Optical system and image display device

Abstract

To provide an optical system which reduces image deterioration in a display image due to an adhesive layer for pasting an optical unit and a lens.SOLUTION: An optical system includes a lens 105 which guides light from a display element 110 to an observation side and which uses a translucent reflection surface 114, a polarization separation surface 116, polarizers 115, 117, and a resin material. The translucent reflection surface or the polarization separation surface and the polarizers are integrated with each other so as to form an optical unit. The optical unit and the lens are joined together through a first adhesive layer 119. The first adhesive layer transmits the light a plurality of times. The thickness d1 (mm) of the first adhesive layer, a refractive index N1 in a d line of the lens, and a refractive index N2 in a d line of the first adhesive layer satisfy conditions of 0.009<N2×d1<0.031 and 0.95≤N1 / N2≤1.10.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to an 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 an optical system, an optical system that folds the optical path by using polarized light and uses an optical unit made by laminating a polarization selection element (polarization separation element), a half mirror, a phase plate, a polarizing plate, etc., attached to a lens is disclosed in Patent Documents 1 and 2. However, there is a risk that the quality of the displayed image may be degraded due to the influence of air bubbles mixed in the adhesive layer between the optical unit and the lens or the birefringence of the adhesive layer itself. [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 describe the adhesive layer between the optical unit and the lens, nor do they describe a method for reducing the effects of air bubbles or birefringence in the adhesive layer.

[0005] The present invention provides an optical system that can reduce image degradation of a displayed image caused by an adhesive layer that bonds an optical unit and a lens together. [Means for solving the problem]

[0006] An optical system according to one aspect of the present invention is an optical system that guides light from a display element to the viewing side, and includes a semi-transmissive reflective surface, a polarized light separating surface, a polarizing element, and a lens made of a resin material. The semi-transmissive reflective surface or the polarized light separating surface and the polarizing element are integrated together to form an optical unit. The optical unit and the lens are bonded together via a first adhesive layer. Light passes through the first adhesive layer multiple times. When the thickness of the first adhesive layer is d1 (mm), the refractive index of the lens at the d-line is N1, and the refractive index of the first adhesive layer at the d-line is N2, 0.009 <N2×d1<0.031 0.95≦N1 / N2≦1.10 The optical system is characterized by satisfying the following conditions: An image display device using the optical system described above also constitutes another aspect of the present invention. [Effects of the Invention]

[0007] According to the present invention, it is possible to reduce image degradation of a displayed image caused by the adhesive layer that bonds the optical unit and the lens together. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram showing the configuration of an image display device equipped with an optical system according to a first embodiment. [Figure 2] FIG. 1 is a diagram showing the configuration of an optical system according to a first embodiment. [Figure 3] FIG. 2 is a diagram showing the optical path of the optical system of the first embodiment. [Figure 4] FIG. 2 is an enlarged view showing the configuration of a joint between an optical unit and a lens in the optical system of the first embodiment. [Figure 5] FIG. 10 is a diagram showing the configuration of an image display device equipped with an optical system according to a second embodiment. [Figure 6] FIG. 10 is a diagram showing the configuration of an optical system according to a second embodiment. [Figure 7] FIG. 10 is a diagram showing the optical path of the optical system of the second embodiment. [Figure 8] FIG. 10 is an enlarged view showing the configuration of a joint between an optical unit and a lens in the optical system of Example 2. [Figure 9] FIG. 10 is a diagram showing the configuration of an image display device equipped with an optical system according to a third embodiment. [Figure 10] FIG. 10 is a diagram showing the configuration of an optical system according to a third embodiment. [Figure 11] FIG. 10 is a diagram showing the optical path of the optical system of the third embodiment. [Figure 12] FIG. 11 is an enlarged view showing the configuration of a joint between an optical unit and a lens in the optical system of Example 3. [Figure 13] FIG. 10 is an enlarged view showing the configuration of the junction between the PBS and the phase plate and the lens in the optical system of Example 3. [Figure 14] FIG. 2 is an external view of the image display device of FIG. 1. DETAILED DESCRIPTION OF THE INVENTION

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

[0010] (Image display device) FIG. 1 shows a top view of an HMD (head mounted display) 101 as an image display device using the optical system (display optical system, observation optical system, eyepiece optical system) of Example 1. Reference numeral 102 denotes the right eye of an observer, and 103 denotes the left eye of the observer. Lenses 104 to 106 form part of the optical system for the right eye, and lenses 107 to 109 form part of the optical system for the left eye. Reference numeral 110 denotes a display element for the right eye, and 111 denotes a display element for the left eye, each of which is formed by an organic EL element that emits unpolarized light.

[0011] The optical system for the right eye magnifies light (virtual image) from the original image displayed on the display element for the right eye 110 and directs it to the right eye 102, and the optical system for the left eye magnifies light from the original image displayed on the display element for the left eye 111 and directs it to the left eye 103.

[0012] The focal length f of the right-eye optical system and the left-eye optical system is 17 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×θ1 is 72°. The distance between the HMD 101 and the observer's eyes (eye relief) is 12 mm.

[0013] (optical system) The optical system of Example 1 is an optical system that folds the optical path using polarized light, and FIG. 2 shows an enlarged view of the optical system for the right eye. In addition to lenses 104 to 106, the optical system for the right eye includes a first polarizing plate 112 and a first phase plate 113, which are arranged between a right-eye display element 110 and the first lens 106, in that order from the display element side, and a half mirror 114 deposited on the display element side surface of the second lens 105. The first polarizing plate 112 and the first phase plate 113 each have a planar shape and are stacked on top of each other and attached to the right-eye display element 110. The half mirror 114 functions as a semi-transmissive reflective surface located between the bonding surfaces of the first and second lenses 106 and 105. That is, the first lens 106 and the second lens 105 are configured as a cemented lens, with the half mirror 114 sandwiched between their bonding surfaces.

[0014] The right-eye optical system further includes a second phase plate 115, a polarization separation element (PBS) 116, and a second polarizing plate 117, which are arranged between the second lens 105 and the third lens 104 in this order from the display element side. The second phase plate 115, the PBS 116, and the second polarizing plate 117 each have a planar shape, and are stacked and bonded together to form a layered optically functional element (hereinafter referred to as an optical unit). The PBS 116 functions as a polarization separation surface.

[0015] The first polarizing plate 112, the first phase plate 113, the second phase plate 115 and the second polarizing plate 117 correspond to a plurality of polarizing elements.

