U.S. patent application number 13/271581 was filed with the patent office on 2012-02-02 for devices and methods for enhancing brightness of displays using angle conversion layers.
This patent application is currently assigned to QUALCOMM MEMS Technologies, Inc.. Invention is credited to Ion Bita, Russell W. Gruhlke, Marek Mienko, Lai Wang, Gang Xu.
Application Number | 20120026576 13/271581 |
Document ID | / |
Family ID | 40613122 |
Filed Date | 2012-02-02 |
United States Patent
Application |
20120026576 |
Kind Code |
A1 |
Bita; Ion ; et al. |
February 2, 2012 |
DEVICES AND METHODS FOR ENHANCING BRIGHTNESS OF DISPLAYS USING
ANGLE CONVERSION LAYERS
Abstract
Various embodiments of the present invention relate to enhancing
the brightness of displays that employ illumination systems. In
some embodiments, the illumination systems include light guides,
diffractive microstructure, and light-turning features. The
diffractive microstructure may be configured to receive ambient
light at a first angle and produce diffracted light at a second
angle greater than the first angle and greater than the critical
angle for of light guide. The light is thereby guided within the
light guide. The light-turning features may be configured to turn
the light guided within the light guide out of a light guide and
onto, for example, a spatial light modulator at near normal
incidence.
Inventors: |
Bita; Ion; (San Jose,
CA) ; Xu; Gang; (Cupertino, CA) ; Mienko;
Marek; (San Jose, CA) ; Wang; Lai; (Milpitas,
CA) ; Gruhlke; Russell W.; (Milpitas, CA) |
Assignee: |
QUALCOMM MEMS Technologies,
Inc.
San Diego
CA
|
Family ID: |
40613122 |
Appl. No.: |
13/271581 |
Filed: |
October 12, 2011 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12369630 |
Feb 11, 2009 |
8040589 |
|
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13271581 |
|
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|
61028145 |
Feb 12, 2008 |
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Current U.S.
Class: |
359/290 ;
359/567 |
Current CPC
Class: |
G02B 6/0018 20130101;
G02B 26/001 20130101; G02B 6/0053 20130101; G02B 6/0038
20130101 |
Class at
Publication: |
359/290 ;
359/567 |
International
Class: |
G02B 26/02 20060101
G02B026/02; G02B 27/44 20060101 G02B027/44 |
Claims
1. A display system, comprising: an array of display elements; and
an angle conversion layer overlying the display elements, wherein
the angle conversion layer is configured to turn ambient light
towards the array of display elements such that the turned light is
reflected and propagates away from the display system at angles
within a field of view of the display system, wherein the turned
light is incident on the angle conversion layer at angles outside
of the field of view of the display system.
2. The system of claim 1, wherein the angle conversion layer
includes a diffractive microstructure.
3. The system of claim 2, wherein the angle conversion layer is a
holographic turning layer and the diffractive microstructure
includes holographic light turning features.
4. The system of claim 3, wherein the holographic light turning
features are part of a volume hologram.
5. The system of claim 2, wherein the turned light is incident on
the diffractive microstructure from a plurality of directions.
6. The system of claim 1, wherein the field of view is within about
.+-.60.degree. of a normal to a first surface of the display.
7. The system of claim 6, wherein the field of view is within about
.+-.45.degree. of the normal to the first surface of the
display
8. The system of claim 1, wherein the display elements are
reflective display elements.
9. The system of claim 8, wherein the display elements include
interferometric modulators, each interferometric modulator
including a surface for reflecting the turned light.
10. The system of claim 1, further comprising: a processor that is
configured to communicate with the display elements, the processor
being configured to process image data; and a memory system that is
configured to communicate with the processor.
11. The system of claim 10, further comprising: a driver circuit
configured to send at least one signal to the display.
12. The system of claim 11, further comprising: a controller
configured to send at least a portion of the image data to the
driver circuit.
13. The system of claim 10, further comprising: an image source
module configured to send the image data to the processor.
14. The system of claim 13, wherein the image source module
includes at least one of a receiver, transceiver, and
transmitter.
15. The system of claim 10, further comprising: an input device
configured to receive input data and to communicate the input data
to the processor.
16. A display system, comprising: a plurality of display elements
configured to transmit reflected incident light outward from an
image-displaying side of the display system to form a displayed
image; and a means for turning light incident on the display system
towards the plurality of display elements such that the turned
light is reflected from the plurality of display means and the
reflected turned light propagates away from the display system at
angles within a field of view of the display system, wherein the
reflected turned light is incident on the means for turning light
at angles outside of the field of view of the display system.
17. The system of claim 16, wherein the plurality of display
elements is a plurality of interferometric modulators.
18. The system of claim 16, wherein the means for turning light
includes a diffractive microstructure.
19. The system of claim 18, wherein the diffractive microstructure
is a volume diffractive microstructure.
20. The system of claim 16, wherein the means for turning light is
a hologram.
21. The system of claim 16, wherein the field of view is within
about .+-.60.degree. of a normal to a first surface of the display
system.
22. A method for manufacturing a display system, comprising:
providing a reflective display having a reflective layer; and
providing an angle conversion layer on the display, the angle
conversion layer including a diffractive microstructure configured
to turn light incident on the display towards the reflective layer
such that the turned light is reflected off the reflective layer
and the reflected turned light propagates away from the display at
angles within a field of view of the display, wherein the reflected
turned light is incident on the angle conversion layer at angles
outside of the field of view of the display.
23. The method of claim 22, wherein providing the angle conversion
layer includes providing a holographic layer.
24. The method of claim 22, wherein providing the angle conversion
layer includes attaching the angle conversion layer to the
reflective display.
25. The method of claim 22, wherein providing the reflective
display includes forming a plurality of interferometric modulators,
the interferometric modulators forming pixels of the display.
Description
PRIORITY
[0001] This application is a continuation of U.S. patent
application Ser. No. 12/369,630, filed Feb. 11, 2009, U.S. Pat. No.
8,040,589 (issue date: Oct. 18, 2011), entitled "DEVICES AND
METHODS FOR ENHANCING BRIGHTNESS OF DISPLAYS USING ANGLE CONVERSION
LAYERS," which claims priority under 35 U.S.C. .sctn.119(e) to U.S.
Provisional Application No. 61/028,145, filed on Feb. 12, 2008,
entitled "DEVICES AND METHODS FOR ENHANCING BRIGHTNESS OF DISPLAYS
USING ANGLE CONVERSION LAYERS," both of which are assigned to the
assignee hereof. The disclosures of the prior applications are
considered part of this disclosure and are incorporated by
reference in their entireties.
