DE4004206A1 - Liq. crystal element, useful as rotating polariser etc. - has LC layer on substrate, with electrodes arranged to produce rotating electric field in plane of LC layer - Google Patents

Abstract

Liq. crystal (LC) element (I) comprises a LC layer on a substrate, and an arrangement of electrodes (E) to produce an electric field in the LC layer; the novelty is that (E) produces a rotating electric field which is basically parallel to the plane of the LC layer. The LC layer consists of a ferroelectric LC (II) in the smectic phase with individual parallel smectic layers one above the other, pref. a chiral smectic phase with layer thickness smaller than the pitch of the chiral helix; the chiral helix is at least partly twisted by the electric field; LC mol. USE/ADVANTAGE - (I) is useful as an optical element which rotates with the frequency, esp. a rotating polariser; specific applications are as amplitude and/or phase modulators, rotating phase elements with adjsutable phase angle, and for determn. of the phase transition of liq. crystals. The invention provides a device in which the spatial orientation of the LC mols can be adjusted.

Description

The invention relates to a liquid crystal element, comprising a liquid crystal layer on a support and an electrode arrangement for generating a electric field in the liquid crystal layer as well various uses of this element.

Such liquid crystal elements are known and are currently used primarily as display elements (liquid crystal display LCD). For this purpose, the liquid crystal element has two discrete states, between which it is possible to switch over by appropriately controlling the electrode arrangement. The field direction of the electric field is perpendicular to the layer plane - for this purpose the carrier is provided with one electrode and a cover plate covering the liquid crystal layer with the counter electrode. Since the molecules of the liquid crystal try to align themselves parallel (with positive dielectric anisotropy) or perpendicular (with negative dielectric anisotropy) to the field direction due to their dielectric anisotropy, different molecule orientations result in the two switching states. The spatial orientation of the physical quantities linked to the molecular direction and describable as tensors changes accordingly. Thus, both liquid crystals in the nematic phase and in the smectic phase can often be treated as optically uniaxial crystals with an optical axis parallel to the molecular direction. Depending on the relative orientation between the optical axis of the liquid crystal and the direction of radiation and the direction of polarization of a light beam passing through the liquid crystal layer, the liquid crystal element can have a different influence on this light beam in the two switching states, in particular due to different birefringence. The ECB-LCDs (electrically controlled birefringence-LCDs) (magazine "Contacts", Darmstadt, 1989 (1), pages 34-48, publisher: Merck, in particular page 42, FIG. 22) are based on this principle, for example. In the case of a liquid crystal with an optically active phase (cholesteric phase or chiral smectic phase), the phase shift of irradiated linearly polarized light is added as a further optical property. The type and size of the phase rotation in turn depends on the course of the molecular orientation along the light beam path and can be influenced by changing the molecular orientation by means of electrical fields (e.g. when switching from one switching state to the other). An LCD element based on this principle is explained on page 35 ( FIG. 3) of the specified magazine "Contacts". The screw rotation of the optical axis is achieved here in that the carrier and cover plate are coated in such a way that the adjacent liquid crystal region is oriented in a predetermined direction. It is then only necessary to arrange the cover plate rotated relative to the carrier.

In the case of liquid crystals in the chiral smectic C phase, the molecular directions of successive smectic layers describe a kind of helical movement on a cone with a cone angle typical of the liquid crystal material. With the direction of the molecules, the polarization vector P of the spontaneous polarization occurring in this phase changes its direction, so that with macroscopic liquid crystals of this type, polarization disappears with a large number of helical turns. In order to nevertheless obtain a macroscopic polarization, which is of particular advantage for the rapid switching of the LCD, an attempt is made to suppress the helix in a special arrangement. In US-PS 43 67 924 the normally occurring helix structure is shown in Fig. 1. In order to avoid this, the smectic layers, according to FIG. 2, are arranged between the carrier and the cover plate such that the smectic individual layers are perpendicular to the carrier surface or cover plate surface. The distance between the carrier and the cover plate is now made so small that the molecular directions n in all individual layers are parallel to the top of the carrier or the underside of the cover plate. This leaves only two possible orientations of n on the cone. A suitable electrical pulse can be used to switch between the two. The direction of polarization of the incident light can now be selected parallel to one of the two orientations, so that in this case there is a beam passage without birefringence and for the other switching state a beam passage with birefringence. A downstream crossed polarizer can then differentiate between the two states (specified magazine "Contacts", page 46, Fig. 35; magazine "Appl. Phys. Lett." 36 (11), pages 899-901; US Pat. No. 4,367,924) .

