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.
In recent years, the moiré imaging device has become one of the hot topics in the field of micro optics due to its strikingly visual three-dimensional (3D) effect which can be easily recognized by naked eye. Traditionally, the moiré imaging film is composed of the superposition of a microlens array(MLA)and a micro pattern array (MPA)with high alignment accuracy. By the combination of the nanoimprinting and nanoprinting techniques, we fabricated a moiré imaging film on a large-format substrate characterized by fluorescent enhancement effect under ultraviolet light illumination. By using a novel virtual mask technique, the MPA can contain more information than traditional one. It is worthy to note that the nanostructure is introduced to the MPA to promote the light efficiency of the fluorescent material. A synthetically magnified moiré image with 3D effect is demonstrated. The moiré imaging film has widely potential applications in 3D imaging, optical anti-counterfeiting, packaging, etc.
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