JP5838049B2 - Light guide plate and surface light source device - Google Patents

Description

  The present invention relates to a light guide plate used for a liquid crystal display or the like, and a surface light source device including the light guide plate.

  Liquid crystal display devices used in personal computers, computer monitors, video cameras, liquid crystal televisions (LCD-TVs), mobile communication terminals, etc. are light-receiving display devices that do not have their own light-emitting ability and are irradiated from the outside. An image is displayed by selectively transmitting illumination light. For this reason, a surface light source device is installed on the back surface of the liquid crystal display device as a backlight serving as a light source.

  In a liquid crystal display device, light emitted from a surface light source device passes through a liquid crystal cell in which a liquid crystal layer is disposed between a pair of polarizing plates whose transmission axes are substantially orthogonal, and this transmitted light is electrically turned on and off. This realizes image display. As a polarizing plate, usually, a polyvinyl alcohol film colored with iodine and uniaxially stretched is used as a polarizer, a protective film such as a triacetyl cellulose film, a coating layer made of an acrylic resin or the like on one or both sides of the polarizer, Alternatively, an absorption type polarizing plate in which a retardation film such as norbornene or polycarbonate is disposed is used.

  However, since such an absorption type polarizing plate has a characteristic of transmitting only the light in the transmission axis direction of the polarizing plate and absorbing the light of the remaining components, in principle, the light use efficiency (light transmittance) is high. In view of the fact that the reflectance of the inner surface is 4%, the maximum limit is 46%. Therefore, effective use of the backlight and improvement in luminance are propositions of the liquid crystal display device in order to achieve low power consumption.

  As one of the methods for solving this, a reflection type polarizing plate using optical reflection interference characteristics is known. The reflective polarizing plate reflects specific polarized light and transmits polarized light having the opposite property. Specifically, the light that has passed through the reflective polarizing plate is aligned so that it passes through the polarizing plate as linearly polarized light, so that only the polarized light in the transmission axis direction is transmitted and the polarized light that has been absorbed by the absorbing polarizing plate Reflect and reuse. Thereby, the utilization efficiency of the light emitted from the backlight can be improved.

  An example of the reflective polarizing plate is a dual brightness enhancement film (DBEF) manufactured by Sumitomo 3M Limited, which is composed of an alternately laminated film of a refractive index isotropic layer and a refractive index anisotropic layer. However, DBEF has a problem that the manufacturing cost is high because several hundreds of polymer films need to be laminated as a whole in order to secure polarization characteristics over the visible light region, and strict control is required.

  As a method for improving light utilization efficiency and polarization separation ability at a lower cost, a technique using a polarization-sensitive scattering element (PSSE) has attracted attention. For example, Patent Document 1 discloses a technique in which a polarized light component in the direction orthogonal to the transmission axis is scattered backward by PSSE to separate the polarized light, and the backward scattered component is reversed by a λ / 4 plate and reused. Has been.

  Patent Document 2 discloses a reflective polarizing plate using a birefringent material made of a fiber having birefringence as PSSE. In this method, a layer (polarizing layer A) in which the refractive index in the cross-sectional direction of the birefringent body (ordinary ray refractive index) and the refractive index of the supporting medium are matched, and the refractive index in the longitudinal direction of the birefringent body (ordinary ray). A layer (polarizing layer B) in which the refractive index of the supporting medium and the refractive index of the support medium are matched is laminated so that the arrangement directions of the birefringents intersect each other, thereby separating polarized light from obliquely incident light and diffused light. Improve performance.

  Further, in Patent Document 3, by integrating an isotropic resin layer in which a birefringent fiber as PSSE is embedded with a light guide plate, only one polarized light is scattered and emitted to the outside. There is also disclosed a method for improving.

  On the other hand, in order to reduce the power consumption of the surface light source device, a backlight using an LED having a long life and a power saving effect as a light source is becoming mainstream.

Japanese Patent Laid-Open No. 11-502036 JP 2009-0478802 A JP 2006-517720 A

  However, in the methods described in Patent Documents 1 to 3, when a light source such as an LED is used, there is a problem that light from the LED light source appears linearly and becomes uneven, resulting in uneven brightness in a liquid crystal display device or the like. In particular, in these documents, although the polarization separation efficiency is improved by PSSE, the direction of light scattered by PSSE is biased only in the direction perpendicular to PSSE such as a fiber. Unevenness occurs.

  Accordingly, an object of the present invention is to provide means for suppressing unevenness in luminance even when a discontinuous light source is disposed on the end face of a light guide plate while improving polarization separation efficiency.

  The present inventors have intensively studied to solve the above problems. As a result, two layers (polarization separation layer and light homogenization layer) in which the refractive index and arrangement direction of the fiber and the refractive index of the holding medium holding the fiber are controlled are laminated on the light guide layer. As a result, the present invention has been completed.

That is, according to one embodiment of the present invention, a light guide layer that introduces light from an incident surface, which is a side surface, and a light guide layer that is stacked on the light guide layer and transmits desired polarized light in the light guide layer. A light guide comprising: a polarization separation layer derived from a light emitting surface which is one main surface of the layer; and a light homogenization layer laminated on the light guide layer. The polarization separation layer includes a plurality of first fibers having birefringence extending in parallel to the incident surface and arranged perpendicular to the incident surface, and holding the first fiber. Including an isotropic first holding medium having a refractive index that matches the light refractive index (no ₁ ) or extraordinary light refractive index (ne ₁ ), wherein the light homogenizing layer extends perpendicularly to the incident surface and A plurality of birefringent second fibers arranged parallel to the incident surface, and a refractive index different from at least one of ordinary ray refractive index (no ₂ ) and extraordinary ray refractive index (ne ₂ ) of the second fiber. An isotropic second holding medium is included.

  According to the present invention, the light is scattered and diffused at various angles in the in-plane direction by the light homogenizing layer in which the second fibers extending perpendicular to the incident surface are arranged, so that a discontinuous light source is used. Even in this case, uniform brightness can be obtained. Furthermore, only a desired polarization component can be selectively extracted with high polarization separation efficiency by the polarization separation layer in which the first fibers extending parallel to the incident surface are arranged.

It is a perspective view which shows schematic structure of the surface light source device which is one Embodiment of this invention. It is drawing for demonstrating the relationship between one fiber and a refractive index. It is drawing for demonstrating the relationship between one fiber and a refractive index. It is a figure which shows the modification of the cross-sectional shape of a fiber. 4A is a right side view of the surface light source device of FIG. 1, and FIG. 4B is an enlarged view of FIG. 4A showing a state of propagation of the s-polarized component incident on the polarization separation layer 40. FIG. 4C is an enlarged view of FIG. 4A showing a state of propagation of the p-polarized component incident on the polarization separation layer 40. It is a bottom view of the surface light source device of FIG. It is drawing which shows schematic structure of the surface light source device of 2nd Embodiment. It is drawing which shows schematic structure of the surface light source device of 3rd Embodiment. It is drawing which shows schematic structure of the surface light source device of 4th Embodiment. It is drawing which shows schematic structure of the surface light source device which is 5th Embodiment. It is drawing which shows schematic structure of the surface light source device which is 6th Embodiment. It is drawing which shows schematic structure of the surface light source device which is 7th Embodiment. 2 is a cross section of a polarization separation layer formed in Example 1. It is drawing which shows the two-dimensional luminance distribution of the light inject | emitted from the upper surface (light emission surface) of the light-guide plate of the surface light source device produced in Example 2. FIG. It is drawing which shows the two-dimensional luminance distribution of the light inject | emitted from the upper surface (light emission surface) of the light-guide plate of the surface light source device produced in the comparative example 1. FIG.

