Sidelobe suppression in chiral optical filters by apodization of the local form birefringence.

Chiral optical filters are characterized by circular Bragg effects, including the preferential reflection and transmission of circular polarization states. The selective response to circularly polarized light is caused by stratified birefringent plates twisted into a helical arrangement, as seen in cholesteric liquid crystals and columnar thin films produced by oblique-angle physical vapor deposition. A refinement of the latter, glancing angle deposition employs substrate rotation to control the optical anisotropy of columnar thin films, and was used in this study to suppress the reflection sidelobes of chiral optical filters by modulating the local birefringence of helically structured thin films using an apodization function. Both theoretical simulations based on Berreman formalism, and experimental results involving evaporated TiO(2) thin films are presented and compared.