Title: Two panel optical engine for projection applications
Abstract: Optical engines using a reduced number of components offer advantages over more complex optical systems. Three panel optical engines have offered the advantage of relatively high throughput but at the cost of complexity and increased components on the bill of materials. Conventional two-panel engines have required the use of complex retarder structures to achieve the dual polarizations state for the three primary colors. The present invention achieves this goal while using simpler optical retarders.
Patent Number: 7,008,064 Issued on 03/07/2006 to McDonald
| Inventors:
|
McDonald; David Charles (Longmont, CO)
|
| Assignee:
|
eLCOS Microdisplay Technology, Inc. (Sunnyvale, CA)
|
| Appl. No.:
|
700643 |
| Filed:
|
November 3, 2003 |
| Current U.S. Class: |
353/84; 353/20; 353/31; 359/891 |
| Current Intern'l Class: |
G03B 21/14 (20060101); G03B 21/00 (20060101); G02B 5/22 (20060101) |
| Field of Search: |
353/30,31,33,34,81,84,94,97,20,122
349/5,8,9
359/490,496,501,502,887,890-892
|
References Cited [Referenced By]
U.S. Patent Documents
| 4500172 | Feb., 1985 | Gagnon et al.
| |
| 5517340 | May., 1996 | Doany et al.
| |
| 5921650 | Jul., 1999 | Doany et al.
| |
| 6309071 | Oct., 2001 | Huang et al.
| |
| 6402323 | Jun., 2002 | Shiue et al.
| |
| 6568815 | May., 2003 | Yano.
| |
| 6773111 | Aug., 2004 | Yamamoto.
| |
| Foreign Patent Documents |
| PCT/US00/13063 | Aug., 2000 | WO.
| |
Primary Examiner: Perkey; W. B.
Assistant Examiner: Sever; Andrew
Attorney, Agent or Firm: Lin; Bo-In
Parent Case Text
This Application is a Formal Application and claim a Priority Date of Nov. 5,
2002 benefited from a Provisional Patent Application 60/424,213 file by one common
inventor of this Patent Application.
Claims
I claim:
1. An optical engine comprising:
a color wheel to alternatively derive at least two separate composite lights;
a dichroic device to sequentially separate said at least two composite lights
into a first color path and a second color path;
an optical retarder to modify a polarization state for one of said first and
second color paths; and
a color combiner for receiving a first and a second beams of light projected
from said first and second light path respectively to reconstitute a combined beam
of light comprising two different colors with mutually orthogonal polarization states.
2. The optical engine of claim 1 further comprising:
a polarizing beam splitter (PBS) for receiving and splitting said combined beam
according to a polarization state for projecting to two microdisplay panels.
3. The optical engine of claim 2 further comprising:
a projection lens to receive and project light from the polarizing beamsplitter.
4. The optical engine of claim 3 further comprising:
a linear polarizer disposed between said polarization beam splitter and said
projection lens for preventing a transmission of selected beam of specific color
and specific polarization.
5. The optical engine of claim 3 further comprising:
a linear polarizer disposed between said polarization beam splitter and said
projection lens for preventing a transmission of a red color beam of a p-polarization.
6. The optical engine of claim 2 further comprising:
a quarter wave plate retarder disposed between at least one of said microdisplay
panels and said polarizing beam splitter (PBS).
7. The optical engine of claim 1 wherein:
said color wheel further drives two composite lights comprising a yellow light
and a magenta light.
8. The optical engine of claim 1 wherein:
said dichroic device separating said composite lights into a red path and a green-or-blue path.
9. The optical engine of claim 1 wherein:
said optical retarder to modify a polarization state for one of said first and
second color paths further comprising a half-wave optical retarder for changing
a polarization by ninety degrees.
10. The optical engine of claim 1 further comprising:
a linear polarizer disposed right after said optical retarder in one of said
first and second color paths.
