JP3552383B2 - Display device - Google Patents

Description

[0001]
【Technical field】
The present invention relates to a display device using a hologram screen, and more particularly to a display device capable of suppressing noise light entering a viewer's eyes and increasing the contrast of a displayed image.
[0002]
[Prior art]
2. Description of the Related Art As a display device for forming an image on a screen, a projector projection type display device using liquid crystal is known. This type of display device irradiates a transmission type or reflection type liquid crystal with light from a predetermined direction, and emits signal light in which an image formed on the liquid crystal is recorded. Then, the display image of the signal light is formed on a screen via an image forming lens or the like, and the transmitted scattered light or the reflected scattered light of the display image emitted from the screen is visually recognized by a viewer.
[0003]
In addition, there is a type in which a CRT projector or the like is used instead of a liquid crystal projector and emits three color beams of R (red), G (green), and B (red) to form a display image on a screen.
As described above, the display device using a normal screen has a problem that, in a bright environment, the contrast of a display image is reduced by light incident on the screen from the surroundings. Therefore, the display device can be used only in a limited place where the illuminance from the environment is low.
[0004]
In order to cope with such a problem, a method has been proposed in which a hologram element is used for a screen, and the hologram is diffracted to exhibit the characteristics of the screen as a scatterer only for specific light incident from a specific direction. ing. That is, a hologram element on which a scatterer is recorded is used as a screen to scatter light only for irradiation light (signal light) incident from a specific direction, and transmit or specularly reflect light incident from other directions.
[0005]
As a result, most of the ambient light is not scattered on the screen, so that the brightness of the background of the screen does not increase, and the contrast of the displayed image is improved (see Japanese Patent Application Laid-Open No. 5-333435).
In addition to the above configuration using a hologram screen, a method has been proposed in which an external light absorbing means (black paint or the like) for absorbing external light is provided inside the hologram screen, thereby absorbing external light. (See JP-A-5-88020).
[0006]
[Problem to be solved]
A display device using a hologram screen has the advantage of improving the contrast of a display image against the background as described above. However, between the hologram screen and the outside air or between the components of the hologram screen, reflection occurs at the boundary surface having a different refractive index, and a part of the reflected light travels in the direction of the viewer. The problem of lowering the contrast and making the image difficult to see still remains.
In particular, in an environment where strong external light such as sunlight or a lighting lamp is present, the decrease in contrast due to the reflected light noise becomes remarkable.
[0007]
As shown in FIG. 5, in the case of a hologram screen 91 using a reflection hologram, the signal light 31 radiated from the projector 93 is diffracted and reflected by the hologram 910 and becomes a regular diffracted light 311 of the viewer 81. Enters the eye. However, the noise extraneous light 390 incident from a specific direction is transmitted through the substrates 911 and 912 sandwiching the hologram 910 and the hologram 910 and then reflected at the interface 913 between the substrate 912 and the outside air. When the angle of incidence on the hologram 910 coincides with the direction opposite to the angle of incidence of the signal light 31 (a difference of 180 degrees), the noise diffracted light 392 of the first reflected light 391 becomes opposite to the normal diffracted light 311 of the signal light 31. You will go toward.
[0008]
Then, the noise diffracted light 392 is reflected again at the interface 913 and becomes harmful noise light 393 visually recognized by the viewer 81. In this case, the noise light 393 reaches the eyes of the viewer 81 through a total of three reflections including reflection due to diffraction. However, since external light such as sunlight is extremely strong light, it is reflected three times. Even afterwards, it still has a strong intensity, which greatly reduces the contrast of the displayed image.
