U.S. patent application number 13/084286 was filed with the patent office on 2011-07-28 for light illumination of displays with front light guide and coupling elements.
This patent application is currently assigned to QUALCOMM Incorporated. Invention is credited to Ion Bita, Alberto Emerico Brewer, Russell Wayne Gruhlke, Marek Mienko, Gang Xu.
Application Number | 20110182086 13/084286 |
Document ID | / |
Family ID | 40352376 |
Filed Date | 2011-07-28 |
United States Patent
Application |
20110182086 |
Kind Code |
A1 |
Mienko; Marek ; et
al. |
July 28, 2011 |
LIGHT ILLUMINATION OF DISPLAYS WITH FRONT LIGHT GUIDE AND COUPLING
ELEMENTS
Abstract
In various embodiments described herein, a display device
includes a front illumination apparatus that comprises a first
light guide disposed forward of an array of display elements, such
as an array of interferometric modulators, to distribute light
across the array of display elements. The light guide panel is edge
illuminated by a light source positioned behind the array display
elements. The light from such a light source is coupled to a second
light guide disposed behind the array of display elements and
positioned laterally with respect to the light source. The light in
the second light guide is coupled into the first light guide using
a small optical coupling element such as a turning mirror. In some
embodiments the second light guide may comprise the backplate of
the display device.
Inventors: |
Mienko; Marek; (San Jose,
CA) ; Xu; Gang; (Cupertino, CA) ; Bita;
Ion; (San Jose, CA) ; Gruhlke; Russell Wayne;
(Milpitas, CA) ; Brewer; Alberto Emerico; (Chula
Vista, CA) |
Assignee: |
QUALCOMM Incorporated
San Diego
CA
|
Family ID: |
40352376 |
Appl. No.: |
13/084286 |
Filed: |
April 11, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
|
|
11952872 |
Dec 7, 2007 |
7949213 |
|
|
13084286 |
|
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Current U.S.
Class: |
362/615 ;
29/592.1 |
Current CPC
Class: |
G02B 6/0038 20130101;
G02B 26/001 20130101; G02B 6/0076 20130101; G02B 6/0028 20130101;
G02B 6/0031 20130101; G02B 17/023 20130101; Y10T 29/49002 20150115;
Y10T 29/49826 20150115 |
Class at
Publication: |
362/615 ;
29/592.1 |
International
Class: |
F21V 8/00 20060101
F21V008/00; H05K 13/00 20060101 H05K013/00 |
Claims
1. A display device comprising: a reflective spatial light
modulator; a light source; a light guide forward of the reflective
spatial light modulator, the light guide having forward and
rearward surfaces; a light bar disposed forward or rearward of the
light guide, the light bar configured to receive light from the
light source and comprising a material through which light from the
light source propagates; and a turning mirror, the light bar
including turning features configured to turn light propagating
therein onto the turning mirror, the turning mirror disposed to
direct light into the light guide, such that the light is total
internally reflected from the forward and rearward surfaces of the
light guide so as to be guided along the length of the light guide,
wherein the light guide is configured to direct the light coupled
therein to the reflective spatial light modulator.
2. The display device of claim 1, wherein the reflective spatial
light modulator includes a microelectromechanical system
(MEMS).
3. The display device of claim 1, wherein the reflective spatial
light modulator includes a plurality of interferometric
modulators.
4. The display device of claim 1, wherein the reflective spatial
light modulator includes a substrate on which a plurality of
modulating elements are formed.
5. The display device of claim 1, wherein the light source includes
a light emitting diode.
6. The display device of claim 1, wherein the light bar is forward
the light guide.
7. The display device of claim 1, wherein the light bar is rearward
the light guide.
8. The display device of claim 2, wherein the light guide further
includes a plurality of turning features in or on the light guide
that direct the light propagating in the light guide onto the
reflective spatial light modulator.
9. The display device of claim 8, wherein the turning features
include grooves.
10. The display device of claim 8, wherein the turning features
include diffractive features.
11. The display device of claim 4, wherein the light guide includes
the substrate on which the plurality of modulating elements are
formed.
12. The display device of claim 1, wherein the light guide includes
a sheet, plate, film, film stack, or combination thereof.
13. The display device of claim 4, further including an isolation
layer between the light guide and the substrate.
14. The display device of claim 1, further including turning
features disposed on or in the light bar to turn the light
propagating therein onto the optical coupler.
15. The display device of claim 1, wherein the optical coupler
includes a turning mirror.
16. The display device of claim 1, wherein the turning mirror
includes a curved reflective surface.
17. The display device of claim 16, wherein the curved reflective
surface is elliptical.
18. The display device of claim 17, wherein the elliptical surface
has foci proximal to ends of the light bar and the light guide.
19. The display device of claim 1, wherein the turning mirror
includes a plurality of planar mirror surfaces oriented at an angle
with respect to each other.
20. The display device of claim 19, wherein the angle is between
about 90 and 120 degrees.
21. The display device of claim 19, wherein the angle is about 90
degrees.
22. The display device of claim 19, wherein the angle is about 120
degrees.
23. The display device of claim 1, further including: a processor
that is configured to communicate with the spatial light modulator,
the processor being configured to process image data; and a memory
device that is configured to communicate with the processor.
24. The display device of claim 23, further including a driver
circuit configured to send at least one signal to the spatial light
modulator.
25. The display device of claim 24, further including a controller
configured to send at least a portion of the image data to the
driver circuit.
26. The display device of claim 25, further including an image
source module configured to send the image data to the
processor.
27. The display device of claim 26, wherein the image source module
includes at least one of a receiver, transceiver, and
transmitter.
28. The display device of claim 27, further including an input
device configured to receive input data and to communicate the
input data to the processor.
29. A display device comprising: a means for reflectively
modulating light; a means for illuminating; a means for guiding
light disposed forward of the reflectively light modulating means,
the means for guiding light having forward and rearward surfaces; a
means for receiving light from the illuminating means, the light
receiving means disposed forward or rearward of the light guiding
means and including a material through which light from the
illuminating means propagates; and a turning mirror, the light
receiving means including means for turning light configured to
turn light propagating therein onto the turning mirror, the turning
mirror disposed to direct light received from the light receiving
means into the light guiding means, such that the light is total
internally reflected from the forward and rearward surfaces of the
means for guiding light so as to be guided along the length of the
means for guiding light, wherein the light guiding means is
configured to direct the light coupled therein to the reflectively
light modulating means.
30. The display device of claim 29, wherein the reflectively light
modulating means includes reflective spatial light modulator.
31. The display device of claim 30, wherein the reflective spatial
light modulator includes a microelectromechanical system
(MEMS).
32. The display device of claim 29, wherein the illuminating means
includes a light emitting diode.
33. The display device of claim 29, wherein the light receiving
means includes a light bar.
34. The display of claim 29, wherein the light guiding means
includes a light guide.
35. The display device of claim 29, wherein the light guiding means
further includes means for turning light.
36. The display device of claim 35, wherein the light turning means
includes grooves.
37. The display device of claim 35, wherein the light turning means
includes diffractive features.
38. The display device of claim 29, wherein the light coupling
means includes a turning mirror.
39. The display device of claim 29, further including a means for
supporting the reflectively light modulating means.
40. The display device of claim 39, further including a means for
isolation disposed between the supporting means and the light
guiding means.
41. The display device of claim 39, wherein the supporting means
includes a substrate.
42. A method of manufacturing a display device, the method
comprising: providing a reflective spatial light modulator;
providing a light source; disposing a light guide forward of the
reflective spatial light modulator, the light guide having forward
and rearward surfaces; disposing a light bar forward or rearward of
the light guide, the light bar configured to receive light from the
light and including a material through which light from the light
source propagates; providing a plurality of turning features on the
light bar; and providing a turning mirror, the turning features on
the light bar configured to direct light towards the turning
mirror, the turning mirror configured to direct light received from
the light bar into the light guide, such that the light is total
internally reflected from the forward and rearward surfaces of the
light guide so as to be guided along the length of the light
guide.
43. The method of claim 42, further includes forming a plurality of
turning features on the light guide.
Description
CROSS-REFERENCE TO RELATED APPLICATIONS
[0001] This application is a divisional of U.S. application Ser.
