Bifurcated overtones of one-way localized Fabry–Pérot resonances in parity-time symmetric optical lattices**Project supported by the National Natural Science Foundation of China (Grant Nos. 11674119, 11404125, and 11574389). X. F. Z acknowledges the financial support from the Bird Nest Plan of HUST, China. P. Z. is supported by One Hundred-Talent Plan of Chinese Academy of Sciences.

Abstract

Since the first observation of parity-time (PT) symmetry in optics, varied interesting phenomena have been discovered in both theories and experiments, such as PT phase transition and unidirectional invisibility, which turns PT-symmetric optics into a hotspot in research. Here, we report on the one-way localized Fabry–Pérot (FP) resonance, where a well-designed PT optical resonator may operate at exceptional points with bidirectional transparency but unidirectional field localization. Overtones of such one-way localized FP resonance can be classified into a blue shifted branch and a red shifted branch. Therefore, the fundamental resonant frequency is not the lowest one. We find that the spatial field distributions of the overtones at the same absolute order are almost the same, even though their frequencies are quite different.