Display optical system and display device

Abstract

To provide a display optical system having small birefringence and hardly causing interference with the face of an observer.SOLUTION: The display optical system guides light from the display element 108 to the observation side. The display optical system includes a first lens 104, a second lens 105 adjacent to the first lens on the display element side, and at least two transmissive reflective surfaces 112 and 114. The first and second lenses are each formed in a non-circular shape when viewed from a direction in which an optical axis of the display optical system extends. When a degree of difference between the non-circular shape and the circular shape is referred to as a non-circularity, the non-circularities of the first and second lenses are different from each other.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a display optical system suitable for a display device such as a head-mounted display (HMD) that guides light from a display element to the eyes of a viewer. [Background technology]

[0002] As such a display optical system, Patent Documents 1 and 2 disclose optical systems that achieve a thinner design and a wider angle of view by folding the optical path using polarized light. When using a resin lens to reduce the weight of such a display optical system, if the resin lens has a large birefringence, an appropriate polarization state cannot be obtained, resulting in a decrease in the amount of light guided to the eye and the generation of unwanted light (ghosts).

[0003] If the resin lens is made circular to reduce birefringence within the lens, the lens will interfere with the viewer's face (nose, forehead, etc.). On the other hand, the non-circular lens used in Patent Document 2 can avoid interference with the viewer's face, but the heat from the display element tends to increase birefringence. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Special Publication No. 2018-512602 [Patent Document 2] Japanese Patent Application Publication No. 2019-053151 Summary of the Invention [Problem to be solved by the invention]

[0005] For these reasons, there is a demand for a display optical system that uses a non-circular resin lens that has small birefringence and can reduce interference with the viewer's face. [Means for solving the problem]

[0006] A display optical system according to one aspect of the present invention guides light from a display element to a viewing side. The display optical system includes a first lens, a second lens adjacent to the first lens on the display element side, and at least two transmissive / reflective surfaces. When viewed in the direction of the optical axis of the display optical system, the first and second lenses are each formed to be non-circular. When the degree of difference between a non-circular shape and a circular shape is referred to as non-circularity, the first and second lenses have different degrees of non-circularity. Note that a display device including the above-described display optical system also constitutes another aspect of the present invention. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a display optical system that suppresses birefringence and is less likely to cause interference with the viewer's face. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view of a display device according to a first embodiment. [Figure 2] FIG. 1 is a cross-sectional view showing the configuration of a display optical system according to a first embodiment. [Figure 3] FIG. 1 is an external view of a display device according to a first embodiment. [Figure 4] FIG. 2 is an optical path diagram of the display optical system according to the first embodiment. [Figure 5] FIG. 2 is a diagram showing a first lens in the first embodiment. [Figure 6] FIG. 3 is an explanatory diagram of a second lens in the first embodiment. [Figure 7] FIG. 10 is a cross-sectional view of a display device according to a second embodiment. [Figure 8] FIG. 10 is a cross-sectional view of a display optical system according to a second embodiment. [Figure 9] FIG. 10 is a diagram showing the optical path of a display optical system according to a second embodiment. [Figure 10] FIG. 10 is a diagram showing a first lens in Example 2. [Figure 11] FIG. 10 is a diagram showing a second lens in Example 2. [Figure 12] FIG. 10 is a diagram showing cemented first and second lenses in Example 2. [Figure 13] FIG. 10 is a cross-sectional view of a display device as a modified example of the second embodiment. [Figure 14] FIG. 10 is a diagram showing a camera and cemented first and second lenses in Example 2. [Figure 15] FIG. 10 is a cross-sectional view of a display device according to a third embodiment. [Figure 16] FIG. 10 is a cross-sectional view of a display optical system according to a third embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, an embodiment of the present invention will be described with reference to the drawings. [Example]

[0010] Fig. 3 shows the appearance of an HMD 101 as a display device of Example 1. Fig. 1 shows the configuration of the HMD 101. Reference numeral 102 denotes the right eye of the observer, and 103 denotes the left eye of the observer.

[0011] The HMD 101 is composed of right eye optical systems (104, 105) and left eye optical systems (106, 107) as display optical systems, and a right eye display element 108 and a left eye display element 109. In the right eye optical systems and left eye optical systems, the side where the eyes 102, 103 are located is called the observation side, and the side where the display elements 108, 109 are located is called the display element side. The direction in which the optical axes of the right eye optical systems and left eye optical systems extend is called the optical axis direction.

[0012] The right-eye optical system has, arranged in order from the observation side, a first lens 104 and a second lens 105 adjacent to the first lens 104 on the display element side. The left-eye optical system has, arranged in order from the observation side, a first lens 106 and a second lens 107 adjacent to the first lens 106 on the display element side. The display elements 108 and 109 are each organic EL displays that emit unpolarized light. The right-eye optical system and the left-eye optical system guide light from the right-eye display element 108 and the left-eye display element 109 to the observer's right eye 102 and left eye 103, respectively, allowing the observer to observe an enlarged virtual image (display image) of the original image displayed on each display element.

[0013] In this example, the focal length of each of the right-eye optical system and the left-eye optical system is 12 mm, the horizontal display angle of view is 55°, the vertical display angle of view is 40°, and the diagonal display angle of view is 65°. The distance between the HMD 101 and the observer's eyes (eye relief) is 20 mm. Note that in order for the observer to observe an image with a high sense of realism, it is preferable that the diagonal display angle of view be 60° or more.

[0014] The distance on the optical axis from the observation-side surfaces of the first lenses 104 and 106 to the display element-side surfaces of the second lenses 105 and 107 is 12.5 mm, resulting in a thin optical system. The first lenses 104 and 106 and the second lenses 105 and 107 are adjacent to each other with an air gap between them. In order to make each optical system thin, it is preferable that the distance on the optical axis from the observation-side surfaces of the first lenses 104 and 106 to the display element-side surfaces of the second lenses 105 and 107 be 15 mm or less.

