Projection device with concave mirror

Abstract

The invention relates to a projection device for generating and displaying an image in an observation field provided for the overlaying of information and images, comprising at least one light source (1) for emitting at least one light beam (2), a microscanner (3) for variable deflection of the at least one light beam (2) in the direction of the observation field, wherein the microscanner (3) has at least one axis of rotation for a rotational oscillating movement for deflecting the at least one light beam (2), a waveguide (4) which is arranged downstream of the microscanner (3) in a beam path of the at least one light beam (2), and a concave mirror (5) which is provided between the at least one light source (1) and the microscanner (3) in the beam path of the light beam (2) and is designed to collimate the at least one light beam (2).

Description

[0001] Projection device with concave mirror

[0002] The invention relates to a projection device for generating and displaying an image on an observation field intended for projecting augmented reality, which field of observation can in particular be a spectacle lens or a retina of a user of augmented reality glasses.

[0003] Augmented reality (AR) refers to the computer-assisted extension of reality perception that addresses at least one of the human sensory modalities. However, AR is often understood only as the visual representation of information, namely the supplementation of images or videos with computer-generated additional information and / or virtual objects by means of overlay or superimposition. In particular, the visual representation or projection of images, user interfaces or information, such as directions, weather information or news, represents a common application of AR and is increasingly being used in so-called AR glasses, which can display images, user interfaces or information directly on the lenses or retina of a user. AR has experienced increasing popularity in recent years, particularly in the areas of entertainment, education and marketing.In the future, further areas of application could be developed, for example in medicine or transport.

[0004] A microscanner (also known as a micro-electro-mechanical system, or MEMS for short) can be used to project images or text information. A light beam, generated by a light source located, for example, in the temple of a pair of glasses and then shaped, is deflected onto the MEMS scanner. The light beam can then be scanned by the MEMS scanner, generating an image in an observation field. Such an imaging system with a MEMS scanner requires comparatively few optical elements, allowing for small and cost-effective projectors. For AR applications, a projector must achieve very good optical resolution and consume very little power. Due to a lack of alternatives, edge emitters are often used as the light source. However, these emit a highly divergent, elliptically shaped light beam that must be collimated.A MEMS scanner is described, for example, in DE 10 2021 1 16 151 B3. The MEMS scanner disclosed therein can perform simultaneous rotational oscillations around two resonant oscillation axes in order to create a nonlinear Lissajous projection into an observation field by deflecting a light beam incident on a deflection element during the oscillations.

[0005] The oscillations scan a field of view (FOV) at high frequencies in a scan pattern resembling a Lissajous figure. Unlike conventional raster scanning methods, which periodically scan the FOV from top to bottom at maximum resolution, this allows hundreds of partial images to be processed simultaneously, enabling smoother motion representation. Furthermore, artifacts in the three-dimensional perception of fast-moving objects are greatly reduced.

[0006] A display for near-eye display of images is disclosed in WO 2021 / 122948 A1. The display comprises a light source for emitting light toward a waveguide, the waveguide, and a first optical element provided on the waveguide and configured to receive light and couple it into the waveguide. Laser beam scanning (LBS) can be used to display the images.

[0007] Due to the high number of required components and the limited miniaturization options, AR glasses are generally heavier and bulkier than conventional eyeglass frames. However, the acceptance of AR glasses depends largely on the design and weight of the AR glasses. Therefore, it is desirable to reduce the required installation space and weight of AR glasses as much as possible.

[0008] Conventional AR glasses require three optical elements—usually two lenses and a mirror—for collimation, achromatization, and deflection of a light beam emitted by a light source onto a scanner. Since the installation space for AR glasses is limited and design aspects play a major role, integrating many optical elements into AR glasses is disadvantageous. Furthermore, the number of components required for assembling the projection device also adversely affects the adjustment effort, which increases with the number of components.

[0009] The object of the invention is therefore to find a new possibility for image generation and image display on an observation field for AR information projection, which requires as few optical elements as possible and takes up very little installation space.

[0010] The object is achieved by a projection device for generating and displaying an image in an observation field provided for the insertion of information and images, comprising at least one light source for emitting at least one light beam, a microscanner for the variable deflection of the at least one light beam in the direction of the observation field, wherein the microscanner has at least one axis of rotation for a rotational oscillating movement for deflecting the at least one light beam, a waveguide which is arranged downstream of the microscanner in a beam path of the at least one light beam, and a concave mirror which is present between the at least one light source and the microscanner in the beam path of the light beam and is designed to collimate the at least one light beam.

