Optical element

Abstract

To enable appropriate distribution of light intensity on a projection surface.SOLUTION: An optical element 10 provided herein is a transparent optical element having multiple aspherical concave lens units 20 formed on a surface thereof to be arranged in matrix. Each lens unit 20 has a stepped portion 24 on an aspherical lens surface 22 to cause a profile extending radially outward from the center O of the lens surface 22 to be discontinuous, where a region of the lens surface 22 radially inside of the stepped portion 24 and a region of the lens surface radially outside of the stepped portion 24 have different conic constants.SELECTED DRAWING: Figure 5

Description

[Technical Field]

[0001] The present invention relates to an optical element. [Background technology]

[0002] Optical elements that diffuse light from a light source are known. For example, Patent Document 1 describes an optical element (lens array) in which a plurality of concave lens portions are arranged in an array and the light incident on each lens portion is diffused. By using such a lens array, the light diffused by each lens portion can be superimposed, making the intensity of the light on the projection surface uniform. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Patent No. 6424418 Summary of the Invention [Problem to be solved by the invention]

[0004] In such optical elements that diffuse light, it is required to appropriately distribute the light intensity on the projection surface.

[0005] The present invention has been made in view of the above-mentioned problems, and has an object to provide an optical element that can appropriately distribute the intensity of light on the projection surface. [Means for solving the problem]

[0006] In order to solve the above-mentioned problems and achieve the objectives, the optical element of the present disclosure is a transparent optical element having a plurality of aspherically recessed lens portions formed in a matrix on one surface, wherein the lens portions include a step portion on the aspherical lens surface where the profile extending radially outward from the center of the lens surface is discontinuous, and the conic constants of a region on the lens surface radially inward from the step portion and a region on the lens surface radially outward from the step portion are different. [Effects of the Invention]

[0007] According to the present invention, the light intensity can be appropriately distributed on the projection surface. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a schematic diagram of an illumination system according to this embodiment. [Figure 2] FIG. 2 is a schematic top view of the optical element according to this embodiment. [Figure 3] FIG. 3 is a cross-sectional view taken along line AA in FIG. [Figure 4] FIG. 4 is a schematic top view of the lens portion according to this embodiment. [Figure 5] FIG. 5 is a cross-sectional view taken along line BB in FIG. [Figure 6] FIG. 6 is a graph illustrating an example of a step portion. [Figure 7] FIG. 7 is a graph showing an example of the light intensity distribution on the projection surface. [Figure 8] FIG. 8 is a schematic diagram showing another example of the step portion. [Figure 9] FIG. 9 is a schematic diagram illustrating a method for manufacturing an optical element according to this embodiment. [Figure 10] FIG. 10 is a schematic diagram for explaining the shape of the lens portion of the optical element in the example. [Figure 11] FIG. 11 is a graph showing the simulation results in Example 1. [Figure 12]FIG. 12 is a graph showing the simulation results in Example 2. [Figure 13] FIG. 13 is a graph showing the simulation results in Example 3. [Figure 14] FIG. 14 is a graph showing the simulation results in Example 4. DETAILED DESCRIPTION OF THE INVENTION

[0009] Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Note that the present invention is not limited to these embodiments, and when there are multiple embodiments, the present invention also includes configurations that are made by combining the respective embodiments. Furthermore, numerical values ​​include the range of rounding.

[0010] (Irradiation system) FIG. 1 is a schematic diagram of an illumination system according to this embodiment. The illumination system 1 according to this embodiment is a device that illuminates light. The illumination system 1 is used for distance measurement using a time-of-flight (TOF) method, but its application is not limited thereto and is arbitrary. As shown in FIG. 1, the illumination system 1 includes an optical element 10 and a light source 100. The light source 100 is a light source that illuminates light L. The light source 100 illuminates laser light, more specifically, vertical cavity surface-emitting laser light, as the light L. That is, the light source 100 is a VCSEL (Vertical Cavity Emitting Laser) light source. The optical element 10 is an optical component provided on the light source 100 in the traveling direction of the light L. The optical element 10 is disposed such that one surface 10A faces the light source 100. The optical element 10 diffuses the light L incident from the surface 10A while transmitting it toward the other surface 10B, and emits the diffused light L from the surface 10B. It should be noted that light source 100 is not limited to a VCSEL light source and may be one that emits any light. Hereinafter, the thickness direction of optical element 10, i.e., the direction from surface 10A to surface 10B, will be referred to as direction Z. Direction Z can also be said to be the optical axis direction of lens portion 20, which will be described later. Furthermore, a direction perpendicular to direction Z will be referred to as direction X, and a direction perpendicular to direction X and direction Z will be referred to as direction Y.

