Optical system and display device

Abstract

[Problem] To provide an optical system that can reduce the angle of emission from a display element. [Solution] An optical system (1000) that guides a light flux from a display surface (1400) to a pupil surface (SP) and has, arranged in order from the pupil surface side to the display surface side, a first lens group (1100), a first transmission / reflection member (A) that has a first transmission / reflection surface, a second lens group (1200), a second transmission / reflection member (C) that has a second transmission / reflection surface, and a third lens group (1300), wherein at least one optical surface serving as an interface with air in the first lens group is a first aspherical surface, and at least one optical surface serving as an interface with air in the third lens group is a second aspherical surface.

Description

Optical Systems and Display Devices

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

[0002] In recent years, display devices (observation devices) such as head-mounted displays (HMDs) have become known that provide a realistic experience by enlarging an original image displayed using a display element such as a liquid crystal display (LCD) through an observation optical system to provide a large-screen image to a user. Because display devices are worn on the head, the observation optical systems used in display devices are 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 by using a cemented lens.

[0003] Patent No. 6984261

[0004] A typical characteristic of display elements is that the amount of light emitted from the display element is greatest in the vertical direction and decreases in proportion to the emission angle. In the optical system disclosed in Patent Document 1, the emission angle from the display element of the light beam at the edge of the field of view is large, so the amount of light at the edge of the field of view decreases, and the user perceives the edge of the field of view as dark.

[0005] SUMMARY OF THE INVENTION It is therefore an object of the present invention to provide an optical system that can reduce the angle of emergence from a display element.

[0006] An optical system according to one aspect of the present invention is an optical system that guides a light beam from a display surface to a pupil plane, and has, arranged in order from the pupil plane 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, wherein at least one optical surface of the first lens group that interfaces with air is a first aspherical surface, and at least one optical surface of the third lens group that interfaces with air is a second aspherical surface.

[0007] Other objects and features of the present invention are illustrated in the following examples.

[0008] According to the present invention, it is possible to provide an optical system that can reduce the angle of emergence from a display element.

[0009] FIG. 1 is a cross-sectional view and aberration diagrams of an optical system in Example 1. FIG. 2 is a schematic diagram showing an optical path of the optical system in Example 1. FIG. 3 is an explanatory diagram of a first transmissive-reflective surface and a second transmissive-reflective surface. FIG. 4 is a diagram showing an exit angle β of a display element relative to a half angle of view α in Example 1. FIG. 5 is a diagram showing the cross-sectional shapes of a first aspherical surface and a second aspherical surface in Example 1. FIG. 6 is a diagram showing local curvatures of the cross-sectional shapes of the first aspherical surface and the second aspherical surface in Example 1. FIG. 6 is a cross-sectional view and aberration diagrams of an optical system in Example 2. FIG. 7 is a schematic diagram showing an optical path of the optical system in Example 2. FIG. 8 is a diagram showing an exit angle β of a display element relative to a half angle of view α in Example 2. FIG. 9 is a diagram showing the cross-sectional shapes of the first aspherical surface and the second aspherical surface in Example 2. FIG. 10 is a diagram showing local curvatures of the cross-sectional shapes of the first aspherical surface and the second aspherical surface in Example 2. FIG. 11 is a cross-sectional view and aberration diagrams of an optical system in Example 3. FIG. 12 is a schematic diagram showing an optical path of the optical system in Example 3. FIG. 13 is a diagram showing an exit angle β of a display element relative to a half angle of view α in Example 3. FIG. 14 is a diagram showing the cross-sectional shapes of a first aspherical surface and a second aspherical surface in Example 3. 10A and 10B are diagrams illustrating the local curvatures of the cross-sectional shapes of the first aspherical surface and the second aspherical surface in Example 3.

[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 a display surface of a display element (panel unit) to an observation surface (pupil plane), and is an observation optical system for observing an image displayed on the display surface. The optical system of each embodiment and the display element constitute a display device. The optical system of each embodiment has, arranged in order from the pupil plane side to the display surface side, a first lens group (pupil plane side optical system), a first transmissive reflective member, a second lens group (transmissive reflective optical system), a second transmissive reflective member, and a third lens group (panel side optical system).

[0012] The first transmissive-reflective member has a flat or curved first transmissive-reflective surface. The second transmissive-reflective member has a curved second transmissive-reflective surface. The lens in the first lens group closest to the display surface and the lens in the second lens group closest to the pupil plane are cemented together via the first transmissive-reflective member. Furthermore, the lens in the second lens group closest to the display surface and the lens in the third lens group closest to the pupil plane are cemented together via the second transmissive-reflective 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 transmission-reflection surfaces (first transmission-reflection surface and second transmission-reflection surface) that serve as both transmission and reflection surfaces. The third lens group is an optical system sandwiched between the second lens group and a display element. The first lens group and the third lens group may not exist. Each embodiment will be described in detail below.

[0014] First, an optical system (observation optical system) 1000 according to a first embodiment of the present invention will be described. Fig. 1A is a cross-sectional view of the optical system 1000. The optical system 1000 has a pupil plane side optical system (first lens group) 1100, a first transmissive reflecting member (A), a transmissive reflecting optical system (second lens group) 1200, a second transmissive reflecting member (C), and a panel side optical system (third lens group) 1300.

[0015] The pupil plane side optical system 1100 has an optical element (first lens) 1101, the transmission / reflection 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. In this manner, in this embodiment, one pupil plane side optical system 1100, two transmission / reflection optical systems 1200, and one panel side optical system 1300 have optical elements (optical elements 1101, 1201, 1202, 1301) that refract, reflect, or diffract light rays.

[0016] Each optical element has two optical surfaces, referred to as the R1 surface and the R2 surface from the pupil plane 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 material of the optical elements 1101, 1202, and 1301 is PMMA (acrylic resin). However, this embodiment is not limited to this, and instead of using acrylic resin as the material of each optical element, acrylic resin may be coated on each optical element.

[0017] A light ray from the panel unit (display surface of the display element) 1400 passes through the panel-side optical system 1300 and the transmission-reflection optical system 1200, is reflected by the first transmission-reflection surface, is reflected by the second transmission-reflection surface, passes through the transmission-reflection optical system 1200 and the pupil-plane-side optical system 1100, and heads toward the pupil plane SP. This makes it possible for the optical system 1000 to observe an optical image of the panel unit 1400 from the pupil plane SP where its exit pupil is located. The light that follows this optical path is designated as desired light, and the rest is designated as unwanted light.

