U.S. patent application number 09/728522 was filed with the patent office on 2002-04-18 for sold state light source augmentation for slm display systems.
Invention is credited to Bohler, Christopher L., Poradish, Frank J., Tew, Claude E..
Application Number | 20020044445 09/728522 |
Document ID | / |
Family ID | 26864370 |
Filed Date | 2002-04-18 |
United States Patent
Application |
20020044445 |
Kind Code |
A1 |
Bohler, Christopher L. ; et
al. |
April 18, 2002 |
SOLD STATE LIGHT SOURCE AUGMENTATION FOR SLM DISPLAY SYSTEMS
Abstract
In an SLM-type display system, a solid state light source can be
used to augment a lamp light source in a least two different ways.
First, a solid state source can be used to augment deficiencies in
a particular spectral region. Typically, lamps are deficient in
red, and a red solid state source would be used. However, the same
concept applies to augmenting any color region. Multiple solid
state sources could be used to augment more than one region.
Second, when the SLM system uses a color wheel, a solid state
source can be used to eliminate "spoke loss". Multiple solid state
sources can be used for providing different colors during the
spokes.
Inventors: |
Bohler, Christopher L.;
(Allen, TX) ; Poradish, Frank J.; (Plano, TX)
; Tew, Claude E.; (Dallas, TX) |
Correspondence
Address: |
Charles A. Brill
Texas Instruments Incorporated
M/S 3999
P.O. Box 655474
Dalls
TX
75265
US
|
Family ID: |
26864370 |
Appl. No.: |
09/728522 |
Filed: |
December 1, 2000 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
60168696 |
Dec 3, 1999 |
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Current U.S.
Class: |
362/293 ;
348/E5.142; 348/E9.027; 362/317 |
Current CPC
Class: |
H04N 9/3114 20130101;
G02B 26/0841 20130101; H04N 5/7458 20130101 |
Class at
Publication: |
362/293 ;
362/317 |
International
Class: |
F21V 009/00 |
Claims
What is claimed is:
1. An illumination system for a spatial light modulator,
comprising: a white light source that provides white light in the
visible spectrum; a solid state light source for providing light in
a desired spectral region; a beam combiner for combining a beam of
light from the white light source with light from the solid state
light source, thereby providing augmented illumination; a color
wheel having multiple color segments, for filtering the augmented
illumination; and at least one lens for focussing the light from
the white light source and the light from the solid state light
source along an optical path to the spatial light modulator.
2. The system of claim 1, further comprising additional solid state
light sources for augmenting additional spectral regions of visible
light.
3. The system of claim 1, further comprising at least one mirror
for folding the optical path.
4. The system of claim 1, further comprising timing circuitry for
switching the solid state light source at least one per revolution
of the color wheel.
5. The system of claim 1, further comprising timing circuitry for
switching the solid state source at segment transitions.
6. A method of augmenting illumination for a spatial light
modulator, comprising the steps of: providing a beam of white light
source in the visible spectrum; augmenting the beam of white light
with light from a solid state light source that provides light in a
desired spectral region, thereby providing augmented illumination;
filtering the augmented illumination with a color wheel having
multiple filter segments, thereby providing filtered and augmented
illumination; and focussing the filtered and augmented illumination
on the spatial light modulator.
7. The method of claim 6, wherein the augmenting step is repeated
for more than one spectral region.
8. The method of claim 6, further comprising the step of switching
the solid state light source during revolutions of the color
wheel.
9. The method of claim 6, further comprising the step of switching
the solid state light source at transitions of the color wheel.
10. The method of claim 6, further comprising the step of switching
the solid state light source to coincide with one or more segments
of the color wheel.
11. An illumination system for a spatial light modulator,
comprising: a white light source that provides white light in the
visible spectrum; a color wheel having multiple color segments, for
filtering the light from the white light source, thereby providing
filtered illumination; a solid state light source for providing
light in a desired spectral region; a beam combiner for combining a
beam of light from the solid state light source with the filtered
illumination, thereby providing augmented illumination; and at
least one lens for focussing the light from the white light source
and the light from the solid state light source along an optical
path to the spatial light modulator.
