Eyepiece optical system and image display device

Abstract

To provide an eyepiece optical system that reduces the phase shift between phase plates to prevent a reduction in optical performance.SOLUTION: In an eyepiece optical system 100, in order from the side of a display element 101, a polarizing plate 102, a first phase plate 103, lenses 104, 105, a second phase plate 106 held in contact by the lens 105, and a PBS 107 that is a polarization separation element. A lens barrel 108 holds the polarizing plate 102, first phase plate 103, and lens 104. The first phase plate 103 has a shape that determines a phase. The contour of the lens 105 has a rotational symmetrical shape, and the second phase plate 106 partially has a non-rotational symmetrical shape that determines a phase on the basis of the rotational symmetrical shape.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to an eyepiece optical system and an image display device using the same. [Background technology]

[0002] As one type of optical system, a polarization optical system is known that achieves size and weight reduction by folding the optical path using polarized light, as described in Patent Document 1. The polarization optical system is configured with two phase plates and lenses, and is also used in HMDs (head-mounted displays), which require size and weight reduction in products. When two phase plates are installed in this way, it is necessary to reduce the phase shift between the phase plates from the perspective of optical performance. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2020-85956 Summary of the Invention [Problem to be solved by the invention]

[0004] In a polarization optical system, in order to make the size more compact, a phase plate disposed on the observer side may be attached to a lens, for example. However, when the outer shape of a lens is rotationally symmetric, it is difficult to determine the phase of the phase plate attached to the lens, which may worsen the phase shift between the phase plates and degrade the optical performance.

[0005] The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide an eyepiece optical system that reduces the phase shift between phase plates and prevents a deterioration in optical performance. [Means for solving the problem]

[0006] The eyepiece optical system of the present invention is an eyepiece optical system for guiding light from a display element to an observer's eye, and includes a first phase plate, a second phase plate, one or more lenses, and a polarization separation element that reflects first linearly polarized light and transmits second linearly polarized light having a polarization direction orthogonal to the polarization direction of the first linearly polarized light. a semi-transmissive reflective surface that transmits light from the first phase plate and reflects light from the second phase plate; The second phase plate is configured to be held in contact with a predetermined lens among the one or more lenses, and the first phase plate is for defining the arrangement of the slow axis of the first phase plate The outer shape of the predetermined lens is a rotationally symmetrical shape. Shape based on and the second phase plate is based on a rotationally symmetric shape, for defining the arrangement of the slow axis of the second phase plate It is characterized by having a partially rotationally asymmetric shape. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide an eyepiece optical system that reduces the phase shift between phase plates and prevents degradation of optical performance. [Brief explanation of the drawings]

[0008] [Figure 1] 1 is a diagram showing an image display device according to a first embodiment. [Figure 2] 1 is a cross-sectional view of an eyepiece optical system according to a first embodiment. [Figure 3] 3A and 3B are diagrams for explaining the inclination of the slow axis of the phase plate in the eyepiece optical system according to the first embodiment and the polarization direction transmitted by the polarizing plate and the polarization separation element. [Figure 4] 3A and 3B are diagrams for explaining a holding configuration for a polarizing plate and a first phase plate of the eyepiece optical system according to the first embodiment. [Figure 5] FIG. 2 is a diagram illustrating a holding configuration for a second phase plate and a PBS in the eyepiece optical system according to the first embodiment. [Figure 6] FIG. 10 is a cross-sectional view of an eyepiece optical system according to a second embodiment. [Figure 7] FIG. 10 is a diagram for explaining a holding configuration of the second phase plate and the PBS in the eyepiece optical system according to the second embodiment. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, preferred embodiments of the present invention will be described with reference to the accompanying drawings. [First embodiment] Fig. 1 is a diagram showing an image display device 10 according to a first embodiment. Fig. 2 is a cross-sectional view taken along line aa in Fig. 1. The image display device 10 includes left and right eyepiece optical systems 100, and is suitable for use in an HMD (head-mounted display) or HHD (handheld display) as shown in Fig. 1. The eyepiece optical system 100 guides light from a display element 101 to the eye 300 of a user who is an observer. The eyepiece optical system 100 enlarges and projects the original image displayed on the display element 101 as a virtual image and guides it to the user's eye 300. In this embodiment, the eyepiece optical system 100 is configured as a common component having a common configuration so that it can be used with either the left or right eye, and the following description will be given without making any distinction between the left and right eye.

