Brewster Mode‐Enhanced Sensing with Hyperbolic Metamaterial

Abstract

Hyperbolic metamaterials (HMMs) are artificial extreme anisotropic media, which are characterized by indefinite or hyperbolic dispersion relation where the out-ofplane dielectric constant has an opposite sign to the in-plane dielectric constants. [1] These effective bulk metastructures are usually composed of metallic and dielectric elements, and display extraordinary optical properties over a wide frequency band from visible to terahertz. The HMMs showing hyperbolic dispersion can be classified based on the sign of their dielectric components, such as type I (−ε ⊥ and ε ll ) and type II (ε ⊥ and − ε ll ). The type I HMM is usually realized using metallic nanowires immersed in a dielectric matrix, [2] while the type II HMM assumes stacked metal/dielectric multilayers. [3] In particular, the type II is the most studied HMM because of its straightforward fabrication using conventional thin film physical vapor deposition (PVD) techniques. Various metal-dielectric multilayer stacks have been proposed to realize hyperbolic dispersion over the frequency band from visible to terahertz. [1][2][3][4][5][6][7] In recent years, the type II multilayered HMMs have received much attention and used as the technological core in many potential applications including ultrasensitive biosensors, [8][9][10] absorbers, [11,12] single photon sources, [13] super-resolution imaging, [14] and Cherenkov radiation. [15] In addition, thermal flux engineering has been achieved using HMMs, [16] which is considered to be the near-field analog of a blackbody. Also, the occurrence of super-Planckian thermal energy transfer has been predicted in HMMs. [17] The overall optical response of HMM can be qualitatively predicted in the framework of the so-called effective medium theory (EMT) since both the layers of HMMs are deeply subwavelength. [18] In particular, HMM is a 1D subwavelength photonic crystal when stacking multiple periodic bilayers of metal/dielectric is formed. The optical response of HMM can be homogenized if the number of bilayers in the stack is large enough and their thickness is deeply subwavelength. Therefore, the overall uniaxial optical response can be described using an effective dielectric permittivity, whose components (parallel and perpendicular to the surface of HMM) can be calculated by applying boundary conditions. [19] HMM supports both radiative and nonradiative guided modes. Bulk plasmon polariton (BPP) [20] or high-k optical Hyperbolic metamaterials (HMMs) are used to demonstrate extreme sensitivity biosensing by exciting their high-k modes. However, momentum couplers, such as subwavelength diffraction grating or bulky high-index prism, are required to excite these nonradiative modes, which is not cost-effective and thus not suitable for point-of-care applications. Here, a cost-effective and scalable HMM-based sensor platform is proposed and experimentally demonstrated, by exciting the Brewster mode of HMM from free-space. The excitation of Brewster modes is shown in a multilayered HMM comprising of alternating thin l...

Perovskite/Metal‐Based Hyperbolic Metamaterials: Tailoring the Permittivity Properties of Coexisting Anisotropies in the Visible Region

“…Another type I HMM comprising alternating layers of TiN/Sb 2 S 3 was presented in Ref. [15], exhibited elliptic to hyperbolic dispersion transition at ≈560 nm but, again, no type II properties within the visible band. A HMM exhibiting coexisting type I and type II regions was presented in Ref.…”

Hyperbolic dispersion metasurfaces for molecular biosensing

“…Hyperbolic metamaterials support both radiative and nonradiative modes. The radiative modes such as Ferrell-Berreman [103,104] and Brewster modes [75,105] can be excited from free space. However, a momentum-matching condition must be satisfied to excite HMM nonradiative modes, such as SPP and BPP modes.…”

“…A phase-sensitive HMM-based biosensor can be developed by exciting the Brewster mode of the HMM because a sudden phase jump occurs at the Brewster angle. In this scheme, the phase shift at the Brewster angle due to the change in RI arising from the presence of the analyte can be recorded as the sensing parameter [75]. However, extreme sensitivity biosensing is only possible by exciting the BPP modes of the HMM.…”

“…This miniaturized multimode sensor exhibited extreme bulk RI sensitivity with a record figure of merit (FOM) and detected biotin concentrations as low as 10 pM. Since then different hyperbolic dispersion metamaterials have been proposed for sensitivity enhancement purposes [72][73][74][75][76][77][78][79][80][81][82].…”

Anisotropic Photonics Topological Transition in Hyperbolic Metamaterials Based on Black Phosphorus

“…In contrast to the closed iso-frequency contour (IFC) of traditional materials, the hyperbolic IFC is open and large wave-vectors can be supported in HMMs [ 15 ]. This special feature has been explored for many prospective applications in hyperlens [ 6 ], spontaneous emission enhancement [ 16 , 17 ], Goos–Hänchen effect [ 18 , 19 ], photonic topological transition [ 20 , 21 , 22 , 23 , 24 ], photonic spin hall effect [ 25 , 26 ], and Casimir force [ 27 , 28 ].…”