BACKGROUND
[0002] 1. Field of the Invention
[0003] Embodiments of the present invention relate to enhancing
brightness of reflective displays. In some embodiments, devices
include a light-turning features and diffractive
microstructure.
[0004] 2. Description of Related Technology
[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] In some embodiments, an illumination apparatus is provided,
the apparatus comprising a light guide that guides light
propagating therein at an angle greater than a critical angle for
the light guide and ejects light from the light guide to provide
illumination; diffractive microstructure disposed to receive
ambient light at a first angle smaller than said critical angle and
to diffract said ambient light to produce diffracted light at a
second larger angle; and light-turning features configured to turn
the diffracted light and direct the turned light out of the light
guide. The second angle may be greater than the critical angle of
the light guide.
[0007] In some embodiments, a method of manufacturing an
illumination apparatus is provided, the method including providing
a light guide that guides light propagating therein at an angle
greater than a critical angle for the light guide and ejects light
therefrom to provide illumination; disposing diffractive
microstructure to receive ambient light at a first angle smaller
than said critical angle and to diffract said ambient light to
produce diffracted light at a second larger angle; and providing
light-turning features configured to turn the diffracted light and
direct the turned light out of the light guide.
[0008] In some embodiments, an illumination apparatus is provided,
the illumination apparatus comprising means for guiding light
propagating therein at an angle greater than a critical angle for
the light guiding means and ejecting light from the light guiding
means to provide illumination; means for diffracting ambient light
received at a first angle smaller than said critical angle to
produce diffracted light at a second larger angle; and means for
turning the diffracted light and directing the turned light out of
said light guiding means.
[0009] In some embodiments, an illumination apparatus is provided,
the illumination apparatus comprising a light guide that guides
light propagating therein at an angle greater than a critical angle
for the light guide and ejects light from the light guide to
provide illumination; and an angle converting structure disposed to
receive ambient light at a first angle greater than said critical
angle and to diffract said ambient light to produce diffracted
light at a second smaller angle, wherein a refractive index of said
angle converting structure is less than a refractive index of said
light guide.
BRIEF DESCRIPTION OF THE DRAWINGS
[0010] 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.
[0011] FIG. 2 is a system block diagram illustrating one embodiment
of an electronic device incorporating a 3.times.3 interferometric
modulator display.
[0012] FIG. 3 is a diagram of movable minor position versus applied
voltage for one exemplary embodiment of an interferometric
modulator of FIG. 1.
[0013] FIG. 4 is an illustration of a set of row and column
voltages that may be used to drive an interferometric modulator
display.
[0014] FIGS. 5A and 5B illustrate one exemplary timing diagram for
row and column signals that may be used to write a frame of display
data to the 3.times.3 interferometric modulator display of FIG.
2.
[0015] FIGS. 6A and 6B are system block diagrams illustrating an
embodiment of a visual display device comprising a plurality of
interferometric modulators.
[0016] FIG. 7A is a cross section of the device of FIG. 1.
[0017] FIG. 7B is a cross section of an alternative embodiment of
an interferometric modulator.
[0018] FIG. 7C is a cross section of another alternative embodiment
of an interferometric modulator.
[0019] FIG. 7D is a cross section of yet another alternative
embodiment of an interferometric modulator.
[0020] FIG. 7E is a cross section of an additional alternative
embodiment of an interferometric modulator.
[0021] FIG. 8A schematically illustrates light incident on a
display device within the field-of-view of the display device such
that light is reflected therefrom to a viewer within the
field-of-view of the display device.
[0022] FIG. 8B schematically illustrates a display device
comprising an array of display elements and having a field-of-view
that is tilted with respect to the array of display elements.
[0023] FIG. 8C schematically illustrates light incident on a
display device at an angle outside the field-of-view of the display
device such that the light is reflected outside the field-of-view
of the display device.
[0024] FIG. 8D schematically illustrates a display device having an
angular conversion layer disposed forward an array of display
elements that redirects light incident on the display device at an
angle outside the field-of-view into an angle more normal to the
array of display elements and within the field-of-view of the
display device.
[0025] FIG. 8E schematically illustrates a display device having an
angular conversion layer forward a plurality of display elements
that redirects light incident on the display device at an angle
outside the field-of-view into a larger (more grazing incidence)
angle such that the light is guided in a light guide forward the
array of display elements.
[0026] FIG. 9 schematically illustrates an illumination apparatus
comprising a light guide forward an array of display elements,
diffractive microstructure that couples light incident on the
display device at an angle outside the field-of-view into so as to
be guided in the light guide, and light turning features that
redirect the light guided by the light guide onto the array of
display elements at near normal incidence.
[0027] FIG. 10 schematically illustrates an illumination apparatus
further comprising an artificial light source such as an light
emitting diode or a light bar for providing supplemental
illumination.
[0028] FIG. 11 schematically illustrates the field-of-view of the
display device and the angular range for optical modes guided
within the light guide.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
[0029] The following detailed description is directed to certain
specific embodiments. However, the teachings herein can be applied
in a multitude of different ways. In this description, reference is
made to the drawings wherein like parts are designated with like
numerals throughout. 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.
[0030] The perceived brightness of reflective displays can depend
on available lighting. In various embodiments of the present
invention, an illumination apparatus for front illuminating
reflective display elements is configured to increase the amount of
ambient light that is incident on the display elements and
reflected therefrom within a usable field-of-view to the viewer.
This illumination apparatus may comprise a light guide,
light-diffractive microstructure, and turning features. The
diffractive microstructure diffracts light incident on the
illumination apparatus at an angle outside the field-of-view away
from the normal to the array of display elements such that ambient
light outside the field-of-view may be coupled into the light
guide. The light turning features turn this light guided within the
light guide to the display elements at an angle near normal to the
array of display elements. Therefore, the amount of ambient light
that can be directed at angles near normal to the array of display
elements and reflected by the display elements at angles near
normal to the array (or otherwise within the desired field-of-view)
can be increased. In various embodiments, the display elements
comprise reflective display elements and in some embodiments, the
display elements comprise reflective interferometric
modulators.
[0031] 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 ("relaxed" or "open") state, the display element
reflects a large portion of incident visible light to a user. When
in the dark ("actuated" 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.
[0032] 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.
[0033] 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.
[0034] 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.
[0035] 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) to form columns 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.
