EP3969957A1

EP3969957A1 - Image generating device for a scanning projection method with bessel-like beams

Info

Publication number: EP3969957A1
Application number: EP20728922.4A
Authority: EP
Inventors: Ulrich Hofmann; Joachim Janes
Original assignee: Oqmented GmbH
Current assignee: Oqmented GmbH
Priority date: 2019-05-15
Filing date: 2020-05-13
Publication date: 2022-03-23
Also published as: US20220197042A1; KR20220008864A; DE102019207073A1; JP2022533380A; SG11202112572WA; CN114072716A; WO2020228907A1; DE102019207073B4; CA3139854A1

Abstract

The invention relates to an image generating device comprising a radiation source (1a) , in particular a laser beam source, for one or more output beams (1) with a Gaussian radiation characteristic, comprising a device (2, 4, 5, 28, 29) for generating Bessel-like beams from one or more output beams, comprising a controllably drivable MEMS scanner (8, 9, 32, 36, 41), the Bessel-like beams being directed at the MEMS scanner and deflected in a targeted manner by the MEMS scanner (8, 9) for the purposes of generating an image, and comprising a display body (10, 16, 18, 20, 22, 24, 26, 30), which is at least partly transmissive for the Bessel-like beams, onto which the Bessel-like beams are steered by the MEMS scanner.

Description

Image generation device for a scanning projection method with besel-like beams

The invention is in the field of optics and imaging. It can be used with particular advantage, for example, for image projectors.

Scanning image projection methods are known in principle. In such methods, a beam, for example a laser beam, is typically deflected in a targeted manner by means of a controllable mirror, and the beam intensity is modulated during the deflection. This creates a recognizable image on a projection surface.

The resolution of known projection methods is not only limited by the imaging optics and the quality of the control of the mirror or other elements that deflect the beam in a targeted manner, but also by the quality, in particular the expansion, of the image-generating rays themselves.

Against the background of the prior art, the present invention is based on the object of creating a scanning projection method and an image generation device which allow images to be generated with the highest possible resolution.

The object is achieved with the features of the invention according to claim 1. Claims 2 to 10 present possible implementations of the device.

Accordingly, the invention relates to an image generating device with a radiation source for one or more output beams with Gaussian radiation characteristics, in particular a laser beam source, with a device for generating Bessel-like beams from one or more output beams, with a controllably drivable MEMS scanner , wherein the Bessel-like beams are directed onto the MEMS scanner and are deflected in a targeted manner by the MEMS scanner to generate an image, and with a display body which is at least partially permeable to the Bessel-like beams and onto which the Bessel-like beams pass the MEMS scanner. The invention is based on the idea that the resolution of the scanning projection method is limited, among other things, by the beam profile of the Gaussian beams usually used, for example in the form of laser beams. The focusing and beam shaping of Gaussian beams to small beam diameters are physically limited in principle.

The solutions to the Helmholtz equation, which basically describes electromagnetic radiation, show that so-called Bessel beams, named after the Bessel functions that describe possible solutions to the Helmholtz equation, permit smaller beam diameters than with the usual Gaussian rays. However, ideal Bessel rays, which are described by the named Bessel functions, cannot be generated in practice any more than ideal Gaussian rays. Therefore, in the description of the present invention, in the following, Bessel-like radiation is turned off, which have properties that come close to the properties of the ideal Bessel radiation. Practical ways of generating Bessel-like rays are known and are based on the use of Gaussian rays and their conversion into Bessel-like rays. The properties of the Bessel rays and Bessel-like rays will be discussed in more detail in connection with the description of the figures.

According to the invention, an image can therefore be made visible on a display body with a high resolution using a MEMS scanner. The pixel resolution can, for example, be in the order of magnitude of approximately 1000 × 1000 pixels per square centimeter.

An advantageous embodiment of the invention can be that a projection device is provided which projects the image from the display body onto a projection surface by means of projection optics. The display body can initially act like a ground glass, on which the image generated by the Bes sel-like rays is visible. This image can be projected onto a larger area by the projection device, for example, in order to make the image more visible and / or more convenient for users. One possible embodiment of the invention can provide that the device for generating Bessel-like beams has at least one axicon. An axicon is understood to be an optical component that can be in a reflective or refractive design, which is designed to be rotationally symmetrical in most cases and which generates ring-shaped beam profiles in the far-field approximation. It is ideal for this that a laser beam, and thus a Gaussian beam, is radiated collinear to the optical axis of an axicon. As a result of the further beam guidance, the ring-shaped beam profile is concentrated, for example focused or collimated, on the smallest possible area. For this purpose, imaging optics or another axicon can be used.

It can be provided that at least one axicon is designed as a mirror or as a light-refracting element, in particular as a lens.

In such a case, the output beam traverses both axicons one after the other, and a combination of two axicons can also be combined with imaging optics.

Specifically, it can be provided that the device for generating Bessel-like beams has at least two axicons aligned coaxially to one another.

In another embodiment, it can also be provided, for example, that the device for generating Bessel-like beams has a diaphragm with an annular gap to which the output beam or beams are directed, with at least one converging lens being provided behind the annular gap, in particular seen from the radiation source is. A Bessel-like beam with an extremely narrow intensity distribution can also be produced by such a device.

In principle, the MEMS scanner used can have one or more drivable, pivotable or rotatable mirrors that can be pivoted about different axes so that the beam can be deflected in two dimensions in order to generate a two-dimensional image. It can make sense be that the axes of the mirror or mirrors are perpendicular to each other. In principle, it is also possible for some applications to provide a mirror, in particular a MEMS mirror, which can only be rotated or pivoted about a single axis.