[0016] The first phase plate 113 and the second phase plate 115 are wave plates with a phase difference of λ / 4. The polarization direction of the polarized light transmitted by the first polarizing plate 112 and the slow axis of the first phase plate 113 are inclined at 45° from each other, and the polarization direction of the polarized light transmitted by the first polarizing plate 112 and the slow axis of the second phase plate 115 are inclined at −45° from each other. The polarization direction of the polarized light transmitted by the first polarizing plate 112 and the polarization direction of the polarized light transmitted by the PBS 116 are orthogonal to each other. The polarization direction of the polarized light transmitted by the second polarizing plate 117 and the polarization direction of the polarized light transmitted by the PBS 116 are consistent with each other.

[0017] In the right-eye optical system, a third lens 104 is disposed between an optical unit composed of a second phase plate 115, a PBS 116, and a second polarizing plate 117 and an exit pupil where the right eye 102 is disposed.

[0018] FIG. 3 shows the optical path of the right-eye optical system configured as described above. Unpolarized light emitted from the right-eye display element 110 passes through the first polarizing plate 112 to become linearly polarized light, and this linearly polarized light passes through the first phase plate 113 to become circularly polarized light. The circularly polarized light that passes through the first lens 106 passes through the half mirror 114, then passes through the second lens 105, and then passes through the second phase plate 115 to become linearly polarized light. Because the polarization direction of this linearly polarized light is perpendicular to the transmission polarization direction of the PBS 116, it is reflected by the PBS 116 and passes through the second phase plate 115 to become circularly polarized light. The circularly polarized light passes through the second lens 105, reflects off the half mirror 114, passes through the second lens 105 again, and then passes through the second phase plate 115 to become linearly polarized light. Because the polarization direction of this linearly polarized light matches the transmission polarization direction of the PBS 116, it passes through the PBS 116, the second polarizing plate 117, and the third lens 104, and is guided to the right eye 102. By providing the second polarizing plate 117, ghost light caused by external light can be reduced, and the contrast of the displayed image can be increased. In the left-eye optical system, light from the left-eye display element 111 follows a similar optical path and is guided to the left eye 103.

[0019] By using an optical system that folds the optical path using polarized light in this way, the optical system can be made thinner and the focal length of the optical system can be shortened, allowing images to be displayed at a wide angle of view. Furthermore, by using a cemented lens for the first and second lenses 106 and 105 and cementing an optical unit to the second lens 105, the optical system can be made even thinner. Furthermore, by placing a third lens 104 in front of the exit pupil, high optical performance can be ensured.

[0020] FIG. 14 shows the appearance of the HMD 101. It is desirable that the head-mounted HMD 101 be lightweight. For this reason, it is desirable that the lenses constituting the right-eye optical system are manufactured (formed) using a resin material whose specific gravity is smaller than that of glass, and in Example 1, all lenses 104 to 106 are made of resin. Note that the resin material referred to here is not limited to a material consisting of resin alone, but may also contain components other than resin, such as inorganic fine particles. In other words, it is sufficient that the main component is resin. This also applies to the other Examples described below.

[0021] The second lens 105 is a plano-convex aspherical lens, which enhances the aberration correction effect. The first lens 106 is also a double-sided aspherical lens. The same applies to the left-eye optical system.

[0022] The characteristic configuration of the lenses in this embodiment will be described. The second lens 105 is a lens with positive refractive power, with a flat lens surface on the observation side (exit pupil side) and an aspherical lens surface on the display element side (the cemented surface with the first lens 106) that is convex toward the display element side. A half mirror 114 is provided as a reflective surface on the lens surface on the display element side of the second lens 105, and the half mirror 114 has positive refractive power, which allows the optical path to be folded, thereby achieving a thin optical system with a wide angle of view. Furthermore, the lens surface on the display element side of the second lens 105 and the lens surface on the observation side of the first lens 106 are cemented together to form a cemented surface, which prevents the condition for total reflection from being met for light incident on the cemented surface compared to when these lens surfaces are in contact with air. Furthermore, the first lens 106 is a double-sided aspherical lens with negative refractive power.

[0023] When the optical power (the reciprocal of the focal length) on the optical axis of the first lens 106 is Φ1 and the optical power on the optical axis of the second lens 105 is Φ2, it is desirable to satisfy the condition of the following formula (1).

[0024] 0.2≦|Φ1 / Φ2|≦0.8 (1) The condition of formula (1) indicates an appropriate relationship between the optical powers of the first and second lenses 106 and 105 that constitute the cemented lens. If |Φ1 / Φ2| exceeds the upper limit of formula (1), the focal length of the entire optical system becomes long, which leads to an increase in the size of the HMD 101, which is undesirable. If |Φ1 / Φ2| falls below the lower limit of formula (1), it becomes difficult to configure an optical system with good optical performance, which is undesirable. In Example 1, Φ1 = -0.0045, Φ2 = 0.0085, and |Φ1 / Φ2| = 0.526. That is, the optical system of Example 1 satisfies the condition of formula (1).

[0025] Furthermore, by placing the third lens 104 with positive refractive power closer to the display element side than the exit pupil, it is possible to correct aberrations that could not be corrected by the first and second lenses 106 and 105. If the third lens 104 is an aspherical lens, higher optical performance can be obtained.

[0026] When resin lenses are used for the lenses 104 to 106, birefringence that occurs during molding of each lens may affect the optical performance of the right-eye optical system. For this reason, an annealing process or the like is performed to set the retardation amount Re (nm) due to birefringence of each lens so that it satisfies the condition of the following formula (2).

[0027] Re≦30 (2) In this embodiment, the phase difference Re of the first lens 106 is 20 nm, the phase difference Re of the second lens 105 is 5 nm, and the phase difference Re of the third lens 104 is 20 nm, which satisfies the condition of formula (2).

[0028] (adhesive layer) 4 shows an enlarged view of adhesive layers 120 to 122 within the optical unit and adhesive layer (first adhesive layer) 119 between the optical unit and lens 105. The second phase plate 115 and PBS 116 are bonded together with adhesive layer 120, and the PBS 116 and second polarizing plate 117 are bonded together with adhesive layer 121. In addition, in order to reduce reflection at the interface between the second polarizing plate 117 and air, an anti-reflection film 118 is bonded to the second polarizing plate 117 with adhesive layer 122. The optical unit having this layered structure is bonded to the second lens 105 with adhesive layer 119.

[0029] When the thickness of adhesive layer 119 is d1 (mm), the refractive index of second lens 105 at the d-line is N1, and the refractive index of adhesive layer 119 at the d-line is N2, adhesive layer 119 satisfies the conditions of the following formulas (3) and (4). Note that the thickness referred to in this specification refers to the width in the optical axis direction.

