One aspect of the invention provides a method of fabricating a mode size converter. The method includes: exposing a photoresist-coated substrate to varying doses of light exposure to produce a profile in the photoresist of a beam mode size converter; and etching the photoresist-coated substrate to remove an equal thickness of the photoresist and substrate. The beam mode sized converter includes: a first surface having a first surface height and a first surface width; a second surface opposite the first surface, the second surface having a second surface height different than the first surface height and a second surface width different than the first surface width; and one or more boundary surfaces connecting the first surface and second surfaces.