Effect of the Cavity Resonance-Gain Offset on the Output Power Characteristics of GaSb-Based VECSELs

In spite of elaborate heat-sinking employing intracavity heat-spreaders, the maximum output power of current (AlGaIn)(AsSb)-based vertical-external-cavity surface-emitting lasers (VECSELs) is still limited by thermal rollover (e.g., 0.8 W at 20degC at a peak emission wavelength of 2.35 mum). To identify the mechanisms underlying this thermal limitation, VECSEL structures with different cavity resonance-gain offsets have been fabricated and characterized. The resulting data have been analyzed using a thermooptical model. The temperature-dependent spectral alignment of quantum-well gain and microcavity resonance (so-called ldquogain offsetrdquo) is found to be one of the key parameters in optimizing high-power performance. A 45% increase in maximum room-temperature output power is obtained if the gain offset is chosen such that the gain spectrum matches the cavity resonance at operating pump power, i.e., at elevated active region temperatures.