Double-handed circular Bragg phenomena in polygonal helix thin films

Oblique-incidence physical vapor deposition has been used to create optical thin films with a polygonal helix-shaped nanostructure. A series of titanium dioxide thin films are investigated, including triangle, square, pentagon, and star-shaped polygonal helices. Experimental optical measurements reveal a double-handed circular Bragg response: at one frequency band a polygonal helix reflects left-handed circularly polarized light, and at a second frequency band reflects right-handed circularly polarized light. The relative wavelength dependence of each reflection band is determined by the physical structure of the polygonal helix, a property that is set during the thin-film deposition process. Spectral-hole polarization filters, produced by adding twist and spacing layer defects to polygonal helix thin films, are also reported.