JP2013101892A - Plane surface lighting device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a plane surface lighting device that can raise use efficiency of light emitted from a light source while thinning the plane surface lighting device.SOLUTION: The plane surface lighting device includes a light source 100, a light guide plate 200 having a light incident end face 212 for entering light emitted from the light source 100 and a light emitting surface 224 for emitting light incident from the light incident end face 212, and a diffractive optical element 230 arranged between the light source 100 and the light incident end face 212. The light guide plate 200 has an inclined part 210 arranged on a light incident end face 212 side and preparing an inclined surface 214 to gradually increase its thickness toward the light incident end face 212, and the diffractive optical element 230 makes light emitted from the light source 100 deflect in an inclination direction of the inclined surface 214 as a whole.

Description

  The present invention relates to a planar illumination device, and more particularly to a sidelight type planar illumination device.

  As a lighting device for a liquid crystal display panel used in a portable information device such as a cellular phone, a sidelight type planar lighting device (backlight) using an LED as a light source is widely used. In a sidelight type planar illumination device, a light source LED is disposed on an end surface (incident surface) of a plate-shaped light guide plate. At this time, if the thickness of the light guide plate is smaller than the thickness of the LED, there is a possibility that a problem such as a decrease in light utilization efficiency may occur. Therefore, the reduction in thickness of the planar lighting device has been restricted by the thickness of the LED.

  On the other hand, in order to cope with further thinning of the portable information device, the planar lighting device is required to be further thinned. Therefore, it has been proposed to form an inclined surface on the light guide plate so that the thickness gradually increases as it approaches the incident surface (see, for example, Patent Document 1). By forming the inclined surface on the light guide plate in this way, it is possible to reduce the thickness of the light emitting surface that emits planar light regardless of the thickness of the LED.

JP 2007-287550 A

  However, when the inclined surface is formed on the light guide plate, the light incident inclining in the inclined surface direction is reflected by the inclined surface, so that the direction of the light changes. Therefore, a part of the incident light leaks from the light guide plate before reaching the light emitting surface, and the use efficiency of the light emitted from the LED may be reduced. This problem is not limited to planar illumination devices using LEDs, but is common to sidelight type planar illumination devices using various light sources.

  The present invention has been made in order to solve the above-described conventional problems, and provides a technique for increasing the utilization efficiency of light emitted from a light source while reducing the thickness of a planar illumination device. Objective.

  In order to achieve at least a part of the above object, the present invention can be realized as the following forms or application examples.

[Application Example 1]
A planar illumination device, comprising: a light source; a light guide plate having a light incident end surface on which light emitted from the light source is incident; a light output plate that emits light incident on the light incident end surface; the light source and the incident light And a diffractive optical element provided between the light end face, the light guide plate is disposed on the light incident end face side, and an inclined surface provided with an inclined surface so that the thickness gradually increases toward the light incident end face And a diffractive optical element that deflects the light emitted from the light source as a whole in the tilt direction of the tilted surface. According to this application example, the light emitted from the light source by the diffractive optical element is deflected in the inclined direction of the inclined surface as a whole, thereby suppressing the light incident on the light guide plate from reaching the inclined surface, or Since the incident angle when reaching the inclined surface is increased, leakage of light from the inclined portion is suppressed. Therefore, it is possible to reduce the thickness of the planar lighting device by providing an inclined surface, to suppress a decrease in light utilization efficiency due to the provision of the inclined surface, and to increase the utilization efficiency of light emitted from the light source. it can.

[Application Example 2]
The planar illumination according to Application Example 1, wherein the diffractive optical element has a diffraction efficiency of diffracted light of a predetermined order deflected in the tilt direction by the diffractive optical element is higher than that of other orders of diffracted light. apparatus. By making the diffraction efficiency of the diffracted light of a predetermined order deflected in the tilt direction higher than the diffraction efficiency of the diffracted light of other orders, the light emitted from the light source as a whole in the tilt direction of the tilted surface more reliably. Can be deflected.

[Application Example 3]
The planar illuminating device according to Application Example 1 or 2, wherein the diffractive optical element is a diffraction grating in which a ridge-shaped convex portion extending in a longitudinal direction of the light incident end surface is formed. Since the convex part of the diffraction grating can be produced by forming a groove in the mold by cutting or the like, the diffractive optical element can be produced more easily.

[Application Example 4]
The planar illumination device according to Application Example 3, wherein the convex portion has an asymmetric cross-sectional shape with respect to the tilt direction. By making the convex part an asymmetric cross-sectional shape with respect to the inclination direction, the light emitted from the light source can be more reliably deflected in the inclination direction of the inclined surface as a whole.

[Application Example 5]
5. The planar illumination device according to any one of application examples 1 to 4, wherein the diffractive optical element is provided in a partial region on the inclined surface side in a region through which light emitted from the light source passes. In the region where the diffractive optical element is not provided, the light incident on the light guide plate does not reach the inclined surface or reaches the inclined surface at a position close to the light exit surface. Light leakage can be sufficiently suppressed.

[Application Example 6]
In the planar illumination device, the light incident end face is provided with a plurality of prisms separated along the longitudinal direction of the light incident end face, and the diffractive optical element is adjacent to the light incident end face. The planar illumination device according to any one of Application Examples 1 to 5, which is provided on a surface between the prisms. According to this application example, the use efficiency of light can be increased by providing the diffractive optical element, and the intensity of light emitted from the light exit surface can be made more uniform by providing the prism.

