This PDF file contains the front matter associated with SPIE Proceedings Volume 6587, including the Title Page, Copyright information, Table of Contents, Introduction, and the Conference Committee listing.

We describe a class of liquid crystalline photonic metamaterials that exhibit tunable negative-zero-positive refractive indices. As a result of the extreme sensitivity of the nematic liquid crystal constituent, these metamaterials also exhibit extraordinarily large optical nonlinearities associated with the optical field induced director axis reorientation and birefringence change. Incorporation of a gain medium such as laser dye reduces losses of the metamaterial.

The ability to generate regular spatial arrangements of particles on different length scales is one of the central issues of the "bottom-up" approach in nanotechnology. Current techniques rely on single atom or molecule manipulation by the STM, colloidal particle manipulation by laser or optoelectronic tweezers, microfluidics, optofluidics, micromanipulation and classical lithography. Of particular interest is self-assembly, where the pre-determined spatial arrangements of particles, such as 3D photonic crystals, could be realized spontaneously. Dispersions of particles in liquid crystals show several novel classes of anisotropic forces between inclusions, which result in an amazing diversity of self-assembled patterns, such as linear chains and 2D photonic crystals of microspheres. The forces between the particles in nematic colloids are extremely strong and long-range, resulting in several thousand times stronger binding compared to the binding in water based colloids. The mechanisms of self-assembly in nematic colloids are discussed, showing this is a novel paradigm in colloidal science, which can lead to new approaches in colloidal self-assembly for photonic devices.

Microstructured photonic crystal fibers have an ability to modify their spectral properties when different materials are inserted into the holes. This paper presents our latest experimental results on spectral properties of photonic crystal fibers infiltrated with liquid crystals. Three different types of photonic crystal fibers host-structures were filled with nematic liquid crystals. The structures consisted of multi-core, isotropic or highly birefringent photonic crystal fibers. The nematic liquid crystals mixtures used as guest materials are characterized by either extremely low or medium material birefringence. This paper demonstrates a prototype multi-core photonic liquid crystal fiber showing strong influence of fluctuations in the fiber's dimensions on the selective propagation bands. The paper discusses the influence of temperature and of external electric field on the spectral properties of the photonic liquid crystal fibers and reports the latest experimental results with highly birefringent Blazephotonicsphotonic crystal fibers also filled with the nematic liquid crystal.

Photonic liquid crystal fibers (PLCFs) combine unique properties of photonic crystal fibers and liquid crystals (LCs). Liquid crystal molecules orientation within the PLCFs has crucial impact on their optical properties since it determines the radial refractive index profile of the LC-filled micro-holes. There are many techniques used for LC molecules orientation control, but most of them are not suitable for application in microstructured fibers characterized by holes with diameters in the order of few micrometers. It seems that the only method that could be applied in PLCFs is using of thin photopolymer layers, in which surface anisotropy can be induced in the way of photochemical reactions. In this paper we present preliminary experimental results of the photoinduced molecular alignment in the PLCF induced by a thin polyvinylcinnamate (PVCi) film irradiated with the linearly polarized ultraviolet light.

We investigated photochemical manipulation of physical properties and colloidal structures in liquid-crystal (LC) colloids containing azobenzene compounds. In a LC suspension where polymeric particles were dispersed in a host LC, we achieved photochemical control of light-scattering properties of the suspension. In a nematic phase, when the suspension was sandwiched with two glass plates, the film became opaque. This would be attributable to an appearance of both multidomain structures of LC alignment and mismatches of refractive indices between the materials. The opaque state turned into a transparent one when a nematic-to-isotropic phase transition was induced by the trans-to-cis photoisomerization of the azo-dye. This will result from a disappearance of both the multidomain structures and the refractive-index mismatches in the isotropic phase. The transparent film went back into the initial opaque film when the nematic phase was obtained by the cis-to-trans photoisomerization. In a LC emulsion in which glycerol or water droplets were dispersed in liquid crystals, we examined photochemical change of defect structures and inter-droplet distances by the photochemical manner. At the initial state, Saturn ring and hedgehog defects were formed around the droplets. For the glycerol droplets, we observed structural transformations between Saturn ring and boojums on irradiation with ultra-violet and visible light. For the water droplets, the inter-droplet distances varied by changing defect size on the irradiation. These phenomena would result from modulation of anchoring conditions of the droplets by the photoisomerization of the azo-dyes.

