Optical element, sensor and display device

Abstract

An optical element (1) is specified, comprising: - a transparent body (2) with a flat light coupling surface (21) configured to couple electromagnetic radiation (3) into the transparent body and a flat light coupling surface (22) configured to couple the electromagnetic radiation (3) out of the transparent body (2), - a first reflective layer (41) on an area of ​​the light coupling surface (21), - a second reflective layer (42) on an area of ​​the light output surface (22), wherein - the light coupling surface (21) and the light coupling surface (22) are parallel to each other, - the first reflective layer (41) has an opening (43) through which the electromagnetic radiation (3) is coupled into the transparent body (2), and - the first reflective layer (41) and the second reflective layer (42) are arranged such that a geometric length of an optical path (5) of the electromagnetic radiation (3) within the transparent body (2) is at least three times greater than a distance (D) between the light coupling surface (21) and the light coupling surface (22). Furthermore, a sensor (10) and a display device (100) are specified, which include the optical element (1).

Description

[0001] An optical element, a sensor, and a display device are described here.

[0002] At least one objective of certain embodiments is to specify a particularly compact optical element for redistributing irradiance. Furthermore, a sensor and a display device incorporating this optical element are specified.

[0003] According to at least one embodiment, the optical element comprises a transparent body with a flat light-input coupling surface configured to couple electromagnetic radiation into the transparent body and a flat light-output coupling surface configured to couple the electromagnetic radiation out of the transparent body. In particular, the transparent body is at least partially transparent to electromagnetic radiation. For example, at least 90% of the electromagnetic radiation coupled into the transparent body is transmitted through the transparent body. In other words, at most 10% of the electromagnetic radiation coupled into the transparent body via the light-input coupling surface is not coupled out of the transparent body via the light-output coupling surface.

[0004] In particular, the light coupling surface and the light coupling surface are planar and located on opposite sides of the transparent body. The transparent body comprises, for example, glass, a plastic material, or a semiconductor material such as silicon, or consists of one of these materials. In particular, a transparent body comprising or consisting of silicon can be used for electromagnetic radiation with wavelengths in the short-wave infrared and / or mid-infrared spectral range, with wavelengths of, for example, at least 1100 nm.

[0005] Electromagnetic radiation can have wavelengths between infrared and ultraviolet light. Electromagnetic radiation includes, for example, electromagnetic laser radiation, or it is laser radiation itself. Electromagnetic laser radiation is generated by a stimulated emission process. Compared to electromagnetic radiation generated by spontaneous emission, electromagnetic laser radiation has a longer coherence length, a narrower spectral width, and / or a higher degree of polarization. Alternatively, the electromagnetic radiation coupled into the optical element can also be focused or collimated electromagnetic radiation generated by spontaneous emission.

[0006] According to at least one further embodiment, the optical element has a first reflective layer on a region of the light coupling surface. The first reflective layer is configured to reflect at least a portion of the electromagnetic radiation propagating in the transparent body. For example, the reflectance of the first reflective layer for the electromagnetic radiation is at least 80%, preferably at least 99%, and particularly preferably at least 99.9%.

[0007] The area of ​​the light coupling surface on which the first reflective layer is arranged can comprise a portion or the entire light coupling surface. In particular, the first reflective layer comprises, or consists of, a metallic layer and / or a dielectric sequence. In particular, the dielectric sequence forms a Bragg mirror.

[0008] The Bragg mirror, for example, has a sequence of alternating dielectric layers with different refractive indices. In particular, the thickness of the dielectric layers and the refractive index contrast between the alternating dielectric layers are adjusted such that the Bragg mirror has a high reflectance for electromagnetic radiation.

[0009] According to at least one further embodiment, the optical element has a second reflective layer on a region of the light-emitting surface. The second reflective layer is configured to reflect at least a portion of the electromagnetic radiation propagating in the transparent body. Preferably, the reflectance of the second reflective layer is lower than that of the first reflective layer. Furthermore, the second reflective layer preferably transmits at least a portion of the electromagnetic radiation propagating in the transparent body. For example, the reflectance of the second reflective layer for electromagnetic radiation is at least 10%, preferably at least 50%, and particularly preferably at least 80%.For example, the transmittance of the second reflective layer for electromagnetic radiation is at most 90%, preferably at most 50% and particularly preferably at most 20%.

[0010] The area of ​​the light-emitting surface on which the second reflective layer is arranged can comprise a portion or the entire light-emitting surface. In particular, the second reflective layer comprises a metallic layer and / or a dielectric sequence, or consists of one or more of these layers. In particular, the dielectric sequence forms a Bragg mirror.

[0011] According to at least one further embodiment of the optical element, the light-input surface and the light-output surface are parallel to each other. In particular, the light-input surface and the light-output surface are parallel to each other within manufacturing tolerances. Here and in the following, the light-input surface and the light-output surface are considered to be parallel if a direction perpendicular to the light-input surface and a direction perpendicular to the light-output surface differ from each other by at most 5°, preferably by at most 1°. For example, the light-input surface and the light-output surface are opposite surfaces of a planar transparent body. Alternatively, the light-input surface and the light-output surface can form an angle. Furthermore, the light-input surface and / or the light-output surface can be curved.

[0012] According to at least one further embodiment of the optical element, the first reflective layer has an aperture through which electromagnetic radiation is coupled into the transparent body. In particular, the light coupling surface within the aperture is free of the reflective layer. The aperture can have any shape, for example, circular, elliptical, oval, square, rectangular, or polygonal. In particular, the diameter of the aperture in the first reflective layer is equal to or greater than a beamwidth of the electromagnetic radiation on the light coupling surface. The beamwidth of the electromagnetic radiation is defined here and in the following as a radial diameter in a plane perpendicular to the direction of propagation in which the intensity of the electromagnetic radiation has decreased to 13% of a maximum intensity within that plane.

[0013] For example, due to the opening in the first reflective layer, only a small portion of the electromagnetic radiation is reflected by the first reflective layer when the electromagnetic radiation is coupled into the transparent body. For example, less than 5%, preferably less than 1%, of the electromagnetic radiation is reflected by the first reflective layer when the electromagnetic radiation is coupled into the transparent body.

