Chiral helix materials have large optical rotatory power, and therefore, their application has been caught much attention for optical elements and/or optical switching devices. Among such helical polymers, chiral poly-lactic acid can be easily synthesized without racemization. However, the film formation of poly-lactic acid for optical application is difficult because of the high crystallinity. We synthesized the chiral oligo-L-lactic acid with the definite degree of polymerization by using GPC fractionation technique and found that the optical rotatory power reached to a saturated constant value even in the octamer. Such oligomers whose repeating units are less than 14 are liquid state at ambient temperature. These results indicate that the helical structure has stably existed even in the low molecular weight oligomers. The oligo-L-lactic acid could be oriented in liquid crystalline cell and by electro-poling treatment. The orientation structure was discussed from ORD spectra and SHG measurement.

Molecules designed to possess large dipole moments have been synthesized and doped into liquid crystals for the purpose of reducing the threshold voltage associated with the Freedericksz transition in nematics. These molecules were tested in the commercial nematic mixture E7 at varying concentrations and the resultant mixtures were evaluated to determine their nematic-isotropic transition temperature, threshold voltage, dielectric anisotropy, and visco-elastic constant as a function of dopant concentration. We have shown that these materials reduce the threshold voltage by up to 25 % at the 10 wt.% doping level but do so via a reduction of the splay elastic constant, not by the increase of the dielectric anisotropy as was expected. As a consequence of this result these dopants have also shown to increase the response time of the dopant/liquid crystal mixture.

The dynamic behavior of a holographic grating induced in a homeotropically aligned dye-doped liquid-crystal film is investigated. In the presence of an applied dc voltage, photoexcited azo dyes induce a photorefractive grating and then diffuse and are absorbed onto cell substrates. The reorientation of liquid crystals as a result of adsorbed dyes leads to a phase grating that is phase shifted 90° from the photorefractive grating. Competition of these two gratings induces two-beam couplings of the writing beams, initially transferring energy from beam 1 to beam 2 and then, after a pause, from beam 2 to beam 1.

A numerical model has been developed that describes the electro-optical switching properties of an optically addressed spatial light modulator (OASLM). The OASLM device comprises of a hydrogenated amorphous silicon photosensitive layer with electrically blocking contacts, and a nematic liquid crystal light modulation layer. The model has been used to investigate the magnitudes of the switching voltages that give the largest operating window between the on (illuminated) and off (dark) states.

We report on theoretical and experimental studies of all-optical polarization conversion of cw 1.55 μm lasers using nematic liquid crystal in their ordered and isotropic phases. Almost complete conversion of the linearly polarized laser is achieved in a 400 μm thick film at mW power.

A dual frequency liquid crystal (DFLC) can be field-driven towards its unperturbed state, which dramatically reduces the overall electro-optical response time. DFLC materials with sub-millisecond switching speed are being used in infrared electro-optical devices at wavelengths up to 3 microns. The performance of devices such as tunable half-wave plates and optical phased arrays in agile beam steering devices, and wavefront controllers for adaptive optics are described. Device issues discussed include drive schemes, field of view, reflective direct drive backplane, infrared-transparent conductors, and antireflection coatings.

We report theoretical and experimental studies of 1-D and 2-d tunable nonlinear photonic crystals made of liquid crystal or liquid crystal infiltrated periodic structures. Theoretical modeling shows that such structures exhibit tunable bandgap, and sugar-prism effect. Experimentally, we have demonstrated the possibility of writing dynamic or permanent [but switchable] index gratings to dye-doped LC films that act as planar waveguides.

We present results of single and three pulse photoselection studies of the dynamics of a fluorescent probe (Oxazine 4) in the nematic phase of the liquid crystal 4-n-pentyl-4'-cyanobiphenyl (5CB). The combination of these techniques with time resolved fluorescence anisotropy measurements allows the unambiguous determination of the full angular motion of the probe together with the ground and excited state degrees of equilibrium (steady state) alignment. The restricted geometry imposed by the nematic host is seen to impart a marked anisotropy in θ and Φ diffusion (γ_φ/γ_θ~4).

A survey of recent results of experiments aimed at understanding the basic mechanism of the photoinduced reorientation phenomena in dye-doped liquid crystals is presented. In particular, I shall focus on experiments based on the isotopic substitution of hydrogen atoms with deuterium in dye molecules, which have shown an unexpected enhancement of the photoinduced reorientation effect by a factor two. The isotopic substitution also changes the dye excited state lifetime and orientational diffusion times. These results are in good agreement with the model proposed for the effect, and confirm the hypothesis that the active photoexcited state in the photoinduced reorientation phenomena is simply the first-excited singlet electronic state of dye molecules.

