Photonic Micro‐ and Nanostructures, Metamaterials

Abstract

Periodic structures with feature sizes comparable to the wavelength of electromagnetic radiation (“photonic crystals”) or feature sizes much smaller than the considered wavelength (“metamaterials”) can have unique optical properties, including ‐ for example ‐ unusual transmission, reflection, and diffraction, enhanced or inhibited transmission of emitters embedded in these structures, or zero and even negative refraction, which offer many opportunities for integrated optics and photonics. This topical field may benefit from liquid crystals in two ways: A mesophase with an intrinsic periodic structure may behave as a natural, self‐organized material of this kind or serve as a template for producing such materials. An artificial structure can be equipped with tunable optical properties by infiltration with liquid crystals owing to their optical nonlinearity or the sensitivity of their dielectric permittivity to external controlling parameters. This chapter gives an overview of the latter type of photonic crystals (including microstructured fibers) and metamaterials. Emerging concepts of possible applications for tunable light sources, integrated tunable filters or switchable optical components, and optical sensors are summarized.

Switchable Plasmonic Holograms Utilizing the Electro-Optic Effect of a Liquid-Crystal Circular Polarizer

“…The development of optical metamaterials , effective media that are composed of different materials and very specifically structured on a subwavelength length scalehas changed some fundamental assumptions about the achievable range of optical properties. For example, a large variability of the magnetic permeability at optical frequencies, extreme values of the refractive index (including negative values), and tailoring of the spatial distribution of the refractive index have been demonstrated. , Possible applications include, for example, the fabrication of super- and hyperlenses with subwavelength resolution, integrated waveguiding by micro- and nanostructured media, and even optical cloaking. − Tunable or switchable optical metamaterials pave the way toward practically applicable and active optical devices. − Two-dimensional structures with subwavelength featuresmetasurfacesare readily accessible by lithographic techniques and enable optical filters or phase plates with unusual properties. Despite their easier fabrication on planar surfaces, metasurfaces have shown great potential in altering the wavefront of light in nearly arbitrarily ways, for example, to form lenses or other phase masks. , …”

Ferroelectric Liquid Crystals in Microcapillaries: Observation of Different Electro-optic Switching Mechanisms

“…The more recent advances in fabricating microstructured fibers and photonic crystal fibers (PCFs) have enabled the design of fibers with low attenuation, endless single-mode fibers, and highly nonlinear fibers for supercontinuum generation. , In addition, the development of sensing or actively tunable fiber segments became possible through infiltration of hollow fibers with liquids or liquid crystals (LCs). − Thermotropic calamitic LCs are ordered liquids, which are composed of rod-like organic molecules. − Preferred parallel alignment of neighboring molecules (along the director n ) results in local birefringence, while the optical axis (parallel to n ) can be realigned by external electric or magnetic fields, thereby enabling controlled changes of the intensity, the spectral distribution, or the state of polarization of the transmitted light. The opportunities of LC mesophases for optical fiber applications have extensively been studied for the nonchiral nematic phase − and its chiral analogues, the cholesteric phase (which shows a twisted, helix-like director field) and blue phases (which exhibit local double-twist and a three-dimensional superstructure). On the basis of dielectric anisotropy, these nematic-like phases enable electro-optic switching with typical switching times in the range of 10–100 ms. − Chiral smectic (Sm) phases can show ferroelectricity and may provide even faster electro-optic response with switching times in the submicrosecond range. − Sm phases are characterized by a layer structure in addition to the orientational order of the molecules.…”