Light control with Weyl semimetals

Weyl semimetals are topological materials whose electron quasiparticles obey the Weyl equation. They possess many unusual properties that may lead to new applications. This is a tutorial review of the optical properties and applications of Weyl semimetals. We review the basic concepts and optical responses of Weyl semimetals, and survey their applications in optics and thermal photonics. We hope this pedagogical text will motivate further research on this emerging topic.Comment: Tutorial review, 53 pages, 12 figure

Tunable Magnetless Optical Isolation with Twisted Weyl Semimetals

Weyl semimetals hold great promise in revolutionizing nonreciprocal optical components due to their unique topological properties. By exhibiting nonreciprocal magneto-optical effects without necessitating an external magnetic field, these materials offer remarkable miniaturization opportunities and reduced energy consumption. However, their intrinsic topological robustness poses a challenge for applications demanding tunability. In this work, we introduce an innovative approach to enhance the tunability of their response, utilizing multilayered configurations of twisted anisotropic Weyl semimetals. Our design enables controlled and reversible isolation by adjusting the twist angle between the anisotropic layers. When implemented in the Faraday geometry within the mid-IR frequency range, our design delivers impressive isolation, exceeding 50 dB, while maintaining a minimal insertion loss of just 0.33 dB. Moreover, the in-plane anisotropy of Weyl semimetals eliminates one or both polarizers of a conventional isolator geometry, significantly reducing the overall dimensions. These results set the stage for creating highly adaptable, ultra-compact optical isolators that can propel the fields of integrated photonics and quantum technology applications to new heights

Metasurface-Based Realization of Photonic Time Crystals

Photonic time crystals are artificial materials whose electromagnetic properties are uniform in space but periodically vary in time. The synthesis of such materials and experimental observation of their physics remain very challenging due to the stringent requirement for uniform modulation of material properties in volumetric samples. In this work, we extend the concept of photonic time crystals to two-dimensional artificial structures -- metasurfaces. We demonstrate that time-varying metasurfaces not only preserve key physical properties of volumetric photonic time crystals despite their simpler topology but also host common momentum bandgaps shared by both surface and free-space electromagnetic waves. Based on a microwave metasurface design, we experimentally confirmed the exponential wave amplification inside a momentum bandgap as well as the possibility to probe bandgap physics by external (free-space) excitations. The proposed metasurface serves as a straightforward material platform for realizing emerging photonic space-time crystals and as a realistic system for the amplification of surface-wave signals in future wireless communications.Comment: 21 pages, 3 figure

Nonreciprocal optical nonlinear metasurfaces

We demonstrate nonreciprocal one-way transmission through a half-a-micron-thick nonlinear silicon-VO2 metasurface for low-power CW excitation. Reciprocity is broken by optically self-induced phase transition of VO2 occurring at different intensities for the opposite directions of illumination

Tunable localization of light using nested invisible metasurface cavities

Funding Information: Research funding: This work was supported in part by the Academy of Finland ( https://doi.org/10.13039/501100002341 ) under grant 330260 and by Nokia Foundation ( https://doi.org/10.13039/501100004181 ) under scholarship 20200224. Publisher Copyright: © 2023 the author(s), published by De Gruyter, Berlin/Boston 2023.An invisible cavity is an open resonant device that confines a localized field without producing any scattering outside of the device volume. By exploiting the scatter-less property of such device, it is possible to nest two invisible cavities, as the outer cavity would simply not notice the presence of the inner one, regardless of their relative position. As a result, the position of the inner cavity becomes a means to easily control the field localized inside the cavity and its quality factor. In this paper, we discuss the properties of nested invisible cavities as a simple method to achieve stronger localized fields and high tunable quality factor. Furthermore, we show that in optics, these cavities can be implemented using nanodisk-based dielectric metasurfaces that operate near their electric resonances.Peer reviewe