Electrically Controlled Nanostructured Metasurface Loaded with Liquid Crystal: Toward Multifunctional Photonic Switch

Abstract

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...

Fundamentals and Applications of Metasurfaces

“…Liquid crystals with broadband optical nonlinearity and birefringence are the most commonly used materials for the dynamic control of the optical properties. The refractive‐index change of a liquid crystal can be externally tuned by temperature, light, and electric or magnetic fields . Phase‐change materials have also been extensively utilized in optical data‐storage systems and nanophotonic systems based on their tunable optical properties.…”

Traditional and emerging materials for optical metasurfaces

“…To this end, significant work has been done in the research and synthesis of new functional materials, and their integration with traditional metamaterial building blocks [128]. Examples include the use of microelectromechanical (MEMs) systems [129][130][131], charge carrier injection [132][133][134][135][136], phase change materials [137][138][139][140][141][142][143][144][145] and liquid crystals [146][147][148] for dynamic reconfigurability.…”

Dual-Core Optical Fiber as Beam Splitter With Arbitrary, Tunable Polarization-Dependent Transfer Function

“…Design and simulation of the fiber was performed using advanced optical modal simulations, based on a full-vector finite element method implemented in Comsol Multiphysics ® , in combination with a custom-made LC model [24] based on the Frank-Oseen continuous elastic theory approach [25]. LC alignment is described by a director l defined by the tilt and twist angles, θ and φ, as shown in Fig.…”