Wide-view video display device

Abstract

This look-in-type wide-field video display device comprises an eyepiece optical system (OC), a polarizing plate, and a display element (D) positioned in the stated order from the user's-eye side. The OC includes a first lens (L1) and a second lens (L2) positioned in the stated order from the user's-eye side. The surface of the L1 on the user's-eye side is aspherical. The D-side surface of the L1 is planar or approximately planar, and a reflection polarizing plate and a 1 / 4-wavelength plate are laminated in the stated order thereon from the user's-eye side. The surface of the L2 on the user's-eye side is aspherical and is convex toward the eye of the user about the optical axis of the OC, or is approximately planar. The D-side surface of the L2 is convex toward the D, is aspherical, and is half-mirror coated. The relationships 0.8×P0≤P2≤1.2×P0 and |P1|<1 / 4×P2 hold true, where P0 and P1 are the respective powers of the OC and the L1, and P2 is the power of the L2 with respect to video light that is emitted from the D and travels along a normal optical path.

Description

Technical Field

[0001] The present invention relates to a peep-type wide-field video display device having a folded optical path.

Background Art

[0002] In recent years, as an example of a peep-type wide-field video display device, an HMD (Head Mounted Display) assumed for VR (Virtual Reality) applications (hereinafter referred to as "VR HMD") has begun to attract attention.

[0003] The VR HMD has a wider FOV (Field Of View) (also referred to as "viewing angle") than a normal HMD for which VR applications are not particularly assumed. For example, the FOV of a normal HMD is generally 45° or less, but the FOV of a VR HMD is often 90° or more. When comparing 90° with 45° for the FOV, the value of the FOV is twice, but the diameter of the virtual screen is 2.4 times and the area is 5.8 times. Therefore, with a VR HMD, a higher sense of presence can be given to the user. Note that the sense of presence increases with an increase in the maximum picture angle (viewing angle) of the video and saturates from around 80° or more, as shown in Non-Patent Document 1.

[0004] As an optical system applicable to such a VR HMD, for example, the optical systems described in Patent Documents 1 and 2 are known.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Patent Document 2

Non-Patent Documents

[0006]

Non-Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0007] In a peephole-type wide-field video display device such as an HMD for VR, it is desired that a user can visually recognize a wide field of view (FOV of 80° or more) and a high-resolution video, that it is small (thin) and lightweight, that it has excellent mass productivity, and that its manufacturing cost is low.

[0008] However, in reality, no device has yet been realized that can meet all of these demands. For example, when realizing a peephole-type wide-field video display device by applying the optical system described in Patent Document 1, the following problems remain.

[0009] In the optical system described in Patent Document 1, a reflective polarizer is disposed on the curved main surface of an optical lens. In order to dispose the reflective polarizer on a curved surface in this way, a special manufacturing method is required, which leads to an increase in cost and further problems with reliability.

[0010] It is difficult to dispose a retarder layer on a curved surface in terms of manufacturing method. In the optical system described in Patent Document 1, the retarder layer is disposed on the flat or substantially flat main surface of an optical lens on the image emitter (so-called display panel) side that emits an image. For this reason, the optical lens on the display panel side cannot correct spherical aberration by configuring the main surface on which the retarder layer is disposed as an aspherical surface with a large sag. The lens that has lost the means to effectively correct aberration cannot have a high power. This is because increasing the power increases aberration, which cannot be compensated for. As a result, the optical system described in Patent Document 1 has a limited magnification. And for this reason, in order to obtain a large FOV (80° or more), it is necessary to increase the size of the display panel, which leaves the following two problems. 1. As the size of the display panel increases, the entire device becomes larger and heavier. 2. As the size of the display panel increases, the light beam (harmful light beam) that exits the display surface and passes straight through without following the normal optical path (i.e., without being reflected even once) becomes thicker, especially within the optical lens adjacent to the display surface. In order to block such light rays and obtain a clear image, it is necessary to reduce the birefringence across the entire region through which the light beam of the optical lens passes. Since plastic lenses are prone to generating birefringence at the peripheral portion, it is impossible to use plastic lenses for the optical lens, and glass lenses must be used. However, glass lenses have a higher manufacturing cost compared to plastic lenses, especially for aspherical lenses. Moreover, glass lenses are heavier than plastic lenses. Also, even for glass lenses, if they are manufactured by, for example, molding, the birefringence becomes large at the peripheral portion of the lens, and it is necessary to devise the manufacturing method.

[0011] Such problems can similarly occur when applying the optical system described in Patent Document 2 to realize a peephole-type wide-field-of-view video display device. In view of the above actual situation, an object of the present invention is to provide a peephole-type wide-field-of-view video display device that can allow a user to visually recognize a wide field of view (FOV of 80° or more) and high-resolution video, and is small (thin), lightweight, has excellent mass productivity, and low manufacturing cost.

Means for Solving the Problems

[0012] One aspect of the present invention is a peephole-type wide-field-of-view video display device, comprising an eyepiece optical system, a circular polarizing plate, and a display element arranged in order from the user's eye side, the eyepiece optical system includes a first lens and a second lens arranged in order from the user's eye side, a first surface, which is the surface on the user's eye side of the first lens, is an aspherical surface, The second surface, which is the surface on the display element side in the first lens, is flat or substantially flat, and a reflective polarizing plate and a quarter-wave plate are laminated in this order from the side of the user's eye. The third surface, which is the surface on the user's eye side in the second lens, is aspherical, and the optical axis portion of the eye optical system on the third surface is convex or substantially flat on the user's eye side, and the outer peripheral portion on the third surface has a smaller curvature than the optical axis portion. However, the curvature is positive when the lens surface is convex toward the user's eye side and negative when it is concave. The fourth surface, which is the surface on the display element side in the second lens, is an aspherical surface convex toward the display element side, and a half mirror is coated thereon. When the power of the eye optical system is P0, the power of the first lens is P1, and the power of the second lens with respect to the video light emitted from the display element and traveling along the normal optical path is P2, 0.8×P0≦P2≦1.2×P0, |P1|<1 / 4×P2, and When the maximum size of the video displayed on the display surface of the display element is DD and the effective diameter of the second lens is ED, DD<0.8×ED, and the material of the second lens is a resin material. This is the gist of the invention.

