DE102021123871A1 - PROJECTION SYSTEM - Google Patents

Abstract

The invention relates to a projection system (1) for the superimposed display of image content, having a substrate (2) on which a VCSEL array (4) is applied, the VCSEL array (4) being an array of surface emitters (6), a lens array (8) downstream of the VCSEL array (4) in the beam path, the lens array (8) being an array of collimator optics (10), a DOE array downstream of the lens array (8) in the beam path Array (12), wherein the DOE array (12) is an array of individual diffractive optical elements (14), each containing an image content to be displayed, and an imaging plane (16) downstream of the DOE array (12) in the beam path, wherein the DOE array (12) is formed so that the image content of the diffractive optical elements (14) are superimposed in the imaging plane (18).

Description

The invention is based on a projection system for the superimposed display of image content.

There are various technical options for displaying an animation of a movement, with individual images usually being displayed one after the other at short intervals, so that the impression of the movement is conveyed when looking at it. Such a representation is also referred to as semi-dynamic.

Examples of the different technical possibilities include a digital micromirror unit ("DMD", Digital Micromirror Device), a liquid crystal display ("LCD", Liquid Crystal Display), liquid crystals on a silicon substrate ("LCoS", Liquid Crystal on Silicon) or an organic light-emitting diode (“OLED”, Organic Light Emitting Diode), with which both projections and displays can be set up.

These technical solutions differ in their resolution, their maximum achievable contrast or their luminance, which are decisive features depending on their application. For example, these technical solutions can be used in home entertainment or in the automotive sector to project warnings, welcome scenarios or to display information on displays.

However, previous solutions in particular do not meet all the requirements with regard to optical efficiency, simple construction and space efficiency.

The object of the present invention is to provide a (semi-)dynamic projection system in particular, which has good optical efficiency and is constructed as simply and compactly as possible.

This object is achieved by a projection system having the features of claim 1, claim 8 and claim 9, respectively.

Particularly advantageous configurations can be found in the dependent claims.

According to the invention, a projection system for the superimposed display of image content is provided. The projection system has a substrate on which a VCSEL array is applied, the VCSEL array being an array of surface emitters. These surface emitters are often referred to by their English term as VCSEL, i.e. vertical-cavity surface-emitting laser. In addition, the projection system has a lens array downstream of the VCSEL array in the beam path, the lens array being an array of lenses/collimator optics. Furthermore, the projection system has a DOE array downstream of the lens array in the beam path, the DOE array being an array of individual diffractive optical elements (DOE, diffractive optical element) each containing image content to be displayed. In addition, the projection system has an imaging plane downstream of the DOE array in the beam path. The projected image content is displayed on the imaging level. According to the invention, the DOE array is designed in such a way that the image contents of the diffractive optical elements are superimposed in the imaging plane.

This means that the projection system is used to display image content on the imaging plane/projection plane, with the image content being spatially superimposed/projected onto the same imaging surface. The projection system comprises the substrate with the VCSEL array, where a VCSEL is a laser diode in which the light is emitted perpendicular to the plane of its semiconductor chip (in contrast to an edge-emitting laser diode, in which the light is emitted at one or two flanks of its semiconductor chip exit). In particular, a VCSEL is an optoelectronic device made up of quantum wells sandwiched between two Distributed Bragg Reflectors (“DBR”). The projection system has the lens array for beam shaping, which is arranged stacked above the VCSEL array, and the DOE array, which is arranged stacked above the lens array and carries the image information to be projected. The diffractive optical elements can be glass carriers on which microstructures are applied by photolithography, so that phase modulations occur in them due to different optical path lengths of the partial beams, which creates interference patterns, with the amplitude being able to be modulated additionally by constructive and destructive superimposition. In general, diffractive optical elements can be used for beam shaping (beam shaping) or for dividing a laser beam into several partial beams (beam splitting). In addition, the projection system has the imaging plane downstream of the DOE array in the beam path, on which the light beams diffracted by the optical grating of the DOE array are imaged and the image information of the DOE array is projected. Each diffractive optical element contains an image (or a partial image), so that sequential or parallel activation of the lasers, i.e. the VCSEL array, and superimposition of the images (or partial images) in the imaging plane/projection plane creates the impression of a moving image can arise. According to the invention, a semi-dynamic projection with VCSEL and DOE is thus proposed.

