Institute of Communications and Connected Systems


The highs and lows of PhD life with Kari Clark and Tom Gerard

25 January 2021

Two of our latest student researchers to successfully defend their theses, Kari Clark and Tom Gerard from the Optical Networks Group, share the best and worst moments of their PhD life.

photo of Kari Clark

Author: Ruth Milne, Transnet Communications Manager

Optical Networks | PhD Life | Q+A

In this Q+A, two of our latest student researchers to successfully defend their theses, Kari Clark and Tom Gerard from the Optical Networks Group, share the best and worst moments of their PhD life. Kari describes a tough second year before going on to develop award winning research, whilst Tom remembers how an experience very early into his PhD left him feeling daunted and bewildered about what lay ahead. Read on to learn more.  

What are your PhD highlights and why?

Tom: The best moments of my PhD were all based around collaboration and engagement – attending international conferences, working with visiting academics, touring the laboratories of other groups, interning with Microsoft Research, and so on. These events demonstrated to me that the days of solo PhD work are over, and that the best (and most fun!) contributions come from collaborating with others and working as a team.

A wonderful example of this was the last days of Dr Yuta Wakayama’s stay with us, who was visiting from KDDI Japan. After a week of intense lab work combining Yuta’s programming experience with our laboratory skills, we had a group picnic with football in the park and a dip in the Hampstead Heath ponds. This tight fit of international collaboration, cutting-edge research, socialising in the group and engaging in cultural activities was amazing fun and totally typical of life within the Optical Networks Group.

Kari: Winning the EPSRC Connected Nation Pioneers award, having my phase caching post-deadline conference paper and its follow-up journal paper accepted by Nature Electronics were all rather significant highlights.

However, the most significant highlight for me, which came before these, was seeing my clock phase caching technique working for the first time, late in the evening in our optical communications laboratory. I had been writing and testing field programmable gate array (FPGA) hardware code to implement the technique for about two months, and it was very satisfying to finally see my idea work. It was a key turning point in my PhD project: from being unsuccessful, to successful.

What’s been the most challenging part of your PhD and why? And the most rewarding?

Kari: The second year of my PhD was extremely challenging. During that year, my original primary and secondary supervisors both left UCL, my father was ill, my grandmother died, I had very little in the way of results, I had no publications and there was uncertainty regarding the funding of the remainder of my PhD. I was advised, and rightly so, to consider not continuing with my studies. I knew that I would regret that however, and so I choose to continue, in the hope that things would improve. They did.

The most rewarding part of my PhD project was managing to get past these difficulties and go on to achieve so much in the later years of my PhD project. I am very thankful to the many people who were instrumental in helping me to do so, but particularly my supervisor Zhixin, Polina, Hitesh and Paolo from Microsoft Research, Radan from the University of Southampton, and my family.

Tom: One of the most challenging moments of my PhD was my very first group meeting. On my first Monday morning I sat down with the team in the meeting room, bright eyed and bushy tailed. The room was packed with almost 30 people, and Prof Bayvel asked Gabriele Liga to give an update on the ongoing experiment. Gabriele looked around the room and said: “I can see we have a few new faces so I’ll give a brief introduction to put the work in context.”

I smiled, relieved, as he continued: “We are investigating DSP for WRONs using SSMF and EDFAs in DWDM scenarios. We know LMS and CMA methods can recover AWGN signals, but here we investigate their limitations with QPSK and M-QAM formats inflicted with PAPR impairments from the DAC and ADC, especially when using DBP…” and he went on like that for 30 minutes.

It was a foreign language; I looked around, but nobody else seemed fazed. Eventually the meeting finished, and I came out completely demoralised. I thought I had made an enormous mistake – how could I ever become an expert in this field, when I could not even understand information as it was presented to me? What possible contribution could I ever make that was on the level targeted by these researchers? How on earth can these guys know so much?

Those feelings came and went throughout the PhD, but it helped when I found out that similar crises of confidence and self-worth are experienced by many (all?) researchers. A key highlight of the PhD was the flip side of this experience.

Just a few months ago, I was helping four Master’s students with their final experiment in the lab. The questions came thick and fast: “How can we measure this? What’s the theory behind that? Why is this effect happening? Where can we find more of these?” I helped where I could, knowing that others had done the same for me years ago, until the last question came:

“Tom, how can you know so much?”

The question surprised me because I had never taken the chance to reflect on how far I had come since that first group meeting. Working with the students gave me perspective on my own progression, and it was a rewarding opportunity to pass on some of that knowledge.

What’s your advice for new students joining the team?

Kari: Do work hard at your PhD, but make sure that you look after your mental and physical health too. A good way to help ensure that is to pursue activities and hobbies outside of your PhD. Get involved in a UCL Student Society, learn a new language, play sports – whatever interests you most. In my case, I really enjoyed playing board games in, and being a committee member of, the UCL Science Fiction and Fantasy Society. Additionally, if you run into difficulties during the PhD, ask for help, since there are plenty of people in the team that would be able to provide it.

Tom: My advice for new students is twofold. Firstly, context is king. You will naturally become the expert on your specific topic – but understanding how your research fits into the wider field will really show its significance and where it has the most potential. Therefore, I advise you to shamelessly question everything you can, especially ‘basic’ questions – what is that device? Can we look inside? Why do we do X/Y/Z? When did that become possible? These questions will help you learn specifics, but also the research trends of the wider field.

Secondly, get involved at every opportunity – poster sessions, academic meets, student teaching, inter-group collaboration, art and poetry competitions, presentation opportunities, and so on. Meeting people, learning about the work of others, and winning small successes along the way will keep the PhD social, creative, and break up the long slogs of difficult solo work that can otherwise dominate your research.


Many congratulations to Tom and Kari, both of whom passed their viva exams in December 2020.

Tom joined the Optical Networks Group as an MPhil/PhD student in October 2016 with funding from Microsoft Research. His thesis title is ‘Optical Switching for Scalable Data Centre Networks’ supervised Professor Polina Bayvel, Head of the Optical Networks Group and Co-Director of the ICCS.

Kari joined the Optical Networks Group in 2014. His PhD research was jointly funded by Inphi Corporation, Microsoft Research UK, the EPSRC AirGuide Photonics Programme Grant (EP/P030181/1) and the EPSRC PhotoDAC Grant (EP/R041792/1). His thesis title is ‘Clock Synchronisation Assisted Clock and Data Recovery for Sub-Nanosecond Data Centre Optical Switching’ supervised by Dr Zhixin Liu, Lecturer in Optical Communications and Networks and member of the Optical Networks Group and ICCS.


Kari Clark
Tom Gerard
Optical Networks Group 
Department of Electronic and Electrical Engineering  
Institute of Communications and Connected Systems