Semiconductor laser structure including quantum dot

A semiconductor laser structure, comprising:

• a first clad layer;
• a first ridge waveguide having a width W formed on the first clad layer, the width W corresponding to a resonance amplitude, wherein “0” and W are the two end positions of a width of the first ridge waveguide, and a lengthwise line along W/2 is the centerline of the first ridge waveguide, and a resonance axis is formed along the lengthwise direction of the first ridge waveguide;
• an active layer formed on the first ridge waveguide;
• a second ridge waveguide formed on the active layer;
• a second clad layer formed on the second ridge waveguide;
• an ohmic contact layer formed on the second clad layer;
• and
• a plurality of gratings formed in at least the first clad layer, making a predetermined angle with respect to the resonance axis of the first ridge waveguide such that the phase shift between the cross section of a grating and the width “0” W and the cross section of the corresponding grating and the width W/2 is λ/4, wherein a single-wavelength output is generated by destructive interference of an output of the semiconductor laser structure along “0” or W and an output of the semiconductor laser structure along W/2, wherein the gratings are periodically arranged in a longitudinal direction of the first ridge waveguide,
• wherein θ=tan−1(2W/λ), where the width W also denotes a resonance amplitude of the first ridge waveguide and λ denotes a wavelength.