We have used video-microscopy to observe the behavior of liquid crystal (LC) droplets within nematic droplet-polymer films (NCAP) as the droplets respond to an applied electric field. The textures observed at intermediate fields yielded information about the process of liquid crystal orientation dynamics within droplets. The nematic droplet-polymer films had low LC content (less than 1 percent) to allow the observation of individual droplets in a 2 - 6 micrometers size range. The aqueous emulsification technique was used to prepare the films as it allows the straightforward preparation of low LC content films with a controlled droplet size range. Standard electro-optical (E-O) tests were also performed on the films, allowing us to correlate single droplet behavior with that of the film as a whole. Hysteresis measured in E-O tests was visually confirmed by droplet orientation dynamics; a film which had high hysteresis in E-O tests exhibited distinctly different LC orientations within the droplet when ramped up in voltage than when ramped down in voltage. Ramping the applied voltage to well above saturation resulted in some droplets becoming `stuck'' in a new droplet structure which can be made to revert back to bipolar with high voltage pulses or with heat.

We studied the electro-optic properties as a function of temperature of a PDLC film composed of either E7 or E43 dispersed as droplets in a polyvinylformal (PVFM) matrix. The dissolved liquid crystal lowers the glass transition temperature, Tg, of the PVFM matrix to about 30 - 35 degree(s)C. The electro-optics of these PDLC films change abruptly at the polymer matrix Tg. In general the drive voltage decreases and the turn off time increases rapidly as the temperature is raised above Tg. Also, the shutter has essentially no hysteresis below, and significant hysteresis above Tg. These temperature effects are completely reversible. The rapid change in electro-optic properties cannot be entirely explained by changes in the polymer dielectric properties or droplet size and shape. We have therefore postulated that changes in the surface anchoring energy of the liquid crystal are primarily responsible for the abrupt changes in the electro-optic response at the matrix Tg.

Several different types of polymer dispersed liquid crystal (PDLC) systems have been developed in recent years. The transmission characteristics of each type depend on the materials used, the method of construction, and the addressing technique used to drive the system. Greater control over the transmittance response as a function of time is important for many display operations. The effect of using dual-frequency addressing and pulsed mode dual frequency addressing in controlling the transmittance response of one type of PDLC film has been investigated. The results suggest that the gray scale inconsistency as well as the hysteresis effect can be reduced by utilizing the frequency dependence of the dielectric anisotropy of the liquid crystal.

Aggregation states and electro-optical effects based on light scattering have been investigated for polymer (liquid crystal) composite films. The composite film was prepared by a solvent- evaporation method. Since a continuous liquid crystalline domain is embedded in a three- dimensional spongy network of polymer matrix, the liquid crystalline material is self- supported in the composite film in spite of its very low viscosity. The composite film composed of poly(methyl methacrylate) and a nematic LC(E44) with positive dielectric- anisotropy exhibited remarkable and reversible light scattering-light transmission switching under the modulation of an ac electric field. A light scattering state was dependent on optical heterogeneities such as a spatial distribution of nematic directors and/or mismatching in refractive indices of the components. Reversible and bistable electro-optical effects were also recognized for a smectic phase of a binary composite system composed of liquid crystalline polymer (LCP) and nematic LC. A light-addressed optical information storage of the LCP/nematic LC/(photoresponsive molecule) ternary composite membrane has also been demonstrated.

We establish some phenomenological relationships for the scattering properties of nematic/droplet polymer films. We find that in powered films film scattering scales exponentially with thickness, indicating that multiple scattering effects appear to be unimportant in powered films. In contrast, multiple scattering effects are very important in strongly scattering unpowered films. We show that for powered films, scattering depends strongly on the refractive index mismatch between the liquid crystal and the polymer matrix. We describe a model which shows a quantitative fit between the model and experiment. We find that the factors influencing scattering differ markedly in powered and unpowered films. In unpowered films, the refractive index gradients between neighboring droplets provides the dominant factor contribution to film scattering, rather than the more familiar LC/polymer refractive index gradient.

