Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2000-05-31
2002-01-08
Epps, Georgia (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C359S621000, C359S490020, C359S490020
Reexamination Certificate
active
06337759
ABSTRACT:
BACKGROUND OF THE INVENTION
Unevenness due to the light distribution characteristics of a light source may be reduced in an illuminating optical system, such as a liquid crystal projector, even if a light source having an irregular light distribution, such as a metal halide lamp, a xenon lamp, a halogen lamp, or the like, is used. A system called a light integrator is known that uses one or more lenticular lens arrays arranged in the light path in order to make the light more even.
FIGS.
10
(A) and
11
(A) are sectional views of portions (namely, from a light source to a polarization converter), of prior art illuminating optical systems. FIGS.
10
(B) and
11
(B) are views of the components shown in FIGS.
10
(A) and
11
(A), respectively, as seen from the light modulator side of a projection-type display device.
More specifically, the prior art illuminating optical systems of FIGS.
10
(A) and
11
(A) each includes a light source
910
formed of a lamp
904
and a reflector
901
, a first integrator plate
911
A (formed of a first lenticular lens array), a second integrator plate
911
B (formed of a second lenticular lens array), a polarization converter
911
C and a field lens (not shown), listed in the order that light progresses through the system. The first integrator plate
911
A is configured by arranging a plurality of lens elements into a two-dimensional array to form a lenticular lens. Similarly, the second integrator plate
911
B is configured by arranging a plurality of lens elements into a two-dimensional array to form a lenticular lens. The first integrator plate
911
A divides the single beam from the reflector
901
, which single beam has a large spatial unevenness of luminosity, into multiple divided light beams, with the number of divided beams being the same as the number of lens elements in the first integrator plate
911
A. The spatial variation of the luminous flux in the divided beams is smaller than the spatial variation of the single luminous flux before the division. Each divided beam is then incident onto a respective region of the second integrator plate
911
B. The second integrator plate and a field lens operate to direct each divided light beam so that all divided light beams overlap one another at an illuminated area, thereby achieving an even illumination in the illuminated area.
Moreover, each member is arranged within an optical system so that the second integrator plate
91
lB and the pupil of a projection lens are at conjugate positions of the optical system and so that the lamp(s)
904
and the first integrator plate
911
A are at conjugate positions of the optical system, thus providing a projection-type display device wherein the second integrator plate serves as a secondary light source. If the light modulator is formed using a liquid crystal light modulator, a liquid-crystal projection-t ype display is thus provided.
The prior art polarization converter
911
C is arranged, relative to the first integrator plate and the second integrator plate, nearer the second integrator plate
911
B. Images of the light source are formed on the second integrator plate, and the polarization converter efficiently converts the unpolarized light from the light source into linearly polarized light having a single polarization direction. Such a polarization converter is disclosed in U.S. Pat. No. 5,986,809 and includes pairs of prisms with each prism supporting a polarizing beam splitter film
971
or a reflection film
972
inclined at an angle relative to an optical axis (FIGS.
10
(A) and
11
(A)). These films are alternately arranged in a row across the light beam. Thus, there are alternately arranged across the light beam polarizing beam splitter surfaces and reflecting surfaces. Such a structure is herein termed a “comb polarization-separation prism array”. Further, half-wave phase retardation plates
963
(hereinafter termed half-wave plates) are arranged on every surface from which the polarized light exits from the comb polarization-separation prism array (i.e., in those light paths of either the transmitted p-polarized component or the reflected s-polarized component so as to rotate the polarization of one of these components 90 degrees, thereby converting the unpolarized light incident on the polarization converter into light exiting the polarization converter that is uniformly polarized.) In
FIGS. 10 and 11
, half-wave plates
963
are arranged only on those surfaces where the p-polarized light exits the comb polarization-separation prism array. Of course, alternatively, the half-wave plates
963
could be arranged instead on those surfaces where the s-polarized light exits the comb polarization-separation prism array.
Japanese Laid-open Patent Application 8-304739 uses an integrator plate having such a lens array, so that the unevenness of illumination onto a light modulator is reduced. Further, the illumination optical system is compact and provides a bright image. By combining an integrator plate and a polarization converter in such a manner, unpolarized light emitted from a light source may be illuminated onto an illuminating area as light having a single polarization without any significant loss of light. Thus, the light from a light source is efficiently used.
Moreover, a light source, a polarization converter and other members are arranged so as to locate an image of the light source(s) near the polarization-separation film of the polarization converter. Thus, even when the unpolarized light from the light source is split into p-component and s-component light fluxes, the luminous flux is not widened and a compact optical system may be provided.
When the shapes of the light source images formed on the second integrator plate are significantly different (depending on the locations of lens array elements, such as near the optical axis versus at the periphery of the array) light is often wasted. Sections having low illumination efficiency may be formed in a polarization converter having polarizing beam splitter films and reflection films arranged only in one direction.
Additionally, when the shapes of each lens array element of the second integrator plate are different and, particularly, when each lens array element is arranged with a relatively fine pitch in the same direction as the arrangement direction of the polarizing beam splitter films and reflection films, a polarization converter has to have its polarizing beam splitter films and reflection films arranged with a correspondingly fine pitch. This is required in order to provide a high illumination efficiency and for compactness.
An illuminating optical system is disclosed in Japanese Laid-open Patent Application 11-108909 by the present applicant. This illuminating optical system uses a plurality of light sources and has a large spatial variation of luminosity among the light sources. Thus, the shapes of the lens array elements of the second integrator plate differ. However, even with a single light source, the luminous flux has a large spatial variation so that the shapes of the lens array elements of the second integrator often differ.
BRIEF SUMMARY OF THE INVENTION
The present invention provides a polarization converter which has a simple structure that can convert unpolarized light to polarized light having a uniform direction of polarization even when the shapes of light source images formed on a second integrator plate are significantly different from each other, due to the location of lens array elements, and even when the shapes of the lens array elements of the second integrator plate differ. The present invention also provides the above-described polarization converter in combination with a projection-type display device.
The polarization converter of the present invention has at least two regions, with each region including adjacent prisms arranged side-by-side in a row. The prisms support films along the row that are arranged in pairs, each film pair including a polarizing beam splitter film and a reflection film. The row of adjacent prisms in one region is oriented n
Arnold Bruce Y.
Arnold International
Epps Georgia
Fuji Photo Optical Co., Ltd.
Lucas Michael A.
LandOfFree
Polarization converter and projection-type display device... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Polarization converter and projection-type display device..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Polarization converter and projection-type display device... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2850779