WO2015098209A1

WO2015098209A1 - Light condensing optical element and light condensing device provided with same

Info

Publication number: WO2015098209A1
Application number: PCT/JP2014/074828
Authority: WO
Inventors: 賢司鎌田; 敏行三原; 金高　健二
Original assignee: 独立行政法人産業技術総合研究所
Priority date: 2013-12-25
Filing date: 2014-09-19
Publication date: 2015-07-02
Also published as: JPWO2015098209A1; JP6385959B2

Abstract

[Problem] To provide: a novel light condensing optical element which is able to have a good balance between high end-face light condensing efficiency and size reduction; and a light condensing device which uses this light condensing optical element and does not require a solar tracking mechanism. [Solution] A light condensing optical element which is provided with a laminate wherein a plurality of light guide bodies are laminated on the main surfaces of one another. Each light guide body has a continuous series of prism structures on at least one main surface thereof. The external light incident on the main surfaces of the light guide bodies is refracted or reflected by the prism structures, travels within the light guide bodies, and is emitted from at least one end face of each light guide body.

Description

Condensing optical element and condensing device provided with the same

The present invention relates to a condensing optical element and a condensing device including the condensing optical element.

Conventionally, solar cells, solar water heaters, solar lighting, etc. that use solar energy effectively are known. For example, in sunlight illumination, a plurality of lenses that collect sunlight, an optical fiber that guides sunlight collected by the lens, an optical sensor that detects the position of the sun, and a detection result of the optical sensor. A device equipped with a sun tracking mechanism for tracking the movement of sunlight by moving the lens is used. In such sunlight illumination, since the light collected by the lens is guided indoors through an optical fiber or the like, it is used as indoor illumination that is difficult for sunlight to reach (see, for example, Non-Patent Document 1). .

However, for example, in sunlight illumination as disclosed in Non-Patent Document 1, since the dependency on the incident angle of sunlight is high, the solar tracking that tracks the movement of the sun with the light incident surface directed toward the sun. A mechanism is needed. There is a problem that the solar light collecting device provided with the sun tracking mechanism is large. Therefore, such a solar light collecting device can be installed on the roof or roof of a building, but it is very difficult to install it on the wall surface of a building, for example, and there is a great restriction on the installation location. There is.

Therefore, various techniques for increasing the light collection efficiency without using the solar tracking mechanism have been studied. As such a technique, for example, a method is known in which light incident at various incident angles from the diurnal sun is reflected inside the condensing optical element to guide the light to a desired position.

For example, Patent Document 1 discloses a transmissive solar diffusion plate installed toward the sky, and sunlight transmitted through the solar diffusion plate installed on the lower surface of the solar diffusion plate, as a light receiving surface. A multi total reflection surface type condensing prism that totally reflects by a plurality of inclined optical surfaces formed on the opposite surface and guides it in a desired direction, and condenses sunlight emitted from the multi total reflection surface type condensing prism There is disclosed a solar condensing device comprising: a condensing condensing lens to be coupled; and an optical fiber for guiding sunlight condensed by the condensing condensing lens.

Further, for example, in Patent Document 2, two light guides each having a prism-shaped portion intermittently formed on the bottom surface are disposed on the top surface, and the top and bottom surfaces of the light guide are flat. A device that guides light toward an end face side by totally reflecting light on the surface is disclosed.

Further, for example, Patent Document 3 includes a light guide, a first layer provided on one surface side of the light guide, and a second layer provided on the other surface side. The first layer and the second layer are made of a material having a light refractive index smaller than that of the light guide, and a concavo-convex structure is formed on the surface of the second layer opposite to the light guide side. A light collecting structure is disclosed. In the light condensing structure of Patent Document 3, light can be guided to the end face side by total reflection of a planar portion in the light guide.

Further, for example, Patent Document 4 discloses a solar cell module including a light guide unit that collects light from the outside and a solar cell element that receives light emitted from the light guide unit. The light guide unit has a refractive index lower than that of the first light guide, which is gradually increased as it approaches the end surface on the light guiding direction side, and is transmitted through the first light guide. What is provided with the 2nd light guide which has a reflective surface in which the reflected light is reflected is disclosed.

JP 2012-225611 A JP 2013-611149 A JP 2012-99681 A JP 2012-156445 A

For example, as in Patent Documents 1 to 4, light incident from above the condensing optical element is reflected in the condensing optical element to guide the light to a desired position, so that the solar tracking mechanism is not used every moment. It is conceivable to improve the light collection efficiency of light from the moving sun. However, for example, Patent Documents 1 to 3 do not discuss the light collection efficiency at the end surface (hereinafter referred to as “end surface light collection rate”), and Patent Document 4 also has one incident angle (35 °). The end-face arrival rate of light is only studied by simulation. As described above, in the present situation, there is insufficient study on a method for efficiently condensing light incident at various incident angles on the end face side. Moreover, when providing other members having a prism structure in addition to the light guide, the condensing optical element becomes large, so that it may be difficult to install on the wall surface of the building. Under such circumstances, there is a need for a novel condensing optical element that can achieve both high end-face condensing efficiency and downsizing for light incident at various incident angles.
The main object of the present invention is to provide a novel condensing optical element capable of achieving both high end-face condensing efficiency and downsizing, and a condensing device that does not require a sun tracking mechanism using the same.

