Display optical system and image display device

Abstract

To provide a display optical system which prevents a deterioration in a local contrast of a display image even if having an adhesive layer for pasting a film element.SOLUTION: A display optical system guides light from a display element 108 to an observation side through a translucent reflection surface 112, a polarization separation surface 114, and a plurality of polarizers 110, 113, 115. At least one of the translucent reflection surface and the polarization separation surface is formed of a film element. The film element is pasted on one of the plurality of polarizers or a lens through a first adhesive layer 118 on its opposite side. The thickness d1 of the first adhesive layer satisfies a condition of 5 μm≤d1<20 μm.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a display optical system suitable for an image display device such as a head-mounted display (HMD), which displays an enlarged version of an original image displayed on a display element. [Background technology]

[0002] As an example of such a display optical system, an optical system that folds the optical path by using polarized light and that uses a polarization selection element (polarization separation element) and a half mirror is disclosed in Patent Documents 1 and 2. However, when the polarization separation element or half mirror is made of a film-like element (hereinafter referred to as a film element), the contrast of the displayed image is locally reduced due to variations in thickness (unevenness) in the in-plane direction of the adhesive layer that attaches the film element to the polarizing element or lens. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2000-275566 [Patent Document 2] Japanese Patent Application Publication No. 2019-148626 Summary of the Invention [Problem to be solved by the invention]

[0004] Patent Documents 1 and 2 do not even mention the adhesive layer between the film element and the polarizing element or lens, nor do they disclose any measures to address the problem of localized contrast reduction due to unevenness in the adhesive layer.

[0005] The present invention provides a display optical system that has little local decrease in contrast of a displayed image even when an adhesive layer for attaching a film element is provided. [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 the viewing side via a semi-transmissive reflective surface, a polarized light separating surface, and a plurality of polarizing elements. At least one of the semi-transmissive reflective surface and the polarized light separating surface is made of a film element. The film element is bonded to one of the plurality of polarizing elements or a lens on the reflective side of the film element via a first adhesive layer, and the thickness d1 of the first adhesive layer is 5μm≦d1<20μm The display optical system is characterized by satisfying the following conditions: Note that an image display device using 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 in which the local decrease in contrast of a displayed image is small even if an adhesive layer for attaching a film element is provided. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 1 is a diagram showing an image observation device equipped with a display optical system according to a first embodiment. [Figure 2] FIG. 2 is a detailed diagram showing the configuration of the display optical system according to the first embodiment. [Figure 3] FIG. 2 is an external view of the image display device of FIG. 1. [Figure 4] FIG. 2 is a partially enlarged view of the display optical system according to the first embodiment. [Figure 5] 10A and 10B are diagrams showing local contrast reduction in a displayed image. [Figure 6] FIG. 10 is a diagram showing an image observation device equipped with a display optical system according to a second embodiment. [Figure 7] FIG. 10 is a detailed diagram showing the configuration of a display optical system according to a second embodiment. [Figure 8] FIG. 10 is a partially enlarged view of the display optical system according to the second embodiment. [Figure 9] FIG. 10 is an enlarged view of another part of the display optical system according to the second embodiment. [Figure 10] FIG. 11 is a detailed diagram showing the configuration of a display optical system according to a third embodiment. [Figure 11] FIG. 11 is a partially enlarged view of a display optical system according to a third embodiment. [Figure 12]FIG. 10 is an enlarged view of another part of the display optical system according to the third embodiment. [Figure 13] 10A and 10B are diagrams showing an example in which local contrast degradation is improved according to an embodiment. DETAILED DESCRIPTION OF THE INVENTION

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

[0010] 1 shows the configuration of an HMD 101 as an image display device using the display optical system of Example 1, viewed from above. Reference numeral 102 denotes the right eye of the observer, and 103 denotes the left eye of the observer. Lenses 104 and 105 constitute a part of the display optical system for the right eye, and lenses 106 and 107 constitute a part of the display optical system for the left eye. Reference numeral 108 denotes a display element for the right eye, and 109 denotes a display element for the left eye, which in this example use an organic EL element.

[0011] The right eye display optical system magnifies light (virtual image) from the original image displayed on the right eye display element 108 and directs it to the right eye 102 located on the observation side, and the left eye display optical system magnifies light from the original image displayed on the left eye display element 109 and directs it to the left eye 103 located on the observation side.

[0012] The focal length f1 of the right-eye display optical system and the left-eye display 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 2×θ1 is 65°. To increase the sense of realism of the observer observing the image, it is desirable that the diagonal display angle of view be 60° or more. The distance (eye relief) E1 between the HMD 101 and the observer's eyes is 25 mm.

[0013] The display optical system of this embodiment is an optical system that folds the optical path by using polarized light, and its specific configuration will be explained using the display optical system for the right eye shown in Fig. 2. The display optical system for the right eye has a first polarizing plate 110 and a first phase plate 111, which are arranged between a right-eye display element 108 and a lens 105 in this order from the display element side. The first polarizing plate 110 and the first phase plate 111 are each formed in a planar shape and are stacked on top of each other.

