JP2002243948A - Hologram light guide plate - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a hologram light guide plate which is capable of conducting bright white illumination by using a single layer of a volume hologram. SOLUTION: The hologram light guide plate 1 has a transparent plate body 2 provided with a hologram 3 on one surface 2' of the transparent plate body 2 and has such a structure that the light introduced from a light source 5 disposed near one end of the plate body 2 propagates as repeatedly subjected to total reflection in the plate body 2 and that a part of the propagating light 6 is diffracted by the hologram 3 to exit to the outside of the plate body 2. In this light guide plate 1, the hologram 3 is a volume hologram consisting of an array of converting holograms 3' in such a manner that the light beams 7R, 7G, 7B diffracted by the hologram 3 form a white illumination region α.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a hologram light guide plate, and more particularly to a hologram light guide plate used for a backlight and a front light for a liquid crystal display device.

[0002]

2. Description of the Related Art The present applicant has disclosed Japanese Patent Application Laid-Open No. H11-109338.
In this issue, we propose a hologram light guide plate that provides a reflection or transmission hologram on one surface of a light guide plate that propagates light while repeating total reflection as a light guide plate for front light and that emits propagation light as illumination light to the outside. I have. It is clear that such a hologram light guide plate can be used as a backlight light guide plate.

On the other hand, it has been proposed, for example, in Japanese Patent Application Laid-Open No. 10-253955 to combine a light guide plate and a volume hologram constituting a condensing hologram array to form a hologram color filter for a liquid crystal display device.

[0004]

In order to configure a conventional hologram light guide plate for white illumination, a conventional hologram light guide plate uses a hologram that is multiplex-recorded to diffract light in a plurality of color regions or has a multi-layer structure. It is necessary and its fabrication is not easy. In the case of multiplex recording, the diffraction efficiency also decreases, and it is not easy to obtain a bright one.

The present invention has been made in view of such problems of the prior art, and has as its object to provide a hologram light guide plate capable of providing bright white illumination using a single-layer volume hologram. That is.

[0006]

A hologram light guide plate according to the present invention for achieving the above object has a transparent plate, a hologram provided on one surface thereof, and a light source arranged near one end of the plate. The hologram waveguide is configured so that light introduced from the hologram propagates while repeatedly totally reflecting in the plate, and a part of the propagated light is diffracted outside the plate by the hologram. In the optical plate, the hologram is formed of a volume hologram composed of an array of light-collecting holograms, and light diffracted by the hologram is configured to form a white illumination region.

In this case, it is necessary that the diffracted light having the smallest diffraction angle in the red region and the diffracted light having the largest diffraction angle in the blue region, which are diffracted by the light-collecting hologram, intersect.

It is desirable that the average diffraction efficiency of the hologram on the light source side be lower than the average diffraction efficiency on the opposite side.

The hologram light guide plate of the present invention can be used as a backlight illuminator or a front illuminator of a liquid crystal display.

In the present invention, since a hologram of the hologram light guide plate is a volume hologram composed of an array of condensing holograms, and the light diffracted by the hologram is configured to form a white illumination area, it is simple. With this configuration, bright white illumination can be achieved, and a backlight and front light guide plate for bright white illumination for a liquid crystal display device or the like can be realized.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS A hologram light guide plate of the present invention will be described below based on embodiments.

FIG. 1 is a cross-sectional view of a hologram light guide plate 1 according to one embodiment of the present invention.
A hologram 3 is attached to the front surface 2 ′ of the light guide plate 2, and diffused light from a white light source 5 disposed opposite to the end face 4 at one end of the light guide plate 2 is introduced into the light guide plate 2 through the end face 4. The light is guided to the other end as transmission light 6 while repeating total reflection between the outer surface of the volume hologram 3 and the surface 2 ″ on the opposite side of the light guide plate 2. The transmission light 6 is diffused light. And has a distribution in the traveling direction.

The volume hologram 3 is a single-layer volume hologram composed of an array of light-collecting holograms 3 ', and has a selectivity of a diffraction angle and a selectivity of a diffraction wavelength. Therefore, as shown in FIG. 1, the component 6 of the wavelength λ _{G in} the G (green) region that enters the light-collecting hologram 3 ′ of the transmission light 6, which is the diffused light, from the light guide plate 2 at the incident angle θ _G.
G is the interference fringes of light-harvesting hologram 3 'condensing hologram 3 as is diffracted as diffracted light 7 _G of satisfies the Bragg condition convergence example the front direction of the volume hologram 3 of the interference fringes' At the incident angle θ _G , light of other wavelengths is transmitted through the interference fringes without being diffracted by the wavelength selectivity, and is totally reflected on the outer surface of the volume hologram 3. The light of wavelength λ _{G in} the G region incident at an angle other than the incident angle θ _G is transmitted through the interference fringes without being diffracted by the angle selectivity, and is totally reflected on the outer surface of the volume hologram 3.

