Optical metamaterials capture the imagination with potential applications such as sub-wave imaging, invisibility cloaking and solar energy collection. The challenge is to learn how to construct and reconfigure a metamaterial with a spatially varying refractive index. We describe an approach based on colloidal dispersion of metal nano-rods in a dielectric fluid placed in a non-uniform electric field. Because of the dielectrophoretic effect, the nano-rods accumulate in the regions with the maximum field and align along the field lines. High concentration of nano-rods lowers the effective local refractive index of the dispersion. The nano-rods are much smaller than the wavelength of light. We illustrate the approach with a dispersion of gold nanorods (length 40-70 nm, diameter 10-20 nm) in toluene, using flat and cylindrical cells. In the first case, the electric field is created by two mutually perpendicular electrodes, in the second case, it is created by two coaxial electrodes. When the field is applied, the initially isotropic dispersion of nanorods transforms into birefringent orientationally ordered structures with the director following the electric field lines. We describe how the optical properties of the field-induced structures are controlled by dichroism and birefringence of the dispersion and determine the spatial variation of the field-induced optical phase retardation. In cylindrical capillaries, the index gradient bends lights around the central electrode, thus reducing its visibility. Our approach can be used as a starting point for the development of self-assembled and reconfigurable optical metamaterials with optical properties controlled by the dielectrophoretic effect on submicron scales.

Holographic laser projection is high efficiency when using analogue phase spatial light modulators and high brightness laser sources. The experimental work reported will describe the use of digitally addressed nematic liquid crystal on silicon devices for the analogue phase holograms. The laser sources are based on the tapered laser concept and have been provided by a European project called WWW.BRIGHTER.EU.

This work studies photo-induced reorientation in azo-dye-doped liquid crystal (ADDLC) films by observing the diffraction patterns produced by self-phase modulation (SPM). The experimental results show that not only the magnitude but also the sign of the refractive index change (Δn) of an ADDLC sample pumped by a green laser can be modulated by the beam intensity (IG). The reason is that different IG give rise to different trans/cis concentration ratios, and then induce different overall torques on LC molecules. The trans and cis isomers contribute negative and positive torques, respectively, that reorient LC molecules perpendicular and parallel to the polarization of the pump laser. The reorientation effect in the ADDLC sample illuminated by the biphotonic lasers (green and red lasers) is also investigated by observing the self-phase modulation diffraction pattern. The results indicate that red light can induce |Δn| to decrease and increase at low and high IG, respectively. Besides, the dye-induced torque can be changed from negative to positive by adding red light. This is due to the fact that cis isomers produce an extra positive torque to the LCs after absorbing red light.

This article focuses on thermotropic cubic phases with bicontinuous type constructed by rod-shaped molecules such as 4'-n-alkoxy-3'-nitrobiphenyl-4-carboxylic acid (ANBC) and 1,2-bis (4'-n-alkoxybenzoyl)hydrazine (BABH). Their phase diagrams as functions of temperature and terminal alkyl chain length were fully established. The common feature of the two series is the Ia3d to Im3m to Ia3d phase sequence on lengthening the terminal chains. The formations are usually understood in analogy with lyotropic cases, but one of the highlighted differences is the structure of the Im3m phase. The structure contains two types of aggregates, spherical shells and a 3-by-3 network, within a lattice. The presence of the two distinguished sites in their dynamically ordered structure is very surprising. Another interesting point in their phase diagram is the Ia3d phase region, which is separated into two. The structures of the two Ia3d regions were also investigated. It was revealed that the network is composed of central core parts of the constituent molecules in both chain regions. This is another interesting feature probably only observed in thermotropic system because in the case of lyotropic system a replacement of location between the two chemically incompatible parts is usually observed. Analogies and differences between the thermotropic and lyotropic cubic phases are discussed.

Chiral smectic C (SmC*) elastomers have attracted both industrial and scientific interests, because of rubber elasticity with anisotropic physical properties such as pyroelectricity, ferroelectricity, SHG and piezoelectricity owing to the point group C₂. In this paper, we discuss their physical properties focused on the stimuli-responsive behavior, such as the biaxial shape memory effect in thermo-mechanical responses, the electric response to mechanical excitation due to the piezoelectric effect, and the electroclinic effect that brings about macroscopic deformation. Additionally, we consider chiral mechanical coupling between tilt and twist in SmC* elastomers.

