Note : Les descriptions sont présentées dans la langue officielle dans laquelle elles ont été soumises.
CA 02326693 2000-11-22
Attorney Docket No.: M-8433 US
EXPRESS MAIL LABEL NUMBER:
EL252928136US
METHOD AND APPARATUS FOR ILLUMINATING A DISPLAY
Milan M. Popovich
Jonathan D. Waldern
This application claims priority to Provisional application entitled METHOD
AND APPARATUS FOR ILLUMINATING A DISPLAY, Serial Number 60/125,924
filed March 23, 1999; Provisional application entitled DEVICE FOR PRODUCING
COLOURED LIGHT AND IMAGE GENERATING APPARATUS INCLUDING
SUCH A DEVICE, Serial Number 60/127,898 filed April 5, 1999; and Provisional
application entitled DEVICE FOR PRODUCING COLOURED LIGHT AND
IMAGE GENERATING APPARATUS INCLUDING SUCH A DEVICE, Serial
Number 60/157,796 filed October S, 1999.
BACKGROUND OF THE INVENTION
Field Of The Invention
The present invention relates generally to a method and apparatus for
illuminating an image display, and more particularly to an apparatus and
method for
illuminating a color sequential image display.
Description of the Related Art
In color sequential displays, a display screen is used to display a sequence
of
monochrome frames corresponding to what will be the red, green and blue
components of a final monochromatic image. A typical color sequential display
may
take form in a reflective LCD micro display. The images generated by the
display are
illuminated in succession by a red, green, and blue light so that the red
light ..
illuminates the red monochromatic frame of the final monochromatic image, the
green
light illuminates the green frame of the final monochrome image, and the blue
light
illuminates the blue frame of the final image. Components of a subsequent
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monochromatic image are illuminated in the same fashion. Switching from one
image to the next is performed very rapidly so that an observer sees what is
effectively a full color image.
The successive illumination of image frames by red, green, and blue light is
typically achieved using a white light source and a rotating color wheel; such
wheels
are prone to mechanical failure. Alternatively, the successive illumination of
monochromatic frames of an image by red, green, and blue light may be achieved
using a white light source and a solid-state device such as a liquid crystal
polarization
switch. Unfortunately this alternative technique has a disadvantage. More
particularly, the solid-state techniques that employ devices such as liquid
crystal
polarization switches work only with polarized light. Accordingly, at least
half of the
light available for illuminating a particular monochromatic frame is
immediately lost.
A more important problem with the mechanical and solid-state techniques for
illuminating color sequential displays is that only a third of the available
white light is
used for illuminating the red, green and blue monochromatic frames of the
image
collectively. In other words, at least two thirds of the available white light
is unused
at any given moment. For example, when the red monochromatic frame of a final
image is displayed, only red light is used to illuminate, while the green and
blue
components of the white light source are filtered out and unused.
Summary of the Invention
The present relates to a device for producing colored light and an image
generating apparatus including such a device. The device includes a switchable
light-
directing apparatus configured to receive light and a first control circuit
coupled to the
switchable light-directing apparatus. The first control circuit provides
control signals
to the switchable light-directing apparatus In response to the switehable
light-
directing apparatus receiving a control signal, the switchable light-directing
apparatus
directs a first portion of the received light to a first region of a plane.
Additionally,
the switchable light-directing apparatus directs second and third portions of
the
received light to second and third regions, respectively, of the plane. The
second
region is positioned between the first and third regions of the plane.
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In one embodiment, the switchable light-directing apparatus comprises a first
group of electrically switchable holographic optical elements comprising
first, second,
and third electrically switchable holographic optical elements each of which
is
electrically switchable between an active state and an inactive state. Each of
the first,
second, and third electrically switchable holographic optical elements is
configured to
diffract light incident thereon when operating in the active state, and each
of the first,
second, and third electrically switchable holographic optical elements
transmits light
incident thereon without substantial alteration when operating in the deactive
state. In
this embodiment, each of the first, second and third electrically switchable
holographic optical elements is activated or deactivated by the first control
circuit.
Brief Description of the Drawin>=s
While the invention is susceptible to various modifications and alternative
forms, specific embodiments thereof are shown by way of example and the
drawings
and will be herein described in detail. It should be understood, however, that
the
drawings and detailed description thereto are not intended to limit the
invention to the
particular form disclosed. On the contrary, the intention is to cover all
modifications,
equivalents and alternatives falling within the spirit and scope of the
present invention
as defined by the appended claims.
The present invention may be better understood, and it's numerous objects,
features, and advantages made apparent to those skilled in the art by
referencing the
accompanying drawings.
Figure 1 shows a first embodiment of a transmissive type device for producing
colored light and an image generating apparatus; --
Figure 2 shows a second embodiment of a transmissive type device for
producing colored light and an image generating apparatus;
Figure 3 shows a third embodiment of a transmissive type device for
producing colored light and an image generating apparatus;
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Figure 4 shows a first embodiment of a reflective type device for producing
colored light and an image generating apparatus;
Figure 5 shows a second embodiment of a transmissive type device for
producing colored light and an image generating apparatus;
Figure 6 shows a third embodiment of a transmissive type device for
producing colored light and an image generating apparatus;
Figures 7A - 7C illustrate operational aspects of one embodiment of the
switchable optics system and image surface employable in the embodiments shown
in
Figures 1 - 6;
Figure 8 illustrates operational aspects of another embodiment of the
switchable optics system and image surface employable in the embodiments shown
in
Figures 1 - 6;
Y
Figure 9 illustrates operational aspects of still another embodiment of the
switchable optics system and image surface employable in the embodiments shown
in
Figures 1- 6;
Figure l0A - lOC show alternative embodiments of the filter employable in
the embodiments shown in Figures 2 and 5;
Figure 11 is a cross sectional view of an electrically switchable holographic
- optical element;
Figure 12 is one embodiment of an electrically switchable holographic optical
element system employable in the switchable optics system of Figures 2, 3, S,
and 6;
Figure 13 is one embodiment of an electrically switchable holographic optical
element system employable in. the switchable optics system of Figures 1 and 4;
Figure 14 is one embodiment of an electrically switchable holographic optical
element system employable in the switchable optics system of Figures 3 and 6;
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Figure 15 is another embodiment of an electrically switchable holographic
optical element system employable in the switchable optics system of Figures
2, 3, 5,
and 6;
Figure 16 is another embodiment of an electrically switchable holographic
optical element system employable in the switchable optics system of Figures 1
and 4;
Figure 17 illustrates one embodiment of the system shown in Figure 2;
Figure 18 illustrates another embodiment of the system shown in Figure 2;
Figure 19 illustrates still another embodiment of the system shown in Figure
2;
Figure 20 illustrates one embodiment of the system shown in Figure 5;
Figure 21 illustrates an electrically switchable holographic optical element
system and an optical diffuser employable in the embodiments shown in Figures
1 -
6;
Figure 22 illustrates an alternative embodiment of the switchable optics
system employable in the embodiment of Figure 2;
Figure 23 illustrates the switchable optics system of Figure 22 with a
modification thereto;
Figure 24 illustrates the switchable optics system of Figure 22 with a
modification thereto;
Figure 25 shows a fourth embodiment of a transmissive type device for
producing colored light and an image generating apparatus;
Figure 26 illustrates operational aspects of the transmissive type device for
producing colored light shown in Figure 25;
Figure 27 shows a fourth embodiment of a reflective type device for producing
colored light and an image generating apparatus.
