U.S. patent application number 12/824435 was filed with the patent office on 2010-10-21 for light filter/modulator and array of filters/modulators.
This patent application is currently assigned to Light Resonance Technologies, LLC.. Invention is credited to Timothy Smith.
Application Number | 20100267920 12/824435 |
Document ID | / |
Family ID | 38802015 |
Filed Date | 2010-10-21 |
United States Patent
Application |
20100267920 |
Kind Code |
A1 |
Smith; Timothy |
October 21, 2010 |
LIGHT FILTER/MODULATOR AND ARRAY OF FILTERS/MODULATORS
Abstract
A light filter or an array of filters can be either one or two
dimensional. The filter or filters use multiple beam interference
by varying an optical path length between semi-reflective surfaces.
The optical path length between the semi-reflective surfaces is
varied by changing a thickness of a polymer film in response to an
electric field formed between two semi-transparent electrodes. The
filter can be configured in either a transmissive or reflective
mode.
Inventors: |
Smith; Timothy; (Hudson,
OH) |
Correspondence
Address: |
RENNER KENNER GREIVE BOBAK TAYLOR & WEBER
FIRST NATIONAL TOWER, SUITE 400, 106 SOUTH MAIN STREET
AKRON
OH
44308-1412
US
|
Assignee: |
Light Resonance Technologies,
LLC.
|
Family ID: |
38802015 |
Appl. No.: |
12/824435 |
Filed: |
June 28, 2010 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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12300817 |
Nov 14, 2008 |
7773291 |
|
|
PCT/US07/12757 |
May 30, 2007 |
|
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12824435 |
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Current U.S.
Class: |
528/26 ; 528/10;
528/25; 528/27; 528/28; 528/30; 528/31; 528/41; 528/42; 528/43;
977/773 |
Current CPC
Class: |
G02B 26/001
20130101 |
Class at
Publication: |
528/26 ; 528/10;
528/25; 528/27; 528/28; 528/30; 528/31; 528/41; 528/42; 528/43;
977/773 |
International
Class: |
C08G 77/14 20060101
C08G077/14; C08G 77/04 20060101 C08G077/04; C08G 77/28 20060101
C08G077/28; C08G 77/18 20060101 C08G077/18; C08G 77/30 20060101
C08G077/30; C08G 77/12 20060101 C08G077/12; C08G 77/24 20060101
C08G077/24 |
Claims
1. A polysiloxane polymer comprising: a reactive group capable of
bonding to an electrode surface; and one or more polar groups,
wherein the polymer is responsive to an electric field.
2. The polymer of claim 1, wherein the reactive group is selected
from the group consisting of silicon hydroxy (Si--OH), silicon
hydride (Si--H), silicon alkoxy, and silicon chloride groups.
3. The polymer of claim 1, wherein the polar group is selected from
the group consisting of anions, cations, zwitterions, and non-ionic
polar functional groups.
4. The polymer of claim 1, wherein the polar group is selected from
the group consisting of sulfonate, sulfate, phosphonate, phosphate,
polyphosphate, carboxylate, carboxylic acid, ammonium,
polypropylene oxide, and polyphenylene oxide.
5. The polymer of claim 1, wherein the polymer includes linear
polymers having a molecular weight of less than about 50,000
amu.
6. The polymer of claim 1, wherein the polymer may be characterized
by a polydispersity of less than about 1.5.
7. The polymer of claim 1, wherein the polymer is a soft solid
having a modulus of less than about 40,000 pascals and a tangent
delta of less than about 0.15.
8. The polymer of claim 1, wherein the polymer includes linear
polysiloxane.
9. The polymer of claim 8, wherein the polymer is grafted to a
polymer selected from the group consisting of polyacrylate,
polyether, polystyrene, polysulphone, polyurea, polyamide,
polyimide, polyamide-imide, polyester, polycarbonate, and epoxy
resins.
10. The polymer of claim 8, wherein the polymer is chemically or
physically bonded to nano particles.
11. The polymer of claim 10, wherein the nano particles are
selected from the group consisting of nanoclay, activated calcium
carbonate, silica, POSS, surface modified silica, and mixtures
thereof.
12. The polymer of claim 1, wherein the polymer further comprises a
chain having a terminus, and wherein said one or more polar groups
are located at or near the terminus of the polymer chain.
13. The polymer of claim 1, wherein the polymer further comprises a
chain, and wherein said reactive group is located at or near the
terminus of the polymer chain.
14. The polymer of claim 1, wherein the polymer further comprises a
chain having a first terminus and a second terminus, wherein said
one or more polar groups are located at or near a first terminus,
and wherein said reactive group is located at or near a second
terminus.
15. The polymer of claim 1, wherein the polymer further comprises a
chain having a midpoint and one or more termini, wherein said
reactive group is located at or near the midpoint of the polymer
chain, and wherein said one or more polar groups are located at or
near each termini.
16. The polymer of claim 1, wherein the polymer further comprises
linear polydimethyl siloxane.
17. The polymer of claim 16, wherein said linear polydimethyl
siloxane has two methyl groups bonded to each silicon atom.
18. The polymer of claim 17, wherein at least one of said methyl
groups is replaced by another substituent on a low percentage of
silicon atoms.
19. The polymer of claim 18, wherein said substituent is selected
from the group consisting of phenyl groups, fluoroalkyl groups,
alkyl groups containing two or more carbon atoms and cyano
groups.
20. The polymer of claim 1, wherein said polysiloxane is bonded at
multiple sites to phenyl silanes selected from the group consisting
of triphenyl silane and triphenyl vinyl silane.
Description
CROSS REFERENCE TO RELATED APPLICATION
[0001] This is a divisional application of Application Ser. No.
12,300,817 filed Nov. 14, 2008, which claims priority of PCT
Application No. PCT/US2007/012757 filed May 3, 2007 and U.S.
provisional application Ser. No. 60/809,873 filed Jun. 1, 2006, and
which is incorporated herein by reference.
TECHNICAL FIELD
[0002] The present invention relates to light filters and arrays
using the light filters. Specifically, the present invention is
directed to light filters that use multiple beam interference by
varying a light beam's optical path length between semi-reflective
surfaces. In particular, the present invention is directed to a
polymer film that changes thickness in response to an electric
field, wherein the change in the film's thickness results in a
corresponding change in the light beam's optical path length as it
passes through the filter.
BACKGROUND ART
[0003] Flat panel and projection devices are areas of rapidly
growing display technology. Many of these technologies involve the
filtering and modulating of light. Better resolution, brighter
display, wider color gamut and greater contrast as well as lower
production cost and lower energy usage are just a few of the goals
of current research and development efforts.
[0004] Direct view flat panel displays include computer monitors
and televisions as well as portable displays in cell phones,
personal data systems, portable games, cameras, global positioning
systems and many others. Current technologies such as plasma and
liquid crystal displays (LCD) require significant energy to operate
and are relatively costly to produce. Plasma is generally limited
to displays over forty inches. The large number of thin film
transistors (TFTs) that are fabricated in typical LCD's leads to
quality control problems, much time spent on product inspection,
and high rejection rates.
[0005] LCD-based displays require significantly brighter backlights
with higher energy usage because of the need for polarization
filters and color absorbance filters. Polarization filters absorb
60% of the source light and color filters absorb up to 75% of the
source light. Along with the absorbance of other components in an
LCD display, typically only about 5% of the source light is
transmitted. As such, these devices have poor light and energy
efficiency.
[0006] The picture quality of LCD displays is not optimal. First,
the response time can be considered slow. Second, current LCD
technology requires subpixels and provides lower resolution for a
given number of electronic components, including thin film
transistors and data drivers. Current LCD technology requires
polarization and color filters that reduce brightness, provide a
small color gamut and limit the number of primary colors that can
be used at a time. And finally, LCD technology requires a fairly
large number of electronic parts, including TFTs at each subpixel
so that there is typically a large amount of black matrix
associated with each pixel that does not transmit the source
light.
[0007] There is a need for a direct view display that provides a
high resolution with fewer subpixels per pixel with a concurrent
reduction in electronic parts, including TFTs and data drivers.
There is also a need for a display where the polarization and color
absorbance filters are eliminated to provide greater brightness, a
wider color gamut, more pure saturated color, and better contrast
ratio. And there is a need for a display that uses light more
efficiently, that eliminates polarization filters and color
absorbance filters and minimizes dark matrix effects.
[0008] Current projection displays, such as digital micromirror
devices (DMD), liquid crystal light valves (LCD) and liquid crystal
on silicon (LCOS) have many of the same drawbacks as flat panel
direct view displays. Current technology requires the use of
polarization filters as used in LCD and LCOS. All three
technologies can use three separate light valves to display three
separate colors leading to increased manufacturing costs. If one
light valve is used, then absorbance filter color wheels must be
used. DMD requires expensive micromachining. Therefore, there is a
need for a technology that offers superior picture quality to LCD,
LCOS and DMD without the shortcomings inherent in these
devices.
[0009] Based on the foregoing, it is clear that there is a need for
light filters used in projection displays that can supply high
contrast, wide color gamut with fewer than three light valves.
There is also a need for technology that eliminates the need for
polarization and color absorbance filters, with the resulting
brighter display with a wider color gamut. It is also desirable to
reduce the number of electronic parts to reduce the "screen door
effect," a negative effect seen in some LCD-based projection
displays. There is also a need for a technology that provides full
color control within one light valve without the use of absorbance
color wheels. And there is also a need to provide more saturated
colors, thus offering a clearer picture at high intensity with less
washout. There is also a need for a projection display with high
light efficiency that will transmit most of the source light.