[0014] According to at least one further embodiment of the optical element, the first reflective layer and the second reflective layer are arranged such that the geometric length of an optical path of the electromagnetic radiation within the transparent body is at least three times greater than the distance between the light coupling surface and the light coupling surface. In particular, the optical path corresponds to a light beam of electromagnetic radiation that is coupled into the transparent body via the light coupling surface and coupled out of the transparent body via the light coupling surface.

[0015] For example, at least some of the electromagnetic radiation coupled into the transparent body via the light-input coupling surface is reflected by the second reflective layer on the light-output coupling surface and deflected to the first reflective layer on the light-input coupling surface. The first reflective layer can further deflect most or all of the incident electromagnetic radiation to the light-output coupling surface, where it is either coupled out of the transparent body or reflected again by the second reflective layer. In particular, at least some of the electromagnetic radiation coupled into the transparent body can be reflected multiple times between the first reflective layer and the second reflective layer before being coupled out of the transparent body.Preferably, different reflected components of the electromagnetic radiation do not interfere within the transparent body. In other words, the optical path of the electromagnetic radiation within the transparent body is such that the different reflected components of the electromagnetic radiation hardly or not at all interfere within the transparent body.

[0016] According to a preferred embodiment, the optical element has: - a transparent body with a flat light coupling surface configured to couple electromagnetic radiation into the transparent body, and a flat light coupling surface configured to couple the electromagnetic radiation out of the transparent body, - a first reflective layer on an area of ​​the light coupling surface, - a second reflective layer on an area of ​​the light output surface, wherein - the light coupling surface and the light coupling surface are parallel to each other, - the first reflective layer has an opening through which the electromagnetic radiation is coupled into the transparent body, and - the first reflective layer and the second reflective layer are arranged such that a geometric length of an optical path of the electromagnetic radiation within the transparent body is at least three times greater than a distance between the light coupling surface and the light coupling surface.

[0017] The optical element described here makes it possible to redistribute the irradiance of electromagnetic radiation by, for example, increasing the cross-sectional area and / or the beam width of the electromagnetic radiation. In particular, the optical element can be used to reduce the maximum irradiance of the electromagnetic radiation near an electromagnetic emitter, while the radiation characteristics of the electromagnetic radiation remain virtually unchanged at large distances from the emitter.

[0018] Advantageously, the optical element can have a particularly small thickness and can be integrated into a compact housing. Here and in the following, the thickness refers to the distance between the light coupling surface and the light output surface of the optical element.

[0019] Electromagnetic radiation is emitted, for example, by a sensor, such as a distance sensor for measuring the distance between the sensor and an external object. In particular, the electromagnetic radiation emitted by the sensor may pass through another element, such as a screen, before being emitted towards the external object. If the irradiance of the electromagnetic radiation on the screen is too high, the screen's luminance may be visibly distorted at the point where the electromagnetic radiation passes through the screen. Such visible distortions can be reduced or eliminated by redistributing the irradiance of the electromagnetic radiation on the screen using the optical element disclosed herein.Furthermore, the performance and / or functionality of the sensor remains unaffected by the optical element, since the properties of the electromagnetic radiation at large distances from the sensor remain virtually unaffected by the optical element.

[0020] According to at least one further embodiment, the optical element reduces the maximum irradiance of electromagnetic radiation on a reference plane downstream of the optical element by at least 50%, preferably by at least 90%. Here and in the following, irradiance denotes the radiant flux of electromagnetic radiation received by a surface, such as the reference plane, per unit area. In particular, irradiance is expressed in W / m². 2 measured.

[0021] In particular, the reference plane refers to a plane downstream of the optical element in which the irradiance can be measured. Preferably, the reference plane is parallel to the light-emitting surface. For example, the distance between the reference plane and the light-emitting surface is less than or equal to the thickness of the optical element.

[0022] Due to the increased geometric length of the optical path of the electromagnetic radiation within the transparent body, the beam width of the electromagnetic radiation coupled out of the optical element increases, for example. Consequently, the irradiance on the reference plane decreases compared to a situation in which no optical element as described here is present.

[0023] According to at least one further embodiment of the optical element, the beam divergence of the electromagnetic radiation coupled out of the optical element is at most 20%, preferably at most 10%, greater or less than the beam divergence of the electromagnetic radiation coupled into the optical element. Here and in the following, beam divergence is an angular measure of the increase in beam width along a propagation direction of the electromagnetic radiation. In particular, beam divergence indicates the opening angle of a cone within which the majority of the electromagnetic radiation propagates.

[0024] Preferably, the optical element does not alter the beam divergence of the electromagnetic radiation. In other words, the optical element does not focus, collimate, or defocus the electromagnetic radiation.

[0025] Preferably, the electromagnetic radiation coupled into the optical element is incident on the light coupling surface in a direction parallel to a surface normal of the light coupling surface. In other words, the electromagnetic radiation preferably strikes the light coupling surface at an angle perpendicular to the light coupling surface. Alternatively, the electromagnetic radiation can be coupled into the optical element at any angle of incidence with respect to the light coupling surface.

[0026] For example, the electromagnetic radiation is coupled into the optical element at such an angle that it propagates laterally within the transparent body, undergoing multiple reflections between the first and second reflecting layers before being coupled out of the optical element. Here and in the following, "lateral" refers to a direction parallel to the light coupling surface and / or parallel to the light coupling surface. In particular, as the electromagnetic radiation propagates laterally, its radiative width increases, thereby reducing the irradiance at the light coupling surface.

[0027] According to at least one further embodiment of the optical element, an antireflection coating is arranged on the light coupling surface within the aperture in the first reflective layer. In particular, the antireflection coating is arranged directly on the light coupling surface of the transparent body. The antireflection coating reduces, for example, a portion of the electromagnetic radiation reflected at the light coupling surface when the electromagnetic radiation is coupled into the transparent body by at least 50%.

[0028] According to at least one further embodiment of the optical element, a first refractive optical element is arranged on the light-input surface and covers the aperture in the first reflective layer. For example, the first refractive optical element can be arranged directly on the light-input surface of the transparent body within the aperture of the first reflective layer, or the first refractive optical element can be arranged directly on the first reflective layer so that it covers the aperture. In particular, an area of ​​the first reflective layer around the aperture can also be covered by the refractive optical element.

