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Claims  |
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I claim:
1. A scrolling liquid crystal light modulator, comprising:
an array of liquid crystal cells capable of assuming different optical
states in response to electrical signals applied to the cells, at least
one of which is an input liquid crystal cell, the state of which is
controlled by input signals applied to the cell from outside the array;
and
clocking means for applying electrical clocking signals to the array cells,
to shift the optical states from cell to cell across and within the array,
without further application of input data signals except to the input
liquid crystal cell or cells.
2. A scrolling liquid crystal light modulator as defined in claim 1,
wherein:
the array of liquid crystal cells is two-dimensional.
3. A scrolling liquid crystal light modulator as defined in claim 1,
wherein:
the clocking means includes means for applying a selected one of three
clocking signals to each of the liquid crystal cells but not to any input
cell, each of the three clocking signals being applied to every third
cell, to propagate the state of the input liquid crystal cell from cell to
cell across the array in a direction away from the input liquid crystal
cell.
4. A scrolling liquid crystal light modulator, comprising:
an array of liquid crystal cells capable of recording binary data as
different optical properties of the cells, the array having an input end;
electrical data input means coupled to the input end of the array to
receive input signals; and
clocking means applied to the array cells to shift binary data across the
array in a form represented by different optical properties, which are
shifted from cell to cell within the array, without the application of
externally provided data signals except those applied to the input end of
the array through the electrical data input means.
5. A scrolling liquid crystal light modulator as defined in claim 4,
wherein:
the liquid crystal cells are ferroelectric smectic C (FSC) liquid crystals.
6. A scrolling liquid crystal light modulator as defined in claim 4,
wherein:
the array of liquid crystal cells is two-dimensional.
7. A scrolling liquid crystal light modulator as defined in claim 6
wherein:
the liquid crystal cells are ferroelectric smectic C (FSC) liquid crystals.
8. A scrolling liquid crystal light modulator as defined in claim 4,
wherein:
the array has at least one input liquid crystal cell, the state of which is
determined by the input signals, which are applied to the input liquid
crystal cell;
the clocking means includes means for applying a selected one of three
clocking signals to each of the liquid crystal cells but not to any input
cell, each of the three clocking signals being applied to every third
cell, to propagate the state of the input liquid crystal cell from cell to
cell across the array in a direction away from the input end.
9. A scrolling liquid crystal light modulator as defined in claim 8,
wherein:
the liquid crystal cells are ferroelectric smectic C (FSC) liquid crystals.
10. A scrolling liquid crystal light modulator as defined in claim 8,
wherein:
each clocking signal has a cycle including three phases;
the input signals are applied to the input cell or cells during two of the
three phases of the clocking signals, the input signals being separated by
a buffer signal applied to turn the input cell to an off state during
every third clocking phase;
each of the clocking signals is in a first condition for one of the three
clock phases, to isolate adjacent signals being propagated, and is in a
second condition for the other two of the three clock phases, the second
condition resulting in propagation of an ON state from an adjacent cell to
the one to which the second condition of the clock signal is applied; and
the three clocking signals are staggered in their times of occurrence of
the first clocking signal condition such that the first clocking signal
condition is applied to a set of cells comprising every third cell, and
the set is advanced cell by cell across the array in synchronism with the
clocking signals.
11. A scrolling liquid crystal light modulator as defined in claim 10,
wherein:
the liquid crystal cells are ferroelectric smectic C (FSC) liquid crystals.
12. A scrolling liquid crystal light modulator as defined in claim 8,
wherein:
the array of liquid crystal cells is two-dimensional;
there are a plurality of input liquid crystal cells and an equal plurality
of rows of clocked liquid crystal cells, each row having a plurality of
column positions at which cells are located; and
identical clocking signals are applied to liquid crystal cells having the
same column position.
13. A scrolling liquid crystal light modulator as defined in claim 12,
wherein:
the liquid crystal cells are ferroelectric smectic C (FSC) liquid crystals.
