Optical element, optical system, and imaging device

Abstract

To provide an optical element in which traces of air pockets formed during manufacturing are reduced and decentering of the optical axis can be prevented with high precision. [Solution] An optical element having an optical surface, a tapered portion located on the outer periphery of the optical surface, with the normal direction from the inside to the outside of the optical element facing the optical axis, and a side portion located on the outer periphery of the tapered portion, wherein, in a cross section including the optical axis and passing through the tapered portion, when the straight-line distance perpendicular to the optical axis from the end point of the tapered portion on the optical axis side to the side portion is A and the height of the tapered portion based on said straight line is B, B / A is greater than 0.2.

Description

[Technical field]

[0001] The present invention relates to an optical element, an optical system, and an imaging device. [Background technology]

[0002] Lens units used in mobile phones (including smartphones) and car-mounted cameras are generally formed by stacking multiple lens elements in the optical axis direction inside a lens barrel. The lens unit must be assembled so that the optical axis of each lens element is not decentered from the central axis of the lens barrel (so that the optical axis does not shift).

[0003] Patent Document 1 describes a lens unit formed by fitting a flange portion provided on a lens element with a flange portion provided on a lens barrel side to prevent the optical axis of the lens element from becoming eccentric. Specifically, a flange portion having a tapered portion is provided on the periphery of the lens element. Also, a flange portion having a tapered portion that fits with the flange portion of the lens element is provided on the lens barrel side. Then, by fitting both flange portions together so that both tapered portions are in contact, the optical axis of the lens element is made to coincide with the central axis of the lens barrel.

[0004] Patent Document 2 describes an optical lens having a flange portion, in which an inclined portion is provided between an effective area (optical surface) and the flange portion outside the effective range of the lens surface, and the inclined surface of the inclined portion is used for alignment during manufacturing. During manufacturing of the optical lens, the central axis of the lens molding die and the optical axis of the lens are aligned by adjusting the lens position according to the contact state between the lens holding portion and the inclined surface.

[0005] Patent Document 3 describes an optical system in which a glass lens and another lens are superimposed and stored in a lens barrel. The glass lens has an optical function part and a flange part (edge ​​part), and an inclined part is provided between the optical function part and the flange part at the periphery of the glass lens, and the tapered part of the inclined part is used for alignment during manufacturing. It is also said that when molding the glass lens, the occurrence of voids in the molding die is prevented. [Prior art documents] [Patent documents]

[0006] [Patent Document 1] Japanese Patent No. 5274881 [Patent Document 2] Japanese Patent No. 4874084 [Patent Document 3] Japanese Patent No. 6280337 Summary of the Invention [Problem to be solved by the invention]

[0007] The optical lens described in Patent Document 2 has a problem in that when the material is glass, it is difficult to obtain sufficient shape precision when forming the tapered portion. This is because glass has a higher viscosity during molding than resin, and gas traps (air pockets) tend to occur.

[0008] The glass lens described in Patent Document 3 has a tapered portion for alignment, but the tapered portion is formed so that the normal line from the inside to the outside of the glass lens faces in a direction away from the optical axis. However, a tapered portion in which the normal line from the inside to the outside faces the optical axis may be desired. It is unclear how the thickness of the flange portion and the angle of the tapered portion described in Patent Document 3 can be applied when forming a tapered portion in which the normal line from the inside to the outside faces the optical axis.

[0009] The present invention aims to provide an optical element that reduces traces of air pockets formed during manufacturing and can prevent decentering of the optical axis with high precision, as well as an optical system including the optical element and an imaging device including the optical element. [Means for solving the problem]

[0010] The optical element according to the present invention has an optical surface, a tapered portion located on the outer periphery of the optical surface, with a normal direction from the inside to the outside of the optical element facing the optical axis, and a side portion located on the outer periphery of the tapered portion, and is characterized in that, in a cross section including the optical axis and passing through the tapered portion, when A is the straight-line distance perpendicular to the optical axis from the end point of the tapered portion on the optical axis side to the side portion and B is the height of the tapered portion based on the straight line, B / A is greater than 0.2.

