Diffusing lens, light source, method for manufacturing light source and method for illuminating a scene

Abstract

The invention describes a diffuse lens (1) comprising an annular first lens segment (2) and an annular second lens segment (4). The first and second lens segments (2, 4) are concentric, and the refractive index of the first and second lens segments in a cross section along a plane including the optical axis of the diffuse lens is described by a refractive index profile (5), the refractive index profile varies in a direction perpendicular to the optical axis and comprises a first sub-profile (12) describing the refractive index profile of the first lens segment (2) and a second sub-profile (14) describing the refractive index profile of the second lens segment (4). The first sub-profile (12) transforms into the second sub-profile (14) at an interface (10), and the first and second sub-profiles (12, 14) have slopes of opposite signs. The invention further describes a light source (50) comprising a VCSEL (70) and such a diffuse lens (1), a method of manufacturing such a light source (50), and a method of illuminating a scene.

Description

Technical Field

[0001] The present invention relates to a diffusing lens. The present invention further relates to a light source comprising a vertical cavity surface emitting laser (VCSEL) and such a diffusing lens for diffusing the light emitted by the VCSEL. The present invention further relates to a method of manufacturing such a light source. The present invention further relates to a method of illuminating a scene, in particular for sensing applications. Background Art

[0002] VCSELs, especially VCSEL arrays with engineered diffusers to form a rectangular beam profile in the camera's field of view (FOV), are now often used as illumination sources for 2D and 3D cameras. There has been extensive research on how to integrate diffusers in VCSEL chips, as such integration typically creates some issues that need to be overcome.

[0003] In order to achieve good uniformity of the preferred rectangular beam profile in the FOV of the camera, the diffuser needs to be small. For example, the diffuser can be an array of diffuse lenses. However, the small size of these diffuse lenses leads to diffraction losses, because the lens array is typically uniformly illuminated, which causes some of the incident beam to not ideally enter the center of each lens. These diffraction losses lead to non-uniformity of the desired beam profile and reduce the quality of the desired sensing application.

[0004] One possibility to overcome these problems is to use larger lenses. Using one or more larger lenses can avoid the diffraction losses in question, but the large aperture of the lens automatically leads to a large height difference of the lens along the optical axis, i.e., a large lens sag. Large lenses with such large height differences in the surface profile are difficult to be integrated into semiconductor chips using manufacturing techniques such as grayscale lithography.

[0005] Fresnel lenses allow the construction of large aperture lenses and reduce the lens sag compared to conventional lenses by dividing the lens into a set of concentric annular segments. The height difference is thus effectively reduced compared to an equivalent standard lens. However, one problem that arises with Fresnel lenses is that the design of Fresnel lenses is typically achieved by dividing the continuous surface of a standard lens into a set of curved surfaces with step-like discontinuities between the curved surfaces. These discontinuities can result in loss and non-uniformity of the desired beam profile.

[0006] Therefore, there remains a need for improved diffusing lenses, particularly for use as illumination sources for 2D and 3D cameras. Summary of the invention

[0007] An object of the present invention is to provide an improved planar diffuser lens for diffusing incident light so that a uniform rectangular profile is achieved in a target area. The resulting uniform beam profile can be matched to the field of view of a camera, for example, thereby allowing reliable sensing applications such as time-of-flight (TOF) measurements.

[0008] Another object of the present invention is to provide a light source having such an improved diffusing lens.

[0009] Another object of the present invention is to provide a method for manufacturing such a light source having an improved diffusing lens.

[0010] Another object of the present invention is to provide a method of illuminating a scene.

[0011] The invention is described in the independent claim. Preferred embodiments are described in the dependent claims or in the subsequent part of the description.

[0012] According to a first aspect of the present invention, there is provided a diffuse lens comprising an annular first lens segment and an annular second lens segment. The first and second lens segments are concentric with respect to each other. The refractive index of the first and second lens segments in a cross section along a plane including the optical axis of the diffuse lens is described by a refractive index profile, which varies in a direction perpendicular to the optical axis. This refractive index profile comprises a first sub-profile describing the refractive index profile of the first lens segment and a second sub-profile describing the refractive index profile of the second lens segment. Further, the first sub-profile transforms to the second sub-profile at an interface and the first and second sub-profiles have slopes of opposite signs.

[0013] The invention is based on the idea of ​​providing a planar diffuser lens which can preferably be used in a VCSEL array to transform incident light so as to uniformly illuminate a scene, such as the field of view of a camera. For this purpose, the diffuser lens comprises at least two annular lens segments, wherein a first lens segment is arranged concentrically with respect to a second lens segment. This means that the first lens segment and the second lens segment share the same center, i.e. the center of the diffuser lens.

[0014] The expression "annular" means that the first lens segment and the second lens segment are annular. The shape of the annulus may preferably be circular, but may also include other shapes formed like annulus, such as an elliptical shape.

[0015] It should be noted that the expression "first and second lens segments" should not be understood as two separate lenses or lens parts, but as segments of a single diffuse lens. Further, the first sub-profile and the second sub-profile are parts of a refractive index profile, which describe the refractive index of the first and second lens segments in a cross section along a plane including the optical axis of the diffuse lens. In other words, the refractive index profile describes a common profile, which describes the diffuse lens refractive index of at least a part of the diffuse lens.