A review of the recent results of our group in the field of light-induced anchoring and reorientation effects in dye-doped liquid crystals (LCs) is presented. In particular, the phenomena of photoinduced anchoring and permanent reorientation over a polymeric boundary surface of a dye-doped LC cell is reported, both in the isotropic phase and in the orientationally ordered nematic phase. The results have been interpreted microscopically in terms of adsorption and desorption of the dichroic azo-dye (methyl-red) molecules onto the illuminated surface during light irradiation. The model proposed is in agreement with recent results on the dynamic and stable grating formation in methyl-red doped LCs .

Electric fields can induce motion of polymer cholesteric liquid crystal (pCLC) flakes suspended in a fluid medium. The platelet-shaped pCLC flakes with a Grandjean texture show strong selective reflection when lying flat in the plane of a conventional cell. As their orientation with respect to normally incident light changes, their selective reflection color shifts toward the blue and diminishes until the flakes are no longer easily visible beyond 7-12° of rotation. Reproducibility and control of motion has been observed in moderately conductive host fluid. Flakes in such hosts do not respond to a DC electric field, but they rotate 90° in an AC field within a given frequency band. The response times and frequency regions for motion depend partially on the field magnitude, the dielectric properties of the host fluid and the flake geometry. We observe flakes reorienting in less than 500 ms in an electric field of 0.17 V_rms/μm, while sub-second reorientation is seen in fields as low as 5x10^-2 V_rms/μm. This response time is comparable with typical electronic-paper applications, but with a significantly lower electric field. Displays using pCLC flakes would not require backlighting, sheet polarizers, color filters or alignment layers. Numerous additional applications for pCLC flakes are envisioned, including filters, polarizers, and spatial light modulators.

We synthesized di-mesogenic liquid crystals with both cholesterol and azobenzene groups by esterification of 10,12-docosadiynedioic acid or docosanedioic acid with 4-alkyl-4'f-hydroxyazobenzene (or 4-hydroxyazobenzene) and cholesterol. Two compounds without an alkyl chain on the azobenzene unit show cholesteric and smectic phases, while five compounds with an alkyl chain from butyl to hexadecyl show only a smectic phase. When the compounds were doped in 2-10 w% to a dicholesteryl ester forming stable cholesteric glass, the mixture became photo-responsive. Upon irradiation at 366 nm, the cholesteric band of the mixtures shifted toward shorter wavelength caused by the photo-isomerization from trans to cis of the azobenzene unit on the dopant. The extent of the shift depends on irradiation energy, temperature and the length of the alkyl chain on the azobenzene unit. When a thin film of the dicholesteryl compounds containing 5w% of the dopant having a heptyl substituent on the azobenzene unit was irradiated at 90°C, the reflection band shifted from 730 nm (infrared) to 490 nm (blue). The mixture went into the glassy state keeping the shifted cholesteric reflection band after rapid cooling from the liquid crystalline temperature to 0°C. The cholesteric glassy state was stable up to 80°C. Since the molecular arrangement of the dicholesteryl compound and the conformation of the doped azobenzene derivatives completely returned to the initial state upon reheating to isotropic temperature, the photo-responsibility and glass-forming property of the mixture is applicable to full-color rewritable recording materials.

Two kinds of chiral diarylethene derivatives were synthesized and used as dopants for photoresponsive liquid crystals. Both derivatives underwent thermally irreversible and fatigue resistant photochromic reactions and exhibited reversible circular diochroism (CD) spectral changes. Large photostimulated pitch chances of chiral nematic K-15 liquid crystals were observed by the addition of the derivatives as dopants. The relation between the optical rotation and the twisting power force was discussed.

Liquid crystalline polymethacrylates with benzanilide and photochromic azobenzene side groups and a related terpolymer containing an additional side group with a phenylethynyl substituted anthracene chromophore were oriented by the irradiation with linearly polarized light. The orientation of both polymers were compared irradiating with polarized visible or, alternatively, UV light. Caused by the co-operativity of the photoorientation process, the light-induced orientation of the azobenzene groups is connected to the alignment of the non-photochromic side groups below the glass transition temperature. The light-induced order generated in the glassy state was significantly amplified by the subsequent annealing of the irradiated films at temperatures in the mesophases. Factors of amplification of about 30 were found in the case of both polymers. The photo-induction process and its amplification by thermotropic self-organization were investigated in dependence on the polymer composition, the irradiation dose and the wavelength of the incident light with respect to the absorption of the dye and its limited photo-stability. The required dose or the irradiation time, respectively, were significantly reduced by the optimization of the light-induced and thermal processing. In this way, dichroic films of co- and terpolymers were created. However, the green fluorescence of the anthracene chromophore is effectively quenched by the azobenzene side group within the film.