[0011] (Optical elements) FIG. 2 is a schematic top view of the optical element according to this embodiment, and FIG. 3 is a cross-sectional view taken along line AA in FIG. 2. The optical element 10 is a transparent (visible light transmissive) plate-like member. In this embodiment, the optical element 10 is made of glass, but may be made of any material, for example, a transparent resin. As shown in FIG. 2, in this embodiment, the optical element 10 is rectangular when viewed from direction Z, with two opposing sides extending along direction X and two other opposing sides extending along direction Y. In this embodiment, the optical element 10 is a horizontally elongated rectangle with the sides extending along direction X longer than the sides extending along direction Y. However, the shape (shape of the periphery) of the optical element 10 when viewed from the Z direction is not limited to this and may be any shape.

[0012] Optical element 10 is a so-called lens array in which a plurality of lens portions 20 are formed in a matrix (array) on surface 10A. Lens portion 20 is an aspherical recessed portion on surface 10A of optical element 10, and can be said to be a portion that constitutes a concave lens. The aspherical concave surface of lens portion 20 on the surface 10A side will hereinafter be referred to as lens surface 22 where appropriate.

[0013] The lens portions 20 are arranged on the surface 10A along the X and Y directions, and in this embodiment, are arranged in a rectangular lattice pattern. The rectangular lattice pattern refers to the fact that, when four lens portions 20 are extracted in two rows and two columns arranged in the X and Y directions, the centers of the lens portions 20 are arranged so as to form vertices of a rectangle when viewed from the Z direction. However, the arrangement of the lens portions 20 is not limited to a rectangular lattice pattern and may be arbitrary.

[0014] Furthermore, the lens portions 20 are not arranged independently of each other, but are arranged so as to be in contact with each other. The lens portions 20 being in contact refers to a state in which a portion of the lens surface 22 of one of two adjacent lens portions 20 is in contact with a portion of the lens surface 22 of the other lens portion 20. Furthermore, the lens portions 20 being in contact refers to a state in which no flat portion is formed between the periphery of the lens surface 22 of one lens portion 20 and the periphery of the lens surface 22 of the other lens portion 20 (see FIG. 3). The flat portion here refers to a flat portion orthogonal to direction Z (along direction X and direction Y). The absence of a flat portion allows light L to be appropriately diffused. However, the arrangement of the lens portions 20 is not limited to this, and they may be arranged so as not to be in contact with each other, i.e., so as to form a flat portion. In this case, it is preferable that the area of ​​the flat portion when viewed from the Z direction (the area of ​​the flat portion in the XY plane on the projection surface) is 5% or less of the total area of ​​the lens portion 20 when viewed from the Z direction (the total area of ​​the lens portion 20 in the XY plane on the projection surface).

[0015] The pitch between adjacent lens portions 20 is preferably 10 times or more the wavelength of light L, preferably 4 μm or more, more preferably 10 μm or more and 500 μm or less, and even more preferably 40 μm or more and 200 μm or less. By setting the pitch within this range, the intensity of light L can be appropriately distributed on the projection surface. The pitch between lens portions 20 refers to the distance between the center O of one lens portion 20 and the center O of the lens portion 20 adjacent to that lens portion 20. The center O of the lens portion 20 refers to the center of the lens portion 20 when viewed from the Z direction. In the example of this embodiment, the pitch between lens portions 20 in the direction X is longer than the pitch between lens portions 20 in the direction Y, but this is not limited thereto, and the larger or smaller relationship may be arbitrary.

[0016] As shown in FIG. 2, the lens portion 20 has a rectangular outer periphery on the surface 10A when viewed from the Z direction. That is, the lens portion 20 is formed so that the boundary between adjacent lens portions 20 is rectangular. In the example of FIG. 2, the length LX of the lens portion 20 in the X direction is longer than the length LY of the lens portion 20 in the Y direction, but the relationship between the lengths LX and LY may be arbitrary. The length LX may be the same as the pitch between the lens portions 20 in the X direction, and the length LY may be the same as the pitch between the lens portions 20 in the Y direction. The length LX refers to the length along the X direction from the boundary between the lens portion 20 and another adjacent lens portion 20 on the opposite side of the X direction. The length LY refers to the length along the Y direction from the boundary between the lens portion 20 and another adjacent lens portion 20 on the opposite side of the Y direction. The outer peripheral shape of the lens portion 20 as viewed in the Z direction is not limited to a rectangle and may be any shape, for example, a polygon other than a rectangle.

