Optical element and video display device using the same

Abstract

To suppress reduction in contrast of an aerial video by shielding light not forming the aerial video, in an optical element.SOLUTION: An optical element 1 includes a base 2 and a plurality of projection-like parts 3 integrally formed with the base 2. The projection-like part 3 has two reflection surfaces 31 and 32 perpendicular to the base 2 and approximately orthogonal to each other, inclined surfaces 33 and 34, and a top surface 35 forming a surface opposite to the base 2. A stereoscopic light shielding mask 5 for shielding a part of light reflected by the reflection surface 31 or the inclined surface 33 is arranged above a groove part 21 between the reflection surface 31 and the inclined surface 33. The stereoscopic light shielding mask 5 has a height in a direction perpendicular to the base 2, is configured so that a side surface 56 located above the reflection surface 31 is inclined so as to project to above the top surface 35, and shields the light reflected by only one of the two reflection surfaces 31 and 32.SELECTED DRAWING: Figure 7

Description

Technical Field

[0001] The present invention relates to an optical element that forms a real image of an object to be observed on one side in a space on the other side, and an image display device using the same.

Background Art

[0002] An optical element has been invented that disposes an object to be projected on one side of a planar body partitioning a certain space and forms a mirror image of the object to be projected at a position that is plane-symmetric in the space on the other side. As a device of this type, an optical element having a structure in which a plurality of two-sided corner reflectors each composed of two minute mirror surfaces (reflective surfaces) orthogonal to each other are assembled in a plane is known (see, for example, Patent Document 1).

[0003] Patent Document 1 discloses an optical element having a two-sided corner reflector array in which a plurality of two-sided corner reflectors are arranged in a lattice pattern on one plane. In this optical element, each mirror surface forming the two-sided corner reflector is arranged perpendicular to the element surface of the optical element. Therefore, the light emitted from an object to be observed disposed on one side of the element surface is reflected twice by the two-sided corner reflector and bent when passing through the optical element, and forms a real image in the space on the other side where there is no object to be observed. As a result, the object to be observed is imaged as an aerial image so as to exist at a symmetric position with respect to the element surface of the optical element.

[0004] In addition, the light incident on the groove portion sandwiched by the protrusions constituting the two-sided corner reflector becomes stray light, which is a factor in reducing the contrast of the aerial image. Therefore, a technique is known in which the groove portion sandwiched by the protrusions is filled with a transparent material added with light-absorbing particles, and the light-absorbing particles absorb the light that becomes stray light, thereby suppressing a decrease in the contrast of the aerial image (see, for example, Patent Document 2).

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

[0006] However, among the two mirror surfaces forming the two-sided corner reflector, the light that is reflected by one mirror surface and then exits from the upper surface of the element without being reflected by the other mirror surface does not contribute to forming the aerial image and becomes a factor in reducing the contrast of the aerial image. Also, such light cannot be absorbed by the light-absorbing material filled in the groove as described in Patent Document 1 above.

[0007] The present invention solves the above problems, and an object thereof is to provide an optical element that can block light that is reflected by one of the two mirror surfaces forming a two-sided corner reflector and exits from the upper surface of the element without being reflected by the other mirror surface, and can suppress a decrease in the contrast of an aerial image, and a video display device using the same. [Means for Solving the Problems]

[0008] To solve the above problems, the present invention provides an optical element that forms a real image of an object to be observed on one side in a space on the other side, including a base formed of a transparent material and forming a flat surface, and a plurality of protruding portions integrally formed with the base so as to protrude from the base. The protruding portion has two reflecting surfaces perpendicular to the base and substantially orthogonal to each other, an inclined surface inclined with respect to the reflecting surface, and a top surface forming a surface opposite to the base and parallel to the base. Above the groove portion between the reflecting surface and the inclined surface, a three-dimensional light-shielding mask for blocking a part of the light reflected by the reflecting surface is disposed. The three-dimensional light-shielding mask has a height in a direction perpendicular to the base, and a side surface located above the reflecting surface is inclined so as to protrude above the top surface, and is characterized by blocking light reflected only by one of the two reflecting surfaces.

[0009] In the above optical element, it is preferable that the side surface of the three-dimensional light-shielding mask located above the inclined surface is parallel to the side surface located above the reflecting surface.

[0010] In the above optical element, it is preferable that fine irregularities are formed on the side surface of the three-dimensional light-shielding mask.

