Liquid Crystal Polarization Research Articles

Freely suspended nematic and smectic films and free-standing smectic filaments in the ferroelectric nematic realm.

We show that stable, freely suspended liquid crystal films can be made from the ferroelectric nematic (NF) phase and from the recently discovered polar, lamellar SmZA and SmAF phases. The NF films display two-dimensional, smectic-like parabolic focal conic textures comprising director/polarization bend that are a manifestation of the electrostatic suppression of director splay in the film plane. In the SmZA and SmAF phases, the smectic layers orient preferentially normal to the film surfaces, a condition never found in typical thermotropic or lyotropic lamellar LC phases, with the SmZA films exhibiting focal-conic fan textures mimicking the appearance of typical smectics in glass cells when the layers are oriented normal to the plates, and the SmAF films showing a texture of plaquettes of uniform in-plane orientation where both bend and splay are suppressed, separated by grain boundaries. The SmAF phase can also be drawn into thin filaments, in which X-ray scattering reveals that the smectic layer planes are normal to the filament axis. Remarkably, the filaments are mechanically stable even if they break, forming free-standing, fluid filaments supported only at one end. The unique architectures of these films and filaments are stabilized by the electrostatic self-interaction of the liquid crystal polarization field, which enables the formation of confined, fluid structures that are fundamentally different from those of their counterparts made using previously known liquid crystal phases.

Polar Order in a Fluid Like Ferroelectric with a Tilted Lamellar Structure – Observation of a Polar Smectic C (SmCP) Phase

AbstractThe spontaneous polarisation of the SmCP phase is over two orders of magnitude larger than that found in conventional ferroelectric SmC phase of chiral materials used in some LCD devices. Fully atomistic molecular dynamics simulations faithfully and spontaneously reproduce the proposed structure and associated bulk properties; comparison of experimental and simulated X‐ray scattering patterns shows excellent agreement. The materials disclosed here have significantly smaller dipole moments than typical polar liquid crystals such as RM734 which suggests the role of molecular electrical polarity in generating polar order is perhaps overstated, a view supported by consideration of other molecular systems.

Polar Order in a Fluid Like Ferroelectric with a Tilted Lamellar Structure - Observation of a Polar Smectic C (SmCP) Phase.

The spontaneous polarisation of the SmCP phase is over two orders of magnitude larger than that found in conventional ferroelectric SmC phase of chiral materials used in some LCD devices. Fully atomistic molecular dynamics simulations faithfully and spontaneously reproduce the proposed structure and associated bulk properties; comparison of experimental and simulated X-ray scattering patterns shows excellent agreement. The materials disclosed here have significantly smaller dipole moments than typical polar liquid crystals such as RM734 which suggests the role of molecular electrical polarity in generating polar order is perhaps overstated, a view supported by consideration of other molecular systems.

Robust optical singularity detection enabled by spin-synchronized shearing interference

Singular beams carrying phase and polarization singularities have been extensively studied for applications in optical communication, quantum information processing, optical imaging, and other fields. However, developing a robust method to detect optical singularity that is insensitive to wavelength, polarization, and illumination position remains a significant challenge. In this study, we propose and demonstrate a robust optical singularity detection scheme based on spin-synchronized shearing interference (SSSI) using spin-dependent gradient phase modulation of a quarter-wave liquid–crystal polarization grating. Since the spin-dependent gradient phase modulation of the polarization grating is wavelength-independent, and the two circular bases of the incident field can be measured simultaneously, the proposed method is robust to wavelength and polarization. Additionally, we have verified that SSSI performs well in detecting multi-singularity cylindrical vector beam. This work provides a practical and straightforward scheme for robust optical singularity detection.

Design and fabrication of an achromatic liquid crystal polarization grating with large deflection angle for visible wavelength

Design and fabrication of an achromatic liquid crystal polarization grating with large deflection angle for visible wavelength

Nonsymmetrical thermal conductivity along the director field in ferroelectric nematic liquid crystals.

