Display device

Abstract

A display device includes a display element, a display optical system configured to guide light from a display surface of the display element to a viewing side, and two optical elements. The display optical system includes a first semi-transmissive reflective surface and a second semi-transmissive reflective surface. Light from the display surface is transmitted through the second semi-transmissive reflective surface, reflected on the first semi-transmissive reflective surface, reflected on the second semi-transmissive reflective surface, transmitted through the first semi-transmissive reflective surface, and guided to the viewing side. An absolute value of a curvature of the second transflective surface is greater than an absolute value of a curvature of the first transflective surface. The display surface has a convex shape toward the observation side in at least one of two cross sections including an optical axis of the display optical system and orthogonal to each other.

Description

Technical Field

[0001] An aspect of the embodiment relates to a display optical system suitable for an image display device such as a head mounted display (HMD) which magnifies and displays an original image displayed on a display element. Background Art

[0002] The display device is required to have a reduced size and a wide viewing angle. Japanese Patent Laid-Open No. 2019-148627 discloses a display optical system using a reflective surface with a reduced size and a wide viewing angle. The display optical system uses a triple-pass configuration and two reflective surfaces that reflect light from a display element (display surface) to achieve a wide viewing angle (high magnification) and reduced thickness.

[0003] In the display optical system disclosed in Japanese Patent Laid-Open No. 2019-148627, the optical material of the lens is selected so that the Petzval field curvature generated at the reflective surface (concave mirror) is offset by the Petzval field curvature generated at the refractive surface. Thus, the entire optical system can correct the field curvature to support a flat display surface.

[0004] Optical materials have a limited range of refractive indices and Abbe numbers, and in cases where the optical material is selected with priority given to correction of the Petzval sum, it may be difficult to correct chromatic aberration. Lateral chromatic aberration can be reduced by electronically correcting the image on the display element.

[0005] When displaying high-definition images with high spatial frequencies, optical performance is degraded due to lateral chromatic aberration within each RGB color channel. In addition, it is difficult to electronically correct longitudinal chromatic aberration.

[0006] The display optical system disclosed in JP 2019-148627 has difficulty in providing a strong light-gathering effect to the reflective surface in order to balance field curvature and chromatic aberration, and the attempt to increase the magnification and reduce the size of the optical system is limited. In addition, since the display optical system includes a single cemented lens composed of a plano-convex lens and a plano-concave lens via a reflective surface disposed therebetween, correction of astigmatism is also limited. Summary of the invention

[0007] A display device according to one aspect of the present disclosure includes: a display element, a display optical system configured to guide light from a display surface of the display element to an observation side, and two optical elements. The display optical system includes a first semi-transmissive reflective surface and a second semi-transmissive reflective surface provided on a bonding surface of the two optical elements. Light from the display surface is transmitted through the second semi-transmissive reflective surface, reflected on the first semi-transmissive reflective surface, reflected on the second semi-transmissive reflective surface, transmitted through the first semi-transmissive reflective surface, and guided to the observation side. The absolute value of the curvature of the second semi-transmissive reflective surface is greater than the absolute value of the curvature of the first semi-transmissive reflective surface. The display surface has a convex shape toward the observation side in at least one of two cross sections that include an optical axis of the display optical system and are orthogonal to each other.

[0008] Further features of various embodiments of the present disclosure will become apparent from the following description of the embodiments with reference to the attached drawings. BRIEF DESCRIPTION OF THE DRAWINGS

[0009] Figure 1 is a ZX cross-sectional view of the display optical system according to Example 1.

[0010] Figure 2 is a YX cross-sectional view of the display optical system according to Example 1.

[0011] Figure 3 : is a longitudinal aberration diagram of the display optical system according to Example 1 in the horizontal viewing angle direction.

[0012] Figure 4 3 is a longitudinal aberration diagram of the display optical system according to Example 1 in the vertical viewing angle direction.

[0013] Figure 5 is a YX cross-sectional view of the display optical system according to Example 2.

[0014] Figure 6 2 is a longitudinal aberration diagram of the display optical system according to Example 2 in the horizontal and vertical viewing angle directions.

[0015] Figure 7 is a YX cross-sectional view of a display optical system according to Example 3.

[0016] Figure 8 2 is a longitudinal aberration diagram of the display optical system according to Example 3 in the horizontal and vertical viewing angle directions.

[0017] Fig. 9 is a YX cross-sectional view of a display optical system according to Example 4.

[0018] Fig.102 is a longitudinal aberration diagram of the display optical system according to Example 4 in the horizontal and vertical viewing angle directions.

[0019] Fig.11 is a YX cross-sectional view of the display optical system according to Example 5.

[0020] Fig.12 2 is a longitudinal aberration diagram of the display optical system according to Example 5 in the horizontal and vertical viewing angle directions.

[0021] Fig.13 The light path using polarized light is shown.

[0022] Fig.14 An HMD using the display optical system according to any one of Examples 1 to 5 is shown. DETAILED DESCRIPTION

[0023] Examples of the present disclosure will be described below with reference to the drawings. First, before describing the display devices according to Examples 1 to 5 in detail, common matters of the respective examples will be explained. Figure 1 and Figure 2 A ZX cross section and an XY cross section of the display device according to Example 1 are shown. Figure 5 , Figure 7 , Fig. 9 and Fig.11 YX cross sections of the display devices according to Examples 2 to 5 are respectively shown.

