Ferroelectric Liquid Crystal Layer Research Articles

Ferroelectric liquid crystal with sub-wavelength helix pitch as an electro-optical medium for high-speed phase spatial light modulators

Deformed-helix ferroelectric liquid crystals (DHFLCs) with sub-wavelength helix pitch usually demonstrate sub-millisecond electro-optical response time, but they cannot provide pure phase modulation. However, here, it is shown experimentally that the planar aligned 50 μm thick layer of ferroelectric liquid crystal (FLC) mixture can be used as an electro-optical medium for the phase spatial light modulators (SLMs) if the mixture exhibits smectic C* phase (SmC*) with the helix pitch around 100 nm or less and operates in DHFLCs electro-optical mode. The electrically controlled spiral phase plate (SPP) was constructed on the base of non-chiral biphenylpyrimidines as liquid crystal smectic C matrix and trifluoromethylalkyl diester of p-terphenyldicarboxylic acid as a non-mesogenic chiral dopant. This SPP is able to form and reconfigure the vortex light fields at the frequency up to 3 kHz that was not yet achieved using known liquid crystal spatial light modulators.

Direct current electric conductivity of ferroelectric liquid crystals–gold nanoparticles dispersion measured with capacitive current technique

ABSTRACT The influence of capped gold nanospheres (GNSs) on the direct current (DC) electric conductivity () of a ferroelectric liquid crystal (FLC) confined in a cell with blocking electrodes was experimentally investigated. In framework of this work, several measurement techniques of , such as dielectric and conductivity spectroscopies, were utilised. However, it was demonstrated that only the capacitive technique allowed estimating values of of both pure FLC and FLC/GNSs nanodispersion confined in the cell with blocking electrodes. The experimental results confirm the assumption that the gold nanoparticles adsorb the impurities' ions in FLC which leads to the decrease in the conductivity of the FLC layer.

P‐11.4: Concept of Electronic Controlling the Ferroelectric Liquid Crystal Shutter at Unequal Durations of its Open and Closed States

Fast transient times of ferroelectric liquid crystal (FLC) modulators (shutters) provide accurate selection of pulse light fluxes, for example, the active selection of view images in the stereoscopic applications. The problem of the electronic control of the FLC shutter appears in the case of unequal durations of its alternating open and closed optical states. Corresponding unequal portions of control electrical power during positive and negative polarities of the control voltage cause the degradation of the FLC performance. Main reason of the degradation is the inequality of the volume ion charges induced into the FLC layer by positive and negative control voltage. In this paper, the concept of solution to this problem is suggested with the corresponding experimental verification. Our method allows to equalize the positive and negative control electrical power values without affecting the optical response of the FLC shutter by introducing the short time gaps into a longer control voltage waveform to lower the corresponding integral electrical power value.

40.3: Inversion Charge for Memory Display under Passively Addressed Driving using Photo‐aligned Ferroelectric Liquid Crystal

A ferroelectric liquid crystal (FLC) panel driven by different driving signals has been test. The FLC layer thickness is 3um. Asymmetric boundary conditions, when only one of the ITO surfaces of the display matrix is covered with the photo‐aligning layer while another is not, have been used for providing high contrast, fast response and steady multiplex operation. The electro‐optical performance driven by different impulse signal is presented to show the minimum charge needed for the inversion of bi‐stable state.

Speckle-noise suppression using electro-optical cell with helix- free ferroelectric LC

The authors develop an original and promising method of suppressing the speckle- noise in images generated by a laser beam by means of a compact despeckler based on an electro-optical cell with the smectic ferroelectric liquid crystal (FLC), realizing spatially inhomogeneous phase modulation of light. The mechanisms of destruction of the phase relations in the laser beam passing through a cell with helix-free FLC are discussed. The electric field induces the light scattering and small-scale randomly distributed gradients of the refractive index in FLC layer. The features and benefits of a despeckler using helix-free FLC compared to helix FLC are indicated.

Ferroelectric C* phase induced in a nematic liquid crystal matrix by a chiral non-mesogenic dopant

We report on a ferroelectric chiral smectic C (C*) phase obtained in a mixture of a nematic liquid crystal (NLC) and a chiral nonmesogenic dopant. The existence of C* phase was proven by calorimetric, dielectric and optical measurements, and also by X-rays analysis. The smectic C* which is obtained in such a way can flow, allowing to restore the ferroelectric liquid crystal layer structure in the electro-optical cells after action of the mechanical stress, as it happens with the cells filled with NLC. The proposed method of obtaining smectic C* material allows us to create innovative electro-optical cell combining the advantages of NLC (mechanical resilience) and smectic C* (high switching speed).