Advantages of the Invention

[0013] According to the present invention, it is possible to allow a user to visually recognize a video with a wide viewing angle (80° or more in FOV) and high resolution, and to provide a peephole-type wide-view video display device that is small (thin), lightweight, excellent in mass productivity, and low in manufacturing cost.

Brief Description of the Drawings

[0014]

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Modes for Carrying Out the Invention

[0015] Hereinafter, embodiments of the present invention will be described with reference to the drawings. FIG. 1 is a diagram illustrating the configuration of a peephole-type wide-field video display device 1 according to an embodiment. FIG. 2 is a diagram illustrating a normal optical path.

[0016] The wide-field video display device 1 illustrated in FIG. 1 is a wide-field video display device that is peeped into and used by a user from the left side of FIG. 1. Note that the wide-field video display device 1 may be provided for each of the user's right eye and left eye, or may be provided only for one of the eyes. Further, the wide-field video display device 1 can be applied to, for example, a VR HMD.

[0017] The wide-field video display device 1 includes an eye optical system OC, a circular polarizing plate CP, and a display element D arranged in this order from the user's eye side. The eye optical system OC includes a first lens L1 and a second lens L2 arranged in this order from the user's eye side.

[0018] A first surface S1, which is the surface on the user's eye side of the first lens L1, is an aspherical surface. A second surface S2, which is the surface on the display element D side of the first lens L1, is a flat surface or an approximately flat surface. Further, a reflective polarizing plate (reflective polarizing film) RP and a quarter-wave plate (quarter-wave film) QWP are laminated in this order from the user's eye side on the second surface S2. The reflective polarizing plate RP is, for example, a wire grid polarizing plate or a cholesteric polarizing plate.

[0019] A third surface S3, which is the surface on the user's eye side of the second lens L2, is an aspherical surface, and the shape is convex on the user's eye side around the optical axis A of the eye optical system OC. Alternatively, the third surface S3 may be approximately flat around the optical axis A. A fourth surface S4, which is the surface on the display element D side of the second lens L2, is an aspherical surface and is convex on the display element D side. Further, a half mirror (semi-transmissive mirror) HM is coated on the fourth surface S4.

[0020] The circular polarizing plate CP is laminated on the display element D. Alternatively, the circular polarizing plate CP may be disposed in the space between the viewing optical system OC and the display element D (more specifically, between the half mirror HM and the display element D) without being laminated on the display element D. The circular polarizing plate CP is, for example, a quarter-wave plate superimposed on a linear polarizing plate.

[0021] The display element D includes a video display surface S5 on which an image is displayed, a cover glass D1 that protects the video display surface S5, and a display element substrate D2 that displays an image on the video display surface S5. The display element D is, for example, a display panel with a large viewing angle such as an OLED (Organic Light Emitting Diode) panel or a micro LED (Light Emitting Diode) panel.

[0022] In the wide-view video display device 1 having such a configuration, the video light emitted from the display element D follows the normal optical path (including the folded optical path) illustrated in FIG. 2 (and FIG. 1) below and enters the user's eye (pupil).

[0023] As illustrated in FIG. 2 (and FIG. 1), the video light emitted from the video display surface S5 of the display element D through the cover glass D1 first passes through the circular polarizing plate CP. As a result, the polarization state of the video light becomes a clockwise or counterclockwise circular polarization state.

[0024] The video light that has passed through the circular polarizing plate CP then partially passes through the half mirror HM, and the rest is reflected by the half mirror HM to become unnecessary light. The video light that has passed through the half mirror HM then passes through the second lens L2 in the order of the fourth surface S4 and the third surface S3.

[0025] The video light that has passed through the second lens L2 then passes through the quarter-wave plate QWP. As a result, the polarization state of the video light changes from a clockwise or counterclockwise circular polarization state to a linear polarization state. Here, the azimuth angle of the polarization plane is set to 0°.

[0026] The image light that has passed through the quarter-wave plate QWP is then reflected by the reflective polarizing plate RP. Here, it is assumed that the reflective polarizing plate RP reflects light in a linearly polarized state with an azimuth angle of 0° and transmits light in a linearly polarized state with an azimuth angle of 90°.

[0027] The image light reflected by the reflective polarizing plate RP then passes through the quarter-wave plate QWP again. As a result, the polarization state of the image light changes from a linearly polarized state with an azimuth angle of 0° to a clockwise or counterclockwise circularly polarized state.

[0028] The image light that has passed through the quarter-wave plate QWP then passes through the second lens L2 again in the order of the third surface S3 and the fourth surface S4. The image light that has passed through the fourth surface S4 of the second lens L2 is then partially reflected by the half mirror HM, and the rest passes through the half mirror HM and becomes unwanted light.

[0029] The image light reflected by the half mirror HM then passes through the second lens L2 again in the order of the fourth surface S4 and the third surface S3. The image light that has passed through the second lens L2 then passes through the quarter-wave plate QWP again. As a result, the polarization state of the image light changes from a clockwise or counterclockwise circularly polarized state to a linearly polarized state with an azimuth angle of 90°.