Dispersions of liquid crystals in polymeric matrices are used as light control devices because of the possibility of varying their light scattering through alignment changes arising from the application of electric fields. The scattering from such systems is very similar to that found with crystalline polymers which have been extensively studied in our laboratory for over 25 years. Studies of the scattering from spherulitic polymers have been modelled as that arising from anisotropic spheres. Theories and measurements have been made with parallel (Vv) and crossed (Hv) polarization as a function of the radii, anisotropy, and volume fraction of spheres, and the refractive index of the matrix.

The optical properties of nematic droplet-polymer films were studied both in the on and off state using Lambert-Beer''s law to characterize their scattering phenomena. For the preparation of the devices, NCAP process was employed with the different diameter, distribution, shape, and density of nematic droplets. Their cell thickness and refractive indices concerning the birefringence of liquid crystals were also controlled. The results showed that the scattering phenomena of nematic droplet-polymer films were likely caused by two types of features. One, related to the surface area of nematic droplets, was the difference of the refractive indices in the interface between liquid crystals and polymer matrix. The other, related to the liquid crystal volume inside the nematic droplets, was the birefringence of liquid crystals. Considering such relations, the extinction coefficient of Lambert-Beer''s law could be described by the sum of the area in the interface multiplied by the difference of the refractive indices between two materials and the liquid crystal volume multiplied by their birefringence. Furthermore, it was found their parallel transmittance in the off state and haze ratio in the on state were well characterized by such extinction coefficient of Lambert-Beer''s law.

Analytical expressions are obtained for spatial distribution of the director and the order parameter in a spherical nematic droplet, as well as for the shift of the phase transition temperature. The cases of small and large values of anchoring are considered. The Green''s function of order parameter fluctuation in isotropic phase is found.

Ever since their invention in 1980 SSFLCs have been considered promising candidates for high resolution displays. However, a number of unexpected fundamental problems have hampered fast development of this technology. We review the major problems, explorations of which have led to enormous headway during the past few years. We discuss the influence of various characteristics on the frame time of FLC displays. We demonstrate the potential of the spontaneous polarization Ps and present addressing schemes which lead to smaller frame times while maintaining moderate voltage levels.

This paper reports the electrical properties of a surface stabilized ferroelectric liquid crystal display provided by an almost ideal bookshelf layer structure. The bookshelf layer structure is obtained by ordinary rubbed polymer film cell by utilizing a particular liquid crystal material; naphthalene-ring contained liquid crystals. First, we show the layer structure of the naphthalene base FLCs analyzed by x-ray diffractions. Second, the electro-optic switchings of the naphthalene base FLCs are discussed. Then the effect of the depolarization field on the polarization switching is mentioned. Some polarization switching phenomena in conjunction with the the conductivity of the orientation layer is shown. Finally, we mention our multiplexed FLC prototype. It has 640 X 201 pixels, shows 40:1 contrast ratio, and 40 transmittance.

New suitable homologues of SmC host materials including different classes of fluorinated and non-fluorinated alkyl-alkyloxy-phenylpyrimidines were developed. Some materials were chosen to develop a new SmC host mixture. Several new chiral dopants have been synthesized. We found an influence of the different ring-systems and various side chains on the physical properties. Chiral dopants with more than one chiral center exhibit interesting properties. One dopant with a fluorine atom at the chiral center and a biphenyl-cyclohexane core showed the best properties and was chosen to introduce, together with the new SmC host mixture, new FLC-mixtures with improved properties. By using low-volt multiplex driving schemes and also high-volt multiplex driving schemes it is shown that these mixtures with an adjustable Ps fulfill the requirements for both methods.

We prepared ferroelectric liquid crystals (FLCs) possessing a newly designed chiral part, 2- fluoro-2-methylalkanoyloxy group. The new chiral moiety was derived from the corresponding chiral epoxides biologically produced. Physical properties of the FLCs with the new chiral moiety were compared to those having another fluorinated chiral moieties. The 2-fluoro-2- methylalkanoyloxy group greatly contributes to producing a large spontaneous polarization (Ps). Effects of core structures in the FLC molecules were also investigated. A prymidine ring in the core part extremely enhances the Ps value. In order to prepare a practical FLC mixture, the novel chiral compound with the large Ps was doped in a base mixture having a wide temperature range of smectic C phase. The mixture exhibits a fast optoelectrical switching time and an appropriate tilt angle. Its performance in a multiplexing device was also investigated.