[0010] The eyepiece optical system 100 is a polarization optical system that folds the optical path using polarized light, and the optical path of this system will be described below. As shown in Fig. 2, in the eyepiece optical system 100, arranged in this order from the display element 101 side are a polarizing plate 102, a first phase plate 103, lenses 104 and 105, a second phase plate 106, and a PBS (polarizing beam splitter) 107, which is a polarization separation element. A lens barrel 108 holds the polarizing plate 102, the first phase plate 103, and the lens 104.

[0011] The outer shapes of lenses 104 and 105 are circular, which is rotationally symmetric. Lenses 104 and 105 are cemented together, and a half mirror 109 is vapor-deposited on the surface of lens 104 facing lens 105. The surface on which half mirror 109 is vapor-deposited acts as a semi-transparent reflective surface.

[0012] The first phase plate 103 and the second phase plate 106 are wave plates with a phase difference of λ / 4. The polarizing plate 102 and the first phase plate 103 are bonded together. The second phase plate 106 and the PBS 107 are bonded together. In order to achieve a slimmer ocular optical system 100, the second phase plate 106 is held in contact with the user-side surface of the lens 105. In this embodiment, the lens 105 corresponds to the "predetermined lens" as defined in the present invention.

[0013] Here, the polarization direction of light transmitted through the polarizing plate 102 is inclined at 45° to the slow axis of the first phase plate 103. The polarization direction of light transmitted through the PBS 107 is inclined at 45° to the slow axis of the second phase plate 106. The polarization direction of light transmitted through the polarizing plate 102 and the polarization direction of light transmitted through the PBS 107 are perpendicular to each other. In this case, the light emitted from the display element 101 passes through the polarizing plate 102 to become linearly polarized light, and passes through the first phase plate 103 to become circularly polarized light. The circularly polarized light that passed through the first phase plate 103 passes through the half mirror 109 and then passes through the second phase plate 106 to become linearly polarized light (referred to as first linearly polarized light). The polarization direction of the first linearly polarized light is orthogonal to the polarization direction of the light that passes through the PBS 107, and the first linearly polarized light is reflected by the PBS 107 and passes through the second phase plate 106 to become circularly polarized light. The circularly polarized light that passed through the second phase plate 106 is reflected by the half mirror 109 and passes through the second phase plate 106 to become linearly polarized light (referred to as second linearly polarized light). The polarization direction of the second linearly polarized light is different from that of the first linearly polarized light and is consistent with the polarization direction of the light that passes through the PBS 107, and the second linearly polarized light passes through the PBS 107 to be guided to the user's eye 300. The user's eye 300 is substantially aligned with the exit pupil of the eyepiece optical system 100 . By using polarized light to fold the optical path in this way, it is possible to make the optical system thin and shorten the focal length, and to realize image observation with a wide angle of view.

[0014] As described above, ideally, as shown in FIG. 3, (A) it is desirable to tilt the slow axis of the first phase plate 103 by 45° relative to the polarization direction of light transmitted by the polarizing plate 102. Also, (B) it is desirable to tilt the slow axis of the second phase plate 106 by 45° relative to the polarization direction of light transmitted by the PBS 107. Also, (C) it is desirable to tilt the polarization direction of light transmitted by the PBS 107 by 90° relative to the polarization direction of light transmitted by the polarizing plate 102. Also, (D) it is desirable to tilt the slow axis of the second phase plate 106 by 90° relative to the slow axis of the first phase plate 103. However, in reality, a phase shift occurs, and this phase shift reduces the optical performance from the ideal state.

[0015] Regarding (A), if the polarizing plate 102 and the first phase plate 103 are each made into a flat plate shape and are bonded together with an adhesive layer, the phase shift can be stably reduced to the attachment precision of each component. Similarly, regarding (B), if the second phase plate 106 and the PBS 107 are each made into a flat plate shape and are bonded together with an adhesive layer, the phase shift can be stably reduced to the attachment precision of each component.

[0016] On the other hand, in the case of (C), since the polarizing plate 102 and the PBS 107 are spaced apart, it is difficult to stably reduce the phase shift, and it is necessary to clearly define the phases of each. Similarly, in the case of (D), since the first phase plate 103 and the second phase plate 106 are spaced apart, it is difficult to stably reduce the phase shift, and it is necessary to clearly define the phases of each. The phase shift in (C) has the effect of increasing the ratio of ghost light to normal light. Furthermore, the phase shift in (D) has the effect of color shift.

