The Goos–Hänchen (GH) shift of the transmitted and reflected defect modes in a structurally chiral medium (SCM) containing a twist defect was theoretically investigated. TheSCMis modeled as an anisotropic dielectric with ¯42m point group symmetry, incorporating a twist defect introduced via a pitch discontinuity at the structure’s midpoint. Our results reveal the presence of a defect mode within the circular Bragg gap for right-handed circularly polarized (RCP) waves. Significant lateral shifts were observed at the defect-mode wavelengths in transmission and reflection. Furthermore, the sign of the GHshift differs between the transmitted and reflected waves.Wealso examined how key optical and structural parameters, including twist angle, incidence angle, and the presence of metallic nanoparticles, affect the wavelength andGHshift of the defect modes. Finally, the impact of slab thickness on the optical behavior was analyzed. The findings indicate that when the slab thickness exceeds a critical threshold, a polarization crossover occurs: the RCP defect modes are replaced by lefthanded circularly polarized (LCP) modes, accompanied by a reversal inGHshift polarity. These features suggest the potential of the proposed structure for use in optical switches, sensors, polarizers, and related photonic applications.
