Optical component and method for manufacturing an optical component

Abstract

The invention relates to an optical assembly and a method for producing an optical assembly. An optical assembly (12) is proposed for an optical sensor device (10), in particular for an optical sensor device (10) for a motor vehicle. The optical assembly (12) has a lens plate (22), a light source (18) and a light receiving unit (20), wherein the lens plate (22) comprises a lens structure (24) on the side associated with the light source (18) and a light extraction structure (26) on the side facing away from the light source (18). The lens structure (24) has different local radii of curvature. In addition, a method for producing an optical assembly (12) is proposed.

Description

Technical Field

[0001] The invention relates to an optical assembly for an optical sensor device, in particular for a motor vehicle, and to a method for producing an optical assembly. Background Art

[0002] Optical sensor devices are used in motor vehicles, for example as rain sensors for detecting the wetting of a windshield.

[0003] Such rain sensors typically include a light source, a lens plate fixed to the windshield, and a light receiver.The lens plate typically has a lens structure on the side associated with the light source and a light extraction structure on the side facing away from the light source.

[0004] The light emitted by the light source enters or is coupled into the lens plate through the lens structure, wherein the light rays propagate substantially parallel inside the lens plate. The light extraction structure then deflects the light rays by about 45 degrees towards the measurement area on the windshield. When the pane is dry, the light rays are completely reflected at the pane, whereas when the pane is wet, some of the light rays escape the pane. Thus, the change in the light intensity of the reflected light enables the wetting of the windshield to be detected.

[0005] However, in lens plates known from the prior art, the sensitivity to light extraction is not uniform in the measurement area, but generally has the shape of a Gaussian distribution (i.e. a clear maximum in the center and a sharp decrease towards the edge). As a result, wetting at the edge of the measurement area leads to a significantly lower drop in the light intensity of the reflected light than wetting in the central part of the measurement area and is therefore more difficult to detect. Therefore, wetting of the windshield cannot be reliably detected over the entire measurement area.

[0006] It is therefore an object of the present invention to provide an optical component and a method of manufacturing which alleviate the disadvantages of the prior art. Summary of the invention

[0007] According to the invention, the above object is achieved by an optical assembly for an optical sensor device, in particular for an optical sensor device for a motor vehicle, the optical assembly comprising a lens plate, a light source and a light receiving unit, wherein the lens plate comprises a lens structure on a side associated with the light source and a light extraction structure on a side facing away from the light source, the lens structure having different local radii of curvature.

[0008] In this context and in the following, "local" is understood to mean "in a predefined environment of a point". Thus, "different local radii of curvature" therefore means that the curvature of the lens structure is likely to be piecewise constant, but varies over the entire lens structure.

[0009] According to the invention, the local radius of curvature is selected such that a predefined distribution of the light emitted by the light extraction structure is achieved, in particular in a measurement area associated with the optical component.

[0010] Here, the light is distributed so that the intensity received at the light receiving unit varies depending only on the total area in the measurement region from which light generated by the light source and emitted through the light extraction structure is extracted.

[0011] Therefore, the intensity variation detected at the light receiving unit does not depend on the position of the extraction of light in the measurement area. Therefore, the light receiving unit is equally sensitive to the extraction of light in the entire measurement area.

[0012] Therefore, the entire measuring area (ie, in particular also its border area) can be used for measurement, in particular for the detection of wetting of the windshield of a motor vehicle. In particular, the wetting of the windshield can therefore be reliably detected in this way in the entire measuring area (including its border area).

[0013] The surface of the lens structure thus presents a varying curvature. If the curvature is substantially constant, the transmission angle (measured opposite to the axial direction of the lens plate) of a light ray emanating from the light source, impinging on the lens structure and entering the lens plate does change due to spherical aberration, but only insignificantly. Due to the variable curvature of the lens plate, the shape of the lens structure and thus the local angle of incidence of the light ray on the lens structure changes, so that the transmission angle of the light ray depends on the position of incidence on the lens structure, which leads to a variation of the intensity distribution in the lens plate and also in the measurement area.