[0017] As shown in Fig. 3, if the depth of the lens portion 20 is defined as depth LZ, in order to suppress interference patterns caused by the periodic structure of the lenses on the projection surface of the diffused light, the variation in depth LZ for each lens portion 20 in the lens array is preferably 0.5 to 20 times the wavelength of the light L, and more preferably 1 to 10 times the wavelength. Note that depth LZ refers to the distance along the Z direction from the most recessed point of the lens portion 20 in the Z direction to the boundary with other lens portions 20 on the surface 10A of the lens portion 20. In this embodiment, the center O of the lens portion 20 when viewed from the Z direction is the most recessed point in the Z direction.

[0018] The optical element 10 may have an anti-reflection film laminated on the surface 10A, that is, on the lens surface 22 of each lens portion 20, for suppressing reflection of the light L.

[0019] The optical element 10 has a flat surface 10B, which is formed so as to be perpendicular to the direction Z (along the direction X and the direction Y). However, the shape of the surface 10B is not limited to being flat and may be any shape; for example, in order to homogenize the light L, the surface 10B may be a scattering surface with high surface roughness, or multiple lens portions may be formed on the surface 10B side.

[0020] (Lens surface shape) The following provides a more detailed description of the shape of the lens surface 22 of the lens portion 20. Fig. 4 is a schematic top view of the lens portion according to this embodiment, and Fig. 5 is a cross-sectional view taken along line BB of Fig. 4.

[0021] Lens surface 22 has an aspheric shape. That is, when the central axis AX of lens surface 22 (an axis passing through the center O of lens surface 22 and extending in the Z direction) is taken as the axial direction, and the profile (position in the Z direction) of each position in the radial direction of lens surface 22 is taken as z, z is expressed by the following equation (1). z can also be considered as the amount of sag.

[0022] z=cr 2 / [1+{1-(1+k)c 2 r 2} 0.5 ] ···(1)

[0023] where c is the curvature of the lens surface 22, r is the distance along the radial direction from the center O (i.e., the position in the radial direction), and k is the conic constant.

[0024] The profile at each position in the radial direction of lens surface 22 does not need to strictly satisfy formula (1), as long as the fitting curve of lens surface 22 satisfies formula (1). In other words, lens surface 22 whose fitting curve satisfies formula (1) can be said to have an aspherical shape. In this case, it is preferable that the deviation in the Z direction of the profile at each position in the radial direction of lens surface 22 from the fitting curve of lens surface 22 is 10 μm or less. The fitting curve of lens surface 22 is a quadratic curve obtained by approximating a line connecting the profiles at each position in the radial direction of lens surface 22 with a quadratic formula. That is, the profile (position in the Z direction) of each position on lens surface 22 along the radial direction from one end of lens surface 22 in the radial direction (the boundary position with the adjacent lens portion 20 on one side along the radial direction) to the other end of lens surface 22 in the radial direction (the boundary position with the adjacent lens portion 20 on the other side along the radial direction) is measured, and the line connecting these profiles is approximated by a quadratic curve, which can be said to be the fitting curve of lens surface 22. The profile of each position on lens surface 22 in the radial direction can be measured using a white light interference microscope, a laser confocal microscope, or the like.

[0025] (Stepped part) A step portion 24 is formed on the lens surface 22. As shown in Fig. 5, the step portion 24 is a portion where the profile of the lens surface 22 is discontinuous. That is, a line drawn along the lens surface 22 in the radial direction from one end of the lens surface 22 in the radial direction to the other end of the lens surface 22 in the radial direction is discontinuous at the position of the step portion 24. In this embodiment, the step portion 24 can also be said to be a corner portion of the lens surface 22 that protrudes toward the opposite side of the direction Z.

[0026] FIG. 6 is a graph illustrating an example of a step portion. The horizontal axis of FIG. 6 indicates the distance from the center O of lens surface 22, and the vertical axis indicates the deviation (difference) between the profile of lens surface 22 (position in the Z direction) and the fitting curve of lens surface 22. That is, FIG. 6 shows an example of the deviation between the profile of lens surface 22 and the fitting curve for each position along the radial direction. Hereinafter, the deviation between the profile of lens surface 22 and the fitting curve will be referred to as the profile deviation. In this case, a broken line connecting the profile deviations for each position along the radial direction may be approximated by a curve, and the section in the radial direction of lens surface 22 where the profile deviation is higher by 0.1 μm or more on the side opposite to the Z direction than the approximate curve may be defined as step portion 24. Note that the approximate curve here may be a least-squares curve of the profile deviation for each position along the radial direction.