[0016] The concept of a lens divided into two or more segments or elements is already known from Fresnel lenses. An ideal Fresnel lens comprises an infinite number of such lens segments, which have curved surfaces and step-like discontinuities between them. At these step-like discontinuities, the surface of the Fresnel lens is oriented parallel to the optical axis of the Fresnel lens. Thus, a standard Fresnel lens comprises (at least) two lens segments adjoining at an interface, wherein one of these lens segments has a curved surface and the other lens segment is oriented parallel to the optical axis of the Fresnel lens, i.e. as a height step oriented along the optical axis.

[0017] B. Kim et al.: "Elimination of flux loss by optimizing the groove angle in modified Fresnellens to increase illuminance uniformity, color uniformity, and flux efficiency," Optics Express, 17(20), pp. 17916-17927 (2009) addresses the problem that Fresnel lenses may generally suffer from flux efficiency loss and illuminance non-uniformity due to secondary refraction at surface discontinuities, particularly along the groove faces, i.e., along height steps. A modified Fresnel lens is disclosed in which the groove angle is optimized to maximize illumination uniformity.

[0018] Unlike the modified lens of B. Kim et al. and unlike a standard Fresnel lens, the diffuser lens according to the present invention preferably does not include a series of annular height steps at the surface of the lens, because the diffuser properties of the diffuser lens according to the present invention are instead caused by different lens segments having different refractive indices. In other words, the diffuser properties of the diffuser lens according to the present invention are caused by having different refractive indices along the width of the diffuser lens.

[0019] The diffuse lens according to the present invention comprises adjacent lens segments whose optical properties are caused by different refractive index profiles in a cross section along a plane including the optical axis of the diffuse lens. Planar Fresnel lenses with different refractive index profiles are known in the art, for example, see T.Suhara et al. "Graded-index Fresnelenses for integrated optics", Applied Optics, 21(11), pp. 1966-1971 (1982). Unlike the gradient refractive index (GRIN) type Fresnel lens disclosed by Suhara et al., the different refractive index profiles of the diffuse lens according to the present invention include adjacent sub-profiles with slopes of opposite signs. This means that the refractive index profile changes from a refractive index profile with a positive finite slope to a refractive index profile with a negative finite slope, or vice versa. The sub-profile can be curved. In this case, this also means that the refractive index profile changes from a convex curved refractive index profile to a concave curved refractive index profile, or vice versa. Therefore, the refractive index profile of the diffusing lens according to the invention does not comprise problematic height steps as known from GRIN-type Fresnel lenses disclosed hitherto.

[0020] The diffuser lens according to the present invention can be a single optical element, which can be integral or monolithic, and which combines the ability to transform the light emitted by any kind of light emitting element into a uniform diffuse beam profile in the target area. This measure provides a simple, non-bulky and low-cost optical device. Preferably, the single integral optical element can be integrated on the VCSEL array chip, but can also be arranged at a distance from the VCSEL array.

[0021] It should be understood that the expression "diffusing lens" means that the lens is configured to diffuse light in one or more directions parallel to the optical axis of the diffusing lens or inclined relative to the optical axis of the diffusing lens.

[0022] Further, the expression "lens" should be understood as any kind of object configured to affect light passing through the lens.

[0023] In the following, preferred embodiments of the diffusing lens will be described. Preferred embodiments are not only those indicated in the dependent claims but also those indicated in the entire disclosure herein.

[0024] In one embodiment, the slope of the first sub-profile describing the refractive index profile of the first lens segment and the slope of the second sub-profile describing the refractive index profile of the second lens segment can be described by the same function, but the signs of the slopes are opposite. As known in the art, the slope of a function is a first-order derivative function of the function. According to this embodiment, the first-order derivative function (slope function) describing the slope of the first sub-profile and the slope of the second sub-profile are the same, but the signs are opposite. In other words, except that the signs of the slopes are opposite, the slope of the first sub-profile and the slope of the second sub-profile are described by the same function. This means that the slope of the first sub-profile is, for example, a positive slope, while the slope of the second sub-profile is a negative slope. For example, when the first sub-profile and the second sub-profile are spherical, this means that the radii of curvature of these sub-profiles can have the same absolute value, but different signs. If the sub-profile is aspherical, the same concept can be applied, wherein the aspherical refractive index profile can be a conical profile or any other aspherical profile. Therefore, the different refractive indices of the first and second lens segments are suitable for transforming the incident light beam so that the same diffuse beam profile is generated.

[0025] The slope function (first-order derivative function) describing the slope of the first sub-contour and the slope of the second sub-contour can be expressed as r n Proportional to, where r is the radius of the diffuse lens and n≥0. Therefore, the slope function (first-order derivative function) can be proportional to a constant of n=0. For example, this is the case if the first sub-profile and the second sub-profile have the shape of a linear function in a cross-section along a plane including the optical axis of the diffuse lens. For example, a conical refractive index profile is such a case, where in a cross-section along a plane including the optical axis, the conical refractive index profile is formed by the straight surface lines of a cone. For n>0, the slope function can also be a polynomial function. The slope is not infinite. When the first and second sub-profiles are curved, the first sub-profile and the second sub-profile can also be described by their curvature functions, which are second-order derivative functions of the sub-profiles. In this case, the curvatures of the first and second sub-profiles can be the same for the first and second sub-profiles, but have different signs relative to each other, for example, one is convexly curved and the other is concavely curved.

