Observation optical system and image display device using the same

Abstract

To provide an observation optical system that is advantageous in reducing ghost light caused by external light while having a wide field of view and a compact size.SOLUTION: There is provided an observation optical system that guides light from a display element displaying an image to an observer and has a first semi-transmissive reflective surface, a first λ / 4 plate, a second semi-transmissive reflective surface, a second λ / 4 plate, and a linear polarization plate arranged sequentially from the display side to the observation side. When the first linear polarization from the display side enters the first semi-transmissive reflective surface, and the polarization direction of the first linear polarization is parallel to the polarization direction of the light passing through the linear polarization plate, the direction of a slow axis of the first λ / 4 plate and the direction of a slow axis of the second λ / 4 plate are parallel. When the polarization direction of the first linear polarization is perpendicular to the polarization direction of the light passing through the linear polarization plate, the direction of the slow axis of the first λ / 4 plate and the direction of the slow axis of the second λ / 4 plate are perpendicular and a prescribed condition is satisfied.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to an observation optical system and an image display device using the same, which is suitable for a wearable image display device such as an HMD (Head Mounted Display). [Background technology]

[0002] 2. Description of the Related Art Conventionally, there has been a demand for observation optical systems used in image display devices such as HMDs to have a wide angle of view while being compact in size.

[0003] For this purpose, Patent Document 1 discloses a configuration in which the optical path is folded by utilizing polarized light. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2005-148655 A Summary of the Invention [Problem to be solved by the invention]

[0005] One configuration in Patent Document 1 has a polarizing beam splitter and a half mirror arranged in this order from the observation side to the display side in order to fold the optical path by using polarized light. As a result, external light entering the observation optical system from the observation side is reflected by the half mirror, reflected by the polarizing beam splitter, and further reflected by the half mirror, and then enters the observer's eye as ghost light that has passed through the polarizing beam splitter.

[0006] Another configuration in Patent Document 1 has a half mirror and a polarizing beam splitter arranged in this order from the observation side to the display side in order to fold the optical path by using polarized light. However, the polarizing beam splitter is flat, and external light entering the observation optical system from the observation side passes through the half mirror, is reflected by the polarizing beam splitter, and passes through the half mirror again to enter the observer's eye as ghost light.

[0007] In addition, the half mirror, which is responsible for the main power of imaging, is a concave mirror on the display side, which tends to increase the diameter.

[0008] SUMMARY OF THE PRESENT EMBODIMENTS An object of the present invention is to provide an observation optical system that has a wide angle of view, is compact, and yet is advantageous in reducing ghost light caused by external light. [Means for solving the problem]

[0009] The observation optical system of the present invention is an observation optical system that guides light from a display element that displays an image to an observer, and has, in order from the display side to the observation side, a first semi-transmissive reflective surface, a first λ / 4 plate, a second semi-transmissive reflective surface, a second λ / 4 plate, and a linear polarizing plate, wherein, of the first semi-transmissive reflective surface and the second semi-transmissive reflective surface, the reflective surface having a smaller absolute value of focal length is designated as reflective surface A, the focal length of reflective surface A is designated as fA, and the air-equivalent distance on the optical axis from the exit pupil position to reflective surface A is designated as LaA, 1.0 <LaA / |fA|<3.0 The present invention is characterized in that the following conditional expression is satisfied: Effect of the Invention

[0010] According to the present invention, it is possible to provide an observation optical system that has a wide angle of view, is compact, and yet is advantageous in that ghost light caused by external light is reduced. [Brief description of the drawings]

[0011] [Figure 1] Main part configuration diagram in embodiment 1 [Diagram 2] Main part configuration diagram in embodiment 2 [Diagram 3] FIG. 1 shows the optical path of polarized light in the first embodiment. [Figure 4] FIG. 13 is a diagram showing the optical path of polarized light in the second embodiment. [Diagram 5] FIG. 13 is a diagram showing the optical path of polarized light in the third embodiment. [Figure 6] FIG. 13 is a diagram showing the optical path of polarized light in the fourth embodiment. [Figure 7] A diagram showing how external light enters the observation optical system. [Figure 8] Diagram showing how ghost light occurs [Figure 9] FIG. 1 shows a configuration in which a light blocking member is arranged. [Figure 10] Optical path diagram for numerical example 1 [Figure 11] Optical path diagram for numerical example 2 [Figure 12] Optical path diagram for numerical example 3 [Figure 13] Optical path diagram for numerical example 4 [Figure 14] Optical path diagram for numerical example 5 [Figure 15] FIG. 1 shows an HMD using the observation optical systems of Examples 1 to 4. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] Hereinafter, embodiments of the present invention will be described with reference to the drawings.

