Circuit-Level Analysis on Opto-Electronic Characteristics of Ferroelectric Liquid Crystal

We propose an electronic model in Spice, instead of traditional mathematical analysis, for analyzing the performance of ferroelectric liquid crystal （FLC） under various working conditions. Using this equivalent circuit model,it is easy to simulate and analyze the behavior of an FLC layer in three different typical parameters,including temperature, input light wavelength, and the frequency of driving voltage. We conclude that the response velocity drops as the wavelength increases in the range of visible light, and for the parameter of temperature, the velocity reaches its lowest value when the temperature reaches a certain degree,meanwhile,the frequency of driving voltage exerts important effects on the response velocity only when the frequency is beyond a critical value. Excellent agreement is achieved between simulation and experimental results.

Macro-circuit simulation and optimal design for ferroelectric liquid crystal based on dielectric properties

A macro-circuit equivalent model for ferroelectric liquid crystal （FLC） is proposed. The model includes both effects of ferroelectric toque and dielectric torque and is utilized to simulate the switching response and memory behavior of a single FLC cell . Simulation results show that the delay time has a minimum while increasing the amplitude of drive voltage and the amplitude of bipolar pulses should be controlled within a certain range to realize the memory behavior. Also the switching angle is successfully enhanced to the reference value of 22.5° by adopting ＂AC stabihzation＂ addressing method.

ORGANOMETALLIC FERROELECTRIC LIQUID CRYSTALS Ⅰ. LIQUID CRYSTAL PROPERTIES OF ORTHO—PALLADATED BINUCLEAR COMPLEXES OF AZINE, IMINE AND AZO DERIVATIVES

The mesomorphie properties of title complexes are investigated by means of DSC and polarizing microscopy. The mesophase temperature ranges of complexes are wider than that of corresponding organic ligands. The bridging groups of the complexes have profoand effects on the mesomorphic behavior, When the bridging groups are opticallhy active. the compleve show chiral smectic

Circuit-level simulation of the hysteresis inversion frequency of the ferroelectric liquid crystals

The V-shaped electro-optical properties control is investigated by an equivalent circuit model.Simu-lation results show that genuine V-shaped form is only observed at hysteresis inversion frequency,and be-low and above this frequency an anomalous and normal hysteresis are observed.And the inversion fre-quency decreases with the resistance of ferroelectric liquid crystal(FLC)layer following logf_i=-alogR_(LC)+b .The results are in good accordance with the reported experimental results.

Helix unwinding in ferroelectric liquid crystals induced by tilted electric field

Helix unwinding in ferroelectric liquid crystals induced by an electric field is theoretically studied on the basis of the continuum theory. By applying a weak electric field tilted to the smectic layers, the contribution of the dielectric interaction energy density to the total free energy density is increased. Approximation methods are used to calculate the free energy for different tilt angles between the electric field and the smectic layers. The obtained results suggest selecting the optimal number of pitches in the film that matches to the minimum of the free energy.

Fabrication and structure of Langmuir-Blodgett films of ferroelectric liquid crystal

The molecular aggregation, orientation, and structure in Langmuir-Blodgett films of ferroelectric liquid crystal were studied by ultraviolet and Fourier transform infrared spectra. The results show that medium strong (H-aggregates) in the Langmuir-Blodgett films of ferroelectric liquid crystal are formed by chromophores where the alkyl chains are nearly perpendicular to the film surface. Compared with the cast films, the CO stretching bands, due to the rotational isomerism around the O—C axis of the chiral part, can be identified clearly in Langmuir-Blodgett films.

Ferroelectric Liquid Crystal Optical Switches

The dynamic response of molecular orientation, and the temperature and pulse shape dependences of the switching behavior in ferroelectric liquid crystal are described. The switching speed and the surface energy of ferroelectric liquid crystal are given.

Kerr effect and Kerr constant enhancement in vertically aligned deformed helix ferroelectric liquid crystals

In this article,we review recently achieved Kerr effect progress in novel liquid crystal（LC） material：vertically aligned deformed helix ferroelectric liquid crystal（VADHFLC）.With an increasing applied electric field,the induced inplane birefringence of LCs shows quadratic nonlinearity.The theoretical calculations and experimental details are illustrated.With an enhanced Kerr constant to 130 nm/V2,this VADHFLC cell can achieve a 2π modulation by a small efficient electric field with a fast response around 100 μs and thus can be employed in both display and photonics devices.

