Tapered-grating single mode lasers and method of manufacturing

A single mode distributed-feedback (DFB) waveguide comprising:

• a semiconductor active region;
• and
• a semiconductor cap stacked on top of the semiconductor active region, wherein semiconductor active region and semiconductor cap form a waveguide,
• wherein the waveguide includes a grating structure distributed along a sidewall of the waveguide, wherein the grating structure protrudes horizontally out of a side of the waveguide,
• wherein the grating structure comprises a tapered grating portion sandwiched between two uniform grating portions,
• wherein each of the uniform grating portions comprise a plurality of uniform ridges with approximately identical height which laterally protrude from the waveguide, and
• wherein the tapered grating portion comprises a plurality of tapered ridges which gradually increase in height from one end to an apex ridge and gradually decrease in height from the apex to the other end.