This PDF file contains the front matter associated with SPIE Proceedings Volume 9004, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

Recently, the liquid crystalline materials with a bent-core mesogen have attracted attentions because their interesting properties such as polarity and biaxiality of the mesophase. There are several types of bent-core mesogenic structures have been reported, for instance, banana-shaped, V-shaped molecules, boomerang-shaped, hockey stick-shaped, and Yshaped molecules. In this study, the liquid crystals and the reactive mesogens with the hockey-stick shaped mesogens will be described concerning with the structure-property relationship.

We investigated the electrooptical properties of a bent-core liquid crystal with a high kink angle. The bent-core liquid crystal showed a bistable memory effect and the memory retention time was over 10 h. A nematic liquid crystal doped with a small amount of bent-core liquid crystal showed flexoelectric anisotropy ~37.5 pC/m much greater than the pure host nematic liquid crystal. We also examined the elastic constant of the bent-core liquid crystal doped nematic mixture vs temperature.

Exciting new directions for liquid crystals (LCs) are emerging on the length scale of the wavelength of light. Two complementary micron-sized systems are formed by LC droplets and by dispersions of colloidal particles in LCs. The dimensions of each of these systems are ideal for laser tweezer manipulation, allowing a new range of photon-addressed LC systems to be envisaged. Trapping and moving micron-sized particles in LCs is a beautiful approach that can build novel colloidal photonic materials. However, it is also a unique way of studying fundamental LC properties, particularly anisotropic viscosity coefficients in the low Ericksen regime, which can be accessed by laser trapping. Rather few nematic materials have been studied using laser traps; we describe two different approaches to deduce the viscosity coefficients of nematic mixtures. Micron-sized LC droplets are emerging as intriguing photonic systems in their own right. Angular momentum can be transferred from laser traps to droplets, with specific polarization properties and droplet geometries resulting in a variety of novel photon-driven effects. Fast optical switches, rotating at speeds >1kHz, can be produced from nematic droplets in circularly polarized beams. Both droplet geometry and beam polarization influence the droplet rotation, allowing control of the phenomenon. Surprisingly, a chiral nematic droplet can sometimes undergo continuous rotation in a linearly polarized trap, a phenomenon caused by optically-induced changes in chirality. We describe this remarkable effect which demonstrates how the control of chirality through polarization can result in an optically driven transducer.

Lasing in liquid crystals has been demonstrated in numerous con gurations and material systems. In most reports the laser light is emitted perpendicular to the liquid crystal layer, using a chiral liquid crystal layer which exhibits a helical structure with a periodicity that gives rise to a stop band in the visible spectrum. The emission of light can then be modeled with one-dimensional models with reasonable accuracy. In the last few years also in-plane lasers have been demonstrated, for example by using a lying helix arrangement. The accurate optical modeling of the light generation in such systems is complex because the materials are optically anisotropic and the con guration should be modeled as two-dimensional. Advanced optical methods are necessary. For these simulations we rely on nite-element calculations of the optical modes in periodic two-dimensional structures including full position dependent anisotropy. The optical modes in a lying helix con guration are calculated as a proof-of-principle for this simulation method. Several interesting features of the optical modes in these structures are found.

Binary blends of phthalocyanine (Pc) LCs, 1, 4, 8, 11, 15, 18, 22, 25-octadecylphthalocyanine (C10PcH₂) and the corresponding Zn complex (C10PcZn) were studied which have the identical hexagonal columnar (Col_h) mesophase and the same order of carrier mobility (~ 10^-1 cm² V^-1 s^-1) in the mesophase. The phase diagram shows a complete miscibility in the Col_h mesophase and no eutectic point was detected. The carrier mobility evaluated by Time-Of-flight (TOF) technique goes down to 10^-2 cm² V^-1 s^-1 in Col_h phase of the initial blends prepared by solution mixing. However, the treatment of these binary systems with repetitive heating and cooling gives recovering of carrier mobility to the original level, though their HOMO and LUMO levels are slightly different in these two mesogenic Pcs. These results indicate that two types of single component column form a hexagonal array in mesophase. Also the blends with PCBM were studied on carrier mobility as well as miscibility and phase separation.

