MEMS projector comprising a waveguide for projecting light

Abstract

The invention relates to an MEMS projector comprising a waveguide (4) for projecting light, said MEMS projector comprising: at least one light source (1) for emitting at least one light beam (2) along an optical axis (O), said at least one light beam (2) having a focal point on the optical axis (O); a microscanner (3) which is positioned on the optical axis (O) so as to variably deflect said at least one light beam (2); a waveguide (4) which is positioned between the light source (1) and the microscanner (3) transversely to the optical axis (O) in a plane near the focal point of the light beam (2) and has a coupling-in element (41) in a region around the optical axis (O); and a lens assembly (5) which is positioned between the waveguide (4) and the microscanner (3) on the optical axis (O) in order to influence the divergence of the light beam (2) in such a way that a light beam (21) deflected by the scanner mirror (31) is collimated or has a predefined divergence after penetrating the lens assembly (5).

Description

[0001] MEMS projector with waveguide for projecting light

[0002] The invention relates to a MEMS projector with a waveguide for projecting light, which can be used in particular in augmented reality glasses.

[0003] Augmented reality (AR) refers to the computer-assisted enhancement 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, i.e., 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, is 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 user's lenses or retina.

[0004] A microscanner (also known as a microelectromechanical system, or MEMS for short) can be used to project images or text information. A beam of light, generated by a light source located, for example, in the temples of AR glasses, is deflected onto the microscanner and then shaped. The light beam can then be scanned by the microscanner, creating an image in an observation field. Such an imaging system with a microscanner requires comparatively few optical elements, allowing for the creation of small and cost-effective projectors.

[0005] A microscanner 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 to create a nonlinear Lissajous projection in an observation field by deflecting a light beam incident on a deflection element during the oscillations.

[0006] 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.

[0007] In W. Davis et al.'s "MEMS-based pico projector display," published in IEEE / LEOS International Conference on Optical MEMs and Nanophotonics, Volume 2008, pp. 31-32, published in 2008, a MEMS projector is described in which light beams in an illumination beam path are reflected via a beam splitter onto a microscanner. The projection beam path is transmitted through the same beam splitter. Thus, the illumination and projection beam paths have only a slight overlap.

[0008] Microscanners are often integrated into optics or beam paths in such a way that at least one light beam is incident on the microscanner at an angle, i.e., not perpendicular to the microscanner in its rest position. This is disadvantageous because it limits the field of view angle in a projection plane that runs parallel to a mirror plane of the microscanner in its rest position. Furthermore, the oblique incidence of the light beam creates distortion. This distortion must subsequently be corrected. Furthermore, the oblique incidence of the light limits the available installation space for additional components, such as apertures, because the microscanner must be deflected further to scan the same space when the light is incident at an angle.

[0009] In addition, an illumination beam path, through which the at least one light beam travels from a light source to the microscanner, and a projection beam path, which the at least one light beam takes after being deflected by the microscanner, often run at least largely separately from each other. This results in the installation space required for the projector being unnecessarily large and wafer-based design approaches for producing the projector being inaccessible or difficult to access, resulting in correspondingly high assembly effort and manufacturing costs for MEMS projectors.

[0010] The object of the invention is therefore to provide a novel MEMS projector for projecting light, which requires very little installation space and can be manufactured very cost-effectively using a wafer-based design.The object is achieved by an M EMS projector with a waveguide for projecting light, comprising at least one light source for emitting at least one light beam along an optical axis, the at least one light beam having a focus on the optical axis, a microscanner arranged on the optical axis in such a way as to variably deflect the at least one light beam, a waveguide arranged between the light source and the microscanner transversely to the optical axis in a plane close to the focus of the light beam and having a coupling element in a region around the optical axis, and a lens arrangement arranged between the waveguide and the microscanner on the optical axis in order to influence the divergence of the light beam such that a light beam deflected by the scanner mirror is collimated after passing through the lens arrangement or has a predetermined divergence.

