Microlens array for an image projector

Abstract

The invention relates to a microlens array (100-A, 100-B) for an image projector (200), the array comprising: a support (105-A, 105-B); a matrix-shaped arrangement (101-A, 101-B) having a plurality of lenses (103-A, 103-B) which are arranged on the support (105-A, 105-B); and an aperture device (121, 131) having a plurality of optical openings (123) for each of the lenses (103-A, 103-B).

Description

[0001] MICRO LENS ARRAY FOR AN IMAGE PROJECTOR

[0002] The invention relates to a microlens array for an image projector, an image projector with a microlens array, and a microlens array arrangement.

[0003] For small projectors built as a stack along the optical axis, a micro lens array (MLA) image projector has been used in recent years, particularly in the automotive sector. This projector typically comprises collimation optics that produce collimated light with a specific, small residual divergence, an optical stack with an illumination lens array, a slide plane (made of a light-absorbing layer) in which the image information is provided through apertures, a substrate with a thickness equal to the focal length, and a projection lens array, which is often identical to the illumination lens array.

[0004] In addition, the image projector comprises electronics, a housing, and a cover plate. This creates a compact multi-channel optic in which each channel can project the entire image with high depth of field.

[0005] German patent application DE 10 2009 024 894 A1 relates to a projection display with a light source and regularly arranged optical channels. The optical channels contain a field lens, each associated with an object structure to be projected and a projection lens. The distance between the projection lenses and their associated object structures corresponds to the focal length of the projection lenses, while the distance between the object structures to be projected and their associated field lens is chosen to enable Köhler illumination of the associated projection lens. This results in the individual projections being superimposed to form the overall image.

[0006] The microlens array according to the invention for an image projector with a carrier of a matrix-shaped arrangement with a plurality of lenses arranged on the carrier; and an aperture device with a plurality of optical openings for the respective lenses offers the technical advantage of improving the sharpness of the projected image and preventing the formation of ghost images.

[0007] In another advantageous embodiment of the microlens array, the openings are circular. This allows the openings to correspond to the shape of the lenses, so that the light can be directed towards the center of the lenses.

[0008] In another advantageous embodiment of the microlens array, the diameter of the openings is smaller than the diameter of the lenses. This prevents crosstalk between the individual light channels.

[0009] In another advantageous embodiment of the microlens array, the diameter of the apertures is less than 500 pm. This makes it possible to effectively suppress ghost images.

[0010] In another advantageous embodiment of the microlens array, the aperture device is arranged inside the carrier. This allows the aperture device to be protected by the surrounding material.

[0011] In another advantageous embodiment of the microlens array, the center point of the apertures and the center point of the lenses are centered relative to each other. This allows the light to be efficiently directed to the lens.

[0012] In another advantageous embodiment of the microlens array, the microlens array is a thermoplastic polymer. This allows the microlens array to also be manufactured using an injection molding process.

[0013] In another advantageous embodiment of the microlens array, the thermoplastic polymer comprises polymethyl methacrylate (PMMA), cycloolefin polymer (COP), polycarbonate (PC), or optical silicone. This allows for the use of particularly suitable materials for the fabrication of the microlens array.

[0014] In a further advantageous embodiment of the microlens array, the aperture device is formed by an aperture layer or by aperture channels. This allows the apertures to be effectively formed. The microlens array arrangement according to the invention, comprising a first microlens array with a plurality of lenses on an illumination side; a second microlens array with a plurality of lenses on a projection side; and an aperture device with a plurality of openings for the respective lenses between the first and second microlens arrays, can be used as a component in an image projector. A slide plane, comprising specially designed openings for the passage of light, can be arranged between the first and second microlens arrays. This results in a further simplified design.

[0015] The inventive image projector with the microlens array arrangement offers the same technical advantages as the microlens array.

[0016] Exemplary embodiments of the invention are explained in more detail with reference to the following figures. These show:

[0017] Fig. 1 shows a schematic representation of an image projector with a microlens array;

[0018] Fig. 2 shows a schematic cross-sectional view of a microlens array arrangement;

[0019] Fig. 3 shows a schematic cross-sectional view of another microlens array arrangement;

[0020] Fig. 4 shows the effect of an aperture device;

[0021] Fig. 5 shows a schematic cross-sectional view of another microlens array arrangement;

[0022] Fig. 6 shows a schematic cross-sectional view of another microlens array arrangement; and

[0023] Fig. 7 shows a schematic cross-sectional view of another microlens array arrangement.

[0024] Fig. 1 shows a schematic representation of an image projector 200 with a microlens array 300 (MLA projector). The microlens array 300 comprises a first microlens array 100-A on an illumination side 107-A and a second microlens array 100-B on a projection side 107-B.

[0025] The image projector 200 projects a static, unchanging image 109 onto a screen, such as a street or a wall. The aim is to generate the highest possible luminous flux (lumens) using the smallest possible image projector 200.

