Lighting devices, optical elements

Abstract

Provided is a lighting device having a sufficiently wide irradiation angle and a uniform light intensity within a prescribed range even in the case in which light having a small spread angle, such as laser light, or a light source similar to a collimated light source is used. This lighting device includes: a light source having at least one light-emitting part; a first optical element that receives light emitted from the light source and that emits the light with an expanded emission angle; and a second optical element that receives the light emitted from the first optical element and that emits the light with a further expanded irradiation angle.

Description

[Technical Field]

[0001] This invention relates to a lighting device. [Background technology]

[0002] Conventionally, lighting devices that increase the radiation angle of light from a light source such as an LED, and furthermore, achieve uniformity of brightness (light intensity) within a certain range, are known, such as those disclosed in Patent Document 1 and Patent Document 2. All of these conventional devices are equipped with a light source such as an LED and a lens that adjusts its orientation, and are configured to greatly broaden the direction in which light is emitted by refracting the light emitted from the LED with the lens.

[0003] A type of meniscus lens is preferably used as the lens. This lens comprises a first surface that receives light from a light source and a second surface that emits light. The first surface has a cavity that encloses the LED element. The lens has an axis (lens optical axis) and is axially symmetric, and is approximately coaxial with the optical axis of the LED. On the second surface, a certain central area including the lens optical axis is concave compared to the rest of the surface.

[0004] However, these technologies can expand the illumination angle by utilizing the properties of lenses and other components, using light sources that inherently have a large radiation angle, such as LEDs. On the other hand, applying these lighting devices to light sources that inherently have a small light irradiation angle, such as laser light sources, is not easy, and expanding the light irradiation angle is difficult.

[0005] Furthermore, similar problems can arise when using light sources other than lasers, such as collimated light sources that emit parallel light with a small beam diameter using a collimating lens. Specifically, because the light emitted from the light source has only optical components parallel to the optical axis, it is difficult to sufficiently increase the irradiation angle of the emitted light. [Prior art documents] [Patent Documents]

[0006]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0007] The present invention has been made paying attention to such conventional problems, and provides a lighting device that has a sufficiently wide irradiation angle and uniform light intensity within a predetermined range even when using light with a small divergence angle such as a laser or a light source close to parallel light.

Means for Solving the Problems

[0008] In order to solve the above problems, a lighting device according to the present invention includes a light source having at least one light emitting portion, a first optical element that receives light emitted from the light source and expands its emission angle for emission, and a second optical element that receives light emitted from the first optical element and further expands its irradiation angle for emission.

Effects of the Invention

[0009] According to the present invention, it is possible to provide a lighting device that has a sufficiently wide irradiation angle and uniform light intensity within a predetermined range even when using light with a small divergence angle such as a laser or a light source close to parallel light.

Brief Description of the Drawings

[0010] [Figure 1A] It is an optical configuration diagram for explaining the overall configuration of a lighting device 100 according to an embodiment. [Figure 1B] It is a graph showing the light intensity characteristics of the emitted light of the lighting device 100. [Figure 2] It is a schematic diagram showing an example of the configuration of a microlens array 10M used as the first optical element 10. [Figure 3A]This is an example of a top view of the microlens array 10M. [Figure 3B] This is a schematic diagram for explaining the virtual circle. [Figure 4] This is a graph with the distance d (d = 0 to RH) from the center C of the virtual circle to the center of the upper surface (lens surface) of each microlens ML on the horizontal axis and the sag z of the microlens ML on the vertical axis. [Figure 5] This shows a cross-sectional view when the microlens ML is cut by a plane including the symmetry axis. [Figure 6] This is a graph showing the relationship between the distance d and the specific tilt angle β for the example of the microlens illustrated in FIG. 4. [Figure 7] This is a graph showing an example of the relationship between the specific tilt angle adjustment coefficient k and the specific tilt angle β. <00OO102> [Figure 8] This is a graph showing an example of the relationship between the distance d and the specific tilt angle adjustment coefficient k of the microlens ML in FIGS. 4 and 6. [Figure 9] This is a graph showing an example of the relationship between the specific tilt angle β of the microlens ML and the distance d from the center C. [Figure 10A] This shows a configuration example of the first optical element 10. [Figure 10B] This shows a configuration example of the first optical element 10. [Figure 10C] This shows a configuration example of the first optical element 10. [Figure 10D] This shows a configuration example of the first optical element 10. [Figure 10E] This shows a configuration example of the first optical element 10. [Figure 10F] This shows a configuration example of the first optical element 10. [Figure 10G] This shows a configuration example of the first optical element 10. [Figure 11A] This is a schematic diagram for explaining the definition of the divergence angle θd. [Figure 11B] This shows a top view of an example of a microlens array having fluctuations in the arrangement of microlenses. [Figure 11C]A top view of an example of a microlens array with fluctuations in the arrangement of microlenses is shown. [Figure 11D] A top view of an example of a microlens array with fluctuations in the arrangement of microlenses is shown. [Figure 12] This is an explanatory diagram illustrating the distance L between the light source 1 and the first optical element 10. [Figure 13A] The light intensity distribution of the light emitted from the NIR-VCSEL used as light source 1 in Example 1 is shown. [Figure 13B] The various numerical values ​​used in Example 1 are shown below. [Figure 14] This graph shows the relationship between distance d and the specific tilt angle adjustment coefficient k in Example 1. [Figure 15] This is a schematic diagram of the microlens array of Example 1. [Figure 16] An example of a fisheye lens used as the second optical element 20 in Example 1 is shown. [Figure 17] This is the simulation result for Example 1. [Figure 18] This is the simulation result for Comparative Example 1. [Modes for carrying out the invention]