The present inventor has intensively studied to solve the above problems. As a result, it is a condensing optical element comprising a laminate in which a plurality of light guides are laminated on the main surface side, and the light guide has a plurality of prism structures continuous to at least one of the main surfaces, Condensing optical element in which external light incident from the main surface side of the light guide is refracted or reflected by the prism structure, propagates through the plurality of light guides, and is emitted from at least one end face of the light guide Found that it is possible to achieve both high end face condensing efficiency and miniaturization for light incident at various incident angles. The present invention has been completed by further studies based on such findings.

That is, this invention provides the invention of the aspect hung up below.
Item 1. A condensing optical element comprising a laminate in which a plurality of light guides are laminated on the main surface side,
The light guide has a plurality of prism structures continuous to at least one of the main surfaces,
External light incident from the main surface side of the light guide is refracted or reflected by the prism structure, propagates through the plurality of light guides, and is emitted from at least one end surface of the light guide. Condensing optical element.
Item 2. The cross-sectional shape in the stacking direction of the prism structure is triangular.
Item 2. The condensing optical element according to Item 1, wherein in the cross-sectional shape of the prism structure, an apex angle protruding from the light guide is in a range of 45 ° to 120 °.
Item 3. The cross-sectional shape in the stacking direction of the prism structure is triangular.
Item 3. The condensing optical element according to

Item

1 or 2, wherein a cross-sectional shape of the prism structure is axisymmetric with respect to a stacking direction.
Item 4. The cross-sectional shape in the stacking direction of the prism structure is triangular.
Item 3. The condensing optical element according to

Item

1 or 2, wherein a cross-sectional shape of the prism structure is non-axisymmetric with respect to a stacking direction.
Item 5. Item 5. The condensing optical element according to any one of Items 1 to 4, wherein the prism structure is formed by a plurality of continuous V-shaped grooves formed on a main surface of the light guide.
Item 6. Item 6. The condensing optical element according to any one of Items 1 to 5, wherein a pitch of the plurality of prism structures is in a range of 0.01 to 1 mm.
Item 7. Item 7. The condensing optical element according to any one of Items 1 to 6, wherein the thickness of each light guide is in the range of 0.1 to 10 mm.
Item 8. Item 8. The condensing optical element according to any one of Items 1 to 7, wherein the number of laminated light guides is in the range of 2 to 6.
Item 9. Item 9. The condensing optical element according to any one of Items 1 to 8, wherein the plurality of light guides have substantially the same refractive index.
Item 10. Item 10. The condensing optical element according to any one of Items 1 to 9, wherein the prism structure is formed on substantially the entire main surface on at least one side of the light guide.
Item 11. The light guide located on the outermost surface side where external light enters in the condensing optical element has the prism structure on the main surface on the outermost surface side,
Item 11. The condensing optical element according to any one of Items 1 to 10, wherein the other light guide has the prism structure on a main surface opposite to the main surface on the outermost surface side.
Item 12. Item 12. The condensing optical element according to any one of Items 1 to 11, wherein the light guide has a rectangular shape or a sector shape when viewed from the stacking direction.
Item 13. Item 13. A condensing device comprising the condensing optical element according to any one of Items 1 to 12.

According to the present invention, it is possible to provide a condensing optical element that can achieve both high end-face condensing efficiency and downsizing for light incident at various incident angles. The condensing optical element can efficiently reflect external light to a desired position by reflecting light incident at various incident angles inside the condensing optical element. For this reason, the condensing apparatus provided with the said condensing optical element does not need to use a sun tracking mechanism, For example, you may install and use on the wall surface etc. of a building.

It is a schematic sectional drawing of an example of the condensing optical element of this invention. It is a schematic exploded view of an example of the condensing optical element of this invention. It is schematic-drawing sectional drawing to which an example of the prism structure of the light guide in this invention was expanded. It is schematic-drawing sectional drawing to which an example of the prism structure of the light guide in this invention was expanded. It is schematic-drawing sectional drawing to which an example of the prism structure of the light guide in this invention was expanded. It is a schematic diagram of the condensing apparatus in this invention. It is a graph which shows the relationship between the end surface condensing efficiency and incident angle in the condensing optical element of the simulation 1 in this invention. It is a graph which shows the relationship between the end surface condensing efficiency and incident angle in the condensing optical element of the simulation 2 in this invention. It is a graph which shows the relationship between the end surface condensing efficiency and incident angle in the condensing optical element of the simulation 3 in this invention. It is a graph which shows the relationship between the end surface condensing efficiency and incident angle in the condensing optical element of the simulation 4 in this invention. 6 is a graph showing the relationship between the incident angle of light and the end face condensing efficiency in the condensing optical element of Example 1. It is a graph which shows the relationship between the incident angle of light in the condensing optical element of Example 2, and an end surface condensing efficiency. 10 is a graph showing the relationship between the incident angle of light and the end face condensing efficiency in the condensing optical element of Example 3. It is a graph which shows the relationship between the incident angle of the light in the condensing optical element of Example 4, and an end surface condensing efficiency. 6 is a graph showing the relationship between the incident angle of light and the end face condensing efficiency in the condensing optical element of Comparative Example 1; It is a graph which shows the relationship between the incident angle of the light in the condensing optical element of Example 5, and an end surface condensing efficiency. It is a graph which shows the relationship between the end surface condensing efficiency and incident angle in the condensing optical element of the simulation 5 in this invention. It is a graph which shows the relationship between the end surface condensing efficiency and incident angle in the condensing optical element of the simulation 6 in this invention.

