Intermittent dynamics switching on the route to chaos in a discrete-mode laser with long time-delayed feedback is experimentally and numerically studied by analyzing the time series, power spectra, and phase portraits. The results show two types of dynamics switching: one or multiple times regular intermittent dynamics switching between stable state and square-wave envelope period-one oscillation within one feedback round time, and the irregular intermittent dynamics switching between stable state and quasi-periodic or multi-states or chaos with higher feedback ratio and bias currents. The relationship between the duty cycle of period-one oscillation and the feedback ratio has been analyzed. The map of the dynamics distribution in the parameter space of feedback ratio and bias current is plotted for a better understanding of dynamics evolution in long external cavity discrete-mode lasers.

Through employing permutation entropy and the self-correlation function, the time-delay signature (TDS) of a vertical-cavity surface-emitting laser (VCSEL) with variable-polarization filtered optical feedback (VPFOF) is evaluated theoretically. The work shows that the feedback rate η, polarizer angle θp, and filter bandwidth Λ have an obvious influence on the TDS. The evolution maps of the TDS in parameter space (η,Λ) and (η,θp) are simulated for searching the chaos with weak TDS. Furthermore, compared with a VCSEL with polarization-preserved filtered optical feedback and a VCSEL with variable-polarization mirror optical feedback, this VPFOF–VCSEL shows superiority in TDS suppression.