PhD defence by Jasper Riebesehl

Abstract

Lasers and optical frequency combs are powerful sources of highly controlled light, forming the backbone of many modern technologies. One prominent example is high-speed internet: to meet growing global demand, we rely on ever more precise light sources to boost the performance of optical communication networks.

However, no light source is perfect. Their frequency fluctuates randomly in a phenomenon known as phase noise, which limits their performance. Understanding and measuring this noise is crucial, but conventional methods often fall short by providing incomplete or biased results.

This PhD thesis introduces new signal processing techniques that offer more accurate ways to measure phase noise in lasers and frequency combs. By using data-driven models, the work improves upon conventional methods by accounting for hidden measurement errors, which produce more accurate noise estimates. Critically, the required experimental setups are kept simple and accessible. A key innovation is the ability to automatically search for noise correlations, which previously would have required significant experimental effort.

In the future, improvements to these techniques could allow for the digital compensation of phase noise, beyond its characterization. This would lower the demands placed on the hardware itself, opening new possibilities for simpler, more cost-effective systems in communications, sensing, and other technologies that rely on ultra-precise light.

Supervisors

• Principal supervisor: Professor Darko Zibar, Department of Electrical and Photonics Engineering, DTU, Denmark

•  Co-supervisor: Associate Professor Michael Galili, Department of Electrical and Photonics Engineering, DTU, Denmark

Evaluation Board

• Associate Professor Haiyan Ou, Department of Electrical and Photonics Engineering, DTU, Denmark

• Professor Laurent Schmalen, Karlsruhe Institute of Technology (KIT), Germany

• Professor Radan Slavik, University of Southampton, United Kingdom

Master of the Ceremony

• Associate Professor Francesco Da Ros, Department of Electrical and Photonics Engineering, DTU, Denmark