[0009]
On the other hand, as shown in FIG. 6, in the case of a hologram screen 92 using a transmission hologram, the signal light 31 radiated from a projector (not shown) is diffracted and transmitted by the hologram 920 and becomes a regular diffracted light 311. And enters the eyes of the viewer 81. However, part of the external light 394 that has entered from a specific direction passes through the substrate 911 that sandwiches the hologram 920, and the angle of incidence on the hologram 920 is opposite (180 degrees) to the angle of incidence of the signal light 31. When they match, the diffraction noise light 395 of the external light 394 travels in the direction opposite to the normal diffraction light 311 of the signal light 31. Then, the diffraction noise light 395 is reflected again at the interface 913 and becomes harmful noise light 396 visually recognized by the viewer 81, and similarly, the contrast of the display image is reduced.
[0010]
Further, other external light noise 397 reflected by the external object 95 or the like passes through the substrates 911 and 912 sandwiching the hologram 920 and the hologram 920, and then is reflected at the interface 913 between the substrate 912 and the outside air. When the incident angle of the noise light 398 to the hologram 920 coincides with the incident angle of the signal light 31 to the hologram 920, the diffraction noise light 399 of the reflection noise light 398 is directed in the same direction as the diffraction light 311 of the signal light 31. , Which becomes another harmful noise light visually recognized by the viewer 81, and similarly reduces the contrast of the displayed image.
[0011]
The present invention has been made in view of such a conventional problem, and an object of the present invention is to provide a display device using a hologram screen that can suppress harmful noise light generated by external light and increase the contrast of a display image. Is what you do.
[0012]
[Means for solving the problem]
In the display device according to the first aspect of the present invention, a translucent anti-reflection member is disposed on the back side of the transmission type hologram screen, and the anti-reflection member has a predetermined angle range in which the signal light is incident. The incident angle of the first noise light (see FIGS. 1 and 6, diffracted noise light 395) incident on the hologram screen from the direction opposite to α and diffracted and transmitted, or the light regularly reflected by the antireflection member is It has a low reflectance with respect to the incident angle of the second noise light (see FIG. 1 and FIG. 6, the external light noise light 397) in the same direction as the predetermined angle range α.
[0013]
Therefore, the light that reflects the first noise light toward the viewer (see FIGS. 1 and 6 and the harmful noise light 396) and the light that reflects and diffracts the second noise light toward the viewer (see FIG. 1). 1, the intensity of the harmful noise light 399) is greatly reduced. That is, according to the present invention, harmful background light generated by external light can be significantly suppressed, and the contrast of a displayed image can be increased.
[0014]
Next, in the display device according to the invention of claim 2 of the present application, a translucent anti-reflection member is disposed on the back side of the reflection type hologram screen, and the anti-reflection member is a positive anti-reflection member. The third noise light (see FIGS. 3, 5, and the outside light 390) or the third noise light in which the reflected light is in the direction opposite to the predetermined angle range β where the signal light is incident is diffracted and reflected by the hologram. It has a low reflectance with respect to the incident angle of the fourth noise light (see FIGS. 3, 5 and the noise diffracted light 392).
Therefore, the intensity of the harmful background noise light (see FIGS. 3, 5, and 393) caused by the third noise light and the fourth noise light is significantly reduced, and the contrast of the display image can be increased. it can.
[0015]
Next, a display device according to a third aspect of the present invention uses a transmission type or reflection type hologram screen having a high diffraction efficiency with respect to light linearly polarized in a predetermined direction. A polarizing optical element is disposed on the side, and the polarizing optical element selectively transmits predetermined linearly polarized light having a high diffraction efficiency by the hologram screen. The polarizing optical element includes, for example, a polarizing plate and a polarizing film.
[0016]
Therefore, external light such as natural light coming from at least the front side toward the hologram screen passes through the polarizing optical element, so that other polarized components are removed, and the intensity is reduced to a fraction. For example, the intensity of external light such as sunlight containing all polarized light components is attenuated to about one third by passing through the polarizing optical element. On the other hand, the linearly polarized light diffracted by the hologram is not attenuated by the presence of the polarizing optical element, so that the brightness of the display image viewed by the viewer does not change. That is, according to the present invention, it is possible to reduce harmful noise light generated by external light while keeping the brightness of the display image unchanged, and thus to enhance the contrast of the display image.
