Narrow-linewidth distributed feedback semiconductor laser and preparation method thereof

The invention provides a distributed feedback semiconductor laser which sequentially comprises an N-surface electrode layer, a substrate layer, a buffer layer, a lower waveguide layer, an active layer, an upper waveguide layer, a secondary epitaxial grating layer, an etching self-stop layer, a cladding layer, an ohmic contact layer, a passivation layer and a P-surface electrode layer from bottom to top. The cladding layer and the ohmic contact layer form a waveguide structure, and the waveguide structure is a ridge waveguide structure. An upper grating structure and a lower grating structure in the vertical direction are used for jointly feeding back mode selection. Secondary epitaxial gratings distributed near the active region are efficiently coupled with a light field so that frequencyselection and line width reduction are realized. The single reflection peak line width of the electrode sampling grating is narrow, the electrode sampling grating is fully coupled with a light field in the waveguide for feedb