[0027] As shown in FIG. 4 , the step portion 24 is formed to surround the center O of the lens surface 22 when viewed from the Z direction. The step portion 24 can be said to form a ridge line on the lens surface 22. The step portion 24 is preferably circular with the center O as the center when viewed from the Z direction. However, the step portion 24 is not limited to being circular and may be any shape surrounding the center O, such as an ellipse or a polygon. The step portion 24 is not limited to being formed around the entire circumference around the center O of the lens surface 22, but may be formed in at least a portion of the entire circumference around the center O of the lens surface 22. For example, the step portion 24 may have a shape in which a portion of the ring around the entire circumference around the center O is missing due to the boundary with the adjacent lens portion 20 (see step portion 24C in FIG. 8 described later). That is, the step portion 24 forms a closed region surrounding the center O. One step portion 24 may form a closed region surrounding the center O, or a closed region may be formed together with the boundary with the adjacent lens portion 20. Furthermore, the step portion 24 is not limited to being formed so as to surround the center O, and may have any shape when viewed from the Z direction.

[0028] The shape of the step portion 24 as viewed from the Z direction can be confirmed as follows: That is, the direction in which the profile of the lens surface 22 is measured (a line along the radial direction tracing the lens surface 22 to measure the profile) is shifted by a predetermined angle at a time to measure the profile over the entire area of ​​the lens surface 22, and of the step portions 24 extracted from each profile, those step portions 24 that are within the same range of distance from the center O are determined to be one step portion 24. For example, if the shape obtained by connecting the step portions 24 determined to be one step portion 24 is annular, then the step portion 24 can be confirmed to be annular.

[0029] In the example of FIG. 4, two step portions 24 are provided: step portion 24A and step portion 24B formed radially outward of step portion 24A. That is, when a plurality of step portions 24 are provided, the step portions 24 are aligned radially. Note that the number of step portions 24 is preferably a plurality, but may be any number, such as one, three, or more. For example, the number of step portions 24 is preferably set so that the value obtained by dividing the pitch between adjacent lens portions 20 by the number of step portions 24 is 10 μm or more.

[0030] As shown in FIG. 5, the width D of the step portion 24 is preferably 5 μm or less, more preferably 2 μm or less, and even more preferably 1 μm or less. Furthermore, the width D is preferably equal to or less than twice the wavelength of the light L, and more preferably equal to or less than the wavelength of the light L. Having the width D within this range suppresses scattering of the light L due to the discontinuous step portion 24, thereby enabling an appropriate distribution of the intensity of the light L on the projection surface. The width D is the radial length of the step portion 24. For example, the width D may be determined as the radial section of the lens surface 22 where the profile deviation is 0.1 μm or more higher on the side opposite to the direction Z, relative to a broken-line approximation curve connecting the profile deviations at each position along the radial direction.

[0031] (Conic constant for each region) Lens surface 22 has a conic constant that is different in a region radially inside step portion 24 and a conic constant that is different in a region radially outside step portion 24. By making the conic constants different between the radially inside and the radially outside step portion 24, the intensity of light L can be appropriately distributed on the projection surface. The conic constant of the radially inner region of the stepped portion 24 may refer to the conic constant of the fitting curve of the radially inner region of the stepped portion 24 of the lens surface 22, and the conic constant of the radially outer region of the stepped portion 24 may refer to the conic constant of the fitting curve of the radially outer region of the stepped portion 24 of the lens surface 22. Also, in the following, the conic constant of a portion of the region included in the lens surface 22 is described, and in this case, the conic constant of the fitting curve of that region of the lens surface 22 may be used as the conic constant of that region. The fitting curve of a region included in the lens surface 22 may be calculated as follows. That is, profiles (positions in the Z direction) are measured at each position along the radial direction from one end to the other end of the region in the radial direction, and the fitting curve of that region is determined by approximating the line connecting these profiles with a quadratic curve.

[0032] It is preferable that the conic constant of lens surface 22 in a region radially inside step portion 24 is larger than the conic constant of a region radially outside step portion 24. In other words, when lens surface 22 is divided into a plurality of regions by step portion 24, it is preferable that the conic constant be larger in a region radially inside (closer to center O) in the lens surface 22. Therefore, in the example of this embodiment, the conic constant increases in the order of the region radially outside step portion 24B, the region radially inside step portion 24B and radially outside step portion 24A (the region between step portion 24B and step portion 24A), and the region radially inside step portion 24A.

