Scientists develop first electrically-driven ‘topological’ laser  February 13, 2020 Previous demonstrations of topological lasers have required an external laser source for optical pumping and have operated in the conventional optical frequency regime. An international team of researchers (Singapore, UK) demonstrated an electrically pumped terahertz quantum cascade laser based on topologically protected valley edge states. Unlike topological lasers that rely on large-scale features to impart topological protection, the compact design makes use of the valley degree of freedom in photonic crystals, analogous to two-dimensional gapped valleytronic materials. With regularly spaced emission peaks lasing occurs in a sharp-cornered triangular cavity, even if perturbations are introduced into the […]