Broadband cholesteric liquid crystal (CLC) reflectors are highly desirable for advanced optical applications, but their polarization behavior under oblique incidence remains underexplored. This study reveals anomalous polarization-selective reflection in broadband pitch-gradient CLCs, including linear polarization selectivity and the reversal of circular polarization handedness under oblique incidence. The pitch-gradient CLC reflects a much wider spectrum than that of a uniform-pitch CLC, covering the full visible range. Under oblique incidence, it exhibits anomalous polarization-selective reflections. Notably, for light incident from the short-pitch (front) side of the element, the reflector preferentially reflects linear polarization of transverse electric (TE) mode over its transverse magnetic (TM) mode and even shows a reversal of circular polarization selectivity at certain angles. When illuminated from the long-pitch (back) side, the device maintains the usual circular polarization preference but splits the broadband reflection band such that TE and TM polarizations dominate different wavelength regions. These phenomena are confirmed by rigorous Berreman 4 × 4 matrix simulations, which replicate the experimental results and indicate that the effects originate from the intrinsic pitch-gradient structure. These findings uncover and elucidate anomalous polarization effects unique to broadband pitch-gradient cholesteric reflectors. The results offer practical design rules for compact broadband polarization control under oblique incidence, particularly for AR display combiners and other polarization-sensitive optical systems.
Nakajima et al. (Wed,) studied this question.