Additionally, it is believed that brighter displays may be achieved
without the heat buildup that is characteristic of prior art
projection display technology.
[0010] There is also a need for technology which improves the use
of laser and LED arrays used as image formers for toner/fuser
printers. For instance, there is a need for technology which allows
for improved, multiple resolutions. Current devices use a
complicated system of lasers and rotating mirrors and lenses, as is
the case with current laser printers. As such, there is a need for
a technology which is not limited by the size of the laser dot, as
with laser technology, nor is it limited by the size of the LEDs in
an LED array. And there is a need for technology which provides a
less costly alternative to laser printers by eliminating the need
for expensive lasers. Additionally, there is a need for greater
speed so that whole lines can be projected across the imaging drum
at a single time. There is also a need for finer detail than is
available from current technologies because of the variation in
light intensity that can be projected on the image drum.
[0011] It is also believed that improved light filters and
associated arrays can be used in an image former for large format
printers including lithography.
[0012] And finally, there is a need for a filter technology that is
adaptable for use with digital cameras, video cameras, and other
image formation devices, such as electronically tunable filters,
spatial light modulators, spectroscopy devices, microscopy devices,
holographics, data bus and wavelength division multiplexing (WDM)
devices and large Fabry Perot interferometers.
[0013] There are a number of prior art devices that use various
forms of polysiloxane which changes its physical properties upon
application of an electric field. For example, a light modulator
has been described having two deformable dielectric layers; where
at least one dielectric layer is a relief-forming gel, such as a
polyorganosiloxane gel, and the other layer is air. Reliefs are
generated at the interface between the layers in response to
signals applied to electrodes provided on either side of the
dielectric layers.
[0014] Another prior art optical switching device manipulates an
incident light wave passing through the device having an
electrically controlled variable thickness plate. The device
comprises a first transparent electrode; a second transparent
electrode; and a layer of dielectric and transparent viscoelastic
material located between the first and second electrodes that
deforms in local thickness in response to an electric field. The
transparent viscoelastic material includes silicone gel, oil,
various polymer materials and other viscous substances that undergo
viscous flow when placed in the presence of an electric field and
relax towards their original form when the electric field
ceases.
[0015] Another type of device is a control element that has been
described having a liquid layer with electroosmotic movement to
attain a geometrically uneven state in response to an electrical
signal, having a high sensitivity to an applied voltage. The liquid
layer contains at least one silicon compound, preferably a
derivative of silane or siloxane including organopolysiloxane.
[0016] Still another device is a solid state light modulator that
includes a charge storage device including a semiconductor
substrate and associated with at least one display electrode; a
deformable elastomer layer, a silica containing gel, such as a
polydimethyl siloxane (PDMS); and a light reflective metal
electrode layer. A potential applied between the display electrodes
and the upper electrode causes the gel layer to deform in a rippled
pattern.
[0017] A transparent film or coating composition blend of
polysiloxane and liquid crystalline components has been used as an
organic nonlinear optical unit in a light modulator device. The
molecular orientation of the polysiloxane molecules can be external
field-induced.
[0018] Some of the above devices require the polymer material to
remain in a fluid or flowable condition. Thus, the completed
assembly must be maintained in a flat, horizontal orientation. Even
in devices where there is some type of adherence between the
polymer material and the substrate, movement of the device may
cause sagging of the polymer material, thus the light-altering
properties of the polymer material cannot be sufficiently
controlled. Some of the above devices require a thickness of more
than 10 microns. Although these devices are believed to be
effective for their stated purpose, their specific attributes and
formulations are not conducive for use in displays. Therefore,
there is a need in the art for a polysiloxane configuration which
is adapted for use in light filters and light modulators that can
be used in display type devices.
SUMMARY OF THE INVENTION
[0019] In light of the foregoing, it is a first aspect of the
present invention to provide a light filter/modulator and array of
filters/modulators.
[0020] Another aspect of the present invention is a light modulator
comprising a pair of opposed substrates having a gap therebetween,
an electrode disposed on each of the substrates, wherein each
paring of the electrode and the substrate has associated therewith
reflective properties, a polymer film disposed on and chemically
bonded to one of the electrodes, wherein application of a voltage
across the electrodes causes a corresponding uniform change in a
thickness of the polymer film.
[0021] Yet another aspect of the present invention is a
polysiloxane polymer comprising a reactive group capable of bonding
to an electrode surface and one or more polar groups wherein the
polymer is responsive to an electric field.
BRIEF DESCRIPTION OF THE DRAWINGS
[0022] For a complete understanding of the objects, techniques and
structure of the invention, reference should be made to the
following detailed description and accompanying drawings
wherein:
[0023] FIG. 1 is a schematic diagram of a light modulator including
a single transmissive filter element according to the concepts of
the present invention;
[0024] FIG. 2 is a schematic diagram of a light modulator providing
two transmissive filter elements of an array according to the
present invention;
[0025] FIG. 3 is a schematic diagram of a light modulator
comprising a two-dimensional array of transmissive filter elements
in accordance with the concepts of the present invention;
[0026] FIG. 4 is a schematic diagram of a light modulator providing
two transmissive filter elements showing a variation in a thickness
of a variable thickness polymer film according to the concepts of
the present invention;
[0027] FIG. 5 is a schematic diagram of a light modulator with a
transmissive filter element wherein the element contains a variable
thickness polymer film associated with each substrate according to
the present invention;
[0028] FIG. 6 is a schematic diagram of a light modulator providing
two transmissive filter elements with variable thickness polymer
films coated continuously on a common electrode according to the
concepts of the present invention;
[0029] FIG. 7 is a schematic diagram of a light modulator showing
two transmissive filter elements with high reflective coatings
disposed on an active electrode according to the concepts of the
present invention;
[0030] FIG. 8 is a schematic diagram of a light modulator utilizing
two transmissive filter elements as part of an array of a direct
view display according to the concepts of the present
invention;
[0031] FIG. 9 is a schematic diagram of a light modulator utilizing
two transmissive filters elements as part of an array of a direct
view display according to the concepts of the present invention,
wherein a fiber optic face plate is utilized according to the
concepts of the present invention;
[0032] FIG. 10 is a schematic diagram of a camera system utilizing
a light modulator, with transmissive filters according to the
concepts of the present invention;
[0033] FIG. 11 is a schematic diagram of a light modulator with a
single filter coupled to a single fiber optic input according to
the concepts of the present invention;
[0034] FIG. 12 is a schematic diagram of a light modulator with an
array of transmissive filters coupled to or associated with a
plurality of fiber optic inputs according to the concepts of the
present invention;
[0035] FIG. 13 is a schematic diagram of a light modulator
utilizing two filter elements wherein the modulator is utilized in
a reflective filter array;
[0036] FIG. 14 is a schematic diagram of a light modulator
utilizing two filter elements and part of a third filter element in
a reflective array with a high reflective film coated on the
electrodes according to the concepts of the present invention;
and
[0037] FIG. 15 is a schematic perspective diagram of an electrode
surface of a light modulator with a polymer film filter element
with grids allowing for expansion of the polymer film according to
the concepts of the present invention.
BEST MODE FOR CARRYING OUT THE INVENTION
[0038] Generally, the present invention is directed to a light
filter or an array of filters that can be either one or two
dimensional. These light filters can be used in a reflectance mode
or in a transmissive mode. In other embodiments, the filters can be
arranged in a series of transmissive filters, in a series of
reflective filters, or in a combination of both reflective and
transmissive filters to increase the filtering capabilities.
[0039] The device to be described works by filtering and/or
modulating light using multiple beam interference which varies the
optical path length between semi-reflective surfaces. The optical
path length is defined by .SIGMA.nd, where n is the refractive
index of individual layers between the reflective surfaces, and d
is the thickness of the individual layers between the reflective
surfaces. The optical path length between the semi-reflective
surfaces is varied by changing the thickness of a polymer layer in
response to an electric field formed between two semi-transparent
electrodes that are associated with the semi-reflective surfaces.
It should also be appreciated that the components shown in the
drawings are not drawn to scale. Moreover, in some instances, the
components of the various light modulator embodiments are shown
spaced apart from one another. However, the components could be
positioned directly adjacent one another if needed. In other words,
components of the devices may be in direct contact with one
another.
[0040] Referring now to the drawings and in particular FIG. 1, it
can be seen that a light modulator according to the concepts of the
present invention is designated generally by the numeral 20. The
modulator 20 shown in FIG. 1 is a basic embodiment for a
transmissive type filter that presents the general teachings for
the present invention. Skilled artisans will appreciate that the
light modulator 20 may be configured in different embodiments, such
as reflective, which are presented in later figures. In the present
embodiment, the modulator 20 provides a single filter which may be
referred to as a picture element or pixel as shown, but could be
provided with multiple pixels as will be described. In such cases,
where multiple filters are utilized, a modulator may be referred to
as a matrix, an array, or array of filters.
[0041] The light modulator 20 includes a programmable multiple beam
interference light filter designated generally by the numeral 22
which is connected to and controlled by a controller 24.
Specifically, the controller 24, which is attached to an electrical
power supply, applies power and generates an appropriate control
signal for operation of the filter 22 or multiple filters. The
controller 24 includes the necessary hardware, software and memory
to enable operation of the modulator 20 and, as such, the filter
22. As will become apparent as the description proceeds, variations
of the filter 22 embodiments may be provided with alphabetic
suffixes.
