Le Thai Son, Yu.I. Alekseev

Semiconductor lasers subjected to optical injection from another laser is known as nonlinear optical systems that can generate chaotic intensity fluctuations and lead to various nonlinear dynamics. Such dynamics have gained a lot of consideration due to their fundamental physical properties and potential for technological applications, including for example, chaotic RADAR, chaotic LIDAR, and secure communications. Several theoretical and experimental investigations of semiconductor lasers in the terms of chaos, transition routes to chaos, nonlinear dynamics, bifurcation and chaotic synchronization have been performed. In the last decade the chaotic regime of an optically injected semiconductor laser has attracted a lot of attention due to its high-performance potential application in optical chaotic communication. An all-optical system approach would be attractive in high-speed and long-haul secure communication because all-optical systems have large bandwidth and low attention. Many semiconductor laser systems have been proposed for chaotic optical communication. In these systems the main require is the stability of chaotic generation. Normally the chaotic region is too small that the system can easily get out of chaotic regime when the laser bias current and temperature change. In order to improve performance of chaotic optical communication this problem is needed to be taken into consideration. In this article we investigate chaotic regime of an optically injected semiconductor laser with AM-optical signals through measurement of the stability map of the system. Mathematical model of the system is built by using Lang and Kobayashi equations for the amplitude and the phase of the electric field and the average density in the active region. Numerical method is used due to its simplicity. The stability maps of the system can be obtained by numerically integrating the Lang and Kobayashi equations using Rungge-Kutta method. We show that the chaotic region of an optically injected semiconductor laser with AM-optical signals is as much larger than that when the amplitude of optical injected signal is constant. We also notice that by changing the modulation frequency we can easily modify the stability and this technique can be used in order to control chaos. The proposal technique is also attractive because of its simplicity. AM-optical signal can be easily obtained by direct modulation laser bias current.