A Survey of Current Optical Security Techniques

In this paper, we describe two types of optical security devices: di ractive anti-counterfeiting devices such holograms and microgratings, and encryption techniques such as double-phase encoding and optoelectronic implementation of conventional algorithms. It is shown that holograms are more easily copied than is widely believed, though advanced techniques may soon make duplication far more di cult. Zero-order microgratings, which produce a distinctive red to green colour shift upon rotation about their own axis, are o ered as a more secure alternative that could gain ascendency. Double-phase encryption allows for simple encoding using a two-lens processor, as well as the possibility of denser holographic storage. Its security, however, is poor because of its linearity. Optoelectronic implementations of operations such as exclusive-or and bit-permutation, which are central to current cryptography, will allow faster parallel instantiations of algorithms for which the security is already well tested.