[Application Example 7]
6. The planar illumination device according to any one of application examples 1 to 5, wherein the diffractive optical element is provided on a light emitting surface of the light source. According to this application example, since the diffractive optical element can be disposed between the light source and the light incident end face regardless of the shape of the light guide plate, the light guide plate can be made to have a more appropriate shape.

[Application Example 8]
The planar illumination device according to any one of application examples 1 to 5, wherein the diffractive optical element is provided on a film disposed between the light source and the light incident end surface. Also according to this application example, since the diffractive optical element can be disposed between the light source and the light incident end face regardless of the shape of the light guide plate, the light guide plate can be formed in a more appropriate shape.

[Application Example 9]
The planar illumination device according to any one of Application Examples 1 to 8, wherein the inclined surface is provided on the light exit surface side. Usually, a diffusion sheet and a light collecting sheet are laminated on the light exit surface side. According to this application example, an increase in the thickness of the light guide plate due to the provision of the inclined surface can be avoided from being added to the thickness of these sheets, so that the planar lighting device can be made thinner.

The perspective view which shows the structure of the planar illuminating device in 1st Embodiment. Sectional drawing of LED and a light-guide plate. Explanatory drawing which shows a mode that the emitted light of LED deflect | deviates with a diffraction grating. Explanatory drawing which shows the optical path of the light ray which injected into the incident light end surface diagonally. Explanatory drawing which shows typically the shape of the diffraction grating evaluated as one Example. Explanatory drawing which shows the conditions and the result of simulation. The graph which shows the measurement result of a far field characteristic. Explanatory drawing which shows the shape of the light-guide plate at the time of performing simulation. Explanatory drawing which shows the structure of the light-guide plate in 2nd Embodiment. The fragmentary sectional view which shows the structure of the diffraction grating in a 1st modification. The fragmentary sectional view which shows the structure of the diffraction grating in a 2nd modification. Explanatory drawing which shows the structure and function of the diffraction grating in a 3rd modification.

Next, modes for carrying out the present invention will be described in the following order.
A. First embodiment:
A1. Configuration of the planar lighting device:
A2. Diffraction grating functions:
A3. Example:
B. Second embodiment:
C. Variations of diffraction grating:
C1. First modification of the diffraction grating:
C2. Second modification of the diffraction grating:
C3. Third modification of the diffraction grating:
D. Variations:

A. First embodiment:
A1. Configuration of the planar lighting device:
FIG. 1 is a perspective view illustrating a configuration of a planar illumination device 10 according to the first embodiment. The planar illumination device 10 is a so-called sidelight type planar illumination device, and includes a plurality of light emitting diodes (LEDs) 100 that are light sources, a substantially rectangular plate-shaped light guide plate 200, a diffusion sheet 300, and a condensing sheet. 400. The planar illumination device 10 causes the LED 100 to face one end face (light incident end face) 212 of the light guide plate 200 and also in a direction (z direction) orthogonal to the main plane of the light guide plate 200. Are sequentially stacked. Although details will be described later, the light emitted from the LED 100 enters the light guide plate 200 from the light incident end face 212 and is emitted from one main plane (light exit surface) 224 of the light guide plate 200 facing the diffusion sheet 300. The amount of light emitted from the light exit surface 224 is made uniform by the diffusion sheet 300 and the light distribution characteristic is adjusted by the light collecting sheet 400. In addition, it is good also as what arrange | positions a reflecting plate in the position on the opposite side to the diffusion sheet 300 on both sides of the light guide plate 200.

  FIG. 2 is a cross-sectional view of the LED 100 and the light guide plate 200, showing a cross section taken along the line AA in FIG. In addition, although LED100 and the light-guide plate 200 are arrange | positioned closely, in FIG. 2, LED100 and the light-guide plate 200 are drawn apart for convenience of illustration. The LED 100 includes an LED chip 110 that emits blue light, a lamp house 120, and a sealing portion 130. The lamp house 120 is provided with a recess 122, and the LED chip 110 is mounted on the bottom of the recess 122. The sealing part 130 is, for example, a transparent thermosetting resin such as an epoxy resin in which a phosphor that emits yellow light is dispersed. The liquid thermosetting resin is filled (potted) in the recess 122 and then heated. Is formed.

  When the LED chip 110 emits blue light by energization, the phosphor dispersed in the sealing portion 130 is excited by the blue light, and the phosphor emits yellow light. White light (pseudo white light) obtained by mixing the yellow light and the blue light emitted from the LED chip 110 is emitted from the surface (light emitting surface) 132 of the sealing portion 130 located at the opening of the recess 122. As the LED, in addition to the pseudo white LED 100 described above, an LED using a plurality of LED chips that respectively emit light of three colors of red, green, and blue, an LED chip that emits ultraviolet light, and a white phosphor Various LEDs can be used, such as an LED using LED.

  The light guide plate 200 is a substantially rectangular plate-shaped transparent member, and is formed using, for example, a polymetal methacrylate resin or a polycarbonate resin. The light guide plate 200 can be formed using various resin molding techniques such as injection molding. The light guide plate 200 has an inclined portion 210 whose thickness gradually increases toward the end surface and a flat portion 220 having a constant thickness. The inclined portion 210 has, as its outer surface, a light incident end surface 212 and an inclined surface 214, and a reflective surface 202 common to the flat portion 220. The flat portion 220 has, as its outer surface, a facing end surface 222 and a light exit surface 224, and a reflective surface 202 common to the inclined portion 210.

