JP5074704B2 - Image projection device - Google Patents

Description

  The present invention relates to a color separation / synthesis system used in an image projection apparatus such as a liquid crystal projector, and more particularly, to a color separation / synthesis system that improves the color tone and color unevenness of an image during black display and improves the contrast characteristics of the image.

At present, liquid crystal projectors are increasing in brightness and contrast. In particular, in recent years, many products with a mode having a high contrast mode have been put on the market for home theater applications. Under such circumstances, a type using an aperture is often used in order to improve the contrast characteristics of an image in cinema viewing or the like. Japanese Patent Application Laid-Open No. 2003-228867 discloses a conventional example using a diaphragm that increases the contrast within the effective image range. In this conventional example, a light source, a parabolic reflector that reflects light from the light source toward the light valve as parallel light, a parallel light beam from the reflector is divided to create a secondary light source image, and the light is superimposed on the light valve for illumination. Optical means is provided, and means for limiting the luminous flux is provided in the vicinity of the secondary light source image. As a result, the angle range of light incident on the optical element sensitive to the incident angle characteristic can be narrowed, so that the contrast characteristic can be improved.
JP 05-303085 A

  However, in the above conventional example, the contrast of the image can be improved, but there is a problem that the light amount is greatly reduced because the light flux is limited in the vicinity of the light source image. In addition, since the luminous flux is limited by the illumination system before color separation and synthesis, the luminous flux cannot be limited for each wavelength, and this is an effective means for black color and color unevenness during black display. Absent.

  Accordingly, an exemplary object of the present invention is to provide an image projection apparatus that is effective for black color and color unevenness, suppresses a decrease in light amount, and realizes low cost.

An image projection apparatus according to one aspect of the present invention includes a light source, an illumination optical system, a color separation / synthesis system, a reflective light valve as an image forming element, and a projection optical system. The illumination optical system has a polarization conversion element and converts non-polarized light from the light source into predetermined polarized light. The color separation / combination system is means for separating the white light from the illumination optical system into RGB and guiding it to a light valve to synthesize each image light. The color separation / synthesis system reflects the RB component of the light emitted from the illumination optical system and transmits the G component to separate the colors, and either one of R and B of the light of the RB component The wavelength-selective phase plate for rotating the R light into S-polarized light and the B light as P-polarized light, and rotating the R light into the R-polarized light A prism-shaped RB polarization beam splitter that reflects the light beam to the light valve side and transmits the B light to the B light valve side, and image light modulated by the light valve , the RB polarization beam A first polarizing plate for analyzing the B light after being emitted from the splitter, and a G-shaped polarizing beam splitter for the G-shaped prism that guides the G light transmitted through the dichroic mirror to the G light valve side When , An image light which has received the image modulated by the light valve G, and a second polarizer for analyzing the light after emitted from the polarization beam splitter for the G is reflected by the polarization beam splitter for G And a composite prism having a function of combining RGB image light and guiding it to the projection optical system and analyzing R light. When the angle of light incident on the G light valve is θ and the refractive index of the polarizing beam splitter for G is n, the light incident angle β on the film surface of the G polarizing beam splitter is β = 45 ° + sin ⁻¹ ( 1 / n × sin θ), the light incident angle α of the dichroic mirror is expressed as α = 45 ° −θ, the plane of polarization transmitted through the second polarizing plate is S-polarized light, and the transmittance in the dichroic mirror W <Wa where W is the wavelength on the long wavelength side and Ts (β) is the S-polarized light transmittance at the light incident angle β on the film surface of the polarizing beam splitter for G. In the wavelength region W, Ts (β) ≦ 5% is satisfied.

An image projection apparatus according to another aspect of the present invention is an image projection apparatus including a light source, an illumination optical system, a color separation / synthesis system, a reflective light valve as an image forming element, and a projection optical system, The illumination optical system has a polarization conversion element, converts non-polarized light from the light source into predetermined polarization, and the color separation / synthesis system separates white light from the illumination optical system into RGB. The color separation / synthesizing system reflects the RB component of the light emitted from the illumination optical system and transmits the G component for color separation. Rotating the polarization plane of one of R and B of the RB component light by 90 ° and changing the polarization plane of the other light without changing the polarization plane, A wavelength-selective phase plate with P light as P-polarized light, Is a prism-shaped RB polarization beam splitter that reflects the light of R to the R light valve side and transmits the B light to the B light valve side, and image light that has undergone image modulation by the light valve, A first polarizing plate for analyzing the B light after exiting from the RB polarizing beam splitter, and a prism shape that guides the G light transmitted through the dichroic mirror to the G light valve side Image light that has undergone image modulation by the G polarization beam splitter and the G light valve, and that has passed through the G polarization beam splitter and is emitted from the G polarization beam splitter. And a second prism that combines the RGB image light and guides it to the projection optical system, and has a function of analyzing the R light. Where the angle of light incident on the G light valve is θ and the refractive index of the G polarizing beam splitter is n, the light incident angle β on the film surface of the G polarizing beam splitter is β = 45 ° + sin ⁻¹ (1 / n × sin θ), the light incident angle α of the dichroic mirror is expressed as α = 45 ° −θ, and the plane of polarization transmitted through the second polarizing plate is P-polarized light. Yes, when the wavelength on the long wavelength side of the wavelength at which the transmittance is 5% in the dichroic mirror is Wa, the P-polarized reflectance at the light incident angle β to the film surface of the G polarization beam splitter Is Rp (β), Rp (β) ≦ 5% is satisfied in the wavelength region W where W <Wa .

