Synchronization And Communication In Cascade And Multichannel Systems With Chaotic VCSELs

With the achievement of the chaos synchronization, secure communications with messages encoded in chaotic waveforms have attracted considerable interest. Semiconductor lasers are able to generate hyper-dimension chaotic carriers with large bandwidth subject to optical feedback or injection. Optical chaotic communication has been a subject of intensive research. Meanwhile, vertical cavity surface emitting lasers (VCSELs), as the new type micro-cavity lasers, have many excellent features, such as circular beams, high efficiency for coupling with fibers, easy to be integrated as high density 2D arrays, single longitude mode operation. Therefor, it can largely promote the performance of chaotic optical communication system. Based on above considerations, synchronization and communication in cascade and multi-channel systems with chaotic VCSELs are theoretically investigated in this thesis.Firstly, the relaying performance in open-loop cascade chaotic optical communication system is investigated. The synchronization condition, correlation degree, synchronization robustness, and spectra of chaotic outputs are analyzed thoroughly. The encoding/decoding processes and performance in chaotic masking (CMS), chaotic modulation (CM), and chaos-shift keying (CSK) are simulated. The chaos-pass filtering (CPF) effects are observed by transmission of sinusoid signals. Multilevel decoding ability for the messages, and the relay of regenerated signals are the issues we focus on. The results indicate that a high synchronization performance between the neighboring two lasers can be guaranteed by sufficient optical injection from the former laser, and is very robust for variations in the mismatch of parameters. With the three encoding methods, the digital signals sent in transmitting part can be well hidden by chaotic carrier and recovered correctly in the receiver. At the same conditions, the decoding performances in CMS and CSK are better than CM. CPF effect is the physical basis for chaotic decoding, and it is relative to the modulation frequency. The signal is attenuated due to the CPF effects, and nearly filtered out after transferring twice. The original message can be extracted correctly in the first two grades because of the notable CPF effects, and can hardly be recovered in the third or later. The multilevel cascade chaotic communication can be realized by regenerating the depleted signal in relaying. A multi-channel chaotic optical communication system is established on the basis of cascade system, in order to investigate the effects of the cross talk on synchronization and decoding. Based on the corresponding rate equations, similarity index is used to evaluate the synchronization performance, and 2.5Gb/s message coding/decoding of chaotic masking method is numerically analyzed. The results show that the system can get better synchronization quality with less relative injection strength and more channel interval. The synchronization performance of dual-channel system decreases obviously compared with master-slave single channel system, and changes little when the channel number increases. The digital and analog signals can be correctly recovered when the synchronization is good enough.