[0014] Furthermore, a half mirror 112 constituting a semi-transmissive reflective surface is formed by vapor deposition on the surface of the lens 104 facing the display element (lens 105). Furthermore, between the lens 104 and the right eye 102, there are arranged, in order from the display element side (lens 104 side), a second phase plate 113, a polarization separation element (PBS) 114 constituting a polarization separation surface, and a second polarizing plate 115. The polarization separation surface is an optically functional surface whose transmittance and reflectance change depending on the polarization direction of incident light. The second phase plate 113, the PBS 114, and the second polarizing plate 115 are each formed in a planar shape and stacked on top of each other. The first phase plate 111 and the second phase plate 113 are each wave plates with a phase difference of λ / 4.

[0015] The polarization direction of the polarized light transmitted by the first polarizing plate 110 and the slow axis of the first phase plate 111 are inclined at 45° from each other. The polarization direction of the polarized light transmitted by the first polarizing plate 110 and the slow axis of the second phase plate 113 are inclined at -45° from each other. The polarization direction of the polarized light transmitted by the first polarizing plate 110 and the polarization direction of the polarized light transmitted by the PBS 114 are orthogonal to each other. The polarization direction of the polarized light transmitted by the second polarizing plate 115 and the polarization direction of the polarized light transmitted by the PBS 114 are consistent with each other.

[0016] In the above configuration, unpolarized light emitted from the right-eye display element 108 passes through the first polarizing plate 110 and becomes linearly polarized light, and this linearly polarized light passes through the first phase plate 111 and becomes circularly polarized light. The circularly polarized light that passes through the half mirror 112 passes through the second phase plate 113 and becomes linearly polarized light, and because the polarization direction of this linearly polarized light is perpendicular to the polarization direction of light passing through the PBS 114, it is reflected by the PBS 114. The reflected linearly polarized light then passes through the second phase plate 113 and becomes circularly polarized light.

[0017] The circularly polarized light reflected by the half mirror 112 passes through the second phase plate 113 and becomes linearly polarized light. This linearly polarized light passes through the PBS 114 because its polarization direction matches the polarization direction of the light passing through the PBS 114, and then passes through the second polarizing plate 115 and is directed to the right eye 102. By providing the second polarizing plate 115, ghost light generated by external light can be reduced, thereby increasing the contrast of the displayed image. The above configuration is the same for the display optical system for the left eye.

[0018] By folding the optical path using polarized light as in this embodiment, the display optical system can be made thinner and the focal length can be shortened, thereby realizing image observation at a wide angle of view.

[0019] FIG. 3 shows the appearance of the HMD 101. Because the HMD 101 is worn on the viewer's head, it is desirable that it be lightweight. For this reason, the lenses that make up the display optical system are desirably made of resin, which has a lower specific gravity than glass, and in this embodiment, the lenses 104 and 106 are made of resin lenses. Furthermore, by making the lenses 104 and 106 aspherical lenses with a plano-convex shape, the aberration correction effect can be improved. The lenses 105 and 107 are double-sided aspherical lenses made of resin.

[0020] The exit pupil position of the display optical system in this embodiment is 35 mm, which is the sum of the eyeball rotation radius of 10 mm and the eye relief of 25 mm, and the exit pupil diameter is 6 mm. This ensures that even when the eyeball rotates to observe up, down, left, or right, light in that direction is incident on the eyeball. It is desirable that the eye relief be 15 mm or more so that observers wearing eyeglasses can also wear the HMD 101. Furthermore, since a longer eye relief increases the outer diameter of the lens and the size of the HMD 101, it is desirable that the eye relief be 25 mm or less.

[0021] 4 shows the second phase plate 113, the PBS 114, and the second polarizing plate 115 laminated and bonded to the observation-side surface of the lens 104. An adhesive layer 117 is provided between the observation-side surface of the lens 104 and the second phase plate 113, an adhesive layer (first adhesive layer) 118 is provided between the second phase plate 113 and the PBS 114, and an adhesive layer 119 is provided between the PBS 114 and the second polarizing plate 115. By laminating the second phase plate 113, the PBS 114, and the second polarizing plate 115 in this manner, the display optical system can be made thinner. An anti-reflection (AR) film 116 for preventing reflection of external light is bonded to the observation-side surface of the second polarizing plate 115 via an adhesive layer 120.

[0022] In this embodiment, the PBS 114 is configured as a thin film element (film element), and if the adhesive layer 118 between the PBS 114 and the second phase plate 113 has thickness variations (unevenness) in the in-plane direction, unevenness corresponding to the unevenness will appear on the PBS 114. In particular, if the thickness of the adhesive layer 118 between the PBS 114 and the second phase plate 113 arranged on the reflection side of the PBS 114 varies periodically, the PBS 114 with the corresponding unevenness will generate local optical power for light reflected by the PBS 114. When local optical power is generated in the PBS 114, a localized focus error occurs in the displayed image, and the displayed image will be observed as a blurred image with reduced contrast.

[0023] 5 shows how the contrast of a displayed image containing vertical lines is locally reduced due to the unevenness of the PBS 114. The contrast of the vertical lines is high near the center of FIG. 5, but the contrast is low on the left and right sides.