[0033] FIG. 7 is a graph showing an example of the light intensity distribution on the projection surface. FIG. 7 shows an example of the intensity of light emitted from the optical element 10 at each distance from the optical axis center when uniform-intensity light is incident on the optical element 10 with a large conic constant radially inside the stepped portion 24. The horizontal axis of FIG. 7 represents the distance from the optical axis center, and the vertical axis represents the light intensity. Furthermore, Y=0 represents the light intensity at each position along the X direction from the optical axis center, and X=0 represents the light intensity at each position along the Y direction from the optical axis center. As shown in FIG. 7, by increasing the conic constant radially inside, it is possible to increase the light intensity at positions farther from the optical axis center, thereby appropriately distributing the intensity of the light L on the projection surface. For example, in a VCSEL, the light intensity significantly decreases with increasing distance from the optical axis center. Therefore, by diffusing the light by the optical element 10 so as to increase the light intensity at positions farther from the optical axis center, the light intensity distribution on the projection surface can be made uniform, which is preferable. However, the lens surface 22 is not limited to having a large conic constant on the radially inner side of the step portion 24, and for example, the conic constant on the radially inner side of the step portion 24 may be smaller than the conic constant on the radially outer side of the step portion 24. In this case, the light intensity at a position close to the center of the optical axis can be increased, and therefore, this can be suitably used when it is required to increase the light intensity at a position close to the center of the optical axis.

[0034] When lens surface 22 is divided into a plurality of regions by step portions 24, each region is defined as a unit region. In this case, the difference in conic constant between adjacent unit regions separated by the same step portion 24, i.e., the difference in conic constant between a region radially outside step portion 24 and a region radially inside step portion 24, is preferably greater than 0 and not greater than 0.2. That is, in the example of this embodiment, the difference in conic constant between a region radially outside step portion 24B and a region radially inside step portion 24B but radially outside step portion 24A is preferably greater than 0 and not greater than 0.2, and the difference in conic constant between a region radially inside step portion 24B but radially outside step portion 24A and a region radially inside step portion 24A is also preferably greater than 0 and not greater than 0.2. Furthermore, the difference in conic constant between adjacent unit areas across the same step portion 24 is more preferably 0 or more and 0.1 or less, and even more preferably 0 or more and 0.05 or less. When the difference in conic constant falls within this range, the light intensity on the projection surface can be appropriately adjusted between the radially inner and outer sides of step portion 24A, while preventing excessive changes in the light intensity on the projection surface.

[0035] Furthermore, the difference in conic constant between the radially innermost unit area and the radially outermost unit area is preferably 0.3 or less, more preferably 0.1 to 0.2 or less, and even more preferably 0.1 to 0.15 or less. By making the difference in conic constant between the innermost and outermost unit areas equal to this value, it is possible to appropriately adjust the light intensity on the projection surface while suppressing excessive changes in the light intensity on the projection surface. In this embodiment, the radially inner area of ​​the stepped portion 24A corresponds to the radially innermost unit area, and the radially outer area of ​​the stepped portion 24B corresponds to the radially outermost unit area.

[0036] The conic constant of the region (innermost unit region) that is radially inward of step portion 24 and includes center O of lens surface 22 is preferably −1.2 or more and −0.8 or less, and more preferably −1.05 or more and −0.95 or less. Setting the conic constant of the innermost unit region within this range is preferable because it makes it possible to make the light intensity on the projection surface, for example, in a region close to the center of the optical axis, more uniform.

[0037] Furthermore, when the pitch between the lens portions 20 in the direction X is longer than the pitch between the lens portions 20 in the direction Y, it is preferable that the conic constant of a unit area overlapping the range from the center O to a position radially outwardly away from the center O by half the value of the pitch between the lens portions 20 in the direction X (i.e., the range of a circle centered on the center O and having a diameter half the pitch in the direction X) is -1.1 or more and -0.9 or less.

[0038] (Another example of a stepped section) Fig. 8 is a schematic diagram showing another example of the step portion. In the above description, two step portions 24 are provided, but as mentioned above, the number of step portions 24 is not limited to two. For example, as shown in Fig. 8, three step portions, 24A, 24B, and 24C, may be provided.

[0039] (Method of manufacturing optical elements) A manufacturing method for the optical element 10 will be described below, but the manufacturing method is not limited to the following description and may be any method. FIG. 9 is a schematic diagram illustrating a manufacturing method for an optical element according to this embodiment. In this manufacturing method, the optical element 10 is manufactured by forming the lens portions 20 in a matrix on the surface 10A of the optical element 10a, which is the optical element 10 before the lens portions 20 are formed. Specifically, an optical element 10a having a flat surface 10A is prepared. Then, as shown in FIG. 9 , laser light La from an irradiation device D is irradiated onto the optical element 10a from the surface 10B side of the optical element 10a so that the optical axis travels in the direction opposite to the Z direction (step S10). The laser light La enters the optical element 10a from the surface 10B side and is emitted to the outside of the optical element 10a through the surface 10A. The optical element 10a is modified at the locations irradiated with the laser light La, and modified regions M are generated at the locations irradiated with the laser light La. The modified regions M refer to locations whose chemical composition has been modified by irradiation with the laser light La.

