PhD defence by Dagmawi Alemayehu Bekele

Title: Photonic crystal fano structures for all-optical signal processing

Principal supervisor: Professor Jesper Mørk, DTU Fotonik
Co-supervisor: Assoc. Prof. Kresten Yvind, DTU Fotonik
Co-supervisor: Dr. Luisa Ottaviano, DTU Fotonik

Evaluation Board
Dr. Lars Hagedorn Frandsen, DTU Fotonik
Dr. William Whelan-Curtin, Cork Institute of Techonology, Ireland
Dr. Alfredo De Rossi, Thales Research and Technology, France

Master of the Ceremony

Assoc. Professor Michael Galili, DTU Fotonik

In the digital age that we live in, the role of internet is increasingly important part of our daily lives. With most of our home appliances, computers, smartphones, vehicles, refrigerators etc., sharing information with each other, the internet traffic and the associated energy consumption have been increasing exponentially. In order to successfully meet these demands of Internet of Things, serious contributions to the advancement of technology must be achieved as the result of synergistic research activities between multidisciplinary fields of science. Surprisingly, the well-established electronic computing technology is reaching its physical limitation due to the high processing speed required to cope up with the exponentially growing internet traffic. As the speed of operation increases, the energy required for interconnection between various electronic processing units becomes very high, especially for longer wire connections.
On the other hand, fiber optics has proved to be the best means of sending large information over long distances, at low loss, and at high speed. Thus, optical interconnect is replacing the lossy electrical wires and substantially mitigating the energy and density problems. However, the next question is whether optics can be used to reduce energy dissipation within racks, chip-to-chip, and possibly on-chip communications.
Furthermore, optical technology has also the opportunity to go beyond being just a convenient pipe for ultrafast data transmission, it can actually perform data signal processing. This involves the efforts for building optical transistors that can perform all-optical switching and logic operations.
A good compromise is to use optically assisted signal processing which exploits optics for what it does well and electronics for what it does best. Optics can perform few functions very fast, and electronics is best for doing accurate complex computations with buffers and memory. Ultimately, electronics and optics in computing are more complementary than competitive.
In this Ph.D. thesis, we investigated a compact and energy efficient photonic integrated circuit, that is capable of performing bit-level all-optical switching such as wavelength conversion and optical time domain demultiplexing. The device is based on a resonant cavity which possesses a unique transmission property known as the Fano resonance, which can be turned ON or OFF using another optical signal on demand. The results show that such photonic integrated system has a potential to be used in next generation optical interconnect systems at low energy budget.


Tue 18 Sep 18
13:30 - 16:30


DTU Fotonik


Lyngby Campus

Bld. 306, aud. 37