Optical system and image display device

Abstract

To make a ghost inconspicuous in an optical system which has a wide angle, is lightweight, and uses polarization light.SOLUTION: An optical system OR1 guides, to an observer, light from a display element 108 for displaying an image, and comprises a first phase plate 111, a translucent reflective surface 112, a lens 104, a second phase plate 113 and a polarization separation element 114 which are arranged in the order from the display element toward the observer. The polarization separation element reflects first linear polarized light while transmits second linear polarized light in a polarization direction orthogonal to a polarization direction of the first linear polarized light. A difference is 7% or less, between a maximum value and a minimum value of reflection rates of the translucent reflective surface in first, second and third wavelengths respectively included in a wavelength rage of 430 nm to 480 nm, a wavelength rage of 520 nm to 570nm, a wavelength rage of 600 nm to 650 nm. One of lenses included in the optical system which is the closest to the display element is a negative lens having a surface convex toward the display element.SELECTED DRAWING: Figure 2

Description

[Technical field]

[0001] The present invention relates to an image display device that allows an observer to observe an image displayed on a display element through an optical system. [Background technology]

[0002] One example of such an image display device is a head-mounted display (HMD) that is worn on the observer's head. In order to present images with a wide angle of view in such an HMD, an eyepiece optical system that folds the optical path using polarized light is sometimes used. However, when a plastic lens is used to reduce the weight of such an eyepiece optical system, the birefringence in the plastic lens disrupts the polarization state of light, resulting in the generation of ghost images.

[0003] Patent Documents 1 and 2 disclose HMDs with eyepiece optical systems that use polarized light to achieve a wide angle of view. In the HMD of Patent Document 1, the direction of the transmission axis of the semi-transmissive polarizing plate in the eyepiece optical system is aligned with the direction in which the observer's eyes are aligned to reduce luminance unevenness. In addition, the HMD of Patent Document 2 achieves a wide angle of view by using a curved polarizing element. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2019-053152 A [Patent Document 2] Special Publication No. 2018-508800 Summary of the Invention [Problem to be solved by the invention]

[0005] However, Patent Document 1 only describes the use of a plastic material with low birefringence in the eyepiece optical system to reduce ghosts caused by birefringence in the plastic lens, and Patent Document 2 does not describe the reduction of ghosts caused by birefringence in the lens.

[0006] The present invention provides an optical system that is suitable for a lightweight eyepiece optical system with a wide angle of view that utilizes polarized light and that can make ghost images less noticeable, and an image display device that includes the optical system. [Means for solving the problem]

[0007] The optical system according to one aspect of the present invention is an optical system that guides light from a display element that displays an image to an observer, and includes a first phase plate, a semi-transmissive reflective surface, a lens, a second phase plate, and a polarization separation element, which are arranged in this order from the display element toward the observer. The polarization separation element reflects a first linearly polarized light and transmits a second linearly polarized light having a polarization direction perpendicular to the polarization direction of the first linearly polarized light. The difference between the maximum and minimum reflectances of the semi-transmissive reflective surface at a first wavelength included in the wavelength range of 430 nm to 480 nm, a second wavelength included in the wavelength range of 520 nm to 570 nm, and a third wavelength included in the wavelength range of 600 nm to 650 nm is 7% or less, and the lens closest to the display element among the lenses included in the optical system is a negative lens having a surface that is convex toward the display element. Note that an image display device having the above optical system and a display element also constitutes another aspect of the present invention. Effect of the Invention

[0008] According to the present invention, ghosts can be made less noticeable in a wide-angle, lightweight optical system that uses polarized light. [Brief description of the drawings]

[0009] [Figure 1] FIG. 1 is a diagram showing the configuration of an HMD according to a first embodiment. [Diagram 2] FIG. 2 is a diagram showing the configuration of an eyepiece optical system in the first embodiment. [Diagram 3] FIG. 2 is an external view of the HMD of the first embodiment. [Figure 4] FIG. 3 is an optical path diagram of the eyepiece optical system in the first embodiment. [Diagram 5] 5A to 5C are diagrams for explaining ghost light in the eyepiece optical system according to the first embodiment. [Figure 6] 4 is a diagram showing the spectral characteristics of a half mirror of the eyepiece optical system in the first embodiment. FIG. [Figure 7] 6 is a diagram showing another spectral characteristic of the half mirror of the eyepiece optical system in Example 1. FIG. [Figure 8] 4 is a diagram showing the spectral characteristics of the lenses and half mirror of the eyepiece optical system in the first embodiment. FIG. [Figure 9] FIG. 11 is a diagram showing the configuration of an HMD according to a second embodiment. [Figure 10] FIG. 11 is a diagram showing the configuration of an eyepiece optical system in a second embodiment. [Figure 11] 10A to 10C are diagrams for explaining ghost light in the eyepiece optical system according to the second embodiment. [Figure 12] 13 is a diagram showing the spectral characteristics of a half mirror of an eyepiece optical system in Example 2. FIG. [Figure 13] 13 is a diagram showing another spectral characteristic of the half mirror of the eyepiece optical system in the second embodiment. FIG. [Figure 14] 4 is a diagram showing the incidence angle characteristics of a half mirror of the eyepiece optical system in the first embodiment. FIG. [Figure 15] 13 is a diagram showing the incidence angle characteristics of a half mirror of an eyepiece optical system in Example 2. FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0010] Hereinafter, embodiments of the present invention will be described with reference to the drawings. EXAMPLES

