Optical: systems and elements – Single channel simultaneously to or from plural channels – By surface composed of lenticular elements
Reexamination Certificate
2000-05-03
2001-08-21
Mack, Ricky (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By surface composed of lenticular elements
C359S569000
Reexamination Certificate
active
06278552
ABSTRACT:
This application is based on applications Nos. H11-131017 and H11-133918 filed in Japan on May 12, 1999 and May 14, 1999 respectively, the entire content of which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polarization separation device used to illuminate a spatial light modulation device such as a liquid crystal panel that utilizes polarization of light. The present invention relates also to a projection-type display apparatus having such a polarization separation device.
2. Description of the Prior Art
Conventionally, as projection-type display apparatuses that project an enlarged image of an original image through a projection lens are known those employing a CRT and those employing a light source and a spatial light modulation device. Here, as spatial light modulation devices are known transmission-type liquid crystal panels that use twisted nematic liquid crystal. Liquid crystal panels of this type are in practical use in various applications because they permit miniaturization of projection-type display apparatuses, because they permit projection of high-resolution images simply if provided with sufficient numbers of pixels, and because their mass-production methods have been well established with those manufactured for direct-view purposes.
A spatial light modulation device such as one using twisted nematic liquid crystal utilizes polarization of light, and therefore has polarizers provided at its entrance and exit sides. Out of the light that illuminates the spatial light modulation device, the linearly polarized light component that has passed through the entrance-side polarizer then has its polarization state modulated spatially while passing inside the spatial light modulation device. This controls the amount of light that passes through the exit-side polarizer, and thereby forms an optical image.
A projection-type display apparatus employing a spatial light modulation device typically uses a lamp that emits natural light to illuminate the spatial light modulation device. If the spatial light modulation device is of a type that utilizes polarization of light, the polarizer provided at its entrance side transmits only about one half of the natural light emitted from the lamp, and the other half of the light is wasted by being reflected or absorbed.
To overcome this inconvenience, various techniques have been proposed that are generally called polarization conversion. According to these techniques, the natural light from a light source is separated beforehand into, on the one hand, a polarized light component (hereafter referred to as the primary polarized light component) polarized in the same way as the light that a spatial light modulation device is designed to use and, on the other hand, a polarized light component (hereafter referred to as the secondary polarized light component) polarized perpendicularly thereto. Then, the polarization plane of the secondary polarized light component, which if left intact the spatial light modulation device cannot use, is rotated through 90° so that the primary and secondary polarized light components are, after their polarization planes are thus made identical, together fed to the spatial light modulation device. In this way, it is possible to use both of the two polarized light components.
Accordingly, a projection-type display apparatus utilizing polarization conversion needs to be provided with a polarization separation device for separating natural light into two polarized light components polarized in directions perpendicular to each other and a polarization plane rotating device for rotating the polarization plane of one of those two separated polarized light components through 90°. As polarization separation devices, polarization separation multilayer films are widely known that utilize the Brewster angle and interference and that are available in plate-shaped and prism-shaped types.
On the other hand, as polarization plane rotating devices, phase films called &lgr;/2 plates are generally known. A &lgr;/2 plate is made by drawing an optically transparent organic film uniaxially so as to give it optical anisotropy. It has its thickness and optical anisotropy so controlled as to give the light passing therethrough a phase difference that corresponds to one half of the wavelength of the light. Accordingly, if linearly polarized light having a polarization plane in a direction 45° with respect to an optical axis enters a &lgr;/2 plate, it exits therefrom as linearly polarized light having a polarization plane rotated further through 90°.
A projection-type display apparatus having a polarization separation device and a polarization plane rotating device as described above is disclosed in Japanese Laid-Open Patent Application H6-202094. The construction of this projection-type display apparatus is shown in FIG.
14
. The natural light radiated from a light source
901
is made into a parallel beam by a parabolic surface mirror
902
, and then enters a polarization separation device
903
. The primary and secondary polarized light components exiting from the polarization separation device
903
travel through a first and a second lens array
904
and
905
, and then illuminate a liquid crystal panel
907
.
The first lens array
904
separates the beam of the illumination light into partial beams, and the thus separated partial beams are enlarged by the second lens array
905
to an appropriate size. The separated partial beams are then superimposed on each other on the liquid crystal panel
907
by a convex lens
908
. Another convex lens
909
provided in the vicinity of the liquid crystal panel
907
makes the principal ray within each angle of view parallel to the optical axis.
The polarization separation device
903
has a structure as shown in
FIG. 15. A
structure composed by putting together a prism having an isotropic refractive index and a prism layer made of a birefringent material in general is widely known as a Wollaston prism. This structure exhibits, at the interface between the prism and the prism layer, different refraction conditions in different polarization directions perpendicular to each other, and thereby permits two polarized light components to travel in different directions.
The polarization separation device
903
has a plurality of such Wollaston prisms arranged in an array. Thus, the polarization separation device
903
is composed of a prism array base plate
911
having a blaze-shaped section, a flat base plate
912
, and a birefringent optical material layer
913
made of an optically anisotropic material. Here, since calcite, which is generally used as an optically anisotropic material, is expensive, a material produced by uniaxially arranging strips of an organic material such as liquid crystal layers, organic films, or monomers is used.
Thus, the polarization separation device
903
separates the light
914
entering it into a primary polarized light component
914
a
and a secondary polarized light component
914
b
that exit therefrom traveling in directions &thgr;′ degrees apart from each other. As a result, the light beams that the first lens array
904
makes converge on the second lens array
905
each form separate spots, a predetermined distance apart from each other in the direction of the angle &thgr;′, for the primary and secondary polarized light components
914
a
and
914
b.
In the vicinity of the second lens array
905
, a phase difference plate
906
is provided that selectively acts on the spots formed by the secondary polarized light component so as to rotate its polarization plane through 90°. As a result, the polarization planes of the primary and secondary polarized light components exiting from the convex lens
908
are made uniform. By aligning the polarization plane of these polarized light components with the polarization direction of the entrance-side polarizer (not shown) of the liquid crystal panel
907
, it is possible to realize an optical system that permits efficient
Hayashi Kohtaro
Ishihara Jun
Mack Ricky
Minolta Co. , Ltd.
Sidley Austin Brown & Wood
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