One-way light flow by spatio-temporal modulation.

The unidirectional flow of electrons that takes place in a conventional electronic diode has been a cornerstone in the development of the field of electronics. Achieving an equivalent one-way flow for light has been a long-standing problem. While a number of concepts have been suggested recently, attaining a unidirectional flow of light in a two-port system (e.g., a waveguiding configuration) is still challenging. Here, we present what we believe to be a novel approach for breaking reciprocity and achieving one-way flow of light. Taking a nanoplasmonic waveguide as an example, we show that a combination of time-dependent interband optical transitions, when in systems exhibiting a backward wave flow, can yield light transmission strictly in one direction. In our configuration, the energy flow is unidirectional: light is fully reflected in one direction of propagation, and is unperturbed in the other. The concept can find use in a range of applications including communications, smart windows, thermal radiation management, and solar energy harvesting.

Optically tunable bianisotropy in a sphere made from an epsilon-near-zero material.

Bianisotropic media can be used to engineer absorbance, scattering, polarization, and dispersion of electromagnetic waves. However, the demonstration of a tunable light-induced bianisotropy at optical frequencies is still lacking. Here, we propose an experimentally feasible concept for a light-induced tunable bianisotropic response in a homogeneous sphere made of an epsilon-near-zero (ENZ) material. By exploiting the large linear absorption and the large possible intensity-dependent changes in the permittivity of ENZ materials, the direction-dependent scattering and absorption cross sections could be obtained. Our findings pave the way for further studies and applications in the optical regime requiring full dynamic control of the bianisotropic behavior.

Nonlocal Cable-Network Metamaterials.

Metamaterials are artificial materials in which the atoms of ordinary solids are replaced by tailored functional building blocks. Therefore, previous work has emphasized tailoring the inside of the building blocks, for example, by exploiting local resonances, to realize unusual effective metamaterial properties. However, the wave properties of a metamaterial are not only determined by its building blocks but also by the interactions between these building blocks. Here, reconfigurable "plug-and-play" electromagnetic metamaterials are introduced for which the building blocks are essentially trivial standard bayonet Neill-Concelman (BNC) connectors and the effective metamaterial properties are solely achieved by tailoring the local and especially the nonlocal interactions mediated by standard coaxial cables. Unprecedented dispersion relations of the lowest band with multiple regions of slow waves and backward waves are demonstrated. Importantly, the dispersion relation of such metamaterials dominated by nonlocal interactions is not limited by the principle of causality in the same way as for metamaterials designed by local resonances of building blocks.