[0042] The light modulator 20 may include a light source 26 which
generates broadband, multiple discrete bands, or monochromatic
forms of light. The light source 26, which may be connected to the
controller 24, or which may be independently controlled, may also
generate near-infrared, infrared or ultraviolet (>300 nm) types
of light. Depending upon the component structure of the light
filter 22, the range of the light source may extend further into
the ultraviolet region. The light source may be cold cathode
fluorescent, hot cathode fluorescent, electro-luminescent,
xenon-based lamps, metal halide, mercury arc, or, in some
embodiments, light emitting diodes of three or more colors with
fairly narrow bandwidths and others. The aforementioned
monochromatic sources may also be light emitting diodes or an
appropriate laser source. Broadband sources may include natural or
artificial light in camera and imaging applications. A broadband
ultraviolet/visible or infrared light source may be used as the
light source in spectroscopic applications.
[0043] The light source 26 generates an input light 28 which has a
wavelength .lamda. such that the optical path length of the filter
22 is an integral multiple of the wavelength at a given time and is
passed. Light that is not an integral multiple at a given time is
reflected. As will be discussed in further detail, the wavelength
.lamda. that is passed is determined by the equation
.SIGMA.nd=m.lamda./2 (1)
Where n is an integer .gtoreq.1. When the optical path length is
such that the input light reflected between the reflective surfaces
is in phase, constructive interference occurs and the filter
transmits the wavelength of light. If this condition does not hold,
destructive interference occurs and transmission will be low and
the wavelength of light will be reflected. Skilled artisans will
appreciate that a change in the optical path length will result in
multiple beam interference, which, in turn, results in a
corresponding change in the wavelength of light transmitted by the
filter or reflected back toward the light source.
[0044] The input light 28 generated by the light source 26 may be
directed into an optics system designated generally by the numeral
30. Light emanating from the optics system may be referred to as
modified input light 28'. In selected embodiments, the optics
system 30 may include lenses to collimate the light. The system 30
may also impart a slight angle, <5.degree., to control the
optical path length in the filter 22. In most embodiments, it is
believed that an angle closer to 0.degree. is beneficial. In direct
view applications, where the light source 26 generates a broad and
diffuse light directly behind the filter 22, focus at infinity may
not be practical. In this instance, an optical system that guides
light 28' into a narrow cone is desired. The optics system 30 may
also filter out or block unwanted wavelengths of light. For
example, ultraviolet and infrared light may be filtered or blocked
from visible light that passes through. The optics system 30 may
also filter bandwidths from a broadband light source where dark
pixels may be formed. It will also be appreciated that the optics
system 30 may be in the form of lenses used by a camera, as will be
discussed in other embodiments.
[0045] The filter 22, which is proximally positioned near the
optics system 30, includes a pair of spaced apart substrates 32 and
34. The substrates 32 and 34 could be in the form of an optically
clear glass, or they may comprise silica or any other transparent
substrate of sufficient mechanical strength, including flexible
transparent polymers such as polyester. The substrates 32 and 34
are spaced apart and provide a gap, designated generally by the
numeral 36, therebetween. The gap 36 is maintained by a plurality
of spacers 38 which may be in the form of spherical glass beads,
glass rods, polymer walls, deposited and etched dielectric, or
other such configurations so as to maintain a defined distance
between the substrates. The spacers 38 provide a uniform distance
between the substrates 32 and 34 which is needed to ensure proper
operation of the filter 22.
[0046] An anti-reflective coating 40 may be provided on the
substrate 32 and positioned in such a manner so as to face the
modified input light 28' that is passed through the optics system
30. The anti-reflective coating may be optimized for broadband
visible light in such applications as direct view displays,
projection and imaging applications. In monochromatic applications,
the anti-reflective coating may be optimized for the particular
wavelength of the modified input light 28'.
[0047] Each substrate 32 and 34 may be provided with a high
reflective (HR) dielectric coating. Specifically, the substrate 32
is provided with a high reflective coating 42 and the substrate 34
is provided with a high reflective coating 43. The coatings 42 and
43 are positioned on their respective substrates so as to face one
another. Each coating 42 and 43 may comprise an alternating stack
of high refractive index and low refractive index films. For broad
light sources, the HR coatings may be optimized across the spectrum
of the source, such as for example, the visible light spectrum. In
displays with RGB light emitting diodes, the HR coatings may be
optimized for the specific wavelengths generated by the light
emitting diodes. If a light source such as cold cathode fluorescent
is used, where phosphors are excited, the HR coatings may be
optimized for the narrow primary bands of the phosphors. The HR
coatings may be continuously coated on the substrates 32 and 34, or
pattern coated as needed. Reflective metal coatings such as silver,
platinum, gold or aluminum may be used. Indeed, combinations of
metallic and dielectric coatings may be used. It will further be
appreciated that HR coating 43 may be made slightly less reflective
than HR coating 42 to allow easier passage of light out of the
front of the filter. In the alternative, as will be discussed in
other embodiments, the HR coatings 42 and 43 may be coated on other
components within the filter 22.
[0048] For display applications, the reflectance R (where
R=r.sup.2, where r is the reflectivity of coatings 42, 43) of the
coatings should be greater than 75% and, more desirably, greater
than 95%. As such, in display applications, the reflectance should
be large enough to create fairly narrow, but not too narrow,
bandwidths of transmitted color. If an LED array of RGB light is
used as the light source 26, the reflectance should be controlled
to make the passed bandwidths match the bandwidths of the LEDs. If
cold cathode fluorescent or other light source with excited
phosphors is used, then the reflectance should be controlled to
match the bandwidths of the primary emission bands of the
phosphors. Higher reflectance provides narrow bandwidths that make
more pure spectral colors and thus, a wider color gamut for display
applications, as well as yields darker dark pixels. Narrow
bandwidths also provide for darker dark pixels in display
applications. Where laser light is used as the light source 26, the
reflectance of coatings 42 and 43 can be matched to specific
wavelengths of the source to give reflectances greater than 99% so
as to pass bandwidths comparable to the laser source, as well as
provide filtering of the laser light. In spectroscopic
applications, it is believed that embodiments can be provided where
the reflectance can be made greater than 99% to provide narrow
spectroscopic bandwidths for good resolution.
[0049] Disposed on each of the coatings 42 and 43, if provided, or
on the substrates 32 and 34 if the coatings are not provided, is a
corresponding electrode. Each electrode, which may be selectively
patterned, is connected to the controller 24. It will further be
appreciated that the electrodes are associated with electronic
components to provide for specific applications of voltage. In
particular, a common electrode 44 of an active matrix is associated
with the substrate 34 and an active electrode 46 of an active
matrix is associated with the substrate 32, wherein the coatings
are disposed between the electrodes and the substrates. However, it
will be appreciated that the electrodes 44 and 46 could be
positionally switched on the substrates as needed by a particular
application. Moreover, it will be appreciated that each electrode
44 and 46 may be further covered with an insulating layer if
required such as Al.sub.2O.sub.3 or SiO.sub.2 to prevent electrical
shorting between the substrates and to provide reactive sites for
the chemical bonding of a polymer film. The electrodes 44 and 46
may comprise semi-transparent metallic oxides, such as indium tin
oxide (ITO). The metallic oxides may also include tin oxide, zinc
oxide, indium zinc oxide, and others. Alternatively, the electrodes
may comprise metal such as gold, silver, platinum, aluminum or
alloys thereof. And these metallic electrodes may be coated with
one or more dielectric materials to enhance reflectivity and/or
bonding to a polymer film (to be discussed) or insulation films. If
metallic electrodes are used, they may also comprise the reflective
coating in the filter 22, thus allowing the elimination of the
dielectric high reflective coatings 42 and 43. The metallic
electrodes may allow for lower voltages for a comparable electric
field. The reflectances of the metallic electrodes may be chosen by
controlling the thickness of the electrodes. Alternatively, a
combination of dielectric and metal electrodes may be used. And, in
certain embodiments, index matched indium tin oxide (IMITO)
electrodes may be used, where the ITO is matched to the substrate
it is attached to or associated with.
[0050] Disposed on or associated with at least one of the
electrodes is a variable thickness polymer film designated
generally by the numeral 48. In most embodiments, the variable
thickness polymer film or film is positioned on the active
electrode 46. The film 48 varies in thickness according to a
voltage that is applied across the electrodes 44 and 46.
Accordingly, as the thickness of the film 48 decreases, a variable
space 49 between the film and the facing common electrode 44
increases in thickness. Likewise, as the film 48 increases in
thickness, the variable space 49 between the film 48 and the
electrode 44 decreases. As such, the changing thickness of the film
and the associated gap varies the optical path length between the
electrodes which is:
.SIGMA.nd=n.sub.gd.sub.g+n.sub.pd.sub.p (2)
where n.sub.g is the refractive index of the air and d.sub.g is the
thickness of the variable space or air gap; and wherein n.sub.p is
the refractive index of the film 48 at thickness d.sub.p. The
refractive index of the film 48 will vary slightly with the
variation in thickness. Indeed, the film's refractive index will
vary slightly with a variation in the thickness according to
.DELTA.n/.DELTA..tau., wherein .DELTA..tau. is the stress placed on
the film as the film is strained by the applied electric field.