Shortcoming of a planar self-emitting device is only a small fraction of light generated in the device available due to a total internal reflection at the air/substrate interface. To increase a luminance efficiency of the device, microlens arrays are most useful: they extract the total internal reflection of light at the air/substrate interface. In this study, we investigated photoinduced reorientation behavior of dye-doped polymerizable liquid crystals to fabricate a novel planar microlens array film as an optical component for a self-emitting device.

It is well known that doping nematic liquid crystals with nanoparticles can alter the electrooptic response of the nematic host as well as the alignment of the liquid crystal molecules on various substrates. In addition, nanoparticles dispersed in a nematic matrix often induce defects and defect patterns justifying the necessity for more detailed optical and electrooptic investigations including effects of nanoparticle size, coating, concentration and core material. We studied the local alignment of nematic LC molecules in such dispersions by means of fluorescence confocal polarizing microscopy. The results of two- and three-dimensional imaging indicate that frequently observed birefringent stripes, which are induced by the presence of metal nanoparticles and semiconductor quantum dots, correspond to twist disclinations located at the LC/substrate interface. The luminescence of dispersed quantum dots shows that the ends of these disclination threads are pinned to conglomerates of nanoparticles that stabilize these line defects. By performing (x,z)-scans, it can be shown that the defects are not walls extending through the entire cell gap, but lines that are located at the substrate surface. Our experiments also confirm, as hypothesized before, that the nanoparticles preferably reside at the liquid crystal/substrate interfaces. Finally, detailed electrooptic investigations also revealed that a contrast inversion observed earlier is initiated by a change from parallel to homeotropic anchoring, thereby causing an instability, which in turn leads to the appearance of convection rolls (Kapustin-Williams domains). This electrohydrodynamic instability is likely an example for the behavior of (+, -) systems predicted by de Gennes, which was only recently experimentally observed for the first time.

Optical trapping and manipulation of micrometric silica particles dispersed in a nematic liquid crystal is reported. Several kind of samples are considered: homeotropic and planar undoped cells and homeotropic and planar cells doped by a small amount of the azo-dye Methyl-Red. The incident light intensity is over the threshold for optical reorientation of the molecular director. The refractive index of the dispersed particles is lower than the ones of the liquid crystal therefore the usual conditions for laser trapping and manipulation are not fulfilled. Nevertheless optical trapping is possible and is closely related to the optical nonlinearity of the hosting liquid crystal¹. Trapping in doped and undoped cells are compared and it is shown that in the first case intensity lower by more than one order of magnitude is required as compared to the one needed in undoped samples. The effect is faster and the structural forces are of longer range. The formation of bubble-gum like defects in doped samples under certain experimental conditions is also reported and discussed.

Stimuli-responsive gas permeation membranes hold substantial potential for industrial processes as well as in analytical and screening applications. Such "smart" membrane systems, although prevalent in liquid mass-transfer manipulations, have yet to be realized for gas applications. We report our progress in developing gas permeation membranes in which liquid crystalline (LC) phases afford the active region of permeation. To achieve rapid and reversible switching between LC and isotropic permeation states, we harnessed the photomechanical action of mesogenic azobenzene dyes that can produce isothermal nematic-isotropic transitions. Both polymeric and low-molecular-weight LC materials were tested. Three different dye-doped LC mixtures with mesogenic azo dyes were infused into commercially available track-etched porous membranes with regular cylindrical pores (0.4 to 10.0 μm). Photoinduced isothermal phase changes in the imbibed material produced large and fully reversible changes in the permeability of the membrane to nitrogen with 5 s of irradiation at 2 mW/cm². Using two measurement tools constructed in-house, the permeability of the photoswitched membranes was determined by both variable-pressure and variable-volume methods. Both the LC and photogenerated isotropic states demonstrate a linear permeability/pressure (ideal sorption) relationship, with up to a 16-fold difference in their permeability coefficients. Liquid crystal compositions can be chosen such that the LC phase is more permeable than the isotropic-or vice versa. This approach is the first system offering reversible tunable gas permeation membranes.