[0011] By arranging all optically active components on the optical axis, the MEMS projector can be manufactured very cost-effectively using a wafer-based design. Because the illumination beam path, through which the at least one light beam travels from a light source to the microscanner, and the projection beam path, which the at least one light beam takes after being deflected by the microscanner, largely overlap, the MEMS projector requires very little installation space.

[0012] Particularly preferably, at least the light source, the microscanner, and the lens arrangement are assembled using wafer-level assembly. Wafer-level assembly refers to a technology in which components are mounted directly on a wafer or as plates with multiple elements and a predetermined pitch (= distance between individual elements). A wafer is a disk made of semiconductor material, such as silicon, or an optical material such as glass or plastic. Wafer-level assembly offers several advantages over conventional chip assembly. By performing the assembly process at the wafer level, production time and costs can be significantly reduced. The plates with the elements arranged in a fixed grid are stacked and then separated.

[0013] The waveguide is essentially plate-shaped and consists of a material through which a light beam emitted by the light source can propagate. The waveguide can also be a curved, parallelepiped layer. The at least one light beam preferably propagates along the planar extent of the waveguide by total internal reflection at the outer surfaces of the waveguide. For this to happen, the light beam must be coupled into the waveguide at an angle greater than the angle of total internal reflection. The angle of total internal reflection depends on the material from which the waveguide is made. The waveguide can consist of several layers or just a single layer. The waveguide is preferably a plate made of glass or transparent optical plastic. The waveguide is particularly preferably a lens of AR glasses or the windshield of a motor vehicle.

[0014] A coupling element is arranged between the microscanner and the waveguide, through which the at least one light beam can be coupled into the waveguide. The coupling element is thus designed to couple the light beam coming from the microscanner into the waveguide. The coupling element advantageously simultaneously reduces or prevents image errors and deflections of the light beam that occur at an entrance surface of the waveguide.

[0015] In or on the waveguide, at least one output coupling element can also advantageously be mounted, at which at least a partial light beam can be output from the waveguide. This is particularly advantageous when the light beam propagates through the waveguide by total internal reflection at the outer sides of the waveguide. In this case, no total internal reflection occurs at the output coupling elements, and the light beam is transmitted through the exit surface. For this purpose, the output coupling element or a number of output coupling elements can, for example, have the same refractive index as the waveguide and a plane extending orthogonally to the light beam.

[0016] Advantageously, the coupling element has a transparent region in a narrowly defined section on the optical axis with a diameter that is larger than the diameter of the light beam on the side of the waveguide facing the microscanner. The transparent region acts as an obstruction when the light beam is coupled into the waveguide. It is therefore essential to the invention to design the transparent region as small as possible. The transparent region advantageously has a diameter of 3 to 3,000 micrometers, preferably a diameter of 3 to 100 micrometers. Particularly preferably, the diameter is a maximum of 10 micrometers. The transparent region is at least transparent to the at least one light beam coming from the light source, and the diameter of the transparent region is adapted to the diameter of the light beam on the side of the waveguide facing the microscanner.This means that the diameter of the transparent area is advantageously only slightly larger than the diameter of the (convergently incident) light beam on the side of the waveguide facing the microscanner.

[0017] The coupling element is therefore designed, particularly in its transparent area around the optical axis, in such a way that it has maximum transmission there and transmits the light beam coming from the light source to the greatest possible extent.

[0018] The transparent region of the coupling element can, for example, be made of the same material as the coupling grating and be unstructured. The transparent region can also be a hole or a recess in the coupling grating. In both cases, no coupling grating is present in the transparent region.

[0019] Advantageously, the waveguide is positioned at the focus of the light beam. When the waveguide is positioned at the focus of the light beam, the transparent area can be very small, since the light beam has its smallest diameter at its focus.

[0020] Preferably, the light source is configured to emit the at least one light beam with a predetermined first polarization. In this case, a polarizing element is arranged between the waveguide and the microscanner to change the polarization of the at least one light beam to a second polarization, and the coupling element is configured to transmit light with the first polarization and reflect light with the second polarization. The first polarization can be, for example, a horizontal linear polarization, and the second polarization can be a vertical linear polarization or a circular polarization.

