Luminous flux control member and metal mold

Abstract

To provide a luminous flux control member which has a vortex surface comprising a plurality of phase control surfaces, and is capable of properly forming light with ring-shaped intensity distribution.SOLUTION: A luminous flux control member includes a vortex surface comprising: a plurality of phase control surfaces that have a spiral shape with a central axis as a center, and that are radially divided with the central axis as a center; and a plurality of step surfaces for each connecting the ends of two adjacent phase control surfaces with each other among the plurality of phase control surfaces. Upper sides of the plurality of step surfaces cross a center part of the vortex surface. In a side view, a curve directed from the center part of the vortex surface toward an outer peripheral part has an inflection point at the center part of the vortex surface.SELECTED DRAWING: Figure 9

Description

[Technical field]

[0001] The present invention relates to a light flux controlling member and a mold for molding the light flux controlling member. [Background technology]

[0002] In recent years, communication devices and systems equipped with multimode optical fibers have been used to transmit and receive large volumes of data at high speeds using optical communication. Multimode optical fibers have a larger core diameter through which light passes than single-mode optical fibers, allowing more light to pass through. In optical communication using such multimode optical fibers, back reflection, in which light is reflected at the end face of the optical fiber and returns toward the light source, is a problem. This is because when reflected light returns to the light source, a phenomenon called back reflection noise occurs, in which the output of the light source fluctuates.

[0003] As a means for improving this problem, it is known to use optical elements called vortex lenses and spiral phase plates (for example, Patent Document 1). A vortex lens (spiral phase plate) is an optical element (light flux control member) having a vortex surface including a spiral-shaped phase control surface and a step surface connecting the ends of the phase control surface. When light having a Gaussian distribution with a high intensity at the center (Gaussian beam) is passed through a vortex lens, it is converted into light having a ring-shaped intensity distribution (vortex beam) with a significantly reduced intensity at the center. Patent Document 1 describes that by making the light incident on a multimode optical fiber into light with a ring-shaped intensity distribution generated using a vortex lens, it becomes difficult for the back-reflected light to reach the light source.

[0004] Non-Patent Document 1 and Non-Patent Document 2 disclose optical communication using a spiral phase mask that has the same function as a vortex lens. In Non-Patent Document 1 and Non-Patent Document 2, a spiral phase mask is realized using a spatial light modulator. In Non-Patent Document 1, phase masks with topological charge numbers l of +4, +8, -8, and +16 are used. In Non-Patent Document 2, phase masks with topological charge numbers l of 1, 2, 3, and 4 are used. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] JP 2016-091014 A [Non-patent literature]

[0006] [Non-Patent Document 1] Jian Wang, et al., "Terabit free-space data transmission employing orbital angular momentum multiplexing", Nature Photonics, Vol. 6, pp. 488-496. [Non-Patent Document 2] Zikun Wang, "Efficient Recognition of the Propagated OrbitalAngular Momentum Modes in Turbulences With the Convolutional Neural Network", IEEE Photonics Journal, Vol. 11, 7903614. Summary of the Invention [Problem to be solved by the invention]

[0007] As disclosed in the above Non-Patent Document 1 and Non-Patent Document 2, phase masks with various topological charge numbers are known. Therefore, the present inventor attempted to manufacture vortex lenses with various topological charge numbers. FIGS. 1A to 1C are diagrams showing examples of phase patterns with different topological charge numbers l, and FIGS. 1D to 1F are diagrams showing the shape of a vortex surface having the phase patterns shown in FIGS. 1A to 1C, the center of which is not crushed, and which can form light with a ring-shaped appropriate intensity distribution. Specifically, FIG. 1D is a diagram showing the shape of a vortex surface having the phase pattern (l=1) shown in FIG. 1A, FIG. 1E is a diagram showing the shape of a vortex surface having the phase pattern (l=2) shown in FIG. 1B, and FIG. 1F is a diagram showing the shape of a vortex surface having the phase pattern (l=4) shown in FIG. 1C.

[0008] When manufacturing optical elements such as lenses using a mold, the surface of the mold that forms the optical surface is generally formed by cutting. Therefore, the present inventor formed the surface of the mold that forms the vortex surface (hereinafter referred to as the "vortex surface forming surface") for molding a vortex lens by cutting. When a vortex lens having the vortex surface (l≧2) shown in FIG. 1E and F was manufactured using the mold obtained in this way, the center of the vortex surface was crushed. In such a vortex lens, the light with a ring-shaped intensity distribution could not be properly formed due to the unintended shape of the center.

[0009] An object of the present invention is to provide a light flux controlling member having a vortex surface including a plurality of phase control surfaces, which can appropriately form light with a ring-shaped intensity distribution. Another object of the present invention is to provide a mold for molding the light flux controlling member. [Means for solving the problem]

[0010] The present invention relates to the following light flux controlling member and a mold for molding the light flux controlling member.

