COLOR SEPARATION OPTICAL SYSTEM AND IMAGE PROJECTION APPARATUS

Abstract

A color separation optical system is disclosed which is effective in improving black color and black unevenness. Linearly polarized light impinging on a dichroic surface at an incident angle smaller than 45 degrees and then impinging on a polarization beam splitting surface at an incident angle larger than 45 degrees is referred to as first incident-angle light. A wavelength which is longer than a wavelength at the maximum transmittance of the dichroic surface for the first incident-angle light and at which the transmittance of the dichroic surface for the first incident-angle light is 10% is referred to as Wa, and a wavelength range shorter than Wa is referred to as W. The polarization beam splitting surface has a characteristic in which its transmittance for the first incident-angle light in the wavelength range W is 5% or lower.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram showing the structure of a liquid crystal projector which is Embodiment 1 of the present invention.

FIG. 2 is a graph showing the characteristic of a wavelength-selective phase plate in Embodiment 1.

FIG. 3 is a graph showing the characteristic of a combination PBS in Embodiment 1.

FIG. 4 is a graph showing the transmittance of a dichroic mirror in Embodiment 1.

FIG. 5 is a graph showing the transmittance of a G-PBS for S-polarized light in Embodiment 1.

FIG. 6 shows the optical path from the dichroic mirror to a G panel in Embodiment 1.

FIG. 7 is a schematic diagram showing the structure of a liquid crystal projector which is Embodiment 2 of the present invention.

FIG. 8 is a graph showing the reflectance of a G-PBS for P-polarized light in Embodiment 2.

FIG. 9 shows the optical path from a dichroic mirror to a G panel in Embodiment 2.

FIG. 10 is a graph showing the transmittance of a conventional G-PBS for S-polarized light.

Claims

1. A color separation optical system comprising: a dichroic surface which transmits light from a light source in a first wavelength band and reflects light therefrom in a wavelength band longer than the first wavelength band; anda polarization beam splitting surface on which the light transmitted through the dichroic surface impinges,wherein, when linearly polarized light impinging on the dichroic surface at an incident angle smaller than 45 degrees and then impinging on the polarization beam splitting surface at an incident angle larger than 45 degrees in an optical path for the light in the first wavelength band is referred to as first incident-angle light, a wavelength which is longer than a wavelength at the maximum transmittance of the dichroic surface for the first incident-angle light and at which the transmittance of the dichroic surface for the first incident-angle light is 10% is referred to as a wavelength Wa, and a range of wavelengths shorter than the wavelength Wa is referred to as W,the polarization beam splitting surface has a characteristic in which its transmittance for the first incident-angle light in the wavelength range W is equal to or lower than 5%.

2. The color separation optical system according to claim 1, wherein the polarization beam splitting surface has a cut wavelength for the first incident-angle light longer than a cut wavelength of the dichroic surface for the first incident angle light.

3. An image display optical system comprising: the color separation optical system according to claim 1;a light modulation element to which the light reflected by the polarization beam splitting surface of the color separation optical system is introduced; anda projection optical system which projects the light from the light modulation element.

4. An image projection apparatus comprising: a light source; andthe image display optical system according to claim 3.

5. An image display system comprising: the image projection apparatus according to claim 4; andan image supply apparatus which supplies image information to the image projection apparatus.

6. A color separation optical system comprising: a dichroic surface which transmits light from a light source in a first wavelength band and reflects light therefrom in a wavelength band longer than the first wavelength band; anda polarization beam splitting surface on which the light transmitted through the dichroic surface impinges,wherein, when linearly polarized light impinging on the dichroic surface at an incident angle smaller than 45 degrees and then impinging on the polarization beam splitting surface at an incident angle larger than 45 degrees in an optical path for the light in the first wavelength band is referred to as first incident-angle light, a wavelength which is longer than a wavelength at the maximum transmittance of the dichroic surface for the first incident-angle light and at which the transmittance of the dichroic surface for the first incident-angle light is 10% is referred to as a wavelength Wa, and a range of wavelengths shorter than the wavelength Wa is referred to as W,the polarization beam splitting surface has a characteristic in which its reflectance for the first incident-angle light in the wavelength range W is equal to or lower than 5%.

7. An image display optical system comprising: the color separation optical system according to claim 6;a light modulation element to which the light reflected by the polarization beam splitting surface of the color separation optical system is introduced; anda projection optical system which projects the light from the light modulation element.

8. An image projection apparatus comprising: a light source; andthe image display optical system according to claim 7.

9. An image display system comprising: the image projection apparatus according to claim 8; andan image supply apparatus which supplies image information to the image projection apparatus.