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Патент USA US3067423

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Dec. 4, 1962
Filed April 27, 1960
2 Sheets-Sheet l
Dec. 4, 1962
Filed April 27, 1960
2 Sheets-Sheet 2
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United States Patent O??ce
Liselntte Fischle, Sindeifingen, Werner Kulcke, Boblingen,
Paul Schweitzer, Sindei?ngen, and Jurgen Trapp, Bob~
lingen, Germany, assignors to International Business
Machines Qorporation, New York, N.Y., a corporation
of New York
Filed Apr. 27, 1960, Ser. No. 25,080
Ciaims priority, appiication Germany May 9, 1959
Patented Dec. 4, 1962
on information having the form of electric pulses, where
in on one or a plurality of electro-optically active crystals
penetrated by a ray beam and arranged between cross
connected polarizers there are arranged, at opposite sur
faces thereof penetrated by said radiation, electrodes and
counter-electrodes which due to their selective connec
tion with an electric voltage source in?uence the ray
beam penetrating them in such a manner that the projec
tion thereof, depending on the electrodes selected, repre
Particular advantages
5 Claims. (Cl. 340-334)
of this arrangement are the very short adjusting time,
the very high light output due to the use of an external
The present invention relates to character display sys
light source, and the possibility of displaying a great
tems and particularly to improved high-speed character
number of alphanumerical characters with a low number
display systems employing arrays of electro-optically ac’
15 of controllable element with good contrasts. Moreover,
tive light controlling devices.
such systems are extremely small and cheap to manu
In data processing machines, the problem of the optical
facture due to the low number of required structural ele
display of intermediate and ?nal results is of outstanding
ments and the possibility of using printed circuits.
importance. Even more important is the problem of the
Another object of the invention is to provide an ar
output devices which register the results and, if necessary,
print explanatory passages and should be adapted to the 20 rangement of the type described which utilizes a minimum
number of character forming elements.
operating speed of the computing systems, which is most
A further object of the invention is to provide an ar
ly very high. In order to meet the great number of dif
rangement of the type described in which mutual inter
ferent requirements to be ful?lled by display and output,
ference between the character forming elements is re
the said problems have so far been realized in separate
25 duced.
Still another object of the invention is to provide an
For the display of information which is mostly present
arrangement of the type described in which the quality
in the form of electric signals, it has so far been cus
of the surface ?nish of the crystals need not be high.
tomary to use glow lamp ?elds which, however, have the
A further object of the invention is to provide an ar
disadvantage of being very di?icult to survey. In order
to avoid this disadvantage of di?icult observation, it has 30 rangement of the type described which is not affected
by humidity or other advance atmospheric conditions.
already been proposed to use mechanically movable digit
A further object of the invention is to provide an im
carriers as display means. However, such systems have
proved electro-optical character display system.
not proved useful for the purposes of data processing
In a particularly simple embodiment of the invention,
machines because of the great number of structural ele
ments to be mechanically moved and the susceptibility 35 the individual electrodes are arranged in the form of line
elements by which it is possible to compose all of the
to trouble caused thereby as well as their inertia. More
characters to be displayed. It has proved particularly
over, it has been proposed to use display devices consist
useful that the entity of all electrically selectable elec
ing of a great number of selectively operable incandes
trodes provided for each display position is mounted in
cent or glow lamps which through slots or masks project
one single plane perpendicular to the direction of irradia
specially designed or normal characters to a ground-glass
tion on one or a plurality of electro-optically active crys
screen. However, in view of their long adjusting times
tals. Accordingly, it is possible to arrange several crystals
and their relative low light output, such arrangements are
in one plane side by side and to mount the electrodes re
not expected to succeed in practice. An additional dis
quired for displaying a character on this crystal surface
advantage of these arrangements is their high susceptibil
composed in the manner of a mosaic. It may, however,
ity to trouble due to the extremely large number of in
also be advisable to arranged the electrically selectable
dividually selectable incandescent or glow lamps used
electrodes provided for each display position in a plu
therein, the complicated control logic and the relatively
rality of planes lying one behind the other perpendicular
great space requirements. A further approach to the
to the direction of irradiation and on a plurality of
problem, which has been used in the past, is a specially
electro-optically active crystals or groups of crystals in
designed cathode ray tube having a phosphorescent screen,
wherein a series of successive de?ection means, electronic
lenses and masks serve to display the characters to be
represented on the screen of said tube. Although that
arrangement has a very high display speed and a good
light output, it is so expensive that it is uneconomic for
most applications.
