JP3233256B2 - Projection type image display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention is applied to, for example, a compact projection type color liquid crystal television system or information display system, and performs color display by one liquid crystal display element without using a mosaic color filter. The present invention relates to a single-panel projection image display device.

[0002]

2. Description of the Related Art As a projection type image display device, a projection type liquid crystal display device has been conventionally known. Since the liquid crystal display element used in this liquid crystal display device does not emit light by itself, it is necessary to separately provide a light source. However, liquid crystal display devices have very excellent characteristics, such as a wide color reproduction range, small size, light weight, and no need for convergence adjustment, as compared with projection type CRT display devices, so future development is expected. .

A projection type color image display system using a liquid crystal display element uses three liquid crystal display elements according to three primary colors.
There are a plate type and a single plate type using only one sheet. In the former three-panel system, an optical system that divides white light into three primary colors of red, green, and blue, and a liquid crystal display element that controls the color lights to form an image are provided independently of each other. This is a method of performing full color display by superimposing.

In this three-plate configuration, the light emitted from the white light source can be used effectively, but the optical system is complicated and the number of parts is increased. In terms of cost and miniaturization, the latter single-plate configuration is used. In general, it is disadvantageous. The latter single-panel type uses a projection optical system to project a liquid crystal display element having a mosaic, stripe, or other three primary color filter pattern, and is disclosed in, for example, JP-A-59-230383. The single-panel type uses only one liquid crystal display element, and the optical system has a simpler configuration than the three-panel type, and is suitable for a low-cost, small-sized projection system. However, the brightness of the screen of a single-panel type using a color filter is reduced to about 1/3 as compared with a three-panel type using an equal light source.

[0005] Brightening the light source is one solution to the reduction in brightness, but when used for consumer use,
It is not preferable to use a light source with large power consumption. When an absorption type color filter is used, the energy of the light absorbed by the color filter is converted into heat.If the light source is brightened unnecessarily, not only will the temperature of the liquid crystal display element rise, but also the color filter will lose its color. Accelerated.

Therefore, how to effectively use a given light beam is an important issue in improving the usefulness of a projection image display device.

[0007] In order to solve the drawbacks of the single-panel type liquid crystal display device, there has been proposed a device which aims to improve the light use efficiency (Japanese Patent Laid-Open No. Hei 4-60538). This is because white light is made incident on a dichroic mirror arranged in a fan shape, split into red, blue, and green (hereinafter, referred to as R, G, and B) light fluxes, and arranged on a light source side of a liquid crystal display element. To the microlens array at different angles. Further, when each incident light beam passes through the microlens according to the incident angle, the light beam is distributed and irradiated for each color to a liquid crystal portion driven by a display electrode to which a corresponding color signal is independently applied. It is a system configured so that: Thereby, the light use efficiency can be improved.

Further, instead of the dichroic mirror, a transmission hologram element corresponding to R, G, B light from a light source is used to improve the light utilization rate. Japanese Patent Application Laid-Open Nos. Hei.
249318 and JP-A-6-222361.

[0009]

However, in the method using the above-mentioned dichroic mirror as the spectral means, a plurality of dichroic mirrors R arranged in a fan shape are used.
There is a problem that color mixing occurs due to multiple reflections occurring between G and B, color purity is reduced, and display quality is adversely affected.

[0010] Such degradation of display quality will be described with reference to FIG. FIG. 6 shows an example in which dichroic mirrors B, G, and R for reflecting light in the wavelength ranges of B, G, and R are arranged in a fan shape in such a manner that they are respectively shifted by an angle θ from the side closer to the white light source. Is shown. The angle at which white light enters the dichroic mirror B is α.

The white light incident on the three dichroic mirrors R, G, and B is divided into three light beams as follows. That is, a blue light beam is generated by being reflected by the dichroic mirror B.

The light passes through the dichroic mirror B, is reflected by the dichroic mirror G, and passes through the dichroic mirror B again to obtain a green light beam.

After passing through dichroic mirrors B and G,
The light is reflected by the dichroic mirror R, passes through the dichroic mirrors B and G again, and a red light beam is obtained.

At this time, the green light flux is different from the blue light flux.
The traveling direction of the red light beam is 2θ with respect to the green light beam.
And is incident on the aforementioned liquid crystal display element.