I review recent results on a novel method for generating helical waves of visible light based on inhomogeneous birefringent plates made of a suitably patterned liquid crystal. These devices, dubbed "q-plates", act on the light wave by converting its spin angular momentum into orbital angular momentum, an optical process not envisioned before. The output helical wave can be easily and rapidly switched between opposite wavefront helicities by switching the input polarization with standard electro-optics devices. The process can be cascaded, so that rapid switching can take place among multiple values of the wavefront helicity. More generally, patterned liquid-crystal devices similar to those realized for generating helical beams may be used for shaping the optical wavefront in any prescribed way, with the possibility of dynamical polarization multiplexing between conjugate wavefronts. This is an application of the Pancharatnam-Berry phase principle, allowing the realization of a novel kind of optical elements for wavefront shaping. Potential developments in the fields of optical communication and quantum computation are briefly discussed.

Heterogeneous liquid crystal (LC) systems are a new class of anisotropic materials which have been intensively studied over the last decade. This article is concerned with two such systems: ferroelectric LC nano-suspensions and LCs with polymer network. The significant implication of ferroelectric LC-colloids is the possibility of a significant reduction in the threshold electric Fredericksz voltage. Here we present a theory of this phenomenon, which agrees qualitatively with experiment. A second example of heterogeneous LC systems is a gradient-polymer-stabilized LC (G-PSLC) structure, which has been proposed for a tunable-focus lens application. We report on theoretical model that describes the dependence of the G-PSLC lens focal length on applied voltage. A previous model is improved by considering light absorption during the polymerization. Again we find qualitative agreement with the experimental data.

The optimal design over a broad spectral range of Liquid Crystal (LC) based Polarisation State Generators (PSG) and Polarisation State Analyzers (PSA), requires detailed knowledge of the spectral behaviour of the LCs. The full Mueller matrix measurement formalism based on the Eigenvalue Calibration Method, does in principle not require an exact modelling of the polarizing components, however, it is required that the condition number for both the PSG and the PSA is close to optimum over a wide spectral range. Two LC technologies are investigated here, Ferroelectric LC (FLC), and Liquid Crystal Variable Retarders (LCVR). In the case of a FLC based PSG, additional components, such as fixed retarders also need to be properly characterised in order for a proper broad spectral optimal design. These issues are here studied by characterizing the FLCs, the LCVRs and the fixed retarders with the help of a commercial visible Mueller matrix ellipsometer, and a polarizer-rotating sample-rotating analyzer near infra red set-up. The results are analyzed in the framework of the optimal condition number over a broad spectral range.

In this paper we present a new method of depolarization of light by using an electrically-controlled liquid crystal rotator in combination with a solid-state crystal with high birefringence. In general, anisotropic crystals depolarize partially temporary coherent light depending on their birefringence and path length of the light passing through them as well as on the azimuth of the optical beam i.e. the angle between the electric vector of the light wave and the birefringence axis of the crystal. Electrically-controlled liquid crystal rotator is a useful tool to introduce changes in azimuth and in the same to control depolarization of the light passing through the crystal placed behind the polarization rotator. Some experimental results of degree of polarization measurements for different light sources as a superluminescent diode and a laser diode are presented. Totally depolarization of light was achieved for the superluminescent diode and lithium niobiate crystal with the liquid crystal electrically controlled rotator.

Photopolymerization-induced phase separation of the constituent components in holographic polymer-dispersed liquid crystals (H-PDLCs) causes a huge variation of the refractive index for light as well as for neutrons. We demonstrated that H-PDLCs with the thickness of only 30 micrometers act as extremely efficient gratings for neutrons. The lightinduced refractive-index modulation for neutrons of about 10^-6 was observed, which is nearly two orders of magnitude larger than found in the best photo-neutron-refractive materials probed up to now. This makes H-PDLCs very promising candidate for fabricating neutron-optical devices.