The synthesis of ferroelectric nematic liquid crystals (FNLCs) concludes the long wait for their existence and potential usage in multiple liquid crystal based applications. In FNLCs, electric polarization in the nematic phase significantly decreases the switching time of in-on display pixels. In this article, we report the occurrence of translation symmetry breaking for heat propagation along the director field n[over ̂] in the ferroelectric nematic phase. Due to the C_{∞V} symmetry of such a phase and close similarity to the bent-core polar liquid crystal phase, a rank-3 tensor describes its scalar order parameter and algebraic deductions. The finite element simulations show the occurrence of the nonsymmetrical thermal conductivity along n[over ̂]. The preferential heat transport in FNLCs can allow them to work as an all-thermal monophase non-nanostructured single-material thermal rectifier. We expect that this study will contribute towards the FNLCs application as functional layers and inks.

Compact binocular holographic near-eye 3D display system based on a liquid crystal polarization grating

Holographic technology is considered as one of the most ideal 3D display technologies and has significant potential in near-eye display. However, binocular holographic near-eye 3D display still faces challenges such as serious visual fatigue and complex system. Here, we propose a compact binocular holographic near-eye 3D display system based on a liquid crystal polarization grating (LCPG). Based on the LCPG, the reconstructed light can be deflected respectively to left and right viewing areas. The proposed system achieves binocular display with only one phase-only spatial light modulator used to load computer-generated hologram, which makes the binocular display system more compact. Simultaneously, the proposed system reduces mismatches in the images perceived by two eyes, thus achieving a better binocular display effect. Experimental results demonstrate the feasibility of the proposed binocular holographic near-eye 3D display system with dual viewing areas. Additionally, based on the time-division multiplexing method, dynamic binocular holographic near-eye display can be achieved. The proposed system has potential applications in holographic virtual reality and augmented reality display.

Optically Isotropic Polymer Stabilized Liquid Crystals with Fast and Large Field‐Induced Refractive Index Variation

AbstractOptically isotropic polymer stabilized liquid crystals with low haze (≈1% at 550 nm), large (≈0.09) field induced refractive index variation, and fast (<0.1 ms) relaxation time are reported. The impressive improvement compared to previous studies using conventional nematic liquid crystals are due to both the addition of novel highly polar ferroelectric nematic liquid crystals that decrease the required field to achieve the theoretically predicted refractive index variation and of the 6 wt.% of chiral dopant with high helical twisting power that suppressed the haze and made the system reversible with fast relaxation. It is also shown that the field induced refractive index variation can be increased over to 0.1 by using high intensity UV light for polymer stabilization. Although such polymer structure is not completely isotropic, it still provides polarization independent optical properties for normal incidence. Since fast and large switching of focal length is essential in AR/VR glasses, these systems offer significant potential for applications in highly tunable microlens arrays.

Electrically Switchable Transmissive and Reflective Liquid Crystal Polarization Gratings Based on Cholesteric Liquid Crystals

Electrically Switchable Transmissive and Reflective Liquid Crystal Polarization Gratings Based on Cholesteric Liquid Crystals

Quarter-wave Pancharatnam-Berry phase gradient liquid crystal-enabled dual-polarization optical edge detection.

Here, we present a novel, to the best of our knowledge, optical edge detection scheme that can be operated in both linear and circular polarization modes, leveraging an optical spatial differentiator constructed by quarter-wave Pancharatnam-Berry (P-B) phase gradient element. After explaining the theoretical mechanism, we utilize a quarter-wave P-B phase liquid crystal polarization grating to validate the dual-polarization optical edge detection capability. We demonstrate that the orientation of linear polarization and the spin of circular polarization dictate the transition between edge and bright-field images. Besides, the linear and circular polarization modes exhibit broadband and monochromatic responsive properties, respectively. This mechanism, dependent on wavelength and polarization, holds promise for applications in color image processing, chiral sensing imaging, and polarization-entangled quantum imaging.

Emergent Antiferroelectric Ordering and the Coupling of Liquid Crystalline and Polar Order

Polar liquid crystals possess 3D orientational order coupled with unidirectional electric polarity, yielding fluid ferroelectrics. Such polar phases are generated by rod‐like molecules with large electric dipole moments. 2,5‐Disubstituted 1,3‐dioxane is commonly employed as a polar motif in said systems, and herein it is shown to suffer from thermal instability as a consequence of equatorial‐trans to axial‐trans isomerism at elevated temperatures. Isosteric building blocks are utilized as potential replacements for the 1,3‐dioxane unit, and in doing so new examples of fluid ferroelectric systems are obtained. For binary mixtures of certain composition, the emergence of a new fluid antiferroelectric phase, a finding not observed for either of the parent molecules, is observed. This study also reveals a critical tipping point for the emergence of polar order in otherwise apolar systems. These results hint at the possibility for uncovering new highly ordered polar liquid‐crystalline phases and delineate distinct transition mechanisms in orientational and polar ordering.