[0026] The image projector 200 comprises a light source 113 and a collimating lens 115 for generating parallel light beams. Nevertheless, the spatial dimensions of the image projector 200, particularly along the axis of light propagation, and the number of components should be kept as small as possible. This is especially advantageous when installation space is limited for automotive lighting systems. For this purpose, the image projector 200 is designed as a multi-aperture design in which miniaturized projectors (channels), each with separate lenses 103-A and 103-B, are arranged in parallel, thus achieving a miniaturized design in terms of thickness.

[0027] Furthermore, a high depth of field can be achieved with the small spatial dimensions of lenses 103-A and 103-B. This enables a sharp image of image 109 to be projected onto an inclined screen at different projection distances without tilting the object and lens planes (Scheimpflug condition).

[0028] In this embodiment, the same microlens arrays 100-A and 100-B with the same focal length are used for lenses 103-A on the illumination side 107-A and lenses 103-B on the projection side 107-B. The focal length is selected such that the respective focus lies on the opposite lens 103-A and 103-B (BL <-> PL). Therefore, for good illumination with appropriate collimation, as little distance as possible between lenses 103-A on the illumination side 107-A and the slide plane 111 is desirable.

[0029] Lenses 103-A and 103-B are manufactured using an injection molding process. The image plane 111 is made of a chromium layer in which the image information is provided through apertures. Glass is frequently used for the chromium layer, and the support 105-A has a near-zero thickness or consists solely of the lens material and is not a separate support (polymer on glass). The support 105-A is manufactured together with the lenses 103-A and positioned on the illumination side 101-A. It typically has a thickness between 400 pm and 800 pm, in this embodiment 550 pm. The support 105-A or 105-B can be made of polymethyl methacrylate (PMMA) or cycloolefin polymer (COP). This has the technical advantage that these materials exhibit low dispersion. This prevents chromatic aberrations and color fringing in polychromatic white projection.The carrier 105-A and 105-B can also be made of polycarbonate or optical silicone. The carrier 105-A and 105-B can have a length between 5 mm and 50 mm and a width between 5 mm and 50 mm, preferably 10 mm by 10 mm.

[0030] The lenses 103-A and 103-B on the support 105-A and 105-B, for example, have a center-to-center distance of 500 pm to 1,000 pm, in this embodiment 800 pm. The lenses 103-A and 103-B are arranged hexagonally on the support 105-A and 105-B and have a focal length between 1.5 mm and 4 mm, in this embodiment 2 mm. The lenses 103-A and 103-B can, for example, be made of the same or a different material as the support 105-A or 105-B. For example, 12 by 12 lenses 103-A and 103-B are arranged on the support 105-A and 105-B, which has dimensions of 10 mm by 10 mm. The focal length of lenses 103-A, 103-B, for example, is greater than the thickness of the support 105.

[0031] The sufficient thickness of the substrate 105-A and 105-B allows the microlens array 100-A and 100-B to be manufactured using injection molding or compression molding. The focal length of the lenses 103-A on the illumination side 107-A can be easily increased to achieve optimal illumination of the slide structures (image information) in the slide plane 111 and the corresponding lenses 103-B on the projection side 107-B. The substrate 105-A and 105-B and the respective lenses 103-A and 105-B of each microlens array 100-A and 100-B can be manufactured from the same material in a single piece.

[0032] In this embodiment, different focal lengths are used for lenses 103-A and 103-B on the illumination and projection sides 107-A and 107-B, such that the focal plane of lens 103-A on the illumination side 107-A lies precisely within the lens 103-B on the projection side 107-B. This results in a maximum acceptable angle of residual collimation divergence. The focal length of lens 103-B on the projection side 107-B is selected such that the focal plane lies within the slide plane 111. This enables a sharp projection with the same advantages, such as a large depth of field, as for projection onto an inclined plane.

[0033] Fig. 2 shows a schematic cross-sectional view of a microlens array 300. The microlens array 300 comprises an aperture layer 121 as an aperture device with a plurality of openings 123 for the respective lenses 103-B. The aperture layer 121 assigns an opening 123 to each lens 103-B, through which the light rays for lens 103-B pass. The openings 123 allow side areas of lens 103-B to be shielded and darkened. This prevents the formation of ghost images and artifacts. The openings 123 also prevent crosstalk in adjacent light channels.

[0034] The aperture layer 121 is formed, for example, by a silver layer with a thickness of 50 nm to 100 nm or a chromium layer with a thickness of 100 nm to 300 nm. This results in high optical density and a high absorption coefficient. The aperture layer 121 is located inside the support 105-B. The arrangement of the openings 123 in the aperture layer 121 corresponds to the arrangement of the lenses 103-B on the support 105-B. The aperture layer 121 is located between the illumination side 107-A and the projection side 107-B of the microlens array 300. The aperture layer 121 is arranged, for example, such that the distance between the diaplane 111 and the aperture layer 121 is greater than or equal to the distance between the aperture layer 121 and the lens 103-B on the projection side 107-B. The aperture layer 121 works better when it is positioned closer to the lenses 103-B on the projection side 107-B.