(First embodiment)
Hereinafter, embodiments of the present invention will be described with reference to the accompanying drawings. In addition, this invention is not restrict | limited only to the following embodiment. The dimensional ratios in the drawings are exaggerated for convenience of explanation, and may differ from actual ratios.

  In the present specification, the term “stacking” may include not only the case of directly stacking but also the case of stacking indirectly through another structure therebetween. In addition, when a member such as a layer, region, or plate is "on top" or "on top" of another member, not only when it is "directly above" another member but also another member in the middle Including some cases. Similarly, when a member such as a layer, region, or plate is “under” or “below” another member, not only when it is “below” another member, but also another member in the middle Including the case where there is.

According to one aspect of the present invention, a light guide layer that introduces light emitted from a light source into an inside from an incident surface that is a side surface; birefringence extending parallel to the incident surface and arranged perpendicular to the incident surface A plurality of first fibers having an optical property and an isotropic property that holds the first fiber and has a refractive index that matches the ordinary ray refractive index (no ₁ ) or extraordinary ray refractive index (ne ₁ ) of the first fiber A polarization separation layer that is laminated on the light guide layer and derives desired polarized light from a light emitting surface that is one main surface of the light guide layer; A plurality of birefringent second fibers extending perpendicular to the incident surface and arranged parallel to the incident surface, and an ordinary ray refractive index (no ₂ ) and an extraordinary ray refractive index (ne ₂ ) of the second fiber. ) Isotropic with a refractive index different from at least one of It includes a holding medium, and the light homogenizing layer is laminated on the light guide layer; comprises a light guide plate is provided.

  First, a basic configuration of a surface light source device to which the light guide plate of this embodiment can be applied will be described with reference to the drawings.

  FIG. 1 is a perspective view showing a schematic configuration of a surface light source device according to an embodiment of the present invention, FIGS. 2A and 2B are drawings for explaining the relationship between one fiber and a refractive index, and FIG. 3 is a fiber. It is a figure which shows the modification of a cross-sectional shape. As shown in FIG. 1, the surface light source device 1 is configured as an edge light type surface light source device, and emits a desired polarization component among light emitted from a light source unit 10 and a light source 11 of the light source unit 10. 20. In the present embodiment, the surface light source device 1 emits light toward the upper side of the paper surface. Although not shown, when the surface light source device 1 is applied to a liquid crystal display, a liquid crystal unit is disposed on the surface light emitting side.

  The light source unit 10 generates light to be supplied to the surface light source device 1 and is arranged on the side of the light guide plate 20 and is configured by intermittently arranging a plurality of light sources 11. In the form shown in FIG. 1, the light sources 11 are arranged one-dimensionally to constitute the light source unit 10, but the light sources may be arranged two-dimensionally. The light source 11 can be configured by, for example, a dot-like LED (light emitting diode).

  The light guide plate 20 has a substantially rectangular parallelepiped plate shape, and includes a light guide layer 30, a polarization separation layer 40 laminated on the light guide layer 30, a light homogenization layer 50 laminated on the light guide layer 30, and a light guide layer. A phase difference plate 60 attached to the optical layer 30 and a reflection plate 70 are provided.

  The light guide layer 30 introduces the light irradiated from the light source 11 into the inside from the incident surface 30a which is a side surface. The introduced light propagates in the light guide layer 30 and only a predetermined polarization component is selectively extracted from the polarization separation layer 40.

  The light guide layer 30 is made of a transparent material that can transmit incident light, and is made of, for example, an optically isotropic material such as polymethyl methacrylate (PMMA) or polycarbonate (PC).

  The polarization separation layer 40 is laminated on the light guide layer 30, derives desired polarized light out of the light in the light guide layer 30 from the light emitting surface 30 b that is one main surface of the light guide layer 20, and is orthogonal to the polarized light. Reflects polarized light. The position of the polarization separation layer is not particularly limited, but is preferably located in the outermost layer.

  The polarization separation layer 40 includes a first fiber 41 and a first holding medium 42 that holds the first fiber 41.

  The first fiber 41 is formed in a shape that extends parallel to the incident surface 30 a of the light guide layer 30. In this specification, “extending parallel to the incident surface” means not only when the extending direction (longitudinal direction) of the first fiber 41 completely coincides with the direction parallel to the incident surface 30a, but also parallel to the incident surface 30a. This includes the case where the extending direction (longitudinal direction) of the first fiber 41 is inclined by ± 45 ° with respect to the other direction.

  In the polarization separation layer 40, a plurality of first fibers 41 are provided and arranged in a direction perpendicular to the incident surface 30 a of the light guide layer 30.

  The light homogenization layer 50 is laminated on the light guide layer 30, and diffuses the light in the light guide layer 30 in the in-plane direction, that is, the direction orthogonal to the light propagation direction a, thereby homogenizing the light direction. To do.

  The light homogenizing layer 50 includes a second fiber 51 and a second holding medium 52 that holds the second fiber 51.

  The second fiber 51 is formed in a shape extending perpendicularly to the incident surface 30 a of the light guide layer 30. In this specification, “extending perpendicular to the incident surface” means not only when the extending direction (longitudinal direction) of the second fiber 51 completely coincides with the direction perpendicular to the incident surface 30a, but also perpendicular to the incident surface 30a. This includes the case where the extending direction (longitudinal direction) of the second fiber 51 is inclined by ± 45 ° with respect to any direction.

  In the light homogenization layer 50, a plurality of second fibers 51 are provided and are arranged in a direction parallel to the incident surface 30 a of the light guide layer 30. That is, the second fibers 51 are arranged in a direction orthogonal to the arrangement direction of the first fibers 41 in the polarization separation layer 40.

  The fibers (41, 51) included in the polarization separation layer 40 and the light homogenization layer 50 have a large extraordinary ray refractive index (ne), which is a refractive index in the longitudinal direction, and an ordinary ray refractive index, which is a refractive index in the cross-sectional direction ( no) has a small birefringence. Here, with reference to FIG. 2A and FIG. 2B, the relationship between one fiber (41, 51) and a refractive index is demonstrated. As shown in FIGS. 2A and 2B, the fibers (41, 51) have a refractive index in the cross-sectional direction (ordinary ray refractive index, no) smaller than a refractive index in the longitudinal direction (extraordinary ray refractive index, ne).