[0026] The diffusing lens may be a gradient refractive index (GRIN) type lens or a metalens. In both cases, the height of the diffusing lens along its optical axis is preferably constant over the width of the diffusing lens.

[0027] If the diffuser lens according to the invention is a GRIN-type lens, the different refractive indices (i.e., the gradient of the refractive index) of the diffuser lens are caused by varying the composition of the material from which the GRIN-type lens is made along the width or radial distance of the diffuser lens. This may be caused, for example, by varying the doping of the material. Several techniques known in the art (such as neutron irradiation, chemical vapor deposition, partial polymerization, ion exchange, ion filling or direct laser writing) are suitable for making such a GRIN-type lens.

[0028] The simple geometry of the GRIN type lenses allows for very cost effective production and substantially simplifies the assembly of the diffusing lens. Further, varying the lens height means a high flexibility in varying or adapting the optical properties.

[0029] If the diffuse lens according to the present invention is a metalens, the different refractive indices of the diffuse lens are caused by some nanostructures built on the surface of the substrate material. The nanostructures can be spatially separated by air gaps between them. The subwavelength-scale nanostructures are made of high-refractive-index materials that interact with the incident light to shape the amplitude and phase of the light. Such metalens provide a broad platform for controlling light in ways that are not possible with conventional lenses.

[0030] The diffuse lens according to the present invention may be a metalens formed of nanostructures arranged such that an annular first lens segment and an annular second lens segment concentric with each other are formed on the surface of a substrate (such as a Fresnel metalens known in the art). Unlike the Fresnel metalens known in the art, the nanostructures are shaped and arranged such that a first sub-profile describing the refractive index profile of the first lens segment and a second sub-profile describing the refractive index profile of the second lens segment have slopes or curvatures of opposite signs.

[0031] In other words, the nanostructures are shaped and arranged so that the refractive index of the entire first lens segment in a cross section along a plane including the optical axis of the diffuse lens is described by a first sub-profile, which has, for example, a negative slope, such as a convex shape. In the second lens segment, the nanostructures are shaped and arranged so that the refractive index of the entire second lens segment in a cross section along a plane including the optical axis of the diffuse lens is described by a second sub-profile, which in turn has a positive slope, such as a concave shape.

[0032] In this case, the first sub-profile describing the refractive index profile of the first lens segment and the second sub-profile describing the refractive index profile of the second lens segment both describe how the different shapes and arrangements of the nanostructures in the first lens segment and the second lens segment cause an overall varying refractive index of the diffuse lens in a direction perpendicular to the optical axis.

[0033] The main advantage of this metalens approach is that the diffuse lens can be very thin (nanometer-scale), which significantly reduces chromatic aberration. Furthermore, metalenses or metasurfaces can be mass-produced in existing CMOS semiconductor foundries, enabling massively parallel wafer-level integration of optical systems.

[0034] Common to both approaches, the GRIN type lens approach and the metalens approach, is that the height of the diffuse lens along its optical axis may preferably be constant over the width of the diffuse lens. However, it should be understood that this is not necessarily the case and that the height of the metalens may vary, for example on a nanometer scale.

[0035] Preferably, the transition from the first sub-profile to the second sub-profile at the interface is continuous and not continuously differentiable. The refractive index profile of the diffuse lens according to the present invention does not have problematic height steps that cause optical losses and inhomogeneities. This provides an advantage over the standard Fresnel lens approach, in which the lens segments have step-like discontinuities between them. Since the sub-profile of the first lens segment and the second sub-profile of the second lens segment have slopes or curvatures of opposite signs, the crossing or transition from the first sub-profile to the second sub-profile at those interfaces is not continuously differentiable in this embodiment.

[0036] The diffusing lens according to the invention may comprise a series of concentric lens segments formed by a first lens segment and a second lens segment and, for example, further lens segments.

[0037] In one embodiment, the diffuser lens may include not only the first and second lens segments, but also a third, fourth or even more lens segments. In contrast to an ideal Fresnel lens having an infinite number of segments or lens segments, the number of lens segments of the present diffuser element is not limited by a maximum number. The diffuser lens may have a circular geometric aperture to form a circular beam. In other configurations, the geometric aperture of the diffuser lens may be rectangular, such as quadratic, to form a rectangular, such as quadratic beam.

[0038] According to a second aspect of the present invention, there is provided a light source comprising a VCSEL arranged on a semiconductor substrate and configured to emit laser light and a diffusion lens according to the first aspect, wherein the diffusion lens is configured to diffuse the laser light emitted by the VCSEL into a target area.

[0039] Preferably, the diffusing lens and the VCSEL are integrated into one device.

[0040] Typically, a VCSEL can be considered as a quasi-point-shaped light emitting element that emits a slightly diverging light cone. The emitted light cone of the VCSEL passes through a transmissive diffuser lens, which transforms the light emitted by the VCSEL into a beam profile with uniform intensity distribution in the target area.

[0041] In one embodiment, the diffuse lens may be integrated in a semiconductor substrate on which the VCSEL is arranged. As described above, the diffuse lens according to the present invention may be a GRIN type lens or a super lens. In the case of a super lens, some nanostructures are formed on the surface of the substrate. In the case of a GRIN type lens, the different refractive indices (i.e., the gradient of the refractive index) of the diffuse lens may be caused by changing the composition (i.e., doping) of the substrate in which the diffuse lens may be integrated.

