Photopolymer based holographic variable data storage system for security applications

摘要

Photopolymer based microholograms are gaining much importance in the field of security imaging, product authentication and prevention of document forgery. Security holograms, mass produced through soft or hard embossing, from electroformed metal master holograms are not amenable to store and retrieve variable data. On the other side, rapid developments in optical and digital technologies result in large scale counterfeiting of conventional security holograms and look-alike holograms of great exactitude is becoming a real threat to original manufacturers. In contrast to conventional recording materials, photopolymer holograms do not need wet processing. They are amenable to replication and, at the same time, can hold variable data. This, apart from security at various levels, facilitates machine readability, automation, easy tracking and effective maintenance of inventory. This paper presents design, development and performance evaluation of a photopolymer based holographic variable data storage system for security applications. A liquid crystal spatial light modulator (SLM) is used to create a modulated optical data beam that varies from hologram to hologram. Photopolymer films in tape form are applied for continuous recording of micro-holograms, synchronous with the variable data content. This is a novel, but simple data storage system and can be used to give added security, in conjunction with conventional holograms. Easy and on site verification by applying special reading devices and dedicated software is the other charm of the proposed system. Moreover, for added protection, variable key based data encryption can be applied effectively. System parameters like diffraction efficiency, recording speed, preprocessing requirements etc. are analyzed and the response of the photopolymer material is also evaluated.