JP2017058400A - Image display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a downsized and easy-to-manufacture image display device that enables an image of high image quality to be superimposed on an external scene at a wide angle.SOLUTION: An image display device GH includes: a display element DP that displays an image IM0; and an observation optical system KK that projects the image IM0 to an observer's eye EY so as to superimpose on an external scene as a virtual image. The observation optical system KK includes: a light guide plate 1; an incidence optical system NK; and incidence/emission side holographic optical elements Hi/Ho. As to a waveguide path composed of the light guide plate, and the incidence/emission side holographic optical elements, expressions: t/2 L<tan(90°-θ1)<2 t/L, tan(90°-θc)<tan(90°-θ2)<4 t/L (t: a waveguide path thickness, L: a waveguide path propagation length of the holographic optical element, θ1: a diffraction reflection angle when vertical light enters into or emits from an end on a side opposite an intermediate image of the waveguide path propagation direction end of the holographic optical element, θ2: a diffraction reflection angle when vertical light enters into or emits from an end on a side of the intermediate image of the waveguide path propagation direction end of the holographic optical element, and θc: a critical angle of the waveguide path) are satisfied.SELECTED DRAWING: Figure 1

Description

  The present invention relates to an image display device. For example, a two-dimensional image of a liquid crystal display (LCD) is projected and displayed on a viewer's eye using a holographic optical element (HOE). The present invention relates to a glasses-type image display device.

  Patent Documents 1 to 5 propose eyeglass-type image display devices that display an image superimposed on an external scene (that is, an external field of view). Since these image display devices are used hands-free, it is important to display information in an optimal situation for the user. On the other hand, it is necessary to meet not only the display image but also the desire to see the outside scene well. There is. Therefore, by using a holographic optical element, see-through display by wavelength selective diffraction reflection is possible.

JP 2012-88715 A JP 2009-151655 A Japanese Patent Laying-Open No. 2015-72435 JP 2002-162598 A

  The holographic optical element used in the image display device described in Patent Document 1 performs incident and output of image light with respect to a waveguide in order to diffract and reflect a parallel light beam in a light guide plate. Therefore, it is necessary to arrange the optical system after a long waveguide. Since the focal length of the optical system is about the length of the waveguide, it is difficult to widen the angle of view.

  The holographic optical element used in the image display device described in Patent Document 2 is disposed obliquely between two prisms. Therefore, there exists a possibility that a bonding surface may be seen and it is difficult to obtain favorable see-through property.

  The image display device described in Patent Document 3 is also a type that forms an intermediate image. In order to project and display on the observer's eye with a curved reflecting mirror, a holographic optical element is bonded to a prism to improve see-through performance. Therefore, there is a problem similar to that of Patent Document 2.

  The image display device described in Patent Document 4 is a type that forms an intermediate image while diffracting and reflecting a light beam in a light guide plate. Since two holographic optical elements are bonded to both surfaces of the thin light guide plate, there is a problem of see-through degradation due to the two holographic optical elements being positioned in front of the eyes. In addition, since the same hologram surface is used for both transmission and reflection, the efficiency is poor and there is a concern that luminance unevenness and ghosting may occur.

  The present invention has been made in view of such circumstances, and an object of the present invention is to provide a see-through display in which an image with a good image quality is superimposed on a bright outside scene with a wide angle of view while being compact and easy to manufacture. The object is to provide a possible image display device.

In order to achieve the above object, an image display device according to a first aspect of the present invention includes a display element that displays an image and an observation that projects and displays the image as a virtual image on a viewer's eye so that the image overlaps an outside scene. An eyeglass-type image display device having an optical system,
The observation optical system includes a light guide plate, an incident optical system that causes the light of the image to enter the light guide plate, and a light having a specific wavelength among the light that has entered the light guide plate is diffracted and reflected to intermediate the image An incident-side holographic optical element that forms an image in the light guide plate, and an emission-side holographic optical element that diffracts and reflects light propagating in the light guide plate after the intermediate image is formed toward the observer's eye Have
The light guide plate is provided so as to be positioned in front of the observer's eye, the incident side holographic optical element and the emission side holographic optical element are provided on the surface of the light guide plate,
Light diffracted and reflected by the incident-side holographic optical element so that the light once incident on the incident-side holographic optical element does not enter again and the light once incident on the exit-side holographic optical element does not enter again. The light guide plate propagates to the exit-side holographic optical element by total reflection,
The incident-side holographic optical element and the exit-side holographic optical element both have a condensing power due to diffraction action,
The following conditional expressions (1) and (2) are satisfied for each of the incident-side holographic optical element and the emission-side holographic optical element and the waveguide constituted by the light guide plate.
t / 2L <tan (90 ° −θ1) <2t / L (1)
tan (90 ° −θc) <tan (90 ° −θ2) <4t / L (2)
However,
t: thickness of the waveguide,
L: the length of the holographic optical element in the waveguide propagation direction,
θ1: diffraction reflection angle when vertical light is incident on or exits from the end of the holographic optical element in the waveguide propagation direction opposite to the intermediate image,
θ2: diffraction reflection angle when vertical light enters or exits the end on the intermediate image side among the ends of the holographic optical element in the waveguide propagation direction,
θc: the critical angle of the waveguide,
It is.