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Description of the Preferred embodiments)
Figure 1 shows one embodiment of a system having a light transmissive type
device for producing colored light and an image generating apparatus. Figure 1
shows a light source 100 for generating white light 102, collimation optics
104,
S switchable optics system 108, image display system 112 having an image
display
surface 114 typically comprising an array of pixels for displaying
monochromatic
data, image control circuit 116, and illumination control circuit 118.
White light 102 generated by light source 100 is received by collimation
optics
104. Collimation optics 104, in turn, collimates white light 102 to produce
collimated
white light 106. Switchable optics system108 receives collimated white light
106 and
produces at least three distinct bandwidths of illumination light in response
thereto.
In the preferred embodiment, switchable optics system 108 generates red (R),
green
(G), and blue (B) bandwidth illumination lights. Switchable optics system108
produces the illumination lights as a result of shaping, filtering, focusing,
and/or
correcting collimated white light 106. Additionally, switchable optics system
208
selectively directs illumination lights onto subsurfaces of the image display
surface.
The switchable optics system 108 simultaneously illuminates at least three
distinct subsurface areas of image display surface 114 with the illumination
lights R,
G, B, respectively. Preferably, the three subsurfaces are of equal size. With
reference
to Figure 1, switchable optics system 108 simultaneously illuminates the
entire
surface 114 by illuminating each of three adjacent subsurfaces 114A-114C with
one
of the illumination lights R, G, B. The switchable optics system 108, or any
of the
switchable optics systems described below, should not be limited to
simultaneously
illuminating the entire surface 114 with the three illumination lights. The
switchable
optics system 108 may simultaneously illuminate three subsurfaces of lesser
size than
that shown in Figure 1. For example, the switchable optics system 108, or any
other
switchable optics system described herein, may simultaneously illuminate each
of
only three lines of pixels on the display surface with a respective one of the
three
illumination lights. Additionally, the switchable optics system 108, or any
other
switchable optics system described herein, may simultaneously illuminate each
of
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only three pixels on the display surface with a respective one of the three
illumination
lights.
Display surface 114 displays monochromatic data of monochromatic images
in accordance with signals generated by image control circuit 116. Each
monochromatic image consists of three monochromatic frames (i.e., a red
monochromatic frame, a green monochromatic frame, and a blue monochromatic
frame). With reference to Figure 1, each monochromatic image is displayed in a
three-stage cycle. In each cycle, a portion of each monochromatic frame is
displayed
on each of the subsurfaces 114A, 114B, and 114C. For example, in the first
stage,
subsurface 114A displays the top monochromatic component of the red frame
while
subsurfaces 114B and 114C display middle and bottom monochromatic components
of the green and blue frames, respectively. In the second cycle, subsurface
114A
displays the top monochromatic component of the green frame while subsurfaces
114B and 114C display middle and bottom monochromatic components of the blue
and red frames, respectively. In the third and last stage of the cycle,
subsurface 114A
displays the top monochromatic component of the blue frame while subsurfaces
114B
and 114C display middle and bottom monochromatic components of the red and
green frames, respectively.
lllumination control circuit 118 is coupled to image control circuit 116 and
switchable optics system 108. Switchable optics system108, operating under
command of control circuit 118, selectively directs each of the illumination
lights R,
G, and B to one of the subsurfaces 114A - 114C. Illumination control circuit
118 is
linked to image control circuit 116 and operates in sync therewith. In the
embodiment
shown in Figure l, switchable optics system 108 operates in a three-stage
cycle. In
the first stage, switchable optics system 108 receives one or more control
signals from
control circuit 118 and, in response thereto, directs illumination light R
onto
subsurface 114A while subsurface 114A displays the top component of the red
monochromatic frame as described above. Switchable optics system108 also
directs
illumination lights G and B onto subsurfaces 114B and 114C, respectively, in
the first
cycle, while subsurfaces 114B and 114C display the middle and bottom component
of
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the green and blue monochromatic frames, respectively. In the second cycle,
switchable optics system 108 receives one or more second control signals and,
in
response thereto, directs illumination light G onto subsurface 114A while
subsurface
114A displays the top component of the green monochromatic frame as described
above. Switchable optics system108 also directs illumination lights B and R
onto
subsurfaces 114B and 114C, respectively, in the second cycle, while
subsurfaces
114B and 114C display the middle and bottom component of the blue and red
frames,
respectively. In the third cycle, switchable optics system 108 receives one or
more
third control signals and, in response thereto, directs illumination light B
onto
subsurface 114A while subsurface 114A displays the top component of the blue
monochromatic frame as described above. Switchable optics system108 also
directs
illumination lights R and G onto subsurfaces 114B and 114C, respectively, in
the
third cycle, while subsurfaces 114B and 114C display the middle and bottom
component of the red and green monochromatic frames, respectively.
Figure 1 shows the second stage of this three-stage cycle in which: subsurface
114A is illuminated with green illumination light G as subsurface 114A
displays the
top monochromatic component of the green frame; subsurface 114B is illuminated
with blue illumination light B as subsurface 114B displays the middle
monochromatic
component of the blue frame, and; 114C is illuminated with red illumination
light R
as subsurface 114C displays the bottom monochromatic component of the red
frame.
If the monochromatic components displayed in the first and third stages are
illuminated in similar fashion, and if the switching rate between the three
stages is fast
enough, than an observer will be able to eye integrate the illuminated
components into
the final image.
When the three stage cycle has completed, image control circuir'116 initiates
a
new three stage cycle for the next image. The present invention should not be
limited
to displaying the monochromatic image in a three stage cycle. The present
invention
could be implemented with three lines of each monochromatic frame being
simultaneously displayed on three lines of pixels of the image display
surface. In this
alternative embodiment, the monochromatic image is scrolled down the display
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surface as it is illuminated with illumination lights R, B, and B.
Additionally, the
present invention could be implemented with three pixels of each monochromatic
frame being simultaneously displayed on three pixels of the image display
surface. In
this alternative embodiment, the monochromatic image is scrolled across and
down
the display surface as it is illuminated with illumination lights R, B, and B.
Figures 7A - 7C illustrate front views of display surface 114 of Figure 1.
Figures 7A - 7C further illustrates how switchable optics system 108 properly
illuminates the monochromatic components of the final image. In Figure 7A,
subsection 114A is illuminated with R when subsection 114A displays what will
be
the red monochrome component of the final image in that subsurface. Subsection
114B is illuminated with G when subsection 114B displays the green monochrome
component of the final image in that section. Subsection 114C is illuminated
with B
when subsection 114C displays the blue monochrome component of the final image
in
that section. Figures 7B and 7C show illumination of the subsections 114A -
114C as
the subsurfaces cycle through what will be the monochromatic components of the
final image.
Figure 2 shows an alternative embodiment of a system having a light
transmissive type device for producing colored light and an image generating
apparatus. The embodiment shown in Figure 2 includes white light source 100
which
generates a white light 102, collimation optics 104, filter 202, switchable
optics
system 206, image display system 112 having an display surface 114, image
control
circuit 116, and illumination control circuit 118. It is noted that the same
reference
number identifies similar components in the Figures.
Collimation optics 104 in Figure 2 collimates white light 102 into collimated
white light 106. Filter 202 receives and filters collimated white light 106 to
produce
at least three spatially separated and bandwidth distinct output lights 2048,
2046, and
204B. In the embodiment shown in Figure 2, output light 2048 constitutes the
red
bandwidth component of collimated white light 106, output light 2046
constitutes the
green bandwidth component of collimated white light 106, and output the light
204B
constitutes the blue bandwidth component of collimated white light 106.
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Switchable optics system 208 shapes, focuses and/or corrects output lights
2048, 2046 and 204B to produce illumination lights R, G and B, respectively.
