Light guide body and image display device

Abstract

To provide a compact light guide body capable of making luminous flux reach the pupil of an observer with high efficiency.SOLUTION: Wherein the light guide body is a light guide body that reflects a light flux on surfaces facing each other and propagates the light flux, and includes a first element light guide body having a first surface on which the light flux is incident and a second surface facing the first surface, and a second element light guide body having a third surface from which the light flux is emitted and a fourth surface facing the third surface, the first element light guide body and the second element light guide body are coupled so that the first surface and the third surface are non-parallel to each other, a principal ray of a luminous flux propagating inside the second element light guide body propagates at an angle smaller than a critical angle, and a dielectric multilayer film having a pupil expanding function is provided on the third surface.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a light guide used in an image display device that displays an image as a magnified virtual image to an observer through an optical system. [Background technology]

[0002] Conventionally, image display devices equipped with a light guide plate have been known. FIG. 9 is a conceptual diagram of a light beam propagating inside a light guide plate 3 in a conventional image display device disclosed in, for example, Patent Document 1. The light beam from the image generating element enters the first deflection means 1, is deflected, and then propagates inside the light guide plate 3 by total reflection. A portion of the light beam that enters the second deflection means 2 is deflected and heads toward the viewer's pupil SP, while another portion is reflected, propagates inside the light guide plate 3 by total reflection, and enters the second deflection means 2. With this configuration, multiple light beams are emitted from the second deflection means 2, expanding the area in which the viewer can observe the light beams. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Publication No. 2017-173487 Summary of the Invention [Problem to be solved by the invention]

[0004] However, in conventional image display devices, the light beam emitted from the second deflection means 2 spreads according to the angular distribution of the light beam, resulting in the generation of a large amount of unnecessary light relative to the effective area, significantly reducing efficiency. When a dielectric multilayer film with angle selectivity is used for the out-coupler to improve efficiency, reducing the exit angle from the light guide plate 3 toward the viewer's pupil SP requires reducing the propagation angle inside the light guide plate 3. Reducing the propagation angle increases the number of reflections and lengthens the optical path length of the propagating light beam inside the light guide plate 3, resulting in a reduction in light guide efficiency.

[0005] An object of the present invention is to provide a small light guide that can guide a light beam to the observer's pupil with high efficiency. [Means for solving the problem]

[0006] One aspect of the present invention provides a light guide that reflects and propagates a light beam at opposing surfaces, comprising a first element light guide having a first surface onto which the light beam is incident and a second surface opposite the first surface, and a second element light guide having a third surface from which the light beam exits and a fourth surface opposite the third surface, wherein the first element light guide and the second element light guide are joined so that the first surface and the third surface are non-parallel, the chief ray of the light beam propagating inside the second element light guide propagates at an angle smaller than the critical angle, and the third surface is provided with a dielectric multilayer film having a pupil expansion function. [Effects of the Invention]

[0007] According to the present invention, it is possible to provide a small light guide that can guide a light beam to the observer's pupil with high efficiency. [Brief explanation of the drawings]

[0008] [Figure 1] FIG. 10 is a configuration diagram of an image display device of a comparative example. [Figure 2] FIG. 2 is a diagram illustrating the configuration of a light guide plate according to the first embodiment. [Figure 3] FIG. 10 is a diagram illustrating the configuration of a light guide plate according to a second embodiment. [Figure 4] FIG. 10 is an enlarged view of the vicinity of a joint between a first component light guide and a second component light guide in Example 2. [Figure 5] FIG. 10 is a diagram illustrating the configuration of a light guide plate according to a third embodiment. [Figure 6] FIG. 10 is a diagram illustrating the configuration of a light guide plate according to a fourth embodiment. [Figure 7] FIG. 10 is an enlarged view of the vicinity of a joint between a first component light guide and a second component light guide in Example 4. [Figure 8] FIG. 10 is a configuration diagram of an image display system equipped with an image display device according to a fifth embodiment. [Figure 9]FIG. 10 is a conceptual diagram of a light beam propagating inside a conventional light guide plate. DETAILED DESCRIPTION OF THE INVENTION

[0009] Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings. In the drawings, the same reference numerals are used to designate the same components, and redundant explanations will be omitted.

[0010] 1 is a structural diagram of an image display device 10 equipped with a light guide plate 13 of a comparative example. The image display device 10 includes a light source unit 11, a condenser lens 12, and a light guide plate 13. The light guide plate 13 includes a first dielectric multilayer film 13a and a second dielectric multilayer film 13b. Light beams L11a, L11b, and L11c represent light beams incident on the light guide plate 13 at angles θa, θb, and θc, respectively. Angles θag, θbg, and θcg represent angles of light beams L12a, L12b, and L12c within the light guide plate 13, respectively.

