Photonic defect modes in a cholesteric liquid crystal with a resonant nanocomposite layer and a twist defect.

We have studied spectral properties of a cholesteric liquid crystal with a combined defect consisting of a nanocomposite layer and a twist. The nanocomposite layer is made of metallic nanoballs dispersed in a transparent matrix and featuring effective resonant permittivity. A solution has been found for the transmission spectrum of circularly polarized waves in the structure. We have analyzed spectral splitting of the defect mode in the band gap of the cholesteric when its frequency coincides with the nanocomposite resonant frequency. Defect modes have characteristics strongly dependent on the magnitude and the sign of the phase difference of the cholesteric helix on both sides of the defect layer. It has been found that the band gap width and the position and localization degree of defect modes can be effectively controlled by external fields applied to the cholesteric.