[0011] This embodiment will be described below with reference to the attached drawings. In the attached drawings, functionally identical elements may be indicated by the same number. The attached drawings show embodiments and implementation examples in accordance with the principles of this disclosure, but they are for the purpose of understanding this disclosure and are not to be used in any way to restrict the interpretation of this disclosure. The descriptions in this specification are merely typical examples and do not limit the claims or applications of this disclosure in any way.

[0012] While this embodiment is described in sufficient detail for those skilled in the art to implement the disclosure, it is important to understand that other implementations and forms are possible, and that the configuration and structure can be modified and various elements replaced without departing from the scope and spirit of the technical idea of ​​this disclosure. Therefore, the following description should not be construed as limiting to this.

[0013] The illumination device according to the embodiment will be described with reference to Figures 1A and 1B. Figure 1A is an optical configuration diagram illustrating the overall configuration of the illumination device according to the embodiment, and Figure 1B is a graph showing the light intensity characteristics of this illumination device. As shown in Figure 1A, this illumination device 100 is broadly composed of a light source 1, a first optical element 10, and a second optical element 20.

[0014] Light source 1 is a light source that emits light with excellent directionality, such as laser light. Instead of a laser light source, light source 1 may be configured by combining a light source that emits light with low directionality, such as an LED, with a collimating lens that makes this light parallel.

[0015] The first optical element 10 has the role of widening the irradiation angle of the light emitted from the light source 1. The second optical element 20 has the role of further widening the irradiation angle of the light emitted by the first optical element 10.

[0016] An example of the light intensity distribution of this lighting device 100 is shown in Figure 1B. In Figure 1B, the horizontal axis represents the light emission angle centered on the optical axis, and the vertical axis represents the light intensity when the maximum intensity is set to 1.

[0017] The light emission angle is synonymous with the divergence angle and spread angle of light emitted from a device, optical apparatus, or lighting device. The magnitude of the emission angle is closely related to the size of the illumination range of the lighting device. In this specification, when measuring or simulating the light intensity distribution (light intensity distribution characteristics) from a device, optical apparatus, or lighting device, the light intensity per unit solid angle is determined relatively according to the light emission angle (the maximum light intensity value is set to 1).

[0018] As shown in Figure 1B, the lighting device 100 according to this embodiment has a light intensity distribution characteristic in which the light intensity when the emission angle of the emitted light is ±90° is 0.5 or higher, preferably 0.55 or higher, and more preferably 0.6 or higher. Furthermore, the light intensity is 0.9 or higher when the absolute value of the emission angle is 45° or less (-45° to 45°), preferably 50° or less, more preferably 55° or less, and particularly preferably 60° or less. The light intensity distribution can be measured using, for example, an orientation measuring device IMS-5000 manufactured by Asahi Spectroscopic Co., Ltd.

[0019] For the illumination device 100 of this embodiment, a laser light source with a relatively small irradiation angle (spread angle) is advantageous. When light source 1 is a laser light source, the laser light source may be a light-emitting array having multiple light-emitting parts within a predetermined area, or it may be a single laser element having only one light-emitting part.

[0020] If light source 1 is a laser light source, the laser light source may be a VCSEL (Vertical Cavity Surface Emitting Laser), or a VCSEL array in which the substantial light-emitting parts are arranged in two or three dimensions. In addition to a laser light source, light source 1 can also be an LED element or an LED array in which the substantial light-emitting parts are arranged in two or three dimensions. In addition to electroluminescent light sources such as laser light sources and LEDs, thermal radiation light sources and discharge light sources may also be used. Thermal radiation light sources include incandescent bulbs and halogen bulbs, while typical discharge light sources include high-pressure mercury lamps, metal halide lamps, and fluorescent lamps. The irradiation angle of the light emitted from light source 1 used is such that the full width at half maximum (FWHM) of the light intensity distribution of the light source is 6° to 40°, preferably 12° to 30°, and more preferably 15° to 24°.

