Electrically controllable optical element, in particular thin-film cell with an optically effective surface profile and method for its production

Abstract

Electrically controllable optical element with a cell (D) filled with Kerr mixture (K) having two substrates (1a, 1b) and a conductive layer (2a, 2b) applied to the inner surface of each substrate (1a, 1b), wherein the Kerr mixture (K) comprises a mixture of rod-shaped molecules with a large dipole moment (5) and semi-mesogens (4) as active components, and wherein the Kerr mixture (K) forms a thin layer with a photopolymerization-produced, wide-mesh, anisotropic network (9) between a structured and / or planar conductive layer (2a, 2b) applied to a substrate (1a, 1b) in a thin-film cell (D), such thatthat, according to the electro-optical Kerr effect, the state of the active composites of semi-mesogens (4) and rod-shaped molecules with a large dipole moment (5) of the Kerr mixture (K) is isotropic without an electric field in the operating temperature range, and a change in the voltage-induced phase shift or refractive index shift in the optical element is generated by electrically continuous adjustment of the voltage U or by applying a constant voltage, characterized in that, in addition to the conductive layer (2a, 2b), an optically effective surface profile (O) is incorporated on the inner surface of a substrate (1a or 1b) or into the substrate (1a or 1b) or of both substrates (1a and 1b).

Description

[0001] The invention relates, according to claim 1, to an electrically controllable optical element, in particular a thin-film cell with an optically effective surface profile, and according to claim 10 to a method for its production based on liquid composites.

[0002] Adjustable optical elements are currently primarily mechanical systems. These are heavy and bulky, and due to the use of mechanical drives, they are prone to malfunctions and often too slow. Non-mechanical optical elements are therefore advantageous and the subject of current development. While solutions have already been commercialized for such optical elements with smaller usable diameters, this is not yet the case for larger apertures.

[0003] The electro-optic Kerr effect (J. Kerr 1875), also known as the quadratic electro-optic effect or electric birefringence, describes the occurrence of birefringence that increases with the square of the electric field strength of an applied field. In this effect, molecules with permanent dipole moments in an isotropic fluid align themselves in the electric field. This alignment makes the material optically anisotropic in the field, exhibiting a higher refractive index in the field direction and a lower refractive index perpendicular to it, compared to the isotropic fluid in its undisturbed state. In a Kerr cell, the refractive and polarization behavior of a material is altered by an externally applied electric field, allowing electrical signals to be converted into optical signals. An electric field is applied across electrode plates in the Kerr fluid, perpendicular to the direction of the transmitted light.The Kerr fluid usually consists of pure nitrobenzene, which has a Kerr constant K of 2.44 × 10 . -12 m / V 2 Nitrotoluene is liquid at room temperature and mixes well with alcohols, ethers, and benzene. For comparison, nitrotoluene has a Kerr constant K of 1.37 × 10⁻⁶. -12 m / V 2 and water has a Kerr constant K of 5.1 × 10 -14 m / V 2 With the aforementioned liquid and typical cell sizes in the centimeter range, electrical voltages in the range of a few kilovolts are required. The front and back of the Kerr cell are made of transparent glass, while the metal side walls serve as electrode plates.

[0004] The technical application of the Kerr cell is thus a capacitor with the Kerr liquid – usually nitrobenzene – as its dielectric. It is placed between crossed polarizers whose principal optical axes are each inclined at 45° to the direction of the electric field. If no voltage is applied to the cell, light cannot penetrate this arrangement.

[0005] In the electric field, the Kerr fluid becomes birefringent, meaning that the component of light oscillating in the direction of the field has a different propagation speed than the component oscillating perpendicular to the field. Therefore, a phase shift δ exists between the two components as they exit the Kerr cell. The optical arrangement then causes the amount of light L to pass through, which is related to δ and the amount of light L0 entering the cell in the following way: L=L0⋅sin2 δ / 2

[0006] The phase shift δ depends on the field strength E, the length l of the light path between the capacitor plates and the Kerr constant of the dielectric B according to the relationship δ=2π⋅B⋅1⋅E2

[0007] This will L=L0⋅sin2⋅(π⋅B⋅1⋅E2)

[0008] To significantly increase the sensitivity of the Kerr cell as a light relay, it is known from DE 555 249-A to impart an additional, unchanging phase shift to the partial beams of the polarized light used, in addition to the voltage-dependent phase shift generated in the Kerr cell. To generate this additional phase shift, a birefringent crystal plate is placed in the light path.

[0009] For liquids—such as nitrobenzene—the observed refractive index difference is very low, even when voltages in the kilovolt range are applied. Due to the small magnitude of the long-known Kerr effect, the fabrication of active optical elements based on it initially appears impossible. For example, the Kerr constant, which quantifies the strength of the Kerr effect, is only about 2.44 × 10⁻⁶ for nitrobenzene (Zinth, W., Optics, Oldenbourg-Verlag, Munich, 2011). -12 mV -2 .

[0010] For many decades, attempts have been made to find liquids with a higher Kerr constant than the previously used nitrobenzene, thereby achieving the same effect at a lower control voltage. For example, DE 622 368-A discloses a Kerr cell liquid in which double or triple substituents of the benzene ring, which are solid at room temperature, are dissolved in a solvent whose Kerr constant is on the order of that of nitrobenzene. The substituent NO₂ is advantageously preferred. According to DE 622 368-A, the following solvents are used, for example: Nitrobenzen meta nitritoluene ortho nitritoluene

[0011] The following substances are proposed for dissolution: ortho Dinitrobenzene, Nitraniline (preferably para), para Nitrotoluene, ortho Chloronitrobenzene, 1-Chloro-2,3-Dintrobenzene, Dichloronitrobenzene 1:2:3, Nitronaphthalene alpha, Dinitronaphthalene 1:8.

[0012] Currently, elements based on macroscopically oriented liquid-crystalline materials are still in use. However, these systems have the disadvantage that they only affect one polarization direction of the light, leaving light with the perpendicular polarization direction almost unaffected. Because of this, absorptive polarizers are combined with such elements. This necessarily leads to a reduction of the light intensity to less than 50%. To overcome this disadvantage, it has been proposed to combine two (or more) identical elements with orthogonal orientations. This results in significantly higher complexity and introduces additional sources of error due to spatial crosstalk, optical losses, and further problems regarding the precise alignment of the elements relative to each other.

[0013] Other isotropic LC states include scattering PDLCs, low-scattering nano-PDLC systems, and isotropic polymer-reinforced blue LC phases. These are characterized by high switching voltages caused by the polymer matrix and domain boundaries. In contrast to reflective elements, such as LC phase modulators, the residual scattering that occurs in transmissive elements is a problem.

[0014] In isotropic liquids with high anisotropy of the dipole moment and a rod-shaped molecular form, significantly larger refractive index differences can be achieved, resulting in Kerr constants that are orders of magnitude higher. This has already been demonstrated, for example, for isotropic phases of liquid crystals at higher temperatures.

[0015] Significantly higher values ​​can be measured in isotropic melts of liquid crystals (J. Chem. Soc, Faraday Trans. 2, 1976, 72, 1447-1458 / DOI: 10.1039 / F29767201447) just above the clarification temperature or in polymer-stabilized isotropic liquid crystals (Appl. Phys. Lett. 98, 023502 (2011) / DOI: 10.1063 / 1.3533396) and polymer-stabilized blue phases of liquid crystals. Here, Kerr constants of up to 300 × 10⁻⁶ were measured. -12 mV -2 measured.

[0016] A major disadvantage of the Kerr effect in such systems, however, is its very strong temperature dependence, as described, for example, for the isotropic melt of the liquid crystal 5CB (Dunmur DA and Tomes A. E., 1981, Mol. Cryst. Liq. Cryst. 76, 231). In polymer-stabilized isotropic liquid crystals, the temperature dependence could be reduced, but only for a very limited temperature range (J. Phys. D: Appl. Phys. 42 (2009) 112002 / DOI: 10.1088 / 0022-3727 / 42 / 11 / 112002). For most of these systems, the required high voltage and long switching times prove to be disadvantageous.

