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UBC Theses and Dissertations

Metal waveguides for multi-axial light guiding at nanometer scales Maqsood, Muhammad Waqas


A basic component of most optical systems is an optical waveguide. There has been an increased interest in nanofabricated optical waveguides that incorporate metal layers due to their fabrication compatibility with existing complimentary-metal-oxide-semiconductor (CMOS) processes and, their ability to sustain sub-wavelength confined electromagnetic modes. In this work, we have developed analytical techniques for designing metal waveguides that achieve tailored optical functionalities. The developed techniques are applied in two design examples which address contemporary problems related to waveguiding at sub-wavelength and nanometer scales.In the first example, we apply our analytical technique to optimize a bi-axial waveguide that can bend light at 90 degree, constructed from two uni-axial metal waveguides. The optimization procedure consists of mapping out wavevector values of the electromagnetic modes sustained by the two waveguides over the operational frequency range. The constituent materials and geometry of the waveguides are selected such that each waveguide sustains only one low-loss mode. The geometry of each of the waveguides is tailored in a way that the in-plane wavevector components for both waveguide modes are matched. The wavevector matching results in efficient coupling between the two modes, yielding predicted bending efficiencies over 90%. In the second example, we apply our analytical technique to optimize a bi-axial waveguide structure for coupling free-space light into surface plasmon polaritons (SPP), electromagnetic excitations bounded to the surface of a metal. We study the simple geometry consisting of a slit in a metal film, filled and covered with a dielectric. We break the configuration down into two uni-axial waveguide components. Using our approach, we optimize the materials and geometry of the slit so that wavevector matching is achieved between the light emanating from the slit and the adjacent SPP modes, yielding coupling efficiency over 68%.

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