[0021] The first optical element 10 comprises a first surface to which light is incident and a second surface to which light is emitted. The first optical element 10 may be, for example, a surface that has the function of diffusing light, and may have a homogenizing effect, or it may be equipped with a homogenizer and a diffuser plate or diffuser element (diffusion function). The diffuser plate or diffuser element has the function of diffusing incident light at a certain angle through refraction or diffraction due to the structure such as minute irregularities on the surface or inside. Similarly, the second surface may be a surface that has a diffusion function, similar to the first surface, or it may be a surface that does not have a diffusion function. However, it is required that at least one of the first surface and the second surface of the first optical element 10 is an element that has a diffusion function.

[0022] The first optical element 10 may be, for example, a microlens array, a cylindrical lens array, a microprism array, or a Fresnel lens array. Each of these can be an optical element in which multiple microlenses, cylindrical lenses, microprisms, or Fresnel lenses are formed on at least one of the first and second surfaces of the first optical element 10. Furthermore, multiple types of optical elements may be mixed and formed within a single first optical element 10.

[0023] Furthermore, microlenses and microprisms may be concave or convex. Microlenses and microprisms may be arranged according to a certain rule or may be randomly distributed. Microlenses and microprisms may be mixed together, differing in curvature, shape, angle, and size.

[0024] Furthermore, the first optical element 10 may be a frosted diffuser plate or the like, with a substrate or support surface that has been roughly ground to create minute irregularities. The first optical element 10 may have a line-symmetric or point-symmetric structure with respect to the center, but is not limited to this. If multiple structures, such as multiple lenses, are formed, it may also have an asymmetric structure.

[0025] Figures 2(a) to (c) show an example of the configuration of a microlens array 10M used as the first optical element 10. The microlens array 10M has a substrate SB having a first surface S1 to which light is incident and to which a plurality of microlenses ML are arranged, and a second surface S2 from which light is emitted. The second surface S2 is planar in shape, so that the microlens array 10M is a substantially flat plate-shaped element. In Figures 2(a) to (c), microlenses ML may be formed on both the first surface S1 and the second surface S2. In this case, there are a total of two surfaces that have the function of acting on light, so an increase in the effect of expanding the illumination angle can be expected.

[0026] Although not shown in the illustrations, the microlens array 10M may be a substantially flat plate shape as illustrated in Figures 2(a) to (c), or it may have a shape that includes curved surfaces such as a curved surface. The material of the microlens array 10M is not limited to any particular material. The material of the microlens array 10M may include resin and glass, and may be an inorganic material, an organic material, or even an inorganic-organic hybrid material.

[0027] The method for manufacturing the microlens array 10M is not limited to a specific method. For example, a mold for transfer may be prepared in advance, and the microlens array 10M may be formed by mold molding. In particular, when the surface to be formed, or the constituent material and / or support containing the surface, is formed of resin or plastic, the mold molding method may include injection molding, blow molding, extrusion molding, casting, vacuum forming, etc.

[0028] Alternatively, a microlens array 10M may be formed by pouring a fluid resin or uncured resin onto a substrate or support made of materials such as glass or resin, transferring microlenses to at least one side of the resin using a mold, and then drying or curing the resin to integrate it with the substrate or support (2P molding).

[0029] Cylindrical lens arrays and microprism lens arrays may also be formed using a similar method.

[0030] Furthermore, the first optical element 10 may be a microlens array 10M, in which the shape of each microlens has a distribution. A top view of such a microlens array 10M is shown in Figure 3A.

[0031] The microlens array 10M shown in Figure 3A has, for example, a roughly square top surface of approximately 1 mm × 1 mm. The size of the microlens array 10M can be changed depending on the size of the light source 1 and the lighting performance required of the lighting device. The shape of the individual microlenses ML may be a roughly square shape as shown in Figure 2, a polygonal shape as shown in Figure 3A, or a circular or elliptical shape.

[0032] In the top view of Figure 3A, each microlens ML in the microlens array 10M has an outer shape that is a circle or a polygon such as a hexagon, with respect to the axis of symmetry, and its lens diameter can be, for example, about 25 μm or less. When the outer shape of the microlens ML is a circle, the diameter of the circle is the lens diameter, and when it is a polygon, the diameter of the circumscribed circle is the lens diameter.

