WO2003012495A2

WO2003012495A2 - Holographic screen for front projection, a projection system and a method for image projection

Info

Publication number: WO2003012495A2
Application number: PCT/DE2002/002488
Authority: WO
Inventors: Thorsteinn Halldorsson
Original assignee: Eads Deutschland Gmbh
Priority date: 2001-07-27
Filing date: 2002-07-06
Publication date: 2003-02-13
Also published as: DE10136786A1; DE10136786B4; WO2003012495A3

Abstract

The invention relates to a holographic screen (110) for front projection, comprising an optically transparent support plate (112), a hologram (111) which is secured to the support plate (112) and which back scatters a front projected, spectrally narrow-banded light at a predetermined spatial angle while the hologram (111) is transparent for broad-banded light. A switchable layer (114, 116) can be interchanged between a first state which is essentially optically transparent and a second state which is essentially optically absorbent and/or reflective.

Description

Holographic screen for front projection, projection system and method for image projection

The invention relates to a holographic screen for auto projection according to the preamble of claim 1, a projection system according to the preamble of claim 15 and a method for image projection according to the preamble of claim 16.

Image projection techniques are increasingly used for presentations and general office work as well as for entertainment in the home. For this purpose, electronic projectors, so-called projectors, can be connected directly to a PC, notebook, television or DVD player. Other applications are, for example, in cinemas and lecture rooms.

Usual image projection screens for reflected light projection, such as. B. white screens have the disadvantage that in addition to the incident light from the projector they also scatter light from the surroundings back to the viewer. The superimposition of this background light reduces the contrast and the color saturation of the projected image.

In order to avoid this disadvantage, holographic screens for front projection have been developed. Such screens selectively scatter spectrally narrowband light from a projector, which is located at a defined location, back to the viewer, who is on the same side as the projector, at a predefined angle. In contrast, spectrally broadband background light from directions other than the projection direction is transmitted largely unaffected. This applies both to background light that falls on the holographic screen from the side of the viewer and to background light that falls on the image screen hologram from the side facing away from the viewer.

A holographic screen for front projection and its production is described for example in DE 197 00 162 AI. In order to produce the holographic screen, for example, a hologram image of a real screen or a scattering surface is made. In other words, a hologram is created, the object of which is recorded when it is recorded real screen or a light-scattering surface. If the hologram is later illuminated with a light beam in the same wavelength range and at the same angle of incidence as in the hologram recording, it is scattered back to the viewer through the grating structure of the hologram. In this way you get a very bright and high-contrast image when projecting with narrow-band light.

Such a holographic au-projection screen, which is applied to a transparent support plate, allows illuminated objects that are located behind the au-projection screen or screen to be viewed. If, on the other hand, a bright image is projected onto the screen, the free view is interrupted by the hologram, i.e. for the viewer, the projected image outshines the view through the screen.

However, this overexposure does not always have to be complete, since areas that are dark or black in the projected image will still be partially transparent to the eye through the screen. A bright object that is behind the screen when viewed by the viewer will therefore significantly degrade the contrast in the projection image.

The disturbing brightening of the space behind the holographic projection screen can be either direct or indirect. It is direct when the room is lit normally. It is indirect if, in the case of a darkened room behind the holographic screen, light is transmitted from the room in front of the holographic screen through the screen and is again scattered back through the screen by bright objects that are behind the screen.

This is particularly annoying when the holographic screen is leaned against a brightly painted wall or when the wall scatters the continuous background light back through the screen to the viewer.

So that the superimposition of the images of objects in view does not disturb the projection projection image, holographic projection projection screens have hitherto been provided with a firmly applied absorbent layer in order to prevent this disturbing or undesired view through the screen when they are used. Such a holographic projection projection screen, which is attached to a living room or office wall and has an absorbing layer on the back, will appear to the viewer as a monotonous dark surface and have a disturbing effect. To remedy this disadvantage, the holographic screen would have to be used when not in use, e.g. B. with a light canvas, such as a z. B. decorative screen, or he should be able to be covered in the wall with sliding or folding doors. However, this is cumbersome and involves additional costs.

It is the object of the present invention to provide a holographic screen which, in the operating state, produces a high-contrast image with little or no interference light, while in the idle state it does not appear to be disturbing to an observer or has an unattractive appearance. Furthermore, a projection system and a method for image projection are to be created with which the same advantages can be achieved.

This object is achieved by the holographic screen according to patent claim 1, by the projection system according to patent claim 15, and by the method for image projection according to patent claim 16. Further advantageous features of the invention result from the dependent claims and the drawings.