12. The system of claim 11, further comprising additional solid
state light sources for augmenting additional spectral regions of
visible light.
13. The system of claim 11, further comprising at least one mirror
for folding the optical path.
14. The system of claim 11, further comprising timing circuitry for
switching the solid state light source at least one per revolution
of the color wheel.
15. The system of claim 11, further comprising timing circuitry for
switching the solid state source at segment transitions.
16. A method of augmenting illumination for a spatial light
modulator, comprising the steps of: providing a beam of white light
source in the visible spectrum; filtering the white light with a
color wheel having multiple filter segments, thereby providing
filtered illumination; augmenting the filtered illumination with
light from a solid state light source that provides light in a
desired spectral region, thereby providing filtered and augmented
illumination; and focussing the filtered and augmented illumination
on the spatial light modulator.
17. The method of claim 16, wherein the augmenting step is repeated
for more than one spectral region.
18. The method of claim 16, further comprising the step of
switching the solid state light source during revolutions of the
color wheel.
19. The method of claim 16, further comprising the step of
switching the solid state light source at transitions of the color
wheel.
20. The method of claim 16, further comprising the step of
switching the solid state light source to coincide with one or more
segments of the color wheel.
21. An illumination system for at least one spatial light modulator
of a display system having two or more spatial light modulators,
comprising: a color light source that provides light in a color
region of the visible spectrum; a solid state light source for
providing light in all or part of the color region; a beam combiner
for combining a beam of light from the color light source with
light from the solid state light source, thereby providing
augmented illumination; and at least one lens for focussing the
light from the color light source and the light from the solid
state light source along an optical path to the spatial light
modulator.
22. The system of claim 21, further comprising a white light
source, a second solid state light source for a second color, a
second beam combiner, and a second lens for providing augmented
illuminated of a second color to a second spatial light modulator,
and further comprising a color wheel having multiple color segments
for filtering the augmented illumination to the second spatial
light modulator.
23. The system of claim 21, further comprising a second and a third
colored light source for a second and third color, a second and
third solid state light source for the second and third color, a
second and third beam combiner, and a second and third lens for
providing augmented illumination to a second and third spatial
light modulator, respectively.
Description
TECHNICAL FIELD OF THE INVENTION
[0001] This invention relates to image displays, and more
particularly to methods of augmenting white light filtered through
a color wheel, or colored lamp light, and used to illuminate the
display.
BACKGROUND OF THE INVENTION
[0002] Spatial light modulators (SLMS) have found application in
many fields, a significant one of which is image displays. In
general, an SLM is an array of light-emitting, light-transmitting,
or light-reflecting elements, which are individually addressable,
usually with electronic signals. Many SLMs are binary, having an
addressing scheme that switches its elements to either an "on" or
"off" state to form the image. A characteristic of SLMs is that
there is no scanning--all pixels are activated at substantially the
same time to generate the entire image or a two-dimensional block
of the image, depending on the size of the image and the SLM.
[0003] One type of SLM is a digital micro-mirror device (DMD), also
known as the digital light processor (DLP), manufactured by Texas
Instruments Incorporated. The DMD has an array of thousands of tiny
tilting mirrors. To permit the mirrors to tilt, each is attached to
one or more hinges mounted on support posts and each is spaced by
means of an air gap over underlying addressing circuitry. The
addressing circuitry provides electrostatic forces, which cause
each mirror to selectively tilt.
[0004] For display applications, the DMD is addressed with image
data. In accordance with this image data, light is selectively
reflected either into a projection pupil or into a "dump". The
combination of light and dark mirrors projected onto a viewing
screen forms an image. Modulation techniques are used to provide
greyscale image "frames". A quick succession of frames is perceived
by the viewer as a full motion display.
