A STUDY ON THE COUPLED-MODE THEORY FOR MICROWAVE AND OPTICAL WAVE CIRCUITS AND ITS APPLICATION

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The purpose of this research project is to investigate an analytical modeling of coupled-waveguide systems based on the coupled-mode theory and to develop its application to the analysis of multilayred and multiconductor transmission lines and coupled linear or nonlinear optical optical waveguides. The main results of the research are summarized as follows :1. For the multilayred and multiconductor transmission lines system, we have proposed a coupled-mode theory using the generalized reciprocity theorem and a coupled-mode theory using the singular perturbation technique, and formulated very efficient analytical and numerical approaches combined with Galerkin's moment method in the spectral domain.2. Using the proposed conpled-mode theory, we have analyzed the dispersion characteristics of the coupled microstrip lines placed on a single plane or dual planes. The results confirmed that the coupled-mode theory yields a good enough approximation over a weak to moderately strong coupling b … More etween the microstrips.3. We developed a vector-wave coupled-mode theory for nonlinear optical fiber coupled and demonstrated the polarization effects in the optical swiching.4. We have proposed a grating-assisted asymmetric three-waveguide coupler as a novel optical wavelength filtering device. The conpler consists of three nonidentical planar waveguides in which the upper and lower surfaces of the intermediate waveguide are corrugated with different periods. It has been shown that the proposed coupler yields a remarkably sharper filtering operation than in the conventional grating-assisted two-wavegiode conpler and the sidelobes in wavelength response are almost completely suppressed.5. The self-consistent first-order conpled-mode equations describing a planar three-waveguide nonlinear directional coupler have been derived in an analytically closed. It has been shown that the output channel for the strong input signal can be swiched between two outermost waveguides by changing the phase of a weak control light launched into the intermediate waveguide. Less