U.S. patent application number 10/247720 was filed with the patent office on 2003-08-14 for discrete element light modulating microstructure devices.
Invention is credited to Romanovsky, Alexander B..
Application Number | 20030151790 10/247720 |
Document ID | / |
Family ID | 25502396 |
Filed Date | 2003-08-14 |
United States Patent
Application |
20030151790 |
Kind Code |
A1 |
Romanovsky, Alexander B. |
August 14, 2003 |
Discrete element light modulating microstructure devices
Abstract
A light modulating or switching array (10) having a plurality of
discrete protrusions (16) formed of electro-optic material, each of
which is electrically and optically isolated from each other. The
protrusions (16) have defined a top face (20), a bottom face (30),
first and second side faces (22, 24), and front and back faces (26,
28). There are a plurality of electrodes (34) associated with each
of the protrusions (16), these electrodes (34) being capable of
inducing an electric field in the electro-optic material for
independently modulating a plurality of light beams which are
incident upon one of the faces (20, 22, 24, 26, 28, 30) of the
protrusions (16). The electro-optic material may be of PLZT, or a
member of any of the groups of electro-optic crystals,
polycrystalline electro-optic ceramics, electro-optic
semiconductors, electro-optic glasses and electro-optically active
polymers. Also disclosed is a light modulating array (10) of the
type having a matrix (136) of electro-optic material which contains
a plurality of embedded adjacent electrodes (134). These electrodes
(134) are capable of inducing an electric field in the
electro-optic material for independently modulating a plurality of
light beams which are incident upon the matrix (136) of
electro-optic material. This matrix (136) can be formed by a
variety of processes, including a sol-gel process. Additionally
disclosed is a system (11) in which light modulating arrays (10)
are used to modulate incident light beams (42) and separate them
into a plurality of data channels (94, 96).
Inventors: |
Romanovsky, Alexander B.;
(San Jose, CA) |
Correspondence
Address: |
KNOBBE MARTENS OLSON & BEAR LLP
2040 MAIN STREET
FOURTEENTH FLOOR
IRVINE
CA
92614
US
|
Family ID: |
25502396 |
Appl. No.: |
10/247720 |
Filed: |
September 19, 2002 |
Related U.S. Patent Documents
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Application
Number |
Filing Date |
Patent Number |
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10247720 |
Sep 19, 2002 |
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10033153 |
Oct 25, 2001 |
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10033153 |
Oct 25, 2001 |
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08959778 |
Oct 29, 1997 |
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6310712 |
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Current U.S.
Class: |
359/245 |
Current CPC
Class: |
G02B 6/3556 20130101;
G02F 1/055 20130101; H04Q 11/0003 20130101; G02F 1/3137 20130101;
G02F 1/0551 20130101; G02F 1/315 20130101; G02B 2006/12145
20130101 |
Class at
Publication: |
359/245 |
International
Class: |
G02F 001/03; G02F
001/07 |
Claims
What is claimed is:
1. A light modulating array comprising: a plurality of discrete
protrusions formed of electro-optic material, each discrete
protrusion being electrically and optically isolated from each
other, said protrusions further having defined a top face, a bottom
face, first and second side faces, and front and back faces; and a
plurality of electrodes associated with each of said protrusions,
said electrodes being capable of inducing an electric field in said
electro-optic material for independently modulating one or more
light beams which are incident upon one of said faces of said
protrusions.
2. The light modulating array of claim 1 wherein: said protrusions
are formed from a single wafer of electro-optic material and said
bottom faces of said protrusions are integral with said wafer.
3. The light modulating array of claim 1 wherein: said protrusions
are formed on a separate substrate layer.
4. The light modulating array of claim 1 wherein: said protrusions
are separated by regions of dielectric material.
5. The light modulating array of claim 1 wherein: each of said
first side faces are angled such that incident light beams are
internally reflected within said protrusions.
6. The light modulating array of claim 5 wherein: said second side
face is angled such that incident light beams are directed to exit
said protrusions.
7. The light modulating array of claim 6 wherein: said first and
second angled faces include a reflective means.
8. The light modulating array of claim 1 wherein: said
electro-optic material is selected from the group consisting of
electro-optic crystals, polycrystalline electro-optic ceramics,
electro-optically active polymers, electro-optic semiconductors and
electro-optic glasses.
9. The light modulating array of claim 8 wherein: said
electro-optic material is PLZT where the lanthanum concentration
lies in the range of 8.5% to 9.0% of the overall composition.
10. The light modulating array of claim 1 wherein: said electrodes
are attached to said first and second side faces of said
protrusions.
11. The light modulating array of claim 1 wherein: said electrodes
are attached to said front and rear faces of said protrusions and
said electrodes include an aperture for passage of light beams.
12. The light modulating array of claim 2 wherein: said wafer
includes a bottom surface; and an electrode is attached to each top
face of each of said protrusions and one or more electrodes contact
said bottom surface of said wafer.
13. The light modulating array of claim 3 wherein: an electrode is
attached to each said top face of each said protrusion and said
substrate layer includes one or more electrodes which contact said
bottom face of each of the protrusions in the array.
14. The light modulating array of claim 1 wherein: each of said
protrusions includes a first portion of said electro-optic material
to which a plurality of electrodes is associated, and each of said
protrusions further includes a second portion composed of material
with an index of refraction matching that of said first portion
when no voltage is applied to electro-optically activate said first
portion, but said index of refraction of said second portion is
less than the index of refraction of said first portion when said
first portion is electro-optically activated by application of
appropriate voltage; said first and second portions are in close
conjunction with each other such that a boundary is formed at the
junction of said first and second portions; and each of said
protrusions is oriented with respect to one or more light beams
such that said each of the light beams enters each first portion of
each protrusion and strikes said boundary between said first and
said second portions at an angle such that each light beam is
totally reflected internally when said first portion is
electro-optically activated by application of sufficient voltage,
but which will pass unreflected through said boundary when said
first portion is not electro-optically activated.