[0024] Therefore, in this embodiment, the thickness of the adhesive layer 118 between the PBS 114 and the second phase plate 113 is reduced to reduce the unevenness (particularly periodic unevenness) of the adhesive layer 118, thereby suppressing the generation of localized optical power in the PBS 114. Specifically, the thickness of the adhesive layer 118 is set to 15 μm, and the amount of variation in the thickness is limited to 6 μm (tolerance ±3 μm). Basically, it is desirable that the thickness d1 of the adhesive layer 118 between the PBS 114, which has a reflective function, and the second phase plate 113 is 5 μm or more and less than 20 μm (satisfying the condition 5 μm≦d1<20 μm). If the thickness of the adhesive layer 118 is 20 μm or more, the thickness variation becomes large, unevenness is likely to appear on the PBS 114, and the optical power generated by the unevenness increases, which is undesirable. On the other hand, if the thickness of the adhesive layer 118 is too thin, less than 5 μm, it becomes difficult to bond the PBS 114 and the second phase plate 113 together, and wrinkles and bubbles are likely to occur during bonding, which is undesirable.

[0025] The thickness d1 of the adhesive layer 118 is more preferably 19 μm or less, even more preferably 18 μm or less, and even more preferably 16 μm or less. This also applies to the thickness d1 of the adhesive layer in other examples described later.

[0026] Furthermore, it is desirable that the thickness variation Δd1 of adhesive layer 118 is less than 10 μm (satisfying the condition 0<Δd1<10 μm). If the thickness variation of adhesive layer 118 is 10 μm or more, unevenness is likely to appear on PBS 114, and the optical power generated by the unevenness increases, which is undesirable.

[0027] Furthermore, the viewer is sensitive to a local decrease in contrast near the center of the displayed image (for example, within a range of 30° horizontally and 20° vertically, which is the effective visual field of the human eye). For this reason, it is desirable that the variation in thickness of the adhesive layer 118 within the width of the light beam incident on the viewer's eye near the optical axis of the display optical system, which corresponds to the vicinity of the center of the displayed image, is as small as possible. Specifically, the ratio of the light beam width Φ1 when the light beam emitted from a pixel on the optical axis of the display optical system among the display elements is reflected by the PBS 114 to the variation amount Δd1 is 0<Δd1 / Φ1<0.002 In this embodiment, the variation Δd1 in the thickness of the adhesive layer 118 near the center is 4 μm, and the diameter (=Φ1) of the pupil of the observer's eye is about 4 mm, so Δd1 / Φ1 is 0.001.

[0028] If the unevenness of the adhesive layer 118 is periodic, it is desirable that the period of the unevenness be at least twice the light beam width Φ1. If the period of the unevenness is less than twice the light beam width Φ1, the optical power of the PBS 114 due to the unevenness of the adhesive layer 118 becomes large, which is not preferable.

[0029] Furthermore, the thickness of the PBS 114, 60 μm, is four times the thickness of the adhesive layer 118. The greater the thickness of the PBS 114 relative to the thickness of the adhesive layer 118, the less likely the unevenness of the adhesive layer 118 will appear in the PBS 114, and the less likely local optical power will be generated. For this reason, it is desirable that the thickness of the PBS 114 be three times or more the thickness of the adhesive layer 118. On the other hand, if the thickness of the PBS 114 is too large, it becomes difficult to slim down the display optical system, so it is desirable that the thickness of the PBS 114 be 15 times or less the thickness of the adhesive layer 118.

[0030] In this way, by reducing the thickness of the adhesive layer 118 between the PBS 114 and the polarizing element (second phase plate 113) adjacent to it on the reflection side and reducing the thickness variation, it is possible to reduce the unevenness that occurs in the PBS 114. Because the PBS 114 has a reflective function, local unevenness has a greater effect on the optical power than on a surface with a transmissive function, and is more likely to cause a local decrease in contrast in the displayed image. Therefore, by reducing the unevenness of the adhesive layer 118 between the PBS 114 and the second phase plate 113 adjacent to it on the reflection side, it is possible to reduce the unevenness of the PBS 114 and reduce the local decrease in contrast in the displayed image.

[0031] FIG. 13(a) shows an example of a display image different from that of FIG. 5, in which local contrast reduction occurs due to unevenness in the adhesive layer 18. The areas where contrast is reduced are shown in black. In this display image, there are multiple areas where contrast is reduced, which creates an unnatural feeling. In contrast, FIG. 13(b) shows a display image in which the unevenness in the adhesive layer 18 is reduced as in this embodiment, thereby improving the local contrast reduction.

[0032] Up to this point, we have explained the thickness of the adhesive layer 118 between the PBS 114 and the second phase plate 113, but it is desirable to also thin the thickness of the adhesive layer 119 between the PBS 114 and the second polarizer 115 to reduce thickness variations. In this embodiment, the thickness of the adhesive layer 119 is 20 μm, and the thickness variation is 8 μm (±4 μm). Furthermore, the thickness variation of the adhesive layer 119 near the center is 5 μm, and the ratio to the light beam width near the center is 0.00125.

[0033] Furthermore, in this embodiment, an AR film 116 is bonded to the observation-side surface of the second polarizing plate 115 via an adhesive layer 120. As with the PBS 114, if there are irregularities at the interface between the AR film 116 and the air, local optical power is generated, reducing the contrast. Therefore, in this embodiment, the thickness of the adhesive layer 120 between the AR film 116 and the second polarizing plate 115 is made thin to reduce the irregularities in the adhesive layer 120.