[0033] In the microlens array 10M shown in Figure 3A, six microlenses are arranged with equal pitch and equal phase for each microlens (referred to as a "hexagonal dense arrangement" in this text; the same applies hereafter). The lens pitch (distance between the centers of two adjacent lenses) is, for example, approximately 25 μm.

[0034] In identifying the microlens array 10M, as shown in Figure 3B, a center C and radius R are defined on the upper surface of the microlens array 10M. H A virtual circle can be assumed to have the following characteristics. The center position and radius of the virtual circle can be determined based on, for example, the shape and size of the microlens array 10M, the size of the light source 1, and the emission angle of the light emitted from the light source 1. In other words, the position and size of the virtual circle can be determined based on the size corresponding to the effective range through which the emitted light is transmitted.

[0035] If the upper surface of the microlens array 10M is circular, the circular shape itself may be considered a virtual circle. If the upper surface of the microlens array 10M is an ellipse, polygon, or any other shape formed by curves or straight lines, the inscribed circle tangent to its contour may be considered a virtual circle. Furthermore, if the upper surface of the microlens array 10M is polygonal, the inscribed circle tangent to any side of the circle or polygon contained within it may be considered a virtual circle.

[0036] The properties of the microlenses ML contained in the microlens array 10M will be explained. As an example, consider the case where the contour of the upper surface of the microlens array 10M is a 1 mm x 1 mm square, as shown in Figure 3A, and the axially symmetric microlenses ML are arranged in a hexagonal, dense arrangement. The virtual circle is the inscribed circle of the contour of the upper surface of the microlens array 10M.

[0037] The center C of the virtual circle may be the geometric center of the microlens array 10M, or the axis of symmetry of a microlens near the geometric center. In the example shown in Figure 3A, the radius R of the virtual circle. H The thickness is 500 μm. Please note that the example in Figure 3A is for ease of understanding and is not intended to limit the scope of the present invention.

[0038] The shape of the microlens ML may change depending on the distance d from the center C of the virtual circle. Figure 4 shows the distance d from the center C of the virtual circle to the center of the upper surface (lens surface) of each microlens ML (d=0~R). H This graph has the horizontal axis representing the sag z of the microlens ML and the vertical axis representing the sag z of the microlens ML, showing the shape of a portion of the cross-section of the microlens ML aligned along the dashed line A-A' in Figure 3A. The example shown illustrates the case where the microlens ML is a concave lens, but this is not intended to be the only case.

[0039] As is clear from the graph of FIG. 4, in this example, the shape of the microlens ML varies depending on its position (distance d) on the microlens array 10M. Specifically, the microlens ML is formed such that the sag z decreases as the distance d increases (at least in part). The sag or sag amount refers to the maximum depth (or maximum height if the microlens is convex) in a direction parallel to the symmetry axis or optical axis of the microlens ML. One further feature of the example in FIG. 4 is that the angle of the tangent plane (the dashed line in FIG. 4) of the microlens ML changes according to the distance d. This is because when light is incident on the microlens ML, the inclination angle of the tangent plane can be used to evaluate the divergence or diffusion angle at which the light exits with respect to the symmetry axis of the microlens ML.

[0040] FIG. 5 shows a cross-sectional view when the microlens ML is cut along a plane including the symmetry axis. When the diameter of the microlens ML is D, the inclination angle of the tangent plane at a predetermined position (for example, a position at a distance of 0.6×D from the center) on the lens surface between the center and the outer edge of the microlens ML is defined as the specific inclination angle β. This specific inclination angle β is one of the indices representing the characteristics of the shape of the microlens ML. The graph of FIG. 6 shows the relationship between the distance d and the specific inclination angle β for the example of the microlens illustrated in FIG. 4. Since the microlens ML is formed discretely in the microlens array 10M, its specific inclination angle β is also discrete with respect to the distance d, and the coordinates (d, β) are any of the points on the dashed line shown in FIG. 6.

[0041] In the example of FIG. 6, the specific inclination angle β is constant within the range of d = 0 to d1 (d1 < R H ), and decreases monotonically as d increases within the range of d = d1 to R H . d1 = 0.6×R H , preferably d1 = 0.5×R H , and more preferably d1 = 0.45×R H . The maximum value β of the specific inclination angle β of the microlens ML within the range of d = 0 to R H maxThe angle is 20° to 40°, preferably 22° to 35°, more preferably 25° to 32°, and particularly preferably 25° to 30°. Also, the specific inclination angle β of the microlens ML is d = 0 to R H The minimum value β within the range min The angle is 5° to 25°, preferably 10° to 20°, and more preferably 12° to 18°. Also, β min / β max The value of is 0.2 to 1.0, preferably 0.4 to 0.8, and more preferably 0.5 to 0.7. In short, in the region where the distance d from a predetermined position is within a predetermined value, the multiple microlenses ML have substantially the same shape, and in the region where the distance d exceeds a predetermined value, the shape of the microlenses ML changes according to the distance d. The specific inclination angle β can be measured using an Olympus OLS4500 industrial microscope (objective lens: magnification 100x) equipped with the function of a scanning laser microscope.