  The light incident end surface 212 is an end surface that faces the light emitting surface 132 of the LED 100 and on which light emitted from the LED 100 enters. The facing end surface 222 is an end surface facing the light incident end surface 212. The reflecting surface 202 is one main plane of the light guide plate 200 that is orthogonal to the light incident end surface 212 and the opposed end surface 222 and extends from the light incident end surface 212 to the opposed end surface 222. The light exit surface 224 is the other main plane facing the reflection surface 202, is orthogonal to the facing end surface 222, and extends from the facing end surface 222 toward the light incident end surface 212. The inclined surface 214 is a surface that extends from the light incident end surface 212 toward the opposite end surface 222 and is inclined at a certain gradient so as to approach the reflecting surface 202 as it is away from the light incident end surface 212. In the present specification and claims, the direction in which the inclined surface 214 approaches as it moves away from the light incident end surface 212 is referred to as the inclined direction of the inclined surface 214. Therefore, the inclination direction of the inclined surface 214 in FIG. 2 is the reflective surface 202 direction (−z direction).

  In the first embodiment, by providing the inclined portion 210, the area of the light incident end face 212 facing the LED 100 can be made larger than when the inclined portion 210 is not provided. Therefore, the incident efficiency of the light emitted from the LED 100 to the light guide plate 200 can be made higher than when the inclined portion 210 is not provided.

  In the light guide plate 200 in the first embodiment, the diffraction grating 230 is formed on the light incident end surface 212. The diffraction grating 230 is a transmission type diffraction grating, and is specifically configured by forming a ridge (ridge) -shaped convex portion 232 extending in the longitudinal direction (x direction) of the light incident end surface 212 on the light incident end surface 212. Has been. The convex part 232 can be formed, for example, by providing a groove in an injection mold for forming the light guide plate 200. In the first embodiment, the cross-sectional shape of the convex portion 232 formed on the light incident end surface 212 is asymmetrical (sawtooth in the example of FIG. 2) with respect to the inclination direction (z direction) of the inclined surface 214, so that the entire incident light is obtained. As described above, the light is deflected in the inclination direction of the inclined surface 214 (that is, in the direction of the reflecting surface 202). A specific function and shape of the diffraction grating 230 will be described later.

  The light emitted from the light emitting surface 132 of the LED 100 enters the light guide plate 200 from the light incident end surface 212 where the diffraction grating 230 is formed. The incident light propagates in the direction of the opposed end surface 222 by repeating total reflection between the inclined surface 214 and the light exit surface 224 and the reflection surface 202 in the light guide plate 200. The traveling direction of the light propagating through the light guide plate 200 is changed by an optical path changing pattern (not shown) formed on the reflecting surface 202 in the flat portion 220. The traveling direction is changed by the optical path changing pattern, and the light that has reached the light exit surface 224 at an angle less than the critical angle is emitted from the light exit surface 224.

A2. Diffraction grating functions:
FIG. 3 is an explanatory diagram showing how the light emitted from the LED 100 is deflected by the diffraction grating 230. In the first embodiment, the diffraction grating 230 is constituted by a ridge-shaped convex portion 232 (FIG. 2) formed on the light incident end face 212. However, for convenience of explanation, the diffraction grating 230 is periodic in the air in FIG. It is depicted as a diffraction grating with slits.

FIG. 3A shows the optical path of a light beam incident obliquely on the diffraction grating 230. By passing through the diffraction grating 230, the light beam incident on the diffraction grating 230 is divided and emitted in the same direction as the incident light and in a plurality of directions different from the incident light. Here, the angle (diffraction angle) φ formed by the emitted light (diffracted light) and the optical axis OO is the slit interval (ie, the lattice interval) d, the light wavelength λ, the incident light and the optical axis O−. As an angle (incident angle) θ formed by O, an integer m (referred to as an order m) is used to be expressed by the following equation. The diffracted light when the order is m is called m-order light.

  As can be seen from the above equation, in the example of FIG. 3A, the 0th-order light travels in the same direction as the incident light, and the diffracted light whose order m is positive is the + z direction (the inclined surface 214 in FIG. Diffracted light having a negative order m is deflected in the −z direction (inclination direction of the inclined surface 214 in FIG. 2, that is, in the direction of the reflecting surface 202) with respect to the incident light. As shown in FIG. 2, in the first embodiment, the cross-sectional shape of the convex portion 232 formed on the light incident end surface 212 is asymmetric with respect to the inclination direction (z direction) of the inclined surface 214. Thereby, the intensity of the diffracted light of a specific negative order m is made stronger than the intensity of the diffracted light of other orders, and the incident light is deflected as a whole in the tilt direction (−z direction) of the tilted surface 214. The sign m of the order m differs depending on the coordinate system and the way of taking the angle, but in this specification, the order m for deflecting the incident light in the tilt direction of the tilted surface 214 will be described as negative.

  FIG. 3B shows how the far field characteristic (FFP) is changed by the diffraction grating 230. Here, the far-field characteristic is a characteristic that represents the relationship between the direction in which the light emitting surface of the light source is viewed and the intensity (luminance) of the light beam in that direction, and represents the light distribution of the light source. In FIG. 3B, the broken line indicates the far field characteristic of the LED 100 alone without the diffraction grating 230, and the solid line indicates the far field characteristic when the diffraction grating 230 is provided. As shown in FIG. 3B, when there is no diffraction grating 230, the intensity of the light beam is maximized in the optical axis OO direction. On the other hand, as described above, when the intensity of the diffracted light of a specific negative order m is made higher than the intensity of the diffracted light of other orders, most of the light that has passed through the diffraction grating 230 is inclined in the direction of inclination of the inclined surface 214 ( -Z direction), the light distribution is inclined in the inclination direction of the inclined surface 214 as shown by the arrow as compared with the case where there is no diffraction grating.