[0018] FIG. 1B 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-plane-side optical system 1100 (the lens surface of the pupil-plane-side optical system 1100 closest to the pupil plane)) is 10 mm and a virtual image is displayed at a position 1600 mm from the pupil plane SP. FIG. 1B shows aberrations for 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. It can be seen from FIG. 1B that although there is some curvature of field and astigmatic difference, imaging performance that is usable is obtained. Here, FIG. 1B shows aberrations in a reverse optical path (reverse tracing) from the pupil plane SP to the panel unit 1400, with the panel unit 1400 as the image plane, rather than the original forward optical path (forward tracing) from the panel unit 1400 to the pupil plane SP. This point is not a problem because it corresponds to the aberration in the case of a forward optical path (forward tracing) when indicating the optical performance of the optical system 1000. Furthermore, for the polarizing plate, quarter-wave plate, and polarization-selective transmission / reflection element, etc., which will be described later, the approximate properties of each element are uniformly expressed as follows, but in reality, the properties may differ. For example, the polarizing plate has a thickness of 0.1 mm, a refractive index of 1.52, and an Abbe number of 50, while the quarter-wave plate and the stacked element of the quarter-wave plate and the polarization-selective transmission / reflection element have a thickness of 0.3 mm, a refractive index of 1.52, and an Abbe number of 50.

[0019] Next, the optical path of the optical system 1000 will be described with reference to Fig. 2. Fig. 2 is a schematic diagram showing the optical path of the optical system 1000, showing the direction of the optical path passing through each surface and the polarization state above it. Note that the optical path of the desired light will be described here, and a description of the optical path of the unwanted light resulting from 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 plane-side optical system 1100, a polarization-selective transmission-reflection element A, a transmission-reflection optical system 1200, a first quarter-wave plate B, a transmission-reflection surface (half mirror) C, a panel-side optical system 1300, and a panel unit 1400. The polarization-selective transmission-reflection element A corresponds to a first transmission-reflection member having a first transmission-reflection surface, and the transmission-reflection surface C corresponds to a second transmission-reflection member having a second transmission-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 display element has a square shape with a diagonal of 1.3 inches (each side is 23.3 mm). The polarizing plate E and the second quarter-wave plate D are arranged in close proximity to each other from the display element toward the pupil plane.

[0021] The unpolarized light emitted from the display element is converted into linearly polarized light by the polarizing plate E, and then converted into circularly polarized light by the second quarter-wave plate D, passes through the panel-side optical system 1300, and heads toward the transmission-reflection optical system 1200. 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, organic EL elements may use a polarizing plate 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 provide a separate polarizing plate E.

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

[0023] The first quarter-wave plate B is disposed with respect to the second quarter-wave plate D such that their slow axes are inclined at 90° to each other, and the slow axis of the first quarter-wave plate B is inclined at 45° to the polarization transmission axis of the polarizing plate E. A transmission-reflection surface (half mirror) C is deposited on the R1 surface of the optical element 1301, and is further bonded to the R2 surface of the optical element 1202. The first quarter-wave plate B is bonded to the R1 surface of the optical element 1201, and is further bonded to the polarization-selective transmission-reflection element A bonded 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 it passed through the polarizing plate E, and to transmit linearly polarized light having a polarization direction perpendicular to the polarization direction. That is, the polarization-selective transmission-reflection element A is a reflective polarizer that separates incident light into reflected light and transmitted light depending on the polarization state, and is, for example, a wire grid polarizer or a laminated birefringent film polarizer. A specific example of a wire grid polarizer is "WGF" manufactured by Asahi Kasei Corporation, and the wire grid-formed 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 transmissive-reflective member is a member that includes a transmissive-reflective surface and is connected to the transmissive-reflective surface, has almost no refractive power, and is mainly responsible for optical functions other than refraction (such as absorption according to the polarization state, change in the polarization state, and anti-reflection) and mechanical functions (such as adhesion and protection). In this embodiment, the polarization-selective transmissive-reflective element A is the first transmissive-reflective member, and the transmissive-reflective surface (half mirror) C is the second transmissive-reflective member. Each transmissive-reflective member may be connected to members having multiple functions.

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

[0027] 3A and 3B are schematic diagrams illustrating the optical path of a ray emitted from an image height (height h) on a display element, the emission angle β of the display element (the angle with respect to the normal to the display surface of the display element), and the half angle of view α on the pupil plane SP, depending on the plano-convex shape of the first transmissive-reflective surface. Here, the effect of refraction is not illustrated, as the effect of reflection is explained. For simplicity, the discussion will proceed using a substantially spherical shape rather than a complex aspherical shape. Details of FIGS. 3A and 3B will be described later.

[0028] Since display elements typically emit Lambertian light, the smaller the emission angle β, the greater the amount of light captured, and the larger the emission angle β, the less light captured. Therefore, if the maximum value of the emission angle β is large within the range of the designed viewing angle, unevenness in the amount of light will occur within the field of view, which is undesirable. As mentioned above, the larger the half angle of view α (i.e., the wider the viewing angle), the greater the sense of immersion, which is desirable, but at the same time, the larger the maximum value of the emission angle β, which is likely to be problematic.

[0029] Although it depends on the characteristics of the display element, generally, when the exit angle β (the maximum absolute value of the exit angle β) is greater than 35°, unevenness in the amount of light is likely to become a problem. For this reason, the exit angle β (the maximum absolute value of the exit angle β) of the chief ray of the light beam passing through the pupil plane SP from the display element is preferably 35° or less. More preferably, the exit angle β is 30° or less. In order to reduce the maximum absolute value of the exit angle β, it is effective to employ a configuration in which an aspherical surface is provided on the optical surface that interfaces with air in the panel-side optical system. This is because the light beams at each angle of view are separated in the panel-side optical system compared to the pupil-plane-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 exit angle β, the curvature of field and astigmatic difference will be inappropriate. To improve this, it is effective to adopt a configuration in which an aspheric surface is provided on the optical surface that interfaces with air in the pupil-plane-side optical system. In a transmission-reflection optical system, even a light beam with the same field angle passes through different optical surfaces along the three folded optical paths, making it difficult to optimize the light beam for each field angle. Furthermore, because the pupil-plane-side optical system is separated from the panel-side optical system, the aspheric surfaces of both optical systems make it easy to adjust the curvature of field and astigmatic difference. However, even if an aspheric surface were provided on the cemented surface rather than on the interface with air, the refractive effect would be weak and the desired effect would not be achieved.

