Device integration for silicon microphotonic platforms

Abstract

Silicon ULSI compatible, high index contrast waveguides and devices provide high density integration for optical networking and on-chip optical interconnects. Four such waveguide systems were fabricated and analyzed: crystalline silicon-on-insulator (SOI) strip, polycrystalline silicon (polySi) strip, silicon nitride strip and SPARROW waveguides. The loss of 15 dB/cm measured through an SOI waveguide was the smallest ever measured for a silicon strip waveguide and is due to improved side-wall roughness. The TM mode of a single mode polySi strip waveguide with a 1:2.5 aspect ratio exhibited, surprisingly, smaller loss than the TE mode. Further, analysis shows that high index contrast waveguides are more sensitive to polarization dependent loss in the presence of surface roughness. Single mode bends and splits in both silicon and silicon nitride were studied. 0.01 dB/turn loss has been measured for 2 micron radius silicon bends. Polarization dependent loss was also observed; the bending loss of a TM mode was, as expected, much larger than that of a TE mode. The splitting losses for two-degree Y-split was 0.15 dB/split. A 1x16 multi-mode interferometer splitter occupied an area of 480 sq-microns and exhibited loss of 3 dB. ULSI compatible waveguide structures integrated with micro-resonators have been studied. Qs of 10000 and efficiencies close to 100% were achieved in high index contrast ring resonators and Qs of 100 million were achieved in microsphere resonators. A thermal and mechanical tuning mechanism was demonstrated for micro-ring resonators.

(cont.) In addition, >95% coupling efficiency between SPARROW waveguides and microspheres was achieved, the first microspheres to be coupled to integrated optics waveguides. 1x4 wavelength division multiplexing devices have been, for the first time, demonstrated in high index contrast silicon and silicon nitride strip waveguide systems. These systems have a component density of 1-million devices/sq-cm. Higher order filters made from multiple rings exhibited flat top responses and the expected steeper roll-off resonance response. Integrated modulators and switches based on waveguides and rings were also studied. Finally, the integration of the components in systems applications was analyzed. A study of the effect of polarization and loss in silicon microphotonics waveguide systems is presented.