This PDF file contains the front matter associated with SPIE Proceedings Volume 9940, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and Conference Committee listing.

We demonstrate an array of the Fabry-Perot (FP) resonators with a liquid crystal polymer (LCP) layer inside each resonant cavity for image selection by polarization of the incident light. In our approach, the LCP molecules in the array of the FP resonators for different images are photo-aligned in different directions. Under unpolarized light, no image is observed. For the incident light polarized parallel to the photo-alignment direction, only the image corresponding to the polarization state among the recorded images is visible due to the difference in the effective refractive index between different image regions in the array of the FP resonators. Our approach based on anisotropic FP resonators will be useful for the realization of highly efficient and low-cost anti-counterfeiting systems and security labels.

We have proposed a hybrid alignment nematic (HAN) liquid crystal cell using a polymer stabilized (PS) technology. The cell shows a reverse mode scattering property. The PS-HAN cell is transparent at any viewing angle in the off-state and has an asymmetrical scattering property at incident angles in the on-state. Applying the cell to a smart glass, it cell can selectively scatter a midday sunlight with a function of window blinds. In this study, two polymerization processes, an irradiation with UV light from planar and vertical aligned sides of the cell have been investigated. UV penetration depth has also been estimated from planar and vertical aligned sides of the cell. LC materials with different UV absorption spectra were prepared. A driving voltage, an optical property and a polymer morphology were measured in PS-HAN cells. The UV intensity profile have an effect on polymer density and particle size, which changed the driving voltage and the light scattering property in the PS-HAN cell. The study on the UV penetration in the polymer stabilized technology can improve their performance.

In this paper we outline that light-induced effects in liquid crystals are still able to provide scientific and technological novelty in spite of a long time investigation started more than thirty years ago. Here we review some recent achievements related to new phenomena that have been studied in the past few years. In the first part of our report we discuss optical trapping of nematic colloids whose origin relies on the elastic properties of liquid crystals rather than on the field gradient that is on the basis of conventional optical tweezing. In the second part we present some recent results obtained in studying the self-phase modulation in bent core nematic liquid crystals, pointing out a peculiar two regimes behavior.

We have investigated the pretilt angle of liquid crystals generated by photoalignment layers of polyimide containing azobenzene in the backbone structure (Azo-PI). Three different photoalignment layers were prepared by performing or not performing alkylamine vapor treatment on the precursor (polyamic acid: Azo-PAA) films. Octadecyamine (ODA) and N,N-dimethylhexadecylamine (DMHDA) were used as a primary and a tertiary alkylamines, respectively. When unpolarized light irradiation of 114 J/cm² was performed at an angle of incidence of 45°, the pretilt angles generated by the conventional (without alkylamine vapor treatment), ODA-treated, and DMHDA-treated photoalignment layers were 1.4°, 19°, and 4.3°, respectively. From these results, we found that the pretilt angle generated by Azo-PI photoalignment layers increased by performing alkylamine vapor treatment but the degree of increase strongly depended on the class of alkylamine. To understand the increase in the pretilt angle by the alkylamine vapor treatments, the alignment behaviour of the Azo-PAA (PI) backbone structure in each preparation step was examined and discussed.

Recently, low-frequency driving of a display panel to reduce the power consumption has drawn much attention, especially in mobile devices. In case a liquid crystal display panel is driven by a fringe-field at a low frequency, the image flickering phenomenon can be observed when the sign of the applied electric field is reversed. Image flicker can be eliminated simply by applying a bias voltage to a liquid crystal cell so that the transmittance during the positive frame is the same as that during the negative frame. However, it may be difficult to employ this technique for practical applications because it requires a bias voltage that is dependent on the gray level. In this talk, we introduce methods to eliminate the image flicker by controlling the material parameters of liquid crystals, such as the flexoelectric anisotropy and the dielectric anisotropy. Methods to eliminate image flicker without controlling the material parameters, such as driving by a bipolar wave and optimization of the electrode spacing, are also introduced.

As opposed to most fluorophores that suffer from aggregation-caused quenching (ACQ), aggregation-induced emissive luminogens (AIEgens) possess very weak fluorescence in solution, but show strong emission upon aggregation due to restriction of intramolecular motion (RIM). Since AIEgens are often comprised of propeller-shaped structures, i.e. polyphenylsiloles or tetraphenylethylene (TPE), the attachment of chiral units has recently proven a powerful tool to fabricate chiral AIEgens exhibiting strong circularly-polarized luminescence (CPL) signal upon aggregation. Different chiral moieties lead to various assembled structures, such as helical nanoribbons, superhelical ropes, hollow and solid micro-/nanospheres. Generally, these structures exhibit enhanced chiroptical properties when compared to their monomeric counterpart. In this context, we report on the tetraphenylsilole and TPE derivatives with side-chains bearing an enantiomerically pure chiral units readily assembled into superhelical ropes upon aggregation, which displayed large CPL dissymmetry factors (g_em) of –0.32 – a record for purely organic chiral materials.