It is particularly advantageous if these intersect with several pivot axes provided. If a beam traverses two pivotable mirrors one after the other, both the reflection losses and errors in the deflection add up. This is partly due to the fact that the beam already deflected by the first mirror travels on the second mirror, so that inhomogeneities on the mirror surface can lead to errors.

Therefore, it can advantageously be provided according to the invention that the MEMS scanner is designed as a 2D MEMS scanner with a mirror that can be rotated or pivoted about several axes. In fundamentally known 2D MEMS scanners, a single mirror is rotated about two different axes by suitable drives in order to generate a two-dimensional image. Errors in image generation can be minimized by using such a 2D MEMS scanner.

A further advantageous embodiment of the invention can provide that an encapsulation wall of the MEMS scanner is designed as a display body, the encapsulation wall for the image generation in particular having a planar section or a spherical cap-shaped section whose center point coincides with a point at which two pivot axes meet cut a MEMS mirror. In many cases, the MEMS scanners described are encapsulated and have an encapsulation wall that is at least partially transparent to the radiation used. The encapsulation can, for example, protect the scanner from environmental influences, and the space in which the drivable mirror moves can also be evacuated, for example, in order to minimize air friction losses and optimize the deflection of the mirror.

A section of the encapsulation wall can be used to serve as a kind of ground glass for the scanning projection on this section to be generated in such a way that it can be recognized from outside the enclosure. A conventional design of the enclosure wall as a ground glass, for example by roughening the enclosure wall on the inside or outside, is often not sufficient, since the possible resolution that can be achieved through the use of Bessel-like rays can exceed the resolution of such a ground glass. The material of the encapsulation wall should therefore advantageously have a structure that enables forward scattering of the incident light with high spatial resolution. For this purpose, the encapsulation wall can, for example, be mixed or coated with a phosphorescent substance, for example also coated with a phosphorescent film. However, any other type of nature of such an encapsulation wall that enables high-resolution forward scattering is also conceivable.

The shape of the encapsulation wall or specifically of the section of the encapsulation wall on which the image can be generated can, for example, correspond to a spherical cap whose center point coincides with the point at which two pivot axes of a MEMS mirror intersect. In such a case, an image is generated that is easy to calculate and has a uniform spatial resolution over the image extent. It is also conceivable to use a flat section of the encapsulation wall for image projection. In this case, distortions of the generated image if the underlying geometry is known during image generation, i.e. H. when setting the respective deflection angle of the MEMS scanner for individual pixels, mathematically to be taken into account in a simple form.

When using a single deflecting mirror / MEMS mirror that can only be pivoted about a single axis, a cylindrical or semi-cylindrical encapsulation housing can also be provided or a cylindrical section of the encapsulation housing. The cylinder axis can then advantageously be aligned parallel to the pivot axis.

In principle, it should also be noted that the image can be generated both on the inside of the encapsulation wall and on the outside or also in a layer lying in between. If a phosphorescent substance is used, it goes without saying that the wavelength of the Bessel-like rays should be placed on the material in such a way that phosphorescence is generated.

Since Bessel-like beams are used in the image generating device according to the invention, which have an annular intensity distribution at least in sections in sections of the beam path, such an annular intensity distribution can also be present during the reflection on the MEMS mirror or mirrors, since the beams only behind the MEMS mirror. Scanner can be compressed to the optimized beam diameter. This means that in many cases the central area of the MEMS mirror or mirrors is not required for a reflection. Such an area can therefore be excluded to reduce the mass of the MEMS mirror or the MEMS mirrors. Such a recess can, for example, be circular or else elliptical if the Bessel-like beams strike the MEMS mirror at a flat angle.

Bessel rays

Bessel rays were theoretically described in 1987 and experimentally generated shortly thereafter. Bessel rays are one of the solutions to the Helmholtz equation, namely an electromagnetic field whose

Amplitude is described with a Bessel function of the first type. In normal usage, the rotationally symmetrical special case m = 0 is called a Bessel beam or, more precisely, a Bessel-like beam. The generation of Bessel rays requires an infinitely extended plane wave which cannot be produced in practice. In the following text, the term Bes sel rays is used in part, whereby Bessel-like rays are meant.

To generate Bessel beams, laser beams (Gaussian beams or Gaussian beams) are reshaped with special lenses. In contrast to laser beams with a Gaussian characteristic, Bessel beams do not have any diffraction effects and the beam geometry does not change as it propagates. The exploitable properties of Bessel rays are that you Central maximum has a high radiance and that this central maximum has a small radial extent.

For the production of Bessel-like beams, Gaussian beams z. B. superimposed with the help of axicons. Axicons are conical, optical compo elements that can be used in a reflective or lens-shaped, refractive design. Axicons are made in both concave and convex shapes. They can be made of any suitable optical material (suitable in terms of wavelength, laser power, etc.). In both reflective and lens-shaped versions, axicons generate ring-shaped beam profiles in the far-field approach as soon as a laser beam is irradiated in, for example, collinear or approximately collinear to the optical axis of an axi cons. The ring width of the ring-shaped beam is then approximately half the diameter of the Gaussian input beam. If either additional axicons or lenses are used on the optical axis, beam profiles with different geometries can be produced.

For the use of axicons in the device described here, it is crucial that the type of Bessel beams generated depends essentially on the axicon angle that defines the beam geometry.

In the same way as this z. B. for laser beams in eye surgery is performed, two axicons are combined to produce a collimated beam with ringförmi ger intensity distribution. The distance between the two axicons then defines the diameter of the annular intensity distribution. For the generation of Bessel rays or specific Bessel-like rays it then also applies that their lateral distribution and their depth depend on the entrance diameter. It is a well-known practice to combine axicons with various optical lenses that are used to define the beam geometry (e.g. as a beam expanders).

