Optical data storage-readout based on fractal encrypting masks

MYRIAN TEBALDI; WALTER FURLAN; ROBERTO TORROBA; NÉSTOR BOLOGNINI

Sidney (Australia)

Congreso; 20th Congress of the International Commission for Optics; 2008

International Comission of Optics

We present a secure optical data storage-readout architecture based on a configuration of a Joint Transform Correlator (JTC), introducing key codes designed with fractal amplitude masks. The goal of information encryption is that one is able to encode information to be sent in such a way that it is difficult for unauthorized party to decode this information without having a proper key(s). In optics, the diffraction properties of fractal objects have been studied extensively ranging from simple one-dimensional objects to complex 2D systems, including fractal zone plates (FZP). A FZP is characterized by its fractal profile along the square of the radial coordinate. When illuminated by a parallel wavefront a FZP produce multiple foci, the main lobe of which coincide with those of the associated conventional zone plate but the internal structure of each focus exhibits a characteristic fractal structure, reproducing the self-similarity of the originating FZP. This contribution presents the use of a fractal zone plate acting as the normal encoding mask under joint transform correlator architecture. The complexity exhibited by fractal zone plates allows including them as secure keys that are an alternative to conventional random phase masks. In fact, their robustness and simplicity fulfill the encrypting masks requirements for high security and easiness respectively. In particular, there is no need for sending the fractal zone plate itself, but a simple set of parameters to reconstruct it, thus avoiding the sending of other complex phase masks, reducing the chance for losses in the transmission stage. In addition, they offer several advantages over previous proposals: they are very difficult to replicate, as they are diffractive optical elements, we can also manipulate the diffraction efficiency depending on the requirements of the optical systems, and they have the property of multiple keys in a single mask as extra security parameters. Both theoretical and experimental results back the soundness of our proposal.