In this study, we comprehensively explored the photoinduced anchoring transition in a nematic liquid crystal containing the azo dendrimers. Because the azo dendrimer in the trans-isomer state spontaneously adsorbed at substrate surfaces in a polar fashion, which was confirmed by optical second harmonic generation (SHG), a homeotropic orientation was established at the first stage. Ultraviolet (UV) light irradiation diminished the SHG intensity due to photoisomerization, resulting in a planar orientation. The monotonic decrease of the effective scalar order parameter with increasing UV light intensity was found by polarized attenuated total reflection infrared (ATR-IR) spectroscopy. The variations of anchoring strength and extrapolation length were evaluated by observing the Freedericksz transition as a function of UV light intensity under a certain visible (VIS) light intensity. Such photoinduced variations were analyzed as a variation of anchoring strength depending on the trans/cis ratio at the surfaces based on a modified Rapini-Papoular model.

 Preview abstract

Planar photonics, like metasurfaces and nanoantennas, has caught immense attention because of the ability of controlling the phase and polarization of light. The tunability of metasurfaces system could be realized by combining with liquid crystals. In this work, several novel devices, like tunable nanoantennas arrays with color, diffraction control of binary gratings metasurfaces, and optical Tamm states would be presented. First, by changing different dimensions of nanoantennas, the anchoring energy of liquid crystal could be adjusted in nanoscale. The different shapes of nanoantennas show the difference in color or monotone change when applying different voltages. Second, the diffraction ratio of metasurface could be controlled by nematic liquid crystal by controlling the polarization direction by applying voltages. Third, optical Tamm states could be realized and adjustable by combining liquid photonic crystal with metasurface. All of those ideas are realized in both modeling and experimental, which could give a great impact to the field of future application in tunable metasurfaces.

 Preview abstract

In this paper, we have investigated a dynamic behavior of the CLC structure according to the applied electric field using a high-speed wavelength-swept laser, where the structure of CLC cell is abruptly varied as soon as the applied electric field to the CLC cell has large enough. Then, the director is rearranged rapidly and the photonic bandgap is changed. In order to investigate the dynamics of a CLC structure, we fabricated a CLC cell which is prepared by mixing the nematic LC (ML-9704) and chiral dopant (S811, Merck). We have successfully measured the variation of the photonic bandgap in the CLC structure using the temporal signals, which correspond to the spectral signals of the wavelength-swept laser.

 Preview abstract

We introduced azobenzene into cholesteric (Ch) liquid crystals (LCs), and we investigated rotation of Ch droplets coexisting with an isotropic phase under UV-light irradiation. Trans-isomer of azobenzene in Ch LCs absorbs UV-light and transfers to cis-isomer. Thus, UV-light intensity is expected to be weaker as thickness deeper, so that a concentration of cis-isomer spatially varies from top to bottom of cell. We found that mass flux of cis isomer along the concentration gradient drive rotation of Ch droplets.

 Preview abstract

Topological defects in liquid crystals are attractive subjects of study, as they allow for the testing of topological theories, and act as scaffolds to trap nano- and micro-sized colloidal objects. Moreover, recent studies have proven that defects not only trap mesoscopic materials, but also low-molecular-weight molecules dissolved in the host nematic liquid crystal. Considering the potential of topological defects as templates for bottom-up assembly of molecular and mesoscopic materials, the technology to create stable topological defects with complex shapes is much in need. We have previously shown that it is possible to induce topological defect lines with controlled shapes and numbers by sandwiching nematic liquid crystals between substrates with orientational easy axis distributions with singular points. However, the previous study only allowed the generation of line defects with ends anchored on one of the substrates of the cell. In this study, a design strategy is presented that allows topological defect loops floating in the bulk of the nematic liquid crystal to be generated.

 Preview abstract

In this paper, we present our numerical attempts to construct confocal microscope images of cholestetric blue phases from their profiles of the dielectric tensor, deduced from the distribution of the orientational tensor order parameter. Instead of resorting to geometrical optics, we solve the Maxwell equations for electromagnetic waves to evaluate the reflected light for incident light with given wavevector, and make an appropriate superposition for different wavevectors of incident light. Our calculated confocal microscope images agree qualitatively with experimental ones in that the symmetry of images is consistent with the ordering of bulk BP I. We also show that the images sensitively depend on the wavelength and the polarization of the incident light. We hope that our theoretical work will extend the applicability of confocal microscopy towards submicron scales.

 Preview abstract

A thermodynamically stable blue phase III (BP III) has been achieved in a host system of bent-core (BC) molecules doped with chiral materials. Utmost 15OC of BPIII was obtained in mixed system. The electro-optic (EO) performance is evaluated in in-plane electric field geometry and stable EO response was observed over temperature range >6 OC. Hysteresis free V-T characteristics is obtained along with high Kerr constant. Kerr constant (K≈8×10-10 mV-2) obtained at low temperature region is the largest among bent-core BP systems reported so far. Dielectric spectroscopy is employed to accurately distinguish isotropic to BP transition. This near room temperature bent-shaped nematogen demonstrates excellent switching properties with sharp rise and fall time (<12mS) and thus becomes a potential candidate for high speed EO devices.

