Brillouin optical-fiber frequency-domain analysis for distributedtemperature and strain measurements

Brillouin optical-fiber frequency-domain analysis is a new sensing technique for the distributed measurement of temperature and strain. Extensive theoretical investigations and experimental results of distributed temperature and strain measurements demonstrate the feasibility of this new concept. In an experimental demonstration, a spatial resolution of 3 m was achieved for a 1 km-long single-mode fiber     

D-Fiber antenna characterization using finite-element analysis

An all-fiber antenna using piezoelectric polymer coated circular core D-fiber has been characterized using finite-element analysis. The response of the D-fiber antenna was determined over a wide frequency range from 1 MHz to 2 GWz. The modeling predicts an electric field induced phase shift of 2.43×10^-6 rad/(V/m) per meter at 5 MHz. At frequencies higher than 8 MHz, the optical response is dominated by radial resonances of the D-fiber/coating composite. Using the simulation results, a minimum detectable electric field of 41 μV/m has been achieved using a 1 km length of coated D-fiber. In addition, a D-fiber antenna network intended for microcellular communications has been analyzed using shot noise limited detection. The D-fiber antenna has potential applications in areas such as electromagnetic compatibility testing and radio-over-fiber networks where it provides a convenient means of optically generating radio signals     

Two-dimensional semiconductor analysis using finite-element method

Two-dimensional simulation of semiconductor devices using a finite-element formulation is described. In the present analysis, Poisson's equation is solved by a finite-element method, based on the variational principle, and current continuity equations are solved by a method of weighted residuals. The advantage of this method is mentioned. In order to demonstrate the validity of this method, a bipolar n-p-n transistor is analyzed, considering the generation-recombination term. Not only voltage-current characteristic, but also junction capacitance and cutoff frequency are calculated. Then transistor behavior under inverse mode by using the n-type buried layer as a common emitter is discussed.     

Quasi-static finite-element analysis of a skewed microstripcrossover

In this work, we present a quasistatic analysis of a microstrip crossover on a dielectric substrate. The microstrips are located at different planes and may cross at an arbitrary angle. Capacitances and inductances are calculated from scalar potentials. For magnetostatic formulation, the boundary conditions for scalar potential are introduced by means of partitioning surfaces. The use of the adaptive finite element method provides the required flexibility with respect to the analyzed geometry, optimal discretization and good efficiency     

A two-dimensional finite-element analysis of reverberation chambers

A two-dimensional (2-D) analysis of reverberation chambers is performed at cutoff. The structure considered is lossless and corresponds to an infinite quality factor (Q) chamber. The concept of frequency stirring is used to generate field data for a discrete set of modes and the resulting statistics are analyzed. The field statistics are examined for TE and TM modes. This analysis yields statistics similar to the expected reverberation chamber statistics for the fields. Mechanical stirring is also examined and a connection to the peak-frequency deviation is presented     

An efficient finite-element analysis of magnetooptic channelwaveguides

A finite-element method based on the scalar-wave approximation is developed for the analysis of magnetooptic waveguides. A simple and efficient iterative method is proposed for solving a nonlinear eigenvalue equation derived from the scalar finite-element approach. To show the validity and usefulness of this method, examples are computed for magnetooptic rib-type and ridge-type waveguides. The waveguide structures which have larger nonreciprocal phase shift are discussed     

Accurate finite-element analysis of dual-mode highlyelliptical-core fibers

A scalar finite-element method is used for investigating propagation characteristics of dual-mode highly elliptical-core fibers. The dispersion property, polarization modal birefringence, and spatial modal birefringence are calculated. To improve the accuracy of solutions, isoparametric curvilinear elements are introduced. The applicability of the scalar finite-element method for highly elliptical-core fibers is assessed by comparing the results obtained with the vector finite-element method. An approximate simple approach, in which an elliptical-core is replaced by an appropriate rectangular-core, is also examined     

