| Summary: | 碩士 === 國立中央大學 === 光電科學與工程學系 === 101 === This thesis describes an analytical approach to analyze subwavelength 90̊ curved waveguide bend in an asymmetric metal/multi-insulator configuration. This approach employs the conformal mapping to first transform a curved waveguide bend into an equivalent straight waveguide structure and then calculate the modal index of the guided mode under the continuously-varying index profile using the transmission line network method. The propagation loss and mode transition loss along the curved waveguide bend are quantified accordingly.
Based on the convergence of the attenuation constant at the operating wavelength of 1550 nm, the width of the silver region is set to 100 nm. We then define the effective transverse width as the integral of the transformed index profile over the transverse axis in the radial direction. When quantified as a function of the bending radius, the newly defined parameter is found to be in good agreement in tendency with the finite-difference-time-domain-method-based numerical simulations and can be used to describe physically the TM wave behavior along the curved bending. In general, the curved bending region along with the input/output straight sections can be treated conceptually as a structure composed of narrow, wide, narrow sections connected in sequence. Significant power loss occurs at the interface going from the wide section to the narrow section.
Following the analytical analysis and power interchange studies, the width of silicon and silica regions are reduced to 150 nm and 50 nm, respectively, and the respective TM and TE transmissions could be up to 90.50% and 93.22% with a curved bending area of 0.2165 /mum^2.
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