The output‘ arrangements used up to now have mostly
been mechanical printing units which, on the one hand,
10 sents a predetermined character.
such a manner that a mutual electric in?uence of overlap
ping or very closely spaced electrodes is avoided. It is
obvious that to each of these planes provided with selec
tively controllable, line-shaped electrodes there is also
associated a transparent counter-electrode which is pref
erably areal. According to another embodiment of the
invention, the counter-electrodes are formed of a plu
rality of selectively electrically controllable, entirely or
partly transparent, electrically conductive elementary
could not be used as display means and, on the other 60
areas which allows a partial activation of the line-shaped
hand, did not operate satisfactorily in many applications
in view of their high technical requirements and their
relatively low printing speed.
An output unit having a very high operating speed
consists of the above mentioned cathode ray tube in con
nection with a xerographic printing device. However,
because of its extremely high cost and its relatively great
susceptibility to trouble, this arrangement is uneconomic
for most applications.
In order to avoid these disadvantages, the present in
vention has for an object the provision of an arrange
ment for the optical display of printed characters based
electrodes arranged on the opposite crystal surface in
such a manner that the number of electrodes required
for representing all characters is reduced.
Thus it is possible to subidivide the counter-electrode,
which consists of a transparent area and comprises a
whole character ?eld, into two rectangular segments, so
that e.g. a circular electrode arranged on the other crystal
surface becomes effective as a semicircular electrode.
has proved particularly useful to make the counter-elec
trodes, too, in the shape of lines and to make them assume
the shape of the electrodes arranged on the crystal surface
facing them. In that arrangement, the line of the counter
electrode may either be uninterrupted or again subdivided
into individual selectively controllable elements. In a
particularly advantageous embodiment of the invention,
the line-shaped counter-electrodes mounted on a crystal
surface perpendicular to the direction of irradiation are
arranged in such a manner that they coincide With the pro
jection of the line-shaped electrodes arranged on the op—
tion they have no noticeable in?uence on the path of
In order to reduce the number of electrodes required
for representing a given number of characters, a special
design of character representation is employed. For that
purpose, there are provided on one 'or a plurality of cry-s—
tals a number of individually controllable electrodes hav
ing the form of straight and bent lines which is smaller
than the number of characters to be represented. By a
range the line-shaped counter-electrodes mounted on a
crystal surface perpendicular to the direction of irradia 10 suitably controlled selection of certain electrode combina
tions, the corresponding characters are rendered visible
tion in staggered relationship to the projection of the line
on the ground-glass screen. It has proved to be of par
shaped electrodes mounted on the opposite crystal surface
ticular advantage to arrange on the controllable crystals
so that the electro-optically modi?ed crystal regions form
posite crystal surface. It is, however, also possible to ar
eifecting the display of the characters line-shaped elec
an acute angle with the rays penetrating the crystal, so that
the lighted area approximately corresponds to the amount 15 trodes in the shape of two superimposed circles, an up
of staggering.
right cross bisecting said circles and a concentric diagonal
cross as well as a rectangle surrounding the aforemen
It has also proved to be of particular advantage that
tioned electrodes.