11. A method for configuring an optical engine comprising:
driving at least two separate composite lights by employing a color wheel for
driving a yellow light and a magenta light;
sequentially separating said at least two composite lights into a first color
path and a second color path with;
employing an optical retarder to modify a polarization state for one of said
first and second color paths; and
receiving a first and a second beams of light projected from said first and second
light path respectively to reconstitute a combined beam of light comprising two
different colors with mutually orthogonal polarization states.
12. The method of claim 11 further comprising:
employing a polarizing beam splitter (PBS) for receiving and splitting said combined
beam according to a polarization state for projecting to two microdisplay panels.
13. The method of claim 12 further comprising:
receive and projecting a beam of light from said polarizing beamsplitter (PBS).
14. The method of claim 13 further comprising:
disposing a linear polarizer between said polarization beam splitter and a projection
lens for preventing a transmission of a selected beam of specific color and specific polarization.
15. The method of claim 13 further comprising:
disposing a linear polarizer disposed between said polarization beam splitter
and a projection lens for preventing a transmission of a red color beam of a p-polarization.
16. The method of claim 11 wherein:
said step of separating said composite lights further comprising a step of employing
a dichroic device for separating said composite lights into a red path and a green-or-blue path.
17. The method of claim 11 wherein:
said step of employing said optical retarder to modify a polarization state for
one of said first and second color paths further comprising a step of employing
a half-wave optical retarder for changing a polarization by ninety degrees.
18. The method of claim 11 further comprising:
disposing a linear polarizer right after said optical retarder in one of said
first and second color paths.
19. The method of claim 11 further comprising:
disposing a quarter wave plate retarder between at least one of said microdisplay
panels and said polarizing beam splitter (PBS).
Description
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention pertains to liquid crystal display (LCD) systems, and more
particularly to improved two panel optical engines using simpler optical retarder
for color display projection.
2. Description of the Prior Art
As earlier research projects in developing microdisplay systems using the liquid
crystal display technologies were mostly for military and specialized applications
with high performance requirements, the systems were generally configured without
much concern for production costs. However, some of the configurations as developed
earlier now become quite costly when the microdisplay systems are commercialized
for high definition TVs and used as monitor for computers. One particular system
is the simplified two panels display configurations while cost savings are achieved
with two instead of three color display panels, the optical components used for
color path separation and polarization modifications as disclosed by the conventional
configurations are specially made thus unduly increases the production cost of
such systems.
It is well known that the complexity of on-axis optical engines has hindered
the
development of cost-effective liquid crystal on silicon display devices for projection
applications. The earliest developments were based on earlier reflective light
valve efforts that were manufactured to high levels of performance at great cost
for industrial and military uses. The more recent approaches have been for application
in commercial display products such as data monitors and television receiving sets.
While much of the earlier work remains relevant to background, improved solutions
of lower cost have been sought.
The earliest attempts to solve this problem have required compromises. For example,
in U.S. Pat. No. 4,500,172, a two-panel reflective display architecture is disclosed
that is limited to modulated light of two primary colors displayed on a constant
background of the third primary color. Two beams of polarized colored light, said
two beams of light having different spectra, are directed onto one surface of a
polarizing beamsplitter. The two reflective displays are arrayed on two remaining
faces of the polarizing beamsplitter. The fourth port of the polarizing beamsplitter
delivers the combined beams to a lens group for projection onto a viewing screen.
Later, Sharp et al disclose in PCT Application WO 00/7-376 a two-panel architecture
requiring the use of color selective retarder stacks that separate linearly polarized
light into orthogonal polarized beams of light based on the spectrum of the light.
The orthogonally polarized beams of light are then separated by a polarizing beamsplitter
(PBS) and directed onto the faces of two different microdisplays for image generation.
The optical architecture therein is efficient and practical, but suffers in application
because of the high cost and limited supply of the color selective retarder stacks.
For these reasons, there is still need and challenge in the art of microdisplay
such as a two-panel liquid crystal on silicon (LCOS) display to provide improved
system architecture and methods for polarization and color separation.
