DE1487779A1 - Arrangement for making information visible by means of a light control cell - Google Patents

Description

, een 29. ^ 068

H87779

WESTINGHOUSE ELECTRIC CORPORATION of East Pittsburgh, Pa., V.St.A.

Arrangement for making information visible by means of a light control cell.

The invention relates to an arrangement for making visible Information by means of a light control cell, which is a layer liquid crystals of the cholesterol type, the optical properties of which can be influenced by temperature changes.

There are various ways of representing an image distribution known, including in particular the normal television reception system. The television receiver is based essentially on the fact that an intensity-modulated according to the image information to be displayed Electron beam accelerated. In the case of screens with large dimensions, however, there are practical limitations to the The beam current density and the beam voltage have an upper limit Image brightness. Another way of displaying images that is currently being developed makes use of electroluminescent phosphors. A screen of a large area based on this, however, has so far proven to be too faint, and so have the associated ones

9Ö9Ö18 / O616

Imaging control devices are complex and expensive.

The object of the invention is to provide a remedy here. the Arrangement according to the invention for making information visible by means of a light control source that creates a layer of fluid Contains cholesterol type crystals, their optical properties can be influenced by temperature changes is characterized in that the light control source is controlled by a beam in accordance with the information

lies, which exerts a heat effect corresponding to the information on the liquid crystal layer.

The light control cells used according to the invention can be of The outside can be brightly illuminated, whereby the general lighting can be used to support a luminous picture by reflection at the light control cell or transmission through the same to create. Here, the temperature dependence of the optical properties of liquid crystals of the cholesterol type Made use of. Liquid crystals are known to have a state between a real crystal and a liquid. the Cholesterol-type liquid crystals form a group thereof which has particularly remarkable optical properties. the most liquid crystals of this type are formed from compounds derived from sterols, although by no means all substances that show the relevant properties belong to this chemical class. When heating a solid substance

U87779

it goes into this kind from a white crystal state a liquid-like phase in which he vigorously is colored.

The cholesterol phase has an index of refraction that corresponds to the direction of propagation the light sways through the fabric. Enforces the light is a thin layer of liquid crystals of the cholesterol type, so is the index of refraction for normal incidence a minimum. The refractive index increases with a larger angle of incidence. In the case of solid crystals, this property is called Denotes birefringence.

When linearly polarized light is in the direction of the optical axis, i.e. the direction in which the refractive index is Is a minimum, the plane of polarization becomes around one Rotated angle, which depends on the layer thickness, the type of material and the respective wavelength. These As is well known, property is referred to as optical activity. It was found that the cholesterol type liquid crystals have the strongest optical activity of all known substances. The rotation of the plane of polarization can be up to 1800 ° each Be millimeters.

Another important property of the liquid cholesterol-type crystals is their iridescent appearance when illuminated with Ambient light. The colors that occur are due to a scattering in the material, which in a certain way is due to the scattering of light

909810/061 $

is similar to an oil film on water. However, there are significant differences. An oil film then scatters light when its thickness is an exact multiple of half a wavelength. The cholesterol layers only scatter one wavelength at a certain angle. The light scattered by an oil film is not polarized, whereas the light scattered by a liquid crystal of the type in question is circularly polarized. Furthermore, it can be seen that circularly polarized light hitting a liquid crystal retains its sense of rotation during reflection or scattering, in contrast to normal mirror reflection. In detail, the conditions are such that right-hand circularly polarized light remains clockwise during reflection and scattering, while counter-clockwise polarized light is not scattered at all, but penetrates the layer. This property is known as circular dichroism. It is found that a liquid crystal absorbs almost no energy, so that almost all of the incident light energy is either transmitted or reflected. At certain wavelengths and perpendicular incidence, around 50 % of the incident light radiation is scattered. At larger angles of incidence, the amount of reflected energy increases and the maximum scattering shifts to shorter wavelengths. If the temperature of the liquid crystal layer changes, then with a temperature increase the maximum of the reflection curve shifts towards shorter wavelengths. This temperature effect is completely reversible. At any temperature the wavelength of the maximum scattering depends on the

909818/0616

_ 5 -

Sum of the angle of incidence of light and the viewing angle.

