JP2004138698A - Off-axis optical element and display device using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical element (a display device using the same) for display optical path control having the optical characteristics that the problem of "mirroring-in" by reflection on the outside surface of the display device is eliminated as the direction to make the luminance of display light highest varies from a specular reflection direction and that the display light can be visually recognized in a way as not to be accompanied by the color change of the display light according to observation directions. <P>SOLUTION: The optical element consists of volume phase transmission diffraction gratings having angle selectivity, has the optical characteristics of transmitting and diffracting the incident light at angles within a specific range non-perpendicular to the major face thereof by deviating the center of the optical axis and consists of the configuration that a plurality of kinds of the diffraction gratings varying in recording conditions are regionally divided and recorded. <P>COPYRIGHT: (C)2004,JPO

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention provides an "off-axis" transmission diffraction characteristic in which the center of the optical axis is strongly different from the incident angle of incident light in a direction different from the incident angle, and the visibility (brightness, contrast, etc.) of a displayed image by applying the same. And a display device with improved characteristics.
[0002]
In the present invention, when the terms “scatter” and “diffusion” are used with respect to light, they are synonymous.
Also, the terms "film" and "sheet" are used synonymously in the present invention.
In addition, “angle selectivity” is an optical property that causes diffraction only for incident light at a specific range of angles, and “directivity” is used in the sense that the direction and range of the diffracted light to be emitted can be controlled. Can be
Hereinafter, the case where the image display element is a liquid crystal panel and the display device is a liquid crystal display device will be mainly described.
[0003]
[Prior art]
In the liquid crystal display device, a viewing angle at the time of observation is secured (that is, a display image is brightly displayed on the front surface of the display device), and the display image is viewed with uniform brightness over the entire display screen. For this purpose, a light scattering film is arranged on the front of the device.
As a conventional light scattering film, a resin film whose surface is processed into a mat shape, a resin film containing a diffusing material inside, and the like are used.
[0004]
However, in the case of the above-mentioned film, it is difficult in principle to have a function of changing the scattering property depending on the incident angle of the incident light (referred to as scattering anisotropy). Therefore, there is a problem that unnecessary scattered light is generated when used in a display device, which causes a reduction in display brightness and contrast, or a phenomenon called a “blur” of a display image.
[0005]
In the case of a light-scattering film whose surface has been processed into a mat shape, the film surface is physically processed by sand blasting or the like to form a matte surface, or chemically treated by dissolution treatment with an acidic or alkaline solution. To form
It is possible to control the emission range / direction (referred to as scattering directivity) of scattered light by controlling the mat surface (shape of unevenness, etc.). Have difficulty.
[0006]
Also, in a light scattering film containing a diffusing agent (fine particles) therein, an attempt has been made to control the refractive index, size, shape, etc. of the diffusing agent in order to control the scattering anisotropy. At present, it is technically difficult and not sufficiently practical.
[0007]
In particular, the above-described film has no scattering anisotropy or off-axis light scattering characteristics, has low directivity of light scattering, and can be applied to a display device to reflect light from the outermost surface of the display device (specular reflection). Direction) or in a direction inappropriate for observation of a display image, causing unnecessary scattered light, which causes a problem of lowering the brightness and contrast of display or causing blur of the display image.
[0008]
Reflection type liquid crystal display device (not a type that obtains display light by irradiating illumination light from the backside of the liquid crystal panel with the built-in light source, but reflected light by incident light from the observer side such as sunlight or indoor illumination light) FIG. 1 schematically shows an example of a conventional configuration of a type in which is a display light.
The type shown in the figure is a display device of a type in which the back electrode of the drive electrodes of the liquid crystal panel also serves as the light reflection layer (referred to as a reflection electrode) as a light reflection layer. 1, a color filter 2 (in the case of a device for performing full color display), a liquid crystal panel 3, and a reflective electrode 5 (included in the liquid crystal panel 3).
Generally, in order to secure a viewing angle at the time of observation, a process for performing diffuse reflection is performed by forming fine irregularities on the surface of the reflective electrode.
