Gain Control of Semiconductor Optical Amplifier Using a Bandpass Filter in a Feedback Loop

The authors present a simple configuration of a gain-clamped semiconductor optical amplifier (GC-SOA) based on automatic intensity control of a feedback light generated by amplified spontaneous emission, using a narrow bandwidth thin-film-tunable filter. Experimental results show that the proposed amplifier has good gain clamping characteristics and the feedback light dramatically reduces steady and transient gain variations. The feedback light operates satisfactorily with the channel's add-drop frequency up to 20.9 kHz. We also examined the performance of the GC-SOA by employing the feedback light at different wavelengths.     

A three-dimensional asymptotic analysis of anisotropic inhomogeneous and laminated cylindrical shells

Summary An asymptotic for anisotropic inhomogeneous cylindrical shells is formulated on the basis of three-dimensional elasticity withouta priori assumptions. The inhomogeneities are considered varying in the radial direction, thus including the important case of laminated composite shells in which the material properties are piecewisely constant through the thickness. Reformulation and nondimensionalization of the basic three-dimensional elasticity equations reveal that the problem can be treated by means of asymptotic expansion. By using asymptotic expansion and successive integration, we show in a natural and consistent manner that the asymptotic theory gives rise to two-dimensional shell equations, in forms similar to those in the classical laminated shell theory (CST), at each level of approximation. Thus the three-dimensional asymptotic solution for the problem is no more difficult to obtain than that based on CST. The asymptotic solution can be improved by determining the higher-order modifications in a systematic way. Various through-thickness effects can be accounted for hierarchically. The performance of the theory is illustrated by comparing the asymptotic solutions with the available numerical results for a homogeneous and for a multilayered cross-ply cylindrical shell under lateral loads.     

Mobile technology as a learning object and an exploration tool in an IS curriculum: an innovative instruction of wireless network security

Information systems (IS) is a fully recognized business discipline. Many IS programs have not given network security appropriate attention; nor have they brought enough hands-on experience of both wireline and wireless networks to the class rooms. This study proposes a systematic framework to cover wireless security attack, detection, and protection. It also includes a learning matrix for educators and practitioners to enhance the IS curriculum. The assessment results show that students are very positive toward this new approach of security education. Implications and suggestions are provided.     

Polarization changing and beam profile deformation of light during the isotropic Raman-nath acousto-optic interaction

A spatial Fourier transform approach is used to study the phenomena of polarization changing and beam profile deformation of light during the Raman-Nath, acousto-optic interaction in isotropic media. Starting from the vector version of the well-known Raman-Nath interaction equation and using a spatial Fourier transform allows analytic solutions that encompass the effects of polarization changing and beam-profile deformation for the multiple scattered light to be found in the spatial-frequency domain. Two kinds of sound wave, longitudinal and shear, are assumed to be interacted with the light, whose transverse spatial profile and state of polarization are arbitrary. It is shown that, for light with an arbitrary spatial profile after interaction with the sound wave in the Raman-Nath regime, the spatial profiles of the scattered light are almost the same shape as those of the input light. For the polarization changing part, it is found that the state of polarization and the direction of rotation can alter, depending not only on the sound amplitude but also on the propagation mode of the sound wave. Simulation results are provided to confirm the validity of this approach.     

薄板弯曲分析中的拟协调元

本文对薄板弯曲的有限元分析提出一个新的构造板单元的一个基本方法——拟协调元法。 按这种方法构造的单元都能保证收敛,即通过分片试验,并且方法简洁、运算量小,便于应用。 文中给出可用于薄板弯曲分析的三种单元的单元刚度矩阵的显式。     

Polarization-mode dispersion effect of an acousto-optic tunable filter

The effect of the polarization-mode dispersion (PMD) of an acousto-optic tunable filter (AOTF) is studied both theoretically and experimentally. A coupled-mode method derived from Maxwell's equations is proposed to study the evolution of the polarization of light and hence the deterministic dynamics of the PMD inside an AOTF. It is found that the PMD value of a typical AOTF is around several picoseconds and is adjustable by tuning the strength of the applied sound signal. A set of experimental data acquired by the wavelength scanning method is employed to check the validity of the proposed method. A high degree of similarity is observed between the experimental and the theoretical data.     