[0029] According to at least one further embodiment of the optical element, the first refractive optical element is configured to reduce the irradiance of the electromagnetic radiation on the light output surface. In particular, the first refractive optical element reduces the maximum irradiance of the electromagnetic radiation on the light output surface. The first refractive optical element comprises, for example, a lens, a microlens, a lens array, and / or a microlens array.

[0030] Furthermore, the first refractive optical element can be configured to reduce light loss. For example, the first refractive optical element is configured to reduce a portion of the electromagnetic radiation that is reflected back from the second reflective layer to the aperture in the first reflective layer and can thus be coupled out of the optical element through the light coupling surface.

[0031] According to at least one further embodiment of the optical element, the first refractive optical element has a concave conical lens, or it is a concave conical lens. In other words, the first refractive optical element has a concave axicon, or it is a concave axicon. In particular, the concave conical lens has a material transparent to electromagnetic radiation, such as glass or a plastic, for example, epoxy. Furthermore, the concave conical lens has a concave conical surface with a fixed apex angle. The concave conical lens, for example, focuses a point light source onto a ring. Compared to a non-conical concave lens, the concave conical lens has a higher alignment tolerance and is therefore easier to position on the light coupling surface.

[0032] According to at least one further embodiment of the optical element, a first diffractive optical element is arranged on the light-input surface and covers the aperture in the first reflective layer. For example, the first diffractive optical element can be arranged directly on the light-input surface of the transparent body within the aperture of the first reflective layer, or the first diffractive optical element can be arranged directly on the first reflective layer so that it covers the aperture. In particular, a region of the first reflective layer around the aperture can also be covered by the first diffractive optical element.

[0033] According to at least one further embodiment of the optical element, the first diffractive optical element is configured to reduce the irradiance of the electromagnetic radiation on the light output coupling surface. In particular, the first diffractive optical element has the same functions as the first refractive optical element. All functional features of the first refractive optical element are also disclosed for the first diffractive optical element, and vice versa.

[0034] The first diffractive optical element, for example, has or consists of a concentric grating or a meta-lens. The meta-lens, for example, has a nanostructured surface. In particular, the nanostructured surface has an aperiodic arrangement of nanopillars designed to impart a spatially dependent phase to the incident electromagnetic radiation. The first diffractive optical element is realized, for example, by nanoimprinting the light coupling surface of the transparent element or by nanoimprinting an at least partially transparent layer on the light coupling surface.

[0035] According to at least one further embodiment of the optical element, the second reflective layer has a first sub-region and a second sub-region, and the reflectance of the first sub-region differs from the reflectance of the second sub-region. In particular, the reflectance indicates the proportion of the incident electromagnetic radiation that is reflected by the respective sub-region. Preferably, the first sub-region and the second sub-region are directly adjacent to each other. For example, the second sub-region has a lower reflectance than the first sub-region, or vice versa. For example, the first sub-region has a reflectance between 90% and 100% inclusive, while the second sub-region has a reflectance between 70% and 90% inclusive.

[0036] The second reflective layer can also have more than two sub-regions with different reflectances and / or transmittances. For example, the second reflective layer may have multiple sub-regions with different reflectances for electromagnetic radiation. The second reflective layer may also have a continuously varying reflectance gradient along a direction parallel to the light-emitting surface. For example, the reflectance of the second reflective layer decreases continuously with increasing radius from the center of the second reflective layer.

[0037] According to at least one further embodiment of the optical element, the second sub-area completely surrounds the first sub-area in a top view of the light-emitting surface. In particular, the first sub-area and the second sub-area are arranged concentrically. For example, the first sub-area is circular and the second sub-area is annular in a top view of the light-emitting surface.

[0038] According to at least one further embodiment of the optical element, a second refractive optical element is arranged on the second reflective layer and / or on the light-emitting surface. The second refractive optical element is, for example, a lens, a microlens, a lens array, or a microlens array. Preferably, the second refractive optical element is arranged directly on the second reflective layer and / or directly on the light-emitting surface of the transparent body.

[0039] According to at least one further embodiment of the optical element, the second refractive optical element is configured to reduce the beam divergence of the electromagnetic radiation coupled out of the optical element. For example, the first refractive optical element increases the beam divergence, while the second refractive optical element decreases it, so that the electromagnetic radiation coupled out of the optical element has the same or a similar beam divergence as the electromagnetic laser radiation coupled into the optical element. In particular, the first refractive optical element and the second refractive optical element are configured such that the beam width of the electromagnetic radiation coupled out of the optical element is increased, while the beam divergence remains unaffected by the optical element.

[0040] The second refractive optical element can be configured to adjust the properties of the electromagnetic radiation exiting the optical element. In particular, the second refractive optical element can be configured to adjust the beam divergence of the electromagnetic radiation. For example, the second refractive optical element can be configured to collimate and / or focus the electromagnetic radiation.

[0041] According to at least one further embodiment of the optical element, the second refractive optical element comprises a convex conical lens. In particular, the convex conical lens comprises a material transparent to electromagnetic radiation, such as glass or a plastic, for example, epoxy. Furthermore, the convex conical lens has a convex conical surface with a fixed apex angle.

[0042] Preferably, the convex conical lens has two or more segments arranged concentrically. For example, each segment comprises a portion of the convex conical surface, and the segments are offset along an axial direction of the convex conical surface. In other words, the convex conical lens is a Fresnel lens. Preferably, in a top view of the light-emitting surface, the shape of a segment coincides with and directly overlaps the shape of a portion of the second reflective layer. In other words, for example, each segment of the convex conical lens is positioned directly on a corresponding portion of the second reflective layer. In particular, a portion of the electromagnetic radiation transmitted through a portion of the second reflective layer propagates further through the corresponding segment of the convex conical lens.

[0043] According to at least one further embodiment of the optical element, the apex angle of the concave conical lens and the apex angle of the convex conical lens are equal. In particular, the apex angles are equal within manufacturing tolerances. For example, the apex angle of the convex conical lens and the apex angle of the concave conical lens may differ by no more than 5°, preferably by no more than 1°. By matching the apex angles of the convex conical lens and the concave conical lens, the beam width of the electromagnetic radiation coupled out of the optical element is increased, while the beam divergence of the electromagnetic radiation remains unaffected.

