Sculptured nematic thin films with periodically modulated tilt angle as rugate filters

The reflectances and transmittances of linearly polarized light are calculated using the piecewise homogeneity approximation for a sculptured nematic thin film (SNTF) with a sinusoidally varying (local) columnar tilt angle. Empirical data on TiO₂, available in the literature, are used to realistically model the variation of the permittivity dyadic with the tilt angle. Wave propagation is taken to occur in the morphologically significant plane of the SNTF. Several Bragg peaks occur, with the fundamental peak making a tilt-modulated SNTF suitable for exploitation similarly to a rugate filter. Additionally, the appearance of a spectral hole in the fundamental Bragg peak is demonstrated with the inclusion of a central defect layer.