JP5549816B2 - Backlight device - Google Patents

Description

  The present invention relates to a backlight device used as illumination in various display devices such as a liquid crystal display device, and more particularly to a backlight device using coherent light such as laser light.

  As a backlight device used for a liquid crystal display device or the like, a direct type backlight system in which a plurality of light sources are arranged in a plane is known. Currently, LEDs are mainly used as the light source of such backlight devices.

  In the system using LEDs as the light source, since the LEDs are uniformly diffused illumination, it is necessary to control the light distribution characteristics of the LEDs, but light with an angle close to parallel to the backlight surface must be effectively extracted. Is difficult. Laser light, which is expected as a next-generation light source, is excellent in straightness, so that it is considered that the light incident efficiency can be increased as compared with the LED. However, when laser light is used as a light source, there is a drawback that speckle noise is generated due to high coherence and it is difficult to view an image.

  Speckle noise is spot-like image noise that occurs when scattered light from minute irregularities on the surface to be irradiated interferes when coherent laser light is used as a light source. In order to reduce this speckle noise, various attempts have been made, such as vibrating the diffusion plate through which the laser beam passes, expanding the wavelength spectrum of the laser spectrum, and vibrating the screen itself that is the target of the laser beam irradiation. . As an attempt to reduce such speckle noise, Patent Document 1 discloses a non-speckle display device that reduces speckle noise by rotating a diffusion element through which coherent light passes.

Japanese Patent Laid-Open No. 6-208089 JP-A-6-301322

  However, in the speckle noise reduction method disclosed in Patent Document 1, speckle noise (interference pattern) generated before reaching the diffusing element can be averaged, but the incident ray angle from the diffusion center to the screen is on the screen. Since it is invariant at any point, the light scattering characteristics at each point on the screen are constant, and as a result, there is a problem that the effect of removing speckle noise generated on the screen is hardly obtained.

  The present invention proposes a new speckle noise reduction method in view of the problem of speckle noise generation in a backlight device. Specifically, a method is adopted in which speckle noise is reduced by temporally changing the incident angle of light within the screen surface to be irradiated.

Therefore, the backlight device according to the present invention is a backlight device including a plurality of unit backlights, and the unit backlight includes an optical fiber, a deflecting unit, and a light diffusing element, and the optical fiber includes an end portion thereof. Is deflectably supported by the deflecting unit, and incident light from a coherent light source is emitted to the light diffusing element side. The deflecting unit deflects an end of the optical fiber to be supported, The light diffusing element scans the emitted light, and diffuses the emitted light from the optical fiber so that the emitted light from the optical fiber incident on each point illuminates substantially the same illumination region. To do.

  Furthermore, in the backlight device according to the present invention, the light diffusing element is a hologram, and light emitted from the optical fiber incident on each point forms substantially the same illumination by forming the same diffusing plate image. The area is illuminated.

  Furthermore, in the backlight device according to the present invention, the hologram uses, as object light, light from a diffuser plate located at the same place as the illumination area, and light conjugate with the emitted light scanned by the optical fiber. It is used for recording.

  Furthermore, in the backlight device according to the present invention, the light diffusing element is a lens array.

  Furthermore, in the backlight device according to the present invention, illumination areas formed by the adjacent unit backlights are adjacent to each other or overlap each other.

  Furthermore, in the backlight device according to the present invention, the light diffusing element is formed of a common member between the unit backlights.

  Furthermore, in the backlight device according to the present invention, the deflection unit deflects the plurality of unit backlights in conjunction with each other.

  As described above, according to the backlight device of the present invention, speckle noise can be effectively invisible with a simple configuration. Moreover, the use efficiency of light can be improved by using a laser beam having high straightness as the light source. Further, since the laser light has a single wavelength oscillation, it is possible to expand the color reproduction region when using laser beams of a plurality of colors.

