High-speed oxide-VCSELs for cryogenic computing applications

Wu, Haonan

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

Description

Title

High-speed oxide-VCSELs for cryogenic computing applications

Author(s)

Wu, Haonan

Issue Date

2025-07-18

Director of Research (if dissertation) or Advisor (if thesis)

Feng, Milton

Doctoral Committee Chair(s)

Feng, Milton

Committee Member(s)

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

Department of Study

Electrical & Computer Eng

Discipline

Electrical & Computer Engr

Degree Granting Institution

University of Illinois Urbana-Champaign

Degree Name

Ph.D.

Degree Level

Dissertation

Keyword(s)

• Cryogenic Photonic Interconnect
• vertical-cavity-surface-emitting-laser (VCSEL)
• Cryogenic Physics
• Opto-Electronic Packaging
• Artificial Intelligence

Abstract

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.

Graduation Semester

2025-08

Type of Resource

Thesis

Handle URL

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

Copyright and License Information

Copyright 2025 Haonan Wu

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