Note that FIG. 1 may not be to scale. In some embodiments, the
spacing between posts 18 may be on the order of 10-100 um, while
the gap 19 may be on the order of <1000 Angstroms.
[0036] 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
(voltage) 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 actuated pixel 12b on the right in FIG. 1.
The behavior is the same regardless of the polarity of the applied
potential difference.
[0037] FIGS. 2 through 5 illustrate one exemplary process and
system for using an array of interferometric modulators in a
display application.
[0038] FIG. 2 is a system block diagram illustrating one embodiment
of an electronic device that may incorporate interferometric
modulators. The electronic device includes a processor 21 which may
be any general purpose single- or multi-chip microprocessor such as
an ARM.RTM., Pentium.RTM., 8051, MIPS.RTM., Power PC.RTM., or
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.
[0039] 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. Note that although FIG. 2 illustrates a
3.times.3 array of interferometric modulators for the sake of
clarity, the display array 30 may contain a very large number of
interferometric modulators, and may have a different number of
interferometric modulators in rows than in columns (e.g., 300
pixels per row by 190 pixels per column).
[0040] FIG. 3 is a diagram of movable minor position versus applied
voltage for one exemplary embodiment of an interferometric
modulator of FIG. 1. For MEMS interferometric modulators, the
row/column actuation protocol may take advantage of a hysteresis
property of these devices as illustrated in FIG. 3. An
interferometric modulator 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. There is thus a range of voltage,
about 3 to 7 V in the example illustrated in FIG. 3, where there
exists a window of applied voltage 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 or bias 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.
[0041] As described further below, in typical applications, a frame
of an image may be created by sending a set of data signals (each
having a certain voltage level) across 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 a first row electrode,
actuating the pixels corresponding to the set of data signals. The
set of data signals is then changed to correspond to the desired
set of actuated pixels in a second row. A pulse is then applied to
the second row electrode, actuating the appropriate pixels in the
second row in accordance with the data signals. The first row of
pixels are unaffected by the second row pulse, and remain in the
state they were set to during the first row 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 image 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 image frames may be used.
[0042] FIGS. 4 and 5 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, 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.
[0043] 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 initially 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.
[0044] 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. The same procedure can be employed for
arrays of dozens or hundreds of rows and columns. 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.
[0045] 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.
[0046] 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, 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.
[0047] 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. However, for purposes of describing the present embodiment,
the display 30 includes an interferometric modulator display, as
described herein.
[0048] 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.
[0049] 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 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, W-CDMA, 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.
[0050] 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.
[0051] 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.
[0052] 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.
[0053] 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.
[0054] 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.
[0055] 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).
[0056] 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, 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.
[0057] 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.
[0058] In some implementations control programmability resides, as
described above, in a driver controller which can be located in
several places in the electronic display system. In some cases
control programmability resides in the array driver 22. The
above-described optimization may be implemented in any number of
hardware and/or software components and in various
configurations.
[0059] 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 its 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
of each interferometric modulator is square or rectangular in shape
and attached to supports at the corners only, on tethers 32. In
FIG. 7C, the moveable reflective layer 14 is square or rectangular
in shape and 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.
[0060] 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. For example, 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.
[0061] Various embodiments of the present invention relate to
increasing the amount of light available to display elements of a
display device. In certain embodiments, a display device comprises
a plurality of reflective display elements having a preferred
field-of-view from which a viewer will view image content displayed
by the display elements. Improved brightness may be achieved in
certain embodiments by increasing the amount of ambient light
output by the display in within the field-of-view of the
device.
[0062] In various embodiments described herein, display devices
comprise a plurality of reflective display elements such as
reflective spatial light modulators. Reflective interferometric
modulators are examples of such reflective spatial light
modulators. In certain embodiments, only light incident on the
display device within the field-of-view of the display device is
reflected within the field-of-view of the device. Accordingly, in
such embodiments ambient illumination of the display device is
generally limited to ambient light incident on the display device
within the field-of-view of the device.
[0063] FIG. 8A schematically illustrates the situation where light
incident on a display device 800 having a field-of-view 830' is
within the field-of-view of the display device and is reflected
from the display device to a viewer 803 at an angle also within the
field-of-view of the device. FIG. 8A shows a plurality of display
elements 801 having a light guide 802 or other optically
transmissive medium disposed forward (on the viewing side) of the
display elements. Light is incident on the light guide 802 or
optically transmissive medium at an angle within the field-of-view
830' of the display device.
[0064] Although the optically transmissive medium 802 is shown as a
single layer, in other embodiments, the optically transmissive
medium may comprises a plurality of layers. For example, one or
more films or layers may form part of the light guide 802. Other
embodiments may include additional layers in addition to the light
guide 802. Alternatively, some embodiments may exclude the light
guide 802. In such embodiments, the optically transmissive medium
802 disposed forward the display elements 801 may comprise, for
example, one or more other optically transmissive layers such a
substrate on which the display elements are formed, a protective
glass or plastic plate or sheet, or one or more other optically
transmissive films, layers, sheets, plates, etc. In other
embodiments, a substrate on which the display elements are formed,
a protective glass or plastic plate or sheet, etc. may also form
part of the light guide 802.
[0065] In general, the optically transmissive medium 802 has a
first surface 805 that defines an interface, which may be an
interface between, for example, air (above or on the viewing side
of the first surface 805) and the optically transmissive medium 801
(below or on a spatial modulator side of the first surface 805).
Alternatively, the interface 805 may be between another medium
above first surface 805 and the optically transmissive medium 801
below first surface 805. In some embodiments, the medium above the
first surface 805 is not part of the display device 800, wherein in
other embodiments, it is.
[0066] An incident light ray 810 can be characterized by a first
incident angle 815 measured with respect to the normal 820 to the
surface 805 and to the array of display elements 801. The incident
light ray 810 is refracted at the surface 805 to produce a
refracted light ray 810a characterized by a first transmission
angle 815a. The refracted light ray 810a is reflected at a second
surface 825 corresponding to the plurality of display elements 801
to produce a reflected light ray 810b. The reflected light ray 810b
encounters the first surface 805 of the reflecting device at a
second incident angle 815b. The reflected light ray 810b is again
refracted and becomes an output light ray 810c, characterized by a
second transmission angle 815c with respect to the normal 820.
