This PDF file contains the front matter associated with SPIE Proceedings Volume 8475 including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

The reflection color of a cholesteric liquid crystal depends on material parameters such as the molecular chirality or the concentration of chiral dopant, the helical pitch of the twisted structure and the optical indices. We show that the color may be selected simply by varying the annealing time of an open cholesteric oligomer film with hybrid anchoring. The 3D representation of the structure is provided by combining complementary imaging techniques. The color selectivity is due to controlled changes of the orientation of the helix axis with respect to the air-material interface. Potential applications are chiral microreflectors and microlenses. Then, we demonstrate the symbiotic association of gold nanoparticles within such cholesteric textures and their long-range self-organized arrangements. We show that the nanoparticles can be patterned on demand only by playing with the film thickness and the interfacial properties of the CLC film. We investigate how the selective reflection is affected by the in situ organization of gold nanoparticles and what is the plasmon response of nanoparticle chains. Potential applications are envisioned in the field of soft nanotechnology and optical materials.

In this study, we investigated self-organized structures and photoinduced motions of microparticles on azobenzenedoped liquid crystal (LC) films with homogeneous or homeotropic alignment structures. In the case of homogeneous alignment, the microparticles formed linear chains oriented along the direction of the bulk LC alignment at air–LC interface in the initial state. Upon irradiation with ultra-violet (UV) light, the linear chains gathered into the irradiated area and formed closely-packed aggregates. The assembled chains diffused outside the irradiated area to reform the chains upon irradiation with visible light. In contrast, on the homeotropically aligned LC films, pseudo-hexagonal lattice structures of microparticles with long interparticle distances have been organized in the initial state. The particles exhibited photoinduced motions in directions opposite to those observed on the homogeneously aligned LC films. Upon irradiation with UV light, lattice structures were expanded by a particle motion away from the photoirradiated area. Irradiation with visible light then induced contraction of lattice structures based on a particle motion toward the irradiated area. The photoinduced particle motions depending on LC alignments would be explained by macroscopic convective flow or deformation of LC surface induced by cis–trans photoisomerization of azobenzene dopant.

High brightness trans-reflective bi-stable displays based on smectic A (SmA) liquid crystals (LCs) can have nearly perfect transparency in the clear state and very high reflection in the scattered state. Because the LC material in use is stable under UV radiation, this kind of displays can stand for strong day-light and therefore be ideal for outdoor applications from e-books to public signage and advertisement. However, the colour application has been limited because the traditional colourants in use are conventional dyes which are lack of UV stability and that their colours are easily photo bleached. Here we present a colour SmA display demonstrator using pigments as colourant. Mixing pigments with SmA LCs and maintain the desirable optical switching performance is not straightforward. We show here how it can be done, including how to obtain fine sized pigment nano-particles, the effects of particle size and size distribution on the display performance. Our optimized pigments/SmA compositions can be driven by a low frequency waveform (~10¹Hz) to a scattered state to exhibit colour while by a high frequency waveform (~10³Hz) to a cleared state showing no colour. Finally, we will present its excellent UV life-time (at least <7.2 years) in comparison with that of dye composition (~2.4 years). The complex interaction of pigment nano-particles with LC molecules and the resulting effects on the LC electro-optical performances are still to be fully understood. We hope this work will not only demonstrate a new and practical approach for outdoor reflective colour displays but also provide a new material system for fundamental liquid crystal colloid research work.

By employing anisotropic fluids and namely liquid crystals, fluid flow becomes an additional degree of freedom in designing optofluidic devices. In this paper, we demonstrate optofluidic liquid crystal devices based on the direct flow of nematic liquid crystals in microfluidic channels. Contrary to previous reports, in the present embodiment we employ the effective phase delay acquired by light travelling through flowing liquid crystal, without analysing the polarisation state of the transmitted light. With this method, we demonstrate the variation in the diffraction pattern of an array of microfluidic channels acting as a grating. We also discuss our recent activities in integrating mechanical oscillators for on-chip peristaltic pumping.

In this paper the concept and design of infrared cloaking using nanosphere dispersed liquid crystal (NDLC) matematerial in cylindrical geometry is presented for TM polarization of incident light. The influence of material losses on the cloaking efficiency is discussed. The loss can be tuned by changing design parameters.

Azobenzene dye-doped liquid crystal elastomers (LCE) are known to give strong photomechanical responses. We review photothermal heating actuated Photomechanical Optical Devices (PODs) and applications to systems by examining successful attempts at cascading macroscopic PODs in a series configuration. Using these results, we present some new design strategies that have the potential of miniaturizing these systems with increases in the response time and system integration.

