Three-dimensional nano-periodic liquid crystals and their application to photonic crystal device

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Three-dimensional nano-periodic structures based on cholesteric and chiral smectic liquid crystals having a self-organized nano-periodic structure have been investigated. The electrically tunable lasing has been observed in a focal conic structure of dye-doped cholesteric liquid crystal. This laser action is based on a helix micro-cavity in focal conic domains. Electrical tuning of the wavelength of the defect mode lasing in a one-dimensional periodic structure has been demonstrated using a stacked layer of NLC and conjugated polymer as a defect layer in the periodic structure. Lasing wavelength is widely tuned upon applying the electric field, which is due to the refractive index change in the defect layer caused by the field-induced realignment of the NLC molecules. Twist defect mode (TDM) and a lasing based on TDM have been experimentally demonstrated in a transmission spectrum of the composite film consisting of two photopolymerized cholesteric liquid crystal (PCLC) layers in which self-organized helical structure of PCLC acts as one-dimensional photonic crystal and a discontinuity of the director rotation around the helix axis at an interface of two PCLC layers induces the TDM. Optically pumped distributed feedback lasing has been proposed in a dye-doped nematic liquid crystal (NLC) waveguide by holographic excitation, in which continuous tuning of the lasing wavelength is performed upon applying electric field.