Optical system, display device, and method of manufacturing optical system

Abstract

[Problem] To provide an optical system having a reduced thickness and high light utilization efficiency. [Solution] An optical system configured to guide light from a display element (11) to an eye point (31), the optical system comprising: a projection unit (12) configured to project light from the display element; and a light guide element (20) configured to guide light from the projection unit toward an eye point. The eyespot is located outside the light guide element. The projection unit forms a first pupil (EP). The light guide element has a reflector (24) configured to form a second pupil (EPc) at the eye point in a first cross-section parallel to the first direction. The following conditional expression is satisfied: 0 < = A1 / flt; f (mm) is the focal length of the reflector in the first cross section of the reflector, and A1 (mm) is the air-equivalent distance on the optical axis from the reflecting surface of the reflector to the first pupil.

Description

Technical Field

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

[0002] Conventionally, an observation optical system is known, which is used in augmented reality (AR) glasses and has a light guide plate such as a transflective laminated light guide plate or a diffractive light guide plate. Patent Document 1 discloses a light guide member for a virtual image display device configured to guide image light from an image display element and emit the image light to display a virtual image, and a retroreflector (recursive reflector) configured to reverse the traveling direction of the image light guided in the light guide member of the light guide member. Patent Document 2 discloses a display system in which retroreflectors are arranged on opposite surfaces of a waveguide layer.

[0003] Prior Art Documents

[0004] Patent Documents

[0005] Patent Document 1: Japanese Unexamined Patent Application Publication No. 2017-146447

[0006] Patent Document 2: International Publication No. 2020 / 112836 Summary of the Invention

[0007] Problems to be Solved by the Invention

[0008] The structures disclosed in Patent Documents 1 and 2 use a light guide plate, which can achieve a thin observation optical system, but the light utilization efficiency of the light guide plate (the ratio of the light projected by the projection unit that reaches the observer's eyes) is low. As a result, it is difficult to achieve brightness that can be used in a bright environment such as outdoors, and it is difficult to lighten the battery.

[0009] Therefore, the present invention can provide an optical system having a reduced thickness and high light utilization efficiency.

[0010] Solutions to the Problems

[0011] An optical system according to one aspect of the present invention is configured to guide light from a display element to an eye point. The optical system includes: a projection unit configured to project light from the display element; and a light guiding element configured to guide the light from the projection unit to the eye point. The eye point is located outside the light guiding element. The projection unit forms a first pupil. The light guiding element has a reflector configured to form a second pupil at the eye point in a first cross section parallel to a first direction. The following conditional expression is satisfied: 0 ≤ A1 / f < 0.5, where f is the focal length of the reflector in the first cross section of the reflector, and A1 is the air equivalent distance on the optical axis from the reflecting surface of the reflector to the first pupil, and the units of f and A1 are mm.

[0012] More objects and features of the present invention will become apparent from the following description of embodiments.

[0013] Effects of the Invention

[0014] The present invention can provide an optical system having a reduced thickness and high light utilization efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0015] Figure 1 are schematic views of display devices in respective embodiments.

[0016] Figure 2 explain the functions of light guide plates in respective embodiments.

[0017] Figure 3 is a front view of a light guide plate in a first embodiment.

[0018] Figure 4 is a side view of a light guide plate in a first embodiment.

[0019] Figure 5 is a perspective view of a light guide plate in a first embodiment.

[0020] Figure 6 is a cross-sectional view of a reconstruction mirror in a first embodiment.

[0021] Figure 7 is a cross-sectional view of a reconstruction mirror according to a first modification of a first embodiment.

[0022] Figure 8 is a cross-sectional view of a reconstruction mirror according to a second modification of a first embodiment.

[0023] Figure 9 is a cross-sectional view of a reconstruction mirror according to a third modification of a first embodiment.

[0024] Figure 10Cross-sectional view of the reconstruction mirror according to the fourth modification of the first embodiment.

[0025] Figure 11 Cross-sectional view of the reconstruction mirror according to the fifth modification of the first embodiment.

[0026] Figure 12 Illustrate the configuration and structure of the reconstruction mirror in the first embodiment.

[0027] Figure 13 Describe the pupil reconstruction mirror unit in the second embodiment.

[0028] Figure 14 Cross-sectional view of the light guide plate in the second embodiment.

[0029] Figure 15 Perspective view of the first pupil reconstruction mirror in the second embodiment.

[0030] Figure 16 Flowchart illustrating a method of manufacturing a light guide plate in the third embodiment.

[0031] Figure 17 Describe the components of the light guide plate in the third embodiment.

[0032] Figure 18 Illustrate pupil reconstruction in the second embodiment.

[0033] Figure 19 Describe a light guide plate using a two-dimensional pupil reconstruction mirror according to a modification of the second embodiment. Detailed Description of the Invention

[0034] Now, with reference to the accompanying drawings, a detailed description of embodiments according to the present invention will be given. Corresponding elements in each figure will be designated by the same reference numerals, and redundant descriptions thereof will be omitted.

[0035] (First Embodiment)

[0036] Now, with reference to Figure 1 , a description of the display device 100 according to the present embodiment will be given. Figure 1 Schematic diagram of the display device 100. The display device 100 includes a projection unit 10 and a light guide plate (light guiding element) 20. In the following description, the horizontal direction (e.g., the direction from the observer's right eye to the left eye) will be set as the X-axis direction (first direction), the vertical direction will be set as the Y-axis direction (second direction), and the direction orthogonal to the X-axis and Y-axis (the direction from the eye point 31 and the observer's eye 30 to the light guide plate 20) will be set as the Z-axis direction. The cross-section including the X-axis and Z-axis will be set as the first cross-section, the cross-section including the Y-axis and Z-axis will be set as the second cross-section, and the cross-section including the X-axis and Y-axis will be set as the third cross-section.