SUMMARY OF THE PRESENT INVENTION
It is therefore an object of the present invention to provide new and simplified
means to process color path separation through polarization modifications and then
recombination to achieve flexibly manageable color intensity adjustments dependent
upon the background color of particular light source. The new and simplified color
path separation and polarization modifications employ dichroic trim filters and
optical retarder that are commercially available and of low cost while achieve
high quality color display effect such that the aforementioned difficulties and
limitations can be overcome.
The present invention is a reduced-cost two-panel projection engine optical architecture
suitable for use as a data monitor, television display device, or front projection
system for application at home or business locations. The invention makes use of
convention materials throughout for reduced cost and good performance.
Briefly, in a preferred embodiment of the present invention, this invention
discloses an optical subsystem to separate color paths of a color-composite light
that includes a dichroic device to separate the color-composite light into a first
color path and a second color path. The optical subsystem further includes an optical
retarder to modify a polarization state for one of the first and second color paths
whereby the lights of transmitted over the first and second light path may be recombined
and processed by a polarization beam splitter (PBS). In a preferred embodiment,
the optical retarder further comprising a half-wave retarder to modify a ninety-degrees
polarization state between light beams transmitted along the first and second color
paths. In another preferred embodiment, the optical subsystem further includes
a color combiner for receiving light beams transmitted along the first and a second
color paths to reconstitute a combined beam of light comprising two different colors
with mutually orthogonal polarization states. In another preferred embodiment,
the optical subsystem further includes a polarizing beam splitter (PBS) for receiving
and splitting the combined beam according to a polarization state for projecting
to two microdisplay panels. In a specific embodiment, the dichroic device further
separating the composite light into a red path and a green-or-blue path. In another
specific preferred embodiment, the optical subsystem further includes a linear
polarizer disposed right after the optical retarder in one of the first and second
color paths.
These and other objects and advantages of the present invention will no doubt
become obvious to those of ordinary skill in the art after having read the following
detailed description of the preferred embodiment, which is illustrated in the various
drawing figures.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 depicts the present invention of a two-panel liquid crystal on silicon
display device, and
FIG. 2 depicted a dichroic color wheel the forms part of the present invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
Referring to FIG. 2 for a two-panel engine
100 of this invention.
The two panel optical engine
100 as shown in FIG. 2 can be divided into
three major subsections. These three subsections are 1) an illumination subsection
101 for providing illumination for the optical engine; 2) a color generation,
polarization and color separating subsection
102 that includes a means for
separating different colors into orthogonal polarization states, and imaging and
3) a projection subsection
103 that includes means for generating composite
color images.
In the illumination subsection
101, a high intensity discharge (HID) lamp
or other suitable illumination generating system generates an illumination beam
of light
55. A reflector, integrating sphere, or other suitable means is
used to focus the light from the HID lamp. Since the specific details of the means
for focusing the light beam is not part of the invention, for the sake of clarity,
these details are not further provided. The illumination beam of light
55
may be un-polarized, linearly polarized or circularly polarized.
The beam of light
55 is directed through color wheel
60. As is
well known in the art, color wheel are used to separate light into color temporally.
The duration of each color is determined by the rotation rate and diameter of the
color wheel at the point of illumination, and by the length of the different color
segments. FIG. 2, described later, presents one embodiment of the color wheel.
For the present example it is assumed that the segments of the color wheel alternatively
pass first red and green light (hereafter referred to as yellow) and then red and
blue light (hereafter referred to as magenta.) Thus exiting beam of light
65
is alternatively color yellow and magenta. The beam of light
65 then passes
through optical component
70. Optical component
70 may perform a
number of different functions by receiving the light from the color wheel and modify
it to a beam as that required by the remainder of the system. The optical component
70 may also include other elements such as a polarization conversion system
(PCS) to take incident unpolarized light
65 and convert it to substantially
polarized light
75. The light then passes from subsection
101 to
subsection
102 for subsequent functions of separation by spectrum and polarization.
