Failure of the α factor in describing dynamical instabilities and chaos in quantum-dot lasers.
We show that the long-established concept of a linewidth-enhancement factor α to describe carrier-induced refractive index changes in semiconductor lasers breaks down in quantum-dot (QD) lasers when describing complex dynamic scenarios, found, for example, under high-excitation or optical injection. By comparing laser simulations using a constant α factor with results from a more complex nonequilibrium model that separately treats gain and refractive index dynamics, we examine the conditions under which an approximation of the amplitude-phase coupling by an α factor becomes invalid. The investigations show that while a quasiequilibrium approach for conventional quantum well lasers is valid over a reasonable parameter range, allowing one to introduce an α factor as a constant parameter, the concept is in general not applicable to predict QD laser dynamics due to the different time scales of the involved scattering processes.
Institut für Theoretische Physik, Technische Universität Berlin, 10623 Berlin, Germany.
Benjamin
B
Lingnau
Kathy
K
Lüdge
Weng W
WW
Chow
Eckehard
E
Schöll