U.S. patent application number 12/183094 was filed with the patent office on 2010-02-04 for balanced light valve.
Invention is credited to Meritt W. Reynolds.
Application Number | 20100027095 12/183094 |
Document ID | / |
Family ID | 41226748 |
Filed Date | 2010-02-04 |
United States Patent
Application |
20100027095 |
Kind Code |
A1 |
Reynolds; Meritt W. |
February 4, 2010 |
BALANCED LIGHT VALVE
Abstract
Radiation from an illumination source (102) is directed to a
total internal reflector (TIR) modulator (10). The modulator
includes a an electro-optic member (213) with a plurality of
individually addressable pixel regions (210) comprised of a
plurality of electrodes arranged in a first and second set. At
least one electrode of the first set is adjacent to at least one
electrode of the second set and at least one of the pixel regions
is controlled to form at least one image pixel on a surface. A
first electric potential is imposed on the first set of electrodes
selected from a first predetermined group of electric potential
values. A second electric potential is imposed on the second set of
electrodes selected from a second predetermined group of electric
potential values. The first and second predetermined groups of
electric potential values together comprise at least three
different electric potential values.
Inventors: |
Reynolds; Meritt W.;
(Burnaby, CA) |
Correspondence
Address: |
Amelia A. Buharin;Patent Legal Staff
Eastman Kodak Company, 343 State Street
Rochester
NY
14650-2201
US
|
Family ID: |
41226748 |
Appl. No.: |
12/183094 |
Filed: |
July 31, 2008 |
Current U.S.
Class: |
359/259 |
Current CPC
Class: |
B41J 2/465 20130101;
G02F 1/195 20130101; G02F 1/315 20130101 |
Class at
Publication: |
359/259 |
International
Class: |
G02F 1/03 20060101
G02F001/03 |
Claims
1. An imaging method comprising: emitting radiation from an
illumination source towards a total internal reflection (TIR)
modulator, the TIR modulator comprising: a member comprising an
electro-optic material; a plurality of individually addressable
pixel regions; and wherein each pixel region comprises a first set
of electrodes arranged in an interdigitated relationship with a
second set of electrodes; controlling at least one of the pixel
regions to form at least one image pixel on a surface; imposing a
first electric potential on the first set of electrodes of a pixel
region in accordance with a first electric potential value selected
from a first predetermined group of electric potential values;
imposing a second electric potential on the second set of
electrodes of the pixel region in accordance with a second
electrical potential value selected from a second predetermined
group of electric potential values; and wherein the first
predetermined group of electric potential values and the second
predetermined group of electric potential values together comprise
at least three different electric potential values.
2. A method according to claim 1, comprising operating a first
voltage source to impose the first electric potential on the first
set of electrodes of the pixel region and separately operating a
second voltage source to impose the second electric potential on
the second set of the electrodes of the pixel region.
3. A method according to claim 1, wherein each of the first
predetermined group of electric potential values and the second
predetermined group of electric potential values comprises a common
electric potential value.
4. A method according to claim 3, wherein the common electric
potential value is selected from each of the first predetermined
group of electric potential values and the second predetermined
group of electric potential values in accordance with a first image
data signal.
5. A method according to claim 1, wherein each of the electric
potential values of the first predetermined group of electric
potential values is different from any of the electric potential
values of the second predetermined group of electric potential
values.
6. A method according to claim 4, wherein the first electric
potential value and the second electric potential value are
different electric potential values and both the first electric
potential value and the second electric potential value are
selected in accordance with a second image data signal that is
different from the first image data signal.
7. A method according to claim 3, wherein each of the first
electric potential value, the second electric potential value and
the common potential value are different electric potential
values.
8. A method according to claim 1, wherein the first electric
potential value is different from the second electric potential
value and an average of the first electric potential value and the
second electric potential value is approximately equal to another
electric potential value of at least one of the first predetermined
group of electric potential values and the second predetermined
group of electric potential values.
9. A method according to claim 1, wherein the first electric
potential value is different from the second electric potential
value, and a sum of the first electric potential value and the
second electric potential value is approximately equal to a sum of
another electric potential value, of the first predetermined group
of electric potential values and another electric potential value
of the second predetermined group of electric potential values.
10. A method according to claim 3, wherein the first electric
potential value is different from the second electric potential
value, and an average of the first electric potential value and the
second electric potential value is approximately equal to a common
electric potential value.
11. A method according to claim 1, wherein each of the first set of
the electrodes and the second set of the electrodes of the pixel
region are formed on a common surface of the member.
12. (canceled)
13. An imaging apparatus comprising: an illumination source adapted
for emitting radiation; a TIR modulator comprising: a member
comprising an electro-optic material; and a plurality of
individually addressable pixel regions wherein each pixel region
comprises a first set of electrodes arranged in an interdigitated
relationship with a second set of electrodes; a first voltage
source adapted to apply voltage to the first set of electrodes of a
pixel region; a second voltage source adapted to apply voltage to
the second set of the electrodes of the pixel region; a first
optical element positioned along a path of the emitted radiation,
extending from the illumination source towards the total internal
reflection (TIR) modulator; a second optical element adapted to
form one or more image pixels on a surface, the one or more image
pixels corresponding to one or more of the pixel regions; and a
controller programmed to: cause a first voltage to be applied to
the first set of the electrodes of the pixel region and cause a
second voltage to be applied to the second set of electrodes of the
pixel region, in accordance with a first image data signal; and
cause the first voltage applied to the first set of electrodes of
the pixel region to be adjusted by a first amount to create an
adjusted first voltage and cause the second voltage applied to the
second set of electrodes of the pixel region to be adjusted by a
second amount to create an adjusted second voltage, in accordance
with a second image data signal; and wherein the sum of the first
voltage and the second voltage is approximately equal to a sum of
the adjusted first voltage and the adjusted second voltage.
14. The imaging apparatus according to claim 13, wherein the
controller is programmed to cause an electric potential difference
to be created between the first voltage and the second voltage that
is different than an electric potential difference that is created
between the adjusted first voltage and the adjusted second
voltage.
15. The imaging apparatus according to claim 14, wherein the
potential difference between the first voltage and the second
voltage is null.
16. The imaging apparatus according to claim 13, wherein each of
the first voltage and the second voltage are approximately equal
voltages.
17. The imaging apparatus according to claim 13, wherein the first
voltage and the second voltage combine to induce an electric field
in the electro-optic material that is different from an electric
field that is induced in the electro-optic material by a
combination of the adjusted first voltage and the adjusted second
voltage.