Liquid crystal (LC) is the promising material for the fabrication of high-performance soft, flexible devices. The fascinating and useful properties arise from their cooperative effect that inherently allows the macroscopic integration and control of molecular alignment through various external stimuli. To date, light-matter interaction is the most attractive stimuli and researchers developed photoalignment through photochemical or photophysical reactions triggered by linearly polarized light. Here we show the new choice based on molecular diffusion by photopolymerization. We found that photopolymerization of a LC monomer and a crosslinker through a photomask enables to direct molecular alignment in the resultant LC polymer network film. The key generating the molecular alignment is molecular diffusion due to the difference of chemical potentials between irradiated and unirradiated regions. This concept is applicable to various shapes of photomask and two-dimensional molecular alignments can be fabricated depending on the spatial design of photomask. By virtue of the inherent versatility of molecular diffusion in materials, the process would shed light on the fabrication of various high-performance flexible materials with molecular alignment having controlled patterns.

Light-controllable azobenzene materials have a remarkable potential for micro- and nanotechnologies as patterning templates, sensors, micropumps and actuators. The photoisomerization between trans and cis states of azo-chromophores is the primary source of photodeformation in azo-polymers. The direction of deformation can be controlled by the light polarization. In our analytical and computer simulation studies, description of the light-induced anisotropy is simplified by applying effective orientation potential to the trans isomers orienting them perpendicular to the light polarization. Using coarse-grained modelling we proved that effective potential approximates well the reorientation of trans isomers under linearly polarized light. The proposed orientation approach is quite promising. It allows not only the explanation of the sign and magnitude of photodeformation in azo-polymers with diverse chemical architecture and topology, but also the prediction of new effects, such as appearance of biaxial deformation in liquid crystal (LC) azo-polymers. A rich behavior is predicted for two-component polymer networks containing azobenzenes and non-chromophoric LC mesogens. Whether such two-component network expands or contracts with respect to the light polarization, depends on the art of attachment of the mesogens to the network strands.

Liquid crystal cells with LiNbO₃:Fe crystals as substrates, are described. The photovoltaic field generated by the substrates is able to reorient the liquid crystal director thus giving rise to a phase shift on the light propagating through the cell, as in liquid crystal light valves. The process does not require the application of an external electric field, thus being potentially useful for applications requiring a high degree of compactness. A detailed characterization of several cells based on lithium niobate crystals with different iron concentration has been carried out. The correlation between the LiNbO₃:Fe characteristics and the liquid crystal reorientation is also discussed.

The texture observation has long been the core technique in liquid crystal (LC)-based bioassays. Its working principle stems from the dark-to-bright texture change induced by the interruption of the initially homeotropic alignment in nematic bulks or from the radial-to-bipolar configuration transition in LC droplets in the presence of biomolecules. One of the drawbacks of this observational scheme, which requires a polarizing optical microscope, is the difficulty in quantitative analysis. In this invited paper, we report on our recent development of alternative optical biosensing techniques based on cholesteric LCs (CLCs) without the use of a polarizer. The increase in structural order in a vertically anchored CLC cell in the quasi-planar state provides a means to allow detection and quantification of the concentration of biomolecules immobilized on the interface between the mesophase and the surfactant DMOAP for LC vertical alignment.

Photo-addressed liquid crystal media allow realizing optical phase detection based on self-adaptive holographic processes. Examples are reported of adaptive holographic systems based on optically addressed liquid crystal spatial light modulators. Owing to the physical mechanisms involved, such liquid crystal based adaptive interferometers adapt to slow phase variations, thus filtering out low frequency noise while transmitting the phase modulations at higher frequencies. This method permits measuring small phase modulations in noisy environments and with distorted and speckled wavefronts. The basic principles of the adaptive interferometer are presented, then, the association with an optical fiber is shown to realize a new class of distributed optical fiber sensors.

Mesomorphic metal alkanoates is very promising yet overlooked class of nonlinear-optical materials. Metal alkanoates can exhibit a broad variety of condensed states of matter including solid crystals, plastic crystals, lyotropic and thermotropic ionic liquid crystals, liquids, mesomorphic glasses, and Langmuir–Blodgett films. Glass-forming properties of metal alkanoates combined with their use as nano-reactors and anisotropic host open up simple and efficient way to design various photonic nanomaterials. Despite very interesting physics, the experimental data on optical and nonlinearoptical properties of such materials are scarce. The goal of the present paper is to fill the gap by discussing recent advances in the field of photonic materials made of metal alkanoates, organic dyes, and nanoparticles. Optical and nonlinear-optical properties of the following materials are reviewed: (i) mesomorphic glass doped with organic dyes; (ii) smectic glass composed of cobalt alkanoates; (iii) semiconductor nanoparticles embedded in a glassy host; (iv) metal nanoparticles - glass (the cobalt octanoate) nanocomposites.