However, not only axicons are used to generate Bessel rays. An alternative manufacturing method is to let a collimated laser beam fall through an annular gap with a suitable diameter. The laser beam is bent at this annular gap. A lens with a focal length, which corresponds approximately to the distance to the annular gap, collimates the annular intensity distribution and thus generates a Bessel-like beam.

MEMS scanner

For applications of the present invention, the generation of images with 2D MEMS scanners is ideal. Such scanners are described, for example, in the following documents:

- DE 199 41 363 B4: method for producing a microactuator component;

- DE 10 2004 060576 B4: optical-electronic laser scanning method and arrangement for its operation;

- DE 10 2006 058536 B3: micromirror actuator with encapsulation possibility and method of production;

- EP 2102 096 B1: hermetic wafer-level package for mobile replaceable optical MEMS;

- DE 10 2008 012384 A1: geometric reflection suppression on encapsulated micromirrors;

- EP 2514 211 Bl: Method and device for single or multi-axis beam deflection;

- EP 2828 701 B1: micromechanical mirror actuator for deflecting high laser power;

- DE 10 2013 206396 A1: resonant micromirror actuator with large oscillation amplitude.

The 2D scanners are not subject to any restrictions with regard to their embodiment and their mode of operation.

MEMS scanners can, for example, be driven electrostatically, piezoelectrically, magnetically, mechanically or in some other way. It only has to be ensured that a sufficiently precise measuring method is provided for the angular position in both directions. An advantageous aspect when choosing a 2D scanner is that both torsion axes in one Lie level and that there is therefore a common pivot point for the deflections in two independent directions.

A structure that uses two 1D scanners and thus also covers the desired solid angle range is also possible, but less advantageous in some applications for geometric reasons.

The scan frequencies on both axes depend on the application. 2D MEMS scanners that are currently being manufactured can reach Oszillationsfre frequencies z. B. from a few 100 Hz on one axis to a few 10 kHz on the other axis. However, 2D MEMS scanners with the same or similar scan frequencies in both directions of vibration can also be used. The frequencies of the two axes define the maximum repetition rate with which a volume is illuminated.

The prerequisite for image generation is precise knowledge of the angular position of the scanner in both axes at all times during image generation. For example, capacitive readout methods, optical position-sensitive detectors, strain gauges, piezoelectric methods and other methods are available for measuring the angular position.

Glass encapsulation / vacuum encapsulation

Various constructions and methods are available for the vacuum-tight covering of MEMS mirror units. An exemplary process for the production of a MEMS mirror arrangement, in which a transparen ter cover with a carrier substrate on which a mirror oscillating about at least one axis is suspended, is hermetically sealed, has the following steps:

- Provision of a silicon wafer,

- Structuring the silicon wafer in such a way that a plurality of depressions Ver are produced, each corresponding to the base area of the lid, - Bonding of a cover wafer made of vitreous material onto the structured silicon wafer, an inert gas being enclosed at a given pressure in the cavities formed by the depressions and the cover wafer,

- Annealing the composite of silicon wafer and cover wafer in such a way that the expansion of the enclosed inert gas forms a plurality of domes,

- After the composite of silicon wafer and cover wafer has cooled, partial or complete removal of the silicon wafer,

- Arranging a mirror wafer, which comprises a plurality of mirrors suspended on the carrier substrate, to the cover wafer in such a way that the mirror centers are each in the center of the domes,

- Joining and hermetically sealed sealing of the lid wafer with the mirror wafer,

- Separation of the composite of lid wafer and mirror wafer in

individual capped MEMS mirror assemblies.

In another method, instead of the silicon wafer, a tool is used which consists of a material preventing a hot glass-like material from sticking or which is coated with a material preventing a hot glass-like material from sticking. This tool is or will be provided with through openings. A lid wafer made of vitreous material is placed on the tool provided with through openings, and a negative pressure is applied to the side facing away from the lid wafer. The tempering of the assembly of tool and lid wafer takes place under atmospheric conditions in such a way that a plurality of domes is formed by sucking the lid wafer into the through openings due to the negative pressure. After the composite of the tool and lid wafer has cooled, the tool is removed. The further steps are the same as in the previously specified procedure. Screen, focusing screen

It is possible to generate a real picture with the proposed device, the following z. B. is projected with a corresponding projection optics on egg NEN screen. The easiest way to create such an image is to use a focusing screen, as was common in photography in the past. The focusing screen is either on the inside or the outside of the glass encapsulation of the MEMS scanner in order to generate a real image there. Against the background, however, that the real image is to be generated with the aid of scanning Bessel rays, i.e. with rays of particularly high lateral resolution, the grain size or the granularity of conventional focusing screens does not fully utilize the available resolution. The pixel resolution possible with Bessel beams would be reduced when using focusing screens.

Depending on the specific application of the device, it is also possible to apply a phosphorescent layer to one of the surfaces of the glass body of the vacuum encapsulation. The phosphorescent layer is typically irradiated with "blue" laser light. A well-known conversion process in the phosphorescent layer results in light with greater wavelengths being emitted from it.

For some years there has been a projection surface called "transparent fluorescent film" or also "superimaging film" ("transparent fluorescent film"). This film essentially consists of nano-particles, which are transparent in the visible wavelength range due to the small diameter of the particles. If this film with laser light z. B. the wavelength of 405 nm is illuminated, then the film emits lines in all Rich and at larger wavelengths, z. B. blue or red, incoherent light. A Bessel beam, which is reflected by the MEMS scanner oscillating in two directions and sweeps over a surface section of the vacuum encapsulation, projects an image onto this small screen in this way.

The generation of an image by scanning a laser beam or a Besel beam, e.g. B. is deflected by a 2D MEMS scanner, and at because the image consists of 2000 x 1000 pixels, for example, requires precise detection of the current angular position of the MEMS mirror in the two scanning directions.

