JPH09325336A - Surface type light source device and passive type display device with same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain apparently the same effect with the provision of the same light source as a light source, provided on one flank of a photoconductor for lighting, on the other flank of the photoconductor for lighting although the surface light source of an edge light type photoconductor system is actually provided with only one light source on one flank of the lighting photoconductor. SOLUTION: This surface type light source device is constituted by putting a lighting photoconductor 10 which is a plate or film type and has high light transmissivity and a high refractive index and a photoconductor 30 for a bypass optical path which is formed of a similar photoconductor and has light reflecting layers provided on both the surfaces, and an optical coupling means 20 which optically couples both the photoconductors 10 and 30 is arranged nearby terminal parts 10b and 30e of both the photoconductors 10 and 30 on the opposite sides from light guide-in terminal parts 10a and 30d.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thin planar light source and a planar light source device widely used for a planar light source of a backlight (backlight) for illuminating a passive display device and the planar light source device. The present invention relates to an illuminated passive display device in which a light source device is arranged on the back surface. More specifically, a light guide plate for illumination is arranged on the back surface of the passive display device, and light rays are incident from the terminal side surface of the light guide plate for illumination. Multiple reflection of light rays on the front surface and the back surface of the light transmissive light guide body. TECHNICAL FIELD The present invention relates to a light guide type (edge light type) planar light source device that utilizes the above, and a passive type display device with illumination in which the planar light source device is arranged on the back surface.

[0002]

2. Description of the Related Art Conventionally, a liquid crystal display device, which is a typical example of a passive display device (passive type display), has a C
Unlike active display devices such as RTs (cathode ray tubes) and electroluminescence display devices, they do not emit light by themselves. Therefore, in order to be able to observe this passive display device in the dark,
It is necessary to use a backlight (back light source) in which a planar light source is arranged on the back surface of the passive display device.

For example, as a typical example of a backlight for a liquid crystal display device, a light guide plate installed on the back surface of the liquid crystal display device,
A light guide type (edge light type) planar light source using a light guide plate, which is combined with a linear light source such as a straight tube fluorescent lamp installed on the side surface of the light guide plate, is widely used. This light guide system allows light rays to enter from the side surface of the light guide made of an acrylic resin, a polycarbonate resin, or the like, which has excellent translucency.
The planar illumination is performed by utilizing multiple reflection of light rays on the front surface and the back surface (front surface and back surface) of the light guide.

The light guide for illumination is a plate-shaped body or a film-shaped body having a rectangular illumination surface in correspondence with the rectangular display surface of the liquid crystal display device. A positional relationship between the light guide for illumination having a rectangular surface having two short sides facing each other and two long sides facing each other, and a linear light source such as a straight tube fluorescent lamp disposed on the side surface thereof. Is! Short side 1 light type in which one light is arranged on the side of the short side of the light guide, "long side 1 light type in which one light is arranged on the side of the long side of the light guide, #side of the short side of the light guide Short side 2 with 2 lights
It can be classified into a light type and a long side two lamp type in which two lights are arranged on the side surface of the long side of the light guide.

In the case where a light source is arranged on either one of the short side and the long side of the light guide for illumination and a light ray is incident from this one side, that is, the above! Short side 1 light type, "long side 1
In the case of the light type, as is well known, a part of the light beam incident on the illumination light guide repeats total internal reflection and is directed toward the side face of the illumination light guide opposite to the terminal side face on the opposite side. Is transmitted, reaches the side surface of the terminal, and the remaining incident light leaks little by little from the surface of the illuminating light guide body for illuminating purposes. Therefore, the surface brightness of the illuminating light beam emitted from the surface of the illuminating light guide decreases rapidly with the distance from the light source. In the vicinity of the side surface of the terminal, the surface brightness becomes slightly higher than that of the terminal portion due to the side surface reflection. Therefore, in the case of this one-lamp type, there is a drawback that the surface brightness is not uniform and the surface brightness is small. Further, in a large-area light guide for illumination, the distance of incident light rays to be transmitted is too long. This is a drawback in that the surface brightness in the vicinity of the end portion of the large-area illumination light guide is extremely insufficient and cannot be put to practical use. Therefore, this one-lamp type is used for small-area liquid crystal displays, for displaying liquid crystal numerals such as watches that do not necessarily require uniform surface brightness, and for monochrome display type liquid crystal displays whose surface brightness may be relatively small. It had limited uses.

On the other hand, for a monitor of a personal computer which requires a uniform surface brightness and a large surface brightness, a monochrome display type, a color display type liquid crystal display used as a television receiver, and a large area liquid crystal display, The above-mentioned #short side 2 lights type and $ long side 2 lights type were adopted. However, the two-lamp system naturally requires two light sources, and thus has the serious drawbacks listed below. % For battery-backed liquid crystal display backlights of portable electronic devices such as notebook type, pocket type personal computers, information communication terminals, etc., the two-lamp type using two fluorescent lamps uses a fluorescent lamp and its inverter power supply. The storage space for power consumption, weight, lamp house, etc. will be twice as large as the one-lamp type. That is, in the case of the two-light type, the battery life is roughly half, the weight is doubled, and the storage space is doubled as compared with the single-light type, and it is a portable electronic device that requires low power consumption, light weight, and compact size. It cannot be put to practical use as a light source for liquid crystal displays for devices. & As is well known for general-purpose fluorescent lamps, the blackened part grows from the vicinity of the electrode toward the center due to aging, and the emission brightness decreases, and the unevenness of the emission brightness varies in the length direction. It depends on the position of. In addition, since the state of aging changes considerably depending on the individual fluorescent lamps, the above-mentioned two-lamp system using two fluorescent lamps has a surface luminance of the illumination light guide due to aging compared to the one-lamp system. Inhomogeneity due to the location and unevenness of the display color increase.

[0007]

The main object of the present invention is to:
The drawbacks of the prior art described above are eliminated.
Another main object of the present invention is to use, as a backlight for a passive display device, a light guide arranged on the back surface of the passive display device, and radiate from a light source arranged on the end side of the light guide. A large area passive display device with a large surface brightness and uniform display brightness by using only one light source in a light guide type (edge light type) planar light source in which light rays are incident from the side surface of the light guide body. It is an object of the present invention to propose a novel planar light source device that enables the above and a passive type display device with illumination including the novel planar light source device.