Accordingly, if .SIGMA.nd is an integral multiple of a source
wavelength, the wavelength of the light will be passed. The
bandwidth of the passed band will be further determined by the
reflectances of the high reflective coatings 42 and 43 or however
the coatings are configured in the filter 22. As seen in FIG. 1,
the film 48 can be provided in an unactivated condition 50 when no
electric field is applied and in an activated condition when an
electric field is applied. The activated condition results in the
film 48 being compressed or extended. Whether the film is
compressed or elongated (also referred to as extended) is dependent
on any number of factors related to the characteristics of the
film. Indeed, the film 48 can have an extended activated condition
52 and a compressed activated condition 53.
[0051] As discussed previously, the modified input light 28' has a
wavelength .lamda. that is an integral multiple of the optical path
length of the filter at the time the light is passed. Light that is
not an integral multiple at a given time is reflected. The
wavelength .lamda. that is passed is determined by equation (1),
wherein .SIGMA.nd is the sum of the optical path lengths of the
layers between the reflective surfaces 42 and 43 and where m is an
integer .gtoreq.1. The optical path length .SIGMA.nd changes with
the variation in thickness of the film 48. The variation of the
thickness of the film is determined by the applied electric field
between the electrodes which is controlled by the controller 24.
Accordingly, when a voltage is applied across the film 48, the film
may be caused to compress, increasing the space 49 between the
spaced apart substrates. As such, the optical path length may pass
one color from the light source, whereas a changed optical path
length may pass another color from the light source. Indeed, at
another voltage, the optical path length may create constructive
interference for a bandwidth not in the light source, and thus
create a dark pixel. As such, with a monochromatic light source,
the filter may act as a modulator, passing or not passing light
from the source. The optical path length may be configured or sized
so as to destructively interfere or constructively interfere with
the monochromatic light source creating digital bits of either zero
or one. In other words, control of the film 48 may generate a dark
pixel or a white pixel.
[0052] Depending upon the spacers and configuration of the
substrates, the total distance of gap 36 between the reflective
surfaces can range from under 1 .mu.m to over 10 .mu.m and in some
cases several millimeters. In most embodiments, it is believed that
the total thickness should be as small as practically possible so
as to minimize the voltages needed to create the electric fields
needed to vary the thickness of the film 48. A low total thickness
will minimize the power consumed as well as decrease the response
time of the filter. Lower voltages would also make the components
in an active matrix smaller, decreasing the dark areas or inactive
areas of the display. Lower total thickness will minimize overlap
between modes (the integer m in Eq.1). In broadband applications,
the optimal total thickness is less than 2 .mu.m. As will be
discussed in other embodiments, the film 48 may be selectively
positioned on the electrodes and pattern coated as needed so as to
provide a desired light output.
[0053] In general, the polymer of the film is a soft solid that is
chemically bound to the electrode surface. That is, the polymer
should have a low modulus and a low tangent delta, where tangent
delta is equal to Loss Modulus/Elastic Modulus. It is believed that
the chemical bonding of the polymer to the electrode, as will be
described, prevents the polymer from flowing or creeping with
respect to the electrode and substrate. It is also believed that
chemical bonding of the film to the electrodes, along with the
other attributes discussed herein, will provide operational
features not present in existing technology. In one or more
embodiments, the modulus of the polymer is less than about 40,000
pascals. In these or other embodiments, the tangent delta is less
than about 0.15. In one embodiment, the tangent delta is less than
about 0.05. A polymer with a low tangent delta has low internal
friction and minimizes heat generated during repeated stressing as
a result of voltage applied and removed across the electrodes. The
elastic modulus of the polymer of the film 48 should be low enough
so that moderate voltages are needed to extend or compress the
film. Chemically bonding the polymer to the plane of the electrode
surface increases the response in the z-direction. Chemically
bonding the polymer film to the electrode surface also prevents the
sagging of the polymer film when held in a vertical position. Thin
films of polymers are known to have significantly lower modulus
than the bulk polymers. In most embodiments, the polymer film
should be coated at as small a thickness as possible in order to
minimize the modulus of the film. As noted above, embodiments that
use a thickness of less than 5 .mu.m, and even less than 1 .mu.m
are well suited for broadband visible applications. In most cases,
the only bonding is of the individual chemical chains to the
electrode surface. In some cases there may be light crosslinking
between polymer molecules. The elastic modulus should, however, not
be so great that large voltages are needed to elongate or compress
the film. However, when the film is extended or compressed, the
energy of compression is stored as elastic energy, which helps the
polymer material restore to its original thickness when the
electric field is removed or released.
[0054] Ideally, the film should undergo a maximum compression of
about 50% and, more ideally, 30%. Voltages applied by the
electrodes should be reversed periodically so as to extend the film
every few cycles to keep the film from developing a compression
set. In other words, application of a voltage of one polarity to
the film causes the film to compress, and application of a voltage
with an opposite polarity causes the film to elongate. The maximum
extension of the film should be less than the compression, with a
maximum of 30%, or more ideally, about 20%. The total thickness of
the filter and the resting thickness of the film 48 can be chosen
so that the smallest variation of the film thickness causes
constructive interference for modes of the wavelengths of
interest.
[0055] In one or more embodiments, the variable thickness polymer
film (polymer film) 48 comprises an elastomeric polymer having a
low glass transition temperature, low modulus, low tangent delta,
high chemical saturation and sufficient light stability. In one
embodiment, the film includes acrylic, polyurethane, saturated
rubber such as polyisobutylene, or polysiloxane polymer, or
copolymers or terpolymers thereof. Other elastomers are possible.
In certain embodiments, the film includes a polymer modified to be
responsive to an electric field. In one embodiment, the film
includes polysiloxane.
[0056] In one or more embodiments, the polysiloxane polymer
includes linear polysiloxane. Linear polydimethylsiloxane molecules
have nearly zero bond rotational energy around the Si--O bond of
the polymer chain, which makes the polymer very flexible.
Polydimethylsiloxane polymer has a glass transition temperature of
less than 120.degree. C. Linear polysiloxane polymers that contain
a low percentage of phenyl have lower crystallinity and impart even
more flexibility.
[0057] Linear polysiloxane has high elongation and compressibility.
Linear polysiloxane has a low modulus and a low tangent delta.
Polysiloxane has a high reflection and gloss and exhibits low light
scattering and low light absorbance. Polysiloxane is stable to heat
and high light flux. The polysiloxane may be compounded to have a
wide range of refractive indices and exhibits low birefringence.
The polymer is moisture resistant and permeable to gas.
Polysiloxane retains flexibility at cold temperatures.
[0058] In one embodiment, the linear polysiloxane polymer includes
Si(CH.sub.3).sub.2 groups, i.e. has two methyl groups bonded to
each silicon atom. In other embodiments, one or both methyl groups
may be replaced by another substituent on a low percentage
(<15%) of silicon atoms. Examples of replacement substituents
include, but are not limited to, phenyl groups, fluoroalkyl groups,
alkyl groups containing two or more carbon atoms, and cyano groups.
Substitutions may be made to change the refractive index,
rheological properties, or electroactive properties. In one or more
embodiments, one or more of the silicon atoms may be replaced with
germanium atoms. Substituting phenyl groups for a small percentage
of methyl groups both lowers the modulus and glass transition
temperature as well as raises the refractive index of the
polymer.
[0059] As stated above, the polymer film includes a polymer that is
responsive to an electric field formed between the electrodes. In
one or more embodiments, the polysiloxane polymer exhibits
sufficient response to an electric field. In other embodiments, the
responsiveness may be increased by the addition of one or more
polar groups to the polysiloxane polymer. In one embodiment the
polymer may contain, or may be modified to contain, polar groups
that will be responsive to the electric field. It will be
understood that polar groups include ionic groups and non-ionic
polar groups. In one or more embodiments, the polymer may have
pendant anions. In other embodiments, the polymer may have pendant
cations. Other ionic configurations, such as zwitterions, are
possible. The polymer may include non-ionic polar functional
groups; and polar groups with unsymmetrical charged distributions,
such as polypropylene oxide, polyphenylene oxide, or polyvinyl
ethers, for example.
[0060] In one or more embodiments, the average number of ionic
groups per polymer molecule is small. In one embodiment, the
average number of ionic groups is up to about 1.5 per polymer
molecule. In other embodiments, the number of ionic groups is less
than about 1.1 per molecule. The number of polar groups should be
sufficient to make the polymer chains active in the electric field,
but not so high as to adversely affect the optical and rheological
properties of the polymer film. Embodiments that contain non-ionic
groups may contain more than one non-ionic monomer per polymer
chain. In one or more embodiments, the polymer includes an average
of from about 2 to about 10 non-ionic polar groups per
molecule.
[0061] Ionic groups may include sulfonate, sulfate, phosphonate,
phosphate, polyphosphate, carboxylate, carboxylic acid, ammonium,
and others. The addition of polar and ionic groups to polysiloxane
may be achieved by methods known in the art of silicone surfactant
chemistry. In one or more embodiments, the behavior of the polymer
film in the electric field will depend to some extent on whether
the polymer has anionic or cationic functionality. If the polymer
has anionic functionality, the film will compress when a positive
charge is placed on the electrode to which it is bonded. The film
will elongate when a negative charge is placed on the electrode to
which it is bonded. If the polymer chain has cationic
functionality, the film will compress when a negative charge is
placed on the electrode to which it is bonded. And the film will
elongate when a positive charge is placed on the electrode to which
it is bonded. To obtain the maximum deformation possible, the
electric field should alternate in polarity so that the polymer
film is both elongated and compressed.
