Gratings formed by anisotropic phase separation of liquid crystals how tremendous promise for switchable optical elements. Formation of useful gratings is linked to the control of the resulting nano-scale morphologies. In an attempt to decrease scatter and improve the electro-optic properties of polymer-dispersed liquid crystal volume transmission gratings were have evaluated the result of altering the relative concentrations of the components in the pre-polymer mixture. Discussion is made concerning the expected effects on polymerization and phase separation and how these changes are reflected in the film morphologies and electro-optical properties. Initial results indicate that changes in the concentration of co-initiator, chain extender, and effective monomer functionality have a significant effect on the size and shape of the LC domains at constant LC loading.

The cholesteric liquid crystal (LC) has a chiral structure defined by pitch length. This unique structure reflects one handedness of circularly polarized light and is used as a circular polarizer. This polarizer can be actively switched between a state that is transparent to light of all polarizations and another state that in only transmissive to one handedness of circularly polarized light. The dual- frequency material is used to reduce the relaxation time. The dual-frequency circular polarizer can be switched from the transparent homeotropic texture by a low frequency driving signal, and switched to the reflecting planar texture by a high frequency signal. This polarizer functions as a switchable shutter for which we have characterized switching process, relaxation time, polarization purity, and extinction ratio.

In recent years, compact, portable information equipment such as notebook computers and PDAs has progressed remarkably. This, in turn, has created a need for bright reflective color liquid crystal displays (LCDs) without a backlight. In responses to this requirement, we have previously proposed a new, achromatic reflective TN-LCD, and STN-LCD with one polarizer and one retardation film. The LCDs enables creation of a reflective color LCD using a color-mixing system such as the micro color filter type. However, the TN-LCD of the normally black mode has the problem that the higher the resolution is, the lower the luminance becomes due to the space between electrodes. In order to solve this problem, we will propose a normally white mode achromatic reflective TN-LCD, composed of the above mentioned normally black mode reflective TN-LCD and one liquid-crystal polymer film with a twist angle of the same magnitude, but with an opposite-handed to the LC layer. The electro-optical properties of the LCD have been numerically analyzed, and it was found that several sets of solutions exist for obtaining an achromatic image with high luminance as well as a high contrast ratio. In this paper, we will focus on the achromatic reflective TN-LCD of normally white mode, which is promising for a new reflective LCD in respect to full color displays, especially for document displays.

A non-rubbing process suitable for active matrix LCDs based on a photo-dimerized monolayer (PDML) has been developed. The PDML yields defect free alignment of nematic liquid crystal molecules. The electro-optic characteristics of LCDs fabricated using the photo-dimerized layers are shown to be comparable to those of a rubbed polyimide alignment layer.

Deformed-helix ferroelectric liquid-crystal media with high molecular tilt angles have been used in spatial light modulators to make them faster and more efficient. A prototype device developed for real-time holography applications has generated diffraction efficiencies as high as 38 percent and response times as short as 600 microsecond(s) ec.

Dried oriented purpose-membrane (PM)-films were fabricated by electrosedimentation of aqueous PM-suspensions on ITO- covered slides. The photoelectric output of illuminated PM- films was optimized by adjusting several deposition parameters and the photoelectric signals were used to switch twisted-nematic (TN)- and ferroelectric (FE) liquid-crystal (LC) cells. Due to the quasi differential behavior of the photocurrent with respect to illumination intensity,l a PM/TN system represents an inherent novelty filter. The use of FE-LC cells for permanent data display is demonstrated. A prototype of a pixelated BR-LC-OASLM is presented and experimental results from a device consisting of a BR-film in direct contact with a LC-cell are discussed.

Electrically-controlled diffraction gratings are developed on the basis of a cholesteric liquid crystal confined between two transparent electrodes. The electrodes are coated with unidirectionally treated alignment layers. The initial state is planar, with the helix axis oriented normally to the electrodes. The applied field causes reorientation of molecules and creates structures modulated in the plane of the cell. Surface alignment provides unidirectional uniformity of the modulation. The parameters of the modulated structures and light diffraction are controlled by the cholesteric pitch, cell thickness and applied voltages. Diffraction regimes of both Raman-Nath and Bragg types are demonstrated. In the Raman-Nath regime, the electric field allows one to control continuously the deflection angle by changing the periodicity of modulations. This effect can be used in various beam steering devices. The variation in the diffracted beam direction can be more than 20 degrees. Typical working voltages are less than 10V. We present both the experimental results and 3D computer simulations of modulated structures caused by the field.

Using a mode-locking Nd:YAG laser, we measured the second harmonic generation (SHG) of polymer stabilized cholesteric texture (PSCT) films. SHG observed in these samples is due to the dielectric gradient which arises from the interfaces between the cholesteric liquid crystal/polymer and those between the adjacent cholesteric focal conic domains having different helical axis. Both of the SHG intensities and the electro-optical characteristics of PSCTs were measured as a function of polymer concentration. In addition, polymer network structures formed in PSCTs were investigated. Good correlations among the SHG measurements, electro-optical characteristics, and the polymer network morphologies were found. It means that SHG measurements could provide us another qualitative, nondestructive method to analyze the PSCT films. In addition, SHG change on polymerization can be used to monitor the polymerization of LC-polymer mixtures.

M-line measurements have been performed on thin films of pyroelectric liquid crystalline polymers (PLCP), in order to determine the magnitude and anisotropy of the refractive index. The films, polymerized under various conditions, are based on materials exhibiting a chiral smectic C phase. The results of the measurements were analyzed and compared with a new numerical method to model the optical properties of anisotropic multilayered thin films. In the model, which is an extension of the analytical approach of Berreman, the eigenmodes and boundary conditions of refracted light waves are handled and solved by numerical matrix manipulations. Model calculations of total reflection measurements for various multi-layered systems were used to investigate the effect of ITO and polyimide aligning layers to the apparent effective index of m-lines.

