共查询到20条相似文献,搜索用时 49 毫秒
1.
Kubo S Gu ZZ Takahashi K Ohko Y Sato O Fujishima A 《Journal of the American Chemical Society》2002,124(37):10950-10951
Recently, photonic band gap (PBG) crystals with lattice parameters comparable to the wavelength of light have attracted much attention, because they offer unique ways in which to control the propagation of light. PBG crystals have applications in laser, quantum optical devices, and so on. For many of these applications, it is important to have the capability of tuning the photonic band structures. The fabrication of such tunable PBG crystals is still a challenge. In this paper, we proposed that switchable PBG crystals could be realized by taking advantage of the phase transition in liquid crystals induced by the photoisomerization of azo dyes. A dynamic change in the optical stop band was demonstrated. Such photoswitchable PBG crystals provide a method by which light can be routed using light. 相似文献
2.
《Liquid crystals》2012,39(15):2159-2166
ABSTRACTWe study the optical properties of a cholesteric liquid crystal doped with a fluorescent dye in the regime of highly distorted helix without full helix unwinding. The distortion was achieved by applying a pulsed AC electric field, perpendicular to the helix axis. If the pulse is in the millisecond range, the helix is deformed but keeps its original pitch even for electric fields higher than the theoretical critical field for helix unwinding. In this field regime, very pronounced high-order photonic band gaps are observed, in agreement with our calculations. We theoretically explore the possibility of obtaining viable laser emission at the second-order photonic band gap, and experimentally find that lasing is not only possible but has a figure of merit similar to that of the usual laser at the main-gap region. Therefore, electric-field-induced high-order photonic band gaps are potentially useful for multiline laser applications. 相似文献
3.
以改进的对流自组装方法制备层数可控的胶体光子晶体, 并通过各向同性氧等离子体(O2 Plasma)刻蚀构造出梯度结构, 进一步通过金(Au)及无定形硅(Si)的可控沉积调节梯度结构胶体光子晶体的光子禁带, 并将该梯度结构用于罗丹明B的荧光发射增强. 相似文献
4.
5.
Roman Dabrowski Katarzyna Garbat Stanisław Urban Tomasz R. Woliński Jerzy Dziaduszek Tomasz Ogrodnik 《Liquid crystals》2017,44(12-13):1911-1928
ABSTRACTSeries of low-birefringence liquid crystal mixtures composed of alkyl alkylbicyclohexyl carbonates and modified mixtures with other compounds have been formulated, their refractive indices and electric permittivity measured upon temperature. They exhibit the ordinary refraction index no lower than the refractive index of silica glass in a different range of temperature. This enables to observe in photonic liquid crystal fibres (PLCFs) a change in the light propagation mechanism from photonic band gap guiding to modified total internal reflection at different temperatures. Selected applications of PLCFs are also discussed. 相似文献
6.
ABSTRACT Complex optical investigations were performed in one-dimensional (cholesteric) and three-dimensional (Blue Phase II) liquid-crystalline photonic crystals. Spectra of optical transmission and luminescence in the range of the photonic stop band contain information about the local anisotropy, characteristics of the photonic stop band, photonic density of states. We determine the photonic density of states in one-dimensional and three-dimensional liquid-crystalline photonic crystals employing measurements of polarised luminescence. The width of the photonic band gap, density of states and the optical characteristics related to the density of states essentially change with temperature in one-dimensional cholesteric photonic crystal. Drastic transformation of the density of states was found at the transition from one-dimensional to three-dimensional (Blue Phase II) photonic crystal. The results of our investigations demonstrate the possibility to employ the applied method for various types of photonic structures. 相似文献
7.
ABSTRACTWe demonstrate a spatially and electrically tunable random lasing based on polymer-stabilized blue phase liquid crystal (PS-BPLC)-wedged cell. The spatially tunable random lasers can be obtained from the laser dye-doped PS-BPLC-wedged cell through changing the pump positions, where the emission wavelength of the random laser can be tuned due to the thickness gradient of the wedged cell, which affects the scattering mean free path. Additionally, applying different electric fields can also tune the laser emission wavelength. The changing of refractive index due to the Kerr effect leads to a change in the scattering mean free path, resulting in shift of lasing wavelength. This PS-BPLC-wedged cell device has a great potential in applications of speckle-free imaging, document coding, biomedicine and other photonic devices. 相似文献
8.