[0034] Specifically, the thickness d2 of the adhesive layer 120 is 14 μm, and the thickness variation Δd2 is 10 μm (±5 μm). Basically, it is desirable that the thickness d2 of the adhesive layer 120 between the AR film 116, which has a light-transmitting property, and the second polarizing plate 115 be 5 μm or more and less than 20 μm (satisfying the condition 5 μm≦d2<20 μm). If the thickness of the adhesive layer 120 is 20 μm or more, the unevenness of the adhesive layer 120 becomes large, and unevenness corresponding to the unevenness also appears on the AR film 116, which is undesirable. If the thickness of the adhesive layer 120 is less than 5 μm, the adhesive layer 120 is too thin, making it difficult to bond the AR film 116 and the second polarizing plate 115, and wrinkles and bubbles are likely to occur during bonding, which is undesirable.

[0035] The thickness d2 of the adhesive layer 120 is more preferably 19 μm or less, even more preferably 18 μm or less, and even more preferably 16 μm or less. This also applies to the thickness d2 of the adhesive layer in other examples described later.

[0036] Furthermore, it is desirable that the thickness variation Δd2 of the adhesive layer 120 is less than 20 μm (satisfying the condition 0<Δd2<20 μm). If the thickness variation is 20 μm or more, the unevenness of the adhesive layer 120 will generate optical power in the AR film 116, which is not desirable.

[0037] Furthermore, near the center, the variation Δd2 in the thickness of the adhesive layer 120 is 8 μm, and when the width of the light beam emitted from a pixel on the optical axis of the display element when it passes through the adhesive layer 120 is Φ2, Δd2 / Φ2 is 0.002. It is desirable that Δd2 / Φ2 is less than 0.005 (satisfying the condition 0<Δd2 / Φ2<0.005).

[0038] The focal length of the display optical system in this embodiment is 12 mm. If the focal length of the display optical system is short and the optical power is high, the difference with the optical power of the PBS 114 and the AR film 116 will be large, and the display optical system will be less susceptible to this influence. For this reason, the focal length of the display optical system is preferably 20 mm or less, and more preferably 16 mm or less. Furthermore, if the focal length is too short, the optical performance will deteriorate and high-quality images will not be observed, so the focal length f is preferably 10 mm or more, and more preferably 12 mm or more. In other words, it is desirable to satisfy the condition 10 mm≦f≦20 mm or 12 mm≦f≦16 mm.

[0039] In this embodiment, the surface of the lens 104 on which the half mirror 112 is vapor-deposited has a convex shape facing the display element side. By vapor-depositing the half mirror on this convex surface, it is possible to achieve a wide angle of view while reducing the thickness of the display optical system. Furthermore, by making the convex surface on which the half mirror 112 is vapor-deposited aspherical, it is possible to improve the aberration correction effect.

[0040] In this embodiment, the observation-side surface of lens 104, on which second phase plate 113 and PBS 114 are laminated, is flat. This is to ensure both sufficient eye relief and a slim display optical system. If this surface were concave toward the observation side, the lens would be thicker to ensure eye relief at the periphery, which is not preferable. If the surface were convex toward the observation side, the lens would be thicker to ensure the thickness of the edge of the lens, which is also not preferable. Therefore, in this embodiment, lens 104 is a plano-convex lens.

[0041] In this embodiment, the first phase plate 111 and the second phase plate 113 are both λ / 4 plates, but the phase difference may be shifted from λ / 4 to cancel the birefringence of the lenses 104 and 105. In this case, it is desirable that the sum of the phase differences of the lens 104 and the second phase plate 113 be 3λ / 20 or more and 7λ / 20 or less. It is also desirable that the sum of the phase differences of the lens 105 and the first phase plate 111 be 3λ / 20 or more and 7λ / 20 or less. If the phase difference is outside this range, the intensity of ghost light increases, making it impossible to observe a natural image, which is not desirable.

[0042] In this embodiment, an organic EL element that emits unpolarized light is used as the display element, but a liquid crystal display that emits linearly polarized light may be used as the display element, eliminating the need for the first polarizer 110 and making the display optical system thinner. [Example]

[0043] 1 shows the configuration of an HMD 201 as an image display device using the display optical system of Example 2, viewed from above. Reference numeral 202 denotes the right eye of the observer, and 203 denotes the left eye of the observer. Lenses 204 and 205 are cemented together to form part of the display optical system for the right eye, and lenses 206 and 207 are cemented together to form part of the display optical system for the left eye. Reference numeral 208 denotes a display element for the right eye, and 209 denotes a display element for the left eye, and in this example, organic EL elements are used.

[0044] The right eye display optical system magnifies light (virtual image) from the original image displayed on the right eye display element 208 and directs it to the right eye 202 located on the observation side, and the left eye display optical system magnifies light from the original image displayed on the left eye display element 209 and directs it to the left eye 203 located on the observation side.

[0045] The focal length f2 of the right-eye display optical system and the left-eye display 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 2 × θ2 is 78°. To increase the sense of realism for the observer viewing the image, it is desirable that the diagonal display angle of view be 75° or more. The eye relief E2 is 18 mm.

[0046] The display optical system of this embodiment is also an optical system that folds the optical path using polarized light, and its specific configuration will be described using the right-eye display optical system shown in Fig. 7. The right-eye display optical system has a first polarizing plate 210 arranged between the right-eye display element 208 and the lens 205, and a PBS 212 arranged between the lenses 204 and 205. It also has a first phase plate 213, a half mirror 214, a second phase plate 215, a second polarizing plate 216, and an AR film 217 arranged between the lens 204 and the right eye 202, in that order from the display element side.

