Patent Application
20230313043
The invention relates to an optical component comprising a liquid crystal (LC) medium, operable in the infrared region of the electromagnetic spectrum. The invention further relates to the use of said LC medium in the infrared (IR) region and to devices comprising said optical component.
Liquid-crystalline media have been used for many years in electro-optical displays (liquid crystal displays: LCDs) in order to display information by amplitude modulation of polarised light in the visible region. Nematic liquid crystals have also been proposed for phase modulation of light: The article Mcmanamon PF, Dorschner TA, Corkum DL, Friedman LJ, Hobbs DS, Holz M, Liberman S, Nguyen HQ, Resler DP, Sharp RC, Watson EA. Optical phased array technology. Proc IEEE. 1996;84:268-298. doi:1 0.11 09/5.482231 describes liquid crystal based optical phased arrays for various types of sensor applications; the article Scott R. Davis, George Farca, Scott D. Rommel, Seth Johnson, Michael H. Anderson, “Liquid crystal waveguides: new devices enabled by >1000 waves of optical phase control,” Proc. SPIE 7618, Emerging Liquid Crystal Technologies V, 76180E (12 Feb. 2010); doi: 10.1117/12.851788 describes refractive beam steering using a waveguide structure.
Increasingly, telecommunications has need of optical components that operate in the infrared range. For example, wavelength-selective-switching (WSS) based reconfigurable optical add-drop multiplexers (ROADMs) are the essential components of dynamic optical networks. The fast growing demand for high-speed broadband communication gave rise to the need for development of the so-called colorless, directionless, contentionless, and gridless (CDC-F) networking architectures. Wavelength selective switch technology, on which the latest generation ROADMs are based on, is envisaged to provide the CDC-F capability which the next-generation optical network relies on. Currently, there are several competing switch engine technologies used in WSSs, one of which are liquid-crystal-on-silicon (LCoS) spatial light modulators (SLMs). LCoS-SLMs have shown advantages including flexible bandwidth adjustment, adaptive optical alignment for WSSs with high port count number, and robustness without mechanical movements.
Another application using liquid crystal based devices is light detection and ranging (Lidar) - a method for measuring distances by illuminating a target with laser light and measuring the reflection with a sensor. Differences in laser return times and wavelengths can then be used to make digital 3-D representations of the target. In WO2019/24052 A1, a holographic LlDAR system is proposed that uses for example an LCoS SLM.
In US 10,665,953 B1 A tunable, optical metasurface is proposed that includes an optically reflective surface to reflect infrared laser light, wherein an array of optical resonant antennas positioned on the reflective surface and voltage-controlled liquid crystal is positioned in the optical field region of each of the optical resonant antennas to attain one-dimensional beam steering or shaping for a LIDAR system.
One of the most important features for a phase-only LCoS device is its use of optically non-linear liquid crystal (LC) materials, which are sensitive to the working temperature. While the main focus of LCoS devices in the past was on optical intensity modulation, which is little affected by temperature variation, for phase-only LCoS devices optical phase modulation of the incident light is an essential performance parameter and it can easily be affected by a small change of working temperature, resulting in a significant change in the outcome of corresponding optical diffractions.
Liquid crystal mixtures optimized for regular display applications such as TV or mobile phones known from prior art are not suitable for applications in the infrared because the birefringence of these mixtures fall-off as wavelength increases so the optical device has to have an extremely high cell gap for modulating IR radiation. Many liquid crystal mixtures suffer from both insufficient birefringence (Δn) and high optical loss in the IR region. The article Fenglin Peng, Yuan Chen, Shin-Tson Wu, Suvagata Tripathi & Robert J. Twieg (2014) Low loss liquid crystals for infrared applications, Liquid Crystals, 41:11, 1545-1552, DOl: 10.1080/02678292.2014.932452 proposes to avoid liquid crystal mixture components with a CN or NCS polar group but to use chlorine or fluorine instead. This problem is particularly acute for devices in which phase modulation has to be achieved at NIR wavelengths. A mixture optimized for birefringence alone is not sufficient for commercial applications and other thermal, optical and electrooptical properties are also important. For outdoor IR applications of liquid crystal attenuators, a wide temperature range and low temperature dependency of the optical properties with temperature is typically required.
A key challenge for the development of next generation of LCoS devices is the creation of a high-speed multi-level phase modulation. Nematic LCoS devices have demonstrated the benefits of the multi-level phase modulation, but are limited by the slow response time of the nematic LC. This is especially the case in telecommunication applications, where the infrared wavelengths used require thicker devices, thus further slowing down the response times. Hence, the main materials challenge for these applications is to find a suitable high-speed LC material capable to deliver the full 2π phase depth required in these applications.
There is a need for liquid crystal based optical components operable in the infrared region of the electromagnetic spectrum with improved overall application relevant properties having high birefringence and fast switching speed.
The invention is devised in the light of the problems of the prior art described herein. Accordingly it is a general object of the present invention to provide a novel and useful device and technique that can solve the problems described herein.
An object of the present invention is an optical component comprising a liquid crystal medium sandwiched between a pair of substrates, wherein the liquid crystal medium comprises one or more compounds of the formulae l, ll, and lll
in which
In the compounds of the formulae l, ll and lll, RL preferably denotes H.
In another preferred embodiment, in the compounds of formulae l, ll and lll, one or two groups RL, preferably one group RL is different from H.
The invention further relates to the use of the medium defined above and below in the infrared region of the electromagnetic spectrum, preferably in the A-band, and/or B-band and/or C-band, for phase modulation of said infrared light.
The invention further relates to a device comprising the optical component according to the invention. Preferred devices are infrared imagers, wavelength selective switches, LCoS-SLM, LIDAR systems, wavelength-division multiplexing (WDM) systems, reconfigurable optical add-drop multiplexer (ROADM), and nonmechanical beam steering, e.g. steerable Electro Evanescent Optical Refraction (SEEOR) prism as published in the article P. McManamon, 2006, “Agile Nonmechanical Beam Steering,” Opt. Photon. News 17(3): 24-29.
According to another aspect of the present invention there is provided a method of spatially modulating infrared light, the method comprising,
According to another aspect of the present invention there is provided a method of manufacturing an optical phase modulator, comprising at least the steps of
The optical component according to the invention is distinguished by excellent operational stability when exposed to the environment because of high clearing temperature, broad nematic phase range and excellent low-temperature stability (LTS) of the liquid crystal medium used therein. As a result, the component and devices containing the component are operable under extreme temperature conditions. Surprisingly, the temperature dependence of the birefringence of said liquid crystal medium is very small, i.e. the Δn changes little with the temperature, which makes a device reliable and easy to control.
The media used in the component according to the invention are distinguished by high values of the dielectric anisotropy and low rotational viscosities. As a result, the threshold voltage, i.e. the minimum voltage at which a device is switchable, is very low. A low operating voltage and low threshold voltage is desired in order to enable a device having improved switching characteristics and high energy efficiency. Low rotational viscosities enable fast switching of the components and devices according to the invention.
As used herein, infrared region of the electromagnetic spectrum is taken to mean the spectral region of electromagnetic radiation having a wavelength in the range of from 0.75 µm to 1000 µm.
As used herein, infrared A (IR-A) is taken to mean the spectral region of electromagnetic radiation having a wavelength in the range of from 0.75 µm to 1.4 µm.
As used herein, infrared B (IR-B) is taken to mean the spectral region of electromagnetic radiation having a wavelength in the range of from 1.4 µm to 3 µm.
As used herein, infrared C (IR-C) is taken to mean the spectral region of electromagnetic radiation having a wavelength in the range of from 3 µm to 1000 µm.
Preferbly, the optical component according to the invention operates at a wavelength in the range of from 750 nm to 2500 nm, in particular from 1530 nm to 1565 nm.
A very preferred light source for applications according to the invention is an IR laser emitting light with a wavelength of 1,55 µm or an lR laser emitting light with a wavelength of 905 nm.
