Masanori Matsuhara

Finite-Element Analysis of Waveguide Modes: A Novel Approach that Eliminates Spurious Modes

An efficient finite-element method for analyzing the propagation characteristics of a wide variety of waveguides is presented. A variational expression suited for the finite-element method is formulated in terms of the transverse electric and magnetic field components. In this approach all guided-mode solutions are real, while the spurious-mode solutions are not real. Therefore, discrimination of the spurious-mode solutions can be achieved merely by imposing the simple condition that guided-mode solutions be real. Three numerical examples, two for the isotropic case and the other for the magnetic anisotropic case, are carried out.

Optical-waveguide band-rejection filters: design.

A method for designing optical-waveguide band-rejection filters is presented that allows side-lobe levels to be reduced by several orders of magnitude while the rolloff rate of the response characteristics is not appreciably degraded. The method is based upon the control of the shape of the perturbation-amplitude envelope. We discuss in detail the particular case where the coupling coefficient of the waveguide filter takes the form of a modified raised cosine function along the length of the waveguide. Side-lobe level and rolloff can be traded off by appropriately choosing the index p of the function. Design curves are included that allow the optimization of filter responses for side-lobe levels or rolloff characteristics.

Analysis of the guided modes in slab-coupled waveguides using a variational method

The waveguiding properties of the slab-coupled waveguides (i.e., the optical stripline and the rib waveguide) are investigated by the vector variational method. The slab-coupled waveguides are low-loss optical waveguides which are easy to fabricate and design. In this paper, the propagation constants and the field intensity distributions of the slab-coupled waveguides are presented, and the effects on the wave-guiding properties caused by changing their geometrical parameters are discussed. The results obtained by employing the variational method are compared with those obtained by using other methods.

Transparent boundary for the finite-element beam-propagation method.

We propose a transparent boundary for the finite-element beam-propagation method to analyze the beam propagation in a finite computational window. In this method, a transparent boundary condition is derived by assuming a beam to be a plane wave in the vicinity of a virtual boundary, which eliminates undesirable reflections from a virtual boundary.

Truncated Parabolic-Index Fiber with Minimum Mode Dispersion

The use of a parabolic-index fiber as an optical transmission line has been receiving extensive attention because of its excellent mode dispersion characteristics. In the present paper, the modal dispersion in the optical fiber with truncated parabolic index distribution is analyzed theoretically in detail by using a variational method. Taking the influence of the cladding upon the propagating modes into consideration, it is found that there exists an optimum index distribution for which the modal dispersion is minimized. The standard deviation of the normalized group delay of propagating modes is used to estimate the modal dispersion behavior of the fiber.

Extended integral equation formulation for scattering problems from a cylindrical scatterer

An extended integral equation is developed for electromagnetic scattering from a perfectly conducting cylinder and a dielectric cylinder. The conventional surface integral equations cannot yield unique solutions when the wavenumber of the electromagnetic wave is equal to an eigenwavenumber of the system. Several methods to overcome this difficulty have been presented, but each method includes some drawbacks. A numerical method is proposed in which the boundary element method is applied to the extended integral equations with the observation points lying on a closed surface inside the scatterer. It is shown that the extended integral equations have unique solutions for any given wavenumber. As examples, plane wave scattering from a perfectly conducting elliptic cylinder, a dielectric elliptic cylinder, and a dielectric rectangular cylinder is numerically analyzed. >

Analysis of wave modes in slab waveguide with truncated parabolic index

The exact wave equation for a lenslike dielectric medium derived from Maxwells equations contains the term of gradient of permittivity e. The purpose of this correspondence is to clarify the effect of the \bigtriangledown \epsilon term on the propagation constants of the modes. We find that the propagation constants of the lower order modes suffer significant modification by taking the \bigtriangledown \epsilon term into account, while for the higher order modes the effects are small enough to be disregarded.

Modal analysis of strip-loaded diffused optical waveguides by a variational method

The propagating modes supported by strip-loaded three-dimensional diffused optical waveguides are analyzed in detail theoretically by using a variational method. Some typical numerical examples of the propagation constants and the field distributions are illustrated. The dependence of propagation characteristics on the geometrical parameters of the loading dielectric strip is discussed.

Analysis of open-type waveguides by the vector finite-element method

A variational expression that is suitable for waveguide analysis is proposed. In addition, a mapping technique for analyzing open-type waveguides is introduced. Any arbitrarily shaped waveguide can be analyzed by the finite-element method with this variational expression and the mapping technique. The dispersion characteristics of the rectangular dielectric waveguide and the microstrip line are demonstrated, and these results show the validity and usefulness of this method.<<ETX>>

Analysis of lightwave propagation in the bent waveguide by the Galerkin Method

A simple method is developed to analyze the bent waveguide, which is described in the cylindrical coordinate system. By means of this method based on the Galerkin method, the sampling spacing can be chosen arbitrarily and it is possible to treat narrow beams. In addition we introduce the absorber using the graded lossy medium. As this lossy absorber can remove the radiation wave from the bend, so we can use the finite computational window. The lightwave propagating phenomena in the uniformly bent slab waveguide and in the nonlinear slab waveguide are demonstrated