Coherent light sources are one of the most crucial foundations in both scientific disciplines and advanced applications. As a prominent platform, ultrahigh-Q whispering-gallery mode (WGM) microcavities have witnessed significant developments of novel light sources. However, the intrinsic chiral symmetry of WGM microcavity geometry and the resulting equivalence between the two directions of laser propagation in a cavity severely limits further applications of microlasers. Continue reading…