[0015] The right-eye optical system and the left-eye optical system of this embodiment are optical systems that fold the optical path using polarized light. The optical path will be explained using FIGS. 1 and 2. FIG. 2 shows a detailed configuration of the right-eye optical system. A polarizing plate 110 and a phase plate 111 are arranged between the right-eye display element 108 and the second lens 105, in that order from the display element side. A half mirror 112 that forms a first transmissive-reflective surface is vapor-deposited on the surface of the first lens 104 facing the second lens 105. Furthermore, on the observation side of the first lens 104, in that order from the display element side, a phase plate 113 and a polarization splitting surface (hereinafter referred to as PBS) 114 that serves as a second transmissive-reflective surface provided with a polarization splitting element are arranged. Both the phase plate 113 and the PBS 114 have a planar shape.

[0016] Both phase plate 111 and phase plate 113 are quarter-wave plates that impart a phase difference of λ / 4 to light passing through them. The slow axis of phase plate 111 is tilted at 45° with respect to the polarization direction of linearly polarized light passing through polarizer 110, and the slow axis of phase plate 113 is tilted at −45° with respect to the polarization direction of linearly polarized light passing through polarizer 110. Furthermore, the polarization direction of linearly polarized light passing through polarizer 110 and the polarization direction of linearly polarized light passing through PBS 114 are perpendicular to each other.

[0017] Of the unpolarized light emitted from the right-eye display element 108, linearly polarized light that passes through the polarizing plate 110 passes through the phase plate 111 and is converted into circularly polarized light. The circularly polarized light passes through the half mirror 112 and then passes through the phase plate 113 and is converted into linearly polarized light. Because the polarization direction of this linearly polarized light is orthogonal to the polarization direction of light passing through the PBS 114, it is reflected by the PBS 114 and passes through the phase plate 113 and is converted into circularly polarized light. The circularly polarized light is reflected by the half mirror 112 and passes through the phase plate 113 and is converted into linearly polarized light. Because the polarization direction of this linearly polarized light matches the polarization direction of light passing through the PBS 114, it passes through the PBS 114 and is directed to the right eye 102. The configuration and optical path of the left-eye optical system are the same as those of the right-eye optical system.

[0018] By folding the optical path using polarized light as described above, it is possible to achieve a thin display optical system with a short focal length and a wide angle of view.

[0019] As shown in Figure 4, the position of the exit pupil of the display optical system is set to 30 mm, which is the eye relief of 20 mm plus the eyeball rotation radius of 10 mm, and the exit pupil diameter is set to 6 mm. This ensures that even when the eyeball rotates to observe up, down, left, or right, light is incident on the eyeball in the direction of the rotation. Because the HMD is worn on the observer's head (in front of the face), and also so that observers wearing eyeglasses can wear it, it is preferable that the eye relief be 15 mm or more. If the eye relief is too long, the outer diameter of the lens will become larger, and the HMD will also become larger. Therefore, it is preferable that the eye relief be 25 mm or less.

[0020] Furthermore, it is preferable that the HMD worn on the head is lightweight. For this reason, it is preferable that the lenses constituting the display optical system are lenses (resin lenses) made of a resin material having a lower specific gravity than glass. In this embodiment, the first lenses 104, 106 and the second lenses 105, 106 are resin lenses, and the first lenses 104, 106 are aspherical lenses with a plano-convex shape, thereby enhancing the aberration correction effect. Furthermore, both surfaces of the second lenses 105, 107 are aspherical.

[0021] 1 are provided with a nose relief portion 101a and a forehead relief portion so that the HMD 101 does not interfere with parts of the face (nose or forehead) when worn by a viewer. For this reason, as shown in Figures 5 and 6, the first lenses 104, 106 and the second lenses 105, 106 are not circular when viewed from the optical axis direction, but are formed in a non-circular shape with the outer shapes on the nose side and forehead side being smaller.

[0022] However, molded resin lenses (especially lenses made of thermoplastic resin) tend to retain birefringence due to residual stress during molding. When a birefringent lens is used, a phase difference is imparted to the light passing through it, preventing the light from maintaining its proper polarization state. This results in the generation of unwanted light (ghost light) that is guided directly to the viewer's eye without being reflected by the PBS 114, rather than following the normal optical path shown in Figure 1. Furthermore, even after reflection by the PBS 114, an unwanted phase difference is imparted to the light along the normal optical path, which may ultimately result in a portion of the light that should be transmitted by the PBS 114 being reflected, reducing the amount of light in the displayed image. Therefore, it is ideal for each lens to have a circular shape as viewed from the optical axis direction. A circular lens shrinks isotropically during molding, reducing the internal birefringence of the lens. However, as mentioned above, each lens must be formed noncircular.

[0023] Therefore, in this embodiment, each lens is formed into a non-circular shape, while reducing the birefringence that occurs during molding of the lens. Specifically, as shown in Figures 5 and 6, the nose-side and forehead-side portions of the first lenses (104, 106) and the second lenses (105, 107) are made non-circular by making the shapes closer to a straight line than the other arc-shaped portions (hereinafter referred to as arc portions) of the lenses.

[0024] Here, the degree of difference (deviation) between a non-circular shape and a circular shape is referred to as non-circularity. In this embodiment, the non-circularity of the first lens and the non-circularity of the second lens are made different from each other. More specifically, the non-circularity of the second lens is made smaller than the non-circularity of the first lens.

[0025] In this embodiment, as shown in Figures 1 and 2, the end face of the non-circular lens on the nose relief side is formed at an angle to the optical axis. Furthermore, the first and second lenses are directly molded as non-circular lenses, rather than cutting the nose-side and forehead-side portions of circular lenses. This simplifies the manufacturing of each lens (eliminating the cutting process).

[0026] As shown in Figures 5 and 6, the non-circular shapes of the first lenses (104, 106) and the second lenses (105, 107) can be said to be shapes in which the distance from the optical axis C (the centers of circles CL1 and CL2 described below) to some of the outer peripheries of the lenses is shorter than the distance from the optical axis C to other parts of the outer peripheries of the lenses. In this example, the distance r11 from the optical axis to the arc-shaped portion of the first lens (the maximum distance from the optical axis to the outer periphery, which is the radius of the circle CL1 in which the first lens is inscribed) is set to 20 mm, and the minimum distance r12 from the optical axis to the non-arcuate portion is set to 15 mm. If the degree of non-circularity is defined as the ratio of the difference between the maximum and minimum values ​​of the above distances to the maximum value, then it is 5 / 20 = 0.25.

