Optical element, display device, and camera

Abstract

To provide an optical element capable of increasing precision of reproducing or acquiring a write field.SOLUTION: An optical element 10 for a write field includes: a first lens array 20 having first multiple unit lenses 21 in which a focal length f1 is a positive value; a second lens array 30 having second multiple unit lenses 31 as diffraction lenses that function as lenses having a focal length f2 relative to first circularly polarized incident light and function as lenses having a focal length -f2 relative to second circularly polarized incident light when one of right circularly polarized light and left circularly polarized light is set as first circularly polarized light and the other that is one of right circularly polarized light and left circularly polarized light and is not the first circularly polarized light is set as second circularly polarized light; and a polarization control member 40 that covers the second multiple unit lenses 31 and transmits right circularly polarized light or left circularly polarized light. The absolute value of the focal length f2 is larger than the focal length f1.SELECTED DRAWING: Figure 3

Description

[Technical field]

[0001] The present disclosure relates to an optical element, a display device, and a camera. [Background technology]

[0002] The concept of a light field, which considers light as a field, is widely known. The concept of a light field is applied to a display device that reproduces a light field, a camera that acquires a light field, and the like (see, for example, Patent Documents 1 and 2).

[0003] Patent Document 1 describes a light field display (light field type display) that virtually reproduces the light rays of a three-dimensional object. The light field display of Patent Document 1 includes a display and a lens array. The display and lens array form a virtual image that is visually recognized by the user.

[0004] Patent Document 2 describes a light field image processing system equipped with a light field optical system having a microlens array and an image sensor. The light field image processing system of Patent Document 2 obtains a three-dimensional image of an object by guiding light from the object to the image sensor via the microlens array. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Patent Publication No. 2023-4538 [Patent Document 2] JP 2023-72914 A Summary of the Invention [Problem to be solved by the invention]

[0006] The accuracy with which a device to which a light field is applied reproduces or acquires a light field is affected by the focal position of an optical element such as a lens array used to reproduce or acquire the light field. For example, in the case of a display device that reproduces a light field, if an image is formed at a position away from the focal position of an optical element such as a lens array, the image is likely to be blurred. In this case, it can be said that the accuracy with which the optical element reproduces the light field is low. In the case of a camera that acquires a light field, if the positional relationship between the position of the object to be photographed relative to an optical element such as a lens array and the focal position of the optical element is not appropriate, the captured image is likely to be blurred. In this case, it can be said that the accuracy with which the optical element acquires the light field is low. For this reason, there is a demand for an optical element that can increase the accuracy with which a light field is reproduced or acquired.

[0007] The present disclosure has been made in consideration of the above points, and aims to provide an optical element that can increase the accuracy of reproducing or acquiring a light field. [Means for solving the problem]

[0008] The embodiments of the present disclosure relate to the following [1] to [8].

[0009] [1] A first lens array having a plurality of first unit lenses each having a positive focal length f1; a second lens array having a plurality of second unit lenses, each of which is a diffractive lens that functions as a lens with a focal length f2 for the first circularly polarized light and a lens with a focal length -f2 for the second circularly polarized light, when one of right-handed circularly polarized light and left-handed circularly polarized light is defined as a first circularly polarized light, and the other of the right-handed circularly polarized light and the left-handed circularly polarized light that is not the first circularly polarized light is defined as a second circularly polarized light; a polarization control member that covers the plurality of second unit lenses and transmits right-handed circularly polarized light or left-handed circularly polarized light; An optical element for a light field, wherein the absolute value of the focal length f2 is greater than the focal length f1.

[0010] [2] the polarization control member has a first surface facing the second lens array and a second surface located on the opposite side to the first surface, The optical element according to [1], further comprising a quarter-wave plate facing the second surface.

[0011] [3] The optical element described in [1] or [2], wherein the polarization control member has a plurality of liquid crystal cells that impart a phase difference of 1 / 2 wavelength to incident light in either a state in which a voltage is applied or a state in which a voltage is not applied.

[0012] [4] a third lens array having a plurality of third unit lenses, each of which is a diffractive lens that functions as a lens with a focal length f3 for the third circularly polarized light and a lens with a focal length -f3 for the fourth circularly polarized light, when one of the right-handed circularly polarized light and the left-handed circularly polarized light that is not the third circularly polarized light is a fourth circularly polarized light; and a second polarization control member that covers the plurality of third unit lenses and transmits right-handed circularly polarized light or left-handed circularly polarized light; The optical element according to any one of [1] to [3], wherein an absolute value of the focal length f3 is greater than the focal length f1 and different from an absolute value of the focal length f2.

[0013] [5] [1] to [4], and a display element overlaid on the optical element, the polarization control member has a first surface facing the second lens array and a second surface located on the opposite side to the first surface, the display element faces a second surface of the polarization control member, A display device in which the display element causes right-handed circularly polarized light or left-handed circularly polarized light to be incident on the optical element.

[0014] [6] [2] The optical element according to the present invention; a display element that is overlaid on the optical element and faces the second surface of the polarization control member with the quarter-wave plate interposed therebetween.

[0015] [7] The display device described in [5] or [6], further comprising an eyepiece lens arranged to sandwich the optical element between the display element and the eyepiece lens.

[0016] [8] [1] to [4], and an imaging element overlaid on the optical element; the polarization control member has a first surface facing the second lens array and a second surface located on the opposite side to the first surface, The imaging element faces the second surface of the polarization control member. Effect of the Invention

[0017] According to an embodiment of the present disclosure, the accuracy of reconstructing or acquiring a light field can be improved. [Brief description of the drawings]

[0018] [Figure 1] FIG. 1 is a cross-sectional view showing a display device according to an embodiment. [Diagram 2] FIG. 2 is a plan view showing a first lens array according to an embodiment. [Diagram 3] FIG. 3 is an enlarged partial cross-sectional view showing a part of the display device according to the embodiment. [Figure 4] FIG. 4 is a plan view illustrating a second unit lens according to an embodiment. [Diagram 5] FIG. 5 is an enlarged view of the area indicated by the reference character V in FIG. 4 and enclosed by a dashed line. [Figure 6] FIG. 6 is a plan view showing a polarization control member according to an embodiment. [Figure 7] FIG. 7 is a diagram illustrating the operation of the optical element according to one embodiment. [Figure 8] FIG. 8 is a diagram illustrating the operation of the optical element according to one embodiment. [Figure 9] FIG. 9 is a cross-sectional view showing a display device according to the first modification. [Figure 10] FIG. 10 is a cross-sectional view showing a display device according to the second modification. [Figure 11A] FIG. 11A is a cross-sectional view showing a display device according to a third modification. [Figure 11B] FIG. 11B is a perspective view showing a display device according to the third modification. [Figure 12] FIG. 12 is a cross-sectional view showing a camera according to the fourth modification. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0019] Hereinafter, an embodiment of the present disclosure will be described with reference to the drawings. In the drawings attached to this specification, the scale and the aspect ratio are appropriately changed and exaggerated from those of the actual objects for the convenience of illustration and understanding.

[0020] In order to clarify the directional relationships between the drawings, common directions are indicated in several drawings by arrows with common symbols. Arrows perpendicular to the plane of the drawings are indicated by a symbol of an X in a circle, as shown in FIG.

[0021] Terms used in this specification that specify shapes and geometric conditions, as well as the degree thereof, such as terms such as "parallel," "perpendicular," and "same," and values ​​of lengths and angles, are not limited to strict meanings, but are interpreted to include a range within which similar functions can be expected. In this specification, terms such as "sheet" and "plate" are not terms that are distinguished from each other based only on the difference in name.

[0022] The optical element 10 according to the present embodiment can be incorporated into a display device 1. FIG. 1 is a cross-sectional view showing the display device 1 including the optical element 10 according to the present embodiment. First, the configuration of the display device 1 including the optical element 10 according to the present embodiment will be described with reference to FIG. 1. As shown in FIG. 1, the display device 1 according to the present embodiment includes the optical element 10 and a display element 60 superimposed on the optical element 10.

[0023] As shown in Fig. 1, the optical element 10 includes a first lens array 20, a second lens array 30, and a polarization control member 40. In the example shown in Fig. 1, the optical element 10 further includes a quarter-wave plate 50. The first lens array 20, the second lens array 30, and the polarization control member 40 are stacked in one direction. The direction in which the first lens array 20, the second lens array 30, and the polarization control member 40 are stacked is referred to as a stacking direction dn.

[0024] The optical element 10 according to the present embodiment is an optical element for a light field. The optical element 10 is incorporated into a device to which a light field is applied, and reproduces or acquires the light field. A light field is a concept that considers light as a field represented by the positions and directions of light rays existing in a space. Reproducing a light field means reproducing a recorded field represented by the positions and directions of light rays in a target space. Acquiring a light field means recording a field represented by the positions and directions of light rays existing in a target space.

[0025] Next, each of the components of the optical element 10 will be described in detail.

[0026] <First lens array> As shown in Fig. 1, the first lens array 20 has a plurality of first unit lenses 21. In the example shown in Fig. 1, the first lens array 20 has a sheet-like first main body portion 22 together with the first unit lenses 21. The plurality of first unit lenses 21 are arranged on one surface 22a of the first main body portion 22. In the example shown in Fig. 1, the surface 22a of the first main body portion 22 is a surface perpendicular to the stacking direction dn.

