Numerical analysis of tunable edge filters based on hyperbolic metamaterials constructed from indium tin oxide and silicon oxide layers

This paper presents and discusses the results of numerical studies of multi-layered hyperbolic metamaterials (HMMs). Such structures are built of alternating thin layers of conductive (e.g., metal or alternative conductive material) and dielectric materials. The thicknesses of these layers are much smaller than the operating wavelength, usually of the order of a few or tens of nanometres. Indium tin oxide (ITO), which is an alternative conductive plasmonic material from the group of transparent conductive oxides (TCOs), was used in the conductive layers. Silica (SiO2) was used as a material in the dielectric layers. As a result of a simulation-based optimization, the layer thicknesses of two components forming the structure were chosen to be 20 nm each. Four variants of multilayer structures with different numbers of elementary cells forming the structure, N, for N = 5, 10, 15, and 20, respectively, were investigated by both analytical methods using the transfer matrix method (TMM) and simulation methods using finite-difference time-domain (FDTD). The results confirmed the hyperbolic dispersion of effective electric permittivity and tunability of the structure in the near-infrared (NIR) range. Moreover, a complete agreement of the results confirmed the complementarity of the two methods – both analytical TMM and simulation FDTD. The proposed HMMs structures may have potential applications as tunable edge filters.