Photonic crystals manipulate light in unique and beneficial ways, acting as waveguides, laser cavities, and facilitating topological light propagation. However, the reconfiguration of photonic crystals has been limited, hindering their versatility. We have recently introduced the concept of pixelated 2D photonic crystals, where a pixelated matrix of the material enables variability in the dielectric profile. By changing the orientation state of liquid crystal molecules within individual pixels an effective refractive index for a specific input polarisation is altered. In this work we numerically show how different distributions of ”on” and ”off” state pixels and therefore different effective refractive index configurations in the periodically repeated unit cell effect the band structure of the material and its optical properties. Considering the size of pixels and unit cells, such photonic crystals would enable dynamic control of THz waves.
Liquid crystals are transparent optically birefringent materials that have the ability to self-assemble into tunable photonic microstructures. They can be modified by adding chiral dopants, by anchoring on confining surfaces, temperature changes, and by external electric or magnetic fields. Cholesteric liquid crystals (CLCs), which have a periodic helical structure, act as photonic crystals and thus partially reflect light with wavelengths comparable to the period of the structure. Possessing these properties, CLCs can be utilized as resonators or even as micro-lasers if doped with organic dye. In this work, we present the findings of a numerical study of light transmission through CLCs with or without isotropic defect layers in different 1D geometries. We also show numerically calculated photonic eigenmodes and their corresponding Q-factors. Overall, this work summarizes the properties of CLC resonators that could be important for the design of liquid crystal micro-lasers and other soft-matter-based photonic devices.
We show photonic responses of selected two-dimensional photonic crystals that are based on a combination of geometrical design and spatial self-similarity. Structures based on multi-layer circles, squares, and triangles are studied, finding a range of local band gaps that can be varied with the self-similarity of the photonic crystal patterns. Selected photonic modes are shown that couple to different geometrical features of the photonic crystal. The role of boundary sharpness between the two dielectric components is emphasized.
Laser beams which carry spin and orbital angular momentum are desired in many applications. They are usually created by manipulating the laser output or by inserting optical components in the laser cavity. Due to their high susceptibility to external fields and birefringent nature, control over the emitted light could be achieved by inserting liquid crystals into the laser cavity. In this work we numerically study lasing in selected nematic liquid crystal director profiles. We use custom written FDFD code to calculate emergent electromagnetic eigenmodes, and show how they are affected by the nematic director field. Control over lasing is of a particular interest with the aim to path the way towards the creation of general arbitrary shaped laser beams.
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