[0027] FIG. 2 is a plan view showing the first lens array 20 according to the present embodiment, observed from the side of the surface 22a of the first main body portion 22. In the example shown in FIG. 2, the first unit lenses 21 are two-dimensionally arranged. In the example shown in FIG. 2, the first unit lenses 21 are arranged at regular intervals in each of the first direction d1 and the second direction d2, which are two different directions on a plane. In the example shown in FIG. 2, the first direction d1 is a direction parallel to the surface 22a of the first main body portion 22. The second direction d2 is a direction parallel to the surface 22a of the first main body portion 22 and perpendicular to the first direction d1. In the example shown in FIG. 2, the first unit lenses 21 are arranged in the first direction d1 and the second direction d2 at a common and constant arrangement pitch P1. In the example shown in FIG. 2, the first lens array 20 is a so-called fly's eye lens.

[0028] In one example, when the first lens array 20 is observed from the stacking direction dn (see FIG. 2), the contour shape of each of the first unit lenses 21 is circular.

[0029] The arrangement and contour shape of the first unit lenses 21 are not limited to the examples shown in FIG. 1 and FIG. 2. Although not shown, the contour shape of the first unit lenses 21 when observed from the stacking direction dn may be a four-fold symmetric shape other than a circle. The contour shape of the first unit lenses 21 may be a quadrangle or a substantially quadrangle. The contour shape of the first unit lenses 21 may be a square or a substantially square. The first unit lenses 21 having a quadrangle or a substantially quadrangle contour shape may be arranged in a lattice shape. In addition, the second direction d2 may be inclined by an angle of 60° with respect to the first direction d1. In this case, although not shown, the contour shape of the first unit lenses 21 when observed from the stacking direction dn may be a six-fold symmetric shape other than a circle. The contour shape of the first unit lenses 21 may be a regular hexagon or a substantially regular hexagon. The first unit lenses 21 having a regular hexagon or a substantially regular hexagon contour shape may be arranged in a honeycomb shape. Although not shown, the multiple first unit lenses 21 may be arranged without gaps between each other, or may be arranged so as not to contact each other. From the viewpoint of increasing the resolution of a device that reproduces or acquires a light field in which the optical element 10 is incorporated, it is preferable that the multiple first unit lenses 21 are arranged without gaps between each other.

[0030] In this specification, the side from the polarization control member 40 toward the second lens array 30 in the stacking direction dn is referred to as the first side dn1. The side from the second lens array 30 toward the polarization control member 40 in the stacking direction dn is referred to as the second side dn2. When a lens and an optical system functioning as a lens focus light traveling in the stacking direction dn toward the first side dn1, the focal length of the lens and the optical system is expressed as a positive value. When a lens and an optical system functioning as a lens diverge light traveling in the stacking direction dn toward the first side dn1, the focal length of the lens and the optical system is expressed as a negative value. Based on the above, the focal length f1 of the first unit lens 21 will be described.

[0031] FIG. 3 is an enlarged cross-sectional view showing one first unit lens 21 of the first lens array 20, a portion of the optical element 10 other than the first lens array 20, and a portion of the display element 60 overlapping with the one first unit lens 21. As shown in FIG. 3, one first unit lens 21 and a portion of the optical element 10 other than the first lens array 20 overlapping with the one first unit lens 21 are collectively referred to as an optical system unit 2. The optical element 10 of the present embodiment includes a plurality of optical system units 2. In the example shown in FIG. 3, one optical system unit 2 includes one first unit lens 21, one second unit lens 31 (described later) corresponding to the one first unit lens 21, one cell 41 (described later) corresponding to the one first unit lens 21, and a part of a quarter-wave plate 50 (described later).

[0032] In this embodiment, the focal length f1 of the first unit lens 21 shown in FIG. 3 is a positive value. The solid line with the symbol L3 shown in FIG. 3 shows an example of an optical path when light traveling parallel to the stacking direction dn toward the first side dn1 passes through the first unit lens 21. In the example shown in FIG. 3, the surface 211 of the first side dn1 of the first unit lens 21 has a shape of a convex lens surface. In the example shown in FIG. 3, the surface 211 of the first unit lens 21 is a curved surface having a shape corresponding to a part of a spherical surface. As a result, the first unit lens 21 focuses the light traveling in the stacking direction dn toward the first side dn1 to a focal point F1 located on the first side dn1 of the first unit lens 21. For this reason, the focal length f1 of the first unit lens 21 is a positive value.

[0033] The first lens array 20 as shown in FIG. 1 to FIG. 3 is manufactured by, for example, the following method. First, a material having fluidity is supplied to one surface of a sheet material. As the material having fluidity, various known materials that can be used for molding can be used. In the following example, an example in which an ionizing radiation curable resin is supplied will be described. Examples of the ionizing radiation curable resin include ultraviolet curable resin, electron beam curable resin, visible light curable resin, and near infrared curable resin. Next, the surface of the sheet material to which the material having fluidity is supplied is pressed against a mold having a shape corresponding to the shape of the first lens array 20 having a plurality of first unit lenses 21. Then, ionizing radiation according to the curing characteristics of the material having fluidity is emitted from the surface of the sheet material to which the material having fluidity is not supplied. In this way, the first lens array 20 can be manufactured. In this case, the first main body portion 22 of the first lens array 20 is formed from the above-mentioned sheet material and a portion where the material having fluidity is cured into a sheet shape. A plurality of first unit lenses 21 are formed from a part of the portion where the material having fluidity is cured.

[0034] <Second lens array> As shown in FIG. 1, the second lens array 30 has a plurality of second unit lenses 31. Either the right-handed circularly polarized light or the left-handed circularly polarized light is the first circularly polarized light, and the other of the right-handed circularly polarized light and the left-handed circularly polarized light that is not the first circularly polarized light is the second circularly polarized light. At this time, the second unit lens 31 functions as a lens with a focal length f2 for the incident first circularly polarized light and functions as a lens with a focal length -f2 for the incident second circularly polarized light. f2 is a positive value. In other words, the second unit lens 31 focuses one of the right-handed circularly polarized light and the left-handed circularly polarized light, and diverges the other. The first circularly polarized light may be right-handed circularly polarized light, and the second circularly polarized light may be left-handed circularly polarized light. The first circularly polarized light may be left-handed circularly polarized light, and the second circularly polarized light may be right-handed circularly polarized light. In the following, unless otherwise specified, a case will be described in which the first circularly polarized light is right-handed circularly polarized light, and the second circularly polarized light is left-handed circularly polarized light. In this case, the second unit lens 31 functions as a lens with a focal length f2 for right-handed circularly polarized light that travels in the stacking direction dn toward the first side dn1 and is incident on the second unit lens 31. The second unit lens 31 functions as a lens with a focal length -f2 for left-handed circularly polarized light that travels in the stacking direction dn toward the first side dn1 and is incident on the second unit lens 31. In addition, the absolute value of the focal length of the second unit lens 31 when right-handed circularly polarized light is incident is equal to the absolute value of the focal length of the second unit lens 31 when left-handed circularly polarized light is incident.

[0035] FIG. 3 shows the focal length f2 and the focal length −f2 when the first circularly polarized light is right-handed and the second circularly polarized light is left-handed. The solid line with the symbol L4 in FIG. 3 shows an example of an optical path when right-handed circularly polarized light traveling parallel to the stacking direction dn toward the first side dn1 passes through the second unit lens 31. When the first circularly polarized light is right-handed and the second circularly polarized light is left-handed, the second unit lens 31 focuses the right-handed circularly polarized light traveling in the stacking direction dn toward the first side dn1 and entering the second unit lens 31. The solid line with the symbol L5 in FIG. 3 shows an example of an optical path when left-handed circularly polarized light traveling parallel to the stacking direction dn toward the first side dn1 passes through the second unit lens 31. When the first circularly polarized light is right-handed and the second circularly polarized light is left-handed, the second unit lens 31 diverges the left-handed circularly polarized light traveling in the stacking direction dn toward the first side dn1 and entering the second unit lens 31. Although not shown, when the first circularly polarized light is left-handed and the second circularly polarized light is right-handed, the second unit lens 31 diverges the right-handed circularly polarized light traveling in the stacking direction dn toward the first side dn1 and entering the second unit lens 31. Furthermore, when the first circularly polarized light is left-handed and the second circularly polarized light is right-handed, the second unit lens 31 focuses the left-handed circularly polarized light traveling in the stacking direction dn toward the first side dn1 and entering the second unit lens 31.

[0036] The absolute value of the focal length f2 is greater than the focal length f1. That is, the second unit lenses 31 function as lenses with a smaller refractive power than the first unit lenses 21.

[0037] FIG. 4 is a diagram showing an example of the second unit lens 31 having the optical action described above. FIG. 4 corresponds to a plan view showing the second unit lens 31 observed from the stacking direction dn. The straight lines in the pattern region 32 in FIG. 4 indicate the direction of the in-plane slow axis. For the sake of simplicity, FIG. 4 avoids strictly illustrating the direction of the in-plane slow axis in a practical second unit lens 31, and illustrates a more simplified direction of the in-plane slow axis. The second unit lens 31 shown in FIG. 4 is a so-called PBP lens (Pancharatnam Berry Phase lens).

[0038] In the example shown in Fig. 4, the contour shape of the second unit lenses 31 when the second lens array 30 is observed from the stacking direction dn is circular. A direction from the geometric center GC of the contour shape of the second unit lenses 31 to the outside of the contour of the second unit lenses 31 when the second lens array 30 is observed from the stacking direction dn is called a radial direction da. A direction going around the geometric center GC of the contour shape of the second unit lenses 31 when the second lens array 30 is observed from the stacking direction dn is called a circumferential direction db. The radial direction da and the circumferential direction db are directions perpendicular to the stacking direction dn.

