Display device

Abstract

Provided is a display device comprising: an eyepiece optical system in which a first lens and a second lens are disposed in order from the eyeball side; and an image display element disposed on the opposite side from the eyeball side with the eyepiece optical system therebetween. The surfaces of the first and second lenses on the image display element side are configured as a Fresnel lens surface.

Description

display device

[0001] The present disclosure relates to a display device.

[0002] Known display devices using image display elements include electronic viewfinders, electronic binoculars, and head-mounted displays (HMDs). In particular, head-mounted displays require small, lightweight eyepieces and a lightweight display device body, since the display device body is worn in front of the eyes for extended periods of time. Furthermore, head-mounted displays are required to present high-resolution images with a wide viewing angle.

[0003] Japanese Patent Application Laid-Open No. 2020-13106

[0004] Therefore, it is known to use a Fresnel lens to reduce the weight and overall length of the eyepiece, but even when a Fresnel lens is used for the eyepiece, conventional techniques have limitations in terms of presenting a wide field of view and a high-resolution image while reducing the weight and overall length.

[0005] Therefore, the present disclosure proposes a display device that is lighter in weight and shorter in overall length, while being capable of presenting a higher-resolution image with a wider viewing angle.

[0006] According to the present disclosure, there is provided a display device comprising an eyepiece optical system in which a first lens and a second lens are arranged in this order from the eyeball side, and an image display element arranged on the opposite side of the eyeball side across the eyepiece optical system, wherein the surfaces of the first and second lenses facing the image display element are configured as Fresnel lens surfaces.

[0007] 1 is a diagram illustrating an example configuration of an eyepiece optical system 802 according to a comparative example, used in, for example, a head-mounted display. FIG. 2 is an explanatory diagram illustrating an example configuration of an eyepiece optical system. FIG. 3 is an explanatory diagram illustrating an example configuration of a Fresnel lens. FIG. 4 is an explanatory diagram illustrating an example configuration of an eyepiece optical system. FIG. 5 is an explanatory diagram (part 1) illustrating the shape of a Fresnel lens. FIG. 6 is an explanatory diagram (part 2) illustrating the shape of a Fresnel lens. FIG. 7 is a cross-sectional view illustrating a display device according to a first embodiment of the present disclosure. FIG. 8 is an explanatory diagram illustrating an emission spectrum of a general image display element. FIG. 9 is an explanatory diagram illustrating the results of analyzing the luminance distribution on a virtual image plane at viewing angles of 20° and 40° when one green pixel is caused to emit light in the first embodiment. FIG. 10 is a cross-sectional view illustrating a display device according to a second embodiment of the present disclosure. FIG. 11 is an explanatory diagram illustrating the behavior of light incident on different media. FIG. 12 is a cross-sectional view illustrating the details of a light beam passing through a Fresnel lens surface formed on the eye side. FIG. 13 is a cross-sectional view illustrating the details of a light beam passing through a Fresnel lens surface formed on the image display element side. FIG. 14 is a diagram illustrating the results of analyzing the luminance distribution on a virtual image plane in a line of sight direction of 30°. FIG. 15 is an explanatory diagram illustrating an example usage form of a PB lens. FIG. 16 is a cross-sectional view illustrating an example configuration of a display device according to Example 1a. FIG. 17 is a cross-sectional view illustrating an example configuration of a display device according to Example 1b. FIG. 1 is a diagram (part 1) showing various aberrations in Example 1a. FIG. 2 is a diagram (part 1) showing various aberrations in Example 1a. FIG. 1 is a diagram (part 2) showing various aberrations in Example 1b. FIG. 2 is a diagram (part 2) showing various aberrations in Example 1b. A cross-sectional view showing an example of the configuration of a display device according to Example 1c. A cross-sectional view showing an example of the configuration of a display device according to Example 1d. FIG. 1 is a diagram (part 1) showing various aberrations in Example 1c. FIG. 2 is a diagram (part 1) showing various aberrations in Example 1d. FIG. 2 is a diagram (part 2) showing various aberrations in Example 1d. An image of a PB lens using a liquid crystal polymer. An explanatory diagram showing an example of the light distribution angle of a PB lens using a liquid crystal polymer. An explanatory diagram explaining an example of a usage form in which two PB lenses are stacked. An explanatory diagram explaining the analysis results of stray light. A cross-sectional view showing an example of the configuration of a display device according to Example 2a. FIG. 1 is a diagram (part 1) showing various aberrations in Example 2a. FIG. 2 is a diagram (part 2) showing various aberrations in Example 2a. 10A and 10B are cross-sectional views showing a configuration example of a display device according to Example 2b, and FIG. 10C are diagrams (part 1) showing various aberrations in Example 2b.FIG. 10 is a diagram showing various aberrations in Example 2b (part 2). FIG. 11 is a cross-sectional view showing an example of the configuration of a display device according to Example 1e. FIG. 12 is a diagram showing various aberrations in Example 1e (part 1). FIG. 13 is a diagram showing various aberrations in Example 1e (part 2). FIG. 14 is a cross-sectional view showing an example of the configuration of a display device according to Example 1f. FIG. 15 is a diagram showing various aberrations in Example 1f (part 1). FIG. 16 is a diagram showing various aberrations in Example 1f (part 2). FIG. 17 is a cross-sectional view showing an example of the configuration of a display device according to Example 3a. FIG. 18 is a diagram showing various aberrations in Example 3a. FIG. 19 is a diagram showing various aberrations in Example 3a (part 2). FIG. 20 is a diagram showing various aberrations in Example 3a. FIG. 21 is a diagram showing the amount of sag versus the distance from the lens center before providing annular zones on each Fresnel lens surface in the third embodiment (Example 2a) and the fourth embodiment (Example 3a). FIG. 22 is a diagram showing the difference between the PSF radius taking into account the spread of light due to diffraction by the annular zones of the Fresnel lens and the PSF radius ignoring the spread of light diffracted by the annular zones of the Fresnel lens, relative to the angle of the line of sight when the eyeball rotates. FIG. 1 is a diagram illustrating an example of a configuration of a head-mounted display to which an embodiment of the present disclosure is applied.

[0008] Hereinafter, embodiments of the present disclosure will be described in detail with reference to the accompanying drawings. In this specification and the drawings, components having substantially the same functional configurations are designated by the same reference numerals, and redundant description will be omitted.

[0009] The drawings referred to in the following description are for explaining and facilitating understanding of one embodiment of the present disclosure, and for the sake of clarity, the shapes, dimensions, ratios, etc. shown in the drawings may differ from the actual ones. Furthermore, the design of the components, etc. shown in the drawings may be modified as appropriate, taking into consideration the following description and known technologies.

[0010] The explanation will be given in the following order: 1. Background 2. Definitions of Terms 3. First Embodiment 4. Second Embodiment 4.1 Background 4.2 Details of the Embodiment 5. Third Embodiment 5.1 Details of the Embodiment 5.2 Modification 6. Fourth Embodiment 7. Examples 8. Summary 9. Application Examples 10. Supplementary Notes

[0011] <<1. Background>> First, the background that led the inventors to create the embodiments of the present disclosure will be described with reference to FIGS. 1 to 3. FIG. 1 is a diagram showing an example configuration of an eyepiece optical system 802 according to a comparative example, which is used in, for example, a head-mounted display. FIG. 2 is an explanatory diagram illustrating image magnification, and FIG. 3 is an explanatory diagram illustrating the configuration of a general Fresnel lens. Here, the comparative example refers to the eyepiece optical system 802 that the inventors studied before creating the embodiments of the present disclosure.

[0012] As shown in FIG. 1 , the eyepiece optical system 802 according to the comparative example includes, in order from the eyepoint E.P. side along the optical axis Z1, an eyepiece lens 801 and an image display element 800. The image display element 800 is, for example, a display panel such as an LCD (Liquid Crystal Display) or an organic EL (Electroluminescence) display. The eyepiece lens 801 is used to enlarge and display an image displayed on the image display element 800. A user (e.g., a user of a head-mounted display) observes the enlarged virtual image Im through the eyepiece lens 801. Note that a seal glass (not shown) or the like for protecting the image display element 800 may be disposed on the front surface of the image display element 800. The eyepoint E.P. corresponds to the position of the user's pupil and also functions as an aperture stop STO.

[0013] The comparative examples include a configuration example in which the size of the image display element 800 is smaller than the lens diameter of the eyepiece lens 801, as shown in Figure 1, but also a configuration example in which the size of the image display element 800 is larger than the lens diameter of the eyepiece lens 801.

[0014] As explained above, for example, in the case of a head-mounted display, the display device body is worn in front of the eyes and used for long periods of time, so there is a strong demand for the image display element 800 to be small, and for the eyepiece optical system 802 to have a wide viewing angle, high magnification, yet be small and lightweight.

[0015] In many head-mounted displays with a wide viewing angle exceeding 70° that use a coaxial eyepiece optical system 802, the image display element 800 is large relative to the lens diameter of the eyepiece lens 801. However, in such head-mounted displays, although the image magnification Mv can be kept low, the focal length f is relatively long, which results in a long overall length of the eyepiece optical system 802. Furthermore, the size of the eyepiece optical system 802 is sometimes determined by the size of the image display element 800 rather than the eyepiece lens 801, making such eyepiece optical systems 802 unsuitable for miniaturization.

[0016] 1 , when the size of the image display element 800 is small, the overall size of the eyepiece optical system 802 is limited by the size of the eyepiece lens 801. Therefore, when the size of the image display element 800 is large, the overall size of the eyepiece optical system 802 is determined by the size of the image display element 800.

[0017] Here, the image magnification Mv is defined as follows. Specifically, as shown in the upper part of FIG. 2, α is the field of view angle when the eyepiece 801 is not present. Also, as shown in the lower part of FIG. 3, α' is the field of view angle (field of view angle relative to the virtual image Im) when the eyepiece 801 is present. In this case, the image magnification Mv can be expressed by the following formula (1). Note that the reference wavelength for the image magnification Mv described in this specification is 546 nm.

[0018] 2, h is the maximum image height of the image to be observed, for example, the maximum image height of the image displayed on the image display element 800. For example, if the image display element 800 is rectangular, h is half the diagonal size of the image display element 800. Furthermore, f is the focal length of the eyepiece lens 801.

[0019] In this case, the image magnification Mv can be expressed by the following equation (2).

