FR2634566A1 - Method and device for fixing the image of an electric field in a material - Google Patents

Abstract

Method for fixing the image of an electric field in a material comprising molecules endowed with electrooptic activity, characterised by the following steps: a) the temperature is raised, in at least one zone of this material, beyond a transition level above which the orientation of these molecules inside the support can be modified by the action of an electric field; b) in this zone, an orienting or writing electric field is applied, the direction and/or strength of which are determined as a function of optical anisotropy characteristics which are desired to be obtained; and c) during the operation b, the temperature of the said zone is lowered below the transition temperature in order to fix the characteristics of the applied field in the material.

Description

METHOD AND DEVICE FOR FREEZING
THE IMAGE OF AN ELECTRIC FIELD IN A MATERIAL
The present invention relates to a method and a device for freezing the image of an electric field in a material and to the products and applications which result therefrom.

It is based on the observation of the properties of certain electro-optical polymer materials.

Crystals have long been known, the optical properties of which are liable to be modified by making an anisotropy appear in the presence of an electric field. These materials are generally gathered under the name of non-linear optical materials. In practice, the anisotropy produced in such materials in the presence of an electric field is manifested by the change in the refractive index of the material in at least one direction. Two types of effect are classically distinguished in this regard. In the first, the phase delay created between the components of the electric field along two axes of incident light polarized as a function of the electric field to which the material is subjected varies linearly with the intensity of the field. This effect is called the Pockels effect. In the other type of effect, the phase delay varies according to the square of the intensity of the electric field. This effect is known as an effect
Kerr.

Different kinds of materials are capable of providing crystals having the properties mentioned above. These crystals, however, are not always easy to use or may be available only in relatively small dimensions. Now, we have seen the appearance for some time of electro-optic materials making it possible to overcome these difficulties, in which the electro-optically active molecules are organic molecules. These molecules can be used in films, fibers, thin or thick layers deposited or not on substrates. There are in particular polymers in which elactrooptically active molecules are incorporated in suitable proportions into a matrix of a support material itself lacking these properties.

In practice, in the absence of special provisions, such materials are amorphous and having no electro-optical effect. No change in index can be observed when an electric field is applied inside these materials. The invention starts from the fact that in order to obtain the manifestation of such a phenomenon, the material should be given an anisotropy which can be obtained when, after having heated it, it is subjected to an electric field and it is cooled. The invention uses the observation that the direction of the electric field used influences the direction in which the electro-optical molecules tend to orient in the material (and therefore on the directional characteristics of the resulting anisotropy) and that the intensity of the electric field applied during this operation also modifies the level of electro-optical activity of the material.

The invention takes advantage of these observations to freeze the image of an electric field to which such a material is subjected with a view to applications such as the recording of data or signals, or the imaging of certain parameters or physical quantities. .

The invention relates in particular to a method in which the temperature is raised in at least one zone of such a material beyond a transition level from which the orientation of the molecules endowed with electro-optical activity of this material can be modified by an external action; an electric field is applied in this zone, the direction and / or intensity of which are determined as a function of optical anisotropy characteristics of the material which it is desired to obtain and, during the application of said field, the temperature in said field is lowered area below the transition temperature to freeze the characteristics of the field applied in the material. This electric field will frequently be referred to as the orienting or polarizing field.

According to one aspect of the implementation of the invention, the intensity of the electric field applied to the material is modulated in at least one direction of space so as to vary an optical anisotropy characteristic of this material along this direction. To this end, it is possible in particular to create a relative displacement, in this direction, of the material and of the source of the electric field. If the modulation of the electric field is produced by a signal or data to be recorded, the variations in the characteristic of optical anisotropy resulting in the material along this direction constitute a recording of this signal or these data according to a parameter which can be represented by the variation of distance in this direction.

To read such a recording, an electric field is necessary to highlight the variations of said anisotropy characteristic of the material along the direction considered. One can, for this purpose, subject the material to an electric field, hereinafter called detector, developer or reading, the intensity of which remains essentially constant along the direction in which one seeks to reveal the anisotropy. An optical detection device measures the variations in the electro-optical activity of the material along said direction to read the information or the signal that initially modulated the orienting electric field. Of course, the modulation of the anisotropy characteristics by this means can be carried out in several directions of the space inside the material. We thus obtain a multidimensional recording. It should be noted here that this technique allows in each elementary zone of the material to carry out either a binary type recording, by all or nothing, or a level recording according to the level of intensity of the field. counselor.

The creation and the modulation of the anisotropy intended to carry out the writing on the material, can be carried out according to two different modes. The first mode consists of heating locally and applying a global electric field. The second mode consists in heating overall and applying a local electric field; according to said second mode, the method makes it possible to record data of analog or quasi-analog type, by globally heating the material and by applying local electric fields of different values; the latter can advantageously be created by local deposition of charges or setting to given potentials.

The method of the invention can be implemented in two ways. Indeed, either the molecules of the material are previously and generally pre-oriented, by simultaneous application of heat and an excitatory electric field and cooling under field, then the material is subjected to the local application of heat under zero electric field, or the molecules of the material are oriented locally by the simultaneous local application of an excitatory electric field and heat.

In the first case, writing is equivalent to locally suppressing the prior global orientation of the molecules of the material; in the second case, we write on the material by locally orienting the molecules; the dopant molecules orient themselves in the electric field and keep their orientation as soon as the material temperature becomes lower than the critical temperature necessary for orientation.

 According to either of the two implementations referred to above, the material has a succession of non-oriented and oriented zones, which constitute the data in the form of bits with two states O or 1.

In addition, the method makes it possible to write at different levels in the thickness of a support of the sheet or strip type. Indeed, it is possible to locally heat each given level under a uniform orienting field. A recording of the information in volume is thus carried out, according to the three dimensions of the medium.

For the reading of the information carried on the support, one carries out the analysis of a light beam crossing the support (placed under an electric field of reading) and of which certain characteristics were modified by the anisotropy of the material (such as birefringence ).

Given the quantitative importance of the optical phenomenon involved, all else being equal, a high level of the optical output signal is obtained, which makes it possible to use very simple reading means.
The invention also relates to the use of a polymer material with electro-optical properties as an information recording medium.

The invention, applied to recording / reading data, has advantages over the prior art.

Indeed, the writing and reading steps can be carried out without contact with the film or the tape, which eliminates the problems of wear. In addition, the cost of the support is low because no deposit is to be made. In addition, reading is made simpler, because it is implemented by transmission of a light beam, therefore without the flatness of the support being a critical point, and above all because the values of electro birefringence -optics can be raised, from ten to several tens of degrees. Reading can also be carried out by reflection of light on one of the faces of the support, after transmission in the material. In addition, the density of information can be high since, on the one hand the size of the bits is only a function dimensions of the area subjected to the local field or locally heated, and on the other hand the material is not conductive. Finally, the chemical stability of the polymers makes it possible to carry out a large number of write / read cycles.

Also, the object of the invention is to propose a device for implementing the method described above, comprising means for creating a controlled optical anisotropy of the material and means for modulating it, and displacement means relative between on the one hand the information medium made up of said material, and on the other hand said means of creation and modulation of anisotropy.

