Topological Valley Hall Edge State Lasing

Topological lasers based on topologically protected edge states exhibit unique features and enhanced robustness of operation in comparison with conventional lasers, even in the presence of disorder, edge deformation, or local defects. Here a new class of topological lasers arising from the valley Hall edge states is proposed, which does not rely on magnetic fields. Specifically, topological lasing occurs at domain walls between two honeycomb waveguide arrays with broken spatial inversion symmetry. Two types of valley Hall edge lasing modes are found by shaping the gain landscape along the domain walls. In the presence of uniform losses and two-photon absorption, the lasing results in the formation of stable nonlinear dissipative excitations localized on the edge of the structure, even if it has complex geometry and even if it is finite. Robustness of lasing edge states is demonstrated in both periodic and finite structures, where such states can circumvent certain corners without scattering losses or radiation into the bulk, as long as the intervalley scattering is absent. The photonic structure and mechanism proposed here for topological lasing is fundamentally different from those previously employed in topological lasers, and can be used for fabrication of practical topological lasers of various geometries.