IMAGE DISPLAY DEVICE

Abstract

Image light is introduced into a light guide through a collimating optical system, reflected by an incident side reflective surface (101) in a substrate (100), and repeatedly reflected between a first surface and a second surface (100a, 100b). The image light reaches a plurality of emission side reflective surfaces (102a to 102c) that constitute a beam splitter. The incident side reflective surface (101) and the emission side reflective surfaces (102a to 102c) are arranged in parallel. Therefore, with respect to the image light (L1, L2) derived from the image light emitted from the same position on a display surface of a display unit and incident on the substrate 100 at the same incident angle 1, the emission angle 2 of the image light (L1, L2) emitted from the substrate (100) becomes equal in both cases when the light is reflected one time by the incident side reflective surface (101) and one time by the emission side reflective surface (102a) and when the light is reflected two times by the incident side reflective surface (101) and two times by the emission side reflective surface (102a). As a result, it is possible to reduce the generation of a ghost image, which in turn can improve the visibility of a virtual image.

Claims

1. An image display device for displaying a virtual image, comprising: a) an image emission unit configured to generate parallel light fluxes that include two-dimensional image information and differ in an angle at each portion of an image and to make the light fluxes incident on a light guide; and b) the light guide, wherein the light guide includes: a transparent substrate having a first surface and a second surface facing each other in parallel; an incident side reflective surface formed inside the substrate so as to be inclined with respect to the first surface and the second surface, the incident side reflective surface being configured to guide image light incident into the substrate through the first surface or the second surface from the image emission unit to an inside of the substrate so as to be reflected by the first surface and the second surface; and one or a plurality of partially reflective surfaces formed in the substrate so as to be inclined with respect to the first surface and the second surface, the one or a plurality of partially reflective surfaces being configured to reflect a part of the image light guided to the inside of the substrate by the incident side reflective surface and transmitted through the inside of the substrate while being reflected by the first surface and the second surface to emit the part of the image light to an outside of the substrate, wherein the incident side reflective surface and the one or a plurality of partially reflective surfaces are each formed so as to be inclined at a same predetermined angle with respect to the first surface or the second surface and formed in parallel with each other.

2. The image display device as recited in claim 1, wherein a plurality of the partially reflective surfaces is provided, and the plurality of partially reflective surfaces is arranged so that the image light transmitted through one partially reflective surface reaches a subsequent partially reflective surface.

3. The image display device as recited in claim 1, wherein the image light is emitted by the partially reflective surface from a side opposite to a side on which the image emission unit is arranged across the light guide.

4. The image display device as recited in claim 2, wherein the image light is emitted by the partially reflective surface from a side opposite to a side on which the image emission unit is arranged across the light guide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0034] FIG. 1 is a schematic configuration diagram of an optical system in an image display device, which is an embodiment of the present invention.

[0035] FIG. 2 is a plan view of a light guide in the image display device of this embodiment when viewed in the y-axis direction.

[0036] FIG. 3 is a diagram illustrating an optical path for a particular image light in the image display device of this embodiment.

[0037] FIG. 4 is a schematic configuration diagram of an optical system in an example of a conventional image display device.

[0038] FIG. 5 is a diagram illustrating an optical path for a particular image light in a conventional image display device.

[0039] FIG. 6 is an explanatory view of a manufacturing process for forming an emission side reflective surface (partially reflective surface) of a light guide.

EMBODIMENTS FOR CARRYING OUT THE INVENTION

[0040] An image display device, which is an embodiment of the present invention, will be described by referring to the attached drawings.

[0041] FIG. 1 is a schematic configuration diagram of an optical system in the image display device of this embodiment, and FIG. 2 is a plan view of a light guide when viewed in the y-axis direction.

[0042] The image display device 1 of this embodiment is provided with a light source 11, a display element 12, a collimating optical system 13, and a light guide 10, similar to the conventional image display device 2 shown in FIG. 4. The light source 11, the display element 12, and the collimating optical system 13 correspond to the image emission unit in the present invention, and these can be the same as the light source 21, the display element 22, the collimating optical system 23 in the conventional image display device 2, but not limited thereto. For example, as the display element 12, instead of a transmissive liquid crystal display element, a reflective liquid crystal display element or an organic EL display, or a DMD (digital macro mirror device), a MEMS mirror, a projector, or the like, may be used.

[0043] When a reflective liquid crystal display element or a DMD is used as the display element 12, the light source 11 is used to illuminate the liquid crystal display element or the DMD from the front side. Further, in the case of using a self-emitting display element such as an organic EL display as the display element 12, it can be considered that the light source 11 is incorporated in the display element 12. Further, in cases where a MEMS mirror for scanning an angle is used as the display element 12, a laser light source for emitting a thin laser beam toward the MEMS mirror is used as the light source 11, the collimating optical system 13 is omitted, or it is sufficient to use the collimating optical system 13 to fine-tune the parallel light. Further, in cases where a projector is used as an image forming unit, the light source 11 can be regarded as a projector, and the display element 12 can be regarded as a projector screen.

[0044] The light guide 10 is provided with a flat cube-shaped substrate 100 having a first surface 100a and a second surface 100b, both parallel to the y-z plane and facing with each other, and a third surface 100c and a fourth surface 100d, both parallel to the x-y plane and facing with each other. The substrate 100 is a transparent body made of, polycarbonate resin or quartz glass. A single incident side reflective surface 101 and a plurality of (three in this embodiment) emission side reflective surfaces 102a to 102c are formed inside the substrate 100.