Said means for creating and modulating the anisotropy include means for local heating and means for generating a general orienting electric field in which the information medium is capable of being placed.

As a variant, said means for creating and modulating the anisotropy include global heating means and means for generating a field locally on the support.

Preferably, the means for creating and modulating the anisotropy are fixed and the displacement means are capable of causing the support to move.

Advantageously, the local heating means comprise a laser beam emitter capable of being focused on the support. In this case, it is possible to provide electrodes on either side of the support; the electrodes are made of a material which is both conductive and capable of letting the light of the laser beam pass. The electrodes are for example made up of two plates having a potential difference between them, in the vicinity of which the support passes.

According to a variant, the electric field generating means are capable of depositing electrostatic charges on the surface of the support; for example, they consist of a source of electrons.

In order to obtain a high density of information, the means of creation and modulation of the anisotropy are able to create several parallel tracks each carrying a series of successive bits. In the case where the heating means consist of lasers, the device advantageously comprises either a laser diode per track, or a single diode associated with means for controlling the direction of the laser beam emitted by the single diode.

The information carrier, made of material with electro-optical property, can be produced in the form of a film, cut for example to form a strip or a disc.

The invention also relates to a device for reading the information recorded on the electro-optical support, comprising means for generating an electric reading field, means for generating a light beam capable of passing through the support and means for analysis. optic of said beam at the exit of the support. Reading can be carried out either by transmission of the light beam or by reflection thereof.

The reading light beam generating means may consist of a laser beam emitter.

The optical analysis means are for example of the polarimetric type and comprise a crossed polarizer and analyzer assembly and a detector. Said optical analysis means can, as a variant, be of the interferometric type.

In order to protect the film from the consequences of breakdown voltage, the excitatory (writing) electric field is less than the reading electric field.

To avoid, when reading, inadvertently changing the orientation of the molecules, the laser transmitter for reading is of lower power than the laser transmitter for writing (local heating).

Advantageously, the support is absorbent for the write wavelength (in order to heat as much as possible) and poorly absorbent (translucent or transparent) for the read wavelength (to allow good transmission of the light beam from reading).

In order to overcome the consequences of temporal drift of the read signals, the device comprises means for recording on the medium reference data and means for comparing between the reference signals and the signals corresponding to the information proper. These reference data are also intended to guide the reading means.

According to a second aspect of implementation of the invention, the direction of the orienting electric field is determined to impose on the structure of the material characteristics of anisotropy preselected in direction. These anisotropy characteristics can in particular be chosen to facilitate the subsequent use of the electro-optical properties of the material under determined operating conditions. This use may relate, for example, to the detection or the revelation of information carried by the material itself as it was previously exposed; it can also have as an object the detection of variations of information specific to the revealing or excitatory electric field with which the material is used. In both cases, it may be useful to predetermine the direction of the orienting field which is frozen in the material with a view to the conditions of use subsequently envisaged for the latter.

To demonstrate the Pockels effect produced by an excitatory electric field in an optically anisotropic material, an incident polarized light is sent into this material and the resulting light is detected after crossing the examined area subjected to the electric field. It has been determined that the direction of the incident light with respect to the direction of the excitation field as well as with respect to the direction of the orienting field initially used to orient the material was not indifferent. It is therefore understandable that the ability to determine and control the latter offers an interesting means of optimizing the operating conditions to be implemented.

In the case of a recording, mentioned above, of an orienting field modulated in intensity, it may thus be advantageous, starting from a non-oriented recording tape, to record a field oriented in a direction not perpendicular to the plane of this strip and, for example, parallel to it. It may also be advantageous to start from a recording tape whose active molecules have been previously oriented in a direction not perpendicular to the plane of the tape and perform the recording of bits by locally heating this tape in the presence of an electric field different from the initial orienting field or of a zero field.

Another typical use envisaged for such an electro-optical material is the detection of an excitatory electric field, or the demonstration of an image of this in the material, by an optical detection means, for example by polarimetry. or interferometry. The operating conditions, in particular the direction of the incidence of the light which can be used to carry out this detection, depend on the relative direction of the field which it is sought to detect or reveal with respect to the initial direction of orientation of the electro-optical molecules of the material.

Thus, the invention, according to this second aspect, can be applied to the imaging of voltages and, in particular of voltages in an electrical circuit for the purpose of measuring the latter or of the functional or dynamic test of the latter. For this type of application, an electro-optical material is then readily used in the form of a two-dimensional element, plate, layer or film, one face of which is disposed in the electrical proximity of the conductors or of the zones of the circuit which it is desired. examine. If one chooses to provide the other face of said sensitive element with a reference electrode, the voltages at the test zones cause the establishment of an electric field across the material in a direction substantially perpendicular to the plane of the electro-optical sensitive element. The detection of the electric fields thus appearing in the material can be carried out by sending an incident light towards the electro-optical element and by collecting a corresponding light reflected near the zone to be tested.

The studies carried out show that it may be advantageous, under these conditions, to have a sensitive electro-optical element whose active molecules are oriented in a direction not perpendicular to its plane, for example-parallel to the plane of the sensitive organ. itself, especially when you want to operate with normal incidence.

The invention will be clearly understood in the light of the following description, with reference to the drawing, in which: FIG. 1 is a block diagram, in side view,
of the device according to the invention for writing and
reading information on a tape Figure 2 shows a first embodiment of the
means for reading the device of FIG. 1; Figure 2bis shows a variation curve of
the light intensity of the output signal of the means of
Figure 2; Figures 3a and 3b illustrate the index anisotropy
an electro-optical material; Figure 4 shows a second embodiment of the
reading means of the device of Figure 1 ;; Figures 5 and 6 schematically represent a
variant of the writing means of the device of the
Figure 1, respectively in section and in top view Figures Sbis, 6bis and 6ter representing
variants of the orientation of molecules in a
direction not orthogonal to the film plane Figure 7 shows a third embodiment
reading means of the device of Figure 1; Figure 8 schematically shows side means
writing allowing to write on several levels in
the thickness of the strip; Figure 9 is a side view of the writing means
allowing the localized application of potential to the
strip surface; Figure 10 is a variant of the device of Figure
9 suitable for writing several tracks in
parallel Figure lcbis shows from above a variant of
the electrode assembly of FIG. 10; Figure 11 is a schematic front view of a shape
reading means capable of allowing the writing of
several parallel tracks; Figure 12 shows the fluctuations in the signal
reading as a function of time; and - Figure 13 shows an example of application of
the invention in the electronic circuit test.

We already know crystals with electro-optical properties; it has already been proposed to use organic materials which have a strong electro-optical activity such as MNA (2 methyl-4-nitroaniline) to produce crystals which can be used to implement this type of properties.

The MNA crystals have a high rn3 / e 'ratio of about 50 in which r is the electro-optical coefficient, n the index, and e' the dielectric constant.