The projection system according to the invention has the advantage that it can be constructed in a particularly compact manner through the use of the diffractive optical elements. Thus, in the projection system according to the invention, the focus is not on the dynamics of the image content, but rather on the compactness, the simple structure and the optical efficiency of the overall system. In contrast to overall systems that work with micromirrors, liquid crystals or the like and can achieve an optical efficiency of approx. 30%, the optical efficiency of a diffractive optical element is more than 80%, depending on the number of stages. In addition, the projection system according to the invention can be constructed less complex and more cost-effectively with regard to the structure of the optical path and the control than the mentioned systems with micromirrors, liquid crystals or the like. In addition, the use of VCSELs in the projection system according to the invention has the advantage that they can be constructed with high positional precision in relation to one another, so that precise superimposition is made possible.

According to a preferred development of the projection system, at least two of the diffractive optical elements can have different image content. The image content of the at least two diffractive optical elements can preferably be slightly different, i.e. partially identical. This has the advantage that the projection system can be used for motion animation by activating the optical channels/paths of the projection system, i.e. the surface emitters/VCSELs individually, in quick succession. In this context, in quick succession in time means that the individual optical paths are activated at intervals of a few milliseconds to a few 100 milliseconds. Alternatively, the image content of the at least two diffractive optical elements can have different structures, such as warnings or symbols, so that (completely) different image content can be displayed with the projection system, depending on the application. In particular, each of the diffractive optical elements can carry its own image content that differs from the other diffractive optical elements.

According to a preferred development of the projection system, at least two of the diffractive optical elements can have an identical image content. This has the advantage that an intensity increase can be achieved by superimposing identical image content in the imaging plane, which can contribute to improving perceptibility in daylight, for example. The overlay can be achieved in particular by simultaneously activating the optical channels/paths of the projection system, i.e. the surface emitters/VCSELs that are connected upstream of the diffractive optical elements with the same image content.

According to a preferred development of the projection system, the diffractive optical elements can be wavelength-dependent, with a first diffractive optical element being designed for red light, a second diffractive optical element being designed for green light, and a third diffractive optical element being designed for blue light. Due to their optical properties, diffractive optical elements can only be optimally designed for a specific wavelength. If a diffractive optical element is provided for red, green and blue for each (different) image content to be displayed and the projections are superimposed in the imaging plane, color mixing can be achieved and any color can be generated with the projection system.

According to a preferred development of the projection system, the diffractive optical elements can be produced on a wafer basis and/or by means of a glass master (stamper). The optical paths of the projection system can be aligned with high positional precision, particularly in wafer-based production.

According to a preferred development of the projection system, a spacer can be arranged between the substrate on which the VCSEL array is applied and the lens array. A particularly exact distance between the two arrays can thus be achieved, so that a compact projection system can be formed.

According to a preferred development of the projection system, a spacer can be arranged between the lens array and the DOE array. A particularly exact distance between the two arrays can thus be achieved, so that a compact projection system can be formed.

According to a preferred development of the projection system, the VCSEL array can be a monochromatic VCSEL array. This means that all surface emitters emit the same wavelength, which is advantageous for the production of all surface emitters on one substrate, since the VCSEL array then has an integrated structure with tight tolerances and can be produced with simple production steps.

According to a preferred development of the projection system, the VCSEL array, particularly if it is a monochromatic VCSEL array, can be followed by a laser crystal with non-linear optics in the beam path for frequency doubling or frequency tripling of light emitted from the surface emitters. This means that the surface emitters only serve as a pump source for laser crystals, with which the desired wavelengths are generated by single-pass frequency doubling (“SHG”, second harmonic generation) or frequency trebling (“THG”, third harmonic generation). The VCSEL array can preferably emit light with a wavelength of 808 nm, since such surface emitters are sufficiently available and their properties are known. Alternatively, wavelengths of 850 nm or 940 nm are also possible for adapted laser crystals. It is therefore possible with the laser crystal, such as Nd:Yag, depending on the doping, to produce red light from light with a wavelength of 808 nm by frequency doubling, i.e. light with a wavelength of 660 nm (in the case of a laser crystal Nd:Yag with a doping of 1320 nm ) or green light, ie light with a wavelength of 530 nm, (for a laser crystal Nd:Yag with a doping of 1060 nm) or by frequency doubling blue light, ie light with a wavelength of 440 nm (for a laser crystal Nd:Yag with a doping of 1320 nm).

With the arrangement described, wavelengths which are not commercially available and at which the mixture collides with the wavelength-dependent design of the diffractive optical elements can also be produced by direct emission. For example, the yellow indicator used in the automotive sector, which has a wavelength of 587 to 597 nm and cannot be generated by mixing a green and a red laser due to the wavelength-dependent design of the diffractive optical elements, can be generated by frequency doubling by using a fundamental wavelength (i.e. a wavelength of the surface emitters) of 1174 nm to 1195 nm is used. Since such surface emitters with wavelengths >1000 nm already exist, turn signal yellow can also be produced with the arrangement described.