[0009]
In the device shown in FIG. 1, illumination light 4 from an external illumination light source (not shown) passes through a polarizing plate 1, a color filter 2, and a liquid crystal panel 3, and is incident on a reflective electrode 5 in the liquid crystal panel. Since the surface of the reflective electrode 5 is uneven, the light is reflected as diffused light 6 having a spread in the regular reflection direction, and is reflected by the liquid crystal panel 3, the color filter 2, and the polarizing plate 1, respectively. After passing again, it is emitted as display light.
For this reason, display light (hereinafter, also referred to as an image) composed of a display pattern defined by the liquid crystal panel is observed brightly from a direction centered on the specular reflection direction (the lower right direction in the figure). Can be.
[0010]
As shown in FIG. 2, the intensity of the diffused light (display light) 6 in the reflection type liquid crystal display device shown in FIG. 1 has an intensity distribution that is the strongest in the regular reflection direction of the incident light.
For this reason, the brightest display light is obtained in the observation direction corresponding to the specular reflection direction. However, in the specular reflection direction, the reflected light 7 specularly reflected on the surface of the apparatus (in general, a cover glass or the like is arranged) is also displayed. There is a problem that the visual light overlaps with the light 6 and the illumination light source is reflected, so that the display light 6 is difficult to observe.
[0011]
According to FIG. 2, the central portion of the range 8a in which a bright image can be observed is in the regular reflection direction, and overlaps with the range 8b in which the illumination light is reflected. Therefore, the range of the range 8c in which bright display light can be continuously observed becomes narrow. However, there has been a problem that the display light is darkened even if the observation direction is slightly changed, or that reflection occurs, making it difficult to observe.
[0012]
As described above, in the conventional reflective liquid crystal device, the direction in which the display light can be viewed brightly overlaps the direction in which the reflection of the illumination light source is most strongly viewed, so that it is difficult to observe an image in that direction and the image is continuously displayed. There is a problem that a range in which a bright image can be observed is narrowed.
In order to solve such a problem, an optical element having off-axis optical characteristics is used to control the display optical path so that the direction in which the display light is visible at the highest luminance is deviated from the specular reflection direction. Proposals have been made for this purpose.
[0013]
Holograms and diffraction gratings are typical examples of optical elements having off-axis optical characteristics.
They are often captured and recorded due to the interference between the object light and the reference light. By controlling the intersection angle between the two, the angle of the reproduced light (corresponding to the object light) can be changed to the illumination light (to the reference light). It is easy to design so as to deviate from the rectilinear direction (or the specular reflection direction), and off-axis optical characteristics are realized.
[0014]
As a configuration in which the hologram is arranged on the observation side of the liquid crystal display device,
With regard to a transmission type liquid crystal display device requiring a backlight, there is a type in which a hologram for diffracting light transmitted by a direct type backlight in a predetermined range and direction is arranged on the front side of a liquid crystal panel. (For example, see Patent Document 1)
Patent Literature 1 does not disclose off-axis in the specular reflection direction of ambient light that is not a backlight.
Further, in Patent Document 1, the hologram is disposed outside (observation side) of the liquid crystal display element, and since there is a distance between the hologram and the liquid crystal display portion (by the thickness of the polarizing plate), the influence of the diffracted light of the hologram. In this case, there is a problem that the display becomes blurred or a double image becomes difficult to see.
[0015]
As a proposal to apply a hologram to a reflective liquid crystal display device that does not require a backlight,
A reflection type liquid crystal display device, wherein a transmission type hologram is arranged on the viewer side opposite to the reflection surface via the liquid crystal panel,
A reflection type liquid crystal display device which employs a volume phase transmission hologram as a hologram, and transmits, without diffracting incident illumination light, and transmits and diffracts emitted display light, due to the angle selectivity of the hologram. Is disclosed. (For example, see Patent Document 2)
In Patent Literature 2, when a hologram is arranged on the display side of a liquid crystal glass substrate in a reflective liquid crystal display device in which display light is viewed using ambient light, the effect of reflection (reflection) is reduced, and display light is reduced. A hologram in which the visible range is appropriately set and a reflection type liquid crystal display device using the hologram are proposed.
