This PDF file contains the front matter associated with SPIE Proceedings Volume 8828, including the Title Page, Copyright information, Table of Contents, Introduction, and Conference Committee listing.

Light-driven supramolecular chiral materials containing an azobenzene moiety as a photoresponsive part and binaphthyl moiety as a chiral part were designed. We found that the dynamic molecular twisting motion of the binaphthyl moiety could be achieved by irradiation of UV or visible light to cause photoisomerization of the azobenzene moiety. The twisting motion induced by the photochromic reaction gave rise to large change in the molecular structure and the value of optical rotation. The chiral materials were demonstrated to behave uniquely as photomodulation of liquid-crystalline helical structures and non-destructive erasable chiroptical memory through photoinduced switching of the dihedral angle of the binaphthyl moiety.

The photorefractive effect in photoconductive ferroelectric liquid crystals (FLCs) that contain oligo-thiophene chiral compounds was investigated. Ter-thiophene and quarto-thiophene compounds with chiral structures were chosen as the photoconductive chiral compounds and mixed with an achiral smectic C liquid crystal. The mixtures exhibit the ferroelectric chiral smectic C phase. The photorefractivity of the mixtures was investigated by two-beam coupling experiments. It was found that the FLCs containing the photoconductive chiral compound exhibit a large gain coefficient of over 990 cm^-1 and a fast response time of 1.7 ms.

Photonic band edge lasers based on cholesteric liquid crystals (CLCs) have attracted considerable interest as selfassembled, tunable, microscopic, coherent light sources. We discuss several ways to improve the lasing performance: lasing threshold and slope efficiency can both be improved by stabilizing the liquid crystalline order to suppress heatinduced distortions during the pumping process. This can be achieved either by photo-crosslinking reactive mesogens, or by applying an electric field along the helical axis of a CLC with negative dielectric anisotropy. Defect mode lasing with exceptionally low lasing threshold can be easily achieved with polymeric systems by insertion of a phase jump in the chiral molecular order. Finally, electrical fine tuning of the laser emission by application of an in-plane electric field electric field will be discussed.

The helical structure of a chiral-nematic liquid crystal (CLC) material produces a number of interesting optical properties, including selective reflection and optical rotatory power. To take advantage of the high optical rotation near the selective reflection peak for applications in the UV, either large concentrations of chiral components or those possessing very large helical twisting powers (HTP’s) are necessary. It is difficult to find chiral twisting agents with high HTP that do not degrade the UV transmission. We report what we believe to be the first experimental observation of extraordinarily high optical rotation (<30°/μm) in the near UV for a long-pitch (13.8-μm) CLC mixture composed of the low-birefringence nematic host ZLI-1646 doped with a low concentration (e.g., 1 wt%) of the chiral dopant CB 15. This experimental finding is verified theoretically using a mathematical model developed by Belyakov, which improves on de Vries’ original model for optical rotation far from the selective reflection peak by taking into account the nonlinearity of optical rotatory power as a function of liquid crystal (LC) layer thickness. Using this model, the optical rotation at λ = 355 nm for the 1% CB 15/ZLI-1646 mixture is determined computationally, with the results in agreement with experimental data obtained by evaluating a series of wedged cells using an areal mapping, Hinds Exicor 450XT Mueller Matrix Polarimeter. This finding now opens a path to novel LC optics for numerous near-UV applications. One such envisioned application for this class of materials would be UV distributed polarization rotators (UV-DPR’s) for largeaperture, high-peak-power lasers.

We report on the investigation of random lasing in blue phase liquid crystals. Multiple scattering and interference effects arising from disordered platelet texture as well as index mismatch between polymer and mesogen contribute the optical feedbacks towards laser action. In pure blue phase liquid crystals, the random laser can be switched between the coherent and incoherent types by executing distinct heating/cooling cycles; and, the randomness of lasing wavelengths can be determined by the platelet size, which can be set by controlling the cooling rate. After the blue phase liquid crystals are polymer-stabilized, coherent random lasing may occur in both the blue phase with an extended temperature interval and the isotropic liquid state; also, the selected modes are constant from one pulse to another. Additionally, if the laser dye is sensitive to temperature, the excitation threshold and the emission spectrum could be altered via thermal control.