The first function of subsection
102 is to polarize the incident light
75 more thoroughly. It is the nature of PCS units as implemented in the
optical component
70 that the resultant light
75 may contain up to
10% or 15% of light that is incorrectly polarized. To convert this to polarized
light with fewer incorrectly polarized components, a polarizing element
80
is included. While element
80 may be considered optional to the design,
the performance without it would normally be of unacceptably low contrast, as is
well known. The vertical arrows
85 depicts that the output beam
90
from the polarizing element
80 is a p-polarized light. For the convenience
of illustration, this convention will be employed through the remaining descriptions
of this invention.
Depending on the time sequencing of the color wheel, the incident p-polarized
beam of light
90 alternates as a light beam that comprises the red and blue
primary colors or the red and green primary colors. When beam of light
90
passes through a dichroic trim filter
140, the resultant light is separated
into p-polarized red beam of light
155 and p-polarized green or blue beam
of light
145. The dichroic trim filter
140 trims blue and green light
and passes red light. The passed beam of light
155 reflects from mirror
150 and projected to color combiner
170. The mirror
150 is
preferably a first surface mirror although other types of mirrors, such as dielectric
mirrors, may also serve the purpose. The color combiner
170 is a red trim
filter that passes blue and green light and reflects red light and is based solely
on spectrum. The spectral characteristics of the color combiner
170 may
be mismatched to that of the color separator
140 to create a notch between
red and green, should that be needed to eliminate objectionable features typical
of high pressure mercury lamps, such as the yellow spike at 578 nanometers wavelength.
The p-polarized beam of light
145 passes from the color separator
140
and is reflected by a mirror
160 and then projected to a retarder device
130. The mirror
160 is, as is the case for mirror
150, preferably
a first surface mirror but alternatively may be a dielectric or other mirror. The
retarder device
130 is a half wave retarder and is arranged to have a particular
orientation such that p-polarized light entering the retarder exits as s-polarized
light. Because the retarder must be able to rotate the polarizations of both green
light and blue light, an achromatic retarder may be preferred. Such retarder designs
are now quite common and are therefore not further described. The orientation of
the first optical axis of retarder device
130 may be aligned at 45 degrees
to the orientation of the incident p-polarized beam
145 as this would normally
result in an exiting beam of light with plane of polarization rotated by 90 degrees
to the plane of polarization of the incident light. For the convenience of illustration
and description, hereafter this light
165 will be referred to as s-polarized
light. The polarizing element
135 is optionally placed adjacent to and after
retarder element
130 to clean up the exiting polarization of the retarder
element and insure that no element of the incident light emerges with the incorrect
polarization. The S-polarized beam of light
165 emerges from retarder element
130 and from optional polarizing element
135 and projects to color
combiner
170. At this point color combiner
170 merges the s-polarized
blue or green beam of light
165 with p-polarized red beam of light
155
to form a composite beam of light
205, where the beam of light
205
comprises light of two different spectra where the two different spectra are of
orthogonal polarization states. The beam of light
205 then exits subsection
102 and enters into subsection
103.
As the beam of light
205, now comprises p-polarized red light and s-polarized
blue or green light, enters into a polarizing beamsplitter
210, the beamsplitter
divides beam
205 into p-polarized red beam of light
232 and s-polarized
green or blue beam of light
222 and then directs those beams to different
ports on the polarizing beamsplitter.
The p-polarized red beam of light passes through PBS
210 to project to
a reflecting microdisplay
230. The reflecting microdisplay
230 is
constructed such that it is optimized to reflect red light. Optionally the design
may include a quarter wave retarder element
235 disposed between polarizing
beam splitter
210 and reflective microdisplay
230. Use of a quarter
wave retarder is highly recommended when the polarizing beam splitter is a traditional
glass device of the MacNeille type. In an alternate embodiment, the quarter wave
retarder
235 may not be necessary when the polarizing beam splitter is a
wire grid polarizer of the type now commercially available by Moxtek Corporation
of Orem, Utah. The advisability of a quarter wave retarder in such applications
is fully disclosed and clearly explained by Rosenbluth et al in their paper "Contrast
Properties of Reflective Liquid Crystal Light Valves in Projection Displays," published
in the IBM Journal of Research and Development, Vol. 42, No. 3/4, dated July 1998,
the disclosures made in the publication are hereby incorporated by reference in
the present Patent Application. The polarized beam of light
232 incident
upon reflecting microdisplay
230 has its polarization state modified in
some respect by the state of the liquid crystal material within microdisplay
230.