[0010]

In order to achieve the above-mentioned object, in a surface light source device of the present invention, an illumination is made of a plate-shaped or film-shaped light guide material having a high refractive index and excellent light transmittance. Superimpose a light guide and a plate-like or film-like light guide for a detour optical path, which is made of a light guide material having a high refractive index and excellent in light transmission, and provided with light reflecting layers on both front and back surfaces. The illumination light guide body and the detour optical path light guide body are provided in the vicinity of a terminal portion of the illumination light guide body and the detour light path light guide body on the side opposite to the light introduction terminal portion. An optical coupling means for optically coupling is arranged.

The optical coupling means can be selected from optical elements having a prismatic, trapezoidal, tapered, rectangular, or U-shaped cross section. Further, one end portion of the light guide for a bypass optical path may be extended, and the extended portion may be bent into a substantially U shape to form the optical coupling means.

It is possible to align one side surface of the light guide for illumination and one side surface of the light guide for detour optical path, and arrange a common linear or point light source on the aligned surface.

Further, in the passive type display device with the planar light source of the present invention, the light guide for illumination made of a plate-shaped or film-shaped light guide material having a high refractive index and excellent in light transmittance, and the light transmittance are provided. The light guide for illumination is formed by superimposing a plate-shaped or film-shaped light guide for a bypass optical path, which is made of a light guide material having an excellent high refractive index and provided with light reflection layers on both front and back surfaces. An optical coupling means for optically coupling the illumination light guide and the detour optical path light guide is arranged in the vicinity of the body and the terminal opposite to the light introduction terminal of the detour light guide. A planar light source device
It is placed on the back of a passive display device such as a liquid crystal display device.

[0015]

In the planar light source device of the present invention, the illumination light guide body of the prior art made of a light guide material having a high refractive index and excellent light transmittance is used, and the light guide body for illumination is arranged on the side surface of the end of the light guide body. In a light guide type (edge light type) planar light source in which a light beam emitted from a light source is incident from the side surface for illumination, a detour optical path made of a light guide material having a high refractive index and excellent light transmittance. A light guide, and the illumination light guide and the detour optical path light guide near the end of the illumination light guide and the detour optical path light guide opposite to the light introducing terminal. And an optical coupling means for optically coupling.

Therefore, by using only one common light source for both the light guide for illumination and the light guide for detour light path, one side portion of the light guide for illumination and the light guide for detour light path is used. A light beam emitted from the arranged light source can be made incident from one side surface portion of the illumination light guide and the detour light guide.
A part of the light beam incident on the light guide for illumination is repeatedly reflected multiple times and is transmitted toward the other side face of the terminal facing the one side face, and the rest of the incident light is guided by the light guide for illumination. It gradually leaks from the surface of the body and becomes an illumination ray. On the other hand, almost all of the light rays that have entered the detour optical path light guide are repeatedly reflected multiple times and are transmitted to the other side surface portion of the terminal facing the one side surface portion with almost no leakage to the outside. The detoured transmitted light beam is optically coupled by the optical coupling means in the vicinity of the other side surface portions of both light guides and is incident on the illumination light guide body, and a part of the incident light beam is transmitted to the illumination light guide body. Multiple reflections are transmitted from the vicinity of the other side surface portion of the light body toward the one side surface portion, and the rest of the incident light rays leak from the surface little by little to become illumination light rays. Since the light guide for the bypass optical path is different from the light guide for illumination in that light rays do not leak in the middle of the optical path, the light guide for illumination is near the other side surface portion (final end) of the light guide for illumination. In addition, it functions as if another light source having almost the same light emission brightness as the one side surface portion is arranged.

Therefore, in the present invention, by providing the detour light guide and the optical coupling means in addition to the conventional light guide for illumination, in reality, only one side surface of the light guide for illumination is provided. Despite the provision of the light source, the same effect as the provision of the same light source as the light source on the other side surface of the illumination light guide is apparently obtained. That is, the surface light source of the one-lamp type light guide system (edge light type) has a surface luminance as large as that of the two-lamp type surface light source, and the display luminance is uniform. Differently, it is possible to provide a novel planar light source device that is energy-saving, lightweight, and enables a large-area illuminated passive display device.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Various embodiments of the present invention will be described below in detail with reference to the drawings. In all drawings, the same or equivalent parts are designated by the same reference numerals. Further, the dimensions in all the drawings are exaggerated and drawn arbitrarily in order to clarify the present invention.

(Embodiment 1) FIG. 1 is an exploded perspective view of a planar light source device FLS showing the basic principle common to various embodiments of the present invention described below. FIG. 2 is an enlarged side sectional view taken along the line AA of FIG. 1 with a part omitted. FIG. 3 is an enlarged side cross-sectional view in which the vicinity of the optical coupling means 20 arranged at the terminal on the right side of FIG. 2 is further enlarged and the light ray transmission path L1 is entered.

1 to 3, the planar light source device F is shown.
The LS is composed of a light guide 10 for illumination, which is made of a plate-shaped or film-shaped light guide material having a high refractive index and excellent in light transmittance, and a light guide material having a high refractive index which is excellent in light transmittance. A plate-shaped or film-shaped detour optical path light guide 30 provided with a reflective layer made of a highly reflective metal material and / or a light reflective layer made of a light guide material having a low refractive index on both front and back surfaces. Light-introducing terminal side face portion 10a of the light guide 10 for illumination, which is formed by overlapping.
The illumination light guide 10 and the detour optical path are provided near the terminal side surface 10b on the opposite side (and the terminal side surface 30e on the opposite side of the light introducing terminal side 30d of the detour optical path light guide 30). An optical coupling means 20 for optically coupling the light guide body 30 is arranged. A known light scatterer 52 is disposed on the back side of the illumination light guide 10 between the back surface of the illumination light guide 10 and the surface of the detour light guide 30. . In addition, a plate-shaped or film-shaped known light diffuser 53 is arranged on the surface side of the illumination light guide 10. The light introducing terminal side surface portion 10a of the illumination light guide 10
And the light introduction terminal side surface portion 30 of the light guide 30 for the detour optical path
A linear light source LS, such as a tubular fluorescent lamp or a tubular incandescent lamp, is arranged near d.

Examples of the light guide material having a high light transmittance and having a high refractive index, which constitutes the light guide 10 for illumination, include polymethylmethacrylate resin (PMMA), polycarbonate resin (PC), polystyrene resin (PS) and the like. The light-transmissive organic resin or the inorganic optical glass is used.