The acquisition of the angular position can be carried out by various methods. These include u. a. capacitive measurements of opposing, conductive surfaces, optical measurements, piezoelectric measurements, or measurements with strain gauges.

Depending on the current angular position of the MEMS mirror, the power of the laser is adjusted so that illuminated pixels are visible at the desired positions on a screen. To achieve this, the laser power is controlled as a function of the angular positions in both pivot directions of the mirror. For this purpose, a control or regulation is provided that brings the position of the 2D MEMS scanner in conjunction with the laser power in order to define the pixel intensity with high spatial resolution.

In the case of the image generating device according to the invention, use can be made of the fact that MEMS scanners are equipped with vacuum encapsulation for many applications. The glass surfaces of the vacuum encapsulation can be used to create a real image on it.

The high pixel resolution is achieved by using known methods a Bessel beam that is reflected by the MEMS scanner in both directions over time and illuminates part of the glass body of the vacuum enclosure as a display body.

In order to generate a real image on a surface of the display body, it is advantageous to design this surface in terms of its optical properties. Surface properties of the vacuum encapsulation of the MEMS scanner can be changed in such a way that the transparent material, e.g. B. glass, sapphire, or quartz, a real image can be generated. Various existing options are available for this.

First of all, it should be emphasized that the surface changes should only be carried out in the section of the vacuum encapsulation on which the real Picture should arise. The area of the vacuum encapsulation through which the lasers pass before being reflected by the MEMS mirror should remain free of changes and as transparent as possible. The surface changes or additions that are addressed here include, for example, the formation of a ground glass screen, the application of

phosphorescent materials and the application of a transparent fluorescent film.

In fact, a real image can also be generated on a completely transparent surface, so that the simple glass surface of the vacuum encapsulation is sufficient as a screen in some cases. With this configuration, a scanned, real image is created on both surfaces of the glass body, and these double images can be a hindrance to use. After all, the image resolution is deteriorated in this way. The easiest way to prepare the surface is to treat it so that it becomes a screen. You can choose which of the two surfaces of the glass body is designed as a ground glass. In this way, it is basically possible to generate a real image. The resolution obtained with a focusing screen, as used in photography in the past, for example. B. was common with system cameras, but is suboptimal. Provided that a suitable material for equipping a surface of the vacuum encapsulation of the MEMS component has been found, one of the most promising applications of the invention is to project the image on this surface onto a large screen with suitable projection optics.

Various methods are available for generating Bessel rays. The use of reflective or lens-like axicons or combinations of these axicons is a known and used procedure. Alternatively, Bessel rays can also be produced in that a laser beam passes through an annular gap and that diffraction patterns arising behind the gap are focused with a suitable lens, so that Bessel rays are created. However, the invention is independent of the method of generating the Bessel rays. The main application of the invention consists in generating a real image on one of the surfaces of the vacuum encapsulation of a 2D MEMS scanner, which is then projected onto a screen using projection optics.

It is important to emphasize that the invention is not limited to 2D MEMS scanners. Applications that only require a 1D MEMS scanner are also included.

Typical projection optics that project a small, real image on the order of a few square centimeters at a distance of a few meters with projection surfaces of a few square meters were used in the past in slide projectors and now in "projectors". They consist of a combination of suitable lenses whose optical properties are adapted to the task at hand. With such a structure, the inven tion is an alternative and a replacement for current "projectors", in which the image generation z. B. is done with DLPs and projection optics.

In the following, the invention is shown using exemplary embodiments in Figu Ren a drawing and explained below. It shows

Fig. 1 shows an optical structure for generating Bessel-like

Rays,

2 shows a calculated distribution of the radiance of Bessel rays,

3 shows a sectional view of a device for generating a real image by means of Bessel-like beams on a spherical glass dome,

4 shows a perspective illustration of a device for generating a real image corresponding to FIG. 3,

5 shows a sectional view of a device for generating a real image by means of scanned Bessel-like beams a screen outside the encapsulation of a MEMS mirror,

6 shows a sectional illustration of a device for generating a real image on the encapsulation wall of a planar vacuum encapsulation of a MEMS component,

7 shows a sectional illustration of a device for generating a real image on a screen outside a planar vacuum encapsulation of a MEMS component,

Fig. 8 is a sectional view of a device for generating a real image on a planar encapsulation wall inclined to the angle of the MEMS component,

FIG. 9 shows a representation analogous to FIG. 8, the image on a

Screen beyond the inclined enclosure wall it is generated,

10 shows a sectional illustration of a device for generating a real image on a spherically shaped encapsulation wall of a MEMS element, the center of which is shifted with respect to the pivot point of the MEMS mirror,

11 shows a sectional illustration of a device for generating a real image on an encapsulation wall with an irregular surface shape,

Fig. 12 is a sectional view of a device for generating images by means of scanned Bessel-like beams, the Bessel-like beams being generated by means of vitreous axicons, and also

Figs. IBa-c possible embodiments of mirrors of a MEMS scanner with cutouts. To produce Bessel rays, specular axicons are used in the first embodiment which, as shown in FIG. 1, are constructed in such a way that they allow the superposition of Gaussian rays. A Gaussian beam 1 passes through beam-shaping optics 2 with which primarily its diameter and beam divergence are set (the beam-shaping optics are only shown symbolically in FIG. 1). After passing through the opening S in the component 5, the beam 1 hits the conically shaped mirror 4, which is referred to as the "axicon". In a mathematical sense, the conical mirror is a cone. The optical function of the conically shaped mirror is to reflect the Gaussian beam 1, so that an annular beam cross-section is created after the reflection. In this sense, it is advantageous that the Gaussian beam runs on the optical axis (cone axis) of the axicon.