[0016]
[Patent Document 1] JP-A-9-152602 [Patent Document 2] JP-A-11-84372
[Problems to be solved by the invention]
By using a hologram having off-axis diffraction characteristics for controlling the display optical path (shifting the direction in which the luminance becomes highest from the specular reflection direction), the above-described problem of “reflection” is solved. New solution issues arise.
That is, “coloring of display light” based on the use of a hologram.
[0018]
The volume phase transmission hologram has a diffraction wavelength width in the visible wavelength range as compared with a volume phase reflection hologram (a so-called Lippmann type hologram) having diffraction wavelength selectivity (a characteristic of generating diffracted light of a specific wavelength = color). It is well known in the art that it is so wide that it does not produce diffracted light of a particular color.
Although the diffraction wavelength width is wide over the visible wavelength range, the wavelength dispersion characteristic of the hologram itself (the wavelength distribution of the diffracted light depends on the relative relationship of the illumination angle / hologram arrangement / observation direction) (A characteristic that changes), the hue at which the diffracted light is viewed changes depending on the viewing conditions.
[0019]
For this reason, the image light originally intended to be displayed on the liquid crystal display device is caused to undergo a color change according to the viewing direction, and this has a particularly large effect when performing full-color display.
SUMMARY OF THE INVENTION It is a main object of the present invention to provide a display device using an optical element having off-axis optical characteristics for controlling a display optical path so that the display device can be viewed without a color change of display light in accordance with an observation direction. And
[0020]
[Means for Solving the Problems]
The off-axis optical element according to the present invention,
It consists of a volume phase transmission type diffraction grating with angle selectivity,
For incident light at a specific range of angles that is non-perpendicular to its main surface, it has the optical property of transmitting and diffracting off the center of the optical axis,
It is characterized in that a plurality of types of diffraction gratings having different recording conditions are divided into regions and recorded.
[0021]
As a typical off-axis optical characteristic, for the incident light at an angle in the range of 25 to 45 degrees with respect to the main surface, the characteristic of emitting the transmitted diffraction light at an angle in the range of -5 to -15 degrees, It is suitable when applied to a display device. (It can also be said that the incident light at an angle in the range of -25 to -45 ° emits transmitted diffracted light at an angle in the range of 5 to 15 °.)
In the optical field, an angle perpendicular to the main surface is set to 0 °, and a clockwise direction is measured in a plus direction.
In FIG. 1, the illumination light 4 is incident at a negative angle, and the diffused light 6 is emitted at a positive angle. In the figure, when the left and right are reversed, incident light at a plus angle exits at a minus angle.
[0022]
BEST MODE FOR CARRYING OUT THE INVENTION
Hereinafter, the off-axis optical element of the present invention will be described in detail with reference to the drawings.
FIG. 3 is an explanatory view schematically showing an embodiment of an off-axis optical element according to the present invention.
In the optical element 9 according to the figure, as a form of area division, a volume phase transmission type diffraction grating 10 of a dot-like portion arranged in a substantially matrix shape and a volume phase transmission type diffraction grating 11 of a non-dot-like portion therearound are provided. It is constituted by.
The recording conditions are different between the volume phase transmission type diffraction gratings 10 and 11 as described below.
[0023]
The optical element 9 is manufactured as follows using an optical duplication technique.
First, two types of diffraction gratings serving as masters for optical duplication are prepared.
1. Using an optical system as shown in FIG. 4A, a laser light (parallel light) 13 from a laser light source (not shown) and a laser light (divergent light) 14 emitted from the same laser light source are placed on a dry plate (photosensitive material) 12. And a diffraction grating is recorded on the dry plate 12 by these interferences.
2. 4B, the diffraction grating is recorded on another dry plate 15 by changing only the incident angle of the diverging light 14 as shown in FIG. 4A.
[0024]
Next, as shown in FIG. 5A, a halftone dot (dot) -shaped portion is substantially arranged in a matrix, and the mask 18 recorded as the light transmitting portion 16 and the non-transmitting portion 17 and the mask 18 A mask 19 in which the light transmitting portion and the non-transmitting portion are in an inverted relationship is prepared.