Holey fiber analysis through the finite-element method

A holey fiber (HF), having very complex hole geometry, is studied by means of a numerical simulator for modal analysis based on the finite-element method (FEM). Polarization and dispersion properties as well as the full vector field distribution of the fundamental mode are investigated. The obtained numerical results show a good agreement with experimental ones reported in literature     

Three-dimensional edge-based finite-element analysis for discretebodies of revolution

An extension to three-dimensional (3-D) edge-based finite-element analysis for modeling electrically large fan-like bodies as discrete bodies of revolution is given. By exploiting the overlapping symmetries between a fan-like body and a modal expansion of the electromagnetic fields, only one lobe of the problem need be solved by the finite-element method without introducing approximations. This computational scaling makes possible the solution of electrically large structures much more efficiently. However, a periodic phase-boundary condition (PBC) must be applied to the faces of the mesh describing a single slice of the body and this condition must be enforced on both the electric and magnetic fields for a robust solution. Details on the implementation of the PBCs are given along with results which validate the overall technique     

Full vectorial finite-element analysis of sharp optical waveguidecorners

The transmission efficiency of optical waves through a guided-wave structure, incorporating a sharp corner, is investigated by using rigorous numerical approaches based on the finite-element method. To show the versatility of the proposed numerical approaches, the modal power transmission coefficient of two rib waveguides is calculated, and the results are compared with those obtained by using other approaches     

The anticipated impact of supercomputers on finite-element analysis

The supercomputers of the 1980's have already impacted large-scale computation. This paper discusses the status and anticipated impact of supercomputers on finite-element analysis which is the primary tool for structural analysis and is also very useful in other areas of engineering analysis. The initial impact has been the significant reduction in turnaround time for large problems and the corresponding opportunity to solve heretofore unsolvable problems. In these cases, emphasis has been placed on employing already-proven computing software which was modifed to take advantage of vector processing and other forms of parallel operations. This trend is expected to continue because the established usage base of commercially available programs is not likely to be quickly dislodged. The near term will see the further use of design optimization, broader use of nonlinear mechanics, and a closer link between designers and analysts because of improved computer turnaround. The economy of scale suggests that solution techniques will be performed not only faster but cheaper than is possible with scalar processors which will further encourage the analysis of larger, more complex structures. The supercomputers of the future are expected to offer additional challenges to today's application systems. A primary factor in this will be the effective use of multiprocessors. Additional influence is expected as Artificial Intelligence matures to the point where Expert Systems become a reality for selected engineering and scientific disciplines. In order to effectively compete, today's software companies must address the possibility of significant changes in the architecture and methodology currently embodied in today's systems. Improved packaging, most likely in the form of pre- and postprocessors, will be necessary to provide industry- or technology-specific systems solutions.     

Approximate scalar finite-element analysis of anisotropic optical waveguides

An approximate scalar finite-element program for the analysis of anisotropic optical waveguides with a diagonal permittivity tensor is described. The accuracy of the method has been checked by calculating the eigenmodes of two-dimensional, anisotropic asymmetric slab waveguides. The results obtained for a channel waveguide embedded in LiNbO3 agree well with the results of the earlier vectorial finite-element method.     

Optical-transmission characteristics of optical-fiber cables and installed optical-fiber cable networks for WDM systems

Many cables containing 1.3-/spl mu/m zero-dispersion single-mode (SM) optical fibers are installed in trunk and access networks. Recently, there have been a number of studies on wavelength-division-multiplexing (WDM) systems designed to increase transmission capacity and flexibility. If we can construct WDM systems using SM optical-fiber cable networks designed to transmit using wavelengths in the 1.3-/spl mu/m window (O-band), this will prove very effective in reducing construction costs. It is therefore important to examine the wavelength dependence of the transmission characteristics of SM optical-fiber cables and networks that have already been installed and in which several optical fibers are joined. In this paper, we describe the measured optical characteristics of SM optical-fiber cables and installed optical-fiber cable networks at various wavelengths. The optical characteristics were stable in the 1.46 to 1.625-/spl mu/m wavelength range and we confirmed that the installed SM optical-fiber cable networks could be used for WDM system applications.     