Dye-doped liquid-crystalline (LC) system is known to enhance its photoinduced reorientation behavior significantly compared to undoped LC system. However, aligned LC system is disturbed by thermal fluctuation at high irradiation intensity, due to excess thermal deactivation excited dye molecules with a low emission quantum yield. In this study, photoresponsive behavior of LC systems doped with photostable fluorescent π-conjugated molecules was investigated by irradiation with a single Ar+ laser beam. When the laser beam was incident on the sample cells, diffraction patterns were observed on a screen for the LC cell doped with coumarin derivatives. Appearance of the diffraction rings indicates photoinduced reorientation of LCs. Coumarin derivatives with long molecular length were found to act as efficient triggers for photoinduced reorientation of LCs.

High helical twisting powerchiral additives are required for an expanding variety of liquid crystal displays and devices. Molecular conformation plays a critical role in determining the helical twisting power, HTP, of chiral additives. We studied additives based on an isosorbide benzoate ester core. Molecular modeling revealed two low energy states with very different conformations for this core The ultra-violet absorption and NMR spectra show two stable isosorbide conformers These spectra reveal how the relative populations of these two conformations change with temperature and how this is related to the helical twisting power. Conformation changes can explain many of the observed anomalous responses of HPT to temperature.

We discuss the effect of a negative refraction at the interface of uniaxial anisotropic media in the case of nanosphere dispersed liquid crystal (NDLC) matematerial. Finite Element (FE) calculations (COMSOL Multiphysics) are used to trace the propagation of the electromagnetic wave. We show that for chosen values of the parameters of nanospheres and of nematic liquid crystal (NLC) host negative refraction can be obtained for a wide range of incident angles.

Incorporating liquid crystal (LC) as a defect layer in a photonic crystal (PC) leads to the electrically tunable optical spectrum in defect modes within the photonic band gap. While the LC defect layer has bi- or multi-stable states, the profile of defect modes in each stable state can be preserved permanently without applied voltage, indicating a feature of low power consumption for photonic applications. In this paper, we report on our recent development of optical and spectral properties of multilayer PC structures containing various types of memory-enabling LC (ME-LC), including a bistable chiral-tilted homeotropic nematic (BHN), a bistable chiral-splay nematic (BCSN), a bistable dual-frequency cholesteric LC (DFCLC), a tristable polymer-stabilized cholesteric texture (PSCT), and a tristable smectic-A liquid crystal as a defect layer. The defect modes of the PC/ME-LC cell can be switched to not only the voltage-sustained states but the memory states. As a result, PC/ME-LC cells reveal several features such as the wavelength tunability, transmission tunability and optical bistability or tristability of defect modes that are of potential for realizing tunable and memorable optical devices such as low-power-consumption multichannel filters, light shutters or electrically controllable intensity modulators with green concept.

A biosensor for the concentration of high-density lipoprotein (HDL) in human serum on a liquid crystal and polymer composite film (LCPCF) is demonstrated. The sensing mechanism is based on a polar-polar interaction between orientation of LC directors and HDL in human serum. The concentration of polar HDL in human serum affects the orientations of LC directors at the interface between LCPCF and the human serum. In addition, the surface free energy of LCPCF changes with the applied voltage due to the electrically tunable orientations of LC directors anchored among the polymer grains of LCPCF. As a result, the droplet motion of human serum on LCPCF under applied voltages can sense the concentration of HDL in human serum.