[0024] The display device according to each example includes a display element and a display optical system, and an image displayed on a display surface ID of the display element is magnified and displayed toward a pupil surface SP on the observation side. The display optical system has a configuration in which a return light path (three-pass path) is formed by two internal reflections. More specifically, the display optical system includes a first semi-transmitting reflection surface PBS, a first quarter-wavelength (λ / 4) plate QWP1, a first lens G1, a second semi-transmitting reflection surface HM, a second lens G2, a second quarter-wavelength plate QWP2, and a polarizing plate POL in sequence from the pupil side (observation side) to the display element side. The pupil surface SP is an observation surface, and the pupil of the observer is placed there.

[0025] The first semi-transmissive reflective surface PBS includes, for example, a wire grid polarizer, and reflects linear polarized light in the same polarization direction as the polarization direction of the linear polarized light passing through the polarizing plate POL, and transmits the linear polarized light in the polarization direction perpendicular thereto. In the wire grid polarizer, a surface on which a wire grid is formed serves as a semi-transmissive reflective surface.

[0026] The first quarter wavelength plate QWP1 and the second quarter wavelength plate QWP2 are arranged so that their respective slow axes (lag axes) are inclined by 90° (90 degrees) relative to each other. The slow axis of the first quarter wavelength plate QWP1 is inclined by 45° relative to the polarization transmission axis of the polarizing plate POL. The second semi-transmissive reflective surface HM is a semi-transmissive reflective mirror formed by, for example, a dielectric multilayer film or metal vapor deposition. The display element can use a liquid crystal display element (LCD), an organic EL element, etc. CG represents a cover glass (glass cover) covering the display surface (screen) ID of the display element.

[0027] Fig.13 The use of polarized light in the display optical system according to various examples is shown. Among the light emitted from the display surface ID, the linear polarized light parallel to the polarization transmission axis of the polarizing plate POL (E) is transmitted through the polarizing plate POL, converted into circular polarized light by the second quarter-wave plate QWP2 (D), and enters the semi-transmitting reflective surface HM (C). A portion of the light that has reached the second semi-transmitting reflective surface HM is reflected, becomes circularly polarized light in the direction opposite to the direction before reflection, and returns to the second quarter-wave plate QWP2. The reverse circularly polarized light that has returned to the second quarter-wave plate QWP2 is converted by the second quarter-wave plate QWP2 into linear polarized light whose polarization direction is perpendicular to the polarization direction when it was originally transmitted through the polarizing plate E, and then returns to the polarizing plate POL and is absorbed by the polarizing plate POL.

[0028] On the other hand, the light that has reached and transmitted through the second semi-transmitting reflective surface HM is converted by the first quarter-wave plate QWP1 (B) into linear polarized light in the same polarization direction as when it was transmitted through the polarizing plate POL, and enters the first semi-transmitting reflective surface PBS (A). The linear polarized light incident on the first semi-transmitting reflective surface PBS is reflected due to the polarization selectivity of the first semi-transmitting reflective surface PBS, converted by the first quarter-wave plate QWP1 into circular polarized light in the direction opposite to the direction of the circular polarized light originally emitted from the second quarter-wave plate QWP2, and enters the second semi-transmitting reflective surface HM.

[0029] The circularly polarized light incident on the second semi-transmitting reflective surface HM is reflected by the second semi-transmitting reflective surface HM, and is converted into circularly polarized light in the direction opposite to the direction before the reflection. The light then enters the first quarter-wave plate QWP1, is converted into linearly polarized light in a polarization direction perpendicular to the polarization direction of the linearly polarized light initially transmitted through the polarizing plate POL, and enters the first semi-transmitting reflective surface PBS. The linearly polarized light incident on the first semi-transmitting reflective surface PBS is transmitted through the first semi-transmitting reflective surface PBS due to the polarization selectivity of the above-mentioned first semi-transmitting reflective surface PBS, and reaches the pupil surface SP.

[0030] By using polarized light as described above, light emitted from the display surface (screen) ID is guided to the pupil surface SP through a three-pass path in which the light is transmitted through the second semi-transmitting reflective surface HM, reflected by the first semi-transmitting reflective surface PBS, reflected by the second semi-transmitting reflective surface HM, and transmitted through the first semi-transmitting reflective surface PBS.

[0031] The characteristics of the display optical system according to each example will now be described. The display optical system adopts a three-pass configuration using two semi-transmitting reflection surfaces (a first semi-transmitting reflection surface PBS and a second semi-transmitting reflection surface HM), and a bonding optical element in which two optical elements (a first semi-transmitting reflection surface G1 and a second semi-transmitting reflection surface G2) are bonded. The semi-transmitting reflection surface (the second semi-transmitting reflection surface) having a larger curvature (absolute value) of the two semi-transmitting reflection surfaces is provided on the bonding surface of the bonding lens. The display surface of the display element has a convex shape toward the observation side in at least one of the two cross sections (ZX cross section and XY cross section) that include the optical axis and are orthogonal to each other.