However, there is actually stray light other than the above, which is generated due to extra reflection. The dichroic mirrors R, G, and B are formed by a well-known multilayer thin film coating technique, and the angle of incidence of a light beam is determined at the time of design. However, when a light beam is incident at an angle different from the designed incident angle, the spectral characteristics change, and as the difference between the designed incident angle and the actual incident angle increases, the spectral characteristics also change. FIG. 7 shows the spectral characteristics of a dichroic mirror B (reflecting the blue wavelength range and transmitting the other wavelength ranges) designed at an incident angle of 45 ° and a light beam incident at an incident angle of 20 ° different from the designed incident angle. And the actual spectral characteristics shown by the dichroic mirror B.
As is apparent from FIG. 7, when a light beam enters at an angle smaller than the set incident angle, the rising wavelength near 500 nm shifts to the longer wavelength side, and the characteristic curve shows ripple (sine wave-like transmittance curve undulation). Occurs.

In this method, the green light reflected by the dichroic mirror G is incident on the dichroic mirror B again at an angle 2θ smaller than the design value α of the incident angle at the dichroic mirror B. , The shift of the reflection region toward the longer wavelength side and an increase in ripples occur. Therefore, part of the green light is reflected by the dichroic mirror B. As a result, a small amount of stray light M is generated as shown in FIG. 8, and this stray light M is generated by the dichroic mirror G.
, Most of which is reflected. The stray light M reflected by the dichroic mirror G again enters the dichroic mirror B at an angle 4θ smaller than the above α, that is, at the same angle as the red light beam reflected by the dichroic mirror R. Therefore, the traveling direction of the stray light M transmitted through the dichroic mirror B is the same as the angle after the red light flux has passed through the dichroic mirror B, as shown in FIG. There is an angle difference of 4θ with respect to the blue light. This is because green stray light M is applied to a pixel that modulates red light of the liquid crystal display element.
Means incident.

Similarly, the red light flux reflected by the dichroic mirror R enters the dichroic mirrors G and B at angles smaller than the design values by 2θ and 4θ, respectively. Therefore, the characteristics of the dichroic mirrors G and B are similarly shifted, and a part of the red light beam is reflected by the dichroic mirrors G and B as shown in FIG. The stray light N generated by this is light reflected by the dichroic mirror R and transmitted through the dichroic mirrors G and B, or light reflected by the dichroic mirror G and transmitted through the dichroic mirror B. This stray light N
Has an angle difference of 2θ from the red light beam, and enters the liquid crystal display element at an angle different from any of the blue, green, and red light beams.

The stray lights M and N are distributed to pixels other than the corresponding pixels of the liquid crystal display element by the micro-lens array, causing color mixing and lowering the color purity.

Further, since a dichroic mirror needs to be manufactured by stacking a plurality of dielectric films, it is very expensive compared to a hologram element for writing interference fringes of light. JP-A-5-249318, JP-A-6-22236
In the method using the transmission type hologram element disclosed in No. 1, one or three hologram elements corresponding to each color are used in close contact with each other, so that stray light due to the above-described cause does not occur, and further, the dichroic mirror is used. The cost can be reduced as compared with the method used.

However, in this method, when the incident angle of light deviates from the design value, not only does the diffraction wavelength shift, but also the diffraction efficiency is greatly reduced, so that the light utilization efficiency is reduced. This is because the diffraction efficiency of the transmission hologram is obtained by the thickness (d) of the hologram element from the equation derived from Kogelnik's couple wave theory described later.
This is because it changes as shown in FIG.

For example, if the incident angle of light deviates from the designed value by Δθ, the light passing distance B passing through the hologram element becomes the light passing distance A at the designed incident angle in the case shown in FIG.
Changes by 1 / cos (△ θ). Therefore, when light having a certain degree of parallelism such as used in liquid crystal projection enters a transmission type hologram element, a high diffraction efficiency can be obtained for the principal ray, but for other light, it is high. The diffraction efficiency decreases as the degree of divergence of light (the opening angle with respect to the principal ray) increases.

In Japanese Patent Application Laid-Open No. Hei 6-222361, the hologram element has a periodic structure corresponding to the pixel pitch of the liquid crystal display element. In addition, the process of manufacturing the master of the hologram element becomes complicated.