The figure which shows the structure of the backlight apparatus which concerns on embodiment of this invention. The figure which shows the mode of the emission light formation which concerns on embodiment of this invention. The figure which shows the structure of the deflection | deviation part which concerns on embodiment of this invention. The figure which shows the mode of the emission light scanning which concerns on embodiment of this invention. The figure which shows the mode of illumination area formation which concerns on embodiment of this invention. The figure for demonstrating the positional relationship of an adjacent illumination area | region. The figure which shows the structure at the time of recording the hologram which concerns on embodiment of this invention. The figure which shows the structure of the backlight apparatus which concerns on other embodiment of this invention. The figure which shows the mode of illumination area formation which concerns on other embodiment of this invention.

  FIG. 1 is a diagram showing a configuration of a backlight device according to an embodiment of the present invention, and FIG. 2 is a diagram showing a state of emission light formation according to the embodiment of the present invention. As shown in FIG. 1, the backlight device according to the present embodiment includes, as main components, a hologram 1 as a light diffusing element and a plurality of deflecting units 2 a to 2 d arranged on the back surface of the hologram 1. Yes. For the sake of convenience, the axial direction of the deflection units 2a to 2d is the X axis, the direction in which the deflection units 2a to 2d are arranged (the depth direction in FIG. 1) is the Y axis, and the front surface as the backlight device is the Z axis. Take it.

  The hologram 1 is parallel to the XY plane and is disposed in front of the deflection units 2a to 2d. In the present embodiment, a plurality of recording areas are formed on one hologram. This recording area is provided for each unit backlight. Although the hologram 1 is used as the light diffusing element, a lens array or a normal diffusing plate may be used as long as the optical element has similar characteristics. Note that a volume hologram is preferably used as the hologram 1 to be used. Since the volume hologram generates diffracted light by interference fringes formed therein, it is not necessary to provide unevenness on the surface, and speckle noise that is secondarily generated in the hologram can be suppressed. Furthermore, since the volume hologram can set the diffraction efficiency high and can effectively suppress the zero-order transmitted light, the intended diffuser plate image can be reproduced accurately.

  FIG. 2 is a diagram showing in detail a part of the deflecting unit 2 a installed on the back surface of the hologram 1 in FIG. 1, and shows how the emitted light is formed on the hologram 1. The deflection unit 2 includes a rotation shaft 21 and an optical fiber support portion 22 formed on the rotation shaft 21 at a predetermined interval. The optical fiber support 22 is formed with a hole for fixing the optical fiber end 31 at the center position of the end, and the optical fiber end 31 is positioned in this hole. A laser light source (coherent light source) is connected to the other end of the optical fiber 3 and outputs emitted light from each optical fiber end portion 31 to the hologram 1 side. A unit backlight is composed of the optical fiber end 31, the deflection unit 2 that deflects the optical fiber end 31, and the hologram 1 on which the diffusion plate image is recorded. The method for guiding light to each optical fiber end portion 31 and the method for fixing the optical fiber end portion 31 to the optical fiber support portion 22 are not limited to such an embodiment, and any appropriate method can be adopted.

  The rotation shaft 21 rotates a predetermined rotation range about the axis as indicated by an arrow in the figure. The optical fiber end portion 31 supported by the optical fiber support portion 22 is deflected so as to draw an arc, and the emitted light irradiated from the optical fiber end portion 31 scans the back surface of the hologram 1 at a predetermined cycle. The turning shaft 21 is turned by a turning mechanism composed of a motor or a cam. Thus, by rotating the plurality of optical fiber support portions 22 with the single rotation shaft 21, it is possible to make the configuration common and to reduce the size and simplification of the apparatus. The rotation mechanism may be configured to share the deflection units 2a to 2d arranged in the Y-axis direction.

