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We report the first experimental observation of anticipating chaotic synchronization in an optical system using two diode lasers as transmitter and receiver. The transmitter laser is rendered chaotic by application of an optical feedback in an external-cavity configuration. It is found that the anticipation time does not depend on the external-cavity round trip time of the transmitter.

An experimental demonstration of optical synchronization of chaotic external-cavity semiconductor laser diodes is reported for what is believed to be the first time. It is shown that at an optimum coupling strength between the master and the slave lasers high-quality synchronization can be obtained.

We report a new type of chaos synchronization:inverse anticipating synchronization, where a time delay chaotic system x can drive another system y in such a way that the driven system anticipates the driver by synchronizing with its inverse future state:y(t) = −x(t + τ ),τ > 0. We extend the concept of inverse anticipating chaos synchronization to cascaded systems. We propose means for the experimental observation of inverse anticipating chaos synchronization in external cavity lasers. PACS number (s) . Application of chaos synchronization can be found in secure communications, optimization of non-linear systems' performance, modeling brain activity and pattern recognition [2]. Synchronization of coupled chaotic systems restricts the evolution of synchronized systems to the synchronization manifold and therefore eliminates some degrees of freedom of the joint system, and thus leading to significant reduction of complexity. In this context new types of chaos synchronization can be considered as a novel ways of reducing unpredictability of chaotic dynamics. Time delay systems are ubiquitous in nature, technology and society due to finite signal transmission times, switching speeds and memory effects [3]. Therefore the study of chaos synchronization in these systems is of high practical importance. Because of their ability to generate high-dimensional chaos time delay systems are also good candidates for secure communications based on chaos synchronization [4]. In addition, time delay systems can be considered as a special case of spatio-temporal systems [5].In this letter we report a new type of synchronization: inverse anticipating synchronization, where a time-delayed chaotic system x drives another system y in such a way that the driven system anticipates the driver by synchronizing with its inverse future state:x(t) = −y(t − τ ) (in conditional representation:x = −y τ ) or equivalently y(t) = −x(t + τ ) with τ > 0. We investigate inverse anticipating synchronization between two coupled systems both with a single delay time and with two characteristic delay times where the delay time in the coupling is different from the delay time in the coupled systems themselves. We extend our findings to cascaded systems. We also propose means for the experimental observation of inverse anticipating synchronization phenomenon using external cavity laser diodes. We define inverse anticipating synchronization as follows: the driver system

Amplitude modulation is used to encode a message into the output of a chaotic laser-diode optical transmitter, and decoding of the message by use of a synchronized chaotic laser-diode receiver is demonstrated experimentally. The chaotic carrier is shown to effectively mask the transmitted message.