[0067] A first angular range 830 corresponding to the field-of-view
830' of the device 800 is shown in FIG. 8A. A second angular range
830a corresponding to the effective field-of-view 830' within the
optically transmissive medium 802 is also shown. The second angular
range 830a is smaller than the first angular range 830 due to
refraction within the optically transmissive medium. A third
angular range 830b symmetrical or, in some embodiments, identical
to the second angular range 830a is also shown displaced to where
the ray 810b is incident on surface 805 and exits from the
optically transmissive medium 802. A fourth angular range 830c
symmetrical or, in some embodiments, identical to the first angular
range 830 is also shown at the location where the ray 810b is
incident on surface 805 and exits from the optically transmissive
medium 802. This fourth angular range 830c corresponds to the
field-of-view 830' of the device 800 and shows whether a given ray
of light reflected from the display device is within the
field-of-view 830' of the device. Similarly, these other angular
ranges 830, 830a, 830b, correspond to the field-of-view 830' of the
device 800 and are replicated at different locations (inside and
outside of the optically transmissive medium 802) as a reference to
show whether a given ray of light incident on, refracted by, or
reflected from portions of the display device 800 is within the
field-of-view 830' of the display device. In the embodiment shown
in FIG. 8A, these angular ranges 830, 830a, 830b, 830c show whether
the first incident angles 815, the first transmitted angles 815a,
the second incident angles 815b and the second transmitted angles
815c will be viewable upon exiting the device 800. Thus, if a light
ray, such as 810 which is within the first angular range 830, it
can be expected that the transmitted light ray 810a, the reflected
light ray 810b, and the output light ray 810c will be oriented at
angles within the first angular range 830a, the second angular
range 830b and the third angular range 830c, respectively.
[0068] In some instances, the second angular range 830a and the
third angular range 830b include substantially the same range of
angles. In some instances, the first angular range 830 and the
fourth angular range 830c include substantially the same range of
angles. In other instances, the second angular range 830a and the
third angular 830b and/or the first angular range 830 and the
fourth angular range 830c do not include substantially the same
range of angles. For example, surface irregularities, tilted
fields-of-view, and/or a plurality of display device components may
contribute to such differences in the angular regions.
[0069] The field-of-view 830' and corresponding angular ranges 830,
830a, 830b, 830c may vary depending on, for example, the design of
the device 800, materials used in the device, how a design is used,
or external device properties. In some embodiments, one or both of
the first angular range 830 and the fourth angular range 830c
include a range of about 0.degree. from the normal to about
60.degree. or about 0.degree. from the normal to about 180.degree.
from the normal. In some embodiments, one or both of the first
angular range 830 and the fourth angular range 830c include a range
of about 0.degree. from the normal to about 60.degree. or about
10.degree. to about 60.degree. from the normal (e.g., from about
0.degree. or 10.degree. from the normal to about 30.degree., to
about 45.degree., or to about 60.degree. depending, for example, on
the usage model of the displays). The angular ranges can depend,
for example, on factors, such as display size and viewing distance.
In some embodiments, one or both of the second angular range 830a
and the third angular range 830b include a range of about 0.degree.
from the normal to about 40.degree. from the normal. In some
embodiments, one or both of the second angular range 830a and the
third angular region 830b include a range of about 0.degree. from
the normal to about 20.degree. from the normal. In certain
embodiments, the range of the second angular range 830a and/or the
third angular range 830b may be less than the range of the first
angular range 830 and the fourth angular region 830c, for example,
as a result of refraction. In other embodiments, the range of the
second angular range 830a and/or the third angular range 830b may
be greater than the range of the first angular range 830 and the
fourth angular region 830c depending on the index of refraction
above and below the interface 805. The fourth angular range 830c
may be approximately 1 to approximately 3 times as large as the
second angular range 830a. For example, the fourth angular range
830c and the second angular range 830a may be about 80.degree. and
about 41.degree., respectively; about 60.degree. and about
35.degree., respectively; about 40.degree. and about 20.degree.,
respectively; about 20.degree. and about 13.degree., respectively;
or about 10.degree. and about 7.degree., respectively, in some
embodiments.
[0070] FIG. 8B shows an embodiment wherein the field-of-view 83W is
tilted and not centered or symmetrical about the normal 820.
Similarly, angular ranges 830, 830a, 830b and 830c are not centered
or symmetrical about the normal 820. Non-symmetric field-of-views
83W may be applicable, for example, to display devices 800 for
viewing at a tilted angle. It will be understood that embodiments
herein are not limited to symmetric viewing cones centered about
the normal 820. The second angular range 830a may be mirror images
of the third angular range 830b. (For example, if third angular
range 830b includes angles between -35.degree. and 45.degree.,
second angular range 830a could include angles between -45.degree.
and 35.degree..) Similarly, the first angular range 830 may include
angles that are substantially mirror images of the fourth angular
range 830d. In other embodiments, however, these angular ranges
830, 830a, 830b, 830c need not be mirror images.
[0071] FIG. 8C schematically illustrates the situation where light
incident on a display device 800 outside the field-of-view 830' of
the display device and is reflected from the display device at an
angle also outside the field-of-view of the device. Light ray 810,
for example, is shown incident on the light guide 802 or optically
transmissive medium at an angle outside the field-of-view 830' of
the display device.
[0072] FIG. 8C also shows four corresponding angular regions 835,
835a, 835b and 835c outside the field-of-view 830'. A first angular
region 835, a second angular region 835a, a third angular region
835b, and a fourth angular region 835c indicate ranges of the first
incident angles 815, the first transmitted angles 815a, the second
incident angles 815b and the second transmitted angles 815c, for
which light will not be within the field-of-view 830' upon exiting
the device. Thus, if a light ray such as 810 is within the first
angular region 835, it can be expected that the transmitted light
ray 810a, the reflected light ray 810b, and the output light ray
810c will be characterized by angles within the second angular
region 835a, the third angular region 835b and the fourth angular
region 835c, respectively and not within the field-of-view
830'.
[0073] Further, FIG. 8C shows first and second forbidden angular
regions 840a, 840b. Light from above the interface 805 will not be
refracted into these forbidden angular regions 840a, 840b if the
index of refraction above the interface is less than the index of
refraction below the interface. For example, even if incident light
ray 810 encountered the surface 805 at the largest angle possible,
refraction would prevent the light from entering the first device
angular region 840a and therefore from being reflected into the
second device angular region 840b. Typically, the angles within the
angular regions 835, 835a, 835b and 835c outside the field-of-view
will be larger than angles within the angular regions 830, 830a,
830b and 830c corresponding to the field-of-view 830' of the device
800, and the angles within the forbidden angular regions 840a and
840b will be larger than angles within the angular regions 835a and
835b outside the field-of-view 830' of the device.
