding layers, and
• a thickness of one of the pair of first cladding layers that is adjacent to the multi-quantum well layer is greater than a thickness of another of the pair of first cladding layers;
• a high refractive index layer configured to not absorb light oscillating in the multi-quantum well layer, under the mesa structure and the buried layer, below the first cladding layer, wherein:
• the high refractive index layer has a higher refractive index than the first cladding layer, and
• the high refractive index layer is one of a pair of high refractive index layers that are alternately stacked with the pair of first cladding layers;
• a diffraction grating layer at least partially constituting a diffraction grating capable of diffracting the light oscillating in the multi-quantum well layer,
• wherein the diffraction grating layer does not contact the high refractive index layer;
• a substrate with the first conductivity type, below the high refractive index layer;
• and
• a second cladding layer with a second conductivity type opposite to the first conductivity type, above the multi-quantum well layer.