  The image display device of a second invention is characterized in that, in the first invention, the total number of reflections in the light guide plate is 3 to 5 times.

  According to a third aspect of the present invention, there is provided the image display device according to the first or second aspect, wherein the incident optical system comprises a transmissive holographic optical element having a positive power and is provided on the surface of the light guide plate. It is characterized by.

  According to a fourth aspect of the present invention, there is provided the image display device according to any one of the first to third aspects, wherein the principal ray conversion angle in the incident-side holographic optical element and the principal ray conversion in the emission-side holographic optical element. The angle is substantially equal.

  The image display device according to a fifth aspect of the present invention is the image display device according to any one of the first to fourth aspects, wherein the shape of the light guide plate is a plane-parallel plate shape or a plate shape in which both surfaces have the same radius of curvature. It is characterized by being.

  According to a sixth aspect of the present invention, in the image display device according to any one of the first to fifth aspects, the intermediate image is formed at a position closer to the exit-side holographic optical element than to the incident-side holographic optical element. It is characterized by that.

  According to the present invention, it is possible to realize an image display device capable of see-through display in which a good image quality is superimposed on a bright outside scene with a wide angle of view while being compact and easy to manufacture.

FIG. 2 is a schematic cross-sectional view showing an optical configuration example of an image display device. The optical path figure which shows the axial light beam in the optical structural example of FIG. The enlarged view which shows the principal part of FIG. FIG. 3 is an optical path development view for explaining diffraction reflection conditions in the optical configuration example of FIG. 2. FIG. 3 is a schematic cross-sectional view showing a specific example of an incident optical system constituting the image display apparatus. 1 is a schematic cross-sectional view showing an embodiment of an optical path horizontal type eyeglass-type image display device. BRIEF DESCRIPTION OF THE DRAWINGS FIG.

  Hereinafter, an image display device and the like according to the present invention will be described with reference to the drawings. In addition, the same code | symbol is mutually attached | subjected to the part which is the same in each embodiment etc., and the corresponding part, and duplication description is abbreviate | omitted suitably.

  FIG. 1 shows an optical configuration example of an image display device GH according to an embodiment of the present invention. FIG. 2 shows an optical path of an axial light beam in the optical configuration example, and an enlarged main part thereof is shown in FIG. . The image display device GH includes a display element DP that displays the image IM0, and an observation optical system KK that projects and displays the image IM0 as a virtual image on the observer eye EY so that the image IM0 overlaps the outside scene. ing. Examples of the display element DP include a reflective or transmissive LCD, a digital micromirror device, and an organic EL display. In the case of the display element DP that needs to be illuminated, a light source (for example, an LED (light emitting diode)) for illuminating the display element DP is arranged, and the display element DP modulates the illumination light from the light source to display the image IM0. Further, an illumination optical system including a lens and a mirror is appropriately disposed between the light source and the display element DP.

  The observation optical system KK includes a light guide plate 1, an incident optical system NK that causes the light of the image IM 0 to be incident on the light guide plate 1, and diffracted and reflected light of a specific wavelength among the light that has entered the light guide plate 1. An incident-side holographic optical element Hi that forms an intermediate image IM1 of IM0 in the light guide plate 1, and an exit side that diffracts and reflects the light propagating through the light guide plate 1 after the formation of the intermediate image IM1 toward the observer's eye EY And a holographic optical element Ho.

  The incident optical system NK is provided on the surface S1 of the light guide plate 1 (a plane on the side of the observer's eye EY) and is composed of a transmissive holographic optical element having a condensing power (that is, positive power) due to diffraction action. (Power: An amount defined by the reciprocal of the focal length). Further, the incident-side holographic optical element Hi and the exit-side holographic optical element Ho are provided on the surface S2 (external scene side plane) of the light guide plate 1, and both of them are condensing power (that is, positive power) due to diffraction action. have. Here, in order to enable see-through display, a transmission-type volume phase holographic optical element is assumed as the incident optical system NK, and the incident-side holographic optical element Hi and the emission-side holographic optical element Ho are assumed. A reflective volume phase holographic optical element is assumed, and a transparent substrate is assumed as the light guide plate 1.