14. A scrolling liquid crystal light modulator as defined in claim 8,
wherein:
each clocking signal has a cycle including three phases;
the input signals are applied to the input cell or cells during one of the
three phases of the clocking signals, the input signals having a first
condition to switch an input cell to an ON state and a second condition to
switch an input cell to an OFF state;
each of the clocking signals is in the second condition for one of the
three clock phases, to isolate adjacent signals being propagated, is in a
third condition during another of the three clock phases, to initiate
propagation of an ON state from an adjacent cell, and is in a fourth
condition during the third of the clock phases, to preserve the state of a
cell from a prior clock phase; and
the three clocking signals are staggered in their times of occurrence of
the second clocking signal condition such that the second signal condition
is applied to a set of cells comprising every third cell, and the set is
advanced cell by cell across the array in synchronism with the clocking
signals.
15. A scrolling liquid crystal light modulator as defined in claim 14,
wherein:
the liquid crystal cells are ferroelectric smectic C (FSC) liquid crystals.
16. A scrolling liquid crystal light modulator as defined in claim 14,
wherein:
the array of liquid crystal cells is two-dimensional;
there are a pluraity of input liquid crystal cells and an equal plurality
of rows of clocked liquid crystal cells, each row having a plurality of
column positions at which cells are located; and
identical clocking signals are applied to liquid crystal cells having the
same column position.
17. A scrolling liquid crystal light modulator as defined in claim 16,
wherein:
the liquid crystal cells are ferroelectric smectic C (FSC) liquid crystals.
18. A scrolling liquid crystal light modulator, comprising:
a two-dimensional array of liquid crystal cells, including a plurality of
rows of cells, each row having an input cell at its first column position;
electrical means for applying binary input signals to the input cells in a
synchronous manner, whereby the input cells are selectively switched to an
ON condition dependent upon the states of the corresponding input signals;
means for applying a first clocking signal to the cells in the second
column position and to every third following cell in each row;
means for applying a second clocking signal to the cells in the third
column position and to every third following cell in each row;
means for applying a third clocking signal to the cells in the fourth
column position and to every third following cell in each row;
wherein the first, second and third clocking signals have a three-phase
cycle, and each input signal is applied to an input cell during at least
one of the three phases, and wherein the state of the input cell is
transferred by the clocking signals to the first and second cells of the
row, and then to the second and third cells of the row, and is thereafter
propagated from cell to cell along the row.
19. A scrolling liquid crystal light modulator as defined in claim 18,
wherein:
each of the first, second and third clocking signals includes a level of a
first type during one of the clock phases and a level of a second type
during at least one of the other two clock phases;
the level of the first type is effective to switch any cell to which it is
applied to an OFF state, and is employed to separate adjacent binary
signals being propagated across the array; and
the level of the second type is effective to propagate an ON state from an
immediately adjacent cell to the cell to which the clocking signal is
applied.
20. A method for scrolling data across an array in optical form, the method
comprising the steps of:
inputting binary electrical signals into an input liquid crystal cell;
selectively switching the input cell to an optical ON state dependent upon
the state of the corresponding input signals; and
applying clocking signals to a succession of liquid crystal cells following
the input cell, in such a manner as to propagate the optical state of the
input cell across the succession of liquid crystal cells, without the
input of electrical data signals to the array other than those applied
through the input liquid crystal cell.
21. A method as defined in claim 20, wherein the step of applying clocking
signals includes:
applying to the first cell following the input cell a signal of a first
level, the effect of which is to propagate the state of the input cell to
the first following cell;
applying to the second cell following the input cell a signal of the first
level, to propagate the state of the input cell from the first cell to the
second cell following the input cell; and
applying a signal of the first level to the third cell following the input
cell, to propagate the input signal from the second cell to the third cell
following the input cell, while simultaneously applying a signal of a
second level to the first cell following the input cell, to isolate the
signal propagated to the second and third cells from a new input signal
now impressed on the input cell. |
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Claims |
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Description |
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BACKGROUND OF THE INVENTION
This invention relates generally to electro-optical devices and, more
specifically, to electro-optical devices employing liquid crystals for the
optical storage of data. Optical data storage is effected by altering the
orientation of the liquid crystal molecules within a liquid crystal cell.