[0030] The image light that has passed through the quarter-wave plate QWP then passes through the reflective polarizing plate RP and passes through the first lens L1 in the order of the second surface S2 and the first surface S1. Then, the image light that has passed through the first lens L1 passes through the pupil plane S0 and enters the user's eye (pupil). Note that the position of the pupil plane S0 is also the position of the assumed user's eye (pupil).

[0031] Also, in the wide-view image display device 1, assuming the power of the eye-piece optical system OC is P0, the power of the first lens L1 is P1, and the power of the second lens L2 with respect to the image light emitted from the display element D and following the above-described normal optical path is P2, the relationship between P0 and P2 satisfies the following formula (1), and the relationship between P1 and P2 satisfies the following formula (2). 0.8×P0≦P2≦1.2×P0 Formula (1) |P1| < 1 / 4 × P2 Equation (2)

[0032] Also, around the optical axis A on the third surface S3 of the second lens L2, when the power P2 of the second lens L2 is 0.06 (unit: 1 / mm) or less, with the power of the third surface S3 being PW3 and the power due to reflection toward the user's eye side by the half mirror HM coated on the fourth surface S4 being PW4R, it is an approximate plane that satisfies the following equation (3). |PW3| > -1 / 10 × PW4R Equation (3)

[0033] Also, the power P0 (unit: 1 / mm) of the eye-piece optical system OC satisfies the following equation (4). 0.05 < P0 < 0.075 Equation (4)

[0034] Also, when the maximum size of the image displayed on the image display surface S5 of the display element D is DD and the effective diameter of the second lens L2 is ED, the relationship between DD and ED satisfies the following equation (5). DD < 0.8 × ED Equation (5)

[0035] Note that DD is also the diameter of the circle circumscribing the display area of the image when the image is displayed on the image display surface S5. Also, ED is also the diameter of the circle circumscribing the area through which the light beam of the image projected onto the user's eye (pupil) passes through the second lens L2.

[0036] Also, preferably, the material of the second lens L2 is a resin material whose refractive index Nd satisfies the following equation (6) and whose Abbe number Vd satisfies the following equation (7). Nd < 1.65 Equation (6) Vd > 50 Equation (7)

[0037] Also, assuming that the position of the pupil plane S0 is 12 mm from the first surface S1 of the first lens L1 toward the user's eye side, when the chief ray passing through the pupil plane S0 and having an inclination of θ with respect to the optical axis A is back-traced from the pupil plane S0 toward the first surface S1, the chief ray that first enters the third surface S3 of the second lens L2 is inclined in a direction away from the optical axis A in the traveling direction, and the chief ray that exits from the fourth surface S4 of the second lens L2 is inclined in a direction approaching the optical axis A in the traveling direction.

[0038] For example, when θ is 40°, letting the incident angle of the chief ray that first enters the third surface S3 with respect to the third surface S3 be θ3 and the exit angle of the chief ray that exits from the fourth surface S4 with respect to the fourth surface S4 be θ4, θ3 satisfies the following formula (8), and / or θ4 satisfies the following formula (9). |θ3| > 30° Formula (8) |θ4| > 30° Formula (9)

[0039] Hereinafter, the operation and effects of the wide-view video display device 1 having such a configuration will be described in detail. In the following description, unless otherwise specified, the description will be based on the premise of back-tracing the light ray from the user's eye side toward the display element D side.

[0040] In the wide-view video display device 1, as is clear from satisfying the above formulas (1) and (2), most of the power of the eyepiece optical system OC is mainly borne by the second lens L2. Focusing on the optical path related to the second lens L2 in the above-described normal optical path (including the folded optical path), the power P2 of the second lens L2 is approximately obtained by the following formula (10).

[0041] P2 ≒ PW4 + PW3_1 + PW3_2 + PW4R + PW3_3 Formula (10) Here, each of the power elements PW4, PW3_1, PW3_2, PW4R, and PW3_3 is as follows. Note that PW3_1, PW3_2, and PW3_3 have the same value PW3.

[0042] PW4 is the power due to refraction at the fourth surface S4 when the image light that has passed through the circular polarizing plate CP and transmitted through the half mirror HM is incident on the fourth surface S4. PW3_1 is Passing through the half mirror HM the power due to refraction at the third surface S3 when the image light incident on the fourth surface S4 However, exits from the third surface S3.

[0043] PW3_2 is the power due to bending at the third surface S3 when the image light reflected by the reflective polarizing plate RP and passing through the quarter-wave plate QWP is incident on the third surface S3. PW4R is the power due to reflection at the half mirror HM when the image light incident on the third surface S3 is reflected by the half mirror HM. This power can be calculated by the following formula (11-3) using the optical formula.

[0044] PW3_3 is the power due to refraction at the third surface S3 when the image light reflected by the half mirror HM and incident on the fourth surface S4 exits from the third surface S3. Note that PW4 can be calculated by the following formula (11-1) using the optical formula. PW4 = (1 - Nd) × C4 Formula (11-1) Here, Nd is the refractive index of the second lens L2, and C4 is the curvature of the fourth surface S4. PW3_1, PW3_2, and PW3_3 have the same value PW3. This power can be calculated by the following formula (11-2) using the optical formula. PW3 = (Nd - 1) × C3 Formula (11-2) Here, C3 is the curvature of the third surface S3. PW4R can be calculated by the following formula (11-3) using the optical formula. PW4R = -2 × Nd × C4 Formula (11-3) Since both the third surface S3 and the fourth surface S4 of the second lens L2 are convex, all the power elements on the right side of the above formula (10) have positive values. From this, the power that the second lens L2 needs to bear can be obtained by combining relatively small power elements. Further, as is clear from comparing the above formula (11-1) and the above formula (11-3), the fourth surface S4 has a particularly gentle curvature and can create the required size of PW4R. As a result, since the second lens L2 is composed of convex surfaces with gentle curvatures and can create a large power that satisfies the above formulas (1) and (4), the occurrence of aberrations can be suppressed to a low level.

