STROOBACH, Pieter (AE Eindhoven, NL-5656, NL)
VAN DER VEER, Jorgen, M. (AE Eindhoven, NL-5656, NL)
STROOBACH, Pieter (AE Eindhoven, NL-5656, NL)
CLAIMS:
1. A beam combiner (1) comprising at least two x-cube prisms (10, 20) arranged adjacent to each other, said prisms having a plurality of faces (12, 13, 21, 22, 24) at which light beams (101, 201, 301, 401, 501) enter the beam combiner and one face (14) being defined as a front face, said beam combiner (1) combining said light beams entering the combiner into a beam (400) exiting through said front face (14).
2. The beam combiner as defined in claim 1, further comprising light sources (Ll, L2, L3, L4, L5) arranged at said plurality of faces (12, 13, 21, 22, 24) for producing said light beams (101, 201, 301, 401, 501).
3. The beam combiner as defined in claims 1 and 2, wherein said x-cube prisms (10 and 20) are arranged adjacent to each other using an index matching glue.
4. The beam combiner as defined in any one of the preceding claims, wherein said x-cube prisms (10, 20) are arranged with at least partially reflecting diagonal surfaces
(15, 16, 25, 26) coated with at least one light-reflecting layer adapted to reflect the light beams (101, 201, 301, 401, 501) entering the beam combiner.
5. The beam combiner as defined in any one of the preceding claims, wherein one or more of said faces (11, 12, 13, 14, 21, 22, 23, 24) of said at least two x-cube prisms
(10, 20) are coated with transmission layers.
6. The beam combiner as defined in any one of the preceding claims, wherein a wide band pass-band filter is arranged at said front face (14).
7. The beam combiner as defined in any one of the preceding claims, wherein at least one face of said at least two x-cube prisms (10, 20) is arranged to shape said exiting beam (400).
8. The beam combiner as defined in any one of the preceding claims, wherein said at least one face of said at least two x-cube prisms (10, 20) is arranged to collimate said exiting beam (400).
9. The beam combiner as defined in any one of the preceding claims, wherein at least one face of said at least two x-cube prisms (10, 20) is arranged with at least one lens for focusing the light beams (101, 201, 301, 401, 501) entering the beam combiner.
10. The beam combiner as defined in any one of the preceding claims, wherein at least one face of said at least two x-cube prisms (10, 20) is arranged with at least one lens for focusing said exiting beam (400).
11. The beam combiner as defined in claims 9 or 10, wherein said at least one lens is a liquid crystal lens for selectively altering the focus of said exiting beam (400).
12. The beam combiner as defined in any one of the preceding claims, wherein said light sources (Ll, L2, L3, L4, L5) are single point light sources or an array of single point light sources.
13. The beam combiner as defined in any one of the preceding claims, wherein said light sources (Ll, L2, L3, L4, L5) are light emitting diodes or laser diodes.
14. The beam combiner as defined in any one of the preceding claims, wherein at least two of said light sources (Ll, L2, L3, L4, L5) emit light of different wavelengths for covering a broad colour spectra.
15. A projection display system comprising at least one beam combiner according to any one of the preceding claims.
16. An illumination system comprising at least one beam combiner according to any one of the preceding claims. |
Beam combiner for multiple light sources
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an optical device, in particular to a beam combiner used for combining light beams emitted from multiple light sources.
BACKGROUND OF THE INVENTION
Illumination systems, projection display systems and other optically based systems typically comprise a plurality of optical elements. One key optical element of such systems is a beam combiner. The function of a beam combiner is to combine the beams of different light sources into one beam. For example, for the purpose of creating a white beam in a projection display system, the beams of light sources emitting blue, red and green light, i.e. the three primary colours, can be combined. Several methods can be used to form a beam combiner. Two of these methods are described below.
One method is to combine the beams using an arrangement of dichroic mirrors. Depending on the wavelength at which the light is emitted, the light that is incident on a dichroic mirror will either be reflected or transmitted. In such beam combiners, the arrangement of the mirrors creates light paths for the different beams so that they are combined into one single beam.
Another method is to use an x-cube prism, which is a prism structure composed of four triangular prisms arranged in the form of a cube having two partially reflecting diagonal surfaces. In such beam combiners, the light emitted from the light sources enter the x-cube prism and then impinges on the partially reflecting diagonal surfaces, which can either reflect or transmit the light, depending on the coatings of these partially reflecting diagonal surfaces. When used in for instance projection display systems, a beam combiner based on an x-cube prism provides three positions at which the light sources can be located and a fourth position at which light exits.