Light rays emitted from the light source LS and incident from the one end side surface portion 10a of the illumination light guide 10 are subjected to multiple reflection between the front surface and the rear surface thereof in order to effectively function as a surface light source. Repeatedly, it is necessary to be efficiently transmitted to the other terminal side surface portion 10b on the opposite side, and at the same time, this light beam is emitted from the surface of the illumination light guide 10 with a predetermined brightness and a predetermined brightness distribution. There is a need. For this purpose, the light-scattering body 52 is brought close to the back surface side, or white paint in a predetermined pattern is directly printed on the back surface, or the rough surface portion is directly formed in a predetermined pattern on the back surface. There is. As shown in FIG. 2, the light beam introduced inside from one end side surface 10a of the light guide 10 for illumination and transmitted to the other end side surface 10b has a predetermined number of predetermined points from the light scatterer 52. Is gradually taken out as scattered light 11. Further, the scattered light beam 11 has a light diffuser 5 arranged adjacent to the front surface side of the illumination light guide 10.
In 3, the diffused light beam 12 is diffused and emitted to serve as a surface light source. This type of surface light source using only one light source LS of the prior art has the same or similar configuration as above.
However, in this configuration, for example, to obtain a surface light source having a high surface luminance and a uniform luminance distribution over the entire surface of the illumination light guide 10 is, for example, the illumination light guide 1 described above.
It was not possible to obtain a large-area surface light source such as when the distance from the one terminal side surface portion 10a to the other terminal side surface portion 10b is long.

In the first embodiment, in addition to the above configuration,
The detour optical path light guide 30 having a substantially parallel plate shape and a film shape, which is substantially the same as the light guide 10 for illumination, is provided. As shown in FIGS. 1, 2 and 3, the detour optical path light guide 30 is
The illumination light guides 10 are arranged on the back surface, that is, on the lower side, close to or in contact with each other and stacked. That is, in the surface light source device FLS according to the first embodiment, the light scatterer 52, the illumination light guide body 10, and the illumination light guide body 10 are sequentially arranged on the upper side of the bypass optical path light guide body 30.
Light diffusers 53 are stacked and arranged. In the exploded perspective view of FIG. 1, the light scatterer 5 is set in the arrow direction (downward) indicated by reference numeral D with reference to the detour light guide 30.
2. The light guide 10 for illumination and the light diffuser 53 are stacked and arranged in this order, and the optical coupling means 20 is arranged in the arrow direction (leftward direction) indicated by the symbol E. At this time, as shown in FIG. 2, in the light source LS, the light beam emitted from the light source LS is
It is arranged at a position where light is effectively incident from both one end side face 10a of the illumination light guide 10 and one end side face 30d of the bypass optical path light guide 30. Moreover, as shown in FIG. 2 and FIG.
A light ray L1 that is multiple-reflected inside the detour optical path light guide body 30 and exits from the other terminal side surface 30d is effectively introduced into the optical coupling means 20 formed of a light-transmitting trapezoidal columnar body having a high refractive index, The optical coupling means 20 is arranged at a position where the light beam which is turned from the optical coupling means 20 and is emitted is effectively introduced from the other end side surface 10b of the illumination light guide 10. As shown in FIG. 3, the other end side surface 3 of the light guide 30 for the detour optical path
The light ray L1 emitted from 0d is effectively introduced into the optical coupling means 20, is reflected and emitted at least once in the light coupling means 20, and is effectively introduced from the other end side surface 10b of the illumination light guide 10. Next, this light ray L1 repeats multiple reflection in the direction from the other end side surface 10b to the one end side surface 10a from the other end surface 10b of the illumination light guide 10, and is gradually emitted from the surface and diffused via the light diffuser 53 so that the surface brightness is increased. It is homogenized and emitted to the outside. The light beam gradually emitted from the back surface is diffusely reflected by the light scatterer 52 to become a scattered light beam La, passes through the illumination light guide 10 and is diffused via the light diffuser 53 to have a uniform surface brightness. Is emitted to the outside. This scattered light L
In a, in order to effectively extract the component emitted in the surface direction of the detour light guide 30 from the surface of the illumination light guide 10, the back surface of the light scatterer 52 and the detour light guide 30 are provided. A light return light reflector may be disposed between the surface and the surface. When the reflection layer 30b provided on the front surface side of the light guide 30 for the detour optical path is made of a light reflecting metal, the reflection layer 30b can also serve as the light returning light reflector.

As the light guide material having a high light transmittance and a high refractive index, which constitutes the light guide 30 for the bypass optical path, as with the light guide 10 for illumination, a polymethylmethacrylate resin (PMMA) or a polycarbonate is used. Light-transmissive organic resin such as resin (PC) and polystyrene resin (PS), or inorganic optical glass is used. While the light guide 10 for illumination needs to gradually radiate the light rays incident from the surface thereof, the light guide 30 for the detour optical path is provided.
Has the sole purpose of efficiently transmitting a light ray incident from the one terminal side surface portion 30d to the other terminal side surface portion 30e on the opposite side thereof by repeating multiple reflection between the surface and the back surface thereof. For this reason, in this embodiment, as shown in FIG. 2 and FIG. 3, the detour optical path light guide 30 is a plate having a high refractive index, which is excellent in light transmittance so that an incident light ray hardly leaks to the outside. -Shaped or film-shaped light guide material is used as a core (core) 30a, and almost all of its front and back surfaces are made of a low-refractive-index fluororesin, a silicon resin light guide material, or a specularly reflective aluminum, It has reflection layers 30b and 30c made of a metal material having a light reflectance such as nickel as a clad. In addition, a reflection layer (not shown) similar to the reflection layers 30b and 30c is provided on all side surfaces except one terminal side surface portion 30d which is a light ray incident portion and the other terminal side surface portion 30e which is a light ray emission portion. It is desirable to further prevent the leakage of

Therefore, as shown in FIG. 2 and FIG. 3, the light ray incident on the core portion 30a from the one end side surface portion 30d of the detour light guide 30 is repeatedly reflected multiple times between the cladding portions 30b and 30c. And is efficiently transmitted to the side surface 30e of the other terminal without leaking to the outside. Other terminal side part 3
The ray reaching 0e enters into the optical coupling means 20 having a trapezoidal columnar cross section in this embodiment, as shown by the symbol L1, and is reflected in the optical coupling means 20 to change the direction of the ray. This converted light ray L1 enters from the other end side surface 10b of the illumination light guide 10 and is introduced into the inside thereof, and is repeatedly reflected multiple times toward the one end side surface 10a, and at the same time, the illumination light guide 10 is illuminated. The light is gradually and gradually emitted from the surface of the optical body 10 to become emitted light rays La (scattered light rays) and Lb (diffused light rays).