[0062] In one or more embodiments, the polymer includes primarily
linear polymers of fairly low molecular weight, i.e. less than
about 50,000 amu. In these or other embodiments, the polymer film
polymer may be characterized by a fairly narrow molecular weight
distribution with polydispersity less than about 1.5, where
polydispersity=Mw/Mn. The molecular weight should be low enough to
minimize molecular chain entanglements. The entanglement molecular
weight refers to the molecular weight associated with or
corresponding to a polymer chain length that is sufficiently large
for entanglements to occur between molecules of undiluted polymer.
This molecular weight can be experimentally derived for a polymer
from the slope of a plot of log viscosity versus log molecular
weight. Experimental techniques for determining the entanglement
molecular weight of a polymer are summarized by W. W. Graessley in
ADV. POLYM. SCI., Vol. 16, 1974, and are known by those skilled in
the art.
[0063] Polysiloxane polymers are liquid up to about 100,000 amu.
The liquid nature of linear polysiloxane polymers is advantageous
for applying the polymer to the electrode surface. The liquid
polymer can be applied without solvents and then chemically bonded
to the electrode surface to form a non-sagging thin film soft
solid. Before coating the ionic groups on the polymer chains may be
reacted with functional groups to form non-polar groups in order to
modify the flow and deposition properties of the liquid polymer.
After deposition and bonding to the electrode surface, the
functional group may be removed and the ionic group released. For
example, a carboxylic acid polar group may be reacted with a long
chain alcohol to form a more non-polar ester before deposition.
After deposition and bonding, the alcohol may be hydrolyzed with a
mild acid to form carboxylic acid.
[0064] In other embodiments, the polysiloxane polymer chains may be
grafted to low molecular weight polymers such as polyacrylate,
polyether, polystyrene, polysulphone, polyurea, polyamide,
polyimide, polyamide-imide, polyester, polycarbonate, epoxy resins,
and others. The purpose of the grafting may be to alter the optical
properties including refractive index, rheological properties, and
electroactive properties. In still other embodiments, the
polysiloxane chains may be bonded chemically or physically to nano
particles. The nano particles may include nanoclay, activated
calcium carbonate, silica, POSS, surface modified silica, and
others. POSS (Polyhedral Oligomeric Silsesquioxane) is a silicate
with dimensions of a few nanometers. POSS can be bonded with
organic groups to change its solubility, as well as with vinyl
groups that allow polymerization into the polymer chains. Linear
polysiloxane with standard designations with M and D may be bonded
to polysiloxane resins with standard designations of T, Q, and MQ
to modify the optical and rheological properties of the polymer
film.
[0065] In other embodiments, the polysiloxane may be reacted with
phenyl silanes. Examples are triphenyl silane, diphenyl alkyl
silane and triphenyl vinyl silane. Triphenyl silane may be reacted
with vinyl groups on the polymer chains. Triphenyl vinyl silane may
be reacted with hydrides on the polymer chains. One purpose of
adding phenyl silanes is to increase the refractive index of the
polymer film without greatly affecting the glass transition
temperature, elastic modulus and tangent delta of the polymer
film.
[0066] The film 48 may be applied to the electrodes by ink jet,
photolithography, e-beam lithography, reactive ion etching, plasma
coating, spin-on coating, extrusion (slit) coating. Ink jet
deposition would be advantageous for deposition on individual
active electrodes. Extrusion coating would be advantageous for
continuous or semi-continuous coating or large areas such as the
common electrode, as will be described subsequently. The film is
then chemically bonded to the electrode via a chemical reaction.
Thus, prior to the bonding, the polymer of the film includes a
reactive group that is capable of reacting to form a chemical bond
with either the electrode or with a coupling agent, as described
hereinbelow.
[0067] It will be understood by one of skill in the art that many
polymers include polymer molecules having chains. In one or more
embodiments, each chain includes a first terminus (i.e. end) and a
second terminus (i.e. end). The one or more polar groups are
located at or near a terminus of the polymer chain. Prior to
bonding with the electrode or a coupling agent, in one or more
embodiments the reactive group is located at or near one end of the
polymer chain, with a polar group at or near the other end. In
other embodiments, the reactive group is located near the midpoint
of the polymer chain, with polar groups at each end. In yet other
embodiments, the reactive group is located partway along the
polymer chain, and both termini of the polymer chain include a
polar group. In these or other embodiments, the length of the
polymer chain between the reactive group and the polar group is
less than the entanglement molecular weight. It may be preferred
that the reactive group is somewhat randomly positioned in the
middle of the polymer molecule. This would stagger the polar groups
on the free ends so that the polar groups are more separated from
each other.
[0068] The electrode surface may be chemically modified to provide
reactive sites for polymer bonding. The surface treatments may
include etching, oxidation, plasma treating and others. The surface
may be coated with a dielectric such as SiO.sub.2 to provide
bonding sites. The SiO.sub.2 coating may be acid etched to increase
reactive sites. After etching, the surface should be dried to an
anhydrous condition. Coating with SiO.sub.2 has other advantages
such as insulating the electrode. This would be especially
advantageous if metallic electrodes such as aluminum are used.
[0069] The reactive groups on the polymer include, but are not
limited to silicon hydroxy (Si--OH), silicon hydride (Si--H),
silicon alkoxy, silicon chloride and others. The reactive group
could include functional groups that would allow bonding using UV
or e-beam radiation.
[0070] In one embodiment, where two polymer film layers are used in
a filter element, their polarities need to be reversed. If the
polymer film applied to the active electrode is anionic, the
polymer film applied to the common electrode may be cationic. If
the polymer film applied to the active electrode is cationic, the
polymer film applied to the common electrode may be anionic. If two
polymer film layers are employed, the variation in thickness in the
two films that is required to produce light filtration across a
broad range of wavelengths may be decreased from that needed when
only one polymer film is utilized.
[0071] When light filtration across a broad range of wavelengths is
desired, as in direct view displays, the refractive index of the
polymer film should be as high as possible. In certain embodiments,
a higher refractive index allows the total deflection of the
polymer film to be made smaller while still achieving filtration
across the wavelength range. In applications with monochromatic
light sources, a polymer film with a lower refractive index may be
preferred. In certain embodiments, a lower refractive index will
allow better control of subtle phase shifts and allow easier
modulation between total constructive and total destructive
interference. It is advantageous to avoid a refractive index
modification that causes a significant increase in the tangent
delta of the polymer film. The refractive index of the polymer
should be matched as much as possible to the electrode or other
surface to which it is bonded.
[0072] The modulus of the polymer film should be low enough that
the change in the refractive index with the stress induced by the
electric field is not too large. In applications where the
electrode area is small, in projection display light valves for
instance, when compressed, the polymer film can expand. FIG. 2
shows electrodes 46A and 46B where a space 56 is provided to allow
the polymer film to expand when compressed by the electric field.
In applications where the area of the filter is large compared to
the thickness, as in a large direct view display, the polymer film
may be pattern coated within the filter 22 to provide areas where
the polymer film can expand when compressed. As seen in FIG. 15,
areas 252 allow for expansion between polymer film 48 components.
The width of the space 252 should be less than a wavelength of
light (50 nm to 400 nm). The rows may be staggered to minimize
continuous stripes of uncoated area. The expansion areas may be
created by pattern coating an alkyl capped silane under anhydrous
conditions. The alkyl groups (methyl, ethyl, etc.) cap off reactive
sites on the electrode surface where the polymer cannot bond when
it is coated on the polymer surface. The alkyl based silane also
provides a non-polar inert surface that prevents interaction of
ions or polar groups in the polymer chains from interacting,
perhaps irreversibly with the electrode surface. Other areas of the
filter that may come in contact with the polymer or polymer film
may be similarly capped.
[0073] In one embodiment, the polymer film may be applied to the
electrode or electrodes in a series of steps. In a first
preparatory step, the alkyl silane capping agent is pattern coated
onto certain areas of the electrode, the areas delineated by 252 of
FIG. 15. These areas will be unreactive in subsequent steps, and
will therefore create expansion areas for the polymer film. In a
subsequent step, the electrode substrate is coated with a silane
coupling agent, which chemically bonds to the electrode where the
capping agent is not present. In a third step, an elastomeric
polymer is applied and chemically bonded to the coupling agent. In
one embodiment, where the elastomeric polymer is capable of bonding
directly with the electrode, the coupling agent may be
eliminated.
[0074] The capping agent used in the first preparatory step
includes a group capable of reacting to form a bond with the
electrode. The capping agent, once bound to the electrode, does not
contain any group capable of reacting with the polymer that is
subsequently applied to the electrode to form the polymer film. In
other words, the capping agent reacts with the electrode substrate
to form a patterned coating over certain areas of the substrate
that will be unreactive to the polymer. Examples of capping agents
include compounds represented by the formula
##STR00001##
where R.sup.1 is selected from alkoxy groups, R.sup.2 is an alkyl
group, R.sup.3 and R.sup.4 are independently selected from alkoxy,
methyl, or other alkyl groups, and x is an integer from 0 to about
18. If R.sup.1, R.sup.3 and R.sup.4 are all three alkoxy, methoxy
for instance, the silane may form a monolayer under anhydrous
conditions. The preferred configuration, however, is a monoalkoxy
where R.sup.3 and R.sup.4 are methyl groups and R.sup.1 is an
alkoxy. This type of silane gives a stable monomeric monolayer
under anhydrous deposition.