The orientation affects the polarization of light passing through the cell
and therefore provides a technique for reading the data optically. In a
number of applications there is a need to convert data from electrical
form to an optical form in which the data will be displayed or further
processed. One such application is in optical computing systems, in which
data elements in optical form are rapidly processed by optical logic
elements.
Processing data in optical form is a particularly attractive approach if
the data can be automatically scrolled across an optical matrix, since
many mathematical manipulations involving matrices can be performed more
simply if the data elements remain in matrix form. The conventional
electronic processing approach to matrix processing involves retrieving
data elements from an electronic memory matrix, and storing intermediate
and final results in the same or a different memory matrix. If the matrix
data elements are stored in optical form, two optical data matrices can be
directly interacted, in optical form, to produce a mathematical result.
Moreover, if one matrix can be shifted or scrolled, a matrix
multiplication can be performed directly, without converting the data back
into electrical form.
Another application for a scrolling optical storage device is the display
of data. Conventional liquid crystal displays employ matrix (x-y)
addressing methods to enter the data, whereby each liquid crystal element
is defined by a unique combination of an x-axis address and a y-axis
address, both of which must be selected to access the element. Such
displays often employ active devices, such as transistors, in the display
structure. When displayed data, which may be textual characters, are
scrolled in a conventional liquid crystal display, the data elements have
to be rewritten into appropriate locations for each incremental scrolling
movement. This requires relatively complex circuitry and is both costly
and inconvenient.
Therefore, there is a need in optical computing and related applications
for a spatial light modulator that has scrolling capability. The present
invention is directed to this end.
SUMMARY OF THE INVENTION
The present invention resides in a scrolling liquid crystal light modulator
for propagating data in optical form. Briefly, and in general terms, the
scrolling liquid crystal light modulator of the invention comprises an
array of liquid crystal cells capable of assuming different optical states
in response to electrical signals applied to the cells, and clocking means
for applying electrical signals to the cells, to shift the optical states
across the array.
More specifically, the array has at least one input liquid crystal cell and
the clocking means includes means for applying three clocking signals to
all of the liquid crystal cells except the input cell. Each clocking
signal is applied to every third liquid crystal cell, to propagate the
state of the input liquid crystal cell in a direction away from the input
cell. At the input end of the array, an input electrode receives a binary
input signal that has either a high voltage state, to input an ON
condition to the array, or a low voltage state, to input an OFF condition
to the array. The low voltage state may, in fact, be a negative voltage.
Adjacent to the input electrode are three clocking electrodes associated
with first, second and third liquid crystal cells. The voltage levels
applied to these three electrodes are stepped through three-phase cycles
in order to propagate the input signals across the array. At the same time
that an input signal is propagated into the first group of three cells,
the contents of the first group of cells is propagated into the second
group of three cells, and so forth.
In one illustrative embodient of the invention, during the first clocking
phase a new data bit is introduced at the input electrode, by placing a
high voltage level or pulse on the input electrode to indicate an ON
condition or a low, or negative, voltage level to indicate an OFF
condition.
It should be noted that the ON switching threshold and the OFF switching
threshold are not simple voltage thresholds, but also have a time
component. For example, switching a cell to the ON condition might be
effected by a high voltage level for a short period or by a lower voltage
for a longer period. In any event, for simplicity, switching to the ON
state is described here as being accomplished with a "high" switching
voltage level, and switching to an OFF state is described as being
accomplished with a "low" switching voltage level. As already mentioned,
the "low" voltage level may be of opposite sign to the high level.
The ON condition can correspond to a binary "1" or a binary "0" depending
on the convention chosen. In the first illustrative embodiment of the
invention to be described, the input data condition is maintained
throughout the first and second clocking phases. During the third clocking
phase, a low voltage is applied to the input electrode to reset the input
condition to "0" and to isolate successive input data bits.
