DD288469A5 - PROCESS FOR PROJECTION AND IMAGE STORAGE WITH OPTICALLY ADDRESSABLE LIQUID CRYSTAL VALVE - Google Patents

Abstract

Method for projection and image storage with optically addressable liquid crystal light valve, suitable for transmitted light as well as reflection projection. The method is mainly used for television and other fields of image reproduction technology. Light blocking layers are not provided. According to the invention, a projection light beam is produced which illuminates a part of the image field. To completely image the image field, this Lichtbuendel performs a scanning movement. At an interval spatially and temporally fixed, an addressing light beam follows the scanning movement of the projection light beam so as to address the field of view which has just been scanned. {Projection; Image storage; Fluessigkristallichtventil; By light; Reflection projection; Watch TV; Image reproduction technology; Light-blocking layers; Projektionslichtbuendel; Image field; scanning; Adressierlichtstrahl}

Description

For this 2 pages drawings

Field of application of the invention

The invention relates to a method of television projection, image storage and slide projection. In addition, the application of the method for storing information for computing is suitable.

Characteristic of the known state of the art

According to the state of the art, liquid crystals have become increasingly important as electro-optically switching substances for image reproduction technology because of their low power requirement and the low control voltages. This also applies to the projection technology.

Liquid crystal displays with thin-film transistors have become the most popular in practice. Their use in projectors has been unsuccessful. In order nevertheless to make the liquid crystal usable for projection purposes, a light valve has been proposed in US 3824002, which is optically addressable. The image is generated by writing the photoconductor through a weak addressing light source. The exposed photoconductive members, which were high-resistance to the liquid crystal in the dark-capable state, become conductive and turn on a current to the liquid crystal to build up an electric field capable of changing the output orientation of the liquid crystal. From the liquid crystal side facing the light of an auxiliary light source is irradiated and modulated. Most of the light is reflected by the mirror while the non-reflected portion of the light is absorbed by the blocking layer. This avoids that the photoconductor is described by the auxiliary light source. However, this system has the following disadvantages. It does not allow transmitted light projection. The blocking layer is an electrically conductive or semiconductive material having a relatively low resistance to obtain the light absorbing properties. At this layer, the charges flow widely and reduce resolution and contrast. The dielectric mirror, in addition, contributes to a loss in resolution due to its thickness and requires AC operation due to its high resistance. The light valve construction proposed in DE 2028235 replaces the blocking layer and mirror with a soot level. Although it allows DC operation, but has an increased due to its high conductivity negative influence on the resolution. Another solution provides for the use of photoconductors, which are largely transparent to white light and addressed with UV or IR radiation. Accordingly, the light source intended for addressing must be filtered out by the projection light source. However, this layer system allows only low luminous fluxes, since there is a residual sensitivity of the photoconductor for white light.

All methods have in common that the measures for neutralizing the light penetration of projection light on the specific photosensitive layer for addressing the resolution, contrast and allowable luminous flux reduce. A first step to avoid the aforementioned deficiencies is gone in DE 2154150. Here, for the first time as a method of electrophotography, a temporal separation of addressing and scanning is proposed. That in this publication

described light valve requires no light-blocking layers despite ordinary white photosensitive photoconductor. However, nematic liquid crystals alone can not be used because the liquid crystal must have a long-term storage capacity. Also, the method does not work without additional switching means, d. H. Optical addressing alone is no longer enough to replace an old picture with a new one. In the present case, a mixture of cholesteric and nematic liquid crystals is used, which has a durable storage device. The image content is optically addressed. The photoconductor switches a DC voltage to the liquid crystal, which orients it. Subsequently, the voltage is externally turned off, the liquid crystal storing the image information. To delete an alternating voltage pulse is sufficient. Diozeitliche separation of addressing and scanning does not allow television because the television is the addressing continuously. Also, this liquid crystal mixture can only influence the directional parameter, d. H. Depending on the orientation of the liquid crystal, the light is scattered or passed through unaffected. However, the directional parameter should remain unchanged, since the distinction of the states "transparent" or "scattering" makes either very large optics or small light-absorbing apertures a condition.

Object of the invention

The aim of the invention was to ensure the use of the liquid crystal light valve for both transmitted light and reflection projection. Here, simple optical systems are to be used. Negative influences on the resolution or luminous flux should be reduced as much as possible.

Explanation of the essence of the invention The object of the invention was to ineffective the penetration of the projection light on the photoconductive layer

although the lightening or lighting of this layer is projected with projection. The object is further, the previously required blocking layers that have prevented the projection light penetration and z. B. too

Resolution losses led to eliminate. The object is achieved as by that first a projection light beam is focused or generated such

that it illuminates only a part of it instead of the entire image field. In order to fully image the image field thereafter, this light beam performs a scan bounce. In a previously spatially and temporally fixed distance follows

Addressing light beam of the scanning movement of the projection light beam, so that it addresses the image field location, which previously

has just been scanned. Both addressing light beams and scanning light beams are simultaneously scanned across the image field, the scanning order being arbitrary, and during a given image presentation period

Image field once completely addressed or completely scanned. The luminous spot size of the addressing light beam is arbitrary, with the upper limit case being a stationary "luminous flock".

which, in the manner of the slide projection from picture change to picture change, projects a faint addressing picture stationarily onto the light valve. The projection light beam carries out the scanning motion on its own.