  FIG. 3 is a diagram showing a configuration of the deflecting unit according to the embodiment of the present invention, and is a view of one of the optical fiber support units 22 arranged on the deflecting unit 2 as viewed from the X-axis direction. As shown in the figure, the deflecting unit 2 rotates around a rotation center O of the rotation shaft 21 in a rotation range as shown. The optical fiber end portion 31 supported by the optical fiber support portion 22 by turning the deflecting portion 2 changes its direction by drawing an arc, and scans the emitted light emitted on the back surface of the hologram 1. The period of the deflection unit 2 is sufficient to be about the frame rate of the image display device to be used (for example, 30 fps).

  FIG. 4 is a diagram illustrating a state of the emitted light scanning according to the embodiment of the present invention, and illustrates a state in the vicinity of the scanning end portion during the back surface scanning of the hologram 1. As shown in the figure, the light emitted from the optical fiber end 31 scans the back surface of the hologram 1. With the hologram 1 that has received the emitted light as reproduction illumination light, the diffusion plate image is reproduced as diffracted light. In this embodiment, since a transmission hologram is employed, the diffuser plate image is formed on the side opposite to the optical fiber end 31. At the time of hologram recording, recording is performed so that the same diffuser plate image is reproduced for any angle of reproduction illumination light. Therefore, the same diffusion plate image is reproduced from the hologram 1 regardless of the orientation of the deflecting unit 2. A method for recording (creating) such a hologram 1 will be described later.

  On the other hand, when attention is paid to one point of the diffuser plate image, it can be seen that the light emitted from the hologram 1 is formed by changing the incident angle with time. For example, if the screen is placed at the position of the diffuser image, the incident angle of light on the screen is temporally different, so the speckle noise is averaged, and an image quality equivalent to that when using a non-coherent light source is obtained. Can do.

  In the present embodiment, the hologram 1 (transmission type hologram) is used as the light diffusing element. However, by using the hologram 1, the same diffusion plate image is always formed as a reproduced image, and the designer intends It is possible to stably form the illumination area to be performed. Further, by adopting the hologram 1, it is possible to increase the degree of freedom of the shape of the beam cross section incident on the hologram 1 and the incident angle of the beam. As the light diffusing element, in addition to the hologram 1, a lens array in which fine lenses are arranged on the array, a normal diffusing plate, or the like can be used.

  In the present invention, any light diffusing element is sufficient as long as it illuminates substantially the same illumination area when irradiated with light emitted from the optical fiber end 31. As for the illumination area, it is possible to form the completely same or almost the same illumination area when using a hologram, but when using a lens array or a diffuser plate, it is completely the same. Since it is difficult to form an illumination area, it is assumed that each point of the light diffusing element is substantially the same because it irradiates the entire illuminated area.

  At the position of the illumination area (diffusion plate image), a liquid crystal panel or the like that forms an image based on the image information is disposed. In this way, by using a backlight device that can sufficiently reduce speckle noise, it is possible to achieve high image quality of the image forming apparatus.

  FIG. 5 is a diagram illustrating a state of forming an illumination area according to the embodiment of the present invention, and is a view in which one optical fiber end 31, that is, an illumination area formed by a unit backlight is viewed from the Z-axis direction. ing. The formation area of the hologram 1 is arranged so as to encompass the scanning range of the emitted light from the optical fiber end 31 by the deflecting unit 2. The diffusion plate image described with reference to FIG. 4 can be reproduced regardless of the position of the light emitted from the optical fiber end 31. The same applies not only to the Y-axis direction but also to the X-axis, that is, the width direction of irradiation light.

  The emitted light applied to the hologram 1 forms an illumination area (diffuser plate image) in the XY plane. FIG. 6 is a diagram for explaining the positional relationship between adjacent illumination areas. In this embodiment, it is comprised so that a part of adjacent illumination area may mutually overlap. In the figure, the illumination area of interest is described in the center, and an overlapping area with adjacent illumination areas is indicated by hatching around the illumination area of interest. In the present embodiment, it is possible to form an illumination area that does not leak on the entire surface of the backlight device by overlapping adjacent illumination areas in this manner. Note that the illumination areas may be substantially adjacent to each other without overlapping each other. In the present embodiment, the illumination areas adjacent to each other between the deflecting units 2a to 2c are positioned up and down. However, the illumination areas adjacent to each other may be shifted from each other.