During the first clocking phase, the first clocking electrode is held in a
low condition, and any ON condition at the adjacent input electrode is not
propagated beyond the input itself. During this first phase, the second
and third clocking electrodes are held in a medium voltage level. The
medium level sustains an already present ON state, and will propagate an
ON state, if one is present, from an adjacent cell, but will not otherwise
initiate an ON state. Therefore, if there was an ON state in the cell
corresponding to th first clocking electrode prior to the first clocking
phase, this ON state would be propagated to the cell corresponding to the
second clocking electrode.
In the second clocking phase, the first clocking electrode is raised to the
medium voltage state, the second is lowered to the low state and the third
is raised to the medium state. This propagates any ON condition from the
input cell to the first cell following the input cell, and simultaneously
propagates any ON state in the second cell to the third cell following the
input cell.
In the third clocking phase of the illustrative embodiment the first and
second clocking electrodes receive a medium voltage pulse and the third
clocking electrode receives a low voltage pulse. During this phase, the
input cell also receives a low voltage pulse. The effect is to propagate
any ON condition from the first cell to the second cell following
following the input cell. The input and third cells are switched to the
OFF or extinguished state. The overall effect of this clocking procedure
is to propagate the input state from cell to cell, in bands that are two
cells wide, separated by an extinguished band that is one cell wide.
There are other variations of this clocking scheme within the scope of the
invention. For example, in another embodiment data bits are not separated
by a low, or negative, pulse applied every third clock cycle. Instead, a
logical "zero" is represented at the input by a negative pulse and a
logical "one" by a high positive pulse. The input cell is then never
turned off except by the input of a "zero" bit. Bit separation is
maintained by applying a negative pulse to each successive clocked cell in
turn, as the data bits are propagated across the array.
In terms of a novel method, the invention comprises the steps of inputting
binary electrical signals into an input liquid crystal cell, selectively
switching the input cell between an optical ON state and an optical OFF
state in response to the input signals, and applying clocking signals to a
succession of liquid crystal cells following the input cell, in such a
manner as to propagate the optical state of the input cell across the
succession of liquid crystal cells. More specifically, in one embodiment
of the invention the step of applying clocking signals includes the steps
of applying to the first cell following the input cell a signal of a first
level, the effect of which is to propagate the state of the input cell to
the first following cell, then applying to the second cell following the
input cell a signal of the first level, to propagate the state of the
first cell to the second cell following the input cell. The next step is
that of applying signals of the first level to both the second and third
cells following the input cell, to propagate the input signal from the
second cell to the third cell following the input cell, while
simultaneously applying a signal of a second level to the first cell
following the input cell, to switch the first cell to an OFF condition and
to isolate the signal contained in the second and third cells from a new
input signal now impressed on the input cell.
Within the scope of the present invention, there are alternatives to the
specific clocking scheme described above. As already mentioned, instead of
applying a "low" or negative pulse to the input cell during every third
phase of operation, to isolate successive data bits, one can apply a low
or negative pulse during the first phase whenever the input data is a
logical "0". Isolation is still provided by applying a low voltage lvel to
the first cell following the input cell during the first clocking phase.
Another variation is to omit any pulsing of the second cell during the
first clocking phase. At this point, the cell already has data in it, i.e.
it is in the ON state if the data is a logical "1," and no pulsing is
needed to sustain the ON state. Further propagation is effected by pulsing
in the adjacent third cell. Similarly, one can omit pulsing of the third
cell during the second clocking phase. Propagation into the fourth cell
occurs as a result of applying a medium pulse to the fourth cell during
the third clocking phase. Moreover, it is desirable to avoid two
successive medium pulses to the same cell, to minimize the risk that the
they may have the same effect as one larger pulse that would switch the
cell to the ON state.
More specifically, in another illustrative embodiment of the invention the
input cell is switched either ON or OFF in the first clocking phase,
depending on the state of the input bit applied to the input cell. During
this first phase, the first clocking cell is pulsed low, or negative, to
ensure data bit separation with an OFF condition. In the second phase, the
input cell has no voltage signal applied to it and the first clocking cell
is pulsed with a medium voltage level, to propagate the content of the
input cell into the first cell. At the same time, the low or negative
condition is applied to the second clocking cell, to maintain separation.
