Abstract
Optically variable devices (OVDs) enable the angle-dependent optical effect for anti-counterfeiting. This paper proposes a multi-image encoding strategy and demonstrates single-, two-, and three-layer OVDs using ultrasonic modulation cutting. An analytical model that incorporates the diffractive intensity spectrum, resonance characteristics of diffraction efficiency, and grating geometry is presented to accurately predict the apparent color information in hue, saturation and brightness. Ultrasonic modulation cutting is proposed for ultrafast pixel-level rendering by tuning the grating spacing. Two-layer image encoding is achieved by interlacing gratings with spatially separated diffractive spectra, while a layer of relief image is added for three-layer image encoding.
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