[0011] FIG. 1 shows the configuration of an HMD 101 as an image display device (image observation device) according to a first embodiment of the present invention. The HMD 101 is worn on the head of an observer. Reference numeral 102 denotes the observer's right eye, and 103 denotes the observer's left eye. Display lenses 104 and 105 constitute an eyepiece optical system for the right eye OR1, and display lenses 106 and 107 constitute an eyepiece optical system for the left eye OL1. Each eyepiece optical system is a coaxial optical system made up of a plurality (two) of display lenses. Note that the number of display lenses included in each eyepiece optical system may be one or more. The observer's right eye 102 is disposed at the exit pupil ER1 of the eyepiece optical system for the right eye OR1, and the observer's left eye 103 is disposed at the exit pupil EL1 of the eyepiece optical system for the left eye OL1.

[0012] Reference numeral 108 denotes a display element for the right eye, and 109 denotes a display element for the left eye. Each display element is a flat-plate type display element, and in this embodiment, an organic EL display panel is used. Figure 3 shows the appearance of the HMD 101 and a personal computer 150 connected thereto. Each display element displays a display image (original image) corresponding to an image signal output from the personal computer 150.

[0013] The eyepiece optical systems OR1 and OL1 guide light from the display elements 108 and 109 to the exit pupils ER1 and EL1, respectively, to project enlarged virtual images of the displayed image onto the observer's right eye 102 and left eye 103. This allows the observer to observe the observation images, which are virtual images of the displayed images on the display elements 108 and 109, through the eyepiece optical systems OR1 and OL1.

[0014] In this embodiment, the focal length of each eyepiece optical system is 12 mm, the horizontal display angle of view is 45°, the vertical display angle of view is 34°, and the diagonal display angle of view is 54°. The eye relief E1, which is the distance between the surface of each eyepiece optical system closest to the exit pupil (observer side) (the surface on the exit pupil side of the polarization separation element 114 described later) and the exit pupil of each eyepiece optical system, is 18 mm.

[0015] The right-eye and left-eye eyepiece optical systems OR1 and OL1 in this embodiment are optical systems that fold the optical path using polarized light, and their configuration will be described using the right-eye eyepiece optical system OR1. As shown in Fig. 2, the right-eye eyepiece optical system OR1 has a polarizing plate 110, a first phase plate 111, a display lens 105, a display lens 104, a second phase plate 113, and a polarization separation element (hereinafter referred to as PBS) 114, which are arranged in this order from the right-eye display element 108 toward the exit pupil ER1. A half mirror 112 is formed as a semi-transmissive reflective surface by deposition on the surface of the display lens 104 facing the display element. The second phase plate 113 and the PBS 114 are provided so as to be stacked on the surface of the display lens 104 facing the exit pupil.

[0016] The polarizing plate 110, the first phase plate 111, the second phase plate 113, and the PBS 114 are all formed in a flat plate shape. The first and second phase plates 111 and 113 are all wave plates with a phase difference of λ / 4. The polarization direction of the first linearly polarized light transmitted through the polarizing plate 110 and the slow axis of the first phase plate 111 are inclined at 45°. The polarization direction of the first linearly polarized light and the slow axis of the second phase plate 113 are also inclined at −45° (i.e., the same angle as the polarization direction of the first linearly polarized light, but on the opposite side to the slow axis of the first phase plate 111). Furthermore, the polarization direction of the first linearly polarized light and the polarization direction of the second linearly polarized light transmitted through the PBS 114 are mutually perpendicular.

[0017] The unpolarized light emitted from the right-eye display element 108 passes through the polarizing plate 110 to become linearly polarized light, passes through the first phase plate 111 to become circularly polarized light, and passes through the display lens 105. The circularly polarized light further passes through the half mirror 112, passes through the display lens 104, and passes through the second phase plate 113 to become first linearly polarized light. Since the first linearly polarized light has a polarization direction perpendicular to the polarization direction passing through the PBS 114, it is reflected by the PBS 114 and passes through the second phase plate 113 to become circularly polarized light. After passing through the display lens 104, the circularly polarized light is reflected by the half mirror 112, passes through the display lens 104 again, and passes through the second phase plate 113 to become second linearly polarized light. Since the second linearly polarized light has a polarization direction that coincides with the polarization direction passing through the PBS 114, it passes through the PBS 114 and is guided to the exit pupil ER1 (right eye 102). Similarly, the light emitted from the left-eye display element 109 is guided to the exit pupil EL1 (left eye 103) by the left-eye eyepiece optical system OL1.

[0018] By configuring each eyepiece optical system in this way to fold the optical path by using polarized light, each eyepiece optical system can be made thinner in the optical axis direction, and the focal length of each eyepiece optical system can be shortened, making it possible to observe images with a wide angle of view.

