Antireflection Spatiotemporal Metamaterials

Abstract

Reflection occurs when light impinges on an interface between two distinct media. Suppression of the reflection is of paramount significance to practical applications in information transfer and conversion. While technologies such as the Brewster effect and material coatings are widely adopted to eliminate the wave reflection from purely spatial or temporal interfaces, how to eliminate the reflection from a spatiotemporal interface remains elusive. Here, a new type of spatiotemporal metamaterial that functions as a global and generalized perspective of quarter‐wave impedance transformers is presented. With the proper geometric design, the proposed spatiotemporal metamaterial can fully suppress the reflection, applicable to arbitrary modulation velocities. Importantly, the tunability of modulation velocity in the spatiotemporal metamaterial allows flexible frequency conversions in high efficiency, indicating that the spatiotemporal metamaterials are much more powerful than the purely spatial or temporal counterparts. These findings not only enhance the controllability of electromagnetic waves but also can be adapted to other classes of physical dynamics, including water surface waves, acoustic, and elastic.

Conformal Spatiotemporal Modulation Enabled Geometric Frequency Combs

“…n t 0 c t 0 (11) in such cases, the amplitude ratio of electric field between successive components of the transmission modes can be approximated as…”

“…The fascinating topic of time-varying medium has garnered significant attention in recent years. − Light matter interaction in a time-varying system is fundamentally distinct from that in the conventional passive medium, as the energy exchanges between the wave and matter are caused by the breaking of time-translational symmetry. The investigation of time-varying matter has been significantly propelled by a range of theoretical and experimental findings, including amplified emission, temporal reflections and transmissions, − temporal double slits, luminal amplification, − temporal antireflection, , momentum bandgaps, − temporal topological phases, temporal aiming, spatiotemporal scatterings, , and harmonic spectrum manipulations. − Time-varying media can generally be categorized into periodic and aperiodic types. In particular, the spatiotemporal periodic modulation of the refractive index of the ring resonators facilitates interband transitions of photon states, analogous to electronic transitions in semiconductors .…”