Optical element, optical system, display device, and method for manufacturing optical element

Abstract

To easily provide an optical element that has high optical performance.SOLUTION: An optical element (10) has a substrate (11) including a curved surface, a plurality of projections (12) arranged in a first direction on the curved surface, and metal layers (13) provided on respective side faces of the plurality of projections. Each of the plurality of projections extends in a second direction perpendicular to the first direction. When the pitch of the plurality of projections is defined as P (nm), the absolute value of the maximum angle difference between central axes of each of the plurality of projections when seen from the second direction as |Δθs| (°), the maximum width in the first direction of each of the plurality of projections as W, and the maximum width of the metal layers in the first direction of each of the plurality of projections as Wm, the following conditional expressions are satisfied. 0<P≤300, 0≤|Δθs|≤15, and 0.3≤(W+Wm) / P≤0.6.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an optical element, an optical system, a display device, and a method for manufacturing an optical element. [Background technology]

[0002] In recent years, a technology has been proposed for using an optical element having a polarization selective transmission and reflection function on a curved surface in a display device such as a head mounted display (HMD) or an electronic viewfinder (EVF). By using an optical element having a polarization selective transmission and reflection function on a curved surface, it is possible to reduce the size of the optical system and improve the design freedom. Patent Document 1 discloses an optical element configured by bonding a film having a polarization selective transmission and reflection function to an optical surface having a curved surface of the optical element. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2022-165579 A Summary of the Invention [Problem to be solved by the invention]

[0004] The optical element disclosed in Patent Document 1 requires that the film be bonded while being stretched in order to bond the film to the curved optical surface. This may result in variations in the spacing, metal width, and direction of the thin metal wires within the optical surface, as well as reduced surface accuracy and reduced optical performance. In addition, the manufacturing process is complicated because a process of bonding the film to the optical element is required.

[0005] SUMMARY OF THE PRESENT EMBODIMENTS An object of the present invention is to provide an optical element that easily exhibits high optical performance. [Means for solving the problem]

[0006] An optical element according to one aspect of the present invention comprises a substrate including a curved surface, a plurality of convex portions arranged on the curved surface in a first direction, and a metal layer provided on a side surface of each of the plurality of convex portions, each of the plurality of convex portions extending in a second direction perpendicular to the first direction, wherein a pitch of the plurality of convex portions is P (nm), an absolute value of a maximum angular difference between central axes of each of the plurality of convex portions when viewed from the second direction is |Δθs| (°), a maximum width of each of the plurality of convex portions in the first direction is W, and a maximum width of the metal layer of each of the plurality of convex portions in the first direction is Wm, 0 <P≦300 0≦|Δθs|≦15 0.3≦(W+Wm) / P≦0.6 The following condition is satisfied.

[0007] Other objects and features of the present invention are illustrated in the following examples. Effect of the Invention

[0008] According to the present invention, it is possible to easily provide an optical element having high optical performance. [Brief description of the drawings]

[0009] [Figure 1] 1A and 1B are a cross-sectional view and a top view of an optical element in Example 1. [Diagram 2] 2 is an enlarged cross-sectional view of the optical element in the first embodiment. FIG. [Diagram 3] FIG. 2 is an explanatory diagram of optical elements in a comparative example and in Example 1. [Figure 4] 3A to 3C are explanatory diagrams of a manufacturing method of the optical element in the first embodiment. [Diagram 5] FIG. 11 is a cross-sectional view of an optical element in Example 2. [Figure 6] FIG. 2 is a cross-sectional view of a display device in each embodiment. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. Note that the drawings shown below may be drawn at a scale different from the actual scale in order to facilitate understanding of each embodiment.

