JP2000206517A - Display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a display device compact in structure, high in the availability of illumination light and satisfactory in the luminance of display light by controlling each of the incident angle of the illumination light to a hologram and the outgoing angle of the transmitted and diffracted light to a specified range and controlling the halfwidth of the diffraction efficiency of the transmitted and diffracted light to a specified range. SOLUTION: The transmitted and diffracted light by a hologram 9 is made incident on this display device 15, and the reflected light 16 from the device is observed as a display image. The incident angle 12 of the illumination light from a illumination light source 10 for the hologram 9 is controlled to the range from 60 deg. to 80 deg. or from -60 deg. to -80 deg. to the normal line direction of the hologram face, while the emitting angle of the transmitted and diffracted light 14 is controlled to the range from 5 deg. to 30 deg. or from -5 deg. to -30 deg. to the normal line direction of the hologram face. The peak wavelength of the diffraction efficiency of the transmitted and diffracted light 14 from the hologram 9 is controlled to be almost equal to the peak wavelength of the emitted light from the illumination light source 10. The halfwidth of the diffraction efficiency of the transmitted and diffracted light 14 from the hologram 9 is controlled to the range from 10 to 30 nm.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device,
In particular, the present invention relates to a display device that achieves compactness and effective use of illumination light by improving the illumination mechanism of a reflective liquid crystal display device.

[0002]

2. Description of the Related Art A typical example of an illumination mechanism in a conventional reflection type liquid crystal display device will be described below. In the first method, as shown in FIG. 1, the reflector 2 disposed on the back surface (the side opposite to the viewer) of the liquid crystal panel 1 is formed into a half mirror shape (both transmitting and reflecting), and the back surface of the reflector 2 is formed. In this method, a part 4 of the illumination light from the illumination light source 3 passes through the reflector 2 to illuminate the liquid crystal panel. Naturally, it is also possible to view a displayed image by reflection of ambient light, and this type is strictly a reflection type (and transmission type) liquid crystal display device.

However, in this method, if the reflectivity of the half-mirror-shaped reflector 2 is low, the reflected light 5 with respect to the surrounding light is weakened.
Conversely, if the reflectance of the reflector 2 is high, the transmitted light 4 to the internal illumination light source 3 is weakened, so that a bright display image cannot be visually observed in display using either ambient light or illumination light alone.

Further, this method cannot be applied to a reflection type liquid crystal display device of a type in which a driving electrode of a liquid crystal panel, which has become popular in recent years, also serves as a reflection plate.

In the second method, as shown in FIG. 2, an illuminating light source 7 is arranged on the front surface (viewer side) of a liquid crystal panel 6, and
This is a method of illuminating the liquid crystal panel with illumination light from the illumination light source 7.

When this method is adopted, if the position of the illumination light source 7 is too far in front of the apparatus (on the side of the observer), the thickness of the apparatus (the distance in the left-right direction in FIG. 1) increases, and the display apparatus has an increased thickness. This hinders downsizing. Therefore, as shown in the figure, it is necessary to arrange the illumination light source 7 at a position that illuminates the liquid crystal panel surface at an angle close to parallel.

Further, as shown in FIG. 1, in a reflection type liquid crystal display device, display light is emitted in the vicinity of the specular reflection direction of illumination light, but in this method, from the front of the display device which is a standard observation condition. The brightness of the display light for observation of is insufficient,
There is a drawback that the utilization efficiency of the illumination light deteriorates.

[0008]

As described above, each of the prior arts has a problem. The present invention is intended to solve these problems. In a reflective liquid crystal display device having an illumination mechanism, the present invention aims at achieving compactness and effective use of illumination light, and can perform display using either ambient light or illumination light. It is an object to provide a display device with sufficient light luminance.

[0009]

A display device according to the first aspect of the present invention has a configuration illustrated in FIG. 3 and includes at least a volume transmission type hologram, a display device, and an illumination light source, and the hologram is a display device. The hologram is illuminated from the front (observer side) by an illumination light source, and transmitted and diffracted light by the hologram is incident on the display device, and reflected light from the display device is visually displayed as a display image. The angle of incidence of the illumination light of the hologram by the illumination light source is 60 ° to 80 ° or −6 ° with respect to the radiation direction of the hologram surface.
0 ° to −80 °, and the emission angle of the transmitted diffracted light from the hologram is in the range of 5 ° to 30 ° or −5 ° to −30 ° with respect to the radiation direction of the hologram surface. The peak wavelength of the diffraction efficiency of the transmitted diffracted light from the hologram is substantially equal to the peak wavelength of the emission of the illumination light source, and the half value width of the diffraction efficiency of the transmitted diffracted light from the hologram is within a range of 10 nm to 30 nm. There is a feature.

