Liquid-crystal-based tunable plasmonic waveguide filters

Abstract

We propose a liquid-crystal-based tunable plasmonic waveguide filter and numerically investigate its filtering properties. The filter consists of a metal-insulator-metal waveguide with a nanocavity resonator. By filling the nanocavity with birefringent liquid crystals (LCs), we could then vary the effective refractive index of the nanocavity by controlling the alignment of the LC molecules, hence making the filter tunable. The tunable filtering properties are further analyzed in details via the temporal coupled mode theory (CMT) and the finite-difference time-domain (FDTD) method. The simulation results show that the resonant wavelengths have linear redshift as the refractive index of the nanocavity increases and the coupling efficiency is more than 65% without considering the internal loss in the nanocavity and waveguides. These achieved results by the FDTD simulations can be also accurately analyzed by CMT. The compact design of our proposed plasmonic filters is especially favorable for integration, and such filters could find many important potential applications in high-density plasmonic integration circuits.

Liquid Crystal Enabled Dynamic Nanodevices

“…So far, several different tuning principles [ 58 , 59 , 60 , 61 , 62 ] based on various types of liquid crystal (LC) molecules, such as chiral [ 63 ], nematic [ 64 ], and smectic [ 65 ] characteristics have been experimentally demonstrated to realize dynamically controllable nanodevices. Since LC-based modulation mechanism can offer an additional advantage because the LC-molecules exhibit a large optical anisotropy [ 66 , 67 , 68 , 69 , 70 , 71 , 72 , 73 , 74 , 75 , 76 , 77 , 78 , 79 , 80 , 81 , 82 , 83 ], investigations on LCs combined with nanostructures [ 84 , 85 , 86 ] or two-dimensional materials [ 87 ] have recently drawn significant attention and interest. Developing tunable optical metamaterials by incorporating nematic LCs as an electro-optic or nonlinear optical constituent has become a popular research topic [ 88 , 89 , 90 , 91 , 92 , 93 ].…”