[0011] The optical element of each embodiment has a polarization selective transmission / reflection function, and has a plurality of convex portions extending in one direction (the second direction, the vertical direction in FIG. 1(b)) on the surface of the curved shape, and a metal layer covering at least a part of each of the plurality of convex portions. With such a configuration, the optical element of each embodiment can reflect or transmit light depending on the polarization state of the light. The optical element of each embodiment has a structure in which, for example, thin metal wires (metal layer) are arranged at specific intervals, and reflects light vibrating in a direction parallel to the thin metal wires and transmits light vibrating in a direction perpendicular to the thin metal wires.

[0012] First, an overview of the optical element 10 in each embodiment will be described with reference to Figs. 1(a) and 1(b). Fig. 1(a) is a cross-sectional view of the optical element 10, and Fig. 1(b) is a top view of the optical element 10. The substrate 11 is, for example, a transparent substrate, and one optical surface (surface) 11a of the substrate 11 has a curved shape as shown in Fig. 1(a). A plurality of convex portions (uneven structure) 12 are arranged on the optical surface 11a. The metal layer 13 covers at least a part of the plurality of convex portions 12. As shown in Fig. 1(b), when viewed from the direction of the central axis Ac of the convex portions 12, the plurality of convex portions 12 covering the metal layer 13 are arranged approximately parallel to each other along a specific direction (first direction, the left-right direction in Figs. 1(a) and 1(b)). That is, the optical element 10 has a substrate 11 including a curved surface and a plurality of convex portions 12 arranged on the curved surface in the first direction.

[0013] In each embodiment, the plurality of convex portions 12 may be arranged on at least one surface (optical surface) of the substrate 11, or may be arranged on both surfaces of the substrate 11. In each embodiment, the plurality of surfaces of the substrate 11 may be curved, or may be curved. In each embodiment, the metal layer 13 may be formed on at least a part of each of the plurality of convex portions 12, or may be formed on only one side surface or only the upper surface (top) of each of the plurality of convex portions 12. Alternatively, the metal layer 13 may be formed on only both side surfaces or both side surfaces and the upper surface of each of the plurality of convex portions 12. However, at least a part of the optical surface (corresponding to the concave portion) located between two adjacent convex portions 12 is not covered with the metal layer 13.

[0014] Next, the configuration of the optical element 10 will be described in detail with reference to Fig. 2. Fig. 2 is an enlarged cross-sectional view of a region α in Fig. 1(a).

[0015] In each embodiment, when the pitch (the distance between two adjacent convex portions) of the plurality of convex portions 12 is P (nm), the following conditional formula (1) is satisfied.

[0016] 0 <P≦300 ···(1) If the pitch P exceeds 300 nm, unnecessary diffracted light is generated, which is undesirable.

[0017] Preferably, the numerical range of conditional expression (1) is set as shown in the following conditional expression (1a).

[0018] 20≦P≦250 (1a) More preferably, the numerical range of conditional expression (1) is set as shown in the following conditional expression (1b).

[0019] 50≦P≦150 (1b) As shown in FIG. 2, the points (intersections) where the side surfaces 12a, 12b of the convex portion 12 intersect with the optical surface 11a are Sa and Sb, respectively, the midpoint between the points Sa and Sb is Sc, and the distance from the midpoint Sc to the apex (highest position) of the convex portion 12 (the height of the convex portion 12) is H. Also, the midpoint between the points Ta, Tb on the side surfaces 12a, 12b of the convex portion 12 at a position 0.1H downward from the apex of the convex portion 12 is Tc. Also, the imaginary line passing through Sc-Tc is the central axis Ac. Note that the direction of the central axis Ac includes the direction of the central axis of any of the multiple convex portions 12, but the direction along the central axis of one representative convex portion (for example, the center of the optical element 10) among the multiple convex portions 12 is referred to as the central axis direction. In this case, in each embodiment, the absolute value |Δθs|(°) of the maximum angle difference (the maximum value of the angle difference between the central axes of any two convex parts) of each of the central axes Ac of the multiple convex parts 12 when viewed from the second direction satisfies the following conditional formula (2). Here, the "angle" refers to, for example, the angle between the central axis of the central convex part in the optical element 10 and the reference axis (angle is 0 degrees), and the angle is a positive value on one side relative to this and a negative value on the other side.