Another reflective axicon 5 is arranged in the beam path in such a way that the ring-shaped intensity distribution of the beam 1 is completely reflected by the conical surface of the axicon 5 after the reflection on the axicon 4. An essential prerequisite for the functioning of the arrangement is that the two optical axes 6 of the two axicons 4 and 5 are ideally collinear. The axicon 5 reflects the ring-shaped intensity distribution in the direction of the optical axis 6. The geometry of the arrangement must ensure that the axicon 4 is not in the beam path of the ring-shaped intensity distribution collimated by the axicon 5. At a distance that depends on the angle of reflection of the axicons 4 and 5, the annular Intensi ity distribution in the volume 7 is superimposed.

The total length of elements 2, 3, 4, 5, 6 and 7 is approx. 15-20 mm in the simulation shown in FIG. 1, and the entrance diameter of the laser beam 1 is here, for example, 1 mm.

The calculated intensity distribution that results from the superposition of the ring-shaped light distribution in the volume 7 is shown in FIG. The calculation is based on ideal conditions such that z. B. was simulated with exactly one wavelength without bandwidth. Furthermore, the input beam has an ideal phase and flat wave fronts. In the representation the simulated radiance is shown as a function of the lateral extent and the axial position in the direction of the axis 6 within the volume 7.

FIG. 2 shows the theoretical beam density distribution of the Bessel beams, which is achieved with the structure shown in FIG. The essential property of the Bessel rays for the task described above is their lateral extension found in the simulation of a few miti for the central maximum and some secondary maxima with intensities of less than 10% of the intensity of the central maximum. In addition, it can be seen in FIG. 2 that the central maximum along the optical axis has only a relatively small variation in intensity.

In Figure 3, the structure according to the invention for the generation of Bessel rays and their projection on a spherical surface is shown as a sectional drawing. A laser la as a radiation source with a (Gaussian) laser beam 1 is adjusted with a beam-shaping optics 2 with regard to its diameter and its divergence. The laser unit la can also consist of a combi nation of lasers which meet the necessary conditions for generating a real image. After passing through the opening 3, the laser beam hits the first axicon 4. The rays reflected by the axicon 4 form a ring-shaped intensity distribution and then hit the second axicon 5. The optical axes of the axicons 4 and 5 are collinear. Likewise, the center of the laser beam 1 ideally, but not necessarily, lies on the optical axis 6. Certain axis deviations of both the laser and the axicons are possible and can be corrected or calculated out later during the image generation.

The pivot point of the MEMS scanner 8 is also advantageously on the optical axis 6. The MEMS scanner is part of the MEMS component 9, which contains the mechanical and electrical functionality of the scanner. The installation angle of the MEMS component 9 relative to the optical axis 6 is defined on the one hand by the application and on the other hand by the optical scanning angle that the scanner mirror 8 is intended to enable. The MEMS component is hen with an optically transparent vacuum encapsulation 10 verses, which is designed here in spherical shape. The vacuum encapsulation 10 increases the Q value of the torsional vibrations of the mirror and thus the Angular amplitudes of the vibrations. It consists of an optically transparent material that must also meet the boundary conditions for process control for MEMS components (e.g. suitable thermal expansion coefficient).

The ring-shaped intensity distribution, which is reflected on the axicon 5, occurs through the spherical material of the vacuum encapsulation 10. Irrespective of the exact geometric shape of the encapsulation 10, also for the embodiments shown below, the material thickness / glass thickness is essentially constant should be. In the event that the glass thickness is variable, lens effects can cause significant distortion of the images generated. Material thicknesses / glass thicknesses of MEMS vacuum encapsulation are approximately in the range from 50 μm to 500 μm, whereby the smallest possible glass thickness is usually aimed for. In the embodiment shown here, the center of the spherical vacuum encapsulation 10 lies on the optical axis 6. The axicon angle of the axicon 5 is set in such a way that the annular intensity distribution is collimated towards the MEMS scanner 8 and then the intensity is superimposed on the vacuum encapsulation 10 takes place in section 11. Bessel rays, the profile of which is simulated and shown in FIG. 2, thus arise in section 11. If the MEMS scanner 8 executes a torsional oscillation in one or two of the possible directions, then the section 11 moves at a constant distance around the pivot point of the MEMS scanner 8 in accordance with the reflection conditions. The result of this is that the intensity distributions shown in FIG. 2 also move around the pivot point of the scanner 8.

To ensure that the optical axes of the axicons 4 and 5 permanently coincide with the pivot point of the MEMS scanner, the axicons 4 and 5 are connected to the holding elements 12 and 13 with the MEMS component.

A transparent fluorescent film is preferably applied to the spherical surface of the encapsulation 10. The film can be applied both to the inner surface and to the outer surface of the encapsulation without impairing the function. The film is illuminated by the scanned Bessel rays. The intensity distribution shown in FIG. 2 is generated pixel by pixel Fluorescent light. If the Bessel rays are scanned in two directions as a function of time with the 2D MEMS scanner 8, a large number of pixels are created. If the laser power is controlled accordingly, a real image is created in the film on the spherical surface through differently bright pixels.

The encapsulation 10 consists of a suitable glass material. For example, Borofloat is used to manufacture vacuum enclosures with a spherical glass dome for process engineering reasons.

Regardless of the thickness of the glass material, there are two surfaces. Both surfaces of the dome-shaped encapsulation section, the outer surface as well as the inner surface, can be selected as the projection surface.

One of these selected surfaces is then z. B. coated with the phosphoreszie-generating material or coated with the fluorescent film or treated by other means. This creates a projection screen on one of the selected surfaces, on which the pixels generated by the scanned Bessel beams create a real image.

Due to the fact that both the axicons 4 and 5 and the pivot point of the scanner mirror 8 should lie as precisely as possible on one axis, it is advantageous to align the corresponding components with one another and to install them firmly. It must be taken into account that the connecting elements do not affect the beam path of the laser la. For this reason, the axicon 4 is installed on a holder 12 which is attached to the dome of the enclosure 10.