Effect of Ferroelectric Nanopowder on Electrical and Acoustical Properties of Cholesteric Liquid Crystal

The composite materials based on nanopowder dispersed liquid crystals are important both from fundamental research and device applications due to their unique properties such as improvement in various properties like electrical,optical,thermal,energy storage and spontaneous polarization etc.The proper selection of nanoparticle and its size which to be dispersed in particular liquid crystals is very important for a particular application.In the present study,a ferroelectric nanopowder of Barium Titanate(BaTiO3)was dispersed in cholesteric liquid crystal and the same was confirmed by Fourier Transform Infrared(FTIR)Spectroscopy.The various acoustical properties like ultrasonic velocity,density,Adiabatic Compressibility,Rao Constant,Wada Constant and Acoustic Impedance were investigated by ultrasonic interferometer at room temperature at fixed frequency.The dielectric constant was determined by Precision Impedance Analyzer.In addition to these investigations,particle size and surface area were also measured.Our investigation shows enhanced in dielectric and acoustical properties which may be useful for device applications extensively in microelectronics,low cost-photovoltaic devices,and custom-shaped containers possibly applied as a coating.

Field-induced phase transitions in chiral smectic liquid crystals studied by the constant current method

In ferroelectric liquid crystals, phase transitions can be induced by an electric field. The current constant method allows these transition to be quickly localized and thus the（E, T） phase diagram of the studied product can be obtained.In this work, we make a slight modification to the measurement principles based on this method. This modification allows the characteristic parameters of ferroelectric liquid crystal to be quantitatively measured. The use of a current square signal highlights a phenomenon of ferroelectric hysteresis with remnant polarization at null field, which points out an effect of memory in this compound.

Influences of nanoparticles and chain length on thermodynamic and electrical behavior of fluorine liquid crystals

Hydrogen-bonded polar nematic liquid crystal series with the general formula n OBAF(n = 7-12) is studied. The mesomorphic characterization is demonstrated through differential scanning calorimetry(DSC) and polarized optical microscopy(POM). The complexes with short alkyl chains(n = 7, 8) present a wide nematic range and monotropic smectic F mesophase, whereas the longer alkyl chain(n = 10-12) analogues show high melting and low clearing mesomorphic liquid crystals. The thermal range of the mesophase and the birefringence increase with chain length decreasing. Furthermore, the effect of the nanoparticles(LiNbO_(3)) on the thermal and the electrical behavior of 8OBAF are investigated. The presence of LiNbO_(3) nanoparticles increases the conductivity and reduces the resistivity of the complex.

FLC编码系统中材料参量设计的电路实验研究

提出用电路模型实验的方法对铁电液晶基相位编码系统进行材料参量设计.建立了编码系统中关于相位分析的铁电液晶电路模型.以铁电液晶材料的典型参数(自发极化强度、转动粘滞系数以及液晶薄膜厚度)为参变量,给出了稳态方位角(表征外加电场引起的铁电液晶折射率变化)与各参变量间的依赖关系,以及各参变量对调制速率的影响.实验结果表明:调制速率随自发极化强度的提高而增加,随转动粘滞系数、液晶薄膜厚度的提高而减慢.控制自发极化强度取值大于38nC/cm3,转动粘滞系数小于210mPa.s,液晶薄膜厚度小于24μm可使稳态方位角满足基于相位编码系统提出的参考值.

液晶电扫描主动成像视场扩展技术研究

针对场景监视、视觉导航等领域亟需解决的大视场高分辨率成像问题,提出了一种液晶电扫描主动成像视场扩展技术,基于液晶电扫描原理设计了基于液晶偏振光栅和铁电液晶的液晶电扫描模块,并搭建了一套主动成像视场扩展系统。通过激光主动照明方式,采用在光源发射端和图像接收端引入液晶电扫描模块的方法,结合液晶偏振时序控制和拼接融合得到了大视场高分辨率的目标图像。实验结果表明,基于液晶电扫描的主动照明成像,实现了分辨率为3840×480、视场角为52°的大视场高分辨率成像,成像视场扩大了6倍。工作实现了非机械式的主动扫描成像,为大视场成像扩展技术提供了一种很好的方法。

高频脉冲激励下SSFLC灰度调制效应的动态研究

通过引入由液晶盒多层结构及驱动电路所导致的阻抗分配效应,将表面稳定型铁电液晶（SSFLC）等效电路模型拓展到对其V字型光电效应的研究当中,在随机高频脉冲（Pτ=25μs）激励下成功地实现了灰度级输出。模拟结果表明,当激励脉冲幅度较小时,输出光透射率随着激励脉冲幅度的提高线性增加,当激励脉冲幅度较大时则透射率趋于饱和,在一定条件下,激励脉冲幅度在2~10 V范围内SSFLC表现出较好的灰度特性。另外,由于铁电液晶的自发极化效应,液晶层压降VLC即使在激励信号VIN=0时也不会消失,且VIN=0时VLC的符号恰好与自发极化强度在电场上分量的符号相反,VLC的大小则与液晶层及定向层的材料参数,以及液晶盒的结构参数相关。