On the other hand, in the transmission light 6 which is a diffused light,
Incident angle θ_GIncident angle θ different from_R(Θ _R> Θ_G)
Wavelength λ in the R (red) region_RIncident light component 6_RIs the light collection
Satisfying the Bragg condition of the interference fringes of the hologram 3 '
Region wavelength λ_GDiffracted light 7_GConvergent diffracted light to the right
7_RIs diffracted as In the transmission light 6 which is a diffused light,
Incident angle θ_B(Θ_B<Θ_GB) (blue) region incident at)
Wavelength λ_BIncident light component 6_BIs a light-collecting hologram 3 '
Satisfies the Bragg condition of the interference fringe_Gof
Diffracted light 7_GDiffracted light 7 to the left_BIs diffracted as

As described above, from the same light-collecting hologram 3 ', convergent diffracted lights 7 _R , R, G, and B regions,
When 7 _G and 7 _B are diffracted at different angles, as is apparent from FIG. 1, the diffracted light 7 having the smallest diffraction angle in the R region is obtained.
As _long as _R diffracted light 7 _B of the largest diffraction angle (left beam of Figure 1) and B region (the right side of the ray of FIG. 1) intersect, within the angle therebetween alpha, the wavelength of the three primary colors lambda _R, lambda _G , Λ _B are simultaneously incident, so that a white illumination area is obtained. As described above, the condition for the existence of such a white illumination area α is that the diffracted light 7 _R having the smallest diffraction angle in the R area and the diffracted light 7 _B having the largest diffraction angle in the B area are the hologram light guide plate 1. Intersect in the space on the illumination side of the white light, and the white illumination area α exists outside the intersection, and the area of the white illumination area α increases as the distance from the intersection increases. Since the white illumination region α exists in correspondence with each of the array-shaped light-collecting holograms 3 ′, the white illumination regions α of adjacent light-collecting holograms 3 ′ are all white Will be illuminated.

The other components that do not satisfy the Bragg condition are not diffracted by the volume hologram 3, are transmitted as transmission light 6 while repeating total reflection as described above, and are incident on the next light-collecting hologram 3 '. Sometimes, the wavelength and angle components that satisfy the Bragg condition are similarly diffracted and emerge from the volume hologram 3, and the diffraction directions of the wavelengths of the respective color regions at that time are the same in any case.
White illumination can be performed at all positions in the transmission direction of the hologram light guide plate 1.

The illumination light (diffraction light) 7 is transmitted through the hologram light guide plate 1 and diffracted by the volume hologram 3.
_R, 7 light amount distribution exiting as _G, 7 _B is higher in the light source 5 side,
Lowers at opposite end. This tendency cannot be avoided even if the shape of the light guide plate 2 is devised. Then, the diffraction efficiency of the volume hologram 3 is given a distribution so that the diffraction efficiency is low on the light source 5 side and high on the opposite side, so that the illumination light (diffracted light) 7 _R , 7 _R exiting from the hologram light guide plate 1. _G, 7 to equalize the light intensity distribution of _B. There are various methods for giving the diffraction efficiency of the volume hologram 3 a distribution. For example, when recording the volume hologram 3 by two-beam interference, the intensity of the recording light is low on the light source 5 side and is high through the gradation mask whose transmittance is gradually changed so as to increase on the opposite side. Just do it. As a modification, the same thing can be obtained even if the volume hologram photosensitive material is pre-exposed before interference exposure using a gradation mask so that the sensitivity of the volume hologram photosensitive material has a distribution.

In the surface of the volume type hologram photosensitive material, the area where the hologram is recorded is made to be discrete, and the area of the area is made smaller on the light source 5 side and made larger on the opposite side, so that the light source is averaged. The diffraction efficiency may be low on the fifth side and high on the opposite side. As a modified example, the area of each hologram recording area may be the same, and the distribution density may be low on the light source 5 side and high on the opposite side. However, in these cases, the area of each hologram recording area must be sufficiently smaller than the size of the light-collecting hologram 3 '. In order to selectively record a hologram in a discrete area, the sensitivity may be lost by exposing a part of the volume hologram photosensitive material other than such an area before the interference exposure.

When a photopolymer is used as a volume hologram photosensitive material for recording a volume hologram,
The distribution of the diffraction efficiency can be provided by providing the distribution of the in-plane temperature or the distribution of the baking time during the baking process after the interference fringe exposure.