15. A light modulating array comprising: a plurality of discrete
protrusions formed of electro-optic material, each discrete
protrusion being electrically and optically isolated from each
other, said protrusions further being formed in a prism shape
having defined a top face, a bottom face, and front and rear faces;
a plurality of electrodes associated with each of said protrusions,
said electrodes being capable of inducing an electric field in said
electro-optic material for independently modulating one or more
incident light beams; and each of said prism shaped protrusions is
oriented with respect to one or more light beams such that each
light beam incident upon said front face of said protrusion enters
each protrusion traveling a first path and emerging at a first
angle from said rear face of said protrusion when no voltage is
applied to electro-optically activate said protrusion, but each
light beam travels a second path and emerges at a second angle from
said rear face of said protrusion when said protrusion is
electro-optically activated by application of appropriate
voltage.
16. A light modulating array comprising: a matrix of electro-optic
material; and said matrix containing a plurality of embedded
adjacent electrodes, said electrodes being capable of inducing an
electric field in said electro-optic material for independently
modulating one or more light beams which are incident upon said
matrix of electro-optic material.
17. A light modulating array as in claim 16 wherein: said
electrodes are embedded in said matrix material by a process
selected from the group consisting of sol-gel deposition, molding,
etching of the matrix followed by electrode placement, and
micro-machining of the matrix.
18. A system for modulating light comprising: one or more discrete
protrusions formed of electro-optic material, each discrete
protrusion being electrically and optically isolated from each
other, said protrusions having defined a top face, a bottom face,
one or more side faces, and front and back faces; a plurality of
electrodes associated with each of said protrusions, said
electrodes being capable of inducing an electric field in said
electro-optic material for independently modulating one or more
light beams incident upon one of said faces of said protrusions,
the light beams being linearly polarized in a first polarization
orientation; a power supply capable of supplying sufficient voltage
to induce a desired polarization shift from a first polarization
orientation to a second polarization orientation in a beam of
polarized light entering said protrusions; conductive means for
conducting electricity from said power supply to said plurality of
electrodes; switching means for controlling application of voltage
to said electrodes through said conducting means; and separation
means for separating light of a first polarization orientation from
light of a second polarization orientation.
19. The system for modulating light of claim 18 wherein: said
conductive means includes conductive pads which are connected to
said electrodes in a configuration to be selected from the group
consisting of two conductive pads on the top surface of each
protrusion, a conductive pad on each side surface of each
protrusion, and a conductive pad on the top surface of each
protrusion and a conductive pad on each of one or more electrodes
which are associated with the bottom of each protrusion,
20. The system for modulating light of claim 18 wherein: said
separation means is an output polarizer having a polarization
orientation, said polarizer being positioned to transmit linearly
polarized light output from said protrusions having the same
polarization orientation as that of said output polarizer.
21. The system for modulating light of claim 18 wherein: said
separation means is a beam splitter, said beam splitter being
positioned so that light of a first polarization orientation is
passed through said beam splitter, and light of a second
polarization orientation is reflected.
Description
TECHNICAL FIELD
[0001] The present invention relates generally to light modulators
and light switches, and more particularly to electro-optic
modulator arrays. The inventor anticipates that primary application
of the present invention will be in high-speed printing and image
processing, although it may also be used in optical interconnects,
telecommunications and flat panel displays.
BACKGROUND ART
[0002] Electro-optic modulators have been well known in the art for
years, but for multi-channel applications they have suffered from
several disadvantages. Prior art modulator arrays have usually been
formed from single wafers of electro-optically active material onto
which surface electrodes have been attached, to form channels which
are defined by the electric field lines within the optical wafer.
Cross-talk, or interference between channels, has been a problem
because electro-optic modulators are vulnerable on at least two
levels. Since the channels are not restricted except by the
electric field lines, activity in one channel can easily induce
electro-optic interference in a nearby channel. This is in addition
to usual electrical cross-talk experienced by closely grouped and
unshielded electrical contacts. Also, previous electro-optic
modulators and light switches have often relied on surface
deposited electrodes, which produce electric field lines that are
fringed, rather than channeled and directed. Due to the exponential
decay of the electric field intensity inside the material, very
high voltages may be required to drive the material to produce the
desired electro-optic effect.
[0003] Electro-optic materials, such as LiNbO.sub.3, can be
expensive, and can require high driving voltages. Liquid crystal
modulators have also been used, but response times for this type
are typically very slow, on the order of milliseconds. Also, the
electro-optic effect exhibited by a material can be of several
different orders, depending on the material. A first order effect,
called the Pockels effect, is linear in its response to increase in
applied voltage. A second order effect, called the Kerr effect, is
quadratic in its response, thus a greater increase in effect can be
produced relative to an increase in voltage. This can theoretically
allow smaller driving voltages in a primarily Kerr effect material
to be applied to produce a comparable electro-optic effect compared
to material which produces primarily Pockels effect.
[0004] Lead zirconate titanate polycrystalline ceramic which is
doped with lanthanum (PLZT) is a relatively inexpensive, optically
transparent ceramic which can be made to exhibit either the
quadratic Kerr effect or the linear Pockels effect, depending on
the composition, and can be formed into wafers easily and used in
sol-gel moldings. The concentrate of lanthanum, or "doping", is
variable, and can lead to varying characteristics in the material.
PLZT that is commercially available is typically made from a
"recipe" which produces a very high dielectric constant .kappa..
Very high .kappa. values produce high capacitance values C, which
in turn produce high power requirements, as power (P) is
proportional to CV.sup.2/2 where V=voltage. High power consumption
in turn generates heat, so that some modulators that require high
voltage also may require cooling. If the proportion of lanthanum
dopant, or other components, in the material is adjusted, the
dielectric constant value and electro-optic constant value, as well
as the type of electro-optic effect (Kerr or Pockels), may also be
varied, with the result affecting capacitance and power
consumption.
[0005] Prior art inventions for modulating light in arrays
generally suffer from common problems experienced by multi-channel
optical and electrical systems in which the channels are not
appropriately isolated. As discussed above, interference is easily
induced in nearby channels resulting in cross-talk which can
distort image clarity and corrupt data transmissions. Additionally,
much of the prior art requires high driving voltages that are
incompatible with TTL level power supplies.