No. 11/952,872, filed on Dec. 7, 2007 and entitled "Light
Illumination of Displays with Front Light Guide and Coupling
Elements," the contents of which are hereby incorporated by
reference in their entirety.
BACKGROUND
[0002] 1. Field
[0003] The present invention relates to microelectromechanical
systems (MEMS), and more particularly to displays comprising
MEMS.
[0004] 2. Description of the Related Art
[0005] Microelectromechanical systems (MEMS) include micro
mechanical elements, actuators, and electronics. Micromechanical
elements may be created using deposition, etching, and/or other
micromachining processes that etch away parts of substrates and/or
deposited material layers or that add layers to form electrical and
electromechanical devices. One type of MEMS device is called an
interferometric modulator. As used herein, the term interferometric
modulator or interferometric light modulator refers to a device
that selectively absorbs and/or reflects light using the principles
of optical interference. In certain embodiments, an interferometric
modulator may comprise a pair of conductive plates, one or both of
which may be transparent and/or reflective in whole or part and
capable of relative motion upon application of an appropriate
electrical signal. In a particular embodiment, one plate may
comprise a stationary layer deposited on a substrate and the other
plate may comprise a metallic membrane separated from the
stationary layer by an air gap. As described herein in more detail,
the position of one plate in relation to another can change the
optical interference of light incident on the interferometric
modulator. Such devices have a wide range of applications, and it
would be beneficial in the art to utilize and/or modify the
characteristics of these types of devices so that their features
can be exploited in improving existing products and creating new
products that have not yet been developed.
SUMMARY
[0006] Various embodiments described herein comprise light guides
for distributing light across an array of display elements. The
light guide may include surface relief features to turn light
propagating in a light guide onto the array of display elements.
The surface relief features may comprise facets that reflect light.
The light guide may be illuminated by a light source placed behind
the array of display elements.
[0007] In one embodiment of this invention, a display device
comprises a reflective spatial light modulator, a light source
rearward of the reflective spatial light modulator, a first light
guide forward of the reflective spatial light modulator and a
turning mirror disposed to receive light from the light source and
direct the light into said first light guide. The first light guide
is configured to direct the light coupled therein to the reflective
spatial light modulator.
[0008] In another embodiment of this invention, a display device
comprises a reflective spatial light modulator, a light source, a
light bar disposed to receive light from the light source, a light
guide forward of said reflective spatial light modulator and an
optical coupler disposed to receive light from the light bar and
direct said light into said light guide. The light guide is
configured to direct the light coupled therein to the reflective
spatial light modulator.
[0009] In one embodiment, a display device comprises a means for
reflectively modulating light. The display device further comprises
a means for illuminating; a means for receiving light from the
illuminating means; a means for guiding light disposed forward of
the reflectively light modulating means; and a means for coupling
light disposed to receive light from the light receiving means and
directing the light into the light guiding means. The light guiding
means is configured to direct the light coupled therein to the
reflectively light modulating means.
[0010] In another embodiment, a display device comprises a means
for reflectively modulating light; a means for illuminating
disposed rearward of the reflectively light modulating means; a
first means for guiding light forward of the reflectively light
modulating means; and a means for reflecting light disposed to
receive light from the illuminating means and direct the light into
the first light guiding means. The first light guiding means is
configured to direct the light coupled therein to the reflectively
light modulating means.
[0011] In a certain embodiment, a method of manufacturing a display
device comprises providing a reflective spatial light modulator.
The method further comprises disposing a light source rearward of
the reflective spatial light modulator, disposing a first light
guide forward of the reflective spatial light modulator and
disposing a turning mirror to receive light from the light source
and direct the light into the first light guide.
[0012] In another embodiment, a method of manufacturing a display
device comprises providing a reflective spatial light modulator.
The method further comprises providing a light source, disposing a
light bar to receive light from the light source and disposing a
light guide forward of the reflective spatial light modulator. The
method also comprises disposing an optical coupler to receive light
from the light bar and direct the light into the light guide.
[0013] In another embodiment, a display device comprises a means
for reflectively modulating light; a means for illuminating
disposed forward of the reflectively light modulating means; a
first means for guiding light forward of the reflectively light
modulating means; and a means for reflecting light disposed to
receive light from the illuminating means and direct the light into
the first light guiding means. The first light guiding means is
configured to direct the light coupled therein to the reflectively
light modulating means.
[0014] In one embodiment, a display device comprises a reflective
spatial light modulator; a light source forward of the reflective
spatial light modulator; a first light guide forward of the
reflective spatial light modulator; and a turning mirror disposed
to receive light from the light source and direct the light into
the first light guide. The first light guide is configured to
direct said light coupled therein to the reflective spatial light
modulator.
[0015] In a certain embodiment, a method of manufacturing a display
device comprises providing a reflective spatial light modulator.
The method further comprises disposing a light source forward of
the reflective spatial light modulator, disposing a first light
guide forward of the reflective spatial light modulator and
disposing a turning mirror to receive light from the light source
and direct the light into the first light guide.
BRIEF DESCRIPTION OF THE DRAWINGS
[0016] Example embodiments disclosed herein are illustrated in the
accompanying schematic drawings, which are for illustrative
purposes only.
[0017] FIG. 1 is an isometric view depicting a portion of one
embodiment of an interferometric modulator display in which a
movable reflective layer of a first interferometric modulator is in
a relaxed position and a movable reflective layer of a second
interferometric modulator is in an actuated position.
[0018] FIG. 2 is a system block diagram illustrating one embodiment
of an electronic device incorporating a 3.times.3 interferometric
modulator display.
[0019] FIG. 3 is a diagram of movable mirror position versus
applied voltage for one exemplary embodiment of an interferometric
modulator of FIG. 1.
[0020] FIG. 4 is an illustration of a set of row and column
voltages that may be used to drive an interferometric modulator
display.
[0021] FIG. 5A illustrates one exemplary frame of display data in
the 3.times.3 interferometric modulator display of FIG. 2.
[0022] FIG. 5B illustrates one exemplary timing diagram for row and
column signals that may be used to write the frame of FIG. 5A.
[0023] FIGS. 6A and 6B are system block diagrams illustrating an
embodiment of a visual display device comprising a plurality of
interferometric modulators.
[0024] FIG. 7A is a cross section of the device of FIG. 1.
[0025] FIG. 7B is a cross section of an alternative embodiment of
an interferometric modulator.
[0026] FIG. 7C is a cross section of another alternative embodiment
of an interferometric modulator.
[0027] FIG. 7D is a cross section of yet another alternative
embodiment of an interferometric modulator.
[0028] FIG. 7E is a cross section of an additional alternative
embodiment of an interferometric modulator.
[0029] FIG. 8 is a top view of a display device comprising a light
source, a light bar reflector and a light guide panel that can
illuminate an array of interferometric modulators.
[0030] FIG. 9 is a cross section of a portion of an embodiment of a
display device comprising of an elliptical turning mirror coupling
light from the light source into the light guide panel.
[0031] FIG. 10 is a perspective view of a curved turning
mirror.
[0032] FIG. 11 is a cross section of a portion of an embodiment of
a display device comprising of a turning mirror having two planar
reflective surfaces angled with respect to each other.
[0033] FIG. 12 is a cross section of a portion of another
embodiment of a display device comprising of a turning mirror
having three planar reflective surfaces angled with respect to each
other.
[0034] FIG. 13 is a cross section of a portion of another
alternative embodiment of a display device wherein an isolation
layer is disposed between the front light guide and the array of
interferometric modulators.
[0035] FIG. 14 is a cross section of a portion of an embodiment of
a display device wherein the substrate on which the array of
interferometric modulators are formed is used as a light guide.
[0036] FIG. 15 is a perspective view of an embodiment of a display
device comprising a light bar disposed on the light guide panel and
a turning mirror configured to couple light from the light bar into
the light guide panel.