In this study we demonstrate the fabrication of one-dimensional porous multilayer photonic crystals made by metal oxide nanoparticles. We show the infiltration of these porous structures with a liquid crystal via a very simple method, resulting in a red shift of the photonic band gap due to increase of the effective refractive index of the medium. Taking advantage of structure thickness of only few micrometers, we have observed a blue shift of the photonic band gap owing the non-linear response of the liquid crystals by applying a very low external electric voltage, i.e. 8 V. The experimental observation of electric voltage tuning on the transmission spectrum has been corroborated by transfer matrix method simulations, by taking into account the non-linear optical properties of the liquid crystal. In this framework, we propose how the optical properties of these structure can be accurately predicted by our simulation software in terms of diffraction efficiency, of photonic band gap position when the porous photonic crystals is doped with a liquid crystal, of modulation of the photonic band gap position (electro-optic tuning) in the presence of applied voltage. According with results carried out by the custom simulation software it is possible to control the optical proprieties of the photonics crystal in very thin structures. Furthermore, the presented device could be very interesting for applications where high sensitivity sensor and selective color tunability is needed with the use of cheap and low voltage power supplies.

Large-scale, high-energy Nd:glass laser systems require beam shapers to control the spatial distribution of the incident intensity. Commercially available liquid crystal (LC) electro-optical spatial light modulators (SLM’s) are frequently employed for this purpose, but their intrinsic requirement for conductive metal or metal-oxide coatings limits their 1054-nm laser-damage thresholds to 230 mJ/cm² (2.4 ns, 5 Hz), relegating them for use only in low-fluence areas of the laser system. Previously, we demonstrated that passive near-IR LC beam shapers employing coumarin alignment layers patterned by contact photolithography are capable of high resolution and contrast and can withstand incident 1054-nm laser-fluence levels of <30 J/cm² (1-ns pulse). An evolutionary step to expand the scope of this simple and robust device would be to identify and incorporate into the device structure photoalignment layers that trigger LC bulk reorientation by undergoing reversible optical switching between two predetermined alignment patterns using low-energy polarized UV/visible incident light and have a high near-IR laser-damage threshold. Such “optically driven” LC beam shapers offer the in-system write/erase flexibility of the electro-optical LC SLM’s while eliminating conductive coatings that compromise the laser-damage threshold and electrical interconnects that increase device fragility and complexity. To this end, we have recently identified and evaluated the 1054-nm laser-damage–resistance and coating properties of several commercial azobenzene-based photoswitchable alignment materials. In 1-on-1 and N-on-1 testing, these new materials displayed 1054-nm laser-damage thresholds that compare very favorably to those of previously tested coumarin photoalignment materials (30 to 60 J/cm²).

The microscope system in combination with a digital image processing is developed for determining all-focused images and depth mapping properties of microscopic objects by using a liquid crystal (LC) lens with a variable focal length. The objects can be selectively illuminated by using a light emitting diode (LED) ring illumination with controllable switching each LED. Three-dimensional distributions of the microscopic objects are determined by applying voltages to the electrodes of the LC lens and tuning a focal plane in a depth direction.

The authors have developed liquid crystalline retardation films to improve certain aspects of LCD image quality such as viewing angle performance and coloration. We have successfully created several types of optical retardation films using a rod-like liquid crystalline polymer. The resulting liquid crystalline polymer films have several advantages over conventional uni- or biaxially stretched retardation films. Precisely controlled structures such as twisted nematic, homogeneous nematic, hybrid nematic and homeotropic structures can provide ideal compensation of various LCD types, such as STN, TN, ECB, VA and IPS-LCDs. Twisted nematic film effectively prevents coloration of STN-LCDs, which is a critical flaw affecting color representation. Short pitch cholesteric film, which utilizes said rod-like liquid crystalline polymer and is the optical equivalent of a negative C-plate, can expand the viewing angle of VA-LCDs. Hybrid nematic film is quite unique in that the film functions not only as a wave plate but also as a viewing angle compensator for TN and ECB-LCDs. Homeotropic film, which acts as a positive-C plate, greatly improves the viewing angle performance of IPS and CPVA-LCDs. Our homeotropically aligned liquid crystalline film, called “NV film”, is the world’s thinnest retardation film. The thickness of the liquid crystalline layer is a mere 1 micrometer. Homeotropic film can be used to expand the viewing angle not only of LCDs but also OLED displays. And NV film, when used in in combination with a quarter wavelength plate, can expand the viewing angles of the circular polarizers used to prevent reflection in OLED displays.