We present a survey on organic composite and hybrid materials suitable for a new family of optical devices like thermo- and electro-tunable multilayer mirrors, microcavities and optical filters. The main component is a tunable and/or switchable Bragg grating. Two different classes of materials have been realized, characterized, and designed in form of prototype devices, namely a) polymer-liquid crystal composite and b) liquid crystal infiltrated porous silicon. Different geometries and patterns can be envisaged, leading to different physical properties and a large number of device potentialities, most of them yet unexplored. Obtained results look promising for both material families, especially for the porous silicon one, which includes an inherent immediate integration with the electronic fabric technology.

Novel liquid crystal-based integrated optical devices with >140GHz electrical tuning are presented. Initial results with Bragg wavelength tuning covering five 25GHz WDM channel spacing have been achieved with 170V (peak-to-peak) sinusoidal voltages applied across electro-patterned ITO-covered glass electrodes placed 60μm apart. These prototype devices were fabricated using direct UV grating writing, with an evanescent field coupling into a liquid crystal overlay through an etched window. Two distinct threshold conditions are observed, manifesting only during the increase of supply voltage and forming a hysteretic tuning curve. The secondary threshold which takes place at higher voltages has never been reported before. We believe these threshold points are related to the formation and bleaching of disclination lines. Geometric and effective index consideration could not explain the similar tuning behaviour displayed by both TE and TM polarised light.

Azobenzene-containing polymer, in which a change in birefringence can be induced by photoisomerization, is one of promising materials for holographic applications. To develop high-performance holographic materials using azobenzene polymers, it is necessary to prepare optically transparent thick films with capability of a large photoinduced change in refractive index to obtain high diffraction efficiency and fast response in the Bragg regime. A number of materials have been studied so far, but no attention has been paid to the combination of thick amorphous copolymers films containing photoresponsive and mesogenic groups in the side chain and polarization gratings formed in the Bragg regime. In this paper, we prepared optically transparent thick polymer films containing an azobenzene moiety with photosensitivity and a tolane moiety with high birefringence, and formed intensity and polarization gratings with linearly polarized beams and orthogonal circularly polarized beams, respectively. It was found that the nearly theoretically maximum diffraction efficiency was successfully achieved, and the recorded hologram could be erased thermally or photochemically. In addition, a large change in refractive index was induced in the polarization grating, and high diffraction efficiency (~90%) and quick response (920 ms) was realized simultaneously.

Holographic data pages were stored in a PVA/acrylamide photopolymer. This material is formed of acrylamide photopolymers which are considered interesting materials for recording holographic memories. A liquid crystal device was used to modify the object beam and store the data pages in the material. During the storage process, some parameters like exposure time, beam ratio and intensity were controlled to obtain high quality images after the reconstruction process. The bit error rate was calculated to determine what parameters improve the quality of the image.

Waveguiding in liquid crystals can be achieved by controlling the molecular orientation by means of external fields or by shaping the geometry of the substrates that contain the liquid crystal material. The creation of these waveguides in liquid crystals can also be achieved by using the optical nonlinear properties of the material. For a sufficient optical power (in the order of a few mW), the beam can induce its own optical waveguide. This is a selfinduced waveguide and the resulting beam is referred to as a soliton beam. In the last few years, the properties of these soliton beams have been studied thoroughly, revealing some interesting phenomena. In this article, simulations are reported on two common configurations in which solitons have been generated experimentally. The soliton beam, for certain configurations, displays an undulative behavior inside the cell, which may be used for large angle steering of the optical beam.

