  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).