The present invention has been made in order to solve the problems of the prior art, and provides a projection type image display device which has a wide color reproduction range and can be reduced in size and cost. The purpose is to:

[0024]

According to a projection type image display apparatus of the present invention, a light source and a light beam emitted from the light source are divided into a plurality of light beams having different wavelength ranges, and the plurality of light beams are respectively different.
Optical means to enter the same area at an angle and different
Divided into each wavelength region incident on the same region at an angle
A plurality of light beams, a converging means for converging each wavelength band, each
A plurality of light beams converged for each wavelength range are input corresponding to each light beam.
A pixel opening for transmitting light, and the light transmitted through the pixel opening.
Liquid crystal display that modulates each bundle to generate the desired image light
Projecting image light generated by the element and the liquid crystal display element
In the projection type image display device and a projection means for,
The optical unit converts the light beam emitted by the light source into a light beam having a different wavelength range.
A first light diffracted in different directions as a plurality of light beams
The hologram element and the first hologram element
Receiving each of the folded light beams, and applying each light beam to the focusing means
Second hologram elements for incidence at different angles
And a small number of the first and second hologram elements.
At least one is a reflective hologram element , thereby achieving the above object.

In the projection type image display device according to the present invention, the light condensing means may be a microlens array or a hologram element.

The operation of the present invention will be described below.

In the present invention, the white light from the light source is split into light beams of a plurality of wavelength ranges by the first hologram element, and the light beams of the plurality of wavelength ranges are mutually separated by the second hologram element. Light is incident on the same liquid crystal display element at different angles. Then, a color display is performed by causing the light beam in each wavelength range to enter the corresponding pixel by the microlens.

As the first and second hologram elements, as shown in FIG. 11, a reflection type hologram element formed by recording interference fringes of two light beams formed on a hologram recording substrate as a difference (Δn) in refractive index. Hologram elements can be used. Here, the angle setting of the two luminous fluxes is described in “Image of Laser”, by Shizuo Tatsuoka (Kyoritsu Shuppan) As described in 77-81, it may be set so that the light in the wavelength range to be used satisfies the Bragg diffraction condition. Further, the diffraction efficiency η of the hologram element can be derived from Kogelnik's couple wave theory. In the reflection type hologram element, the waveform is shown in FIG. 9B, that is, expressed by the following equation (1).

Η = tanh ² (πΔnd / λcosθ) (1) In the transmission type hologram element, the waveform shown in FIG. 9A, that is, represented by the following equation (2).

Η = sin ² (πΔnd / λcos θ) (2) where d is the thickness of the hologram element, λ is the wavelength of the diffracted light, and θ is the angle formed by the two light beams.

As a result, in the reflection type hologram element, the diffraction efficiency monotonously increases with the increase of d, and Δnd / λcos
In the range where θ exceeds 1, the diffraction efficiency is almost 100%, whereas in the transmission hologram, when d deviates from the design value, the diffraction efficiency decreases.

The illuminating light of the liquid crystal projection has a certain degree of parallelism. Among them, the light having a larger opening angle with respect to the principal ray is, as described above, that is, FIG.
As shown by (2), the distance that the light passes through the hologram element changes, and the difference (Δd) from the distance that the principal ray passes through the hologram element increases.

Therefore, in the case of a transmission type hologram element, when the illumination light for projection is used, the diffraction efficiency decreases as the parallelism becomes worse. However, when a reflection type hologram element is used as in the present invention, Δnd / λcos θ > 1
By setting to, not only high diffraction efficiency can be maintained even for light with poor parallelism, but also light that goes straight without undergoing diffraction (light of the valley between the zero-order diffracted light and the diffracted wavelength) It does not fall on the projection lens to lower the color purity.

Further, in the present invention, by using a hologram element as compared with the case of using a dichroic mirror,
There are the following advantages.

(1) Cost can be reduced.

(2) No stray light is generated.

Further, the hologram element used in the present invention does not need to be patterned, does not need to be aligned with the pixels of the liquid crystal display element, and is easy to manufacture. Furthermore, by using a microlens A L'<br/> b or hologram element as the condensing means, it may be made incident light from the second hologram element in a pixel opening efficiently liquid crystal display device.

