TiO₂ Nanodisk Arrays as All-Dielectric Huygens’ Metasurfaces for Engineering the Wavefront of Near-UV Light

Abstract

Electromagnetic components are important for ultraviolet (UV) applications. However, due to the limitation in the materials’ intrinsic responses, there are fewer electromagnetic components in high-frequency regimes than in low-frequency ones. Conventional UV components manipulate the wavefront via geometric phase accumulation; thus, they are significantly bulky and inefficient. In this study, we demonstrate all-dielectric Huygens’ metasurface (ADHMS) at a near-ultraviolet (NUV) regime. The NUV-ADHMS is comprised of resonant titanium dioxide (TiO2) nanodisks, with the ultrathin thickness of the fifth wavelength. In addition, by modulating the diameter of the resonant TiO2 nanodisks, we can simultaneously excite and control both electric and magnetic dipoles, achieving a powerful wavefront engineering of the near-unity transmittance and a full range of the 2π phase coverage. Finally, we employed the NUV-ADHMS to bend a normal incident beam, demonstrating a deflection angle of 11° at a wavelength of 405 nm.

Chiroptical Enhancement in Hybrid Core–Shell Nanoresonators

“…To achieve near-field enhancement of individual particles through resonator coupling between adjacent units and to circumvent structural chirality induced by asymmetrical particle distributions, , we arrange the cubic gold core and silicon shell structures into a two-dimensional array with identical periodicity (Figure a). When the period length of the metasurface is set at 500 nm, the highest optical chirality density within the spacer is attained (Figure b).…”

Revisiting Optical Material Platforms for Efficient Linear and Nonlinear Dielectric Metasurfaces in the Ultraviolet, Visible, and Infrared

“…At near-UV frequencies (λ > 315 nm), TiO 2 , Nb 2 O 5 , and optimized SiN x have been used as optical materials for dielectric metasurfaces. TiO 2 exhibits a high n (>2.4) at near-UV frequencies and has been used as a constituent of beamsteering metasurfaces whose measured and simulated deflection efficiencies approach 15.4% and 80% at λ = 405 nm, respectively 38 (Figure 2c.i). Furthermore, its high n enables optical resonance within an ultrathin layer (approximately λ/ 5), thereby enabling phase manipulation with 2π coverage even when located in a silicon dioxide (SiO 2 ) background medium.…”

“…(c) SEM images of UV metasurfaces represented with various optical materials: (c.i) TiO 2 . Adapted from ref . Copyright 2021 American Chemical Society.…”

Review of Metasurfaces and Metadevices: Advantages of Different Materials and Fabrications

“…Therefore, the development of high-efficiency metasurfaces shifted focus to TiO 2 in 2016 [78,146], with work mainly done by the Capasso group. With a high refractive index and low optical loss, TiO 2 -based metasurfaces exhibit exceptional properties in the visible wavelength range [147][148][149][150][151][152][153][154][155][156][157][158][159][160][161][162][163].…”