A display device according to a second aspect of the present invention includes at least a volume transmission type hologram, a light guide plate in close contact with the hologram, a display device, and an illumination light source, and the hologram is provided on a front surface (observer side) of the display device. Is installed, and a light guide plate is installed in front of the hologram (observer side). The illumination light source illuminates the hologram via the light guide plate, and transmitted and diffracted light by the hologram is incident on the display device. The reflected light from the hologram is viewed as a display image, and the angle of incidence of the illumination light of the hologram by the illumination light source is 60 ° to 80 ° or −60 ° to −8 with respect to the radiation direction of the hologram surface.
0 °, and the angle of emission of the transmitted diffracted light from the hologram is 5 ° with respect to the radiation direction of the hologram surface.
-30 ° or -5 ° to -30 °, the peak wavelength of the diffraction efficiency of the transmitted diffracted light from the hologram is substantially equal to the peak wavelength of the emission of the illumination light source,
The half width of the diffraction efficiency of the transmitted diffracted light from the hologram is in the range of 10 nm to 30 nm.

In a display device according to a third aspect of the present invention, a white illumination light source having a peak wavelength in each of R, G, and B regions is used as an illumination light source, and R, G, and R of the illumination light source are used as a hologram. 3. The display device according to claim 1, wherein three types of volume transmission holograms having a peak of diffraction efficiency of transmitted diffraction light at a wavelength corresponding to the peak wavelength of B are used.

[0012]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention relates to a display device such as a liquid crystal panel for defining a display image on a display device.
In this configuration, illumination is performed using diffracted light from a volume transmission hologram.

The volume transmission type hologram has an incident angle selectivity (a characteristic of emitting diffracted light only for incident light from a specific angle), and the incident angle of illumination light matches the diffraction condition of the hologram. In this case, the diffracted light is strongly emitted in the direction designed in advance. The conditions depend on the hologram imaging conditions.

As shown in FIG. 3, an illuminating light 11 from an illuminating light source 10 is incident on the hologram 9 at an angle 12 nearly parallel to the surface of the hologram 9 and a diffracted light 14 reproduced at an angle 13 close to the front of the display device is used for display. When the device 15 is illuminated, the display device can be illuminated in a compact size at an angle close to the front.

Since the hologram 9 is disposed in front of the display device 15 (on the observer side), the reflected light 16 from the display device 15 serving as display light is observed through the hologram 9. The reflected light 16 is the hologram 9
When the light is diffracted when passing through, the illumination light 11 is diffracted twice with a diffraction efficiency of less than 100%, and the display light becomes dark. However, the volume transmission type hologram has the above-mentioned characteristic of the incident angle selectivity. Therefore, when the display light exits through the hologram, the display light passes through without being diffracted.

As described above, the incident angle selectivity depends on the hologram imaging conditions. That is, the hologram photographed and recorded by causing the object light and the reference light to interfere with each other, when the illumination light enters from a direction (a conjugate direction) corresponding to the reference light at the time of photographing, is shifted in a direction corresponding to the object light at the time of photographing. Diffracted light is emitted. (And vice versa)

Therefore, the incident angle selectivity (graph of the incident angle-diffraction efficiency) of the hologram of FIG. 3 is shown in FIG. As shown in the figure, light incident from the vicinity of each of the angle 12 at which the illumination light enters the hologram and the angle 13 at which the diffracted light exits is strongly diffracted, and light from other angles is hardly diffracted. Because there is a (penetrate) characteristic,
By controlling the incident angle selectivity of the hologram, bright display light can be emitted in a direction according to the observation conditions of the display device.

As a result of studying the above control, the angle 12
Is effective in reducing the size of the display device if it is close to being parallel to the hologram surface, and is 60 ° to 80 ° or −60 °.
It is preferable to be within the range of -80 °. (Positive / negative is the difference between whether the illumination light source 10 is above or below in FIG. 3) The angle 13 should be slightly off the front (0 °),
It has been confirmed that a range of 5 ° to 30 ° or −5 ° to −30 ° is preferable. That is, the light illuminating the display device 15 from the front (0 °) direction is reflected by the display device 15 and strongly reflected in the front (0 °) direction, so that it is diffracted again when passing through the hologram. This is because the light intensity is reduced by the second diffraction and the display light is blurred.

The volume transmission type hologram has a wavelength of the diffracted light which is higher than that of a volume reflection type hologram (a so-called Lippmann hologram) having strong diffraction wavelength selectivity (a characteristic of reproducing only a diffracted light of a specific wavelength and color). Although the width is wide, the diffraction efficiency is not uniform over the entire visible wavelength range, and has a diffraction efficiency peak in a specific wavelength range. (See Fig. 5)

In the present invention, it is necessary to use an illumination light source having a peak in light emission in a specific wavelength range. When a typical cold cathode tube is used as the light source, a specific wavelength as shown in FIG. It has a light emission characteristic in which the light intensity shows a peak at 17, and by adjusting the peak 18 of the diffraction wavelength of the hologram having the diffraction wavelength selectivity as shown in FIG. Become.