[0037] The projection unit 10 includes a display element 11 such as an organic light emitting diode (OLED), and a projection optical system (projection unit) 12. The projection optical system 12 includes a freeform prism and enables a high acceptance angle and miniaturization. However, the present embodiment is not limited to this example, and the projection optical system 12 may use a general optical system instead of the freeform prism. The light guide plate 20 is configured to form a second pupil EPc of a first pupil (exit pupil) EP of the reconstruction projection unit 10 (projection optical system 12) at the position of the eye point 31 (the pupil of the observer's eye 30) in a one-dimensional direction (for example, in a first cross section parallel to the first direction). In the present embodiment, the projection optical system 12 and the light guide plate 20 constitute an optical system (observation optical system) configured to guide the light from the display element 11 to the eye point 31.

[0038] The light beam incident on the light guide plate 20 from the projection optical system 12 has a width equivalent to the thickness of the light guide plate 20 in the thickness direction of the light guide plate 20, and has a beam width narrower than the width of the light guide plate 20 in the width direction of the light guide plate. Such a light beam travels while being internally reflected by the inner surface within the light guide plate 20 (two light guide substrates holding the pupil reconstruction mirror 24, for example, Figure 17 the planar substrates 291 and 292 in

[0039] In the present embodiment, the ratio of the viewing angles in the horizontal cross section (X-axis cross section) and the vertical cross section (Y-axis cross section) of the display device 100 is 16:9. Since the second pupil EPc is preferably formed at least in the direction with a wider viewing angle to improve the light utilization efficiency, the light guide plate 20 forms the second pupil EPc by reconstructing the first pupil (exit pupil) EP in the horizontal cross section. However, the present embodiment is not limited to this example, and the second pupil EPc may be formed in the vertical cross section (Y-axis cross section) instead of the horizontal cross section.

[0040] Now referring to Figure 2 , an explanation of the function of the light guide plate 20 will be given. Figure 2Describe the function of the light guide plate 20. The light guide plate 20 is a pupil reconstruction light guide plate that forms a second pupil EPc by reconstructing the first pupil (exit pupil) EP of the projection unit 10 (projection optical system 12) at the eye point 31 where the observer's eye 30 is located. In the present embodiment, the state of reconstructing the second pupil EPc similar to the first pupil (exit pupil) EP of the projection unit 10 at the position of the eye point 31 will sometimes be referred to as "pupil reconstruction". This indicates a state where the perspective light beam emitted from the first pupil and diffused converges and overlaps again, rather than forming a second pupil as a conjugate image formed by imaging the first pupil. Since the perspective light beam is not affected by imaging and has no optical power, the light emitted as a parallel beam from the first pupil converges on the second pupil as a parallel beam.

[0041] The light guide plate 20 has a pupil reconstruction mirror (reflector) 24, and forms a second pupil EPc at the eye point 31 by reconstructing the first pupil EP of the projection unit 10 in a one-dimensional direction (within the first cross-section, or within the second cross-section orthogonal to the first cross-section, in the horizontal or vertical direction). The reflecting surface of the pupil reconstruction mirror 24 is inclined with respect to the surface of the light guide substrate in the second cross-section, and the light reflected by the pupil reconstruction mirror 24 passes through the light guide substrate and is emitted to the outside of the light guide plate 20. The pupil reconstruction mirror 24 includes a plurality of reflecting surfaces arranged in a second direction orthogonal to the first direction, and the angles formed by the plurality of reflecting surfaces and the surface of the light guide substrate are equal to each other.

[0042] The observer places his eye 30 at the eye point 31. Thereby, the wasted light that does not enter the observer's eye 30 can be reduced, and thus the ratio of the light reaching the observer's eye 30 in the light projected from the projection unit 10 (light utilization efficiency of the light guide plate 20) can be increased. The place where the second pupil EPc is formed is the position of the eye point 31, but as long as the second pupil EPc is located near the eye point 31 to a certain extent, the effects of the present embodiment can be fully obtained.

[0043] The pupil reconstruction mirror 24 having a pupil reconstruction function in a one-dimensional direction (first direction, horizontal direction) preferably has the following structure. That is, in the direction (second direction, vertical direction) where the pupil reconstruction mirror 24 does not have a pupil reconstruction function, it is preferable to use a structure in which light is incident on the pupil reconstruction mirror 24 at an angle other than the vertical angle and is reflected in a direction different from the incident direction. Thereby, the second pupil EPc can be arranged at a place different from the first pupil EP, and thus the second pupil can be formed at the eye point outside the light guide element.

[0044] In this embodiment, the pupil reconstruction lens (lens) 24 reconstructs a new pupil while keeping the light beam substantially parallel by reflecting the light beam twice on the pupil reconstruction lens. Now, assume that: f (mm) is the focal length of the pupil reconstruction lens 24 in the first cross-section, and A1 (mm) is the air equivalent distance on the optical axis from the reflecting surface (e.g., the center of the reflecting surface) of the pupil reconstruction lens 24 to the first pupil EP. Then, the optical system according to this embodiment satisfies the following conditional expression (1).

[0045] 0.0 ≤ A1 / f < 0.5 … (1)

[0046] Here, the optical axis corresponds to the optical path of the chief ray projected onto the YZ cross-section, and the air equivalent distance corresponds to the following: the actual distance (for A1, the optical path length of the chief ray when projected onto this cross-section) / the refractive index of the light guiding element.

[0047] Conditional expression (1) means that the focal length of the pupil reconstruction lens 24 is longer than twice the optical path length (A1), and the optical power (refractive power) of the pupil reconstruction lens 24 is small enough.

[0048] In the light guiding element, the optical element is divided into multiple elements to reduce the plate thickness of the light guiding element. When the optical element for reconstructing the pupil is divided into multiple elements, the distances from the first pupil to each optical element are different. In this case, when the light guiding element uses its refractive power to form a conjugate pupil, due to the different distances from the first pupil to each optical element, there is a problem of different degrees of convergence of the light beams for each divided optical element. When changing the refractive power for each divided optical element, the degree of convergence of the light beam can be uniform, but the viewing angle expands or shrinks for each divided optical element, and there is an offset of the viewing angle. In contrast, by setting the refractive power of the pupil reconstruction lens to satisfy conditional expression (1), even if the pupil reconstruction lens includes multiple optical elements, the light beam can be directed as a substantially parallel light beam to the second pupil without changing the degree of convergence of the light beam and without changing the viewing angle.

[0049] Preferably, the numerical range of conditional expression (1) is set as the following conditional expression (1a).