The lower limit is a spot of size that corresponds to a single pixel to be addressed. It will be a Projector used with a light valve. The light valve consists of the following layers: Substrate carrier, electrode, photoconductor with orientation layer, liquid crystal, electrode with orientation layer and Substrate carrier. In principle, all conventional layer systems, including those with dielectric mirror and / or Use insulation layers. Both by Adressiei light and by projection light of the photoconductor is switched electrically conductive and the Liquid crystal, starting from a homogeneous initial orientation or a disordered liquid crystal volume

an electric field oriented. However, since the entire image field is not illuminated by the projection light but a part remains unexposed, the liquid crystal volume relaxes at these darkened spots. Only one in the darkened

Image field part directed addressing light beam is able to maintain the photoconductive state at struck locations

and to prevent relaxation. After taking the field-free output orientation in the non-addressed by the addressing light beam, the switched-off image field portion of the projection light scan is suspended.

By the projection light of the photoconductor is switched uniformly in the image field section and the liquid crystal begins

again to take its orientation corresponding to the electric field. It can be scanned as long as the

Reorientation, i. the liquid crystal is turned on and all liquid crystals of the liquid crystal are completed Image field section are again uniformly oriented, or the next addressing begins. Thus, the superfluous Use of blocking layers or dielectric mirrors. By this method, the temporal separation of Addressing and sampling realized. Furthermore, it is the use of purely nematic liquid crystals in layer systems

possible, which were previously reserved exclusively for electrophotography. Last but not least, all switching operations of the liquid crystal, which have a negative effect on the image quality, can be faded out.

The method can according to the invention by a third method step "the voltage isolation of image field parts"

be extended regardless of the photoconductor state. At least one of the field electrodes of the image field is divided into a plurality of independent sectors.

According to the invention, a voltage is first applied to the unexposed field of view sector. Then he becomes optical

addressed. Thereafter, it is disconnected from the power supply and finally scanned with the projection light beam.

By this method, not the turn-on delay, but the turn-off delay of the liquid crystal for the Image storage used. The condition here is that addressing and projection light bundles in their scanning on Dom Do not encounter image field. In addition, live sectors and projection beams should not be allowed

encounter if maximum image contrast is to be achieved.

When non-nematic liquid crystals (for example smectic, cholesteric) are used, according to the invention a fourth process step can be carried out in the presence of sectored electrodes, "the setting of erase voltages." Especially in the case of cholesteric liquid crystals, the nature of the turn-on voltage (eg direct current) differs. To set the erase voltage, this must either be set so high that it overcomes the locked photoconductor, or it must be radiated light into the sector, which, however, against projection to the screen The step "setting extinguishing voltages" is further representative of local, d. H. resistive heating performed across the sector electrode to effect a phase change, localized heat radiation or transmission, ultrasonic irradiation or generation, or a combination thereof.

As a means for switching off, for example, serve impellers whose wings, however, may only partially cover the picture. Similarly, fixed sector size electrooptical light valves may be used, or the scanning light beam is simply focused on sector size and deflected by scanner.

As addressing means faint monochromatic picture tubes, LED rows and others can be used. The photoconductor used are photoresist layers or photodiode layers and other transducers which can switch electrical currents as a function of light irradiation.

embodiments

Fig. 1: Overall view of the projector

Fig. 2: Detail sketch of the layer system

Fig. 3: Detail sketch of the sectored layer system

The image field according to Flg. 2 consists of O, 6mm thick glass substrates 21, each having a transparent electrode 22 of indium oxide / tin oxide. On a substrate, a ca, 1 μιη thick CdS layer 23 is applied. This is already sufficiently transparent for a scanning luminous flux, but on the other hand has a sufficiently large absorption coefficient for the addressing. The liquid crystal 24 in this example is of the nematic type called E 5 (Merck). The layer thickness is typically 1 to 20μπΊ but preferably 6-8 μιυ. On the CdS layer 23, an orientation layer 25 of 150 to 200 Å in thickness consisting of a maleic anhydride copolymer obtained from the reaction of maleic anhydride-vinyl acetate with butylamine is applied by dipping. This layer system has the size of an image field 16 and is arranged stationary in the projector according to FIG. The image field is located in the light path of the scanning light from the light source 11. The scanning light is collected by the capacitor 12 so that it completely illuminates the entire image field, so that from the entire image field on projection lens 17, an image can be generated on the screen. Before and behind the image 16 polarizers 13 are arranged. Immediately before the image field, a slit diaphragm band 14 is threaded, which hides the scanning light beam to sector size. On the opposite side of the image field 16, the addressing light source, a picture tube 18 with the addressing lens 19, arranged such that the optical axes of frame 16, addressing lens 19 and picture tube 18 are parallel to each other to completely exclude distortion. The method of image formation is as follows. First, the lower part of the image field is shaded by the slit band 14, since because of the reversed representation in projection, the image must be built from below.