[0011] An optical system according to the present invention is characterized by comprising the optical element described above.

[0012] An imaging device according to the present invention includes the optical element described above. Effect of the Invention

[0013] According to the present invention, there is provided an optical element in which traces of air pockets formed during manufacturing are reduced, making it possible to prevent decentering of the optical axis with high precision. [Brief description of the drawings]

[0014] [Figure 1] FIG. 1 is a cross-sectional view showing an optical element according to one embodiment of the present invention. [Diagram 2] FIG. 2 is an enlarged cross-sectional view showing a flange portion of the optical element shown in FIG. [Diagram 3] FIG. 3 is an enlarged cross-sectional view of the flange portion. [Figure 4] FIG. 4 is an explanatory diagram that shows a schematic diagram of how a glass lens is molded. [Diagram 5] FIG. 5 is an explanatory diagram showing the results of a simulation of the spread of glass during forming, performed by the finite element method. [Figure 6] FIG. 6 is an explanatory diagram showing the results of a simulation of the spread of glass during forming, performed by the finite element method. [Figure 7] FIG. 7 is an explanatory diagram for explaining the reason why the air pocket area becomes smaller as the value of B / A increases. [Figure 8] FIG. 8 is an explanatory diagram showing the shape of the glass lens of the first embodiment. [Figure 9] FIG. 9 is a cross-sectional view illustrating a schematic example of a lens unit. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

[0016] EMBODIMENT 1 Fig. 1 is a cross-sectional view showing an optical element according to one embodiment of the present invention. Fig. 2 is a cross-sectional view showing an enlarged flange portion of the optical element in Fig. 1. The glass lens 10 shown in Figs. 1 and 2 is an example of an optical element.

[0017] Glass lens 10 has, at the center, a convex first aspherical portion 11 and a concave second aspherical portion 12 facing the first aspherical portion 11. In Fig. 1, the optical axis of glass lens 10 is indicated by a dashed line. Fig. 1 illustrates a glass lens 10 in which the radius of curvature of first aspherical portion 11 at the optical axis is smaller than the radius of curvature of second aspherical portion 12 at the optical axis. Note that glass lens 10 illustrated in Fig. 1 is a meniscus type convex lens.

[0018] Hereinafter, the side of first aspheric surface portion 11 may be referred to as the upper portion, and the side of second aspheric surface portion 12 may be referred to as the lower portion. Moreover, first aspheric surface portion 11 and second aspheric surface portion 12 are referred to as optical surfaces.

[0019] The glass lens 10 has a flange portion 13 on the outside of the center portion. The glass lens 10 also has a side portion 16 (the outer peripheral side portion of the flange portion 13).

[0020] The flange portion 13 has a convex portion 14 that protrudes downward from the side surface portion 16. A tapered portion 15 is formed on the convex portion 14 on the second aspheric portion 12 side. The tapered portion 15 is formed as an inner peripheral portion (inner wall) of the convex portion 14 so that the direction of the normal of the tapered portion 15 from the inside to the outside of the flange portion 13 (see the arrow in FIG. 2) faces the optical axis. The angle between the tapered portion 15 and a plane perpendicular to the optical axis is θ. In addition, the portion between the second aspheric portion 12 and the tapered portion 15 in the flange portion 13 is called a bottom portion 17. The bottom portion 17 may be inclined from the horizontal axis (axis perpendicular to the optical axis) in a cross-sectional view. The angle θ of the tapered portion 15 may be 45° or more and 90° or less (or less than 90°). Furthermore, the angle that bottom 17 makes with the horizontal axis (axis perpendicular to the optical axis) in a cross-sectional view may be any angle that is not less than 0° and not more than 30°.

[0021] 1 and 2 show glass lens 10 having tapered portion 15 formed in the lower portion, glass lens 10 may have a tapered portion in the upper portion, or may have tapered portions in both the lower portion and the upper portion.