According to a preferred development of the projection system, an independent laser crystal for frequency doubling or frequency trebling can be mounted in front of each of the surface emitters, or several surface emitters can be provided with a common laser crystal. The diffractive optical element downstream of the respective surface emitter and laser crystal is designed according to the wavelength emitted by the laser crystal.

Alternatively, another excitation source could be used instead of a VCSEL array, whereby the laser crystal with the non-linear optics can also be placed in the resonator in order to achieve higher frequency conversion efficiency. This can be done, for example, via externally optically pumped disk lasers or via internally pumped systems, each with an external resonator mirror.

According to a further aspect of the invention, a projection system for the superimposed representation of structures is provided, with a substrate on which a VCSEL array is applied, the VCSEL array being an array of surface emitters, a DOE directly downstream of the VCSEL array in the beam path Array, wherein the DOE array is an array of individual diffractive optical elements, each containing an image content to be displayed, wherein the VCSEL array and the DOE array are designed such that emission angles of the VCSEL array are within acceptance angles of the DOE array, and an imaging plane downstream of the DOE array in the beam path, the DOE array being designed in such a way that the image contents of the diffractive optical elements are superimposed in the imaging plane. In terms of structure, the projection system essentially corresponds to the projection system already described, the projection system according to the further aspect having no lens arrays arranged between the VCSEL array and the DOE array. The lens array can be dispensed with if the emission angles/divergence angles of the surface emitters match the acceptance angles of the diffractive optical elements, so that no beam shaping by the lens array is required. The divergence angles of the surface emitters/lasers can be in the range of a few degrees.

According to another aspect of the invention, a projection system for the superimposed representation of structures is provided, with a laser, a movable micromirror downstream of the laser in the beam path, a DOE array downstream of the micromirror in the beam path, the DOE array being an array of individual, respectively is diffractive optical elements containing an image content to be displayed, and an imaging plane downstream of the DOE array in the beam path, characterized in that the projection system has a control unit for controlling a movement of the micromirror, which is designed to move the micromirror in such a way that the Laser-emitted light is deflected onto individual diffractive optical elements, and that the DOE array is designed such that the image contents of the diffractive optical elements are superimposed in the imaging plane.

This means that the DOE array is used in combination with a micromirror as a controllable laser deflection unit to create a motion animation. The laser beam is guided sequentially over the segmented DOE structure and activated at defined points in time.

According to a preferred development of the projection system, the control unit for activating the laser can be designed in such a way that it synchronizes the movement of the micromirror and the activation of the laser. The movement of the micromirror is thus activated by the activation of the laser via the control unit, so that the laser is activated precisely when the micromirror is moved or is aligned with another diffractive optical element. The temporally offset superimposition of the projection in the imaging plane creates the impression of a moving image.

According to a preferred development of the projection system, at least two of the diffractive optical elements can have different image content. The image content of the at least two diffractive optical elements can preferably be slightly different, i.e. partially identical. This has the advantage that the projection system can be used for motion animation by activating the optical channels/paths of the projection system, i.e. the surface emitters/VCSELs individually, in quick succession. In this context, in quick succession in time means that the individual optical paths are activated at intervals of a few milliseconds to a few 100 milliseconds. In particular, each of the diffractive optical elements can carry its own image content that differs from the other diffractive optical elements.

In summary, the projection system according to the invention has the advantages that imaging optics are not required after the diffractive optical element, that diffractive optical elements offer a very efficient option for projection, that a very flat, compact structure is possible, that the use of arrays (VCSEL -Array, lens array, DOE array) a very high level of precision can be achieved when aligning the optical elements to one another, that all colors are mixed through the combination of diffractive optical elements for defined wavelengths RGB, which are superimposed in the imaging plane that due to the infinite depth of focus of the image of the diffractive optical elements, this is advantageous for oblique projection, and that high luminance levels can be achieved, which can improve perceptibility in daylight.

In addition to image projection, the approach described can also be used, for example, for a stripe projection for object recognition/for 3D scans, in order to present strips or knife patterns of different widths and thereby improve the detection accuracy using a camera, which is particularly important when using lasers in the infrared wavelength range can be beneficial.