FIG. 7 is a diagram showing a configuration (interference exposure) when recording (creating) a hologram according to the embodiment of the present invention. Laser light is irradiated from the back side of the diffusing plate 51, and the object light Ob diffused forward is made incident from one surface of the hologram recording material 11. At that time, diffused light from each point of the diffusing plate 51 is diffused so as to illuminate at least the entire use region of the hologram recording material 11. Then, the reference light R condensed by the condensing optical system 52 is irradiated from the same surface of the hologram recording material 11. The focal position of the condensing optical system 5 is arranged so as to coincide with the divergence point of the irradiated light by the optical fiber 3 at the time of reproduction. The object light Ob and the reference light R are simultaneously incident and interfered in the hologram recording material 11. The hologram recording material 11 is subjected to post-processing such as heating and ultraviolet irradiation to produce a transmission hologram that reproduces the diffuser plate image at the same position at each point on the surface.

  The created hologram may be mounted on the backlight device by arranging it for each unit backlight. However, the created hologram covers one surface of the backlight device as shown in FIG. It is preferable to arrange in an array on the material, expose the recording material, and create a single hologram on which a plurality of regions for reproducing the diffusion plate image are formed. Compared with the case where a plurality of holograms are arranged, it is not necessary to position each hologram. Furthermore, it becomes possible to improve productivity by duplicating this hologram.

  In FIG. A, the state of the deflecting unit 2 during hologram reproduction is shown as a reference. An image of the diffuser plate 51 is formed by forming light (reproduction illumination light) conjugate with the reference light R (the direction is the same and the opposite direction) by scanning the light emitted from the optical fiber end 31 by the deflecting unit 2. (Diffusion plate image) can be reproduced. In the present embodiment, interference fringes are recorded (interference exposure) by causing the object beam Ob and the reference light R to interfere with each other. However, the interference fringes calculated by the computer are directly recorded on the recording material 11. A so-called computer generated hologram may be employed.

Table 1 shows speckle contrast under various conditions. (1) and (2) are for comparison, and are measurement results in the case where only a laser parallel light is used and a monochromatic LED is used. (3) and (4) are measurement results according to the embodiment of the present invention, and are measurement results when a volume hologram and a computer generated hologram are used as the light diffusing element, respectively. The speckle contrast is expressed by the following formula (1). For measurement, an image was projected on a screen using a DPSS laser (532 nm) as a light source. The volume hologram used in this measurement was prepared so that the diffusion angle, that is, the apex angle of the cone formed by the light beam incident on one point of the screen was 20 °. A photopolymer material having sensitivity at 532 nm (the material described in Example 1 of Patent Document 2 cited as the prior art document) is used as the recording material for each hologram.
SC = σ / I × 100
= 1 / (Modes) ^0.5 x 100 (1)
SC: speckle contrast σ: standard deviation of luminance I: luminance average value Modes: number of patterns (number of statistically independent speckles)

  In the case of laser parallel light, about 20 and the monochromatic LED is 4, whereas in the case of the light diffusing element (volume hologram, computer generated hologram) of the present invention, an extremely good result of less than 4 was obtained. About the point that speckle contrast is better than in the case of the single color LED, since the light diffusion element is not used for the illumination of the single color LED, there is a slight luminance unevenness compared to the case where the light diffusion element is used. Conceivable.

  As described above, the embodiment of the present invention has been described by taking as an example the case where the transmission hologram 1 is adopted as a light diffusing element. Is also possible. Further, not only a transmission type hologram but also a reflection type hologram can be adopted.