Additionally, switchable optics system 208 selectively directs illumination
lights onto
subsurfaces of the image display surface. Image display system 112 displays
monochromatic images in the same fashion described with reference to Figure 1.
Illumination control circuit 118 controls switchable optics system 208 in
synchronization with the monochromatic components displayed on display surface
114.
Switchable optics system208 operates in a three-stage cycle. In the first
stage
of the three-stage cycle, switchable optics system 208 directs illumination
lights R, G,
and B onto display surfaces 114A, 114B, and 114C, respectively, as image
subsurfaces 114A, 114B, and 114C, display the appropriate monochromatic
components of the final image. In the second stage of the three-stage cycle,
switchable optics system 208 directs illumination lights R, G and B onto image
subsurfaces 114C, 114A and 114B, respectively, while image subsurfaces 114C,
114A and 114B display the appropriate monochromatic components of the final
image. In the third stage of the three-stage cycle, switchable optics system
208 directs
illumination lights R, G, and B onto subsurfaces 114B, 114C and 114A,
respectively,
while subsurfaces 114B, 114C, and 114A display the appropriate monochromatic
components of the final image. It is noted in Figures 1 and 2 that all or
substantially
all of collimated white light 106 is used to illuminate display surface 114 as
display
surface 114 displays the final image.
Figure 1 shows another embodiment of a system having a light transmissive
type device for producing colored light and an image generating apparatus.
Figure 3
shows light source 100, collimation optics 104, switchable optics system 308,
image
display system 112 having an display surface 114, image control circuit 116,
and
illumination control circuit 11$. With the exception of switchable optics
system 308
the embodiments of Figures 1 and 3 are identical. The main difference between
the
systems of Figures 1 and 3 relates to the intensity of illumination lights R,
G, and B
produced by switchable optics system 308. Unlike the embodiments shown in
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Figures land 2, switchable optics system 308 shown in Figure 3 illuminates the
entire
display surface 114 with less than substantially all available collimated
white light
106 at any given time.
The embodiments shown in Figures 1 through 3 include a transmissive-type
switchable optics system. The present invention can be employed with a
reflective
type switchable optics system. Figure 4 shows the embodiment of Figure 1 with
switchable optics system 108 replaced by switchable optics system 408, and
with
image display system 112 repositioned to take advantage of the reflective
properties
of switchable optics system 408. Except for its reflective properties,
switchable optics
system 408 operates in a manner substantially similar to switchable optics
system 108
shown in Figure 1.
In Figure l, switchable optics system 108 emits illumination lights R - B from
a surface opposite a surface that receives collimated white light 106. In
contrast,
reflective-type switchable optics system 408 emits illumination lights R - G
from the
same surface that receives collimated white light 106. Figure 5 shows the
system of
Figure 2 with switchable optics system 208 replaced by switchable optics
system 508,
and with image display system 112 repositioned to take advantage of the
reflective
properties of switchable optics system 508. Switchable optics system 508 is a
reflective-type system, whereas switchable optics system 208 shown in Figure 2
is a
transmissive-type system. Figure 6 shows the system of Figure 3 with the
transmissive switchable. optics system 308 replaced by reflective-type
switchable
optics system 608. Again, like the system shown in Figure 3, switchable optics
system 608 shown in Figure 6 illuminates surface 114 with less than
substantially all
of collimated white light 106.
Figures 7A through 7C illustrate one mode in which monochromatic
components of the final image image are displayed and illuminated on image
surface
114. As shown display surface 114 is divided into three areas of equal size,
each-of
which is cyclically and sequentially illuminated with red, green, and blue
illumination
light as the appropriate monochromatic component is displayed thereon. The
present
invention should not be limited thereto. Figure 8 shows a front-view of
display
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surface 114 which is divided into six subsurfaces 114A through 114F. In this
embodiment subsurfaces 114A and 114D sequentially and cyclically display in
monochrome what will be red, blue and green components of the final image in
those
subsurfaces, subsurfaces 114B and 114E sequentially and cyclically display in
S monochrome what will be green, red and blue components of the final image in
those
regions, and subsurfaces 114C and I 14F sequentially and cyclically display in
monochrome what will be blue, green and red components of the final image in
those
regions. Moreover, when subsurfaces 114A and 114D are displaying their red
monochromatic components, subsurfaces 114B and 114E display their green
monochromatic components and subsurfaces 114C and 114F display their blue
monochromatic components, and so on. To illuminate the monochromatic
components of the final image displayed in the subsurfaces 114A through 114F,
as
shown in Figure 8, the switchable optics system of Figures 1 through 6 must be
modified to produce two separate groups of red, green, and blue illumination
lights.
In this embodiment, the first group of red, green and blue illumination lights
are
selectively directed to each of the subsurfaces 114A through 114C, while the
second
group of red, green and blue illumination lights are selectively directed to
each of the
subsurfaces 114D through 114F. Thus, the modified switchable optics system
directs
the red illumination lights to the two subsurfaces which display their red
monochromatic components of the image at that time, while directing the green
illumination lights to the two subsurfaces displaying their green
monochromatic
subcomponent image and the blue illumination lights to the two subsurfaces
displaying their blue monochromatic subcomponent of the image at the time. The
modified switchable optics systems operate in a cyclic manner so that the red,
green,
and blue illumination lights of the first group are directed to subsurfaces
14A through
. 14C in synchronism with the display thereon of red, green, and blue
monochromatic
components of the final image. Similarly the modified switchable optics
systems
operate in a cyclic manner so that the red, green, and blue illumination
lights of the
second group are directed to subsurfaces 114D through 114F in synchronism with
the
display thereon of red, green, and blue monochromatic components of the final
image.
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Figures 9A through 9F show a front-view of image display surface 114
operating in accordance with another embodiment. In this embodiment, surface
114
is divided into six subsurfaces 114 A through 114F of equal size. It is noted
that
display surface 114 can be further divided into regions each of which occupies
a line
S of pixels. However, the present invention will be illustrated with the image
display
divided into six distinct but equal-sized subsurfaces.
Whereas the display surface described above operate in a three-stage cycle to
complete a full image, surface 114, shown in Figures 9A through 9F, operates
in a
six-stage cycle to completely display a final monochromatic image. Each
subsurface
114A through 114F displays in monochrome what will be the red, green, and blue
components of the final-image in that section. However, the display of the
red, blue,
and green components does not occur sequentially or cyclically as described
above.
In this embodiment only three of the subsurfaces 114A through 114F at any
given
point in time display a red, green, and blue component of the final image. The
display
of the components of the final image scrolls down the display surfaces 114A
through
114F as shown in Figures 9A through 9F. Figure 9A illustrates the first stage
of the
six-stage cycle. In Figure 9A, .subsurfaces 14A through 14C display in
monochrome
what will be the red, green, and blue components of the final image,
respectively, in
those subsurfaces. In the second stage of the six-stage cycle as shown in
Figure 9B,
subsurfaces 114B through 114D display the red, green, and blue components of
the
final image, respectively, in those sections. In the third stage of the six-
stage cycle, as
shown in Figure 9C, subsurfaces 114C through 114E display in monochrome what
will be the red, green, and blue components of the final image, respectively,
in those
sections. In the fourth stage, as shown in Figure 9D,, subsurfaces 14D through
14F
display in monochrome what will be the red, green, and blue components of the
final
image, respectively, in those sections. In Figure 9E, subsurfaces 114E, 114F,
and
114A display in monochrome what will be the red, green, and blue components of
the
final image, respectively, in those sections. In the last stage, as shown in
Figure 9F,
subsurfaces 114F, 114A, and 114B display the red, green, and blue components
of the
final image, respectively, in those sections.
