Donor-acceptor structures have recently gained great popularity for the design of low band gap polymeric organic semiconductors. Presented here is a first systematic study of organic semiconductors based on columnar liquid crystals that consist of discotic and board-shaped donor-acceptor structures. The discotic benzotristhiophenetricarboxamide and hexaphenyldiquinoxalinophenazine derivatives form hexagonal columnar mesophases over wide temperature ranges while the board-shaped tetraphenylquinoxalinophenanthrophenazine derivative displays rectangular and hexagonal columnar mesophases. All compounds are designed to preferentially conduct electrons and not holes because the central acceptor parts, which are the sole contributors to the unoccupied frontier orbitals, show strong intermolecular electronic interactions within columnar stacks whereas the donor parts at the periphery of the cores, the sole contributors to the occupied frontier orbitals, are too far apart to provide sufficient electronic interactions. The absence of hole conduction is confirmed by charge carrier mobility measurements based on time-resolved microwave conductivity and time-of-flight methods that reveal intrinsic electron mobility values of about 10^-2 cm² V^-1 s^-1. The board-shaped compound is also highly fluorescent not only in solution but also in its mesophases. Interstingly, the fluorescence quantum yield of its mesophases reversibly increases with decreasing temperature, which is reasoned with changes in molecular mobility and intracolumnar packing within columnar stacks.

In confined blue phases numerous quasi 2D disclination networks ranging from rings to double helices can be stable. We have recently demonstrated how such networks act as arrays of trapping sites that can lead to easy assembling of colloidal particles in complex 2D lattice structures. In this short overview we summarize main results of our Landau - de Gennes modeling combined with topology that was proven to be useful in bulk blue phase colloids. Effects of confinement, particle anchoring, and particle sizes that can range from micron to nanometre scale are presented. Quasi 2D colloidal crystals that can be easily manipulated by external stimuli via affecting liquid crystal and/or colloidal particles are expected to have possible photonic applications.

We demonstrate a new material composed of isotropic liquid crystal (ILC) blended with semiconductor nanoparticles, which could result in a novel high-speed, multiple-notch broadband passive optical switch to selectively discriminate bands of electromagnetic radiation in intelligence, surveillance, or reconnaissance systems. The new material has been demonstrated high nonlinear 3rd order optical Kerr coefficients (light-induced refractive index change, n₂) exceeding 100 times of classic nonlinear material CS₂ with n₂ = 1.2E-11 esu. Details of fabrication and experimental results are presented.

Since 10 years spatial optical solitons are studied for application in optical steering and routing. We propose here another potential use of solitons: a localized spectral probe in colloids. We show the feasibility of this concept by collecting the fluorescence signal escaping from in a cell filled with a mixture of liquid crystal (5CB) and dye (quinizarin), excited either by a spatial soliton obtained by thermal self-focusing or by a freely propagating beam. We find that the fluorescence signal collected at the output of the soliton is larger than the one collected on the same optical path in the linear regime. A model based on waveguide considerations confirms such a behavior. Finally we discuss how polystyrene particles can be detected in colloids by using spatial solitons.

This paper demonstrates formation of surface relief (SR) gratings and crossed SR gratings with molecularly oriented structure using photo-cross-linkable liquid crystalline copolymer films by means of holographic exposure of 325 nm He- Cd laser beams combined with linearly polarized (LP) UV light. For the intensity holography using He-Cd laser, SR gratings were formed after annealing the exposed films, where the molecular migration from the lower to the higherexposed region occurred. The reorientational part and SR height were dependent on degree of the photoreaction. When the exposure doses were low, molecular reorientation at the convex region was generated. In contrast, higher exposing doses resulted in the molecular reorientation at the concave area. The resulting gratings showed polarization sensitivity for diffraction efficiencies of the probe light beam according to the molecularly reorientation direction. Furthermore, multi-holographic exposure yielded crossed SR gratings with reoriented structure according the polarization direction of He-Cd laser beams, which exhibited multi-functional diffractions. Furthermore, when combining the multi-holographic exposure and the unidirectional LPUV light exposure, crossed SR grating with multi-directionally oriented film structure was generated., where the whole area was reoriented.