[0031] In this embodiment, it is assumed that the maximum half angle of view is 50° as the design field angle in the design nominal design. Specifically, the maximum angle of the chief ray of the light beam passing through the pupil plane SP is 50°. In general, if the maximum half angle of view (the maximum angle of the chief 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 angle of view is 40° or more. The wider the field angle, the greater the effect of this embodiment.

[0032] FIG. 4 shows the exit angle β (angle with respect to the normal to the display element) of the chief ray with respect to the half angle of view α of the optical system 1000 in this embodiment. In FIG. 4, the horizontal axis represents the angle of view (°), and the vertical axis represents the exit angle β (°). As shown in FIG. 4, the exit 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 toward the optical axis. From FIG. 4, it can be seen that the exit angle β at the maximum half angle of view (α=50°) is −24.6°, and the maximum absolute value of the exit angle β is smaller than 30° (when evaluating light intensity unevenness, the evaluation is based on the absolute value, not on positive or negative). In other words, the configuration of this embodiment can achieve the effect of reducing light intensity unevenness.

[0033] Furthermore, as in this embodiment, when the output angle β at the maximum half angle of view is negative (i.e., when the light beam is emitted in a direction away from the optical axis at the edge angle of view 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 view of 30° or more, it is preferable that the shape of the display element is such that the diagonal length of the circumscribing square of the display element is 1.6 inches or less (one side of the circumscribing square is 28.7 mm or less).

[0034] Next, details of FIGS. 3A and 3B will be described. FIG. 3A illustrates a case where the first transmission-reflection surface has a planar shape and the second transmission-reflection surface has a concave shape toward the pupil plane. This case is suitable for increasing the half angle of view α but not for reducing the exit angle β. FIG. 3B illustrates a case where both the first transmission-reflection surface and the second transmission-reflection surface have a concave shape toward the pupil plane. This case is suitable for reducing the exit angle β and the half angle of view α. That is, considering only the effect of reflection, a configuration where both the first transmission-reflection surface and the second transmission-reflection surface have a concave shape toward the pupil plane, as shown in FIG. 3B, is preferable in terms of the exit angle β and the half angle of view α. In other words, a configuration where the first transmission-reflection surface has a planar shape, as in this embodiment, is particularly effective for reducing the exit angle β due to the effect of refraction. Furthermore, a configuration where the first transmission-reflection surface is planar is easier to manufacture than a configuration where the first transmission-reflection surface is curved.

[0035] In this embodiment, the optical element 1101 (the lens in the first lens group closest to the display surface) and the optical element 1201 (the lens in the second lens group closest to the pupil surface) which are refractive optical elements are cemented together via a first transmissive-reflective member including a first transmissive-reflective surface. Also, the optical element 1201 (the lens in the second lens group closest to the display surface) and the optical element 1301 (the lens in the third lens group closest to the pupil surface) which are refractive optical elements are cemented together via a second transmissive-reflective member including a second transmissive-reflective surface.

[0036] In this way, by sandwiching the transmissive-reflective member including the transmissive-reflective surface between refractive optical elements, the refractive power of the transmissive-reflective surface can be reduced compared to when 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 consider the influence of the reflective power, which increases the degree of freedom in optical design and enables the imaging performance to be improved while reducing the exit angle β.

[0037] In particular, when attempting to ensure imaging performance over a wide viewing angle, a configuration in which the second transmissive-reflective surface has a concave shape on the pupil plane side and a large reflective power, as in this embodiment, is preferable. In other words, the above-described configuration is highly effective. On the other hand, when the first transmissive-reflective surface has a flat shape, as in this embodiment, the above-described configuration is less effective in terms of reducing the exit angle β and improving imaging performance. However, since no unnecessary space is provided, there are advantages in that the total optical length can be shortened, that manufacturing and maintenance can be simplified, and that durability, as described below, can be improved. The effects of this embodiment can be obtained even without adopting the above-described bonding configuration.

[0038] This embodiment is configured with a total of three optical elements: one for each of the pupil-plane-side optical system, the transmissive-reflective optical system, and the panel-side optical system. Specifically, the first lens group includes a first lens (optical element 1101), the second lens group includes a second lens (optical element 1201), and the third lens group includes a third lens (optical element 1301). The first and second lenses are cemented together via a first transmissive-reflective member, and the second and third lenses are cemented together via a second transmissive-reflective member. This configuration minimizes the number of optical elements required to achieve the above-described effects, making it preferable from the standpoints of cost and manufacturing efficiency. Here, "cementing" refers not only to bonding using an adhesive but also to methods such as vapor deposition and pressure bonding. Furthermore, this refers to bonding at least within a portion of the effective area through which light passes, and does not necessarily include bonding over the entire effective area or outside the effective area. This embodiment ensures flexibility in optical design and achieves the effect of achieving high-resolution images.

[0039] As mentioned above, the observation optical system used in the display device is also required to be small (thin). Specifically, in order to make the observation optical system small (thin), 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] To achieve such a small (thin) size, it is necessary to shorten the focal length to approximately the same as the distance from the optical surface facing the pupil plane SP to the display screen. In other words, to make the observation optical system small (thin), it is preferable that the focal length of the observation optical system is 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). At a wide viewing angle, shortening the focal length tends to deteriorate field curvature and astigmatic difference. Therefore, the smaller (thinner) the device, the greater the effect of this embodiment.

[0041] An effective means for shortening the focal length is to configure the pupil-plane-side optical system (first lens group) and the panel-side optical system (third lens group) so that their respective on-axis powers (refractive powers near the optical axis) are positive. In terms of imaging performance, the axial power of the transmission-reflection optical system is positive, so that all three optical systems have positive axial powers, making it easier to shorten the focal length compared to a configuration in which the axial power of either the pupil-plane-side optical system or the panel-side optical system, or both, is negative. In this example, the focal length of the pupil-plane-side optical system is 103.7 mm, and the focal length of the panel-side optical system is 31.3 mm, both of which are positive.

