High-speed oxide-VCSELs for cryogenic computing applications

The rapid growth of artificial-intelligence workloads and the emergence of superconducting and quantum processors are pushing data-movement requirements far beyond what conventional electrical links can sustain—especially inside cryogenic environments, where thermal budgets are exceptionally tight. This dissertation advances vertical-cavity-surface-emitting-laser (VCSEL) technology from its traditional role in room-temperature data centers to a new generation of energy-efficient optical transmitters capable of operating at temperatures down to 2.6 K. After reviewing VCSEL lasing physics and oxide-aperture design trade-offs, the work introduces a custom epitaxial platform and fabrication flow that enable reliable cryogenic operation. A fully packaged 4 K optical link directly driven by a superconducting single-flux-quantum circuit is demonstrated, followed by a record-setting 128 Gb/s PAM-4 link at 2.8 K—the fastest cryogenic optical transmission reported to date. To further reduce heat dissipation, a sub-micron-aperture architecture is developed. Shrinking the oxide aperture to 0.9 µm yields an unprecedented threshold current of 50 µA at 3 K and an energy cost of only 45.5 fJ bit⁻¹ while sustaining 112 Gb/s modulation, establishing a new benchmark for cryogenic optical interconnects. Because even microwatt-scale self-heating can degrade performance at deep-cryogenic temperatures, this dissertation also presents a novel experiment–simulation co-design framework that combines Cryo-VCSEL wavelength-shift thermometry with nonlinear three-dimensional finite-element Cryo-VCSEL thermal modeling. The model captures temperature-dependent thermal behavior of the Cryo-VCSELs from 2.6 K to 130 K, accurately predicting cavity temperatures and guiding design rules to mitigate thermal rollover. Collectively, these results show that oxide-confined VCSELs can deliver terabit-per-second-class bandwidth with femtojoule-level energy efficiency at cryogenic temperatures, paving the way for scalable optical I/O in superconducting and quantum computing systems. The thesis concludes with a roadmap for high-power single-mode cryogenic VCSELs, large-scale VCSEL arrays, and integrated electro-optic–thermal design tools that will further unlock the potential of cryogenic photonic interconnects.

Name thesis:degree_name

Ph.D.

Level thesis:degree_level

Dissertation

Discipline thesis:degree_discipline

Electrical & Computer Engr

Grantor

University of Illinois Urbana-Champaign

Year dc:date

2025

Author dc:creator

• Wu, Haonan

Contributors dc:contributor

• Feng, Milton
• Dallesasse, John
• Jin, Jianming
• Dragic, Peter

• Cryogenic Photonic Interconnect
• Vertical-cavity-surface-emitting-laser (vcsel)
• Cryogenic Physics
• Opto-electronic Packaging
• Artificial Intelligence

Statement dc:rights

• Copyright 2025 Haonan Wu

Language dc:language

en, eng

Handle dc:identifier

https://hdl.handle.net/2142/130152

OAI record oai:identifier

https://www.ideals.illinois.edu/oai-pmh?verb=GetRecord&metadataPrefix=etdms&identifier=oai%3Awww.ideals.illinois.edu%3A2142%2F130152