[0013] In describing each embodiment of the present invention, the state represented by concepts such as linear polarization, circular polarization, and phase difference of λ / 4, which indicate the polarization state of light, means a wide state having a certain range. Therefore, the essential effect of the present invention is not hindered by these errors. In addition, the phase difference generated by each optical element is a phase difference related to light of wavelength λ, and the wavelength λ can be any wavelength in the visible light range, for example, λ=580 nm, but is not limited to this.

[0014] [Example 1] Hereinafter, a first embodiment will be described with reference to Figs. 1 and 3. Fig. 1 is a diagram showing the main components of the first embodiment, in which 1000 denotes an observation optical system. The observation optical system 1000 has a lens element 100 consisting of a plano-concave lens 101 and a plano-convex lens 102. Furthermore, 40 denotes a display element, such as a liquid crystal panel or an organic EL panel. The display element 40 has a display surface 41 and an optical flat plate portion 42 including a cover glass or the like.

[0015] The optical flat plate section 42 includes a linear polarizing plate, and light from the image displayed on the display surface 41 becomes a predetermined linearly polarized light through the optical flat plate section 42 and is guided to the exit pupil S via the observation optical system 1000. The position of the exit pupil S represents the position where the central ray of the light beam guided from the maximum object height on the display surface 41 to the exit pupil S intersects with the optical axis.

[0016] In order to fold the optical path, the observation optical system 1000 has, in order from the display element 40 side to the exit pupil S side, a first semi-transmissive reflective surface 21, a first λ / 4 plate 31, a second semi-transmissive reflective surface 22, a second λ / 4 plate 32, and a linear polarizing plate 11. Here, the first semi-transmissive reflective surface 21 and the second semi-transmissive reflective surface 22 are half mirrors. The half mirror is an element that transmits a part of light and reflects a part of light regardless of polarization. The ratio of transmission and reflection of light incident on the half mirror does not have to be 50:50, and may be, for example, 30:70 or 70:30.

[0017] A λ / 4 plate is a wave plate that imparts a phase difference of λ / 4 to two orthogonal polarized light components. A linear polarizer transmits a specific linearly polarized light and absorbs linearly polarized light that is orthogonal to the specific linearly polarized light.

[0018] The first semi-transmissive reflective surface 21 is formed between the plano-concave lens 101 and the plano-convex lens 102. In addition, the second semi-transmissive reflective surface 22 is formed between the first λ / 4 plate 31 and the second λ / 4 plate 32. With this configuration, it is possible to appropriately adjust the polarization direction of the light emitted from the display element 40 and fold the optical path. The reason for this will be explained with reference to FIG. 3(A).

[0019] 3(A) shows the optical path of polarized light in the observation optical system 1000. The display element 40 is a liquid crystal display element that emits a first linearly polarized light that vibrates in a direction parallel to the paper. The lower part of the figure shows the inclinations of the slow axes of the first and second λ / 4 plates when viewed from the exit pupil S side, and they are arranged at inclinations of +45° and -45° with respect to the vibration direction of the first linearly polarized light, respectively.

[0020] Therefore, the first and second λ / 4 plates 31 and 32 are arranged so that their slow axes are perpendicular to each other. The axis direction of the light transmission for the linear polarizer 11 is shown downward in the figure. The linear polarizer 11 is configured to transmit light that vibrates in a direction perpendicular to the first linearly polarized light.

[0021] 3(A), light emitted from display surface 41 of display element 40 passes through optical flat plate portion 42, becomes linearly polarized light that vibrates in a direction parallel to the page, and becomes right-handed circularly polarized light at first λ / 4 plate 31. The right-handed circularly polarized light is reflected by second semi-transmissive reflective surface 22, becomes linearly polarized light that vibrates in a direction perpendicular to the page at first λ / 4 plate 31, is reflected by first semi-transmissive reflective surface 21, and becomes left-handed circularly polarized light at first λ / 4 plate 31.

[0022] The left-handed circularly polarized light is converted by the second λ / 4 plate 32 into linearly polarized light that vibrates in the direction perpendicular to the page, passes through the linear polarizer 11, and is guided to the exit pupil S. At the semi-transmissive reflective surface, reflected light and transmitted light are generated, but unnecessary reflected light and transmitted light are blocked by the polarizer 11 or the like and are not guided to the exit pupil S, or are attenuated by passing through the semi-transmissive reflective surface multiple times and are difficult to perceive.

[0023] The above configuration makes it possible to fold the optical path.

[0024] Moreover, the observation optical system 1000 of the present invention is configured so as to satisfy the following conditional expression. 1.0 <LaA / |fA|<3.0···(1)

[0025] Here, when the reflecting surface A is the one having the smaller absolute value of the focal length between the first semi-transmissive reflecting surface 21 and the second semi-transmissive reflecting surface 22, fA is the focal length of reflecting surface A, and LA is the air-equivalent distance on the optical axis from the position of the exit pupil S to the reflecting surface A.

