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

Abstract

The invention discloses an optical element, an optical system, a display device, and a manufacturing method of the optical element. The optical element includes a substrate having a curved surface, a plurality of protrusions arranged on the curved surface in a first direction, and 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. A predetermined inequality is satisfied.

Description

Technical Field

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

[0002] Recently, a technology for using an optical element with a polarization selective transmissive reflection function on a curved surface in a display device such as a head-mounted display (HMD) or an electronic viewfinder (EVF) has been proposed. Using an optical element with a polarization selective transmissive reflection function on a curved surface can reduce the size of the optical system and increase the degree of freedom in design. Japanese Patent Publication No. 2022-165579 discloses an optical element configured by bonding a film with a polarization selective transmissive reflection function to an optical surface having a curved surface of the optical element. Summary of the invention

[0003] An optical element according to one aspect of the present disclosure includes a substrate having a curved surface, a plurality of convex portions arranged on the curved surface in a first direction, and a metal layer provided on each side surface of the plurality of convex portions. Each of the plurality of convex portions extends in a second direction perpendicular to the first direction. The following inequality may be satisfied:

[0004] 0≤|Δθs|≤15

[0005] wherein |Δθs| (°) is the absolute value of the maximum angular difference between the central axes of the plurality of convex portions when viewed from the second direction. An optical system and a display device each having the above-described optical element also constitute another aspect of the present disclosure.

[0006] Further features of various embodiments of the present disclosure will become apparent from the following description of the embodiments with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0007] Figure 1A and Figure 1B are a cross-sectional view and a top view of an optical element according to Example 1.

[0008] Figure 2 is an enlarged cross-sectional view of an optical element according to Example 1.

[0009] Figure 3A and 3B Optical elements according to Comparative Example and Example 1 are described.

[0010] Figure 4A and 4B A method of manufacturing an optical element according to Example 1 is described.

[0011] Figure 5 is a cross-sectional view of an optical element according to Example 2.

[0012] Figure 6 is a cross-sectional view of a display device according to each example. DETAILED DESCRIPTION

[0013] Now referring to the accompanying drawings, a detailed description of examples according to the present disclosure will be given. In order to facilitate understanding of each example, the drawings shown below may be drawn in a different scale from the actual drawings.

[0014] The optical element according to each example has a polarization selective transflective function and includes a first direction (a second direction or a second direction) on a surface of a curved shape. Figure 1B A plurality of protrusions extending in a direction (vertical direction in the middle), and a metal layer covering at least a portion of each of the plurality of protrusions. Due to this configuration, the optical element according to each example can reflect or transmit light according to the polarization state of the light. The optical element according to each example has, for example, a structure in which thin metal wires (metal layers) are arranged at specific intervals (or distances), and light vibrating in a direction parallel to the thin metal wires is reflected, and light vibrating in a direction perpendicular to the thin metal wires is transmitted.

[0015] Reference now Figure 1A and Figure 1B , a description will be given of an overview of the optical element 10 according to each example. Figure 1A is a cross-sectional view of the optical element 10, and Figure 1B 1 is a top view of the optical element 10. The substrate 11 is, for example, a transparent substrate. Figure 1A As shown in FIG. 1 , one optical surface (front surface) 11a of the substrate 11 has a curved shape. A plurality of convex portions (uneven structures) 12 are arranged on the optical surface 11a. The metal layer 13 covers at least a portion of the plurality of convex portions 12. Figure 1B As shown in FIG. 1 , when viewed from the direction of the central axis Ac of the convex portion 12, the plurality of convex portions 12 covered with the metal layer 13 are arranged along a specific direction (a first direction or Figure 1A and Figure 1B That is, the optical element 10 includes a substrate 11 including a curved surface and a plurality of convex portions 12 arranged on the curved surface in a first direction.

