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Microwave properties of Ba_0.5Sr_0.5TiO₃ thin film coplanar phase shifters

JOURNAL OF APPLIED PHYSICS 2006年第10期99卷 104101.1-104101.7页

作者： Suherman, PM Jackson, TJ Tse, YY Jones, IP Chakalova, RI Lancaster, MJ Porch, A Univ Birmingham Sch Engn Birmingham B15 2TT W Midlands England Cardiff Univ Sch Engn Cardiff CF24 3AA Wales

Coplanar waveguide transmission lines have been used to show that the temperature dependent properties of Ba0.5Sr0.5TiO3 thin films used for microwave phase shifters in the frequency range 45 MHz-50 GHz are correlated strongly with the microstructure of the films. The highest tunability and figure of merit of the phase shifters were obtained for films with the narrowest ferroelectric-paraelectric phase transition range, lowest mosaic spread, and widest columnar microstructure. The study also showed that the operating temperature plays an important role in achieving the optimum phase shift for microwave applications. (c) 2006 American Institute of Physics.

关键词： wave-guides DIELECTRIC-PROPERTIES PERMITTIVITY TEMPERATURE TRANSITION FREQUENCY SUBSTRATE

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Confinement loss in adiabatic photonic crystal fiber tapers

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS 2006年第9期23卷 1965-1974页

作者： Kuhlmey, Boris T. Nguyen, Hong C. Steel, M. J. Eggleton, Benjamin J. Univ Sydney CUDOS Sydney NSW 2006 Australia Univ Sydney Sch Phys Sydney NSW 2006 Australia RSoft Desing Grp Inc Chippendanle NSW 2008 Australia

We numerically study confinement loss in photonic crystal fiber (PCF) tapers and compare our results with previously published experimental data. Agreement between theory and experiment requires taking into account hole shrinkage during the tapering process, which we measure by using a noninvasive technique. We show that losses are fully explained within the adiabatic approximation and that they are closely linked to the existence of a fundamental core-mode cutoff. This cutoff is equivalent to the core-mode cutoff in depressed-cladding fibers, so that losses in PCF tapers can be obtained semiquantitatively from an equivalent depressed-cladding fiber model. Finally, we discuss the definition of adiabaticity in this open boundary problem. (c) 2006 Optical Society of America.

关键词： MICROSTRUCTURED-OPTICAL-FIBERS SUPERCONTINUUM GENERATION FUNDAMENTAL MODE MULTIPOLE METHOD HOLEY FIBERS wave-guides CUTOFF INDEX

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Structural analysis of hybrid titania-based mesostructured composites

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JOURNAL OF THE AMERICAN CHEMICAL SOCIETY 2005年第27期127卷 9721-9730页

作者： Boettcher, SW Bartl, MH Hu, JG Stucky, GD Univ Calif Santa Barbara CNSI Dept Chem & Biochem Santa Barbara CA 93106 USA Univ Calif Santa Barbara Mat Res Lab Santa Barbara CA 93106 USA

High-optical-quality titania-based mesostructured films with cubic or 2D-hexagonal symmetry were fabricated by combining trifluoroacetate (TFA)-modified titanium precursors with amphiphilic triblock poly(ethylene oxide)-poly(propylene oxide) -poly(ethylene oxide) (PEO-PPO-PEO) copolymers. The distribution, dynamics, and local environments of the TFA-modified titania, PEO, and PPO components of the hybrid were investigated. IR/Raman spectroscopy, in situ small-angle X-ray scattering, and transmission electron microscopy studies indicate that TFA coordinates the titanium center and forms a stable complex that is subsequently organized by the block copolymer species into ordered mesostructures. Solid-state NMR F-19 -> H-1 cross-polarization, C-13{H-1} two-dimensional heteronuclear correlation, and H-1 relaxation techniques were used to determine that PEO is predominantly incorporated within the TFA-modified titania, and that PPO environments encompass both microphase separated regions and interfacial regions composed of mixed PPO and TFA-modified titania. NMR F-19 multiple-quantum spin counting measurements suggest that -CF3 groups of the trifluoroacetate ligands do not form clusters but instead randomly distribute within the inorganic component of the hybrid.

关键词： SOLID-STATE-NMR MULTIPLE-QUANTUM NMR MESOPOROUS MOLECULAR-SIEVES THIN-FILMS TRIFLUOROACETIC-ACID METAL-OXIDES POLY(ETHYLENE OXIDE) VIBRATIONAL-SPECTRA CROSS-POLARIZATION wave-guides

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Dependence of nonlinearity enhancement on power density in photonic crystals characterized by numerical Z-scan experiments based on the finite-difference time-domain technique

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS 2008年第4期25卷 555-563页

作者： Meng, Zi-Ming Liu, Hai-Ying Dai, Qiao-Feng Wu, Li-Jun Guo, Qi Hu, Wei Liu, Song-Hao Lan, Sheng Trofimov, V. A. S China Normal Univ Lab Photon Informat Technol Sch Informat & Optoelect Sci & Engn Guangzhou 510006 Guangdong Peoples R China Moscow MV Lomonosov State Univ Dept Computat Math & Cybenet Moscow 119992 Russia

