Wetting-layer-pumped continuous wave surface emitting quantum dot laser

We report a continuous wave 1 μm laser based on InAs Stranski-Krastanov quantum dots (SK-QD) which is optically pumped on a wetting layer absorption band at 915 nm. The slope efficiency of this laser relative to absorbed pump power was measured to be 56% with wetting layer pumping, 1.75 times larger than when pumped with 830 nm light absorbed into the barriers between the SK-QD layers. Compared to barrier pumping, wetting layer pumping benefits from a smaller quantum defect, with less heat deposited in the active region, at the expense of weaker pump absorption in the thin (~1 nm) wetting layer. When a 50 μm thick intracavity diamond heatspreader was contacted to the optically pumped gain structure, a 10-fold increase in output power, up to 2.25W, was obtained in the barrier pumped case. A much smaller 2-fold increase in power, to a maximum of 0.35 W, was seen for the wetting layer pumped case. The diamond heatspreader is more effective in removing heat from the active region, where it is deposited by barrier pumping, than from the substrate, which absorbs residual pump radiation in the barrier pumping case. A gain sample with a doubly periodic DBR to back reflect pump radiation, will allow the full potential of wetting layer pumping to be realised, both by increasing pump absorption due to the double pass through the active region, and by localising heat generation in the active region.