| 摘要 |
<p>1408791 Modulating light LICENTIA PATENT-VERWALTUNGS GmbH 6 Nov 1972 [6 Nov 1971] 51156/72 Heading H4F In a variable colour filter, a homotropically aligned nematic liquid crystal layer is subjected to an A.C. field of an intensity and frequency such as to distort (tilt) the nematic alignment without producing dynamic scattering, whereby the layer, which initially appears optically isotopic to an incident polychromatic light beam, becomes birefringent, and the layer is disposed between crossed or parallel polarizers for selectively transmitting interference colours in the energized state. Parts of the layer may be selectively addressed, e.g. by X and Y strip electrodes on respective sides of the layer, for a colour display on a dark or light background. By applying A.C. voltages of the same frequency to both electrodes and varying the phase at one electrode, the magnitude of the resultant field and hence the colour transmitted may be controlled. The brightness at any point may be controlled by time multiplexing. To display both primary and non-primary colours, three adjacent elemental points constituting a single image point may be independently operated with different predetermined fields. Alternatively an arrangement of three sequential layers with interposed polarizers, providing three primary colours, may be used. With low A.C. voltages, the filter acts as a grey scale (intensity) modulator. Such a filter may be used in series with the colour filter, the intermediate polarizer being common, and the electrodes being in register if shaped. In a projection arrangement, the filter may be positioned at the slide position of a still projector, being preceded by a heat protective filter, and the image is received on a screen or matt disc. For small angle transmission a fibre optic disc replaces the matt disc. As particularly described, the nematic material may be methoxy-benzylidene-p-n-butylaniline, the polarizers are cemented to glass plates bounding the liquid crystal layer, and glass-air surfaces are anti-reflection coated. The A.C. frequency may be 1 kHz to 30 kHz and is preferably 5 kHz. The nematic layer is preferably controlled to be at a temperature above ambient, e.g. by resistance heating using transparent conductive sheets externally of the glass plates, or the X-Y conductors themselves. The latter enable selective heating, for example for correcting colour deviations arising out of variations in the thickness of the nematic layer. If the intended homotropic alignment is not actually at 90 degrees to the surfaces of the nematic layer, the layer must be tilted until the alignment and optical path are parallel.</p> |