 Preview abstract

We investigate the hybrid Tamm microcavity states, which underlie the recently proposed WOLEDs, organic solar cells of a new design, and enhancement of the nonlinear optical effects. In this work, we theoretically demonstrate the possibility of controlling the hybrid Tamm microcavity states in a photonic crystal with the 5CB NLC defect bounded by a silver film. The position of the resonant wavelengths corresponding to hybrid modes can be controlled by a temperature or electric field applied to the NLC defect.

 Preview abstract

In this work,We use microfluidic system to prepare BPs microdroplets with the uniform size from few tens to hundreds μm. By employing the polymer-stabilized method ,we extend the temperature range over 50°C and keep the sample in BPs at room temperature without temperature controller. Moreover, We applied spatially resolved micro-photoluminescence spectroscopy(μ-PL) to observe small region of lasing emission and CCD image of polymer stabilized BPs microdroplets. There are two types of lasing emission we obtained, band-edge lasing and whispering gallery modes(WGMs). In band-edge lasing, the wavelength of lasing emission can be change when we focus the pumping region on different lattice plane. WGMs can be observed on the edge of the droplets due to the light waves are guided round by optical total internal reflection.

 Preview abstract

We investigated phase behavior, self-assembled structure and electric responsivity of a liquid crystal (LC) compound bearing 1,3-dioxane unit in the mesogen core part (DIO) by differential scanning calorimetry, polarized optical microscopy, X-ray diffraction, dielectric relaxation, polarization switching and second harmonic generation (SHG) studies, and also proposed a possible mechanism why DIO showed the anomalously large dielectric permittivity Δεwhich was several thousand at 10 kHz and more than 10 thousand at 1 kHz in a specific mesophase MP.

 Preview abstract

Cybotactic nematic phase (Ncyb) has attracted much attention; however, almost all molecules under investigation have had a bent-shaped structure or mixture of rod and disc shaped molecules. Recently, a U-shaped compound possessing two 1,4-diphenyl-2,3-difluorobenzene units was found to exhibit an Ncyb phase with a temperature range of 20 K and an semctic C (SmC) phase [1]. Also, the rod-like compound, 4-[4-(6-hydroxyhexyloxy)phenyl]-1-(4-hexyloxyphenyl)-2,3-difluorobenzene, was found to exhibit an Ncyb with a temperature range of 25 K and an SmC phase. Dielectric spectroscopic studies have been performed to investigate the molecular dynamics of U-shaped and rod shaped Ncyb nematic phases. Electric field induced Ncyb-SmC phase transition temperature has been observed. Moreover, application of external electric phases induces a collective mode relaxation process in U-shaped Ncyb phase.

 Preview abstract

We report a method to stabilize blue phase liquid crystals (BPLCs) by photo-polymerizing the doped chiral polymers at isotropic phase. Such a method is called “Surface-stabilized blue phase liquid crystals (SSBP-LCs)”. SSBP-LCs can simplify the conventional manufacturing process of extending the temperature range of BP-LCs because the temperature of BPLCs does not have to precisely control in the narrow range during photo-polymerization. Also, we compare the electro-optical properties of SSBP-LCs with those of conventional polymer-stabilized BPLCs [1], the results show that the response time, the operation voltage, and others, can be improved. Accordingly, we believe that such an approach can improve the development of BP-LCs in LC technology

 Preview abstract

This study is aimed to clarify the optimal frequency regime for well-aligned ULH structure via the voltage-induced EHD effect. According to the complex dielectric and the tan δ spectra, three frequencies designated fL, fR, and fH can be acquired at a given temperature. These frequencies are meaningful to characterize transport behaviors of ion charges under the application of a probe ac electric field within distinct frequency regimes. Based on measurements of voltage- and frequency-dependent transmission spectra and observations of optical textures, it can be summarized that the frequency regime (fL,< f < fR), where electrical charges can apparently oscillate in the bulk of the cell with less ion-accumulation on the electrode surfaces, is adequate to obtain well-structured ULH due to the effective induction of the EHD flow by appreciable voltages. As a result, this work is helpful to obtain a more uniform ULH alignment so as to enhance the optical contrast of the proposed devices and promote their practical uses.

