Optimized grating coupler with fully etched slots

A grating coupler with fully etched slots is optimized for fiber coupling into SOI slab waveguides. Such coupler can be produced in one lithography step together with other SOI components. Theoretical maximal coupling efficiency of 49% is demonstrated with a 3 dB bandwidth of 35 nm. Strong reflection from the fully etched grating was avoided through an antireflection interface. Constructive interference is used to decrease radiation into the substrate and the filling factor is optimized for optimal power coupling into the fiber mode. It was also demonstrated, that the chirped grating approach is inapplicable for fully etched gratings.