RESUMO
Under white light illumination, gratings produce an angular distribution of wavelengths dependent on the diffraction order and geometric parameters. However, previous studies of gratings are limited to at least one geometric parameter (height, periodicity, orientation, angle of incidence) kept constant. Here, we vary all geometric parameters in the gratings using a versatile nanofabrication technique, two-photon polymerization lithography, to encode hidden color information through two design approaches. The first approach hides color information by decoupling the effects of grating height and periodicity under normal and oblique incidence. The second approach hides multiple sets of color information by arranging gratings in sectors around semicircular pixels. Different images are revealed with negligible crosstalk under oblique incidence and varying sample rotation angles. Our analysis shows that an angular separation of ≥10° between adjacent sectors is required to suppress crosstalk. This work has potential applications in information storage and security watermarks.
RESUMO
Two-dimensional (2D) metasurfaces hold great promise to enable multiplexing and multifunctional optical devices due to their artificial freedom in design, device miniaturization, etc. Various multiplexing and multifunctional metasurfaces have been extensively studied, including polarization multiplexing, wavelength multiplexing, and orbit angular momentum (OAM) multiplexing. However, due to the lack of angular encoding freedom, angular multiplexing switchable nanoprinting has rarely been studied or demonstrated yet to the best of our knowledge. Here, we realize angular multiplexing switchable nanoprinting functionality with independent amplitude encryption based on visible-frequency metasurfaces. By screening a large number of structural designs and breaking the angular correlation, we eventually obtain optimal metasurface designs to realize dual-channel arbitrary image encryption. Furthermore, we illustrate that the proposed scheme would serve as an optical information concealment/retrieval strategy by combining the structural color and amplitude modulation. Overall, we believe that angular multiplexing metasurfaces would easily find promising applications, including optical information encryption/concealment, multifunctional switchable devices, and advanced eyeglass-free three-dimensional (3D) stereoscopic displays.