Optical system and display device

Abstract

To provide an optical system capable of decreasing an angle of emission from a display element.SOLUTION: An optical system (1000) for guiding a light flux from a display surface (1400) to a pupil surface (SP) includes the following arranged in order from a pupil surface side to a display surface side: a first lens group (1100); a first transmission / reflection member (A) having a first transmission / reflection surface; a second lens group (1200); a second transmission / reflection member (C) having a second transmission / reflection surface; and a third lens group (1300). At least one optical surface served as an interface between air and itself in the first lens group is a first aspherical surface, and at least one optical surface served as an interface between air and itself in the third lens group is a second aspherical surface.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an optical system and a display device.

Background Art

[0002] In recent years, a display device (observation device) such as a head-mounted display (HMD) that provides an immersive experience by magnifying and displaying an original image displayed using a display element such as a liquid crystal display (LCD) through an observation optical system and presenting a large-screen image to a user has been known. Since the display device is used by being worn on the head, the observation optical system used in the display device is required to be small (thin) while having a wide field of view and high optical performance. Patent Document 1 discloses an optical system that reduces chromatic aberration using a cemented lens.

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0004] As a characteristic of a general display element, the amount of light of a light beam emitted from the display element is the largest in the vertical direction and decreases in proportion to the emission angle. In the optical system disclosed in Patent Document 1, since the emission angle of the light beam at the end field angle from the display element is large, the amount of light at the end field angle decreases, and the user feels dark at the end of the field of view.

[0005] Therefore, an object of the present invention is to provide an optical system capable of reducing the emission angle from the display element.

Means for Solving the Problems

[0006] The optical system as one aspect of the present invention is an optical system that guides a light beam from a display surface to a pupil surface, and includes, in order from the pupil surface side to the display surface side, a first lens group, a first transmissive-reflective member having a first transmissive-reflective surface, a second lens group, a second transmissive-reflective member having a second transmissive-reflective surface, and a third lens group. At least one optical surface that forms an interface with air in the first lens group is a first aspherical surface, and at least one optical surface that forms an interface with air in the third lens group is a second aspherical surface.

[0007] Other objects and features of the present invention will be described in the following embodiments.

Effects of the Invention

[0008] According to the present invention, it is possible to provide an optical system capable of reducing the emission angle from a display element.

Brief Description of the Drawings

[0009]

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Mode for Carrying Out the Invention

[0010] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

[0011] The optical system of each embodiment is an optical system (bending optical system) that guides a light beam from the display surface of a display element (panel portion) to an observation surface (pupil surface), and is an observation optical system for observing an image displayed on the display surface. A display device is configured by the optical system and the display element of each embodiment. The optical system of each embodiment includes a first lens group (pupil-side optical system), a first transmission-reflection member, a second lens group (transmission-reflection optical system), a second transmission-reflection member, and a third lens group (panel-side optical system) arranged in order from the pupil surface side to the display surface side.

[0012] The first transmission-reflection member has a first transmission-reflection surface that is flat or curved. The second transmission-reflection member has a second transmission-reflection surface that is curved. The lens closest to the display surface side in the first lens group and the lens closest to the pupil surface side in the second lens group are joined via the first transmission-reflection member. Also, the lens closest to the display surface side in the second lens group and the lens closest to the pupil surface side in the third lens group are joined via the second transmission-reflection member.

[0013] The first lens group is an optical system sandwiched between the pupil plane and the second lens group. The second lens group is an optical system sandwiched between two transmissive-reflective surfaces (a first transmissive-reflective surface and a second transmissive-reflective surface) that serve as both a transmissive surface and a reflective surface. The third lens group is an optical system sandwiched between the second lens group and the display element. The first lens group and the third lens group may not exist in some cases. Hereinafter, each embodiment will be described in detail.

Embodiment

[0014] First, the optical system (observation optical system) 1000 in Embodiment 1 of the present invention will be described. FIG. 1(A) is a cross-sectional view of the optical system 1000. The optical system 1000 includes a pupil-side optical system (first lens group) 1100, a first transmissive-reflective member (A), a transmissive-reflective optical system (second lens group) 1200, a second transmissive-reflective member (C), and a panel-side optical system (third lens group) 1300.

[0015] The pupil-side optical system 1100 has an optical element (first lens) 1101, the transmissive-reflective optical system 1200 has an optical element (second lens) 1201 and an optical element (third lens) 1202, and the panel-side optical system 1300 has an optical element (fourth lens) 1301. Thus, in this embodiment, there is one pupil-side optical system 1100, two transmissive-reflective optical systems 1200, one panel-side optical system 1300, and optical elements (optical elements 1101, 1201, 1202, 1301) that refract, reflect, or diffract light rays.

[0016] Each optical element has two optical surfaces, which are referred to as the R1 surface and the R2 surface from the pupil side. The R1 surface of the optical element 1101 is a curved surface, and the R2 surface is a flat surface. The R1 surface of the optical element 1201 is a flat surface, and the R2 surface is a curved surface. The R1 surface and the R2 surface of the optical element 1301 are both curved surfaces. The materials of the optical elements 1101, 1202, and 1301 are PMMA (acrylic resin). However, this embodiment is not limited thereto, and instead of using acrylic resin as the material of each optical element, acrylic resin may be applied to each optical element.

[0017] The light rays from the panel section (display surface of the display element) 1400 pass through the panel-side optical system 1300 and the transmissive-reflective optical system 1200, are reflected by the first transmissive-reflective surface, are reflected by the second transmissive-reflective surface, pass through the transmissive-reflective optical system 1200 and the pupil-side optical system 1100, and head towards the pupil plane SP. Thereby, the optical system 1000 can observe the optical image of the panel section 1400 from the pupil plane SP where its exit pupil is located. The light following the optical path at this time is regarded as desired light, and the rest is regarded as unnecessary light.

[0018] Figure 1(B) is an aberration diagram of the optical system 1000 when the eye relief (the distance from the pupil plane SP to the pupil-facing surface of the pupil-side optical system 1100 (the lens surface closest to the pupil side among the pupil-side optical systems 1100)) is 10 mm and a virtual image is displayed at a position 1600 mm from the pupil plane SP. Figure 1(B) shows the aberrations at the wavelengths of the d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm), which are the design reference wavelengths. From Figure 1(B), it can be seen that although there is some field curvature and astigmatism, an imaging performance that can withstand use is obtained. Here, Figure 1(B) shows the aberration with the panel section 1400 as the image plane in the reverse optical path (reverse trace) from the pupil plane SP towards the panel section 1400, rather than the forward optical path (forward trace) from the original panel section 1400 towards the pupil plane SP. This point is not a problem because it corresponds to the aberration in the case of the forward optical path (forward trace) when showing the optical performance of the optical system 1000. Also, regarding the polarizing plate, quarter-wave plate, and polarization-selective transmissive-reflective element, etc. to be described later, as an example of the approximate properties of each element, they are uniformly described as follows, but the actual properties may be different. For example, the polarizing plate has a thickness of 0.1 mm, a refractive index of 1.52, an Abbe number of 50, the quarter-wave plate, and the laminated element of the quarter-wave plate and the polarization-selective transmissive-reflective element have a thickness of 0.3 mm, a refractive index of 1.52, and an Abbe number of 50.

[0019] Next, with reference to Figure 2, the optical path of the optical system 1000 will be described. Figure 2 is a schematic diagram showing the optical path of the optical system 1000, and shows the direction of the optical path passing through each surface and the polarization state above it. Here, the optical path of the desired light will be described, and the description of the optical path of the unnecessary light caused by each component of the optical system 1000 will be omitted.

[0020] The optical system 1000 includes, in order from the pupil plane SP, a pupil-side optical system 1100, a polarization-selective transmission and reflection element A, a transmission and reflection optical system 1200, a first quarter-wave plate B, a transmission and reflection surface (half mirror) C, a panel-side optical system 1300, and a panel unit 1400. The polarization-selective transmission and reflection element A corresponds to a first transmission and reflection member having a first transmission and reflection surface, and the transmission and reflection surface C corresponds to a second transmission and reflection member having a second transmission and reflection surface. The panel unit 1400 includes a display element (light modulation element) such as a liquid crystal display element or an organic EL element, a polarizing plate E, and a second quarter-wave plate D. The shape of the display element is a square with a diagonal of 1.3 inches (side length 23.3 mm). The polarizing plate E and the second quarter-wave plate D are arranged in this order close to the display element on the pupil side.

[0021] The unpolarized light rays emitted from the display element become linearly polarized by the polarizing plate E, are converted into circularly polarized light by the second quarter-wave plate D, pass through the panel-side optical system 1300, and head toward the transmission and reflection optical system 1200. Note that the polarizing plate E may be integrated with the image display element. For example, many liquid crystal display elements include a polarizing plate in their configuration. Also, in the case of an organic EL element, a polarizing plate may be used for the purpose of anti-reflection, and in this case, the light emitted from the image display element becomes linearly polarized. In these cases, there is no need to separately provide the polarizing plate E.