[0042] Here, we will explain the aspherical shapes of the optical surfaces that form interfaces with air in the pupil-plane-side optical system (first lens group) and the panel-side optical system (third lens group). To improve the field curvature and astigmatic difference while reducing the exit angle β, at least one optical surface in the effective light beam area must have a high-order aspherical shape. Specifically, the cross-sectional shape including the optical axis must be a shape that cannot be expressed by a conic section (i.e., an ellipse, a parabola, or a hyperbola).

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

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

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

[0046] 6A and 6B, both the first aspherical surface and the second aspherical surface have a shape in which the on-axis curvature crosses zero (i.e., inverts) as it moves off-axis (i.e., a shape having an inflection point). By providing a shape with such a local power distribution, it is possible to obtain the effect of improving the curvature of field and astigmatic difference while reducing the exit angle β. In this embodiment, both the first aspherical surface and the second aspherical surface have an inflection point in their cross sections, but this is not a limitation. It is sufficient that at least one cross section of the first aspherical surface or the second aspherical surface, including the optical axis, has an inflection point.

[0047] Furthermore, as can be seen from FIG. 6B , the local curvature has five extreme values ​​within the effective diameter. By adopting a shape that finely changes the local power so that the local curvature has three or more extreme values, the effect of improving the exit angle β, field curvature, and astigmatic difference is achieved across the entire angle of view. In particular, for a particularly wide field of view, 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-order derivative of the shape. Therefore, a local curvature having three or more extreme values ​​is equivalent to a second-order derivative of the shape having three or more extreme values. In other words, in this embodiment, it is preferable that at least one cross section of the first or second aspherical surface, including the optical axis, has a shape in which the second-order derivative has three or more extreme values.

[0048] In Fig. 5A, the shape of the paraxial curvature surface of the cross section including the optical axis of surface R1 of optical element 1101 is shown by a dotted line, and the difference from the cross section is shown by a double-chain line. Similarly, in Fig. 5B, the shape of the paraxial curvature surface of the cross section including the optical axis of surface R2 of optical element 1301 is shown by a dotted line, and the difference from the cross section is shown by a double-chain line. Note that the paraxial curvature surface means a spherical surface defined by the curvature near 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 asphericity). Although it is not proportional to the asphericity, it can be said that the effect of the present invention is greater when the asphericity is somewhat greater. Generally, the asphericity increases toward the maximum effective diameter end, and the effect of this embodiment is easily obtained if the asphericity is 30% or more at the maximum effective diameter end. More preferably, the effect of this embodiment can be fully obtained if the asphericity is 50% or more.

[0050] In this embodiment, in a cross section including the optical axis of at least one of the R1 surface of the optical element 1101 or the R2 surface of the optical element 1301, the sag amount of the shape of the paraxial curvature surface at the maximum effective diameter end is defined as SagR, and the sag amount of the aspheric surface (cross-sectional shape including the optical axis) is defined as SagA. In this case, 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, the effects of this embodiment can be fully obtained by setting the asphericity to 30% or more for the two aspheric surfaces, the surface R1 of the optical element 1101 and the surface R2 of the optical element 1301. In particular, the asphericity of the surface R2 of the optical element 1301 is 50% or more, which makes the effect even greater.

[0054] In this embodiment, the Abbe number of optical element 1201, referenced to the d-line, is v12, and the Abbe number of optical element 1301, which is cemented to optical element 1201 across the second transmissive-reflective surface, referenced to the d-line, is v13. In this case, v12 = 56.0, v13 = 22.38, and |v12 - v13| = 33.62. In this way, by using glass materials with an Abbe number difference of 20 or more on either side of the cemented surface, it is possible to reduce chromatic aberration while shortening the overall optical length. In this case, the effects of this embodiment can be obtained regardless of the combination of optical elements sandwiching any cemented surface in the optical system.

[0055] Here, as in this embodiment, it is also possible to adopt such a configuration in order to obtain the effect of reducing off-axis chromatic aberration rather than reducing chromatic aberration in the vicinity of the on-axis direction. With a cemented surface in the optical system sandwiched between them, the Abbe number of one optical element (one of two adjacent lenses) referenced to the d-line is denoted as v1, and the Abbe number of the other optical element (lens) referenced to the d-line is denoted as v2. In this case, 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 conditional expression (2) is set as in the following conditional expression (2a).

[0057] 25≦|ν1−ν2| (2a) More preferably, the numerical range of 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 bonding the external shapes of the optical elements 1101 and 1201 (P in FIG. 1A) and does not come into contact with air (does not touch air). In this way, by configuring the transmission-reflection surface not to come into direct contact with air, it is possible to prevent performance degradation and durability degradation due to moisture absorption. However, this embodiment is not limited to this, and it is preferable that at least one of the first transmission-reflection member or the second transmission-reflection member does not touch air.

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

[0060] In this embodiment, PMMA (acrylic resin), which has higher hardness and chemical resistance than ordinary resins, is used as the material for the optical element 1101 having the optical surface facing the pupil plane SP. Because the optical surface facing the pupil plane SP is likely to be touched by the observer, it generally meets strict anti-fouling standards. This eliminates the need for hard coating or anti-fouling glass, even in cases where the anti-fouling standards are stricter than usual, resulting in cost reduction.

[0061] Next, an optical system (observation optical system) 2000 according to a second embodiment of the present invention will be described. Note that in this embodiment, descriptions common to those in the first embodiment will be omitted. Fig. 7A is a cross-sectional view of the optical system 2000. The optical system 2000 has a pupil plane side optical system (first lens group) 2100, a first transmissive reflecting member (A), a transmissive reflecting optical system (second lens group) 2200, a second transmissive reflecting member (C), and a panel side optical system (third lens group) 2300.

[0062] The pupil plane side optical system 2100 has an optical element (first lens) 2101, the transmission / reflection 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. As described above, this embodiment has one pupil plane side optical system 2100, two transmission / reflection optical systems 2200, and one panel side optical system 2300, and optical elements (optical elements 2101, 2201, 2202, 2301) that refract, reflect, or diffract light rays. The R1 and R2 surfaces 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 and R2 surfaces of the optical element 2301 are both curved surfaces. The material of the optical element 2101 is PMMA (acrylic resin).