A nonuniform FDTD technique for efficient analysis of propagationcharacteristics of optical-fiber waveguides

In this paper, we present a highly efficient one-dimensional cylindrical nonuniform finite-difference time-domain (1-D CNUFDTD) method, which utilizes the unsplit anisotropic perfectly matched layer (APML) for mesh truncation along the radial direction to analyze axisymmetric optical-fiber waveguides. As a first step, we validate the proposed FDTD algorithm by analyzing a uniform dielectric waveguide of circular cross section and show that the results are in excellent agreement with the conventional mode theory solutions. Next, we apply the algorithm to analyze propagation characteristics of a number of commonly used optical-fiber waveguides, i.e., step-index multimode, graded-index multimode, and single-mode step-index configurations     

Polarization-holding single-mode optical-fiber cables

Polarization-holding properties of low-loss and highly birefringent single-mode fibers inserted into two kinds of cable are presented. Variation of the properties and microbending loss during cabling processes were investigated. No degradation in extinction ratio between two orthogonal polarizations was measured in cabling processes for the both cables. Furthermore, length dependence of the extinction ratio was examined theoretically and experimentally by splicing fibers over a 10-km optical transmission line, and the experimental results were found to be in good agreement with those evaluated from the coupled-wave equation.     

Longitudinal analysis of semiconductor lasers with low reflectivity facets

An analysis is made of longitudinal effects in semiconductor lasers with low facet reflectivities. For this purpose, a self-consistent model is used based on the beam propagation method, which takes into account both the lateral and longitudinal dimension. The calculations show that longitudinal effects have a significant influence on the output fields in the laser.     

Simple and efficient finite-element analysis of microwave andoptical waveguides

A simple and efficient finite-element method for the analysis of microwave and optical waveguiding problems is formulated using three components of the electric or magnetic field. In order to eliminate spurious solutions, edge elements are introduced. In the edge element approach the nodal parameters are not limited to the magnetic field as in the conventional three-component formulation for the dielectric waveguiding problem. An eigenvalue equation that involves only the edge variables in the transversal plane and can provide a direct solution for the propagation constant is derived. To show the validity and usefulness of this approach, computed results are illustrated for microstrip transmission lines and dielectric waveguides     

Automated finite-element analysis for deformable registration of prostate images

Two major factors preventing the routine clinical use of finite-element analysis for image registration are: 1) the substantial labor required to construct a finite-element model for an individual patient's anatomy and 2) the difficulty of determining an appropriate set of finite-element boundary conditions. This paper addresses these issues by presenting algorithms that automatically generate a high quality hexahedral finite-element mesh and automatically calculate boundary conditions for an imaged patient. Medial shape models called m-reps are used to facilitate these tasks and reduce the effort required to apply finite-element analysis to image registration. Encouraging results are presented for the registration of CT image pairs which exhibit deformation caused by pressure from an endorectal imaging probe and deformation due to swelling.     

Coupling matrices for high-order finite-element analysis of acoustic-wave propagation

Finite-element coupling matrices, independent of element geometry and material properties, are presented for the high-order finite-element analysis of acoustic-wave propagation in homogeneous isotropic media. Some new results for ridge guides are used to illustrate the formulation.     

Estimation of submarine optical-fiber cable elongation

The tensile strain on a submarine optical-fiber cable may reach a nonlinear elastic region when recovered from the sea floor. In this paper, a method is shown to characterize cable elongation up to the nonlinear plastic region by extending wire theory previously developed to evaluate cable strain in the elastic linear region. The results of applying this method to several optical-fiber cables agrees well with tensile test results of the cables when cable ends are prevented from twisting, as well as when they are free to rotate. Also, by evaluating the dependence of cable strain on cable materials, such as stranded-strength members and pressure-resistant conductor pipe, a practical submarine optical-fiber cable structure for deep-sea use is determined.