Silicon photonics has gained significant advancement over the past two decades. In this thesis, we experimentally study silicon sub-bandgap photodetectors in the telecommunications wavelengths of 1550 nm in silicon waveguides and microring resonators using surface-state absorption (SSA) and defect-state absorption (DSA). We integrate such photodetectors into silicon microring resonators as a photomonitor to actively stabilize the microring resonances for emergent optical switch fabrics applications in optical interconnects for datacenter applications.

For characterizing SSA, we propose and demonstrate a modulated photocurrent-transmission spectroscopy method to measure the linear SSA coefficient from the photocurrent extracted from a PIN-diode-integrated silicon waveguide, while u...[ Read more ]

Silicon photonics has gained significant advancement over the past two decades. In this thesis, we experimentally study silicon sub-bandgap photodetectors in the telecommunications wavelengths of 1550 nm in silicon waveguides and microring resonators using surface-state absorption (SSA) and defect-state absorption (DSA). We integrate such photodetectors into silicon microring resonators as a photomonitor to actively stabilize the microring resonances for emergent optical switch fabrics applications in optical interconnects for datacenter applications.

For characterizing SSA, we propose and demonstrate a modulated photocurrent-transmission spectroscopy method to measure the linear SSA coefficient from the photocurrent extracted from a PIN-diode-integrated silicon waveguide, while using the nonlinear two-photon-absorption coefficient measured from the modulated transmission spectrum as a reference. Our experiments reveal a responsivity of ~1.4 mA/W/mm from an air-clad waveguide photodetector upon -1 V, indicating an SSA coefficient of 0.013 ~ 0.017 mm^-1.

We have designed and integrated PIN photodetectors in silicon microrings. The microring is integrated with an air-clad photodetector and an electrically isolated silica-clad photodetector as a control. Our experiments reveal a responsivity of 0.9 ~ 2.9 mA/W/mm upon -1 V from the air-clad photodetector, and of only 0.13 ~ 0.19 mA/W/mm from the control photodetectors. Likewise, we have integrated ion-implantation-induced DSA-based PIN photodetectors in microrings. Our experiments reveal a responsivity of 7.0 ~ 65.0 mA/W/mm upon -1 V using B-, P-, and Ar-ion implantations.

In order to obtain actively stabilized silicon microrings, we utilize the SSA/DSA-based photodetectors to monitor the spectral alignment between the microring resonance and a carrier wavelength. Feedback-controlled integrated electro-optic and thermo-optic tuners, along with a threshold-detection/slope-detection method are used for actively stabilizing the microring. We demonstrate a reduced transmission power variation of < 2.5 dB over a 14^oC on-stage temperature modulation. We observe open eye-diagrams with a 30Gb/s data transmission through an actively stabilized microring array.