However, further optical devices in addition to a prism or an arrangement of mirrors are needed in order to accomplish an operative beam combiner or a final product such as a projection display system. US 2005/0219476 discloses such a system in which an x- cube prism is used to combine the light emitted from three light-recycling illumination
systems. Before light beams emitted from the recycling illumination systems enter the x-cube prism, the light beams pass through light-collimating means. In another embodiment, the light also passes through a beam-splitting prism polarizer.
A problem of the projection display system set forth in US 2005/0219476 is that each individual component introduces a power loss in the system, thus resulting in low efficiency. Another problem is that alignment of several optical elements is required, thus making assembly of such a system difficult.
SUMMARY OF THE INVENTION An objective of the invention is to solve or at least mitigate the above- mentioned problems of prior art and to provide a beam combiner which is more efficient, and/or easy to assemble, and/or which also enables control of the light beam exiting the beam combiner.
The present invention is based on the understanding that a beam combiner can be formed by arranging a plurality of x-cube prisms adjacent to each other in an inventive manner. This enables combining of light beams, produced for instance by a plurality of light sources, impinging on the faces of the x-cube prisms.
According to a first aspect of the present invention, there is provided a beam combiner comprising at least two x-cube prisms arranged adjacent to each other, said prisms having a plurality of faces at which light beams enter the beam combiner and one face being defined as a front face, said beam combiner combining light beams entering the combiner into a beam exiting through said front face.
A great advantage of this beam combiner as compared to prior art beam combiners is that it enables usage of additional light sources without introducing corresponding loss of light power. Thus, the beam combiner of the present invention is more efficient and is further easily expandable to a combiner employing a great number of x-cube prisms.
According to another embodiment of the present invention, there is provided a beam combiner comprising x-cube prisms arranged adjacent to each other, wherein at least one face of the x-cube prisms is arranged to shape or to collimate the exiting beam. In addition, lenses can be arranged at the faces of the x-cube prisms to focus the light emitted from the light sources or to focus the exiting beam. Hence, the present invention provides a beam combiner for combining light emitted from a plurality of light sources into an exiting beam and for shaping, collimating and focusing this exiting beam.
As compared to currently used beam combiners, a great advantage of the integration of optical functions in or at the faces of the x-cube prisms is that it reduces the power loss usually induced at each interface between two non-integrated separate components and therefore improves the system efficiency. Further, this beam combiner does not require any alignment of different interacting optical components since principal functionalities (collimating, focusing and shaping) are integrated in a single optical structure. Another advantage is that the beam combiner becomes very compact and therefore enables production of, for instance, very compact projection display systems.
In another embodiment of the invention, there is provided a beam combiner wherein the lens arranged at one or more faces of the x-cube prisms is a liquid crystal lens for selectively altering the focus of the exiting beam. Thus, one and the same illumination system could one the one hand be used for illuminating an entire room and on the other be used as a reading lamp.
In another embodiment of the invention, there is provided a beam combiner using single point light sources such as light emitting diodes (LEDs) or laser diodes at the faces of the x-cube prisms. The use of LEDs and laser diodes enable provision of optical systems that are smaller as compared to prior art systems which e.g. uses high pressure lamps, since these lamps are bulky in comparison to LEDs and laser diodes. Another advantage of LEDs and laser diodes is that their light distributions are relatively narrow in comparison to other light sources. Thus, requirements on collimation of the light are milder for LEDs and laser diodes than for many other light sources. As a consequence, beam combiners based on LEDs and laser diodes can be combined with high resolution imaging devices in e.g. projection display systems. Further, characteristics of the LEDs and the laser diodes, such as wavelength and intensity, are easily controllable. Another advantage provided by the beam combiner arrangement comprising several x-cube prisms is that almost all colours of the visible spectrum can be obtained and that a more "warm" white exiting beam can be produced when using light sources of different wavelengths from each other. Thus, the colour of the exiting beam to a greater extent covers the full spectra that is visible to the human eye. In current CRT televisions and even in LCD televisions, only three colours are used to create a full colour image. However, this full colour picture does not comprise all the colours perceptible by the human eye. By using the arrangement of x-cube prisms in accordance with an embodiment of the present invention, more than three colours can be used.
