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...

Epsilon near zero (ENZ) materials exhibit strongly confined optical modes and plasmonic response around and beyond the ENZ wavelength (λENZ). In order to exploit the novel properties of ENZ materials for real-world applications, it is important to develop material platforms that offer continuous tuning of λENZ. We report octave span, controllable, and reversible tuning of λENZ from 1280 nm to 2900 nm in commercially available thin films of indium tin oxide (ITO), employing a low temperature annealing protocol. Electrical, spectroscopic, and optical measurements establish the physical basis of the observed tunability in free electron density by over an order of magnitude and quantify the real and imaginary components of the refractive index for ITO thin films. Excitation of surface plasmon polaritons (SPPs) in the metallic regime of ITO probes its infrared plasmonic response demonstrating continuous tunability of SPP frequency and crossover to the tunable ENZ plasmon mode in ultrathin films. Finally, dispersion tuning of optical fiber modes by optical coupling with a tunable λENZ platform is demonstrated by investigating modal interference in a tapered silica fiber in contact with various custom tuned ITO films.

We demonstrate the tunability of the intensity and directionality of scattered light in a soft colloidal dielectric metamaterial. The system consists of high-refractive-index sub-micrometer-sized particles dispersed homogeneously in a nematic liquid crystal. The refractive index modulation of the nematic liquid crystals achieved by the application of an ac electric field provides tunable Mie resonant forward scattering of the particles in the optical wavelength regime following Kerker’s first condition. The unique scattering properties exhibited by the system are established using the heterodyne near-field scattering (HNFS) imaging technique. The analysis of the Mie coefficients, simulation of near- and far-field scattering based on Mie theory, and finite element method elucidate the enhancement and tunability of forward scattering.

High refractive index (n > 2.5) dielectric particles support strong electric and magnetic Mie resonances in the visible region enabling optical properties such as directional scattering, anapole modes, and Fano resonances with applications in nanophotonics. Selenium particles, which possess a high refractive index at optical frequencies, have been synthesized using a controlled approach involving a moderate reduction of selenious acid to obtain particles of the desired size. The extinction spectra from UV–vis spectroscopy in conjunction with theoretical simulations confirm the presence of highly size‐dependent dipole and quadrupole Mie resonances in the visible region. Dynamic tuning of magnetic and electric Mie resonances and swapping of electric and magnetic dipoles are observed in a colloidal dispersion of 250 nm‐sized selenium particles in a nematic liquid crystal due to the anisotropic nature of the latter. Theoretical simulations reveal the presence of unidirectional scattering and photonic‐nanojet formation, attributed to generalized Kerker's effects in nanophotonics and meta‐optics, due to the swapping phenomena leading to the superposition of dipole and quadrupole resonances. The manipulation of Mie resonances in the liquid crystal based colloidal metamaterial has the potential for large‐scale and cost‐effective nanophotonic device applications.

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