 Preview abstract

Liquid crystal (LC) micro-particles can be fabricated by polymerizing pre-aligned pohotopolymerizable LC molecules in the LC state, and are functional materials possessing optical and dielectric anisotropy. When the particles are dispersed in nematic LC hosts, they spontaneously rotate to match their inner molecular alignment along the host alignment, because they possess an anchoring potential along their inner molecular alignment. Moreover, reversible orientation switching of particles is possible in LC hosts by an electric field, and the rotation angle of particles is determined so as to minimize the free energy of the system, which comprises the electrostatic energy generated by the dielectric anisotropy of the LC particles and the elastic energy generated by the director deformation of the host LC induced around the particles. Here we investigate orientation of LC micro-particles in a dual-frequency LC (DFLC) host. Rectangular parallelepiped micro-particles with inner molecular alignment along the long axis are fabricated via two-photon excited direct laser writing, and dispersed in a DFLC to be electrically driven by a voltage applied in the in-plane direction of the cell. Interestingly, it was found that the particle rotates either clockwise or anticlockwise to align the inner molecular alignment parallel or perpendicular to the applied field.

 Preview abstract

Negative dielectric nematic liquid crystals (LCs) doped with two azobenzene materials provide electrically switchable and permanently stable scattering mode light modulators based on dynamic fingerprint chiral textures (DFCT) with inhomogeneously helical axes. These light modulators can be switched between transparent states and scattering states. This study is the first report on the advantages of the light scattering mode of DFCT, including low operating voltage, permanently stable transmission.

 Preview abstract

In recent years, manipulation of tiny particle which size ranges from nanometer to millimeter is an attractive and important topic for scientists. To achieve the manipulation of tiny particles, such as sorting, handling, transport, and trapping, a number of innovative methods, including electrophoresis and dielectrophoresis (DEP) [1], optical tweezers [2], magnetic tweezers [3,4], acoustic wave [5], and fluidics [6], has been developed. In this work, we report the observation of DEP in liquid crystal (LC) droplets on a photoconductive substrate. By illuminating the photoconductive polymer layer on a glass substrate with ultraviolet light and a binary mask, a non-uniform electric field distribution can be induced on the photoconductive substrate. The non-uniform electric field induces the dipoles in LC droplets and provides a static-electric force for transporting the LC droplets. The whole process is based on the principle of DEP and thus it is not necessary for the manipulation of LC droplets occurring with any extra electric field. Fig. 1 shows the dynamic and the corresponding of the polarizing microscope images of the DEP process for the LC droplets. This study provides a new route for developing DEP-based LC device being potentially applied on optics.

 Preview abstract

A bistable negative lens with a large aperture size (~10mm) by integrating a polarization switch of ferroelectric liquid crystals (FLCs) with a passively anisotropic focusing element is demonstrated. The proposed lens not only exhibits electrically tunable bistability but also fast response time of sub-milliseconds. The tunable lens power ranges rom 0 to -1.74 Diopters. The electro-optical properties and imaging performances are demonstrated. In our previous work, the bistable lens is designed for red light due to the chromaticity of FLC-wave retarders. In order to extend the range of operating wavelength, we design a FLC-wave retarder with a proper cell gap. According to the simulation, it is able to operate in visible range with the response time of 171 us. The impact of this study is to provide a solution of electrically bistable liquid crystal lenses for the applications of portable devices, wearable devices and colored ophthalmic lenses. The design of the FLC-wave retarder can also be applied to the wavelength control of low level light therapy.

 Preview abstract

In this paper, we have studied the ionic behaviors of a rubbed-polyimide(PI)-vertical-aligned (VA) cell whose ions were originated from both liquid crystal mixture and PI layers within the same VA cell. We have used a LCR meter to measure the capacitances of the VA cell and heterodyne interferometry[1] to measure the phase change versus voltage at 1 kHz and the phase change versus time by applying a mid-grayscale square-wave voltage at 0.1 Hz to the VA cell. The latter were converted into the ionic-charge densities (or voltages) versus time accumulated adjacent to the PI-to-LC interfaces contributed from PI- and LC-sides, respectively. We have observed that the measured interfacial ionic-charge densities versus time were dominated by the ions generated within PI-alignment layers rather than the LC mixture in the same VA cell. The measured data were fitted to analytic solutions[2,3] for the derivations of ionic physical parameters for liquid crystal mixture and PI-alignment layers, respectively. We have also measured anchoring energies of two such VA cells with same LC mixture but two different PI-alignment materials, and observed a substantial difference in anchoring energies between them.

 Preview abstract

A lyotropic liquid crystal is a mixture of a surfactant in an appropriate solvent at a specific concentration and temperature. After leaving for a while, lyotropic liquid crystal textures are formed from the mixture, and can be observed under a polarizing optical microscope (POM), Figure 1. Generally, the textures are observed sandwiched between two parallel glass plates i.e., a microscope slide and a cover glass. In this work, we employed Triton X-100, lecithin and commercial detergents as surfactants and water as a solvent to study their free-standing films compare to those sandwiched between glass plates. A hole (3 nm in diametre) in an acrylic slide (2.5 cm x 7.5 cm) was dropped with an aqueous surfactant mixture and the lyotropic textures were observed under a polarizing optical microscope, Figure 2. The results showed that for Triton X-100 in water, the surfactant molecules which formed hexagonal columns aligned randomly between two glass plates. On the other hand, due to an interaction with the surface of the free standing film, the columns tried to lie down along the radius of the film, thus forming twisting textures.