[0027] Meanwhile, the distance r21 from the optical axis to the arc portion of the second lens (the maximum distance from the optical axis to the outer periphery, which is the radius of the circle CL2 inscribed in the second lens) is set to 20 mm, and the minimum distance r22 from the optical axis to the non-arc portion is set to 17.5 mm. If the non-circularity is defined as the ratio described above, it is 2.5 / 20 = 0.13. Thus, the non-circularity of the second lens is smaller than that of the first lens. In other words, the shape of the second lens is closer to a circle than that of the first lens.

[0028] The degree of non-circularity of the first lens, as defined above, is preferably 0.2 or more and 0.3 or less. If the degree of non-circularity is less than 0.2, the relief amount of the nose relief portion 101a and the forehead relief portion becomes too small, causing the HMD 101 to interfere with the viewer's nose or forehead, which is undesirable. If the degree of non-circularity is greater than 0.3, the birefringence of the first lens becomes large, causing ghost light and significant reduction in light intensity, which is undesirable.

[0029] Furthermore, the degree of non-circularity of the second lens, as defined above, is preferably 0.1 or more and less than 0.2. If the degree of non-circularity is less than 0.1, the relief amount of the nose relief portion and the forehead relief portion becomes too small, causing the HMD 101 to interfere with the observer's nose or forehead, which is undesirable. If the degree of non-circularity is 0.2 or more, the birefringence of the second lens becomes large, causing ghost light and significant reduction in light intensity, which is also undesirable.

[0030] In a display optical system using polarized light as in this embodiment, it is preferable from the perspective of aberration correction that the resin material of the first lens has a low refractive index and low dispersion, and that the resin material of the second lens has a higher refractive index and higher dispersion than the material of the first lens. However, because the materials mixed with the resin material to increase its refractive index have a large birefringence, resin materials with a high refractive index tend to have a large birefringence. Table 1 shows the refractive index at the d-line, Abbe number based on the d-line, and photoelastic coefficient of the resin materials of the first lens 104 (106) and the second lens 105 (107) in this embodiment.

[0031] [Table 1]

[0032] As can be seen from Table 1, the refractive index of the second lens 105 is greater than the refractive index of the first lens 104, and therefore the birefringence of the second lens 105 is greater than the birefringence of the first lens 104. Specifically, the photoelastic constant of the first lens 104 is 8×10 -12 [1 / Pa], the second lens 105 is 48 x 10 -12 [1 / Pa], and the second lens 105 is larger.

[0033] In order to reduce the birefringence of the non-circular lens, the photoelastic constant of the first lens 104 is 10×10 -12 [1 / Pa] or less, and the photoelastic constant of the second lens 105 is preferably 50×10 -12 It is preferable that the value is [1 / Pa] or less.

[0034] In order to reduce the birefringence of the display optical system, it is necessary to make second lens 105, which is made of a resin material with high birefringence, into a shape with small non-circularity. For this reason, the non-circularity of second lens 105 is made smaller than the non-circularity of first lens 104.

[0035] By doing so, the first lens and the second lens can be made non-circular so that the HMD 101 does not interfere with the viewer's nose or forehead, and birefringence that occurs when molding each lens can be kept small.

[0036] Considering the shape of the viewer's face, the relief amounts of the nose relief and forehead relief areas can be small when they are farther away from the eyes. For this reason, the HMD 101 will not interfere with the viewer's face even if the non-circularity of the second lens is smaller than that of the first lens, thereby reducing the relief amounts.

[0037] 5 and 6, the non-circularity of the first lenses (104, 106) and the second lenses (105, 107) can be said to be such that a portion of the outer periphery of the lens is closer to the optical axis than the circles CL1 and CL2 inscribed in the lenses. In this case, the non-circularity can also be defined as the ratio of the difference between the areas A1' and A2' of the first and second lenses, respectively, and the areas A1 and A2 of the circles CL1 and CL2 to the areas A1 and A2 of the circles CL1 and CL2. In this example, the non-circularity of the first lens is 0.07, and the non-circularity of the second lens is 0.03, which is smaller than the non-circularity of the first lens.

[0038] As described above, when the non-circularity is expressed as a ratio of area, the non-circularity of the first lens is preferably 0.06 or more and 0.10 or less. If the non-circularity is less than 0.06, the amount of clearance becomes too small, causing the HMD 101 to interfere with the viewer's face, which is undesirable. If the non-circularity is greater than 0.10, the birefringence of the first lens becomes large, causing ghost light and significant reduction in light intensity, which is also undesirable.

[0039] Furthermore, when the non-circularity is expressed as a ratio of area, the non-circularity of the second lens is preferably 0.01 or more and less than 0.06. If the non-circularity is less than 0.01, the amount of relief becomes too small, causing the HMD 101 to interfere with the observer's face, which is undesirable. If the non-circularity is 0.06 or more, the birefringence of the second lens becomes large, causing ghost light and significant reduction in light intensity, which is undesirable.

[0040] Furthermore, the non-circularity may be defined as the ratio of the volume reduced from the circular lenses (lenses whose entire outer edges are inscribed in the circles CL1 and CL2) that form the bases of the first lenses (104, 106) and the second lenses (105, 107) to the volume of the circular lenses in order to make them non-circular. In this example, the non-circularity of the first lens is 0.04, and the non-circularity of the second lens is 0.01, so the non-circularity of the second lens is smaller than the non-circularity of the first lens.

[0041] As described above, when the non-circularity is expressed as a volume ratio, the non-circularity of the first lens is preferably 0.03 or more and 0.05 or less. If the non-circularity is less than 0.03, the amount of relief becomes too small, causing the HMD 101 to interfere with the observer's face, which is undesirable. If the non-circularity is greater than 0.05, the birefringence of the first lens becomes large, causing ghost light and significant reduction in light intensity, which is also undesirable.

[0042] Furthermore, when the non-circularity is expressed as a ratio of the volume, the non-circularity of the second lens is preferably 0.005 or more and less than 0.03. If the non-circularity is less than 0.005, the amount of relief becomes too small, causing the HMD 101 to interfere with the observer's face, which is undesirable. If the non-circularity is 0.03 or more, the birefringence of the second lens becomes large, causing ghost light and significant reduction in light intensity, which is undesirable.