[0045] Also, the second lens L2 can create the required power even if it is a lens made of a material with a relatively small refractive index Nd. Therefore, as the material of the second lens L2, a material with a large Abbe number Vd, that is, a small dispersion, can be selected. By selecting a material with a small dispersion, the occurrence of chromatic aberration of the second lens L2 can be suppressed to a low level.

[0046] Specifically, the material of the second lens L2 is preferably selected from among the materials included in the range that satisfies the above formulas (6) and (7). And by selecting an injection-moldable resin material included in this range, it becomes possible to manufacture the second lens L2 easily and at low cost.

[0047] Furthermore, since the third surface S3 of the second lens L2 and the first surface S1 of the first lens L1 are both aspherical and face the air, they have a large aberration correction effect, and these surfaces can correct the aberrations of the entire ocular optical system OC to a practically sufficient level.

[0048] Note that for the ocular Optical system When the power P0 of OC is 0.06 (unit: 1 / mm) or less, the power of the second lens L2 is for the ocular Optical system Since it is almost the same as the power P0, that is, the power required for the second lens L2 may also be 0.06 (unit: 1 / mm) or less. And this power is a magnitude that can be reasonably created only by PW4R calculated by the above formula (11-3). In this case, if the third surface S3, which is an aspherical surface, satisfies the above formula (3), the shape around the optical axis A may be an approximate plane close to a plane.

[0049] In addition, since the power P2 of the second lens L2 has a positive value, the above formula (2) can be transformed as follows into the following formula (12). -1 / 4×P2<P1<1 / 4×P2 Formula (12)

[0050] Furthermore, when the power P1 of the first lens L1 has a positive value, the above formula (12) can be expressed as the following formula (13), and when the power P1 of the first lens L1 has a negative value, the above formula (12) can be expressed as the following formula (14). P1<1 / 4×P2 Formula (13) -1 / 4×P2<P1 Formula (14)

[0051] In order to create a large FOV from the small display element D, when increasing the power P0 of the eyepiece optical system OC, since the focal length becomes shorter, in order to ensure sufficient eye relief for the eyepiece optical system OC and the distance from the display element D, as described below, it is important to satisfy the above formulas (13) and (14).

[0052] Since the FOV is large, the outer diameter (DL1) of the first lens L1 that can be estimated by the following formula (15) is large. DL1≒2×eye relief×tan(FOV / 2) Formula (15)

[0053] Therefore, when the first lens L1 has a positive power, when increasing the power P1 of the first lens L1, it is necessary to greatly increase the central thickness in order to ensure the edge thickness. The increase in the thickness of the first lens L1 has the effect of reducing the eye relief. In addition, from the above formula (4), the eyepiece Optical system The focal length of the OC is less than 20 mm. Therefore, if the power of the first lens L1 exceeds a certain value, it becomes difficult to ensure eye relief.

[0054] Also, as for the power balance between the first lens L1 and the second lens L2, if the power of the first lens L1 is increased and the power of the second lens L2 is decreased, the rear focal position of the ocular optical system OC moves toward the inside of the ocular optical system OC. For this reason, when the positive power of the first lens L1 with respect to the second lens L2 exceeds a certain limit, the rear focal position dives into the inside of the ocular optical system OC. Since it is necessary to project a virtual image far away, it is necessary to arrange the video display surface S5 of the display element D near the rear focal position of the ocular optical system OC. Therefore, in order to avoid physical interference, the rear focal position of the ocular optical system OC must be on the outer side (the right side in FIG. 1 or FIG. 2) of the ocular optical system OC with respect to the fourth surface S4 of the second lens L2.

[0055] On the other hand, when the first lens L1 has a negative power, the larger the negative power of the first lens L1, the larger the light beam diameter of the video light passing through the second lens L2. Moreover, since the second lens L2 needs to cancel the negative power of the first lens L1, it is necessary to increase the positive power. For this reason, when the negative power of the first lens L1 exceeds a certain limit, the peripheral video light that should pass through the second lens L2 and head toward the display element D undergoes total reflection at the fourth surface S4 of the second lens L2.

[0056] Also, in the first lens L1, the second surface S2 is a plane or an approximate plane, and the first surface S1 is an aspherical surface. This aspherical surface corrects the tangential field curvature generated in the negative direction by the second lens L2, and thus the curvature becomes strongly negative toward the outer periphery. For this reason, especially in a large FOV, the outer periphery of the first surface S1 protrudes toward the user's eye side (see, for example, FIG. 1). The larger the negative power of the first lens L1, the larger the protruding amount, and it becomes easier to cause interference with the user's face.

[0057] The first lens L1 has a first surface S1 that is aspherical and plays an important role in canceling out the aberrations generated by the second lens L2. However, as described above, if its power is not set appropriately, problems such as the inability to ensure sufficient eye relief and the distance between the second lens L2 and the display element D will occur. However, by satisfying the above equations (13) and (14), these problems can be avoided. In this way, the first lens L1 is thin and has little reduction in eye relief.

[0058] In the wide-view video display device 1, since the second surface S2 of the first lens L1 is a plane or an approximate plane, even if a reflective polarizing plate RP and a quarter-wave plate QWP are laminated on the surface, good adhesion can be maintained.

[0059] Let the diameter of the lamination surface of the second surface S2 on which the reflective polarizing plate RP and the quarter-wave plate QWP are laminated be DL, and the maximum value of the sag of the second surface S2 be SL. Then, the second surface S2, which is a plane, spherical surface, or aspherical surface, satisfies the following equation (16). 0.05 × DL > |SL| Equation (16)

[0060] For example, even when the second surface S2 is a spherical surface and the maximum value of its sag is near the limit defined by the above equation (16), the reflective polarizing plate (reflective polarizing film) RP and the quarter-wave plate (quarter-wave film) QWP can be laminated on the second surface S2 by expanding and contracting the circumferential dimension by about 0.6%. Such expansion and contraction is a reasonable value for a reflective polarizing plate (reflective polarizing film) RP and a quarter-wave plate (quarter-wave film) QWP based on a resin film.