[0042] The shape of each microlens ML is, for example, an axially symmetric aspherical shape represented by [Equation 1] below.

[0043]

number

[0044] Here, z is the sag, r is the distance from the axis of symmetry, K is the aspherical coefficient, R is the radius (paraxial radius) when the surface near the axis of symmetry is approximated as a sphere, α2, α4, and α6 are higher-order coefficients, and k is a coefficient for adjusting the specific tilt angle β of the microlens ML (specific tilt angle adjustment coefficient).

[0045] For each microlens ML, the shape of the microlens ML can be adjusted by adjusting the coefficient k, which is included in common in the terms of each order. Even if the coefficient k changes to a different value, the lens shape will remain similar as long as it follows [Equation 1]. Creating similar microlenses ML with different values ​​for coefficient k is cost-effective even when manufacturing the microlens array 10M using a transfer mold. By making the shape of the axially symmetric microlens ML conform to [Equation 1], it is possible to represent a microlens ML with a desired specific inclination angle β simply by changing the value of the specific inclination angle adjustment coefficient k, which is rational when manufacturing transfer molds, etc. An example of the relationship between the specific inclination angle adjustment coefficient k and the specific inclination angle β can be represented, for example, as shown in the graph in Figure 7, using a predetermined coefficient.

[0046] Figure 8 shows an example of the relationship between the distance d of the microlens ML in Figures 4 and 6 and the specific tilt angle adjustment coefficient k. The specific tilt angle adjustment coefficient k of the microlens ML is given by d = 0 to d1 (d1 <R H It is constant within the range of ) and d=d1~R H It increases monotonically within the range d1 = 0.6 × R. H Preferably, d1 = 0.5 × R H And more preferably, d1 = 0.45 × R H That is the case.

[0047] The specific tilt angle adjustment coefficient k of the microlens ML is d = 0 to R H Maximum value k within the range max When the specific tilt angle adjustment coefficient k is set to 1 within the above range where the specific tilt angle adjustment coefficient k is constant, the value is 1.2 to 2.7, preferably 1.5 to 2.5, and particularly preferably 1.7 to 2.2.

[0048] Furthermore, the specific tilt angle β of the microlens ML may have a distribution as shown in Figures 9(a) to (c) with respect to the distance d from the center C.

[0049] Specific configuration examples of the first optical element 10 will be explained with reference to Figures 10A to 10G. In the configuration example in Figure 10A, a concave microlens ML is formed only on one side of the resin material forming the microlens ML, and the substrate is omitted. Figure 10B shows a configuration example in which the resin material forming the concave microlens ML is formed only on the first surface S1 side of the substrate SB. Figure 10C shows an example in which concave microlenses ML1 and ML2 are formed on both sides of the first surface S1 and the second surface S2 of the substrate SB.

[0050] In the configuration example shown in Figure 10D, the convex microlens ML is formed only on one side of the resin material forming the microlens ML, and the substrate is omitted. Figure 10E shows a configuration example where the resin material forming the convex microlens ML is formed only on the first surface S1 side of the substrate SB. Figure 10F shows an example where convex microlenses ML1 and ML2 are formed on both sides of the first surface S1 and the second surface S2 of the substrate SB. Furthermore, Figure 10G shows an example where a concave microlens ML1 is formed on one side of the resin material and a convex microlens ML2 is formed on the opposite side (the substrate is omitted).

[0051] As mentioned above, the specific tilt angle β of the microlens ML corresponds to the divergence angle θd when light is incident on and exits the microlens ML. The divergence angle θd is defined as the exit angle corresponding to the half value of the largest light intensity when the light intensity per unit solid angle is measured or calculated in relation to the exit angle for light that is incident on and exits the microlens ML (see Figure 11A).

[0052] The divergence angle θd is measured with respect to the axis of symmetry of the microlens ML. The specific inclination angle β of the microlens ML is measured with respect to a plane perpendicular to the axis of symmetry of the microlens ML. When the microlens ML is formed on one of the main planes of a flat substrate having two parallel main planes, the angle between the main plane and the tangent plane may be used as the specific inclination angle.