  The divergent light from the image IM0 displayed on the display element DP enters the light guide plate 1 as substantially parallel light by the condensing power of the incident optical system NK. The substantially parallel light is diffracted and reflected in the oblique direction by the incident side holographic optical element Hi and condensed by the light condensing power to form an intermediate image IM1 in the waveguide constituted by the light guide plate 1. The light after forming the intermediate image IM1 diverges and enters the exit-side holographic optical element Ho. And it becomes substantially parallel light by the condensing power of the exit-side holographic optical element Ho, exits from the pupil EP, and enters the observer's eye EY. Note that “substantially parallel light” means that the deviation from parallel is 0.5 degrees or less in terms of angle, and more specifically, when the pupil diameter is 3 mm, the distance of the virtual image is 500 mm or more.

  In the observation optical system KK, the light of the image IM0 is guided by the waveguide constituted by the light guide plate 1, and the wavelength selectivity of the incident side holographic optical element Hi and the emission side holographic optical element Ho is used. Therefore, high see-through performance can be obtained. In addition, the incident-side holographic optical element Hi and the emission-side holographic optical element Ho both have a condensing power due to diffraction action, thereby forming an intermediate image IM1 in the waveguide constituted by the light guide plate 1. Therefore, the focal length of the exit-side holographic optical element Ho is not affected by the length of the waveguide. Therefore, even if a long waveguide is secured in order to obtain high sheathability, a large angle of view can be obtained with a small configuration. In FIG. 1, a design example with an angle of view of 20 ° × 6 ° is shown as a cross section of the optical path on the 6 ° side.

  Light diffracted and reflected by the incident-side holographic optical element Hi so that the light once incident on the incident-side holographic optical element Hi does not enter again and the light once incident on the exit-side holographic optical element Ho does not enter again. The light guide plate 1 is configured to propagate to the exit-side holographic optical element Ho by total reflection. That is, the light hits the entrance-side holographic optical element Hi and the exit-side holographic optical element Ho only once. Thereby, an efficient see-through display can be realized. A holographic optical element with positive power requires the same number of reflections at all angles of view. If the holographic optical element acts twice, the portion of the light is displaced by the holographic optical element, or a part of the light is diffracted in another direction by diffraction of the holographic optical element. Accordingly, when light once incident on the incident-side holographic optical element Hi or the emission-side holographic optical element Ho is incident again, luminance unevenness and color unevenness are caused.

From the above viewpoint, since it is preferable that both the incident-side holographic optical element Hi and the exit-side holographic optical element Ho are subjected to the diffraction action once, in this image display device GH, the incident-side holographic optical element Hi is used. Each of the emission-side holographic optical elements Ho and the waveguide constituted by the light guide plate 1 satisfy the following conditional expressions (1) and (2).
t / 2L <tan (90 ° −θ1) <2t / L (1)
tan (90 ° −θc) <tan (90 ° −θ2) <4t / L (2)
However,
t: thickness of the waveguide,
L: the length of the holographic optical element in the waveguide propagation direction,
θ1: diffraction reflection angle when vertical light is incident on or exits from the end of the holographic optical element in the waveguide propagation direction opposite to the intermediate image,
θ2: diffraction reflection angle when vertical light enters or exits the end on the intermediate image side among the ends of the holographic optical element in the waveguide propagation direction,
θc: the critical angle of the waveguide,
It is.

  FIG. 3A shows an enlarged diffraction reflection at the incident side holographic optical element Hi, and FIG. 3B shows an enlarged diffraction reflection at the exit side holographic optical element Ho. The range defined by conditional expressions (1) and (2) regarding the diffraction reflection is shown in the optical path development view of FIG.

In FIG. 4, a solid line indicating 2t / L in the conditional expression (1) indicates a condition necessary for light to propagate through the waveguide. On the other hand, the broken line indicating t / 2L in the conditional expression (1) means that if the diffraction reflection angle θ1 is further increased, the amount of aberration generated due to diffraction increases, so that necessary optical performance cannot be obtained. ing. Also, as shown in FIG. 2, when total reflection is performed three times in the light guide plate 1, the conditional expression (2) defines that the intermediate image IM1 is formed by the fourth reflection corresponding to the thickness of four sheets. Yes. Therefore, a two-dot chain line indicating 4 t / L in the conditional expression (2) indicates a condition for condensing light up to a thickness of 4 t even at 90 ° -θ1. If the refractive index of the light guide plate is n, the critical angle θc of the waveguide is represented by θc = sin ⁻¹ (1 / n).

