Stepwise Dual‐Fabry–Pérot Nanocavity for Grayscale Imaging Encryption/Concealment with Holographic Multiplexing

Abstract Metal–insulator–metal (MIM) nanocavity, as a lossy Fabry–Pérot (FP) scheme, has been widely studied for color filter and perfect absorber functionality, which can be integrated into functional photonic devices. However, such triple‐layered MIM still lacks the ability to induce multiple intensity levels for meticulous grayscale imaging because of strong spectral sensitivity to cavity thickness variation. Moreover, the MIM stack remains unexplored to multiplex a near‐field nanoprinting and holographic imaging because it is challenging to break the mutual dependence relation between the intensity and phase shift. Herein, a new film stack of dual‐Fabry–Pérot (DFP) nanocavity is proposed to create triple‐fold freedom in light modulations: intensity, phase shift and operation wavelength, which can be respectively modulated by the top/bottom/total cavity length. By spatially arranging the stepwise nanocavities, the designed DFP pattern can show multiplexing dual‐channel imaging, which encrypts/conceals a grayscale nanoprinting image and simultaneously projects a far‐field holographic image. Such DFP strategy allows for new possibility of independent light modulation and creates new dimensional degree of freedom for thin‐film nanocavity. The proposed functional DFP strategy enriches the subwavelength building block design for metasurfaces and thin‐film stacks, which would promisingly empower advanced applications in information multiplexing, imaging encryption/concealing, and many other related fields.