DETAILED DESCRIPTION OF CERTAIN PREFERRED EMBODIMENTS
[0037] The following detailed description is directed to certain
specific embodiments of the invention. However, the invention can
be embodied in a multitude of different ways. In this description,
reference is made to the drawings wherein like parts are designated
with like numerals throughout. As will be apparent from the
following description, the embodiments may be implemented in any
device that is configured to display an image, whether in motion
(e.g., video) or stationary (e.g., still image), and whether
textual or pictorial. More particularly, it is contemplated that
the embodiments may be implemented in or associated with a variety
of electronic devices such as, but not limited to, mobile
telephones, wireless devices, personal data assistants (PDAs),
hand-held or portable computers, GPS receivers/navigators, cameras,
MP3 players, camcorders, game consoles, wrist watches, clocks,
calculators, television monitors, flat panel displays, computer
monitors, auto displays (e.g., odometer display, etc.), cockpit
controls and/or displays, display of camera views (e.g., display of
a rear view camera in a vehicle), electronic photographs,
electronic billboards or signs, projectors, architectural
structures, packaging, and aesthetic structures (e.g., display of
images on a piece of jewelry). MEMS devices of similar structure to
those described herein can also be used in non-display applications
such as in electronic switching devices.
[0038] In various embodiments described herein, a display device
includes a front illumination apparatus that comprises a light
guide disposed forward of an array of display elements, such as an
array of interferometric modulators, to distribute light across the
array of display elements. For example, a light guide panel may
comprise a transparent sheet or plate and a turning film thereon.
The light guide panel is edge illuminated by a light source and at
least a portion of this light is delivered uniformly across the
array of display elements. For many portable display applications,
however, it is useful for the display to be compact. Accordingly,
in various embodiments described herein, the light source is
positioned directly behind the array display elements to reduce the
footprint of display device. In certain embodiments, for example,
two light guide panels may be used. A first light guide is disposed
forward to the display elements and a second light guide is
disposed rearward to the display elements. The second light guide
is edge illuminated by the light source. The first guide comprises
the substrate supporting the array of display elements and a
turning film formed thereon. A small optical coupling element such
as, for example, a turning mirror is used to couple light from the
second light guide to the first light guide. The second light guide
may comprise the substrate supporting the display elements or the
backplate of the display device in certain embodiments. In some
embodiments, the first light guide comprises the substrate and the
second light guide comprises the backplate. Such designs may be
useful in addressing the size or form factor restrictions. The
second light guide is thin as compared to the substrate and the
array of display elements. As a consequence, the overall thickness
of the entire display is only slightly increased beyond that of the
display elements themselves which are formed on a substrate. The
footprint however is reduced by locating light sources behind the
display element rather than on the side thereof
[0039] One interferometric modulator display embodiment comprising
an interferometric MEMS display element is illustrated in FIG. 1.
In these devices, the pixels are in either a bright or dark state.
In the bright ("on" or "open") state, the display element reflects
a large portion of incident visible light to a user. When in the
dark ("off" or "closed") state, the display element reflects little
incident visible light to the user. Depending on the embodiment,
the light reflectance properties of the "on" and "off" states may
be reversed. MEMS pixels can be configured to reflect predominantly
at selected colors, allowing for a color display in addition to
black and white.
[0040] FIG. 1 is an isometric view depicting two adjacent pixels in
a series of pixels of a visual display, wherein each pixel
comprises a MEMS interferometric modulator. In some embodiments, an
interferometric modulator display comprises a row/column array of
these interferometric modulators. Each interferometric modulator
includes a pair of reflective layers positioned at a variable and
controllable distance from each other to form a resonant optical
gap with at least one variable dimension. In one embodiment, one of
the reflective layers may be moved between two positions. In the
first position, referred to herein as the relaxed position, the
movable reflective layer is positioned at a relatively large
distance from a fixed partially reflective layer. In the second
position, referred to herein as the actuated position, the movable
reflective layer is positioned more closely adjacent to the
partially reflective layer. Incident light that reflects from the
two layers interferes constructively or destructively depending on
the position of the movable reflective layer, producing either an
overall reflective or non-reflective state for each pixel.
[0041] The depicted portion of the pixel array in FIG. 1 includes
two adjacent interferometric modulators 12a and 12b. In the
interferometric modulator 12a on the left, a movable reflective
layer 14a is illustrated in a relaxed position at a predetermined
distance from an optical stack 16a, which includes a partially
reflective layer. In the interferometric modulator 12b on the
right, the movable reflective layer 14b is illustrated in an
actuated position adjacent to the optical stack 16b.
[0042] The optical stacks 16a and 16b (collectively referred to as
optical stack 16), as referenced herein, typically comprise several
fused layers, which can include an electrode layer, such as indium
tin oxide (ITO), a partially reflective layer, such as chromium,
and a transparent dielectric. The optical stack 16 is thus
electrically conductive, partially transparent, and partially
reflective, and may be fabricated, for example, by depositing one
or more of the above layers onto a transparent substrate 20. The
partially reflective layer can be formed from a variety of
materials that are partially reflective such as various metals,
semiconductors, and dielectrics. The partially reflective layer can
be formed of one or more layers of materials, and each of the
layers can be formed of a single material or a combination of
materials.
[0043] In some embodiments, the layers of the optical stack 16 are
patterned into parallel strips, and may form row electrodes in a
display device as described further below. The movable reflective
layers 14a, 14b may be formed as a series of parallel strips of a
deposited metal layer or layers (orthogonal to the row electrodes
of 16a, 16b) deposited on top of posts 18 and an intervening
sacrificial material deposited between the posts 18. When the
sacrificial material is etched away, the movable reflective layers
14a, 14b are separated from the optical stacks 16a, 16b by a
defined gap 19. A highly conductive and reflective material such as
aluminum may be used for the reflective layers 14, and these strips
may form column electrodes in a display device.
[0044] With no applied voltage, the gap 19 remains between the
movable reflective layer 14a and optical stack 16a, with the
movable reflective layer 14a in a mechanically relaxed state, as
illustrated by the pixel 12a in FIG. 1. However, when a potential
difference is applied to a selected row and column, the capacitor
formed at the intersection of the row and column electrodes at the
corresponding pixel becomes charged, and electrostatic forces pull
the electrodes together. If the voltage is high enough, the movable
reflective layer 14 is deformed and is forced against the optical
stack 16. A dielectric layer (not illustrated in this Figure)
within the optical stack 16 may prevent shorting and control the
separation distance between layers 14 and 16, as illustrated by
pixel 12b on the right in FIG. 1. The behavior is the same
regardless of the polarity of the applied potential difference. In
this way, row/column actuation that can control the reflective vs.
non-reflective pixel states is analogous in many ways to that used
in conventional LCD and other display technologies.
[0045] FIGS. 2 through 5B illustrate one exemplary process and
system for using an array of interferometric modulators in a
display application.
[0046] FIG. 2 is a system block diagram illustrating one embodiment
of an electronic device that may incorporate aspects of the
invention. In the exemplary embodiment, the electronic device
includes a processor 21 which may be any general purpose single- or
multi-chip microprocessor such as an ARM, Pentium.RTM., Pentium
II.RTM., Pentium III.RTM., Pentium IV.RTM., Pentium.RTM. Pro, an
8051, a MIPS.RTM., a Power PC.RTM., an ALPHA.RTM., or any special
purpose microprocessor such as a digital signal processor,
microcontroller, or a programmable gate array. As is conventional
in the art, the processor 21 may be configured to execute one or
more software modules. In addition to executing an operating
system, the processor may be configured to execute one or more
software applications, including a web browser, a telephone
application, an email program, or any other software
application.
[0047] In one embodiment, the processor 21 is also configured to
communicate with an array driver 22. In one embodiment, the array
driver 22 includes a row driver circuit 24 and a column driver
circuit 26 that provide signals to a display array or panel 30. The
cross section of the array illustrated in FIG. 1 is shown by the
lines 1-1 in FIG. 2. For MEMS interferometric modulators, the
row/column actuation protocol may take advantage of a hysteresis
property of these devices illustrated in FIG. 3. It may require,
for example, a 10 volt potential difference to cause a movable
layer to deform from the relaxed state to the actuated state.
However, when the voltage is reduced from that value, the movable
layer maintains its state as the voltage drops back below 10 volts.
In the exemplary embodiment of FIG. 3, the movable layer does not
relax completely until the voltage drops below 2 volts. Thus, there
exists a window of applied voltage, about 3 to 7 V in the example
illustrated in FIG. 3, within which the device is stable in either
the relaxed or actuated state. This is referred to herein as the
"hysteresis window" or "stability window." For a display array
having the hysteresis characteristics of FIG. 3, the row/column
actuation protocol can be designed such that during row strobing,
pixels in the strobed row that are to be actuated are exposed to a
voltage difference of about 10 volts, and pixels that are to be
relaxed are exposed to a voltage difference of close to zero volts.