[0032] Each example uses a three-pass configuration to reduce the thickness of the display optical system. One of the two semi-transmissive reflective surfaces that shares the main optical power (the inverse of the focal length) of the entire display optical system is set on the bonding surface. This configuration avoids total reflection on the semi-transmissive reflective surface, which becomes a problem when seeking a high magnification of the display optical system. In addition, since the risk of the bonding surface being exposed to the external environment is low, it is beneficial in terms of environmental resistance when a semi-transmissive reflective mirror made of a metal film or a dielectric multilayer film is used as the semi-transmissive reflective surface.

[0033] Here, in the attempt of high magnification of the display optical system, it is effective to increase the optical power of the semi-transmissive reflective surface, that is, to give the semi-transmissive reflective surface a larger curvature (absolute value). At this time, the problem of total reflection can be avoided by arranging the semi-transmissive reflective surface on the bonding surface. However, it becomes difficult to correct the Petzval sum in the entire optical system, and the image field curvature still exists. Using a display element having a display surface formed as a convex surface toward the observation side to compensate for the residual image field curvature can realize a display optical system with excellent optical performance on the entire display screen.

[0034] A known method for realizing a curved display surface is to process the end face of a fiber optic plate (FOP) into a curved surface. In addition, another known example is to convert the display surface into a cylindrical or foldable shape using a flexible processing technology for LCD or OLED. Here, considering resolution and cost, it is better to use a display element such as an LCD or OLED with a curved display surface than to use a FOP.

[0035] Another known example is a combination of a curved display surface and a display optical system including a dioptric optical system. In this example, the main focal length of the entire optical system is borne by the refractive surface. On the other hand, the display optical systems according to the various examples are different in that the main focal length of the entire optical system is borne by the reflective surface. Since the signs of the Petzval terms generated on the refractive surface and the reflective surface are opposite, the signs of the generated field curvature are also opposite. Therefore, in the combination of a curved display surface and a display optical system including a dioptric optical system, the curvature direction of the display surface can be convex toward the display optical system side.

[0036] As described above, the respective examples realize a display device with a reduced size and a wide viewing angle using a display optical system having a high magnification and a reduced thickness to achieve high optical performance and a display element having a curved display surface.

[0037] In each example, two optical elements joined at a joining surface provided with a semi-transmissive reflective surface are made of a resin material. Using a resin material for the optical elements is better in terms of weight reduction than using a glass material.

[0038] In the above configuration, fG1 is the focal length of the first optical element in air, which is calculated based on the curvature radius of the reference spherical surface of the first optical element (G1) disposed on the observation side of the two optical elements (wherein the curvature radius of the reference spherical surface will be referred to as the reference curvature radius). fG2 is the focal length of the second optical element (G2) in air, which is calculated based on the reference curvature radius of the second optical element (G2) disposed on the display element side of the two optical elements. Ndp is the d-line refractive index of the optical element with a positive focal length of the two optical elements. vdp is the Abbe number of the d-line based on the optical element with a positive focal length of the two optical elements. Rhm is the reference curvature radius of the semi-transmissive reflective surface (the second semi-transmissive reflective surface) with a larger curvature (absolute value) of the two semi-transmissive reflective surfaces. f is the focal length of the entire display optical system. Rp is the reference curvature radius of the display surface. The reference curvature radius of each optical element and the semi-transmissive reflective surface is the radius of the reference spherical surface determined by the surface vertex on the optical axis and the maximum optical effective diameter (effective diameter). The reference curvature radius of the display surface is the minimum value of the curvature radius (absolute value) of the reference spherical surface determined by the surface vertex on the optical axis and the end of the effective area of ​​the display surface.

[0039] Then, the display optical system according to each example may satisfy at least one of the following inequalities (1) to (5):

[0040] fG1 / fG2 < 0 (1)

[0041] 1.4 ≤ Ndp < Ndn ≤ 1.9 (2)

[0042] 1.0 < νdp / νdn ≤ 4.0 (3)

[0043] 1.0 < |Rhm| / f ≤ 5.0 (4)

[0044] 0.1 ≤ |Rhm| / |Rp| ≤ 2.0 (5)

[0045] Inequality (1) defines the appropriate ratio of the focal lengths of the positive lens and the negative lens when a semi-transmitting reflective surface is set for the bonding surface in two optical elements (which form a bonded lens composed of a positive lens and a negative lens). The bonded lens composed of a positive lens and a negative lens can correct chromatic aberration occurring on the refractive surface of the bonded lens. When fG1 / fG2 becomes higher than the upper limit of inequality (1), both optical elements become positive lenses or negative lenses, and achromatism cannot be achieved. Although no lower limit is set in inequality (1), when fG1 / fG2 becomes too small, the optical power becomes too biased towards one lens, which is not conducive to correcting chromatic aberration. The bonding surface can have a convex shape toward the display element side. Setting the semi-transmitting reflective surface to a concentric shape relative to the pupil surface is conducive to astigmatism correction. At this time, the lens on the observation side can be a positive lens, and the lens on the display element side can be a negative lens.