[0017] To create improved electro-optical elements in combination with planar waveguides or optical fibers for optical communication applications requiring modulation, attenuation, polarization control, and switching of optical signals, a waveguide device is known from WO 2004 / 046796-A1. This device comprises an optical waveguide core and a cladding optically coupled to the core. The cladding includes an optically functional zone with a Kerr-effect medium having a refractive index that varies in response to a control signal applied to the optically functional zone. The refractive index of the optically functional zone is lower than that of the optical waveguide core at the optical wavelength and temperature during device operation.The sheath comprises an optically functional zone defined by an unpolarized, substantially isotropic or substantially anisotropic polymeric sheath material. In particular, the sheath material is a polymeric / chromophoric lining characterized by chromophoric mobility sufficient to enable the optically functional zone to undergo a passive transition from a substantially oriented state to a substantially isotropic state in less than about one second. Specifically, the polymeric / chromophoric lining contains at least about 5 wt% and about 20 wt% of chromophore and is plasticized, and the Kerr effect medium comprises a polymer selected from polycarbonate, terpolymer, PMMA, and polycyclohexane. Preferably, the chromophore includes a donor component, a bridging component with a conjugated and / or aromatic component, and an acceptor component.Specifically, 12 different structural formulas of the Kerr-effect medium are given. Furthermore, a controller is provided that is configured to control or regulate the operating temperature of the waveguide device. The polymeric plating or lining medium is characterized by an effective glass transition temperature that is lower than the operating temperature of the device. It should be noted that the effective glass transition temperature of a material is the temperature at which the reorientation mobility of the chromophore shows a relatively large increase as a function of the material's temperature. The effective glass transition temperature of an electro-optical material can be determined by measuring the electro-optical response of the material as a function of its temperature.The plating medium exhibits an acceptable degree of chromophore mobility and physical stability, either by incorporating a plasticizing agent into the plating medium or by ensuring that the effective glass transition temperature of the plating medium is lower than the operating temperature of the device. Specifically, the plating media of WO 2004 / 046796 A1 are characterized by effective glass transition temperatures below approximately 120°C, down to 20°C. To achieve sufficient chromophore mobility, a solvent is provided in the plating medium. In the case of a polymeric plating medium containing a chromophore and a base polymer, suitable solvents dissolve both the chromophore and the polymer. In many cases, the use of such solvents results in suitable operating temperatures of the devices at or near room temperature.An electric field E is generated in the optically functional zone of the plating using control electrodes. Alternatively, the control signal can produce a thermal signal, with the optically functional zone of the plating responding to the magnitude of the thermal signal. In either case, the waveguide device includes a suitable controller configured to independently modify the optical properties of optically functional sections of the optically functional zone. In particular, applying a control voltage to an electro-optic polymer plating or coating also induces successive phase shifts Δ□ in the optical signal; however, successive phase shifts of the same value are induced with progressively smaller increases in the control voltage V (E approximately sin Δ□). 2 □, where □ = BV 2Therefore, in the case of successive phase shifts Δ□ of 180°, the magnitude of the successive control voltage increments Vπ required to index successive phase shifts of 180° decreases with increasing magnitude of the control voltage V. To operate a Mach-Zehnder interferometer (i.e., a beam splitter with two arms for measuring phase shifts or for modulating light by selective phase modulation in one arm of the interferometer, or for wavelength-dependent demultiplexing) over a 180° phase shift, approximately 340 volts are required for the waveguide device of WO 2004 / 046796-A1. However, the next 180° phase shift at approximately 520 volts is achieved simply by increasing the drive voltage by approximately 180 volts (the difference between 520 volts and 340 volts). A third 180° phase shift occurs at approximately 610 volts, an increase of only about 90 volts.A simple extrapolation suggests that with a bias voltage of approximately 3000 volts, a Vπ drive voltage of approximately 4 volts can be achieved. By improving the polymer plating or coating medium and refining the electrode configuration used as control electrodes, a 180° phase shift can be achieved with drive voltages of less than 5 volts and a bias voltage of approximately 1000 volts.

[0018] Another technical application of the electro-optical Kerr or Pockels effect in the field of optical transmission or communication is the use of gratings with electrically adjustable refractive index and electrically adjustable spatial periodicity as input / output couplers, waveguide coupling elements (interfaces), mode / polarization converters, mode / polarization filters, deflectors or reflectors, and reflectors. For this purpose, a diffraction grating with an electrically adjustable refractive index and an electrically adjustable spatial frequency is known from EP 1 155 355 B1, wherein the grating comprises: • a substrate; • an electro-optical structure extending over the substrate, wherein the electro-optical structure includes a waveguide with a propagation axis; • a first and a second electrode structure for generating an electric field between them, wherein the electric field induces the diffraction grating in the waveguide, wherein the first and second electrode structures are arranged on opposite sides of the electro-optic structure and each extends in a plane parallel to the propagation axis of the waveguide, wherein the first electrode structure comprises a first and a second set of fingered fingers, wherein the first set of fingers is under a potential V0 and the second set of fingers is under a potential V0 + ¢ V, wherein V0 is variable for adjusting the refractive index of the diffraction grating and is variable for switching the spatial periodicity of the grating between discrete values.

[0019] Alternatively, the diffraction grating can be used to modify externally incident light: • a substrate; • an electro-optical structure that extends over the substrate; • a first and a second electrode structure for generating an electric field between them, wherein the electric field induces the diffraction grating in the electro-optic structure, wherein the first and second electrode structures extend along superimposed planes parallel to each other and to the electro-optic structure and are arranged on opposite sides of the electro-optic structure, wherein the first electrode structure comprises a first and a second set of fingered fingers, wherein the first set of fingers is under a potential V0 and the second set of fingers is under a potential V0 + ¢ V, wherein V0 is variable for adjusting the refractive index of the diffraction grating and is variable for switching the spatial periodicity of the grating between discrete values.

[0020] In specific instances, the diffraction grating of EP 1 155 355 B1 can be configured to act as a Bragg filter, or the grating can be used for collinear reverse coupling for a reflector function, serving as an active optical filter for distributed feedback (DFB) or distributed Bragg reflection (DBR) lasers. Other embodiments relate to applications in wavelength division multiplexing (WDM) systems for fiber optic communication. The grating can be used alone or in combination with other electro-optical components to form integrated structures.The lattice comprises an electro-optical structure, for example, an electro-optical rod made of a material such as LiNbO3 or an electro-optical polymer, preferably with a thickness of approximately 0.5 to 2 µm and a width of about 5 µm, extending over a substrate. First and second electrode structures are provided on opposite sides of the electro-optical structure, parallel to the direction of propagation. The first and second electrode structures, which are particularly comb-like in shape, are subjected to different potentials to generate an electric field between them and thus the periodicity resulting from the electric field. Modern nanofabrication technologies enable fingered electrode structures with submicron finger spacing.The fingered electrodes are made of a transparent conductive material and indium tin oxide (ITO), for example, with a width a = 105 µm and an ITO thickness of 0.1 µm. The gaps between the waveguide and the electrode fingers are filled with buffer layers of a dielectric material, such as SiO₂, which has a lower refractive index than that of the waveguide. These buffer layers form the cladding of a waveguide within the electro-optic rod and protect the guided wave from lossy interactions with the electrodes.

[0021] Furthermore, in the technical field of stereo television, the utilization of the electro-optical Kerr effect in conjunction with prismatic lenses of polarizing glasses is known from DE 28 28 910-A1. For this purpose, a polarizing device is arranged and dimensioned such that it extends over the entire surface of the screen of a television set, its polarization plane being rotatable for selective alignment with the polarization plane of the left or right lens of the viewer's polarizing glasses. The rotation of the polarization plane of the polarizing device is preferably achieved by a Kerr effect cell consisting of an optically active material that rotates the polarization plane of the transmitted polarized light depending on a voltage applied to opposite electrodes of the cell by a control voltage source.It is possible to reverse the role of the left or right lens, whereby in one state of the polarizing device the left lens transmits the light passing through the polarizing device, while the right lens acts as a dark filter, and in the other state of the device the lenses block or transmit the light passing through the polarizing device. Furthermore, at the viewer's discretion, either the left or the right lens can be selected to act as a dark filter, thus making the image appear closer or farther away from the viewer as desired. The control voltage source can supply the aforementioned voltage depending on a command signal, which can be provided along with a television signal (in the case of television signal playback) or depending on a signal recorded on a film (in the case of film playback).The Kerr-effect cell can be made from PLZT (polycrystalline lanthanum-modified lead zirconate tanate) or other known ferroelectric ceramic materials.

[0022] Another application for non-polarizing, electrically adjustable or switchable optical lenses is in visual aids and switchable magnification systems (telescopic glasses). Traditional visual aids, including bifocal systems, are increasingly being equipped with additional functions. A crucial aspect is the development of active, i.e., intelligent, switchable, or adjustable optical systems. This development is currently also influenced by the development of head-mounted displays (HMDs) and LCD systems for the rapidly developing field of augmented reality (AR is a technology that combines images of the real world with computer-generated information, thus augmenting real-world images with virtual information). The foundation of this development is LCD-based microdisplays.In a modified form, this technology can also revolutionize other areas of optics and lead to the replacement of classic refractive elements such as lenses, prisms and other passive elements.

[0023] Under the two aspects of customizable or adjustable lenses and extended functionality, for example, a binocular electronic spectacle with a frame is known from EP 1 463 970 B1. The frame is designed as a dustproof, closed housing to which the temples are hinged, and the spectacle includes at least one electronic video camera arranged within the housing, a lens with forward-facing lenses, and a CCD sensor. Specifically, a motor-adjustable, front-mounted lens system with plastic lenses and a guide for adjustment by bending and / or rotating the individual lenses, which is connected to the electronic camera, is provided.An electrical control unit is connected to the lens system and camera, and this unit contains a memory that stores the manual preset values ​​for both eyes as target values ​​for automatic correction of refractive errors and interpupillary distance during operation. Refractive errors are corrected by adjusting the refractive power of the lenses and / or focusing, including automatic adjustment to reading or working distance. Contrast-controlled focusing is achieved by the control unit being designed to maintain this focus continuously. The lens system consists of four lenses, and the magnification range is between 2.5x and 10x. The control unit controls the motor, and a gearbox is located on the output side of the motor to increase the adjustment speed.For power, a rechargeable battery is integrated into the eyeglass frame, and the frame features a charge level indicator. An interface circuit connected to the camera allows for the connection of recording devices. Furthermore, a radio receiver and / or a call receiver, connected to the display, are located in the temple area. Before using the eyeglass system for the first time, the wearer sets the interpupillary distance and, if necessary, their diopter values. These settings are saved in the system and serve as the basis for all subsequent, now automatically controlled, processes. Focusing for zooming from a reading distance of approximately 25 cm to infinity takes only seconds. The mechanical lens system is capable of continuously zooming in on objects up to 2.4x.The objects are automatically focused sharply – regardless of the zoom level, which can be adjusted at the touch of a button (similar to a digital camera). These autofocus glasses work through a mechatronic interplay of a chip-controlled camera, motor, and specially surface-treated lenses. Additional features may include a memory button, microphone, voice control, speakers in the temple, external battery packs, storage for long-term video and audio recording, and a spotlight.