[0061] In the wide-view video display device 1, the above equation (5) is satisfied. This contributes to suppressing the generation of ghosts, as will be described below. Figure 3 is a diagram illustrating straight light. The straight light is emitted from the display element D and does not follow the normal optical path as illustrated in FIG. 2 (and FIG. 1) (i.e., without being reflected even once) to the pupil Surface The light passing through S0 is stray light that can generate ghosts.

[0062] In the wide - field video display device 1, such straight light is blocked (light - shielded) by the reflective polarizing plate RP and the quarter - wave plate QWP laminated on the second surface S2 of the first lens L1. However, if there is retardation in the second lens L2, the light in the circularly polarized state that exits the display element D and passes through the circularly polarizing plate CP may have its polarization state disrupted while passing through the second lens L2, and there is a risk that the light - shielding action by the reflective polarizing plate RP and the quarter - wave plate QWP will not function sufficiently.

[0063] Therefore, not only is the second lens L2 made of a material with low birefringence, but since retardation is proportional to birefringence and optical path length, it is important to shorten the optical path length in the peripheral part of the lens where residual internal stress remains and birefringence is likely to occur due to the photoelastic effect. The second lens L2, in which both the third surface S3 and the fourth surface S4 have a convex shape, has a shape suitable for this.

[0064] Furthermore, as illustrated in FIG. 3, the straight light that exits the display element D and passes through the eyepiece optical system OC without being reflected even once and reaches the pupil Surface The straight light passing through S0 is convergent light traveling from the display element D toward the user's eye, including subordinate light rays. The size of the region of this light beam passing through the second lens L2 is smaller than the size of the image displayed on the video display surface S5.

[0065] Therefore, by the wide - field video display device 1 satisfying the above formula (5), the straight light that exits the video display surface S5 and passes through the pupil surface S0 passes through the second lens L2 while avoiding the peripheral part where birefringence becomes large. From this, the allowable amount of birefringence in the peripheral part of the second lens L2 can be greatly relaxed. Retardation is preferably 10 nm or less at the central part of the second lens L2, but there is no problem even if it is about several tens of nm at the peripheral part.

[0066] Since the third surface S3 of the second lens L2 is an aspherical surface, considering mass productivity, molding is preferred as the manufacturing method. In molding, thermal stress remains in the peripheral part of the lens, and the birefringence tends to increase significantly due to the photoelastic effect. However, if the above formula (5) is satisfied, it is possible to manufacture by molding using not only glass but also resin materials with relatively low birefringence. As the resin material used at this time, for example, resin materials such as Optimas (registered trademark) of Mitsubishi Gas Chemical Company, AZP (registered trademark) announced by Asahi Kasei Corporation in 2014, and APEL (registered trademark) of Mitsui Chemicals, Inc. can be used. Note that all of these are acrylic-based materials that satisfy the above formulas (6) and (7).

[0067] Also, in the wide-field video display device 1, the above formula (4) is satisfied. Here, the reason why the power P0 of the ocular optical system OC is set to less than 0.075 (unit: 1 / mm) is that although the second lens L2 can produce a strong power as a single lens, the aberration increases as the power increases. In particular, when it exceeds 0.075 (unit: 1 / mm), the aberration becomes significantly large.

[0068] Also, the reason why the power P0 of the ocular optical system OC is set to be greater than 0.05 (unit: 1 / mm) is that the smaller the power of the second lens L2, the better the aberration state. However, if the power of the ocular optical system OC is set to 0.05 (unit: 1 / mm) or less, the DD (the maximum size of the image displayed on the image display surface S5) on the left side in the above formula (5) becomes too large, making it difficult to satisfy the above formula (5).

[0069] Also, in the wide-field video display device 1, the relationship between the focal length and the FOV considering image distortion is as shown in the following formula (17). EFL = (DD / 2) / {(1 + Dis / 100) × tan(FOV / 2)} Formula (17)

[0070] Here, EFL is the focal length of the ocular optical system OC. Dis (unit: %) is the percent distortion at the video edge part of the ocular optical system OC defined by the following formula (18).

[0071] Dis = (actual maximum image height - ideal maximum image height) / (ideal maximum image height) × 100 Formula (18) FOV is the field of view angle of the ocular optical system OC. DD is the maximum size of the video displayed on the video display surface S5 as described above. Note that DD / 2 is the image height of the video.

[0072] The optical formula that holds for an optical system without image distortion is as follows in formula (19). Ideal image height = focal length × tan (field of view angle) Formula (19) The relationship between the actual image height and the ideal image height when there is image distortion is as follows in formula (20). Actual image height = (1 + Dis / 100) × ideal image height Formula (20)

[0073] From the above formulas (19) and (20), the following formula (21) can be derived. Actual image height = focal length × tan (field of view angle) × (1 + Dis / 100) Formula (21) By transforming the above formula (21), the above formula (17) can be derived. The relationship between the power P0 of the ocular optical system and the image distortion is expressed as follows in formula (22) using the above formula (17). P0 = 1 / EFL = {(1 + Dis / 100) × tan (FOV / 2)} / (DD / 2) Formula (22)

[0074] When comparing ocular optical systems with the same FOV, an ocular optical system with negative Dis can reduce the power of the ocular optical system compared to an ocular optical system without Dis. For example, if Dis is -30%, the power of the ocular optical system can be reduced by 30% compared to the case without Dis.