18. The imaging apparatus according to claim 13, wherein the first
voltage and the second voltage combine to impart a birefringent
state in the electro-optic material that is different than a
birefringent state imparted in the electro-optic material by a
combination of the adjusted first voltage and the adjusted second
voltage.
19. The imaging apparatus according to claim 13, wherein the
controller is programmed to cause both the first voltage applied to
the first set of electrodes of the pixel region and the second
voltage applied to the second set of electrodes of the pixel region
to be adjusted by approximately the same amount in accordance with
the second image data signal.
20. The imaging apparatus according to claim 13, wherein the
controller is programmed to cause the first amount to be within 10
Volts or less of the second amount.
21. (canceled)
22. The imaging apparatus according to claim 13, wherein the first
set of electrodes and the second set of electrodes of the pixel
region are arranged on a common surface of the member.
23. The imaging apparatus according to claim 13, wherein each pixel
region of the plurality of individually addressable pixel regions
is electrically coupled to a corresponding group of voltage sources
and each of the groups of voltage sources is independently
controllable from one another.
24. The imaging apparatus according to claim 13 wherein the
controller is programmed to: determine an operating electric
potential difference; determine a difference between the sum of the
adjusted first voltage and the adjusted second voltage and the sum
of the first voltage and the second voltage; and operate the first
voltage source and the second voltage source to cause a ratio
between the difference and the operating potential difference to be
50% or less.
25. The imaging apparatus according to claim 13, wherein the
controller is programmed to: determine an operating electric
potential difference; determine a difference between the sum of the
adjusted first voltage and the adjusted second voltage and the sum
of the first voltage and the second voltage; and operate the first
voltage source and the second voltage source to cause a ratio
between the difference and the operating potential difference to be
30% or less.
26. The imaging apparatus according to claim 13, wherein the
controller is programmed to: determine an operating electric
potential difference; determine a difference between the sum of the
adjusted first voltage and the adjusted second voltage and the sum
of the first voltage and the second voltage; and operate the first
voltage source and the second voltage source to cause a ratio
between the difference and the operating potential difference to be
20% or less.
27. An imaging apparatus comprising: a radiation source adapted for
emitting radiation; a light modulator comprising: a member
comprising an electro-optic material; and a plurality of
individually controllable pixel regions including a pixel region
comprising a plurality of electrodes arranged in a first set and in
a second set, wherein the electrodes of the first set of the
electrodes are arranged in an interdigitated relationship with the
electrodes of the second set of the electrodes; a first optical
element positioned along a path of the emitted radiation extending
from the illumination source towards the TIR modulator; a second
optical element adapted to form one or more image pixels on a
surface, the one or more image pixels corresponding to one or more
of the pixel regions; and a controller programmed to: create an
electric potential difference between the first set of the
electrodes and the second set of the electrodes to impart a first
birefringent state onto a portion of the electro-optic material;
and vary the electric potential difference between the first set of
the electrodes and the second set of electrodes by varying a
voltage applied to the first set of the electrodes by a first
amount and by varying a voltage applied to the second set of the
electrodes by a second amount to impart a second birefringent state
onto the portion of the electro-optic material, wherein the second
amount is approximately equal to the first amount.
28. The imaging apparatus according to claim 27, wherein the
controller is programmed to control a first voltage source to
increase the voltage applied to the first set of the electrodes by
the first amount while controlling a second voltage source to
decrease the voltage applied to the second set of the electrodes by
the second amount to impart the second birefringent state onto the
portion of the electro-optic material, wherein the second amount is
equal to the first amount to within 10 Volts or less.
29. The imaging apparatus according to claim 27, wherein the
controller is programmed to control a first voltage source to
impose electric potential on the first set of the electrodes and
control a second voltage source to impose electric potential on the
second set of the electrodes, wherein a first sum of the electric
potentials imposed on the first set of the electrodes and on the
second set of the electrodes while imparting the first birefringent
state onto the portion of the electro-optic material approximately
equals a second sum of the electric potentials imposed on the first
set of the electrodes and on the second set of the electrodes while
imparting the second birefringent state onto the portion of the
electro-optic material.
30. The imaging apparatus according to claim 29, wherein the
controller is programmed to: determine an operating electric
potential difference; determine a difference between the second sum
of the electric potentials and the first sum of the electric
potentials; and operate the first voltage source and the second
voltage source to cause a ratio between the difference and the
operating potential difference to be 50% or less.
31. (canceled)
32. An imaging method comprising: emitting radiation from an
illumination source towards a TIR modulator, the TIR modulator
comprising: an electro-optic material; and a plurality of
individually addressable pixel regions including a pixel region
comprising a plurality of electrodes arranged in a first set and in
a second set, and wherein the electrodes of the first set of the
electrodes are arranged in an interdigitated relationship with the
electrodes of the second set of the electrodes; controlling at
least one of the pixel regions to form at least one image pixel on
a surface; maintaining electric potential information specifying a
first combination of electric potentials to impose on the first set
of the electrodes and the second set of the electrodes in the event
that a first activation state is desired and specifying a second
combination of electric potentials to impose on the first set of
the electrodes and the second set of the electrodes in the event
that a second activation state different from the first activation
state is desired, wherein the first combination of electric
potentials comprises a plurality of electric potentials that are
not common with any of the electric potentials of the second
combination of electric potentials; determining a desired
activation state; and imposing electric potential on each of the
first set of the electrodes and the second set of the electrodes
according to the electric potential information corresponding to
the determined desired activation state.
33. A method according to claim 31, comprising separately operating
a first voltage source coupled to the first set of the electrodes
and a second voltage source coupled to the second set of the
electrodes to impose the electric potential on each of the first
set of the electrodes and the second set of the electrodes
according to the electric potential information corresponding to
the determined desired activation state.
Description
FIELD OF THE INVENTION
[0001] The invention relates to an apparatus for forming images on
a surface, and more particularly to improvements to an
electro-optic light modulator.
BACKGROUND OF THE INVENTION
[0002] Electro-optic materials are those whose optical properties
change in accordance with the strength of an electric field
established within them. These materials make possible an
electrically controlled electro-optic modulator for use in a light
valve array.
[0003] One well known form of electro-optic modulator arrays are
total internal reflection (TIR) modulators which can be employed in
laser-based imaging systems for example. FIGS. 1A and 1B
schematically show plan and side views of a conventional TIR
modulator 10 comprising a member 12 which includes an electro-optic
material and a plurality of electrodes 15 and 16 arranged in an
interdigitated relationship on a surface 18 of member 12. Surfaces
20 and 22 are arranged to cause input radiation 25 to refract and
undergo total internal reflection at surface 18.