  FIG. 4 is an explanatory diagram showing an optical path of a light beam incident obliquely on the light incident end face 212. In the first embodiment, since the diffraction grating 230 is formed on the light incident end surface 212 of the light guide plate 200, the incident light is refracted at the light incident end surface 212 and divided into a plurality of diffracted lights. The 0th order light (m = 0) is the same as the optical path without the diffraction grating 230, and the mth order light (m = −1 to −3) is more inclined as the absolute value of the order m increases. It is deflected in the direction of inclination of the surface 214. In the example of FIG. 4, the third-order light (m = -3) having a large deflection amount reaches the flat portion 220 without being reflected by the inclined surface 214, but the zero-order light (m = 0), −1 The secondary light (m = −1) and the secondary light (m = −2) are reflected by the inclined surface 214.

  As described above, since the inclined surface 214 is inclined in the direction of the reflecting surface 202 (−z direction), when light incident from the light incident end surface 212 is reflected by the inclined surface 214, the light travels. The angle formed between the direction and the direction of the reflecting surface 202 is increased. In the example of FIG. 4, zero-order light (m = 0) is reflected by the inclined surface 214 and then enters the reflecting surface 202 at a critical angle or less. Therefore, a part of the reflection surface 202 leaks from the light guide plate 200. Although not shown, the light reflected by the reflecting surface 202 also enters the inclined surface 214 at a critical angle or less, and therefore leaks from the inclined surface 214 as well. On the other hand, the −1st order light (m = −1) and the −2nd order light (m = −2) are deflected by the diffraction grating 230 in the inclination direction of the inclined surface 214, so that the light guide plate 200 is formed by the inclined portion 210. The flat portion 220 is reached without leaking outside.

  As described above, in the first embodiment, the diffraction grating 230 is formed on the light incident end surface 212 to deflect the incident light as a whole in the tilt direction (−z direction) of the tilt surface 214, that is, in the direction of the reflection surface 202. In addition, it is possible to further increase the incident efficiency of light emitted from the LED 100 to the light guide plate 200 and to suppress leakage of light to the outside of the light guide plate 200 in the inclined portion 210.

A3. Example:
FIG. 5 is an explanatory diagram schematically showing the shape of the diffraction grating 500 evaluated as an example. FIG. 5A shows a state where the diffraction grating 500 is viewed from the surface on which the convex portions 522 are formed. FIG. 5B shows a state where the diffraction grating 500 is viewed from the + x direction of FIG. 5A, and FIG. 5C is a partially enlarged view of FIG. 5B. FIG. 5D shows an optical path of a light beam incident perpendicularly (y direction) to the diffraction grating 500 shown in FIGS. 5A to 5C.

  The evaluated diffraction grating 500 is a diffraction grating in which a convex portion 522 having a right-angled triangular cross section is formed on one surface of a resin plate 510 made of polymethyl methacrylate resin. In this diffraction grating 500, the angle between the inclined surface 524 constituting the convex portion 522 and the main plane of the diffraction grating 500 is 40 ° (that is, 50 ° with respect to the direction perpendicular to the diffraction grating 500 (y direction)). The vertex 528 of the convex portion 522 is located on the −z direction side of the convex portion 522. Further, the interval between the convex portions 522 (that is, the lattice interval) was 2.69 μm, and the height (that is, the depth of the lattice groove) was 2.25 μm.

As the evaluation of the diffraction grating 500, as shown in FIG. 5D, the diffraction efficiency for each order m was evaluated by simulation for the light beam perpendicularly incident on the diffraction grating 500. Here, the diffraction efficiency refers to the ratio of the intensity of diffracted light to the intensity of incident light. The sign of the order m is such that the order m of the diffracted light deflected in the + z direction is positive and the order m of the diffracted light deflected in the −z direction is negative. Table 1 shown below shows the evaluation results when the wavelength λ of the incident light is 550 nm.

  As shown in Table 1, the diffraction grating 500 shown in FIGS. 5A to 5C has the highest diffraction efficiency of 62.83% when the order m is −2, and the other orders m The diffraction efficiency was -1st order 7.00% at the maximum. From this, it was found that by using the diffraction grating 500, most of the incident light can be deflected in the −z direction.

  Next, the change in far-field characteristics caused by arranging the diffraction grating 500 on the light emitting surface 132 side of the LED 100 (FIG. 2) was evaluated. In the evaluation, first, a far-field image representing far-field characteristics was obtained using simulation. Here, the far-field image is an image that two-dimensionally represents the far-field characteristics in the biaxial direction. FIG. 6 is an explanatory diagram showing simulation conditions and results. FIG. 6A shows the arrangement of the LED 100 and the diffraction grating 500 when the simulation is performed. As shown in FIG. 6A, in the embodiment, the diffraction grating 500 is disposed with the light emitting surface 132 (FIG. 2) of the LED 100 opposed to the surface on which the convex portion 522 is formed. FIG. 6B shows a far field image when the diffraction grating 500 is not disposed as a comparative example, and FIG. 6C shows a far field image in the example. In FIG. 6B and FIG. 6C, the white circle on the outer periphery represents the direction horizontal to the light emitting surface 132 of the LED 100 (direction on the zx plane), and each direction of xyz is a white circle. Represents the direction at the center of.