[0021] The waveguide can preferably be a diffractive waveguide. A diffractive optical waveguide is a special type of waveguide based on the principle of light diffraction. The diffractive properties of the waveguide are used primarily for coupling and decoupling the light beam.

[0022] 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 equipped with elements for beam shaping and focusing. Surface emitters and fiber-coupled light sources have the advantage that the light beams emitted by these light sources are generally less divergent than those emitted by edge emitters. However, the acquisition costs of surface emitters and fiber-coupled light sources are generally significantly higher than those of edge emitters.

[0023] The at least one light source can be designed to emit a plurality of light beams with pairwise different spectral compositions. 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 by means of 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 an image in two dimensions can then be generated by simultaneously controlling a line light source and the one-dimensional microscanner.

[0024] Advantageously, an aperture can be provided to limit the light beam, mounted in a direction of incidence of the light beam at a defined position relative to the microscanner. An optical aperture is a mechanical component that controls the amount of incident light in an optical system and / or spatially limits a light beam. It is, for example, a round or polygonal opening embedded in an aperture material. The aperture material can be metal or plastic, for example. The aperture can be introduced into the MEMS mirror device, in particular, by wafer-level assembly; however, it can also be created by coating a transparent substrate with an absorbing material or an absorbing surface structure. By introducing the aperture, the contrast when generating an image can be improved.

[0025] Preferably, at least the scanner mirror of the microscanner is arranged within an encapsulation. The encapsulation hermetically encloses the scanner mirror, and an interior of the encapsulation has a gas pressure reduced compared to normal conditions. The encapsulation can either completely enclose the scanner mirror of the microscanner itself or completely enclose the scanner mirror together with other components, such as the waveguide or the microscanner. The encapsulation of the scanner mirror is intended to protect the moving mechanical and optical components of the microscanner and is essential for protecting it from external influences and contamination. Arranging the scanner mirror in a vacuum serves to reduce friction, avoid airborne particles, and mitigate thermal effects, such as heat input through convection.

[0026] The microscanner can be designed, in particular, as a micro-electro-mechanical system (MEMS) and configured to effect a nonlinear Lissajous projection into an 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 motion representation. Furthermore, the user's perception of artifacts in the three-dimensional representation of fast-moving objects is greatly reduced.

[0027] The lens arrangement preferably comprises one or more planar optical elements with a diffractive effect. The lens arrangement can also advantageously comprise one or more elements made of an optical metamaterial. Alternatively or additionally, the lens arrangement can comprise one or more metal lenses or one or more refractive optical lenses.

[0028] A diffractive optical effect refers to the phenomenon of the diffraction of light striking a periodic structure. When light strikes a periodic arrangement of structures, such as gratings, stripes, or grooves, it is diffracted and deflected in different directions.

[0029] An optical metamaterial is a man-made material that exhibits optical properties not found in natural materials. Optical metamaterials are engineered so that their optical properties are controlled by the deliberate arrangement of submicroscopic structures. Unlike conventional materials, which exhibit their optical properties due to the interaction of atoms or molecules with light, optical metamaterials are based on the control of light-matter interactions at wavelengths smaller than the wavelength of the light they influence. By deliberately designing the structure, optical metamaterials can exhibit unusual and tailored optical phenomena.

[0030] Optical metal lenses are lenses made of metal that can manipulate light. Unlike conventional lenses, which are usually made of transparent materials such as glass or plastic, optical metal lenses consist of specially shaped metallic structures. These metallic structures are microscopically small and have complex shapes that are capable of refracting and focusing light in a similar way to conventional lenses. Through the precise design of the metallic structures, optical metal lenses can create various optical effects, such as focusing light to a point or concentrating light beams. For example, optical metal lenses can be highly efficient for specific wavelength ranges of light or be capable of manipulating polarized light. Furthermore, they can be manufactured in very compact designs and small sizes.

