High‐Q Nanophotonics over the Full Visible Spectrum Enabled by Hexagonal Boron Nitride Metasurfaces. Issue 13 (21st February 2023)

• Record Type: Journal Article
• Authors: Kühner, Lucca; Sortino, Luca; Tilmann, Benjamin; Weber, Thomas; Watanabe, Kenji; Taniguchi, Takashi; Maier, Stefan A.; Tittl, Andreas
• Is Part Of: Advanced materials. Volume 35:Issue 13(2023)
• Page Start: n/a
• Page End: n/a
• Publication Date: 2023-02-21
• Subjects: bound states in the continuum -- hexagonal boron nitride -- high‐Q resonances -- low index photonics; Materials -- Periodicals; Chemical vapor deposition -- Periodicals; 620.11
• DOI: 10.1002/adma.202209688
• Languages: English
• ISSNs: 0935-9648

Abstract

Abstract: All‐dielectric optical metasurfaces with high quality ( Q ) factors have been hampered by the lack of simultaneously lossless and high‐refractive‐index materials over the full visible spectrum. In fact, the use of low‐refractive‐index materials is unavoidable for extending the spectral coverage due to the inverse correlation between the bandgap energy (and therefore the optical losses) and the refractive index ( n ). However, for Mie resonant photonics, smaller refractive indices are associated with reduced Q factors and low mode volume confinement. Here, symmetry‐broken quasi bound states in the continuum (qBICs) are leveraged to efficiently suppress radiation losses from the low‐index ( n ≈ 2) van der Waals material hexagonal boron nitride (hBN), realizing metasurfaces with high‐ Q resonances over the complete visible spectrum. The rational use of low‐ and high‐refractive‐index materials as resonator components is analyzed and the insights are harnessed to experimentally demonstrate sharp qBIC resonances with Q factors above 300, spanning wavelengths between 400 and 1000 nm from a single hBN flake. Moreover, the enhanced electric near fields are utilized to demonstrate second‐harmonic generation with enhancement factors above 10 2 . These results provide a theoretical and experimental framework for the implementation of low‐refractive‐index materials as photonic media for metaoptics. Abstract : The authors demonstrate how the combination of low‐refractive‐index resonator materials such as hexagonal boron nitride and symmetry‐broken bound states in the continuum overcomes the lack of high‐refractive‐index and lossless materials in the visible region. Following this approach, high‐ Q photonic resonances over the full visible spectrum are realized and used to enhance second‐harmonic generation in the ultraviolet region.