Abstract
Information transmission plays a crucial role in the actual society of technology. Two of the major and more important issues are privacy and security. Traditionally, public key cryptosystems based on software techniques have covered these two issues. A complementary and simple way to improve the security can be realized by additionally encoding at the physical layer using chaotic carriers generated by components operating in the nonlinear regime [1]. Semiconductor lasers are ideal candidates for the realization of these non-linear emitter and receiver systems. They are already inherently non-linear devices that under various operation conditions exhibit nonlinear dynamical behavior associated with, e.g., fast irregular pulsations of the optical power. Optical communication using chaotic carriers is possible when two spatially separated chaotic lasers synchronize to each other; synchronization means that the irregular time evolution of the emitter laser can be well reproduced by the receiver laser. Once the two lasers have synchronized, the chaotic output of the emitter can be used as the carrier on which the message is encoded. The other laser, in the receiver system, allows the message to be extracted by acting as a non-linear filter for the message. By comparing the input of the receiver, that contains the carrier and the message, with its output, that contains only the carrier, the message can be extracted.
© 2003 Optical Society of America
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