The replacement of a highly fluorinated tail group for one or both of the hydrocarbon tails in thermotropic liquid crystal systems has a dramatic effect on mesomorphic behavior and other physical properties. The nematic phase is greatly suppressed, often totally lost, in all systems that have been examined. A large enhancement of the smectic behavior is usually observed. The preferred phases are (chiral) smectic A and C for systems which incorporate a partially, but highly fluorinated, tail. This creation of smectic C behavior has made these fluorinated materials interesting for use in ferroelectric liquid crystal devices. Fluorination, it is well known, alters certain physical properties of organic compounds. For example, chemical and thermal stability, lower viscosity, and lower birefringence being realized.

Ferroelectric liquid crystalline polymers (FLCP) were synthesized. These ferroelectricities were confirmed directly by measuring the polarization reversal currents and other electro- optical properties. The smectic layer structure of FLCP was also studied. A chevron structure similar to that of low molecular weight FLC was observed even in the FLCP cell. But the zigzag defects were not so sharp, which means it is easy to get a good orientation even in large area displays. We succeeded in making a FLCP display of 15 cm X 40 cm without any alignment layers.

Electro-optic properties of new liquid crystalline polymers exhibiting a ferroelectric phase over a wide range of temperature are reported. The materials exhibit bistable electro-optic switching in the smectic C* phase and a pronounced linear electroclinic effect in the smectic A phase. The response times are very fast, of the order of 100 microseconds.

Ferroelectric smectic C* liquid crystals have been shown to exhibit high speed, multistate electro-optic and display device applications, particularly when incorporated into the surface stabilized ferroelectric liquid crystal (SSFLC) light valve. The SSFLC geometry results in two distinct stable states. Unfortunately, the lack of intermediate electrically addressed states precludes a natural gray-scale effect. The recently discovered Deformed Helix Ferroelectric liquid crystal (DHFLC) effect opens the door to linear gray scale or linear phase modulation in a ferroelectric liquid crystal device on a microsecond time-scale. One drawback of currently available DHFLC materials is that their alignment quality is limited due to the lack of a nematic phase above their smectic A phase. While alignment can be improved by the use of shear techniques, this represents an undesirable option for a manufacturing process. We show that DHFLC mixtures can possess a nematic phase with a long N* pitch and tight C* pitch in the C* phase. These new easily aligned DHFLC mixtures are discussed as well as their use in beam-steering devices that can benefit from analog optical response.

Liquid crystals are utilized in many display applications. The use of liquid crystals in electro- optic phase devices, spatial light modulators and laser optics is becoming increasingly more common. Critical to most of these applications is the uniform macroscopic alignment of the liquid crystals. We have discovered a new process of controlling the local macroscopic alignment of liquid crystal molecules using polarized light. This discovery gives an additional degree of freedom in controlling liquid crystal alignment. In addition, complex devices (i.e., binary phase devices) that would be difficult to achieve using conventional alignment techniques (i.e., buffing, deposition, etc.) may be readily attainable using optical techniques. The optically induced alignment described in this paper possesses memory, write-rewrite capability, and high spatial resolution on the order of micrometers or less.

It is well known that oriented systems may possess physical properties that exceed those of the isotropic species by orders of magnitude. Examples of improved performance through orientation include enhanced mechanical properties, thermal and electrical conductivity, piezo- electric properties, and optical transparency. In this paper we present a simple and versatile method using thin highly ordered films of poly(tetrafluoroethylene) PTFE to orient a wide variety of crystalline and liquid crystalline species and its application to some systems. The morphology of the polymeric substrate layer is also briefly discussed.