  FIGS. 8 and 9 are diagrams showing an embodiment using a reflection hologram as a light diffusing element. FIG. 8 shows a configuration of a backlight device similar to FIG. The figure which shows the mode of illumination area formation is shown. As shown in FIG. 8, the hologram 1 as the optical diffusing element is opposite to the deflecting unit 2, that is, opposite to the irradiation direction as the backlight device, as compared with the case where the transmission hologram is used. Placed on the side. About the detail of the deflection | deviation part 2, only the rotation direction and the rotation range differ, The outline of a structure is as substantially the same as having demonstrated in FIG.

  FIG. 9 shows a part of the configuration of the backlight device as viewed from the X-axis direction. Outgoing light traveling toward the hologram 1 is output from the end of the optical fiber supported by the optical fiber support 22a disposed in each of the deflection units 2a and 2b. The emitted light scans a predetermined region on the hologram 1 by temporally deflecting at the optical fiber end portion by the deflecting portions 2a and 2b. For example, the light emitted from the optical fiber support 22a scans the region 1a of the hologram 1, and the light emitted from the optical fiber support 22b scans the region 1b of the hologram 1.

  In each of the areas 1a and 1b, an illumination area a and an illumination area b are recorded as diffusion plate images, and these are reproduced using the emitted light from the end of the optical fiber as reproduction illumination light. In the present embodiment, the illumination areas a and b are adjacent to each other to perform backlight illumination with no leakage as a whole. However, as in the previous embodiment, the illumination areas may be partially overlapped. Good. In addition, it is preferable that the positional relationship be such that the optical path is not obstructed even when each of the deflecting units 2a and 2b rotates. In the present embodiment, the areas 1a and 1b of the hologram 1 are reduced with respect to the illumination areas a and b with respect to the Y-axis direction, so that the deflection units 2a and 2b are provided between the optical paths formed by unit backlights adjacent in the Y-axis direction. Is formed (a triangular space in which 21, 21 is accommodated in FIG. 9), and the optical path is not obstructed even when the deflecting portions 2a, 2b are rotated.

  As described above, even when a reflection hologram is employed as the light diffusing element, the illumination area (diffuser plate image) is formed by the reproduction light from the hologram 1 whose angle changes with time, and therefore, coherent. It is possible to effectively suppress speckle noise caused by being a light source.

  Note that the present invention is not limited to these embodiments, and embodiments configured by appropriately combining the configurations of the respective embodiments also fall within the scope of the present invention.

1 ... Hologram (light diffusion element)
DESCRIPTION OF SYMBOLS 11 ... Recording material 2 ... Deflection part 21 ... Turning axis 22 ... Optical fiber support part 3 ... Optical fiber 31 ... Optical fiber end part 4 ... Laser light source (coherent light source)
51 ... Diffusing plate 52 ... Condensing optical system

Claims (7)

A backlight device in which a plurality of unit backlights are arranged in parallel,
The unit backlight includes an optical fiber, a deflection unit, and a light diffusing element,
The optical fiber has an end that is deflectably supported by the deflecting unit, and emits incident light from a coherent light source toward the light diffusing element.
The deflecting unit deflects an end of the optical fiber to be supported, and scans light emitted from the optical fiber,
The backlight device, wherein the light diffusing element diffuses the light emitted from the optical fiber so that the light emitted from the optical fiber incident on each point illuminates substantially the same illumination area. The light diffusing element is a hologram, and emitted light from the optical fiber incident on each point illuminates substantially the same illumination region by reproducing the same diffusion plate image. The backlight device according to 1. The hologram is recorded using diffused light from a diffusion plate located at the same place as the illumination area as object light, and using light conjugate with emitted light scanned by the optical fiber as reference light. The backlight device according to claim 2. The backlight device according to claim 1, wherein the light diffusing element is a lens array. 5. The backlight device according to claim 1, wherein illumination regions formed by the adjacent unit backlights are adjacent to each other or overlap each other. The backlight device according to any one of claims 1 to 5, wherein the light diffusing element is formed of a common member between the unit backlights. The backlight device according to any one of claims 1 to 6, wherein the deflecting unit deflects the plurality of unit backlights in conjunction with each other.

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