This PDF file contains the front matter associated with SPIE Proceedings Volume 7955, including the Title Page, Copyright information, Table of Contents, and the Conference Committee listing.

Liquid Crystal Photonic Crystal Fibers (LC-PCFs) known also as Photonic Liquid Crystal Fibers (PLCFs) are advanced specialty fibers that benefit from a combination of "passive" photonic crystal fiber host microstructures infiltrated with "active" liquid crystal guest materials and are responsible for a diversity of new and uncommon spectral, propagation, and polarization properties. This combination has simultaneously reinvigorated research in both fields of Liquid Crystals Photonics and Fiber Optics by demonstrating that optical fibers can be more "special" than previously thought. Simultaneously, photonic liquid crystal fibers create a new class of optical waveguides that utilizes unique guiding properties of the micro-structured photonic crystal fibers and attractive tunable properties of liquid crystals. Comparing to the conventional photonic crystal fibers, the photonic liquid crystal fibers can demonstrate greatly improved control over their optical properties. The paper describes basic physics including guiding mechanisms, spectral properties, polarization phenomena, thermal, electrical and optical controlling effects as well as innovative emerging technology behind these developments. Some examples of novel LC-PCFs highly tunable photonic devices as: attenuators, broadband filters, polarizers, waveplates, and phase shifters recently demonstrated at the Warsaw University of Technology are also presented. Current research progress in the field indicates that a new class of emerging liquid crystals tunable photonics devices could be expected.

A liquid crystalline phthalocyanine semiconductor, 1, 4, 8, 11, 15, 18, 22, 25-hexahexylphthalocyanine (C6PcH2) was studied on the drift mobility of charged carriers by a Time-Of-Flight (TOF) method. It was found that this compound exhibits an ambipolar nature for charge transport and the hole and electron mobilities were determined to be in the order of 10^-1 cm² V^-1 s^-1 for polydomain films of the hexagonal disordered columnar (Colh_d) mesophase. This is comparable to that of the octyl homologue (C8PcH₂) reported by Hanna et al. However, C6PcH₂ did not show any tendency to form the homeotropic alignment between ITO-coated glass substrates, though C8PcH₂ so clearly and easily does. Clear decay curves of the transient photocurrents could be obtained in TOF measurements even for polydomain films of the crystalline solid phase to give a strongly temperature-dependent mobility of holes which reaches to 1.1 cm² V^-1 s^-1 at room temperature (RT) as the temperature goes down, whilst the electron mobility slightly increases to be 0.5 cm² V^-1 s^-1at RT. This compound could easily form thin films by spin-coating technique with the toluene solution and a simple bulk-heterojunction thin film solar cell was fabricated to give a good performance such as 3.1 % of power conversion efficiency and > 70 % of external quantum efficiency.

This study investigates an optically switchable band gap of photonic crystal that is based on an azobenzene-doped liquid crystal blue phase. The trans-cis photoisomerization of azobenzene deforms the cubic unit cell of the blue phase and shifts the photonic band gap. The fast back-isomerization of azobenzene was induced by irradiation with different wavelengths light. The crystal structure is verified using Kossel diffraction diagram. An optically addressable blue phase display, based on Bragg reflection from the photonic band gap, is also demonstrated. The tunable ranges are around red, green and blue wavelengths and exhibit a bright saturated color.

In this work we show that nematic liquid-crystal droplets can be used as low-loss and highly tunable whisperinggallery mode (WGM) optical microcavities. They are spontaneously formed by mixing the liquid crystal with an immiscible liquid. The optical modes can be tuned either by applying an electric field, changing the temperature or by mechanical deformation. The tuning range for the electric field is as high as 20 nm at 2.6 V/μm for a ~ 600 nm WGM in 17 μm diameter droplets. Tuning is fast and almost linear with the applied voltage. In the case of the temperature tuning, we can shift the modes by more than 15 nm at a temperature change of 30 K. Further, we can also apply mechanical deformation to a free standing film of PDMS polymer containing the liquid crystal droplets. At 15% strain the mode shift is more than 30 nm. In all the three cases the tuning exceeds the free spectral range of the resonators and is completely reversible.

A finite element framework is presented to combine advanced three-dimensional liquid crystal director calculations with a full-vector beam propagation analysis. This approach becomes especially valuable to analyze and design structures in which disclinations or diffraction effects play an important role. The wide applicability of the approach is illustrated in our overview from several examples including small pixel LCOS microdisplays with homeotropic alignment.