[0017] The following describes a configuration for reducing the phase shifts (C) and (D). 4, the structure of the lens barrel 108 for holding the polarizing plate 102 and the first phase plate 103 will be described. FIG. 4 is a cross-sectional view taken along the line bb in FIG. The polarizing plate 102 and the first phase plate 103 have the same flat plate shape and are bonded together with an adhesive layer to form an integrated component. This flat plate shape is based on a rotationally symmetric circular shape, with a partially asymmetric shape that determines the phase. Specifically, the polarizing plate 102 has a tab portion 102a on its side that protrudes laterally and is thickened in part. The first phase plate 103 has a tab portion 103a on its side that protrudes laterally and is thickened in part. The tab portions 102a and 103a define the inclination between the polarization direction of light transmitted by the polarizing plate 102 and the slow axis of the first phase plate 103. Lens barrel 108 corresponds to the rotationally symmetric shapes of polarizing plate 102 and first phase plate 103, and has holes 108b that do not block light from display element 101, and grooves 108a into which tab portions 102a and 103a are fitted. This makes it possible to define the phase of polarizing plate 102 and the phase of first phase plate 103 with respect to lens barrel 108. Polarizing plate 102 and first phase plate 103, which are integrated components, may be attached to lens barrel 108 with an adhesive layer, but the holding structure is not limited thereto.

[0018] Next, a holding configuration of the second phase plate 106 and the PBS 107, which are held in contact with the lens 105, will be described with reference to Fig. 5. Fig. 5 is a diagram of the eyepiece optical system 100 as seen from the user's eye 300 side. The second phase plate 106 and the PBS 107 have the same flat plate shape and are bonded together with an adhesive layer to form an integrated component. This flat plate shape is based on a rotationally symmetric circular shape, with a partially asymmetrical shape that determines the phase. Specifically, a D-cut portion 106a is formed by partially cutting out a side portion of the second phase plate 106, where the thickness is reduced. Similarly, a D-cut portion 107a is formed by partially cutting out a side portion of the PBS 107, where the thickness is reduced. The slow axis of the second phase plate 106 and the polarization direction of light transmitted by the PBS 107 are determined based on the D-cut portions 106a and 107a. Then, the D-cut portions 106a and 107a are aligned horizontally so that the second phase plate 106 is held in contact with the lens 105. This allows the phase of the second phase plate 106 and the phase of the PBS 107 to be defined relative to the lens barrel 108. The second phase plate 106 may be attached to the lens 105 with an adhesive layer, but the contact and holding structure is not limited thereto. After the second phase plate 106 integrated with the PBS 107 is attached to the lens 105, the phase shift of the second phase plate 106 and the PBS 107 relative to the lens barrel 108 can be detected and clarified based on the degree of inclination of the D-cut portions 106a of the second phase plate 106 and the D-cut portions 106a of the PBS 107.

[0019] With the above-described configuration, the phase shift between (C) and (D) can be clearly defined. Therefore, the angle between the polarization direction of light transmitted through the polarizing plate 102 and the polarization direction of light transmitted through the PBS 107 can be made substantially perpendicular (for example, within a range of 90±5°). Furthermore, the angle between the slow axis of the first phase plate 103 and the slow axis of the second phase plate 106 can be made substantially perpendicular (for example, within a range of 90±5°). By reducing the phase shift between (C) and (D) in this way, it is possible to provide an eyepiece optical system 100 that prevents degradation of optical performance.

[0020] In this embodiment, the display element 101 is an organic EL element that emits unpolarized light, but it may be a liquid crystal display that emits linearly polarized light. If the display element emits linearly polarized light, the polarizing plate 102 is not required, which leads to a thinner display and reduced costs, but it is preferable to adjust the phase of the display element 101 so as to reduce the phase shift between (A) and (C).

[0021] Furthermore, while lenses 104 and 105 are preferably made of resin to reduce weight, they may also be made of glass. Glass lenses have very low birefringence, enabling high-quality image observation. Furthermore, by making lens 105 a plano-convex aspherical lens and lens 104 a double-sided aspherical lens, aberration correction can be enhanced. Because the outer shapes of lenses 104 and 105 are rotationally symmetric, there is no need to determine the phase; however, there is a concern that the gate may degrade optical performance. Therefore, it is preferable to position the gate at the smaller of the horizontal and vertical angles of view determined by the eyepiece optical system 100 and the display element 101. Furthermore, lens 105 may be in contact with lens barrel 108. While UV adhesive or the like may be used to hold lens 104 or lens 105 by lens barrel 108, the holding structure is not limited thereto.