[0011] By using the concave mirror, several optical components can be combined into one component, thus drastically reducing the number of optical elements required and the space required for them.

[0012] The concave mirror is preferably made of glass or ceramic. The concave mirror is advantageously a parabolic mirror. A parabolic mirror is a concave mirror in the shape of a paraboloid of revolution. The parabolic mirror can, in particular, be an off-axis parabolic mirror. Off-axis parabolic mirrors are a type of parabolic mirror that has a special shape and orientation. Unlike a conventional parabolic mirror, off-axis parabolic mirrors are not aligned with an axis, but have an eccentricity or off-axis positioning that distinguishes them from conventional parabolic mirrors. Off-axis parabolic mirrors have the advantage of having a large clear aperture. In addition, off-axis parabolic mirrors can also reduce distortions that can be caused by conventional parabolic mirrors when the light is not precisely focused on the axis of the parabolic mirror.This makes off-axis parabolic mirrors a useful option in optical systems where distortion must be avoided.

[0013] The concave mirror can advantageously be an ellipsoidal mirror, i.e., it can have the shape of a section of a three-dimensional ellipse of revolution. It is usually made of glass or metal and has a smooth, polished surface that reflects light. An ellipsoidal mirror also enables the finite-to-finite imaging of a point into a real intermediate image. A real intermediate image just before the projector is useful or necessary in various applications: in AR glasses with a (holographic) combiner instead of a waveguide, in projection devices equipped with so-called birdbath optics, and in HUD (head-up display) applications. Birdbath optics is an optical structure with a curved mirror and a beam splitter that ensures that the light hits the curved mirror (almost) on the optical axis (perpendicular to the curvature).Such a birdbath optic enables the dynamic change of the focus of the virtual image displayed to a user, with low power consumption and no moving (mechanical) parts.

[0014] In addition to collimation, the concave mirror can also have other functionalities. For example, the concave mirror can be provided with a coating, preferably a diffractive coating, which ensures that the concave mirror is designed to shape a beam cross-section of the at least one light beam in order to reduce the ellipticity of the at least one light beam and / or ensures that the concave mirror is designed to influence astigmatisms of the at least one light beam. A diffractive coating is a special type of coating that is applied to optical surfaces and modifies the optical properties.In contrast to conventional coatings, which primarily serve to minimize or maximize reflections and scattering, a diffractive coating is designed to redirect the incident light in a specific way, thereby fulfilling a defined optical function. A diffractive coating consists of a large number of micro- or nanostructures arranged on the optically effective surface of the concave mirror. These structures are usually arranged periodically and have different depths and profiles. When light hits the coating, it is diffracted by these structures and deflected in different directions. By specifically designing the structures, the light can be redirected in a specific way, for example to achieve a wavelength-dependent deflection of the light.

[0015] The generation and display of images, within the meaning of the invention, is to be understood as the generation and display of one image, multiple images, or a sequence of images. A device according to the invention can also be used to display user interfaces or information, such as directions, weather information, or news, on the observation field.

[0016] The observation field is advantageously a screen mounted, for example, on a windshield or dashboard of a motor vehicle. Alternatively, the observation field can be the retina of a user's eye.

[0017] Advantageously, the at least one light source is a laser diode configured as an edge emitter or surface emitter, or a fiber-coupled laser light source. A surface emitter is a type of semiconductor light source, also known as a vertical cavity surface emitting laser (VCSEL). In contrast to an edge emitter, in which the light is emitted laterally from a thin edge of the semiconductor crystal, a surface emitter radiates the light perpendicular to the surface of the semiconductor crystal. Surface emitters and fiber-coupled light sources have the advantage that the light beams emitted by these light sources are generally rotationally symmetrical, which is not the case with light beams emitted by edge emitters. Furthermore, they feature a compact design and high efficiency.