If the display device of FIG. 3 does not have the illumination light source 10 and the display device is observed with ambient light as shown in FIG. 7, the optical path of the peripheral light is as shown in FIG. Although a part of the incident light is diffracted, generally, the ambient light is not light only in a specific wavelength range, but has a flat light intensity distribution over the entire visible wavelength range. As shown in the graph, light other than the diffraction wavelength band of the hologram contributes to the reflection from the display device, and the utilization efficiency of the ambient light does not decrease so much.

As an index indicating the wavelength selectivity of the hologram (the relationship between the diffraction wavelength and the diffraction efficiency), there is a half-value width (bandwidth between wavelengths at which the diffraction efficiency becomes に お け る at the wavelength where the diffraction efficiency reaches a peak). In a cold cathode tube, the band (wavelength) width at which the light intensity shows a peak is slightly less than 10 nm, the half width of the hologram is desirably 10 nm or more, and the peripheral light is 7 nm.
If you intend to use about 0% or more, the half width is 30 nm.
It is desirable to do the following.

<First Embodiment> FIG. 9 is an explanatory diagram showing an outline of an example of an optical system for photographing and recording a hologram mounted on the display device shown in FIG. The light emitted from the laser light source 19 is split into two beams by a beam splitter 20, respectively, is spread by a lens via mirrors, and is incident on a dry plate 21.

The angles of the two incident laser beams (average incident angles with respect to the normal direction of the dry plate) 22 and 23 are the incident angles when a laser light source having the same wavelength as the peak wavelength of the cold cathode tube does not exist. By changing it, the wavelength is corrected.

For example, assuming that a cold-cathode tube having a peak wavelength of 545 nm is used for the illumination light, a hologram that is diffracted to −15 ° when illuminated from 75 ° is produced by using a 532 nm wavelength of a YAG laser. In the case of photographing and recording with the above light, light is incident from 72.5 ° and -14 °.

The incident angle selectivity and the wavelength selectivity of the hologram produced at this time are determined by the thickness of the recording material of the hologram.
In the case of μm, the incident angle selectivity of about ± 2 ° and 17 nm
A wavelength selectivity of about half width is obtained.

FIG. 1 shows an outline of an example of the display device according to claim 1 on which the hologram thus produced is mounted.
0 is shown. In the figure, light 25 emitted from a cold cathode tube 24 as an illumination light source illuminates a hologram 26 at an angle substantially parallel (large) to the hologram surface, and diffracted light 27 from the hologram 26 illuminates a display device 28. .

As described above, in order to make the apparatus compact, it is better to have a large hologram illumination angle.
An angle of 60 ° or more is desirable. However, if the angle is too large (exceeds the critical angle), the surface reflection sharply increases and the light quantity loss increases, so it is preferable to suppress the angle to about 80 °.

In the display device based on the above assumption, the angle for illuminating the hologram is 75 ° and the angle for illuminating the display device is -15 °. Needless to say, each angle depends on the imaging conditions shown in FIG. 9, and the angle (75 °) of the hologram illumination light 25 is equal to the laser light incident angle 2
2, and the angle (−15 °) of the diffracted light 27 corresponds to the laser light incident angle 23.

FIG. 6 shows the light quantity distribution of a green monochromatic cold cathode tube. When the cold cathode tube is used as illumination light and the hologram is illuminated, about 70% of the illumination light of the hologram is used. Of light will be available.

In a display device having these illumination light sources and holograms (see FIG. 10), the light 29 reflected by the display device 28 reaches the observer's eyes 30 through the hologram. ± 2 hologram angle selectivity
When the angle is about °, the light 29 passes through the hologram without being diffracted again.

On the other hand, when observing a display device using ambient light, assuming that the light amount distribution is substantially flat over the entire visible wavelength range, about 82% of ambient light can be used in the hologram. Therefore, a bright display image can be visually recognized by both the ambient light and the light from the illumination light source.

In the above description, the incident angles of 75 ° and -15 ° and the diffraction efficiency peak at a wavelength of 545 nm
Although a hologram having a thickness of μm has been described, the present invention is not limited to this.

<Embodiment 2> Next, a display device having a light guide plate according to a second aspect of the present invention will be described. FIG.
FIG. 2 is an explanatory diagram showing an outline of an example of an optical system for photographing and recording a hologram mounted on the display device.

In this system, a glass block 3 is provided in front of the dry plate.
The hologram is photographed and recorded by putting light from a different surface with 1 placed. Other than that is the same as the first embodiment.