  As shown in FIG. 6B, the far-field image without the diffraction grating 500 was brightest at the center of the white circle, which is the direction perpendicular to the light emitting surface 132 of the LED 100 (FIG. 2). On the other hand, in the example in which the diffraction grating 500 is arranged, as shown in FIG. 6C, the far-field image is brightest at a position shifted in the −z direction from the center. From this, it was found that the light emitted from the LED 100 can be deflected in a specific direction (here, the −z direction) by using the diffraction grating 500.

  Next, for each of the comparative example and the example, the far field characteristics were measured under the same conditions as in the simulation. FIG. 7 is a graph showing the measurement results of the far field characteristics. In FIG. 7, the circumferential direction represents the angle formed with the direction (y direction) perpendicular to the light emitting surface 132 (FIG. 2) of the LED 100, and the radial direction represents the relative value (maximum value = 1) of the light intensity. . In addition, the solid line in FIG. 7 indicates the far field characteristic of the example, and the broken line indicates the far field characteristic of the comparative example.

  As shown in FIG. 7, the far-field characteristic without the diffraction grating 500 is maximum at about 0 °, and the shape of the graph is substantially circular. Thus, the light distribution of the comparative example was a Lambert distribution which is a normal LED light distribution. On the other hand, in the example in which the diffraction grating 500 is disposed, the light distribution is deviated from the Lambertian distribution, and the intensity peak moves in the −z direction. From this, it was confirmed that the light emitted from the LED 100 can be deflected in a specific direction (here, the −z direction) by using the diffraction grating 500.

Furthermore, the effect of providing the diffraction grating 230 was investigated by simulation for the light guide plate 200 (FIG. 2) of the first embodiment. FIG. 8 is an explanatory diagram showing the shape of the light guide plate 200 when a simulation is performed. In the simulation, as the shape of the light guide plate 200, the height of the light incident end surface 212 is 0.58 mm, the thickness of the flat portion 220 is 0.43 mm, the length of the inclined portion 210 is 1.10 mm, the inclined surface 214 and the light exit surface 224. And the distance (full length) between the light incident end face 212 and the opposing end face 222 was 78 mm. As a comparative example, the inclined surface 214 and the light exit surface are formed in a state in which no diffraction grating is provided on the light incident end face 212 and in a state in which a convex portion 522 having the same shape as the diffraction grating 500 shown in FIG. The amount of light (light flux) emitted from each of 224 was evaluated. Table 2 shown below shows the evaluation results when the amount of light emitted by the LED 110 is the same value. In Table 2, the amount of light is shown in arbitrary units (AU). Further, the amount of change indicates the percentage of increase / decrease in the amount of emitted light by providing the diffraction grating 230 with reference to the amount of emitted light without the diffraction grating 230.

  As shown in Table 2, the amount of light emitted from the inclined surface 214 was 0.042 AU in the comparative example in which the diffraction grating was not provided, but decreased to 0.024 AU in the example in which the diffraction grating was provided. Further, the amount of light emitted from the light exit surface 224 was 35.112 AU in the comparative example, but increased to 35.806 AU in the example. That is, by providing a diffraction grating on the light incident end face 212, light leakage from the inclined surface 214 was reduced by about 42%, and the amount of light emitted from the light exit surface 224 was improved by about 2%. For this reason, a diffraction grating that is asymmetric with respect to the tilt direction (z direction) of the tilted surface 214 is provided on the light incident end surface 212, and the incident light as a whole is deflected in the tilt direction (−z direction) of the tilted surface 214 (FIG. 2). As a result, it was confirmed that light leakage from the inclined surface 214 can be suppressed and the amount of light emitted from the light exit surface 224 can be increased.

B. Second embodiment:
FIG. 9 is an explanatory diagram showing the configuration of the light guide plate 200a in the second embodiment. FIG. 9A is a perspective view showing the entire light guide plate 200a, and FIG. 9B is a partially enlarged view of an area surrounded by a dotted line in FIG. 9A. The second embodiment is different from the first embodiment in that the shape of the light incident end surface 212a of the light guide plate 200a is different. Other points are the same as in the first embodiment.

  Specifically, in the second embodiment, a plurality of triangular prisms 240 are formed on the light incident end face 212a facing the LED 100 (FIG. 2). The plurality of prisms 240 are arranged at intervals in the longitudinal direction (x direction) of the light incident end surface 212a. Thus, the light incident end surface 212a is configured by the gap surface 242 between the adjacent prisms 240 and the two prism surfaces 244 and 246 that each prism 240 has. As shown in FIG. 9B, a diffraction grating having a shape similar to that of the first embodiment is formed on the gap surface 242.

  At this time, when a light beam is incident on the prism surfaces 244 and 246 of the prism 240, the incident light beam is refracted in the longitudinal direction (x direction) of the light incident end surface 212a according to the incident direction. Thereby, in 2nd Embodiment, since the light inject | emitted from LED100 is spread in the longitudinal direction of the light-incidence end surface 212a, the intensity | strength of the x direction of the light inject | emitted from the light-emitting surface 224 becomes more uniform.

  Further, by forming a diffraction grating asymmetric with respect to the inclination direction (z direction) of the inclined surface 214 on the gap surface 242, the light incident on the gap surface 242 is deflected in the inclination direction of the inclined surface 214 (FIG. 2) as a whole. Is done. Therefore, similarly to the first embodiment, it is possible to prevent light incident on the gap surface 242 from leaking from the inclined surface 214.