[0031] The problem is further solved by augmented reality glasses containing a MEMS projector according to one of the described embodiments.

[0032] The invention will be described in more detail below by means of exemplary embodiments based on the drawings. These show:

[0033] Fig. 1 A view of a first embodiment of a MEMS projector with waveguide for projecting light,

[0034] Fig. 2A is a side view of the first embodiment of the MEMS projector with an illumination beam path,

[0035] Fig. 2B is a section of the side view of the first embodiment of the MEMS projector from Fig. 2A,

[0036] Fig. 3 a side view of the first embodiment of the MEMS projector with a projection beam path,

[0037] Fig. 4 is a side view of a second embodiment of the MEMS projector, comprising a lens arrangement with a diverging lens and a converging lens, Fig. 5 is a view of a third embodiment of the MEMS projector, comprising a polarizing element,

[0038] Fig. 6 is a side view of a fourth embodiment of the MEMS projector, wherein the lens arrangement comprises two metal lenses,

[0039] Fig. 7 is a view of a fifth embodiment of the MEMS projector with an aperture arranged in front of the scanner mirror and an encapsulation enclosing the scanner mirror.

[0040] A first embodiment of a MEMS projector for projecting light is shown in Fig. 1. The MEMS projector has a light source 1 that emits a light beam 2 along an optical axis O in the direction of a microscanner 3. The MEMS projector also has the microscanner 3, which is arranged on the optical axis O in order to variably deflect the at least one light beam 2. The microscanner 3 comprises a scanner mirror 31, which is suspended via two connecting elements from a frame surrounding the scanner mirror 31. Due to its suspension, the scanner mirror 31 is capable of oscillation and is designed to effect a nonlinear Lissajous projection of the light beam 2 into an observation field.

[0041] A flat, oval-shaped waveguide 4 is arranged between the light source 1 and the microscanner 3. The waveguide 4 comprises, in a region around the optical axis O, a coupling element 41 mounted on a side facing the microscanner 3, through which the light reflected by the microscanner 3 is to be coupled into the waveguide 4 as effectively as possible. A coupling grating or another suitably structured surface area on the surface of the waveguide 4 facing the microscanner 3 is preferably suitable for this purpose.

[0042] The coupling element 41 has a transparent region B on the optical axis O with a diameter that is larger than a diameter of the light beam 2 coming from the light source 1 on the side of the waveguide 4 facing the microscanner 3. Since the transparent region B represents a singular disturbance of the coupling element 41 for coupling the light reflected by the microscanner 3 into the waveguide 4 and limits its effective area, it is important to design the transparent region B as small as possible. In order to keep the transparent region B small, the waveguide 4 is positioned near a focus of the light beam 2 coming from the light source 1, which is referred to as divergent in its overall path. The light beam 2 is transmitted through the transparent region B in the direction of the microscanner 3 without being influenced by the coupling element 41.To minimize the diameter of the transparent region B, the light source 1 is configured such that the divergent light beam 2 has a focus exactly in the region of the transparent region B of the coupling element 41. This makes it possible to limit the transparent region B, which can have a diameter between 3 pm and 3 mm, to less than 100 pm or even to a maximum of 10 pm.

[0043] To ensure that the transparent region B around the optical axis O has maximum transmission, in this example it is formed as a hole or recess in the coupling element 41. However, the transparent region B can also consist of a material like the coupling element 41, but which is not structured.

[0044] Between the waveguide 4 and the microscanner 3, a lens arrangement 5 is also arranged on the optical axis O. This lens arrangement serves to influence the divergence of the light beam 2 such that a light beam 21 deflected by the scanner mirror 31 is collimated after passing through the lens arrangement 5. In the first embodiment, the lens arrangement 5 comprises only a single converging lens 51. The light beam 2 is transmitted once through the lens arrangement 5, and the deflected light beam 21 is also transmitted once through the lens arrangement 5. The converging lens 51 of the lens arrangement 5 is matched to the light source 1 and arranged in such a way as to release the divergent light beam 2 emitted by the light source 1 in a collimated state after passing through it twice.

