WO2007014551A1

WO2007014551A1 - Apparatus for switchable image projection with diffractive optical elements

Info

Publication number: WO2007014551A1
Application number: PCT/DE2006/001339
Authority: WO
Inventors: Ulrich Babst; Thorsteinn Halldorsson; Andreas Prücklmeier
Original assignee: Airbus Deutschland Gmbh
Priority date: 2005-08-04
Filing date: 2006-08-01
Publication date: 2007-02-08
Also published as: DE102005037435B4; DE102005037435A1

Abstract

An apparatus for switchable image projection (10) comprises diffractive optical elements (16, 16a) which in each case generate a pattern for image projection upon impingement of a narrowband light beam (13) by diffraction, a light source (11) for generating the narrowband light beam (13) for the image projection, and a device (50) for moving the light beam over the diffractive optical elements (16, 16a) in order to generate successively different patterns. In this case, the device (50) for moving the light beam (13) comprises a lens (12) and a pivotable mirror (14) arranged at the focus of the lens (12), the lens (12) being arranged between the pivotable mirror (14) and the diffractive optical elements (16, 16a).

Description

Device for switchable image projection with diffractive optical elements

The invention relates to a device for switchable image projection with diffractive optical elements according to the preamble of patent claim 1 and a method for switchable image projection with diffractive optical elements according to the preamble of patent claim 17.

Switchable image projections can be used, for example, in aircraft passenger cabins to display changing information to the passenger on surfaces or on objects. For example, seat occupancy can be displayed by projection on interior walls or on the seats themselves. Furthermore, for example, current flight information, logos of the airline or even current purchase offers the passengers can be displayed by image projections. In addition, it is also possible to give a different optical design through switchable colored projections or pattern passenger spaces in a flexible manner.

Also in other rooms, such as in trains, waiting rooms or other common rooms, or on walls and other surfaces, changing image projections are used to inform people and for flexible optical design.

Diffractive optical elements (DOEs) illuminated by narrow-band light offer the possibility of projection-independent image generation and cheap mass production. They can be used in many applications, especially where defined stationary image patterns, such as characters, logos, pictograms, logos or frames, are to be projected with lasers onto a surface as information, entertainment, warning or advertisement. Another advantage of this type of projection over classical shadow or slide projection is that it uses all incident light, not just part of it is allowed through. Compared with a scanned laser projection, the DOE as an imaging element also has the advantage that it requires no complicated dynamic deflection and intensity modulation.

Diffractive optical elements or DOEs, also called synthetic holograms, are known to be used for beam splitting and beam shaping and thus also for pattern and image generation with laser beams. Here, the result of the classical diffraction theory of light is exploited, that any desired light wave corresponds to a diffractive surface structure or a complex transmission function - with which it can also be produced in a simple manner.

The static images, which are initially imprinted as diffraction patterns into an optical carrier material and which are projected onto image surfaces by division and deflection of collimated laser beams after passing through a carrier material, are switched over by successively illuminating different diffractive optical elements , This is done by means of turning and feeding devices.

When using DOEs, lasers are essentially used as the light source because they very well presuppose defined wavefronts, i. good bundling and a narrow spectral width that can be achieved with lasers of sufficient quality.

With a corresponding interpretation of the far field diffraction or

Fraunhof diffraction, which describes diffraction patterns at infinity, can be used to split a collimated laser beam into a flock of rays of specific intensity and direction using a DOE. Almost any two-dimensional pattern can be imaged that is sharp regardless of the distance on a projection screen. In contrast, in a beam-forming DOE, the diffracted light is imaged in a specific position behind the diffractive structure, ie in the near field, convergent or divergent (Fresnel diffraction). This function of DOEs can then be used to model the function of classical optical elements such as lenses and mirrors in the imaging of monochromatic laser light.

Today, DOEs are calculated wave-theoretically in the computer and exposed using microlithography technology of modern electronics as a master. Subsequently, they are transferred and duplicated using a stamping technique, similar to the production of surface holograms, on permeable or reflective surfaces of plastics or glasses.