[0063] A light ray from the panel unit (display surface of the display element) 2400 passes through the panel-side optical system 2300 and the transmission-reflection optical system 2200, is reflected once each by the first transmission-reflection surface and the second transmission-reflection surface, passes through the transmission-reflection optical system 2200 and the pupil-plane-side optical system 2100, and proceeds toward the pupil plane SP. As a result, the optical system 2000 of this embodiment makes it possible to observe an optical image of the panel unit 2400 from the pupil plane SP where its exit pupil is located. The light that follows this optical path is designated as desired light, and the rest is designated as unwanted light.

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

[0065] The configuration of the panel unit 2400 is the same as that of the panel unit 1400 of Example 1. The transmissive-reflective surface (half mirror) C is vapor-deposited on the R1 surface of the optical element 2301. The first quarter-wave plate B is bonded to the R2 surface of the optical element 2201 and the R1 surface of the optical element 2201. The polarization-selective transmissive-reflective element A is bonded to the R2 surface of the optical element 2101 of the pupil-plane-side optical system 2100 and the R1 surface of the optical element 2201 of the transmissive-reflective optical system. In this example, 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.

[0066] 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. Note that, since this is the same as in Example 1, the explanation will be omitted.

[0067] In this embodiment, the nominal design field angle is also assumed to be a maximum half angle of 50°. Specifically, the maximum angle of the chief ray of the light beam passing through the pupil plane is set to 50°.

[0068] FIG. 9 shows the exit angle β (angle with respect to the normal to the display element) of the chief ray with respect to the half angle of view α of the optical system 2000 in this embodiment. In FIG. 9, the horizontal axis represents the half angle of view α (°), and the vertical axis represents the exit angle β (°). As shown in FIG. 9, the exit angle β is negative (−) when the light is emitted in a direction away from the optical axis, and positive (+) when the light is emitted in a direction toward the optical axis. From FIG. 9, it can be seen that the exit angle β at the maximum half angle of view is −23.3°, and the maximum absolute value of the exit angle β is less than 30° (when evaluating unevenness in light intensity, the evaluation is made using the absolute value, not positive or negative). In other words, by adopting the configuration of this embodiment, unevenness in light intensity can be reduced.

[0069] As described above, when only the influence of reflection is considered, a configuration in which both the first and second transmission-reflection surfaces have a concave shape toward the pupil plane, as shown in FIG. 3B, is preferable in terms of the output angle β and the half angle of view α. The configuration of this embodiment is less effective than that of Example 1, but is still sufficiently useful. Note that the manufacturing difficulty increases because the first transmission-reflection member is bonded to a curved surface. On the other hand, making the first quarter-wave plate curved would further increase the manufacturing difficulty, so it is not laminated on the first transmission-reflection member but is kept separate and remains flat.

[0070] In this embodiment, the optical elements 2101 and 2201, which are refractive optical elements, are bonded together via a first transmissive-reflective member including a first transmissive-reflective surface, and the optical elements 2202 and 2301, which are refractive optical elements, are bonded together via a second transmissive-reflective member including a second transmissive-reflective surface. As in the first embodiment, by sandwiching the transmissive-reflective member including the transmissive-reflective surface between the refractive optical elements, the refractive power of the transmissive-reflective surface can be reduced compared to when 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 consider the influence of the reflective power, which increases the degree of freedom in optical design and enables the imaging performance to be improved while reducing the exit angle β.

[0071] In particular, in this embodiment, unlike in Example 1, the first transmissive-reflective surface also has a concave shape on the pupil plane side, and is configured to have a large reflective power, which makes it easier to ensure imaging performance at a wide viewing angle. In other words, the above-described configuration is highly effective. As a result, as shown in FIG. 7B , this embodiment can achieve better imaging performance, including field curvature, than Example 1. According to this embodiment, it is possible to ensure freedom in optical design and achieve the effect of achieving high-definition images.

[0072] In this embodiment, the distance from the pupil-facing surface to the display element is 15.5 mm, which is sufficiently small (thin) as in Example 1. Also, in this embodiment, the focal length is 14.5 mm, which is sufficiently small (thin) as in Example 1. Also, in this embodiment, the focal length of the pupil-plane-side optical system is 206.8 mm, and the focal length of the panel-side optical system is 23.7 mm, both of which are positive. This allows the focal length to be shortened, and therefore the device can be made small (thin) as in Example 1.

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

[0074] 11A shows the local curvature of the cross-sectional shape of the R1 surface of the optical element 2101, which includes the optical axis. FIG. 11B shows the local curvature of the cross-sectional shape of the R2 surface of the optical element 2301, which includes the optical axis. In FIGS. 11A and 11B, the horizontal axis represents the distance y (mm), and the vertical axis represents the curvature (1 / mm). As in Example 1, both the R1 surface and the R2 surface have a shape in which the curvature of the on-axis curvature is inverted as it moves off-axis (i.e., a shape having an inflection point). By providing a shape with such a local power distribution, it is possible to obtain the effect of improving the field curvature and astigmatic difference while reducing the exit angle β.

[0075] 11A and 11B, the local curvature has five extreme values ​​within the effective diameter, as in Example 1. By providing a shape that allows the local power to be varied finely so that the local curvature has three or more extreme values, the exit angle β, field curvature, and astigmatic difference can be improved over the entire range of the angle of view. In particular, in the case of a particularly wide viewing angle, as in this example, it is preferable to have at least one such aspherical surface.

[0076] 10A further shows by dotted lines the shape of the paraxial curvature surface of the cross section including the optical axis of surface R1 of optical element 2101, and the difference from the cross section is shown by double-chain lines. Similarly, Fig. 10B further shows by dotted lines the shape of the paraxial curvature surface of the cross section including the optical axis of surface R2 of optical element 2301, and the difference from the cross section is shown by double-chain lines.

[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 surface R2 of 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, the effect of this embodiment can be fully obtained by setting the asphericity to 30% or more on the R2 surface (one aspheric surface) of the optical element 2301. Furthermore, in this embodiment, the asphericity is 50% or more, which provides an even greater effect.