  A variety of materials having birefringence can be used as the fibers (41, 51), but they are manufactured by stretching a polymer because of excellent stability and durability of the cross-sectional shape and easy control of orientation. It is preferable that the polymer fiber be made.

  Specific polymer fiber materials include polyolefin fibers such as polyethylene (PE), polytetrafluoroethylene (PTFE), and polypropylene (PP), polyvinylidene fluoride (PVdF), polyvinyl fluoride (PVF), and polyvinyl chloride. (PVC), polyvinyl fibers such as polyvinyl alcohol (PVA), acrylic fibers such as polyacrylonitrile (PAN), nylon 6 (N6), nylon 6, 6 (N66), nylon 4, 6 (N46), nylon 6 , 10 (N610), etc., poly (m-phenylene isophthalamide) (PMPIA), poly (p-phenylene terephthalamide) (PMPTA) and other aromatic polyamide fibers (aramid fiber), polyethylene terephthalate (PET), Li ethylene naphthalate (PEN), polyester fibers such as polyethylene -ε- caprolactone, silk, wool, animal fibers such as spider silk, cupro, cellulosic plant fibers, such as rayon fibers, and the like. The types of the first fiber and the second fiber are selected so as to satisfy the relationship of refractive index described later, and the same type may be used, or different types may be used. In some cases, a plurality of types of fibers may be used in the polarization separation layer 40 and the light homogenization layer 50.

  Preferably, a polymer fiber having a large difference (Δn) between the extraordinary ray refractive index (ne) and the ordinary ray refractive index (no) is preferably used. As the refractive index difference is larger, the polarization separation efficiency of the polarization separation layer 40 and the light diffusion efficiency of the light homogenization layer 50 can be improved. Specifically, Δn is 0.03 or more, preferably 0.05 or more, more preferably 0.1 or more.

  The ordinary ray refractive index (no) and extraordinary ray refractive index (ne) of these polymer fibers adjust the tensile speed and tensile rate when the polymer is drawn, the material of the polymer, the thickness (diameter) and density of the fiber. Is controlled.

  Table 1 shows the ordinary ray refractive index (no) and extraordinary ray refractive index (ne) of typical stretched polymer fibers. The refractive indexes (no, ne) in Table 1 are obtained by immersing the fiber in liquids of various refractive indexes, and using a polarizing microscope to adjust the liquid in which the fiber line becomes assimilated with the liquid and becomes invisible. The refractive index of the fiber was measured by using a digital Abbe refractometer DR-A1 manufactured by Atago Co., Ltd. (wavelength 589 nm). No and ne can be measured by measuring each of the transmission axes of polarized light.

  The thickness of the fibers (41, 51) is not particularly limited, and is controlled in accordance with the size of the display to be applied and to obtain a desired refractive index. For example, the thickness is 1 to 200 μm. The arrangement interval of the fibers (41, 51) is not particularly limited, and may be appropriately selected according to the size of the display so as to be smaller than the pixel pitch of the applied liquid crystal display device. The arrangement interval of the fibers (41, 51) may be regular or irregular. The fibers (41, 51) may have a single layer structure or a multilayer structure.

  Preferably, the first fibers are arranged from coarse to dense as the distance from the light source 11 increases. That is, it is preferable that the density of the first fibers 41 in the polarization separation layer 40 increases continuously or stepwise as the distance from the light source 11 increases. Since the amount of light decreases as the distance from the light source 11 increases, the first fibers 41 are densely arranged in a region away from the light source 11 with a small amount of light, and the first fibers 41 are roughly arranged in the vicinity of the light source 11 having a large amount of light. The uniform light can be extracted from the entire upper surface (light emitting surface) of the light guide plate.

  The length of the fibers (41, 51) may be determined according to the size of the polarization separation layer 40 or the light homogenization layer 50 in which the fibers (41, 51) are arranged. However, the length of the fibers (41, 51) does not have to be continuous over the length direction of the polarization separation layer 40 or the light homogenization layer 50. That is, a part of the fibers (41, 51) may be divided and discontinuous. Furthermore, there may be a portion where some of the fibers (41, 51) overlap.

  The fibers (41, 51) may be circular in cross section as shown in FIG. 1, but need not be circular and may have other cross sectional shapes. As other cross-sectional shapes, for example, regular and irregular polygons such as triangles, rectangles and hexagons, or cross-sectional shapes combining curved and straight sides can be used as shown in FIG. . In the present specification, the “polygon” includes not only a figure in which each side is a straight line but also a figure in which each side has a slight curvilinearity. That is, the polygonal cross section of the polymer fiber (41, 51) may have some curvilinearity at each side or apex, and such a cross sectional shape is also included in the cross sectional shape that is a “polygon”. And

  Preferably, the cross-sectional shape of the first fiber 41 is a polygon. In the polarization separation layer 40, as described later, only the polarization component of specific light is selectively scattered by the first fiber 41 and extracted from the light emitting surface 30b. In this case, it is often scattered in the waveguide direction. , Scattered light in a direction perpendicular to the light traveling direction is reduced. When the light guide plate of the present invention is used as a surface light source and as a backlight of a liquid crystal display, the cross-sectional shape of the first fiber 41 is made polygonal, so that the scattering angle becomes various and the direction perpendicular to the waveguide direction is varied. By increasing the scattered light, light having a more uniform angular distribution can be obtained.

  The shape of the outer peripheral surface of the fiber (41, 51) is not particularly limited. However, the surface roughness (Rz) of the outer peripheral surface of the first fiber is preferably 0.1 to 10 μm. In such a case, the scattering angle of light by the first fiber varies, and light having a more uniform angular distribution can be obtained. “Surface roughness (Rz)” means the maximum height of a smooth surface defined by JIS B 0601-2001.

  The holding medium (42, 52) serves to hold the fiber (41, 51) and is made of a material having optical isotropy. Therefore, the material of the holding medium (42, 52) is not particularly limited as long as it shows good adhesion to the fiber (41, 51) and has optical transparency. For example, a curable resin that undergoes polymerization / crosslinking reaction by heat or radiation can be used. Specifically, UV curable resin made of a compound having acryloyl group, methacryloyl group, vinyl group, allyl group, styryl group, thiol group, epoxy group, vinyl ether group, oxetanyl group; silicone resin, allyl ester, acrylic type And thermosetting resins composed of resins, epoxy resins, polyimides, urethane resins, and the like; and mixtures of two or more of these. Further, acrylic resins such as poly (methyl methacrylate) (PMMA), polyolefin resins such as polyethylene (PE) and polypropylene (PP) cycloolefin polymer (COP), polyester resins such as polyethylene terephthalate (PET), polyphenylene oxide (PPO) Polyethers such as polyvinyl alcohol, polyvinyl alcohol (PVA), polystyrene, polycarbonate, polyurethane, polyamide, polyimide, epoxy resin, copolymers using two or more monomers constituting these, and polymer blends thereof May be used. By mixing a plurality of resins, the refractive index (nm) of the holding medium (42, 52) can be controlled to a desired value.