Optical spatio-temporal X-wave-like pattern formation is investigated in a voltage-controlled array of channel waveguides in nematic liquid crystals and in generic optically dispersive nonlocal nonlinear media as well. The nonlinear response of the system is governed by the spatio-temporal diffusion equation for the medium's response to the optical field, while the respective equation for the evolving light pulse may incorporate normal temporal dispersion. The associated discrete nonlinear Schr&diaero;dinger equation which governs the evolution of the temporal profiles of a discrete set of modes is derived and is studied numerically. The results are obtained via full numerical investigation of the array with beam propagation techniques.

Optical pattern formation in space and time in slab nematic liquid crystal cells is investigated. The nonlinear response of the system is governed by the spatiotemporal diffusion equation for the molecular reorientation while the respective coupled equation for the evolving light pulse may incorporate normal or anomalous temporal dispersion, for the sake of generality in potential applications. Continuous-wave background enhancement of pattern formation is demonstrated. Evolution of the optical field is studied numerically via the beam propagation technique.

The first experimental evidence of random laser action in a partially ordered, dye doped nematic liquid crystal with long-range dielectric tensor fluctuations is reported. Above a given pump power the fluorescence curve collapses and discrete sharp peaks emerge above the residual spontaneous emission spectrum. The spectral linewidth of these emission peaks is narrow banded, typically around 0.5nm. The unexpected surviving of interference effects in recurrent multiple scattering of the emitted photons provide the required optical feedback for lasing in nematic liquid crystalline materials. Light waves coherent backscattering in orientationally ordered nematics manifests a weak localization, strongly supporting the diffusive laser action phenomenon in the presence of a gain medium. Unlike distributed feedback mirror-less laser, this system can be considered as a cavity-less microlaser where the disorder unexpectedly plays the most important role, behaving as randomly distributed feedback laser. The far field spatial distribution of the emission intensity shows a huge number of bright tiny spots spatially overlapped and the intensity of each pulse strongly fluctuates in time and space. Here, we report the main characteristics of this novel systems for various confinement geometries and under different conditions. A brief presentation of boundary-less systems such as free standing and freely suspended dye doped nematic films and droplets is also introduced, revealing unique emission features because of the complete absence of confining borders.

In this work, we examine the phenomenon of random lasing from the smectic A liquid crystal phase. We summarise our results to date on random lasing from the smectic A phase including the ability to control the output from the sample using applied electric fields. In addition, diffuse random lasing is demonstrated from the electrohydrodynamic instabilities of a smectic A liquid crystal phase that has been doped with a low concentration of ionic impurities. Using a siloxane-based liquid crystal doped with ionic impurities and a laser dye, nonresonant random laser emission is observed from the highly scattering texture of the smectic A phase which is stable in zero-field. With the application of a low frequency alternating current electric field, turbulence is induced due to motion of the ions. This is accompanied by a decrease in the emission linewidth and an increase in the intensity of the laser emission. The benefit in this case is that a field is not required to maintain the texture as the scattering and homeotropic states are both stable in zero field. This offers a lower power consumption alternative to the electric-field induced static scattering sample.

Kinetics of the photoexcitation of azo-dye doped liquid crystals (ADDLCs) is observed by the improved attenuated total reflection leading a pump light into a coupling prism, namely pumped ATR (PATR) experiment. The technique of ATR could be applied on an LC cell based on that the guide mode is overcome by the usage of an isotropic surface, which is also a usual way to observe the reaction involving the adsorption effect. The evanescent wave of the pump light induces the photoexcitation of azo dye at the limited effective depth, and the evanescent wave of the probe light detects the dynamic behavior in real time. The time response of the photoexcitation in ADDLCs in the pumped ATR experiment is less than 2ms and believed the reaction occur in the local region of 100-nm. This result is a witness of that the reaction in this local region is free of the influence of the elastic continuum of the whole LC cell. With the help of the local sensitivity and local disturbance, the detailed reactions during the photoexcitation process are clearly observed and the dynamics equation are expressed to illustrate the oscillation phenomena of LC directors as the pump light irradiates on this region.

