Polarization- and angle-dependent topological interface states in one-dimensional photonic crystal heterostructures containing birefringent materials

In this work, we present a numerical analysis of a one-dimensional topological photonic crystal heterostructure composed of isotropic (amorphous silicon carbide) and birefringent (aligned liquid crystal elastomer) layers, designed as a tunable narrow-bandpass filter operating in the telecommunication wavelength range. By exploiting the polarization- and incident-angle-dependent refractive index of the liquid crystal elastomer, we achieve dynamic tuning of the photonic bandgaps under both TE and TM polarizations. Toward the aim of overlapping bandgaps, two different photonic crystal structures are constructed, one being topologically trivial and the other topologically non-trivial, characterized by the Zak phases of their respective bands. At normal incidence, the concatenated structure exhibits robust topological interface states at the interface between the two photonic crystals at 1501.86 nm for TE polarization and 1590.10 nm for TM polarization. Angular-dependent analysis shows that the topological interface states are tunable across the O to S band for TE polarization, while for TM polarization, the tunability is enhanced across the O to L band. Our device possesses a low reflection loss and a high polarization contrast ratio across its operating range. Furthermore, the temperature-dependent refractive indices of the constituent layers are used to tune the topological interface states across a short wavelength interval, with an exceptional sensitivity, the figure of merit, and a polarization contrast ratio. We also investigate the robustness of the interface states by introducing random thickness disorders of upto ±20nm in the layers adjacent to the interface. Our findings offer the prospect of incorporating these topological heterostructures as polarization-selective, incident-angle-dependent, and thermally controlled narrowband filters.