JPH05181108A - Video device for liquid crystal image - Google Patents

Abstract

(57) [Summary] [Object] An object of the present invention is to develop a video device capable of obtaining a high-quality video by using a plurality of dichroic mirrors with a single cutoff wavelength and having a low cost. To do. [Structure] Four dichroic mirrors each having one cutoff wavelength are used, and red light is emitted by a first optical system including first, third and fourth dichroic mirrors (60, 63, 64). With the second optical system including the first, second, third, and fourth dichroic mirrors (60 to 64) to emit green light to the first, second, and fourth dichroic mirrors (60,
The third optical system including 61, 63) separates blue light.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a video device such as a liquid crystal video projector and a liquid crystal projection television, and more particularly to a video device using a dichroic mirror.

[0002]

2. Description of the Related Art FIG. 3 shows an example of a liquid crystal video projector. 1 is a light source for projecting white light, and 2, 3, 4,
Reference numeral 5 is a dichroic mirror (hereinafter referred to as DM) that reflects light in a specific wavelength range, transmits light in other wavelength ranges, and separates color light by wavelength. Reference numerals 6, 7, and 8 denote liquid crystal panels, and 9 Numerals 10 and 11 are condenser lenses for condensing the red, green, and blue color lights separated by the respective DMs on the liquid crystal panels 6, 7, and 8, 12 and 13 are total reflection mirrors, and 14 is a projection lens. is there.

The four DMs 2, 3, 4, and 5 are DMs as blue reflection DM-B in which the DM 2 selectively reflects the color light blue.
3, DM4 is a red reflection DM-R that selectively reflects the color light red.
DM5 is a green reflection DM that selectively reflects the color light green.
-G respectively assigned. The blue reflection DM2, the red reflection DM3, 4 and the green reflection DM5 described above are shown in FIG.
It has unique characteristics shown in (A), (B), and (C), and the characteristics are determined as follows.

The white light from the light source 1 is extracted in the visible light range (about 380 to 780 nm) using a bandpass filter or the like, and the chromaticity of colored light blue, colored light red, and colored light green is specified by NTSC. , A wavelength of light that is substantially the same as the chromaticity of red of color light and green of color light. As a result, the color light blue ≈ 500 nm or less, the color light red ≈ 600 nm or more, and the color light green ≈ 500 to 550 nm or less, and based on this, the blue reflection DM2, the red reflection DM3, 4,
The characteristics of the green reflection DM5 are defined.

In the case of the red reflection DMs 3 and 4, when the limit wavelength (λR) on the short wavelength side in the color light red is longer than the limit wavelength (λG ₁ ) on the long wavelength side in the color light green, that is, in FIG. When λR> λG ₁ in A) and (B),
Let λG be the cutoff wavelength (the separation point between the wavelength of the reflected light and the wavelength of the transmitted light) of the red reflection DMs ₃ and 4, and λR <λ
When G _1, the cutoff wavelength is λR and the red reflection DM3,
4 characteristics are defined. The result of this procedure is shown in FIG.
It has the characteristics shown in.

In the case of the green reflection DM5, the cutoff wavelength on the long wavelength side and the cutoff wavelength on the short wavelength side are determined. The cutoff wavelength on the long wavelength side is λR when λG ₁ <λR, and λG ₁ When> λR, λG ₁ is set. Further, the cutoff wavelength on the short wavelength side is when the short wavelength side limit wavelength (λG ₂ ) of the color light green is longer than the long wavelength side limit wavelength (λB) of the color light blue, that is, λG ₂ >.
and .lambda.B when .lambda.B, and .lambda.G ₂ when λG ₂ ≦ λB.
The characteristics obtained by this procedure are the characteristics shown in FIG.

In the case of blue reflection DM2, the cutoff wavelength is λG ₂ when λB <λG ₂ , and λB when λB ≧ λG ₂ . The characteristics obtained by this procedure are the characteristics shown in FIG.

