Virtual boundary method for the analysis of elliptically cross-sectional photonic-crystal fibers with elliptical pores

This paper introduces a new semianalytical method for the analysis of propagation characteristics of elliptically cross-sectional photonic-crystal fibers (PCFs) with elliptical pores. This method known as a virtual boundary method (VBM) is based on the equivalency between an actual PCF and a three-layered, transversely inhomogeneous waveguide. The complicated refractive-index profile of the PCF is written as a double Fourier series, and an approximate separable wave equation is found in an elliptical coordinate system for the longitudinal field components. The exact solution to the derived equation is expressed in terms of higher order transcendental functions, such as regular and irregular Coulomb-wave functions and Mathieu functions. After having expressed all the field components, boundary conditions are imposed on the boundaries, and then, a transcendental equation for the propagation constant is derived, which is solved numerically. The validity of the method is ensured by comparing various quantities, such as effective indexes, modal birefringences, and electromagnetic field distributions, with those from an accurate full-vector finite-element method (FEM) simulator, showing relatively good agreement between the results. The method correctly confirms some of the unique PCFs' properties, such as strong localization of light within the fiber and enhancement of modal birefringence as a function of the topology of hole arrangement.     

Cobalt-based bulk glassy alloy with ultrahigh strength and soft magnetic properties

Bulk metallic glasses--formed by supercooling the liquid state of certain metallic alloys--have potentially superior mechanical properties to crystalline materials. Here, we report a Co(43)Fe(20)Ta(5.5)B(31.5) glassy alloy exhibiting ultrahigh fracture strength of 5,185 MPa, high Young's modulus of 268 GPa, high specific strength of 6.0 x 10(5) Nm kg(-1) and high specific Young's modulus of 31 x 10(6) Nm kg(-1). The strength, specific strength and specific Young's modulus are higher than previous values reported for any bulk crystalline or glassy alloys. Excellent formability is manifested by large tensile elongation of 1,400% and large reduction ratio in thickness above 90% in the supercooled liquid region. The ultrahigh-strength alloy also exhibited soft magnetic properties with extremely high permeability of 550,000. This alloy is promising as a new ultrahigh-strength material with good deformability and soft magnetic properties.     

Finite-element analysis of edge resonance in a semi-infinite elastic plate

A finite-element analysis is presented for reflection of the fundamental symmetric Lamb wave at the free edge of a semi-infinite elastic plate. It is shown that the edge resonance phenomenon is very sensitive to the value of Poisson's ratio. For a smaller value of Poisson's ratio, this phenomenon occurs at a lower frequency and the solutions vary more rapidly with frequency.     

Finite-element calculation of the transmission probability and theresonant-tunneling lifetime through arbitrary potential barriers

A numerical method for the calculation of the transmission probability through a potential barrier or structure and of the lifetime of a resonant state in a double- or multiple-barrier structure is presented. This method is based on a combination of the finite-element method and the analytical approach. A generalized boundary condition of the heterointerface is introduced by use of the interface matrix, and thus the method is applicable to the potential barriers made of arbitrary semiconductors. The validity of the method is confirmed by calculating the transmission probability of rectangular potential barriers and double barrier structures. Numerical results on sinusoidal barriers and voltage-applied barriers are also presented     

Finite-element analysis of the miniband structures of semiconductorsuperlattices with arbitrary periodic potential profiles

The method is based on the Galerkin procedure, and the third-order Hermitian line elements are used for finite elements. The periodic boundary condition is applied to the edges of one period of the periodic potential. A generalized boundary condition at the heterointerface is also introduced by use of the interface matrix. The validity of the method is confirmed by calculating the miniband structures and the envelope functions in rectangular superlattices made of GaAs-AlGaAs and GaSb-InAs. Numerical results for a biperiodic structure, a superlattice with graded interfaces, and a modulation-doped superlattice are presented     

Approximate scalar finite-element beam-propagation method withperfectly matched layers for anisotropic optical waveguides

The perfectly matched layer boundary condition for arbitrary anisotropic media is incorporated into the approximate scalar beam propagation method. The procedure is based on a finite-element method for three-dimensional anisotropic optical waveguides with off-diagonal elements in a permittivity tensor. In order to treat a wide-angle beam propagation, the Pade approximant operator is employed. To show the validity and usefulness of this approach, numerical results are presented for Gaussian beam propagation in free space and Gaussian beam excitation on a three-dimensional anisotropic optical waveguide     

Strong infrared radiation through passive dispersive wave generation and its control

We observe strong infrared (IR) radiation as a result of passive dispersive wave generation for a realistic microstructured fiber having two zero-dispersion wavelengths. The IR radiation frequency can be suitably controlled by varying the operational wavelength, which falls in the first normal dispersion regime. The amplitude of the radiation can be significantly increased by introducing a suitable amount of chirp in the input pulse. This strong phase-matching radiation can be considered as an alternative solution for the IR laser for different applications.     

Organic solvent based TiO<Subscript>2</Subscript> dispersion paste for dye-sensitized solar cells prepared by industrial production level procedure

In order to prepare the TiO₂ liquid dispersions for the electrodes of dye-sensitized solar cells with industrial mass production level at a reasonable cost, the present study investigates the preparation of TiO₂ liquid dispersions by a general industrial dispersion technique using readily available P25. To determine the TiO₂ dispersion offering the best light–electricity energy conversion efficiency, the suitability of various types of solvents and resins for use in TiO₂ dispersion are tested. In general, organic solvent based TiO₂ dispersions are found to allow the formation of more uniform thin films in comparison with water-based dispersions. A preparation using ethyl cellulose as the resin and the terpineol as the solvent is found to exhibit the best conversion efficiency. We have also found that using two kinds of resins of different molecular weights gave rise to better efficiency. Among 26 metal compounds tested in this study, the best metal dopant was Ag. XRD and XPS measurements confirm that the Ag exists as metal Ag and silver oxide.