Viewing angle switching panels using large optically anisotropic behaviours of twisted-nematic liquid-crystal layers

Abstract

This work proposes a viewing angle switching (VAS) panel using twisted-nematic liquid-crystals (TN-LCs). Calculations reveal that, in a low voltage regime, a TN-LC behaves optically as a high twisted (∼90°) TN-LC in a vertical direction but as a low twisted (<25°) TN-LC in a horizontal direction. Additionally, a large difference in phase retardation of TN-LC from different viewing directions occurs at applied voltage 1.5Vth ⩽ V ⩽ 1.7Vth, where Vth is the threshold voltage of director reorientation. The large differences in the twisted angle and the phase retardation from different directions result in a large optically anisotropic behaviour of a TN-LC layer. The proposed VAS panel is developed using this large optically anisotropic behaviour of a TN-LC layer. Optical films are also used in the proposed VAS panel to enhance the optical anisotropy of a TN-LC layer. With the proposed panel, a display is only perceived clearly at a downward direction in a narrow viewing angle mode to ensure high privacy protection. Additionally, the proposed VAS panel achieves a high transmittance of 95%, making it highly promising for mobile device applications.