The writing beam emanating from the picture tube 18 then addresses the shadowed picture field portion while scanning the overlying portion. In the shaded field part, the unaddressed photoconductor sites assume their dark-conducting state, causing the liquid crystals to relax. At the sites addressed, the power supply of the liquid crystals as they existed since the projection light scan continues to exist, so that the liquid crystals retain their orientation caused by an electric field. The electric field can be maintained in the addressed pixel by several factors. Such are the luminescence time of the luminophore matched to the switching time of the liquid crystal, a small switch-off delay of the photoconductor and the capacitive storage of the charges on the liquid crystal volume as a dielectric. The openings of the slit diaphragm band 14 follow by a continuous transport movement at a fixed distance from the writing light beam 120 and slot and their direction of movement are shown in FIG. 1. Instead of a CdS photoconductor, it is also possible to use a photoconductor which is considerably more transparent for white light but requires UV light or IR light for its addressing. Such a photoconductor is, for example, ZnS for UV light. In addition, photoconductors that are self-reflective may be used and eliminate other mirrors for reflectance projection. Such a photoconductor is made of silicon, for example. In principle, it is also possible to install dielectric mirrors, which, however, somewhat diminishes the desired effect of the resolution improvement, increases the production outlay and requires AC operation with all the problems of impedance matching. Likewise, one of the electrodes can also be a metallic mirror and at the same time a substrate carrier. This is particularly advantageous if a heating current pulse or simply an extinguishing current impulse is to be conducted through these electrodes. The latter is particularly important in the case of sectored electrodes.

The method of imaging with sectored image field 16 according to FIG. 3 is initially described on the premise of the further use of nematic liquid crystals. The image field 16 is again addressed from bottom to top. The slit of the aperture band 14 has left the sector electrode and is opposite the sector electrode 352. The freshly shaded sector electrode 351 is de-energized. Photoconductor and liquid crystal have the possibility to take the rest state. Thereafter, the sector electrode 352 is shaded by the constant transport movement of the slit band 14, while at the same time the supply voltage is applied to the sector electrode 351 and the addressing is started. The slot is opposite to the sector electrode 353. Subsequently, the slot travels to the sector electrode 354 while continuing the power supply and addressing of the sector electrode 352. The sector electrode 351 still remains off and has time to complete the switching associated with the addressing. The supply voltage can still remain applied when the photoconductor his

stores the excited state for a short time, as is usually the case with photoresist layers, but it can already be turned off when fast switching photodiode layers are used. Subsequently, the slot moves out of the frame at the top, while from below a new one moves into the image field and releases the sector electrode for di6 scanning. This process is repeated constantly.

As already anticipated, the sector electrodes 351 to 354, which divide the image field into corresponding sectors, can be made metallic and specular.

Thus, they are also advantageous as heating electrodes for bringing about phase changes in the liquid crystal volume usable. The Heizstromimpuls is always set in the timing of image generation when the slot has just left the image field part.

Usually one more sector is needed until addressing. On the other hand, the sector is unnecessary after the addressing to sampling, since, for example, smectic liquid crystals switch several orders of magnitude faster than nematic. In principle, an overlap of sampling and heating is allowed. This is especially true when the scanning light beam itself is to contribute to the heating. In this case, however, it is advisable to use a second aperture slit band on the opposite field side, which has narrower slits than the first, the upper edges run synchronously with each other, so that the switching process is hidden. Last but not least, it should be added that the layer system may also be larger than an image field, which increases the switching times or allows simultaneous operation of several sectors. However, in principle, an objective 17 is additionally required for each sector which exceeds an integer multiple of an image field.

Claims (3)

1. Method for projection and image storage with optically addressable Flüssigkribtallichtventll, suitable for both transmitted light and reflection projection by using a photoconductive or switching material for optical addressing, characterized in that first a projection light beam is generated, which only partially illuminates the image field and then to a scanning movement is initiated, which simultaneously follows an addressing light beam in a previously spatially and temporally fixed distance, such that the image field is completely scanned once from image change to image change from both the projection light beam and the addressing light beam. 2. Method for projection and image spokes mg according to claim 1, characterized in that instead of the turn-on delay of the liquid crystals, the turn-off delay for obtaining the image information can be made available by at least one of the electrode surfaces is formed sectoriort, and to these electrode sectors only a switching voltage is applied when the field sector corresponding to this electrode sector is being addressed, or after its addressing to the scan for the completion of the switching process still an electric field is required, but then for the subsequent projection light scanning the electric field is removed. 3. A method for projection and image storage according to claims 1 and 2, characterized in that the triggering dos-off operation using, for example, non-nematic liquid crystals, the electrode sectors are used, such that the electrode sectors with an erase voltage, with an electrical heating current or an AC voltage for the z. B. piezoceramic ultrasound generation are always connected in the image field sections that are just left by the scanning light bundle or have already been abandoned by the Adressier'ichtstrahl, however, have not yet been reached or influenced.