Tri-Functional Metasurface for Phase, Amplitude, and Luminescence Control

TL;DR

This paper presents a metasurface capable of controlling phase, amplitude, and luminescence simultaneously, enhancing optical anti-counterfeiting security by integrating multiple optical responses into a single device.

Contribution

The work introduces a novel anisotropic gap-plasmon metasurface that combines multiple optical functionalities, including color, holography, and luminescence, with unclonable features for security applications.

Findings

Achieved simultaneous control of phase, amplitude, and luminescence.

Enabled generation of multiple optical responses with simple equipment.

Created a physically unclonable fingerprint using nanoparticle distribution.

Abstract

In optical anti-counterfeiting, several distinct optically variable devices (OVDs) are often concurrently employed to compensate for the insufficient security level of constituent OVDs. Alternatively, metasurfaces that exhibit multiple optical responses effectively combine multiple OVDs into one, thus significantly enhancing their security and hindering fraudulent replication. This work demonstrates the simultaneous control of three separate optical responses, i.e., phase, amplitude, and luminescence, using anisotropic gap-plasmon metasurfaces. Due to the incorporated geometric anisotropy, the designed structure exhibits distinct responses under x- and y-polarized light, revealing either a color image, or a holographic projection in the far field. Furthermore, inserting upconversion nanoparticles (UCNPs) into the dielectric gaps of the structures, the designed metasurface is able to generate a third luminescent image upon illumination with the near-infrared light. The stochastic distribution of the UCNPs constitutes a unique fingerprint, achieving a physically unclonable function (PUF) layer. Crucially, our triple-mode metasurface requires only readily attainable equipment such as a macro-lens/camera and a laser pointer to read most of the channels, thus paving the way towards highly secure and easy-to-authenticate metasurface-driven OVDs (mOVDs).