• 1 einen schematischen Aufbau eines Projektionssystems gemäß einem ersten Ausführungsbeispiel;
• 2 einen schematischen Aufbau des Projektionssystems gemäß einer Modifikation des ersten Ausführungsbeispiels;
• 3 einen schematischen Aufbau des Projektionssystems gemäß einer weiteren Modifikation des ersten Ausführungsbeispiels;
• 4 eine schematische Querschnittsdarstellung des Projektionssystems gemäß der weiteren Modifikation, entlang der Linie IV-IV in 3; und
• 5 einen schematischen Aufbau des Projektionssystems gemäß einem zweiten Ausführungsbeispiel.

The invention is to be explained in more detail below using exemplary embodiments. The figures show:

• 1 a schematic structure of a projection system according to a first embodiment;
• 2 a schematic structure of the projection system according to a modification of the first embodiment;
• 3 a schematic structure of the projection system according to a further modification of the first embodiment;
• 4 a schematic cross-sectional representation of the projection system according to the further modification, along the line IV-IV in 3 ; and
• 5 a schematic structure of the projection system according to a second embodiment.

1 until 4 show a schematic structure of a projection system 1 according to the invention according to a first embodiment with different modifications.

The projection system 1 is used for the superimposed display of image content. The projection system 1 has a plurality of optical paths/channels/projection paths which are aligned with one another through the use of arrays. In the illustrated embodiment, the projection system has 1 arrays that form 3x2 projection paths.

The projection system 1 has a substrate 2 on which a VCSEL array 4 is applied. The VCSEL array 4 is an array of surface emitters/VCSEL, ie vertical-cavity surface-emitting laser, 6. In addition, the projection system 1 has a lens array 8 downstream of the VCSEL array 4 in the beam path. The lens array 8 is an array of lenses/collimator optics 10. Furthermore, the projection system 1 has a DOE array 12 downstream of the lens array 8 in the beam path. The DOE array 12 is an array of individual diffractive optical elements 14, each containing an image content to be displayed. In addition, the projection system 1 has an image downstream of the DOE array 12 in the beam path level/projection level 16 on. The projected image content is displayed on the imaging plane.

According to the invention, the DOE array 12 is designed in such a way that the image contents of the (individual) diffractive optical elements 14 are superimposed in the imaging plane 16 .

The image content of the (individual) diffractive optical elements 14 can be different, so that different image content can be projected. If the various image contents are successively projected onto the imaging plane 16 at short time intervals, i.e. at intervals between a few and a few 100 milliseconds, the impression of an animation can be generated. Alternatively, the image content of the (individual) diffractive optical elements 14 can be identical, so that the same image content can be projected into the imaging plane 16, with the same image content being able to be displayed with a higher luminance through temporal superimposition.

2 shows a modification of the in 1 illustrated first embodiment, in which the diffractive optical elements 14 are wavelength-dependent. A first diffractive optical element 14a is designed for red light, a second diffractive optical element 14b is designed for green light, and a third diffractive optical element 14c is designed for blue light. In addition, the respective surface emitters emit light of a specific wavelength. A first surface emitter 6a emits red light, a second surface emitter 6b green light and a third surface emitter 6c blue light. Thus, for each image content to be displayed, a diffractive optical element 14 is provided for red, green and blue, with the projection of which in the imaging plane 16 color mixing can be achieved.

3 shows a modification of the in 1 illustrated first exemplary embodiment, in which a first spacer 18 is arranged between the substrate 2 and the lens array 8 and in which a second spacer 20 is arranged between the lens array 8 and the DOE array 12 .

In addition, 3 It can be seen that the surface emitters 6 have a diameter 22 of 200 µm and are arranged at a distance 24 of 1000 µm. Thus, the distance 24 is about five times as large as the diameter 22 of the surface emitters 6.

Furthermore, in 3 It can be seen that the surface emitters 6 have a radiation cone 26 whose divergence angle 28 is approximately 10° in the exemplary embodiment shown. The emission cone strikes the collimator optics 10 and emerges from the lens array 8 and into the DOE array 12 in an almost parallel bundle of rays 30 .

In 4 it can be seen that the surface emitters 6 are arranged in the 2×3 array, with the distances 24 between the surface emitters 6 being equal. The first spacer 18 is arranged around the surface emitters 6 .

5 shows a schematic structure of a projection system 32 according to the invention according to a second embodiment.

The projection system 32 has a laser 34 . In addition, the projection system 32 has a movable micromirror 36 downstream of the laser 34 in the beam path. Furthermore, the projection system 32 has a DOE array 40 downstream of the micromirror 36 in the beam path. The DOE array 40 is an array of individual diffractive optical elements 42, each containing an image content to be displayed. In addition, the projection system 32 has an imaging plane 44 downstream of the DOE array 40 in the beam path.