the crystals provided with electrodes are individually or
The path of radiation in?uenced by the above described
in groups brought into an immersion bath having a high
dielectric strength. This method has the advantage that 20 means is rendered visible, e.g., through a Fresnel lens (an
nular lens), through a ground-glass screen, through ?uo
the electrodes which are individually and separately con
rescent layers or by the illumination of photosensitive
trolled may be arranged in a very closely spaced relation
substances. By using photosensitive substances or by the
ship without the danger of an electric breakdown to non
additional use of Xerographic methods, respectively, it is
controlled electrodes on the application of high electric
voltages. A further advantage obtained by using an im 25 possible to employ the arrangement of the present inven
tion successfully as a high-speed printer.
mersion bath consists in the fact that it is possible to se
The electro-optically active crystals employed in the
above described arrangement may preferably comprise
compounds of the type of the primary alkaline phos
mains without effect, so that crystals having not ?nely
worked surfaces may be used. That eliminates the neces 30 phates and the isomers thereof, for example NH4I-I2PO4,
sity of polishing the crystals or taking care of the quality
KH2PO4, KD2PO4, the alkaline tartrates and the isomers
of their surfaces in any other manner. In order to reach
thereof, for example Rochelle salt C4H4O6NaK or the
barium titanates and the isomers thereof, for example
this object, it is necessary that the index of refraction of
BaTiO3. The compensation crystals to be used in accord
the immersion ?uid correspond about to the mean value
35 ance with the invention preferably consist of compounds
of the refractive indices of the immersed crystal.
An additional advantage may be reached with immer
of the types NH4NO3, K2S206, IiHCzOQ, Na3PO4,
sion, i.e. it is possible in this manner to dissipate the heat
or rutile.
The foregoing and other objects, features and advan
produced in the crystal. This heat dissipation may be fur
tages of the invention will be apparent from the follow
ther improved by moving the immersion ?uid with re
spect to the crystal, which may be achieved e.g. by ?ow 40 ing more particular description of preferred embodi
ments of the invention, as illustrated in the accompany
ing or forced rotating of this ?uid. If it is desired in the
lect an immersion ?uid having such an optical index of
refraction that any unevenness of the crystal surface re
arrangement of the invention to use electromagnetic ra
ing drawings.
diations of a given frequency range, a ?ne-granular sub
In the drawings:
stance of the nature of a Christiansen ?lter may be added
FIG. 1 is a diagrammatic representation of an electro
to the immersion ?uid. A further advantage of the im 45 optical shutter, illustrating the basic phenomena utilized
in the invention.
mersion bath resides in the fact that it is also possible to
FIG. 2 illustrates one embodiment of the arrangement
use hygroscopic or air-sensitive crystals.
according to the invention, comprising a plurality of
It is well known that for achieving a high contrast of
electrodes mounted on a corresponding plurality of sep
the characters to be represented the occurrence of diver~
gent radiation should be avoided as far as possible. For 50 arate crystals.
FIG. 3 shows an arrangement designed in accordance
this purpose, honeycomb diaphragms for eliminating any
stray light causing lightening of the background are pro
with the invention for displaying specially designed char
acters by means of twenty-seven selectively controllable
electrodes arranged on two crystals succeeding each
In order to make full use of the divergent radiation em 65 other within the path of radiation.
FIGS. 4 and 5 are a schematic representation of the
anating from a point-shaped light source, it is also possible
electrodes used in the arrangement of FIG. 3.
to provide birefringent compensation crystals the thick
FIG. 6 graphically represents certain of the characters
ness and refractive index difference of which are so se
which can be displayed by means of the arrangement
lected that the phase difference occurring in the control
lable crystals, when in their uncontrolled condition and 60 shown in FIGS. 3, 4 and 5.
FIG. 7 is a diagrammatic fragmentary view of another
in the presence of divergent rays due to birefringence, is
embodiment of the invention in which the crystals are
vided at one or a plurality of positions in the path of ra
A particularly simple embodiment of the arrangement
according to the invention is obtained by providing a num
immersed in a suitable immersion bath.