[0014] The invention is based on the basic idea that not only do the light rays propagating parallel to each other in the axial direction of the lens plate reach the measurement area, but also the light extraction structure has an acceptance angle range within which the light rays propagating through the lens plate still reach the measurement area after leaving the light extraction structure. Changing the local curvature of the lens structure will change the local transmission angle of the lens structure. Here, the local curvature of the lens structure is selected so that: on the one hand, as many light rays as possible are within the acceptance angle range of the light extraction structure, thereby achieving the highest possible light output, and on the other hand, the light receiving unit can uniformly detect the extraction of light in the entire measurement area, i.e., a uniform distribution of the useful light in the measurement area is achieved.

[0015] Preferably, the different local radii of curvature are therefore selected so that: the light emitted by the light extraction structure is distributed at least within a measuring area associated with the optical component, so that when the light is coupled out in the measuring area, the intensity change received at the light receiving unit depends only on the total area from which the light is extracted in the measuring area.

[0016] On the one hand, it is provided that the lens structure constitutes a Fresnel lens. In particular, as described above, the local curvature radius of the groove of the Fresnel lens is selected so that when light is extracted in the measurement area, the intensity change received at the light receiving unit depends only on the total area of ​​the light extracted in the measurement area. Compared to conventional lens structures, the configuration of the lens structure as a Fresnel lens enables a particularly compact design of the optical component.

[0017] According to another aspect, the local radius of curvature of the lens structure is described in segments by a linear function or a nonlinear function. The linear or nonlinear function indicates the local curvature of the lens structure as a function of the horizontal distance from a predefined point of the lens structure, for example from the center of the lens structure. Therefore, starting from the predefined point, the curvature of the lens structure and therefore the local transmission angle changes linearly or nonlinearly. This means that by selecting a function, the local transmission angle can be adjusted so that when light is extracted in the measurement area, the intensity change received at the light receiving unit depends only on the total area from which the light is extracted in the measurement area. In addition, by selecting a function, the transmission angle can be adjusted so that as much light as possible is within the acceptance angle range of the light extraction structure.

[0018] In one configuration of the invention, the above function is monotonic, in particular strictly monotonic. Therefore, the transmission angle also changes monotonically, in particular strictly monotonically. For example, the function decreases (strictly) monotonically, so that the transmission angle increases (strictly) monotonically.

[0019] A further development of the invention provides that at least one groove of the Fresnel lens is described by the function. The linear or non-linear function thus indicates the local curvature of the groove of the Fresnel lens as a function of the horizontal distance from a predefined point of the lens structure, for example from the starting point of the groove, i.e. the point of the groove closest to the center of the Fresnel lens.

[0020] The plurality of grooves of a Fresnel lens can each be described by the same function or by different functions. This means, more particularly, that functions are defined piecewise.

[0021] According to various aspects, the light source is arranged at the focus of the lens structure. In this way, the light efficiency of the optical component is increased. Here, the focus is understood to mean in particular a point which is the focus in the case of a constant curvature of the lens structure.

[0022] In another configuration of the invention, the lens structure comprises an anti-transmission feature in certain areas. More specifically, the anti-transmission feature is configured to prevent light from the light source from entering the lens plate or at least to attenuate the light intensity. The anti-transmission feature is formed, for example, by an absorbing coating of the lens structure. Preferably, the anti-transmission feature is arranged so that the central maximum intensity in the measurement area is attenuated. In combination with the design of the lens structure according to the invention with respect to the local curvature radius, a particularly uniform sensitivity of the light receiving unit to the light extraction in the measurement area is obtained.