[0025]
Next, as shown in FIG. 6, the diffraction grating 12 = the mask 18 is superimposed on the dry plate 12 in FIG. 4A, and the photosensitive material 9 having a certain thickness is placed in close contact with the pattern surface of the mask 18.
In this state, when the laser light 20 is irradiated from the direction opposite to the parallel light when the diffraction grating 12 is photographed, the diffraction grating 12 separates the transmitted light 21 and the diffracted light 22.
The two lights 21 and 22 respectively reach the photosensitive material 9 after passing through the mask 18, and a volume phase transmission type diffraction grating is recorded on the photosensitive material 9 by interference of the two lights.
At this time, since light passes only through the light transmitting portion 16 of the mask 18, a diffraction grating having the same characteristics as the diffraction grating 12 is duplicated only in the corresponding portion of the photosensitive material 9.
[0026]
Next, as shown in FIG. 7, the diffraction grating 15 = the mask 19 is overlaid on the dry plate 15 in FIG. 4A, and the photosensitive material 9 on which the diffraction grating 12 is duplicated is brought into close contact with the pattern surface of the mask 19. Install.
At this time, the light transmitting portion of the mask 19 (corresponding to the non-transmitting portion 17 of the mask 18) is arranged so as to correspond to the portion of the photosensitive material 9 where no hologram is recorded.
When laser light is incident in this state, a diffraction grating having the same characteristics as the diffraction grating 15 is duplicated only in the light transmitting portion of the mask 19 in the same manner as in the previous recording.
As described above, two types of diffraction gratings are recorded on the photosensitive material 9 while being divided into dot-like / non-dot-like regions.
[0027]
FIG. 8 shows an outline of an example in which the optical element 9 obtained above is used for a liquid crystal display device.
The display device shown in the figure has a configuration in which an off-axis optical element 9 is inserted between the polarizing plate 1 and the color filter 2 as compared with the conventional liquid crystal display device (FIG. 1).
[0028]
In the figure, a light 4 incident from an obliquely upward direction by an external illumination light source (not shown) passes through the polarizing plate 1 and is then diffracted by the diffraction grating 10 in the optical element 9, and a diffracted light 23 off the optical axis. The light travels in a direction different from the straight traveling direction of the original illumination light.
After passing through the color filter 2 and the liquid crystal panel 3, the diffracted light 23 is reflected by the reflective electrode 5 to become display light 24 that spreads in the vicinity of the regular reflection direction of the diffracted light 23. (The emission direction of the display light 24 is different from the regular reflection direction of the illumination light 4 in the same figure.)
[0029]
The display light 24 enters the optical element 9 after passing through the liquid crystal panel 3 and the color filter 2 again. However, since the volume phase transmission type diffraction grating constituting the optical element 9 has an angle selectivity, the display light 24 is again optically. When passing through the element 9, the light passes without undergoing diffraction and is emitted to the outside through the polarizing plate 1.
Therefore, bright display light can be observed from a direction close to the regular reflection direction of the diffracted light 23 in FIG. Since this direction is different from the regular reflection direction of the illumination light 4 in which the regular reflection light 7 reflected on the device surface advances, the reflection of the illumination light is not felt at the position where the display light can be observed brightest.
[0030]
As described above, holograms and diffraction gratings have wavelength dispersion characteristics, and when illuminated with white light, they are diffracted in different directions (mainly, up and down) for each color.
If only one type of diffraction grating is used, the color of the image will appear to be greatly changed corresponding to the seven colors of the rainbow, even if the observation position is slightly changed.
In the optical element according to the present invention, in order to eliminate such a color change, a method of reducing the color change by mixing diffracted lights emitted to different positions in the vertical direction is adopted.
[0031]
In the case of the above embodiment, since the diffracted light from the diffraction grating 11 is diffracted in a direction different from the diffracted light from the diffraction grating 10 in the vertical direction, as shown in FIG. The diffracted light (in the range from red to blue) and the chromatically dispersed diffracted light from the diffraction grating 11 overlap with a slight shift.
In a region where two lights overlap, different colors overlap and cancel each other's colors, so that a change in color is reduced.