It is demonstrated that the photoinduced gliding of the easy axis for nematics doped with various azo dyes on rubbed polyimide involves the formation of a second easy axis on the polyimide surface. While some azo dyes, such as disperse orange 3, do not exhibit large surface induced nonlinear effects, other dyes, such as methyl red, do. The amount of reorientation of the easy axis on rubbed polyimide is determined by the relative anchoring strengths of the easy axis formed from adsorbed dye and that formed from rubbing. One question of interest is what is the source of the anchoring strength? In this paper, we discuss the formation of easy axes via the photo-induced adsorption of azo dye. We will compare the anchoring strengths between dyed nematic liquid crystals and the easy axes formed by photoinduced adsorption of three isomers of the methyl red azo dye, ortho, meta, and para, as well as disperse orange 3. We will also discuss the impact of the carboxyl group position in the dye molecule on the anchoring strength.

Liquid crystal (LC) based sensors have been investigated over the past decades in an effort to develop low cost, portable, field-deployable, highly selective chemical and biological sensors. Due to the collective behavior and the highly anisotropic properties of liquid crystal molecules, detection of very low levels (ppbs) of chemical and biological agents is possible. However, present LC sensors rely on a threshold concentration of a targeted analyte to cause a surface driven molecular reorientation of the LC molecules. In this paper, we present techniques using capacitive transduction to monitor anchoring energy that improve sensitivity of LC based sensors.

We discuss the concept of infrared cloaking using nanosphere dispersed liquid crystal (NDLC) matematerial in cylindrical geometry for TM polarization. The system consists of six layers of NDLC with different values of ordinary refractive index. Finite element calculations (COMSOL Multiphysics) show that scattering from the hidden object is strongly limited in the presence of the cloak.

Nanocomposites composed of a self prepared Ferroelectric Liquid Crystalline (FLC) matrix and different nanomaterials show pronounced reduction of important parameters like spontaneous polarization, switching time but no change of the tilt angle. As a typical subject silver nanoparticles where characterized. A pronounced increase of resistivity where described by comparing the pure FLC mixture with properties of FLC nanocomposites. Ion capturing due to silver particles has been discussed. Photoluminescence originated by the terphenyl compound and enhanced due to the Silver Surface Plasmon Resonance has been described.

We report on the fabrication and characterization of a micro periodic structure realized in soft-composite materials containing metallic nanoparticles. The particles are used to infiltrate a passive polymer template realized by combining a holographic curing setup and a microfluidic etching process. In other experiments, small amounts of nanoparticles are dissolved in the original mixture utilized for the realization of polymer-liquid-crystal-polymer-slices gratings (POLICRYPS); this enables to fabricate POLICRYPS-like structures showing novel electromagnetic properties. Obtained structures are characterized in term of impinging probe polarization in the UV/visible range. Correlation between the optical response and external perturbations (electric field, temperature) is also reported. These first attempts are oriented to the fabrication of devices with tunable metamaterial properties.

Photo-responsive multi-bilayered film consisting of azobenzene polymer liquid crystals (PAzo) and polyvinylalcohol (PVA) was prepared on a glass substrate by spin coating of the polymer solutions alternately. The reflectivity of the multi-bilayered film disappeared by annealing at 80 °C. The disappearance of the reflection by the annealing was related to the thermal out-of-plane molecular orientation of PAzo even in the multi-bilayered film, leading to a very small difference in refractive indices between PAzo and PVA. The reflectance of the multi-bilayered film was increased again by UV irradiation because of the transformation from the out-of-plane orientation to the in-plane random orientation, resulting in the restoration of difference in the refractive indices. In this way, the on-off switching of the reflection was achieved by combination of the thermally spontaneous out-of-plane molecular orientation and following photoisomerization of PAzo comprising the multi-bilayered film.

By replacing common buffers with anisotropic liquids in microfluidics, an enhanced range of optofluidic functionalities is enabled. Such an anisotropic liquid is nematic liquid crystals (NLC), which exhibits optical properties that can be tuned by optical, electrical or mechanical fields, such as flow. We demonstrate an optofluidic modulator based on direct flow of nematic liquid crystals in microfluidic channels. We discuss this optofluidic paradigm both under steady state conditions, and under flow. Rapid pulsatile flows are detrimental towards more compact and ultra-fast devices. These were enabled via peristaltic pumps, demonstrating liquid crystal modulators operating above the limit of 3 kHz. We discuss the latter results, but also assess the feasibility of performing ultra-fast optics and additional functionalities for on- and off-chip imaging.