However, such a body can be used not only in the form of a crystal, but also in a form combined with a support material in which molecules of such an electro-optically active compound are incorporated. It is thus possible, for example, to use PMMA poly (methyl, methacrylate) support material with an MNA density of approximately 15%. MNA is therefore used as a dopant, the molecules of which are retained in the PMMA matrix, in order to render the composition electro-optical. Other possible dopants having electro-optical properties are for example the following
DAN [4- (N, N-dimethylamino) -3- acetamidomitrobenzene]
COANP [2-cyclo-octylamino -5- nitropyridine)
PAN (4-N-pyrrolydina -3- acetaminomitrobenzene] MBANP (2- (alpha-methylbanzylanino) -5-nitropyridine)
This type of polymer compound is currently the subject of numerous developments by several companies, universities and research centers in this field such as Lockheed Missiles and Space Company, Inc., Hoechst Celaneses Corporation and other large companies in the chemical field. (See for example the communication from the symposium entitled: NATO advanced work shop = "Polymer for non linear optics", Sophia Antipolis June 19-24, 1988).

The polymers obtained can be used to form films, fibers or thin or thick layers on any substrate.

A particularly interesting characteristic of these polymers is the possibility of using them in the form of films capable of being produced in large quantities and at reasonable costs. These films can be used either in a thickness of a few microns (for example 10 microns) on transparent supports, for example in glass. They can also be delivered directly in the form of flexible films composed by the juxtaposition of several thicknesses of elementary films, (for example 500 microns thick). Values ranging from 10 to 50 µm / V can be obtained for the electro-optical constant r of these materials.

After drying, the molecules of electro-optically active products are trapped in a support material in the amorphous state, without any particular orientation. To make the material electro-optical, it is necessary to heat it to a temperature sufficient to allow the active molecules to recover a certain mobility inside the matrix. The value of this transition temperature can vary depending on the polymer but can typically be around 100 to 120 C. In this state, they can undergo an orientation relative to the support under the effect of an electric field. Molecules tend to orient in the direction of the orienting field, The stronger the orienting field, the higher the proportion of active molecules oriented in the direction of the field. Field values of the order of 10 to 100 kvolt / millimeter can be implemented.

When the temperature is lowered again while the molecules are oriented under the effect of a field, they keep their orientation. The material thus retains an oriented structure which can be revealed by an optically anisotropic behavior (Pockels effect) in the presence of an electric field (developer or reading).

Thus, when the material is struck by an incident light linearly polarized in the absence of an electric field, the light transmitted or reflected by the material does not undergo any modification of polarization. On the contrary, in the presence of an electric field, the transmitted light undergoes an elliptical polarization linked linearly to the applied field intensity.

The following description is made with reference to a recording medium in the form of a film or tape, it being understood that the invention is not limited to this type of medium; the support can also consist of a disc. Figure 1 shows from the side (seen in its thickness) a strip 1 consisting of a polymer matrix of the type mentioned above. The strip has, by way of illustration, a thickness of 10 to 100 microns, and a width (transverse to the plane of the figure) of 5 to 300 mm.

The device shown schematically in FIG. 1 comprises the writing means 2 and the reading means 3.

According to the example shown, the writing means 2 comprise, on the one hand, means for generating a global electric field comprising two electrodes made up of two conductive plates 4,5 capable of being connected respectively to ground and to a direct writing potential, and on the other hand local heating means consisting of a laser beam emitter 6 capable of being focused on a defined area 8 (from 1 to a few microns) of the strip 1; said electrodes 4 and 5 are further capable of letting the light of the laser beam pass (for example facing an opening or a slot not shown); the direction of the writing laser beam 7 is orthogonal to the plane of the film. The plates 4 and 5, for example of tin oxide (Sn 02), are arranged opposite one another and are separated from each other. one from the other by a distance slightly greater than the thickness of the strip, in order to allow the strip 1 to pass between them. The strip is capable of being driven in a translational movement, in the longitudinal direction, indicated by the arrow f, by drive means known per se and not shown; similarly, scrolling means also known per se and not shown, are provided to cause the strip to follow a given path relative to the writing / reading device of the invention.

The reading means 3, arranged for example downstream of the writing means 2, comprise electric field generating means comprising two electrodes constituted by two transparent conductive plates 11, 12 arranged face to face so as to provide a space in which the strip is likely to pass, and likely to be connected to ground and to a potential respectively
Reading The reading means also comprising a laser beam emitter 13, focused on a given zone 15 of the strip, and means 16 for analyzing and processing the output signal.

The areas 8 and 15 respectively affected by the writing laser beam 7 and by the reading laser beam 14, are of dimensions (in the longitudinal direction) substantially identical (namely one to a few microns).

The basic operation of the device in FIG. 1 is described below according to a first form of implementation.

The strip 1, brought to pass (at a constant speed of a few tens of cm / s to a few m / s) opposite the writing means 2, has no particular orientation of the electro-active molecules. The upper electrode plate 5 is brought to the positive potential Vwriting; the strip is subjected between the electrode plates 4 and 5 to an electrical field called writing t the laser transmitter 6 emits a light pulse 7 focused on an area 8 of the strip which is thus brought to a given temperature T higher at a critical temperature Tc defined as the limit temperature necessary to cause, in the presence of an electric field, a given orientation of the molecules; the heated zone 8, by the heating light pulse of approximately 10-6s, moves to the right of the figure, and remains at a temperature T greater than Tc for a period of between lms and O, lms, always in being subjected to the electric writing field; during this period, the orientation of the molecules of zone 8 is effected, which cools under said electric field: zone 8 thus presents a modification of the orientation of the molecules, while the rest of the strip presents no modification to this regard; zone 8 then defines information in the form of a bit assigned to state 1, the non-electro-optical part of the strip being assigned to state 0.

The information is thus recorded, or written, on the tape in the form of a succession of bits consisting of respectively oriented and non-oriented areas.

The power of the write laser transmitter is for example between 10 and 50 mW. The duration of the time interval during which the heated zone must remain subject to the writing field, in order to freeze the orientation of molecules, is for example between 10-3s and 10-4s; -accounting for the values the tape running speed (a few m / s), the "useful" length of the writing electrodes, between the writing beam and the downstream edge thereof, is for example between 0.1 mm and 5 mm. On the other hand, the determination of the length of the reading electrodes is less critical, insofar as the reading is carried out by "instantaneous" optical analysis of the state of the zone examined, without the latter having to stay for a given time under the reading field.

The reading of this information can be carried out by the means 3 shown in FIG. 2, arranged downstream of the writing means 2 described above. The writing means comprise optical analysis means 16 of the interferometric type as based on the use of a so-called Fabry-Perot analyzer. The reading beam 14, orthogonal to the plane of the film, emitted by the transmitter 13, partly crosses the strip and is partly reflected on semi-transparent mirrors arranged on either side of the strip 1 t said mirrors are consisting of thin film segments 24a, 24b, 24c, 25a, 25b, 25c deposited on the lower and upper sides of the strip. The film segments forming the mirrors are conductive and connected, respectively, for each side of the strip, to a potential Reading by an electrode 12 and to ground by an electrode 11. The thin films 24 and 25 are regularly interrupted along the strip by spaces 28, 29 separating two consecutive film segments in fact, it is necessary to avoid that the upper face (at the potential Vleading) is electrically in contact with the lower face, when the strip is wound on a reel for example.