All of the above Common to liquid crystal elements is that they are each are only switchable between two states and the Direction of the electrical switching Field perpendicular to the surface of the carrier and thus to Layer level of the liquid crystal layer runs. For this the carrier is just as necessary as that cover plate to be provided with a corresponding electrode Mistake. The top of the carrier and the cover plates below Page is specially treated to the desired orien orientation of the molecular direction. In the case of Liquid crystal element according to US-PS 43 67 924 must be very small plate spacing, for example in the area of 1-3µm are observed.

The invention is based on the object Liquid crystal element of the type mentioned specify which is an analog setting of the Spatial orientation of the molecular direction and thus of the Molecular orientation linked material properties, especially optical properties.

This object is achieved in that the Electrode arrangement essentially to the layer plane parallel electrical rotating field generated in the layer.

Because of the effects of the rotating field on the molecules These molecules strive with their forces Molecular directions to follow the motion of the rotating field. The tensorial linked to the molecular direction Material sizes, such as dielectric constant and Refractive index (birefringence) will be accordingly forced to move. The liquid crystal layer can vary depending on the structure of the Single molecules and how they are coupled as optical uniaxial or biaxial crystal behave with corresponding influencing of the liquid crystal penetrating light beam according to the analog adjustable parameters (frequency and field strength) of the Rotating field.

It is preferably provided that the liquid crystal layer from a ferroelectric liquid crystal in the smectic phase is formed with the layer plane in the essentially parallel superimposed smectic Single layers. Because in contrast to the known Liquid crystal elements the rotation of the molecular direction not restricted in the individual layers but in Contrary is desired at least at one helix end, there is no need to limit the possible Molecular orientations through appropriate Surface treatment of both the carrier and the  Cover plate or the provision of a very small distance between carrier and cover plate. According to the Cover plate u. U. also completely omitted, especially since they are carriers is not required for one of the electrodes.

The preferred use of a liquid crystal with ferroelectric smectic phase compared to one nonferroelectric smectic phase or one The nematic phase lies in the much stronger one Coupling between the spontaneously polarized smectic Layers. Because of this strong coupling are only low field strength required (often enough a field strength of 500 V / cm), albeit higher Field strengths can be advantageous, especially for Influencing the helix shape. A total frequency range of 10 V / cm to 1 MV / cm is advantageous.

There is also a large range of rotational frequencies, in particular between 0.1 Hz and 10 MHz, better between 0.1 Hz and 10 kHz possible, in which the molecule can be taken along Orientation of the liquid crystal layer takes place. At a liquid crystal phase without ferroelectricity on the other hand, essential due to the weaker coupling higher field strengths required (electroclinic effect).

A liquid crystal layer is particularly preferred a ferroelectric liquid crystal in the chiral smectic phase as this leads to a further, depend on the respective molecular orientation leads optical parameters, namely the Phase shift property according to the actual Length of the chiral helix in the liquid crystal in relation to the helix pitch.

To turn the helix rapidly under the influence of the Maintaining the rotating field is particularly preferred Embodiment of the invention provided that the thickness  the liquid crystal layer is smaller than the pitch the chiral helix. Would the pitch of the chiral helix for example the thickness of the liquid crystal layer correspond, u. U. the rotation of the helix abolish initiating forces. To still be with one such a liquid crystal to rotate the helix can be obtained according to a further embodiment use a correspondingly strong electrical rotating field, which then at least partially the chiral helix winds up (and thus increases the pitch accordingly).