Thin ferroelectric liquid crystal layers: mechanical stability and fast electro-optical response, connection between molecule design and surface properties

The storage of information after mechanical stimuli even without applied electrical field is based on the elastic properties of the ferroelectric liquid crystal (FLC) material and the anchoring energy. It is favourable for chiral molecules with extended length, such as 4,4′-di-substituted quaterphenyls and 4,4′-di-substituted quinquephenyls, which have in series-connected benzene rings, but not separated by bridging fragments. To obtain the required stability with a reasonable switching speed of about 50 μs 4,4′-di-substituted chiral quaterphenyls with two chiral centres on the same wing has been synthesised. Here, the switching is much faster compared to compounds with same quaterphenyl fragment, but only with one chiral centre.

Wavelength Tunable Operation in Si Waveguide Grating That Has a Ferroelectric Liquid Crystal Cladding

We obtained the wavelength selective operation in a grating Si rib waveguide that has an ferroelectric liquid crystal (FLC) cladding. The FLC cladding gives a phase shift change for the traveling lightwave in the waveguide in accordance with the polarity of the applied voltage. We propose the wavelength selective filter using this operation and demonstrate the selective switching and the tunable operation of our fabricated device. We also report its time response and dependence on the applied voltage and propose a new operating method to achieve a continuous phase change by using the FLC layer that has binary characteristics.

Anchoring energy and orientational elasticity of a ferroelectric liquid crystal

The dielectric susceptibility of a helix-free ferroelectric liquid crystal layer has been experimentally and theoretically studied as a function of the layer thickness. The investigation has been performed on the inner branch of the polarization hysteresis loop, in the region of a linear dependence of the polarization on the electric field. The experimental results are explained using the notion of effective layer thickness, which involves the characteristic distance ξ over which the orienting effect of interfaces is operative. Comparison of the experimental data and theoretical results made it possible to estimate this distance as ξ = 41 μm and evaluate the anchoring energy (W = 2.8 × 10−3−1.1 × 10−2 J/m2) and the intralayer elastic constant (K″ ≈ 1 × 10−8−3 × 10−7 N).

Preparation of Zigzag Free Surface Stabilized Ferroelectric Liquid Crystals: Filling the Liquid Crystal in the Right Direction

The effects of surface characteristics of rubbed polyimide alignment layer on the product of zigzag free ferroelectric liquid crystals have been studied. Rubbing causes anisotropy in wettability on the polyimide surface. The flowing direction of the liquid crystal during cell filling is found to influence the molecular alignment in the resultant ferroelectric liquid crystal layer. Better aligned ferroelectric liquid crystal layer with fewer zigzag defects can be produced when the ferroelectric liquid crystal is allowed to flow into the cell toward the direction in which the alignment surface exhibits higher hydrophobicity.

Rubbed Polyimide Thin Films for Zigzag Free Surface Stabilized Ferroelectric Liquid Crystal

We investigate the effects of rubbing on the surface free energies of polyimide thin films, and how the surface energetic properties influence the molecular alignment of ferroelectric liquid crystals and the formation of zigzag defects. Rubbing breaks the uniformity in free energy at the surface of polyimide thin film. By properly rubbing the polymer, a diminishment of the difference between the polar part of the surface energies along and against the rubbing direction, respectively, can be achieved, and will favour the formation of zigzag free ferroelectric liquid crystal layer.

Fast beam steering with a ferroelectric-liquid-crystal optical phased array

We demonstrate fast, efficient beam steering using a single 1x32 analog ferroelectric liquid crystal (FLC) spatial light modulator. A high-tilt FLC material with 82 degrees optic-axis switching provides, in a reflective-mode device with a passive quarter-wave retarder between a half-wave FLC layer and a mirror, 91% of full 0-2pi phase modulation. Electronic drive based on applied charge gives 200 micros response-time analog modulation.

Preparation of zigzag-free ferroelectric liquid crystal between rubbed polyimide thin films

Conditions for producing a zigzag-free chiral smectic C phase ferroelectric liquid crystal layer have been investigated based on the consideration of the surface free energy of rubbed polyimide alignment films. Rubbing breaks the azimuthal uniformity in the surface free energy of the polymer alignment layer and induces in-line anisotropy in the surface free energy in the rubbing direction. This anisotropy in the surface free energy is found to have a significant effect on the formation of zigzag lines. Properly rubbing the polymer surface can eliminate or reduce the difference between the surface free energies along and against the rubbing direction, respectively, and favours the formation of a single domain chevron structure and a zigzag-free smectic C layer in the cell.