[0011] [1] A light flux controlling member having a vortex surface having a spiral shape centered on a central axis and including a plurality of phase control surfaces divided radially around the central axis, and a plurality of step surfaces connecting ends of two adjacent phase control surfaces among the plurality of phase control surfaces, wherein upper sides of the plurality of step surfaces intersect at a center of the vortex surface, and in a side view, a curve extending from the center of the vortex surface to an outer periphery has an inflection point at the center of the vortex surface. [2] The light flux controlling member according to [1], wherein the shortest distance between an extension line of an upper side of each of the plurality of step surfaces and the central axis, and the shortest distance between an extension line of a lower side of each of the plurality of step surfaces and the central axis are all 5 μm or less. [3] The light flux controlling member according to [1] or [2], wherein the number of the plurality of phase control surfaces is the same as the number of topological charges of the vortex surface. [4] The light flux controlling member according to any one of [1] to [3], wherein the plurality of phase control surfaces have the same shape. [5] The light flux controlling member according to any one of [1] to [4], wherein the multiple phase control surfaces are arranged in the same height range. [6] A mold for molding a light flux controlling member, the light flux controlling member having a spiral shape centered on a central axis, and having a vortex surface including a plurality of phase control surfaces divided radially around the central axis, and a plurality of step surfaces connecting ends of two adjacent phase control surfaces among the plurality of phase control surfaces, upper sides of the plurality of step surfaces intersect at a center of the vortex surface, and in a side view, a curve extending from the center of the vortex surface to an outer periphery has an inflection point at the center of the vortex surface. Effect of the Invention

[0012] According to the present invention, it is possible to provide a light flux controlling member having a vortex surface including a plurality of phase control surfaces, which can appropriately form light with a ring-shaped intensity distribution. [Brief description of the drawings]

[0013] [Figure 1] 1A to 1C are diagrams showing examples of phase patterns with different topological charge numbers, and FIGS. 1D to 1F are diagrams showing the shapes of vortex surfaces having the phase patterns shown in FIGS. 1A to 1C. [Diagram 2] FIG. 2 is a cross-sectional view showing a configuration of a mold according to an embodiment. [Diagram 3] FIG. 3A is a bottom view of a mold (lower mold) according to the embodiment, and FIG. 3B is a cross-sectional view taken along line AA shown in FIG. 3A. [Figure 4] FIG. 4A is a perspective view showing how a die is manufactured using a conventional cutting tool, and FIG. 4B is a perspective view showing how a die is manufactured using the cutting tool according to the embodiment. [Diagram 5] FIG. 5 is a photograph of the center of a vortex surface of a prototype vortex lens having the vortex surface shown in FIG. 1D. [Figure 6] FIG. 6 is a photograph of the mold (vortex surface molding surface) according to the embodiment. [Figure 7] FIG. 7 is a photograph of the mold (vortex surface molding surface) according to the embodiment. [Figure 8] FIG. 8 is a flowchart of a method for manufacturing a light flux controlling member according to an embodiment. [Figure 9] FIG. 9 is a perspective view of a light flux controlling member according to an embodiment. [Figure 10] 10A is a plan view of a light flux controlling member according to an embodiment, FIG. 10B is a front view, a right side view, a back view, and a left side view of the light flux controlling member according to the embodiment, and FIG. 10C is a cross-sectional view taken along lines BB and CC in FIG. 10A. [Figure 11] FIG. 11 is a photograph of the vicinity of the center of a vortex surface in a light flux controlling member according to an embodiment. [Figure 12] FIG. 12A is a diagram showing the intensity distribution of light emitted from a light flux controlling member having a vortex surface with a crushed center, and FIG. 12B is a diagram showing the intensity distribution of light emitted from a light flux controlling member in accordance with an embodiment. [Figure 13]13A and 13B are schematic plan views showing vortex surfaces of a light flux controlling member in which the topological charge number l is 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0014] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, preferred embodiments of the present invention will be described in detail with reference to the accompanying drawings.

[0015] (Mold and its manufacturing method) First, a description will be given of mold 100 according to an embodiment of the present invention. As shown in Fig. 2, mold 100 is used to mold light flux controlling member 200 according to an embodiment of the present invention.

[0016] FIG. 2 and FIGS. 3A and 3B are diagrams showing the configuration of a mold 100. As shown in FIG. 2, the mold 100 has an upper mold 101 and a lower mold 102. The upper mold 101 and the lower mold 102 form a cavity 120 and a gate 121. FIGS. 3A and 3B show only a piece (lower mold 102) of the mold 100 that includes a vortex surface molding surface 110. FIG. 3A is a bottom view of the mold 100 (lower mold 102), and FIG. 3B is a cross-sectional view taken along line AA shown in FIG. 3A. The gate 121 is omitted in FIGS. 3A and 3B.

[0017] As shown in FIGS. 3A and 3B, the mold 100 has a vortex surface molding surface 110 and a cavity 120.