[0005] There are at least two approaches to generating color
displays with the DMD display system. One approach is to generate
multiple images with multiple SLMs, typically one SLM each for red,
green and blue. Each image has a desired intensity, and the images
are combined to result in the correctly colored display. A second
approach is to use a single SLM and generate images for each color
(red, green, and blue) sequentially. A white light source is
filtered through a revolving color wheel, such that a desired color
illuminates the corresponding image. The differently colored images
are generated so quickly that the eye integrates them into the
correctly colored frame.
[0006] An issue with lamps used in display systems is that they
tend to be deficient in the red spectrum of the visible light
region. This limits the number of lumens that can be projected onto
a viewing screen while maintaining esthetically pleasing color
balance.
SUMMARY OF THE INVENTION
[0007] One aspect of the invention is an illumination system for a
spatial light modulator that is illuminated with light from a color
wheel and sequentially displays differently colored images. In one
embodiment, the solid state light source is "forward" of the color
wheel, relative to a white light source. The white light source,
such as a lamp, provides white light in the visible spectrum. A
solid state light source augments the white light by providing
light in a desired spectral region. A beam combiner overlays the
light from the white light source with the light from the solid
state light source. This combined beam is focused through the color
wheel, which has multiple color segments for filtering the light.
Various timing alternatives may be implemented such that the
augmentation is during the complete revolution of the color wheel
or only during part of each revolution. Various lens and mirrors
may be used to focus the light from the white light source and the
light from the solid state light source along an optical path to
the spatial light modulator.
[0008] In other embodiments, the solid state light source may be
"behind" the color wheel. Also, in each embodiment, multiple solid
state light sources could be used to augment different colors.
[0009] An advantage of the invention is that it can be used to
provide good color balance in displays generated with a color wheel
display system. For example, solid state illumination can be used
to augment red lamp illumination without throwing away blue and
green lamp illumination. Additionally, a solid state source can be
used to compensate light loss during transitions between segments
of the color wheel. In sum, the solid state source enhances picture
quality, without adding undue expense or complexity to the display
system.
[0010] The high switching speeds and longevity of solid state
sources make them a good supplement to any lamp source in an SLM
display system, whether the lamp be a white light lamp in a color
wheel system (sequential colored images) or a color lamp in a
multiple SLM (concurrent colored images) system.
BRIEF DESCRIPTION OF THE DRAWINGS
[0011] FIG. 1 illustrates a portion of a SLM-based display system,
namely the SLM and the optical components used to illuminate the
SLM, having solid state augmentation in accordance with the
invention.
[0012] FIG. 2 illustrates the same system as FIG. 1 but with an
alternative placement of the solid state source.
[0013] FIG. 3 illustrates an alternative embodiment of the solid
state light source of FIGS. 1 or 2.
[0014] FIG. 4 illustrates a second alternative embodiment of the
solid state light source of FIGS. 1 or 2.
[0015] FIG. 5A illustrates a color wheel having one segment for
each color.
[0016] FIG. 5B illustrates the timing of the illumination provided
by the color wheel of FIGURE SA, augmented with a solid state light
source.
[0017] FIG. 6A illustrates a color wheel having multiple segments
for each color.
[0018] FIG. 6B illustrates the timing of the illumination provided
by the color wheel of FIG. 6A, augmented with a solid state light
source.
[0019] FIG. 7 illustrates a portion of an SLM-based display that
uses two SLMs.
DETAILED DESCRIPTION
[0020] Color Wheel Display System with Solid State Augmentation for
Lamp Deficiency
[0021] The following description is in terms of a SLM-type display
system that uses a color wheel to filter "field sequential" images.
As described in the Background, with each image frame, the color
wheel filters white light so as to illuminate the SLM with
differently colored light. This permits the SLM to generate a
sequence of differently colored images, which are perceived by the
viewer as a correctly colored display.
[0022] FIG. 1 illustrates a portion of the display system 10,
namely the SLM 120 and the optical elements that provide light to
be reflected from the SLM 120. These optical elements are referred
to herein as the "illumination system" 10, and include elements
that provide solid state light augmentation in accordance with the
invention.