The hologram light guide plate 1 of the present invention as described above is, as shown in FIG.
And can be used as a backlight illumination device. In that case, as shown in FIG. 1, the transmission type liquid crystal display element 10 has a distance in which the diffracted lights 7 _R , 7 _G , and 7 _B from the hologram light guide plate 1 overlap to form a white illumination area,
In other words, it is separated from the position where the diffracted light 7 _R (the left ray in FIG. 1) having the smallest diffraction angle in the R area and the diffracted light 7 _B (the right ray in FIG. 1) having the largest diffraction angle in the B area intersect. Need to be placed in position.

Then, the scattering layer 11 is disposed integrally or separately on the observation side of the transmission type liquid crystal display element 10 opposite to the hologram light guide plate 1. When such a scattering layer 11 is not disposed, an invisible pixel appears or an angle range in which a display can be viewed is narrow depending on a direction in which the transmission type liquid crystal display element 10 is viewed. Therefore, by disposing the scattering layer 11 as described above, the observer EA can observe a bright display image without color distribution within a relatively wide angle range and without skipping pixels.

In the configuration of FIG. 1, the image displayed on the transmission type liquid crystal display element 10 is observed from the opposite side of the observer EB through the hologram light guide plate 1 by making the scattering layer 11 a reflection type scattering layer. You can do it. This is because the volume hologram 3 has a selectivity of the diffraction angle,
Because the selectivity of the diffraction wavelength is narrow, the white light scattered by the reflective scattering layer 11 is transmitted without being diffracted by the volume hologram 3 and transmitted through the light guide plate 2. In this case, the hologram light guide plate 1 is used as a front light illumination device.

Although the hologram light guide plate of the present invention has been described based on the embodiments, the present invention is not limited to these embodiments, and various modifications can be made.

[0024]

As is apparent from the above description, according to the hologram light guide plate of the present invention, the hologram of the hologram light guide plate uses a volume hologram composed of an array of condensing holograms, and the light diffracted by the hologram is obtained. Since it is configured to form a white illumination region, bright white illumination can be achieved with a simple configuration, and a backlight and front light guide plate for bright white illumination for a liquid crystal display device or the like can be realized.

[Brief description of the drawings]

FIG. 1 is a sectional view of a hologram light guide plate according to one embodiment of the present invention.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Hologram light guide plate 2 ... Light guide plate 2 '... Front surface of a light guide plate 2 "... Opposite surface of a light guide plate 3 ... Volume hologram 3' ... Condensing hologram 4 ... Light guide plate end surface 5 ... White light source 6 ... Transmission light 6 _R … incident light component in R region 6 _G … incident light component in G region 6 _B … incident light component in B region 7 _R … Diffraction light in R region 7 _G … Diffraction light in G region 7 _B … B region Diffraction light 10: Transmissive liquid crystal display element 11: Scattering layer (reflective scattering layer) α: White illumination area EA: Observer of transmissive liquid crystal display EB: Observer of reflective liquid crystal display

Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat II (reference) G09F 9/00 336 G09F 9/00 336J // F21Y 103: 00 F21Y 103: 00 F term (reference) 2H038 AA55 BA06 2H049 CA01 CA05 CA08 CA15 CA17 CA22 2H091 FA14Z FA23X FA23Z FA41X FA41Z FD06 LA16 5G435 AA03 BB12 BB15 BB16 EE27 FF02 FF03 FF08 GG24

Claims (5)

[Claims] A hologram is provided on one surface of a transparent plate, and light introduced from a light source disposed near one end of the plate is repeatedly totally reflected in the plate. In a hologram light guide plate configured to propagate and a part of the propagated light is diffracted outside the plate by the hologram, the hologram is a volume hologram composed of an array of condensing holograms. Wherein the light diffracted by the hologram is configured to form a white illumination region. 2. The apparatus according to claim 1, wherein the diffracted light having the smallest diffraction angle in the red region and the diffracted light having the largest diffraction angle in the blue region diffracted by the light-collecting hologram intersect. Item 3. A hologram light guide plate according to Item 1. 3. The hologram light guide plate according to claim 1, wherein the average diffraction efficiency of the hologram on the light source side is lower than the average diffraction efficiency on the opposite side. 4. The hologram light guide plate according to claim 1, wherein the hologram light guide plate is used as a backlight illumination device for a liquid crystal display device. 5. The hologram light guide plate according to claim 1, wherein the hologram light guide plate is used as a front light illumination device for a liquid crystal display device.