[0004] In this typical conventional configuration, various
electrodes 15 and 16 are grouped into electrode groups S.sub.1,
S.sub.2, S.sub.3, S.sub.4 . . . S. which are collectively referred
to as electrode groups S. Each of the electrodes 15 in each of the
groups are coupled together and driven with corresponding one of
individually addressable voltages sources V.sub.1, V.sub.2,
V.sub.3, V.sub.4 . . . V.sub.n which are operated in accordance
with various image data signals. To simplify interconnect and
driver requirements, all electrodes 16 are interconnected to a
common source (e.g. a ground potential). In this case, electrodes
16 are coupled in a serpentine fashion among all the groups S.
[0005] Upon the application of a suitable voltage by one of the
voltage sources V.sub.1, V.sub.2, V.sub.3, V.sub.4 . . . V.sub.n to
a corresponding one of the electrode groups S.sub.1, S.sub.2,
S.sub.3, S.sub.4 . . . S, an electric field is established in a
portion of the of the electro-optic material referred to as a pixel
region. The application of the voltage alters the refractive index
of the electro-optic material, thereby changing a birefringent
state of the pixel region. Under the application of the
corresponding drive voltage, the arrangement of electrodes 15 and
16 in each of the electrode groups S.sub.1, S.sub.2, S.sub.3,
S.sub.4 . . . S causes each of the electrode groups to behave in a
manner similar to a diffraction grating. A birefringent state of
the each of the pixel regions can therefore be changed in
accordance with the selective application of various voltages by
corresponding voltage sources V.sub.1, V.sub.2, V.sub.3, V.sub.4 .
. . V.sub.n. For example, in this case when no voltage is applied
to a particular electrode group S, the corresponding pixel region
assumes a first birefringent state in which output radiation 27 is
emitted from surface 22 and is directed by one or more lenses (not
shown) towards a surface of a recording media (also not shown) to
form an image pixel thereon. In the case when a suitable voltage is
applied to a particular electrode group S, the corresponding pixel
region assumes a second birefringent state in which output
radiation 27 is emitted from surface 22 in a diffracted form which
can be blocked by an obstruction such as an aperture to not form an
image pixel.
[0006] Various image features are formed on a recording media by
combining image pixels into arrangements representative of the
image features. It is a common desire to form high quality images
with reduced levels of artifacts. In particular, the visual quality
of the formed image features is typically dependant on the visual
characteristics of the formed image pixels themselves. For example,
one important characteristic is the contrast between an image
feature and surrounding regions of the recording media. Poor
contrast can lead to the formation of various image features whose
edges lack sharpness or are otherwise poorly defined. Another
important characteristic is the accurate placement of the image
pixels on the recording media.
[0007] The conventional method of driving the arrangement of
electrodes 15 and 16 as previously described can lead to various
problems which can adversely impact a desired visual characteristic
of the final image. For example, the sharpness of feature edges can
suffer or an undesired deflection of output radiation 27 can arise.
FIG. 1C schematically shows a subset of electrode groups S.sub.1,
S.sub.2, S.sub.3, and S.sub.4 driven with various voltage levels by
their corresponding voltage sources as follows: (V.sub.1:V);
(V.sub.2:V); (V.sub.3:0); and (V.sub.4:V). Voltage level V
corresponds to a drive voltage level selected to cause substantial
diffraction to be created by a pixel region whereas voltage level 0
corresponds to a voltage level (i.e. a ground potential in this
case) selected to not cause substantial diffraction to be created
by a pixel region. When a pixel region is made non-diffracting
(e.g. the pixel region corresponding to electrode group S.sub.3)
the average electric potential of the electrodes 15 and 16 of the
pixel region is null. However, when a pixel region is made
diffracting (e.g. the pixel regions corresponding to electrode
groups S.sub.1, S.sub.2 and S.sub.4) the average electric potential
of the electrodes 15 and 16 of the pixel region is approximately
V/2. This creates an electric potential difference of V/2 between
the average voltages of non-diffracting and diffracting regions of
TIR modulator 10. This can give rise to long-range electric fields
that deflect radiation that is propagated within the electro-optic
material to produce a beam steering effect. Although the long-range
fields can be relatively weak, they typically interact with the
radiation over a longer path length than the shorter range
diffraction grating fields.
[0008] One possible consequence of this deflection is that image
pixels formed on the recording media can be shifted and a placement
error arises. The degree of the placement error can vary in
accordance with the image data which controls the selective
application of the drive voltages. Another possible consequence can
include an increase in the diffraction broadening of an image pixel
since the output radiation 27 is deflected to one side in the pupil
of the imaging system, thereby reducing the effective aperture of
the system. Other possible consequences can include an increased
sensitivity to aberrations in the imaging system.
[0009] There is, therefore, a need for improved TIR modulators that
can mitigate beam steering effects. There is also a need for
improved TIR modulators that can reduce occurrences of improperly
formed image pixels.
SUMMARY OF THE INVENTION
[0010] Briefly, according to one aspect of the present invention
radiation from an illumination source is directed to a total
internal reflector (TIR) modulator. The modulator includes a an
electro-optic member with a plurality of individually addressable
pixel regions comprised of a plurality of electrodes arranged in a
first and second set. At least one electrode of the first set is
adjacent to at least one electrode of the second set and at least
one of the pixel regions is controlled to form at least one image
pixel on a surface. A first electric potential is imposed on the
first set of electrodes selected from a first predetermined group
of electric potential values. A second electric potential is
imposed on the second set of electrodes selected from a second
predetermined group of electric potential values. The first and
second predetermined groups of electric potential values together
comprise at least three different electric potential values.
[0011] The invention and its objects and advantages will become
more apparent in the detailed description of the preferred
embodiment presented below.
BRIEF DESCRIPTION OF THE DRAWINGS
[0012] Embodiments and applications of the invention are
illustrated by the attached non-limiting drawings. The attached
drawings are for purposes of illustrating the concepts of the
invention and may not be to scale.
