Optical mode loss and gain of multiple-layer quantum-dot lasers

Using an electrically pumped multisection technique, we have directly measured the internal optical mode loss of semiconductor-laser structures containing 1, 3, 5, and 7 layers of uncoupled InGaAs quantum dots. The optical loss does not increase with the number of dot layers so higher net modal gain can be achieved by using multiple layers. The maximum modal gain obtained from the ground state increases with dot layer number from 10±4 cm^-1 for a single layer to 49±4 cm^-1 for the 7 layer sample, which is typical of the threshold gain requirement of a 350 μm long device with uncoated facets.