The condensing optical element of the present invention is a condensing optical element including a laminated body in which a plurality of light guides are laminated on the main surface side, and the light guide includes a plurality of continuous light beams on at least one of the main surfaces. External light that has a prism structure and is incident from the main surface side of the light guide is refracted or reflected by the prism structure, propagates through the plurality of light guides, and is emitted from at least one end face of the light guide. It is characterized by that. Hereinafter, the condensing optical element of the present invention and the condensing device provided with the same will be described in detail.

For example, as shown in FIGS. 1 and 2, the condensing optical element 1 of the present invention includes a laminated body in which a plurality of light guides 2 are laminated on the

principal surfaces

2a and 2b. Each light guide 2 includes the

main surfaces

2a and 2b, at least one

end surface

2c and 2d from which light is emitted, and a width direction x (a direction in which a plurality of prism structures 2g described later are continuously formed). It is a transparent substrate having

side surfaces

2e and 2f extending in the direction of the end surface from which light is emitted. 1 and 2, each light guide 2 has a rectangular shape when viewed from the stacking direction y. However, in the present invention, for example, a fan shape may be used. When the shape of each light guide 2 is a fan shape, light can be concentrated on the end surface having the smaller area, and strong light can be emitted from the small end surface.

The thickness of each light guide (length in the stacking direction y) is not particularly limited, but is preferably 0.1 to 10 mm from the viewpoint of achieving both high end face light collection efficiency and downsizing of the light collection optical element. A range of about 0.2 to 3 mm is preferable.

The length in the width direction x of each light guide is not particularly limited, but is preferably about 50 to 500 mm, more preferably from the viewpoint of achieving both high end face condensing efficiency and downsizing of the condensing optical element. The range is about 50 to 150 mm. As the length of the light guide in the width direction x increases, for example, the distance from the external surface incident from the main surface 2a shown in FIG. 1 to the end surfaces 2c and 2d increases, and thus the light collection efficiency decreases. It becomes easy. In the present invention, the light collection efficiency refers to end face light collection efficiency (ECE), which is a value (%) calculated by end face emission light power ÷ incident light power × 100. Here, the optical power corresponds to a value obtained by integrating the light intensity (optical power density) over the entire area of the incident surface or the exit surface.

The length of each light guide in the depth direction z is not particularly limited. However, if the length in the depth direction is increased, the area of the end face from which light is emitted increases, so that the number of optical fibers 5 and the like for guiding outgoing light from the end face as shown in FIG. There is a problem that the optical element becomes large. For example, since the number of optical fibers is normally assumed to be about 10 to 200, the length in the depth direction z of each light guide is preferably in the range of about 10 to 200 mm. .

For example, when 80 condensing optical elements having a width direction of 100 mm and a depth direction of 100 mm are combined, the light receiving area is 0.8 m ² . In this light receiving area, when the average illuminance of 98000 lux of outdoor light at noon on a clear day is received, the total incident light flux to the condensing optical element is calculated as illuminance × light receiving area, and is 78400 lumens. For example, in a condensing optical element having an end face condensing efficiency of 5%, 5% of the total incident light flux is emitted from the end face, so the illuminance of light emitted from the end face is 3920 lumens. When a 10 m ² room (about 6 tatami mats) is illuminated with the emitted light flux, the illuminance is calculated as light flux ÷ irradiation area, and thus becomes 392 lux.

For example, as shown in FIG. 3, each light guide 2 has a plurality of continuous prism structures 2g on at least one of the

main surfaces

2a and 2b. In the present invention, the plurality of continuous prism structures 2g means that at least two, preferably three or more adjacent prism structures that refract or reflect light do not pass through a flat surface extending in the width direction x. More preferably, it refers to a structure in which four or more are formed.

The plurality of continuous prism structures may be formed only on one main surface of each light guide, or may be formed on both main surfaces. When a plurality of continuous prism structures are formed only on one main surface of the light guide, the other main surface is preferably a flat surface (mirror surface). Further, as the laminated structure of the condensing optical element of the present invention, (1) a laminated structure in which only a light guide having a prism structure formed on only one main surface is laminated, and (2) both main surfaces. Laminated structure in which only light guides having prism structures are laminated, or (3) A light guide having prism structures formed only on one main surface and a light guide having prism structures formed on both main surfaces. A laminated structure in which both bodies are laminated is mentioned. Among these laminated structures, the laminated structure of the above (1) or (3) is preferable, and the laminated structure of the above (1) is more preferable from the viewpoint of simplification of the member used and cost reduction.

Furthermore, in the condensing optical element of the present invention, among the laminated structure of (1), a prism structure is formed on the main surface on the incident surface side of the external light, and the main surface on the back surface side is a flat surface. The light body is denoted as “F”, the light guide on which the principal surface on the incident surface side of the external light is a flat surface and the prism structure is formed on the principal surface on the back surface side is denoted as “B”. A particularly preferable laminated structure from the viewpoint of achieving both high end-face condensing efficiency and downsizing of the optical optical element is as follows.

