Effect In Ferroelectric Liquid Crystals Research Articles

Photorefractive Effect of Ferroelectric Liquid Crystals with Application of a Biased Alternating Electric Field

The photorefractive effect of a ferroelectric liquid crystal (FLC) was investigated with application of a biased alternating electric field. A two-beam coupling gain coefficient of 96 cm−1 was obtained for a 10 µm-thick sample. The gain coefficient obtained was found to be much larger than those obtained with application of a DC electric field.

Photorefractive Effect of Ferroelectric Liquid Crystals with an Applied Alternating Electric Field

The photorefractive effect of ferroelectric liquid crystals (FLCs) with application of an alternating electric field was investigated. The consecutive switching motion of the director of a FLC under an alternating electric field was modulated by the photoinduced internal electric field at the interference fringe. The grating based on the difference in the switching motion of the FLC was formed, and it was confirmed to operate as a diffraction grating.

Thickness-independent memory effect in ferroelectric liquid crystals

Memory in ferroelectric liquid crystals (FLCs) is well known in the literature where thickness of the cell is less than the pitch value of the material. Here, we report a thickness independent memory in a class of FLCs called the de Vries electroclinic liquid crystals. Thickness independency of memory effect is observed by dielectric spectroscopy and texture observation. The memory observed in SmC* phase of de Vries material is entirely different from conventional FLCs. In the former case, it is the inherent property of the material but in the latter it is dependent on the cell geometry. In de Vries material, it is probably the randomization that is playing a major role.

Photorefractive effect of ferroelectric liquid crystals

This paper reviews our recent work on the photorefractive effect of ferroelectric liquid crystals (FLCs). The photorefractive effect is defined as the optical modulation of the refractive index of a medium as a result of a variety of processes. The interference of two laser beams in a photorefractive material establishes a refractive index grating. This phenomenon enables the creation of different types of photonic applications. FLCs exhibit fast electric field response, and the orientation of the molecular axis of FLCs changes its direction according to the change in direction of the spontaneous polarization (Ps). When two laser beams interfere in a photoconductive FLC, an orientational grating is formed. The mechanism of the formation of the grating is based on the response of the Ps to the photoinduced internal electric field. The time of formation of the refractive index grating is significantly shorter in FLC materials.

Influence of the Laser Incidence Conditions on the Spontaneous Polarization Reorientation Photorefractive Effect of Ferroelectric Liquid Crystals

The photorefractivity of a ferroelectric liquid crystal (FLC) mixed with a photoconductive compound was investigated in detail. FLCs are anisotropic media, so that laser beam incidence conditions strongly affect the formation of the refractive index grating. Effects of intersection angles of the laser beams, sample angle, sample rotation angle, sample thickness, and polarization of the laser beams on the photorefractivity of FLCs were examined.

The effect of rotational viscosity on the memory effect in ferroelectric liquid crystal

Memory effect in deformed helix ferroelectric liquid crystal (DHFLC) is not a new phenomenon. Although it was reported 12 years ago yet its exact physical behavior is not explained. It has been thought by various researchers all over the world that it might be a transient memory effect. In the present study, it has been observed and predicted that memory effect is of long duration and shows remarkable dependencies on the voltage and frequency of the driving electrical pulse, which is entirely different from the memory effect in surface-stabilized ferroelectric liquid crystal (SSFLC). The memory effect in SSFLC is primarily due to surface effect but in DHFLC, its ultra-short pitch plays a dominant role. So, it has been observed that the memory effect in DHFLC is due to its high viscosity and inter/intra layer dipolar interactions.

Memory effect of ferroelectric liquid crystal stabilized by polymer fibers

AbstractWe investigated the bistable state of the molecular orientation of ferroelectric liquid crystal that is formed between micro‐polymer fibers, and demonstrated the occurrence of a memory effect when the smectic layer structure is corrected. In this study, we introduced high‐pretilt alignment layer and formed polymer fibers in the liquid crystal by using the photopolymerization phase separation method in order to make the creasing and bending of the layer in the direction of thickness unidirectional. In addition, we treated the composite film of the liquid crystal and the polymer fiber by applying an AC voltage in order to hold the cone axis of the liquid crystal molecule in a rubbing direction during the gradual cooling process in which the liquid crystal molecule tilt (phase transition from the smectic A phase to the smectic C* phase). The results of trial production confirmed an alleviation of the bending of the smectic layer in the horizontal plane and the occurrence of a memory effect, resulting in a minute distribution of bistable switching domains and a memory function involving area‐wise grayscale. © 2004 Wiley Periodicals, Inc. Electron Comm Jpn Pt 2, 87(4): 16–24, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/ecjb.10082