[0018] Vortex surface forming surface 110 is a surface that forms vortex surface 210 of light flux controlling member 200. As will be described later, vortex surface (also referred to as optical vortex generating surface) 210 of light flux controlling member 200 has a spiral shape centered on central axis CA2 of light flux controlling member 200, and includes a plurality of phase control surfaces 211 divided radially around central axis CA2, and a plurality of step surfaces 212 that each connect end portions of two adjacent phase control surfaces 211 among the plurality of phase control surfaces 211 (see FIG. 9 ). The vortex surface molding surface 110 has a shape complementary to the vortex surface 210, has a spiral shape centered on the central axis CA1 of the mold 100, and includes a plurality of phase control surface molding surfaces 111 radially divided around the central axis CA1, and a plurality of step surface molding surfaces 112 that connect the ends of two adjacent phase control surface molding surfaces 111 among the plurality of phase control surface molding surfaces 111. In this specification, "radially dividing" means dividing an object so that multiple dividing lines extend radially from one point when viewed in a plane. The area generated by dividing is fan-shaped.

[0019] Each of the plurality of phase control surface molding surfaces 111 is a surface for molding phase control surface 211 of light flux controlling member 200. Since each of the plurality of phase control surfaces 211 of light flux controlling member 200 has a spiral shape centered on central axis CA2 of light flux controlling member 200 (see FIG. 9), each of the plurality of phase control surface molding surfaces 111 of mold 100 has a spiral shape centered on central axis CA1 of mold 100. The number of the plurality of phase control surface molding surfaces 111 is the same as the number of the plurality of phase control surfaces 211 of light flux controlling member 200. In the example shown in FIG. 3A, vortex surface molding surface 110 includes four phase control surface molding surfaces 111. These plurality (four) phase control surface molding surfaces 111 are arranged so as to be rotationally symmetric (four-fold symmetric) about central axis CA1 of mold 100. Therefore, the plurality (four) phase control surface molding surfaces 111 have the same shape and are arranged in the same height range. Here, the height in the mold 100 means the position in the direction along the central axis CA1.

[0020] Plural step surface molding surfaces 112 are surfaces for molding step surface 212 of light flux controlling member 200. Plural step surfaces 212 of light flux controlling member 200 connect end portions of two adjacent phase control surfaces 211 to each other (see FIG. 9), and thus plural step surface molding surfaces 112 of mold 100 connect end portions of two adjacent phase control surface molding surfaces 111 to each other. Furthermore, plural step surfaces 212 of light flux controlling member 200 are planes extending in the radial direction from central axis CA2 of light flux controlling member 200 to the outer edge (see FIG. 7), and thus plural step surface molding surfaces 112 of mold 100 are planes extending in the radial direction from central axis CA1 of mold 100 to the outer edge. The number of plural step surface molding surfaces 112 is the same as the number of plural phase control surfaces 211 of light flux controlling member 200 and the number of plural phase control surface molding surfaces 111 of mold 100. In the example shown in the present embodiment, vortex surface molding surface 110 includes four step surface molding surfaces 112. These multiple (four) step surface molding surfaces 112 are arranged to be rotationally symmetric (four-fold symmetric) about central axis CA1 of mold 100. Therefore, multiple (four) step surface molding surfaces 112 have the same shape and are arranged in the same height range. Note that in the following description, of the sides of step surface molding surface 112, the side corresponding to the upper side of step surface 212 of light flux controlling member 200 is referred to as the upper side of step surface molding surface 112, and the side corresponding to the lower side of step surface 212 of light flux controlling member 200 is referred to as the lower side of step surface molding surface 112. Light flux controlling member 200 has first surface 220 for receiving light from a light source or for emitting light that has traveled inside to the outside, and vortex surface (second surface) 210 for receiving light or for emitting light that has received at first surface 220 to the outside (see FIGS. 10B and 10C). In this specification, the first surface 220 side (light source side) of light flux controlling member 200 is defined as the downward direction, and the vortex surface 210 side of light flux controlling member 200 is defined as the upward direction (see FIGS. 10B and 10C). Therefore, the upper side of step surface 212 of light flux controlling member 200 is farther from first surface 220 (light source side surface) than the lower side of step surface 212 of light flux controlling member 200.

[0021] The above-mentioned Fig. 1F shows an example of a preferable vortex surface 210. As shown in Fig. 1F, the phase control surface 211 located between the two step surfaces 212 in the circumferential direction is preferably a gently continuous surface, and more preferably a mirror surface.

[0022] As in the case of a conventional general processing method, when vortex surface molding surface 110 of mold 100 is formed by cutting in a concentric circle, an annular processing mark is formed. As a result, an annular processing mark is also formed on vortex surface 210 of light flux controlling member 200. This processing mark is formed not only on the outer periphery of vortex surface 210 but also in the center. When a processing mark is formed in the center of vortex surface 210 in this way, the upper sides of each of multiple step surfaces 212 do not intersect at the center of vortex surface 210. In light flux controlling member 200 having a processing mark in the center of vortex surface 210, it is not possible to appropriately form light with a ring-shaped intensity distribution due to the unintended processing mark.

