José Carlos Pizolato

Chaotic Communication Based on the Particle-in-a-Box Electronic Circuit

A secure communication system based on the error-feedback synchronization of the electronic model of the particle-in-a-box system is proposed. This circuit allows a robust and simple electronic emulation of the mechanical behavior of the collisions of a particle inside a box, exhibiting rich chaotic behavior. The required nonlinearity to emulate the box walls is implemented in a simple way when compared with other analog electronic chaotic circuits. A master/slave synchronization of two circuits exhibiting a rich chaotic behavior demonstrates the potentiality of this system to secure communication. In this system, binary data stream information modulates the bifurcation parameter of the particle-in-a-box electronic circuit in the transmitter. In the receiver circuit, this parameter is estimated using Pecora-Carroll synchronization and error-feedback synchronization. The performance of the demodulation process is verified through the eye pattern technique applied on the recovered bit stream. During the demodulation process, the error-feedback synchronization presented better performance compared with the Pecora-Carroll synchronization. The application of the particle-in-a-box electronic circuit in a secure communication system is demonstrated.

Zeroth-order phase-contrast technique

What we believe to be a new phase-contrast technique is proposed to recover intensity distributions from phase distributions modulated by spatial light modulators (SLMs) and binary diffractive optical elements (DOEs). The phase distribution is directly transformed into intensity distributions using a 4f optical correlator and an iris centered in the frequency plane as a spatial filter. No phase-changing plates or phase dielectric dots are used as a filter. This method allows the use of twisted nematic liquid-crystal televisions (LCTVs) operating in the real-time phase-mostly regime mode between 0 and p to generate high-intensity multiple beams for optical trap applications. It is also possible to use these LCTVs as input SLMs for optical correlators to obtain high-intensity Fourier transform distributions of input amplitude objects.

Phase-only optical encryption based on the zeroth-order phase-contrast technique

A phase-only encryption/decryption scheme with the readout based on the zeroth-order phase-contrast technique ZOPCT, without the use of a phase-changing plate on the Fourier plane of an optical system based on the 4f optical correlator, is proposed. The encryption of a gray-level image is achieved by multiplying the phase distribution ob- tained directly from the gray-level image by a random phase distribution. The robustness of the encoding is assured by the nonlinearity intrinsic to the proposed phase-contrast method and the random phase distribution used in the encryption process. The experimental system has been implemented with liquid-crystal spatial modulators to generate phase- encrypted masks and a decrypting key. The advantage of this method is the easy scheme to recover the gray-level information from the de- crypted phase-only mask applying the ZOPCT. An analysis of this de- cryption method was performed against brute force attacks.

The Zero-Order Phase-Contrast Technique

A new Phase-Contrast Technique without a phase-changing plate (phase dielectric dot) on the Fourier plane of a 4f optical correlator is proposed. The advantages of this method are the easy scheme to recover the gray level information encoded on a phase-only mask and the high diffraction efficiency of the recovered image.

Application of the particle in a box electronic circuit in a spread spectrum communication system

A spread spectrum communication system based on the electronic model of the particle in a box system is proposed. This electronic system allows a robust and simple electronic emulation of the mechanical behaviour of the collisions of a particle inside a box, exhibiting rich chaotic behaviour. The required non-linearity to emulate the box walls is implemented in a simple way when compared with other analogue electronic chaotic circuits. In this system, a stream of binary data is transformed in the frequency modulated signal by the binary frequency shift keying (BFSK) modulator. The chaotic signal of the particle in a box electronic circuit is used to generate a broadband signal in the voltage controlled oscillator (VCO) of the transmitter. The frequency hopping signal sent to receiver is generated by mixing the binary frequency shift keying and the broadband signal. The demodulation process is done when the VCOs of transmitter and receiver are synchronised by a phase locked loop (PLL) circuit. The performance of the demodulation process is verified through the eye pattern technique applied on the recovered bit stream. A binary data stream was sent through a transmission channel with the following lengths: 2,000 metres and 8,000 metres. The experimental results demonstrated that the particle in a box electronic circuit can be used in a spread spectrum communication system.

Optical implementation of image encryption using the zero-order phase-contrast technique

An encryption/decryption scheme based on a new Phase-Contrast Technique, without the use of a phase-changing plate (phase dielectric dot) on the Fourier plane of a 4f optical correlator is proposed. The encryption of a gray level image is achieved by multiplying the phase distribution obtained directly from the gray level image by a random phase distribution. The encoding is obtained without any iterative calculation to generate the encrypted phase-only mask. The robustness of the encoding is assured by the non-linearities intrinsic to the phase-contrast method and the random phase distribution used in the encryption process. The advantage of this method is the easy scheme to recover the gray level information from the decrypted phase-only mask applying the proposed Zero-Order Phase-contrast Technique.