[0022] The polarization-selective transmission and reflection element A and the transmission and reflection surface (half mirror) C are two transmission and reflection surfaces (a first transmission and reflection surface and a second transmission and reflection surface) that serve as both a transmission surface and a reflection surface. The transmission and reflection surface (half mirror) C is formed of a dielectric multilayer film or a metal film and functions as the transmission and reflection surface (the second transmission and reflection surface). The thickness of the transmission and reflection surface (half mirror) C is usually 1000 nm or less, and at most 5000 nm or less. In each numerical example, the thickness of the transmission and reflection surface is shown without considering the thickness (omitting the thickness).

[0023] The first quarter-wave plate B is arranged with respect to the second quarter-wave plate D such that their slow axes are inclined by 90° to each other, and the slow axis of the first quarter-wave plate B is inclined by 45° with respect to the polarization transmission axis of the polarizing plate E. The transmission-reflection surface (half mirror) C is deposited on the R1 surface of the optical element 1301 and is further adhered to the R2 surface of the optical element 1202. The first quarter-wave plate B is adhered to the R1 surface of the optical element 1201 and is further adhered to the polarization-selective transmission-reflection element A adhered to the R2 surface of the optical element 1101.

[0024] The polarization-selective transmission-reflection element A is an element configured to reflect linearly polarized light having the same polarization direction as when passing through the polarizing plate E and transmit linearly polarized light having a polarization direction orthogonal thereto. That is, the polarization-selective transmission-reflection element A is a reflection polarizer that separates incident light into reflected light and transmitted light according to the polarization state, and is, for example, a wire grid polarizer or a laminated birefringent film polarizer. As a wire grid polarizer, specifically, there is "WGF" manufactured by Asahi Kasei Corporation, and the wire grid formation surface functions as the transmission-reflection surface. The thickness of the polarization-selective transmission-reflection element A is usually 0.5 mm or less, and at most 1 mm or less.

[0025] The transmission-reflection member includes a transmission-reflection surface and is a member continuous with the transmission-reflection surface. It has substantially no refractive power and mainly bears optical functions other than refraction (absorption according to the polarization state, change in polarization state, antireflection, etc.) and mechanical functions (adhesion, protection, etc.). In this embodiment, the polarization-selective transmission-reflection element A is the first transmission-reflection member, and the transmission-reflection surface (half mirror) C is the second transmission-reflection member. Each transmission-reflection member may be a continuous member having a plurality of functions.

[0026] Of the light incident on the reflection surface (half mirror) C, the desired light is transmitted through it and converted into linearly polarized light with the same polarization direction as when passing through the polarizing plate E by the first quarter-wave plate B, and then enters the polarization-selective transmission and reflection element A. This linearly polarized light is reflected by the polarization selectivity of the polarization-selective transmission and reflection element A. The light reflected by the polarization-selective transmission and reflection element A is converted into the same circularly polarized light as when it was first converted into circularly polarized light by the second quarter-wave plate D by the first quarter-wave plate B, enters the transmission and reflection surface (half mirror) C, and is reflected here. The light reflected by the transmission and reflection surface (half mirror) C becomes circularly polarized light rotating in the opposite direction to the light before reflection, enters the first quarter-wave plate B again, and is converted into linearly polarized light having a polarization direction orthogonal to the polarization direction when passing through the polarizing plate E for the first time, and then enters the polarization-selective transmission and reflection element A. This linearly polarized light passes through the polarization-selective transmission and reflection element A due to its polarization selectivity and is guided to the pupil plane SP.

[0027] Figs. 3(A) and (B) are schematic diagrams for explaining the optical path of the light rays emitted from the image height (height h) on the display element, the emission angle β (the angle formed with the normal of the display surface of the display element), and the half angle α on the pupil plane SP according to the plano-convex shape of the first transmission and reflection surface. Here, to explain the influence of reflection, the influence of refraction is not shown. Also, for the sake of simplicity of explanation, the discussion is advanced with a substantially spherical shape instead of a complex aspherical shape. The details of Figs. 3(A) and (B) will be described later.

[0028] Since the display element usually emits Lambertian light, the smaller the emission angle β, the larger the amount of light captured, and the larger the emission angle β, the smaller the amount of light captured. Therefore, in the range of the designed viewing angle, if the maximum value of the emission angle β is large, light amount unevenness occurs in the visual field, which is not preferable. As described above, the larger the half angle α (that is, the wider the viewing angle), the more the sense of immersion can be obtained, which is preferable. However, at the same time, the maximum value of the emission angle β tends to be large, which tends to cause problems.

[0029] Although it depends on the characteristics of the element, generally, when the emission angle β (the maximum value of the absolute value of the emission angle β) is greater than 35°, light quantity unevenness is likely to become a problem. For this reason, the emission angle β (the maximum value of the absolute value of the emission angle β) of the principal ray of the light beam passing through the pupil plane SP from the display element is preferably 35° or less. More preferably, the emission angle β is 30° or less. In order to reduce the maximum value of the absolute value of the emission angle β, it is effective to adopt a configuration in which an aspherical surface is provided on the optical surface that is the interface with air of the panel-side optical system. This is because the light beams for each field angle are separated in the panel-side optical system as compared with the pupil-side optical system or the transmissive-reflective optical system.

[0030] On the other hand, if the configuration of the panel-side optical system is designed with priority given to the emission angle β, the field curvature and the astigmatism become inappropriate. To improve this, it is effective to adopt a configuration in which an aspherical surface is provided on the optical surface that is the interface with air of the pupil-side optical system. In the transmissive-reflective optical system, even for light beams of the same field angle, since they pass through different positions of the optical surface in the three-times folded optical path, it is difficult to optimize the light beams for each field angle. Also, since the pupil-side optical system is separated from the panel-side optical system, it is easy to adjust the field curvature and the astigmatism by the aspherical surfaces they have. Here, even if an aspherical surface is provided on the joint surface instead of the interface with air, the refraction effect is weak and the desired effect cannot be obtained.

[0031] In this embodiment, it is assumed that the maximum half field angle is 50° as the design field angle in the design designation. Specifically, the maximum angle of the principal ray of the light beam passing through the pupil plane SP is 50°. Generally, if the maximum half field angle (the maximum angle of the principal ray of the light beam passing through the pupil plane SP) is 30° or more, it is an optical system with a wide field angle. More preferably, the maximum half field angle is 40° or more. The wider the field angle, the higher the effect of this embodiment.

[0032] FIG. 4 shows the emission angle β (angle with respect to the normal of the display element) of the principal ray with respect to the half angle α in the optical system 1000 of the present embodiment. In FIG. 4, the horizontal axis represents the angular field (°), and the vertical axis represents the emission angle β (°). As shown in FIG. 4, the emission angle β is negative (-) when the light beam is emitted in a direction away from the optical axis, and positive (+) when the light beam is emitted in a direction approaching the optical axis. From FIG. 4, it can be seen that the emission angle β at the maximum half angle (α = 50°) is -24.6°, and the maximum value of the absolute value of the emission angle β is smaller than 30° (when evaluating the light quantity unevenness, it is evaluated by the absolute value rather than the positive and negative). That is, by adopting the configuration of the present embodiment, the effect of reducing the light quantity unevenness can be obtained.

[0033] Also, as in the present embodiment, when the emission angle β at the maximum half angle is negative (that is, when the light beam is emitted in a direction away from the optical axis at the end angular field of the display element), the size of the display element can be reduced, which is preferable from the viewpoints of weight and cost. Specifically, assuming a maximum half angle of 30° or more, the shape of the display element is preferably such that the diagonal length of the square circumscribing the display element is 1.6 inches or less (one side of the circumscribing square is 28.7 mm or less).

[0034] Next, the details of FIGS. 3(A) and (B) will be described. FIG. 3(A) shows a case where the first transmission-reflection surface has a planar shape and the second transmission-reflection surface has a concave shape on the pupil side. In this case, it is suitable for increasing the half angle α, but not suitable for reducing the emission angle β. FIG. 3(B) shows a case where both the first transmission-reflection surface and the second transmission-reflection surface have concave shapes on the pupil side. In this case, the emission angle β is small and it is suitable for increasing the half angle α. That is, considering only the influence of reflection, as shown in FIG. 3(B), the configuration in which both the first transmission-reflection surface and the second transmission-reflection surface have concave shapes on the pupil side is preferable from the viewpoints of the emission angle β and the half angle α. In other words, the configuration in which the first transmission-reflection surface has a planar shape, as in the present embodiment, is particularly effective for reducing the emission angle β due to the influence of refraction. Also, the configuration in which the first transmission-reflection surface is planar is easier to manufacture compared to the configuration with a curved surface.

