Optical properties of bistable Ch reflective displays

2 Optical properties of bistable Ch reflective displays 10.6.2.1 Reflection 

Bistable Ch reflective displays are operated between the reflecting planar state and the nonreflecting focal conic state. When a Ch hquid crystal is in the planar texture, the refractive index varies periodically in the cell normal direction. The refractive index oscillates between the ordinary refractive index and the extraordinary refractive index rig. The period is PJ2 because n and - n are equivalent. The liquid crystal exhibits Bragg reflection at the wavelength 2o = 2h Po/2)=hPo for normally incident hght [28], where h= ne + no)/2 is the average refractive index. The reflection bandwidth is given by AmPq, where An = is the birefrin- 

The deviation of the helical axis from the cell normal direction in the poly-domain planar texture depends on the amount of the dispersed polymo-. In the regular polymer stabilized cholesteric 

In a cholesteric display with a single layer of cholesteric hquid crystal, only a single color can be displayed. In order to make multiple color displays, Ch LCs with a variety of pitches must be 

Multiple color displays from one layer can be made from pixelation of colors. The displays have three alternating types of stripes of Ch liquid crystals with three different pitches reflecting blue, green and red light. Partition or some other means of preventing inter-stripe diffusion must be used. Polymer walls, especially field-induced polymer walls, are good candidates. The different pitches can be achieved by two methods. In the first method, three cholesteric liquid crystals with different pitches are filled into empty cells with partitions. The second method is photo color tuning [62,63]. A photosensitive chiral dopant is added to the liquid 

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