Robust single-mode lasing in topologically protected cavities

We demonstrate a novel approach to achieving robust, single-mode lasing in a trivial Su-Schrieffer-Heeger (SSH) microring array by leveraging non-Hermitian defect engineering and localized pumping. Unlike traditional topological lasers that require non-trivial bulk topology and uniform gain to excite edge-localized modes, our method introduces a coupling defect and selectively pumps a single microring to induce an exceptional point (EP). This generates a localized defect mode within the bandgap, enabling low-threshold, spectrally isolated lasing without edge states or high pump power. Theoretical analysis and experimental validation confirm the emergence of topologically protected lasing behavior rooted in the system’s non-Hermitian degeneracy rather than its Hermitian topology. This work provides a scalable, energy-efficient path toward topological laser arrays and integrated photonic platforms.