Generally, all terms used in the claims are to be interpreted according to their ordinary meaning in the technical field, unless explicitly defined otherwise herein. All references to "a/an/the [element, device, component, means, step, etc]" are to be interpreted openly as referring to at least one instance of said element, device, component, means, step, etc., unless explicitly stated otherwise.
Other objectives, features and advantages of the present invention will be apparent from the following detailed disclosure, from the attached dependent claims as well as from the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
The above, as well as additional objects, features and advantages of the present invention, will be better understood through the following illustrative and non- limiting detailed description of preferred embodiments of the present invention, with reference to the appended drawings, in which: Fig. 1 is a top view of a beam combiner comprising two x-cube prisms arranged adjacent to each other to form a beam combiner for multiple light sources in accordance with an embodiment of the present invention.
Fig. 2 is a top view of a beam combiner comprising two x-cube prisms arranged adjacent to each other to form a beam combiner for multiple light sources, wherein the faces of the x-cube prisms are curved, in accordance with another embodiment of the present invention.
DETAILED DESCRIPTION OF EMBODIMENTS OF THE INVENTION
With reference to Fig. 1, a first embodiment of the invention will be described below.
In Fig. 1, two x-cube prisms 10 and 20 are arranged adjacent to each other. Each x-cube prism is made of four prisms also arranged adjacent to each other. These four prisms are preferably triangular but may alternatively have other shapes. The x-cube prisms 10 and 20 each have two partially reflective diagonal surfaces, 15 and 16, and 25 and 26, respectively, as well as four active faces, 11, 12, 13 and 14, and 21, 22, 23 and 24, respectively, which are not perpendicular to their respective diagonal surfaces.
In the present embodiment, the beam combiner 1 further comprises five light sources Ll, L2, L3, L4 and L5 emitting light at five different wavelengths. These light sources are positioned at faces 12, 13, 21, 22 and 24 of the x-cube prisms 10 and 20, leaving
one face 14 free from light source (this face is referred to as front face in the following). The joint faces 11 and 23 of the two x-cube prisms 10 and 20 are preferably flat. As compared to a system comprising one single x-cube prism, the beam combiner of the present embodiment provides two more positions at which additional light sources can be placed. Thus, the total output power of the beam combiner 1 is increased. In addition, this arrangement provides higher flexibility in choice of colours.
The diagonal surfaces 15, 16, 25 and 26 of the x-cube prisms 10 and 20 can be coated to adequately reflect or transmit light emitted from the light sources Ll, L2, L3, L4 and L5. In the following, two of such coatings are presented in more detail. Coatings of the partially reflective diagonal surfaces may be standard "DC blue" and "DC red" coatings, as provided by Unaxis. Such a DC blue coating reflects light having a wavelength below 500 nm, i.e. blue light, and transmits light having a wavelength in the range 500-800 nm, i.e. green and red light. Similarly, the DC red coating reflects light having a wavelength above 650 nm, i.e. red light, and transmits light having a wavelength in the range 400-575 nm, i.e. green and blue light. In a glass/coating/air arrangement, reflection coefficients of these coatings are in the range of 90-95%. However, in a glass/coating/glass arrangement such as in embodiments of the present invention, these values would be slightly lower. It will be appreciated by a person skilled in the art that other coatings than the two coatings presented here can be used and that the used coatings may cover other reflection and transmission ranges in terms of wavelength.
In addition, the faces 11, 12, 13, 14, 21, 22, 23 and 24 of the x-cube prisms 10 and 20 may be coated with transmission layers suitable for the selected wavelengths of the light sources Ll, L2, L3, L4 and L5. The front face 14 would preferably be coated with a wide band pass-band filter for transmitting all wavelengths emitted from the light sources Ll, L2, L3, L4 and L5.
It will be appreciated by a person skilled in the art that more than one layer could be deposited on the diagonal surfaces 15, 16, 25 and 26 and on the faces 11, 12, 13, 14, 21, 22, 23 and 24 of the x-cube prisms 10 and 20 in order to improve the quality of the coatings. This is of particular importance in the case of beam combiners comprising multiple light sources since light beams of at least two different wavelengths may impinge on the same diagonal surface 15, 16, 25 or 26. Layers having different properties could then be arranged on top of each other in order to form a coating suitable for the selected wavelengths of the impinging light beams.