The device physics of this rotation according to the designs of the display dictates
the degree and type of modifications and that is a way by which information is
encoded by the microdisplay into the beam of light. Reflected beam of light
233
now consists of a number of differing time-variant polarization states based on
the continuing drive state of reflective microdisplay
230. Reflected beam
of light
233 enters polarizing beamsplitter
210, where the s-polarized
components of said beam of light are reflected to form part of composite beam of
light
245. Thus the polarization states encoded in beam of light
233
are converted into intensity variations within beam of light
245.
Likewise the s-polarized beam of light
222 is directed by the polarizing
beamsplitter
210 to a reflective microdisplay
220. As previously
mentioned, the s-polarized beam of light
222 is alternatively green or blue
and the alternations of colors depending on the time sequence of color wheel
60
described earlier. The beam of light
222 may pass through a quarter wave
retarder
225 for transmitting to the reflective microdisplay
220.
Again, the quarter wave retarder
225 is optional and depends on the types
of PBS
210 implemented in the optical engine as described above. It may
be necessary to implement the quarter wave retarder
225 as an achromatic
retarder having a retarding wavelength across the green and blue spectrum because
of the need to perform its function across a somewhat wider spectrum of light than
is required of quarter wave retarder
235. The reflected beam of light
223
is returned to polarizing beam splitter
210. The beam of light
223
comprises a number of time-variant polarization states, and the polarization states
depending solely on the drive state of the liquid crystal array in reflecting microdisplay
220. As beam of light
223 passes through polarizing beamsplitter
210, the p-polarized components of beam of light
223 are separated
by the PBS
210 to form part of composite beam of light
245. Thus
the polarization states encoded on beam of light
223 are converted into
intensity variation within composite beam of light
245.
As a design option, a color polarizer
250 is disposed between polarizing
beamsplitter
210 and projection lens
250. This filter may be relocated
to other positions within the projection path, but the described position is preferred
so that plastic lenses and the like may be used in the projection lens design without
concern for the ultimate quality of the image. Because composite beam of light
245 includes s-polarized red light and because said s-polarized red light
is analyzed by polarizing beamsplitter
210 in reflection, it is possible
that there may be some first surface reflections of red light within the composite
beam that are of the orthogonal polarization. Failure to remove these components
may result in a final image with lower contrast in the red color than is desirable.
The function of optional red polarizer
250 is to remove said unwanted components
without disturbing the blue or green p-polarized light components. Such polarizers
are well known in the art. It would be acceptable for the polarizing function of
the red polarizer to start at wavelengths as low as approximately 560 nanometers
so as to insure that the polarizer is full polarizing up to a wavelength around
610 nanometers. This may attenuate a slight amount of the green light, but the
bulk of the luminance of green light in high-pressure mercury lamps is located
in a spike at 550 nanometers. Invariably projection systems built using such lamps
must severely attenuate green light to achieve proper color balance.
Based on the foregoing, composite beam of light
255 emerges from optional
red polarizer
250 and enters projection lens
260. The composite beam
of light
255 is identical to composite beam of light
245 if optional
red polarizer
250 is removed. The projection lens
260 modifies beam
of light
255 by magnification and focus and results in a new composite beam
of light
270 that is delivered to the view screen.
FIG. 2 shows a preferred embodiment of the color wheel for this invention. The
color wheel
60 as that depicted in FIG. 1 includes a set of dichroic filter
segments
40 arrayed circumferentially around the hub of the wheel. These
dichroic elements may consist of two or more segments, the length of the segments
varying according to the specific color requirements of the design. In the specific
example of FIG. 2, dichroic color filter
45 may be yellow, in that it passes
both red and green and reflects blue, and dichroic color filter
50 may be
magenta, in that it passes both red and blue and reflects green. Thus as the color
wheel rotates, the spectrum of the light passing through the dichroic segments
alternates between two states. In alternative embodiments, different color segments
may be used. For example, it may be preferred to reduce noise by lowering the rotation
rate. The color field rate may be maintained by increasing the number of color segments.