As used herein, halogen is F, Cl, Br or l, preferably F or Cl, particularly preferably F.
Herein, alkyl is straight-chain or branched and has 1 to 15 C atoms, is preferably straight-chain and has, unless indicated otherwise, 1, 2, 3, 4, 5, 6 or 7 C atoms and is accordingly preferably methyl, ethyl, n-propyl, n-butyl, n-pentyl, n-hexyl or n-heptyl.
Herein, branched alkyl is alkyl having a secondary and/or tertiary, preferably secondary, carbon atom and is preferably isopropyl, s-butyl, isobutyl, isopentyl, 2-methylhexyl or 2-ethylhexyl, 2-methylpropyl, 2-pentyl, 3-pentyl, 2-methylbutyl, 3-methylbutyl.
Herein, a cyclic alkyl group is taken to mean a cycloalphatic radical or an alkyl group in which a methylene group is replaced with a cycloalphatic group (i.e. a cycloalkylalkyl or alkylcycloalkylalkyl), which may be saturated or partially unsaturated, and preferably denotes cyclopropyl, methylcyclopropy, cyclobutyl, methylcyclobutyl, cyclopentyl, methylcyclpoentyl, cyclopent-1-enyl, cyclopropylmethyl, cyclopropylethyl, cyclobutylmethyl, cyclobutylethyl, cyclopentylmethyl, cyclopentylethyl, cyclopent-1-enylmethyl.
Herein, an alkoxy radical is straight-chain or branched and contains 1 to 15 C atoms. It is preferably straight-chain and has, unless indicated otherwise, 1, 2, 3, 4, 5, 6 or 7 C atoms and is accordingly preferably methoxy, ethoxy, n-propoxy, n-butoxy, n-pentoxy, n-hexoxy or n-heptoxy.
Herein, an alkenyl radical is preferably an alkenyl radical having 2 to 15 C atoms, which is straight-chain or branched and contains at least one C-C double bond. It is preferably straight-chain and has 2 to 7 C atoms. Accordingly, it is preferably vinyl, prop-1- or -2-enyl, but-1-, -2- or -3-enyl, pent-1-, -2-, -3- or -4-enyl, hex-1-, -2-, -3-, -4-or -5-enyl, hept-1-, -2-, -3-, -4-, -5- or -6-enyl. If the two C atoms of the C-C double bond are substituted, the alkenyl radical can be in the form of E and/or Z isomer (trans/cis). In general, the respective E isomers are preferred. Of the alkenyl radicals, prop-2-enyl, but-2- and -3-enyl, and pent-3- and -4-enyl are particularly preferred.
Herein, alkynyl is taken to mean an alkynyl radical having 2 to 15 C atoms, which is straight-chain or branched and contains at least one C-C triple bond. 1- and 2-propynyl and 1-, 2- and 3-butynyl are preferred.
In case RF denotes a halogenated alkyl-, alkoxy-, alkenyl or alkenyloxy it can be branched or unbranched. Preferably it is unbranched, mono- poly or perfluorinated, preferably perfluorinated and has 1, 2, 3, 4, 5, 6 or 7 C atoms, in case of alkenyl 2, 3, 4, 5, 6 or 7 C atoms.
RP preferably denotes CN, NCS, Cl, F, —(CH2)n—CH═CF2, -(CH2)n-CH=CHF, —(CH2)n—CH═Cl2, -CnF2n+1, —(CF2)n—CF2H, —(CH2)n—CF3, -(CH2)n-CHF2, —(CH2)nCH2F, —CH═CF2, —O(CH2)n—CH═CF2, -O(CH2)nCHCl2, -OCnF2n+1, —O(CF2)n—CF2H, —O(CH2),CF3, -O(CH2)n-CHF2, —O(CF)nCH2F, -OCF=CF2, -SCnF2n+1, —S(CF)n—CF3, wherein n is an integer from 0 to 7.
Preferably, the medium comprises one or more compounds of formula RO
in which
In a preferred embodiment, RRO in formula RO denotes straight chain alkyl or alkenyl having up to 7 C atoms.
In another preferred embodiment, RRO in formula RO denotes branched alkyl or alkenyl having up to 10 C atoms.
In yet another preferred embodiment, RRO in formula RO denotes cyclic alkyl having up to 10 C atoms.
Preferably, the compounds of formula RO are selected from the group consisting of the formulae RO-1 to RO-7
More preferred compounds of formulae RO-1 to RO-7 are selected from the group consisting of the formulae RO-2, RO-3, RO4 and RO-5, very preferred RO-2;
particularly preferably, the medium comprises one or more n-alkoxy derivatives of formula RO-2 selected from the sub-formulae RO-2-1 a to RO-2-1l and/or one or more branched alkoxy derivatives of formula RO-2 selected from the sub-formulae RO-2-2a to RO-2-2m and/or one or more cycloalkoxy derivatives of formula RO-2 selected from the sub-formulae RO-2-3a to RO-2-3p:
In a preferred embodiment of the present invention, the compounds of formula l are selected from the group of compounds of the formulae l-1 to l-5:
in which
The media preferably comprise one or more compounds of formula l-1, which are preferably selected from the group of the compounds of the formulae l-1a to l-1d, preferably of formula l-1b:
in which R1 has the meaning indicated above for formula l and preferably denotes alkyl having 1 to 7 C atoms or alkenyl having 2 to 7 C atoms.
The media preferably comprise one or more compounds of formula l-2, which are preferably selected from the group of the compounds of the formulae l-2a to l-2e, preferably of formula l-2c:
in which R1 has the meaning indicated above for formula l and preferably denotes alkyl having 1 to 7 C atoms or alkenyl having 2 to 7 C atoms.
The media preferably comprise one or more compounds of formula l-3, which are preferably selected from the group of the compounds of the formulae l-3a to l-3d, particularly preferably of formula l-3b:
in which R1 has the meaning indicated above for formula l and preferably denotes alkyl having 1 to 7 C atoms or alkenyl having 2 to 7 C atoms.
The media preferably comprise one or more compounds of formula l-4, which are preferably selected from the group of the compounds of the formulae l-4a to l-4e, particularly preferably of formula l-4b:
in which R1 has the meaning indicated above for formula l and preferably denotes alkyl having 1 to 7 C atoms or alkenyl having 2 to 7 C atoms.
The media preferably comprise one or more compounds of formula l-5, which are preferably selected from the group of the compounds of the formulae l-5a to l-5d, particularly preferably of formula l-5b:
in which R1 has the meaning indicated above for formula l and preferably denotes alkyl having 1 to 7 C atoms or alkenyl having 2 to 7 C atoms.