The alignment of these components to one another and the alignment of the axicon axis on the pivot point of the scanner mirror 8 is carried out with the known in-situ adjustment methods. The axicon 5 is installed in a cylinder-shaped bracket 13, for example. It is important that here, too, the axicon axis and the cylinder axis are collinearly adjusted to one another. The holder 13 together with the axicon 5 are then also aligned with the known in-situ adjustment methods relative to the axis on which the pivot point of the scanner mirror 8 and the axis of symmetry of the axicon 4 lie, and on the surface of the glass dome of the encapsulation 10 attached. The use of axicons and the resulting ring-shaped intensity distribution of the laser light enables an advantageous embodiment of the scanner mirror 8. Since in the embodiment described here, the ring-shaped intensity distribution can also be found on the mirror surface of the scanner mirror 8, it can also be in the form of an elliptical one Rings are made with a central recess. This also includes the shape of a circular ring. The annular intensity distribution of the laser beam 1, which strikes a scanner mirror 8 at an angle of incidence (here, for example, 45 °), results in an elliptical intensity distribution on the mirror surface. The advantage of a recess in relation to the scanner mirror 8 is that an elliptical ring with a defined outer boundary has a lower mass than a scanner mirror 8, which is designed as a full elliptical disk. The lower mass of the scanner mirror 8 means that a smaller torque is required in order to achieve the same angle amplitudes than in the case of a scanner mirror made from solid material. Regardless of the type of drive of the scanner mirror 8, this means a lower drive force and according to the drive types z. B. lower drive voltages or lower drive currents (see Figures IBa-c).

For pixel-accurate generation of a real image, it is necessary to determine or detect the angular position of the MEMS scanner 8 in both directions of oscillation and the necessary illuminance of a pixel that is projected exactly in the direction of the corresponding angular position of the MEMS scanner 8, to regulate or control. The detection and control unit 14 links the angular position of the MEMS scanner 8 with the control of the laser la to control the laser intensity for each pixel to be projected. The detection and regulation unit 14 can also be designed for the control or regulation of a combination of lasers.

The image generated on the glass dome of the encapsulation 10 has an area of at most a few square centimeters (1 cm ² - 2 cm ² ) and can, depending on the pixel resolution achieved by the Bessel rays within the projection area, have a pixel density of up to 2000 pixels per Centimeters in one direction. Such a real image can be compared with a usual Projection optics z. B. projected onto a large screen at a usual distance of a few meters from the MEMS mirror.

FIG. 4 shows the structure, which is already presented as a sectional drawing in FIG. 3, in a perspective illustration. The laser beam 1 and the subsequent annular intensity distributions are shown as a section in a vertical plane for illustrative reasons. The dashed lines on the axicons 4 and 5 and on the MEMS scanner 8 indicate the areas which are illuminated either by the laser beam 1 or by the subsequent annular intensity distributions. The MEMS scanner 8 is shown here as a 2D MEMS mirror with the torsion axes indicated.

FIG. 5 shows a sectional drawing which essentially shows the same structure for generating Bessel rays as FIG. 3. Only the axicon angle of the axicon 5 is set in such a way that the overlap area of the annular intensity distribution 14 is outside the spherical vacuum encapsulation 10 and thus at a greater distance from the axicon 5 than in Fi gur 3. A similar constellation can of course also be achieved by adapting the distances between the axicons 4 and 5 and the axicon angle of the axicon 4. Within the overlap volume of the annular intensity distribution, Bessel rays are also formed here, as they are simulated and shown in FIG. The Bessel rays then hit a screen 15 which serves to make the intensity distribution, as indicated in FIG. 2, visible. In this structure, too, the torsional vibrations of the MEMS scanner cause the Bessel rays to sweep over the screen 15 in accordance with the Reflexionsbe conditions. In this embodiment, in contrast to the embodiment shown in FIG. 3, the screen is coated with the phosphorescent material or provided with the fluorescent film. A real image created in this way can in turn with a conventional projection optics z. B. be projected on a large screen at a usual distance of, for example, a few meters.

The geometric shape of the vacuum encapsulation is not limited to spherical designs. FIG. 6 shows an embodiment of the vacuum encapsulation with a flat glass plate 16, which is arranged parallel to the MEMS component 9. The axicon angles of axicons 4 and 5 and their spacing are set in such a way that the superimposition of the annular intensity distribution and, therefore, the formation of Bessel-like rays in area 17 takes place. In this way, the intensity distribution of the Bessel rays shown in FIG. 2 arises on the planar glass cover 16. When the MEMS scanner executes torsional vibrations, the area 17 of the superimposed intensity distribution is shifted accordingly and thus sweeps over the flat glass cover. In contrast to the embodiment in FIG. 3, the distance between the pivot point of the MEMS scanner and the position of the area 17 on the planar glass cover 16 also changes with the scanning angle of the MEMS scanner.

In FIG. 2 it can be seen that the intensity distribution of the Bessel beam occurs in a certain range of the distance (e.g. from the axicons) (in the simulation of FIG. 2 this distance is approximately 10 mm). The distance range depends primarily on the diameter of the laser beam 1 and the crossing angle of the annular intensity distribution in FIG. The generation of a real image on the planar glass cover 16 then takes place in the same way as in the exemplary embodiment in FIG. B. applied a phosphorescent layer on the outside or on the inside of the glass cover 16, or one of the two sides is provided with a fluorescent film, or another method for producing a real image is used.

The fastening and adjustment of the axicons 4 and 5 on a common axis, which also runs through the pivot point of the MEMS scanner 8, must be solved individually for individual MEMS scanner systems.