  In view of the above, it is possible to realize an image display device GH capable of see-through display in which an image with a good image quality and a wide angle of view is superimposed on a bright outside scene while being compact and easy to manufacture. For example, a bright image can be displayed with low power consumption, and an image can be displayed without deterioration in image quality due to unnecessary light, although a good lateral view can be secured.

  The total number of reflections in the light guide plate 1 is preferably 3 to 5, and more preferably 3 times. If the total number of reflections is small (for example, once or twice), the distance from the entrance-side holographic optical element Hi to the exit-side holographic optical element Ho becomes short. Then, there is a possibility that the display element DP or the like hits around the eyes. On the other hand, if the distance becomes too long, the image quality deteriorates due to the planarity of the waveguide, or the influence of image quality deterioration due to blurring of the total reflection condition due to dirt, water droplets, or the like increases.

  It is preferable that the incident optical system NK is composed of a transmissive holographic optical element having positive power and is provided on the surface of the light guide plate 1. When the incident optical system NK composed of a holographic optical element is used, it becomes possible to cause the incident optical system NK to generate chromatic aberration in a direction that cancels chromatic aberration caused by diffraction reflection at the incident-side holographic optical element Hi. An observation optical system KK in which chromatic aberration is corrected well can be realized. For this purpose, the intermediate image IM1 is preferably formed at a position closer to the exit-side holographic optical element Ho than the entrance-side holographic optical element Hi (that is, the pupil EP side).

  The incident optical system NK may be configured to bend the optical path with a prism having positive power instead of the holographic optical element having positive power. FIG. 5 shows a specific example of the incident optical system NK configured by the prism NP having positive power. By using the prism NP in this way, the incident optical system NK can be configured compactly together with the display element DP. The incident optical system NK may be configured by combining a transmissive holographic optical element having positive power and the prism NP, or may be configured by combining the positive lens and the prism NP. Good.

  The principal ray conversion angle θ at the incident side holographic optical element Hi (FIG. 3A) and the principal ray conversion angle θ ′ at the exit side holographic optical element Ho (FIG. 3B) are substantially equal. It is preferable that (θ≈θ ′), and it is more preferable that the principal ray conversion angles θ and θ ′ are equal (θ = θ ′). By setting the principal ray conversion angles θ and θ ′ in this way, chromatic aberration can be canceled by the incident-side holographic optical element Hi and the exit-side holographic optical element Ho. That is, chromatic aberration generated in the reflection direction due to diffraction reflection can be canceled out, so that a high-performance observation optical system KK without chromatic aberration can be realized. In FIG. 3, the optical axis AX of the observation optical system KK corresponds to the screen center chief ray with respect to the holographic optical elements Hi and Ho (the chief ray emitted from the screen center of the display element DP).

  The shape of the light guide plate 1 is preferably a parallel flat plate shape, or a plate shape having both surfaces having the same curvature radius, and more preferably the surface of the light guide plate 1 has a curvature radius of 500 mm or more. In order to obtain the see-through property so that the outside scene can be seen straight forward, it is preferable to employ the light guide plate 1 having a plane-parallel plate shape. However, if the curvature radii of both surfaces are 500 mm or more, there is no significant difference from the parallel flat plate, and it is possible to obtain substantially the same operation.

  The intermediate image IM1 is preferably formed at a position closer to the exit-side holographic optical element Ho than to the entrance-side holographic optical element Hi. This is because the position of the intermediate image IM1 is easy to ensure high optical performance closer to the exit-side holographic optical element Ho than to the entrance-side holographic optical element Hi.

  FIG. 6 shows a schematic cross-sectional structure of an optical path rotation type glasses-type image display device GH as viewed from above, and FIG. 7 shows an outline appearance of an optical path rotation type glasses-type image display device GH. The structure is shown as seen from diagonally above. These image display devices GH are configured to have the display element DP and the observation optical system KK shown in FIG. 1 and the like symmetrically with respect to the observer eye EY. Since the image display device GH is in the form of glasses, the temples 2 that are respectively located on the sides of the left and right observer eyes EY and the light guide plates that are located in front of the left and right observer eyes EY are provided. 1 (for example, a glass flat plate) and a bridge 3 for connecting the left and right light guide plates 1.