[0006] U.S. Pat. No. 4,746,942 by Moulin shows a wafer of PLZT
electro-optic ceramic material with a large number of surface
mounted electrodes. This invention suffers from the disadvantage of
cross-talk between channels, although there is discussion of
attempts to decrease cross-talk by use of large electrodes and
increased space of the electro-optic windows. This results in less
efficient use of the material. Although typical driving voltages
are not given, with larger areas of material, higher applied
voltages become necessary to provide the necessary electric field
density in the wafer.
[0007] U.S. Pat. No. 4,867,543 by Bennion et al. describes a
spatial light modulator made of a solid sheet layer of
electro-optic material such as PLZT, which has paired surface
electrodes. This has the disadvantage of requiring a driving
voltage of approximately 20 volts to produce a phase retardation of
PI radians. U.S. Pat. No. 4,406,521 by Mir et al. discloses a panel
of electro-optic material which uses electrodes to define pixel
regions. It speaks of using voltages in the range of 100-200 volts.
U.S. Pat. No. 5,033,814 by Brown et al. also shows a single slab of
electro-optic material which requires a driving voltage of 150
volts. U.S. Pat. No. 5,528,414 to Oakley discloses a single wafer
of Pockels crystal with surface mounted electrodes requiring a 70
volt driving voltage. Besides being obviously incompatible with TTL
voltage levels, none of these inventions have any mechanism for
confining electric field lines. Also, in general, use of higher
driving voltages will generate heat in the electro-optic material,
which can mean that a cooling system may be required.
[0008] U.S. Pat. No. 5,220,643 by Collings discusses an array of
optical modulators which are built into a neural network. These
modulators are mostly of liquid crystal type, although use of PLZT
is mentioned. U.S. Pat. No. 4,560,994 by Sprague shows a single
slab of electro-optic material with an array of electrodes which
create fringe electric fields, which are not channeled. Sarraf's
U.S. Pat. No. 5,521,748 also discloses a modulator array in which
mirror-like devices deflect or deform when electrostatic force is
applied. U.S. Pat. No. 4,367,946 to Varner also discusses a light
valve array, with one specifically preferred material being PLZT.
However, all four of these inventions can be expected to have the
same problems of cross-talk, which the present invention is
designed to eliminate.
[0009] For the foregoing reasons, there is a need for an array of
discrete light modulating elements which can operate at TTL voltage
levels, and at high speeds, with almost no cross-talk, and which
can be used to produce small pixels or which can be grouped
together to create larger pixels and large two dimensional panels
or sheets.
DISCLOSURE OF THE INVENTION
[0010] Accordingly, it is an object of the present invention to
provide an array of discrete modulated elements of electro-optic
material.
[0011] Another object of the invention is to provide arrays of
electro-optically modulators that can be driven by TTL voltages,
and thus be compatible with standard TTL power supplies.
[0012] Yet another object of the invention is to produce arrays of
electro-optic modulators which have very little cross-talk between
channels.
[0013] Still another object of the present invention is to provide
an array with very fast response and switching time.
[0014] A further object of the present invention is to provide an
array of pixels which can be of very small dimensions to reduce
problems of aliasing in optical displays.
[0015] A yet further object of the present invention is to produce
light modulating arrays that can be manufactured by conventional
methods very inexpensively.
[0016] Briefly, one preferred embodiment of the present invention
is a light modulating array having a number of discrete protrusions
formed of electro-optic material, each of which is electrically and
optically isolated from each other. The protrusions each can be
viewed as having a top face, a bottom face, first and second side
faces, and front and back faces. Each array also has a number of
electrodes associated with each of the protrusions, the electrodes
being capable of inducing an electric field in the electro-optic
material for independently modulating a number of light beams which
are incident upon one of the faces of the protrusions. The
protrusions can be made from any number of electro-optic materials
including electro-optic crystals, polycrystalline electro-optic
ceramics, electro-optically active polymers, electro-optic
semiconductors and electro-optic glasses. The protrusions can be
integral with a substrate wafer, or formed upon a substrate of a
second material. The electrodes can be attached in a variety of
positions including on the sides, top and bottom, and on the front
and back faces if electrodes with apertures are used.
[0017] A second preferred embodiment of the present invention is a
light modulating array having a number of discrete protrusions
formed of electro-optic material, each of which is electrically and
optically isolated from each other, each protrusion being formed in
a prism shape. Each protrusion has a top face, a bottom face, and
front and rear faces. Each array also has a number of electrodes
associated with each of the protrusions, the electrodes being
capable of inducing an electric field in the electro-optic material
for independently modulating a plurality of incident light beams.
Each of the prism shaped protrusions is oriented with respect to a
number of light beams such that each light beam incident upon the
front face of each protrusion enters the protrusion traveling a
first path and emerging at a first angle from the rear face of the
protrusion when no voltage is applied to electro-optically activate
the protrusion. However, each light beam travels a second path and
emerges at a second angle from the rear face of the protrusion when
the protrusion is electro-optically activated by application of
appropriate voltage.
[0018] A third preferred embodiment of the present invention is a
light modulating array having a matrix of electro-optic material,
with each matrix containing a number of embedded adjacent
electrodes. The electrodes are each capable of inducing an electric
field in the electro-optic material for independently modulating a
number of light beams which are incident upon the matrix of
electro-optic material.
[0019] A fourth preferred embodiment of the present invention is a
system for modulating light having a number of discrete protrusions
formed of electro-optic material and a number of electrodes, as
above. The system also includes a power supply capable of supplying
sufficient voltage to induce a desired polarization shift from a
first polarization orientation to a second polarization orientation
in a beam of polarized light entering the protrusions. Also
included are a switches for controlling application of voltage to
the electrodes through a conductor and a separator for separating
light of a first polarization orientation from light of a second
polarization orientation. The separator could be any of a number of
mechanisms, such as beam splitters, cross-polarizers, etc.
[0020] An advantage of the present invention is that it may be
operated with TTL voltages or lower.
[0021] Another advantage of the invention is that because of the
low voltage requirements, heating of the elements is reduced and
requirements for cooling are minimized.
[0022] Yet another advantage of the present invention is that very
small elements may be produced, thus allowing for very fine image
resolution.
[0023] A further advantage of the present invention is that
cross-talk between channels is nearly eliminated.