[0047] The first phase plate 213, the half mirror 214, the second phase plate 215, and the second polarizing plate 216 are formed in a planar shape and stacked on top of each other. The first phase plate 213 and the second phase plate 215 are each a wave plate with a phase difference of λ / 4.

[0048] The polarization direction of the polarized light transmitted by the first polarizing plate 210 and the polarization direction of the polarized light transmitted by the PBS 212 are aligned with each other, and the slow axis of the first phase plate 213 is tilted at 45° with respect to these polarization directions. The polarization direction of the polarized light transmitted by the first polarizing plate 210 and the slow axis of the second phase plate 215 are tilted at -45° with respect to each other. Furthermore, the polarization direction of the polarized light transmitted by the PBS 212 and the polarization direction of the polarized light transmitted by the second polarizing plate 215 are aligned with each other.

[0049] In the above configuration, unpolarized light emitted from the right-eye display element 208 passes through the first polarizing plate 210 and becomes linearly polarized light. This linearly polarized light passes through the PBS 212 and then passes through the first phase plate 213 to become circularly polarized light. The circularly polarized light reflected by the half mirror 214 passes through the first phase plate 213 to become linearly polarized light. Because the polarization direction of this linearly polarized light is perpendicular to the polarization direction of the polarized light passed by the PBS 212, it is reflected by the PBS 212 and then passes through the first phase plate 213 to become circularly polarized light. The circularly polarized light passed through the half mirror 214 passes through the second phase plate 215 to become linearly polarized light. Because the polarization direction of this linearly polarized light matches the polarization direction of the polarized light passed by the second polarizing plate 216, it passes through the second polarizing plate 216 and then passes through the AR film 217 to be guided to the right eye 202.

[0050] In this embodiment, a second polarizing plate 216 is provided to absorb the light that is emitted from the right-eye display element 208 and first passes through the half mirror 214. The above configuration is the same for the left-eye display optical system.

[0051] By folding the optical path using polarized light as in this embodiment, the display optical system can be made thinner and the focal length can be shortened, thereby realizing image observation at a wide angle of view.

[0052] In this embodiment, in order to reduce weight, lenses 204, 205, 206, and 207 are all made of resin lenses, and by using aspherical lenses, the aberration correction effect is enhanced. The exit pupil position of the display optical system in this embodiment 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, and the exit pupil diameter is set to 6 mm.

[0053] 8 shows a first phase plate 213, a half mirror 214, a second phase plate 215, and a second polarizing plate 216 that are laminated and bonded together on the observation-side surface of the lens 104. An adhesive layer 218 is provided between the observation-side surface of the lens 204 and the first phase plate 213, an adhesive layer (first adhesive layer) 219 is provided between the first phase plate 213 and the half mirror 214, and an adhesive layer 220 is provided between the half mirror 214 and the second phase plate 215. In addition, an adhesive layer 221 is provided between the second phase plate 215 and the second polarizing plate 216.

[0054] In this way, the display optical system can be made thinner by laminating the first phase plate 213, the half mirror 214, the second phase plate 215, and the second polarizing plate 216. An anti-reflection (AR) film 217 for preventing reflection of external light is attached to the observation side surface of the second polarizing plate 216 via an adhesive layer 222.

[0055] In this embodiment, the half mirror 214 is made of a film element. If there is unevenness (concavities and depressions) in the thickness of the adhesive layer 219 between the half mirror 214 and the adjacent first phase plate 213 on the reflection side, unevenness corresponding to the unevenness will appear on the half mirror 214. If there are concaves and convexes on the half mirror 214, local optical power will be generated in the half mirror 214 with respect to the light reflected by the half mirror 214, causing local defocusing of the displayed image, which will be observed as a blurred image with reduced contrast.

[0056] Therefore, in this embodiment, the thickness of the adhesive layer 219 between the half mirror 214 and the first phase plate 213 is reduced to reduce the unevenness of the adhesive layer 219, thereby suppressing the generation of local optical power in the half mirror 214. Specifically, as in the first embodiment, the thickness of the adhesive layer 219 is set to 10 μm, and the amount of variation in the thickness is limited to 5 μm (±2.5 μm). Basically, it is desirable that the thickness (d1) of the adhesive layer 219 between the half mirror 214 having a reflective function and the first phase plate 213 be equal to or greater than 5 μm and less than 20 μm. Also, as in the first embodiment, it is desirable that the amount of variation in the thickness (Δd1) of the adhesive layer 219 be less than 10 μm.

[0057] Furthermore, similar to Example 1, it is desirable that the thickness variation of the adhesive layer 219 be as small as possible within the width of the light beam incident on the viewer's eye near the optical axis of the display optical system, which corresponds to the vicinity of the center of the displayed image. Specifically, the ratio (Δd1 / Φ1) of the light beam width (Φ1) of the light beam emitted from a pixel on the optical axis of the display optical system among the display elements when reflected by the half mirror 214 to the thickness variation (Δd1) is desirably less than 0.002. In this example, the thickness variation of the adhesive layer 219 near the center is 3 μm, and since the diameter of the pupil of the viewer's eye is approximately 4 mm, the ratio is 0.00075. Furthermore, the thickness of the half mirror 214, 40 μm, is four times the thickness of the adhesive layer 219. It is desirable that the thickness of the half mirror 214 be 3 times or more and 15 times or less the thickness of the adhesive layer 219.