[0023] Therefore, in the present embodiment, vortex surface molding surface 110 of mold 100 is formed by radially cutting. In this case, as shown in FIG. 3A, radial processing grooves (processing marks) 113 may be slightly formed on the outer periphery of vortex surface molding surface 110. In contrast, in center 114 of vortex surface molding surface 110, processed regions overlap and the same region is repeatedly processed, so processing grooves 113 disappear. Therefore, center 114 of vortex surface molding surface 110 becomes an approximately mirror surface. In addition, the upper sides of multiple step surface molding surfaces 112 intersect at center 114 of vortex surface molding surface 110. Therefore, center 214 of vortex surface 210 of light flux controlling member 200 also becomes an approximately mirror surface, and the upper sides of multiple step surfaces 212 intersect at the center of vortex surface 210, making it possible to appropriately form light with a ring-shaped intensity distribution. In this specification, center 114 of vortex surface molding surface 110 means the range from central axis CA1 of vortex surface molding surface 110 (mold 100) to a distance of 1 / 10 of the radius of vortex surface molding surface 110. Similarly, in this specification, center 214 of vortex surface 210 means the range from central axis CA2 of vortex surface 210 (light flux controlling member 200) to a distance of 1 / 10 of the radius of vortex surface 210.

[0024] Furthermore, when cutting the vortex surface molding surface 110 of the die 100 radially using a conventional general cutting tool (bite) 130, the boundary between the phase control surface molding surface 111 and the step surface molding surface 112 becomes a curved surface (R surface) 112R at the upper end of the step surface molding surface 112 (the portion corresponding to the upper side of the step surface molding surface 112) as shown in Fig. 4A. Therefore, the position of the upper side of the step surface molding surface 112 and the position of the lower side of the step surface molding surface 112 are largely misaligned in the horizontal direction, and at least one of the upper side and the lower side of the step surface molding surface 112 is separated from the central axis CA1 of the die 100. As a result, when light flux controlling member 200 is manufactured using die 100 formed by conventional general cutting tool 130, at least one of the shortest distance between an extension line of an upper side of step surface 212 of light flux controlling member 200 and central axis CA2 of light flux controlling member 200 and the shortest distance between an extension line of a lower side of step surface 212 of light flux controlling member 200 and central axis CA2 of light flux controlling member 200 is 7 μm or more, as shown in FIG. 5. That is, step surface 212, which should extend radially from central axis CA2 in the design, is formed at a position away from central axis CA2. In such light flux controlling member 200, light with a ring-shaped intensity distribution cannot be appropriately formed due to the unintended shape of step surface 212. Note that in FIG. 5, step surface 212 shows one vortex surface 210 in order to make the relationship between step surface 212 and central axis CA2 easier to see.

[0025] Therefore, in this embodiment, when cutting the vortex surface molding surface 110 of the mold 100 radially, a cutting tool according to this embodiment having a vertical cutting edge on one side is used instead of a conventional cutting tool 130 having curved (R-shaped) cutting edges on both sides. By doing so, as shown in FIG. 4B, it is possible to prevent the boundary between the phase control surface molding surface 111 and the step surface molding surface 112 from becoming a curved surface (R surface) 112R at the upper end of the step surface molding surface 112. Therefore, the position of the upper side of the step surface molding surface 112 and the position of the lower side of the step surface molding surface 112 are prevented from shifting in the horizontal direction, and the upper side and the lower side of the step surface molding surface 112 are also prevented from moving away from the central axis CA1 of the mold 100. As a result, the shortest distance between an extension line of the upper side of each of multiple step surface molding surfaces 112 and central axis CA1 of mold 100, and the shortest distance between an extension line of the lower side of each of multiple step surface molding surfaces 112 and central axis CA1 of mold 100 are both 0 μm or more and 5 μm or less. When light flux controlling member 200 is manufactured using mold 100 formed by the cutting tool according to the present embodiment, the shortest distance between an extension line of the upper side of each of multiple step surfaces 212 of light flux controlling member 200 and central axis CA2 of light flux controlling member 200, and the shortest distance between an extension line of the lower side of each of multiple step surfaces 212 of light flux controlling member 200 and central axis CA2 of light flux controlling member 200 are both 0 μm or more and 5 μm or less (see FIG. 11 ). That is, multiple step surfaces 212 are formed to extend radially from central axis CA2 as designed.

[0026] The die 100 according to this embodiment can be manufactured, for example, by cutting the die base material radially from a predetermined point as the center to form the vortex surface molding surface 110. At this time, it is preferable to use the cutting tool according to this embodiment described above.

[0027] The material constituting the mold base material is not particularly limited and can be appropriately selected from known materials. Examples of materials constituting the mold base material include steel, zinc alloy, and aluminum alloy. From the viewpoint of durability, it is preferable that the mold base material contains steel.