[0080] Here, the asphericity of surface R1 of optical element 2101 is 30% or less, and although the effect of this embodiment is obtained, the effect is not significant. As described above, this embodiment is configured such that both the first transmissive-reflective surface and the second transmissive-reflective surface have a concave shape toward the pupil plane, and is advantageous compared to Example 1 in terms of the exit angle β and half angle of view α. Therefore, the effect of this embodiment can be sufficiently obtained even without providing multiple surfaces with an asphericity of 30% or more. In this way, the effect of this embodiment can be obtained as long as at least one surface has the above-mentioned aspherical surface.

[0081] In this embodiment, the Abbe number of the optical element 2101 based on the d-line is defined as v21, and the Abbe number of the optical element 2201 bonded to the optical element 2101 across the first transmitting-reflecting surface is defined as v22 based on the d-line. In this case, v21 = 57.4, v22 = 27.0, and |v21 - v22 | = 30.4. Similarly, the Abbe number of the optical element 2101 based on the d-line is defined as v22, and the Abbe number of the optical element 2202 bonded to the optical element 2101 across the first quarter-wave plate B is defined as v23 based on the d-line. In this case, v22 = 27.0, v23 = 56.0, and |v22 - v23 | = 29.0. Similarly, the Abbe number of the optical element 2202 with respect to the d-line is v23, and the Abbe number of the optical element 2301 bonded to the optical element 2202 with the second transmission-reflection surface therebetween is v24 with respect to the d-line. In this case, v23=56.0, v24=22.38, and |v23-v24|=33.62.

[0082] In this way, by using glass materials with an Abbe number difference of 20 or more on either side of the cemented surface, it is possible to reduce chromatic aberration while shortening the overall optical length. As a result, in this embodiment, chromatic aberration can be improved over a wider range of angle of view than in Example 1, as shown in FIG.

[0083] In this embodiment, the presence of a cemented surface where the optical element 2101 and the optical element 2202 are cemented with the first quarter-wave plate B sandwiched therebetween in the transmissive-reflective optical system 2200 contributes to reducing chromatic aberration. The shapes of the first transmissive-reflective surface and the second transmissive-reflective surface contribute to the overall imaging performance, and therefore do not have design freedom primarily aimed at reducing chromatic aberration. In other words, the cemented lens sandwiching the first transmissive-reflective surface and the second transmissive-reflective surface has the effect of reducing chromatic aberration, but the effect is limited.

[0084] In this embodiment, at least one of the pupil plane side optical system, the transmission / reflection optical system, and the panel side optical system has a cemented surface (a cemented lens formed by cementing together multiple lenses). In this case, the shape of the cemented surface has a degree of freedom in design with the primary objective of reducing chromatic aberration, and therefore a high chromatic aberration reduction effect can be obtained. In particular, if the transmission / reflection optical system has a cemented surface, the effect is even greater because light rays pass through the cemented surface three times.

[0085] In this example, similar to Example 1, 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 and does not come into contact with air by bonding (P in FIG. 7A ) the outer shapes of the optical element 2101 and the optical element 2201. This makes it possible to prevent performance degradation and durability degradation due to moisture absorption.

[0086] In this embodiment, PMMA (acrylic resin) is used as the material of the optical element 2101 that forms the pupil-facing surface that faces the pupil plane SP, as in embodiment 1. This eliminates the need to provide a hard coating or anti-fouling glass, even in cases where anti-fouling standards are stricter than usual, and provides the effect of reducing costs.

[0087] Next, an optical system (observation optical system) 3000 according to a third embodiment of the present invention will be described. Note that in this embodiment, descriptions common to those in the first embodiment will be omitted. Fig. 12A is a cross-sectional view of the optical system 3000. The optical system 3000 has a pupil plane side optical system (first lens group) 3100, a first transmissive reflecting member (A), a transmissive reflecting optical system (second lens group) 3200, a second transmissive reflecting member (C), and a panel side optical system (third lens group) 3300.

[0088] The pupil plane 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. As described above, this embodiment has one pupil plane 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 surface and the R2 surface of the optical element 3301 are both curved surfaces. The material of the optical element 3101 is PMMA (acrylic resin).

[0089] A light ray from the panel unit (display surface of the display element) 3400 passes through the panel-side optical system 3300 and the transmission-reflection optical system 3200, is reflected once each by the first transmission-reflection surface and the second transmission-reflection surface, passes through the transmission-reflection optical system 3200 and the pupil-plane-side optical system 3100, and proceeds toward the pupil plane SP. As a result, the optical system 3000 of this embodiment makes it possible to observe an optical image of the panel unit 3400 from the pupil plane SP where its exit pupil is located. The light that follows this optical path is designated as desired light, and the rest is designated as unwanted light.

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

[0091] In particular, the field curvature (imaging performance) is better than in Example 1, and the reason for this will be described later.

[0092] The configuration of the panel unit 3400 is the same as that of the panel unit 1400 of Example 1. The transmissive-reflective surface (half mirror) C is vapor-deposited on the R1 surface of the optical element 3301. The first quarter-wave plate B is bonded 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 bonded to the R2 surface of the optical element 3101 of the pupil-plane-side optical system 3100. In this example, 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] 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. Note that since this is the same as in Example 1, the description will be omitted.

[0094] In this embodiment, too, a maximum half angle of 50° is assumed as the design nominal field of view. 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 of the chief ray (angle relative to the normal to the display element) relative to the half angle of view α of the optical system 3000 in this embodiment. In FIG. 14, the horizontal axis represents the half angle of view α (°), and the vertical axis represents the exit angle β (°). As shown, the exit angle β is negative (−) when emitted in a direction away from the optical axis, and positive (+) when emitted in a direction toward the optical axis. From FIG. 14, it can be seen that the exit angle β at the maximum half angle of view is −29.1°, and the maximum absolute value of the exit angle β is less than 30° (when evaluating light intensity unevenness, the evaluation is based on the absolute value, not on positive or negative). In other words, the configuration of this embodiment can reduce light intensity unevenness.