[0043] The degree of non-circularity may be defined using a value other than the distance from the optical axis, the area, and the volume. Depending on the definition, the degree of non-circularity of the second lens may be greater than the degree of non-circularity of the first lens, but it is sufficient if the shape of the second lens is closer to a circle than the first lens.

[0044] In the display optical system of this embodiment, the surface on which the half mirror 112 is vapor-deposited preferably has a convex shape facing the display element side. By vapor-depositing the half mirror 112 on this convex lens surface, the display optical system can be made thinner while achieving a wider angle of view. Furthermore, by making the convex lens surface on which the half mirror 112 is vapor-deposited aspherical, the aberration correction effect can be improved.

[0045] Furthermore, in order to reduce ghost light and increase the contrast of the displayed image, a polarizing plate may be disposed on the observation side of the PBS 114 (between the PBS 114 and the exit pupil where the observer's eye is located).

[0046] Furthermore, it is preferable that the observation-side surface of the first lens (104, 106) on which the phase plate 113 and the PBS 114 are provided is flat. This allows the display optical system to be made thinner while ensuring a sufficiently long eye relief. If this surface is concave toward the observation side, the first lens will be thicker to ensure the eye relief at the periphery of the first lens. If this surface is convex toward the observation side, the first lens will be thicker to ensure the thickness of the edge of the first lens. In this embodiment, as described above, a plano-convex lens with a flat surface on the observation side is used as the first lens.

[0047] Furthermore, in this embodiment, the phase difference imparted to light by the phase plates 111 and 113 is λ / 4, but the phase difference imparted may be shifted from λ / 4 so that the birefringence of the first lens and the second lens is canceled by the phase plates. In this case, it is preferable that the sum of the phase differences of the first lens and the phase plate 113 is 3λ / 20 or more and 7λ / 20 or less. It is also preferable that the sum of the phase differences of the second lens and the phase plate 111 is 3λ / 20 or more and 7λ / 20 or less. If the sum of the phase differences is outside these ranges, the intensity of ghost light increases, making it impossible to observe a natural image, which is undesirable.

[0048] Although this embodiment uses an organic EL display that emits unpolarized light as the display element, a liquid crystal display that emits linearly polarized light may also be used as the display element. In this case, the polarizing plate 110 on the display element side is not required, and the display optical system can be made thinner.

[0049] In this embodiment, the PBS 114 is used as the second transmissive-reflective surface, which transmits or reflects linearly polarized light depending on the polarization direction of the linearly polarized light. However, a polarization separation element may be used that transmits or reflects circularly polarized light depending on the direction of circularly polarized light. In this case, the phase plate 113 is not required, and the display optical system can be made thinner.

[0050] In this embodiment, the half mirror 112 is disposed between the first and second lenses as the first transmissive-reflective surface, and the PBS 114 is disposed on the observation side of the first lens, but other arrangements are also possible. For example, a curved PBS may be disposed between the first and second lenses, and a half mirror may be disposed on the observation side of the first lens.

[0051] The above-described preferred configurations (non-circularity and other configurations), conditions that are preferably satisfied, and alternative configurations are similarly applicable to other embodiments described later. [Example]

[0052] 7 shows the configuration of an HMD 201 according to Example 2. Reference numeral 202 denotes the right eye of the observer, and 203 denotes the left eye of the observer.

[0053] The HMD 201 is composed of right-eye optical systems (204, 205) and left-eye optical systems (206, 207) as display optical systems, and a right-eye display element 208 and a left-eye display element 209. The right-eye optical system has, arranged in order from the observation side, a first lens 204 and a second lens 205 adjacent to (cemented with) the first lens 204 on the display element side. The left-eye optical system has, arranged in order from the observation side, a first lens 206 and a second lens 207 adjacent to (cemented with) the first lens 206 on the display element side. The display elements 208 and 209 are each an organic EL display.

[0054] The right eye optical system and the left eye optical system guide light from the right eye display element 208 and the left eye display element 209 to the observer's right eye 202 and left eye 203, respectively, allowing the observer to view an enlarged virtual image (display image) of the original image displayed on each display element.

[0055] In this example, the focal length of the right-eye optical system and the left-eye optical system is 13 mm, the horizontal display angle of view is 60°, the vertical display angle of view is 60°, and the diagonal display angle of view is 78°. The eye relief is 18 mm. To enable the observer to observe an image with a high sense of realism, it is preferable that the diagonal display angle of view be 75° or greater.

[0056] The distance on the optical axis from the observation side surfaces of the first lenses 204 and 206 to the display element side surfaces of the second lenses 205 and 207 is 13.5 mm, forming a thin optical system.

[0057] The position of the exit pupil of each optical system is set to 28 mm, which is the sum of the eye relief of 18 mm and the radius of rotation of the eyeball of 10 mm, as shown in FIG. 9, and the exit pupil diameter is set to 6 mm.

[0058] The right-eye optical system and the left-eye optical system of this embodiment are optical systems that fold the optical path using polarization, as in Example 1. FIG. 8 shows a detailed configuration of the right-eye optical system. As in Example 1, a polarizing plate 210 and a phase plate 211 are arranged between the right-eye display element 208 and the second lens 205, in that order from the display element side. A half mirror 212 that forms a first transmissive-reflective surface is vapor-deposited on the surface of the first lens 204 facing the second lens 205. Furthermore, on the observation side of the first lens 204, in that order from the display element side, a phase plate 213 and a PBS 214 that serves as a second transmissive-reflective surface are arranged. Both the phase plate 213 and the PBS 214 have a planar shape.

[0059] Both phase plate 211 and phase plate 213 are quarter-wave plates. The slow axis of phase plate 211 is tilted at 45° with respect to the polarization direction of linearly polarized light that is transmitted through polarizing plate 210, and the slow axis of phase plate 213 is tilted at −45° with respect to the polarization direction of linearly polarized light that is transmitted through polarizing plate 210. Furthermore, the polarization direction of linearly polarized light that is transmitted through polarizing plate 210 and the polarization direction of linearly polarized light that is transmitted through PBS 214 are perpendicular to each other.