[0035] In this embodiment, an optical element 1101 (the lens closest to the display surface among the first lens group), which is a refractive optical element, and an optical element 1201 (the lens closest to the pupil surface among the second lens group), which is a refractive optical element, are joined via a first transmissive-reflective member including a first transmissive-reflective surface. Further, an optical element 1201 (the lens closest to the display surface among the second lens group), which is a refractive optical element, and an optical element 1301 (the lens closest to the pupil surface among the third lens group), which is a refractive optical element, are joined via a second transmissive-reflective member including a second transmissive-reflective surface.

[0036] Thus, by adopting a configuration in which the transmissive-reflective member including the transmissive-reflective surface is sandwiched between the refractive optical elements, the refractive power at the transmissive-reflective surface can be reduced as compared with the case where the transmissive-reflective surface is in contact with air. As a result, when determining the shape of the transmissive-reflective surface, it is only necessary to mainly consider the influence of the reflective power, the degree of freedom in optical design is improved, and the imaging performance can be improved while reducing the emission angle β.

[0037] In particular, when attempting to ensure imaging performance at a wide viewing angle, as in this embodiment, the second transmissive-reflective surface preferably has a concave shape on the pupil surface side and has a large reflective power. That is, the effect of the above-described configuration is high. On the other hand, when the first transmissive-reflective surface has a planar shape as in this embodiment, the effect of the above-described configuration is low from the viewpoints of reducing the emission angle β and improving the imaging performance. However, since no unnecessary space is provided, there are advantages such as shortening the overall optical length, simplifying manufacturing and holding, and leading to an improvement in durability described later. Note that the effects of this embodiment can be obtained without adopting the above-described joining configuration.

[0038] In addition, this embodiment is composed of a total of three optical elements, one for each of the pupil-side optical system, the transmissive-reflective optical system, and the panel-side optical system. That is, the first lens group has a first lens (optical element 1101), the second lens group has a second lens (optical element 1201), and the third lens group has a third lens (optical element 1301). Further, the first lens and the second lens are joined via a first transmissive-reflective member, and the second lens and the third lens are joined via a second transmissive-reflective member. According to such a configuration, the number of optical elements for obtaining the above-described effects can be minimized, which is preferable from the viewpoints of cost and manufacturing. Here, joining includes not only adhesion using an adhesive but also vapor deposition, pressure bonding, etc. Further, it refers to joining at least a part within the effective region through which light rays pass, and does not necessarily include joining over the entire effective region or outside the effective region. According to this embodiment, it is possible to secure the degree of freedom in optical design and obtain the effect of achieving high definition of an image.

[0039] As described above, the observation optical system used in the display device is also required to be small (thin). Specifically, in order to miniaturize (thin down) the observation optical system, the distance from the optical surface facing the pupil plane SP to the display surface of the display element is preferably 20 mm or less. More preferably, the distance from the optical surface facing the pupil plane SP to the display surface of the display element is 17 mm or less. In this embodiment, the distance from the optical surface facing the pupil plane SP to the display surface is 15.5 mm, which is sufficiently small (thin).

[0040] In order to achieve such miniaturization (thin down), it is necessary to shorten the focal length to approximately the same extent as the distance from the optical surface facing the pupil plane SP to the display surface. In other words, in order to miniaturize (thin down) the observation optical system, the focal length of the observation optical system is preferably 20 mm or less. More preferably, the focal length of the observation optical system is 17 mm or less. In this embodiment, the focal length is 14.3 mm, which is sufficiently small (thin). When the focal length is shortened at a wide viewing angle, the field curvature and the astigmatism are likely to deteriorate. Therefore, the smaller (thinner) the size, the higher the effect of this embodiment.

[0041] As a means of shortening the focal length, a configuration in which the powers (refractive powers in the vicinity of the optical axis) on the optical axes of the pupil-side optical system (the first lens group) and the panel-side optical system (the third lens group) are both positive is effective. In terms of imaging performance, since the on-axis power of the transmissive-reflective optical system is positive, thereby, in all three optical systems, the on-axis power becomes positive, and it is easier to shorten the focal length compared to a configuration in which the on-axis power of either one or both of the pupil-side optical system and the panel-side optical system is negative. In this embodiment, the focal length of the pupil-side optical system is 103.7 mm, and the focal length of the panel-side optical system is 31.3 mm, and both are positive.

[0042] Here, the aspherical shapes of the optical surfaces that form the interfaces with air of the pupil-side optical system (the first lens group) and the panel-side optical system (the third lens group) will be described. In order to reduce the exit angle β while improving the field curvature and the astigmatism, at least one optical surface in the effective ray region requires a higher-order aspherical shape. Specifically, the cross-sectional shape including the optical axis cannot be expressed by a conic curve (i.e., any one of an ellipse, a parabola, or a hyperbola).

[0043] FIG. 5(A) shows, by a solid line, the cross-sectional shape including the optical axis of the R1 surface of the optical element 1101. FIG. 5(B) shows, by a solid line, the cross-sectional shape including the optical axis of the R2 surface of the optical element 1301. In FIGS. 5(A) and 5(B), the position in the optical axis direction is represented as z (positive from the pupil side toward the panel side), the radial distance is represented as y, and the vertex of the surface is set to z = 0 mm. In FIGS. 5(A) and 5(B), the horizontal axis represents the distance y (mm), and the vertical axis represents the position z (mm) in the optical axis direction, respectively. Also, the scale of the graph is different for each surface. As can be seen from FIGS. 5(A) and 5(B), both cross-sectional shapes cannot be expressed by a conic curve.

[0044] Thus, in this embodiment, at least one optical surface that forms the interface with air among the first lens group is the first aspherical surface, and at least one optical surface that forms the interface with air among the third lens group is the second aspherical surface. Preferably, the cross-section including at least one optical axis of the first aspherical surface or the second aspherical surface has a shape that cannot be expressed by a conic curve.

[0045] To consider the optical action of such a shape, the curvature proportional to the power in the local optical axis direction is evaluated. FIG. 6(A) shows the local curvature of the cross-sectional shape including the optical axis of the R1 surface (first aspherical surface) of the optical element 1101. FIG. 6(B) shows the local curvature of the cross-sectional shape including the optical axis of the R2 surface (second aspherical surface) of the optical element 1301. Here, the radial distance is denoted as y. In FIGS. 6(A) and 6(B), the horizontal axis represents the distance y (mm), and the vertical axis represents the curvature (1 / mm).

[0046] As can be seen from FIGS. 6(A) and 6(B), both the first aspherical surface and the second aspherical surface have a shape in which the curvature crosses zero (i.e., reverses) as it goes off-axis with respect to the on-axis curvature (i.e., a shape having an inflection point). By adopting a shape having such a local power distribution, the effect of reducing the exit angle β while improving the field curvature and the astigmatism is obtained. In this embodiment, both cross-sections of the first aspherical surface and the second aspherical surface have an inflection point, but it is not limited thereto, and it is sufficient that at least one cross-section including the optical axis of the first aspherical surface or the second aspherical surface has an inflection point.

[0047] Also, as can be seen from FIG. 6(B), within the effective diameter, the local curvature has five extreme values. Thus, by adopting a shape in which the local power is finely changed so that the local curvature has three or more extreme values, the effect of improving the exit angle β, the field curvature, and the astigmatism over the entire angular field is obtained. In particular, in the case of a particularly wide viewing angle as in this embodiment, it is preferable to have at least one such aspherical surface. Note that the local curvature is correlated with the second derivative value of the shape. Therefore, the fact that the local curvature has three or more extreme values is synonymous with the fact that the second derivative value of the shape has three or more extreme values. That is, in this embodiment, it is preferable that at least one cross-section including the optical axis of the first aspherical surface or the second aspherical surface has a shape in which the second derivative value has three or more extreme values.

[0048] In FIG. 5(A), further, the shape of the paraxial curvature surface of the cross-sectional shape including the optical axis of the R1 surface of the optical element 1101 is indicated by a dotted line, and the difference from the cross-sectional shape is indicated by a double-dotted line. Similarly, in FIG. 5(B), further, the shape of the paraxial curvature surface of the cross-sectional shape including the optical axis of the R2 surface of the optical element 1301 is indicated by a dotted line, and the difference from the cross-sectional shape is indicated by a double-dotted line. Note that the paraxial curvature surface means a spherical surface defined by the curvature in the vicinity of the optical axis.

[0049] The absolute value of the ratio of this difference to the shape of the paraxial curvature surface indicates the degree of aspherization (referred to as the asphericity). Although it is not proportional to the asphericity, it can be said that the effect of the present invention is higher when the asphericity is relatively large. Generally, the asphericity increases toward the maximum effective diameter end, and if it is 30% or more at the maximum effective diameter end, the effect of this embodiment is easily obtained. More preferably, if it is 50% or more, the effect of this embodiment can be sufficiently obtained.