[0039] The second lens array 30 is a half-wave plate having a plurality of second unit lenses 31. In the optical element 10, the second lens array 30 is arranged so that the surface of the second lens array 30 is perpendicular to the stacking direction dn. The second unit lenses 31 are diffractive lenses. The second unit lenses 31 have a plurality of pattern regions 32. Each of the plurality of pattern regions 32 spreads in the circumferential direction db. The plurality of pattern regions 32 are arranged along the radial direction da. In the example shown in FIG. 4, the plurality of pattern regions 32 include a first pattern region 32a, a second pattern region 32b, and a third pattern region 32c. The first pattern region 32a is the pattern region 32 located at the innermost position (closest to the geometric center GC) in the radial direction da. In the example shown in FIG. 4, the first pattern region 32a is a circular region including the geometric center GC. In the example shown in Fig. 4, the second pattern region 32b is an annular region surrounding the first pattern region 32a from the outside in the radial direction da. In the example shown in Fig. 4, the third pattern region 32c is an annular region surrounding the second pattern region 32b from the outside in the radial direction da.

[0040] FIG. 5 is an enlarged view of the region surrounded by the dashed line marked with the symbol V in FIG. 4. FIG. 5 is an enlarged view of a part of the periphery of the second pattern region 32b in FIG. 4. The straight lines in the pattern region 32 in FIG. 5 indicate the direction of the slow axis in the plane. As shown in FIG. 4 and FIG. 5, each of the pattern regions 32 has a plurality of optical axis pattern regions Pa in which the angles of the slow axis direction with respect to the direction extending along any straight line perpendicular to the stacking direction dn are different from each other. The direction dc shown in FIG. 4 and FIG. 5 is a direction extending along a straight line perpendicular to the stacking direction dn. This direction dc is also referred to as the reference direction dc. At this time, each of the pattern regions 32 has a plurality of optical axis pattern regions Pa in which the angles of the slow axis direction with respect to the reference direction dc are different from each other. For example, as shown in FIG. 5, the second pattern region 32b has a plurality of second optical axis pattern regions Pa2 in which the angles of the slow axis direction with respect to the reference direction dc are different from each other. In the example shown in FIG. 5, the second pattern region 32b has n second optical axis pattern regions Pa2 from region Pa21 to region Pa2n. FIG. 5 shows region Pa1n, which is the first optical axis pattern region Pa1 located at the outermost position in the radial direction da among the multiple optical axis pattern regions Pa of the first pattern region 32a, together with the n second optical axis pattern regions Pa2. Furthermore, FIG. 5 shows region Pa31, which is the third optical axis pattern region Pa3 located at the innermost position in the radial direction da among the multiple optical axis pattern regions Pa of the third pattern region 32c. The multiple optical axis pattern regions Pa are arranged along the circumferential direction db. Each of the multiple optical axis pattern regions Pa spreads in the circumferential direction db. The multiple optical axis pattern regions Pa are lined up along the radial direction da. Within one optical axis pattern region Pa spreading in the circumferential direction db, the angle that the direction of the slow axis makes with respect to the direction extending along any straight line perpendicular to the stacking direction dn is constant. Therefore, within one optical axis pattern area Pa extending in the circumferential direction db, the angle that the direction of the slow axis makes with respect to the reference direction dc is constant.

[0041] In the example shown in Fig. 4, the direction of the slow axis in the pattern region 32 gradually changes in the radial direction da. Consider a case where the second unit lens 31 is observed in order along the radial direction da from the optical axis pattern region Pa located at the innermost position in one pattern region 32 to the optical axis pattern region Pa located at the innermost position in another pattern region 32 that contacts the one pattern region 32 from the outside. In this case, the direction of the slow axis in the optical axis pattern region Pa gradually changes so as to rotate 180° from the optical axis pattern region Pa located at the innermost position in one pattern region 32 to the optical axis pattern region Pa located at the innermost position in the other pattern region 32.

[0042] As a specific example, in the example shown in FIG. 5, the second pattern region 32b has a region Pa21 as the optical axis pattern region Pa located at the innermost position in the radial direction da in the second pattern region 32b. The third pattern region 32c corresponds to a pattern region 32 other than the second pattern region 32b, which contacts the second pattern region 32b from the outside in the radial direction da. The third pattern region 32c has a region Pa31 as the optical axis pattern region Pa located at the innermost position in the radial direction da in the third pattern region 32c. The second pattern region 32b has n second optical axis pattern regions Pa2 from region Pa21 to region Pa2n as the optical axis pattern region Pa. Consider the case where the second unit lens 31 shown in FIG. 5 is observed in sequence from region Pa21 to region Pa31 along the radial direction da. In this case, n second optical axis pattern regions Pa2 from region Pa21 to region Pa2n are observed in sequence, and then region Pa31 is observed. Therefore, n+1 optical axis pattern regions Pa are observed. At this time, the direction of the slow axis in the optical axis pattern region Pa gradually changes so as to rotate 180° from the region Pa21 to the region Pa31.

[0043] The width of the pattern region 32 in the radial direction da is smaller in the pattern region 32 located further outward in the radial direction da. In the example shown in Fig. 4, the second pattern region 32b is located further outward in the radial direction da than the first pattern region 32a. The width w2 of the second pattern region 32b is smaller than the width w1 of the first pattern region 32a. Furthermore, the third pattern region 32c is located further outward in the radial direction da than the second pattern region 32b. The width w3 of the third pattern region 32c is smaller than the width w2 of the second pattern region 32b.

[0044] The action of the second unit lens 31 described above will be explained. The second lens array 30, which is a half-wave plate, has the second unit lens 31 described above. Therefore, the second unit lens 31 changes the incident right-handed circularly polarized light to left-handed circularly polarized light, and changes the incident left-handed circularly polarized light to right-handed circularly polarized light. More specifically, the second unit lens 31 changes the right-handed circularly polarized light that travels in the stacking direction dn toward the first side dn1 and enters the second unit lens 31 to left-handed circularly polarized light. The second unit lens 31 changes the left-handed circularly polarized light that travels in the stacking direction dn toward the first side dn1 and enters the second unit lens 31 to right-handed circularly polarized light. The width of the pattern area 32 of the second unit lens 31 in the radial direction da becomes smaller in the pattern area 32 located further outward in the radial direction da. Therefore, the circularly polarized light that enters the second unit lens 31 is diffracted so as to make a larger angle with respect to the stacking direction dn in the pattern area 32 located further outward in the radial direction da. As a result, the second unit lens 31 functions as a lens that focuses or diffuses the incident circularly polarized light. The direction of the slow axis in the optical axis pattern area Pa gradually changes so as to rotate 180° from the optical axis pattern area Pa located at the innermost position in one pattern area 32 to the optical axis pattern area Pa located at the innermost position in another pattern area 32 that contacts the one pattern area 32 from the outside. As a result, the second unit lens 31 focuses one of the right-handed circularly polarized light and the left-handed circularly polarized light and diverges the other. As a result, the second unit lens 31 having the above-mentioned characteristics can function as a lens with a focal length f2 for the incident first circularly polarized light, and can function as a lens with a focal length -f2 for the incident second circularly polarized light.

[0045] In this embodiment, the second unit lenses 31 are two-dimensionally arranged. In this embodiment, the second unit lenses 31 are arranged at regular intervals in each of two different directions, a first direction d1 and a second direction d2, on a plane, similar to the first unit lenses 21.

[0046] The arrangement and contour shape of the second unit lenses 31 are not limited to the above example. The arrangement and contour shape of the second unit lenses 31 may be the same as the arrangement and contour shape of the first unit lenses 21 described above, unless there is a contradiction.

[0047] The second lens array 30 having the second unit lenses 31 shown in FIG. 4 and FIG. 5 can be manufactured by, for example, the following method. First, an alignment film is formed. The alignment film plays a role in facilitating alignment of a liquid crystal compound described later in the second lens array 30 when the second lens array 30 is formed. The alignment film has a means for imparting an alignment regulating force corresponding to the slow axis in the optical axis pattern region Pa of the second unit lenses 31 of the second lens array 30. As an example, the means for imparting an alignment regulating force is unevenness formed on the surface of the alignment film and corresponding to the slow axis in the optical axis pattern region Pa of the second unit lenses 31 of the second lens array 30. In this case, the unevenness of the alignment film can be formed by, for example, an imprint method. That is, the unevenness of the alignment film can be formed by shaping a layer containing a resin using a plate having a shape complementary to the surface shape of the alignment film. The material for forming the alignment film is, for example, a resin composition such as a UV-curable resin.

[0048] Next, the second lens array 30 is formed on the alignment film. The second lens array 30 can be formed, for example, by applying a composition constituting the second lens array 30 on the alignment film, and then drying and curing the composition. As an example, the second lens array 30 contains a liquid crystal compound. In this case, the second lens array 30 can be formed by applying a composition containing a liquid crystal compound on the alignment film, and then drying and curing the composition. By forming the second lens array 30 containing a liquid crystal compound on an alignment film having concaves and convexes as a means for imparting an alignment regulating force, the liquid crystal compound can be aligned in a predetermined direction along the concaves of the concaves and convexes. After the second lens array 30 is formed, the alignment film is removed. As a result, the second unit lenses 31 having the optical axis pattern region Pa in which the direction of the slow axis is oriented in a desired direction can be formed in the second lens array 30.

[0049] As shown in FIG. 1, each of the first unit lenses 21 of the first lens array 20 and each of the second unit lenses 31 of the second lens array 30 have a corresponding relationship. In the example shown in FIG. 1, one second unit lens 31 is provided corresponding to one first unit lens 21. In the examples shown in FIG. 1 and FIG. 3, one first unit lens 21 and one second unit lens 31 corresponding to one first unit lens 21 overlap in the stacking direction dn. In this embodiment, the shape of the outline of the first unit lens 21 when the first lens array 20 is observed from the stacking direction dn and the shape of the outline of the second unit lens 31 when the second lens array 30 is observed from the stacking direction dn have the same shape. The focal point when one second unit lens 31 corresponding to one first unit lens 21 shown in FIG. 3 functions as a lens with a focal length f2 is defined as a focal point F2. The focal point when one second unit lens 31 corresponding to one first unit lens 21 shown in FIG. 3 functions as a lens with a focal length -f2 is defined as a focal point F3. 3, the focal points F1, F2, and F3 of the first unit lenses 21 are aligned on a straight line L1. The straight line L1 is a straight line parallel to the stacking direction dn.