  As described above, the second embodiment can suppress the light incident on the gap surface 242 from leaking from the inclined surface 214 and can make the intensity in the x direction of the light emitted from the light exit surface 224 more uniform. More preferable than the first embodiment. On the other hand, 1st Embodiment is more preferable than 2nd Embodiment at the point which can suppress the leakage from the inclined surface 214 about the whole light which injected into the light-incidence end surface 212. FIG.

  In the second embodiment, the diffraction grating is formed only on the gap surface 242, but the diffraction grating may be formed on the prism surfaces 244 and 246 in addition to the gap surface 242. However, when a diffraction grating is formed on the prism surfaces 244 and 246, it is not always easy to manufacture a mold or the like for forming the light guide plate. Therefore, it is preferable to form a diffraction grating only on the gap surface 242 in that the light guide plate 200a can be formed more easily.

C. Variations of diffraction grating:
In the first embodiment, as shown in FIG. 2, the diffraction grating 230 is formed on the entire surface of the light incident end surface 212 of the light guide plate 200. In general, the diffraction grating is composed of the light emitting surface 132 of the LED 100 and the light guide plate 200. It is provided between the light incident end surface 212 and the light emitted from the LED 100 may be deflected as a whole in the tilt direction of the tilted surface 214, and the configuration of the diffraction grating can be variously modified as shown in the following modifications. Is possible.

C1. First modification of the diffraction grating:
FIG. 10 is a partial cross-sectional view showing the configuration of the diffraction grating 230b in the first modification. In the first modified example, as shown in FIG. 10, the diffraction grating 230b is formed only in the region on the inclined surface 214 side of the light incident end surface 212b in the light incident end surface 212b that is a region through which the light emitted from the LED 100 passes. The diffraction grating 230b is not formed in the region on the reflective surface 202 side. Other points are the same as in the first embodiment.

  In general, the light incident on the reflecting surface 202 side does not reach the inclined surface 214 or reaches the inclined surface 214 at a position close to the flat portion 220, so that leakage from the inclined surface 214 is small. On the other hand, the light incident on the inclined surface 214 side is deflected in the inclination direction of the inclined surface 214 by the diffraction grating 230b, so that leakage of light from the inclined surface 214 is suppressed. Therefore, even if the diffraction grating 230b is formed only on the inclined surface 214 side of the light incident end surface 212b, leakage of light from the inclined surface 214 can be suppressed.

  When the diffraction grating 230b is formed only on a part of the light incident end face 212b as in the first modification, it is possible to reduce the processing amount of a mold or the like for forming the light guide plate 200b. Therefore, the light guide plate 200b of the first modification can be manufactured more easily than the light guide plate 200 of the first embodiment in which the diffraction grating 230 is formed on the entire surface of the light incident end surface 212. On the other hand, according to the first embodiment, the light incident on the reflecting surface 202 side is also deflected in the tilt direction of the tilted surface 214, so that the arrival of light on the tilted surface 214 can be more reliably suppressed. Therefore, light leakage from the inclined surface 214 can be more reliably suppressed.

  In addition, when the diffraction grating 230 is provided on the entire surface of the light incident end face 212 as in the first embodiment, light incident on the reflecting surface 202 side in an inclined direction toward the reflecting surface 202 (inclination direction of the inclined surface 214) is incident. The light is further deflected in the direction of the reflecting surface 202 by the diffraction grating 230. Then, after the deflected light is reflected by the reflecting surface 202, it may reach the inclined surface 214 at a small incident angle and leak from the inclined surface 214. Therefore, unlike the first modification, by not providing the diffraction grating 230b in the region on the reflecting surface 202 side of the light incident end surface 212b, the reflecting surface 202 direction (inclination direction of the inclined surface 214) in the region on the reflecting surface 202 side. ) Is incident on the reflecting surface 202 and is prevented from leaking out from the inclined surface 214.

  In the first modification, no prism is formed on the light incident end surface 212b. However, even when the prism 240 is formed on the light incident end surface 212a as in the second embodiment, diffraction is performed only on the inclined surface 214 side. A lattice may be formed.

C2. Second modification of the diffraction grating:
FIG. 11 is a partial cross-sectional view showing the configuration of the diffraction grating 610 in the second modification. In the second modification, as shown in FIG. 11, no diffraction grating is formed on the light incident end face 212 c of the light guide plate 200 c, and the film 600 on which the diffraction grating 610 is formed is used as the light emission of the light incident end face 212 c and the LED 100. It is arranged between the surface 132. Other points are the same as in the first embodiment.

  The film 600 on which the diffraction grating 610 is formed can be formed using a known transfer technique such as roll transfer. In this case, since a large-area film can be produced by a production method such as a roll-to-roll system, a large-area film is formed in advance, and a film of a predetermined size is cut out from the film, thereby reducing the cost. The film 600 of the second modification can be produced.

  In the second modification, the diffraction grating 610 is formed on the film 600, which is a separate member from the light guide plate 200c, so that the light incident end surface 212c and the light emitting surface 132 are not affected by the shape of the light guide plate 200c. A diffraction grating 610 can be disposed therebetween. Therefore, the existing light guide plate can be used with almost no change. Even when the prism 240 is formed on the light incident end face 212a as in the second embodiment, the entire light emitted from the LED 100 can be incident on the diffraction grating 610. In this case, since it is possible to omit the gap surface 242 between the prisms 240, it becomes easier to make the intensity in the x direction of the light emitted from the light exit surface 224 more uniform and the light emitted from the LED 100. Leakage from the inclined surface 214 can be suppressed as a whole.

  Furthermore, in the second modification, the diffraction grating 610 is formed on the film 600 that is a separate member from the light guide plate 200c, so that the light distribution characteristics of the LED 100 and the optical characteristics of the light guide plate 200c are more appropriate. Since the diffraction grating 610 having diffraction characteristics can be used, it is possible to more effectively suppress the leakage of light from the inclined surface 214 side and the occurrence of unevenness in the amount of light emitted from the light exit surface 224.

  In the second modified example, the diffraction grating 610 is formed on the entire surface of the film 600. However, as in the first modified example, the inclination of the entire surface of the film 600 (the region through which the emitted light from the LED 100 passes). The diffraction grating 610 may be formed only in a partial region on the surface 214 side. Further, the film 600 having the diffraction grating 610 formed on the entire surface may be disposed only in a partial region on the inclined surface 214 side. In the latter case, the diffraction grating 610 is not formed, and a film having the same thickness as the film on which the diffraction grating 610 is formed may be disposed on the reflecting surface 202 side.

C3. Third modification of the diffraction grating:
FIG. 12 is an explanatory diagram showing the configuration and function of the diffraction grating 140 in the third modification. 12A is a partial cross-sectional view showing the configuration of the diffraction grating 140 in the third modification, and FIG. 12B is an enlarged cross-sectional view in which the region surrounded by the dotted line in FIG. 12A is enlarged. It is.

  In the third modification, as shown in FIG. 12A, the diffraction grating 140 is formed on the light emitting surface 132d of the LED 100d without forming the diffraction grating on the light incident end surface 212c of the light guide plate 200c. The LED 100d in which the diffraction grating 140 is formed on the light emitting surface 132d can be manufactured by forming the sealing portion 130d using a sealing technique using a mold such as transfer molding or compression molding.

  In the third modification, the convex portion 142 constituting the diffraction grating 140 is formed on the light guide surface 200c side of the light emitting surface 132d, and the light emitted from the LED 100d travels in the direction in which the convex portion 142 is formed. As described above, in the third modification example, the traveling direction of the light beam and the forming direction of the convex portion are different from those of the above-described embodiments, and thus the convex portion 142 having a different cross-sectional shape from the convex portion in each of the above-described embodiments is formed. . Specifically, as shown in FIG. 12B, the convex portion 142 includes a surface 144 on the reflecting surface 202 side having a steep inclination and a surface 146 on the inclined surface 214 side having a gentle inclination. . Therefore, the vertex 148 of the convex portion 142 is located on the inclined surface 214 side of the convex portion 142.

  FIG. 12C shows a state in which the light distribution characteristic is changed by providing the LED 100d with the diffraction grating 140. FIG. In FIG. 12C, the broken line indicates the far field characteristic of the LED 100 in which the diffraction grating 140 is not formed, and the solid line indicates the far field characteristic of the LED 100d in which the diffraction grating 140 is formed on the light emitting surface 132d. As shown in FIG. 12C, the intensity of the emitted light from the LED 100 in which the diffraction grating 140 is not formed becomes maximum in the optical axis OO direction. On the other hand, the intensity of the light emitted from the LED 100d on which the diffraction grating 140 shown in FIG. 12B is formed becomes maximum in the direction inclined in the inclination direction (−z direction) of the inclined surface 214 with respect to the optical axis OO.

  As described above, by providing the diffraction grating 140 on the light emitting surface 132d of the LED 100d, it is possible to deflect the emitted light of the LED 100d as a whole in the direction of inclination of the inclined surface 214 (direction of the reflecting surface 202). Therefore, leakage of light from the inclined surface 214 can also be reduced by the third modification.

  Further, in the third modification, by forming the diffraction grating 140 on the light emitting surface 132d of the LED 100d, the light deflected by the diffraction grating 140 is made incident on the light incident end surface 212c regardless of the shape of the light guide plate 200c. Can do. Therefore, the existing light guide plate can be used with almost no change as in the second modification. Further, even when the prism 240 is formed on the light incident end surface 212a as in the second embodiment, the deflected light can be incident on the light incident end surface 212a. Therefore, it is possible to omit the gap surface 242 between the prisms 240, so that it becomes easier to further uniform the intensity in the x direction of the light emitted from the light exit surface 224, and the entire light emitted from the LED 100d. Leakage from the inclined surface 214 can be suppressed.

  In the third modified example, the diffraction grating 140 is formed on the entire surface of the light emitting surface 132d. However, as in the first modified example, of the entire surface of the light emitting surface 132d (the region through which the light emitted from the LED 100d passes). The diffraction grating 140 may be formed only in a partial region on the inclined surface 214 side. Also in this case, as in the first modification, the amount of processing of a mold or the like used for sealing can be reduced, and thus the LED 100d in which the diffraction grating 140 is formed can be manufactured more easily. .

D. Variations:
The present invention is not limited to the above-described embodiments, and can be implemented in various modes without departing from the gist thereof. For example, the following modifications are possible.