[0050] In this embodiment, in a cross-section including at least one optical axis of the R1 surface of the optical element 1101 or the R2 surface of the optical element 1301, let the sag amount of the shape of the paraxial curvature surface at the maximum effective diameter end be SagR, and the sag amount of the aspherical surface (cross-sectional shape including the optical axis) be SagA. At this time, it is preferable to satisfy the following conditional expression (1).

[0051] 0.3 ≦ |(SagA - SagR) / SagR| …(1) In this embodiment, the sag amount SagA at the maximum effective diameter end (Φ32) of the R1 surface of the optical element 1101 is 1.30 mm, the sag amount SagR is 2.57 mm, and the asphericity is calculated as follows.

[0052] |(SagA - SagR) / SagR| = 0.495 (49.5%) Similarly, the sag amount SagA at the maximum effective diameter end (Φ26) of the R2 surface of the optical element 1301 is -0.46 mm, the sag amount SagR is -5.14 mm, and the asphericity is calculated as follows.

[0053] |(SagA - SagR) / SagR| = 0.910 (91.0%) In this way, in the two aspherical surfaces of the R1 surface of the optical element 1101 and the R2 surface of the optical element 1301, by setting the asphericity to 30% or more, the effects of this embodiment can be fully obtained. In particular, for the R2 surface of the optical element 1301, the asphericity is 50% or more, and the effect is even greater.

[0054] In this embodiment, let the Abbe number based on the d-line of the optical element 1201 be ν12, and the Abbe number based on the d-line of the optical element 1301 joined to the optical element 1201 across the second transmission-reflection surface be ν13. At this time, ν12 = 56.0, ν13 = 22.38, and |ν12 - ν13| = 33.62. In this way, by using optical materials with an Abbe number difference of 20 or more across the joint surface, it is possible to reduce chromatic aberration while shortening the overall optical length. At this time, the effects of this embodiment can be obtained for any combination of optical elements sandwiching any joint surface of the optical system.

[0055] Here, rather than reducing the axial chromatic aberration as in this embodiment, it is also conceivable to adopt such a configuration to obtain the effect of reducing off-axis chromatic aberration. Let the Abbe number based on the d-line of one optical element (one of the two adjacent lenses) sandwiching the joint surface of the optical system be ν1, and the Abbe number based on the d-line of the other optical element (lens) be ν2. At this time, it is preferable to have at least one combination that satisfies the following conditional expression (2).

[0056] 20 ≦ |ν1 - ν2| …(2) More preferably, the numerical range of the conditional expression (2) is set as in the following conditional expression (2a).

[0057] 25 ≦ |ν1 - ν2| …(2a) Even more preferably, the numerical range of the conditional expression (2) is set as in the following conditional expression (2b).

[0058] 30 ≦ |ν1 - ν2| …(2b) In this embodiment, the side surface of the first transmission-reflection member including the polarization-selective transmission-reflection element A in the direction perpendicular to the optical axis is sealed by the joining of the outer shapes of the optical element 1101 and the optical element 1201 (P in Fig. 1(A)) and does not come into contact with air (is not exposed to air). By adopting such a configuration where the transmission-reflection surface does not directly contact air, it is possible to prevent performance degradation and durability degradation due to moisture absorption. However, this embodiment is not limited thereto, and it is preferable that at least one of the first transmission-reflection member or the second transmission-reflection member is not exposed to air.

[0059] In this embodiment, the diameter of the first transmission-reflection member is smaller than the diameters of the optical element 1101 and the optical element 1201 and has the above-described configuration, but this is not essential. For example, the diameter of the transmission-reflection member may be made equal to the diameter of the refractive optical element joined thereto, and a protective film may be provided on the side surface of the transmission-reflection member in the direction perpendicular to the optical axis, or it may be covered with another member.

[0060] In this embodiment, PMMA (acrylic resin), which has higher hardness and higher chemical resistance than ordinary resins, is used as the material of the optical element 1101 having an optical surface facing the pupil plane SP. Since the optical surface facing the pupil plane SP may be touched by the observer, generally, the anti-fouling standard is strict. As a result, even in the case of a more stringent anti-fouling standard than usual, there is no need to provide hard coating or anti-fouling glass, and the effect of cost reduction can be obtained.

Embodiment

[0061] Next, the optical system (observation optical system) 2000 in Embodiment 2 of the present invention will be described. In this embodiment, the description common to Embodiment 1 will be omitted. Fig. 7(A) is a cross-sectional view of the optical system 2000. The optical system 2000 includes a pupil-side optical system (first lens group) 2100, a first transmission-reflection member (A), a transmission-reflection optical system (second lens group) 2200, a second transmission-reflection member (C), and a panel-side optical system (third lens group) 2300.

[0062] The pupil-side optical system 2100 has an optical element (first lens) 2101, the transmissive-reflective optical system 2200 has an optical element (second lens) 2201 and an optical element (third lens) 2202, and the panel-side optical system 2300 has an optical element (fourth lens) 2301. Thus, in this embodiment, there is one pupil-side optical system 2100, two transmissive-reflective optical systems 2200, one panel-side optical system 2300, and optical elements (optical elements 2101, 2201, 2202, 2301) that refract, reflect, or diffract light rays. The R1 surface and the R2 surface of the optical element 2101 are curved surfaces. The R1 surface of the optical element 2201 is a curved surface and the R2 surface is a flat surface. The R1 surface of the optical element 2202 is a flat surface and the R2 surface is a curved surface. The R1 surface and the R2 surface of the optical element 2301 are both curved surfaces. The material of the optical element 2101 is PMMA (acrylic resin).

[0063] Light rays from the panel portion (display surface of the display element) 2400 pass through the panel-side optical system 2300 and the transmissive-reflective optical system 2200, are reflected once each at the first transmissive-reflective surface and the second transmissive-reflective surface, pass through the transmissive-reflective optical system 2200 and the pupil-side optical system 2100, and head towards the pupil plane SP. Thereby, the optical system 2000 of this embodiment can observe the optical image of the panel portion 2400 from the pupil plane SP where its exit pupil is located. The light following the optical path at this time is taken as the desired light, and the rest is taken as unnecessary light.

[0064] Figure 7(B) is an aberration diagram of the optical system 2000 when the eye relief (distance from the pupil plane SP to the pupil-facing surface of the pupil-side optical system 2100 (the lens surface closest to the pupil plane in the pupil-side optical system 2100)) is 10 mm and a virtual image is displayed at a position 1600 mm from the pupil plane SP. It can be seen from Figure 7(B) that good imaging performance is obtained. In particular, compared with Example 1, the field curvature and chromatic aberration are good, and the reason for this will be described later.

[0065] The configuration of the panel unit 2400 is equivalent to that of the panel unit 1400 in the first embodiment. The transmissive and reflective surface (half mirror) C is deposited on the R1 surface of the optical element 2301. The first quarter-wave plate B is adhered to the R2 surface of the optical element 2201 and the R1 surface of the optical element 2201. The polarization-selective transmissive and reflective element A is adhered to the R2 surface of the optical element 2101 included in the pupil-side optical system 2100 and the R1 surface of the optical element 2201 included in the transmissive and reflective optical system. In this embodiment, the transmissive and reflective surface (half mirror) C is the second transmissive and reflective member, and the polarization-selective transmissive and reflective element A is the first transmissive and reflective member.

[0066] Similar to the first embodiment, FIG. 8 shows the direction of the optical path passing through each surface and the polarization state of the desired light passing through the optical system 2000. Since it is the same as the first embodiment, the description is omitted.

[0067] Also in this embodiment, as the design field angle in the design designation, a maximum half angle of 50° is assumed. Specifically, the maximum angle of the principal ray of the light beam passing through the pupil plane is 50°.

[0068] FIG. 9 shows the exit angle β (angle with respect to the normal of the display element) of the principal ray with respect to the half angle α of the optical system 2000 in this embodiment. In FIG. 9, the horizontal axis represents the half angle α (°), and the vertical axis represents the exit angle β (°). As shown in FIG. 9, the exit angle β is negative (-) when emitted in a direction away from the optical axis and positive (+) when emitted in a direction approaching the optical axis. From FIG. 9, it can be seen that the exit angle β at the maximum half angle is -23.3°, and the maximum value of the absolute value of the exit angle β is less than 30° (when evaluating the light quantity unevenness, it is evaluated by the absolute value rather than the positive or negative value). That is, by adopting the configuration of this embodiment, the light quantity unevenness can be reduced.