[0046] Inequality (2) defines the appropriate relationship and range of the refractive indexes of the two optical elements. The refractive index of the positive lens is less than the refractive index of the negative lens, which can help select a low-dispersion material for the positive lens and a high-dispersion material for the negative lens. This refractive index configuration is not conducive to using the Petzval term generated at the refractive surface to compensate for the Petzval term generated at the reflective surface (concave mirror). However, the display optical system combined with the display element having a curved display surface according to various examples can have a configuration that gives priority to chromatic aberration correction over field curvature correction. In the case where Ndp or Ndn becomes lower than the lower limit of inequality (2), the refractive index of the optical element becomes too low, and it becomes difficult to correct monochromatic aberrations such as spherical aberration. In the case where Ndp or Ndn becomes higher than the upper limit of inequality (2), the refractive index of the optical element becomes too high. Accordingly, a material with a high specific gravity must be selected as the optical material, and it is difficult to reduce the weight of the display optical system.

[0047] Inequality (3) defines an appropriate range for the ratio of the Abbe numbers of two optical elements. Selecting a low-dispersion material for the positive lens and a high-dispersion material for the negative lens to provide a joined lens with an achromatic configuration can correct longitudinal chromatic aberration and lateral chromatic aberration. Achromatism in the lens is crucial for a display optical system with a three-pass configuration because chromatic aberration does not appear on the reflective surface. In the case where νdp / νdn becomes lower than the lower limit of inequality (3), the Abbe number of the positive lens becomes much smaller than the Abbe number of the negative lens, and the correction of chromatic aberration is not sufficient. In the case where νdp / νdn becomes higher than the upper limit of inequality (3), the Abbe number of the positive lens becomes much larger than the Abbe number of the negative lens. In this case, a material with an extremely low refractive index must be selected for the positive lens, or a material with an extremely high dispersion must be selected for the negative lens, and the correction of monochromatic aberrations and the reduction of transmittance of the optical system will become a problem.

[0048] Inequality (4) defines an appropriate range of the ratio of the radius of curvature of the semi-transmissive reflective surface disposed on the bonding surface to the focal length of the entire optical system. Each example disposes the semi-transmissive reflective surface on the bonding surface, thereby avoiding the total reflection condition, allowing the semi-transmissive reflective surface to share the strong light focal length, and increasing the magnification of the display optical system. In the case where |Rhm| / f becomes lower than the lower limit of inequality (4), the radius of curvature of the semi-transmissive reflective surface becomes too small relative to the focal length of the entire optical system, and it becomes difficult to use the curved display surface to compensate for the image field curvature that occurs in the optical system. In the case where |Rhm| / f becomes higher than the upper limit of inequality (4), the radius of curvature of the semi-transmissive reflective surface becomes too large relative to the focal length of the entire optical system. Accordingly, the optical focal length shared by the reflective surface (concave mirror) in the semi-transmissive reflective surface decreases, and it becomes difficult to increase the magnification of the optical system.

[0049] Inequality (5) defines an appropriate range of the ratio of the radius of curvature of the semi-transmitting reflective surface disposed on the bonding surface to the radius of curvature of the display surface. Properly setting both the radius of curvature of the semi-transmitting reflective surface and the radius of curvature of the display surface can correct the field curvature of the entire display device, and can achieve the amount of curvature of the display element manufactured as a device. In the case where |Rhm| / |Rp| becomes lower than the lower limit of inequality (5), the radius of curvature of the semi-transmitting reflective surface becomes too small relative to the radius of curvature of the display surface, and the field curvature of the entire display device cannot be fully corrected. In the case where |Rhm| / |Rp| becomes higher than the upper limit of inequality (5), the radius of curvature of the semi-transmitting reflective surface becomes too large relative to the radius of curvature of the display element surface. In this case, it is difficult to increase the magnification of the optical system, the field curvature of the entire display device may be over-corrected, and it becomes difficult to manufacture the display element.

[0050] Inequalities (1) to (5) can be replaced by the following inequalities (1a) to (5a):

[0051] -3.0≤fG1 / fG2≤-0.2(1a)

[0052] 1.45≤Ndp <Ndn≤1.8(2a)

[0053] 1.4≤νdp / νdn≤3.5(3a)

[0054] 1.0<|Rhm| / f≤4.0(4a)

[0055] 0.2≤|Rhm| / |Rp|≤1.7(5a)

[0056] Inequalities (1) to (5) can be replaced by the following inequalities (1b) to (5b):

[0057] -1.5≤fG1 / fG2≤-0.4(1b)

[0058] 1.5≤Ndp <Ndn≤1.7(2b)

[0059] 1.8≤νdp / νdn≤3.0(3b)

[0060] 1.0<|Rhm| / f≤3.6(4b)

[0061] 0.3≤|Rhm| / |Rp|≤1.4(5b)

[0062] The display optical system according to Example 1, Example 2 and Example 4 has an aspherical refractive surface (lens surface) having an inflection point within the optically effective diameter. The inflection point is a point (line) where the refractive power on the refractive surface changes from positive to negative. In Example 1, Example 2 and Example 4, the configuration uses a display element with a curved display surface to compensate for the field curvature of the display optical system, but astigmatism is to be corrected within the display optical system. The aspherical refractive surface with an inflection point can significantly change the divergence and convergence of the refractive surface near and outside the optical axis, and is effective for correcting astigmatism while allowing field curvature in the display optical system.