[0074] In order to, for example, enhance the brightness of the
display device 800, it can be advantageous to redirect light
incident on the display device outside the field-of-view (e.g., in
first angular region 835) into the field-of-view 830' (e.g., into
second angular region 830a, third angular region 830b, and fourth
angular region 830c). Therefore, more incident (e.g., ambient)
light can directed to the viewer 803 upon reflection from of the
plurality of display elements 801. FIG. 8D shows a strategy to
increase the amount of ambient light collected using an angle
converting device 845, such as a diffractive layer. The angle
converting device 845 re-directs light outside the field-of-view
830' by changing the direction of the transmitted light rays
towards the surface normal 820 (e.g., by reflective or transmissive
diffraction). In some embodiments, an index of refraction of the
angle conversion layer 845 comprises a holographic or diffractive
layer. Thus, at least some of the incident light (e.g., light ray
810) that would have been within the first angular region 835a
outside the effective field-of-view is re-directed, such that the
transmitted light (e.g., transmitted light ray 810b) is within the
first angular 830a inside the effective field-of-view. This light
is reflected from the array of display elements 801 into the third
angular region 830b and output into the fourth angular region 830c
within the field-of-view 83W of the display device 800. This light
is therefore directed to a viewer 803. In essence, the first
angular range 830 is redefined as a larger angular region 831. More
light can be collected and directed into the field-of-view 830',
831 and be used to convey image content to the viewer 803. The
display device is thus brighter.
[0075] As illustrated in FIG. 8E, various embodiments of the
present invention include an angle converting device 850 that
re-directs light by changing the direction of the transmitted light
rays away from the surface normal 820. The angle converting device
850 may therefore increase the angle of the transmitted ray 810a as
measured with respect to the normal 820. For example, the angle
converting device 850 receives light ray 810 and transmits light
ray 810a to be within the first forbidden angular region 840a.
Thus, in some instances, the light is re-directed to an angle
greater than a critical angle, such as for example the critical
angle associated with the boundaries of the light guide 802. This
light is therefore coupled into the light guide 802 so as to be
guided therein by total internal reflection. The light is optically
guided in the light guide 802 via total internal reflection in a
customary manner for waveguides. In certain embodiments, turning
features are included to eject light from the light guide 802 at
near normal angles. This light then reflects from the array of
display elements 801 through the light guide 802 at near normal
angles and out of the display device 800 within the field-of-view
83W to a viewer 803.
[0076] FIG. 9 shows an embodiment of a display device 900
comprising an illumination apparatus 900' and a plurality of
display elements 901 such as intereferometric modulators. The
illumination apparatus 900' is forward of the plurality of display
elements 901 and assists in front illumination thereof. The
illumination apparatus 900' of the display device 900 may include a
light guide or light guide region 902 that guides light propagating
therein (e.g., light ray 920) at an angle greater than a critical
angle for the light guide. The light 920 is ejected from the light
guide 902, for example, to provide illumination of the array of
display elements 901 rearward of the light guide. The light guide
902 may comprise one or more layers and/or components. These layers
may comprise glass or polymeric material or other substantially
optically transparent material. In some embodiments the light guide
902 comprises one or more of glass, polycarbonate, polyether or
polyester such as, e.g., PET, acrylic or acrylate and acrylate
polymers and copolymers including but not limited to
polymethymethacrylate (PMMA), styrene-acrylic copolymer, and
poly(styrene-methylmethacrylate) (PS-PMMA), sold under the name of
Zylar, and other optically transmissive plastics although other
materials may also be used. In some embodiments the light guide
region 902 has a thickness in the range of between about 100 .mu.m
and about 1 cm, e.g. between 0.1 mm and 0.4 mm, although the
thickness may be larger or smaller. In some embodiments, the light
guide region 902 has a thickness of less than about 400 .mu.m, such
as, for examples, embodiments in which the light guide does not
include a substrate. In some embodiments, the substrate is part of
the light guide region 902 and thus the thickness of the light
guide region 902 may be larger, such as about 100 .mu.m to about 1
cm.
[0077] The light guide region 902 may include a substrate 915 in
certain embodiments. This substrate 915 may comprise substantially
optically transmissive material such as for example glass or
plastic or other materials. As described above, the material may
comprise aluminum silicate or borosilicate glasses although other
materials may also be used. For example polycarbonate, polyether
and polyesters such as, e.g., PET or PEN, acrylics or acylates and
acrylate polymers and copolymers including but not limited to PMMA,
poly(styrene-methylmethacrylate) (PS-PMMA) sold under the name of
Zylar, and other optically transmissive plastics may be used. The
materials that may be employed, however, are not limited to those
specifically recited herein. The substrate 915 may have a thickness
between about 0.1 mm and about 1 cm, (e.g. between 0.1 mm and 0.4
mm), although the thickness may be larger or smaller. In some
embodiments, the substrate 915 may have a thickness sufficient to
support other layers or films thereon.
[0078] The illumination apparatus 900' may also include
light-turning features 903. A light-turning layer 905 may comprise
a plurality of light-turning features 903. The light-turning
features 903 may include, for example, prismatic and/or diffractive
features. The light-turning features 903 may be shaped and/or
oriented to turn light such that light guided within the light
guide 902 is directed out of the light guide. Additionally,
light-turning features 903 may be shaped and/or oriented such that
the angle as measured with respect to the normal 920 to the light
guide 902 and/or array of display elements 901 of the turned light
is reduced and is therefore more normal, for example, as compared
to light prior to interacting with the turning features. In some
embodiments, the light-turning features 903 may be shaped and/or
oriented to increase the amount of light within the field-of-view
of the display device 900 and/or to increase the percentage of
incident and/or ambient light that is output into the field-of-view
of the display device. Alternatively, the light-turning features
903 may be shaped and/or oriented to reduce the angular size of the
field-of-view of the display device 900. For example, the
light-turning features 903 may assist in concentrating light output
or reflected from display device 900 into a smaller angular
region.
[0079] In FIG. 9, the light-turning features are shown as arranged
on a layer. This layer forms an upper portion, and in particular,
an upper boundary of the light guide 902. The light-turning
features 903 need not be disposed at an upper portion of the
light-guide 902 but may be located elsewhere, for example, in the
middle or low portions of the light guide closer to the display
elements 901. In some embodiments, the light-turning features 903
need not be included in a single layer.
[0080] In some embodiments the light-turning features 903 are
reflective. Light guided within the light guide region 902 may be
turned upon reflecting from such light-tuning features 903.
