Non-reciprocal lasing action in topological cavities of arbitrary geometries

Topological insulator is a material in which helical conducting states exist on the surface of the bulk insulator. These states can transport electrons or photons at the boundary without any back scattering, even in presence of obstacles enabling to make topological cavities with arbitrary geometries that light can propagate in one direction. Here, we present the demonstration of the first experimental non-reciprocal topological laser that operates at telecommunication wavelengths. The unidirectional stimulated emission from edge states is coupled to a selected waveguide output port with an isolation ratio of 11 dB. Topological cavities are made of hybrid photonic crystals (i.e., two different photonic crystals) with distinct topological phase invariants, which are bonded on a magnetic material of yttrium iron garnet to break the time-reversal symmetry. Our experimental demonstration, paves the way to develop complex nonreciprocal topological devices of arbitrary geometries for integrated and robust generation and transport of light in classical and quantum regimes.