Through thermodynamic analyses of several liquid crystals (LCs) and related compounds, discussed are the roles played by alkyl chains attached to mesogenic cores. The roles identified include, i) an extension of molecular length, enhancing the shape anisotropy required for the formation of LCs by excluded volume effects, ii) an entropy reservoir, which, through the entropy term in Gibbs energy, stabilizes mesophases and governs the phase relation, and iii) intramolecular solvent (self-solvent), which induces micro-phase separated LCs including SmA phase. The last aspect opens the possibility that science and technology of thermotropic and lyotropic LCs be combined under the unified view of LCs.

Liquid crystals have been employed for several decades in devices such as phase shifters, Fabry-Perot filters, polarizers, phase gratings, and Bragg switches at optical frequencies. However it is only recently that such devices have been demonstrated at terahertz frequencies. This is because of several fundamental frequency dependent relationships between device properties and frequency of operation. When designing liquid crystal devices, we need to find liquid crystals with high birefringence, low viscosity and low absorption at terahertz frequencies. In this paper we will present some measurements and simulations of potentially suitable liquid crystal mixtures.

Conventional liquid-crystalline (LC) semiconductors have been molecules consisting of a π-conjugated moiety and alkyl chains. For example, phenylterthiophene derivatives bearing alkyl chains exhibit ordered smectic phase at room temperature and are applied to field-effect transistors. In this paper, we report a molecular designs of LC electronic materials based on nanosegregation. Terthiophene derivatives bearing an imdazolium moiety exhibit supremolecular smectic phases, in which hole- and ion-conductive layers are formed separately. In the LC phase, electrochrmism is observed under the application of a DC bias without any electrolyte solutions. In simple side-chain LC polysiloxanes bearing terthiophene pendant groups, suprastructures based on nanosegregation are observed. The presence of flexible sublayers consisting of the polysiloxane backbones can relax the applied strain and decrease defect density, resulting in high hole mobility on the order of 10^-2 cm²/Vs. For perylene tetracarboxylic bisimide (PTCBI) derivatives bearing oligosiloxane chains, nanosegregation between the rigid aromatic cores and flexible oligosiloxane chains promotes the formation of columnar and layer structures, in which efficient electron transport is observed. The electron mobility in the columnar phase of the PTCBI derivative bearing four trisiloxane chains exceeds 10^-3 cm²/Vs at room temperature.

We report linear and crosslinked azobenzene containing liquid-crystalline polymers which can be applied to high-density optical storage and photomechanical analysis. We introduced a molecular design concept of multicomponent systems composed of photoresponse, refactive-index change amplification, and transparency units. Taking advantage of characteristics of liquid crystals (optical anisotropy and cooperative motion), polarization holograms were recorded, which enabled us higher-density holographic storage. On the other hand, crosslinked liquid-crystalline azobenzene polymer films were fabricated to investigate the photomechanical behavior. We have found that a large change in Young’s modulus is induced by several mol%-cis form production. Furthermore, a unique bending behavior, which cannot be explained by the conventional bending mechanism, was observed in the crosslinked liquid-crystalline polymer films with azobenzene in the side chain.

A unique feature of liquid crystals (LCs) is orientational order of molecules that can be controlled by electromagnetic fields, surface modifications and pressure gradients. We describe a new effect in which the orientation of LC molecules is altered by thermal expansion. Thermal expansion (or contraction) causes the LC to flow; the flow imposes an orienting torque on the LC molecules and the optical axis. The optical and mechanical responses activated by a simple temperature changes can be used in sensing, photonics, microfluidic, optofluidic and lab-on-a-chip applications as they do not require externally imposed gradients of temperature, pressure nor electromagnetic fields.

This paper presents a micro electromechanical system (MEMS) based micro optical switch for display devices. The size of the micro optical switch was 254 μm × 254 μm. The micro optical switch moves vertically by electrostatic force and consists of two parallel plate electrodes which have rectangular aperture array. The lower electrode was directly patterned on a glass substrate and the upper electrode was suspended by cantilever spring which was supported by anchors. The electrodes were made of thin aluminum film and the gap between two electrodes was 3.3 μm. The thickness of the electrodes was 0.3 μm respectively and the lower electrode was covered with 0.3 μm silicon dioxide. The width of the aperture and the metal were 8 μm and 5 μm respectively. The upper aperture array was aligned with the lower aperture array with 6.5 μm offset horizontally and the overlapping width of the two electrodes was 1.5 μm. The micro optical switch is in open state when no voltage is applied and the light passes through the two electrodes by the leakage or the reflection between the two electrodes. The micro optical switch is in close state when voltage is applied and the light is reflected to the backlight unit. The required voltages for pull in and pull out were 16.0 V and 11.4 V respectively. The switching time was 30 μs from the open state to the closed state and 50 μs from the closed state to the open state.