A particularly effective way to take the preferred direction of the smectic single layers with clearer Amplitude modulation of a linearly polarized Light beam in time with the rotational frequency of the rotating field results when using a ferroelectric Liquid crystal, the molecules of which have two chiral centers include. This particularly preferably comprises Liquid crystal molecules of the following formula (see also EP-A2-01 59 872):

With such a liquid crystal, the result is wide frequency range from 0.1 Hz to about 10 kHz Molulation depth (ratio of the modulated intensity to the unmodulated intensity) of about 25%.

To generate the rotating field with structurally simple means it is proposed that the electrode arrangement at least three symmetrically arranged phase-rigid controllable  Electrodes. One is particularly preferred Electrode arrangement consisting of four electrodes with 90 ° Phase difference of successive electrodes are controllable.

Due to the relatively small thickness of the Liquid crystal layer is used for the electrodes of the Electrode arrangement only requires a small height. These can be obtained in a simple manner in that the Electrodes of the electrode arrangement on the carrier are evaporated. You preferably get one for thickness parallel height of the liquid crystal layer in the range of 0.6-2µm. A distance has proven particularly useful opposing electrodes between 1µm and 500µm, better between 20µm and 140µm.

The liquid crystal can be directly in the center of the Electrode arrangement on the plate-shaped in particular Carrier are dropped on. Because of the low it is not absolutely necessary for the required layer thickness required to pass the liquid crystal through sidewalls in the Keep center of the electrode assembly. In a another embodiment of the invention comprises the carrier Housing with a substantially cylindrical recess for Recording of the liquid crystal with arrangement of the electrodes of the electrode arrangement on the inner circumferential side of the Recess. With this arrangement one comes because of the in effective capillary forces under the narrow recess Possibly both without a cover plate at one end of the receptacle also without a carrier plate at the other end of the holder. These cylindrical arrangement is particularly suitable for use in an optical fiber system, since the respective The light guide is only to be coupled to one end of the recess.

The electrodes can be easily moved from to Cylindrical axis of the recess formed parallel wires be.  

The carrier particularly preferably comprises a piece of pipe inner diameter between 50 and 1000µm, preferably about 300 microns, and preferably a length from 1-5 mm, ideally about 3 mm.

The carrier can have a recess at one end have final plate.

As described above, the from the molecular directions of the successive Individual layers of the liquid crystal formed by helix Application of the rotating field on the one hand according to the Rotate the selected rotational frequency as a whole and to others depending on the applied field strength deform, especially wind up to the pitch to increase accordingly. One can according to another Embodiment of the invention, however, also an end of determine the chiral helix in a manner known per se (by appropriate treatment of the top of the corresponding Carrier). In contrast to the prior art, however not also fixed the other helix end so that it is can freely adjust its rotational orientation. Now according to the invention, the rotating field is switched on, this results the possibility to wind the helix (direction of rotation of the Rotating field opposite to the winding direction of the helix, based on the fixed helix end). Runs the Direction of rotation of the rotating field, however, in the direction of the turns the helix, the helix is wound more strongly (reduction the pitch). This certain "elasticity" of the helix results from the not too strong directional coupling successive smectic individual layers. The The pitch of the helix can thus be increased continuously or reduce. This also allows the angle between the molecular direction of the smectic single layer on fixed helix ends and the molecular direction of the continuously increase the smectic layer at the other end or reduce and thus the phase rotation angle to  which the direction of polarization of light is twisted, if this at the specified end of the helix in the Liquid crystal occurs. The liquid crystal element leaves itself as a phase shift element with optional use adjustable angle of rotation. This element rotates the electrical polarization vector of an incoming Lightwave.

The liquid crystal element described above leaves as an optical element rotating at the rotational frequency, especially use a rotating polarizer. This is just select a liquid crystal material which looks like an optically uniaxial or biaxial Crystal or behaves as a phase rotator.