[0050] <Polarization control material> The polarization control member 40 is a member that covers the plurality of second unit lenses 31 and transmits right-handed or left-handed circularly polarized light. FIG. 6 is a plan view showing an example of the polarization control member 40 observed from the stacking direction dn. In this embodiment, the polarization control member 40 has a plurality of cells 41. The state of each of the plurality of cells 41 can be switched between a first state in which the incident right-handed circularly polarized light is changed to left-handed circularly polarized light and the incident left-handed circularly polarized light is changed to right-handed circularly polarized light, and a second state in which the incident right-handed circularly polarized light and the left-handed circularly polarized light are transmitted without changing the polarization state. In this embodiment, the state of each of the plurality of cells 41 can be switched between a first state and a second state independently of the other cells 41. For example, a part of the plurality of cells 41 can be set to the first state, and the other cells 41 not included in the part can be set to the second state.

[0051] In the example shown in FIG. 1 and FIG. 3, the polarization control member 40 is located on the second side dn2 of the second lens array 30 in the stacking direction dn. The polarization control member 40 is stacked on the second lens array 30 in the stacking direction dn without any other member sandwiched therebetween. In the example shown in FIG. 3, the polarization control member 40 has a first surface 40a and a second surface 40b located on the opposite side to the first surface 40a. The first surface 40a of the polarization control member 40 faces the second lens array 30. As a result, by switching the state of the cell 41 of the polarization control member 40 between the first state and the second state, it is possible to switch whether right-handed circularly polarized light or left-handed circularly polarized light is incident on the second unit lens 31. For example, when right-handed circularly polarized light traveling toward the first side dn1 in the stacking direction dn is incident on the cell 41, the left-handed circularly polarized light can be incident on the second unit lens 31 by switching the state of the cell 41 to the first state. By setting the state of the cell 41 to the second state, right-handed circularly polarized light can be made incident on the second unit lens 31 .

[0052] In this embodiment, the polarization control member 40 has a plurality of liquid crystal cells 42 that impart a phase difference of 1 / 2 wavelength to the incident light in either a state where a voltage is applied or a state where a voltage is not applied. In this embodiment, the above-mentioned cell 41 is a liquid crystal cell 42. The liquid crystal cell 42 imparts a phase difference of 1 / 2 wavelength to two vertically polarized components of the incident light in either a state where a voltage is applied or a state where a voltage is not applied. As a result, the liquid crystal cell 42 changes the incident right-handed circularly polarized light to left-handed circularly polarized light and the incident left-handed circularly polarized light to right-handed circularly polarized light in either a state where a voltage is applied or a state where a voltage is not applied. In the other state, the liquid crystal cell 42 transmits the incident right-handed circularly polarized light and the incident left-handed circularly polarized light without changing the polarization state. As an example, in a state where a voltage is not applied, the liquid crystal cell 42 changes the incident right-handed circularly polarized light to left-handed circularly polarized light and the incident left-handed circularly polarized light to right-handed circularly polarized light. When a voltage is applied to the liquid crystal cell 42, the liquid crystal cell 42 transmits the incident right-handed and left-handed circularly polarized light without changing the polarization state. In this case, the liquid crystal cell 42 is in a first state when no voltage is applied, and in a second state when a voltage is applied.

[0053] The form of the liquid crystal cell 42 is not particularly limited as long as it can impart a phase difference of 1 / 2 wavelength to the incident light in either a state where a voltage is applied or a state where a voltage is not applied. As an example, the liquid crystal cell 42 has a liquid crystal material filled between two alignment films. In this case, by switching between a state where a voltage is applied and a state where a voltage is not applied, the alignment of the liquid crystal material changes, and the first state and the second state are switched. As an example, the liquid crystal cell 42 is of a TN (Twisted Nematic) type. The liquid crystal cell 42 may be of a VA (Vertical Alignment) type.

[0054] 6, the plurality of cells 41 are arranged two-dimensionally. In this embodiment, the plurality of cells 41 are arranged at regular intervals in each of the first direction d1 and the second direction d2, which are two different directions on a plane, similar to the first unit lens 21 and the second unit lens 31. As a description of the arrangement of the plurality of cells 41, the above-mentioned descriptions of the arrangement of the plurality of first unit lenses 21 and the arrangement of the plurality of second unit lenses 31 can be applied unless contradicted.

[0055] As shown in FIG. 1, each of the second unit lenses 31 of the second lens array 30 and each of the cells 41 of the polarization control member 40 have a corresponding relationship. In the example shown in FIG. 1, one cell 41 is provided corresponding to one second unit lens 31. In the examples shown in FIG. 1 and FIG. 3, one second unit lens 31 and one cell 41 corresponding to one second unit lens 31 overlap in the stacking direction dn. As a result, each of the first unit lenses 21 of the first lens array 20 and each of the cells 41 of the polarization control member 40 have a corresponding relationship. In the example shown in FIG. 1, one cell 41 is provided corresponding to one first unit lens 21. In the examples shown in FIG. 1 and FIG. 3, one first unit lens 21 and one cell 41 corresponding to one first unit lens 21 overlap in the stacking direction dn.

[0056] <1 / 4 wavelength plate> The quarter-wave plate 50 is a retardation plate that imparts a phase difference of a quarter wavelength to incident light. The quarter-wave plate 50 imparts a phase difference of a quarter wavelength to two perpendicularly polarized components of light traveling in the stacking direction dn toward the first side dn1 and incident on the quarter-wave plate 50. This causes the quarter-wave plate 50 to change the incident linearly polarized light into circularly polarized light. The quarter-wave plate 50 changes the linearly polarized light traveling in the stacking direction dn toward the first side dn1 into circularly polarized light, which is then incident on the polarization control member 40.

[0057] In the example shown in FIG. 1, the first lens array 20 is located on a first side dn1 of the second lens array 30 and the polarization control member 40. The first lens array 20 may be located on a second side dn2 of the second lens array 30 and the polarization control member 40. In the example shown in FIG. 1, the quarter-wave plate 50 is located on the second side dn2 of the second lens array 30 and the polarization control member 40. The quarter-wave plate 50 is located on the second side dn2 of the first lens array 20. In the optical element 10 shown in FIG. 1, the quarter-wave plate 50, the polarization control member 40, the second lens array 30, and the first lens array 20 are laminated in this order from the second side dn2 toward the first side dn1.

[0058] Next, a description will be given of the display device 1 including the optical element 10. The display device 1 includes the optical element 10 and a display element 60 superimposed on the optical element 10.

[0059] <Display element> The display element 60 displays an image of a three-dimensional object on which a light field is to be reproduced. The display element 60 faces the second surface 40b of the polarization control member 40. In particular, the light exit surface 60a of the display element 60 faces the second surface 40b of the polarization control member 40. In the example shown in FIG. 1, the display element 60 is overlaid on the optical element 10 and faces the second surface 40b of the polarization control member 40 with the quarter-wave plate 50 sandwiched therebetween. The display element 60 is located on the second side dn2 of the optical element 10.

[0060] In the example shown in FIG. 1, the display element 60 has a plurality of elemental image regions 61. In this embodiment, the elemental image regions 61 are arranged two-dimensionally. In this embodiment, the plurality of elemental image regions 61 are arranged at regular intervals in each of the first direction d1 and the second direction d2, which are two different directions on a plane, similar to the first unit lenses 21, the second unit lenses 31, and the cells 41. As a description of the arrangement of the plurality of elemental image regions 61, the above-mentioned descriptions of the arrangement of the plurality of first unit lenses 21, the arrangement of the plurality of second unit lenses 31, and the plurality of cells 41 can be applied, unless contradicted.

[0061] As shown in FIG. 1, each of the elemental image regions 61 of the display element 60 and each of the first unit lenses 21 of the first lens array 20 have a corresponding relationship. In the example shown in FIG. 1, one elemental image region 61 is provided corresponding to one first unit lens 21. Each of the elemental image regions 61 of the display element 60 and each of the second unit lenses 31 of the second lens array 30 have a corresponding relationship. In the example shown in FIG. 1, one elemental image region 61 is provided corresponding to one second unit lens 31. Furthermore, each of the elemental image regions 61 of the display element 60 and each of the cells 41 of the polarization control member 40 have a corresponding relationship. In the example shown in FIG. 1, one elemental image region 61 is provided corresponding to one cell 41. In the example shown in Figure 1, one first unit lens 21, one second unit lens 31 corresponding to the one first unit lens 21, one cell 41 corresponding to the one first unit lens 21, and one elemental image area 61 corresponding to the one first unit lens 21 are overlapped in the stacking direction dn.

[0062] Each of the elemental image regions 61 displays a part of an image of a three-dimensional object for which a light field is to be reproduced. The light emitted from each of the elemental image regions 61 is incident on the optical element 10, whereby the light field is reproduced. That is, the position and direction of light rays that are visually recognized when the three-dimensional object for which the light field is to be reproduced is viewed from a specific viewpoint are reproduced. This allows the user of the display device 1, who visually recognizes the light rays whose position and direction have been reproduced, to visually recognize a three-dimensional image of the target object.