[0050] 0.0≤A1 / f<0.3…(1a)

[0051] More preferably, the numerical range of conditional expression (1) is set as the following conditional expression (1b). Conditional expression (1b) means that the refractive power of the pupil reconstruction lens 24 is zero (no refractive power). In this embodiment, the pupil reconstruction lens 24 without refractive power can reconstruct the pupil while maintaining the incident light as a parallel light beam, and better optical performance can be achieved.

[0052] A / f = 0.0…(1b)

[0053] Now referring to Figures 3 to 5 (a) of Figure 5 and (b) of Figure 3 will give an explanation of the structure of the light guide plate 20. Figure 4 is the front view of the light guide plate 20. Figure 5 (a) of Figure 5 and (b) of Figure 3 are perspective views of the light guide plate 20. As Figure 4 illustrated, the light guide plate 20 includes a light guide substrate 21, a head (entrance portion) 22, a bending mirror (first reflector) 23, and a pupil reconstruction mirror (extraction mirror) 24.

[0054] The bending mirror 23 is a first reflector configured to deflect the light from the projection optical system 12. The pupil reconstruction mirror 24 is a second reflector that emits the light reflected by the two inner side surfaces facing each other, the first reflection surface, and these two inner side surfaces to the outside of the light guide plate 20. The first reflector includes a first reflection surface orthogonal to the two inner side surfaces, and the second reflector includes a plurality of reflection surfaces arranged in a direction parallel to the two inner side surfaces, and the first reflection surface is inclined with respect to the direction parallel to the two inner side surfaces in a cross section parallel to the two inner side surfaces.

[0055] The pupil reconstruction mirror 24 includes a first retroreflective (retroreflective or recursive) mirror 241, a second retroreflective mirror 242, and a third retroreflective mirror 243. In order to reduce the thickness of the light guide plate 20, three retroreflective mirrors 241, 242, and 243 are arranged, and the retroreflective mirrors 241, 242, and 243 each form a second pupil for reconstructing the first pupil EP. However, this embodiment is not limited to this example, and the number of retroreflective mirrors constituting the pupil reconstruction mirror 24 may be other than three.

[0056] As Figure 3 and Figure 5 (a) of

[0057] The observation optical system according to this embodiment uses a bending mirror 23 to bend the optical path in the light guide plate, and the angle between the optical paths before and after the bending mirror 23 is set to an acute angle of θc = 69°. Thereby, the height (distance) of the light guide plate in the vertical direction (Y-axis direction) can be reduced. The angle of the optical path from the first pupil (exit pupil) EP of the projection optical system to the bending mirror 23 is set to θa = 21°, and the light is guided at an angle upward from the horizontal direction (θa = 0°). Thereby, the tilt angle of the bending mirror 23 is set to θb = 34°, which is closer to the horizontal direction than 45°, and the height of the terminal of the bending mirror 23 is reduced.

[0058] The observation optical system according to this embodiment can form a second pupil EPc, which is formed by reconstructing the first pupil (exit pupil) EP of the projection unit 10 at the position of the eye point 31 outside the light guide plate 20 in the horizontal direction. As Figure 5 illustrated in (b) of [], each of the three retroreflective mirrors 241, 242, and 243 is a right-angle mirror array in which a plurality of right-angle mirrors are arranged along a first direction (the horizontal direction in the local coordinate system of the retroreflective mirror) in which the angle formed by two reflecting surfaces in the first direction is a right angle. In this embodiment, the three retroreflective mirrors 241, 242, and 243 are arranged along the vertical direction (the first direction). That is, the pupil reconstruction mirror 24 includes a plurality of right-angle mirrors each having two reflecting surfaces forming a right angle in a first cross section, and the plurality of right-angle mirrors are arranged along the first direction.

[0059] Now, assume that: A1 (mm) is the air equivalent distance from the reflecting surface of the pupil reconstruction mirror 24 to the first pupil (exit pupil) EP (the root 22a of the head 22) of the projection unit 10, and A2 (mm) is the air equivalent distance from the reflecting surface of the pupil reconstruction mirror 24 to the optical axis of the eye point (pupil) 31. The eye point 31 is the position where the second pupil EPc is formed, and in this embodiment, it corresponds to the position of the observer's eye 30. The eye point 31 is located, for example, at a distance of about 12 mm to 18 mm from the exit surface of the light guide plate 20 (while the eye distance is 12 mm to 18 mm), but is not limited to this example and varies according to the size of the display device and whether it is compatible with vision correction glasses.

[0060] As Figure 3As illustrated, assume that L1a is the distance from the position of the root 22a of the head 22 in the light guide substrate 21 to the position of the bending mirror 23. L1b is the distance from the position of the bending mirror 23 in the light guide substrate 21 to the position of the pupil reconstruction mirror 24 (which corresponds to the center of the second retroreflector 242 in this embodiment, the height position of the observer's eye 30, or the position where the chief ray at the perspective center reaches the pupil reconstruction mirror 24). N is the refractive index of the light guide substrate 21 with respect to the d line. In this case, the air equivalent distance A1 is expressed as A1 = (L1a / N) + (L1b / N).

[0061] As Figure 4 illustrated, L2a is the distance from the position of the pupil reconstruction mirror 24 in the light guide substrate 21 (which corresponds to the center position of the pupil reconstruction mirror 24 in the thickness direction of the light guide plate 20 or the center position of the second retroreflector 242 in this embodiment) to the position of the exit surface 20a of the light guide plate 20. L2b is the distance in air from the exit surface 20a of the light guide plate 20 to the eye point 31. In this case, the air equivalent distance A2 is expressed as A2 = (L2a / N) + L2b.

[0062] In this embodiment, in order to reconstruct the first pupil (exit pupil) EP of the projection optical system 12 at the position of the eye point 31 (for pupil reconstruction), the relationship between the air equivalent distances A1 and A2 preferably satisfies the following conditional expression (2).

