Optics: image projectors – Polarizer or interference filter
Reexamination Certificate
2002-06-20
2004-05-25
Adams, Russell (Department: 2851)
Optics: image projectors
Polarizer or interference filter
C353S031000, C353S084000, C353S033000
Reexamination Certificate
active
06739724
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of Invention
The present invention relates to an illumination optical system which uniformizes in-plane illuminance distribution of the light emitted from a light source, and to a projector having such an optical system.
2. Description of Related Art
Currently, for liquid crystal projectors, so-called three-plate type reflective liquid crystal projectors, which use three reflective liquid crystal panels, is known. The three-plate type reflective liquid crystal projector separates the light emitted from a light source into lights of three colors, that is, three primary colors, red (R), green (G), and blue (B) by a color separation system. Then the separated three color lights illuminate three reflective liquid crystal panels for each color light, the three primary colors modulated by each of the reflective liquid crystal panels are synthesized, and the color image obtained by the synthesis is projected, in an enlarged form, onto a screen by the projection lens.
In the above-described reflective liquid crystal projectors, miniaturization of the apparatus is considered to be important, so that optical elements having dichroic planes disposed at 45° to the optical axis are often used for color separation and color synthesis. However, these projectors have a problem in that chrominance non-uniformity often occurs: by the polarization dependency of light separation characteristics of dichroic planes, thereby making it difficult to improve image quality.
Under this circumstance, several optical systems, which seldom cause chrominance non-uniformity in consideration of the characteristics of dichroic planes, and thus realize image quality improvement, have been proposed. For example, in Japanese Unexamined Patent Application Publication Nos. 7-84218 and 11-64794, optical systems have been proposed, in which a polarized beam splitter having a wavelength selection retardation film and a light separation function are used instead of dichroic planes for light separation. However, there remains a problem in that with a polarized beam splitter having a wavelength selection retardation film and light separation function, it is difficult to realize light separation which varies steeply, and that the cost becomes too high.
SUMMARY OF THE INVENTION
Accordingly, it is an object of the present invention to provide an illumination optical system which efficiently generates illumination light having specific color light with the polarization direction which is different by 90° to the polarization direction of the other color light, so that such illumination light can provide the illuminated area with uniform illuminance distribution. Furthermore, it is another object of the present invention to provide a projector to which such an illumination optical system is applied, thus in which the polarization dependency of dichroic planes which constitute the color separation/synthesis optical system is reduced, and high quality projection image is displayed.
According to a first aspect of the present invention, there can be provided an illumination optical system including a luminous flux division optical element which divides the light from a light source into a plurality of partial luminous fluxes and collects each partial luminous flux, a color light separation optical element which separates each of the partial luminous fluxes into first color partial luminous flux and second color partial luminous flux, and emits the first color partial luminous flux and the second color partial luminous flux in different directions with each other or in a direction parallel to each other, a polarization change element which includes a polarization beam splitter array in which a plurality of polarization separation films and a plurality of reflective films are arranged alternately, and a polarization direction rotation element which is disposed either at a position where light transmitted through the polarization separation film is emitted or at a position where light reflected by the reflective film is emitted. The first color partial luminous flux incident on the polarization separation film is uniformed in a first polarization direction, and the second color partial luminous flux incident on the reflective film is uniformed in a second polarization direction. The invention can also include a transmission optical element which is disposed either at an incident side or at an emitting side of the polarization change element, and transmits an image formed by the luminous flux division optical element to an illuminated area, and a superposition optical element for superposing partial luminous flux emitted from the polarization change element at the illuminated area.
With this arrangement, first, the light from a light source is divided into a plurality of partial luminous fluxes and collected by the luminous flux division optical element, and each of the partial luminous fluxes is separated into the first color partial luminous flux and the second color partial luminous flux. The separated first color light and second color light enter the polarization change element having the polarization beam splitter array and the polarization direction rotation element, and are transformed into the first color partial luminous flux and second color partial luminous flux, each luminous flux having desired polarization state for each color light. Here, the polarization beam splitter array has a structure in which a plurality of pairs of polarization separation film and reflective film are arranged, and the polarization direction rotation elements are disposed at the emitting side of the polarization beam splitter array by selecting the positions corresponding to the positions of the polarization separation films or those of the reflective films.
For example, the polarization direction rotation elements are disposed only at the emitting side of the polarization separation films. Accordingly, of the first color partial luminous flux and the second color partial luminous flux, one enters a polarization separation film, and the other enters a reflective film selectively. Furthermore, the first color partial luminous flux and second color partial luminous flux are individually separated at the polarization beam splitter array into two kinds of polarization luminous fluxes, that is, a partial luminous flux having the first polarization direction which allows transmission of the polarization separation film and a partial luminous flux having the second polarization direction which is reflected by the polarization separation film.
Of the two kinds of polarization luminous fluxes, the polarization direction of one of the polarization luminous fluxes is rotated about 90° by passing through a retardation film (polarization direction rotation element) such as a &lgr;/2 wavelength plate. Since the first color partial luminous flux and the second color partial luminous flux enter different films (polarization separation film and reflective film), respectively, the first color partial luminous flux and the second color partial luminous flux are uniformed in different polarization directions such that the first color partial luminous flux is uniformed in a first polarization direction and the second color partial luminous flux is uniformed in a second polarization direction.
For example, every first color partial luminous flux is arranged in S polarization light and every second color partial luminous flux is arranged in P polarization light. Then these partial luminous fluxes are superposed at the illuminated area through the superposition optical element. The transmission optical element has a function to transmit each partial luminous flux to the illuminated area The transmission optical element can be disposed either at the incident side or at the emitting side of the polarization change element. If the transmission optical element is disposed at the incident side of the polarization change element, each partial luminous flux becomes possible to enter the polarization change element at a predetermined angle,
Adams Russell
Seiko Epson Corporation
Sever Andrew
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