Abstract
This paper presents theoretical and experimental study of ultra-compact Si-wire Optical Directional
Couplers (ODCs) on Silicon-on-Insulator wafer for optical signal processing. The presence of the controllable
evanescent light strongly confined in the region bounded by the Si nano-wires has a large impact on the optical power
coupling between waveguides. The characteristics of coupling length and power transmission in ODCs based on
separation, wavelength, light field propagation distance and geometry of waveguides are described in detail by the
coupled mode theory, 3-D finite-difference time-domain analysis and beam propagation method, and are confirmed by
experiments. The exponential dependency of coupling length on the separation of coupled waveguides and wavelength
shows interesting high-sensitivity optical sensing, switching and multiplexing properties. Custom spectral properties
can be achieved by the configuration of coupled nano-wire waveguides based on their separation and lengths. We show
that optimization of ODCs based on the physics of the coupled waveguides will lead to short optical devices which can
be integrated as building blocks within high-density photonic circuits with the desired spectral characteristics. In
the end, two new systems based on Mach–Zehnder structure and Micro-Ring Resonators are proposed in which ODCs
are implemented as embedded tunable devices resulting in more functional optical sensing and signal processing
devices.
© 2013 IEEE
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