Reflective LCDs

Similarly, the reflective LCDs can be subdivided into direct-view and projection displays. In principle, a direct-view reflective LCD does not require a backlight so that it is light in weight and its power consumption is low. A major drawback is poor readability under weak ambient light. Thus, a reflective LCD is more suitable for projection TVs employing liquid-crystal-on-silicon (LCoS) microdisplay panels. In an LCoS, the reflector employed is an aluminum metallic mirror. The viewing angle is less critical in projection displays than in direct-view displays. 

For outdoor applications, the displayed images of a transmissive LCD could be washed out by sunlight A reflective LCD would be a better choice. However, such a reflective display is unreadable in dark ambient conditions. Transflective LCDs integrate the features... 

Polymer-dispersed LC (PDLC) [30], polymer-stabilized cholesteric texture (PSCT) [31], and LC gels [32] all exhibit optical scattering characteristics and have wide applications in displays and optical devices. The LC gel-based reflective LCD can also be extended to transflective... 

The 90° TN cell can be used not only in transmissive and reflective LCDs [38], but also in transflective LCDs [39]. Figure 9.11(a) shows the device configuration of a transflective TN LCD. A 90° TN LC cell, which satisfies the Gooch-Tarry minima conditions [40], is sandwiched between two crossed polarizers. In addition, a transflector is laminated at the outer side of the bottom polarizer and a backlight is intended for dark ambient. 

Let us design a normally black reflective LCD using a 45° twisted nematic cell for projection displays. We want the display to be independent of beta angle ( ) the angle between the top LC rubbing direction and the incoming polarization axis. What is the required d n value at 2 = 550 nm ... 

The feasibility of a photoswitchable bistable reflective LCD based on an azodye doped LC film has been successfully demonstrated [42]. Its bright/dark states... 

Figure 6.2 A bistable photoswitchable reflective LCD. POL, DDLC, QWP, and TRM are the linear polarizer, dye-doped liquid crystal, quarter-wave plate, and transflective mirror respectively [2]. Reproduced from T.-H. Lin, H.-C. Jan, S.-Y. Hung, H.-R. Fuh, and A. Fuh, Photoaddressable bistable reflective liquid crystal display. Applied Physics Letters 89, 021116 (2006), American Institute of Physics...

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