Therefore, in the surface light source device FLS of this embodiment, the common light source LS for both the light guide for illumination and the light guide for the detour optical path is used, and the light guide for illumination 10 is used. And a light beam emitted from the light source LS arranged on the one end side surface portions 10a and 30d of the light guide body 30 for the bypass optical path,
The light can be incident from one side surface portion of the light guide body 10 for illumination and the light guide body 30 for the detour optical path. The illumination light guide 10
A part of the light beam incident on is repeatedly transmitted multiple times toward the other side surface of the terminal facing the one side surface, and the rest of the incident light is gradually emitted from the illumination light guide 10. The light leaks from the surface to become light rays La and Lb. On the other hand, almost all of the light rays incident on the light guide 30 for the detour optical path are repeatedly reflected multiple times and are transmitted to the other side surface portion 30e of the terminal facing the one side surface portion 30d with almost no leakage to the outside. It The detoured transmitted light rays are optically coupled by the optical coupling means 20 in the vicinity of the other side surface portions 10b and 30e of both the light guide bodies 10 and 30, and are incident into the illumination light guide body 10. A part of the incident light beam is transmitted by multiple reflection from the vicinity of the other side surface part 10b of the illumination light guide 10 toward the one side surface part 10a, and the rest of the incident light beam leaks little by little from the surface. And become illumination light beams La and Lb. The detour light guide 30 is
Unlike the light guide 10 for illumination, since light rays do not leak in the middle of the optical path, the light guide 10 for illumination has one side surface near the other side surface portion (final end) 10b. It functions as if another light source having the same emission brightness as the light source LS arranged in the portion 10a is arranged.

Therefore, according to the present invention, by providing the light guide for the detour optical path and the optical coupling means, although only one light source is actually provided on one side of the light guide for illumination,
Apparently, the same effect as providing the same light source as the light source is provided on the other side surface of the light guide for illumination. That is, it is a surface light source of the above-mentioned one-lamp type light guide method (edge light type) and has a surface luminance as large as that of the above-mentioned two-lamp type surface light source, a uniform surface luminance distribution, energy saving, light weight, and large area. It has become possible to provide the above-mentioned planar light source device. Further, when the planar light source device is provided on the back surface of the transmissive passive display device to be used as a backlight of the display device, the surface light source is large and the distribution of the surface brightness is uniform using only one light source. It is possible to provide an energy-saving, lightweight, large-area passive type display device with illumination.

Next, various embodiments which are modifications of the first embodiment will be described. (Embodiment 2) FIGS. 1, 4 and 5 show another embodiment of the present invention. FIG. 1 is an exploded perspective view of a second embodiment, which is common to the first embodiment of the present invention except that the optical coupling means and the arrangement location thereof are different. FIG. 4 is an enlarged side sectional view taken along the line AA of FIG. 1 with a part omitted. FIG. 5 is an enlarged side sectional view in which the vicinity of the optical coupling means 21 arranged at the terminal on the right side of FIG. 4 is further enlarged and the light ray transmission path L2 is entered. The second embodiment is different from the first embodiment in the optical coupling means 22.
The structure and the location are different and the rest are almost the same. Therefore, here, for the same parts as those of the first embodiment, the description thereof will be omitted as much as possible for the sake of simplicity.

As shown in FIGS. 1, 4 and 5, the planar light source FLS according to the second embodiment is provided with a plate-like or film-like detouring optical path light guide body 30 on the front surface side thereof for sequentially illuminating and guiding light. The body 10, the light scatterer 52, the illumination light guide 10 and the light diffuser 53 are arranged. Further, on the surface side of the light guide for illumination 10,
The light diffuser 53 is disposed. Similar to the first embodiment, one end side surface of both light guides 10 and 30, that is, the light introducing end side surfaces 10a and 30d, have their end surfaces aligned at substantially the same position in the column direction, and have a tubular shape in the vicinity thereof. A linear light source LS such as a fluorescent lamp or a tubular incandescent lamp is arranged.

On the other hand, unlike the first embodiment, in the second embodiment, the long side of the detour light guide 30 is set to be shorter than the long side of the illumination light guide 10. That is, the other terminal side surface portion 30e of the detour light guide 30 is shorter than the other terminal side surface portion 10b of the illumination light guide 10. Further, in the second embodiment, unlike the first embodiment, a columnar body formed of a prism having a triangular cross section is used as the optical coupling means 21. As shown in FIGS. 4 and 5, the first side of the triangular prism is adjacent to the other terminal side surface 30e of the detour optical path light guide 30, and the second side thereof is the other terminal side surface of the illumination light guide 10. Part 1
The optical coupling means 21 is arranged so as to be adjacent to a part of the rear surface 10c near 0b.

Therefore, as shown in FIGS. 4 and 5, the light beam incident on the core portion 30a from the one side surface portion of the light guide 30 for the bypass optical path repeats multiple reflection between the cladding portions 30b and 30c. , And is efficiently transmitted to the side surface 30e of the other terminal without leaking to the outside. The light beam that has reached the side surface portion 30e of the other terminal is connected to the optical coupling means 20 as indicated by the symbol L2.
Which is incident on and reflected within the optical coupling means 20 of this embodiment, which redirects the light rays. This converted light ray L2 enters from a part 10c of the back surface of the illumination light guide 10 and is introduced into the inside thereof, and repeats multiple reflections toward the one terminal side face portion 10a, and at the same time, the illumination light guide is formed. The emitted light beam La is emitted gradually from the surface of the body 10
(Scattered light) and Lb (diffused light).