Photosensitive, liquid crystalline (LC) polymers were prepared by in-bulk polymerization of phytomonomers such as cinnamic acid derivatives. The p-coumaric acid (4HCA) homopolymer showed a thermotropic LC phase where a photoreaction of [2+2] cycloaddition occurred by ultraviolet irradiation. LC phase was exhibited only in a low molecular weight state but the polymer was too brittle to materialize. Then we copolymerized 4HCA with multifunctional cinnamate, 3,4 dihydroxycinnamic acid (caffeic acid; DHCA), to prepare the hyperbranching architecture. Many branches increased the apparent size of the polymer chain but kept the low number-average molecular weight. P(4HCA-co-DHCA)s showed high performances which may be attained through the entanglement by in-bulk formation of hyperbranching, rigid structures. P(4HCA-co-DHCA)s showed a smooth hydrolysis, an in-soil degradation and a photoreaction cross-linking from conjugated cinnamate esters to aliphatic esters. The change in photoconversion degree tuned the polymer performance and chain hydrolysis.

This investigation researches and developes two spatial filters based on dye-doped liquid crystal films. One is made with a dye-doped liquid crystal (DDLC) film, and is polarization controllable. The other is transflective, and is fabricated with an azo dye doped cholesteric liquid crystal (DDCLC) film. The fabrication of the former type relies on the fact that the various intensities of the diffracted orders are responsible for various changes of the polarization state induced by the photo-aligned DDLC film. Particular spatial orders in the Fourier optical signal process can be filtered using an analyzer placed behind the sample by controlling the polarization state of the diffracted orders. The latter is based on the photoisomerization effect in a DDCLC film with a concomitant lowering of phase transition temperature from a cholesteric to an isotropic phase (T_Ch-I). The fabrication relies on the fact that the various intensities of the diffracted orders are responsible for various degree of transparency induced by the photoisomerized DDCLC film. Particular spatial orders in the Fourier optical signal process can be filtered to trans- or reflect- part at the same time. Simulations are also performed for the two-type spatial filters, and the results agree closely with experimental data.

We have fabricated a series of polymer stabilized chiral nematic test cells for use as flexoelectro-optic devices. The devices fabricated were based on commercial chiral nematic mixtures which were polymer stabilized so as to enhance the uniformity and stability of the uniform lying helix texture in the cells. During fabrication and test procedures a series of unusual scattering states have been observed within the devices at different viewing angles. The observations made so far indicate that the properties of the scattering state lies somewhere between the focal conic texture and the Grandjean or planar texture and that the devices exhibit both a helical pitch selective reflection and scattering effect. What is even more dramatic is that the wavelength selectivity of the scattering effect can be tuned by an applied field. In addition, we show that it is possible to achieve good uniform lying helix textures from such devices. Moreover, we show that in certain cases the spontaneous alignment of the helix in the plane of the device opens up the possibility of a new mode of switching.

The simplified elasticity of a B₂ - phase is based on elastic free energy density of biaxial nematic liquid crystal with four elastic constants. No layer deformations are supposed. Simplest solutions describing twist deformations in one dimension which can be induced by an external influence in synclinic and anticlinic, ferroelectric and antiferroelectric B₂ structures were given as examples of the use of the proposed simplified elastic free energy density.

We report an efficient method for extraction of anionic polysaccharides (PS) from cyanobacteria, Aphanothece sacrum; we used a hot alkaline solution (0.01 N NaOH) as an elution solvent in the first step of the extraction and isopropanol as a precipitation solvent in the last step. Thin fibers of PS were obtained at a high yield (50-80 % to the weight of the raw cyanobacterial sample). The spectroscopy and elemental analyses indicated the PS contains fucose, uronic acids (14.2 % by a carbazole-sulfuric acid method), a sugar unit containing amides. The solution of PS with a concentration of 1 wt% showed a very high viscosity (80 000cps) implying a high molecular weight, and a strong macroscopic birefringence with a texture typical of nematic liquid crystals was confirmed by crossed-polarizing microscopy (more than 0.5 wt%). The PS from A. sacrum may form a special structure rigid-rod enough to show LC phase and macroscopic birefringence.

