Highly-efficient grating couplers based on transfer-printing technology

We propose a new approach that allows highly efficient fiber-to-chip coupling using transfer-printing technology. The novelty of the approach relies on the integration of a mirror between a top (source) grating coupler circuit and a bottom (target) photonic integrated circuit (PIC) and on a wide directional coupler to transfer the light between the two waveguide layers before tapering the waveguide to single mode widths. We propose an apodized, partially etched, grating coupler integrated with a directional coupler implemented in amorphous Si, while a crystalline 220nm Silicon-on-Insulator (SOI) platform is used for the target PIC. We achieve a simulated 2D coupling efficiency of 96.2% (-0.17 dB) with a 1 dB bandwidth of 45 nm. The bandwidth takes into account the broadband directional coupler, which is very compact. The alignment tolerance along the direction orthogonal to the light propagation is better than +/- 2 μm to achieve an insertion loss penalty lower than 1 dB, which is well within reach with transfer printing