[0044] According to at least one further embodiment of the optical element, a second diffractive optical element is arranged on the second reflective layer and / or on the light-emitting surface. Preferably, the second diffractive optical element is arranged directly on the second reflective layer and / or directly on the light-emitting surface of the transparent body.

[0045] According to at least one further embodiment of the optical element, the second diffractive optical element is configured to reduce beam divergence of the electromagnetic radiation coupled out of the optical element. In particular, the second diffractive optical element has the same functions as the second refractive optical element. All functional features of the second refractive optical element are also disclosed for the second diffractive optical element, and vice versa.

[0046] The second diffractive optical element comprises, for example, a concentric grating or a meta-lens. The meta-lens, for example, has a nanostructured surface. In particular, the nanostructured surface has an aperiodic arrangement of nanopillars designed to impart a spatially dependent phase to the incident electromagnetic radiation. The second diffractive optical element is realized, for example, by nanoimprinting the light-emitting surface of the transparent body, or by nanoimprinting the second reflective layer arranged on the light-emitting surface of the transparent body, or by nanoimprinting an at least partially transparent layer arranged on the light-emitting surface and / or on the second reflective layer.

[0047] Furthermore, a sensor is described here. Preferably, the sensor includes an optical element described herein. All features of the optical element are also disclosed for the sensor, and vice versa.

[0048] According to at least one embodiment, the sensor has an optical element. In particular, the sensor has an optical element as described above.

[0049] According to at least one further embodiment, the sensor has an emitter for emitting electromagnetic radiation. The emitter emits, for example, electromagnetic radiation with wavelengths between infrared and ultraviolet light. The emitter particularly comprises a laser diode or a light-emitting diode. The laser diode, for example, has an optical resonator and an epitaxial semiconductor layer stack with a pn junction. The pn junction, together with the optical resonator, is configured to convert an electric current into electromagnetic laser radiation. In contrast, the light-emitting diode does not have a resonator and generates electromagnetic radiation by spontaneous emission.

[0050] According to at least one further embodiment, the sensor has a detector configured to detect at least a portion of the electromagnetic radiation reflected by an external object. In particular, the electromagnetic radiation emitted by the emitter and coupled out of the sensor is partially reflected by the external object. At least a portion of the reflected electromagnetic radiation is coupled into the sensor and detected by the detector. In particular, the detector converts the incident electromagnetic radiation into an electrical signal.

[0051] According to at least one further embodiment of the sensor, the emitter, the optical element and the detector are arranged such that the electromagnetic radiation emitted by the emitter passes through the optical element before being coupled out of the sensor, and the electromagnetic radiation coupled into the sensor does not pass through the optical element before it hits the detector.

[0052] The sensor is, for example, a distance sensor, a heart rate sensor, or an oxygen saturation sensor. Specifically, the distance sensor measures the distance between the sensor and the external object. For example, the distance sensor measures the travel time of a laser pulse emitted by the sensor towards the external object, reflected by the external object, and finally detected by the detector. Alternatively or additionally, the sensor can determine the distance to the external object by measuring the intensity of the detected electromagnetic radiation.

[0053] The heart rate sensor or the oxygen saturation sensor can determine a heart rate or an oxygen saturation in the blood, for example, by measuring a relative change in the intensity of the reflected electromagnetic radiation.

[0054] According to at least one further embodiment of the sensor, the emitter comprises a vertical cavity surface-emitting laser diode. Specifically, the surface-emitting laser diode emits electromagnetic laser radiation in a direction perpendicular to a principal plane of extension of the semiconductor layers in the semiconductor stack. In other words, the electromagnetic laser radiation is emitted in a direction parallel to an epitaxial growth direction of the semiconductor stack.

[0055] Advantageously, a radial beam profile of the electromagnetic laser radiation emitted by the surface-emitting laser diode exhibits a dip in the beam center. In other words, the intensity of the electromagnetic laser radiation is higher at small, but finite, emission angles than the intensity of the electromagnetic laser radiation emitted at an emission angle of zero degrees in the forward direction. The dip in the beam profile at the beam center can be advantageously used to reduce the proportion of electromagnetic laser radiation that is reflected back to the emitter by the optical element and thus lost.

[0056] According to at least one further embodiment of the sensor, the detector comprises a photodiode, a phototransistor, a single-photon avalanche diode, a photodiode array, and / or a single-photon avalanche diode array. For example, the detector comprises an epitaxial semiconductor layer stack with a pn junction configured to convert incident electromagnetic radiation into an electrical output current. In particular, the photodiode array comprises a plurality of photodiodes, arranged, for example, in a plane. The single-photon avalanche diode array comprises a plurality of single-photon avalanche diodes, arranged, for example, in a plane.

[0057] Furthermore, a display device is described here. Preferably, the display device includes a sensor as described above. All features of the sensor are also disclosed for the display device, and vice versa.

[0058] According to at least one embodiment, the display device includes a sensor. In particular, the display device includes a sensor as described above. The sensor is, for example, a distance sensor, a heart rate sensor, and / or an oxygen saturation sensor.

[0059] According to at least one further embodiment, the display device has a partially transparent screen arranged such that the electromagnetic radiation emitted by the sensor is transmitted through the screen before being coupled out of the display device towards the external object. In particular, the screen is at least partially transparent to the electromagnetic radiation emitted by the sensor.

[0060] The screen emits electromagnetic radiation in the visible spectral range. Preferably, the screen and the sensor have the same or a similar direction of emission for their respective electromagnetic radiation. The sensor is, for example, a distance sensor, and the display device changes the information shown on the screen according to the distance between the sensor and an external observer.

[0061] According to at least one further embodiment of the display device, the screen has a plurality of individually addressable pixels. The screen is, for example, configured to display information in the form of an image. In particular, the plurality of individually addressable pixels is arranged in the form of a two-dimensional array.