[0011] In the above optical element, a groove filling portion made of a medium having a refractive index lower than that of the transparent material forming the protruding portion is disposed in the groove portion, and it is preferable that the three-dimensional light-shielding mask is placed on the groove filling portion.

[0012] In the above optical element, it is preferable that the upper surface of the groove filling portion is formed to be lower than the top surface.

[0013] The above optical element is preferably used in an image display device.

Advantages of the Invention

[0014] According to the optical element of the present invention, since the side surface of the three-dimensional light-shielding mask is inclined so as to protrude above the top surface of the protruding portion, the incident angle on the reflecting surface is large, and the light that is reflected only once on the reflecting surface is shielded by the side surface. Therefore, the light that does not form an aerial image is shielded, and it is possible to suppress a decrease in the contrast of the aerial image.

Brief Description of the Drawings

[0015]

Figure 1

Figure 2

Figure 3

Figure 4

Figure 5

Figure 6

Figure 7

Figure 8

Embodiments for Carrying Out the Invention

[0016] An optical element according to an embodiment of the present invention will be described with reference to the drawings. As shown in FIG. 1, the optical element 1 of the present embodiment has a two-sided corner reflector 30 formed of mirror surfaces (reflecting surfaces 31 and 32) that are perpendicular to a base 2 forming a plane and are substantially orthogonal to each other. A plurality of two-sided corner reflectors 30 are arranged in a lattice pattern on the base 2 to form a two-sided corner reflector array 30S.

[0017] When an object O to be observed is arranged on one surface side of the optical element 1, the optical element 1 forms a real image (real mirror image P) of the object O to be observed in the space on the other surface side of the element surface 1S of the optical element 1. That is, the optical element 1 forms a real mirror image P of the object O to be observed at a position that is plane-symmetric with respect to the element surface 1S as a symmetric plane. Here, the element surface 1S refers to a virtual plane that is perpendicular to the two reflecting surfaces 31 and 32 constituting the two-sided corner reflector 30. Note that compared to the overall size of the optical element 1 being on the order of cm or m, the two-sided corner reflector 30 is very fine on the order of μm, and in FIG. 1, the aggregate of the two-sided corner reflectors 30 is conceptually shown in a V shape.

[0018] The imaging mode by the two-sided corner reflector array 30S will be described with reference to FIGS. 2(a) and 2(b). In FIG. 2(a), the light emitted from the point light source o as the object to be projected is assumed to travel three-dimensionally from the back side of the paper surface to the front side of the paper surface. The light (solid line arrow) emitted from the point light source o is reflected by one reflecting surface 31 that constitutes the two-sided corner reflector 30 when passing through the optical element 1 (omitted in FIG. 2(a)), and then further reflected by the other reflecting surface 32, and then passes through the element surface 1S (see FIG. 2(b)). The light (dashed-dotted line arrow) thus emitted from the optical element 1 passes through and spreads at the position p that is symmetric to the point light source o with respect to the element surface 1S. As a result, the transmitted light of the optical element 1 converges at the position p that is symmetric to the point light source o with respect to the element surface 1S, and forms an actual mirror image P (see FIG. 1).

[0019] FIGS. 3 and 4 show the specific configuration of the optical element 1 of the present embodiment. The optical element 1 includes a main body portion 10 that constitutes the above two-sided corner reflector array 30S, and a three-dimensional light shielding mask 5 disposed on the light emitting surface side of the main body portion 10. In the following description, it is assumed that an object to be projected (not shown) that emits light exists on the side of the main body portion 10 opposite to the surface on which the three-dimensional light shielding mask 5 is provided, and the direction in which the light is led out is referred to as upward.

[0020] The main body portion 10 includes a base 2 and a plurality of protruding portions 3 formed so as to protrude from the base 2. The base 2 is formed of a transparent material and forms a flat surface. The plurality of protruding portions 3 are integrally formed with the base 2 by the same transparent material as the base 2. In addition, a groove filling portion 4 is provided in the groove portion 21 between adjacent protruding portions 3. The groove filling portion 4 is composed of a medium having a lower refractive index than the transparent material constituting the main body portion 10. In FIG. 4, the illustration of the groove filling portion 4 is omitted.

