Development of Moiré imaging film based on diffraction grating

Abstract

Micro-nano optical device based on the moiré imaging effect has been widely used in the visual security and anticounterfeiting due to the unique visual effect. However, the micro-pattern array in the state-of-art moiré imaging device is based on nanoimprint lithography and the gravure printing technique which cannot achieve multi-color effect. Even worse, the volatile organic compounds in the printing ink does harm to the environment and human health. Therefore, it is urgently needed to develop a moiré imaging device free of ink. In this paper, we propose to integrate the diffraction grating into the moiré imaging device. Grating MPA is formed by rasterizing the micro-pattern array layer, and combined with the microlens array to construct a moiré imaging device, which was a hybrid refraction-diffraction structure. In the experiment, a diffraction grating with a period of 2 μm and a cylindrical lens array with a focal length of 90 μm were integrated on both sides of a 50 μm thick film to realize the imaging device. A formula that can predict the intensity of diffraction dispersion is derived, and the colorful moiré image related to the orientation of the grating and the position of the light source is achieved, in which the color can cover the whole visible spectrum under different viewing angle.