WO2001016624A2

WO2001016624A2 - Lighting system using an afocal cylinder lens system

Info

Publication number: WO2001016624A2
Application number: PCT/DE2000/002622
Authority: WO
Inventors: Horst Linge; Bernward Bretthauer
Original assignee: Isco-Optic Gmbh
Priority date: 1999-08-31
Filing date: 2000-08-05
Publication date: 2001-03-08
Also published as: WO2001016624A3; DE19941272A1

Abstract

The invention relates to a lighting system using an afocal cylinder lens system. The invention especially relates to a lighting system that combines the light beams of two light sources. Said lighting system consists of two lamps that produce unpolarized light, two reflectors for focusing the light, two systems of at least two respective cylinder lenses that compress the ray beam in one coordinate direction so that the two ray beams, after having been guided in parallel, are combined to form a ray beam the aspect ratio of which is 1 to 1.6. The lighting system further comprises an optical integrator or bar integrator that guarantees that the object is evenly illuminated. The invention further relates to a lighting system for producing polarized light. Said lighting system consists of a lamp that produces unpolarized light, a reflector that focuses the light, a system that consists of at least two cylinder lenses that compress the ray beam in a coordinate direction, a polarized beam splitter that splits the compressed ray beam into two ray beams of polarized light, and an optical integrator or bar integrator that guarantees that the object is evenly illuminated. The cylinder lenses are designed in such a way that the two ray beams that leave the polarizing beam splitter are combined to form a ray beam the aspect ratio of which is 1 to 1.6. The inventive lighting systems have an especially compact design and have especially good optical properties.

Description

Illumination system using an afocal cylindrical lens system

B e s c h r e i b u n

The invention relates to a lighting system using an afocal cylindrical lens system, in particular for guiding light in projectors.

An afocal cylindrical lens system is used to compress the beam cone emerging from a reflector in approximately one half of the width in one direction. The purpose of the compression is either to convert the beam into a beam of polarized light whose width corresponds approximately to its height by means of a polarizing beam splitter, or to combine the light from two reflectors into a common beam cone so that the resulting beam in turn has a width, which roughly corresponds to its height. It is preferably used in combination with an optical integrator.

LCD projectors are usually equipped with optical integrators, which consist of two integrator plates. Each integrator plate consists of a group of lenses, the shape of the lenses of the first plate corresponding to the field to be illuminated. Each lens of the first plate corresponds to a lens of the second plate. Each lens of the first integrator plate focuses the light from the reflector onto the associated lens of the second plate. Every lens of the second plate, together with the condenser lens, images the corresponding lens of the first plate onto the LCD panel. Because the shape of the lens shown corresponds to that of the LCD panel, the illuminated area also has the right shape. Since the light cones of all lenses overlap in the field, there are irregularities in the illuminance. This enables uniform illumination of a rectangular window with high efficiency. The field lens can be omitted if an ellipsoid reflector is used instead of a parabolic reflector.

The bar integrator is an alternative to the optical integrator. The light is focused on the entrance surface of the bar integrator. The light is repeatedly totally reflected on the side surfaces within the glass rod. As a result, the unevenness in the beam profile between the entry surface and the exit surface of the integrator rod is continuously reduced. The longer the integrator rod, the better the uniformity of the beam profile at the exit of the integrator. Since the total reflection is lossless, high uniformity can be achieved with good efficiency and simple construction. However, the rod integrator has the disadvantage of being very long.

In the LCD projector, the LCD panel is illuminated with polarized light depending on the system. Polarizing filters reduce the light output by at least 50%.