[0045] The light beam 2 emitted by the light source 1 first passes through an illumination beam path, which is illustrated in Fig. 2A and Fig. 2B. Fig. 2A shows the entire illumination beam path of the light beam 2. The divergence of the light beam 2 present after passing through the waveguide 4 decreases as it is transmitted through the lens arrangement 5. However, the light beam 2 is still divergent after transmission.

[0046] Fig. 2B shows the transparent region B through which the light beam 2 is transmitted unaffected by the coupling element 41. After reflection and deflection by the scanner mirror 31, the deflected light beam 21 passes through a projection beam path, which is shown in Fig. 3. Since the deflected light beam 21 has been deflected or reflected by the scanner mirror 31 in the direction of the optical axis O, the illumination and projection beam paths largely overlap. The deflected light beam 21 is still divergent after deflection by the scanner mirror 31 of the microscanner 3. Only after the divergent light beam 2 has passed through the lens arrangement 5 twice is the deflected light beam 21 collimated.The lens arrangement 5 is thus designed such that the deflected light beam 21 is always collimated after its transmission through the lens arrangement 5, regardless of the direction in which the deflected light beam 21 is deflected by the scanner mirror 31.

[0047] The collimated, deflected light beam 21 is coupled into the waveguide 4 by the coupling element 41, which is preferably designed as a coupling grating. The deflected light beam 21 is guided in the waveguide 4. The light can be guided in the waveguide 4 by total internal reflection at the outer sides of the waveguide 4, as shown in Fig. 3.

[0048] The lens arrangement 5 can also consist of several lenses, for example, a converging lens 51 and a diverging lens 52, as in the second embodiment shown in Fig. 4. The interaction of the converging lens 51 and the diverging lens 52 collimates the deflected light beam 21. In the configuration shown in Fig. 4, the scanner mirror 31 of the microscanner 3 is deflected from its rest position, and the deflected light beam 21 does not run along the optical axis O.

[0049] A coupling element 41 which does not have a transparent region B is shown in Fig. 5. The third embodiment shown in Fig. 5 contains a polarizing element 6 arranged between the waveguide 4 and the microscanner 3. The light source 1 is designed to emit a light beam 2 with a predetermined first polarization. The polarizing element 6 is designed to change the polarization of the light beam 2 to a second polarization. The coupling element 41 is designed to transmit light with the first polarization and to reflect light with the second polarization. The light beam 2 emitted by the light source 1 is thus transmitted through the coupling element 41, while the deflected light beam 21 is reflected by the coupling element 41 and thus coupled into the waveguide 4.

[0050] Instead of conventional optical lenses, the lens arrangement 5 can also contain metal lenses and / or elements made of optical metamaterial. A fourth embodiment of the MEMS projector, comprising a first metal lens 53 and a second metal lens 54, is shown in Fig. 6. The first metal lens 53 acts as a diverging lens, and the second metal lens 54 as a converging lens. Similar to the second embodiment, the collimated, deflected light beam 21 is collimated by the interaction of the first metal lens 53 and the second metal lens 54 and is then coupled into the waveguide 4 by the coupling element 41, which in this example is designed as a coupling grating.

[0051] Fig. 7 shows a fifth embodiment of the MEMS projector. Similar to the second embodiment, the fifth embodiment has a converging lens 51 and a diverging lens 52, which together form the lens arrangement 5. The fifth embodiment has an aperture 7 located between the scanner mirror 31 and the converging lens 51 for limiting the light beam 2 or the deflected light beam 21. The aperture 7 must be dimensioned and arranged such that the scanner mirror 31 does not come into contact with the aperture 7 during its deflection.

[0052] Furthermore, the scanner mirror 31 is arranged within an encapsulation 8, which hermetically encloses the scanner mirror 31 together with the microscanner 3 and the waveguide 4. The interior of the encapsulation 8 has a gas pressure that is reduced compared to normal conditions.