In the above projector, the white light emitted from the light source 1 is first reflected by the blue reflection DM2 to have a wavelength of about 500 nm or less, and the color light blue is selected. The selected color light blue is reflected by the total reflection mirror 12, condensed by the condenser lens 9 and incident on the liquid crystal panel 6. Then, it becomes blue image light and passes through the red reflection DM 4 and the green reflection DM 5 and enters the projection lens 14.

When the above color light blue is selected by the blue reflection DM2, the wavelengths of the color light red and the color light green are also included due to light leakage. That is, the transmittance in the transmission band of the dichroic mirror is about 90% on average, and it is difficult to increase the transmittance beyond this. Therefore, the blue light DM2 is reflected in the colored light blue reflected by the blue reflection DM2. This is because about 10% of the non-selected wavelengths of colored light red and colored light green are included.

However, this colored light blue reflects the red DM4.
Since the light having a wavelength of about 550 nm or more is reflected by transmitting the light having a wavelength of about 500 nm to 600 nm, the light having a wavelength of about 500 nm to 600 nm is reflected by transmitting the green reflection DM5. The wavelength is pure color light blue.

Approximately 500n transmitted through the blue reflection DM2
Light having a wavelength of m or more is then transmitted by the red reflection DM3 to about 5
The color light red is selected by reflecting light having a wavelength of 50 nm or more.
The selected color light red wavelength light is condensed by the condenser lens 10 and enters the liquid crystal panel 7, becomes red image light, is reflected by the red reflection DM4 again, and is further transmitted through the green reflection DM5 to be projected. It is incident on the lens 14.

When the above-mentioned color light red is also selected by the red reflection DM3, the wavelength of the color light green is included due to light leakage. However, this color light red is reflected by the red reflection DM4 that reflects and selects the same wavelength light again, so that the wavelength light of the color light green has a light leakage of 10% out of 10%, that is, 1%. Then, by transmitting the green reflection DM5, about 6
The light having a wavelength of 00 nm or more becomes almost pure colored light red.

The light transmitted through the blue reflection DM2 and the red reflection DM3 has a wavelength in the range of about 500 nm to 550 nm, becomes almost pure color green, and is condensed by the condenser lens 11 to enter the liquid crystal panel 8. Then, it becomes green image light, is reflected by the total reflection mirror 13, is further reflected and selected by the green reflection DM 5, and enters the projection lens 14.

Since the red, blue, and green color lights selected in this way contain almost no intermediate color, the composite image projected onto the screen from the projection lens 14 has a good color tone.
The image quality is highly accurate.

[0015]

Problems to be Solved by the Invention Dichroic mirror
Is formed by forming a plurality of special thin films on the glass surface and selectively reflecting light in a specific range depending on the thickness of the films. From this, as compared with the dichroic mirror having only one cutoff wavelength such as the blue reflection DM2 and the red reflection DM3 and 4, those having two cutoff wavelengths such as the green reflection DM5 have a complicated structure, The green reflection DM5 is more than twice as expensive as the blue reflection DM2 and the red reflection DM3, 4. Therefore, the provision of such a green reflection DM 5 poses a problem in reducing the cost of the video device.

In view of the above situation, the present invention uses a low-cost dichroic mirror with one cut-off wavelength instead of the high-cost green reflection DM5 to obtain a high-quality image device. The purpose is to develop.

[0017]

In order to achieve the above object, the present invention has a first dichroic mirror for reflecting the light of a light source to separate the first color light. A first optical system that transmits the third and fourth dichroic mirrors and guides them to a projection lens, and a first dichroic mirror.
Has a second dichroic mirror that reflects the light that has passed through and separates the second color light. The second color light is reflected by the third dichroic mirror and transmitted by the fourth dichroic mirror. A second optical system for guiding the light to the light projecting lens, and a third optical system for guiding light having passed through the first and second dichroic mirrors by the fourth dichroic mirror to guide the third color light to the light projecting lens. In addition to the above, in a liquid crystal image imaging device that separates the liquid crystal images of the liquid crystal members arranged in each optical system into color lights of the three primary colors and then synthesizes them,
The first and second dichroic mirrors change from transmission to reflection,
The third and fourth dichroic mirrors are switched from reflection to transmission respectively, and the second dichroic mirror is set to the short wavelength side and the third dichroic mirror is set to the first dichroic mirror. A video device characterized in that the cutoff wavelength is set on the long wavelength side and the cutoff wavelength of the fourth dichroic mirror is set to the same or the long wavelength side with respect to the second dichroic mirror. suggest.