[0016] In each example, the plurality of protrusions 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 example, at least one surface of the substrate 11 may be a curved surface, or both surfaces of the substrate 11 may be curved surfaces. In each example, the metal layer 13 may be formed on at least a portion of each of the plurality of protrusions 12, and may be formed only on one side surface of each of the protrusions 12 or only on the top surface (top) of each of the protrusions 12. Alternatively, the metal layer 13 may also be formed only on the two side surfaces of each of the protrusions 12 or on the two side surfaces and the top surface. However, at least a portion of the optical surface (corresponding to the recess) located between two adjacent protrusions 12 is not covered by the metal layer 13.

[0017] Reference now Figure 2 , a detailed description will be given of the configuration of the optical element 10. Figure 2 yes Figure 1A An enlarged cross-sectional view of region α in FIG.

[0018] In each example, the following inequality (1) can be satisfied:

[0019] 0 < P ≤ 300 (1)

[0020] Here, P (nm) is the pitch of the plurality of protrusions 12 (the distance between two adjacent protrusions).

[0021] In the case where the pitch P becomes larger than 300 nm, unnecessary diffracted light is generated.

[0022] Inequality (1) can be replaced by the following inequality (1a):

[0023] 20≤P≤250(1a)

[0024] Inequality (1) can be replaced by the following inequality (1b):

[0025] 50≤P≤150(1b)

[0026] like Figure 2As shown in , Sa, Sb are the points (intersections) where the side surfaces 12a and 12b of each convex portion 12 intersect with the optical surface 11a, Sc is the midpoint between points Sa and Sb, and H is the distance from the midpoint Sc to the top (highest position) of the convex portion 12 (the height of the convex portion 12). Tc is the midpoint of points Ta and Tb on the side surfaces 12a and 12b of the convex portion 12 at a position 0.1H downward from the top of the convex portion 12. The imaginary line passing through Sc-Tc is the central axis Ac. The direction of the central axis Ac includes the direction of the central axis of any convex portion among the plurality of convex portions 12, and the direction along the central axis of a representative convex portion (for example, the center of the optical element 10) among the plurality of convex portions 12 is referred to as the central axis direction. Each of the first direction and the second direction is perpendicular to the central axis Ac of the convex portion at the center of the optical axis 10 as a reference axis.

[0027] At this time, in each example, the absolute value |Δθs| (°) of the maximum angle difference of the convex portion 12 when viewed from the second direction (the maximum value of the angle difference between the central axes of any two convex portions) can satisfy the following inequality (2). Here, "angle" indicates the angle between the reference axis (angle 0 degrees) of the central axis of the central convex portion in the optical element 10 and another convex portion, for example, and the angle is positive on one side and negative on the other side:

[0028] 0 ≤ |Δθs| ≤ 15 (2)

[0029] Inequality (2) can be replaced by the following inequality (2a):

[0030] 0≤|Δθs|≤10(2a)

[0031] Inequality (2) can be replaced by the following inequality (2b):

[0032] 0≤|Δθs|≤5(2b)

[0033] In each example, the following inequality (3) can be satisfied:

[0034] 0.3 ≤ (W + Wm) / P ≤ 0.6 (3)

[0035] Wherein W (nm) is the maximum width of the plurality of protrusions 12 in the first direction, and Wm (nm) is the maximum width of the metal layer 13 (the metal layer 13 formed on the side surface) of the plurality of protrusions 12 in the first direction.

[0036] When the value becomes lower than the lower limit of inequality (3), the S-polarized light reflectance and optical performance decrease. On the other hand, when the value becomes higher than the upper limit of inequality (3), the P-polarized light transmittance and optical performance decrease.

[0037] Inequality (3) can be replaced by the following inequality (3a):

[0038] 0.2≤(W+Wm) / P≤0.5(3a)

[0039] Inequality (3) can be replaced by the following inequality (3b):

[0040] 0.1≤(W+Wm) / P≤0.4(3b)

[0041] When the metal layer 13 is formed on both side surfaces 12a and 12b of the protrusion 12, the maximum width Wm of the metal layer 13 in the inequalities (3), (3a), and (3b) is the sum of the widths formed on the side surfaces 12a and 12b.