After the strobe, the pixels are exposed to a steady state voltage
difference of about 5 volts such that they remain in whatever state
the row strobe put them in. After being written, each pixel sees a
potential difference within the "stability window" of 3-7 volts in
this example. This feature makes the pixel design illustrated in
FIG. 1 stable under the same applied voltage conditions in either
an actuated or relaxed pre-existing state. Since each pixel of the
interferometric modulator, whether in the actuated or relaxed
state, is essentially a capacitor formed by the fixed and moving
reflective layers, this stable state can be held at a voltage
within the hysteresis window with almost no power dissipation.
Essentially no current flows into the pixel if the applied
potential is fixed.
[0048] In typical applications, a display frame may be created by
asserting the set of column electrodes in accordance with the
desired set of actuated pixels in the first row. A row pulse is
then applied to the row 1 electrode, actuating the pixels
corresponding to the asserted column lines. The asserted set of
column electrodes is then changed to correspond to the desired set
of actuated pixels in the second row. A pulse is then applied to
the row 2 electrode, actuating the appropriate pixels in row 2 in
accordance with the asserted column electrodes. The row 1 pixels
are unaffected by the row 2 pulse, and remain in the state they
were set to during the row 1 pulse. This may be repeated for the
entire series of rows in a sequential fashion to produce the frame.
Generally, the frames are refreshed and/or updated with new display
data by continually repeating this process at some desired number
of frames per second. A wide variety of protocols for driving row
and column electrodes of pixel arrays to produce display frames are
also well known and may be used in conjunction with the present
invention.
[0049] FIGS. 4, 5A, and 5B illustrate one possible actuation
protocol for creating a display frame on the 3.times.3 array of
FIG. 2. FIG. 4 illustrates a possible set of column and row voltage
levels that may be used for pixels exhibiting the hysteresis curves
of FIG. 3. In the FIG. 4 embodiment, actuating a pixel involves
setting the appropriate column to -V.sub.bias, and the appropriate
row to +.DELTA.V, which may correspond to -5 volts and +5 volts,
respectively Relaxing the pixel is accomplished by setting the
appropriate column to +V.sub.bias, and the appropriate row to the
same +.DELTA.V, producing a zero volt potential difference across
the pixel. In those rows where the row voltage is held at zero
volts, the pixels are stable in whatever state they were originally
in, regardless of whether the column is at +V.sub.bias, or
-V.sub.bias. As is also illustrated in FIG. 4, it will be
appreciated that voltages of opposite polarity than those described
above can be used, e.g., actuating a pixel can involve setting the
appropriate column to +V.sub.bias, and the appropriate row to
-.DELTA.V. In this embodiment, releasing the pixel is accomplished
by setting the appropriate column to -V.sub.bias, and the
appropriate row to the same -.DELTA.V, producing a zero volt
potential difference across the pixel.
[0050] FIG. 5B is a timing diagram showing a series of row and
column signals applied to the 3.times.3 array of FIG. 2 which will
result in the display arrangement illustrated in FIG. 5A, where
actuated pixels are non-reflective. Prior to writing the frame
illustrated in FIG. 5A, the pixels can be in any state, and in this
example, all the rows are at 0 volts, and all the columns are at +5
volts. With these applied voltages, all pixels are stable in their
existing actuated or relaxed states.
[0051] In the FIG. 5A frame, pixels (1,1), (1,2), (2,2), (3,2) and
(3,3) are actuated. To accomplish this, during a "line time" for
row 1, columns 1 and 2 are set to -5 volts, and column 3 is set to
+5 volts. This does not change the state of any pixels, because all
the pixels remain in the 3-7 volt stability window. Row 1 is then
strobed with a pulse that goes from 0, up to 5 volts, and back to
zero. This actuates the (1,1) and (1,2) pixels and relaxes the
(1,3) pixel. No other pixels in the array are affected. To set row
2 as desired, column 2 is set to -5 volts, and columns 1 and 3 are
set to +5 volts. The same strobe applied to row 2 will then actuate
pixel (2,2) and relax pixels (2,1) and (2,3). Again, no other
pixels of the array are affected. Row 3 is similarly set by setting
columns 2 and 3 to -5 volts, and column 1 to +5 volts. The row 3
strobe sets the row 3 pixels as shown in FIG. 5A. After writing the
frame, the row potentials are zero, and the column potentials can
remain at either +5 or -5 volts, and the display is then stable in
the arrangement of FIG. 5A. It will be appreciated that the same
procedure can be employed for arrays of dozens or hundreds of rows
and columns. It will also be appreciated that the timing, sequence,
and levels of voltages used to perform row and column actuation can
be varied widely within the general principles outlined above, and
the above example is exemplary only, and any actuation voltage
method can be used with the systems and methods described
herein.
[0052] FIGS. 6A and 6B are system block diagrams illustrating an
embodiment of a display device 40. The display device 40 can be,
for example, a cellular or mobile telephone. However, the same
components of display device 40 or slight variations thereof are
also illustrative of various types of display devices such as
televisions and portable media players.
[0053] The display device 40 includes a housing 41, a display 30,
an antenna 43, a speaker 45, an input device 48, and a microphone
46. The housing 41 is generally formed from any of a variety of
manufacturing processes as are well known to those of skill in the
art, including injection molding and vacuum forming. In addition,
the housing 41 may be made from any of a variety of materials,
including, but not limited to, plastic, metal, glass, rubber, and
ceramic, or a combination thereof. In one embodiment, the housing
41 includes removable portions (not shown) that may be interchanged
with other removable portions of different color, or containing
different logos, pictures, or symbols.
[0054] The display 30 of exemplary display device 40 may be any of
a variety of displays, including a bi-stable display, as described
herein. In other embodiments, the display 30 includes a flat-panel
display, such as plasma, EL, OLED, STN LCD, or TFT LCD as described
above, or a non-flat-panel display, such as a CRT or other tube
device, as is well known to those of skill in the art. However, for
purposes of describing the present embodiment, the display 30
includes an interferometric modulator display, as described
herein.
[0055] The components of one embodiment of exemplary display device
40 are schematically illustrated in FIG. 6B. The illustrated
exemplary display device 40 includes a housing 41 and can include
additional components at least partially enclosed therein. For
example, in one embodiment, the exemplary display device 40
includes a network interface 27 that includes an antenna 43, which
is coupled to a transceiver 47. The transceiver 47 is connected to
a processor 21, which is connected to conditioning hardware 52. The
conditioning hardware 52 may be configured to condition a signal
(e.g., filter a signal). The conditioning hardware 52 is connected
to a speaker 45 and a microphone 46. The processor 21 is also
connected to an input device 48 and a driver controller 29. The
driver controller 29 is coupled to a frame buffer 28 and to an
array driver 22, which in turn is coupled to a display array 30. A
power supply 50 provides power to all components as required by the
particular exemplary display device 40 design.
[0056] The network interface 27 includes the antenna 43 and the
transceiver 47 so that the exemplary display device 40 can
communicate with one or more devices over a network. In one
embodiment, the network interface 27 may also have some processing
capabilities to relieve requirements of the processor 21. The
antenna 43 is any antenna known to those of skill in the art for
transmitting and receiving signals. In one embodiment, the antenna
transmits and receives RF signals according to the IEEE 802.11
standard, including IEEE 802.11(a), (b), or (g). In another
embodiment, the antenna transmits and receives RF signals according
to the BLUETOOTH standard. In the case of a cellular telephone, the
antenna is designed to receive CDMA, GSM, AMPS, or other known
signals that are used to communicate within a wireless cell phone
network. The transceiver 47 pre-processes the signals received from
the antenna 43 so that they may be received by and further
manipulated by the processor 21. The transceiver 47 also processes
signals received from the processor 21 so that they may be
transmitted from the exemplary display device 40 via the antenna
43.