[0020] ω': Half value of maximum field of view angle (rad) h: Maximum image height L: Total length (distance from eye point E.P. to image)

[0021] Here, the image refers to, for example, an image displayed on the image display element 800. As described above, when the image display element 800 is rectangular, for example, h is half the diagonal size of the image display element 800. Furthermore, L corresponds to, for example, the total length of the eyepiece optical system 802 described above (the distance from the eyepoint E.P. to the display surface of the image display element 800).

[0022] By setting the image magnification Mv at a high magnification of 2.1x or more and making the size of the image display element 800 smaller than the lens diameter of the eyepiece lens 801, as in the configuration example shown in Figure 1, it is possible to reduce the volume occupied by the eyepiece optical system 802. However, in such a case, the high magnification increases the amount of aberrations such as field curvature and distortion, and in order to ensure sufficient image definition, it may become necessary to use at least three lenses in the eyepiece lens 801. This inevitably increases the weight and overall length of the eyepiece lens 801.

[0023] Therefore, using a Fresnel lens is considered as a means for reducing the weight and overall length of the eyepiece lens 801. By using a Fresnel lens, it is possible to achieve a lighter weight and a shorter overall length compared to eyepiece optical systems using standard lenses. For example, by making the lens surface closest to the eye concave and a Fresnel lens surface, it is possible to improve imaging performance. However, such a configuration example results in a longer overall length of the eyepiece optical system and a larger lens diameter to ensure a sufficient distance between the eye and the lens closest to the eye.

[0024] Here, the configuration and operation of a general Fresnel lens 300 will be described with reference to FIG. 3. The Fresnel lens 300 is a lens in which concentric notches are made in the lens surface and the cuts are made at an angle. In detail, as shown in FIG. 3, the Fresnel lens 300 has a plurality of ring zones 301 formed concentrically around the optical axis Z1. A step surface 302 is formed at each boundary between the plurality of ring zones 301. The Fresnel lens surface Fr of the Fresnel lens 300 has a sawtooth cross-sectional shape.

[0025] 3, in the Fresnel lens 300, each annular zone 301 functions individually as a refractive surface, so that the optical path of parallel light rays can be bent and the light can be focused at a predetermined focal position. Therefore, the Fresnel lens 300 has high imaging performance, even though it is physically thin and lightweight.

[0026] However, in an eyepiece optical system using a Fresnel lens 300, stray light (unintended light) traveling in a direction different from the design path occurs due to the step surface 302, as shown in Figure 3. This stray light is therefore perceived as ghosts or flares, leading to degradation of image quality (particularly contrast).

[0027] As described above, even when a Fresnel lens 300 is used in an eyepiece, sufficient optical effects may not be obtained depending on the surface and shape of the Fresnel lens 300. In light of this situation, the present inventors conducted extensive research to realize an eyepiece that uses a Fresnel lens 300 to reduce weight and overall length, while achieving a wide field of view and good aberration correction. As a result of their research, the present inventors have come up with the embodiments of the present disclosure described below. Details of the embodiments of the present disclosure created by the present inventors will be described below.

[0028] <<2. Definition of Terms>> Next, before describing the details of the embodiments of the present disclosure, definitions of terms used in this specification will be described with reference to Figs. 4 to 6. Fig. 4 is an explanatory diagram illustrating the configuration of an eyepiece optical system 400. Figs. 5 and 6 are explanatory diagrams illustrating the shape of a Fresnel lens 300, and in detail, Fig. 6 is an enlarged view of area A shown in Fig. 5.

[0029] In this specification, as shown in FIG. 4 , the i-th lens from the eyeball side (eyepoint E.P. side) is referred to as Li. For example, the lens closest to the eye side is referred to as the first lens L1. In addition, for each lens L, the surface on the eyepoint E.P. side (eye side) is referred to as the R1 surface, and the surface on the image side (image display element 700 side) magnified by the eyepiece is referred to as the R2 surface. For example, the surface of the first lens L1 on the eyepoint E.P. side is referred to as the L1(R1) surface, and the surface of the first lens L1 on the image side is referred to as the L1(R2) surface, etc.

[0030] In this specification, a general lens surface that is not a Fresnel lens surface Fr is referred to as a “standard lens surface.” Standard lens surfaces include not only spherical surfaces but also aspherical surfaces other than Fresnel surfaces.

[0031] 5 and 6, the surface of the Fresnel lens surface Fr that is not the effective lens surface 304 is referred to as the step surface 302. The height of each of the multiple concentrically divided annular zones 301 on the Fresnel lens surface Fr is referred to as the annular zone height Rh, and the distance between the vertices of two adjacent annular zones 301 is referred to as the annular zone pitch Rp. Furthermore, as shown in FIG. 6, the angle of the step surface 302 (standing wall) with respect to the optical axis Z1 of the Fresnel lens surface Fr is referred to as the inclined step surface angle θd. Note that the step surface angle θd has a positive value in the direction in which the vertex angle of the annular zone 301 becomes obtuse.

[0032] Furthermore, in this specification, the axial distance between the eyepoint E.P. and the lens surface (L1 (R1) surface) of the eyepiece lens closest to the eyepoint E.P. is referred to as the eye relief E.R.

[0033] <<3. First Embodiment>> First, details of a display device 102 according to an embodiment of the present disclosure will be described with reference to Fig. 7. Fig. 7 is a cross-sectional view illustrating the display device 102 according to this embodiment, with an enlarged view of region B in the left drawing shown on the right side of the figure. This embodiment can be applied to, for example, a head-mounted display, similar to the comparative example described above.

[0034] As shown in Figure 7, the display device 102 according to this embodiment includes, in order from the eyepoint E.P. along the optical axis Z1, an eyepiece optical system 400 and an image display element 700. The eyepiece optical system 400 includes a first lens L1 and a second lens L2 arranged opposite each other. The first lens L1 has a first Fresnel lens surface Fr1 formed entirely from the center to the periphery on the lens surface facing the second lens L2, i.e., the lens surface facing the image display element 700. The second lens L2 also has a second Fresnel lens surface Fr2 formed entirely from the center to the periphery on the lens surface facing the first lens L1, i.e., the lens surface facing the eye. In this embodiment, by using two Fresnel lenses 300 and arranging the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 opposite each other, an optical system with a short overall length can be realized. Furthermore, in this embodiment, the eyepiece optical system 400 further includes a third lens L3 disposed closer to the image (image display element 700) than the first lens L1 and the second lens L2. The third lens L3 is a standard lens that does not use a Fresnel lens surface Fr. The third lens L3 is preferably an aspherical lens having an aspherical surface with an inflection point formed on at least one surface. Furthermore, although not shown in FIG. 7 , a type of diffractive lens that utilizes in-plane phase difference, known as a Pancharatnam-Berry lens, may be provided between the second lens L2 and the third lens L3 to correct chromatic aberration. In this embodiment, it is preferable that at least one refractive lens be disposed between the Pancharatnam-Berry lens and the image display element 700. Note that hereinafter, the Pancharatnam-Berry lens will be referred to as a PB lens, and details of the PB lens will be described later.

[0035] It is also preferable that each of the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 has a positive refractive power, which allows for efficient correction of aberrations and enables reduction in overall length and weight.

[0036] Furthermore, it is preferable that at least one of the first lens L1 and the second lens L2 has an aspherical surface with an inflection point. In the first lens L1 and the second lens L2, by using one or more aspherical surfaces other than the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2, and by having one or more aspherical surfaces with an inflection point, astigmatism, field curvature, and distortion can be efficiently corrected even with a small number of lenses. Furthermore, by using an aspherical surface shape with an inflection point, distortion can be efficiently corrected.

[0037] From the viewpoint of ease of processing the Fresnel lens surface Fr and the aspherical surface, it is desirable to use a resin material such as an acrylic, polyolefin, or polycarbonate as the material for the first lens L1 and the second lens L2. By constructing the first lens L1 and the second lens L2 only from a resin material, it is possible to achieve a lighter weight and smaller size compared to a configuration including one or more glass lenses. This is because the high-refractive-index glass material used to obtain refractive power can be replaced with the thin and lightweight Fresnel lens 300.

[0038] In this embodiment, as described above, two Fresnel lens surfaces Fr, the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2, are arranged opposite each other. By using the lens surface of the first lens L1 facing the image display element 700 and the lens surface of the second lens L2 facing the eye, which require a refractive index, as Fresnel lens surfaces Fr, light rays can be refracted with high space efficiency. As a result, this embodiment makes it possible to minimize the overall length and lens weight.

[0039] Furthermore, in this embodiment, by appropriately adjusting the step surface angles θd of the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 with respect to the optical axis Z1, it is possible to suppress the occurrence of stray light and to inhibit the occurrence of ghosts and flares.

[0040] Furthermore, by applying this embodiment to a head-mounted display, the overall length (the distance from the eye point E.P. to the image) can be shortened, and therefore the head-mounted display itself can be made smaller and lighter while providing high-definition images with a wide viewing angle.

[0041] <<4. Second Embodiment>> <4.1 Background> Next, the background that led the inventors to create the second embodiment of the present disclosure will be described with reference to Fig. 8 and Fig. 9 . Fig. 8 is an explanatory diagram showing the emission spectrum of a typical image display element 700, specifically the emission spectrum of a green pixel. Fig. 9 is an explanatory diagram showing the results of analyzing the luminance distribution on the virtual image plane at viewing angles of 20° and 40° when one green pixel is caused to emit light in the first embodiment.

[0042] Incidentally, when the second Fresnel lens surface Fr2 is formed on the eye-side lens surface, as in the second lens L2 of the first embodiment described above, the ring line formed by the annular zone 301 of the second Fresnel lens surface Fr2 becomes easily visible. Specifically, the right diagram in FIG. 7 shows a light beam passing through the second Fresnel lens surface Fr2 formed on the eye-side lens surface, with a line of sight direction of 30°. The light beam passing through the second Fresnel lens surface Fr2 formed on the eye-side lens surface is partially eclipsed by the stepped surface 302 of the second Fresnel lens surface Fr2, resulting in a noticeable difference in brightness within the light beam, which is perceived as a ring line. Such noticeable brightness and darkness can cause uneven brightness and be a major factor in degrading image quality.

[0043] In the first embodiment described above, the inclined step surface angle θd is set so as to suppress unnecessary light (stray light) entering the eye due to refraction at step surface 302, making it difficult to avoid the phenomenon of some light being vignetted at step surface 302 of second Fresnel lens surface Fr2. Therefore, it is conceivable to suppress the visibility of ring lines by appropriately designing the annular zone pitch Rp of the annular zones 301 of second Fresnel lens surface Fr2. However, because the light beam passing through second Fresnel lens surface Fr2 formed on the lens surface closest to the eye exhibits significant differences in brightness and darkness, fine ring lines may remain even if the annular zone pitch Rp is appropriately designed.