Modeling Electrooptical Effects in Ferroelectric Liquid Crystals. 1. Basic Equations and Experimental Tests

Electrooptical effects in ferroelectric liquid crystal cells have been simulated and the calculation results have been compared with experiments. Two sets of equations have been solved numerically: (1) the dynamic equations for the director coupled with the electric current equation; (2) the Maxwell equations which allow the calculations of the optical transmission T for different polarization, wavelength and coherency of light incident onto a cell. The anisotropy of elastic, viscous and dielectric properties and arbitrary anchoring conditions have been taken into account. The experimental data on the director switching and the electroclinic effect in the Smectic C∗ phase agree quantitatively with the modeling, and novel features of these effects are discussed.

Modeling electrooptical effects in Ferroelectric Liquid Crystals. 2. V-Shape Switching in the SmC* phase

The thresholdless, hysteresis-free V-shape electrooptical switching in surface stabilized ferroelectric liquid crystal (FLC) cells has been modeled and the results compared with experimental data. High frequency V-shape switching (at f>100 Hz) was experimentally demonstrated and simulated numerically. The key role of the capacitance C of FLC aligning layers has been underlined: thin layers with large C promote the well known bistability effect, thick layers, on the contrary, are necessary for V-shape switching. The results of modeling are in quantitative agreement with experiment.

Spontaneous Polarization Reorientation Photorefractive Effect in Ferroelectric Liquid Crystals

The photorefractive effect of a series of low-molecular-weight ferroelectric liquid crystals (FLCs) doped with photoconductive compounds was investigated using two-beam coupling experiments. Asymmetric energy exchange was observed only in the ferroelectric phase, and the refractive index formation time was found to be ∼30 ms, which is faster than that of nematic photorefractive LCs. These results indicate that the mechanism of the photorefractive effect in FLCs is different from that in nematic LCs. The photorefractivity of a photoconductive polymer and FLC mixture was also investigated, and the effects of temperature, the strength of the applied electric field and spontaneous polarization on the diffraction efficiency were examined.

Optomechanical effect in ferroelectric liquid crystal freely suspended films

Optomechanical effect in vibrating ferroelectric liquid crystal freely suspended films have been observed. In the experiment the liquid crystal films are doped with a photochromic dye which undergoes trans-cis isomerization. Photoisomerization induces the change both in a switching potential of the host liquid crystal and the film surface tension. We observed also a nonlinear dependence of photoinduced variation of the surface tension as function of the dye concentration. Such dependence strongly supports the possibility of amplification of photochemical effect in liquid crystals. The optomechanical effect might be exploited for the remote control of the sensors using freely suspended films, and more generally for the investigation of the cooperative phenomena in liquid crystals.

PD05 強誘電性液晶のフォトリフラクティブ効果 : 光導電性化合物の構造の効果(フォトニクス・光デバイス)

PD05 強誘電性液晶のフォトリフラクティブ効果 : 光導電性化合物の構造の効果(フォトニクス・光デバイス)

3A09 光導電性色素をドープした強誘電性液晶のフォトリフラクティブ効果(フォトニクス・光デバイス)

3A09 光導電性色素をドープした強誘電性液晶のフォトリフラクティブ効果(フォトニクス・光デバイス)

Spontaneous Polarization Vector Reorientation Photorefractive Effect in Dye-Doped Ferroelectric Liquid Crystals

The photorefractive effect of a series of low-molecular-weight ferroelectric liquid crystals (FLCs) doped with photoconductive compounds was investigated through two-beam coupling experiments. Asymmetric energy exchange was observed only in the ferroelectric phase, and the refractive index formation time was found to be ∼30 ms, which is faster than that of nematic photorefractive LCs. These results indicate that the mechanism of the photorefractive effect in FLCs differs from that in nematic LCs. The photorefractivity of a photoconductive polymer and FLC mixture was also investigated, and the effects of temperature, the strength of the applied electric field, and spontaneous polarization on the diffraction efficiency were examined.

