Abstract

A focusing waveguide grating coupler (FWGC)^[1] implements simultaneously two optical functions. One is to couple out the guided-wave propagating in the waveguide structure; the other is to focus the outgoing beam into a small spot. Although combining two optical functions into a single diffractive optical element is quite attractive, the submicron feature sizes necessary to implement high–numerical–aperture focusing elements impose a significant burden on the lithography. Therefore, focusing waveguide grating couplers with high numerical aperture (NA> 0.25) have been rarely reported^[2]. Furthermore, fabrication of such FWGCs usually relies upon direct–write electron beam lithography.

© 1996 Optical Society of America