[0019] It is desirable that the HMD is lightweight so that the observer wears it on his / her head. For this reason, it is desirable that the display lenses constituting the eyepiece optical system and the imaging lenses constituting the imaging optical system are made of a resin material having a smaller specific gravity than glass. In this embodiment as well, the display lenses 104 to 107 are resin lenses made of a resin material. Moreover, the display lenses 104 and 106 closest to the exit pupil are plano-convex lenses having a convex surface on the display element side, and the convex surface is aspheric, thereby enhancing the aberration correction effect. Moreover, the display lenses 105 and 107 are resin lenses having aspheric surfaces on both sides.

[0020] The display lenses 105 and 107 may be glass lenses because they have a small outer diameter and little effect on weight. The birefringence of glass lenses is very small, making it possible to observe high-quality images.

[0021] In the HMD 101 of this embodiment, it is desirable that the eye relief is 15 mm or more so that even observers who wear glasses can wear it. On the other hand, if the eye relief is too long, the outer shape of the display lens becomes large and the HMD also becomes large, so it is desirable that the eye relief is 25 mm or less. In other words, the eye relief E1 is 15mm≦E1≦25mm (1) It is preferable to satisfy the following conditions.

[0022] In the HMD 101 of this embodiment, as shown in FIG. 4, the position of the exit pupil ER1' of the right eye eyepiece optical system OR1 when the eyeball (pupil) of the right eye 102 is facing (looking at) the left and right ends of the display surface of the right eye display element 108, that is, the eye relief E1', is set to 28 mm, which is the sum of the eyeball rotation radius of 10 mm and the eye relief E1=18 mm when the eyeball is facing the center of the display surface as shown in FIG. 1. The exit pupil diameter is set to 6 mm. The same is true for the exit pupil of the left eye eyepiece optical system OL1. By setting in this way, even if the eyeball rotates to observe the left and right ends (similarly the top and bottom ends) of the display surface, light can be made to enter the eyeball from the direction in which the eyeball is facing.

[0023] Next, the generation of ghost light as unwanted light in the eyepiece optical systems OR1 and OL1 that use polarized light in this embodiment will be described with reference to Fig. 5. Here, the description will be given using the right-eye eyepiece optical system OR1, but the same applies to the left-eye eyepiece optical system OL1.

[0024] In the eyepiece optical system OR1, due to birefringence in the display lenses 104 and 105 and the polarization characteristics of the polarizing plate 110, the phase plates 111 and 113, and the PBS 114, the light emitted from the display element 108 may not follow the normal optical path shown in FIG. 1 or FIG. 4, but may be guided directly to the right eye 102 without being reflected by the PBS 114 as shown in FIG. 5. This light becomes ghost light. More specifically, the circularly polarized light transmitted through the first phase plate 111 becomes elliptically polarized light due to birefringence in the display lenses 104 and 105, and the polarization direction of the linearly polarized light after transmitting through the second phase plate 113 is tilted from the original direction. Then, this linearly polarized light transmits the PBS 114 and is guided to the right eye 102, becoming ghost light. Even if there is no birefringence in the display lenses 104 and 105, ghost light may occur if the polarization characteristics of the polarizing plate 110, the phase plates 111 and 113, and the PBS 114 are not good.

[0025] Here, the normal light path shown in Fig. 1 and Fig. 4 is compared with the ghost light path shown in Fig. 5. Light (normal light) that is emitted from the right-eye display element 108 and follows the normal light path is transmitted and reflected by the half mirror 112. However, in the ghost light path, the ghost light is only transmitted by the half mirror 112. For this reason, if there is a difference in reflectance of the half mirror 112 for each wavelength, a difference occurs between the spectral characteristics of the half mirror 112 in the normal light path and the spectral characteristics of the half mirror 112 in the ghost light path. As a result, the color shift between the normal light and the ghost light becomes large, making the ghost light more noticeable.

[0026] For example, when the half mirror 112 has the reflectance and transmittance shown in Fig. 6, the spectral characteristics of normal light by the half mirror 112 are shown in a graph of transmittance x reflectance, and the spectral characteristics of ghost light by the half mirror 112 are shown in a graph of transmittance. As can be seen from Fig. 6, the difference in transmittance x reflectance for each wavelength is small within the visible light range, but the difference in transmittance for each wavelength is large within the visible light range, and the transmittance of blue light around 450 nm is high. For this reason, the ghost light appears bluer than the normal light to the observer, making the ghost light more noticeable.

[0027] Therefore, in this embodiment, the reflectance and transmittance of the half mirror 112 at an incident angle of 0° are set as shown in Fig. 7. Fig. 7 also shows the reflectance x transmittance of the half mirror 112 at an incident angle of 0°. In this way, the difference in reflectance for each wavelength within the visible light range is reduced, and the difference in the spectral characteristics of the half mirror 112 for normal light and the spectral characteristics of the half mirror 112 for ghost light is reduced. This reduces the color shift between the normal light and the ghost light, making the ghost light less noticeable.

[0028] In this embodiment, the dominant wavelength (first wavelength) of the blue light emitted from the display element 108 is 450 nm, the dominant wavelength (second wavelength) of the green light is 525 nm, and the dominant wavelength (third wavelength) of the red light is 610 nm. In contrast, the reflectance of the half mirror 112 at the first, second, and third wavelengths of 450 nm, 525 nm, and 610 nm is 45%, 44%, and 50%, respectively, and the difference between the maximum and minimum reflectance at these wavelengths is 6%. This difference is preferably 7% or less, and if it is 7% or less, the color shift between the normal light and the ghost light due to the spectral characteristics of the half mirror 112 is small, and the ghost light can be made less noticeable. Furthermore, in order to further reduce the color shift between the normal light and the ghost light, it is more preferable that the above difference is 5% or less.