Liquid crystals (LC) are particularly well suited for the manipulation of the angular momentum of light. Only recently, the possibility of coupling the LCs and the so-called orbital angular momentum (OAM) of light has been identified. OAM is associated with a light beam having a helical wavefront and an optical vortex at its axis. A singular-patterned LC plate, named “q-plate”, can be used for generating and controlling helical beams of light, or “vortex beams”. The qplate can be also used in the quantum regime, for controlling the OAM of single photons, leading to several applications in the quantum information field.

Some of our recent progress on liquid crystal (LC) gratings, from nematic to blue phase, is reviewed in this invited talk. The first kind of grating is fabricated by periodically adjusting the LC directors to form alternate micro phase retarders and polarization rotators in a cell placed between crossed polarizers. The second one is demonstrated by means of photoalignment technique with alternate orthogonal homogeneously-aligned domains. To improve the response time of the gratings, several approaches are also proposed by using dual-frequency addressed nematic LC, ferroelectric LC and blue phase LC, which shows great performance including high transmittance, polarization independency and submillisecond response. At last, to obtain other controllable LC microstructures rather than simple 1D/2D gratings, we develop a micro-lithography system with a digital micro-mirror device as dynamic mask forms. It may instantly generate arbitrary micro-images on photoalignment layers and further guides the LC molecule orientations. Besides normal phase gratings, more complex patterns such as quasicrystal structures are demonstrated. Some new applications such as tunable multiport optical switching and vector beam generations are expected.

We demonstrate a hysteresis-free PSBP-LCs by inveistagating crystal growth and phase separation process of PSBP-LCs. By enlarging the domain size and uniformity of the crystal orientations of PSBP-LC, the hysteresis of PSBP-LCs can be eliminated. The large domain size and uniform crystal orientations of PSBP-LCs reduce the mismatch of the crystal orientations of PSBP-LCs. Based on this study, we also demonstrate a hysteresis-free electro-optical switch using dye-doped PSBP-LCs. Hysteresis-free PSBP-LC is important in many applications, such as displays, electro-optical switches, and electrically tunable focusing lenses.

A polarization-independent liquid crystal (LC) phase modulation using polymer-network liquid crystals with orthogonal alignments layers (T-PNLC) is demonstrated. T-PNLC consists of three layers. LC directors in the two layers near glass substrates are orthogonal to each other. In the middle layer, LC directors are perpendicular to the glass substrate. The advantages of such T-PNLC include polarizer-free, larger phase shift (~0.4π rad) than the residual phase type (<0.05π rad), and low operating voltage (< 30V_rms). It does not require bias voltage for avoiding scattering because the refractive index of liquid crystals matches that of polymers. The phase shift of T-PNLC is affected by the cell gap and the curing voltages. The potential applications are laser beam steering, spatial light modulators and electrically tunable micro-lens arrays.

We present our recent theoretical and numerical studies concerning the properties of cholesteric blue phases (BPs). One is on the effect of the variation of the Frank elastic constants on the stability of BPs. Our study is based on a classical and well-known theory of Meiboom et al. that gave a rough estimate of the temperature range of stable BPs in the case of equal elastic constants. We extend it to take into account the difference of the elastic constants. We show that the stability of BPs is greatly enhanced when the bend elastic constant K33 is smaller, which agrees well with recent experiments. We also show that larger splay (K11) and twist (K22) elastic constants are also favorable for the stability of BPs. The other subject of the present paper is the response of BPs in a parallel cell to an applied electric field. We carry out numerical calculations for the investigation the dynamics of orientational order and associated disclination lines. Our calculations are based on a Landau-de Gennes theory describing the orientational order of the liquid crystal by a second-rank tensor. Our preliminary calculations demonstrate that a non-uniform electric field induced by comb-like electrodes gives rise to non-trivial dynamics of disclination lines.

Liquid crystal (LC) optical elements have proven themselves as robust and cost-effective components for high-peakpowerlaser systems such as the 60-beam, 40-TW OMEGA Nd:glass laser system at the University of Rochester’sLaboratory for Laser Energetics. Although buffed nylon 6/6 alignment layers are the de facto standard for high-peak-power applications, photoalignment coatings based on coumarin materials have demonstrated exceptionally high near-IR laser-damage resistance. Using conventional photolithographic patterning techniques, high-resolution, photoaligned, nematic LC beam-shaper devices with a contrast ratio of 430:1, a pixel size of 10 μm, an interpixel resolution of 1.7 μm, and laser-damage resistance of 30 J/cm² (1054-nm, 1-ns pulse) have been demonstrated. Recently, we have extended this photoalignment process to other existing and potential high-peak-power LC optical devices that have previously used buffed alignment coatings. In addition to fabricating photoaligned LC wave-plate prototypes that meet all optical and performance specifications of LC devices currently used on OMEGA, novel LC polarization converters with continuously varying radial or azimuthal polarization states have been fabricated using the same high-damage-threshold materials. These polarization converters have applications not only in high-peak-power lasers but also in microscopy, electron acceleration, and machining.