[0081] In one example, the light-turning features 903 comprise
prismatic features. Such prismatic features may reflect light off
of multiple facets via total internal reflection. FIG. 9 shows an
example of such facets that form prismatic features. These
prismatic features may be disposed in a film. This film may be
substantially optically transmissive. In some embodiments, this
film comprises a polymeric material such as, e.g., PC, PET, or
PMMA, although other materials may also be used. In some
embodiments, the film comprises a UV-curable resins molded on a
plastic carrier film, such as, e.g., PC, PET or PMMA. Accordingly,
the film may comprise polymeric material such as an optically
transmissive material including but not limited to polycarbonate,
acrylics or acrylates and acrylate polymers and copolymers
including but not limited poly(styrene-methylmethacrylate)
(PS-PMMA), sold under the name of Zylar, and other optically
transmissive plastics. The materials that may be employed, however,
are not limited to those specifically recited herein. This film may
be between about 50 .mu.m and about 500 .mu.m (e.g. 100 .mu.m and
about 500 .mu.m) thick or may have a thickness outside this range.
In some embodiments the light turning features are between about 1
.mu.m and about 50 .mu.m deep and in some embodiments may be
between about 0.5 and 50 .mu.m wide although the light turning
features may have other sizes in other embodiments. These features
903 have been exaggerated in size in FIG. 9 for illustrative
purposes. Likewise the size, shape, arrangement, and other
characteristics may be different. Moreover, the light-turning
features 903 may comprise different structures in other
embodiments.
[0082] The illumination apparatus 900 may also include diffractive
microstructure, which may be included in a diffractive layer 910.
This diffractive layer 910 may comprise one or more diffractive or
holographic layers that provide the angle conversion as described
above with respect to FIG. 8 (e.g. FIG. 8E). The diffractive
microstructures may comprise surface and/or volume features that
form, for example, one or more surface and/or volume diffractive
optical elements or holograms. Such a diffractive layer 910 may be
transmissive in certain embodiments and may operate on light
transmitted therethrough. The diffractive layer 910 may operate on
light incident thereon from forward of the display device 900 and
may be customized to operate on light incident from a particular
angle or set of angles such as ambient light incident on the
illumination apparatus 900' at large angles with respect to the
normal. As described above, this light may be incident on the
illumination apparatus 900' and diffractive layer 910 at angles
outside the field-of-view of the device 900.
[0083] The diffractive layer 910 may comprise, for example,
holographic recording films or coatings, such as mixtures of
acrylates and vinyl copolymers, or other photopolymers. The
diffractive layer may include a holographic material such as, for
example, a silver halide material, a dichromated gelatin material,
a photoresist material, and/or a photorefractive crystal. Other
materials may include those described in, for example, J. E. Boyd
et al., Applied Optics. vol 39, iss. 14, p. 2353-2358 (10 May
2000), references cited therein, and/or
www.hololight.net/materials.html. In various embodiments wherein
the diffractive features 910 are surface features, the diffractive
layer 910 may further comprise a planarized layer and/or a coating
positioned over or under the diffractive microstructure. The
planaraization layer may comprise a wet-coated polymeric coating or
a spin-on glass in certain embodiments although the material need
not be limited to such material. The diffractive layer 910 may be
of any suitable thickness, such as, for example, between about 10
and about 100 microns although values outside this range are
possible as well.
[0084] The diffractive microstructure and/or the diffractive layer
910 may be located below or rearward of the light-turning features
902 and/or light-turning layer 905 with respect to incident light
on the display device 900. Thus, ambient light may be transmitted
through the light-turning features 902 prior to being received by
the diffractive microstructure. The diffractive microstructure
and/or the diffractive layer 910 may be configured to receive light
at a first angle smaller than a critical angle for the light guide
902 and to diffract the light to produce diffracted light at a
second larger angle. The first and second angles may be measured
with respect to the normal. The second larger angle may be greater
than the critical angle of the light guide 902 such that the light
is coupled into the light guide so as to be propagated therein by
total internal reflection. In some embodiments, the refractive
index of the light-turning layer 905 is similar to or the same as
the index of refraction of the diffractive layer 910. Reflection of
light passing through the interface between the light-turning layer
905 and the diffractive layer 910 can thereby be reduced. In other
embodiments the refractive index of the diffractive layer 910 is
lower than or higher (which, in some embodiments, is advantageous
over "lower") than that of the light-turning layer 905. The
light-turning features 902 may be configured such that light
traveling from the diffractive layer 910 to the light-turning
features 902 is turned to be directed out of the light guide 902
and/or to reduce the angle with respect to the normal to the
illumination apparatus 900' or display device 900.
[0085] As described above, in some embodiments, the illumination
apparatus 900 includes a substrate 915. This substrate 915 may
provide support for the diffractive layer 910 and/or the
light-turning layer, for example during fabrication or use. The
diffractive layer 910 and/or the light-turning layer 905 may be
formed over, for example, deposited on or applied (e.g., laminated)
to the substrate 915 or one or more layers formed on the substrate.
In some embodiments, the diffractive layer 910 may be formed over,
for example, deposited on or applied (e.g., laminated) to the
substrate 915 or one or more layers formed thereon and the
light-turning layer 905 may be formed over, for example, deposited
on or applied (e.g., laminated) to the diffractive layer 910 or one
or more layers formed thereon. Accordingly, in some embodiments the
substrate 915 may be located beneath the diffractive microstructure
and/or the diffractive layer 910 with respect to incident light. In
other embodiments, the diffractive microstructure and/or the
diffractive layer 910 is formed below or rearward of the substrate
915. In other embodiments, the illumination apparatus 900 does not
include a substrate 915.
[0086] In some embodiments the substrate 915 forms part of the
light guide 902. In the embodiment shown in FIG. 9, the critical
angle for the lower or rearward boundary of the light guide 902 is
determined by the interface of the substrate 915 and an optical
medium rearward of the substrate 915. In the embodiment shown in
FIG. 9, an air gap 916 is disposed rearward of the substrate and
illumination apparatus 900' and forward of one or more or an array
of display elements 901. The interface between the substrate 915
and the air gap in this embodiment determines the critical angle
for reflection from the lower or rearward boundary of the light
guide 902.
[0087] In other embodiments, this gap 916 may be filled with
material Likewise, in certain embodiments, one or more layers may
be attached to the substrate 915 rearward of the substrate and form
port of the light guide 902. These layers may or may not be part of
the light guide region 902 depending, for example, on the index of
refraction of these layers.
