Engineering the light coupling between metalens and photonic crystal resonators for robust on-chip microsystems

Abstract. We designed an on-chip transformative optic system with a broadband metalens coupler on a foundry compatible silicon photonic platform. By adjusting the on-chip metalens’ focusing length and mode dimension, the insertion loss between the metalens and the photonic crystal waveguide (PhC WG) structures is reduced to 2 dB by matching the mode on the metalens focal plane to the PhC WG mode. Alternatively, the integrated metalens allow for direct coupling from a multi-mode WG to the PhC cavity. The on-resonance transmission in a lens–cavity–lens microsystem achieves 60%. These micro-systems do not involve any single-mode silicon nanowire WG, and even a suspended PhC structure can be mechanically robust against vibrations. The proposed microsystem can be a new platform for miniaturized chemical and biosensor applications operating in air or solution environments.