Illumination device and display device

Abstract

To provide an illumination device with improved light use efficiency, and a display device including the illumination device.SOLUTION: A display device includes a light source, a light guide plate, a first retardation plate, a holographic optical element, and a second retardation plate. The light source, the light guide plate, the first retardation plate, the holographic optical element, and the second retardation plate are stacked in this order. The holographic optical element reflects incident light with a predetermined incidence angle, and does not reflect light with the incidence angle other than the predetermined incidence angle.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] FIELD OF THE DISCLOSURE The present invention relates to a lighting device and a display device. [Background technology]

[0002] Liquid crystal display panels are one of the most widely used flat panel displays today. A liquid crystal display panel consists of two substrates on which pixel electrodes and a common electrode are formed, and a liquid crystal layer placed between them. An electric field is generated in the liquid crystal layer by applying a voltage to the electrodes, and this determines the orientation of the liquid crystal molecules in the liquid crystal layer, thereby controlling the polarization of the incident light, thereby displaying an image.

[0003] In a transmissive liquid crystal display panel, an illumination device is placed on the back surface, and the light emitted from the illumination device is modulated by the liquid crystal layer to display an image. In this case, the light from the illumination device is absorbed by the polarizing plates provided above and below the liquid crystal display panel. This type of display panel has the problem of poor light utilization efficiency and low display brightness. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] JP 2007-004182 A Summary of the Invention [Problem to be solved by the invention]

[0005] The present embodiment provides an illumination device with improved light utilization efficiency and a display device including the same. [Means for solving the problem]

[0006] An illumination device according to an embodiment includes: A light source; A light guide plate; A first retardation plate; A holographic optical element; A second retardation plate; Equipped with the light source, the light guide plate, the first phase difference plate, the holographic optical element, and the second phase difference plate are laminated in this order; The holographic optical element reflects incident light having a predetermined angle of incidence and does not reflect incident light having angles other than the predetermined angle of incidence.

[0007] Moreover, the display device according to one embodiment includes: A light source; A light guide plate; A first retardation plate; A holographic optical element; A second retardation plate; A lighting device comprising: A reflective polarizer; A first polarizing plate; A display panel; A second polarizing plate; Equipped with the light source, the light guide plate, the first phase difference plate, the holographic optical element, and the second phase difference plate are laminated in this order; the reflective polarizing plate, the first polarizing plate, the display panel, and the second polarizing plate are laminated in this order; the display panel is a liquid crystal display panel, The holographic optical element reflects incident light having a predetermined angle of incidence and does not reflect incident light having angles other than the predetermined angle of incidence. [Brief description of the drawings]

[0008] [Figure 1] FIG. 1 is a cross-sectional view showing a schematic configuration of a display device according to an embodiment. [Diagram 2] FIG. 2 is a cross-sectional view showing a schematic configuration of a display device of a comparative example. [Diagram 3] FIG. 3 is a cross-sectional view showing a schematic configuration of a display device of a comparative example. [Figure 4] FIG. 4 is a cross-sectional view showing another configuration example of the display device according to the embodiment. [Diagram 5]FIG. 5 is a cross-sectional view showing a schematic configuration example of a liquid crystal lens. [Figure 6] FIG. 6 is a cross-sectional view showing a schematic configuration example of a liquid crystal lens. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0009] Hereinafter, each embodiment of the present invention will be described with reference to the drawings. Note that the disclosure is merely an example, and those who are skilled in the art can easily come up with appropriate modifications while maintaining the gist of the invention, which are naturally included in the scope of the present invention. In addition, in order to make the explanation clearer, the drawings may show the width, thickness, shape, etc. of each part in a schematic manner compared to the actual embodiment, but these are merely examples and do not limit the interpretation of the present invention. In addition, in this specification and each figure, elements similar to those described above with respect to the previous figures may be given the same reference numerals, and detailed explanations may be omitted as appropriate.

[0010] DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The embodiments described in this specification are not general, but are embodiments describing the same or corresponding special technical features of the present invention.

