Propagation of electromagnetic waves through liquid crystals with defect-based interfaces

We present a theoretical study of electromagnetic surface wave modes along a dielectric interface that includes a cholesteric liquid crystal-based layer, and a metallic layer. The cholesteric liquid crystal layer has a twist defect and metallic inclusions. The system is modeled by Maxwell's equation and we propose a Maxwell-Garnett theory for the dielectric response of the cholesteric liquid crystal layer. Surface waves satisfy a Marcuvitz-Schwinger system that we solve numerically assuming continuous fields at interfaces. The dispersion relation shows the existence of localized modes associated with defect-tuned resonances. Field distributions for the electric, magnetic, and the Poynting vector components imply enhanced confinement near the defect region, with strong amplification at resonant frequencies and clear evidence of energy trapping. We also observe the existence of a region of negative group velocity in the dispersion relation analogous to what is seen in metamaterials. The comparison between single-period and multi-period cholesteric liquid crystal layers demonstrates that increasing periodicity reinforces localization and mode stability. These results highlight the role of structural defects in tailoring light propagation through anisotropic composite waveguides and open perspectives for tunable photonic devices based on liquid crystals.