[0011] The light beam emitted from the light source unit 11 is image light from a liquid crystal panel or a MEMS (Micro Electro Mechanical Systems), etc. Alternatively, the image light may be from an OLED (Organic Light Emitting Diode) in which a light source is arranged for each pixel, or a small LED. The light source of the light source unit 11 is assumed to be a laser light source of 450 nm, 520 nm, or 635 nm.

[0012] The first dielectric multilayer film 13a has a characteristic of reflecting a light beam in a predetermined wavelength band within a predetermined angle range, while the second dielectric multilayer film 13b has a characteristic of reflecting the light beam in the predetermined wavelength band at an angle θ equal to or greater than a predetermined angle θ and partially transmitting the light beam at an angle less than the predetermined angle θ, and also has a characteristic of decreasing the angle θ along the x-direction.

[0013] A light beam from the light source unit 11 is condensed by the condenser lens 12 onto the light guide plate 13 and then enters the light guide plate 13. The light beam that entered the light guide plate 13 is guided along the x direction via the first dielectric multilayer film 13a and the second dielectric multilayer film 13b, and is split into multiple split light beams by the second dielectric multilayer film 13b, which then exit the light guide plate 13 and guide them to the pupil SP. The light beams L12a, L12b, and L12c that exit the light guide plate 13 almost overlap at the position of the pupil SP, thereby achieving high light utilization efficiency. Furthermore, the pupil expansion function of the second dielectric multilayer film 13b, which emits multiple split light beams, allows the observer to view the image without any loss even when the observer's pupil SP moves.

[0014] 1, if the angle of incidence on the observer's pupil SP is to be made shallower, the propagation angle within the light guide plate 13 must be made shallower, and more reflections are required to propagate the light to the observer's pupil SP. If the number of reflections is large, efficiency will decrease due to absorption losses, etc., even if a dielectric multilayer film is used. Therefore, in the present invention, adjacent element light guides are joined non-parallel to change the propagation angle within the light guide plate 13.

[0015] In the following examples, the specific configuration of the light guide plate will be described. Note that the configuration of the image display device other than the light guide plate is the same as that of the comparative example, and therefore the description thereof will be omitted. [Example]

[0016] FIG. 2 is a structural diagram of a light guide plate (light guide) 20 of this embodiment. The light guide plate 20 is configured by joining a first element light guide 21 and a second element light guide 22, and reflects and propagates a light beam at opposing surfaces. The first element light guide 21 has a first surface 21a and a second surface 21b opposite the first surface 21a. The second element light guide 21 has a third surface 22a and a fourth surface 22b opposite the third surface 22a. The first element light guide 21 and the second element light guide 22 are joined such that the angle θ between the first surface 21a and the third surface 22a is 150.2 degrees. The first element light guide 21 and the second element light guide 22 may be joined by adhesive or by bonding such as optical contact.

[0017] The first element light guide 21 and the second element light guide 22 are made of the same medium, and their refractive index is 1.5168. The light beam from the light source unit 11 enters the first element light guide 21 so that the propagation angle β is 60°. The light beam entering the first element light guide 21 satisfies the total reflection condition and is guided by total reflection between the first surface 21a and the second surface 21b (at an angle greater than or equal to the critical angle). The light beam propagates through the first element light guide 21 and enters the second element light guide 22 via the junction. The propagation angle of the light beam is deepened by the third surface 22a and the fourth surface 22b, which are inclined relative to the first surface 21a and the second surface 21b. Specifically, the propagation angle within the first element light guide 21 is 60°, and the propagation angle within the second element light guide 22 is 28.6°. This widens the propagation distance, reduces the effect of absorption, and allows the light beam to propagate efficiently.

[0018] A dielectric multilayer film equivalent to the second dielectric multilayer film 13b is provided on the third surface 22a, and a dielectric multilayer film equivalent to the first dielectric multilayer film 13a is provided on the fourth surface 22b. The light beam incident on the second element light guide 22 propagates between the third surface 22a and the fourth surface 22b at an angle smaller than the critical angle, and is split into multiple light beams by the dielectric multilayer film provided on the third surface 22a. The split light beams are emitted from the third surface 22a and directed to the pupil SP. The pupil expansion function of the dielectric multilayer film provided on the third surface 22a, which outputs multiple split light beams, makes it possible to view the image without any loss even when the observer's pupil SP moves.

[0019] It is preferable that the light guide plate 20 satisfy the following conditional expression (1).