Polarizing beam splitters (PBS) are an alternative to polarizing filters. For example, the light is split into a vertical portion and a portion polarized parallel to the plane of the drawing using a multiple coating; this is done with a high degree of efficiency. The portion polarized perpendicular to a plane is reflected by the coating, the portion polarized parallel to the plane transmits the layer. This portion is deflected with the aid of a mirror layer and also converted into light polarized perpendicular to the aforementioned plane with the aid of a λ / 2 plate. This arrangement has the following Part: The light cone gets twice the dimension in one dimension thanks to the beam splitter, which makes the integrator plates twice as wide as they are high. However, the aperture of the projection lens is circular. In order to be able to use the light cone, which is twice as wide as it is high, for the projection, a lens must be used whose aperture is approximately twice as large as when using polarizing films. This large aperture makes the lens large and heavy and, with the same optical effort, leads to a deterioration in the imaging performance. The large aperture is only used in one direction.

A second possibility is to keep the aperture constant by doubling the distance between the second integrator plate and the LCD panel. As a result, however, the entire projector becomes very large and the aperture of the objective is in turn only fully used in one direction. Since the lenses of the second integrator plate map the lenses of the first integrator plate onto the LCD panel, the imaging equation must also be used

Image size = image width

Item size Item width

the distance between the integrator plates can also be doubled. However, this also enlarges the image of the luminous field of the lamp that the first integrator plate produces on the second integrator plate. This in turn leads to a drop in efficiency, since the image of the light field is no longer completely captured by the lenses of the second plate. Another disadvantage is the high weight of the beam splitter, which must correspond to that of the reflector in its horizontal dimension.

A better solution is described in EP 0 753 780 AI. A small strip-shaped beam splitter is attached behind each lens of the second integrator plate according to the above principle. As a result, the entire light cone is only widened by half a lens width. Reflection and polarization coatings alternate in the strip-shaped beam splitter, so that only every second Strips can take up useful light, which contributes to efficiency. However, since the light is already concentrated at this point through the lenses of the first integrator plate, the conversion takes place with only a small additional space requirement. However, this solution only works in conjunction with an optical integrator consisting of two lenticular screens and cannot be used independently of these.

The conventional approach for merging two light sources is to guide two parallel beams next to one another onto the condenser optics. However, this cannot be used because it leads to the same problems with the aperture of the projection objective as the polarization by means of a beam splitter prism with the alternative of the polarizing beam splitter (PBS).

Against this background, it is an object of the present invention to provide an illumination system using an afocal cylindrical lens system which is structurally particularly compact with particularly good optical properties.

According to a first solution to the aforementioned task, an illumination system is proposed that combines the luminous flux of two light sources, consisting of:

- two lamps that produce unpolarized light,

- two reflectors for focusing the light,

two systems of at least two cylindrical lenses each, which compress the beam cone in one coordinate direction, so that the two beam cones, after they have been guided next to one another, together form a beam cone whose aspect ratio is 1 to 1.6,

- an optical integrator or a rod integrator, which ensures uniform illumination of the object. According to a second solution to this problem, an illumination system for generating polarized light is proposed, consisting of:

- a lamp that produces unpolarized light,

- a reflector for focusing the light,

a system of at least two cylindrical lenses that compress the beam cone in one coordinate direction,

a polarizing beam splitter which splits the compressed beam cone into two beam cones made of polarized light,

an optical integrator or a rod integrator, which ensures uniform illumination of an object,

- The cylindrical lenses are designed such that the two beam cones, which leave the polarizing beam splitter, together form a beam cone, the aspect ratio of which is approximately 1 to 1.6.

The beam cone formed from the two beam cones preferably has an aspect ratio of 1 to 1.2, in particular 1, in the case of both solution variants. With the latter value, the greatest compactness in the light cone is guaranteed.

In the case of an illumination system which combines the luminous flux of two light sources, it is considered to be particularly advantageous if, in addition, a polarization conversion system according to EP 0 753 780 AI is used to generate polarized light.

Further features of the lighting system according to the invention using an afocal cylindrical lens system are shown in the description of the figures, the figures and in the subclaims, it being noted that all individual features and all combinations of individual features are essential to the invention.

