On-chip intra- and inter-layer grating couplers for three-dimensional integration of silicon photonics

We present on-chip intra- and inter-layer grating couplers fabricated on double-layer, single crystalline silicon nanomembranes. The silicon nanomembranes were fabricated using an adhesive bonding process. The grating couplers are based on subwavelength nanostructures operating at the transverse-electric polarization. Such nanostructures can be patterned in a single lithography/etching process. Simultaneous intra-layer coupling to separate silicon photonic layers is demonstrated through grating couplers with peak efficiencies of 18% and 44% per grating coupler for bottom and top layer, respectively, at 1550 nm wavelength. The inter-layer grating coupler has an efficiency of 25% at 1560 nm wavelength with a 3 dB bandwidth of 41 nm.