Tunable photonic switches and filters employing liquid crystals (LC) or LC-composites can be used in several fields of application such as optical communications, sensors and imaging systems. Their excellent electro-optic, thermo-optic and nonlinear optical responses can be exploited for producing components in guided-wave microstructures operating at low optical and electric powers. This review deals with various integrated optics structures, some of them already experimentally demonstrated for optical processing, including routers, Bragg filters and all-optical switches. A compact (160μm long) two-way router in a nematic liquid crystal (NLC) waveguide was designed and demonstrated operating in the near infrared with voltage modulation as low as 0.21 V. Wavelength-tunable voltage-controlled Bragg reflectors were analyzed in different geometries: one has a reflectivity above 80% in a 14 nm range (1530-1550 nm) with bias voltages from 2.5 to 3.0 V; another one exploits coplanar comb electrodes to achieve an extended tuning range of about 104 nm (1521-1625 nm) with reflection above 50% for voltages from 2.9 to 10.2 V. Tunable gratings made with microslices of polymers and NLC on glass waveguides were also characterized in the 1.55 μm spectral window, demonstrating electro-optic filters adjustable over 4 nm for bias fields of about 3 V/μm. An alloptically tunable filter was also demonstrated in dye-doped NLC with tuning range over 6.6 nm when illuminated with a green laser beam of a few mW.

Phototropic liquid crystals (PtLC), in which the phase transition can be controlled by the light, are a new class of liquid crystal materials possessing number of potential applications, especially in photonic devices. So far a significant majority of PtLC materials has been realized by the doping a classical liquid crystal with a photochromic dye. Here we report PtLCs comprising a single compound. Liquid-crystalline and photochromic properties have been accomplished in alkylo-alkoxy derivatives of azobenzene. Such compounds show a rich polymorphism which can be controlled by the light. The phenomenon of the photochemical phase transition has been investigated by means of holographic grating recording.

Spatially confined liquid crystals (LCs) exhibit non-uniform alignment, often accompanied by self-organized topological defects of non-trivial shape in response to imposed boundary conditions and geometry. Here we show that a nematic LC, when confined in a sinusoidal microwrinkle groove, exhibits a new periodic arrangement of twist deformations and a zigzag line defect. This periodic ordering results from the inherent LC elastic anisotropy and the antagonistic boundary conditions at the top flat LC and the curved LC-groove interfaces. The effect of the LC thickness on the stability of the line defect is also shown.

An overview of the results obtained from the most recent experiments performed for revealing the structure of the twistbend nematic N_tb phase will be presented at the conference. This new phase provides typical X-ray diffraction pattern for the nematic phase and is found at temperatures below the conventional nematic phase in odd-chain hydrocarbon linked mesogenic dimers. The materials in the Ntb phase form self-deformed striped pattern parallel to the rubbing direction in planarly aligned rubbed cells with a well-defined period. The period is found to depend on the cell spacing. The selfdeformation stripes appear without any external electromagnetic field or thickness gradient across the cell. Although the materials are composed of non-chiral molecules, the low temperature nematic phase exhibits fast linear optical response of the order of a few microseconds. This response is reminiscent of the phase exhibiting chirality. Moreover, at higher fields some of the materials form striped domains with opposite direction of the optical response. These stripes appear normal to the rubbing direction and their periodicity depends on voltage and frequency. The Freedericksz transition in this phase also shows unusual properties and this is proven to be of the first order. The techniques to characterize this phase include polarized microscopy observation and optical contrast spectroscopy. Possible causes of the phenomena will be discussed.