Complex optical field-induced defect structures are presented in nematic and chiral nematic liquid crystals, as imprinted by Laguerre–Gaussian (LG) laser beams. Our modeling study is based on the phenomenological free energy approach, which dielectrically couples the nematic optical axis with the polarization of the LG beams. The symmetry of the presented structures proves to be conditioned by the beam helical indices. The beam intensity, strength of the nematic elastic constant, and local intensity-induced control of the nematic order via absorption of the light are demonstrated as possible mechanisms for producing, imprinting, and tuning of the field-induced complex defect structures in achiral and chiral nematics.

Optodielectrophoresis has been shown to be an interesting tool for massive manipulation of microparticles using external electric fields. Here, no electrode fabrication is need it since they are created by the light distribution incident onto a photoconducting material. We propose the use of this device for the recording of dynamic holograms in hydrogenated amorphous silicon (a:Si-H)-liquid crystals hybrid devices. The device consists of 5CB liquid crystal sandwiched between a photoconductive a:Si-H substrate and an ITO covered glass-plate. Diffraction efficiency of 3.3% is obtained when holograms are recorded with a low power He-Ne laser.

To improve electrooptical characteristics of the vertical aligned (VA) liquid crystal displays (LCDs), the monomer material and in-plane switching (IPS) field produced by interdigital electrodes are employed in LC cells. The fast switching response and well optical transmittance of the VA-IPS display mode are successfully achieved by mixing the nematic LC with polymer networks, attributed to the surface anchoring, and the molecular orientation of the LC cell will be further governed, especially under the greater applied voltage. Furthermore, the high concentration doping of the monomer can effectively improve the response behavior, but it also results in the transmittance sacrificed due to the light scattering, and the threshold voltage (V_th) increased.

Optical materials based on cholesteric liquid crystals (LCs) doped with fluorescent CdSe/ZnS quantum dots (QDs) have been developed and demonstrated to have a wide photonic band gap. It has been shown that the fluorescence emission of QDs embedded in LCs is circularly polarized and that the dissymmetry factor of this polarization may be optically or electrically controlled via conformational changes in the helical structure of the LC matrix. The possibility of photochemical patterning or image recording using these materials has been demonstrated; the recorded information can be read through changes in the dissymmetry factor of circular polarization of QDs emission. The developed photo- and electro-active materials with a controlled degree of fluorescence circular polarization may be used as on-demand single photon sources in photonics, optoelectronics, and quantum cryptography, as well as for development of nanophotonic systems capable of low-threshold lasing.

A concentration photovoltaic (CPV) system adopting a liquid crystal light modulation is demonstrated. The LC light modulation adjusts the optical power density of the incident light based on the electrically controllable distribution of LC directors. The electrically tunable concentration ratio of the LC light modulation can help to achieve the highest and a fixed efficiency of the CPV system because the LC light modulation helps to increase the photocurrent at a low illumination and prevent the effect of the series resistance at a high illumination. This study opens a window in solar cells by using LC light modulations.

Deformable Helix Ferroelectric Liquid Crystal (DHFLC) devices with nanodimensionally short pitch are examined for the purpose of applications in biomedical optical imaging. While nematic Liquid Crystal (NLC) devices have been used in our previous research as retarders, optical filters and polarization rotators and integrated into biomedical optical imaging systems, the current research is devoted to DHFLCs and to highlight the advantages that these devices can offer. Ferroelectric Liquid Crystal (FLC) devices are considerably faster than Nematic LC devices, the DHFLC sub group possesses other, more desired effects. The desired electro-optical response of the device is continuous, hysteretic-free and insensitive to the sign of the applied voltage. This can be achieved by using the DHFLC V-shaped switching effect which is observed when the helix pitch magnitude is shifted to nanoscale below 400nm (sub-wavelength) down to 150 nm. DHFLC cells with a sub-wavelength helix pitch have small light scattering in the visible spectral range when the applied voltage is below the critical level of the helix unwinding. Designs, experimental results and simulations are presented particularly for the reflectivity at oblique incidence showing some unique properties including polarization independent modulation, faster response and surface waves excitation.

We investigate spectral peculiarities of multilayer system, consisting of two identical CLC layers and a Rhodamine 6G doped polymethyl metacrylate thin film sandwiched between them. We measure transmission and reflection spectra of the system. A small mismatch between Selective reflection band and corresponding dip in transmission spectrum is observed. Also we investigate luminescence spectrum of this system at pulsed and CW mode pumping at various temperatures. The results show that maximal intensity of luminescence spectrum at constant pumping power is observed at 18°C and the weakest luminescence is observed at 20°C, the luminescence spectra at higher and lower temperatures are “confined” between these two spectral curves.