We investigate the enhancement of nonlinearity in one-dimensional (1D) photonic crystals (PCs) with Kerr nonlinearity by numerical Z-scan experiments based on the finite-difference time-domain technique. Focused Gaussian beams with well-defined waists and Rayleigh lengths necessary for Z-scan experiments are generated through a conjugated manipulation of the Gaussian beams propagating in free space. The Z-scan measurements used for bulk materials are naturally extended to 1D PCs after incorporating the frequency- and power-density-dependent reflections into their linear and nonlinear absorptions. The closed- and open-aperture Z-scan traces for the 1D PCs are obtained and a symmetric method is employed to modify the asymmetric closed-aperture traces. The nonlinearity enhancement factors at different frequencies in the first and second bands are derived numerically and analytically. A good agreement is found between the numerical and analytical results in the case of weak nonlinearity. Moreover, the dependences of the enhancement factor on the incident power density for different frequencies in the 1D PCs are extracted and they are found to be much different from those in bulk materials. It is revealed that the variation of the group velocity with increasing power density is responsible for the power-density dependence of the enhancement factor. It indicates that in practice one must deliberately choose the working frequency and power density of PC-based devices in order to achieve a maximum enhancement of nonlinearity. (C) 2008 Optical Society of America.

关键词： ULTRASHORT OPTICAL PULSES wave-guides KERR NONLINEARITY BANDGAP STRUCTURE DELAY-LINES SUPERPRISM DESIGN EMISSION DEFECT BEAM

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Induced focusing of two laser beams in cubic quintic nonlinear media

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PHYSICA SCRIPTA 2004年第6期70卷 354-360页

作者： Jana, S Konar, S Birla Inst Technol Dept Appl Phys Ranchi 835215 Bihar India

This paper presents an investigation of induced focusing of two laser beams (i.e., a pump beam and another probe beam) in a medium possessing cubic quintic nonlinearity. Third and fifth order nonlinear susceptibilities in presence of two interacting waves have been evaluated. These susceptibilities are then employed to derive two coupled nonlinear Schrodinger equations. Variational formalism has been employed to derive relevant equations which govern different characteristics of propagating beams. Extensive numerical simulation has been performed to investigate the influence of the pump beam on the propagation characteristics of the probe beam. Among several important findings. most noteworthy one is that a very weak probe beam can be guided and focused with a pump beam even if its power is well below threshold Value of focusing of the pump beam alone. It has been found that induced focusing of the probe beam is more effective when its wavelength is smaller and initial beam width larger than the corresponding quantities of the pump. The roles of fifth order nonlinear coefficient on induced focusing have been investigated. Particularly. it has been established that even an initially defOCUsing pump can focus a very weak probe.

关键词： PARA-TOLUENE SULFONATE OPTICAL FIBERS wave-guides VARIATIONAL APPROACH SOLITARY waveS RING FORMATION PROPAGATION INDEX COLLAPSE PULSES

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AN FD-BPM WITH ADAPTIVE MESH FOR LONGITUDINALLY VARYING OPTICAL STRUCTURES

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OPTICAL AND QUANTUM ELECTRONICS 1995年第10期27卷 951-959页

作者： MASSINI, C BELLANCA, G BASSI, P SORRENTINO, R UNIV BOLOGNA DIPARTIMENTO ELETTRON INFORMAT & SISTEMISTI-40136 BOLOGNAITALY

A finite difference beam propagation method (FD-BPM) algorithm using an adaptive mesh is proposed for optimal use of computer memory and minimization of CPU times in three-dimensional longitudinally varying guiding structures. Preliminary results confirming its feasibility and the advantages of the new algorithm both in CPU and computer memory requirements are described in a 2D case using a Y-junction.

关键词： Beam propagation method Finite-difference wave-guides computer memory Finite differences Beam propagation method central processing units waveguide Device Component Y junction

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Low-shrinkage, high-hardness, and transparent hybrid coatings: Poly(methyl methacrylate) cross-linked with silsesquioxane

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CHEMISTRY OF MATERIALS 2003年第18期15卷 3481-3489页

作者： Harreld, JH Esaki, A Stucky, GD Univ Calif Santa Barbara Dept Chem & Biochem Santa Barbara CA 93106 USA Mitsubishi Chem Corp MCC Grp Sci & Technol Res Ctr Precis Coating & Surface Modificat Lab Aoba Ku Yokohama Kanagawa 2278502 Japan

Copolymers of trimethoxysilylpropyl methacrylate (TMSPM) and methyl methacrylate (MMA) with varied composition and molecular weight were prepared as building blocks for transparent organic-inorganic hybrid materials. Thermally and chemically induced condensation of these network precursors after solvent evaporation results in optically clear coatings as thick as 1.0 mm with extremely low lateral shrinkage. Many interacting variables such as acid catalyst concentration, polymer molecular weight, polymer composition, and thermal treatment combine to produce materials having controllable shrinkage, hardness, transparency, and thermal stability. By selectively defining these variables, the syntheses of these materials are optimized such that silsesquioxane-cross-linked acrylic polymers are produced that exhibit desirable properties such as low optical loss in the visible spectrum, low lateral shrinkage, high scratch hardness, and no glass transition temperature. The available combinations, interrelationships, and limitations of these properties are discussed.

