High Birefringence Liquid Crystals Research Articles

Thermal tuning nanoprinting based on liquid crystal tunable dual-layered metasurfaces for optical information encryption.

Dynamic tuning metasurfaces represent a significant advancement in optical encryption techniques, enabling highly secure multichannel responses. This paper proposes a liquid crystal (LC) tunable dual-layered metasurface to establish a thermal-encrypted optical platform for information storage. Through the screening of unit cells and coupling of characteristics, a dynamic polarization-dependent beam-steering metasurface is vertically cascaded with an angular multiplexing nanoprinting metasurface, separated by a dielectric layer. By integrating high-birefringence LCs into dual-layered metasurfaces, the cascaded meta-system can achieve dynamic thermal-switching for pre-encoded nanoprinting images. This work provides a promising solution for developing compact dynamic meta-systems for customized optical storage and information encryption.

Synthesis and properties of biphenyl liquid crystal diluters terminated by 2,2-difluorovinyloxyl for high birefringence liquid crystals

ABSTRACT A series of liquid crystal (LC) diluters containing a rigid biphenyl core with a lateral fluorine substituent, a 2,2-difluorovinyloxyl terminal group and a flexible n-alkyl chain were designed and synthesised through classical organic synthetic reactions. Their chemical structures were characterised and confirmed by traditional methods. Meanwhile, the effects of alkyl-chain length, terminal group and lateral fluorine substituent on the melting point (T m), birefringence (Δn), dielectric anisotropy (Δε) and rotational viscosity (γ 1) of LC diluters were investigated. Density functional theory (DFT) calculations were employed to obtain the molecular polarisability, dipole moment, frontier orbitals, biphenyl dihedral angle and aspect ratio. Furthermore, their comprehensive properties in low-Δn LC mixture 002 and high-Δn LC mixture P01-F were further evaluated, and it was found that the 2,2-difluorovinyloxyl LC diluter 3FV have a significant advantage in reducing the T m and γ 1 of LC mixtures, and increasing the values of Δn and Δε. The research results provide technical support and theoretical guidance for the molecular design of new LC diluters and the development of fast response liquid crystals.

Synthesis and performance evaluation of fluorinated biphenyl diluters for high birefringence liquid crystals

ABSTRACT Liquid crystal (LC) mixtures with high birefringence (∆n) and low rotational viscosity play an essential role for fast-response LC devices. However, high birefringence and low rotational viscosity are a pair of contradictory performance parameters. In this work, two high-∆n LC diluters are proposed to achieve a fine balance between them. These two terminal olefin diluters containing a rigid biphenyl core with a lateral fluorine substituent, a buty-3-enyl terminal group and a flexible n-alkyl chain were designed and synthesised through classical organic synthetic reactions. Meanwhile, their comprehensive properties were further evaluated in a LC mixture P02-F containing fluoro-tolane and a LC mixture P12-ISO containing isothiocyano-tolane. The results show that the biphenyl diluters 2BBF2V and 3BFB2V could effectively decrease the T m of LC mixture P12-ISO to below −25°C, while maintain high ∆n and large Δε, which are suitable for the high-∆n LC mixtures containing isothiocyano-tolane. Furthermore, DFT calculations of molecular conformation and polarisability components were utilised to correlate the experimental findings.

47.2: An Essential Role of Diluters on the Fast Response Time for High Birefringence Liquid Crystals

A new liquid crystal diluter was designed and synthesized to balance trade‐offs between low viscosity, high Δn, and large Δε in the LC mixture. Research results indicated that this diluter had excellent properties of low melting point, high Δn, and large Δε. Meanwhile, in a high‐Δn LC mixture, it could effectively reduce the viscoelastic coefficient (γ1/K11), and increase the As while maintaining an equivalent LC phase temperature range and Δn. It means that the LC diluter plays an essential role to improve the response time of LCs.

P‐12.12: Development and Application of High Birefringence Liquid Crystal Materials

The development of new liquid crystal optoelectronic devices, including laser phase modulation, microwave and terahertz devices, requires liquid crystal materials with high birefringence. In this paper, three new molecular design strategies are proposed, including the introduction of olefin chain, lateral fluorine substitution and new ring core. Four new series of isothiocyanate liquid crystal compounds with high birefringence, low melting point and wide nematic temperature range were synthesized. Based on these new liquid crystal compounds, a liquid crystal mixture with nematic temperature range of ‐40~146 ºC and birefringence of 0.42 was developed. At 19 GHz, the new liquid crystal mixture shows excellent dielectric properties, with dielectric anisotropy of 1.28 and dielectric loss of 0.0087. The new liquid crystal mixture also has very low viscoelastic coefficient. The results at 1550nm and 60 ºC show that the response speed can reach 3.6 milliseconds with 2π phase modulation in the reflection mode.