[0026] However, the air-equivalent distance on the optical axis from the position of the exit pupil S to the reflecting surface A is the sum of the thickness of each element through which the light passes divided by the refractive index of each of the elements.

[0027] In the case of ghost light caused by external light, the light that is reflected two or more times by the first semi-transmissive reflective surface 21 can be reduced by the arrangement of the polarizing element, and the light that is reflected once by the first semi-transmissive reflective surface 21 can be mainly reduced by conditional formula (1). The reason for this will be explained.

[0028] 3B shows the optical path of external light in the observation optical system 1000. Of the external light incident on the observation optical system 1000 from the exit pupil S side, linearly polarized light oscillating in a direction parallel to the paper surface is absorbed by the linear polarizer 11, and linearly polarized light oscillating in a direction perpendicular to the paper surface is transmitted through the linear polarizer 11. The light transmitted through the linear polarizer 11 is converted to left-handed circularly polarized light by the second λ / 4 plate 32 and transmitted, and is converted to linearly polarized light oscillating in a direction perpendicular to the paper surface by the first λ / 4 plate 31 and transmitted. The transmitted light is reflected by the first semi-transmissive reflective surface 21 and converted to left-handed circularly polarized light by the first λ / 4 plate 31.

[0029] The left-handed circularly polarized light is branched into a first ghost light which is left-handed circularly polarized light and transmits through the second semi-transmissive reflective surface 22, and a second ghost light which is right-handed circularly polarized light and reflects through the second semi-transmissive reflective surface 22. The first ghost light is converted to linearly polarized light oscillating in the direction perpendicular to the paper surface by the second λ / 4 plate 32 and transmits therethrough, then transmits through the linear polarizer 11 and emerges towards the pupil S. The second ghost light is converted to linearly polarized light oscillating in the direction parallel to the paper surface by the first λ / 4 plate 31 and transmits therethrough, is reflected by the first semi-transmissive reflective surface 21, and becomes right-handed circularly polarized light by the first λ / 4 plate 31.

[0030] The right-handed circularly polarized light is branched into a third ghost light which is right-handed circularly polarized light that is transmitted by the second semi-transmissive reflective surface 22, and a fourth ghost light which is left-handed circularly polarized light that is reflected by the second semi-transmissive reflective surface 22. The third ghost light is converted by the second λ / 4 plate 32 into linearly polarized light that vibrates in the direction parallel to the page, is transmitted, and is absorbed by the linear polarizer 11.

[0031] Moreover, the fourth ghost light guided to the exit pupil S is further reflected once each by the first semi-transmissive reflective surface 21 and the second semi-transmissive reflective surface 22 relative to the third ghost light, so that the light intensity is weakened and the observer finds it difficult to view the fourth ghost light. Compared to the fourth ghost light, the ghost light that is reflected more times by the first semi-transmissive reflective surface 21 has an even weaker light intensity than the fourth ghost light, making it even more difficult for the observer to view it.

[0032] As described above, in the case of ghost light caused by external light, light that is reflected two or more times by the first semi-transmissive reflective surface 21 is reduced by the arrangement of the polarizing element.

[0033] 7 and 8, it will be described how the first ghost light guided to the exit pupil S, i.e., the light reflected once by the first semi-transmissive reflective surface 21, can be reduced by appropriately setting the focal length of the first semi-transmissive reflective surface 21. In Figs. 7 and 8, the Z axis is defined as the optical axis direction, the X axis is defined as a direction perpendicular to the optical axis and parallel to the paper surface, and the Y axis is defined as a direction perpendicular to the paper surface.

[0034] 7 is a diagram showing a state when external light incident on the right-eye observation optical system 1000R from the exit pupil S side is incident on the first semi-transmissive reflecting surface 21R. External light rays Ri, Rc, and Ro are light rays that pass near the right eye side of the face and are incident on the innermost, center, and outermost parts of the semi-transmissive reflecting surface 21R, respectively. The intersections of Ri, Rc, and Ro are gathered near a predetermined position near the face. In the case of external light, light that passes near the right eye side of the face and is reflected by the semi-transmissive reflecting surface 21R has a small angle with respect to the optical axis, and is therefore relatively easily guided to the observer's eye.

[0035] Fig. 8 is a diagram showing how ghost light occurs. In order to simply show how the light rays Ri, Rc, and Ro shown in Fig. 6 enter the observation optical system 1000R and are reflected by the semi-transmissive reflecting surface 21R, the concave mirror of the semi-transmissive reflecting surface 21R is treated as an ideal lens A that is a plane, and the light rays Ri, Rc, and Ro intersect at an intersection point PA. In other words, it shows the state when the intersection point PA is the object point of the ghost light. The dashed line shows the light refracted by the ideal lens A, and the light reflected by the ideal lens A is shown by inverting the above-mentioned dashed line with respect to the ideal lens A.

