Optical mode loss and gain of multiple layer quantum dot lasers

Summary form only given. We report direct measurements of the optical loss and gain of structures employing 1, 3, 5 and 7 layers of quantum dots using an electrically pumped multi-section technique. The structures consist of layers of InGaAs quantum dots embedded in GaAs quantum wells with an AlGaAs waveguide core whose thickness is adjusted in each case to maintain a constant average confinement factor per layer. We plot the optical mode loss for structures containing different numbers of dot layers. The results indicate that in fact the optical mode loss, /spl alpha//sub 1/, is independent of the number of quantum dot layers. On the other hand, the peak-gain does scale with the number of layers. The peak-gain per layer at low current densities is similar for structures with 1, 3, 5, and 7 layers of quantum dots. This means the net-modal gain (gain-/spl alpha//sub 1/) of the dot ground state can be increased by using multiple quantum dot layers in the active region. At high current densities the gain per layer of quantum dots does not scale with layer number in a simple fashion and we also discuss the origin of this effect.