Finite-difference time-domain analysis of cholesteric blue phase II using the Landau-de Gennes tensor order parameter model.

We numerically calculated the photonic band structure of a cholesteric blue phase II (BPII) liquid crystal using two models, the tensor order parameter model and the double-twist cylinder (DTC) model. The tensor order parameter model was derived numerically from the Landau-de Gennes theory, whereas the DTC model simply assumed a three-dimensional stack of ordered cylinders. The two models yielded similar photonic band structures; however, the polarization dependence of the transmission spectrum through the (100) direction in BPII was different. The results from the tensor order parameter model gave a better qualitative agreement with experiments on the transmission spectrum. This demonstrates the importance of a precise orientation model in the analysis of the optical properties of cholesteric blue phases.