[0095] In this embodiment, the optical elements 3101 and 3201, which are refractive optical elements, are bonded together via a first transmissive-reflective member including a first transmissive-reflective surface, and the optical elements 3201 and 3301, which are refractive optical elements, are bonded together via a second transmissive-reflective member including a second transmissive-reflective surface. As in the first embodiment, by sandwiching a transmissive-reflective member including a transmissive-reflective surface between refractive optical elements, the refractive power of the transmissive-reflective surface can be reduced compared to when 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 consider the influence of the reflective power, which increases the degree of freedom in optical design and allows for improved imaging performance while reducing the exit angle β. This embodiment ensures the degree of freedom in optical design and can achieve the effect of achieving high-resolution images.

[0096] Furthermore, this embodiment is configured with a total of three optical elements, one for each of the pupil plane side optical system, the transmission / reflection optical system, and the panel side optical system, and is therefore preferable from the standpoints of cost and manufacturing because it is the minimum number of optical elements required to obtain the effects described above.

[0097] In this embodiment, the distance from the pupil-facing surface to the display element is 17.0 mm, which is sufficiently small (thin) as in Example 1. Also, in this embodiment, the focal length is 15.0 mm, which is sufficiently small (thin) as in Example 1. Also, in this embodiment, the focal length of the pupil-plane-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. This allows the focal length to be shortened, and therefore the device can be made small (thin) as in Example 1.

[0098] As in Example 1, the aspheric shapes of the optical surfaces that form interfaces with air in the pupil plane side optical system and the panel side optical system will be described. Fig. 15(A) shows, with a solid line, the cross-sectional shape of surface R1 of optical element 3101, including the optical axis. Fig. 15(B) shows, with a solid line, the cross-sectional shape of surface R2 of optical element 3301, including the optical axis. In Figs. 15(A) and 15(B), the horizontal axis represents distance y (mm), and the vertical axis represents position z (mm) in the optical axis direction. As in Example 1, both surfaces R1 and R2 have shapes that cannot be expressed by a conic section.

[0099] FIG. 16A shows the local curvature of the cross-sectional shape of the R1 surface of the optical element 3101, including the optical axis. FIG. 16B shows the local curvature of the cross-sectional shape of the R2 surface of the optical element 3301, including the optical axis. In FIGS. 16A and 16B, the horizontal axis represents the distance y (mm), and the vertical axis represents the curvature (1 / mm). As in Example 1, both the R1 surface and the R2 surface have a shape in which the curvature inverts as the curvature on the axis moves off-axis (i.e., a shape having an inflection point). By providing a shape with such a local power distribution, it is possible to obtain the effect of improving the field curvature and astigmatic difference while reducing the exit angle β.

[0100] 16B, the local curvature has five extreme values ​​within the effective diameter, as in Example 1. By providing a shape that allows the local power to be varied finely so that the local curvature has three or more extreme values, the exit angle β, field curvature, and astigmatic difference can be improved over the entire range of the angle of view. In particular, in the case of a particularly wide viewing angle, as in this example, it is preferable to have at least one aspherical surface.

[0101] 15A further shows by dotted lines the shape of the paraxial curvature surface of the cross section including the optical axis of surface R1 of optical element 3101, and the difference from the cross section is shown by double-chain lines. Similarly, Fig. 15B further shows by dotted lines the shape of the paraxial curvature surface of the cross section including the optical axis of surface R2 of optical element 3301, and the difference from the cross section is shown by double-chain lines.

[0102] At the maximum effective diameter end (Φ34) of the R1 surface of the optical element 3101, the sag amount SagA of the cross-sectional shape including the optical axis 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] Similarly, at the maximum effective diameter end (Φ30) of surface R2 of 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, the effects of this embodiment can be fully achieved by providing an asphericity of 30% or more for one aspheric surface, the R2 surface of the optical element 3301. Here, the asphericity of the R1 surface of the optical element 3101 is 30% or less, and while the effects of this embodiment are achieved, they are not significant. This is because, as can be seen from FIG. 12B or FIG. 14 , emphasis is placed on the imaging performance in terms of the balance between imaging performance and the exit angle β, compared to Example 1, and the exit angle β is allowed. Thus, although the effects vary depending on the design concept, the effects of this embodiment can be achieved as long as there is at least one aspheric surface as described above.

[0105] In this embodiment, the Abbe number of the optical element 3201 with respect to the d-line is v32, and the Abbe number of the optical element 3301 cemented to the optical element 3201 with the second transmitting-reflecting surface therebetween is v33 with respect to the d-line. In this case, v32 = 57.4, v33 = 22.38, and |v32 - v33| = 33.62. In this way, by using glass materials with an Abbe number difference of 20 or more on both sides of the cemented surface, it is possible to reduce chromatic aberration while shortening the overall optical length.

[0106] In this example, similar to Example 1, 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 and does not come into contact with air by bonding (P in FIG. 12A ) the outer shapes of the optical elements 3101 and 3201. This makes it possible to prevent performance degradation and durability degradation due to moisture absorption.

[0107] In this embodiment, PMMA (acrylic resin) is used as the material of the optical element 3101 that forms the pupil-facing surface that faces the pupil plane SP, as in embodiment 1. This eliminates the need to provide a hard coating or anti-fouling glass, even in cases where anti-fouling standards are stricter than usual, and provides the effect of reducing costs.

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

[0109] An asterisk (*) next to a surface number indicates that the surface has an aspherical shape. The aspherical shape is expressed by the following equation, where x is the displacement in the optical axis direction at a position of height h from the optical axis relative to the vertex of the surface, 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]

