(1) Field of the Invention
The present invention relates to an optical unit which, according to a video signal, intensity-modulates light emitted from a light source using transmissive liquid crystal panels and which enlarges and projects optical images formed on the liquid crystal panels, and more particularly, to the structure of output polarizing plates of the transmissive liquid crystal panels.
(2) Description of the Related Art
A projection-type display device has been known which includes an optical unit accommodated in an enclosure together with a drive circuit, a power supply circuit, and a cooling fan, the optical unit intensity-modulating, by using light valves according to a video signal, light emitted from a light source and enlarging and projecting formed optical images.
Generally, in a related-art projection-type display device including transmissive liquid crystal panels (hereinafter referred to simply as “liquid crystal panels”) to be used as light valves, polarizing plates for different polarization directions (for example, mutually perpendicular directions) are provided upstream and downstream (on the light input side and the light output side) of each of the liquid crystal panels. The polarizing plates are absorption-type polarizing plates formed of a uniaxially-stretched organic film prepared by uniaxially stretching a polymer film with low temperature resistance. The absorption-type polarizing plates generate heat by absorbing unnecessary polarized light, so that they are, along with the liquid crystal panels with low heat resistance, cooled by cooling fans for reliability enhancement. An output polarizing plate to be disposed on the light output side of a liquid crystal panel, in particular, absorbs most light when black is displayed, so that its heat resistance is required to be enhanced. Under such circumstances, devices have been put in use which include polarizing plates formed of an inorganic material of high heat resistance. The wire-grid type polarizing plate disclosed in JP-A No. 2007-33746 is among such known inorganic polarizing plates.
When external air is blown to an optical component, for example, a liquid crystal panel by a cooling fan, dust contained in the air may attach to the liquid crystal panel. Dust attached to the liquid crystal panel may be displayed as a black dot on the screen to degrade the quality of image display. JP-A No. H09-105901 discloses a configuration in which a liquid crystal panel is supported by a support frame and is placed in a sealed state with its front and back sides covered with a front side glass and a back side glass also supported, at their peripheries, by the support frame.