Optical nonlinearities can arise as the result of intense electromagnetic radiation fields inducing either changes in electron or nuclear configurations. Indeed, as is discussed in this paper, several mechanisms, including mechanisms depending upon electron-phonon coupling, may be elicited from the same material. The precise contribution that a given mechanism makes to observed optical nonlinearity is often dependent upon pulse conditions employed in transient nonlinear optical experiments. The ability to control optical nonlinearity by pulse conditions is demonstrated and analyzed for a high symmetry ladder polymer where contributions from coherent parametric mixing, excitons, and bipolarons are observed. The different timescales associated with various mechanisms for index of refraction and absorption changes are discussed. The utilization of photo-induced changes occurring on widely different timescales is demonstrated in the realization of efficient second harmonic generation by quasi- phase matching. The role of chemical synthesis in engineering multi-functional materials is discussed.

In order to obtain oriented liquid crystalline films which maintain the alignment of monomeric species from whence they are derived, it is necessary to induce rapid, isothermal polymerization processes. In recent studies, monofunctional and difunctional mesogenic methacrylate monomers with nematic and smectic phases have been aligned and polymerized to yield macroscopically oriented polymers. In some cases, the orientation is maintained even after the polymer is heated above its clearing temperature. By utilizing a thin-foil calorimeter, we have succeeded in measuring polymerization rates in macroscopically oriented liquid crystalline monomers. Although the macroscopic structure of the aligned system may be locked-in during polymerization, this does not necessarily result in enhanced rates compared to non-oriented samples. The experimental techniques used to measure the polymerization exotherms of oriented liquid crystals are described. Initial results which illustrate the effect of macroscopic alignment are discussed with respect to polymerization kinetic rates. Implications for polymerization of oriented liquid crystals are briefly discussed in the context of optical properties of the final films.

Image storage into polymer liquid crystals (PLCs) on the basis of an isothermal phase transition is presented. Photochromic guest molecules are incorporated into PLCs just physically or covalently at concentrations below several mole and irradiated so as to bring about a photoisomerization. In the case where azobenzenes are used as guests, a trans-cis photoisomerization caused by photoirradiation acts as a trigger to induce nematic (N) to isotropic (I) phase transition at the irradiated sites owing to lowering of the N-I phase transition temperature (TNI) by accumulation of the sphere-like cis-form of the azobenzenes. This photochemical phase transition is reversible and the cis to trans isomerization restores the system to the initial state. The photochemical phase transition depends on such factors as temperature, structures of guests, and hosts. Guest molecules with high affinity to hosts induce the photochemical phase transition effectively and hosts with low order parameters are also effective for the phase transition. Unlike the response to electric field, PLCs show a similar photoresponsiveness to low-molecular-weight LCs.

We describe the use of liquid crystals in a Fabry-Perot cavity to produce optical modulation. It is shown that these devices can be used not only as electrically tunable wavelength filters but also as narrow wavelength optical switches with high contrast. The performance of the device is illustrated by experiments using nematic and smectic liquid crystals. Using nematic liquid crystals, for example, it is shown that the device can be used to produce an optical pulse of 10 microsecond(s) at low voltages.

Various nematic liquid crystal (LC) operating schemes have been proposed to improve nematic LC response beyond video rate. Several high contrast nematic liquid crystal modulators with fast response time have been developed and successfully demonstrated. The transient nematic effect represents the recent effort for developing high speed liquid crystal modulators.

This paper reviews recent development and application of the infrared version of the liquid crystal light valve (LCLV). We describe delivered IR image projectors for advanced end-to- end laboratory testing of IR seeker and sensor systems. System performance characteristics are given. A newly developed version of the device has much higher contrast with low IR background image capability.

Recently there has been much interest in a new polymer nematic dispersion technology, often called as NCAP, PDLC, PNLC, LCPC, etc., since projection displays using this technology have been shown to produce much brighter display images than projectors using conventional twisted nematic (TN) lightvalves. For commercializing projection displays based on this polymer nematic dispersion technology, the new materials must not only meet various electro- optic requirements, e.g., operational voltage, `off-state'' scattering angle, voltage holding ratio and hysteresis, but must also be stable over the lifetime of the product. This paper reports recent progress in the development of NCAP based projection displays and discusses some of the key commercialization issues.