[0023] According to another aspect, each groove of the Fresnel lens is provided with an anti-transmission feature. More specifically, the anti-transmission feature is configured to prevent light from the light source from entering the lens plate through the grooves of the Fresnel lens or at least to attenuate the light intensity. The anti-transmission feature is formed, for example, by an absorbing coating of the grooves of the Fresnel lens. Preferably, the anti-transmission feature is arranged such that the central maximum intensity in the measurement area is attenuated. In combination with the design of the lens structure according to the invention with respect to the local curvature radius, a particularly uniform sensitivity of the light receiving unit to the light extraction in the measurement area is obtained.

[0024] According to the invention, the object is also achieved by a method for manufacturing an optical assembly, in particular an optical assembly as described above, the optical assembly comprising a lens plate, a light source and a light receiving unit, wherein the lens plate comprises a lens structure on a side associated with the light source and a light extraction structure on a side facing away from the light source, the method comprising the following steps:

[0025] specifying the focal length and transmission function of the lens structure; and

[0026] determining a curvature function describing a local curvature of the lens structure;

[0027] The curvature function is such that the power density of light coming from the focus of the lens structure and passing through the lens structure corresponds to a specified transmission function.

[0028] In particular, the above-mentioned optical component according to the present invention can be obtained by the method for manufacturing an optical component according to the present invention.

[0029] The transmission function thus describes the intensity of the light entering the lens plate through the lens structure, in particular as a function of the horizontal distance from a predefined point of the lens structure, for example the center of the lens structure, or, in the case of a lens structure in the form of a Fresnel lens, from the start of the grooves of the Fresnel lens. Expressed in terms of geometrical optics, this means that the light rays impinging on the lens structure starting from the light source are each assigned a transmission angle such that a desired distribution of the light generated by the light source, in particular a desired intensity distribution of the useful light component (i.e. a desired power density), is obtained in the lens plate. In particular, here the light rays do not propagate parallel within the lens plate.

[0030] Here, the transmission function may depend on a plurality of parameters of the optical assembly and / or the sensor device. These parameters include, for example, one or more of the following variables: the distance between the light source and the light receiving unit (measured in the lateral direction of the lens plate), the thickness of the lens plate (measured in the axial direction of the lens plate), the thickness of the (windshield) window plate (measured in the axial direction), the thickness of the coupling structure (measured in the axial direction), the refractive index of the lens plate, the refractive index of the coupling structure, the refractive index of the (windshield) window plate and / or the acceptance angle range of the light extraction structure.

[0031] Preferably, the transmission function is such that when light is extracted in the measurement area, the intensity received at the light receiving unit varies depending only on the total area over which the light is extracted in the measurement area. With regard to the advantages, reference is made to the previous discussion. BRIEF DESCRIPTION OF THE DRAWINGS

[0032] Further advantages and features will become apparent from the following description and accompanying drawings, to which reference is made, in which:

[0033] Figure 1 shows a cross section taken through a prior art rain sensor having an optical assembly;

[0034] Figure 2 a detailed view showing a portion of an optical assembly according to the present invention; and

[0035] Figure 3 A schematic flow chart showing the steps of the method according to the present invention; DETAILED DESCRIPTION

[0036] Figure 1 A sensor device 10 from the prior art is shown which, in the variant shown here, is in the form of a rain sensor for a motor vehicle.

[0037] The sensor device 10 comprises an optical component 12 which is mounted to a window panel 16, more particularly a windshield of a motor vehicle, via a coupling layer 14. The coupling layer 14 preferably has a refractive index similar to that of the window panel 16 here.

[0038] The optical assembly 12 includes a light source 18 , a light receiving unit 20 , and a lens plate 22 .

[0039] The lens plate 22 comprises a first lens structure 24' on the light source side, which is disposed on the side of the lens plate 22 associated with the light source 18. In addition, the lens plate 22 comprises a light extraction structure 26 on the light source side, which is disposed on the side of the lens plate 22 associated with the window plate 16.

[0040] Preferably, here, the light source 18 is arranged at the focus of the first lens structure 24 ′.