The self-organization of the helical structure of chiral nematic liquid crystals combined with their sensitivity to electric fields makes them particularly interesting for low-threshold, wavelength tunable laser devices. We have studied these organic lasers in detail, ranging from the influence specific macroscopic properties, such as birefringence and order parameter, have on the output characteristics, to practical systems in the form of two-dimensional arrays, double-pass geometries and paintable lasers. Furthermore, even though chiral nematics are responsive to electric fields there is no facile means by which the helix periodicity can be adjusted, thereby allowing laser wavelength tuning, without adversely affecting the optical quality of the resonator. Therefore, in addition to studying the liquid crystal lasers, we have focused on finding a novel method with which to alter the periodicity of a chiral nematic using electric fields without inducing defects and degrading the optical quality factor of the resonator. This paper presents an overview of our research, describing (i) the correlation between laser output and material properties,(ii) the importance of the gain medium,(iii) multicolor laser arrays, and (iv) high slope efficiency (>60%) silicon back-plane devices. Overall we conclude that these materials have great potential for use in versatile organic laser systems.

Color filter (CF), one of the key components for liquid crystal display (LCD), is costly to make from repeated lithography processes. The defects may be created during the repeated lithography processes. The recycling defect CF panels are environmental unfriendly and not cost-effective process. CF repairing is an important cost-effective technical process to improve product yield. In this study, a solvent-less repaired ink system was studied. The optimized formulas of red, green, blue, and black inks have passed the quality control, reliability, and life-time tests. The new solvent-free ink system possesses the balance characteristics in liquid fluidic, UV reactivity, and color saturation. The energy has been conserved without high temperature process for removing organic solvent. The new system exhibits the state-ofthe- art fabrication process without unnecessary energy waste. As a result, the solvent-less CF repair inks offer a promising result for contributing to a low carbon process in the near future.

Polymer-stabilized optically isotropic liquid crystal exhibits a fairly large Kerr constant and has potential to become next-wave display technology. The underlying physical mechanism is the Kerr-effect-induced isotropic-to-anisotropic transition. Wavelength and temperature effect on the Kerr constant of optically isotropic liquid crystal composites are investigated. Our experimental results indicate that as the wavelength or temperature increases, K decreases. The proposed physical models fit very well with the experimental data.

A combination of front-scattering film and directional backlight has been proposed as a system for wide-viewing-angle transmissive liquid-crystal display (LCD). This system does not require precisely controlled phase difference film presently used in commercial LCDs, which is expected to make LCDs simpler and less expensive. However, this system has not, as far as we know, been put into practical use due to the blurring of images and the whitening of the scattering film that causes the degradation of contrast. In this article, we designed a scattering film that causes little blurring of images and whitening by optimizing conditions of light-scattering particles added to a polymer film and addition of the dye. The blurring of images was inhibited by doping polymer film with particles of high relative refractive index. The whitening of the scattering film was inhibited by the addition of the dye. The film in which particles were dispersed and accumulated showed different luminance properties and blurring of images at the same particle concentration. Finally, a directional backlight covered with the optimized scattering film showed equivalent luminance properties to those of a commercial backlight and demonstrated the feasibility of this system.

We report wide temperature range blue phase liquid crystals for display applications. Systematical analysis of the relationship of dielectric anisotropy value (Δε) and the blue phase liquid crystal (BPLC) temperature range shows that the BP temperature range increases as the Δε decrease. Additionally, we also find that as the chiral concentration of the blue phase increases, the BP temperature range decreases. The studied BPLCs also exhibit fast response time of 400 μs using IPS cells with a fixed cell gap and electrode line and space of 10 μm. These results can be explained based on the defect theory and would give effective guidance during the application of BPLC. Detailed physical, optical, dielectric and electro-optical study will be presented.

Liquid crystal alignment is a crucial step in display manufacture. Photo-alignment of liquid crystal media figures among several non-contact methods under study as potential alternatives to mechanical rubbing of polymer films. Obliquely deposited silica has also been studied as an alignment surface. We report initial studies on a non-contact approach that combines the advantages of both polymers and silica in a photosensitive spin-on type hybrid organic-inorganic glass film. We have discovered a form of nonresonant photo-induced anisotropy (PIA) in these glasses that will align nematic 4-pentyl-4'-cyanobiphenyl (5CB) liquid crystal. Optical self-writing with polarized guided waves in the glasses produces birefringence that can be "read out" by waveguide Raman scattering. 5CB spontaneously orders on the waveguides and indicates that PIA in the self-written glasses propagates to the surface of the film. PIA with polarized light at 488 nm also orients 5CB in a conventional twist cell fabricated from hybrid glasses derived from acrylates and arenes covalently bound to silicon. Electro-optic measurements on the hybrid glasses yield liquid crystal EO parameters that depend in complex ways on PIA, the chemical composition of the glass and the processing conditions of the films.