In the case of image reproduction, usually a collimated laser beam whose diameter is typically 1.5 mm falls on a square DOE whose side length is approximately 2 mm and whose structure width is approximately 0.1 μm to 10 μm. Mostly, the DOE is structured in binary form as a diffraction grating on the surface. Traversing through this structure of the DOE, the laser beam diffracts in the desired manner. The diffraction structure can be designed so that the entire laser power in only one of the low diffraction order, z. B. the + 1-th order of diffraction is concentrated. For elements in which also portions of the -1-th or the O-th diffraction order arise, these disturbance orders can be suppressed by additional suppression in the beam path.

In most applications, multiple DOEs with different images are grouped together on a rectangular, translucent glass or plastic panel side-by-side in rows and columns, where they are sequentially illuminated during image display. This arrangement of the elements in rows and columns is particularly advantageous because they are exposed horizontally and vertically also with a usual for electron lithography feed mode. Thus, even the cheapest playback is either the translational horizontal and vertical movement of the substrate plate of the DOEs in front of a stationary laser beam, or the translational movement of the laser beam itself along the substrate.

These horizontal and vertical movements to switch from one DOE to the other have hitherto been performed by means of a stepper motor driven XY table. This construction is too costly and too expensive for the small DOEs and in mass production very cheap elements for many applications.

The object of the invention is to provide a device for image projection with DOEs, in which the switching between the DOEs is realized simpler, more compact and less expensive. Furthermore, a corresponding method for switchable image projection with DOEs is to be specified, which is simple and inexpensive to carry out with a compact design.

This object is achieved by the apparatus for switchable image projection with diffractive optical elements according to claim 1 and by the method for switchable image projection with diffractive optical elements according to claim 17. Further advantageous features, aspects and details of the invention will become apparent from the dependent claims, the description and the drawings.

The switchable image projection device according to the invention comprises diffractive optical elements which generate a pattern for image projection upon impact of a narrowband light beam or laser beam, a light source for generating the narrowband light beam for the image projection, and a device for moving the light beam via the diffractive optical elements to produce successively different patterns, the means for moving the light beam comprising a lens and a pivotable mirror disposed in the focus of the lens, and wherein the lens is disposed between the pivotable mirror and the diffractive mirror is arranged optical elements.

The invention exploits the property of a condenser lens that all sub-beams of an incident, parallel to the lens axis and collimated beam in the focus of the lens, i. at the focal point on the lens axis. After reflecting on a mirror - whose plane contains the focal point - the rays are thrown back to the lens and leave the lens in the opposite direction than a parallel and collimated beam with the incoming rays (cat's eye reflection principle).

This principle is used according to the invention to perform a translatory movement over an extended substrate area of an array of DOEs, thereby achieving a simpler, more compact and less expensive switchable image projection.

Preferably, the pivotable mirror is designed as a biaxial micro-electro-mechanical mirror scanner and fixed, for example, in a two-axis gimbal.

With the help of the biaxial deflection of very compact and cost-effective micromirrors results in a particularly compact and very cost-effective design.

The mirror preferably has an electrostatic, magnetic or piezoelectric drive. Advantageously, the axes of rotation of the mirror are aligned in alignment with the arrangement of the DOEs in rows and columns. The axes of rotation of the mirror are preferably aligned substantially orthogonal to each other. The orthogonal axes intersect, for example, in a point in space and can, for example, be moved by an angle of up to +/- 15 ° Depending on the design, the mirror scanner can be operated in two different ways, either resonantly, ie with a fixed deflection frequency as so-called "digital micromirror", or analogously as a so-called "analog micromirror" for deflection to defined, fixed scan angles in a switching time of a few milliseconds. wherein for the invention, the second mode, that is, the switching to many different discrete positions, is particularly suitable.

Preferably, the diffractive optical elements are arranged in a planar array. Advantageously, the planar arrangement of diffractive optical elements is arranged parallel to the lens on the side of the lens opposite the mirror.

The lens may in particular be designed as a holographic lens. However, it is also possible to use a conventional refractive optical lens.

The lens and the mirror are arranged in the beam path of the laser beam, for example, such that the laser beam is reflected back onto the lens after passing through the lens and permeates again, in order subsequently to depend on the mirror position on one of the diffractive optical elements located behind the lens hold true.