In this paper we demonstrate laser emission from emulsion-based polymer dispersed liquid crystals. Such lasers can be easily formed on single substrates with no alignment layers. Remarkably, it is shown that there can exist two radically different laser emission profiles, namely, photonic band-edge lasing and non-resonant random lasing. The emission is controlled by simple changes in the emulsification procedure. Low mixing speeds generate larger droplets that favor photonic band edge lasing with the requisite helical alignment produced by film shrinkage. Higher mixing speeds generate small droplets, which facilitate random lasing by a non-resonant scattering feedback process. Lasing thresholds and linewidth data are presented showing the potential of controllable linewidth lasing sources. Sequential and stacked layers demonstrate the possibility of achieving complex, simultaneous multi-wavelength and "white-light" laser output from a wide variety of substrates including glass, metallic, paper and flexible plastic.

Direct synchrotron x-ray scattering measurements of the orientational order parameter, S, corresponding to the siloxane and hydrocarbon parts of the molecule, smectic layer spacing, and director tilt angle with respect to the smectic-C (SmC) layer normal in the de Vries smectics-A (SmA) and SmC phases of two organosiloxane mesogens are reported. The results reveal that (i) the SmC (tilt) order parameter exponent β = 0.26 ± 0.01 for 2nd order SmA-SmC transition in excellent agreement with the tricritical behavior, (ii) the siloxane and hydrocarbon parts of the molecules are segregated and oriented parallel to the director with different degree of orientational order, and (iii) thermal evolution of the effective molecular length is different in the two phases contrary to the conventional wisdom.

Optical elements with spatially varying transmission are required for laser engineering and imaging systems. Although refractive systems can transform the Gaussian energy distribution of a laser beam into a "top-hat" distribution, they lack the versatility to produce the more-complex and precise intensity distributions required for high-peak-power laser systems such as the OMEGA and OMEGA EP Laser Systems at the University of Rochester's Laboratory for Laser Energetics and the National Ignition Facility at Lawrence Livermore National Laboratory. Previously, distributions of opaque metal pixels on a transparent glass substrate have been used for such beam-shaping efforts, but laser-damage thresholds of the order of 200-700 mJ/cm² in the nanosecond regime limit their applicability. By applying photolithographic patterning of coumarin-based photoalignment layers using polarized UV light to generate spatially varying molecular orientation in a nematic liquid crystal (LC) device, we have developed and demonstrated highresolution beam-shaper devices for such high-peak-power laser applications in the near-IR region. Operating at 1054 nm, these devices demonstrated a contrast ratio ranging from 280:1 to 540:1, a pixel size of 10 m with an interpixel resolution of 1.7 μm, and laser-damage resistance ranging from 20 to 40 J/cm² at 1054 nm (1-ns pulse width) using a 10-μm layer of commercially available nematic LC materials. Coupled with the ability to generate an almost infinite variety of binary and gray-scale apodization and beam-shaping profiles by the photoalignment process, the high laser-damage threshold of these devices makes them attractive and useful tools for a multitude of laser applications.

Liquid crystal (LC) gratings consisting of twisted nematic orientation domains have been demonstrated. The LC cells exhibited bistability in its LC molecular orientation behavior, which can be divided into two types of twist orientations; that is, ±90° or ±180° twist orientation states. The former can be produced by the nematic-isotropic phase transition (heating and cooling the LC cell). The latter is constantly obtained by a suitable voltage application. Based on this experimental result, switching scheme between these two orientation states were proposed. Furthermore, diffraction properties of the LC cell as a grating and the possibility as LC bistable grating were discussed.

The study of band-edge lasing from dye-doped chiral nematic liquid crystals has thus far been largely restricted to visible wavelengths. In this paper, a wide range of commercially available laser dyes are examined for their suitability as infrared emitters within a chiral nematic host. Problems such as poor solubility and reduced quantum efficiencies are overcome, and successful band-edge lasing is demonstrated within the range of 735-850 nm, using the dyes LD800, HITC-P and DOTC-P. This paper also reports on progress towards widely tuneable liquid crystal lasers, capable of emission in the region 460- 850 nm. Key to this is the use of common pump source, capable of simultaneously exciting all of the dyes (both infrared and visible) that are present within the system. Towards this aim, we successfully demonstrate near-infrared lasing (800 nm) facilitated by Förster energy transfer between the visible dye DCM, and the infra-red dye LD800, enabling pump wavelengths anywhere between 420 and 532 nm to be used. These results demonstrate that small and low-cost tuneable visible to near-infrared laser sources are achievable, using a single common pump source. Such devices are envisaged to have wide-ranging applications including medical imaging (including optical coherence tomography), point-of-care optical medical diagnostics (such as flow cytometry), telecommunications, and optical signatures for security coatings.

