INTERVIEW towards real applications. Interestingly, most of the spin-offs originating from our group are in sensing, which again reflects the potential we see in that field.
From your perspective, what has been the major success of integrated photonics? If we look at impact, the major success of silicon photonics is clearly its use in high-speed optical transceivers for data centres. Today, with the massive interconnect requirements associated with AI and the move towards co-packaged optics, this has become an enormous application for the field. I hope that in the coming years we will see a similar development in at least a few sensing applications.
What are the main challenges for the future? The major challenge, in my view, concerns material diversity. For a long time, integrated optics involved many different material platforms such as silica, glass, lithium niobate, III-V semiconductors just to cite a few. Silicon photonics created the attractive idea that perhaps we could do a very large number of things on one common platform. Today, however, we are moving again towards increasing material diversity. For very good reasons, researchers want to combine silicon or silicon nitride with many other materials in order to obtain new functionalities. Scientifically, it is a dream and industrially, it is a nightmare.
How can this material diversity be made compatible with industrial manufacturing? Moving a process from a research laboratory into reliable industrial manufacturing is already difficult. If every new function requires another material and another specific process flow, the complexity can become enormous. Integrated photonics is still small compared with the semiconductor industry in terms of wafer volumes. If we introduce too much diversity while the markets remain relatively modest, there is a risk that industry simply cannot support it. The challenge is therefore to benefit from material diversity while keeping as much of the manufacturing process as possible generic. This is one reason why I am enthusiastic about approaches such as micro-transfer printing: the different materials can remain in their natural technological environments for most of the process and only be brought together relatively late. I also believe this evolution will create opportunities for new industrial actors. We may need companies positioned somewhere between the foundry and the final product manufacturer, specializing in these heterogeneous integration steps. If we find sensible industrial value chains that can manage this diversity, then the opportunities are enormous.
You have supervised many generations of PhD students and young researchers. What is your approach to mentoring? It starts with selecting the right students. Whenever a master ' s student asked me about doing a PhD, I would tell them that it is probably the hardest choice they can make. They are often surprised by that! A PhD is a very particular challenge. In Belgium, you typically have four years, and you have only four years to surprise the world with something that nobody has done before you. That requires intellectual ability, of course, but also motivation and mental strength. Almost every PhD student goes through a difficult period, often somewhere around the middle of the thesis. You may have spent two years working without the results you expected, perhaps without publications, while suddenly realizing that the time to start writing is getting closer. That can be daunting. As a supervisor, I have always disliked micromanagement. Initially, perhaps I simply did not have time for it because the team became too large! But with experience, I became convinced that giving researchers trust and independence is actually the right approach. For most people, it works extremely well. Of course, when someone runs into trouble, you need to be there. Sometimes the scientific problem is simply harder than expected; sometimes motivation becomes difficult. Mentoring, for me, is about giving people freedom to develop independently while being ready to support them when they really need it.
What role can professors play in attracting young people to photonics? Individual professors can have an enormous influence on the direction a student takes. In my own case, Paul Lagasse in Ghent was one of the people who introduced me to fibre optics and photonics. At the time, these subjects felt very new compared with many of the other courses we were taking, and students are naturally attracted by something new. At Stanford, Joe Goodman was another important influence. Even though I only did a relatively small project with him, working with such a personality was inspiring. Because of those experiences, I became very conscious of the role a professor can play as a role model. I have always enjoyed teaching, both to larger groups and to smaller classes, and I tried not only to explain the science but also to convey enthusiasm for the field. Whether I succeeded is something you would have to ask my former students! But I was certainly aware that inspiring students is an important part of teaching.
What advice would you give to a young researcher starting a career in photonics today? I would definitely encourage young researchers to move into photonics. But if they have the opportunity to work on something genuinely novel, I would strongly encourage them to grasp it. There will always be many research opportunities driven by the major trends of the moment. But there is something very special about entering a field when it is still emerging, when you do not yet know whether it will become important. If I were starting a PhD again today, I would probably still choose integrated photonics, but I would try to move into a completely new type of application. For example, I find the idea of using an integrated photonic circuit to support photochemical processes at the surface of a chip very intriguing. It is still an embryonic idea in my mind, but that is precisely what makes such directions exciting. For a young researcher, the thrill of doing something that could become important while being among the pioneers is difficult to beat.
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