[0062] According to at least one further embodiment of the display device, each pixel comprises an organic light-emitting diode and / or a micro-LED. In particular, the organic light-emitting diode comprises an organic functional layer stack configured to convert an electric current into electromagnetic radiation. The organic functional layer stack includes a layer of organic molecules that are organic semiconductors.

[0063] Alternatively or additionally, each pixel can have a light-emitting semiconductor diode and / or a thin-film transistor. The screen is, for example, a micro-LED display or a liquid crystal display with thin-film transistors (TFT). In particular, each pixel of the micro-LED display has a light-emitting semiconductor diode with an edge length of at most 50 µm, preferably at most 20 µm. For example, each micro-LED has an edge length of approximately 12 µm.

[0064] According to at least one further embodiment of the display device, the optical element reduces the maximum irradiance of the electromagnetic radiation emitted by the sensor onto the screen, such that the screen's luminance changes by no more than 2%, preferably no more than 0.5%, due to the electromagnetic radiation. The electromagnetic radiation emitted by the sensor can, for example, lead to a visible distortion of an image displayed on the screen. Advantageously, the optical element reduces the maximum irradiance of the electromagnetic radiation on the screen to such an extent that no visible distortions can be observed on the screen by an external viewer. Furthermore, the optical element preferably does not significantly alter the emitter's directional characteristic.Accordingly, the functionality of the sensor is not impaired by the optical element.

[0065] Further advantageous embodiments and further embodiments of the optical element, the sensor and the display device will become apparent from the following exemplary embodiments, which are described in connection with the figures. Fig. Figure 1 shows a schematic cross-section of an optical element according to an exemplary embodiment. Fig. Figure 2 shows a schematic top view of a light output surface of an optical element according to an exemplary embodiment. The Fig. 3 and Fig. Figure 4 shows schematic irradiance distributions of electromagnetic laser radiation coupled from an optical element according to an exemplary embodiment. Fig. Figure 5 shows a schematic cross-section of an optical element according to a further embodiment. Fig. Figure 6 shows a schematic top view of a light output surface of an optical element according to a further embodiment. Fig. Figure 7 shows a schematic irradiance distribution of electromagnetic laser radiation coupled out of an optical element according to a further embodiment. The Fig. Figures 8 to 10 show schematic cross-sections of optical elements according to further embodiments. Fig. Figure 11 shows a schematic perspective view of a second refractive optical element of an optical element according to an embodiment. Fig. Figure 12 shows a schematic irradiance distribution according to an example. Fig. Figure 13 shows a schematic irradiance distribution according to an exemplary embodiment. Fig. Figure 14 shows a schematic cross-section of a sensor according to an exemplary embodiment. The Fig. 15 and Fig. Figure 16 shows schematic cross-sections of a display device according to exemplary embodiments.

[0066] Elements that are identical or similar, or have the same effect, are marked with the same reference symbols in the figures. The figures and the proportions of the elements depicted in the figures are not to scale. Rather, individual elements, especially layer thicknesses, may be exaggerated for clarity and / or better understanding.

[0067] The optical element 1 according to the in Fig. The embodiment shown in Figure 1 comprises a transparent body 2, a first reflective layer 41, and a second reflective layer 42. The transparent body 2 is made of glass and has a flat light-input surface 21 and a flat light-output surface 22 parallel to the light-input surface 21 on opposite sides of the transparent body 2.

[0068] The first reflective layer 41 is arranged directly on the light coupling surface 21. The first reflective layer 41 completely covers the light coupling surface 21 except for an opening 43 through which electromagnetic laser radiation 3 is coupled into the transparent body 2. The opening 43 has a circular shape or a shape corresponding to a beam profile of the electromagnetic laser radiation 3. In particular, the diameter of the opening 43 is equal to or greater than a beam width of the electromagnetic laser radiation 3 on the light coupling surface 21. The first reflective layer 41 comprises a metallic layer or a Bragg mirror and preferably has a reflectance of at least 99.9% for the electromagnetic laser radiation 3.

[0069] The second reflective layer 42 is arranged directly on the light output surface 22. It covers a circular area of ​​the light output surface 22 opposite the aperture 43 in the first reflective layer 41. The second reflective layer 42 has a metallic layer or a Bragg mirror and preferably has a reflectance of at least 80% for the electromagnetic laser radiation 3.

[0070] The electromagnetic laser radiation 3 is emitted by an emitter 11 that is not part of the optical element 1. The electromagnetic laser radiation 3 has a beam divergence α before it is coupled into the optical element 1. The optical element 1 does not change the beam divergence α of the electromagnetic laser radiation 3. In particular, the electromagnetic laser radiation 3 coupled out of the optical element 1 has the same beam divergence α as the electromagnetic laser radiation 3 coupled into the optical element 1.

[0071] One diameter of the second reflective layer 42 corresponds to the beam width of the electromagnetic laser radiation 3 on the light output surface 22 before the electromagnetic laser radiation 3 is at least partially reflected by the second reflective layer 42. In other words, all of the electromagnetic laser radiation 3, which is coupled into the transparent body 2 via the aperture 43 in the first reflective layer 41 and transmitted through the transparent body 2, reaches the second reflective layer 42.

[0072] Furthermore, in Fig. Figure 1 shows optical paths 5 or light rays of the electromagnetic laser radiation 3. In particular, at least a part of the electromagnetic laser radiation 3, which is coupled into the transparent body 2 through the aperture 43 in the first reflective layer 41, propagates through the transparent body 2 and is reflected back to the first reflective layer 41 by the second reflective layer 42. The first reflective layer 41 further deflects the electromagnetic laser radiation 3 towards the light output surface 22, where it is coupled out of the optical element 1.

[0073] Accordingly, the geometric length of at least some optical paths 5 within the transparent body 2 is at least three times the distance D between the first reflecting layer 41 and the second reflecting layer 42. Here, the distance D corresponds to the thickness of the transparent body 2. The optical element 1 thus limits an irradiance distribution of the electromagnetic laser radiation 3 at a fixed distance from the emitter 11. In particular, the beamwidth of the electromagnetic laser radiation 3 coupled out of the optical element 1 is increased by the optical element 1. Consequently, the irradiance of the electromagnetic laser radiation 3 is decreased by the optical element 1.

