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Applied Optics

Encrypted optical storage with angular multiplexing

Osamu Matoba, Bahram Javidi

Published Dec 10, 1999• 129 citations
Publisher

Abstract

We present the first, to our knowledge, demonstration of an encrypted optical storage based on double-random phase encoding by using angular multiplexing in a photorefractive material. Original two-dimensional data are encrypted by use of two random phase codes located in the input and the Fourier planes and are then stored holographically in a LiNbO(3):Fe crystal. The retrieval of the original data can be achieved with a phase-conjugated readout scheme. We demonstrate the encryption and the decryption of multiple frames of two-dimensional digital data by using angular multiplexing. We also evaluate numerically the influence of the bandwidth of the optical system on the decrypted digital data. The bit error rate as a function of the optical system bandwidth is presented.

DOI
10.1364/ao.38.007288

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We present the first, to our knowledge, demonstration of an encrypted optical storage based on double-random phase encoding by using angular multiplexing in a photorefractive material. Original two-dimensional data are encrypted by use of two random phase codes located in the input and the Fourier planes and are then stored holographically in a LiNbO(3):Fe crystal. The retrieval of the original data can be achieved with a phase-conjugated readout scheme. We demonstrate the encryption and the decryption of multiple frames of two-dimensional digital data by using angular multiplexing. We also evaluate numerically the influence of the bandwidth of the optical system on the decrypted digital data. The bit error rate as a function of the optical system bandwidth is presented.
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We implement an optical encryption system based on double-random phase encoding of the data at the input and the Fourier planes. In our method we decrypt the image by generating a conjugate of the encrypted image through phase conjugation in a photorefractive crystal. The use of phase conjugation results in near-diffraction-limited imaging. Also, the key that is used during encryption can also be used for decrypting the data, thereby alleviating the need for using a conjugate of the key. The effect of a finite space-bandwidth product of the random phase mask on the encryption system's performance is discussed. A theoretical analysis is given of the sensitivity of the system to misalignment errors of a Fourier plane random phase mask.
We propose a new optical encryption technique using the fractional Fourier transform. In this method, the data are encrypted to a stationary white noise by two statistically independent random phase masks in fractional Fourier domains. To decrypt the data correctly, one needs to specify the fractional domains in which the input plane, encryption plane, and output planes exist, in addition to the key used for encryption. The use of an anamorphic fractional Fourier transform for the encryption of two-dimensional data is also discussed. We suggest an optical implementation of the proposed idea. Results of a numerical simulation to analyze the performance of the proposed method are presented.
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