[0075] In the wide-field video display device 1, since the power of the ocular optical system OC and the power of the second lens L2 are substantially the same, it can be said that the power of the second lens L2 can be reduced by about 30%. As described above, the second lens L2 can produce a strong power. However, the higher the power, the greater the aberration. Therefore, in order to obtain excellent resolution performance, it is preferable that the power of the second lens L2 is small. In particular, when the power of the second lens L2 is 0.075 (unit: 1 / mm) or more, the aberration becomes significantly large.

[0076] That is, a negative Dis can realize an ocular optical system OC with higher resolution performance while maintaining the FOV. In other words, a negative Dis can realize an ocular optical system OC with a larger FOV while maintaining the resolution performance.

[0077] Also, in the wide-field video display device 1, as described above, assuming that the position of the pupil plane S0 is 12 mm from the first surface S1 of the first lens L1, when the chief ray having an inclination of θ with respect to the optical axis A passes through the pupil plane S0 and is back-traced from the pupil plane S0 toward the first surface S1, the chief ray that first enters the third surface S3 of the second lens L2 is inclined in a direction away from the optical axis A in the traveling direction, and the chief ray that exits the fourth surface S4 of the second lens L2 is inclined in a direction approaching the optical axis A in the traveling direction.

[0078] FIG. 4 is a diagram illustrating a chief ray having an inclination of θ with respect to the optical axis A passing through the pupil plane S0. As illustrated in FIG. 4, when the chief ray is back-traced from the pupil plane S0 toward the first lens L1, the chief ray CR4 that exits the fourth surface S4 of the second lens L2 is inclined in a direction approaching the optical axis A in the traveling direction. Moreover, since the fourth surface S4 is convex toward the display element D side, the exit angle θ4 of the chief ray CR4 from the fourth surface S4 has a large angle clockwise. For this reason, a large negative spherical aberration is generated in the chief ray at the fourth surface S4. Furthermore, the chief ray CR3 that first enters the third surface S3 of the second lens is inclined in a direction away from the optical axis A in the traveling direction, and since the third surface S3 is convex or approximately planar around the optical axis A toward the user's eye side, the incident angle θ3 of the chief ray CR3 to the third surface S3 is ReflectionIt has an angle in the clockwise direction. For this reason, negative spherical aberration occurs in the principal ray on the third surface S3. In particular, when the third surface S3 is convex toward the user's eye side, the incident angle θ3 becomes large, and a large negative spherical aberration occurs.

[0079] When negative spherical aberration occurs in the principal ray traced backward from the pupil plane S0 toward the first lens L1 by the second lens L2 in this way, for example, the height at which the principal ray emitted from the pupil plane S0 at an inclination angle of 40° (θ = 40°) crosses the image display surface S5 of the display element D can be reduced. That is, the effect of creating a negative Dis is generated. As described above, this is preferable in designing an ocular optical system OC with a large FOV while maintaining the resolution performance.

[0080] In this case, by satisfying the above formula (8) and / or (9), it is possible to create a sufficient negative Dis that enables a design with an FOV exceeding 80° while suppressing the power of the second lens L2 to less than 0.075 (unit: 1 / mm).

[0081] The reason for assuming that the position of the pupil plane S0 is 12 mm from the first surface S1 of the first lens L1 is that θ3 and θ4 change when the position of the pupil plane S0 changes. Therefore, in order to quantitatively define θ3 and θ4, it is necessary to assume the position of the pupil plane S0. Generally, glasses are adjusted so that the distance between the eye and the spectacle lens is 12 mm. This is to prevent the spectacle lens from being soiled by the splash of tears generated by blinking. Also, in the wide-view video display device 1, it is preferable to widen the distance between the ocular optical system OC and the eye to 12 mm or more.

[0082] As described above, in the wide-view video display device 1 according to one embodiment, the third surface S3 of the second lens L2 has a convex shape or an approximately flat surface, and the fourth surface S4 has a convex shape, and it has a substantially five-surface positive power element (see the above formula (10)) by a folded optical path created using polarization and reflection. Thereby, the second lens L2 can create a strong positive power with a gently curved convex surface and suppress the occurrence of aberrations. In addition, since a sufficiently strong positive power can be created using a material with a low refractive index, a low-dispersion material can be selected, and the occurrence of chromatic aberration can be suppressed.

[0083] Further, the first surface S1 of the first lens L1 and the third surface S3 of the second lens L2 are aspherical surfaces facing air. Since facing air means that the refractive index difference at the interface is large, the first surface S1 and the third surface S3 can strongly correct aberrations even with a relatively gentle aspherical shape. For this reason, it is possible to design an ocular optical system OC with excellent resolution, and the sag can be reduced to make the ocular optical system OC thin.

[0084] Also, since both the third surface S3 and the fourth surface S4 of the second lens L2 have a convex shape, a large incident angle θ3 and exit angle θ4 of the chief ray are obtained, and negative image distortion is created in reverse tracing. Thereby, while suppressing the power of the second lens L2, a large-FOV video can be projected from a display element D with a small video display surface size. Also, the video display surface size can be designed to be smaller than the outer diameter of the second lens L2. And thereby, stray light traveling straight inside the ocular optical system OC travels inside the second lens L2 while avoiding the lens peripheral portion where birefringence is likely to occur greatly. Therefore, the allowable amount of birefringence of the outer peripheral portion of the second lens L2 can be increased, and the second lens L2 can be manufactured by resin molding. According to molding, even an aspherical lens can be manufactured at low cost.

[0085] Also, by the power distribution of the first lens L1 and the second lens L2, it becomes possible to secure sufficient eye relief and design to avoid buffering between the ocular optical system OC and the display element D. As described above, in the wide-view video display device 1 according to one embodiment, it is possible to allow a user to visually recognize a wide-view (FOV of 80° or more) and high-resolution video, and effects such as being small (thin), lightweight, excellent in mass productivity, and low in manufacturing cost can be obtained.