[0057] In an alternative embodiment, the transceiver 47 can be
replaced by a receiver. In yet another alternative embodiment,
network interface 27 can be replaced by an image source, which can
store or generate image data to be sent to the processor 21. For
example, the image source can be a digital video disc (DVD) or a
hard-disc drive that contains image data, or a software module that
generates image data.
[0058] Processor 21 generally controls the overall operation of the
exemplary display device 40. The processor 21 receives data, such
as compressed image data from the network interface 27 or an image
source, and processes the data into raw image data or into a format
that is readily processed into raw image data. The processor 21
then sends the processed data to the driver controller 29 or to
frame buffer 28 for storage. Raw data typically refers to the
information that identifies the image characteristics at each
location within an image. For example, such image characteristics
can include color, saturation, and gray-scale level.
[0059] In one embodiment, the processor 21 includes a
microcontroller, CPU, or logic unit to control operation of the
exemplary display device 40. Conditioning hardware 52 generally
includes amplifiers and filters for transmitting signals to the
speaker 45, and for receiving signals from the microphone 46.
Conditioning hardware 52 may be discrete components within the
exemplary display device 40, or may be incorporated within the
processor 21 or other components.
[0060] The driver controller 29 takes the raw image data generated
by the processor 21 either directly from the processor 21 or from
the frame buffer 28 and reformats the raw image data appropriately
for high speed transmission to the array driver 22. Specifically,
the driver controller 29 reformats the raw image data into a data
flow having a raster-like format, such that it has a time order
suitable for scanning across the display array 30. Then the driver
controller 29 sends the formatted information to the array driver
22. Although a driver controller 29, such as a LCD controller, is
often associated with the system processor 21 as a stand-alone
Integrated Circuit (IC), such controllers may be implemented in
many ways. They may be embedded in the processor 21 as hardware,
embedded in the processor 21 as software, or fully integrated in
hardware with the array driver 22.
[0061] Typically, the array driver 22 receives the formatted
information from the driver controller 29 and reformats the video
data into a parallel set of waveforms that are applied many times
per second to the hundreds and sometimes thousands of leads coming
from the display's x-y matrix of pixels.
[0062] In one embodiment, the driver controller 29, array driver
22, and display array 30 are appropriate for any of the types of
displays described herein. For example, in one embodiment, driver
controller 29 is a conventional display controller or a bi-stable
display controller (e.g., an interferometric modulator controller).
In another embodiment, array driver 22 is a conventional driver or
a bi-stable display driver (e.g., an interferometric modulator
display). In one embodiment, a driver controller 29 is integrated
with the array driver 22. Such an embodiment is common in highly
integrated systems such as cellular phones, watches, and other
small area displays. In yet another embodiment, display array 30 is
a typical display array or a bi-stable display array (e.g., a
display including an array of interferometric modulators).
[0063] The input device 48 allows a user to control the operation
of the exemplary display device 40. In one embodiment, input device
48 includes a keypad, such as a QWERTY keyboard or a telephone
keypad, a button, a switch, a touch-sensitive screen, or a
pressure- or heat-sensitive membrane. In one embodiment, the
microphone 46 is an input device for the exemplary display device
40. When the microphone 46 is used to input data to the device,
voice commands may be provided by a user for controlling operations
of the exemplary display device 40.
[0064] Power supply 50 can include a variety of energy storage
devices as are well known in the art. For example, in one
embodiment, power supply 50 is a rechargeable battery, such as a
nickel-cadmium battery or a lithium ion battery. In another
embodiment, power supply 50 is a renewable energy source, a
capacitor, or a solar cell including a plastic solar cell, and
solar-cell paint. In another embodiment, power supply 50 is
configured to receive power from a wall outlet.
[0065] In some embodiments, control programmability resides, as
described above, in a driver controller which can be located in
several places in the electronic display system. In some
embodiments, control programmability resides in the array driver
22. Those of skill in the art will recognize that the
above-described optimizations may be implemented in any number of
hardware and/or software components and in various
configurations.
[0066] The details of the structure of interferometric modulators
that operate in accordance with the principles set forth above may
vary widely. For example, FIGS. 7A-7E illustrate five different
embodiments of the movable reflective layer 14 and it's supporting
structures. FIG. 7A is a cross section of the embodiment of FIG. 1,
where a strip of metal material 14 is deposited on orthogonally
extending supports 18. In FIG. 7B, the moveable reflective layer 14
is attached to supports at the corners only, on tethers 32. In FIG.
7C, the moveable reflective layer 14 is suspended from a deformable
layer 34, which may comprise a flexible metal. The deformable layer
34 connects, directly or indirectly, to the substrate 20 around the
perimeter of the deformable layer 34. These connections are herein
referred to as support posts. The embodiment illustrated in FIG. 7D
has support post plugs 42 upon which the deformable layer 34 rests.
The movable reflective layer 14 remains suspended over the gap, as
in FIGS. 7A-7C, but the deformable layer 34 does not form the
support posts by filling holes between the deformable layer 34 and
the optical stack 16. Rather, the support posts are formed of a
planarization material, which is used to form support post plugs
42. The embodiment illustrated in FIG. 7E is based on the
embodiment shown in FIG. 7D, but may also be adapted to work with
any of the embodiments illustrated in FIGS. 7A-7C, as well as
additional embodiments not shown. In the embodiment shown in FIG.
7E, an extra layer of metal or other conductive material has been
used to form a bus structure 44. This allows signal routing along
the back of the interferometric modulators, eliminating a number of
electrodes that may otherwise have had to be formed on the
substrate 20.
[0067] In embodiments such as those shown in FIG. 7, the
interferometric modulators function as direct-view devices, in
which images are viewed from the front side of the transparent
substrate 20, the side opposite to that upon which the modulator is
arranged. In these embodiments, the reflective layer 14 optically
shields the portions of the interferometric modulator on the side
of the reflective layer opposite the substrate 20, including the
deformable layer 34. This allows the shielded areas to be
configured and operated upon without negatively affecting the image
quality. Such shielding allows the bus structure 44 in FIG. 7E,
which provides the ability to separate the optical properties of
the modulator from the electromechanical properties of the
modulator, such as addressing and the movements that result from
that addressing. This separable modulator architecture allows the
structural design and materials used for the electromechanical
aspects and the optical aspects of the modulator to be selected and
to function independently of each other. Moreover, the embodiments
shown in FIGS. 7C-7E have additional benefits deriving from the
decoupling of the optical properties of the reflective layer 14
from its mechanical properties, which are carried out by the
deformable layer 34. This allows the structural design and
materials used for the reflective layer 14 to be optimized with
respect to the optical properties, and the structural design and
materials used for the deformable layer 34 to be optimized with
respect to desired mechanical properties.
[0068] As described above, the interferometric modulators are
reflective display elements and can rely on ambient lighting in
daylight or well-lit environments. In addition, an internal source
of illumination can be provided for illuminating these reflective
display elements in dark ambient environments. The illumination for
reflective displays may be provided by a front illuminator. FIG. 8
shows the top view of a portion of a display device 80 comprising
an illumination apparatus configured to provide front illumination.
The display device 80 comprises a light source 82, a light bar 81
and a light guide panel 83. The light source 82 in this particular
embodiment comprises an LED. The light bar 81 is disposed with
respect to the light source 82 to receive light therefrom.
Reflective sections 85a and 85b are disposed with respect to the
side and end of the light bar 81. Reflectors may also be included
above and/or below the light bar 81. The light bar 81 comprises
substantially optically transmissive material that supports
propagation of light along the length thereof. Light emitted from
the light emitter 82 propagates into the light bar 81 and is guided
therein, for example, via total internal reflection at sidewalls of
the light bar, which form interfaces with air or some other
surrounding medium. The light bar 81 includes turning
microstructure 84 on one side that is opposite the light guide
panel 83. The turning microstructure 84 is configured to turn a
substantial portion of the light incident on that side of the light
bar 81 and to direct a portion of this light out of the light bar
81 into the light guide panel 83. In certain embodiments, the
illumination apparatus may further comprise a coupling optic (not
shown) between the light bar 81 and the light guide panel 83. For
example, the coupling optic may collimate light propagating from
the light bar 81. Other configurations are also possible.
