S. Sivaprakasam

Lag synchronization in time-delayed systems

We present the first analytical investigation of lag chaos synchronization between two unidirectionally coupled identical time-delayed systems in the case when these systems are governed by two characteristic times: the delay time in the coupling is generally different from the delay time in the coupled systems. Also, for the first time we demonstrate that parameter mismatches can explain the fact that the lag time is equal to the coupling delay. These findings can be helpful to explain coupling-delay lag time in chaos synchronization.

Demonstration of optical synchronization of chaotic external-cavity laser diodes.

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.

SIGNAL MASKING FOR CHAOTIC OPTICAL COMMUNICATION USING EXTERNAL-CAVITY DIODE LASERS

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.

Message encoding and decoding using chaotic external-cavity diode lasers

Synchronization of chaotic external-cavity diode lasers has been studied in a master-slave configuration. A message is encoded into the chaotic master laser by amplitude modulation and transmitted to the slave laser. A scheme for decoding the message at the slave is demonstrated.

Dual-channel chaotic optical communications using external-cavity semiconductor lasers

We experimentally demonstrate that two chaotic optical communication channels can be configured over a single transmission path by using two external-cavity laser diodes as transmitter lasers and a single stand-alone receiver laser. The two chaotic communication channels are shown to operate independently. Two messages, at different modulation frequencies, generated via direct-current modulation of the transmitter lasers, can be masked by the chaos and recovered at the receiver laser by the use of a decoder laser. The decoder laser is used to select the channel to be utilized. We show that there is good message recovery with little cross talk between the two channels. The channels operate at different laser wavelengths and thus constitute a wavelength-division-multiplexing scheme.

Comparison of closed-loop and open-loop feedback schemes of message decoding using chaotic laser diodes

An experimental study of a chaotic optical communication scheme using an external cavity laser diode to encode a message is reported. The message is decoded in closed- and open-loop receiver schemes. Both schemes show effective decoding of a 1-GHz message. The synchronization and effectiveness of encoding are compared in both schemes.

Inverse anticipating chaos synchronization.

We report a new type of chaos synchronization:inverse anticipating synchronization, where a time delay chaotic system can drive another system in such a way that the driven system anticipates the driver by synchronizing with its inverse future state. 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.

Lag times and parameter mismatches in synchronization of unidirectionally coupled chaotic external cavity semiconductor lasers.

We report an analysis of synchronization between two unidirectionally coupled chaotic external cavity master/slave semiconductor lasers with two characteristic delay times, where the delay time in the coupling is different from the delay time in the coupled systems themselves. We demonstrate for the first time that parameter mismatches in photon decay rates for the master and slave lasers can explain the experimental observation that the lag time is equal to the coupling delay time.

Regimes of chaotic synchronization in external-cavity laser diodes

Chaotic synchronization is investigated experimentally 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. Experimental conditions are found under which the synchronization diagram makes a transition from a positive to a negative gradient. A regime of operating conditions is identified in which the receiver laser is found to anticipate the dynamics of the transmitter laser. The anticipation time does not depend on the external-cavity length, but rather on the time of flight between the two lasers. Changes in the spectrum of the synchronized system are shown to be associated with the transition between anticipating and lag synchronization.

Cascaded synchronization of external-cavity laser diodes

An experimental demonstration of optical synchronization of a chain of chaotic external-cavity laser diodes is reported for what is believed to be the first time. The experiment is performed in the low-frequency-fluctuation regime.