When the condensing optical element of the present invention has two layers of light guides, a laminated structure of BF and a laminated structure of FB are preferable in order from the back side of the condensing optical element. Moreover, when it has 3 layers of light guides, the laminated structure of BBF and the laminated structure of FFB are preferable in order from the back surface side of a condensing optical element. When a four-layer light guide is provided, a BBBF laminated structure and an FFFB laminated structure are preferable in this order from the back side of the condensing optical element. In the case of having five layers of light guides, a BBBBF stacked structure and a FFFFB stacked structure are preferable in this order from the back side of the condensing optical element. In the case of having six layers of light guides, a BBBBBBF stacked structure and a FFFFFB stacked structure are preferable in this order from the back side of the condensing optical element.

For example, as shown in FIG. 2, the laminated structure of “BBBF” refers to the main surface 2 a on the incident light side of the light guide 21 located on the outermost surface side where external light is incident among the plurality of light guides 2. A prism structure 2g is formed (F), and a prism structure 2g is formed on the main surface 2b on the back side of the other light guides 22 to 24 (BBB). That is, the light guide located on the outermost surface side where external light is incident in the condensing optical element has the prism structure on the main surface on the outermost surface side, and the other light guide is the main surface on the outermost surface side. By having a prism structure on the main surface on the opposite side (back side), as will be described later, external light incident from the vicinity in the vertical direction (stacking direction y, incident angle 0 °) is easily reflected by the corner cube of the prism structure. . For this reason, it can suppress that the light perpendicularly incident on the condensing optical element escapes from the back surface side without being guided to the end surface, and can exhibit higher end surface condensing efficiency and downsizing.

One prism structure formed on the light guide is not particularly limited as long as the light incident on the light guide 2 is refracted or reflected, but the light collecting optical element has high end face light collection efficiency and downsizing. From the viewpoint of achieving both, a triangular prism structure is preferable. That is, for example, as shown in FIG. 3, the cross-sectional shape of the prism structure 2g in the stacking direction y and the width direction x (xy plane) of the light guide 2 is preferably triangular. Such a prism structure can be provided by forming a plurality of continuous V-shaped grooves on the

main surface

2a or 2b of the light guide 2 as shown in FIG. A plurality of continuous V-shaped grooves are formed by a method of cutting a transparent base material of a light guide having a flat surface, a method of pouring a resin into a mold having a corresponding shape, and the like. Can do. In FIG. 2, the V-shaped groove is formed substantially parallel (parallel) to the end faces 2 c and 2 d so as to extend in the depth direction z. In addition, when the shape when the light guide is viewed from the stacking direction y is a fan shape, the V-shaped groove forming the prism structure is formed concentrically with the end surface side having the smaller area as the center. It is preferable that

When the cross-sectional shape of the prism structure 2g in the stacking direction y and the width direction x (xy plane) is triangular, the cross-sectional shape of the prism structure 2g is line-symmetric with respect to the stacking direction y as shown in FIG. It may be non-axisymmetric as shown in FIG. 5, for example. Further, when the cross-sectional shape of the prism structure 2g is line symmetric as shown in FIG. 4, the apex angle a protruding from the light guide 2 in the cross-sectional shape of the prism structure 2g is not particularly limited. From the viewpoint of achieving both high end face light collection efficiency and downsizing, it is preferably in the range of about 45 ° to 120 °, more preferably about 85 ° to 95 °. When the cross-sectional shape of the prism structure 2g is non-symmetrical as shown in FIG. 5, the smaller one of the angles b and c formed by the apex angle protruding from the light guide 2 and the straight line in the stacking direction y. The angle b is not particularly limited, but is preferably 0 ° to about 1/2 ° of the angle c, more preferably 0 ° to 0 °, from the viewpoint of achieving both high end-face condensing efficiency and downsizing. A range of about 2 ° is mentioned. Further, the angle of the larger angle c is not particularly limited, but is preferably about 50 ° to 65 °, more preferably 58 ° to 62 ° from the viewpoint of achieving both high end surface light collection efficiency and downsizing. A range of degrees is mentioned.

From the viewpoint of achieving both high end-face condensing efficiency and downsizing of the condensing optical element, the prism structure on at least one of the principal surfaces of the light guide 2 is provided on substantially the entire surface (entire surface) of at least one of the principal surfaces. It is preferable. The plurality of prism structures may have the same shape or different shapes. Further, the size of the prism structure may be the same or different.

The pitch p (interval) of the plurality of prism structures is not particularly limited, but preferably from about 0.01 to 1 mm, more preferably from 0.05 to 1 mm, from the viewpoint of achieving both high end-face condensing efficiency and downsizing. The range is about 0.15 mm.

The material constituting the light guide is not particularly limited as long as it has high transparency, and preferably includes a transparent organic material such as acrylic resin and polycarbonate resin, or a transparent inorganic material such as glass. In the condensing optical element of the present invention, only light guides made of the same material may be used, or light guides made of different materials may be used in combination. In the present invention, the term “transparent” means that at least visible light is transmitted. As the light guide, for example, a light having a transmittance of 90% or more for light having a wavelength of about 360 nm to 800 nm is preferable.

The refractive index of the light guide is not particularly limited, but is preferably about 1.3 to 1.6, more preferably about 1.4 to 1.5. In the condensing optical element of the present invention, light guides having substantially the same refractive index may be used, or light guides having different refractive indexes may be used in combination.