[0018] The at least one light source can be designed to emit a plurality of light beams with pairwise different spectral compositions or wavelengths. Alternatively, the at least one light source can be supplemented by further similar light sources, so that a plurality of light beams with the same spectral composition are emitted. The distance between the light beams emitted by the light source or light sources can preferably be adjusted using an additional optical element. The use of a light source that emits a plurality of light beams, or of a plurality of light sources, is particularly useful when the microscanner is designed to be rotatable about only one axis of rotation, since a two-dimensional image can then be generated by simultaneously controlling the line light source and the microscanner.

[0019] It is advantageous if the concave mirror is designed to deflect all emitted light beams simultaneously towards the microscanner. A field angle generally remains between the light beams, preventing them from being combined into a single beam. The light sources are then controlled so that they each light up at the correct time. The light sources must be close to one another because the concave mirror, whether parabolic or ellipsoidal, only produces a good image on or near its axis. Therefore, the light source is advantageously a multiple point light source, with the individual sources very closely packed, meaning the individual sources are very close together.

[0020] This can be achieved by mounting the laser diodes close together or by guiding the light to the focal point of the collimator via optical fibers. These fibers can be conventional glass fibers or monolithically integrated waveguides.

[0021] The concave mirror is preferably designed as a front surface mirror. A front surface mirror, also called a front mirror, is a mirror in which the reflective layer is applied to the front side of the mirror. By applying the reflective layer to the front side of the mirror, it is avoided that the light has to pass through glass or another transparent carrier layer twice, which can lead to distortions and image errors. Alternatively, the concave mirror is designed as a rear surface mirror. A rear surface mirror is a mirror in which the reflective layer is applied to the back side of a mirror substrate. The design as a rear surface mirror is particularly useful when a light beam is guided from the light source to the concave mirror in glass or another optical medium, since this prevents the light beam from being guided in different media or from being reflected at their interfaces (e.g.between air and glass).

[0022] The microscanner can, in particular, be embodied as a micro-electro-mechanical system (MEMS) and configured to effect a nonlinear Lissajous projection into the observation field. The microscanner is configured to scan the light beam across the observation field, thereby generating an image on the observation field. By scanning the at least one light beam along a Lissajous figure, hundreds of partial images can be processed simultaneously, enabling a smoother representation of motion. Furthermore, artifacts in the user's three-dimensional perception of fast-moving objects are greatly reduced. A MEMS scanner is a small, integrated system used for optical scanning and imaging of objects. The system consists of tiny movable mirrors controlled by micro-electro-mechanical systems (MEMS).A MEMS mirror is typically only a few hundred micrometers or a few millimeters in size and can be moved very quickly and precisely to reflect the light beam coming from at least one light source. The movement of the MEMS mirror can be controlled by electrical signals sent to the microscanner from a computer or other control unit, which may also be part of the projection device. MEMS microscanners offer the advantages of high speed, accuracy, and reliability while maintaining low power consumption and a small footprint.

[0023] Particularly advantageously, the microscanner is designed for rotational oscillations around exactly two axes of rotation that are orthogonal to each other, and oscillates at its natural frequency around the two axes of rotation. The microscanner can also be designed for rotational oscillations around only one axis of rotation, in which case the at least one light source is designed to emit several adjacently arranged light beams in a line pattern.

[0024] Advantageously, the waveguide is a lens of augmented reality glasses. The object is further achieved by augmented reality glasses containing a projection device for generating and displaying images according to one of the described embodiments.

[0025] The invention will be described in more detail below by means of exemplary embodiments based on the drawings. These show:

[0026] Fig. 1 A side view of a first embodiment of a projection device with a concave mirror,

[0027] Fig. 2 is a view of a second embodiment of a projection device with a dome-shaped encapsulation,

[0028] Fig. 3 is a side view of a third embodiment of a projection device with a micro-interface connector,

[0029] Fig. 4 is a side view of a fourth embodiment of a projection device with a micro-interface connector, and

[0030] Fig. 5 is a view of a fifth embodiment of a projection device.

[0031] Fig. 1 shows a first embodiment of a projection device. The projection device is used to generate and display an image in an observation field intended for the display of information and images. The projection device comprises a light source 1 for emitting a light beam 2. The light beam 2 is deflected onto a microscanner 3. A waveguide 4 is arranged downstream of the microscanner 3 in the beam path of the light beam 2. The light beam 2 is deflected onto the microscanner 3 by a concave mirror 5, which in this example is a parabolic mirror and is arranged in the beam path of the light beam 2 between the light source 1 and the microscanner 3. The concave mirror 5, designed as a parabolic mirror, also serves to collimate the light beam 2. The parabolic mirror is designed here as a rear surface mirror on the back of a glass substrate 10.