[0020] |θ out |-|θ eye |>10 (1) where θ out is the angle of emergence [°] of the chief ray of the light beam emerging from the third surface 22a with respect to the surface normal of the third surface 22a. eyeis the angle of incidence [°] of the chief ray of the light beam emitted from the third surface 22a onto the viewer's pupil SP. Note that the chief ray is the ray that passes through the center of the light beam.

[0021] In this embodiment, the exit angle θ out is 46.5°, and the incident angle θ eye is 15°, which satisfies conditional expression (1).

[0022] The smaller the angle θ between the first surface 21a and the third surface 22a, the greater the change in the propagation angle, but if it is made too small, there is a risk of interference between the second element light guide 22 and the viewer. Therefore, it is preferable to set the angle θ [°] between the first surface 21a and the third surface 22a so as to satisfy the following conditional expression (2).

[0023] 130<θ<175 (2) Although the effect of the second element light guide 22 alone can only enlarge the pupil in one dimension, it is possible to enlarge the pupil in two dimensions by providing the first element light guide 21 with a pupil enlargement configuration in a direction perpendicular to the second element light guide 22. For example, a configuration such as a half mirror array may be incorporated. [Example]

[0024] 3 is a diagram showing the configuration of a light guide plate 20 of this embodiment. The basic configuration of the light guide plate 20 of this embodiment is the same as that of Example 1, except that a dielectric multilayer film with angle selectivity is provided at the joint between the first element light guide 21 and the second element light guide 22. In this embodiment, only the configuration different from Example 1 will be described, and a description of the configuration similar to Example 1 will be omitted.

[0025] When the first element light guide 21 and the second element light guide 22 are joined non-parallel, a light beam that can cause a large loss of light intensity occurs near the joint depending on the angle of the joint and the manner in which the incident light beam is incident. The occurrence of light intensity loss and the configuration of this embodiment will be explained below. Figure 4 is an enlarged view of the vicinity of the joint between the first element light guide 21 and the second element light guide 22.

[0026] FIG. 4(a) shows a case where the first component light guide 21 and the second component light guide 22 are joined together so as to satisfy the following formula (3).

[0027] α=90-{β-2×(180-θ)} (3) Here, α is the angle between the first surface 21a and a plane including the line segment AB connecting the intersection line between the first surface 21a and the third surface 22a and the intersection line between the second surface 21b and the fourth surface 22b, shown by the dotted line, when viewed from the y direction.

[0028] In Figure 4(a), the light beam L4a reflected by the second surface 21b near the joint of the first element light guide 21 passes through the inside of the second element light guide 22 without hitting the third surface 22a or the fourth surface 22b, and becomes unwanted light because it does not head toward the viewer's pupil SP. This results in a loss of light intensity. Furthermore, when the first element light guide 21 and the second element light guide 22 are joined so that the angle α exceeds the value of the right-hand side of Equation (1), the light beam L4a is incident on the third surface 22a, but is different from the light beam incident at a normal incident angle, and therefore becomes unwanted light.

[0029] 4(b) shows a case where the first element light guide 21 and the second element light guide 22 are joined so that the angle α is smaller than the value of the right-hand side of Equation (1). In this case, a part L4b of the light beam reflected by the first surface 21a near the joint of the first element light guide 21 and incident on the fourth surface 22b is incident on the first surface 21a again, but because it does not satisfy the total reflection condition, it escapes outside the first element light guide 21. This causes a loss of light quantity.

[0030] As described above, there is a possibility of light loss occurring regardless of the angle α. Therefore, in this embodiment, a dielectric multilayer film with angle selectivity is provided at the joint between the first element light guide 21 and the second element light guide 22.

[0031] In this embodiment, the first element light guide 21 and the second element light guide 22 are joined together so as to satisfy the following formula (4).

[0032] α≧90−{β−2×(180−θ)} (4) Figure 4(c) shows a case where the first element light guide 21 and the second element light guide 22 are joined so as to satisfy formula (4). In Figure 4(c), the angle α is the same as in Figure 4(a). In Figure 4(c), a dielectric multilayer film with angle selectivity is provided on a plane including the line segment BC (a plane extending from the first surface 21a to the fourth surface 22b).