15‐3: Reflective Liquid Crystal Polarization Volume Grating for SWIR with High Diffraction Efficiency and Large Diffraction Angle and Sensor Application

We have developed a reflective polarization volume grating using liquid crystal polymer for SWIR with high efficiency and a large diffraction angle. By using this grating and a lightguide system, we demonstrated a sensor system that can capture identical images simultaneously in both visible and SWIR light.

75‐1: Invited Paper: Liquid Crystal Polarization Hologram for Eye Tracking Application

Eye‐tracking is vital in AR/VR/MR systems for display correction, rendering, accommodation, and more. However, existing eye‐tracking solutions fall short in accuracy, efficiency, form factor, and population coverage. Using Liquid crystal polarization hologram (LCPH) for eye‐tracking purposes offers a compact form‐factor with excellent performance.

Memorizable Electro‐Birefringence Effect Exhibited by Transparent Liquid Crystal/Polymer Composite Materials

AbstractPolymer‐dispersed liquid crystals (PDLCs) with nano‐phase‐separated structures, in which nanometer‐sized liquid crystal (LC) domains are dispersed within a polymer matrix (nano‐PDLCs), are transparent solid materials whose optical properties can be modulated by applying an electric field (E‐field). Because the proportion of LC that can respond to an electric field is small, the specific surface area of the phase‐separated interface of nano‐PDLCs is larger than that of conventional PDLCs, resulting in higher drive voltages than those of conventional PDLCs. To lower the driving voltage of nano‐PDLCs, highly polar LCs (C3DIO) are used with a large dielectric anisotropy (>10000), and prepared nano‐PDLCs using DIO mixtures obtained by mixing them with related compounds as the host LC. Nano‐PDLCs employing DIO mixtures exhibit higher E‐field responsivity than those using conventional LC. In addition, the electro‐optical Kerr coefficient at visible wavelength is significantly high, reaching 10−8 m V−2. Furthermore, nano‐PDLCs using the DIO mixture exhibit a memory effect in which the induced birefringence remains even after the removal of the in‐plane E‐field. Memorized birefringence can be erased by heating or applying an E‐field perpendicular to the substrate surface. Nano‐PDLCs using a DIO mixture can be rewritable electro‐birefringence‐responsive materials that can memorize arbitrary birefringence values.

Performance and compensation method of first-order liquid crystal beam-steering system under continuous wave laser irradiation

The effects of laser irradiation thermal deposition on the performance degradation of liquid crystal (LC) devices in high-power laser systems are extremely vital. In this study, the first-order beam-steering system (FBS) was developed using a passive liquid crystal polarization grating (LCPG) and liquid crystal adjustable wave-plate (LCAW). The LCPG was prepared by holographic exposure technology, and the LCAW was prepared using the standard LC cell preparation process. We investigated the influences of diffraction efficiency of FBS under a 1070-nm continuous-wave (CW) laser irradiation. The energy is concentrated in the −1st order at first. When the half-wave retardation was reached, all the energy is concentrated in the +1st order (∼97 %), and the beam is deflected. Once the phase retardation decreases below the half-wave retardation, the energy gradually reconcentrates in the −1st order. When the LCAW fails, the diffraction the energy is refocused to the −1st order by the LCPG. The results indicated that both thermal deposition and driving voltage reduce the phase retardation of the LCAW, generating a variation of energy between in ±1st orders. By reducing the driving voltage, this half-wave retardation can be recovered under a certain half-wave voltage and laser power density, and the diffraction efficiency of the +1st order can be compensated to ∼97 %. If the reduced phase retardation is not less than half-wave, the FBS can still be modulated in high-power continuous lasers. Our research provides a reference for the development of beam-steering technology based on LC materials in high-power laser systems.

