Asulab S.a.

Peter Kipfer

Joachim Grupp

Rolf Klappert

Hans Peter Herzig

Toralf Scharf

Christian Bohley

An optical device ( ) is provided using at least one film ( ) of cholesteric liquid crystal to reflect at least one predetermined wavelength band from an incident light. This device is characterized in that a non zero birefringence gradient is present in a portion or the entire thickness of said film. The gradient may be obtained in particular by superposing layers ( ) having increasing or decreasing respective birefringence coefficients. The birefringence gradient has the effect of removing the lateral bands of the reflection spectrum, hence making the color of the reflected light more brilliant and more saturated. The effect is particularly advantageous in the case of the color red, for which the lateral band located on the yellow side is perceived strongly by the human eye.

Bragg reflection optical device and methods for the manufacturing thereof

The invention concerns a liquid crystal display device intended, in particular, to form a colour image display screen, of the type including: a first substrate which is transparent on a front side situated on the side of the viewer; and a second substrate arranged on a back side facing the first substrate and extending parallel to the latter. The first substrate is connected to the second substrate in order to delimit between them a cavity in which at least one film of liquid crystal is arranged. The liquid crystal has at least a first state in which it reflects the light of a range of wavelengths of a predetermined colour and at least a second state in which it is transparent. The surface of each substrate facing the other substrate includes electrodes to allow the liquid crystal to pass at least from the first state to the second state or conversely, by selective application of a control voltage to the electrodes. The liquid crystal display includes a filter absorbing at least the visible neighbouring wavelengths of the range of wavelengths of the predetermined colour and the closest to the wavelength 555 nm with the exception of the wavelengths of said predetermined colour. The filter is arranged on the side of the viewer with respect to the film of liquid crystal.

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Berneck, Switzerland

Peter Kipfer