[0022] Furthermore, there is a concern that the D-cut portions 106a and 107a may cause vignetting of the optical effective diameter. By arranging the D-cut portions 106a and 107a at the smaller of the horizontal and vertical angles of view determined by the eyepiece optical system 100 and the display element 101, the effect of vignetting can be reduced or eliminated. Furthermore, since the rotationally symmetric shape of the second phase plate 106 is the same as the rotationally symmetric shape of the lens 105, the relative positions are easily determined. Furthermore, since there is no step between the second phase plate 106 and the lens 105, quality can be improved. Furthermore, since the eyepiece optical system 100 is a common component for both the left and right eyes, the D-cut portions 106a and 107a in the eyepiece optical system 100 for the left eye and the D-cut portions 106a and 107a in the eyepiece optical system 100 for the right eye are arranged in approximately the same positions.

[0023] Although the rotationally asymmetric shape partially possessed by the first phase plate 103 is the tab portion 103, it may be a D-cut portion. In this case, as described above, the D-cut portion is preferably disposed at the smaller of the horizontal and vertical angles of view determined by the eyepiece optical system 100 and the display element 101. The first phase plate 103 does not necessarily have to be based on a rotationally symmetric shape, as long as it has a shape that determines the phase. Furthermore, the polarizing plate 102 and the first phase plate 103, which are integrated components, only need to be located between the lens 104 and the display element 101 and not necessarily held by the lens barrel 108, but it is necessary to be able to detect the degree of inclination of the shape that determines the phase.

[0024] Furthermore, because the rotationally asymmetric shapes partially possessed by the second phase plate 106 and the PBS 107 are D-cut portions, the lens barrel 108 does not need to contact the second phase plate 106 and the PBS 107 to determine the phase. Therefore, the lens barrel 108 can be made smaller and lighter. However, the shape may be extended in the optical axis direction to block external light entering the interior from the outer diameter of the lens 104. Furthermore, by positioning the lens barrel 108 farther from the user's eye 300 in the optical axis direction than the PBS 107, the surface closest to the user's eye 300 can be the PBS 107, which is the final optical surface. This prevents the substantial eye relief from being shortened by components of the image display device 10, even if the eyepiece optical system 100 has a long eye relief designed with eyeglass users in mind. Furthermore, components of the image display device 10 may be positioned slightly closer to the user's eye 300 than the PBS 107 to prevent the eyepiece optical system 100 from striking the user's eye 300 first when dropped, while minimizing the impact on the eyeglass user.

[0025] Furthermore, although the lens 105 and the second phase plate 106 held in contact therewith have been described as having a circular rotationally symmetric shape, the present invention is not limited to this. In n-fold rotationally symmetric shapes, particularly when n≧3, it becomes difficult to determine the phase of the second phase plate attached to the lens 105, and in such cases the present invention is preferably applied.

[0026] [Second embodiment] Next, an eyepiece optical system 200 according to a second embodiment will be described with reference to Figures 6 and 7. Note that the same components as those in the first embodiment are given the same reference numerals, and the description thereof will be omitted. Fig. 6 is a cross-sectional view of the eyepiece optical system 200, corresponding to Fig. 2 in the first embodiment. As shown in Fig. 6, in the eyepiece optical system 200, a polarizing plate 102, a first phase plate 103, lenses 104 and 105, a second phase plate 206, and a PBS 207 are arranged in this order from the display element 101 side. A lens barrel 208 holds the polarizing plate 102, the first phase plate 103, the lens 104, the second phase plate 206, and the PBS 207. The polarization direction of light transmitted through the polarizer 102, the slow axis of the first phase plate 103, the slow axis of the second phase plate 206, and the tilt of the polarization direction of light transmitted through the PBS 207 are the same as those in the first embodiment.

[0027] The structure for holding the polarizing plate 102 and the first phase plate 103 by the lens barrel 208 is the same as in the first embodiment.

