| Photonic crystals are ordered microstructure with dielectric constant change periodically,thus controlling the propagation of light.The physical properties of liquid crystals are extremely sensitive to external conditions and the transition between different phases can also trigger the change of their optical properties.By controlling the orientation or phase state of liquid crystals under an external field,the refractive index of the composite structure prepared by combining liquid crystal and photonic crystal is tunable,therefore the light is controlled.However,to date,the liquid crystal materials used in the composite system are mostly limited to the nematic phase or liquid crystalline elastomer.The cholesteric and the blue phase have not been reported in this field.This thesis is devoted to the preparation and investigation of the optical properties of liquid crystal-photonic crystal composite structure,which may provide theoretical support for the development of functional optoelectronic devices with tunable band gap.The research contents are as follows:(1)Polydisperse microspheres with unsatisfactory sphericity were assembled into ordered opal photonic crystal film using negative pressure to control the vertical deposition process.Results showed that negative pressure can accelerate the solvent evaporation and balance between the solvent evaporation and the sphere precipitation,making the polydisperse microspheres form tightly packed film.This research laid the foundation for the subsequent preparation of tunable devices base on photonic crystals.(2)A novel responsive device composed of inverse opal-chiral nematic liquid crystal was fabricated by combining the liquid crystalline cholesteric phase as a one-dimensional photonic crystal with the inverse opal as the three-dimensional photonic structure.The device showed reversible,dual-responsive band gap under thermal and electrical condition,which provides a novel idea for studying the reversible conversion between different photonic crystals.(3)Blue phase liquid crystal is filled into the inverse opal structure and the photonic band gap of this composite structure is tuned by using the different refractive indices of blue phase Ⅱ and blue phase Ⅰ at different temperatures.On the other hand,the introduction of inverse opal structure also improved the properties of blue phase materials.(4)Standard Kerr constant and the electro-optical coefficient perpendicular to the electric field were measured in blue phase.It is found that the electro-optical coefficients vertical to the electric field is comparable to that in the direction along the electric field,indicating the electrostriction effect and phase transition in the field-normal direction also contribute to the field-induced anisotropy of blue phase. |