In the third clocking phase, the input cell remains at zero voltage level,
the first clocking cell is also switched to a zero voltage level, thereby
sustaining its previous condition, and the second clocking cell is pulsed
with a medium voltage, allowing the content of the first clocking cell to
propagate into the second. In the next phase, which is another "first"
phase, the second clocking cell has a zero voltage applied to it and the
third has a medium voltage pulse, thereby propagating the content of the
second cell to the third. The first clocking cell is pulsed with a low or
negative signal again, for data separation, and the input cell is pulsed
with either a positive or a negative data phase to input the next data
bit.
In a preferred form of the invention, the array of liquid crystal cells is
two-dimensional and there ar multiple input electrodes, to which multiple
input signals are simulaneously applied.
It will be appreciated from the foregoing that the present invention
represents a significant advance in the field of optical data processing.
In particular, the invention provides a technique for modulating an
optical device with a two-dimensional matrix of data, and rapidly
scrolling the data in optical form across an array. Other aspects and
advantages of the invention will become apparent from the following more
detailed description, taken in conjunction with the accompanying drawings.
BRIEF DESCRIPTION OF THE DRAWINGS
FIG. 1 is a diagrammatic view of a two-dimensional spatial light modulator
in accordance with the invention;
FIGS. 2a-2f together illustrate how the array of the invention is
controlled by three-phase clocking signals.
FIG. 3 is graph showing the variation of optical transmission
characteristics with voltage in a typical bistable liquid crystal cell;
FIG. 4 is a graph showing the voltage-time relationship for switching a
liquid crystal cell; and
FIGS. 5a-5d are data and clocking signal waveforms for an alternative
clocking scheme in accordance with the invention.
DESCRIPTION OF THE PREFERRED EMBODIMENT
As shown in the drawings for purposes of illustration, the present
invention is concerned with devices for scrolling of data in optical form,
for use in optical computing and related applications. Prior to this
invention, there has not been any convenient technique for rapidly
scrolling of data in optical form.
In accordance with the invention, binary signals in electrical form are
used to control a liquid crystal modulator array, and the binary signals,
encoded as different orientations of liquid crystal molecules, are
scrolled across the device by means of clocking signals applied to cells
of the array. As shown in FIG. 1, the device of the invention in its
preferred form is a two-dimensional array of liquid crystal cells. The
array is indicated by reference numeral 10 and the individual cells by
reference numeral 12. The array 10 has an input end 14 into which binary
data signals in binary form are input, as indicated at 16. A data signal
input at one row of the array 10 is propagated sequentially across the row
of the array to the opposite side. The liquid crystal cells 12 are
controlled by clocking signals on three clocking signals lines 18a, 18b
and 18c, which are applied to clocking electrodes in each of the cells.
The input signals are used to modulate the state of an input liquid crystal
cell, in an input zone or region indicated at 19. FIG. 1 shows five
additional data positions in each row of the array 10, indicated at 20.1,
20.2, 20.3, 20.4 and 20.5. Each position in the array has three associated
cells, indicated at 20.1a, 20.1b, 20.1c, and so forth to 20.5c. Clocking
signals are applied to these cells over clock signal lines 18a, 18b and
18c. That is to say, line 18a is connected to electrodes located adjacent
to all of the cells designated with an "a" suffix, line 18b is connected
to electrodes adjacent to all of the "b" cells and line 18c is connected
to electrodes located adjacent to all of the "c" cells.
By applying an appropriate sequence of clocking signals to the lines 18a,
18b, and 18c, as will be discussed more fully with reference to FIG. 2,
data stored in the input cells of the device can be transferred to the
first position 20.1, and data in the first position can be transferred to
the second position 20.2, and so forth, the whole device functioning very
much like a shift register, but with the data stored as different
orientations of the liquid crystal molecules, so that it may be read
optically.