[0069] The light guide panel 83 is disposed with respect to the
light bar 81 so as to receive light that has been turned by the
turning microstructure 84 and directed out of the light bar 81. In
certain embodiments, for example, the light guide panel 83
comprises a sheet or plate having a prismatic film thereon that
reflects light from the light bar 81 onto a plurality of display
elements (not shown) beneath the light guide panel in FIG. 8. The
plurality of display elements may comprise, for example, a
plurality of spatial light modulators (e.g. interferometric
modulators, liquid crystal elements, etc.).
[0070] To reduce the footprint of display device, in certain
embodiments the light bar 81 which is disposed adjacent to one edge
of the light guide panel 83 in FIG. 8 may be replaced with another
smaller optical coupling element such as, for example, a turning
mirror. Removing the light bar 81 from the side of the light guide
panel 83 reduces the footprint by reducing the dimension of the
display device in the X-Y plane. Moreover, the light bar 81 need
not be included thereby reducing device complexity and possible
cost. Such a configuration may also allow the light source 82 to be
positioned behind the plurality of display elements possibly
further reducing the footprint. Such designs may be useful in
addressing the size or form factor restrictions or other
considerations. Various approaches described herein may therefore
use a light source behind the display elements and a turning mirror
to front illuminate a reflective display element.
[0071] FIG. 9 illustrates a cross section of a portion of one
embodiment of a display device 90 wherein the light bar 81 of FIG.
8 is replaced with an optional coupling element. The display device
90 in FIG. 9 comprises a reflective display comprising a plurality
of reflective elements 96 such as reflective spatial light
modulators. In the embodiment shown in FIG. 9, the reflective
display elements 96 comprise interferometric modulators, although
other types of display elements may be used in the device. Other
examples of display elements include MEMS and liquid crystal
structures. The display elements 96 may be formed on an optically
transmissive substrate 95. This substrate 95 may provide structural
support during and after fabrication of the display elements 96
thereon. The substrate 95 may be substantially transparent such
that a viewer can see the display elements 96 through the
substrate. In some embodiments the substrate 95 may comprise glass
or plastic although other materials may also be used.
[0072] In the embodiment shown in FIG. 9, the substrate 95 has a
turning film 94 formed thereon. The turning film 94 may comprise,
for example, a prismatic film that includes turning features formed
therein. In some embodiments, the turning film 94 may comprise a
plastic film laminated onto the substrate 95. Adhesive may be used
to affix the turning film 94 to the substrate 95. Pressure
sensitive adhesive may be used. The adhesive may provide index
matching in some embodiments as well. Other methods of attaching
the turning film 94 to the substrate 95 may be used. In certain
embodiments the turning film 94 can be a multilayer stack instead
of a single layer. In case of a multilayer stack, the refractive
indices of the different layers may be close so that light is
transmitted through the various layers without being substantially
reflected or refracted. The film or films may be rigid or flexible.
In certain embodiments the film or films have an index of
refraction substantially similar to that of the substrate 95.
[0073] The substrate 95 and the turning film 94 together form a
first light guiding element 97 that is located above the
interferometric modulators 96 of the display device 90. In certain
embodiments wherein the turning film 94 is attached to the
substrate 95 with index matching adhesive, the first light guiding
element 97 is increased in thickness. Some advantages of a thicker
first light guiding element 97 are the relative ease in achieving
uniformity in brightness and increasing the efficiency of the light
coupled into the first light guiding element 97.
[0074] In some other embodiments, the turning film 94 may be joined
to the substrate 95 by an adhesive layer that has substantially
lower refractive index than the refractive index of the turning
film 94. Other layers or film such as optical isolation layer,
diffuser layer or color filter layer may be disposed between the
adhesive layer and the substrate. Light is guided in the turning
film 94 by total internal reflection at the interface between the
turning film and the adhesive layer. In such embodiments, the first
light guiding element is formed by the turning film 94 only.
[0075] The plurality of turning features in the turning film 94
redirect light normally guided in the light guide 97 such that the
light is directed out of the light guide towards the display
elements 96. The direction of the turned light forms an angle
smaller than 45 degrees from the normal to the surface of the
display elements. In various embodiments, light is redirected
through the thickness of the first light guide 97 substantially
normal to the light guide and the array of display elements 96.
Accordingly, such light is no longer totally internally reflected
at the lower sidewall of the light guide and exits therethrough.
Likewise, the light is transmitted to the interferometric
modulators preferably at normal incidence or close thereto.
[0076] In some embodiments, the turning features may comprise a
plurality of microprisms extending along the length of the first
light guide 97. The microprisms may be configured to receive light
propagating along the length of the turning film 94 and turn the
light through a large angle, usually between about 70-90.degree.
with a plurality of grazing incidence reflections. The prismatic
microstructures may comprise two or more turning facets angled with
respect to one another for reflecting the light at the air/facet
interface via total internal reflection and causing the light to be
turned toward the array of display elements 96 at near normal
incidence or close thereto.
[0077] In an alternative embodiment, the turning features may
comprise one or more diffractive optical elements or hologram
(e.g., volume or surface holograms or grating) configured to
receive light normally guided in the first light guide 97 and turn
the light such that the light is redirected towards the display
elements 96. In certain embodiments, the propagation direction of
the turned light forms an angle smaller than 45 degrees from the
normal to the display elements 96.
[0078] A light source 92 is disposed rearward of the
interferometric modulators 96 on a first side (side 1) of the
display device 90. A second light guide 98 is disposed with respect
to the light source 92 to receive light injected therein by the
light source 92. In certain embodiments, the second light guide 98
may comprise the backplate of the display device. In certain other
embodiments, the second light guide 98 may comprise an existing
backlight in the display device 90. This light source 92 could be a
single LED or an array of LEDs extending along an edge of the
second light guide 98. In certain embodiments, for example, the
light source 92 may comprise a plurality of LEDs parallel to the
x-axis that emit light parallel to the y axis (e.g., in the
negative y direction) to illuminate the second light guide 98
uniformly. In other embodiments, the light source 92 may comprise
an LED emitting in a direction parallel to the x-axis (e.g. in the
negative x direction) coupled to a light bar which has turning
features that turn a substantial amount of light propagating
parallel to the x axis in a direction parallel to the y axis (e.g.
in the negative y direction). Other types of emitters may also be
used. Additionally, in some embodiments optical lens or other
optical components may be used to couple the light from the light
source 92 into the second light 98. Optical features may also be
included to expand the width of or diverge the beam of light from
the light source 92 propagating in the second light guide 98. Such
features may be on the input end of the light guide near the light
source 92 in some embodiments.
[0079] Light emitted from the light source 92 is guided within the
second light guide 98 by total internal reflection from side 1 to
side 2. In some embodiments, the second light guide 98 may comprise
glass or transparent plastic or some other optically transmissive
material. In embodiments, for example wherein the second light
guide 98 is comprised of glass, the thickness of the second light
guide 98 may be from 200 .mu.m to 1 mm. In certain other
embodiments, for example wherein the second light guide is
comprised of plastic or other flexible material, the thickness of
the second light guide may be from 100 .mu.m to 1 mm. Other
materials and thicknesses may be used. In certain embodiments, the
length of the second light guide 98 is sufficiently long as to
allow the light from the light source 92 to spread uniformly across
the width of the second light guide 98 (e.g., on side 2 shown in
the embodiment depicted in FIG. 9), for example parallel to the
x-axis. In some embodiments the second light guide 98 may comprise
the transparent backplate of the display device 90. The backplate
of the device may be the packaging enclosing and/or supporting the
display elements 96. In some embodiments the backplate may form the
hermetically sealed package. In certain other embodiments, wherein
the backplate of the display device 90 is not transparent, a second
light guide 98 may be disposed forward of the backplate. In such
embodiments, the second light guide 98 may incorporate refractive
features to diverge the light from the light source 92. In some
embodiments comprising a main display element and a sub-display
element, wherein the main display element is illuminated with a
backlight, the second light guide 98 may comprise the backlight. In
embodiments, for example wherein the light guide is comprised of a
backplate, the thickness of the light guide may be from 400 to 700
.mu.m or may be up to 1 mm or greater. In certain embodiments, for
example wherein the light guide is comprised of a separate
component rearward of the display, the thickness of the light guide
may be 100 to 700 .mu.m. Values outside these ranges are also
possible.
[0080] Advantageously, the light source 92 and the second light
guide 98 are disposed beneath the plurality of display elements 96.