  According to the present invention, when displaying a black image, it is possible to improve the color and unevenness of black and increase the contrast of the image. Furthermore, since the polarizing plate can be eliminated, the cost can be reduced, and at the same time, the deterioration at the time of durability due to the polarizing plate can be eliminated, which is very effective.

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

FIG. 1 shows the configuration of a liquid crystal projector (image projection apparatus) that is Embodiment 1 of the present invention. The projector according to the present embodiment includes a light source 1, an illumination optical system 2, a color separation / synthesis optical system 3, reflection type liquid crystal panels 6, 7 and 8 (light valves) as image forming elements, a projection lens 4, and the like. Consists of. The illumination optical system 2 is an optical system that guides light from the light source 1 to the liquid crystal panels 6, 7, and 8.

The liquid crystal panels 6, 7, and 8 are reflective RGB liquid crystal panels. The color separation / combination system 3 separates white light from the illumination system 2 into RGB and guides it to each RGB panel, and image light from each panel. Are combined and guided to the projection optical system 4. The projection optical system 4 is an optical system that projects the display image of each panel toward the screen 5. Light emitted from the light source 1 is a non-polarized light, by a non-illustrated polarization conversion element included in the illumination system 2, the (P-polarized light in this embodiment) predetermined polarization.

  The color separation / combination system 3 includes three prism-shaped polarization beam splitters (hereinafter referred to as PBS). In the following, 10 is G-PBS, 11 is RB-PBS, and 12 is synthetic PBS.

The color separation / combination system 3 reflects red (R component) and blue (B component) light and transmits green (G component) light by the dichroic mirror 9 out of white light from the illumination system 2. Thus, the RB optical path and the G optical path are separated. In addition, a wavelength selective phase plate 15 is provided in the RB optical path in order to separate RB component light reflected by the dichroic mirror into Red and Blue. The wavelength-selective phase plate has the characteristics shown in FIG. 2, whereby one ( Red in this embodiment ) light changes its polarization state from P-polarized light to S-polarized light (the polarization plane is rotated by 90 °) . The other ( Blue in this embodiment ) light remains P-polarized light.

The Red light after passing through the wavelength-selective phase plate is S-polarized light, reflected by RB-PBS11 (polarization beam splitter for RB) , and guided to the Red panel 8. The light guided to the Red panel 8 (R light valve side) is image-modulated by the panel to become P-polarized light, passes through the RB-PBS 11, and reaches the combined PBS 12. On the other hand, Blue light is incident on the RB-PBS 11 as P-polarized light, passes through the RB-PBS 11, and is guided to the Blue panel 7 (B light valve side) . The light incident on the panel 7 undergoes image modulation, becomes S-polarized light, is reflected by the RB-PBS 11, and reaches the combined PBS 12.

  The combined PBS 12 has the characteristics shown in FIG. 3 and has a function of a polarizing beam splitter for Red light, and is a prism-shaped optical element having a dichroic film function for Blue and Green. is there. Between this synthetic PBS and the RB-PBS, a polarizing plate 16 for analyzing the blue light is disposed. After the blue light is analyzed by this polarizing plate, it enters the synthetic PBS 12 and is transmitted therethrough. Then, the projection system 4 is reached. Further, the red light is detected and transmitted by the detection characteristics shown in FIG. 3 of the synthetic PBS 12 and reaches the projection system 4.

On the other hand, the Green light transmitted through the dichroic mirror 9 is P-polarized light, passes through the G-PBS 10 (G polarization beam splitter) , and enters the Green panel 6. The light incident on the green panel 6 undergoes image modulation by the panel to become S-polarized light, is reflected by the G-PBS 10, and enters the combined PBS 12. A polarizing plate for detecting the green light is arranged between the synthetic PBS 12 and the G-PBS 10, and after detecting the green light, it is reflected by the synthetic PBS 12 and guided to the projection system 4. .