The polarization separation layer 40 is configured such that the refractive index (nm ₁ ) of the first holding medium 42 matches the ordinary ray refractive index (no ₁ ) or extraordinary ray refractive index (ne ₁ ) of the first fiber 41. The In the following description, it is assumed that the refractive index (nm ₁ ) of the first holding medium 42 matches the ordinary ray refractive index (no ₁ ) of the first fiber 41.

In this specification, “refractive index n _A matches refractive index n _B ” means that n _A and n _B match with an accuracy of two decimal places or more, more preferably 3 digits or more. That coincide with each other, and more preferably, n _A = n _B ± 0.003.

In the light homogenization layer 50, the refractive index (nm ₂ ) of the second holding medium 52 is different from at least one of the ordinary ray refractive index (no ₂ ) and the extraordinary ray refractive index (ne ₂ ) of the second fiber. Configured. In the following description, it is assumed that the refractive index nm ₂ of the second holding medium 52 is different from both the ordinary ray refractive index no ₂ and the extraordinary ray refractive index ne _{2 of} the second fiber 51.

  The phase difference plate 60 is attached to the side surface opposite to the incident surface 30 a of the light guide layer 30, and converts the polarization direction of light propagating through the light guide layer 30. In the present embodiment, the phase difference plate 60 is, for example, a λ / 4 plate that shifts the phase by λ / 4. In the present invention, the phase difference plate is not essential, and a form not including the phase difference plate can be preferably used.

  In order to prevent light in the light guide layer 30 from leaking from other than the light emitting surface 30b, the reflecting plate 70 is laminated on the side surface other than the incident surface 30a of the light guide layer 30 and the main surface opposite to the light emitting surface 30b. Is done. In the present embodiment, as shown in the drawing, they are laminated and attached to the phase difference plate 60 and the light homogenization layer 50. Although not shown, in the present embodiment, the reflecting plate 70 is also provided on two side surfaces other than the incident surface 30a of the light guide layer 30 and the surface opposite to the incident surface 30a. Moreover, although not shown in figure, the reflecting plate 70 may be provided between the several light sources 11 or up and down.

  Next, the principle of extracting light from the light source as surface light emission in the surface light source device 1 will be described.

  4A is a right side view of the surface light source device of FIG. 1, and FIG. 4B is an enlarged view of FIG. 4A showing a state of propagation of the s-polarized component incident on the polarization separation layer 40. FIG. 4C is an enlarged view of FIG. 4A showing a state of propagation of the p-polarized component incident on the polarization separation layer 40. As shown in FIG. 4A, light is incident from the light source 11 to the incident surface 30 a of the light guide layer 30. The incident light propagates through the light guide layer 30 while repeating total internal reflection at the interfaces of the polarization separation layer 40, the light homogenization layer 50, and the phase difference plate 60, as indicated by the alternate long and short dashed lines. . The light is also reflected by the reflection plate 70 attached to the outside of the phase difference plate 60, the lower part of the light homogenization layer 50, and the side surface of the light guide layer 30, so that light is not leaked from other than the light emitting surface 30b side. Propagation continues in the optical layer 30.

  The light generated by the light source 11 is natural light, and light of various polarization components is mixed. In the following, in FIG. 4, the polarization component that vibrates in the same plane as the paper surface indicated by the one-dot chain line and the black circle is referred to as the p-polarization component, and the polarization component that vibrates in the plane perpendicular to the paper surface indicated by the two-dot chain line and the arrow. Is called an s-polarized component. In the present embodiment, the polarization separation layer 40 selectively extracts the s-polarized component from the light emitting surface 30b side.

The polarization separation layer 40 includes the first fiber 41 as described above. As shown in FIG. 2A, the first fiber 41 has an extraordinary ray refractive index (ne ₁ ) in the longitudinal direction and an ordinary ray refractive index (no ₁ ) in the cross-sectional direction. Since the s-polarized component vibrates in a plane parallel to the cross section of the first fiber 41 cut in the longitudinal direction, the s-polarized component can be influenced by the extraordinary ray refractive index (ne ₁ ) in the longitudinal direction of the first fiber 41, but in the cross-sectional direction. Is not affected by the ordinary ray refractive index (no ₁ ). Conversely, the p-polarized component oscillates in a plane parallel to the cross section of the first fiber 41, so that it can be affected by the ordinary ray refractive index (no ₁ ) in the cross section direction of the first fiber 41, but is abnormal in the longitudinal direction. It is not affected by the light refractive index (ne ₁ ).

Here, the first holding medium 42 holding the first fiber 41 is formed so that the refractive index (nm ₁ ) matches the ordinary ray refractive index (no ₁ ) of the first fiber 41. Therefore, when light is incident on the first fiber 41 from the first holding medium 42 or on the first holding medium 42 from the first fiber 41, a material having the same refractive index is propagated for the p-polarized component. become. For this reason, the p-polarized light component travels straight without affecting the ordinary ray refractive index (no ₁ ). In other words, the p-polarized component of the light is the same as the first fiber 41 is not present in the first holding medium 42. Therefore, the p-polarized component indicated by the two-dot chain line in FIG. 4 is not refracted by the first fiber 41, and as a result, is reflected according to the internal total reflection condition of the first holding medium.

On the other hand, the first holding medium 42 is formed so that the refractive index (nm ₁ ) is different from the extraordinary ray refractive index ne _{1 of} the first fiber 41. Accordingly, when light is incident on the first fiber 41 from the first holding medium 42 or on the first holding medium 42 from the first fiber 41, materials having different refractive indexes are propagated for the s-polarized component. become. For this reason, the s-polarized component of light is refracted and reflected under the influence of the extraordinary ray refractive index (ne ₁ ). Therefore, the s-polarized component indicated by the one-dot chain line in FIG. 4 is refracted or reflected by the first fiber 41, and partly deviates from the internal total reflection condition of the first holding medium 42 and enters the interface at an acute angle. 1 It is taken out from the holding medium 42. In this way, by laminating the polarization separation layer 40 on the light guide layer 30, only the s-polarized component can be selectively scattered and extracted from the light emitting surface 30b side. As a result, only the polarization component necessary for the liquid crystal unit can be selectively extracted.

In the above description, the refractive index (nm ₁ ) of the first holding medium 42 matches the ordinary ray refractive index (no ₁ ) of the first fiber 41 and is different from the extraordinary ray refractive index (ne ₁ ). The refractive index (nm ₁ ) of the first holding medium 42 may be the same as the extraordinary ray refractive index (ne ₁ ) of the first fiber 41 and the ordinary ray refractive index (no ₁ ). In this case, only the p-polarized component can be selectively scattered and extracted from the light emitting surface 30b side. However, since the s-polarized component that does not vibrate in the same plane as the light guiding direction is superior to the p-polarized component that vibrates in the same plane as the light guiding direction, the first holding medium It is preferable that the refractive index (nm ₁ ) of 42 coincides with the ordinary ray refractive index (no ₁ ) of the first fiber 41.