[0042] The VCSEL may be a bottom emitter arranged to emit laser light through a semiconductor substrate. In this case, the diffusing lens may be provided on or integrated into a surface of the semiconductor substrate that is arranged opposite to the substrate surface on which the VCSEL is arranged.

[0043] The VCSEL may also be a top emitter arranged to emit laser light in the direction away from the semiconductor substrate. In this embodiment, the diffuse lens may include a transparent material disposed on top of the semiconductor layer structure of the VCSEL. The material is transparent in the wavelength range of the laser light (e.g., in the wavelength range between 750nm-1200nm). The transparent material may be disposed on top of the mesa of the VCSEL.

[0044] The light source may further include a VCSEL array arranged on a common semiconductor substrate. The VCSELs in the array are configured to emit laser light and are associated with one or more diffusion lenses. The one or more diffusion lenses are configured to diffuse the laser light emitted by the VCSELs.

[0045] VCSELs can be characterized by having a 3 μm 2 With 10000μm 2 The active laser emission area of ​​the area between the VCSELs included in the VCSEL array may be between 20 μm and 250 μm. The density of the VCSELs and / or the size of the light emitting area may be different depending on the position in the VCSEL array and / or the shape of the common optical structure illuminated by the respective VCSELs, so that the intensity of the illumination pattern can be adapted.

[0046] At least a portion of the VCSELs may be arranged to be individually controlled to emit laser light. Each VCSEL or groups of two, three, four or more VCSELs in a VCSEL array may be arranged to be individually turned on or off so as to illuminate one or more regions of an illumination pattern in a defined sequence. The VCSEL array comprises corresponding electrodes so that the VCSELs or groups of VCSELs can be individually controlled. Individual control of VCSELs or groups of VCSELs (subarrays) may allow electronic adjustment of the illumination pattern.

[0047] According to a third aspect of the present invention, there is provided a method of manufacturing such a light source. The method comprises the steps of providing a VCSEL arranged on a semiconductor substrate and integrating a diffusing lens according to the first aspect with the VCSEL.

[0048] These steps are not necessarily performed in the order presented above.

[0049] According to a fourth aspect of the present invention, there is provided a method of illuminating a scene, comprising the steps of providing a VCSEL, providing a diffusion lens according to the first aspect, causing the VCSEL to emit laser light, and diffusing the laser light emitted by the VCSEL into a target area through the diffusion lens.

[0050] Likewise, the steps do not necessarily have to be performed in the order presented above.

[0051] It shall be understood that a preferred embodiment of the invention can also be any combination of the dependent claims with the respective independent claim.

[0052] It shall further be understood that the claimed diffusing lens, light source and method have similar and / or identical preferred embodiments, in particular as defined in the dependent claims and as disclosed herein.

[0053] Further advantageous embodiments are defined below. BRIEF DESCRIPTION OF THE DRAWINGS

[0054] These and other aspects of the invention will become apparent and elucidated with reference to the embodiments described hereinafter with reference to the accompanying drawings, in which:

[0055] Figure 1 shows a schematic diagram of a cross section along a plane including the optical axis of a Fresnel lens known in the art;

[0056] Figure 2 Shown with Figure 1 Schematic diagram of the same Fresnel lens and the light path of the incident light through the diffuse Fresnel lens;

[0057] Figure 3 shows a schematic diagram of a cross section along a plane including the optical axis of a gradient refractive index (GRIN) type Fresnel lens known in the art;

[0058] Figure 4 A schematic diagram showing a cross section along a plane including the optical axis of a diffusion lens according to the present invention;

[0059] Figure 5 A schematic diagram showing a 3D representation of a diffusing lens with a quadratic lens aperture according to the present invention;

[0060] Figure 6shows a schematic diagram of a standard diffusing lens used in the prior art;

[0061] Figure 7 A schematic diagram showing a refractive index profile of a diffuse lens according to the present invention;

[0062] Figure 8 A schematic diagram showing a simulated light beam transformed by a diffuse lens according to the present invention;

[0063] Fig. 9 Schematically shows a graph demonstrating the irradiance of a diffusing lens according to the invention (top) and a standard diffusing lens (bottom) on a flat target screen;

[0064] Fig.10 shows a schematic diagram of a light source according to the present invention;

[0065] Fig.11 A principle flow chart showing a method for manufacturing a light source according to the present invention; and

[0066] Fig.12 A principle flow chart of the method for illuminating a scene according to the present invention is shown. DETAILED DESCRIPTION

[0067] Figure 1 A schematic diagram of a cross section along a plane including the optical axis of a Fresnel lens 100 known in the art is shown. The dependence of the height of the Fresnel lens 100 on its radius is shown.

[0068] Unlike the continuous surface of a standard lens, the surface of the Fresnel lens 100 is divided into a set of curved surfaces with step-like discontinuities between the curved surfaces. Figure 1 , where at least the first lens segment 112 , the second lens segment 114 , the third lens segment 116 and the fourth lens segment 118 form the overall structure of the Fresnel lens 100 .

[0069] Figure 1 The inset in shows a top view of the same Fresnel lens 100 and demonstrates that a known Fresnel lens 100 is typically composed of a series of concentric grooves etched into the material forming the Fresnel lens 100. Fresnel lenses 100 are usually made of glass or plastic, but modern Fresnel lenses can also be composed of all refractive materials.