[0069] As described above, considering only the influence of reflection, as shown in Fig. 3(B), a configuration in which both the first transmissive reflection surface and the second transmissive reflection surface have a concave shape on the pupil side is preferable in terms of the exit angle β and the semi-aperture angle α. Although the configuration of this embodiment has less effect than that of the first embodiment, it is sufficiently useful. Note that since the first transmissive reflection member is adhered to a curved surface, the manufacturing difficulty has increased. On the other hand, since curving the first quarter-wave plate further increases the manufacturing difficulty, laminating it on the first transmissive reflection member has been stopped, and it is held separately and kept flat.

[0070] In this embodiment, the optical element 2101 and the optical element 2201, which are refractive optical elements, are joined via a first transmissive reflection member including a first transmissive reflection surface, and the optical element 2202 and the optical element 2301, which are refractive optical elements, are joined via a second transmissive reflection member including a second transmissive reflection surface. Similar to the first embodiment, by adopting a configuration in which a transmissive reflection member including a transmissive reflection surface is sandwiched between refractive optical elements, the refractive power at the transmissive reflection surface can be reduced as compared with the case where the transmissive reflection surface is in contact with air. As a result, when determining the shape of the transmissive reflection surface, it is only necessary to mainly consider the influence of the reflection power, the degree of freedom in optical design is improved, and the imaging performance can be improved while reducing the exit angle β.

[0071] In particular, in this embodiment, different from the first embodiment, the first transmissive reflection surface also has a concave shape on the pupil side and has a large reflection power, making it easier to ensure imaging performance at a wide viewing angle. That is, the effect of adopting the above-described configuration is high. As a result, as shown in Fig. 7(B), in this embodiment, the imaging performance including field curvature can be improved as compared with the first embodiment. According to this embodiment, it is possible to secure the degree of freedom in optical design and obtain the effect of achieving high definition of an image.

[0072] In this embodiment, the distance from the pupil-facing surface to the display element is 15.5 mm, and as in Embodiment 1, it is sufficiently small (thin). Also in this embodiment, the focal length is 14.5 mm, and as in Embodiment 1, it is sufficiently small (thin). Also in this embodiment, the focal length of the pupil-side optical system is 206.8 mm, and the focal length of the panel-side optical system is 23.7 mm, both being positive. As a result, as in Embodiment 1, the focal length can be shortened, and thus, it can be made small (thin).

[0073] Similar to Embodiment 1, the aspherical shape of the optical surfaces that form the interfaces with air of the pupil-side optical system and the panel-side optical system will be described. Fig. 10(A) shows, by a solid line, the cross-sectional shape including the optical axis of the R1 surface of the optical element 2101. Fig. 10(B) shows, by a solid line, the cross-sectional shape including the optical axis of the R2 surface of the optical element 2301. In Figs. 10(A) and (B), the horizontal axis represents the distance y (mm), and the vertical axis represents the position z (mm) in the optical axis direction. Similar to Embodiment 1, both the R1 surface and the R2 surface have shapes that cannot be expressed by conic curves.

[0074] Fig. 11(A) shows the local curvature of the cross-sectional shape including the optical axis of the R1 surface of the optical element 2101. Fig. 11(B) shows the local curvature of the cross-sectional shape including the optical axis of the R2 surface of the optical element 2301. In Figs. 11(A) and (B), the horizontal axis represents the distance y (mm), and the vertical axis represents the curvature (1 / mm). Similar to Embodiment 1, both the R1 surface and the R2 surface have shapes in which the curvature is reversed (i.e., shapes having inflection points) as going away from the axis with respect to the curvature on the axis. By adopting such shapes having such local power distributions, the effect of improving the image surface curvature and the astigmatism while reducing the emission angle β can be obtained.

[0075] Also, as can be seen from FIGS. 11(A) and 11(B), similar to Example 1, within the effective diameter, the local curvature has five extreme values respectively. In this way, by making the shape such that the local power varies finely so that the local curvature has three or more extreme values, the exit angle β, the field curvature, and the astigmatism can be improved over the entire angular field. In particular, in the case of a particularly wide viewing angle as in this embodiment, it is preferable to have at least one such aspherical surface.

[0076] FIG. 10(A) further shows the shape of the paraxial curvature surface of the cross-sectional shape including the optical axis of the R1 surface of the optical element 2101 with a dotted line, and shows the difference from the cross-sectional shape with a double-dotted line. Similarly, FIG. 10(B) further shows the shape of the paraxial curvature surface of the cross-sectional shape including the optical axis of the R2 surface of the optical element 2301 with a dotted line, and shows the difference from the cross-sectional shape with a double-dotted line.

[0077] At the maximum effective diameter end (Φ34) of the R1 surface of the optical element 2101, the sag amount SagA of the cross-sectional shape including the optical axis is 1.41 mm, and the sag amount SagR of the shape of the paraxial curvature surface is 1.52 mm. The asphericity is calculated as follows.

[0078] |(SagA - SagR) / SagR| = 0.071 (7.1%) Similarly, at the maximum effective diameter end (Φ28) of the R2 surface of the optical element 2301, the sag amount SagA of the cross-sectional shape including the optical axis is -1.97 mm, and the sag amount SagR of the shape of the paraxial curvature surface is -11.03 mm. The asphericity is calculated as follows.

[0079] |(SagA - SagR) / SagR| = 0.822 (82.2%) In this way, in the R2 surface (one aspherical surface) of the optical element 2301, by setting the asphericity to 30% or more, the effects of this embodiment can be sufficiently obtained. Also in this embodiment, the asphericity is 50% or more, and the effect is greater.

[0080] Here, although the asphericity of the R1 surface of the optical element 2101 is 30% or less and the effects of this embodiment are obtained, the effects are not significant. As described above, in this embodiment, both the first transmission-reflection surface and the second transmission-reflection surface have a concave shape on the pupil side, and from the viewpoints of the emission angle β and the semi-aperture angle α, it is advantageous compared to Example 1. Therefore, even if a plurality of surfaces with an asphericity of 30% or more are not provided, the effects of this embodiment can be sufficiently obtained. Thus, if at least one of the above-described aspherical surfaces is provided, the effects of this embodiment can be obtained.

[0081] In this embodiment, let the Abbe number based on the d-line of the optical element 2101 be ν21, and the Abbe number based on the d-line of the optical element 2201 joined to the optical element 2101 across the first transmission-reflection surface be ν22. At this time, ν21 = 57.4, ν22 = 27.0, and |ν21 - ν22| = 30.4. Similarly, let the Abbe number based on the d-line of the optical element 2101 be ν22, and the Abbe number based on the d-line of the optical element 2202 joined to the optical element 2101 across the first quarter-wave plate B be ν23. At this time, ν22 = 27.0, ν23 = 56.0, and |ν22 - ν23| = 29.0. Similarly, let the Abbe number based on the d-line of the optical element 2202 be ν23, and the Abbe number based on the d-line of the optical element 2301 joined to the optical element 2202 across the second transmission-reflection surface be ν24. At this time, ν23 = 56.0, ν24 = 22.38, and |ν23 - ν24| = 33.62.

[0082] Thus, by using optical materials with an Abbe number difference of 20 or more across the joint surface, it is possible to reduce chromatic aberration while shortening the overall optical length. As a result, as shown in Fig. 1(B), in this embodiment, chromatic aberration can be improved over a wide range of field angles compared to Example 1.

[0083] In this embodiment, in particular, as the transmissive-reflective optical system 2200, having a joint surface where the optical element 2101 and the optical element 2202 are joined with the first quarter-wave plate B interposed therebetween contributes to reducing chromatic aberration. Since the shapes of the first transmissive-reflective surface and the second transmissive-reflective surface contribute to overall imaging performance, they do not have a degree of design freedom mainly aimed at reducing chromatic aberration. That is, the cemented lens sandwiching the first transmissive-reflective surface and the second transmissive-reflective surface has an effect of reducing chromatic aberration, but the effect is limited.

[0084] In this embodiment, at least one of the pupil-side optical system, the transmissive-reflective optical system, and the panel-side optical system has a joint surface (has a cemented lens in which a plurality of lenses are joined). In this case, since its shape has a degree of design freedom mainly aimed at reducing chromatic aberration, a high chromatic aberration reduction effect can be obtained. In particular, when the transmissive-reflective optical system has a joint surface, since the light beam passes three times, the effect is further enhanced.

[0085] In this embodiment, similar to the first embodiment, the side surface of the first transmissive-reflective member including the polarization-selective transmissive-reflective element A in a direction perpendicular to the optical axis is sealed by the joining of the outer shapes of the optical element 2101 and the optical element 2201 (P in FIG. 7(A)) and does not come into contact with air. Thereby, performance degradation and durability degradation due to moisture absorption can be prevented.