In the condensing optical element of the present invention, the light guides may be laminated so that they are in contact with each other, or at least a part of the light guides may be laminated. Air may exist between the light guides. Note that the light guides may be optically connected to each other. In that case, the optically connected light guides together constitute one light guide.

In the condensing optical element of the present invention, light may be emitted from one end face, or light may be emitted from both end faces. When light is emitted from one end face, a light reflector is disposed on the end face opposite to the end face from which the emitted light is emitted, and the light that has reached the opposite end face is reflected to the exit end face. Is preferred. Further, when light is emitted from the end face on one side, as shown in FIG. 5, when the cross-sectional shape of the prism structure 2 g is axisymmetric with respect to the stacking direction y, the high end face condensing of the condensing optical element 1 is performed. From the viewpoint of achieving both efficiency and miniaturization, it is preferable to emit light from the end face on the smaller angle b side.

The external light incident on the condensing optical element is not particularly limited and may be appropriately selected depending on the light to be collected, and preferably includes sunlight.

For example, in a transparent substrate having a refractive index higher than that of the surroundings and a main surface on which external light is incident is parallel and flat, light propagating at a critical angle or more is efficiently guided to the end face by total reflection. The However, since light incident from the outside of the transparent base material is always below the critical angle inside the transparent base material, it is not possible to guide the light to the end face by repeating total reflection inside the transparent base material. Therefore, in order to propagate the light incident from the main surface of the transparent base material to the end face efficiently through the inside of the transparent base material, it is necessary to change the direction of the light beam when incident on the transparent base material or after the incident. There is. As a simple approach for changing the direction of the light beam, there is a method in which some kind of light scatterer is disposed on or inside the transparent substrate. By providing the light scatterer, a part of the incident light becomes less than the critical angle in the transparent base material and is easily guided to the end face. However, since the light scatterer itself hinders total reflection and becomes a loss when light is guided to the end surface within the transparent base material, the light scatterer is used as a condensing optical element having high end surface condensing efficiency. It is difficult.

On the other hand, in the condensing optical element 1 of the present invention, as shown in FIGS. 1 and 3, for example, the main part on the incident light side of the light guide 2 located on the outermost surface side of the condensing optical element 1 is used. From the surface 2a, external light enters at various incident angles and travels along various optical paths A. The incident light is repeatedly reflected and refracted by the prism structure 2g formed on the light guide 2 and the flat surface of the main surface opposite to the main surface on which the prism structure 2g is formed, so that the end surfaces 2c, 2d The light is guided in the direction, and light is emitted from the end faces 2c and 2d. In the present invention, a part of incident light is refracted by the continuous prism structure formed in the light guide, and light reaching the flat surface of the light guide at a critical angle or more is 100% efficient by total reflection. Reflected. Thereafter, the light reaches the surface having the prism structure again and is transmitted or reflected, but a certain percentage of the light again travels toward the flat surface at an angle greater than the critical angle with respect to the flat surface. By repeating such refraction, reflection and transmission in the light guide, light reaches the end face of the light guide. Light with an angle less than the critical angle is also reflected, although the reflectance is lower than that of total reflection, and is reflected again, and the traveling direction can be changed again by the prism structure. To reach. In the condensing optical element of the present invention, since a plurality of light guides having such a specific structure are laminated, external light is repeatedly reflected, refracted, and transmitted within the light guide, and is emitted from the end face with high light collection efficiency. It is considered to be done.

In general, most of the incident light incident on the transparent substrate passes through all the light guides and exits to the outside from the back side of the condensing optical element, leading to a condensing loss. From the viewpoint of suppressing such light condensing loss and further improving light condensing efficiency, in the condensing optical element of the present invention, it is more preferable that a prism structure is formed on the back side of the light guide. preferable. In that case, when the incident light from the outside is normal incidence (stacking direction, incident angle 0 °) or close to it, a part of the incident light is known as a corner cube as in the optical path A shown at the left end of FIG. It returns to the incident side in the same manner as the reflection structure. The remaining light enters the next light guide as in the central optical path A in FIG. 3, or travels through the light guide in the right optical path A in FIG. The light incident on the next light guide repeats the same action. In this way, the amount of light traveling to the end face increases when the number of light guides stacked is increased, but by further increasing the number of light guides stacked, the amount of light is increased from the back surface of the condensing optical element to the outside. Since the amount of emitted light decreases, the effect of improving the light collection efficiency accompanying the increase in the number of stacked light guides becomes gradually limited. When all the light guides are arranged so that the back side has a prism structure, when the incident light from the outside is perpendicularly incident (stacking direction, incident angle 0 °) or close to it, it returns to the incident side. The light increases, and the end face condensing efficiency at the incident angle decreases.