[0024] A still further advantage of the present invention is that
standard micro-machining operations can be used, allowing for
inexpensive manufacture.
[0025] A yet further advantage of the present invention is that
sol-gel processes can be used to create arrays very
inexpensively.
[0026] Yet another advantage of the present invention is that
sol-gel processes can be used to make displays which are both thin
and flexible. These molding processes can produce arrays with large
numbers of elements quickly and for very low cost.
[0027] These and other objects and advantages of the present
invention will become clear to those skilled in the art in view of
the description of the best presently known mode of carrying out
the invention and the industrial applicability of the preferred
embodiment as described herein and as illustrated in the several
figures of the drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
[0028] The purposes and advantages of the present invention will be
apparent from the following detailed description in conjunction
with the appended drawings in which:
[0029] FIG. 1 is a perspective view of a system for modulating and
switching light beams which uses a light modulating array, showing
the modulation of impinging light beams;
[0030] FIG. 2 is a perspective view of a modulator array, and
electrical circuit showing an alternative location for conductive
pads;
[0031] FIG. 3 is a perspective view of a modulator array, and
electrical circuit showing the elements mounted on a substrate of
different material;
[0032] FIG. 4 is a perspective view of a modulator array and
electrical circuit in which electrodes have been attached to the
top and bottom wafer surfaces;
[0033] FIG. 5 is a perspective view of a modulator array and
electrical circuit showing an alternate location for conductive
pads;
[0034] FIG. 6 is a perspective view of an alternate embodiment of a
modulator array and electrodes;
[0035] FIG. 7 is a perspective view of another alternative
embodiment of a modulator array and electrodes;
[0036] FIG. 8 is a perspective view of system for modulating and
switching light beams which uses a modulator array and
beamsplitters to separate modulated and unmodulated beams into
different channels;
[0037] FIG. 9 is a plan view of a system for modulating and
switching light beams, which shows a single element of a modulator
array used as an alternate mechanism for separating modulated and
unmodulated beams into different channels;
[0038] FIG. 10 is a perspective view of a system for modulating and
switching light beams which shows a single element of a different
version of a modulator array used as an alternate mechanism for
separating modulated and unmodulated beams into different
channels;
[0039] FIG. 11 is a perspective view of a modulator array in which
electrodes have been placed so as to produce an electric field
which is collinear with the direction of light propagation; and
[0040] FIG. 12 is a cross-sectional view of an embedded electrode
array in a sol-gel matrix of electro-optic material.
BEST MODE FOR CARRYING OUT THE INVENTION
[0041] A preferred embodiment of the present invention is an array
of light modulating and switching microstructure devices. The
present invention solves many of the problems of the prior art by
using lanthanum doped lead zirconate titanate crystal (PLZT), which
is an optically transparent ceramic that becomes birefringent when
proper voltage is applied. PLZT has a quadratic electro-optic
response to voltage increase thus allowing lower driving voltages.
In addition, the present invention uses an optimized compositional
"recipe" in which the proportion of lanthanum dopant and matrix
elements has been designed to produce low dielectric constant
.kappa.; higher electro-optic efficiency, and thus low power
requirements. Additionally, the electro-optic elements are
3-dimensional and of very small size, generally 10 .mu.m-200 .mu.m
in the light propagation direction, or much less, depending on the
design. This allows production of very high-density electric fields
in these elements by using small voltages, including TTL levels of
approximately 5 volts, and lower. This has advantages because power
supplies that are already set up for TTL level digital components
can supply the electro-optic modulators as well. Cross-talk has
been nearly eliminated by the use of grooves or regions which are
filled with air or other dielectric materials. These physically
separate at least a portion of the elements, thus directing and
channeling electric field lines more closely. PLZT, as well as
other electro-optic materials, also allows for pico-second response
time, thus theoretically allowing very high switching frequencies
of 100 GHz and more.
[0042] The use of embedded electrodes produces more uniform
electric field strength in the elements. This allows a much lower
driving voltage and a much more predictable and controllable
electric field.
[0043] The present invention is also useful when using standard
recipe electro-optic materials, in which the dielectric constant
has not been minimized, and also in a variety of other
electro-optic materials beside PLZT. Electro-optic materials fall
generally into five categories, 1) electro-optic crystals, 2)
polycrystalline electro-optic ceramics, 3) electro-optically active
polymers, 4) electro-optic semiconductors, and 5) electro-optic
glasses. Although the electro-optic properties of the materials are
variable depending on composition, the present invention can be
implemented with materials of any of these three categories.
Specific examples of electro-optic materials besides PLZT which may
be used include, but are not limited to, LiNbO.sub.3, LiTaO.sub.3,
BSN, PBN, KTN, KDP, KD*P, KTP, BaTiO.sub.3,
Ba.sub.2NaNb.sub.5O.sub.15, GaAs, InP, CdS, AgGaS.sub.2, and
ZnGeP.sub.2. The very small dimensions of the elements result in
very low element capacitance even when using material having a
relatively large dielectric constant .kappa..
[0044] As illustrated in the various drawings herein, and
particularly in the view of FIG. 1, a form of this preferred
embodiment of the inventive device is depicted by the general
reference character 10.
[0045] FIG. 1 illustrates an array of light modulating
microstructures 10 as well as a system 11 for modulating or
switching light in a number of independent channels. In this
preferred embodiment, the array 10 is formed from a wafer 12 of
PLZT. PLZT has been chosen for its large electro-optic effect and
low absorption for thin wafers.
[0046] If PLZT is used, the relative proportion of the Lanthanum
dopant in the ceramic can be very important in determining the
driving voltage required for the elements. The composition also is
important in establishing the optical properties such as
transparency, grain size and pore size, speed, power dissipation,
operating temperature and for maximizing both the linear and the
quadratic electro-optic coefficients of the material. Commercial
recipes for PLZT have largely used Lanthanum concentrations of 9.0%
to 12%. If Lanthanum concentration is varied in the range of 8.5%
to 9.0% of the PLZT ceramic and the concentration of Zirconium and
Titanium are unchanged from typical ratios of 65/35, it may be
possible to achieve a higher quadratic electro-optic coefficient
(R) in the PLZT for the La dopant percentage closer to 8.5%. For
the PLZT compositions, where Zr and Ti are maintained in a 65/35
ratio and the overall percentage of La is varied:
La=9.5%, R=1.5.times.10.sup.-16 m.sup.2/V.sup.2;
La=9.0%, R=3.8.times.10.sup.-16 m.sup.2/V.sup.2.
