Focusing of Hyperbolic Phonon Polaritons by Bent Metal Nanowires and Their Polarization Dependence

Lei Ma, Anping Ge, Liaoxin Sun, Feng Liu and Wei Lu

ACS Photonics 10, 1841 (2023)
Manipulating in-plane hyperbolic phonon polaritons on biaxial van der Waals crystals provides an opportunity for the development of planar photonic devices. Recent studies show that nanometal disks constructed on the surface of hyperbolic media can focus phonon polaritons, which is a remarkable breakthrough in planar photonics. Here, we demonstrate that using bent metal nanowires made by strain engineering not only produces the focusing of hyperbolic phonon polaritons but also introduces a new modulation factor, the polarization of incident light, which shows a clear affection on focusing. In this study, we investigate the operating mechanism and applicability of this nanolens from the perspective of device size, incident light frequency, and polarization, where the effect of polarization is unprecedented for this type of surface engineering. With the support of super-resolution technology, the foci with high confinement are clearly observed and the focal length from 0.7 to 2.01 μm is achieved. Moreover, the angle between the in-plane polarization direction and the axial direction of the nanowires directly affects the intensity of the local field. This approach provides a new idea to control electromagnetic fields in a two-dimensional plane, which is beneficial to further promote the design of planar optical functional devices.