The Transmission Of Two-dimensional Messages And The Preference Of Chaotic Synchronization In Chaotic Lasers

The chaotic synchronization of a nonlinear coupled laser system and the digital communication through chaotic synchronization are investigated in this paper. Firstly, the digital communication of two-dimensional messages using chaotic synchronization in two multi-mode coupled lasers is investigated. A new scheme of multi-channel communication using chaotic synchronization in a multi-mode laser system has been proposed. By introducing the time derivation of the intensity difference between the receiver and the transmittal, the messages can be decoded successfully. It is found that one digit can be encoded and decoded on one pulse at any location since the width of the signal is much narrower than that of the pulse of the transmitter. To increase the efficiency of utilizing the pulse of the transmitter, the method of decoding messages has been improved. Therefore, several digits can be encoded and decoded on a single pulse. If different height of the signals can represent a group of different binary bits, a two-dimensional message in the form of a matrix can be encoded and decoded correctly on a single pulse. Our numerical simulations of chaotic communication in a two three-mode laser system shows that one dimensional data, two dimensional information and a static two-dimensional gray-scale image have successfully been transmitted. By these improvements on the methods of encoding and decoding the messages, not only the transmission rate can be increased but also the privacy can be enhanced greatly in secure communication using chaotic multi-mode lasers. Secondly, the phenomenon of preference of chaotic synchronization in a laser system has been analyzed. The phenomenon and the rule of chaotic synchronization have attracted further investigations due to its potential applications in many fields. We study a coupled laser system that is composed of three loss-modulated sing-mode Nd:YAG lasers. In the coupled laser system, two separate lasers act as the transmitters while the third one acts as the receiver. The outputs of the transmitter laser are injected into the receiver laser. It means that there exists coupling between the transmitters and the receiver. The numerical simulations show an interesting phenomenon of the preference of chaotic synchronization. The chaotic synchronization between the transmitters and the receiver depends on the coupling strength between them. The intensity output of the receiver can be controlled by adjusting the coupling strength between the transmitter lasers and the receiver laser.