Polarized beam splitter and projection-type image display using it
View Patent ↗A polarized beam splitter includes an inclined intermediate layer between two glass prisms. The intermediate layer includes an adhesive layer and a polarized light separating membrane. The intermediate layer may be wedge-shaped in order to compensate for or to cancel astigmatism of light transmitted by the polarized beam splitter caused by the inclination of the intermediate layer. The polarized beam splitter may also be formed with the refractive indexes of the glass and the adhesive of the adhesive layer chosen to reduce astigmatism. Embodiments of three-color projection image display devices that use the polarized beam splitter are also disclosed. The three-color projection image display devices may use one or three polarized beam splitters with a Philips prism or use two polarized beam splitters with a COLORQUAD.
1. A polarized beam splitter comprising:
a first prism that includes a first surface and a second surface inclined with respect to said first surface;
a second prism that includes a third surface that faces said second surface;
an intermediate layer between said second surface and said third surface that includes an adhesive layer that bonds said first prism to said second prism and a polarized light separating membrane; and
wherein the following conditions are satisfied:
Nc≧1.75
Np≧1.85
| Np−Nc |>0.2
where
Np is the refractive index of said first prism and said second prism, and
Nc is the refractive index of the adhesive forming said adhesive layer.
2. The polarized beam splitter of claim 1 , wherein the intermediate layer is wedge-shaped and the thicker part of the wedge is located farther from said first surface than is the thinner part of the wedge so that transmission of a light beam that is incident on said first surface and thereafter transits through the intermediate layer compensates for astigmatism of a light beam caused by the inclination of said second surface with respect to said first surface.
3. The polarized beam splitter of claim 2 , wherein the transmission of the light beam through said intermediate layer substantially cancels astigmatism caused by the inclination of said second surface.
4. A projection image display device including the polarized beam splitter of claim 1 .
5. A projection image display device including the polarized beam splitter of claim 2 .
6. A projection image display device including the polarized beam splitter of claim 3 .