[0028] For example, when forming the vortex surface molding surface 110 by cutting, a point that will be the center of the spiral may be determined on one main surface of the mold base material, and cutting may be performed radially toward the center. Conversely, a point that will be the center of the spiral may be determined on one main surface of the mold base material, and cutting may be performed radially from the center. In either case, a plurality of grooves 113 that are arranged radially toward the center of the spiral may be formed on the outer periphery of the vortex surface molding surface 110.

[0029] When forming the phase control surface molding surface 111, the height of the tip of the tool is changed to cut one groove 113 so that the depth of the adjacent groove in the rotation direction of the spiral is deeper or shallower. For example, when cutting grooves in a clockwise direction in order so that the angle between adjacent grooves is 0.2° when viewed in a plane, cutting is performed so that a groove deeper or shallower than the depth of the groove is formed at a position 0.2° forward clockwise from the formed groove. By performing this continuously over a predetermined angle range (for example, 90°), the phase control surface molding surface 111 is formed on the main surface of the mold base material. The rotation direction of the spiral can be determined arbitrarily, and cutting can be performed by changing the height of the tip of the tool according to the rotation direction.

[0030] When forming the step surface molding surface 112, the cutting tool according to the present embodiment is positioned so that the vertical cutting edge is positioned on the step surface molding surface 112 side (see FIG. 4B). As a result, the step surface molding surface 112 is formed on the main surface of the mold base material. The step surface molding surface 112 may be parallel to the central axis CA1, or may be slightly inclined with respect to the central axis CA1 (draft taper).

[0031] In the vortex surface molding surface 110 thus formed, the multiple phase control surface molding surfaces 111 are each a concave curved surface, and in a side perspective view, the curve extending from the center 114 of the vortex surface molding surface 110 toward the outer periphery has an inflection point at the center 114 of the vortex surface molding surface 110. That is, in a cross section including the central axis CA1, the curve which is the cross section of the phase control surface molding surface 111 has an inflection point at the center 114 of the vortex surface molding surface 110. More specifically, in a cross section including the central axis CA1, in the region other than the center 114 of the vortex surface molding surface 110, the phase control surface molding surface 111 has a smaller inclination (becoming closer to perpendicular to the central axis CA1) as it approaches the central axis CA1, but in the center 114 of the vortex surface molding surface 110, the phase control surface molding surface 111 includes a portion where the inclination becomes larger (the angle with respect to the central axis CA1 becomes smaller) as it approaches the central axis CA1. However, this does not apply to the center 114 of the vortex surface molding surface 110 in the immediate vicinity of the step surface molding surface 112. Therefore, in Fig. 3B, the phase control surface molding surface 111 is not shown to be curved.

[0032] FIG. 6 is a photograph of the mold 100 (vortex surface molding surface 110) manufactured as described above. FIG. 7 is a photograph of the center of the vortex surface molding surface 110 enlarged (1000 times). As described above, the vortex surface molding surface 110 of the mold 100 is radially cut to form the center 114 of the vortex surface molding surface 110 into a substantially mirror-like surface. In addition, since the vortex surface molding surface 110 is machined without continuously pressing a cutting tool against the center 114 of the vortex surface molding surface 110, it is possible to prevent large machining marks (destruction) from being formed in the center of the vortex surface molding surface 110. Furthermore, by using the cutting tool of this embodiment having a vertical cutting edge on one side, it is possible to prevent the boundary between the phase control surface molding surface 111 and the step surface molding surface 112 from becoming a curved surface (R surface) 112R at the upper end of the step surface molding surface 112. Therefore, the upper sides of each of the multiple step surface molding surfaces 112 intersect at center 114 of vortex surface molding surface 110. Additionally, each of the multiple phase control surface molding surfaces 111 is a concave curved surface, and in a side see-through view, the curve extending from center 114 of vortex surface molding surface 110 toward the outer periphery has an inflection point at center 114 of vortex surface molding surface 110. Furthermore, the shortest distance between an extension line of the upper side of each of the multiple step surface molding surfaces 112 and central axis CA1 of mold 100, and the shortest distance between an extension line of the lower side of each of the multiple step surface molding surfaces 112 and central axis CA1 of mold 100 are both 0 μm or more and 5 μm or less.

[0033] (Light flux controlling member and method for manufacturing same) FIG. 8 is a flowchart of a method for manufacturing light flux controlling member 200 according to the present embodiment.

[0034] 8, light flux controlling member 200 according to the present embodiment has, for example, (1) a step (step S10) of injecting a molding material into cavity 120 of die 100 described above, (2) a step (step S20) of solidifying the molding material in cavity 120, and (3) a step (step S30) of releasing and taking out the solidified molding material from die 100. Each step will be described below.

[0035] First, a molding material is injected into the cavity 120 of the mold 100 (step S10). For example, the above-mentioned mold 100 is used as a fixed mold, and after closing with a movable mold disposed so as to face the fixed mold, the molding material is injected from a molding material injection port.

