This PDF file contains the front matter associated with SPIE Proceedings Volume 6487, including the Title Page, Copyright information, Table of Contents, Introduction (if any), and the Conference Committee listing.

Beyond conventional electrooptic applications, liquid crystals become increasingly important in the topical field of organic electronics. Here, some fundamental findings are reviewed and two examples for the combination of liquid crystals and organic semiconductors are described in more detail. The first part of the paper describes the electroluminescent properties of very thin layers of aligned p-(phenylene vinylene) oligomers, which are embedded in a stack of thin organic semiconductor layers and sandwiched between two electrodes. Both the wavelength of the emitted luminescence (varying from green to red) and the dichroic ratio increase with increasing length of the aromatic backbone of the molecules. High brightness and low threshold voltages could be achieved. The photorefractive system described in the second part of the paper consists of small droplets of a low molar mass liquid crystal, which are dispersed in a photoconducting polymer. Two-beam coupling experiments indicate a high performance at reasonable external voltages. From dynamic diffraction measurements, the amplitude of the internal space charge field can be estimated.

THz time-domain spectroscopy is used to measure the frequency dependent (0.2-2.0 THz) complex refractive index of a pure liquid crystal (LC), 4'-n-pentyl-4-cyanobiphenyl (5CB), and its LC colloids with SiO₂ particles. While the refractive index of the pure LC is found to vary markedly due to distinct spatial inhomogeneities consisting of oriented domains within the sample, the LC colloids provide us with a spatially much more homogeneous dielectric response which is very stable and reproducible, from which we can reliably deduce the optical constants of pure 5CB using effective medium theory. While the absorption coefficient is found to be very small, the refractive index of 5CB decreases considerably over our probe frequency range.

We have measured the terahertz (THz) absorption spectra of MBBA (4-Methoxybenzylidene-4'-n-butylaniline) and its homologues by using THz time-domain and polarized fourier transform far-infrared (FT-IR) spectroscopy, and observed the absorption peak due to the permanent dipole moments perpendicular to the molecular long axis. In addition, we also measured the THz absorption spectra of CCN47 (4'-trans-butyl-4-cyano-4-trans-heptyl-1,1'-bicyclohexane) which has a large permanent moment perpendicular to the long axis, by using polarized far-infrared FT-IR spectroscopy. The relation between the vibration modes and the absorption in the THz region is discussed.

In this work, we report recent progress in liquid-crystal-based electrically tunable THz optical devices. Tunable phase shift up to 360° at 1 THz is demonstrated using electrically controlled birefringence in a vertically aligned nematic liquid crystal (E7) cell, 1.83 mm in thickness. The driving voltage and corresponding field required for a phase shift of 360° at 1 THz are 100 V and 90.5 V/cm, respectively. A sandwiched NLC cell about 2 mm in total thickness is used to increase the interaction length while minimizing Fresnel losses at the interfaces. A phase shift of 367° is demonstrated at 1.05 THz, significantly improving the dynamic response of the device.

The investigation of dye-doped liquid crystal systems for lasing applications has become a burgeoning topic in recent years. To date, reports have been made of the tunability of cholesteric liquid crystal lasers by means of temperature, photochemical processes and mechanical forces. The application of an in-plane electric field on a cholesteric liquid crystal results in an unwinding and elongation of the cholesteric pitch. This change in pitch length shifts the reflection band of the cholesteric liquid crystal. We report on the tunability of a cholesteric liquid crystal laser in an in-plane switching mode cell. Tunabilities of up to 15 nm have been achieved in these cells. Electrical tuning methods have significant advantages over the other techniques by which cholesteric lasers can be tuned, especially with regards to the potential applications of liquid crystal lasers.

In this paper, we demonstrated a new dye-doped cholesteric liquid crystal (CLC) photonic band edge laser with emission enhanced by an external cholesteric resonator. As one-dimensional photonic crystal, the 5-&mgr;m dye-doped cholesteric liquid crystal cell generates circularly polarized laser emission at its photonic band edge. When sandwiched between two 5-&mgr;m cholesteric liquid crystal mirrors whose reflection band reflects the laser emission from the central dye-doped CLC laser, the emission can be enhanced by ~800X. In experiment, a second-harmonic Q-switched Nd-YAG pulsed laser is used to pump the CLC laser assembly at normal incidence. The detected laser emission is elliptically polarized and is still located at the band edge wavelength of the central CLC cell. The beam divergence is decreased by ~10X due to an increased cavity length. Theoretical analysis using 4x4 transfer matrix and scattering matrix has shown that the circular resonator produces transmission peaks based on Fabry-Perot effect inside reflection band and, moreover, the transmission peak at the band edge of central CLC can be well-preserved. Both experiment results and simulation results are present in good agreement.