[0017]
In addition, as described in claim 4, the invention of claim 3 can be applied to the display device of claim 1 or claim 2, and the effects of both inventions can be exhibited synergistically. That is, after the hologram of the hologram screen has a high diffraction efficiency with respect to the linearly polarized light, the polarizing optical element is arranged at least on the front surface of the hologram screen of the display device according to claim 1 or 2. Thus, the intensity of external light incident on the hologram screen can be attenuated at the entrance, so that harmful noise light can be further reduced and the contrast of the displayed image can be increased.
[0018]
According to a fifth aspect of the present invention, in the display device according to any one of the first to fourth aspects, the hologram screen is further surrounded by the hologram screen so as not to obstruct the optical path of regular signal light entering and exiting the hologram screen. Is preferably covered with a light absorbing member. With this configuration, external light incident on the hologram screen by reflection, that is, external light other than the external light directly incident on the hologram screen, can be further reduced.
[0019]
It is preferable that the hologram screen is of a transmission type, and that the light projecting means is provided with a reflection optical element for projecting the signal light obliquely above or below the hologram screen. The signal light is projected obliquely from above or below the hologram screen, so that the 0th-order diffracted light of the hologram can be prevented from entering the viewer's eyes, and the reflective optical element is arranged. Thus, the display can be prevented from protruding from above and below the hologram screen (see FIG. 4). As a result, each component of the display device can be accommodated in a case having a size substantially the same as the vertical and horizontal dimensions of the hologram screen. Can be configured.
[0020]
Some of the displays include a liquid crystal device and a light source that irradiates the liquid crystal device with light from a predetermined direction. The liquid crystal device can change the display by controlling the recorded display image by adding an electric signal from the outside.
[0021]
BEST MODE FOR CARRYING OUT THE INVENTION
Embodiment 1
In this example, as shown in FIG. 1, a display 28 that emits signal light 31 on which display information is recorded, and a signal light 31 that forms a transmission type hologram 11 and is incident from a predetermined angle range α are directed to a viewer 81. The display device 1 includes a hologram screen 10 having a directivity for diffracting and transmitting light to the hologram screen 10 and a light projecting unit (imaging lens) 29 for projecting the signal light 31 emitted from the display 28 onto the hologram screen 10.
[0022]
On the back side of the hologram screen 10, a translucent anti-reflection member 21 is arranged. The anti-reflection member 21 is incident on the hologram screen from a direction opposite to the predetermined angle range α and diffracted and transmitted. The reflectance is low with respect to the incident angle of the first noise light 395 or the incident angle of the second noise light 397 in which the light 398 specularly reflected by the antireflection member 21 is in the same direction as the predetermined angle range α. have.
[0023]
The hologram 11 of the hologram screen 10 has a high diffraction efficiency with respect to light linearly polarized in a predetermined direction, and a polarization optical element 22 is arranged on the front side of the hologram screen 10. The polarizing optical element 22 is a polarizing plate or a polarizing film through which the hologram screen 10 selectively transmits the predetermined linearly polarized light having high diffraction efficiency.
[0024]
The following is a supplementary explanation for each.
The display 28 has a light source 281, a liquid crystal element 282 that records an image, and a reflector 283 that converts divergent light emitted from the light source 281 into parallel light.
The hologram screen 10 is such that a hologram 11 is sandwiched between transparent substrates 12 and 13 as shown in FIG.
[0025]
The hologram 11 is a transparent transmission hologram, and irradiates the hologram 11 with a signal light 31 from an imaging lens 29 obliquely below to prevent the 0-order diffracted light from entering the eyes of the viewer 81. The angle of the irradiated signal light 31 is bent by diffraction, and the diffracted light 311 is scattered about a substantially horizontal direction so that the viewer 81 can visually recognize the display image (see reference numeral 311 in FIG. 4). The bending angle between the signal light 31 and the diffracted light 311 is about 30 to 40 ° at the center of the hologram screen 10.
