Researchers at Technische Universität Wien in Austria report in the June 3 issue of Applied Physics Letters the relative performance of GaAs/AlGaAs quantum cascade lasers fabricated with Fabry-Perot, distributed feedback or microcylinder resonators. They found that the laser with a microcylinder quadrupolar geometry displayed similar characteristics to the others with ridge-shaped cavities.They fabricated the lasers using solid-source molecular beam pitaxy on an N-doped GaAs substrate. The microcylinder laser (above) displayed a normalized spectrum at 78 K blue-shifted by 20 cm-1 from the 12.50-µm wavelength of the Fabry-Perot laser, which they attributed to a lower threshold current density. The maximum operating temperature of 54 °C for the microcylinder laser was slightly higher than that of those with a distributed feedback design and 57 °C higher than previously reported for InP-based microcylinder lasers.