Numerous alternatives to the choices described above may be made without
exceeding the bounds of the present invention. For example, it may be desirable
to make blue the color that is always on and reduce the time available for red.
In that case, a different dichroic configuration may direct blue to one microdisplay
and red and green alternatively to the other. These alternatives will be obvious
to those skilled in the art.
According to FIGS. 1 and 2 and above descriptions, this invention discloses
an optical engine that includes a color wheel to alternatively derive at least
two separate composite lights. The optical engine further includes a dichroic device
to sequentially separate the at least two composite lights into a first color path
and a second color path and an optical retarder to modify a polarization state
for one of the first and second color paths. The optical engine further includes
a color combiner for receiving a first beam and a second beam of light projected
from the first and second light path respectively to reconstitute a combined beam
of light comprising two different colors with mutually orthogonal polarization
states. In a preferred embodiment, the optical engine further includes a polarizing
beam splitter (PBS) for receiving and splitting the combined beam according to
a polarization state for projecting to two microdisplay panels. In a preferred
embodiment, the color wheel further drives two composite lights comprising a yellow
light and a magenta light. In a preferred embodiment, the dichroic device separating
the composite lights into a red path and a green-or-blue path. In a preferred embodiment,
the optical engine further includes a projection lens to receive and project light
from the polarizing beamsplitter. In a preferred embodiment, the optical retarder
to modify a polarization state for one of the first and second color paths further
comprising a half-wave optical retarder for changing a polarization by ninety degrees.
In a preferred embodiment, the optical engine further includes a linear polarizer
disposed right after the optical retarder in one of the first and second color
paths. In a preferred embodiment, the optical engine further includes a linear
polarizer disposed between the polarization beam splitter and the projection lens
for preventing a transmission of selected beam of specific color and specific polarization.
In a preferred embodiment, the optical engine further includes a linear polarizer
disposed between the polarization beam splitter and the projection lens for preventing
a transmission of a red color beam of a p-polarization. In a preferred embodiment,
the optical engine further includes a quarter wave plate retarder disposed between
at least one of the microdisplay panels and the polarizing beam splitter (PBS).
In essence this invention further discloses a method to configure an optical
subsystem
to separate color paths of a color-composite light that includes steps of disposing
a dichroic device to separate the color-composite light into a first color path
and a second color path and employing an optical retarder to modify a polarization
state for one of the first and second color paths whereby the lights of transmitted
over the first and second light path may be recombined and processed by a polarization
beam splitter (PBS). In a preferred embodiment, the step of employing the optical
retarder further comprises a step of employing a half-wave retarder to modify a
ninety-degrees polarization state between light beams transmitted along the first
and second color paths. In a specific embodiment, the method further includes a
step of employing a color combiner for receiving light beams transmitted along
the first and a second color paths to reconstitute a combined beam of light comprising
two different colors with mutually orthogonal polarization states. In another embodiment,
the method further includes a step of employing a polarizing beam splitter (PBS)
for receiving and splitting the combined beam according to a polarization state
for projecting to two microdisplay panels. In another preferred embodiment, the
step of separating the composite light with the dichroic device further comprising
separating the composite light into a red path and a green-or-blue path. In another
preferred embodiment, the method further includes a step of disposing a linear
polarizer right after the optical retarder in one of the first and second color paths
Although the present invention has been described in terms of the presently
preferred embodiment, it is to be understood that such disclosure is not to be
interpreted as limiting. Various alternations and modifications will no doubt become
apparent to those skilled in the art after reading the above disclosure. Accordingly,
it is intended that the appended claims be interpreted as covering all alternations
and modifications as fall within the true spirit and scope of the invention.
*