Referring to FIG. 1, there is shown a basic arrange
ber ‘of crystals arranged successively in the radiation path 65 ment for utilizing the electro-optical effect, which in the
corresponding to the number of characters provided for
each display position, which crystals, besides the counter
electrodes, include line-shaped electrodes corresponding
pertinent technical literature is referred to as an electro
optical shutter. In this ?gure, an electro-optically active
crystal 5 is arranged between a polarizer 4 and an ana
lyzer 8. The forward directions of the polarizer 4 and
to the shape of the individual characters. In this arrange
of the analyzer 8 form an angle of 90°, as indicated by
ment, each crystal carries a controllable electrode repre
the double arrows. In front of analyzer 8, there is
senting a given character. If a given electrode is con
arranged a ground-glass screen 9. The light coming
nected to a voltage source, the image of the respective
from a bright, point-source of light 1 is set parallel by
character will appear on the ground-glass screen. The
a collimater lens 2 and directed through the arrangement
electrodes are so designed that in their unselected condi 75 as a parallel ray beam 3. In the embodiment of FIG. 1,
the crystal 5 is an optically uniaxial ammonium-dihydro
gen-phosphate crystal cut perpendicularly to its optical
axis. Consequently, the polarization state of the light
passing through the crystal in the direction of its optical
axis is not changed in the ?eld-free crystal. Therefore,
normally no light will reach the ground-glass screen 9
through the crossed polarizers 4 and 8. The irradiated
Referring to FIG. 2, there is shown an arrangement
wherein the radiation emanating from a point-source of
light 1 passes through a condenser lens 32. Beyond the
lens 32 there is arranged an apertured diaphragm 33
beyond which an additional lens 2 is provided for col
linearizing the light. Beyond this lens 2 there is arranged
a polarizer 4 which passes only light having the direction
of polarization shown by the double arrow. The linearly
polarized light leaving the polarizer 4 passes through ten
surfaces 5a and 5b of the crystal 5 are covered in a well
ltnown manner with semitransparent electrodes 6 and 7,
one of which is grounded, whereas the other one may 10 crystals 56 to 59 (only ?ve of which are shown in FIG. 2
in order to simplify the drawing) which besides a trans
be connected with an electric voltage source 10 through
parent counter-electrode 60 to 69 covering an entire crystal
a switch 11. Due to the electro-optical effect, the crystal
surface, each have one of ten different electrodes 70‘ to 79
is thereby rendered optically anisotropic in the direction
having the shape of the digtis “l,” “2,” “3” . . . “9” and
of irradiation and changes the polarization state of the
light beam originally linearly polarized in the forward 15 “0.” Beyond the crystal '59 there is arranged an analyzer
8 the forward direction of which forms an angle of 90°
with the forward direction of the polarizer 4. The crys
tals 50 to 59 consist of compounds cut perpendicularly
direction of the polarizer 4. Depending on the voltage
applied to the crystal, it is possible to direct more or less
light through the analyzer 8, so that the ground-glass
to the optical axis and optically isotropic in that direction,
so that the polarization state of the light is not changed
in these crystals in the ?eld-free condition thereof. In
this manner, no light will pass through the analyzer 8
to the ground-glass screen 9 arranged beyond the latter.
screen 9 is lighted as a function of the applied voltage.
The maximum brightness, which theoretically corre
sponds to one half of the light directed into the arrange
ment, is obtained when the voltage applied across the
crystal 5 equals the M2 voltage characteristic for the
The electrodes 70 to 79 of the crystals 50 to 59‘ are provid
crystal. As is known, the M2 voltage is the voltage in
the presence of which the path lengths of the two radia 25 ed with conductors 80 to 89 by means of which they may
be selectively connected through the high voltage power
tion components in the direction of the axes of the index
ellipsoid of the crystal on passing through the crystal
supply unit 90 to electric voltages. The semitransparent
have a path length difference of one half wave length.
Exemplary A/ 2 voltages are:
counter-electrodes 60 to 69 provided on the opposite
crystal surfaces are grounded through the conductor 92.
