Nonlinear dynamics induced by external optical injection in semiconductor lasers

Abstract

External optical injection of semiconductor lasers changes the resonant coupling characteristics between the circulating optical field in the laser cavity and the free carriers (gain medium). Changes in the characteristic resonance frequency and damping of the system can lead to dynamic instabilities and deterministic chaos and to enhancement of the modulation bandwidth. The changes induced depend on key dynamic parameters of the semiconductor laser such as the photon and carrier decay rates, gain characteristics and the linewidth enhancement factor, and the operating point of the laser determined by the injection current (pump) level, circulating optical power, the amplitude of the external optical injection and the frequency offset between the master and injected lasers. Here, we describe a mapping of the typical dynamics induced in a nearly single-mode semiconductor laser biased well above the threshold for laser oscillation as the amplitude and frequency offset of the master laser are changed. We also present results on a laser initially biased near threshold in a free-running condition where it displays a near-Gaussian optical lineshape. The external optical injection induces spectral holes and spikes, as well as spectral shifts. All features that we observe can be recovered in a standard coupled equation model of semiconductor laser operation.