[0088] In the embodiment shown in FIG. 9, the critical angle for
the upper or forward boundary of the light guide 902 is determined
by the interface of the light-turning layer 905 and an optical
medium forward of the light-turning 905 or illumination apparatus
90W. In the embodiment shown in FIG. 9, an air layer is disposed
rearward of the substrate and illumination apparatus 900' and
forward of an array of display elements 901. The interface between
the light-turning film 905 and the air in this embodiment
determines the critical angle for reflection from the upper or
forward boundary of the light guide 902.
[0089] In other embodiments, the light-turning layer 905 is not the
uppermost or forwardmost layer. In such embodiments, one or more
layers forward the light-turning layer 905 may determine the
critical angle for the upper or forward boundary of the light guide
902 depending on index of refraction. Likewise, in certain
embodiments, one or more layers may be attached to the light
turning layer forward of the light-turning layer 905 and form part
of the light guide 902 or define a boundary of the light guide 902.
A planarization layer may be disposed on the light-turning layer
905. The layer or layers forward the light-turning layer 905 may or
may not be part of the light guide region 902 depending, for
example, on the respective indices of refraction.
[0090] More generally, the critical angle for the upper or forward
boundary of the light guide 902 may be determined by the interface
of the forward most layer of the light guide 900 and the optical
medium directly forward of the forwardmost layer. The critical
angle for the lower or rearward boundary of the light guide 902 may
be determined by the interface of the rearwardmost layer of the
light guide 900 and the optical medium directly rearward of the
rearwardmost layer.
[0091] In some embodiments, an isolation layer is disposed between
the light guide region 902 and the plurality of display elements
901. This isolation layer, for example, may comprise a material
having an index of refraction lower than the light guide 902. In
the absence of the air gap 916 or isolation layer, the light guide
902 may be disposed directly on the array of display elements 901.
In such a configuration, light guided within the light guide 902
may be incident on the array of display elements 901 may be
absorbed.
[0092] FIG. 9 shows an example trajectory of a ray of light 920
through the illumination apparatus 900. The light ray 920 enters
the illumination apparatus 900 at the top surface of the
light-turning layer 905. Due to a difference in refractive indices,
the light beam 920 is refracted as shown by transmitted light ray
920a. In this example, the light ray 920a is transmitted through
the light-turning layer 905 into the diffractive layer 910. The
diffractive layer 910 diffracts and re-directs of the light ray
920a, producing a diffracted light ray 920b directed at an angle
930 from the normal to the display apparatus 900' and one or more
or an array of display elements 901. This angle 930 is larger than
the angle 925 of an undiffracted ray that would result in the
absence of the diffractive layer 925.
[0093] The diffracted light beam 920b is totally internally
reflected at the interface between the substrate 915 and the air
gap 916 to produce the reflected light beam 920c. The reflected
light beam 920c travels through the diffractive layer 910 into the
light-turning layer 905. The light-turning features 902 then turn
the light, such that the turned light beam 920d has a reduced angle
with respect to the normal as compared to the angle with respect to
the normal of the reflected light beam 920c. The turned light beam
920d is then transmitted through the diffractive layer 910 and the
substrate 915 to exit the illumination apparatus 900 and is
incident on the array of display elements 901. Although not shown,
the turned light beam 920d may be reflected from the array of
display element 901 depending, for example, on the state of the
reflective light modulators. Accordingly, the turned light beam
920d may be directed out of the display device toward a viewer in a
direction near normal to the array of display element 901 and
within the field-of-view of the display device 900. Thus, the
diffractive layer 910 redirects light from a first set of angles
into a second set of angles and thereby enables ambient light
directed into a light guide region to be redirected into an angle
that is guided by the light guide region and otherwise forbidden
from being directly accessed by ambient light.
[0094] FIG. 10 shows a display device 1000 comprising an
illumination apparatus 1000' in which the diffractive layer 910 is
separated from the light-turning layer 905. One or more separation
layers 1007 may separate the diffractive layer 910 and the
light-turning layer 905. The one or more separation layers 1007 is
substantially optically transmissive and may be diffusive in some
embodiments. The one or more separation layers 1007 may have a
refractive index lower than that of the light-turning layer 905
such that the light-turning layer 905 can guide light therein. The
one or more separation layers 1007 may have a refractive index
greater than that of the diffraction layer 910.
[0095] The one or more separation layers 1007 may material selected
from the group of acrylics, polyesters, polyethers, or cycloolefin
polymers. In some embodiments, for example, the separation layers
1007 may comprise an optically transmissive material such as, e.g.,
polycarbonate, acrylics or acrylates and acrylate polymers and
copolymers including but not limited polymethymethacrylate (PMMA),
poly(styrene-methylmethacrylate) (PS-PMMA), sold under the name of
Zylar, and other optically transmissive plastics. In some
embodiments, the one or more separation layers 1007 may comprise a
pressure sensitive adhesive. The one or more separation layers 1007
may be of any suitable thickness, such as, for example, between
about 1 to about 100 microns (e.g., between about 1 and 30 microns)
although values outside this range are also possible.
[0096] The embodiment shown in FIG. 10 also includes a light source
1002 that provides light to the illumination apparatus 1000. The
light source 1002 may comprise an edge light source, located
adjacent to the illumination apparatus 1000 so as to inject light
into an edge thereof. The light source 1002 may comprise for
example one or more light emitters such as LED and may comprise,
for example, a linear array of LEDs. In certain embodiments, the
light source 1002 may also comprise a light bar and one or more
emitters disposed to inject light into the light bar.
[0097] The separation layer 1007 forms a light guiding region 1004
for the light emitted from the light source 1002. This light
guiding region 1004 may comprise, for example, the light-turning
layer. Light 1035 from the light source 1002 may enter the
light-turning layer 905 as represented by a first light ray 1035a
and may be guided by totally internally reflection within the
light-turning layer 905, until a light-turning feature 902 turns
the first light ray 1035a. An example turned light beam 1035b is
shown directed to the array of display elements 901.
[0098] The separation layer 1007 forms a boundary for the light
guiding region 1004 for the light emitted from the light source
1002. In the embodiment shown in FIG. 10, the separation layer 1007
optically decouples the light turning layer 905 from the
diffractive layer 910. The separation layer 1007 may reduce or
prevent interactions of the light emitted 1035a from the light
source 1002 with the diffractive layer 910.