[0036] In this embodiment, a resin material can be used as the molding material. The type of resin material can be appropriately selected from materials that are translucent to the light to be used. Examples of resin materials include polymethylmethacrylate (PMMA), polycarbonate (PC), epoxy resin (EP), modified polyphenylene ether (m-PPE), cycloolefin polymer (COP), and cyclic olefin copolymer (COC).

[0037] Next, the molding material injected into the cavity 120 is solidified (step S20). For example, if a thermoplastic resin is injected into the cavity 120, the thermoplastic resin may be cooled and solidified. Also, if a thermosetting resin is injected into the cavity 120, the resin in the cavity 120 may be heated and solidified (cured).

[0038] Finally, the molding material solidified in step S20 is released and taken out from the mold 100 (step S30).

[0039] By the above procedure, it is possible to manufacture light flux controlling member 200 having vortex surface 210 which is the inverse of the shape of vortex surface molding surface 110 of mold 100. Light flux controlling member 200 will be described below.

[0040] Fig. 9 and Fig. 10A-C are diagrams showing light flux controlling member 200 according to the present embodiment. Fig. 9 is a perspective view of light flux controlling member 200, Fig. 10A is a plan view of light flux controlling member 200, Fig. 10B is a front view, right side view, rear view, and left side view of light flux controlling member 200, and Fig. 10C is a cross-sectional view taken along lines BB and CC in Fig. 10A.

[0041] As shown in FIG. 9 and FIGS. 10A to 10C, light flux controlling member 200 has vortex surface 210 and first surface 220.

[0042] The vortex surface (optical vortex generating surface) 210 has a spiral shape centered on the central axis CA2, and includes a plurality of phase control surfaces 211 divided radially around the central axis CA2, and a plurality of step surfaces 212 connecting the ends of two adjacent phase control surfaces 211 among the plurality of phase control surfaces 211. The light passing through the vortex surface 210 is converted into light having a phase difference in the circumferential direction and a ring-shaped intensity distribution (see FIG. 12B). In this embodiment, as shown in FIG. 10A, the vortex surface 210 (phase control surface 211) also includes a plurality of ridges 213 corresponding to the plurality of processing grooves 113 of the mold 100. Note that the plurality of ridges 213 are omitted in FIG. 9 and FIG. 10B.

[0043] Each of the plurality of phase control surfaces 211 has a spiral shape centered on central axis CA2 of light flux controlling member 200. Here, the spiral shape may be a smoothly continuous spiral shape or a stepped spiral shape. The number of phase control surfaces 211 is not particularly limited. In the present embodiment, vortex surface 210 includes a plurality (four) of phase control surfaces 211, the number of which is the same as the number of topological charges l of vortex surface 210. These plurality (four) of phase control surfaces 211 are arranged to be rotationally symmetric (four-fold symmetric) about central axis CA2. Therefore, the plurality of phase control surfaces 211 have the same shape and are arranged in the same height range. Here, the height in light flux controlling member 200 means the position in the direction along central axis CA2.

[0044] Each of the multiple phase control surfaces 211 is a convex curved surface, and in a side view, a curve extending from the center 214 of the vortex surface 210 toward the outer periphery has an inflection point at the center 214 of the vortex surface 210. That is, in a cross section including the central axis CA2, the curve which is the cross section of the phase control surface 211 has an inflection point 215 at the center 214 of the vortex surface 210. More specifically, in a cross section including the central axis CA2, in a region other than the center 214 of the vortex surface 210, the phase control surface 211 has a smaller inclination (becoming closer to perpendicular to the central axis CA2) as it approaches the central axis CA2, but in the center 214 of the vortex surface 210, the phase control surface 211 includes a portion where the inclination becomes larger (the angle with respect to the central axis CA2 becomes smaller) as it approaches the central axis CA2 (see FIG. 10B). However, this does not apply even to central portion 214 of vortex surface 210 in the immediate vicinity of step surface 212. Therefore, in Figure 10C, phase control surface 211 is not shown to be curved.

[0045] The step surfaces 212 connect the ends of two adjacent phase control surfaces 211. In this embodiment, the step surfaces 212 are planes extending radially from the central axis CA2 to the outer edge. The upper sides of the step surfaces 212 intersect at the center 214 of the vortex surface 210. The number of step surfaces 212 is the same as the number of phase control surfaces 211. For example, when the vortex surface 210 includes two phase control surfaces 211, the vortex surface 210 includes two step surfaces 212, and each step surface 212 connects the ends of two adjacent phase control surfaces 211. In the example shown in this embodiment, the vortex surface 210 includes four step surfaces 212. These multiple (four) step surfaces 212 are arranged to be rotationally symmetric (four-fold symmetric) around the central axis CA2. Therefore, the multiple (four) step surfaces 212 have the same shape and are arranged in the same height range.