[0070] The surface profiles of the first lens segment 112 and the third lens segment 116 are convexly curved, while the second lens segment 114 arranged at the first radial distance 124 and the fourth lens segment 118 arranged at the second radial distance 128 form height steps or discontinuities between the convexly curved lens segments. The curvature of the surface profile 122 of the first lens segment 112 is the same as the curvature of the surface profiles of other curved lens segments, such as the third lens segment 116. Therefore, the surface shape of other curved lens segments, such as the third lens 116, can be achieved by projecting the surface profile 122 of the first lens segment 112 along a direction parallel to the optical axis of the Fresnel lens 100. In other words, the continuous refractive surface of the conventional optical device is divided and folded onto the bottom plane to obtain a surface profile such as Figure 1 Fresnel lens 100 is shown. This is indicated by arrows 130 from the dashed curve representing the surface profile 122 of the first lens segment 112 to the surfaces of the other curved lens segments.

[0071] As is clear from the symmetry, the rest of the Fresnel lens 100 is Figure 1 This also comes from Figure 1 The entrance in becomes apparent.

[0072] The Fresnel lens 100 has a reduced lens sag compared to conventional lenses and ideally includes an unlimited number of segments or lens sections. Figure 1 Four lens segments are shown by way of example 112, 114, 116, 118. Their thin, lightweight construction and availability in a variety of sizes make Fresnel lenses useful in a variety of applications.

[0073] By using Figure 1 A problem with the conventional diffuse Fresnel lens 100 shown is that the height step formed by the second lens segment 114 and the fourth lens segment 118 causes an inhomogeneity in the diffuse beam profile and energy loss in this area. This is subsequently Figure 2 A schematic illustration is given in .

[0074] Figure 2 Shown with Figure 1 FIG. 1 is a schematic diagram of the same Fresnel lens 100 and the optical path of the incident light 150 passing through the Fresnel lens 100. The incident light 150 is Figure 2 , showing how the Fresnel lens 100 known in the art diffuses incident light. The diffraction of the incident light 150 by the Fresnel lens 100 indicated by these arrows is calculated by applying Snell's law. Circles 140 indicate areas of height difference, i.e., sections where a convex surface with the same curvature is interrupted by a discontinuity.

[0075] Some of the light transmitted through each discontinuous surface is deflected due to secondary refraction, which causes most of the optical loss at the outer regions in the target area. This is due to Figure 2 The dashed arrows in exemplarily show that the optical efficiency and uniformity of the beam profile in the target area are significantly reduced due to the height step.

[0076] Figure 3 A schematic diagram of a cross section along a plane including the optical axis of a gradient refractive index (GRIN) type Fresnel lens 100 ′ known in the art is shown. Figure 3 The lower figure in shows the dependence of the refractive index difference Δn in the cross section of the GRIN type Fresnel lens 100 ′ on its radius. The upper figure shows the dependence of the constant height of the GRIN type Fresnel lens 100 ′ on its radius.

[0077] As disclosed in T. Suhara et al., "Graded-index Fresnel lenses for integrated optics," Applied Optics, 21(11), pp. 1966-1971 (1982), it is known in the art that a GRIN type Fresnel lens 100' can also be manufactured by a gradient refractive index (GRIN) profile, wherein the refractive index n of the material constituting the GRIN type Fresnel lens 100' varies according to the radius of the Fresnel lens. This is Figure 3 , where the refractive index profile 105 describes the refractive index of the different lens segments 112, 114, 116 (see Figure 3 , upper and lower figures in the figure).

[0078] See also Figure 1 The description of the varying height of the classical Fresnel lens 100 applies mutatis mutandis to the following: Figure 3 The varying refractive index profile 105 of the GRIN type Fresnel lens 100' is shown and therefore will not be repeated.

[0079] However, from Figure 3 It becomes apparent from the above figure that Figure 1 Unlike the illustrated Fresnel lens 100, the GRIN type Fresnel lens 100' is flat and does not include any height differences. Therefore, the optical properties of this GRIN type Fresnel lens 100' are only due to the different refractive indices along its radius.

[0080] Figure 4 A schematic diagram showing a cross section along a plane including the optical axis of the diffusion lens 1 according to the present invention is shown. Figure 4The lower figure in shows the refractive index difference Δn in the cross section. The upper figure shows the preferred constant height of the diffusing lens according to the present invention.

[0081] The refractive index profile 5 depicting the refractive index of the diffusion lens 1 in a cross section along a plane including the optical axis of the diffusion lens 1 and varying in a direction perpendicular to the optical axis (ie, along a radius) includes at least a first sub-profile 12 and a second sub-profile 14 . Figure 4 The first, second and third sub-profiles 12, 14, 16 describe the refractive index profiles of the first lens segment 2, the second lens segment 4 and the third lens segment 6. Figure 4 In the above figure, the planar diffuser lens 1 is exemplarily shown as a segment or section of the planar diffuser lens 1. The three lens segments 2, 4, 6 shown are only exemplary, and the diffuser lens 1 according to the invention may comprise more lens segments.

[0082] exist Figure 4 The following figure further shows that the first sub-profile 12 transitions to the second profile 14 at the interface 10. It is clear to those skilled in the art that all sub-profiles of all lens segments are adjacent at their respective interfaces and that the transition or intersection between different lens segments is continuous. Further, it is clear to those skilled in the art that, by symmetry, the rest of the diffuse lens 1 is Figure 4 Mirror image shown.

