Bistable reflective cholesteric displays are a liquid crystal display technology developed to fill a market need for very low power displays on a low-cost, high resolution passive matrix. Their unique look, high reflectivity, bistability, and simple structure make them an ideal flat panel display choice for handheld or other portable devices where small lightweight batteries with long lifetimes are important. We discuss recent advances in cholesteric display technology at Kent Displays such as progress towards single layer black and white displays, standard products, lower cost display modules, and various interface options for cholesteric display applications. It will be shown that inclusion of radio frequency (rf) control options and serial peripheral interface (spi) can greatly enhance the cholesteric display module market penetration by enabling quick integration into end devices. Finally, some discussion will be on the progress of the development of flexible reflective cholesteric displays. These flexible displays can dramatically change industrial design methods by enabling curved surfaces with displays integrated in them. Additional discussion in the paper will include applications of various display modes including signs, hand held instrumentation, and the electronic book and reader.

TN-LCDs fabricated by doping metal nanoparticles of such as Pd, Ag, Au, or Ag-Pd composite are shown to exhibit a frequency modulation electro-optic response with short response time of ms or sub-ms order. These devices are called FM-LCDs. The frequency range spreads from 40 Hz to 2 KHz around a dielectric relaxation frequency that increases with increasing the concentration of metal nanoparticles. This behavior is explained by the equivalent circuit model of heterogeneous dielectrics, for the first time, formulated by the present authors. Further, we discuss the origin of the fast response and the value of electrical conductivity of metal nanoparticles.

Single or dual panel microdisplay systems are becoming more popular in the marketplace. Consequently, Liquid Crystal on Silicon (LCoS) microdisplays are constantly being pushed to achieve faster switching times as well as higher contrast, while becoming simpler and allowing simpler optics engine design. Currently, most products use a Twisted Nematic (TN) mode with a retardation film. The most promising solution in research now is the Vertically Aligned Nematic (VAN) mode, which does not require a retarder.

We propose a high-speed optical measurement method for determining cell parameters such as cell thicknesses and twist angles of reflective liquid crystal (LC) cells. A polarization-converting device prepared using a circularly-homogeneously aligned LC (CH-LC) cell and a charge couple device (CCD) camera are used. The spatial light intensity distribution from the reflective LC cell through the CH-LC cell and the local minimum point are measured. Then the cell parameters can be derived by using the coordinate values of the point and the Jones matrix analysis.

A paper-like cholesteric liquid crystal (ChLC) display has been developed by photo-induced polymer/ liquid crystal phase separation process. Depending on this process, the homogeneous mixture of ChLC and pre-polymer would separate into polymer walls and ChLC rich region. Polymer walls formed by photopolymerization of pre-polymer provide several advantages of flexible display applications such as good mechanical properties and low cell gap tolerance. The ChLC rich region was a composite combined by the ChLC and dispersed polymer. This dispersed polymer was derived from the residue polymer in the display area after the phase separation process. This dispersed polymer was used to disturb the alignment of ChLC, and break the planar structure into multi-domain planar structure which would present the white appearance in the planar state. The electro-optical properties were measured by Otsuka LCD 5100 and Eldim EZ Contrast 160RH. The relationship between phase separation process and electro-optical properties was also been developed.

Liquid crystal networks change their dimensions when the degree of order is altered. Upon decreasing order, e.g. as a result of temperature increase, the linear dimension decreases in the direction along the director and increases orthogonal to that. When the director changes as a function of position, the local dimensional changes cause stresses that effect in deformation of the sample. In the case of thin films with a twisted molecular orientation over their cross-section a change in the order parameter results in a double, saddle-like, bending of the film as the linear expansion is different for both in-plane axes. For geometric reasons this bending is uncontrolled and irregular. When the linear expansion is chosen to be different along one in-plane axis, but is kept the same for the other axis, the deformation becomes orderly and controlled. Therefore, films of liquid crystal networks with a splayed molecular alignment over their cross-section provide a well-controlled bending deformation as a function of a changing order parameter. In a liquid crystal network the order parameter can be modulated by temperature. The direction- and order parameter dependent linear expansion than comes on top of the volume expansion as caused by induced thermal molecular motions and decreased secondary molecular forces. Besides by temperature the order parameter can also be modulated by light in the presence of photo-sensitive moieties in the liquid crystal network. The deformation behavior is anticipated to be of relevance for polymer based MEMS technology.