[0060] Of the unpolarized light emitted from the right-eye display element 208, linearly polarized light that passes through the polarizing plate 210 passes through the phase plate 211 and is converted into circularly polarized light. The circularly polarized light passes through the half mirror 212 and then the phase plate 213, where it is converted into linearly polarized light. Because the polarization direction of this linearly polarized light is perpendicular to the polarization direction of light passing through the PBS 214, it is reflected by the PBS 214 and passes through the phase plate 213, where it is converted into circularly polarized light. The circularly polarized light is reflected by the half mirror 212, passes through the phase plate 213, and is converted into linearly polarized light. Because the polarization direction of this linearly polarized light matches the polarization direction of light passing through the PBS 214, it passes through the PBS 214 and is directed to the right eye 202. In this embodiment, a polarizing plate 219 is located closer to the observation side than the PBS 214 to reduce ghost light and increase the contrast of the displayed image. The configuration and optical path of the left-eye optical system are similar to those of the right-eye optical system.

[0061] By folding the optical path using polarized light as described above, it is possible to achieve a thin display optical system with a short focal length and a wide angle of view.

[0062] As in Example 1, the first lenses 204 and 205 and the second lenses 206 and 207 in this example are made of resin lenses to reduce weight and aspherical lenses to enhance aberration correction. Furthermore, in this example, the first and second lenses are cemented together to form a cemented lens. Forming the first and second lenses into a cemented lens makes it easier to hold the first and second lenses. Furthermore, by forming the first and second lenses into a cemented lens, the surface on which the half mirror 212 is vapor-deposited may be the observation-side surface of the second lens. Even in this case, the surface on which the half mirror 212 is vapor-deposited has a convex shape facing the display element side.

[0063] The HMD 201 of this embodiment also has nose and forehead reliefs to prevent interference with the viewer's nose and forehead when worn on the head. The first lenses 204, 205 and the second lenses 206, 207 are also formed as noncircular lenses, as shown in FIGS. 10 and 11 . Specifically, the noncircular portions of the first and second lenses are made more linear than the other circular portions, resulting in a noncircular shape. In this embodiment, the noncircularity of the first and second lenses is also different from each other. More specifically, the noncircularity of the second lens is smaller than that of the first lens. As a result, a step is created when the first and second lenses are cemented together. In this embodiment, the end faces of the noncircular lenses on the nose relief side are formed parallel to the optical axis, as shown in FIGS. 7 and 8 .

[0064] In this example, the distance r11 from the optical axis to the arc portion of the first lens (the radius of the circle CL1 inscribed in the first lens) is 21 mm, and the minimum distance r12 from the optical axis to the non-arc portion is 15 mm. If the degree of non-circularity is defined as the ratio of the difference between the maximum and minimum values ​​of the above distance to the maximum value, then it is 6 / 21 = 0.29.

[0065] Meanwhile, the distance r21 from the optical axis to the arc portion of the second lens (the radius of the circle CL2 inscribed in the second lens) is 22 mm, and the minimum distance r22 from the optical axis to the non-arc portion is 18 mm. If the non-circularity is defined as the ratio described above, then 4 / 22 = 0.18. Thus, the non-circularity of the second lens is smaller than the non-circularity of the first lens. In other words, the shape of the second lens is closer to a circle than the first lens.

[0066] In this embodiment, as in the first embodiment, the refractive index of the second lens is greater than that of the first lens, and therefore the birefringence of the second lens is greater than that of the first lens. Specifically, the photoelastic constant of the first lens is 5×10 -12 [1 / Pa], the second lens is 35x10 -12 [1 / Pa], and the second lens is larger. In order to reduce the birefringence of the display optical system, the second lens, which is made of a resin material with high birefringence, must have a shape with small non-circularity. For this reason, the non-circularity of the second lens is made smaller than that of the first lens.

[0067] By doing so, the first lens and the second lens can be made non-circular so that the HMD 201 does not interfere with the viewer's nose or forehead, and birefringence that occurs when molding each lens can be kept small.

[0068] Alternatively, the degree of non-circularity may be expressed as the ratio of the difference between the areas A1', A2' of the first lenses (204, 206) and the second lenses (205, 207) when viewed from the optical axis direction and the areas A1, A2 of the circles CL1, CL2 to the areas A1, A2 of the circles CL1, CL2. In this example, the degree of non-circularity of the first lens is 0.09, and the degree of non-circularity of the second lens is 0.05, which is smaller than the degree of non-circularity of the first lens.

[0069] Furthermore, the non-circularity may be defined as the ratio of the volume reduced from the circular lenses (lenses whose entire outer edges are inscribed in the circles CL1 and CL2) that form the bases of the first and second lenses to the volume of the circular lenses in order to form the non-circular lenses. In this example, the non-circularity of the first lens is 0.05, and the non-circularity of the second lens is 0.02, which is smaller than the non-circularity of the first lens.

[0070] In this embodiment, the first lens (204, 206) and the second lens (205, 207) are bonded together with an adhesive. As shown in FIG. 12, the outer shape of the second lens is larger than that of the first lens, and the surface of the second lens facing the first lens is concave, as shown in FIG. 8. Therefore, the area of ​​the concave surface outside the first lens serves as a reservoir of adhesive, preventing excess adhesive from adhering to the lens surfaces. Furthermore, in order to position the first lens and the second lens relative to each other when they are bonded together, it is preferable that the non-arcuate portions of the first lens and the second lens be linear.

[0071] 13 , the HMD 201 may further be provided with a right-eye infrared light source 215, a left-eye infrared light source 217, a right-eye infrared camera 216, and a left-eye infrared camera 218 to detect the observer's line of sight. The infrared light emitted from the right-eye infrared light source 215 passes through the first lens 204 and the second lens 205 and is irradiated onto the observer's right eye (eyeball) 202, and the right-eye infrared camera 216 captures an image of the right eye 202 illuminated with the infrared light through the first lens 204 and the second lens 205. Similarly, the infrared light emitted from the left-eye infrared light source 217 passes through the first lens 206 and the second lens 207 and is irradiated onto the observer's left eye (eyeball) 203, and the left-eye infrared camera 218 captures an image of the left eye 203 illuminated with the infrared light through the first lens 206 and the second lens 207.