[0053] Furthermore, as the first optical element 10, a microlens array 10M with a hexagonal dense arrangement as described above, and a microlens array with an arrangement based on that arrangement, in which the center positions of individual microlenses ML are shifted in the X, Y, or Z directions, can be used. The X and Y directions are orthogonal directions in the plane of a substantially flat microlens, and the Z direction is perpendicular to the plane of the microlens array. Alternatively, the Z direction is the axis of symmetry of the microlens ML, and the X and Y directions are perpendicular to the axis of symmetry and orthogonal to each other. Figure 11B shows a top view of an example of such a microlens array. In the example of Figure 11B, as schematically shown in Figure 11C, the arrangement of individual microlenses ML is randomly varied within a range of ±4 μm in the X and Y directions and ±1 μm in the Z direction (the lenses are moved in the direction of the arrows). In other words, the microlens array according to Figure 11B can be said to have a moderate fluctuation in the arrangement of hexagonally densely arranged microlenses. Figure 11D schematically shows the case where the microlens ML has a rectangular shape and similar fluctuations are applied.

[0054] Next, the distance L between the light source 1 and the first optical element 10 will be explained with reference to Figure 12. Increasing the distance L between the light source 1 and the first optical element 10 increases the cross-sectional area of ​​the light beam that should be incident on the first surface S1 of the first optical element 10, which tends to increase the overall dimensions of the lighting device. Conversely, if the distance L is made excessively small, the number of individual structures such as microlenses and microprisms through which light passes decreases, making it easier for unevenness to occur in the light emitted from the first optical element 10.

[0055] It is preferable that at least 10 microlenses ML are included within the cross-sectional area of ​​the light beam received by the first optical element 10 from the light source 1. Let L be the distance from the light source 1 to the first optical element 10, let θo be the divergence angle of the light emitted from the light source 1 (where θo = FWHM / 2), and let D be the average value of the radii of the microlenses. A In this case, it is preferable that the following equation is satisfied. 10 < π × (L × tanθ 0) 2 / πDA 2 √10 <L×tanθo / D A Furthermore, 10 <L×tanθo / D A It is more preferable to satisfy these conditions.

[0056] If the second optical element 20 is a lens, it is preferable to use a fisheye lens as the second optical element in order to provide the function of emitting light at a wider angle and illuminating a wider area. A fisheye lens is a type of equidistant projection lens. In a typical fisheye lens, the angle of incidence of light θ and the image height h at the image formation position are proportional, but in this embodiment, it is preferable to emit light to the second optical element 20 which is made of such a fisheye lens to expand the illumination angle of the emitted light.

[0057] The fisheye lens used as the second optical element 20 has a field of view W (total angle) of 150° or more, preferably 160° or more, more preferably 180° or more, and particularly preferably 200° or more.

[0058] The lens constituting the second optical element 20 may be adjusted in relation to the light source 1 so that its optical axis is approximately parallel to or overlaps with the optical axis of the light source 1. When the optical axis of the second optical element 20 and the optical axis of the light source 1 are adjusted to approximately coincide, it is expected that highly symmetrical and uniform illumination light can be obtained.

[0059] Fisheye lenses that may be used in this embodiment include fisheye lenses used in interchangeable lens cameras and fisheye lenses used in camera modules built into smartphones and mobile devices (including lenses that are attached to the front of an existing camera using a conversion method).

[0060] Light from light source 1 is converted by the first optical element 10 into light with a predetermined irradiation angle and uniform irradiation intensity within the plane. By refracting this light with a lens (e.g., a fisheye lens) constituting the second optical element, an illumination device with a wide irradiation angle and uniform irradiation intensity in each direction can be provided. The illumination device of this embodiment is useful in 3D sensing technologies such as facial recognition systems, in-vehicle cameras, and LiDAR applications, which have been under development in recent years. A representative method of 3D sensing technology is the Time of Flight (TOF) method, which is a technique that obtains three-dimensional information by measuring the time it takes for illumination light to hit an object and return. In this case, more information can be obtained if the illumination light is irradiated at a wider angle, so it is important for the illumination device to radiate light from the light source at a wide angle. According to the illumination device of this embodiment, the light intensity can be kept constant regardless of the illumination angle (divergence angle), making TOF analysis easier. [Examples]

[0061] Next, embodiments of the present invention will be described below.

[0062] [Example 1] The lighting device according to Example 1 was fabricated based on the following components. A Vixar NIR-VCSEL (Part Number: V0081) was used as light source 1. This light source emits near-infrared light with a dominant wavelength of 940 nm. It is a hexagonal, densely packed, multimode array consisting of a total of 281 VCSEL light-emitting units. The FWHM is typically 18°, and the size of the light-emitting unit is 0.9 mm × 1 mm.

[0063] Figure 13A shows the light intensity distribution of the light emitted from the NIR-VCSEL used as light source 1. The light intensity distribution of the light emitted from this light source has a low light intensity in the center, exhibiting a roughly donut-shaped distribution.

