Liquid-Crystalline Nanostructured Optical Metamaterials

Abstract

In this chapter, we present a complete self-contained discussion on all the electromagnetic and material fundamentals needed to understand the synthesis and properties of tunable metamaterials made possible by inclusion of liquid crystals as a constituent material, and a thorough discussion of the reflection and transmission properties at interfaces formed between positive and negative index materials. Two principal classes of metamaterials are treated: (1) metamaterials made of nematic liquid crystals containing nanoparticulates and (2) metamaterials made of nanostructures infiltrated with liquid crystals. We also studied the special case involving laser dye-doped nematic liquid crystals that could provide optical gain; it is shown that the overall loss can be minimized, while the effective real part of the refractive index can be tailored toward the desired value (positive or negative). In comparison with other metamaterial systems that tend to be passive and nonreconfigurable, the presence of electro-optic active and nonlinear optical materials, such as liquid crystals, enable tremendous tuning flexibility and new forms/shapes enabled by their dual (fluid/crystalline) physical properties. As a result of the broadband birefringence of liquid crystals, the operation wavelengths of these metamaterials cover the entire visible–near infrared–far infrared to terahertz and microwave regime. These tunable optical metamaterials, which combine the unique properties of liquid crystals and specific properties from engineered nanoparticulates and nanostructures, will enable a wide range of application possibilities in next-generation reflective, transmissive, modulation, and switching elements and devices.