Materials with time-varying permittivity are an emerging research area in the electromagnetics and optics communities. From Maxwell's equations, the electric displacement (D) must be continuous in the time domain. However, this requirement is not satisfied for some conventional time domain solvers, which were developed for time-invariant simulations. Here we briefly review several commercial and open-source software packages. Some of them employ a so-called time-static simplification, which works well for time-invariant materials but will fail for time-varying materials. Read more Wending Mai*, Jingwei Xu, Douglas H. Werner

The quarter-wavelength matching technique is widely used because it minimizes the reflection while it maximizes the transmission. The recently introduced antireflection temporal coatings (ATCs) [Optica7, 323 (2020)10.1364/OPTICA.381175] have been considered as its temporal analog. However, our study shows that by introducing an ATC, not only will the reflection be reduced but also the transmission. This phenomenon is opposite its spatial counterpart, which indicates that ATCs are more than simply a temporal dual of quarter-wavelength matching. This is a direct consequence of the different physical phenomena that are manifested in the temporal and spatial domains. Read more Wending Mai,* Jingwei Xu,…

It is well known that control over the polarization of electromagnetic waves can be achieved by utilizing artificial anisotropic media such as metamaterials. However, most of the related research has been focused on time-invariant systems. Inspired by the concept of temporal boundaries, we propose a method to realize polarization conversion in real time by employing time-variant materials, whose permittivity or permeability switches between isotropic and anisotropic values. The criteria for complete polarization conversion are studied for several polarization angles, both analytically and numerically. Read more Jingwei Xu,* Wending Mai, AND Douglas H. Werner

Chiral mirrors are a class of metamaterials that reflect circularly polarized light of a certain helicity in a handedness-preserving manner, while absorbing circular polarization of the opposite handedness. However, most absorbing chiral mirrors operate only in a narrow frequency band, as limited by the causality principle. Instead of absorbing the undesired waveform, here we propose a transparent chiral mirror that allows undesired waves to pass through. In particular, the handedness-preserving band of the transparent chiral mirror is free of the causality limit, thus enabling broadband functionality. Furthermore, since electromagnetic waves outside the handedness-preserving band may transmit through the proposed chiral…