自发极化强度对VFLC电光迟滞曲线影响的电路级模拟

提出了关于V字型铁电液晶(V-shaped Ferroelectric Liquid Crystal,VFLC)的等效电路模型,旨在将EDA技术引入对VFLC光电集成系统进行研究、开发和设计。该模型考虑了由铁电液晶盒多层结构和驱动电路引起的阻抗分配效应,以及极化与非极化锚定能对VFLC光电响应特性的影响。演示了电光迟滞曲线的反常迟滞、V字型及正常迟滞状态,并着重就自发极化强度对电光迟滞曲线的影响给出了模拟结果和分析。结果表明:强制电压随驱动信号频率的提高而增加,但增加速度随自发极化强度的提高而减慢;强制电压和迟滞反转频率随自发极化强度的变化均存在一个拐点,强制电压在自发极化强度为80nC/cm2时取到最小值(-0.084V),迟滞反转频率在自发极化强度为90nC/cm2时达到最大值(6.4Hz);自发极化强度小于80nC/cm2时,迟滞反转频率随自发极化强度准线性增加。模拟结果从量级和趋势上均与实验结果吻合。

反铁电液晶显示器（AFLCD）

本文描述了一种可显示灰度的反铁电液晶显示器。在ＡＦＬＣＤ的矩阵驱动中，交替地使用了双滞回环的正边和负边，避免了净离子漂移影响和弹性稳定作用。

Ferroelectric liquid crystals for fast switchable circular Dammann grating [Invited]

Diffractive optical elements attract a considerable amount of attention, mainly due to their potential applications in imaging coding, optical sensing, etc. Application of ferroelectric liquid crystals(FLCs) with photoalignment technology in diffractive optical elements results in a high efficiency and a fast response time. In this study we demonstrate a circular Dammann grating(CDG) with a diffraction efficiency of 84.5%. The achieved response time of 64 μs is approximately two orders of magnitude faster than the existing response time of nematic liquid crystal devices. By applying a low electric field(V = 6 V) to the FLC CDG, it is switched between the eight-order diffractive state and the transmissive diffraction-free state.

Dynamic modulation performance of ferroelectric liquid crystal polarization rotators and Mueller matrix polarimeter optimization

A ferroelectric liquid crystal polarization rotator(FLCPR)has been widely used in polarization measurement due to its fast and stable modulation characteristics.The accurate characterization of the modulation performance of FLCPR directly affects the measurement accuracy of the instrument based on liquid crystal modulation.In this study,FLCPR is accurately characterized using a self-developed high-speed Stokes polarimeter.Strong linear and weak circular birefringence are observed during modulation processes,and all the optical parameters of FLCPR are dependent on driving voltage.A dual FLCPR-based Mueller matrix polarimeter is designed on the basis of the Stokes polarimeter.The designed polarimeter combines the advantages of the high modulation frequency of FLCPR and the ultrahigh temporal resolution of the fast polarization measurement system in the Stokes polarimeter.The optimal configuration of the designed polarizer is predicted in accordance with singular value decomposition.A simulated thickness measurement of a 24 nm standard SiO2 thin film is performed using the optimal configuration.Results show that the relative error in thickness measurement caused by using the unsatisfactory modulation characteristics of FLCPR reaches up to−4.34%.This finding demonstrates the importance of the accurate characterization of FLCPR in developing a Mueller matrix polarizer.

Effect of dichroic azo-dye doped on ferroelectric liquid crystals

In order to study the effect of mixing dye in ferroelectric liquid crystal （FLC） materials, the phase transition temperature and electro-optical properties of azo dye doped FLC samples have been investigated. All the properties have been found to be changed drastically. The results have revealed that not only the SmC^＊- SmA^＊ transition temperature decreased markedly by the addition of azo-dye, but also dye-doped FLC had lower threshold voltage and saturation voltage than the pure FLC.

Analysis of Dielectric and Electro-optic Responses of Nanomaterials Doped Ferroelectric Liquid Crystal Mixture

Dielectric and rotational viscosity measurements of a multi-component ferroelectric liquid crystal mixture were performed by adding a small concentration （0.01 wt%） of silica and multi walled carbon nanotubes （MWCNTs）. Liquid crystals turn out to be outstanding hosts for nanomaterials. A remarkable increase in the rotational viscosity was noticed in CNT doped system as compared to silica doped same liquid crystal system. Comparison of dielectric studies shows higher value of permittivity and dielectric losses for silica-doped sample than those of CNT doped sample. The results have been interpreted both experimentally and theoretically.