[0013] FIG. 1A is a prior art schematic plan view of a conventional
TIR modulator;
[0014] FIG. 1B is a prior art schematic side view of the
conventional TIR modulator of FIG. 1A;
[0015] FIG. 1C is a prior art schematic showing a subset of
electrode groups of the conventional TIR modulator of FIG. 1A
driven by various voltage levels;
[0016] FIG. 2 schematically shows an imaging apparatus as per an
example embodiment of the invention;
[0017] FIG. 3A is a schematic plan view of a light modulator as per
an example embodiment of the invention;
[0018] FIG. 3B is a schematic side view of the light modulator of
FIG. 3A;
[0019] FIG. 4 schematically shows a subset of electrode groups of
the modulator of FIG. 3A driven by various voltage levels;
[0020] FIG. 5 is graph comparing simulated exposure profiles at the
boundary of diffracting and non-diffracting regions created in a
balanced light modulator of the present invention and in an
unbalanced conventional TIR light modulator;
[0021] FIG. 6A is a graph simulating two period pixel exposure
profiles associated with the formation of an image pixel as
compared between a balanced light modulator of the present
invention and an unbalanced conventional TIR light modulator;
[0022] FIG. 6B is a graph simulating one period pixel exposure
profiles associated with the formation of an image pixel as
compared between a balanced light modulator of the present
invention and an unbalanced conventional TIR light modulator;
and
[0023] FIG. 7 shows a graph which simulates how radiation emitted
by an illumination source is utilized by a balanced light modulator
of the present invention and by an unbalanced conventional TIR
light modulator.
DETAILED DESCRIPTION OF THE INVENTION
[0024] The present invention will be directed in particular to
elements forming part of, or in cooperation more directly with the
apparatus in accordance with the present invention. It is to be
understood that elements not specifically shown or described may
take various forms well known to those skilled in the art.
[0025] FIG. 2 schematically shows an imaging apparatus 100 employed
by an example embodiment of the invention. Imaging apparatus 100
includes an illumination source 102 which can include a laser for
example. Suitable lasers can include laser diode arrays which are
relatively easy to modulate, have relatively low cost and have
relatively small size. The choice of illumination source 102 can be
motivated by the properties of recording media 130 that is to be
imaged by imaging apparatus 100. One or more optical elements 110
are positioned along the path of radiation 125 emitted by
illumination source 102 towards light modulator 200. Optical
elements 110 can include one or more lenses employed to condition
radiation 125 in various ways. For example, when diode laser arrays
are employed, various degrees of beam divergence can exist along a
plurality of directions. Beam divergence can include fast axis
divergence and slow axis divergence for example. Optical elements
110 can include various lenses adapted to correct these divergences
such as micro-lenses or crossed cylindrical lenses. Optical
elements 110 can include various elements adapted to mix or reflect
various radiation beams such as light pipes and fly's eye
integrators for example. Optical elements 110 can include various
lenses adapted to focus or redirect radiation 125 emitted by
illumination source 102.
[0026] Radiation 125 that is directed onto light modulator 200 is
modulated in accordance with controller 160 which selectively
controls various pixel regions 210 of light modulator 200 to form
various radiation beams. Image data 120 is employed by controller
160 to generate various radiation beams which are directed along a
path towards an imageable surface of a recording media 130 to form
various image pixels 140 thereon as required by image data 120.
Other radiations beams not required by the formation of various
image pixels 140 are directed elsewhere. In this illustrated
embodiment, the radiation beams required to form image pixels 140
pass through an aperture 150 while radiation beams not required to
form image pixels 140 are obstructed by aperture 150. One or more
lenses (not shown) may be employed to direct radiation beams from
light modulator 200 towards aperture 150. One or more optical
elements 170 are employed to direct various radiation beams onto
the imageable surface of recording media 130. Various other
embodiments of the invention need not employ aperture 150, and
radiation beams not required by the formation of various image
pixels 140 may fall by design outside the entrance pupil of a lens
of optical elements 170.
[0027] Radiation beams can be used to form image pixels 140 on
recording media 130 by different methods. For example, radiation
beams can be used to ablate a surface of recording media 130.
Radiation beams can be used to cause transference of an
image-forming material from a donor element to a surface of
recording media 130 (e.g. a thermal transfer process). Recording
media 130 can include an image modifiable surface, wherein a
property or characteristic of the modifiable surface is changed
when irradiated by a radiation beam.
[0028] Interactions between the radiation beams and the recording
media 130 can vary during the formation of corresponding image
pixels 140. For example, various arrangements of image pixels 140
can be formed from plurality of imagings referred to as "shots."
During each shot, imaging apparatus 100 is positioned relative to a
region of recording media 130. Once positioned, light modulator 200
is activated to form a first group of image pixels 140 on the
region of recording media 130. Once these image pixels 140 are
formed, relative movement between light modulator 200 and recording
media 130 is effected to position apparatus 100 in the vicinity of
an adjacent region and another shot is taken to form a next group
of image pixels 140 on the adjacent region. Various image pixels
140 can also be formed by scanning. Scanning can include
establishing relative movement between light modulator 200 and
recording media 130 as the light modulator 200 is activated to form
the desired image pixels 140. Relative movement can include moving
one or both of light modulator 200 and recording media 130. In some
example embodiments of the invention, scanning can be performed by
deflecting radiation beams emitted by light modulator 200 relative
to recording media 130 to form the image pixels 140.
[0029] FIGS. 3A and 3B schematically show corresponding plan and
side views of one exemplary embodiment of light modulator 200. In
this example embodiment of the invention, light modulator 200 is a
TIR light modulator. Light modulator 200 includes a member 212
comprising an electro-optic material 213. Electro-optic material
213 can include lithium niobate (LiNbO.sub.3) or lithium tantalate
(LiTaO.sub.3) for example. Electro-optic material 213 can include a
suitably chosen material which exhibits birefringent
characteristics in response to the application of a suitable
electric field. A plurality of electrodes 215 and 216 are arranged
on a surface 218 of member 212. Member 212 includes surfaces 220
and 222 which are arranged to cause radiation 125 to refract and
undergo total internal reflection at surface 218. Other example
embodiments of the invention can employ other orientations between
various ones of surfaces 218, 220, and 222 and radiation 125 to
cause the total internal reflection.
[0030] As shown in FIG. 3A, each of the electrodes 215 and 216 are
elongate in form and extend along directions that are substantially
parallel to an overall direction of travel 126 of radiation 125.
Electrodes 215 and 216 are electrically conductive elements that
can be formed on a common contiguous surface by various techniques
known in the art. In some example embodiments, electrodes 215 and
216 are formed by sputtering metal (e.g. gold) on surface 218.