The number of x-cube prisms to be arranged in the beam combiner can be expanded and each added x-cube prism provides two additional light source positions, i.e. two further possible colours or wavelengths. In other words, a beam combiner with one single x-cube prism offers three positions, a beam combiner with two x-cube prisms offers five positions and a beam combiner with three x-cube prisms would offer seven positions, and so forth. For a beam combiner containing more than two x-cube prisms, it will be appreciated by the person skilled in that art that several dispositions of the x-cube prisms are possible.
Again with reference to Fig. 1, it is easier to add a light source to the beam combiner 1 of the present invention than in currently used mirror-based beam combiners since it does not introduce an additional interface (for mirror-based beam combiners, each new added light source introduces at least two new interfaces in the light path). As can be seen in Fig. 1, each beam produced by a light source will pass through two interfaces only, i.e. faces 21 and 14 for Ll, faces 22 and 14 for L2, faces 24 and 14 for L3, faces 12 and 14 for L4 and faces 13 and 14 for L5. Thus, the number of light sources to be added to the beam combiner may, at least theoretically, be unlimited.
Current available coatings can filter light having a minimum wavelength difference in the order of 20 nanometres. Thus, in applications where light wavelength ranges from 400 to 700 nanometres, a maximum of 15 wavelengths (i.e. 15 light sources) could be used.
The x-cube prisms 10 and 20 can be joined together with an index-matching glue, which inhibits light power loss.
In the following, the principle of the beam combiner 1 shown in Fig. 1 is explained. In this embodiment, the light sources Ll, L2, L3, L4 and L5 emit light at 440, 405, 470, 532 and 650 nm, respectively. Thus, light sources Ll, L2 and L3 correspond to blue light while light sources L4 and L5 correspond to green and red light, respectively. The diagonal surfaces 15 and 16 of the x-cube prism 10 are coated with the above-described "DC red" and "DC blue" coatings, respectively. In the x-cube prism 20, the diagonal surface 25 is coated to transmit light having a wavelength below 450 nm and to reflect light having wavelengths in the range 450-700 nm while the diagonal surface 26 is coated to reflect light having a wavelength below 420 nm and to transmit light having wavelengths in the range 420-700 nm.
Thus, as illustrated in Fig. 1, the blue beam 101 entering the x-cube prism 20 through the face 21 is transmitted through the diagonal surfaces 25 and 26 of the x-cube
prism 20, and enters the x-cube prism 10 through the faces 23 and 11 of the x-cube prisms 20 and 10, respectively. On the other hand, the blue beam 201 enters the x-cube prism 20 through the face 22. If this blue beam 201 first impinges on the diagonal surface 25 of the x- cube prism 20, it will be transmitted and subsequently impinge on the diagonal surface 26, against which it will be reflected to finally enter the x-cube prism 10 through the faces 23 and 11 of the x-cube prisms 20 and 10, respectively. If this blue beam 201 impinges directly on the diagonal surface 26 of the x-cube prism 20, it will be reflected and finally enter the x- cube prism 10 through the faces 23 and 11 of the x-cube prisms 20 and 10, respectively. Similarly, the blue beam 301 enters the x-cube prism 20 through the face 24 and is reflected against the diagonal surface 25 of the x-cube prism 20 to finally enter the x-cube prism 10 through the faces 23 and 11 of the x-cube prisms 20 and 10, respectively. If this blue beam 301 first impinges on the diagonal surface 25 of the x-cube prism 20, it will be transmitted and subsequently be reflected against the diagonal surface 26 of the x-cube prism 20 to finally enter the x-cube prism 10 through the faces 23 and 11 of the x-cube prisms 20 and 10, respectively.
After they have entered the x-cube prism 10, the three blue beams 101, 201 and 301 impinge on the diagonal surface 16 of the x-cube prism 10, against which they are reflected, to eventually exit the x-cube prism 10 via the front face 14. If these beams 101, 201, and 301 first impinge on the diagonal surface 15, they will be transmitted and subsequently reflected against the diagonal surface 16 of the x-cube prism 10 to finally exit via the front face 14.
In a similar manner, the red beam 501 enters the x-cube prism 10 via the face 13 and is then reflected against the diagonal surface 15. If this beam 301 first impinges on the diagonal surface 16, it will be transmitted and subsequently reflected against the diagonal surface 15. In any case, the red beam 301 will eventually exit the x-cube prism 10 through the front face 14, as for the three blue beams 101, 201 and 301. In its turn, the green beam 401 enters the x-cube prism 10 via the face 12 and is transmitted trough the diagonal surfaces 15 and 16, as these surfaces are arranged to reflect blue and red beams only. This beam 401 eventually exits the x-cube prism 10 via the front face 14. As a result, the blue, green and red beams 101, 201, 301, 401 and 501 are combined together to form an exiting beam 400, which, in this case, would result in a white beam.