The media preferably comprise one or more compounds of formula ll, which are preferably selected from the group of the compounds of the formulae ll-1 to ll-3, very preferably selected from the group of the compounds of the formulae ll-1 and ll-2:
in which the occurring groups have the meanings given under formula ll above and preferably
The compounds of formula ll-1 are preferably selected from the group of the compounds of the formulae ll-1a to ll-1f:
in which
The compounds of formula ll-2 are preferably selected from the group of the compounds of the formulae ll-2a and ll-2b:
in which
The compounds of formula ll-3 are preferably selected from the group of the compounds of the of formulae ll-3a to ll-3d:
in which
The compounds of formula lll are preferably selected from the group of the compounds of the formulae lll-1 to lll-6, more preferably of the formulae selected from the group of the compounds of the formulae lll-1, lll-2, lll-3 and lll-4, and particularly preferably of formula lll-1:
in which
The compounds of formula lll-1 are preferably selected from the group of the compounds of the formulae lll-1 a to lll-1l, more preferably selected from the group of the compounds of the formulae lll-1 a, lll-1 b, lll-1 h and lll-1 i, particularly preferably of formula Ill-1b and/or lll-1h:
in which
The compounds of formula lll-2 are preferably compounds of formula lll-2a to lll-2l, very preferably lll-2b and/or lll-2j:
in which
Very preferably, the medium comprises one or more compounds of the formula lll-2j selected from the following sub-formulae lll-2j-1 to lll-2j-15:
The compounds of formula lll-5 are preferably selected from the compounds of formula lll-5a:
The compounds of formula lll-6 are preferably selected from the compounds of the formulae lll-6a to lll-6l
In a preferred embodiment, the media according to the invention comprise one or more compounds selected from the group of compounds of the formulae IIA-1-1 to IIA-1-12, very preferably IIA-1-1 or llA-1-2:
in which
Additionally, the liquid-crystalline media according to the present invention in a certain embodiment, which may be the same or different from the previous preferred embodiments preferably comprise one or more compounds of formula IV,
in which
In a preferred embodiment of the present invention, the liquid-crystal medium additionally comprises one or more compounds selected from the group of compounds of the formulae V, VI, VII, VIII and IX:
in which
In a preferred embodiment of the present invention, the liquid-crystal medium comprises one or more compounds of the formula V, preferably selected from the group of the compounds of the formulae V-1 to V-3, preferably of the formulae V-1 and/or V-2 and/or V-3, preferably of the formulae V-1 and V-2:
in which the occurring groups have the respective meanings indicated above for formula V and preferably
The compounds of the formula V-1 are preferably selected from the group of the compounds of the formulae V-1a to V-1d, preferably V-1c and V-1d :
in which the parameters have the respective meanings indicated above for formula V-1 and in which
The compounds of the formula V-2 are preferably selected from the group of the compounds of the formulae V-2a to V-2e and/or from the group of the compounds of the formulae V-2f and V-2g:
The compounds of the formula V-3 are preferably compounds of the formula V-3a:
in which the parameters have the respective meanings indicated above for formula V-1 and in which preferably
The compounds of the formula V-1a are preferably selected from the group of the compounds of the formulae V-1a-1 and V-1a-2:
in which
The compounds of the formula V-1b are preferably compounds of the formula V-1b-1:
in which
The compounds of the formula V-1c are preferably selected from the group of the compounds of the formulae V-1c-1 to V-1c-4, particularly preferably selected from the group of the compounds of the formulae V-1c-1 and V-1c-2:
in which
The compounds of the formula V-1d are preferably selected from the group of the compounds of the formulae V-1d-1 and V-1d-2, particularly preferably the compound of the formula V-1d-2:
in which
The compounds of the formula V-2a are preferably selected from the group of the compounds of the formulae V-2a-1 and V-2a-2, particularly preferably the compounds of the formula V-2a-1:
in which
Preferred combinations of (R5′ and R52), in particular in the case of formula V-2a-1, are (CnH2n+1 and CmH2m+1), (CnH2n+1 and O-CmH2m+1), (CH2═CH—(CH2)Z and CmH2m+1), (CH2═CH—(CH2)Z and O-CmH2m+1) and (CnH2n+1 and (CH2)Z—CH═CH2).
Preferred compounds of the formula V-2b are the compounds of the formula V-2b-1:
in which
The preferred combination of (R51 and R52) here is, in particular, (CnH2n+1 and CmH2m+1).
Preferred compounds of the formula V-2c are the compounds of the formula V-2c-1:
in which
The preferred combination of (R51 and R52) here is, in particular, (CnH2n+1 and CmH2m+1).
Preferred compounds of the formula V-2d are the compounds of the formula V-2d-1:
in which
The preferred combination of (R51 and R52) here is, in particular, (CnH2n+1 and CmH2m+1).
Preferred compounds of the formula V-2e are the compounds of the formula V-2e-1:
in which
The preferred combination of (R51 and R52) here is, in particular, (CnH2n+1 and O-CmH2m+1).
Preferred compounds of the formula V-2f are the compounds of the formula V-2f-1:
in which
The preferred combinations of (R51 and R52) here are, in particular, (CnH2n+1 and CmH2m+1) and (CnH2n+1 and O-CmH2m+1), particularly preferably (CnH2n+1 and CmH2m+1).
Preferred compounds of the formula V-2g are the compounds of the formula V-2g-1:
in which
The preferred combinations of (R51 and R52) here are, in particular, (CnH2n+1 and CmH2m+1) and (CnH2n+1 and O-CmH2m+1), particularly preferably (CnH2n+1 and O-CmH2m+1).
The compounds of the formula VI are preferably selected from the group of the compounds of the formulae VI-1 to VI-5:
in which
The compounds of the formula VI-1 are preferably selected from the group of the compounds of the formulae VI-1a and VI-1b, more preferably selected from compounds of the formula VI-1a:
in which
The preferred combinations of (R61 and R62) here are, in particular, (CnH2n+1 and CmH2m+1) and (CnH2n+1 and O-CmH2m+1), in the case of formula VI-1a particularly preferably (CnH2n+1 and CmH2m+1) and in the case of formula VI-1b particularly preferably (CnH2n+1 and O-CmH2m+1).
The compounds of the formula VI-3 are preferably selected from the compounds of the formula VI-3a to VI-3e:
in which the parameters have the meaning given above under formula VI-3 and preferably
The compounds of the formula VI-4 are preferably selected from compounds of the formulae VI-4a to VI-4e:
in which the parameters have the meaning given above under formula VI-4 and preferably
The compounds of the formula VI-5 are preferably selected from the compounds of the formulae VI-5a to VI-5d, preferably VI-5b:
in which the parameters have the meaning given above under formula VI-5 and preferably
The compounds of the formula VII are preferably selected from the group of the compounds of the formulae VII-1 to VII-6:
The compounds of the formula VII-1 are preferably selected from the group of the compounds of the formulae VII-1a to VII-1d:
in which X72 has the meaning given above for formula VII-2 and
The compounds of the formula VII-2 are preferably selected from the group of the compounds of the formulae VII-2a and VII-2b, particularly preferably of the formula VII-2a:
in which
The preferred combinations of (R71 and R72) here are, in particular, (CnH2n+1 and CmH2m+1) and (CnH2n+1 and O-CmH2m+1), particularly preferably (CnH2n+1 and CmH2m+1).
The compounds of the formula VII-3 are preferably compounds of the formula VII-3a:
in which
The preferred combinations of (R71 and R72) here are, in particular, (CnH2n+1 and CmH2m+1) and (CnH2n+1 and \O-CmH2m+1), particularly preferably (CnH2n+1 and CmH2m+1).
The compounds of the formula VII-4 are preferably compounds of the formula VII-4a:
in which
The preferred combinations of (R71 and R72) here are, in particular, (CnH2n+1 and CmH2m+1) and (CnH2n+1 and O-CmH2m+1), particularly preferably (CnH2n+1 and CmH2m+1).
The compounds of the formula VII-5 are preferably selected from the group of the compounds of the formulae VII-5a and VII-5b, more preferably of the formula VII-5a:
in which
The preferred combinations of (R71 and R72) here are, in particular, (CnH2n+1 and CmH2m+1) and (CnH2n+1 and O—CmH2m+1), particularly preferably (CnH2n+1 and CmH2m+1).
The compounds of the formula VII-6 are preferably selected from the group of the compounds of the formulae VII-6a and VII-6b:
in which
The preferred combinations of (R71 and R72) here are, in particular, (CnH2n+1 and CmH2m+1) and (CnH2n+1 and O—CmH2m+1), particularly preferably (CnH2n+1 and CmH2m+1).
The compounds of the formula VII-7 are preferably selected from the group of the compounds of the formulae VII-7a to VII-7d:
in which
The compounds of the formula VIII are preferably selected from the group of the compounds of the formulae VIII-1 to VIII-3, more preferably these compounds of the formula VIII predominantly consist, even more preferably essentially consist and very particularly preferably completely consist thereof:
in which one of
The preferred combinations of (R81 and R82) here are, in particular, (CnH2n+1 and CmH2m+1) and (CnH2n+1 and O—CmH2m+1), particularly preferably (CnH2n+1 and CmH2m+1).
The compounds of the formula VIII-1 are preferably selected from the group of the compounds of the formulae VIII-1a to VIII-1c:
in which
The preferred combinations of (R81 and R82) here are, in particular, (CnH2n+1 and CmH2m+1) and (CnH2n+1 and O—CmH2m+1), particularly preferably (CnH2n+1 and CmH2m+1).
The compounds of the formula VIII-2 are preferably compounds of the formula VIII-2a:
in which
The preferred combinations of (R81 and R82) here are, in particular, (CnH2n+1 and CmH2m+1), (CnH2n+1 and O—CmH2m+1) and (CH2═CH—(CH2)Z and CmH2m+1), particularly preferably (CnH2n+1 and CmH2m+1).
The compounds of the formula VIII-3 are preferably compounds of the formula VIII-3a:
in which
The preferred combinations of (R81 and R82) here are, in particular, (CnH2n+1 and CmH2m+1) and (CnH2n+1 and O—CmH2m+1).
The compounds of the formula IX are preferably selected from the group of the compounds of the formulae IX-1 to IX-3:
in which the parameters have the respective meaning indicated above under formula IX and preferably
The preferred combinations of (R91 and R92) here are, in particular, (CnH2n+1 and CmH2m+1) and (CnH2n+1 and O—CmH2m+1).
The compounds of the formula IX-1 are preferably selected from the group of the compounds of the formulae IX-1a to IX-1e:
in which the parameters have the meaning given above and preferably
The compounds of the formula IX-2 are preferably selected from the group of the compounds of the formulae IX-2a and IX-2b:
in which
The preferred combination of (R91 and R92) here is, in particular, (CnH2n+1 and CmH2m+1).
The compounds of the formula IX-3 are preferably compounds of the formulae IX-3a and IX-3b:
in which
The preferred combinations of (R91 and R92) here are, in particular, (CnH2n+1 and CmH2m+1) and (CnH2n+1 and O—CmH2m+1), particularly preferably (CnH2n+1 and O—CmH2m+1).
In a preferred embodiment of the present invention the medium comprises one or more compounds of formula X
in which
Preferably, the compounds of formula X are selected from the sub-formulae X-1 and X-2
in which the occurring groups and parameters have the meanings given above for formula X.
Particularly preferably, the media according to the invention comprise one or more compounds selected from the group of compounds of the formulae X-1-1 to X-1-9
In a preferred embodiment, the medium according to the invention comprises one or more compounds of formula XI
in which
Preferably, the compounds of formula XI are selected from the group of compounds of the formulae XI-1 to XI-24:
in which the occurring groups have the meanings given above for formula XI and preferably
Preferably, the medium according to the invention comprises one or more compounds of formula T
in which
In a preferred embodiment, the liquid crystalline media according to the invention comprise one or more compounds selected from the group of compounds of the formulae T-1a to T-3b below:
in which
In a particularly preferred embodiment of the present invention the media comprise one or more compounds selected from the compounds of the formulae T-1a and T-2a.
Preferred compounds of formula T-1a are selected from the group of compounds of the following sub-formulae:
in which n is 1, 2, 3 or 4, preferably 1.
Preferred compounds of formula T-2a are selected from the group of compounds of the following sub-formulae:
in which n is 1, 2, 3 or 4, preferably 1.
Very preferably, the medium comprises one or more compounds of formula T-1a-5.
Preferably, the medium comprises a compound of formula C
in which
The compounds of formula C are preferably selected from the compounds of the following sub-formulae:
in which
Preferably, one of the groups ZC1 and ZC2 of formula C denotes a single bond and the other one of ZC1 and ZC2 denotes -C≡C-.
Very preferred compounds of the formula C are selected from the compounds of the following sub-formulae:
in which RC has the meanings given above and preferably denotes alkyl having 1 to 7 C atoms or CF3O.
Very particularly preferred compounds are the compounds of the formulae C-7-1, C-9-1, C-9-4, C-10-1, C-10-2, C-10-3, C-10-4, C-10-5, C-10-6, and C-10-7.
Preferably, the medium comprises one or more compounds of formula U a compound of formula U
in which
The compounds of formula U are preferably selected from the compounds of the following sub-formulae:
In a preferred embodiment of the present invention, the compounds of formula U are selected from the compounds of the formulae U-1 to U-20, very preferably from the compounds of the formulae U-1 to U13:
in which the occurring groups have the meanings indicated above for formula U and its subformulae and preferably RU denotes alkyl having 1 to 7 C atoms, Y1, Y2, Y3, and Y4, identically or differently, denote H, F, Cl, methyl, ethyl, n-propyl, isopropyl, cyclopropyl, cyclobutyl, cyclopentyl or cyclopentenyl, and more preferably Y1 and Y2 independently denote H or F, in particular H, and Y3 and Y4 very preferably denote H, and L1 and L2, identically or differently, very preferably denote H, F, methyl or ethyl, in particular H.
According to one embodiment of the present invention the compounds of formula U are used in which RU denotes H, alkyl or alkoxy having 1 to 12 C atoms, or alkenyl, alkenyloxy or alkoxyalkyl having 2 to 12 C atoms, in which one or more CH2-groups may be replaced by
preferably alkyl having 1 to 12 C atoms.
According to another embodiment of the present invention compounds of formula U are used in which the group RU denotes RP, where RP denotes halogen, CN, NCS, RF, RF—O— or RF—S—, and wherein RF denotes fluorinated alkyl or fluorinated alkenyl having up to 9 C atoms, preferably CF3 or OCF3.
Preferably, the medium comprises one or more compounds of formula UF
The present invention relates to a compound of formula U
in which
The compounds of formula UF are preferably selected from the following subformulae:
in which
According to one embodiment of the present invention the compounds of formula UF are used in which RU denotes H, alkyl or alkoxy having 1 to 12 C atoms, or alkenyl, alkenyloxy or alkoxyalkyl having 2 to 12 C atoms, in which one or more CH2-groups may be replaced by
preferably alkyl having 1 to 12 C atoms.
According to another embodiment of the present invention compounds of formula UF are used in which the group RU denotes RP, where RP denotes halogen, CN, NCS, RF, RF-O- or RF-S-, and wherein RF denotes fluorinated alkyl or fluorinated alkenyl having up to 9 C atoms, preferably CF3 or OCF3.
The media according to the present invention comprise one or more chiral dopants. Preferably these chiral dopants have an absolute value of the helical twisting power (HTP) in the range of from 1 µm-1 to 150 µm-1, preferably in the range of from 10 µm-1 to 100 µm-1. In case the media comprise two or more chiral dopants, these may have opposite signs of their HTP-values. This condition is preferred for some specific embodiments, as it allows to compensate the chirality of the respective compounds to some degree and, thus, may be used to compensate various temperature dependent properties of the resulting media in the devices. Generally, however, it is preferred that most, preferably all of the chiral compounds present in the media according to the present invention have the same sign of their HTP-values.
Preferably the chiral dopants present in the media according to the instant application are mesogenic compounds and most preferably they exhibit a mesophase on their own.
In a preferred embodiment of the present invention, the medium comprises two or more chiral compounds which all have the same algebraic sign of the HTP.
The temperature dependence of the HTP of the individual compounds may be high or low. The temperature dependence of the pitch of the medium can be compensated by mixing compounds having different temperature dependencies of the HTP in corresponding ratios.
For the optically active component, a multitude of chiral dopants, some of which are commercially available, is available to the person skilled in the art, such as, for example, cholesteryl nonanoate, R- and S-811, R- and S-1011, R- and S-2011, R- and S-3011, R- and S-4011, or CB15 (all Merck KGaA, Darmstadt).
Particularly suitable dopants are compounds which contain one or more chiral groups and one or more mesogenic groups, or one or more aromatic or alicyclic groups which form a mesogenic group with the chiral group.