[0063] As an example, each of the multiple elemental image regions 61 has multiple pixels. By adjusting which of the multiple pixels in one elemental image region 61 is to be lit, the position and direction of the light rays incident on the cell 41, the first unit lens 21, and the second unit lens 31 corresponding to the one elemental image region 61 can be adjusted. This allows the display device 1 to display various images of three-dimensional objects. Furthermore, the position and direction of the light rays viewed from the viewpoint of the user viewing the display device 1 can be reproduced in accordance with the viewpoint of the user. Therefore, even if the viewpoint of the user viewing the display device 1 is not fixed to a specific position and it is expected that the user will view the display device 1 from various positions, the light field can be reproduced in accordance with the viewpoint of the user viewing the display device 1. In such a case, the display device 1 may further include an eye tracking device that detects the position of the user's viewpoint. By including the eye tracking device in the display device 1, the light field can be reproduced in accordance with the viewpoint detected by the eye tracking device. A specific example of a case in which it is expected that the user will view the display device 1 from various positions is a case in which the display device 1 is a stationary display.

[0064] The display element 60 of the present embodiment emits linearly polarized light. The display element 60 emits linearly polarized light traveling in the stacking direction dn toward the first side dn1 in each of the multiple elemental image regions 61. The display element 60 includes, for example, an organic EL (Electro Luminescence) display. The display element 60 may include a metal layer, a support substrate, a resin substrate, a thin film transistor (TFT), and an organic EL layer, which are not shown. When the display element 60 includes an organic EL display, the display element 60 may further include a circular polarizing plate provided on the light exit surface side of the organic EL display. The circular polarizing plate is composed of a retardation plate that functions as a quarter-wave plate, and a polarizing plate located on the light exit surface side of the retardation plate. The circular polarizing plate works as follows. When external light incident on the organic EL display from the surroundings passes through the polarizing plate, linearly polarized light having a polarization plane in a specific direction is transmitted, and linearly polarized light having a polarization plane perpendicular to the retardation plate is absorbed. The linearly polarized light transmitted through the polarizing plate is subjected to the action of the retardation plate, and becomes circularly polarized light whose polarization plane rotates. When the light that has passed through the retardation plate is reflected by the internal structure of the organic EL display, it becomes circularly polarized light whose rotation direction is reversed. The reflected light again enters the retardation plate, and when passing through it, it is converted into linearly polarized light by the action of the retardation plate and is absorbed by the polarizing plate. Therefore, the light does not return to the outside. As described above, the circular polarizing plate can prevent external light from being reflected by the organic EL display and reaching the user's eyes. Such a display element 60 having an organic EL display and a circular polarizing plate can emit linearly polarized light. The display element 60 may include a liquid crystal display. Even when the display element 60 includes a liquid crystal display, the display element 60 can emit linearly polarized light. In the display device 1 of this embodiment, the linearly polarized light emitted from the display element 60 is converted into circularly polarized light by the quarter-wave plate 50, and then enters the polarization control member 40.

[0065] The operation of the display device 1 and the optical element 10 of the present embodiment will be described. As an example, the operation of the display device 1 and the optical element 10 will be described when the linearly polarized light emitted from the display element 60 is changed to right-handed circularly polarized light by the quarter-wave plate 50, and the first circularly polarized light is right-handed circularly polarized light and the second circularly polarized light is left-handed circularly polarized light. In particular, the operation of the display device 1 and the optical element 10 will be described when linearly polarized light traveling parallel to the stacking direction dn toward the first side dn1 is emitted from the display element 60. FIG. 7 is a diagram showing an optical path L2 of light emitted from one elemental image region 61 of the display element 60 when the cell 41 is in the first state. FIG. 8 is a diagram showing an optical path of light emitted from one elemental image region 61 of the display element 60 when the cell 41 is in the second state. In FIGS. 7 and 8, the light is right-handed circularly polarized light in the portion of the optical path L2 indicated by the dashed line. The light is left-handed circularly polarized light in the portion of the optical path L2 indicated by the dashed line.

[0066] As shown in FIG. 7, when the cell 41 is in the first state, the right-handed circularly polarized light output from the quarter-wave plate 50 is converted to left-handed circularly polarized light by the cell 41 and then enters the second unit lens 31. Since the first circularly polarized light is right-handed and the second circularly polarized light is left-handed, the second unit lens 31 functions as a lens that focuses the right-handed circularly polarized light and diverges the left-handed circularly polarized light. Therefore, the light is diverged by the second unit lens 31 as shown by the optical path L2 in FIG. 7. The light output from the second unit lens 31 is further entered into the first unit lens 21. The absolute value of the focal length f2 is greater than the focal length f1. Therefore, the first unit lens 21 functions as a lens with a greater refractive power than the second unit lens 31. As a result, the light diverged by the second unit lens 31 is focused by the first unit lens 21. Due to the above action, when the cell 41 is in the first state, one optical system unit 2 of the optical element 10 functions as a lens that focuses light traveling parallel to the stacking direction dn toward the first side dn1 to a focal point F4.

[0067] As shown in FIG. 8, when the cell 41 is in the second state, the right-handed circularly polarized light output from the quarter-wave plate 50 is incident on the second unit lens 31 without the polarization state being changed by the cell 41. As described above, the second unit lens 31 functions as a lens that focuses the right-handed circularly polarized light. Therefore, the light is focused by the second unit lens 31 as shown by the optical path L2 in FIG. 8. The light output from the second unit lens 31 is further incident on the first unit lens 21. As a result, the light focused by the second unit lens 31 is further focused by the first unit lens 21. Due to the above action, when the cell 41 is in the second state, one optical system unit 2 of the optical element 10 functions as a lens that focuses the light traveling toward the first side dn1 in parallel to the stacking direction dn to a focal point F5 as a whole. In FIG. 7, the second unit lens 31 diverges the light, whereas in FIG. 8, the second unit lens 31 focuses the light. Therefore, when cell 41 is in the second state as shown in FIG. 8, one optical system unit 2 of optical element 10 functions as a lens with a smaller focal length overall compared to when cell 41 is in the first state as shown in FIG. 7.

[0068] The accuracy with which a device to which a light field is applied reproduces or acquires a light field is affected by the focal position of the optical element used to reproduce or acquire the light field. For example, in the case of a display device that reproduces a light field, if an image is formed at a position away from the focal position of the optical element, the image is likely to be blurred. In contrast, according to the optical element 10 of the present embodiment, by switching the state of the cell 41 between the first state and the second state, one optical system unit 2 of the optical element 10 can function as a lens with a different focal length as a whole. This allows the focal position of the optical element 10 to be adjusted to a position more preferable for reproducing or acquiring the light field. As described above, the accuracy with which the optical element 10 reproduces or acquires the light field can be increased. When the display device 1 includes the optical element 10 as shown in FIG. 1, the accuracy with which the optical element 10 reproduces the light field can be increased. This allows the user to visually recognize a clear image of a three-dimensional object.

[0069] The display device 1 of the present embodiment has a plurality of optical system units 2. In addition, the state of each of the plurality of cells 41 can be switched between a first state and a second state independently of the other cells 41. Therefore, a part of the plurality of optical system units 2 and the other optical system units 2 not included in the part can be made to function as lenses with different focal lengths. This provides the following effects. It is assumed that a user is required to visually recognize an image having a plurality of parts at different distances from the user's viewpoint. For example, it is assumed that a user is required to visually recognize an image having a first part and a second part that is farther away from the user's viewpoint than the first part. In this case, the optical system unit 2 involved in the formation of the first part of the image can be made to function as a lens with a smaller focal length, and the optical system unit 2 involved in the formation of the second part of the image can be made to function as a lens with a larger focal length. This allows each of the first and second parts of the image to be displayed more clearly. In this way, it is possible to display an image having a plurality of parts at different distances from the user's viewpoint more clearly.

[0070] The optical element 10 of the present embodiment described above includes a first lens array 20 having a plurality of first unit lenses 21 with a positive focal length f1, a second lens array 30 having a plurality of second unit lenses 31 that are diffractive lenses that function as a lens with a focal length f2 for the first circularly polarized light and a lens with a focal length -f2 for the second circularly polarized light when either one of the right-handed circularly polarized light and the left-handed circularly polarized light that is not the first circularly polarized light is the second circularly polarized light, and a polarization control member 40 that covers the plurality of second unit lenses 31 and transmits right-handed circularly polarized light or left-handed circularly polarized light. The absolute value of the focal length f2 is greater than the focal length f1. This allows the position of the focal point of the optical element 10 to be adjusted to a position more preferable for reproducing or acquiring a light field. As described above, the optical element 10 can increase the accuracy with which the light field is reproduced or acquired.

[0071] In the present embodiment, the polarization control member 40 has a first surface 40a facing the second lens array 30 and a second surface 40b located on the opposite side to the first surface 40a. The optical element 10 further includes a quarter-wave plate 50 facing the second surface 40b. This allows circularly polarized light to be incident on the polarization control member 40.

[0072] In this embodiment, the polarization control member 40 has a plurality of liquid crystal cells 42 that impart a phase difference of 1 / 2 wavelength to incident light in either a state where a voltage is applied or a state where a voltage is not applied. This allows the state of the liquid crystal cells 42 to be switched between a state where a voltage is applied and a state where a voltage is not applied, thereby switching between allowing right-handed circularly polarized light or left-handed circularly polarized light to be incident on the second unit lenses 31. As a result, it is possible to switch between allowing the second unit lenses 31 to function as a lens with a focal length f2 or a lens with a focal length -f2.