[0047] It is known that for La<8.0%, PLZT loses quadratic
electro-optic properties. It is therefore expected that somewhere
around 8.5% La there should be a maximum for R around
(5-40).times.10.sup.-16 m.sup.2/V.sup.2.
[0048] This enhanced value of electro-optic coefficient provides
many advantages. It will permit lower required driving voltages,
and thus lower power dissipation in the material and hence lower
heating of the device. This in turn allows the device to be driven
at significantly higher frequencies, even without external cooling.
Also, the use of lower La concentrations (which is a free electron
donor) will result in a reduced "charge screening" effect. The
overall result is higher modulation efficiency of devices
manufactured from this material.
[0049] The wafer 12 has regions or grooves 14 formed to produce
protrusions 16 from the original thickness 18 of the wafer 12. The
grooves 14 may be formed by any number of means, such as mechanical
machining with micro-saws, chemical etching using photo-resist
masks, or laser ablation, or the array may be molded in shape from
polycrystalline ceramic, among other methods. The grooves 14
provide isolation between the channels of the array 10, serve to
direct and channel the electric field lines in the electro-optic
material and thus allow the array to operate with nearly zero
cross-talk.
[0050] Each protrusion 16 has a top face 20, a first side face 22
and a second side face 24, a front face 26 and a rear face 28. The
grooves 14 can be cut through the entire original thickness 18 of
the wafer 12, in which case, the protrusions will have an
independent bottom face 30, or if the groove is not cut through the
entire original thickness 18, the bottom face 30 will be integral
with the wafer 12, as shown by the dotted line in FIG. 1.
[0051] The faces of the wafer 32 can be polished either before or
after the grooves 14 are formed, to prevent scattering of light
entering or leaving the wafer 12. Electrodes 34 are attached to the
protrusions 16 by any of a number of ways, but one preferred method
is to embed the electrodes 34, as this may produce a more uniform
electrical field. It is also possible that the material of the
electrode 34 may completely fill the grooves 14. Conductive pads 36
of gold or some other metal or conductive material are used to
attach electrical leads 38 to the electrodes 34, which connect them
in turn to the electrical power supply 40. An electrical field is
thus established which is oriented in a transverse direction
relative to the direction of the incoming light beams 42. The width
of electro-optic material between the grooves 14 in the protrusions
16 establishs the electrode gap 44 in this configuration of
electrode 34 placement.
[0052] For ease of reference, an assembly containing a protrusion
16, attached electrodes 34, and conductive pads 36 shall be
referred to as an "element". The size of the wafer 12, the
protrusions 16 and the electrode gaps 44 will depend on the
material chosen, and the desired range of applied voltages to be
used. The electro-optic effect exhibited by an element of a
particular material depends on the electric field strength within
that element. The density of that field will in turn depend on the
amount of applied voltage, the material chosen, and the physical
dimensions of the element in which the electric field is contained.
Using very small elements allows a large concentration of electric
field density by use of small to moderate voltages. In the present
invention, in order to use voltages in the TTL range, around 5V, it
is estimated that the physical size of the elements, if made of
PLZT, will be on the order of 20 .mu.m.times.20 .mu.m.times.200
.mu.m. The grooves 14 can be made very small, and indeed may be
limited by the size of machining tools used to form them. Excellent
results in terms of near zero cross-talk have been achieved using
micro-sawing methods where the kerf size of the saw cuts are around
25 .mu.m. Effective reduction of cross-talk between channels may be
achieved with grooves as small as 5 .mu.m.
[0053] Such tiny elements can produce modulated beams of very small
size, producing such fine image resolution that the unaided eye is
incapable of distinguishing it. It may have applications where
microscopic images are required, or where multiple beams are
combined in groups of 5 or 10 elements to make up 1 pixel in a
display device.
[0054] The size of the elements will also depend on whether the
beam is transmitted through the element or reflected from a rear
surface, in which case, the length or the driving voltage can be
cut roughly in half to produce the same degree of modulation.
Materials with smaller electro-optic properties may require greater
size or increased applied voltage to achieve proper modulation
results.
[0055] In FIG. 1, a first element 46 and a second element 48 are
shown, which in this preferred embodiment, will be assumed to be
composed of PLZT. Between the first element 46 and the voltage
supply line, an open switch 50 is shown to represent that the
element 46 has no voltage applied, and is in an inactive state. It
is, of course, to be understood that nothing so primitive as
throw-switches need be used to practice the invention. Most likely,
very high frequency (perhaps as much as 100 GHz or more) square
waves of appropriate voltage will be used, but throw-switches are
used here as an easy means of illustrating the state of the applied
voltage.
[0056] The incoming light beams 42 having incoming linear
polarization 54 which is aligned with the upper tip 45 degrees to
the left of vertical, (which shall be referred to as "R"
polarization) impinge on both elements 46 and 48. This incoming
light may be linearly polarized laser light, or it may be initially
unpolarized light, perhaps even including light from an
incandescent bulb, which has been transmitted through a polarizer
to produce linearly polarized light. First element 46 is inactive,
thus the outgoing polarization 56 of the first element 46 is
unchanged. It passes through an R aligned polarizer 60 and is
detected by a light sensor or photo detector 62, perhaps to be
recognized as a digital "1".
[0057] In contrast, switch 52 is closed leading to the second
element 48, thus the supply voltage is applied and the element 48
is active. The element 48 becomes bilefringent under the influence
of the applied electric field. Birefringence causes an incoming
beam 42 which is linearly polarized at a 45 degree angle relative
to the direction of the applied electric field to split into two
orthogonal components which are respectively parallel and
perpendicular to the electric field lines. These components travel
along the same path but at different velocities. The electro-optic
effect thus will cause a phase shift between the two components, as
one is retarded in relation to the other. After traveling through
the element 48, the components re-combine with the result that the
polarization of the emergent beam 58 is changed. If the voltage is
sufficient to cause a .lambda./2 shift in polarization, the
polarization will be rotated by 90 degrees, relative to its
original orientation. In FIG. 1, it is assumed that a .lambda./2
voltage of 5 volts has been applied which produces a 90 degree
phase shift to give a linearly polarized output beam 58, which is
oriented with the upper tip now 45 degrees to the right of vertical
(which shall be referred to as "S" polarization). This S polarized
light is now blocked by the R aligned polarizer 60, which allows no
light to reach the detector 62. This may be recognized by a digital
device as a "0".