Suitable chiral groups are, for example, chiral branched hydrocarbon radicals, chiral ethane diols, binaphthols or dioxolanes, furthermore mono- or polyvalent chiral groups selected from the group consisting of sugar derivatives, sugar alcohols, sugar acids, lactic acids, chiral substituted glycols, steroid derivatives, terpene derivatives, amino acids or sequences of a few, preferably 1-5, amino acids.
Preferred chiral groups are sugar derivatives, such as glucose, mannose, galactose, fructose, arabinose and dextrose; sugar alcohols, such as, for example, sorbitol, mannitol, iditol, galactitol or anhydro derivatives thereof, in particular dianhydrohexitols, such as dianhydrosorbide (1,4:3,6-dianhydro-D-sorbide, isosorbide), dianhydromannitol (isosorbitol) or dianhydroiditol (isoiditol); sugar acids, such as, for example, gluconic acid, gulonic acid and ketogulonic acid; chiral substituted glycol radicals, such as, for example, mono- or oligoethylene or propylene glycols, in which one or more CH2 groups are substituted by alkyl or alkoxy; amino acids, such as, for example, alanine, valine, phenylglycine or phenylalanine, or sequences of from 1 to 5 of these amino acids; steroid derivatives, such as, for example, cholesteryl or cholic acid radicals; terpene derivatives, such as, for example, menthyl, neomenthyl, campheyl, pineyl, terpineyl, isolongifolyl, fenchyl, carreyl, myrthenyl, nopyl, geraniyl, linaloyl, neryl, citronellyl or dihydrocitronellyl.
The media according to the present invention preferably comprise chiral dopants which are selected from the group of known chiral dopants. Suitable chiral groups and mesogenic chiral compounds are described, for example, in DE 34 25 503, DE 35 34 777, DE 35 34 778, DE 35 34 779 and DE 35 34 780, DE 43 42 280, EP 01 038 941 and DE 195 41 820. Examples are also compounds listed in Table F below.
Chiral compounds preferably used according to the present invention are selected from the group consisting of the formulae shown below.
Particular preference is given to chiral dopants selected from the group consisting of compounds of the following formulae A-I to A-III and A-Ch:
in which
Particular preference is given to dopants selected from the group consisting of the compounds of the following formulae:
in which
Particularly preferred compounds of formula A are compounds of formula A-III.
Further preferred dopants are derivatives of the isosorbide, isomannitol or isoiditol of the following formula A-IV:
Examples of compounds of formula IV are:
The compounds of the formula A-IV are described in WO 98/00428. The compounds of the formula A-V are described in GB-A-2,328,207.
Very particularly preferred dopants are chiral binaphthyl derivatives, as described in WO 02/94805, chiral binaphthol acetal derivatives, as described in WO 02/34739, chiral TADDOL derivatives, as described in WO 02/06265, and chiral dopants having at least one fluorinated bridging group and a terminal or central chiral group, as described in WO 02/06196 and WO 02/06195.
Particular preference is given to chiral compounds of the formula A-VI
in which
Particular preference is given to chiral binaphthyl derivatives of the formula A-VI-1
The concentration of the one or more chiral dopant(s), in the LC medium is preferably in the range from 0.001% to 20%, preferably from 0.05 % to 5%, more preferably from 0.1% to 2%, and, most preferably from 0.5% to 1.5%. These preferred concentration ranges apply in particular to the chiral dopant S-4011 or R-4011 (both from Merck KGaA) and for chiral dopants having the same or a similar HTP. For Chiral dopants having either a higher or a lower absolute value of the HTP compared to S-4011 these preferred concentrations have to be decreased, respectively increased proportionally according to the ratio of their HTP values relatively to that of S-4011.
The pitch p of the LC media or host mixtures according to the invention is preferably in the range of from 5 to 50 µm, more preferably from 8 to 30 µm and particularly preferably from 10 to 20 µm.
Preferably, the media according to the invention comprise a stabiliser selected from the group of antioxidants, preferably hindered phenol antioxidants, and hindered amine light stabilisers (HALS), more preferably selected from the group of compounds of the formulae ST-1 to ST-18.
in which
Of the compounds of the formula ST, special preference is given to the compounds of the formulae
In the compounds of the formulae ST-3a and ST-3b, n preferably denotes 3. In the compounds of the formula ST-2a, n preferably denotes 7.
Very particularly preferred mixtures according to the invention comprise one or more stabilisers from the group of the compounds of the formulae ST-2a-1, ST-3a-1, ST-3b-1, ST-8-1, ST-9-1 and ST-12:
The compounds of the formulae ST-1 to ST-18 are preferably each present in the liquid-crystal mixtures according to the invention in amounts of 0.005 - 0.5%, based on the mixture.
If the mixtures according to the invention comprise two or more compounds from the group of the compounds of the formulae ST-1 to ST-18, the concentration correspondingly increases to 0.01 - 1% in the case of two compounds, based on the mixtures.
However, the total proportion of the compounds of the formulae ST-1 to ST-18, based on the mixture according to the invention, should not exceed 2%.
According to another aspect of the present invention, the optical component comprises a polymer network liquid crystal obtained by polymerisation of one or more compounds of formula P defined below, in the liquid crystal host mixture comprising one or more compounds selected from the group consisting of the compounds of the formulae I, II and III as defined above. A is described in for example Peng, Fenglin, Chen, Haiwei, Tripathi, Suvagata, Twieg, Robert, Wu, Shin-Tson. (2015). Fast-response infrared phase modulator based on polymer network liquid crystal. Optical Materials Express. Vol. 5, Issue 2, pp. 265-273. doi: 10.1364/OME.5.000265.
in which the individual radicals have the following meanings:
The polymerisable group Pa,b is a group which is suitable for a polymerisation reaction, such as, for example, free-radical or ionic chain polymerisation, polyaddition or polycondensation, or for a polymer-analogous reaction, for example addition or condensation onto a main polymer chain. Particular preference is given to groups for chain polymerisation, in particular those containing a C═C double bond or —C≡C— triple bond, and groups which are suitable for polymerisation with ring opening, such as, for example, oxetane or epoxide groups.
Preferred groups Pa,b are selected from the group consisting of CH2═CW1—CO—O—, CH2═CW1—CO—,
CH2═CW2—(O)k3-, CW1═CH—CO—(O)k3—, CW1═CH—CO—NH—, CH2═CW1—CO—NH—, CH3—CH═CH—O—, (CH2=CH)2CH-OCO-, (CH2=CH-CH2)2CH-OCO-, (CH2═CH)2CH—O—, (CH2═CH—CH2)2N—, (CH2═CH—CH2)2N—CO—, HO—CW2W3—, HS—CW2W3—, HW2N—, HO—CW2W3—NH—, CH2═CW1—CO—NH—, CH2═CH—(COO)k1—Phe—(O)k2—, CH2═CH—(CO)k1—Phe—(O)k2—, Phe—CH═CH—, HOOC—, OCN— and W4W5W6Si—, wherein W1 denotes H, F, Cl, CN, CF3, phenyl or alkyl having 1 to 5 C atoms, in particular H, F, CI or CH3, W2 and W3 each, independently of one another, denote H or alkyl having 1 to 5 C atoms, in particular H, methyl, ethyl or n-propyl, W4, W5 and W6 each, independently of one another, denote Cl, oxaalkyl or oxacarbonylalkyl having 1 to 5 C atoms, W7 and W8 each, independently of one another, denote H, Cl or alkyl having 1 to 5 C atoms, Phe denotes 1,4-phenylene, which is optionally substituted by one or more radicals L as defined above which are other than P-Sp-, k1, k2 and k3 each, independently of one another, denote 0 or 1, k3 preferably denotes 1, and k4 denotes an integer from 1 to 10.