[0024] An important optical function of such multifunctional eyeglasses is the magnification system. Conventional telescope eyeglasses use a lens system to magnify viewed objects, which is attached to the lower part of the glasses. A characteristic of these eyeglasses is the fixed magnification system, which only allows the use of a rather limited area of ​​the total field of view. Generally, depending on the requirements, either a Keplerian or a Galilean system is used for magnification: Galilean systems allow for the direct realization of upright and laterally correct magnification, whereas Keplerian systems are characterized by larger fields of view. However, the Keplerian telescope produces a mirror-inverted image, which may be corrected by additional optical elements (prism or lens). If the depth of the magnification system is critical, the Galilean telescope is preferable.

[0025] The principles used so far for developing adjustable optical elements, especially lenses, are based on elastic membranes in combination with suitable fluids, the electrowetting principle of liquid lenses, or the electrically induced reorientation of liquid crystals. In elastomer membranes, a fluid is pumped into a cavity formed by a thin elastomer film or released into a reservoir to cause a change in the membrane's curvature. Membrane lenses can also be integrated into microscope systems (see Biomed. Opt. Express 5(2), 645-652 (2014) or Biomed. Opt. Express 5(6), 1877-1885 (2014)). However, this mechanical solution offers only moderate switching times, as the membrane cavity must be filled or emptied with fluid during the switching process. Furthermore, the stability of the elastomer membrane must be tested over a high number of switching cycles.Furthermore, the periphery of membrane lenses is relatively bulky due to the reservoir, pumps, and motors. Adjustable vision aids based on membrane lenses have also been introduced to the market, in which the pumping process is performed manually. Such systems are inherently very slow.

[0026] Liquid lenses, based on the principle of electrowetting, offer an alternative to membrane lenses. These controllable optical autofocus liquid lenses are used in smartphones, webcams, and other applications.

[0027] The range of tunable refractive power of the lenses is quite large, extending from -12 to 12 diopters. The switching times of 20 ms are fast enough for a number of applications, but not sufficient for the high clock rates required in machine vision. However, different requirements apply to optical focusing elements in machine vision applications with regard to aperture, speed, and resolution. The state of the art for focusing in industrial applications is the mechanical focusing of the lenses. This reaches its limits due to the masses that need to be moved (speed) as well as in terms of long-term stability (wear of the mechanical elements). Another disadvantage of this solution is that the unloaded state is not optically neutral, but rather represents a diverging lens.Furthermore, the free aperture is limited in relation to the overall diameter of the lens element, so that the ring-shaped supply unit dominates the lens element, especially in head applications.

[0028] Therefore, both elements based on the electrowetting principle and membrane lenses are not very suitable for hybrid optics, visual aids or telescopic glasses due to their design with bulky supply units and their weight.

[0029] Switchable lenses based on liquid crystals (LC) do not exhibit these disadvantages. A switchable bifocal lens based on liquid crystals typically works by changing the orientation of a thin liquid crystal layer within a conventional refractive lens using a field-induced change. In the switched state, the refractive index contrast activates an additional lens element, which enables sharp near vision. In the switched state, this lens element is inactive, and sharp distance vision is provided by the refractive lens. Switching between the states can be done manually or via a tilt detector.

[0030] For applications in webcams or mobile phone cameras, lenses with a diameter of only a few millimeters are sufficient, which greatly simplifies the technical problem. Limitations include the strong polarization dependence of the effect used, which either reduces the light output through the use of additional polarizers or makes the design of the elements significantly more complex due to the alternative orthogonal combination of two elements, introducing additional sources of error in manufacturing. The advantage of LC-based lenses is that they enable the realization of, for example, telescope systems or focusing devices that require no mechanical elements whatsoever, thus enabling robust and maintenance-free optics and also leading to a reduction in installation depth and weight.

[0031] In refractive lenses, the possible refractive power is generally determined by the radius of curvature of the phase boundary between the optically denser and less dense medium and the refractive index gradient. A similar principle applies to GRIN lenses (gradient index lenses), and planar liquid crystal lenses can also be considered as such. Here, the radial refractive index gradient, from the center to the edge, in conjunction with the diameter, are the determining factors. For all these lens types, the required lens diameter limits the achievable refractive power if the thickness of the medium is to remain constant. If the lens diameter is to be increased for a given refractive power, the medium thickness must also be increased. However, in liquid crystal lenses, this leads to a quadratic increase in the required switching voltages while simultaneously decreasing the switching speed.

[0032] These limitations can only be overcome by diffraction lenses, or more precisely, phase zone plates. Unlike Fresnel zone plates, which rely on amplitude modulation, phase zone plates utilize a phase shift of half the wavelength to achieve the lens function. Therefore, their light transmission is significantly higher, as all of the incident light is used, instead of just half as with amplitude zone plates. Furthermore, by implementing them as Gabor holograms (sinusoidal rather than binary zone transitions), the typical periodicity of the focal length can be reduced to a specific focal length.

[0033] Conventional rigid optical elements made of inorganic materials, such as glass lenses or crystalline beam splitters, are increasingly being replaced by organic materials. While the former offer the advantage of excellent optical properties and high stability, they are bulky and require complex manufacturing technologies. Organic materials are significantly easier to process and modify, especially to structure (injection molding, printing, nanoimprinting, 3D printing, laser structuring). Another crucial advantage is that many organic materials respond to external stimuli such as light, electrical voltage, temperature, etc., thereby permanently or reversibly altering their physical properties.The voltage-induced reorientation of liquid crystals in LCDs is the most prominent example of the use of electrically switchable and adjustable optical elements based on the electro-optical orientation effects of liquid crystals. Voltage-induced changes in the thickness or length of elastomers, usable in actuators or tunable grids, are another example. This enables active optical systems or intelligent systems that can be precisely adjusted or actively react to external conditions.

[0034] The problem of polarization dependence, however, could be solved by specific LC systems that are macroscopically isotropic in the direction of transmission. This applies, for example, to PDLC systems (polymer dispersed liquid crystal) or polymer-stabilized liquid crystals with blue phases (isotropic LC phase with a complex 3D structure). However, due to increased interactions with the polymer walls, high switching voltages are required. In addition, increased scattering of the transmitted light occurs due to phase separation, which significantly limits the suitability of these basic solutions for imaging optical systems. Intensive work is also being done on concepts for reducing switching times, although these are currently limited to the sub-millisecond range in the state of the art, with a significant switching range.

[0035] The voltage-induced orientation of polar molecules in liquids has long been known as the optical Kerr effect. However, the Kerr constants of conventional liquids such as nitrobenzene or carbon disulfide are orders of magnitude too low for use in lenses, and the switching voltage is orders of magnitude too high.

[0036] Significantly higher Kerr constants are observed in isotropic liquid crystals. Switching times are in the single-digit millisecond range or below. Some of these problems of liquid-crystalline systems and conventional Kerr fluids can be overcome by liquid crystals in their isotropic phase above the clearing point. This utilizes pre-orientation effects of the liquid crystals in isotropic melts just above the clearing point. This leads to polarization-free, fast-switching, and sufficiently efficient Kerr systems. However, a major disadvantage is the extremely strong temperature dependence of the effect. In summary, all variants based on the electrowetting principle, LC orientation, or Merribran fluidics exhibit sometimes considerable limitations in their optical or geometric parameters.

[0037] As the preceding review of the prior art demonstrates, various devices utilizing the electro-optical Kerr effect, particularly for light modulation, are known. However, the effect's strong temperature dependence, combined with high operating voltages, is a disadvantage for widespread industrial application.

[0038] An electrically controllable optical element made of an optically isotropic liquid, in particular a lens, and a method for its production based on liquid composites are known from the unpublished German patent application DE 10 2015 015 436 A1 or the unpublished WO 2017 / 092877 A1 of the applicant. Specifically, a Kerr mixture comprises a mixture of dipolar, rod-shaped molecules and semi-mesogens as active components.The Kerr mixture forms a thin layer with a photopolymerized, open-mesh, anisotropic network between a structured and / or planar conductive layer applied to a substrate within a thin-film cell. This network is structured such that, according to the electro-optical Kerr effect, the state of the active composites, consisting of semi-mesogens and dipolar, rod-shaped molecules of the Kerr mixture, is isotropic without an electric field within the operating temperature range. A change in the voltage-induced phase shift or refractive index shift within the optical element is generated by continuously adjusting the voltage U or by applying a constant voltage. Specifically, the thin-film cell comprises two glass or polymer substrates, each with an inner surface coated with a conductive ITO electrode as the conductive layer, and this electrode with an orientation layer.The production of a wide-mesh, anisotropic polymer network in the cooled Kerr mixture is achieved by adding photoinitiators, aliphatic monomers, and reactive mesogens, and by UV irradiation. When a voltage U is applied, the rod-shaped molecules align along the field lines. This has the advantage that, surprisingly, the strength of the dielectric anisotropy is not reduced when approximately half of the molecular framework of the semi-mesogens is mesogenic and approximately the other half is non-mesogenic. Furthermore, the deviation from the rod-shaped structure does not suppress the pronounced interactions with the mesogenic components of the composites. The orientation layer, which leads to a homeotropic orientation, also contains crosslinkable or polymerizable groups.The anisotropic network is preferably covalently fixed to the two substrate interfaces, thus maintaining the long-term stability of the network in its anisotropic form even when the Kerr liquid is isotropized by raising the temperature to the operating temperature range. This has the advantage that, surprisingly, below the operating temperature range, the effect of the aligning layers reinforces a homeotropic orientation (i.e., the molecules align perpendicular to the substrates), and the network remains fixed to the two substrate interfaces within the thin-film cell.

