From Asymmetrical to the Nonreciprocal Isolator Using Time-varying Metasurfaces

We present an emulation design method for converting asymmetric isolators to nonreciprocal ones using time-varying metasurfaces. To illustrate the model, we design a structure using a combination of the photonic crystal (PhC) and time-varying metasurface. Moreover, we propose a general approach for numerical analysis of the time-modulated proposed structure using the extension of the transfer matrix method (TMM) which consists of working through the device one layer at a time and calculating an overall transfer matrix including the time-variation of the permittivity and permeability in each layer. Also, we use an optimization algorithm that is less used in the field of electromagnetism but is suitable for fast and accurate parameter optimization. The results show that the proposed method, using pure time-varying metasurfaces which cannot prepare full nonreciprocity alone, is a promising procedure for breaking the Lorentz reciprocity in the general isolator system as well as maintaining the previously asymmetric designed structure.