[0073] In this embodiment, the polarization control member 40 has a plurality of liquid crystal cells 42 that impart a phase difference of 1 / 2 wavelength to incident light in either a state where a voltage is applied or a state where a voltage is not applied. This allows the state of the liquid crystal cells 42 to be switched between a state where a voltage is applied and a state where a voltage is not applied, thereby switching between allowing right-handed circularly polarized light or left-handed circularly polarized light to be incident on the second unit lenses 31. As a result, it is possible to switch between allowing the second unit lenses 31 to function as a lens with a focal length f2 or a lens with a focal length -f2.

[0074] The display device 1 of the present embodiment includes an optical element 10 and a display element 60 that is overlaid on the optical element 10 and faces the second surface 40b of the polarization control member 40 across a quarter-wave plate 50. Thus, linearly polarized light emitted from the display element 60 is converted into circularly polarized light by the quarter-wave plate 50 and then incident on the polarization control member 40.

[0075] <<Modifications>> Next, various modified examples of this embodiment will be described with reference to Figures 9 to 12. In Figures 9 to 12, the same parts as those in the embodiment shown in Figures 1 to 8 are given the same reference numerals and detailed description thereof will be omitted.

[0076] <Variation 1> In the above embodiment, the optical element 10 including the quarter-wave plate 50 has been described. However, as shown in FIG. 9, the optical element 10 does not need to include the quarter-wave plate 50. In this case, the display element 60 may cause right-handed or left-handed circularly polarized light to be incident on the optical element 10. In the example shown in FIG. 9, the display element 60 faces the second surface 40b of the polarization control member 40. In the example shown in FIG. 9, the display element 60 faces the second surface 40b of the polarization control member 40 without sandwiching another member such as the quarter-wave plate 50 therebetween. Even in this case, the display element 60 causes right-handed or left-handed circularly polarized light to be incident on the optical element 10, thereby realizing a display device 1 capable of adjusting the position of the focal point of the optical element 10. The display element 60 that causes right-handed or left-handed circularly polarized light to be incident on the optical element 10 may have, for example, the above-mentioned organic EL display or liquid crystal display, and a quarter-wave plate provided on the light exit surface side of the display. As the explanation of the quarter-wave plate provided on the light exit surface side, the explanation of the quarter-wave plate 50 of the optical element 10 described above can be applied, unless there is a contradiction. The quarter-wave plate converts linearly polarized light emitted from the organic EL display or liquid crystal display into right-handed circularly polarized light or left-handed circularly polarized light, which is then incident on the optical element 10.

[0077] <Variation 2> As shown in FIG. 10, the optical element 10 may further include a third lens array 70 having a plurality of third unit lenses 71, and a second polarization control member 80 covering the plurality of third unit lenses 71.

[0078] Either the right-handed or left-handed circularly polarized light is the third circularly polarized light, and the other of the right-handed or left-handed circularly polarized light that is not the third circularly polarized light is the fourth circularly polarized light. The third lens array 70 includes a plurality of third unit lenses 71 that function as a lens with a focal length f3 for the incident third circularly polarized light and a lens with a focal length -f3 for the incident fourth circularly polarized light. f3 is a positive value. The third circularly polarized light may be right-handed circularly polarized light, and the fourth circularly polarized light may be left-handed circularly polarized light. The third circularly polarized light may be left-handed circularly polarized light, and the fourth circularly polarized light may be right-handed circularly polarized light. In the following, unless otherwise specified, the case where the third circularly polarized light is right-handed circularly polarized light, and the fourth circularly polarized light is left-handed circularly polarized light will be described. In this case, the third unit lens 71 functions as a lens with a focal length f3 for the right circularly polarized light that travels in the stacking direction dn toward the first side dn1 and enters the third unit lens 71. The third unit lens 71 functions as a lens with a focal length −f3 for left-handed circularly polarized light that travels in the stacking direction dn toward the first side dn1 and is incident on the third unit lens 71.

[0079] FIG. 10 shows the focal length f3 and the focal length −f3 when the third circularly polarized light is right-handed and the fourth circularly polarized light is left-handed. When the third circularly polarized light is right-handed and the fourth circularly polarized light is left-handed, the third unit lens 71 focuses the right-handed circularly polarized light that travels in the stacking direction dn toward the first side dn1 and enters the third unit lens 71. When the third circularly polarized light is right-handed and the fourth circularly polarized light is left-handed, the third unit lens 71 diverges the left-handed circularly polarized light that travels in the stacking direction dn toward the first side dn1 and enters the third unit lens 71. The third circularly polarized light may be left-handed and the fourth circularly polarized light may be right-handed. In this case, although not shown, the third unit lens 71 diverges the right-handed circularly polarized light that travels in the stacking direction dn toward the first side dn1 and enters the third unit lens 71. Furthermore, when the third circularly polarized light is left-handed circularly polarized light and the fourth circularly polarized light is right-handed circularly polarized light, the third unit lens 71 focuses the left-handed circularly polarized light that travels in the stacking direction dn toward the first side dn1 and enters the third unit lens 71.

[0080] The absolute value of the focal length f3 is greater than the focal length f1. That is, the third unit lens 71 functions as a lens having a smaller refractive power than the first unit lens 21. Furthermore, the absolute value of the focal length f3 is different from the absolute value of the focal length f2. That is, the third unit lens 71 functions as a lens having a different refractive power from the second unit lens 31. In the example shown in FIG. 10, the absolute value of the focal length f3 is smaller than the absolute value of the focal length f2. In this case, the third unit lens 71 functions as a lens having a larger refractive power than the second unit lens 31. Although not shown, the absolute value of the focal length f3 may be greater than the absolute value of the focal length f2. In this case, the third unit lens 71 functions as a lens having a smaller refractive power than the second unit lens 31. In the second modification, the optical system unit 2 is configured to function as a lens that converges light as a whole, even if both the second unit lens 31 and the third unit lens 71 function as lenses that diffuse light. By making the focal length f1 of the first unit lens 21 sufficiently small compared to the absolute value of the focal length f2 of the second unit lens 31 and the absolute value of the focal length f3 of the third unit lens 71, the optical system unit 2 as a whole can function as a lens that focuses light.

[0081] As an explanation of the characteristics of the third lens array 70 and the third unit lenses 71 other than the focal length f3, the explanation of the second lens array 30 and the second unit lenses 31 described above can be applied, unless there is a contradiction.

[0082] As shown in FIG. 10, each of the first unit lenses 21 of the first lens array 20 and each of the third unit lenses 71 of the third lens array 70 have a corresponding relationship. In the example shown in FIG. 10, one third unit lens 71 is provided corresponding to one first unit lens 21. In the example shown in FIG. 10, one first unit lens 21 and one third unit lens 71 corresponding to one first unit lens 21 overlap in the stacking direction dn. In this embodiment, the contour shape of the first unit lens 21 when the first lens array 20 is observed from the stacking direction dn and the contour shape of the third unit lens 71 when the third lens array 70 is observed from the stacking direction dn have the same shape. The focal point when one third unit lens 71 corresponding to one first unit lens 21 shown in FIG. 10 functions as a lens with a focal length f3 is defined as a focal point F6. The focal point when one third unit lens 71 corresponding to one first unit lens 21 shown in FIG. 10 functions as a lens with a focal length -f2 is defined as a focal point F7. In the example shown in Fig. 10, the focal points F1, F6, and F7 are aligned on a straight line L1 parallel to the stacking direction dn. In the example shown in Fig. 10, the focal points F1, F6, F7, F2, and F3 are aligned on a straight line L1 parallel to the stacking direction dn.

[0083] The second polarization control member 80 is a member that covers the multiple third unit lenses 71 and transmits right-handed circularly polarized light or left-handed circularly polarized light. The second polarization control member 80 has multiple second cells 81. As with the above-mentioned cell 41, the state of each of the multiple second cells 81 can be switched between a first state in which incident right-handed circularly polarized light is changed to left-handed circularly polarized light and incident left-handed circularly polarized light is changed to right-handed circularly polarized light, and a second state in which incident right-handed circularly polarized light and left-handed circularly polarized light are transmitted without changing their polarization state.

[0084] The second polarization control member 80 has a plurality of second liquid crystal cells 82 that impart a phase difference of 1 / 2 wavelength to incident light in either a state in which a voltage is applied or a state in which a voltage is not applied. In the present embodiment, the above-mentioned second cells 81 are the second liquid crystal cells 82.

[0085] As the explanation of the second polarization control member 80, the second cell 81 and the second liquid crystal cell 82, the explanation of the polarization control member 40, the cell 41 and the liquid crystal cell 42 mentioned above can be applied unless there is a contradiction.

[0086] In the example shown in FIG. 10, the second polarization control member 80 is located on the second side dn2 of the third lens array 70 in the stacking direction dn. The second polarization control member 80 is stacked on the third lens array 70 in the stacking direction dn without any other member therebetween. As a result, by switching the state of the second cell 81 of the second polarization control member 80 between the first state and the second state, it is possible to switch whether right-handed circularly polarized light or left-handed circularly polarized light is incident on the third unit lens 71. For example, when right-handed circularly polarized light traveling toward the first side dn1 in the stacking direction dn is incident on the second cell 81, the state of the second cell 81 can be changed to the first state to cause left-handed circularly polarized light to be incident on the third unit lens 71. The state of the second cell 81 can be changed to the second state to cause right-handed circularly polarized light to be incident on the third unit lens 71.

[0087] In the example shown in Figure 10, one optical system unit 2 includes one first unit lens 21, one second unit lens 31 corresponding to the one first unit lens 21, one cell 41 corresponding to the one first unit lens 21, one third unit lens 71 corresponding to the one first unit lens 21, one second cell 81 corresponding to the one first unit lens 21, and a portion of a quarter-wave plate 50.