[0029] The first, second and third wavelengths when defining the difference in reflectance of the half mirror 112 are desirably matched to the dominant wavelengths of the blue, green and red light from the display element 108. This makes it possible to reduce the color shift between the normal light and the ghost light in accordance with the spectral characteristics of the light from the display element 108. However, when the difference in reflectance for each wavelength of the half mirror 112 is small as in this embodiment, the first to third wavelengths do not need to be matched to the dominant wavelengths of the blue, green and red light from the display element 108.

[0030] The dominant wavelength of the blue light from the display element 108 is often in the range of 430 nm to 480 nm, and the dominant wavelength of the green light is often in the range of 520 nm to 570 nm. The dominant wavelength of the red light is often in the range of 600 nm to 650 nm. For this reason, it is desirable that the first wavelength is in the range of 430 nm to 480 nm, the second wavelength is in the range of 520 nm to 570 nm, and the third wavelength is in the range of 600 nm to 650 nm. This can reduce color shifts between the blue light, the green light, and the red light.

[0031] The half mirror 112 of this embodiment includes a layer made of silver (silver layer). This reduces the difference in reflectance and transmittance depending on the polarization state. In an optical system that uses polarized light as in this embodiment, if there is a difference in reflectance and transmittance depending on the polarization state, a loss of light occurs. For this reason, it is desirable for the half mirror 112 to include a metal layer that has a small difference in reflectance and transmittance depending on the polarization state, and in particular a silver layer that has a small loss due to absorption.

[0032] Furthermore, in order to improve adhesion between the silver layer of the half mirror 112 and the resin of the display lens 104, a dielectric multilayer film (dielectric film) may be provided between the silver layer and the display lens 104. Furthermore, in order to improve durability of the silver layer, a dielectric multilayer film may be provided on the surface of the silver layer opposite to the display lens 104.

[0033] The film configuration (material, refractive index, and film thickness) of the half mirror 112 of this embodiment is shown in Table 1. By making the half mirror 112 a multilayer film as shown in Table 1, it is possible to reduce the difference in reflectance for each wavelength in the visible light range. The dielectric multilayer film between the silver layer (Ag) of the half mirror 112 and the display lens (substrate) 104 contains silicon oxide (SiO2), zirconium oxide (ZrO2), titanium oxide (TiO2), and aluminum oxide (AlO3). In addition, the dielectric multilayer film on the silver layer of the half mirror 112 opposite the display lens 104 contains aluminum oxide and silicon oxide.

[0034] [Table 1]

[0035] Furthermore, the number of times that light passes through the display lens 104 differs between the normal light path and the ghost light path. Specifically, normal light passes through the display lens 104 three times, whereas ghost light passes through it only once. For this reason, similar to the half mirror 112, by reducing the difference in the spectral transmittance of the display lens 104 for each wavelength within the visible light region, it is possible to reduce the color shift between the normal light and the ghost light.

[0036] The normal light emitted from the display element 108 passes through the half mirror 112, then passes through the display lens 104 twice, is reflected by the half mirror 112, and passes through the display lens 104 again. On the other hand, the ghost light emitted from the display element 108 passes through the half mirror 112, then passes through the display lens 104 once. Therefore, the difference in the spectral characteristics of the lens 104 and the half mirror 112 between the normal light path and the ghost light path is Transmittance of the display lens 104×reflectance of the half mirror 112×transmittance of the display lens 104 It can be expressed as:

[0037] 8 shows the transmittance of the display lens 104, the reflectance of the half mirror 112, and the value of the transmittance of the display lens 104 × the reflectance of the half mirror 112 × the transmittance of the display lens 104. The transmittance of the display lens 104 indicates the transmittance when there is no Fresnel reflection on the surface of the display lens 104.

[0038] As can be seen from Fig. 8, the values ​​of the transmittance of the display lens 104 x the reflectance of the half mirror 112 x the transmittance of the display lens 104 at 450 nm, 525 nm, and 610 nm are 44%, 45%, and 49%, respectively. Therefore, the difference between the maximum and minimum values ​​at the dominant wavelengths of the blue light, green light, and red light from the display element 108 is 5%. It is desirable that this difference be 10% or less. If it is 10% or less, the color shift between the normal light and the ghost light due to the spectral characteristics of the display lens 104 and the half mirror 112 becomes small, and the ghost light can be made less noticeable.