[0074] Fig. Figure 2 shows a top view of the light output surface 22 of the optical element 1 according to the diagram in conjunction with Fig. The second reflective layer 42 is circular and covers only a portion of the light-emitting surface 22. A circular second reflective layer 42 advantageously results in an approximately radially symmetrical beam profile of the electromagnetic laser radiation 3 coupled out of the optical element 1.

[0075] The Fig. 3 and Fig. Figure 4 shows schematic irradiance distributions E of the electromagnetic laser radiation 3 coupled out of the optical element 1 according to the one in conjunction with Fig. The embodiment described in 1 is shown in particular. Fig. 3 and Fig. 4 the irradiance distribution E in the top view of the light output surface 22 at a fixed distance to the light output surface 22.

[0076] The in Fig. The irradiance distribution E shown in Figure 3 corresponds to an optical element 1 in which both the first reflective layer 41 and the second reflective layer 42 have a reflectance of nearly 100% and a transmittance of nearly 0%. Accordingly, the electromagnetic laser radiation 3 exhibits a ring-shaped irradiance distribution E, where the irradiance E between the inner and outer diameters of the ring is finite and the irradiance E elsewhere is approximately zero.

[0077] In contrast, the one in Fig. Figure 4 shows the irradiance distribution E of an optical element 1, in which the first reflective layer 41 has a reflectance of 100%, while the second reflective layer 42 has a reflectance of 90% and a transmittance of 10% for the electromagnetic laser radiation 3. Accordingly, the irradiance E is, in comparison to Fig. 3 within the inner diameter of the ring due to the fraction of electromagnetic laser radiation 3 which is transmitted through the second reflective layer 42, finally.

[0078] As opposed to Fig. 1 has the optical element 1 according to the embodiment in Fig. 5 a second reflective layer 42 with a first sub-area 421 and a second sub-area 422, which directly adjoins and completely surrounds the first sub-area 421. In particular, the first sub-area 421 is like the one associated with Fig. 1. The second reflective layer 42 is configured as described above. The second sub-area 422 is annular and has an inner diameter corresponding to the diameter of the first sub-area 421. The outer diameter of the second sub-area 422 is configured such that an optical path 5 of the electromagnetic laser radiation 3 incident at the edge of the first sub-area 421 is redirected through the first reflective layer 41 to an outer edge of the second sub-area 422, away from the first sub-area 421.

[0079] The first sub-area 421 has a reflectance of 90% and a transmittance of 10%, while the second sub-area 422 has a reflectance of 80% and a transmittance of 20% for the electromagnetic laser radiation 3. Accordingly, the in Fig. The optical element 1 shown in section 5 has a wider irradiance distribution than that associated with Fig. 1 disclosed optical element 1. In particular, some optical paths 5 of the electromagnetic laser radiation 3 have a geometric length that is at least five times greater than a distance D between the first reflecting layer 41 and the second reflecting layer 42.

[0080] Fig. Figure 6 shows a top view of the light output surface 22 of the device in conjunction with Fig. 5 described optical element 1. The second reflective layer 42 has a circular first sub-area 421 and a ring-shaped second sub-area 422, which are directly adjacent to each other.

[0081] Fig. Figure 7 shows a schematic irradiance distribution E of the electromagnetic laser radiation 3 coupled out of the optical element 1 according to the one in conjunction with Fig. 5 described embodiment. In particular, in Fig. Figure 7 shows the irradiance distribution E in a top view of the light output surface 22 at a fixed distance from the light output surface 22. The irradiance distribution E has a circular inner region and two concentric annular outer regions.

[0082] In particular, the inner circular region exhibits electromagnetic laser radiation 3, which is transmitted through the first subregion 421 of the second reflecting layer 42, while the inner annular region exhibits electromagnetic laser radiation 3, which is transmitted through the second subregion 422 of the second reflecting layer 42. The outer annular region of the irradiance distribution E exhibits electromagnetic laser radiation 3, which is reflected by the second subregion 422 of the second reflecting layer 42 towards the first reflecting layer 41 and is further deflected by it towards the light output coupling surface 22.

[0083] The optical element 1 according to the embodiment in Fig. 8 shows, in comparison to the one in connection with Fig. In the embodiment described in Figure 5, a first refractive optical element 61 is further described. The first refractive optical element 61 is a concave conical lens arranged on the light coupling surface 21 of the transparent body 2. In particular, the concave conical lens covers the aperture 43 in the first reflective layer 41 and is configured to increase the beam diameter of the electromagnetic laser radiation 3. An antireflection layer (44) can be arranged between the first refractive optical element 61 and the light coupling surface 21. Furthermore, the concave conical lens reduces light losses by decreasing the proportion of the electromagnetic laser radiation 3 that is reflected by the second reflective layer 42 and coupled out of the optical element 1 through the aperture 43 in the first reflective layer 41 on the light coupling surface 21.

[0084] Compared to the one associated with Fig. The optical element disclosed in section 8 has the optical element according to the exemplary embodiment in Fig. 9 furthermore, a second reflective layer 42 with an additional third sub-area 423. The third sub-area 423 is arranged concentrically around the second sub-area 422. The reflectance and transmittance of the first, second, and third sub-areas 421, 422, 423 can be adjusted, for example, to achieve a more homogeneous irradiance distribution of the electromagnetic radiation 3 coupled out of the optical element 1.

[0085] Furthermore, the optical element 1 comprises a second refractive optical element 62. The second refractive optical element 62 is a convex conical lens and is arranged directly on the second reflective layer 42. The second refractive optical element 62 is configured to re-collimate the electromagnetic laser radiation 3. In particular, the second refractive optical element 62 reduces beam divergence of the electromagnetic laser radiation 3. For example, the second refractive optical element 62 compensates for an increase in beam divergence caused by the first refractive optical element 61. Advantageously, the apex angle φ of the conical surface of the first reflective optical element 61 is, within manufacturing tolerances, equal to the apex angle φ of the conical surface of the second refractive optical element 62.By adjusting the apex angles φ of the concave conical lens and the convex conical lens, the beam divergence of the electromagnetic laser radiation 3 passing through the optical element 1 remains unaffected by the optical element 1.

