A novel method for realizing multi-layer diffractive optical variable devices via oblique elliptical vibration texturing

Optically variable devices (OVD) are esteemed security elements renowned for their capacity to produce structural color effects reliant on multiple angle-dependent information channels. In this paper, based on the patterning of single-point diamond ultrasonic oblique elliptical vibration texturing, a novel strategy for micro/nano grating structure encoding for multi-layer high-definition structural color images is proposed and demonstrated. The innovation of this paper lies in the design of a rotating stable bracket equipped with ultrasonic vibration tool, allowing for the flexible adjustment of the tool angle to generate an oblique elliptical vibration texture. Firstly, this paper establishes a mathematical model of grating spatial diffraction, extending it from a two-dimensional plane to three-dimensional space, and determines the variation trend of grating diffraction efficiency in different directions within the spatial observation domain. Secondly, the relationship between grating and structural color is established via the micro-optical theoretical model, so as to determine the mapping between pixel color information and cutting velocity. Finally, single-point diamond ultrasonic oblique elliptical vibration texturing is used to achieve ultra-fast pixel-level drawing of sub-micron gratings with controllable spacing. Simultaneously, the tool deflects at set angles to machine grating structures for different images. This method flexibly controls the convergence direction of diffracted light, thereby realizing three-layer image encoding. The research results show that OVD exhibits the ability to selectively display target image information from various observation angles, indicating that the three-layer image encoding is decoupled.