Spectral hole-burning and carrier-heating dynamics in InGaAs quantum-dot amplifiers

The ultrafast gain and index dynamics in a set of InAs-InGaAs-GaAs quantum- dot (QD) amplifiers are measured at room temperature with femtosecond resol ution. The role of spectral hole-burning (SHB) and carrier heating (CH) in the recovery of gain compression is investigated in detail. An ultrafast re covery of the spectral hole within similar to 100 fs is measured, comparabl e to bulk and quantum-well amplifiers, which is contradicting a carrier rel axation bottleneck in electrically pumped QD devices. The CH dynamics in th e QD is quantitatively compared with results on an InGaAsP bulk amplifier. Reduced CH for both gain and refractive index dynamics of the QD devices is found, which is a promising prerequisite for high-speed applications. This reduction is attributed to reduced free-carrier absorption-induced heating caused by the small carrier density necessary to provide amplification in these Low-dimensional systems.