[0072] In this case, as shown in Fig. 14, by placing the right-eye infrared camera 216 closer to the viewer's nose, the robustness of gaze detection improves when the right eye moves up, down, left, or right. The same applies to the left-eye camera 218. However, if the non-arcuate portions of both the first and second lenses are large, it becomes difficult to place the infrared camera so that it does not extend beyond the non-arcuate portions toward the nose. Furthermore, even when multiple infrared light sources are placed, they cannot be placed in the non-arcuate portions, which reduces the accuracy of gaze detection.

[0073] Therefore, by making the non-circularity of the second lens smaller than that of the first lens and making the outer shape of the second lens closer to a circle, it becomes possible to place the infrared camera and infrared light source in appropriate positions, thereby improving the accuracy of gaze detection.

[0074] As mentioned above, in this embodiment, the first lenses (204, 206) and the second lenses (205, 207) are resin lenses, and when a temperature distribution occurs within each lens due to a rise in the temperature of the HMD 201, birefringence increases. In particular, non-circular lenses do not expand isotropically, so birefringence is likely to increase significantly. As mentioned above, the second lens is made of a resin material whose birefringence is greater than that of the first lens, but because the second lens is close to the display element, which is a heat source, its temperature is likely to rise, so birefringence is more likely to increase.

[0075] In order to minimize the temperature distribution within each lens, it is preferable to hold the cemented lens with a holding member capable of transmitting heat, such as a lens barrel. In this case, by holding the second lens on the holding member by adhesive or the like, it is possible to minimize the temperature distribution within the second lens. In order to hold the second lens with the holding member, it is preferable to make the outer shape of the second lens larger than the outer shape of the first lens.

[0076] As mentioned above, the surface on which the half mirror 212 is vapor-deposited is a convex surface facing the display element side. By vapor-depositing the half mirror on this convex surface, it is possible to achieve a wider angle of view while reducing the thickness of the display optical system. Furthermore, by making the convex surface on which the half mirror 212 is vapor-deposited aspherical, it is possible to improve the aberration correction effect.

[0077] When vapor-depositing the half mirror 212 on the surface of the second lens, if the vapor-deposited area of ​​the half mirror 212 is larger than the outer shape of the first lens, the vapor-deposited surface may be exposed, causing ghost light and deterioration due to oxidation of the vapor-deposited surface. For this reason, it is preferable that the vapor-deposited area of ​​the half mirror 212 is smaller than the outer shape of the first lens. [Example]

[0078] 15 shows the configuration of an HMD 301 according to Example 3. Reference numeral 302 denotes the right eye of the observer, and 303 denotes the left eye of the observer.

[0079] The HMD 301 is composed of right-eye optical systems (304-307) and left-eye optical systems (308-311) as display optical systems, and a right-eye display element 312 and a left-eye display element 313. The right-eye optical system has, arranged in order from the observation side, a lens 304, a first lens 305, a second lens 306 adjacent to the first lens 305 on the display element side, and a lens 306. The left-eye optical system has, arranged in order from the observation side, a lens 308, a first lens 309, a second lens 310 adjacent to the first lens 309 on the display element side, and a lens 311. The display elements 312 and 313 are each an organic EL display.

[0080] The right eye optical system and the left eye optical system guide light from the right eye display element 312 and the left eye display element 313 to the observer's right eye 302 and left eye 303, respectively, allowing the observer to view an enlarged virtual image (display image) of the original image displayed on each display element.

[0081] In this embodiment, the focal length of the right-eye optical system and the left-eye optical system is 11 mm, the horizontal display angle of view is 70°, the vertical display angle of view is 60°, and the diagonal display angle of view is 84°. The eye relief is 15 mm. The distance on the optical axis from the observation-side surfaces of lenses 304 and 308 to the display-element-side surfaces of lenses 307 and 311 is 20 mm, resulting in a thin optical system. The first lenses 305 and 309 and the second lenses 306 and 310 are adjacent to each other with an air gap between them. The distance on the optical axis from the observation-side surfaces of first lenses 305 and 309 to the display-element-side surfaces of second lenses 306 and 310 is 15 mm.

[0082] The position of the exit pupil of each optical system is set to 25 mm, which is the sum of the eye relief of 15 mm and the radius of rotation of the eyeball of 10 mm, and the exit pupil diameter is set to 6 mm.

[0083] The right-eye optical system and the left-eye optical system of this embodiment are optical systems that fold the optical path by using polarized light, as in Example 1. Fig. 16 shows the detailed configuration of the right-eye optical system. A polarizing plate 314 and a phase plate 315 are arranged between the lens 307 and the second lens 306, in that order from the display element side. A half mirror 316 that forms a first transmissive-reflective surface is vapor-deposited on the surface of the second lens 306 facing the first lens 305.

[0084] Furthermore, a phase plate 317 and a PBS 318 serving as a second transmission / reflection surface are arranged, in that order from the display element side, between the first lens 305 and the lens 304. Both the λ / 4 plate 317 and the PBS 318 have a planar shape.

[0085] Both phase plate 315 and phase plate 317 are quarter-wave plates. The slow axis of phase plate 315 is tilted at 45° with respect to the polarization direction of linearly polarized light that is transmitted through polarizing plate 314, and the slow axis of phase plate 317 is tilted at −45° with respect to the polarization direction of linearly polarized light that is transmitted through polarizing plate 314. Furthermore, the polarization direction of linearly polarized light that is transmitted through polarizing plate 314 and the polarization direction of linearly polarized light that is transmitted through PBS 318 are orthogonal to each other.

[0086] Unpolarized light emitted from the right-eye display element 312 passes through the lens 307, then through the polarizing plate 314 to become linearly polarized light, and then through the phase plate 315 to be converted to circularly polarized light. This circularly polarized light passes through the second lens 306, the half mirror 316, and the first lens 305, and then through the phase plate 317 to be converted to linearly polarized light. Because the polarization direction of this linearly polarized light is perpendicular to the polarization direction of light passing through the PBS 318, it is reflected by the PBS 318 and passes through the phase plate 317 to be converted to circularly polarized light. The circularly polarized light passes through the first lens 305, is reflected by the half mirror 316, passes through the first lens 305, and then passes through the phase plate 317 to be converted to linearly polarized light. Because the polarization direction of this linearly polarized light matches the polarization direction of light passing through the PBS 318, it passes through the PBS 318 and is directed to the right eye 302. The configuration and optical path of the left-eye optical system are the same as those of the right-eye optical system.