[0030] 0.009 <N2×d1<0.031 (3) 0.95≦N1 / N2≦1.10 (4) The condition of formula (3) indicates the appropriate range of the optical path length N2×d1 when light passes through the adhesive layer 119. If N2×d1 exceeds the upper limit of formula (3), the thickness of the adhesive layer 119 becomes too thick, which is undesirable because the birefringence of the adhesive layer 119 causes a deterioration in the quality of the displayed image. If N2×d1 falls below the lower limit of formula (3), the thickness of the adhesive layer 119 becomes too thin, which makes it more likely for air bubbles to form in the adhesive layer 119 due to the influence of surface shape errors of the resin lens and variations in surface shape errors due to the annealing process. This results in a deterioration in the quality of the displayed image, which is undesirable.

[0031] The condition of formula (4) indicates an appropriate relationship between the refractive indices N1 and N2 of second lens 105 and adhesive layer 119. When N1 / N2 is within the numerical range of formula (4), the difference in refractive index between adhesive layer 119 and second lens 105 can be reduced, and the influence of the difference in refractive power on optical performance can be reduced.

[0032] In this example, the thickness d1 of the adhesive layer 119 is 0.015 mm (tolerance ±0.003 mm), the refractive index N1 of the second lens 105 is 1.54, and the refractive index of the adhesive layer 119 is 1.48. Therefore, N2×d1=0.022 and N1 / N2=1.045, which respectively satisfy the conditions of formulas (3) and (4).

[0033] Note that d1 is preferably 0.020 mm or less, more preferably 0.019 mm or less, even more preferably 0.018 mm or less, and even more preferably 0.016 mm or less. This also applies to the thickness d1 of the adhesive layer in other examples described later.

[0034] Furthermore, the thickness d1 of the adhesive layer 119 satisfies the condition of the following formula (5), where f (mm) is the focal length of the entire optical system: 0.0002≦d1 / f≦0.0020 (5) The condition of formula (5) indicates an appropriate relationship between the thickness d1 of the adhesive layer 119 and the focal length f of the entire system. By satisfying this condition, it is possible to reduce the influence of the adhesive layer 119 on the optical performance of the entire system. In this example, the focal length f is 17 mm and the thickness d1 of the adhesive layer 119 is 0.015 mm, so d1 / f=0.0009, which satisfies the condition of formula (5).

[0035] In an optical system that folds the optical path using polarized light, the adhesive layer 119 has a large effect on optical performance because the light beam traveling from the right-eye display element 110 toward the observation side passes through the adhesive layer 119 multiple times (three times). Therefore, by satisfying the conditions of formulas (3) to (5), it is possible to effectively suppress degradation of the quality of the displayed image caused by the joint where the optical unit and the lens 105 are bonded together with the adhesive layer 119.

[0036] The adhesive layers 120 to 122 in the optical unit will be described. When the thickness of the adhesive layer (second adhesive layer) 120 that bonds the second phase plate 115 and the PBS 116 together is d2, the condition of the following formula (6) is satisfied.

[0037] 0.005mm≦d2<0.020mm (6) The condition in formula (6) indicates an appropriate range for the thickness d2 of the adhesive layer 120. Because the PBS 116 is a thin film-like element (hereinafter referred to as a film element), if the adhesive layer 120 has thickness variations (unevenness) in the in-plane direction, unevenness corresponding to the unevenness will also appear on the PBS 116. If the adhesive layer 120 has periodic unevenness, localized optical power will be generated for the light reflected by the PBS 116. 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. In particular, because the PBS 116 functions as a reflective surface, it is more likely to affect the displayed image than a transmissive surface. If d2 exceeds the upper limit of formula (6), the unevenness of the adhesive layer 120 will become large, and the unevenness appearing on the PBS 116 will also become large, increasing the optical power for the light reflected by the PBS 116, which is undesirable. If d2 is below the lower limit of the formula (6), the adhesive layer 120 becomes too thin, making it difficult to bond the second phase plate 115 and the PBS 116 together, and wrinkles and bubbles tend to form in the adhesive layer 120, which is undesirable.

[0038] In this embodiment, the thickness d2 of the adhesive layer 120 is 0.010 mm (±0.003 mm), which satisfies the condition of formula (6).

[0039] It is more preferable that d2 be 0.019 mm or less, even more preferably 0.018 mm or less, and even more preferably 0.016 mm or less. This also applies to the thickness d2 of the adhesive layer in other examples described later.

[0040] Furthermore, in this embodiment, the thickness of adhesive layer 121 that bonds PBS 116 and second polarizing plate 117 together is set to 0.025 mm (±0.003 mm), and the thickness of adhesive layer 122 that bonds second polarizing plate 117 and anti-reflection film 118 together is set to 0.025 mm (±0.003 mm), thereby reducing the effect of unevenness on the optical performance of each adhesive layer. [Example]

[0041] (Image display device) 5 shows an HMD 201 as an image display device using the optical system of Example 2, viewed from above. 202 denotes the observer's right eye, and 203 denotes the observer's left eye. Lenses 204 and 205 constitute part of the optical system for the right eye, and lenses 206 and 207 constitute part of the optical system for the left eye. 208 denotes a display element for the right eye, and 209 denotes a display element for the left eye, each of which is composed of an organic EL element that emits unpolarized light.

[0042] The optical system for the right eye magnifies light (virtual image) from the original image displayed on the display element for the right eye 208 and directs it to the right eye 202, and the optical system for the left eye magnifies light from the original image displayed on the display element for the left eye 209 and directs it to the left eye 203.

[0043] The focal length f of the right-eye optical system and the left-eye optical system is 17 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×θ1 is 78°. The distance between the HMD201 and the observer's eyes (eye relief) is 18 mm.

[0044] (optical system) The optical system of Example 2 also folds the optical path using polarized light. FIG. 6 shows an enlarged view of the optical system for the right eye. In addition to the lenses 204 and 205, the optical system for the right eye includes a first polarizing plate 210 and a first phase plate 211, which are arranged between the right-eye display element 208 and the first lens 205, in that order from the display element side, and a half mirror 212 deposited on the display element side surface of the second lens 204. The first polarizing plate 210 and the first phase plate 211 each have a planar shape and are stacked on top of each other. The half mirror 212 functions as a semi-transmissive reflective surface located between the bonding surfaces of the first and second lenses 205 and 204. That is, the first and second lenses 205 and 204 are configured as a cemented lens with the half mirror 212 sandwiched between them.

