New metasurface shows different images depending on light source

The three-channel device is an advance with potential applications in anticounterfeiting, or to offer a new way of securely delivering encrypted information.

“Metasurfaces are artificial materials with tiny nanostructures that can be used to manipulate light,” said research team member Qi Dai. “In this work, we exploited both the size and orientation of the nanostructures to design a metasurface with three working modes.”

The team’s work is described in Optics Express. They also showed that the metasurface would generate a holographic image or a structural-colour nanoprinting image with or without polarisation-dependent watermarks.

“Our tiny metasurface could be easily attached to currency, ID cards, credit cards, certificates, watches or rings for anticounterfeiting,” Dai said in a statement. “Because this multi-functional metasurface features twofold safeguards, it could provide a simple but effective approach to fight against counterfeiting.”

Metasurface-based anticounterfeiting devices have been developed, but the hidden information is usually retrieved either on the surface or via a far-field holographic image. To create a more secure three-channel metasurface, the researchers merged watermarked structural-colour nanoprinting with holographic imaging into a device, which is made of tiny nanobricks arranged on a transparent substrate.