[0011] In this embodiment, the first direction X, the second direction Y, and the third direction Z are perpendicular to each other, but may intersect at an angle other than 90 degrees. The direction toward the tip of the arrow of the third direction Z is defined as up or upward, and the direction opposite to the direction toward the tip of the arrow of the third direction Z is defined as down or downward. The first direction X, the second direction Y, and the third direction Z may also be called the X direction, the Y direction, and the Z direction, respectively.

[0012] Furthermore, in the case of "a second member above the first member" and "a second member below the first member," the second member may be in contact with the first member or may be located away from the first member. In the latter case, a third member may be interposed between the first and second members. On the other hand, in the case of "a second member above the first member" and "a second member below the first member," the second member is in contact with the first member.

[0013] Also, it is assumed that an observation position for observing the display device is located at the tip side of the arrow in the third direction Z, and a planar view refers to a view from this observation position toward the XY plane defined by the first direction X and the second direction Y. A cross-sectional view refers to a view of a cross section of the display device in the XZ plane defined by the first direction X and the third direction Z, or in the YZ plane defined by the second direction Y and the third direction Z.

[0014] [Embodiment] Fig. 1 is a cross-sectional view showing a schematic configuration of a display device according to an embodiment. The display device DSP shown in Fig. 1 includes a display panel PNL, a polarizing plate POL1, a polarizing plate POL2, a reflective polarizing plate DF, and an illumination device ILD. The illumination device ILD includes a light source LS, a light guide plate LG, a retardation plate RD1, a holographic optical element HE, and a retardation plate RD2. Note that no prism sheet is provided between the light guide plate LG and the retardation plate RD1.

[0015] The reflective polarizer DF, the polarizer POL1, the display panel PNL, and the polarizer POL2 are laminated in this order along the third direction Z. The reflective polarizer DF may be, for example, a reflective polarizing film (Dual Brightness Enhancement Film: DBEF).

[0016] The light source LS, the light guide plate LG, the retardation plate RD1, the holographic optical element HE, and the retardation plate RD2 are laminated in this order along the third direction Z. Each of the retardation plates RD1 and RD2 may be a 1 / 4λ plate.

[0017] The display panel PNL is a liquid crystal display panel including two transparent substrates and a liquid crystal layer sandwiched between the transparent substrates. A plurality of pixels are provided on the display panel PNL. However, the display panel PNL is not limited to a liquid crystal display panel. The display panel PNL may be any display panel that displays an image by modulating light emitted from the illumination device ILD.

[0018] When linearly polarized light enters a 1 / 4λ plate, if the vibration direction of the incident light is at an angle of θ=+45° with respect to the slow axis of the 1 / 4λ plate, the light exiting the 1 / 4λ plate becomes right-handed (clockwise) circularly polarized light. On the other hand, if the vibration direction of the incident light and the slow axis of the 1 / 4λ plate form an angle of θ=-45°, the light exiting the 1 / 4λ plate becomes left-handed (counterclockwise) circularly polarized light.

[0019] The holographic optical element HE has an interference fringe pattern and a refractive index with a period according to the wavelength in the thickness direction (third direction Z). Such a holographic optical element HE reflects and diffracts a portion of the incident light and has a lens action to focus the light. The holographic optical element HE is configured to reflect light incident at a specific incident angle and transmit light incident at an incident angle different from the specific incident angle.

[0020] The light emitted from the light source LS is incident on the light guide plate LG. Since the light emitted from the light source LS is linearly polarized light, the light incident on the light guide plate LG is also linearly polarized light. Since the polarization axis does not change in the light guide plate LG, the light emitted from the light guide plate LG is also linearly polarized light. The polarization axis of the linearly polarized light is assumed to be in the direction from the front to the back of the paper.

[0021] The light emitted from the light guide plate LG is incident on the retardation plate RD1. As described above, since the retardation plate RD1 is a ¼ λ plate, the light emitted from the retardation plate RD1 becomes counterclockwise circularly polarized light.

[0022] The light emerging from the retardation plate RD1 is incident on the holographic optical element HE. The polarization axis does not change in the holographic optical element HE. Therefore, the light emerging from the holographic optical element HE is left-handed circularly polarized light.