Liquid crystal/polymer dispersions have widely recognized promise as light modulators in projection displays for high definition video. Achieving switching voltages compatible with active matrix display drivers while maintaining good on-screen contrast remains an area of active material research. As the driving voltage depends linearly on the liquid crystal/polymer dispersion thickness, one simple method to lower driving voltage is to operate with thinner dispersions. This approach has a significant impact on contrast ratio. We report on the results of a study of the dependence of the driving voltage and contrast ratio as a function of thickness. For very thin samples the voltage does not decrease with thickness and the contrast is greatly reduced, indicating a clear limit to this approach.

Cadmium selenide devices are reported with mobilities in excess of 200 cm2 v-1 sec-1 and off currents of -14 amps. Shift registers have been fabricated which operate at 1 MHz and buffers with rise times of 2 microsecond(s) ecs when driving a 60 pF load, which make them suitable for driving the rows of high resolution complex displays.

In a previous paper, we described an optical interconnection system in which two arrays of mutually coherent sources are used for the recording of holographic gratings that form weighted interconnection between another source array and a detector array. Mutually coherent source arrays are required for the writing of holographic gratings. The generation of coherent diffracted light beams from a single laser source using programmable SLMs is an attractive and simple method. Two-dimensional surface-emitting laser arrays can be used to readout the written holograms but not for recording them, as individual lasers have yet to be made mutually coherent. There are numerous other applications for programmable source arrays. They could for example drive optically pumped surface-emitting laser diode arrays or optically controlled smart pixels of a spatial light modulator. Their potential use in three- dimensional display systems and in wavelength division multiplexing applications is also being studied. Each of the modulators described in this paper has programmable features suitable for a variety of applications. Four methods to generate programmable coherent source arrays using addressable liquid crystal spatial light modulators and two-dimensional arrays of Fresnel lenses that produce multiple diffracted light beams are described in this paper. These include an optically addressed light modulator, a matrix-addressed pixellated (television) display with thin-film transistors, and two modulators fabricated at Bellcore that are electrically addressed through specially designed electrode patterns. Implementations with binary-amplitude and binary-phase Fresnel lenses are discussed identifying programmable features and resolution limits of each type of modulator.

We review the nonlinear joint transform correlator (JTC) including the kth law nonlinear JTC, and the binary nonlinear JTC. The implementation of the nonlinear JTC using an optically addressed SLM in the Fourier plane is described.

A compact crossbar switch array based on matrix-vector multiplication is proposed. The crossbar is composed of beam splitting and beam combining holographic structures in substrate mode waveguides and a liquid crystal spatial light modulator. A design of a 4 X 4 crossbar is presented.

Liquid crystals (LC) have been known for more than a century. These materials different from both liquids and solids have a molecular disposition intermediate between chaos and perfect order. Their anisotropic optical properties were quickly revealed but without special applications. Tothy LC are in every day life and their applications are more and more numerous. To respond to users'' needs new products are continuously appearing on the market and many improvements have been made. In this paper we will introduce a technique which allows the improvement of a variable retarder LC cell response time. The switching speed between two retardation states is of primary importance for many applications (polarimeters variable attenuators shutters. . . ). In our particular case this improvement was proved essential in order to make the cell compatible with an underwater polarimetric imaging application. The cell is here used as a variable retarder and switching between two retardation states must occur between two successive expositions. By modifying the electric field control which tunes the retardance of the cell the switching speed can be improved.

Benzocyclobutene (BCB) is being developed to planarize both substrate glass, color filters and active devices for flat panel displays. In addition, the material is being evaluated as the alignment layer and acceptable pre-tilt angles are reported. The results of the current study have shown the BCB to exhibit superior planarization to polyimide with efficiencies 90. As an example, a typical P-V (peak-valley) of a color filter is reduced from about 1.4 (mu) initially to about 1200 angstroms with the application of 1.2 (mu) of BCB. In addition to efficiently smoothing the color filters, the BCB can also be employed to planarize the substrate glass, while acting as a Na+ barrier. For this particular example, the BCB coated glass is subjected to ITO deposition and the resultant film still exhibits excellent optical clarity with transmissions of approximately 92 respectively before and after ITO. The glass substrate is also efficiently planarized to the point that the directionality of the float direction becomes ambiguous.