Recently is has been discovered that some types of liquid crystals exhibit very fast electronic conduction whose charge carrier transport are characterized by high mobility over 10^-2 cm²/Vs independent of electric field and temperature. Now, the liquid crystals are being recognized as a new class of organic semiconductors, in addition to the recognition as the display material. The liquid crystal enjoys superior properties to conventional amorphous materials in terms of the organic semiconductors for large-area devices, thanks to its liquid-like fluidity and crystal-like molecular alignment. In this articles, a new aspect of liquid crystals as a Self-organizing molecular semiconductors are reviewed on the basis of our experimental results on smectic liquid crystals and discuss their high potential for organic electronic devices.

The thermal polymerization of aziridine monomers without a mesophase was performed in rubbing and non-treated sandwich cells. Cross-linked polymers, having homogeneous and homeotropic structures, were prepared. The thermal polymerization process was examined by X-ray diffraction measurements and polarizing microscopy. The cross-linked polymers exhibited a smectic A layered structure. In the rubbing sandwich cell, an aziridine monomer with an ethanol terminal group gave a cross-linked polymer having a homogeneous alignment. The homeotropic structure was obtained by thermal polymerization of an aziridine monomer with a nitro terminal group in a non-treated sandwich cell. The homeotropic structure was also formed on the surface of a glass plate and an aluminum thin film. A uniaxial-optical property of the homeotropic structure was characterized by conoscopic observation. The X-ray diffraction measurements showed the formation of the smectic A domain within an isotropic fluid by thermal polymerization at 100°C as well as optical texture observations. The X-ray diffraction pattern of the homeotropic structure was composed of first, second, and third inner reflections and a wide-angle halo, corresponding to the smectic A fluid phase.

The mechanism of photo-aligning (PA) of azodye molecules is investigated. We show that PA takes place due to the pure reorientation of the molecular absorption oscillators perpendicular to the UV-light polarization. The model of the rotational diffusion of the azodye molecules in the field of polarized UV-light was used to explain the formation of the photo-induced order in azodye layers. We constructed a special experimental set-up, based on a photo-elastic modulator, that allows to make accurate measurements of the phase retardation δ of thin film as a function of the exposure time t_exp and exposure power W (W/cm²). The optical anisotropy was induced by a pump beam of Ar⁺ laser (λ=457 nm). Fitting the experimental curves d(t_exp) for different power values W, we can estimate the coefficient of rotational diffusion D and azodye order parameter S(t_exp).

We propose a two-dimensional (2D) and hyperfine measurement method for precisely determining cell parameter distributions such as a cell thickness and twist angle in color liquid crystal (LC) displays. The 2D cell thickness and twist angle distributions can easily be determined by measuring Stokes parameters of all pixels for red, green and blue in LCD panel at a wavelength of near-infrared region, because the transmission light at the wavelength is not absorbed by each color filter. In addition, the spatial resolution can be improved by increasing the magnification of the objective lens in front of a high resolution CCD camera. These cell parameters of each pixel in the practical LCD panel are compared and discussed.

The formation of mirrors reflecting a single colour or reflecting the whole visible spectrum by application of a liquid crystalline layer followed by UV polymerisation (photo-polymerisation) is described. Also, the formation of patterned films obtained by a sequence of UV exposure steps is discussed. Such films play an important role in the improvement of the performance of liquid crystal displays.

Chiral helical polymethylphenylethylcarbodiimides (Poly-PhEMCDI) and polymethylcyclohexylethylcarbodiimides (Poly-ChEMCDI) have been synthesized by insertion polymerization of corresponding monomeric carbodiimide using copper complex as initiator. Their circular dichroism, optical rotation power induced by ordered rigid main chain helical structure in solution and casting films were obtained and molecular weight dependent circular dichroism were studied. Primary results about Second Harmonic Generation (SHG) of casting films of polycarbodiimides prepared by different solvents were measured and chloroform was the best solvent to prepare casting films with preferential orientation of molecular helical structure. Polycarbodiimides can form lyotropic liquid crystal in chloroform, THF solution etc.