[0023] The light emitted from the holographic optical element HE is incident on the retardation plate RD2. Since the retardation plate RD2 is a 1 / 4 λ plate, the left-handed circularly polarized light incident on the retardation plate RD2 is changed to linearly polarized light. The polarization axis of the linearly polarized light is in the left-right direction with respect to the paper surface.

[0024] The linearly polarized light is emitted from the retardation plate RD2 and enters the reflective polarizer DF. The light that enters the reflective polarizer DF is reflected downward at a reflection angle θ, passes through the retardation plate RD1, and enters the holographic optical element HE.

[0025] The light that is emitted from the reflective polarizer DF and enters the retardation plate RD1 is changed from linearly polarized light to left-handed circularly polarized light.

[0026] Light that is incident on the holographic optical element HE is reflected at an incident angle θ and emitted upward. The incident angle θ on the holographic optical element HE is the same as the reflection angle θ at the reflective polarizer DF. Light that is incident on the holographic optical element HE at an angle other than the incident angle θ is not reflected by the holographic optical element HE and is not emitted upward.

[0027] The left-handed circularly polarized light that enters the holographic optical element HE is changed to right-handed circularly polarized light and emitted upward. The right-handed circularly polarized light that exits the holographic optical element HE enters the retardation plate RD2 and is changed back to linearly polarized light. The polarization axis of this linearly polarized light is oriented from the front to the back of the paper.

[0028] The linearly polarized light emitted upward from the retardation plate RD2 passes through the reflective polarizer DF, polarizer POL1, display panel PNL, and polarizer POL2, and is emitted upward from the display device DSP. The linearly polarized incident light, which has a polarization axis that runs from the front to the back of the paper, changes its polarization axis as it passes through polarizers POL1 and POL2. The polarization axis runs left to right with respect to the paper. The emitted light, which has a polarization axis that runs left to right with respect to the paper, leaves the display device DSP and enters the user's eyes. This allows the user to view the displayed image.

[0029] Fig. 2 is a cross-sectional view showing a schematic configuration of a display device of a comparative example. The display device DSPr shown in Fig. 2 includes an illumination device ILDr, a reflective polarizer DF, a polarizer POL1, a display panel PNL, and a polarizer POL2.

[0030] The illumination device ILDr of the display device DSPr shown in Fig. 2 includes a light source LS, a prism sheet PM, and a diffusion plate DS. The prism sheet PM is provided with a plurality of prisms and has a function of lifting the light incident from below upward. The diffusion plate DS has a function of diffusing the incident light and emitting it.

[0031] The light emitted from the light source LS is incident on the prism sheet PM. The light that has entered the prism sheet PM is lifted upward and then exits. The light that has exited from the prism sheet PM is incident on the diffusion plate DS.

[0032] The diffusion plate DS diffuses the light incident on a plane perpendicular to the third direction Z. The light exiting the diffusion plate DS is incident on the reflective polarizer DF.

[0033] The light emitted from the reflective polarizer DF passes through the polarizer POL1, the display panel PNL, and the polarizer POL2, and is emitted above the display device DSP.

[0034] 2, light emitted from the light source LS is emitted linearly upward along the third direction Z. At this time, the light is absorbed by the polarizing plates POL1 and POL2 while passing through the polarizing plates POL1 and POL2.

[0035] Furthermore, the light emitted from the light source LS does not necessarily travel in a straight line. There is also light traveling from the light source LS in a diagonal direction with respect to the third direction Z. The light traveling in a diagonal direction is not visible to the user. The presence of light traveling diagonally makes the displayed image darker. In other words, the illumination device ILDr does not utilize all of the light emitted from the light source LS.

[0036] 3 is a cross-sectional view showing a schematic configuration of a display device of a comparative example. The display device DSPr shown in FIG. 3 has the same configuration as the display device DSPr shown in FIG.

[0037] Light emitted from the light source LS passes through the light guide plate LG, the prism sheet PM, and the diffusion plate DS, and is emitted to the reflective polarizer DF.