[0086] In this embodiment, similar to the first embodiment, PMMA (acrylic resin) is used as the material of the optical element 2101 forming the pupil-facing surface facing the pupil plane SP. Thereby, even in the case of stricter antifouling standards than usual, it is not necessary to provide hard coating or antifouling glass, and the effect of cost reduction can be obtained.

Embodiment

[0087] Next, the optical system (observation optical system) 3000 in Example 3 of the present invention will be described. In this example, descriptions common to Example 1 will be omitted. FIG. 12(A) is a cross-sectional view of the optical system 3000. The optical system 3000 includes a pupil-side optical system (first lens group) 3100, a first transmission-reflection member (A), a transmission-reflection optical system (second lens group) 3200, a second transmission-reflection member (C), and a panel-side optical system (third lens group) 3300.

[0088] The pupil-side optical system 3100 has an optical element (first lens) 3101, the transmission-reflection optical system 3200 has an optical element (second lens) 3201, and the panel-side optical system 3300 has an optical element (third lens) 3301. Thus, in this example, there is one pupil-side optical system 3100, one transmission-reflection optical system 3200, one panel-side optical system 3300, and optical elements (optical elements 3101, 3201, 3301) that refract, reflect, or diffract light rays. The R1 surface of the optical element 3101 is a curved surface, and the R2 surface is a flat surface. The R1 surface of the optical element 3201 is a flat surface, and the R2 surface is a curved surface. The R1 and R2 surfaces of the optical element 3301 are both curved surfaces. The material of the optical element 3101 is PMMA (acrylic resin).

[0089] Light rays from the panel portion (display surface of the display element) 3400 pass through the panel-side optical system 3300 and the transmission-reflection optical system 3200, are reflected once each at the first transmission-reflection surface and the second transmission-reflection surface, pass through the transmission-reflection optical system 3200 and the pupil-side optical system 3100, and head toward the pupil plane SP. Thereby, the optical system 3000 of this example can observe the optical image of the panel portion 3400 from the pupil plane SP where its exit pupil is located. The light following the optical path at this time is regarded as desired light, and the rest is unnecessary light.

[0090] FIG. 12(B) is an aberration diagram of the optical system 3000 when the eye relief (distance from the pupil plane SP to the pupil-facing surface of the pupil-side optical system 3100 (the lens surface closest to the pupil plane among the pupil-side optical system 3100)) is 10 mm and a virtual image is displayed at a position 1400 mm from the pupil plane SP. It can be seen from FIG. 12(B) that good imaging performance is obtained.

[0091] In particular, compared with Example 1, the field curvature (imaging performance) is good, and the reason will be described later.

[0092] The configuration of the panel unit 3400 is equivalent to that of the panel unit 1400 in Example 1. The transmissive reflective surface (half mirror) C is deposited on the R1 surface of the optical element 3301. The first quarter-wave plate B is adhered to the R1 surface of the optical element 3201 and the polarization selective transmissive reflective element A. The polarization selective transmissive reflective element A is adhered to the R2 surface of the optical element 3101 included in the pupil plane side optical system 3100. In this embodiment, the transmissive reflective surface (half mirror) C is the second transmissive reflective member, and the polarization selective transmissive reflective element A is the first transmissive reflective member.

[0093] Similar to Example 1, FIG. 13 shows the direction of the optical path passing through each surface and the polarization state of the desired light passing through the optical system 3000. Since it is the same as Example 1, the description is omitted.

[0094] Also in this embodiment, as the design field angle in the design designation, a maximum half angle of 50° is assumed. Specifically, the maximum angle of the chief ray of the light beam passing through the pupil plane is 50°. FIG. 14 shows the exit angle β (angle with respect to the normal of the display element) of the chief ray of the optical system 3000 in this embodiment with respect to the half angle α. In FIG. 14, the horizontal axis represents the half angle α (°), and the vertical axis represents the exit angle β (°). As shown in the figure, the exit angle β is negative (-) when exiting in a direction away from the optical axis and positive (+) when exiting in a direction approaching the optical axis. From FIG. 14, it can be seen that the exit angle β at the maximum half angle is -29.1°, and the maximum value of the absolute value of the exit angle β is less than 30° (when evaluating the light amount unevenness, it is evaluated by the absolute value rather than the positive and negative). That is, by adopting the configuration of this embodiment, the light amount unevenness can be reduced.

[0095] In this embodiment, the optical element 3101, which is a refractive optical element, and the optical element 3201 are joined via a first transmissive-reflective member including a first transmissive-reflective surface, and the optical element 3201, which is a refractive optical element, and the optical element 3301 are joined via a second transmissive-reflective member including a second transmissive-reflective surface. Similar to Embodiment 1, by adopting a configuration in which the transmissive-reflective member including the transmissive-reflective surface is sandwiched between the refractive optical elements, the refractive power at the transmissive-reflective surface can be reduced as compared with the case where the transmissive-reflective surface is in contact with air. As a result, when determining the shape of the transmissive-reflective surface, it is only necessary to mainly consider the influence of the reflective power, which improves the degree of freedom in optical design and enables improvement of the imaging performance while reducing the emission angle β. According to this embodiment, it is possible to secure the degree of freedom in optical design and obtain the effect of achieving high definition of the image.

[0096] In addition, this embodiment is composed of a total of three optical elements, one for each of the pupil-side optical system, the transmissive-reflective optical system, and the panel-side optical system, and is the minimum number of optical elements for obtaining the above-described effects, which is preferable from the viewpoints of cost and manufacturing.

[0097] In this embodiment, the distance from the pupil-facing surface to the display element is 17.0 mm, and like Embodiment 1, it is sufficiently small (thin). Also in this embodiment, the focal length is 15.0 mm, and like Embodiment 1, it is sufficiently small (thin). Further in this embodiment, the focal length of the pupil-side optical system is 112.2 mm and the focal length of the panel-side optical system is 179.8 mm, both of which are positive. Thereby, like Embodiment 1, the focal length can be shortened, and by extension, it can be made small (thin).

[0098] Similar to Embodiment 1, the aspherical shape of the optical surface that is the interface with air of the pupil-side optical system and the panel-side optical system will be described. FIG. 15(A) shows, by a solid line, the cross-sectional shape including the optical axis of the R1 surface of the optical element 3101. FIG. 15(B) shows, by a solid line, the cross-sectional shape including the optical axis of the R2 surface of the optical element 3301. In FIGS. 15(A) and 15(B), the horizontal axis represents the distance y (mm), and the vertical axis represents the position z (mm) in the optical axis direction. Similar to Embodiment 1, both the R1 surface and the R2 surface have shapes that cannot be expressed by conic curves.

[0099] FIG. 16(A) shows the local curvature of the cross-sectional shape including the optical axis of the R1 surface of the optical element 3101. FIG. 16(B) shows the local curvature of the cross-sectional shape including the optical axis of the R2 surface of the optical element 3301. In FIGS. 16(A) and 16(B), the horizontal axis represents the distance y (mm), and the vertical axis represents the curvature (1 / mm). Similar to Example 1, both the R1 surface and the R2 surface have a shape in which the curvature is inverted as it goes away from the axis with respect to the curvature on the axis (that is, a shape having an inflection point). By adopting such a shape having a local power distribution, an effect of improving the image plane curvature and the astigmatism while reducing the emission angle β can be obtained.

[0100] Also, as can be seen from FIG. 16(B), similar to Example 1, within the effective diameter, the local curvature has five extreme values respectively. In this way, by adopting a shape in which the local power is finely changed so that the local curvature has three or more extreme values, the emission angle β, the image plane curvature, and the astigmatism can be improved over the entire angular field of view. In particular, in the case of a particularly wide viewing angle as in this embodiment, it is preferable to have such an aspherical surface on at least one surface.

[0101] FIG. 15(A) further shows the shape of the paraxial curvature surface of the cross-sectional shape including the optical axis of the R1 surface of the optical element 3101 by a dotted line, and shows the difference from the cross-sectional shape by a double-dotted line. Similarly, FIG. 15(B) further shows the shape of the paraxial curvature surface of the cross-sectional shape including the optical axis of the R2 surface of the optical element 3301 by a dotted line, and shows the difference from the cross-sectional shape by a double-dotted line.

[0102] The sag amount SagA of the cross-sectional shape including the optical axis at the maximum effective diameter end (Φ34) of the R1 surface of the optical element 3101 is 2.08 mm, and the sag amount SagR of the shape of the paraxial curvature surface is 2.68 mm. The asphericity is calculated as follows.

[0103] |(SagA−SagR) / SagR| = 22.3% Similarly, at the maximum effective diameter end (Φ30) of the R2 surface of the optical element 3301, the sag amount SagA of the cross-sectional shape including the optical axis is -0.89 mm, and the sag amount SagR of the shape of the paraxial curvature surface is -1.32 mm. The asphericity is calculated as follows.