[0045] The right-eye optical system further includes a second phase plate 213, a PBS 214, and a second polarizing plate 215, which are arranged in this order from the display element side, on the observation side of the lens 204. The second phase plate 213, the PBS 214, and the second polarizing plate 215 each have a planar shape, and are stacked and bonded together to form an optical unit.

[0046] The first phase plate 211 and the second phase plate 213 are wave plates with a phase difference of λ / 4. The polarization direction of the polarized light transmitted by the first polarizing plate 210 and the slow axis of the first phase plate 211 are inclined at 45° from each other, and the polarization direction of the polarized light transmitted by the first polarizing plate 210 and the slow axis of the second phase plate 213 are inclined at −45° from each other. 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 214 are orthogonal to each other. The polarization direction of the polarized light transmitted by the second polarizing plate 215 and the polarization direction of the polarized light transmitted by the PBS 214 are consistent with each other.

[0047] FIG. 7 shows the optical path of the right-eye optical system configured as described above. Unpolarized light emitted from the right-eye display element 208 passes through the first polarizing plate 210 to become linearly polarized light, and this linearly polarized light passes through the first phase plate 211 to become circularly polarized light. The circularly polarized light that passes through the first lens 205 passes through the half mirror 212 and then the second lens 204, and then passes through the second phase plate 213 to become linearly polarized light. Because the polarization direction of this linearly polarized light is perpendicular to the transmission polarization direction of the PBS 214, it is reflected by the PBS 214 and passes through the second phase plate 213 to become circularly polarized light. The circularly polarized light passes through the second lens 204, reflects off the half mirror 212, passes through the lens 2204 again, and then passes through the second phase plate 213 to become linearly polarized light. Because the polarization direction of this linearly polarized light matches the transmission polarization direction of the PBS 214, it passes through the PBS 214 and then through the second polarizer 215 to be guided to the right eye 202. By providing the second polarizer 215, ghost light caused by external light can be reduced, thereby increasing the contrast of the displayed image. In the left-eye optical system, light from the left-eye display element 209 follows a similar optical path and is guided to the left eye 203.

[0048] By using an optical system that folds the optical path using polarized light in this way, the optical system can be made thinner, the focal length of the optical system can be shortened, and images can be displayed at a wide angle of view. Furthermore, by using a cemented lens for the first and second lenses 205 and 204 and cementing the optical unit to the second lens 204, the optical system can be made even thinner.

[0049] It is desirable for the head-mounted HMD 201 to be lightweight. For this reason, it is desirable for the lenses constituting the optical system for the right eye to be made of a resin material, which has a lower specific gravity than glass, and in Example 2, all lenses 204 and 205 are made of resin. Furthermore, the second lens 204 is a plano-convex aspherical lens, thereby improving the aberration correction effect. Furthermore, the first lens 205 is also a double-sided aspherical lens. The same applies to the optical system for the left eye.

[0050] The characteristic configuration of the lenses in this embodiment will be described. The right-eye optical system of this embodiment has two lenses 204 and 205. The second lens 204 is a lens with positive refractive power, with a flat lens surface on the observation side and an aspherical lens surface on the display element side (the surface bonded to the first lens 205) that is convex toward the display element side. A half mirror 212 is provided as a reflective surface on the lens surface on the display element side of the second lens 204, and the half mirror 212 has positive refractive power, which allows the optical path to be folded, thereby achieving a thin optical system with a wide angle of view.

[0051] Furthermore, since the lens surface of the second lens 204 facing the display element and the lens surface of the first lens 205 facing the observation side are cemented together to form a cemented surface, it is possible to avoid the condition for total reflection of light incident on the cemented surface being met, as compared to when these lens surfaces are in contact with air. Furthermore, the first lens 205 is a double-sided aspherical lens with negative refractive power.

[0052] When the optical power on the optical axis of the first lens 205 is Φ1 and the optical power on the optical axis of the second lens 204 is Φ2, it is desirable to satisfy the condition of formula (1) described in Example 1. In this example, Φ1=-0.0044, Φ2=0.0128, and |Φ1 / Φ2|=0.346. That is, the optical system of Example 2 satisfies the condition of formula (1).

[0053] The display element-side surface of the first lens 205 has a convex shape toward the display element side in a central region including the optical axis, but the curvature becomes gentler as it moves away from the optical axis, and has an inflection point within the optically effective region, which is the region through which effective light rays that contribute to image formation pass. The inflection point is the point where the surface changes from convex to concave toward the display element side. In other words, the inflection point is the point at which the value of the curve representing the display element-side surface of the lens 205, when differentiated twice, becomes zero in a cross section of the first lens 205 along the optical axis.

[0054] By making the central region of the display element-side surface of the first lens 205, including the optical axis, convex toward the display element side, the focal length of the optical system is shortened. Furthermore, by making the curvature of the display element-side surface of the first lens 205 gentler as it moves away from the optical axis, the output angle from the right-eye display element 208 in the peripheral area can be reduced. By providing such an aspherical shape to the display element-side surface of the first lens 205, an optical system with a short focal length and a wide field of view can be achieved, while also reducing the output angle from the right-eye display element 208 in the peripheral area, thereby suppressing deterioration in the viewing angle characteristics of the display element and reducing color shift. Furthermore, by reducing the angle of incidence to the first polarizing plate 210 and the second phase plate 211, factors that degrade image quality, such as a decrease in light intensity, uneven light intensity, and color unevenness, can be reduced.

[0055] The aspheric shape of the first lens 205 on the display element side has an inflection point in order to reduce the angle of emission from the peripheral right-eye display element 208 and shorten the focal length of the optical system at the same time. When the distance from the optical axis to the inflection point is Yip and the maximum distance from the optical axis (effective diameter) of the optically effective area of ​​the display element side surface of the first lens 205 is Yea, the aspheric shape satisfies the condition of the following formula (7).

[0056] 0.20 <Yip / Yea<0.75 (7) The condition of formula (7) indicates the appropriate position of the inflection point on the aspheric surface on the display element side of the first lens 205. If Yip / Yea exceeds the upper limit of formula (7), the inflection point will be at the periphery of the optically effective area, which is undesirable because it reduces the effect of reducing the output angle from the right-eye display element 208 in the periphery. If Yip / Yea falls below the lower limit of formula (7), the inflection point will be close to the optical axis, which reduces the optical power near the optical axis and makes it impossible to shorten the focal length of the optical system, which is undesirable.

