BACK PROJECTION DISPLAY

摘要

A back projection display has a reflecting means (7) which reflects image light from an image projector (4) toward the back side of a diffusion screen (3), a light separating means (8) which is provided on the back side of the diffusion screen (3) and reflects the image light toward the reflecting means (7), and a 1st reflecting mirror (6) which is a total reflecting mirror. The reflecting means (7) is composed of a 2nd reflecting mirror (72) which is a total reflecting mirror and a 1/4-wavelength plate (71) and reflects the incident image light with 90 degrees polarization. The light separating means (8) is composed of a plane-polarization mirror and transmits P-wave polarized light only and reflects light of other polarization. If P-wave image light is emitted from the image projector (4), the light is changed to S-wave image light. Therefore, the image light traveling toward the screen (3) is reflected by the light separating means (8) and travels toward the reflecting means (7) again. As the image light is subjected to further 90 degrees polarization by the reflecting means (7), the light is changed to P-wave polarized light and travels toward the screen (3). As the separating means (8) transmits the P-wave polarized light, the image light is transmitted by the separating means (8) and reaches the screen (3). As the reflection is repeated a plurality of times between the reflecting means and the light separating means (8), a long optical path can be obtained even if the display is thin.