Effects of Gain Saturation on Orbital Instability of Chaotic Laser Diode with External Pseudorandom Signal

In a laser diode (LD) system with optical injection, the effects of gain saturation of the LD on the orbital instability of the system are analyzed numerically. For the optical injection LD system without signal application, it is shown that the effect of optical injection is suppressed in the system with gain saturation and small optical injection, and that a higher amount of optical injection is necessary to obtain similar dynamics. Next, in the optical injection LD system with a pseudo-random signal applied to the LD drive current, it is confirmed that when the dynamics are a periodic window between chaotic and chaotic regions, chaotic dynamics are actualized as the standard deviation of the applied signal becomes larger. Furthermore, it is suggested that this phenomenon can be explained by linear stability analysis, and it is shown by introducing randomly varying tentative gain coefficients that gain fluctuations that lead to an expansion of the chaotic region. Hence, the results of this study provide research on the effects of gain saturation on chaotic oscillation in LDs with pseudo-random signals applied and contribute to the generation of more complex chaotic signals, chaotic secure communication, and random number generation.