Due to the fact that it extends over five powers of ten Rotational frequency range can be the inventive Liquid crystal element with advantage also as amplitude and / or phase modulator can be used. To Amplitude modulation can also result in loss of light inner suggestions of the liquid crystal contribute to their Size of the respective orientation of the electrical Polarization vector of the incoming light wave relative to the current molecular direction of the smectic Individual layers is dependent. Mostly with parallel Orientation the interaction to be maximal and at vertical arrangement minimal. If no light source for Polarized light is available conventional polarizer the liquid crystal element be upstream. If necessary, one can also Pair of polarizers on both sides of the liquid crystal element order, especially to suppress the modulated light component.

Liquid crystals can often be a variety of different Go through phases, knowing the exact location the phase transitions for the further development of  Liquid crystals, especially for display liquid crystal Elements that is of great importance. With the help of the invention contemporary liquid crystal element with liquid crystal in the ferroelectric smectic phase, the two phase boundaries to the two subsequent phases determine with high accuracy by just that Disappearance of the polarization effects due to the rotating field the phase boundary is tracked.

The invention is preferred in the following Exemplary embodiments explained with reference to the drawing. It shows:

Figure 1 is a rough schematic principle illustration of an arrangement for light modulation by means of a charged with a rotary electric field liquid crystal element; FIG.

Figure 2 is a schematic view of the electrode arrangement of the liquid crystal element showing the individual electrode excitation voltages.

Fig. 3 is a vertical section through two mutually opposite electrodes (section line III-III in Fig. 2);

... 4A and 4B with the arrangement of Figure 1 received waveforms at a rotational frequency of 500 Hz (Fig. 4A) and 60 Hz (Fig. 4B); and

Fig. 5 is a perspective view similar to Fig. 2 of another embodiment of the invention.

The liquid crystal element according to the invention is generally designated 10 in the figures . It consists of a support 12 in the form of a flat horizontal glass plate onto which an electrode arrangement 14 is applied, preferably vapor-deposited. The electrode arrangement in turn consists of four electrodes 16 , 18 , 20 , 22 , which are opposite each other in pairs at a distance a ( FIG. 3), both pairs 16 , 20 and 18 , 22 crossing each other at right angles (see also FIG. 5). . In other words, the electrodes 16 , 18 , 20 and 22 run cross-wise from a free measuring volume V with a square base (side length a). The height b of the measurement volume V corresponds to the electrode height. In order to avoid direct contact or rollover between adjacent electrodes, the width c of the electrodes is smaller than the electrode spacing a.

For example, quartz glass with a diameter of 20 mm, a thickness of 2 mm and a surface quality of λ / 10 is used as the carrier 12 . The electrode arrangement is vapor-deposited onto this carrier using the photoresist technique. The electrode height b is between 0.6 µm and 2 µm. Electrode arrangements with the following dimensions have proven themselves: a = 20 µm and b = 10 µm; a = 70µm and b = 50µm; a = 140µm and b = 100µm. For temperature measurement in the immediate vicinity of the sample in the sample volume V, an indicated in FIG . B. incorporated downwardly open blind hole 24 in the plate 12 (in particular ultrasonic drilling). A thermocouple 26 (NiCrHi) is inserted into this blind hole 24 , the lead wires 28 of which are also indicated in FIG. 2.

To control the four electrodes 16 , 18 , 20 and 22 , they are connected to a corresponding voltage source (lines 32 ) shown as block 30 in FIG. 1. The aim is to generate a rotating field in the sample volume V with an axis of rotation 38 running through the center of the sample volume V and perpendicular to the flat upper side 36 of the carrier 12 . In the four-electrode arrangement shown, the electrodes ( 16 , 18 , 20 , 22 ) which follow one another in the desired direction of rotation are each provided with a corresponding, for. B. sinusoidal control voltage supplied with a constant phase difference of + 90 ° between the respective electrode and the next electrode. In FIG. 2, which are the individual electrodes 16, 18, indicated 20 and 22 associated control voltages of the respective next electrode.

