Optical Image Multiplexing Encryption Using Digital Holography in a JTC Architecture Edgar Rueda 1 , John F. Barrera 1 , Rodrigo Henao 1 , Roberto Torroba 2 1. Grupo de Óptica y Fotónica, Instituto de Física, Universidad de Antioquia, A.A. 1226, Medellín, Colombia. 2. Centro de Investigaciones Ópticas (CONICET-CIC) and UID OPTIMO, Facultad de Ingeniería, Universidad de la Plata, P.O. Box (124) 1900, La Plata. elgaral@gmail.com , jbarrera@fisica.udea.edu.co , rhenao@fisica.udea.edu.co , robertot@ciop.unlp.edu.ar Abstract: An optical scheme that uses a digital holographic technique in a Joint transform correlator architecture to encrypt and decrypt images is presented. A filtering procedure is implemented to improve the multiplexing capabilities of the system. ©2009 Optical Society of America OCIS codes: (060.4785) Optical security and encryption, (070.0070) Fourier optics, (090.1995) Digital holography, (100.2000) Digital image processing. 1. Introduction Encryption and decryption of images using the double random phase encoding (DRPE) technique has arisen as a promising method for securing information. Among the alternative architectures that work with this technique, the Joint Transform Correlator (JTC) architecture [1] is attractive in the sense that it does not require the accurate optical alignment of methods like the 4f architecture [2], although it generates unwanted terms in the output. Digital holographic techniques have been implemented in different optical security systems. In particular, for the 4f architecture Nomura et al. [3] proposed a system for securing information using a digital holographic technique that allows the encrypted image to be stored, transmitted and decrypted digitally. Numerous multiplexing techniques to store multitude of images into a single storing device without cross talk have been proposed [4-6]. In some multiplexing techniques there are restrictions over the number of stored images due to the presence of background noise or limitations in the recording device. In this work we present: a system for securing information using a digital holographic technique in a JTC architecture, a filtering procedure to eliminate the unwanted terms in the output plane, and an increase in the number of recovered images in multiplexing techniques thanks to the elimination of the background noise. 2. Optodigital procedure for encryption and decryption of images The setup is basically a Mach-Zender with one arm corresponding to a JTC configuration and the other to a reference plane wave beam (Fig. 1). Plane O is the input plane where the image to be encrypted and the phase key are placed; plane K corresponds to the Fourier plane of the input plane where the recording device (CCD camera) is located. Fig1. Optical setup (Mach-Zender). B1 and B2 are beamsplitters, Plane O is the input plane, L is a positive lens, plane K is the joint power spectrum plane, f is the lens focal distance, M1 and M2 are mirrors. The encryption step is done optically. First, blocking the reference arm the Joint Power Spectrum (JPS) intensity pattern is stored using the CCD camera, thus storing the encrypted image; next, unblocking the reference arm the hologram of the Phase Key Fourier Transform (PKFT) is stored; and finally, the intensity of: the original image, the PKFT and the reference plane wave are recorded separately. The decryption step is done digitally. First, using the stored intensities, the noisy terms on the encrypted image and on the hologram of the PKFT are removed. These noise-free images are then multiplied and inverse Fourier transformed. The result will have four spatially differentiated terms, one corresponding to the original image. The spatial position of each term is controlled with the input plane windows separation (Fig. 1) and the angle of incidence of the reference plane wave. a357_1.pdf JTuB3.pdf © 2009 OSA/DH/FTS/HISE/NTM/OTA 2009 JTuB3.pdf