Other metal deposition methods can include evaporation. Coated
surface 218 is then coated with a suitable photo-resist which is
patterned by exposure to light (e.g. ultraviolet light) through a
suitable mask. A development of the photo-resist removes the
photo-resist locally according to the pattern, and the electrodes
215 and 216 are formed by chemically etching away metal that is not
protected by the photo-resist. Other embodiments of the invention,
may employ a lift-off technique in which a photo-resist is first
applied to surface 218 and is patterned. Metal is then sputtered
onto both surface 218 and the patterned photo-resist. The
photo-resist is then dissolved so that the metal deposited on the
photo-resist is removed while leaving other metal attached to
surface 218 in areas where the photo-resist was absent during
sputtering. In this illustrated embodiment of the invention,
electrodes 215 and 216 are jointly formed on a single uniform
surface.
[0031] In this illustrated embodiment, various electrodes 215 are
coupled to one another to form a plurality of first electrode sets
X.sub.1, X.sub.2, X.sub.3, X.sub.4 . . . X.sub.n (collectively
referred to as first electrode sets X) while various electrodes 216
are coupled to one another to form a plurality of second electrode
sets Y.sub.1, Y.sub.2, Y.sub.3, Y.sub.4 . . . Y.sub.n (collectively
referred to as second electrode sets Y). Each of the first and
second electrode sets X and Y include four (4) respective
electrodes 215 and 216. Other example embodiments of the invention
can include first and second electrode sets X and Y made up of
other suitable numbers of electrodes. The electrodes 215 within a
given first electrode set X are electrically driven by a
corresponding one of individually controllable first voltage
sources: V.sub.X1, V.sub.X2, V.sub.X3, V.sub.X4 . . . V.sub.Xn
(collectively referred to as first voltage sources V.sub.X). Each
of the electrodes 216 within a given second electrode set Y are
electrically driven by a corresponding one of individually
controllable second voltage sources: V.sub.Y1, V.sub.Y2, V.sub.Y3,
V.sub.Y4 . . . V.sub.Yn (collectively referred to as second voltage
sources V.sub.Y).
[0032] First and second electrode sets X and Y are arranged such
that an electrode 215 is adjacent to an electrode 216. In this
example embodiment of the invention, each of the first electrodes
sets X are arranged with another of the electrode sets Y such that
their respective electrodes are interdigitated with respect to one
another. In this example embodiment of the invention, each of the
interdigitated electrode sets X and Y belongs to an electrode group
T (i.e. one of electrode groups T.sub.1, T.sub.2, T.sub.3, T.sub.4
. . . T.sub.n). Each of the various pixels regions 210 of light
modulator 200 include a portion of electro-optic material 213 and
one of the electrode groups T. Accordingly, in this example
embodiment of the invention, each of the pixel regions 210 includes
an electrode group T which includes first and second electrode sets
X and Y that are separately drivable with respect to one another.
That is, an electric field can be established with the
electro-optic material 213 corresponding to a given pixel region
210 by appropriately driving one or both of the voltage sources
V.sub.X and V.sub.Y corresponding to the given pixel region 210. In
this illustrated embodiment, both voltage sources V.sub.X and
V.sub.Y corresponding to given pixel region 210 are driven to
impart various birefringent states on the portion of the
electro-optic material associated with the given pixel region 210.
Each of the pixel regions 210 is individually addressable by
controlling a corresponding group of voltage sources V.sub.X and
V.sub.Y. In this regard, various groups of voltage sources V.sub.X
and V.sub.Y can be operated independently of other groups of
voltage sources V.sub.X and V.sub.Y.
[0033] Each of the groups of voltage sources V.sub.X and V.sub.Y is
selectively operated by controller 160 (not shown in FIG. 3A) to
activate a corresponding pixel region 210 between various states.
Controller 160, which can include one or more controllers is used
to control one or more systems of imaging apparatus 100 including,
but not limited to, the light modulator 200. In this example
embodiment, controller 160 is programmed to address light modulator
200 in accordance with image data 120 which includes information
representing an image to be formed. Various systems can be
controlled using various control signals and by implementing
various methods. Controller 160 can be configured to execute
suitable software and can include one or more data processors,
together with suitable hardware, including by way of non-limiting
example: accessible memory, logic circuitry, drivers, amplifiers,
A/D and D/A converters, input/output ports and the like. Controller
160 can comprise, without limitation, a microprocessor, a
computer-on-a-chip, the CPU of a computer or any other suitable
microcontroller.
[0034] FIG. 4 schematically shows a subset of the electrode groups
T (i.e. electrode groups T.sub.1, T.sub.2, T.sub.3, and T.sub.4) of
light modulator 200 driven by their corresponding voltage sources
V.sub.X and V.sub.Y to establish various electric potentials on
each of the first electrode sets X and on each of the second
electrode sets Y associated with each of the electrode groups T. In
particular, first voltage sources V.sub.X1, V.sub.X2, and V.sub.X4
are driven to apply a voltage V.sub.A to each of their
corresponding first electrode sets X.sub.1, X.sub.2, and X.sub.4 to
impose an electric potential P.sub.A thereon. Second voltage
sources V.sub.Y1, V.sub.Y2, and V.sub.Y4 are driven to apply a
voltage V.sub.B to each of their corresponding second electrode
sets Y.sub.1, Y.sub.2, and Y.sub.4 to impose an electric potential
P.sub.B thereon. First and second voltage drives V.sub.X3 and
V.sub.Y3 are driven to apply a voltage V.sub.C to each of their
corresponding first and second electrode sets X.sub.3 and Y.sub.3
to impose an electric potential P.sub.C thereon. It is understood
that only the subset of electrode groups T.sub.1, T.sub.2, T.sub.3,
and T.sub.4 is depicted for clarity and other electrode groups T of
light modulator 200 can be activated in a similar fashion.
[0035] In various example embodiments of the invention, electric
potentials P.sub.A, P.sub.B, and P.sub.C are selectively imposed on
the first and second electrode sets X and Y of each of the
electrode groups T in accordance with a desired activation state of
a pixel region 210 associated with each of the electrode groups T.
Activation states can include for example: an ON state in which a
pixel region 210 is activated to form an image pixel 140 on
recording media 130 and an OFF state in which a pixel region 210 is
activated not to form a corresponding image pixel 140 on recording
media 130. In various example embodiments of the invention, various
ones of electric potentials P.sub.A, P.sub.B, and P.sub.C are
selectively applied to the first and second electrode sets X and Y
of each of the electrode groups T to impart a desired birefringent
state on a portion of the electro-optic material 213 associated
with each of the electrode groups T. In this example embodiment,
electric potentials P.sub.A, P.sub.B, and P.sub.C are each
different from one another.