30 The voltage supply unit 90 is controllable by means of a
device 93 to which the information is supplied via the
conductors 94 in the form of electric pulses. If now a
Ammonium-dihydrogen-phosphate ____ _.. 8.75 kv.,
Potassium-dihydrogen-phosphate ______ _.. 7.1 kv.,
and for
Potassium - dihydrogen - phosphate substi
tuted with heavy water ___________ __
voltage is applied through the voltage supply unit 90 to
one of the electrodes 70 to 79, the crystal region between
the areal counter-electrode and the electrode to which a
2.5 kv.
voltage is applied becomes optically anisotropic, so that
the polarization state of the light passing through this
crystal region is changed. The light the polarization state
As substantial brightening effects occur already at
lesser path length differences than one half wave length,
02-fold values of the above indicated >\/2 values may
also be sufficient in certain circumstances.
The arrangement shown in FIG. 1 is based on the
assumption that the crystal 5 in its voltage-free condition
is isotropic in the direction of irradiation. It is, how
ever, also possible to use crystals which are birefringent
in the direction of irradiation already in the voltage-free
condition. In that case, a second crystal may be placed
in front of or behind the electro-optically active crystal
of which has been changed in this manner can now pass
through the analyzer 8, so that the ?gure corresponding
to the electrode to which a voltage is supplied is rendered
visible on the ground-glass screen 9. Due to the fact that
the electrodes representing the individual characters con
sist of very thin conductors and hardly obstruct the beam
passing through the crystal, the brightness of the digits
projected to the ground-glass screen is very great. More
over, the ?gure appearing on the ground-glass screen is
not disturbed by the line-shaped electrodes arranged on
for cancelling the original birefringency.
The effect described in the above example is composed
of two partial effects: The direct action of the electric
?eld on the electron con?guration of the crystal building
blocks (direct electro-optical effect) and the effect see
the other crystals. In order to avoid stray light disturbing
the contrast of the image, the honeycomb diaphragm 95
is arranged between the analyzer 8 and the ground-glass
ondarily produced by the piezoelectric deformation
screen 9.
(elasto-optical effect). Of these, the former is inde
pendent of frequency in the range of radio waves, where
displaying specially designed representations of characters,
Referring to FIG. 3, there is shown an arrangement for
kilocycles per second. Of the entire electro-optical effect,
wherein the number of controllable electrodes is substan
tially lower than the number of characters to be dis
played. The light from source 1 is projected through the
condenser lens 32 to the apertured diaphragm 33. The
approximately 70% are due to the direct, 30% due to
the elasto-optical effect. If only a very small part of
the crystal surface is covered with electrodes and the
ing through the polarizer 4, the crystal 96, the crystal 97,
as the latter will disappear above the mechanical reso- ,
nant frequency of the crystal, which for a crystal having
a size of approximately 1 cm. is in the order of 100
predominant part is free of electrodes, the electrode-free
regions will obstruct the piezoelectrical deformations and
thus cause the elasto-optical effect to disappear. If in
this case the frequency of the applied voltage is not just
equal to one of the mechanical inherent frequencies of
the crystal, brightening will occur in an arrangement
according to FIG. 1 only immediately between the elec
trodes and within a narrow margin of approximately
0.5 mm. about the electrodes. According to the present
invention, this effect is utilized for displaying alpha
numerical characters. Of course, the arrangement illus
trated in FIG. 1 may also be designed with a plurality
of successive crystals without the individual crystals dis
turbing each other.
image of this apertured diaphragm is converted by the
collimator lens 2 into a parallel path of radiation 3 pass
the analyzer 8 and the honeycomb diaphragm 95. The
crystals 96 and 97 are provided with individually con
trollable electrodes 120 to 127 and 101 to 119 which,
depending on their selective control, in?uence the light
beam in such a manner that one of the characters repre
sented in FIG. 6 will appear on the ground-glass screen 9.