[0041] Furthermore, in the variant shown, the lens plate 22 comprises, on the light receiver side, a second lens structure 28 , which is arranged on the side of the lens plate 22 associated with the light receiving unit 20 .

[0042] The lens plate 22 further comprises, on the light receiver side, a light injection structure 30 which is arranged on the side of the lens plate 22 associated with the window plate 16 .

[0043] Preferably, the light receiving unit 20 is arranged at the focus of the second lens structure 28 .

[0044] exist Figure 1 In the illustrated variant, the two lens structures 24' and 28 are each formed as a Fresnel lens, while the light extraction structure 26 and the light injection structure 30 are each configured as a Fresnel prism. However, the lens structure 24', the lens structure 28, the light extraction structure 26 and the light injection structure 30 may each have any other suitable shape.

[0045] Figure 1 The mode of operation of the illustrated sensor device 10 is explained as follows.

[0046] The light source 18 emits light rays 32 which are refracted by the first lens structure 24' so that they propagate substantially parallel inside the lens plate 22 along the axial direction A of the lens plate 22. In other words, the first lens structure 24' thus has a substantially constant curvature.

[0047] The light extraction structure 26 deflects the light 32 by approximately 45 degrees toward a measurement area 34 on the window panel 16 associated with the sensor device 10 .

[0048] When the window pane is dry (ie, not wetted), the light 32 is totally reflected at the transition from the window pane 16 to the environment, injected into the lens plate 22 through the light injection structure 30 , and focused on the light receiving unit 20 by the second lens structure 28 .

[0049] On the other hand, when the window plate 16 is wet, total reflection does not occur in the wetted area due to the smaller difference between the refractive index of the window plate 16 and the refractive index of water, which is why at least some of the light 32 leaves the window plate 16. The light intensity of the light 32 reaching the light receiving unit 20 is thus reduced and the wetting of the window plate 16 can thereby be detected.

[0050] exist Figure 1 In the variant of the sensor device 10 shown, the power density of the light in the measurement area 34 generally presents a substantially Gaussian distribution shape. Thus, in the center of the measurement area 34, the light intensity is high, whereas towards the edge of the measurement area 34, the light intensity decreases sharply. The sensitivity of the light receiving unit 20 to receive the light from the measurement area 34 also generally has a substantially Gaussian distribution shape. Therefore, the detection sensitivity of the light extraction can be determined on the measurement area 34 substantially follows the product of two Gaussian functions. Due to the sharp increase in sensitivity generated in the center and the sharp decrease in sensitivity at the edge, not the entire measurement area 34 can be used to detect the wetting of the window panel 16. In addition, due to the difference in sensitivity, it is not possible to reliably determine how large the area of ​​any light extraction is, that is, the size of the water droplets on the measurement area 34 cannot be determined with certainty.

[0051] Through Figure 2 The change in the design of the first lens structure 24 shown in the example solves this problem. The purpose of the above change is to change the power density of the light on the measurement area 34 so that the product of the power density in the measurement area 34 and the sensitivity distribution of the light receiving unit 20 produces a substantially constant distribution.

[0052] Therefore, the variation of the intensity received at the light receiving unit 20 when extracting light in the measurement region 34 depends only on the total area from which the light is extracted in the measurement region 34 (eg due to wetting of the window plate 16 ).

[0053] Figure 2 The first lens structure 24 shown is Figure 1 The variant shown differs in that the local curvature of the first lens structure 24 is not constant but position dependent. In other words, the local curvature of the first lens structure 24 is a function of the horizontal distance from a predefined point, such as the center of the first lens structure 24 or the start point of the groove (measured along the transverse direction T of the first lens structure 24).

[0054] As a result, not all light rays 32 emitted by the light source 18 and entering the lens plate 22 through the first lens structure 24 propagate in the lens plate 22 parallel to the axial direction A, but all light rays 32 include a transmission angle θ about the axial direction A that depends on the local curvature of the first lens structure 24 .