[0039] The process according to the applicant's unpublished or unpublished WO 2017 / 092877 A1 for producing an electrically controllable optical element with a cell filled with Kerr mixture, comprising two substrates and a conductive layer applied to the inner surface of each substrate, is characterized in that: a) the Kerr mixture comprises a mixture of dipolar, rod-shaped molecules and semi-mesogens as active components, reactive mesogens, photoinitiators and aliphatic monomers, b) the Kerr mixture is filled into a thin-film cell, c) the Kerr mixture is cooled to a temperature T lower than room temperature RT, at which a liquid crystalline phase with a homeotropic orientation forms, and d) by UV irradiation of the homeotropically oriented layers, radicals are generated which cause polymerization of the oriented reactive mesogens, such that a wide-meshed, loosely anisotropic network of reactive mesogens cross-linked with the aliphatic monomers is formed in the Kerr mixture.

[0040] The invention is based on the objective of designing or manufacturing an electrically controllable optical element in such a way that, based on the electro-optic Kerr effect, a low threshold and operating voltage, a minimized temperature dependence of the effect and a low response time are achieved.

[0041] This problem is solved in an electrically controllable optical element, according to the preamble of claim 1, by incorporating an optically effective surface profile on the inner surface of a substrate or into the substrate or both substrates, in addition to the conductive layer.

[0042] Furthermore, this problem is solved in a method for producing an electrically controllable optical element with a cell filled with Kerr mixture, comprising two substrates and a conductive layer applied to the inner surface of the respective substrate according to claim 10, by the fact that a) the Kerr mixture comprises a mixture of rod-shaped molecules with a large dipole moment and semi-mesogens as active composites, reactive mesogens, photoinitiators and aliphatic monomers, b) the Kerr mixture is filled into a thin-film cell, c) the Kerr mixture is cooled to a temperature T lower than room temperature RT, at which a liquid-crystalline phase with a homeotropic orientation is formed, d) by UV irradiation of the homeotropically oriented layers, radicals are generated which cause polymerization of the oriented reactive mesogens, such that a wide-meshed, loosely anisotropic network of reactive mesogens cross-linked with the aliphatic monomers is formed in the Kerr mixture, and e) an optically effective surface profile extending parallel to the conductive layer is incorporated on the inner surface of a substrate or into the substrate or both substrates, such that without voltage U in the operating temperature range RT the composite of rod-shaped molecules with a large dipole moment and semi-mesogens is again isotropic and when the voltage U is applied the molecules of the composite orient themselves in the direction of the field lines of the electric field.

[0043] The present invention utilizes the electro-optical Kerr effect (see also the online encyclopedia Wikipedia, https: / / de.wikipedia.org / wiki / Kerr-Effekt) in isotropic liquids. Therefore, these are not liquid-crystalline states. In particular, the optical element according to the invention enhances the optical Kerr effect through self-organization based on a preformable, open-mesh, loosely anisotropic network. Thus, the disadvantages of the classical Kerr effect can be surprisingly overcome by using the composites according to the invention and the manufacturing technology according to the invention, which leads to specific cell configurations in the thin-film cell according to the invention. The state of the active composites according to the invention is isotropic in the operating temperature range without an electric field. No domains or microdomains of ordered molecules exist that could lead to scattering.In particular, additionally fixed mesogen clusters (nanoparticles) can be used as a component of a precursor mixture to further enhance the Kerr effect and minimize its temperature dependence. The entire composite remains in a liquid, isotropic state when no stress is applied.

[0044] The optical thin-film elements based on the invention are electrically continuously adjustable phase modulators, lenses, and visual aids, or alternatively, phase modulators that can be switched between defined states. They are characterized by being optically isotropic, i.e., polarization-free and non-scattering. They are realized with electro-optically active composites that can be applied without polarization in the transmission direction and are characterized by a high electrically induced phase shift and / or refractive index shift. Particularly for the application of visual aids, the operating voltage range U is between 5 V and 40 V, preferably between 5 V and 25 V.

[0045] Using the inventive method, polarization-free, electrically switchable optical elements based on thin-film cells with novel electroactive liquids are produced. The orientation of these elements is enhanced by the interaction of polar, rod-shaped molecules in anisotropic polymer networks. Through molecular design and enhancement of the Kerr effect due to self-organization, significantly higher refractive index modulations or phase shifts are achieved at short switching times and low voltages. Examples of electrically switchable or adjustable lenses, particularly for visual aids, include: a) Electrically fast-switching optical elements for visual aids b) tunable, individually adjustable visual aids c) Switchable magnification system for telescope glasses

[0046] In a further development of the invention, according to claim 3, the electrodes are either applied under the surface profile, integrated into it or arranged on it.

[0047] Furthermore, the thin-film cell has two glass or polymer substrates, the inner surface of which is each provided with a conductive ITO electrode as a conductive layer and this with an orientation layer, and that the pre-formation of a wide-mesh, anisotropic polymer network in the cooled Kerr liquid takes place by means of added photoinitiators, aliphatic monomers and reactive semi-mesogens, and UV irradiation, whereby when a voltage U is applied, the rod-shaped molecules are aligned along the field lines.

[0048] This has the advantage that, surprisingly, the strength of the dielectric anisotropy is not reduced when approximately half of the molecular framework of the semi-mesogens is designed to be mesogenic and approximately the other half of the molecular framework is non-mesogenic, whereby the deviation from the rod-shaped structure does not suppress the pronounced interactions with the mesogenic components of the composites.

[0049] Furthermore, the orientation layer leading to a homeotropic orientation contains crosslinkable or polymerizable groups, and the anisotropic network is preferably covalently fixed to the two substrate interfaces, whereby the long-term stability of the network in its anisotropic form is maintained even when the Kerr liquid is isotropized by increasing the temperature to the operating temperature range.

[0050] This has the advantage that, surprisingly, below the operating temperature range, the effect of the aligning layers reinforces a homeotropic orientation (i.e., the molecules align themselves perpendicular to the substrates) and the network in the thin-film cell is fixed to the two substrate interfaces.

[0051] Further advantages and details can be found in the following description of a preferred embodiment of the invention with reference to the drawing. The drawing shows: Fig. 1 A preferred embodiment of the electrically controllable optical element, left in the initial state, right after pre-marking, Fig. 2 the optical element after Fig. 1 at approximately room temperature RT, left without voltage U and right after applying voltage U, Fig. 3 the composition of the isotropic Kerr composites, Fig.4 the architecture of a preferred embodiment of the semi-mesogen, Fig. 5a, Fig. 5b an embodiment for connecting the anisotropic network to the substrates and Fig. 6a - 6d different embodiments for an optically effective surface profile and structuring of the electrodes.

[0052] The Fig. 1 to Fig.Figure 2 shows a preferred embodiment of the electrically controllable optical element, particularly for illustrating the Kerr effect according to the invention of isotropic composites of a Kerr liquid K based on mixtures of rod-shaped molecules 5 and non-rod-shaped molecules 4 in anisotropic networks 9. Hereinafter, "isotropic mixture" is understood to mean a mixture of liquid crystals and semi-mesogen that is isotropic in the operating temperature range. The "precursor mixture" (involving components 4 to 8) consists of the isotropic mixture, reactive mesogens, aliphatic monomers, and a photoinitiator. The "precursor mixture" is converted into the composite according to the invention by the formation of the anisotropic network through in-situ UV irradiation, as shown in Figure 2. Fig. 1 to 3 are shown.

[0053] The Kerr liquid K composites according to the invention are characterized by a suitable combination of rod-shaped molecules 5 with a large dipole moment, as well as non-rod-shaped, dipolar molecules 4, which prevent the formation of ordered states such as liquid crystal phases, photocrosslinkable mono-, bi-, and trifunctional molecules, in particular reactive mesogens 8, and photoinitiators 6. Photoinitiators are chemical compounds that decompose in a photolysis reaction after absorption of (UV) light, thus forming reactive species that initiate a reaction; in the case of the Kerr liquid K according to the invention, a polymerization. The reactive species are radicals or cations. Further components, such as molecules with non-covalent interactions and fixed mesogen clusters, significantly improve the desired properties.

[0054] The non-rod-shaped dipolar molecules (semi-mesogens) 4 suppress the formation of a liquid-crystalline phase at room temperature (RT) or in the operating temperature range. Their function is to induce a clearing point depression in the liquid-crystalline phases of the rod-shaped molecules 5. Such a balanced clearing point depression can be achieved, for example, by bulky wing groups, lateral substituents, a smaller length-to-width ratio, deviations from the rod-shaped structure, and other factors.

[0055] On the other hand, the molecular shape of the semimesogens 4, their molecular interactions and their concentration are designed such that they function at low temperatures below the operating temperature range (T <RT) die Ausbildung einer homöotropen Orientierung der Mischung erlauben. Eine Hälfte des Molekülgerüstes ist also mesogen und durch ausgeprägte Wechselwirkungen mit den Mesogenen der Komposite gekennzeichnet und die andere ist nicht-mesogen, wobei die Abweichung von der stäbchenförmigen Struktur nicht die Stärke der dielektrischen Anisotropie herabsetzt. Diese Moleküle sind ebenfalls durch ein möglichst hohes Dipolmoment gekennzeichnet, wodurch sie zur Stärke des Kerr-Effektes des Komposits beitragen.

[0056] UV irradiation (preferably with UV power diodes) of the homeotropically oriented layers generates radicals that cause polymerization of the oriented reactive mesogens 8. This results in a loosely dispersed, anisotropic network 9. At room temperature or within the operating temperature range RT, the composite of rod-shaped molecules with a large dipole moment and non-rod-shaped, dipolar molecules becomes isotropic again. When a voltage U is applied, the molecules 4 and 5 of the composite orient themselves in the direction of the electric field lines (homeotropically, i.e., perpendicular to the substrate surfaces) ( Fig. 2 right).

[0057] In one embodiment, an aligning / orientation layer 3, which leads to homeotropic orientation, contains crosslinkable or polymerizable groups. In this case, the anisotropic network 9 is preferably covalently fixed to the two substrate interfaces, whereby the network retains its anisotropic form to a particularly high degree even when the composite 4, 5 is isotropized by increasing the temperature to the working range, thus ensuring long-term stability. Photocrosslinkable or photopolymerizable groups can also be used within the scope of the invention.