To generate these four control voltages, for example, two phase-coupled frequency generators can be used using two voltage inverters. However, the four voltage curves can also be entered in a memory element (EPROM) and read out triggered by a function generator. With both arrangements, modulation effects due to the rotating field can be determined on a liquid crystal in the chiral smectic phase, as will be explained below with reference to FIGS. 4A and 4B.

The electrical contact to the fine electrodes 16 , 18 , 20 , 22 of the electrode arrangement 14 and the electrical feed lines 32 was produced by the silver application 40 indicated in FIG. 2. For the metrological detection of the bilateral phase boundaries of the chiral smectic phase used, it is necessary to maintain the sample volume V at a precisely specifiable temperature. This is achieved by connecting or installing the support plate 12 in a thermostat.

The measuring arrangement shown in FIG. 1. It can be seen a light source (laser) 42 which emits a light beam 44. This passes through a linear polarizer 46 . A double arrow 48 in FIG. 1 symbolizes the resulting direction of polarization of the light. This is followed by a converging lens arrangement 50 for focusing the light beam 44 onto the sample volume V in the subsequent liquid crystal element 10 . In order to allow the light beam 44 to reach the sample volume V as freely as possible, the carrier 12 is accordingly designed to be transparent.

A further converging lens arrangement 54 follows, which concentrates the light emitted by the sample in the sample volume V into a subsequent detector 56 .

To evaluate the measurements, both the detector 56 and the function generator 30 are connected to an evaluation device 62 via corresponding lines 58 , 60 . A screen 64 for displaying the measurement curves is indicated in FIG. 1.

The sample material on which the measurement curves according to FIGS . 4A and 4B were obtained consists of a pure liquid crystal sample with two chiral centers with the structure (4- (3 - (S) -methyl-2 (S) -bromopentanoyloxy) - 4'-octyloxy-biphenyl). The synthesis was carried out according to known methods (SU Vallerien, F. Kremer, H. Kapitza, R. Zentel, W. Frank Physics Letters A, 138, 219 (1989); SU Vallerien. R. Zentel, F. Kremer, H. Kapitza , EW Fischer Proceedings of the Second Ferroelectric Liquid Crystal Conference (2. FLCC) at Göteborg, Sweden (1989) Ferroelectrics, in press; SU Vallerien, F. Kremer, H. Kapitza, R. zentel, EW Fischer Proceedings of the Seventh International Meeting on Ferroelectricity (IMF-7) at Saarbrücken, FRG (1989) Ferroelectrics, in press; K. Yoskino, M. Ozaki, S. Kishio, T. Sakurai, N. Mikami, R. Higuchi, M. Honma Mol. Cryst Liq. Cryst. 144, 87 (1987)). The formula expression is:

The lower phase transition temperature of the smectic phase S _C * (towards the crystal phase) is 293K; the upper phase transition temperature (to the orthogonal phase S _A *) at 315K.

To carry out the measurement curves shown in FIG. 4A and 4B resulting measurements of the supports was warmed to about 80 ° C for 12, and then a small amount of liquid crystal material (less than 1 mg) is filled into the sample volume V. Here, the sample surface ended approximately with the top of the electrodes 16 , 18 , 20 , 22 . Due to the low sample material height, there is no fear of the sample material flowing out of the sample volume V open between the electrodes.

The electrical rotating field was then generated by the described control of the electrodes 16 , 18 , 20 and 22 and the sample was cooled to the temperature range of the S _C * phase. At low rotational frequencies (below 10 Hz), a polarization effect following the rotation of the field could be observed directly with the aid of a polarization microscope aimed at the sample. Electrical field strengths in the range of 500 V / cm were sufficient for this.

In another arrangement, not shown, for higher ones Rotational frequencies became a stroposcopic arrangement selected with direct observation of the sample volume and intermittent interruption of the observation beam through a breaker disc (chopper). With more suitable Setting the chopper frequency resulted in a standing Observation image. From the chopper frequency derive that the frequency with which the image of the Sample in the polarizing microscope changes the rotational frequency corresponded to the stimulating field.