[0075] The coupling agent includes alkoxyl groups, or other groups
capable of reacting to form a bond with the electrode substrate,
and a functional group capable of reacting to form a bond with the
polymer that is subsequently applied to the electrode to form the
polymer film. In one or more embodiments, the functional group is a
vinyl group. In one embodiment, the coupling agent includes
compounds that may be represented by the following formula
##STR00002##
where R.sup.1 is selected from alkoxy groups, R.sup.2 is a vinyl
group, R.sup.3 and R.sup.4 are independently selected from alkoxy,
methyl, or other alkyl groups, and x is an integer of from 0 to
about 10. Both the silane capping agent and the silane coupling
agent are best applied under anhydrous conditions that create a
monolayer. If R.sup.1, R.sup.3 and R.sup.4 are all three alkoxy,
methoxy for instance, the silane may form a monolayer under
anhydrous conditions. The preferred configuration, however, is a
monoalkoxy where R.sup.3 and R.sup.4 are methyl groups and R.sup.1
is an alkoxy. This type of silane gives a stable monomeric
monolayer under anhydrous deposition. Trialkoxy silane coupling
agents produce polymeric multilayered structures under hydrous
conditions.
[0076] As stated above, in one or more embodiments the coupling
agent includes alkoxyl groups, or other groups capable of reacting
to form a bond with the electrode substrate, and a functional group
capable of reacting to form a bond with the siloxane polymer that
is subsequently applied to the electrode to form the polymer film.
The polymer, prior to reaction, includes a reactive group that is
capable of reacting with the coupling agent. For example, where
R.sup.2 of the coupling agent is a vinyl group, it can react with a
silicon hydride group on the siloxane polymer chain. Other
combinations of functional groups on the silane coupling agent and
the siloxane polymer are possible.
[0077] The order in which these bonds are formed is not
particularly limited. Thus, in one embodiment a siloxane polymer is
reacted with the coupling agent after it is bound to the electrode.
In another embodiment, the coupling agent may be reacted with the
polymer before the coupling agent is applied to and bonded with the
electrode. In one or more embodiments, the reaction may be an
addition cure, catalyzed by platinum (Pt) or rhodium (Rh). The cure
may be induced by UV radiation, and may involve either cationic or
free radical species. The cure may be through electron beam (EB) or
reactive ion itching.
[0078] In another embodiment, as stated above, the coupling agent
may not be necessary. That is, a low molecular weight
dimethysiloxane polymer that includes a reactive group may be
bonded directly to the electrode. In these or other embodiments,
the polymer may be chemically bonded to the electrode via a
condensation reaction, involving hydroxyl or other reactive
groups.
[0079] For purposes of this specification, the term chemically
bonded will be understood to also include electrostatic attractions
and hydrogen bonding.
[0080] Skilled artisans will appreciate that a number of different
embodiments can be configured based upon the embodiments shown in
FIGS. 1 and 2. And from these different embodiments, a number of
end-use devices can be improved upon by use of the disclosed
technologies. Indeed, as seen in at least FIG. 3, multiple filters
can be configured on the facing substrates so as to provide a
matrix of filters. An exemplary matrix of filters can be configured
for any conceivable end use appreciated by a skilled artisan.
Although a number of embodiments are presented herein, they should
not be construed as limiting.
[0081] In another active matrix embodiment, a light modulator
designated generally by the numeral 20A is shown in FIG. 2. The
modulator 20A, wherein the alphabetic suffix is an indication of an
embodiment with a variation of some type, includes an electrode 44
that is a common electrode of an array so as to provide a common
reference voltage. Active electrodes 46A and 46B may be controlled
by an active matrix addressing scheme that is generated by the
controller 24. Indeed, a number of active electrodes 46 may be
provided, all of which are connected to the controller 24. It will
further be appreciated that a space 56 may be provided between each
of the active electrodes 46A and 46B so that thin film transistors,
addressing lines, storage capacitors and the like may be associated
therewith. Alternatively, in a single filter, or where a relatively
small number of filter elements in an array are used, a segmented
voltage control, where the voltages are applied directly to the
electrodes by the controller may be used. In some embodiments, a
passive matrix control may be used.
[0082] An exemplary modulator designated generally by the numeral
20B is shown in FIG. 3 and comprises an array of filters 22A and
22B and as many as are needed in an end-use application. As can be
seen, the array comprises a plurality of filters 22 arranged in a
matrix of rows and columns. A network of row select and data lines
57 and 58 supply a voltage to each filter 22 as deemed appropriate
by the controller. Surrounding each filter 22, or picture element,
is an electronics area 59 which typically receives input or control
signals from the data lines. The area 59 typically receives input
or control signals from row select and data lines. The area 59 may
also provide for a location of additional electronic elements that
control operation of each respective filter.
[0083] FIG. 4 shows two filter elements 22A and 22B in an array
designated generally by the numeral 60. When configured in this
manner, each film forms a pixel, also referred to as a picture
element, or a defined filter in the array. Specifically, an active
electrode 46A is coated with film 48A, forming gap 49A. An active
electrode 46B is coated with film 48B, forming gap 49B. In this
embodiment electrode 46A has a resting voltage with a resting
thickness for film 48A. Electrode 46B has voltage applied, which
creates an electric field between electrode 46B and common
electrode 44. In this embodiment, application of the electric field
causes the film 48B to compress, increasing gap 49B. The optical
path length of filter 22A may pass one color from the light source.
The optical path length of filter 22B may pass another color from
the light source. At another voltage, the optical path length of
filter 22B may create constructive interference for a bandwidth not
in the light source and thus create a dark pixel. With a
monochromatic light source, the filter may act as a modulator,
passing or not passing light from the source. The optical path
length of filter 22A may destructively interfere or constructively
interfere with the monochromatic light source, creating digital
bits zero and one.
[0084] The total distance between the reflective surfaces 42 and 43
can range from under 1 .mu.m to over 10 .mu.M, and in some cases
several mm. The total thickness should be as small as practically
possible to minimize the voltages needed to create the electric
fields needed to vary the thickness of the films 48A and 48B. Low
total thickness minimizes the power consumed as well as decreasing
the response time of the filter. Lower voltages also make the
active matrix components smaller decreasing dark areas in a
display. Lower total thickness minimizes overlap between modes (the
integer m in Eq.1). In a broadband application, the optimal total
thickness is less than 2 .mu.m.
[0085] Referring now to FIG. 5, it can be seen that an alternative
light modulator is designated generally by the numeral 70. As
shown, the modulator 70 provides only a single filter 22C, but an
array with multiple filters 22C could be used. This embodiment is
similar to the modulator shown in FIG. 1, except that a variable
thickness polymer film 72, which has the same characteristics as
film 48, may be coated on the common electrode 44, and, as before,
the film 48 is pattern coated on the active electrode 46. If a
variable thickness polymer film is coated on both electrodes, the
polymer film layers will have opposite polarity as will be
discussed subsequently. This embodiment allows for finer control of
the optical path length and potentially improved response
times.
[0086] Referring now to FIG. 6, it can be seen that another light
modulator is designated generally by the numeral 80. As shown, the
modulator 80 provides two filters designated by the numeral 22D and
22E, but a single filter or an array of filters could be used. In
this embodiment, a variable thickness polymer film 82, which has
the same characteristics as film 48, is associated with the common
electrode 44. Specifically, FIG. 6 shows the film 82 coated as a
continuous layer or semi-continuous layer on the common electrode
44. The localized electric field created between electrodes 44 and
46 extends or compresses the film 82 in a manner previously
discussed. The space 56 between electrodes 46A and 46B provides an
area for the film 82 to transition in thickness between the
electrodes. In other words, when a voltage is applied across common
electrode 44 and active electrode 46A, but not across electrode 44
and electrode 46B, an angular transition is formed in the film 82.
As such, the film 82 is shown in an extended activated condition on
juxtaposition to film 48 A and in an unactivated condition in
juxtaposition to film 48B. This transition from where the film
expands to areas where the film does not expand, which might
otherwise provide an undesirable change in the optical length, is
diminished in view of the gap 56.
[0087] In another embodiment, shown in FIG. 7, a light modulator is
designated by the numeral 90. In this embodiment, the modulator 90
provides two filters designated as 22F and 22G. In this variation,
instead of applying the high reflective coating to an entire
surface of the substrate, the HR coatings 42A and 42B are coated
directly on corresponding electrodes 46A and 46B. In other words,
the filter 22F includes coating 42A, electrode 46A and film 48A;
and filter 22G includes coating 42B, electrode 46B and film 48B in
addition to the other components previously discussed. Of course,
other combinations of electrodes, reflective coatings and polymer
film layers within a modulator are possible.
[0088] Referring now to FIG. 8, it can be seen that a direct view
light modulator is designated generally by the numeral 120. In this
embodiment, the modulator may be edge lit or back lit, as is
typical for direct view displays such as computer monitors,
televisions and portable devices. A light source 102 may be cold
cathode fluorescent, hot cathode fluorescent, xenon flat lamp or
other white light source. An optimal light source is a plurality of
LEDs with three or more colors, including the primary colors red,
blue and green. Other colors may be chosen. Other colors outside
the gamut of the three primaries may be added to increase the gamut
of the display, for instance, violet, deep red, or orange. Colors
that are inside the gamut of the primaries may also be added. The
LEDs should have a fairly narrow bandwidth, especially if more than
three colors are utilized, preferably 20 nm to 60 nm. There should
be dark areas in the total spectrum to allow the filters 22A and
22B to create constructive interference in a dark bandwidth of the
spectrum to create a dark pixel.