Light Localization and Lasing Characteristics in One-dimensional Photonic Crystal with a Helix Defect of Ferroelectric Liquid Crystal

We have investigated light localization in one-dimensional photonic crystal with a helix defect of ferroelectric liquid crystal (FLC) and experimentally observed particular defect mode peaks at the photonic band edge of FLC. The appearance of particular defect modes was confirmed by theoretical calculations. The single-mode laser action has been observed in the one-dimensional photonic crystal with a helix defect of FLC doped the laser dye. The single-mode laser action was observed at the edge wavelength of photonic band gap of FLC, which is based on a strong optical confinement into the FLC layer.

Bistable and multistable states in ferroelectric liquid crystals

The effect of memorizing the structural states in a ferroelectric liquid crystal (FLC), known as biand multistability, is based on the existence of a domain structure that changes its properties under the action of an applied voltage. The criterion for the bistability steadiness of the optical-transmission states of FLC electrooptic cells is developed. This criterion is related to the hysteresis-loop parameters of the FLC layer. The conditions for the existence and steadiness of the hysteresis-free switching of the memorized optical-transmission states of multistable electrooptic cells are formulated.

Pyroelectric investigations of a hydrogen bonded ferroelectric liquid crystal gel by LIMM

AbstractThe laser intensity modulation method (LIMM) is employed to determine spatially resolved polarization distributions in sandwich cells containing a hydrogen‐bonded ferroelectric liquid crystal (FLC) gel. At no external electric fields, contributions to the distributions at the surface of the FLC layer are dominating in all the samples with different concentration of gel former. These are attributed to non‐vanishing polarization due to surface interaction. In this case, the effect of hydrogen‐bonded network on the polarization distribution is not visible. In external electric fields, additional contribution to the resulting distribution caused by the induced polarization due to unwinding the FLC helix has been observed. Furthermore, the influence of hydrogen‐bonded network on the polarization distribution is also detected when the gel former content is increased up to 5.0 wt%. Therein the shape of the measured pyrospectra is completely different to other FLC gel samples with lower gel former concentration, where their maximum distributions still locate at the surface of FLC layer which is comparable to the initial field‐free state. These result indicate that the helical structure and orientation director of FLC are able to be stabilized effectively by the gel network even under strong external electric field. Copyright © 2004 John Wiley & Sons, Ltd.

Optimization of photo‐aligned ferroelectric liquid‐crystal display under passively addressed driving

Abstract— A ferroelectric liquid‐crystal (FLC) passively addressed 64 × 64 display based on the photo‐alignment technique has been developed. The display matrix has dimensions of 33 × 33 mm2, and the FLC layer thickness is about 5 μm. Asymmetric boundary conditions, when only one of ITO surfaces of the display matrix is covered with the photo‐aligning layer while another one is not, have been used for providing both high contrast ratio and steady multiplex operation. The electro‐optical performance of the 5‐μm FLC display is presented, including bistable switching in static operation, optimization in multiplexing operation, and gray‐scale generation.

垂直配向強誘電性液晶を用いたプロジェクションディスプレイ用高解像度化素子

A new resolution-enhancing device has been developed based on a novel structure and a unique principle of operation, which shifts the optical path of projected light from pixel arrays by a half pitch at a fast switching speed. The device has a Vertically Aligned Ferroelectric Liquid Crystal (VA-FLC) layer and Multiple Line-shaped Transparent Electrodes (MLTE) that apply a uniform electric field to the VA-FLC layer. These features provide good optical performance in this optical path shift device and produce excellent projection images.

Dynamic Properties of In-Plane Switching of Ferroelectric Liquid Crystals

A detailed study of electro-optical response has been carried out over wide range of the thickness of homeotropically aligned ferroelectric liquid crystal layers for in-plane electric field between inter-digitated electrodes. The field dependencies of switching times, optical transmission and contrast ratio have been measured. The physical mechanisms of the observed effects are discussed.

Fast Switching Characteristics of Surface-Relief Microlens Array Based on a Ferroelectric Liquid Crystal

We demonstrated a fast switching microlens array that is composed of a ferroelectric liquid crystal (FLC) and a UV curable polymer. The electrically controlled microlens array was fabricated by preparing the FLC layer on one of two substrates in a sandwiched cell which has a pre-processed surface-relief structure of the UV curable polymer. Using the FLC as an active layer to modulate the refractive index, fast switching characteristics together with good focusing properties were obtained. The response time was found to be a few hundred microseconds. Moreover, the well-defined surface-relief structure of the UV curable polymer on one of the substrates allows for easy and inexpensive fabrication of the microlens array. The optical devices with such microlens array would be suitable for future optical communication components.