[0063] In Examples 1 to 4, the semi-transmissive reflective surface having the smaller curvature of the two semi-transmissive reflective surfaces is configured as a flat surface. Fig.13The configuration using polarization shown joins the polarizing element to a flat surface and reduces the thickness of the display optical system. In addition, the flat joining surface joined to the polarizing element can facilitate the joining process of the polarizing element. In addition, the two semi-transmissive reflective surfaces as described in Example 5 are curved surfaces so that two reflective surfaces with optical power can be placed in the display optical system and increase the degree of freedom in design. This is conducive to increasing the higher magnification of the display optical system.

[0064] In Examples 1 to 3 and 5, the optical element having optical power included in the display optical system is composed of a cemented lens. Therefore, it is possible to achieve the required optical performance with a minimum configuration, and the weight of the display optical system can be reduced.

[0065] In various examples, when the interocular distance is 15 mm, the diopter is 0 diopter, and the viewing angle is 30 degrees, the absolute value of the angle between the pupil center ray (ray passing through the center of the pupil plane) and the normal to the display surface is 30 degrees or less. In the case where the display surface has a rotationally asymmetric shape with respect to the optical axis, the angle is evaluated based on the direction in which the radius of curvature (absolute value) of the spherical surface defined by the surface vertex on the optical axis of the display surface and the effective area of ​​the display surface has a minimum value.

[0066] Conventional display optical systems with a three-pass configuration using two semi-transmissive reflective surfaces have problems in that field curvature increases and the incident angle of light on the display surface increases when high magnification is attempted.

[0067] Using a display element with a curved display surface can reduce the incident angle of light relative to the normal of the display surface and improve the brightness shadow and color shift of the image (screen). As described in each example, the angle (absolute value) between the pupil center light and the normal of the display element surface can be 20 degrees or less. As described in Examples 1, 3 to 5, the angle (absolute value) between the pupil center light and the normal of the display element surface can be 10 degrees or less.

[0068] In various examples, at least one of the two transflective surfaces includes a polarization selective transflective element. Fig.13 The configuration using polarized light is shown. That is, the use of polarized light can shield unnecessary light from the display surface that is not reflected by the two semi-transmissive reflective surfaces but is transmitted and reaches the pupil surface. Examples of polarized light selective semi-transmissive reflective elements include wire grid elements such as WGF (registered trademark) manufactured by Asahi Kasei, reflective linear polarizing elements such as IQP-E manufactured by 3M, and circularly polarized reflective elements using cholesteric liquid crystal. When using a reflective linear polarizing element, a quarter-wave plate is placed between the two semi-transmissive reflective surfaces.

[0069] A description will now be given of Examples 1 to 5 and corresponding Numerical Examples 1 to 5. Numerical Examples 1 to 5 will be described together after Example 5. Numerical values ​​in the numerical examples will be described later.

[0070] Example 1

[0071] according to Figure 1 and Figure 2 The display device of Example 1 (Numerical Example 1) shown has a horizontal viewing angle of about 90 degrees. The display optical system according to this example includes a joined lens consisting of a plano-convex lens G1 arranged on the observation side and an aspheric lens G2 arranged on the display element side, and a second semi-transmitting reflection surface HM having an aspheric surface and a concave surface facing the observation side is arranged on the joined surface of the joined lens. The first semi-transmitting reflection surface PBS is arranged on the surface (plane) on the observation side of the lens G1. Due to this configuration, the lens G1 can be used as a three-pass, and a high magnification and reduced thickness of the display optical system can be achieved. Using a resin material as the material of the lens G1 and the lens G2 can reduce the weight of the display optical system. In addition, joining the lens G1 (which is a positive lens made of a low-dispersion material) and the lens G2 (which is a negative lens made of a high-dispersion material) can satisfactorily correct the chromatic aberration of the display optical system. In addition, the aspheric surface of the display element side of the lens G2 has an inflection point within the optical effective diameter to satisfactorily correct the astigmatism.

[0072] The display element has a rectangular-shaped display surface ID, whose active area has an aspect ratio of about 16:9, and the display surface ID is Figure 1 The ZX cross section (horizontal viewing angle direction parallel to the longitudinal direction of the display surface) shown has a cylindrical shape with the convex surface facing the observation side. As a result, the image field curvature remaining in the display optical system can be compensated by the curved display surface ID, and a display device with excellent image plane characteristics in the horizontal viewing angle direction can be realized.

[0073] The display optical system according to Numerical Example 1 satisfies all of Inequalities (1) to (5).

[0074] Figure 3 and Figure 4The longitudinal aberrations (spherical aberration, astigmatism, distortion, and chromatic aberration) of the display optical system according to numerical example 1 in the horizontal field angle direction and the vertical field angle direction are respectively shown. In the spherical aberration diagram, EPD / 2 represents the radius of the pupil surface SP, the solid line represents the spherical aberration amount of the d-line (wavelength 587.6nm), and the double-dashed line represents the spherical aberration amount of the C-line (wavelength 656.3nm). The dashed line represents the spherical aberration amount of the F-line (wavelength 486.1nm). In the astigmatism diagram, the solid line ΔS represents the astigmatism amount on the sagittal image plane, and the dotted line ΔM represents the astigmatism amount on the meridional image plane. The distortion aberration shows the distortion amount of the d-line. The chromatic aberration diagram shows the lateral chromatic aberration amount of the C-line and the F-line. ω represents the half viewing angle (°).

