An optical configuration for a horizontally-switched reflective LCD that could provide high reflectance as well as high contrast is proposed. We have shown that the proposed configuration can provide a flat reflection spectrum with very high reflectance in the bright state experimentally and theoretically.

Application of in-plane switching of liquid crystal director to reflective LCD was not effective previously due to low aperture ratio. However, recently developed fringe-field switching (FFS) mode developed by us made it possible, owing to an advantage of high transmittance. The device shows wide viewing angle intrinsically. IntroductionThe role of reflective liquid crystal displays (R-LCDs) is becoming important because LCDs are believed to be suitable devices for mobile information tools (MITs). [1,2] Recently, several approaches such as R-TN [3,4], R-OCB[5], and stacked guest-host display [6] have been introduced. However, in order for R-TN and R-OCB to exhibit high image quality, the addition and optimization of optical compensation films are necessary and also there is a difficulty in an application to transflective LCD without modifying pixel structure and optical system. The transmissive type display, in-plane switching (IPS)[7], shows wide viewing angle intrinsically owing to in-plane rotation of LC director. However, it shows low transmittance problem. Recently we developed "fringe-field switching (FFS)" mode to overcome low transmittance problem, i.e., exhibiting both wide viewing angle and high transmittance simultaneously. [8][9][10] Taking an advantage of in-plane rotation of LC director that allows wide viewing angle intrinsically, we apply the FFS mode to reflective system. There are several ways of designing reflective FFS display. In this paper, we will discuss about electro-optical characteristics of the reflective FFS display in different systems. Simulational and Experimental ResultsFor reflective LCDs using the FFS mode, three different types are considered in this paper. The first is one with two polarizers.In this case, normally white (NB) and normally black (NB) modes can be achieved. Fig. 1 shows cell configurations of both modes. In the NW mode, the rubbing direction of the cell is coincident to the transmission axes of the polarizers. Therefore when the voltage is not applied, the linearly polarized incident light by analyzer at normal direction is reflected without loss of light intensity except the absorption of the polarizers. As the voltage is applied, the polarization of the incident light is 90 o rotated through the LC layer, and the polarizer absorbed the light so that the cell appears black. In the NB mode, the axis of the analyzer is orthogonal to the polarizer. As a result, the polarizer blocks the linearly polarized light that passed the LC layers and the cell appears black. When the voltage is applied, the optic axis of the LC director deviates from the analyzer and the linearly polarized light becomes elliptic such that some of light passes polarizer and reflects from reflector.The electro-optical characteristics of the reflective FFS cell are simulated based on Berreman's 4X4 method. The retardation value of the cell is 0.3✙m which is effectively similar value to half wavelength. The cell and electrode condition refers to previous work. 9 Fig. 2 shows voltage-dependent ref...