| dc.description.abstract | In this thesis, we report that the electro-optical properties of surface-relief gratings, having the period of about 30 μm and the width of the SU-8 structures of about 16.4 μm, based on periodic SU-8 structures onto an induim tin oxide (ITO) substrates by photolithography process. After photolithography process, the period structures are spin-coated with polyvinylalcohol (PVA) thin flim and treated with rubbing process. Another ITO-coated substrate is also coated with PVA thin film and treated with the same rubbing process. An empty cell is fabricated by assembling the two substrates, and then filled with nematic liquid crystals (LCs) to be electrically tunable LC gratings.
First, SU-8 possesses strong shielding effect for DC electric field, but weak for AC electric field according to our experimental results, and can be clearly understood by electrical double layer theory and RC circuit model. When a DC or AC electric field is applied, LCs in the region with SU-8 will be rotated by a weak effective electric field, and those in the other region will be rotated by a strong electric field. Furthermore, each region has its respective potential, which yields a transverse electric field due to the potential difference. Such transverse electric fields cause the LCs near the SU-8 structures but not on the surface of PVA thin film to be twisted from its initial alignment direction. Accorfing to the elastic continuum theory of LCs, the alignment of LCs should be continuously distributed, which changes the phase retardation and polarization state of the diffraction light. Finally, the methods of measurement and theory of electrically induced hybrid twisted nematic structure reported by He et al. is used for analyzing the diffraction efficiency and polarization state of diffraction light. | en_US |