  Next, the principle of diffusing the light in the light guide layer 30 in the in-plane direction by the light homogenizing layer 50 will be described. FIG. 5 is a bottom view of the surface light source device of FIG.

  As shown in FIG. 5, since the LED that is the light source 11 emits point light, the amount of light between the adjacent light sources 11 is reduced, and a dark portion is likely to occur in the inter-light source region 12 near the light source 11. In the present embodiment, the light propagating in the light guide layer 30 is scattered in the in-plane direction by the light homogenization layer 50, thereby homogenizing the direction distribution of the light in the light guide layer 30.

The light homogenization layer 50 includes the second fiber 51 as described above, and the second fiber 51 has an extraordinary ray refractive index (ne ₂ ) in the longitudinal direction and an ordinary ray refractive index (no ₂ ) in the cross-sectional direction. Have. The second fiber 51 is arranged such that its longitudinal direction coincides with the light guiding direction. For this reason, the light incident on the second fiber is affected by the ordinary ray refractive index (no ₁ ) and the effective extraordinary ray refractive index (ne 2 — _eff ).

Here, as shown in FIG. 2B, in the light homogenization layer, when the light guided in the longitudinal direction of the second fiber 51 enters the second fiber 51 at an incident angle θ, the effective anomaly that the second fiber 51 has. The light refractive index ne _{2_eff} is represented by the following formula (A).

In the above formula, no ₂ is the ordinary ray refractive index of the second fiber, ne ₂ is the extraordinary ray refractive index of the second fiber, and θ is the incident angle of light to the second fiber (longitudinal direction).

Since the p-polarized component vibrates in a plane parallel to the cross section of the second fiber 51 cut in the longitudinal direction, the p-polarized component can be affected by the effective extraordinary ray refractive index (ne _{2_eff} ) of the second fiber 51 in the longitudinal direction. It is not affected by the ordinary refractive index (no ₂ ) of the direction. Conversely, since the s-polarized component vibrates in a plane parallel to the cross section of the second fiber 51, it can be affected by the ordinary ray refractive index (no ₂ ) in the cross-sectional direction of the second fiber 51, but the effective in the longitudinal direction. It is not affected by the extraordinary ray refractive index (ne _{2_eff} ).

That is, when light is incident on the second fiber 51 from the second holding medium 52 or on the second holding medium 52 from the second fiber 51, the p-polarized component is affected by the effective extraordinary ray refractive index (ne _{2_eff} ). The s-polarized component is refracted and reflected under the influence of ordinary ray refractive index (no ₂ ). At this time, in the light homogenization layer 50, since the second fiber 51 is arranged so that the longitudinal direction of the second fiber 51 is parallel to the waveguide direction, the second fiber 51 and the second holding member into which light enters. The interface with the medium 52 is not orthogonal to the waveguide direction, and the angle distribution in the in-plane direction of light changes when the p-polarized component or the s-polarized component is refracted / reflected at the interface. That is, light is angled to the left and right of the waveguide direction. Thereby, the light propagating through the light guide layer 30 is scattered and diffused at various angles, and the light direction distribution can be homogenized.

  In the light homogenization layer, light is refracted and spread only in the left-right direction, and the angle in the vertical direction does not change. Therefore, the light homogenization layer does not satisfy the total reflection condition for both p and s polarized light. In other words, the light homogenization layer functions only to spread light left and right and eliminate unevenness of the LED, and the polarization separation layer changes the vertical refraction angle of only s-polarized light, so that only desired single polarized light is guided. Both taking out from the light plate and improving the light unevenness of the LED are compatible.

In order to exhibit the light homogenizing function, the refractive index (nm ₂ ) of the second holding medium 52 should be different from the ordinary ray refractive index (no ₂ ) and extraordinary ray refractive index (ne ₂ ) of the second fiber 51. That's fine.

However, the light homogenizing layer 50 preferably acts more strongly as an s-polarized homogenizing layer. From this point of view, the difference in refractive index between no ₂ and nm ₂ is preferably 0.03 or more, more preferably 0.05 or more, and still more preferably 0.1 or more.

Further, in order to scatter and diffuse both the s-polarized component and the p-polarized component in a balanced manner, the ordinary ray refractive index (no ₂ ) and extraordinary ray refractive index (ne ₂ ) of the second fiber, and the refraction of the second holding medium. The rate (nm ₂ ) preferably satisfies the following formula (1).

More preferably, the refractive index (nm ₂ ) of the second holding medium is desirably smaller than the effective extraordinary ray refractive index (ne _{2_eff} ) of the second fiber.

That is, it is preferable that the refractive index (nm ₂ ) of the second holding medium satisfies the following formula (3). In such a case, since the refractive index (nm ₂ ) of the second holding medium is smaller than the effective extraordinary ray refractive index (ne _{2_eff} ) of the second fiber, it is possible to scatter and diffuse the p-polarized component. It is. Therefore, it can act as a light uniformizing layer that effectively diffuses and scatters both p-polarized light and s-polarized light.

In the above formula, no ₂ is the ordinary ray refractive index of the second fiber, ne ₂ is the extraordinary ray refractive index of the second fiber, and nl is the refractive index of the light guide layer.

  Here, the above formula (3) is derived from the above formula (2), the above formula (A), and the following formulas (B) to (F).

In the above formula, no ₂ is the ordinary ray refractive index of the second fiber, ne ₂ is the extraordinary ray refractive index of the second fiber, ni is the refractive index of the external medium of the light guide plate, and nl is the light guide layer. the refractive index of, theta _i is the incident angle of light incident on the light guide layer, theta _i is the incident angle of light incident on the light guide layer, theta _l is refraction of light incident on the light guide layer Is an angle, θ _in is an incident angle of light incident on the light homogenizing layer, and θ _out is a refraction angle of light incident on the light homogenizing layer. Usually, the light guide plate is disposed in the air, and the refractive index ni of the external medium of the light guide plate is equal to the refractive index of air (= 1) and is expressed by (B) above.

In the above formula (A), when nm ₂ = ne _{2_eff} and formula transformation is performed using the above formulas (B) to (E), the above formula (F) is derived. And the said Formula (3) is derived | led-out from the said Formula (2) and the said Formula (F). When nm ₂ = ne ₂ — _eff, the incident light component (θ _{i ≈π} / 2) having the maximum angle among the p-polarized light does not _travel straight without being refracted and reflected by the second fiber of the light homogenizing layer. The light homogenizing layer cannot exhibit a light homogenizing action for such light. In this case, the effective refractive index for light with a small angle (θ) takes a value close to no ₂ .

  When the above formula (5) is satisfied, it is possible to exert a light homogenizing action on incident light components incident on the second fiber at all angles (θ).

Particularly preferably, from the viewpoint of further improving the effect of the p-polarized component as a homogenizing layer, the difference in refractive index between nm ₂ and ne 2 — _eff represented by the above formula (F) is preferably different by 0.03 or more.

