WO2009144251A1

WO2009144251A1 - Optical light valve having an input aperture

Info

Publication number: WO2009144251A1
Application number: PCT/EP2009/056465
Authority: WO
Inventors: Nico Coulier
Original assignee: Barco N.V.
Priority date: 2008-05-30
Filing date: 2009-05-27
Publication date: 2009-12-03
Also published as: GB2460457A; GB0809903D0

Abstract

The invention relates to an optical light valve device, comprising a light valve (1) which (5) is adapted for being irradiated with incident light (3) and for modulating the incident light (3) by predetermined image data, and an aperture (2) with a light-transmissive area (7) for transmitting part of the incident light (3) and a light-blocking means (6) for blocking another part of the incident light (3), wherein the light blocking means is thin to avoid reflections from the edge of the aperture. This has the advantage that uncontrolled stray (10) light is avoided and, thus, no deterioration of image quality due to such stray light occurs. Also the surface of the light-blocking area (6) which is facing away from the light valve (1) is specularly reflective. This also has the advantage that uncontrolled stray light is (15) avoided and, thus, no deterioration of image quality due to such stray light occurs.

Description

OPTICAL LIGHT VALVE HAVING AN INPUT APERTURE

The invention relates to an optical light valve device, especially for an optical projection system as well to a method of operating and manufacturing the same. In particular the invention relates to an aperture for an optical light valve device, especially for use of the aperture in an optical projection system.

TECHNICAL BACKGROUND

A light valve is understood to be an optical device which can be used to vary the amount of light which reaches a target like an optical screen. One type of light valve comprises an array of switching means which selectively block incident light from reaching the target or direct the incident light onto the target, respectively. Examples for light valves are digital micro mirror arrays (DMD arrays) and LCOS (liquid crystal on silicon) devices. DMD arrays and LCOS devices are both reflective light valves, i. e. light incident on the light valve is either reflected onto the target, e. g. a screen, or away from the target, e. g. onto an optical sink which typically also acts as a heat sink. However, there are also transmissive light valves like LCDs (liquid crystal displays).

When incident light is irradiated onto a light valve, a problem exists in that not only the active area of the light valve, i. e. the image forming area, is irradiated, but also parts of the light valve different from the image forming area, like the light valve packaging which surrounds the active area. Typically, this is due to stray light which results from optical components, like optical lenses, and cannot be totally avoided. Such stray light deteriorates the image quality and has further disadvantages since the light valve system is heated. Heating of the light valve system adversely effect reliability and lifetime of the light valve, especially of its electronic parts.

In order to address this problem, conventionally, metal apertures are used in order to block incident light from falling onto areas of the light valve different from its active area. However, such metal apertures heat up due to absorbed light which is then irradiated onto the light valve as heat. Heat is very important to control for lifetime and reliability issues of the light valve system. Further, due to diffuse reflection at such apertures, further stray light is generated which might reach the light valve and further deteriorates the image quality. This aperture always has a certain thickness (few tenths of mm) and a certain surface roughness causing stray light to become diffuse meaning optically out of control.

SUMMARY OF THE INVENTION

Accordingly, it is the object of the invention to provide an optical light valve device, especially for an optical projection system as well a method of operating and manufacturing the same. An advantage of the present invention is to provide a possibility to remove disturbing stray light outside the active area of a light valve and, further, to keep heat away from the light valve system. This disturbing stray light is coming from light of the incoming beam which is not getting to the chip because of imperfections of the optical system (typical the light valve, e.g. DMD window being too small to accept a small focal length light beam or a defocused beam spot). Some of the heat getting to the light valve system is coming from the same light as this light that is not getting to the light valve and is absorbed by the light valve system.

This object is addressed by an optical light valve device, comprising a light valve which is adapted for being irradiated with incident light and for modulating the incident light by predetermined image data and having a black level, and an aperture with a light- transmissive area for transmitting part of the incident light in a direction towards the light valve and a light-blocking means for blocking another part of the incident light from falling onto the light valve, wherein the light-blocking means has a thickness such that any light reflected from the edge of the light-blocking means into the aperture is less than the black level of the light valve.