The measurement curves according to FIGS . 4A and 4B were obtained with the arrangement according to FIG. 1. FIG. 4A shows the measurement at 500 Hz and FIG. 4B shows the frequency of the rotating field at 60 Hz. The time t is plotted on the right and the voltage U of the sinusoidal excitation voltage (at one of the electrodes 16 , 18 , 20 , 22 ) or the intensity I of the radiation picked up by the detector 56 is plotted upwards.

When measuring at 500 Hz, the intensity is I with the Frequency of the rotating field modulated corresponding frequency. For the approximately sinusoidally modulated portion there is an non-modulated intensity component added to a typical modulation strength (ratio of the modulated Intensity to unmudolated intensity) of 25%.

In the measurement according to FIG. 4B at 60 Hz, there was an intensity modulation that deviated from the pure sinusoidal shape, but also here with a modulation frequency corresponding to the rotational frequency of the field. Instead of the usual sine minimum, there is a secondary maximum 66 , which is attributed to internal excitation mechanisms (Goldstone Mode), since their excitation frequency is close (approx. 100 Hz).

It is assumed that the measured modulation of the polarization following the electrical rotating field or of the intensity picked up by the detector 56 can be attributed to the following effects:

The liquid crystal in the sample volume V is oriented in its smectic S _C * phase in such a way that the individual layers 70 are arranged parallel to the carrier surface 36 and are stacked one above the other according to FIG. 3. Each smectic individual layer 70 has a main direction n, to which all elongate molecules are arranged in parallel. The directions n of the layers 70 each lie on the cone surface of an upwardly open cone 72 with a cone angle typical of the material used. Progressing from layer to layer, the individual directions n describe a helix with a pitch that is also characteristic of the material. With the material used, this amounts to about 6-8 µm and is therefore significantly larger than the height of the sample volume V (determined by the electrode thickness b in the range between 0.6 µm and 2 µm). Accordingly, the directions n of the individual layers 70 in the sample volume V in the projection onto the surface 36 are limited to a relatively small angular range. Accordingly, there is also spontaneous polarization, which leads to a strong coupling with the exciting rotating field. For a given field direction, the molecular directions n will accordingly try to orient themselves in the field. If the field rotates, the directions n are taken along.

From the respective orientation of the molecular direction n important physical properties now depend on this Layer from, especially the dielectric constant and Birefringence. Because the molecules used are optically active (two chiral centers each) also results one of the current position of the molecular direction n dependent phase shift of a sample passing through Light beam. In this case it works Liquid crystal element than with the excitation frequency rotating phase rotator. The angle at which the Phase is rotated depends on the height of the sample volume (actual height of the helix) compared to the pitch the helix.

If this pitch is in the range of the sample volume height or is even lower, there may be the possibility by creating a rotating field with increased field strength Turning the helix more or less, d. H. the pitch enlarge accordingly. Then here is the one Condition for carrying the molecular directions fulfilled.  

Due to the birefringent properties of the individual layers, depending on the molecular and layer structure, the liquid element can also be viewed as a single- or biaxial optical crystal, of which a main axis rotates on the cone 72 in time with the rotating field.

The modulation of the intensity I of the light received by the detector 56 after passing through the polarizer 46 and the liquid crystal element 10 is primarily attributed to the fact that an interaction takes place between the irradiated linearly polarized light and the liquid crystal, which stimulates the liquid crystal The consequence is a corresponding loss of energy in the light emerging from the liquid crystal element. However, this interaction depends on the relative orientation of the current polarization direction of the light and the molecular directions. For example, the dipole moment induced by the electric field vector of light is only maximum for certain molecular arrangements and is minimal in this regard in the position rotated by 90 °.

In Fig. 5, a further 110 designated liquid crystal element is shown in simplified form, in which also the rotation effect of the rotating electric field to the molecular orientations of the smectic individual layers is utilized 170, but here while fixing the lower in Fig. 5 Helix end.

