Ghost-induced exact degeneracies

We show that the recently discovered "ghost coupling" (Opt. Lett. 46, 1708-1711 (2021)) – a new type of mode interaction mediated by a special class of nonuniform waves in biaxial anisotropic media – can lead to exact frequency degeneracies in guided modes. In addition to explaining the mode interaction through a coupled mode analysis, we also show that the interaction can lead to emergence of exceptional points which can offer a new approach to optical sensing with better performance.