This object is also addressed by an optical light valve device, comprising a light valve which is adapted for being irradiated with incident light and for modulating the incident light by predetermined image data, and an aperture with a light-transmissive area for transmitting part of the incident light in a direction towards the light valve and a light- blocking means for blocking another part of the incident light from falling onto the light valve and having an edge facing towards the aperture, wherein the light-blocking means has a thickness of < 1000 nm, more preferably a thickness < 500 nm or <250 nm. Accordingly, it is an essential idea of the invention to avoid stray light that gets into the projection lens and is projected also on the screen or at least to reduce any such light so that it is lower in intensity than the black level of the light valve. If the intensity of the stray light is less, e.g. significantly less than the black level of the light valve then the stray light cannot be distinguished. The reflected light stays under control which means that any such light even if directed into the projection lens and projected onto the screen cannot be distinguished against the background of the black level.

The surface of the light-blocking area of the aperture which is facing away from the light valve can be made specularly reflective.

This avoids diffuse reflection of the blocked light. Instead, since the surface of the light- blocking area of the aperture which is facing away from the light valve is specularly reflective, the reflected light stays under control which means that this light is not unintentionally directed onto the active area of the light valve.

The feature that the surface of the light-blocking area of the aperture which is facing away from the light valve is specularly reflective does not necessarily mean that the light-blocking ability of the aperture is essentially based on reflection. In contrast to that, preferably this feature is meant to keep those reflections which actually cannot be avoided under control. Thus, in general, this means that the light-blocking feature is preferably not achieved by reflection but by another effect. Especially, this means that it is preferred that light-blocking is achieved by a light absorbing opaque area. Further, it is preferred that the specular reflective ability of the aperture is only used for avoiding diffused stray light from rest reflectiveness.

Generally, this concept can be used for any kind of light valve. To operate at high light output levels calls for reflective micro-display technology that allows a high fill factor with the driving electronics buried under the pixel and an effective cooling from the back of the micro-display, this could either be based on DMD or LCOS display technology. Hence, the light valve can be a liquid crystal display but it is preferred that the light valve is a digital micro mirror array or a LCOS device. It is preferred that the light valve is used for an optical light valve device of an optical projection device, e.g. a digital luminating device or light.

As already stated further above, the light valve typically comprises an active area for modulating the incident light by predetermined image data. With respect to this, according to a preferred embodiment of the invention, the aperture is adapted for blocking incident light from being irradiated onto another part of the light valve than the active area. In this way, it can be avoided to heat up the light valve system which is necessary for driving the active area of the light valve, e. g. the micro mirrors in case of a DMD array. If the heating of the light valve system, especially the electronics, is avoided, reliability and lifetime of the optical light valve device are improved.

Since the light which is reflected from the surface of the light-blocking area of the aperture which is facing away from the light valve is not diffuse, this reflected light can be directed away from the projection lens (and/or the light valve) in a controlled manner, i. e. away from the active area of the light valve in order to avoid negative effects due to a stray light, and away from the light valve system in order to avoid heating. With respect to this, according to a preferred embodiment of the invention, the light reflected from the aperture is directed onto an optical sink and/or onto a heat sink. Especially, it is preferred that a combined optical and heat sink is provided. In this way, the undesired part of the light which is irradiated in a direction towards the light valve is eliminated in a controlled way.

As already stated above, the light-blocking ability of the aperture may be based on different effects. However, according to a preferred embodiment of the invention, the light-blocking area of the aperture comprises a dark coating, preferably a black coating, e.g. a black chrome coating. This means, that according to this preferred embodiment of the invention, light blocking is achieved by an opaque coating while, additional to that, a specular reflection is provided by other means. With respect to this, according to a preferred embodiment of the invention, the aperture comprises a glass plate. Furthermore, according to a preferred embodiment of the invention, the dark coating is provided on that surface of the glass plate which is facing towards the light valve. This provides for the following possibilities: According to a preferred embodiment of the invention, the aperture comprises a glass plate which is partly coated with a dark coating, especially a black coating, on its side which is different from the side on which the light is irradiated. Due to the dark coating, a light-blocking area is formed. This light-blocking area preferably surrounds a light- transmissive opening through the glass which allows that part of the incident light which is directed onto the light-transmissive are to reach the active area of the light valve. In this way, most of the incident light falling onto the light-blocking area of the aperture is eliminated since it is absorbed by the dark coating. However, the part of the light which is falling onto the light-blocking area but which is not absorbed by the dark coating can be reflected in a controlled way, i. e. by specular reflection since the glass plate can be provided with a very even surface.