[0038]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a schematic diagram showing a projection type image display apparatus for color display according to the present embodiment. As the light source 1 used in the present embodiment, a metal halide lamp having a power of 150 W, an arc length of 5 mm, and an arc diameter of 2.2 mm was arranged so that the arc was perpendicular to the paper surface. As the light source 1, a halogen lamp or a xenon lamp can be used.

A spherical mirror 2 is arranged on the back of the light source 1, and a condenser lens 3 having a diameter of 80 mm and a focal length of 60 mm is arranged on the front. The center of the spherical mirror 2 is the light source 1
And the light source 1
Are arranged so as to coincide with the focal point of the condenser lens 3. With this arrangement, the parallelism of the light emitted from the light source 1 through the condenser lens 3 is about 2.2 ° in the arc length direction (the direction perpendicular to the plane of FIG. 1) and about 1 ° in the direction of the arc diameter. is there.

In front of the condenser lens 3, a light source 1
A reflection hologram element 4 for diffracting R, G, and B light contained therein in different directions; receiving R, G, and B diffracted light from the reflection hologram element 4; And a reflection type hologram element 5 that diffracts so as to be incident on the liquid crystal display element 7 having the same at different angles. In the present embodiment, one micro lens 6 a in the micro lens array 6 corresponds to three pixels of the liquid crystal display element 7. The incident angles of the R, G, and B lights on the liquid crystal display element 7 are obtained from the pixel pitch P of the liquid crystal display element 7 and the focal length f of the micro lens 6a, which will be described later.

In the present embodiment, as shown in FIG.
The Lippmann hologram corresponding to each light of B
The reflection hologram elements 4 and 5 are formed by superposing the holograms such that the R hologram reflects visible light of about 600 nm or more, the B hologram reflects visible light of about 500 nm or less, and the G hologram reflects 500 nm to 570 nm. Set to. As hologram elements 4 and 5, R,
A single multiplexed hologram element having the above-described spectral characteristics by performing multiple exposure of the G and B lights may be used. By arranging the optical system in this manner, the R, G, and B lights are diffracted by the corresponding reflection hologram elements 4 and 5, and then enter the microlens array 6 attached to the liquid crystal display element 7. When the incident angle of the light beam of each color at this time is appropriately selected so as to satisfy the following condition, the light beam is distributed to pixels corresponding to each color by the microlens array 6 as shown in FIG. These conditions are R, G, B
For any two colors of light, if the difference between the incident angles of the light flux and the microlens is θ, the focal length of the microlens 6a in the air is f, and the horizontal pixel interval of the corresponding color is P, then tan θ = P / f (3)

The hologram elements 4 and 5 in the present embodiment
In this method, two parallel light beams are irradiated with an argon laser (wavelength: 488 nm) while adjusting the angle between them using OmniDex 600 manufactured by DuPont, and interference fringes generated at this time are recorded. . The hologram elements 4, 5
Is a polymer recording film containing a monomer, an initiator, and a sensitizing dye.
Interference fringes corresponding to G and B can be recorded on the hologram element.

(A) Exposure with laser light: 20 mJ / cm ² (sum of object light intensity and reference light intensity) (b) UV irradiation: 100 mJ / cm ² (c) Heating: 140 ° C. (2 hours) The monomer is uniformly distributed in the recording film. However, when the exposure is performed by the laser beam based on the above (a), the monomer moves from the surroundings as the monomer is polymerized and polymerized in the exposed portion. I do. Therefore, the density of the monomer increases in the exposed portion, and decreases in the other areas. At this time, if the refractive indices of the polymer and the monomer are different, a refractive index distribution corresponding to the interference fringe is generated.

Next, based on the above (b), the entire surface is irradiated with ultraviolet rays to complete the polymerization of the monomer of the red reaction. Finally, the refractive index modulation is enhanced by heating based on the above (c).

As a light source for recording interference fringes on the hologram element, an He—N
An e-laser, a YAG laser, a Kr laser, or the like can be used. Further, as the material for the hologram element, in addition to the photopolymerizable photopolymer such as the above-mentioned materials, any material can be used as long as it can produce a volume hologram such as gelatin dichromate or silver halide. .

Further, the hologram element used in the present invention converges the light corresponding to the pixels of the liquid crystal display element by the microlens array, so that the periodicity corresponding to the pixel pitch is not required in the plane of the hologram element. The recording of interference fringes can be performed by one recording.