Nematic liquid crystals can switch the orientation of the director under influence of an electric field. Liquid crystals can be combined with waveguides in many different ways: the liquid crystal can be in the core, in the cladding or in both. In the recent past liquid crystals have been combined with glass fibers and with silicon-on-insulator waveguides. Important progress has been achieved in the modeling of liquid crystals near inhomogeneous boundaries and the modeling of optical waveguides with anisotropic materials. This paper discusses these recent advancements and illustrates how waveguides with voltage tuned cutoff may be designed.

We report on the realization and characterization of a polymeric template sculptured in photosensitive material, on a chemical inert surface. The structure is devoted to micro/nanoconfinement and stabilization of a wide range of organic and nano-particle components with selfarrangement properties at the nanoscale [1]. High quality morphology of a polymeric, micropatterned, array is obtained by combining a, nano-precision level, optical holographic setup and a multi-step chemico-physical process. The "universal" template represents the basic platform to be filled with different organic materials, which can also include metallic nano-particles. The long range self-organization is induced without making use of any kind of surface chemistry. Due to their capability of exhibiting self organization, light responsive Liquid Crystals (LC) [2] and short pitch Cholesterics LC [3] have been exploited, and experimental studies have been carried out in order to investigate the photo-optical and elecro-optical response of obtained composite structures for the realization of photonic devices. Finally, the possibility of including metallic nano-particles has been also investigated, with the aim of inducing a "metamaterial" behavior of the realized structure.

Design and synthesis of a bent-core mesogen possessing the achiral ferroelectric SmAP_F phase is reported. The design approach is based upon the discovery of Sadashiva and Reddy, et al. that bent-core mesogens possessing only one tail gave biaxial SmA phases shown to be antiferroelectric (SmAP_A). The SmAP_A phase shows antiferroelectric layer stacking with synclinic layer interfaces, as expected based upon typical behavior seen in most bent-core mesogens. In order to obtain the target ferroelectric phase, several tails known to allow the formation of anticlinic layer interfaces were incorporated into the basic Sadashiva/Reddy structure. These tails are thought to suppress out of layer fluctuations, thereby removing the strong entropically driven tendency for synclinic layer interfaces, and allowing formation of anticlinic layer stacking driven by a more subtle, and unknown, factor in the free energy of the system. In the event, the tricarbosilane-terminated alkoxy tail proved effective, providing the first known low molar mass SmAP_F material.

A polarization beam splitter and tunable retarders were combined into a single element by using Si pentaprisms and liquid crystal (LC). An LC layer that was sandwiched between the two pentaprisms acted as a polarization beam splitter that reflected s-polarized light and transmitted p-polarized light. The other two LC layers that were attached to the outer surfaces of the pentaprisms acted as tunable retarders; i.e., they changed the polarization states of the reflected and transmitted light beams. When these beams were reflected back to the former LC layer (the beam splitter), wavelength selection took place owing to the wavelength dependence of the polarization state. This performance was confirmed by optical experiments in the infrared region.

Large-area glass facades are widely spread in contemporary architecture. They meet demands for natural light illumination of rooms and satisfy esthetic requirements of modern architecture. However, larger glass facades increase transfer of energy into the building. Since this has to be compensated by the intense use of air conditioning, modulation of the energy passing through the glazing is essential. The authors have been developing a corresponding system. It consists of a modified twisted nematic (TN) liquid crystal (LC) cell which is embedded in a double glazing. Since a conventional outside film polarizer is susceptible to heat, the authors substituted this component for an inside coatable polarizer. Long term outdoor weathering tests demonstrated that the concept is viable. Part of the current research is the integration of the TN LC cell into double-glazing. A further demand for such a system is a cost-efficient manufacturing process. It has been investigated to use the coatable polarizer at the same time as an alignment layer for the liquid crystal. Aluminum zinc oxide (AZO) is to be used for the electrode material substituting conventionally used indium tin oxide (ITO) which is expensive. Currently the authors are looking into the coating process for the inside polarizer.

