Polariton: What is the mission of your institute?
Prof. Leuthold: At IEF, we aim to develop the smallest, fastest, and most energy-efficient devices for optical communications and applications in the THz regime. In practice, that means inventing and developing novel concepts, chip-level design, chip fabrication, characterization, and system-level performance testing. Offering this environment that includes the whole cycle from invention up to system levels to our students is challenging and rewarding at the same time. Yet, in the end, I am convinced that we are excelling in time-to-publication, and our students get the bigger picture of what a development cycle means.
POL: When did you first get in touch with plasmonics?
JL: I started with this topic as a Professor at the KIT (Karlsruhe Institute of Technology). In 2009 Professor Fujii was a visiting scientist from Japan when I got interested in this subject. He was a theoretician and looking for new topics. So I asked him to investigate the dispersion relations of plasmons. Plasmonic research at that time had a bad reputation. It kind of was a “forbidden” subject due to the high losses of metallic waveguides. We ended up with a theoretical paper with Masafumi Fujii as the first author. I found the outcome sufficiently interesting. My own back-of-the-envelope calculations told me that super-fast modulation should be doable. At that time, we got a student, Argishti Melikyan, interested in working on a Master’s thesis with us. The common wisdom was not to work on this subject. And indeed, I found that my PhD did not supervise him well. So I decided to support Argishti myself. By 2010 we had the first concept paper presented at CLEO (Conference on Lasers and Electro-Optics). We published an absorption modulator employing ITO (Indium Tin Oxide). Said work was popularized later under the name “epsilon-near-zero” research. In 2011 we had the first proof-of-concept experiment. However, it was slow, and the modulation was weak. The deposition of ITO turned out to be difficult. We were also researching silicon-organic hybrid (SOH) modulators at this time. A research that started in 2008 with Jan-Michael Brosi. We then combined the plasmonic with the SOH technology. This took a lot of time, but in 2014 we made it to Nature Photonics. It was then the first Plasmonic modulator paper. The numbers were poor, but the concept was already there.
POL: Who funded that research?
JL: The German funding agencies were not particularly lenient at the time. So we went for an EU grant which got magically accepted. When I visited Brussels for the grant negotiation, I was welcomed with a cold dismissal, “This proposal should never have been accepted.” Well, let me say that the wish to prove that expert wrong was much of a motivation for the entire team.
POL: And what made you think that starting a company about plasmonics would be a good idea?
JL: We brought down the plasmonic losses from 40 dB to the twenties, and knowing that the fundamental losses would be smaller than 5 dB convinced us that it would have a market potential. Like for many technology projects, such loss reduction becomes a matter of engineering and stamina. Miniaturization and material research merged with visionary people. Then, the three musketeers (the Polariton Founders) took over.
POL: That’s an interesting subject. How did that work out?
JL: The “later” Founders were Master’s students when I was at KIT. I am still surprised that they followed me to Zurich. Wolfgang (Heni) was the device wizard, Claudia (Hössbacher) focused on characterization, and Benedikt (Bäuerle) developed the system-level aspects. They adopted the challenge and worked as a team, and it’s when we developed the company’s idea.
POL: Did the Founders have to be convinced to come to Switzerland?
JL: No! I told them about Toggenburg (smiles – Jürg’s region of origin).
POL: What can you tell about the Founders that not many know?
JL: With pleasure. Claudia discovered the first atomic-scale switch in the search for a modulator. This was the first optical memristor, for which we are still looking for an application. But welcome! Also, Claudia used to tell me that plasmonic modulators would not work. Today she leads a 30 people company. It’s been nice to push her ahead. While Benedikt has developed signal processing algorithms for coherent communication that were much better than any state of the art in terms of processing speed, and still are. So we are still employing them in the institute today. Finally, Wolfgang has my admiration for helping so many people in the institute and becoming a co-author of 146 papers so far. I guess he was laying the foundation for his later role as an entrepreneur.
POL: Coming back to you, what is your current role at Polariton?
JL: I love talking to the team once per month and covering the role of Scientific Advisor.
POL: Finally, what do you do when you are not thinking of work?
JL: Biking! When I was a kid, I had to cycle uphill twice a week as the church was on top of it, and I guess this helped to develop my passion for mastering alpine crossings. In the past year, we conquered as a family the Furka, Grimsel, or the Albula. All of which are worthwhile rides. Unfortunately, I am not as energetic anymore as I was once. I think I got lazy in my time in the USA. So, I am not much of an outdoor person anymore, but I like certain activities, like my yearly ski vacation. I remember I was on the slopes when you called me last time.
POL: Yes, you still picked up your phone. Thank you for that!
Interview by Stephan Koch.