Realization of Bound States in the Continuum and Exceptional Points in Rectangular Microcavities

Abstract Rectangular cavities are central building blocks in photonic circuits due to their excellent optical performance and facile fabrication procedure. Though the performance of the rectangular cavity is high enough for coherent light sources. However, for communication and signal processing, the introduction of a waveguide is inevitable. In this sense, leakage appears, and the quality ( Q ) factors are strongly spoiled. Herein, the possibility of manipulating the leakage losses in a waveguide‐microcavity system is explored. It is confirmed that obvious Fabry‐Perot (F‐P) bound states in the continuum (BIC) are established and the Q factors are significantly improved. Furthermore, by purposely introducing defects in the central areas of two cavities, the resonance behaviors of the symmetric and asymmetric modes of the cavities can be effectively modulated. With varying the intervals between two resonators, the eigenvalues and eigenvectors of the symmetric and the asymmetric modes periodically coalesce, clearly indicating the emergence of exceptional points (EPs). Surprisingly, strong chirality is also accomplished simultaneously at each EP. It is believed that findings provide a new platform to investigate the rich physics regarding non‐Hermiticity in rectangular cavities and substantially broaden the application potential of such resonators in high‐performance lasers and ultrasensitive EP sensors.