[0028] Next, a holding configuration of the second phase plate 206 and the PBS 207, which are held in contact with the lens 105, will be described with reference to Fig. 7. Fig. 7 is a diagram of the eyepiece optical system 200 as seen from the user's eye 300 side. The second phase plate 206 and the PBS 207 have the same flat plate shape and are bonded together with an adhesive layer to form an integrated component. This flat plate shape is based on a rotationally symmetric circular shape, with a partially asymmetric shape that determines the phase. Specifically, the second phase plate 206 has a tab portion 206a, which is a protrusion that protrudes laterally and is partially thickened, on its side. The PBS 207 has a tab portion 207a, which is a protrusion that protrudes laterally and is partially thickened, on its side. The tab portions 206a and 207a define the slow axis of the second phase plate 206 and the polarization direction of light transmitted by the PBS 207. The lens barrel 208 corresponds to the rotationally symmetric shapes of the second phase plate 206 and the PBS 207, and has a hole 208b that does not block light from the display element 101, and a groove 208a into which the tab portions 206a and 207a are fitted. This makes it possible to define the phase of the second phase plate 206 and the phase of the PBS 207 with respect to the lens barrel 208. The second phase plate 206 may be attached to the lens 105 with an adhesive layer, but the contact holding structure is not limited thereto. In the second embodiment, the lens barrel 208 has a shape that determines the phases of the polarizing plate 102, the first phase plate 103, the second phase plate 206, and the PBS 207 as a single component, so the phase shifts of (C) and (D) can be reduced more easily than in the first embodiment.

[0029] Although the present invention has been described above with reference to the embodiments, the above embodiments are merely illustrative of specific examples of how the present invention can be implemented, and the technical scope of the present invention should not be construed as being limited by these embodiments. In other words, the present invention can be implemented in various forms without departing from its technical concept or main features. [Explanation of symbols]

[0030] 10: image display device, 100, 200: eyepiece optical system, 101: display element, 102: polarizing plate, 103: first phase plate, 104, 105: lenses, 106, 206: second phase plate, 107, 207: PBS, 108, 208: lens barrel

Claims

1. An eyepiece optical system for guiding light from a display element to an observer's eye, a first phase plate; and a second phase plate; and one or more lenses; a polarization separation element that reflects a first linearly polarized light and transmits a second linearly polarized light having a polarization direction orthogonal to the polarization direction of the first linearly polarized light; a semi-transmissive reflective surface that transmits light from the first phase plate and reflects light from the second phase plate, the second phase plate is configured to be held in contact with a predetermined lens among the one or more lenses, the first phase plate has a shape for defining the arrangement of a slow axis of the first phase plate; the outer shape of the predetermined lens is a shape based on a rotationally symmetric shape, An eyepiece optical system, characterized in that the second phase plate has a rotationally symmetric shape as a base and partially has a non-rotationally symmetric shape for defining the arrangement of the slow axis of the second phase plate.

2. 2. The eyepiece optical system according to claim 1, wherein the second phase plate and the polarization separation element have the same shape and are bonded together.

3. 3. The eyepiece optical system according to claim 1, wherein the rotationally symmetric shape of the second phase plate is the same as the rotationally symmetric shape of the predetermined lens.

4. 4. The eyepiece optical system according to claim 1, wherein the rotationally asymmetric shape partially possessed by the second phase plate is a D-cut portion formed on the second phase plate.

5. 4. The eyepiece optical system according to claim 1, wherein the non-rotationally symmetric shape partially possessed by the second phase plate is a protrusion provided on a side of the second phase plate and protruding laterally.

6. 6. The eyepiece optical system according to claim 1, wherein the angle between the slow axis of the first phase plate and the slow axis of the second phase plate is 90±5°.

7. 7. The eyepiece optical system according to claim 1, further comprising a polarizing plate that transmits light from the display element.

8. 8. The eyepiece optical system according to claim 7, wherein the polarizing plate and the first phase plate have the same shape and are bonded together.

9. 9. The eyepiece optical system according to claim 7, wherein the angle between the direction of polarization transmitted by said polarizing plate and the direction of polarization transmitted by said polarization separation element is 90.+-.5 degrees.

10. 10. The eyepiece optical system according to claim 1, wherein the first phase plate is disposed on the display element side, and the second phase plate is disposed on the viewer side.

11. An image display device comprising the display element and the eyepiece optical system according to any one of claims 1 to 10.

12. the rotationally asymmetric shape partially possessed by the second phase plate is a D-cut portion formed on the second phase plate, 12. The image display device according to claim 11, wherein the D-cut portion is disposed at a smaller of a horizontal angle of view and a vertical angle of view determined by the eyepiece optical system and the display element.

13. 13. The image display device according to claim 11, wherein the display element emits unpolarized light.

14. 14. The image display device according to claim 11, wherein the gate of the lens is arranged at a smaller of a horizontal angle of view and a vertical angle of view determined by the eyepiece optical system and the display element.

15. 15. The image display device according to claim 11, wherein the eyepiece optical system for the left eye and the eyepiece optical system for the right eye are configured as a common component.

Images