Optical: systems and elements – Single channel simultaneously to or from plural channels – By partial reflection at beam splitting or combining surface
Reexamination Certificate
2002-05-30
2004-03-09
Epps, Georgia (Department: 2873)
Optical: systems and elements
Single channel simultaneously to or from plural channels
By partial reflection at beam splitting or combining surface
C359S640000, C359S618000, C359S629000, C359S636000, C359S834000
Reexamination Certificate
active
06704144
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to the image display systems that utilize color separation prisms. More particularly, this invention relates to an improved method and configuration for assembling a color separation prism assembly compensated for contrast enhancement and implemented as reflective imager.
BACKGROUND OF THE INVENTION
A technical difficulty of compound angle depolarization is still confronted by those of ordinary skill in the art in designing and assembling reflective imager type projection display systems implemented with a polarization beam splitter (PBS). Color separation prisms are placed between quarter wave plate (QWP) and imager cause undesirable phase changes at the tilted dichroic and total internal reflection (TIR) surfaces. System performance is degraded because of the poor contrast. A quarter wave plate (QWP) placed between polarization beam splitter (PBS) and reflective imager will correct compound angle depolarization. However, the process required to glue the QWP adds to the processing complexities that causes difficulties in mass production. Thin films with optical characteristics to control phase difference can be coated on the total internal reflection and dichroic reflection surfaces to mitigate the effects caused by undesirable phase changes. However, existing color separation prism assemblies, as will described below, are faced with the difficulties that the assemblies become quite massive and occupy a large volume in order to provide color separation for a third color channel.
The limitation can be understood by examining a prior art patent issued to Bryars et. al. U.S. Pat. No. 6,144,498, entitled “Color Separation Prism Assembly and Method for Making Same”. This patent discloses a color separation device assembled from three prisms in an arrangement that provides for air equivalent thickness adjustment for each color. The air equivalent thickness adjustment provides for the correction of deviations in any of the three prisms, as well as providing a method to correct for the chromatic aberration arising from other optical elements in the information display system. The color separation device is disclosed to improve the image quality and provides opportunities to lower the display system cost by using low tolerance components and/or plastic optical components normally having a high chromatic aberration.
As discussed in Bryars et al. the combination of dichroic filters and prisms is commonly used in color imaging and display systems as a way to separate colors or combine the primary colors into the final image. A compact optical element that accomplishes this purpose is known as a Philips prism. The Philips prism assembly is commonly known, and various uses thereof are described in U.S. Pat. Nos. 2,392,978, 3,659,918, 4,009,941, 4,084,180, and 4,913,528, the disclosures of of these patents and that by Bryars et al. in U.S. Pat. No. 6,144,498 are incorporated herein by reference.
Referring to
FIG. 1A
for a perspective view of a conventional Philips prism assembly
10
. The prism assembly
10
includes a first triangular prism
12
and a second triangular prism
14
, with a third prism
16
having at least four sides. The triangular prisms
12
and
14
are positioned with respect to each other to provide an air gap
18
at their interface. The second triangular prism
14
and third prism
16
are optically cemented at an interface
20
of these prisms. As indicated in
FIG. 1
, prism
12
is configured to separate red light (R), prism
14
is configured to separate blue light (B), and prism
16
is configured to receive green light (G). The light ray paths through prism assembly
10
are shown in FIG.
1
. An incident ray i passes into prism
12
, with a portion thereof (e.g. red light) internally reflected and emerging from prism
12
as r
1
. The remaining portion of the incident light passes into prism
14
, with a portion thereof (e.g., blue light) internally reflected and emerging from prism
14
as r
2
. The remaining portion of the incident ray (e.g., green light) emerges from prism
16
as r
3
. A color separation into red, green and blue (RGB) is therefore achieved with this Philip prism.
For a purpose to correct for the chromatic aberration of the optical system components, U.S. Pat. No. 6,144,498 discloses a color separation prism assembly as that shown in FIG.
1
B.
FIG. 1B
is a ray diagram for a prism assembly
30
where prism
14
is assembled with an offset with respect to prisms
12
and
16
from the nominal position. The dashed arrowhead line in prism
14
represents the physical path for a prism assembly having no deviation from the nominal design. The dashed line in prism
12
represents the nominal position for the now longer side of prism
12
forming the exit facet adjacent prism
14
. The solid segment lines in prism
30
represent the actual physical path caused by the deviations in prisms
12
and
14
utilized to assemble prism
30
in the corrective offset position. The prisms are offset in one dimension whereby the parallel relationship between connected facets is maintained and the path lengths are equalized such that: (ABCD)new=(ABA‘B’C‘D’)new. The prism
16
is displaced a distance away from the common edge with prism
14
by translating its common facet parallel to the interface. The amount of displacement for prism
16
is calculated such that: (ABCD)new=(ABA‘B’A“B”) new. The prisms as disclosed above all have large volume. In the Philip prism assemblies described above, compensating foils on the reflection surface are used and the third prism is cut into two and one tilted interface is added to properly control the differential phase shift incurred in optical transmission. The assemblies are made with prisms of different shapes thus requires more complex assembling processes that lead to higher production cost and lower product yield and poor reliability.
Referring to
FIGS. 1C and 1D
for alternate prior art color separation prism assemblies disclosed by Greenberg and Bryars that comprises three prisms of distinctly shapes. The third prism is modified such that the third prism is a mirror image of the second prism. A total internal reflection (TIR) surface for the third channel is introduced. This modified prism assembly has an advantage that the prism assembly is more compact than the regular Philip prism assembly described above. However, the modified assembly creates another problem of introducing aberrations due to addition of extra components. Corrections of aberrations through differential phase shifts through transmission cannot be conveniently achieved. Furthermore, as the modified prism assembly still requires more than one types of prisms, the increase of manufacturing costs due to processes in handling different types of prisms is still not resolved.
Therefore, a need still exists in the art to provide a new and improved color separation prism assembly to overcome the above difficulties and limitations. A simplified, more compact and more economical color separation prism assembly would be desirable to further advance the state of the art of prism assembly for color separation applications.
SUMMARY OF THE PRESENT INVENTION
It is therefore an object of the present invention to provide a color separation prism assembly that is more compact in size and weight and can be more conveniently manufactured and assembled such that the difficulties and limitations encountered by the prior art can be resolved.
Specifically, it is an object of the present invention to provide a new and improved prism assembly configured with three triangular prisms of identical size and shape. These three triangular prisms are further assembled into a combined prism with internal interfacing surfaces coated with dichroic filtering film for separating light into color beams. The combined prism assembled with three prisms of same shape and size is more compact and can be more conveniently manufactured and assembled by simplified processes with reduced production cost.
Another obj
Dinh Jack
Epps Georgia
Lin Bo-In
LandOfFree
Color separation prism assembly compensated for contrast... does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Color separation prism assembly compensated for contrast..., we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Color separation prism assembly compensated for contrast... will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-3212604