Liquid crystal spatial light modulators (SLM) often suffer from defects that need to be compensated for demanding phase modulation applications. Usually the calibration map used to correct the SLM are determined at the factory or on a dedicated optical bench, but either way the measurement is done away from the experimental setup. So this correction map can’t reflect any temporal modification of defects, or correct for defects induced by the experimental setup itself or the environment. With a liquid crystal SLM, the read-out beam phase is modulated by tuning locally the birefringence. We present here a method where we record the birefringence map with a second superimposed light beam which uses the SLM in intensity modulation. In a first experiment we use the birefringence map to deduce the complete phase response of the SLM and optimize its parameters. In a second experiment we demonstrate the correction of externally induced defects: after a comparison between the measured and desired birefringence maps, SLM defects are compensated via a feed-back on the addressed hologram. As SLM monitoring is done in-place we can control time-dependant defects like those induced by a powerful read-out beam or a thermal drift. This method allows us to measure the defects of the SLM with spatial and phase resolutions comparable to interferometric methods. As it relies on polarization modulation, vibrations and misalignments are not critical, therefore supplying robustness. Furthermore, this method provides in-situ measurement, so that it’s easy to compensate day to day defects variation or aging. Finally the demonstrated method is a way open to closed-loop phase correction.

Silicon photonics is a rapidly evolving field allowing for optical devices to be made cost effectively using standard semiconductor fabrication techniques and integrated with microelectronic chips. Active tuning of silicon photonic devices has been demonstrated using thermal, electrical and optical means in the form of injection of free carriers through two-photon absorption. This work explores active electrical and optical tuning of silicon photonic devices using silicon strip waveguides combined with nematic liquid crystal (NLC) claddings. Simulation and experimental studies are presented.

Head-up display (HUD) commonly uses liquid crystal to generate images. However, the intensity of the light decreases a lot because of passing through the polarizers. Therefore, polarizer-free display is a way to enhance the light efficiency. We demonstrate the feasibility of using Polymer Dispersed Liquid Crystal (PDLC), which consists of polymer and liquid crystal, as an optical switch to fabricate a simple see-through projected display device. Due to the unique E-O characteristics of PDLC, it can be a role to define the projected image shape. In our device, we use the ultra-bright collimated LED as a backlight source so that the projected image can also be seen clearly in broad daylight. Besides, PDLC do not need to utilize polarizers. It is achieved to obtain very high light efficiency (~70%). In this paper, we show some results of projected images with various colors (RGB) that can be applied to see-through projected display. From our experiment result, the see-through projected display device by PDLC can achieve high contrast ratio (~1000:1) and response time is about 15~20 ms. The driving voltage is around 20~25 V. Further improvement can be achieved by optimizing the LC material/monomer concentration or others parameters.

A considerable body of knowledge has been developed on the general behavior of cholesteric liquid crystal (CLC) materials in electric fields. One approach that has been reported to achieve tunability in optical filters based on CLCs with a positive dielectric anisotropy and in the planar homogeneous state involves the application of electric fields perpendicular to the axis of the CLC helix. The field leads to a progressive unwinding of the helix and a corresponding red-shift in the position of the reflection band of the CLC. In this work, a microspectrophotometer was employed to probe the spatial heterogeneity of the optical spectra of the CLC in cells with interdigitated electrodes. We will show that a complex behavior of the Bragg reflection band is obtained in the gap between electrodes for certain parameters of cells with interdigitated electrodes as a function of the applied field. This is ascribed to variations in the field magnitude and direction in the cell, which lead to a spatial variation of helix unwinding.

We propose a liquid crystal (LC) micro-lens array with two-divided and hexagonal-hole-patterned electrodes for varying a focal length and a beam deflection angle. The possibilities of lens-like refractive index distributions in the hexagonal region of the LC micro-lens array are discussed. We investigate the optical properties such as the focal length and beam deflection of the micro-lens array by measuring the refractive index distributions and the transmitted light intensity distributions.

We study the electro-optical properties of the nematic liquid crystal (LC) cells such as a homogenously aligned nematic LC cell and twisted nematic (TN) LC cell fabricated with polished silicon wafers in a far-infrared wavelength region. The birefringence of the nematic LC material at the wavelength of about 10 μm is estimated by applying a voltage to the homogenously aligned LC cell under crossed infrared-wire-grid polarizers. The application of the TN LC cell into an optical shutter in the far-infrared region for electrically controlling the transmitted light intensity is demonstrated and discussed.