[0020] 0≦|Δθs|≦15 (2) Preferably, the numerical range of conditional expression (2) is set as shown in the following conditional expression (2a).

[0021] 0≦|Δθs|≦10 (2a) More preferably, the numerical range of conditional expression (2) is set as in the following conditional expression (2b).

[0022] 0≦|Δθs|≦5 (2b) In each embodiment, when the maximum width in the first direction of each of the multiple protrusions 12 is W (nm) and the maximum width in the first direction of each of the multiple protrusions 12 of the metal layer 13 (metal layer 13 formed on the side surface) is Wm (nm), the following conditional formula (3) is satisfied.

[0023] 0.3≦(W+Wm) / P≦0.6 (3) If the lower limit of condition (3) is exceeded, the S-polarized light reflectance decreases, degrading the optical performance, which is undesirable, whereas if the upper limit of condition (3) is exceeded, the P-polarized light transmittance decreases, degrading the optical performance, which is undesirable.

[0024] Preferably, the numerical range of conditional expression (3) is set as shown in the following conditional expression (3a).

[0025] 0.2≦(W+Wm) / P≦0.5 (3a) More preferably, the numerical range of conditional expression (3) is set as in the following conditional expression (3b).

[0026] 0.1≦(W+Wm) / P≦0.4 (3b) In addition, when a metal layer 13 is formed on both side surfaces 12a, 12b of the protrusion 12, the maximum width Wm of the metal layer 13 in conditional formulas (3), (3a), and (3b) is the sum of the widths formed on the side surfaces 12a and 12b.

[0027] The metal layer 13 is preferably made of a material having a high reflectance in the visible light region (for example, wavelengths of 400 to 700 nm). The metal layer 13 is, for example, an alloy containing at least one of aluminum, silver, copper, chromium, and gold as a main component. From the viewpoints of durability and low cost, the metal layer 13 is more preferably made of aluminum.

[0028] In each embodiment, when the absolute value of the maximum half open angle of the curved surface of the optical element is |θl| (°), it is preferable to satisfy the following conditional expression (4).

[0029] 0<|θl|<40 (4) Here, the maximum half aperture angle is the maximum value of the angle between the center line (optical axis) of the optical element and the surface normal at any position within the effective diameter of the optical element. If the upper limit of conditional expression (4) is exceeded, the in-plane variation of metal layer 13 becomes large, which is not preferable.

[0030] More preferably, the numerical range of conditional expression (4) is set as in the following conditional expression (4a).

[0031] 0<|θl|<30 (4a) More preferably, the numerical range of conditional expression (4) is set as in the following conditional expression (4b).

[0032] 0<|θl|<25 (4b) The substrate 11 and the protrusions 12 are preferably made of a single member (the same material). The substrate 11 and the protrusions 12 are preferably made of a resin material whose main component is a thermoplastic resin, such as a polycarbonate resin, a polymethacrylic acid acrylic resin, or a cycloolefin polymer resin. It is more preferable to use a cycloolefin polymer resin that has low water absorption. Here, the main component means that the content is 51% or more by mass, and preferably 90% or more.

[0033] Example 1 Next, the optical element 10 in Example 1 will be described. The optical element 10 has a substrate 11 having a spherical shape as shown in Fig. 1. One surface (optical surface 11a) of the substrate 11 has a spherical shape with a radius of curvature of 115.2 mm, and a maximum half open angle |θl| of 10°. In addition, on the optical surface 11a, convex portions 12 are formed with a pitch P=130 nm, a height H of the convex portion=170 nm, and a maximum width W of the convex portion 12=25 nm.

[0034] In this embodiment, the pitch P is 300 nm or less, so that the generation of unnecessary diffracted light can be suppressed. In addition, (W+Wm) / P is 0.37, so that a good polarization selective transmission reflection function can be obtained. In addition, in this embodiment, a spherical substrate 11 as shown in FIG. 3(b) is used. The maximum half open angle |θl| at the end of the effective area (effective diameter) of the optical element 10 is 10°, so that the in-plane variation can be suppressed.