Nowadays Liquid Crystal Displays (LCD) takes the very important place among different visualization devices. It's are used in many standard applications such as computer or video screens. In May 2006, 100" LCD TV monitor had been shown by LG. But beside of this main direction of display development, very interesting - because of insignificant electro-magnetic disturbances - is the possibility of it's applications in motorization and aviation. An example of it can be a glass cockpit of U2 , Boeing 777 or many different car dashboards. On this field beside LCD we have now many another display technologies, but interesting for us are 3 of them: FEDs (Field Emission Displays), OLEDs (Organic Light Emitting Diode), PLEDs (Polymer Light Emitting Diode). The leading position of LCD is a result of LCD unique advantages of flat form, weight, power consumption, and reliability, higher (than CRT) luminance, luminance uniformity, sunlight readability, wide dimming range, fault tolerance and a large active display area with a small border. The basis of starting our investigation was the comparison of passive LCD and the other technology, which can be theoretically used on motorization and aviation field. The following parameters are compared: contrast ratio, luminance level, temperature stability, life-time, operating temperature range, color performance, and depth, viewing cone, technology maturity, availability and cost. In our work an analysis of Liquid Crystal Displays used in specific applications is done. The possibilities of the applications such a display under high lighting level are presented. The presented results of this analysis are obtained from computer program worked by authors, which makes it possible to calculate the optical parameters of transmissive and reflective LCD working in quasi-real conditions. The base assumption of this program are shown. This program calculate the transmission and reflection coefficient of a display taking into account the interference phenomena occurring into the display, different direction of ordinary and extraordinary wave vectors and its polarization vector, dispersion phenomena of refractive indices and absorption coefficient of the display layers.

In this paper we analyze the performance of a fibre Bragg grating (FBG) interrogation system based on a liquid crystal tunable filter (LCTF), which acts as a channel dropper for multiple FBG sensors coupled to a simple all-fibre ratiometric wavelength measurement scheme in which a macrobending single-mode fibre is utilized as an edge filter. We present a model of the proposed interrogation scheme and analyse the optimum design parameters for the LCTF. From the model, the optimum ratio between the number of FBG sensors and the tunable filter bandpass can be found. Experimental results for the wavelength interrogation system are presented to validate the theoretical predictions. The model should be also suitable for similar interrogation systems using other forms of tunable bandpass filters.

We present the characterization and the optimization of the phase and amplitude modulation of a liquid crystal display (LCD) applied to holographic data storage. We discuss the main LCD modulation regimes demanded in the literature in the application to holographic memories: binary amplitude, binary phase and hybrid ternary modulation (HTM). We show how to obtain optimally these modulation regimes with a LCD. In our strategy it is essential the accuracy demonstrated by the model we use to describe the modulation properties of the LCD. This accuracy allows for a reliable computer search of the configurations enabling for an optimum LCD complex amplitude modulation. Results are given for the calibration of a commercial LCD. Optimum configurations close to the ideal for each of the modulation regimes are also obtained and the values of the various parameters characterizing the quality of these configurations are provided. We have also analyzed the performance of these configurations to perform the Fourier transform (FT) of a binary data page. We see that the optimum configurations obtained for the binary phase and the HTM regimes produce a homogeneous distribution of the energy in the Fourier plane with no DC peak.

We propose the use of low cost alphanumeric liquid crystal displays (LCD) not only as an educational tool, to introduce students the insights of the electrooptic performance of liquid crystals, but also as a device able to be used in research to validate models describing the performance of LCDs and to be used in applications requiring monopixel optical modulation. High resolution LCDs have usually focused the research attention because of their capabilities to be used as SLMs. However low cost LCDs with a low number of pixels and directly addressed, such as segmented alphanumeric displays, may also be appealing devices. We show the characterization of one of the segments. The model applied had previously been demonstrated with high resolution LCDs, which are thin LCDs. The segmented LCD is found to be a thick LCD, thus, allowing us to verify the validity of the model in another range of conditions. Furthermore, we show that low cost alphanumeric LCDs can be used as monopixel LCDs. This is interesting since there are a number of applications, as in polarimetry or in interferometry, where monopixel LCDs may proof necessary. We optimize the modulation of the LCD both in the transmissive and in the reflective geometry to obtain amplitude-only and phase-only modulations which are useful for a number of applications.

