This thesis presents the findings of a numerical study into the chaos synchronization and current modulation of semiconductor lasers. A system of coupled semiconductor lasers is simulated using a complex set of coupled differential equations.
The initial focus of the investigations is the chaos synchronization process. A
proportion of the chaotic output of the first semiconductor laser is injected into a second and if the parameters of the lasers are sufficiently similar the dynamics of the second laser can lock to the dynamics of the first. The simulation model is verified by producing time domain outputs that can easily be compared with previous studies. The synchronization quality is assessed via the correlation coefficient and this is then used to obtain the widely used injection locking diagram.
The injection locking regime is studied in the frequency domain and, for the first time, frequency based injection locking diagrams are presented, providing added insight into the synchronization process. The subtle variations in the con-elation of the laser dynamics observed across the injection locking region are attributed to low power spectral components at high frequencies.
The second half of the thesis focuses on the current modulation of a semiconductor laser and the use of chaos to mask the applied message. The extraction process at the receiver, commonly referred to as chaos pass filtering, is analysed. The difference between the frequency dependent current and optical modulation responses of the semiconductor lasers used in the transmitter and receiver is shown to be key to the extraction process.
A realistic digital message is applied to the transmitter laser and the simulations have shown that a fine balance exists between the quality of extraction of the message at the receiver and the masking of the message in the transmitted signal.