[0022] 2, in a cross section including the optical axis and passing through the tapered portion, the horizontal linear distance between the end point of tapered portion 15 on the optical axis side and side portion 16 is defined as A. Also, the height of convex portion 14 (corresponding to the height of tapered portion 15) is defined as B.

[0023] When glass lens 10 is molded using a glass mold or the like, deterioration of the mold or shrinkage occurring during the molding process may cause bottom portion 17 and tapered portion 15 to shrink to form a curved surface with a certain radius of curvature. Taking such a possibility into consideration, as shown in Fig. 3, in a cross section that includes the optical axis and passes through the tapered portion, the intersection of an extension of bottom portion 17 and an extension of tapered portion 15 may be taken as a reference point, and the straight-line distance in the horizontal direction between the reference point and side portion 16 may be taken as A. In Fig. 3, this distance is indicated as A'.

[0024] From the viewpoint of manufacturing the glass lens 10 described below, it is preferable that the relationship between the distance A and the height B be as follows. Specifically, when the relationship is as follows, the occurrence of air pockets is reduced when the glass lens 10 is molded using a glass mold or the like.

[0025] That is, it is preferable that B / A>1 / 5, it is more preferable that B / A>1 / 4, and it is even more preferable that B / A>1 / 2.

[0026] On the other hand, if the value of height B is large, there is a high possibility that the glass material will get caught in the mold when the temperature of the glass material is lowered from a high temperature to a low temperature during molding of glass lens 10. Therefore, it is preferable that B / A<10, and it is more preferable that B / A<5. The specific value of B is preferably 500 μm or less in order to prevent cracking during molding of the glass, preferably 250 μm or less, and more preferably 125 μm or less. The specific value of A is set so as to satisfy the ratio B / A.

[0027] Various types of glass can be used as the glass material to be molded into the glass lens 10. However, in order to prevent the glass material from getting caught in the mold, it is preferable to select a glass material with a small linear expansion coefficient. For example, the linear expansion coefficient of the glass material is 10×10 -6 / ℃ or less, and 9×10 -6 / ℃ or less, more preferably 8×10 -6 It is more preferable that the temperature is 100° C. or less.

[0028] In addition, the tapered portion 15 is preferably formed over a range of 360° around the optical axis of the glass lens 10, but there is a possibility that a part of it may be chipped due to variations during manufacturing or the occurrence of air pockets. In such a case, the tapered portion 15 is preferably formed over a range of 270° or more.

[0029] In a cross section including the optical axis and passing through the tapered portion, the length of the tapered portion 15 is preferably 30 μm or more. If it is 30 μm or more, it is possible to perform alignment with other lenses with high precision. From the same viewpoint, it is more preferable that the length of the bottom portion 17 in a cross-sectional view is 50 μm or more.

[0030] In this embodiment, the optical element is a glass lens 10, but is not limited to this and may be a lens made of a light-transmitting material, for example, a light-transmitting resin. Also, the shape of the lower part of the glass lens 10 is aspheric, but it may be spherical or flat.

[0031] Furthermore, although the tapered portion 15 is provided on the flange portion 13, when the optical element does not have the flange portion 13, the tapered portion 15 may be provided on the bottom portion 17 of this embodiment. Regardless of the presence or absence of the flange portion 13, the tapered portion 15 is located on the outer circumferential side of the optical surface (the second aspheric portion), and the portion formed by the optical surface (specifically, the second aspheric portion 12) and the bottom portion 17 and the tapered portion 15 may be concave.

[0032] In order to reliably form the tapered portion 15, it is preferable that the outer diameter of the glass lens 10 is small. For example, it is preferable that the outer diameter is 10 mm or less, and more preferably 6 mm or less. The outer diameter of the glass lens 10 is preferably 1 mm or more.