Molecular stacking of discotic liquid crystals through self-assembly on solid substrates is observed. During the molecular stacking, thermal conditions can strongly affect the arrangement of discotic molecules. For ordered molecular stacking of discotic molecules slow and smooth variation in temperature is necessary. By carefully controlling cooling rate below 0.3°C min^-1, orientational molecular stacking of discotic molecules and uniaxial aggregation of discotic columns can be produced on planar glass and indium-tin-oxide surfaces. If the temperature of discotic compound drops too fast, ordered molecular stacking may be destroyed by thermal turbulence due to fast change of temperature in adjacent regions.

The wavelength-dependent Jones matrix representation of a twisted-nematic liquid crystal (TN-LC) cell contains four independent parameters. The absolute values of these parameters and two mutual sign relationships can be determined from comparatively simple transmission measurements of the TN-LC cells sandwiched between two rotatable polarizers. The physical parameters of the cell (twist angle α, director orientation ψ, birefringence β) can be retrieved if the Jones matrix is known for more than one wavelength. We have measured the Jones matrices of the TN-LC cells of a translucent Sony LCX-016 microdisplay for six wavelengths ranging from 488nm to 1064nm and determined the physical parameters of the cell. We have also measured the Jones matrices for one wavelength for a number of applied voltages. These experimental results show that it is not sufficiently exact to calculate the Jones matrix from the known physical parameters of the cell assuming a voltage-dependent birefringence only. We attribute the deviations from the theoretical model to edge effects which are not taken into account. The direct experimental determination of the Jones matrix components is therefore preferable and permits a more accurate simulation of the TN-LC microdisplay in experimental configurations involving other polarization-dependent optical components.

In the last years, many efforts have been devoted to use electrically addressed spatial light modulators (SLMs) in Adaptative Optics. In this contribution we have optimized a low-cost SLM based on a liquid crystal (LC) device for the compensation of eye aberrations. This kind of devices is seldom used in ophtalmic applications due to the relatively low dynamic range of the phase retardation that can be introduced at each pixel. Here, we have optimized the phase modulation response of a commercial twisted nematic liquid crystal display (TNLCD) by means of a polarimetric arrangement that includes retarder plates and polarizers. Furthermore, we describe an efficient four-level phase encoding scheme that allows us to use these conventional SLMs for the compensation of optical aberrations as those typically found in human eyes. For obtaining experimental compensation results we have used artificial aberrated eyes simulated with refractive phase plates. This proof-of-concept is the first step to develop a low-cost real-time system for the correction of eye aberrations.

In this contribution we describe a method for achieving a phase-only modulation regime with an off-the-shelf twisted nematic liquid crystal display (TNLCD). The keystone of this procedure involves illumination of an addressed TNLCD with circularly polarized light. The analysis of the distribution of the output polarization states in the S₁-S₂ plane as the applied voltage is changed suggests a simple way to optimize the liquid crystal phase response. For this purpose, a properly oriented quarter-wave plate followed by an analyzer is used behind the TNLCD. Laboratory results for a commercial display are presented. Our experiments show a phase modulation depth of 240º for a wavelength of 514 nm with a residual intensity variation lower than 4%.