  FIG. 4 shows the characteristics of the dichroic mirror 9 in this embodiment. The solid line indicates the transmittance at an incident angle of 45 °, the dotted line indicates the transmittance when the incident angle is greater than 45 °, and the one-dot broken line indicates the incident angle. Is the transmittance when is less than 45 °. FIG. 5 shows the S-polarized light transmission characteristics of G-PBS.

Here, the solid line indicates the transmittance at a light incident angle of 45 °, the dotted line indicates the transmittance when the light incident angle is smaller than 45 °, and the one-dot broken line indicates the transmittance when the light incident angle is larger than 45 °. . As shown in FIG. 6, when the light incident angle α of the dichroic mirror 9 is smaller than 45 ° , the light incident on the film surface of the G-PBS 10 is larger than 45 °.

  In this embodiment, most of the light incident on the color separation / combination system 3 is P-polarized light, but actually, it is slightly mixed with S-polarized light component. When this slight S-polarized component is incident on the G-PBS 10 in the Green optical path, light on the long wavelength side is transmitted through the G-PBS 10 due to the S-polarized light transmission characteristics shown in FIG. Since this transmitted light enters the green panel 6 and is not modulated during black display, it exits as S-polarized light, enters the G-PBS 10, is reflected, guided to the combining prism 12, and passes through the projection system to the screen 5. It reaches. The light leakage of the long wavelength component generated from the Green optical path deteriorates the color tone and color unevenness of the image during black display, and causes a decrease in contrast.

Here, in FIG. 6, when the panel incident angle is θ 2 and the refractive index of G-PBS is n , the light incident angle β on the film surface of G-PBS is expressed as follows.

β = 45 ° + sin ⁻¹ (1 / n × sin θ)

When the S-polarized light transmittance of G-PBS at the incident angle β is Ts (β),
Ts (β) ≦ 5%
By satisfying the above, it is possible to reduce leakage light during black display without providing a polarizing plate on the incident side of the G-PBS. This makes it possible to reduce costs and avoid deterioration of the polarizing plate during durability.

  For reference, FIG. 10 shows the S-polarized light transmittance characteristics of a conventional G-PBS.

  FIG. 7 shows the configuration of a liquid crystal projector that is Embodiment 2 of the present invention. The basic configuration is the same as in the first embodiment, but the polarized light after exiting the illumination system is S-polarized light. The separation of RB and G by the dichroic mirror 9 is the same as in the first embodiment, but the red light remains S-polarized by the wavelength-selective phase plate, but the blue light is changed from S-polarized light to P-polarized light. The polarization state is changed. The subsequent optical action is the same as that of the first embodiment. In the G optical path, the Green light transmitted through the dichroic mirror 9 is incident on the G-PBS 10, reflected by the film surface of the G-PBS 10 due to S polarization, and incident on the Green panel 6. The light incident on the panel 6 is image-modulated to become P-polarized light, passes through the G-PBS 10, and is emitted to the synthetic PBS 12 side. The image light emitted from the G-PBS 10 is analyzed by the polarizing plate 17 between the G-PBS 10 and the synthetic PBS 12, enters the synthetic PBS 12, is reflected by the film surface of the synthetic PBS 12, and is guided to the projection system 4. 5 is reached. Here, the synthetic PBS 12 has the same characteristics as in the first embodiment.

  Most of the light emitted from the illumination system 2 is S-polarized light, but actually, a P-polarized component is slightly mixed. This P-polarized light is almost transmitted through the film of the G-PBS 10, but actually has a component that reflects on the short wavelength side as shown in FIG. As shown in FIG. 9, when the panel incident angle is θ, the G-PBS incident angle β is expressed as follows.

β = 45 ° + sin ⁻¹ (1 / n × sin θ)

When the P-polarized reflectance of G-PBS at the incident angle β is Rp (β),
Rp (β) ≦ 5%
By satisfying the above, it is possible to reduce leakage light during black display without providing a polarizing plate on the incident side of the G-PBS. This makes it possible to reduce costs and avoid deterioration of the polarizing plate during durability.