The difficulty of aligning bent-core liquid crystals at a surface is addressed from three directions: We form Langmuir monolayers of bent core molecules at the air-water interface, and explore their orientation and packing. We transfer these films by Langmuir-Schaefer techniques to a solid surface, and test them for the alignment of bulk liquid crystal. We use atomistic molecular dynamics simulations to directly probe possible molecular orientation at the water surface, for comparison with experiments. We find that relatively small changes in the bent-core molecule affect both the stability of the films and their ability to promote alignment within liquid crystal cells.

Nematic liquid crystals (NLCs) have traditionally been used in displays and other electro-optical applications where the orientation of NLC is manipulated by using an external electric field to display the information. In recent years, there have been significant advances in unconventional applications of NLCs in photonics, sensors, and diagnostics. In this paper, the application of NLCs for detection of vapor phase chemicals and biological entities is presented. When NLCs are in contact with another medium (solid, liquid or air) the delicate interplay between the properties of medium and NLCs determines the nature of the alignment assumed by NLCs at the interface. Interfaces functionalized with select chemical or biological entities promote alignment of NLCs in predetermined orientations (perpendicular or parallel to that interface) that are primarily dictated by local interactions at the interface. When these interfaces are exposed to target analytes, the interactions at the interfaces are perturbed and the NLC films undergo orientational transitions from perpendicular to parallel alignment, or vice versa. The orientational transition can be detected by viewing the film of NLCs between crossed polarizers (optical signal) or by measuring the differential capacitance associated with the change in alignment of NLCs (electrical signal). By engineering surfaces with different interfacial properties, sensors based on this principle have been demonstrated to selectively detect a wide variety of chemical and biological analytes that have relevance in industrial hygiene, environmental monitoring, homeland security, diagnostics, and biomedical applications.

In this paper, we focused on polarity of smectic mesophase and biaxiality of nematic mesophase formed by V-shaped bent-core mesogens which have an acute-subtended angle (60°) instead of an obtuse-subtended angle (120°). Their switching properties of the former mesogens were investigated and compared with the latter mesogens. On the basis of the electro/optical data a plausible model for the smectic mesophase alignments was proposed. However, we have not confirmed yet the biaxiality of their nematic phases by our experimental data.

Traditionally LC/polymer composite, such as polymer dispersed liquid crystal (PDLC), holographic PDLC (H-PDLC), and polymer stabilized liquid crystal (PSLC) etc. is primarily used as display devices. Recently, with electrical, optical and thermal tunability, easy fabrication and fast response time, they have attracted much attention in photonics devices (grating, diffractive optical elements, optical switches etc.) with potential applications in communications, imaging, and biology. The intrinsic tunable property of LC/polymer composite (by means of mechanic, electronic, magnetic, thermal stimulus) makes it an attractive material used in dynamic photonics devices. In this paper, we will first introduce the preparation of LC/polymer material for various objectives. Then two essential fabrication approaches i.e. multibeams interference lithography for periodic structures and programmable projection lithography for specific designed patterns are introduced respectively. At last, our recent results in applying LC/polymer composite in photonic devices, such as tunable 3D photonics crystals, 2D tunable lasing source, focusing elements and binary Airy beams generation etc. are reviewed.

Crosslinked liquid-crystalline polymer film (CLCP) was prepared by thermal polymerization of the mixture of an acrylate monomer and diacrylate crosslinker containing azotolane chromophores. Mesomorphic properties were studied using a polarizing optical microscope and a polarized UV-Vis absorption spectrometer. Due to a longer conjugated structure of the azotolane moieties in side chains, the CLCP film underwent photoinduced bending upon exposure to short-wavelength visible light at 436 nm and the deformable film returned to its initial flat state completely by alternating visible light to 577 nm. It was also observed that the bending process was accelerated by increasing the light intensity and the temperature. And the maximum force generated in the film upon photoirradiation decreased with the increase of the temperature and increased with the increment of the light intensity. In addition, a visible-light-driven microrobot was prepared from CLCP and polyethylene bilayer films, which could successfully lift and move an object through its "head".

We demonstrate the fabrication and characterization of optically-tunable and stimuli-responsive electrospun microfibers endowed with liquid crystal (LC) functionality. The highly flexible LC microfibers are electrospun from a solution of 4- pentyl-4'-cyanobiphenyl (5CB) and polylactic acid (PLA) in chloroform/acetone solvent. In the electrospinning process, the low molecular weight 5CB phase-separates and self-assembles to form a planarly aligned nematic core within a PLA shell. Most importantly, the orientation of LC domains and, therefore, the optical properties of the 5CB/PLA fibers can be tuned by application of an external electric field. These properties of LC fibers may, in turn, be utilized to fabricate a variety of photonic textiles, and ultimately may introduce an entirely new manufacturing process where weaving will reach well beyond the roll-to-roll manufacturing envisioned for the currently emerging flexible displays printed on flexible plastic substrates.