关键词： Organic-inorganic nanocomposites Sol-gel materials Mechanical-properties Composite-materials Optical-properties wave-guides Chemistry Trimethoxysilylpropylmethacrylate Tetramethoxysilane Polymerization

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Numerical analysis of coupled wedge plasmons in a structure of two metal wedges separated by a gap

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JOURNAL OF APPLIED PHYSICS 2006年第1期100卷 13101-1-13101-页

作者： Pile, D. F. P. Gramotnev, D. K. Haraguchi, M. Okamoto, T. Fukui, M. Univ Tokushima Dept Opt Sci & Technol Fac Engn Tokushima 7708506 Japan Queensland Univ Technol Appl Opt Program Sch Phys & Chem Sci Brisbane Qld 4001 Australia

This paper presents the results of the numerical finite-difference time-domain analysis of a strongly localized antisymmetric plasmon, coupled across a nanogap between two identical metal wedges. Dispersion, dissipation, field structure, and existence conditions of such coupled wedge plasmons are determined and investigated on an example of the fundamental coupled mode. It is shown that in the general case there exist three critical wedge angles and a critical gap width (separation between the wedge tips). If the gap width is larger than the critical separation, then the antisymmetric wedge plasmons can exist only in the ranges between the first and the second critical angles, and between the third critical angle and 180 degrees. If the gap width is smaller or equal to the critical separation, then the third and the second critical angles merge, leaving only one interval of wedge angles within which the antisymmetric coupled wedge plasmons can exist. The effect of rounded wedge tips is also investigated and is shown to be similar to that of different wedge angles. Feasibility of using these plasmons for the design of efficient subwavelength waveguides is discussed. (c) 2006 American Institute of Physics.

关键词： wave-guides ELECTROMAGNETIC ENERGY SURFACE POLARITONS GROOVES TRANSPORT MODES LIGHT

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Experimental and theoretical observations of the slow-light effect on a tunable photonic crystal

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JOURNAL OF THE OPTICAL SOCIETY OF AMERICA B-OPTICAL PHYSICS 2007年第6期24卷 1416-1422页

作者： Roussey, Matthieu Baida, Fadi I. Bernal, Maria-Pilar Inst FEMTO ST Dept Opt PM Duffieux F-25030 Besancon France

We describe how the susceptibility of a nonlinear material, such as lithium niobate, can change when the material is nanostructured. Indeed, we show, by the calculation of the local-field factor inside a photonic crystal, a significant augmentation of the susceptibility, especially at the edges of the photonic bandgap. In addition, and for the case of lithium niobate, we observe an increase of the second-order nonlinear coefficient. The experimental realization of an electro-optic tunable photonic crystal, based on a square lattice of holes, shows that the measured phenomenon completely agrees with the theoretical predictions. (C) 2007 Optical Society of America

关键词： wave-guides BAND-EDGE SUPERCONTINUUM SPECTROSCOPY ENHANCEMENT GENERATION

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Using a quantum well heterostructure to study the longitudinal and transverse electric field components of a strongly focused laser beam

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JOURNAL OF APPLIED PHYSICS 2006年第2期100卷 23112-1-23112-页

作者： Rurimo, G. Kihara Schardt, M. Quabis, S. Malzer, S. Dotzler, Ch. Winkler, A. Leuchs, G. Dohler, G. H. Driscoll, D. Hanson, M. Gossard, A. C. Pereira, S. F. Univ Erlangen Nurnberg Max Planck Res Grp Inst Opt Informat & Photon D-91058 Erlangen Germany Univ Calif Santa Barbara Dept Mat Santa Barbara CA 93116 USA Delft Univ Technol Fac Sci Appl Opt Res Grp NL-2628 CJ Delft Netherlands

We report a method to measure the electric energy density of longitudinal and transverse electric field components of strongly focused polarized laser beams. We used a quantum well photodetector and exploited the polarization dependent optical transitions of light holes and heavy holes to probe the electric field distribution in the focal region. A comparison of the measured photocurrent spectra for radially and azimuthally polarized beams at the light and heavy hole absorption peaks provides a measure of the amount of the longitudinal electric field component. (c) 2006 American Institute of Physics.

关键词： FOCAL REGION OPTICAL-PROPERTIES SINGLE MOLECULES wave-guides POLARIZATION LIGHT ELECTROABSORPTION MICROSCOPE AMPLITUDE SYMMETRY

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