Observation of orientation dependence of electrorheology effect in ferroelectric liquid crystal using shear horizontal wave

The electrorheology (ER) effect of ferroelectric liquid crystals is observed under shear-horizontal (SH) wave propagation. The ER effect is strongly dependent on the orientation direction of the liquid-crystal molecule. The apparent viscosity is evaluated through the numerical analysis result on the propagation characteristics of a SH wave in a trilayer structure including a ferroelectric liquid-crystal (Chisso, CS1014) layer between two glass plates. The ER effect is examined by the relation between the orientation of smectic layers and the propagation direction of the SH wave.

Diffraction light modulator based on transverse electro-optic effect in short-pitch ferroelectric liquid crystals

A diffraction modulator that exploits the transverse electro-optic effect in ferroelectric liquid crystals is proposed for applications in displays and in spatial light modulators. Experiments with a short-pitch ferroelectric liquid crystal aligned homeotropically show an achromatic contrast ratio of greater than 100:1 available with oblique readout. The sources of the contrast deterioration and the tolerance of the proposed scheme to this deterioration are analyzed. For selected directions of readout the light output obtains low sensitivity to the polarization of the readout light. Nonlaser light sources can be used in a practical display setup based on the proposed principle.

Application of Pyroelectric Sensor and IR-Chopper with Ferroelectric Liquid Crystal for Human Detection.

Infrared chopper elements have been fabricated, utilizing the transient light scattering effect of ferroelectric liquid crystal with asymmetric waveform voltage drive. New elements can performed 12% of modulation degrees in around 10 microns region. A combination of an IR-chopper and a pyroelectric sensor is used to measure radiation intensity from black body at various temperatures to detect human body stationary. The new type of IR detector allows a pyroelectric sensor array easily to be developed to measure temperature distribution over large area. The detection has achieved 0.55°C noise equivalent temperature difference (NETD).

The IR modulator utilizing light scattering effect with ferroelectric liquid crystal for gas analysis

Experimental infrared modulator elements have been fabricated utilizing the transient light scattering effect of ferroelectric liquid crystal with asymmetric waveform voltage drive. The new elements perform 80% modulation degrees at the 632.8nm. We have also achieved 30% modulation degrees in the 4 to 5µ m region where the strongest CO2 absorption bands exist. A new type of analyzer which monitors ambient air quality has been developed. This analyzer uses non-dispersive infrared absorption method and composes of a double-beam, a single detector and a pair of liquid crystal light modulator as the IR chopper. The detection has achieved 10ppm noise equivalent concentration.

Advanced in Development IR Modulators of Ferroelectric Liquid Crystals Utilizing Transient Light Scattering Effects

Abstract The highly efficient IR-modulation has been achieved using LC electro-optic elements. Experimental infrared modulator elements have been fabricated and demonstrated utilizing the transient light scattering effect of ferroelectric liquid crystal with asymmetric waveform voltage drive. The new elements performed 80%, 50%, 40% and 25% modulation degree in the 632.8nm, 2, 3-5 and 8-12 μm region. And we observed micro domain structure under the scattering state by a polarizing microscope to understand the mechanism of the domain switching. In addition, we evaluated properties of the scattering angular and temperature dependence quite important for the design of optics for the application in the infrared range.

The Domain Mode in Ferroelectric Liquid Crystals a Novel Electrooptical Process

ABSTRACTNovel electrooptical effects in ferroelectric liquid crystals with high spontaneous polarization (Ps ) are observed. They are connected with the formation of a modulated distribution of the macroscopic dipole moments of smectic layers if going along the layer normal. The period (D) of this modulation (ferroelectric domains) near the electrode surfaces (DS) and in the bulk (DB) of a FLC-specimen can differ appreciably, depending on an applied external voltage. The main role of the value of the effective spontaneous polarization is established. A variuos number of domain structures and corresponding diffraction patterns are observed under variation of frequency and amplitude of the external electric field. A simple explanation of the new electrooptical responses is proposed on the basis of interference and incommensurability of bulk and surface domains.