[0023] The SLM of FIG. 1 is a DMD type SLM, which as explained in
the Background, reflects light it receives out of the color wheel
109. Thus, the particular optical path described herein is
configured for a reflective type SLM. However, the optical path,
with its mirrors and lenses, could be rearranged for other types of
SLMs.
[0024] Furthermore, the particular optical path of FIG. 1 is
designed to provide a compact design. For example, the two mirrors
115 and 118 serve to fold the optical path. However, in essence,
the illumination system 10 provides an optical path from a white
light source 101 to the SLM 120. Along this path, the white light
is filtered with a color wheel 109 and augmented with at least one
solid state illumination source 104.
[0025] The white light source is implemented with lamp 101.
Examples of suitable lamps are arc lamps and metal halide lamps. A
possible alternative might be a solid state white light source,
such as a white light LED (light emitting diode), provided its
intensity is sufficient.
[0026] The light from lamp 101 is focussed through the color wheel
109 using a condensing lens pair, which is comprised of a
collimating lens 102a and a focussing lens 102b.
[0027] Solid state light source 104 provides red, green, or blue
augmentation. In the example of this description, light source 104
is a red light source to compensate for deficiencies of lamp 101 in
the red spectral region. However, augmentation could be provided
for other spectral regions.
[0028] In the example of FIG. 1, solid state source 104 is a
fiber-coupled laser diode. A laser diode 104 is coupled to lens 105
using optical fiber 104a and an optical coupler 104b. Other
examples of a suitable solid state source 104 are LEDs, vertical
cavity surface emitting lasers, or superlumiscent diodes. Two
examples of alternative solid state light sources are discussed
below in connection with FIGS. 3 and 4.
[0029] The light beams from lamp 101 and solid state source 104 are
combined using a beam combiner 103. A lens 106 focuses the light
from the solid state source 104 to beam combiner 103. After being
combined, the beam from the solid state source 104 and the beam
from lamp 101 follow the same path through lens 102b.
[0030] An example of a suitable beam combiner 103 is a dichroic
beam combiner, which reflects the solid state light in the desired
direction. It is "notched" to reflect a desired region of the light
spectrum from solid state source 104. Typically, this spectrum is
narrow relative to the corresponding color from lamp 101. For
example, in the case of red augmentation, a red solid state source
might provide a fairly narrow range, such as 620-650 nanometers. In
comparison, the lamp 101 provides a broad red spectrum. The notch
is sufficiently wide to ensure that a desired spectral region from
solid state source 104 is combined with the lamp light. However,
because the same range of lamp light will be reflected out of the
light path, the notch is sufficiently narrow to limit this loss. In
other words, the range of the notching permits the solid state
light to be combined with the lamp beam, without undue loss of
light from the lamp. Even though some red lamp light is lost,
overall, the amount of red light is increased by the combination of
light from the two sources.
[0031] Other examples of suitable beam combiners 103 are
holographic beam combiners (HOEs) and gratings.
[0032] A solid state source timing circuit 105 (which may be part
of a larger timing circuit), controls the on and off times of the
solid state source. There are many possible timing alternatives.
For example, a red solid state source 104 could be on continuously
or on during only the red segment(s) of the color wheel. It might
even be the case that color wheel 109 has a "clear" segment during
which the solid state source 104 is on. An additional use of solid
state source 104 to augment color wheel transitions, as well as
lamp deficiency, is discussed below in connection with FIGS.
5A-6B.
[0033] Color wheel 109 has a motor and control electronics (not
shown) that cause it to revolve at a pre-determined rpm rate. As a
simple example, color wheel 109 has three segments, one red, one
green, one blue. It revolves once for every frame generated by SLM
120 so that each color (red, green, or blue) is displayed for 1/3
of the frame time. Variations on this simple example include
revolving the color wheel at n>1 times the frame time, and
dividing the red, green, and blue segments into multiple
non-contiguous segments. These variations are designed to reduce
artifacts associated with "field sequential" color wheel
displays.
[0034] After passing through color wheel 109, the light is
integrated using integrator 111. This removes "hot spots" and
provides a smooth light beam to be transmitted to the SLM 120.