[0046] The total height of multiple step surfaces 212 can be set appropriately according to topological charge number l, which relates to what type of vortex light Gaussian light is converted into. When the topological charge number is l, the wavelength of light passing through vortex surface 210 is λ, and the difference in refractive index at wavelength λ of light between the material of light flux controlling member 200 and the surrounding medium (e.g., air) is Δn, the total height d of multiple step surfaces 212 can be found from the following formula (1). The total height d of multiple step surfaces 212 is set according to the topological charge number l to be imparted, and is, for example, 1 μm or more and 10 μm or less. d=l×λ / Δn (1)

[0047] The multiple protrusions 213 are a pattern transferred from the multiple processing grooves 113 of the mold 100. As shown in FIG. 10A, the multiple protrusions 213 are arranged radially from the central axis CA2 on the vortex surface 210. Therefore, the closer the multiple protrusions 213 are to the central axis CA2, the narrower the interval between the adjacent protrusions 213, and they eventually overlap. Accordingly, the grooves formed between the adjacent protrusions 213 also become shallower as they approach the central axis CA2. Therefore, the height of the protrusions 213 becomes lower as they approach the center. As a result, the center 214 of the vortex surface 210 becomes a substantially mirror surface. Here, the "height of the protrusions 213" does not mean the absolute height of the protrusions 213 (for example, the height relative to the first surface 220), but the height relative to the bottom of the grooves on both sides of the protrusions 213.

[0048] Light flux controlling member 200 according to the present embodiment can be manufactured using die 100 according to the present embodiment described above. As described above, in die 100 according to the present embodiment, the upper sides of multiple step surface molding surfaces 112 intersect at center 114 of vortex surface molding surface 110, and the shortest distance between an extension line of each of the upper sides of multiple step surface molding surfaces 112 and central axis CA1 of die 100, and the shortest distance between an extension line of each of the lower sides of multiple step surface molding surfaces 112 and central axis CA1 of die 100 are both 0 μm or more and 5 μm or less. Therefore, also in light flux controlling member 200 according to the present embodiment, the upper sides of multiple step surfaces 212 intersect at center portion 214 of vortex surface 210, and the shortest distance between an extension line of the upper side of each of multiple step surfaces 212 and central axis CA2 of light flux controlling member 200, and the shortest distance between an extension line of the lower side of each of multiple step surfaces 212 and central axis CA2 of light flux controlling member 200 are both 0 μm or more and 5 μm or less. In other words, step surfaces 212 are formed to extend radially from central axis CA2 as designed.

[0049] FIG. 11 is a photograph of the vicinity of the center of vortex surface 210 in light flux controlling member 200 according to the present embodiment. Here, vortex surface 210 with one step surface 212 is shown in order to make the relationship between step surface 212 and central axis CA2 easier to see. It can be seen from FIG. 11 that the upper and lower sides of step surface 212 are not far from the central axis (center of the spiral) (compare with FIG. 5). In the example shown in FIG. 11, the shortest distance between the extension line of the upper side of step surface 212 and central axis CA2 of light flux controlling member 200, and the shortest distance between the extension line of the lower side of step surface 212 of light flux controlling member 200 and central axis CA2 of light flux controlling member 200 were both 1 μm or less.

[0050] Fig. 12A is a diagram showing the intensity distribution of light emitted from light flux controlling member 200 having vortex surface 210 with a crushed central portion as shown in Fig. 5, and Fig. 12B is a diagram showing the intensity distribution of light emitted from light flux controlling member 200 in accordance with the present embodiment. Both diagrams show the intensity distribution of light at the focal position of light flux controlling member 200. As shown in Fig. 12B, light flux controlling member 200 in accordance with the present embodiment can generate light having a desired ring-shaped intensity distribution.

[0051] Vortex surface 210 of light flux controlling member 200 according to the present embodiment is preferably n-fold symmetric (n is an integer of 2 or more), and n is preferably the same number as topological charge number l of vortex surface 210. For example, when topological charge number l is 4, as shown in FIG. 9 and FIG. 10A, vortex surface 210 is preferably 4-fold symmetric, that is, includes four phase control surfaces 211 of the same shape and four step surfaces 212 of the same shape. These four phase control surfaces 211 and four step surfaces 212 are arranged in the same height range. In this way, the difference in thickness within light flux controlling member 200 is reduced, and therefore stress distortion during cutting of die 100 and molding of light flux controlling member 200 is suppressed, and the molding accuracy of light flux controlling member 200 is improved.