 Preview abstract

Prior publications on the measurements and interpretations of residual direct current (RDC) voltages in polyimide(PI)-film-aligned LC cells have been based on assumption that ions existed only in the LC medium but not in the PI-films. The RDC voltages were caused by the LC-to-PI-interfacial trapped ions originated only from the LC side. Based on the above assumption, Masanobu Mizusaki et al.[1] published a paper on generation mechanism of RDC voltage in a liquid crystal display and its evaluation parameters related to liquid crystal and alignment-layer materials. In this paper, for the first time, we report the measurements of RDC voltage in LC cells with ionic properties dominated by PI-alignment films [2] such that there are more ions driven to the PI-to-LC interfaces from PI sides than from LC side. We will discuss the interpretations of our data in comparison to the results published by Masanobu Mizusaki et al.

 Preview abstract

We consider photo-induced trans–cis isomerization of a chiral-azobenzene dye and propose an azo-chiral-doped liquid crystal (ACDLC) enabling photoswitching among the planar-nematic (N), the fingerprint (FP) and the planar (P)-cholesteric (CLC) states. The N with unwound molecular orientation and the P-CLC with helical pitch of ~900 nm can readily be achieved by illuminating the ACDLC cell with ultraviolet (UV, λ = 365 nm) and green (λ = 532 nm) lights, respectively. Noticeably, because dye molecules tend to be oriented in the state with the lowest absorptivity for the incident light, it is found that a metastable FP state is realized during the photo-induced textural transition between the N and the P states (Fig. 1). Furthermore, the ACDLC is employed as a central defect layer of a 1D PC. Since the ACDLC in the N, FP, and the P states possesses effective refractive indices of ne, no, and (ne + no)/2, respectively, three photoswitchable sets of defect modes in the 1D-PC/ACDLC cell are realized according to the photoswitching mechanism of the ACDLC. As a result, the proposed PC/ACDLC hybrid structure is promising for developing a multifunctional photonic device with unique optically switchable and electrically tunable spectral properties of defect-mode peaks.

 Preview abstract

By means of temperature-dependent dielectric spectroscopy and observations of optical textures, our results show that the PS-ULH structure with excellent uniformity and stability, as examined after cycles of temperature tests, can be obtained in the temperature range covering both the CLC and the SmA phases. While the ULH state is regarded as a uniaxial crystal in the CLC phase, the voltage-dependent transmission (VT) curve of the cell under crossed polarizers as shown in Fig. 1 exhibits hysteresis-free electro-optical responses, suggesting the ability of linear gray-levels. Noticeably, the switching time between the PS-ULH and the homeotropic states measured in the order of a submillisecond can be reduced by increasing the concentration of the monomer doped into the cell. In the present work, the response time of the cell can be promoted to ~10 ms when the monomer concentration is 7 wt%. Consequently, the proposed PS-ULH structure, with high contrast ratio, hysteresis-free responses and millisecond order response time, is potentially applicable for developments of electro-optical devices, such as phase modulators and displays. Other remarkable results including phase behaviors and improved electro-optical properties of the PSULH structure based on our proposed approach will be clarified accordingly.

 Preview abstract

We investigate motions of spherical micro-particle in non-uniform director fields. In this study, we mix a particle into nematic liquid crystal. The director alignment on the particle is homeotropic boundary condition. The particle has to induce dipole or quadrupolar configuration. The dipole configuration accompanies a hyperbolic hedgehog defect and the quardrupolar configuration is encircled by a Saturn-ring disclination ring around particle [1,2]. We construct a liquid crystal cell. One substrate is prepared to have striped alignment patterns. To make a pattern we use a photo-alignment technique [3]. At this system, boundaries of striped pattern induce a distortion of liquid crystal. When the single particle locates in a position of the alignment pattern, it shows various dynamic motions. There seems to be an interaction between distortion of liquid crystal and particle configuration. In this report, we would like to show the interaction and its results.

 Preview abstract

Cholesteric liquid crystals (CLCs) with uniformly lying helix (ULH) structure are well-known for their superior electro-optical characteristics, including fast flexoelectric switching and tunable birefringence that are potentially for a variety of optoelectronic and photonic applications. Unfortunately, simple device geometry is unavailable to permit the ULH structure as a minimum energy state so that it has been proven difficultly in creating a defect-free ULH alignment. In considering the prospective developments, we propose an approach to the formation of a stable and switchable ULH structure. Here, CLC mixtures with distinct helical pitches were individually injected into 90-twisted cells. When sustaining the cell in the homeotropic state by an external voltage, turning off the voltage quickly and switching directly to a lowered voltage, result in the formation of planar and focal conic states, respectively. Noticeably, a stable ULH texture can be created by descending the voltage slowly to zero, due to the generation of twist deformation of LC molecules near the substrates during the nematic–CLC transition. Accordingly, by utilizing the aforementioned tristable-switching mechanism together with the feature of electrically controllable birefringence in the ULH state, the proposed CLC cell is potentially applicable as a tunable phase modulator and an energy-efficient photonic device.