The electrodes 12% to 127 arranged on the crystal 96
correspond to the electrode arrangement shown in FIG. 5
and are connected through eight separate conductors 178
to 177 to the voltage supply unit 90. On the opposite
surface of the crystal 96 there is provided the same ar
rangement of electrodes (not visible in FIG. 3) with the
exception that those electrodes are commonly connected
and grounded via one single conductor 180‘. The elec
75 trodes 101 to 119 arranged on the crystal 97 correspond
to the electrode arrangement shown in FIG. 4 and are
c! inected through nineteen conductors 151 to 169 to the
voltage supply unit 99. On the rear side of this crystal
there is provided the same arrangement of electrodes with
the exception that there the electrodes are connected in
common and ‘grounded via the conductor 181. For the
control of the voltage supply unit 90 there is provided a
control unit
to which the information to be displayed
of the electrodes, which decreases the over-all size of the
apparatus and provides better resolution of the displayed
By selection of a fluid having an index of refraction
which is comparable vwith that of the crystals, a higher
degree of surface roughness of the crystals can be tolerat~
ed. Additionally, by dispersion of suitable granular ma
terial therein, a Christiansen ?lter effect can be obtained
to render the apparatus more effective in a given portion
is applied in the form of electric pulses through the lines
9%. If a given character is supplied to the control unit 10 of the spectrum. Immersion of the crystals also removes
any adverse effects thereon due to atmospheric conditions.
93 in the form of electric pulses, the voltage supply unit
a ii is operated in such a manner that it supplies a voltage
A further advantage of immersion of the crystals is that
the heat energy generated therein is readily dissipated by
to all of those electrode elements 101 to 127 which are
the bath. Natural convection can be used, or as shown
required for the optical representation of that character.
if e.g. the digit “8” isapplied in the form of electric 15 in FIG. '7, a forced circulation may be obtained by use of
pulses through the seven conductors 94 to the control unit
93, the voltage supply unit 98 is set up so that it supplies
a voltage to the conductors leading to the electrodes 120 to
127. As the counter-electrode is connected to ground
a circulatory pump 195, driven by a suitable motor 197,
and connected to the tank or container by conduits 198
and 199.
It is, of course, possible in the instance where multiple
potential, an electric ?eld is produced between the elec 20 displays are provided, to utilize a common bath for all
of the crystals, since there is no interaction. Also, it
trodes and counter~electrodes which in?uences the crystal
is apparent that in the case of multiple displays, many
regions included therein in such a manner that they be
of the components may be common to more than one set
come optically anisotropic and which changes the polariza
of crystals, for example, the light source, collimating
tion state of the linearly polarized radiation passing
through the polarizer 4. This radiation, which when 25 lenses, polarizers, analyzers, honeycomb ?lter and display
passing through the uninfluenced crystal regions has such
From the foregoing, it is apparent that the present in
a position with respect to the forward direction of the
vention provides an improved electro-optical display sys
analyzer that no light whatever can pass, is so changed
in the regions which have become anisotropic that it can
pass through the analyzer 8 and causes the image of the
electrodes 12-6 to 1.217 shown in FIG. 5 to become visible
tem which utilizes a minimum number of character form
on the groundglass screen 9 as a light image of the digit
In this connection it should be noted that the elec
trodes provided on the two crystals are so thin and in the
interference therebetween.
ing elements, which by location on a plurality of succes
sively disposed optically active crystals, reduces the mutual
Also provision of such an ar
rangement in an immersion bath of high dielectric strength
permits closer spacing of electrodes/ with resultant de
ncnselected condition disturb the path of radiation to such 35 crease in size and increase in resolution, reduced tolerance
of crystal surface ?nish, and better heat dissipation.
