2025 Theses Doctoral

Applied Performance, Variation, and Control of Silicon Photonic Micro-Resonators and Links

Robinson, James Thomas

Over the past decade, silicon photonics have greatly matured and present an increasingly complete solution to the bandwidth-power bottleneck challenge faced by modern data-centers and high-performance supercomputers. As these computational systems have grown, both physically and architecturally, their performance has been increasingly limited by internal bandwidth between compute nodes and memory as opposed to in-node compute power.

This has generated a demand for higher and higher amounts of relatively long-reach bandwidth without the proportional increase in power consumption typically required of conventional electrical interconnects. One solution to this challenge is the usage of optical interconnects enabled by silicon photonic transceivers. Integrated silicon photonic links using optical frequency combs and micro-resonators enable dense wavelength division multiplexing (DWDM) on a single photonic integrated chip (PIC) which can be closely co-integrated with compute or memory nodes, increasing bandwidth density and reducing electrical I/O power demands.

Existing work clearly demonstrates that such interconnects are achievable, however, the many-channel low-data-rate approach of DWDM requires very high numbers of components that are relatively sensitive to fabrication imperfections and temperature variations. The impact of component variation on practical transceiver implementations is less thoroughly explored, particularly the interplay of this variation and certain selected control schemes, especially when paired with statistical measurements of fabricated devices.

This work seeks to address several concerns regarding silicon photonic micro-resonator-based interconnects, with a primary focus on thermal controls and their usage in compensating for component variation, as well as the general characterization of that variation and its impact on other features of interconnects. First, a general review of the motivation for and architecture of DWDM silicon photonic links will be presented as background.

Next, in order to ground the requirements of thermal controls and variation management, several practical custom photonic transceivers will be presented, and various features of their performance characterized. Then, a broad and deep evaluation of the statistical variation of several silicon photonic devices will be presented, with discussion of variation and their consequences to controls at the reticle, wafer, and inter-wafer scale.

This variation data will be used to inform several computational models of transceiver performance, primarily of their thermal controls, under realistic variation and power consumption restrictions, providing a novel understanding of expected device and module yield and limitations as a function of the variation of directly measurable parameters such as resonant frequency, free spectral range, and thermal tuning efficiency. This will primarily focus on evaluation of performance in the link initialization stage. Finally, an analysis of an architecture for implementing a multi-channel wide-band RF mixing platform using a modified version of the transceiver architecture discussed thus far will be presented.