In this paper, it is shown that a suitable choice of the geometrical parameters of a silicon-wire waveguide micro-racetrack resonator structure can lead to a substantial improvement in the control of coupling coefficients and, hence, the design of ultracompact devices for high-performance channel add-drop filters and all-optical switching applications. On the one hand, some simple theoretical arguments and simulation results indicate that the reduction of the silicon-wire rectangular waveguide cross-section area (width x height) is possible, from standard (450 nm x 220 nm) to (380 nm x 200 nm) on both the bus and the resonator waveguides; this action, apart from still guaranteeing a quasi-TE single-mode operation, would provide an effective improvement into scale-ofintegration by a 1.30 factor per device volume. On the other hand, it will be shown by a semianalytical method (analytical calculation + numerical simulation) that achieving the waveguide-racetrack optimal coupling condition for a particular application can be reduced to a prime calculation of the main resonator geometrical parameters (bend radius, straight length, air gap and overall coupling length). In particular, the design of high-performance ultracompact waveguide-racetrack resonator structures, with pre-established Q factor (Q >= 2000), free spectral range (FSR >= 15 nm), full width at half-maximum (FWHM <= 5 nm), finesse (F >= 40) or extinction ratio signals (ER >= 20 dB) can be systematically obtained with this procedure. (C) 2019 Optical Society of America.
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