Particularly preferred groups Pa,b are selected from the group consisting of CH2═CW1—CO—O—, in particular CH2═CH—CO—O—, CH2═C(CH3)—CO—O— and CH2═CF—CO—O—, furthermore CH2═CH—O—, (CH2═CH)2CH—O—CO—, (CH2═CH)2CH—O—,
and
Very particularly preferred groups Pa,b are selected from the group consisting of acrylate, methacrylate, fluoroacrylate, furthermore vinyloxy, chloroacrylate, oxetane and epoxide groups, and of these preferably an acrylate or methacrylate group.
Preferred spacer groups Spa,b are selected from the formula Sp″-X″, so that the radical Pa/b-Spa/b- conforms to the formula Pab-Sp“X″-, where
Typical spacer groups Sp″ are, for example, —(CH2)p1—, —(CH2CH2O)q1—CH2CH2—, —CH2CH2—S—CH2CH2—, —CH2CH2—NH—CH2CH2— or -(SiR00R000-O)p1-, wherein p1 is an integer from 1 to 12, q1 is an integer from 1 to 3, and R00 and R000 have the meanings indicated above.
Particularly preferred groups -Sp“-X″- are -(CH2)p1-, —(CH2)p1—O—, —(CH2)p1—O—CO—, —(CH2)p1—O—CO—O—, wherein p1 and q1 have the meanings indicated above.
Particularly preferred groups Sp″ are, for example, in each case straight-chain ethylene, propylene, butylene, pentylene, hexylene, heptylene, octylene, nonylene, decylene, undecylene, dodecylene, octadecylene, ethyleneoxyethylene, methyleneoxybutylene, ethylenethioethylene, ethylene-N-methyliminoethylene, 1-methylalkylene, ethenylene, propenylene and butenylene.
Particularly preferred monomers of formula P are the following:
in which the individual radicals have the following meanings:
In a particularly preferred embodiment of the present invention the LC mixture comprises one or more compounds or formula P10-1
wherein the parameters are defined as described above and P1 and P2 preferably denote acrylate or methacrylate.
Particularly preferred compounds of formula P10-1 are selected from the group of the following subformulae
wherein each n4 denote independently of each other an integer between 2 and 10, preferably 3,4,5 or 6.
In one embodiment of the present invention the liquid crystal composition is injected between the first and second substrates or is filled into the cell by capillary force after combining the first and second substrates. In an alternative embodiment, the liquid crystal composition may be interposed between the first and second substrates by combining the second substrate to the first substrate after loading the liquid crystal composition on the first substrate.
The total amount of the compounds of formula P in the medium is in the range of from >0% to 20%, preferably 2% to 15%, very preferably 3% to 10%, in particular 4%, 5%, 6%, 7% or 8%.
The polymerisable compounds are polymerised or crosslinked (if a polymerisable compound contains two or more polymerisable groups) by in-situ polymerisation in the LC medium between the sub¬strates of the optical component, optionally with application of a voltage. The poly¬merisation can be carried out in one step or in more than one step (“end curing”).
Suitable and preferred polymerisation methods are, for example, thermal or photopolymerisation, preferably photopolymerisation, in particular UV photo¬polymerisation. One or more initiators can optionally also be added here. Suitable conditions for the polymerisation and suitable types and amounts of initiators are known to the person skilled in the art and are described in the literature. Suitable for free-radical polymerisation are, for example, the commercially available photoinitiators Irgacure651®, Irga-cure184®, Irgacure907®, Irgacure369® or Darocure1173® (BASF SE). If an initiator is employed, its proportion is preferably 0.001 to 5% by weight, par¬ticularly preferably 0.001 to 1% by weight.
The polymerisable compounds according to the invention are also suitable for polymerisation without an initiator, which is associated with considerable advantages, such as, for example, lower material costs and, in particular, reduced contamination of the LC medium by possible residual amounts of the initiator or degradation products thereof. The polymerisation can thus also be carried out without addition of an initiator. The LC medium thus, in a preferred embodiment, comprises no polymerisation initiator.
The polymerisable component or the LC medium may also comprise one or more stabilisers in order to prevent undesired spontaneous polymerisation of the RMs, for example during storage or transport. Suitable types and amounts of stabilisers are known to the person skilled in the art and are described in the literature. Particularly suitable are, for example, the com¬mer¬cially available stabilisers from the Irganox® series (BASF SE), such as, for example, Irganox® 1076. If stabilisers are employed, their propor¬tion, based on the total amount of the RMs or the polymerisable component, is preferably 10 - 10,000 ppm, particularly preferably 50 - 500 ppm.
Other mesogenic compounds which are not explicitly mentioned above can optionally and advantageously also be used in the media in accordance with the present invention. Such compounds are known to the person skilled in the art.
In a preferred embodiment of the present invention, the liquid-crystalline medium comprises in total 30% or more, preferably 40% or more and particularly preferably 50% or more compounds of formula l, preferably selected from the group of compounds of the l-1, l-2 and l-3, particularly preferably selected from the compounds of the formulae l-2 and l-3.
In another preferred embodiment of the present invention, the liquid-crystalline medium comprises in total 20% or less, preferably 18% or less and particularly preferably 15% or less compounds of formula l, preferably selected from the group of compounds of the l-1, l-2 and l-3, particularly preferably selected from the compounds of the formulae l-2 and l-3.
Preferably, the proportion of the compounds if formula l-1 in the medium is 20% or less, more preferably 15% or less, particularly preferably 10% or less and very particularly preferably 5% or less.
In a preferred embodiment, the medium comprises one or more compounds of formula l-2 in a total concentration in the range of from 5% to 25%, more preferably from 7% to 25%, and particularly preferably from 10% to 20%.
In another preferred embodiment, the medium comprises one or more compounds of formula l-2 in a total concentration of 10% or less, preferable of 5% or less and particularly preferably of 2% or less.
In a preferred embodiment, the medium comprises a compound of the formula l-3, preferably in the range of from 5% to 50%, more preferably from 10% to 40%, and particularly preferably from 15% to 35%.
In a preferred embodiment, the total concentration of the compounds of formula l-3 in the media according to the present invention is 20% or more, more preferably 25% or more and particularly preferably 30% or more.
In a preferred embodiment of the present invention the medium comprises one or more compounds of formula ll and/or RO-2, preferably ll-1 and/or RO-2, in a total concentration of 5% to 40%, more preferably 10% to 37%, particularly preferably 15% to 35%.
Preferably, the medium comprises one or more the compounds of the formula ll-1.
In a preferred embodiment of the present invention the medium comprises one or more compounds of formula ll-1 in a total concentration of 25% or less, more preferably 20% or less, particularly preferably 15% or less, very particularly preferably 10% or less.
In a preferred embodiment of the present invention the medium comprises one or more compounds of formula lll, preferably lll-1, very preferably of formula lll-1 b in a total concentration of 2% to 30%, more preferably 5% to 25%, very preferably 10% to 25%, and in particular 10% to 20%.
In a preferred embodiment of the present invention the medium comprises one or more compounds of formula RO in a total concentration in the range of from 2% to 35%, more preferably from 5% to 30%, particularly preferably from 7% to 25%.
In a preferred embodiment of the present invention, the liquid-crystalline media preferably comprise in total 5% to 35%, preferably 10% to 32% and particularly preferably 20% to 30% of compounds of formula T.
In a preferred embodiment of the present invention, the liquid-crystalline medium comprises in total 30% or less, preferably 15% or less and particularly preferably 10% or less compounds of formula T.
Preferably, the medium comprises one or more compounds of formula C, preferably in a total concentration in the range of from 5% to 50%, preferably from 10% to 40% and particularly preferably from 15% to 30%.
Further preferred embodiments of the present invention, taken alone or in combination with one another, are as follows, wherein some compounds are abbreviated using the acronyms given in Table C:
The liquid-crystal media in accordance with the present invention preferably have a clearing point of 90° C. or more, more preferably 100° C. or more, more preferably 110° C. or more, more preferably 120° C. or more, more preferably 130° C. or more, particularly preferably 140° C. or more and very particularly preferably 150° C. or more.