[0087] By folding the optical path using polarized light as described above, it is possible to achieve a thin display optical system with a short focal length and a wide angle of view.

[0088] As in the first embodiment, the lenses 304 to 311 in this embodiment are made of resin to reduce weight, and are aspherical lenses to enhance the aberration correction effect.

[0089] The HMD 301 of this embodiment also has nose recesses and forehead recesses so as not to interfere with the viewer's nose or forehead when worn on the head, and lenses 304, 305, 306, 308, 309, and 310 are formed as non-circular lenses. Specifically, the non-circular shapes of lenses 304, 305, 306, 308, 309, and 310 are formed by making the non-circular arc-shaped portions on the nose side and forehead side closer to a straight line than the other arc-shaped portions. Furthermore, as shown in Figures 15 and 16, the end faces of the non-circular lenses on the nose recess side are formed at an angle with respect to the optical axis.

[0090] The lenses 307, 311 closest to the display element are circular because they have a small outer shape and do not affect the nose and forehead relief areas. In this embodiment, the first lenses (305, 309) and the second lenses (306, 310) have different degrees of non-circularity. More specifically, the degree of non-circularity of the second lens is smaller than that of the first lens. Furthermore, the lenses (304, 308) closest to the viewing side have the largest degree of non-circularity in order to increase the amount of relief in the nose and forehead relief areas.

[0091] In this example, it is necessary to reduce the birefringence of the first and second lenses disposed between the polarizing plate (314) and the PBS (318). The distance from the optical axis to the arc-shaped portion of the first lens (the radius of the circle inscribed in the first lens) is set to 23 mm, and the minimum distance from the optical axis to the non-arcuate portion is set to 18 mm. If the degree of non-circularity is defined as the ratio of the difference between the maximum and minimum values ​​of the above distance to the maximum value, then it is 5 / 23 = 0.22.

[0092] On the other hand, the distance from the optical axis to the arcuate portion of the second lens (the radius of the circle inscribed in the second lens) is 24 mm, and the minimum distance from the optical axis to the non-arcuate portion is 21.5 mm. If the non-circularity is defined as the ratio described above, then 2.5 / 24 = 0.1. Thus, the non-circularity of the second lens is smaller than the non-circularity of the first lens. In other words, the shape of the second lens is closer to a circle than the first lens.

[0093] In this embodiment, as in the first embodiment, the refractive index of the second lens is greater than that of the first lens, and therefore the birefringence of the second lens is greater than that of the first lens. Specifically, the photoelastic constant of the first lens is 7×10 -12 [1 / Pa], the second lens is 45x10 -12 [1 / Pa], and the second lens is larger. In order to reduce the birefringence of the display optical system, the second lens, which is made of a resin material with high birefringence, must have a shape with small non-circularity. For this reason, the non-circularity of the second lens is made smaller than that of the first lens.

[0094] By doing so, the first lens and the second lens can be made non-circular so that the HMD 301 does not interfere with the viewer's nose or forehead, and birefringence that occurs when molding each lens can be kept small.

[0095] Alternatively, the degree of non-circularity may be expressed as the ratio of the difference between the area of ​​each of the first lens and the second lens and the area of ​​the circle in which they are inscribed to the area of ​​the circle. In this example, the degree of non-circularity of the first lens is 0.06, and the degree of non-circularity of the second lens is 0.02, which is smaller than the degree of non-circularity of the first lens.

[0096] Furthermore, the non-circularity may be defined as the ratio of the volume reduced from a circular lens (a lens whose entire outer periphery is inscribed in a circle) that serves as the base for the first and second lenses to the volume of the circular lens. In this example, the non-circularity of the first lens is 0.03, and the non-circularity of the second lens is 0.008, which is smaller than the non-circularity of the first lens.

[0097] In the above embodiments, the display optical system is described as folding the optical path using two transmissive-reflective surfaces, but the display optical system may be configured as folding the optical path using three or more transmissive-reflective surfaces.

[0098] The above embodiment includes the following configurations.

[0099] (Configuration 1) A display optical system that guides light from a display element to an observation side, A first lens; a second lens adjacent to the first lens on the display element side; at least two transmissive-reflective surfaces; When viewed from a direction in which an optical axis of the display optical system extends, the first and second lenses are each formed in a non-circular shape; When the degree of difference between the non-circular shape and a circular shape is called non-circularity, the display optical system is characterized in that the non-circularity of the first and second lenses differ from each other. (Configuration 2) each of the first and second lenses is formed in a non-circular shape such that a distance from the optical axis to a portion of an outer periphery of the lens is shorter than a distance from the optical axis to another portion of the outer periphery of the lens; When the non-circularity is defined as a ratio of a difference between the maximum value of the distance and the minimum value of the distance for each of the first and second lenses, 2. The display optical system according to configuration 1, wherein the degree of non-circularity of the second lens is smaller than the degree of non-circularity of the first lens. (Configuration 3) the degree of non-circularity of the first lens is 0.2 or more and 0.3 or less, 3. The display optical system according to configuration 2, wherein the degree of non-circularity of the second lens is equal to or greater than 0.1 and less than 0.2. (Configuration 4) a part of an outer circumferential edge of each of the first and second lenses is formed in a non-circular shape that is closer to the optical axis than a circle in which the lens is inscribed, When the degree of non-circularity is defined as the ratio of the difference between the area of ​​each of the first and second lenses and the area of ​​the circle to the area of ​​the circle, 2. The display optical system according to configuration 1, wherein the degree of non-circularity of the second lens is smaller than the degree of non-circularity of the first lens. (Configuration 5) the degree of non-circularity of the first lens is 0.06 or more and 0.10 or less, 5. The display optical system according to configuration 4, wherein the degree of non-circularity of the second lens is 0.01 or more and less than 0.06. (Configuration 6) 6. The display optical system according to any one of configurations 1 to 5, wherein the first and second lenses are resin lenses. (Configuration 7) 7. The display optical system according to any one of configurations 1 to 6, wherein the refractive index of the second lens is greater than the refractive index of the first lens. (Configuration 8) 8. The display optical system according to any one of configurations 1 to 7, wherein the birefringence of the second lens is greater than the birefringence of the first lens. (Configuration 9) The photoelastic constant of the first lens is 10×10 -12 [1 / Pa] or less, The photoelastic constant of the second lens is 50×10 -12 The display optical system according to configuration 8, characterized in that the refractive index is [1 / Pa] or less. (Configuration 10) 10. The display optical system according to any one of configurations 1 to 9, wherein the shape of the portion of the outer periphery is closer to a straight line than to an arcuate shape. (Configuration 11) 11. The display optical system according to any one of configurations 1 to 10, wherein the first and second lenses are cemented together. (Configuration 12) In the first and second lenses cemented together, the outer shape of the second lens is larger than the outer shape of the first lens, 12. The display optical system according to configuration 11, wherein the second lens is held by a holding member. (Configuration 13) 13. The display optical system according to any one of configurations 1 to 12, wherein one of the at least two transmission-reflection surfaces is a polarization separation surface that reflects or transmits light depending on its polarization state. (Configuration 14) The display optical system described in configuration 13 is characterized in that light from the display element is transmitted through the second lens, transmitted through a half mirror that is one of the at least two transmission-reflection surfaces, transmitted through the first lens, reflected by the polarization separation surface, transmitted through the first lens, reflected by the half mirror, transmitted through the first lens, transmitted through the polarization separation surface, and directed to the observation side. (Configuration 15) The diagonal display angle of view of the display optical system is 60° or more, 15. The display optical system according to any one of configurations 1 to 14, wherein the distance on the optical axis from the observation side surface of the first lens to the display element side surface of the second lens is 15 mm or less. (Configuration 16) a display optical system according to any one of configurations 1 to 15; and The display element, A display device that is placed in front of the viewer's face. (Configuration 17) 17. The display device according to configuration 16, wherein the part of the outer periphery of the first and second lenses is located on at least one of the nose side and the forehead side of the viewer. (Configuration 18) 17. The display device according to configuration 16, further comprising a camera disposed on the nose side of the viewer, for capturing an image of the viewer's eye through the first and second lenses.

