JPH09166709A - Color separation system and projection type display device using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a color separation system having dichroic mirrors capable of preventing the loss of light quantity in a process for transmitting or reflecting elliptically polarized light consisting of S polarized light and P polarized light by each dichroic mirror and causing no change in a color tone and a display device provided with a color separation system. SOLUTION: Each of dichroic mirrors constituted by combination with the color separation system is formed by a light transmitting base and high refractive index substances and low refractive index substances formed on the base so as to be alternately repeated. When incident light converted into an incident angle in air is made incident on the dichroic mirror at >=20 deg. or a complex number, the mirror has a high reflection factor of >=90% when a wavelength difference for separating incident light into transmission and reflection between the S polarized light and the P polarized light is <=5nm, 480 to 580nm, or 590 to 680nm.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a color separation system for a polarization optical system and a projection type display device using the same.

[0002]

2. Description of the Related Art FIG. 10 shows a basic structure of a projection type display device using a conventional polarization optical system. 1 is a metal halide lamp as a light source, 2 is a condenser lens,
3 is a polarization beam splitter (hereinafter referred to as PBS), 4
Is a conventional red dichroic mirror, 5 is a conventional green dichroic mirror, 6 is a reflective liquid crystal display element for red, 7 is a reflective liquid crystal display element for green, 8 is a reflective liquid crystal display element for blue, and 9 is a projection. The lens, 10 is a screen.

Therefore, the irradiation light from a powerful light source such as a metal halide lamp is condensed by a condenser lens and then enters a PBS to be separated, and unnecessary P-polarized light is passed to a dichroic mirror. Is incident. Of the S-polarized light reflected by the PBS, first, only the red S-polarized light is reflected by the conventional red dichroic mirror and enters the red reflective liquid crystal display element. The green light and the blue light transmitted through the conventional red dichroic mirror are separated by the conventional green dichroic mirror and are incident on the reflective liquid crystal display elements of the respective colors. The S-polarized light of each color is modulated by the reflective liquid crystal display element of each color, and becomes light (elliptically polarized light) in which P-polarized light in which information is written and S-polarized light is mixed, and is synthesized in the optical path opposite to the above.
It is incident on the BS. Only the P-polarized light necessary for information is transmitted by this PBS, magnified by the projection lens and projected on the screen.

[0004]

However, the PBS is
The S-polarized light separated by is transmitted or reflected by the dichroic mirror, is incident on the reflective liquid crystal display element of each color, is modulated, and becomes elliptically polarized light composed of S-polarized light and P-polarized light of each color, but the opposite of the above. In the optical path, there is a problem that the amount of light is lost and the color tone is changed in the process of transmitting or reflecting the dichroic mirror.

That is, FIG. 11 shows the 45-degree incident spectral reflectance of the conventional red dichroic mirror. It can be seen that the wavelengths for separating incident light into transmitted light and reflected light are shifted by about 25 nm for S-polarized light and P-polarized light. . When the red S polarized light is 100% modulated by the red reflective liquid crystal display element to become the red P polarized light, the proportion of the red S polarized light reflected by the red dichroic mirror and returning as the red P polarized light is the red dichroic mirror. Is the product of the S-polarized reflectance and the P-polarized reflectance of. This characteristic is shown in FIG. 580-6
It can be seen that there is a difference in output at 20 nm. In the film structure of the conventional red dichroic mirror, the incident light is converted into the incident angle in air and is incident on the dichroic mirror at 20 degrees or a complex number (for example, incident angle of 45 degrees in glass (1.52)). In the case of total reflection, there is no angle in the air (computation is a complex number)), and the wavelength that separates into transmission and reflection is about 25 nm or less for S-polarized light and P-polarized light, and 480-580 nm. It was impossible to achieve a high reflectance of 90% or more.

The same applies to the conventional green dichroic mirror. The present invention has been made in view of the above problems, elliptically polarized light consisting of S-polarized light and P-polarized light does not lose the amount of light in the process of transmitting or reflecting the dichroic mirror, and also has a dichroic mirror whose color tone does not change. An object of the present invention is to provide a color separation system and a projection display device including the same.