[0044] Furthermore, if a plastic lens is used in the eyepiece optical system 400 to reduce weight and cost, unlike glass, a low-dispersion (high Abbe number) material cannot be selected for the plastic lens, and there is a high probability that large chromatic aberrations (axial chromatic aberration and lateral chromatic aberration) will occur. Chromatic aberrations are aberrations that occur when the focal length changes depending on the color of light, and this can cause image distortion and blurring.

[0045] Furthermore, when the eyepiece optical system 400 and the image display element 700 are combined and used as the display device 102, it is possible to correct chromatic aberration of magnification by appropriately changing the image displayed by each of the red, green, and blue pixels. However, as shown in Figure 8, for example, the emission spectrum of a typical image display element 700 has a bandwidth of about several tens of nanometers at half maximum, which results in a deterioration in definition at the periphery of the field of view.

[0046] As described above, FIG. 9 is an explanatory diagram showing the results of an analysis (simulation analysis) of the luminance distribution on the virtual image plane at viewing angles of 20° and 40° when one green pixel is illuminated in the first embodiment. Specifically, the upper part of the figure shows the results reflecting the emission spectrum of the green pixel of the standard image display element 700, while the lower part shows the results of analysis at a single wavelength of 546 nm. As can be seen from FIG. 9 , when the emission spectrum of the green pixel of the standard image display element 700 is reflected, the blur of one pixel is relatively large due to the influence of lateral chromatic aberration, and the definition is degraded, compared to the analysis results at a single wavelength. Therefore, because the blur due to the broadening of the emission spectrum of the image display element 700 occurs on a pixel-by-pixel basis, there are limitations to correcting it on the image side.

[0047] A commonly known solution to this problem is to use a cemented lens made of glass materials with different refractive indices and Abbe numbers. However, the overall length of the lens optical system in the high-magnification eyepiece optical system 400 is short, and there is insufficient space for a cemented lens. As a result, only one cemented lens can be used, making it difficult to ensure sufficient correction. Furthermore, there are few variations in resin materials, making it difficult to cement together resin lenses for manufacturing reasons.

[0048] As described above, in the first embodiment in which the second Fresnel lens surface Fr2 is formed on the lens surface closest to the eye, the ring lines are easily visible, and there is a limit to how much deterioration in definition caused by chromatic aberration can be suppressed.

[0049] In view of this situation, the present inventors have come up with the second embodiment of the present disclosure, which will be described below. According to the second embodiment of the present disclosure, it is possible to make the ring lines less visible and to suppress deterioration of definition caused by chromatic aberration. Details of the second embodiment of the present disclosure created by the present inventors will be described below.

[0050] 4.2 Details of the Embodiment Next, details of the display device 102 according to a second embodiment of the present disclosure will be described with reference to Fig. 10. Fig. 10 is a cross-sectional view illustrating the display device 102 according to this embodiment, and an enlarged view of region C in the left drawing is shown on the right side of the drawing.

[0051] 10 , the display device 102 according to this embodiment includes, in order from the eyepoint E.P. along the optical axis Z1, an eyepiece optical system 400 and an image display element 700. Also in this embodiment, the eyepiece optical system 400 includes a first lens L1 and a second lens L2 on which Fresnel lenses are formed. However, unlike the first embodiment, in the second embodiment, both the first lens L1 and the second lens L2 include a first Fresnel lens surface Fr1 and a second Fresnel lens surface Fr2 formed entirely from the center to the periphery on the lens surface on the image display element 700 side.

[0052] More specifically, in this embodiment, the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 are formed on the concave lens surfaces of the first lens L1 and the second lens L2. In this embodiment, by forming the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 on the lens surfaces of the first lens L1 and the second lens L2 that face the image display element 700, it is possible to suppress the occurrence of significant differences in brightness and darkness in the light beam that passes through the Fresnel lens surface Fr. As a result, this embodiment makes it possible to make the ring lines less visible.

[0053] In this embodiment, the eyepiece optical system 400 further includes a third lens L3, a fourth lens L4, and a fifth lens L5, which are located closer to the image (image display element 700) than the first lens L1 and the second lens L2, in this order from the eye point E.P. along the optical axis Z1. The third lens L3 and the fifth lens L5 are refractive lenses that do not have a Fresnel lens surface Fr.

[0054] Furthermore, in this embodiment, the eyepiece optical system 400 may include a PB lens (chromatic aberration compensation element) as the fourth lens L4 to further correct chromatic aberration. In this embodiment, it is preferable that at least one refractive lens (fifth lens L5 in FIG. 10) is disposed between the PB lens (fourth lens L4 in FIG. 10) and the image display element 700. For example, in the example of FIG. 10, a third lens L3 is disposed between the second lens L2 and the fourth lens L4 which is the PB lens, and a fifth lens is disposed between the fourth lens L4 which is the PB lens and the image display element 700. In addition, the focal length f of the PB lens is Ｄ For example, the distance is 240 mm at a reference wavelength of 550 nm (see Table 19). In this embodiment, a diffractive lens, a hologram lens, or the like may be used instead of the PB lens.

[0055] In this embodiment, the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 are formed as concave lens surfaces, but the present invention is not limited to this and they may be formed as flat surfaces (flat-shaped surfaces) or convex lens surfaces with extremely small power.

[0056] Furthermore, this embodiment is not limited to the configuration shown in Fig. 10. For example, the eyepiece optical system 400 may include three or more Fresnel lenses 300, may not include a PB lens, may have a different position for the PB lens, or may further include a seal glass for protecting the image display element 700.

[0057] By applying this embodiment to a head-mounted display, it is possible to provide an image with high definition from the center to the periphery of the field of view, while still providing high magnification, making it difficult to see the ring lines caused by the Fresnel lens 300.

[0058] The second embodiment corresponds to Examples 1a to 1f, which will be described later, and the embodiment shown in Fig. 10 corresponds to Example 1a. Specific configuration examples and lens data for each of Examples 1a to 1f will be described later.

[0059] (Reason why ring lines are less visible) Next, with reference to FIGS. 10 to 14, the effect of suppressing the occurrence of ring lines caused by the Fresnel lens 300 according to this embodiment will be described.

[0060] 10 shows a light beam passing through first Fresnel lens surface Fr1 and second Fresnel lens surface Fr2 in the second embodiment (more specifically, Example 1a) in a line of sight direction of 30°. A portion of the light beam that passes through first Fresnel lens surface Fr1 and second Fresnel lens surface Fr2 formed on the lens surface facing image display element 700 is vignetted by step surfaces 302 of first Fresnel lens surface Fr1 and second Fresnel lens surface Fr2, but compared to the first embodiment, the occurrence of significant brightness and darkness within the light beam can be suppressed.

[0061] Fig. 11 is an explanatory diagram illustrating the behavior of light incident on different media. The left diagram shows the behavior of light when a Fresnel lens surface Fr is formed on the eye side and light enters from the resin toward the air, while the right diagram shows the behavior of light when a Fresnel lens surface Fr is formed on the image display element 700 side and light enters from the air toward the resin. Fig. 12 is a cross-sectional view showing details of the light beam passing through the Fresnel lens surface Fr formed on the eye side, with an enlarged view of region D in the left diagram on the right side. Fig. 13 is a cross-sectional view showing details of the light beam passing through the Fresnel lens surface Fr formed on the image display element 700 side, with an enlarged view of region E in the left diagram on the right side.

[0062] As shown in the left diagram of Figure 11, the light beam incident on the Fresnel lens surface Fr formed on the eye side enters through the resin and exits into the air. That is, the light beam enters from the side with the higher refractive index and exits from the side with the lower refractive index, resulting in a narrowing (densification) of the light beam. More specifically, as shown in Figure 12, when the Fresnel lens surface Fr is formed on the eye side, the angle of incidence on the Fresnel lens surface Fr becomes very large in the peripheral region of the field of view (the line of sight direction of 30° in Figure 12), resulting in a large refraction angle. Therefore, in this case, the light passing through the effective lens surface 304 becomes dense, resulting in significant variations in brightness and darkness within the light beam.

[0063] On the other hand, as shown in the right diagram of FIG. 11 , the light beam incident on the Fresnel lens surface Fr formed on the image display element 700 side enters from the air and exits from the resin. That is, the light beam enters from the side with the smaller refractive index and exits from the side with the larger refractive index, resulting in a spread (sparse) light beam. More specifically, as shown in FIG. 13 , when the Fresnel lens surface Fr is formed on the image display element 700 side, the angle of incidence on the Fresnel lens surface Fr is relatively small in the peripheral region of the field of view (the line of sight direction of 30° in FIG. 13 ), and therefore the refraction angle is also small. Therefore, in this case, the light passing through the effective lens surface 304 does not become very dense, and as a result, the occurrence of significant brightness and darkness within the light beam can be suppressed.

[0064] In this manner, in this embodiment, by forming a Fresnel lens surface Fr on the lens surface on the image display element 700 side, it is possible to suppress the occurrence of significant differences in brightness and darkness within the light beam passing through the Fresnel lens surface Fr, making it possible to make the ring line less visible.

[0065] FIG. 14 shows the results of analyzing the luminance distribution on the virtual image plane at a 30° line of sight. Specifically, the effective area of ​​the image display element 700 is fully white, and the luminance distribution on the virtual image plane is analyzed within a ±8° field of view at a 30° line of sight. The center of the image in the figure corresponds to the 30° line of sight. (a) of FIG. 14 shows the results for the first embodiment, and (b) of FIG. 14 shows the results for the second embodiment. For comparative verification, the annular zone height Rh was set to 150 μm (constant) in both the first and second embodiments, and the step surface angle θd was set to an angle that reduces the generation of stray light. From FIG. 14 , it can be seen that the second embodiment suppresses the generation of low- and high-frequency brightness and darkness compared to the first embodiment.

[0066] (Functions and Effects of Forming a Fresnel Lens Surface Fr on a Concave Lens Surface) In the second embodiment, by forming a first Fresnel lens surface Fr1 and a second Fresnel lens surface Fr2 on the concave lens surfaces of the first lens L1 and the second lens L2, it is possible to ensure high definition even in a high-magnification eyepiece optical system 400 that has a wide field of view and a small image display element 700. Below, with reference to FIG. 10 , the functions and effects of forming the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 on the concave lens surfaces of the first lens L1 and the second lens L2 will be described.

