Extraordinary Figure‐of‐Merit of Magnetic Resonance from Ultrathin Silicon Nanohole Membrane as All‐Dielectric Metamaterial

Abstract

index, [4][5][6][7][8] optical chirality, [9][10][11][12][13] or unusual high-index. [14] Those unique optical properties facilitate new optical systems such as multifunctional optical filter, phase modulator, gradient index lens, perfect/ super lens, and optical clocking supported by transformation optics or even active optical devices so called "meta-devices". Those metamaterial has been successfully demonstrated by using various metallic subwavelength structures based on a split ring resonator, metallic cut-wire arrays, and double fishnet structures. [1,8,15,16] However, passive metallic metamaterials at optical frequencies typically exhibit considerable conduction loss due to their metallic nature, which impedes practical device applications. Furthermore, their intrinsic geometrical asymmetry causes high angular dependency, which restricts wide-angle operation and 3D assembly as well. Recently, all-dielectric metamaterials actively move onto an emerging and attractive approach for controlling electromagnetic (EM) fields to take full benefits of low-loss, bandwidth enhancement, and isotropic responses. [17][18][19] Theoretical concept was first proposed by Lewin [20] and the dielectric metamaterials have experimentally demonstrated at microwave and infrared region by using high-index subwavelength structures such as silicon, [21][22][23][24][25] dielectric composite, [26] TiO 2 , [27] and tellurium cubic arrays. [28] Moreover, all-dielectric metamaterials have been employed for zero-index metamaterial, [29] gradient optical elements, [30,31] or optomechanical metamaterial with free-standing silicon membrane, [25] but still not for biosensor. All-dielectric metamaterial based on silicon realized the high figure-of-merit (FOM) of 103 by using electromagnetically induced transparency at the working wavelengths over 1.3 µm. [23] However, the previous work has limitations in practical use such as biosensing, because the conventional siliconbased spectrum systems cannot be applied at the wavelength larger than 1.3 µm.Here we report a silicon dielectric metamaterial providing a magnetic resonance at near-infrared frequencies and label-free sensing with an extraordinarily resolvable shift of magnetic resonance. This all-dielectric metamaterial consists of subwavelength nanohole arrays in a square lattice on an ultrathin Metamaterial allows novel nanophotonic applications such as negative permeability, negative refractive index, and near-zero index. In particular, all-dielectric metamaterials recently create new opportunities for manipulating electromagnetic fields, taking full advantage of low-loss, bandwidth enhancement, and isotropic responses. Here a silicon dielectric metamaterial is reported in near-infrared region, exhibiting extraordinarily figure-ofmerit, defined by sensitivity (resonance shift/refractive index change) over full width at half maximum, from magnetic resonance shift depending on index changes of surrounding medium. This silicon dielectric metamaterial comprises subwavelength nanohole arrays in a...