Optical isolator based on backward Brillouin scattering

Abstract

We propose to realize an optical isolator based on backward Brillouin scattering in a whispering-gallery-mode (WGM) cavity that supports both traveling optical and acoustic waves. When the WGM cavity is optically driven in one direction, the time-reversal symmetry for light transmission is broken due to the unidirectional photon–phonon coupling. We show that the signal light is either transmitted or completely absorbed depending on whether it propagates in the same or opposite direction as the strong pump laser. The perfect absorption can be interpreted as a phase transition in a parity–time–symmetric Hamiltonian with the balanced gain and loss. The present work paves a way for the realization of an on-chip optical isolator with the high degree of isolation, large bandwidth, and low insertion loss simultaneously.