[0036] 8A shows a diagram when the distance from the exit pupil S of the observation optical system 1000 to the ideal lens A is fA. That is, it shows the case where LaA is equal to |fA|. Assume that the intersection PA of the light rays Ri, Rc, and Ro is located at a position dX away from the center of the exit pupil S in the negative direction with respect to the Z axis. When LaA is equal to |fA|, the light is reflected parallel to the reflected light of the light ray connecting the intersection PA of the reflecting surface A and the optical axis and the center of the pupil S.

[0037] Therefore, when the display angle of view of the observation optical system 1000 is wide, that is, when the diameter of the ideal lens A is large, it is not preferable because at least a part of the ghost light reflected once by surface A enters the exit pupil S. The same is true when |fA| is small relative to LaA.

[0038] 8B shows the case where LaA=2×|fA| is satisfied. The light emitted from the intersection point PA is focused at a point at dX in the positive direction of the Z axis, and does not enter the exit pupil S. In other words, ghost light can be suppressed.

[0039] 8C shows a case where LaA=3×|fA| is satisfied. The light emitted from the intersection point PA is collected in the Z-axis direction at a position relatively close to the reflecting surface A with respect to the position of the exit pupil S. Therefore, when the display angle of view of the observation optical system 1000 is wide, that is, when the diameter of the semi-transmissive reflecting surface 21 is large, at least a part of the ghost light reflected once by the A surface enters the exit pupil S, which is not preferable. The same is true when LaA>3×|fA|.

[0040] With the above configuration, it is possible to obtain an observation optical system that has a wide angle of view, is compact, and yet is advantageous in that ghost light caused by external light is reduced.

[0041] It is preferable that at least one of the upper limit and the lower limit of the numerical range of conditional expression (1) is set to the numerical value of the following conditional expression (1a). 1.1 <LaA / |fA|<2.5···(1a)

[0042] Furthermore, it is more preferable that at least one of the upper limit and the lower limit of the numerical range of conditional formula (1) satisfies the range of the following conditional formula (1b). 1.2 <LaA / |fA|<2.3···(1b)

[0043] Next, a preferred configuration of the observation optical system 1000 will be described.

[0044] It is preferable that the reflecting surface A is concave toward the exit pupil S. By being concave toward the exit pupil S, the reflecting surface A has a concentric shape toward the exit pupil S, which makes it easier to correct off-axis aberrations. This is also advantageous for reducing the diameter.

[0045] Next, conditions that are preferably satisfied in the observation optical system 1000 will be described.

[0046] It is preferable that the observation optical system 1000 satisfies at least one of the following conditional expressions. 0.60<|fA| / f<1.50 (2) 0°<ω<45° (3) -6.0 <R / f<-1.0 ···(4)

[0047] Here, f is the focal length of the observation optical system 1000, ω is the absolute value of the angle of the external light incident on the observation optical system 1000 with respect to the optical axis, and R is the radius of curvature of the reflecting surface A.

[0048] If the focal length of reflecting surface A is too long, exceeding the upper limit of condition (2), the optical path length becomes too long, which makes it difficult to reduce the size, which is not preferable.If the focal length of reflecting surface A is too short, below the lower limit of condition (2), the off-axis aberrations generated by reflecting surface A become large, which is not preferable.

[0049] If the upper limit of condition (3) is exceeded, the angle of the external light incident on the observation optical system 1000 with respect to the optical axis becomes too large, which is undesirable because ghost light is likely to be incident on the eye opposite to the eye into which the external light is incident.

[0050] If the absolute value of the radius of curvature of reflecting surface A becomes too small by exceeding the upper limit of conditional formula (4), it is undesirable because it increases the off-axis aberrations generated at reflecting surface A. If the absolute value of the radius of curvature of reflecting surface A becomes too large by falling below the lower limit of conditional formula (2), it is undesirable because it makes it difficult to reduce the size of the system due to the long optical path length.

[0051] It is preferable that at least one of the upper and lower limits of the numerical ranges of the conditional expressions (2) to (4) is set to the numerical value of the following conditional expression (2a). 0.63<|fA| / f<1.40 (2a) 5°<ω<35° (3a) -5.0 <R / f<-1.5 ···(4a)

[0052] Furthermore, it is more preferable that at least one of the upper limit and the lower limit of the numerical range of conditional formula (2) satisfies the range of the following conditional formula (2b). 0.66<|fA| / f<1.30 (2b) 10°<ω<25° (3a) -4.0 <R / f<-2.0 ···(4a)

[0053] [Example 2] Example 2 will be described below with reference to Figs. 2 and 4. Differences from Example 1 will be mainly described. In Fig. 2, the observation optical system 1000 differs from Example 1 in that the display element 40 does not include a linear polarizer, and unpolarized light that is not polarized in a specific direction is incident on the observation optical system 1000. For this reason, a linear polarizer 12 that transmits light that vibrates in a direction parallel to the paper surface is disposed between the first semi-transmissive reflective surface 21 and the display element 40.