[0058] The polymer-based anisotropic matrix or anisotropic network 9 serves to support the electrically induced switching state and reduces the switching voltage. It is generated in the precursor mixture by a special process involving components 4 to 8. The generation of the assisting network 9 does not cause any macroscopically perceptible phase separation, as is the case with polymer-stabilized blue phases, polymer-stabilized isotropic phases, and isotropic polymer-dispersed phases.

[0059] The wide-mesh, anisotropic polymer network 9 with its orientation function (bulk alignment, orientation layer 3) results in lower temperature dependence, low switching voltages and an enhancement of the optical Kerr effect through self-organization.

[0060] In extreme cases, a liquid crystalline phase forms when a sufficiently high voltage U is applied and suitable intermolecular interactions occur with the precisely matched composition of the composite, and only through this process.

[0061] To achieve a lower temperature dependence through stabilization resulting from the fixation of order in the Kerr fluid K, the Kerr effect of isotropic composites can be achieved with nanoscale clusters and nanoparticles of shape-anisotropic molecules with a large dipole moment in the open-mesh anisotropic polymer network 9. For this purpose, nanoscale clusters and nanoparticles of shape-anisotropic molecules 4, which are fixed in their ordered arrangement by covalent bonds or intermolecular interactions, are used as components of the precursor mixture. Such nanoscale anisotropic clusters and nanoparticles extend the aforementioned approach of the Kerr effect of isotropic composites based on mixtures of rod-shaped and non-rod-shaped molecules 4, 5 in anisotropic networks 9.The difference lies in the fact that the rod-shaped molecules with a large dipole moment 5 are fixed in the form of nanoscale clusters or nanoparticles in an ordered arrangement (analogous to the pre-ordering effect of swarms just above the clearing point of nematic phases). Such clusters and nanoparticles are nanoscopically small (1 nm to 200 nm, preferably 5 to 20 nm). Due to their nanoscopic size, they do not cause scattering of the composite. Rod-shaped molecules with reactive groups (reactive mesogens) 8 can be fixed by photopolymerization in formed droplets, nanoparticles, or nematic pre-order swarms just above the clearing point. Instead of fixation through covalent bonds, this can also occur through non-covalent intermolecular interactions (hydrogen bonds, ionic interactions, or ππ interactions), which also leads to more stable, ordered nanoscopic molecular arrangements. Such molecular clusters, orSpherical or aspherical nanoparticles are dispersed in the precursor mixture (comprising components 4 to 8). The resulting composites are isotropic, non-scattering liquids.

[0062] Orderly fixed clusters and nanoparticles based on shape-anisotropic molecules, on the one hand, increase the Kerr effect through their high stable orientation order and, in particular, minimize the pronounced temperature dependence of the Kerr effect in solutions or LC materials above the clearing point.

[0063] To achieve a lower temperature dependence by exploiting the different temperature dependencies of intermolecular complex formation and the pre-orientation effect in the Kerr liquid K, the Kerr effect of isotropic composites based on the complex formation of shape-anisotropic molecules 5 with large dipole moments can be achieved through intermolecular interactions in the open-mesh anisotropic polymer network 9. For this purpose, the rod-shaped molecules 5 with large dipole moments are initially formed through intermolecular interactions such as hydrogen bonds, ionic interactions, or ππ interactions (e.g., pyridine / acid, acid / acid, etc.). The different temperature dependencies of intermolecular interactions and the pre-orientation effect are used to stabilize the effect.The ordering tendency of the rod-shaped molecules 5 is increased—according to the above approach of the Kerr effect in isotropic composites based on mixtures of rod-shaped and non-rod-shaped molecules 4, 5—by non-covalent intermolecular interactions. Accordingly, a strain-induced ordering or reinforcement effect is caused by self-organization, leading to high Kerr constants.

[0064] To achieve a lower temperature dependence by exploiting the different temperature dependencies of intermolecular complex formation and the pre-ordering effect in the Kerr liquid K, the thermal stabilization of the Kerr effect of isotropic composites with non-form-anisotropic molecules formed by intermolecular interactions can be achieved. The non-rod-shaped semi-mesogens 4 are formed only through intermolecular interactions, such as hydrogen bonds or ionic or ππ interactions. The formation of the semi-mesogens 4 generates an isotropic phase at room temperature RT or within the operating temperature range. An increase in temperature weakens the non-covalent interactions, and the complexes are (partially) degraded. This reduces their concentration, thus enabling control of the ordering tendency. The thermally induced degradation of the complexes, i.e.,The reduced formation of, for example, hydrogen bonds counteracts the charge blurring caused by complex formation, and the fragments acquire a higher dipole moment. In this way, the composite gains higher dielectric anisotropy with increasing temperature, and the Kerr effect is enhanced.

[0065] By utilizing the active composites according to the invention and applying them in thin layers between structured and / or planar electrodes 2, a variety of applications can be realized: • Refractive and diffractive optical elements, • Electrically continuously adjustable lens or lens switchable between two states, • Electrically continuously adjustable and locally modifiable lens (corrective lens, aspheric lenses), • Locally and continuously adjustable visual aid or visual aid switchable between two states (switchable near vision section), • Electrically controllable diffraction gratings, • Polarization-independent phase modulators.

[0066] The structure of the electrically controllable optical element according to the invention is described in detail below with reference to Fig. 1 and Fig. 2 described. Cell substrates 1:

[0067] The cell substrates can be made of glass or plastic. The substrates can be planar, concave, or convex, or they can also contain microlenses. The substrates 1 are held at a uniform distance of a few micrometers by spacers (pieces of glass or plastic fibers, beads, or lithographically produced polymer structures). Optical adhesive is used to fix the two substrates 1 to each other at their end faces. Electrodes 2:

[0068] The glass or plastic substrates 1 are provided with transparent electrodes 2. These are preferably electrodes made of ITO, metals, or conductive polymers, which are applied to the substrates 1 by sputtering, vapor deposition, printing, etc. The electrodes 2 can be large-area or structured, the structuring being achieved by printing, by means of masks during electrode application, or by subsequent (lithographic) etching. Alternatively, large-area electrodes can be structured within the scope of the invention. Alignment layer 3:

[0069] Thin layers of aligning layers 3 (20 nm to 1 µm) are applied to the ITO electrodes 2, which ensure the homeotropic orientation of the composite at low temperatures or below the operating temperature range (T <RT). Dafür werden im Rahmen der Erfindung Polymere wie Polyimide, Polyvinylalkohol, photosensitive Polymere, Lecithin u.a. eingesetzt.

[0070] Optionally, the aligning layers contain 3 (photo-)crosslinkable groups that allow the covalent connection of the reactive mesogens or networks formed therefrom 9. Isotropic mixtures 4 and 5:

[0071] The isotropic mixture is isotropic within the operating temperature range. An anisotropic state is achieved by interface orientation using orientation layers at temperatures below the operating temperature range. This anisotropic intermediate state is required exclusively for the synthesis of the anisotropic network 9 by photopolymerization of the reactive mesogens 8. Within the operating temperature range, the isotropic state of the polar, rod-shaped, and non-rod-shaped molecules 4 and 5 is then restored.

[0072] The conditions during the manufacture and operation of the electrically controllable optical element according to the invention are: 1. Isotropic initial state of the precursor mixture (components 4 to 8) between substrates 1 at room temperature RT. 2. Homeotropic state at temperatures below the operating temperature range before photopolymerization (see Fig. 1 left). 3. Homeotropic state through photopolymerization below the operating temperature range of an anisotropic network (see Fig. 1 right). 4. Isotropic state with anisotropic network in the operating temperature range without voltage U (see Fig. 2 links). 5. Orientation of the composite by applying an electrical voltage U. The orientation is supported by the anisotropic network 9 ( Fig. 2 right).

[0073] By combining mixtures with novel high-Δn materials, ordering-inducing or -degrading components contributing to the Kerr effect, and the in-situ generation of anisotropic polymer networks 9, the composites according to the invention exhibit a significant increase in the stress-induced modulation of the polarization-independent optical properties compared to the use of the Kerr effect in typical liquids. The composites are composed of various functional components: These are, firstly, rod-shaped molecules 5 with a large dipole moment, whose ordering tendency in the operating temperature range is reduced by dipolar molecules with limited mesogenicity (semi-mesogens 4). The semi-mesogens 4 play the crucial role here, as they act as a kind of perturbation to the rod-shaped, high-Δn compounds, thus partially lowering their ordering tendency in the operating temperature range and preventing the formation of ordered states, such as LC phases. However, since they also exhibit high dielectric anisotropy, they contribute cooperatively to the Kerr effect.

[0074] Another essential component is the photocrosslinkable reactive mesogens 8, combined with a photoinitiator 6. Below the operating temperature range, the starting mixtures exist in a nematic LC phase, which can be homeotropically oriented by interfacial effects and / or electrical voltage. UV irradiation in this state leads to the photopolymerization of the reactive mesogens 8, resulting in the formation of a loosely woven, anisotropic network 9 that acts as an orienting agent. The resulting composites are isotropic, non-scattering, and optically transparent at room temperature or within the operating temperature range. However, if a sufficiently high electrical voltage is applied, the polar, rod-shaped molecules 5 of the isotropic liquid orient themselves along the field lines perpendicular to the substrates, thereby changing the refractive index.Here, the anisotropic network 9 supports the alignment of the rod-shaped, polar molecules 5 of the composite through a pre-ordering effect, thus enhancing the optical Kerr effect. As a result, a significantly stronger refractive index modulation is achieved at lower switching voltages compared to the prior art. Furthermore, the temperature dependence of the process is substantially reduced, thus enabling its technical application. The necessary voltage-induced refractive index shift or phase shift is generated in the composites according to the invention based on the electro-optical Kerr effect. The voltage-induced refractive index shift in the composites according to the invention is characterized by very short switching times.