[0040] In the step of irradiating the laser light La, the laser light La is irradiated in a conical shape that is focused at the center of the optical axis, and the laser light La is irradiated so that the focal point of the laser light La is located at a position that overlaps with the surface 10A or on the opposite side of the Z direction from the surface 10A. As a result, the intensity of the laser light La increases toward the opposite side of the Z direction (toward the surface 10A) within the optical element 10a, and the degree of modification of the modified portion M increases toward the surface 10A.

[0041] In the step of irradiating the laser beam La, the laser beam La is irradiated while the irradiation position is moved in the X direction and the Y direction, thereby forming modified regions M in a matrix.

[0042] In the step of irradiating the laser light La, one pulse of the laser light La is irradiated to one position (one modified portion). The pulse width of the laser light La is preferably 25 ps or less. This allows for a quasi-non-heating process in which the degree of heating of the optical element 10a is small. The laser light La may be an oscillating light from a solid crystal laser such as Nd:YAG, Nd:YLF, or Nd:YVO4, or a second harmonic light or third harmonic light obtained by wavelength conversion of the oscillating light.

[0043] By forming the modified region M by irradiating the laser light La in this manner, a plurality of modified lines M1 extending in the Z direction are formed in the modified region M. The modified lines M1 are portions that are more highly modified than other regions of the modified region M, and have a shape that extends axially in the Z direction. The length of the modified lines M1 in the Z direction is 100 μm or more, and the lengths (widths) in the X and Y directions are 10 μm or less. The modified lines M1 can be confirmed as lines extending in the Z direction in a photograph of a cross section of the modified region M.

[0044] After the modified portions M are formed, the optical element 10a is etched to form openings OP (step S12). In this step, wet etching is performed by applying an etching liquid to the optical element 10a. The etching liquid used is one that removes the modified portions M but does not easily remove the portions of the optical element 10a other than the modified portions M (unmodified portions). For example, a mixed aqueous solution of hydrofluoric acid, hydrochloric acid, and nitric acid is used as the etching liquid. The etching time, which is the time from when the etching liquid is applied to when the etching liquid is removed, may be set arbitrarily, but may be, for example, two hours or less.

[0045] Once the etching liquid has been applied, the modified portion M of the optical element 10a is removed, and an opening OP is formed in the portion where the modified portion M has been removed. Here, the degree of modification of the modified portion M increases toward the front surface 10A, and therefore the area from which the modified portion M is removed increases toward the front surface 10A, forming a conical opening OP with a larger diameter toward the front surface 10A. Furthermore, because etching progresses at the location of the modified line M1, a step is formed in the opening OP at the location of the modified line M1.

[0046] In step S12, anisotropic etching is performed on the modified region M to form an opening OP. In this manufacturing method, an etching process is then performed on the opening OP to form a lens portion 20 (lens surface 22) (step S16). That is, after anisotropic etching is performed on the modified region M to form the opening OP, isotropic etching is performed on the area around the opening OP that is not the modified region to form the lens portion 20. This results in the manufacture of an optical element 10 with the lens portion 20 formed thereon. In this step, an etching liquid is applied to the opening OP to remove the portion around the opening OP of the optical element 10a, and material is removed from the opening OP more widely and deeply, thereby forming an aspherical lens surface 22. In this case, material is removed from the conical opening OP by the same depth, resulting in the formation of an aspherical lens surface 22 and a step portion 24 at the location of the step portion that was included in the opening OP. The etching liquid used in this step is one that can remove the optical element 10a, such as a mixed aqueous solution of hydrofluoric acid, hydrochloric acid, and nitric acid. The etching time, which is the time from application of the etching liquid to removal of the etching liquid, may be set arbitrarily, for example, to 2 hours or less. By setting the etching time within this range, the etching time is prevented from becoming too long, and the risk of losing the smoothness of the processed surface can be suppressed.

[0047] (effect) As described above, optical element 10 according to this embodiment is a transparent optical element having a plurality of aspherically recessed lens portions 20 formed in a matrix on one surface 10A. Lens portion 20 includes, on aspherical lens surface 22, step portions 24 whose profile extending radially outward from center O of lens surface 22 is discontinuous, and the region of lens surface 22 radially inward from step portions 24 has a different conic constant from the region of lens surface 22 radially outward from step portions 24.

[0048] The optical element 10 according to this embodiment includes a step portion 24 on the lens surface 22, and the conic constant differs between the radially inner and outer sides of the step portion 24. This makes it possible to appropriately distribute the intensity of the light L emitted from the optical element 10 on the projection surface.

[0049] The step portion 24 is formed to surround the center O of the lens surface 22 when viewed from the optical axis direction (direction Z) of the lens portion 20. By forming the step portion 24 to surround the center O, it is possible to make the distribution of the intensity of the light L emitted from the optical element 10 on the projection surface more appropriate.