The liquid-crystal media in accordance with the present invention preferably have a clearing point of 160° C. or less, more preferably 140° C. or less, particularly preferably 120° C. or less, and very particularly preferably 100° C. or less.
The nematic phase of the media according to the invention preferably extends at least from 0° C. or less to 90° C. or more. It is advantageous for the media according to the invention to exhibit even broader nematic phase ranges, preferably at least from -10° C. or less to 120° C. or more, very preferably at least from -20° C. or less to 140° C. or more and in particular at least from -30° C. or less to 150° C. or more, very particularly preferably at least from -40° C. or less to 170° C. or more.
The Δε of the liquid-crystal medium according to the present invention, at 1 kHz and 20° C., is preferably 10 or more, more preferably 15 or more and very preferably 18 or more.
The birefringence (Δn) of the liquid-crystal media according to the present invention, at 589 nm (NaD) and 20° C., is preferably 0.280 or more, more preferably 0.300 or more, even more preferably 0.320 or more, very preferably 0.330 or more and in particular 0.350 or more.
The Δn of the liquid-crystal media according to the present invention, at 589 nm (NaD) and 20° C., is preferably in the range from 0.200 to 0.900, more preferably in the range from 0.250 to 0.800, even more preferably in the range from 0.300 to 0.700 and very particularly preferably in the range from 0.350 to 0.600.
In a preferred embodiment of the present application, the Δn of the liquid-crystal media in accordance with the present invention is preferably 0.50 or more, more preferably 0.55 or more.
The compounds of the formulae l to lll in each case include dielectrically positive compounds having a dielectric anisotropy of greater than 3, dielectrically neutral compounds having a dielectric anisotropy of less than 3 and greater than -1.5 and dielectrically negative compounds having a dielectric anisotropy of -1.5 or less.
The compounds of the formulae l, ll and lll are preferably dielectrically positive.
In some embodiments, however, liquid crystals having a negative value of the dielectric anisotropy can also advantageously be used.
Preferably, the optical component according to the invention is arranged and configured as an optical phase modulator.
In a preferred embodiment, the optical component according to the invention is designed and configured for use in a transparent device for phase modulation of IR radiation.
In another preferred embodiment, the optical component according to the invention is designed and configured for use in a reflective device for phase modulation of IR radiation.
A typical electro-optical modulator comprises conducting, infrared transmitting windows consisting for example of Ge, separated from one anther by spacers and having a cell gap in the range of from 1 mm to 5 mm.
According to another aspect of the present invention there is provided a LIDAR scanning system as described in WO2018/156643 A1, including a laser configured to emit pulses of light at an operating wavelength in the infrared. The LIDAR scanning system includes a transmit reconfigurable-metasurface configured to reflect an incident pulse of light from the laser as an illumination beam pointing at a selected portion of a field of view, preferably a two dimensional field of view. The pointing of the illumination beam is responsive to a first selected holographic beam steering pattern implemented in the transmit reconfigurable-metasurface. The system further includes a receive reconfigurable-metasurface configured to reflect a return of the illumination beam from the selected portion of the field of view as a relay beam pointing at an optical detector. The pointing of the relay beam is responsive to a second selected holographic beam steering pattern implemented in the receiving reconfigurable-metasurface. The system includes an optical detector comprising an array of detector pixels. Each detector pixel includes (i) a photodetector configured to detect light in the return of the illumination beam and (ii) a timing circuit configured to determine a time of flight of the detected light. The optical detector is also configured to output a detection signal indicative of the detected light and a time of flight of the detected light for each pixel of the array. The transmit reconfigurable-metasurface includes a plurality of dynamically adjustable high-Q dielectric resonators arranged on a surface of the reconfigurable-metasurface with inter-element spacing less than the operating wavelength of the laser, where the surface of the reconfigurable-metasurface includes a conducting surface, and the plurality of resonators have a corresponding plurality of adjustable reflection phases providing a dynamically adjustable reflected wave responsive to an incident wave, wherein the conducting surface and the plurality of resonators define a metasurface. Each of the plurality of dielectric resonators includes (i) a pair of regions having high refractive index; and (ii) an electrically-adjustable material disposed in a gap between the regions, wherein the electrically-adjustable material is a liquid crystal material as set forth above and below.
According to another aspect of the invention and referring to
Said LCoS device is useful for the integration into optical devices. Preferred devices are a wavelength selective switch (WSS), LIDAR scanner, infrared scene projector, as well as other beam steering applications as shown in the article Micallef, F. (2019). Middle infrared beam-steering using liquid crystals for spatial light modulation (Doctoral thesis). https://doi.org/10.17863/CAM.39602 (https://www.repository.cam.ac.uk/handle/1810/292443).
In the present application, the expression “dielectrically positive” means compounds or components where Δε > 3.0, dielectrically neutral means those where -1.5 ≤ Δε ≤ 3.0 and dielectrically negative means those where Δε < -1.5. Δε is determined at a frequency of 1 kHz and at 20° C. The dielectric anisotropy of the respective compound is determined from the results of a solution of 10 % of the respective individual compound in a nematic host mixture. If the solubility of the respective compound in the host mixture is less than 10 %, the concentration is reduced to 5 %. The capacitances of the test mixtures are determined both in a cell having homeotropic alignment and in a cell having homogeneous alignment. The cell thickness of both types of cells is approximately 20 µm. The voltage applied is a rectangular wave having a frequency of 1 kHz and an effective value of typically 0.5 V to 1.0 V, but it is always selected to be below the capacitive threshold of the respective test mixture.
Δε is defined as (ε || - ε⊥), while εave. is (ε || + 2 ε⊥) / 3.
The host mixture used for the determination of physical constants of pure compounds by extrapolation is ZLI-4792 from Merck KGaA, Germany. The absolute values of the dielectric constants, the birefringence (Δn) and the rotational viscosity (γ1) of the compounds are determined from the change in the respective values of the host mixture on addition of the compounds. The concentration in the host is 10% or in case of insufficient solubility 5%. The values are extrapolated to a concentration of 100% of the added compounds.
In the examples, the phase sequences of pure compounds are given using the following abbreviations:
K: crystalline, N: nematic, SmA: smectic A, SmB: smectic B, l: isotropic.
Components having a nematic phase at the measurement temperature of 20° C. are measured as such, all others are treated like compounds.
The expression threshold voltage in the present application refers to the optical threshold and is quoted for 10% relative contrast (V10), and the expression saturation voltage refers to the optical saturation and is quoted for 90% relative contrast (V90), in both cases unless expressly stated otherwise. The capacitive threshold voltage (V0), also called the Freedericks threshold (VFr), is only used if expressly mentioned.
The parameter ranges indicated in this application all include the limit values, unless expressly stated otherwise.
The different upper and lower limit values indicated for various ranges of properties in combination with one another give rise to additional preferred ranges.
Throughout this application, the following conditions and definitions apply, unless expressly stated otherwise. All concentrations are quoted in per cent by weight and relate to the respective mixture as a whole, all temperatures are quoted in degrees Celsius and all temperature differences are quoted in differential degrees. All physical properties are determined in accordance with “Merck Liquid Crystals, Physical Properties of Liquid Crystals”, Status November 1997, Merck KGaA, Germany, and are quoted for a temperature of 20° C., unless expressly stated otherwise. The optical anisotropy (Δn) is determined at a wavelength of 589.3 nm. The dielectric anisotropy (Δε) is determined at a frequency of 1 kHz. The threshold voltages, as well as all other electro-optical properties, are determined using test cells produced at Merck KGaA, Germany. The test cells for the determination of Δε have a cell thickness of approximately 20 µm. The electrode is a circular ITO electrode having an area of 1.13 cm2 and a guard ring. The orientation layers are SE-1211 from Nissan Chemicals, Japan, for homeotropic orientation (ε||) and polyimide AL-1054 from Japan Synthetic Rubber, Japan, for homogeneous orientation (ε⊥). The capacitances are determined using a Solatron 1260 frequency response analyser using a sine wave with a voltage of 0.3 Vrms. The light used in the electro-optical measurements is white light. A set-up using a commercially available DMS instrument from Autronic-Melchers, Germany, is used here. The characteristic voltages have been determined under perpendicular observation. The threshold (V10), mid-grey (V50) and saturation (V90) voltages have been determined for 10%, 50% and 90% relative contrast, respectively.