[0083] In this embodiment, the sub-profiles describing the refractive index profile of the lens segment are all curved. Figure 3 The known GRIN type Fresnel lens 100' shown is essentially different in that the curved sub-profiles are divided by vertical steps therebetween (see Figure 3 ). Instead of being curved, the refractive index profiles 12, 14, 16 of the lens segments of the lens 1 may not be curved but may be straight in a cross section along a plane including the optical axis of the lens 1. For example, the refractive index profiles 12, 14, 16 of the lens segments may be conical when viewed in three dimensions, such that the refractive index sub-profiles in a cross section along a plane including the optical axis of the lens 1 are formed by surface lines of the corresponding cones.

[0084] For simplicity, the following description will be mainly given for the case of a lens segment having a curved refractive index profile as shown in the figure.

[0085] The first sub-profile 12 may be formed, for example, by the function Description, where n1 is the refractive index of the first sub-profile 12, n0 is the offset refractive index and Δn is the refractive index difference, for simplicity, this is Figure 4 It is shown in and is exemplarily proportional to the square of the radius r of the diffuse lens. is a constant used for normalization.

[0086] The second sub-contour 14 can be represented by the function The curvature of the first sub-contour 12 and the second sub-contour 14 is ±n0A (second-order derivative) for this example. Therefore, the curvature of the first sub-contour 12 and the second sub-contour 14 is determined by the same curvature function (n″) 1，2 =±n0A), but with opposite signs. Figure 4 It is shown that we can project the function along the ordinate to obtain the second sub-contour 14. This is indicated by arrow 30b.

[0087] The third sub-profile 16 can be described by the same function as that used to describe the first sub-profile 12. Figure 4 As shown, only the function Projection along the ordinate. This is indicated by arrow 30a.

[0088] More generally, the function describing the slope of the first sub-profile 12 and the second sub-profile 14 may be, for example, related to r n , where r is the radius of the diffuse lens and n≥0. Therefore, the slope function (first-order derivative function) may be proportional to a constant of n=0. For example, this is the case if both the first sub-profile and the second sub-profile have the shape of a linear function in a cross section along a plane including the optical axis, such as is the case with a conical refractive index profile. For n>0, the slope function may be a polynomial function.

[0089] like Figure 4 The diffuser lens 1 shown provides the same advantages as the known Fresnel lens, but additionally overcomes the following problems: Figure 1 , Figure 2 and Figure 3 The problem caused by secondary reflection at height steps in a known Fresnel lens is shown.

[0090] In addition to following Figure 4 The radius of the diffuser lens 1 shown changes the refractive index in addition to the refractive index in the azimuthal direction.

[0091] Figure 5 Schematic diagram of a 3D representation of a diffusing lens 1 with a secondary lens aperture 20 according to the present invention is shown. In addition to the secondary aperture 20, the diffusing lens 1 can be connected with Figure 4The diffuser lens 1 is identical to that shown in FIG. 1 . The diffuser lens 1 consists of four planar lens segments 2, 4, 6, 8 having planar surfaces through which the light exits. Each lens segment may, for example, have a radial width of 50 μm, so that the inner segment, i.e. the first lens segment 2, goes from r=0 μm to r=50 μm, the second lens segment 4 from r=50 μm to r=100 μm, etc. Since the lens segments 2, 4, 6, 8 are preferably flat and not noticeable, since they differ only in their refractive index profile, the transitions from different lens segments 2, 4, 6, 8 are determined by Figure 5 The dotted circle in is shown.

[0092] Figure 6 A schematic diagram of a standard diffuse lens used in the prior art is shown. The diffuse lens 200 is illuminated by parallel incident light 150, and each portion of the diffuse lens 200 redirects the light to a certain angle. The different angles are represented by -X3, -X2, -X1, X1, X2 and X3. All positive angles, i.e., X1 to X3, are to the right of the lens center of the diffuse lens 200, and the same angles but with opposite signs can be found to the left of the lens center of the diffuse lens 200. For large diffusion angles, the surface slope becomes very large at the sides of the lens, and the total height difference or sagitta of the lens is too large to be achieved in a semiconductor substrate by common methods such as grayscale lithography.

[0093] Figure 7 A schematic diagram of the refractive index profile 5 of the diffuser lens according to the present invention is shown to demonstrate how parallel incident light rays 150 are redirected by the diffuser lens according to the present invention. Figure 6 and Figure 7 It becomes apparent from the comparison of the above that in each segment of the diffuser lens according to the present invention, Figure 6 Compared to the prior art lens 200 shown, the signs of the emission angles of the redirected light rays 150 alternate. This means, for example, that at a location where a +X3 angle is generated for the prior art lens 200, a -X3 angle is generated for the diffuser lens according to the present invention. At a location where a -X3 angle is generated for the prior art lens 200, a +X3 angle is generated for the diffuser lens according to the present invention.

[0094] Figure 8A schematic diagram of a simulated light ray 150 transformed by a diffuse lens 1 according to the invention is shown. The diffuse lens 1 according to the invention is also shown with a secondary lens aperture 20. A large number of light rays are exemplarily simulated by ray tracing, wherein the light path is simulated by taking into account the interaction of the light with the diffuse lens 1 according to the invention. The simulation shows that the first lens segment 2 and the third lens segment 6 are focusing the light ray 150, while the second lens segment 4 and the fourth lens segment 8 are defocusing the light ray 150. Overall, this produces a uniform beam profile in the far field by the overlap of light rays transformed differently by the different lens segments.