[0088] In the example shown in FIG. 10, the third lens array 70 and the second polarization control member 80 are located on the first side dn1 of the second lens array 30 and the polarization control member 40. Although not shown, the third lens array 70 and the second polarization control member 80 may be located on the second side dn2 of the second lens array 30 and the polarization control member 40. In the example shown in FIG. 10, the first lens array 20 is located on the first side dn1 of the second lens array 30, the polarization control member 40, the third lens array 70, and the second polarization control member 80. Although not shown, the first lens array 20 may be located on the second side dn2 of the second lens array 30, the polarization control member 40, the third lens array 70, and the second polarization control member 80. Although not shown, the first lens array 20 may be located between the second lens array 30 and the polarization control member 40 and the third lens array 70 and the second polarization control member 80. 10, the quarter-wave plate 50 is located on the second side dn2 of the second lens array 30, the polarization control member 40, the third lens array 70, and the second polarization control member 80. In the optical element 10 shown in Fig. 10, the quarter-wave plate 50, the polarization control member 40, the second lens array 30, the second polarization control member 80, the third lens array 70, and the first lens array 20 are laminated in this order from the second side dn2 toward the first side dn1.

[0089] The following describes the operation of the display device 1 and the optical element 10 of the modified example 2. As an example, the following describes the operation of the display device 1 and the optical element 10 when the linearly polarized light emitted from the display element 60 is changed to right-handed circularly polarized light by the quarter-wave plate 50, the first circularly polarized light is right-handed circularly polarized light, the second circularly polarized light is left-handed circularly polarized light, the third circularly polarized light is right-handed circularly polarized light, and the fourth circularly polarized light is left-handed circularly polarized light, and the absolute value of f3 is smaller than the absolute value of f2.

[0090] When the cell 41 and the second cell 81 are both in the first state, the right-handed circularly polarized light output from the quarter-wave plate 50 is converted to left-handed circularly polarized light by the cell 41 and then enters the second unit lens 31. Since the first circularly polarized light is right-handed and the second circularly polarized light is left-handed, the second unit lens 31 functions as a lens that focuses the right-handed circularly polarized light and diverges the left-handed circularly polarized light. For this reason, the light is diverged by the second unit lens 31. The light is converted to right-handed circularly polarized light by the second unit lens 31 and then enters the second cell 81. The right-handed circularly polarized light output from the second unit lens 31 is converted to left-handed circularly polarized light by the second cell 81 and then enters the third unit lens 71. Since the third circularly polarized light is right-handed and the fourth circularly polarized light is left-handed, the third unit lens 71 functions as a lens that focuses the right-handed circularly polarized light and diverges the left-handed circularly polarized light. For this reason, the light is diverged by the third unit lens 71. The light emitted from the third unit lens 71 is further incident on the first unit lens 21. In the second modification, the focal length f1 of the first unit lens 21 is set to be sufficiently smaller than the absolute value of the focal length f2 of the second unit lens 31 and the absolute value of the focal length f3 of the third unit lens 71 so that the optical system unit 2 as a whole functions as a lens that focuses light. This allows the light diverged by the second unit lens 31 and the third unit lens 71 to be focused by the first unit lens 21. Due to the above action, one optical system unit 2 of the optical element 10 as a whole functions as a lens that focuses the light emitted from the display element 60 when the cell 41 and the second cell 81 are both in the first state.

[0091] When the cell 41 and the second cell 81 are both in the second state, the right-handed circularly polarized light output from the quarter-wave plate 50 is incident on the second unit lens 31 without the polarization state being changed by the cell 41. As described above, the second unit lens 31 functions as a lens that focuses the right-handed circularly polarized light. Therefore, the light is focused by the second unit lens 31. The light is changed to left-handed circularly polarized light by the second unit lens 31 and then further enters the second cell 81. The left-handed circularly polarized light output from the second unit lens 31 is incident on the third unit lens 71 without the polarization state being changed by the second cell 81. As described above, the third unit lens 71 functions as a lens that diverges the left-handed circularly polarized light. Therefore, the light is diverged by the third unit lens 71. The light output from the third unit lens 71 is further entered into the first unit lens 21. As a result, the light focused by the second unit lens 31 and diverged by the third unit lens 71 is focused by the first unit lens 21. By the above action, when the cell 41 and the second cell 81 are both in the second state, one optical system unit 2 of the optical element 10 functions as a lens that focuses the light emitted from the display element 60 as a whole. At this time, the optical system unit 2 functions as a lens with a shorter focal length as a whole than when the cell 41 and the second cell 81 are both in the first state, by the amount of light focused by the second unit lens 31.

[0092] When the cell 41 is in the first state and the second cell 81 is in the second state, the right-handed circularly polarized light output from the quarter-wave plate 50 is converted to left-handed circularly polarized light by the cell 41 and then enters the second unit lens 31. As described above, the second unit lens 31 functions as a lens that diverges left-handed circularly polarized light. Therefore, the light is diverged by the second unit lens 31. The light is converted to right-handed circularly polarized light by the second unit lens 31 and then further enters the second cell 81. The right-handed circularly polarized light output from the second unit lens 31 enters the third unit lens 71 without having its polarization state changed by the second cell 81. As described above, the third unit lens 71 functions as a lens that focuses right-handed circularly polarized light. Therefore, the light is focused by the third unit lens 71. The light output from the third unit lens 71 further enters the first unit lens 21. As a result, the light diverged by the second unit lens 31 and focused by the third unit lens 71 is focused by the first unit lens 21. By the above action, when the cell 41 is in the first state and the second cell 81 is in the second state, one optical system unit 2 of the optical element 10 functions as a lens that focuses the light emitted from the display element 60 as a whole. At this time, the optical system unit 2 functions as a lens with a shorter focal length as a whole than when the cell 41 and the second cell 81 are both in the second state, by the amount that the absolute value of f3 is smaller than the absolute value of f2.

[0093] When the cell 41 is in the second state and the second cell 81 is in the first state, the right-handed circularly polarized light output from the quarter-wave plate 50 is incident on the second unit lens 31 without the polarization state being changed by the cell 41. As described above, the second unit lens 31 functions as a lens that focuses the right-handed circularly polarized light. Therefore, the light is focused by the second unit lens 31. The light is converted to left-handed circularly polarized light by the second unit lens 31 and then further enters the second cell 81. The left-handed circularly polarized light output from the second unit lens 31 is converted to right-handed circularly polarized light by the second cell 81 and then enters the third unit lens 71. As described above, the third unit lens 71 functions as a lens that focuses the right-handed circularly polarized light. Therefore, the light is focused by the third unit lens 71. The light output from the third unit lens 71 is further entered into the first unit lens 21. As a result, the light focused by the second unit lens 31 and the third unit lens 71 is focused by the first unit lens 21. By the above action, when the cell 41 is in the second state and the second cell 81 is in the first state, one optical system unit 2 of the optical element 10 functions as a lens that focuses the light emitted from the display element 60 as a whole. At this time, the optical system unit 2 functions as a lens with a shorter focal length as a whole than when the cell 41 is in the first state and the second cell 81 is in the second state, by the amount of light focused by the second unit lens 31.

[0094] As described above, according to the display device 1 and the optical element 10 of the second modification, by combining the switching of the state of the cell 41 and the switching of the state of the second cell 81, the focal length of one optical system unit 2 of the optical element 10 can be switched between three or more different focal lengths. In particular, the focal length f1 of the first unit lens 21 is set to be sufficiently small so that the optical system unit 2 functions as a lens that focuses light as a whole. This allows the focal length of one optical system unit 2 of the optical element 10 to be switched between four different focal lengths while functioning as a lens that focuses light as a whole. This allows the focal position of the optical element 10 to be adjusted to a position more preferable for reproducing or acquiring a light field.

[0095] The optical element 10 may further include an additional lens array similar to the second lens array 30 or the third lens array 70, except as described below. The absolute value of the focal length of the additional lens array is different from the absolute value of the focal length f2 and the absolute value of the focal length f3. The optical element 10 may further include an additional polarization control member similar to the polarization control member 40 or the second polarization control member 80, except as described below. The additional polarization control member causes right-handed circularly polarized light or left-handed circularly polarized light to be incident on the additional lens array. By the optical element 10 further including the additional lens array and the additional polarization control member, the focal length of one optical system unit 2 of the optical element 10 can be switched between five or more different focal lengths. This allows the position of the focal point of the optical element 10 to be adjusted to a position more preferable for reproducing or acquiring a light field.

[0096] <Variation 3> 11A, the display device 1 may further include an eyepiece lens 3 arranged to sandwich the optical element 10 between it and the display element 60. In the display device 1 shown in Fig. 11A, the display element 60, the optical element 10, and the eyepiece lens 3 are layered in this order from the second side dn2 toward the first side dn1.

[0097] 11A, the first lens array 20 is located on the second side dn2 of the second lens array 30 and the polarization control member 40. In the optical element 10 shown in Fig. 11A, the quarter-wave plate 50, the first lens array 20, the polarization control member 40, and the second lens array 30 are laminated in this order from the second side dn2 toward the first side dn1.

[0098] The eyepiece 3 magnifies the image formed by the display element 60 and the optical element 10. In the example shown in FIG. 11A, the surface 3a of the eyepiece 3 on the first side dn1 has the shape of a convex lens surface. In the example shown in FIG. 11A, the surface 3a of the eyepiece 3 is a curved surface having a shape corresponding to a part of a spherical surface. Therefore, the eyepiece 3 focuses light traveling in the stacking direction dn toward the first side dn1. This allows the eyepiece 3 shown in FIG. 11A to magnify the image formed by the display element 60 and the optical element 10. In the example shown in FIG. 11A, the eyepiece 3 is a convex lens in which both the surface 3a of the first side dn1 and the surface 3b of the second side dn2 are curved surfaces having a shape corresponding to a part of a spherical surface.

