Hierarchical Metasurfaces with Significant Reductions in Aspect Ratio Based on Geometrically Compensated Phase

Abstract Since the groundbreaking demonstration one decade ago, metasurfaces have widely reformed applications with continuously extended scopes. Somewhat unexpectedly, traditional metasurfaces are usually confronted with problems of challenging fabrications due to the large height/width aspect ratio of unit cells to cover full phase range. Here, a concept of geometrically compensated phase is introduced. A microscale grating as primary structure is designed to provide π phase compensation, and the unit cells as secondary structure are only required to provide a phase delay of 0–π. As proofs‐of‐concept, beam deflection and focusing are demonstrated with all‐glass hierarchical metasurfaces. It is found that the metasurface beam deflectors maintain high efficiencies, while the maximum aspect ratio of the unit cell is significantly reduced from 23.4 and 30 to 8.4 and 8.7 by up to 71% for 5.04° and 3.78° beam deflectors, respectively. Furthermore, numerical investigations verify the hierarchical metasurfaces present good robustness to fabrication errors. The dependences of the proposed metasurfaces on the incident angle, operation wavelength, and grating height are analyzed quantitatively. The near‐diffraction‐limited focusing confirms the generic capability of this hierarchical metasurface besides beam deflections. This work represents an accessible design strategy for metasurfaces with broad material compatibility and promotes the advances of metasurfaces.