Transient nonlinear dynamics in an electrically modulated quantum cascade laser with optical injection

Based on rate equations, we mainly simulate the transient instability characteristics of an 8 mu m quantum cascade laser (QCL) subject to optical injection with alternating current (AC) electrical modulation. Simulation results show that the period-one oscillation of the optical injection-locked QCL is broken by applying an AC current to the direct current (DC) bias. Combining an external optical injection and induced period current modulation can cause period-one oscillation dropouts and can display chaotic states outside the stable locking region, owing to the cooperative interplay between the AC frequency and the periodic oscillation frequency caused by the optical injection. To give a clear physical picture of the chaos under different line-width enhancement factors (LEFs), we use temporal series, Poincare bifurcation diagrams, Fourier spectra, phase portraits, and first return maps to carefully analyze. These analytical methods are effective for the dynamical behaviors of QCLs with low LEFs, which show that the chaos of QCLs strongly rely on external modulation compared with class-B laser systems. This work paves a new way for realizing chaotic signal generation and has an important application in secure communication in the mid-infrared and terahertz frequency band.