Strain engineered bilayers for extending the operating wavelength of quantum dot lasers

The analysis of molecular-beam epitaxy (MBE) grown bilayer quantum dot (QD) laser material is reported here. Specifically, gain characteristics of 5× ´bilayer´ QDs with GaAs caps and 5× ´single´ QD layers with InGaAs caps were studied experimentally. A transition of lasing from the ground state to lasing via the first excited state, and subsequently the second excited state is observed with increasing threshold gain for both the laser structures. A 50% increase in saturated modal gain is observed for bilayer laser as compared to single-layer samples. Further analysis of the bilayer sample using the multi-section technique allows the gain and absorption spectrum to be obtained.