[0038] The light that reaches the reflective polarizer DF is reflected by the reflective polarizer DF and emitted downward. The light that has exited from the reflective polarizer DF passes through the diffusion plate DS and the prism sheet PM, and is reflected by the light guide plate LG.

[0039] The light incident on the light guide plate LG is reflected at an angle φ with respect to the third direction Z. The light reflected at the angle φ travels upward while maintaining the angle φ. The light is emitted from the display device DSPr along a direction inclined at an angle φ with respect to the third direction Z, passing through the prism sheet PM and the diffusion plate DS, as well as the reflective polarizer DF, the polarizer POL1, the display panel PNL, and the polarizer POL2.

[0040] The light emitted from the display device DSPr at the angle φ does not reach the user's eyes. In other words, if the light reflected obliquely increases, the amount of light that is not visible to the user increases. Thus, the display device DSPr of the comparative example has a problem that the light utilization efficiency is poor and the display brightness is low.

[0041] On the other hand, in the display device DSP of the embodiment (see FIG. 1), the holographic optical element HE reflects and collects light incident at an angle θ. In the display device DSPr of the comparative example, even oblique light that is not utilized can be utilized in the display device DSP of the embodiment. The display device DSP of the embodiment has a higher light utilization efficiency than the display device DSPr of the comparative example. Therefore, the display device DSP of the embodiment can obtain a display image with high brightness.

[0042] According to the embodiment, it is possible to provide a display device in which the luminance of the display panel PNL is greatly improved by significantly increasing the efficiency of use of the light emitted from the light source LS. Also, according to the embodiment, it is possible to obtain an illumination device ILD that can significantly increase the efficiency of use of light.

[0043] <Configuration example 1> Fig. 4 is a cross-sectional view showing another example of the configuration of the display device in the embodiment. The example of the configuration shown in Fig. 4 is different from the example of the configuration shown in Fig. 1 in that a liquid crystal lens is provided.

[0044] In the display device DSP shown in Fig. 4, the illumination device ILD is the same as that in Fig. 1. The display device DSP shown in Fig. 4 differs from the display device DSP shown in Fig. 1 in that a liquid crystal lens LNS is provided between the reflective polarizer DF and the polarizer POL1.

[0045] In FIG. 4, a reflective polarizer DF, a liquid crystal lens LNS, a polarizer POL1, a display panel PNL, and a polarizer POL2 are laminated in this order along the third direction Z.

[0046] By providing the liquid crystal lens LNS, it is possible to control the viewing angle of the display device DSP. Hereinafter, the optical action of the liquid crystal lens LNS will be described with reference to Figs. 5 and 6. Note that Figs. 5 and 6 show only the configuration necessary for the description. Figs. 5 and 6 are cross-sectional views showing schematic configuration examples of the liquid crystal lens.

[0047] The liquid crystal lens LNS shown in Figures 5 and 6 includes a polarizer POL3, an electrode LE, an insulating layer INS, a liquid crystal layer LC1, an electrode UE, and a polarizer POL4. The insulating layer INS and the electrodes LE are provided in the same layer. The liquid crystal layer LC1 includes liquid crystal molecules LM1.

[0048] FIG. 5 is a diagram showing a schematic diagram of the liquid crystal lens LNS in an off state (OFF) where no electric field is applied to the liquid crystal layer LC1.

[0049] Of the illumination light emitted from the illumination device ILD, the p-polarized light LP is incident on the liquid crystal lens LNS. Note that the s-polarized light is not modulated by the liquid crystal layer LC1, so its description is omitted.

[0050] In the liquid crystal layer LC1 in the off state, the liquid crystal molecules LM1 are initially aligned. In this off state, the liquid crystal layer LC1 has a nearly uniform refractive index distribution. Therefore, the p-polarized light LP that is incident on the liquid crystal lens LNS passes through the liquid crystal layer LC1 with almost no refraction (or divergence).

[0051] Therefore, when the liquid crystal lens LNS is in the off state, illumination light with a relatively small degree of divergence can be formed, and an image display in the narrow viewing angle mode can be realized by the light transmitted through the display panel PNL.