[0007]

SUMMARY OF THE INVENTION The first aspect of the present invention is to provide "a dichroic mirror comprising at least a light-transmitting substrate and alternating high and low refractive index substances formed on the light-transmitting substrate. A color separation system consisting of a combination of these, when incident light is converted into an incident angle in air and is incident on the dichroic mirror by 20 degrees or more or by a complex number, it is incident as S-polarized light and P-polarized light. A color separation system (claim 1) characterized by having a wavelength difference of 5 nm or less for separating light into transmission and reflection and having a high reflectance of 90% or more at 480 to 580 nm or 590 to 680 nm. To do.

Secondly, the present invention relates to a "projection type display device using a polarizing optical system having a light source, a polarization beam splitter and a color separation system, wherein the color separation system is at least a light-transmitting substrate and the light-transmitting substrate. A color separation system comprising a dichroic mirror formed by alternately repeating a high refractive index substance and a low refractive index substance formed on a substrate, or a combination thereof, wherein the incident light is converted into an incident angle in the air. When incident on the dichroic mirror at 20 degrees or more or in complex numbers,
The difference between the wavelengths for separating incident light into transmitted light and reflected light between S-polarized light and P-polarized light is 5 nm or less, and 480 to 580 nm or 590.
A projection type display device (claim 2) having a high reflectance of 90% or more at 680 nm.

[0009]

1 is a block diagram of the first embodiment of the present invention. In FIG. 1, 11 is a red dichroic mirror in the present invention and 12 is a green dichroic mirror in the present invention, which are installed at an angle of 45 degrees with respect to the optical axis. . FIG. 2 shows an example of the film structure and optical film thickness of the red dichroic mirror in the present invention. Alternating layers of SiO ₂ of the TiO ₂ with a refractive index of 1.47 of the refractive index 2.3 over the flat glass having a refractive index of 1.52 is formed, the total number of layers is 66 layers. The optical film thickness is shown as a coefficient of wavelength λ = 580 nm. Further, an antireflection film for transmitting green light and blue light is provided on the back side of the substrate. FIG. 3 shows an example of the film structure and optical film thickness of the green dichroic mirror in the present invention. Refractive index 2.on top of flat glass with refractive index 1.52.
Alternating layers of Ta ₂ O _{5 of} 1 and SiO ₂ of 1.47 are formed, the total number of layers is 66. Wavelength λ as optical film thickness
= Shown as a coefficient of 480 nm. In addition, an antireflection film for blue light that is transmitted is provided on the back side of the substrate.

The film formation method is a vacuum deposition method of 2 × 10.^-FourTorr
The film is formed in an atmosphere and the deposition rate is 0.2 to 0.5 mm / s.
Was. Film composition is only alternating layers of low and high refractive index materials
However, other combinations are possible. Low refractive index material
As SiO_Two, MgF_Two, Ti as a high refractive index material
O_Two, Ta_TwoO _Five, ZrO_Two, HfO_TwoIs mentioned.

45 of the dichroic mirror in the present invention
The degree incident spectral reflectance is shown in FIGS. The wavelengths that separate incident light into transmitted light and reflected light are S-polarized light and P-polarized light, and the difference is 5 nm or less. That is, in the red dichroic mirror according to the present invention, the wavelength difference separating the transmission and the reflection between the red S polarized light and the red P polarized light is substantially equal to or less than 5 nm, and shows a high reflectance of 90% or more at 590 to 680 nm. . Further, in the dichroic mirror for green according to the present invention, green S-polarized light and green P-polarized light are used.
The difference between the wavelengths for separating the transmission and the reflection for polarized light is substantially equal to 5 nm or less, and a high reflectance of 90% or more is shown at 480 to 580 nm. For example, if the red S polarized light is 100% modulated by the red reflective liquid crystal display element to become P polarized light, the red S polarized light is reflected by the red dichroic mirror to produce red P polarized light.
The ratio of returning as polarized light is the product of the S-polarized reflectance and the P-polarized reflectance of the red dichroic mirror. This characteristic is shown in FIG.

The wavelength range of red is 590 to 680 nm
It turns out that a very high output is obtained. Therefore, the S-polarized light is modulated by the reflective liquid crystal display element and becomes the light in which the P-polarized light and the S-polarized light in which the information is written is mixed (elliptical polarized light), but the light in which the P-polarized light and the S-polarized light are mixed is There is no loss of light amount when transmitting and reflecting with the dichroic mirror in.

