3.5-μm radius race-track microlasers operating at room temperature with 1.3-μm quantum dot active region

We present detailed studies of optically pumped InAs/InGaAs quantum dot based racetrack microlasers with 3.5-μm bend radius operating at room temperature. Q factor over 8000 and room temperature threshold power in the mW-range were achieved in the racetrack microlasers with straight section length ranging from 0 to 4 μm. A systematic investigation of the influence of the racetrack straight section length on spatial distribution of optical modes is presented. The microcavity eigenmodes and electromagnetic field distribution calculated by means of three-dimensional numerical simulation demonstrate a good agreement with the experimental results obtained by micro-photoluminescence and scanning near-field optical microscopy. The racetracks demonstrate zigzagging behavior of the modes inside the cavity and the energy switching between the radial maxima in second-order modes. Higher-order modes are found to be suppressed in micro-photoluminescence spectra.