The holographic screen according to the invention is suitable for Auφrojektion and comprises an optically transparent carrier plate, as well as a hologram, which is attached to the carrier plate and backscattered Auφrojizierter, spectrally narrow-band light in a predetermined spatial angle, while the hologram is transparent for broadband light, a switchable Layer is provided which can be switched back and forth between a first, essentially optically transparent state and a second, essentially optically absorbing and / or reflecting state.

As a result, holographic projection screens which can be used very flexibly can be provided in a particularly simple and inexpensive manner, which deliver an excellent image quality while avoiding stray light in the operating state, while in the state in which they are provided, when no images are being projected, they do not have a disturbing effect, but rather appear transparent and one Allow visibility. The screen can be electronically darkened or illuminated without influencing the projected image. So-called switchable absorbent glazing can be used. Switchable glazing systems are glass plates with embedded material layers that can be switched either electronically or chemically between a state that is optically transmittable and absorbing or reflecting in the visible and near infrared region of the spectrum.

The switchable layer preferably has an absorption capacity which can be set in the visible region of the spectrum. Furthermore, the switchable layer preferably has a reflection or backscattering capacity which can be set in the visible region of the spectrum.

In particular, a plurality of switchable layers can be provided, the absorption capacity and / or reflection or backscattering capacity of which can be set separately in the visible region of the spectrum.

The carrier plate advantageously has several layers, between which the hologram is sealed. This allows hologram materials such as Silver halide and dichromate gelatin, which are sensitive to environmental influences such as oxygen and air humidity, are effectively protected. They are preferably sealed between glass plates or plastic plates.

The hologram or screen hologram can therefore be applied both to the surface of a carrier plate and sealed within the carrier plate or between different layers of the carrier plate, depending on the resistance of the hologram to environmental influences.

An electrode arrangement is preferably provided which serves to generate an electrical field within the switchable layer, the switchable layer comprising light-scattering or light-absorbing particles which can be aligned by applying the electrical field. ,

The switchable layer can comprise, for example, hydrochromic or electrochromic material. A device for introducing a reaction gas into the switchable layer is advantageously provided, the switchable layer comprising oxidic material which colors when it comes into contact with the reaction gas.

The switchable layer can also comprise, for example, a viologen system or an electroreflective metal hydride layer. The switchable layer may also preferably comprise a PDLC layer (polymer dispersed liquid crystals), and / or it may comprise an SPD layer (suspended particle device).

The carrier plate is preferably made of glass or plastic or in multiple layers from both material components, the hologram being connected to the carrier plate for example by lamination or gluing. This ensures a very high optical quality of the screen surface. The hologram is made, for example, from a photopolymer.

The holographic screen is advantageously used as a partition for separating rooms or as part of them. For example, it can also be used as external glazing for buildings or vehicles or as a window or as part of it.

This results in a large number of possible applications, in which e.g. a wall can alternately be used as a transparent wall or as a screen as needed.

A transmitting partition of rooms can e.g. alternately allow a clear view of an adjoining room or let the light through from one room to the other, and then switch to the state of light absorption, in which it serves as a darkened projection screen.

Stained-glass windows in living rooms can be designed as transparent for daylight during the day and as darkened projection screens in the evening. Large glass facades of buildings can also be used as projection screens during the day or at night. Furthermore, compartments of airplanes or trains with transparent walls can be subdivided, which can be used darkened as projection walls if necessary.

A switchable layer can advantageously be arranged between two holograms. This means that projections can be made from both sides of the screen at the same time, without the projections being interfered with by both sides. It is therefore possible to use the area on both sides, i.e. with holograms for projection on both sides of the transparent support plate, which results in a considerable saving in space.

Optical switches are preferably used as the switchable layer, which are effective in the entire visible range, which comprises the red-green-blue wavelength range of the usual image projectors. It can be switched back and forth in the range between a highest transmission of 50% -70% and a lowest transmission in the absorbing state of 1% to 10%, which is sufficient for the purpose discussed here.

In one embodiment of the invention, reflective glazing systems can be used as switches, which can be switched from a transmitting state to a reflecting or reflectively scattering state. In combination with holographic rear projection screens, such layers can be used in certain cases to switch from a mirror to a projection screen.

Furthermore, a combination of a first and a second absorbent layer in the same carrier plate is possible, which enables switching between transmitting, reflecting or absorbing projection wall in a single carrier plate. The reflection factor of usable reflective layers is usually 50% - 70%, which is sufficient for the areas of application discussed here.

According to another aspect of the invention, a projection system is provided, with a projector for projecting images with spectrally narrow-band light in one or more wavelength ranges, and with a screen for displaying the projected images, the screen being a holographic screen according to the invention, as described above is generally described and described in detail below. This essentially results in the advantages which have already been mentioned in connection with the holographic screen according to the invention.

Projectors with lamps, LEDs or lasers can preferably be used for the projection onto the AuφiOjECTION hologram.

