Extraordinary transmission in an add–drop filter configuration driven by nonconservative coupling

We proposed a nonconservative coupling scheme based on the add–drop filter configuration, in which a high Q factor passive microtoroid resonator is indirectly driven by an active unit, thus providing an additional coupling which might be comparable to a mode decay rate. Extraordinary scattering points are predicted when one of the supermodes becomes lossless. Specifically, when the inherent coupling strength is set at half of the mode’s total decay rate, controllable transmission peaks can be realized by tuning the nonconservative coupling strength and phase delay. Our theoretic research might find potential application in tunable light steering based on non-Hermitian resonator systems.