[0057] In this embodiment, Yip is 4 mm and Yea is 12 mm, so Yip / Yea=0.33, which satisfies the condition of formula (7). More preferably, Yip / Yea is 3≦Yip / Yea≦0.7 (7a) It is preferable to satisfy the following conditions.

[0058] Furthermore, the aspherical shape of the first lens 205 on the display element side changes monotonically with increasing distance from the optical axis, and has no maximum or minimum values ​​within the effective optical area other than at points on the optical axis. This aspherical shape achieves both a smaller output angle from the right-eye display element 208 in the peripheral area and a shorter focal length of the optical system. Furthermore, by minimizing the change in the aspherical shape, the change in optical performance from the center to the periphery can be reduced, making it possible to present a display image that is easy to observe and improving the processing accuracy of the aspherical shape. The above description of the first lens 205 also applies to the first lens 207 in the left-eye optical system.

[0059] Also in this embodiment, the first and second lenses 205 and 204 are made of resin, and birefringence that occurs during molding of each lens may affect the optical performance of the right-eye optical system. For this reason, an annealing process or the like is performed to set the retardation amount Re due to birefringence of each lens so as to satisfy the condition of formula (2) described in Example 1. In this embodiment, the retardation amount Re of the first lens 205 is 18 nm, and the retardation amount Re of the second lens 204 is 7 nm, which satisfies the condition of formula (2).

[0060] (adhesive layer) 8 shows an enlarged view of adhesive layers 218-220 within the optical unit and adhesive layer 217 between the optical unit and lens 204. The second phase plate 213 and PBS 214 are bonded together with adhesive layer 218, and the PBS 214 and second polarizing plate 215 are bonded together with adhesive layer 219. In addition, in order to reduce reflection at the interface between the second polarizing plate 215 and air, an anti-reflection film 216 is bonded to the second polarizing plate 215 with adhesive layer 220. The optical unit having this layered structure is bonded to the second lens 204 with adhesive layer (first adhesive layer) 217.

[0061] When the thickness of the adhesive layer 217 is d1, the refractive index of the second lens 204 at the d-line is N1, and the refractive index of the adhesive layer 217 at the d-line is N2, the adhesive layer 217 satisfies the conditions of formulas (3) and (4) as in Example 1. In this example, the thickness d1 of the adhesive layer 217 is 0.015 mm (±0.003 mm), the refractive index N1 of the second lens 204 is 1.54, and the refractive index of the adhesive layer 217 is 1.46. Therefore, N2×d1=0.022 and N1 / N2=1.058, which respectively satisfy the conditions of formulas (3) and (4).

[0062] Furthermore, when the focal length of the entire optical system is f, the thickness d1 of the adhesive layer 217 satisfies the condition of formula (5) as in Example 1. In this example, the focal length f is 13 mm, the thickness d1 of the adhesive layer 217 is 0.015 mm (±0.003 mm), and d1 / f=0.0012. Therefore, the condition of formula (5) is satisfied.

[0063] In an optical system that folds the optical path using polarized light, the adhesive layer 217 has a large effect on optical performance because the light beam traveling from the right-eye display element 208 to the observation side passes through it three times. Therefore, by satisfying the conditions of formulas (3) to (5), it is possible to effectively suppress degradation of the quality of the displayed image caused by the joint where the optical unit and the lens 204 are bonded together with the adhesive layer 217.

[0064] The adhesive layers 218 to 220 in the optical unit will now be described. When the thickness of the adhesive layer 218 that bonds the second phase plate 213 and the PBS 214 is d2, it satisfies the condition of formula (6) as in Example 1. In this example, the thickness d2 of the adhesive layer 218 is 0.015 mm (±0.003 mm), which satisfies the condition of formula (6).

[0065] Furthermore, in this embodiment, the thickness of adhesive layer 219 that bonds PBS 214 and second polarizing plate 215 together is set to 0.020 mm (±0.003 mm), and the thickness of adhesive layer 220 that bonds second polarizing plate 215 and anti-reflection film 216 together is set to 0.025 mm (±0.003 mm), thereby reducing the effect of unevenness on the optical performance of each adhesive layer. [Example]

[0066] (Image display device) 9 shows an HMD 301 as an image display device using the optical system of Example 3, viewed from above. Reference numeral 302 denotes the observer's right eye, and 303 denotes the observer's left eye. Lenses 304 and 305 constitute part of the optical system for the right eye, and lenses 306 and 307 constitute part of the optical system for the left eye. Reference numeral 308 denotes a display element for the right eye, and 309 denotes a display element for the left eye, each of which is constituted by an organic EL element that emits unpolarized light.

[0067] The optical system for the right eye magnifies light (virtual image) from the original image displayed on the display element for the right eye 308 and directs it to the right eye 302, and the optical system for the left eye magnifies light from the original image displayed on the display element for the left eye 309 and directs it to the left eye 303.

[0068] The focal length f of the right-eye optical system and the left-eye optical system is 16 mm, the horizontal display angle of view is 65°, the vertical display angle of view is 65°, and the diagonal display angle of view 2×θ1 is 84°. The distance between the HMD301 and the observer's eyes (eye relief) is 20 mm.

[0069] (optical system) The optical system of Example 3 also folds the optical path using polarized light. FIG. 10 shows an enlarged view of the optical system for the right eye. In addition to the lenses 304 and 305, the optical system for the right eye includes a first polarizing plate 310 disposed between the right-eye display element 308 and the first lens 305, and a PBS 312 and a first phase plate 313 disposed between the first and second lenses 305 and 304, in that order from the display element side. The PBS 312 and the first phase plate 313 each have a curved surface and are stacked and bonded together to form a first optical unit. The PBS 312 functions as a polarization splitting surface disposed between the cemented surfaces of the first and second lenses 305 and 304. That is, the first and second lenses 305 and 304 are cemented together with the half mirror 114 sandwiched between their cemented surfaces, forming a cemented lens.

[0070] Further, on the observation side of the second lens 304, there are provided a half mirror 314, a second phase plate 315, and a second polarizing plate 316, which are film elements arranged in this order from the display element side. The half mirror 314, the second phase plate 315, and the second polarizing plate 316 each have a planar shape and are stacked and bonded together to form a second optical unit. The half mirror 314 functions as a semi-transmissive reflective surface.

