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We present gain measurements and calculations for InAs/GaAs quantum dot injection lasers. Measurements of the modal gain and estimation of the confinement factor by transmission electron microscopy yield an exceptionally large material gain of 6.8(±1)×104 cm−1 at 80 A cm−2. Calculations including realistic quantum dot energy levels, dot size fluctuation, nonthermal coupling of carriers in different dots, and band filling effects corroborate this result. A large maximum differential gain of 2×10−12 cm2 at 20 A cm−2 is found. The width of the gain spectrum is determined by participation of excited quantum dot states. We record a low transparency current density of 20 A cm−2. All experiments are carried out at liquid nitrogen temperature.

We report on 980nm InGaAs∕AlGaAs lasers with a broad waveguide based on a longitudinal photonic band crystal concept. The beam divergence measured as full width at half maximum was as narrow as <5° (vertical). Broad area 100μm multimode devices demonstrated >15W pulsed operation as limited by the current source. Significantly increased modal spot size enabled stable single lateral mode operation in broad ridge 10μm stripes. Maximum continuous wave power in single mode regime of 1.3W for 10μm wide stripe lasers was obtained, being limited by the catastrophic degradation of the unpassivated laser facets.

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