[0099] In the example shown in Fig. 11A, the eyepiece 3 overlaps with a plurality of first unit lenses 21 in the stacking direction dn. As a result, the eyepiece 3 overlaps with a plurality of optical system units 2 in the stacking direction dn. In the example shown in Fig. 11A, the eyepiece 3 covers all of the plurality of first unit lenses 21 of the first lens array 20. As a result, the eyepiece 3 covers all of the plurality of optical system units 2 in the stacking direction dn.

[0100] As an example, the eyepiece 3 is provided in a display device 1 in which the viewpoint of a user viewing the display device 1 is expected to be fixed at a specific position. In this case, the position of the eyepiece 3 relative to the display element 60 and the optical element 10 is set so that the image formed by the display element 60 and the optical element 10 can be easily viewed from the expected viewpoint position.

[0101] A specific example of a case where the viewpoint of a user viewing the display device 1 is expected to be fixed at a specific position is a case where the display device 1 is a head-mounted display as shown in FIG. 11B. The display device 1, which is a head-mounted display shown in FIG. 11B, includes a display element 60, an optical element 10, and an eyepiece 3, and a mounting device 1a that holds the display element 60, the optical element 10, and the eyepiece 3. The display element 60, the optical element 10, and the eyepiece 3 are held in the mounting device 1a so that the surface 3a of the eyepiece 3 faces the user's eyes when the user of the display device 1 wears the mounting device 1a on his / her head. The user of the display device 1 can view an image formed by the display element 60 and the optical element 10 and magnified by the eyepiece 3 by wearing the mounting device 1a on his / her head. The display device 1, which is a head-mounted display, may use VR (Virtual Reality) technology or MR (Mixed Reality) technology. The display device 1, which is a head-mounted display, may be VR glasses.

[0102] <Modification 4> In the above-described embodiment and each modified example, an example in which the optical element 10 is incorporated in the display device 1 has been described. However, the use of the optical element 10 is not limited thereto. The optical element 10 may be incorporated in a camera 4 as shown in FIG. 12. The camera 4 is a camera capable of acquiring a light field. In the example shown in FIG. 12, the camera 4 includes the optical element 10 and an image sensor 4a superimposed on the optical element 10. The image sensor 4a faces the second surface 40b of the polarization control member 40. In the example shown in FIG. 12, the image sensor 4a is superimposed on the optical element 10 and faces the second surface 40b of the polarization control member 40 with the quarter-wave plate 50 interposed therebetween. The image sensor 4a is located on the second side dn2 of the optical element 10. In the example shown in FIG. 12, the image sensor 4a has an image sensor 4b. The image sensor 4b detects light that travels from the first side dn1 to the second side dn2 and reaches the image sensor 4b.

[0103] The camera 4 shown in FIG. 12 further includes a lens 4c arranged to sandwich the optical element 10 between the imaging element 4a and the lens 4c. In other words, in the camera 4 shown in FIG. 12, the imaging element 4a, the optical element 10, and the lens 4c are stacked in this order from the second side dn2 toward the first side dn1. The lens 4c adjusts the overall focal length of the optical system including the optical element 10 and the lens 4c to a size preferable for photographing the three-dimensional object O located on the second side dn2 of the camera 4. In the example shown in FIG. 12, the lens 4c is a convex lens in which both the surface on the first side dn1 and the surface on the second side dn2 are curved surfaces having a shape corresponding to a part of a spherical surface.

[0104] 12, the lens 4c overlaps with a plurality of first unit lenses 21 in the stacking direction dn. As a result, the lens 4c overlaps with a plurality of optical system units 2 in the stacking direction dn. In the example shown in Fig. 12, the lens 4c covers all of the plurality of first unit lenses 21 of the first lens array 20. As a result, the lens 4c covers all of the plurality of optical system units 2 in the stacking direction dn.

[0105] 12, the first lens array 20 is located on the second side dn2 of the second lens array 30 and the polarization control member 40. In the optical element 10 shown in Fig. 12, the quarter-wave plate 50, the first lens array 20, the polarization control member 40, and the second lens array 30 are laminated in this order from the second side dn2 toward the first side dn1.

[0106] Although not shown, the camera 4 may include a measurement unit that measures the distance between the three-dimensional object O, which is the subject of the image capture, and the camera 4. In this case, the measurement unit may have a sensor that measures distance, such as LiDAR. As a result, the measurement unit can measure the distance between the three-dimensional object O and the camera 4 using the sensor. The measurement unit may measure the distance between the three-dimensional object O and the camera 4 by the following method. First, the camera 4 captures the three-dimensional object O multiple times while switching the focal position of the optical element 10. Next, the focal position of the optical element 10 when the image of the three-dimensional object O is most clearly formed is identified. Next, the distance between the three-dimensional object O and the camera 4 is calculated from the identified focal position of the optical element 10 when the image of the three-dimensional object O is most clearly formed.

[0107] The operation of the camera 4 shown in FIG. 12 will be described. As an example, the operation of the camera 4 when the camera 4 is used to capture an image of a three-dimensional object O located on the second side dn2 of the camera 4 will be described. The three-dimensional object O is captured by the camera 4 by light from the three-dimensional object O passing through the lens 4c and the optical element 10 and reaching the image sensor 4b of the imaging element 4a. At this time, the light from the three-dimensional object O reaches the image sensor 4b by tracing the optical path in reverse, which was described in the example in which the optical element 10 is incorporated in the display device 1, through which the light passes through the optical element 10 and reaches the user's eye. The light from the three-dimensional object O is decomposed by the optical element 10 when tracing the optical path in reverse, which was described in the example in which the optical element 10 is incorporated in the display device 1. By causing the light decomposed by the optical element 10 to reach the image sensor 4b and detecting it in this way, information regarding the position and direction of the light beam from the three-dimensional object O can be obtained. That is, a light field regarding the light beam from the three-dimensional object O can be obtained.

[0108] One optical system unit 2 of the optical element 10 is made to function as a lens with a different focal length as a whole. Therefore, even when the optical element 10 is incorporated in the camera 4, the precision with which the optical element 10 acquires the light field can be improved by adjusting the focal position of the optical element 10 to a position more favorable for acquiring the light field. In particular, the precision with which the optical element 10 acquires the light field can be improved by measuring the distance between the three-dimensional object O and the camera 4 by the above-mentioned measuring unit and adjusting the focal position of the optical element 10 according to the measured distance between the three-dimensional object O and the camera 4. This allows a clearer image to be captured using the camera 4.

[0109] It is also possible to combine the multiple components disclosed in the above embodiment and each modification as necessary. Alternatively, some components may be deleted from all the components shown in the above embodiment and each modification. [Explanation of symbols]

[0110] 1 Display device 2 Optical system unit 3 Eyepiece 4. Camera 4a Image sensor 10 Optical elements 20 First lens array 21 First unit lens 30 Second lens array 31 Second unit lens 40 Polarization control material 41 Cell 42 Liquid crystal cell 50 1 / 4 wave plate 60 Display element 70 3rd lens array 71 Third unit lens 80 Second polarization control member 81 Cell 2 82 2nd Liquid Crystal Cell

Claims

1. A first lens array including a plurality of first unit lenses each having a positive focal length f1; a second lens array having a plurality of second unit lenses, each of which is a diffractive lens that functions as a lens with a focal length f2 for the first circularly polarized light and a lens with a focal length −f2 for the second circularly polarized light, when one of right-handed circularly polarized light and left-handed circularly polarized light is defined as a first circularly polarized light, and the other of the right-handed circularly polarized light and the left-handed circularly polarized light that is not the first circularly polarized light is defined as a second circularly polarized light; a polarization control member that covers the second unit lenses and transmits right-handed circularly polarized light or left-handed circularly polarized light; An optical element for a light field, wherein the absolute value of the focal length f2 is greater than the focal length f1.

2. the polarization control member has a first surface facing the second lens array and a second surface located on the opposite side to the first surface, The optical element of claim 1 , further comprising a quarter wave plate facing the second surface.

3. 3. The optical element according to claim 1, wherein the polarization control member has a plurality of liquid crystal cells that impart a phase difference of ½ wavelength to incident light in either a state in which a voltage is applied or a state in which a voltage is not applied.

4. a third lens array including a plurality of third unit lenses, each of which is a diffractive lens that functions as a lens with a focal length f3 for the third circularly polarized light and a lens with a focal length -f3 for the fourth circularly polarized light, when one of the right-handed circularly polarized light and the left-handed circularly polarized light that is not the third circularly polarized light is a fourth circularly polarized light; and a second polarization control member that covers the plurality of third unit lenses and transmits right-handed circularly polarized light or left-handed circularly polarized light; The optical element according to claim 1 , wherein an absolute value of the focal length f3 is greater than the focal length f1 and is different from an absolute value of the focal length f2.

5. The optical element according to claim 1 ; a display element overlaid on the optical element, the polarization control member has a first surface facing the second lens array and a second surface located on the opposite side to the first surface, the display element faces a second surface of the polarization control member, A display device in which the display element causes right-handed circularly polarized light or left-handed circularly polarized light to be incident on the optical element.

6. The optical element according to claim 2; a display element that is overlaid on the optical element and faces the second surface of the polarization control member with the quarter-wave plate interposed therebetween.

7. The display device according to claim 5 , further comprising an eyepiece arranged to sandwich the optical element between the display element and an eyepiece lens.

8. The optical element according to claim 1 ; an imaging element overlaid on the optical element; the polarization control member has a first surface facing the second lens array and a second surface located on the opposite side to the first surface, The imaging element faces the second surface of the polarization control member.

Images