[0071] The first phase plate 313 and the second phase plate 315 are wave plates with a phase difference of λ / 4. The polarization direction of the polarized light transmitted by the first polarizing plate 310 and the slow axis of the first phase plate 313 are inclined at 45° from each other, and the polarization direction of the polarized light transmitted by the first polarizing plate 310 and the slow axis of the second phase plate 315 are inclined at −45° from each other. The polarization direction of the polarized light transmitted by the first polarizing plate 310 and the polarization direction of the polarized light transmitted by the PBS 312 are consistent with each other. The polarization direction of the polarized light transmitted by the second polarizing plate 316 and the polarization direction of the polarized light transmitted by the PBS 312 are consistent with each other.

[0072] FIG. 11 shows the optical path of the right-eye optical system configured as described above. Unpolarized light emitted from the right-eye display element 308 passes through the first polarizer 310 and becomes linearly polarized light. This linearly polarized light then passes through the first lens 305 and PBS 312 and then the first phase plate 313, becoming circularly polarized light. A portion of the circularly polarized light that passes through the second lens 304 is reflected by the half mirror 314 and passes through the second lens 304 and the first phase plate 313, becoming linearly polarized light. Because the polarization direction of this linearly polarized light is perpendicular to the transmission polarization direction of the PBS 312, it is reflected by the PBS 312, passes through the second lens 304, and then passes through the first phase plate 313, becoming circularly polarized light. The circularly polarized light then passes through the first lens 304, the half mirror 314, and the second phase plate 315, becoming linearly polarized light. The polarization direction of this linearly polarized light matches the transmission polarization direction of the second polarizer 316, so it passes through the second polarizer 316 and is guided to the right eye 302. By providing the second polarizer 316, ghost light caused by external light can be reduced, thereby increasing the contrast of the displayed image. In the left-eye optical system, light from the left-eye display element 309 follows a similar optical path and is guided to the left eye 303.

[0073] By using an optical system that folds the optical path using polarized light in this way, the optical system can be made thinner, and the focal length of the optical system can be shortened, allowing images to be displayed at a wide angle of view. Furthermore, by using first and second lenses 305 and 304 as cemented lenses, disposing a first optical unit between them, and cementing a second optical unit to second lens 304, the optical system can be made even thinner.

[0074] It is desirable for the head-mounted HMD 301 to be lightweight. For this reason, it is desirable for the lenses constituting the optical system for the right eye to be made of resin, which has a lower specific gravity than glass, and in Example 3, all lenses 304 and 305 are made of resin. In addition, the second lens 304 is a plano-convex aspherical lens, thereby improving the aberration correction effect. Furthermore, the first lens 305 is also a double-sided aspherical lens. The same is true for the optical system for the left eye.

[0075] The characteristic configuration of the lenses in this embodiment will be described. The right-eye optical system of this embodiment has two lenses 304 and 305. The second lens 304 is a lens with positive refractive power, with a flat lens surface on the observation side and an aspherical lens surface on the display element side (the surface bonded to the first lens 305) that is convex toward the display element side. A PBS 312 is provided as a reflective surface on the display element side of the second lens 304, and because the PBS 312 has positive refractive power, the optical path can be folded, resulting in a thin optical system with a wide angle of view.

[0076] In addition, the lens surface of second lens 304 facing the display element and the lens surface of first lens 305 facing the observation side are cemented together to form a cemented surface, which makes it possible to avoid the condition for total reflection of light incident on the cemented surface being met, compared to when these lens surfaces are in contact with air. Furthermore, first lens 305 is a double-sided aspherical lens with negative refractive power.

[0077] When the optical power on the optical axis of the first lens 305 is Φ1 and the optical power on the optical axis of the second lens 304 is Φ2, it is desirable to satisfy the condition of formula (1) described in Example 1. In this example, Φ1=-0.0075, Φ2=0.0112, and |Φ1 / Φ2|=0.673. That is, the optical system of Example 3 satisfies the condition of formula (1).

[0078] In addition, the surface of the first lens 305 facing the display element has a convex shape toward the display element in the central region including the optical axis, but the curvature becomes gentler as it moves away from the optical axis, and has an inflection point within the optical effective region, which is the region through which effective light rays that contribute to image formation pass.

[0079] When the distance from the optical axis to the inflection point is Yip and the maximum distance from the optical axis (effective diameter) of the optically effective area of ​​the display element side surface of first lens 305 is Yea, the condition of formula (7) described in Example 2 is satisfied. In this example, Yip is 6 mm, Yea is 13 mm, and Yip / Yea = 0.46, which satisfies the condition of formula (7).

[0080] Furthermore, the aspherical shape of the first lens 305 on the display element side changes monotonically with increasing distance from the optical axis, and has no local maximum or minimum values ​​other than at points on the optical axis within the effective optical area. This aspherical shape reduces the output angle from the right-eye display element 308 in the peripheral area and shortens the focal length of the optical system. Furthermore, by reducing the change in the aspherical shape, the change in optical performance from the center to the periphery is reduced, making it possible to present a display image that is easy to observe and improving the processing accuracy of the aspherical shape. The above description of the first lens 305 also applies to the first lens 307 in the left-eye optical system.

[0081] Also in this embodiment, the first and second lenses 305 and 304 are made of resin, and birefringence that occurs during molding of each lens may affect the optical performance of the right-eye optical system. For this reason, an annealing process or the like is performed to set the retardation amount Re due to birefringence of each lens so as to satisfy the condition of formula (2) described in embodiment 1. In this embodiment, the retardation amount Re of the first lens 305 is 20 nm, and the retardation amount Re of the second lens 304 is 5 nm, satisfying the condition of formula (2).

[0082] (adhesive layer) 12 shows an enlarged view of adhesive layers 325-327 in the second optical unit and adhesive layer 324 between the second optical unit and second lens 304. Half mirror 314 and second phase plate 315 are bonded together with adhesive layer 325, and second phase plate 315 and second polarizing plate 316 are bonded together with adhesive layer 326. In addition, in order to reduce reflection at the interface between polarizing plate 316 and air, anti-reflection film 317 is bonded to polarizing plate 316 with adhesive layer 327. The second optical unit having this layered structure is bonded to lens 304 with adhesive layer (first adhesive layer) 324.

[0083] When the thickness of the adhesive layer 324 is d1, the refractive index of the second lens 304 at the d-line is N1, and the refractive index of the adhesive layer 324 at the d-line is N2, the adhesive layer 324 satisfies the conditions of formulas (3) and (4) as in Example 1. In this example, the thickness d1 of the adhesive layer 324 is 0.020 mm (±0.003 mm), the refractive index N1 of the second lens 304 is 1.49, and the refractive index of the adhesive layer 324 is 1.478. Therefore, N2×d1=0.029 and N1 / N2=1.006, which respectively satisfy the conditions of formulas (3) and (4).