[0055] By referring to the following Figures 1 to 3 The described method adjusts the shape of the first lens structure 24 so that when light is extracted in the measurement area 34 , the intensity received at the light receiving unit 20 varies only depending on the total area from which light is extracted in the measurement area 34 (eg, due to wetting of the window plate 16 ).

[0056] First, a desired focal length and a desired transmission function of the first lens structure 24 are specified (step S1 ).

[0057] The light source 18 is arranged to be spaced apart from the first lens structure 24 by a desired focal length in the axial direction A, particularly relative to the center of the first lens structure 24 .

[0058] The transmission function describes the intensity of light entering the lens plate 22 through the first lens structure 24, and in particular describes the intensity of the light as a function of the horizontal distance from a predefined point of the first lens structure 24, such as the center of the first lens structure 24 (measured in the transverse direction T), or as described in the following example, as a function of the horizontal distance from the start point of the grooves of the first lens structure 24 formed as a Fresnel lens.

[0059] The surface of the first lens structure 24 is adjusted at the starting point of the groove of the first lens structure 24 so that the refracted light propagates along the axial direction A in the lens plate 22 (step S2). Therefore, the transmitted light includes θ about the axial direction A. i = a transmission angle of 0 degrees. Here, the starting point of the groove should be understood to mean the center of the first lens structure 24 or the point of the groove closest to the center.

[0060] Starting from the starting point, the surface of the first lens structure 24 is now adjusted such that the transmission angle θ increases monotonically, in particular strictly monotonically, in the transverse direction T (step S3). In other words, the surface of the first lens structure 24 thus has a curvature that varies along the transverse direction T. In the case of a substantially constant curvature, the transmission angle θ does change due to spherical aberration, but only insignificantly.

[0061] This means that the local curvature of the first lens structure 24 is a monotonic function, in particular a strictly monotonic function, of the horizontal distance from the start point of the groove, measured in the transverse direction T. This function is determined in step S3.

[0062] Therefore, at the end point of the groove, that is, at the point of the groove farthest from the center of the first lens structure 24, the transmission angle θf is the biggest.

[0063] Preferably, in θ i With θ f Between and including θ i and θ f All angles of the lens plate 22 are within the acceptance angle range of the light extraction structure 26, thereby ensuring the highest possible light efficiency. Here, the acceptance angle range is understood to mean such an angle range (measured opposite to the axial direction A) that the light passing through the lens plate 22 is refracted by the light extraction structure 26 towards the measurement area 34 and also reaches the measurement area 34.

[0064] Steps S2 and S3 can now be repeated for the other grooves of the first lens structure 24 (via Figure 3 Here, the local curvature of each groove can be described by the same or different functions.

[0065] Here, the shape of each groove is adjusted so that the power density of light entering the lens plate 22 through the first lens structure 24 corresponds to a specified transmission function.

[0066] In this way, it is ensured that when light is extracted in the measurement area 34 , the intensity received at the light receiving unit 20 varies depending only on the total area over which light is extracted in the measurement area 34 .

[0067] Here, the transmission function may depend on a plurality of parameters of the sensor device 10. These parameters may include one or more of the following variables: the distance between the light source 18 and the light receiving unit 20 (measured in the transverse direction T), the thickness of the lens plate 22 (measured in the axial direction A), the thickness of the window plate 16 (measured in the axial direction A), the thickness of the coupling structure 14 (measured in the axial direction A), the refractive index of the lens plate 22, the refractive index of the coupling structure 14, the refractive index of the window plate 16 and / or the acceptance angle range of the light extraction structure 26.