Fluorination Improves the Electro-Optical Properties of Benzoxazole-Terminated Liquid Crystals in High Birefringence Liquid Crystal Mixtures: Experimental and Theoretical Investigations.

Aromatic heterocyclic liquid crystal (LC) materials have received much attention from LC chemists for their high birefringence and large dielectric anisotropy, yet few have reported their properties in LC mixtures. In this work, a series of fluorinated benzoxazole liquid crystal compounds were synthesized to evaluate their electro-optical properties in high birefringence LC mixtures, with the expectation of further establishing the theoretical basis and experimental evidence for their applications in LC photonics. Firstly, the effects of the lateral fluorine substituent positions on the molecular synthetic yield, mesomorphic and solubility properties were comparatively investigated. Afterwards, we focused on the fluorination effects on the core electro-optical properties, including birefringence, dielectric anisotropy and further investigation of the viscoelastic coefficient of high birefringence LC mixtures. Research results showed that the benzoxazole liquid crystal compounds possess low melting points, wide nematic phase intervals and good solubility by appropriate lateral fluorine substitution, which is beneficial to further improve the electro-optical properties of high birefringence LC mixtures. Meanwhile, the theoretical and experimental results corroborate each other to well reveal the structure-property relationship. This study demonstrates that fluorination would promote promising applications of benzoxazole-terminated liquid crystals in emerging LC optical devices.

Bis-tolane liquid crystals terminated by 2,2-difluorovinyloxyl with high birefringence and large electrical anisotropy

A series of liquid crystals (LCs) containing bis-tolane, lateral fluorine substituents and 2,2-difluorovinyloxyl group were designed and synthesized. Their LC phase behavior, birefringence, dielectric anisotropy and viscosity properties were discussed by comparing with previously reported LCs with high birefringence and large electrical anisotropy. Meanwhile, the effects of lateral fluorine numbers on the melting point, birefringence and dielectric anisotropy of these LCs were explored, and density functional theory (DFT) calculations of molecular conformation and polarizability were used to correlate the experimental results. Research results indicated that the 2,2-difluorovinyloxyl terminal group decreased the melting points of these LCs, and these LCs showed relatively low melting point (<113.7 ℃), broad nematic-phase temperature interval, high birefringence (>0.4), and large dielectric anisotropy (35.87). Furthermore, performance in high birefringence LC mixture demonstrated that they could effectively improve the birefringence and dielectric anisotropy, and maintain low viscosity, which is expected to possess widespread applications in fast response LC optical devices.

High birefringence liquid crystals with a wide temperature range and low melting point for augmented reality displays

Precise molecular tailoring was applied to obtain high performance liquid crystal materials for the broad temperature adaptability of LCoS devices in AR displays.

Topological steering of light by nematic vortices and analogy to cosmic strings.

Liquid crystals are widely known for their technological uses in displays, electro-optics, photonics and nonlinear optics, but these applications typically rely on defining and switching non-topological spatial patterns of the optical axis. Here, we demonstrate how a liquid crystal's optical axis patterns with singular vortex lines can robustly steer beams of light. External stimuli, including an electric field and light itself, allow us to reconfigure these unusual light-matter interactions. Periodic arrays of vortices obtained by photo-patterning enable the vortex-mediated fission of optical solitons, yielding their lightning-like propagation patterns. Predesigned patterns and spatial trajectories of vortex lines in high-birefringence liquid crystals can steer light into closed loops or even knots. Our vortex lattices might find technological uses in beam steering, telecommunications, virtual reality implementations and anticounterfeiting, as well as possibly offering a model system for probing the interaction of light with defects, including the theoretically predicted, imagination-capturing light-steering action of cosmic strings, elusive defects in cosmology.

A high birefringence liquid crystal for lenses with large aperture

This work presents the application of an experimental nematic liquid crystal (LC) mixture (1929) in a large aperture lens. The LC material is composed of terphenyl and biphenyl derivatives compounds with an isothiocyanate terminal group and fluorinated lateral substituents. The substitution with a strongly polar isothiocyanate group and an aromatic rigid core provides pi-electron coupling, providing high birefringence (Delta n = 0.3375 at 636 nm and 23 °C) and low viscosity (eta = 17.03 mPa s). In addition, it also shows high values of birefringence at near infrared (0.318 at 1550 nm). The synthesis process is simple when comparing materials with high melting temperatures. The excellent properties of this LC mixture are demonstrated in a large aperture LC-tunable lens based on a transmission electrode structure. Thanks to the particular characteristics of this mixture, the optical power is high. The high birefringence makes this LC of specific interest for lenses and optical phase modulators and devices, both in the visible and infrared regions.

