  Microcavity polaritons are strongly interacting hybrid light-matter
quasiparticles, which are promising for the development of novel light sources
and active photonic devices. Here, we report polariton lasing in the UV
spectral range in microring resonators based on GaN/AlGaN slab waveguides, with
experiments carried out from 4 K up to room temperature. Stimulated polariton
relaxation into multiple ring resonator modes is observed, which exhibit
threshold-like dependence of the emission intensity with pulse energy. The
strong exciton-photon coupling regime is confirmed by the significant reduction
of the free spectral range with energy and the blueshift of the exciton-like
modes with increasing pulse energy. Importantly, the exciton emission shows no
broadening with power, further confirming that lasing is observed at
electron-hole densities well below the Mott transition. Overall, our work paves
the way towards development of novel UV devices based on the high-speed slab
waveguide polariton geometry operating up to room temperature with potential to
be integrated into complex photonic circuits.
