Nonlinear Optical Information Encoding with Grayscale Lithography Enabled Metasurfaces

Optical information encoding is promising for many applications in sensing, data storage, and computing. Recently, various strategies have been suggested to encode optical information in planar devices. Among these, optical metasurfaces represent a flexible platform for manipulating multiple degrees of freedom of light with subwavelength scale meta-atoms. However, to realize both amplitude and phase control of light with metasurfaces, usually multiple meta-atoms per unit cell are required, so information density will be greatly reduced. Here, we develop a novel approach of nonlinear optical information encoding with grayscale lithography enabled hybrid metasurfaces composed of gold plasmonic meta-atoms deposited on an epsilon-near-zero material. By controlling the spacer layer thickness with electron beam grayscale lithography and varying orientation angles of the meta-atoms, we can control at the single-pixel level both the amplitude and phase of the generated second-harmonic waves. The proposed method opens new avenues for developing advanced nonlinear nanophotonic sources.