 Preview abstract

The concept supporting the aforementioned results can be explained as follows. In a dye-doped LC cell, dye molecules follow the director of the LC host in that they are squeezed by and attached to the long axes of LC molecules. From the point of view of material design, the rod-like LC with larger refractive index as well as dielectric anisotropy typically reflects longer molecular conjugation and higher ordering. Accordingly, promoted CR and reduced operating voltages are expected in a guest–host LC device comprising a high- nematic host, presumably due to the enhancement in ordering of dye molecules. As a result, our work provides a promising pathway to a high contrast and energy-efficient guest–host device for the application in, say, smart windows.

 Preview abstract

In this study, we explore a cholesteric liquid crystal device with a three-terminal electrode structure that can be switched between standing-helix (SH) and lying-helix (LH) molecular configurations by in-plane and vertical electrical field. The ITO interdigital electrode arrays with a width of 8𝜇m and separation of 12𝜇m are fabricated on the bottom glass substrate to produce in-plane electric field, and the uniform ITO thin film is deposited on the top glass substrate as the sheet electrode to create nonuniform vertical electric field. The ChLC cell with a three-terminal electrode structure exhibits interesting optical characteristics. Both Bragg reflection and phase retardation can be electrically switched.

 Preview abstract

In this paper, we calculate liquid crystal director field in circularly confined capsules by using Q-tensor method, which can calculate not only the LC director field in bulk area but the local phase transition in high elastic distortion area. We calculated LC director filed in colloidal capsule with the boundary condition of both homogeneous state and homeotropic state.

 Preview abstract

Recently, two-photon absorption (TPA) in diacrylate mesogens, RM82 and RM257, was reported [1]. However, the authenticity that the TPA happened in the mesogens has been questioned. A major feature that distinguishes TPA from one-photon absorption is that TPA is, as being classified, a third-order nonlinear optical process at a wavelength λ [2]. Z-scan is a simple and highly sensitive single-beam experimental technique, and has been widely used to measure both nonlinear absorption and nonlinear refraction [3]. Recently, we employed Z-scan technique to verify the nonlinear optical property of diacrylate. In the present study, a 21 mW HeNe laser operated at wavelength 632.8nm was used to provide probe beam. Sample was mounted in a holder which was controlled to move along the laser beam. Data were acquired when the samples were at difference temperature. Marked response signals were observed from both diacrylate compounds RM82 and RM257, and indicate the existence of nonlinear optical process in the mesogens.

 Preview abstract

Nanoscale plasmonic structures have attracted much attention owing to their strong absorption at visible-light regime [1-3]. The strong absorption arises from the collective oscillation of the electrons at the surfaces of nanoscale metal structures, and the wavelengths of their absorption peaks depend on the refractive indices of the media that surround the structures. As a result, the nanoscale plasmonic structures can be used to develop biomedical sensors [1-3]. This work fabricates an electrically construable optical filter using silver nanoslits embedded with liquid crystal. The intensity (wavelength) of the filter can be tuned at a low (high) voltage region between 1 (5) V and 3 (50) V due to the strong anchoring energy of the nanoslits, as presented in Fig. 1(a) [1(b)]. The optical filter, together with an LED, functions as a single-wavelength light source. Such a light source can be used to develop lab-on-chips for biomedical detection and photonic integrated circuits.

 Preview abstract

We experimentally studied the thermal and optical properties of the laser lines and fluorescent spectrum generated by a thermally tunable cholesteric liquid crystal (CLC) laser. High-quality perovskite quantum dots with cubic structure were simply synthesized by a novel low temperature solvothermal pathway. Relationship between band edge effect and threshold energy has been investigated in optical emission using perovskite quantum dots embedded in the one dimensional photonic crystal device (CLC). Upon 532nm pulse laser excitation, amplified spontaneous emission (ASE) and optical gain were observed, for the first time, perovskite quantum dots doping cholesteric liquid crystal (PDCLC). This work demonstrates a thermally tunable perovskite quantum dots-doped cholesteric liquid crystal distributed feedback (DFB) laser or ASE. Such a tunable optical can be used in the fabrication of tunable optical sources and biosensors, and in integrated photonic circuits, optical communication, and displays.