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Figures 9A through 9F represent snapshots of the display surface 114 during
each stage of the six-stage cycle. Switchable optics systems 108, 208, 308,
408, 508
and 608 (described above) can be modified in order to illuminate only those
subsurfaces 114A through 114F which display monochromatic components of the
S final image with the appropriate illumination light at any given time. More
particularly, the modified switchable optics systems in this embodiment
operate in a
six-stage cycle. In the first stage of the six-stage cycle, the switchable
optics systems
direct the red, green, and blue illumination lights to subsurfaces 114A
through 114C,
respectively, as subsurfaces 114A through 114C display their red, green, and
blue
monochromatic components of the final image, respectively, as shown in Figure
9A.
In the second stage, the modified switchable optics systems direct the red,
green, and
blue illumination lights to subsurfaces 114B, 114C, and 114D, respectively, as
subsurfaces 114B, 114C; and 114D display their red, green, and blue
monochromatic
components of the final image, respectively as shown in Figure 9B. In the
third stage
of the six-stage cycle, the modified switchable optics systems direct red,
green, and
blue illumination lights to subsurfaces 114C, 114D and 114E, respectively, as
subsurfaces 114C, 114D and 114E display their red, green, and blue
monochromatic
components of the final image, respectively as shown in Figure 9C. In the
fourth
stage of the six-stage cycle, a modified switchable optics systems direct the
red,
green, and blue illumination lights to subsurfaces 114D, 114E and 114F,
respectively,
as subsurfaces 114D, 114E and 114F display their red, green, and blue
monochromatic components of the final image, respectively as shown in Figure
9D.
In the fifth stage of the six-stage cycle, the modified switchable optics
systems direct
the red, green, and blue illumination lights onto subsurfaces 114E, 114F, and
114A,
respectively, as subsurfaces 114E, 114F, and 114A display their red, green,
and blue
monochromatic components of the final image, respectively as shown i~ Figure
9E.
In the last stage of the six-stage cycle modified switchable optics systems
direct their
red, green, and blue illumination lights onto subsurfaces 114F, 114A, and
114B,
respectively, as subsurfaces 114F, 114A, and 114B display their respective
red, green,
and blue components of the final image, respectively as shown in Figure 9F.
The
switching or cycling of the modified switchable optics system and the display
surface
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is such that an observer sees what is effectively the final image without any
visible
divisions between the subsurfaces 114A through 114F.
Figures l0A through lOC show alternative embodiments of the filter 202
employed in Figures 2 and 5. In Figure 10A, filter 202 includes three dichroic
filters
1002, 1004, and 1006 arranged in sequence along an optical path from the light
source
100 (not shown in Figures l0A through lOC). More particularly, filter 1002
receives
collimated white light 106 and reflects the red bandwidth component thereof
sideways
to produce output light 2048. Remaining components of collimated white light
106
pass through filter 1002 substantially unaltered. Filter 1004 receives the
light
transmitted through filter 1002 and reflects the green bandwidth component
thereof
sideways to produce green output light 2046 while transmitting the blue
bandwidth
component without substantial alteration. The remaining blue bandwidth
component
of collimated white light is reflected sideways by filter 1006 to produce
output light
204B.
Filter 202 shown in Figure lOB is similar to that shown in Figure 10A.
However, dichroic filter 108 receives collimated white light and transmits the
red
bandwidth component thereof to produce output beam 2048 while deflecting
sideways the remaining blue and green bandwidth components of collimated white
light. Filters 1004 and 1006 reflect the green and blue bandwidth components,
respectively, of the light deflected by filter 1008 to produce output beams
2046 and
204B, respectively, in the same fashion as shown in Figure 10A.
Figure lOC shows filter 202 including a dichroic prism 1012 with dichroic _
layers on its interfaces and a pair of plane mirrors 1014 and 1016. One
example of
the dichroic prism which can be employed in Figure IOC, is manufactured by
Nitto
Optical of Japan under the name Cross Dichroic Prism. Such a prism is
typically
fabricated from glass such as DK7, and operates over the visible band from
420nm to
680nm and has a reflectivity of at least 94% for polarized light at normal
incidence. It
is also possible to employ prisms that have high transmission and are
relatively
insensitive to the polarization state of the incident light. Prism 1012 has an
input face
1018 that receives collimated white light 106, and three output faces 1020,
1022, and
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1024. The red bandwidth component of collimated white light 106 is deflected
to one
side by reflection and filtration at the prism interfaces, to emerge from
output face
1020 as output light 2048. This light is then deflected 90 degrees by plane
mirror
1014 towards the switchable optics system. The green bandwidth component of
collimated white light 106 passes straight through prism 112 without
substantial
alteration to emerge as output light 2046 from surface 1022. The blue
bandwidth
component of collimated white light 106 is deflected to one side by reflection
and
filtration at the prism interfaces to emerge from output face 1024 as
illumination light
204B. 204B is deflected through 90 degrees by plane mirror 1026.
As noted above switchable optics systems 108, 208, 308, 408, 508, and 608
can direct the red, green, and blue illumination lights onto display surfaccs
114A -
114C. Typically, switchable optics systems 108, 208, 308, 408, 508, and 608
also
focus illumination lights onto the subsurfaces. Additionally switchable optics
systems
108, 308, 408 and 608 may filter collimated white light 106. The switchable
optics
systems may be base on solid state switching techniques using acousto-optic
materials, liquid crystals or alternatively, opto mechanical devices such as
rotating
prisims, mirrors, or gratings. In the preferred embodiment, the switchable
optics
systems are based on electrically switchable holographic optical technology.
Accordingly, the switchable optics systems described above includes an
electrically switchable holographic optical element (ESHOE) system having at
least
three groups of three electrically switchable holographic elements that
perform the
illumination light directing functions described above. The ESHOE system may
additionally perform the functions of filtering the collimated white light 106
to
produce separated red, green, and blue illumination lights, or focusing the
illuminations lights onto the subsurfaces of display surface 114.
Addit'ronally, the
ESHOE system may perform the functions of light shaping and light correction.
However, these last functions are preferably performed by conventional optics
embodied in glass or plastic separate and apart from the ESHOE system. The
function of focusing the illumination light onto the subsurfaces of the image
display
may also be performed by conventional optics.
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Figure 11 shows the cross-sectional view of an exemplary switchable
holographic optical element that can be used in the ESHOE system. The
switchable
holographic optical element of Figure 11 includes a pair of substantially
transparent
and electrically non-conductive layers 1102, a pair of substantially
transparent and
S electrically conductive layers 1104, and a switchable holographic layer 1106
formed,
in one embodiment, from the polymer dispersed liquid crystal material
described in
U.S. Patent Application 09/478,150 entitled Optical Filter Employing
Holographic
Optical Elements And Lnage Generating System Incorporating The Optical Filter,
filed January 5, 2000, which is incorporated herein by reference. In one
embodiment,
the substantially transparent, electrically non-conductive layers 1102
comprise glass,
while the substantially transparent, electrically conductive layers 1104
comprise
indium tin oxide (ITO). An anti-reflection coating (not shown) may be applied
to
selected surfaces of the switchable holographic optical element, including
surfaces of
the TTO and the electrically nonconductive layers, to improve the overall
transmissive
efficiency of the optical element and to reduce stray light. As shown in the
embodiment of Figure 1 l, all layers 1102-1106 are arranged like a stack of
pancakes
on a common axis 408. The layers may be flexible.