The schematic block diagram of 1st Example of this invention. The characteristic view of the wavelength-selective phase plate in 1st Example of this invention. The characteristic view of synthetic | combination PBS in 1st Example of this invention. The angle characteristic figure of the dichroic mirror in 1st Example of this invention. The S polarization | polarized-light transmittance characteristic figure of G-PBS in 1st Example of this invention. 1 is a schematic diagram from a dichroic mirror to a green panel in a first embodiment of the present invention. The schematic block diagram of 2nd Example of this invention. The P polarization | polarized-light reflectance characteristic of G-PBS in 2nd Example of this invention. Schematic from the dichroic mirror to the Green panel in 2nd Example of this invention. The S polarization | polarized-light transmittance characteristic figure of conventional G-PBS.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Light source 2 Illumination system 3 Color separation synthesis system 4 Projection optical system 5 Screen 6 Green liquid crystal panel 7 Blue liquid crystal panel 8 Red liquid crystal panel 9 Dichroic mirror 10 G-PBS
11 RB-PBS
12 Synthetic PBS
15 Wavelength selective phase plate 16 B polarizing plate 17 G polarizing plate

Claims (2)

An image projection apparatus comprising a light source, an illumination optical system, a color separation / synthesis system, a reflective light valve as an image forming element, and a projection optical system,
The illumination optical system includes a polarization conversion element converts unpolarized light from the light source into a predetermined polarization,
The color separation / synthesis system is a means for separating the white light from the illumination optical system into RGB, guiding it to the light valve, and synthesizing each image light,
The color separation / synthesis system is:
Reflects the RB components of the light emitted from the illumination optical system, by transmitting the G component, and the dichroic mirror for color separation,
By rotating the plane of polarization of either R or B of the RB component light by 90 ° and changing the plane of polarization of the other light, the R light is S-polarized and the B light is P-polarized. A wavelength-selective phase plate and
A prism-shaped RB polarizing beam splitter that reflects R light to the R light valve side and transmits B light to the B light valve side;
Wherein an image light received images modulated by the light valve, a first polarizer for analyzing the light of B after emitted from the polarization beam splitter for the RB,
By transmitting light of G that has passed through the dichroic mirror, a polarization beam splitter for G prism-shaped guiding the light valve side of the G,
Wherein an image light received images modulated by the light valve G, a second polarizer for analyzing the light after emitted from the polarization beam splitter for the G is reflected by the polarization beam splitter for the G When,
The RGB image light is combined and guided to the projection optical system, and composed of a combining prism having an action of analyzing R light,
When the light ray incident on the G light valve is θ and the refractive index of the G polarizing beam splitter is n, the light incident angle β on the film surface of the G polarizing beam splitter is:
β = 45 ° + sin ⁻¹ (1 / n × sin θ)
And the light incident angle α of the dichroic mirror is
α = 45 ° -θ
And
The plane of polarization transmitted through the second polarizing plate is S-polarized light,
Of the wavelength at which the transmittance is 5% at the dichroic mirror, the wavelength of the long wavelength side Wa, the S-polarized light transmittance at light incident angle beta to the membrane surface of the polarizing beam splitter for the G Ts (beta) When
In the wavelength range W where W <Wa,
Ts (β) ≦ 5%
An image projection apparatus characterized by satisfying An image projection apparatus comprising a light source, an illumination optical system, a color separation / synthesis system, a reflective light valve as an image forming element, and a projection optical system,
The illumination optical system has a polarization conversion element, converts non-polarized light from the light source into predetermined polarized light,
The color separation / synthesis system is a means for separating the white light from the illumination optical system into RGB, guiding it to the light valve, and synthesizing each image light,
The color separation / synthesis system reflects a RB component of light emitted from the illumination optical system, transmits a G component, and performs color separation, and
By rotating the plane of polarization of either R or B of the RB component light by 90 ° and changing the plane of polarization of the other light, the R light is S-polarized and the B light is P-polarized. A wavelength-selective phase plate and
A prism-shaped RB polarizing beam splitter that reflects R light to the R light valve side and transmits B light to the B light valve side;
A first polarizing plate that detects image light that has undergone image modulation by the light valve and that has exited from the polarization beam splitter for the RB; and
A G-shaped polarization beam splitter in the form of a prism that guides the G light transmitted through the dichroic mirror to the G light valve side;
A second polarizing plate that detects image light that has undergone image modulation by the G light valve and that has passed through the G polarization beam splitter and is emitted from the G polarization beam splitter. When,
The RGB image light is combined and guided to the projection optical system, and composed of a combining prism having an action of analyzing R light,
When the light ray incident on the G light valve is θ and the refractive index of the G polarizing beam splitter is n, the light incident angle β on the film surface of the G polarizing beam splitter is:
β = 45 ° + sin ⁻¹ (1 / n × sin θ)
And the light incident angle α of the dichroic mirror is
α = 45 ° -θ
And
The polarization plane that passes through the second polarizing plate is P-polarized light,
The dichroic among wavelengths at which the transmittance is 5% in the dichroic mirror, when the wavelength on the long wavelength side was Wa, P-polarized light the reflectivity at the light incident angle β to the membrane surface of the polarizing beam splitter for the G Is Rp (β),
In the wavelength range W where W <Wa,
Rp (β) ≦ 5%
An image projection apparatus characterized by satisfying