Broadband reflective terahertz linear cross-polarization converter with refractive-index sensing capability

Abstract A broadband reflective linear cross-polarization converter with refractive-index sensing capability is investigated for terahertz operation. The proposed unit cell consists of an asymmetric gold resonator placed on a polyimide spacer backed by a continuous gold ground plane. The simulated results show that the structure converts the incident linearly polarized wave into its orthogonal reflected component from 1.56 to 2.67 THz , with both P C R x and P C R y remaining above 90%. The conversion behavior is examined through the reflected amplitudes and phase difference along the rotated u and v axes, as well as electric-field and surface-current distributions at representative frequencies. These results indicate that the broadband response is associated with localized field concentration, induced current paths, and phase retardation between the orthogonal components. The converter maintains stable polarization conversion under oblique incidence up to 45 ∘ for both ϕ = 0 ∘ and ϕ = 90 ∘ . A refractive-index sensing analysis is also performed by comparing the lower and upper 90% P C R band edges with identifiable minima in the co-polarized reflection spectrum. For an analyte thickness of 3 μ m , the upper 90% P C R band edge provides the highest sensitivity of approximately 1.085 THz/RIU . The effect of analyte thickness is further examined, showing that the sensitivity increases with analyte thickness and gradually approaches a weaker rate of change at larger thicknesses.