Accordingly, it is especially preferred that the glass plate, at least on one side, i. e. the side facing the light valve, preferably on both sides, is polished. With respect to this, it is especially preferred that the surface roughness of the aperture is < 10 nm, preferably

< 1 nm. The average surface roughness can be 1 nm. Within this context, the term "surface roughness" is understood to be representative of the center-line mean roughness of the surface of the aperture, e. g. the glass plate.

In other words, this means that surface roughnesses of the surface of the glass plate on which the coating is provided can be avoided and, thus, no diffuse reflection occurs. Further, it is preferred that the coating has a very small thickness, preferably a thickness

< 1000 nm, more preferably a thickness < 500 nm or <250 nm. The coating can be a black chrome coating The thickness of a black chrome coating is typically 200 nm.

According to a preferred embodiment of the invention, the aperture comprises one single glass plate. This means that the light-transmissive part of the aperture is formed by the area of the glass plate which is not covered with a dark coating. This is advantageous since reflective surfaces of a bore in the glass plate, i.e. side walls of the bore, which might lead to further stray light, can be avoided.

A further advantage of a glass plate for the aperture is that glass is a bad heat conductor compared to metal. Accordingly, the light valve system is heated by the glass aperture to a lesser degree compared with conventional metal apertures, leading to higher reliability and longer lifetime of the device as already stated above.

The aperture, e.g. a suitably transparent part of a glass plate, is optionally retractable or moveable away from the light valve. Alternatively or additionally, an additional aperture can be provided that has a differently shaped transparent part, i.e. the one aperture with reduced disturnbing light according to the present invention may be moved to one side and replaced with another aperture.

The present invention also provides a method of remove disturbing stray light outside the active area of an optical light valve device which is adapted for being irradiated with incident light and for modulating the incident light by predetermined image data and having a black level, the disturbing stray light being derived from light of an incoming beam, the method comprising the steps of: transmitting a first part of the incident light in a direction towards the light valve through an aperture, blocking second part of the incident light from falling onto the light valve, wherein the light-blocking means has a thickness such that any light reflected from the edge of the light-blocking means into the aperture is less than the black level of the light valve.

These and other aspects of the invention will be apparent from and elucidated with reference to the embodiments described hereinafter.

BRIEF DESCRIPTION OF THE DRAWINGS

Fig. 1 schematically shows an optical light valve device according to a preferred embodiment of the invention, and

Fig. 2 schematically depicts the aperture of the optical light valve device according to a preferred embodiment of the invention in a cross sectional view.

Fig. 3 schematically depicts an assembly including the aperture of the optical light valve device according to another embodiment of the invention.

Fig. 4 schematically depicts apertures of the optical light valve device according to another embodiment of the invention.

DESCRIPTION OF THE ILLUSTRATIVE EMBODIMENTS

The present invention will be described with respect to particular embodiments and with reference to certain drawings but the invention is not limited thereto but only by the claims. The drawings described are only schematic and are non-limiting. In the drawings, the size of some of the elements may be exaggerated and not drawn on scale for illustrative purposes. Where the term "comprising" is used in the present description and claims, it does not exclude other elements or steps. Where an indefinite or definite article is used when referring to a singular noun e.g. "a" or "an", "the", this includes a plural of that noun unless something else is specifically stated.

The term "comprising", used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. Thus, the scope of the expression "a device comprising means A and B" should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.

Furthermore, the terms first, second, third and the like in the description and in the claims, are used for distinguishing between similar elements and not necessarily for describing a sequential or chronological order. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other sequences than described or illustrated herein.

Moreover, the terms top, bottom, over, under and the like in the description and the claims are used for descriptive purposes and not necessarily for describing relative positions. It is to be understood that the terms so used are interchangeable under appropriate circumstances and that the embodiments of the invention described herein are capable of operation in other orientations than described or illustrated herein. It is to be noticed that the term "comprising", used in the claims, should not be interpreted as being restricted to the means listed thereafter; it does not exclude other elements or steps. It is thus to be interpreted as specifying the presence of the stated features, integers, steps or components as referred to, but does not preclude the presence or addition of one or more other features, integers, steps or components, or groups thereof. Thus, the scope of the expression "a device comprising means A and B" should not be limited to devices consisting only of components A and B. It means that with respect to the present invention, the only relevant components of the device are A and B.