[0035] The openings 123 in the aperture layer 121 are circular and have a diameter smaller than the diameter of the lenses 103-B. For example, the diameter of the openings 123 is less than 500 pm. The center point of the openings 123 and the center point of the lenses 103-B coincide. In general, the openings 123 in the aperture layer 121 can also have a different shape or be adapted to the graphic used in the slide plane 111. The openings 123 in the aperture layer 121 can also be graphically adapted to the images in the slide plane 111. The aperture layer 121 can be used to shape the illuminated area of ​​the lens 103-B. Fig. 3 shows a schematic cross-sectional view of another microlens array 300 with a beam path indicated. The microlens array arrangement 300 can include more than one aperture layer 121.The light 125 passing through the openings 123 of the aperture layer 121 emerges as useful light at the projection side 107-B. Divergent light 127 outside an acceptable angular range of the lens 103-B is blocked by the aperture layer 121.

[0036] In this way, blurring and ghosting caused by light hitting the area between two adjacent lenses 103-B can be prevented.

[0037] Fig. 4 shows the effect and principle of the aperture layer 121 with circular openings 123 when projecting the image 109. By using the aperture layer 121, the ghost light 125 can be reduced by more than 80%. With a typical light distribution on the illumination side 107-A, a reduction of the ghost light 125 of over 95% is possible with an aperture layer 121 located close (100 pm - 300 pm) to the projection lens 103-B.

[0038] Fig. 5 shows a schematic cross-sectional view of another microlens array 300. In this microlens array 300, no support 105-A is used, which serves as a disk for the lenses 103-A on the illumination side 107 A. Here too, an aperture layer 121 is located inside the support 105-B.

[0039] Fig. 6 shows a schematic cross-sectional view of another microlens array 300. In this microlens array 300, two aperture layers 121 are used, which are spaced apart from each other. By using two aperture layers 121, blurring and ghosting can be further reduced.

[0040] Fig. 7 shows a schematic cross-sectional view of another microlens array 300. In this embodiment, the aperture device is not formed by a layer, but by absorbing walls 129, which are arranged between the lenses 103-B inside the microlens array 300 and extend along the optical axis. The walls 129 extend perpendicular to the diaplane 111. Aperture channels 131 are formed by the walls 129, each extending in front of the lenses 103-B.

[0041] The aperture channels 131 can be used to shape the illuminated area of ​​the lenses 103-B on the projection side 107-B. The aperture channels 131 create longitudinal apertures that effectively prevent crosstalk. This allows for increased projection sharpness and optimization of the aperture position.

[0042] Due to its dimensions, the described microlens array 300 is particularly suitable for the automotive sector, for example as a light source for a light carpet or the projection of a turn signal onto the road, as symbol projection in hotels, as safety projection in aircraft, as

[0043] Effect lighting, as guidance projection or as hazard area projection in buildings.

[0044] All features explained and shown in connection with individual embodiments of the invention can be provided in different combinations in the object according to the invention in order to simultaneously realize their advantageous effects.

Claims

PATENT CLAIMS 1. Microlens array (100-A, 100-B) for an image projector (200), with: - a carrier (105-A, 105-B); - a matrix-shaped arrangement (101-A, 101-B) with a plurality of lenses (103-A, 103-B) arranged on the support (105-A, 105-B); and - an aperture device (121 , 131 ) with a plurality of optical apertures (123) for the respective lenses (103-A, 103-B).

2. Microlens array (100-A, 100-B) according to claim 1, wherein the openings (123) are circular.

3. Microlens array (100-A, 100-B) according to claim 2, wherein the diameter of the apertures (123) is smaller than the diameter of the lenses (103-A, 103-B).

4. Microlens array (100-A, 100-B) according to any one of the preceding claims, wherein the diameter of the apertures (123) is less than 500 pm.

4. Microlens array (100-A, 100-B) according to one of the preceding claims, wherein the aperture device (121) is arranged inside the carrier (105-A, 105-B).

5. Microlens array (100-A, 100-B) according to one of the preceding claims, wherein a center point of the openings (123) and a center point of the lenses (103-A, 103-B) is centered relative to each other.

6. Microlens array (100-A, 100-B) according to any of the preceding claims, wherein the microlens array (100-A, 100-B) is a thermoplastic polymer.

7. Microlens array (100-A, 100-B) according to claim 6, wherein the thermoplastic polymer comprises a polymethyl methacrylate (PMMA), cyclo-olefin polymer (COP), polycarbonate (PC) or optical silicone.

8. Microlens array (100-A, 100-B) according to one of the preceding claims, wherein the aperture device (121 , 131 ) is formed by an aperture layer (121 ) or by aperture channels (131 ).

9. Microlens array arrangement (300), comprising: a first microlens array (100-A) with a plurality of lenses (103-A) on an illumination side (107-A); and a second microlens array (100-B) with a plurality of lenses (103-B) on a projection side (107-B); and - an aperture device (121 , 131 ) with a plurality of openings (123) for the respective lenses (103-A, 103-B) between the first microlens array (100-A) and the second microlens array (100-B).

10. Image projector (200) with a microlens array arrangement (300) according to claim 9.

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