Abstract: The Application describes a method and devices for manufacturing a broadband cholesteric polarizer having a well-defined bandwidth and edge position. To this end, a liquid-crystalline cholesterically ordered layer comprising reactive chiral monomers and reactive nematogenic monomers having a different reactivity is polymerized by exposure to radiation. The invention is characterized in that the intensity of the radiation is increased substantially, preferably by a factor of 10 or more, when a desired edge position of the band is reached. As a result, the bandwidth and edge position of the reflection band reached at that moment are frozen as it were. A monochromatic sensor can be used to determine whether said edge position has been reached, the wavelength used by the sensor corresponding to the wavelength of the desired edge position of the band. Broadband, cholesteric polarizers having a well-defined bandwidth and edge position can very advantageously be used in a display.

Abstract: The invention relates to a color filter layer of a cholesterically ordered material, in which the axis of the molecular helix is directed perpendicularly to said layer. According to the invention, the color filter layer comprises at least one dye which is able to absorb undesired colors caused by color shifts. A correct choice of the bandwidth of the primary colors of the color filter layer and the dyes significantly alleviates the problem of undesired color shift. The invention also relates to a liquid crystal color display device of the reflective type, which is provided with such a color filter layer.

Abstract: A compensator (for example, for a liquid-crystal display device) comprising a retardation foil with a tilted optical main axis and, in addition, a second optically active layer, can be manufactured in a simple manner by providing the retardation foil and the second layer on different sides of a transparent support.

Abstract: A liquid-crystalline cholesterically ordered layer comprising reactive chiral monomers and reactive nematogenic monomers having a different reactivity is polymerized by exposure to radiation. The intensity of the radiation is increased substantially, preferably by a factor of 10 or more, when a desired edge position of the band is reached. As a result, the bandwidth and edge position of the reflection band reached at that moment are frozen as it were. A monochromatic sensor can be used to determine whether said edge position has been reached, the wavelength used by the sensor corresponding to the wavelength of the desired edge position of the band. Broadband, cholesteric polarizers having a well-defined bandwidth and edge position can very advantageously be used in a display.

Abstract: An illumination system has an active layer which includes an electroluminescent material, the active layer being located between an optically transparent electrode layer and a reflective electrode layer. A reflective polarizer is present at a side of the transparent electrode layer facing away from the active layer. A sub-beam incident on the polarizer and having an unwanted polarization is reflected back to the active layer, where it is again partially depolarized to recover a component having the desired state of polarization. The invention also relates to a flat-panel picture display device which includes such an illumination system.

Abstract: An illumination system (3) comprises an optical waveguide (9) of an optically transparent material having an exit surface (19) and four end faces (13, 14, 15, 16). The light from a light source (11) is coupled into the optical waveguide (9) via at least one of the end faces (13). The illumination system, for an LCD, further has a reflective polarizer (21) in combination with a diffuser (23) for polarizing the light supplied by the light source (11). The reflective polarizer (21) is integrated with the optical waveguide and constitutes the surface (25) of the optical waveguide (9) which is located opposite the exit surface (19). The diffuser (23) is present on a surface of the polarizer (21) remote from the optical waveguide (9).

Abstract: A liquid crystal display cell having a compensation layer of (polymer) material deposited from the gaseous phase. To obtain a smaller angle dependence, the birefringence of the compensation layer is rendered complementary to that associated with a given voltage across the liquid crystal cell by giving the optical axis of the compensation layer an angle to the direction transverse to the cell.

Abstract: The Application relates to an illumination system comprising a fluorescent lamp and a broadband, cholesteric polarizer. Such a polarizer contains a layer of a polymeric material having a cholesteric order, which material is ordered in such a way that the axis of the molecular helix extends at right angles to the layer. The broadband character of the polarizer is obtained by causing the pitch of the molecular helix to increase from a minimum value at a first surface of the cholesteric layer to a maximum value at the second surface of the layer. In accordance with the invention, the polarizer should be positioned in the illumination system in such a manner that the cholesteric layer is directed towards the fluorescent lamp with its first surface. In addition, the value of the product p.sub.max.n.sub.e of the maximum value of the pitch in the cholesteric layer p.sub.max and of the extraordinary refractive index n.sub.e must range between 0.61 micron and 0.76 micron.

Abstract: Flat-panel picture display device comprising a picture display panel for modulating the state of polarization of polarized light coupled into said panel in conformity with a picture to be displayed. The light is polarized by means of a reflective polarizer which is integrated or not integrated with the picture display panel. At least a part of the picture display panel functions as an optical waveguide, notably for the beam component b.sub.2 having the state of polarization which is not suitable for modulation. An analyzer is present at a first surface of the picture display panel. The polarizing means in the form of a reflective polarizer are present at a second surface of the picture display panel, which surface is located opposite the first surface.

Abstract: In a liquid crystal display device the number of grey levels is increased by means of a compensation foil comprising a layer having a cholesteric ordering with a helix pattern, in which the pitch of the helix is smaller than (0.26-0.31..DELTA.n) .mu.m, in which .DELTA.n is the optical anisotropy of the anisotropic layer. Moreover, the viewing angle dependence will be more symmetrical by patterning the cholesteric ordering.

