This proposal focuses on advancing silicon photonics (SiPh) optical communication systems for operation in extreme environments, including radiation-intensive settings and cryogenic applications. By ensuring robust performance at both the component and system levels, SiPh technology could unlock significant benefits in these challenging domains. Building on preliminary research that has characterized transient and cumulative radiation effects on silicon Mach-Zehnder modulators (MZMs), the proposed work will expand the study of transient effects to encompass entire optical transceiver systems. This research will investigate the propagation and impact of single-event transients throughout the system, providing insights into their influence on signal integrity and reliability. Additionally, the proposal seeks to evaluate the performance of surface-illuminated photodetectors and high-performance phototransistors under cryogenic conditions. These efforts aim to drive advancements in cryogenic sensing and quantum computing applications, positioning SiPh as a key enabler for next-generation technologies.