[0075] In the configuration described above, all switching states are symmetrical with respect to the direction of transmission and thus polarization-independent. Overall, the composites according to the invention allow the use of the electro-optic basic effect for the fabrication of thin-film elements with lens functionality, since the refractive index modulation is significantly increased, switching times are reduced, and the required switching voltage is lowered. Within the scope of the invention, patterns of addressed diffractive lenses can be produced as basic elements using novel composites. Alternatively, the production of active Fresnel or phase-zone plates requires the fabrication of ring-shaped aperiodic electrode structures and their contacting. The ring electrodes can be fabricated using ITO.Both methods are suitable for realizing switchable lenses, Fresnel structures in the substrate or in the active material, wherein the switchable diffractive thin-film lens according to the invention can be designed and adapted for various optical applications.

[0076] As explained above, switchable lenses based on the electrowetting principle and elastomer membranes are poorly suited for visual aids and telescopic spectacles due to their weight, bulky supply components, and limited aperture. These approaches are also of limited use for the production of hybrid optics.

[0077] Switchable lenses based on liquid crystals do not exhibit these disadvantages. However, the polarization dependence of oriented liquid crystals severely limits this approach. To overcome this disadvantage, additional optical components such as polarizers or multiple LC elements with opposing LC orientations (see AYG; Ko, SW; Huang, SH; Chen, YY; Lin, TH, Opt. Express 2011, 19, 2294-2300) or opposing oriented layers (see especially Ren, H.; Lin, YH; Fan, YH; Wu, ST Appl. Phys. Lett. 2005, 86, 141110; Lin, YH; Ren, H.; Wu, YH; Zhao, Y.; Fang, J.; Ge, Z.; Wu, ST Opt. Express 2005, 13, 8746-8752; Wang, B.; Ye, M.; Sato, S., Opt. Commun. 2005, 250, 266-273) must be used. However, this reduces the light output, makes the system design significantly more complex, and creates additional sources of error in manufacturing.

[0078] Isotropic LC elements based on PDLC exhibit significant scattering due to the differing orientation of the droplets in the OFF initial state. Nano-PDLC systems, which are optically nearly transparent in both states, also exhibit residual scattering. Furthermore, the required switching voltage is comparatively high, and the switching times are considerably longer than those of other LC elements due to the interaction of the nanometer-sized droplets with the surrounding polymer matrix.

[0079] Since the process of dielectric reorientation (especially in the field-free state) is generally relatively slow in LC elements, numerous approaches have been pursued in recent years to achieve shorter switching times of LCDs and other LC elements. Examples include: optimizing the viscoelastic parameters of NLCs, overdriving the system (see D.-K. Yang and S.-T. Wu, Fundamentals of Liquid Crystal Devices (John Wiley, New York, 2006)), "realigning" an NLC in sub-µm polymer network templates (see J. Xiang and OD Lavrentovich, Appl. Phys. Lett. 103, 051112 (2013)), or through "dual frequency" LCs (DFLCs) (see B. Golovin, SV Shiyanovskii, and OD Lavrentovich, Appl. Phys. Lett. 83, 3864 (2003)), surface-stabilized ferroelectric LCs (SSFLCs), or chiral smectic LCs (see G. Polushin, VB Rogozhin, and EI Ryumtsev Doklady Physical Chemistry, 2015, Vol. 465, Part 2, pp. 298-300).

[0080] The Kerr effect, which is based on the alignment of polar molecules (see, for example, Bing-Xiang Li, Volodymyr Borshch, Sergij V. Shiyanovskii, Shao-Bin Liu; Oleg D. Lavrentovich, Appl. Phys. Lett. 104, 201105 (2014)) and does not require the dielectric reorientation of the LC director of oriented liquid crystals (Frederiks effect), exhibits switching times in the nanosecond range (1–33 ns). However, the switching voltage required in conventional Kerr liquids is several hundred volts (300 to 900 V, E = ~10 8 V / m), achieving electrically induced birefringence values ​​of 0.001 to 0.01. These approaches are limited by more complex control circuits, hysteresis behavior, and unstable switching states (Su Xu, Yan Li, Yifan Liu, Jie Sun, Hongwen Ren, Shin-Tson Wu, Micromachines 2014, 5, 300-324).

[0081] An alternative is blue LC phases, which exhibit a complex 3D structure but are optically isotropic in the field-free state. They are characterized by short switching times but are unsuitable for lens applications due to the very small thermal existence regions of the phases. Polymer-reinforced blue phases (PSBP, see Su Xu, Yan Li, Yifan Liu, Jie Sun, Hongwen Ren, Shin-Tson Wu, Micromachines 2014, 5, 300-324) show higher refractive index modulation with application-relevant existence regions, but exhibit relatively high switching voltages and significant scattering effects (see Y. Haseba and H. Kikuchi, Mol. Cryst. Liq. Cryst., 2007, 470,1; Young-Cheol Yang and Deng-Ke Yang Applied Physics Letters 98, 023502, 2011) in the OFF state.

[0082] The orientation of polar molecules in an electric field has long been known as the optical Kerr effect. However, the Kerr constants of conventional liquids such as nitrobenzene or carbon disulfide are orders of magnitude too low for lens applications, and the switching voltage is orders of magnitude too high for relevant layer thicknesses. Significantly higher Kerr constants, with switching times in the millisecond and sub-millisecond range, are exhibited by isotropic melts of nematic liquid crystals (see F. Costache, M. Blasl, Optik & Photonik, Volume 6, Issue 4, pages 29–31, December 2011). This leads to polarization-free, fast-switching, and efficient Kerr systems. The effect apparently has two causes: firstly, the rod-shaped, polar liquid crystals with an elongated π-system result in high Kerr constants, and secondly, the cause lies in the nematic pre-orientation effect of molecular swarms above the clearing point.The resulting extremely strong temperature dependence of the effect is a significant disadvantage of this approach.

[0083] The disadvantages described are overcome by the isotropic composites according to the invention. By combining the isotropic mixture of mesogens and semi-mesogens with the anisotropic network 9, high values ​​of refractive index modulation are achieved at fast switching times and moderate switching voltages. This novel material concept can be used to manufacture electrically switchable or adjustable optical lenses and other optical elements based on the optical Kerr effect.

[0084] For this purpose, liquid-crystalline compounds with very high refractive index anisotropy were selected, and isotropic semi-mesogens were developed and mixed with these compounds so that the resulting mixtures of both components exhibit only latent liquid-crystalline properties. In particular, these exist as isotropic liquids in the operating temperature range without the application of an electrical voltage. The semi-mesogens 4 according to the invention represent a new class of functional materials in terms of their structure, combination of properties, and function. The adjustment of the required properties through suitable molecular design and efficient synthesis is described in more detail below.

[0085] The composites according to the invention require precise adjustment of the optical and dynamic properties as well as the intermolecular interactions of the main components of these mixtures (see Fig. 3), consisting of: - liquid crystalline compounds with high refractive index anisotropy, - Semi-mesogens 4 for establishing order as well as - (photo-)polymerizable reactive mesogen 8 for the formation of an anisotropic network 9.

[0086] According to the invention, the Kerr mixtures contain rod-shaped liquid crystals 5 with high refractive index anisotropy. Their high ordering tendency, as well as their high melting and clearing points, are lowered by mixing with semi-mesogens 4 such that the mixtures exist as isotropic liquids in the operating temperature range (especially room temperature RT). In elaborate series of experiments, various molecular approaches for adjusting this combination of properties were tested: for example, by adjusting suitable length-to-width ratios, varying the length of the rigid aromatic ring systems, the length and branching of the wing groups, and by varying the polarity of the head group, i.e., generally by adjusting suitable intermolecular interactions that suppress the LC phase.The polar semi-mesogens 4 were designed to also be oriented in an electric field, but to suppress the liquid-crystalline properties of the mesogens 5 in the mixture. They are isotropic liquid and exhibit only latent liquid-crystalline properties.

[0087] With regard to the required optical and electro-optical properties of the Kerr mixtures, the semi-mesogens 4 cannot be replaced by any solvent. According to the invention, the orientational order of the liquid crystals is reduced and adjusted in a defined manner. Thus, the final mixtures should exist as an optically isotropic liquid in the working range, but exhibit a nematic pre-orientation tendency. At low temperatures, however, they should be liquid-crystalline and be able to be homeotropically aligned by means of an aligning layer or by applying an electric field. This defined orientational order is necessary for the formation of the anisotropic network by photopolymerization at low temperatures.

[0088] The semi-mesogens 4 have further functions to fulfill; according to the invention, their molecular design also contributes to the optical Kerr effect. Therefore, they should also exhibit high dielectric anisotropy, contribute to high refractive index anisotropy, and support the cooperative orientation of the mixtures in an electric field. This combination of these different properties is made possible by the following structural features: (1) The breakdown of the liquid crystalline order can be achieved by secondary or tertiary branching of the alkyl wing group and / or by lateral substituents. (2) High dielectric anisotropy, high Kerr constants or high refractive index anisotropies are achieved by varying the polar head group and by introducing heterocycles in the rigid part of the molecule.

[0089] The basic architecture of the Semi-Mesogene4 is Fig. 4 can be seen.

[0090] The described functionality of the isotropic semi-mesogens 4 can be achieved using suitably substituted biphenyls. In particular, branched wing groups drastically increase the width of a molecule and lead to a significant reduction in transition temperatures. The altered length-to-width ratio can prevent the formation of nematic phases or significantly reduce the extent of existence of such a phase. This is achieved by incorporating, for example, methyl and ethyl groups as branches of the aliphatic wing group, with the position of the branch on the wing group being crucial.