Kim SH Lee SY Yi GR Pine DJ Yang SM 《Journal of the American Chemical Society》2006,128(33):10897-10904
Monodisperse aqueous emulsion droplets encapsulating colloidal particles were produced in the oil phase, and controlled microwave irradiation of the aqueous drop phase created spherical colloidal crystals by so-called evaporation-induced self-organization of the colloidal particles. Unlike usual colloidal crystals, colloidal crystals in spherical symmetry (or photonic balls) possessed photonic band gaps for the normal incident light independent of the position all over the spherical surface. While the consolidation of colloidal particles in emulsion droplets in an oven took several hours, the present microwave-assisted evaporation could reduce the time for complete evaporation to a few tens of minutes. Under the microwave irradiation, the aqueous phase in emulsions was superheated selectively and the evaporation rate of water could be controlled easily by adjusting the microwave intensity. The result showed that the packing quality of colloidal crystals obtained by the microwave-assisted self-organization was good enough to show photonic band gap characteristics. The reflectance of our photonic balls responded precisely to any change in physical properties including the size of colloidal particles, refractive index mismatch, and angle of the incident beam. In particular, for polymeric particles, the photonic band gap could be tuned by the intensity of microwave irradiation, and the reflection color was red-shifted with stronger microwave irradiation. Finally, for better photonic band gap properties, inverted photonic balls were prepared by using the spherical colloidal crystals as sacrificial templates. 相似文献
9.
Wu G Jiang Y Xu D Tang H Liang X Li G 《Langmuir : the ACS journal of surfaces and colloids》2011,27(4):1505-1509
Liquid-crystal elastomers together with nematic liquid crystals have been used as inverse opal materials to fabricate thermoresponsive photonic crystal directly. In the vicinity of the phase-transition point of the mixture, the photonic band gaps of such inverse opal films exhibited a strong temperature dependence. As the molar ratio of liquid-crystal elastomers and nematic liquid crystals changed, the character of their PBGs also changed with increasing temperature. Such a temperature-tuning effect in the photonic band gap should be of great interest in thermal switches and thermal sensors. 相似文献
10.
用旋涂法将聚苯乙烯微球组装成光子晶体,研究了此光子晶体的特点,并分析了在单一微球粒径下旋涂参数对光子带隙的影响.结果表明:旋涂法制备的光子晶体具有各向同性特点,其光子带隙由旋涂参数决定.光子晶体的反射波段取决于乳液中微球的质量分数,而反射强度取决于旋涂层数.因此,在设计光子晶体时,可以根据需要,通过微球的质量分数和旋涂... 相似文献
11.
Seiji Kurihara Masaki Moritsugu Sun-nam Kim Takamasa Nonaka 《European Polymer Journal》2007,43(12):4951-4960
A photochemically tunable photonic crystal was prepared by infiltration of the polymer liquid crystal (LC) having azo-chromophores in a SiO2 inverse opal structure. The SiO2 inverse opal film infiltrated with the polymer LC reflected a light corresponding to the periodicity as well as the refractive indices of the inverse opal structure. Linearly polarized light irradiation caused the shift of the reflection band to longer wavelength more than 15 nm. This is caused by the formation of uniaxially anisotropic molecular orientation of the polymer LC. The switched state was stable under interior light, and reversible switching of the reflection band can be achieved by the linearly and circularly polarized light irradiation. This photoswitching property will be suitable not only for various optical materials, but also for introduction of defects in the photonic crystals. 相似文献
12.
13.
14.
Kan Zhu Zhengwen Yang Dong Yan Zhiguo Song Dacheng Zhou Rongfei Wang Jianbei Qiu 《Journal of Sol-Gel Science and Technology》2012,62(2):149-152
Tb3+–Yb3+ co-doped Ca5(PO4)3F inverse opal photonic crystals were prepared by a self-assembly technique in combination with a sol–gel method. Upconversion
luminescence characteristics of the inverse opals were investigated. The results indicate that photonic band gap has a significant
effect on upconversion luminescence of Tb3+–Yb3+ co-doped Ca5(PO4)3F inverse opal. Significant inhibition of the green or blue upconversion luminescence was inspected if the photonic band gap
overlapped with the emission band of Tb3+ ions. 相似文献
15.
16.