FIG. 7 shows a sectional drawing which essentially shows the same structure for generating Bessel rays as FIG. 6. Only the axis angles of axicons 4 and 5 are set in such a way that the area of overlap of the annular intensity distribution outside the planar glass cover 18 lies. Adjusting the spacing of axicons 4 and 5 achieves this same goal. Bessel rays are also formed here within the overlap volume of the annular intensity distribution, as they are simulated and shown in FIG. The Bessel rays then hit a screen 19, which serves to make the intensity distribution visible. In this structure, too, the torsional vibrations of the MEMS scanner cause the intensity distribution of the Bessel rays to sweep across the screen 19 in accordance with the reflection conditions. In this embodiment, in contrast to the embodiment shown in FIG. 6, the screen 19 is coated with a phosphorescent material or provided with the fluorescent film.

Analogous to the exemplary embodiment of FIG. 6, FIG. 8 shows an embodiment in which a planar vacuum encapsulation 20 of the MEMS component is present, but in contrast to FIG. 6, this encloses an angle greater than 0 ° with the surface of the component. Such a construction of the vacuum encapsulation is used in order to be able to set the direction of reflex spots in laser projection methods (see DE 10 2008 012 384 A1). In the same way as in the embodiment shown in FIG

is shown, an intensity distribution similar to that which is shown in FIG. 2 arises in region 21.

A real image is then generated on the inclined, planar glass cover 20 in the same way as in the exemplary embodiment in FIG. B. applied a phosphorescent layer on the outside or on the inside of the glass cover, or one of the two Be th is provided with a fluorescent film, or another method for producing a real image is used. The real image can then be projected further onto a screen, not shown, by means of projection optics 46, which are shown schematically in FIG. 8, and made visible there in enlarged form.

In a manner analogous to that shown in FIG. 7, the screen can be set up outside the scanner system, as shown in FIG. This figure shows essentially the same structure for generating Bessel rays as Figure 7. Only the axicon angles of axicons 4 and 5 are chosen in such a way that that the area of overlap of the annular intensity distribution 23 lies outside the planar glass cover 22.

Adjusting the spacing of axicons 4 and 5 can lead to the same situation. Within the overlap volume of the annular intensity distribution, Bessel rays or specifically Bessel-like rays are also formed here, as they are simulated and shown in FIG. The Bessel rays then hit a screen 23, which is used to make the Intensitätsvertei development visible. Also in this structure, the

Torsional vibrations of the MEMS scanner that the intensity distribution of the Bessel rays sweeps over the screen 23 according to the reflection conditions. In this exemplary embodiment, in contrast to the embodiment shown in FIG. 7, the screen 23 is coated with the phosphorescent material or provided with the fluorescent film.

An exemplary embodiment is shown in FIG. 10 in which the vacuum encapsulation is produced without a centrally symmetrical geometry. The center of the still spherical glass dome 24 is no longer in the pivot point of the scanner mirror. This means that the passage of the annular intensity distribution is no longer axially symmetrical to the glass dome 24.

FIG. 10 shows a sectional drawing in which the optical structure for generating Bessel beams is essentially the same as that shown in FIG. The center of the spherically shaped glass dome 24 can be displaced ver relative to the plane of the MEMS component 9 in the x, y or z direction. In the same way as in the embodiment shown in FIG. 3, in the case shown in FIG. 10 either part of the inside or part of the outside of the dome 24 is equipped with the optical properties that enable the generation of a real image in FIG enable.

In FIG. 3, the annular intensity distribution runs symmetrically through the glass dome of the vacuum encapsulation. The wave fronts thus experience the same phase shifts everywhere. This is also the case for planar glass covers, regardless of the angle the cover has to the beam. In the situation shown in FIG. 10, this is no longer the case. The one in the Sectional drawing shown beam path in the upper part dargestell th rays have a different angle of passage through the glass dome than in the lower part. This means that the rays shown in the upper part experience a different phase shift. The intensity distribution of the Bessel rays therefore looks completely different from the distribution shown in FIG. 2 for the symmetrical case. For reasons of manufacturing technology for the spherical glass dome 24 described here, this is the most common case. The fact that the center of the spherical glass dome and the pivot point coincide is a desired but unfortunately not always achievable special case.

FIG. 11 shows an embodiment of the glass encapsulation 26 of the MEMS scanner with an irregular geometry. The geometry shown here is representative of any number of irregular geometric shapes. This should also include those geometric shapes that are not irregular in the mathematical sense. For this purpose, for example, glass encapsulations in an elliptical embodiment, in a cylindrical execution form u. a. are counted.

The generation of the Bessel rays takes place with the laser la and the Strahlfor mungsoptik 2 as well as with the axicons 4 and 5. Analogously to the embodiment from FIG metric to the glass dome 26. Since the overlap area 27 also lies on the irregularly shaped surface 26, the real images generated there must be rectified with image control algorithms in accordance with the surface shape.

FIG. 12 shows a possible embodiment of a device for producing Bessel beams using glass-shaped axicons 28, 29 made of an optically transparent, light-refracting material. A laser 1 a with a laser beam 1 with a Gaussian characteristic is set with beam shaping optics 2 primarily with regard to its diameter and its divergence. It then encounters an axicon 28 which is made of light-refracting material which is transparent in the optical range and which is cut concavely conically (conically) on (at least) one side is. As a result, the laser beam la is given an annular intensity distribution which strikes the axicon 29 at a suitable distance and at a suitable angle. The axicon 29 also consists of a light-refracting material and has a convex conical (conical) shape on both sides. The optical axes 6 of the axicons 28 and 29 as well as the beam shaping optics and the central axis of the laser beam la are collinear. The axicon angles of the axicon 28, 29 are set such that the ring-shaped intensity distribution is collimated after passing through the axicon 29.