[0039] As can be seen from FIG. 4, in the eyepiece optical system OR1 using polarized light, the exit angle of light from the peripheral part of the display element 108 is large in order to make the optical system thin, and the peripheral light amount is greatly reduced. In the ghost optical path, the angle of incidence to the half mirror 112 is small, but the angle of incidence to the half mirror 112 when the normal light from the peripheral part is transmitted is large at about 60°. For this reason, as shown in FIG. 14, the angle of incidence characteristic of the transmittance of the half mirror 112 is set so that the transmittance at the incident angle of 60° is higher than the transmittance at the incident angle of 0° at the second wavelength of 545 nm. In other words, the transmittance of the half mirror 112 is set so that the larger the angle of incidence to the half mirror 112 is, the higher the transmittance of the half mirror 112 is. This makes it possible to increase only the light utilization efficiency in the normal optical path from the peripheral part of the display element 108, and to brighten the peripheral part of the observed image without brightening the ghost light. In this embodiment, the transmittance at the incident angle of 60° is higher than the transmittance at the incident angle of 0° even for the first wavelength of 450 nm and the third wavelength of 610 nm.

[0040] Here, the transmittance of the half mirror 112 for each incident angle is a value for wavelengths in the visible light region, and if it differs for each wavelength, it may be an average value, or it may be a value for a representative wavelength with high relative luminosity such as the wavelength of green light as in this embodiment. Also, if the spectral characteristics of the half mirror 112 differ depending on the incident angle, it may be a value at an incident angle of 0° as in this embodiment, or it may be a value at the incident angle of ghost light.

[0041] The surface of the display lens 104 on which the half mirror 112 is deposited is a surface that is convex toward the display element 108. By depositing the half mirror 112 on this convex surface, it is possible to realize a wide angle of view while making the eyepiece optical system OR1 thinner. Furthermore, by making the convex surface on which the half mirror 112 is deposited aspheric as described above, it is possible to improve the aberration correction effect. By depositing the half mirror 112 on the convex and aspheric surface of the display lens 104 that faces the display element 108 in this way, the half mirror 112 also becomes a surface that has a convex and aspheric shape toward the display element 108.

[0042] In order to reduce ghost light as external light and increase the contrast of the observed image, a polarizing plate may be disposed between the PBS 114 and the exit pupil ER1.

[0043] Furthermore, by making the surface on the exit pupil side of the display lens 104 on which the second phase plate 113 and the PBS 114 are formed flat, the eye relief can be lengthened and the eyepiece optical system OR1 can be made thinner. If this surface is concave on the exit pupil side, the display lens 104 becomes thicker in order to ensure the eye relief in the peripheral area. If this surface is convex on the exit pupil side, the display lens 104 becomes thicker in order to ensure the thickness of the edge portion of the display lens 104. For this reason, in this embodiment, the display lens 104 is a plano-convex lens.

[0044] As described above, the first and second phase plates 111 and 113 are wavelength plates with a phase difference of λ / 4, but the phase difference may be shifted from λ / 4 so as to cancel the birefringence of the display lenses 104 and 105. In this case, it is desirable that the sum of the phase difference of the display lens 104 and the phase difference of the second phase plate 113 is 3λ / 20 or more and 7λ / 20 or less. It is also desirable that the sum of the phase difference of the display lens 105 and the phase difference of the first phase plate 111 is 3λ / 20 or more and 7λ / 20 or less. If the sum of the respective phase differences is out of the above range, the intensity of ghost light increases, making it impossible to observe a natural image.

[0045] As described above, each display element in this embodiment uses an organic EL display panel that emits unpolarized light. However, if a liquid crystal display that emits linearly polarized light is used, the polarizing plate 110 on the display element side will not be necessary, making it possible to make the display even thinner. EXAMPLES

[0046] 9 shows the configuration of an HMD 201 according to a second embodiment of the present invention. Reference numeral 202 denotes an observer's right eye, and 203 denotes the observer's left eye. Display lenses 204 and 205 constitute an eyepiece optical system for the right eye OR2, and display lenses 206 and 207 constitute an eyepiece optical system for the left eye OL2. Each eyepiece optical system is a coaxial optical system made up of two display lenses. The observer's right eye 202 is disposed at the exit pupil ER2 of the eyepiece optical system for the right eye OR2, and the observer's left eye 203 is disposed at the exit pupil EL2 of the eyepiece optical system for the left eye OL2.

[0047] Reference numeral 208 denotes a display element for the right eye, and 209 denotes a display element for the left eye. Each display element is a flat-plate type display element, and in this embodiment, an organic EL display panel is used. Each display element displays a display image (original image) corresponding to an image signal output from a personal computer (not shown).

[0048] The eyepiece optical systems OR2 and OL2 guide light from the display elements 208 and 209 to the exit pupils ER2 and EL2, respectively, to project enlarged virtual images of the display images displayed on the display elements 208 and 209 onto the observer's right eye 202 and left eye 203. This allows the observer to observe the observation images, which are virtual images of the display images displayed on the display elements 208 and 209, through the eyepiece optical systems OR2 and OL2.

[0049] In this embodiment, the focal length of each eyepiece optical system is 13 mm, the horizontal display angle of view is 60°, the vertical display angle of view is 60°, and the diagonal display angle of view is 78°. The eye relief E2, which is the distance between the surface of each eyepiece optical system closest to the exit pupil (the surface on the exit pupil side of a polarization separation element 214 described later) and the exit pupil of each eyepiece optical system, is 20 mm. In this embodiment, too, for the same reasons as in embodiment 1, it is desirable for the eye relief E2 to be 15 mm or more and 25 mm or less.