[0058] If the applied voltage causes a .lambda./4 rotation, the
outgoing polarization 58 will be made into circular polarization,
as the tip of the resultant electric field vector will describe a
circle as it propagates. Intermediate voltage values will result in
elliptical polarization. These will be incompletely blocked by the
polarizer 60, which will allow only the R aligned component to
pass. Thus, the light seen by the detector 62 may be theoretically
controlled anywhere in the range from undiminished incoming
intensity to total extinction, to produce analog-type output
signals if the appropriate control voltage is applied.
[0059] FIG. 2 illustrates a different version of the modulator
array 10. A wafer 12 is shown with attached or embedded electrodes
34, and in this embodiment, the conductive pads 36 are located in a
different configuration for attachment to electrical leads 38.
[0060] FIG. 3 illustrates another version of the modulator array
10, in which the grooves 14 have been extended completely through
the original thickness 18 of the wafer. The elements 64 here are
composed of the protrusion 16 portions of the wafer 12 and their
respective attached or embedded electrodes 22 and conductive pads
24 (see FIG. 1). A number of elements 64 have been formed on a
substrate 66 made from a different material which the bottom faces
30 now contact. This substrate 66 is preferably a low dielectric
material that is not electro-optically active, such as SiO.sub.2,
for one example among many. The protrusions 16 may be attached or
glued to the substrate 66 prior to machining or attachment of the
electrodes 34 and pads 36, or the completed elements 64 may be
assembled prior to attachment to the substrate 66.
[0061] FIG. 4 shows yet another version of the modulator array 10.
In this embodiment, electrodes 34 are attached to the top faces 20
of the protrusions 16 and a single large electrode 68 is positioned
on the bottom side 70 of the wafer 12. It is to be understood that
a plurality of appropriately placed individual electrodes could be
used on the bottom side 70 of the wafer 12 in place of the single
large electrode 68 pictured here and in the following FIG. 5.
Conducting pads 36 are attached to the top and bottom electrodes
34, 68 as attachment points for the electrical leads 38. Polished
front faces 26 are indicated as before, and incoming light beams 42
are shown to indicate orientation. The polarization direction has
not been shown, as the principles of phase retardation operate much
the same as in FIG. 1, with a .lambda./2 shift producing a 90
degree rotation, etc. This placement of electrodes 34, 68 produces
a different orientation of transverse electrical fields, but still
retains the advantage of channel separation and minimization of
cross-talk which was unavailable in the prior art.
[0062] FIG. 5 shows a variation of the configuration in FIG. 4, in
which the upper conductive pads 36 are located in a different
orientation relative to the wafer 12. The top and bottom electrodes
34, 68 are positioned as in FIG. 4, to produce a transverse
electric field. The polished front faces 26 and incoming light
beams 42 are again shown for orientation purposes.
[0063] Although not pictured here, it is to be understood that this
arrangement of top and bottom electrodes and the variations in
conductive pad locations seen in FIGS. 4 and 5 can be used with
elements which have been positioned on a different substrate
material, in the manner suggested by FIG. 3, if the substrate
material has the proper conductive properties. It may also be
possible for elements to be directly attached to a single large
bottom electrode which can act as a substrate to support and
position the elements. Alternately, the electrodes may be attached
or embedded on both sides of the electro-optic material directly
before mounting the assembled elements onto a substrate.
[0064] FIG. 6 shows another version of an array 10 of modified
protrusions 72 which have either been formed on the original wafer
12 or formed separately on a substrate of different optically
transparent material 66 in a similar manner to the embodiment shown
in FIG. 3. The modified protrusions 72 are shown to be oriented
with their long sides parallel to the long edge of the wafer 12 or
substrate 66, but it should be understood that they may also be
oriented with the long sides of the protrusions 72 transverse to
the long edge of the wafer 12 or substrate 66. An incoming
polarized light beam 42 enters from the bottom side 70 of the wafer
12 or substrate 66 and is internally reflected on the angled first
side face 74 and angled second side face 76 to reemerge from the
bottom side 70 of the wafer 12. If appropriate voltage has been
applied to the electrodes 78, the resulting polarization of the
emergent light beam 80 will be modulated in the manner described
above. The angles of the faces here are chosen to allow total
internal reflection, but it is to be understood that if a
reflective coating is applied to the faces, a variety of other
angles may be used as well.
[0065] FIG. 7 illustrates yet another version of a modulator array
10 in which the protrusions 82 have been modified in another manner
such that the angled second side face 84 of each has been angled to
direct the emergent beam 86 out of the top face 20 of each
protrusion 82. As in FIG. 6, the protrusions may be oriented in a
transverse direction, a different substrate material may be used,
and a reflective coating may be applied to reflecting faces.
[0066] FIG. 8 shows a system 11 for modulating or switching light
beams which uses the modulator array 10 in much the same
configuration as in FIG. 1. An incoming linearly polarized beam 42
of polarization "R" enters a first element 46 which is inactive due
to an open switch 50, so that its exiting polarization 56 is
unchanged. This enters a beamsplitter 88 that has been positioned
so that light of R polarization will be reflected out of the
beamsplitter at angle .phi., as shown by reflected beam 90. In a
second element 48, which is active, the voltage is assumed to be
such as to produce a .lambda./2 shift, the polarization is rotated
90 degrees to "S" orientation, and this passes through the
beamsplitter 88, as shown by unreflected beam 92. These beams can
be used to carry separate digital information, and may be
designated "channel 1" 94 and "channel 2" 96. It is to be
understood that beamsplitters can be used as a channel separation
device with any of the various embodiments illustrated herein.