The lens and the mirror are in particular arranged in the beam path of the laser beam, that the incoming laser beam penetrates the lens parallel to the lens axis and after reflection on the pivoting mirror and re-lens passage, the lens parallel to the incoming laser beam leaves to then in response to the mirror position on a meet behind the lens located diffractive optical elements.

Preferably, a deflection mirror is provided, which is arranged on the lens axis, in order to align the incident laser beam in such a way that it lies on the Lens axis through the center of the lens meets the pivoting mirror.

The light source comprises, for example, means for generating RGB laser beams, which are guided together through the lens onto the pivotable mirror. This results in a colored image projection.

In order to project a colored pattern, it is particularly preferable in each case to arrange a plurality of diffractive optical elements with different feature sizes in close proximity. As a result, size differences in the projection can be compensated for with different wavelengths.

The device for moving the laser beam may, for example, also comprise a plurality of holographic lenses, which are preferably arranged as stacks, each holographic lens serving to image an RGB wavelength and transmitting remaining RGB wavelengths largely without interference.

The method according to the invention serves for switchable image projection with diffractive optical elements, which generate a pattern for image projection upon impact of a narrow-band light beam or laser beam by diffraction, respectively, and comprises the steps:

Generation of the narrowband light beam for image projection; Moving the light beam across the diffractive optical elements to produce successively different patterns; wherein the light beam is moved with a pivotable mirror over the diffractive optical elements, and wherein the mirror is arranged in the focus of a lens, which is located between the diffractive optical elements and the mirror.

Advantageously, the method is carried out with a device according to the invention. The invention will be described by way of example with reference to the figures, in which

Fig. 1 shows an apparatus for switchable image projection according to a first preferred embodiment of the invention;

Fig. 2 is a plan view of a DOE array;

Fig. 3 shows a reversible image projection apparatus according to a second preferred embodiment of the invention with a holographic lens;

Fig. 4 shows a switchable image projection apparatus according to a third preferred embodiment of the invention for projecting multicolor images;

Fig. 5 shows an apparatus for switchable image projection according to a fourth preferred embodiment of the invention with a stack of holographic lenses.

In the various figures, components and elements having substantially the same functions or properties are identified by the same reference numerals.

1 shows a device 10 for switchable image projection as a first variant of the construction of a DOE projector with only one monochromatic laser 11 as the light source and with a lens 12 for focusing the laser beam 13 generated by the laser 11 onto a pivotable micromirror 14.

The micromirror 14 is designed as a MEMS scanner. The mirror or

Micromirror 14 mirrors the incident, collimated laser beam 13, which is focused on the optical axis of the lens 12 at its focal point to the double angle of incidence back. The mirroring back is done in such a way that the back-mirrored laser beam 15 after passing through the lens 12 has the same diameter as the incident laser beam 13 before passing through the lens 12 and with the optical axis of the lens 12 is exactly parallel but in the opposite direction.

Parallel to the lens, a plurality of diffractive optical elements 16 (DOEs) are arranged as a planar array on a substrate 17 such that the reflected laser beam 15 strikes the DOE surface after passing through the lens 12.

The arrangement comprising the lens 12 and the mirror or micromirror 14 forms a device 50 for moving the light beam or laser beam 13, 15 via the diffractive optical elements 16.

Upon rotation of the scan or micromirror 14, the laser beam 13 incident along the lens axis is translated in two directions over the DOEs 16 on the substrate surface, such that each angular coordinate (φi.ψ _j ) is a spatial coordinate (Xj ₁ Vj). , as shown in Fig. 1, corresponds to the substrate 17. In traversing the DOE 16a, the incident beam in the diffraction structure is split and deflected in the desired manner.

With this arrangement and appropriate control of the micromirror 14, the individual DOEs 16 of the array are illuminated one behind the other discretely in any order. As a result, the images stored in them are called in succession or projected onto a surface not shown in the figure.