[0021] As shown in FIG. 4, the protruding portion 3 has three or more side surfaces that are angled with respect to the base 2. The protruding portion 3 of the present embodiment has a frustum shape and has four side surfaces consisting of two surfaces (reflective surfaces 31, 32) perpendicular to the base 2 and two surfaces (inclined surfaces 33, 34) inclined with respect to the base 2, and a top surface 35 that forms a plane parallel to the base 2. Of the above side surfaces, the two reflective surfaces 31, 32 are adjacent to each other, and the two inclined surfaces 33, 34 are adjacent to each other. Further, the reflective surfaces 31, 32 are arranged so as to be substantially orthogonal to each other. In the illustrated example, there are inclined surfaces 33, 34 in front of the paper surface, and reflective surfaces 31, 32 are located behind, hidden by the inclined surfaces 33, 34. The light incident on the protruding portion 3 from the base 2 is totally reflected twice on the inner wall surfaces of the reflective surfaces 31, 32 and exits from the top surface 35 of the protruding portion 3.

[0022] The top surface 35 is defined by the respective ridge lines with the reflective surfaces 31, 32 and the inclined surfaces 33, 34, and their lengths are substantially equal, and it is substantially square when viewed from above. The reflective surface 31 (32) is, in side view, a trapezoid having the boundary line with the base 2 as the lower base, the ridge line with the top surface 35 as the upper base, the ridge line with the inclined surfaces 33, 34 as the hypotenuse, and the ridge line with the adjacent reflective surface 32 (31) as the vertical side.

[0023] As shown in FIGS. 5(a) and 5(b), a plurality of protruding portions 3 having the above-described shape are arranged in a lattice pattern on the base 2 of the main body portion 10. For adjacent protruding portions 3, one reflective surface 31 faces the other inclined surface 33, and one reflective surface 32 faces the other inclined surface 34. In other words, a lattice-shaped groove portion 21 is formed between the opposing reflective surfaces 31, 32 and inclined surfaces 33, 34 of the plurality of protruding portions 3.

[0024] The groove portion 21 is filled with a groove filling portion 4 made of a medium having a refractive index lower than that of the transparent material forming the main body portion 10 (see FIGS. 3 and 5(b)). Therefore, the groove filling portion 4 is in contact with each of the reflective surfaces 31 (32) and inclined surfaces 33 (34) that form at least a two-sided corner reflector. Of the groove filling portion 4, the surface opposite to the base 2, that is, the upper surface 41 of the groove filling portion 4 is flat and is formed to be slightly lower than the top surface 35, for example, 50 μm lower.

[0025] In a top view of one pitch of the protruding portion 3 including the groove portion 21, the width W of one side is, for example, 100 to 1000 μm, and the pitch width W is set according to the protrusion distance of the real image video P (see FIG. 1). For example, when the protrusion distance is 10 cm, it is about 300 μm. Among these, the width L of the upper side of the reflecting surface 31 (two-sided corner reflector) is 200 μm (see FIG. 5(b)), and the width of the groove portion 21 is set to 100 μm. The plate thickness of the optical element 1 including the substrate 2 and the protruding portion 3 is generally 1 to 3 mm. The height H of the protruding portion 3 (depth of the groove portion 21) from the substrate 2 (bottom surface 22 of the groove portion 21) is set to 1 to 3 times the pitch width W.

[0026] The inclination angle θ1 of the inclined surface 33 with respect to the normal of the substrate 2 is at least 1° or more, and preferably 5° or more. By providing this inclination angle θ1, a necessary draft can be ensured, and it is possible to easily remove the two-sided corner reflector array 30S from the mold. However, if the inclination angle θ1 is too large, the top surface 35 that emits light becomes small. For example, 20° it is preferably within. The numerical values shown here are representative values shown as an example of this embodiment, and the present invention is not limited to these numerical values.

[0027] As the medium of the substrate 2 and the protruding portion 3 constituting the optical element 1, a transparent material having a light transmittance of 80% or more, a refractive index of 1.3 or more, and little alteration due to heat and humidity is used. Examples of such a transparent material include acrylic resin and glass. In the optical element 1 of this embodiment, it is particularly preferable to use a cycloolefin polymer (COP), which is a hydrocarbon-based polymer having low water absorption, being amorphous, and having an alicyclic structure. Examples of the cycloolefin polymer include the product name: ZEONOR (registered trademark) (grade: 1020R, light transmittance 92%, refractive index 1.53) manufactured by Nippon Zeon Co., Ltd. Further, in order to reduce the critical angle at the reflecting surface 31 (32) of the groove filling portion 4 and make total reflection likely to occur, the refractive index of the medium is desirably 1.4 or less. Examples of such a medium include a fluorine coating agent, and in addition, hollow silica particles, mesoporous silica particles, etc. may be appropriately applied.

