Single-mode robust defect-based laser

Non-Hermitian systems can exhibit unique topological effects that can be realized in photonic crystals, metamaterials, and coupled resonators. In our theoretical and experimental work, by utilizing non-Hermitian degeneracies known as the exceptional points (EP) and a locally embedded defect in a trivial array of microring resonators, we form a single-mode robust defect-based laser emission that is immune from disorder in the couplings in the array. Our proposed design facilitates going beyond edge mode lasing and bypasses the requirements sought to be evaded in previous approaches towards achieving topological lasing modes.