The switchable image projection apparatus 10 further comprises an arrangement of deflecting mirrors 18a, 18b which guide the narrowband light beam generated by the laser 1 1 to the lens 12 so as to be incident on the lens axis or parallel to the lens axis, the lens 12 penetrates. In the apparatus 10 shown here, the deflection mirror 18b is fixed to a window 19 at a position lying on the lens axis. Through the window 19, the diffracted by the DOEs 16 light beams leave the projector or the device 10th

By a switching arrangement or mirror control, which outputs a corresponding signal and is not shown in the figures, the mirror 14 is driven in order to effect the pivoting movements and thereby the switching between the DOEs.

According to a particularly preferred embodiment of the invention, the control of the mirror 14 takes place in such a way that the image of each DOE in the projection is set into a randomized or randomly controlled movement in two axes. The rashes of this movement are in the order of magnitude of the roughness of the surface, which is typically in the range of 10 .mu.m to 100 .mu.m. However, they are well below the pixel size of the image of the DOE and the resolution limit of the eye on the projection screen, i. typically well below the order of 1000μm.

Through this movement, an averaging of speckles in the eye of the beholder takes place. Such image speckies generally arise in an image projection with lasers on a rough surface. That is, by the above-described special control of the mirror, the emergence of Bildspeckeis is solved due to image roughness in the eye of the beholder.

The randomized two-dimensional movement over the image surface and thus over the surface of each DOE can be accomplished by superimposing a corresponding Randomsignals to the already existing signal to control the mirror of the 2-axis microscanner with simple electronic means. FIG. 2 shows a top view of the array of DOEs 16, which are arranged on the substrate 17 in rows and columns. It is shown schematically how the beam 13 coming from the laser 11 penetrates the substrate 17 from its front side at an opening 4 in the center is then reflected at the pivotable mirror 14 located behind the DOE array or substrate 17, and then penetrates the substrate 17 from the rear side at the DOE 16a defined by the mirror position, the beam being diffracted by the DOE 16a and selected pattern for image projection generated.

A particular advantage of these DOE-projected laser images is that they are sharp at any distance. They increase with increasing distance due to the angular spread of the deflected rays, but still take on the same angle of view in the eye of a fixed observer. With an oblique projection on smooth surfaces and with projection on curved surfaces, the resulting image distortion can be taken into account by a predistortion of the image during the production of the DOEs.

FIG. 3 shows a further variant of the structure with a monochromatic light source 11 or laser source. In this case, instead of the lens 12 of the construction shown in FIG. 1, a holographic lens 22 is provided as a DOE for beam focusing or beam shaping. Preferably, the holographic lens 22 is fabricated with a volume phase hologram as a transmission structure. As a result, even greater advantages in terms of compact design and standardization of the techniques used can be achieved.

4 shows a further variant of the construction with three monochromatic RGB lasers 11 for the projection of multicolor images with three DOEs 16r, 16g, 16b of different structure size for three RGB wavelengths for canceling the different diffraction angle as a function of the wavelength, and for the projection of multicolored pictures. Since the projection takes place due to light diffraction, an image remains exactly the same geometrically when using different laser wavelengths, but it increases in size - since the diffraction angle is wavelength-dependent - at a fixed projection distance, to or from. With a simultaneous three-color laser illumination, red, green and blue (RGB), therefore, a DOE produces exactly the same images with the scaling of the different wavelengths of different sizes.

In order to avoid this effect in a desired projection of multicolor images, as shown in Figure 4, three DOEs 16r, 16g, 16b for a pattern are in close proximity, but corresponding to the different wavelengths, each having a different feature size, applied as arrays on the common carrier 17. In the far field, due to the natural divergence of the colored single rays, the rays overlap to form a uniform image of equal size for all wavelengths in the projection.

Fig. 5 shows a variant of the structure of Fig. 4, wherein the common lens is replaced by a stack 52 of three holographic lenses 22, and each of the individual lenses 22 as volume phase holograms contributes to the imaging only for one of the three RGB wavelengths and lets others through without interference.

It goes without saying that the beam path between DOE and micromirrors can be shortened with a conventional convolution with deflecting mirrors, and chromatically corrected lenses can be used for the imaging of multicolor laser beams.