[0053] List of reference symbols

[0054] 1 light source

[0055] 2 light beams

[0056] 21 deflected light beam

[0057] 3 micro scanners

[0058] 31 scanner mirrors

[0059] 4 waveguides

[0060] 41 Coupling element

[0061] 5 lens arrangement

[0062] 51 Converging lens

[0063] 52 Diverging lens

[0064] 53 first metal lens

[0065] 54 second metal lens

[0066] 6 polarizing element

[0067] 7 aperture

[0068] 8 Encapsulation

[0069] O optical axis

[0070] B transparent area

Claims

Patent claims 1 . MEMS projector with waveguide (4) for projecting light, comprising - at least one light source (1) for emitting at least one light beam (2) along an optical axis (O), wherein the at least one light beam (2) has a focus on the optical axis (O), - a microscanner (3) arranged on the optical axis (O) in such a way as to variably deflect the at least one light beam (2), - a waveguide (4) arranged between the light source (1) and the microscanner (3) transversely to the optical axis (O) in a plane close to the focus of the light beam (2) and having a coupling element (41) in a region around the optical axis (O), and - a lens arrangement (5) arranged between the waveguide (4) and the microscanner (3) on the optical axis (O) in order to influence the divergence of the light beam (2) in such a way that a light beam (21) deflected by the scanner mirror (31) is collimated or has a predetermined divergence after passing through the lens arrangement (5).

2. MEMS projector according to claim 1, wherein the coupling element (41) has a transparent region (B) on the optical axis (O) with a diameter that is larger than a diameter of the light beam (2) on the side of the waveguide (4) facing the microscanner (3).

3. MEMS projector according to claim 2, wherein the transparent region (B) is formed from the same material as the coupling element (41) and is not structured.

4. MEMS projector according to claim 2, wherein the transparent region (B) is a hole or a recess in the coupling element (41).

5. MEMS projector according to claim 1, wherein - the light source (1) is designed to emit the at least one light beam (2) with a predetermined first polarization, - a polarizing element (6) is arranged between the waveguide (4) and the microscanner (3) in order to change the polarization of the at least one light beam (2) to a second polarization, and - the coupling element (41) is designed to transmit light with the first polarization and to reflect light with the second polarization.

6. MEMS projector according to one of claims 1 to 5, wherein the waveguide (4) is positioned at the focus of the light beam (2).

7. MEMS projector according to one of claims 1 to 6, wherein the waveguide (4) is a diffractive waveguide.

8. MEMS projector according to one of claims 1 to 7, wherein the at least one light source (1) is designed as an edge emitter, a surface emitter or a fiber-coupled light source and is equipped with beam shaping and focusing.

9. MEMS projector according to one of claims 1 to 8, wherein in the beam path of the light beam (2) there is at least one aperture (7) mounted in a defined relative position to the microscanner (3) as a function of a direction of incidence of the light beam (2) for limiting the light beam (2).

10. MEMS projector according to one of claims 1 to 9, wherein at least the scanner mirror (31) is arranged within an encapsulation (8), the encapsulation (8) hermetically encloses the scanner mirror (31) and an interior of the encapsulation (8) has a gas pressure reduced compared to normal conditions.

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

12. MEMS projector according to one of claims 1 to 11, wherein the lens arrangement (5) comprises one or more planar optical elements with a diffractive effect.

13. MEMS projector according to one of claims 1 to 12, wherein the lens arrangement (5) contains one or more elements consisting of optical metamaterial.

14. The MEMS projector according to any one of claims 1 to 13, wherein the lens arrangement (5) includes one or more metal lenses (53, 54).

15. The MEMS projector according to any one of claims 1 to 14, wherein the lens arrangement (5) includes one or more refractive optical lenses (51, 52).

16. Augmented reality glasses containing a MEMS projector for generating and displaying images according to one of claims 1 to 15.

Images