As shown in Fig. 1, the light sources of the beam combiner can be regrouped by colour, thus creating e.g. a blue side in the arrangement of x-cube prisms. As was the case for a previous embodiment, it is advantageous to add further light sources at the blue side of
the arrangement since the power output of blue light sources currently is a limiting factor. Thus, adding an extra x-cue prism in the arrangement increases the total output power of the beam combiner 1 without having to increase the power of the light sources Ll, L2 and L3. In addition, it is advantageous to employ three light sources of slightly different wavelengths, such as Ll, L2 and L3, since this enables achievement of a more colourful exiting beam 400. It will be understood by a person skilled in the art that, similarly, several red light sources of slightly different wavelengths could be added to the arrangement by adding an x-cube prism at the red side of the beam combiner 1. Further, a green side may be provided.
In another embodiment, one or more of the faces 12, 13, 14, 21, 22 and 24 of the x-cube prisms 10 and 20 are arranged to shape, collimate and focus the exiting beam 400 and the beams of the light sources Ll, L2, L3, L4 and L5.
As can be seen in Fig. 2, the faces 12, 22 and 24 of the x-cube prisms 10 and 20 are arranged to collimate the light beams 201, 301 and 401 emerging from the light sources L2, L3 and L4, respectively. Similarly, the faces 13 and 21 could also be arranged to collimate the light beams 101 and 501 emerging from the light sources Ll and L5. In addition to this, the face 14 can be arranged for collimating and shaping the light beam 400 exiting the beam combiner 1 through the front face 14. In a preferred embodiment, the faces 12, 13, 14, 21, 22 and 24 of the x-cube prisms 10 and 20 can be curved and may include several different curvatures along horizontal, vertical as well as diagonal directions of each face of the x-cube prisms 10 and 20.
The fact that a number of different functionalities, such as shaping and collimating, are integrated in each x-cube prism 10 and 20 further reduces the loss of light power as compared to systems comprising a plurality of separate, non- integrated optical components. In such multi-component beam combiners based on e.g. mirrors, each mirror (or each optical element) introduces a power loss of at least 1% per side of the mirror. This means that when three mirrors are used, the system has a power loss of about 6%. Integrating components within the faces 12, 13, 14, 21, 22 and 24 of the x-cube prisms 10 and 20 reduces the number of optical interfaces in the light path and thereby reduces the light power loss. Hence, throughout embodiments of the present invention, a beam combiner 1 is provided where each light path passes through two interfaces only, for instance faces 21 and 14 for the beam 101, faces 22 and 14 for the beam 201, faces 24 and 14 for the beam 301, faces 12 and 14 for the beam 401, and faces 13 and 14 for the beam 501, which advantageously results in a light power loss of about 2% only.
The x-cube prisms 10 and 20 combine the beams, but since the angle of incidence for the light sources Ll, L2, L3, L4 and L5 with respect to the faces 21, 22, 24, 12 and 13, respectively, may be mutually different, only a small portion of a cross-section of the exiting beam 400 would comprise white light. Thus, lenses can be arranged at the faces 21, 22, 24, 12 and 13 at which the light sources Ll, L2, L3, L4 and L5 are positioned in order for the incoming beams 101, 201, 301, 401 and 501 to coincide. The integration of lenses at the faces 21, 22, 24, 12 and 13 of the x-cube prisms 20 and 10 reduces the size of the beam combiner 1 considerably in comparison to beam combiners where separate, non-integrated components are used for collimating the incoming beams before entering an x-cube prism. In addition, in such multi-component systems, a relatively large distance is required between the light sources and the collimating components, which further increases the size of the beam combiner.
In an embodiment of the invention, the lens incorporated at the front face 14 of the x-cube prism 10 is a liquid crystal lens. Such a lens enables selective altering of the focus of the exiting beam 400, which enables implementation of illumination systems adapted to both room illumination conditions and reading illumination conditions.
