Theses Doctoral

Ultra-Broadband Silicon Photonic Link Design and Optimization

James, Aneek

Carbon emissions associated with deep learning and high-performance computing have reached critical levels and must be addressed to mitigate the potential damage to the environment. Optical solutions have been widely accepted as a necessary part of any comprehensive intervention, primarily in the form of ultra-broadband wavelength-division multiplexing (WDM) optical interconnects to connect spatially distanced compute nodes and, in the further term, as dedicated photonic deep learning accelerators and photonic quantum computers.

Silicon photonic interconnects provides the most promising platform for satisfying the required performance, device density, and total wafer throughput by leveraging the same mature complementary metal–oxide–semiconductor (CMOS) infrastructure used to fabricate modern electronic chips. However, implementing these links at scale requires unprecedented levels of integration density in the associated silicon photonic integrated circuit (PICs). The potential explosion in PIC density poses a significant design challenge towards guaranteeing that designers are capable of both an exhaustive design space exploration and rigorous design optimization within reasonable design cycles. Higher level design abstractions—that is, representations of designs that accurately capture system behavior while simultaneously reducing model complexity—are needed for moreefficient design and optimization of PICs.

This work contributes two novel design abstractions for the rapid optimization of ultra-high-bandwidth silicon photonic interconnects. The first contribution is a novel process variation-aware compact model of strip waveguides that is suitable for circuit-level simulation of waveguide-based process design kit (PDK) elements. The model is shown to describe both loss and—using a novel expression for the thermo-optic effect in high index contrast materials—the thermo-optic behavior of strip waveguides. Experimental results prove the reported model can self-consistently describe waveguide phase, loss, and thermo-optic behavior across all measured devices over an unprecedented range of optical bandwidth, waveguide widths, and temperatures.

The second contribution is a generalized abstraction for designing WDM links in the multi-freespectral range (FSR) regime, a technique for avoiding aliasing while using microresonators with FSRs smaller than the total optical bandwidth of the link. Extensive simulation and experimental results prove that the aforementioned abstractions described collectively provide a powerful toolset for rapid interconnect design and optimization. The advances in this thesis demonstrate the utility of higher-level design abstractions for fully realizing the potential silicon photonics holds for keeping pace with ever-growing bandwidth demands computing systems in the post-Moore’s Law era and beyond.


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More About This Work

Academic Units
Electrical Engineering
Thesis Advisors
Bergman, Keren
Ph.D., Columbia University
Published Here
May 3, 2023