[0052] 13A and 13B are schematic plan views showing vortex surface 210 of light flux controlling member 200 in which topological charge number l is 4. Vortex surface 210 shown in FIG. 13A includes one phase control surface 211 and one step surface 212. On the other hand, vortex surface 210 shown in FIG. 13B includes four phase control surfaces 211 and four step surfaces 212. Here, as shown in FIGS. 13A and 13B, it is assumed that vortex surface 210 is divided into four regions A to D. In vortex surface 210 shown in FIG. 13A, region A corresponds to a phase difference ΔΦ of 0 to 2π, region B corresponds to a phase difference ΔΦ of 2 to 4π, region C corresponds to a phase difference ΔΦ of 4 to 6π, and region D corresponds to a phase difference ΔΦ of 6 to 8π. In vortex surface 210 shown in Fig. 13A, step surface 212 exists only between region A and region D, and the height of step surface 212 is, for example, 5.2 µm (= 1.3 µm × 4). On the other hand, in vortex surface 210 shown in Fig. 13B, regions A to D all correspond to phase differences ΔΦ of 0 to 2π. In vortex surface 210 shown in Fig. 13B, step surfaces 212 exist respectively between region A and region B, between region B and region C, between region C and region D, and between region D and region A, and the height of these step surfaces 212 is, for example, 1.3 µm each (total height is 5.2 µm). 13A, the difference in thickness between the portions adjacent to step surface 212 is as much as 5.2 μm, whereas in light flux controlling member 200 shown in Fig. 13B, the difference in thickness between the portions adjacent to step surface 212 is only 1.3 μm. In this way, in light flux controlling member 200 shown in Fig. 13B, the difference in thickness between the portions adjacent to step surface 212 is small, and therefore stress distortion during cutting of die 100 and molding of light flux controlling member 200 is suppressed, improving the molding accuracy of light flux controlling member 200.

[0053] (effect) As described above, in the present embodiment, vortex surface molding surface 110 of mold 100 is formed by cutting in a radial manner, so that central portion 114 of vortex surface molding surface 110 can be made into a substantially mirror surface. Moreover, since vortex surface molding surface 110 is machined without continuously pressing a cutting tool against central portion 114 of vortex surface molding surface 110, it is possible to prevent large machining marks (destruction) from being formed in central portion 114 of vortex surface molding surface 110. Furthermore, by using the cutting tool of the present embodiment having a vertical cutting edge on one side, it is possible to prevent the boundary between phase control surface molding surface 111 and step surface molding surface 112 at the lower end of step surface molding surface 112 from becoming curved surface (R surface) 112R. As a result, light flux controlling member 200 according to the present embodiment can generate light having a desired ring-shaped intensity distribution.

[0054] (Modification) In the above embodiment, light flux controlling member 200 having one vortex surface 210 has been described; however, a light flux controlling member according to the present invention may be a lens array having a plurality of vortex surfaces 210.

[0055] Furthermore, the light flux controlling member of the present invention may be a light flux controlling member in which vortex surface (second surface) 210 functions as the incident surface and first surface 220 functions as the exit surface, or a light flux controlling member in which first surface 220 functions as the incident surface and vortex surface (second surface) 210 functions as the exit surface. [Industrial Applicability]

[0056] According to the present invention, it is possible to provide a light flux controlling member that can appropriately form light having a ring-shaped intensity distribution. The light flux controlling member according to the present invention is useful, for example, in optical communications. [Explanation of symbols]

[0057] 100 Molds 101 Upper mold 102 Lower mold 110 Vortex surface molding surface 111 Phase control surface molding surface 112 Step surface molding surface 112R curved surface 113 Machining groove 114 Center of the vortex surface molding surface 120 Cavity Gate 121 130 Conventional cutting tools 200 Light flux control member 210 Vortex Surface (Second Surface) 211 Phase Control Surface 212 Step surface 213 Convex strip 214 Center of the vortex surface 215 Inflection point of phase control surface 220 Page 1 CA1 Central axis of the mold CA2 Central axis of light flux control member

Claims

1. A vortex surface includes a plurality of phase control surfaces having a spiral shape centered on a central axis and divided radially around the central axis, and a plurality of step surfaces each connecting ends of two adjacent phase control surfaces among the plurality of phase control surfaces, the upper sides of the plurality of step surfaces intersect at a center of the vortex surface, When viewed from the side, a curve extending from the center of the vortex surface to the outer periphery has an inflection point at the center of the vortex surface. Light flux control member.

2. 2. The light flux controlling member according to claim 1, wherein the shortest distance between an extension line of an upper side of each of the plurality of step surfaces and the central axis, and the shortest distance between an extension line of a lower side of each of the plurality of step surfaces and the central axis are each 5 μm or less.

3. 2. The light flux controlling member according to claim 1, wherein the number of the plurality of phase control surfaces is the same as the number of topological charges of the vortex surface.

4. The light flux controlling member according to claim 1 , wherein the plurality of phase control surfaces have the same shape.

5. 5. The light flux controlling member according to claim 1, wherein the plurality of phase control surfaces are arranged in the same height range.

6. A mold for molding a light flux controlling member, the light flux controlling member has a spiral shape centered on a central axis, and has a vortex surface including a plurality of phase control surfaces divided radially around the central axis, and a plurality of step surfaces each connecting ends of two adjacent phase control surfaces among the plurality of phase control surfaces, the upper sides of the plurality of step surfaces intersect at a center of the vortex surface, When viewed from the side, a curve extending from the center of the vortex surface to the outer periphery has an inflection point at the center of the vortex surface. Mold.

Images