On-chip optical interconnects is one promising technology to replace conventional electrical interconnects for large-data-capacity and low-power-consumption communications on integrated circuit (IC) chips. Among various nascent technology platforms for optical interconnects, silicon photonics leveraging the mature silicon nanoelectronics fabrication processes offers the key advantage of a potentially manufacturable integration of optical interconnects on silicon IC chips.

In this thesis, we propose and demonstrate a number of functional silicon photonic devices for on-chip optical interconnect applications including (i) electro-optical tunable delay lines, (ii) photocurrent monitors for silicon microresonator-based switches and modulators and (iii) epitaxially grown III-V-on-si...[ Read more ]

On-chip optical interconnects is one promising technology to replace conventional electrical interconnects for large-data-capacity and low-power-consumption communications on integrated circuit (IC) chips. Among various nascent technology platforms for optical interconnects, silicon photonics leveraging the mature silicon nanoelectronics fabrication processes offers the key advantage of a potentially manufacturable integration of optical interconnects on silicon IC chips.

In this thesis, we propose and demonstrate a number of functional silicon photonic devices for on-chip optical interconnect applications including (i) electro-optical tunable delay lines, (ii) photocurrent monitors for silicon microresonator-based switches and modulators and (iii) epitaxially grown III-V-on-silicon photodetectors.

Silicon tunable time delay lines are key components for optical networks. We demonstrate electro-optical tunable time delay and advance using silicon feedback-microring microresonators integrated with p-i-n diodes. By controlling the feedback and round-trip phase shifts through the carrier injection-based free-carrier dispersion effect, we obtain a large dynamic time tuning range (−88 ps to 110 ps) upon dc bias voltage change in the range of few tens of millivolts at a given resonance wavelength. We also demonstrate tunable time delay and advance at different resonance wavelengths within 0.76nm wavelength range.

Silicon microresonators also act as essential building blocks in the form of filters, switches and modulators for on-chip optical interconnects. However, the resonance wavelengths of silicon microresonators are susceptible to optical carrier wavelength drift and environmental temperature variation. An adaptive feedback-based solution to actively stabilize the resonance wavelength is desirable. To this end, we propose to use on-chip all-silicon photodetectors to monitor the resonance wavelengths of silicon microresonators. We study the on-chip all-silicon photodetectors employing sub-bandgap surface-state absorption and two-photon absorption induced photocarrier generation. We integrate the photodetectors with silicon microresonators in order to monitor the spectral alignment between the optical carrier wavelength and the resonance. We demonstrate real-time in-microresonator photocurrent monitoring for silicon microring carrier-injection switches. We also demonstrate real-time in-microresonator photocurrent monitoring for silicon feedback-microring carrier-injection modulators.

Given that silicon is essentially transparent in the 1300-1550nm telecommunications wavelengths, it constitutes a low-loss material for integrated waveguides in the telecommunications window but not an efficient photodetector. One way to enable photodetection on silicon chips in the telecommunications wavelengths is to hybrid-integrate III-V semiconductor photodetectors on silicon chips. On this front, we develop epitaxially grown III-V-on-silicon normal-incidence and silicon waveguide butt-coupled photodetectors by metalorganic chemical vapor deposition (MOCVD). The waveguide butt-coupled device with a 20μm × 20μm area shows a dark current of 2.5 μA and a responsivity of 0.17 A/W at 1550nm wavelength upon -1V bias voltage, a 3dB bandwidth of 9 GHz upon -4V bias voltage and an open eye diagram at 10Gb/s data rate upon -4V bias voltage. The photodetectors show promising performances for on-chip optical interconnects applications. The developed epitaxial III-V-on-silicon technology with silicon waveguide integration can be naturally extended into integration with more sophisticated silicon photonic devices.