[0050] The right-eye and left-eye eyepiece optical systems OL2 and OL2 in this embodiment are optical systems that fold the optical path using polarized light, as in the first embodiment, and their configuration will be described using the right-eye eyepiece optical system OL2. As shown in FIG. 10, the right-eye eyepiece optical system OL2 has a polarizing plate 210, a first phase plate 211, a display lens 205, a display lens 204, a second phase plate 213, and a PBS 214, which are arranged in this order from the right-eye display element 208 toward the exit pupil ER2. A half mirror 212 is formed as a semi-transmissive reflecting surface by deposition on the convex surface of the display lens 204 facing the display element. The second phase plate 213 and the PBS 214 are provided so as to be stacked on the surface of the display lens 204 facing the exit pupil.

[0051] The polarizing plate 210, the first phase plate 211, the second phase plate 213, and the PBS 214 are all formed in a flat plate shape. The first and second phase plates 211 and 213 are all wave plates with a phase difference of λ / 4. The polarization direction of the first linearly polarized light transmitted through the polarizing plate 210 is inclined at 45° to the slow axis of the first phase plate 211, and the polarization direction of the first linearly polarized light is inclined at −45° to the slow axis of the second phase plate 213. In addition, the polarization direction of the first linearly polarized light and the polarization direction of the second linearly polarized light transmitted through the PBS 214 are perpendicular to each other.

[0052] The unpolarized light emitted from the right-eye display element 208 passes through the polarizing plate 210 to become linearly polarized light, passes through the first phase plate 211 to become circularly polarized light, and passes through the display lens 205. The circularly polarized light further passes through the half mirror 212, passes through the display lens 204, and passes through the second phase plate 213 to become first linearly polarized light. Since the first linearly polarized light has a polarization direction perpendicular to the polarization direction passing through the PBS 214, it is reflected by the PBS 214 and passes through the second phase plate 213 to become circularly polarized light. After passing through the display lens 204, the circularly polarized light is reflected by the half mirror 212, passes through the display lens 204 again, and passes through the second phase plate 213 to become second linearly polarized light. Since the second linearly polarized light has a polarization direction that coincides with the polarization direction passing through the PBS 214, it passes through the PBS 214 and is guided to the exit pupil ER2 (right eye 202). Similarly, the light emitted from the left-eye display element 209 is guided to the exit pupil EL2 (left eye 203) by the left-eye eyepiece optical system OL2.

[0053] In this embodiment, as in the first embodiment, each eyepiece optical system is configured to fold the optical path by using polarized light, thereby making it possible to make each eyepiece optical system thinner and shortening the focal length of each eyepiece optical system, thereby enabling the observation of wide-angle images.

[0054] In this embodiment, the thickness of the optical axis direction is reduced by cementing two display lenses in each eyepiece optical system. By cementing the two display lenses, the display lenses can be easily held by the main body of the HMD 201.

[0055] Furthermore, in this embodiment as well, the display lenses 204 to 207 are made of resin lenses in order to reduce weight, and the display lenses 204 to 207 are made of aspheric lenses in order to improve the effect of correcting aberrations.

[0056] In the HMD 201 of this embodiment, the position of the exit pupil of the right eye eyepiece optical system OR2 when the eyeball (pupil) of the right eye 202 is facing (looking at) the left and right ends of the display surface of the display element 208, i.e., the eye relief, is set to 30 mm, which is the sum of the eyeball rotation radius of 10 mm and the eye relief E2=20 mm when the eyeball is facing the center of the display surface. The exit pupil diameter is set to 6 mm. The same is true for the exit pupil of the left eye eyepiece optical system OL2. By setting in this way, even if the eyeball rotates to observe the left and right ends (similarly the top and bottom ends) of the display surface, light can be made to enter the eyeball from the direction in which the eyeball is facing.

[0057] As shown in FIG. 11, ghost light is also generated in each of the eyepiece optical systems OR2 and OL2 of this embodiment for the same reason as in the first embodiment. For example, in the eyepiece optical system OR2, due to birefringence in the display lenses 204 and 205 and the polarization characteristics of the polarizing plate 210, the phase plates 211 and 213, and the PBS 214, the light emitted from the display element 208 may not follow the normal optical path shown in FIG. 9, and may be guided directly to the right eye 202 without being reflected by the PBS 214 as shown in FIG. 11. This light becomes ghost light. More specifically, the circularly polarized light transmitted through the first phase plate 211 becomes elliptically polarized light due to birefringence in the display lenses 205 and 204, and the polarization direction of the linearly polarized light after transmitting through the second phase plate 213 is tilted from the original direction. Then, this linearly polarized light transmits through the PBS 214 and is guided to the right eye 202, becoming ghost light. Even if there is no birefringence in the display lenses 204 and 205, ghost light will occur if the polarization characteristics of the polarizer 210, the phase plates 211 and 213, and the PBS 214 are not good. Ghost light will also occur in the left-eye eyepiece optical system OL2.

[0058] Therefore, in this embodiment, the reflectance and transmittance of the half mirror 212 at an incident angle of 0° are as shown in Fig. 12. Fig. 12 also shows the reflectance x transmittance of the half mirror 212 at an incident angle of 0°. In this way, the difference in reflectance for each wavelength within the visible light range is reduced, and the difference in the spectral characteristics of the half mirror 212 for normal light and the spectral characteristics of the half mirror 212 for ghost light is reduced. This reduces the color shift between the normal light and the ghost light, making the ghost light less noticeable.

