Optical characteristics of twisted nematic liquid crystals: Application to the improvement of the scanning capability in matrix displays

摘要

The scanning limitations of a liquid‐crystal matrix display due to the lack of sharpness of the transmission characteristic can be extended in the case of the twisted nematic configuration. Indeed, the output polarization from an electrically excited cell, generally elliptic, can be made linear when the linear input polarization is rotated from the molecular alignment at the entrance of the cell. Thus it is possible to decrease the transmission of the nonselected dots while keeping a suitable transmission for the selected dots. A theoretical treatment of the output polarization versus the input polarization and the π/2‐twisted nematic parameter u=2dΔn/λ shows the existence of linear output polarizations. Experiments made on a 64×64‐dot matrix display agree with the predictions. With a duty cycle equal to 1/128, the contrast ratio is 20 : 1, while the response time is 100 ms at 20 °C; the address and the data pulses, applied to the rows and to the columns, respectively, are V1=12.4 V and V2=±1.1 V.