In the present application, the term compounds is taken to mean both one compound and a plurality of compounds, unless expressly stated otherwise.
All mixtures according to the invention are nematic. The liquid-crystal media according to the invention preferably have nematic phases in preferred ranges given above. The expression have a nematic phase here means on the one hand that no smectic phase and no crystallisation are observed at low temperatures at the corresponding temperature and on the other hand that no clearing occurs on heating from the nematic phase. At high temperatures, the clearing point is measured in capillaries by conventional methods. The investigation at low temperatures is carried out in a flow viscometer at the corresponding temperature and checked by storage of bulk samples: The storage stability in the bulk (LTS) of the media according to the invention at a given temperature T is determined by visual inspection. 2 g of the media of interest are filled into a closed glass vessel (bottle) of appropriate size placed in a refrigerator at a predetermined temperature. The bottles are checked at defined time intervals for the occurrence of smectic phases or crystallisation. For every material and at each temperature two bottles are stored. If crystallisation or the appearance of a smectic phase is observed in at least one of the two correspondent bottles the test is terminated and the time of the last inspection before the one at which the occurrence of a higher ordered phase is observed is recorded as the respective storage stability. The test is finally terminated after 1000 h, i.e. an LTS value of 1000 h means that the mixture is stable at the given temperature for at least 1000 h.
The liquid-crystal media in accordance with the present invention may comprise further additives and chiral dopants in the usual concentrations. The total concentration of these further constituents is in the range from 0 % to 10 %, preferably 0.1% to 6%, based on the mixture as a whole. The concentrations of the individual compounds used are each preferably in the range from 0.1% to 3%. The concentration of these and similar additives is not taken into consideration when quoting the values and concentration ranges of the liquid-crystal components and liquid-crystal compounds of the liquid-crystal media in this application.
Preferably the media according to the present invention comprise one or more chiral compounds as chiral dopants in order to adjust their cholesteric pitch. Their total concentration in the media according to the instant invention is preferably in the range 0.05 % to 15%, more preferably from 1% to 10% and most preferably from 2% to 6%.
Optionally the media according to the present invention may comprise further liquid crystal compounds in order to adjust the physical properties. Such compounds are known to the skilled person. Their concentration in the media according to the instant invention is preferably 0% to 30%, more preferably 0.1% to 20% and most preferably 1% to 15%.
The response times are given as rise time (τon) for the time for the change of the relative tuning, respectively of the relative contrast for the electro-optical response, from 0% to 90% (t90 - t0), i.e. including the delay time (t10 - t0), as decay time (τoff) for the time for the change of the relative tuning, respectively of the relative contrast for the electro-optical response, from 100% back to 10% (t100 - t10) and as the total response time (τtotal = τon + τoff), respectively.
The liquid-crystal media according to the invention consist of a plurality of compounds, preferably 3 to 30, more preferably 4 to 20 and very preferably 4 to 16 compounds. These compounds are mixed in a conventional manner. In general, the desired amount of the compound used in the smaller amount is dissolved in the compound used in the larger amount. If the temperature is above the clearing point of the compound used in the higher concentration, it is particularly easy to observe completion of the dissolution process. It is, however, also possible to prepare the media in other conventional ways, for example using so-called pre-mixes, which can be, for example, homologous or eutectic mixtures of compounds, or using so-called “multibottle” systems, the constituents of which are themselves ready-to-use mixtures.
All temperatures, such as, for example, the melting point T(C,N) or T(C,S), the transition from the smectic (S) to the nematic (N) phase T(S,N) and the clearing point T(N,l) of the liquid crystals, are quoted in degrees Celsius. All temperature differences are quoted in differential degrees.
In the present invention and especially in the following examples, the structures of the mesogenic compounds are indicated by means of abbreviations, also referred to as acronyms. In these acronyms, the chemical formulae are abbreviated as follows using Tables A to D below. All groups CnH2n+1, CmH2m+1 and ClH2l+1, and CnH2n, CmH2m and ClH2l denote straight-chain alkyl or akylene, respectively, in each case having n, m or l C atoms, wherein n and m, independently are 1, 2, 3, 4, 5, 6 or 7 and l is 1, 2 or 3. Table A lists the codes used for the ring elements of the core structures of the compounds, while Table B shows the linking groups. Table C gives the meanings of the codes for the left-hand or right-hand end groups. Table D shows illustrative structures of compounds with their respective abbreviations.
in which n and m each denote integers, and the three dots “..” are placeholders for other abbreviations from this table.
The following table shows illustrative structures together with their respective abbreviations. These are shown in order to illustrate the meaning of the rules for the abbreviations. They furthermore represent compounds which are preferably used.
The following illustrative structures are compounds, which are preferably additionally used in the media:
in which m and n, identically or differnetly, are 1,2,3,4,5,6 or 7.
Preferably, the medium according to the invention comrises one or more compounds selected from the compounds of Table C.
The following table, Table D, shows illustrative compounds which can be used as alternative stabilisers in the mesogenic media in accordance with the present invention. The total concentration of these and similar compounds in the media is preferably 5% or less.
In a preferred embodiment of the present invention, the mesogenic media comprise one or more compounds selected from the group of the compounds from Table D. The following table, Table E, shows illustrative compounds which can preferably be used as chiral dopants in the mesogenic media in accordance with the present invention.
In a preferred embodiment of the present invention, the mesogenic media comprise one or more compounds selected from the group of the compounds of Table E.
The mesogenic media in accordance with the present application preferably comprise two or more, preferably four or more, compounds selected from the group consisting of the compounds from the above tables.
Without further elaboration, it is believed that one skilled in the art can, using the preceding description, utilize the present invention to its fullest extent. The following examples are, therefore, to be construed as merely illustrative, and not limitative of the remainder of the disclosure in any way whatsoever. From the description, one skilled in the art can easily ascertain the essential characteristics of this invention and, without departing from the spirit and scope thereof, can make various changes and modifications of the invention to adapt it to various usages and conditions.
Comparative Mixture C1 and Example mixtures N1 to N22 for use according to the invention having the compositions and properties as indicated in the following tables are prepared and characterized with respect to their general physical properties and their applicability in optical components.
An optical component comprising the media according to the invention as defined in clam 1, and fabricated according to the process as defined in claim 12 is distinguished by excellent operational stability when exposed to the environment because of high clearing temperature, broad nematic phase range and excellent low-temperature stability (LTS) of the liquid crystal medium used therein. As a result, the component, and devices containing the component, are operable under extreme temperature conditions. Surprisingly, the temperature dependence of the birefringence of said liquid crystal medium is very small, i.e. the Δn changes little with the temperature which makes a device reliable and easy to control.
The birefringence of comparative mixture C-1 and of mixture examples N-1 and N-2 are determined at 20° C. and 60° C. The results are shown in Table 1.
Surprisingly, the ratio Δn20/Δn60 is favorably smaller for the media according to the invention, i.e. they show less variation of the birefringence with temperature compared to the medium of the state of the art.
Furthermore, the media according to the invention are distinguished by a high clearing temperature in combination with excellent low temperature stability, i.e. they have a very broad operating temperature range.
Furthermore, the media according to the invention show a surprisingly low threshold voltage V0.
Surprisingly, a medium comprising a compound RO with an alkoxy side chain has an even higher birefringence and higher clearing temperature than a medium comprising exclusively compounds with an alkyl side chain.
| Number | Date | Country | Kind |
|---|---|---|---|
| 20184700.1 | Jul 2020 | EP | regional |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/EP2021/068574 | 7/6/2021 | WO |