[0100] The embodiments described above are merely representative examples, and various modifications and alterations are possible to each embodiment when implementing the present invention. [Explanation of symbols]

[0101] 101,201,301 HMD 102,202,302 Right eye 103,203,303 left eye 104,106,204,206,305,309 First lens 105,107,205,207,306,310 Second lens 108,208,312 Right eye display element 109,209,313 Left eye display element 112,212,316 Half mirror 114,214,318 PBS

Claims

1. A display optical system that guides light from a display element to an observation side, A first lens; a second lens adjacent to the first lens on the display element side; at least two transmissive-reflective surfaces; When viewed from a direction in which an optical axis of the display optical system extends, the first and second lenses are each formed in a non-circular shape; When the degree of difference between the non-circular shape and a circular shape is called non-circularity, the degree of non-circularity of the first and second lenses is different from each other.

2. each of the first and second lenses is formed in a non-circular shape such that a distance from the optical axis to a portion of an outer periphery of the lens is shorter than a distance from the optical axis to another portion of the outer periphery of the lens; When the non-circularity is defined as a ratio of a difference between the maximum value of the distance and the minimum value of the distance for each of the first and second lenses to the maximum value of the distance, 2. The display optical system according to claim 1, wherein the degree of non-circularity of the second lens is smaller than the degree of non-circularity of the first lens.

3. the degree of non-circularity of the first lens is 0.2 or more and 0.3 or less, 3. The display optical system according to claim 2, wherein the degree of non-circularity of the second lens is equal to or greater than 0.1 and less than 0.

2.

4. a part of an outer circumferential edge of each of the first and second lenses is formed in a non-circular shape that is closer to the optical axis than a circle in which the lens is inscribed, When the degree of non-circularity is defined as a ratio of a difference between the area of ​​each of the first and second lenses and the area of ​​the circle to the area of ​​the circle, 2. The display optical system according to claim 1, wherein the degree of non-circularity of the second lens is smaller than the degree of non-circularity of the first lens.

5. the degree of non-circularity of the first lens is 0.06 or more and 0.1 or less, 5. The display optical system according to claim 4, wherein the degree of non-circularity of the second lens is equal to or greater than 0.01 and less than 0.

06.

6. 2. The display optical system according to claim 1, wherein the first and second lenses are resin lenses.

7. 2. The display optical system according to claim 1, wherein the refractive index of the second lens is greater than the refractive index of the first lens.

8. 2. The display optical system according to claim 1, wherein the birefringence of the second lens is greater than the birefringence of the first lens.

9. The photoelastic constant of the first lens is 10×10 －１２ [1 / Pa] or less, The photoelastic constant of the second lens is 50×10 －１２ 9. The display optical system according to claim 8, wherein the optical density is 1 / Pa or less.

10. 2. The display optical system according to claim 1, wherein the shape of the portion of the outer periphery is closer to a straight line than to a circular arc.

11. 2. The display optical system according to claim 1, wherein the first and second lenses are cemented together.

12. In the first and second lenses cemented together, the outer shape of the second lens is larger than the outer shape of the first lens, 12. The display optical system according to claim 11, wherein the second lens is held by a holding member.

13. 2. The display optical system according to claim 1, wherein one of the at least two transmission / reflection surfaces is a polarization separation surface that reflects or transmits light depending on its polarization state.

14. 14. The display optical system according to claim 13, wherein light from the display element is transmitted through the second lens, transmitted through a half mirror that is one of the at least two transmission-reflection surfaces, transmitted through the first lens, reflected by the polarization separation surface, transmitted through the first lens, reflected by the half mirror, transmitted through the first lens, transmitted through the polarization separation surface, and guided to the observation side.

15. The diagonal display angle of view of the display optical system is 60° or more, 2. The display optical system according to claim 1, wherein the distance on the optical axis from the observation side surface of the first lens to the display element side surface of the second lens is 15 mm or less.

16. a display optical system according to claim 1; The display element, A display device that is placed in front of the viewer's face.

17. 17. The display device according to claim 16, wherein the portions of the outer peripheries of the first and second lenses are located on at least one of the nose side and the forehead side of the viewer.

18. 17. The display device according to claim 16, further comprising a camera arranged on the nose side of the viewer, for capturing an image of the viewer's eye through the first and second lenses.

Images