Claims

claims

1 . Device for switchable image projection with diffractive optical elements (16, 16a), which is incident upon the arrival of a narrowband

Light beam (13) by diffraction each generate a pattern for image projection, a light source (11) for generating the narrow-band light beam

(13) for image projection, and means (50) for moving the light beam across the diffractive optical elements (16, 16a) to produce successively different patterns, characterized in that the means (50) for moving the light beam (13 ) a lens

(12; 22) and a pivotable mirror (14) arranged in the focus of the lens (12; 22), the lens (12; 22) being arranged between the pivoting mirror (14) and the diffractive optical

Elements (16, 16a) is arranged.

2. Apparatus according to claim 1, characterized in that the pivotable mirror (14) as a biaxial micro-electro-mechanical

Mirror scanner is designed.

3. Apparatus according to claim 1 or 2, characterized in that the pivotable mirror (14) is fixed in a two-axis gimbal.

4. Device according to one of the preceding claims, characterized in that the mirror (14) comprises an electrostatic, magnetic or piezoelectric drive.

5. Device according to one of the preceding claims, characterized in that the axes of rotation of the mirror (14) in their Alignment are movable.

6. Device according to one of the preceding claims, characterized in that the axes of rotation of the mirror (14) are aligned substantially orthogonal to each other.

7. Device according to one of the preceding claims, characterized in that the diffractive optical elements (16, 16 a) are arranged like an array as an array.

8. Device according to one of the preceding claims, characterized in that the lens (22) is designed as a holographic lens.

9. Device according to one of the preceding claims, characterized in that the lens (12; 22) and the mirror (14) are arranged in the beam path of the light beam such that the light beam after passing through the lens (12; 22) back to the lens is reflected and penetrates again, in order subsequently to hit, depending on the mirror position, on one (16a) of the diffractive optical elements (16) located behind the lens (12;

10. Device according to one of the preceding claims, characterized in that the lens (12; 22) and the mirror are arranged in the beam path of the light beam such that the incoming

Light beam (13) penetrates the lens (12; 22) parallel to the lens axis and, after reflection on the pivotable mirror (14) and again lens passage, leaves the lens (12; 22) parallel to the incoming light beam and then, depending on the mirror position on a ( 16a) of the diffractive optical elements (16) located behind the lens (12; 22).

11. Device according to one of the preceding claims, characterized in that a planar arrangement of diffractive optical elements (16) parallel to the lens (12; 22) on the mirror (14) opposite side of the lens (12; 22) is arranged ,

12. Device according to one of the preceding claims, characterized by a deflection mirror (18a, 18b) which is arranged on the lens axis in order to align the incident light beam (13) in such a way that it passes through the center of the lens (12, 22) on the lens axis. on the pivoting mirror (14) meets.

13. Device according to one of the preceding claims, characterized in that the light source (11) comprises means for generating RGB laser beams which are guided together by the lens (12; 22) on the pivotable mirror (14).

14. Device according to one of the preceding claims, characterized in that for the projection of a pattern in each case a plurality of diffractive optical elements (16r, 16b, 16g) are arranged with different feature sizes in close proximity to

To compensate for size differences in the projection with different wavelengths.

15. Device according to one of the preceding claims, characterized in that the means for moving the light beam comprises a plurality of holographic lenses (22) which are arranged as a stack (52), wherein each holographic lens (22) is used to image an RGB wavelength and transmits other RGB wavelengths largely without interference.

16. Device according to one of the preceding claims, characterized by a mirror control, the mirror during the illumination of a DOE (16a) is set in motion about two axes to average out image speckles by moving the image of the DOE (16a).

17. Method for switchable image projection with diffractive optical

Elements which generate a pattern for image projection by diffraction when a narrow-band light beam (13, 15) hits, comprising the steps of: generating the light beam (13, 15) for the image projection, and moving the light beam (13, 15) over the diffractive one optical

Elements (16) for generating successively different patterns, characterized in that the light beam (13, 15) is moved with a pivoting mirror (14) over the diffractive optical elements (16), the mirror (14) being in focus Lens (12; 22) is located between the diffractive optical elements (16) and the mirror (14).

18. The method according to claim 16, characterized in that it is carried out with a device according to one of claims 1 to 15.