Cornerstone Research Group Inc. (CRG) will present a brief overview on our recent efforts in developing liquid crystal (LC) network polymers for various applications. These efforts cover different aspects of the LC network polymer material technology in optical, structural and other novel applications. Liquid crystal network polymers have demonstrated great potential in producing high-performance optical components and smart materials, such as actuators. We will discuss the potential applications of these materials as optical filters, reflectors for lightweight space-based mirrors, and structural resins to improve toughness. The potential to capitalize on the templating capability of these materials to produce novel all-polymer conducting composites will also be discussed. Various possibilities and directions for future research and applications of liquid crystal network polymers will also be presented.

The recently discovered stressed liquid crystals (SLCs) are of a great interest because they provide the largest phase retardation shift achievable within the shortest time interval. This was accomplished by decoupling the speed of a liquid crystal layer from its thickness. SLCs easily switch 5 microns of phase retardation at sub-millisecond speeds. We have produced phase shifts as large 50 microns in several milliseconds. SLCs are therefore able to modulate IR light with response frequencies higher than 10 kHz. The SLCs are polymer/liquid crystal composites; however, their electro-optic properties differ significantly from previously developed polymer dispersed liquid crystals and polymer network/stabilized liquid crystals. An applied mechanical stress aligns the liquid crystal domains, eliminating scattering and hysteresis at the same time. The phase shift is highly linear with the applied voltage, greatly simplifying the drive electronics. The SLCs pose intriguing basic scientific questions and may be used in a host of new electro-optical applications (micro-displays, diffractive optical elements, beam steering devices).

Surface effects on the phase separation dynamics, morphologies, and electro-optic properties of thin polymer-dispersed liquid crystal (PDLC) cells are investigated. Four types of surface alignment layers were studied: ITO only, Polyimide (PI) without rubbing, homogeneous cell, and 90° twisted nematic (TN) cell. The ITO-only and non-rubbed PI cells do not provide enough anchoring force to prevent LC droplets flow and coalesce. As a result, the droplets are larger and less uniform. For the homogeneous and TN cells with sufficiently high anchoring energy, almost all the nucleated LC droplets grow at a fixed position during phase separation. The appearance of the coalescence is not obvious and the formed LC droplets are relatively uniform. For the rubbed cells with polar anchoring energy >2x 10^-4 J/m², the droplet size is smaller and more uniform than those in the conventional PDLC cell. The phase separation dynamics determine the final composite morphology which affects the electro-optic properties of a PDLC device. The morphologies in the homogeneous and TN cells are similar, but the TN cell is polarization independent while the homogeneous cell is polarization dependent. Moreover, the TN PDLC cell exhibits a higher contrast ratio. The light shutter made of TN PDLC shows no haze and 5-10 ms response time.

Liquid crystal and polymer dispersions (LCPD) have potential application as flat panel displays, switchable lenses, optical switches, Bragg gratings, photonic crystals, diffractive optics, hyper-spectral filters, and etc. Precise morphological control of the phase-separated morphology of LCPDs is required to meet the rigorous requirements for the numerous applications. Liquid crystal and polymer dispersions (LCPDs) are micro or nano-structured materials fabricated using one of several phase separation techniques. The micro- or nano-structured morphology of LCPDs ranges from a polymeric network suspended in a liquid crystal solvent (polymer stabilized liquid crystals [PSLC] to random or spatially periodic micron or sub-micron sized liquid crystal droplet dispersions in a solid polymer matrix of polymer dispersed liquid crystals (PDLC) and the holographically formed PDLC (H-PDLC). The goal of this investigation is to identify the material properties and processing conditions required for more precise control of the phase-separated morphology of PDLCs. The investigation entailed construction of thermal phase diagrams for liquid crystal and monomer/pre-polymer mixtures to identify the compositionally dependent phase separation temperatures. The investigation also entailed inducing phase separation of the mixtures via ultra-violent light initiated polymerization at carefully chosen cure temperatures based on the thermal phase diagrams. The phase-separated morphology was correlated with the cure temperature, liquid crystal component, and mixture composition.

We discussed the effect of polymer concentration and localization on flexoelectro-optical device using short pitch cholesterics oriented in uniform lying helix texture. By using a small concentration of photoreactive liquid crystal monomer with various concentrations and selecting the illumination conditions, we have been able to create a localized polymeric network at both substrate surfaces. We can stabilized the two switching modes and eliminating at the same time the effect of the residual birefringence of the polymeric network in the field-unwound state of the sample. The device has two operating modes: amplitude and phase modulation mode, respectively. The amplitude modulation mode is a fast in-plane switching of the device optic axis that enables to achieve a 100 % modulation of the transmitted light intensity whereas the phase mode gives a continuous change of the refractive index and thus of the phase shift of the transmitted light.

We describe the development of fiber chiral gratings and discuss salient similarities and differences from planar chiral structures. Planar chiral structures include cholesteric liquid crystals and structured thin films produced by oblique deposition of dielectric materials on a rotating substrate. These are composed of uniform anisotropic planes with 180 degrees rotation symmetry which rotate uniformly with displacement perpendicular to the planes so that the pitch is equal to twice the period. The sinusoidal modulation of the structure which possesses double-helix symmetry results in a single band gap for co-handed light with the same sense of circular polarization as the handedness of the helical structure. Orthogonally polarized light is freely transmitted. Within the band gap the wavelength in the medium equals the structure pitch. Double-helix symmetry may also be implemented into a fiber geometry by twisting glass optical fiber with noncircular core cross section as it passes through a miniature oven. In addition to the polarization-selective resonant band observed in planar chiral gratings, we observe two additional modes of optical interaction when the pitch exceeds the wavelength in the fiber. In chiral long period gratings, dips in transmission are observed at wavelengths associated with coupling of the core mode and distinct cladding modes mediated by the chiral grating. In chiral intermediate period gratings, a broad scattering band is observed due to scattering out of the fiber into a continuum of states. Gratings with uniform pitch as well as with a specially designed pitch profile can be utilized to produce a variety of polarization selective devices. In addition to describing optical chiral gratings, we describe studies of microwave planar and fiber gratings, which played a key role in the development of optical fiber chiral gratings.

Optical switching allows us to make the photonic network flexible and expandable. We have been studying two types of optical switches incorporating ferro-electric liquid crystals (FLCs). One type of them is a polarization-controlled free-space optical switch whose operation principle is based on the polarization switching by FLC cells. It has a novel integrated structure consisted with FLC polarization control devices (FLC-PCDs), thin-film beam-splitters and mirrors. The FLC-PCD with a metal mirror electrode is the key element in this switch. The design theory for the FLC-PCD to achieve an accurate 90-degree polarization switching for the oblique incident light has been developed and verified by experiments. 2x2 and 4x4 optical switches were fabricated for optical communication wavelengths of 1300 and 1550nm and their feasibility was demonstrated. The other switch type is a waveguide switch composed of an optical waveguide having FLC claddings. The FLCs in the cladding layer change their effective refractive index corresponding to the applied voltage polarity, providing the phase shift of the travelling lightwave in the waveguide. The operation principle of the switch has been confirmed by an experimental Si waveguide Mach-Zehnder interferometer (MZI) having FLC claddings.

The photorefractivity of a ferroelectric liquid crystal (FLC) mixed with a photoconductive compound was investigated in detail. FLCs are anisotropic media, so that laser beam incidence conditions strongly affect the formation of the refractive index grating. Effects of intersection angles of the laser beams, sample angle and sample thickness on the photorefractivity of FLCs were examined. The motion-mode photorefractive efffect of a FLC was also investigated.

This letter examines a planar cholesteric cell (CLC) doped with a collocation of two laser dyes as a one-dimensional photonic crystal. Adding the photo-tunable chiral material-AzoB allows the CLC photonic crystal can be lased at the band edges of the photonic band gap with a tuning range of over 100nm. Tuning is performed by irradiating the chiral AzoB material with UV light so that it undergoes trans-cis isomerization in the CLC film. The tuning range is the visible region from 563nm to 667nm. Moreover, the tuning is reversible.