The field of ferroelectric liquid crystals (FLCs) is one of the most fascinating aspects of the Science of Materials for their interesting electro-optic applications. Among different chemical and physical properties those related to the molecular dynamics are very stimulating due to the relationship between molecular motions and macroscopic response to external fields, such as electric and magnetic ones. In this work, the molecular dynamics of a ferroelectric smectogen, namely the (S)-2-methylbutyl-[4'-(4"-heptyloxyphenyl)-benzoyl-4-oxy-(S)-2-((S)-2')-benzoyl)-propionyl)]-propionate (ZLL 7/*) has been investigated by means of ²H NMR and dielectric relaxation techniques. The first method allows us to get information on the molecular motions in the fast motion regime, in particular the diffusion reorientational motions of the whole molecule, as well as of the internal motions affecting the phenyl and biphenyl fragments. The second technique, which covers the slow motion regime, has been used to detect collective motions and fluctuation modes. This study allows us to have a complete idea of molecular motions in the different smectic phases formed by the ZLL 7/* mesogens, in particular the paraelectric smectic A (SmA), the ferroelectric smectic C* (SmC*), the antiferroelectric smectic C*_A (SmC*_A) and the re-entrant ferroelectric smectic C* (SmC*_r) phases. This last phase has been investigated for the first time in this work, from the point of view of the dynamic behaviour. All results will be discussed in the framework of the molecular dynamics of ferroelectric liquid crystals, reported in the literature so far.

In this paper we investigate a dye guest-host liquid crystal device based upon the bistable electro-optic effect in the smectic A phase. The dye used is a pentamethyldisiloxane-grafted disperse red 1 moiety; the liquid crystal host is an organosiloxane liquid crystal based upon cyanobiphenyl. It is shown that extremely high dye solubilities can be achieved e.g. greater than 38 % w/w, without dye separation or adverse effect on device electro-optic properties. The typical solubility limit in liquid crystals is of the order of several percent. It is proposed that the beneficial degree of dye accommodation is the result of microsegregation of constituent moieties into siloxane, alkyl chain and cyanobiphenyl core/chromophore regions.

We have studied several compounds of non-chiral mesogens composed of symmetrically and non-symmetrically bent-shaped molecular core with thermally stable ester linkages and laterally substituted by methoxy group. Recently, mesomorphic properties have been described and the SmCP (B₂) phase has been identified in a wide temperature range below the isotropic phase. Additionally, symmetrical bent-shaped mesogens exhibit the B₇ phase on cooling from the B₂ phase. Herein we concentrated on nonlinear optical properties in the observed mesophases. Second harmonic generation (SHG) supports the idea that the ground state of the B₂ phase in studied bent-shaped mesogens has antiferroelectric character and demonstrates the switching from antiferroelectric to ferroelectric state under applied electric field.

The differences and similarities between the flexoelectro-optic effect in chiral nematic liquid crystals in the uniform lying helix geometry and the standing helix geometry have been considered. We present results on the response times measured for a bimesogenic liquid crystal in the uniform lying helix and compare this with the response observed for the standing helix geometry for similar field strengths. For the standing helix geometry an electric field is applied perpendicular to the helix axis by means of parallel gold deposited electrodes which were coated on the surface of one substrate. These electrodes provide a uniform electric field across the sample. From theoretical simulations we find that the response for the two geometries should be identical although, experimentally, some differences are observed. Furthermore, solutions to the governing equations reveal that, unlike the uniform lying helix geometry, the direction of the applied field relative to the alignment of the liquid crystal at the surface boundaries is of importance to the overall response. These results are compared with experimental observations.

The origin of optical diffraction in holographic polymer-dispersed liquid crystal (H-PDLC) transmission gratings was investigated by optical two beam-coupling analysis based on the linear phase-shift technique. Gratings with the pitch of 1 micrometer and the thickness of 50 micrometers were fabricated from a UV curable mixture of commercially available constituents. Photopolymerization in the interference field of two laser beams produces not only a periodic variation of the refractive index, but also a periodic modulation of optical extinction due to light scattering. Both of them contribute to the diffraction efficiency of the gratings. The magnitudes and relative phases of the two contributions were measured as a function of a recording time of the grating and as a function of an applied external electric field. During the initial stage of the grating formation phase modulation is predominant, while at longer exposures both contributions have the same order of magnitude. They are phase shifted with respect to each other for around π/2. Application of an external electric field causes a strong decrease of the amplitude modulation, while phase modulation is much less perturbed.