The tunable liquid crystal (LC) lens designed for a holographic projection system is demonstrated. By using a single patterned electrode LC lens, a solid lens and an encoded Fresnel lens on the LCoS panel, we can maintain the image size of the holographic projector with different wavelengths (λ674nm, 532nm and 445nm) . The zoom ratio of the holographic projection system depends on the lens power of the solid lens and the tunable lens power of the LC lens. The optical zoom function can help to solve the image size mismatching problem of the holographic projection system.

An electrically tunable depth-of-field (DOF) endoscope using a liquid crystal lens (LC lens) as an active focusing element is demonstrated. The optical mechanism of the electrically-tunable DOF endoscope adopting a two-mode switching LC lens is introduced. The two-mode switching LC lens provides not only a positive lens power but also a negative lens power. Therefore, we could extend the range of DOF originally from 27 mm ~ 55 mm to 12.4 mm ~ 76.4 mm by using the two-mode switching LC lens as an active focusing element. The detail derivations of the optical mechanism of the endoscopic system adopting a LC lens are invistgated. The more detail experimental results are demonstrated. We believe this study can provide a more detail understanding of an endoscopic system adopting a tunable focusing lens.

In this paper, we demonstrated an electrically tunable optical zoom system with separated focusing and zooming functions. The optical mechanism is discussed. The focusing distance and magnification of the image can be controlled separately by focusing lenses and zooming lenses. As a result, the zoom ratio is independent of objective distance and only depends on the tunable range of the lens power of the active-optical elements. This study helps designing many applications with an optical zoom function, such as cell phones, holographic projectors, pico projectors and endoscopes.

The increasing interest in the terahertz frequency range is motivated by the unique property of sub-millimeter waves to penetrate any nonmetallic materials such as fabric and plastic, and sense objects distinctive signatures. Furthermore, because of its low photon energy, terahertz radiation can be used in medical applications for accurate imaging without damaging tissues. For these reasons there is a growing need of devices dedicated to control the radiation in this frequency range. Current established technology uses non-tunable, mesh-like filters and mechanical mirrors to filter and manipulate THz radiation. We study electrically-controlled beaming and filtering abilities of sub-wavelength metallic gratings. The geometry consists of a finite array of slits in a metallic film separated by spacers and filled with liquid crystal (LC). We exploit the Fabry-Perot (FP) like resonances of the slits to filter THz radiation. We then simulate the application of an external voltage across the metallic grating in order to generate an electro-optic torque force on the LC molecules and change the dielectric constant inside the slits. This results in a large tuning effect on the FP resonances. We also predict that a linear voltage distribution across the grating induces a linear phase delay resulting in a beamsteering action for radiation incoming at grazing incidence.

In this work, cholesteric liquid crystal (CLC) laser emission from two different liquid crystal hosts doped with the same laser dye was studied. For both systems, the lasing thresholds were measured and the energy output was studied at different pump energies and at different temperatures. When the pump energy was increased, a shift of lasing wavelength and a decrease of emission in one sample were observed. We argue that this phenomenon is associated with thermal degradation of the distributed-feedback cavity caused by laser heating and the temperature induced changes of the cholesteric pitch.

The concentration level of bile acids is a useful indicator for the diagnosis of liver diseases since individual suffering from liver diseases often has a sharp increase in bile acid concentration. Here we present a sensor platform based on the anchoring transition of nematic liquid crystal (LC), 4’, 4-alkylcyanobiphenyls (nCB, n=5-8), at the surfactant-laden LC/aqueous interfaces for the detection of cholic acid (CA) in aqueous solution. In the sensor platform, the competitive adsorption of CA at the surfactant-laden LC/aqueous interface triggers a homeotropic-to-planar anchoring transition of the LC at the interface. We find the detection limit, which is the minimum concentration of CA required to trigger the LC transition, increases with the increase of the chain length of nCB.