[0032]
It is particularly effective to make the diffracted light achromatic (white) in order to eliminate the phenomenon that the hue of the diffracted light changes according to the observation direction by mixing the colors.
In order to make the color close to white when the two colors of light are combined, it is desirable to make complementary colors such as blue and yellow, red and cyan overlap each other.
In FIG. 9, a portion of the diffracted light from the diffraction grating 10 close to blue and a portion of the diffracted light from the diffraction grating 11 close to red overlap.
In order to make the complementary colors overlap each other, considering the standard viewing conditions of the display device and the size of the display device, when assuming observation at a distance of 300 to 1000 mm, the diffracted light of each other is obtained. Are different by about 5 °.
[0033]
It is effective to use not only the superposition of two colors but also the superposition of more colors to obtain achromatic diffracted light with less color change depending on the viewing direction.
In the above embodiment, two types of diffraction gratings are used: a dot-like portion (10) arranged in a substantially matrix shape and a non-dot-like portion (11) around the dot-like portion (10). It is also possible to combine a plurality of types of dot portions arranged in a substantially matrix shape.
For example, at the time of photographing and recording, while changing (exchanging) the mask on the photosensitive material so that the openings of the mask do not overlap, sequentially changing the exposure conditions, finally forming a diffraction grating on substantially the entire surface of the photosensitive material. Is done.
[0034]
By the way, the diffraction grating can have a lens function, but if the diffraction grating used in the present invention has a lens function of condensing light at a distance corresponding to the observation position, the diffraction grating at the peripheral portion and the central portion can be provided. Brightness can be made uniform.
Since a reflection type liquid crystal display device is usually observed from a distance of about 300 mm to 1000 mm, if a lens function of condensing light at a focus position of that degree is provided, the brightness of a display image becomes uniform and the display image becomes easy to see. Become.
[0035]
On the other hand, it is desirable that the display image can be viewed so that the display light has the highest luminance as close to the front as possible (at an angle perpendicular to the main surface of the display device). If the function of emitting diffracted light is applied to a display device, as shown in FIG. 10, the light is transmitted and diffracted by an off-axis optical element (diffraction grating), travels at 0 ° to the reflective electrode, and then reflects. The light reflected from the electrode is again incident on the off-axis optical element at 0 °, which matches the angle selectivity of the off-axis optical element (diffraction grating), so that transmission diffraction occurs again, resulting in illumination. The display light returns to the direction of the light 4, and the display light hardly returns to the front direction of the apparatus.
[0036]
For this reason, the off-axis diffraction characteristic of the diffraction grating preferably diffracts light in a direction slightly deviated from the front direction, and is suitably diffracted in a direction deviated from the front by about 5 to 15 °.
Further, in order to provide the diffraction grating with an appropriate angle selectivity, it is necessary to form such grating fringes inside. In the case of a volume type, a photosensitive material having a thickness of about 3 to 20 μm is used. It is suitable.
[0037]
The off-axis optical element according to the present invention is not only used as an optical path control element disposed on the front side (viewer side) of the liquid crystal panel, but also on the back side of the liquid crystal panel, as shown in the above embodiment. It is also effective to use as a light reflection layer instead of the reflection electrode in the embodiment.
[0038]
【The invention's effect】
As described above, according to the optical element (and the display device using the same) according to the present invention,
Since the direction in which the brightness of the display light becomes highest is different from the specular reflection direction, the problem of “reflection” due to reflection on the outer surface of the display device is eliminated, and the color of the display light changes depending on the observation direction. In particular, when displaying a full-color image, it is possible to view with a hue faithful to the original display image.
[0039]
[Brief description of the drawings]
FIG. 1 is an explanatory view schematically showing a configuration example of a conventional reflective liquid crystal display device.
FIG. 2 is a graph showing a change in luminance of display light according to a viewing direction in a conventional reflective liquid crystal display device.
FIG. 3 is an explanatory view schematically showing an embodiment of an off-axis optical element according to the present invention.
FIG. 4 is an explanatory view showing an example of a method for producing a diffraction grating master used for producing an off-axis optical element according to the present invention.
FIG. 5 is an explanatory view showing a mask used for manufacturing the optical element shown in FIG.