[0054] 4(A), the inclination of the slow axis of the second λ / 4 plate 32 when viewed from the exit pupil S side is set to +45°, and the linear polarizer 11 is configured to transmit light that vibrates in a direction parallel to the first linearly polarized light. With this configuration, it is possible to appropriately change the polarization direction and fold the optical path, as in the first embodiment.

[0055] The reason why ghost light caused by external light that is reflected two or more times by the first semi-transmissive reflective surface 21 can be reduced by the arrangement of the polarizing element in the second embodiment will be described.

[0056] 4(B) shows the optical path of external light in the observation optical system 1000. Of the external light incident on the observation optical system 1000 from the exit pupil S side, linearly polarized light oscillating in a direction perpendicular to the paper surface is absorbed by the linear polarizer 11, and linearly polarized light oscillating in a direction parallel to the paper surface is transmitted through the linear polarizer 11. The light transmitted through the linear polarizer 11 is converted to left-handed circularly polarized light by the second λ / 4 plate 32 and transmitted, and is converted to linearly polarized light oscillating in a direction perpendicular to the paper surface by the first λ / 4 plate 31 and transmitted. The transmitted light is reflected by the first semi-transmissive reflective surface 21 and converted to left-handed circularly polarized light by the first λ / 4 plate 31.

[0057] The left-handed circularly polarized light is branched into a first ghost light which is left-handed circularly polarized light and transmits through the second semi-transmissive reflective surface 22, and a second ghost light which is right-handed circularly polarized light and reflects through the second semi-transmissive reflective surface 22. The second ghost light is converted to linearly polarized light that vibrates in the direction parallel to the page by the first λ / 4 plate 31 and transmits through the first λ / 4 plate 31, is reflected by the first semi-transmissive reflective surface 21, and becomes right-handed circularly polarized light by the first λ / 4 plate 31.

[0058] The right-handed circularly polarized light is branched into a third ghost light which is right-handed circularly polarized light that is transmitted by the second semi-transmissive reflective surface 22, and a fourth ghost light which is left-handed circularly polarized light that is reflected by the second semi-transmissive reflective surface 22. The third ghost light is converted by the second λ / 4 plate 32 into linearly polarized light that vibrates in the direction perpendicular to the page, is transmitted, and is absorbed by the linear polarizer 11.

[0059] Moreover, the fourth ghost light guided to the exit pupil S is further reflected once each by the first semi-transmissive reflective surface 21 and the second semi-transmissive reflective surface 22 relative to the third ghost light, so that the light intensity is weakened and the observer finds it difficult to view the fourth ghost light. Compared to the fourth ghost light, the ghost light that is reflected more times by the first semi-transmissive reflective surface 21 has an even weaker light intensity than the fourth ghost light, making it even more difficult for the observer to view it.

[0060] [Example 3] Hereinafter, the third embodiment will be described with reference to Figs. 5(A) and (B). The differences from the first embodiment will be mainly described. The first semi-transmissive reflective surface 21P is a polarizing beam splitter that transmits light that vibrates in a direction parallel to the paper surface and reflects light that vibrates in a direction perpendicular to the paper surface. Here, the polarizing beam splitter is an element that transmits a first linearly polarized light and reflects a second linearly polarized light whose polarization direction is orthogonal to the first linearly polarized light.

[0061] By changing the half mirror in the configuration of Example 1 to a polarizing beam splitter, it is possible to reduce the number of optical paths that are reflected by the polarizing beam splitter, as in the optical path in Figure 5(A), resulting in a configuration in which unnecessary light is less likely to be directed toward the exit pupil S.

[0062] In the case of ghost light caused by external light, the amount of light that reaches the first semi-transmissive reflective surface 21P can be reduced by the arrangement of the polarizing element in the third embodiment. The reason for this will be explained.

[0063] 5(B) shows the optical path of external light in the observation optical system 1000. Of the external light incident on the observation optical system 1000 from the exit pupil S side, linearly polarized light oscillating in a direction parallel to the paper surface is absorbed by the linear polarizer 11, and linearly polarized light oscillating in a direction perpendicular to the paper surface is transmitted through the linear polarizer 11. The light transmitted through the linear polarizer 11 is converted to left-handed circularly polarized light by the second λ / 4 plate 32 and transmitted, and is converted to linearly polarized light oscillating in a direction perpendicular to the paper surface and transmitted through the first λ / 4 plate 31. The transmitted light is reflected by the first semi-transmissive reflective surface 21P and converted to left-handed circularly polarized light by the first λ / 4 plate 31.

