Photonic crystals based on liquid crystal structuresŠtimulak, Mitja (Avtor) Ravnik, Miha (Mentor) liquid crystalsphotonic crystalsanisotropycolloidstunabilityband gapnematic liquid crystalblue phase Iblue phase IIgyroidheliconical liquid crystalThis thesis investigates the flow of light in liquid crystal photonic crystals, with a focus on three-dimensional photonic crystals with cubic unit cells. The main results are a precise model and understanding of the photonic band structure and electromagnetic eigenfields for photonic crystals formed by self-organized cholesteric liquid crystals in (i) heliconical liquid crystals, (ii) blue phase I, (iii) blue phase I and blue phase II with dispersed colloidal particles, and (iv) gyroid photonic templates. A notably original contribution of the thesis is the calculation of photonic bands and eigenfields of three-dimensional liquid crystals combined with dielectric material. This is achieved by solving Maxwell's equations for arbitrary wavevectors in liquid crystal photonic crystals using the plane wave expansion approach, thanks to our custom enhancement of the established numerical solver to support materials with general spatially variable birefringence. We first apply this method to investigate one-dimensional heliconical liquid crystals, showing tunable optical properties leading to a photonic bandgap. We calculate photonic eigenmodes of the light and find the emergence of electric field components along the propagation axis of light for both left and right-hand polarization, resulting in a strongly spatially varying Poynting vector, tunable with various material parameters and external electric fields. Second, we show a complete band diagram of blue phase I, which includes higher band gaps. We investigate the corresponding photonic eigenmodes, as well as their polarization state. Interestingly, at different wavelengths, the same photonic eigenmode can have left or right-handed polarization. Furthermore, we demonstrate the density of photon states in blue phase I. Third, we identify blue phase colloidal crystals as materials whose photonic response is influenced by the interaction of two symmetries - the colloid lattice and blue phase unit cells. We compare photonic bands of blue phase colloidal crystals to (no-particle) blue phases and particles in an isotropic background arranged in face-centered cubic and body-centered cubic lattices, demonstrating that photonic bands and local band gaps can be tuned and even created by changing particle size. Specifically, larger particles lead to more significant local band gaps. Fourth, we demonstrate that nematic and cholesteric liquid crystals in a gyroid-shape template can form a variety of mesophases. We show that material parameters such as liquid crystal volume fraction, chiral liquid crystal pitch, and dielectric contrast between the liquid crystal and gyroid template can be used to tune the size of the band gap and shape of the photonic bands. More generally, this work contributes to the field of spatially dispersive anisotropic dielectric photonic crystals capable of controllable and tunable photonic properties.20222022-08-03 10:09:21Doktorsko delo/naloga138619VisID: 123534COBISS_ID: 111620099sl