[0075] Example 2

[0076] according to Figure 5 The display device of Example 2 (Numerical Example 2) shown has horizontal and vertical viewing angles of about 85 degrees. The basic configuration of the display device according to this example is the same as that of Example 1, but the specifications of the display element and the display optical system are different from those of Example 1.

[0077] The display element has a display surface ID in a square shape, an active area thereof has an aspect ratio of about 1:1, and the display surface ID is Figure 5 The YX cross section shown and the ZX cross section not shown have a spherical surface with a convex surface facing the observation side. Thus, the image field curvature remaining in the display optical system can be compensated by the curved display surface ID, and a display device with excellent image plane characteristics in the horizontal viewing angle direction can be realized.

[0078] The display optical system according to Numerical Example 2 satisfies all of Inequalities (1) to (5). Figure 6 Longitudinal aberrations of the display optical system according to Numerical Example 2 in the horizontal and vertical viewing angle directions are shown.

[0079] Example 3

[0080] Figure 7 The display device according to Example 3 (Numerical Example 3) shown has horizontal and vertical viewing angles of about 120 degrees. The basic configuration of the display device according to this example is the same as that of Example 2, but the specifications of the display element and the display optical system are different from those of Example 2.

[0081] The display element has a display surface ID in a square shape, an active area thereof has an aspect ratio of about 1:1, and the display surface ID is Figure 7The YX cross section shown and the ZX cross section not shown have a spherical surface with a convex surface facing the observation side. Thus, the image field curvature remaining in the display optical system can be compensated by the curved display surface ID, and a display device with excellent image plane characteristics in the horizontal viewing angle direction can be realized.

[0082] The display optical system according to Numerical Example 3 satisfies all of Inequalities (1) to (5). Figure 8 Longitudinal aberrations of the display optical system according to Numerical Example 3 in the horizontal and vertical viewing angle directions are shown.

[0083] Example 4

[0084] according to Fig. 9 The display device of Example 4 (Numerical Example 4) shown has horizontal and vertical viewing angles of about 90 degrees. The basic configuration of the display device of this example is the same as that of Example 1, but the specifications of the display element and the display optical system are different from those of Example 1.

[0085] In the display optical system according to this example, the incident and exit surfaces of a bonding lens having a second semi-transmitting reflection surface HM arranged on its bonding surface are made into flat surfaces, and an aspherical lens G3 made of a resin material and arranged on the display element side of the bonding lens is responsible for aberration correction.

[0086] This example sets the first semi-transmissive reflective surface PBS on the surface (plane) on the observation side of the lens G1, uses the lens G1 for three passes, thereby achieving high magnification and reduced thickness of the display optical system. The aspherical surface on the display element side of the lens G3 has an inflection point within the optical effective diameter, and can satisfactorily correct astigmatism.

[0087] The display element has a display surface ID in a square shape, an active area thereof has an aspect ratio of about 1:1, and the display surface ID is Fig. 9 The YX cross section shown and the ZX cross section not shown have a spherical shape with the convex surface facing the observation side. Thus, the image field curvature remaining in the display optical system can be compensated by the curved display surface ID, and a display device with excellent image plane characteristics in the horizontal viewing angle direction can be realized.

[0088] The display optical system according to Numerical Example 4 satisfies all of Inequalities (1) to (5). Fig.10 Longitudinal aberrations of the display optical system according to Numerical Example 4 in the horizontal and vertical viewing angle directions are shown.

[0089] Example 5

[0090] Fig.11The display device according to Example 5 (Numerical Example 5) shown has a horizontal and vertical viewing angle of about 100 degrees. The basic configuration of the display device according to this example is the same as that of Example 1, but this example is different from Example 1 in that the two semi-transmissive reflective surfaces PBS and HM are curved surfaces. The first semi-transmissive reflective surface PBS provided as a curved surface on the surface of the observation side of the lens G1 can realize a higher magnification of the display optical system.

[0091] The display element has a display surface ID in a square shape, an active area thereof has an aspect ratio of about 1:1, and the display surface ID is Fig.11 The YX cross section shown and the ZX cross section not shown have a spherical shape with the convex surface facing the observation side. Thus, the image field curvature remaining in the display optical system can be compensated by the curved display surface ID, and a display device with excellent image plane characteristics in the horizontal viewing angle direction can be realized.

[0092] The display optical system according to Numerical Example 5 satisfies all of Inequalities (1) to (5). Fig.12 Longitudinal aberrations of the display optical system according to Numerical Example 5 in the horizontal and vertical viewing angle directions are shown.

[0093] The aspect ratio and shape of the effective area of ​​the display element (display surface) according to each example can be set arbitrarily. For example, in addition to a rectangle (or square), the shape of the effective area of ​​the display element can be circular or polygonal, etc. In addition, in addition to a cylindrical or spherical shape, the curved surface shape of the display element can be set to a deformed surface shape, an aspherical shape, a free-form surface shape, etc.

[0094] Numerical Examples 1 to 5 will be described below. In each numerical example, surface number i represents the order of the surface counted from the object side. r represents the radius of curvature (mm) of the i-th surface from the object side, d represents the lens thickness or air distance (mm) between the i-th surface and the (i+1)-th surface, and nd is the d-line refractive index of the optical material between the i-th surface and the (i+1)-th surface. νd is the Abbe number based on the d-line of the optical material between the i-th surface and the (i+1)-th surface.

