Atomic-Void van der Waals Channel Waveguides

Abstract

Layered van der Waals materials allow creating unique atomic-void channels with subnanometer dimensions. Coupling light into these channels may further advance sensing, quantum information, and single molecule chemistries. Here, we examine theoretically limits of light guiding in atomic-void channels and show that van der Waals materials exhibiting strong resonances, excitonic and polaritonic, are ideally suited for deeply subwavelength light guiding. We predict that excitonic transition metal dichalcogenides can squeeze >70% of optical power in just <λ/100 thick channel in the visible and near-infrared. We also show that polariton resonances of hexagonal boron nitride allow deeply subwavelength (<λ/500) guiding in the mid-infrared. We further reveal effects of natural material anisotropy and discuss the influence of losses. Such van der Waals channel waveguides while offering extreme optical confinement exhibit significantly lower loss compared to plasmonic counterparts, thus paving the way to low-loss and deeply subwavelength optics.

Ultrathin WS2 Polariton Waveguide for Efficient Light Guiding

“…[22] However, they still have strong exciton resonances at K or K' valleys, [27] which results in high dielectric constants near the exciton energies. [28] Therefore, numerous types of passive photonic components have been proposed and investigated both theoretically [29,30] and experimentally. Experimentally demonstrated components include photonic crystals, [31][32][33][34] Mie resonators, [35][36][37][38] metalenses, [39] and whispering gallery cavities.…”

Nanostructured Transition Metal Dichalcogenide Multilayers for Advanced Nanophotonics

“…[ 5,11–13 ] At even lower energies (longer wavelengths) where the refractive index remains large but the material's absorption coefficient quickly vanishes, these materials can be exploited for lossless waveguiding and light confinement. [ 12–19 ] Furthermore, all TMDs are naturally anisotropic due to their vdW nature, endowing them with an inherent optical uniaxial permittivity with $$\varepsilon _{xx}=\varepsilon _{yy}\ne \varepsilon _{zz}$$. [ 8,13,14,17,20 ] In certain materials (e.g., in ReS 2 ) a distortion of the planar hexagonal lattice leads to biaxial anisotropy with different values of the in‐plane permittivity tensor elements, that is, $$\varepsilon _{xx}\ne \varepsilon _{yy}$$ and both being different from the out‐of‐plane $$\varepsilon _{zz}$$.…”

“…In this regard, careful testing and optimization of the fabrication procedures, applicable not only for semiconducting but also for metallic TMDs, and tested on various challenging to work with substrates, are of particular interest. This fabrication‐oriented progress, together with theoretical efforts [ 16,18,19 ] and knowledge of basic optical constants, [ 13 ] is essential for the development of all‐TMD nanophotonics.…”

van der Waals Materials for Overcoming Fundamental Limitations in Photonic Integrated Circuitry

“…However, further miniaturization of photonic devices meets fundamental limitations imposed by the wave nature of light . Plasmonics was previously considered a very promising approach to overcoming these limitations, yet absorption losses become increasingly severe in highly confined plasmonic modes and resonances. − With the moderate progress in overcoming the losses using excitonic materials, − the attention has been shifted to new photonic materials and all-dielectric platforms …”