JP2007310036A - Image projection device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an image projection device effective to color tint and irregular color of black, and restraining the lowering of light quantity. <P>SOLUTION: In a color separation and composing system, white light from an illumination system is separated to RGB and guided to light valves, so that respective image light beams are composed. When the angle of a light beam made incident on the light valve is defined as θ, and the refractive index of a polarizing beam splitter prism of an optical path G is defined as n, a light beam incident angle β on the film surface of the prism is expressed as β=45°+sin<SP>-1</SP>(1/n×sinθ). In a wavelength region W meeting W<Wa when wavelength that transmittance on a long wavelength side is 5% is defined as Wa in an incident angle on a dichroic mirror α=45°-θ, light made incident on the film surface of the polarizing beam splitter of the optical path G at the angle of β is shown as follows. In a rate in which the light is guided to the light valve G, a rate that light whose plane of polarization is rotated by 90° is made incident on the light valve is ≤5% when light whose predetermined plane of polarization is made incident on the light valve is 100%. <P>COPYRIGHT: (C)2008,JPO&INPIT

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 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. Thereby, 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 system has a polarization conversion element, and 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 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 system and transmits the G component to separate the colors, and the light of either R or B of the light of the RB component. Is a wavelength-selective phase plate that does not change the plane of polarization, the R light is S-polarized, the B light is P-polarized, and the R light is analyzed. A prism-shaped polarizing beam splitter that reflects the R light valve and simultaneously detects the B light and transmits it to the B light valve side. A polarizing plate for analyzing the B light after being emitted, a G-shaped prism-shaped polarization beam splitter for detecting the G light transmitted through the dichroic mirror and guiding it to the G light valve side, and an image with the G light valve Modulated A polarizing plate for analyzing the image light that has exited from the polarizing beam splitter, and a combining prism that combines the RGB image light and guides it to the projection optical system, and has the function of detecting only the R light. It is configured.

When the light beam incident on the light valve is θ and the refractive index of the polarizing beam splitter prism in the G optical path is n, the light beam incident angle β on the film surface of the prism is
β = 45 ° + sin ⁻¹ (1 / n × sin θ)
And the incident angle α of the dichroic mirror:
α = 45 ° -θ
In this case, when the wavelength at which the transmittance on the long wavelength side is 5% is Wa, the light of the G light is incident on the film surface of the polarization beam splitter in the G optical path at an angle β in the wavelength region W where W <Wa. When the light with which the predetermined plane of polarization is incident on the light valve is defined as 100% in the ratio of the light guided to the bulb, the ratio of the light with 90 ° rotation of the plane of polarization incident on the light valve is 5% or less. It is characterized by that.

  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 that is Embodiment 1 of the present invention. The projector of this embodiment includes a light source 1, an illumination optical system 2, a color separation / synthesis optical system 3, reflective liquid crystal panels 6, 7, and 8 as image forming elements, and a projection lens 4. . 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. The light emitted from the light source 1 is non-polarized light but becomes P-polarized light by a polarization conversion element (not shown) included in the illumination system 2.

  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 separates the RB optical path and the G optical path by reflecting Red and Blue light and transmitting Green light from the white light from the illumination system 2 by the dichroic mirror 9. . 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 Red light changes its polarization state from P-polarized light to S-polarized light, while Blue light remains P-polarized light.

  The Red light after passing through the wavelength selective phase plate is S-polarized light, reflected by the RB-PBS 11, and guided to the Red panel 8. The light guided to the Red panel 8 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, the blue light enters the RB-PBS 11 as P-polarized light, passes through the RB-PBS 11, and is guided to the blue panel 7. 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 arranged. After the blue light is analyzed by this polarizing plate, it enters the synthetic PBS 12 and is transmitted therethrough. To the projection system 4. 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 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 beam incident angle of 45 °, the dotted line indicates the transmittance when the incident angle is smaller than 45 °, and the one-dot broken line indicates the transmittance when the incident angle is larger than 45 °. As shown in FIG. 6, when the angle of light incident on the dichroic mirror 9 is smaller than 45 °, the angle of light incident on the film surface of the G-PBS 10 becomes 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 is incident on the green panel 6 and is not modulated during black display, it is emitted as S-polarized light, incident on the G-PBS 10, reflected, guided to the combining prism 12, and applied to the screen 5 through the projection system. 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, the incident angle β of 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, leakage light at the time of black display can be reduced 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, leakage light at the time of black display can be reduced 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. P polarization reflectance characteristics of G-PBS in the second embodiment of the present 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 the 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 (3)

It consists of a light source, illumination optical system, color separation / synthesis system, reflective light valve as an image forming element, and projection optical system,
The illumination system has a polarization conversion element, converts non-polarized light from the light source into predetermined polarized light,
The color separation / synthesis system is means for separating the white light from the illumination system into RGB, guiding it to the light valve, and synthesizing each image light,
The color separation / combination system reflects a RB component of light emitted from the illumination system and transmits a G component to separate colors, and either one of R and B of light of the RB component. A wavelength-selective phase plate that rotates the plane of polarization of light by 90 °, and the other light does not change the plane of polarization. R light is S-polarized light, B light is P-polarized light, and R light is analyzed. A prism-shaped polarization beam splitter that detects the B light and transmits it to the B light valve side at the same time as reflecting the light beam to the R light valve side. A polarizing plate for analyzing the B light after exiting the polarizing beam splitter;
G-polarized polarizing beam splitter that detects G light transmitted through the dichroic mirror and guides it to the G light valve side, and image light modulated by the G light valve, the polarizing beam splitter Polarizing plate for analyzing the light after exiting
The RGB image light is combined and guided to the projection optical system, and composed of a combining prism having an action of detecting only R light,
When the light beam incident on the light valve is θ and the refractive index of the polarizing beam splitter prism in the G optical path is n, the light beam incident angle β on the film surface of the prism is
β = 45 ° + sin ⁻¹ (1 / n × sin θ)
And the incident angle α of the dichroic mirror:
α = 45 ° -θ
In this case, when the wavelength at which the transmittance on the long wavelength side is 5% is Wa, the light of the G light is incident on the film surface of the polarization beam splitter in the G optical path at an angle β in the wavelength region W where W <Wa. When the light with which the predetermined polarization plane is incident on the light valve is defined as 100% in the ratio at which the light is guided to the bulb, the ratio at which the light rotated 90 degrees with respect to the polarization plane enters the light valve is 5% or less. An image projection apparatus characterized by that. When the predetermined polarization plane is P-polarized light and the transmittance with S-polarized light at an incident angle β to the film surface of the polarization beam splitter in the G optical path is Ts (β),
Ts (β) ≦ 5%
The image projection apparatus according to claim 1, wherein: The predetermined polarization plane is S-polarized light, and when the reflectance with P-polarized light at an incident angle β on the film surface of the polarizing beam splitter in the Green optical path is Rp (β),
Rp (β) ≦ 5%
The image projection apparatus according to claim 1, wherein: