Gain and Loss in Active Waveguides Based on Lithographically Defined Quantum Dots

We report on the optical gain and loss of waveguides containing lithographically defined quantum dots. Lasing action has previously been demonstrated in a nominally identical structure. Measurements are made by monitoring the transmission of a resonant pulse while varying the injection current. We measure a maximum modal gain of 1.8 cm^-1 at the peak of the ground state emission for a two-layer structure. The peak gain is insufficient for ground state lasing to be achieved in a structure with as-cleaved facets, but the gain per dot is comparable with that demonstrated in self-assembled quantum dots.