[0091] These structural properties are shown below a) for a wing group with secondary branching, R = CN and b) for a wing group with tertiary branching, R = CN.

[0092] The goal of synthesizing isotropic semi-mesogens 4 with high dielectric and optical anisotropy, i.e., high Δε and Δn values, can be promoted, for example, by a polar head group. Particularly suitable groups that, on the one hand, make a high contribution to electrically inducible birefringence and, on the other hand, contribute to high dielectric anisotropy, are the following substituents in the para position of the biphenyl structure, namely substitution of the mesogenic unit with polar head groups:

[0093] Furthermore, the permanent dipole moment, and thus the dielectric anisotropy Δε, of semi-mesogens 4 can be increased by replacing phenyl rings with heteroaromatic nuclei. While the molecular geometry changes only slightly with heteroaromatic nuclei, a strong influence on the dielectric properties is expected according to A. Boller, M. Cereghetti, H. Scherrer, Z. Naturforsch., Part B, 33, 433 (1978). The position of the heteroatoms, or the heteroaromatic ring, relative to the head group must be chosen such that the dipole moments are additive. In addition to the increase in dielectric anisotropy, an increase in polarizability anisotropy, and thus higher birefringence, is also expected. This is illustrated below, particularly for a semi-mesogen 4 with a pyrimidine ring and a variation of the head group.

[0094] The dielectric anisotropy can be further increased by polar groups on the rigid rings. Lateral substituents can simultaneously counteract partial compensation of the dipole moments through dimer formation.

[0095] In particular, the introduction of two fluorine atoms in the 3,5-position increases the dielectric anisotropy by 8.5 units (see P. Kirsch, A. Hahn, Eur. J. of Org. Chem. (2005), (14), 3095-3100). In the case of lateral 3,5-substitution, the partial electric charge along the longitudinal axis of the molecule is retained (i.e., a dipole moment parallel to the longitudinal axis), resulting in a positive dielectric anisotropy. Simultaneously, the lateral substituents lower the transition temperatures. The increase in dielectric anisotropy through the introduction of polar substituents is shown below.

[0096] According to the invention, the field-induced alignment of the isotropic mixture is supported by an anisotropic polymer network 9. The orienting memory effect of the network 9 in combination with the nematic pre-ordering effect of the latent liquid crystalline composites enhances the optical Kerr effect.

[0097] Another important function of network 9 is to significantly reduce the temperature dependence of the switching process. To construct network 9, aromatic reactive mesogens 8 and aliphatic monomers are introduced into the isotropic mixture consisting of mesogens and semi-mesogens 4. These are then polymerized by photopolymerization in the homeotropically ordered state of the composite at low temperatures, forming a loosely woven anisotropic network 9. The addition of the reactive mesogens 8 requires the adjustment of the intermolecular interactions in the initial mixtures as well as in the final composites after network structure formation. To further enhance the stability of network 9, it is covalently linked to the substrates by functionalizing the aligning layer 3. Fig. Figure 5 shows the generation of a multidimensional, anisotropic network, namely: a) isotropic mixture with reactive mesogens in homeotropic mixture (precomposite) (see Fig. 5a) and b) Covalent linkage of network 9 and aligning layer 3 with network-stabilized molecules (see Fig. 5b).

[0098] The covalent anchoring of network 9 at the interfaces of the aligning layers 3 leads to a significant improvement in electro-optical switching behavior and long-term stability. For this purpose, the aligning material is functionalized with temperature-stable, reactive groups (e.g., OH groups) so that it can bond with the bifunctional reactive mesogens 8. The network formation triggered by radical photopolymerization encloses the bond with the two functionalized aligning layers 3, so that the anisotropic network 9, stabilized at the interfaces, permanently spans the cell. The necessary concentration of binding sites at the interfaces must be appropriately adjusted.For this purpose, the aligning layers 3 can be modified with appropriate reactive solutions after coating and drying, functional compounds can already be contained in the coating material, or the surface of the aligning layers can be functionalized accordingly by plasma processes.

[0099] In addition to improving the properties of the composites through network formation based on aliphatic and aromatic reactive mesogens respectively, possible demixing phenomena are also suppressed.

[0100] The Kerr composites according to the invention meet the following requirements profile, for example for the application fields of lenses, in particular for visual aids and telescopic glasses: - high Kerr constant - high dielectric anisotropy - isotropic and fluid within the operating temperature range due to the semi-mesogens 4 - High electrically inducible refractive index modulation by rod-shaped molecules 5 and polar semi-mesogens 4 - good homogeneity (miscibility of substances, low tendency to phase separation) across the entire operating temperature range - Short switching times due to low rotational viscosity - low absorption in the visible spectral range - high (photo)chemical stability.

[0101] Furthermore, the polarization independence and fast switching times of this approach are significant advantages compared to liquid crystal-based approaches. The composites according to the invention combine the advantages of liquid-crystalline systems, which are characterized by large Kerr constants of rod-shaped polar molecules and a high tendency towards order, with those of isotropic liquids, which are characterized by low rotational viscosity and very short switching times.

[0102] One embodiment of the invention, which is in Fig.The device shown in Figure 6a is characterized in that an optically active surface profile O is located on or incorporated into the inner surface of a substrate 1b or into both substrates 1a and 1b. This surface profile O can, for example, be a Fresnel lens, a phase plate, or a surface grating. The surface profile O is optically inactive in the de-stressed state of the filled thin-film cell because the material has an almost identical refractive index to the (electroactive) composite K according to the invention. By applying a voltage U, the refractive index of the electro-optically active material changes, thus fulfilling an optical function. In the case of the Fresnel lens, a voltage-dependent refractive power of the thin-film cell D is generated. The magnitude of the refractive power of the lens depends on the magnitude of the applied voltage U.In the case of surface gratings, beam splitters, beam combiners, monochromators, multiplexers or demultiplexers are implemented.

[0103] Substrates 1a and 1b are provided on their inner surfaces with transparent electrodes 2a, 2b, which consist of ITO or other (partially) transparent electrically conductive materials. These electrodes 2a, 2b are insulated with an insulating material 3 (see Fig. 1) coated in such a way that it simultaneously insulates and aligns the active components 4, 5 and the reactive mesogens 8 of the precursor mixture of the electro-active composite K perpendicular to the surfaces (homeotropically) below the operating temperature range. The electrodes 2a, 2b are either applied under the surface profile O (see Fig. 6a), integrated into it or arranged on it (see Fig. 6b). In this embodiment of the invention, planar electrodes 2a, 2b are preferably used.

[0104] Another embodiment of the invention is characterized in that one electrode 2b or both electrodes 2a, 2b are structured, or one or both electrodes 2a, 2b represent a set of individual electrodes that are controlled individually, in groups, or as a whole (see Fig. 6c and Fig. 6d). A further development of this design is characterized in that a (lower) electrode is a set of ring electrodes 2b (see Fig.6c) and the other (upper) electrode is designed as a planar electrode 2a. The widths and diameters of the ring electrodes 2b are preferably designed to meet the requirements of a zone plate. When a voltage U is applied to the filled thin-film cell D with the described electrodes 2, areas are created in the electroactive material between the upper and lower electrodes 2a and 2b that have a different refractive index than the areas that are not under the influence of the electric field. In this way, a refractive index profile is created in the electroactive composite K according to the invention, which generates an optical function. In this further development of the invention, a phase zone plate is thus realized that acts as a diffractive lens on transmitted light ( Fig. 6c).

[0105] Another embodiment of the invention is characterized in that both electrodes 2a and 2b are designed as sets of strip electrodes ( Fig. 6d). If both sets 2a and 2b are arranged orthogonally to each other and can be individually controlled, pixels with different phase shifts can be generated by applying a voltage U. The entire thin-film cell D acts as a variably structurable phase mask. If both sets 2a and 2b are arranged in parallel, refractive index gratings can be realized by applying a voltage, acting as beam splitters, beam combiners, monochromators, multiplexers, or demultiplexers.

[0106] For visual aids, the lens according to the invention features a polarization-free, electrically adjustable near field of view with moderate switching times and, depending on the application, non-critical switching voltages of < 42V. The lens diameter allows for an adequate field of view, and the refractive power of the switchable lens is in the single-digit diopter range. The optical function is essentially independent of the wavelength of light, and the diffraction efficiency is quite high, thus preventing ghosting. Furthermore, the lens according to the invention can be combined with typical spectacle lenses and has a low weight and compact size for controlling the element, so that it can be integrated together with a normal spectacle lens or in a spectacle frame.

[0107] Within the scope of the invention, the use for visual aids can be extended to a tunable, individually adjustable visual aid. By using pixelated electrode grids, similar to that of a transmissive LCD, the optical properties can be individually adjusted for very small areas. This makes it possible to create diffractive lenses that, for example, have a direction-dependent refractive power, as required for correcting astigmatism. The lens setting can then be individually adjusted and saved, as described in the binocular electronic glasses of EP 1 463 970 B1.

[0108] Within the scope of the invention, the lens according to the invention can be used in a switchable magnification system for telescopic glasses. The magnification system has some similar requirements to those in the field of visual aids. However, the refractive power of the eyepiece and objective lenses must be significantly stronger. The requirements for the necessary aperture, particularly for the eyepiece lens, are considerably lower. A magnification factor of 2.5 is sufficient for the magnification system. As with the individual element, the system can also be implemented with the lowest possible weight to ensure the desired high level of wearing comfort. This is where the solution according to the invention differs significantly from currently available telescopic glasses. Another significant advantage is, of course, that the entire field of vision is available in the off state; the integrated control and supply elements do not restrict this.

