Here we report the robust propagation, refraction and reflection of optical spatial solitons at the interface between two regions of a nematic liquid crystal. The ability to independently tune the optical properties of each region enables us to steer the beams by refraction and total internal reflection by as much as −18 and +22 degrees, respectively. Moreover, the extended (nonlocal) and anisotropic response of our system supports polarization healing of the solitons across the interface as well as non-specular filament reflection. Finally, exploiting the inherent and alloptically tunable birefringence, we demonstrate unprecedented nonlinear Goos-Hänchen lateral shifts in excess of 0.5 mm.

and absorb light with no diffraction. Planar metamaterials offer unprecedented fl exibility in the design and control of light propagation, replacing bulk optical components, [1][2][3][4][5] and exhibiting exotic optical effects, such as asymmetric transmission [ 6 ] and extrinsic optical activity, [ 7 ] whereas recent demonstrations of anomalous refl ection and refraction by metasurfaces have opened a new exciting chapter in photonic research. [ 8,9 ] Metasurfaces can be readily fabricated using existing planar technologies, while hybridization of their fabric with naturally available functional materials should enable dynamic control over their optical properties, dramatically expanding the range of potential metamaterial applications. [ 10,11 ] Among the existing functional materials, liquid crystals (LCs) possess arguably the strongest and most broadband optical non-linearity and birefringence, which can be externally controlled by temperature, light, and electric or magnetic fi elds. [ 12 ] That has made liquid crystals, and nematics in particular, one of the fi rst and most popular active ingredients considered for hybrid metamaterial and plasmonic designs. [13][14][15][16][17][18][19][20][21] Although the refractive index changes attainable in liquid crystals are extraordinarily large, the effi ciency of spectral tuning in the nematic phase may be reduced substantially due to strong surface anchoring of LC molecules. The latter, in fact, presents a serious problem for nanostructured LC-loaded metasurfaces operating in the visible and near-IR, and so far has made controlling the wavelength of their optical response practically impossible. [21][22][23] In this paper, we introduce a design of a near-IR active metasurface functionalized with a nematic LC, which allowed us to overcome the problem of strong anchoring and engage for the fi rst time the mechanism of electrically controlled nanoscale in-plane switching of the LC director. As a result, the resonant response of the demonstrated metamaterial hybrid could be controlled both in terms of its magnitude and wavelength with the spectral tunability approaching the theoretical limit of 9%. Active Metamaterial-LC Hybrid: Design and FabricationAlthough the in-plane LC switching has been experimentally demonstrated on the microscale for applications in LC Achieving an effi cient spectral tuning in liquid-crystal (LC)-loaded active photonic metamaterials has so far remained a challenge due to strong surface anchoring of LC molecules. This paper reports on a novel approach in the development of hybrid metamaterials that enables to overcome this problem and engage for the fi rst time in-plane switching of liquid-crystal molecules on the nanoscale. Combined with the usual volume switching, it unlocks the full potential of the liquid crystals as a functional component of active metamaterial hybrids operating at optical frequencies. As a result, the resonant response of an active metasurface can now be controlled both in terms of its magnitude and wavelength with the...

We present a detailed experimental and theoretical study of the optical response of suspensions of ferromagnetic nanoparticles (''ferroparticles'') in nematic liquid crystals (''ferronematics''), concentrating on the magnetic field-induced Frederiks transition. Even extremely low ferroparticle concentrations (at a volume fraction between 2 Â 10 À5 and 2 Â 10 À4 ), induce a significant additional ferronematic linear response at low magnetic field (<100 G) and a decrease in the effective magnetic Frederiks threshold. The experimental results demonstrate that our system has weak ferronematic behavior. The proposed theory takes into account the nematic diamagnetism and assumes that the effective magnetic susceptibility, induced by the nanoparticles, no longer dominates the response. The theory is in good agreement with the experimental data for the lowest concentration suspensions and predicts the main features of the more concentrated ones. The deviations observed in these cases hint at extra effects due to particle aggregation, which we have also observed directly in photographs.

We experimentally demonstrate efficient electro-optical control in an active nano-structured plasmonic metamaterial hybridised with a liquid-crystal cell. The hybridisation was achieved by simultaneously replacing the polarizer, transparent electrode and molecular alignment layer of the liquid-crystal cell with the metamaterial nano-structure. With the control signal of only 7 V we have achieved a fivefold hysteresis-free modulation of metamaterial transmission at the wavelength of 1.55 µm.

We investigate spatial optical solitons propagating in a medium with a saturable but adjustable nonlinearity and a fixed degree of nonlocality. We employ nematic liquid crystals in a planar cell with optical properties tuned by an external voltage and solitons excited in the near infrared. We also demonstrate soliton self-bending versus excitation due to nonlinear variations in walk-off. A theoretical model accounting for the longitudinal derivatives is employed to compute the refractive index distribution and is found in excellent agreement with the experimental data

We investigate the interaction between two beams differing in wavelength and the properties of dual-frequency spatial solitons in nonlocal birefringent reorientational media. We report the first experimental observations of anisotropic nonlocal vector solitons in unbiased nematic liquid crystals. Model and simulations, based on the paraxiality along the Poynting vectors, include joint walk-off and breathing.

Functional materials based on ferroelectric, inorganic nanoparticles, and low refractive index nematic liquid crystals show strong induced birefringence and dielectric anisotropy. Birefringence can increase by a factor of 2 and dielectric anisotropy by a factor of 3 as compared with nominally pure liquid crystals. The enhancement of the electro-optic performance is higher in liquid crystals with Sn2P2S6 (SPS) nanoparticles than with BaTiO3 nanoparticles. The shape and size distribution of both types of ferroelectric particles were characterized using atomic force microscopy. The average size of SPS nanoparticles was 45nm and of BaTiO3 nanoparticles was 20nm.

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