[0064] The left-handed circularly polarized light is branched into a first ghost light, which is left-handed circularly polarized light that is transmitted by the second semi-transmissive reflecting surface 22, and a second ghost light, which is right-handed circularly polarized light that is reflected by the second semi-transmissive reflecting surface 22. The second ghost light is converted into linearly polarized light that vibrates in the direction parallel to the paper surface by the first λ / 4 plate 31, and is transmitted through the first semi-transmissive reflecting surface 21. Therefore, light that is reflected two or more times by the first semi-transmissive reflecting surface 21P can be suppressed, and the ghost light can be reduced.

[0065] [Example 4] Hereinafter, Example 4 will be described with reference to Fig. 6. Differences from Example 1 will be mainly described. Example 4 is intended to further suppress ghost light reflected by the display element 40, in comparison with Example 1. For this purpose, a second linear polarizing plate 12 that transmits light that vibrates in a direction parallel to the paper surface in order from the exit pupil S side, and a third λ / 4 plate 33 whose slow axis is inclined at -45° with respect to the vibration direction of the first linearly polarized light are disposed between the first semi-transmissive reflective surface 21 and the display element 40.

[0066] As a result, of the light emitted from the display element 40, the light reflected by the first semi-transmissive reflective surface 21 passes through the third λ / 4 plate 33 and becomes right-handed circularly polarized light, and is reflected by the display element 40 and becomes left-handed circularly polarized light. The left-handed circularly polarized light passes through the third λ / 4 plate 33 and becomes linearly polarized light that vibrates perpendicular to the paper surface, and is suppressed by the second linear polarizer 12. In other words, ghost light reflected by the display element 40 can be suppressed.

[0067] As a variation of the fourth embodiment, the first semi-transmissive reflective surface 21 may be a polarizing beam splitter 21P. In particular, when the polarizing beam splitter 21P is formed of a wire grid, a part of the linearly polarized light vibrating in a direction parallel to the paper surface is reflected by the polarizing beam splitter 21P, so that the light reflected by the display element 40 is prevented from returning to the polarizing beam splitter 21P, and the generation of unnecessary light can be suppressed.

[0068] 9 is a diagram showing a configuration for reducing ghost light caused by external light entering the observation optical system 1000 from a direction having a large angle with respect to the optical axis, i.e., shallow external light. 500 is a light-shielding wall, and 600 is a louver element in which a plurality of rectangular light-shielding portions are arranged. Since the configurations of Examples 1 to 3 suppress ghost light caused by external light entering the observation optical system 1000 from a direction nearly parallel to the optical axis, the thickness of the light-shielding wall 500 or the light-shielding portion in the louver element 600 in the Z-axis direction can be reduced. As a result, ghost light caused by shallow external light can be suppressed without much bothersomeness due to the arrangement of the light-shielding wall 500 or the louver element 600.

[0069] Numerical Examples 1 to 5 are shown below. Figures 10 to 14 are optical path diagrams corresponding to Numerical Examples 1 to 5, respectively. Numerical Examples 1 to 5 show specific surface data for the configurations of any of Examples 1 to 4. However, in Numerical Examples 1 to 5, the second semi-transmissive reflective surface 22, the first λ / 4 plate 31, the second λ / 4 plate 32, and the linear polarizer 11 in Examples 1 to 4 are regarded as a single flat plate.

[0070] In the surface data of each numerical example, r represents the radius of curvature of each optical surface, and d (mm) represents the axial distance (distance on the optical axis) between the mth surface and the (m+1)th surface. Here, surface number 1 is the position of the exit pupil S, and m is the surface number counted from the exit pupil S side. Also, nd is represented by the refractive index of each optical member with respect to the d line. The S numbers in Figures 10 to 14 correspond to the surface number m in the numerical example.

[0071] The aspheric shape is defined as follows: X-axis is in the direction of the optical axis, H-axis is perpendicular to the optical axis, the direction of light travel is positive, R is the paraxial radius of curvature, and A, B, C, and D are the aspheric coefficients. X=(H 2 / R) / [1+{1-(H / R) 2} 1 / 2 ]+A×h 4 +B×h 6 +C×h 8 +D×h 10 The symbol * indicates a surface with an aspheric shape. "Ex" is 10 -x This means:

[0072] [Numerical example 1] Unit: mm Surface number rd nd νd 1∞17.0 2∞1.01.516364.1 3 ∞ 10.0 1.5163 64.1 4 -50.000 2.0 1.5163 64.1 5∞2.026 Display surface ∞ 0

[0073] [Numerical example 2] Unit: mm Surface number rd nd νd 1∞29.0 2∞1.01.516364.1 3 ∞ 10.0 1.5163 64.1 4* -50.000 2.0 1.5163 64.1 5∞2.285 Display surface ∞ 0 4th side A= 2.376E-06 B= -8.480E-09 C= 1.367E-11 D= -6.993E-15