Such a configuration may be useful in reducing the footprint
occupied by the display devices as compared to devices with a light
source and light being disposed in the side of the front light
guide panel such as in FIG. 8.
[0081] In some embodiments spacers 99 may be used to separate the
display element 96 from the second light guide 98. In some
embodiments, the spacers 99 may structurally support the second
light guide 98 to the rigid substrate 95. In certain other
embodiments, the spacers 99 could be other peripheral adhesive
features that attach the backplate to the substrate 95.
[0082] A turning mirror 91 is disposed to receive light from the
edge of the second light guide 98 which is distal to the light
source 91 (side 2) and to direct the light into the edge of the
first light guide 97 that is proximal to the turning mirror, in
those embodiments wherein the turning film 94 is attached to the
substrate 95 with an adhesive layer that has substantially lower
refractive index than the turning film 94. Alternatively, when the
turning film 94 is attached to the substrate 95 with an index
matched adhesive layer, the turning mirror 91 is configured to
direct light from the edge of the second light guide 98 into the
edge of the substrate 95 that is proximal to the turning mirror. In
the embodiment shown in FIG. 9, the turning mirror 91 redirects
light propagating generally in the negative y direction and cause
it to rotate by 180 degrees and propagate generally in the positive
y direction by reflecting a substantial portion of the light. In
some embodiments greater than 90% of the light may be reflected by
the turning mirror 91.
[0083] The turning mirror 91 comprises a reflective surface in the
shape of a cylinder. In the embodiment shown in FIG. 9, the
reflective surface has a curved cross-section in the Z-Y plane
(i.e., parallel to the length of the cylinder that is parallel to
the X axis). The curved cross-section may be circular, elliptical,
other conics or aspheric. The curved cross-section may be smooth or
facetted. The facets can be planar or non-planar. The curved
surface may be multifaceted comprising, for example, three, four,
five, ten or more facets. In the embodiment shown in FIG. 9, the
cross section of the surface of the turning mirror 91 is
elliptical. The turning mirror 91 also has an optical aperture that
overlaps both the edge of the first light guide 97 and the edge of
the second light guide 98 in its optical path. In the embodiment
shown, the aperture is larger than the thicker of the first and
second light guide. In particular, the aperture is as large as
first and second light guides and spacers. The height of the
turning mirror (e.g., height of aperture) may be between 0.5 and
2.0 mm. In other embodiments, the height of the turning mirror may
be between 0.25 and 1.0 mm. In some embodiments, the turning mirror
may have width from 0.25 to 1 or to 3 or 4 millimeters. The turning
mirror can have other sizes.
[0084] In this particular embodiment, the elliptical cross section
of the turning mirror 91 has two line foci, represented by points
9A and 9B in the cross sectional view to FIG. 9. The foci are
disposed in the middle of the first light guide 97 and second light
guide 98 respectively. If the rays of light that emerge from the
edges of the second light guide 98 pass through the first focus 9A,
the rays of light will after reflection from the mirror 91 pass
through the second focus 9B and be injected into the first light
guide 97 with good efficiency, e.g. greater than 50%. The light
distribution at the edge of the second light guide 98 towards side
2 will be imaged at the edge of the first light guide 97 towards
side 2. Other configurations are possible. For example, the foci
9A, 9B need not be disposed precisely at the center or edge of the
first and second light guide. Additionally, in certain embodiments,
the mirror has different shape such that first and second line foci
are not provided.
[0085] Regardless of the shape of the turning mirror 91, light is
coupled from the second light guide 98 to the first light guide 97
by the turning mirror. For example, light from light source 92 can
be coupled into the second light guide 98 at the side 1. The light
propagates within the second light guide 98 from the input edge
side 1 to output edge side 2 by total internal reflection. The
light rays that are incident on the turning mirror 91 are reflected
by the turning mirror 91 into the first light guide 97. The turning
film 94 turns light guided in the light guide 97 such that the
light is redirected towards the display elements 96. The redirected
light passes through the guiding portion 97 substantially normal to
the light guide and the array of display elements 96 and is
transmitted to the interferometric modulators 96 preferably at
normal incidence or close thereto.
[0086] In another embodiment the reflective surface of the turning
mirror may have a parabolic cross-section. In case of the parabolic
turning mirror, the light passing through a line focus of the
parabolic reflecting surface will emerge in a direction
perpendicular to a directrix of the parabola after reflection. In
those embodiments having a parabolic turning mirror, the size and
shape of the parabolic reflecting surface can be adjusted to
increase or maximize the efficiency of coupling light from the
second light guide 98 to the first light guide 97.
[0087] In some embodiments, the turning mirror can be solid as
compared to a hollow shell. The turning mirror, for example, may
comprise a rod of substantially optically transmissive material
such as glass or plastic. FIG. 10 illustrates an embodiment of a
solid cylindrical turning mirror 100 with a first curved surface
101 and a second planar surface 102. The curved surface 101 has an
elliptical cross section along the Z-Y plane (i.e., perpendicular
to the length of the cylinder). The planar surface 102 of the
turning mirror is flat and can be contacted to the edge of the
display device. The curved surface 101 is coated with a reflective
layer. In some embodiments, the reflective layer may be metallic.
Other reflective coatings including dielectric coating,
interference coating, etc. may be used. Light enters the solid
turning mirror through the second planar surface 102 and is
reflected at the first curved surface 101.
[0088] In some embodiments, the turning mirror may be hollowed out
and comprise, for example, a shell having two curved surfaces. One
of the curved surfaces may be reflective. In one embodiment, for
example, where the turning mirror comprises optically transmissive
material such as plastic, one of the curved surfaces may be
metalized or have a dielectric or interference coating formed
thereon. In other embodiments, the turning mirror may comprise
metal with one of the curved surfaces being polished to increase
reflectivity.
[0089] In certain embodiments, the turning mirror may comprise
multiple planar reflecting surfaces disposed at an angle with
respect to each other. The particular embodiment illustrated in
FIG. 11, for example, shows two reflecting planar surfaces angled
with respect to each other. The angle between the two planar
surfaces can vary between, for example, 90 and 120 degrees or
between 90 and 100 degrees or between 90 and 110 degrees. In
certain embodiments, the planar mirror surfaces are oriented at an
angle of 90, 95100, 105, 110, 115 or 120 degrees with respect to
each other. Examples include 97 and 117 degrees. The angles are not
limited to those of these particular examples or ranges. The
turning mirror described in FIG. 11 comprises a solid rod or be it
may be hollowed out as described above. The turning mirror may
comprise optically transmissive material such as glass, plastic. In
other embodiments, the mirror may be metal. In some other
embodiments, the reflecting surface can comprise a metal film or a
dielectric film. In some embodiments the reflecting film comprises
an interference coating. The two reflecting surfaces can be fused,
adhered, or affixed together. In some embodiments, for example, the
mirror may be formed by extruding or molding an elongate structure
with the planar surfaces thereon. Other methods of forming the two
reflecting surfaces may be used.
[0090] In operation, light from light source 112 is coupled into
the second light guide 118. The light propagates within the second
light guide 118 from the input edge side 1 to output edge side 2 by
total internal reflection. The light rays from the second light
guide 118 are incident on the first reflecting plane 111A of the
planar turning mirror 111. After reflection, the light rays are
incident on the second reflecting plane 111B. After being reflected
by the second reflecting surface 111B, the light rays are incident
on the input of the first light guide 117 on side 2. The turning
film 114 further comprises a plurality of turning features for
turning light guided in the light guide 117 such that the light is
redirected towards the display elements 116. The redirected light
passes through the guiding portion 117 substantially normal to the
light guide 117 and the array of display elements 116 and is
transmitted to the interferometric modulators 116 preferably at
normal incidence or close thereto.