[0033] The dielectric multilayer film disposed on the plane including the line segment BC has the property of reflecting light beams with large incident angles and transmitting light beams with small incident angles. Therefore, when the light beam L4a described as unwanted light in FIG. 4(a) is incident on the dielectric multilayer film, it is reflected by the dielectric multilayer film, reflected by the fourth surface 22b, and corrected to a normal propagation angle. When it again enters the dielectric multilayer film, it is transmitted through the dielectric multilayer film. This suppresses the generation of unwanted light. In this embodiment, the angle α is set to 92.9°, but the present invention is not limited to this. [Example]

[0034] 5 is a diagram illustrating the configuration of a light guide plate 20 of this embodiment. The basic configuration of the light guide plate 20 of this embodiment is the same as that of the first embodiment. In the first embodiment, the first element light guide 21 propagates the light beam by total reflection, but in this embodiment, the light beam is propagated by reflection by the dielectric multilayer films provided on the first surface 21a and the second surface 22b. In this embodiment, only the configuration different from the first embodiment will be described, and the description of the configuration similar to the first embodiment will be omitted.

[0035] In this embodiment, by making the propagation angle within the first element light guide 21 larger than the propagation angle within the second element light guide 22, the number of reflections of the light beam can be reduced, the effect of absorption can be reduced, and the light beam can be propagated efficiently.

[0036] In this embodiment, a dielectric multilayer film is provided on the first surface 21a and the second surface 21b. The first element light guide 21 and the second element light guide 22 are coupled so that the angle θ between the first surface 21a and the third surface 22a is 155°. The first element light guide 21 and the second element light guide 22 are made of the same medium, and their refractive index is 1.5168. The light beam from the light source unit 11 is incident on the first element light guide 21 so that the propagation angle β is 40°. The light beam incident on the first element light guide 21 is reflected and guided by the dielectric multilayer film provided on the first surface 21a and the second surface 21b. The light beam propagates through the first element light guide 21 and enters the second element light guide 22 via the joint, and the propagation angle is deepened by the third surface 22a and the fourth surface 22b that are inclined with respect to the first surface 21a and the second surface 21b. Specifically, the propagation angle in the first element light guide 21 is 40°, and the propagation angle in the second element light guide 22 is 21.4°. This widens the propagation distance, reduces the effect of absorption, and enables efficient propagation of the light beam.

[0037] A dielectric multilayer film corresponding to the third dielectric multilayer film 13b is provided on the third surface 22a, and a dielectric multilayer film corresponding to the first dielectric multilayer film 13a is provided on the fourth surface 22b. The light beam incident on the second element light guide 22 is split into a plurality of light beams at the third surface 22a, and then emerges from the second element light guide 22 and is guided to the pupil SP. In this embodiment, the emergence angle θ out is 33.6°, and the incident angle θ eye is 15°, which satisfies conditional expression (1).

[0038] As explained above, even when the first surface 21a and the second surface 21b of the first element light guide 21 are provided with a dielectric multilayer film, it is possible to improve the efficiency. [Example]

[0039] Fig. 6 is a structural diagram of the light guide plate 20 of this embodiment. Fig. 7 is an enlarged view of the vicinity of the joint between the first element light guide 21 and the second element light guide 22 of this embodiment. The basic structure of the light guide plate 20 of this embodiment is the same as that of Example 3, except that a dielectric multilayer film with angle selectivity is provided at the joint between the first element light guide 21 and the second element light guide 22. In this embodiment, only the structure different from Example 3 will be described, and a description of the structure similar to Example 3 will be omitted.

[0040] In this embodiment, the first element light guide 21 and the second element light guide 22 are joined to satisfy the above formula. In this embodiment, the angle α is set to 87.2°. In this embodiment, a dielectric multilayer film with angle selectivity is provided on a plane including the line segment BC. The dielectric multilayer film has the property of reflecting light beams with large incident angles and transmitting light beams with small incident angles. Therefore, when the light beam L4a described as unwanted light in FIG. 4(a) enters the dielectric multilayer film, it is reflected by the dielectric multilayer film, reflected by the fourth surface 22b, and corrected to a normal propagation angle. When it enters the dielectric multilayer film again, it is transmitted through the dielectric multilayer film. This suppresses the generation of unwanted light. [Example]

[0041] 8 is a diagram showing smart glasses as an example of an image display system equipped with an image display device 500 including the light guide plate 20 of each embodiment. The image display device 500 may be equipped in a head-mounted display (HMD) or the like.

[0042] The frame 700 holds the image display devices 500 in front of both eyes of the observer 1000. Light beams emitted from each image display device are guided to the eyes of the observer 1000. This allows the observer 1000 to view a display image 1100. By presenting display images with parallax to the left and right eyes, the observer 1000 can also view a stereoscopic image. Also connected to the frame 700 is a control unit 730 that controls the driving of the image generation elements in the image generation section and the light intensity of the light source unit 11. The control unit 730 may be arranged outside the frame 700 as shown in the figure and connected to the image generation section 100 so as to be able to communicate with it via wire or wirelessly, or it may be arranged inside the frame 700.

