New phase contrast techniques in the verification of encrypted patterns

Author(s)

José Carlos Pizolato Junior

• Document type: Doctoral Thesis
• Press: São Carlos.
• Institution: Universidade de São Paulo (USP). Escola de Engenharia de São Carlos (EESC/SBD)
• Defense date: 2006-02-10

Examining board members

Luiz Gonçalves Neto; Jarbas Caiado de Castro Neto; Amílcar Careli César; Luciano da Fontoura Costa; Liliane Ventura

• Advisor: Luiz Gonçalves Neto

Abstract

In this work, an encryption and decryption scheme based on a new phase contrast technique is proposed. This new technique, called the zero order phase contrast technique, transforma the phase modulation to intensity without the necessity of a phase-changing plate (phase dielectric dot) on the Fourier plane of a 4f optical correlator. A codification process, which does not use any iterative calculation, is applied directly in a gray level image to generate a phase distribution. After this, an encryption process is applied multiplying the phase distribution by a random phase distribution. The advantage of this method is the easy scheme to recover the gray level information from the decryption phase mask. The encrypted phase mask and the key of the system were implemented on Spatial Light Modulators of the kind LCTV. The encoding ways were investigated to generate the phase masks from gray level image, by implementing two kinds of phase Diffractive Optical Elements, operating in transmission and reflection modes. Experimental results show the successfully application of the zero order phase contrast technique in the visualization of encoded information both in Spatial Light Modulators and in phase only Diffractive Optical Elements as well as in the verification of encrypted patterns. (AU)