Evidence of Tunable Fano Resonance in a Liquid Crystal‐Based Colloidal Metamaterial

Abstract

behavior gives a characteristic dip in the scattering spectrum along with an asymmetric spectral profile. [1,3] Fano resonance is a ubiquitous physical phenomenon observed in a wide range of systems [2][3][4] such as autoionized atoms, Bose-Einstein condensates, quantum dots, photonic crystals, plasmonic nanostructures, and high refractive index microspheres. The unique Fano line shape and the spectral dip have the potential to enable applications [5] such as slow-light devices, [6] optical switches, [7] optical sensors, [8,9] and nanoantennas. [10] In metamaterials, Fano resonance was mostly observed in plasmonic systems, where the interference between a superradiant bright mode, which is directly excited by incident light and a sub-radiant dark mode, indirectly excited by near-field coupling with the bright mode, lead to the Fano spectral profile. [4] Systems such as ring-disk cavities, asymmetric split-ring resonators, and plasmonic oligomers were fabricated to realize this feature in the THz, microwave and NIR regimes. [11,12] However, at NIR and visible frequencies, the quality factor of the Fano resonance is limited by strong absorption and dissipation losses in metals. [12] On the other hand, in dielectric nanostructures, apart from electric, strong magnetic resonant modes are also excited, generating resonant scattering with low energy loss in the visible region of the spectrum. [13,14] Hence, all dielectric metamaterials are being studied as viable alternatives to achieve energy-efficient Fano resonance in the optical regime. [15,16] Miroshnichenko and coworkers have demonstrated one of the first all dielectric metamaterial systems exhibiting Fano resonance, where the asymmetric spectral profile is due to the interference between the Mie resonances of the middle and surrounding particles in a heptametric arrangement of sub-micrometer-sized Si spheres. [15,17] Fano resonance has also been demonstrated in systems like metal core (Au)/dielectric (ZnS) shell, [18] where the narrow plasmon resonance of the core interferes with the broad Mie resonance of the shell; dielectric (Si) core/dielectric (SiO 2 ) shell, [19] where the narrow magnetic dipole of Si interferes with the broad electric dipole of SiO 2 ; and in a variety of systems with nanostripes, [20] split bar resonators, [21] metasurfaces [22] and microstructures. [23] However, in all these systems, tuning of the strength of Fano resonance and the spectral position of its characteristic dip, which is inevitable A colloidal metamaterial composite, realized by dispersing sub-micrometersized high refractive index dielectric resonators (selenium) in a nematic liquid crystal medium, exhibits electrically tunable Mie resonances in the optical regime. Darkfield hyperspectral imaging reveals that when the nematic liquid crystal (NLC) molecules reorient from the pristine planar state on application of an AC electric field, the scattered image from the particle splits into two, owing to the birefringence of the NLC medium. At higher voltages, a doughnut-shaped s...

[Retracted] The Study of Midinfrared Extremely Narrow Dual‐Band Absorber Based on a Novel Metamaterial Structure

“…The detector can also be used for flammable, toxic, and harmful gases such as CH 4 , CO, and C 2 H 6 in the midinfrared region and SO 2 F 2 and SF 6 in the far-infrared [28]. It can also be used in thermal imaging [29], hyperspectral imaging [30], meteorology [31], free-space light [32], communication [33], remote sensing [34], and lasers [35] and for identifying biological compounds [36].…”

A Review of Tunable Electromagnetic Metamaterials With Anisotropic Liquid Crystals

“…As mentioned in Section 3, LC reorientations would result in a dramatic change in the refractive index of LC, which in turn, would further change the response to electromagnetic waves. In nematic LCs, the crystal is in a rod-shape and the external stimulations such as thermal heating, pressure, and the magnetic and electric field, can control its directional order, resulting in good refractive index tunability [42,59,[74][75][76][77][78][79][80][81][82][83][84][85][86][87][88][89][90][91]. Therefore, LCs are extensive used as the liquid background of solid metamaterials [51,52,92].…”

Photo-tunable epsilon-near-zero behavior in a self-assembled liquid crystal – nanoparticle hybrid material

“…On the other hand, soft materials such as polymers, colloidal dispersions, fluids, and liquid crystals offer immense scope in terms of processability and tunability. 24 Among soft materials, liquid crystals (LCs) are preferred as materials of choice to bring about tunability in metaproperties [25][26][27] due to their responsiveness to a wide range of stimuli, viz., thermal, mechanical, electrical, magnetic, and optical fields. 28,29 Liquid crystal-nanoparticle hybrid systems are interesting materials to be used for this purpose.…”