Layers 1102-1106 may have substantially thin cross-sectional widths, thereby
providing a substantially thin aggregate in cross-section. More particularly,
switchable holographic layer 1106 may have a cross-sectional width of 5 - 12
microns (the precise width depending on a spectral bandwidth and required
diffraction
efficiency), while non-conductive glass layers 1102 may have a cross-sectional
width
of .4 - .8 millimeters. Obviously, ITO layers 1104 must be substantially thin
to be
transparent. It should be noted that holographic layers may be deposited on
thin
plastic substrates. The plastic substrates may also be flexible.
With ITO layers 1104 coupled to a first voltage, an electric field is
established
within the switchable holographic layer 1106, and the switchable holographic
element
operates in the inactive state described above. However, when the TTO layers
1104
arc coupled to a voltage below the first voltage, the switchable holographic
optical
element operates in the active state as described above. When~active, the
electrically
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switchable holographic optical element diffracts, for example, the red
bandwidth
component of collimated incident light 112 while passing the remaining
components
of collimated incident light 112, including green and blue bandwidth
components,
without substantial alteration.
S The switchable holographic optical element shown in Figure 11 may be
reflective or transmissive type. Figure 11 shows the switchable holographic
optical
element with oppositely facing front and back surfaces 1110 and 1112. Whether
reflective or transmissive type, collimated white light 106 falls incident on
the front
surface 1110 at normal incidence angle. If the switchable holographic optical
element
is configured as transmissive type, diffracted light components emerge from
back
surface 1112. In contrast, if the electrically switchable holographic optical
element is
configured as reflective type hologram, diffracted light components emerge
from
front surface 1110. Transmissive type electrically switchable holographic
optical
elements can be employed in the switchable optics systems shown in Figures 1,
2 and
3, while reflective type electrically switchable holographic optical elements
can be
employed in the switchable optics systems shown in Figures 4, 5 and 6.
Switchable holographic layer 1106 records a hologram using conventional
techniques. In one embodiment, the resulting hologram is characterized by a
high
diffraction efficiency and a fast rate at which the optical element can be
switched
between active and inactive states. In the embodiment of switchable
holographic
layer 1106 formed from polymer dispersed liquid crystal (PDLC) material, the
recorded hologram can be switched from a diffracting state. to a transmitting
state with
the creation and elimination of the electric field mentioned above.
Preferably, the
holograms recorded in the switchable holographic layer 1106 would be Bragg
(also
know as thick or volume phase) type in order to achieve high diffraction
efficiency.
Raman-Nath or thin phase type holograms may also be employed.
The hologram recorded in switchable holographic layer 1106 can be based on
PDLC materials described in the 09/478,150 application which, as noted above,
is
incorporated herein by reference. The hologram, in one embodiment, results in
an
interference pattern created by recording beams, i.e., a reference beam and an
object
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beam, interacting within switchable holographic layer 1106. Interaction of the
beams
with the PDLC material causes photopolymerization. Liquid crystal droplets
become
embedded in the dark regions of the fringe patterns that are formed by the
intersection
of the recording beams during the recording process. Stated differently, the
recording
material may be a polymer dispersed liquid crystal mixture which undergoes
safe
separation during the recording process, creating regions densely populated by
liquid
crystal microdroplets, interspersed by regions of clear photopolymer. When a
voltage
of sufficient magnitude is supplied to TTO layers I 104, the liquid crystal
droplets
reorient and change the refractive index of the switchable holographic layer
1106,
thereby essentially erasing the hologram recorded therein so that all
collimated white
light 106 incident thereon passes without noticeable alteration. The material
used
within switchable holographic layer 1106 is configured to operate at a high
switching
rate (e.g., the material can be switched in tens of microseconds, which is
very fast
when compared with conventional liquid crystal display materials) and a high
diffraction efficiency.
Figure 12 is a block diagrams representing an embodiment of an ESHOE
system employable in the switchable optics system used in Figures 2 and 3.
More
particularly, the ESHOE system shown in Figure 12 includes three groups of
three
electrically switchable holographic optical elements. The first group,
designated
1202, consists of three holographic optical elements 1202A - 1202C stacked one
upon
another. The second group of holographic optical elements, designated 1204,
consists
of three holographic optical elements 1204A - 1204C stacked one upon another.
The
third group of holographic elements, designated 1208, consists of three
holographic
optical elements 1208A - 1208C stacked one upon another.
In operation, the ESHOE system shown in Figure 12 is used to direct the red,
green, and blue illumination lights onto the subsurfaces 114A - 114C, ag shown
in
Figures 7A through 7C. During each stage in the three-stage cycle described
with
reference to Figures 7A through 7C, each of the electrically switchable
holographic
optical elements in one of the three groups 1202 through 1208 is activated.
More
particularly, stage one described above is implemented by activating the
electrically
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switchable holographic optical elements 1202A through 1202C of group 1202. The
second stage of the illumination cycle described above is implemented by
activating
the electrically switchable holographic optical elements 1204A - 1204C of
group
1204. The third stage in the three-stage cycle described above is implemented
by
S activating each of the electrically switchable holographic optical elements
1208A -
1208C of the third group 1208. Illumination control circuit 118 sequentially
and
cyclically activates and deactivates groups 1202 through 1208 by providing the
appropriate activation or deactivation voltages thereto so that only one group
is
activated at any one point in time.
With reference to Figure 2, electrically switchable holographic optical
elements 1202A, 1204A and 1208A diffract output light 2048 when activated onto
subsurfaces 114A~.114B and 114C, respectively. Electrically switchable
holographic
optical elements 1202B, 1204B and 1208B, when activated, diffract the output
light
2046 onto subsurfaces 114B, 114C and 114A, respectively. Activated holographic
optical elements 1202C, 1204C, and 1208C diffract output light 204B onto
subsurfaces 114C, 114B and 114A, respectively.
With continuing reference to Figure 12 and with further reference to Figure 3,
electrically switchable holographic optical elements 1202A, 1204A and 1204A
diffract the red bandwidth component of collimated white light 106 onto
subsurface
114A, 114B and 114C, respectively, while passing the remaining components of
collimated white light 106 incident thereon without substantial alteration.
The
portions of collimated white light 106 which pass through activated
electrically
switchable holographic optical elements enter free space and do not fall
incident upon
the display surface 114. This is because diffracted light emerges from the
electrically
switchable holographic optical element at an angle with respect to the light
that passes
without substantial alteration, and the display surface is positioned to take
advantage
of this fact. Electrically switchable holographic optical elements 1202B,
1204B and
1208B diffract the green bandwidth portion of collimated white light 106
incident
thereon, the diffracted light falling incident upon subsurfaces 114B, 114C,
and 114A,
respectively. The remaining portions of collimated white light 106 incident
upon
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activated optical elements 1202B, 1204B, and 1208B, transmit therethrough
without
substantial alteration and enter free space. Likewise activated optical
elements 1202C,
1204C, and 1208C diffract the blue bandwidth component of collimated white
light
106 incident thereon, the diffracted blue bandwidth component falling incident
upon
subsurfaces 114C, 114B and 114A, respectively.
Figure 13 shows an ESHOE system for use in the embodiments of Figures 1
and 4. The ESHOE system of Figure 13 includes three groups of three
electrically
switchable holographic optical elements. The first group 1302 includes three
electrically switchable holographic optical elements 1302A, 1302B and 1302C,
each
of which is configured to diffract red bandwidth light when active while
transmitting
green and blue bandwidth light without alteration. When deactivated, each of
the
electrically switchable holographic optical elements 1302A, 1302B, and 1302C
passes
the red, green, and blue bandwidths without alteration. Diffracted red
bandwidth light
emerges from electrically switchable holographic optical elements 1302A, 1302B
and
1302C at distinct exit angles to illuminate subsurfaces 114A - 114C,
respectively.