Between the layers 24 and 25 parallel, are established on either side of the film interference; the light beam coming from the film is directed towards the optical analysis means 26 able to measure the intensity of the light signal 29. In a known manner, the intensity of the interference light is a function of the distance separating the mirrors, c ie the thickness "e" of the film, the wavelength "lambda" and the refractive index "n" of the material constituting the film. However the index "n" varies according to the orientation of the molecules of the film.

The reflected light intensity is modulated by the electric voltage applied to the electro-optical film according to a so-called Airy law. Measuring the intensity of the output light signal provides a measure of the V potential.

In order to overcome the consequences of possible differences in thickness of the film or of the electro-optical strip, on the part covered with semi-transparent mirrors, it is possible to use a light source capable of emitting a light beam of wavelength ( lambda) variable; this allows to move the operating point of the device on the characteristic curve (figure 2bis) of the intensity as a function of PHI = (2PVlamb.dai ne, from a point A located on a first part of the curve where
I = Imax whatever PHI (therefore of zero sensitivity) at a point B located on a second part of the curve where I (between Imax and O) varies strongly as a function of
PHI; the sensitivity is a function of this variation of I around the point B on this second part of the curve preferably, the point B corresponds to approximately Imax / 2. Once the point B determined, the measurements are then carried out with the length of wave corresponding to the point
B.

Alternatively, according to the invention, the reading means are of the polarimetric type.

However, polarimetric analysis means cannot be used without some precautions in the case illustrated in FIG. 1 where the active molecules are oriented in writing according to a field of direction orthogonal to the plane of the film and where the revealing field applied by the electrodes 11,12 is also orthogonal to the film plane.

Indeed, the anisotropy of the material is defined by the ellipsoid of the refractive indices, comprising several axes.

In FIG. 3a, the distribution of the indices has been represented in an electro-optical film 500 produced with a polymer of the type previously discussed, the molecules of which have been oriented by the application of an electric field, called the orientator, in one direction. normal to its surface while its temperature was lowered below the critical temperature above which the electro-optical dopant molecules lose their mobility. In 502 an ellipsoid has been represented describing the distribution of the refractive indices of the material when an electric field (called reading or revealing) is applied to it perpendicular to its plane. This ellipsoid describes the variations in the refractive index of the material in the directions of space. It has a symmetry of revolution with respect to the normal 504 in the plane of the film 500 which reflects the fact that the material is optically isotropic parallel to the shot of the film.

If the film 500 is illuminated with a polarized beam 506 of normal incidence to the film, the light retransmitted by the film (by transmission or after reflection on the opposite face 508 of the film) will not see its polarization state modified. This explains why we cannot determine whether the molecules are oriented or not. On the other hand, an incident beam 510 oblique to the plane of the film will see its polarization state modified.

In order to be able to use polarimetric analysis means, it is therefore necessary for the molecules to be oriented in writing in a direction which is not parallel to the direction of the field and / or of the reading laser beam. This leads to an alternative, namely either to write while orienting the molecules in a direction orthogonal to the plane of the film and to read using an oblique laser beam, or else to write using a field parallel to the plane of the film and read using a laser beam orthogonal to the plane of the film.

 FIG. 4 schematically represents polarimetric reading means, according to the first branch of the alternative mentioned above, making it possible to reveal the anisotropy of the material previously oriented using a field and a laser beam of writing orthogonal to the film plane (writing means 2 in FIG. 1).

To this end, the strip 1 subjected to the reading field orthogonal to the plane of the film, is illuminated by a laser beam 14 for reading emitted by the laser transmitter 131 and oblique with respect to the normal to the film 1; in the position shown, the incident beam is necessarily directed in a plane parallel to the longitudinal direction of the strip 1. It can be provided to incline this beam obliquely in a plane perpendicular to this longitudinal direction, which reduces the size of the device of reading in the longitudinal direction. The upper plate 12 is brought to a positive potential Vleading so as to place the strip in an electric field known as reading normal to the plane of the strip. The reading beam 14 ′ after having crossed the strip, is received by the means of analysis 16 of the polarimetric type and comprising a lens 17 focusing the intensity beam Iot a polarization splitter 18 (for example in the form of a Wollaston prism), two photodetectors 19 and 20 (receiving respective intensities I2 and I1) whose outputs are connected to a differential amplifier 21 driving a processing circuit 22 of the electrical signals. The beam 14 ′ coming from the film is oblique with respect to the normal to the film and likewise for the optical axis of the optical elements 17, 18, 19 and 20.

Reading is based on the detection and measurement of the rotation of the polarization of the light induced by the electro-optical effect of the material constituting the strip.

The analysis means 16 therefore detect a succession (and alternation) of so-called oriented and non-oriented areas such as the hatched area 15. The signal S detected at the output of the amplifier 21 is
S = I1- I2 = 1o sin TETA, with TETA the angle of polarization t we have
TETA = A Vlecture, with
A = B Write where B is a constant representative of the physical parameters of the tape.

According to the second branch of the alternative set out above1 in order to allow the use of polarimetric analysis means, a strip is used whose molecules are oriented parallel to the plane of the film.

In a first embodiment, this strip is cut from a film, the molecules of which have been generally pre-oriented, the writing being carried out by locally heating the film in the absence of a field. A method for obtaining such a preoriented film is described below with reference to FIGS. 5 and 6, showing respectively in section and from above a device allowing such pre-orientation.

A strip of polymer film 800 is admitted into a tunnel oven 801 heated to a temperature T around 100-C (slightly higher than the critical temperature mentioned above). The strip is guided in the air gap between two metal plates facing each other 802 and 804 which are maintained at the same continuous electrical potential + V.

At the outlet 805 of the tunnel oven, the film enters a second tunnel 810 delimited by two facing metal plates 812 and 814 which are maintained for example at zero potential. As a result, the interval 815 between the heating tunnel outlet 801 and the second tunnel 810 is subjected to a substantially uniform electric field parallel to the plane of the band 800 which passes through this interval 815. The electro-optically active molecules of the film tend to orient themselves parallel to this direction under the effect of this field immediately at the exit 805 of the tunnel 801. Two series of nozzles 818 and 819 on either side of the film 800 open in the interval 815 where they deliver a current 820 of inert gas for example argon or a sulfur hexafloride SF6 cooled to -40-C on the two faces of the film 800. The gas is sucked between the plates of the second tunnel by a device not shown. The temperature of the film 800 drops below the critical temperature in the interval 815. The active molecules retain a preferential orientation in the plane of the film which finishes cooling in the second tunnel.

In FIG. 3b, the ellipsoid of the indices obtained in the same material has been shown in 512 under the action of an electric detector field, or developer, normal to the plane of the film when the molecules of the film 500 have been oriented beforehand. parallel to the plane of this film by the orienting electric field. In this case the ellipsoid of the indices 512 has a symmetry of revolution with respect to an axis 513 in the plane of the film 500. A normal incident beam 506 then sees its angle of polarization modified as a function of the difference of the indices n2 and n3 according to the main axes of the ellipse in the film plane. Under these conditions, the assembly of FIG. 1 (that is to say with normal incidence of the light used in reading) with reading means of the polarimetric type , makes it possible to exploit the effect created by the electric field and the reading laser beam in the polymer film.

