Chaos synchronization and communications in semiconductor lasers

Chaos synchronization is not only of great theoretical interest but may be used in practice, e.g. for novel communication schemes. In this dissertation issues related to practical uses of synchronization are discussed.; The question of bounds on the synchronization error for the case of nearly identical nonlinear systems is addressed and an analytic bound for a simple sub-class of systems, which includes Lur'e systems, is presented showing that the bound grows as the largest singular value of the linearized system increases. Then, the Lorenz system is taken as an example to demonstrate that the phenomenon is not restricted to the sub-class for which the analytic result holds.; In the main part of the dissertation, an optical communication scheme using synchronized chaotic lasers with optoelectronic feedback is investigated in detail. The discussion proceeds in four steps. First, the presence of chaos in the model is established by calculating the Lyapunov exponent spectrum. It is shown that the route to chaos observed in the model and the experiment are identical. Second, the robustness of chaos synchronization in the presence of small parameter mismatches and noise is investigated, where an open-loop receiver configuration is found to be least sensitive. Robust synchronization is a perquisite for successful communications. In the third step communication strategies for arbitrary amplitude of modulation onto the chaotic signals are discussed, and the bit-error rate for one such scheme is evaluated as a function of noise in the optical channel. Finally, both chaos synchronization and the ability to communicate is demonstrated using analog circuitry implementing the model.; In the final portion of the dissertation a method to design dynamically optimal light pulses by shaping the laser pump current is proposed and it is shown that this can improve the communication performance of semiconductor lasers in a conventional communication setup.