In yet a further embodiment, alignment of the light sources Ll, L2, L3, L4 and L5 is performed to create a uniform exiting beam 400. The diameter of the cross-section of the exiting beam 400 can be varied by adjusting the distance between the light sources Ll, L2, L3, L4 and L5 and the faces 21, 22, 24, 12 and 13, respectively. By adjusting the position and the tilt of the light sources Ll, L2, L3, L4 and L5 with regard to the faces 21, 22, 24, 12 and 13, respectively, the angle and the shape of the exiting beam 400 can be varied.
In the following, shaping of an exiting beam 400 created from a combination of laser diode beams is described. A laser diode usually has an elliptical beam profile. Using different curvatures along e.g. two directions of a face of an x-cube prism and rotating the laser diode so that its orientation matches its light-distributing angle enables alteration of elliptical profile of a beam. By adjusting the distance between a laser diode and a corresponding face of the x-cube prism, the profile of the beam can be narrowed, and an exiting beam having for instance a circular cross-section can be created. Other shapes may be achieved using different designs for the optics, i.e. using different types of curvatures for the faces of the x-cube prisms. It is possible to obtain beam profiles of any shapes e.g. square, rectangular or triangular. The main purpose of the shaping is to adapt the exiting beam profile to the final application. For instance, a circular beam profile is suitable for an illumination system while square,
rectangular and even triangular beam profiles are more suitable for beamers and head up displays. Depending on the curvature of the faces, a Gaussian profile of a diode laser can also be changed to a flattop profile. This could be of interest for illuminating a well-defined area in which each part of the illuminated area needs to be uniformly illuminated. It will be appreciated by a person skilled in the art that any type of light sources may be used in combination with the x-cube prisms 10 and 20 of the present invention. In a preferred embodiment, however, light emitting diodes or laser diodes are used. These types of light sources are small and therefore enable compact beam combiners. An advantage of using diodes is that they emit light with a narrow beam distribution, thus enabling creation of a narrow exiting beam which can be directed to individual pixel positions on a screen (not shown in the Figures). Therefore, the use of LEDs enables combination of the beam combiner with high resolution imaging devices such as LCD panels or LCOS panels. As compared to LEDs, the use of laser diodes is even more preferable since laser beams per se are collimated. Thus, the image stays sharp regardless of the distance between the beam combiner and the display. Further, the use of laser diodes is advantageous for reaching the spectral coverage to which the human eye is sensitive, since laser diodes emit light of separate colours as compared to conventionally used fluorescent materials emitting mixed colours.
In addition, different wavelengths can be employed in order to obtain a complete light spectrum. By using six light sources having six different wavelengths, the complete visible spectrum to which the human eye is sensitive could virtually be covered. The spectrum may further be extended by changing the individual power of each light source.
In an above described embodiment of the present invention, the light sources Ll, L2, L3, L4 and L5 emit blue, green and red light. These are the three primary colours which, after passing through the x-cube prisms 10 and 20, result in a white exiting beam 400 suitable for projection display systems or illumination applications. However, it will be appreciated by a person skilled in the art that other wavelengths can be used and that a white exiting beam 400 can be obtained by the combination of other colours than blue, green and red. The x-cube prisms 10 and 20 can be manufactured using conventional methods such as grinding and polishing, hot glass pressing and plastic injection moulding. In some cases, lenses located at the faces 12, 13, 14, 21, 22 and 24 of the x-cube prisms 10 and 20 are directly incorporated during the production process, thus providing a cheap technique to produce the beam combiner. In other cases, these lenses are added later by gluing them
onto the faces 12, 13, 14, 21, 22 and 23 of the x-cube prisms 10 and 20 with optical transparent adhesives.
In one embodiment, a projection display system is realized using a beam combiner of the present invention. Using a beam combiner equipped with several x-cube prisms having curved faces, lenses and appropriate coatings on their diagonal surfaces and faces, only a scanner mirror is needed to fully realize the projection display system. Further, such a projection display system would preferably be provided with light sources such as LEDs or laser diodes since the spatial modulation required to compose the image on the display easily can be controlled by electrical modulation of the LEDs or laser diodes. This is advantageous as compared to systems where the modulation only can be effected in the display device.
In another embodiment, an illumination system is provided using a beam combiner of the present invention.
The present invention is applicable in various display technologies applied in e.g. television sets, computers, automotive industry products and mobile phones and also for lighting applications in which LEDs or laser diodes are used.
The invention has mainly been described above with reference to a number of explicitly disclosed embodiments. However, as is readily appreciated by a person skilled in the art, other embodiments than the ones disclosed above are equally possible within the scope of the invention, as defined by the appended patent claims.
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