  As shown in FIG. 5, in the light homogenization layer 50, the density of the second fiber located on the center line between the adjacent light sources is larger than the density of the second fiber located on the axis of the light irradiation direction of the light source. It is preferable. The amount of light between the light sources is small, and a dark portion tends to occur in the inter-light source region 12 near the light sources. Therefore, by arranging the second fibers densely in these regions, a further light homogenizing effect can be achieved.

  In the polarization separation layer 40 described above, the first fiber is arranged so that the longitudinal direction of the first fiber 41 is orthogonal to the waveguide direction. Therefore, the cross-sectional shape of the first fiber 41 in the diameter direction is substantially the same regardless of where the first fiber 41 is cut in the length direction. Since the first fiber 41 does not change its shape in the length direction, when the p-polarized component or the s-polarized component is refracted / reflected by the first fiber 41, the light is viewed in the waveguide direction when viewed from the plane. There is virtually no scattering on both sides. Scatter in a plane along the waveguide direction. That is, the angular distribution in the in-plane direction does not change substantially. The invention according to the present embodiment enables light to be scattered in the in-plane direction by the second fiber extending perpendicularly to the incident surface 30a in the light homogenizing layer 50. In the invention according to the present embodiment, it is possible to obtain scattering in the in-plane direction of light that cannot be sufficiently obtained only by using the PSSE of the first fiber 41 extended in parallel with the incident surface.

  When only the s-polarized component is extracted, light having a phase close to the p-polarized component remains in the light guide layer 30. The remaining light is disposed on the phase difference plate 60 in order to effectively use the remaining light.

  In the embodiment shown in FIG. 1, the retardation plate 60 is a λ / 4 plate, and is formed to have a thickness that shifts the phase of light incident on the retardation plate 60 at a right angle by 90 degrees. The light totally internally reflected in the light guide layer 30 does not enter the retardation plate 40 at a right angle, as can be seen from FIG. The phase of the p-polarized component is shifted so as to approach the s-polarized component. Conversely, the s-polarized component may be converted into the p-polarized component, but since the s-polarized component is selectively emitted to the outside, the rate of conversion from the p-polarized component to the s-polarized component is higher. Thus, since the light remaining in the light guide layer 20 is also converted into the s-polarized component, the extraction efficiency of the s-polarized component is increased, that is, the light utilization efficiency is increased.

  As the phase difference plate, an appropriate one can be used according to the wavelength range, for example, polycarbonate (PC), polysulfone (PS), polymethyl methacrylate (PMMA), polyvinyl alcohol (PVA), polyamide, polyester, and the like. A birefringent sheet obtained by stretching a film formed from the above, a support sheet for a liquid crystal polymer alignment layer, or a multilayer laminate thereof can be used. In addition, a sheet in which fibers (41, 51) used in the polarization separation layer 40 and the light homogenization layer 50 are arranged in a holding medium can be used as a retardation plate.

(Second Embodiment)
FIG. 6 is a drawing showing a schematic configuration of the surface light source device of the second embodiment.

  In the first embodiment shown in FIG. 4, the light homogenization layer 50 is provided on the lower surface of the light guide layer 30. However, the light homogenization layer 50 may be laminated on the light guide layer 30. As in the surface light source device 1 illustrated in FIG. 6, the light homogenization layer 50 may be provided between the light guide layer 30 and the polarization separation layer 40.

(Third embodiment)
FIG. 7 is a drawing showing a schematic configuration of the surface light source device of the third embodiment.

  As in the surface light source device 1 illustrated in FIG. 7, the light homogenization layer 50 may be provided on the upper surface of the polarization separation layer 40.

(Fourth embodiment)
FIG. 8 is a drawing showing a schematic configuration of the surface light source device of the fourth embodiment.

  In the first embodiment shown in FIG. 4, the retardation plate 60 is attached to the side surface opposite to the incident surface 30 a of the light guide layer 30. However, the phase difference plate 60 can be attached to at least one of the main surface of the light guide layer 30 on the side opposite to the laminated surface of the polarization separation layer 40 and the side surface other than the incident surface 30 a of the light guide layer 30.

  For example, as in the surface light source device 1 shown in FIG. 8, the phase difference plate 60 is provided on the main surface of the light guide layer 30 on the opposite side to the laminated surface of the polarization separation layer 40, that is, on the lower surface of the light guide layer 30. Can be. However, when the phase difference plate 60 is provided on the main surface or the side surface of the light guide layer 30 perpendicular to the light guiding direction as shown in FIG. 8, the phase difference plate 60 is a λ / 2 plate. The thickness of the light incident on the phase difference plate 60 at a right angle is shifted by 180 degrees.

  As a result, even if light is refracted and reflected on the light guide layer 30 side in the polarization separation layer 40 and is incident on the phase difference plate 60 at an acute angle, the phase is changed by approximately 180 degrees, and the light of the s-polarized component is The s-polarized component is maintained. The light is reflected by the reflection plate 70, returns to the light guide layer 30 again, and is emitted from the polarization separation layer 40. This prevents the p-polarized component light from being emitted. As described above, the light guided in the light guide layer 30 does not normally enter the phase difference plate 60 at a right angle. Therefore, the λ / 2 phase difference plate 60 appropriately changes the p polarization component to the s polarization component. Converted.

(Fifth embodiment)
FIG. 9 is a diagram showing a schematic configuration of the surface light source device of the fifth embodiment.

  FIG. 9 is a partial cross-sectional view of the surface light source device 1 including the polarization separation light homogenization layer 80 as viewed from the direction A in FIG. The same configuration as that of the first embodiment will be described with the same reference numerals.

  In the first to fourth embodiments, the polarization separation layer 40 and the light homogenization layer 50 are formed separately. However, a polarization separation light homogenization layer 80 in which the polarization separation layer 40 and the light homogenization layer 50 are integrated as shown in FIG. 9 may be used.

  As shown in FIG. 9, the polarization separation light homogenization layer 80 includes a first fiber 81, a second fiber 82, and a third holding medium 83 that holds the first fiber 81 and the second fiber 82. The first fibers 81 extend in parallel to the incident surface 30a of the light guide layer 30, and a plurality of first fibers 81 are arranged in a direction perpendicular to the incident surface 30a. The second fibers 82 extend perpendicularly to the incident surface 30a of the light guide layer 30, and a plurality of second fibers 82 are arranged in parallel to the incident surface 30a. That is, the first fiber 81 and the second fiber 82 are extended and arranged in directions orthogonal to each other, and the third holding medium 83 is in a state where the first fiber 81 and the second fiber 82 are knitted together. Is held in.

In the polarization separation light homogenization layer 80, the ordinary ray refractive index (no ₁ ) and extraordinary ray refractive index (ne ₁ ) of the first fiber, and the ordinary ray refractive index (no ₂ ) and extraordinary ray refractive index (ne) of the second fiber. ₂ ) and the refractive index (n _matrix3 ) of the third holding medium satisfy the following expressions (4) and (5).