According to a further aspect of the invention, a method for projecting images onto a screen is specified, in which images are projected onto a holographic screen with spectrally narrow-band light in one or more wavelength ranges, the narrow-band light being scattered back into a previously determined solid angle, and wherein, at the beginning or during the process, the holographic screen is brought from a first state, in which it is optically substantially transparent, to a second state, in which it is essentially optically absorbent.

The advantages of this method correspond essentially to the advantages which are achieved with the holographic screen according to the invention.

The projection is advantageously carried out on a partition or a window which is designed as a holographic screen or comprises a holographic screen, the holographic screen being non-transparent to spectrally broadband light during the projection, while it is transparent to spectrally broadband light before or after the projection is.

A holographic screen according to the invention, described in detail below, is advantageously used to carry out the method according to the invention.

The invention is described below by way of example with reference to the figures, in which:

Figures la and lb schematically show a holographic screen and its structure as a first preferred embodiment of the invention in a perspective view;

2a and 2b schematically show the structure of a holographic screen according to the invention according to a second preferred embodiment in a transparent or absorbent state; and Fig. 3 shows schematically a third embodiment of the invention, in which the

Holographic screen has a chemically optically switchable carrier material.

1a and 1b show the structure of a holographic screen 110. The holographic screen 110 has a first transparent support plate 112 made of glass, on the surface of which a hologram 111 is applied. The hologram 112 is a screen hologram that scatters or diffracts incident, spectrally narrow-band light of a predetermined wavelength back into a predefined solid angle, while broadband ambient light is transmitted. For further details in the production of the hologram for image projection, reference is made to the already mentioned publication DE 19700162 AI.

On the back of the carrier plate 112 there is a first transparent electrode 113, which is connected to a first switchable layer 114. The switchable layer 114 is an electrochromic layer. The switchable layer 114 is followed by an activation layer 115, which is made of a polymer electrolyte and forms a means for activating the electrochromic layer.

When the switchable layer 114 is activated, it changes from an essentially transparent state to a state in which it absorbs or blocks broadband light. In the transparent state, broadband light 120 or stray light can penetrate the holographic screen 110, as shown by the arrows 120 and 121 in FIG. 1b. In the blocked state or non-transparent state, no or only a very small proportion 122 of the stray light or broadband ambient light 120 can penetrate the holographic screen 110.

In the embodiment shown here, an arrangement of switchable layer, carrier plate and transparent electrode is provided on both sides of the activation layer 115. That is, on the back of the activation layer 115 there is a second electrochromic switchable layer 116, followed by a second layer-shaped transparent electrode 117, which in turn is followed by a second carrier plate 118 in the form of a glass layer. FIG. 1 a shows the eye 140 of a viewer looking at the front of the holographic screen 110. Ambient light 120, which may be daylight or stray light, passes through the screen in its transmitting state. In its switched state, the stray light is blocked or at least very strongly attenuated, so that no or only a very small proportion of light can penetrate the screen 110 and reach the viewer's eye 140. In contrast, projected, narrowband light 130 in one or more visible wavelength ranges is scattered back from the holographic screen 110 to the eye 140 of the viewer, so that projected images or information become visible.

FIGS. 2a and 2b show the structure of a holographic screen 210 in cross section, according to another preferred embodiment. FIG. 2a shows the holographic screen in the transparent state, while FIG. 2b shows the screen in the non-transparent state.

The holographic screen 210 has an active or switchable layer 214 in the center, in the form of a so-called suspended particle device (SPD). The switchable layer 214 comprises a matrix made of a polymer, in which there are particles 215 in the manner of a suspension, which align when an electric field is applied.

A layer-shaped transparent electrode 213, 216 is arranged on both sides of the switchable layer 214. Via a voltage supply circuit 230, which is electrically connected to the electrodes 213, 216, an electrical field is generated between the electrodes 213, 216 if necessary, which acts on and aligns the particles 215 of the switchable layer 214, so that the switchable layer 214 and so that the holographic screen 210 is transparent.

When the voltage supply 230 'is open or interrupted, the particles are not aligned, so that the light 220' passing through is weakened or blocked by absorption in the switchable layer 214 (FIG. 2b).

On both sides of the layer arrangement, a layer-shaped hologram 212, 218 is sealed between two glass plates, which form a carrier material or a carrier plate 211, 219. That is, there is a seal of an au hologram on both of them Sides of the holographic screen. A two-sided image display is thus possible, that is to say that an au-projection and viewing of the au-projected images can take place on both sides of the holographic screen 210.

3 shows a third possible embodiment of the invention, in which a chemically optically switchable carrier material is used in a holographic lock 310. The holographic screen 310 comprises a carrier plate 311, to which a channel adjoins which can be filled or flowed through with a reaction gas 312.