[0086] Hereinafter, as a specific example of the wide-view video display device 1 according to one embodiment, a specific example in the case where the periphery of the optical axis A of the third surface S3 of the second lens L2 is convex toward the user's eye side is shown as Example 1, and a specific example in the case where the periphery of the optical axis A of the third surface S3 of the second lens L2 is an approximate plane is shown as Example 2. Note that the configuration tables shown in each example are numbered in the direction of tracing the optical path of the video light in reverse. Also, in each example, regarding the optical specifications and performance, those obtained by tracing the optical path in reverse in view of the law of reverse propagation of light are shown. Further, in each example, the material of the second lens L2 is Optimas (registered trademark) 7500 of Mitsubishi Gas Chemical Company, Inc.

[0087] <Example 1> In the wide-view video display device 1 according to Example 1, its configuration, normal optical path, straight optical path that can generate ghosting, and the principal ray having an inclination of θ (40°) with respect to the optical axis A passing through the pupil plane S0 are the same as those shown in FIGS. 1, 2, 3, and 4.

[0088] FIG. 5 is a diagram illustrating a configuration table regarding the optical system of the wide-view video display device 1 according to Example 1. FIG. 6 is a diagram illustrating the coefficients of the aspherical equation according to Example 1. The configuration table illustrated in FIG. 5 shows the type of the surface corresponding to each serial number, the radius of curvature around the optical axis A, the thickness around the optical axis A, the material (Nd, Vd), and the effective diameter. The sag of each aspherical surface can be obtained by the following aspherical equation (23). Sag=(Y^2 / R) / [1+SQRT{1-(1+k)×(Y / R)^2}]+a×Y^2+b×Y^4+c×Y^6+d×Y^8+e×Y^10 Equation (23)

[0089] Here, Y (unit: mm) is the distance from the optical axis A. R (unit: mm) is the radius of curvature around the optical axis A. Sag (unit: mm) is the coordinate in the direction of the optical axis A with the center of the optical axis of the surface at the origin in terms of Y. The coefficients k, a, b, c, d, and e for each aspherical surface are as shown in FIG. 6.

[0090] Also, in the wide-field video display device 1 according to the first embodiment, P0, P1, P2, PW3, and PW4R are as follows. P0: 0.0624 (unit: 1 / mm) P1: 0.0062 (unit: 1 / mm) P2: 0.0608 (unit: 1 / mm) PW3: 0.013161 (unit: 1 / mm) PW4R: 0.031616 (unit: 1 / mm)

[0091] Here, P2 = 0.97 × P0, |P1| = 0.10 × P2, which satisfies the above formulas (1) and (2), and also satisfies the above formula (4). Also, the material of the second lens L2 is Optimas (registered trademark) 7500 of Mitsubishi Gas Chemical Company, Inc., and also satisfies the above formulas (6) and (7).

[0092] Also, in the wide-field video display device 1 according to the first embodiment, FOV, DD, Dis, θ3, and θ4 are as follows. FOV: 80° DD: 22.8 mm Dis: -30% θ3: 42.9° θ4: 35.3°

[0093] Here, DD is 22.8 mm, and from the effective diameter of the second lens L2 in the configuration table shown in FIG. 5, the above formula (5) is also satisfied. Also, since θ3 is 42.9° and θ4 is 35.3°, both of the above formulas (8) and (9) are satisfied.

[0094] As an illustration of the performance of the ocular optical system OC according to Example 1, a graph showing the relationship between the focus shift and the absolute value of the OTF (Optical Transfer Function) is illustrated in FIG. 7, and a graph showing the relationship between the field curvature and the field angle and a graph showing the relationship between the percent distortion and the field angle are illustrated in FIG. 8. Note that the graph illustrated in FIG. 7 is for the case where the spatial frequency is 40 cycles / mm, the wavelength is 525 μm, the pupil diameter is 4 mm, and the pupil position is 15 mm. The graph illustrated in FIG. 8 is for the case where the pupil position is 15 mm. Both graphs show that the resolution performance of the ocular optical system OC according to Example 1 is good.

[0095] <Example 2> FIG. 9 is a diagram illustrating the configuration of the wide-field video display device 1 according to Example 2. FIG. 10 is a diagram illustrating the normal optical path according to Example 2. FIG. 11 is a diagram illustrating a straight optical path that can generate ghosting according to Example 2. FIG. 12 is a diagram illustrating a chief ray passing through the pupil plane S0 and having an inclination of θ with respect to the optical axis A in Example 2.

[0096] In the wide-field video display device 1 according to Example 2, as illustrated in FIG. 9, the periphery around the optical axis A of the third surface S3 of the second lens L2 is an approximate plane. Also, the normal optical path is an optical path as illustrated in FIG. 10 (and FIG. 9), and the straight optical path that can generate ghosting is an optical path as illustrated in FIG. 11. Also, the chief ray passing through the pupil plane S0 and having an inclination of θ (40°) with respect to the optical axis A is as illustrated in FIG. 12.

[0097] FIG. 13 is a diagram illustrating a configuration table regarding the optical system of the wide-field video display device 1 according to Example 2. FIG. 14 is a diagram illustrating the coefficients of the aspherical equation according to Example 2. In the configuration table illustrated in FIG. 13, the sag of each aspherical surface can be obtained by the aspherical equation of the above formula (23). Here, the coefficients k, a, b, c, d, and e for each aspherical surface are as shown in FIG. 14.

