Optical assembly and method of manufacturing an optical assembly

Abstract

An optical assembly for an optical sensor device has a lens plate, a light source, and a light receiving unit. The lens plate includes 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 has different local radii of curvature.

Claims

1. An optical assembly for an optical sensor device of a motor vehicle, comprising: a lens plate; a light source; and a light receiving unit, wherein the lens plate includes 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, and wherein the different local radii of curvature are selected such that light exiting through the light extraction structure is, at least in a measurement region associated with the optical assembly, distributed such that when light rays are coupled out in the measurement region, an intensity change received at the light receiving unit is only dependent on a total area on which the light rays are extracted in the measurement region.

2. The optical assembly of claim 1 wherein the lens structure constitutes a Fresnel lens.

3. The optical assembly of claim 1 wherein a local radius of curvature of the lens structure is described in sections by a linear function or by a non-linear function.

4. The optical assembly of claim 3 wherein the function is monotonic.

5. The optical assembly of claim 3, wherein the lens structure constitutes a Fresnel lens, and wherein at least one groove of the Fresnel lens is described by the function.

6. The optical assembly of claim 5 wherein a plurality of grooves of the Fresnel lens are each described by the same function or by different functions.

7. The optical assembly of claim 1 wherein the light source is arranged in a focal point of the lens structure.

8. The optical assembly of claim 1 wherein the lens structure has anti-transmission features in some regions.

9. The optical assembly of claim 8, wherein the lens structure constitutes a Fresnel lens, and wherein individual grooves of the Fresnel lens are provided with anti-transmission features.

10. A method of manufacturing an optical assembly that includes a lens plate, a light source, and a light receiving unit, wherein the lens plate includes 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, comprising the steps of: specifying a focal length and a transmission function of the lens structure; and determining a curvature function that describes the local curvature of the lens structure; wherein the curvature function is such that a power density of light coming from a focal point of the lens structure and passing through the lens structure corresponds to the specified transmission function, and wherein the transmission function is such that light exiting through the light extraction structure is, at least in a measurement region associated with the optical assembly, distributed such that when light rays are coupled out in the measurement region, an intensity change received at the light receiving unit is only dependent on a total area on which the light rays are extracted in the measurement region.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further advantages and characteristics will be apparent from the description below and the drawings, to which reference is made and in which:

(2) FIG. 1 shows a cross section taken through a rain sensor with an optical assembly from the prior art;

(3) FIG. 2 shows a detail view of a portion of an optical assembly according to embodiments of the disclosure; and

(4) FIG. 3 shows a schematic flow chart of the steps of a method according to embodiments of the disclosure.

DETAILED DESCRIPTION

(5) FIG. 1 shows a sensor device 10 from the prior art, which, in the variant shown here, is in the form of a rain sensor for a motor vehicle.

(6) The sensor device 10 comprises an optical assembly 12 which, by means of a coupling layer 14, is mounted to a pane 16 which more particularly is a windshield of the motor vehicle. The coupling layer 14 here preferably has a refractive index similar to that of the pane 16.

(7) The optical assembly 12 comprises a light source 18, a light receiving unit 20 and a lens plate 22.

(8) The lens plate 22 includes a first lens structure 24′ on the light source side, which is provided on a side of the lens plate 22 associated with the light source 18. Furthermore, the lens plate 22 comprises a light extraction structure 26 on the light source side, which is provided on a side of the lens plate 22 associated with the pane 16.

(9) The light source 18 can be arranged in a focal point of the first lens structure 24′ here.

(10) In addition, in the variant shown, the lens plate 22 includes a second lens structure 28 on the light receiver side, which is provided on a side of the lens plate 22 associated with the light receiving unit 20.

(11) The lens plate 22 further comprises a light injection structure 30 on the light receiver side, which is provided on a side of the lens plate 22 associated with the pane 16.

(12) The light receiving unit 20 can be arranged in a focal point of the second lens structure 28.

(13) In the variant shown in FIG. 1, the two lens structures 24′, 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 structures 24′, 28, the light extraction structure 26, and the light injection structure 30 may also each have any other suitable shape.

(14) The mode of operation of the sensor device 10 shown in FIG. 1 is set forth below.

(15) The light source 18 emits light rays 32 which are refracted by the first lens structure 24′ in such a way that within the lens plate 22, they run substantially parallel along an axial direction A of the lens plate 22. In other words, the first lens structure 24′ thus has a substantially constant curvature.

(16) The light extraction structure 26 deflects the light rays 32 by about 45 degrees towards a measurement region 34, associated with the sensor device 10, on the pane 16.

(17) When the pane is dry (that is, not wetted), the light rays 32 are totally reflected at the transition from the pane 16 to the environment, injected back into the lens plate 22 by means of the light injection structure 30, and focused on the light receiving unit 20 by means of the second lens structure 28.

(18) When the pane 16 is wetted, on the other hand, no total reflection occurs in the wetted areas due to the smaller difference between the refractive indices of the pane 16 and water, which is why at least some of the light rays 32 exit the pane 16. A light intensity of the light rays 32 which reach the light receiving unit 20 is therefore reduced and the wetting of the pane 16 can therefore be detected.