[0095] and Figure 4 and Figure 7 The diffuser lens 1 shown is different, such as Figure 8 The diffuser lens 1 shown has lens segments in different orders with convex and concave sub-profiles describing the refractive index of the lens segments. Figure 8 The first lens segment 2 of the diffuser lens 1 shown has a first sub-profile of convex shape, while the second lens segment 4 has a second sub-profile of concave shape, and so on. In contrast, Figure 4 and Figure 7 The first lens segment 2 of the diffuser lens 1 shown has a first sub-profile of concave shape, while the second lens segment has a second sub-profile of convex shape. This difference demonstrates that the diffuser lens 1 according to the invention is not limited to a specific alternating sequence of convex and concave sub-profiles.

[0096] Fig. 9 Schematic diagram showing a diffuser lens 1 according to the invention (top) and a standard diffuser lens (bottom), such as Figure 6 A graph of the irradiance of the diffuser lens 200 shown on a flat target screen. Both irradiance profiles provide the same functionality and uniformity, but the diffuser lens according to the invention has a much smaller height. In the case where the diffuser lens according to the invention is a metalens, the height can be in the nanometer range. Therefore, the same functionality and uniformity can be achieved using a thinner diffuser lens.

[0097] Fig.10A schematic diagram of a light source 50 according to the present invention is shown. A substrate 60 may include a semiconductor material, in particular a III-V compound semiconductor, in particular gallium arsenide (GaAs). On one side of the substrate 60, a VCSEL 70 is arranged, which may include an optical resonator, the optical resonator including a first reflector such as a distributed Bragg reflector (DBR) 74, an active layer 76 and a second reflector such as a DBR 78. The first DBR 74, the active layer 76 and the second DBR 78 may include a plurality of layers forming a layer structure of the VCSEL 70. The first DBR 74 is arranged on the substrate 60, and the active layer 76 is sandwiched between the first DBR 74 and the second DBR 78. The first DBR 74 and the second DBR 78 may include multiple pairs of layers with different refractive indices to provide reflectivity. The active layer 76 may include one or more quantum well layers. The optical resonator formed by the DBRs 74 and 78 and the active layer 76 is characterized by a mesa structure, which is etched down to the middle layer of the first DBR 74. The second DBR 78 is covered by an electrical contact 80 to contact the VCSEL 70. Another contact 92 provides electrical contact to the substrate 60. The electrical contact 92 is separated from the first DBR 74 by an electrical spacer 94. An electrical bond 96 is conductively connected to the electrical contact 92.

[0098] like Fig.10 As shown, the diffuser lens 1 according to the present invention can be integrated in the substrate 60. In other words, by Figure 4 The refractive index of the substrate material 60 is changed as shown, and the diffusing lens 1 is "buried" in the substrate 60.

[0099] like Fig.10 The VCSEL 70 shown is a so-called bottom emitter, ie the laser emission generated in the optical resonators 74 , 76 , 78 is transmitted through the substrate 60 and through the diffusing lens 1 integrated in the substrate 60 .

[0100] The VCSEL may also be a top emitter, for example, and a diffusing lens may be provided on top of the semiconductor layer structure of the VCSEL 70 , such as on top of the second DBR 78 .

[0101] Further, it should be understood that the present invention is not limited to a light source 50 having one VCSEL 70 and one diffusing lens 1. The present invention also relates to an array of VCSELs 70 arranged on a common semiconductor substrate 60, each VCSEL 70 being configured to emit laser light, and at least one diffusing lens 1 associated with a VCSEL 70 in the VCSEL array and configured to diffuse the laser light emitted by the VCSEL 70 (not shown).

[0102] Fig.11A principle flow chart of a method for manufacturing a light source according to the present invention is shown.

[0103] At S2, a VCSEL 70 is provided, which is arranged on a semiconductor substrate 60. The semiconductor substrate 60 has an initial surface which is preferably planar. The semiconductor substrate 60 may include GaAs.

[0104] At S4, a diffusion lens 1 is provided which is integrated with the VCSEL 70. The diffusion lens 1 is arranged to transform the laser light emitted by the VCSEL 70 so that a uniform beam profile is achieved in the target area. Fig.10 As shown, the diffusing lens 1 may be integrated within the material of the substrate 60 .

[0105] Fig.12 A principle flow chart of the method for illuminating a scene according to the present invention is shown.

[0106] At S12, a VCSEL 70 is provided. At S14, a diffusion lens 1 according to the present invention is provided. At S16, the VCSEL 70 is caused to emit laser light, and at S18, the laser light emitted by the VCSEL 70 is diffused by the diffusion lens 1 into a target area.

[0107] Although the present invention has been shown and described in detail in the drawings and the foregoing description, such showing and description are to be considered illustrative or exemplary rather than restrictive; the present invention is not limited to the disclosed embodiments. Other variations to the disclosed embodiments may be understood and effected by those skilled in the art in practicing the claimed invention from a study of the drawings, the disclosure, and the appended claims.