[0067] As shown in FIG. 10 , light emitted from the image display element 700 passes through the fifth lens L5, the fourth lens L4, and the third lens L3 (lens group) in this order before reaching the second Fresnel lens surface Fr2 formed on the surface (concave lens surface) of the second lens L2 facing the image display element 700. The light then passes through the second lens L2 and reaches the first Fresnel lens surface Fr1 formed on the surface (concave lens surface) of the first lens L1 facing the image display element 700. By forming Fresnel lens surfaces Fr on the concave lens surfaces of the first lens L1 and the second lens L2, off-axis light can be incident on the Fresnel lens surface Fr at a position close to the image display element 700 (on the outer periphery of the lens). In this embodiment, the Fresnel lenses (first lens L1, second lens L2) are designed to have relatively large refractive power, which means that aberrations are more likely to occur than with other lenses. However, by making the light incident on the Fresnel lens surface Fr at a position close to the image display element 700, the light ray height (distance from the optical axis Z1) at the Fresnel lens surface Fr can be kept low. Generally, it is known that the occurrence of aberration increases exponentially as the light ray height increases, but in this embodiment, the occurrence of aberration can be reduced by keeping the light ray height low. As a result, this embodiment can further improve the definition.

[0068] In a third embodiment, which will be described later, the Fresnel lens surface Fr is formed as a flat surface. In such a case, light is incident on the Fresnel lens surface Fr at a position far from the image display element 700, and the height of the light rays increases, making aberrations more likely to occur. However, in the third embodiment, the image magnification Mv is lowered compared to the second embodiment (this embodiment), thereby suppressing the occurrence of aberrations.

[0069] Furthermore, forming the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 on the concave lens surfaces of the first lens L1 and the second lens L2 has the additional effect of making ring lines less visible. Referring to FIG. 13 , light emitted from the image display element 700 passes through the fifth lens L5, the fourth lens L4, and the third lens L3 (lens group) before reaching the second Fresnel lens surface Fr2 formed on the surface of the second lens L2 facing the image display element 700. When the second Fresnel lens surface Fr2 has a concave lens shape, the angle of incidence on the Fresnel lens surface Fr is smaller than when it has a flat shape, and the refraction angle can also be made relatively small. Therefore, as described above, the light passing through the effective lens surface 304 is not so dense, thereby suppressing the occurrence of significant light and dark variations in the light beam. As a result, forming the Fresnel lens surface Fr on the concave lens surface makes ring lines less visible.

[0070] As described above, in a high-magnification eyepiece optical system 400 with a wide viewing angle and a small image display element 700, it is preferable that the surface forming the Fresnel lens surface Fr has a concave lens shape.

[0071] (Regarding the PB Lens) The PB lens will be described with reference to FIG. 15. FIG. 15 is an explanatory diagram illustrating an example of how the PB lens is used. As described above, the PB lens is a type of diffractive lens known as a Pancharatnam-Berry lens or a Pancharatnam-Berry phase lens, which utilizes an in-plane phase difference. Since the diffraction angle increases with wavelength, the refraction angle increases with wavelength in a diffractive lens such as a PB lens. Therefore, the PB lens has an inverse wavelength dispersion to the other refractive lenses used in the eyepiece optical system 400. Therefore, in the second embodiment, by using such a PB lens, chromatic aberration caused by the refractive lenses in the eyepiece optical system 400 can be corrected.

[0072] Because a PB lens is a diffractive lens that utilizes an in-plane phase difference, stray light occurs when the PB lens is used alone. Specifically, the PB lens functions as a diffractive lens for diffracted light of the so-called +1st diffraction order, but diffracted light of other orders, such as 0th, +2nd, and −1st orders, becomes stray light. Therefore, when using a PB lens, it is preferable to use it in combination with a circular polarizer to suppress stray light. For example, as shown in FIG. 15 , a PB lens is used in a configuration in which the PB lens is sandwiched between a right-handed circular polarizer and a left-handed circular polarizer. A circular polarizer is a combination of a linear polarizer and a λ / 4 plate. More specifically, as shown in FIG. 15 , various polarizers and the PB lens may be arranged in the following order: incident polarizer, −λ / 4 plate, PB lens, +λ / 4 plate, and exit polarizer.

[0073] (Effect of the PB Lens) In the second embodiment, chromatic aberration can be effectively reduced by disposing the above-described PB lens in the eyepiece optical system 400. The effect of the PB lens will be described below with reference to FIGS. 16 to 19B. FIG. 16 is a cross-sectional view showing an example configuration of a display device 102 according to Example 1a, and FIG. 17 is a cross-sectional view showing an example configuration of a display device 102 according to Example 1b. FIGS. 18A and 18B are diagrams showing various aberrations in Example 1a, and FIGS. 19A and 19B are diagrams showing various aberrations in Example 1b. Each aberration is obtained by ray tracing from the eyepoint E.P. side. FIGS. 18A and 19A show (a) astigmatism (curvature of field) diagrams and (b) distortion diagrams. FIGS. 18B and 19B show (c) axial aberration diagrams and (d) chromatic aberration of magnification diagrams. The astigmatism diagram, distortion diagram, and lateral chromatic aberration diagram show values ​​at wavelengths of 473 nm, 542 nm, and 639 nm, while the axial aberration diagram shows values ​​at a wavelength of 542 nm. Furthermore, in the astigmatism diagram, the solid line shows values ​​at the tangential image plane, and the dashed line shows values ​​at the sagittal image plane. The same applies to the aberration diagrams of the other examples below.

[0074] Specifically, to verify the effect of the PB lens, the optical characteristics of Examples 1a and 1b below, obtained by simulation analysis, were compared. Example 1a, as shown in FIG. 16 , includes a PB lens as the fourth lens L4 and has a configuration similar to that of the second embodiment described above with reference to FIG. 10 . On the other hand, Example 1b, as shown in FIG. 17 , does not include a PB lens and has an optical system optimized to provide good definition. For comparison, Examples 1a and 1b share the same maximum viewing angle (105°), eye relief (13 mm), and image display element (display panel) size (1.28 inches (approximately 3.25 cm)). Furthermore, in Example 1a, the lens surface of the third lens L3 facing the image display element 700 is flat to facilitate placement of the PB lens and prevent the overall length from becoming unnecessarily long. On the other hand, in Example 1b, since a PB lens is not provided, the lens surface of the third lens L3 on the side of the image display element 700 is made aspherical. Specific lens data and the like for Examples 1a and 1b will be described later.

[0075] As can be seen from Figures 18A and 19A, the astigmatism and distortion characteristics were roughly equivalent in Examples 1a and 1b. On the other hand, as can be seen from Figures 18B and 19B, with regard to the axial chromatic aberration and lateral chromatic aberration, Example 1a was able to significantly suppress the occurrence of axial chromatic aberration and lateral chromatic aberration compared to Example 1b.

[0076] As described above, it has been found that by arranging a PB lens in the eyepiece optical system 400, chromatic aberration can be significantly improved without significantly changing the overall length of the optical system or the lens shape, while maintaining the astigmatism and distortion characteristics almost unchanged. Furthermore, by arranging a PB lens in the eyepiece optical system 400, image quality, particularly definition, can be significantly improved. Note that in this embodiment, the eyepiece optical system 400 is not limited to including one PB lens, but may include two or more PB lenses. Even in this case, each PB lens is used in a configuration sandwiched between a pair of circular polarizers.

[0077] In addition, since Example 1b does not have a PB lens in the eyepiece optical system 400, the definition is inferior to Example 1a, but it has the advantages of high brightness (high efficiency) and low cost.

[0078] (Optimal Position of the PB Lens) As described above, in the display device 102, chromatic aberration can be significantly improved by placing a PB lens in the eyepiece optical system 400. Furthermore, the position of the PB lens in the eyepiece optical system 400 can affect the chromatic aberration correction effect of the PB lens and the focal length f of the PB lens. Ｄ The specifications of the lens aperture and the lens diameter change. Therefore, the optimal placement position of the PB lens will be described with reference to FIGS. 18A, 18B, and 20 to 23B. FIG. 20 is a cross-sectional view showing an example of the configuration of a display device 102 according to Example 1c, and FIG. 21 is a cross-sectional view showing an example of the configuration of a display device 102 according to Example 1d. Furthermore, FIGS. 22A and 22B are diagrams showing various aberrations in Example 1c, and FIGS. 23A and 23B are diagrams showing various aberrations in Example 1d.

[0079] Specifically, in verifying the optimal placement position of the PB lens, the optical characteristics of Examples 1c and 1d below were compared in addition to Example 1a, which is an example including a PB lens as the fourth lens L4. As shown in FIG. 20, Example 1c is an example including a PB lens as the fifth lens L5 (an example in which the PB lens is placed immediately before the image display element 700). On the other hand, as shown in FIG. 21, Example 1d is an example including a PB lens as the second lens L2. For comparison, Examples 1a, 1c, and 1d have the same maximum viewing angle (105°), eye relief (13 mm), and image display element (display panel) size (1.28 inches (approximately 3.25 cm)). Specific lens data and the like for Examples 1c and 1d will be described later.

[0080] Comparing the results of Example 1a and Example 1c obtained by simulation analysis, as can be seen from Figures 18A and 22A, the astigmatism and distortion characteristics of Example 1a and Example 1c were roughly equivalent. Also, as can be seen from Figures 18B and 22B, the axial chromatic aberration and lateral chromatic aberration of Example 1c were larger than those of Example 1a. At this time, the focal length f of each PB lens Ｄ is 240 mm in Example 1a and 110 mm in Example 1c at a reference wavelength of 550 nm. As described above, in Example 1c, which is an example including a PB lens as the fifth lens L5, i.e., an example in which the PB lens is disposed immediately before the image display element 700, the effect of correcting chromatic aberration is limited compared to Example 1a. In addition, in Example 1c, in order to sufficiently improve chromatic aberration, the focal length f Ｄ In other words, in Example 1c, the refractive power of the PB lens is required to be relatively large. However, the focal length f Ｄ Making the length extremely short is not desirable because it makes manufacturing difficult and leads to deterioration in quality.

[0081] 24 and 26, the focal length f of the PB lens is Ｄ The reason why it is not desirable to make the length extremely short will be explained below. Fig. 24 is an image diagram of a PB lens using a liquid crystal polymer, and Fig. 25 is an explanatory diagram showing an example of the orientation angle distribution of a PB lens using a liquid crystal polymer. Fig. 26 is an explanatory diagram explaining an example of a usage form in which two PB lenses are stacked.