[0068] Optionally, the first lens structure 24 may be at least partially provided with an anti-transmission feature. More particularly, the anti-transmission feature is configured to prevent light 32 from the light source 18 from entering the lens plate 22, or at least to attenuate the light intensity. The anti-transmission feature is formed, for example, by an absorbing coating of the first lens structure 24. Preferably, the anti-transmission feature is arranged so that the central maximum intensity in the measurement area 34 is attenuated.

[0069] In particular, each groove of the first lens structure 24 is provided with an anti-transmission feature.

[0070] The above-described method steps can of course also be applied to lens structures that do not constitute a Fresnel lens but have a different shape that is suitable for the optical component 12 .

Claims

1. An optical assembly (12) for an optical sensor device (10), the optical assembly comprising a lens plate (22), a light source (18) and a light receiving unit (20), wherein: The lens plate (22) comprises a lens structure (24) on a side associated with the light source (18) and a light extraction structure (26) on a side facing away from the light source (18), the lens structure (24) having different local radii of curvature, The different local radii of curvature are selected so that: the light emitted by the light extraction structure (26) is distributed at least in a measurement area (34) associated with the optical component (12), so that when the light is coupled out in the measurement area (34), the intensity change received at the light receiving unit (20) depends only on the total area of ​​the light extracted in the measurement area (34), and The local curvature of the lens structure is a monotonic function of the horizontal distance from the center of the lens structure (24) or from the starting point of the groove of the lens structure (24) measured along the transverse direction (T), so that the transmission angle (θ) in the transverse direction (T) increases monotonically from the transmission angle θ about the axial direction (A) of the lens plate (22) i = 0 degrees increases to the transmission angle θ f , where, in θ i With θ f Between and including θ i and θ f All angles are within the acceptance angle range of the light extraction structure (26).

2. The optical component (12) according to claim 1, characterized in that The lens structure (24) constitutes a Fresnel lens.

3. The optical component (12) according to claim 1, characterized in that The function is strictly monotonic.

4. The optical component (12) according to claim 2, characterized in that At least one groove of the Fresnel lens (24) is described by the function.

5. The optical component (12) according to claim 4, characterized in that The plurality of grooves of the Fresnel lens (24) are each described by the same function or different functions.

6. The optical component (12) according to claim 1, characterized in that The light source (18) is arranged at the focus of the lens structure (24).

7. The optical component (12) according to claim 1, characterized in that The lens structure (24) has anti-transmission features in some areas.

8. The optical component (12) according to claim 2, characterized in that The lens structure (24) has anti-transmission features in some areas, and each groove of the Fresnel lens (24) is provided with an anti-transmission feature.

9. The optical component (12) according to claim 1, characterized in that The optical sensor device (10) is an optical sensor device for a motor vehicle.

10. A method for manufacturing an optical assembly (12) according to claim 1, the optical assembly comprising a lens plate (22), a light source (18) and a light receiving unit (20), wherein: The lens plate (22) comprises a lens structure (24) on a side associated with the light source (18) and a light extraction structure (26) on a side facing away from the light source (18), the method comprising the following steps: specifying the focal length and transmission function of the lens structure (24); and determining a curvature function describing a local curvature of the lens structure (24); wherein the curvature function is such that the power density of light from the focus of the lens structure (24) and passing through the lens structure (24) corresponds to a specified transmission function, The curvature function is a monotonic function of the horizontal distance from the center of the lens structure (24) or from the starting point of the groove of the lens structure (24) measured along the transverse direction (T), so that the transmission angle (θ) in the transverse direction (T) increases monotonically from the transmission angle θ about the axial direction (A) of the lens plate (22) to i = 0 degrees increases to the transmission angle θ f , where, in θ i With θ f Between and including θ i and θ f All angles of are within the acceptance angle range of the light extraction structure (26), and The transmission function is such that the light emitted through the light extraction structure (26) is distributed at least in a measurement area (34) associated with the optical component (12), so that when the light is coupled out in the measurement area (34), the intensity change received at the light receiving unit (20) depends only on the total area from which the light is extracted in the measurement area (34).

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