JPH0561130A - Screen projection type picture display device - Google Patents

Abstract

PURPOSE:To obtain an inexpensive polarizing prism which has little internal skewness and is excellent in polarizing characteristic and to obtain excellent image quality. CONSTITUTION:This device is constituted of an image forming means for forming an image which selectively reflects an incident polarizing beam, a polarizing prism 101 which reflects the polarizing beam from a light source toward the image forming means and transmits the reflected beam from the image forming means, and a screen where a projected picture is formed by receiving the beam transmitted through the prism 101; and the prism 101 is constituted of a housing 101h formed of a transparent material, a transparent plane parallel plate 101g which is disposed to form a specified incident angle in the housing 101h and forms an incident surface, and transparent liquid 101l having specified refractive index with which the housing 101h is filled. Thus, the medium of the prism 101 is made uniform and aberration caused by the skewness and stria is prevented, then the polarizing prism 101 is obtained, whose molding is simplified, which is made inexpensive, and which has little internal skewness because of the stability of the temperature distribution of liquid which is the medium.

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD The present invention relates to a screen projection type image display device, and more particularly to a screen projection type image display device for projecting an image on a screen via a polarizing prism.

[0002]

2. Description of the Related Art FIG. 5 is a block diagram showing a color liquid crystal display device using three photoconductive liquid crystal light valves and one polarizing prism as an example of a screen projection type image display device. is there. In the figure, such a liquid crystal display device shows a red CRT (cathode ray tube) 1 for generating a red image.
A red photoconductive liquid crystal light valve (hereinafter referred to as a light valve) 2R for writing red light as a writing light is coupled to each other with an optical fiber 3R interposed therebetween, and a first color is provided.
You are configuring a channel. Similarly, the CRT 1G for green, the light valve 2G for green and the optical fiber 3G constitute the second color channel, and the CRT for blue is used.
1B, blue light valve 2B and optical fiber-3B
Constitutes the third color channel.

On the other hand, the light source 4 emits incident light to each light valve in the first to third color channels, and the incident light is first guided to the polarizing prism 5. The polarization prism 5 bends only the S-polarized (Senkrecht polarized light) component of the incident light at a right angle to the traveling direction and guides it to the dichroic mirror 9. The dichroic mirror 9 has a spectral characteristic of reflecting red light and transmitting blue light and green light. The blue light and green light transmitted through the dichroic mirror 9 reach the dichroic mirror 10 and are reflected by the red light. Is reflected by the total reflection mirror 11 and guided to the red light valve 2R. The dichroic mirror 10 has a spectral characteristic of reflecting blue light and transmitting green light, and guides each primary color light to the blue light valve 2B and the green light valve 2G.

Each of the light valves converts the incident S-polarized readout light into P-polarized light (Parallel) corresponding to the CRT output image.
Polarized light) The light is modulated by including the reflected component. This reflected reading light, that is, each color
The output projection light of the channel is the dichroic mirror 9 again.
Or, it enters the polarizing prism 5 via 10 and is combined into one image. The polarization prism 5 transmits only the P-polarized light corresponding to the image in the combined projection light, and projects the image on the screen 8 via the projection lens 7.

The polarizing prism used here is made of glass and is a spatial modulation element 1-2.
According to the size of the light valve of about inch, the size of the polarizing prism must be relatively large, ³⁰ to 50 mm ³ . Further, in order to prevent the occurrence of aberration due to distortion or striae in this polarizing prism, it is necessary to use glass of a uniform material, and the glass material itself is expensive. Further, in such a prism, the temperature must be raised to about 400 degrees Celsius during vapor deposition of the polarizing film, and since the shape of the polarizing prism as described above is large, it takes time to heat and cool and it becomes expensive. ..

On the other hand, since the temperature rises due to the irradiation of light from the light source, internal distortion will occur due to fluctuations in the temperature distribution. Since such internal distortion has optical directionality, it causes birefringence, which significantly affects the polarization characteristics. In the end, it has been found that such a polarizing prism made of glass is not so preferable in a screen projection type image display device in which a compact size and a low cost are required and a relatively strong light is incident and used.