Analogously to the embodiment of FIG. 3, the ring-shaped intensity distribution hits the MEMS mirror 8 within the MEMS component 9. The MEMS mirror 8 executes torsional vibrations along its oscillation axes, which lead to the deflection of the ring-shaped intensity distribution. The pivot point of the MEMS mirror is ideally on the optical axis 6 of the optical components 2, 28 and 29. In the exemplary embodiment shown here, the MEMS component 9 with the MEMS mirror 8 is provided with a spherically shaped vacuum encapsulation 30. Both the axicon angles and the respective distances between the components are set in such a way that the ring-shaped intensity distribution overlaps in the area 31 around the spherical glass dome and forms the Besel rays described in FIG.

As already mentioned in relation to FIG. 3, the ring-shaped intensity distribution which is caused by the axicons has a great advantage with regard to the layout of the 2D (also 1D) MEMS scanners.

Because the MEMS mirror is only illuminated in its edge area, it is only necessary to design it to deflect the annular intensity distribution. The mirror therefore only has to reflect in an annular area.

A comparison of the geometry of a standard MEMS mirror with a MEMS mirror for ring-shaped illumination is shown in FIG. In FIG. 13a, a circular standard MEMS mirror 32 without the spring suspensions is shown by way of example. The MEMS mirror converts torsional vibrations the axes 33 and 34 off. The ring-shaped intensity distribution meets the MEMS mirror within the area 35, which is delimited by the dashed line. Outside this area 35, the MEMS mirror is not illuminated. For this reason, it is possible and advantageous to design the MEMS mirror 32 in an adapted form with a mass-saving recess.

A MEMS mirror 36 in this adapted form is shown by way of example in FIG. 13b. The MEMS mirror 36 performs torsional oscillations about the two axes 37 and 38. The area 39, which is delimited by the dashed line, indicates the area on the MEMS mirror 36 which is illuminated by the annular intensity distribution. The MEMS mirror 36 has the recess 40 within the area of the MEMS mirror 36 that is not illuminated. This means that the MEMS mirror 36 has a lower mass than the MEMS mirror 32 in FIG. 13a, with the same outer radius. Because of the lower mass, the MEMS mirror 36 has a lower moment of inertia than the MEMS mirror 32 without a recess. The MEMS mirror 36 therefore needs a lower drive force to maintain the two torsional vibrations about the axes 37 and 38 than the MEMS mirror 32 in FIG. 13b. Overall, the recess 40 has a positive effect on the mirror performance.

FIG. 13c shows an analogous embodiment of the MEMS mirror for the more general case that the ring-shaped intensity distribution has a larger angle of incidence relative to the surface normal of the MEMS mirror (10 ° -80 °). For larger angles of incidence, the area illuminated by the ring-shaped intensity distribution has a pronounced elliptical shape.

The MEMS mirror 41 advantageously has an elliptical embodiment and oscillates about the torsion axes 42 and 43. Because of the angle of incidence of the annular intensity distribution on the MEMS mirror 41, the illuminated area 44 delimited by the dashed line is correspondingly elliptical.

The recess 45 is also advantageously designed to be correspondingly elliptical. The recess 45 is designed to be elliptical, regardless of the outer, geometric shape of the MEMS mirror 41. With the described image generation device, high-resolution images can be generated by scanning with justifiable effort, which images can be appropriately further processed.

Claims

1. Image generating device with a radiation source (la) for one or more output beams (1) with Gaussian radiation characteristics, in particular a laser beam source,

with a device (2, 4, 5, 28, 29) for generating Bessel-like beams from one or more output beams,

with a controllably drivable MEMS scanner (8, 9, 32, 36,

41),

wherein the Bessel-like beams are directed at the MEMS scanner and are specifically deflected by the MEMS scanner (8, 9) to generate an image,

and with an at least partially permeable to the Bessel-like rays display body (10, 16, 18, 20, 22, 24, 26, 30) on which the Bessel-like rays are directed by the MEMS scanner.

2. Image generating device according to claim 1, characterized by a projection device (46) which projects the image from the display body (10, 16, 18, 20, 22, 24, 26, 30) onto a projection surface by means of projection optics.

3. Image generating device according to claim 1 or 2, characterized in that the device for generating Bessel-like beams has at least one axicon (4, 5, 28, 29).

4. Image generating device according to claim 3, characterized in that at least one axicon (4, 5, 28, 29) is designed as a mirror or as a lichtbre related element, in particular a lens.

5. Image generating device according to claim 3 or 4, characterized in that the device for generating Bessel-like beams has at least two axicons (4, 5, 28, 29) aligned coaxially to one another.

6. Image generating device according to claim 1 or 2, characterized in that the device for generating Bessel-like beams has a diaphragm with an annular gap on which the or the output beams are directed, with at least one converging lens being provided behind the annular gap, in particular as seen from the radiation source.

7. Image generating device according to one of the preceding claims, characterized in that the MEMS scanner is designed as a 2D MEMS scanner (8, 9, 32, 36, 41) with a mirror that can be rotated or pivoted about several axes.

8. Image generating device according to one of the preceding claims, characterized in that an encapsulation wall of the MEMS scanner (8, 9, 32, 36, 41) as a display body (10, 16, 18, 20, 22, 24, 26, 30 ) is formed, wherein the encapsulation wall for the image generation in particular has a planar section or a spherical cap-shaped section whose center point coincides with a point at which two pivot axes of a MEMS mirror (8, 32, 36) intersect.

9. Image generating device according to one of the preceding and workman che, characterized in that the display body (10, 16, 18, 20, 22, 24, 26, 30) designed as a focusing screen or with a phosphorescent or fluorescent substance, in particular a phosphorescent or fluorescent film is coated.

10. Image generating device according to one of the preceding claims, characterized in that the or at least one MEMS mirror (36, 41) has an in particular circular or elliptical recess (40, 45).