Some embodiments of the invention are presented below explained with reference to the drawing. Are in it

1 shows the schematic representation of an imaging arrangement according to the invention;

Fig. 2 is an illustration of a modified imaging arrangement;

3 is a graph for explaining the properties the liquid crystal layer;

Fig. 4 is a graph for explaining the mode of operation the arrangement of Figures 1 and 2;

5 shows the schematic representation of a further according to the invention Imaging arrangement in which the reflective properties the liquid crystal layer can be used; and

Fig. 6 is a schematic representation of a color television device according to the invention.

Fig. 1 shows a projection system with a polarizer 11 and an analyzer 13 arranged in parallel to each other. The polarizer and analyzer can be seen from tourmaline, Nicol's Prisms or other known arrangements for the passage of light exist in only one plane of polarization.

A light modulation cell 15 is located between the polarizer 11 and the analyzer 13. The modulation cell 15 contains a layer 17 which is capable of electromagnetic wave distortion

909818/0616

to absorb division and convert it into a thermal image. The layer 17 absorbs the wavelengths used for modulation, but lets through the light used for projection. In the present exemplary embodiment, the modulation wavelength is in the "ultraviolet" range, while the projection is in the visible Part of the spectrum takes place. A suitable material for the layer 17 is tartrazine in a thickness of a few microns. Numerous organic and inorganic dyes with corresponding absorption properties are also suitable. For in the ultraviolet range, anthracene and phenanthrene are also suitable. A carrier layer serves as a base for the layer 17 19 with low heat capacity that is transparent to at least the visible part of the spectrum. The layer has a thickness of approximately microns and is made, for example, of polyvinyl fluoride.

On the other side of the layer 19 is a layer of a material which binds liquid crystals of the cholesterol type. The layers 21 and 19 are in good heat transfer. For example, the layer 21 consists of a mixture of 20 % by weight cholesteryl benzoate, 30% cholesteryl nonanoate and 50 % cholesteryl oil carbonate. Other suitable materials are, for example, described in US Pat. No. 3,114,836. On the other side of the liquid crystal layer 21 there is a further final layer 23 made of polyvinyl fluoride and the whole can be enclosed in some way around the

909818/0616

1487773

Liquid 21 between the two layers 19 and 23 to keep.

A cathode ray tube 27 serves to direct the modulating light onto the modulation cell 15. The cathode ray tube

27 has a luminescent screen 28 which generates ultraviolet light when bombarded with electrons. An electron gun 26 is used to generate the electron beam Deflection device for the electron beam and a light control electrode connected to a video signal source in FIG provided in a known manner.

Optics 31 are located between the cathode ray tube 27 and the cell 15 in order to absorb the ultraviolet light from the fluorescent screen

28 focus on cell 15. Outside the polarizer 11 a light source 35 is arranged. In the present embodiment Spiel the light source 35 is monochromatic and provides light with a wavelength of about 5700 ft. Zur If necessary, appropriate filters are provided to suppress this wavelength. Optical means 37 and 39 serve to convey the light from the light source 35 onto the cell 15 and the light from the cell 15 onto a projection screen 41.

To explain the method of operation of the invention, reference is made to FIG referenced. Curves 40 and 42 show the rotation of the plane of polarization through layer 21 at two different ones Temperatures. The curve 40 applies to 27 ° C and the curve 42 to

909818/0616

29 ° C. So at 27 ° C the plane of polarization is 45 ° turned. Polarizer 11 and analyzer 13 can now be set in this way be that at this temperature practically no light from the light source 35 onto the projection screen 41 can get. If the temperature is increased to 29 ° C., the polarization plane only rotates according to curve 42 about 15 ° C, so that with the same setting of the analyzer 13 now a significant amount of light on the projection screen got. By modulating the intensity of the electron beam in the cathode ray tube 27, that emitted by the fluorescent screen 28 is transmitted modulated ultraviolet light accordingly. The ultraviolet incident on layer 17 of light control cell 15 Radiation determines the temperature thereof and thus the amount of light transmitted from the light source 35 to the luminescent screen 41. In this way, a high-intensity visible image corresponding to the video information on the screen 41 can be designed will. The ultraviolet radiation used for modulation can have a much lower intensity than the modulated visible radiation Light that was linearly polarized in the polarizer 11, its ι

