Perfect light absorber with a PT phase transition via coupled topological interface states

Recently,the concepts of parity–time(PT)symmetry and band topology have inspired many novel ideas for light manipulation in their respective directions.Here we propose and demonstrate a perfect light absorber with a PT phase transition via coupled topological interface states(TISs),which combines the two concepts in a onedimensional photonic crystal heterostructure.By fine tuning the coupling between TISs,the PT phase transition is revealed by the evolution of absorption spectra in both ideal and non-ideal PT symmetry cases.Especially,in the ideal case,a perfect light absorber at an exceptional point with unidirectional invisibility is numerically obtained.In the non-ideal case,a perfect light absorber in a broken phase is experimentally realized,which verifies the possibility of tailoring non-Hermiticity by engineering the coupling.Our work paves the way for novel effects and functional devices from the exceptional point of coupled TISs,such as a unidirectional light absorber and exceptional-point sensor.