PhD defence by Kristian Seegert

Abstract

Lasers are found in countless technologies, from barcode scanners to the optical fibers that carry data across the internet. As our society increasingly depends on digital communication and high-performance computing, the demand for smaller, faster, and more energy-efficient lasers is growing. This PhD thesis investigates a new class of microscopic lasers— nanostructured Fano lasers—that use interference effects at the nanoscale to control light in novel ways.

Unlike conventional lasers, Fano lasers exploit a special effect called Fano interference, where light bouncing in a tiny cavity interacts with a broader waveguide. This makes the laser mirror frequency-dependent, enabling unusual and tunable dynamics. The thesis introduces a new theoretical framework that explains how these dispersive mirrors shape laser behavior, predicting when lasers are stable and when they spontaneously start pulsing or switching between modes. While such instabilities are normally seen as problems, this work shows that they can be harnessed to create useful features, such as generating ultrafast pulses or operating two colors of light at once.

The research goes beyond theory by designing and testing nanobeam Fano lasers, confirming several predicted effects in the lab. It also explores the microscopic physics of the quantum well materials that power these devices and demonstrates a new way to produce sharp optical pulses by coupling two nanolasers together.

The results point toward future applications in energy-efficient data communication, optical signal processing, and neuromorphic computing, where lasers may act as “photonic neurons” that mimic the brain’s spiking activity. By showing how to engineer and exploit the rich dynamics of nanostructured lasers, this work contributes to the foundation of next-generation photonic technologies that could complement or even surpass electronics in speed and efficiency.

Supervisors

• Principal supervisor: Professor Jesper Mørk, DTU Electro, Denmark
• Co-supervisor: Senior Researcher Yi Yu, DTU Electro, Denmark
• Co-supervisor: Senior Researcher Mikkel Heuck, DTU Electro, Denmark

Evaluation Board

• Associate Professor Francesco da Ros, DTU Electro, Denmark
• Professor Jan Wiersig, Otto-von-Guericke-Universität Magdeburg, Germany
• Associate Professor Nicolas Volet, Aarhus University, Denmark

Master of the Ceremony

• Professor Martijn Wubs, DTU Electro, Denmark