[0082] Specifically, one type of PB lens is a liquid crystal lens formed using a liquid crystal polymer. Because liquid crystal polymers have birefringence, the phase difference can be changed by varying the orientation angle of the liquid crystal polymer. Therefore, as shown in FIG. 24 , by changing the orientation angle of the liquid crystal polymer in the plane, an in-plane phase difference distribution can be achieved. The structure of a liquid crystal lens, for example, as shown in the right diagram of FIG. 24 , consists of an orientation film formed on a transparent substrate and a liquid crystal polymer layer formed on the orientation film. Furthermore, since a PB lens is a polarizing optical element, the transparent substrate must be a substrate that has no birefringence or very little birefringence, such as glass.

[0083] The alignment film is a layer that controls the in-plane orientation angle of the liquid crystal polymer in a desired direction. A type of alignment film, known as a photo-alignment film, is made of a type of UV-curable resin that hardens when exposed to polarized UV (UltraViolet) light. Therefore, by applying a liquid photosensitive liquid crystal monomer onto the cured photo-alignment film, the liquid crystal polymer can be oriented in a direction perpendicular to the polarization direction of the polarized UV light. In this case, the alignment direction is determined by the alignment film only for the bottommost liquid crystal polymer in contact with the alignment film. However, generally, the liquid crystal monomer stacked on top of the bottommost liquid crystal polymer will attempt to align with the alignment direction of the liquid crystal monomer in the lower layer. Therefore, the orientation angle of the liquid crystal monomer is determined by both the angle of the UV irradiation direction of the alignment film and the orientation angles of the surrounding and underlying liquid crystal monomers. If the aligned liquid crystal monomer is photosensitive, the liquid liquid crystal monomer will harden while maintaining its orientation angle when exposed to light (UV light). In other words, by providing an in-plane distribution in the irradiation direction of the polarized UV light so that it corresponds to the in-plane distribution of the desired orientation angle of the liquid crystal polymer, the desired in-plane distribution of the orientation angle of the liquid crystal polymer can be achieved.

[0084] However, as shown in the cross-sectional view of Figure 24, the liquid crystal polymer in the bottom layer has a different orientation from that defined by the alignment film and that of the adjacent liquid crystal polymers (located to the right and left in the figure), making it difficult to rapidly change the orientation angle in the in-plane direction. Therefore, the in-plane change in the liquid crystal orientation angle must be somewhat gradual. In other words, when attempting to manufacture a PB lens in which the orientation angle rapidly changes in the in-plane direction, liquid crystal orientation defects, i.e., defects in which the liquid crystal does not achieve the desired liquid crystal orientation angle, may occur. Furthermore, in the areas of the orientation defects, the desired phase lens characteristics cannot be exhibited, causing degradation of the image on the display device 102.

[0085] On the other hand, in designing the orientation angle of the liquid crystal polymer in the PB lens, the orientation angle is set to α ０ Then, the following formula (3) should be satisfied at a position at a distance r from the center of the PB lens.

[0086] λ Ｄ : Design wavelength f Ｄ : Focal length at the design wavelength

[0087] FIG. 25 shows the specific orientation angle α ０ In detail, an example of the distribution of the design wavelength λ Ｄ is 550 nm, and the focal length at the design wavelength is f Ｄ 25 shows the vicinity of the center of the lens in a PB lens with a distance r of 240 mm. As can be seen from FIG. 25, when the distance r is large, the orientation angle α ０ It can be seen that the change in the orientation angle α is large with respect to the distance r from the center of the PB lens. ０ The extent to which changes can be determined from the absolute value of the derivative shown in the following equation (4).

[0088] As can be seen from equation (4), the focal length f Ｄ The smaller the value of the absolute value of the derivative shown in Equation (4), the larger the focal length f Ｄ The shorter the liquid crystal orientation angle α ０ This means that the change in the surface is large.

[0089] Therefore, the focal length f Ｄ The PB lens with a short orientation angle α ０ Since the change in the in-plane direction of the focal length f is large, alignment defects of the liquid crystal are likely to occur in the manufacturing process of the PB lens, making it difficult to exhibit the desired optical characteristics. Ｄ Therefore, a PB lens having a long length is used, and the PB lens is disposed at a position distant from the image display element 700 .

[0090] Here, as an example, Example 1a and Example 1c are compared. In Example 1c, in which the PB lens is disposed immediately before the image display element 700, the focal length f of the PB lens is shorter than in Example 1a, in which the fifth lens L5 is disposed between the PB lens (fourth lens L4) and the image display element 700. Ｄ Therefore, in order to suppress the occurrence of alignment defects in the PB lens, the focal length f Ｄ In order to shorten the time, it is preferable to arrange at least one refractive lens between the PB lens and the image display element 700.

[0091] Next, when the results of Example 1a and Example 1d obtained by simulation analysis are compared, as can be seen from Figures 18A and 23A, the astigmatism and distortion characteristics of Example 1a and Example 1d are roughly equivalent. Also, as can be seen from Figures 18B and 23B, the axial chromatic aberration and lateral chromatic aberration of Example 1d were larger than those of Example 1a. At this time, the focal length f of each PB lens Ｄ is 240 mm in Example 1a and 300 mm in Example 1d at a reference wavelength of 550 nm. As described above, it was found that Example 1d, which includes a PB lens as the second lens L2, has a longer optical system than Example 1a and can obtain a high correction effect with a relatively small refractive power.

[0092] That is, in Example 1d, which includes a PB lens as the second lens L2, the chromatic aberration characteristics are inferior to those of Example 1a, but the focal length f ＤSince the time is long, alignment defects of the liquid crystal are unlikely to occur, and the PB lens has the advantage of being highly manufacturable (yield).

[0093] In the above description, the focal length f Ｄ It has been mentioned that it is difficult to manufacture a PB lens with a short focal length f Ｄ When the absolute value of the differential shown in the above formula (4) and FIG. 25 show that the orientation angle α ０ In other words, although the size of the PB lens is increased, the change in the orientation angle α ０ Furthermore, in the future, it will be possible to realize a short focal length f Ｄ If the PB lens described above can be realized, it will be possible to improve the optical performance and reduce the physical size of the display device 102 itself.

[0094] Furthermore, the focal length f Ｄ By combining two PB lenses with long lengths, the overall focal length (composite focal length) can be shortened. However, as explained above, each PB lens is used in a configuration sandwiched between a pair of circular polarizers. In detail, as shown in FIG. 26, the arrangement is in the following order from the light incident side: polarizer 1, -λ / 4 plate, PB lens, +λ / 4 plate, polarizer 2, +λ / 4 plate, PB lens, -λ / 4 plate, and polarizer 3. Note that, as shown in FIG. 26, the transmission axes of polarizer 1 and polarizer 3 are set in the same direction. In this way, the composite focal length can be shortened by the focal length f of the PB lens. Ｄ can be shortened to about half of the

[0095] As described above, by disposing the PB lens at a position where the light beam spreads in the optical system, as in the eyepiece optical system 400 of Examples 1a and 1d, the PB lens has a relatively long focal length f Ｄ Although specific design details will be omitted, for the same reasons as those described above, the second embodiment may include an example in which the third lens L3 is a PB lens.

[0096] As explained above, since the PB lens is a type of diffraction lens, the same effect as that of the PB lens can be obtained even if a lens that utilizes diffraction, such as a diffraction lens or a hologram lens, is used instead of the PB lens.

[0097] As described above, the display device 102 according to the second embodiment includes the eyepiece optical system 400 and the image display element 700. The eyepiece optical system 400 includes two or more Fresnel lenses 300, each having a Fresnel lens surface Fr formed on the lens surface facing the image display element 700, and further includes a PB lens. In this embodiment, it is preferable that the Fresnel lens surface Fr is formed as a concave lens surface, and it is also preferable that at least one refractive lens be disposed between the PB lens and the image display element 700.

[0098] (Regarding the step surface angle θd that suppresses the generation of stray light) As shown in FIG. 3 , in an eyepiece optical system 400 that uses a Fresnel lens 300, some of the light incident on the Fresnel lens surface Fr may strike the step surface 302 and travel in a direction different from the design path, resulting in stray light. This stray light is perceived as ghosts or flare, and contributes to degrading image quality (particularly contrast). Therefore, to suppress the generation of such stray light, it is necessary to suitably design the step surface angle θd with respect to the optical axis Z1 at the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 of the first lens L1 and the second lens L2. This makes it possible to prevent stray light from entering the pupil, thereby suppressing the generation of ghosts and flare.

[0099] In this embodiment, in order to suppress the generation of stray light, it is preferable that the step surface angle θd is set within the following range. In detail, in the first Fresnel lens surface Fr1, the step surface angle θd (θ １ ) is preferably set to 15° or more and 40° or less, and the step surface angle θd (θ １1 ) is calculated by dividing the step surface angle θd (θ １２ ) or less. In addition, in the second Fresnel lens surface Fr2, the step surface angle θd (θ２ ) is preferably set to 0° or more and 30° or less, and the step surface angle θd (θ ２1 ) is calculated by dividing the step surface angle θd (θ ２２ ) or more. Furthermore, in the annular zone 301 that is 5 mm or more away from the center, the step surface angle θd (θ １ ) is the step surface angle θd (θ ２ ) or more.

[0100] According to simulation analysis by the inventors, in an observation configuration in which the pupil is located at the designed viewing position (eye relief 13 mm), even if the eyeball rotates within a range of ±30°, by setting the step surface angle θd within the above-mentioned range, it is possible to suppress the occurrence of stray light that significantly degrades image quality.

[0101] Referring to Figure 27, we will explain the results of verifying that the effect of suppressing the generation of stray light can be achieved by setting the step surface angle θd within the above-mentioned range. Figure 27 is an explanatory diagram illustrating the results of a simulation analysis of stray light. In detail, Figure 27 shows the ratio of the intensity of stray light (components that hit the step surface 302 of the Fresnel lens surface Fr one or more times) to the signal (components that pass through the effective lens surface 304 of the Fresnel lens surface Fr) in the luminance distribution of the virtual image plane when white is displayed in the effective area of ​​the image display element 700, with smaller values ​​(darker colors) indicating smaller stray light. The upper part (a) of Figure 27 shows the results when the step surface angle θd of the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 is set within the above-mentioned predetermined angle range (this embodiment). 27(b) shows the results for a comparative example in which the step surface angle θd of the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 was set outside the above-mentioned predetermined angle range (θd = 0°, which was constant). Note that Fig. 27 shows the results for three levels of eyeball rotation angle (0°, 15°, and 30°), with the center of the image corresponding to the line of sight.