NEMP fields inside a metallic container with an aperture in onewall

The finite-difference time-domain (FDTD) method was used to study the nuclear electromagnetic pulse (NEMP) waves coupling into one metallic container through a small aperture in one face of the container. The incident electric fields of NEMP waves were expressed by double exponential forms with two different decay constants. The time-domain behavior of the electric field inside the metallic container excited by the waves was obtained by the FDTD method. The electric field distributions on various layers for the area of the aperture of 10×10 cm² were also calculated. It was found that the shielding effectiveness is greatly improved by a factor of 255 by reducing the area of the aperture from 10×10 to 1×1 cm² . The aperture filled with dielectric materials was also studied for shielding effectiveness. The coupled electric field inside the metallic container was round to be a nonlinear function of the relative dielectric constant of insulators filled in the aperture     

Descent algorithms for optimal periodic output feedback control

Periodic output feedback is investigated in the context of linear-quadratic regulation for finite-dimensional time-invariant linear systems. Discrete output samples are multiplied by a periodic gain function to generate a continuous feedback control. The optimal solution is obtained in two steps by separating the continuous-time from the discrete-time structure. First, the optimal pole placement problem under periodic output feedback is solved explicitly under the assumption that the behavior at the sample times has been specified in terms of a gain matrix G. Then the minimum value, which depends on G, is substituted into the overall objective. This results in a finite-dimensional nonlinear programming problem over all admissible gain matrices G. The solution defines the optimal periodic output feedback control via the formulas of the optimal pole placement problem. A steepest descent and a direct iterative method for solving this problem are formulated and compared. Numerical examples show that the performance using periodic output feedback is almost equivalent to that using optimal continuous-state feedback     

Determination of dynamic contact angles within microfluidic devices

Here, we report a single-point detection method for the determination of dynamic surface conditions inside microfluidic channels. The proposed method is based on monitoring fluorescence amplitude as a function of the convolution of a laser beam with segmented flow consisting of two immiscible liquids, one containing fluorescent dye. The fluorescence amplitude is determined by the flow rate and the droplet shape, which is affected by the channel surface properties. We modeled the interaction of a droplet and a laser beam via computer-aided design software, using the laser beam location in relation to the droplet shape as a parameter. The method was applied to fused silica capillaries with both unmodified and modified surfaces, with segmented flow exhibiting water contact angles of ≈?30° and ≈?100°, respectively. The method allows discrimination between hydrophillic and hydrophobic surfaces, as well as the quality of the treatment. The results were verified using fluorescence imaging of the droplets via a stroboscopic technique. We also applied this method to the analysis of microfabricated channels with non-circular cross sections. We demonstrated that the technique enables the determination of the hydrophobicity of channel surfaces, a crucial property required for the generation of segmented flow or emulsions for applications such as digital PCR.     

On the design of output regulators for nonlinear systems

This paper considers the output regulation problem for nonlinear systems. By adding the assumption that the decoupling matrix of the system under consideration has maximum rank, the general results presented in Isidori and Byrnes (IEEE Trans. Automat. Control 35(2) (1990) 131–140) have been improved in three ways. Firstly, the precise form of the regulators is presented for multi-input multi-output affine nonlinear systems. Secondly, the number of unknown functions in the controller parameterization has been reduced. Finally, by introducing a hyperbolic realization and constructing auxiliary systems, a sufficient and generically necessary condition for the existence of the unknown functions is obtained. This condition is easily verifiable using only algebraic computation. These results provide a complete solution to the output regulation problem, for a class of nonlinear systems. It is also shown that for this class of systems, the output regulation problem is always generically solvable.