Under the above conditions, the pixel pitch is 130 μm ×
Using a liquid crystal display element of 130 μm, focal length f = 720
μm (in a glass substrate, the thickness of the opposite substrate of the liquid crystal display element is 1.
When a microlens (corresponding to 1 mm) is used, the difference θ between the incident angles is as follows from the equation (3).

Θ = tan ⁻¹ (P / f) = tan ⁻¹ (130/720) {10} Therefore, when the conditions of the hologram elements 4 and 5 are set as shown in FIG. 4, R, G, B 90% for each luminous flux
The above-described high diffraction efficiency was obtained, and a single-panel liquid crystal projection with a wider color reproduction range than before was realized.

In the embodiment described above, the hologram element 4,
4, the R, G, and B lights are made incident at the angles shown in FIG. 4. If the value of θ satisfies the condition of Expression (3), the incident angle and the incident order of the illumination light to the hologram element are It is not limited to this.

In this embodiment, the two hologram elements 4 and 5 are respectively arranged in parallel. However, they may be arranged in a C shape as shown in FIG.
As shown in (b), one of the two hologram elements is constituted by the reflection hologram element 4 and the other is constituted by the transmission hologram element 11, and the transmission hologram is formed in the area where the light reflected by the reflection hologram element 4 passes. The element 11 may be provided.

[0052]

As described above, according to the present invention, the hologram element separates white light into R, G, and B light, and makes each light incident on the corresponding liquid crystal display element through a microlens. A color projection type image display device that has a high utilization rate, a wide color reproduction range, and can be reduced in size and cost can be realized at low cost.

[Brief description of the drawings]

FIG. 1 is a schematic view showing a projection type image display device for color display according to an embodiment.

FIG. 2 is an explanatory diagram of a Lippmann hologram constituting the reflection hologram element used in the present embodiment.

FIG. 3 is a sectional view of a main part of the liquid crystal display element used in the embodiment.

FIG. 4 is a diagram showing detailed setting conditions of a hologram element used in the embodiment.

FIGS. 5A and 5B are diagrams showing another method of installing a hologram element.

FIG. 6 is a diagram showing an arrangement of dichroic mirrors in a conventional example.

FIG. 7 is a diagram showing spectral characteristics when light enters a dichroic mirror at an angle different from the design.

FIG. 8 is a diagram illustrating a principle of generation of color mixture in a system using a dichroic mirror.

FIG. 9 is a diagram showing the diffraction efficiency of a hologram element according to Kogelnik's couple wave theory.

FIG. 10 is a diagram illustrating a relationship between an incident angle of light and a thickness of a hologram element through which light passes.

FIG. 11 is a diagram illustrating a method of writing a hologram by two-beam interference.

[Explanation of symbols]

1 light source 2 spherical mirror 3 condenser lens 4 hologram element 5 hologram element 6 microlens array 6a microlenses 7 a liquid crystal display element 8 field lens 9 projection lens 10 screen 11 hologram element

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁷ , DB name) G02F 1/13 G02B 5/32 G02B 27/18 G02F 1/1335 H04N 5/74

Claims (2)

(57) [Claims] 1. A light source, and a light beam emitted by the light source is divided into a plurality of light beams having different wavelength ranges, and the plurality of light beams are divided into different regions at different angles.
For each wavelength region that is incident on the same region at different angles
A plurality of light fluxes divided into a plurality of light fluxes, and a focusing means for converging the light fluxes for each wavelength range, and a plurality of light fluxes converged for each wavelength range corresponding to each light flux.
Having an incident pixel opening, and transmitting through the pixel opening.
A liquid crystal display that modulates each light beam to generate the desired image light
Display element , and projection for projecting image light generated by the liquid crystal display element
And a light source emitted from the light source having a different wavelength range.
A first light diffracted in different directions as a plurality of light beams
The hologram element and the first hologram element
Receiving each of the folded light beams, and applying each light beam to the focusing means
Second hologram elements for incidence at different angles
And a small number of the first and second hologram elements.
At least one of the projection type image display devices is a reflection type hologram element . 2. The projection type image display device according to claim 1, wherein said light collecting means is a microlens array or a hologram element.