[0035] 4(a) and (b) are explanatory diagrams of a manufacturing method of the optical element 10 in this embodiment. As shown in FIG. 4(a), the substrate 11 and the convex portion 12 are molded by injection molding using a cycloolefin polymer resin. In the injection molding, an injection molding piece 14 on which the optical surface 11a and the inverted convex portion 14a of the convex portion 12 are formed is used. The inverted convex portion 14a can be formed on the curved shape of the injection molding piece 14 by forming a photoresist film on the injection molding piece 14, patterning it by a two-beam interference exposure method, and dry etching it. The injection molding piece 14 having the inverted convex portion 14a can be incorporated into an injection molding device, and a substrate 11 on which the convex portion 12 is formed on the optical surface 11a by injection molding can be obtained.

[0036] In this manner, in this embodiment, the substrate 11 and the multiple protrusions 12 are integrally molded by injection molding. Next, a metal layer 13 is formed on at least a portion of each of the multiple protrusions 12 by performing vacuum deposition from an oblique direction relative to the direction of the central axis Ac of each of the multiple protrusions 12. In this manner, the optical element 10 can be manufactured.

[0037] FIG. 3(a) shows the configuration of the substrate 110 and the plurality of protrusions 120 as a comparative example in which |Δθs} does not satisfy conditional expression (2). Meanwhile, FIG. 3(b) shows the configuration of this embodiment in which |Δθs| satisfies conditional expression (2). The plurality of protrusions 120 in FIG. 3(a) cannot be stably molded because the central axis Ac10 and the central axis Ac20 are not parallel. Meanwhile, the plurality of protrusions 12 in FIG. 3(b) can be stably molded because the central axis Ac1 and the central axis Ac2 are approximately parallel. In this way, the substrate 11 and the protrusions 12 are integrally molded by injection molding, thereby making it possible to reduce costs.

[0038] The metal layer 13 that covers a part of the protrusion 12 is formed by obliquely depositing aluminum by vacuum deposition from a direction at an angle θd with respect to the central axis Ac of the protrusion 12 so as to have a maximum width Wm = 23 nm. This allows the metal layer 13 to be formed so as to cover at least a part of the protrusion 12.

[0039] The degree of polarization was evaluated as the polarization selective transmission and reflection function of the optical element 10 of this example. Light was incident from the convex portion 12 side, and the parallel transmittance Tp and the crossed transmittance Ts at a wavelength of 550 nm were used to calculate the degree of polarization (%) as follows:

[0040] Polarization degree (%)=(Tp-Ts)) / (Tp+Ts)×100 The results are shown in Table 1.

[0041] [Table 1]

[0042] As shown in Table 1, a high degree of polarization of 99.9% or more is achieved at both the center and end portions of the optical element 10. With this configuration, the optical element 10 can achieve good optical performance at low cost without reducing the surface accuracy of the optical surface 11a.

[0043] In this embodiment, the two-beam interference exposure method is used in the process of forming the uneven structure on the curved surface of the injection molded piece, but this embodiment is not limited to this, and for example, electron beam exposure method may be used. Also, in this embodiment, the metal layer 13 is formed by the vacuum deposition method, but this embodiment is not limited to this, and sputtering method or wet method may be used.

[0044] Example 2 Next, the optical element 20 in Example 2 will be described. FIG. 5 is a cross-sectional view of the optical element 20. As shown in FIG. 5, the optical element 20 has a substrate 21 with an aspherical shape. One surface (optical surface 21a) of the substrate 21 has an aspherical shape, and the maximum half open angle |θl|=20°. Furthermore, on the optical surface 21a, convex portions 22 are formed with a pitch P=100 nm, a height H of the convex portions 22=139 nm, and a maximum width W of the convex portions 22=27 nm. The metal layer 23 that covers at least a part of the convex portions 22 is formed so as to have a maximum width Wm=30 nm.