FIG. 6 is an explanatory view showing an example of a method of manufacturing an off-axis optical element according to the present invention.
FIG. 7 is an explanatory view showing an example of a method for manufacturing an off-axis optical element according to the present invention.
FIG. 8 is an explanatory view showing an outline of an example in which off-axis optics according to the present invention is used in a liquid crystal display device.
FIG. 9 is an explanatory diagram showing an outline of optical characteristics (chromatic dispersion) when the off-axis optical element according to the present invention is used in a liquid crystal display device.
FIG. 10 is an explanatory diagram showing optical paths of illumination light, diffracted light, and display light when off-axis optical characteristics are not suitable.
[Explanation of symbols]
DESCRIPTION OF SYMBOLS 1 ... Polarizer 2 ... Color filter 3 ... Liquid crystal panel 4 ... Illumination light 5 ... Reflection electrode 6 ... Diffusion light (display light)
7 Specular reflected light 9 Optical elements 10 and 11 Diffraction gratings 12 and 15 Dry plate (photosensitive material)
13: Parallel light (reference light)
14 divergent light (object light)
16: transmissive portion 17: non-transmissive portions 18, 19: mask 24: display light

Claims (11)

An off-axis optical element consisting of a volume phase transmission type diffraction grating having angle selectivity, wherein the optical element is off-center with respect to incident light at a specific range of angles that is non-perpendicular to its main surface. And has optical characteristics of transmission and diffraction.
An off-axis optical element having a configuration in which a plurality of types of diffraction gratings having different recording conditions are divided into regions and recorded. The off-axis optical element according to claim 1, wherein the optical element has a characteristic that a center angle of an optical axis of transmitted diffracted light is different by 5 ° or more at one end and the other end of the optical element. The off-axis optical element according to claim 1, wherein the optical element has an optical characteristic having a light-condensing function such that a position at a distance of 300 to 1000 mm becomes a focal point. The optical element has an optical property of emitting transmitted diffraction light at an angle in a range of -5 to -15 degrees with respect to incident light at an angle in a range of 25 to 45 degrees with respect to a main surface thereof. The off-axis optical element according to claim 1, wherein The off-axis optical element according to claim 1, wherein the optical element has a configuration in which a diffraction grating is recorded on a translucent material having a thickness of 3 to 20 μm. The off-axis optical element according to any one of claims 1 to 5, wherein the area is divided into a dot portion and a non-dot portion arranged in a substantially matrix shape. The off-axis optical element according to any one of claims 1 to 5, wherein a plurality of types of dot-like portions arranged in a substantially matrix shape are provided as a form of area division. A configuration in which the off-axis optical element according to any one of claims 1 to 7 is arranged on a display surface side (observer side) of the image display element,
The optical element reflects ambient light incident on the device with a light reflection layer disposed on the back side of the image display element (the side opposite to the observer), and then emits the display light with a regular reflection direction. A display device designed to have an off-axis characteristic such that light is transmitted and diffracted with a different direction as the center of the optical axis. A configuration in which the off-axis optical element according to any one of claims 1 to 7 is arranged on a display surface side (observer side) of the image display element,
The display, wherein the optical element is designed to have an off-axis characteristic such that when ambient light is incident on the image display element, the light is diffracted through the center of the optical axis in a direction different from the straight traveling direction. apparatus. The off-axis optical element according to any one of claims 1 to 7, wherein a light reflecting layer is formed on the surface on the back side (the side opposite to the observer) of the image display element,
The optical element reflects the ambient light passing through the image display element by a light reflection layer disposed on the back side of the optical element (opposite to the observer), and then emits the display light as specular reflection. A display device designed to have an off-axis characteristic of transmitting and diffracting light with a direction different from the direction as the center of the optical axis. The off-axis optical element according to any one of claims 1 to 7, wherein a light reflecting layer is formed on the surface on the back side (the side opposite to the observer) of the image display element,
The optical element is off-axis such that when ambient light that has passed through the image display element enters the optical element, the light is transmitted and diffracted around the optical axis in a direction different from the straight traveling direction before reaching the light reflecting layer. A display device characterized by being designed to have characteristics.

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