(19) In the variant of the sensor device 10 shown in FIG. 1, the power density of the light rays in the measurement region 34 typically exhibits substantially the shape of a Gaussian distribution. In the center of the measurement region 34, the light intensity thus is high, whereas it decreases strongly towards the edges of the measurement region 34. The sensitivity with which the light receiving unit 20 receives light rays from the measurement region 34 also typically has substantially the shape of a Gaussian distribution. The detection sensitivity with which a light extraction can be determined on the measurement region 34 thus essentially follows a multiplication of two Gaussian functions. Because of the strong sensitivity exaggeration produced in the center and the strong drop at the edge, not the entire measurement region 34 can be utilized for detecting a wetting of the pane 16. Moreover, due to the difference in sensitivity, it cannot be reliably established how large the area of any light extraction was, i.e. the size of a water drop on the measurement region 34 cannot be determined with certainty.

(20) This problem is solved by a change in the design of the first lens structure 24, as is shown by way of example in FIG. 2. The purpose of the alteration is to change the power density of the light rays on the measurement region 34 in such a way that the multiplication of the power density in the measurement region 34 with the sensitivity distribution of the light receiving unit 20 results in a substantially constant profile.

(21) As a result, a change in intensity received at the light receiving unit 20 when light is extracted in the measurement region 34 is only dependent on the total area on which the light rays are extracted in the measurement region 34 (for example because of a wetting of the pane 16).

(22) The first lens structure 24 shown in FIG. 2 differs from the variant shown in FIG. 1 in that a local curvature of the first lens structure 24 is not constant, but rather location-dependent. In other words, the local curvature of the first lens structure 24 is a function of the horizontal distance (measured along a transverse direction T of the first lens structure 24) from a predefined point, for example from a center of the first lens structure 24 or from a starting point of a groove.

(23) The result is that not all of the light rays 32 emitted by the light source 18 and entering the lens plate 22 through the first lens structure 24 run parallel to the axial direction A in the lens plate 22, but rather include a transmission angle θ with the axial direction A depending on the local curvature of the first lens structure 24.

(24) The shape of the first lens structure 24 is adapted by means of the method described below with reference to FIGS. 1 to 3 in such a way that, when light is extracted in the measurement region 34, a change in intensity received at the light receiving unit 20 is only dependent on the total area on which the light rays are extracted in the measurement region 34 (for example because of a wetting of the pane 16).

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

(26) The light source 18 is provided spaced away from the first lens structure 24 by the desired focal length in the axial direction A, in particular opposite a center of the first lens structure 24.

(27) The transmission function describes an intensity of the light that enters the lens plate 22 through the first lens structure 24, in particular as a function of a horizontal distance from a predefined point of the first lens structure 24 (measured in the transverse direction T), for example from the center of the first lens structure 24 or, as described in the following example, from a starting point of a groove of the first lens structure 24 formed as a Fresnel lens.

(28) The surface of the first lens structure 24 is adapted at the starting point of a groove of the first lens structure 24 in such a way that the refracted light ray runs along the axial direction A in the lens plate 22 (step S2). The transmitted light ray thus includes a transmission angle of θ.sub.i=0 degrees with the axial direction A. The starting point of a groove here is understood to mean a center of the first lens structure 24 or that point of the groove which is closest to the center.

(29) Proceeding from the starting point, the surface of the first lens structure 24 is now adapted such that the transmission angle θ increases monotonically in the transverse direction T, in particular strictly monotonically (step S3). In other words, the surface of the first lens structure 24 thus has a curvature that changes along the transverse direction T. In the case of a substantially constant curvature, the transmission angle θ would indeed change due to spherical aberration, but only insignificantly.

(30) This means that a local curvature of the first lens structure 24 is a monotonic function of the horizontal distance (measured in the transverse direction T) from the starting point of the groove, in particular a strictly monotonic function. This function is ascertained in step S3.

(31) The transmission angle θ.sub.f is therefore largest at an end point of the groove, i.e. at that point of the groove which is farthest from the center of the first lens structure 24.

(32) In embodiments, all angles between and including θ.sub.i and θ.sub.f are within an acceptance angle range of the light extraction structure 26, so that as high a luminous efficiency as possible is ensured. The acceptance angle range here is understood to mean the angular range (measured counter to the axial direction A) in which light rays passing through the lens plate 22 are refracted by the light extraction structure 26 toward the measurement region 34 and also reach the latter.

(33) Steps S2 and S3 can now be repeated for further grooves of the first lens structure 24 (indicated by the dashed arrow in FIG. 3). The local curvature of the individual grooves may be described here by the same or by different functions.

(34) The shape of the individual grooves is adapted here in such a way that a power density of light that enters the lens plate 22 through the first lens structure 24 corresponds to the specified transmission function.

(35) In this way, it is ensured that when light is extracted in the measurement region 34, an intensity change received at the light receiving unit 20 is only dependent on the total area on which the light rays are extracted in the measurement region 34.

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

(37) Optionally, the first lens structure 24 may be provided, at least in sections, with anti-transmission features. More particularly, the anti-transmission features are configured to prevent the light rays 32 coming from the light source 18 from entering the lens plate 22 or at least to attenuate the light intensity. The anti-transmission features are formed, for example, by an absorbent coating of the first lens structure 24. In embodiments, the anti-transmission features are arranged such that a central maximum intensity in the measurement region 34 is attenuated.

(38) In particular, individual grooves of the first lens structure 24 are provided with the anti-transmission features.

(39) The method steps described above may, of course, also be applied to lens structures that do not constitute a Fresnel lens but have a different shape suitable for the optical assembly 12.