The second group 1304 includes three electrically switchable holographic
optical elements 1304A, 1304B and I304C, each of which is configured to
diffract
green bandwidth light when active while transmitting red and blue bandwidth
light
without alteration. When deactivated, each of the electrically switchable
holographic
optical elements 1304A, 1304B and 1304C passes the red, green, and blue
bandwidths
without alteration. The second group 1304 includes three electrically
switchable
holographic optical elements 1304A, 1304B and 1304C, each of which is
configured
to diffract green bandwidth light when active while transmitting red and blue
bandwidth light without alteration. When deactivated, each of the electrically
switchable holographic optical elements 1304A, 1304B and 1304C passes the red,
green, and blue bandwidths without alteration. Diffracted green bandwidth
light
emerges from electrically switchable holographic optical elements I304A,
1304B,
and 1304C at distinct exit angles to illuminate subsurfaces 114A through 114C,
respectively.
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The third group 1306 includes three electrically switchable holographic
optical
elements 1306A, 1306B and 1306C, each of which is configured to diffract blue
bandwidth light when active while transmitting red and green bandwidth light
without
alteration. When deactivated, each of the electrically switchable holographic
optical
elements 1306A, 1306B, and 1306C passes the red, green, and blue bandwidths
without alteration. Diffracted blue bandwidth light emerges from electrically
switchable holographic optical elements 1306A, 1306B, and 1306C at distinct
exit
angles to illuminate subsurfaces 114A through 114C, respectively.
The ESHOE system shown in Figure 13, acting under control of control circuit
118, operates to illuminate the display surface 114 as shown in Figures 7A
through
7C. In this mode, control circuit activates only one electrically switchable
holographic optical element in each of the groups 1302 through 1306. More
particularly, the control circuit in the first cycle activates electrically
switchable
holographic optical elements 1302A, 1304B, and 1306C to illuminate display
surface
114 as shown in Figure 7A. Control circuit in the second cycle activates
electrically
switchable holographic optical elements 1302C, 1304A, and 1306B to illuminate
display surface 114 as shown in Figure 7B. Control circuit in the third cycle
activates
electrically switchable holographic optical elements 1302B, 1304C, and 1306A
to
illuminate display surface 114 as shown in Figure 7C.
Figure 14 shows the ESHOE system of Figure 12 with the electrically
switchable holographic optical elements stagered. The ESHOE of Figure 14 can
be
used to direct collimated white light 106.
The switchable optics systems can employ a pair of the ESHOE systems
described in Figures 12 and 13 to increase the intensity of illumination
lights for
illuminating the monochromatic components of the display surface. More
particularly, the ESHOE system of Figure 13 or 14 could be duplicated, the two
ESHOE systems placed side by side with a polarization rotator in between. In
this
arrangement, each of the s and p polarized components of collimated light 106
or the
output lights 2048 - -204B will be diffracted by one of the two ESHOE systems
with
the rotator therebetween. Alternatively, the ESHOE system of Figure 13 or 14
could
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be duplicated and placed side by side, with the diffraction gratings in each
of the
electrically switchable holographic optical elements of one of the ESHOE
systems
aligned orthogonal to the diffraction gratings of each electrically switchable
holographic optical elements of the other ESHOE system. These arrangements are
more fully described in U.S. Patent Application 09/478,150 which is
incorporated
herein in its entirety.
The ESHOE systems above are employable to illuminate a display surface
divided into three separate subsurfaces with R, G, and B illumination lights.
Alternative ESHOE systems may be employed, for example, to illuminate a
display
surface divided into six separate subsurfaces as shown in Figures 9A - 9F.
Figures 1 S
and 16 show ESHOE systems which can be employed to produce the illumination
patterns shown in Figures 9A - 9F. The ESHOE system of Figure 15 is employable
in the systems of Figures 2 and 5 while the ESHOE system of Figure 15 is
employable in the systems of Figure 1, 3, 4 and 6. In general, the total
number of
electrically switchable holographic optical elements needed in each ESHOE
system
(configured to diffract only one of the s or p polarization components of
collimated
light 106 or output lights 2048 - 204B) equals the number of distinct
illumination
lights (normally three) multiplied by the number of subsurfaces of the display
surface
114 that display monochromatic components of the final image.
Figure 17 shows one embodiment of the system shown in Figure 2. Figure 17
shows 202B receiving collimated white light 106 from collimation lens 104.
Filtered
output lights 20R - 204B are subsequently received by ESHOE system 1200. As
noted in Figure 12, ESHOE system1200 comprises three stacks of electrically
switchable holographic optical elements stacked one upon another. Each of
these
elements directs and focuses a respective wavelength band of output light
received
from the filter 202B onto one of the subsurfaces 114A - 114C. The situation
shown
in Figure 17 is achieved by illumination control circuit 118 activating the
electrically
switchable holographic optical elements 1202A - 1202C (see Figure 12) and
deactivating electrically switchable holographic optical elements 1204A -
1204C and
1206A - 1206C.
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Figure 18 shows a another embodiment of the system shown in Figure 2. In
this embodiment, light from an source 100 is collimated and projected onto
filter
202A. The output lights 2048 - 204B are received and redirected by ESHOE
system
1200 mounted on the front surface of a transparent (e.g. glass) plate 1802 to
produce
illumination lights. After being redirected, the illumination lights are
totally
internally reflected by a rear face of the plate 1802 and are incident upon a
device
1804 (also mounted on the front of the plate 1802) which focuses the
illumination
lights and corrects chromatic dispersion in the latter. The illumination
lights are then
projected on to subsurfaces 114A - 114C. With reference to Figure 12, the
ESHOE
system 1200 of Figure 18 includes three stacks of three electrically
switchable
holographic optical elements. Illumination control circuit (not shown in
Figure 18)
activates the electrically switchable holographic optical elements in only one
stack to
illuminate the subsurfaces.
Because the electrically switchable holographic optical elements of ESHOE
system1200 operate off axis and over appreciable spectral bandwidths, some
correction of chromatic and geometrical aberration will be necessary, and this
function is performed by the device 1804. In a particular example, device 1804
comprises a stack of holographic diffraction elements which are designed to
act on
red, green and blue bandwidth light, respectively. Because the angular
separation
between R, G, and B illumination lights is relatively large (indeed, larger
than the
angular bandwidth of the Bragg holograms in these elements), the Bragg angular
and
wavelength selectivity will be sufficient to ensure that there is no
appreciable cross-
talk between the red, green and blue wavelengths. Under these circumstances,
there is
no need for these elements of device 1804 to be made switchable on and off.
As noted above, electrically switchable holographic optical elements will act
efficiently only on the p-polarised component of the incident light, with the
s-
polarised component being substantially unaffected, i.e. undiffracted by the
electrically switchable holographic optical elements . As a consequence, half
of the
available light power will be lost. To prevent this from happening, the single
ESHOE
system 1200 of Figure 18 can be replaced with a pair of ESHOE systems 1200 and
a
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polarisation rotator optically interposed therebetween. In this alternative
embodiment, the p-polarised component of the light incident upon the
electrically
switchable holographic optical elements of the first ESHOE system is
diffracted
whilst the s-polarised component passes therethrough substantially unaffected.
The
polarisation rotator ( which can be an achromatic half-wave plate) is designed
to
rotate by 90 degrees the polarisation direction of light passing therethrough.