[0058] Furthermore, it is desirable to reduce the thickness of the adhesive layer 220 between the half mirror 214 and the second phase plate 215 to reduce thickness variations. In this embodiment, the thickness of the adhesive layer 220 is 10 μm, and the thickness variation is 5 μm (±2.5 μm). The thickness variation of the adhesive layer 220 near the center is 3 μm, and the ratio to the light beam width near the center is 0.00075.

[0059] 9, in this embodiment, an adhesive layer 223 for bonding the lens 205 and the PBS 212 together is provided between them, and an adhesive layer 224 is provided between the PBS 212 and the lens 204. By bonding the PBS 212 to the lenses 204 and 205 in a curved shape in this way, the degree of freedom in designing the display optical system is improved, and a thinner design and a wider angle of view can be achieved.

[0060] In this embodiment, the PBS 212 is also made of a film element. Therefore, if there are irregularities in the adhesive layer 224 between the PBS 212 and the adjacent lens 204 on the reflection side, irregularities corresponding to those irregularities will appear on the PBS 212, causing local optical power in the PBS 212 against the light reflected by the PBS 212. As a result, the displayed image will be locally out of focus, and the displayed image will be observed as a blurred image with reduced contrast.

[0061] Therefore, in this embodiment, the thickness of the adhesive layer (first adhesive layer) 224 is also reduced to reduce the thickness variation, thereby reducing the unevenness of the adhesive layer 224. In this embodiment, the thickness of the adhesive layer 223 between the PBS 212 and the lens 205 is also reduced in a similar manner. Specifically, the thickness (d1) of the adhesive layers 223 and 224 is 15 μm, and the thickness variation (Δd1) is 8 μm (±4 μm). Basically, the thickness of the adhesive layer 224 between the PBS 212, which has a reflecting function, and the lens 204 is preferably 5 μm or more and less than 20 μm. Furthermore, the thickness variation of the adhesive layer 224 is preferably less than 10 μm.

[0062] Furthermore, the thickness variation of the adhesive layers 223, 224 near the center is 3 μm, and since the size of the pupil of the observer's eye is approximately 4 mm, the ratio to the luminous flux width (Δd1 / Φ1) near the center is 0.00075. This ratio is preferably less than 0.002. Furthermore, the thickness of the PBS 212 is 80 μm, which is 5.3 times the thickness of the adhesive layers 223, 224. The thickness of the PBS 212 is preferably 3 times or more and 15 times or less the thickness of the adhesive layers 223, 224.

[0063] In this way, the thickness of the adhesive layer between the half mirror 214 or the PBS 212 and the polarizing element (first phase plate 213) or the lens 204 adjacent thereto on the reflection side is thinned to reduce thickness variations. This makes it possible to reduce unevenness occurring in the half mirror 214 or the PBS 212. Because the half mirror 214 or the PBS 212 has a reflective function, local unevenness has a greater effect on the optical power than on a surface with a transmissive function, and is more likely to cause local contrast reduction in the displayed image. Therefore, by reducing the unevenness of the adhesive layer between the half mirror 214 or the PBS 212 and the first phase plate 213 or the lens 204 adjacent thereto on the reflection side, it is possible to reduce the unevenness of the half mirror 214 or the PBS 212 and reduce local contrast reduction in the displayed image.

[0064] In this embodiment, the AR film 217 is bonded to the second polarizing plate 216 via an adhesive layer (second adhesive layer) 222. As with the half mirror 214 and the PBS 212, if the AR film 217 has unevenness at its interface with the air, local optical power is generated in the AR film 217, reducing the contrast of the displayed image. Therefore, in this embodiment, the thickness of the adhesive layer 222 between the AR film 217 and the second polarizing plate 216 is reduced to reduce thickness variations, thereby reducing the unevenness of the AR film 217.

[0065] In this embodiment, the adhesive layer 222 has a thickness of 10 μm, and the thickness variation is 10 μm (±5 μm). Essentially, the thickness (d2) of the adhesive layer 222 between the AR film 217, which has a transmitting effect, and the second polarizer 216 is 5 μm or more and less than 20 μm, and the thickness variation (Δd2) is preferably less than 20 μm. Furthermore, the thickness variation (Δd2) of the adhesive layer 222 near the center is 10 μm, and the ratio (Δd2 / Φ2) to the luminous flux width (Φ2) near the center is 0.0025. This ratio is preferably less than 0.005.

[0066] In this embodiment, the lenses 204 and 205 and the lenses 206 and 207 are cemented lenses. Using cemented lenses makes it easier to hold them inside the HMD 201, even if they are separate lenses. For this reason, the lens surface on which the half mirror 212 is vapor-deposited may be the observation-side surface of the lens 205. Even in this case, the surface on which the half mirror 212 is vapor-deposited has a convex shape facing the display element side. By vapor-depositing the half mirror 212 on the convex surface, it is possible to achieve a wide 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 an aspheric shape, it is possible to improve the aberration correction effect.

[0067] The observation-side surface of the lens 204, on which the first phase plate 213, the PBS 214, etc. are laminated, has a flat shape. This allows the display optical system to be made thinner while ensuring sufficient eye relief. The lens 204 is a plano-convex lens.