FIG. 3 shows a typical relationship between the voltage applied to a
bistable liquid crystal cell and the resulting optical transmission
characteristics. As the voltage is first applied and increased positively,
the optical transmission increases only slightly from zero. When a
threshold voltage +V.sub.T is reached, the optical transmission of the
cell jumps to a much higher value and remains there even when the voltage
is subsequently reduced to zero or below. The optical transmission of the
cell is not significantly reduced again until the voltage is reduced to a
negative threshold level -V.sub.T, at which point the optical transmission
falls to zero and remains there until the voltage is raised to +V.sub.T
again. In the context of this hysteresis curve, a "high" voltage pulse is
one above V.sub.T and a "low" voltage pulse is one of a higher negative
value than -V.sub.T. A "medium" pulse is a positive pulse lower than
+V.sub.T.
FIG. 3 is not a completely accurate depiction of the behavior of a bistable
liquid crystal cell, because the voltage required to effect a transition
in optical properties depends on the duration as well as the magnitude of
the applied pulse. As shown in FIG. 4, a cell can be switched optically
with a one-volt pulse lasting 1,000 microseconds or so, but the same cell
can also be switched with a ten-volt pulse lasting only several
microseconds.
An important aspect in the construction of the array of the invention is
the selection of a suitable liquid crystal cell that permit propagation of
its ON state from one cell to an adjacent cell. One type of cell that
meets these requirements is the ferroelectric smectic C (FSC) liquid
crystal cell, of the type described in a paper entitled "Submicrosecond
Bistable Electro-optic Switching in Liquid Crystals," by Noel A. Clark and
Sven T. Lagerwall, published in Applied Physics Letters, 36(11), pp.
899-901, 1 June, 1980.
The devices described in the paper meet the principal requirements for the
scrolling array application of the invention, such as microsecond
switching speed, bistability, domain wall propagation, and appropriate
threshold behavior. The threshold behavior of the device determines the
conditions by which the ON state of a device cell can be propagated to an
adjacent cell. Basically, the invention requires that, when a cell is in
the ON state and an adjacent cell is pulsed to an intermediate voltage
level, the ON state will propagate to the adjacent cell. The FSC cells
have the necessary domain wall propagation properties for this action to
occur.
A necessary property of the selected liquid crystal cell is that there be
associated with it three bias levels having three distinct functions. A
high bias level will initiate switched to the ON state of the device. A
low bias level will immediately extinghish the ON state. And finally, an
intermediate bias state will result in an ON state only if the immediately
preceding adjacent cell is in the ON state. The intermediate bias level
permits propagation of data from one cell to the next across the array.
FIG. 2 shows in more detail how the array 10 is clocked to achieve
scrolling of data entering the array at the input lines 16. FIG. 2a shows
the conditions during the first phase of the clocking cycle, with a data
bit bit applied to input line 16 in the form of a high bias voltage,
causing an ON condition in the input cell. The first clocking signal, on
line 18a is in a low condition during this phase. The other signals on
lines 18b and 18c are in the medium condition, but have no effect in this
first clocking cycle. The low condition on line 18a ensures that the data
ON bit stored in the input zone remains only in that zone for the first
phase.
In the second phase of the clocking cycle, shown in FIG. 2b, the levels on
lines 18a, 18b, and 18c are switched to medium, low and medium,
respectively, and the input line remains high. The medium level on line
18a results in the propagation of the ON condition from the input cell to
the first cell, located beneath the first clocking electrode associated
with line 18a. The low condition on line 18b ensures that the previous
state of the cell beneath the first clocking electrode is not transferred
any further.
In the third phase of the clocking cycle, shown in FIG. 2c, the clocking
signals on lines 18a, 18b and 18c are switched to medium, medium, and low,
respectively, and the input line is pulsed to a low condition to turn it
off and isolate successive bits of input data. This set of conditions
results in the propagation of data from the input cell to the first
following cell, and from the first following cell to the second. The low
signal applied to the third cell ensures an OFF condition in that cell for
the third phase of the cycle.
FIGS. 2d-f show the sequence of events during the next clocking cycl | | |