[0050] The width D of the step portion 24 is preferably 5 μm or less. By setting the width D in this range, it is possible to suppress scattering of the light L due to the discontinuous step portion 24, while ensuring an appropriate distribution of the intensity of the light L on the projection surface.

[0051] In lens surface 22, the conic constant of the region radially inward from step portion 24 is larger than the conic constant of the region radially outward from step portion 24. By increasing the conic constant on the radially outer side, it is possible to increase the light intensity on the projection surface at a position away from the center of the optical axis, and it is possible to appropriately distribute the intensity of light L on the projection surface.

[0052] It is preferable that the difference between the conic constant of the region radially inside step portion 24 and the conic constant of the region radially outside step portion 24 of lens surface 22 be 0.2 or less. By setting the difference within this range, it is possible to appropriately adjust the light intensity on the projection surface between the radially inside and outside step portion 24A, while also preventing excessive changes in the light intensity on the projection surface.

[0053] It is preferable that the conic constant of lens surface 22 is -1.2 or more and -0.8 or less in a region (innermost unit region) that is radially inward of step portion 24 and includes center O of lens surface 22. By setting the innermost conic constant within this range, it is possible to make the light intensity on the projection surface, for example, in a region close to the center of the optical axis, closer to uniform.

[0054] The optical element 10 is preferably made of glass, which can improve heat resistance and moisture resistance.

[0055] The optical element 10 is preferably used to diffuse laser light emitted from a light source 100 that emits vertical cavity surface emitting laser light, thereby enabling the intensity of VCSEL type laser light to be distributed appropriately.

[0056] The method for manufacturing an optical element 10 according to this embodiment is for manufacturing a transparent optical element 10 having a plurality of aspherically recessed lens portions 20 formed in a matrix on one surface 10A of the optical element 10. This manufacturing method includes the steps of modifying a portion of the optical element 10a on one surface 10A side by irradiating the transparent optical element 10a with laser light La from the other surface 10B side, etching the modified portion (modified portion M) of the optical element 10a so that the etching proceeds anisotropically to form a conical opening OP on one surface 10A of the optical element 10a, and etching a portion that is not the modified portion so that the etching proceeds isotropically to form the aspherically recessed lens portions 20. In this manufacturing method, the lens portions 20 having a desired shape can be formed by appropriately adjusting the etching time, concentration of the etching solution, modification conditions, and the like. In the step of forming lens portion 20, lens portion 20 is formed so that aspheric lens surface 22 of lens portion 20 includes step portion 24 where the profile extending radially outward from center O of lens surface 22 is discontinuous, and the conic constant differs between a region of lens surface 22 radially inward from step portion 24 and a region of lens surface 22 radially outward from step portion 24. This manufacturing method makes it possible to manufacture optical element 10 that can appropriately distribute the intensity of light L on the projection surface.

[0057] (Example) Next, an example will be described.

[0058] (Example 1) Fig. 10 is a schematic diagram illustrating the shape of a lens portion of an optical element in an example. In Example 1, which is an example, a simulation model of optical element 10 was prepared, which had lens portion 20 in which stepped portions 24A, 24B, and 24C were arranged radially outward from center O, as shown in Fig. 10. In Example 1, the length LX of one lens portion 20 in the X direction was 100 μm, the length LY in the Y direction was 80 μm, the radius of curvature R (the reciprocal of curvature c) of lens surface 22 was 45 μm, the diameter of a circle centered at center O and having stepped portion 24A as its periphery as viewed from the Z direction was 50 μm, the diameter of a circle centered at center O and having stepped portion 24B as its periphery as viewed from the Z direction was 60 μm, and the diameter of a circle centered at center O and having stepped portion 24C as its periphery as viewed from the Z direction was 70 μm. In addition, the conic constant of the region radially inward from step portion 24A was set to -1, the conic constant of the region between step portion 24A and step portion 24B was set to -1.05, the conic constant of the region between step portion 24B and step portion 24C was set to -1.1, and the conic constant of the region radially outward from step portion 24C was set to -1.15.

[0059] 11 is a graph showing the simulation results for Example 1. In the simulation, a model of optical element 10 of Example 1 prepared as described above was irradiated with light of uniform intensity, and the intensity distribution on the projection surface of the light emitted from the model of optical element 10 was analyzed. For the simulation, a method was used in which the wavefront phase of incident light, which is a plane wave, after passing through optical element 10 was Fourier transformed, and the simulation conditions were that the wavelength of the incident light was 940 nm and the refractive index of the material of optical element 10 was 1.515. Figure 11 shows the analysis results of the intensity distribution on the projection surface of light, with the horizontal axis representing the distance (angle) from the center of the optical axis and the vertical axis representing the normalized light intensity. Furthermore, Y=0 refers to the light intensity at each position along the X direction from the center of the optical axis, and X=0 refers to the light intensity at each position along the Y direction from the center of the optical axis. As shown in Figure 11, by providing a step and varying the conic constants inside and outside the step, the light intensity distribution becomes uniform within a certain range at a small distance from the center of the projection surface, and only a certain range at a large distance exhibits high intensity.