The invention is illustrated in the figures on the basis of several embodiments, without being limited to these. It is also to better understanding, the relevant state of the art is documented in drawings. It shows:

1 is an optical integrator system according to the prior art,

2 shows a possibility of polarizing the light emerging from a reflector in accordance with the prior art,

3 shows an improved possibility of polarizing the light in accordance with the prior art,

4 shows a first embodiment of the afocal optics which is part of the present invention,

5 shows a variant of the invention, which is used to generate polarized light,

6 shows a further embodiment of the invention for generating polarized light,

7 shows the light field which the variant according to the embodiment according to FIG. 6 generates on the input surface of an integrator rod,

8 shows an embodiment of the invention for combining the light of two lamps, in which the light is subsequently polarized by means of a system according to the prior art,

9 shows a further embodiment of the invention for combining the light of two lamps,

10a and 10b the images of the luminous field of the lamp, which a system according to the embodiment of FIG. 8 generates on the second integrator plate, 11 shows a possible embodiment of the LCD projector using the invention and

Fig. 12 shows an embodiment of the invention together with a rod integrator.

LCD projectors are usually equipped with optical integrators as shown in FIG. 1. The integrator consists of two integrator plates 101 and 102. Each integrator plate consists of a group of lenses, the lenses of the first plate 101 corresponding in shape to the field 104 to be illuminated. Each lens of the first plate corresponds to a lens of the second plate. Each lens of the first integrator plate 101 focuses the light from the reflector 100 onto the associated lens of the second plate. The beam cone is drawn in for a lens in FIG. 1. Each lens of the second plate 102, together with the condenser lens 103, images the corresponding lens of the first plate 101 onto the LCD panel 104. Because the shape of the lens shown corresponds to that of the LCD panel, the illuminated area also has the right shape. Since the light cones of all lenses overlap in the field 104, there are irregularities in the illuminance. This enables uniform illumination of a rectangular window with high efficiency. The field lens 103 can be omitted if an ellipsoid reflector is used instead of a parabolic reflector. In the LCD projector, the LCD panel 104 is illuminated with polarized light, depending on the system. Polarizing filters reduce the light output by at least 50%.

Fig. 2 shows an alternative to polarizing filters, a polarizing beam splitter (Polarizing Beam Splitter, PBS). With the aid of a multiple coating 201, the light is split into a portion polarized perpendicularly and parallel to the plane of the drawing. This is done with a high degree of efficiency. The portion polarized perpendicular to the plane of the drawing is reflected by the coating 201, the portion polarized parallel to the plane of the drawing transmits the layer. This portion is converted using a mirror layer 202 steers and with the help of a λ / 2 plate 203 also converted into polarized light perpendicular to the plane of the drawing.

3 shows a modified design in which a small strip-shaped beam splitter 301 is attached behind each lens of the second integrator plate 102 according to the above principle. As a result, the entire light cone is only widened by half a lens width. Reflection 302 and polarization coatings 303 alternate in the strip-shaped beam splitter 301, so that only every second strip can receive the light which contributes to the efficiency. However, since the light through the lenses of the first integrator plate 101 is already concentrated at this point, the conversion takes place with only a small additional space requirement. However, the solution only works in conjunction with an optical integrator consisting of two lenticular grid plates and cannot be used independently of these. The reference number 304 denotes the λ / 2 plate.

Fig. 4 shows an embodiment of the afocal optics, which is part of the present invention. The system consists of a lamp, reflector and beam shaping optics. The unit 1, consisting of a lamp la and a parabolic reflector lb, emits an approximately parallel cone of light. Instead of a parabolic reflector, a reflector of a different shape can also be used. The light has a divergence, which essentially depends on the size of the light field of the lamp used. As a result, the light cone diverges with increasing distance from the unit 1. This divergence affects the desired effect of the invention, namely the deformation of the light cone onto a cone that is twice as high as it is wide. Therefore, the construction of the following optical elements should be as short as possible, which also benefits the compact form of the entire device.

