Single etch fibre-to-chip grating couplers for high-volume production in SOI

Fibre-to-chip grating couplers are an efficient means for injecting and extracting light from silicon-wire waveguides. Here we present the design of single-etch couplers, based on effective media implemented with sub-wavelength gratings. We show that the pitch of these sub-wavelength structures can be increased to make their fabrication compatible with deep-ultraviolet lithography, without compromising their effective medium behavior. We experimentally demonstrate fully-etched grating couplers fabricated with DUV lithography.