Thus, the
p-polarised light diffracted by the first ESHOE system becomes s-polarised,
whilst the
undiffracted s-polarised light becomes p-polarised. On encountering the second
ESHOE system, the (now) p-polarised component is diffracted whilst the (now) s-
polarised component passes therethrough substantially unaffected. The
properties of
electrically switchable holographic optical elements in the two ESHOE systems
are
chosen such that the emission angle of diffracted light is the same in each
case, so that
both the p- and the s-polarised components are emitted in the same direction.
In an alternative arrangement, the polarisation rotator is omitted and instead
the fringes of the holograms recorded in the electrically switchable
holographic
optical elements in the two ESHOE systems are arranged to be mutually crossed,
so
that the electrically switchable holographic optical elements in the first
ESHOE
system act on the p-polarised component whereas those in the second ESHOE
system
act on the s-polarised component. Again, the properties of the holograms in
each
ESHOE system are chosen such that the diffracted p- and s- polarised
components are
emitted in the same direction.
Figure 19 shows a further embodiment of the system shown in Figure 2. Here
filter 202C of Figure lOC is employed to filter collimated white light
received from
collimation lens 104. Additionally, the switchable optics system includes the
ESHOE
1200 and an optical corrector 1902 is optically interposed between the filter
202C and
the ESHOE 1200, its purpose being to correct for aberrations introduced~by the
latter.
Figure 20 shows a side view and a top view of an embodiment of the system
shown in Figure 5 in which a reflective ESHOE 1200. The system shown in Figure
20 is similar to that shown in Figure 19 in that filter 202C is employed to
filter
collimated light from collimation lens 104. The top view shows how output
lights
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204GR, G, and B are diffracted by ESHOE 1200 to produce illumination lights R,
G,
and B which subsequently illuminate display surface 114. Further, the top view
shows that illumination lights (i.e. the diffracted output lights) emerge from
ESHOE
system at angle measured with respect to the angle at which output lights fall
incident
on the input surface of ESHOE system 1200. An appreciable diffraction angle is
needed for the electrically switchable holographic optical elements to achieve
high
diffraction efficiency. Further, it is noted that reflective type electrically
switchable
holographic optical elements are not sensitive to the polarization state of
the incident
light at moderate incidence and diffraction angles. Accordingly, no special
measures
are needed to avoid polarization loses.
Figure 21 shows an arrangement where, instead of being directed to an image
surface, illumination lights R, G, and B are projected on to an intermediate
optical
diffuser 2102. The diffuser can be used to control the beam characteristics to
generate
identical polar diagrams for the illumination light. The diffuser can be
conventional,
but is preferably a holographic light-shaping diffuser, which can be composed
of a
stack of non-switchable holographic optical elements.
Figure 22 shows an alternative embodiment of the system shown in Figure 2.
The switchable optics system of Figure 22 employs the ESHOE system 1200 of
Figure 12. However, the groups of electrically switchable holographic optical
elements not arranged side by side. Rather, the groups of electrically
switchable
holographic optical elements 1202, 1204, and 1206 are individually positioned
adjacent input faces of a dichroic prism. Collimated light 106 is filtered
into output
lights 2048 - 204B by filter 202B. Output light 2048 is deflected 90 degrees
by a
plane mirror 2204 and falls incident upon an input face of the dichroic prism
after
being diffracted by one of the activated electrically switchable holographic
optical
elements in group 1202. Similarly, output light 204B is deflected 90 degrees
by a
plane mirror 2206 and falls incident upon another input face of the dichroic
prism
after being diffracted by. Output light 2046 falls incident on a third input
face of the
dichroic prism after being diffracted by one of the activated electrically
switchable
holographic optical elements in group 1204. The dichroic prism redirects the
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diffracted lights (i.e., the illumination lights R, G, and B) to a color
correction element
2202, disposed optically immediately after the output face of the dichroic
prism,
before illuminating image surface 114. Figure 23 depicts a modification of the
system
shown in Figure 22 in which the plane mirrors 2204 and 2206 are replaced by
total
S internal reflection prisms 2304 and 2306. Figure 24 illustrates a further
embodiment
of Figure 22 in which the dichroic filter elements of filter 202B and the
plane
mirror2206 are rearranged so that output lights 2048 - 204B fall incident on
the
groups of electrically switchable holographic optical elements 1202 - 1206,
respectively, at an angle greater than 90 degrees. It is noted that plane
mirror 2204 is
removed from this alternative. In each case the output beams are angled so
that
diffracted light is emmitted normally to the output surfaces of the
electrically
switchable holographic optical elements.
The arrangement shown in Figure 18 is such that the illumination lights
incident at any point on the display surface, overlap exactly and appear to
have been
generated from a common point. This is an important requirement in many
reflective
display devices, where the brightness of the final projected image depends o
specular
reflection at the display rather than diffusion (as would be the case, for
example, with
transmissive L,CDs). In embodiments described above, the output lights are not
matched in this way and may need to be modified using diffusion screens (such
as
shown in Figure 21 ) before they could be used to illuminate a reflective non-
diffusing
display.
Figure 25 shows an alternative embodiment employing the present invention.
Figure 25 shows image surface 114 comprises an array of pixels 2502. The
pixels are
divided among three sets, with pixels in each set being evenly distributed
across the
image surface 114. Figure 25 shows is a cross sectional view of one line-of
pixels in
the arrayed image surface. Image control circuit controls the display of
monochrome
images on surface 114 so that,_at any time, the pixels in each set display (in
monochrome) either the red, green, or blue component of the final image, and
also
such that the pixels in each set display these final image components in
succession.
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Client Refeeenee: O1P035
CA 02326693 2000-11-22
Attomcy locket No.: M-84ii US
Figure 25 also shows an ESHOE system 2504 having groups of three
electrically switchable holographic optical elements 2504A - 2504C used for
illuminating the pixels with illumination lights R, G, or B. Although not
shown, the
number of groups of three electrically switchable holographic optical elements
2504A
- 2504C equals the number of pixels in a line of pixels. Figure 25 shows one
group
of three electrically switchable holographic optical elements 2504A - 2504C.
Essentially, the ESHOE system 2504 receives collimated white light 106 from a
collimation lens (not shown). ESHOE 2504 filters, directs, and focuses the
collimated
white light 106 by diffraction to illuminate each of pixels with R, G, or B
illumination
light. The red illumination lights R are directed to those pixels 2502 which
are, at the
time, displaying red monochromatic components of the final image. The green
illumination lights G are directed to those pixels 2502 which are, at the
time,
displaying green monochromatic components of the final image. The blue
illumination lights B are directed to those pixels 2502 which are, at the
time,
displaying blue monochromat~~ components of the final image.
ESHOE system 2504 is controlled by circuit 118 so that only one of the
electrically switchable holographic optical elements 2504A - 2504C in each
group is
active at a given point in time. Moreover, control circuit is in synchronism
with
image control circuit 116 so that only those pixels 2502 displaying red,
green, or blue
monochrome components of the final image are illuminated with R, G, or B
illumination light.
Each of the electrically switchable holographic optical elements 2504A -
2504C in each group, includes three stacks of holographic lenses (preferably
microlenses) formed in the holographic recording medium therein. The lenses in
each
stack operate on the red, green, and blue bandwidth components, respeetively,
of
collimated light 106 when activated by the appropriate signal generated by
illumination control circuit 118. In Figure 25, each of the holographic lenses
that
diffract red bandwidth light is shown cross hatched, each of the holographic
lenses
that diffract green bandwidth light is shown plain, and each of the
holographic lenses
that diffract blue bandwidth light is shown dotted. The three stacks of lenses
in each
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CA 02326693 2000-11-22
Attomcy Docker No.: M-8411 US
electrically switchable holographic optical element are positioned between a
pair of
electrode (ITO) layers so that all lenses therebetween are activated by the
control
signal provided to the pair of electrodes by the control circuit 118.