The requirement for a short construction requires a compression of the beam in a short way and therefore a high refractive power of the cylindrical lenses directly behind the unit 1. Realize high refractive power with the help of two positive cylindrical lenses 2 and 3, the first lens 2 making the greatest possible contribution to the total refractive power. After the positive cylindrical lenses, the light cone is convergent. A negative cylindrical lens 4 ensures that the light becomes parallel again. Since this lens has a smaller width than the lenses 2 and 3 due to the cone of rays narrowed, it can have a greater curvature, so that only one instead of two cylindrical lenses are required for the dispersion. Because of the divergence of the light, it can be advantageous not to design the system consisting of the cylindrical lenses 2, 3 and 4 exactly afocal, but to ensure a low residual convergence of the light cone after the lens 4. This is particularly useful for the design with a beam splitter prism, since there is still a longer light path to the optical integrator.

5 shows the polarization / conversion for the invention using the beam splitter prism. A beam splitter prism 6 according to FIG. 5 is placed behind the described system 11 according to FIG. 4. The polarizing coating 7 within the beam splitter 6 divides the light into a portion polarized perpendicularly and parallel to the plane of the drawing. The perpendicularly polarized portion is reflected in the direction of the integrator plate 8, the portion which is polarized parallel to the plane of the drawing is reflected on the mirror 9 in the direction of the integrator plate, and is converted on the λ / 2 plate 10 into light polarized perpendicularly to the plane of the drawing. As a result, the integrator plate is only hit by light that is polarized essentially perpendicular to the plane of the drawing. The light cone that strikes the integrator plate preferably has an aspect ratio of approximately 1, thus a height to width ratio of approximately 1. If the light cone is reduced to approximately half its width by the afocal system 11, the horizontal dimensions of the beam splitter can also be changed can be reduced by half, which results in a saving of glass and thus weight by a factor of 4.

Fig. 6 shows the embodiment of the invention using a rod integrator. Polarization with the help of the afoka len system over the known polarization conversion system the advantage that it works without an optical integrator. This makes it possible to use it in conjunction with the rod integrator shown in FIG. 6. There the condenser lens 41 is flooded with light which is polarized essentially perpendicular to the plane of the drawing. The light cone that enters the condenser lens has an aspect ratio of approximately 1, thus a height to width ratio of approximately 1. The condenser lens 41 focuses the light on the entry surface of the integrator rod 42 or on a point within the integrator rod just behind the entry surface. The integrator rod is generally a cuboid glass rod, the cross section of which has the shape of the surface to be illuminated. Repeated total reflection within the integrator rod 42 achieves a high uniformity of the light flow through the exit surface 43 of the integrator rod. Since the amount of the angle of the light beams with respect to the optical axis is not changed by the total reflections, the aperture does not change by the integrator rod 42 either. In this embodiment, too, the invention provides the same advantages over a polarizing beam splitter without an afocal system according to the prior art: the beam splitter is smaller and the aperture is better utilized.

FIG. 7 shows the image of the luminous field of the lamp (lines of the same luminance) as is generated by the system comprising the reflector, afocal cylindrical lenses, the beam splitter and the condenser lens 41 according to the embodiment in FIG. 6 on the entry surface of the integrator rod. Thanks to the cylindrical lenses, the light field is no longer rotationally symmetrical, but wider than it is high. However, since the area to be illuminated in projectors and thus also the integrator rod has a width to height ratio of typically 4 to 3, this image of the illuminated field can be coupled into the integrator rod with high efficiency.

While the embodiments according to the previously described figures show a Ξin lamp system, the written figures systems that work with two lamps. The Fig.

8 through 11 illustrate systems with an optical integrator.

According to the embodiment according to FIG. 8, two systems 13 and 14 constructed according to the embodiment according to FIG. 4 are arranged such that they illuminate a common integrator plate 15. The beam cones at the exit of systems 13 and 14 are significantly narrower than at the exit of the reflectors due to the intended narrowing. However, since the beam cones should hit the integrator plate 15 directly next to one another, one or both of the systems 13 and 14 must be tilted.

The integrator plate 15 must be struck by light which is essentially parallel to the optical axis. However, since systems 13 and 14 are tilted, beam deflection is required. It can take place in a space-saving manner by means of two prisms 61 and 62. Alternatively, a deflection by mirror 19, as z. B. in Fig.