[0033] Next, we will explain how to mold the glass lens 10. Figure 4 is an explanatory diagram that shows a schematic diagram of how to mold the glass lens 10. The glass lens 10 is molded using a glass mold.

[0034] As shown in FIG. 4(a), a glass material (preform) 24 is placed on a second die 22 that defines the first aspheric portion 11. The preform 24 is heated to a temperature equal to or higher than the glass transition point, and the preform 24 is pressed by a first die 21 that defines the second aspheric portion 12. As a result, a glass member 25 is obtained as shown in FIG. 4(b). The glass member 25 thus formed corresponds to the glass lens 10. The outer diameter of the glass member 25 is determined by a cylindrical third die 23.

[0035] 5 and 6 show the results of a simulation using the finite element method of the spread of glass during molding of a glass lens 10 with an outer diameter of 4 mm. That is, the state of a preform 24 during molding of the glass lens 10 is shown.

[0036] In Fig. 5, (a1) and (a2) show example 1. In Fig. 5, (b1) and (b2) show example 2. In Fig. 5, (c1) and (c2) show example 3. In Fig. 6, (a1) and (a2) show example 4. In Fig. 6, (b1) and (b2) show example 5. In Fig. 6, (c1) and (c2) show example 6.

[0037] In Example 1, θ (see FIG. 1) was 55°, distance A (see FIG. 2) was 0.5 mm, and height B (see FIG. 2) was 0.1 mm. (a1) of FIG. 5 shows the state when the preform 24 comes into contact with the bottom of the recess (the portion for transferring the protrusion 14 of the flange portion 13) in the first mold 21. (a2) of FIG. 5 shows the state when the preform 24 has flowed further.

[0038] In Example 2, θ was 55°, distance A was 0.35 mm, and height B was 0.1 mm. Fig. 5(b1) shows the state when the preform 24 comes into contact with the bottom of the recess in the first mold 21. Fig. 5(b2) shows the state when the preform 24 has flowed further.

[0039] In Example 3, θ was 55°, distance A was 0.2 mm, and height B was 0.1 mm. Fig. 5(c1) shows the state when the preform 24 contacts the bottom of the recess in the first mold 21. Fig. 5(c2) shows the state when the preform 24 has flowed further.

[0040] As shown in (a1), (b1), and (c1) of Figure 5, when the preform 24 comes into contact with the bottom of the recess in the first mold 21, an air pocket 26 appears in the recess in the first mold 21. The air pocket 26 appears prominently in the example shown in (a1) of Figure 5, but becomes smaller as the value of B / A increases (see (b1) and (c1) of Figure 5).

[0041] FIG. 6 shows an example in which the value of B / A is increased compared to the example shown in FIG.

[0042] Specifically, in Example 4, θ was 55°, distance A was 0.35 mm, and height B was 0.1 mm (Note: same as Example 2). Figure 6 (a1) shows the state when the preform 24 contacts the bottom of the recess in the first mold 21. Figure 6 (a2) shows the state when the preform 24 has flowed further.

[0043] In Example 5, θ was 55°, distance A was 0.35 mm, and height B was 0.16 mm. Fig. 6(b1) shows the state when the preform 24 contacts the bottom of the recess in the first mold 21. Fig. 6(b2) shows the state when the preform 24 has flowed further.

[0044] In Example 6, θ was 55°, distance A was 0.35 mm, and height B was 0.24 mm. Fig. 6(c1) shows the state when the preform 24 contacts the bottom of the recess in the first mold 21. Fig. 6(c2) shows the state when the preform 24 has flowed further.

[0045] The values ​​for Examples 1 to 6 are shown in the table below.

[0046] [Table 1]

[0047] When comparing the examples shown in FIG. 5 with the examples shown in FIG. 6, it can be seen that the larger the value of B / A, the smaller the area of ​​the air pocket 26 becomes.

[0048] For example, in Examples 2 and 4, air pockets 26 are generated, but the size of the air pockets 26 is tolerable. In Examples 3 and 5, the size of the air pockets 26 is small. In Example 6, the generation of the air pockets 26 is hardly observed.