[0045] In this embodiment, the pitch P is 300 nm or less, so that the generation of unnecessary diffracted light can be suppressed. In addition, (W+Wm) / P is 0.57, so that good optical performance can be obtained. In addition, the maximum half-open angle |θl| is 20°, so that the in-plane variation can be suppressed.

[0046] The optical performance of the optical element 20 is shown in Table 2.

[0047] [Table 2]

[0048] As shown in Table 2, a high degree of polarization of 99.9% or more is achieved at both the center and the end of the optical element 20. With such a configuration, the optical element 20 can obtain good optical performance at low cost without reducing the surface accuracy of the optical surface 21a.

[0049] In each embodiment, only the metal layers 13, 23 are provided on the protrusions 12, 22, but an adhesive layer may be formed between the protrusions 12, 22 and the metal layers 13, 23, and a protective layer may be formed on the metal layers 13, 23. The adhesive layer and the protective layer are not limited to being formed obliquely, and may be formed at θd=0°.

[0050] Next, a display device 40 including the optical element of each embodiment will be described with reference to Fig. 6. Fig. 6 is an explanatory diagram of the display device 40. The display device 40 has an optical system 30 and a display element (image display surface) 33. That is, the display device 400 has the optical element of each embodiment and the display element 33 that emits light toward the optical element.

[0051] The optical system 30 is an observation optical system that guides a light beam from a display element 33 to an observer, and includes a first optical element 31 having optical surfaces 31a and 31b, and a second optical element 32 having optical surfaces 32a and 32b. For example, a plurality of convex portions 12 (or a plurality of convex portions 22) in each embodiment are formed on the optical surface 31b of the first optical element 31. A λ / 4 plate (not shown) is disposed between the optical surface 31b and the optical surface 32b. The λ / 4 plate is, for example, bonded to the optical surface 32a.

[0052] According to each embodiment, it is possible to easily provide an optical element, an optical system, a display device, and a method for manufacturing an optical element having high optical performance.

[0053] The disclosure of each embodiment includes the following configurations and methods. (Configuration 1) A substrate including a curved surface; A plurality of convex portions arranged in a first direction on the curved surface; a metal layer provided on each side surface of the plurality of protrusions; Each of the plurality of protrusions extends in a second direction perpendicular to the first direction, Let P (nm) be the pitch of the multiple protrusions, |Δθs| (°) be the absolute value of the maximum angular difference between the central axes of the multiple protrusions when viewed from the second direction, W be the maximum width of each of the multiple protrusions in the first direction, and Wm be the maximum width of the metal layer in the first direction of each of the multiple protrusions. 0 <P≦300 0≦|Δθs|≦15 0.3≦(W+Wm) / P≦0.6 An optical element characterized by satisfying the following conditional expression: (Configuration 2) When the absolute value of the maximum half open angle of the curved surface is |θl| (°), 0<|θl|<40 2. The optical element according to configuration 1, which satisfies the following condition: (Configuration 3) 3. The optical element according to claim 1, wherein the substrate and the plurality of convex portions are made of the same material. (Configuration 4) 4. The optical element according to any one of configurations 1 to 3, wherein the substrate and the plurality of convex portions are made of a resin material. (Configuration 5) 5. The optical element according to any one of configurations 1 to 4, wherein the substrate and the plurality of convex portions are integrally formed. (Configuration 6) 6. The optical element according to any one of configurations 1 to 5, wherein a main component of the metal layer is at least one of aluminum, silver, copper, chromium, and gold. (Configuration 7) 7. The optical element according to any one of configurations 1 to 6, wherein the plurality of convex portions are arranged only in the first direction. (Configuration 8) The optical element according to any one of configurations 1 to 7, wherein the first and second projections are provided on the apexes of the plurality of projections. (Configuration 9) An optical system having a plurality of optical elements, 9. An optical system, wherein at least one of the plurality of optical elements is an optical element according to any one of configurations 1 to 8. (Configuration 10) 9. A display device comprising the optical element according to any one of configurations 1 to 8, and a display element that emits light toward the optical element. (Method 1) A step of integrally molding a substrate including a curved surface and a plurality of convex portions arranged in a first direction on the curved surface by injection molding; forming a metal layer on each side surface of the plurality of protrusions by performing vacuum deposition from an oblique direction with respect to a direction of a central axis of each of the plurality of protrusions; Each of the plurality of protrusions extends in a second direction perpendicular to the first direction, Let P (nm) be the pitch of the multiple protrusions, |Δθs| (°) be the absolute value of the maximum angular difference between the central axes of the multiple protrusions when viewed from the second direction, W be the maximum width of each of the multiple protrusions in the first direction, and Wm be the maximum width of the metal layer in the first direction of each of the multiple protrusions. 0 <P≦300 0≦|Δθs|≦15 0.3≦(W+Wm) / P≦0.6 The method for producing an optical element according to the present invention is characterized in that the following conditional expressions are satisfied:

