Optical Properties of Cholesteric Liquid Crystals with Functional Structural Defects.

The authors numerically investigate the optical transmission properties of cholesteric liquid crystals with a local modulation of pitch and refractive indices. The transmittance spectra of structures with various defect thickness, refractive indices and pitch are calculated using the 4 × 4 matrix method. Calculation results showed that single or multiple transmittance peaks arise in the selective reflection band for light incidence with the same circular handedness as the material, and their spectral positions depend strongly on the physical parameter of the defect. A pitch shortening or elongation at the defect causes the defect mode to shift in the shorter or longer wavelength region, respectively, and the tuning range of the defect mode becomes larger for a thicker defect. We also show that efficient tuning is achieved by a defect medium with a smaller birefringence, allowing the defect mode to be sweeped through the photonic band gap with a smaller modulation of pitch. [ABSTRACT FROM AUTHOR]