  Thus, the first fiber 81 (warp yarn) functions to selectively scatter only the s-polarized light component and derive it from the light emitting surface which is the upper surface of the polarization separation light homogenization layer 80, and the second fiber 82 (weft yarn) The light propagating in the light guide layer 30 is diffused in the in-plane direction to achieve the function of homogenizing the direction distribution of the light.

That is, the refractive index (nm ₃ ) of the third holding medium 83 matches the ordinary ray refractive index (no ₁ ) of the first fiber 81 and is different from the extraordinary ray refractive index (ne ₁ ). Therefore, the p-polarized component of the light travels straight without being refracted by the first fiber 81, and only the s-polarized component of the light is refracted and reflected under the influence of the extraordinary ray refractive index (ne ₁ ) of the first fiber 81, A part is derived from the light emitting surface.

On the other hand, the refractive index (nm ₃ ) of the third holding medium 83 is different from the ordinary ray refractive index (no ₂ ) of the second fiber 82 and different from the extraordinary ray refractive index (ne ₂ ). Accordingly, the s-polarized component of light travels straight without being refracted by the second fiber 82, and only the p-polarized component of light is refracted and reflected by the influence of the extraordinary ray refractive index (ne ₁ ) of the second fiber 82. Diffused in the inward direction.

  As the fiber (81, 82) and the third holding medium 83 in the present embodiment, the fiber (41, 51) and the holding medium (42, 52) exemplified above can be preferably used as well. However, in this embodiment, the first fiber 81 and the second fiber 82 are formed of different materials so as to satisfy the above relational expressions (4) and (5) of the refractive index.

(Sixth embodiment)
FIG. 10 is a diagram showing a schematic configuration of a surface light source device according to a sixth embodiment.

  In the various first to fifth embodiments (FIGS. 1 to 9) described above, the light guide layer 30 is formed of a material different from that of the first holding medium 42 and the second holding medium 52. However, the light guide layer 30 may be formed of the same material as at least one of the first holding medium and the second holding medium. The sixth embodiment shown in FIG. 10 corresponds to the light guide layer 34 in the embodiment shown in FIG. 4 when the light guide layer 30 of the first embodiment is made of the same material as the first holding medium 32. . Alternatively, although not shown, the light guide layer of the first embodiment may be formed of the same material as the second holding medium, and may be formed as an integrated layer of the light guide layer and the light homogenization layer. Alternatively, although not shown, the light guide layer, the first holding medium, and the second holding medium of the first embodiment are all formed of the same material, and the light guide layer, the polarization separation layer, and the light homogenization layer It is good also as an integral layer. Furthermore, in the form in which the polarization separation layer and the light homogenization layer shown in FIG. 9 are integrated, the light guide layer is formed of the same material as the third holding medium, and the polarization separation light homogenization layer and the light guide layer are formed. It is good also as an integral layer. As described above, by integrating the light guide layer with the polarization separation layer and / or the light homogenization layer, the manufacturing becomes easy, the cost can be reduced, and the device can be thinned because the thickness can be reduced. Excellent in terms.

  In the form of FIG. 10, the first fibers are arranged in the upper region in the integrated layer of the light guide layer and the polarization separation layer, but the first fibers may be arranged in the entire integrated layer. The first fiber may be arranged in another region in the integral layer.

(Seventh embodiment)
FIG. 11 is a drawing showing a schematic configuration of the surface light source device of the seventh embodiment.

  In various 1st-6th embodiment (FIGS. 1-10) mentioned above, the light source part 10 is arrange | positioned at one side by the side of the short axis of the light guide layer 30 which comprises the light guide plate 20. As shown in FIG. However, the surface light source device 1 may include a plurality of light source units 10. For example, as in the surface light source device 1 illustrated in FIG. 11, the light source unit 10 may be disposed on both side surfaces of the light guide layer 30 constituting the light guide plate 20 on the short axis side. The fifth embodiment shown in FIG. 11 corresponds to the case where the light source unit 10 is provided in place of the reflecting plate 70 in the fourth embodiment shown in FIG. Although not shown, the light source unit 10 may be arranged on both side surfaces of the light guide layer 30 on the short axis side in the same manner as in the third embodiment, for example, the first, second, and fourth embodiments. Good. Furthermore, depending on the case, you may arrange | position the additional light source part 10 in side surfaces other than the light emission surface by the side of the long axis of the light guide layer 30. FIG.

  The effects of the present invention will be described using the following examples and comparative examples. However, the technical scope of the present invention is not limited only to the following examples.

[Example 1]
(1) Preparation of light guide layer As the light guide layer, PMMA (size: 6 cm × 9 cm) was prepared.

(2) Formation of polarization separation layer PET fiber (material: polyethylene terephthalate, no = 1.5449, ne = 1.7200, outer surface roughness Rz = 2 μm on the upper surface of the light guide layer. , Cross-sectional shape: circle having a diameter of 20 μm) arranged in a thickness of 15 layers so that there is no gap in the same direction, and UV curing as a first holding medium designed so that the refractive index after curing is 1.545 Resin (EA-F5503 manufactured by Osaka Gas Chemical Co., Ltd .; 40 parts by weight, MK ester A-400 manufactured by Shin-Nakamura Chemical Co., Ltd .; 58 parts by weight, and photopolymerization initiator Irgacure 184 manufactured by Ciba Specialty Chemicals; 2 parts by weight) Infiltrated. Remove the air between the fiber and the UV resin by vacuum degassing, then cover the upper part with a glass plate that has been subjected to mold release treatment, cure the resin using a UV lamp, and then peel off the glass plate Thus, a polarization separation layer was formed on the light guide layer. When the cross section of the polarization separation layer was observed with a laser microscope (device: VK-9600 manufactured by Keyence Corporation), as shown in FIG. 11, the first fiber aligned in the same direction was held by the UV curable resin as shown in FIG. It was confirmed to have a structure.

(3) Formation of light homogenization layer N610 fiber (material: nylon 6,10, no = 1.5217, ne = 1.5711, cross-sectional shape: circle with a diameter of 50 μm) as the second fiber on the lower surface of the light guide layer ) Is arranged with a thickness of three layers so that there is no gap in the direction orthogonal to the arrangement direction of the first fibers in the polarization separation layer, and the second holding designed to have a refractive index after curing of 1.571 UV curable resin as medium (MK Ester A-BPE-4, Shin-Nakamura Chemical Co., Ltd., 74 parts by weight, MK Ester A-LEN-10, Shin-Nakamura Chemical Co., Ltd., 24 parts by weight; Polymerization initiator Irgacure 184, 2 parts by weight of mixture) was infiltrated. Then, in the same manner as the formation of the polarization separation layer, the light homogenization layer was formed on the light guide layer by curing the resin.

(4) Arrangement of light source part, phase difference plate and reflector Next, on the side surface of the light guide layer, a light source part in which nine LEDs as light sources are arranged one-dimensionally (in series) is installed on the short axis side of the light guide layer. . At this time, the side surface of the light guide layer on which the light source unit is installed is a surface parallel to the longitudinal direction of the first fiber in the polarization separation layer and perpendicular to the cross-sectional direction of the second fiber in the light homogenization layer. The LED is arranged in a direction parallel to the longitudinal direction of the first fiber in the polarization separation layer.

