Toroidal dipole bound states in the continuum metasurfaces for terahertz nanofilm sensing

Abstract

A novel terahertz nanofilm sensor consisting of toroidal dipole bound states in the continuum (TD-BIC) inspired Fano resonance metasurface is proposed and investigated, which exhibits both the TD character and BIC feature. When the mirror symmetry of the unit cell was broken, the TD resonance was excited and demonstrated by anti-aligned magnetic dipoles and calculated scattering powers and the BIC mode was verified with the quality factor satisfying the inverse square law. Combined with the amplitude difference referencing technique, the TD-BIC inspired Fano resonance was utilized for nanofilm sensing at THz frequencies for the first time. Simulation results show that the amplitude difference can be easily observed by comparing the resonance frequency shift under difference thicknesses of germanium overlayer. Moreover, by coating with a 40 nm-thick analyte overlayer, the sensitivity of amplitude difference can achieve 0.32/RIU, which is a significant value and more suitable for sensing nanofilm analytes than the traditional frequency shift method. These advantages make our proposed structure have potential applications in sensing nanofilm analytes.

Photonic and Plasmonic Metasensors

“…[387,388] Figure 13 shows drawings of various forms of toroidal-resonant metastructures that have been engineered for next-generation nanophotonic and plasmonic applications. [389][390][391][392][393][394][395][396][397][398][399] Squeezing electromagnetic fields within an extremely small spot and possessing exquisite sensitivity to the environmental perturbations, toroidal scatterers allow for the creation of high-precision biochemical sensors and immunobiosensing instruments. [24] In the following, we consider recently conducted studies for devising toroidal biochemical and thermal sensors.…”

“…h) Reproduced with permission. [396] Copyright 2020, Optica Publishing Group. i) Reproduced with permission.…”

“…Copyright 2020, Optica Publishing Group. h) Reproduced with permission [396]. Copyright 2020, Optica Publishing Group.…”

Simultaneous Measurements of Refractive Index and Methane Concentration through Electromagnetic Fano Resonance Coupling in All-Dielectric Metasurface

“…With the rapid development of nanotechnology, different metasurface sensors based on Fano resonance also have been reported, such as refractive index sensors [ 8 , 9 , 10 , 11 , 12 ], biosensors [ 13 , 14 , 15 , 16 , 17 , 18 , 19 , 20 ], and gas sensors [ 21 ]. However, quite a lot of metasurface structures are based on a metal layer [ 22 , 23 , 24 , 25 ], which would produce higher Joule losses and lower quality factor. All-dielectric materials can solve the above problem because they have much lower Joule losses.…”

Bound states in the continuum in periodic structures with structural disorder

“…In the last two decades, BICs have been observed in many photonic structures such as photonic crystals, metasurfaces, [2][3][4], chains of coupled resonators [5][6][7][8], waveguides [9][10][11][12][13] and even single subwavelength resonators supporting quasi-BIC in a form of supercavity modes [14][15][16]. A divergent radiative quality (Q) factor, strong spatial localization, and drastic enhancement of the incident field make BICs very prospective for many applications including lasers [17][18][19][20][21][22][23][24][25], optical filters [26][27][28], biological and chemical sensors [29][30][31][32][33], and non-linear photonics [34][35][36][37][38][39][40][41][42][43].…”