P‐90: Student Poster: High Birefringence Liquid Crystal for Fast‐Response Phase Modulators

We report a high birefringence and low viscosity nematic liquid crystal for phase‐only spatial light modulators (SLMs). To achieve 2π phase change at λ = 633 nm with 5 V operation voltage, the measured response time is 2.2 ms at 50°C. Meanwhile, our mixture exhibits no sign of photodegradation for a total dosage of 20 MJ/cm2 at a blue laser wavelength λ = 465 nm Widespread applications of this material for high brightness SLMs, LIDAR, near‐eye displays, and head‐up displays are foreseeable.

40‐2: Distinguished Student Paper: Compact, Fast‐Response, Continuous and Wide‐Angle Laser Beam Steerers

A liquid crystal‐cladding waveguide with resistive electrode configuration is proposed for laser beam steering applications. It can achieve wide‐angle continuous coverage two‐dimensional beam control with fast response time. With numerical validation, we find that in comparison with previous prismatic electrode approach, our device demonstrates higher compatibility with high birefringence liquid crystal materials, and thus a more compact form factor can be realized. Such a beam steerer is attractive for a wide range of applications including automotive LiDAR, eye‐tracking for near‐eye displays, and high‐precision 3D printing.

Compact, fast‐response, continuous, and wide‐angle laser beam steerers

AbstractA liquid crystal‐cladding waveguide with resistive electrode configuration is proposed for laser beam steering applications. It can achieve wide‐angle, continuous coverage, two‐dimensional beam control with fast response time. With numerical validation, we find that in comparison with previous prismatic electrode approach, our device demonstrates higher compatibility with high birefringence liquid crystal materials, and thus, a more compact form factor can be realized. Such a beam steerer is attractive for a wide range of applications including automotive LiDAR, eye‐tracking for near‐eye displays, and high‐precision 3D printing.

Synthesis and properties of 5,6-dihydro-4H-cyclopenta[b]thiophene-based nematic liquid crystals: A new access to mesogens with high birefringence and large dielectric anisotropy

A novel liquid crystal core unit 5,6-dihydro-4H-cyclopenta[b]thiophene was designed and synthesized in four steps and three mesogens containing terminal cyano group were then obtained. The effects of this skeleton on the mesophase and physical properties of liquid crystals were then investigated by compared with two series of reference compounds based on 1,4-disubstituted phenylene and disubstituted phenylcyclohexane and found this unit can benefit the formation of the nematic phase. Besides, both the birefringence (Δn) and dielectric anisotropy (Δε) values were increased after the introduction of this core unit. Density function theory calculations suggested that the combination of thiophene and cyclopentane had increased the height/width ratio and linearity of the mesogens which can stabilise the liquid crystal phase. Five different liquid crystals based on this new core were synthesized at last to further illustrate the usefulness of this core in constructing high birefringence and large dielectric anisotropy liquid crystals with wide nematic phase interval.

Synthesis and properties of novel 6,7-dihydrocyclopenta[5,6-b]benzofuran-based liquid crystal compounds

ABSTRACT A novel liquid crystal core unit 6,7-dihydrocyclopenta[5,6-b]benzofuran was designed and three different kinds of liquid crystals 2MUF, 2MP4, 2MYO2 were synthesised through a facile route which employed palladium-catalysed cascade Sonogashira coupling/cyclisation as a key step. Initially, density function theory calculation illustrated that a compound based on this new unit possessed almost a linear structure. The mesophase and physical properties of these novel compounds were measured and the impacts of the newly designed core unit on these properties were investigated by comparing with two series of analogous materials which contained classical mesogenic cores 1,4-disubstituted benzene and trans-cyclohexyl benzene, finding that the introduction of 6,7-dihydrocyclopenta[5,6-b]benzofuran into liquid crystals tended to promote the formation of nematic phase while increasing both the melting points and the clearing points of target molecules. Meanwhile, the newly synthesised liquid crystals presented higher birefringences when compared with their corresponding reference compounds, indicating that 6,7-dihydrocyclopenta[5,6-b]benzofuran can be a hopeful candidate for the construction of high birefringence liquid crystals.