Abstract: Cholesteric polarizer and the manufacture thereof. A broadband cholesteric polarizer is described, as well as a method of manufacturing such a polarizer. Said polarizer comprises an optically active layer of a polymer material having a cholesteric order, said material being oriented so that the axis of the molecular helix extends transversely to the layer. In accordance with the invention, the polarizer is characterized in that the pitch of the molecular helix in the layer is varied in such a manner that the difference between the maximum pitch and the minimum pitch is at least 100 nm. The optically active layers are preferably provided on substrates which bring about a conversion of circularly polarized light into linearly polarized light. Three different methods of manufacturing such broadband polarizers are described.

Abstract: An illumination system comprises a radiation source and a broadband, cholesteric polarizer. Such a polarizer includes a layer of a polymeric material having a cholesteric ordering, the material being ordered such that the axis of the molecular helix is oriented transversely to the layer. The broadband character of the polarizer is obtained by increasing the pitch of the molecular helix from a minimum value at a first surface of the cholesteric layer to a maximum value at the second surface of the layer. The polarizer must be positioned in the illumination system in such a manner that the second surface of the cholesteric layer faces the radiation source. By virtue thereof, the illumination system attains a surprisingly low viewing-angle dependence of the brightness and the colour. This property is further improved by using a quarter lambda plate having a negative an isotropy in the refractive index.

Abstract: An illumination system (3) includes an optical waveguide (11) and a light source (9) whose light is coupled into the optical waveguide (11) via at least one end face (13) of the optical waveguide (11). The optical waveguide (11) is provided with recesses (19) which are subsequently filled up with a material which is different from that of the optical waveguide (11). One of the two materials is isotropic and has refractive index n.sub.p and the other material is anisotropic and has refractive indices n.sub.o and n.sub.e. For the refractive indices it should hold that n.sub.o or n.sub.e is equal or substantially equal to n.sub.p in order that there is separation of polarization at the interfaces between isotropic and anisotropic material. Further, a flat-panel picture display device includes such an illumination system.

Abstract: An image projection apparatus which comprises an illumination unit, an image display unit, a projection lens and an electro-optical deflection unit arranged between the display unit and the projection lens and being switchable between a first mode and a second mode and comprising a polarization switch and a birefringent element, whereby the light rays from the display unit passing through the deflection unit if the deflection unit is in the first mode are shifted relative to said light rays passing through the deflection unit if this unit is in the second mode. The birefringent element comprises at least one birefringent oriented polymer layer.

Abstract: Radiation-dose indicator as well as a lamp and a tanning apparatus comprising such a radiation-dose indicator.The invention provides a novel type of radiation-dose indicator which is reliable and accurate. The indicator comprises an optically active layer which includes a liquid-crystalline material as well as a radiation-sensitive compound. This compound is converted under the influence of radiation in such a way as to change the order of the liquid-crystalline material. Preferably, a trans-isomer is used as the radiation-sensitive compound, which is converted to the corresponding cis-isomer under the influence of radiation. In this way, the order of the liquid-crystalline material is broken. Indicators in accordance with the invention can very advantageously be used in UV- and IR-lamps as well as in tanning apparatus.

Abstract: A liquid crystal display cell having a compensation layer of (polymer) material deposited from the gaseous phase. To obtain a smaller angle dependence, the birefringence of the compensation layer is rendered complementary to that associated with a given voltage across the liquid crystal cell by giving the optical axis of the compensation layer an angle to the direction transverse to the cell.

Abstract: The invention relates to an optical temperature indicator. The indicator comprises an optically active layer of a transparent polymeric material in which liquid-crystalline material is dispersed. The molecules of the liquid-crystalline material form part of a polymeric structure via covalent bonds, for example as side-chain groups. The polymeric structure is preferably based on a siloxane. Such an indicator exhibits a good mechanical stability, while the opacity is preserved for a long period of time.

Abstract: A molecularly oriented synthetic resin composition whose coefficient of linear thermal expansion in two mutually perpendicular directions, below the glass-transition temperature, is at least a factor of 3 smaller than in a third direction extending perpendicularly to the first two directions, is manufactured by curing a liquid-crystalline composition having a helicoidal order of molecules, so as to form a polymer network. The resins thus obtained are suitable for use as claddings on materials having a coefficient of thermal expansion which is smaller than that of most synthetic resins.

Abstract: A conjugated poly(p-phenylene vinylene) is manufactured by means of CVD and using simple monomers. Such a polymer is particularly adaptable for use as an active layer in electroluminescent devices, such as a light-emitting diode.

Abstract: The invention relates to an illumination system (7) for a colour image projection device (1). The illumination system (7) comprises a radiation source (3) for generating an unpolarized radiation beam (5) and at least a cholesteric mirror (9, 10, 11, 12, 13, 14) for wavelength-selective splitting of the radiation beam (5) into at least two sub-beams of different wavelengths. A composite circular polarizer (35) for directly converting the unpolarized radiation beam (5) into circularly polarized sub-beams jointly forming one beam is arranged in the path of the unpolarized radiation beam (5) between the radiation source (3) and the cholesteric mirror (9). The composite circular polarizer (35) comprises a polarization-sensitive beam splitter (43) which splits the unpolarized radiation beam (5) into two mutually perpendicularly and linearly polarized sub-beams, and a polarization converter (51, 53; 59, 61).