Phys.org 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 underlying structure, because of the existence of topologically protected valley edge states that circulate around the cavity without experiencing localization. The laser based on valley edge states may open routes to the practical use of topological protection in electrically driven laser sources…read more. TECHNICAL ARTICLE
The electrically-driven topological laser prototype in the lab measures a tiny 4mm in length. A Singapore 5 cent coin was placed above it for size comparison. Credit: NTU Singapore