(Embodiment 3) FIGS. 1, 6 and 7 show another embodiment of the present invention. FIG. 1 is an exploded perspective view of a third embodiment common to the first embodiment of the present invention. FIG.
It is the expanded side sectional view which cut | disconnected along the AA line of FIG. 1, and abbreviate | omitted a part. FIG. 7 is an enlarged side cross-sectional view in which the vicinity of the optical coupling means 22 arranged at the terminal on the right side is further enlarged and the transmission path L3 of the light beam is entered. As shown in FIGS. 6 and 7, the planar light source device FLS of the third embodiment has a tapered structure in which only one surface of the other end portion of the other end portion of the detour optical path light guide 40 having a parallel plate shape is inclined. This tapered portion is used as the optical coupling means 22. The other end portion of the parallel-plate-shaped detour optical path light guide body 40 having the core portion 40a and the clad portions 40b and 40c formed on the front surface and the back surface thereof is obliquely cut or polished, thereby It is possible to manufacture the detour light guide 40 for the detour optical path, in which only one surface of the terminal portion is inclined to form a tapered structure, and most of the remaining portion is a parallel plate shape. In order to manufacture a large number of parallel-plate-shaped light guides that are tapered by sloping only one surface of this terminal part, a large number of light guide plates are closely stacked, and the stacked stacks are stacked. Temporarily fix the block and keep it at a specified angle with a saw to cut it. After that, it is desirable to polish the conventional polishing agent such as silicon carbide smoothly. When the light guide body is, for example, an acrylic resin plate that is easily melted by heating, a linear heating wire is heated and melted while being pressed and cut in the laminated block while maintaining a predetermined angle. In this case, the cut surface, that is, the tapered surface becomes a smooth smooth surface, and the subsequent polishing step is unnecessary.

As shown in FIGS. 6 and 7, the light beam incident on the core portion 40a from one end side surface portion of the light guide 40 for the bypass optical path repeats multiple reflection between the cladding portions 40b and 40c, The light is efficiently transmitted to the portion immediately before the tapered optical coupling portion 22 near the other terminal portion without leaking to the outside. Next, this transmitted light beam indicated by reference numeral L3 in FIG. 7 is emitted from the tapered portion of the optical coupling portion 22, and as in the second embodiment, a portion of the rear surface near the other terminal side surface portion of the light guide 10 for illumination. Is incident on the inside of the light guide 10 for illumination. The incident light ray L3 is repeatedly reflected multiple times inside the illumination light guide 10 toward one side surface of the terminal, and is gradually emitted from the surface of the illumination light guide 10 little by little, and emitted light La is emitted. (Scattered light) and Lb (diffused light).

(Embodiment 4) FIGS. 1, 8 and 9 show another embodiment of the present invention. FIG. 1 is an exploded perspective view of a third embodiment common to the first embodiment of the present invention. FIG.
It is an expanded side sectional view which cut | disconnected along the AA line of FIG. 1, and abbreviate | omitted a part. FIG. 9 is an enlarged partial side cross-sectional view in which only the vicinity of the optical coupling means 23a and 23b arranged at the terminal on the right side is further enlarged and the light transmission path L4 is entered. The second embodiment is different from the first embodiment in that the optical coupling means 23a,
The structure of 23b is different from that of the arrangement, and the rest is almost the same. Therefore, here, for the sake of simplicity, the description of the portions common to the already described first to third embodiments will be omitted as much as possible.

As shown in FIGS. 8 and 9, the planar light source device FLS according to the fourth embodiment includes a parallel plate-shaped detour optical path light guide member 4.
0 has a tapered structure on the back side of the other end portion, and also has a tapered structure on the surface side of the other end portion of the parallel-plate-shaped light guide 10 for illumination. . Then, a pair of tapered portions in both of them is combined to form optical coupling means 23a and 23b.
A surface that is a flat surface on which the tapered portion of the other end portion of the detour optical path light guide 40 is not formed, and a back surface that is a flat surface that does not form the tapered portion on the other end portion of the illumination light guide 10. Both are arranged adjacent to each other with a light diffuser interposed therebetween. The reflecting mirror 62 indicated by reference numeral 62 in FIG.
The cross section is a V-shape that is rotated 90 degrees counterclockwise. The reflecting mirror 62 is used for the detour optical path light guide 40.
Of the light coupling means 23a helps to reflect the light rays emitted to the right of the tapered portion of the light coupling means 23a to enter the light coupling means 23b, and also reflects the light rays emitted to the outside from the light coupling means 23b to illuminate the light guide body 10 for illumination. Help get back in. One surface of each of the other end portions is formed by obliquely cutting or polishing one surface of each of the other end portions of the parallel plate detour light guide 40 and the parallel plate illumination light guide 10. The light guide 40 for the detour optical path and the light guide 10 for illumination are formed by sloping only at the side to form a tapered structure, and most of the remaining part is a parallel plate.
And can be easily manufactured.

Referring again to FIGS. 8 and 9, the light beam incident on the core portion 40a from one end side surface portion of the light guide 40 for the bypass optical path repeats multiple reflection between the cladding portions 40b and 40c. , And is efficiently transmitted to the portion immediately before the tapered optical coupling portion 23a near the other terminal portion without leaking to the outside. Next, this transmitted light ray (indicated by reference numeral L4 in FIG. 9) is reflected by the tapered surface of the optical coupling portion 23a, the direction of the light ray is converted, and the light ray enters the illumination light guide 10. Next, the incident light ray L4 is reflected by the light coupling portion 2 of the illumination light guide 10.
It is reflected by the taper surface of 3b and changes the light beam direction. Next, the light ray L4 whose light beam direction is changed is transmitted by repeating multiple reflections toward the side surface of one end of the light guide body 10 for illumination, and from the surface of the light guide body 10 for illumination. The light rays La (scattered light rays) and Lb are emitted gradually.
(Diffused rays).

(Embodiments 5 to 9) FIGS. 10 and 1
1, FIG. 12, FIG. 13 and FIG. 14 are diagrams for explaining the fifth embodiment, the sixth embodiment, the seventh embodiment, the eighth embodiment and the ninth embodiment of the present invention, respectively. The other end portions of the optical body, the vicinity thereof, and only various kinds of optical coupling means for optically coupling the both are shown, and the remaining portion such as the one end portion and the central portion of the both are cut out and enlarged. It is a sectional side view. It should be noted that description of the same or equivalent parts using the same reference numerals as those already described in the first to fourth embodiments will be omitted as much as possible to avoid unnecessary duplication.

