Optics: image projectors – Polarizer or interference filter
Reexamination Certificate
1996-10-17
2002-05-21
Dowling, William (Department: 2851)
Optics: image projectors
Polarizer or interference filter
C353S031000, C353S084000, C349S009000
Reexamination Certificate
active
06390626
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to image projection engines. More particularly, the present invention relates to an image projection engine that provides a polarized image for use in, for instance, a “folded” projection system.
2. Description of the Related Art
High power lamps are used for illumination applications beyond typical incandescent and fluorescent lamps. One type of lamp known as a high intensity discharge (HID) lamp consists of a glass envelope which contains electrodes and a fill which vaporizes and becomes a plasma when the lamp is operated.
Recently, a patent issued for a high power lamp that utilizes a lamp fill containing sulfur or selenium or compounds of these substances. U.S. Pat. No. 5,404,076, issued to Dolan et al. and entitled “Lamp Including Sulfur” discloses an electrodeless lamp utilizing a fill at a pressure at least as high as one atmosphere. The fill is excited at a power density in excess of 50 watts per square centimeter. A lamp utilizing the fill is excited at a power density of at least 60 watts per square centimeter. The Dolan et al. patent is incorporated herein by reference. Other pressures and power densities can be employed.
Projecting systems are used to display images on large surfaces, such as movie or television screens and computer displays. For example, in a front projection system, an image beam is projected from an image source onto the front side of a reflection-type angle transforming screen, which then reflects the light toward a viewer positioned in front of the screen. In a rear projection system, the image beam is projected onto the rear side of a transmission-type angle transforming screen and transmitted toward a viewer located in front of the screen.
Projection engine designs are not new. For example, in U.S. Pat. No. 5,453,859 (hereby incorporated by reference), a system is shown that uses a polarization beam splitter along with a dichroic “X-cube” to create a color image. Referring to FIG. 14 of that patent, it is seen that polarized light from a light source 91 is reflected by a polarization beam splitter to a dichroic prism 95. The reflected light is S-polarized, or polarized normal to the plane of incidence within the prism 93. This S-polarized light is then passed through a quarter wave plate 94, which circularly polarizes that S-polarized light. For each pixel that is in the “off” position, that circularly polarized light is reflected unchanged by the corresponding pixel of a reflective LCD 96, 97, and 98. Then, that circularly polarized light is restored to its original S-polarized state on the return path through the quarter wave plate 94. That light is then reflected back towards the light source by the prism 93.
For pixels that are to be lit, the LCDs 96, 97, and 98 convert some of the circularly polarized light to elliptically polarized light. When this light is passed through the quarter wave plate 94, the light passed will not be solely S-polarized, but will instead include a P-polarized component, which is passed through the prism 93, through a projection lens 99, and into whatever projection system is used.
Displaytech, Inc., in a 6-page technical disclosure entitled “FLC/VLSI Display Technology” and dated Dec. 1, 1995; Parfenov et al., in “Advanced optical schemes with liquid crystal image converters for display applications,” SPIE Proceedings, Volume 2650, pages 173-179 (Jan. 29-31, 1996); and Baur et al., in “High performance liquid crystal device suitable for projection display,” SPIE Proceedings, Volume 2650, pages 226-228 (Jan. 29-31, 1996), disclose background information on the use of liquid crystal devices to process video images. These papers are hereby incorporated by reference.
SUMMARY OF THE INVENTION
The present invention provides an improved projection engine. Polarized light from a light source is reflected by a polarizer/analyzer (such as a 3M DBEF material) which reflects only the S-polarized components of light and transmits P-polarized components of light.
One of the polarized components of light is passed to an image engine that forms an image by shifting the polarity of portions of the light. For example, the S-polarized light can be passed to a dichroic X-cube beam splitter/combiner (or other beam splitter/combiner for splitting the S-polarized light into red, green, and blue components when light passes through the beam splitter/combiner in a first direction and for combining red, green, and blue components when light passes through the beam splitter/combiner in a second direction) which provides red, green, and blue light to spatial light modulator type liquid crystal displays. Alternatively, the beam splitter/combiner could be omitted and a color sequential technique could instead be used to provide colored light. In addition, a combination of the two techniques can be employed. The liquid crystal displays alter the polarity of the S-polarized light so that the reflected light is S-polarized, P-polarized, or elliptically polarized with both S-polarized and P-polarized components, depending on the amount of light that is to be transmitted to the display and the type of spatial light modulator. This light, if the polarity is unchanged, is reflected back to the light source by the polarizer/analyzer. Any P-polarized components, however, are passed through the polarizer/analyzer and on to the display.
Using this system, a variable intensity of each color can be applied with each pixel, and each resulting pixel is generated through the coaligned colors of light. Further, the optics are highly efficient, because virtually all of the source light of an “on” pixel is transmitted for display and virtually all of the source light of an “off” pixel is returned to the lamp where its energy may be recovered.
The beam splitter/combiner is chosen such that there is either no alteration of the polarity of light passing therethrough (the preferred situation) or a consistent, predictable alteration of the polarity so that compensation for the alteration of polarity can be made by controlling the LCDs. For example, if a beam splitter/combiner that is chosen for use alters the polarity of green light passing back and forth through it one quarter wave total, the LCDs for the green light would be adjusted such that if one wanted a dark pixel, one would cause the LCD to alter the polarity back one quarter wave in the opposite direction to end up with a green light beam that is reflected back at the source from the DBEF reflective surface.
The present invention preferably comprises a projection display apparatus comprising:
a source of rays of polarized light;
a 3M DBEF reflecting polarizer aligned at an angle to the rays of polarized light for passing substantially all of the rays of polarized light which are polarized in a first direction and for reflecting substantially all of the rays of polarized light which are polarized in a second direction;
a beam splitter/combiner, having a first, primary incidence plane aligned with the reflected polarized light for splitting the rays of polarized light which are polarized in the second direction into blue, green, and red light rays;
a first reflecting polarizing LCD for receiving the blue light rays from the beam splitter/combiner, shifting the polarization of none, some, or all of the blue light rays, and directing the blue light rays back into the beam splitter/combiner;
a second reflecting polarizing LCD for receiving the green light rays from the beam splitter/combiner, shifting the polarization of none, some, or all of the green light rays, and directing the green light rays back into the beam splitter/combiner;
a third reflecting polarizing LCD for receiving the red light rays from the beam splitter/combiner, shiffing the polarization of none, some, or all of the red light rays, and directing the red light rays back into the beam splitter/combiner; and
a lens for receiving and transmitting substantially all of the rays of polarized light which are polarized in the first direction and which have passe
Dowling William
Duke University
Fleshner & Kim LLP
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