Holographic PDLCs

Schematic diagram showing how the holographic PDLC is used for reflective displays. 

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The spectral response of a holographic PDLC to applied electric fields is shown in Figure 11.27, where white incident hght is used [37]. At 0 V, due to the periodic refractive index, the cell has a high narrow reflection peak. When the applied voltage is increased, the liquid crystal is ahgned toward the layer normal direction. The amplitude of the oscillation of the refractive index decreases and the reflection of the cell also decreases. The drive voltage is approximately equal to the product of the field threshold of the Freedericksz transition of the liquid crystal layer and the cell thickness. 

Figure 11.27 Reflection spectra of the holographic PDLC under various applied voltages. Reproduced with permission from Wiley.

D photonic crystals can be made by holographic lithography. Switchable photonic crystals ° can be made by electrically switchable Bragg gratings or holographic polymer dispersed LCs (Fl-PDLC). i... 

Holographic polymer dispersed liquid crystals (H-PDLCs) are obtained by photopolymerisation of a hquid crystal-prepolymer mixture in the interference field of two or more laser beams [14,15]. This induces phase separation in which hquid crystalline material predominantly congregates in dark regions of the optical interference pattern [16,17]. As a result, holographic gratings with extremely high refractive-index contrast are formed. In addition, the diffraction efficiency of these gratings is electrically switchable the apphcation of an electric field results in reorientation of the nematic director field within... 

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