Optics: image projectors – Polarizer or interference filter
Reexamination Certificate
2001-04-23
2003-07-08
Adams, Russell (Department: 2851)
Optics: image projectors
Polarizer or interference filter
C353S031000, C353S033000, C353S081000, C349S009000, C359S487030, C359S490020, C359S490020
Reexamination Certificate
active
06588905
ABSTRACT:
INCORPORATION BY REFERENCE
The disclosure of the following priority application is herein incorporated by reference:
Japanese Patent Application No. 10-280165 filed Oct. 1, 1998.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a polarizing device and a projector More specifically, it relates to a polarizing device which is utilized when performing a polarization splitting on light fluxes corresponding to a plurality of colors resulting from a color separation performed on light emitted from a light source, guiding the light fluxes having undergone polarization splitting to a plurality of light valves and analyzing the light fluxes corresponding to the plurality of colors that have been modulated at the individual light valves, and a projector that composes (synthesizes) the light fluxes analyzed by using the polarizing device at a color composition optical system and projects the composed light on a screen via a projection lens.
2. Description of the Related Art
Projectors employed to project an image onto a screen in the known art include the projector disclosed in Japanese Patent Publication No. 2599309. To explain this projector in reference to
FIG. 7
, light source light emitted from a light source
61
undergoes color separation at dichroic mirrors
62
and
63
and thus becomes separated into R light, G light and B light which are then guided to polarization beam splitters
64
R,
64
G and
64
B provided in correspondence to the different color light. Only the polarization split light in the light guided to the polarization beam splitters
64
R,
64
G and
64
B is guided to reflection type light valves
65
R,
65
G and
65
B. The light having entered the light valves
65
R,
65
G and
65
B are modulated in correspondence to color signals input to the individual light valves when they are reflected at the light valves
65
R,
65
G and
65
B. The light having been modulated and reflected at the light valves
65
R,
65
G and
65
B are respectively guided to the polarization beam splitters
64
R,
64
G and
64
B and only the modulated light are analyzed at the polarization beam splitters
64
R,
64
G and
64
B and extracted. The analyzed light fluxes are then color-composed at a cross-dichroic prism
66
and a full color projected image is projected onto a screen (not shown) by a projection lens
67
.
To explain the different color light fluxes obtained through the color separation achieved at the dichroic mirrors
62
and
63
in further detail, the optical axes of these different color light fluxes respectively enter the polarization splitter portions of the polarization beam splitter
64
R,
64
G and
64
B with an angle of incidence of 45°. The light that has entered each polarization splitter portion undergoes polarization splitting and is separated into S-polarized light to be reflected at the polarization splitter portion and P-polarized light to be transmitted through the polarization splitter portion. The S-polarized light are allowed to enter the reflection type light valves
65
R,
65
G and
65
B provided near the exit surfaces of the polarization beam splitters
64
R,
64
G and
64
B provided in correspondence to the individual color light. The individual color light having been modulated and reflected at the reflection type light valves
65
R,
65
G and
65
B re-enter the polarization splitter portions of the polarization beam splitters
64
R,
64
G and
64
B respectively. The light fluxes having re-entered the polarization splitter portions undergo an analyzing and, as a result, the P-polarized light fluxes that are the modulated light fluxes are detected as transmitted light and are extracted. The analyzed light fluxes corresponding to the different colors then undergo a color composition at the cross dichroic prism
66
. As explained above, the polarization beam splitters
64
R,
64
G and
64
B are each constituted to function both as a polarization splitting optical system and as an analyzing optical system.
The polarization beam splitters
64
R,
64
G and
64
B each assume a structure achieved by inserting a polarization splitter film between two isosceles right-triangular prisms and bonding them together, and they have a roughly square sectional shape.
The polarization beam splitters
64
R,
64
G and
64
B provided in correspondence to the different colors of light are each formed in a cubic shape or a rectangular parallelopiped shape which is achieved by inserting a polarization splitter film between two isosceles right-triangular prisms with identical sectional shapes. In other words, the polarization beam splitters
64
R,
64
G and
64
B may each be regarded as a block of optical glass. A problem arises when the three blocks are provided in correspondence to the different colors of light since the volumetric space occupied by the optical systems and the weight of the optical systems are bound to increase.
In addition, while the polarization beam splitters
64
R,
64
G and
64
B fulfill a crucial function as analyzing optical systems as explained above, it is desirable to ensure that when the light that have been modulated while being reflected at the light valves
65
R,
65
G and
65
B (linearly polarized light) are transmitted through transparent optical members (glass portions) constituting the polarization beam splitters
64
R,
64
G and
64
B, they do not adversely affect the states of the polarization. Otherwise, the states of the polarization will change while the modulated to light fluxes are transmitted through the glass portions and, a result, modulated light different from the original modulated light will be detected, thereby reducing the contrast of the projected image.
While a glass prism material with a low photoelastic constant may be used to constitute the prisms to reduce the degree to which the polarization states change, the use of such a material which has a particularly large specific gravity among various optical glass materials will lead to an increase in the weight of the optical systems.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a more compact and lightweight polarizing device and a more compact and lightweight projector which employees the polarizing device for polarization splitting and light analyzing.
In order to attain the above object, a polarizing device according to the present invention comprises: a first prism substantially formed in a triangular shape; a second prism substantially formed in a triangular shape and bonded to the first prism; a polarization splitter film provided at a bonding surface at which the first prism and the second prism are bonded to each other; and a shape of a section of the first prism being determined so as to allow an optical axis of light having entered through one surface of the first prism to enter the polarization splitter film with an angle of incidence smaller than 45°.
Another polarizing device according to the present invention comprises: a triangular first prism having a section substantially formed in an isosceles triangular shape having a first interior angle which is an obtuse angle and a second interior angle and a third interior angle which are acute angles equal to each other; a triangular second prism having a section substantially formed in a triangular shape having a first interior angle equal to the second interior angle and the third interior angle of the first prism; and a polarization splitter film provided at a bonding surface at which a first surface of the first prism facing opposite the first interior angle and one surface of the second prism, which is one of two surfaces enclosing the first interior angle of the second prism, are bonded to each other, and a second surface and a third surface respectively faces opposite the second interior angle and the third interior angle of the first prism, an angle of incidence at the polarization splitter film of an optical axis of light having entered through the second surface is equal to the second interior angle and the third interior angle of the firs
Adams Russell
Koval Melissa J
Nikon Corporation
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