There is a great increase of interest in the nematic defect structures, where interplay of confinement, elasticity, anchoring, and chirality leads to complex ordering fields with singular topological defects and nonsingular solitonic deformations. Beside numerous advanced microscopy techniques, the standard polarized optical microscopy is still an elementary first-to-take tool in use. To fully capture its potential and understand the limitations in unveiling the details of complex structures, we apply a recently extended Jones matrix approach based on ray-tracing that allows to include also effects of focusing and numerical aperture. The approach is illustrated with results of recent studies of cholesteric droplets.

The molecular interaction sometimes propagates in a collective manner, reaching for a long distance on the order of millimeters. Such interactions have been well known in the field of strongly-correlated electron systems in a beautiful crystal interleaved by donor and acceptor layers, induced by photo-stimulus. The other examples can be found in liquid crystals (LCs), which could be found in many places in nature such as bio-membrane. Different from crystals, LCs features “softness”, which enables it to be a curved structure such as a cell. In LCs, even a small molecular change would trigger the overall structural change by the propagation of the molecular interaction. Here we will show, for the first time, how long and how fast the molecular interaction propagates in LCs. The patterned phase transition was induced in a LC, causing the phase transition propagation in a controlled way and the propagation was measured with an time-resolved optical technique, called the transient grating. A LC sample doped with azobenzene was put into a thermally controlled LC cell. A grating pattern of a pulse light with 355 nm was impinged to the LC cell, and the light was absorbed by the dyes, releasing heat or photomechanical motion. We could observe the fringe spacing dependence on the phase transition response, which indicates that phase transition was delayed as the fringe spacing due to the delay by the phase transition propagation. This is the first direct evidence of the molecular interaction propagation of the LC molecules.

A low f /# lens and zoom lens system based on Pancharatnam phase are presented. The design, fabrication, and characterization of these devices are shown. The unique characteristics of these devices is made possible by the use of azo-dye photoalignment to align reactive mesogens. The wavelength dependence on the image quality is evaluated and shown to be satisfactory from red light to near infrared machine vision systems. A demonstration device is shown with a 4x zoom ratio.

Blue phase liquid crystal (BPLC) has been attractive for display and photonic applications for its sub-millisecond response time, no need for surface alignment, and an optically isotropic dark state. Because of these advantages, diffractive devices based on blue phase liquid crystals have great potential for wide applications. In this work, we present several BPLC diffractive devices. The operation principles, fabrication and experimental measurements will be discussed in details for two BPLC gratings realized by holographic method and a BPLC Fresnel lens using a spatial light modulator projector. All of these devices exhibit several attractive features such as sub-millisecond response, relatively high spatial resolution and polarization-independence.

Dye-sensitized solar cells (DSSCs) are a type of organic solar cell often cited for their high efficiency and easy fabrication. Recent studies have shown that modification of the standard liquid electrolyte DSSC architecture by the changing one of the components or the addition of additives often results in the improvement in one of the photovoltaic parameters and hence the overall efficiency. Here we explore a dielectric liquid crystal material which is a known insulator but possesses a high degree of order and optical anisotropy. In the presence of an applied electric field, the equilibrium of positive and negative charges are displaced in opposite directions. In this work, different mixtures with different dielectric anisotropies ranging from negative, zero and positive are formulated. These mixtures are then used to prepare polymer dispersed liquid crystal (PDLC) electrolytes and subsequently DSSC devices based on these PDLC electrolytes are fabricated. The morphology of the PDLC is observed through polarizing optical microscopy (POM) and the electrical/photovoltaic characterizations are performed through current density-voltage (J-V) measurements and electrochemical impedance spectroscopy.