[0063] 0.5 < A2 / A1 < 2.0 … (2)

[0064] When A2 / A1 becomes higher than the upper limit of the conditional expression (2), the pupil is formed in front of the observer's eye 30, and the observer cannot view the image with a wide viewing angle as expected (while the observable viewing angle becomes narrower). When A2 / A1 becomes lower than the lower limit of the conditional expression (2), the pupil is formed behind the observer's eye 30, and the observer cannot view the image with a wide viewing angle as expected (while the observable viewing angle becomes narrower). Regarding the distance L1b, in the case where multiple retroreflectors are provided, for the distances L1b to all (three in this embodiment) retroreflectors (for example, the distance to the center of the first retroreflector 241), it is preferable to satisfy the conditional expression (2).

[0065] Preferably, the numerical range of the conditional expression (2) is set as in the following conditional expression (2a).

[0066] 0.6 < A2 / A1 < 1.5 (2a)

[0067] More preferably, the numerical range of the conditional expression (2) is set as in the following conditional expression (2b).

[0068] 0.8 < A2 / A1 < 1.2 (2b)

[0069] Now referring to Figure 6 (a) of Figure 6 and (b) of Figure 6 (a) of Figure 6 and (b) of Figure 6 are cross-sectional views of the retroreflector 241 that constitutes the pupil reconstruction lens. As illustrated in (a) of

[0070] The retroreflector 241 is formed by arranging a plurality of right-angle mirrors 25 in the X-axis direction (horizontal direction) in the local coordinates of the retroreflector. That is, in a cross-section (first cross-section) along the horizontal direction (X-axis direction), the heights (distances) of the plurality of right-angle mirrors 25 from the bottom peak (valley portion) to the top peak (mountain portion) are equal (constant in the horizontal direction).

[0071] According to Figure 6 the retroreflector 241 illustrated in (b) of

[0072] In a horizontal cross-section, the light incident on the right-angle mirror 25 is reflected by the second mirror 25b and the first mirror 25a, and is reflected in the same direction as the incident light. Thus, the light reflected by the right-angle mirror 25 has the retroreflective property of returning to the original direction.

[0073] The pupil reconstruction lens using the right-angle mirror array does not have a refractive power. Therefore, even if it is divided in the vertical direction, the pupil can be reconstructed without changing the convergence or viewing angle of the light beam at each retroreflector.

[0074] On the other hand, Figure 6 the retroreflector 241 illustrated in (b) of

[0075] Referring to Figure 7 (a) toFigure 7 In (c) of this, a description will be given of the structure of the pupil reconstruction mirror 24a according to the first modification of the present embodiment. Figure 7 In (a) to Figure 7 In (c) is a cross-sectional view of the pupil reconstruction mirror 24a. As Figure 7 Illustrated in (a), the pupil reconstruction mirror 24a is configured such that in two surfaces of the two right-angle mirrors 25, the inner surface (first mirror 25a) is wider than the outer surface (second mirror 25b). The root of the outer surface is cut off, and the cut surface 28 is formed parallel to the reflected light. The pupil reconstruction mirror 24a is configured such that as the position approaches the peripheral portion (outer side) from the central portion C (inner side), the right-angle mirror 25 becomes higher.

[0076] In other words, in this modification, in at least one of the plurality of right-angle mirrors 25, in a cross-section along the horizontal direction, the first mirror 25a is wider than the second mirror 25b. At least one of the second mirrors 25b has a cut surface 28 cut at an angle different from the angle of the mirror surface. As the position approaches the peripheral portion from the central portion C of the pupil reconstruction mirror 24, the height (distance) from the bottom peak (valley portion) to the top peak (mountain portion) of each right-angle mirror 25 among the plurality of right-angle mirrors 25 becomes higher (longer).

[0077] Due to this structure, as Figure 7 Illustrated in (b), the gap G2 of the light beam reflected by the pupil reconstruction mirror 24a can be made smaller than the gap G1 of the light beam reflected by the pupil reconstruction mirror 24. The cut surface 28 of the outer surface (second mirror 25b) of the right-angle mirror 25 parallel to the reflected light can minimize the gap G2. As Figure 7 Illustrated in (c), the pupil reconstruction mirror 24a is configured such that the light beam reflected by one surface (inner surface) of the right-angle mirror 25 passes through the other surface (outer surface), passes through one surface (inner surface) of the adjacent right-angle mirror 25, and is reflected by the other surface (outer surface). Thereby, the light utilization efficiency can be increased by, for example, about 10%. The pupil reconstruction mirror 24a is formed such that as the position approaches the outer side (peripheral portion) from the inner side (central portion C), the right-angle mirror 25 becomes higher, so that even if the light reflected to the outer side travels obliquely, the amount of light reflected by the right-angle mirror 25 increases again.

[0078] Now referring to Figure 8 In (a) and Figure 8 In (b), the structure of the pupil reconstruction mirror 24b according to the second modification of the present embodiment will be described. Figure 8 In (a) and Figure 8 In (b) are cross-sectional views of the pupil reconstruction mirror 24b. As Figure 8As illustrated in (a) of , the pupil reconstruction mirror 24b is configured such that, among the two surfaces of the two right-angle mirrors 25, the inner surface (the first mirror 25a) is wider than the outer surface (the second mirror 25b). The root of the outer surface is cut off, and the cut surface 29 is arranged to be orthogonal to the arrangement direction (horizontal direction) of the right-angle mirror 25 (the normal direction of the cut surface 29 is parallel to the arrangement direction of the right-angle mirror 25). The pupil reconstruction mirror 24b is configured such that as the position approaches the peripheral part (outer side) from the central part C (inner side), the right-angle mirror 25 becomes higher.

[0079] Due to this structure, as Figure 8 illustrated in (b) of , the gap G3 of the light beam reflected by the pupil reconstruction mirror 24b becomes smaller than the gap G1 of the light beam reflected by the pupil reconstruction mirror 24. The gap G3 of the light beam reflected by the pupil reconstruction mirror 24b is slightly larger than the gap G2 of the light beam reflected by the pupil reconstruction mirror 24a, but the molding process of the pupil reconstruction mirror 24b is easier than the molding process of the pupil reconstruction mirror 24a during molding.