[0064] Furthermore, as the first optical element 10, a microlens array was used, with an external size of 1 mm × 1 mm and a thickness of 0.4 mm, in which microlenses ML were arranged in a hexagonal, dense arrangement with a basic pitch of 24 μm. The external shape of the microlenses ML is hexagonal, its size D is a maximum of φ23 μm, and it has the shape represented by [Equation 1], with the coefficients shown in Figure 13B.

[0065] Furthermore, considering the inscribed circle of the contour of the first optical element 10 as a virtual circle, the center C of the virtual circle is also the geometric center of the microlens array 10M, and simultaneously coincides with the microlens ML which has an axis of symmetry. The radius R of the virtual circle H The value is 500 μm. The relationship between the distance d from the center C of the virtual circle and k related to [Equation 1] is shown in Figure 14. Note that the actual value of d is discrete, corresponding to the arrangement of the symmetry axes of the microlenses formed for each formed pitch.

[0066] In the range of d=0 to 200 μm (d1=200 μm), k=1 and d=R H At 500 μm, k = 1.91, and within the range where k changes in correspondence with d (d = 200 to 500 μm), the average rate of change of k is 3 × 10⁻¹⁰ -3 [ / μm]. The microlens ML was designed to have fluctuations of ±4μm in the XY direction and ±1μm in the Z direction (sag direction) relative to a basic pitch of 24μm.

[0067] Furthermore, the microlens array 10M was manufactured by preparing a mold in advance with the lens shape of the microlens array 10M reversed, and then casting it onto a glass substrate with resin. The glass substrate used was a borosilicate glass substrate (Corning D263 T eco) with a thickness of 0.4 mm. The resin used was a photocurable resin (Daicel Corporation's Celoxide 2021P, with 3',4'-epoxycyclohexylmethyl 3,4-epoxycyclohexanecarboxylate as the main component).

[0068] Figure 15 shows a schematic cross-section of the microlens array fabricated in this manner. Note that Figure 15 is a schematic diagram for the purpose of easily understanding the distribution of sag, and the number and size of microlenses ML, the scale ratio to the outer shape of the microlens array, and the scale ratio of the thickness to the sag of the microlenses ML differ from the actual shape.

[0069] Furthermore, a fisheye lens, as shown in Figure 16, was used as the second optical element 20. This fisheye lens has a field of view of 210°.

[0070] The light intensity distribution of the irradiated light from the illumination device (Example 1) shown in Figure 1, which was fabricated using the light source 1, the first optical element 10, and the second optical element 20 as described above, was determined by simulation. The results are shown in Figure 17. The simulation was performed using Zemax OpticsStudio Ver20.1, and the light intensity distribution of the irradiated light from a light source with an emission surface of 0.9 mm × 1 mm was determined by simulation, specifically 1 × 10⁻¹⁰. 7 The light rays were virtually emitted and tracked, weighted according to the light intensity distribution of the light source 1, to determine the light intensity distribution. In the light intensity distribution characteristics of the illumination device according to Example 1, the light intensity was 0.68 when the emission angle was 90° or -90°, and the emission angle at which the light intensity was 0.9 was ±65~66°. According to Example 1, an illumination device can be provided that emits illumination light with a sufficiently wide irradiation angle and uniform light intensity within a predetermined range, based on laser light from the light source 1.

[0071] (Comparative Example 1) Next, a comparative example of Example 1 will be described. In the comparative example, the first optical element 10 is the same as the first optical element 10 used in Example 1, which is a microlens array, where d1=R H Except for setting the thickness to 500 μm, the conditions are the same. That is, the first optical element 10, the microlens array 10M in Comparative Example 1, is uniform (k=1) throughout the shape of the microlens ML, and the divergence angle θd and specific inclination angle β of the microlens ML are constant throughout.

[0072] In the lighting device according to Comparative Example 1, the light source 1 and the second optical element 20 are the same as those in Example 1, except for the microlens array 10M of the first optical element 10, and the spacing and coaxiality of these constituent elements are also the same as in Example 1.

[0073] The light intensity distribution of the irradiated light from the lighting device according to Comparative Example 1, which was fabricated using the light source 1, first optical element 10, and second optical element 20 as described above, was determined by simulation. The results are shown in Figure 18. In the simulation, as in Example 1, OpticsStudio Ver20.1 from Zemax was used to determine the light intensity distribution of the irradiated light from the light source 1 having an emission surface of 0.9 mm × 1 mm, and a distribution of 1 × 10⁻¹⁰ 7 The light rays were virtually emitted and tracked, weighted according to the light intensity distribution of light source 1, to determine the light intensity distribution. The light intensity was 0.15 when the emission angle was 90° or -90°, and the emission angle at which the light intensity was 0.9 was ±32~33°.