[0042] The metal layer 13 may be made of a material having high reflectivity in the visible light region (e.g., a wavelength of 400 to 700 nm). The metal layer 13 is made of, for example, an alloy whose main component is at least one of aluminum, silver, copper, chromium, and gold. From the perspective of durability and low cost, the metal layer 13 may be made of aluminum.

[0043] In each example, the following inequality (4) can be satisfied:

[0044] 0 < |θl| < 40 (4)

[0045] where |θl| (°) is the absolute value of the maximum half-opening angle of the curved surface of the optical element.

[0046] Here, the maximum half angle is the maximum angle between the surface normal at any position within the effective diameter of the optical element and the center line (optical axis) of the optical element. When the value becomes higher than the upper limit of inequality (4), the in-plane variation of metal layer 13 increases.

[0047] Inequality (4) can be replaced by the following inequality (4a):

[0048] 0<|θl|<30(4a)

[0049] Inequality (4) can be replaced by the following inequality (4b):

[0050] 0<|θl|<25(4b)

[0051] The substrate 11 and the protrusion 12 may be made of a single member (same material). The substrate 11 and the protrusion 12 may be made of a resin material whose main component is a thermoplastic resin (such as a polycarbonate resin, a polymethacrylic acid resin, and a cycloolefin polymer resin). The cycloolefin polymer resin may have low water absorption. Here, the main component means containing 51% or more, or 90% or more by mass ratio.

[0052] Example 1

[0053] A description will now be given of an optical element 10 according to Example 1. As shown in FIG. 1 , the optical element 10 includes a substrate 11 having a spherical shape. 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°. The optical surface 11a has a convex portion 12 with a pitch P = 130 nm, a height H of the convex portion of 170 nm, and a maximum width W of the convex portion 12 of 25 nm.

[0054] In this example, the pitch P is 300 nm or less, so that the generation of unnecessary diffracted light can be suppressed. In addition, since (W+Wm) / P is 0.37, a good polarization selective transflection function can be obtained. Figure 3B As shown in , this example uses a substrate 11 having a spherical shape. At the end of the effective area (effective diameter) of the optical element 10, the maximum half-open angle |θl| is 10°, and the in-plane variation can be suppressed.

[0055] Figure 4A and Figure 4B A method for manufacturing the optical element 10 according to this example is described. Figure 4A As shown in , the substrate 11 and the convex portion 12 are molded by injection molding using a cycloolefin polymer resin. In the injection molding, an injection-molded piece 14 formed with an optical surface 11a and an inverted convex portion 14a of the convex portion 12 is used. A photoresist is formed on the injection-molded piece 14, and the inverted convex portion 14a can be formed on the curved shape of the injection-molded piece 14 by patterning and dry etching using a double-beam interference exposure method. The injection-molded piece 14 having the inverted convex portion 14a is incorporated into an injection molding apparatus, and the substrate 11 having the convex portion 12 formed on the optical surface 11a by injection molding can be obtained.

[0056] Therefore, in this example, the substrate 11 and the plurality of convex portions 12 are integrally molded by injection molding. Next, a metal layer 13 is formed on at least a portion of each of the convex portions 12 by performing vacuum deposition from an inclined direction relative to the direction of the central axis Ac of each of the convex portions 12. Thus, the optical element 10 can be manufactured.

[0057] Figure 3A The diagram shows the arrangement of the substrate 110 and the plurality of protrusions 120 according to a comparative example in which |Δθs| does not satisfy the inequality (2). Figure 3B The diagram shows the configuration of this example in which |Δθs| satisfies inequality (2). Since the central axis Ac10 is not parallel to the central axis Ac20, Figure 3AThe plurality of convex portions 120 in the mold cannot be stably formed. On the other hand, since the central axis Ac1 is substantially parallel to the central axis Ac2, Figure 3B The plurality of convex portions 12 in the substrate 11 can be stably molded. Therefore, the substrate 11 and the convex portions 12 are integrally molded by injection molding, which allows cost reduction.