[0049] The fact that the area of ​​the air pocket 26 is smaller means that the trace of the air pocket 26 in the molded product (glass lens 10) is smaller, and the shape of the recess in the first mold 21 is accurately transferred to the preform 24. In other words, this leads to the tapered portion 15 being formed with high precision.

[0050] The reason why the area of ​​the air pocket 26 becomes smaller as the value of B / A increases will be described with reference to the explanatory diagram of FIG.

[0051] If the value of B / A is small, as shown in FIG. 7(a), the pressurized preform 24 comes into contact with the bottom of the recess in the first die 21 before coming into contact with the inner wall of the third die 23. In that case, an air pocket 26 is generated between the preform 24 and the bottom of the recess in the first die 21. As a result, the shape of the recess in the first die 21 is not accurately transferred to the preform 24. That is, the convex portion 14 (see FIG. 1) in the flange portion 13 of the glass lens 10 does not have the desired shape. That is, the accuracy of the shape of the tapered portion 15 decreases.

[0052] When the value of B / A is large, as shown in FIG. 7(b), the pressurized preform 24 comes into contact with the inner wall of the third die 23 before coming into contact with the bottom of the recess in the first die 21. By causing the preform 24 to flow in this state, the preform 24 is more likely to flow down evenly toward the bottom of the recess in the first die 21. As a result, the possibility of air pockets 26 occurring decreases. Thus, the convex portion 14 (see FIG. 1) in the flange portion 13 of the glass lens 10 has an approximately desired shape. That is, the tapered portion 15 is formed with high precision.

[0053] The method for molding the glass lens 10 and the shape of the mold used for molding will be explained again.

[0054] In the first die 21, a portion of the protrusion 14 of the flange portion 13 that forms the tapered portion 15 is formed as an inclined portion in which the normal direction from the inside to the outside of the die faces away from the optical axis. That is, it is formed so that the shape of the protrusion 14 can be transferred to the preform 24. The portion of the first die 21 is formed so as to satisfy B / A>0.2.

[0055] Using a mold including the first die 21 having the portion thus formed, the tapered portion 15 is molded with high transfer accuracy. EXAMPLES

[0056] A specific example of the glass lens 10 of the first embodiment will be described below. As shown in FIG. 8, this example uses a glass lens 10 in which the first aspherical portion 11 is convex toward the top and the second aspherical portion 12 is concave toward the bottom. The first aspherical portion 11 is called the convex surface, and the second aspherical portion 12 is called the concave surface. The approximate radius of curvature of the convex aspherical surface is 1.13 mm. The approximate radius of curvature of the concave aspherical surface is 1.76 mm. FIG. 8(a) shows the shape of a portion of the glass lens 10 of this example.

[0057] As described above, the shape shown in Fig. 8(a) was transferred to the preform 24 using a glass mold. The shape was such that θ=68.8° and B / A=0.52.

[0058] The shape of the formed glass lens 10 is shown in Fig. 8(b). As shown in Fig. 8(b), A = 0.226 mm, B = 0.117 mm. In addition, A' = 0.187 mm. B / A = 0.52, and B / A' = 0.63. In other words, both satisfy the condition B / A > 0.2.

[0059] Fig. 9 is a cross-sectional view showing a schematic example of a lens unit. The lens unit 30 shown in Fig. 9 has a structure in which a glass lens 10 and another lens element 32 are assembled into a lens barrel 33. Note that Fig. 9 shows a biconvex glass lens 10 as an example. The glass lens 10 and the lens element 32 are aligned such that the tapered portion of the glass lens 10 comes into contact with the tapered portion of the lens element 32.

[0060] As described above, the tapered portion of the glass lens 10 is formed into a desired shape with high precision, so that the glass lens 10 and the lens element 32 are aligned with high precision. That is, in the lens unit 30, decentering of the optical axes of the glass lens 10 and the lens element 32 can be easily prevented.