Liquid crystal (LC) display and photonics devices based on photo-alignment and photo-patterning LC cells are developed. A fast switchable grating based on ferroelectric liquid crystals and orthogonal planar alignment by means of photo alignments. Both 1D and 2D gratings have been constructed. The proposed diffracting element provides fast response time of around 20 μs, contrast of 7000:1 and high diffraction efficiency, at the electric field of 6V/μm. A switchable LC Fresnel zone lens was also developed with the efficiency of ~42% that can be further improved, and the switching time for the 3 μm thick cell is ~6.7 ms which is relatively fast in comparison of existing devices. Thus, because of the photoalignment technology the fabrication of Fresnel lens became considerably simpler than others. A thin high spatial resolution, photo-patterned micropolarizer array for complementary metal–oxide–semiconductor (CMOS) image sensors was implemented for the complete optical visualization of so called “invisible” objects, which are completely transparent (reflective) and colorless. Four Stokes parameters, which fully characterized the reflected light beam can be simultaneously detected using the array of photo-patterned polarizers on CMOS sensor plate. The cheap, high resolution photo-patterned LC matrix sensor was developed to be able successfully compete with the expensive and low reliable wire grid polarizer patterned arrays currently used for the purpose.

Colloidal platelets are explored as elementary building blocks for the shape-controlled assembly of crystalline and quasicrystalline tilings. Using three-dimensional (3D) numerical modelling based on the minimization of Landau-de Gennes free energy for modelling of colloids combined with Finite Difference Time Domain calculations for optics, we demonstrate the self-assembly and optical (transmission) properties of triangular, square and pentagonal sub-micrometer sized platelets in a thin layer of nematic liquid crystal. Interactions between platelets are explored, providing an insight into the assembly process. Two-dimensional tilings of various-shaped colloidal platelets are demonstrated, and their use as diffraction layers is explored by using FDTD simulations. Designing symmetry-breaking surface anchoring profiles on pentagonal platelets opens also a possibility to achieve interactions that could lead to tilings with non-crystalline symmetry.

Femtosecond pulse shapers are an important tool for the manipulation of ultrashort pulses. Two-Liquid-Crystal (LC)- Panel Spatial Light Modulator (SLM) pulse shapers⁵ are especially useful, as they permit simultaneous control of phase and amplitude of spectral components, thereby allowing for a wide range of possible manipulations of the temporal shape of ultrashort pulses. In this work, a detailed description of the alignment of a pulse shaper optimized for modelocked semiconductor lasers is presented. Several methods to calibrate the phase-retardance-LC-voltagerelationship are reviewed and a calibration method is presented which is robust to non-idealities of the components of the setup.

Cholesteric liquid crystals (CLCs) have been used for a reflective display because of their reflective nature in the planar state. In a reflective display, the planar and the focal-conic states are used for the bright state and the dark state, respectively. In this paper we introduce a long-pitch CLC device, in which a selective wavelength of the reflected light is shifted to infrared (IR) wavelengths by controlling the pitch. The planar state of a long-pitch CLC device is transparent over the entire visible wavelengths in the field-off state. Omni-directional achromatic reflection through light scattering in the focal-conic state can be achieved without a polarizer. Compared to conventional CLC cells that reflect the visible light in the planar state, a long-pitch CLC device has a longer pitch, of which the operating voltage for switching between the two state is much lower so that achromatic reflective displays and light shutters with low power consumption can be realized using long-pitch CLC devices. By coupling with a reflector, the light efficiency of a longpitch CLC cell in the focal-conic state can be enhanced, by which higher brightness can be obtained for application to reflective displays. A dye-doped long-pitch CLC device can be placed behind a transparent organic light-emitting diode display for use as a light shutter to block the ambient light.

