MESA+ University of Twente
Research Business & Innovation About MESA+ Storyline Education

Sergei Sokolov

In this thesis experimental investigations and control of properties, of single and coupled photonic crystal nanocavities are presented. Photonic crystal nanocavities play an important part in the future of nanophotonics.

‘We have built a state-of-the art setup for our experiments from scratch’ Sergei Sokolov says. ‘We discovered several new phenomena, leading to new insights as to the essential parameters to be tuneable in photonic crystal systems.’

It was, for example, discovered that by changing the ambient media, from nitrogen to helium, a change in the width of temperature distributions in these crystal chains occurs, up to 30%. ‘This allows for an increase of the integration density of nanocavities on a photonic chip,’ Sergei says. ‘Also this allows more efficient laser induced thermal tuning.’

Also it was demonstrated that several coupled nanocavities can be controlled independently, in the presence of thermal crosstalk. ‘By restoring the intended state of the system completely, we were able to demonstrate full tunability,' Sergei says. ‘The coupling constant between the nanocavities could be changed experimentally by using two different methods.’

Experimental work was the main part of Sergei Sokolov’s PhD project.

‘I like performing experiments designed from understanding the physics underlying the experiments,’ he says. ‘In this field of research one has to be ready for complications, as there are no experiments without calculations. From the combination of literature study, theoretical understanding and clever experiments you can learn a lot. This can lead to new views on key aspects.’

Challenging field of research

In the second half of his PhD project, Sergei started to feel more free as to follow his own ideas and intuition.

Sergei: ‘From analysing the literature research in the field, I found out some aspects hadn’t been addressed yet, and that achievable experiments were not performed as to that time.’

This led to new experiments to be performed. Sergei: ‘There is not one way towards success. Sometimes in real experiments, dependencies show to have opposite effects then thought of beforehand. Also it is possible that effects that had been left out in the usual analyses, do nevertheless show significant influence on the measurement outcomes. Also, insights about experimental outcomes can come from numerical analysis. All of these processes contribute to this challenging and surprising field of research which I love so very much.’


In his PhD project Sergei collaborated with Thales Research & Technology, located in Paris.

‘They are experts in fabricating photonic crystal nanostructures,’ Sergei explains. ‘According to our requirements they fabricated the nanostructures, allowing us to focus solely on the research and experimental part of the job.’

Creatively designing and building optical experimental setups, Sergei added to his skills during his PhD work. ‘Also I gained descent experience on using simulation tools regarding complex photonic systems,’ he says. ‘Further, I am very glad every chapter in my PhD thesis is a substantive part on its own.’


After a short post-doc term (‘to finalize some aspects of this PhD research’) Sergei is looking forward to go and work in industry.

Sergei: ‘I would like to work in industry and see what challenges lie ahead of me. Mesa+ is an institution that is renowned internationally as well as it is within the Netherlands itself. This I noticed during my last PhD year in which I spent most of my time working at the University of Utrecht and attending the leading event: Physics@Veldhoven, as organised by FOM (Fundamenteel Onderzoek der Materie).’