Design and fabrication of ultrathin lighting responsive security device based on moiré imaging phenomenon

Security authentication of high- and low-value products is a pressing issue. Security technologies should be upgraded before they are counterfeited. In this study, an ultrathin lighting responsive moiré imaging device, which is different from traditional security device is developed for security authentication. Some interesting lighting responsive moiré imaging phenomena including light-activated three-dimensional floating imaging and light-controlled image transformation have been developed as covert security features for advanced authentication. These security features can be verified instantly using a point light source such as a white light-emitting diode configured in a smart phone. A compact defocus optical structure consisting of a micro lens-mirror array (MLMA) and a micro-pattern array is designed to fabricate the lighting responsive moiré imaging device. The structure makes the device ultrathin, which enables the easy integration of the device. The MLMA also overcame the difficulty in the fabrication of high numerical aperture micro-lens array required in traditional moiré imaging system. Flexible devices with 78-μm thickness were fabricated by photolithography, imprinting, and gravure-like techniques. Such thin device allows its potential integration with banknotes, currency, or other valuable documents/products.