[0102] Stray light can cause flare and ghosting, so ideally it is desirable that it not be generated, that is, it is desired that the amount of stray light be made as close to 0 as possible. As shown in Fig. 27, according to this embodiment, the generation of stray light can be suppressed by setting the step surface angle θd within the above-mentioned predetermined angle range.

[0103] (Simulation conditions for the amount of stray light generated) The analysis results shown in Fig. 27 were obtained by simulating the amount of stray light generated under the following conditions: Light distribution characteristic of image display element 700: Lambertian Size of image display element 700: 21.8 mm x 24.2 mm (length x width) Pupil diameter: φ4 mm Shape of Fresnel lens surface Fr: annular zone height Rh = 150 µm (constant) (annular zone pitch Rp is unequal) Reference wavelength: 546 nm

[0104] <<5. Third Embodiment>> <5.1 Details of the Embodiment> Next, a third embodiment of the present disclosure will be described with reference to Fig. 28, Fig. 29A, and Fig. 29B. Fig. 28 is a cross-sectional view showing an example configuration of a display device 102 according to Example 2a, which is one of the present embodiment. Also, Fig. 29A and Fig. 29B are diagrams showing various aberrations in Example 2a.

[0105] 28 , the display device 102 according to this embodiment includes, in order from the eyepoint E.P. along the optical axis Z1, an eyepiece optical system 400 and an image display element 700. Also in this embodiment, the eyepiece optical system 400 includes a first lens L1 and a second lens L2 arranged opposite each other. Furthermore, in this embodiment, both the first lens L1 and the second lens L2 include a first Fresnel lens surface Fr1 and a second Fresnel lens surface Fr2, respectively, formed entirely from the center to the periphery on the lens surface facing the image display element 700. However, this embodiment differs from the second embodiment in that the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 are formed as flat surfaces.

[0106] In this embodiment, the eyepiece optical system 400 further includes a third lens L3, a fourth lens L4, and a fifth lens L5, which are located closer to the image (image display element 700) than the first lens L1 and the second lens L2, in this order from the eye point E.P. along the optical axis Z1. The fourth lens L4 and the fifth lens L5 are refractive lenses that do not have a Fresnel lens surface Fr.

[0107] Furthermore, in this embodiment, the eyepiece optical system 400 includes a PB lens (chromatic aberration compensation element) as the third lens L3 to further correct chromatic aberration. In this embodiment, it is preferable to dispose at least one refractive lens (fourth lens L4 and fifth lens L5 in FIG. 28) between the PB lens (third lens L3 in FIG. 28) and the image display element 700. In addition, the focal length f of the PB lens is Ｄ For example, the distance is 340 mm at a reference wavelength of 550 nm. In this embodiment, a diffractive lens or a hologram lens may be used instead of the PB lens. Specific lens data for Example 2a will be described later.

[0108] Furthermore, this embodiment is not limited to the configuration shown in Fig. 28. For example, the eyepiece optical system 400 may not include a PB lens, or may further include a seal glass that protects the image display element 700.

[0109] Example 2a, which is an example of the third embodiment, has a maximum viewing angle of 110°, an eye relief of 13 mm, and an image display element (display panel) size of 1.7 inches (approximately 4.32 cm). In the third embodiment, the image display element size is larger than that of the second embodiment (1.28 inches), and the image magnification Mv (2.10) of the eyepiece optical system 400 is lower than that of the second embodiment (Example 1a: 2.39) (see Table 19).

[0110] As in the second embodiment described above, in a high-magnification eyepiece optical system 400, it is desirable to form the surface forming the Fresnel lens surface Fr as a concave lens surface in order to improve definition while suppressing the visibility of ring lines. However, as in this embodiment, if the image magnification Mv of the eyepiece optical system 400 is relatively low, the surface forming the Fresnel lens surface Fr may be flat. Furthermore, by forming the surface forming the Fresnel lens surface Fr as a flat surface, the overall length of the eyepiece optical system 400 (the distance from the eye-side surface of the first lens L1 to the image display element 700) can be shortened. Furthermore, forming the Fresnel lens surface Fr on a flat surface is relatively easier to manufacture than forming it on a curved surface, making it possible to obtain a Fresnel lens 300 with high shape accuracy.

[0111] 29A , the results of simulation analysis of Example 2a, which is an example of the third embodiment, show that Example 2a also has a lower image magnification Mv of the eyepiece optical system 400 than Example 1a, which is an example of the second embodiment, and therefore, even if the Fresnel lens surface Fr is formed on a flat surface, good astigmatism (curvature of field) and distortion can be ensured. Furthermore, as shown in FIG. 29B , Example 2a includes a PB lens, and therefore good chromatic aberration can be ensured.

[0112] By applying this embodiment to a head-mounted display, it is possible to provide an image with high definition from the center to the periphery of the field of view, while still achieving a relatively high magnification, making it difficult to see the ring lines caused by the Fresnel lens 300.

[0113] As will be described later, in this embodiment, as shown in Figure 28, a PB lens is included as the third lens L3, but if the usage mode is such that the occurrence of chromatic aberration can be tolerated to a certain extent, a PB lens does not have to be included.

[0114] 5.2 Modifications Next, a modification of this embodiment will be described with reference to Fig. 30, Fig. 31A, and Fig. 31B. Fig. 30 is a cross-sectional view showing an example of the configuration of a display device 102 according to Example 2b, which is a modification of this embodiment, and Fig. 31A and Fig. 31B are diagrams showing various aberrations of Example 2b.

[0115] As shown in Figure 30, the display device 102 according to this modification differs from the present embodiment in that it does not include a PB lens. Because this modification does not include a PB lens, the chromatic aberration characteristics are inferior, but the cost of the display device 102 can be reduced while achieving high brightness (high efficiency). Furthermore, in this modification, the image magnification Mv (2.08) of the eyepiece optical system 400 is lower than that of the second embodiment (Example 1a: 2.39) (see Table 19). Specific lens data for Example 2b will be described later.

[0116] 31A, the results of simulation analysis of Example 2b, which is an example of this modified example, show that Example 2b also ensures good astigmatism (field curvature) and distortion aberration equivalent to those of Example 2a, which is an example of this embodiment. Furthermore, as shown in FIG. 31B, Example 2b does not include a PB lens, and therefore, although its chromatic aberration is inferior to that of Example 2a, it is still able to ensure relatively good chromatic aberration.

[0117] (The focal length of the PB lens is f Ｄ Now, with reference to FIGS. 32 to 35B, the focal length f of the PB lens Ｄ 32 is a cross-sectional view showing a configuration example of a display device 102 according to Example 1e, which is an example of the second embodiment, and FIGS. 33A and 33B are diagrams showing various aberrations in Example 1e. Also, FIG. 34 is a cross-sectional view showing a configuration example of a display device 102 according to Example 1f, which is an example of the second embodiment, and FIGS. 35A and 35B are diagrams showing various aberrations in Example 1f.

[0118] The appropriate focal length f in the eyepiece optical system 400 Ｄ However, the optimal focal length of the PB lens is f Ｄchanges depending on the image magnification Mv of the eyepiece optical system 400. For example, an eyepiece optical system 400 with a relatively low magnification generates relatively little chromatic aberration, so the optimal focal length f of the PB lens is Ｄ On the other hand, the eyepiece optical system 400 with a relatively high magnification generates a relatively large amount of chromatic aberration, so the optimum focal length f of the PB lens is Ｄ That is, when the image magnification Mv is high, the occurrence of chromatic aberration increases, and accordingly, the focal length f Ｄ Since the value of becomes shorter, the focal length f Ｄ It can be said that is dependent on the image magnification Mv. Here, the optimal focal length f of the PB lens is Ｄ In order to consider the above, the focal length f of the PB lens is calculated as shown in the following formula (5). Ｄ The following explanation will be given by introducing an index ε obtained by dividing by the image magnification Mv. The reference wavelength of the index ε is 546 nm. The index ε is also calculated by dividing the focal length f of the PB lens by Ｄ The lower limit of the optimum index ε can be determined by considering an optical system in which the image magnification Mv is high.

[0119] Optimal focal length f of PB lens Ｄ In order to examine this point, the optical characteristics of Example 1a described above were compared with those of Example 1e described below. As shown in Fig. 32, Example 1e has an eyepiece optical system 400 in which the maximum angle of view of Example 1a is increased from 105° to 110°, thereby increasing the image magnification Mv. Specific lens data for each Example 1e will be described later.

[0120] As shown in Figures 33A and 33B, according to the results of simulation analysis of Example 1e, it was found that Example 1e was inferior to Example 1a due to its high image magnification Mv, but was able to ensure relatively good aberration.

[0121] However, as will be described later in the description of the fourth embodiment, in an eyepiece optical system 400 with a high image magnification Mv, the refractive power required of the Fresnel lens 300 is large, and therefore it is necessary to increase the sag amount of the Fresnel lens 300. In addition, in this embodiment, it is necessary to form a relatively large number of annular zones 301 in order to suppress the visibility of ring lines. Here, the "sag amount" refers to the distance from the surface of the lens surface to the apex of the lens surface along the optical axis Z1 of the lens. For example, in the case of a convex lens, the "sag amount" is the distance from the surface of the lens surface at the maximum radius of the lens to the apex at the center of the lens along the optical axis Z1 of the lens. Furthermore, the "sag amount" of a Fresnel lens refers to the sag amount in the shape expressed by the aspherical formula before being divided into Fresnel lenses.

[0122] Furthermore, when a relatively large number of annular zones 301 are formed, the pitch of the annular zones 301 becomes narrower, and the influence of diffraction becomes dominant. Therefore, particularly in the peripheral region of the field of view where many annular zones 301 are formed, light passing through the annular zones 301 may spread due to diffraction, resulting in a deterioration in definition. Example 1e has specifications that can be said to be approximately the limit of the range in which such deterioration in definition at the periphery of the field of view due to the influence of diffraction can be tolerated. Furthermore, if the image magnification Mv is set higher than that of Example 1e, the influence of diffraction becomes even more dominant, resulting in a significant deterioration in definition at the periphery of the field of view. Therefore, since the index ε of Example 1e is approximately 86.3 (see Table 19), it is considered preferable that the index ε be 86.3 or greater in this embodiment.