[0052] FIG. 6 is a diagram showing a schematic diagram of the liquid crystal lens LNS in an on state (ON) where an electric field is generated in the liquid crystal layer LC1.

[0053] For example, if the liquid crystal layer LC1 has positive dielectric anisotropy, in the on-state where an electric field is formed in the liquid crystal layer LC1, the liquid crystal molecules LM1 are oriented so that their major axes are aligned along the electric field. For example, in the liquid crystal layer LC1, an electric field is formed according to the potential difference between the adjacent electrodes LE and the potential difference between the electrodes LE and UE.

[0054] When such an electric field acts on the liquid crystal layer LC1, regions are formed in the liquid crystal layer LC1 where the liquid crystal molecules LM1 stand almost perpendicular to the substrate, regions where the liquid crystal molecules LM1 are maintained in their initial orientation, and regions where the liquid crystal molecules LM1 stand diagonally to the substrate.

[0055] The liquid crystal molecules LM1 have a refractive index anisotropy Δn. Therefore, the liquid crystal layer LC1 in the on state has a refractive index distribution or retardation distribution according to the alignment state of the liquid crystal molecules LM1. Here, retardation is expressed as Δn·d, where d is the thickness of the liquid crystal layer LC1.

[0056] In such an on-state, the p-polarized light LP is diverged due to the refractive index distribution of the liquid crystal layer LC1 when it passes through the liquid crystal layer LC1. The degree of divergence of the transmitted light can be controlled by the voltage applied to the liquid crystal layer LC1.

[0057] Therefore, when the liquid crystal lens LNS is in the ON state, it is possible to form illumination light with a relatively large degree of divergence, and it is possible to realize image display in the wide viewing angle mode by the light transmitted through the display panel PNL. This configuration example also provides the same effects as the embodiment.

[0058] Although some embodiments of the present invention have been described, these embodiments are presented as examples and are not intended to limit the scope of the invention. These novel embodiments can be implemented in various other forms, and various omissions, substitutions, and modifications can be made without departing from the spirit of the invention. These embodiments and their modifications are included in the scope and spirit of the invention, and are included in the scope of the invention and its equivalents described in the claims. [Explanation of symbols]

[0059] DF...reflective polarizing plate, DS...diffuser plate, DSP...display device, HE...holographic optical element, ILD...illumination device, LNS...liquid crystal lens, LS...light source, PM...prism sheet, PNL...display panel, POL1...polarizing plate, POL2...polarizing plate, RD1...phase difference plate, RD2...phase difference plate.

Claims

1. A light source; A light guide plate; A first retardation plate; A holographic optical element; A second retardation plate; Equipped with the light source, the light guide plate, the first retardation plate, the holographic optical element, and the second retardation plate are laminated in this order; The holographic optical element reflects incident light having a predetermined angle of incidence and does not reflect light having an angle of incidence other than the predetermined angle of incidence.

2. The illumination device according to claim 1 , wherein the first retardation plate and the second retardation plate are each a ¼λ plate.

3. The illumination device according to claim 1 , wherein the illumination device does not include a prism sheet between the light guide plate and the first retardation plate.

4. A light source; A light guide plate; A first retardation plate; A holographic optical element; A second retardation plate; A lighting device comprising: A reflective polarizer; A first polarizing plate; A display panel; A second polarizing plate; Equipped with the light source, the light guide plate, the first retardation plate, the holographic optical element, and the second retardation plate are laminated in this order; the reflective polarizing plate, the first polarizing plate, the display panel, and the second polarizing plate are laminated in this order; the display panel is a liquid crystal display panel, The display device, wherein the holographic optical element reflects incident light having a predetermined angle of incidence and does not reflect incident light having angles of incidence other than the predetermined angle of incidence.

5. The display device of claim 4 , further comprising a liquid crystal lens between the reflective polarizer and the first polarizer.

6. The display device according to claim 4 , wherein the first retardation plate and the second retardation plate are each a ¼λ plate.

7. The display device according to claim 4 , wherein the illumination device does not have a prism sheet between the light guide plate and the first retardation plate.

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