[0095] The Abbe number νd is expressed as νd=(Nd-1) / (NF-NC), where Nd, NF and NC are the refractive indices of the d line (587.6nm), F line (486.1nm) and C line (656.3nm) in the Fraunhofer line. The effective diameter is the diameter (mm) of the area on the i-th surface where light rays contributing to imaging (image display) from the display surface are incident. The various numerical examples show the focal length, pupil diameter and total viewing angle of the display optical system.

[0096] An asterisk "*" attached to a surface number indicates that the surface has an aspherical shape. The shape of the aspherical shape is expressed as follows, where x is the displacement from the surface vertex in the direction of the optical axis, h is the height from the optical axis in a direction orthogonal to the optical axis, R is the paraxial radius of curvature, k is the conic constant, and A4, A6, A8, A10, and A12 are aspheric coefficients. "ex" in the conic constant and aspheric coefficient means ×10 -x .

[0097] x=(h 2 / R) / [1+{1-(1+k)(h / R) 2} 1 / 2 ]+A4·h4+A6·h6+A8·h8+A10·h10+A12·h12

[0098] Table 1 summarizes the values ​​corresponding to inequalities (1) to (5) in Numerical Examples 1 to 5.

[0099] Tables 2 and 4 show various numerical values ​​used in numerical examples 1 to 5 (the exit angle and incident angle in Table 4 are the exit angle and incident angle used for reverse ray tracing), and Table 3 shows the inflection points in numerical examples 1, 2, and 4.

[0100] Numerical Example 1

[0101] Unit: mm

[0102] Surface data

[0103]

[0104]

[0105] Display surface (Z, Y) = (37.000, ∞)

[0106] Aspheric surface data

[0107] Surface 6

[0108] K=0.00000e+00 A4=1.07930e-07 A6=-1.20647e-09

[0109] A8=9.57432e-12 A10=-2.62069e-14 A12=3.48383e-17

[0110] Surface 10

[0111] K=0.00000e+00 A4=1.07930e-07 A6=-1.20647e-09

[0112] A8=9.57432e-12 A10=-2.62069e-14 A12=3.48383e-17

[0113] Surface 11

[0114] K=0.00000e+00 A4=5.45637e-05 A6=-6.07318e-07

[0115] A8=2.74780e-09 A10=-6.65150e-12 A12=6.85403e-15 Various data

[0116] Lens unit data

[0117] Single lens data

[0118] Numerical Example 2

[0119] Unit: mm

[0120] Surface data

[0121]

[0122] Display surface 100.000

[0123] Aspherical Data 6th Surface

[0124] K=0.00000e+00 A4=-1.32805e-06 A6=3.76169e-09 Surface 10

[0125] K=0.00000e+00 A4=-1.32805e-06 A6=3.76169e-09

[0126] Surface 11

[0127] K=0.00000e+00 A4=4.12993e-04 A6=-4.91892e-06

[0128] A8=2.28817e-08 A10=-3.78901e-11

[0129] Various data

[0130]

[0131] Lens unit data

[0132] Single lens data

[0133] Numerical Example 3

[0134] Unit: mm

[0135] Surface data

[0136]

[0137]

[0138] Display surface 53.300

[0139] Aspheric surface data Surface 6

[0140] K=0.00000e+00 A4=1.69732e-07 A6=-4.58512e-10 A8=1.04438e-12 A10=-1.18179e-15 A12=5.77673e-19 Surface 10

[0141] K=0.00000e+00 A4=1.69732e-07 A6=-4.58512e-10 A8=1.04438e-12 A10=-1.18179e-15 A12=5.77673e-19 Surface 11

[0142] K=0.00000e+00 A4=2.90606e-05 A6=-6.94977e-08 A8=9.77055e-11 A10=-7.27403e-14 A12=1.95997e-17

[0143] Various data

[0144]

[0145] Lens unit data

[0146] Single lens data

[0147] Numerical Example 4

[0148] Unit: mm

[0149] Surface data

[0150]

[0151]

[0152] Display surface 42.500

[0153] Aspheric surface data Surface 6

[0154] K=0.00000e+00 A4=-1.38181e-07 A6=7.61577e-10 A8=1.97719e-12 A10=-1.54347e-14 A12=2.91621e-17 Surface 10

[0155] K=0.00000e+00 A4=-1.38181e-07 A6=7.61577e-10

[0156] A8=1.97719e-12 A10=-1.54347e-14 A12=2.91621e-17

[0157] Surface 14

[0158] K=0.00000e+00 A4=-1.07263e-04 A6=2.05131e-07

[0159] Surface 15

[0160] K=0.00000e+00 A4=-1.04715e-04 A6=2.21415e-07 Various data

[0161]

[0162] Lens unit data

[0163]

[0164] Single lens data

[0165]

[0166] Numerical Example 5

[0167] Unit: mm

[0168] Surface data

[0169]

[0170] Display surface 43.960

[0171] Aspheric surface data

[0172] Surface 6

[0173] K=0.00000e+00 A4=7.86898e-08 A6=-9.99204e-09

[0174] A8=6.36425e-11 A10=-2.20795e-13 A12=2.88649e-16

[0175] Surface 10

[0176] K=0.00000e+00 A4=7.86898e-08 A6=-9.99204e-09

[0177] A8=6.36425e-11 A10=-2.20795e-13 A12=2.88649e-16

[0178] Surface 11

[0179] K=0.00000e+00 A4=-1.14287e-04 A6=5.91339e-07 A8=-2.28815e-09 A10=5.16921e-12 A12=-5.11210e-15 Various data

[0180]

[0181] Lens unit data

[0182]

[0183] Single lens data

[0184]

[0185] Table 1

[0186]

[0187] Table 2

[0188]

[0189] Table 3

[0190]

[0191] Table 4

[0192]

[0193]

[0194] Fig.14 There is shown a head mounted display (HMD) as the display device according to any one of Examples 1 to 5. The HMD is mounted on the head of the observer (in front of his eyes) by a mounting headgear not shown.