It is not essential that the light from the cathode ray tube 27 have a different wavelength from that from the light source 35, although it is advantageous. Instead of a dye or some other chemical substance with For the layer 17, a metal layer can also be used for selective absorption with an electrical sheet resistance of about 377 ohms can be used. Such a layer absorbs about half

909818/0616

H87779

of all incident rays, so the light from the light source 37 and from the cathode ray tube 27, and lets in Quarter of the rest through. Under these circumstances, the light source 35 can be used together with the cathode ray tube 27 in order to bring the temperature of the layer 21 to a suitable base value at which the main light of of the light source 35 passes through the analyzer 13. if one twentieth of the total energy required to achieve the optimum layer temperature from the cathode ray tube 27 is supplied, this energy component is more than sufficient to ensure the permeability of the arrangement modulate.

It is also possible to use the circular dichroic properties of the layer 21. For this purpose, instead of the polarizer 11 and the analyzer 13, a circular polarizer is used between the light source 35 and the light control cell 15. The light source 35 supplies a wavelength of 5400 8, for example. At a temperature of 27 ° C., the permeability of the layer is almost zero in this case, as curve 43 in FIG. 3 shows. If the temperature rises to 29 ° C., the permeability increases to about 85 % , as curve 44 shows. The polarizer and the liquid crystal layer should have the same polarization rotation, i.e. either left-handed or right-handed,

If the light source 35 is constructed so that it does not emit a single wavelength, but a wavelength band, so

909618/0618

H87779

For example, the arrangement can be used in the following manner: For example, the light source 35 emits light in the region of the spectrum between the infrared end thereof and about 625O 8. This is shown in FIG. 4 by curve 49. Curve 50 shows the transmission properties of polarizer 11, analyzer 13 and light control cell 15 for a temperature of 27.degree. Curve 52 shows the permeability of the same arrangement at a temperature of 29 ° C. By shifting the temperature of the light control source 15 to a higher value, the passage of light through the arrangement can therefore be completely prevented. If the temperature is lowered again to about 27 ° C., the light from the light source 35 again passes through the arrangement and reaches the screen 41. In this case too, however, only about 50 % of the light emanating from the light source 35 is allowed through. This is due to the fact that the circular dichroism always occurs in the optical activity area of the layer 21, so that only the right-handed or left-handed part of the light is transmitted, while the other part is reflected by the liquid crystal layer 21.

In Fig. 2, a modified control arrangement is shown in which the light control cell 59 is within an evacuated Piston 60 is located so that an electron beam generated there can impinge directly on it. The one as a light control cell formed screen 59 consists here of translucent layers 62 and 64 of polyvinyl chloride, between which

909818/0616

a thin layer 65 of a cholesterol type liquid crystal material is located. A clear electrode 66 made of tin oxide or gold is on the outside of the layer. The electron beam bombards the electrode 66 and generates a thermal image that affects the layer 21. In the case of this direct control by the electron beam, a Gain of at least a hundred can be achieved.

The mode of operation of the arrangement according to FIG. 2 corresponds to that according to FIG. 1. The speed of response of the arrangement can be influenced by lining the inner surface of the tubular piston with a plastic film of such a thickness that the correct thermal conductivity results, in order to reduce the thermal time constant of the arrangement as much as possible. This can be achieved without making a great sacrifice in terms of the energy sensitivity of the liquid crystal layer. It is also possible to apply a plastic layer on the side of the screen facing the electron beam, the material of the plastic having a zero crossing of its secondary emission curve at high voltage, so that maximum energy is absorbed from the electron beam. The maximum permeability of the entire cell for the wavelength to be amplified of the light from the light source should be made as high as possible in this case. By arranging the electron gun 26 at an angle to the screen, the polarized light from the high-intensity light source 35 passing through the light control cell 59 can be modulated. _A "