Reference throughout this specification to "one embodiment" or "an embodiment" means that a particular feature, structure or characteristic described in connection with the embodiment is included in at least one embodiment of the present invention. Thus, appearances of the phrases "in one embodiment" or "in an embodiment" in various places throughout this specification are not necessarily all referring to the same embodiment, but may. Furthermore, the particular features, structures or characteristics may be combined in any suitable manner, as would be apparent to one of ordinary skill in the art from this disclosure, in one or more embodiments.

Similarly it should be appreciated that in the description of exemplary embodiments of the invention, various features of the invention are sometimes grouped together in a single embodiment, figure, or description thereof for the purpose of streamlining the disclosure and aiding in the understanding of one or more of the various inventive aspects. This method of disclosure, however, is not to be interpreted as reflecting an intention that the claimed invention requires more features than are expressly recited in each claim. Rather, as the following claims reflect, inventive aspects lie in less than all features of a single foregoing disclosed embodiment. Thus, the claims following the detailed description are hereby expressly incorporated into this detailed description, with each claim standing on its own as a separate embodiment of this invention.

Furthermore, while some embodiments described herein include some but not other features included in other embodiments, combinations of features of different embodiments are meant to be within the scope of the invention, and form different embodiments, as would be understood by those in the art. For example, in the following claims, any of the claimed embodiments can be used in any combination.

In the description provided herein, numerous specific details are set forth. However, it is understood that embodiments of the invention may be practiced without these specific details. In other instances, well-known methods, structures and techniques have not been shown in detail in order not to obscure an understanding of this description.

Electronic projection display apparatuses for use with the present invention can have several designs. One such optical design comprises mirrors that split an incoming light beam, which typically is a white light beam, in three different colour beams, typically a red, green and blue color beam, modulates the different colour beams with a spatial light modulating means for each of the three different colours, and recombines the three modulated light beams in a dichroic prism, like e.g. an x-cube, to form a single light beam to be projected on a screen through a projection lens. Such a setup is e.g. described in patent application U.S. Pat. No. 5,934,778. The system has some specific advantages, as the light paths between the color splitting/recombining means and the light modulating means can be very small, as the light modulating means typically are positioned adjacent the X-cube dichroic prism, in slits attached to the X-cube dichroic prism. The group of a dichroic prism combination such as an X-cube, possible additional filters and the light modulating means with their holders, typically is called a convergence system.

In one aspect the present invention provides components for a convergence system of a projector. An exemplary and non-limiting example of a convergence system comprises various components such as an X-cube, one to three (or more) intermediate parts for three (or more) different colors or color ranges and light modulating means such as a light valve for all three (or more) or for each of these three (or more) different colors. An X-cube is typically a dichroic prism which allows recombination of three outgoing beams having a different color or color range into one beam. Some prisms however act as splitting and recombining mirrors at the same time, e.g. for reflective DMD's or reflective LCD's, such as LCOS-technology. Typically, these colors correspond with the primary colours, i.e. green, red and blue.. The three intermediate parts, i.e. an intermediate part for color green, an intermediate part for color red and an intermediate part for colour blue, are suited for receiving e.g. filters, analyzers or polarizers. For each color, a spatial light modulating means such as a light valve is provided which can be any suitable device which comprises an array of individually addressable and individually drivable light modulating pixels, which can be driven to represent an arbitrary image. The spatial light modulating can be e.g. a digital mirror device (DMD) or a liquid crystal on silicon (LCOS) device, but is not limited thereto.

As can be seen from Fig. 1, according to the preferred embodiment of the invention, an spatial light modulating means such as an optical light valve device with a light valve 1 formed by a DMD array and an aperture 2 for partly blocking light 3 directed onto the light valve 1 is provided. As can be seen from Fig. 1, and more in detail from Fig. 2, the aperture 2 comprises a polished glass plate 4 which is coated with a black coating 5 on its backside. The black coating is thin, e.g. < 1000 nm, more preferably a thickness < 500 nm or <250 nm. A black chrome can be used, e.g. a 200 nm thick black chrome coating. Due to the black coating 5, a light-blocking area 6 and a light-transmissive area 7 through the glass are provided. The light-transmissive area 7 and the light-blocking area 6 of the coating 5 on the glass plate 4 are adapted in such a way that light 3 directed towards the light valve 1 is blocked or transmitted, respectively, in such a manner that very little incident light 3 reaches the complete light valve 1. Preferably, the amount of light which reflects off the edge of the coating is less than the black value of the light valve. The black value of a spatial light modulating means such as a light valve is a well known quantity and is the light intensity reflected when the light value is displaying all black pixels. The light-transmissive area can be circular, oval or any other shape although the DMD is often rectangular.

