Optically pumped passively modelocked vertical external-cavity surface-emitting lasers (VECSELs) can generate pulses as short as 100 fs with an intracavity semiconductor saturable absorber mirror (SESAM). Very stable soliton modelocking can be obtained, however, the high-Q-cavity, the short gain lifetime, and the kinetic-hole burning can also support rather complex multipulse instabilities which we analyze in more details here. This onset of multipulse operation limits the maximum average output power with fundamental modelocking and occurs at the roll-over of the cavity round trip reflectivity. Unfortunately, such multipulse operation sometimes can mimic stable modelocking when only limited diagnostics are available.
We experimentally and theoretically investigate the pulsed emission dynamics of a three section tapered semiconductor quantum dot laser. The laser output is characterized in terms of peak power, pulse width, timing jitter and amplitude stability and a range of outstanding pulse performance is found. A cascade of dynamic operating regimes is identified and comprehensively investigated. We propose a microscopically motivated traveling-wave model, which optimizes the computation time and naturally allows insights into the internal carrier dynamics. The model excellently reproduces the measured results and is further used to study the pulse-generation mechanism as well as the influence of the geometric design on the pulsed emission. We identify a pulse shortening mechanism responsible for the device performance, that is unique to the device geometry and configuration. The results may serve as future guidelines for the design of monolithic high-power passively mode-locked quantum dot semiconductor lasers.
We investigate the emission dynamics of mutually coupled nanolasers and predict ways to optimize their stability, i.e., maximize their locking range. We find that tuning the cavity lifetime to the same order of magnitude as the dephasing time of the microscopic polarization yields optimal operation conditions, which allow for wider tuning ranges than usually observed in conventional semiconductor lasers. The lasers are modeled by Maxwell–Bloch type class-C equations. For our analysis, we analytically determine the steady state solutions, analyze the symmetries of the system and numerically characterize the emission dynamics via the underlying bifurcation structure. The polarization lifetime is found to be a crucial parameter, which impacts the observed dynamics in the parameter space spanned by frequency detuning, coupling strength and coupling phase.
Efficient simulation of the timing jitter in passively mode-locking lasers is key to their numerical investigation and optimization. We introduce a method based on the pulse-period fluctuation auto-correlation function and compare it against established methods with respect to their estimate error. Potential improvements of the computational cost by about two orders of magnitude are reported. This advantage may facilitate larger parameter studies of passively mode-locked lasers on small-scale clusters or even desktop computers and, thereby, guide the target-oriented design of future lasers with ultra-low timing jitter.
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