[0123] Furthermore, the upper limit of the index ε is determined by considering an optical system with a low image magnification Mv and a relatively low occurrence of chromatic aberration. To examine the upper limit of the index ε, the optical characteristics of Example 1f described below were investigated. As shown in FIG. 34 , Example 1f has an eyepiece optical system 400 in which the image magnification Mv is reduced by narrowing the maximum angle of view from 105° to 80° in the eyepiece optical system 400 of Example 1a. Specific lens data for each Example 1f will be described later.

[0124] As shown in Figures 35A and 35B, the results of simulation analysis for Example 1f show that Example 1f also effectively corrects chromatic aberration. It is generally considered desirable for the eyepiece optical system 400 to suppress lateral chromatic aberration to 10 to 13 minutes or less. For the eyepiece optical system 400 of Example 1f, the lateral chromatic aberration is 13 minutes at the very periphery of the field of view (corresponding to a deviation between red and blue pixels of 39 μm), which is within the standard, and therefore the PB lens can be said to provide sufficient correction of lateral chromatic aberration. Therefore, since the index ε for Example 1f is approximately 530.5 (see Table 19), it is considered preferable for the index ε to be 530.5 or less in this embodiment.

[0125] 6. Fourth Embodiment Next, a fourth embodiment of the present disclosure will be described with reference to Fig. 36, Fig. 37, and Fig. 37B. Fig. 36 is a cross-sectional view showing an example configuration of a display device 102 according to Example 3a, which is one of the present embodiments. Fig. 37A and Fig. 37B are diagrams showing various aberrations in Example 3a.

[0126] As shown in Fig. 36, a display device 102 according to Example 3a, which is an example of this embodiment, includes, in order from the eyepoint E.P. side along the optical axis Z1, an eyepiece optical system 400 and an image display element 700. In this embodiment, the eyepiece optical system 400 includes, in order from the eyepoint E.P. side, a first lens L1, a second lens L2, a third lens L3, and a fourth lens L4. Furthermore, unlike the embodiments described so far, this embodiment includes, in addition to the first Fresnel lens surface Fr1 and the second Fresnel lens surface Fr2 of the first lens L1 and the second lens L2, a third Fresnel lens surface Fr3 formed entirely from the center to the periphery on the lens surface of the third lens L3 facing the image display element 700. Furthermore, in this embodiment, as in the third embodiment, the first Fresnel lens surface Fr1, the second Fresnel lens surface Fr2, and the third Fresnel lens surface Fr3 are formed as flat surfaces. In Example 3a, the maximum viewing angle, eye relief, and image display element (display panel) size are the same as those in Example 2a of the third embodiment (see Table 19). Specific lens data for Example 3a will be described later.

[0127] As shown in FIGS. 37A and 37B , according to the results of the simulation analysis of Example 3a, it was found that Example 3a using three Fresnel lenses 300 also ensured relatively good aberration equivalent to that of Example 1a.

[0128] In this embodiment, by using three Fresnel lenses 300 instead of two, the definition of the peripheral field of view can be improved. As described above, the Fresnel lens surface Fr is formed with annular zones 301. However, narrowing the pitch of the annular zones 301 causes light passing through the annular zones 301 to spread due to the wave-like behavior of light (diffraction), which is a major factor in degrading the definition. Because the lens sag increases toward the periphery of the Fresnel lens 300, more annular zones 301 must be formed at the periphery than at the center of the Fresnel lens surface Fr. Therefore, particularly in the peripheral region of the field of view where many annular zones 301 are formed, light passing through the annular zones 301 may spread due to diffraction, resulting in degraded definition. One possible way to avoid this degradation of definition due to diffraction is to widen the pitch of the annular zones 301. However, widening the pitch of the annular zones 301 increases the step size of the annular zones 301. Therefore, the vignetting of light at the step surface 302 becomes large, and the difference in brightness within the light beam becomes more pronounced, resulting in the ring line becoming more visible. In other words, there is a trade-off between the definition of peripheral vision and the degree to which the ring line is visible.

[0129] In order to resolve this trade-off relationship and make the ring lines less visible while improving the definition of the peripheral vision, this embodiment uses three Fresnel lenses 300. In detail, Example 3a is a configuration in which the third lens L3 in Example 2b of the third embodiment is changed to a Fresnel lens 300, and the refractive power that would be borne by the Fresnel lens 300 in the eyepiece optical system 400 is distributed and borne by three Fresnel lenses 300 instead of two Fresnel lenses 300.

[0130] FIG. 38 is a diagram showing the amount of sag (simulation analysis results) versus distance from the lens center before providing annular zones 301 on each Fresnel lens surface Fr in the third embodiment (Example 2a) and the fourth embodiment (Example 3a). In FIG. 38, the first lens L1 is referred to as "L1," the second lens L2 as "L2," and the third lens L3 as "L3." As shown in FIG. 38, it can be seen that the amount of sag is kept small in the fourth embodiment (Example 3a) compared to the third embodiment (Example 2a). Reducing the amount of sag of the Fresnel lens 300 allows the number of annular zones 301 to be reduced and the pitch of the annular zones 301 to be widened, thereby suppressing the effects of diffraction.

[0131] Furthermore, to verify the effect of improving the definition of peripheral vision by including three Fresnel lenses 300 in the eyepiece optical system 400, a simulation analysis was performed to examine the extent to which diffraction occurs due to the annular zones 301 of the Fresnel lens 300 in Example 2a, which is an example of the third embodiment, and Example 3a, which is an example of this embodiment. Here, the analysis was performed under the condition that the annular zone height Rh was 75 μm (constant) in the third embodiment (Example 2a) and the fourth embodiment (Example 3a). Figure 39 is a diagram showing the difference between the PSF (Point Spread Function) radius, which takes into account the spread of light due to diffraction by the annular zones 301 of the Fresnel lens surface Fr, and the PSF radius, which ignores the spread of light diffracted by the annular zones 301 of the Fresnel lens surface Fr, relative to the angle of the line of sight during eye rotation. The larger the difference, the greater the influence of diffraction, indicating that the definition is degraded by diffraction. The PSF radius is a root mean square (RMS) value based on the center of gravity of the PSF in the tangential direction, where the influence of diffraction is dominant. As shown in Fig. 39, in the fourth embodiment (Example 3a) that can reduce the sag amount of the Fresnel lens 300, it was found that the spread of light due to diffraction can be reduced and the deterioration of peripheral definition can be suppressed.

[0132] Furthermore, by using three Fresnel lenses 300 as in this embodiment, the overall length of the eyepiece optical system 400 can be shortened. For example, the overall length of the eyepiece optical system 400, i.e., the distance from the eye-side surface of the first lens L1 to the image display element 700, is 43.5 mm in Example 2b, while it is 42.3 mm in Example 3a, which is shorter. This is because Example 3a is an example in which the refractive lens of the third lens L3 in Example 2b is replaced with the Fresnel lens 300, making it possible to reduce the thickness of the third lens L3, thereby shortening the overall length.

[0133] The eyepiece optical system 400 according to this embodiment may also include a PB lens. In this case, it is preferable to arrange at least one refractive lens between the PB lens and the image display element 700. By including a PB lens, it is possible to significantly reduce axial chromatic aberration and lateral chromatic aberration compared to Example 3a while maintaining astigmatism and distortion equivalent to those of Example 3a. Furthermore, in this embodiment (Example 3a), the Fresnel lens surface Fr is formed on a flat surface. However, this is not limited thereto; the Fresnel lens surface Fr may also be formed on a concave lens surface. This can improve resolution and make ring lines less visible. Furthermore, in this embodiment, the eyepiece optical system 400 may include four or more Fresnel lenses 300.

[0134] That is, this embodiment is not limited to the configuration shown in Fig. 36. For example, the eyepiece optical system 400 may further include a seal glass that protects the image display element 700.

[0135] By applying this embodiment to a head-mounted display, it is possible to provide an image with high definition from the center to the periphery of the field of view, while still providing a high magnification, and making it difficult to see the ring lines caused by the Fresnel lens 300.

[0136] <<7. Examples>> Next, lens data of the eyepiece optical system 400 included in the display device 102 according to each example, which is a specific example of each embodiment of the present disclosure described above, will be described. Note that the example described below is an example of an embodiment of the present disclosure, and each embodiment of the present disclosure is not limited to the example described below.

[0137] The display devices 102 according to the following Examples 1a to 1f correspond to the second embodiment described above, the display devices 102 according to the following Examples 2a and 2b correspond to the third embodiment described above, and the display device 102 according to the following Example 3a corresponds to the fourth embodiment described above.

[0138] The symbols used in the following tables have the following meanings: "Si" indicates the i-th surface number, with the eye point E.P. being number 1 and the symbols increasing sequentially toward the image side. "R" indicates the paraxial radius of curvature (mm) of each surface. "D" indicates the distance (mm) on the optical axis between the i-th surface and the (i+1)-th surface. "Nd" indicates the refractive index value at the d-line (wavelength 587.6 nm) of the material (medium) of the optical element of each surface. "νd" indicates the Abbe number value at the d-line of the material of the optical element of each surface. Furthermore, a surface with a radius of curvature of "∞" indicates a flat surface or a diaphragm surface (aperture diaphragm STO). Furthermore, the "Comment" column lists the type of lens surface, etc.

[0139] Furthermore, the lenses according to each example include an aspherical surface. The aspherical shape is defined by the following aspherical formula (6). Note that in each table showing the aspherical coefficients below, "E-n" represents an exponential expression with base 10, that is, "10 to the power of -n." For example, "0.12345E-05" represents "0.12345 x (10 to the power of -5)."

[0140] Z: depth of aspherical surface Y: height from the optical axis R: paraxial radius of curvature K: conic constant Ai: ith-th aspherical coefficient (i is an integer of 3 or more)

[0141] Example 1a Table 1 shows basic lens data for each lens included in the eyepiece optical system 400 according to Example 1a. Table 2 also shows data for aspherical surfaces.

[0142] Example 1b Table 3 shows basic lens data for each lens included in the eyepiece optical system 400 according to Example 1b. Table 4 also shows data for aspherical surfaces.

[0143] Example 1c Table 5 shows basic lens data for each lens included in the eyepiece optical system 400 according to Example 1c. Table 6 also shows data for aspherical surfaces.

[0144] Example 1d Table 7 shows basic lens data for each lens included in the eyepiece optical system 400 according to Example 1d. Table 8 shows data for aspherical surfaces.

[0145] Example 1e Table 9 shows basic lens data for each lens included in the eyepiece optical system 400 according to Example 1e. Table 10 shows data for aspherical surfaces.

[0146] Example 1f Table 11 shows basic lens data for each lens included in the eyepiece optical system 400 according to Example 1f. Table 12 shows data for aspherical surfaces.