[0080] Now referring to Figure 9 (a) of and Figure 9 the structure of the pupil reconstruction mirror 24c according to the third modification example of the present embodiment will be described. Figure 9 (a) of and Figure 9 (b) of are cross-sectional views of the pupil reconstruction mirror 24c. In this modification example, in a cross-section along the horizontal direction, as the position approaches the peripheral part from the central part C, the rotation angle of the two right-angle mirrors 25 of the pupil reconstruction mirror 24c increases (the angle rotates inward). That is, as Figure 9 illustrated in (a) of , the angles of the plurality of right-angle mirrors 25 vary according to the distance from the central part C of the pupil reconstruction mirror 24c. The central part may be arranged at a position offset from the width center of the pupil reconstruction mirror 24c. The angle of each right-angle mirror 25 is preferably configured such that a ray parallel to the principal ray of the perspective light beam reaching each right-angle mirror 25 is incident on the end of the first mirror 25a, is reflected, is incident on the end of the second mirror 25b, and is reflected. The angular error of each right-angle mirror may be 5° or less than 5°. Due to this structure, the gap G4 of the light beam reflected by the Figure 9 pupil reconstruction mirror 24c illustrated in (b) of can be smaller than the gap G1 of the light beam reflected by the Figure 6 pupil reconstruction mirror 24 illustrated in (b) of .

[0081] Now referring to Figure 10 , a description of the structure of the pupil reconstruction mirror 24d according to the fourth modification example of the present embodiment will be given. Figure 10 is a cross-sectional view of the pupil reconstruction mirror 24d. As Figure 10As illustrated, in addition to the structure of the pupil reconstruction lens 24c, the pupil reconstruction lens 24d further includes a light shielding member 26a disposed between adjacent right-angle lenses (at the bottom peaks of the respective right-angle lenses) so as to extend to the peaks of the respective right-angle lenses. Each of the plurality of light shielding members 26a is arranged parallel to the perspective light beam (such that as the position approaches the peripheral portion from the central portion C, the normal direction of the surface of the light shielding member 26a is away from the arrangement direction (horizontal direction) of the right-angle lenses).

[0082] In the pupil reconstruction lens 24c where the angles of the respective right-angle lenses are changed, the display light transmitted and reflected by the adjacent orthogonal lenses may become ghost light. However, according to the structure of this modification example, the ghosting can be reduced by cutting off (blocking) the light from the adjacent right-angle lenses. When the perspective light reflected by the pupil reconstruction lens 24d is directed toward the observer's eye 30, this perspective light becomes ghost light. Therefore, this modification example can reduce the ghosting by cutting off the reflected light of the optical perspective light.

[0083] Next, with reference to Figure 11 , the structure of the pupil reconstruction lens 24e according to the fifth modification example of the present embodiment will be described. Figure 11 is a cross-sectional view of the pupil reconstruction lens 24e. As Figure 11 illustrated, in addition to the structure of the pupil reconstruction lens 24c, the pupil reconstruction lens 24e further has a light shielding member 26b disposed between adjacent right-angle lenses (at the bottom peaks of the respective right-angle lenses) so as to extend to the peaks of the respective right-angle lenses. The plurality of light shielding members 26b are configured such that the normal direction of the surface of the light shielding member 26b is parallel to the arrangement direction (horizontal direction) of the right-angle lenses. Therefore, according to this modification example, compared with the pupil reconstruction lens 24d having the light shielding member 26a, it is easier to manufacture by metal forming.

[0084] Now, with reference to Figure 12 in (a) and Figure 12 in (b), an explanation will be given of the arrangement of the plurality of retroreflective mirrors (the first retroreflective mirror 241, the second retroreflective mirror 242, and the third retroreflective mirror 243) constituting the reconstruction lens in the present embodiment. Figure 12 in (a) illustrates the arrangement of the plurality of retroreflective mirrors in the present embodiment. As Figure 12 illustrated in (a) of Figure 12 , the plurality of retroreflective mirrors are arranged such that they have the same phase in the vertical direction (the peaks and bottom peaks of the right-angle lenses constituting the retroreflective mirrors 241, 242, and 243 are aligned). However, the present embodiment is not limited to this example, and for example, a structure as illustrated in

[0085] Figure 12 in (b) can be adopted. Figure 12As illustrated in (b) of , in this modification, the second retroreflector 242 is arranged such that it has a phase different from those of the first retroreflector 241 and the third retroreflector 243 in the vertical direction. This modification can provide a higher-quality image by reducing the gap formed between the first retroreflector 241 or the third retroreflector 243 and the second retroreflector 242 and reducing artifacts.

[0086] This embodiment can provide a thin observation optical system with high light utilization efficiency. Each condition or modification described in this embodiment also applies to the second embodiment described below.

[0087] (Second Embodiment)

[0088] The second embodiment of the present invention will be described. In the first embodiment, the light guide plate (one-dimensional pupil reconstruction light guide plate) 20 forms a second pupil at the eye point 31 by reconstructing only the exit pupil of the projection optical system 12 in one dimension (e.g., the horizontal direction). In this embodiment, the light guide plate (two-dimensional pupil reconstruction light guide plate) forms a second pupil at the eye point 31 by reconstructing the exit pupil of the projection optical system 12 in two dimensions (e.g., both the horizontal direction and the vertical direction).

[0089] Now referring to Figure 13 of (a) and Figure 13 of (b), a description will be given of the two-dimensional pupil reconstruction mirror unit 34 in this embodiment. Figure 13 of (a) and Figure 13 of (b) illustrate the pupil reconstruction mirror unit 34 in this embodiment. The light guide plate in this embodiment has a plurality of two-dimensional pupil reconstruction mirror units 34 (i.e., two-dimensional pupil reconstruction mirrors) two-dimensionally arranged along the horizontal direction (X-axis direction) and the vertical direction (Y-axis direction). As Figure 13 illustrated in (a) of , one pupil reconstruction mirror unit 34 constituting the two-dimensional pupil reconstruction mirror has a right-angle mirror 25 composed of a first mirror 25a and a second mirror 25b orthogonal to each other, and a plane mirror (third mirror) 51. The plane mirror 51 is, for example, a semi-transmissive semi-reflective mirror.

[0090] As Figure 13 illustrated in (b) of , the plane mirror 51 is arranged to form an angle θ (degrees) with the ridge line (edge line) 41 of the right-angle mirror 25. The angle θ (degrees) preferably satisfies the following conditional expression (3) to reduce the gap between light beams from directions including, for example, vertical components.