[0032] The microscanner 3 deflects the light beam toward the observation field. For this purpose, the microscanner 3 has two axes of rotation for a rotational oscillation. The scanning mirror of the microscanner 3 can oscillate around these axes of rotation, thus deflecting the light beam in different directions. After the light beam 2 has been deflected by the microscanner 3, it is preferably coupled into the waveguide 4. To couple the light beam 2 into the waveguide 4, a coupling grating 6 can be attached to the waveguide 4.

[0033] The light beam is guided toward the observation field by the waveguide 4. The waveguide 4 is preferably made of glass and is transparent to the light beam 2. Particularly preferably, the waveguide 4 is a lens of augmented reality glasses.

[0034] Fig. 2 shows a second embodiment of the projection device with a dome-shaped encapsulation 7, which together with a base plate 8 forms a cavity. The cavity is sealed gas-tight by the encapsulation 7 and the base plate 8, and the gas pressure in the cavity is lower than under normal conditions.

[0035] The light source 2 is arranged in the cavity and emits a light beam 2 in the direction of the concave mirror 5. The light beam 2 is reflected by the concave mirror 5 in the direction of the microscanner 3. In the second embodiment of the projection device, the concave mirror 5 is designed as a front surface mirror. Located in the beam path of the light beam 2 is the encapsulation 7, through which the light beam 2 is transmitted.

[0036] The microscanner 3 is designed as a MEMS scanner. The MEMS scanner is a silicon component. It is manufactured using a semiconductor process. The mirror of the MEMS scanner is suspended in solid-state joints etched from a bulk material. Layer stacks are applied, structured, and contacted to springs of the MEMS scanner. The MEMS scanner has piezo elements for driving the mirror and measuring the mirror's deflection. Bond pads 11 are provided on the microscanner 3 for contacting the piezo elements. Fig. 3 shows a third embodiment of the projection device. In the third embodiment, the light source 1 (not shown) is a fiber-coupled light source and is connected to an optical fiber connector 9. By using the optical fiber connector 9, the installation space required for the projection device can be reduced, since the light source 1 does not have to be arranged directly on the parabolic mirror 5.The light beam 2 exits the fiber optic connector 9 toward the parabolic mirror 5. In the third embodiment shown in Fig. 3, the fiber optic connector 9 is based on a standard ferrule with a diameter of 2.5 mm. A ferrule (also called a "retaining sleeve") is a small cylindrical component used in the fiber optic, electronics, construction, and mechanical engineering industries as a connecting element to connect two or more components. The ferrule provides space for a screw, rivet, or connecting rod. Ferrules are made from various materials such as ceramic, steel, copper, brass, aluminum, and plastic and can have a variety of shapes and sizes depending on the application.

[0037] The microscanner 3, the concave mirror 5, and the guide cylinder of the fiber optic connector 9, into which the fiber of the light source 1 is inserted (directly or glued into a ferrule), are preferably held by a common housing (not shown). With the ferrule, a fiber-based light source 1 is easier to handle than without. The focal point of the concave mirror 5 is located where the fiber end is located. The concave mirror 5 is thus aligned so that it is centered relative to the guide cylinder.

[0038] If the ferrule is omitted and the fiber-based light source 1 is inserted directly into a hole with a suitable (smaller) diameter, the structure of the projection device can be further reduced in size.

[0039] The concave mirror 5 is arranged so that the (largely) collimated beam is deflected toward the microscanner 3. The encapsulation 7 of the microscanner 3 has a (negative) refractive power. One or more light beams 2i-2a should exit the projection device collimated (or at least decollimated as defined by the application). In order for the light beam 2 or the light beams 2i-2a to exit the projection device collimated, the light beam 2 must be slightly convergent after the concave mirror 5. Since the refractive power of the encapsulation 7 fluctuates due to manufacturing tolerances, system collimation must be adjusted as the final adjustment step. By guiding the fiber in a guide cylinder in which the fiber itself is held centered, a pure Z-alignment can be easily achieved without having to consider any lateral drift of the light source 1. The ferrule is then not used as a “connector” but as a “linear guide”.The distance found during adjustment must then be fixed.

