Doctor of Philosophy (PhD)
Electrical and Computer Engineering
In this dissertation, we introduce compact absorption switches consisting of plasmonic metal-dielectric-metal (MDM) waveguides coupled to multisection cavities. The optimized multisection cavity switches lead to greatly enhanced modulation depth compared to optimized conventional Fabry-Perot cavity switches. We find that the modulation depth of the optimized multisection cavity switches is greatly enhanced compared to the optimized conventional Fabry-Perot cavity switches due to the great enhancement of the total electromagnetic field energy in the cavity region. We then investigate how to improve the computational efficiency of the design of nanoplasmonic devices. More specifically, we show that the space mapping algorithm, originally developed for microwave circuit optimization, can enable the efficient design of nanoplasmonic waveguide devices which satisfy a set of desired specifications. Space mapping utilizes a physics-based coarse model to approximate a fine model accurately describing a device. Here the fine model is a full-wave finite-difference frequency-domain (FDFD) simulation of the device, while the coarse model is based on transmission line theory. We demonstrate that, when the iterative space mapping algorithm is used, it converges fast to a design which meets all the specifications. In addition, full-wave FDFD simulations of only a few candidate structures are required before the iterative process is terminated. Use of the space mapping algorithm therefore results in large reductions in the required computation time when compared to any direct optimization method of the fine FDFD model. We finally introduce a method for the sensitivity analysis of active nanophotonic waveguide devices to variations in the dielectric permittivity of the active material. More specifically, we present an analytical adjoint sensitivity method for the power transmission coefficient of nano optical devices, which is directly derived from Maxwell's equations, and is not based on any specific numerical discretization method. We apply the derived formula to calculate the sensitivity of the power transmission coefficient with respect to the real and imaginary parts of the dielectric permittivity of the active material for two-dimensional and three-dimensional plasmonic devices, and compare the results with the ones obtained by directly calculating the sensitivity.
Document Availability at the Time of Submission
Student has submitted appropriate documentation to restrict access to LSU for 365 days after which the document will be released for worldwide access.
Dastmalchi, Pouya, "Design and Optimization of Nanoplasmonic Waveguide Devices" (2015). LSU Doctoral Dissertations. 891.