We examine the possibilities to use the intrinsic 3D defect networks in blue phases I and II as arrays of trapping sites for colloidal particles. Our approach based on the phenomenological Landau-de Gennes description and topological theory has proven to be extremely useful in dealing with nematic colloids. A perturbed orientational order leads to effective anisotropic long range inter-particle coupling and consequently to numerous organizations of colloidal particles not present in simple liquids. Recent developments that led to the blue phases with extended stability range make them more attractive for use. In these phases the competition between nematic ordering and intrinsic tendency to form double twisted deformations yields complex director patterns and disclination networks. The spatially deformed order that mediates the attraction of particles to the network sets the ground for a possible self-assembling of 3D superstructures with extended stability ranges. Here we first describe the trapping mechanism on the case of a single discilination line and then use the results to demonstrate the trapping in the blue phase II. Effects of particle sizes ranging from submicron to 50 nanometers are examined. The assembling in blue phases is expected to form photonic crystals that can be easily manipulated via affecting the liquid crystal matrix and/or colloidal particles.

Extremely strong dispersion of light is characteristic of the frequency domain of photonic band gap (PBG) boundary that in case of a chiral nematic liquid crystal (CLC) results in a strong frequency dependence of the optical activity of a CLC layer. In the present work the nonlinear behaviour of the rotation of light polarisation plane is investigated in the spectral region of the selective reflection (SR) band when the light-induced modulation of the helical pitch is achieved by means of the either temperature pitch dependence or photo-stimulated changes of the molecular conformation of the chiral dopant. Nonlinear optical modulation of the optical activity allows for recording of dynamic diffraction gratings with peculiar polarisation states of the diffracting orders. At the edge of the SR band the change of phase retardation between circular eigen waves of differing handedness well exceeds pi/2 even for a few-micron-thick LC layer. Given the proper choice of the experimental parameters the effective parameter of cubic nonlinearity in such a system could surmount by orders of magnitude that characteristic of the "giant" optical nonlinearity of liquid crystals. Chiral nematic LC with light-controlled helical pitch were investigated from the standpoint of diffraction grating recording. The experimental data have shown a strong potential of these media in different aspects of optical signal processing, all-optical switching and photonics. Theoretical modelling has provided an excellent agreement with the experiment, the role of elastic constrains on the grating formation has been also taken into consideration.

Monte Carlo studies of the field induced complex refractive index changes in nano-dispersed nematic liquid crystals exhibiting negative - positive refractive indices^{1, 2} have been performed for various cases of applied field strengths,³ anchoring profiles and temperatures over a broad spectral regime. The resultant induced spatially inhomogeneous molecular order and the corresponding metamaterial properties are obtained for various wavelengths, applied field strengths, anchoring forces and temperatures below and above the Freedericksz transition. In general, the director axis reorientation and the resultant refractive index distribution are spatially inhomogeneous, even under an uniform applied field. The detailed computation have identified parameter sets for obtaining negative index of refraction and maximal index modulations that can be more than an order of magnitude larger than those obtainable from pure NLC systems.

A droplet manipulation on a switchable surface using a liquid crystal and polymer composite film (LCPCF) based on phase separation is developed recently. The wettability of LCPCF is electrically tunable because of the orientation of liquid crystal directors anchored among the polymer grains. A droplet on LCPCF can be manipulated owning to the wettability gradient induced by spatially orientation of LC directors. We discuss the droplet manipulation on LCPCF and demonstrate several applications of LCPCF, such as polarizer-free displays, and human semen sensing.

Biphenyl-containing diazides and diynes carrying tetraphenylethylene units are designed and synthesized. Their "click" polymerizations are initiated by Cu(PPh3)3Br in THF or DMF, affording soluble, regioregular polytriazoles in high yields (up to 94.8%) with narrow molecular weight distributions. The structures and properties of the polymers are evaluated and characterized by IR, NMR, UV, PL, TGA, DSC, POM and XRD measurements. All the polymers are almost nonluminescent when dissolved in solutions but become highly emissive when aggregated in poor solvents or fabricated as thin films in the solid state, displaying a novel phenomenon of aggregation-induced emission. The photophysical properties of the polymers are sensitive to their molecular structures and their solid-state quantum yields decrease with an increase in the spacer length. All the polymers enjoy high thermal stability, with 5% weight loss occurring at temperatures up to 406 °C. They are mesomorphic. While polymers with rigid main chains exhibit nematicity, those with longer spacer lengths show better mesogenic packing and hence form sematic phases at higher temperatures.