The purpose of this study was to investigate the effect of varying the pump efficiency of dye-doped chiral nematic liquid crystal lasers, through the dependence on absorption efficiency. Two dyes from the rhodamine subset of the xanthene family (rhodamine B and rhodamine 6G) with similar chemical properties but different absorption and emission spectra have been compared for a fixed pumping wavelength (532nm). Each dye was dissolved in E49 (a commercial nematic mixture from Merck NB-C) and the resulting mixtures characterised in terms of their absorption and laser induced fluorescence spectra. A high twisting power chiral dopant (BDH1281, also from Merck NB-C) was used to induce 1-D photonic band gaps with the high and low energy edges corresponding to the fluorescence maximum for each dye. Laser action was induced in the resulting four mixtures and typical laser parameters such as slope efficiency and threshold energy were examined for each one. The results indicate that the mixtures doped with rhodamine 6G had an absolute absorption ~ 57% greater than those doped with rhodamine B. Rhodamine 6G-doped mixtures therefore had the highest pump efficiency and lased more than 6 times more efficiently then those doped with rhodamine B. We believe that the performance of rhodamine 6G is also influenced by its greater degree of alignment with the liquid crystal host and a possible input energy dependence of the quantum efficiency of the dyes (indicated by the fluorescence characteristics of the achiral dye-doped mixtures). Further experimentation is needed to determine exactly which parameters are responsible for the superior performance of rhodamine 6G in chiral nematic lasers.

In order to develop a fine angular beam steering technique (milliradian and less), we propose a nematic liquid crystal cell with a continuous gradient of the refractive index. This continuous gradient is controlled by applying the driving voltage to non-patterned indium-tin oxide electrodes. We employed the dual-frequency nematic liquid crystal in the cell with high pretilt alignment. The experiments with dual-frequency nematic confirmed that non-patterned electrically controlled nematic cell with the continuous gradient of refractive index is capable of angular beam steering in the milliradian range.

Since the human eye is insensitive to polarization, there is a large amount of information in many situations which is not readily utilized. Measuring the polarization state of light is useful in many research fields including biology, chemistry, astronomy and remote sensing. The first portion of the paper discusses the simple application of accurately measuring the retardance value and fast axis position of an unknown waveplate. We will mention some of the many other polarimetry applications especially in the context of non-mechanical, liquid crystal based polarimeter experimental technique. Some of these examples are from biology showing tissue birefringence changes, astronomy for solar imaging, polarimetric visualization and landmine detection.

Liquid crystal (LC) wavefront correctors with modal addressing are described. Three different approaches are considered. The first one is based on a continuous thin-film resistive layer. This layer is used for forming of the local voltage profile that controls the phase distribution across the corrector’s aperture. The second approach is a modification of the first one, where the continuous resistive coating is replaced by a network of discrete resistors. It is based on silicon technology. The third approach makes use of distributed electric field in thick dielectric layers for forming of the modal response of an actuator. Technologies, methods of control and experimental results are discussed for each case.

Long-range forces between ultra-fine particles imbedded in liquid crystal (LC) result in intriguing colloids. Embedded inorganic particles in LC contribute to the properties of the LC matrix. Large (>>mkm) colloidal particles form defects in LC matrices due to strong director deformations and ensembles of these particles and defects can form complex structures. Small particles at its high concentration (> 2-3% by weight) create almost a rigid LC suspension. We show that at low concentrations LC submicron colloids appear similar to a pure LC with no readily apparent evidence of dissolved particles, but possess unique properties. The diluted suspensions are stable, because the small concentration of submicron particles does not significantly perturb the director field in the LC, and interaction between the particles is weak. At the same time, the submicron particles share their intrinsic properties with the LC matrix due to the anchoring with the LC. We report on the development and unique properties of the diluted suspensions of ferroelectric submicron particles. Our results show that doping a nematic LC matrix with ferroelectric submicron particles results in a suspension, which possesses an enhanced dielectric anisotropy and reveals ferroelectric and paraelectric properties inherent to the submicron particles. In particular, we observed essential decrease of the driving voltage of the quadratic dielectric response and non-usual linear dipole response of the suspensions on the application of ac-field. We present a theoretical model of dielectric properties of ferroelectric suspensions.