(Fifth Embodiment) FIG. 10 shows a fifth embodiment of the present invention.
And the other terminal side surface of the illumination light guide 10 and the other terminal side surface of the detour optical path light guide 40 are substantially aligned,
Both of them 10 and 40 are arranged close to each other and parallel to each other. The optical coupling means 24 of the fifth embodiment is a columnar body having a rectangular cross section, straddling the side surfaces of the other terminals 10 and 40, and
It is arranged adjacent to the other terminal side surface of 0, 40. In order to effectively use the light leaked to the outside, a V-shaped deformed and rotated reflecting mirror 63 is arranged over the optical coupling means 24. In this embodiment, the clad is not formed on both sides of the core of the detour light guide 40, and air having a lower refractive index than the core is used as the clad. The light rays incident on the inside of one end side surface portion of the detour light guide 40 are multiplexed between the front surface and the back surface of the detour light guide 40 having a high refractive index due to the presence of air having a low refractive index. Repeating reflections, light guide 4 for detour optical path
0 is efficiently transmitted to the non-side surface portion of the other end. Next, a part of the component of this transmitted light ray (shown by reference numeral L5 in FIG. 10) is emitted from the other side surface of the terminal and has a rectangular cross section.
It is made to enter in 4. The incident light ray L5 is reflected at least once on the surface and the side surface of the rectangular optical coupling means 24, and is incident from the terminal side surface portion of the illumination light guide 10. Further, a light ray that is incident on the optical coupling means 24 and leaks to the outside, which is indicated by, for example, a straight line with an arrow L5, is converted by a reflecting mirror,
The light is again incident on the optical coupling means 24 and is incident on the side surface of the terminal of the illumination light guide 10.

(Sixth Embodiment) FIG. 11 shows a sixth embodiment of the present invention.
And the terminal side surface of the illuminating light guide body 10 and the terminal side surface part of the detour light guide 30 are substantially aligned and extended from both terminal parts to the vicinity of the inside thereof.
Spacers 30 are interposed between the optical coupling means 25 in the form of a parallel plate, which is thinner than the both, so as to be in contact with or in close contact with each other. If no air enters between the surface of the light guide 30 for the bypass optical path and the rear surface of the light guide 10 for illumination that come into contact with or adhere to both surfaces of the spacer type optical coupling means 25, the most efficient light beam is obtained. Communication can be achieved. For this purpose, an optical adhesive can be used as the side surface of the terminal. That is, a non-hardened or semi-hardened curable optical adhesive is applied to at least one of the spacers 10 and 30 to have a predetermined spacer thickness, and the adhesive is interposed between the adhesives 10 and 30. , Cure while applying pressure. An optical adhesive transmitting light beam L6 having an appropriate refractive index as the optical coupling means 25 passes through the spacer type optical coupling means 25,
In order to allow light to effectively enter from the surface near the terminal side surface of the detour optical path light guide 30 to the back surface near the terminal side surface of the illumination light guide 10, the detour optical path light guide 30 and the lighting It is desirable to set the refractive indexes of the light guide 10 and the optical coupling means 25 to be the same or similar. Further, a light-reflecting metal such as aluminum or nickel is vacuum-deposited on the terminal side surface of the detour optical path light guide 30, the terminal side surface of the spacer-type optical coupling means 25, and the terminal side surface of the illumination light guide body 10. Reflective layer 64
Can be formed. The reflection layer 64 efficiently reflects the light ray L6 reaching the terminal side surface of the detour optical path light guide 30 to change its direction, and guides the light ray L6 for illumination via the spacer type optical coupling means 25. It is made incident on the body 10.

In the sixth embodiment, the clad is not formed on both sides of the core of the detour light guide 30, and air having a lower refractive index than the core is used as the clad.
The light rays that have entered the inside from one end side surface portion of the detour light guide 30 are multiplexed between the front surface and the back surface of the detour light guide 30 having a high refractive index due to the presence of air having a low refractive index. By repeating the reflection, the light is efficiently transmitted to the vicinity of the side surface of the other end of the detour light guide 30. Of course, clad portions may be formed on both surfaces of the core portion of the detour optical path light guide 30, but in the portion corresponding to the spacer type optical coupling means 25,
It is desirable to remove the cladding so that the light rays are emitted efficiently. Next, the transmitted light ray L6 is emitted from the surface of the spacer intervening portion in front of the other side surface portion of the terminal, passes through the spacer type optical coupling means 25, and the illumination light guide 10 is provided.
The light is incident on the inside of the light guide 10 for illumination from the back surface of the spacer intervening portion in front of the side surface portion of the terminal. Next, the light ray L6 whose light ray direction is changed is transmitted by repeating multiple reflections toward the side surface of one end of the inside of the light guide 10 for illumination, and from the surface of the light guide 10 for illumination. It is gradually emitted little by little to become emitted light rays La (scattered light rays) and Lb (diffused light rays).

(Seventh Embodiment) FIG. 12 shows a seventh embodiment of the present invention.
And the other terminal side surface of the illumination light guide 10 and the other terminal side surface of the detour optical path light guide 30 are substantially aligned,
Both 10, 30 are arranged close to each other and parallel to each other. Like the illumination light guide 10 and the detour optical path light guide 30, the optical coupling means 26 of the seventh embodiment is composed of a plate-shaped or film-shaped light guide having good light transmittance and a high refractive index. However, the shape of the optical coupling means 26 is not a flat shape, but the light guide 10 for illumination,
Unlike the light guide 30 for the bypass optical path, the light guide has a curved surface, and as shown in FIG. 12, a light guide having a substantially U-shaped cross section is rotated 90 degrees to the left. . The curved optical coupling means 26 fixes the parallel plate-shaped plate-shaped or film-shaped light guide to a fixing device while keeping the curved state by applying a force to both terminals, or it is curved by a method such as heating. You can make it. One end side surface of the curved optical coupling means 26 faces the other terminal side surface portion of the detour optical path light guide 30, and the other end side surface of the optical coupling means 26 faces the other terminal side surface portion of the illumination light guide 10. So that the light coupling means 26 is connected to both light guides 3
It is arranged adjacent to the side surfaces of the other terminals of 0 and 10. It is desirable to provide a reflective layer on both surfaces of the curved optical coupling means 26 like the detour light guide 30 in order to reduce the leakage of light rays.

A light beam entering from one end side surface of the detour optical path light guide 30 to the inside thereof is repeatedly reflected multiple times and is efficiently transmitted to the other terminal side surface part of the detour light guide 30. Next, the transmitted light ray L7 is emitted from the other side surface of the terminal and is incident into the optical coupling means 24 having a curved cross section. The incident light ray L7 is reflected at least once between both surfaces in the curved optical coupling means 24, and is incident from the terminal side surface portion of the illumination light guide 10. Next, the light ray L7 whose direction has been changed is transmitted by repeating multiple reflections toward the side surface of one end of the light guide 10 for illumination, and from the surface of the light guide 10 for illumination. It gradually emerges little by little and becomes an outgoing ray.