a small extent that they do not become visible on the
While the invention has been particularly shown and
groundglass screen 9. For the representation of other
described with reference to preferred embodiments there
characters, electrodes of the crystals 96 and/ or the crystal
of, it will be understood by those skilled in the art that
97 are simultaneously connected to the high voltage
various changes in form and details may be made therein
source, so that the resulting light image represents a pre
without departing from the spirit and scope of the inven
determined character. Thus, e.g., the digit “9” is repre
sented by applying a voltage to the electrodes 120‘ to 123,
What is claimed is:
Mid, 125 and 126. In the same manner, the digit “3”
1. An electro-optical character display system com
is represented by supplying the electrodes 101, 102, 113,
prising a plurality of electro-optically active crystals dis
124», i.- and 126 with voltage, and the digit “6” is repre
posed between crossed polarizers and traversed by a beam
sented by supplying the electrodes 120, 123, 109, 110 and
of nadiation, a plurality of character segment forming
125:‘ to 127 with voltage. In a similar manner, the letter
electrodes disposed on one face of each of said crystals,
“A” is represented by supplying the electrodes 108, 199,
116), 12s, 1123, 143d, 1%, 114 and 118 with voltage, the
letter “B” is represented by supplying the electrodes 108
to 111, 101, 12%, 121, 113, 124, 125 and 167 with voltage,
the letter “C’ is represented by supplying the electrodes
1&9, 11¢}, 12%,
125 and 12.6 with voltage, etc. Cer
tain of the characters are shown in H6. 6, and it will be
a counter electrode disposed on the other face of each
of said crystals, means for selectively connecting said elec
trodes and counter electrodes across a source of potential
whereby selected portions of said beam are in?uenced dur
ing passage through said crystal, means for receiving said
selected portions of said beam, and immersion bath means
apparent from these examples that well-formed numerals, 55 for immersing said crystals in an immersion bath ?uid
having a high dielectric strength.
letters, and special symbols can. be readily formed by en
2. An electro-optical character display system as
ergizaticn of selected electrodes.
claimed in claim 1, in which the immersion bath ?uid has
FIG. 7 illustrates one manner in which the electro
an index of refraction ‘substantially the same as the mean
optical active crystals such as 96, 97, may be immersed
in a suitable bath. The remainder of the apparatus is 60 index of refraction of said crystals.
3. An electro-optioal character display system as
not shown, in order to simplify the drawing, but can be
claimed in claim 1, in which the immersion ?uid is cir
arranged as shown in FIG. 6.
Crystals 96 and 97 are suspended, by supporting means
culated in said immersion bath to remove heat produced
in said crystals.
not shown, in a container 199, at least two walls 191
4. An electro-optical character display system. as
and 193 of which are transparent to the radiant energy.
claimed in claim 1, in which the immersion ?uid con
Suitable feed-throughs or bushings permit the wires from
tains ?ne granular substance to form a Christiansen ?lter,
the electrodes
counter-electrodes to pass out of the
whereby only radiation of a predetermined spectral re
container. The container is ?lled, at least sufficiently to
gion is permitted to pass.
fully immerse the crystals, with a liquid of high dielectric
5. An electro-optical character display system, comprise
strength, such as a suitable oil, having optical properties 70
ring at least one electro-optically active crystal disposed
ich permit passage of .he radiant energy with the least
between crossed polarizers and traversed by a beam of
.e loss.
The use of a ?uid of high dielectric strength lessens
the chance of breakdown occurring between electrodes at
radiation, an electrode disposed on one surface of said
crystal and a counter electrode disposed on the other sur
different potentials, ‘therefore permitting closer spacing
face of said crystal, at least one of said electrodes being
in the form of a line segment representative of at least
aportion of a character, means for selectively connecting
due to birefringence in the controllable crystals when
in their uncontrolled condition in the presence of di
said electrode and said counter electrode ‘across a source
Vergent rays is cancelled,
of potential whereby a selected portion of said beam is
in?uenced during passage through said crystal, and means
References Cited in the ?le of this patent
‘for receiving said selected portion of said bearn, further
compnslng at least one birefringent compensation crystal
provided in ‘a divergent path of radiation, the thickness
and refractive index difference of said compensation crys-
tals ‘being selected so that the phase difference occurring 10
Boswau ______________ __ Jan. 3, 1939
Wiley _______________ __ Feb. 12, 1957
Anderson ____________ __ Mar. 8, 1960
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