[0059] In this embodiment, the dominant wavelength (first wavelength) of the blue light emitted from the display element 208 is 470 nm, the dominant wavelength (second wavelength) of the green light is 545 nm, and the dominant wavelength (third wavelength) of the red light is 605 nm. In contrast, the reflectance of the half mirror 212 at the first, second, and third wavelengths of 470 nm, 545 nm, and 605 nm is 55%, 53%, and 57%, respectively, and the difference between the maximum and minimum values ​​of the reflectance at these wavelengths is 4%. As described in the first embodiment, this difference is preferably 7% or less. If it is 7% or less (more preferably 5% or less), the color shift between the normal light and the ghost light due to the spectral characteristics of the half mirror 212 is small, and the ghost light can be made less noticeable.

[0060] In this embodiment, the half mirror 212 also includes a silver layer. Furthermore, in this embodiment, the half mirror 212 has a characteristic that the reflectance at the first, second, and third wavelengths is higher than the transmittance. Therefore, the thickness (film thickness) of the silver layer of the half mirror 212 is thicker than usual. By making the silver layer thicker, the film can be formed stably and the durability of the silver layer is improved.

[0061] Similarly to the first embodiment, in order to improve adhesion between the silver layer of the half mirror 212 and the resin of the display lens 204, a dielectric multilayer film may be provided between the silver layer and the display lens 204. In order to improve the durability of the silver layer, a dielectric multilayer film may be provided on the surface of the silver layer opposite to the display lens 204.

[0062] The film configuration of the half mirror 212 of this embodiment is shown in Table 2. By making the half mirror 212 a multilayer film as shown in Table 2, it is possible to reduce the difference in reflectance for each wavelength within the visible light range. As in Example 1 (Table 1), the dielectric multilayer film between the silver layer of the half mirror 212 and the display lens (substrate) 204 contains silicon oxide, zirconium oxide, titanium oxide, and aluminum oxide. In addition, the dielectric multilayer film on the silver layer of the half mirror 212 opposite the display lens 204 contains aluminum oxide and silicon oxide.

[0063] [Table 2]

[0064] In this embodiment, in order to reduce ghost light, the reflectance of the half mirror 212 at the second wavelength of 545 nm is set to 53% and the transmittance is set to 44%, so that the reflectance is higher than the transmittance. As shown in FIG. 11, the ghost light only passes through the half mirror 212 and is not reflected by the half mirror 212. Therefore, by lowering the transmittance of the half mirror 212 at the second wavelength of 545 nm, the intensity of the ghost light can be reduced. In this case, it is desirable that the transmittance of the half mirror 212 at the second wavelength of 545 nm is 45% or less. However, if the transmittance of the half mirror 212 is lower than 25%, the light utilization efficiency of the normal light decreases and the observed image becomes dark. Therefore, it is desirable that the transmittance of the half mirror 212 at the second wavelength of 545 nm is 25% or more.

[0065] That is, the transmittance T of the half mirror 212 at any one of the first, second, and third wavelengths is 25%≦T≦45% (2) It is desirable to satisfy the following conditions.

[0066] In order to further reduce ghost light, the thickness of the silver layer of the half mirror 212 may be made thicker than the thickness shown in Table 2 as shown in Table 3, so that the reflectance of the half mirror 212 at the second wavelength of 545 nm is 65% and the transmittance is 32%, as shown in FIG. 13.

[0067] [Table 3]

[0068] In this embodiment, as in the first embodiment, the transmittance of the half mirror 212 at an incident angle of 60° is set higher than the transmittance at an incident angle of 0° at the second wavelength of 545 nm, as shown in FIG. 15. In other words, the transmittance of the half mirror 212 is set higher as the incident angle to the half mirror 212 increases. This makes it possible to increase only the light utilization efficiency in the normal light path from the periphery of the display element 208, and to brighten the periphery of the observed image without brightening the ghost light. In this embodiment, the transmittance at an incident angle of 60° is set higher than the transmittance at an incident angle of 0° even for the first wavelength of 470 nm and the third wavelength of 605 nm.

[0069] In this embodiment, the transmittance of the half mirror 212 for each incident angle is a value for wavelengths in the visible light region, and if it differs for each wavelength, it may be an average value, or it may be a value for a representative wavelength with high relative luminosity, such as the wavelength of green light. Also, if the spectral characteristics of the half mirror 212 differ depending on the incident angle, it may be a value at an incident angle of 0°, or a value at the incident angle of ghost light.

[0070] In this embodiment, the surface on which the half mirror 212 is vapor-deposited has a convex shape facing the display element 208. By vapor-depositing the half mirror 212 on this convex surface, it is possible to realize a wide angle of view while making the optical system thinner. Furthermore, by making the convex surface on which the half mirror 212 is vapor-deposited aspheric, the aberration correction effect is improved.

[0071] In addition, the display lenses 204 and 205 are cemented together. Therefore, the surface on which the half mirror 212 is deposited may be the surface on the exit pupil side of the display lens 205. Even in this case, the surface on which the half mirror 212 is deposited is a surface that is convex toward the display element 208. By depositing the half mirror 212 on the display lens 204 or the display lens 205 that is convex and aspherical toward the display element 208 in this way, the half mirror 212 also has a surface that is convex and aspherical toward the display element 208.