D1. Modification 1:

  In each of the above embodiments and each modification of the diffraction grating, a single type of diffraction grating 230, 230b, 610, 140 is provided between the light emitting surfaces 132, 132d of the LEDs 100, 100d and the light incident end surfaces 212, 212a-212c. However, a different type of diffraction grating may be provided for each partial region of the region through which the light emitted from the LEDs 100 and 100d passes. For example, it is possible to provide diffraction gratings having different diffraction characteristics between the region on the inclined surface 214 side of the light incident end surface and the region on the reflective surface 202 side of the light incident end surface 212. In this case, a diffraction grating having a short grating interval may be formed in the region on the inclined surface 214 side, and a diffraction grating having a long grating interval may be formed in the region on the reflecting surface 202 side. In this case, it is possible to suppress leakage of light incident in the direction of the inclined surface 214 from the inclined surface 214, and to reduce the amount of deflection of light incident from a region close to the reflecting surface 202, thereby reducing the diffraction grating. As in the first modification example, the light incident on the reflection surface 202 side in the direction of the reflection surface 202 (inclination direction of the inclined surface 214) is further deflected in the direction of the reflection surface 202 by the diffraction grating 230b. Leakage from the inclined surface 214 can be suppressed.

D2. Modification 2:
In each of the above embodiments and each modification of the diffraction grating, the inclined surface 214 is provided on the light exit surface 224 side. However, it is also possible to provide an inclined surface on the reflection surface 202 side and make the light exit surface 224 side flat. . Even in this case, light leakage from the inclined surface can be suppressed by deflecting light emitted from the LED as a whole in the inclined direction of the inclined surface 214 by the diffraction grating. However, in this case, as shown in FIG. 1, the increase in thickness of the light guide plate 200 due to the provision of the inclined surface is added to the increase in thickness due to the lamination of the diffusion sheet 300 and the light collecting sheet 400. The thickness of the illumination device 10 increases. Therefore, it is more preferable to provide the inclined surface 214 on the light exit surface 224 side, as shown in each of the above embodiments and each modification of the diffraction grating.

D3. Modification 3:
In each of the above embodiments and modifications, the diffraction gratings 230, 230b, 610, and 140 are used to deflect the light emitted from the LEDs 100 and 100d as a whole in the inclination direction of the inclined surface 214. It is also possible to use various diffractive optical elements in place of 230b, 610, and 140. As the diffractive optical element, for example, a holographic optical element formed on a photopolymer material using a hologram can be used. However, since the diffraction gratings 230, 230b, 610, and 140 can be produced by forming grooves in the mold by cutting using a diamond tool, they can be produced more easily than holographic optical elements.

D4. Modification 4:
In each of the above-described embodiments and modifications, substantially point light source LEDs 100 and 100d are used as the light source of the surface illumination device 10, but as the light source, in addition to the LEDs 100 and 100d, an LED array, a cold cathode ray tube, Or various light emitting elements, such as an electroluminescence (EL: Electro Luminescence) element, can also be used.

10 ... Planar illumination device 100 ... LED
DESCRIPTION OF SYMBOLS 110 ... LED chip 120 ... Lamp house 122 ... Concave part 130, 130d ... Sealing part 132, 132d ... Light emission surface 140 ... Diffraction grating 142 ... Convex part 144, 146 ... Surface 148 ... Apex 200, 200a, 200b, 200c ... Light guide plate 202 ... Reflecting surface 210 ... Inclined portion 212, 212a, 212b, 212c ... Light incident end surface 214 ... Inclined surface 220 ... Flat portion 222 ... Opposing end surface 224 ... Light exiting surface 230, 230b ... Diffraction grating 232 ... Convex portion 240 ... Prism 242 ... Gap surface 244,246 ... Prism surface 300 ... Diffusion sheet 400 ... Condensing sheet 500 ... Diffraction grating 510 ... Resin plate 522 ... Convex part 524 ... Slope 528 ... Vertex 600 ... Film 610 ... Diffraction grating

Claims (9)

A planar lighting device,
A light source;
A light guide plate having a light incident end surface on which light emitted from the light source is incident, and a light output surface that emits light incident from the light incident end surface;
A diffractive optical element provided between the light source and the light incident end face;
The light guide plate is disposed on the light incident end surface side, and has an inclined portion provided with an inclined surface so that the thickness gradually increases toward the light incident end surface,
The diffractive optical element deflects the light emitted from the light source as a whole in the inclination direction of the inclined surface,
Planar lighting device.   2. The planar illumination according to claim 1, wherein the diffractive optical element has a diffraction efficiency of a diffracted light of a predetermined order deflected in the tilt direction by the diffractive optical element is higher than a diffraction efficiency of a diffracted light of another order. apparatus.   3. The planar illumination device according to claim 1, wherein the diffractive optical element is a diffraction grating in which a ridge-shaped convex portion extending in a longitudinal direction of the light incident end surface is formed.   The planar illumination device according to claim 3, wherein the convex portion has an asymmetric cross-sectional shape with respect to the tilt direction.   5. The planar illumination device according to claim 1, wherein the diffractive optical element is provided in a partial region on the inclined surface side in a region through which light emitted from the light source passes. A planar lighting device,
The light incident end face is provided with a plurality of prisms separated along the longitudinal direction of the light incident end face,
The diffractive optical element is provided on a surface between adjacent prisms of the light incident end surface,
The planar illumination device according to any one of claims 1 to 5.   6. The planar illumination device according to claim 1, wherein the diffractive optical element is provided on a light emitting surface of the light source.   The planar illuminating device according to any one of claims 1 to 5, wherein the diffractive optical element is provided on a film disposed between the light source and the light incident end surface.   The planar illumination device according to any one of claims 1 to 8, wherein the inclined surface is provided on the light exit surface side.