In this paper, we demonstrated two types of novel displays: light waveguide display and arrayed waveguide display. In the light waveguide display, light emitted from commercial LEDs propagates in a glass planar waveguide with a polymer dispersed liquid crystal (PDLC) upper layer. When the voltage is off, light would be partially scattered via PDLC and that pixel becomes bright and opaque. When the voltage is on, PDLC is properly aligned so that light would not be scattered, showing a transparent pixel. By electrically controlling the PDLC, a counting seven-segment pattern is clearly displayed. Arrayed waveguide display had been theoretically proposed to be a full color display with high light-use efficiency. Light of three primary colors from an emitter array could be coupled into a waveguide array upon which is the PDLC switches. In our design, the core of the waveguide is made of SU-8 photoresist while the side and under cladding is polymethyl methacrylate (PMMA). The upper cladding PDLC is controlled pixel by pixel so that the light can be selectively scattered. Both displays were carefully patterned and packaged with their driving circuits. Furthermore, since most materials are transparent and low weight, the displays are applicable for see-through headmounted displays.

We report tunable single-mode lasing with an improved slope efficiency from a cholesteric liquid crystal (ChLC) cavity with a three-layered structure. The device consists of one photopolymerized ChLC layer with a wide reflection band, another ChLC layer with a notch reflection band and a Rhodamine-6G-doped ionic liquid layer acting as the gain medium. Single-mode lasing can be obtained in this device structure because the ChLC layer with the notch reflection band strongly reflects only one of the Fabry-Perot cavity modes. Tuning of the lasing wavelength is achieved by tuning the reflection band of the notch ChLC. The device showed a maximum slope efficiency of 16%, which was found to be approximately 1.5 times larger than that of ordinary ChLC lasers doped with the pyrromethene 597 laser dye.

In this paper, we first investigated the degradation of the performance of liquid crystals display (LCD) units after driving by a DC bias. Missed segments were found in the test LCD units. By carefully investigating the alignment layer and ITO layer separately, an explanation of the ITO failure is proposed: voltages applied to the liquid crystal cell causes accumulation of charged impurities or ions, resulting in a decomposition reaction of ITO in regions where segment and common planes overlap and there are scratches on the PI layer. Consequent, missing segments in the corresponding regions is generated. To prevent this kind of degradation, we studied the correlation between the alignment layer and ions adsorption. Both organic alignment layer (PI2555, SE1211, and FPI) and inorganic alignment layer (SiOx, SiO2, and Al203) are analyzed by residual DC and voltage holding ratio measurement. A correlation between ion adsorption and the dielectric constant of the alignment layer is demonstrated. Alignment layer with a smaller dielectric constant is good for reducing ion adsorption in the alignment layer. Alignment layer with a bigger dielectric constant is good for reducing mobile ions in the LC device, and could be used in non-active areas of the liquid crystal device to remove ion from the active area.

When left and right circularly polarized beams of light from a pump laser interfere in a nematic liquid crystal doped with azo dye, a polarization twisted nematic (PTN) grating is formed in the sample. The same is not true when linearly polarized light interferes, regardless of the polarization. For circularly polarized light, the easy axis is rotated toward the polarization direction of interfering beams. The irradiance is uniform so there is less contribution to refractive index variations. In the latter case the diffraction grating arises from variation in refractive index. Gratings written with Disperse Orange 3 (DO3) as the dopant disappear after removal of the pump beams, whereas grating written with Methyl Red (MR) as the dopant tend to be semi-permanent.

In this work we have experimentally investigated optical properties of multilayered structure, consisting of two right handed Cholesteric Liquid Crystal layers with the same pitch and Rhodamine 6G (R6G) doped polymethyl metacrylate (PMMA) thin film sandwiched between them. Particularly transmission spectrum dependence on temperature is studied. The 10 nm of CLC selective reflection band tuning is achieved. The photoluminescence of R6G is registered.

An optically switchable photoluminence (PL) photonic material using azobenzene-doped cholesteric liquid crystal (CLC) -dispersed quantum dots (QDs) is demonstrated in the film and capillary tube, respectively. In the film, upon the light irradiation the trans-to-cis photoisomerization of azobenzene makes the QD-dispersed CLC cell highly transparent thus allowing most excitation photon to pass through the CLC cell and decreases the intensity of PL. In the capillary tube, there are two situations upon the light irradiation: the intensity of PL decreases when the irradiation applied on the PL excitation position; the intensity of PL increases when the irradiation applied ahead the PL excitation position. In view of the considerable interests in PL of QDs for photonic applications, our study on optically switchable PL from azobenzene doped CLC-dispersed QDs introduces a new approach of controlling emission of QDs by means of light. This may open the door to new exploitation for applications of QD such as light switchable, emission based liquid-crystal display (LCD) or optical communication device.