This paper provides research progress in the development of fast electro-optic gratings for high energy laser beam attenuations. The electro-optic phase grating is formed by the phase separation of small liquid crystals droplets from a polymerizing organic matrix using holographic interference technique. The formed grating separates the incident laser beam into two output beams: the transmitted and diffracted beam, whose intensities can be electrically adjusted through electro-optic effect. The fast electro-optic gratings have a very fast electro-optic response time of 50 &mgr;s is with diffraction efficiency above 99%.

This investigation establishes two spatial filters based on dye-doped liquid crystal films. One is made with a dye-doped liquid crystal (DDLC) film, and is polarization controllable. The other is transflective, and is fabricated with an azo dye doped cholesteric liquid crystal (DDCLC) film. The fabrication of the former type relies on the fact that the various intensities of the diffracted orders are responsible for various changes of the polarization state induced by the photo-aligned DDLC film. Particular spatial orders in the Fourier optical signal process can be filtered using an analyzer placed behind the sample by controlling the polarization state of the diffracted orders. The latter is based on the photoisomerization effect in a DDCLC film with a concomitant lowering of phase transition temperature from a cholesteric to an isotropic phase (T_Ch-I). The fabrication relies on the fact that the various intensities of the diffracted orders are responsible for various degree of transparency induced by the photoisomerized DDCLC film. Particular spatial orders in the Fourier optical signal process can be filtered to trans- or reflect- part at the same time. Simulations are also performed for the two-type spatial filters, and the results agree closely with experimental data.

In this original review we briefly consider the novel azo-dye photo-aligning technology: history and the perspectives for future applications in liquid crystal (LC) devices. The review describes the following items. The brief introduction to the history of photoalignment and the basic classes of the photoaligning materials: photosensitive polymers, azodyes and monolayers will follow with an introduction to the physical mechanisms of the photo-aligning and photo-patterning technology. The advantages and drawbacks of various photo-aligning materials are analyzed from the point of view of practical applications. The detail description of the diffusion photo-aligning in azo-dye materials is provided. The characteristics of azo-dye photoaligning LC layers are compared with those ones prepared by polyimide rubbing method. The characterization of LC-surface interaction, such as pretilt angle and azimuthal anchoring energy is discussed. The newly developed materials should have a controllable pretilt angle and anchoring energy, thus enabling to develop a new generation of the LC devices: with low voltage, fast response and wide viewing angles. The problem of image sticking can be considerably reduced due to the high anchoring energy of azo-dye materials. Promising results, obtained for voltage holding Ratio (VHR) and residual DC voltage (RDC) in azodye photo-aligning materials are also shown. This implies that the azo-dyes can be applied as aligning layers in active matrix liquid crystal displays (AM-LCDs). The possibility to use the photo-aligning layers for new types of liquid crystal displays such as FLCD, VAN-LCD, &pgr;-BTN LCD, optical rewritable memory, microdisplays, and TN-LCD on plastic substrates is demonstrated. The photoaligning of liquid crystal polymers (LCP) and the new classes of devices based on them (optical retarders and compensators) is discussed. Special types of 3D LC alignment, LC alignment inside thin micro tubes, and grating surface were concerned. New superthin photo-aligned polarizers based on azo-dye layers were demonstrated. The polarizers are based both on photo-aligned lyotropic LC as well as pure azo-dye layers. The polarizers can be patterned and put inside LC display cell to serve as internal polarizers. Both color and neutral internal polarizers can be fabricated with the thickness 0.3-0.7 &mgr;m. The electo-optic response of TN-LCD with internal polarizers is practically the same as in case of usual external polarizers. New applications in transflective and 3D displays are envisaged.