[0036] In this example embodiment of the invention, it desired that
each pixel region 210 corresponding to electrode groups T.sub.1,
T.sub.2, and T.sub.4 be activated in accordance with an OFF state
while the pixel region 210 corresponding to electrode group T.sub.3
be activated in accordance with an ON state. In this example
embodiment, the electric potentials applied to each of the first
electrode sets X are selected from a first group comprising a
plurality of predetermined electric potential values including
values corresponding to each of electric potentials P.sub.A and
P.sub.C. The electric potentials applied to each of the second
electrode sets Y are selected from a second group comprising a
plurality of predetermined electric potential values including
values corresponding to each of electric potentials P.sub.B and
P.sub.C. In this example embodiment, electric potentials values
corresponding to each of electric potentials P.sub.A and P.sub.B
are different from one another. In this example embodiment, the
electric potential values corresponding to each of the electric
potentials P.sub.C are different from the electric potential values
corresponding to each of the electric potentials P.sub.A and
P.sub.B. In this example embodiment, the first group of electric
potential values includes at least one electric potential value
that is not common with any of the electric potential values of the
second group of electric potential values. In this example
embodiment, the second group of electric potential values includes
at least one electric potential value that is not common with any
of the electric potential values of the first group of electric
potential values. In this example embodiment, the first group of
electric potential values and the second group of electric
potential values together comprise three different electric
potential values. The electric potential values can be the same or
different from the electric potentials that are imposed as a result
of their selection. In some cases, various losses can cause
differences.
[0037] In various example embodiments, electric potential
information is maintained. The electric potential information can
specify a first combination of electric potentials to impose on
associated first and second set of the electrodes X and Y in the
event that a first activation state is desired. The electric
potential information can specify a second combination of electric
potentials to impose on the first and second sets of the electrodes
X and Y in the event that a second activation state different from
the first activation state is desired. In some of these
embodiments, the first combination of electric potentials comprises
a plurality of electric potentials that are not common with any of
the electric potentials of the second combination of electric
potentials. A desired activation state is determined and electric
potential imposed on each of the first and second sets of the
electrodes X and Y according to the electric potential information
corresponding to the determined desired activation state.
[0038] The selection of an electric potential value from each of
the predetermined first and second groups of electric potential
values can be based at least on image data 120. In an illustrated
embodiment, controller 160 (not shown in FIG. 4) has selected a
combination of electric potential values corresponding to common
electric potentials P.sub.C according to a first image data signal
(i.e. an ON image data signal) and a combination of different
electric potential values corresponding to electric potentials
P.sub.A and P.sub.B according to a different second image data
signal (i.e. an OFF image data signal).
[0039] In this example embodiment, an electric potential difference
between the combination of electric potentials P.sub.C applied to
electrode group S.sub.3 is substantially null and a first
birefringent state corresponding to this electric potential
difference is imposed on the associated pixel region 210. This
first birefringent state can be selected to not cause substantial
diffraction in the radiation emitted from the associated pixel
region 210. In this example embodiment, an electric potential
difference between the combination of electric potentials P.sub.A
and P.sub.B applied to each of the electrode groups T.sub.1,
T.sub.2, and T.sub.4 is sufficient to impose a second birefringent
state on each of their associated pixel regions 210. This second
birefringent state can be selected to cause substantial diffraction
in the radiation emitted from each of the associated pixel regions
210.
[0040] In various example embodiments of the invention, each of the
electric potentials P.sub.A, P.sub.B, and P.sub.C is selected such
that an average of the electric potentials applied to an electrode
group T to impart a first birefringent state onto its associated
pixel region 210 is approximately equal to an average of the
electric potentials applied to an electrode group T to impart a
second birefringent state onto its associated pixel region 210. In
this example embodiment, the values of P.sub.A, P.sub.B, and
P.sub.C are selected such that the sum of electric potentials
P.sub.C and P.sub.C is approximately equal to the sum of electric
potentials P.sub.A and P.sub.B. For example, in this illustrated
embodiment, first and second voltage sources V.sub.X3 and V.sub.Y3
are driven to apply a voltage V.sub.C impose an electric potential
P.sub.C of approximately 0 Volts (i.e. a ground potential) on each
of their corresponding first and second electrode sets X.sub.3 and
Y.sub.3. Each of first voltage drives V.sub.X1, V.sub.X2, and
V.sub.X4 are driven to apply a voltage V.sub.A to each of their
corresponding first electrode sets X.sub.1, X.sub.2, and X.sub.4 to
impose an electric potential P.sub.A of +V/2 Volts thereon. Each of
second voltage drives V.sub.Y1, V.sub.Y2, and V.sub.X4 are driven
to apply a voltage V.sub.B to each of their corresponding second
electrode sets Y.sub.1, Y.sub.2, and Y.sub.4 to impose an electric
potential P.sub.B of -V/2 Volts thereon. In this example embodiment
of the invention, voltages V.sub.A and V.sub.B impose corresponding
electric potentials P.sub.A and P.sub.B that are different from one
another. Specifically, electric potentials P.sub.A and P.sub.B are
each substantially equal in magnitude, but comprise different
polarities.
[0041] Accordingly, an electric potential difference sufficient to
establish the first desired birefringent state (i.e. 0 Volts in
this example) exists in electrode group T.sub.3 while an electric
potential difference sufficient to establish the second
birefringent state (i.e. V Volts in this example) exists in each of
electrode groups T.sub.1, T.sub.2, and T.sub.4. In this example
embodiment, light modulator 200 is driven such that the sums of the
electric potentials combinations used to create each of the
different birefringent states are approximately equal to one
another. That is, a first sum of electrical potentials P.sub.C and
P.sub.C (i.e. the sum of 0 Volts and 0 Volts) approximately equals
a second sum of electrical potentials P.sub.A and P.sub.B (i.e. the
sum of +V/2 Volts and -V/2 Volts). Unlike the aforementioned
conventional TIR modulator 10 in which a variance of V/2 Volts was
created in the average electrical potentials between
non-diffracting and diffracting regions of TIR modulator 10, such
variances are reduced in the light modulator 200 of the present
invention. Light modulator 200 is driven in a balanced manner as
opposed to the un-balanced manner that conventional light TIR
modulator 10 was driven.
[0042] Numerous advantageous can accompany light modulators
produced or operated as per various embodiments of the invention.