[0084] Furthermore, when the focal length of the entire optical system is f, the thickness d1 of the adhesive layer 324 satisfies the condition of formula (5) as in Example 1. In this example, the focal length f is 16 mm, the thickness d1 of the adhesive layer 324 is 0.020 mm (±0.003 mm), and d1 / f = 0.0013. Therefore, the condition of formula (5) is satisfied.

[0085] 13 also shows an enlarged view of adhesive layer 322 within the first optical unit and adhesive layers 321 and 323 between the first optical unit and lenses 304 and 305. PBS 312 and first phase plate 313 are bonded together with adhesive layer 322, first phase plate 313 is bonded to second lens 304 with adhesive layer (first adhesive layer) 321, and PBS 312 is bonded to first lens 305 with adhesive layer 323.

[0086] When the thickness of adhesive layer 321 is d1, the refractive index of second lens 304 at the d-line is N1, and the refractive index of adhesive layer 321 at the d-line is N2, the conditions of formulas (3) and (4) are satisfied, as in Example 1. In this example, the thickness d1 of adhesive layer 324 is 0.015 mm (±0.003 mm), the refractive index N1 of lens 304 is 1.49, and the refractive index of adhesive layer 321 is 1.46. Therefore, N2×d1=0.022 and N1 / N2=1.018, which respectively satisfy the conditions of formulas (3) and (4).

[0087] Furthermore, when the focal length of the entire optical system is f, the thickness d1 of the adhesive layer 321 satisfies the condition of formula (5) as in Example 1. In this example, the focal length f is 16 mm, the thickness d1 of the adhesive layer 321 is 0.015 mm (±0.003 mm), and d1 / f = 0.0009. Therefore, the condition of formula (5) is satisfied.

[0088] In an optical system that folds the optical path using polarization, the light rays traveling from the right-eye display element 308 to the observation side pass through the adhesive layers 321, 324 at least three times, and therefore have a significant impact on optical performance. Therefore, by satisfying the conditions of formulas (3) to (5), it is possible to effectively suppress degradation of the quality of the displayed image caused by the joints where the optical units and lenses are bonded together with the adhesive layers 321, 324.

[0089] The adhesive layers 325 to 327 in the first and second optical units will now be described. The thickness of adhesive layer 322 bonding PBS 312 and first phase plate 313, adhesive layer 325 bonding half mirror 314 and second phase plate 315, and adhesive layer 326 bonding second phase plate 315 and second polarizer 316 are denoted by d2. In this case, the condition of formula (6) is satisfied, as in Example 1. In this example, the thickness of adhesive layer 322 is 0.010 mm (±0.003 mm), and the thickness of adhesive layer 325 is 0.015 mm (±0.003 mm), both of which satisfy the condition of formula (6).

[0090] Furthermore, in this embodiment, the thickness of adhesive layer 326 is 0.015 mm (±0.003 mm), and the thickness of adhesive layer 327 that bonds second polarizer 316 and antireflection film 317 is 0.015 mm (±0.003 mm), thereby reducing the effect of unevenness on the optical performance of each adhesive layer.

[0091] The above embodiment includes the following configurations.

[0092] (Configuration 1) An optical system that guides light from a display element to an observation side, The optical system has a semi-transmissive reflective surface, a polarized light separating surface, a polarizing element, and a lens made of a resin material, the semi-transmissive reflective surface or the polarizing separation surface and the polarizing element are integrated with each other to form an optical unit, the optical unit and the lens are bonded to each other via a first adhesive layer; the light is transmitted through the first adhesive layer multiple times; When the thickness of the first adhesive layer is d1 (mm), the refractive index of the lens at the d line is N1, and the refractive index of the first adhesive layer at the d line is N2, 0.009 <N2×d1<0.031 0.95≦N1 / N2≦1.10 An optical system characterized by satisfying the following conditions: (Configuration 2) When the retardation amount due to birefringence of the lens is Re (nm), Re≦30 The optical system according to configuration 1, characterized in that the following condition is satisfied: (Configuration 3) When the focal length of the optical system is f (mm), 0.0002≦d1 / f≦0.0020 3. The optical system according to configuration 1 or 2, wherein the following condition is satisfied: (Configuration 4) 4. The optical system of any one of configurations 1 to 3, wherein the light passes through the first adhesive layer three times. (Configuration 5) at least one of the semi-transmissive reflective surface and the polarization separation surface is configured by a film element, and the film element is attached to any one of the plurality of polarization elements via a second adhesive layer; When the thickness of the second adhesive layer is d2 (mm), 0.005≦d2<0.020 5. The optical system according to any one of configurations 1 to 4, wherein the following condition is satisfied: (Configuration 6) a first lens on the display element side and a second lens on the observation side, each of which is a resin lens, are cemented together, and the semi-transmissive reflective surface is disposed at the cemented portion between the first and second lenses; The optical system described in any one of configurations 1 to 5, characterized in that the optical unit including the polarization separation surface is bonded to the observation-side surface of the second lens via the first adhesive layer. (Configuration 7) a first lens on the display element side and a second lens on the observation side, each of which is a resin lens, are bonded to each other, and a first optical unit including the polarization separation surface is attached to the bonding surface of the second lens with the first lens via a first adhesive layer; The optical system described in any one of configurations 1 to 5, characterized in that a second optical unit including the semi-transmissive reflective surface is bonded to the observation-side surface of the second lens via the first adhesive layer. (Configuration 8) 8. The optical system described in any one of configurations 1 to 7, wherein the lens surface in the optical system closest to the display element has a convex shape toward the display element in a central region including the optical axis of the optical system, and is an aspheric surface having an inflection point within an optically effective region. (Configuration 9) When the distance from the optical axis to the inflection point on the aspheric surface is Yip and the maximum distance from the optical axis to the optical effective area is Yea, 0.2≦Yip / Yea≦0.75 9. The optical system according to configuration 8, wherein the following condition is satisfied: (Configuration 10) a first lens on the display element side and a second lens on the observation side, each of which is a resin lens, are cemented together, and the semi-transmissive reflective surface or the polarization separation surface is disposed at the cemented portion of the first and second lenses; When the optical power of the first lens on the optical axis of the optical system is Φ1 and the optical power of the second lens on the optical axis is Φ2, 0.2≦|Φ1 / Φ2|≦0.8 10. The optical system according to any one of configurations 1 to 9, wherein the following condition is satisfied: (Configuration 11) a first lens on the display element side and a second lens on the observation side, each of which is a resin lens, are cemented together, and the semi-transmissive reflective surface or the polarization separation surface is attached to the cemented surface of the second lens with the first lens via an adhesive layer; the observation side surface of the second lens is flat, 11. The optical system according to any one of configurations 1 to 10, wherein the cemented surface is an aspherical surface that is convex toward the display element side. (Configuration 12) a first polarizing plate, a first phase plate, a first lens with negative refractive power, the semi-transmissive reflective surface, a second lens with positive refractive power, a second phase plate, the polarization separation surface, a second polarizing plate, and a third lens with positive refractive power are arranged in this order from the display element side to the observation side; 12. The optical system according to any one of configurations 1 to 11, wherein the second phase plate is bonded to the second lens via the first adhesive layer. (Configuration 13) a first polarizing plate, a first phase plate, a first lens having a negative refractive power, a semi-transmissive reflective surface, a second lens having a positive refractive power, a second phase plate, the polarization separation surface, and a second polarizing plate are arranged in this order from the display element side to the observation side; 12. The optical system according to any one of configurations 1 to 11, wherein the second phase plate is bonded to the second lens via the first adhesive layer. (Configuration 14) a first polarizing plate, a first lens having a negative refractive power, the polarization separation surface, a first phase plate, a second lens having a positive refractive power, the semi-transmissive reflective surface, a second phase plate, and a second polarizing plate are arranged in this order from the display element side to the observation side; 12. The optical system according to any one of configurations 1 to 11, wherein the first phase plate is bonded to a display element side surface of the second lens via the first adhesive layer, and the semi-transmissive reflective surface is bonded to an observation side surface of the second lens via the first adhesive layer. (Configuration 15) The optical system according to any one of configurations 1 to 14; and An image display device comprising the display element.