A transparent catalyst layer 313 and a hydrochromic functional layer 314 cause the holographic screen 310 to be switched from a transparent to a non-transparent state when it is filled with the reaction gas 312, which increasingly darkens the switchable layer.

A sealed hologram layer 315 is located within a carrier plate 316 in order to backscatter the image projected with a spectrally narrow-band light source in one or more wavelengths, for example in the three primary colors, at a predetermined angle to the viewer.

It is understood that also Viologen systems with switchable absorption or reflective systems and hybrid absorptive and reflective layers can be constructed analogously to these designs.

In summary, the invention shows in particular a holographic projection projection screen which is connected to an optical carrier plate and an active optical layer which is also connected to the carrier plate, wherein the transmission of the carrier plate can be switched electronically or chemically. The absorption of the active optical layer is e.g. switched in the visible part of the spectrum.

Claims

claims

1. Holographic screen for projection, with an optically transparent carrier plate (112, 118; 211, 219; 311.315), a hologram (111; 212, 218; 315) which is attached to the carrier plate and projected, spectrally narrow-band light into one Scattered previously determined solid angle, while the hologram is transparent for (l ll; 212, 218; 315) broadband light, characterized by a switchable layer (114, 116; 214; 314) which is between a first, essentially optically transparent state and a second, essentially optically absorbing and / or reflecting state can be switched back and forth.

2. Holographic screen according to claim 1, characterized in that the switchable layer (114, 116; 214; 314) has an absorption capacity which is adjustable in the visible region of the spectrum.

3. Holographic screen according to claim 1 or 2, characterized in that the switchable layer (114, 116; 214; 314) has a reflectivity or backscattering capacity which is adjustable in the visible region of the spectrum.

4. Holographic screen according to one of the preceding claims, characterized in that a plurality of switchable layers (114, 116; 214; 314) are provided, the absorption capacity and / or reflection or backscattering capacity of which can be set separately in the visible region of the spectrum.

5. Holographic screen according to one of the preceding claims, characterized in that the carrier plate (112, 118; 211, 219; 311, 315) has a plurality of layers (114, 116; 214; 314), between which the hologram is sealed.

6. Holographic screen according to one of the preceding claims, characterized by an electrode arrangement (113, 117; 213, 216) for generating an electrical field within the switchable layer (114, 116; 214), wherein the switchable layer (114, 116; 214) comprises light-scattering or light-absorbing particles (215) which can be aligned by applying the electrical field

7. Holographic screen according to one of the preceding claims, characterized in that the switchable layer (114, 116; 214; 314) comprises hydrochromic or electrochromic material.

8. Holographic screen according to one of the preceding claims, characterized by an egg device for introducing a reaction gas (312), wherein the switchable layer (314) comprises oxidic material which is colored on contact with the reaction gas.

9. Holographic screen according to one of the preceding claims, characterized in that the switchable layer (114, 116; 214; 314) comprises a viologist system.

10. Holographic screen according to one of the preceding claims, characterized in that the switchable layer (114, 116; 214; 314) comprises an electroreflective metal hydride layer.

11. Holographic screen according to one of the preceding claims, characterized in that the switchable layer (114, 116; 214; 314) comprises a PDLC layer and / or an SPD layer.

12. Holographic screen according to one of the preceding claims, characterized in that the carrier plate (112, 118; 211, 219; 311,315) is made of glass or plastic, the hologram (111; 212, 218; 315), by lamination or adhesive is connected to the carrier plate.

13. Holographic screen according to one of the preceding claims, characterized in that it is used as a partition for separating rooms or as part thereof.

14. Holographic screen according to one of the preceding claims, characterized in that it is used as external glazing of buildings or vehicles or as a window or as part thereof.

15. Projection system, with a projector for projecting images with spectrally narrow-band light in one or more wavelength ranges, and a screen (110; 210; 310) for displaying the projected images, characterized in that the screen (110; 210; 310) is a holographic screen according to any one of claims 1 to 14.

16. A method for projecting images onto a screen, in which images are projected onto a holographic screen (110; 210; 310) with spectrally narrow-band light in one or more wavelength ranges, the narrow-band light being transmitted through a predetermined spatial angle is scattered back, characterized in that the holographic screen (110; 210; 310) at the beginning or during the process from a first state in which it is optically essentially transparent to a second state in which it is essentially optically absorbent , is brought.

17. The method according to claim 16, characterized in that the projection takes place on a partition or a window which is designed as a holographic screen or comprises a holographic screen (110; 210; 310), the holographic screen (110; 210; 310 ) is not transparent to spectral broadband light during projection, while it is transparent to spectral broadband light before or after projection.

18. The method according to claim 16 or 17, characterized in that a holographic screen (110; 210; 310) according to one of claims 1 to 14 is used.