[0007]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned points and provides a screen projection type image display device having a good image quality by obtaining a polarizing prism having a good polarization characteristic which is inexpensive and has a small internal distortion. The purpose is to provide.

[0008]

A screen projection type image display device according to the present invention comprises an image forming means for forming an image which selectively reflects an incident polarized beam, and a polarized light beam from a light source directed to the image forming means. -A polarizing prism that reflects a beam and transmits a reflected beam from the image forming means, and a screen that receives the beam transmitted through the polarizing prism to form a projection screen
A screen projection type image display device comprising
The polarizing prism includes a housing formed of a transparent material, a transparent parallel plate that is disposed to form a predetermined incident angle in the housing and forms an incident surface,
It is characterized by being composed of a transparent liquid having a predetermined refractive index and filling the inside of this housing.

[0009]

The screen projection type image display apparatus according to the present invention has a housing made of a transparent material, which is filled with a transparent liquid as a medium of a polarizing prism having a predetermined refractive index. The incident light from the light source and the reflected light from the image forming means are incident on a transparent parallel plate which is arranged to form a predetermined incident angle inside and forms an incident surface having a polarization characteristic. Polarization is separated by.

[0010]

1 is a diagram showing the construction of a polarizing prism in a screen projection type image display apparatus according to an embodiment of the present invention. In the figure, the polarizing prism 101 is
It has a rectangular parallelepiped frame or housing 101h made of a transparent material such as glass.
The transparent liquid 101l is filled in 1h. Then, in consideration of the refractive index of the liquid, a transparent parallel flat plate 101g such as a glass plate on which a multilayer film having polarization characteristics is vapor-deposited,
The housing 101h is erected so as to stand on a diagonal line on the bottom surface of the housing 101h. In the figure, the upper surface member of the housing 101h is cut away to clarify the position of the parallel plate 101g.

The liquid filled in the housing must be transparent, and in addition, low toxicity, low volatility (vapor pressure), high flash point, and cost performance are taken into consideration. It For example, ethylene glycol C ² H ⁶ O ² (refractive index n = 1.43) and glycerin C ³
H ⁵ O ³ (n = 1.474) is used as a matching liquid for CRT projection, but is also suitable as the liquid here. Other liquids include benzyl alcohol C ⁷ H ⁸ O (n = 1.54).

FIG. 2 schematically shows this polarizing prism and shows how the incident light is polarized and separated with an incident angle of 45 °. In the figure, the light from the light source is incident from the right side of the figure, and the parallel plate 1 is incident on the polarizing prism 101.
Only S-polarized light is reflected at a right angle on the incident surface formed by the multilayer film of 01 g. At this time, the incident angle θ is kept at 45 °, and the reflected S-polarized light is guided to the spatial modulation element 102. The S-polarized light that has reached the spatial modulation element 102 is reflected in the same direction as the incident optical path, including P-polarized light that corresponds to a so-called modulation signal. Only the P-polarized light is transmitted through the reflected light that has returned to the incident surface of the polarization prism 101 again.

At this time, since the housing 101h is filled with the transparent liquid made of the above-mentioned uniform material, it is possible to suppress the occurrence of aberrations due to distortion and striae. Further, the molding process is easier than that of the polarizing prism formed of glass, which is advantageous in terms of cost. Further, since the medium is a liquid, internal strain caused in the crystal does not occur even if the temperature rises due to incident light.

FIG. 3 shows the polarization characteristics when the refractive index n of the liquid to be filled is low at an incident angle of 45 °. In the figure, the horizontal axis λ [nm] is the wavelength of incident light, and the vertical axis R [%] is the reflectance. The curve Rs shows the reflectance characteristic of S-polarized light, and the curve RP shows the reflectance characteristic of P-polarized light. As can be seen from this figure, only S-polarized light cannot be reflected over the entire wavelength range, and the wavelengths of 450 to 620
A maximum of 40% of P-polarized light in the incident light of nm will be reflected. Therefore, the polarization prism in this case causes the P-polarized component to enter the light valve which is the spatial modulation element, which is not preferable.