[0040] Fig. 4 shows a fourth embodiment of the projection device. In the fourth embodiment, the light source 1 (not shown) is also a fiber-coupled light source and is connected to a micro-interface connector 9. However, in the fourth embodiment, the micro-interface connectors 9 are based on a standard ferrule with a diameter of 1.25 mm.

[0041] In principle, the standard ferrule can also have any other diameter. Using smaller diameters is particularly useful, as this further reduces the space required for the projection device.

[0042] The ferrule, in which the fiber is mounted, can be located in a tube along which the collimation can be adjusted (as shown in Fig. 3). However, the ferrule itself can also be used for this purpose if the fiber is not initially glued into it and can thus be moved within a hole in the ferrule.

[0043] Fig. 5 shows a fifth embodiment of the projection device. In the fifth embodiment, a glass substrate 10 is arranged between the light source 1 and the parabolic mirror 5, into which the light from the light source 1 is coupled. This minimizes transitions at interfaces and the associated optical aberrations. The parabolic mirror 5 is arranged on a rear surface of the glass substrate 10.

[0044] In the fifth embodiment, the projection device comprises several light sources 1, which are designed as surface emitters and each emit a light beam 2. The light beams 2i-2a have different wavelengths or wavelength ranges. The three light beams 2i-2a are combined into a single light beam 2 by the parabolic mirror 5. The combined light beam 2 is deflected by the parabolic mirror 5 toward the microscanner 3.

[0045] In the second, third, fourth and fifth embodiments, the microscanner 3 is designed as a micro-electromechanical system (MEMS) and is configured to effect a non-linear Lissajous projection into the observation field.

[0046] Reference symbol

[0047] 1 light source(s)

[0048] 2, 2I-23 light beam

[0049] 3 micro scanners

[0050] 4 waveguides

[0051] 5 concave mirrors

[0052] 6 coupling gratings

[0053] 7 Encapsulation

[0054] 8 Base plate

[0055] 9 fiber optic connectors

[0056] 10 Glass substrate

Claims

Patent claims 1. Projection device for generating and displaying an image in an observation field intended for displaying information and images, comprising: - at least one light source (1) for emitting at least one light beam (2), - a microscanner (3) for the variable deflection of the at least one light beam (2) in the direction of the observation field, wherein the microscanner (3) has at least one axis of rotation for a rotary oscillating movement for deflecting the at least one light beam (2), - a waveguide (4) arranged downstream of the microscanner (3) in a beam path of the at least one light beam (2), and - a concave mirror (5) located between the at least one light source (1) and the microscanner (3) in the beam path of the light beam (2), which is designed to collimate the at least one light beam (2).

2. Projection device according to claim 1, wherein the concave mirror (5) is a parabolic mirror.

3. Projection device according to claim 1, wherein the concave mirror (5) is an ellipsoidal mirror.

4. Projection device according to claim 1, wherein the at least one light source (1) is designed as a surface emitter, edge emitter or as a fiber-coupled light source.

5. Projection device according to one of claims 1 to 4, wherein the projection device comprises a plurality of light sources (1 ) and each light source (1 ) emits a light beam (2i-2s).

6. Projection device according to claim 5, wherein the light beams (2i-2a) have different wavelengths from one another.

7. Projection device according to claim 5 or 6, wherein the concave mirror (5) is designed to deflect all light beams (2i-2s) simultaneously in the direction of the microscanner (3).

8. Projection device according to one of claims 1 to 7, wherein the concave mirror (5) is designed as a front surface mirror.

9. Projection device according to one of claims 1 to 7, wherein the concave mirror (5) is designed as a rear surface mirror.

10. Projection device according to one of claims 1 to 9, wherein the microscanner (3) is designed as a micro-electromechanical system (MEMS) and is configured to effect a non-linear Lissajous projection into the observation field.

11. Projection device according to one of claims 1 to 10, wherein the spectacle lens of the AR glasses is a waveguide (4).

12. Projection device according to claim 1 1, wherein the waveguide (4) also serves as a combiner.

13. Projection device according to claim 11 or 12, wherein the waveguide (4) also serves as imaging optics.

14. Augmented reality glasses containing a projection device for generating and displaying images according to one of claims 1 to 13.

Images