For example, the presence of the aforementioned long-range electric
fields can be reduced. Image pixel positional variances associated
with beam steering effects can be reduced. Improvements in the edge
sharpness of formed image pixels 140 can also be achieved. For
example, FIG. 5 is graph comparing simulated exposure profiles at
the boundary of a diffracting and non-diffracting region created in
a balanced light modulator 200 of the present invention and in an
unbalanced conventional TIR light modulator. Each of the diffracted
and non-diffracted regions is shown to be approximately three
periods wide, wherein one period corresponds to a pair of the
electrodes (i.e. one first electrode X and one second electrode Y).
The boundary transition for the balanced light modulator 200 of the
present invention is steeper (i.e. sharper) than that of the
unbalanced conventional TIR light modulator. A steeper boundary
transition can lead to better defined image feature edges.
[0043] Other advantages can include improvements in the exposure
profiles associated with the formation of a given image pixel 140.
For example, FIGS. 6A and 6B are graphs simulating the exposure
profiles associated with the formation of an image pixel as
compared between a balanced light modulator 200 of the present
invention and an unbalanced conventional TIR light modulator. FIG.
6A compares exposure profiles formed by pixel regions 210
comprising two pairs of first and second electrodes X and Y (i.e. a
two period pixel exposure profile). The exposure profile associated
with the balanced light modulator 200 of the present invention is
shown to be "fuller" than that of the unbalanced conventional TIR
light modulator. A fuller profile can lead to less variation in the
image pixels 140 as a consequence of variations in the
exposure.
[0044] FIG. 6B compares exposure profiles formed by pixel regions
210 comprising a single pair of first and second electrodes X and Y
(i.e. a one period pixel exposure profile). In this case, the
exposure profile associated with the un-balanced conventional TIR
light modulator is significantly deficient in its overall exposure
and is likely not suitable for forming a corresponding image pixel
140. In contrast, the balanced light modulator 200 of the present
invention provides significantly greater exposure. Various light
modulators 200 provided by the present invention might therefore be
used to form image pixels 140 with higher resolutions, and in this
case, resolutions as small as those associated with a single pair
of first and second electrodes X and Y.
[0045] It is to be noted the various profiles of the TIR light
modulator 200 in FIGS. 6A and 6B exceed unity. The intensity of
imaging radiation associated with the various exposure profiles
plotted in FIGS. 6A and 6B is relative to the intensity of an
un-diffracted radiation beam emitted by an associated pixel region.
When image data 120 is imposed by a TIR light modulator, imaging
radiation appears at angles intermediate between zero and first
diffraction orders. Subsequent diffraction of the imaging radiation
by an order blocker (e.g. aperture 150) causes the final exposure
profile to have an oscillatory form. This effect is responsible for
the overshoot of the final intensity at the transition between
diffracting and non-diffracting regions of the TIR light modulator.
In some cases, this effect can cause the peak intensity to exceed
unity.
[0046] One possible reason for the improvements provided by various
embodiments of the invention is that a balanced light modulator 200
makes better use of the pupil of a lens used to image radiation
emitted by the light modulator 200 (e.g. a lens associated with
optical element 170). Light modulators 200 of the present invention
can also make better use of the illumination. FIG. 7 shows a graph
which simulates how radiation emitted by illumination source 102 is
utilized by a balanced light modulator 200 of the present invention
and by an unbalanced conventional TIR light modulator. In this case
each of the modulators is modeled with a two period pixel
configuration. Typically, the utilization of the radiation varies
with the angle at which the radiation passes through the system. In
FIG. 7, the angle is expressed as a fraction of the diffraction
angle and the illumination is shown extending from -0.25 to +0.25.
In the case of the unbalanced conventional TIR modulator, the
illumination contribution varies quite strongly as a function of
the angle. This can lead to various problems such as those
previously mentioned in regards to exposure profile shape and
overall exposure levels. These problems can be especially sensitive
to the details of the illumination angular distribution. In the
case of the balanced light modulator 200 of the present invention,
FIG. 7 shows that the illumination contribution does not vary
significantly as a function of the angle, a result which can lead
to enhanced imaging characteristics.
[0047] In other example embodiments of the invention, light
modulator 200 can be driven using different techniques. For
example, a common electric potential P.sub.C imposed on each of the
first and second electrode sets X and Y of a particular electrode
group T need not be selected to be a null or a ground potential. A
first voltage source V.sub.X and its corresponding second voltage
source V.sub.Y can be driven to apply voltages V.sub.C to impose
non-zero electric potentials of V.sub.O Volts on each of the
corresponding first and second electrode sets X and Y in accordance
with a first desired birefringent state. When a change from the
first birefringent state to a second birefringent state is desired
(i.e. for example when change in a image data signal is
encountered), the first voltage source V.sub.X can be driven to
adjust voltage V.sub.C applied to the first electrode set X by a
first amount (e.g. V/2 Volts) to create an adjusted voltage equal
to V.sub.C+V/2, and the second voltage source V.sub.Y can be driven
to adjust the voltage applied to the second electrode set Y by a
second amount (e.g. V/2 Volts) to create an adjusted voltage equal
to V.sub.C-V/2. The applied voltages are selected such that the sum
of the voltages applied to the first and second electrode sets X
and Y during the establishment of the first birefringent state
(i.e. the sum of V.sub.O and V.sub.O) approximately equals the sum
of the adjusted voltages applied to the first and second electrode
sets X and Y during the establishment of the second birefringent
state (i.e. the sum of V.sub.O+V/2 and V.sub.O-V/2). Each of the
initially applied voltages are selected to create an electric
potential difference suitable for the establishment of the first
birefringent state and each of the adjusted applied voltages are
selected to create an electric potential difference suitable for
the establishment of the second birefringent state. In this example
embodiment, each of the applied voltages is selected to cause each
of the electric potentials applied to each of the first and second
electrodes X and Y during the establishment of either birefringent
state to be uni-polar in nature. A uni-polar drive can be employed
to simplify drive requirements.
[0048] In some example embodiments of the invention, the sum of the
electric potentials applied to each of the first and second
associated electrodes sets X and Y is adjusted to be equal for each
birefringent state while approximating an electric potential
difference required by a particular state. For example, an electric
potential of 50 Volts can be imposed on a first electrode set X
while imposing an electric potential of 40 Volts on an associated
second electrode set Y to create a 10 volt electric potential
difference required by a first birefringent state. A second
birefringent state requiring at least an 80 Volt electric potential
difference can be achieved by changing the electric potential
imposed on the first set of electrodes X to 90V and by changing the
electric potential imposed on the second set of the electrodes Y to
0 Volts to create the necessary electric potential difference
required by the second birefringent state while maintaining equal
sums (i.e. in this example embodiment, a first sum of 50+40 Volts
is approximately equal to a second sum of 90+0 Volts). In this
example embodiment, all of the electric potentials are selected
from electric potential values that are different from each
other.
