Purdue University Graduate School
Final Thesis.pdf (7.29 MB)

Microcombs for Timekeeping and RF Photonics

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posted on 2023-09-27, 19:16 authored by Nathan Patrick O'MalleyNathan Patrick O'Malley

Optical frequency combs have revolutionized metrology and advanced other fields such as RF photonics and astronomy. While powerful, they can be bulky, expensive, and difficult to manufacture. This tends to limit uses in real-world scenarios. Within the last decade or so, coherent frequency combs have begun to be generated in millimeter-scale, CMOS fabrication-compatible nonlinear crystals. These so-called “microcombs” have led to hopes of overcoming deployability constraints of more traditional bulk combs.

One of the first applications for \textit{bulk} frequency combs after their explosion in 2000 was the optical atomic clock. It promised extreme long-term time stability better than that of the Cesium clock that currently defines the SI second. More recently, interest in a fully portable optical atomic clock has grown. Such a device could reliably keep time even without the aid of GPS references, and potentially with greater accuracy than current GPS synchronization can provide.

Frequency combs have also been used to sample electrical signals more rapidly than traditional electronics can accomplish. This has been used to achieve dramatically increased effective frequency bandwidths for signal detection architectures. One can imagine how this capability would be beneficial in a portable (microcomb-driven) form: a lightweight, comb-enhanced receiver able to capture a broadband snapshot of its surrounding electromagnetic environment could be a powerful tool.

Timekeeping and RF photonics are the primary applications of microcombs focused upon here. I will attempt to roughly summarize important concepts and highlight relevant work in both subjects in the Introduction. Then I will move a step closer to the hands-on lab work that has largely kept me preoccupied over the last several years and describe important or commonly-employed Methods for experiments. A collection of three journal manuscripts (two published, and the third recently submitted) will follow in the Publications chapter, highlighting some experimental results. Finally, I will conclude with a brief Outlook.



AFOSR grant FA9550-20-1-0283

US Naval Research Laboratory


Degree Type

  • Doctor of Philosophy


  • Electrical and Computer Engineering

Campus location

  • West Lafayette

Advisor/Supervisor/Committee Chair

Andrew Weiner

Additional Committee Member 2

Sunil Bhave

Additional Committee Member 3

Jason McKinney

Additional Committee Member 4

Minghao Qi