Applications Of Circuit Model For Ferroelectric Liquid Crystal Functional Devices

The advantages of fast response,high contrast ratio,high resolution and abundant information display promise FLC(Ferroelectric Liquid Crystal:FLC) devices a broad prospect in fields of display,telecommunication and optical data processing applications.Thus,investigations on predicting and optimizing various optoelectric response properties of the FLC devices and about its driving circuit and driving waveform design are significant in both fundamental and technological points of view.In this paper,the equivalent circuit model technique,which is different from the usually used numerical technique,is introduced to predict and optimize FLCs' various nonlinear switching behaviors.The equivalent circuit model for FLC is established according to its physical model and able to predict the basic response properties of a single FLC cell,such as the switching response property,the memory characteristic and the response properties under dielectric anisotropy condition.Then with taking into account the voltage divider composed of alignment layer,liquid crystal layer,and the driving circuit,the model is improved and has the ability to study the V-shaped switching behavior which has recently aroused extensive concern.And with introducing a typical structure of the OASLM(Optically Addressed Spatial Light Modulator:OASLM),the model is further improved and thus an equivalent circuit model for a FLC-OASLM is proposed.Moreover,with the equivalent circuits proposed in this paper,the driving circuit and driving waveform designs are designed for JOERS-ALVEY addressing scheme,and for optimizing the hysteresis inversion frequency and the gray scale properties of FLC-OASLM.For the basic response properties of FLC,the memory characteristic,the effects of typical parameters on response velocity and the response properties under dielectric anisotropy condition are simulated and analyzed.And the waveforms of driving voltage are designed for theτ-V_minmode and AC stabilization technique of JOERS-ALVEY addressing scheme.For the V-shaped switching properties of FLC,we try to provide answers to the following questions:ⅰ)if the V-shaped switching is observed only at one characteristic frequency(called hysteresis inversion frequency)and is accompanied by an inversion of the hysteresis direction;ⅱ)if the output light intensity always shows a hysteresis when it is plotted as a function of the voltage on liquid crystal layer;andⅲ)how do typical parameters influence the hysteresis inversion frequency.And then the driving circuit is designed for the purpose of optimizing the hysteresis inversion frequency.For the switching properties of FLC-OASLM,the effects of control image and driving voltage on response velocity,the function of erase light and the gray scale properties are investigated.And the driving waveform for optimizing the gray scale properties is designed.The simulation results are as following:ⅰ)the FLC has shown good memory characteristic;the response velocity quickens up as the spontaneous polarization increases,however increasing other typical parameters(rotational viscosity,and the thickness of liquid crystal layer)slows down the velocity; the switching eventually stops with increasing the amplitude of driving voltage under both condition of positive and negative dielectric anisotropy;with implementing the driving circuit designed for JOERS-ALVEY addressing scheme, the operation ofτ-V_minmode is successfully carded out,and the optical contrast ratio optimization and switching process accomplishment are realized by the AC stabilization technique.ⅱ)V-shaped switching is observed only at the hysteresis inversion frequency and is accompanied by an inversion of the hysteresis direction;the output light,intensity always shows a hysteresis when it is plotted as a function of the voltage on the liquid crystal layer;the hysteresis inversion frequency is increasing with increasing conductivity of liquid crystal layer and the amplitude of applied voltage,and the function according to which hysteresis inversion frequency is varying with the root of conductivity of liquid crystal layer is almost linear;hysteresis inversion frequency has a maximum when it is varying with increasing spontaneous polarization;the dependences of hysteresis inversion frequency on the conductivity of liquid crystal layer,the amplitude of applied voltage and spontaneous polarization for chevron structure are as the same as those for bookshelf structure,however the frequency is higher for the chevron structure;with the driving circuit designed for optimizing the hysteresis inversion frequency,the value of the hysteresis inversion frequency enhances about three orders of magnitude comparing to the case without the driving circuit. ⅲ)The response velocity quickens up as the write light intensity and driving voltage amplitude increase,and as the erase light intensity and driving voltage frequency decrease;the erase light is used not only to erase the image recorded by the devices in the previous frame,but also to keep the OASLM from switching when not illuminated during the write period and to adjust the switching time of the FLC;with the simulation parameters used in the paper, good gray scale properties are observed by employing the control light injected synchronously with the negative pulse as the write light,and good switching properties are shown if the control image injected synchronously with the positive pulse is employed as the write light,furthermore,the gray scale properties are sensitive with the driving voltage frequency;with implementing the driving waveform designed for optimizing the gray scale properties,more than ten gray scales are observed in the FLC-OASLM.Thus it is concluded that the equivalent circuit models proposed in the paper are able to efficiently predict and analyze various switching behavior of FLC devices,and to design and optimize the driving circuit and driving voltage waveform.And the modeling technique provides an effective way to simulate other optoelectric devices.