[0061] In the lens unit 30 illustrated in FIG. 9, the glass lens 10 is combined with one other lens element 32, but the glass lens 10 according to the present invention can also be applied to the production of a lens unit in which the glass lens 10 is combined with multiple other lens elements.

[0062] Although the embodiments and examples of the optical element of the present invention have been described, the optical elements of the above embodiments and examples can be applied (for example, incorporated) into various optical systems.

[0063] The optical system may include, for example, lenses that cooperate with the above optical elements, optical filters such as anti-reflection filters and bandpass filters, cover glasses, apertures, etc. However, these are merely examples, and the application of the above optical elements is not limited to these.

[0064] It is also envisioned that the above optical element will be applied to an imaging device such as a camera.

[0065] Although the present invention has been described in detail and with reference to specific embodiments, it will be apparent to those skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope of the invention. This application is based on Japanese Patent Application No. 2018-067047 filed on March 30, 2018, the contents of which are incorporated herein by reference. [Explanation of symbols]

[0066] 10 Glass Lens 11 First aspheric portion 12 Second aspheric portion 13 Flange 14 Convex 15 Tapered section 16 Side part 17 Bottom 21 First Type 22 Second Type 23 The third type 24 Preform 25 Glass materials 26 Gas trap 30 Lens unit 32 Lens Element 33 Telescope tube

Claims

1. The optical surface, a tapered portion located on an outer periphery side of the optical surface; a side surface portion located on an outer circumferential side of the tapered portion, a protrusion formed on the outer side of the optical surface and protruding from the optical surface side; the tapered portion has a tapered surface that is inclined with respect to the optical axis and that forms an inner wall of the convex portion, The side surface portion is formed as an outer wall of the protrusion, the tapered portion has a normal direction from inside the optical element through the tapered surface to the outside facing the optical axis side, In a cross section including the optical axis and passing through the tapered portion, a straight line perpendicular to the optical axis is drawn from an end point of the tapered portion on the optical axis side to the side portion, and a straight line distance A is drawn. A is a height of the tapered portion based on the straight line. B / A is greater than 0.2 and smaller than 10. A glass lens, an optical element.

2. The optical element of claim 1 , wherein B / A is greater than 0.

25.

3. The optical element of claim 2 , wherein B / A is greater than 0.

5.

4. 4. The optical element according to claim 1, wherein the value of B is 500 μm or less.

5. a flange portion on the outer side of the optical surface; 5. The optical element according to claim 1, wherein the convex portion is provided on the flange portion.

6. a bottom portion between the optical surface and the tapered portion; 6. The optical element according to claim 1, wherein the length of the bottom portion is 50 μm or more.

7. The optical element according to claim 6 , wherein an angle between the bottom and a horizontal axis perpendicular to the optical axis is equal to or greater than 0° and equal to or less than 30°.

8. The optical surface includes a first optical surface and a second optical surface opposed to the first optical surface, The convex portion protrudes from the second optical surface side.

8. The optical element according to claim 6 or 7.

9. An optical system comprising the optical element according to any one of claims 1 to 8.

10. An imaging device comprising the optical element according to any one of claims 1 to 8.

11. A manufacturing method for molding an optical element that is a glass lens using a glass mold, comprising the steps of: The molding of the glass lens is a first mold defining a first optical surface; a second mold defining a second optical surface opposing the first optical surface; and and a third mold that defines a side portion of the glass lens, and the preform is pressed using the third mold. The optical element includes a tapered portion located on an outer circumferential side of the second optical surface; a side surface portion located on an outer circumferential side of the tapered portion, The optical element has a cross section including the optical axis and passing through the tapered portion, and the linear distance A is a linear distance when a straight line perpendicular to the optical axis is drawn from an end point of the tapered portion on the optical axis side to the side portion, and the height of the tapered portion based on the straight line is B, where B / A is greater than 0.2 and smaller than 10.

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