Micro-transfer printed silicon nitride grating couplers for efficient on-chip light coupling

Abstract

We demonstrate a new post-processing approach to efficiently couple light in silicon nitride (Si3N4) photonic integrated circuits (PIC) via grating couplers. Thin-film coupons of apodised Si3N4 grating couplers functionalized with metallic bottom reflectors and adiabatic couplers are micro-transfer printed onto the input and output of Si3N4 waveguides, providing efficient coupling without jeopardizing the rest of the PIC. Two-dimensional FDTD simulations predict coupling efficiencies as large as 78% (-1.1 dB) at a wavelength of 785nm. As a proof-of-concept, we report an experimental coupling efficiency above -4.6 dB, which is almost 3 dB better than the values obtained with standard designs of grating couplers.