Parameters Controlling Optical Feedback of Quantum-Dot Semiconductor Lasers

Abstract

A simple model to describe the dynamics of a single mode semiconductor laser subject to a coherent optical feedback is proposed in 1980 by Lang and Kobayashi (LK). Feedback loop depends on external mirror and creates a passive external cavity, which is explicitly taken into account via the complex delayed electric field variable ( )   E t fed back into the laser. The round trip time is the main feature of the LK model of the laser beam. The LK model has open the door to a very complex dynamics since the system phase space has infinite dimensions and sustain a chaotic regime [1]. Optical feedback consist of two subjects, coherent and incoherent feedback, depending on whether the coherence time of the laser light is larger or smaller than the delay time (τ) respectively [2]. There are five distinct regimes that are defined by the level of the feedback power ratio, this is discusses in section 2. The great importance for dynamics of semiconductor lasers with optical feedback is due to the potential applications of such lasers for secure communications by means of chaotic synchronization. External perturbations such as injected signal, feedback, or pump current modulation are required to achieve a chaotic output. From a practical point of view, optical feedback provided by a back reflecting mirror is one of the simplest ways to achieve chaotic oscillations from a semiconductor laser, even weak optical feedback leads to complex dynamics. In particular, it can sustain a chaotic regime of low-frequency fluctuations with sudden irregular intensity dropouts followed by a gradual intensity recovery [6].