(Embodiment 8) FIG. 13 shows an embodiment 8 of the present invention.
And the other terminal side surface of the illumination light guide 10 and the other terminal side surface of the detour optical path light guide 30 are substantially aligned,
Both 10, 30 are arranged close to each other and parallel to each other. As shown in FIG. 13, the optical coupling means 27 of the eighth embodiment is composed of a light guide body having a cross section of a substantially semi-circle and having a high light transmittance and a high refractive index. The flat portion of the semi-circular light coupling means 27 is straddled over the side surface of the other end of the light guide 30 for the bypass optical path and the side surface of the other end of the light guide 10 for illumination, and the light coupling means 26 is connected to both light guides. 30 and 10 are arranged adjacent to the side surface of the other terminal. In the semi-circular portion of the semi-circular optical coupling means 27, it is desirable to provide a reflective layer like the detour optical path light guide 30 in order to reduce leakage of light rays. A light ray that has entered from one end side surface portion of the detour light guide 30 to the inside thereof is repeatedly reflected multiple times and is efficiently transmitted to the other end side surface portion of the detour light guide 30. Next, the transmitted light ray L8 is emitted from the other side surface of the terminal and is incident on the optical coupling means 27 having a semicircular cross section. The incident light ray L8 is reflected at least once in the curved optical coupling means 27 and is incident from the terminal side surface portion of the illumination light guide 10. Next, the light ray L8 whose light ray direction is changed is transmitted by repeating multiple reflections toward the side surface of one end of the inside of the light guide 10 for illumination, and from the surface of the light guide 10 for illumination. It gradually emerges little by little and becomes an outgoing ray.

(Ninth Embodiment) FIG. 14 shows a ninth embodiment of the present invention.
The light guide 10 for illumination is made of a light guide in the form of a parallel plate, and the light guide 50 for the bypass optical path has a side near the other terminal like an umbrella handle or a handle as shown in the figure. The light coupling portion 28 is curved to form the optical coupling portion 28, and the remaining portion has a parallel plate shape.
It is desirable to form a light reflecting layer on both curved surfaces.
The terminal side surface of the optical coupling portion 28 is arranged adjacent to the other end surface portion of the light guide 10 for illumination. The light ray that has entered the inside from one end side surface portion of the detour optical path light guide 50 repeats multiple reflections and is efficiently transmitted to the curved optical coupling portion 28 near the other terminal portion of the detour light path light guide 50. To be done. Next, the transmitted light ray L9 is reflected at least once in the curved light coupling portion 28, and is incident from the terminal side surface portion of the illumination light guide 10. The incident light ray L9 is reflected at least once in the curved light coupling portion 28 and is incident from the terminal side surface portion of the illumination light guide 10. Next, the light ray L9 whose light ray direction is converted is
The light is repeatedly transmitted in the interior of the light guide for illumination 10 toward the side surface of one end thereof, and is gradually emitted from the surface of the light guide for illumination 10 little by little to become an emission light beam. .

FIG. 15 shows the various embodiments described above.
Specific examples of various kinds of incident optical means for entering a light beam from the light source LS to one end side surface portion of the illumination light guide 10 and the detour optical path light guide 30 for entering the light beam are shown. It is a schematic side sectional view explaining. A, B of FIG.
In C, D, and E, the light-incident light guide 10 and the detour optical path light guide 30 are arranged such that the light-incident one-end side surface portions are aligned in almost a line and overlap each other. A linear light source such as a cold cathode tubular fluorescent lamp or a hot cathode tubular fluorescent lamp is used as the light source LS.

The incident optical means shown in FIG. 15A comprises a tubular fluorescent lamp LS and a reflecting mirror 94. The tubular fluorescent lamp LS is provided in the vicinity of a side surface of one end of the light guide 10 for illumination and the light guide 30 for the detour optical path for incident light, and the reflecting mirror 94 is the tubular fluorescent lamp L.
Provided behind S. The tubular fluorescent lamp LS is a general tubular fluorescent lamp in which a phosphor layer b is formed on the entire inner wall of a glass tube a. The light beam emitted from the tubular fluorescent lamp LS is incident on one of the light guides 10 and the light guide 30 on one end side face for light incidence, either directly or after being reflected by the reflecting mirror 94 and aligned.
The incident optical means shown in FIG. 15B has a tubular fluorescent lamp LS, a light guiding body 92 of both of them, and a light guide body 92 having a trapezoidal cross section between the light guiding body 10 and one end side surface of the light guiding body 30. , The emitted light rays are converged and efficiently incident on the side surface of one terminal. The incident optical means shown in FIG. 15C is a tubular fluorescent lamp LS.
In the aperture type tubular fluorescent lamp LS, the phosphor layer b is provided on the inner surface of the glass tube a, and the reflecting mirror 95 made of a metal film having a high reflectance such as aluminum is provided on the glass tube a except the opening C. is there. Because of the reflecting mirror 95, the light beam emitted from the phosphor layer b of the tubular fluorescent lamp LS is emitted only from the opening c. This emitted light beam is directly or reflected by the mirror 95.
Is incident on one of the light guides 10 and the light guide 30 which are aligned by reflecting the light. In the incident optical means shown in FIG. 15D, a tubular fluorescent lamp LS is provided in the vicinity of one end side surface portion of the light guide 10 for illumination, and the prism 9 having a triangular cross section.
8 is provided in the vicinity of a side surface of one end of the light guide 30 for the bypass optical path for incident light, and a reflecting mirror 98 having a shape shown in FIG. 15D that is common to both the tubular fluorescent lamp LS and the prism 98 is provided. One component of the light beam emitted from the tubular fluorescent lamp LS is incident on one end side surface of the illumination light guide 10. The remaining component of the light beam emitted from the tubular fluorescent lamp LS is incident on the prism 98, and after changing the direction of the light beam by 90 degrees in the prism 98, is incident on one side surface portion of one end of the detour light guide 30. To do. The incident optical means shown in FIG. 15E is different from the incident optical means shown in FIG. 15D in that the prism 98 and the tubular fluorescent lamp LS.
The positions of and are reversed. That is, the tubular fluorescent lamp LS is provided in the vicinity of the side surface of one end of the light guide 30 for detour light incidence for incident light, and the prism 98 is provided in the vicinity of the side surface of one end of the light guide 10 for illumination. A reflecting mirror 98 having a shape shown in FIG. 15E, which is common to both the tubular fluorescent lamp LS and the prism 98, is provided. One component of the light emitted from the tubular fluorescent lamp LS is
The light enters the side surface of one end of the light guide 30 for the bypass optical path. The remaining components of the light beam emitted from the tubular fluorescent lamp LS are incident on the prism 98, and after changing the direction of the light beam by 90 degrees in the prism 98, they are incident on one end side surface of the illumination light guide 10. .

