Low‐density diffractive optical memories for document security

Abstract

A low-density diffractive optical write-once, read multiple times memory (WORM) is demonstrated that authenticates and secures documents. Furthermore, by encoding the machine-readable optical code, information can be linked to the document. The proposed solution leads to a reliable, high security machine-readable information carrier that is fully compatible with the requirements of typical security docu- ments, such as payment substrates, fiduciary papers, passports, and identity cards. The information carrier is a juxtaposition of diffractive structures. Data are written permanently in an optical memory; the dif- fractive structure is changed irreversibly through the interaction of a dif- fractive surface with a beam of laser light. A prototype low-density optical memory based on diffractive structures that are resilient against copying or reorigination is realized for use in securing official travel documents. © 1996 Society of Photo-Optical Instrumentation Engineers.