High-Numerical Aperture Metalenses with High Quality Factor

In highly resonant optical elements, attaining a high quality factor typically comes at the cost of limited spatial control over the wavefront. Here, we report on dielectric, higher-order Mie-resonant metasurfaces that break this paradigm by realizing high-numerical aperture wavefront manipulation with high-quality factors. Our structure consists of high-index dielectric nanoparticles exhibiting a spectrally overlapped electric dipole and electric octupole mode, which allows for local wavefront manipulation. By appropriately tailoring the nanoparticle dimensions over a range of 545 – 555 nm with a period of 736 nm, we imposed a paraboloidal phase profile at an interface to realize radial metalenses for operation at near-infrared wavelengths with linear TE or TM polarization. The structures were fabricated from an amorphous silicon thin film on a glass substrate by a single step electron beam lithography and dry etching process. We have experimentally demonstrated dielectric metalenses with numerical apertures of up to 0.8 and quality factors of up to 880, in some cases with diffraction-limited performance. Our findings represent a significant advancement compared to previous approaches that have been limited to low numerical apertures or one-dimensional wavefront manipulation.