[0068] In this embodiment, the first and second phase plates 213 and 215 are both λ / 4 plates, but the phase difference may be shifted from λ / 4 to cancel the birefringence of the lenses 204 and 205. In this case, it is desirable that the sum of the phase differences of the lens 204 and the second phase plate 215 be 3λ / 20 or more and 7λ / 20 or less. It is also desirable that the sum of the phase differences of the lens 205 and the first phase plate 213 be 3λ / 20 or more and 7λ / 20 or less. If the phase difference is outside this range, the intensity of ghost light increases, making it impossible to observe a natural image, which is not desirable.

[0069] In this embodiment, an organic EL element that emits unpolarized light is used as the display element, but a liquid crystal display that emits linearly polarized light may be used as the display element, eliminating the need for the first polarizer 210 and making the display optical system thinner. [Example]

[0070] 10 shows a display optical system according to a third embodiment. This embodiment is a modification of the second embodiment, and the same components as those in the second embodiment are designated by the same reference numerals.

[0071] In this embodiment, a PBS 312 and a first phase plate 313 are disposed between the lens 204 and the lens 205, and a half mirror 314, a second phase plate 315, a second polarizing plate 316, and an AR coating 317 are laminated on the observation side surface of the lens 204. The half mirror 314 is deposited by vapor deposition on the display element side surface of the lens 204, and the AR coating 317 is deposited by vapor deposition on the observation side surface of the second polarizing plate 316.

[0072] 11, an adhesive layer 319 is provided between the second phase plate 315 and the second polarizing plate 316 to bond them together. Also, an adhesive layer 318 is provided between the second phase plate 315 and the half mirror 314 deposited on the lens 204 to bond them together.

[0073] 12, an adhesive layer 322 is provided between the PBS 312 and the first phase plate 313 to bond them together. In addition, an adhesive layer 321 is provided between the PBS 312 and the lens 205, and an adhesive layer 323 is provided between the first phase plate 313 and the lens 204.

[0074] Here, the PBS 312 is composed of a film element, and if there are irregularities in the adhesive layer 322 between the PBS 312 and the adjacent polarizing element (first phase plate 313) on the reflection side, irregularities corresponding to the irregularities will appear on the PBS 312. As a result, local optical power is generated in the PBS 312 with respect to the light reflected by the PBS 312. As a result, localized defocus occurs in the displayed image, and the displayed image is observed as a blurred image with reduced contrast.

[0075] Therefore, in this embodiment, the thickness of the adhesive layer (first adhesive layer) 322 between the PBS 312 and the first phase plate 313 is reduced to reduce thickness variation, thereby reducing the unevenness that appears on the PBS 312. In this embodiment, the thickness (d1) of the adhesive layer 322 is 10 μm, and the thickness variation (Δd1) is 8 μm (±4 μm). Basically, it is desirable that the thickness of the adhesive layer 322 be equal to or greater than 5 μm and less than 20 μm, and that the thickness variation be less than 10 μm.

[0076] Furthermore, the thickness of adhesive layer 322 near the center varies by 4 μm, and since the size of the pupil of the observer's eye is approximately 4 mm, the ratio (Δd1 / Φ1) to the light beam width (Φ1) near the center is 0.001. This ratio is preferably less than 0.002. Furthermore, the thickness of PBS 312 is 45 μm, which is 4.5 times the thickness of adhesive layer 322. The thickness of PBS 312 is preferably 3 times or more and 15 times or less the thickness of adhesive layer 322.

[0077] It is also desirable to reduce the thickness of the adhesive layer 321 between the PBS 312 and the lens 205 to reduce thickness variation. In this embodiment, the thickness of the adhesive layer 321 is 15 μm, and the thickness variation is 6 μm (±3 μm). The thickness variation of the adhesive layer 321 near the center is 4 μm, and the ratio to the light beam width near the center is 0.001.

[0078] The above embodiment includes the following configurations.