[0099] In some embodiments, the separation layer 1007 is excluded
and the refractive index of the light-turning layer 905 is higher
than that of the diffractive layer 910. In such embodiments the
light-turning layer 905 may guide light therein via in part by
total internal reflection from the interface between the
light-turning layer 905 and the diffractive layer 910.
[0100] The embodiment shown in FIG. 10 also includes an optical
isolation layer 1008 disposed between the substrate 915 and the
array of display elements 901. This optical isolation layer 1008
may have an index of refraction lower than that of the layer
forward of the optical isolation layer, which in this case is the
substrate 915. Although the optical isolation layer 1008 is shown
as a single layer, in other various embodiments the optical
isolation layer comprises a multilayer stack. This optical
isolation layer 1008 may comprise for example, acrylic or acrylate
and acrylate polymers and copolymers including but not limited to
polymethymethacrylate (PMMA) and poly(styrene-methylmethacrylate)
(PS-PMMA), sold under the name of Zylar, fluorine containing
polymers, and polycarbonate, other optically transmissive plastics
or silicon oxide, although other materials may be used. In some
embodiments, the optical isolation layer 1008 may comprise pressure
sensitive adhesive. The isolation layer 1008 may be of any suitable
thickness, such as, for example, between about 1 and about 100
microns or between about 1 and about 30 microns, although the
isolation layer may be thicker or thinner. In another embodiment,
the isolation layer 1008 may be in close vicinity of the display
element 901, and comprise inorganic material with different index
than the substrate 915.
[0101] In the absence of the isolation layer 1008, light diffracted
by the diffractive layer 910 such as ray 920b may be incident on
the array of display elements 901 instead of or in addition to
being reflected as ray 920c toward the light-turning layer 905
where the light such as ray 920d is turned at near normal angles
toward the display elements. The light (ray 920b) prematurely
incident on the plurality of display elements 901 may be absorbed
by the display elements or reflected at angles outside the
field-of-view of the display device 1000. In certain embodiments,
separation layer 1007 forms the lower boundary for the light from
LED, while the isolation layer 1008 forms the lower boundary for
the "converted" beam by the diffractive layer 910 from the ambient
light 920. In certain embodiments they may be combined.
Accordingly, in various embodiments, the isolation layer 1008 is
positioned below the diffractive layer 910. In some embodiments,
the substrate 915 may comprise the isolation layer 1008 or the
optical isolation layer may be disposed elsewhere. Additionally, in
some embodiments, a second substrate may be provided between the
isolation layer 1008 and the display elements 901. The second
substrate may serve to support the display pixels 901, while the
substrate 915 may support films attached to the display.
[0102] FIG. 11 schematically illustrates how the illumination
apparatus 1000' shown in FIG. 10 can operate. FIG. 11 includes an
angular region 1115 corresponding to the direction of light within
the light guiding region 1004 into which ambient light can be
coupled in the absence of the angle conversion layer 910. This
light, however, is not guided in the light guiding region 1004 by
total internal reflection. The boundaries 1105 of this angular
region 1115 are defined by the critical angle established by the
interface between the light-turning layer 905 and the air above.
Angles greater than this critical angle 1105 as measured from the
normal (z-axis) are generally forbidden or not accessible from air
without, for example, the angle conversion layer 910. This critical
angle 1105 defining the angular boundary 1105 may be about
20.degree., about 25.degree., about 30.degree., about 35.degree.,
about 40.degree., about 45.degree. or about 50.degree. in certain
embodiments although the angle should not be so limited.
[0103] FIG. 11 also includes an angular region 1120 corresponding
to the direction of light within the light guiding region 1004 that
is guided by the light guide region 1004. Thus, light within
angular region 1120 totally internally reflects both at the
interface between the light-turning layer 905 and the air above and
at the interface between the light-turning layer 905 and the
separation layer 1007. The boundaries 1110 of this region 1120 are
defined by the critical angle established by an interface between
the light-turning layer 905 and the separation layer 1007 and/or by
an interface between the light-turning layer 905 and the
diffractive layer 910 below. Angles greater than this critical
angle 1110 as measured from the normal (z-axis) are guided by the
light guide region 1004. Light incident at angles greater than this
critical angle 1110 totally internally reflect at the interface
between the light-turning layer 905 and the separation layer 1007.
This critical angle 1110 defining the angular boundary 1110 may be
approximately about 40.degree., about 50.degree., about 60.degree.,
about 65.degree., about 70.degree., about 75.degree., or about
80.degree. although the angle should not be so limited.
[0104] Arrow 1123 shows the effect of another embodiment of the
angle conversion layer 910. Such an angle conversion layer 910 may
redirect light from a first set of angles into a third set of
angles and enable ambient light directed into the light guide
region 1004 to be redirected into an angle that is guided by a
light guide region 1010 comprising the light-turning layer 910, the
angle conversion layer 910 and the substrate 915.
[0105] Whether the ambient light turned by the angle conversion
layer 910 is directed into either of the light guide regions 1004,
1010 may be determined at least in part by the angle conversion
layer. Additionally, the selection of materials and corresponding
index of refraction of the layers within the illumination apparatus
100W, such as the index of refraction of the angle conversion layer
910 itself may affect whether the light is guided within the
light-turning layer 905 alone or is guided within the light-turning
layer, the separation layer 1007, the angle conversion layer 910
and the substrate 915 or elsewhere. Alternative configurations are
also possible.
[0106] A wide variety of different embodiments of the invention are
possible. For example, components (e.g., layers) may be added,
removed, or rearranged. Similarly, processing and method 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.
[0107] In certain embodiments, the light-turning features 903 may
comprise different structures and may be diffractive or holographic
optical elements, for example. In various embodiments, the
light-turning features 903 may turn light transmitted through the
light-turning features. The light-turning features 903, for
example, may comprises transmissive diffractive or holographic
layers that redirect light as the light is transmitted through the
diffractive or holographic layer.
[0108] In some embodiments the diffractive layer 910 may be
disposed forward the light-turning features 903. In various
embodiments, the diffractive layer 910 may be reflective.
[0109] Still other variations are also possible.
[0110] Accordingly, while the above detailed description has shown,
described, and pointed out novel features of the invention as
applied to various embodiments, it will be understood that various
omissions, substitutions, and changes in the form and details of
the device or process illustrated may be made by those skilled in
the art without departing from the spirit of the invention. The
scope of the invention is indicated by the appended claims rather
than by the foregoing description. All changes which come within
the meaning and range of equivalency of the claims are to be
embraced within their scope.
* * * * *
References