[0026]
The hologram 11 has interference fringes formed by the optical system shown in FIG. 2. The photosensitive material 51 is made of dichromated gelatin, and the object to be recorded has a surface roughness of about $ 1,000 (the vicinity of the wavelength of the irradiation light). It is a frosted glass 40 having (surface roughness).
That is, the optical path of the coherent light 35 emitted from the laser light source 41 is bent by the mirror 42 and then split by the half mirror 43 into an optical path toward the object light 36 and an optical path toward the reference light 37. The light 351 exiting on one side (left side of the paper) is converted into parallel light through a mirror 441, an objective lens 442, and an off-axis parabolic mirror 443, and then passes through the frosted glass 40 as a diffusion plate to generate an object light. 36, and enters the photosensitive material 51 via the half mirror 47.
[0027]
On the other hand, the other light 352 exiting the half mirror 43 passes through mirrors 461 and 462, is converted into divergent light by the objective lens 463, and then enters the photosensitive material 51 as reference light 37 through the half mirror 47. As a result, a transmission type hologram in which the rubbed glass 40 is recorded is formed on the photosensitive material 51. As a result, if the hologram 11 is irradiated with reproduction light from the direction of the reference light 37 in FIG. 2, the diffracted light transmitted through the hologram 11 becomes light similar to the light diffused by the rubbing glass 51.
[0028]
The diffraction efficiency of the hologram 11 of this example is about 30 to 40%, and the half angle at half maximum of the scattering of the diffracted light 311 (the difference between the angle of the scattered light at which the intensity is half the value and the angle of the scattered light at which the intensity is the maximum) is The angle is about 6 °, and the screen gain of the hologram screen 10 is about 9.
The display 28 includes, for example, a light source 281 such as a metal halide lamp and a transmissive liquid crystal element 282. For example, when a metal halide lamp of 20 W (total luminous flux: 1300 lm) and a 1.3-inch color liquid crystal element 282 having a transmittance of 3% are used, the efficiency of the illumination system such as the reflector 283 is 50%, and the efficiency of the imaging lens 29 is 50%. Assuming that the efficiency is 80%, the total luminous flux emitted from the imaging lens 29 is 13 lumens (lm).
[0029]
As a result, when the screen size of the hologram screen 10 is 10 inches (0.03 m ² ), the illuminance on the screen by the light beam (13 lm) is 433 lx (lm / m ² ). Then, since the screen gain of the hologram screen 10 is 9, the display luminance is 1240 cd / m ² (display luminance = illuminance × screen gain ÷ π... (1)).
[0030]
This display luminance is a sufficiently large value considering that the display luminance of a CRT display or a direct-view type liquid crystal panel is 100 to 200 cd / m ² . However, in the display device 1 of the present embodiment, since the background light is transmitted through the hologram screen 10, it is necessary to study from the viewpoint of the contrast between the background and the display image.
[0031]
For example, considering that the display device 1 is used outdoors, the illuminance in the case of direct sunlight is 10 ⁵ lx, and the display luminance calculated from the above equation (1) is 28.6 × 10 ⁴ cd. corresponding to the / ^{m 2.} Therefore, if the antireflection member 21 and the polarization optical element 22 are not provided as shown in FIG. 6, if the reflectance at the interface 131 between the substrate 13 and air (reference numeral 913 in FIG. 6) is 4%, The light 39 is incident on the hologram screen 10 from a direction opposite to the predetermined angle range α where the signal light 31 is incident, becomes the first noise light 395, and the surface noise when this is reflected by the interface 131 is 1 .14 × 10 ⁴ cd / m ² .
[0032]
This value reaches about nine times the surface luminance of the display image, and the display image is completely erased and is washed out.
