Optical Metasurfaces for Designing Planar Cassegrain-Schwarzschild Objectives

Reflective objectives are widely used in many imaging systems, but can hardly be compact, due to their curved mirrors. To address this problem, the authors planarize the mirrors in a Cassegrain-style objective by substituting geometric-phase-based flat metasurfaces for conventional curved mirrors. These reflective metasurface objectives are intrinsically free of residual light, and thus less demanding in terms of precision in illumination and nanofabrication, compared to refractive metalenses. This planar metasurface design can potentially reshape and simplify the core components of many microscopes and telescopes, and opens an avenue to ultracompact optics.