As shown in Fig. 1, light valve 1 comprises an active area 8 for modulating incident light 3 by predetermined image data in order to form an image on a screen 9 due to reflected modulated light 10. The active area 8 of the light valve 1 is surrounded by a light valve packaging 11. Further, the light valve 1 comprises a light valve system 12 which incorporates the electronics for driving the light valve, i. e. for controlling the micro mirrors of the DMD array. As can be seen from Fig. 1, since part of the incident light 3 is blocked by the light- blocking area 6 of the aperture 2, the irradiation of other parts of the light valve 1 than the active area 8, i. e. irradiation of the light valve packaging 11 and/or the light valve system 12 is essentially avoided. Thus, practically no heating due to undesired light falling onto these parts of the light valve 1 occurs.

Further, as also can be seen from Fig. 1, part of the light which is incident onto the light-blocking area 6 of the aperture 2 is reflected back. Since the surface of the glass plate 4 on which the black coating 5 is provided is very flat, i. e. polished to a surface roughness of less than < 10 nm, e.g. < 1 nm practically only controlled reflections, i. e. specular reflections, occur. This means that uncontrolled stray light due to diffuse reflection from the aperture 2 is almost totally avoided and, thus, no such stray light reaches the active area 8 of the light valve 1 which would deteriorate the image quality. Instead, such reflected light 14 is directed onto an optical sink 13 which also acts as a heat sink, for a controlled elimination of this reflected part of the incident light 3.

As a result an easily viable possibility is provided for directing disturbing stray light away from the active area of the light valve and to keep heat away from the light valve system in order to enhance reliability and lifetime of the complete system.

Fig. 3 illustrates a further embodiment of the present invention. Fig. 3 shows an assembly 20 that can form part of a convergence system of a projector. It comprises one or more connectors 16 and one or more flexible strip conductors 15, 17 for connection to a light valve 1 such as an LCOS panel and any electronics associated thereto. A light valve 1 such as an LCOS panel is located in a holder 18. Set into the holder 18 is a ledge 19 onto which the aperture 2 is fixed to thereby form an airtight compartment above the light valve 1. This has the advantage that dust cannot form directly on the light valve one but only on the aperture at some distance away. This avoids dust being visible in focus on the projection screen. In Fig. 3 the aperture 2 is shown removed from its operating position for clarity reasons. The aperture 2 may be, e.g. a glass plate with a transparent zone in the middle and a black coating on the side towards the light valve as described in previous embodiments. For example, the aperture 2 comprises a polished glass plate which is coated with a black coating on its backside. The black coating is thin, e.g. < 1000 nm, more preferably a thickness < 500 nm or <250 nm. A black chrome can be used, e.g. a 200 nm thick black chrome coating. Due to the black coating a light-blocking area and a light-transmissive area through the glass are provided. The surface of the glass plate on which the black coating is provided is preferably very flat, i. e. polished to a surface roughness of less than < 10 nm, e.g. < 1 nm practically only controlled reflections, i. e. specular reflections, occur. This means that uncontrolled stray light due to diffuse reflection from the aperture 2 is almost totally avoided and, thus, no such stray light reaches the active area of the light valve 1 which would deteriorate the image quality. Instead, such reflected light is directed onto an optical sink (not shown) which also acts as a heat sink, for a controlled elimination of this reflected part of the incident light.

In the lighting business, there is need for a spot, e.g. a circular spot since moving a rectangle on a projection surface gives odd shapes. A circular image can be created by a light valve such as a DMD (or an LCOS device), but due to stray light, the rectangular shape of the DMD is still visible when projecting in a dark environment, even when all mirrors are in the off state. Inserting a circular aperture makes it possible to have a circular spot when all mirrors are in the off state. The circular aperture will suffer from heat since a big part of the light is blocked. This results in heat stress which can cause deformation. A mechanical design is provided by the present invention that provides an as thin as possible plate as the aperture. The plate can be retractable when a rectangular image is required. Fig. 4 shows schematically a mechanical system for moving the aperture between two positions. In a first position the aperture defined by the glass plate and the coating is controlling the light entering the aperture. In a second position the glass plate is retracted to one side and optionally another type of aperture may be moved in or no aperture is used. The aperture shape can be any desired shape, e.g. round, oval, quadratic etc. The glass plate and coating may be moved to one side, e.g. by running or sliding on guides or slides which control the direction of movement of the aperture. Alternatively, the aperture may swing about a hinge to be brought into alignment with the light valve. Also alternatively the aperture may rotate into place, e.g. being located in an aperture wheel, e.g. with other apertures that can be brought into alignment with the light valve by rotation of the wheel. The movement of the aperture may be motorised.