[0195] The HMD includes a right-eye display element RID and a left-eye display element LID, a right-eye display optical system ROS configured to guide display light from the right-eye display element RID to the right eye of an observer, and a left-eye display optical system LOS configured to guide display light from the left-eye image display element LID to the left eye of the observer.

[0196] The configurations described in Examples 1 to 5 can realize an HMD that is reduced in size and weight and enables observation of high-quality images.

[0197] Although the present disclosure has described exemplary embodiments, it is to be understood that some embodiments are not limited to the disclosed embodiments.The scope of the following claims is to be accorded the broadest interpretation so as to encompass all such modifications and equivalent structures and functions.

[0198] The display optical system having a three-pass configuration according to the respective examples can satisfactorily correct chromatic aberration, field curvature, and astigmatism, and at the same time provide a reflective surface having a strong light-condensing effect for achieving high magnification and reduced thickness.

Claims

1. A display device, comprising: Display components; a display optical system configured to direct light from a display surface of the display element to an observation side; as well as Two optical elements, The display optical system comprises a first semi-transmissive reflective surface and a second semi-transmissive reflective surface provided on the joint surface of the two optical elements. wherein light from the display surface is transmitted through the second semi-transmissive reflective surface, reflected on the first semi-transmissive reflective surface, reflected on the second semi-transmissive reflective surface, transmitted through the first semi-transmissive reflective surface, and guided to the observation side, wherein the absolute value of the curvature of the second semi-transmissive reflective surface is greater than the absolute value of the curvature of the first semi-transmissive reflective surface, and The display surface has a convex shape toward the observation side in at least one of two cross sections that include the optical axis of the display optical system and are orthogonal to each other.

2. The display device according to claim 1, characterized in that Each of the two optical elements is made of a resin material.

3. The display device according to claim 1, characterized in that The following inequality is satisfied: fG1 / fG2<0.0 Wherein fG1 is the focal length in air of the first optical element on the observation side of the two optical elements, and fG1 is calculated based on the curvature radius of the reference spherical surface of the first optical element, and fG2 is the focal length in air of the second optical element on the display element side of the two optical elements, and fG2 is calculated based on the curvature radius of the reference spherical surface of the second optical element.

4. The display device according to claim 1, characterized in that The following inequality is satisfied: 1.4≤Ndp <Ndn≤1.9 Wherein Ndp is the d-line refractive index of the optical element with a positive focal length in air among the two optical elements, and Ndp is calculated based on the radius of curvature of the reference spherical surface, and Ndn is the d-line refractive index of the optical element with a negative focal length in air among the two optical elements, and Ndn is calculated based on the radius of curvature of the reference spherical surface.

5. The display device according to claim 4, characterized in that: The optical element on the observation side of the two optical elements has a positive focal length, and the optical element on the display element side of the two optical elements has a negative focal length.

6. The display device according to claim 1, characterized in that: The following inequality is satisfied: 1.0<νdp / νdn≤4.0 Wherein νdp is calculated based on the Abbe number of the d-line of the optical element with a positive focal length in air among the two optical elements, and the curvature radius of the reference sphere, and νdn is calculated based on the Abbe number of the d-line of the optical element with a negative focal length in air among the two optical elements, and the curvature radius.

7. The display device according to claim 1, characterized in that: The following inequality is satisfied: 1.0<|Rhm| / f≤5.0 Wherein Rhm is the radius of curvature of the reference sphere of the second semi-transmissive reflective surface, and f is the focal length of the display optical system.

8. The display device according to claim 1, characterized in that: The following inequality is satisfied: 0.1≤|Rhm| / |Rp|≤2.0 Wherein Rhm is the radius of curvature of the reference spherical surface of the second semi-transmissive reflective surface, and Rp is the radius of curvature of the reference spherical surface of the display surface.

9. The display device according to claim 1, characterized in that: The display optical system has an aspherical refractive surface having an inflection point within an optically effective diameter.

10. The display device according to claim 1, characterized in that The first semi-transmissive reflective surface is a flat surface.

11. The display device according to claim 1, characterized in that: The display optical system includes a cemented lens composed of the two optical elements as a dioptric element.

12. The display device according to claim 1, characterized in that: When the interocular distance is 15 mm, the diopter is 0 diopter, and the viewing angle is 30 degrees, the absolute value of the angle between the pupil center ray and the normal to the display surface is 30 degrees or less.

13. The display device according to any one of claims 1 to 12, characterized in that: At least one of the first transflective surface and the second transflective surface includes a polarization selective transflective element.

Images