[0147] Example 2a Table 13 shows basic lens data for each lens included in the eyepiece optical system 400 according to Example 2a. Table 14 also shows data for aspherical surfaces.

[0148] Example 2b Table 15 shows basic lens data for each lens included in the eyepiece optical system 400 according to Example 2b. Table 16 shows data for aspherical surfaces.

[0149] Example 3a Table 17 shows basic lens data for each lens included in the eyepiece optical system 400 according to Example 3a. Table 18 also shows data for aspherical surfaces.

[0150] Furthermore, Table 19 shows a summary of the specifications of the display device 102, the lens arrangement, numerical data, etc. in each example.

[0151] <<8. Summary>> As described above, the eyepiece optical system 400 according to each embodiment of the present disclosure can shorten the overall length (the distance from the eyepoint E.P. to the image), and can provide high-definition images with a wide viewing angle while keeping the size of the display device 102 small.

[0152] <<9. Application Example>> An application example of an embodiment of the present disclosure will be described with reference to Fig. 40. Fig. 40 is a diagram showing an example configuration of a head-mounted display 100 as an example of a display device to which an embodiment of the present disclosure is applied, and in detail, (a) in the upper part of Fig. 40 shows a perspective view of the head-mounted display 100, and (b) in the lower part of Fig. 40 shows a side view of the head-mounted display 100.

[0153] 40 , the head-mounted display 100 has a display surface (display panel) Ds placed in front of the eyes of a user (observer), and an ocular optical system 400 according to an embodiment of the present disclosure. The display surface Ds is, for example, a liquid crystal display device, an organic EL display device, a micro OLED (organic light-emitting diode) display device, or the like. When the ocular optical systems 400 are mounted on the head-mounted display 100, the two ocular optical systems 400 are arranged side by side.

[0154] The display device 102 including the eyepiece optical system 400 according to the embodiment of the present disclosure is not limited to the head-mounted display 100, and may be, for example, an electronic viewfinder for a camera, etc. In this case, the number of installed eyepiece optical systems 400 may be one.

[0155] <<10. Supplementary Information>> Although the embodiments of the present disclosure have been described above in detail with reference to the accompanying drawings, the technical scope of the present disclosure is not limited to such examples. It is clear that a person skilled in the art of the present disclosure can conceive of various modified or altered examples within the scope of the technical idea described in the claims, and it is understood that these also naturally fall within the technical scope of the present disclosure.

[0156] Furthermore, the effects described herein are merely descriptive or exemplary and are not limiting. In other words, the technology according to the present disclosure may achieve other effects that will be apparent to those skilled in the art from the description of this specification, in addition to or in place of the above-described effects.

[0157] The present technology can also be configured as follows. (1) A display device including an eyepiece optical system having a first lens and a second lens arranged in this order from the eyeball side, and an image display element arranged on the opposite side of the eyeball side with the eyepiece optical system in between, wherein surfaces of the first and second lenses facing the image display element are configured as Fresnel lens surfaces. (2) The display device according to (1) above, wherein the Fresnel lens surface of at least one of the first and second lenses is provided on a flat-shaped surface. (3) The display device according to (1) above, wherein the Fresnel lens surface of at least one of the first and second lenses is provided on a concave lens surface. (4) The display device according to any one of (1) to (3) above, wherein the eyepiece optical system further includes one or more third lenses arranged on the image display element side of the second lens, and wherein surfaces of the third lenses facing the image display element are configured as Fresnel lens surfaces. (5) The display device according to (4), wherein the Fresnel lens surface of the third lens is provided on a flat surface or a concave lens surface. (6) Each of the first Fresnel lens surface of the first lens and the second Fresnel lens surface of the second lens has a plurality of ring zones, and a step surface is formed at each boundary portion of the plurality of ring zones, and the step surface has an angle θ with respect to the optical axis of the first Fresnel lens surface. １ is 15° or more and 40° or less, and the angle θ of the step surface with respect to the optical axis in the annular zone 5 mm away from the center １1 is the angle θ of the step surface with respect to the optical axis in the annular zone 10 mm away from the center １２ and on the second Fresnel lens surface, the angle θ of the step surface with respect to the optical axis is ２ is 0° or more and 30° or less, and the angle θ of the step surface with respect to the optical axis in the annular zone 5 mm away from the center ２1 is the angle θ of the step surface with respect to the optical axis in the annular zone 15 mm away from the center ２２ In an annular zone that is 5 mm or more away from the center, the angle θ of the step surface of the first Fresnel lens surface with respect to the optical axis １is the angle θ of the step surface of the second Fresnel lens surface with respect to the optical axis. ２ The display device according to any one of (1) to (5) above, wherein the eyepiece optical system further comprises a chromatic aberration compensation element. (7) The display device according to any one of (1) to (6) above, wherein the eyepiece optical system further comprises a chromatic aberration compensation element. (8) The display device according to (7), wherein the eyepiece optical system further comprises at least one or more refractive lenses located between the chromatic aberration compensation element and the image display element. (9) The display device according to (8), wherein the chromatic aberration compensation element is arranged between the second lens and the image display element. (10) The display device according to (9), wherein the eyepiece optical system further comprises another refractive lens located between the second lens and the chromatic aberration compensation element. (11) The display device according to (8), wherein the chromatic aberration compensation element is arranged between the first lens and the second lens. (12) The display device according to (7), wherein the eyepiece optical system further comprises a plurality of the chromatic aberration compensation elements. (13) The display device according to (7), wherein the focal length f of the chromatic aberration compensation element is Ｄ The display device according to any one of (7) to (12) above, wherein an index ε obtained by dividing by an image magnification Mv is 86.3 or more and 530.5 or less. (14) The display device according to any one of (7) to (13) above, wherein the chromatic aberration compensation element is made of a Pancharatnam-Berry lens. (15) The display device according to (14) above, wherein the eyepiece optical system further includes a pair of circular polarizers sandwiching the Pancharatnam-Berry lens. (16) The display device according to (12) above, wherein the plurality of chromatic aberration compensation elements are made of a plurality of Pancharatnam-Berry lenses, and each of the Pancharatnam-Berry lenses is sandwiched between a pair of polarizers. (17) The display device according to any one of (14) to (16) above, wherein the Pancharatnam-Berry lens is made of a liquid crystal lens. (18) The display device according to any one of (7) to (13), wherein the chromatic aberration compensation element is a diffractive lens. (19) The display device according to any one of (7) to (13), wherein the chromatic aberration compensation element is a hologram lens.

[0158] 100 Head-mounted display 102 Display device 400, 802 Eyepiece optical system 300 Fresnel lens 301 Annular zone 302 Step surface 304 Effective lens surface 700, 800 Image display element 801 Eyepiece lens Ds Display surface E.R. Eye relief E.P. Eye point Fr, Fr1, Fr2 Fresnel lens surface Im Virtual image L1, L2, L3, L4, L5 Lens R Surface Z1 Optical axis

Claims

1. A display device comprising: an eyepiece optical system arranged in the order of a first lens and a second lens from the eyeball side; and an image display element arranged on the opposite side of the eyeball side, with the eyepiece optical system in between; wherein the surfaces of the first and second lenses facing the image display element are configured as Fresnel lens surfaces.

2. The display device according to claim 1, wherein the Fresnel lens surface of at least one of the first and second lenses is provided on a flat surface.

3. The display device according to claim 1, wherein the Fresnel lens surface of at least one of the first and second lenses is provided as a concave lens surface.

4. The display device according to claim 1, wherein the eyepiece optical system further comprises one or more third lenses arranged on the image display element side of the second lens, and the surface of the third lens on the image display element side is configured as a Fresnel lens surface.

5. The display device according to claim 4, wherein the Fresnel lens surface of the third lens is provided on a flat surface or a concave lens surface.

6. The first Fresnel lens surface of the first lens and the second Fresnel lens surface of the second lens each have a plurality of ring zones, and a step surface is formed at the boundary portion of each of the plurality of ring zones, and on the first Fresnel lens surface, an angle θ of the step surface with respect to the optical axis is １ is 15° or more and 40° or less, and the angle θ of the step surface with respect to the optical axis in the annular zone 5 mm away from the center １1 is the angle θ of the step surface with respect to the optical axis in the annular zone 10 mm away from the center １２ or less, and in the second Fresnel lens surface, the angle θ of the step surface with respect to the optical axis is ２ is 0° or more and 30° or less, and the angle θ of the step surface with respect to the optical axis in the annular zone 5 mm away from the center ２1 is the angle θ of the step surface with respect to the optical axis in the annular zone 15 mm away from the center ２２ In an annular zone that is 5 mm or more away from the center, the angle θ of the step surface of the first Fresnel lens surface with respect to the optical axis １ is the angle θ of the step surface of the second Fresnel lens surface with respect to the optical axis. ２ The display device according to claim 1 .

7. The display device according to claim 1, wherein the eyepiece optical system further comprises a chromatic aberration compensation element.

8. The display device according to claim 7, wherein the eyepiece optical system further comprises at least one refractive lens located between the chromatic aberration compensation element and the image display element.

9. The display device according to claim 8, wherein the chromatic aberration compensation element is disposed between the second lens and the image display element.

10. The display device according to claim 9, wherein the eyepiece optical system further comprises another refractive lens located between the second lens and the chromatic aberration compensation element.

11. The display device according to claim 8, wherein the chromatic aberration compensation element is disposed between the first lens and the second lens.

12. The display device according to claim 7, wherein the eyepiece optical system further comprises a plurality of the chromatic aberration compensation elements.

13. The focal length f of the chromatic aberration compensation element Ｄ The display device according to claim 7 , wherein an index ε obtained by dividing by an image magnification Mv is equal to or greater than 86.3 and equal to or less than 530.

5.

14. The display device according to claim 7, wherein the chromatic aberration compensation element is a Pancharatnam-Berry lens.

15. The display device according to claim 14, wherein the eyepiece optical system further includes a pair of circular polarizers sandwiching the Pancharatnam-Berry lens.

16. The display device according to claim 12, wherein the plurality of chromatic aberration compensation elements are comprised of a plurality of Pancharatnam-Berry lenses, and each of the Pancharatnam-Berry lenses is sandwiched between a pair of polarizing plates.

17. The display device according to claim 14, wherein the Pancharatnam-Berry lens is a liquid crystal lens.

18. The display device according to claim 7, wherein the chromatic aberration compensation element is a diffractive lens.

19. The display device according to claim 7, wherein the chromatic aberration compensation element is a hologram lens.

Images