Polarization switchable lateral shift of the transmitted and reflected defect modes from a structurally chiral medium with a twist defect

Abstract 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. The SCM is modeled as an anisotropic dielectric with <mml:math xmlns:mml="http://www.w3.org/1998/Math/MathML" overflow="scroll"> <mml:mover accent="true"> <mml:mn>4</mml:mn> <mml:mo>¯</mml:mo> </mml:mover> </mml:math> 2m 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 GH shift differs between the transmitted and reflected waves. We also examined how key optical and structural parameters, including twist angle, incidence angle, and the presence of metallic nanoparticles, affect the wavelength and GH shift 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 left-handed circularly polarized (LCP) modes, accompanied by a reversal in GH shift polarity. These features suggest the potential of the proposed structure for use in optical switches, sensors, polarizers, and related photonic applications.