[0028] The three-dimensional light-shielding mask 5 has a mask body 50 with a predetermined thickness and a through-hole 51 penetrating the mask body 50. As shown in FIGS. 6(a) to (e), the through-hole 51 is composed of a rectangular lower surface opening 52 and an upper surface opening 53, and four side surfaces 54 to 57 connecting them. In FIGS. 6(a) and (d), the front side of the paper surface is the upper surface (light-emitting side) of the three-dimensional light-shielding mask 5. The lower surface opening 52 and the upper surface opening 53 are both openings with substantially the same shape, and are formed so as to be displaced from each other so as to partially overlap in the thickness direction of the mask body 50, and are connected by the inclined side surfaces 54 to 57 with respect to the base 2 (see FIG. 6(d) in particular).

[0029] The lower surface opening 53 has substantially the same dimensions as the top surface 35 of the protruding portion 3, and since the upper surface 41 of the groove filling portion 4 around the top surface 35 is lower, the top surface 35 fits into the lower surface opening 53 (see also FIG. 7 described later). Thereby, the three-dimensional light-shielding mask 5 is arranged on the main body portion 10 without being displaced. Among the side surfaces 54 to 57 of the through-hole 51, there are side surfaces 54 and 55 located above the inclined surfaces 33 and 34 of the protruding portion 3, and side surfaces 56 and 57 located above the reflecting surfaces 31 and 32 of the protruding portion 3 (see also FIG. 4). Among these side surfaces 54 to 57, the side surfaces 56 and 57 located above the reflecting surfaces 31 and 32 are inclined so as to protrude above the top surface 35. The thickness of the three-dimensional light-shielding mask 5 is, for example, 100~300μm as follows. Also, the inclination angle θ2 of the side surfaces 54 to 57 with respect to the top surface 35 is, for example, 50~70° as follows.

[0030] The three-dimensional light-shielding mask 5 is manufactured by using a resin material containing a black pigment (such as ABS resin or PLA resin, etc.) through a 3D printer or resin molding so as to have the above structure. It is preferable that fine irregularities are formed on the side surfaces 54 to 57 of the through holes 51 of the three-dimensional light-shielding mask 5. When the three-dimensional light-shielding mask 5 is manufactured by a 3D printer, since the 3D printer forms a shaped object by laminating resins, fine irregularities are naturally formed on the three-dimensional side surfaces formed in the lamination direction. Also, in the case of resin molding, fine irregularities can be formed on the surface of the molded body by dispersing light-absorbing particles in the resin material. Note that the fine irregularities referred to here preferably have a size of 1~10μm .

[0031] The operation of the optical element 1 configured in this way will be described with reference to FIG. 7. Note that in FIG. 7, the hatching drawing is omitted in the side cross section of the base 2 and the protruding portion 3. The light incident on the base 2 is guided into the main body portion 10 and reaches the reflecting surface 31. Since the reflecting surface 31 is in contact with the groove filling portion 4 made of a low refractive index material, the light incident on the reflecting surface 31 at an incident angle exceeding a predetermined critical angle is totally reflected by the reflecting surface 31. Since the protruding portion 3 has a certain height, if the incident angle α1 on the reflecting surface 31 is within a predetermined range, the light L1 that has undergone the first total reflection at the reflecting surface 31 is emitted from the top surface 35 after undergoing the second total reflection at the other reflecting surface 32 (see FIG. 4). However, the light L2 whose incident angle α2 on the reflecting surface 31 is larger than the predetermined range is emitted from the top surface 35 without being reflected by the other reflecting surface 32 after being reflected by the reflecting surface 31. Such once-reflected light does not contribute to the formation of the aerial image, but in the conventional optical element, the once-reflected light L2 cannot be blocked, which has been a factor in reducing the contrast of the aerial image.

[0032] On the other hand, according to the optical element 1 in the present embodiment, the three-dimensional light-shielding mask 5 is provided on the light-emitting surface side of the main body portion 10. Among the side surfaces constituting the through holes 51 of the three-dimensional light-shielding mask 5, the side surface 56 located above the reflecting surface 31 is inclined so as to project above the top surface 35. Therefore, the incident angle α2 to the reflecting surface 31 is large, and the light L2 that has been reflected only once by the reflecting surface 31 is shielded by the side surface 56. Further, since the side surface 54 located above the inclined surface 33 is also inclined, the light L1 that has been reflected twice by the reflecting surface 31 and the reflecting surface 32 is emitted from the optical element 1 without being shielded by the three-dimensional light-shielding mask 5. Thus, according to the optical element 1, the light L1 that forms an aerial image is emitted from the optical element 1, and the light L2 that does not form an aerial image is shielded, so that it is possible to suppress a decrease in the contrast of the aerial image. Note that, similarly, on the other reflecting surface 32, the light that has been reflected only once by the reflecting surface 32 is shielded by the side surface 57 (not shown).