The proposed paper describes a deflector-chopper based on electrically controlled total internal reflection (TIR) . Thin positive nematic liquid crystal layer Merck 1132 is used as an electrooptic medium. The most interesting advantage of TIR based devices is their high contrast (or s2gnalto--noise ratio). The investigations performed are devoted to the behavior of image contrast vs. applied electric field.

A new type of liquid crystal device was developed by applying a concept of liquid crystal phase gratings (LCPGs). LCPGs are composed of square-wave phase gratings constructed with poly(methyl methacrylate) and liquid crystals which fill the grating grooves. The typical sizes of the phase grating are 10 micrometers in width and 2 micrometers in depth. The transmitted light wavelength can be easily controlled by changing applied voltage. The transmittance varied from less than 1 for monochromatic polarized light, when applied voltage varied from 0 V to 5 V. Rise times for the light varied from 0.2 ms to 7 ms with applied voltage, and were inversely proportional to the square of the applied voltage. Decay times, which depend slightly on the applied voltage, were about 4 ms. A transmitted light, i.e., an observed color (e.g., R,G,B and white), was dependent on not only applied voltage but also grating depth. When two of the LCPGs were combined in such a way that their grating lines were oriented perpendicular to each other, these LCPGs were applicable to nonpolarized light.

We consider the addressing requirements associated with some analogue and binary electro- optic effects in chiral smectic liquid crystals driven from silicon VLSI backplanes. This class of liquid crystals offers major improvements in switching speed over electro-optic effects in nematic liquid crystals, but their non-RMS response to impressed voltages leads to addressing difficulties. Their spontaneous polarization also leads to limitations in using pixel drive circuits resembling dynamic random access memory cells (DRAMs), which are commonplace in display technology. Some illustrative examples of the performance of electro-optic effects with currently available materials are given, followed by a discussion of the problems associated with the charging phenomena occurring when ferroelectric liquid crystals are driven from active backplane drive circuits. Addressing schemes are then considered, particularly those that are aimed at providing electro-optic modulators with continuous optical access and with no temporal noise in their transfer characteristic, such as might be needed in optical switching devices. Some examples of experimental pixel circuits are given.

Polymer-dispersed liquid crystal (PDLC) films are useful in light control applications because they can be switched electrically between light scattering and transparent states. PDLC films are also being considered for solar heat load reduction because they can be made to backscatter the solar radiation. Since the size of the PDLC film required for such applications could be as large as one or more square meters, special consideration must be given to the electrical power required to activate those (mostly capacitive) films. We measured the electrical response of PDLC films to applied voltages of amplitude and frequency in the range of those typically used in most applications. A voltage-dependent and materials-based RC circuit was developed to model the PDLC film and its circuit parameters were adjusted to fit the data. We found that the model and the fitted values of the circuit parameters are useful for understanding the electrical properties of PDLC films and identifying sources of power consumption. In addition, the values obtained for the circuit parameters allowed us to estimate several previously unknown PDLC material parameters.

Gray scale was obtained with a ferroelectric liquid crystal (FLC) cell in which the twisted state of FLC molecules is gradually unwound by an applied voltage. The cell has an extinction ratio of 60 at 632. 8 nm and a response time of 300 jtsec. A spatial light modulator (SLM) with 256 x 256 pixels was fabricated by incorporating the FLC cell with an amorphous silicon thin film transistor array. This offers us a promising technology to realize a FLC-SLM with gray scale a fast frame time of 300 psec and a pixel number as large as 1000 x 1000.

Hysteresic properties of cholesteric-nematic phase transition in liquid crystals is investigated. It is established that the surface orientation influences the relative value of the hysteresis loop. The strongest dependence of the relative value of the hysteresis loop from the concentration of cholesteric admixture was observed for the orientation coating on the basis of SiO