  As shown in FIGS. 6 and 7, the incident optical system NK, the incident side holographic optical element Hi, and the emission side holographic optical element Ho are held on the surfaces S1 and S2 (FIG. 1 and the like) of the light guide plate 1. Yes. The display element DP is housed in the housing 5 together with the illumination light source 4 (FIG. 6) and the like. In the image display device GH shown in FIG. 6, the display element DP is held by the temple 2 by fixing the housing 5 to the temple 2, and in the image display device GH shown in FIG. The display element DP is held on the light guide plate 1 by being fixed to the light guide plate 1.

  Since the observer can hold the image display device GH in front of the eyes with the temple 2, the observer can view the outside scene through the light guide plate 1 in the same manner as normal glasses while observing the image IM0 of the display element DP as a virtual image. it can. Although it is very difficult to construct an image display device in a small and limited structure called glasses, it is essential to achieve a reduction in size and thickness in a spectacle-type image display device worn on the head. Particularly, if there is a heavy object on the front side, the wearability is not good. Therefore, in this image display device GH, wearability is improved by using holographic optical elements Hi, Ho, NK that effectively use the diffraction action. Realized downsizing and thinning. Therefore, it is possible to realize an image display device GH capable of see-through display that is compact and has an image superimposed on a wide screen on a bright outside scene. In addition, if the above characteristic observation optical system KK is used, the above-mentioned effect can be achieved in image display devices such as HMD (head mounted display), HUD (headup display), etc., other than the spectacles of the horizontal optical path rotation / optical path rotation type. It is possible to get.

GH Image display device KK Observation optical system NK Incident optical system Hi Incident side holographic optical element Ho Exit side holographic optical element DP Display element IM0 Image IM1 Intermediate image AX Optical axis (principal ray emitted from the center of the screen)
S1, S2 Surface of light guide plate 1 Light guide plate 2 Temple 3 Bridge 4 Light source 5 Case EP Pupil EY Observer eye

Claims (6)

An eyeglass-type image display device comprising: a display element that displays an image; and an observation optical system that projects and displays the image as a virtual image on a viewer's eye so that the image overlaps an outside scene.
The observation optical system includes a light guide plate, an incident optical system that causes the light of the image to enter the light guide plate, and a light having a specific wavelength among the light that has entered the light guide plate is diffracted and reflected to intermediate the image An incident-side holographic optical element that forms an image in the light guide plate, and an emission-side holographic optical element that diffracts and reflects light propagating in the light guide plate after the intermediate image is formed toward the observer's eye Have
The light guide plate is provided so as to be positioned in front of the observer's eye, the incident side holographic optical element and the emission side holographic optical element are provided on the surface of the light guide plate,
Light diffracted and reflected by the incident-side holographic optical element so that the light once incident on the incident-side holographic optical element does not enter again and the light once incident on the exit-side holographic optical element does not enter again. The light guide plate propagates to the exit-side holographic optical element by total reflection,
The incident-side holographic optical element and the exit-side holographic optical element both have a condensing power due to diffraction action,
An image display characterized by satisfying the following conditional expressions (1) and (2) for each of the incident-side holographic optical element and the emission-side holographic optical element and the waveguide constituted by the light guide plate: apparatus;
t / 2L <tan (90 ° −θ1) <2t / L (1)
tan (90 ° −θc) <tan (90 ° −θ2) <4t / L (2)
However,
t: thickness of the waveguide,
L: the length of the holographic optical element in the waveguide propagation direction,
θ1: diffraction reflection angle when vertical light is incident on or exits from the end of the holographic optical element in the waveguide propagation direction opposite to the intermediate image,
θ2: diffraction reflection angle when vertical light enters or exits the end on the intermediate image side among the ends of the holographic optical element in the waveguide propagation direction,
θc: the critical angle of the waveguide,
It is.   The image display device according to claim 1, wherein the total number of reflections in the light guide plate is 3 to 5 times.   The image display apparatus according to claim 1, wherein the incident optical system includes a transmissive holographic optical element having positive power and is provided on a surface of the light guide plate.   4. The chief ray conversion angle in the incident-side holographic optical element is substantially equal to a chief ray conversion angle in the emission-side holographic optical element. 5. Image display device.   5. The image display device according to claim 1, wherein the light guide plate has a parallel flat plate shape or a plate shape in which both surfaces have the same radius of curvature.   The image display apparatus according to claim 1, wherein the intermediate image is formed at a position closer to the exit-side holographic optical element than to the incident-side holographic optical element.

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