In writing, the strip 1, cut from a film having previously undergone an orientation of the molecules parallel to its plane, is brought to pass before the writing means 2 in which the electric field is zero, the writing = 0. The areas locally subjected to writing laser beam 7 see the prior orientation of the molecules removed after the transition temperature has passed, while the rest of the strip retains the prior orientation. Reading is carried out with polarimetric analysis means of the type of means 16 in FIG. 4. However, for the reasons explained with reference to FIG. 3b, in this case a polarized reading beam of zero incidence (orthogonal) is used. at the film plane) and no longer oblique. The write bits corresponding to a write heating will be characterized by the absence of modification of the polarization state of the light passing through them.

In this form of implementation (the molecules being previously and generally "preoriented"), the writing consists in locally suppressing the imposed orientation.

According to a second embodiment, a strip is used whose molecules are not oriented at the start writing consists in locally orienting the molecules parallel to the plane of the film. Writing means making it possible to achieve this goal are shown in FIG. 5a. A strip 1 (whose thickness has been enlarged in the drawing for reasons of clarity) passes from a supply reel 100 to a take-up reel 101, between which are arranged means for local orientation of the molecules, comprising a first electrode 102, connected to a potential V +, disposed opposite one face of the strip, and a second electrode 104 disposed opposite the other face of the strip but offset with respect to the first electrode 104; the second electrode 104 is connected to ground. The electrodes are spaced from each other so as to provide a space 106 where an electric writing field prevails substantially parallel to the longitudinal axis of the strip or more exactly slightly oblique to said axis. Opposite said space 106 are arranged on the one hand a laser beam emitter 6 focused on a delimited area 8 of the strip 1, and on the other hand (downstream of the emitter 6) a nozzle 108 capable of delivering a stream of neutral gas (for example argon) cooled to a temperature much lower than the critical temperature Tc (for example -40 # C). The zone 8 subjected to the laser beam 7 is thus heated by the latter above the temperature Tc, while being subjected to the electric field prevailing between the electrodes 102 and 104; the nozzle 108 is directed so as to cool the area 8 immediately after it has been heated by the writing laser beam 7, while ensuring the cooling of the area 8 under electric field, to freeze the orientation of the molecules of zone 8.

Figures 6bis and 6ter show schematically, respectively from above and from the front, a variant of writing means, making it possible to orient the molecules in an oblique direction relative to the transverse axis thereof. The device comprises two lateral electrodes 110 and 111 placed on either side of the strip, one 110 facing one side of the strip and the other 111 facing the other side of the strip but offset transversely to the first electrode 110 so as to provide between the electrodes an air gap 113 elongated in the longitudinal direction of the strip 1. The electrodes 110 and 111 are connected respectively to a positive potential V + and to ground. The electrodes thus create an electric field somehow crossing the strip right through its thickness and in an inclined direction relative to the plane of the strip or substantially in the plane of the latter. A laser emitter 6 disposed above the strip emits a beam 7 (orthogonal to the plane of the figure) capable of heating a defined zone 8 of the strip, which then cools under field inside the air gap 113.

With reference to FIG. 1, according to an advantageous embodiment, the writing and reading means are brought together in a single unit; the writing and reading electrodes are then constituted by the same lower plates 4.11 connected to ground and upper 5.12 brought to a potential, ie writing for writing, and
Reading for reading.

In the foregoing description (relating to FIGS. 1 to 6), the devices described carry out the writing, by local heating under an electric field applied uniformly and globally. As a variant, these respective writing operations can be carried out by uniform heating (no longer by laser, but by an oven for example) and by local application of an electric field, for example by depositing electrostatic charges on the surface of the strip (thanks to an electron gun for example).

The writing is preferably carried out at a wavelength where the strip material is relatively absorbent and the reading at a wavelength where the strip material is not very absorbent (to allow satisfactory transmission of the reading beam ). For example, He-Ne (633nm) and Krypton (647nm) lasers can be used as a focused light (heat) source.

FIG. 7 shows a third embodiment of the reading means, comprising, in addition to electrodes 11 and 12, polarimetric analysis means simplified compared to the means 16 shown in FIG. 2 (taking into account the quantitative importance of the signal detected). The analysis means consist of a polarizer P disposed between the emitter 13 of the laser beam 14 and the support, and of an analyzer A disposed on the opposite side of the support, as well as of a single photo-detector 23. The measured parameter is the intensity of the output light signal. The orientation of the molecules in the recorded band is parallel to the plane of this band.

FIG. 8 shows another exemplary embodiment making it possible to write in the thickness of the strip at several levels. For reasons of clarity, the drawing is not to scale in the sense that the strip and the electrodes have been shown enlarged.

The strip 1 passes between the electrodes 4,5 connected respectively to the ground and to the writing potential and capable of letting the light of a writing beam pass.

Several laser transmitters, in this case four, referenced 30,31,32,33, are capable of emitting a beam respectively 34,35,36,37; semi-transparent mirrors (aligned along an oblique axis with respect to the longitudinal axis of the strip) 38,39,40,41 returning the four respective beams in a single direction 42 oblique with respect to the longitudinal axis of the strip on the path of which there is a lens 400 which focuses the beam 43 passing through it in a zone 44 (hatched in the figure) of the strip located at a given level (in the thickness of the strip, that is ie in the plane of FIG. 4. The emitters 30,31,32,33 emit light beams at different respective wavelengths, and such that each beam is focused at a given level 44,45,46 or 47. The beam 43 focused by the lens 400 heats an area of a given level under the electric field applied by the electrodes 4 and 5, which modifies the orientation of the molecules of said area. The active molecules of the written areas are therefore oriented in an electric field orthogonal to band plan.

Reading is carried out in the same way, by successively focusing an oblique reading beam in the direction of alignment of the zones of increasing depth recorded at the time of writing on each of the zones. The reading means then comprise the same members as those shown in FIG. 2, namely two reading electrodes and the polarimetric optical analysis means 16 already described with reference to FIG. 2.

Preferably, the bits of the same oblique in the thickness of the strip are sufficiently distant from each other, so that, during reading, the influence of the bits located above and below the bit on which is focused the reading beam is negligible. By way of illustrative example, the bits have a height dimension (in the direction of the thickness of the strip) of 1 to 5 microns; the number of levels can be between five and ten.

In the context of the description of FIG. 8, the same result, namely focusing a beam at different depths in the thickness of the strip, can be achieved, as a variant, using a single emitting laser transmitter a beam of given wavelength and a lens with variable focal length placed between the emitter and the band.

FIG. 9 shows another embodiment of the device making it possible to create a local electric field by depositing electric charges located on the surface of the strip 1. The electric field can be modulated either in all or nothing or in a quasi-analog manner; in the second case, information is recorded in an analog or quasi-analog manner, that is to say that in each recording area an electric field is applied, the value of which can vary as a function of that of a signal variable analog to record. In the quasi-analog mode, the value of the writing electric field in each discrete recording zone is selected from a number of discrete values in a range of variations of analog signal to be recorded. Reading the information recorded according to the invention involves physical phenomena which are, on the one hand of great amplitude, for example of the order of ten to several tens of degrees of birefringence, and on the other hand proportional to writing tension. Thus, it is possible to distinguish one from the other two zones which have been oriented by different writing voltages.

