Nanophotonic devices based on two-dimensional crystals enable various technological applications, ranging from biosensing to quantum communication. In those devices, plasmonic antennas have been extensively explored in the photon-polariton conversion, as they allow field confinement within subdiffraction volumes. Despite the wide-reaching potential of polaritonics, essential rules for engineering polariton launchers are still to be developed, as the influence of the antenna geometry and source parameters on the polariton directivity is unknown. Here, we address this issue by combining concepts of radio-frequency antenna design with established polariton modeling. As an input for the model, we simulate hyperbolic phonon polariton waves in hexagonal boron nitride launched by metallic antennas. By adapting a Fresnel and Fraunhofer field regions formalism to polaritonics, we optimize the model accuracy and graphically represent several launching parameters as radiation patterns. Furthermore, we demonstrate how our framework can be applied to real antennas by employing it to experimental near-field images of polaritons reported in the literature. Our results show that the antenna geometry, its resonance order, and the angle of incidence of the light can strongly influence the polariton-wave pattern in the crystal. We foresee that our framework can add to further studies approaching optimized polariton launching and help the engineering of nanophotonic chips.
Bibliographical noteFunding Information:
We thank A. H. Castro Neto for bringing insightful thoughts to the work. We also thank Rainer Hillenbrand and the authors of Ref. for providing the s-SNOM data. We thank LNLS and Unicamp for supporting us with the infrastructure for this project. R.M. and R.F. acknowledge support from the São Paulo Research Foundation (FAPESP) through Grants No. 2019/08818-9 and No. 2020/15740-3. R.M. thanks Coordenação de Aperfeiçoamento de Pessoal de Nível Superior - Brasil (CAPES) (Finance Code 001) for financial support. R.F. acknowledges financial support from FAPESP through the Young Investigator Grant No. 2019/14017-9 and from the National Council for Scientific and Technological Development (CNPq) research productivity Grants No. 311564/2018-6 and No. 309946/2021-2. I.D.B., F.H.F., and F.C.B.M. acknowledge the support from CNPq through Grants No. 311327/2020-6, No. 140594/2020-5, and No. 313672/2021-0, respectively. A.R. acknowledges the support by the National Research Foundation, Prime Minister Office, Singapore, under its Medium Sized Centre Programme and the support by Yale-NUS College (through Grant No. A-0003356-42-00).
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