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High‐Efficiency Optical Sparse Aperture Metalens Based on GaN Nanobrick Array

A flat and compact metasurface‐based optical metalens with superior performance can be widely used for focusing and imaging. However, the realization of a large‐aperture metalens, which is composed of billions of nanoscale building blocks, poses significant challenges for both process technology and manufacturing cost. Herein, an unconventional optical sparse‐aperture (UOSA) metalens is developed with a Wiener filtering algorithm to obtain a high‐quality image. The proposed UOSA metalens consists of three identical and concentric annular sectors sub‐aperture metalens based on a gallium nitride nanobrick array, which can effectively focus the unpolarized visible light into the same point. An effective aperture of 0.72 mm with lower cost is realized by utilizing less than 1/2 processing area. The experimental imaging results show that this all‐dielectric UOSA metalens with a diffraction‐limited resolution of 11.36 µm under 632.8 nm illumination is consistent with the simulated results. Furthermore, a relatively high focusing efficiency (≈51.2%) can also be achieved under the incident light of any polarization state. The approach with less area process, time‐saving, high efficiency, and large‐aperture characteristics offers vast potential applications in the fields of integrated optical systems, near‐eye imaging devices, and wearable optics.