[0033] Further, since the surfaces of the side surfaces 54 to 57 of the three-dimensional light-shielding mask 5 have minute unevenness, the light absorption efficiency is high, the reflection of light at the side surfaces 54 to 57 is reduced, and a decrease in the contrast of the aerial image can be more effectively suppressed.

[0034] Also, the light L3 that enters the bottom surface 22 of the groove portion 21 between the protruding portions 3 instead of the protruding portions 3 from the base 2, and the light L4 that enters the groove filling portion 4 without total reflection at the reflecting surface 31 because the incident angle to the reflecting surface 31 is smaller than the critical angle do not form an aerial image and become stray light. However, according to the optical element 1, since the three-dimensional light-shielding mask 5 is disposed on the groove portion 21 between the protruding portions 3, these lights L3 and L4 can also be shielded.

[0035] Next, a video display device according to an embodiment of the present invention will be described with reference to FIG. 8. The video display device 1A specifically applies the above-described optical element 1 and includes a housing 12 having an opening 11 on its upper surface and a video display unit 13 provided on the inner surface of the housing 12. The optical element 1 is attached to the opening 11 of the housing 12. In the illustrated example, the video display unit 13 uses, for example, a liquid crystal display device and displays the letter "A" in an inverted posture with the top and bottom reversed. The light emitted from the video display unit 13 is bent and reflected by the optical element 1 to form an aerial image of the letter "A". When the observer places the viewing point Ep at a position diagonally above the video display device 1A and looks into the optical element 1, the aerial image of the letter "A" can be visually recognized as an aerial image.

[0036] The present invention is not limited to the above embodiment and can be variously modified as long as the three-dimensional light-shielding mask 5 has a predetermined height in a direction perpendicular to the base 2 and a part of the side surfaces 54 to 57 is inclined so as to protrude above the top surface 35 of the protruding portion 3. The thickness of the three-dimensional light-shielding mask 5 and the angle θ2 of the side surfaces 54 to 57 are appropriately determined according to the positional relationship between the video display unit 13, which is the object to be projected, and the optical element 1, the pitch interval, height, and the angles θ1 of the inclined surfaces 33 and 34 of the protruding portion 3, and are not limited to the above-described numerical values.

Explanation of Reference Numerals

[0037] 1 Optical element 10 Main body portion 1A Video display device 2 Base 21 Groove portion 3 Protruding portion 31, 32 Reflecting surface 33, 34 Inclined surface 35 Top surface 4 Groove filling portion 41 Upper surface 5 Three-dimensional light-shielding mask 54, 55, 56, 57 Side surface

Claims

1. An optical element that forms a real image of an object to be observed on one side on a space on the other side, comprising: a substrate formed of a transparent material and forming a plane, and a plurality of protruding portions integrally formed with the substrate so as to protrude from the substrate; each of the protruding portions has two reflecting surfaces perpendicular to the substrate and substantially orthogonal to each other, an inclined surface inclined with respect to the reflecting surface, and a top surface on the side opposite to the substrate and parallel to the substrate; above the groove portion between the reflecting surface and the inclined surface, a three-dimensional light-shielding mask for shielding a part of the light reflected by the reflecting surface is disposed; the three-dimensional light-shielding mask has a height in a direction perpendicular to the substrate, and a side surface located above the reflecting surface is inclined so as to protrude above the top surface, and shields light reflected only by one of the two reflecting surfaces. An optical element characterized by that.

2. The optical element according to claim 1, wherein a side surface of the three-dimensional light-shielding mask located above the inclined surface is parallel to a side surface located above the reflecting surface.

3. The optical element according to claim 1 or claim 2, wherein fine irregularities are formed on the side surface of the three-dimensional light-shielding mask.

4. In the groove portion, a groove filling portion made of a medium having a refractive index lower than that of the transparent material forming the protruding portion is disposed; The optical element according to any one of claims 1 to 3, wherein the three-dimensional light-shielding mask is placed on the groove filling portion.

5. The optical element according to claim 4, wherein an upper surface of the groove filling portion is formed to be lower than the top surface.

6. A video display device using the optical element according to any one of claims 1 to 5.

Images