 Preview abstract

Compared to planar alignment, the homeotropic alignment is not ease to obtain the anchoring strength for large background signal. Here, the anchoring strength of the homeotropic alignment is obtained by measuring the reflected light from the liquid crystal cell in reflection mode of the optical microscope and modelling the cell response. We prepared a cell made of two substrates of homeotropic alignment. One substrate has the alignment layer we have interest in. The other has weak anchoring. The liquid crystal we used has a positive dielectric anisotropy in nematic phase and the electrodes are prepared to apply planar electric field. The depth of focus of the objective lens is selected to be less than the cell gap and light was focused on the interested substrate. With applying the electric field, the director near weak anchoring substrate responds rapidly. In contrast, the director near interested substrate responds slowly. The reflected light from the cell is mostly from the near the interface of interested substrate. The process of the director response is modelled and the change of reflection can be obtained for different anchoring strength. Finding appropriate anchoring strength, we obtain well fitted calculation result to the experiment.

 Preview abstract

Diacrylate, compounds RM257 and RM82 are liquid crystal reagents. They are light sensitivity and two-photon absorption activity can be polymerized when initiated by ultraviolet irradiation. In previous studies , their non-linear characteristics were reported and optical interference patterns can be produced in the compounds.In this study, we studied effects of optical irradiation on the diacrylate reagents using a two-beam interference field that was produced using a He-Ne laser with a power of 21 mW and a wavelength of 632.8 nm. Samples of the diacrylate reagents were irradiated at the position where the interference fringes formed. In additional, a three-beam interference pattern was also used in order to form a spatial periodic structure in the samples. In this report, discussions on the relevant observations are provided.

 Preview abstract

The diffraction-tuned circular gratings with the cholesteric liquid crystals (CLCs) have been investigated by using circular alignment method. The phase-grating like fingerprint texture of CLCs can be obtained by operating at the low voltage under a suitable d/p ratio (d/p ≤ 3) and two types of the fingerprint texture are defined with various range of d/p ratio [1,2]. Fingerprint texture with d/p ratio of 0.5~1.0 is the developable-modulation (DM) type and the stripes simultaneously appear across the whole sample. For the cell with d/p ratio of 1.5~3.0 is growing-modulation (GM) type and the stripes slowly extend to the whole sample along the rubbing direction from defects. In this study, the pitch of CLC sample fabricated with GM type can be easily tuned by varying voltage. The tuning maximum angle of second-order diffraction achieves 20.9 degrees with the CLC sample under the condition of d/p = 2.5. The circular gratings have the polarization-independent property because its stripe exhibits the circular symmetrical structure. According to above characteristics, the CLC circular gratings are polarization-insensitive and can be potentially applied in optical switching devices for widely tunable feature.

 Preview abstract

A simple method of fabricating high-reflective display with the polymer-stabilized blue phase liquid crystals (PS-BPLCs) is proposed. The PS-BPLCs are formed from the polymer monomer-doped BPLCs curing by the UV light, resulting in the more stable structure and the wider temperature range of the BPLCs. The uniform reflective color and high Bragg's reflection of the BPLCs can be obtained by rubbing the surface of sample. In this work, three PS-BPLC samples are produced as the basic sub-pixels of the display, which can reflect the red (R), green (G), and blue (B) lights, respectively. The results show that the G- and B-sub-pixel of the PS-BPLC samples have a good behavior of photoelectric when applied voltage. The reflectances of three PS-BPLC samples (R, G, and B) are about 50, 77, and 60 %, respectively. Moreover, the major problem of PS-BPLCs with high operating voltage is expected to improve in the further study.

 Preview abstract

For twisted nematic(TN) liquid crystal (LC) displays, the pretilt angle of the TN LC medium within the cell has a significant impact on display qualities such as viewing angles and response times as well as shifting the light leaking disclination lines into the black-matrix area within pixels of thin-film-transistor driven TN panel for high contrast ratio. In this paper, we have developed an optical method to determine TN pretilt angle free of entanglement with TN cell gap based on heterodyne measurements of phase versus incident angle of a thin TN cell subjected to out-of-plane rotations. We believe that our method of measuring phases has advantages of a simpler setup, better stability, higher signal-to-noise ratio, and less sensitive to ambient EMI than the conventional method of measuring intensity[1].

 Preview abstract

type of liquid-crystalline phases called the blue phases (BPs) was observed back in 1888. While BPIII is believed to be an amorphous network of disclination lines, BPII and BPI possess distinct three-dimensional cubic lattice structures induced by self-assembled double twist cylinders, exhibiting selective Bragg reflections in accordance with the cubic lattice. BPs appear in a temperature range between a chiral nematic phase and an isotropic phase, which has been recognized as a scientific fact. However, with technology advancing continually, an unusual phase sequence of BP liquid crystals (LCs) has been observed and some researchers termed a unique phase situated between the BP and isotropic phases as the sphere phase [1, 2]. Here, we show and elucidate the “corrected” phase sequence for BPs based on our experimental observations. The BP actually originates from a very narrow temperature range of a chiral phase near the isotropic phase in the cooling process. The random isotropic phase first transforms to a disclination-rich chiral phase, and then LC molecules become connected, pairing helices to produce a double twist cylinder. Finally a BP lattice grows.

