Optics: image projectors – Polarizer or interference filter
Reexamination Certificate
2001-02-14
2002-12-10
Adams, Russell (Department: 2851)
Optics: image projectors
Polarizer or interference filter
C353S031000, C353S034000, C353S038000, C353S099000, C349S007000, C349S009000, C359S894000
Reexamination Certificate
active
06491396
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a projector which separates a luminous flux from a light source into a plurality of partial luminous fluxes and modulates the plurality of partial luminous fluxes according to image information by means of an electro-optic device.
2. Description of Related Art
As a projector capable of projecting and displaying a color image, in addition to a projector of a three-plate type provided with an electro-optic device for each of three color lights, a projector of a single-plate type forming a color image by means of a single electro-optic device has been put to practical use.
A projector of a single-plate type has an advantage of making it possible to easily make a projector apparatus smaller in size and lower in cost.
There are various forms of single-plate type projectors, and among them a single-plate type projector which irradiates a single liquid crystal display device (electro-optic device) provided with a microlens array with color lights obtained by color separation by means of three dichroic mirrors (a color separation optical element) arranged at specific positions like a color liquid crystal display device disclosed in Japanese Patent Laid-Open Publication No. Hei 4-60,538 is well known (hereinafter an electro-optic device of such a composition is called an electro-optic device of a spatial color separation type). A projector of such a form attracts public attention in that it has a high efficiency of light utilization and can easily provide a bright projected image in spite of its single-plate type.
Further, a single-plate type projector as described above is contrived so as to arrange various optical elements such as a luminous flux separation optical element, a polarization transforming element, a color separation optical element and the like in an optical path from a light source to an electro-optic devise, utilize light of the light source without waste, and thereby form a projected image being not irregular in brightness and color.
A luminous flux separation optical element is an optical element which separates a luminous flux from a light source into a plurality of partial luminous fluxes, forms a plurality of light source images in a virtual plane nearly perpendicular to a virtual optical axis of illumination passing nearly the center of the said luminous flux separation optical element, superposes luminous fluxes from the plurality of light source images on an electro-optic device by considering them as pseudo-light sources, and thereby obtains illuminating luminous fluxes being uniform in distribution of intensity. Concretely, as a luminous flux separation optical element, a bar-type optical conductor which reflects a luminous flux inputted from the entrance end by plural pairs of reflecting faces, separates the luminous flux into a plurality of partial luminous fluxes according to different positions of reflection and outputs them from the exit end, a lens array having a plurality of lenses arranged in a plane opposite to the pixel area of an electro-optic device, or the like is adopted.
A polarization transforming element is an optical element which separates an incident luminous flux being random in direction of polarization direction into two polarized luminous fluxes, rotates the polarization direction at least one of the two polarized luminous fluxes, and thereby outputs luminous fluxes being uniform in direction of polarization. Concretely, a polarization transforming element comprises a polarization separating film which transmits one of two polarized luminous fluxes being different in direction of polarization from each other and reflects the other, a reflecting film which reflects the other polarized luminous flux separated, and a retardation plate which turns either of the two polarized luminous fluxes in direction of polarization.
A color separation optical element is an optical element which separates an incident luminous flux into a plurality of color lights such as R, G, B and the like for example, in which three dichroic mirrors to respectively reflect red, green and blue lights are arranged at different angles from one another with respect to the direction of incidence of a luminous flux and the respective color lights separated by the three dichroic mirrors are outputted at different angles from one another.
An electro-optic device of a spatial color separation type modulates each of luminous fluxes separated by said color separation optical element according to its image information for each color light and forms a color image. In the electro-optic device, three rectangular sub-pixels respectively corresponding to R, G and B lights are arranged side by side, and one microlens is formed for these three sub-pixels. The respective color lights incident upon the microlens at different angles are condensed by the microlens, enter their corresponding sub-pixels and are modulated for their respective colors and then outputted through a projection lens to form a color image projected.
Thus, a pixel area obtained by combining R, G and B sub-pixels in an electro-optic device is formed into a nearly square shape, and a sub-pixel to be modulated for each color light is formed by dividing said nearly square-shaped pixel area along the direction of incidence of each color light. In other words, a sub-pixel is formed into the shape of a rectangle having its short sides in the direction of color separation performed by the color separation optical system.
However, since a sub-pixel for each color light is formed into the shape of a rectangle in a single-plate type projector of such a structure, when a inclined light in the short-side direction of the rectangle is entered, a different color light is mixed into an adjacent sub-pixel and the color light leaks to a sub-pixel for another color light to generate a color mixture, and as a result, an image projected on a screen is degraded in contrast and color reproducibility. In a single-plate type projector, therefore, it is important how the angular distribution of lights incident on an electro-optic device in the short-side direction. is controlled.
SUMMARY OF THE INVENTION
An object of the present invention is to provide a single-plate type projector using an electro-optic device of a spatial color separation type, said projector preventing a color mixture and being high in contrast and color reproducibility.
(1) A projector according to the present invention is a projector comprising;
a luminous flux separation optical element that separates a luminous flux from a light source into a plurality of partial luminous fluxes,
a polarization transforming element that separates each of said plurality of partial luminous fluxes into two polarized luminous fluxes and then converts the two luminous fluxes into a single polarized luminous fluxes being uniform in direction of polarization,
an electro-optic device that modulates an illuminating luminous flux outputted from said polarization transforming element, said electro-optic device having a plurality of long and narrow pixels respectively corresponding to color lights and being arranged adjacently to one another, and
a projection lens that projects a luminous flux modulated by said electro-optic device, and
a direction of polarization separation of said plurality of partial luminous fluxes performed by said polarization transforming element coincides nearly with the long-side direction of said pixel.
In case of disposing a polarization transforming element between a light source and an electro-optic device for the purpose of improving the efficiency of utilizing light, an angular distribution of light is spread in direction of polarization separation due to separation of polarization by the polarization transforming element. In the present invention, however, since the direction of polarization separation by the polarization transforming element corresponds to the long-side direction of a pixel in an electro-optic device, an angular distribution of illuminating fluxes is spread in
Ito Yoshitaka
Karasawa Joji
Adams Russell
Cruz Magda
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