[0086] The convex conical lens is a Fresnel-type lens with a circular central segment surrounded, in the top view of the light-emitting surface 22, by two concentric ring-shaped segments. Segments of the convex conical lens overlap with corresponding portions of the second reflective layer 24 in the top view of the light-emitting surface 22. By using a Fresnel-type convex conical lens, the optical element 1 is advantageously more compact.

[0087] Fig. Figure 10 shows optical paths 5 of electromagnetic laser radiation 3, which connect an optical element 1 according to the one in conjunction with Fig. The process is carried out as described in the embodiment 9. First, the electromagnetic laser radiation 3 is deflected by the first refractive optical element 61 such that the beam width of the electromagnetic laser radiation 3 within the transparent body 2 is increased. Furthermore, the electromagnetic laser radiation 3 is partially transmitted and partially reflected by the first sub-region 421 of the second reflective layer 42. The transmitted portion of the electromagnetic laser radiation 3 is re-collimated by a first segment of the second refractive optical element 62 and coupled out of the optical element 1.

[0088] The portion of the electromagnetic laser radiation 3 reflected by the first sub-area 421 is deflected by the first reflective layer 41 onto the second sub-area 422. The electromagnetic laser radiation 3 incident on the second sub-area 422 is partially transmitted and partially reflected. The transmitted portion is re-collimated by a segment of the second refractive optical element 62 and coupled out of the optical element 1. The reflected portion is further deflected by the first reflective layer 41, coupled out by the third sub-area 423, and re-collimated by a third segment of the second refractive optical element 62 before being coupled out of the optical element 1. In this example, the third sub-area 423 does not reflect the incident electromagnetic radiation 3.

[0089] The second refractive optical element 62 of an optical element 1 according to the one described in Fig. The embodiment shown in Figure 11 is a Fresnel-type convex conical lens. In particular, the convex conical lens has conical surface segments that are arranged concentrically offset along an axial direction. Each conical surface segment has the same apex angle.

[0090] The in Fig. The irradiance distribution E shown in Figure 12 corresponds to the irradiance E of the electromagnetic laser radiation 3 emitted by a surface-emitting laser diode (VCSEL). Specifically, the irradiance E is shown as a contour diagram over a surface perpendicular to the direction of propagation of the electromagnetic laser radiation 3 at a fixed distance from the surface-emitting laser diode. In addition, corresponding line diagrams of the irradiance E along an x-direction and along a perpendicular y-direction are shown.

[0091] The electromagnetic laser radiation 3 has an approximately circular beam profile, and the irradiance E exhibits a dip at the beam center. In other words, the electromagnetic laser radiation 3 emitted by the surface-emitting laser diode is not a Gaussian beam with an irradiance maximum E at the beam center. In contrast, the irradiance E is maximal along a ring-shaped contour that is concentric with the beam center.

[0092] The in Fig. The irradiance distribution E shown in Figure 13 corresponds to the irradiance E of a surface-emitting laser diode as in Fig. 12 shown, after it was transmitted through an optical element 1 according to an exemplary embodiment. In comparison to the one in Fig. The irradiance distribution E shown in Figure 12 exhibits the irradiance distribution in Fig. 13 a larger spatial extent in the x and y directions and the maximum irradiance E is lower.

[0093] The sensor 10 according to the in Fig. The embodiment shown in Figure 14 comprises an emitter 11 and a detector 12 arranged on a support 13. The emitter 11 is a surface-emitting laser diode and the detector 12 is a photodiode, while the support 13 is a printed circuit board with electrical contacts for the emitter 11 and the detector 12. Alternatively, the emitter 11 can, for example, comprise a light-emitting semiconductor diode and focusing or collimating optics.

[0094] During operation, the emitter 11 emits electromagnetic laser radiation 3 in a direction perpendicular to the substrate. The electromagnetic laser radiation 3 passes through an optical element 1 to redistribute the irradiance E in lateral directions parallel to the main surface of the substrate 13. Electromagnetic laser radiation 3 that is reflected from an external object and strikes the detector 12 does not pass through the optical element 1.

[0095] The optical element 1 is connected to the carrier 13 by a housing 14, for example, a frame. The housing 14, the optical element 1, and the carrier 13 form, for example, a hermetic seal to protect the emitter 11 from environmental influences such as moisture, pollutants, and / or mechanical forces. By using the optical element 1 as a cover for the emitter 11, the sensor 10 can be installed in a particularly compact housing. Similarly, a cover 15 is arranged over the detector 12. The cover 15 is a window transparent to the electromagnetic laser radiation 3, which protects the detector 12 from environmental influences such as moisture, pollutants, and / or mechanical forces.

[0096] The display device 100 according to the in Fig. The embodiment shown in Figure 15 has a sensor 10, as is used in connection with the [unclear text] Fig. The embodiment described in Figure 14 includes a screen 101. The screen 101 is arranged above the sensor 10. The sensor 10 can also be arranged directly on the screen 101. In particular, the electromagnetic laser radiation 3 emitted by the sensor 10 is at least partially transmitted through the screen 101 before it propagates towards an external object.

[0097] The screen 101 has a large number of individually addressable pixels to display information, for example, in the form of an image. Each pixel has an organic light-emitting diode (OLED) that emits electromagnetic radiation in the visible spectral range. In contrast, the sensor 10 emits electromagnetic laser radiation 3 in the infrared spectral range. The sensor 10 is, for example, a distance sensor configured to measure the distance between the screen 101 and an external object. One emission direction of the electromagnetic radiation from the screen 101 coincides with the emission direction of the electromagnetic laser radiation 3 from the sensor 10.

[0098] The optical element 1 in the sensor 10 is configured to reduce the irradiance of the electromagnetic laser radiation 3 on the screen 101. In particular, the irradiance is reduced such that the electromagnetic laser radiation 3 does not cause any visible distortion in the image displayed on the screen 101. However, beam divergence of the electromagnetic laser radiation 3 is not affected by the optical element 1, so the sensor 10 remains functional.

[0099] Fig. Figure 16 shows numerically simulated optical paths 5 or light beams of electromagnetic laser radiation 3, which are emitted by an emitter 11 and pass through an optical element 1 and a screen 101 of a display device 100 according to an exemplary embodiment (the detector 12 of the display device 100 is in Fig. 16 not shown). Optical element 1 corresponds to the one in connection with Fig.9 described embodiment.

