Optics: image projectors – Polarizer or interference filter
Reexamination Certificate
2003-05-15
2004-07-20
Gray, David (Department: 2851)
Optics: image projectors
Polarizer or interference filter
C353S033000, C353S081000, C349S009000, C359S488010, C359S490020, C359S490020, C359S490020, C359S885000
Reexamination Certificate
active
06764182
ABSTRACT:
TECHNICAL FIELD
The present invention relates to a projector for displaying images, and more specifically pertains to a polarizer that is disposed on a light-incoming side and/or a light-outgoing side of a liquid crystal device.
BACKGROUND ART
Projectors have a liquid crystal light valve including a liquid crystal device (a liquid crystal panel). Polarizers are generally disposed on a light incoming surface and a light outgoing surface of the liquid crystal device. The polarizer functions to transmit a predetermined polarized light component, while removing the other light components.
A light absorbing-type polarizing plate is generally used for the polarizer in the projector. A typical example of the light absorbing-type polarizing plate is obtained by uniaxially orienting a film including iodine or dye molecules. The light absorbing-type polarizing plate has a relatively high extinction rate and relatively small incident angle dependency but poor light resistance and heat resistance.
The recent demand for the enhanced brightness of projected images and the size reduction of the projector leads to higher output of the light source device and size reduction of the liquid crystal device. This increases the luminous flux of light entering the polarizing plate and thereby raises the luminous flux density. Namely this raises the intensity of light entering the polarizing plate per unit area.
The raised intensity of light entering the polarizing plate per unit area undesirably increases thermal load applied to the polarizing plate. The light absorbing-type polarizing plate removes a non-required light component by absorption and converts the absorbed light component into heat. The light absorbing-type polarizing plate has poor light resistance and heat resistance and accordingly has difficulties in maintaining the polarization characteristics over a long time period. The disadvantage of the prior art projector is thus incapability of stably displaying high-contrast, bright images over a long time period.
DISCLOSURE OF THE INVENTION
The object of the present invention is thus to solve the drawbacks of the prior art technique discussed above and provide a projector that stably displays high-contrast, bright images by improving light resistance and heat resistance of a polarizer.
At least part of the above and the other related objects is attained by a projector as a first apparatus of the present invention. The projector includes: a light source device; an electro-optic device that modulates light emitted from the light source device; two polarizers that are disposed respectively on a light incoming side and a light outgoing side of the electro-optic device; and a projection optical system that projects light output from the electro-optic device. At least one of the two polarizers is a structural birefringent polarizing plate.
The structural birefringent polarizing plate may also be called a shape birefringent polarizing plate or a form birefringent polarizing plate.
This projector utilizes the structural birefringent polarizing plate, which hardly absorbs light and has relatively high light resistance and heat resistance. The projector thus stably displays high-contrast, bright images, even when the light entering the polarizer has a high intensity per unit area, due to an increase in light output of the light source device or due to reduction of the size of the electro-optic device.
When non-polarized light enters the polarizer disposed on the light incoming side of the electro-optic device, the thermal load applied to the polarizer on the light incoming side becomes heavier than the thermal load applied to the polarizer on the light outgoing side. In such cases, it is preferable that the structural birefringent polarizing plate is provided at least on the light incoming side of the electro-optic device.
When a predetermined polarized light enters the polarizer disposed on the light incoming side of the electro-optic device, the thermal load applied to the polarizer on the light outgoing side becomes heavier than the thermal load applied to the polarizer on the light incoming side. In such cases, it is preferable that the structural birefringent polarizing plate is provided at least on the light outgoing side of the electro-optic device.
In the above projector, the structural birefringent polarizing plate may be a wiregrid polarizing plate.
The wiregrid polarizing plate has a simple structure, which facilitates manufacture of the structural birefringent polarizing plate.
In accordance with one preferable application of the above projector, the structural birefringent polarizing plate includes a light transmissive crystal substrate and a fine periodic structure periodically formed in a predetermined direction on the light transmissive crystal substrate.
The light transmissive crystal substrate has a relatively high thermal conductivity and thus quickly releases heat generated by absorption of light by the structural birefringent polarizing plate. A sapphire substrate or a rock crystal substrate are typical examples of the light transmissive crystal substrate.
In accordance with another preferable application of the above projector, the structural birefringent polarizing plate is inclined to a center axis of light illuminating the electro-optic device.
The inclined layout of the structural birefringent polarizing plate practically decreases the pitch of the fine periodic structure relative to the incident light, thus improving the optical characteristics of the structural birefringent polarizing plate.
In the above application, the structural birefringent polarizing plate may be arranged at an inclination of about 45 degrees relative to the center axis.
When the light transmitted through the structural birefringent polarizing plate is utilized for the electro-optic device, this arrangement causes a non-required light reflected by the structural birefringent polarizing plate to be emitted in the direction of about 90 degrees to the center axis. This arrangement prevents adverse effects of the non-required light on other optical elements. This arrangement further enables the light reflected by the structural birefringent polarizing plate to be utilized for the electro-optic device.
In accordance with still another preferable application of the above projector, the structural birefringent polarizing plate is divided into a plurality of areas, and at least one of the plurality of areas is inclined to a center axis of light illuminating the electro-optic device.
This arrangement relatively decreases the thickness of the inclined structural birefringent polarizing plate (that is, the dimension in the direction perpendicular to the light incoming surface of the electro-optic device). Part of the plurality of areas may be arranged perpendicular to the center axis of the light illuminating the electro-optic device (that is, parallel to the light incoming surface of the electro-optic device).
In the above application, at least one of the plurality of areas in the structural birefringent polarizing plate may be arranged at an inclination of about 45 degrees relative to the center axis.
When the light transmitted through the structural birefringent polarizing plate is utilized for the electro-optic device, this arrangement causes the light reflected by the structural birefringent polarizing plate to be emitted in the direction of about 90 degrees to the center axis. This effectively prevents adverse effects of the reflected light on other optical elements. For the effective use of the light reflected by the structural birefringent polarizing plate, the reflected light may be returned to the light source device for recycling.
In accordance with one preferable embodiment of the above projector, a light absorbing polarizing plate is further arranged on a light outgoing side of the structural birefringent polarizing plate.
The optical characteristics of the structural birefringent polarizing plate have relatively large incident angle dependency and wavelength dependency. The optical characteristics
Ito Yoshitaka
Sakata Hidefumi
Beyer Weaver & Thomas LLP
Cruz Magda
Gray David
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