Silicon Photoinc Devices for On-chip Optical Interconnects

Silicon photonics is potentially a viable technology to replace copper-based interconnects in multi-core computing chips with swelling demands on communication capacity and energy efficiency. This thesis proposes and demonstrates several building blocks for silicon photonic optical interconnects.;On the photodetection front, we study the surface-state absorption (SSA) and the two-photon absorption (TPA) generated photocurrent in p-i-n diode embedded silicon microresonators. The microring resonator has large mode-field to waveguide surface overlapping which facilitates SSA-dominated photocurrent. We show 20-fold cavity-enhanced photocurrent generation with 0.12 mA/W responsivity in a Q~8000 microring resonator. The microdisk resonator supports high-Q multimode resonances (~105) showing TPA-dominant photocurrent. The photocurrent at on-resonance wavelength is exceeding three orders of magnitude higher than that at off-resonance wavelength. We study microdisk photocurrent spectra with various p-i-n diode intrinsic region widths along the microdisk rim. Both devices are capable for wavelength-dependent optical power detection. The demonstrated cavity enhancement significantly improves the energy harvesting efficiency.;On the passive coupler front, we demonstrate three types of interference-based devices. 1) We design and fabricate a compact multimode-interference (MMI) based waveguide crossing. The MMI-crossing shows 0.4-dB insertion loss compared to 1.1-dB in plain crossing with a significantly suppressed crosstalk. 2) We fabricate and characterize an MMI-based 1 x 64 power splitter in a large-core square-shaped silicon waveguide in order to demonstrate the feasibility of two-dimensional (2-D) MMI couplers. The splitter shows 2-dB transmission flatness over a large number of 2-D array output ports. 3) We design an ultra-compact triplexer (a 1 x 3 wavelength-division multiplexer) using a photonic crystal (PhC) surface waveguide coupled with a conventional waveguide.