Lyotropic chromonic liquid crystals (LCLCs) are formed by molecules with rigid polyaromatic cores and ionic groups at the periphery that form aggregates while in water. Most of the LCLCs are not toxic to the biological cells and can be used as an amplifying medium in real-time biosensors. The detector is based on the principle that the immune aggregates growing in the LCLC bulk trigger the director distortions. Self-assembly of LCLC molecules into oriented structures allows one to use them in various structured films. For example, layer-by-layer electrostatic deposition produces monomolecular layers and stacks of layers of LCLC with long-range in-plane orientational order which sets them apart from the standard Langmuir-Blodgett films. We demonstrate that divalent and multivalent salts as well as acidic and basic materials that alter pH of the LCLC water solutions, are drastically modifying the phase diagrams of LCLC, from shifting the phase transition temperatures by tens of degrees, to causing condensation of the LCLC aggregates into more compact structures, such as birefringent bundles or formation of a columnar hexagonal phase from the nematic phase.

Flexible Cholesteric liquid crystal displays have been rapidly maturing into a strong contender in the flexible display market. Encapsulation of the Cholesteric liquid crystal permits the use of flexible plastic substrates and roll-to-roll production. Recent advances include ultra-thin displays, laser-cut segmented displays of variable geometry, and smart card applications. Exciting technologies such as simultaneous laser-edge sealing and singulation enable high volume production, excellent quality control and non-traditional display geometries and formats.

Liquid crystals have had a large presence in the display industry for several decades, and they continue to remain at the forefront of development as the industry delves into flexible displays and electronic paper. Among the emerging technologies trying to answer this call are polymer cholesteric liquid crystal (PCLC) flakes. The motion of PCLC flakes suspended in a host fluid is controlled with an electric field, whereby the flakes reorient to align parallel with the applied field. A PCLC device easily switches from a bright state, where light of a given wavelength and polarizationis selectively reflected, to a dark, non-reflective state. The device returns to a bright state when the flakes relax to their original orientation after removal of the applied field. Progress has been made in addressing several key device issues: the need to switch flakes back to a reflective state quickly, the development of bistability, the ability to produce flexible devices, and the necessity to produce both high brightness and a large contrast ratio. Improvements in the technology have been made by addressing the optical, mechanical, chemical, and electrical features and characteristics of the PCLC flake/fluid host system. The manufacture of "custom" flakes by the process of formation of specific flake shapes, the addition of dopants, or the formation of layered flake composites results in particles with improved reflectivity and response times along with the ability to respond to both AC and DC fields. Specially designed driving waveforms provide a new means for controlling flake motion. PCLC flake micro-encapsulation allows for the possibility of flexible and potentially bistable devices. Here we report on the wide variety of approaches toward improving PCLC flake devices and their results.

We describe wide temperature range new bimesogenic nematic liquid crystals with high flexoelectro-optic coefficients (e/K),of the order of 1.5- 2.0 CN^-1 m^-1, high switching angles, > 100° and microsecond response times which may be used to give gray scale devices in both the ULH texture, with an optimum optical in plane switch of 45° at fields of 4V&mgr;m^-1 or less, and in the USH or Grandjean texture (with a unique optically isotropic "field off" black state and contrast ratios of > 1000:1), using "in plane" electric fields, with switching times of the order of 20&mgr;s. The new materials and devices give &mgr;s level to level switching and the real potential for colour filter free frame sequential colour switching. New highly reflective Blue Phase devices, stable over a 50°C temperature range, in which an electric field is used to switch the reflection from red to green, for example, will be described. Full RGB reflections may be obtained with switching times of a few milliseconds. Finally we will briefly mention potential applications including high efficiency RGB liquid crystal laser sources.

With hole-patterned electrodes separated from liquid crystal layers it becomes possible to fabricate liquid crystal lens of high quality and large size. The properties of the lens of this kind of electrode structure are discussed. The modifications to the original structure to realize lenses of improved quality, that are polarization-independent and having focus movable in focal plane are also discussed.

Optical waveguides are widely used in the telecom industry for long distance data transport. Glass fibers are designed to have minimal losses. Different functionalities have been integrated in waveguides, such as wavelength filtering, amplitude modulation and routing. Liquid crystals are promising, because their optical properties can be modified by applying a small voltage or by illumination with light. The variation in optical properties can be exploited in different kinds of waveguide systems. It is possible to generate a wave guide in bulk liquid crystal by modulating the director orientation in an appropriate pattern. Some guided modes in such pure liquid crystals are discussed. Because the liquid crystals are anisotropic, the modes have some unusual properties. The influence of light can lead to director reorientation and modify the waveguiding properties. This optical non-linearity determines largely the light propagation. In hybrid waveguides, liquid crystal are used in combination with a material with higher (in the core) or lower (in the cladding) refractive index. Silicon on insulator waveguides are convenient components to study the tuning possibilities in combination with liquid crystals.