[0104] |(SagA - SagR) / SagR| = 32.8% Thus, in the single aspherical surface of the R2 surface of the optical element 3301, by setting the asphericity to 30% or more, the effects of this embodiment can be sufficiently obtained. Here, the asphericity of the R1 surface of the optical element 3101 is 30% or less. Although the effects of this embodiment are obtained, the effects are not significant. As can be seen from FIG. 12(B) or FIG. 14, in terms of the balance between the imaging performance and the exit angle β, compared with Example 1, the imaging performance is emphasized and the exit angle β is tolerated. Thus, although the effects vary according to the design concept, as long as at least one of the aforementioned aspherical surfaces is provided, the effects of this embodiment can be obtained.

[0105] In this embodiment, let the Abbe number based on the d-line of the optical element 3201 be ν32, and the Abbe number based on the d-line of the optical element 3301 joined to the optical element 3201 across the second transmission and reflection surface be ν33. At this time, ν32 = 57.4, ν33 = 22.38, and |ν32 - ν33| = 33.62. Thus, by using optical materials with an Abbe number difference of 20 or more across the joining surface, it is possible to reduce chromatic aberration while shortening the overall optical length.

[0106] In this embodiment, similar to Example 1, the side surface in the direction perpendicular to the optical axis of the first transmission and reflection member including the polarization-selective transmission and reflection element A is sealed by the outer shape joining (P in FIG. 12(A)) of the optical element 3101 and the optical element 3201 and does not come into contact with air. Thereby, performance degradation and durability degradation due to moisture absorption can be prevented.

[0107] In this embodiment, similar to Embodiment 1, PMMA (acrylic resin) is used as the material of the optical element 3101 forming the pupil-facing surface facing the pupil plane SP. As a result, even in the case of stricter anti-fouling standards than usual, it is not necessary to provide hard coating or anti-fouling glass, and the effect of cost reduction can be obtained.

[0108] Hereinafter, Numerical Examples 1 to 3 corresponding to Embodiments 1 to 3 are shown. In the surface data of each numerical example, the surface number i indicates the i-th surface when counted from the pupil plane side. r is the radius of curvature (mm) of the i-th surface, d is the lens thickness or air gap (mm) between the i-th and (i + 1)-th surfaces, nd is the refractive index at the d-line of the material of the i-th optical member. νd is the Abbe number based on the d-line of the material of the i-th optical member. The Abbe number νd is expressed as νd = (Nd - 1) / (NF - NC), where Nd, NF, and NC are the refractive indices at the d-line (587.6 nm), F-line (486.1 nm), and C-line (656.3 nm) of the Fraunhofer lines, respectively. The effective diameter indicates the maximum diameter of the region through which light from the original drawing passes on each surface.

[0109] The "*" attached to the surface number means that the surface has an aspherical shape. The aspherical shape is expressed by the following formula, where the displacement in the optical axis direction at the position of the height h from the optical axis is x with respect to the surface vertex, R is the paraxial radius of curvature, k is the conic constant, and Ai: (i = 4, 6, 8...) are the aspherical coefficients of each order.

[0110] [Number]

[0111] [Numerical Example 1] Unit: mm Surface data Surface number r d nd νd 1 (Diaphragm) ∞ 10.00 2* 51.000 2.70 1.49171 57.4 3 ∞ 0.30 1.52000 50.0 4 * ∞ 7.80 1.54390 56.0 5 * -50.470 -7.80 6 ∞ -0.30 -1.52000 50.0 7 ∞ 0.30 8 * ∞ 7.80 1.54390 56.0 9 * -50.470 2.90 1.64220 22.4 10 * -19.000 1.00 11 ∞ 0.30 1.52000 50.0 12 ∞ 0.10 1.52000 50.0 13 ∞ 0.40 1.51633 64.1 14 ∞ (Variable) Image plane ∞ Aspherical data Second surface K = -1.00000e+00 A4 = -3.67428e-05 A6 = 1.66514e-07 A8 = -4.76007e-10 A10 = 5.37368e-13 A12 = -5.04034e-16 Fifth surface K = -3.00000e+00 A4 = -6.65066e-06 A6 = 5.18014e-09 A8 = 6.70726e-12 A10 = -3.76426e-14 Ninth surface K = -3.00000e+00 A4 = -6.65066e-06 A6 = 5.18014e-09 A8 = 6.70726e-12 A10 = -3.76426e-14 Tenth surface K = -1.00000e+00 A4 = 4.75733e-04 A6 = -4.01516e-06 A8 = 1.58652e-08 A10 = -2.29360e-11 Focal length 14.27 [Numerical Example 2] Unit: mm Surface data Surface number r d nd νd 1 (Diaphragm) ∞ 10.00 2* 96.000 3.50 1.49171 57.4 3* -97.800 0.30 1.52000 50.0 4* -97.800 1.50 1.60700 27.0 5 ∞ 0.30 1.52000 50.0 6 ∞ 6.10 1.54390 56.0 7* -38.200 -6.10 8 ∞ -0.30 -1.52000 50.0 9 ∞ -1.50 1.60700 27.0 10* -97.800 -0.30 -1.52000 50.0 11* -97.800 0.30 12* -97.800 1.50 1.60700 27.0 13 ∞ 0.30 1.52000 50.0 14 ∞ 6.10 1.54390 56.0 15* -38.200 2.00 1.64220 22.4 16* -14.400 1.00 17 ∞ 0.30 1.52000 50.0 18 ∞ 0.10 1.52000 50.0 19 ∞ 0.40 1.51633 64.1 20 ∞ (Variable) Image plane ∞ Aspherical data Second surface K = -1.00000e+00 A4 = 3.60054e-06 A6 = -9.35703e-08 A8 = 5.14016e-10 A10 = -8.55095e-13 Third surface K = 6.00000e+00 A4 = 8.43436e-06 A6 = 1.55821e-09 A8 = 1.89611e-11 The 4th surface K = 6.00000e+00 A 4= 8.43436e-06 A 6= 1.55821e-09 A 8= 1.89611e-11 The 7th surface K =-1.00000e+00 A 4= 1.42878e-06 A 6=-1.21058e-08 A 8= 3.83502e-11 The 10th surface K = 6.00000e+00 A 4= 8.43436e-06 A 6= 1.55821e-09 A 8= 1.89611e-11 The 11th surface K = 6.00000e+00 A 4= 8.43436e-06 A 6= 1.55821e-09 A 8= 1.89611e-11 The 12th surface K = 6.00000e+00 A 4= 8.43436e-06 A 6= 1.55821e-09 A 8= 1.89611e-11 The 15th surface K =-1.00000e+00 A 4= 1.42878e-06 A 6=-1.21058e-08 A 8= 3.83502e-11 The 16th surface K =-1.00000e+00 A 4= 3.25883e-04 A 6=-1.72091e-06 A 8= 3.57618e-09 Focal length 14.45 [Numerical Example 3] Unit: mm Surface data Surface number r d nd νd 1 (Aperture) ∞ 10.00 2* 55.189 3.85 1.49171 57.4 3 ∞ 0.30 1.52000 50.0 4 ∞ 7.45 1.54390 56.0 5* -50.388 -7.45 6 ∞ -0.30 -1.52000 50.0 7 ∞ 0.30 8 ∞ 7.45 1.54390 56.0 9* -50.388 2.70 1.64220 22.4 10* -85.752 1.75 11 ∞ 0.30 1.52000 50.0 12 ∞ 0.10 1.52000 50.0 13 ∞ 0.40 1.51633 64.1 14 ∞ (variable) Image plane ∞ Aspherical data Second surface K = 0.00000e+00 A 4=-5.49562e-06 A 6= 1.36131e-09 A 8=-9.48412e-12 A10=-5.32998e-14 Fifth surface K = 0.00000e+00 A 4=-2.07747e-07 A 6= 2.51349e-10 A 8=-2.99711e-12 Ninth surface K = 0.00000e+00 A 4=-2.07747e-07 A 6= 2.51349e-10 A 8=-2.99711e-12 Tenth surface K = 0.00000e+00 A 4= 4.97609e-05 A 6=-2.65664e-07 A 8= 3.67150e-10 Focal length 14.99 The disclosure of each embodiment includes the following configuration. (Configuration 1) An optical system that guides the light beam from the display surface to the pupil surface, A first lens group, a first transmissive-reflective member having a first transmissive-reflective surface, a second lens group, a second transmissive-reflective member having a second transmissive-reflective surface, and a third lens group, which are arranged in order from the pupil surface side to the display surface side. At least one optical surface that forms an interface with air in the first lens group is a first aspherical surface. An optical system, wherein at least one optical surface that forms an interface with air in the third lens group is a second aspherical surface. (Configuration 2) The optical system according to Configuration 1, wherein the first transmissive-reflective surface is a plane. (Configuration 3) The optical system according to Configuration 1 or 2, wherein a cross section including at least one optical axis of the first aspherical surface or the second aspherical surface has a shape that cannot be expressed by a conic curve. (Configuration 4) The optical system according to any one of Configurations 1 to 3, wherein a cross section including at least one optical axis of the first aspherical surface or the second aspherical surface has a shape having an inflection point. (Configuration 5) The optical system according to any one of Configurations 1 to 4, wherein a cross section including at least one optical axis of the first aspherical surface or the second aspherical surface has a shape in which the second derivative value has three or more extreme values. (Configuration 6) In a cross section including at least one optical axis of the first aspherical surface or the second aspherical surface, when the sag amount of the paraxial curvature surface at the maximum effective diameter end is SagR and the sag amount of the aspherical surface is SagA, 0.3 ≦ |(SagA - SagR) / SagR| The optical system according to any one of Configurations 1 to 5, which satisfies the conditional expression. (Configuration 7) The optical system according to any one of Configurations 1 to 6, wherein the refractive power in the vicinity of the optical axis of each of the first lens group and the third lens group is positive. (Configuration 8) The lens closest to the display surface among the second lens group and the lens closest to the pupil surface among the third lens group are joined via the second transmissive reflection member, and the optical system according to any one of Configurations 1 to 7, characterized in that. (Configuration 9) The lens closest to the display surface among the first lens group and the lens closest to the pupil surface among the second lens group are joined via the first transmissive reflection member, and the optical system according to any one of Configurations 1 to 8, characterized in that. (Configuration 10) The first lens group has a first lens, The second lens group has a second lens, The third lens group has a third lens, The first lens and the second lens are joined via the first transmissive reflection member, The second lens and the third lens are joined via the second transmissive reflection member, and the optical system according to any one of Configurations 1 to 9, characterized in that. (Configuration 11) The distance from the optical surface facing the pupil surface to the display surface is 20 mm or less, and the optical system according to any one of Configurations 1 to 10, characterized in that. (Configuration 12) The focal length of the optical system is 20 mm or less, and the optical system according to any one of Configurations 1 to 11, characterized in that. (Configuration 13) The maximum angle of the chief ray of the light beam passing through the pupil surface is 30° or more, The absolute value of the maximum value of the exit angle of the chief ray from the display element is 35° or less, and the optical system according to any one of Configurations 1 to 12, characterized in that. (Configuration 14) The exit angle of the chief ray passing through the pupil surface from the display element is in a direction away from the optical axis at the end angle of the display element, The diagonal length of the square circumscribing the display element is 1.6 inches or less, and the optical system according to any one of Configurations 1 to 13, characterized in that. (Configuration 15) When the Abbe number based on the d-line of one of two adjacent lenses is ν1 and the Abbe number based on the d-line of the other lens is ν2, 20 ≦ |ν1 - ν2| The optical system according to any one of Configurations 1 to 14, characterized by having at least one combination that satisfies the conditional expression. (Configuration 16) The optical system according to any one of Configurations 1 to 15, characterized in that at least one of the first lens group, the second lens group, or the third lens group has a cemented lens in which a plurality of lenses are cemented. (Configuration 17) The optical system according to any one of Configurations 1 to 16, characterized in that at least one of the first transmissive - reflective member or the second transmissive - reflective member is not in contact with air. (Configuration 18) The optical system according to any one of Configurations 1 to 17, characterized in that the optical element closest to the pupil side in the first lens group is formed of an acrylic resin. (Configuration 19) A display device, characterized by having the optical system according to any one of Configurations 1 to 18 and a display element.