[0043] Also attached to the frame 700 is a first information acquisition unit 710 including a camera that acquires pupil information indicating the position and movement (viewpoint or line of sight) of the observer 1000's pupil. A control unit 730 corrects the position of the display image 1100 (the position at which the image is generated on the image generation element) based on the pupil information. Furthermore, a second information acquisition unit 720 including a camera that acquires external world (surroundings) information is also attached to the frame 700. The control unit 730 adjusts the brightness of the display image 1100 according to the brightness of the external world obtained from the external world information.

[0044] The disclosure of this embodiment includes the following configuration. (Configuration 1) A light guide that reflects and propagates a light beam on an opposing surface, a first light guide element having a first surface onto which the light beam is incident and a second surface opposite to the first surface; a second element light guide having a third surface from which the light beam emerges and a fourth surface opposite to the third surface; the first element light guide and the second element light guide are coupled together such that the first surface and the third surface are non-parallel to each other; a chief ray of the light beam propagating inside the second element light guide propagates at an angle smaller than a critical angle; A light guide body, characterized in that the third surface is provided with a dielectric multilayer film having a pupil enlarging function. (Configuration 2) 2. The light guide according to configuration 1, wherein a chief ray of the light beam propagating inside the first element light guide propagates at an angle equal to or greater than a critical angle. (Configuration 3) The angle of emergence [°] of the chief ray of the light beam emerging from the third surface with respect to the surface normal of the third surface is defined as θ out , the angle of incidence to the observer's pupil [°] is θ eye When |θ out |-|θ eye |>10 3. The light guide according to configuration 1 or 2, which satisfies the following conditional expression: (Configuration 4) When the angle [°] between the first surface and the third surface is θ, 130<θ<175 4. The light guide according to any one of configurations 1 to 3, wherein the following condition is satisfied: (Configuration 5) When the angle [°] formed between the first surface and a plane including an intersection line between the first surface and the third surface and an intersection line between the second surface and the fourth surface is α, and the incident angle [°] of the chief ray of the light beam onto the first surface inside the first element light guide is β, α≧90-{β-2×(180-θ)} 5. The light guide according to any one of configurations 1 to 4, wherein the following condition is satisfied: (Configuration 6) 6. The light guide according to configuration 5, further comprising an angle-selective dielectric multilayer film provided on a surface extending from the first surface to the fourth surface. (Configuration 7) A light guide according to any one of configurations 1 to 6; a light source that emits a light beam onto the light guide.

[0045] Although the preferred embodiments of the present invention have been described above, the present invention is not limited to these embodiments, and various modifications and changes are possible within the scope of the gist of the present invention. [Explanation of symbols]

[0046] 20 Light guide plate (light guide) 21 First element light guide 21a First Side 21b Second Side 22 Second element light guide 22a Third Face 22b Fourth Face

Claims

1. A light guide that reflects and propagates a light beam on an opposing surface, a first light guide element having a first surface onto which the light beam is incident and a second surface opposite to the first surface; a second element light guide having a third surface from which the light beam emerges and a fourth surface opposite to the third surface; the first element light guide and the second element light guide are coupled together such that the first surface and the third surface are non-parallel to each other; a chief ray of the light beam propagating inside the second element light guide propagates at an angle smaller than a critical angle; A light guide body, characterized in that the third surface is provided with a dielectric multilayer film having a pupil enlarging function.

2. 2. The light guide according to claim 1, wherein a chief ray of the light beam propagating inside the first element light guide propagates at an angle equal to or greater than a critical angle.

3. The angle of emergence [°] of the chief ray of the light beam emerging from the third surface with respect to the surface normal of the third surface is defined as θ ｏｕｔ , the angle of incidence to the observer's pupil [°] is θ ｅｙｅ When |θ ｏｕｔ |-|θ ｅｙｅ |>10 3. The light guide according to claim 1, wherein the following condition is satisfied:

4. When the angle [°] between the first surface and the third surface is θ, 130<θ<175 3. The light guide according to claim 1, wherein the following condition is satisfied:

5. When the angle [°] formed between the first surface and a plane including an intersection line between the first surface and the third surface and an intersection line between the second surface and the fourth surface is defined as α, and the incident angle [°] of the chief ray of the light beam onto the first surface inside the first element light guide is defined as β, α≧90−{β−2×(180−θ)} 3. The light guide according to claim 1, wherein the following condition is satisfied:

6. 6. The light guide according to claim 5, further comprising an angle-selective dielectric multilayer film provided on a surface extending from the first surface to the fourth surface.

7. The light guide according to claim 1 or 2; a light source that emits a light beam onto the light guide.

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