Non-reciprocity using quadrature-phase time-varying slab resonators

In this paper, it is shown that non-reciprocity can be observed in time-varying media without employing spatiotemporal modulated permittivities. We show that by using only two one-dimensional Fabry–Perot slabs with time-periodic permittivities having quadrature-phase difference, it is possible to achieve considerable non-reciprocity in transmission at the incidence frequency. To analyze such a scenario, generalized transfer matrices are introduced to find the wave amplitudes of all harmonics in all space. The results are verified by in-house finite-difference time-domain simulations. Moreover, in order to have a simple model of such time-varying slab resonators, a time-perturbed coupled-mode theory is developed for multiple resonances, and it is shown that the results obtained by this method and the analytical method are in excellent agreement.