The device in FIG. 9 comprises means for overall heating of the strip, known in themselves, such as a tunnel oven 200. Writing means described below are provided downstream of the oven 200 for carrying locally the upper part of the strip at a given potential. The strip 1 comprises, on one of its faces, a conductive and transparent film 50 constituting an electrode connected to ground, and on the other face a layer 51 of a polymer material having photoconductive properties, that is to say say whose conductivity depends on the illumination. Opposite and in contact with the transparent photoconductive layer 51, is arranged a transparent electrode 52 connected to potential v, either all or nothing modulated, or of the analog or quasi-analog type. A laser emitter 53 capable of emitting pulsed laser beams 54 focused on a given area 56 of the strip 1. Under the effect of the beam 54, a conduction channel is created between the area 55 in the upper part of the photoconductive layer brought to the potential v, and the zone 56 in the upper part of the strip where the control beam 54 is focused; zone 56 is therefore then at potential v and accumulates electrical charges which are maintained in zone 56 due to the non-conductivity of the polymer constituting the strip 1 by creating an electric field in the thickness of the strip under the effect from which the electro-active molecules orient themselves. The strip is brought, upstream of the writing means, to a temperature such that it remains at a temperature above the critical temperature Tc for a sufficient time after the appearance of the potential. v on the zone to be polarized, so that the orientation of the molecules takes place. This is frozen during the subsequent cooling of the strip.

Reading is carried out using reading means such as those shown in FIG. 2 or those shown in FIG. 4.

The photoconductive effect being almost instantaneous and without remanence, as soon as the beam 54 has disappeared, the photoconductive layer is no longer conductive. It is possible to vary the potential v according to discrete values representative of the variations of an analog signal.

The form of implementation described with reference to FIG. 9 (making it possible to bring the surface of the strip locally to a given potential) has the advantage of using a low power laser transmitter.

FIG. 10 shows a variant of the device in FIG. 9, enabling information to be written on the strip along tracks parallel to the longitudinal axis of the strip. An assembly 520 forming a first electrode is provided, consisting of a parallelepiped plate in rigid and transparent material (such as glass) arranged so that its largest dimension is orthogonal to the longitudinal axis of the strip 1. The underside of the electrode plate 520, is arranged in electrical proximity (a few microns) to the upper face of a photoconductive layer 220 itself arranged on the strip 1; the face of the strip opposite layer 220 is coated with a layer 210 of conductive material (transparent for example) constituting a second electrode, connected to ground. The underside of electrode pad 520 is provided with pads or pads 538 541 square in a conductive and transparent material (such as Yttrium oxide) each connected to a given potential (writing or mass). Each pad constitutes a unitary electrode, of dimensions for example 0.5 mm × 0.5 mm, corresponding to a bit on a given track.

A laser emitter 530 is placed at a distance from the electrode assembly 520 and capable of emitting a laser beam 532 passing through a lens 531 and striking a diffraction grating 533. The latter is thus capable of generating a plurality of beams 534 to 537, in number equal to the number of unit electrodes 538 to 541, and respectively focused on each of the latter.

The strip is previously heated by a tunnel furnace, not shown, located just upstream from the electrode assembly 520 and optical means 530,531,533, relative to the direction of travel of the strip (arrow f). Each strip section arriving at the base of the electrode assembly 520 is at a temperature above the critical temperature. The laser beams 534-537 pass through the photoconductive layer directly above the electrodes 538-541, which causes the conduction thereof, and therefore creates a kind of conduction well towards the base of the photoconductive layer 220, where the charges are deposited above the unit electrodes. On the face of the electro-optical layer forming the strip 1, in contact with the photoconductive layer, localized charge deposits are formed, which create with the second lower electrode, 210 connected to ground, localized electric fields and directions orthogonal to the plane of band 1.

The distance ~ separating two unitary electrodes must be large compared to the distance separating each electrode from the surface of the photoconductive layer, in order to avoid any crosstalk between the electrodes. The surface of the electrodes is chosen to be large enough relative to the light spot of the focused beams 534-537, to allow them to focus on the electrodes despite the relative distance (in the direction orthogonal to the plane of the strip) from the points focusing created by the network 533 and arranged on a circle centered on the latter.

At the base of each unitary electrode, a bit is created on the strip 1. The unitary electrodes are supplied or connected to a write potential (bit 1) or zero (bit 0). It is thus written that the strip 1 a plurality of bits aligned along tracks parallel to each other and to the longitudinal axis of the strip.

The example of embodiment described in FIG. 10 comprises for reasons of clarity four parallel tracks. It is understood that the number of tracks may be higher.

However, taking into account the lower limits mentioned above, the dimensions of the electrodes and the distances between electrodes, the number of tracks reaches limits of the order of, for example, a few units. In order to increase the number of tracks without prohibitively increasing the dimensions of the electrode assembly 520, it is produced as shown in FIG. 10bis showing a top view of the strip 1 and an electrode assembly 550 of parallelepiped shape whose side of the largest dimension is orthogonal to the axis of the strip and of length equal to the width of the strip 1. The assembly 550 consists of a block of glass bearing on its underside, near strip 1, a plurality of pads or pads formed from a square film (0.5 mm × 0.5 mm for example), arranged in rows parallel and orthogonal to the axis of strip 1; each pad forms a unitary electrode; the example shown comprises three rows, the first row four unit electrodes (551 to 554), the second row three (555 to 557) and the third row four (558 to 561), so that the centers of the unit electrodes, corresponding at the write bits, are offset from each other in a direction orthogonal to the axis of the strip; in other words, the individual electrodes are offset so that they are not strictly aligned along the axis of the strip 1.

Each 551-561 unit electrode is connected to a potential
Write or ground and corresponds to a bit and therefore a track; tracks a, b, c, d, e, f, g, h, i, j and k are parallel to the longitudinal axis of the strip; thus the recording of several tracks (in this case eleven) is obtained using an electrode assembly 550 of relatively small dimensions.

FIG. 11 shows, in front view, the strip 1 being represented in cross section, a device for reading the tracks recorded using the writing device shown in FIG. 10. A laser transmitter 6 emits a beam of writing 7 successively passing through a lens 60, a polarizer 61, and an optical grating 62 of diffraction (known in itself) capable of generating several parallel beams 63,64 focused, by a lens 67, in distinct zones 65,66, aligned from one edge to the other of the strip (that is to say transversely to the axis of the strip). Two reading electrodes 4 and 5 are arranged on either side of the strip 1 and close to it, and respectively connected to the reading potential and to ground. The respective beams coming from the network 62 are focused on a succession bits aligned transversely to the longitudinal axis of the strip. The bits are read using optical analysis means A and 23 such as those shown in FIG. 7, comprising a photodetector for each write electrode, that is to say one photoconductor per bit.

In order to overcome the consequences of any untimely movement of the strip, the reading device of FIG. 11 may include means (not shown) for monitoring the position of the bits on the strip. For example, said means comprise a member for detecting the position of the edge of the strip and means suitable for moving the light beam by a value corresponding to the untimely movement of the strip. If the strip were to be translated transversely to its axis, the displacement means control the translation of the transmitter 6 by the same value. In the event that the strip expands, the displacement means cause the inclination of the optical networks 62 in order to enable the position of the bits to be found.