[0091] 40 < θ < 80 … (3)

[0092] When θ becomes higher than the upper limit of the conditional expression (3) or lower than the lower limit of the conditional expression (3), the gap between the light beams from a direction including, for example, the vertical component cannot be sufficiently reduced.

[0093] Preferably, the numerical range of the conditional expression (3) is set as in the following conditional expression (3a).

[0094] 50 < θ < 70…(3a)

[0095] More preferably, the numerical range of the conditional expression (3) is set as in the following conditional expression (3b).

[0096] θ = 60…(3b)

[0097] Therefore, in this embodiment, the right-angle mirror 25 is used to achieve pupil reconstruction in the horizontal direction, and the right-angle mirror 25 and the flat mirror 51 arranged to form an angle θ with the ridge line 41 of the right-angle mirror 25 are used to achieve pupil reconstruction in the vertical direction. Thus, the second pupil can be reconstructed in both the horizontal direction and the vertical direction.

[0098] More specifically, in the horizontal direction, in this embodiment, each perspective beam emitted from the exit pupil of the projection optical system is reflected by using the right-angle mirror array, and the retroreflective function of the right-angle mirror array is used to reconstruct the second pupil.

[0099] In the vertical direction, in this embodiment, it is discussed that for the ridge line 41 of the right-angle mirror 25, the flat mirror 51 is set to θ = 60°. The two-dimensional pupil reconstruction mirror is arranged such that the ridge line 41 of the right-angle mirror 25 is parallel to the incident light. The incident light is first reflected by the flat mirror 51 and then reflected by the two surfaces of the right-angle mirror 25, and the reflected light is reflected in a direction substantially parallel to the flat mirror 51.

[0100] Figure 18 The pupil reconstruction in the pupil reconstruction mirror unit 34 is illustrated in the vertical section. When the perspective beams emitted from the first pupil EP of the projection optical system and diffused are reflected by different pupil reconstruction mirror units 34, the distance between the reflected perspective beams becomes narrower as they travel, and the perspective beams converge at substantially the same position and overlap with each other to form the second pupil EPc. Thus, even in the vertical direction, the two-dimensional pupil reconstruction mirror can form the second pupil reconstructed from the first pupil of the projection optical system. Since, as described above, the flat mirror 51 is set to have an angle θ with respect to the ridge line 41 of the right-angle mirror 25, the second pupil can be reconstructed at a location different from the first pupil in the vertical section.

[0101] In this embodiment, a second pupil reconstructed from the first pupil (exit pupil) of the projection optical system can be formed in two-dimensional directions in a horizontal cross-section and a vertical cross-section. When the second pupil is formed at the position of the eye point, light from the display element can be efficiently guided to the observer's eyes. Thereby, the light utilization efficiency can be further improved.

[0102] Figure 14 FIG. 4 is a cross-sectional view (YZ cross-section) of a light guide plate (light guide element) 70 having a two-dimensional pupil reconstruction mirror 35 in this embodiment. The light guide plate 70 has a two-dimensional pupil reconstruction mirror 35 on a light guide substrate 71, and the two-dimensional pupil reconstruction mirror 35 includes a plurality of pupil reconstruction mirror units 34 arranged along the horizontal direction and the vertical direction. In this embodiment, the two-dimensional pupil reconstruction mirror 35 includes a first pupil reconstruction mirror, and the first pupil reconstruction mirror includes a plurality of pupil reconstruction mirror units 34 arranged in a row along the horizontal direction, and the first pupil reconstruction mirror is arranged in a row along the vertical direction.

[0103] Figure 15 FIG. 5 is a perspective view of the first pupil reconstruction mirror. As Figure 15 illustrated, the first pupil reconstruction mirror has 39 pupil reconstruction mirror units 34 arranged along the horizontal direction (X-axis direction). However, the number of pupil reconstruction mirror units 34 is not limited to this example. As Figure 14 illustrated, the two-dimensional pupil reconstruction mirror 35 is formed by arranging 12 first pupil reconstruction mirrors along the vertical direction (Y-axis direction) on a cylindrical surface 72 formed on the light guide substrate 71. However, the number of first pupil reconstruction mirrors is not limited to this example. The pupil reconstruction mirror units 34 on the cylindrical surface 72 are also arranged such that as the position approaches the peripheral portion from the central portion in the vertical direction, the rotation angle increases (rotates inward). In the case not limited to the arrangement on the cylindrical surface 72, the pupil reconstruction mirror units 34 can be arranged by even partially rotating inward. This structure can form a second pupil while reducing the gap between the light beams reflected by the two-dimensional pupil reconstruction mirror 35 in both the horizontal direction and the vertical direction.

[0104] As a modification of the second embodiment, Figure 19 a light guide substrate 71 using a two-dimensional pupil reconstruction mirror that realizes Maxwell vision is illustrated.

[0105] The size of each pupil reconstruction mirror unit 34 is set to 2 mm or less than 2 mm, and adjacent pupil reconstruction mirror units 34 are spaced apart and sparsely arranged in a third cross-section of the light guide substrate 71 including the X-axis and the Y-axis. Thereby, a light guide plate using a two-dimensional pupil reconstruction mirror that realizes Maxwell vision can be configured by setting the light beam reflected by each pupil reconstruction mirror unit to 1 mm or less than 1 mm.