[0089] Light 104 generated by the source 102 passes through
diffuser 106 and an optional filter 108. The diffuser 106 mixes the
light colors and creates a uniform distribution of light across the
filter(s) 22. The diffuser 106 may be polymer film, holographic or
any other commonly used diffusers. The optional filter may remove
unwanted wavelengths, such as UV and IR from visible light. It may
also clean up the output spectrum of light source 102. In
particular, the filter 108 may clean up areas of the spectrum
between the primary color bandwidths. It may supply a sharp cutoff
at a particular wavelength, 660 nm, for instance, where dark pixels
can be created. This will help increase the contrast of the
modulator 120.
[0090] Since the filters 22H and 22I are configured as an
interference filter, it requires that the viewer be decoupled from
the cells. Otherwise the optical path length will vary with the
viewer's angle. This can be accomplished with one or more diffusing
films 109 placed on an outer surface of substrate 34 of FIG. 8. The
diffusing films can be any of standard holographic,
microreplicated, and other diffusing films. Alternatively, the
outer surface of glass 34 may be ground to create diffusion. In
lower cost displays, where viewing angle is not important, no
diffusers may be used. Another advantage of diffusing films is to
provide a matte look and decrease specular reflection from
reflective layers with the pixels. Alternatively, substrate 34 may
be in the form of a fiber optic faceplate.
[0091] Since the filters 22H and 22I are configured as an
interference filter, it requires a fairly narrow range of input
angles. A light direction film 110 directs modified light 104' into
a narrow range of angles before entering the filters 22 of the
modulator. The light direction films may include one or more 3M
BEF, IDF, TRAF films, as well as holographic films. Alternatively,
a rear fiber optic faceplate 122 may take the place of
antireflective layer of FIG. 8. The fiber optic faceplate 122
directs the backlight into a narrow cone. A collimated backlight
may also be used.
[0092] As discussed previously, light 104' enters the filter
elements of the array. The light 114 that exits each filter element
is colored depending on the optical path length set for each filter
at a particular time. The optical path length of each filter
element is electronically set to pass one of the three or more
wavelengths of source 102. The optical path length of each filter
element is determined by the thickness of the corresponding film
48, which is controlled by the localized electric field formed
between active electrode 46 and common electrode 44. The optical
path length of each filter element is set via the voltage to pass
one of the colors of the light source 102 at a given time. Light
that is not passed is reflected. For instance, if the light source
102 consists of RGB LEDs, and the optical path length of a filter
is set to transmit blue, the filter will reflect red and green. If
the optical path length of the filter is set to transmit green, the
filter will reflect blue and red. If the optical path length of the
filter is set to transmit red, the filter will reflect green and
blue. The reflected light passes back through the light direction
film 110, back to the diffuser 106, where the light is reflected
back to the array of filters until it encounters a filter that is
tuned to pass the particular wavelength. Light is recycled until it
is used.
[0093] Dark pixels are created by tuning the optical path length of
a filter 22 to pass a wavelength that is not in the spectrum of the
light source 102. For instance, if light source 102 is RGB LED, the
wavelength of the dark pixel can be set between the red and green
or the green and blue bandwidths as long as the wavelength is in a
clean area outside the baseline wavelengths of the colors. If a
more broadband light source is used, the dark pixel can be set at a
wavelength above or below the bandwidth of the source, above 400 nm
or below 700 nm, for example. Filter 108 can cut off the spectrum
below 660 nm and the dark pixel set at 700 nm, for instance. Filter
108 can also clean up the spectrum and provide a dark baseline
between red and green or green and blue, for instance. If a cold
cathode fluorescent or other light source that employs excited
phosphor as a light source, the filter 108 can clean up an area in
the bandwidth outside of the primary emission bands.
[0094] A palette of colors can be created by rapidly cycling each
filter 22 through the primary colors of the light source. The
viewer will see a time average color. Including the dark pixel
wavelength in the pixel color cycling can control the contrast of
the displayed colors. Each pixel will appear as a time average
solid color. The colors can smoothly change from one color to
another by subtle changes in the filter timing. White light can be
created by cycling between complementary colors, red and green or
blue and yellow or cycling between red, blue and green with equal
periods. Grey can be created by cycling through equal parts of red,
blue and green with varying periods of black.
[0095] It is believed that high resolution and better picture
quality can be achieved by the elimination of sub pixels because
the electronics of each pixel can be reduced by two-thirds. The
pixels can assume a square shape in which there is a wider aperture
and less dark matrix in each pixel, and the screen door effect that
is typical of LCD and plasma displays is reduced thereby improving
picture quality.
[0096] Because the filter array creates pure spectral colors, the
gamut of the display is greater than typical LCD, which rely on
fairly unsaturated absorption filters. This leads to washout of
colors at higher light intensity levels. The human eye varies in
response to different colors. The eye is much more sensitive to
yellow and green than to red and blue. It is least sensitive to
blue. Standard LCD screens with red, green, and blue subpixels in
the standard stripe configuration cannot easily compensate for or
exploit these differences in perception.
[0097] One skilled in the art can appreciate that a number of
variants can be constructed. A pixel may be comprised of two
subpixels where one subpixel changes between red, green, and black
while the other subpixel changes between yellow, blue, and black.
Alternatively, three subpixels may be used, as in standard
displays, where the first pixel changes between red and black, the
second between green and black and the third between blue and
black. An array of filters can be used in parallel with an LCD
matrix, where the LCD matrix varies the light throughput and the
disclosed array acts simply as a color filter. The filter array may
be used with a field sequential pulse backlight.
[0098] The filters described above can be used in a number of
different applications, some of which are described herein. In one
embodiment, as seen in FIG. 9, a camera system is designated
generally by the numeral 130. The camera, or any other optical
imaging equipment, passes the observed light through a lens system
132. After passing through the lenses of the lens system, the light
is projected through an array of filters, designated by the numeral
134, wherein the array comprises a light modulator with any of the
filters as described above with any number of picture elements.
Light is transmitted through the array of modulators onto a light
recording matrix designated by the numeral 136, such as CCD or
CMOS. The camera may record a still image or a moving video. The
array 134 collects a wider gamut of color than absorbance filters
currently in use. The CCD or CMOS can essentially be monochromatic
and the color filtering can be chosen according to the needs of the
photographic device.
[0099] The filters 22 of the array cycle through a series of
colors. The array may cycle through red, blue and green, for
instance. If a CCD or CMOS array that may be associated with the
modulator 20B is less sensitive to red or blue, for example, the
filters can be programmed to collect more light from these
wavelengths than from green. A matrix array of modulators 20B may
be chosen or one set of pixels may collect red and green and
another set of pixels collect blue and yellow.
[0100] In other applications, it will be appreciated that the
filter 22 as shown in FIG. 10, or the array 134 shown in FIG. 11
may be coupled to fiber optic inputs. In FIG. 10, a single fiber
optic input 150 may provide an input light to the filter 22, which
may be in the form of any of the filters described herein, which
then generates an output light that is coupled to a single fiber
optic output 152. Likewise, in a manner similar to that shown in
FIG. 11, multiple fiber optic inputs 150A-D are associated with an
array 134 with any embodiment of filter 22 which is also associated
with a corresponding fiber optic output 152A-D. Use of fiber optic
inputs and outputs with a single filter or an array of filters
allows for fast switching using a relatively inexpensive
configuration. The embodiments described can be used as a tunable
filter and optical modulator in wavelength division multiplexing
(WDM) and data bus applications.
[0101] By varying the optical path length of the filter or an array
of filters, optical tuning can be obtained over a wide wavelength
range. These embodiments allow the tuning to a particular
wavelength of a multiplexed optical signal. Light from a
monochromatic source can be modulated into a series of ones and
zeros for digital data transmission.
[0102] The previously described embodiments are transmissive,
wherein bright bands appear on a dark background. However, it will
be appreciated that the described filters can also be used in
reflective mode. FIG. 12 shows two filters 22J and 22K utilized in
a reflective configuration. The filters may be a single unit or,
more preferably, an element of an array. The array can be one or
two dimensional.
[0103] The configuration shown in FIG. 12 is for a reflective
modulator designated generally by the numeral 200. The modulator
200 is constructed in a manner similar to the transmissive
modulator shown in FIGS. 1 and 2; however, several changes to the
overall construction are provided so as to provide a modulator that
is reflective instead of transmissive. The modulator 200 is
controlled by a controller 24 as in the previous embodiments. The
significant changes to the modulator are in the use of an
anti-reflective coating 202 on the substrate 34 which faces the
light source. The anti-reflective coating 202 is constructed of the
materials as previously discussed for the anti-reflective layer 40.
Another difference between this construction and the previous
embodiments is the use of an absorption layer 204 on the substrate
32 opposite the substrate 34 with the anti-reflective coating.
Although the electronics associated with each variable thickness
polymer film 48 may be in close proximity, it will also be
appreciated that control electronics 214 may be mounted on the
absorption layer 204 to control the activation and deactivation of
the voltage across the electrodes using appropriate
electronics.
[0104] Light source 206 may be broadband, multiple discrete, or
broad or narrow band monochromatic. The source 206 may be visible,
NIR, IR or UV. The source may be standard metal halide or mercury
arc or, more preferably, light emitting diode (LED) of three or
more colors with fairly narrow bandwidths. Monochromatic sources
may include LED or laser. Broadband UV/visible or IR light sources
may be used in spectroscopic applications.
