Nonlinear dynamics of a quantum cascade laser subject to negative optoelectronic feedback

In this Letter, we experimentally investigate the nonlinear dynamics of a quantum cascade laser (QCL) under negative optoelectronic feedback (NOEF). Results show that as the feedback strength increases, the dynamical behaviors of the QCL undergo an evolution sequentially from steady state to periodic oscillation, intermittent oscillation, and finally square-wave oscillation. In the periodic oscillation regime, the oscillation period is approximately twice the feedback delay time, where the harmonic component intensity enhances with the increase of the feedback strength. The intermittent oscillation is characterized by alternating between the pulse clusters and laminar regions in the time series. For the square-wave oscillation, its period depends on both the bias current and feedback strength, while the duty cycle remains around 50%.