Ryukoku University, Japan
Liquid Crystal, Polarization, Optical Rotation, Scattering, Refractive Index.
Photonic and Optoelectronic Materials and Devices
Photonics, Optics and Laser Technology
Cholesteric liquid crystal usually exhibits an optical rotation owing to its chirality. In the infrared region, however, the optical rotation power disappears, since the light wavelength is too long to recognize the refractive-index change of the nanometer-sized chiral structure. Consequently, the cholesteric liquid crystal exhibits a polarization-independent refractive index in the long-wavelength infrared range. The effective refractive index takes a value between the ordinary and extraordinary indices regardless of the polarization direction. The refractive index decreases to the ordinary index, when a phase transition takes place by application of an electric voltage (the electro-optical effect). This polarizer-free device operation, however, used to be limited to the wavelength range beyond 4 μm, since the optical rotation remained in the short wavelength range. In addition, a heavy scattering occurred during the phase transition process. In this study, experiments were conducted
to examine how the chiral pitch and the thickness of the liquid crystal layer affected these optical characteristics. When a liquid crystal with a chiral pitch of 5 μm was enclosed in a cell with a 3 μm gap, both the rotation power and scattering loss were reduced successfully in a wide spectral range extending to 2 μm wavelength.