Cascaded metasurface structures

Metasurfaces are well known as a single-layer subwavelength structure with superior capability in wavefront shaping, and cascaded metasurfaces with multi-layer structures resulting in compact optical devices will further improve the performance and also bring in new functionalities, such as image correction, optical transformation and processing. However, in order to realize such cascaded metasurfaces, a key issue is to achieve high precision alignment of the structures in each layer usually with large distance in between. Here we propose and experimentally confirm two schemes based on optical alignment and electron-beam alignment respectively to align the frontside and backside of a wafer in order to realize cascaded metasurfaces on these two sides. Except for cascaded metasurface structures, these approaches may also have a wide range of applications in need of other cascaded structures for specific functionality.