The surface light source device of the present invention is a liquid crystal display device,
It is used as a planar light source for passive display devices such as electro-chromic display devices and electrophoretic display devices. Further, the surface light source device of the present invention is, for example, a viewer for observing a photographic film, a thin surface light source for general illumination, and a surface for transmission type illumination used for advertising, advertisement and guidance. It can be used in a wide variety of fields such as a circular light source.

[0048]

In the surface light source device of the present invention, by adding the detour optical path light guide and the optical coupling means to the conventional illumination light guide, the above-mentioned illumination light guide is actually used. Despite the fact that only one light source is provided on one side surface, the same effect is apparently provided by providing the same light source as the light source on the other side surface of the illumination light guide. Therefore, in the planar light source device of the present invention, although the one-light type light guide system (edge light type) is used, the surface brightness is as large as that of the two-light type light guide system and the display brightness is uniform. There is an advantage that a planar light source can be obtained. Further, in the surface light source device of the present invention, the above 2
Unlike the light guide system of the light type, there is an advantage that it is possible to obtain an energy-saving and lightweight planar light source like the one light guide system.

[Brief description of drawings]

FIG. 1 is an exploded perspective view showing a planar light source device FLS according to a first embodiment.

FIG. 2 is an enlarged side sectional view showing an embodiment 1 which is cut along the line AA of FIG. 1 and a part of which is omitted.

3 is an optical coupling means 20 arranged at the terminal on the right side of FIG.
FIG. 6 is an enlarged side sectional view showing Example 1 in which the vicinity of is further enlarged and a transmission path of light rays is entered.

FIG. 4 is an enlarged side sectional view of a second embodiment.

FIG. 5 is an enlarged side cross-sectional view showing a second embodiment in which the vicinity of the optical coupling means 21 is further enlarged and the transmission paths of light rays are entered.

FIG. 6 is an enlarged side sectional view showing a third embodiment.

FIG. 7 is an enlarged side sectional view showing a third embodiment in which the vicinity of the optical coupling means 22 is further enlarged and a transmission path of light rays is entered.

FIG. 8 is an enlarged side sectional view showing a fourth embodiment.

FIG. 9 is an enlarged side sectional view showing an embodiment 4 in which the vicinity of the optical coupling means 23a, 23b is further enlarged and a transmission path of light rays is entered.

FIG. 10 is an enlarged side sectional view showing the vicinity of another optical coupling means 24 according to the fifth embodiment.

FIG. 11 is an enlarged side sectional view showing the vicinity of another optical coupling means 25 according to the sixth embodiment.

FIG. 12 is an enlarged side sectional view showing the vicinity of another optical coupling means 26 according to the seventh embodiment.

FIG. 13 is an enlarged side sectional view showing the vicinity of another optical coupling means 27 according to the eighth embodiment.

FIG. 14 is an enlarged side sectional view showing the vicinity of another optical coupling means according to the ninth embodiment.

FIG. 15 is a schematic side cross-sectional view showing various incident optical means for causing a light beam to be incident from the light source LS to one end side surface portion of the light guide body for illumination 10 and the light guide body for detour optical path 30 for light beam incidence. Is.

[Explanation of symbols]

10 ... Light guide for illumination (Light guide f
or illumination) 10a ... One end of one terminal side part
side surface 10b ... Side portion of other terminal (Another end)
of side surface) 20, 22, 23a, 23a, 24, 25, 26, 2
7, 28, 29 ... Optical coupling means (Light cou
Plumbing means 30, 40, 50, 60, 70 ... Light guide for by-pass (light guide for by-pass)
light way 30a ... cores 30b, 30c ... clad (Clad or Shea)
th) 30d ... One end side of one terminal
side surface) 30e ... Side portion of other terminal (Another end)
of side surface 52 ... Light scatterer (Light scatterin)
g member) 53 ... Light diffuser (Light diffusible)
e member) LS ... Light source (Light source) FLS ... Planar light source device (Flat type li)
ght source device) L1, L2, L3, L4, L5, L6, L7, L8, L
9 ... Light transmission path
(ion light passage way)

Claims (6)

[Claims] 1. A light guide for illumination comprising (a) a plate-like or film-like light guide material having a high refractive index and excellent in light transmittance,
(B) Stacked with a plate-like or film-like light guide for a bypass optical path, which is made of a light guide material having a high refractive index with excellent light transmittance and provided with light reflecting layers on both front and back surfaces. Then
(C) The illumination light guide and the detour optical path light guide are lighted in the vicinity of a terminal portion of the illumination light guide and the detour optical path light guide opposite to the light introduction terminal. A planar light source device characterized in that an optical coupling means for coupling is arranged. 2. The planar light source device according to claim 1, wherein the light coupling means is selected from optical elements having a prism-shaped, trapezoidal, tapered, rectangular, or U-shaped cross section. The planar light source device. 3. The planar light source device according to claim 1, wherein one end of the detour light guide is extended, and the extended portion is bent into a substantially U-shape to form the optical coupling means. A planar light source device characterized by: 4. The planar light source device according to claim 1, wherein one side surface of the light guide for illumination and one side surface of the light guide for detour light path are aligned, and a linear or dot shape common to the aligned surfaces. 2. A planar light source device, characterized in that the light source of FIG. 5. The planar light source device according to claim 1, wherein the light reflecting layer includes a light reflecting material or is made of a light transmitting material having a lower refractive index than that of the light guide for the bypass optical path. A planar light source device comprising a light reflection layer. 6. (a) A light guide for illumination made of a plate-shaped or film-shaped light guide material having a high refractive index and excellent in light transmittance,
(B) Stacked with a plate-like or film-like light guide for a bypass optical path, which is made of a light guide material having a high refractive index with excellent light transmittance and provided with light reflecting layers on both front and back surfaces. Then
(C) The illumination light guide and the detour optical path light guide are lighted in the vicinity of a terminal portion of the illumination light guide and the detour optical path light guide opposite to the light introduction terminal. A passive display device with a planar light source, characterized in that a planar light source device having an optical coupling means for coupling is disposed on the back surface of a passive display device such as a liquid crystal display device.