Adaptive printing using VO2 optical antennas with subwavelength resolution

Abstract

Adaptive pixel operating in the infrared region enables the encoding of invisible information and extraction using specific inputs. Recently, the formation of an adoptive image by utilizing VO2 having the property of phase transitions has been demonstrated. However, the improvement of its pixel resolution is challenging, and a simple geometry is needed to ensure accuracy and reproducibility of the optical function of the pixel; therefore, the proposal of a different working principle is required. Here, we demonstrate adaptive printing based on active tuning between Mie and plasmon resonances excited in VO2 nanostructures with subwavelength resolution. The dielectric constant of the fabricated VO2 changes from positive to negative at infrared wavelengths when the material is heated. By nanostructurizing and arranging VO2, Mie and plasmon resonances are excited at low and high temperatures, respectively, and the measured reflection spectra vary depending on the temperature. Using resonators with the tuning characteristics as pixels, we construct an image with high resolution exceeding 39 000 dpi at λ = 1.5 μm and demonstrate the concealment and extraction of encoded information. Our designed tunable pixels can be applied to functional devices, including tunable displays, anticounterfeiting, and clarifications.