The inability of the eye to focus on nearby objects, presbyopia, is suffered by ~100% of people over the age of 50. Liquid crystal (LC) spectacle lenses have shown great potential for correcting presbyopia. However, correcting presbyopia in contact lens users has proven elusive and existing commercial options suffer significant compromises in vision and comfort. We describe a novel contact lens that includes a liquid crystal element that offers to correct presbyopia without the compromises associated with other technologies. We fabricated variable focus lenses using a balanced optical system, providing the additional optical power presbyopes require for near vision (typically +1.00 D to +2.00 D). The system uses positive optical power from the two substrates and variable negative optical power from the LC layer to form a balanced optical system which, when unpowered, corrects distance vision. Upon voltage application, the liquid crystal layer decreases in refractive index, resulting in additional optical power in the system, offering correction equivalent to reading glasses. Our new technology is based on a traditional contact lens material which could be placed directly on the eye. The liquid crystal lens employed is well suited to the small optical areas associated with contact lenses. We compare several different LC materials and geometries which are suitable for our application, and discuss the influence of material and geometry on switching times, optical quality and operating voltage. Our contact lenses typically switch ±2.00D in response to < 10 V_rms with response times of the order of a second.

Adaptive interferometers based on dynamic holography within a nonlinear medium allow to precisely measuring phase modulations in noisy environments. Thanks to its adaptive behavior, the hologram follows slow external perturbations cancelling the low frequency phase mismatches between the two arms of the interferometer, while it appears static at high frequencies, hence, converting phase into intensity modulation. As a holographic medium, we use a liquid crystal light valve combining a photoconductor with a liquid crystal layer. The effective refractive index and, thus, the phase shift, depend both on the incident optical intensity and the bias voltage. By characterizing the response of the light valve, we show that low frequency noise can be filtered out within a voltage-controlled frequency bandwidth. This feature can be useful for applications where the signal of interest is limited by external noise such as temperature fluctuations and/or vibrations.

Compact and easy-manufacturable wavelength selectors are desired for various types of optical equipments. Our optical wavelength selectors, which possess holographic structure consisting of liquid crystal (LC) and polymer phases, or socalled holographic polymer dispersed liquid crystals (HPDLCs), are switchable in Bragg diffraction wavelength due to polarization states. In the HPDLCs, LC submicrometer droplets are spatially periodically dispersed in polymer matrix with highly-orientational order of LC molecules in the droplets. Such structure is not difficult to be fabricated, that is, it is formed by photo-polymerization and consequent phase separation due to interferometric exposure. Furthermore, the orientation of LC is self-organized during the phase separation process.

Recently, active studies on a transparent organic light-emitting diode (OLED) are in progress as a next generation display. However, since it is not possible to obtain a dark state using a transparent OLED, it exhibits poor visibility. This inevitable problem can be solved by placing a light shutter behind a transparent OLED display. In this paper, we propose a light shutter using dye-doped liquid crystals (LCs) whose Bragg reflection wavelength is chosen to be infrared by controlling the pitch of cholesteric liquid crystals (ChLCs). The proposed light shutter is switchable between the dark planar state and the transparent homeotropic state. The proposed light shutter has the advantages of the high transmittance, low operation voltage, and easy fabrication process compared with previous light shutter devices using liquid crystals. It is expected that the proposed light shutter can be applied to realize high visibility transparent OLEDs and emerging smart windows.

A holographic polymer-dispersed liquid crystal (HPDLC) memory to record multi-context information for an optically reconfigurable gate array is formed by the angle-multiplexing recording using a successive laser exposure in liquid crystal (LC) composites. The laser illumination system is constructed using the half mirror and photomask written by the different configuration contexts placed on the motorized stages under the control of a personal computer. The fabricated holographic memory implements a precise reconstruction of configuration contexts corresponding to the various logical circuits such as OR circuit and NOR circuit by the laser illumination at different incident angle in the HPDLC memory.

In this study, faster response speed of ON/OFF switching of multi-bilayered films containing azo-functionalized polymer liquid crystal and polyvinyl alcohol, PVA, is investigated. The multi-bilayered films were found to reflect a light of specific wavelength, and showed reversible change in the reflection intensity by irradiation with non-polarized visible light and UV light. The multi-bilayered film having high absorbance around 300-500 nm due to stacking several decades of azobenzene containing layer. So, the change in reflection intensity of multi-bilayered film takes long time by light irradiation. We synthesized polyacrylates copolymers with azobenzene and biphenyl side chains where biphenyl groups is having no absorbance at UV and visible region. Multi-bilayered films were fabricated by spin-coating method and the switching time of reflection was investigated comparing to the multi-bilayered film containing azobenzene homopolymer, the ON switching times of reflection for the copolymers were faster than homopolymer needing 900 s. It is attributed to that inducing UV light (λ = 365 nm) easily entered into the film by introducing of biphenyl groups.

