Asymmetric modal coupling in a passive resonator towards integrated isolators

Asymmetric response is essential to form a nonlinearity-based nonreciprocal device. Here, we studied the asymmetric modal coupling in a passive resonator driven by the nonconservative coupling add-drop filter (NCC-ADF). When light is incident from either port, the proposed configuration can selectively excite supermodes and realize an asymmetric stored optical energy in the passive resonators. Such asymmetry can be tuned on demand by varying the amplitude and phase delay of the mirror system. Furthermore, by introducing the thermal-optic nonlinearity effect in the proposed configuration, an optical isolator with low-power and broadband nonreciprocal optical transmission can be realized. The linear and nonlinear mode dynamics in the NCC-ADF configuration with asymmetric modal couplings were effectively described through a temporal coupled mode theory. The theoretical result will find potential application in on-chip integrated isolators as well as microcavity-based applications.