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Generalized modal analysis of electromagnetic- and quantum-waveguide structures and discontinuities

Generalized modal analysis techniques for the characterization and modeling of
dissipationless planar waveguide structures and discontinuities encountered in microwave
and optical integrated circuits, as well as of quantum waveguide structures and devices,
are presented.
The frequency-dependent transmission properties of the curved microstrip bend
are derived by utilizing a second-order perturbation analysis of the equivalent modified
curved waveguide model and a mode-matching method which includes the higher order
modes. An extension of the mode-matching method for characterization of microstrip
right-angle bends and T junctions having a rectangular notch is formulated.
The modal solutions for an arbitrary graded-index dielectric slab waveguide are
derived by applying the generalized telegraphist's equations to the equivalent inhomogeneous
parallel-plate waveguide model with electric or magnetic walls. These modal
solutions are employed in a mode-matching procedure to calculate the transmission
properties of a step discontinuity in typical diffused optical dielectric slab waveguides.
Power loss calculations for an abrupt offset in a diffused optical waveguide show a
smooth increase in radiation loss whereas a sharp transition from almost zero to nearly
total radiation loss is found for an abrupt change in diffusion depth.
In the analysis of quantum waveguide structures, the modal expansions of the
wave function together with a mode-matching technique are utilized. The computed
generalized scattering matrices (GSMs) of junctions and uniform waveguide sections
are combined via an extended GSM technique to obtain the scattering parameters of
composite quantum waveguide structures. Results for cascaded right-angle bends and
periodic multi-waveguide structures in a split-gate configuration are presented assuming
hard wall confinement. For the multisection structures, strong resonant behavior similar
to that in resonant tunneling diodes is found. Calculated current-voltage characteristics
for a double constriction in GaAs are shown, exhibiting a region of negative differential
resistance for temperatures up to approximately 60K with a maximum peak-to-valley
ratio of over 80:1. Finally, a uniform narrow constriction with an assumed parabolic -
like lateral potential confinement is analyzed by utilizing the modal expansion
techniques developed for dielectric waveguides. / Graduation date: 1991
Date29 March 1991
CreatorsWeisshaar, Andreas
ContributorsEngelbrecht, Rudolf S., Tripathi, Vijai K.
Source SetsOregon State University
Detected LanguageEnglish

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