Matjaž Humar 《Liquid crystals》2016,43(13-15):1937-1950
ABSTRACTThe use of liquid-crystal droplets as optical microcavities and lasers is reviewed and possible applications are discussed. Liquid-crystal droplets are prepared by simple methods that enable scalable production since their internal structure is formed by self-assembly. Light is trapped in droplets due to total internal reflection on the surface due to refractive index mismatch or because of a photonic bandgap structure in cholesteric liquid crystals (CLCs). Light confinement gives rise to a variety of optical modes and by employing a fluorescent dye end external optical pumping, lasing can be achieved. Liquid-crystal-droplet cavities are largely tunable by applying an electric field or a temperature change. Such cavities can be used as temperature and chemical sensors, and tunable light sources and filters in future integrated soft photonic circuits. 相似文献
17.
《Journal of Polymer Science.Polymer Physics》2018,56(15):1087-1093
Polymerization of crosslinkable liquid crystal monomers in chiral liquid crystalline media stabilizes the phase and enables distinct electro‐optic properties relative to small‐molecule analogs. Particularly interesting are cases where the polymerization forms a crosslinked polymer network that maintains a “structural” chirality. Recent reports have employed this methodology to realize a diverse set of electro‐optic responses in polymer stabilized cholesteric liquid crystals (PSCLCs) including reflection bandwidth broadening, reflection wavelength tuning, and dynamic scattering modes. It has been proposed that the mechanism at the root of these electro‐optic responses is an ion‐mediated, electromechanical deformation of the stabilizing and structurally chiral polymer network. In an effort to better understand the nature of these deformations, here we have characterized the electro‐optic response of PSCLCs with different polymer concentrations and crosslink densities. The dynamic response of PSCLCs to electric fields exhibits a time‐dependent behavior reminiscent of the creep of polymeric materials to mechanical deformations. The electro‐optic response can be described as the superposition of two contributions: the fast deformation of a relatively soft component of the polymer network (1–2 s) and the slower (10–20 s) deformation of a harder component. © 2018 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2018 , 56, 1087–1093 相似文献
18.
ABSTRACTWe demonstrate nematic and cholesteric liquid crystal (LC) gyroids and show their photonic properties as photonic crystals by using numerical modelling. The LC gyroids are designed as composite optical materials, where we take one labyrinth of passages to be a solid dielectric, whereas the other (complementing) labyrinth of passages is taken to be filled by chiral or achiral nematic LC, with the intermediate gyroid surface imposing homeotropic (perpendicular) surface anchoring. The nematic inside the gyroid matrix is shown to exhibit a variety of possible orientational profiles which are characterised by complex networks of topological defects – from ordered, semi-ordered, to completely disordered. The diversity of possible nematic states is shown to lead to a rich structure of photonic bands, which can be tuned by the LC volume fraction and the cholesteric pitch, including control over full – direct and indirect – band gaps. 相似文献
19.
Planar films of cholesteric liquid crystals exhibit several types of instabilities in electric fields. A periodic equilibrium structure can appear when the field is parallel to the helix axis. Conditions for the occurrence of the modulated phase have been derived by an analytical theory, which describes long wavelength distortions in the vicinity of Lifshitz points. 相似文献
20.
Fabrication and optical characterization of imprinted broad‐band photonic films via multiple gradient UV photopolymerization 下载免费PDF全文
Yan‐Song Zhang A. V. Emelyanenko Jui‐Hsiang Liu 《Journal of Polymer Science.Polymer Physics》2017,55(19):1427-1435
A structured broad‐band photonic film is fabricated by a novel method using multiple gradient UV‐induced polymerization in the presence of cholesteric liquid crystals (CLCs). Here, imprinting and broadening of the reflection band of chiral nematic mesophase cells are achieved via controlled UV polymerization. The intensity gradient of UV light is modified by the distance between UV lamp and sample cell, which affects the polymerization rate and leads to the formation of imprinted helical constructions with different pitches. In this study, a comparison of new design process with traditional UV polymerization process is carried out. After seven cycles of gradient UV polymerization, the imprinted photonic construction exhibited a broadened reflection band and Bragg reflection, even for isotropic materials. Because of this, the reflection bandwidth showed a 70% improvement. Additionally, two stacked imprinted cells with different pitches can reflect incident light with a bandwidth over the visible wavelength range of 480–680 nm. A broad‐band photonic polymer film can be imprinted using multiple gradient UV photopolymerization in the presence of CLCs. Forming a UV intensity gradient and controlling the rate of photopolymerization are key factors in broadening the reflection band. © 2017 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017, 55, 1427–1434 相似文献