[0054] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0055] 10, 20 Optical elements 11, 21 Board 12, 22 Convex 13, 23 metal layer

Claims

1. A substrate including a curved surface; A plurality of convex portions arranged in a first direction on the curved surface; a metal layer provided on each side surface of the plurality of protrusions; Each of the plurality of protrusions extends in a second direction perpendicular to the first direction, Let P be the pitch of the plurality of protrusions (nm), |Δθs| (°) be the absolute value of the maximum angular difference between the central axes of the plurality of protrusions when viewed from the second direction, W be the maximum width of each of the plurality of protrusions in the first direction, and Wm be the maximum width of the metal layer in the first direction of each of the plurality of protrusions. 0<P≦300 0≦|Δθs|≦15 0.3≦(W+Wm) / P≦0.6 An optical element characterized by satisfying the following conditional expression:

2. When the absolute value of the maximum half open angle of the curved surface is |θl| (°), 0<|θl|<40 2. The optical element according to claim 1, which satisfies the following condition:

3. 3. The optical element according to claim 1, wherein the substrate and the plurality of convex portions are made of the same material.

4. 3. The optical element according to claim 1, wherein the substrate and the plurality of convex portions are made of a resin material.

5. 3. The optical element according to claim 1, wherein the substrate and the plurality of convex portions are integrally formed.

6. 3. The optical element according to claim 1, wherein a main component of the metal layer is at least one of aluminum, silver, copper, chromium, and gold.

7. The optical element according to claim 1 , wherein the plurality of convex portions are arranged only in the first direction.

8. 3. The optical element according to claim 1, wherein the first and second projections are provided on the tops of the plurality of projections.

9. An optical system having a plurality of optical elements, 3. An optical system, wherein at least one of the plurality of optical elements is the optical element according to claim 1.

10. 3. A display device comprising: the optical element according to claim 1; and a display element that emits light toward the optical element.

11. a step of integrally molding a substrate including a curved surface and a plurality of convex portions arranged in a first direction on the curved surface by injection molding; forming a metal layer on each side surface of the plurality of protrusions by performing vacuum deposition from an oblique direction with respect to a direction of a central axis of each of the plurality of protrusions; Each of the plurality of protrusions extends in a second direction perpendicular to the first direction, Let P be the pitch of the plurality of protrusions (nm), |Δθs| (°) be the absolute value of the maximum angular difference between the central axes of the plurality of protrusions when viewed from the second direction, W be the maximum width of each of the plurality of protrusions in the first direction, and Wm be the maximum width of the metal layer in the first direction of each of the plurality of protrusions. 0<P≦300 0≦|Δθs|≦15 0.3≦(W+Wm) / P≦0.6 The method for producing an optical element according to the present invention is characterized in that the following conditional expressions are satisfied:

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