The tremendous growth in computer processing power as a result of the microelectronics scaling demands corresponding increase in communications bandwidth that is approaching the limits of traditional electrical interconnects. Optical links, traditionally limited to only long-hual communications, are therefore replacing electrical cables at increasingly small distances, down to only a few tens of centimeters already. In the near future, optical interconnects on the chip level for inter- and intra-chip communications, with length scales of few centimeters to few millimeters, are projected to be imperative. For this goal, silicon photonics has been rapidly emerging for the vision of building integrated photonic circuits on the same chip as the microelectronics for on- and off-chip communications. This dissertation is part of the on-going effort in developing a fully integrated silicon photonic circuit. It contains works on two parts of such a circuit. The first part is the demonstration of resonators with bandwidth dynamically reconfigurable over a very broad range, targeted for functionalities such as reconfigurable filters and tunable optical delays, etc. The second part is the demonstration of the fastest germanium photodetectors integrated with silicon photonic circuits through a novel process compatible with the microelectronics, and of an integrated WDM detection system that can potentially provide over tera-bit per second bandwidth with a small footprint on chip.