Compact silicon photonic resonance-sssisted variable optical attenuator.

A two-part silicon photonic variable optical attenuator is demonstrated in a compact footprint which can provide a high extinction ratio at wavelengths between 1520 nm and 1620 nm. The device was made by following the conventional p-i-n waveguide section by a high-extinction-ratio second-order microring filter section. The rings provide additional on-off contrast by utilizing a thermal resonance shift, which harvested the heat dissipated by current injection in the p-i-n junction. We derive and discuss a simple thermal-resistance model in explanation of these effects.

Wideband silicon-photonic thermo-optic switch in a wavelength-division multiplexed ring network.

Using a compact (0.03 mm(2)) silicon-photonic bias-free thermo-optic cross-bar switch, we demonstrate microsecond-scale switching of twenty wavelength channels of a C-band wavelength-division multiplexed optical ring network, each carrying 10 Gbit/second data concurrently, with 15 mW electrical power consumption (no temperature control required). A convenient pulsed driving scheme is demonstrated and eye patterns and bit-error rate measurements are shown. An algorithm is developed to measure the power-division ratio between the two output ports, the insertion and switching losses, and non-ideal phase deviations.

3D branched nanowire heterojunction photoelectrodes for high-efficiency solar water splitting and H2 generation.

We report the fabrication of a three dimensional branched ZnO/Si heterojunction nanowire array by a two-step, wafer-scale, low-cost, solution etching/growth method and its use as photoelectrode in a photoelectrochemical cell for high efficiency solar powered water splitting. Specifically, we demonstrate that the branched nanowire heterojunction photoelectrode offers improved light absorption, increased photocurrent generation due to the effective charge separation in Si nanowire backbones and ZnO nanowire branching, and enhanced gas evolution kinetics because of the dramatically increased surface area and decreased radius of curvature. The branching nanowire heterostructures offer direct functional integration of different materials for high efficiency water photoelectrolysis and scalable photoelectrodes for clean hydrogen fuel generation.