9 is possible.

Each lens on the first integrator plate 15 has a corresponding lens on the second integrator plate 16. The lenses of the first integrator plate map the light field onto the corresponding lenses of the second plate. However, the reflector and the cylindrical lenses of the afocal system 13 and 14 are also involved in the illustration.

Since the lenses of the first integrator plate 15 are imaged on the field to be illuminated by the corresponding lenses of the second integrator plate 16 and the condenser lens 17, their shape must correspond to that of the field to be illuminated. This restriction does not apply to the lenses of the second integrator plate 16; In order to avoid excessive decentering of the lenses of the first integrator plate (15), the lenses of the second plate (16) are preferably designed in shape and size similar to the lenses of the first integrator plate 15. For the widespread XGA format results There is therefore a height to width ratio of 4: 3 for the lenses of both plates.

10a and 10b show the outlines 20 and 21 of the luminous field images, as they are generated on two different lenses of the second integrator plate 16, and the outlines 22 and 23 of the lenses. The lamp used in this simulation has a cylindrical illuminated field with a length to diameter ratio of approximately 1. The afocal factor of the cylindrical lens system causes these images of the illuminated field to be pulled apart in the horizontal direction. This must be taken into account if a polarization conversion system (PCS) according to EP 0 753 780 AI is to be used. The PCS halves the usable area of the lenses in the second integrator plate. Depending on the direction of installation, the entry surface is halved vertically or horizontally (dashed lines in the outlines 22 and 23 of the lenses). 10a and 10b show that the lowest power loss results from horizontal installation of the PCS. However, the results may vary depending on the lamp used.

According to the embodiment according to FIG. 8, the light is finally guided to the field 18 to be illuminated through the lenses of the second integrator plate (16) and through the condenser lens 17. The beam path is sketched for the lenses 16a and 16b. The lens 16a and the neighboring lenses are illuminated by the system 13, lens 16b and the neighboring lenses by the system 14. However, since both lens groups illuminate the same field 18, the light cones of systems 13 and 14 were combined. Reference number 160 denotes the PCS arranged between the integrator plate 16 and the condenser lens 17.

11 shows a possible embodiment of an LCD projector using the invention. In this context, reference is also made to the illustration in FIG. 9. The dichroic filters 61 and 62 split the light into a red, green and blue component. Each of these color components now illuminates one of the LCD Panels 63. The dichroic beam splitter cube 64 combines the three colors again. The reference number 65 denotes mirrors, and the reference number 66 denotes a lens.

Based on the illustration in FIG. 8, FIG. 12 shows an embodiment of the invention using a rod integrator. A rod integrator can be used instead of the optical integrator if polarized light can be dispensed with for certain purposes. This is e.g. B. the case with DLP projectors. The design and the coupling of the light into the integrator rod 42 is completely analogous to the embodiment according to FIG. 6. The difference is that the two beam cones, which are compressed in width and are to be combined, come from different lamps, instead of from one polarizing beam splitter Beam to be generated. The system according to FIG. 12 thus provides about twice as much light as the single lamp system described above, but the light is not polarized here.

Claims

Patent claims

1. Illumination system using an afocal cylindrical lens system consisting of:

- two lamps that produce unpolarized light,

- two reflectors for focusing the light,

- an optical integrator or rod integrator, which ensures uniform illumination of the object.

2. Illumination system using an afocal cylindrical lens system consisting of:

- a lamp that produces unpolarized light,

- a reflector for focusing the light,

- an optical integrator or rod integrator, which ensures uniform illumination of the object,

the cylindrical lenses being designed such that the two beam cones, which leave the polarizing beam splitter, together form a beam cone, the aspect ratio of which is 1 to 1.6.

3. Lighting system according to claim 1 or 2, wherein the two beam cones together form a beam cone whose aspect ratio is 1 to 1.2, in particular 1.

4. Lighting system according to claim 1 or 3 with two lamps and optical integrator, wherein in addition a polarization conversion system is used to generate polarized light.