In order to suppress a decrease in the end face light collection efficiency in such a case, the orientation of the main surface on which the prism structure of the light guide located on the outermost surface side is formed and the prism structure of other light guides It is preferable to reverse the direction of the formed main surface, a light guide having a prism structure formed on the incident light side is laminated on the outermost surface side, and the other light guides are prisms on the back surface side. More preferably, a structure is formed. For example, as shown in FIG. 2, a prism structure is formed on the main surface 2a on the incident light side of the light guide 21 (first light guide 21) located on the outermost surface side, and the main surface on the back surface side. The surface 2b is a flat surface, and the main surface on the incident light side of the light guide 22 (second-layer light guide 22) positioned immediately below is a flat surface, and a prism structure is formed on the main surface on the back surface side. In the condensing optical element 1, the light vertically incident on and transmitted through the first light guide 21 is bent in the traveling direction by the prism structure 2 g of the first light guide 21. When the light enters the light guide 22, it is not perpendicular incidence. As a result, the light incident on the second-layer light guide 22 is guided to the end face of the light guide 22. Further, by arranging the third and fourth light guides 23 and 24 in the same manner as the second light guide 22, the third and fourth light guides 23 and 24 are also two. The same effect as that of the light guide 22 of the layer is exhibited, and a certain amount of light returned from the light guide closer to the rearmost surface is also guided to the end surface, and as a result, the light is guided to the end surface. The total amount of light flux to be increased increases, and the return light from the resurface to the incident light direction can be suppressed.

In the optical element of the present invention, as the number of stacked light guides 2 increases, the light collection efficiency increases. For example, even if the number of stacked layers exceeds 6, the effect of improving the light collection efficiency is reduced, but the thickness is reduced. The disadvantage of becoming larger becomes larger. The number of laminated light guides is not particularly limited as long as it is 2 or more, but is preferably 2 to 6 and more preferably 2 to 2 from the viewpoint of achieving both high end face condensing efficiency and downsizing of the condensing optical element. 5, more preferably 3 to 5, particularly preferably 4 to 5.

The condensing optical element of the present invention may be laminated with a light guide without a prism structure in addition to the light guide with the prism structure described above. From the viewpoint of achieving both high end surface light collection efficiency and miniaturization, it is preferable that only light guides having a prism structure are stacked.

In addition, what is necessary is just to provide a light reflection board in the end surface of the other side, when light is emitted from the end surface of the one side of a condensing optical element. Furthermore, in order to further improve the light collection efficiency of the light collecting optical element, it is preferable to provide light reflecting plates on the back surface side and the side surface side.

The light collecting device of the present invention includes the above-described light collecting optical element. Specifically, as shown in FIG. 6, for example, the condensing device 10 includes a condensing optical element 1, a lens that condenses light emitted from the end face of the condensing optical element 1, or a function equivalent to this. And the optical fiber 5 that guides the light transmitted through the lens and the like. In the condensing optical element 1, a light reflection plate 3 is disposed on a main surface on the side where external light is incident and on a surface other than an end surface from which the light is emitted.

When the light collecting device of the present invention is used for, for example, sunlight illumination, the sunlight can be guided into the room by the optical fiber 5. Moreover, when using the condensing apparatus of this invention for a solar cell etc., a photoelectric conversion element can be arrange | positioned instead of the optical fiber 5, for example. Moreover, when using the condensing apparatus of this invention for a solar water heater etc., sunlight can be guide | induced to a water storage tank with the optical fiber 5, and the water in a water storage tank can be heated.

According to the condensing device of the present invention, since the above-described condensing optical element having both high end-face condensing efficiency and downsizing is provided, light incident at various incident angles is contained inside the condensing optical element. The light can be reflected and efficiently guided to a desired position. For this reason, it is not necessary to use this solar tracking mechanism, the restriction of the installation location is reduced, and solar energy can be effectively used as a panel-type light collecting device that is installed on the wall surface of a building, for example.

Hereinafter, the present invention will be described in detail with reference to Examples and Comparative Examples. However, the present invention is not limited to the examples.

[Simulation 1]
First, with respect to the condensing optical element in which a plurality of light guides are stacked as described above, the light condensing efficiency in the case where light incident from the main surface side at various incident angles is guided to the end surface was simulated. The simulation was a computer-simulation by the ray tracing method (Software used: LightTool manufactured by Synopsys, USA). The simulation conditions are as follows. As shown in FIG. 4, the light guide is transparent in which a V-shaped groove is provided on the entire main surface on one side so that the cross-sectional shape of the prism structure is axisymmetric with respect to the stacking direction. A substrate was used. In the condensing optical element, as shown in FIG. 2, the light guide in the first layer is arranged with the prism structure facing the incident surface in order from the light incident direction (denoted as F). The light guide of the 5th layer arranges the same prism structure on the opposite side (back side) from the entrance surface (represented as B), and is a laminate of 5 layers (with a light reflector on the back side) BBBBF laminated structure from the back side). With respect to such a condensing optical element, the efficiency of light emitted from one end face of the laminated body (end face condensing efficiency) was simulated in the case where external light was incident with the incident angle changed. The stacking direction of the stacked body is an incident angle of 0 °. The prism structure of each layer has apex angle a = 90 °, pitch p = 0.1 mm, thickness L = 2.0 mm of each light guide, refractive index 1.49 (acrylic resin) of the light guide, incident light The wavelength λ is 632 nm, and the divergence angle of incident light is 1 ° (in FIG. 7 to FIG. 12, expressed as “Aim1 °”). In addition, a simulation was performed in the case where light rays of external light were incident from the end face at positions of 5 mm, 10 mm, and 20 mm, respectively. The results are shown in the graph of FIG. As is apparent from the graph shown in FIG. 7, a high end face condensing efficiency exceeding several percent is obtained with a low angle dependency over an incident angle of −40 ° to + 40 °.

