Active, Tunable, and Reconfigurable Nanophotonics

Nanophotonic devices composed of sub‐wavelength‐sized structures, including metasurfaces, have contributed to the development of bringing flat optics into reality for applications such as sensors, holographic displays, anticounterfeit labels, ultracompact cameras, and microscopy. In this chapter, various approaches for the demonstration of active nanophotonic devices are introduced. In the first section, liquid crystal (LC)‐integrated devices will be presented. Liquid crystals (LCs) are well‐known tunable materials that can provide active functionality to the nanophotonic devices through the control of polarization or refractive index. In the second section, optically tunable devices will be highlighted. The many degrees of freedom of light such as polarization, amplitude, spin, and orbital angular momentum enables multiplexing nanophotonic devices. In the third section, diverse phase change materials (PCMs) will be discussed, with optical (or electrical) properties that can be modulated upon the application of various external stimuli. In the fourth section, a straightforward approach to electromechanically or mechanically tunable devices will be introduced. By compressing or expanding an elastic material, the integrated nanophotonic devices can exhibit reconfigurable optical characteristics. In the fifth section, material engineering, such as ion doping, and biomaterials, is presented for tunable biophotonic devices. Finally, electrically tunable devices are covered, with a particular focus on the transparent conductive oxide (TCO) and indium tin oxide (ITO).