dc.description.abstract | The topics in this thesis include the following two sections. In the first section, electrically and optically controllable absorption-mode liquid crystal (LC) light shutters are discussed in detail. To achieve the absorption state, dichroic dyes (S428)-doped LCs with negative dielectric anisotropy (HNG30400-200) are filled into the empty LC cell, whose substrates are coated with vertical alignment films with mechanical rubbing process or not, to demonstrate the “Rubbed vertical alignment dye-doped nematic LCs (RVA-DdNLC)” and “Vertical alignment dye-doped nematic LCs (VA-DdNLC)” light shutters. The comparisons of the switching mechanism, driving voltages, and response times of the two LC light shutters are also discussed. In the aspect of the switching mechanism and driving voltage, the transparent and absorption states of the two LC light shutters, as well as the absorption coefficients α_⊥ and α_∥ are determined by examining the transmittance versus applied voltage curves. The model of calculating the transmittance of VA-DdNLC applied with 5 Vrms@1 KHz square wave based on the Beer-Lambert law is proposed in this thesis. The alignments of LCs and dichroic dyes of VA-DdNLC are determined by connecting the model and the curve of polarization-selective absorption. In the aspect of the response time, the rise and decay times of the two LC light shutters are determined by the measurements of these transmittance versus time curves. Eventually, the proposed RVA-DdNLC light shutter is connected with the light dependent resistor (LDR) in series to control its grayscales optically.
The second section in this thesis is the study of electrically controllable scattering-mode LC light shutters. To achieve the scattering state, the same LCs in the first section doped with few ionic materials (SDS′) are filled into the empty LC cell, whose substrates are coated with vertical alignment films, to demonstrate the “Vertical alignment of ion-doped nematic LCs (VA-IdNLC)” light shutters. The comparisons of the switching mechanism and driving voltage of DC or AC square waves with different frequencies, as well as the dynamic structures and response times by applying a voltage of 1 KHz square wave onto the VA-IdNLC are discussed. In the aspect of the switching mechanism and driving voltage, the transparent and scattering states are determined by examining the transmittance versus applied voltage (DC and 1 KHz square waves) curves. Regarding the dynamic structures, the model for calculating the position (distribution) of the bright and dark stripes of VA-IdNLC applied with 31.5 Vrms@1 KHz square wave based on the combination of the Carr-Helfrich and the model in the first section is proposed. The alignment of LCs of VA-IdNLC is speculatively clarified by connecting the model, patterns observed under a polarized optical microscope with an analyzer or not, and the curves of polarization-selective scattering. In the aspect of the response time, the rise and decay times of VA-IdNLC are determined by the measurements of its transmittance versus time curves.
The third section in this thesis is the study of electrically controllable absorption-/scattering-mode LC light shutters. To achieve the absorption-/scattering state, the same LCs in the first two sections doped with dichroic dyes (S428) and few ionic materials (SDS′) are filled into the empty LC cell, whose substrates are coated with vertical alignment films, to demonstrate the “Vertical alignment of ion and dye-doped nematic LCs (VA-IDdNLC)” light shutters. The comparisons of the switching mechanism and driving voltage of DC or AC square waves with different frequencies, as well as the dynamic structures and response times by applying a voltage of 1 KHz square wave onto the VA-IDdNLC are discussed. In the aspect of the switching mechanism and driving voltage, the transparent and absorption-/scattering state are determined by examining the transmittance versus applied voltage (DC and 1 KHz square waves) curves. Regarding the dynamic structures, the model for calculating the position (distribution) of the bright and dark stripes of VA-IdNLC applied with 27.5 Vrms@1 KHz square wave based on the second section is proposed. The alignment of LCs and dichroic dyes of VA-IdNLC is speculatively clarified by connecting the model, patterns observed under a polarized optical microscope with an analyzer or not, and the curves of polarization-selective absorption-/scattering. In the aspect of the response time, the rise and decay times of VA-IDdNLC are determined by the measurements of its transmittance versus time curves. | en_US |