 Preview abstract

Our experimental results of real-time measurements indicated that both the TiO2-doped and undoped LC cells exhibit promoted ion densities and reduced voltage holding ratios (VHRs) during the UV exposure. After turning off the UV light, the VHR of TiO2-doped LC cells can recover over time (in hours). For instance, we found that the VHR of TiO2-doped LC decreased from 71% to 43% by 2-mW/cm2 UV irradiation for 60 min but it was remarkably recovered to 61% in the UV-off condition for 180 min. The recovery of UV-degraded electrical properties over time in TiO2-doped LC cells is believed to be attributable to the regained ion-trapping ability of TiO2 NPs. For LC-based devices, cells exposed to the ultraviolet light often lead to the deterioration in electro-optical performance caused by the natural LC-material degradation and ion injection from the aligning materials. Accordingly, the proposed LC/TiO2 colloids can be regarded as a promising system for the use of outdoor LC devices characterized by regained excellence in electrical performance after UV exposure.

 Preview abstract

Surface-stabilized ferroelectric liquid crystal (SSFLC) possesses the advantages of ultra-fast response and bistability. However, the main key point is the extremely thin gap (usually < 2 m) of the LC cell, which is difficult to be fabricated. In this study, we found that the cell gap to achieve SSFLC can be increased if the dopant with high electric dipole moment is doped. Here, the employed dopant is an azobenzene material, whose electric dipole moment at cis-isomer is higher than that at trans-isomer. Briefly, the selected cell gap of the homogeneous alignment LC cell herein was about 5 m, and the material was azobenzene-doped FLC. Figure 1(a)-1(c) show the observations under cross-polarizer polarized optical microscope before being treated with UV illumination, as known as trans-isomers. Clearly, no bistability can be obtained. Moreover, after being treated with UV illumination, the trans-isomers having low electric dipole moment have been transferred to cis-isomers having high electric dipole moment so that the FLC can be stabilized at zero voltage application as shown in Figs. 1(d)-1(f) [1-3]. Reversely, by heating the FLC sample, the bistable characteristic of FLC can be removed.

 Preview abstract

Liquid crystals textures are the main implementation for liquid crystal phase classifications. By doing so, a mesogen is placed between two glass plates, i.e. a microscope glass slide and a cover slide, and the textures can be observed under a polarizing optical microscope (POM), with or without a temperature controller. According to this report, we dissolved 5CB in dichloromethane and the mixture was dropped a hole (2 nm in diameter) in a microscope slide (2.5 cm x 7.5 cm). The mixture was left to dry at room temperature for 2 hours, where the 5CB free standing film was developed in the hole. The textures of the film were observed under a polarizing optical microscope, Figure 2. On the other hand, 5CB was also observed under the microscope using the conventional method, Figure 1. It is concluded that 5CB molecules placed between two glass plates exhibited classical and colorful textures with some defects due to the birefringent properties of the compound. Contradictly, the textures of the free standing film were almost colorless with a defect point. The model of both textures, in sandwiched glass plates and in free standing film, will be presented and discussed in the presentation.

 Preview abstract

This study presents an optically tunable focal length of Fresnel lens with PVK/C60 layer and Sagnac interferometer. The PVK doped with C60 can enhance the absorbance in visible wavelength range. By using Sagnac interferometer with visible wavelength, a Fresnel-like pattern can be induced on the PVK/C60 layer which results in conductive and nonconductive structures corresponding to bright and dark regions. Thus, a Fresnel lens can be constructed through the mismatch of refractive index between adjacent zones with an external voltage. The focal length of the proposed Fresnel lens can be easily tuned by varying the size of the Sagnac pattern and the focusing efficiency can also be controlled optically.

 Preview abstract

The orientation of liquid crystals and the formation of topological defects of liquid crystals in confined geometries are determined by the nematic elasticity, chirality and surface anchoring [1-3]. Here we report the deformations of the inner orientation in cholesteric liquid crystal (CLC) microdroplets with short- and long-pitch deposited on polymeric fibers, as shown in Fig. 1. Two kinds of surface anchoring, perpendicular anchoring at the air-CLC droplet interface and planar anchoring at the fiber-CLC droplet interface, coexist in this system. We observed the equilibrium structures of the CLC microdroplets thermally cooled down from isotropic phase to chiral nematic phase. In addition to the thermal dependent deformations of the CLC microdroplets, this study also discusses the photo-dependent deformations of the azo-CLC microdroplets, which are composed of azo-LC-doped CLCs or azo-chiral-doped CLCs. The UV-irradiation induced trans to cis isomerization of the azo-materials can disturb the orientations of the LCs or the pitch of the CLCs inside the microdroplets and thus the disclinations, as shown in Fig. 2. The photo-controlled deformations of the CLC microdroplets on polymeric fibers presented in this work can be used to achieve topological remote control and open a route to develop devices based on topologically structured soft media.

