Super Birefringent Effect LCDs

Prototype SBE-LCDs combined a chiral nematic mixture with large twist angle, O 240°-270° with a low ratio of the cell gap to pitch djp 0.75), a positive 

Upon the application of an operating voltage just above the threshold voltage results in a modest realignment ( 10%) of the nematic director in the middle of 

The major difference between the configuration of the OMI sandwich cell and other STN-LCDs is that the optical path difference (5 = And 1 pm) is much lower. There is no requirement for a significant pretilt (0 0 5°), the twist angle of the chiral nematic layer is lower (180°), the front polariser is parallel to the nematic director (a = 0°) and the polariser and analyser are crossed (P = 90°). The 180° twist gives rise to strong interference between the two elliptically polarised rays. If the optical path difference is small, e.g. 0.4 m, a bright, white, non-dispersive off-state is produced. The chiral nematic mixture should be of positive dielectric anisotropy, low birefringence and exhibit a low cell gap to pitch ratio dip 0.3). 

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The super birefringent effect (SBE-LCD) reported by Scheffer and Nehring from Brown Boveri in Baden, Switzerland, uses the optical interference of two normal, elliptically polarised modes of transmitted light generated by a high-tilt, highly-twisted nematic structure viewed between two polarisers set in an unusual way, i.e. the input polarisation direction is not parallel to the nematic director at either substrate surface and the polarisers are not crossed at 90°, see Figure 3.10. 

Compared to the conventional transmissive TN LCD, the above transflective TN LCD only requires one additional transflector between the bottom polarizer and the TN LC layer. Naturally, this transflective LCD device configuration can also be extended to an STN-based transflective LCD [42]. In contrast to the so-called polarization rotation effect in TN LCD, the STN LCD uses the birefringence effect of the super-twisted nematic LC layer [43]. Therefore, a larger twist angle (180 270°), a thicker LC cell gap, and a different polarizer/analyzer configuration are required. 

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