Nonlinear optical properties of chiral liquid crystalline media are in scope of our interest since several years. Our previous observations in the subject were already reported, where the effect of light interaction with chiral nematic structure was examined by reflected-probe-beam technique. The present contribution is a continuation of that work. Now the concept of modulation of light by light is presented as an example of potential application of previously achieved results. This paper just considers the use of reflected- probe-beam arrangement in combination with optical fiber technique for 'in line' controlling of high-intensity light beams. The idea utilizes nonlinear optical effect in combination with selective light reflection in chiral liquid crystals. The preliminary results of experimental examination of the 'all optical modulator' are demonstrated. Also some practical aspects and application problems are defined.

The second harmonic generations (SHG) of liquid crystalline main-chain type polymers were investigated. The sample polymers are copolymers of 2-hydroxy-6-naphtoic acid with 4-hydroxy-benzoic acid, in various composition ratios. SHGs for the samples prepared by applying electric fields in some different manners at the liquid crystalline temperature were compared. The nonlinear optical coefficients d_exp evaluated by Maker Fringe Method of electrically poled samples are 2-3 times larger than that of mechanically oriented sample whose d_exp is about 5pm/V. Quasi-phase matching was performed by piling mechanically oriented thin films with alternatively directed machine direction. Using liquid crystal as the space between films and surfaces and tuning refractive index of the liquid crystals by applying adequate electric field, SH intensity increased up to 12-15 from one sheet of film.

Ultrafast transient absorption studies of intramolecular photoinduced charge separation and thermal charge recombination were carried out on a molecule consisting of a 4-(N-pyrrolidino)naphthalene-1,8-imide donor (PNI) covalently attached to a pyromellitimide acceptor (PI) dissolved in the liquid crystal 4'-(n-pentyl)-4- cyanobiphenyl (5CB). The temperature dependencies of the charge separation and recombination rates were obtained at temperatures above the nematic-isotropic phase transition of 5CB, where ordered microdomains exist and scattering of visible light by these domains is absent. We show that excited state charge separation is non-adiabatic, and obtain the unexpected result that charge separation is dominated by molecular reorientation of 5CB perpendicular to the director within the liquid crystal microdomains relative to the orientation of PNI⁺-PI^-. We also report the result of time resolved electron paramagnetic resonance studies of photoinduced charge separation in a series of supramolecular compounds dissolved in oriented liquid crystal solvents. These studies permit the determination of the radical pair energy levels as the solvent reorganization energy increase from the low temperature crystalline phase, through the soft glass phase, to the nematic phase of the liquid crystal.

Optical nonlinearity of liquid crystals (LC) in the isotropic phase can be enhanced by one order of magnitude by dissolving 0.1 percent of anthraquinone dye in the LC. The enhancement decrease when the LC transforms into the nematic phase. The same guest-host effect also exists in non-LC liquids. It can be explained by a model based on selective excitation of dye molecules and the change of guest-host interaction induced by optical excitations of the dye.

We report orientational photorefractive effects observed in photoconductive liquid crystals (LCs) contained with three kinds of polymer, i.e., poly(methyl methacrylate) (PMMA), poly(vinyl alcohol) (PVA) and a side-chain liquid crystalline polymer (SLCP1). The morphology of the photorefractive composites depended on the kind of polymer strongly. In both PMMA and PVA cases, LC and polymer were phase-separated and the composite showed memory effects. In SLCP1 case, the phase-separation in the composite dose not occur and the high resolution could be achieved. In this case, the photorefractive Bragg gratings were generated and a high two-beam coupling gain coefficient with a low applied field of 4 V/micrometers was observed.

A new molecular reorientation effect in nematic liquid crystals is investigated. The nonlinear optical effect occurs under the combined application of DC-electrical fields and low power illumination and has a very huge photosensitivity. Rather large nonlinear optical coefficients up to 6 cm²/W are obtained. Light intensities as low as 10^-3 W/cm² are sufficient for a strong photo-induced reorientation. Even a microscope lamp or a small torch provides enough illumination to induce remarkable changes in birefringence. The effect was first observed in liquid crystals of discotic molecules but is also present with calamatic, i.e. rod-like molecules.

Using nematic liquid crystal films doped with photocharge producing dyes, we have demonstrated the feasibility of optical limiting of long pulse - cw lasers at nanowatt power, and clamped transmission of < < 1(mu) J. We also demonstration incoherent-coherent image conversion capability with optical intensity in the (mu) Watt/cm² level.

A polarization-insensitive, tunable nematic liquid crystal Fabry-Perot filter incorporating polymer liquid crystal waveplates within the Fabry-Perot cavity is presented. The performance of the filter is evaluated experimentally, and theoretically verified using computational modeling techniques. Fabrication tolerance parameters are considered through theoretical experiments using the numerical model. A typical experimental filter yielded 12 nm tuning range with 13 VAC of applied voltage, with a finesse of 7 at the design wavelength 1550 nm.

An original idea of external parameters monitoring is presented. After a short introduction to theoretical analysis of the light modulation in a liquid crystal-core anisotropic fiber the latest experimental results are reported. Due to measurands-induced changes in birefringence and propagation conditions the liquid crystal-core fiber uniting unique advantages of liquid crystal sand quality of fiber technology acts as a sensing medium and can be used for continuous monitoring of different external parameters.