Synthesis and study of physicochemical properties of relatively high birefringence liquid crystals: Tolane-type with symmetric alkoxy side groups

A Liquid Crystal (LC) consisting of rigid unit, tolane, and flexible alkoxy side groups, R = OC6H13, is synthesized. The purity of the product is verified by elemental analysis. Its chemical structure is characterized by, NMR and FT-IR spectroscopy. Their physicochemical properties are investigated by Polarizing Optical Microscope (POM) and Differential Scanning Calorimetry (DSC). The compound exhibits nematic phase, with good thermal stabilities and high birefringence. In addition, it has two smectic phases. The sequences of phases in the obtained results of POM are in good accordance with the results realized by DSC.

Spectroscopic studies on liquid crystalline n-hexyloxy-cyanobiphenyl with dispersed citrate-capped gold nanoparticles in visible region

ABSTRACTIn the present manuscript, the characterisation was done on liquid crystalline n-hexyloxycyanobiphenyl (6ocb) compound with dispersed citrate-capped gold nanoparticles (Au NPs) at different concentrations. It is observed that the birefringence enhances with increase in concentration of Au NPs. Also, strong Vander Waal’s interaction takes place due to well capping between the Au NPs and 6ocb molecules. The refractive indices are determined by using modified spectrometer at different wavelengths. The orientational order parameter has been determined from various theoretical molecular internal field models namely, Kuczynski, Effective geometry, Haller’s extrapolation and Vuks. The dispersive power ω is estimated for two consecutive wavelengths for the case of <n>, ne and no at different wavelengths found to be constant with temperature. The values of cross-over temperature, TCO determined from the temperature gradients of ne and no. Further, the refractive indices measured are fitted with two and three coefficient Cauchy model. Three coefficient Cauchy model is favourable than two coefficient Cauchy model for high birefringence liquid crystals. The results obtained are compared and discussed. Further, the phase transitions can be easily identified by GMSD Image processing method with Matlab tool to reduce the costly equipment’s usage in finding the heat flow with respect to temperature.

Characterization of the spatially anamorphic phenomenon and temporal fluctuations in high-speed, ultra-high pixels-per-inch liquid crystal on silicon phase modulator.

High-birefringence liquid crystal (LC) in ultrathin LCOS panels was adopted to prepare high phase precision (mSTD =λ/50) and phase accuracy (mAPAE% ∼8%) with suppressed pixel-level crosstalk effects. In conjunction with optimized digital driving scheme, the zero order light loss was found directly related to the phase accuracy error. Meanwhile, the world's fastest pure phase modulation LCOS with a response time of ∼0.87 ms at 45 °C was also achieved. The low-temporal flicker (P-P ∼2.0%) with high-speed LC responses was demonstrated by applying new digital driving scheme. Finally, the 4K2 K LCOS-SLM (∼7000 PPI) was evaluated its difficulties and opportunities.

77‐5: Late‐News Paper: Advanced phase distribution algorithm in blazed grating for continuous beam steering

The electrically tunable beam deflector have been researched and developed for lots of purpose. For the transmission type beam deflector, an indium‐tin‐oxide (ITO) has been developed with blazed grating patterns. The ITO layer was designed and generated on the lower substrate for transmission type beam deflector. A pixel pitch of ITO grating patterns is 6um, the electrode width is 3um with 3um spacing. With this small pixel pitch, the maximum diffraction angle is 2.541° at a wavelength of 532nm. A minimum cell gap is 2.5um for the enough 2π phase modulation with high birefringence liquid crystal which is delta n, 0.31. Total 720‐ ITO line which was patterned on the lower substrate is controlled individually by driving integrated circuit (IC) from driving module. Beam deflector driving module with driving IC is designed for continuous beam steering. Driving algorithm is developed and applied to the driving system for high angular resolution and continuous beam steering.

Electrically tunable transmission-type beam deflector using liquid crystal with high angular resolution.

Highly efficient transmission-type beam deflectors that have high angular resolution have been widely used for various applications. Continuously tunable beam deflectors have also been needed for many purposes. An indium-tin-oxide (ITO), widely used for transparent electrodes, was placed on the upper and lower glass substrate. The ITO layer on the lower substrate was patterned by the contact mask aligner for relatively wide input and output pad compared to main grating ITO patterns in the active area. These input and output pads on the lower substrate are connected to each driving integrated circuit (IC), which has 360 channels for continuous control. A small pixel pitch of grating patterns of 6 μm (the electrode width is 3 μm with a 3 μm spacing) was developed, and the maximum diffraction angle is calculated and measured at 2.541° with a wavelength of 532 nm. A minimal cell gap of 2.5 μm was applied for the full 2π phase modulation by using a high-birefringence liquid crystal. A driving module for continuous beam steering is also developed and applied to the beam deflector system. A diffraction efficiency of about 50.9% is observed at an angle of diffraction about 2.541°.