[0106] (Third Embodiment)

[0107] Reference Figure 16 and Figure 17 a description of a method for manufacturing the observation optical system (light guide plate 20) in the present embodiment will be given. Figure 16 is a flowchart illustrating a method for manufacturing the light guide plate 20. Figure 17 (a) of Figure 17 and (b) of Figure 17 illustrate the components constituting the light guide plate 20. Figure 17 (a) of

[0108] First, in step S101, a first light guide unit 201 (first formation step) having a light guide substrate 21, a head (incident portion) 22, and a pupil reconstruction mirror 24 is formed. At this time, a reflective film or a semi-transmissive semi-reflective mirror film is formed on the reflective surface 27 of the pupil reconstruction mirror 24. In the case where the first light guide unit 201 has a plurality of pupil reconstruction mirrors 24, the characteristics of the reflective film or the semi-transmissive semi-reflective mirror film are made different for each pupil reconstruction mirror 24 to adjust the brightness corresponding to the viewing angle of the display image (so that the brightness of the display image viewed by the observer is constant). Here, the characteristics of the reflective film or the semi-transmissive semi-reflective mirror film include, for example, transmittance characteristics and reflectance characteristics. That is, the reflectance of the film formed on the lower pupil reconstruction mirror 24 is made high and the transmittance is made low. For example, the reflectance of the film formed on the third retroreflective mirror 243 is higher than the reflectance of the film formed on the first retroreflective mirror 241, and the transmittance of the film formed on the third retroreflective mirror 243 is lower than the transmittance of the film formed on the first retroreflective mirror 241. The present embodiment is not limited to this example, and a semi-transmissive semi-reflective mirror having the same characteristics can be used.

[0109] The head (incident portion) 22 can be formed integrally with the light guide substrate 21, or can be formed separately and then joined to the light guide substrate 21. When the head (incident portion) 22 is formed by injection molding, the former can achieve the positional accuracy between the light guide substrate 21 and the head 22, while the latter has the advantage of improving the surface accuracy during molding due to the reduction of the thickness difference in the molding part.

[0110] Next, in step S102, a second light guide unit 202 (second formation step) having a pupil reconstruction mirror interpolation portion 84 having a shape similar to the shape of the pupil reconstruction mirror 24 is formed.

[0111] Next, in step S103, the first light guide unit formed in step S101 and the second light guide unit formed in step S102 are joined together using an adhesive to form a light guide plate 20 (third forming step). At this time, the pupil reconstruction lens 24 and the pupil reconstruction lens interpolation unit 84 are joined together to form the light guide plate 20. An adhesive having a refractive index similar to that of the molded product can reduce the visibility of the joint surface. Thus, the pupil reconstruction lens 24, which is the internal structure of the light guide plate 20, is difficult to identify, and the transparency of the joined molded product can be improved.

[0112] Thus, the light guide plate 20 is divided into two molded products (the first light guide unit 201 and the second light guide unit 202) with a reflecting surface or a half mirror surface as the boundary. Then, a reflective film or a half mirror film is vapor-deposited on one molded product (the first light guide unit 201), and the other molded product (the second light guide unit 202) is formed into a shape similar to the shape of the reflecting surface or the half mirror surface. A gap of 0.05 mm is provided between the two molded products, and the positioning projection 85 contacts the positioning surface 281 when they are joined.

[0113] Thereby, one molded product can be positioned relative to the other molded product with high precision. More specifically, the inclination of the light guide plane 86 on the opposite side of the eye point of the second light guide unit 202 is set to be parallel to the flat substrate 291 on the opposite side of the eye point (plane substrate 292) of the light guide substrate 21 of the first light guide unit 201 with an accuracy of less than 1 arc minute.

[0114] A reflecting surface or a half mirror surface can be provided on the molded product closer to the eye point 31 among the divided molded products (the first light guide unit 201). In the light guide plate 20, the light beam reflected by the plane substrate 292 on the side closer to the eye point 31 is reflected by the pupil reconstruction lens 24 and guided to the eye point 31. Thus, the joint surface of the reflective film or the half mirror film becomes a molded product. The joint surface becomes the surface directly vapor-deposited with the molded product, and good reflection characteristics can be easily obtained.

[0115] The molded product provided with the reflecting surface or the half mirror surface can be the same molded product as the light guide substrate 21. This is because the light guide substrate 21 is thicker than the pupil reconstruction lens part, and by providing the reflecting surface 27 of the pupil reconstruction lens 24 in the first light guide unit 201 where the light guide substrate 21 exists, it is easier to stabilize the surface accuracy and the inclination accuracy. The pupil reconstruction lens interpolation unit 84 that does not require surface accuracy can be provided in the second light guide unit 202 that tends to be thin.

[0116] In this embodiment, the light guide plate 20 is manufactured by bonding two molded products (the first light guide unit 201 and the second light guide unit 202), so mass production can be achieved and the optical performance of the light guide plate 20 can be maintained.

[0117] A modified example of this embodiment can manufacture the light guide plate 20 using the following steps.

[0118] In step S101, a first light guide unit 201 is formed. The first light guide unit 201 includes a light guide substrate 21, a head (incident portion) 22, a pupil reconstruction lens 24, and a pupil reconstruction lens interpolation unit 84 having a similar shape (first formation step).

[0119] Next, in step S102, a second light guide unit 202 having a pupil reconstruction lens 24 is formed (second formation step).

[0120] Next, in step S103, the first light guide unit formed in step S101 and the second light guide unit formed in step S102 are joined together using an adhesive to form the light guide plate 20 (third formation step).

[0121] In this modified example, deposition is performed on the pupil reconstruction lens 24 of the second light guide unit 202. In this case, since the second light guide unit 202 is smaller than the first light guide unit 201, many second light guide units 202 can be installed in the deposition furnace, and the number of films that can be formed in a single deposition process can be increased. As a result, cost reduction can be achieved.

[0122] The optical systems according to the embodiments include a light guide plate (pupil reconstruction light guide plate) that forms a second pupil at the position of the observer's eye by reconstructing the first pupil of the projection unit at the position of the observer's eye. Therefore, the battery can be made lightweight and the brightness that can be used in a bright environment such as outdoors can be maintained. The embodiments can provide an optical system, a display device, and a manufacturing method of the optical system, each having a reduced thickness and a high light utilization efficiency (the ratio of the light projected by the projection unit that reaches the observer's eye).

[0123] The above embodiments are merely representative examples, and various modifications and changes can be made to the embodiments when implementing the present invention.

Claims

1. An optical system configured to guide light from a display element to an eye point, the optical system comprising: a projection unit configured to project light from the display element; and a light guide element configured to guide the light from the projection unit to the eye point, wherein the eye point is located outside the light guide element, wherein the projection unit forms a first pupil, wherein the light guide element has a reflector configured to form a second pupil at the eye point in a first cross-section parallel to a first direction, and wherein the following conditional expression is satisfied: 0≤A1 / f<0.5, where f is the focal length of the reflector in the first cross-section of the reflector, and A1 is the air equivalent distance on the optical axis from the reflecting surface of the reflector to the first pupil, and the units of f and A1 are mm.