[0018]

In the first optical system, the light having a wavelength of 550 nm or more, which is reflected and selected by the first dichroic mirror, contains almost no other color light by passing through the third dichroic mirror, for example, 600 nm or more. , That is, the color light is red. In the second optical system,
For example, 550 transmitted through the first dichroic mirror.
When the wavelength light having a wavelength of nm or less is reflected by the second dichroic mirror, for example, the wavelength light in the band of 500 to 550 nm, that is, the color light green, is further reflected by the third dichroic mirror and the fourth dichroic mirror. By passing through, the light becomes a green color light that contains almost no other color light. Further, in the third optical system, the light transmitted through the first and second dichroic mirrors contains almost no other color light, for example, light having a wavelength of 500 nm or less, that is, color light blue. Therefore, the image device can obtain a high quality image without using a green reflection dichroic mirror having two cutoff wavelengths.

[0019]

Embodiments of the present invention will now be described with reference to the drawings. FIG. 1 is an optical system diagram in which the present invention is applied to a liquid crystal video projector, and FIG. 2 is a characteristic diagram of four dichroic mirrors (hereinafter referred to as DM) provided in this projector. This projector, like the conventional example, has a light source 50, three liquid crystal panels 51, 52 and 53, and a condenser lens 5 provided corresponding to each liquid crystal panel 51, 52 and 53.
4, 55, 56, two total reflection mirrors 57, 58, a projection lens 59, and light from the light source 50 are divided into red, blue, and green.
It is composed of four DMs 60, 61, 62, 63 for separating colored light into colors.

The above four DMs 60, 61, 62, 6
3 has the characteristics shown in FIG. That is, the first
The DM 60 has a characteristic point shown in FIG. 2 (A) where the cutoff wavelength λR is 550 nm, which is the separation point between the reflected light wavelength and the transmitted light wavelength, and the second DM 61 has the cutoff wavelength λG ₁ . The third DM 62 has a cutoff wavelength λG ₂ of 600 n and a characteristic shown in FIG.
2C, and the fourth DM 63 has the cutoff wavelength λB of 500 nm and the characteristics shown in FIG. 2D.

Then, these DMs 60, 61, 62,
63 is arranged as shown in FIG. That is, the first DM 60 includes a total reflection mirror 57, a condenser lens 54,
Together with the liquid crystal panel 51, the third and fourth DMs, and the projection lens 59, a first optical system for separating red light is formed. The second DM 61 includes the first, third and fourth DMs and the condenser lens 5
5, liquid crystal panel 52, total reflection mirror-58, projection lens 5
A second optical system for separating green light is formed together with 9. The third DM 63 includes the first DM, the second DM, and the condenser lens 5.
6, liquid crystal panel 53, total reflection mirror-58, projection lens 5
A third optical system for separating blue light is formed together with 9.

In the projector thus constructed, the white light emitted from the light source 50 is first emitted from the first DM6.
0 reflects light having a wavelength of about 550 nm or more. The light selected for reflection is totally reflected by the total reflection mirror 57, condensed by the condenser lens 54, and incident on the liquid crystal panel 51. Then, the image light of the liquid crystal panel 51, the light having a wavelength of 600 nm or more, passes through the third DM 62, and further the fourth DM.
The light passes through 63 and enters the projection lens 59. The selective light, which has become a wavelength light of about 550 nm or more by the first DM 60, is transmitted by the third DM 62, and thus the selected light is transmitted by about 60 nm.
Light with a wavelength of 0 nm or more, that is, color light red,
The color light is red, which contains almost no other colored light.

