| 摘要 |
<p>1478592 Controlling light DEFENCE SECRETARY OF STATE FOR 28 Feb 1975 [1 March 1974] 9489/74 Heading G2F In a "twist" liquid crystal cell, a layer of naturally optically active liquid crystal material with a natural molecular helical pitch of the order of or greater than twice the thickness of the layer is disposed between electrode substrates, the substrate surface being arranged such that at one surface of the layer the average molecular alignment is parallel to the surface and at the other surface the alignment is tilted. Fig. 2 (d) shows an analogous arrangement for a non-twisted device i.e. the alignments adjacent the surfaces LU and LR appear parallel when viewed along a normal to the surfaces. Rotation of one surface about an angle # # 90 degrees would give a "twist" cell. Due to the initial tilt, all molecules tend to rotate in the same sense when a field is applied across the layer. Use of an optically active material precludes the formation of domains of reverse twist. The substrate surface for inducing parallel alignment is prepared by oblique evaporation of a dielectric material in a direction making an angle of 45-75 degrees relative to the surface normal. The molecules tend to align transversely to the projection of the evaporation direction on the surface. The second substrate surface of unidirectional tilted alignment is prepared (a) as the first substrate surface followed by uni-directional rubbing transversely of the evaporation direction; (b) simple uni-directional rubbing of the surface; or (c) oblique evaporation of a dielectric material at a grazing angle of 0-15 degrees. In (a) and (b) the projection of the molecular alignment direction is parallel to the rubbing direction and in (c) it is parallel to the evaporation direction. The molecular alignment direction at one layer surface is arranged to be at an angle e.g. 90 degrees to that of the other surface. As described, the cell may be disposed between polarizers and the electrodes may be sloped or segmented e.g. in a coincidence addressed matrix.</p> |