[0060] (Example 2) In Example 2, which is an embodiment, a model of optical element 10 was prepared having the same shape as Example 1, except that the conic constant of the region radially inward from step portion 24A was set to -1, the conic constant of the region between step portion 24A and step portion 24B was set to -1, the conic constant of the region between step portion 24B and step portion 24C was set to -1.05, and the conic constant of the region radially outward from step portion 24C was set to -1.15.

[0061] Fig. 12 is a graph showing the simulation results for Example 2. In Example 2, a simulation was also performed on the model of Example 2 under the same conditions as in Example 1. As shown in Fig. 12, by providing a step portion and making the conic constant different between the inside and outside of the step portion, it can be seen that the light intensity distribution becomes uniform within a certain range at a small distance from the center of the projection surface, and the light intensity becomes high only within a certain range at a large distance.

[0062] (Example 3) In Example 3, which is an embodiment, a model of optical element 10 was prepared having the same shape as Example 1, except that the diameter of a circle centered at center O and having step portion 24A as its outer periphery when viewed from the Z direction was 60 μm, the diameter of a circle centered at center O and having step portion 24B as its outer periphery when viewed from the Z direction was 70 μm, and the diameter of a circle centered at center O and having step portion 24C as its outer periphery when viewed from the Z direction was 80 μm.

[0063] Fig. 13 is a graph showing the simulation results for Example 3. In Example 2, a simulation was also performed on the model of Example 3 under the same conditions as in Example 1. As shown in Fig. 13, by providing a step portion and making the conic constant different between the inside and outside of the step portion, it can be seen that the light intensity distribution becomes uniform within a certain range at a small distance from the center of the projection surface, and the light intensity becomes high only within a certain range at a large distance.

[0064] (Example 4) In Example 4, which is an embodiment, a model of optical element 10 was prepared having the same shape as Example 2, except that the diameter of a circle centered at center O and having step portion 24A as its outer periphery when viewed from the Z direction was 60 μm, the diameter of a circle centered at center O and having step portion 24B as its outer periphery when viewed from the Z direction was 70 μm, and the diameter of a circle centered at center O and having step portion 24C as its outer periphery when viewed from the Z direction was 80 μm.

[0065] Fig. 14 is a graph showing the simulation results for Example 4. In Example 4, a simulation was also performed on the model of Example 3 under the same conditions as in Example 1. As shown in Fig. 14, by providing a step portion and making the conic constant different between the inside and outside of the step portion, it can be seen that the light intensity distribution becomes uniform within a certain range at a small distance from the center of the projection surface, and the light intensity becomes high only within a certain range at a large distance.

[0066] Although the embodiments of the present invention have been described above, the embodiments are not limited to the contents of these embodiments. Furthermore, the above-described components include those that can be easily imagined by a person skilled in the art, those that are substantially the same, and those that are within the scope of what is called equivalents. Furthermore, the above-described components can be combined as appropriate. Furthermore, various omissions, substitutions, or modifications of the components can be made without departing from the spirit of the above-described embodiments. [Explanation of symbols]

[0067] 10 Optical Elements 10A surface 20 Lens section 22 Lens surface 24 Step O center

Claims

1. An optical element having a plurality of aspherical recessed lens portions formed on one surface, The lens portion has a profile that is discontinuous from the center of the lens surface toward the radially outward side, and the conic constant of a first region on the radially inner side of the lens surface is larger than the conic constant of a second region on the lens surface that is radially outward from the first region. Optical elements.

2. 2. The optical element according to claim 1, wherein a difference between the conic constant of the first region and the conic constant of the second region is 0.2 or less.

3. 3. The optical element according to claim 2, wherein the conic constant of the first region including the center of the lens surface is not less than −1.2 and not more than −0.

8.

4. The optical element according to claim 1 , wherein the lens portion has a step portion.

5. The optical element according to claim 4 , wherein the width of the step portion is 5 μm or less.

6. The optical element according to claim 4 , wherein the step portion is formed so as to surround the center of the lens surface when viewed in the optical axis direction of the lens portion.

7. 7. The optical element according to claim 1, which is made of glass.

8. 10. The optical element according to claim 1, which is used to diffuse laser light emitted from a light source that emits vertical cavity surface emitting laser light.

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