Furthermore, according to an advantageous embodiment (not shown), the device, in accordance with any of the embodiments shown and described above, comprises, on the one hand, means capable of recording on the bit tape of reference made up of zones directed and / or not oriented at a constant level, and on the other hand, associated with the means of reading, means of comparison of the signals resulting respectively from the bits of information (curve a, figure 12) and reference bits (curve b, FIG. 12) so as to deliver an output signal (curve c) formed of "peaks" above an average level substantially equal to zero. Curve b is representative of the reference signals and therefore of the fluctuations in time of the output signals in the absence of correction using reference bits.

FIG. 13 represents an automatic test equipment in which an aspect of the invention is implemented.

An automatic test equipment which implements an aspect of the invention comprises (FIG. 13) a layer of an electro-optical polymer 350 of dimensions substantially equal to those of an assembled circuit, such as a printed circuit board 351 to testar, the assembly being combined in such a way that the electro-optical medium is electrically close to the surface 352 of the card 351 which carries the electric circuit, the latter comprising components such as 355. The surface 352 carries conductors such as 354 and 357 which connect the components to each other, and thus constitute the electrical nodes of the circuit.

The layer of polymer 350 is coated on its face intended to be placed near the conductors 356, 357 with a reflective layer 360 capable of returning light reaching it from the other face of this polymer layer 350. This layer 350 is cut out and has openings such as 361 and 362 in which the welds such as 363 can be accommodated at the ends of component pins or components such as 365 mounted on the face 352 of the card 351. For the test, the reflective layer 360 is placed in contact with or in the electrical vicinity of the surface of conductors 357 and 356. It is insulating. The reflecting surface. 360 is essentially insulating, at least in the sense that an electrical potential applied at a point on this surface is not propagated at other points on it. It can also be produced by conductive pads reflective isolated or separate from each other.

The emission light of a laser 330 (for example a laser
633 nm wavelength HeNe) is linearly polarized by a polarizer 331 and routed, via a lens 332, to an acousto-optic deflector 333 so as to be directed, via a lens 334, to an inspection point 335 of the reflecting surface 360 of the polymer film 350. The acousto-optical deflector 333, known per se, is controlled by a DC voltage signal emitted by an ATE control member (not shown), so as to deflect the light that it receives on any point from the electro-optical medium whose examination is desired.

In a preferred embodiment, two acousto-optical deflectors can be placed in series. A first voltage signal then controls the deflection of the beam in a first direction, corresponding for example to one of the two dimensions of the card to be tested, and the other voltage signal controls the deflection in a second direction, preferably perpendicular to the first and corresponding for example to the other dimension of the map.

Such use of two deflectors makes it possible to reduce the time required to pass from one observation point 335 to another at times of the order of a few microseconds at most.

A transparent electrode 301, for example constituted by a deposit of gold or aluminum, is arranged in a layer on the first face, encountered by the incident light from the electro-optical polymer film 350 and this electrode is kept at ground potential. M which is the reference for potentials; thus, if the electrical potential of the test point examined differs from this reference, the polarization of the light coming from the film is, due to the electric field applied according to the thickness of the electro-optical polymer film 350, different from that of the light incident, and this difference is detected.

 In the film 350, the phase delay of the light due to the electro-optical effect undergone is proportional to the potential difference between the faces of the film 350 at the point of observation.

The reflected light is returned to the quarter-wave plate 302 Ear a separator 303; downstream of the blade 302, the light is conveyed, by a lens 304, to a Wollaston analyzer 305, from which two beams reach the respective photoelectric detectors 308 and 309, which, on their outputs 306 and 307, produce respective electrical signals 11 and 12.

This type of polarimetric detection leads to the following relationships
Il = I. (l + m) and I2 = I. (lm)., In which I is a quantity proportional to the light intensity of the laser 330 and in which m is the detected phase delay, expressed in radians and assumed small.

A differential amplifier 310 receiving the signals from outputs 306 and 307 produces on its output 311 a signal Il
I2, therefore equal to 2.Im Insofar as, during a test, the possible variations in light intensity of the laser 30 correspond to frequencies much lower than the frequencies of variation of m, the quantity m can be directly obtained by adequate filtering of the electrical signal available on the output 311 of the amplifier 310. As a variant, a signal Il + I2 can be used to control the light intensity of the source.

A configuration of test signals can be applied to external nodes of the card 351 in order to excite the circuit and so as to cause a response from the circuit to the conductive node such as 357 which is subjected to electro-optical observation. , which results in the appearance of an image of this response on output 311.

Thanks to a preliminary theoretical analysis of the circuit to be tested, the ideal theoretical output signal, for the circuit to be tested and the configuration of test signals applied, can be determined in advance as is commonly done with ATEs of the prior art, and the expected ideal signal 378 can be compared, by a comparator 379, to the output signal 311 actually obtained.

If this comparison reveals a difference, the comparator 379 produces on its output 380 the indication of a fault revealed by the test.

The lens 334 is a field lens placed in the immediate vicinity of the film 350. Its dimensions are of the same order as that of the circuit boards to be tested. It has the effect of redirecting the beam 339 coming from the deflector 333 towards the film 350 under a practically normal incidence. In this way, the beam reflected by the reflecting face 360, the state of polarization of which is influenced by the electric field in the film at the point examined 336, essentially follows the same return path as the incident beam, up to the separator 303 .

For the reasons mentioned above, with reference to FIGS. 3a and 3b, the film 350 has been previously oriented parallel to its plane. To this end, it has undergone a treatment for example by the method mentioned with reference to FIGS. 5 and 6.

 The excitation field created by the potential difference between the faces of the electro-optical film 350, that is to say between the conductor 357 facing the point 335 and the reference electrode 301, is normal to the plane of the film 350. Thanks to the orientation of the active molecules in the film plane, the polarization state of the perpendicular incidence beam 339 is modified by the voltage appearing during the test on the conductor 357. With an orientation of the active molecules normal to the plane of the film 350, a beam of oblique incidence light can be used. Alternatively, an interferometry method as described with reference to Figure 2 can be used.