[0035] A collimating lens 113 receives the output of integrator 111
and provides a collimated beam. This beam is reflected from a first
folding mirror 115, passes through a relay lens 117, and is
reflected from another folding mirror 118. As stated above, mirrors
115 and 118 are used to shape the light path into a compact path. A
focussing lens 119 focuses the light on the surface of the SLM 120.
A simpler design might simply use lens 113 to focus the light from
the integrator onto the SLM 120.
[0036] FIG. 2 illustrates the same system as FIG. 1, but with an
alternative positioning of the solid state source. In the system 20
of FIG. 2, the solid state source 204 is "behind" the color wheel
109, relative to the lamp 101. A lens 205 focuses the solid state
light to beam combiner 215. Beam combiner 215 combines the solid
state light with the filtered light out of the color wheel 109 and
integrator 111.
[0037] FIG. 3 illustrates an alternative embodiment of the solid
state light source 104 or 204 of either FIG. 1 or FIG. 2,
respectively. Instead of a fiber-coupled laser diode 104 (or 204),
the light source 30 is an LED array 31. A focussing lens 32 focuses
the light from array 31 to an integrator 33, which couples to lens
106 (or 206).
[0038] FIG. 4 illustrates how multiple laser diodes (LDs) may be
ganged to provide the solid state light source 104 (or 204). The
laser diodes 41 are fiber optically connected to a telescope lens
system 42 having a diffuser 43. The output of the diffuser 43 is
combined with the beam from lamp 101 by beam combiner 103. If
desired, heat sinks may be used to conduct heat from the laser
diodes.
[0039] Although the above description is directed toward a system
10 or 20 having a single SLM and a color wheel, solid state light
augmentation can also be used in multiple SLM systems. These
include systems having two SLMs, one with a two-color color wheel
and one for a third color. Systems having three SLMs use one SLM
for each color. When two or more SLMs are used, each SLM is
simultaneously illuminated with a different color, and a
combination of these images is displayed.
[0040] Typically, in a multiple SLM system, even when an SLM is
dedicated to a single color and does not use a color wheel, the
light source is a lamp. However, the addition of solid state light
can ease the problem of overdriving the lamps. The illumination
system for the SLM would be similar to that of FIGS. 1 and 2, but
with the lamp providing only one color and with no color wheel. The
solid state light source would be used to augment the lamp
color.
[0041] Solid State Augmentation for Color Wheel Spoke Losses
[0042] FIG. 5A illustrates an example of color wheel 109. In the
example of FIG. 5A, the color wheel 109 has only three segments,
one for each color (red, green, and blue). The transitions between
segments are referred to as "spokes". As explained in the
Background, the use of a color wheel 109 is based on physiological
traits that cause the viewer's eye to integrate sequentially
colored images (red, green, and blue) as being a single image of
the correct color. There are numerous "tricks" for enhancing the
viewer's perception of image quality, such as by subdividing the
segments or by spinning the wheel faster.
[0043] A problem to be dealt with when using a color wheel for
motion displays is that the time between segments--the spoke
time--is lost for purposes of illuminating the display. Various
techniques may be used to reduce spoke artifacts, and in one
approach, SLM 120 is simply turned off during transitions between
color wheel segments. This results in diminished overall
brightness.
[0044] Thus, although it is desirable to divide each segment into
sub-segments, such division results in more spokes. Solid state
light can be used to compensate for lost illumination resulting
from the spokes.
[0045] A characteristic of solid state light sources, such as light
source 104, is that they may be switched on and off very quickly.
For LEDs and LDs, the switching time is virtually instantaneous.
For this reason, a solid state source may be used with color wheel
109 to reduce spoke time losses. The off time of the solid state
source can be precisely timed to begin or end at a color wheel
transition so that it illuminates the SLM 120 during the
transitions.
[0046] FIG. 5B illustrates the timing (at the SLM 120) of the
illumination provided by the white light from lamp 101 through
color wheel 109, as well as the illumination provided by the solid
state source 204 of FIG. 2. The "on" times of the filtered white
light illustrate the effect of the spokes. As indicated, there is a
short period (exaggerated for purposes of illustration) of time
during which the filtered white light illumination is lost.