According to the invention, the projection system 32 has a control unit 46 for controlling a movement of the micromirror 36 . The control unit 46 is designed to move the micromirror 36 in such a way that light emitted by the laser 34 is deflected onto the individual diffractive optical elements 42 . In addition, the DOE array 40 is designed in such a way that the image contents of the diffractive optical elements 42 are superimposed in the imaging plane 44 . The control unit 46 for activating the laser 34 is preferably designed in such a way that it synchronizes the movement of the micromirror 36 and the activation of the laser 34 . In particular, the control unit 46 is connected via a mirror driver 48 to the micromirror 36 for its movement control. In addition, the control unit 46 is connected to the laser 34 in particular via a laser driver 50 in order to activate it.

Reference List

1; 32

projection system

2

substrate

4

VCSEL array

6

Surface Emitter/VCSEL

6a

first surface emitter

6b

second surface emitter

6c

third surface emitter

8th

lens array

10; 38

Lens/Collimator Optics

12; 40

DOE array

14; 42

diffractive optical element

14a

first diffractive optical element

14b

second diffractive optical element

14c

third diffractive optical element

16; 44

imaging plane/projection plane

18

first spacer

20

second spacer

22

diameter

24

Distance

26

radiation cone

28

divergence angle

30

bundle of rays

34

Laser

36

micromirror

46

control unit

48

mirror driver

50

laser driver

Claims (10)

Projection system (1) for the superimposed display of image content, having a substrate (2) on which a VCSEL array (4) is applied, the VCSEL array (4) being an array of surface emitters (6), a VCSEL Array (4) downstream lens array (8) in the beam path, wherein the lens array (8) is an array of collimator optics (10), a lens array (8) downstream in the beam path DOE array (12) , wherein the DOE array (12) is an array of individual diffractive optical elements (14), each containing an image content to be displayed, and an imaging plane (16) downstream of the DOE array (12) in the beam path, characterized in that the DOE -Array (12) is designed such that the image contents of the diffractive optical elements (14) are superimposed in the imaging plane (18). Projection system (1) according to claim 1 , characterized in that at least two of the diffractive optical elements (14) have a different image content. Projection system (1) according to claim 1 or 2 , characterized in that at least two of the diffractive optical elements (14) have an identical image content. Projection system (1) according to one of Claims 1 until 3 , characterized in that the diffractive optical elements (14) are wavelength-dependent, with a first diffractive optical element (14a) being designed for red light, a second diffractive optical element (14b) being designed for green light, and a third diffractive optical element Element (14c) is designed for blue light. Projection system (1) according to one of Claims 1 until 4 , characterized in that the diffractive optical elements (14) are produced on a wafer basis and/or by means of a glass master. Projection system (1) according to one of Claims 1 until 5 , characterized in that a spacer (18) is arranged between the substrate (2), on which the VCSEL array (4) is applied, and the lens array (8) and/or that between the lens array (8 ) and the DOE array (12) a spacer (20) is arranged. Projection system (1) according to one of Claims 1 until 6 , characterized in that the VCSEL array is a monochromatic VCSEL array, wherein the VCSEL array for frequency doubling or frequency tripling of light emitted from the surface emitters is followed by a laser crystal with non-linear optics in the beam path. Projection system for the superimposed display of image content, with a substrate on which a VCSEL array is applied, the VCSEL array being an array of surface emitters, a DOE array directly downstream of the VCSEL array in the beam path, the DOE array being an array of individual diffractive optical elements each containing an image content to be displayed, the VCSEL array and the DOE array being designed in such a way that emission angles of the VCSEL array are within acceptance angles of the DOE array, and an imaging plane downstream of the DOE array in the beam path , characterized in that the DOE array is designed in such a way that the image contents of the diffractive optical elements are superimposed in the imaging plane. Projection system (32) for the superimposed display of image content, having a laser (34), a movable micromirror (36) downstream of the laser (34) in the beam path, a DOE array (40) downstream of the micromirror (36) in the beam path, the DOE array (40) is an array of individual diffractive optical elements (42), each containing an image content to be displayed, and an imaging plane (44) downstream of the DOE array (40) in the beam path, characterized in that the projection system (32) has a control unit (46) for controlling a movement of the micromirror (36), which is designed to move the micromirror (36) in such a way that light emitted by the laser (34) is deflected onto individual diffractive optical elements (42), and that the DOE array (40) is designed in such a way that the image contents of the diffractive optical elements (42) are superimposed in the imaging plane (44). Projection system (32) according to claim 9 , characterized in that the control unit (46) for activating the laser (34) is designed in such a way that it synchronizes the movement of the micromirror (36) and the activation of the laser (34).

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