We developed an electrically switchable mirror based on polymer-stabilized, short-pitched cholesteric liquid crystals using electro-optical cells with planar alignment. The devices enable the switching of a pre-selected reflective wavelength of the cholesteric to reflect a different wavelength in corresponding to the magnitude of applied electric field. The principle of the wavelength shift to a shorter wavelength is a result of field-induced pitch shortening near the boundaries. The spectral wavelength shift of the reflected wavelength is about 140-nm and the wavelength shift is linearly proportional to the magnitude of applied voltage. The optical response of the device is also studied.

The study of optical solitons and light filaments steering in liquid crystals requires utilization of particular cells designed for top view investigation and realized with an input interface which enables both to control the molecular director configuration and to prevent light scattering. Up to now, the director orientation imposed by this additional interface has been only estimated by experimental observations. In this paper, we report on the design and characterization of liquid crystal cells for investigation of optical spatial solitons as well as on a simple model describing the configuration of the molecular director orientation under the anchoring action of multiple interfaces. The model is based on the elastic continuum theory and only strong anchoring is considered for boundary conditions. Controlling of the director orientation at the input interface, as well as in the bulk, allows to obtain configurations that can produce distinct optical phenomena in a light beam propagating inside the cell. For a particular director configuration, it is possible to produce two waves: the extraordinary and the ordinary one. With a different director configuration, the extraordinary wave only is obtained, which propagates inside the cell at an angle of more than 7° with respect to the impinging wave vector direction. Under this peculiar configuration and by applying an external voltage, it is possible to have a good control of the propagation direction of the optical spatial soliton.

Ferroelectric nanoparticles significantly improve properties of existing liquid crystals and benefit the performance of many devices. By changing a concentration and a type of ferroelectric particles one can affect physical properties of the nematic, smectic, and cholesteric liquid crystal materials, including the dielectric constants, the birefringence, the phase transition temperatures, and even the order parameter. We demonstrate the performance of these new materials in various devices, including displays, light modulators, and beam steering devices.

Recently, active researches on carbon Nanotube (CNT)-doped liquid crystal (LC) mixtures are progressing. Based on experimental observations, CNTs are known to align parallel to the LC director and experience orientational deformation associated with the LC deformation under an electric field. Theoretical calculation also shows that the LC is strongly anchored on CNT in a way that the LC director is parallel to the CNT long axis. Many experimental results have been reported regarding to CNT effects on electro-optic characteristics of the LC device such as threshold voltage, residual dc and response time, and physical properties of a nematic LC such as rotational viscosity, dielectric anisotropy, elastic constants and clearing temperature, although some are still controversial. In this talk, historical reviews as well as our achievements on CNT-LC mixtures will be discussed.

Bragg gratings yield a single diffracted order when irradiated by a coherent beam at the appropriate Bragg angle. In many cases, nearly all of the energy of the incident beam can be coupled to the diffracted beam. Hence these gratings can form many useful optical elements, and this has been realized in 1-D, 2-D, and 3-D photonic crystals. Bragg gratings made with liquid crystals offer the added dimension of dynamic properties through the large electro-optical effect in liquid crystals. Applications for spatial light modulators are numerous, including optical switches, modulators, active optical elements (e.g., lenses), laser sources, and tunable filters. We have been exploring a number of approaches for making liquid crystal Bragg gratings, including holographic polymer-dispersed liquid crystals, cholesteric liquid crystals, and homogenous nematic liquid crystals in hybrid devices. We have studied the dynamic properties of these Bragg gratings by electrical, thermal, and optical stimulation. Modification and control of optical and dynamic properties have been obtained through combinations of liquid crystals with polymers, combinations of various dopant materials, and interactions of liquid crystals with organic and inorganic interfaces. We discuss the materials, fabrication, characterization, and physics of liquid crystal Bragg gratings and present the results of various devices we have studied in our lab. We will also discuss potential applications.

