Treffer: Examination of acousto-optic chaos and application to RF signal encryption and recovery

In communication systems, there are different coding schemes such as linear predictive coding, block coding, and veterbi coding that can be used to encode data for different purposes. One of the techniques to encode/encrypt data for security purposes is to use chaos. Chaotic systems can be manipulated, via arbitrarily small time-dependent perturbations, to generate controlled chaotic orbits whose symbolic representation corresponds to the encoding of a desirable message. An advantage of this type of communication strategy is that the nonlinear chaotic oscillator that generates the wave form for transmission can remain simple and efficient, while all the necessary electronics controlling encoding of the signal remain at the low-powered microelectronic level. Moreover, since the chaotic dynamics can be recovered from a chaotic signal, which in principle can be noisy, by using standard dynamical data analysis techniques, communicating with chaos is also more robust and better behaved against channel noise. Signal encryption and recovery using chaotic optical waves has been a subject of active research in the past 10 years. Since an acousto-optic Bragg cell with zeroth- and first-order feedback exhibits chaotic behavior past the threshold for bistability, such a system was examined for possible chaotic encryption using a low-amplitude sinusoidal signal applied via the bias input of the sound cell driver. Subsequent recovery of the message signal was carried out via a heterodyne strategy employing a locally generated chaotic carrier, with threshold parameters matched to the transmitting Bragg cell. The simulation results, though encouraging and extend to the following (i) increasing the chaos frequency using appropriate parameter control; (ii) carefully examining the system sensitivity to three system parameters, viz., feedback delay, feedback gain, and dc bias level; (iii) examine signal recoverability relative to shifts in the three parameters mentioned above relative to the transmitter; and (iv) determining the ...