Approximately 550 that have passed through the first DM 60.
About 5 nm or less of wavelength light, the second DM 61 causes about 5
The wavelength light in the band of 00 nm to 550 nm, that is, the color light green is reflected and selected. This color light green is condensed by the condenser lens 55 and enters the liquid crystal panel 52, becomes image light of the liquid crystal panel 52, is reflected by the third DM 62, is further transmitted through the fourth DM 63, and is transmitted to the projection lens 59. Incident. The light leakage of this colored light green is cut off by the third DM 63, and becomes almost pure colored light green.

Then, the first DM 60 and the second DM 61
The color light blue that has passed through the light source and has become a wavelength light of about 500 nm or less is condensed by the condenser lens 56 and enters the liquid crystal panel 53. Then, the image light of the liquid crystal panel 53 is totally reflected by the total reflection mirror 58, and further reflected and selected by the fourth DM 63, resulting in a color light blue with almost no light leakage, and the projection lens 5
It is incident on 9.

As a result, the image projected on the screen contains almost no intermediate colors and becomes an image with a good color tone. With such a configuration, the image device is capable of producing high quality images without using a dichroic mirror having two cutoff wavelengths.

Although the front projection type liquid crystal video projector has been described in the above embodiment, the same can be applied to the rear projection type liquid crystal projection television or the like.

[0027]

As described above, according to the image device of the present invention, four dichroic mirrors each having one cutoff wavelength separate the light from the light source into the three primary colors, thereby producing a high quality image. Since it can be obtained, the image device is extremely advantageous in reducing the production cost.

[Brief description of drawings]

FIG. 1 is an optical system diagram in which the present invention is applied to a liquid crystal video projector.

2A and 2B are characteristic diagrams of four dichroic mirrors provided in the projector, where FIG. 2A is a characteristic diagram of the dichroic mirror 60, FIG. 2B is a characteristic diagram of the dichroic mirror 61, and FIG. Mira-62 characteristic diagram,
(D) is a characteristic diagram of the dichroic mirror-63.

FIG. 3 is an optical system diagram of a liquid crystal projector shown as a conventional example.

FIG. 4 is a characteristic diagram of a dichroic mirror provided in the projector of the conventional example, (A) is a characteristic diagram of red reflection dichroic mirrors-3, 4 and (B) is a characteristic diagram of green reflection dichroic mirror-5. , (C) are characteristic diagrams of the blue reflection dichroic mirror-2.

[Explanation of symbols]

 50 light source 51, 52, 53 liquid crystal panel 54, 55, 56 condenser lens 57, 58 total reflection mirror 59 projection lens 60 first dichroic mirror 61 second dichroic mirror 62 third dichroic mirror 63 third 4 dichroic mirrors

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁵ Identification code Internal reference number FI Technical indication H04N 5/74 A 9068-5C 9/31 C 8943-5C

Claims (1)

[Claims] 1. A first dichroic mirror for reflecting light from a light source to separate a first color light, the first color light being transmitted through a third dichroic mirror and a fourth dichroic mirror. It has a first optical system that guides it to the lens and a second dichroic mirror that reflects the light that has passed through the first dichroic mirror and separates the second color light. The second optical system that reflects the light from the mirror and transmits the fourth dichroic mirror and guides it to the projection lens, and the light that has passed through the first and second dichroic mirrors is reflected by the fourth dichroic mirror. And a third optical system for guiding the third color light to the light projecting lens, and a liquid crystal image imaging device for separating the liquid crystal images of the liquid crystal members arranged in each optical system into the three primary color lights and then synthesizing the images. At
The first and second dichroic mirrors change from transmission to reflection,
The third and fourth dichroic mirrors are switched from reflection to transmission respectively, and the second dichroic mirror is set to the short wavelength side and the third dichroic mirror is set to the first dichroic mirror. A video device characterized in that the cutoff wavelength is set on the long wavelength side and the cutoff wavelength of the fourth dichroic mirror is set to the same or the long wavelength side with respect to the second dichroic mirror.