This paper presents an optical sensor based on the surface plasmon resonance (SPR) phenomenon, involved with liquid crystal (LC) sensitive layer. This sensor has potential applications in chemical and biological systems. We present a tracking method for the state of alignment and degree of ordering of the partially ordered LC film. This can be achieved via the SPR propagation constant and the critical angle at the interface between a metal and an LC film. The proposed idea is also investigated experimentally. For this purpose, we fabricated gold nano-dots array on an optical fiber tip for localized SPR sensing. The spectral position of the maximum loss in the transmission spectra depends on the refractive index of the medium surrounding the sensor fiber tips. This allows for tracking the LC profile parameters.

We report the design and study of new liquid crystalline block copolymers (LC-BCPs) with which unusual properties and functions can be obtained. On the one hand, we prepared the first LC-BCP comprising regioregular poly(3- hexylthiophene) (P3HT) and a side-chain liquid crystalline polymer (SCLCP) bearing azobenzene mesogens (PAzoMA). With the SCLCP block having a clearing temperature above the high crystal melting temperature of P3HT, surface- and photoinduced orientation of mesogens in PAzoMA can be used to align stripe nanodomains of P3HT on a macroscopic scale. This study demonstrates a promising pathway to achieving and manipulating macroscopically ordered nanodomains of π-conjugated polymers. On the other hand, by using a rationally designed diblock copolymer composed of two SCLCPs, photoinduced microphase separation in BCPs was achieved for the first time. In this case, the miscibility of the two LC blocks is promoted by the miscibility between the two types of mesogenic side groups, while upon UV light irradiation inducing the trans-cis isomerization of azobenzene mesogens on one block, the shape incompatibility of bent cis isomers with an ordered LC phase drives the two blocks to separate from each other resulting in a microphase separated morphology. This study shows the perspective of using light to process and organize BCP morphology and related nanostructures in a lithography-free manner.

Bragg filters or gratings have the advantages of spectrally selective reflection and high diffraction efficiency, which make them useful for a variety of applications. Liquid crystal Bragg gratings possess an additional interesting and useful feature in that they are switchable or tunable. In switchable filters the reflection notch can be switched on and off, while in a tunable filter it can be scanned through a broad spectral range. We have explored these types of filters for several years and present a review of some of their more intriguing aspects. Two types of filter have been studied: holographic polymer-dispersed liquid crystals and cholesteric liquid crystals. We describe the Bragg diffraction of these two types of filter and explore their similarities and differences. Here we will focus on switching and tuning by external stimuli such as electric fields as well as thermal and mechanical mechanisms. We further describe the physics of these devices and point out some new features we have observed as well as open questions concerning their behavior.

Nano Crystalline Cellulose (NCC) in aqueous suspension gives rise to anisotropic order that leads to iridescence from the fluid phase. Phase separation and order formation were studied using polarized optical microscopy and laser diffraction. Factors affecting liquid crystal phase separation, such as hydrolysis time, wood pulp species, sonication are discussed. Long range order and a physical grating structure are important to produce iridescence in the bulk fluid liquid crystal phase Stereomicroscopy showed that retardation lines propagate through the bulk of the fluid. Laser diffraction light experiments reveal features of the time evolution of the bulk grating. The grating structure may be used as tool to cast a chiral iridescence grating for security applications.

Holographic polymer dispersed liquid crystal (HPDLC) has a feature that can control diffraction of light by applying electric field. HPDLC can be used for optical elements such as an optical switch, or a polarized beam splitter etc. One of the reactive systems for making HPDLC is well known photopolymerization-induced phase separation (PIPS). The performance of HPDLC by PIPS is dependent on distribution of oriented liquid crystal (LC) molecules, or size and shape of LC droplets. These are controlled by chemical structure or functional group of polymer matrix. In this report, Organic-inorganic hybrid materials having sensitivity at 532 nm were synthesized. Polymer matrix was formed with co-polymerization of siloxane-containing materials and poly (propylene glycol) derivatives functionalized with methacrylate groups. Siloxane chain was introduced in polymer matrix to encourage phase separation of LC and stabilize grating structure. In addition, poly (propylene glycol) derivatives were designed to control polymerization rate and extent of phase separation of LC. The characterization of HPDLC was evaluated in terms of diffraction efficiency, contrast between diffraction and transparency modes by applying voltage, and switch speed. As a result, the separation ratio of p-polarized light and s-polarized light was 100:1. The value of ▵n was 0.075, and the index matching of both polymer-rich layer and LC-rich layer was completed at voltage of 17V/μm.