[0100] The optical element 1 increases the beam width and thus reduces the irradiance of the electromagnetic laser radiation 3 on the screen 101. The optical properties of the electromagnetic laser radiation 3, such as the beam divergence, remain unchanged by the optical element 1.

[0101] This patent application claims priority over German patent application DE 102022121629.2, the disclosure content of which is hereby incorporated by reference.

[0102] The invention is not limited to the exemplary embodiments described by reference to them. Rather, the invention encompasses every new feature and every combination of features, including, in particular, every combination of features in the claims and every combination of features in the exemplary embodiments, even if that feature or combination itself is not expressly stated in the claims or exemplary embodiments. Reference sign 1 optical element 2 transparent bodies 21 Light coupling area 22 Light extraction area 3 electromagnetic radiation 41 first reflective layer 42 second reflective layer 421 first sub-area 422 second sub-area 423 third sub-area 43 Opening 44 Anti-reflective coating 5 optical path 61 first refractive optical element 62 second refractive optical element 10 Sensor 11 emitters 12 Detector 13 carriers 14 cases 15 Cover 100 Display device 101 screen Distance E Irradiance α Beam divergence φ Apex angle QUOTES INCLUDED IN THE DESCRIPTION

[0000] This list of documents cited by the applicant was automatically generated and is included solely for the reader's convenience. The list is not part of the German patent or utility model application. The DPMA accepts no liability for any errors or omissions. Cited patent literature

[0000] DE 102022121629.2

[0101]

Claims

[1] Optical element (1), comprising: - a transparent body (2) with a flat light coupling surface (21) which is designed to couple electromagnetic radiation (3) into the transparent body, and a flat light coupling surface (22) which is designed to couple the electromagnetic radiation (3) out of the transparent body (2), - a first reflective layer (41) on a region of the light coupling surface (21), - a second reflective layer (42) on a region of the light output surface (22), wherein - the light coupling surface (21) and the light coupling surface (22) are parallel to each other, - the first reflective layer (41) has an opening (43) through which the electromagnetic radiation (3) is coupled into the transparent body (2), and - the first reflective layer (41) and the second reflective layer (42) are arranged such that a geometric length of an optical path (5) of the electromagnetic radiation (3) within the transparent body (2) is at least three times greater than a distance (D) between the light coupling surface (21) and the light coupling surface (22). [2] Optical element (1) according to the preceding claim, wherein the optical element (1) reduces a maximum irradiance (E) of the electromagnetic radiation (3) on a reference plane downstream of the optical element (1) by at least 50%. [3] Optical element (1) according to one of the preceding claims, wherein a beam divergence (α) of the electromagnetic radiation (3) coupled out of the optical element (1) is at most 10% greater or smaller than a beam divergence (α) of the electromagnetic radiation (3) coupled into the optical element (1). [4] Optical element (1) according to one of the preceding claims, wherein an anti-reflection coating (44) is arranged on the light coupling surface (21) within the opening (43) in the first reflective layer (41). [5] Optical element (1) according to the preceding claim, wherein - a first refractive optical element (61) and / or a first diffractive optical element is arranged on the light coupling surface (21) and covers the opening (43) in the first reflective layer (41), and - the first refractive optical element (61) and / or the first diffractive optical element is configured to reduce an irradiance (E) of the electromagnetic radiation (3) on the light output surface (22). [6] Optical element (1) according to the preceding claim, wherein the first refractive optical element (61) comprises a concave conical lens. [7] Optical element (1) according to one of the preceding claims, wherein - the second reflective layer (42) has a first partial region (421) and a second partial region (422), and - a reflectance of the first sub-area (421) differs from a reflectance of the second sub-area (422). [8] Optical element (1) according to the preceding claim, wherein the second partial region (422) completely surrounds the first partial region (421) in a plan view of the light output surface (22). [9] Optical element (1) according to one of the preceding claims, wherein - a second refractive optical element (62) and / or a second diffractive optical element is arranged on the second reflective layer (42) and / or on the light output surface (22), - the second refractive optical element (62) and / or the second diffractive optical element is configured to reduce a beam divergence (α) of the electromagnetic radiation (3) coupled out of the optical element (1). [10] Optical element (1) according to the preceding claim, wherein the second refractive optical element (62) comprises a convex conical lens. [11] Optical element (1) according to claims 6 and 10, wherein an apex angle (φ) of the concave conical lens and an apex angle (φ) of the convex conical lens are equal. [12] Sensor (10), comprising: - an optical element (1) according to one of claims 1 to 11, - an emitter (11) for emitting electromagnetic radiation (3), and - a detector (12) which is designed to detect at least part of the electromagnetic radiation (3) reflected by an external object, wherein the emitter (11), the optical element (1) and the detector (12) are arranged such that the electromagnetic radiation (3) emitted by the emitter (11) passes through the optical element (1) before being coupled out of the sensor (10), and the electromagnetic radiation (3) coupled into the sensor (10) does not pass through the optical element (1) before impinging on the detector (12). [13] Sensor (10) according to the preceding claim, wherein - the emitter (11) comprises a surface-emitting laser diode, and - the detector (12) comprises a photodiode, a phototransistor, a single-photon avalanche diode, a photodiode array and / or a single-photon avalanche diode array. [14] Display device (100), comprising: - a sensor (10) according to one of claims 12 or 13, and - a partially transparent screen (101) arranged such that the electromagnetic radiation (3) emitted by the sensor (10) is transmitted through the screen (101) before being coupled out of the display device (100) in the direction of the external object. [15] Display device (100) according to the preceding claim, wherein - the screen (101) has a plurality of individually addressable pixels, and - each pixel has an organic light-emitting diode and / or a micro-LED. [16] Display device (100) according to one of claims 14 or 15, wherein the optical element (1) reduces a maximum irradiance (E) of the electromagnetic radiation (3) emitted by the sensor (10) onto the screen (101), so that a luminance of the screen (101) changes by at most 2% due to the irradiation by the electromagnetic radiation (3).

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