A design approach to obtaining highly polar liquid crystal dimers

ABSTRACT The synthesis and characterisation of 10 members of the [4[(E)-[4-[4-[ω-(4-cyanophenyl)phenoxy]alkyloxy]-3-nitrophenyl]methylideneamino]phenyl] 2,4-dimethoxybenzoates is reported in which the number of methylene units in the flexible spacer is increased from three to twelve. The mesogenic units are based on cyanobiphenyl and 3-nitrobenzylideneaniline benzoate and linked by the spacer such that their dipoles are parallel giving rise to a large longitudinal dipole moment. All 10 members of the series show a nematic phase, and the nematic-isotropic transition temperatures, TNI, and associated entropy changes show a strong dependence on the length and parity of the spacer. This behaviour is attributed to the average shapes of the molecules and their flexibility. The heptyl member was further characterised using dielectric spectroscopy revealing a high value of dielectric permittivity reflecting the large dipole moment of the molecules and possibly indicating local short-range ferroelectric order. The synthesis and characterisation of two members of the [4[(E)-[4-[4-[3-(ω-cyanophenyl)phenoxy]alkyloxy]-4-nitrophenyl]methylideneamino]phenyl] 2,4-dimethoxybenzoates are also described for which the difference in shape between odd and even members is reduced. Both dimers are exclusively nematogenic and the difference between TNI for the odd and even member is smaller reflecting the more similar molecular shapes. The potential for developing dimers that exhibit the ferroelectric nematic phase is discussed.

Freeform Liquid–Crystal Polarization Imaging Optics: A Practical Approach from Design to Fabrication

AbstractFreeform liquid–crystal polarization imaging optics (LPIOs) have vast potential for application in next‐generation interactive displays like augmented reality and virtual reality. However, tailoring the phase profile of a freeform LPIO for flexible aberration correction and diffraction efficiency control is still a big challenge due to the difficulties arising from the non‐zero étendue of an imaging system and the finite bandwidth of LPIOs. Here, a practical approach to creating freeform LPIOs from design to fabrication is proposed. A freeform polarization exposure is developed to produce a flexible, precise, and ultra‐high‐resolution photoalignment pattern for a freeform LPIO. A cooperative optimization is performed between the freeform LPIO and the freeform polarization exposure system to find the optimal phase of the freeform LPIO and the optimal surface profiles of the freeform lenses employed in the exposure system to produce freeform wavefronts. The optimal phase of the freeform LPIO is then achieved by superposition interference of the engineered freeform wavefronts via freeform polarization exposure. The effectiveness of the approach and the advantages of freeform LPIOs is experimentally demonstrated. The proposed approach will significantly promote the widespread applications of freeform LPIOs in the field of optics and photonics.

Design and fabrication of a liquid crystal polarization grating for mid- and far-infrared wavelengths.

A lot of research on liquid crystal polarization gratings (LCPGs) that can separate circularly polarized light with 100% diffraction efficiency has been conducted in the visible and near-infrared wavelength regions. In this paper, we tried to design and fabricate the LCPGs that are available for use in the mid- and far-infrared (MIR and FIR) wavelength regions. The materials for making LCPGs were selected in view of low absorption characteristics measured by the use of a Fourier-transform infrared (FT-IR) spectrometer. LCPGs designed for 3.88µm and 9.5-10.6µm were fabricated, and we evaluated their diffraction properties experimentally. The MIR and FIR LCPGs should open new application fields of LC technologies including polarimetry, spectroscopy, and beam steering.

Liquid-Crystal Polarization Volume Gratings Technology and its Applications in Diffractive Optical Waveguides Systems for Augmented Reality

Liquid-Crystal Polarization Volume Gratings Technology and its Applications in Diffractive Optical Waveguides Systems for Augmented Reality

Dual Role of Beam Polarization and Power in Nematic Liquid Crystals: A Comprehensive Study of TE- and TM-Beam Interactions.

Optical spatial solitons are self-guided wave packets that maintain their transverse profile due to the self-focusing effect of light. In nematic liquid crystals (NLC), such light beams, called nematicons, can be induced by two principal mechanisms: light-induced reorientation of the elongated molecules and thermal changes in the refractive index caused by partial light absorption. This paper presents a detailed investigation of the propagation dynamics of light beams in nematic liquid crystals (NLCs) doped with Sudan Blue dye. Building on the foundational understanding of reorientational and thermal solitons in NLCs and the effective breaking of the action-reaction principle in spatial solitons, this study examines the interaction of infrared (IR) and visible beams in a [-4-(trans-4'-exylcyclohexyl)isothiocyanatobenzene] (6CHBT) NLC. Our experimental results highlight the intricate interplay of beam polarizations, power levels, and the nonlinear properties of NLCs, offering new insights into photonics and nonlinear optics in liquid crystals.