[0045] The incident side reflective surface 101 is perpendicular to the third surface 100c and the fourth surface 100d and inclined at an angle a with respect to the first surface 100a. Also, the plurality of emission side reflective surfaces 102a to 102c are similarly perpendicular to the third surface 100c and the fourth surface 100d, respectively, and inclined at an angle a with respect to the first surface 100a. The incident side reflective surface 101 is a reflective surface such as a mirror, and the emission side reflective surfaces 102a to 102c each are a partially reflective surface having a predetermined reflectance. As described above, since the incident side reflective surface 101 and the plurality of emission side reflective surfaces 102a to 102c are both inclined at an angle a with respect to the first surface 100a, the incident side reflective surface 101 and the plurality of emission side reflective surfaces 102a to 102c are parallel to each other.

[0046] In the image display device 1 of this embodiment, the image light emitted from the display screen of the display element 12 upon receiving the illumination light from the light source 11 is substantially collimated by the collimating optical system 13, passes through the first surface 100a, and is introduced into the substrate 100 of the light guide 10. The image light introduced from the collimating optical system 13 to the light guide 10 is a set of parallel light fluxes that contain information of different parts of two-dimensional images, each formed on the display surface of display element 12, and incident on the light guide 10 at different angles.

[0047] After being reflected by the incident side reflective surface 101, the image light is reflected one or more times by the first surface 100a and the second surface 100b, and is transmitted through the inside of the substrate 100, and reaches the emission side reflective surface 102a located closest to the incident side reflective surface 101. The emission side reflective surface 102a reflects a part of the arrived light flux and transmits the remainder. The transmitted light reaches the subsequent emission side reflective surface 102b, a part of its light flux is reflected and the rest is transmitted. The same applies to the emission side reflective surface 102c. Therefore, the light flux transmitted through the substrate 100 of the light guide 10 is reflected by the plurality of the emission side reflective surfaces 102a to 102c, respectively, and is transmitted through the second surface 100b of the substrate 100 to be emitted to the outside. As a result, the light flux introduced into the substrate 100 of the light guide 10 is enlarged and emitted from the substrate 100, and an image formed on the display surface of display element 12 is displayed as a virtual image in front of the eyes E of the observer.

[0048] In the image display device 1, since the incident side reflective surface 101 and the plurality of emission side reflective surfaces 102a to 102c of the light guide 10 are parallel to each other, a ghost image generated in a conventional device can be avoided. FIG. 3 is a diagram showing an optical path for a particular image light in the image display device 1 of this embodiment, which corresponds to FIG. 5 in a conventional device.

[0049] Since the image light emitted from a predetermined position on the display surface of the display element 12 in different directions is collimated by the collimating optical system 13, the collimated light is incident on the first surface 100a at a constant incident angle 1 as shown in FIGS. 3(a) and (b). FIG. 3 (a) is an optical path in the case of reflecting the image light only once at the incident side reflective surface 101 and reflecting the image light once at the emission side reflective surface 102a to emit the image light through the second surface 100b. FIG. 3(b) is a light path in the case of reflecting the light image twice at the incident side reflective surface 101 and also reflecting the image light twice at the emission side reflective surface 102a to emit the image light through the second surface 100b. Since the incident side reflective surface 101 and the emission side reflective surface 102a are parallel, the emission angle 2 of the image light to be emitted becomes equal.

[0050] That is, in this image display device 1, in cases where the number of reflections at the incident side reflective surface 101 and that at the emission side reflective surfaces 102a to 102c are the same, the image light incident on the light guide 10 in parallel is emitted in parallel from the light guide 10. The image information contained in the image light emitted from the light guide 10 is displayed at the same position as viewed by the observer. Therefore, the virtual image formed by such image light will not become a ghost image but become a normal virtual image. As described above, according to a conventional device, since the image light under the condition causing a ghost image does not form a ghost image, it is possible to improve the visibility of the virtual image displayed in front of the eyes of the observer.

[0051] When the incident side reflective surface 101 and the emission side reflective surfaces 102a to 102c are parallel, the thickness of the substrate 100 between the incident side reflective surface 101 and the emission side reflective surface 102a in the y-axis direction becomes even. Therefore, when manufacturing a light guide by the method described in Patent Document 2 or the like as described above, it is unnecessary to use a transparent plate having a non-uniform thickness (thickness gradually increases), and it is only necessary to use a transparent plate having a uniform thickness, which can suppress the manufacturing costs.

[0052] Note that in the image display device of the above-described embodiment, the number of the emission side reflective surface is three, but the number can be arbitrarily determined as long as long as it is 1 or more.

[0053] In the device of the above-described embodiment, the third surface 100c and the fourth surface 100d of the substrate 100 are parallel with each other, but the third surface 100c and the fourth surface 100d need not be parallel to the x-y plane. That is, the first surface 100a, the second surface 100b, the incident side reflective surface 101, and the emission side reflective surface 102a to 102c, the third surface 100c, and the fourth surface 100d need not be perpendicular, and the angles therebetween and the shapes of the surfaces of the third surface 100c and the fourth surface 100d can be arbitrarily determined.

[0054] It should be also noted that the above-mentioned embodiments are merely examples of the present invention, and it is needless to say that it is encompassed within the scope of the claims of the present application even if it is appropriately changed, modified or added within the scope of the present invention.

DESCRIPTION OF SYMBOLS

[0055] 1: Image display device [0056] 10: Light guide [0057] 100: Substrate [0058] 100a: First surface [0059] 100b: Second surface [0060] 100c: Third surface [0061] 100d: Fourth surface [0062] 101: Incident side reflective surface [0063] 102a102c: Emission side reflective surface [0064] 11: Light source [0065] 12: Display element [0066] 13: Collimating optical system