Similarly, when the anti-reflection member 21 and the polarization optical element 22 are not provided as shown in FIG. 6, the sunlight 39 is reflected by the light 398 specularly reflected at the interface 131 between the substrate 13 and the air. The surface luminance when the second noise light 397 in the same direction as the above is reflected by the interface 131 is 1.14 × 10 ⁴ cd / m ² , and the displayed image is completely washed out.
[0033]
However, in this example, the antireflection member 21 and the polarization optical element 22 are provided, and as described below, it is possible to prevent the washout of the display image due to such noise light 395, 397.
The anti-reflection member 21 of this example is a so-called multilayer interference film in which interference films are formed in multiple layers to enable broadband reflection suppression. The thickness of the multilayer interference film is set so as to exhibit an excellent reflection suppressing effect at the angle of incidence of the signal light 31 on the hologram screen 10.
[0034]
It is easy for the antireflection member 21 to make the reflectance of the noise light 395, 397 equal to or less than one-tenth of the reflectance at the interface 131 between the substrate 13 and the air. The surface luminance of 399 is about 1.14 × 10 ³ cd / m ² (the dashed lines of the harmful noise light 396 and 399 in the figure schematically indicate that the intensity is low). Since this surface luminance is almost the same level as the surface luminance of the display image, the display image becomes visible.
[0035]
Also, as shown in FIG. 1, the polarizing optical element 22 cuts light that is orthogonal to the polarization axis and converts unpolarized sunlight 39 (shown by elliptical arrows) into linearly polarized light (shown by linear arrows). (Shown). Therefore, the intensity of the sunlight 39 attenuates to about one third at the stage when the sunlight 39 passes through the polarization optical element 22 and enters the hologram screen 10. Therefore, the surface luminance of the harmful noise light 396, 399 is about 367 cd / m ² .
[0036]
On the other hand, the light diffracted by the hologram 11 with high efficiency is not attenuated by the polarization optical element 22, so that the surface luminance of the display image remains unchanged (1240 cd / m ² ). Therefore, according to this example, it is possible to obtain an excellent display device 1 that can clearly display a display image even in an environment where extremely strong external light such as direct sunlight.
[0037]
Embodiment 2
As shown in FIG. 3, this embodiment is another embodiment in which the hologram 14 of the hologram screen 10 is a reflection hologram in the first embodiment.
In the display device 1 of the present embodiment, a translucent anti-reflection member 21 is disposed on the back side of the hologram screen 10 having the reflection type hologram 14. The incident angle of the third noise light 390 in which the reflected light 391 is in a direction opposite to the predetermined angle range β in which the signal light 31 is incident, or the fourth noise light 390 diffracted and reflected by the hologram 14 It has a low reflectance with respect to the incident angle of the noise light 392.
[0038]
Therefore, the intensity of the harmful noise light 393 caused by the third noise light 390 and the fourth noise light 392 is greatly reduced, and the contrast of the display image with respect to the background can be increased.
Further, since the third noise light 390 is transmitted through the polarization optical element 22, it is weakened to about one third of the intensity of the sunlight 39, so that the contrast of the display image with respect to the background can be further increased. .
Others are the same as the first embodiment.
[0039]
Embodiment 3
In the present embodiment, as shown in FIG. 4, the display device 1 is a box storage type in the first embodiment, and the size of the box 27 is substantially the same as the hologram screen 10 in the vertical and horizontal directions. Therefore, the display devices 1 can be stacked vertically and horizontally to configure a large-sized large-screen display device. Further, the inner surface 271 and the partition 272 of the box 27 are covered with a light absorbing member (black paint) to prevent outside light from entering from other than the front and to suppress the generation of reflected light noise inside the box 27. be able to.
[0040]
The display 28 and the imaging lens 29 are accommodated in the box 27, and the signal light 31 is made incident on the hologram screen 10 from the same angle as in FIG. 1 so that the zero-order diffracted light does not enter the visual field of the viewer 81. For this purpose, in this example, the mirror 26 is arranged on the optical path between the imaging lens 29 and the hologram screen 10. In the figure, reference numerals 284 and 285 denote a power supply wire such as the light source 281 and a signal line for controlling the liquid crystal element 282.