The present invention may be used in any type of projection device with a light valve, e.g. as part of a GoBo. The projection device may include one or more light valves according to the present invention, e.g. a one-light valve projection device or a three light- valve projection device.

While the invention has been illustrated and described in detail in the drawings and foregoing description, such illustration and description are to be considered illustrative or exemplary and not restrictive; the invention is not limited to the disclosed embodiments.

Claims

1. An optical light valve device, comprising a light valve (1) which is adapted for being irradiated with incident light (3) and for modulating the incident light (3) by predetermined image data and having a black level, and an aperture (2) with a light-transmissive area for transmitting part of the incident light (3) in a direction towards the light valve (1) and a light-blocking means (6) for blocking another part of the incident light (3) from falling onto the light valve (1), wherein the light-blocking means (6) has a thickness and an edge facing towards the aperture such that any light reflected from the edge of the light-blocking means into the aperture is less than the black level of the light valve.

2. Optical light valve device according to claim 1, wherein the thickness of the light blocking means (6) is < 1000 nm, preferably < 500 nm or <250 nm.

3. An optical light valve device, comprising a light valve which is adapted for being irradiated with incident light and for modulating the incident light by predetermined image data, and an aperture with a light-transmissive area for transmitting part of the incident light in a direction towards the light valve and a light-blocking means for blocking another part of the incident light from falling onto the light valve, wherein the light-blocking means has a thickness of < 1000 nm, more preferably a thickness < 500 nm or <250 nm.

4. Optical light valve device according to any previous claims, wherein the surface of the light-blocking area (6) of the aperture (2) which is facing away from the light valve (1) is specularly reflective.

5. Optical light valve device according to any previous claim, wherein the light valve (1) comprises an active area (8) for modulating the incident light (3) by the predetermined image data, and the aperture (2) is adapted for blocking incident light (3) from being irradiated onto another part of the light valve (1) than the active area (8).

6. Optical light valve device according to any previous claim, wherein light (14) reflected back from the aperture (2) is directed onto an optical sink (13) and/or onto a heat sink.

7. Optical light valve device according to any previous claim, wherein the light- blocking means (6) of the aperture (2) comprises a dark, preferably a black, coating (5).

8. Optical light valve device according to any of claims 1 to 6, wherein the aperture (2) comprises a glass plate (4).

9. Optical light valve device according to claim 7 or 8, wherein the dark coating (5) is provided on the surface of the glass plate (4) which is facing towards the light valve (1).

10. Optical light valve device according to any previous claim, wherein the light- transmissive area (7) of the aperture (2) comprises a glass plate (4).

11. Optical light valve device according to claim 10, wherein the aperture (2) comprises one single glass plate (4).

12. Optical light valve device according to any of claims 8 to 11, wherein at least the surface of the glass plate (4) which is facing the light valve (1) is polished.

13. Optical light valve device according to any previous claims, wherein the surface roughness of the aperture (2) is < 10 nm, preferably < 1 nm.

14. Optical light valve device according to any previous claim, wherein the aperture (2) forms with a holder an airtight compartment adjacent to the light valve.

15. Optical light valve device according to any previous claim, wherein the aperture is retractable away from the light valve.

16. Optical light valve device according to any previous claim, wherein the light valve is a spatial light modulating means.

17. A convergence system for a projector having an optical light valve device according to any previous claim.

18. A projection device including the optical light valve device of any of the claims 1 to 16.

19. The projection device of claim 18, wherein the device is a digital luminair or light.

20. A method of remove disturbing stray light outside the active area of an optical light valve device which is adapted for being irradiated with incident light and for modulating the incident light by predetermined image data and having a black level, the disturbing stray light being derived from light of an incoming beam, the method comprising the steps of: transmitting a first part of the incident light in a direction towards the light valve through an aperture, blocking second part of the incident light from falling onto the light valve, wherein the light-blocking means has a thickness such that any light reflected from the edge of the light-blocking means into the aperture is less than the black level of the light valve.

21. The method of claim 20, wherein light (14) reflected back from the aperture (2) is directed onto an optical sink (13) and/or onto a heat sink.