[0098] In addition, in the wide-view video display device 1 according to the second embodiment, P0, P1, P2, PW3, and PW4R are as follows. P0: 0.0542 (unit: 1 / mm) P1: 0.0081 (unit: 1 / mm) P2: 0.0510 (unit: 1 / mm) PW3: 0.001976 (unit: 1 / mm) PW4R: 0.044283 (unit: 1 / mm)

[0099] Here, P2 = 0.94 × P0, |P1| = 0.16 × P2, which satisfies the above formulas (1) and (2), and also satisfies the above formula (4). In addition, here, P2 is 0.06 (unit: 1 / mm) or less, and from the values of PW3 and PW4R, the area around the optical axis A on the third surface S3 is an approximate plane that satisfies the above formula (3). Also, the material of the second lens L2 is Optimas (registered trademark) 7500 of Mitsubishi Gas Chemical Company, Inc., as in the first embodiment, and also satisfies the above formulas (6) and (7).

[0100] Also, in the wide-view video display device 1 according to the second embodiment, FOV, DD, Dis, θ3, and θ4 are as follows. 2 FOV: 80° DD: 12.0 mm Dis: -24% θ3: 38.4° θ4: 28.3° θ4: 28.3°

[0101] Here, DD is 12.0 mm, and from the effective diameter of the second lens L2 in the configuration table illustrated in FIG. 13, the above formula (5) is also satisfied. In addition, since θ3 is 38.4° and θ4 is 28.3°, although the above formula (9) is not satisfied, the above formula (8) is satisfied.

[0102] As an illustration of the performance of the ocular optical system OC according to Example 2, a graph showing the relationship between the focus shift and the absolute value of the OTF is exemplified in FIG. 15, and a graph showing the relationship between the field curvature and the field angle and a graph showing the relationship between the percent distortion and the field angle are exemplified in FIG. 16. Note that the graph exemplified in FIG. 15 is for the case where the spatial frequency is 40 cycles / mm, the wavelength is 525 μm, the pupil diameter is 4 mm, and the pupil position is 15 mm. The graphs exemplified in FIG. 16 are for the case where the pupil position is 15 mm. All of the graphs show that the resolution performance of the ocular optical system OC according to Example 2 is good.

[0103] As described above, the present invention is not limited to the above-described embodiments as they are, and at the implementation stage, the components can be modified and embodied without departing from the gist thereof. Also, various inventions can be formed by appropriately combining a plurality of components disclosed in the above-described embodiments. For example, some of the components shown in the embodiments may be deleted. Further, components from different embodiments may be appropriately combined.

Explanation of Reference Numerals

[0104] 1 Wide-field video display device OC Ocular optical system CP Circular polarizing plate A Optical axis D Display element D1 Cover glass D2 Display element substrate L1 First lens L2 Second lens RP Reflective polarizing plate QWP 1 / 4 wavelength plate HM Half mirror S0 Pupil plane S1 First surface S2 Second surface S3 Third surface S4 Fourth surface S5 Video display surface CR3, CR4 Chief ray

Claims

1. An in-line wide-field video display device, comprising: an eye-piece optical system, a circular polarizing plate, and a display element, which are arranged in this order from the side of the user's eye; the eye-piece optical system includes a first lens and a second lens, which are arranged in this order from the side of the user's eye; a first surface, which is the surface on the side of the user's eye of the first lens, is an aspherical surface; a second surface, which is the surface on the side of the display element of the first lens, is a flat surface or substantially flat surface, and a reflective polarizing plate and a quarter-wave plate are laminated in this order from the side of the user's eye; a third surface, which is the surface on the side of the user's eye of the second lens, is an aspherical surface, and a portion of the optical axis of the eye-piece optical system on the third surface is convex or substantially flat on the side of the user's eye, and a curvature of an outer peripheral portion on the third surface is smaller than that of the optical axis portion; however, the curvature is defined as positive when the lens surface is convex on the side of the user's eye and negative when the lens surface is concave; a fourth surface, which is the surface on the side of the display element of the second lens, is an aspherical surface convex on the side of the display element, and a half mirror is coated thereon; assuming that a power of the eye-piece optical system is P0, a power of the first lens is P1, and a power of the second lens with respect to video light emitted from the display element and traveling along a normal optical path is P2, 0.8×P0 ≤ P2 ≤ 1.2×P0, |P1| < 1 / 4×P2, and assuming that a maximum size of a video displayed on a display surface of the display element is DD and an effective diameter of the second lens is ED, DD < 0.8×ED, and a material of the second lens is a resin material, characterized in that it is a wide-field video display device.

2. The circular polarizing plate is laminated on the display element or is arranged in a space between the eye-piece optical system and the display element. The wide-field video display device according to claim 1, characterized in that.

3. A refractive index Nd and an Abbe number Vd of the second lens satisfy Nd < 1.65, Vd > 50, and The wide-field video display device according to claim 1 or 2, characterized in that.

4. The power P0 (unit: 1 / mm) of the eye-piece optical system satisfies 0.05 < P0 < 0.075, and The wide-field video display device according to claim 1 or 2, characterized in that.

5. Assume that the position of the pupil plane is 12 mm from the first surface toward the user's eye side. When the chief ray passing through the pupil plane and having an inclination of θ with respect to the optical axis is back-traced from the pupil plane toward the first surface, the chief ray that first enters the third surface is inclined in a direction away from the optical axis in the traveling direction, and the chief ray that exits the fourth surface is inclined in a direction approaching the optical axis in the traveling direction. The wide-view video display device according to claim 1 or 2, characterized by the above.

6. When θ is 40°, assuming that the incident angle of the chief ray that first enters the third surface with respect to the third surface is θ3, and the exit angle of the chief ray that exits the fourth surface with respect to the fourth surface is θ4, |θ3| > 30°, and / or |θ4| > 30°, it is as follows. The wide-view video display device according to claim 5, characterized by the above.

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