FIG. 12 is an explanatory diagram showing an outline of an example of the display device according to the present embodiment. In this case, the illumination light 33 is incident from the side surface of the light guide plate 32, and the light 34 that has passed through the light guide plate illuminates the hologram 35, but other configurations are the same as in the first embodiment.

In the display device according to the present embodiment, the hologram is illuminated by the light that has passed through the light guide plate, so that the influence of surface reflection is small and the hologram can be illuminated at a larger angle. There is an advantage that you can.

<Third Embodiment> In the display device according to the third aspect, the display device for a color (the liquid crystal panel is driven according to the three primary color pixels) is provided.
The hologram imaging optical system is the same as in FIGS. 9 and 11, and the outline of the configuration of the display device is the same as in FIGS. 10 and 12.

However, the hologram is composed of cold cathode fluorescent lamps R, G,
B, 432 nm, 545 nm, 61
It is produced by superimposing or multiplex-recording those produced according to three wavelengths of 2 nm. In addition, a cold cathode fluorescent lamp corresponding to white light of three wavelengths is used. In this case, a device capable of observing a display image in full color is provided.

[0040]

As described above, according to the present invention,
In a reflection type liquid crystal display device having an illumination mechanism, a compact display device and an effective use of illumination light are provided, and a display device with sufficient display light luminance is provided for display using either ambient light or illumination light.

[0041]

[Brief description of the drawings]

FIG. 1 is an explanatory view showing an example of an illumination mechanism in a conventional reflective liquid crystal display device.

FIG. 2 is an explanatory diagram showing an example of an illumination mechanism in a conventional reflective liquid crystal display device.

FIG. 3 is an explanatory diagram showing an outline of a configuration example of a display device of the present invention.

FIG. 4 is an explanatory diagram showing incident angle selectivity of a hologram.

FIG. 5 is an explanatory diagram showing diffraction wavelength selectivity of a hologram.

FIG. 6 is an explanatory diagram showing an example of light intensity of a cold cathode tube.

FIG. 7 shows a display device according to the present invention, which is illuminated with ambient light (external light). Explanatory drawing which shows a state.

FIG. 8 is a graph showing that light outside the diffraction wavelength band passes through the hologram due to the diffraction wavelength selectivity of the hologram.

FIG. 9 is an explanatory diagram illustrating an outline of an example of an optical system that captures and records a hologram.

FIG. 10 is an explanatory diagram showing an outline of an example of a display device of the present invention.

FIG. 11 is an explanatory diagram illustrating an outline of an example of an optical system that captures and records a hologram.

FIG. 12 is an explanatory diagram showing an outline of an example of a display device of the present invention.

Claims (3)

[Claims] At least a volume transmission type hologram, a display device, and an illumination light source, wherein the hologram is a front surface (a viewer side) of the display device
The illumination light source illuminates the hologram from the front side (observer side), transmission diffracted light by the hologram is incident on the display device, and reflected light from the display device is viewed as a display image. The incident angle of the illumination light of the hologram by
It is within the range of 60 ° to 80 ° or −60 ° to −80 ° with respect to the radiation direction of the hologram surface, and the emission angle of the transmitted diffracted light from the hologram is 5 ° with respect to the radiation direction of the hologram surface. ° to 30 ° or -5 °
The peak wavelength of the diffraction efficiency of the transmitted diffracted light from the hologram is substantially equal to the peak wavelength of the emission of the illumination light source, and the half-width of the diffraction efficiency of the transmitted diffracted light from the hologram. Is in the range of 10 nm to 30 nm. 2. A hologram having at least a volume transmission type hologram, a light guide plate in close contact with the hologram, a display device, and an illumination light source, wherein the hologram is installed on a front surface (observer side) of the display device, A light guide plate is installed on the observer side), the illumination light source illuminates the hologram via the light guide plate, and the transmitted and diffracted light by the hologram is incident on the display device, and the reflected light from the display device is visually displayed as a display image. The incident angle of the illumination light of the hologram by the illumination light source,
It is within the range of 60 ° to 80 ° or −60 ° to −80 ° with respect to the radiation direction of the hologram surface, and the emission angle of the transmitted diffracted light from the hologram is 5 ° with respect to the radiation direction of the hologram surface. ° to 30 ° or -5 °
The peak wavelength of the diffraction efficiency of the transmitted diffracted light from the hologram is substantially equal to the peak wavelength of the emission of the illumination light source, and the half-width of the diffraction efficiency of the transmitted diffracted light from the hologram. Is in the range of 10 nm to 30 nm. 3. A white illumination light source having peak wavelengths in R, G, and B regions as an illumination light source, and a hologram having a wavelength corresponding to the peak wavelengths of R, G, and B of the illumination light source. 3. The display device according to claim 1, wherein three types of volume transmission holograms having a peak of diffraction efficiency of transmitted diffraction light are used.