[0074] [Numerical example 3] Unit: mm Surface number rd nd νd 1∞17.0 2∞1.01.516364.1 3∞8.0 1.5446 56.2 4* -52.338 2.0 1.6418 22.5 5* 69.472 5.585 Display surface ∞ 0 4th side A= -5.3524E-07 B= -3.1573E-10 C= 1.9983E-12 D= -6.6842E-17 5th side A= -3.1426E-05 B= 2.5264E-08 C= 2.6340E-11 D= -4.0278E-14

[0075] [Numerical example 4] Unit: mm Surface number rd nd νd 1∞17.0 2 -94.522 1.0 1.5163 64.1 3* -94.522 8.0 1.5446 56.2 4* -37.697 2.0 1.6418 22.5 5* -848.438 4.1875 Display surface ∞ 0 3rd side A= 1.3125E-06 B= 3.7125E-10 C= -2.5851E-13 D= -3.4224E-16 4th side A= -3.6185E-08 B= -1.7627E-09 C= 5.4487E-12 D= -5.8886E-16 5th side A= -2.1211E-05 B= 1.5352E-08 C= 2.2357E-11 D= -2.0642E-14

[0076] [Numerical example 5] Unit: mm Surface number rd nd νd 1∞15.0 2 200.000 1.0 1.5163 64.1 3 200.000 10.0 1.5446 56.2 4* -67.109 2.0 1.6418 22.5 5 1082.122 3.7612 Display surface ∞ 4th side A= -6.7130E-07 B= 1.7585E-09 C= -2.0854E-12 D= 1.4048E-15

[0077] The table below gives various values ​​for each example.

[0078] [Table 1]

[0079] 15 shows an HMD as an image display device using the observation optical system of Examples 1 to 4. The HMD is worn on the observer's head by a wearing gear (not shown).

[0080] The HMD has image display elements RID and LID for the right and left eyes, a right-eye observation optical system ROS that guides display light from the right-eye image display element RID to the observer's right eye, and a left-eye observation optical system LOS that guides display light from the left-eye image display element LID to the observer's left eye.

[0081] By using the observation optical systems shown in Examples 1 to 4 as the right-eye and left-eye observation optical systems ROS and LOS, it is possible to realize an HMD that has a wide angle of view, is compact, and yet is advantageous in reducing ghost light caused by external light.

[0082] The disclosure of each embodiment includes the following configuration.

[0083] (Configuration 1) An observation optical system that guides light from a display element that displays an image to an observer, The liquid crystal display device has a first semi-transmissive reflective surface, a first λ / 4 plate, a second semi-transmissive reflective surface, a second λ / 4 plate, and a linear polarizer, which are arranged in this order from the display side to the observation side, a first linearly polarized light is incident on the first semi-transmissive reflective surface from a display side; When the polarization direction of the first linearly polarized light is parallel to the polarization direction of light transmitted through the linear polarizer, the direction of the slow axis of the first λ / 4 plate is parallel to the direction of the slow axis of the second λ / 4 plate, When the polarization direction of the first linearly polarized light and the polarization direction of the light transmitted through the linear polarizer are perpendicular to each other, the direction of the slow axis of the first λ / 4 plate and the direction of the slow axis of the second λ / 4 plate are perpendicular to each other, Among the first semi-transmissive reflective surface and the second semi-transmissive reflective surface, the reflective surface having the smaller absolute value of the focal length is designated as reflective surface A, the focal length of the reflective surface A is designated as fA, and the air-equivalent distance on the optical axis from the exit pupil position to the reflective surface A is designated as LA. 1.0 <LaA / |fA|<3.0 1. An observation optical system characterized in that the following condition is satisfied:

[0084] (Configuration 2) When the focal length of the observation optical system is f, 0.60 <fA / f<1.50 2. The observation optical system according to configuration 1, wherein the following condition is satisfied:

[0085] (Configuration 3) 3. The observation optical system according to configuration 1 or 2, wherein the first and second semi-transmissive reflective surfaces are half mirrors.

[0086] (Configuration 4) the first semi-transmissive reflective surface is a polarizing beam splitter; 3. The observation optical system according to configuration 1 or 2, wherein the second semi-transmissive reflective surface is a half mirror.

[0087] (Configuration 5) 5. The observation optical system according to any one of configurations 1 to 4, wherein the reflecting surface A is concave toward the observation side.

[0088] (Configuration 6) 6. The observation optical system according to any one of configurations 1 to 5, wherein the observation optical system has a light blocking member disposed on the most observation side.

[0089] (Configuration 7) 7. The observation optical system according to configuration 6, wherein the light blocking member is a rectangular louver element disposed perpendicular to the optical axis.