[0108] In the claims, the word "comprising" does not exclude other elements or steps and the singular does not exclude a plurality. A single element or other unit may fulfill the functions of several items recited in the claims. The mere fact that certain measures are recited in mutually different dependent claims does not indicate that a combination of these measures cannot be used to advantage.

[0109] Any reference signs in the claims should not be construed as limiting the scope.

Claims

1. A diffusion lens (1), comprising: The first lens segment (2) is annular and the second lens segment (4) is annular, wherein the first lens segment (2) and the second lens segment (4) are concentric. The refractive index of the first lens segment (2) and the second lens segment (4) in a cross section along a plane including the optical axis of the diffuse lens is described by a refractive index profile (5), which varies in a direction perpendicular to the optical axis and includes: a first sub-profile (12) describing a refractive index profile of a first lens segment (2) and a second sub-profile (14) describing a refractive index profile of a second lens segment (4), wherein the first sub-contour (12) transforms into the second sub-contour (14) at the interface (10), and wherein the first sub-contour (12) and the second sub-contour (14) have slopes of opposite signs, wherein, in a cross section along a plane including the optical axis of the diffuse lens, one of the first sub-profile and the second sub-profile (12, 14) is convexly curved, and the other of the first sub-profile and the second sub-profile (12, 14) is concavely curved, The slope of the first sub-contour (12) and the slope of the second sub-contour (14) are described by the same slope function, but the signs of the slopes are opposite. Wherein, the transition from the first sub-contour (12) to the second sub-contour (14) at the interface (10) is continuous and not continuously differentiable.

2. The diffusion lens according to claim 1, in, The slope function describing the slope of the first sub-contour (12) and the slope of the second sub-contour (14) is related to r n Proportional to, where r is the radius of the diffusing lens (1), and n≥0.

3. The diffusion lens according to claim 1 or 2, in, The diffusing lens is a gradient refractive index GRIN type lens or a super lens.

4. The diffusion lens according to claim 1 or 2, further comprising a third lens segment, a fourth lens segment or more lens segments, wherein: The lens segments are circularly concentric.

5. The diffusion lens according to claim 1 or 2, wherein: The geometric aperture (20) of the diffusing lens is rectangular.

6. A light source (50), comprising a vertical cavity surface emitting laser (VCSEL) (70) arranged on a semiconductor substrate (60) and configured to emit laser light, and a diffusion lens (1) according to any one of the preceding claims 1 to 5, wherein: The diffusion lens (1) is configured to diffuse laser light emitted by the VCSEL (70).

7. The light source according to claim 6, wherein The diffusion lens (1) is formed integrally with the VCSEL (70).

8. The light source according to claim 6 or 7, in, The diffusion lens (1) is integrated into a semiconductor substrate (60) on which a VCSEL (70) is arranged.

9. The light source according to any one of claims 6 or 7, in, The VCSEL (70) is a bottom emitter arranged to emit laser light through a semiconductor substrate (60), wherein the diffusion lens (1) is arranged on a surface of the semiconductor substrate (60) arranged opposite to the VCSEL (70) or is integrated into the semiconductor substrate (60).

10. The light source according to claim 6 or 7, in, The VCSEL (70) is a top emitter arranged to emit laser light in a direction away from the semiconductor substrate (60), wherein the diffusing lens (1) is arranged on top of the semiconductor layer structure of the VCSEL (70).

11. A light source according to claim 6 or 7, comprising an array of VCSELs (70) arranged on a common semiconductor substrate (60), the VCSELs (70) being configured to emit laser light, and one or more diffusing lenses (1) associated with VCSELs in the array of VCSELs and configured to diffuse the laser light emitted by the associated VCSELs.

12. A method for manufacturing a light source, the method comprising the following steps: Providing a vertical cavity surface emitting laser (70) VCSEL arranged on a semiconductor substrate (60); A diffusion lens (1) is integrated with a VCSEL (70), wherein the diffusion lens (1) comprises: The first lens segment (2) is annular and the second lens segment (4) is annular, wherein the first lens segment (2) and the second lens segment (4) are concentric. The refractive index of the first lens segment (2) and the second lens segment (4) in a cross section along a plane including the optical axis of the diffuse lens is described by a refractive index profile (5), which varies in a direction perpendicular to the optical axis and includes: a first sub-profile (12) describing a refractive index profile of a first lens segment (2) and a second sub-profile (14) describing a refractive index profile of a second lens segment (4), wherein the first sub-contour (12) transforms into the second sub-contour (14) at the interface (10), and wherein the first sub-contour (12) and the second sub-contour (14) have slopes of opposite signs, wherein, in a cross section along a plane including the optical axis of the diffuse lens, one of the first sub-profile and the second sub-profile (12, 14) is convexly curved, and the other of the first sub-profile and the second sub-profile (12, 14) is concavely curved, The slope of the first sub-contour (12) and the slope of the second sub-contour (14) are described by the same slope function, but the signs of the slopes are opposite. Wherein, the transition from the first sub-contour (12) to the second sub-contour (14) at the interface (10) is continuous and not continuously differentiable.

13. A method of illuminating a scene, the method comprising the steps of: Providing a vertical cavity surface emitting laser (70) VCSEL; A diffusion lens (1) according to any one of claims 1 to 5 is provided. causing the VCSEL (70) to emit laser light; as well as The laser light emitted by the VCSEL (70) is diffused into a target area through the diffusion lens (1).

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