[0105] The light source 206 may be oriented at an angle 0.degree.
to 90.degree. to the modulator or, in other embodiments, between
10.degree. and 60.degree.. An optics system 210 collimates input
light 208 generated by source 206. The optics system can also
filter out unwanted wavelengths, UV and IR from visible, for
instance. Dichroic mirrors may also be used as part of the optics
system 210. The optics system 210 may also filter wavelengths where
dark pixels may be formed. Input light 208' enters filters 22J and
22K. The light source 206 generates an input light 208 which has a
wavelength .lamda. such that the optical path length of the filter
22 is an integral multiple of the wavelength at a given time. The
light that is reflected is determined by an
.SIGMA.nd cos .theta.=m.lamda./2 (3)
.SIGMA.nd is a sum of the optical path length between reflective
surfaces 42 and 43, m is an integer .gtoreq.1, .theta. is the angle
from the perpendicular light 208' strikes the filters 22, .SIGMA.nd
changes with the variation in thickness of the polymer film 48. The
variation in thickness of polymer film 48 is determined by the
localized electric field formed between electrodes 44 and 46. The
voltage between electrodes 44 and 46 is controlled by the
microprocessor control system 24. Light that is not reflected is
absorbed by the filter(s).
[0106] Modified light 208' enters the filters 22. As before, the
filter(s) are structurally built on optically clear substrates 32
and 34. Substrate 32 can also comprise silica, silicon, or other
semi-reflective substrate. Substrate 32 is coated with a dielectric
high reflective coating 42. The high reflective coating may
comprise an alternating stack of high refractive index and low
refractive index films. Coating 42 may also comprise a combination
of dielectric HR film with a reflecting and absorbing metallic
film. The metallic film may comprise aluminum, silver, gold,
platinum, or other suitably reflective metals. Alternatively, as
seen in FIG. 13, the HR coating associated with specific pixels may
be coated on the active electrode 46.
[0107] Substrate 32 can have an absorption layer 204 bonded to it.
The absorption layer will absorb light that is transmitted through
substrate 32. The absorption layer 204 may be bonded continuously
or bonded in a pattern in areas that transmitted light will
penetrate, which is dependent on pixel element location and the
angle of light source 206. The substrate 32 may also have an
attached control area 214 which may contain transistors, storage
capacitors and other electronics as an alternative to placing
electronics in space 56 between elements of the array. Placing the
electronics in control area 214 instead of space 56 allows the film
48 components of the array to be placed closer together. Each
control area 214, which works in tandem with the electrode(s), is
connected to the controller 24.
[0108] The substrate 34 is coated with anti-reflective film 202.
The anti-reflective film 202 may be optimized across the wavelength
range for a broadband source. In monochromatic applications, it may
be optimized for the particular wavelength of the light source. In
applications with light sources that have multiple discrete colors,
the AR coating may be optimized for the individual wavelengths. The
opposite side of substrate 34 is coated with a high reflective
dielectric coating 43. The dielectric coating comprises alternating
layers of high refractive index and low refractive index films.
Alternatively, as seen in FIG. 13, the HR coating 42 may be coated
on the active electrode 46. As such, modulator 200' utilizes
filters 22L and 22M.
[0109] For projection applications, the reflectance (R=r.sup.2,
where r is the reflectivity of the coatings) of the HR coatings 42
and 43 should be greater than 75%, or, in other embodiments,
greater than 95%. The reflectance of HR coating 42 may be made a
little less than HR coating 43 to allow filtered light to more
easily egress from the top of the filter. In any event, as
described previously, if .SIGMA.nd is an integral multiple of a
source wavelength, the reflected light 220 will be directed through
a lens system 230. The bandwidth of the reflected light will be
determined by the reflectance of the reflective layers. The total
spacing between reflective layers or coatings can range from under
1 .mu.m to over 10 .mu.m. As noted previously, the total thickness
of the film should be minimized to reduce power consumption and
decrease response time.
[0110] In summary, direct view displays include computer monitors
and televisions, as well as portable displays in cell phones,
PDA's, portable games, GPS devices and many others. It is believed
that the disclosed technology has several advantages over prior art
such as LCD and plasma, particularly that it will yield superior
picture quality, require significantly less energy to operate, and
will be less costly to produce.
[0111] The embodiments shown will incur lower production costs than
LCD or plasma because the number of electronics parts needed is cut
by one-half or more (including capacitors, thin film transistors,
and data drivers). Additionally, using fewer TFTs translates to a
lower rejection rate for screens, which is a manufacturing problem
for current TFT-based active matrix LCD displays.
[0112] The energy savings comes from the fact that the present
technology eliminates the need for many of the polarization and
absorbance filters. Color absorbance filters can absorb 75% of the
source light. Polarization filters, such as those used in LCD
displays, can absorb 60% of the source light. The display using
this invention has a high light efficiency and will transmit almost
the entire source light. A lower power source light may be used and
give the same luminance as an LCD display with a higher power light
source. Additionally, higher power, more bright light sources that
give brighter displays may be used without heat buildup.
[0113] The present technology offers superior picture quality to
LCD and plasma for a variety of reasons. First, the disclosed light
modulators allow for quicker response time, which translates to
fast motion without blurriness. Secondly, unlike LCD and plasma,
the present technology does not require sub-pixels; therefore, the
display is able to provide a higher resolution. The present
technology also eliminates the need for polarization and absorbance
filters, resulting in brighter picture, wider color gamut, more
pure spectral colors, and the ability to use more than three
primary colors at a time. And, because the disclosed modulators
require less than half of the electronics parts used in traditional
LCD or plasma technologies, the present modulators will accommodate
a larger display area and eliminate the "screen door" effect common
with LCD and plasma displays.
[0114] The disclosed embodiments are also believed to have multiple
advantages over current projection displays, such as digital
micromirror devices (DMD), liquid crystal (LCD), and liquid crystal
on silicon (LCOS). Again, the predominant benefits include the need
for less energy to operate, lower production costs, and improved
picture quality.
[0115] The invention will use less energy than current technology
because of the elimination of polarization filters and because of
the elimination of absorbance filters.
[0116] Production costs will be lower with the present technology
because of the reduced number of necessary electronics parts, which
will be cut by more than one-half Full color control within one
light valve can be attained without the use of absorbance color
wheels. Additionally, the present technology will be simpler to
manufacture than DMD.
[0117] The invention has many additional advantages over current
toner/fuser printer technologies, including laser and LED array.
For instance, the present technology allows for improved, multiple
resolutions. With the present invention, there is no need for a
complicated system of lasers and rotating mirrors and lenses, as is
the case with current laser printers. Furthermore, the present
invention is not limited by the size of the laser dot, as with
laser technology, nor is it limited by the size of the LEDs in an
LED array.
[0118] The present technology also provides a less costly
alternative to laser printers by eliminating the need for expensive
lasers. Additionally, greater speed is achievable because whole
lines can be projected across the imaging drum at a single
time.
[0119] The invention allows for finer detail than is available from
current technologies because of the variation in light intensity
that can be projected on the image drum. In contrast, current LED
array printers and laser printers work in a single "on" or "off"
mode.
[0120] This invention can also be used as a filter for digital
cameras, video cameras, and other image formation devices.
[0121] The invention is an improvement over current technologies
because it will eliminate the need for individual fixed absorbance
filters on the CCD or CMOS, thereby providing a broader color gamut
in image formation. The present invention can compensate for the
response of the CCD or CMOS to different wavelengths of light.
Additionally, the invention can collect specified wavelengths in
low light situations and compensate for differing lighting
conditions.
[0122] The invention can be used as an electronically tunable
filter that can rapidly control spectral output. Some of the
advantages are: fast response time, polarization insensitivity,
small thickness, low loss, random access to wavelengths, broad
spectral range, low power consumption, stability in harsh
environments (heat and humidity).
[0123] With a monochromatic light source such as laser or LED, the
invention can be used as a spatial light modulator that can
modulate a beam of light into a spatial pattern of light and dark
controlled electronically. It has many advantages over LCD and
DMD.
[0124] The invention can be used as an optical filter for
UV/visible, NIR and IR spectroscopy, including usage as an
interferometer in Fourier transform spectrometers.
[0125] In microscopy, control of both the input and the output
light, both illumination and collection in bright field, dark
field, phase contrast, confocal, as well as interference
microscopy.
[0126] The invention can be used as a spatial light modulator for
holographic applications including holographic data storage and
holographic displays. The invention can be used as a tunable filter
and optical modulator in wavelength division multiplexing (WDM) and
data bus applications. The invention can also be used to compensate
for lack of parallelism and other aberrations in large Fabry Perot
etalons and interferometers. Filter elements can be tuned across an
area to compensate for lack of parallelism and other defects.
[0127] Other possible uses include, image former for large format
printers including lithography, near-to-eye displays, optical
computing elements, white light color temperature adjuster,
saturated color maker for stage lighting, tunable laser, and
micro-chemical systems/DNA arrays.
[0128] Thus, it can be seen that the objects of the invention have
been satisfied by the structure and its method for use presented
above. While in accordance with the Patent Statutes, only the best
mode and preferred embodiment has been presented and described in
detail, it is to be understood that the invention is not limited
thereto and thereby. Accordingly, for an appreciation of the true
scope and breadth of the invention, reference should be made to the
following claims.
* * * * *