[0049] In some example embodiments of the invention, the equality
of the sums (or averages) of the electrode electric potentials
between first and second birefringent states is not exact, but
rather approximate. For example, a first birefringent state in
which an electric potential of 40 Volts is imposed on each of the
first and second electrode sets X and Y can be changed to second
birefringent state in which the electric potential imposed on the
first electrode set X is adjusted to 85 Volts (i.e. the electric
potential of 40V is increased by an amount equal to 45 Volts) while
the electric potential imposed on the second electrode set Y is
adjusted to 5 Volts (i.e. the electric potential of 40 Volts is
decreased by an amount equal to 35 Volts). In this example,
embodiment, the applied voltages are not varied by the same amount
but by amounts which are approximately equal to one another to
within 10 volts. Although the sums of the electrical potentials are
not exact but approximate (i.e. a difference of 5 Volts exists),
the difference is significantly less than the 35V difference that
would exist in conventional TIR modulator 10 operated under the
same conditions. In some example embodiments of the invention, the
lesser of the sums (or averages) of the electric potentials
associated with each of two different birefringent states is at
least 80% of the greater of the sums (or averages) of the electric
potentials associated with each of the two different birefringent
states. In other example embodiments of the invention, the lesser
of the sums (or averages) of the electric potentials associated
with each of two different birefringent states is at least 90% of
the greater of the sums (or averages) of the electric potentials
associated with each of the two different birefringent states. In
yet other example embodiments, the lesser of the sums (or averages)
of the electric potentials associated with each of two different
birefringent states is at least 95% of the greater of the sums (or
averages) of the electric potentials associated with each of the
two different birefringent states.
[0050] In some example embodiments of the invention, a plurality of
different birefringent states can be imposed in the electro-optic
material 213 of a given pixel region 210 such that various degrees
of diffraction are established for each of the states. In some
example embodiments, a first birefringent state can be associated
with an electric potential difference that is not null but some
value associated with a diffraction amount that is tolerable by the
required activation state. A first birefringent state can be used
to create a partial diffractive state that can be used to adjust
the output radiation emitted from an associated pixel region 210.
The partial diffraction state can be associated with an ON
activation state and can differ from a diffraction state associated
with an OFF activation state. For example, in various embodiments
of the invention an electric potential difference in the range of 0
to 20 Volts between associated first and second electrodes sets X
and Y can be associated with an ON activation state while an
electric potential difference of about 80 Volts can be associated
with an OFF activation state. A ratio of the electric potential
differences associated with two different birefringent states or
two different activation states can be 25% or less in some example
embodiments, 12% or less in other example embodiments, and 5% or
less in yet other example embodiments. In some example embodiments,
different ratios can be associated with different pixel regions
210.
[0051] The greater of the electric potential differences created
between the electrodes of an associated electrode sets X and Y
(e.g. the previously described 80 Volt difference associated with
an OFF activation state) is typically referred to as the operating
potential difference. A difference between the sums of the electric
potentials applied to each of the first and second associated
electrodes sets X and Y during different activation states can
arise and in some example embodiments a ratio of this difference to
the operating potential difference associated with the first and
second associated electrodes sets X and Y can be 50% or less. In
other example embodiments, this ratio can be 30% or less, and even
20% or less in yet other embodiments. Alternatively, when
considering a difference between the averages of the electric
potentials applied to each of the first and second associated
electrodes sets X and Y during different activation states, a ratio
of the average voltage differences to the operating potential value
can be 25% or less in some embodiments, 15% or less in other
embodiments and 10% or less in yet other embodiments.
[0052] The invention has been described in detail with particular
reference to certain preferred embodiments thereof, but it will be
understood that variations and modifications can be effected within
the scope of the invention.
PARTS LIST
[0053] 10 TIR modulator [0054] 12 member [0055] 15 electrodes
[0056] 16 electrodes [0057] 18 surface [0058] 20 surface [0059] 22
surface [0060] 25 input radiation [0061] 27 output radiation [0062]
100 imaging apparatus [0063] 102 illumination source [0064] 110
optical element(s) [0065] 120 image data [0066] 125 radiation
[0067] 126 direction of travel [0068] 130 recording media [0069]
140 image pixel [0070] 150 aperture [0071] 160 controller [0072]
170 optical element(s) [0073] 200 light modulator [0074] 210 pixel
region [0075] 212 member [0076] 213 electro-optic material [0077]
215 electrode [0078] 216 electrode [0079] 218 surface [0080] 220
surface [0081] 222 surface [0082] P.sub.A electric potential [0083]
P.sub.B electric potential [0084] P.sub.C electric potential [0085]
S.sub.1 electrode group [0086] S.sub.2 electrode group [0087]
S.sub.3 electrode group [0088] S.sub.4 electrode group [0089]
S.sub.n electrode group [0090] T.sub.1 electrode group [0091]
T.sub.2 electrode group [0092] T.sub.3 electrode group [0093]
T.sub.4 electrode group [0094] T.sub.n electrode group [0095]
V.sub.1 voltage source [0096] V.sub.2 voltage source [0097] V.sub.3
voltage source [0098] V.sub.4 voltage source [0099] V.sub.n voltage
source [0100] V.sub.A voltage [0101] V.sub.B voltage [0102] V.sub.C
voltage [0103] V.sub.X1 first voltage source [0104] V.sub.X2 first
voltage source [0105] V.sub.X3 first voltage source [0106] V.sub.X4
first voltage source [0107] V.sub.Xn first voltage source [0108]
V.sub.Y1 second voltage source [0109] V.sub.Y2 second voltage
source [0110] V.sub.Y3 second voltage source [0111] V.sub.Y4 second
voltage source [0112] V.sub.Yn second voltage source [0113] X.sub.1
first electrode set [0114] X.sub.2 first electrode set [0115]
X.sub.3 first electrode set [0116] X.sub.4 first electrode set
[0117] X.sub.n first electrode set [0118] Y.sub.1 second electrode
set [0119] Y.sub.2 second electrode set [0120] Y.sub.3 second
electrode set [0121] Y.sub.4 second electrode set [0122] Y.sub.n
second electrode set
* * * * *