On-chip integration of achromatic metalens arrays

Broadband achromatic metalenses and metalens arrays hold promise for enabling high-performance optical imaging in a compact form factor. Conventional visible-light achromatic metalenses are composed of transparent and high-refractive-index TiO2 or GaN nanopillars, but are strongly limited in mainstream silicon-based complementary metal-oxide-semiconductor (CMOS) processes. Herein, we report the realization of high-efficiency Si3N4 achromatic metalenses in the visible range and demonstrate their integration onto a commercial imaging chip. By improving nanofabrication techniques, we have dramatically increased the aspect ratio of Si3N4 nanostructures from ~17 to a high value of 43.33. Consequently, the group delay of the Si3N4 nanostructures is significantly increased and the averaged focusing efficiency of a Si3N4 metalens with a numerical aperture of 0.155 reaches 80.39%. Owing to the CMOS-compatibility of Si3N4, such high-quality metalenses have been integrated with commercial imaging sensors and demonstrated the capability of full-color optical imaging. This research paves a critical step towards chip-integrated meta-devices.