Tunable metamaterial enables on-chip optical encryption which hides, rewrites, and stores multilevel information using different light fields

https://www.eurekalert.org/news-releases/1105998

"coumarin-based metamaterial, dynamic control... text, watermarks, graphics invisible under white light/ revealed by specific UV... 60 second write/erase cycles without chemicals/ mechanical wear.... features small as 700 nm via 2-photon polymerization/ grayscale-gradient processing... independent optical channels as separate passwords for different data levels... contrast remains >3× after 20 write–erase loops, readable >10 days... banknotes, pharmaceuticals, ID chips with time-dependent codes... reconfigurable barcodes"