[0067] FIG. 9 shows a top plan view of another system 11 for
modulating or switching light beams which uses a different version
of a light modulating array 10. A single protrusion 16 is shown,
which is composed of a first block 98 or portion of material having
an index of refraction N.sub.1, and a second block 100 of material
having index of refraction N.sub.2. A boundary 102 is formed at the
junction of the two materials. One of the two blocks, in this case
the first block 98, has top and bottom electrodes 104. First block
98 is composed of electro-optic material such that when electrodes
104 are uncharged, the electro-optic material is inactive, and
N.sub.1=N.sub.2. When voltage is applied to electrodes 104, the
first block 98 becomes active and the index of refraction changes
for polarization components which are aligned with the electric
field lines so that for this polarization, N.sub.1>N.sub.2. When
first block 98 is inactive, an incoming beam 106 is projected into
the first block 98 at entry angle .epsilon. to a normal such that
the beam passes through the boundary between the two blocks 98, 100
and emerges as unreflected light ray 108. When first block 98 is
active the index of refraction is increased such that total
internal reflectance (TIR) occurs, and the beam is reflected back
into the first block 98 at the boundary 102, and emerges as
reflected light ray 110. The two emergent beams 108 and 110 are
separated by angle .delta., which has been greatly exaggerated
here. These separated beams 108, 110, can be detected by sensors
112, and thus be used to establish channel separation for data
transmission.
[0068] Alternatively, the protrusion 16 can be made from a single
integral block of material, which has been electro-optically
divided into portions or sections. A first section 98 may have
electrodes 104 attached to induce a different index of refraction
in this section. An incoming beam 106 will then be totally
internally reflected, as described above, at the interface between
the activated 98 and unactivated sections 100. This interface or
boundary 102 can be established more definitely by having the
second section 100, be of a different thickness than the first 98.
This serves to direct the electric field lines better so that less
fringing is produced, and a sharper interface boundary 102 is
established.
[0069] FIG. 10 shows a perspective view of another system 11 for
modulating or switching light beams which uses yet another version
of the light modulating array 10 to perform channel separation. A
single prism-shaped protrusion 114 is shown, which can be
electro-optically activated by electrodes 116 to increase the index
of refraction. This causes the light beam to be bent towards the
normal upon entry slightly differently than when the material is an
inactive state. Thus when the element is active, the light beam
will follow a first path 118, and will emerge at a slightly
different angle relative to the normal upon leaving the element,
thus following a first exiting path 120. In contrast, when the
element is inactive, the light follows a second path 122 upon
entry, and follows a second exiting path 124. Both of these second
paths are shown in dashed line in FIG. 10. These first and second
exiting paths 120, 124 are separated by angle .beta., and they can
be further directed by mirrored surfaces 126 to sensors 128 to
produce separate channels. The separation of the paths and the
separation angle has been exaggerated in the FIG. 10.
[0070] FIG. 11 illustrates yet another version of the present light
modulating array 10 in which end-mounted electrodes 130 each having
an aperture 132 have been attached to the front faces 26 and rear
faces 28 of the protrusions 16. In this configuration, the electric
field lines are collinear with the direction of incoming light
beams 42. The application of appropriate applied voltage results in
the change in polarized output in a manner similar to that
discussed above. It is to be understood that the above mentioned
methods of splitting the output into separate channels, or using an
external polarizer and sensor may be used, as well as mounting of
elements on different substrate material, and variations in
conductive pad placement.
[0071] It is also possible to have a light-producing element, such
as a diode laser, with a modulating element physically attached at
the laser's output, in order to produce a single integrated
element.
[0072] Another variation of the preferred embodiment uses sol-gel
processing to create an array of elements that are fixed in a
flexible medium. Sol-gel processing is a chemically based,
relatively low temperature (400-800 degrees C.) method that can
produce ceramics and glasses with better purity and homogeneity
than higher temperature (2,000 degrees C.) conventional
processes.
[0073] When using molding processes, two approaches are possible.
In the first approach, a non electro-optic, optically transparent
or non-transparent matrix is prepared. Electrodes are deposited on
the side walls. Then it is filled with soft, curable electro-optic
material of sol-gel type or polymer resin. It is then cured to
produce an array of electro-optic modulators separated spatially by
non electro-optic material.
[0074] In the second approach, an electro-optically active matrix
of solid or flexible material is prepared. Electrodes are deposited
on the side walls. Then it is filled with soft, curable non
electro-optic material, of optically transparent or non
transparent, sol gel type or polymer resin. Then it is cured to
produce an array of electro-optic modulators separated spatially by
non electro-optic material.
[0075] For the PLZT thin films made by the sol-gel process with 1-2
.mu.m spacing between embedded adjacent electrodes, .lambda./2
voltages range from 20-30 Volts for 0.5 .mu.m thick films, to TTL
levels (4-5 Volts) for 1-2 .mu.m film thickness. This idea is very
attractive for large area flat panel display applications, which
function like CRT tubes and which may successfully compete with
them. Because electrode spacing is necessarily very small to
achieve low driving voltages, resulting pixel size is also very
small, which makes this embodiment ideal for high-resolution flat
panel displays or spatial light modulators. This fine pixel
structure is below typical resolution capability of the human eye,
so for consumer applications, sub-micron and micron size
substructures may be aggregated to produce standard sized pixels
(usually dozens or hundreds of microns). To simplify the
manufacturing process and make it compatible with existing flat
panel technology, the pixel size can be made larger. In this case,
each pixel represents an interdigital pattern of PLZT embedded
shutter electrodes.
[0076] FIG. 12 shows a top plan view of a modulator array 10
composed of embedded electrodes 134 that are contained in a sol-gel
matrix 136. The arrow lines indicate electric field lines 138. The
height of the electrodes 134 (out of drawing plane) is defined by
the thickness of the film. In the figure, light also travels
perpendicular to the drawing plane. For non-polarized light, the
modulator array 10 is placed in between two cross polarizers (not
shown).
[0077] The electrode structures can be deposited either prior to
the sol-gel film deposition, or after it, using standard etching or
micro-machining techniques. Using etching techniques and molding
processes, the height of the electrodes 134 can be much higher, 10
.mu.m or more with the same 1-2 .mu.m spacing between electrodes.