 Preview abstract

A series of non-chiral bent-core molecules with different alkoxy chain at the terminal positons were prepared, and we carried out doping experiments in a cholesteric liquid crystal (ChLC) phase mixed with the bent-core homologues. The helical twisting power (HTP) of the doped bent-core molecule in the ChLC strongly depended on the terminal alkoxy chain length of the bent-core molecules used in this study; Bent-core molecule with the longer alkoxy chain length shows the stronger HTP in a chiral circumstance such as a ChLC. Namely, not only the axial conformations at wings linked to bent central unit [1] but also the length of the alkoxy chain at the terminal positons of the bent-core molecules play an important role in showing the unusual chiral behavior. Details will be discussed in ACLC 2017.

 Preview abstract

Chirality in a mixture system consisting of bent-core molecule (P8-O-PIMB) and rod-like molecule (8CB) molecules has been studied using circular dichroism (CD) observations. The observed CD spectra indicate as follows: (1) the CD signals originate from chiral-segregated helical nano filament (HNF) [1] of binary mixtures comprising bent-core P8−O−PIMB and rodlike 8CB molecules, where 8CB is in the isotropic phase; (2) the enhanced CD signal is detected in the BX1 phase of the binary achiral mixtures, where 8CB is in the nematic phase; (3) furthermore, remarkably enhanced CD signal emerged in the BX2 phase of the binary achiral mixtures, where 8CB is in the smectic phase. Details will be discussed in ACLC 2017.

 Preview abstract

Optical tweezers are achieved by using a highly focused laser beam and can be used to grab micrometer-scale particles. When the particle is transparent and its refractive index is larger than the surroundings, a single focused laser beam can attract it to the focused point through momentum transfer. Due to the non-contact and non-destructive properties, optical tweezers are widely applied in biomedical and materials sciences. The interaction between the microspheres (MSs) and the incident light field of optical tweezers can make the manipulation of microspheres in more diverse ways. This study aims to investigate orbital motions of azo-dye doped nematic liquid crystal (NLC) MSs under the manipulation of optical vortex tweezers (OVTs) and UV irradiation. Home-made q-plates (QPs) are integrated into the optical tweezers system for modulating the phase of laser and generating the optical vortex beam. The laser beam of the OVTs possesses spin and orbital angular momentum simultaneously. Two types of azo-dye-doped NLC MSs, bipolar and radial NLC MSs, are investigated. With the illumination of UV light, the internal orientations of NLC molecules in the azo-dye doped NLC MSs and thus the rotation behaviors of the azo-dye-doped NLC MSs change.

 Preview abstract

Although the material used in this study does not show any LC phases, it is one of the typical soft-matter materials with unique shape. Here we demonstrate how such soft-matter molecules form an orientational structure in a confined thin film, and how such structures can be analyzed, which can be applicable to LC phases as well. We have observed anisotropy with respect to the polar angle in vacuum-deposited amorphous films using cross-shaped molecules with an accompanying effect on carrier mobility by means of variable angle spectroscopic ellipsometry (VASE), sum-frequency generation spectroscopy (SFG) and impedance spectroscopy (IS). We study molecular orientations of the uniquely shaped molecule, keeping it in mind whether or not anisotropy can be observed with relatively bulky molecules. We make a difference in a more quantitative analysis over how the molecules sit in a thin film on average, introducing the advanced technique beyond linear optics; SFG has been used to deduce more detailed molecular orientations. We also make clear how anisotropy accompanies an effect on carrier mobility at the end.

 Preview abstract

Polymer dispersed Liquid crystal (PDLC) based smart windows have been studied widely for the use as curtain-free windows. Their integration with luminescent solar concentrator (LSC) device is a promising approach towards development of self-sustainable smart windows. The electricity produced by the LSC could potentially be employed for switching operation of smart window. In this study, we have presented a novel configuration of LSC-PDLC smart window. The presented system comprises of two parts, LSC and PDLC as outer and inner part respectively, partitioned by the small air gap. LSC-PDLC smart window was evaluated on the base of spectral contents of power emitted by the edges. PDLC in OFF mode acts as a backside scatterer. Firstly, it reflects the untrapped light back into LSC part, enhancing the edge emissions. Second, it redirects light that is not absorbed towards the edges, and thus to the attached solar cell. Further, the effect of applied voltage on LSC-PDLC smart window has been discussed. Our results are of great interest in view of a possible use of LSC as an onboard power generator for smart window.

 Preview abstract

In this research, we successfully design a novel microlithography system to conduct photo-alignment, and the concept of meta-q-plate featured by arbitrarily space-variant optical axes is proposed. Furthermore, correspondingly special fields including elliptical, asymmetrical, multi-ringed and hurricane transverse profiles are demonstrated.

 Preview abstract