[0109] The lens according to the invention meets the technical requirements for: a) polarization-free, electrically adjustable near vision field for visual aids, in particular visual aids with switchable near vision section, b) tunable, individually adjustable visual aids (visual aids with pixel-wise control using µm-structured electrodes, similar to a transmissive active matrix display) and c) Switchable magnification system for telescopic glasses or multifunctional glasses, as can be seen from the following table. a) b) c) Switching times < 10ms < 10ms < 10ms Switching voltage < 42V < 42V < 42V diameter > 25mm > 25mm > 4mm (eyepiece) > 20mm (lens) Diffraction efficiency > 80% > 80% > 80% Refractive power or focal length > 4 diopters > 8 diopters (aspheric) < (-)30mm (eyepiece)< 75 mm (objective)

[0110] Further requirements that are met include high transparency, reproducibility, high reliability, and a high fill factor to avoid ghosting, as well as polarization-independent functionality. In addition, the individual elements are optically neutral in the off state. For applications according to the invention in switchable lenses for technical devices, such as lenses not used on the body, higher switching voltages up to 100V are also acceptable.

[0111] The invention is not limited to the illustrated and described embodiments, but also includes all embodiments that have the same effect in the sense of the invention.

[0112] For example, a synthesis based on laterally substituted biphenyls can be carried out to prepare semi-mesogens, and a catalyst for the final coupling reaction to prepare the substituted biphenyls can be synthesized; to prepare five semi-mesogens, a synthesis and characterization of five substituted arylboronic acids can be carried out; to mold stepped lenses in various materials, surface characterization of available stepped lenses can be carried out using a profilometer, including the preparation of PDMS casts (fabrication of molds of surface gratings and microlens arrays, including an epoxy mixture for molding surface gratings in Sylgard 184 (silicone elastomer kit) and fabrication of replicas with NOA65 (optical adhesive: viscosity 1200 (cps), refractive index n)). d1.52), in particular blazed gratings (method for molding surface gratings with a sawtooth profile to produce linear surface gratings, which serve as model structures for corresponding Fresnel zone plates); the molding of the surface gratings is carried out using a master (commercial diffraction grating), which was molded as a negative copy in POMS and with this “stamp” positive replicates can then be produced via a further molding step with NOA, which are suitable, among other things, for the construction of switchable optical elements; application of corresponding mechanisms of the aryl-aryl coupling according to Suzuki-Miyaura (synthesis of biphenyls or biphenyl derivatives by formation of a CC bond) or analogous reactions and application of chromatographic purification of intermediate compounds (in particular multi-step synthesis with intermediate purification operations).The application areas of the electrically controllable optical element according to the invention extend to many fields of technology, in particular:. Measurement technology - Analysis of samples using a Kerr cell in the measuring head - Wafer inspection systems - Polarizer in microscopes or endoscopes - Measurement of electric field strength Manufacturing technology - microlithographic projection exposure system for ICs or LCDs - Light modulator for exposing printing plates - Polarization direction rotating element during recording on CD or DVD Communication technology - Fast light switch with ceramic cell and with or without downstream polarization filter for digitizing signals up to 100 GHz (optical signal) Medical technology - optical modulator in an MRI system (magnetic resonance imaging system) - Polarizer in microscopes or endoscopes

[0113] Furthermore, the invention is not limited to the combination of features defined in claims 1 and 9, but can also be defined by any other combination of specific features from all disclosed individual features. This means that, in principle, virtually any individual feature of claims 1 and 9 can be omitted or replaced by at least one individual feature disclosed elsewhere in the application. Reference symbol list: 1a, 1b Substrate 2a, 2b conductive layer (conductive ITO electrode) 3. Alignment layer, insulator 4 non-rod-shaped molecules (active composite, semi-mesogen, precursor mixture) 5 rod-shaped molecules (active composite, precursor mixture) 6 photoinitiators 7 aliphatic monomers 8 reactive mesogens 9 anisotropic network (polymer network) 10 interconnected mesogens D thin-film cell K Kerr fluid, electro-active composite O Surface profile RT operating temperature range U voltage

Claims

[1] Electrically controllable optical element with a cell (D) filled with Kerr mixture (K) having two substrates (1a, 1b) and a conductive layer (2a, 2b) applied to the inner surface of each substrate (1a, 1b), wherein the Kerr mixture (K) comprises a mixture of rod-shaped molecules with a large dipole moment (5) and semi-mesogens (4) as active components and wherein the Kerr mixture (K) forms a thin layer with a photopolymerization-produced, wide-mesh, anisotropic network (9) between a structured and / or planar conductive layer (2a, 2b) applied to a substrate (1a, 1b) in a thin-film cell (D), such thatthat, according to the electro-optic Kerr effect, the state of the active composites of semi-mesogens (4) and rod-shaped molecules with a large dipole moment (5) of the Kerr mixture (K) is isotropic without an electric field in the operating temperature range, and that a change in the voltage-induced phase shift or refractive index shift in the optical element is generated by electrically continuous adjustment of the voltage U or by applying a constant voltage. characterized by , that in addition to the conductive layer (2a, 2b) an optically effective surface profile (O) is incorporated on the inner surface of a substrate (1a or 1b) or into the substrate (1a or 1b) or of both substrates (1a and 1b). [2] Electrically controllable optical element according to claim 1, characterized by, that the surface profile (O) on the inner surface of a substrate (1a or 1b) is a fret lens, a phase plate or a surface grating with a material of nearly the same refractive index as the filled thin-film cell (D) in the stress-free state and is optically inactive in this state like the Kerr mixture (K) and that by applying a voltage U the refractive index of the Kerr mixture changes so that an optical function is fulfilled. [3] Electrically controllable optical element according to claim 1 or 2, characterized by that electrodes (2a, 2b) are either applied under the surface profile (O), integrated into it or arranged on it. [4] Electrically controllable optical element according to claim 1, characterized by, that the thin-film cell (D) has two glass or polymer substrates (1a, 1b) whose inner surface is each provided with a conductive ITO electrode (2a, 2b) as a conductive layer and this with an orientation layer (3) and that the production of a wide-mesh, anisotropic polymer network in the cooled Kerr mixture (K) is carried out by means of added photoinitiators, aliphatic monomers (7) and reactive mesogens (8) and UV irradiation, wherein when a voltage U is applied, the rod-shaped molecules are aligned along the field lines. [5] Electrically controllable optical element according to claim 4, characterized by, that the orientation layer (3) leading to a homeotropic orientation contains crosslinkable or polymerizable groups and that the anisotropic network (9) is preferably covalently fixed to the two substrate interfaces, whereby the long-term stability of the network in its anisotropic form is maintained even when the Kerr mixture is isotropized by increasing the temperature to the operating temperature range. [6] Electrically controllable optical element according to claim 1, characterized by, that the rod-shaped molecules (5) with a large dipole moment as active components of the Kerr mixture (K) partially or entirely in the form of nanoscale clusters or nanoparticles, and wherein the clusters or spherical and aspherical nanoparticles are dispersed in a starting mixture (4, 5, 6, 7, 8), thereby achieving, on the one hand, an increase in the Kerr effect through high stable orientational order of the orderedly fixed clusters or nanoparticles, and, on the other hand, minimizing the temperature dependence of the Kerr effect in solutions or liquid-crystalline materials above the clearing point, and that the intermolecular interactions of the rod-shaped molecules (5) with a large dipole moment are based on hydrogen bonds,ionic interactions or ππ interactions of pyridine / acid or of acid / acid are formed, and the different temperature dependence of the intermolecular interactions and the preorientation effect is used to stabilize the Kerr effect. [7] Electrically controllable optical element according to claim 1, characterized by , that the semi-mesogens (4) are formed as active components of the Kerr mixture (K) by intermolecular interactions and that an increase in temperature leads to a weakening of the non-covalent interactions, with the complexes being partially degraded. [8] Electrically controllable optical element according to claim 1, characterized by , that in order to synthesize isotropic semi-mesogens (4) with high dielectric and optical anisotropy, substituents are inserted into the para-position of a biphenyl structure according to a polar head group. [9] Electrically controllable optical element according to claim 1 or 8, characterized by , that by exchanging phenyl rings for heteroaromatic nuclei in semi-mesogens (4) with pyrimidine ring and varying the head group according to the permanent dipole moment and thus the dielectric anisotropy of the semi-mesogens (4) are increased. [10] Method for producing an electrically controllable optical element with a cell filled with Kerr mixture having two substrates (1a, 1b) and a conductive layer (2a, 2b) applied to the inner surface of each substrate (1a, 1b), wherein: a) the Kerr mixture (K) comprises a mixture of rod-shaped molecules with a large dipole moment (5) and semi-mesogens (4) as active components, reactive mesogens (8), photoinitiators (6) and aliphatic monomers (7), b) the Kerr mixture (K) is filled into a thin-film cell (D), c) the Kerr mixture (K) is cooled to a temperature T lower than room temperature RT, at which a liquid crystalline phase with a homeotropic orientation is formed, d) by UV irradiation of the homeotropically oriented layers radicals are generated which cause polymerization of the oriented reactive mesogens (8) such that a wide-meshed, loosely anisotropic network (9) of reactive mesogens (10) cross-linked with the aliphatic monomers (7) is formed in the Kerr mixture (K), and e) an optically effective surface profile (O) extending parallel to the conductive layer (2a, 2b) is incorporated on the inner surface of a substrate (1a or 1b) or into the substrate (1a or 1b) or both substrates (1a and 1b), such that without voltage U in the operating temperature range RT the composite of rod-shaped molecules (5) with large dipole moment and semi-mesogens (4) is again isotropic and when the voltage U is applied the molecules of the composite orient themselves in the direction of the field lines of the electric field. [11] Method according to claim 10, characterized by , that one or both orientation layers leading to a homeotropic orientation (3) contain photocrosslinkable or photopolymerizable groups.

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