In this case, sol-gel can fill the spacings between electrodes 134
and the thin film can still be thin enough (a few microns) to
guarantee the same fabrication process and similar process
conditions. This will allow driving or switching voltages on the
TTL level (4-5 Volts) or below (1-3 Volts and even lower). The
arrays thus fabricated can be used in either transmissive or
reflective modes. Additionally, the sol-gel material can either be
used to completely fill the gap between electrodes, or it can
instead be deposited on the sides of the electrodes as a coating.
If used as a coating, an additional electrode can be added on the
outer side of the sol-gel coating to make a complete element, each
element being separated from its neighbor by a gap or groove.
[0078] In addition to the above mentioned examples, various other
modifications and alterations of the inventive device 10 may be
made without departing from the invention. Accordingly, the above
disclosure is not to be considered as limiting and the appended
claims are to be interpreted as encompassing the true spirit and
the entire scope of the invention.
INDUSTRLAL APPLICABILITY
[0079] The present device 10 is well suited for application in a
wide range of fields in which light modulators and high speed light
switching devices are used, such as in high-speed printing, image
processing and telecommunications. The present invention 10 is also
especially suited for use in flat panel displays and projection
television.
[0080] Although the basic array structures 10 discussed above are
in a one-dimensional line configuration, these may be configured
and arranged to form two-dimensional sheets of large size.
Additionally, by use of the sol-gel process, they may be used to
make a kind of thin flexible display material almost like cloth,
which may be used to cover three dimensional forms or perhaps even
to make clothing.
[0081] The materials presently used in flat panel displays respond
very slowly to changes in display information. This leads to the
commonly observed problem, especially in flat panel displays of
laptop computers, that the display of a moving object will leave
trails behind, due to the lag in the response of the display. The
present invention, by contrast, is capable of switching speeds of
100 GHz and more, producing such fast response that it is beyond
the ability of the human eye to register individual steps in a
display of motion.
[0082] Prior art displays also may exhibit the problem of aliasing,
or the jagged edges sometimes seen around the outline of a
displayed object due to the comparatively large size of pixels in a
digital display. By contrast, the elements of the present invention
10 may be made as smaller than 1 .mu.m.times.1 .mu.m in cross
section, each element being capable of producing an independent
signal. Thus each element is potentially an independent pixel. The
use of the present invention completely eliminates the problem of
aliasing down to the microscopic scale. Indeed, the human eye
cannot resolve such small elements. Thus for use on the scale of
ordinary unaided human vision, the elements may be grouped into
larger pixels, whose overall size can still be small enough to
provide far better image resolution than is presently available.
There may also be applications in which microscopic pixel size is
advantageous, such as making microscopic photo masks for microchip
manufacture. The ungrouped pixels of the present invention are
uniquely suited for such uses.
[0083] The very small size of the elements allows low driving
voltages to be used to produce the necessary electric field density
to induce the desired electro-optic effect. TTL levels may be used
with some materials. The use of TTL level voltages has many
significant advantages. TTL level power supplies have been well
developed over many years and are commonly available "off the
shelf". Thus power supplies can be easily obtained for systems that
utilize the present invention 10, without having to provide a
customized power supply. This also allows easier introduction of
the present invention 10 into equipment that uses TTL devices and
already has the appropriate power supply in place.
[0084] The present invention 10 also may be designed to utilize
sub-TTL levels. It is useful in many applications in which these
smaller driver voltages are supplied.
[0085] Prior art light modulators and optical switches that are
fabricated on a common wafer without benefit of any feature to
channel the electric field lines commonly suffer from problems with
cross-talk between the channels. This interferes with image clarity
and can corrupt transmitted data. By contrast, by utilizing the
discrete elements of the present invention 10, cross-talk between
channels is practically eliminated, resulting in cleaner image
production and improved accuracy and integrity of data
transmission. This has very many industrial applications in a wide
variety of devices such as printers, teleconmunications, and visual
displays.
[0086] In addition, for telecommunications applications, prior art
diode lasers which have been used, have typically suffered from the
problem of "chirping" which is interference which can be produced
when the voltage supplied to a diode laser is rapidly modulated. In
contrast, the present invention 10 modulates the optical output
rather than the diode laser itself. This greatly reduces
interference and can eliminate the problem of chirping. This can be
an important advantage for telecommunications applications.
[0087] Another feature that makes the present invention 10
especially desirable for industrial applications is its ease of
manufacture and low cost. It can be made using existing technology
by varying methods such as micro-machining, laser ablation,
selective etching in an electric field, and molding by conventional
means or using a sol-gel process. For micro-machining, the same
kinds of micro-saws as are presently used in trimming silicon
wafers can be used to form the slots between the projections.
[0088] Another method for manufacturing light modulating arrays 10
is the use of sol-gel processing to create an array of elements
that are fixed in a flexible medium. Sol-gel processing is a
chemically based, relatively low temperature method that can
produce ceramics and glasses with better purity and homogeneity
than higher temperature conventional processes. Another of the
attractive features of the sol-gel process is the capability to
produce compositions not possible with conventional methods.
[0089] Thin films of PLZT electro-optic ceramic made with the
sol-gel process have a number of advantages relative to PLZT
ceramics prepared from powders. Large surface areas of thin film
can be created which have very uniform (homogeneous) material
structure. Small grain sizes are achievable, in the range of 10's
of nm, with much less porosity compared with PLZT ceramics prepared
from powders. A wide range of film thickness from a few nanometers
to a few microns can be produced.
[0090] Sol-gel manufacture also easily lends itself to high volume
production. It is inexpensive, suitable for large area spatial
light modulators or flat panel displays and can utilize
micro-machining fabrication processes which are standard in the
industry. It can be used for bright, ultra high-speed flat panel
displays or spatial light modulators suitable for computer
interconnects and high-speed telecommunications with very wide
viewing angles which may eventually be used to replace cathode ray
tubes.
[0091] For the above, and other reasons, it is expected that the
device 10 of the present invention will have widespread industrial
applicability. Therefore, it is expected that the commercial
utility of the present invention will be extensive and long
lasting.
* * * * *