[0090] (Configuration 8) When the absolute value of the angle of the external light incident on the observation optical system from the observation side with respect to the optical axis is ω, 0°<ω<45° 8. The observation optical system according to any one of configurations 1 to 7, wherein the following condition is satisfied:

[0091] (Configuration 9) When the focal length of the observation optical system is f and the radius of curvature of the reflecting surface A is R, -6.0 <R / f<-1.0 9. The observation optical system according to any one of configurations 1 to 8, wherein the following condition is satisfied:

[0092] (Configuration 10) When the focal length of the observation optical system is f, 0.60<|fA| / f<1.50 10. The observation optical system according to any one of configurations 1 to 9, wherein the following condition is satisfied:

[0093] (Configuration 11) 11. An image display device comprising: the observation optical system according to any one of configurations 1 to 10; and the display element.

[0094] Although the preferred embodiments and examples of the present invention have been described above, the present invention is not limited to these embodiments and examples, and various combinations, modifications, and changes are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0095] 1000 Observation Optical System 11 Linear polarizer 21, 22 First and second semi-transmissive reflecting surfaces 31, 32 First and second λ / 4 plates 40 Display element

Claims

1. An observation optical system that guides light from a display element that displays an image to the observer, The observation optical system has lenses with different radii of curvature between the display side and the observation side. It has a first semi-transparent reflective surface, a first λ / 4 plate, a second semi-transparent reflective surface, a second λ / 4 plate, and a linear polarizer, arranged in order from the display side to the observation side. Of the first semi-transparent reflective surface and the second semi-transparent reflective surface, the reflective surface with the smaller absolute value of its focal length is defined as reflective surface A, the focal length of reflective surface A is defined as fA, and the air-equivalent distance on the optical axis from the exit pupil position to reflective surface A is defined as LaA. 1.0<LaA / |fA|<3.0 An observation optical system characterized by satisfying the following conditional equation.

2. When the focal length of the observation optical system is f, 0.60<|fA| / f<1.50 The observation optical system according to claim 1, characterized in that it satisfies the following conditional equation.

3. The observation optical system according to claim 1, characterized in that the first and second semi-transparent reflective surfaces are half-mirrors.

4. The first semi-transparent reflective surface is a polarizing beam splitter, The observation optical system according to claim 1, characterized in that the second semi-transparent reflective surface is a half-mirror.

5. The observation optical system according to claim 1, characterized in that the reflective surface A is concave toward the observation side.

6. The observation optical system according to claim 1, characterized in that the observation optical system has a light-shielding member positioned closest to the observation side.

7. The observation optical system according to claim 6, characterized in that the light-shielding member is strip-shaped and a louver element arranged perpendicular to the optical axis.

8. A first linearly polarized light is incident on the first semi-transparent reflective surface from the display side. The observation optical system according to claim 1, characterized in that the polarization direction of the first linearly polarized light and the polarization direction of the light transmitted through the linear polarizer are parallel, and the direction of the slow axis of the first λ / 4 plate and the direction of the slow axis of the second λ / 4 plate are parallel.

9. A first linearly polarized light is incident on the first semi-transparent reflective surface from the display side. The observation optical system according to claim 1, characterized in that the polarization direction of the first linearly polarized light and the polarization direction of the light transmitted through the linear polarizer are perpendicular, and the direction of the slow axis of the first λ / 4 plate and the direction of the slow axis of the second λ / 4 plate are perpendicular.

10. The observation optical system according to claim 1, characterized in that the light from the display element passes through the first semi-transparent reflective surface, the first λ / 4 plate, is reflected by the second semi-transparent reflective surface, passes through the first λ / 4 plate, is reflected by the first semi-transparent reflective surface, and is transmitted through the first λ / 4 plate, the second semi-transparent reflective surface, the first semi-transparent reflective surface, the second λ / 4 plate, and the linear polarizer, in that order from the display side.

11. When ω is the absolute value of the angle of the ambient light incident on the observation optical system from the observation side with respect to the optical axis, 0° < ω < 45° The observation optical system according to claim 1, characterized in that it satisfies the following conditional equation.

12. When the focal length of the observation optical system is f and the radius of curvature of the reflective surface A is R, -6.0<R / f<-1.0 The observation optical system according to claim 1, characterized in that it satisfies the following conditional equation.

13. When the focal length of the observation optical system is f, 0.60<|fA| / f<1.50 An observation optical system according to any one of claims 3 to 12, characterized in that it satisfies the following conditional expression.

14. The first and second semi-transparent reflective surfaces are half-mirrors, When the focal length of the observation optical system is f, 0.60<|fA| / f<1.50 An observation optical system according to any one of claims 5 to 12, characterized in that it satisfies the following conditional expression.

15. The first semi-transparent reflective surface is a polarizing beam splitter, The second semi-transparent reflective surface is a half-mirror, When the focal length of the observation optical system is f, 0.60<|fA| / f<1.50 An observation optical system according to any one of claims 5 to 12, characterized in that it satisfies the following conditional expression.

16. An image display device characterized by having an observation optical system according to any one of claims 1 to 12 and the display element.

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