[0074] As can be seen from Figure 18, if the divergence angle of the microlenses ML included in the first optical element 10, the microlens array 10M, is uniform within the range of a virtual circle, a uniform light intensity distribution cannot be obtained. This is because, although a wide angular range can be illuminated by using a fisheye lens as the second optical element 20, reflection at the interface increases as the angle of incidence of light to the lens or element increases, so the transmittance decreases as the light irradiated by the fisheye lens at a wide angle increases.

[0075] On the other hand, in an illumination device that does not include a first optical element 10, but has a light source 1 using a VCSEL and a fisheye lens as the second optical element 20, the intensity of light irradiated at a predetermined angle is proportional to the light intensity of the light emitted from a predetermined position of the light source 1. That is, while ensuring the coaxiality between the axis of symmetry of the light source 1, such as a VCSEL array that emits light having a constant light emission area and a substantially axially symmetric light intensity distribution, and the optical axis of the fisheye lens, which is the second optical element 20, light near the axis of symmetry of the light source 1 (the optical axis of the device) is emitted from the illumination device at a small emission angle, and light relatively far from the axis of symmetry of the light source 1 is emitted from the illumination device at a relatively large emission angle. Therefore, in order to make the light intensity distribution of the emitted light (illumination intensity distribution) uniform in the illumination device (to obtain illumination light with uniform brightness), it is necessary to suppress the light intensity originating from the light emitted from the part of the light source 1 near the axis of symmetry, and to increase, maintain, or suppress the decrease of the light intensity originating from the light emitted from the part far from the axis of symmetry.

[0076] The first optical element 10 used in the lighting device according to the present invention has a diffusion function, and by making the divergence angle θd by the structure near the center (center) of the first optical element 10 large and the divergence angle θd by the structure in the part away from the center (periphery) small, the lighting device can provide uniform brightness illumination. Furthermore, since the lighting device according to this embodiment can use a light source such as a laser that emits light with high light intensity, the problem of the entire illumination becoming darker due to the large illumination range can be eliminated.

[0077] [others] The present invention is not limited to the embodiments described above, and includes various modifications. For example, the embodiments described above are described in detail to make the present invention easier to understand, and are not necessarily limited to those having all the configurations described. Furthermore, it is possible to replace parts of the configuration of one embodiment with the configuration of another embodiment, and it is also possible to add configurations from other embodiments to the configuration of one embodiment. In addition, it is possible to add, delete, or replace parts of the configuration of each embodiment with other configurations. [Explanation of symbols]

[0078] 1...light source, 10...first optical element, 20...second optical element.

Claims

1. A light source having at least one light-emitting part, A first optical element that receives light emitted from the aforementioned light source, amplifies its emission angle, and emits it; A second optical element receives light emitted from the first optical element and further expands the irradiation angle before emitting it, A lighting device including, The first optical element comprises a microlens array in which a plurality of microlenses are arranged, The microlens array is such that the specific tilt angle β of a microlens included in a first region where the distance from a predetermined position is within a first value is constant, and the specific tilt angle β of a microlens included in a second region where the distance from the predetermined position exceeds the first value decreases monotonically. The aforementioned specific inclination angle β represents the inclination angle of the tangent plane at the lens surface located at a distance of 0.6 × D (where D is the diameter of the microlens in a plan view) from the center of the microlens. A lighting device characterized by the following features.

2. When the two orthogonal directions within the plane on which the microlens array is provided are defined as the X and Y directions, and the direction perpendicular to the X and Y directions is defined as the Z direction, On the surface on which the microlens array is provided, the microlenses are arranged at positions where their arrangement is randomly varied, based on the regular arrangement of hexagonal dense or rectangular grid points, within a range of ±4 μm in the x and y directions and ±1 μm in the z direction from the grid point positions. The lighting device according to feature 1.

3. The lighting device according to claim 1 or 2, wherein, in the light intensity distribution of the light emitted from the lighting device, the light intensity when the emission angle is ±90° is 0.5 times or more the maximum light intensity in the light intensity distribution.

4. The illumination device according to any one of claims 1 to 3, wherein the second optical element is a fisheye lens.

5. Let L be the distance from the light source to the first optical element, and let θ be the angle of spread of the light emitted from the light source. 0 (However, θ 0 = FWHM / 2), and the average value of the radius of the microlens is D Ａ In that case, 10<π×(L×tanθ) 0 ) ２ / πD Ａ ２ The lighting device according to any one of claims 1 to 4.

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