Illusion Optics via Phase-Gradient Metasurfaces

Optical phase-gradient metasurfaces have garnered significant attention for enabling flexible light manipulation, with applications across diverse domains. In this work, we will demonstrate that the metasurfaces with phase gradient modulation can be used to achieve illusion optics, featured with the advantages of simple geometric structure and feasible implementation compared with the well-known transformation optics method. The underlying mechanism is anomalous diffraction law caused by the phase gradient, which provides a theoretical basis for freely manipulating the propagation path of light. By considering a specific example, we will demonstrate that the phase gradient can transform the spatial coordinates in the real space into the illusion space, thereby converting a plane in the real space into a curved surface structure in the illusion space to achieve the illusion effect. This approach provides a viable alternative to transformation optics for designing illusion devices.