The liquid crystal element 10 consists of a tube piece 180 with an axial length of approximately 3 mm and a clear inner diameter of approximately 300 μm. The electrode arrangement 114 now consists of four wire-shaped electrodes 116 , 118 , 120 and 122 , each of which is mounted in a radial section offset by 90 ° relative to the cylinder axis 182 of the pipe section 180 and parallel to the pipe section inside 184 . In each case, a dash-dot line indicates electrical lines for connecting these electrodes 116 , 118 , 120 and 122 to the voltage source 30 (components in FIG. 5 which correspond in function to components in FIGS. 1-4 carry the same Reference numbers, however, each increased by the number 100).

The electrodes 116 , 118 , 120 and 122 are gold wires with a diameter of 5 µm.

The light beam 144 enters the sample volume V within the pipe section 180 along the axis 182 . It is linearly polarized in the direction of the double arrow 148 . If liquid crystal material is therefore poured into the sample volume V, which remains in the sample volume V due to the capillary forces, a rotating field applied to the electrodes 116-122 corresponding to FIGS. 1-4 leads to the polarization effects and amplitude modulation effects described there. As described, the rotating field takes along the helix of the molecular directions n.

However, one end of the helix can also be fixed, in particular in that the sample volume V in FIG. 5 is closed at the bottom by a plate 188 , the upper side 190 of which faces the sample volume V is treated in such a way that the one lying directly on the upper side 190 smectic single layer aligns itself with its molecular directions in the given direction. This direction is symbolized by arrow 192 in FIG. 5. This direction corresponds to the projection of the molecular direction n lying on the cone onto a plane perpendicular to the axis 182 . The individual smectic layers 170 are arranged one above the other in the direction of the axis 182 with a layer plane perpendicular to the axis 182 .

Without an electric field, the screw movement along the helix already described results for the molecular directions of the successive smectic individual layers 170 . The directional arrow 194 assigned to the uppermost individual layer 170 in FIG. 5 (again as a projection of the molecular direction n) is rotated by a certain angle α with respect to the starting direction 192 in accordance with the normally occurring helical pitch.

The chirality of the smectic phase has the result that the direction of polarization (double arrow 148 ) of the light passing through the sample volume V is rotated by the same angle α, provided that its direction of polarization coincides with the initial direction 192 when the light enters.

Due to the more or less strong directional coupling of successive smectic individual layers 170 , the helix shape can now be changed by rotating forces acting on the helix, because a helix end is fixed. If, for example, a rotating field rotating in the direction of the angle α in FIG. 5 is applied to the electrodes 116-122 , the helix is rotated to a greater extent - the angle α is correspondingly larger. If a rotating field is applied in the opposite direction, the angle α is accordingly reduced. The result is a phase rotation element with an optionally adjustable rotation angle. The angle of rotation can be adjusted continuously so that the element can be used as an analog optical element.

Liquid crystal elements according to the invention can thus be used as optical elements with birefringent, phase-shifting or amplitude-modulating properties, which acts as if it were physically rotating with the rotational frequency of the exciting field (with the main axis rotating around the cone). By appropriately switching the liquid crystal element into the beam path of a linearly polarized light beam (for example a glass fiber light guide), phase modulation or amplitude modulation of the emitted light beam can be achieved. The non-modulated intensity component of the emitted light can possibly be suppressed by connecting a polarizer which is parallel or crossed to the direction of polarization of the incident light. Since the observed effect is linked to the presence of a certain smectic phase, in particular S _C *, the phase transition temperature to the next or previous phase can be determined with high accuracy by observing the disappearance of the effect with increasing or falling temperature. The liquid crystal elements according to the invention can be used as polarization controllers, in particular in optical communication technology. By changing the helix shape (helix slope) by applying correspondingly strong fields or by fixing a helix end and applying the rotating electrical field, the phase rotation angle of the liquid crystal element can be varied analogously in the desired manner.