Alternatively, each
stack of lenses, or each lens in the electrically switchable holographic
optical
elements may be separately switchable into or out of the active state.
However, such
an alternative embodiment requires that each separate lens or each separate
stack of
lenses by sandwiched between its own set of TTO layers.
Figures 26A - -26C illustrate operational aspects of the ESHOE system 2504
shown in Figure 25. Figures 26A - 26C show only pixels 2502A - 2502C and one
holographic lens from the lens stack of each of the electrically switchable
holographic
optical elements of groups 2504A - 2504C. Figure 26A shows a first stage of a
three'
stage cycle in which pixels 2502A - 2502C display green, red, and blue
monochrome
components, respectively, of the final image. Also in this stage, the
holographic
lenses in the first group 2504A are all activated by control circuit 118 so
that the red
lens contained in first group 2504A directs and focuses the red bandwidth
component
of collimated white light 106 incident thereon onto pixels 2502A while passing
light
of other bandwidths incident thereon without noticeable alteration, the green
lens
contained in first group 2504A directs and focuses the green bandwidth
component of
collimated white light 106 incident thereon onto pixels 2502B while passing
light of
other bandwidths incident thereon without noticeable alteration, and the blue
lens
contained in first group 2504A directs and focuses the blue bandwidth
component of
collimated white light 106 incident thereon onto pixels 2502C while passing
light of
other bandwidths incident thereon without noticeable alteration. Lenses shown
in
broken lines are deactivated by control circuit 118. These lenses pass all
incident
light with out substantial alteration.
In the second stage of the three stage cycle illustrated in Figure 26B, pixels
2502A - 2502C display red, blue, and green monochrome components,
respectively,
of the final image. Also in this stage, the holographic lenses in the second
group
2504B are all activated by control circuit 118 so that the red lens contained
in first
group 2504B directs and focuses the red bandwidth component of collimated
white
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CIkM Retaena: DLP07s
CA 02326693 2000-11-22
Anomey Docket No.: M-8433 US
light 106 incident thereon of pixels 2502A while passing light of other
bandwidths
incident thereon without noticeable alteration, the green lens contained in
first group
2504B directs and focuses the green bandwidth component of collimated white
light
106 incident thereon onto pixels 2502C while passing light of other bandwidths
incident thereon without noticeable alteration, and the blue lens contained in
first
group 2504B directs and focuses the blue bandwidth component of collimated
white
light 106 incident thereon onto pixels 2502B while passing light of other
bandwidths
incident thereon without noticeable alteration.
In the last stage of the three stage cycle illustrated in Figure 26C, pixels
2502A - 2502C display blue, green, and red monochrome components,
respectively,
of the final image. Also in this stage, the holographic lenses in the second
group
2504C are all activated by control circuit 118 so that the red lens contained
in first
group 2504C directs and focuses the red bandwidth component of collimated
white
light 106 incident thereon onto pixels 2502C while passing light of other
bandwidths
incident thereon without noticeable alteration, the green lens contained in
first group
2504C directs and focuses the green bandwidth component of collimated white
light
106 incident thereon onto pixels 2502B while passing light of other bandwidths
incident thereon without noticeable alteration, and the blue lens contained in
first
group 2504C directs and focuses the blue bandwidth component of collimated
white
light 106 incident thereon onto pixels 2502A while passing light of other
bandwidths
incident thereon without noticeable alteration.
The three stage cycle is then repeated for the next final images, with the
switching between the various stages being performed rapidly. In this fashion
the
image surface 114 is perceived by a viewer as displaying a full color image,
and with
the red, green and blue components of collimated white light 114 being-fully
used at
all times. It is to be understood that, where a particular pixel displays
at~any given
time a part of the final image where one or more of the monochromatic
components
are missing, then no illumination light is directed and focused onto that
pixel during
that particular operation, then no light of those particular colors) is
focused onto that
pixel during that particular cycle. For example, if a given pixel displays a
part of the
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Attorney Docket No.: M-8413 US
image having only a red spectral component, then no green or blue illumination
light
is focused thereon.
A further embodiment of the image generating apparatus is shown in figure
27, where the image surface 114 is pixellated like that described in Figure 25
and
S operates under the action of control circuit 116. In this embodiment,
however,
collimated light 106 is reflected by ESHOE system 2702 towards a directing
device
2704, which then directs red, green and blue illumination lights onto the
pixels 2502.
More particularly, the ESHOE system 2702 is composed of three reflective,
electrically switchable holographic optical elements. In one embodiment,
electrically
switchable holographic optical elements 2702A-2702C can be arranged similar to
that
shown in Figure 25 save that each group of electrically switchable holographic
optical
element consists of three arrays of holographic mirrors. In an alternative
each
electrically switchable holographic optical element can be embedded as three
large
holographic mirrors. It should be understood that reflective electrically
switchable
1 S holographic optical elements operate in a manner similar to mirrors in
that light emits
from the same surface that receives the incident light. However, reflective
electrically
switehable holographic optical elements operate by diffracting incident light,
the
diffracted light emitting from the same surface that receives the incident
light.
Each of the electrically switchable holographic optical elements is arranged
to
diffract the red, green and blue components of the light 106 at three
predetermined
emission angles, as indicated by arrows A, B and C. Control circuit 118
activates
each of the electrically switchable holographic optical elements 2702A - 2702C
in
sequence, i.e. so that when one element is activated while the other two are
deactivated. When the element 2702A is activated, red illumination light is
emitted in
the direction of arrow A whilst green and blue illumination light is emitted
respectively in the direction of arrows B and C. When the element 2702B is
activated, red illumination light is emitted in the direction of arrow B
whilst green and
blue illumination lights are emitted respectively in the direction of arrows C
and A.
When the element 2702C is activated, red light is emitted in the direction of
arrow C
whilst green and blue light is emitted respectively in the direction of arrows
A and B.
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CA 02326693 2000-11-22
Attorney Docker No.: M-8433 US
The directing device 2704 comprises essentially a passive optical element
(such as an array of prismatic elements, lens-like elements or holographic
device)
which deflects light incident thereon to a degree dependent upon its
wavelength. The
device 2704 is arranged to direct light received in the direction of arrow A
onto one
set of pixels 2502, and to direct light received in the direction of arrows B
and C onto
second and third sets of the pixels. These sets of pixels are controlled by
the control
circuit 116 such that each set displays at any given time either a "red",
"green" or
"blue" monochromatic component of the final image, with each set displaying
all of
these image components in sequence. Operation of the control circuits 116 and
118 is
synchronized such that, by way of example, when electrically switchable
holographic
optical element 2702A is activated, device 2704 directs red light onto those
pixels
which are at the time displaying a red monochromatic component of the final
image,
and so on. Otherwise, operation of the apparatus of this embodiment is
analogous to
that described above with reference to Figure 25.
In a preferred example of the above apparatus, the directing device 2704 is
composed of a stack of three holographic elements each of which is optimised
to act
upon the re, green and blue wavelengths, respectively.
Whereas the invention has been described in relation to what are presently
considered to be the most practicable and preferred embodiments, it is to be
understood that the invention is not limited to the disclosed arrangements but
rather is
intended to cover various modification and equivalent construction included
within
the spirit and scope of the invention.
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Client Reference: DLP035