[Simulation 2]
A simulation was performed in the same manner as in Simulation 1 except that one layer of the light guide on the back surface side was removed and a four-layer structure (BBBF structure from the back side, refractive index 1.52 (BK7)) was used. . The results are shown in the graph of FIG. As is apparent from the graph shown in FIG. 8, even in the case of a four-layer structure, a high end face condensing efficiency exceeding several percent is obtained with a low angle dependency over an incident angle of −40 ° to + 40 °. The incident angle dependency was almost the same as that of the five-layer structure.

[Simulation 3]
Simulation 2 except that the first and second light guides are in optical contact with each other and that the refractive index of the light guide is 1.49 (acrylic resin). A similar simulation was performed. The results are shown in the graph of FIG. The simulation 3 corresponds to the case where one layer of a double-thickness light guide body in which the first layer and the second layer are combined and prism structures are formed on both main surfaces is used. In simulation 3, the end face light collection efficiency near an incident angle of −45 ° was improved. The end face condensing efficiency at other incident angles was not significantly different from those of

simulations

1 and 2.

[Simulation 4]
As the light guide, as shown in FIG. 5, a simulation is performed except that a transparent base material provided with a V-shaped groove so that the cross-sectional shape of the prism structure is axisymmetric with respect to the stacking direction is used. The simulation was performed in the same manner as in 1. In the apex angle of FIG. 5, b = 0 °, c = 60 °, and the pitch p = 0.3 mm. In addition, the end face from which the light is emitted was calculated as the b side of the apex angle in FIG. The results are shown in the graph of FIG. In the simulation 4, a high end face condensing efficiency was obtained in a wide range of incident angles from −40 ° to + 40 °.

[Example 1]
Plate-shaped acrylic resin with a V-shaped groove (prism structure) with a width of 1 cm and apex angle of 90 ° provided on the entire main surface on one side (refractive index of 1.49, dimensions are 4 cm width x depth 1 cm x thickness 2 mm) is used as a light guide, and a laminate (stacked structure of FFFFF from the back side) is produced by stacking the light guides in a five-tiered manner with the prism structure facing the incident light side (denoted as F). An optical optical element was obtained. In the condensing optical element, a light diffuse reflection plate was provided on the back surface (surface opposite to the incident side) of the laminate. Next, a light beam having a ribbon shape of 632 nm (width 1 mm, height 1 cm, height parallel to the depth direction of the laminate) was incident. The incident positions of the light beams were distances d ′ from the outgoing end face = 5 mm, 10 mm, and 20 mm, respectively. In each case, the output light power from the end face was measured with a detector arranged on the end face, and the end face condensing efficiency was calculated. However, at an angle exceeding d20 = + 20 ° of d ′ = 5 mm, measurement was excluded because the detector itself shielded incident light. The results are shown in the graph of FIG. As shown in the graph of FIG. 11, high end face light collection efficiency was obtained in a wide range of incident angles of −40 ° to + 40 ° in any case where d ′ = 5 mm, 10 mm, and 20 mm. The incident angle of light was set to minus on the side where the angle formed by the incident surface of the condensing optical element and the incident light was less than 90 °, and vertical incidence was set to 0 °.

[Example 2]
As shown in FIG. 2, in order from the incident direction of light, the first-layer light guide is arranged with the prism structure facing the incident surface (F), and the second to fifth-layer light guides are the same. The concentrating optical element is a five-layered laminate (laminated structure of BBBBF from the back side) with the prism structure arranged on the opposite side of the incident surface (B) and a light reflector on the back side. Except for the above, in the same manner as in Example 1, the output light power from the end face was measured with a detector arranged on the end face, and the end face condensing efficiency was calculated. The results are shown in the graph of FIG. As shown in the graph of FIG. 12, high end face light condensing efficiency was obtained in a wide range of incident angles of −40 ° to + 40 ° in any case of d ′ = 5 mm, 10 mm, and 20 mm.

[Example 3]
The light guide is arranged with the prism structure facing the side opposite to the incident light side (B), and a five-layered structure (stacked structure of BBBBB from the back side) with a light reflector on the backside is collected. Except for the optical optical element, the output light power from the end face was measured with a detector arranged on the end face in the same manner as in Example 1, and the end face condensing efficiency was calculated. The results are shown in the graph of FIG. As shown in the graph of FIG. 13, in any case where d ′ = 5 mm, 10 mm, or 20 mm, high end face light collection efficiency was obtained in a wide range of incident angles from −40 ° to + 40 °. However, since all of them have a B laminated structure, the end face light condensing efficiency near an incident angle of 0 ° was lowered.

[Example 4]
In the condensing optical element of Example 2, the size of the light guide is 9.8 cm wide × 9.5 cm deep × 8 mm thick, and one light guide located on the back surface is removed, and a four-layer structure (back surface) BBBF from the side) is used as a condensing optical element, and pseudo sunlight (AM1.5) is applied to the F-side surface of this condensing optical element in the xy plane as shown in FIG. Except that the incident angle was changed and the incident angle was changed, the output light power from the end face was measured with a detector disposed on the end face, and the end face condensing efficiency was calculated in the same manner as in Example 1. As a result, as shown in FIG. 14, the end face condensing efficiency is an average of 4.4% in the range of the incident angle of −40 to + 20 °, and the end face condensing is as high as 5.3% at the incident angle of −10 °. Showed efficiency.