[0093] 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]

[0094] 101,201,301 HMD 102,202,302 Right eye 103,203,303 left eye 104~106,107~109,204,205,206,207,304,305,0,307 Lens 110,208,308 Display element for right eye 111,209,309 Display element for left eye 112,117,210,215,310,316 Polarizing plate 113,115,211,213,313,315 Phase plate 114,212,314 Half mirror 116,214,312 Polarization splitting surface (PBS) 119~122,217~220,321~327 Adhesive layer

Claims

1. An optical system that guides light from a display element to an observation side, The optical system has a semi-transmissive reflective surface, a polarized light separating surface, a polarizing element, and a lens made of a resin material, the semi-transmissive reflective surface or the polarizing separation surface and the polarizing element are integrated with each other to form an optical unit, the optical unit and the lens are bonded to each other via a first adhesive layer; the light is transmitted through the first adhesive layer multiple times; When the thickness of the first adhesive layer is d1 (mm), the refractive index of the lens at the d line is N1, and the refractive index of the first adhesive layer at the d line is N2, 0.009<N2×d1<0.031 0.95≦N1 / N2≦1.10 An optical system characterized by satisfying the following conditions:

2. When the retardation amount due to birefringence of the lens is Re (nm), Re≦30 2. The optical system according to claim 1, wherein the following condition is satisfied:

3. When the focal length of the optical system is f (mm), 0.0002≦d1 / f≦0.0020 2. The optical system according to claim 1, wherein the following condition is satisfied:

4. 2. The optical system of claim 1, wherein the light passes through the first adhesive layer three times.

5. at least one of the semi-transmissive reflective surface and the polarization separation surface is configured by a film element, and the film element is attached to any one of the plurality of polarization elements via a second adhesive layer; When the thickness of the second adhesive layer is d2 (mm), 0.005≦d2<0.020 2. The optical system according to claim 1, wherein the following condition is satisfied:

6. a first lens on the display element side and a second lens on the observation side, each of which is a resin lens, are cemented together, and the semi-transmissive reflective surface is disposed at the cemented portion of the first and second lenses; 2. The optical system according to claim 1, wherein the optical unit including the polarization splitting surface is bonded to the observation side surface of the second lens via the first adhesive layer.

7. a first lens on the display element side and a second lens on the observation side, each of which is a resin lens, are bonded to each other, and a first optical unit including the polarization separation surface is attached to the bonding surface of the second lens with the first lens via a first adhesive layer; 2. The optical system according to claim 1, wherein a second optical unit including the semi-transmissive reflective surface is bonded to the observation side surface of the second lens via the first adhesive layer.

8. The optical system according to claim 1, wherein the lens surface closest to the display element in the optical system has a convex shape toward the display element in a central region including the optical axis of the optical system, and is an aspheric surface having an inflection point within the optically effective region.

9. When the distance from the optical axis to the inflection point on the aspheric surface is Yip and the maximum distance from the optical axis to the optical effective area is Yea, 0.2≦Yip / Yea≦0.75 9. The optical system according to claim 8, wherein the following condition is satisfied:

10. a first lens on the display element side and a second lens on the observation side, each of which is a resin lens, are cemented together, and the semi-transmissive reflective surface or the polarization separation surface is disposed at the cemented portion of the first and second lenses; When the optical power of the first lens on the optical axis of the optical system is Φ1 and the optical power of the second lens on the optical axis is Φ2, 0.2≦|Φ1 / Φ2|≦0.8 2. The optical system according to claim 1, wherein the following condition is satisfied:

11. a first lens on the display element side and a second lens on the observation side, each of which is a resin lens, are cemented together, and the semi-transmissive reflective surface or the polarization separation surface is attached to the cemented surface of the second lens with the first lens via an adhesive layer; the second lens has a flat surface on the observation side; 2. The optical system according to claim 1, wherein the cemented surface is an aspherical surface that is convex toward the display element side.

12. a first polarizing plate, a first phase plate, a first lens with negative refractive power, the semi-transmissive reflective surface, a second lens with positive refractive power, a second phase plate, the polarization separation surface, a second polarizing plate, and a third lens with positive refractive power are arranged in this order from the display element side to the observation side; 2. The optical system according to claim 1, wherein the second phase plate is bonded to the second lens via the first adhesive layer.

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

14. a first polarizing plate, a first lens having a negative refractive power, the polarization separation surface, a first phase plate, a second lens having a positive refractive power, the semi-transmissive reflective surface, a second phase plate, and a second polarizing plate are arranged in this order from the display element side to the observation side, 2. The optical system according to claim 1, wherein the first phase plate is bonded to a display element side surface of the second lens via the first adhesive layer, and the semi-transmissive reflective surface is bonded to an observation side surface of the second lens via the first adhesive layer.

15. The optical system according to any one of claims 1 to 14; An image display device comprising the display element.

Images