| High-power photodetectors are crucial components in analog optical links for applications, such as cable televisions, phased array antennas, antenna remoting, photonic signal processing, and future wireless communication systems. The link performance, which includes link gain, noise figure, and spurious free dynamic range, can be improved by increasing the optical carrier power and using a high-power photodetector. In this dissertation, an analysis of the limiting factors of photodiode output power is presented. Based on this analysis, improved photodiode structures that can suppress space charge effect and loading effect were designed and experimentally studied. Record high values of RF output power were obtained. In order to suppress laser relative intensity noise (RIN), which limits the dynamic range of the link at high optical power, high-power top-illuminated and evanescently-coupled waveguide balanced photodetectors were demonstrated. High saturation current, broad bandwidth, high responsivity and good broadband common mode rejection ratio were achieved. Bonding photodiode to Si using a gold intermediate layer was demonstrated to improve the device heat handling capability. The responsivity of the bonded photodiode was also increased significantly due to the resonant cavity introduced by the gold bonding layer.; Avalanche photodiodes (APDs) are key components for optical communication, imaging and various photon counting applications. In the second part of this work, a novel avalanche photodiode structure with undepleted absorber was proposed and experimentally studied. Theoretical analysis shows that this structure could have orders of magnitude lower dark current than the APDs with depleted absorber. It also has the advantage of high low-gain bandwidth and no multiplication in the absorber. For the fabricated devices, low dark current performance was observed. Because of this property, the structure has potential to be used as a high performance photon counter. |