[0058] Each metal layer 13 covering a portion of each convex portion 12 is formed by vacuum deposition to obliquely deposit aluminum at an angle θd relative to the central axis Ac of the convex portion 12 so that the maximum width Wm is 23 nm. Thus, the metal layer 13 can be formed to cover at least a portion of each convex portion 12.

[0059] For the optical element 10 according to the present example, the polarization degree was evaluated as a polarization selective transflection function. Light was incident from the convex portion 12 side, and the polarization degree (%) was evaluated as follows using the parallel transmittance Tp and the orthogonal transmittance Ts at a wavelength of 550 nm.

[0060] Polarization degree (%) = (Tp-Ts) / (Tp+Ts)×100

[0061] Table 1 shows the results.

[0062]

[0063]

[0064] As shown in Table 1, the optical element 10 has a high polarization degree of 99.9% or more at both the central portion and the end portions. Due to this structure, the optical element 10 can obtain good optical performance at low cost without reducing the surface accuracy of the optical surface 11a.

[0065] This example uses a double beam interference exposure method in the process of manufacturing an uneven structure on the curved surface shape of the injection molded part, but is not limited to this example, and an electron beam exposure method can be used. This example forms the metal layer 13 by vacuum deposition, but is not limited to this example, and a sputtering method or a wet method can be used.

[0066] Example 2

[0067] A description will now be given of an optical element 20 according to Example 2. Figure 5 is a cross-sectional view of the optical element 20. Figure 5As shown in , the optical element 20 includes a substrate 21 having an aspherical shape. One surface (optical surface 21a) of the substrate 21 has an aspherical shape, and the maximum half-open angle is |θl|=20°. The convex portions 22 having a pitch P of 100nm, a height H of each convex portion 22 of 139nm, and a width W of each convex portion 22 of 27nm are formed on the optical surface 21a. The metal layer 23 covering at least a portion of each convex portion 22 is deposited so that the maximum width Wm is 30nm.

[0068] In this example, the pitch P is 300 nm or less, so that the generation of unnecessary diffracted light can be suppressed. In addition, since (W+Wm) / P is 0.57, good optical performance can be obtained. The maximum half-open angle |θl| is 20°, and the in-plane variation can be suppressed.

[0069] Table 2 shows the optical performance of the optical element 20.

[0070]

[0071] As shown in Table 2, the optical element 20 has a high polarization degree of 99.9% or more at both the central portion and the end portions. Due to this structure, the optical element 20 can obtain good optical performance at low cost without reducing the surface accuracy of the optical surface 21a.

[0072] Each embodiment forms the metal layers 13 and 23 only on the protrusions 12 and 22, but an adhesive layer may be formed between each of the protrusions 12 and 22 and each of the metal layers 13 and 23, and a protective layer may be formed on each of the metal layers 13 and 23. In addition, the adhesive layer and the protective layer are not limited to being formed obliquely, and may be formed at θd = 0°.

[0073] Reference now Figure 6 , a description will be given of a display device 40 including an optical element according to each example. Figure 6 The display device 40 is explained. The display device 40 includes the optical system 30 and the display element (image display surface) 33. That is, the display device 400 includes the optical element according to each example, and the display element 33 configured to emit light toward the optical element.

[0074] The optical system 30 is an observation optical system configured to guide 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 concave portions 22) according to each example are formed on the optical surface 31b of the first optical element 31. A quarter wave plate not shown is disposed between the optical surfaces 31b and 32b. For example, the quarter wave plate is bonded to the optical surface 32a.

[0075] Each example can easily provide an optical element having high optical performance, an optical system, a display device, and a method for manufacturing the optical element.

[0076] Although the present disclosure has described examples, it is to be understood that some examples are not limited to the disclosed examples.The scope of the following appended claims is to be accorded the broadest description so as to encompass all such modifications and equivalent structures and functions.