High diffraction efficiency and large diffraction angle are two major concerns in designing a liquid crystal (LC) phase grating for its applications in beam diffractive devices. High-spatial-frequency grating is capable of providing a large diffraction angle. However, fringing-field effect becomes more severe when the grating pitch size decreases, which imposes a limitation on the phase modulation depth and the diffraction efficiency of the LC grating. In this paper, a novel LC grating with striped electrodes patterned on both the top and bottom sides was proposed and fabricated. By using a specified biasing configuration, vertical electric fields are generated and well confined between the facing electrodes. Meanwhile, horizontal electrical fields are created between adjacent electrodes which help reducing the undesirable deformation of the LC director axis resulting from the fringing filed. Computer simulations show, in our novel structure, a maximum phase modulation depth of 4.15 rad (for 1.55 μm) can be achieved, which is large enough to satisfy the 1.17 π phase-shift requirement for maximum first order diffraction in sinusoidal phase gratings. Both the conventional single-sided and the novel double-sided LC gratings were fabricated and tested. Measurements showed, there was an efficiency enhancement of 77 times achieved by the double-sided structure comparing the conventional structure. A first order diffraction with diffraction angle at 14.5o and diffraction efficiency of ~31% is experimentally achieved, of which the efficiency approaches the theoretical upper limit at 33.8% for a sinusoidal phase grating.

Liquid crystal variable phase retarders have been incorporated into prototype devices for optical communications system applications, both as endless polarization controllers1,2,3, and as holographic beam steerers4. Nematic liquid crystals allow continuous control of the degree of retardation induced at relatively slow switching speeds, while ferroelectric liquid crystal based devices allow fast (sub millisecond) switching, but only between two bistable states. The flexoelectro-optic effect5,6 in short-pitch chiral nematic liquid crystals allows both fast switching of the optic axis and continuous, electric field dependent control of the degree of rotation of the optic axis. A novel geometry for the flexoelectro-optic effect is presented here, in which the helical axis of the chiral nematic is perpendicular to the cell walls (grandjean texture) and the electric field is applied in the plane of the cell. This facilitates deflection of the optic axis of the uniaxial negatively birefringent material from lying along the direction of propagation to having some component in the polarization plane of the light. The device is therefore optically neutral at zero field for telecommunications wavelengths (1550nm), and allows a continuously variable degree of phase excursion to be induced, up to 2π/3 radians achieved so far in a 40μm thick cell. The retardation has been shown both to appear, on application of the field, and disappear on removal, at speeds of 100-500 μs. The direction of deflection of the optic axis is also dependent on the direction of the field, allowing the possibility, in a converging electrode "cartwheel cell", of endless rotation of the liquid crystal waveplate at a higher rate than achievable through dielectric coupling to plain nematic materials.

We demonstrate an electro-optic switch and a variable attenuator for telecommunication applications at λ=1550nm by employing the ferroelectric and electroclinic properties of an organosiloxane liquid crystal. In the ferroelectric SmC* phase an optical switch has been realised with an extinction ratio of 36dB between crossed polarisers. The switching time was ~200microseconds. In the SmA* phase the analogue nature of the electroclinic effect was employed to obtain a variable attenuator. The maximum attenuation range between crossed polarisers was 35dB for an applied electric field of +-9V/micron. The response time of the device was about 100microseconds, independent of the applied electric field. Both devices where demonstrated in the same 21.5micron thick cell which provided a retardance of λ/2 at λ=1550nm.

We propose a laser manipulation (optical tweezers) system for controlling microscopic objects by using a liquid crystal (LC) optical device with variable focusing and beam deflection properties. The focused spot, that is the position of the trapped particles can be controlled and moved by the change of the optical properties of the LC optical device by applying the voltage to the LC cell.

The application of the Liquid Crystal Display (LCD) to TV application needs faster response time to reduce trailing effect of moving picture. Due to the strong anchoring energy of liquid crystals on the alignment layer, the overall response time is increased. Therefore the control of the anchoring strength of the Liquid Crystals at the surface layer in display device could improve the response time of LCD. From the previous research of various kinds of hydroxyl functional perfluorinated additives [1], we chose the monohydroxylated additives for further study. In this research the effects of degree of fluorination in additives on the performance of Liquid Crystal Displays were investigated for the structure-property relationship with respect to weak anchoring property. The overall electro-optical and physical properties were measured to determine the role of the additive in Liquid Crystal mixtures. The molecular structure of the additive was changed to impose different polarity and interaction with the Liquid Crystal and alignment layer. The additives reduced the operating voltage of host liquid crystal materials and produced a slippery surface without any phase separation.