Electro-optic (EO) modulation of the amplitude and phase of electromagnetic waves using liquid crystals (LCs) is commonplace in the optical and infrared regions. This effort has led to commercially available components used in spectral filtering, polarization management, beam steering, transmitters, displays, etc. However, electro-optic techniques have had limited success in the terahertz (THz) region due to several practical design challenges. The growth in applications has led to an interest in the development of a spatial light modulator (SLM) for the terahertz region. In the visible region, the most common SLMs use electro-optic materials such as liquid crystals to spatially modulate a beam. However, this approach to achieve a practical SLM in the terahertz regime has been difficult. The primary barrier for components is the long interaction lengths required to modulate a THz wave. Since the EO modulation depth is directly proportional to the multiplication of the change of permittivity and the ratio of interaction length over wavelength, THz systems with wavelengths ranging from 150 μm to 1mm pose a challenge. To overcome this barrier, longitudinal stratified sub-wavelength liquid crystal structures have been engineered and fabricated. The stratified structures introduce the challenge in the selection and design of the electrodes. By using multiple layers the tunable films can be maintained at manageable thicknesses (25 to 200 μm). The reduced individual film thickness will significantly improve the requisite drive voltage and response time. However, the layered structure with multiple conducting layers adds considerable challenges to the design of the transparent electrode. Both simulation and experimental data will be presented.

Surface plasmons in graphene possess stronger mode confinement and lower propagation loss. One way to excite the surface plasmons is placing a periodic array of graphene nano-ribbons on top of a dielectric substrate. However once the system is fabricated it is not possible to change its optical properties. Liquid crystals (LC) are a uniaxial medium with an optical axis easily controlled by external stimuli. We suggest tuning the surface plasmons in an array of graphene ribbons by placing a LC slab on top of the ribbons. A voltage applied to the LC layer shifts the graphene ribbons plasmonic notch and changes its depth.

Direct Laser Writing (DLW) by two-photon photopolymerization (TPP) enables the fabrication of micron-scale polymeric structures in soft matter systems. The technique has implications in a broad range of optics and photonics; in particular fast-switching liquid crystal (LC) modes for the development of next generation display technologies. In this paper, we report two different methodologies using our TPP-based fabrication technique. Two explicit examples are provided of voltage-dependent LC director profiles that are inherently unstable, but which appear to be promising candidates for fast-switching photonics applications. In the first instance, ~1 μm-thick periodic walls of polymer network are written into a planar aligned (parallel rubbed) nematic pi-cell device containing a nematic LC-monomer mixture. The structures are fabricated when the device is electrically driven into a fast-switching nematic LC state and aberrations induced by the device substrates are corrected for by virtue of the adaptive optics elements included within the DLW setup. Optical polarizing microscopy images taken post-fabrication reveal that polymer walls oriented perpendicular to the rubbing direction promote the stability of the so-called optically compensated bend mode upon removal of the externally applied field. In the second case, polymer walls are written in a nematic LC-optically adhesive glue mixture. A polymer- LCs-polymer-slices or ‘POLICRYPS’ template is formed by immersing the device in acetone post-fabrication to remove any remaining non-crosslinked material. Injecting the resultant series of polymer microchannels (~1 μm-thick) with a short-pitch, chiral nematic LC mixture leads to the spontaneous alignment of a fast-switching chiral nematic mode, where the helical axis lies parallel to the glass substrates. Optimal contrast between the bright and dark states of the uniform lying helix alignment is achieved when the structures are spaced at the order of the device thickness, which was also found to be the case for the achiral system. The high resolution DLW technique limits structures to the focal spot size of the beam, ~1 μm in diameter, such that the transmittance is expected to be significantly enhanced relative to other stabilization techniques. Moreover, both devices remain stable under electrical and thermal cycling.

Recently, photo-alignment technology has been the focus of research efforts because lowering the pre-tilt angle is essential for complete elimination of the off-axis light leakage. However, even though photo-alignment can provide zero pre-tilt angle, it has not yet been widely applied in mass production because of its weak surface anchoring, high curing energy, and strong image sticking. In this paper, we demonstrate that the zero pre-tilt angle can be obtained by employing the field-induced UV-alignment method. We have shown electro-optical characteristics and parameters related to the image quality of a fringe-field switching cell fabricated using the proposed method as functions of the monomer concentration and the UV irradiation time.

The effects of the combination of cholesteric liquid crystal (CLC) cells on selective wavelength are investigated by the spectroscopic analysis under thermal modulation. The several kinds of CLC cells are formed by using the chiral dopants with different magnitudes and signs of helical twisting power (HTP). The combination of CLC cells with different temperature dependence shows that the infrared light range longer than 700nm is widely reflected and the visible light is little modulated when the temperature increase from 25 °C to 45 °C. The results demonstrate that the thermal modulation of selective transmittance spectra is controllable by the combination of CLC cells with different temperature dependence.

We have found the solution of the boundary value problem for reflectance and transmittance of normal circularly polarized light impinges on a cholesteric elastomer film with a twist defect. We have found a tunable resonant mode in the reflectance band for right and left circularly polarized light. When the values of chiral twist defect are increased in the cholesteric elastomer film, the resonant modes changes to shorter wavelength until the edge band is reached.