Dyakonov–Tamm (DT) waves are highly sensitive to the constitutive properties of the partnering materials near the interface. DT waves are excited at the interface of two dielectric materials of which at least one is anisotropic and periodically nonhomogeneous normal to their interface. Sculptured nematic thin film (SNTF) is a good candidate for the periodically nonhomogeneous dielectric partner for optical sensing of a fluid due to its porosity. The nanoscale parameters of an uninfiltrated SNTF obtained from the inverse Bruggeman homogenization formalism were used in the forward Bruggeman homogenization formalism to determine the constitutive parameters for the infiltrated SNTF. The sensitivity of DT waves to the refractive index was analyzed for two possible sensing modalities and it was found that the sensitivity was comparable to that of the chiral sculptured thin films (STFs) made of the same material as of the SNTF. This implies that the sensing with DT waves is robust, is independent of the morphology of the partnering nonhomogeneous dielectric material and could make the sensing easier since SNTFs are easier to fabricate than the chiral STFs.
By using a piecewise uniform approximation method, the reflectance and transmittance of light for an obliquely incident circularly polarized plane wave on a tilt-modulated chiral sculptured thin film (STF) were computed. The circular Bragg phenomenon was found to vanish when the amplitude of the modulation was high enough for oblique incidence. The tilt-modulated chiral STF then acts like a conventional mirror in the Bragg regime.