909818/0616

H87779

Fig. 6 shows a projection system with three separate arrangements 31 ι 63 and 67 according to FIG. 1, the three light sources 35, 35a and 35b emitting red, green and blue light, respectively. Thus, a red image is generated by the arrangement 6i on the luminescent screen, which is a red color separation of the video signal is equivalent to. Correspondingly, the arrangement 63 provides a green and the arrangement 67 a blue image. The three Color separations can appear one after the other or simultaneously on the projection screen and result in a color television picture high intensity,

Fig. 5 shows a further embodiment of the invention in which use is made of reflection. A picture tube of the usual type consists of a face plate 70, a piston part 72 and a quay part 74. In the neck part there is an electron gun 76 with a control grid 77 and deflection device. The screen 81 located behind the face plate 70 is designed as a light control line. A transparent electrode 78, for example made of tin oxide, is first attached to the inside of the faceplate. This is followed by a liquid crystal layer 80, for example composed of a mixture of 45% by weight cholesteryl nonanate, 45% oleyl cholesteryl carbonate and 10% cholesteryl benzoate. The thickness of this layer is about 25 microns. On the inside, the liquid crystal layer 80 is bounded by a layer 84 of polyvinyl fluoride, which has a black coating on its surface facing the layer 80. A layer 82 similar to the layer 66 in FIG. 2 is on

909818/0616

U87779

the surface of the polyvinyl fluoride layer facing the interior of the tube 84 applied. A conductive wire mesh can also be located between the screen 81 and the electron gun 76 8 6 for the acceleration and concentration of the electron beam are located. A white light source 88 is positioned outside the envelope to illuminate the screen 81.

In operation, the electron beam is directed from the electron gun 7 6 onto the screen and generates a heat distribution in the layer 82 corresponding to the video information that the control grid 77 is fed. The thermal image generated in the layer 82 influences the layer 80, which is in reflection provides a visible image when illuminated by light source 88. By appropriate choice of the thermal conductivity of the Screen 81, the response speed can be brought to the desired value. By the intensity of the video signal the basic color can be chosen. The color intensity can be changed by simply modulating the electron beam, see above that a multicolor image results. The luminescent screen can can be viewed under strong general lighting. The brighter the ambient light, the brighter the display on the screen. It is also possible to have a single color on it rush to create a black background when the light source provides monochromatic light.

909818/06 16

Claims (9)

G. Wnhfom * Munich, the * * Jum 1968 H87779 WESTINGHOUSE ELECTRIC CORPOATION in East Pittsburgh, Pa., V.St.A. Claims 1. An arrangement for making information visible by means of a light control cell which contains a layer of liquid crystals of the cholesterol type, the optical properties of which can be influenced by temperature changes, characterized in that the light control cell (15) is in the path of a beam controlled in accordance with the information, which is one of the Information corresponding heat effect exerts on the liquid crystal layer (21). 2. Arrangement according to claim 1, characterized in that the control beam is supplied from a cathode ray tube (27) whose light spot is mapped onto the light control cell (15). 3. Arrangement according to claim 1, characterized in that the control beam is supplied by an electron beam source (26, 76) which generates an electron beam scanning the light control cell (59, 81). 909818/0618 4. Arrangement according to one of the preceding claims, characterized in that the light control cell is a with the liquid crystal layer (21, 65, 80) in thermal contact and the control beam source facing layer (17, 66, 82) which can absorb the control beam and convert it into heat. 5. Arrangement according to one of the preceding claims, characterized in that the light control cell is in the way a light beam emanating from a light source (35, 88) is located. 6. Arrangement according to claims 4 and 5, characterized in that the layer absorbing the control beam (17, 66) faces the light source and is transparent to the light emanating from it. 7. Arrangement according to claim 5 or 6, characterized in that a polarizer (11) between the light source and the Light control cell is arranged. 8. Arrangement according to claim 6 or 7, characterized in that a projection screen (41) behind the light control cell is arranged. 9. Arrangement according to claims 6 and 7 or 8, characterized in that that the liquid crystal layer is the plane of polarization of the passing light according to their 909818/0616 Warming turns that behind the light control cell Analyzer (13) is arranged and that the polarizer and analyzer are oriented to each other that in a At a certain temperature of the liquid crystal layer, the light passing through is extinguished in the analyzer. 909818/0616