[0079] (Configuration 1) A display optical system that guides light from a display element to a viewing side via a semi-transmissive reflecting surface, a polarization separation surface, and a plurality of polarizing elements, At least one of the semi-transmissive reflective surface and the polarization separation surface is formed by a film element, the film element is bonded to any one of the plurality of polarizing elements or the lens via a first adhesive layer on the reflection side of the film element; The thickness d1 of the first adhesive layer is 5μm≦d1<20μm A display optical system characterized by satisfying the following conditions: (Configuration 2) The thickness variation Δd1 in the in-plane direction of the first adhesive layer is 0<Δd1<10μm 2. The display optical system according to configuration 1, wherein the following condition is satisfied: (Configuration 3) The light beam width Φ1 and the variation amount Δd1 when the light beam emitted from the pixel on the optical axis of the display optical system among the display elements is reflected by the film element are 0<Δd1 / Φ1<0.002 3. The display optical system according to configuration 2, wherein the following condition is satisfied: (Configuration 4) When the thickness variation amount changes periodically in the in-plane direction, 3. The display optical system according to configuration 2, wherein the period of change in the amount of variation in thickness is at least twice the light beam width Φ1. (Configuration 5) 5. The display optical system according to any one of configurations 1 to 4, wherein the thickness of the film element is 3 times or more and 15 times or less the thickness of the first adhesive layer. (Configuration 6) a first polarizing plate, a first phase plate, the semi-transmissive reflective surface, a second phase plate, the polarization separation surface, and a second polarizing plate are arranged in this order from the display element side; 6. The display optical system according to any one of configurations 1 to 5, wherein the film element constituting the polarization separation surface is bonded to the second phase plate via the first adhesive layer. (Configuration 7) a first polarizing plate, the polarization separation surface, a first phase plate, the semi-transmissive reflective surface, a second phase plate, and a second polarizing plate are arranged in this order from the display element side; 6. The display optical system according to any one of configurations 1 to 5, wherein the film element constituting the semi-transmissive reflective surface is bonded to the first phase plate via the first adhesive layer. (Configuration 8) a first polarizing plate, the polarization separation surface, a lens, a first phase plate, the semi-transmissive reflective surface, a second phase plate, and a second polarizing plate are arranged in this order from the display element side; 6. The display optical system according to any one of configurations 1 to 5, wherein the film element that constitutes the polarization separation surface is bonded to the lens via the first adhesive layer. (Configuration 9) a polarizing plate is provided on the most observation side, and an anti-reflection film is attached to the polarizing plate via a second adhesive layer; The thickness d2 of the second adhesive layer is 5μm≦d2<20μm 9. The display optical system according to any one of configurations 1 to 8, wherein the following condition is satisfied: (Configuration 10) The thickness variation Δd2 in the in-plane direction of the second adhesive layer is 0<Δd2<20μm 10. The display optical system according to configuration 9, wherein the following condition is satisfied: (Configuration 11) The luminous flux width Φ2 of the luminous flux emitted from a pixel on the optical axis of the display optical system of the display element when passing through the second adhesive layer and the variation amount Δd2 are 0<Δd2 / Φ2<0.005 11. The display optical system according to configuration 10, which satisfies the following condition: (Configuration 12) The focal length f of the display optical system is 10mm≦f≦20mm 12. The display optical system according to any one of configurations 1 to 11, wherein the following condition is satisfied: (Configuration 13) The display optical system according to any one of configurations 1 to 12; and and an image display device comprising the display element. The above-described embodiments are merely representative examples, and various modifications and changes can be made to each embodiment when implementing the present invention. [Explanation of symbols]

[0080] 101,201 HMD 102,202 Right eye 103,203 left eye 104~107, 204~207 lenses 108,208 Display element for right eye 109,209 Display element for left eye 110,115,210,216,316 Polarizing plate 111,113,213,215,313,315 Phase plate 112,214,314 Half mirror 114,212,312 PBS

Claims

1. A display optical system that guides light from a display element to a viewing side via a semi-transmissive reflecting surface, a polarization separation surface, and a plurality of polarizing elements, At least one of the semi-transmissive reflective surface and the polarization separation surface is formed by a film element, the film element is bonded to any one of the plurality of polarizing elements or the lens via a first adhesive layer on the reflection side of the film element; The thickness d1 of the first adhesive layer is 5μm≦d1<20μm A display optical system characterized by satisfying the following conditions:

2. The thickness variation Δd1 in the in-plane direction of the first adhesive layer is 0<Δd1<10 μm 2. The display optical system according to claim 1, wherein the following condition is satisfied:

3. The light beam width Φ1 and the variation amount Δd1 when the light beam emitted from a pixel on the optical axis of the display optical system among the display elements is reflected by the film element are 0<Δd1 / Φ1<0.002 3. The display optical system according to claim 2, wherein the following condition is satisfied:

4. When the thickness variation amount changes periodically in the in-plane direction, 3. The display optical system according to claim 2, wherein the period of change in the amount of variation in thickness is at least twice the light beam width Φ1.

5. 2. The display optical system according to claim 1, wherein the thickness of the film element is 3 times or more and 15 times or less the thickness of the first adhesive layer.

6. a first polarizing plate, a first phase plate, the semi-transmissive reflective surface, a second phase plate, the polarization separation surface, and a second polarizing plate are arranged in this order from the display element side; 2. The display optical system according to claim 1, wherein the film element constituting the polarization separation surface is bonded to the second phase plate via the first adhesive layer.

7. a first polarizing plate, the polarization separation surface, a first phase plate, the semi-transmissive reflective surface, a second phase plate, and a second polarizing plate are arranged in this order from the display element side; 2. The display optical system according to claim 1, wherein the film element constituting the semi-transmissive reflective surface is bonded to the first phase plate via the first adhesive layer.

8. a first polarizing plate, the polarization separation surface, a lens, a first phase plate, the semi-transmissive reflective surface, a second phase plate, and a second polarizing plate are arranged in this order from the display element side; 2. The display optical system according to claim 1, wherein the film element constituting the polarization separation surface is bonded to the lens via the first adhesive layer.

9. a polarizing plate is provided on the most observation side, and an anti-reflection film is attached to the polarizing plate via a second adhesive layer; The thickness d2 of the second adhesive layer is 5μm≦d2<20μm 2. The display optical system according to claim 1, wherein the following condition is satisfied:

10. The thickness variation Δd2 of the second adhesive layer in the in-plane direction is 0<Δd2<20 μm 10. The display optical system according to claim 9, wherein the following condition is satisfied:

11. The luminous flux width Φ2 of the luminous flux emitted from a pixel on the optical axis of the display optical system of the display element when passing through the second adhesive layer and the variation amount Δd2 are 0<Δd2 / Φ2<0.005 11. The display optical system according to claim 10, wherein the following condition is satisfied:

12. The focal length f of the display optical system is 10 mm≦f≦20 mm 2. The display optical system according to claim 1, wherein the following condition is satisfied:

13. The display optical system according to any one of claims 1 to 12; An image display device comprising the display element.

Images