In this paper we investigate Photonic Band Edge (PBE) lasing from a homologous series of non-symmetric bimesogen liquid crystals (the mesogenic units are not identical) with varying physical parameters. A homologous series was synthesised, where the number of methylene units in the linking flexible spacer chain ranged from 6 to 12. Our results show a clear odd-even effect within the threshold values and slope efficiencies, of the PBE lasers, when plotted as a function of the number of methylene units in the spacer chain. The even spacer bimesogen PBE lasers performed with an overall higher efficiency (< 2μJ/pulse threshold values and 8% slope efficiency) than the odd spacer bimesogens PBE lasers (3.5μJ/pulse threshold values and 1% slope efficiency). We believe that this odd-even effect is due to the odd-even effect observed within the host physical parameters; a consequence of the molecular shape anisotropy

Nonresonant random lasing from a dye-doped smectic A* scattering device is demonstrated. The field-induced scattering state of a low molar mass liquid crystal in the smectic A* phase is found to provide sufficient feedback to generate random lasing when a gain material, such as a fluorescent dye, is doped into the liquid crystal host. Furthermore, we found that the emission intensity of the random laser at a given excitation energy can be adjusted by altering the strength of the applied electric field so as to modify the scattering texture and consequently the transport mean free path. This change in the transport mean free path results in a change in the random lasing threshold. Large values for the transport mean free path, which indicate a weak scattering strength, result in large threshold values and vice-versa. Finally, we discuss the benefits of controlling the scattering strength with an applied electric field in terms of potential device applications.

Organosiloxane liquid crystals have previously been shown to have much potential in bistable smectic-A devices; in this paper we aim to optimise the device performance by reducing threshold voltages and response times. Our results show that mixtures of novel organosiloxanes with enhanced dielectric coupling can significantly these key parameters. The molecules used were of the A/B and A/B/A type, where B refers to the number of siloxane units, and A to the mesogenic unit(s) attached. The molecule 5/2, which has a pentamethyldisiloxane (PMDS) group laterally attached to a pentyl-oxycyanobiphenyl (5OCB) mesogenic unit, was chosen as host for the mixtures. Of the A/B type, two napthylene-core molecules were chosen, which are designated Si₂-4-ONEBN and Si₃(iso)-4-ONEBN. These molecules have identical cores and alkyl chain lengths but differ in the number and conformation of the siloxane moiety. Of the A/B/A type, 5/2/5 was selected. This molecule consists of two 5OCB units joined via a PMDS group. The concentrations used were 0.3 mol (A/B type) and 0.15 mol (A/B/A type). Threshold voltages of the mixtures were measured as a function of shifted temperature; the response times were measured at fixed temperature as a function of applied voltage. It was found that all the mixtures gave favourable results, with the 0.3 mole fraction Si₂-4-ONEBN response times of 20 ms were achieved - an order of magnitude faster than pure 5/2. Threshold voltages were shown to be reduced by approximately 25% for all mixtures with no degradation in mesogenic behaviour.

In this paper, we review our recent experimental work on coherent and incoherent liquid crystal lasers. For the coherent lasers, results are presented on thin-film photonic band edge lasing using dye-doped low molar mass liquid crystals in the self-organised chiral nematic phase. We show that potentially high Q-factor lasers can be fabricated from these materials by demonstrating that a single mode output with a very narrow linewidth is readily achievable in well-aligned monodomain samples. Moreover, from our investigations we have found that the performance of the laser, i.e. the slope efficiency and the excitation threshold, are dependent upon the physical parameters of the low molar mass liquid crystal. Specifically, the slope efficiency was found to vary from 1% to 12% depending upon the liquid crystalline material employed. Using this information, the important parameters of the host liquid crystal are highlighted. As regards to the functionality, we demonstrate how the wavelength of the laser can be tuned using an in-plane electric field in a direction perpendicular to the helix axis. Finally, for the incoherent lasers, we summarise our findings on random lasers that are fabricated from liquid crystals which exhibit a smectic A* phase.