[0047] However, because of the fast switching times of the solid
state source 204, it may remain "on" until the transition to the
next color is complete. In the example of FIG. 5B, a red solid
state source is on during the whole "on" time of the red component
of the white light and continues "on" during the color wheel
transition to green. The solid state light source 204 is switched
at the transition "edge". In this manner, the red-to-green spoke
loss is compensated by the red solid state source.
[0048] In other embodiments, the solid state source could be on
only during the transitions to red, or from red, or both. Or, the
solid state source could be continuously on.
[0049] In practice, more than one solid state source could be
used-for color wheel spoke compensation. For example, three solid
state sources, one for each color could be used. Each solid state
source would be associated with an appropriate lens and beam
combiner to merge the solid state light onto the optical path. In
the case of the blue and green solid state source, augmentation
during the entire "on" time of the filtered light may not be
necessary, and it may be desired to switch them on during only the
transition time.
[0050] In some cases, it may be desirable to limit the "on" time of
the solid state source, for example, to only the transition times.
An advantage of reducing the total on time for the solid state
source is that it may then be driven "harder", that is, with more
current, without adverse effects on its longevity.
[0051] FIG. 6A illustrates another embodiment of color wheel 109.
In this embodiment, color wheel 109 has multiple segments for each
color. In this embodiment, color wheel 109 has 16 segments, which
are equal in size. Four segments are red, four are blue, and eight
are green.
[0052] FIG. 6B illustrates the timing of the illumination provided
by system 20 using the color wheel 109 of FIG. 6A. As illustrated,
red light is augmented using a solid state light source. In the
example of FIG. 6B, the red light is "behind" the color wheel 109
as in the configuration of FIG. 2, and also compensates for the
spoke times on both sides of the red segments. In other words, the
solid state source is on during the entire time that red light is
transmitted through the color wheel 109, as well as during the
transition time before and after the red segments.
[0053] Augmentation of Multiple Colors
[0054] As indicated above, solid state sources can be used to
augment more than one color. This can be achieved with either the
configuration of FIG. 1 or FIG. 2.
[0055] For example, when red augmentation is achieved with a solid
state source, the green light may be increased without adversely
affecting overall color balance. In the example of FIG. 6A and 6B,
the total duration of green light per revolution is doubled
relative to the other colors. This permits the total lumens for the
display on SLM 120 to be increased for higher image brightness.
[0056] Multiple SLM Display Systems with Solid State Augmentation
for Lamp Deficiency
[0057] As stated in the Background, the use of three SLMs is an
alternative to a color wheel in generating color displays. The
images for each color are generated concurrently rather than
sequentially. Or, a two-SLM system can be implemented in which one
SLM is used with a color wheel to sequentially generate two images
for two colors and a second SLM is used without a color wheel to
concurrently generate a third color image. In both cases, the
outputs from the SLMs are overlaid to provide a full color
image.
[0058] FIG. 7 illustrates an example of a "two-chip" display system
70 that used multiple SLMs 120 to generate the display. The same
concepts as described above may be used to augment any of the
colors. In the example of FIG. 7, a solid state light source 104 is
used to augment the light from the SLM 120 generating the red
image. The light source 71 for the red image may be a red lamp or
other light source such as an LED, or a red-filtered light
source.
[0059] In a "three-chip" system, each color is generated by a
different SLM 120. Thus, there would be three light paths to the
image plane, each providing a differently colored image. Each SLM
120 is illuminated by a differently colored light source 71. Each
would have an optical path similar to that of the red SLM 120 of
FIG. 7. Any one or more of the image could be augmented with a
solid state light source 104 of the appropriate color.
[0060] Other Embodiments
[0061] Although the present invention has been described in detail,
it should be understood that various changes, substitutions, and
alterations can be made hereto without departing from the spirit
and scope of the invention as defined by the appended claims.
* * * * *