Mixed amplitude- and phase-encryption digital processor

JOHN FREDY BARRERA; RODRIGO HENAO; MYRIAN TEBALDI; ROBERTO TORROBA; NESTOR BOLOGNINI

Campinas (San Pablo, Brasil)

Congreso; VI Reunión Iberoamericana de Óptica (VI RIAO) y IX Encuentro Latinoamericano de Óptica, Lásers y sus Aplicaciones (IX OPTILAS); 2007

Instituto de Física Gleb Wataghin (IFGW) - UNICAMP

We introduce the simultaneous use of a phase- and amplitude-encrypting mask in a classical 4f encrypting architecture. This encrypting mask o®ers a new alternative of multiplexing di®erent input objects without changing the original phase mask. We encrypt and multiplex the images by means of a ground glass covered with amplitude screens. We can design these screens with di®erent degrees of complexity. Modifying or changing the amplitude mask is equivalent to present di®erent encoding masks in the same architecture, provided the alteration is enough to produce a result equivalent to generate a decorrelation among these masks. We employ a digital phase conjugation setup to generate the recovering wavefronts. Only by knowing the right amplitude screens allows the appropriate retrieval of the true encoded information separately. To secure the information data from unauthorized users we add some trivial images to what appears to hackers as information. In this way, the publicly delivered content images looks just like ordinary pictures, though some random noise is present as background. The absence of the amplitude mask or a slight mispositioning of it, prevents the correct retrieving of the multiplexed images. In addition, a small change in the optical parameters (wavelength, geometrical distances, etc) also yields an unrecognizable image. We carried out digital experiments to demonstrate the feasibility of our proposed technique.