[0111] [Numerical Example 1] Unit: mm Surface data Surface number rd nd νd 1 (Aperture) ∞ 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 surface ∞ Aspheric surface data Surface 2 K =-1.00000e+00 A 4=-3.67428e-05 A 6= 1.66514e-07 A 8=-4.76007e-10 A10= 5.37368e-13 A12=-5.04034e-16 Surface 5 K =-3.00000e+00 A 4=-6.65066e-06 A6= 5.18014e-09 A8= 6.70726e-12 A10=-3.76426e-14 9th surface K =-3.00000e+00 A4=-6.65066e-06 A6= 5.18014e-09 A8= 6.70726e-12 A10=-3.76426e-14 10th 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 rd nd νd 1(Aperture) ∞ 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 surface ∞ Aspheric surface data Surface 2 K =-1.00000e+00 A 4= 3.60054e-06 A 6=-9.35703e-08 A 8= 5.14016e-10 A10=-8.55095e-13 3rd side K = 6.00000e+00 A 4= 8.43436e-06 A 6= 1.55821e-09 A 8= 1.89611e-11 4th side K = 6.00000e+00 A 4= 8.43436e-06 A 6= 1.55821e-09 A 8= 1.89611e-11 7th side K =-1.00000e+00 A 4= 1.42878e-06 A 6=-1.21058e-08 A 8= 3.83502e-11 10th side K = 6.00000e+00 A 4= 8.43436e-06A 6= 1.55821e-09 A 8= 1.89611e-11 11th side K = 6.00000e+00 A 4= 8.43436e-06 A 6= 1.55821e-09 A 8= 1.89611e-11 12th side K = 6.00000e+00 A 4= 8.43436e-06 A 6= 1.55821e-09 A 8= 1.89611e-11 Surface 15 K =-1.00000e+00 A4= 1.42878e-06 A6=-1.21058e-08 A8= 3.83502e-11 Surface 16 K =-1.00000e+00 A4= 3.25883e-04 A6=-1.72091e-06 A8= 3.57618e-09 Focal length 14.45 [Numerical Example 3] Unit: mm Surface data Surface number rd 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 surface ∞ Aspheric surface data Surface 2 K = 0.00000e+00 A 4=-5.49562e-06 A 6= 1.36131e-09 A 8=-9.48412e-12 A10=-5.32998e-14 Surface 5 K = 0.00000e+00 A 4=-2.07747e-07 A 6= 2.51349e-10 A 8=-2.99711e-12 Surface 9 K = 0.00000e+00 A 4=-2.07747e-07 A 6= 2.51349e-10 A 8=-2.99711e-12 Surface 10 K = 0.00000e+00 A4= 4.97609e-05 A6=-2.65664e-07 A8= 3.67150e-10 Focal length 14.99 Although preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments and various modifications and variations are possible within the scope of the invention.

[0112] For example, when combined with a display element such as an OLED (organic light-emitting diode) or LCD (liquid crystal display), electrical processing may be added to the display side depending on the amount of distortion aberration and lateral chromatic aberration. In each embodiment, one of the first and second transmission-reflection surfaces is preferably a polarization-selective transmission-reflection element (reflective polarizer) PBS. In this case, the other of the first and second transmission-reflection surfaces is preferably a half mirror with a transmittance-to-reflectance ratio of 1:1. However, the transmittance-to-reflectance ratio may be changed as necessary. The optical system of each embodiment may further include another optical system (lens) on the pupil plane side of the first lens group. Similarly, the optical system of each embodiment may further include another optical system (lens) on the display surface side of the third lens group. In the optical system of Example 1, at least one other lens may be inserted in the gap of the second lens group (between the second lens and the third lens).

Claims

1. An optical system that guides a light beam from a display surface to a pupil surface, comprising, arranged 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, wherein at least one optical surface of the first lens group that interfaces with air is a first aspheric surface, and at least one optical surface of the third lens group that interfaces with air is a second aspheric surface.

2. The optical system according to claim 1, wherein said first transmissive reflecting surface is a flat surface.

3. The optical system according to claim 1 or 2, characterized in that a cross section including the optical axis of at least one of said first aspheric surface or said second aspheric surface has a shape that cannot be expressed by a conic section.

4. The optical system according to any one of claims 1 to 3, characterized in that a cross section including the optical axis of at least one of the first aspheric surface or the second aspheric surface has a shape having an inflection point.

5. The optical system according to any one of claims 1 to 4, characterized in that a cross section of at least one of the first aspheric surface or the second aspheric surface, which cross section includes the optical axis, has a shape in which the second-order differential has three or more extreme values.

6. The optical system according to any one of claims 1 to 5, characterized in that in a cross section including the optical axis of at least one of the first aspheric surface or the second aspheric surface, the condition 0.3≦|(SagA-SagR) / SagR| is satisfied, where SagR is the sag amount of the paraxial curvature surface at the maximum effective diameter end, and SagA is the sag amount of the aspheric surface.

7. The optical system according to any one of claims 1 to 6, characterized in that the refractive power of each of the first lens group and the third lens group in the vicinity of the optical axis is positive.

8. An optical system described in any one of claims 1 to 7, characterized in that the lens in the second lens group closest to the display surface and the lens in the third lens group closest to the pupil surface are cemented together via the second transmissive reflecting member.

9. An optical system described in any one of claims 1 to 8, characterized in that the lens in the first lens group closest to the display surface and the lens in the second lens group closest to the pupil surface are cemented together via the first transmissive reflecting member.

10. The optical system described in any one of claims 1 to 9, characterized in that 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 cemented together via the first transmissive reflecting member, and the second lens and the third lens are cemented together via the second transmissive reflecting member.

11. The optical system according to any one of claims 1 to 10, characterized in that the distance from the optical surface opposing the pupil plane to the display surface is 20 mm or less.

12. The optical system according to any one of claims 1 to 11, characterized in that the focal length of the optical system is 20 mm or less.

13. An optical system according to any one of claims 1 to 12, characterized in that the maximum angle of the chief ray of the light beam passing through the pupil plane is 30° or more, and the absolute value of the maximum value of the exit angle of the chief ray from the display element is 35° or less.

14. An optical system according to any one of claims 1 to 13, characterized in that the exit angle of the chief ray passing through the pupil plane from the display element is in a direction away from the optical axis at the end angle of view of the display element, and the diagonal length of a square circumscribing the display element is 1.6 inches or less.

15. An optical system according to any one of claims 1 to 14, characterized in that it has at least one combination that satisfies the condition: 20≦|ν1-ν2|, where ν1 is the Abbe number based on the d-line of one of two adjacent lenses and ν2 is the Abbe number based on the d-line of the other lens.

16. The optical system according to any one of claims 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 together.

17. The optical system according to any one of claims 1 to 16, characterized in that at least one of the first transmissive reflecting member and the second transmissive reflecting member is not in contact with air.

18. The optical system according to any one of claims 1 to 17, characterized in that the optical element in the first lens group closest to the pupil plane is made of acrylic resin.

19. A display device comprising the optical system according to any one of claims 1 to 18 and a display element.

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