PhD defence by Quentin Saudan

Title: Advances in all-optical switching using Fano resonance photonic crystal nanocavities

Supervisors
Principal supervisor: Associate Professor Michael Galili, Department of Electrical and Photonics Engineering, DTU, Denmark
Co-supervisor: Professor Kresten Yvind, Department of Electrical and Photonics Engineering, DTU, Denmark
Co-supervisor: Postdoc Dagmawi Alemayehu Bekele, Department of Electrical and Photonics Engineering, DTU, Denmark

Evaluation Board
Senior Researcher Mikkel Heuck, Department of Electrical and Photonics Engineering, DTU, Denmark
Dr. Research Engineer Mathilde Gay, Centre National de la Recherce Scientifique (CNRS), France.
Dr. Senior Researcher Alfredo De Rossi, Thales Research and Technology, France.

Master of the Ceremony
Associate Professor Nicolas Leitherer-Stenger, Department of Electrical and Photonics Engineering, DTU, Denmark

Abstract
As more and more users and devices are connected to the internet, the amount of data transmitted and processed around the globe is continuously growing, which has significantly increased the demand for computer chips with higher speeds and efficiencies.
In this work, we investigate the implementation of “optical transistors” using photonic crystal nanocavities. These devices could replace their electrical counterparts for specific applications, which might lower the overall power consumption of computers. However, two key challenges still need to be addressed: the recovery rate of such cavities after excitation and the spectral proximity of the pump with the probe during operation.
By using advanced cavity designs, we demonstrate the wavelength conversion of an optical signal using two modes instead of one, which improves the signal quality and the power efficiency. Additionally, we show, both in simulations and experiments, that electrical PIN junctions are promising structures to accelerate the switching process. Finally, we design, fabricate and characterize a photonic crystal cavity with a bowtie. The light is tightly confined at the center of the bowtie, which might increase the speed and efficiency of the switching process.
Our thesis paths the way for further developments in this field and may lead to the implementation of optical switches in computers for a more sustainable internet.