[0091] In certain other embodiments, the turning mirror 121 may
have a cross-section in the shape of a trapezoid as illustrated in
FIG. 12. One advantage of a trapezoidal geometry for the turning
mirror 121 is that the dimension of the turning mirror parallel to
the y-axis can be reduced in comparison to the turning mirror 111
of FIG. 11. The trapezoidal turning mirror 121 is formed by three
reflecting surfaces 121a, 121b and 121c. Reflecting surfaces 121a
and 121c are angled with respect to reflecting surface 121b. The
angular separation between reflecting surfaces 121a and 121b may be
equal to the angle between reflecting surfaces 121b and 121c. The
angle between the reflecting surfaces 121a and 121b may vary
between 90 degrees and 151 degrees. The angle between the
reflecting surfaces 121b and 121c may vary between 90 degrees and
151 degrees. In various embodiments, the angular separation between
the reflecting surfaces 121a and 121b may be greater than 151
degrees. Similarly in various other embodiments the angular
separation between the reflecting surfaces 121b and 121c may be
greater than 151 degrees.
[0092] In certain embodiments, the interferometric modulators may
be absorptive to light rays traveling at an angle of 45-90 degrees
measured from the normal to the interferometric modulators that are
guided within the first light guide. Thus, some of the light
propagating through first light guide may be substantially absorbed
by the interferometric modulators after a sufficient number of
reflections. An optical isolation layer may reduce, minimize, or
prevent this loss of light due to absorption. A display device 130
comprising an optical isolation layer 1301 is illustrated in FIG.
13. The turning film 134 of display device 130 is separated from
the substrate 135 on which a plurality of interferometric
modulators 136 are formed by an optical isolation layer 1301. The
display device 130 comprises from front to rear the second light
guide 134, optical isolation layer 1301, the substrate 135 and the
interferometric modulators 136. Intervening layers may also be
included. In these embodiments, the front light guide 137 comprises
the turning film 134. The optical isolation layer 1301
advantageously has an index of refraction substantially lower than
the glass substrate 135, such that light traveling through the
first light guide 137 and striking the glass/optical isolation film
interface at an oblique or grazing angle, for example, greater than
the critical angle (e.g., greater than 40.degree. or 50.degree. as
measured with respect to the normal), will be totally internally
reflected back into the first light guide 137 of the illumination
apparatus 130. However, light propagating through the first light
guide 137 at steep angles (closer to the normal to the array of
display elements 136), such as light turned substantially normal to
the first light guide 137 by the turning film 134 will be
transmitted through the glass/optical isolation film interface.
This normally incident light or near normally incident light
preferably loses less than about 0.5% of its intensity, and more
preferably loses less than about 0.1% of its intensity. Thus the
optical isolation layer 1201 forms a boundary for the first light
guide 137 such that the light propagating through the first light
guide 137 at oblique or grazing angles prior to being turned by the
turning film 134 may reflect back into, and continue to propagate
through the first light guide 137 until it is turned toward the
interferometric modulators 136 by the turning features at near
normal incidence, thereby providing an increasingly illuminated
display device.
[0093] In certain other embodiments, wherein the turning film 144
is separated from the substrate 145 by an optical isolation layer
1401, the substrate 145 on which a plurality of interferometric
modulators 146 are formed may be used as the second light guide as
illustrated in FIG. 14. The display device 140 comprises from front
to rear the turning film 144, optical isolation layer 1401, the
substrate 145, the interferometric modulators 146 and the backplate
148. Intervening layers may also be included. A light source 142 is
disposed to one side of the substrate 145, for example, side 1. The
substrate 145 functions as the second light guide and guides light
from the source 142 on side 1 to the turning mirror 141 on side 2.
This configuration may be particularly advantageous in reducing the
overall thickness of the display device 140.
[0094] In various embodiments, the second light guide may be
replaced with a light bar. The turning mirror may be used to couple
light from the light bar to an edge of the front light guide panel.
FIG. 15 illustrates a perspective view of a particular embodiment
of a display device 150 comprising of a LED 152, a light bar 154, a
turning mirror 151, a light guide panel 155 and a turning film 153.
The display device 150 comprises of a reflective display comprising
a plurality of reflective elements 156 such as reflective spatial
light modulators. A light guide panel 155 is forward of the
plurality of reflective elements 156. The light guide panel 155
includes a turning film 153 comprising, for example, a prismatic
film. Other methods of forming the turning film 153 and attaching
it to the light guide panel 155 such as are described herein may be
used as well. As discussed above, the turning film directs light
propagating through the light guide panel 155 onto the display
elements 156. Light reflected from the display elements 156 then
transmitted out of the light guide panel 155 towards the viewer.
This design is particularly advantageous in reducing the dimension
in the X-Y plane.
[0095] In the device shown in FIG. 15, a light source 152 is
disposed forward of the light guide panel 155 and the array of
display elements 156. The light source 152 is configured so that
the direction of emission is parallel to the negative x axis. The
light source 152 may comprise an LED. The light bar 154 is disposed
with respect to the light source 152 to receive light into the end
proximal to the light source 152. The light bar 154 comprises
substantially optically transmissive material that supports
propagation of light along the length of the light bar 154. Light
emitted from the light emitter 152 propagates into the light bar
154 parallel to negative x-axis and is guided therein, for example,
via total internal reflection at sidewalls thereof which form
interfaces with air or some other surrounding medium. Accordingly,
light travels from the end proximal to the light source 152 to a
second end distal to the light source 152 of the light bar 154.
Reflective sections 158 may be disposed with respect to the side
and end of the light bar 154 as shown. Reflectors may also be
included above and/or below the light bar 154. The light bar 154 is
disposed on a first side (side 1) of the light guide panel 155 and
array of display elements 156.
[0096] The light bar 154 includes a turning microstructure on one
sidewall closer to side 2 in FIG. 15. The light bar 154 is disposed
on a first side (side 1) of the light guide panel 155 and array of
display elements 156. The turning microstructure is configured to
turn at least a substantial portion of the light incident on that
side wall of the light bar 154 and to direct a portion of light out
of the light bar 154 toward side 1 (in the negative
y-direction).
[0097] The turning microstructure of the light bar 154 comprises a
plurality of turning features. The turning features may comprise
triangular facets as shown in FIG. 15. The features shown in FIG.
15 are schematic, not to scale and exaggerated in size and spacing
there between. In some embodiments, some or all of the faceted
features of the turning microstructure could be formed in a film
that is formed on, or laminated to, the light bar 154. In other
embodiments, the light bar 154 is formed by molding and the facets
are formed in this molding process. The facets or sloping surfaces
of the turning features are configured to scatter light out of the
light bar 154 along the negative y-axis. Light may, for example,
reflect by total internal reflection from a portion of the sidewall
of the light bar parallel to the length of the light bar to one of
the sloping surfaces. This light may reflect from the sloping
surface in a direction out of the light bar 154 toward side 1 of
the display in the negative y-direction.
[0098] A turning mirror 151 is disposed to receive light
propagating in the negative y-direction out of the light bar 154
and turn toward side 1 in the opposite direct (e.g., about by 180
degrees) to propagate along the positive y-direction into the light
guide panel 155 toward side 2 of the display. The turning mirror
151 redirects the light by reflection. FIG. 15 illustrates a
particular embodiment of a turning mirror 151, formed by two planar
reflecting surfaces 151 A and 151B disposed at an angle with each
other. Alternate embodiments of the turning mirror such as
described above may also be used. As described herein,
configurations are provided that can produce reduced footprint.
Various embodiments employ a turning mirror to accomplish the
reduced size. Not all the embodiments need to use a turning mirror
or need to produce reduce footprint.
[0099] A wide variety of other variations are also possible. Films,
layers, components, and/or elements may be added, removed, or
rearranged. Additionally, processing steps may be added, removed,
or reordered. Also, although the terms film and layer have been
used herein, such terms as used herein include film stacks and
multilayers. Such film stacks and multilayers may be adhered to
other structures using adhesive or may be formed on other
structures using deposition or in other manners.
[0100] The examples described above are merely exemplary and those
skilled in the art may now make numerous uses of, and departures
from, the above-described examples without departing from the
inventive concepts disclosed herein. Various modifications to these
examples may be readily apparent to those skilled in the art, and
the generic principles defined herein may be applied to other
examples, without departing from the spirit or scope of the novel
aspects described herein. Thus, the scope of the disclosure is not
intended to be limited to the examples shown herein but is to be
accorded the widest scope consistent with the principles and novel
features disclosed herein. The word "exemplary" is used exclusively
herein to mean "serving as an example, instance, or illustration."
Any example described herein as "exemplary" is not necessarily to
be construed as preferred or advantageous over other examples.
* * * * *