Crystal structures of mono-substituted ferrocene derivatives,ω-[4-(4-methoxyphenoxycarbonyl)phenoxy]alkoxycarbonyl ferrocene (mMAF-n, n = 3-8, 11, where n is the number of carbon atoms in the alkyl spacer), are newly determined. The molecular structures of mMAF-n are divided into three groups; (i) a bent shape containing a doublegauche conformation (n = 2, 4, 6), (ii) a linear shape containing a kink (n = 3, 5, 7), and (iii) an extended linear shape adopting an all-trans conformation (n = 8, 11). The difference of the molecular shape between group (i) and (ii) is highly correlated with the parity of the number of carbon atoms in the alkyl spacer (odd-even effects). In both group (i) and (ii), the high entropic contribution of gauche conformations is introduced in the alkyl spacer, which is consistent with the non-liquid crystallinity of mMAF-n (n = 2-7). In group (iii), it is found out that there is a border at mMAF-8 on the mesomorphism of mMAF-n (n = 2-12).

We review electro-optical properties and discuss possible applications of bent-core liquid crystals. There are three different electro-optical switching modes in the polar tilted smectic (SmCP) phase, relying on chirality, birefringence and induced biaxiality. During switching from transparent to scattering state a racemic antiferroelectric structure is driven to a ferroelectric state, whereas while switching from a transparent to a racemic state a chiral antiferroelectric state is driven to a ferroelectric one. Importantly the racemic and chiral states can be interchanged after applying electric fields with proper waveforms. The anticlinic (racemic ferroelectric and chiral antiferroelectric) states have low birefringence (in certain anticlinic states it can even be zero) whereas the synclinic (racemic antiferroeectric and chiral ferroelectric) states have large birefringences, which offers switching between optically isotropic and birefringent states. This type of switching can also be achieved in samples with vertical alignment and in plane electrodes. This latter effect is a field induced polar or dielectric switching between uniaxial and biaxial smectic structures.

Ferroelectric liquid crystals (FLCs) were known to possess fast response time under 1 ms. The low contrast ratio yielding from defect alignment, however, limited their display application. Based on FLC elastic free energy, the asymmetrical surface polarity controlled alignment was able to suppress the horizontal chevron defects in a half Vshaped switching FLC cell. It is due to the FLC's spontaneous polarization (Ps) pointed to one direction inducing by the opposite surface polarity in asymmetrical hybrid cell. The experimental approach of different alignment materials and different strengths of surface anchoring energies were evaluated in this study. The highest contrast ratio of 780:1 at saturation voltage under 5 V was obtained. The asymmetrical surface polarity controlled alignment technique provided a promising FLC well alignment and fast switching result for TFT-LCD application.

The development history of polarization gratings (PGs), with origins in holography and Bragg gratings, accentuated and reinforced their perception as gratings. We highlight their nature as waveplates - diffractive waveplates (DWs) - and stress their family connection to vector vortex waveplates. This approach provides a straightforward understanding of the unusual properties of PGs, such as nearly 100% diffraction in thin material layers, the presence of only one diffraction order for a circularly polarized beam, wide diffraction bandwidth and the possibility of achromatic behavior. With technology being ripe for applications such as beam steering, and optical switching, we characterize the resistance of DWs to optical radiation, the effects of temperature and deformations. We also show that the boundary effects in the manufacturing process make it necessary to use substrates larger than the desired aperture of the DW. The multicomponent systems are discussed for developing normally transmissive switchable imaging systems, beam scanning, and achromatic diffraction.

In this work we present numerical results on the propagation of high power laser beams in nematic liquid crystals. The optical nonlinearity of the liquid crystal gives rise to self-focusing and the generation of spatial optical solitons. We consider only configurations in which no bias voltage is necessary for the generation of the spatial optical soliton. One of the configurations considered here is one where the liquid crystal twists along the thickness of the layer over an angle of 180°. This configuration leads to spiraling solitons when the beam is injected with a certain offset with respect to the middle of the liquid crystal layer. The sign of the initial angle of the beam is depending on the sign of the offset.

Liquid crystals are characterized by a strong anisotropy of their physical properties, which is at the origin of their high birefringence. By performing two-wave mixing experiments in a liquid crystal light-valve, we show that the anisotropic nature of the beam coupling occurring in the liquid crystal layer leads to a slow-light birefringence phenomenon, that is, orthogonal polarization states of the input pulse travel at very different group velocities. Such a slow-light birefringence effect comports a large difference in the group index for the ordinary and the extraordinary wave. The resulting high contrast of the group index can be exploited for realizing a common-path polarization interferometer working at enhanced sensitivity, where very small phase variations can be efficiently detected.