Claims (24)

1. liquid crystal element ( 10 ; 110 ) comprising a liquid crystal layer on a carrier ( 12 ) and an electrode arrangement ( 14 ; 114 ) for generating an electric field in the liquid crystal layer, characterized in that the electrode arrangement ( 14 ; 114 ) generated in the layer essentially parallel rotating electrical field to the layer plane. 2. Liquid crystal element according to claim 1, characterized in that the liquid crystal layer is formed by a ferroelectric liquid crystal in the smectic phase with the layer plane essentially parallel superimposed smectic individual layers ( 70 ; 170 ). 3. Liquid crystal element according to claim 2, characterized by a chiral smectic phase. 4. Liquid crystal element according to claim 3, characterized characterized in that the thickness of the Liquid crystal layer is smaller than the pitch the chiral helix. 5. Liquid crystal element according to at least one of the preceding claims, characterized in that the chiral helix from the rotating electrical field at least partially wound up. 6. Liquid crystal element according to one of the claims 3-5 characterized in that the ferroelectric liquid crystal molecules with two includes chiral centers.   7. Liquid crystal element according to claim 6, characterized by a ferroelectric liquid crystal with molecules of the following formula: 8. Liquid crystal element according to claim 7, characterized by a ferroelectric liquid crystal with molecules of the following formula: 9. Liquid crystal element according to at least one of the preceding claims, characterized in that the electrode arrangement ( 14 ) has at least three symmetrically arranged, phase-rigidly controllable electrodes. 10. Liquid crystal element according to claim 9, characterized in that the electrode arrangement ( 14 ) has four electrodes ( 16 , 18 , 20 , 22 ) which can be controlled with a 90 ° phase difference of successive electrodes. 11. Liquid crystal element according to at least one of the preceding claims, characterized in that the electrodes ( 16 , 18 , 20 , 22 ) of the electrode arrangement ( 14 ) are evaporated onto the carrier ( 12 ). 12. A liquid crystal element according to claim 11, characterized in that the electrodes ( 16 , 18 , 20 , 22 ) have a height (b) parallel to the thickness of the liquid crystal layer in the range between 0.6 and 2 µm. 13. Liquid crystal element according to at least one of claims 1-10, characterized in that the carrier comprises a housing with a substantially cylindrical recess for receiving the liquid crystal, and that the electrodes ( 116 , 118 , 120 , 122 ) on the inner peripheral side ( 184 ) the recess are arranged. 14. Liquid crystal element according to claim 13, characterized in that the electrodes ( 116 , 118 , 120 , 122 ) of the cylinder axis ( 182 ) whose recess parallel wires are formed. 15. Liquid crystal element according to claim 14, characterized in that the carrier comprises a tube piece ( 180 ) with a light inner diameter between 50 and 1000 µm, preferably about 300 µm, and preferably a length of 1-5 mm, preferably about 3 mm. 16. A liquid crystal element according to at least one of claims 13-15, characterized in that the carrier has a plate ( 188 ) which closes off the recess at one end. 17. Liquid-crystal element according to at least one of the preceding claims, characterized in that the contact surface ( 190 ) of the support lying directly on the liquid crystal and parallel to the layer plane of the smectic individual layers ( 170 ) is treated in such a way that the contact surface ( 190 ) immediately adjacent smectic single layer ( 170 ) oriented in a predetermined direction ( 192 ). 18. Liquid crystal element according to at least one of the preceding claims, characterized in that the rotational frequency of the rotating field between 0.1 Hz and 10 MHz, better between 0.1 and 10 kHz. 19. Liquid crystal element according to at least one of the preceding claims, characterized in that the amplitude of the rotating field of a field strength is between 10 V / cm and 1 MV / cm and ideally approximately Is 500 V / cm. 20. Liquid crystal element according to at least one of the preceding claims, characterized in that the distance (a) from each other Electrodes is between 20 µm and 140 µm. 21. Use of the liquid crystal element after at least one of the preceding claims as with the rotational frequency rotating optical element, especially as a rotating polarizer. 22. Use of the liquid crystal element after a of claims 1-20 as amplitude and / or Phase modulator. 23. Use of the liquid crystal element after a of claims 1-20 as a phase shift element optionally adjustable angle of rotation α. 24. Use of the liquid crystal element after at least one of claims 1-20 Phase transition determination of the liquid crystal.