45 of the conventional red dichroic mirror
It can be seen that even when compared with the degree incident spectral reflectance, the performance is clearly improved and the output is increased. The present inventor has found that the use of the color separation system according to the present invention improves the performance particularly remarkably. That is, when the incident light is incident on the dichroic mirror at 45 degrees in terms of the incident angle in the air, the wavelength difference for separating the incident light into the transmitted light and the reflected light by the S-polarized light is 5 nm or less. , And 480-580
Only when there is a high reflectance of 90% or more in nm or 590 to 680 nm is there a noticeable improvement in performance.

FIG. 7 is a block diagram of a color separation system according to the second aspect of the present invention. This can be used in the projection display device shown in FIG. In the Philips type, an antireflection film is formed on the slope 11a of the prism a, the surface 12a and the slope 11b of the prism b, the surface 12b and the surface 12c of the prism c, and the surface 13a of the prism a is a dichroic mirror for red according to the present invention. And the dichroic mirror for green of the present invention is formed on the surface 13b of the prism b. Further, the red dichroic mirror of the present invention formed on the surface 13a and the antireflection film formed on the slope 11b are arranged with a constant distance (air gap) therebetween, and the green of the present invention formed on the surface 13b. The dichroic mirror and the slope 11c are bonded with an adhesive. BK7 (1.52) is used as the glass material for the prisms a, b, and c. As the adhesive (1.52), a commercially available adhesive such as epoxy type is used.

The S-polarized light separated by the PBS is incident on the surface 11a, and the red S-polarized light is separated by the red dichroic mirror of the present invention formed on the surface 13a.
At the surface 12a, the green S-polarized light is separated by the dichroic mirror for green in the present invention formed on the surface 13b, is totally reflected at the surface 11b, and is emitted from the surface 12b. Emit from 12c.

After that, the S-polarized light of each color is modulated by the reflective liquid crystal display element of each color to become a light (elliptical polarized light) in which P-polarized light and S-polarized light in which information is written is mixed, and the red elliptically polarized light is the surface 12a. Is synthesized by the red dichroic mirror in the present invention formed in, green elliptically polarized light,
The elliptically polarized light, which is synthesized by the green dichroic mirror of the present invention formed on the surface 13b, is emitted from 11a.

S-polarized light is incident on the red dichroic mirror of the present invention formed on the surface 13a of the prism a in FIG. 7 at an incident angle of 27.7 degrees in glass, but Snell's law (1.52 × SIN (27.7deg) = Converting from 1.0 × SIN (θ) to the angle of incidence in air, the incident angle is 45 degrees.
Therefore, the red dichroic mirror (FIG. 2) shown in the first aspect can be used.

The S-polarized light obtained by separating the red S-polarized light is incident on the dichroic mirror for green according to the present invention formed on the surface 13b of the prism b in FIG. 7 at an incident angle of 14 degrees in the glass. Snell's law (1.52 x SIN (14deg) = 1.
Converted to an incident angle in air from 0 x SIN (θ) of 21.5
It will be incident at a degree. FIG. 8 shows the film structure and optical film thickness of the green dichroic mirror in the present invention. Alternating layers of SiO ₂ of the TiO ₂ with a refractive index of 1.47 of the refractive index 2.3 is formed on the prism of refractive index of 1.52, the total number of layers 66
It is a layer. The optical film thickness is shown as a coefficient of wavelength λ = 480 nm.

FIG. 9 shows the 21.5 degree incident spectral reflectance of the green dichroic mirror in the present invention. In the present invention, the dichroic mirror for green is green.
The difference between the wavelengths for separating transmission and reflection between S-polarized light and green P-polarized light is almost equal to 5 nm or less, and 90 at 480 to 580 nm.
It shows a high reflectance of at least%. When the elliptically polarized light of each color is transmitted or reflected by the dichroic mirror in the present invention, there is no loss of light amount and no change in color tone.

The present inventor has found that the use of the color separation system according to the present invention results in a remarkable improvement in performance. That is, when the incident light is converted into an incident angle in air and is incident on the dichroic mirror at 21.5 degrees or 45 degrees, the difference between the wavelengths for separating the incident light into transmitted light and reflected light with S-polarized light and P-polarized light is 5 nm or less and 480 to 580 nm or 5
When the high reflectance of 90% or more at 90 to 680 nm,
For the first time there is a noticeable improvement in performance.