With this paper we present a new developed phase-only LCOS (Liquid Crystal On Silicon) spatial light modulator (SLM) based on an electrically controlled birefringence (ECB) liquid crystal mode for dynamic diffractive optics applications, optical tweezing, wave front control, digital holography and beam/pulse shaping. This device is the first phase-only SLM showing HDTV resolution and a small pixel pitch of only 8&mgr;m (87% fill factor) on a digital silicon back plane. Here the LC molecules are aligned parallel to the electrodes and an applied electric field forces them to tilt in the direction of the field. In this way, the refractive index seen by the light is changed for one polarization direction. This leads to a pure phase modulation without any polarization change (<1%) if the incident light is polarized linearly parallel to the director axis of the LC molecules. We have investigated two versions of this new SLM. One version is optimized for the visible wavelength region (420-800nm) and the other one is designed for 2&pgr; phase retardation up to 1064nm. We will discuss the optical modulation and show measurements on reflectivity, diffraction efficiency as well as measurements of the surface quality (flatness). With user software one is able to adapt the electro-optical response of the system to different wavelengths and applications. Furthermore, we discuss the optical effect of different sequence encoding for the phase modulation properties.

We developed a liquid-crystal-on-silicon (LCOS) spatial light modulator (SLM) for phase-only modulation. The SLM was designed mainly for wavefront control in adaptive optics, optical manipulation, laser processing, etc. A dielectric multilayer mirror was incorporated into the device to enhance the reflectivity. The number of pixels was 792 x 612 and their size was 20 x 20 microns square. The range of the phase modulation exceeded one wavelength, and the light-utilization efficiency for monochromatic light was approximately 90%. The silicon backplane of the SLM was mechanically weak and its surface was not flat. The poor flatness degraded the output wavefront from the SLM. The device was driven by electronics composed of a digital-visual-interface (DVI) receiver, a field programmable gate array, and 12-bit digital-to-analog converters (DACs). The converted analog voltage signals from the DACs were transmitted to the pixels of the SLM and created phase changes. The driver had several kinds of control modes for the device, according to the level of flatness compensation. In one of the modes, the driver received 12-bit data and transferred them directly to the DACs. This 12-bit control mode enabled highly flexible control of the device characteristics. In the presentation, we report details of the device and experimental results on compensation of distortion in the output wavefront from the device.

For years, the technology of TFT-LCDs (thin-film-transistor liquid crystal displays) has grown very rapidly, especially in the market share and technical development of FPD industries. To effectively promote the industry's capacity for the mass production and quality control, it is urgent to design and develop LC cell optical parameter measurement systems. The goal of this paper is to develop a multiple-functional and cost-effective measurement system to lower the manufacturing cost for the industry. The optical parameters includes the pretilt angle, liquid crystal (LC) cell gap (or phase retardation), and twist angle, which highly influence the display quality. In this paper, we first study the past approaches and analyze their measurement performance. Then, a simple and cost-effective method is proposed to achieve the multiple functions. That is, in addition to the precise measurement of the three important optical parameters, the proposed system can measure the voltage-transmittance (V-T) curve. In our approach, the theoretical study, simulation, and experiment are performed to show the feasibility of the system implementation. Finally, the proposed system is developed to automatically measure the LC cell parameters. Experimental results indicate that the proposed measurement system gives a satisfactory result.

A new type of diffractive spatial optical modulators, named SOM, has been developed by Samsung Electro-Mechanics for laser projection display. It exhibit inherent advantages of fast response time and high-performance light modulation, suitable for high quality embedded laser projection displays. The calculated efficiency and contrast ratio are 75 % and 800:1 respectively in case of 0^th order, 67 % and 1000:1 respectively in case of ±1st order. The response time is as fast as 0.7 &mgr;s. Also we get the displacement of 400 nm enough to display full color with single panel in VGA format, as being 10 V driven. Optical module with VGA was successfully demonstrated for its potential applications in mobile laser projection display such as cellular phone, digital still camera and note PC product. Electrical power consumption is less than 2 W, volume is less than 13 cc. Brightness is enough to watch TV and movie in the open air, being variable up to 6 lm. Even if it's optimal diagonal image size is 10 inch, image quality does not deteriorate in the range of 5 to 50 inch because of the merit of focus-free. Due to 100 % fill factor, the image is seamless so as to be unpleasant to see the every pixel's partition. High speed of response time can make full color display with 24-bit gray scale and cause no scan line artifact, better than any other devices.