Claims

1. An optical element, comprising: a substrate having a curved surface; a plurality of protrusions arranged on the curved surface in a first direction; as well as a metal layer provided on each side surface of the plurality of protrusions, It is characterized in that each of the plurality of protrusions extends in a second direction perpendicular to the first direction, The following inequalities are satisfied: 0 ≤ |Δθs| ≤ 15 Here, |Δθs| (°) is the absolute value of the maximum angular difference between the central axes of the plurality of convex portions when viewed from the second direction.

2. The optical element according to claim 1, characterized in that The following inequalities are satisfied: 0 < P ≤ 300 Wherein P (nm) is the pitch of the plurality of protrusions.

3. The optical element according to claim 1, characterized in that The inequality is satisfied: 0.3 ≤ (W + Wm) / P ≤ 0.6 Wherein P (nm) is the pitch of the plurality of protrusions, W is the maximum width of the plurality of protrusions in the first direction, and Wm is the maximum width of the metal layer of the plurality of protrusions in the first direction.

4. The optical element according to claim 2, characterized in that The inequality is satisfied: 0.3 ≤ (W + Wm) / P ≤ 0.6 Wherein W is the maximum width of the plurality of protrusions in the first direction, and Wm is the maximum width of the metal layer of the plurality of protrusions in the first direction.

5. The optical element according to claim 1, characterized in that The following inequalities are satisfied: 0 < |θl| < 40 Wherein |θl| (°) is the absolute value of the maximum half-opening angle of the curved surface.

6. The optical element according to claim 1, characterized in that The substrate and the plurality of protrusions are made of the same material.

7. The optical element according to claim 1, characterized in that The substrate and the plurality of protrusions are made of a resin material.

8. The optical element according to claim 1, characterized in that The substrate and the plurality of protrusions are integrated.

9. The optical element according to claim 1, characterized in that The main component of the metal layer is at least one of aluminum, silver, copper, chromium and gold.

10. The optical element according to claim 1, characterized in that The plurality of protrusions are arranged only in the first direction.

11. The optical element according to claim 1, characterized in that The plurality of protrusions are provided on tops of the plurality of protrusions.

12. An optical system comprising: Multiple optical components, It is characterized in that at least one optical element among the plurality of optical elements is the optical element according to any one of claims 1 to 11.

13. A display device, comprising: The optical element according to any one of claims 1 to 11; as well as A display element is configured to emit light toward the optical element.

14. A method for manufacturing an optical element, comprising the following steps: integrally molding a substrate and a plurality of protrusions by injection molding, the substrate including a curved surface, the plurality of protrusions being arranged on the curved surface in a first direction; forming a metal layer on each side surface of the plurality of convex portions by performing vacuum deposition from an oblique direction with respect to the direction of each central axis of the plurality of convex portions, It is characterized in that each of the plurality of protrusions extends in a second direction perpendicular to the first direction, The following inequalities are satisfied: 0 ≤ |Δθs| ≤ 15 Here, |Δθs| (°) is the absolute value of the maximum angular difference between the central axes of the plurality of convex portions when viewed from the second direction.

15. An optical element, comprising: a substrate having a curved surface; a plurality of protrusions arranged on the curved surface in a first direction; as well as a metal layer provided on each side surface of the plurality of protrusions, The invention is characterized in that each of the plurality of protrusions extends in a second direction perpendicular to the first direction.

16. The optical element according to claim 15, characterized in that The following inequalities are satisfied: 0 < P ≤ 300 Wherein P (nm) is the pitch of the plurality of protrusions.

17. The optical element according to claim 15, characterized in that The following inequalities are satisfied: 0.3 ≤ (W + Wm) / P ≤ 0.6 Wherein P (nm) is the pitch of the plurality of protrusions, W is the maximum width of the plurality of protrusions in the first direction, and Wm is the maximum width of the metal layer of the plurality of protrusions in the first direction.

18. The optical element according to claim 16, characterized in that The inequality is satisfied: 0.3 ≤ (W + Wm) / P ≤ 0.6 Wherein W is the maximum width of the plurality of protrusions in the first direction, and Wm is the maximum width of the metal layer of the plurality of protrusions in the first direction.

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