Claims (51)

1 - Method for freezing the image of an electric field in  a material comprising molecules endowed with activity  electrooptics, characterized by the following stages  a) the temperature is raised in at least one zone of this  material beyond a transition level from  which orientation of these molecules inside  of the support can be modified by the action of a  electric field  b) an electric field is applied in this zone  counselor or writer whose direction and / or  intensity are determined based on  optical anisotropy characteristics that one  wishes to obtain; and  c) during the operation b) the temperature is lowered  said area below the temperature of  transition to freeze the characteristics of the field  applied in the material. 2 - Method according to claim 1, characterized in that  that we modulate the electric field applied to the points of the  material in at least one direction of space for  varying an optical anisotropy characteristic  material in this direction. 3 - Method according to claim 2, characterized in that  the field is modulated in intensity. 4 - Method according to one of claims 2 or 3,  characterized in that the modulation is carried out between  two levels. 5 - Method according to the preceding claim, characterized  in that one of said levels is zero. 6 - Method according to one of claims 2 to 5,  characterized in that the modulation is made on a  range of levels. 7 - Method according to the preceding claim, characterized  in that said levels are discontinuous. 8 - Method according to one of the preceding claims,  characterized in that the material is packaged under  the shape of a layer or film. 9 - Method according to claim 8, characterized in that  modulation is performed in two dimensions  parallel to the layer plane. 10- Method according to claim 8, characterized in that  modulation is carried out at least in one dimension  parallel to the layer plane and in the thickness  of the diaper. 11- Method according to one of claims 8 to 10,  characterized in that the molecules are oriented at  using an electric field not perpendicular to the  layer plane. 12- Method according to claim 11, characterized in that  that we orient the molecules substantially in the  layer plane. 13- Method for reading the record of a field  modulated electric, produced according to the process  according to one of claims 8 to 12, characterized in  what we subject the layer or film to a field  electric reading device capable of revealing anisotropy  optics of the material and this anisotropy is detected by  optical means. 14- Method according to claim 13, characterized in that  that we perform the analysis of a light beam  passing through the material (placed under the electric field  of reading) and some parameters of which are modified  by anisotropy. 15- Method according to one of the preceding claims,  characterized in that a local anisotropy is created  by applying heat locally and from the field  electrical orienter or overall writing and then  cooling under said field. 16- Method according to one of claims 1 to 14,  characterized in that globally removed  the anisotropy of the material by simultaneous application of  heat and a field, then we create an anisotropy  local under zero electric field. 17- Method according to one of claims 15 or 16,  characterized in that the material is subjected to a  local application of heat under said field  electric writing system. 18- Method according to claim 16, characterized in that  that anisotropy is created by global application of  heat and a local electric field. 19- Method according to claim 18, characterized in that  that the material is subjected to a local electric field  by deposition of charges, a potential given to the  material surface. 20- Method according to claim 17, characterized in that  that we heat the material by focusing on  defined areas of the latter located at levels  different in the thickness of the film or layer. 21- Method according to claim 18, characterized in that  that we heat the material globally and submit  the latter to local electric fields of values  different. 22- Method according to claim 8, characterized in that  the material is in the form of a strip or disc. 23- Method according to one of the preceding claims,  characterized in that the material consists of a  polymer matrix doped with electro-active molecules. 24- Method for transferring charges  electric, under the effect of a light beam of  command, between the first side of an element in one  photoconductive material connected to a source of  loads, and the second face of said element arranged at  electrical proximity to one side of a layer of  dielectric material. 25- Method according to claims 19 and 22, characterized  in that the deposit of charges is carried out by transfer  of charges between a face of a layer of a material  photoconductor connected to a charge source and  the other side of said layer disposed close  of one side of the strip. 26- Device for implementing the method according to  one of the preceding claims, comprising  means of creation and modulation of the anisotropy of the  material and relative displacement means between the  support formed of the material on the one hand and the means of  creation and modulation of the anisotropy of the material  on the other hand. 27- Device according to the preceding claim,  characterized in that the means of creation and  modulation is the anisotropy of the material include  heating means and field generating means  electric writing in which is likely to  bathe the support.  28- Device according to claim 25, characterized in that  that the means of creation and modulation of  heating include local heating means of the  material. 29- Device according to one of claims 26 to 28,  characterized in that the means of creation and  modulation and the anisotropy of the material are fixed and  the displacement means are capable of causing displacement  the support. 30- Device according to claim 28, characterized in that  that the local heating means include a  laser beam emitter capable of being focused on a  given area of the support. 31- Device according to claims 27 and 30,  characterized in that the field generating means  electrical include material electrodes  conductive and able to pass the laser beam,  arranged on either side of the support, and brought to  different potentials. 32- Device according to claim 27, characterized in that  that the electric field generating means are  suitable for depositing electrostatic charges  on the surface of the support. 33- Device according to one of claims 26 to 32,  characterized in that the means of creation and  modulation of the anisotropy are able to create  multiple parallel tracks each carrying a  series of successive bits. 34- Device according to claims 30 and 33,  characterized in that it comprises either a laser diode  per track, i.e. a single diode associated with means  for modulating the direction of the emitted laser beam  by the single diode. 35- Device for implementing the method according to  one of claims 1 to 23, characterized in that  that it also includes means for reading  information recorded on the material  electro-optic, comprising means generating  electric field of reading, means of generating a  light beam able to pass through the support and  means of optical analysis of said beam, suitable for  reveal the optical anisotropy of the material  representative of the information recorded. 36- Device according to claim 35, characterized in that  that the field generating means include  electrodes integrated either into said means or into  support itself. 37- Device according to claim 35, characterized in that  that the light beam generating means of  reading consist of a beam emitter  laser. 38- Device according to claim 35, characterized in that  that the optical analysis means are of the type  polarimetric and include a polarizer assembly and  crossed analyzer and a photodetector. 39- Device according to claim 35, characterized in that  that the optical analysis means are of the type  interferometric and include a set of mirrors  semi-transparent in contact with the respective faces  of the support, a light source and means  optical analysis capable of measuring the intensity of the ray  bright from the support. 40- Device according to claims 27 and 35,  characterized in that the value of the electric field  writing is less than the field value  electric reading. 41- Device according to claims 30 and 37,  characterized in that the laser transmitter for reading  is of lower power than the laser transmitter for  1 writing. 42- Device according to claims 30 and 37,  characterized in that the support is absorbent for the  wavelength of the writing light beam and little  absorbent (translucent or transparent) for the length  of the reading light beam. 43- Device according to claims 26 and 35,  characterized in that it comprises means  to save reference data on the medium  (corresponding to a given modulation of anisotropy)  and means of comparison between the signals of  reference and the signals corresponding to the information  proper, resulting from the optical analysis of  reading. 44- Device according to one of claims 26 to 43,  characterized in that the support is made of a material  electro-optical, consisting of a doped polymer matrix  conductive molecules. 45- Device according to one of claims 26 to 44,  characterized in that the support is in the form of a strip  or disc. 46- Device according to claim 32, characterized in that  that it includes means for transferring charges between  one side of a layer of photoconductive material  connected to a source, load and the other side of said  layer placed in electrical proximity to one of the faces  support. 47- A method according to claim 13, characterized in that  that we scroll the layer or film in a field  substantially constant reading and we detect  optically the variations in the layer index or  movie in this field to read the recording of the field  writing. 48- Method according to claim 1, characterized in that  the direction of the orienting electric field is  determined to impose on the structure of the material  characteristics of anisotropy preselected in  direction. 49- Method of manufacturing a transducer specific to  provide a picture of voltages in a circuit  electric and containing a layer of material  comprising molecules endowed with activity  electro-optics, one side of which is intended to be  placed in electrical proximity to the circuit areas including  one wishes to obtain an image of tension, characterized in  what we orient said molecules using  method according to one of claims 11 or 12.  50- Device according to claim 39, characterized in that  that semi-transparent mirrors are made of  layers of transparent and conductive material,  deposited on each side of the support, and connected  respectively to a positive potential and to ground. 51- Device according to the preceding claim,  characterized in that the mirror layers are  consisting of segments of given length (in the  support scrolling direction), two segments  consecutive being separated by a length space  small in front of that of said segments.