Nonlinear and Dynamical Processes in Complex Lasers

Aug 28, 2017, 10:00 am11:30 am
E-Quad J401
Event Description

Advancements in semiconductor fabrication technology have led to the increased miniaturization of photonic systems and the need for small, stable, and efficient laser light sources is growing. Modern lasers targeting on-chip applications can have complex cavity geometries that can easily give rise to unfavorable nonlinear modal interactions that limit laser output efficiency. In the first part of this thesis, we discuss a universal method for controlling these nonlinear interactions by spatially selectively pumping the laser cavity to turn on only its most optimally emitting mode (or modes). Our method applies to lasers of any shape and arbitrary openness, fully taking into account all nonlinearities. We demonstrate our method in a variety of laser systems, most notably in micro-disk lasers where output emission is enhanced by over two orders of magnitude.
Nonlinearities can also significantly impact the stability of a laser. In particular, lasers with fast gain-recovery, such as quantum cascade lasers (QCLs), feature strong four-wave mixing interactions that cause sudden transitions in the laser output spectrum. In the second part of this thesis, we develop the Constant Flux Time Domain (CFTD) method, an efficient computational framework for studying nonlinear interactions in the dynamical regime. Using this method, we study frequency-comb instabilities in ring and Fabry-Perot cavities, fully taking into account all nonlinearities and openness. We discuss the role of gain relaxation rate and cavity decay rate in the formation of these instabilities, and numerically simulate the hysteresis effect seen in experiments. We also predict sudden transitions to stable frequency-comb regimes from within chaotic plateaus.