[0072] In addition, in order to reduce ghost light as external light and increase the contrast of the observed image, a polarizing plate may be disposed between the PBS 214 and the exit pupil ER2.

[0073] In addition, by forming the surface of the display lens 204 on the exit pupil side, on which the second phase plate 213 and the PBS 214 are formed, as a flat surface, it is possible to lengthen the eye relief and reduce the thickness of the eyepiece optical system OR2. For this reason, the display lens 204 is a plano-convex lens.

[0074] Also, similarly to the first embodiment, the phase difference of the first and second phase plates 211, 213 may be shifted from λ / 4 so as to cancel the birefringence of the display lenses 204, 205. In this case, it is desirable that the sum of the phase difference of the display lens 204 and the phase difference of the second phase plate 213 is 3λ / 20 or more and 7λ / 20 or less. It is also desirable that the sum of the phase difference of the display lens 205 and the phase difference of the first phase plate 211 is 3λ / 20 or more and 7λ / 20 or less.

[0075] Also in this embodiment, if a liquid crystal display that emits linearly polarized light is used as each display element, the polarizing plate 210 on the display element side becomes unnecessary, making it possible to further reduce the thickness.

[0076] According to each of the above-described embodiments, ghosts can be made less noticeable in a wide-angle, lightweight eyepiece optical system that utilizes polarized light.

[0077] The embodiments described above are merely representative examples, and various modifications and alterations are possible for each embodiment when implementing the present invention. [Explanation of symbols]

[0078] 101,201 HMD 104,105,106,107,204,205,206,207 Display lens 108,109,208,209 Display element 111,211 First phase plate 113,213 Second phase plate 112,212 Half mirror OR1, OR2 Right eye eyepiece optical system OL1, OL2 Eyepiece optical system for left eye ER1, ER2, EL1,EL2 Exit pupil

Claims

1. An optical system for directing light from a display element that displays an image to an observer, arranged in sequence from the display element to the viewer, A first phase plate; and A semi-transmissive reflective surface; Lenses and A second phase plate; and a polarization separation element; the polarization separation element reflects a first linearly polarized light and transmits a second linearly polarized light having a polarization direction perpendicular to the polarization direction of the first linearly polarized light; a difference between a maximum value and a minimum value of a reflectance of the semi-transmissive reflective surface at each of a first wavelength included in a wavelength range of 430 nm to 480 nm, a second wavelength included in a wavelength range of 520 nm to 570 nm, and a third wavelength included in a wavelength range of 600 nm to 650 nm is 7% or less; An optical system, wherein the lens closest to the display element among the lenses included in the optical system is a negative lens having a convex surface facing the display element.

2. The optical system of claim 1 , wherein the difference is 5% or less.

3. At each of the first wavelength, the second wavelength, and the third wavelength, Transmittance of the lens × reflectance of the semi-transmissive reflective surface × transmittance of the lens 3. The optical system according to claim 1, wherein the difference between the maximum and minimum values ​​of the value of is 7% or less.

4. 4. The optical system according to claim 1, wherein the lens is made of a resin material.

5. 5. The optical system according to claim 1, wherein the semi-transmissive reflective surface has a convex aspheric shape facing the display element.

6. 6. An eyepiece optical system according to claim 1, wherein the semi-transmissive reflective surface includes a layer made of silver.

7. 7. The optical system according to claim 6, wherein the semi-transmissive reflective surface has a dielectric film containing any one of silicon oxide, zirconium oxide, titanium oxide, and aluminum oxide.

8. 8. The optical system according to claim 1, wherein the lens closest to the viewer among the one or more lenses included in the optical system is a plano-convex lens having a convex surface facing the display element.

9. 9. The optical system according to claim 1, wherein the reflectance of the semi-transmissive reflective surface is higher than the transmittance at the first, second and third wavelengths.

10. When the transmittance of the semi-transmissive reflective surface at at least one of the first, second, and third wavelengths is T, 25%≦T≦45% 10. The optical system according to claim 9, which satisfies the following condition:

11. 11. The optical system according to claim 1, wherein the transmittance of the semi-transmissive reflective surface at at least one of the first, second and third wavelengths is higher as the angle of incidence to the semi-transmissive reflective surface is larger.

12. 12. The optical system according to claim 1, wherein a slow axis of the first phase plate and a slow axis of the second phase plate are inclined in opposite directions relative to the polarization direction of the first linearly polarized light.

13. 13. The optical system according to claim 1, further comprising a polarizing plate disposed between the polarization separation element and the viewer, the polarizing plate transmitting the second linearly polarized light.

14. When the eye relief of the optical system is E, 15mm≦E≦25mm 14. The optical system according to claim 1, wherein the following condition is satisfied:

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

16. 16. The image display device according to claim 15, wherein the first, second and third wavelengths are dominant wavelengths of blue light, green light and red light emitted from the display element, respectively.

17. unpolarized light is emitted from the display element; 17. The image display device according to claim 15, wherein the optical system has a polarizing plate disposed between the display element and the first phase plate, the polarizing plate transmitting the first linearly polarized light.

Images