  Thereafter, a λ / 4 phase difference plate is disposed on the side surface of the light guide layer opposite to the surface on which the light source unit is installed, and all the surfaces other than the upper surface (light emitting surface) of the polarization separation layer and the surface on which the light source unit is installed A reflector was attached to the surface. This produced the surface light source device. Note that the surface light source device of this example corresponds to the first embodiment shown in FIG.

[Example 2]
A light homogenization layer is formed on the upper surface of the light guide layer, and a polarization separation layer is formed on the upper surface of the light homogenization layer, and a PET fiber (material: Polyethylene terephthalate, no = 1.5449, ne = 1.700, outer surface roughness Rz = 2 μm, cross-sectional shape: circle with a diameter of 20 μm), and the refractive index after curing is 1. UV curable resin designed to be 605 (a mixture of Osaka Gas Chemical Co., Ltd. EA-F5503; 68 parts by weight, benzyl acrylate; 30 parts by weight, and Ciba Specialty Chemicals photopolymerization initiator Irgacure 184; 2 parts by weight) A surface light source device was produced in the same manner as in Example 1 except that was used. Note that the surface light source device of this example corresponds to the second embodiment shown in FIG.

[Example 3]
A surface light source device was produced in the same manner as in Example 2 except that a polarization separation layer was formed on the top surface of the light guide layer and a light homogenization layer was formed on the top surface of the polarization separation layer. The surface light source device of this example corresponds to the third embodiment shown in FIG.

[Example 4]
PET fiber (material: polyethylene terephthalate, no = 1.5449, ne = 1.700, outer surface roughness Rz = 2 μm, cross-sectional shape: equilateral triangle with a side of 10 μm) as the first fiber constituting the polarization separation layer A surface light source device was produced in the same manner as in Example 2 except that it was used.

[Comparative Example 1]
A surface light source device was produced in the same manner as in Example 1 except that the light homogenization layer was not formed on the lower surface of the light guide layer.

[Evaluation]
In the surface light source devices obtained in the above examples and comparative example 1, the luminance, luminance unevenness, and degree of polarization of light emitted from the light emitting surface were measured. Here, measurement of luminance and luminance unevenness, and measurement of polarization degree are performed by using a two-dimensional color luminance meter Konica Minolta CA-2000 or AUTRONIC-MELCHERS GmbH's Conoscope 80 in combination with a polarizing plate. The ratio of the components was determined. The luminance was measured by driving nine LEDs arranged in series with a constant current of 30 mA, and the front luminance at the center of the light emitting surface of the light guide plate of light emitted at that time was measured. The results are shown in Table 2. FIG. 13 and FIG. 14 show the two-dimensional luminance distribution of light emitted from the upper surface (light emitting surface) of the light guide plate of the surface light source device manufactured in Example 2 and Comparative Example 1 measured by CA-2000. In other Examples 1, 3 and 4, the same two-dimensional luminance distribution as that in FIG. 13 was obtained on the upper surface (light emitting surface) of the light guide plate.

  In the surface light source devices of Examples 1 to 4 having a light homogenization layer, as shown in FIG. 13, streaks are not observed in the light emitted from the upper surface of the laminate, and the LED is a discontinuous light source. It was found that luminance unevenness can be eliminated even when using the. Moreover, it was confirmed that the surface light source devices obtained in these examples can achieve high polarization separation ability.

  On the other hand, in the surface light source device manufactured in Comparative Example 1, the polarization separation ratio was the same as that in the example. However, as shown in FIG. Was clearly observed.

  Furthermore, in the surface light source device of Example 4 in which the cross-sectional shape of the first fiber constituting the polarization separation layer is an equilateral triangle, the surface light source device of Example 2 in which the cross-sectional shape of the first fiber is a circle is introduced. The intensity (luminance) of light in the direction perpendicular to the light layer (light emitted from the upper surface of the laminate) was twice as large.

  From the above, it was confirmed that the surface light source device of the present invention can achieve high polarization separation ability and can prevent unevenness of light even when a discontinuous light source such as an LED is used.

1 surface light source device,
10 light source units,
11 Light source,
12 area between light sources,
20 light guide plate,
30, 34 Light guide layer,
30a incident surface,
30b light emitting surface,
40 polarization separation layer,
41, 81 first fiber,
42 first holding medium 50 light homogenization layer,
51, 82 second fiber,
52 second holding medium,
60 phase difference plate,
70 reflector,
80 polarization separation light homogenization layer,
83 Third holding medium.

Claims (8)

A light guide layer for introducing light emitted from a light source into an inside from an incident surface which is a side surface;
A plurality of first fibers having a birefringence extending parallel to the incident surface and arranged perpendicular to the incident surface; and an ordinary ray refractive index (no ₁ ) of the first fiber holding the first fiber; An isotropic first holding medium having a refractive index that matches the extraordinary ray refractive index (ne ₁ ), and is laminated on the light guide layer to guide the desired polarized light out of the light in the light guide layer. A polarization separation layer derived from the light emitting surface which is one main surface of the optical layer;
A plurality of birefringent second fibers extending perpendicular to the incident surface and arranged parallel to the incident surface, and an ordinary ray refractive index (no ₂ ) and an extraordinary ray refractive index (ne ₂ ) of the second fiber. An isotropic second holding medium having a refractive index different from that of at least one of the above and a light homogenizing layer laminated on the light guide layer;
A light guide plate comprising: The ordinary ray refractive index (no ₂ ) and extraordinary ray refractive index (ne ₂ ) of the second fiber, and the refractive index (nm ₂ ) of the second holding medium satisfy the following formula (1). Light guide plate.
The light guide plate according to claim 1 or 2 , wherein a surface roughness (Rz) of an outer peripheral surface of the first fiber is 0.1 to 10 µm. The radial cross-sectional shape of the first fiber is a polygonal light guide plate according to any one of claims 1-3. A retardation plate attached to the light guide layer and converting a polarization direction of light in the light guide layer;
A reflector that is laminated on at least one of the main surface of the light guide layer opposite to the laminated surface of the polarization separation layer and the side surface other than the incident surface of the light guide layer, and reflects light inward of the light guide layer; ;
The light guide plate according to any one of claims 1 to 4 , further comprising: The light guide plate according to any one of claims 1 to 5 , wherein the light guide layer is formed of the same material as at least one of the first holding medium and the second holding medium. A light source unit in which a plurality of light sources are intermittently arranged one-dimensionally or two-dimensionally;
The light guide plate according to any one of claims 1 to 6 ;
A surface light source device comprising: 8. The surface light source device according to claim 7 , wherein a density of the second fiber positioned on a center line between adjacent light sources is larger than a density of the second fiber positioned on an axis line in a light irradiation direction of the light source.