Inverse synchronization in diode lasers

Summary form only given.Laser systems have been given much attention in the development of novel techniques for secure transmission of data using chaotic optical sources. The underlying concept for the work is that the transmitted message should be encoded within the noise-like output of a chaotic transmitter. Extraction of the message requires a receiver in which the same chaos is generated as in the transmitter, which can be achieved by synchronization of the chaos of the transmitter and the receiver. Useful progress has been made towards experimental encryption and decryption by use of a novel form of wavelength chaos. A successful demonstration of chaotic transmission of a message by use of a fiber laser was reported recently. Because of the ease of operation of semiconductor lasers, it is of considerable interest to develop a chaotic communication system utilising these lasers as the source of optical chaos. Encoding and effective decoding of a message largely depends on the quality of synchronization. Hence, synchronization and its dependence on various experimental parameters are of paramount importance. In this paper, we report what we believe to be the first observation of a negative gradient in a synchronization diagram and discuss its implications for chaotic communication.