Device physics and electro-optical properties of emerging polymer-stabilized blue-phase liquid crystal displays (BPLCDs) are investigated. The novel protruded electrodes generate strong horizontal electric fields which penetrate deeply into the bulk LC layer. As a result, the operating voltage is reduced from over 50V_rms to ~10 V_rms, which for the first time enables the BP-LCDs to be addressed by amorphous silicon thin-film-transistors (TFTs). Kerr constant effect from the material side is also evaluated quantitatively. Widespread application of TFT BP-LCDs is foreseeable.

Non-symmetric broadening (to the blue side) of a cholesteric reflection notch was observed when a cell containing diacrylate and monoacrylate nematic LC monomers, a chiral dopant, nematic LC and a photoinitiator was exposed to very low intensity (microwatts) of 335 nm UV light. At very low intensity, the polymerization rate is very slow and takes a long time to complete as observed by real-time monitoring experiments. The polymerized scaffold templates the original liquid crystal helical structure. The 335 nm light is highly absorbed by the system which generates an intensity gradient throughout the thickness of the cell. This gradient produces a free radical density gradient in the later stage of the polymerization when diffusion is slowed by the growing polymer network. Since more monomer is consumed at the front half of the cell, a counter diffusion of chiral dopant towards the cell backside is observed. This leads to a local increase in the HTP causing a local blue shift of the notch wavelength. The net result observed in transmission is a broadening of the reflection bandwidth from 70 nm to 200 nm where the broadening occurs only to the blue side of the original notch. By varying the intensity of the UV source on one side of the substrate, the broadening magnitude could be controlled. Simultaneous UV illumination from both sides of the cell reduced the broadening considerably. The broadened notch was switchable at high electrical field (20V/μm).

This paper reports on linear and nonlinear optical properties of channel waveguides made of micromachined SiO2/Si Vgrooves filled with nematic liquid crystal E7. Experiments demonstrate operation of the waveguides in the C-band (1530 - 1565 nm). Molecular reorientation of the NLC, induced either by an applied low frequency electric field or by the electric field of the light itself, changes the LC refractive index distribution then allowing the control of guided light. Design criteria and techniques of channel waveguides for both electro-optical and all-optical switching and modulation will be discussed. Experiments are presented where it is showed that light at 1550 nm, fiber-coupled to the LC waveguide is optically modulated by an optical beam with an input power below 25 mW. All-optical switching of a signal at 1510 nm with a contrast over 10 dB is also demonstrated by using a copropagating control signal at 1560 nm. A model of the waveguide is also presented able to explain linear and nonlinear experimental results.

A liquid crystal (LC) cylindrical lens array with electrically tunable focal length is proposed, which is first fabricated. And its optical focusing characteristics are got in tests. The LC cylindrical lens array is driven by applied voltage. It composes of two ITO glasses substrates and LC layer. The top electrode pattern is fabricated by the methods of lithography and hydrochloric acid etching, which has 128×128 elements. Every element is a 60μm×200μm rectangle. The 20μm-thickness-spacer is used to control the LC thickness. When the external electric field is applied, the LC molecules begin to rotate. Then the gradient refractive index forms in the LC cell. The LC cylindrical lens array is a convergent lens array. The parallel white light is used to test its optical characteristics. It comes to a conclusion that the focal length of the LC cylindrical lens array and the external applied voltage has an inverse proportion relationship. The range of the focal length is from 60μm to 450μm, when the applied voltage varies from 1.54 Vrms to 5.0 Vrms. And the response time is up to sub-microsecond. The unique focusing phenomenon of LC cylindrical lens array is that the focusing beams in the top and bottom of every element rectangle are like the image "V".

A simple, full-field method to characterize phase modulation property of translucent twisted nematic spatial light modulator (TN-LCSLM) is presented using Digital Holography (DH). Generally, amplitude and phase modulation is coupled due to simultaneous distortion in twist alignment and tilt order with applied field. The change in birefringence of liquid crystal material with respect to input grey scale produces phase modulation of wavefront transmitted through TNLCSLM. Most existing techniques for phase modulation characterization of LCSLM are complex requiring lengthy calculations and measure a very small region of total active region of SLM. In this paper, a transmission Digital Holographic system is used to extract phase information from the digitally recorded and numerically reconstructed wavefront. The advantage of phase modulation characterization using DH is that the phase value from larger area inside the active region of TN-LCSLM can be visualized and quantified in real time.

We experimentally investigated optical Kerr gating effect by co-propagating a pump beam and a weak signal beam in a nonlinear photonic crystal fiber. It is shown that optical Kerr gating can be observed by using femtosecond pump pulses with only a few milliwatts of average power.