US Patent 7706422 - Graded density q-dot laser

http://www.freepatentsonline.com/7706422.html

This patent from Mitsubishi Electric teaches a way to increase the emission efficiency of quantum dot lasers by altering the quantum dot distribution. Claim 1 reads:

1. A semiconductor optical element comprising an active layer including quantum dots, wherein density of the quantum dots in a resonator direction in a portion of the active layer in which density of photons is relatively high is higher relative to the density of the quantum dots in a portion of the active layer in which the density of photons is relatively low.