[0112] As described above, the preferred embodiments of the present invention have been explained, but the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist.

[0113] For example, when combined with a display element such as an OLED (Organic Light Emitting Diode) or an LCD (Liquid Crystal Display), electrical processing may be applied to the display side depending on the amount of distortion aberration or the amount of magnification chromatic aberration. Also, in each embodiment, it is preferable that one of the first transmission-reflection surface and the second transmission-reflection surface is a polarization-selective transmission-reflection element (reflection polarizer) PBS. At this time, it is preferable that the other of the first transmission-reflection surface and the second transmission-reflection surface is a half mirror having a transmittance-to-reflectance ratio of 1:1. However, the ratio of transmittance to reflectance may be changed as necessary. Also, the optical system of each embodiment may further have another optical system (lens) on the pupil surface side of the first lens group. Similarly, the optical system of each embodiment may further have another optical system (lens) on the display surface side of the third lens group. In the optical system of Embodiment 1, at least one other lens may be inserted into the gap of the second lens group (between the second lens and the third lens).

Explanation of Signs

[0114] 1000, 2000, 3000 Optical system 1100, 2100, 3100 Pupil surface side optical system (first lens group) 1200, 2200, 3200 Transmission-reflection optical system (second lens group) 1300, 2300, 3300 Panel side optical system (third lens group) 1400, 2400, 3400 Panel part (display surface) A Polarization-selective transmission-reflection element (first transmission-reflection member) C Transmission-reflection surface (second transmission-reflection member) SP Pupil surface

Claims

1. An optical system that guides a light beam from a display surface to a pupil surface, comprising a first lens group, a first transmissive-reflective member having a first transmissive-reflective surface, a second lens group, a second transmissive-reflective member having a second transmissive-reflective surface, and a third lens group, which are arranged in order from the pupil surface side to the display surface side, at least one optical surface that forms an interface with air in the first lens group is a first aspherical surface, and at least one optical surface that forms an interface with air in the third lens group is a second aspherical surface. An optical system characterized by this.

2. The optical system according to claim 1, wherein the first transmissive-reflective surface is a flat surface.

3. The optical system according to claim 1, wherein a cross section including at least one optical axis of the first aspherical surface or the second aspherical surface is a shape that cannot be represented by a conic section.

4. The optical system according to any one of claims 1 to 3, wherein a cross section including at least one optical axis of the first aspherical surface or the second aspherical surface is a shape having an inflection point.

5. The optical system according to any one of claims 1 to 3, wherein a cross section including at least one optical axis of the first aspherical surface or the second aspherical surface is a shape in which the second derivative value has three or more extreme values.

6. In a cross section including at least one optical axis of the first aspherical surface or the second aspherical surface, when the sag amount of the paraxial curvature surface at the maximum effective diameter end is SagR and the sag amount of the aspherical surface is SagA, 0.3 ≤ |(SagA - SagR) / SagR| The optical system according to any one of claims 1 to 3, characterized by satisfying the conditional expression.

7. The optical system according to any one of claims 1 to 3, wherein the refractive power near the optical axis of each of the first lens group and the third lens group is positive.

8. Among the lenses of the second lens group closest to the display surface and the lens of the third lens group closest to the pupil surface, they are joined via the second transmissive-reflective member. The optical system according to any one of claims 1 to 3, characterized in that.

9. Among the lens of the first lens group closest to the display surface and the lens of the second lens group closest to the pupil surface, they are joined via the first transmissive-reflective member. The optical system according to any one of claims 1 to 3, characterized in that.

10. The first lens group has a first lens, The second lens group has a second lens, The third lens group has a third lens, The first lens and the second lens are joined via the first transmissive-reflective member, The second lens and the third lens are joined via the second transmissive-reflective member. The optical system according to any one of claims 1 to 3, characterized in that.

11. The distance from the optical surface facing the pupil surface to the display surface is 20 mm or less. The optical system according to any one of claims 1 to 3, characterized in that.

12. The focal length of the optical system is 20 mm or less. The optical system according to any one of claims 1 to 3, characterized in that.

13. The maximum angle of the chief ray of the light beam passing through the pupil surface is 30° or more, The absolute value of the maximum value of the exit angle of the chief ray from the display element is 35° or less. The optical system according to any one of claims 1 to 3, characterized in that.

14. The exit angle of the chief ray passing through the pupil surface from the display element is in a direction away from the optical axis at the end field angle of the display element, The diagonal length of the square circumscribing the display element is 1.6 inches or less. The optical system according to any one of claims 1 to 3, characterized in that.

15. When the Abbe number based on the d-line of one of two adjacent lenses is ν1 and the Abbe number based on the d-line of the other lens is ν2, 20 ≦ |ν1 - ν2| The optical system according to any one of claims 1 to 3, characterized by having at least one combination that satisfies the conditional expression.

16. The optical system according to any one of claims 1 to 3, characterized in that at least one of the first lens group, the second lens group, or the third lens group has a cemented lens in which a plurality of lenses are cemented.

17. The optical system according to any one of claims 1 to 3, characterized in that at least one of the first transmissive reflective member or the second transmissive reflective member is not in contact with air.

18. The optical system according to any one of claims 1 to 3, characterized in that the optical element closest to the pupil side in the first lens group is formed of an acrylic resin.

19. A display device, characterized by having the optical system according to any one of claims 1 to 3 and a display element.

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