The holographically-formed polymer dispersed liquid crystal (H-PDLC) has been widely studied in recent years. In this paper, we analyze the major factors contributing to the efficiency of volume gratings base on the basic optical theory. With regard to the feature of the special exposure material-PDLC, we have conducted some experiments to investigate the impacts of four major factors, such as different recipes of PDLC, exposing time of PDLC cells, thickness of film and the degree of two laser beams, which contribute to obtain the higher diffraction efficiency. As a result, under the same conditions, it is found that the most significant affecting factor is the recipe of PDLC. The diffraction efficiency is enhanced substantially after new chemistry reagent is mixed into the polymer precursors. Shorter cure time and comparative smaller degree of two laser beams give rise to higher diffraction efficiency. Finally, using 17degree of two laser beams, 50mw power of laser with the wavelength of 441.6 nm and exposing time about 30 seconds, we can obtain about 90% efficiency of the H-PDLC volume grating. Furthermore, we researched the relationship between the applied voltage and the diffraction efficiency.

In this paper, we have developed a novel optical switch based on the electronically switchable Bragg gratings (ESGB) in holographical polymer dispersed liquid crystals (H-PDLC), which is adopted in the U.S. Patent (NO.09/963, 939). This optical switching can be produced by the superposition of H-PDLC Bragg gratings with different spatial frequencies and very high diffraction efficiency. It can provide switching speeds faster than 5ms, so that the technique can be widely applied in telecommunication to improve the transmission speed effectively.

The Quetelet-type ring pattern is observed in liquid crystal polymer dispersion (LCPD) films. The clusters of the polymer network and liquid crystal (LC) domains with different director axes in the LCPD films serve as scatterers. Cells with unidirectional and multidirectional rubbins are fabricated. Experimental results show that the polarization of incident light, the applied voltage and the ambient temperature significantly affect the ring intensities. However, the contribution of the LC domains is not evident until the voltage is applied. Finally, rubbing the cells in multiple directions reveals that measurement of the Quetelet-type ring intensity can be used to readily identify the orientation of the liquid crystals. This finding also reveals that the LCs in an LCPD mixture are aligned closer to the final rubbing direction than are pure LCs in a multidirectional rubbed cell. A simple model was proposed to explain the observations.

We develop the novel optical device for controlling the polarization state using liquid crystal (LC) and eight-divided hole-patterned electrodes which are coated with weak anchoring alignment films. The LC director can be reoriented by applying in-plane electric fields and the other electric fields across a cell thickness layer, and then polarization state of light transmitted trough the hole-patterned region can be controlled. The design and the electrical and optical properties of the LC device are briefly discussed.

Colloid-liquid crystal composites are a novel type of soft condensed matter, formed from dispersions of colloidal particles in liquid crystalline hosts. Here, we investigate the kinetics of network formation in mixtures of the thermotropic liquid crystal 5CB and nearly hard sphere colloids (polymethylmethacrylate particles), occurring as the liquid crystal moves from the isotropic to the nematic state. In the isotropic phase the particles (volume fraction < 0.2) are homogeneously distributed. While cooling through the isotropic-nematic phase transition the particles are expelled by the liquid crystal, forming a three dimensional network. Using time-resolved laser scanning confocal microscopy (LSCM) we image the dynamics of the network formation at single particle resolution. The particles perform Brownian motion in the isotropic phase, whereas in the network they remain frozen in position. We observe a broad distribution of the size of the liquid crystal domains, up to a few micrometers. DSC measurements show that the particles do not change the temperature of the phase transition, indicating that the particles do not alter the bulk properties of the liquid crystal.

Molecular dynamics of a nematic liquid crystal, 4n-octylcyanobiphenyl, confined to two types of SBA-type nanoporous molecular sieves were studied by broadband dielectric spectroscopy in order to obtain information about the liquid crystal-surface interactions. The temperature interval of the dielectric measurements was large, covering all the states of the bulk liquid crystal. It is found that there are several relaxation processes covering the large frequency range. A bulk-like relaxation comes from the liquid crystal molecules located in the center of the pores, which rather do not feel the effect of the pore walls. Another relaxation comes from the molecules located in the surface layer. The latter process is much slower than the bulk-like relaxation. The differences observed between the dynamic behavior of the liquid crystal confined to the two types of nanoporous materials are related to pore size, pore shape and liquid crystal-surface interactions.