As described above, when the refractive index n of the liquid is low, proper polarization characteristics cannot be obtained in the structure having an incident angle of 45 °. In order to eliminate this, the incident angle θ is increased and FIG.
As described above, if the polarization prism 101 'is formed with θ = 50 °, almost ideal polarization characteristics can be obtained. However, there are drawbacks such that when the incident angle is deviated from θ = 45 °, the shape of the prism becomes large, and since incident light is swung by a desired angle, the structure becomes complicated with an optical system corresponding to that.

In view of this, if the above-mentioned benzyl alcohol with n> 1.48 is adopted as a transparent liquid in order to achieve proper polarization characteristics, an incident angle of 45 ° can be obtained. It is also possible to use a mixed solution of benzyl alcohol and another solution (ethylene glycol, glycerin, etc.). In the above embodiments, only the color liquid crystal display device using the light valve has been described, but the present invention is not limited to this, and the liquid crystal panel element and the Japanese Patent Application No.
It is also applied to an image display device using a photoconductive liquid crystal light valve utilizing electroluminescence as described in No. 284970.

[0017]

As described above in detail, the screen of the present invention
According to the projection-type image display device, a predetermined incident angle is formed in a housing formed of a transparent material through a transparent liquid as a medium of a polarizing prism having a predetermined refractive index. The incident light from the light source and the reflected light from the image forming means are made incident on a transparent parallel plate which is arranged in this way and forms an incident surface having a polarization characteristic, and polarization is separated by the polarization characteristic of this incident surface. Therefore, the medium of the polarization prism can be made uniform, and the occurrence of aberration due to distortion or striae can be prevented. In addition, the molding of the polarizing prism is simple and inexpensive, and the stability of the temperature distribution of the liquid that is the medium makes it possible to configure a polarizing prism having good polarization characteristics with little internal distortion. As a result, a screen projection type image display device with good image quality can be obtained.

[Brief description of drawings]

FIG. 1 is a perspective view showing a configuration of a polarizing prism in a screen projection type image display device according to an embodiment of the present invention.

FIG. 2 is a diagram schematically showing the polarization prism in FIG. 1 in which an incident angle is 45 ° and incident light is polarized and separated.

FIG. 3 is a polarization characteristic diagram when the refractive index n of the liquid to be filled is low at an incident angle of 45 ° of the polarizing prism in FIG.

FIG. 4 is a diagram schematically showing the polarization prism in FIG. 1 with an incident angle of 50 ° and showing how incident light is polarized and separated.

FIG. 5 is a block diagram showing an example of a screen projection type display device.

[Explanation of symbols for main parts]

1R, 1G, 1B ... CRT for red, green and blue 2R, 2G, 2B ... Photoconductive liquid crystal light valve for red, green and blue 4 ... Light source 5 ... Polarizing prism 7 ... Projection lens 8 ... Screen 9 …… Red light reflecting dichroic mirror 10 …… Blue light reflecting dichroic mirror 11 …… Total reflection mirror 101 …… Polarizing prism 101h …… Housing 101g …… Parallel plate 101l …… Liquid 102… ... Spatial modulator

Claims (2)

[Claims] 1. An image forming means for forming an image that selectively reflects an incident polarized beam, and a polarized beam from a light source toward the image forming means and a reflection from the image forming means. A screen projection type image display device comprising a polarizing prism which transmits a beam and a screen which receives a beam transmitted through the polarizing prism to form a projection screen, wherein the polarizing prism is A housing made of a transparent material, a transparent parallel flat plate arranged to form a predetermined incident angle in the housing and forming an incident surface, and a transparent parallel plate having a predetermined refractive index and filling the housing. A screen projection type image display device characterized by comprising a liquid. 2. The screen projection type image display device according to claim 1, wherein the predetermined refractive index is 1.48 or more.