After separating the light from the light source with PBS,
The dichroic mirror in the present invention can also be used in the case of a polarization optical system in which polarized light is discarded and P-polarized light is incident on the dichroic mirror, and the same effect as described above can be obtained.

[0022]

By using the color separation system in which the dichroic mirror of the present invention is formed in a projection type display device, a good color tone can be obtained without loss of light quantity. Furthermore, the influence of stray light can be reduced by reducing the reflected light.

[Brief description of the drawings]

FIG. 1 is a configuration diagram of a projection display device including a dichroic mirror according to the present invention.

FIG. 2 shows a film structure and an optical film thickness of a red dichroic mirror in the present invention.

FIG. 3 shows a film configuration and an optical film thickness of a green dichroic mirror in the present invention.

FIG. 4 is a 45 ° incident spectral reflectance characteristic diagram of S-polarized light and P-polarized light of the red dichroic mirror in the present invention.

[Fig. 5] Red S-polarized light is 100 for a red reflective liquid crystal display device.
In the case of being% -modulated into red P polarized light, the ratio of red S polarized light reflected by the red dichroic mirror in the present invention and returned as red P polarized light is shown.

FIG. 6 is a 45 ° incident spectral reflectance characteristic diagram of S polarization and P polarization of the dichroic mirror for green in the present invention.

FIG. 7 is a cross-sectional view when a dichroic mirror of the present invention is formed in a Philips type color separation system.

FIG. 8 shows a film structure and an optical film thickness of a green dichroic mirror in the present invention.

FIG. 9 is a 21.5 degree incident spectral reflectance characteristic diagram of S-polarized light and P-polarized light of the dichroic mirror for green in the present invention.

FIG. 10 is a configuration diagram of a projection type display device including a conventional dichroic mirror.

FIG. 11 is a 45-degree incident spectral reflectance characteristic diagram of S polarization and P polarization of a conventional red dichroic mirror.

[Fig. 12] Red S-polarized light is a red reflective liquid crystal display device.
In the case where the light is modulated by 00% to become red P polarized light, the ratio of red S polarized light reflected by a conventional red dichroic mirror and returned as red P polarized light is shown.

[Explanation of symbols]

1 ... Light source 2 ... Condenser lens 3 ... Polarization beam splitter 4 ... Conventional red dichroic mirror 5 ... Conventional green dichroic mirror 6 ... Red reflective liquid crystal display element 7 ... green reflective liquid crystal display element 8 ... blue reflective liquid crystal display element 9 ... projection lens 10 ... screen 11 ... red dichroic mirror 12 in the present invention 12 ... in the present invention Dichroic mirror for green

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification code Internal reference number FI Technical display location G09F 9/00 360 G09F 9/00 360Z H04N 9/31 H04N 9/31 C

Claims (2)

[Claims] 1. A color separation system comprising at least a translucent substrate and a dichroic mirror formed by alternately repeating a high refractive index substance and a low refractive index substance formed on the translucent substrate, or a combination thereof. When incident light is converted into an incident angle in air and incident on the dichroic mirror at 20 degrees or more or in a complex number, the difference in wavelength between S-polarized light and P-polarized light that separates the incident light into transmission and reflection. Less than 5nm and 48
A color separation system having a high reflectance of 90% or more at 0 to 580 nm or 590 to 680 nm. 2. A projection type display device using a light source, a polarization beam splitter, and a polarization optical system having a color separation system, wherein the color separation system is at least a translucent substrate and a high refraction index formed on the translucent substrate. A color separation system consisting of a dichroic mirror consisting of alternating repetition of a refractive index substance and a low refractive index substance or a combination thereof, wherein the incident light is 20 degrees with respect to the dichroic mirror in terms of the angle of incidence in air. When the above or a complex number is incident, the difference between the wavelengths for separating the incident light into transmitted light and reflected light is 5 nm or less between S-polarized light and P-polarized light, and 4
A projection type display device having a high reflectance of 90% or more at 80 to 580 nm or 590 to 680 nm.