2. The optical system according to claim 1, wherein the following conditional expression is satisfied: 0.5<A2 / A1<2.0, where A2 is the air equivalent distance on the optical axis from the reflecting surface to the eye point, and the unit of A2 is mm.

3. The optical system according to claim 1 or 2, wherein the light guide element includes a light guide substrate for holding the reflector, wherein the reflecting surface is inclined with respect to the surface of the light guide substrate in a second cross-section orthogonal to the first cross-section, and wherein the light reflected by the reflector passes through the light guide substrate and exits to the outside of the light guide element.

4. The optical system according to claim 3, wherein the reflector includes a plurality of reflecting surfaces arranged in a second direction orthogonal to the first direction, and the angles formed between the plurality of reflecting surfaces and the surface of the light guide substrate are equal to each other.

5. The optical system according to any one of claims 1 to 4, wherein the reflector includes a plurality of right-angled mirrors, each of the right-angled mirrors in the plurality of right-angled mirrors having two reflecting surfaces forming a right angle with each other in the first cross-section, and the plurality of right-angled mirrors are arranged along the first direction.

6. The optical system according to claim 5, wherein the distances from the bottom peak to the top peak of the plurality of right-angled mirrors are equal to each other.

7. The optical system according to claim 5 or 6, wherein in the first cross-section, the distances from the bottom peak to the top peak of the plurality of right-angled mirrors increase from the central portion to the peripheral portion of the reflector.

8. The optical system according to any one of claims 5 to 7, wherein a first mirror including the inner reflecting surface of each of the right-angled mirrors in the plurality of right-angled mirrors is wider than a second mirror including the outer reflecting surface of each of the right-angled mirrors in the plurality of right-angled mirrors.

9. The optical system according to claim 8, wherein at least one of the second mirrors of the plurality of right-angled mirrors has a cut surface cut at an angle different from the angle of the mirror surface.

10. The optical system according to any one of claims 5 to 9, wherein in the first cross-section, the rotation angle of the angle of the plurality of right-angled mirrors increases from the central portion to the peripheral portion.

11. The optical system according to any one of claims 5 to 10 further includes a light shielding member disposed between adjacent right-angle mirrors among the plurality of right-angle mirrors.

12. An optical system configured to guide light from a display element to an eye point, the optical system comprising: a projection unit configured to project light from the display element; and a light guide element configured to guide light from the projection unit to the eye point, wherein the eye point is located outside the light guide element, wherein the projection unit forms a first pupil, and wherein the light guide element has a reflector configured to form a second pupil at the eye point in a first cross-section parallel to a first direction and in a second cross-section orthogonal to the first cross-section.

13. The optical system according to claim 12, wherein the reflector includes: an array of right-angle mirrors in which a plurality of right-angle mirrors are arranged along the first direction, each right-angle mirror including a first mirror and a second mirror forming a right angle in the first direction, and a third mirror that is a plane mirror, wherein the following conditional expression is satisfied: 40 < θ < 80, where θ is the angle formed by the ridge line between the first mirror and the second mirror and the third mirror, and the unit of θ is degrees.

14. The optical system according to claim 13, wherein the third mirror is a semi-transmissive semi-reflective mirror.

15. The optical system according to any one of claims 12 to 14, wherein a plurality of two-dimensional pupil reconstruction mirrors each including an array of right-angle mirrors and a third mirror are arranged in a second direction.

16. The optical system according to claim 15, wherein the two-dimensional pupil reconstruction mirrors arranged in the second direction have different tilt angles from each other in the second cross-section.

17. An optical system configured to guide light from a display element to an eye point, the optical system comprising: a projection unit configured to project light from the display element; and a light guide element configured to guide light from the projection unit to the eye point, wherein the eye point is located outside the light guide element, wherein the light guide element includes a first reflector configured to deflect light from the projection unit, two inner side surfaces facing each other, and a second reflector for emitting the light reflected by the first reflector and the two inner side surfaces to the outside of the light guide element, wherein the first reflector includes a first reflecting surface orthogonal to the two inner side surfaces, wherein the second reflector includes a plurality of reflecting surfaces arranged in a direction parallel to the two inner side surfaces, and wherein the first reflecting surface is inclined with respect to the direction parallel to the two inner side surfaces in a cross-section parallel to the two inner side surfaces.

18. The optical system according to claim 17, wherein in a cross-section parallel to the two inner side surfaces, the angle formed by the optical path from the projection unit to the first reflector and the optical path from the first reflector to the second reflector is an acute angle.

19. A method for manufacturing an optical system, the manufacturing method Comprising: A first forming step for forming a first light guiding unit, the first light guiding unit including a light guiding substrate and a pupil reconstruction mirror; A second forming step for forming a second light guiding unit, the second light guiding unit including a pupil reconstruction mirror interpolation unit having a shape similar to the shape of the pupil reconstruction mirror; And A third forming step for forming a light guiding element by joining the first light guiding unit and the second light guiding unit, wherein the first forming step includes forming a reflective film or a semi-transmissive semi-reflective mirror film on the mirror surface of the pupil reconstruction mirror, and wherein the third forming step includes forming the light guiding element by joining the pupil reconstruction mirror and the pupil reconstruction mirror interpolation unit to each other.

20. A manufacturing method of an optical system, the manufacturing method Comprising: A first forming step for forming a first light guiding unit, the first light guiding unit including a pupil reconstruction mirror; A second forming step for forming a second light guiding unit, the second light guiding unit including a light guiding substrate and a pupil reconstruction mirror interpolation unit having a shape similar to the shape of the pupil reconstruction mirror; And A third forming step for forming a light guiding element by joining the first light guiding unit and the second light guiding unit, wherein the first forming step includes forming a reflective film or a semi-transmissive semi-reflective mirror film on the mirror surface of the pupil reconstruction mirror, and wherein the third forming step includes forming the light guiding element by joining the pupil reconstruction mirror and the pupil reconstruction mirror interpolation unit to each other.

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