A few research group reports formation of ordered structures of colloidal particles due to topological defects in a nematic liquid crystal. In this paper, we describe the photochemical phase transition of a nematic liquid crystal by the photoisomerization of azobenzene dyes, focusing especially on the dynamical effect of the trans–cis–trans photoisomerization cycle of a push-pull azobenzene dye. Then, we discuss the effects of light irradiation on the motion of small objects dispersed in the nematic and smectic liquid crystals contatining a push-pull azobenzene dye, and successfully manipulate those objects by pushing, trapping and dragging them.

A microperiodic structure composed of polymer and liquid crystal (LC) phases, called holographic polymer dispersed liquid crystal (HPDLC), was fabricated based on a photo-induced phase separation technique by laser interferometric exposure. The diffraction wavelength of HPDLC gratings formed by different LC composites and grating structures was experimentally investigated by spectroscopic measurements as a function of temperature at around 30 °C. The HPDLC gratings composed of nematic LC having low nematic to isotropic temperature (T_NI) and film thickness of 25 μm showed the switch of diffraction wavelength between visible and infrared lights by the change of temperature. The optical characteristics achieved in HPDLC gratings are expected to be applicable for the basis of diffractive type of thermodriven light controller which can supply visibility constantly for solar-ray control windows.

We have visualized the internal structure of electrospun polymer fibers, having liquid crystals in the core, using focused ion beam milling. In this way we were able to correlate observed selective reflection and optical texture, in a specific fiber location, with the corresponding cavity dimensions and shape. It was found that cholesteric liquid crystals exhibit peculiar optical behavior, distinctively different from the one in bulk, when they are confined in sub-micrometer cavities. Because of the reduced dimensions, the pitch of the helix has to change even for tiny variations in cavity size, resulting in changes in the wavelength of the selective reflection. The ion beam milling is a destructive process and it is relevant to consider possible side effects and consequences on the polymer sheath and thus on the revealed cavities. We analyze the heating due to the ion beam exposure calculating the subsequent temperature increase in the polymer and at a polymer-liquid crystal interface. The derived increase of temperature is very small and is not expected to induce any notable change in the polymer cavities.

Discotic liquid crystal (LC) can arrange in columnar structures along which electrical conduction occurs via π-π interaction between adjacent molecular cores. The efficiency of the conductivity is strongly dependent on the overlap of the orbitals of neighbor molecules and, in general, on the structural arrangements. The understanding of the factors that influence the organization is crucial for the optimization of the final conductive properties of the self-assembled columns. In this paper we present a study on the self-organization into molecular wires of a discotic LC using a solution based method. In particular, we focus on the effect of solvents used for preparing the LC solution. The resulting morphologies were investigated by atomic force microscopy (AFM) and optical microscopy, showing that diverse structures result from different solvents. With suitable conditions, we were able to induce very long fibers, with several tents of micrometer in length that, in turn, self-organize assuming a common orientation on a macroscopic scale.

Lyotropic Liquid Crystals (LCs) are attractive materials as host systems for nanoparticles, in particular for carbon nanotubes (CNTs), due to the LC templating and dispersing action. Since carbon nanotubes have many remarkable properties their presence could also influence the aligning hosts and such effects need to be taken into account in CNTLC composites. CNTs can be dispersed efficiently in surfactant-based lyotropic hosts that can be removed after their templating action, being water based. However, residual surfactant has a detrimental effect on the nanotube properties and it becomes important to find ways to minimize its amount in CNT composites. In the present work we use, for CNT alignment, a lyotropic nematic LC host with a very low surfactant concentration, based on charge combination of cationic and anionic surfactant molecules. Small variations in the molar ratio of the two surfactants, still at a fixed total surfactant amount, yield a very different LC behavior. CNTs could be successfully dispersed in the host forming an overall low-surfactant composite. Interestingly, the presence of nanotubes strongly influences the behavior of the host, bringing a stabilization of the LC phase.