[Comparative Example 1]
Except that a plate-like acrylic resin (refractive index 1.49, width 9.5 cm × depth 9.5 cm × thickness 2 mm) having no prism structure was used as the light guide, the same as in Example 4. Then, the output light power from the end face was measured with a detector arranged on the end face, and the end face condensing efficiency was calculated. As a result, as shown in FIG. 15, the end face light collection efficiency was an average of 0.9% in the range of the incident angle of −40 to + 20 °.

[Example 5]
As shown in FIG. 5, a V-shaped groove is provided so that the cross-sectional shape of the prism structure is axisymmetric with respect to the stacking direction, and b = 0 ° and c = 60 at the apex angle of FIG. A laminated body having a five-layer structure (a laminated structure of BBBBB from the back side) with a pitch p = 0.3 mm is used as a condensing optical element, and the dimensions of the laminated body are 9.4 cm wide × 9.4 cm deep × 10 mm thick Further, except that the end surface from which light is emitted is on the b side of the apex angle in FIG. 5, the output light power from the end surface is measured with a detector arranged on the end surface in the same manner as in Example 4. The end face light collection efficiency was calculated. As a result, as shown in FIG. 16, the end face condensing efficiency is an average of 11.6% in an incident angle range of −40 to + 20 °, and the end face condensing efficiency is a maximum of 13.8% at an incident angle of −11 °. showed that.

[Simulation 5]
An air layer was introduced between the planes of the first light guide and the second light guide that were optically separated, and the dimensions of the light guide were 10 cm wide × 10 cm deep, and the thickness of the laminate. The simulation was performed in the same manner as in the simulation 3 except that white light having a color temperature of 5770 K was incident on the entire surface. The results are shown in the graph of FIG. This was a simulation of the conditions corresponding to Example 4, and the end face condensing efficiency was as high as an average of 7.5% in the incident angle range of −40 to + 20 °.

[Simulation 6]
As shown in FIG. 5, a V-shaped groove is provided so that the cross-sectional shape of the prism structure is axisymmetric with respect to the stacking direction, and b = 0 ° and c = 60 at the apex angle of FIG. A 5-layer structure (stacked structure of BBBBB from the back side) with a pitch p = 0.3 mm is used as a condensing optical element, and the thickness of the stack is 10 mm (each layer is 2 mm thick). The simulation was performed in the same manner as in the simulation 5 except that the exit end face was on the b side of the apex angle in FIG. The results are shown in the graph of FIG. This was a simulation of the conditions corresponding to Example 5, and obtained a result close to Example 5 with an end surface light collection efficiency of 11.1% on average in the incident angle range of −40 to + 20 °.

DESCRIPTION OF SYMBOLS 1 Condensing optical element 2

Light guide

2a,

2b Main surface

2c,

2d End surface

2e, 2f Side surface 2g Prism structure 21 1st layer light guide 22 2nd layer light guide 23 3rd layer light guide 24 Fourth-layer light guide 3 Light reflector 4 Light condensing structure 5 Optical fiber A Optical path

Claims

A condensing optical element comprising a laminate in which a plurality of light guides are laminated on the main surface side,
The light guide has a plurality of prism structures continuous to at least one of the main surfaces,
External light incident from the main surface side of the light guide is refracted or reflected by the prism structure, propagates through the plurality of light guides, and is emitted from at least one end surface of the light guide. Condensing optical element.
The cross-sectional shape in the stacking direction of the prism structure is triangular.
The condensing optical element according to claim 1, wherein in the cross-sectional shape of the prism structure, an apex angle protruding from the light guide is in a range of 45 ° to 120 °.
The cross-sectional shape in the stacking direction of the prism structure is triangular.
The condensing optical element according to claim 1, wherein a cross-sectional shape of the prism structure is axisymmetric with respect to a stacking direction.
The cross-sectional shape in the stacking direction of the prism structure is triangular.
The condensing optical element according to claim 1, wherein a cross-sectional shape of the prism structure is non-axisymmetric with respect to a stacking direction.
5. The condensing optical element according to claim 1, wherein the prism structure is formed by a plurality of continuous V-shaped grooves formed on a main surface of the light guide.
The condensing optical element according to any one of claims 1 to 5, wherein a pitch of the plurality of prism structures is in a range of 0.01 to 1 mm.
The condensing optical element according to any one of claims 1 to 6, wherein the thickness of each light guide is in the range of 0.1 to 10 mm.
The condensing optical element according to any one of claims 1 to 7, wherein the number of laminated light guides is in the range of 2 to 6.
The condensing optical element according to any one of claims 1 to 8, wherein the plurality of light guides have substantially the same refractive index.
The condensing optical element according to any one of claims 1 to 9, wherein the prism structure is formed on substantially the entire main surface on at least one side of the light guide.
The light guide located on the outermost surface side where external light enters in the condensing optical element has the prism structure on the main surface on the outermost surface side,
The condensing optical element according to claim 1, wherein the other light guide has the prism structure on a main surface opposite to the main surface on the outermost surface side.
The condensing optical element according to any one of claims 1 to 11, wherein the light guide has a rectangular shape or a sector shape when viewed from the stacking direction.
A condensing device comprising the condensing optical element according to any one of claims 1 to 12.