Others are the same as the first embodiment.
[0041]
【The invention's effect】
As described above, according to the present invention, it is possible to obtain a display device using a hologram screen that can suppress harmful noise light generated by external light and increase the contrast of a display image.
[Brief description of the drawings]
FIG. 1 is a system configuration diagram of a display device according to a first embodiment.
FIG. 2 is a diagram illustrating an optical system in a hologram exposure process according to the first embodiment.
FIG. 3 is a system configuration diagram of a display device according to a second embodiment.
FIG. 4 is a system configuration diagram of a display device according to a third embodiment.
FIG. 5 is a diagram showing optical paths of signal light and noise light in a conventional display device using a reflection hologram.
FIG. 6 is a diagram showing optical paths of signal light and noise light in a conventional display device using a transmission hologram.
[Explanation of symbols]
10. . . Hologram screen,
21. . . Anti-reflective member,
22. . . Polarization optics,
31. . . Signal light,
395, 397. . . Noise light,

Claims (7)

A display for emitting signal light on which display information is recorded, a hologram screen having a directivity for forming a transmission hologram and diffracting and transmitting the signal light incident from a predetermined angle range α toward a viewer, and the display A projection device for projecting the signal light emitted from the hologram screen onto the hologram screen,
On the back side of the hologram screen opposite to the viewer , a translucent anti-reflection member is disposed.
The anti-reflection member is configured to emit the first noise light that is incident on the hologram screen from the direction opposite to the predetermined angle range α and is diffracted and transmitted, or the light that is regularly reflected by the anti-reflection member is in the predetermined angle range α. A display device having a low reflectance with respect to an incident angle of a second noise light in the same direction as α. A display for emitting signal light on which display information is recorded, a hologram screen having a directivity for forming a reflection type hologram and diffracting and reflecting the signal light incident from a predetermined angle range β toward a viewer, and the display A projection device for projecting the signal light emitted from the hologram screen onto the hologram screen,
On the back side of the hologram screen opposite to the viewer , a translucent anti-reflection member is disposed.
The anti-reflection member is a third noise light in which light regularly reflected by the anti-reflection member is in a direction opposite to the predetermined angle range β, or a third noise light in which the third noise light is diffracted and reflected by a hologram. 4. A display device having a low reflectance with respect to the incident angle of the noise light of No. 4. A display device that emits signal light recording display information and a directivity that has a high diffraction efficiency for light linearly polarized in a predetermined direction and diffracts signal light incident from a predetermined angle range in a viewer direction. A display device comprising: a transmission type or reflection type hologram screen, and light projecting means for projecting the signal light emitted from the display unit onto the hologram screen,
A polarizing optical element is bonded to at least the front side of the hologram screen that is the viewer side, and the polarizing optical element selectively converts the predetermined linearly polarized light having a high diffraction efficiency to the hologram screen. A display device characterized by transmitting light. 3. The display device according to claim 1, wherein the hologram screen has a high diffraction efficiency with respect to light linearly polarized in a predetermined direction, and is located on the viewer side of the hologram screen. A display device comprising the polarizing optical element according to claim 3 disposed on a front side. 5. The hologram screen according to claim 1, wherein the hologram screen is covered with a light absorbing member so as not to obstruct an optical path of a normal signal light entering and exiting the hologram screen. A display device characterized by the above-mentioned. 5. The hologram screen according to claim 1, wherein the hologram screen is of a transmission type, and the light projecting means projects the signal light from an obliquely upper side or an obliquely lower side of the hologram screen. A display device comprising a reflective optical element, wherein each component of the display device is housed in a case having substantially the same vertical and horizontal dimensions as the hologram screen. 7. The display device according to claim 1, wherein the display has a liquid crystal device and a light source that irradiates the liquid crystal device with light from a predetermined direction.

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