SCHOOL OF ENGINEERING, TOHOKU UNIVERSITY Driving Force THE POWER TO MAKE TOMORROW INTERVIIEW REPORT
SCHOOL OF ENGINEERING, TOHOKU UNIVERSITY Driving Force THE POWER TO MAKE TOMORROW INTERVIIEW REPORT

Shaping the Future by Utilizing Light

Professor
Department of Electronic Engineering
Graduate School of Engineering,
Tohoku University
Kyoko Kitamura REPORT #36

© School of Engineering, Tohoku University

A career in researching light began with a 'Really?!' moment.

The Photonic Device Engineering Lab, the Department of Electronic Engineering at the Graduate School of Engineering, Tohoku University, is headed by Professor Kyoko Kitamura who first arrived at this university in September 2023. The word “photonic” in the lab’s name refers to “light.” Professor Kitamura mainly studies structures called photonic crystals, and she is engaged in the research and development of such structures from both the science and engineering perspectives. First successfully created in the world in 2000 by Japanese researchers, photonic crystals are artificial structures made of regularly arranged semiconductor nanostructures in a sequence of several hundred nanometers (one billionth of a meter) which is the same as the wavelength of light. A photonic crystal has a property of not permitting light of a certain frequency range to penetrate. By deftly designing a frequency range which does not permit light to penetrate (a photonic band gap) or by introducing an intentional disturbance (a structural defect) into the regular structure of a crystal, it is possible to control light at will, which leads to possible applications in optical circuit devices such as optical storage and optical switches, and in quantum information processing and communication such as quantum computers.

A graduate of Kyoto University’s Undergraduate School of Chemical Science and Technology, one of Professor Kitamura’s options for graduate school was to specialize in a field related to semiconductor fabrication. What led her to a career in optical device research was something she once heard during a lecture. She learned that if you periodically make holes in a semiconductor, you can manipulate light at will. She recalls, “I learned that you can freely control light just by making patterns on a semiconductor substrate using an electron beam and creating nano-level holes with plasma. I honestly thought, ‘How can that be?! There’s no way that’s possible!’ That was my first encounter with photonic crystals, and I thought if that was truly possible, then it would be fascinating, so I decided to study it.”

The lecturer at the time was Professor Susumu Noda of Kyoto University’s Department of Electronic Science and Engineering who later became her mentor. Professor Kitamura focused her research on photonic crystals at Professor Noda’s lab and after she received her doctorate degree, she moved her research base to the Faculty of Electrical Engineering and Electronics of the Kyoto Institute of Technology, developing technology for designing laser beams using photonic crystals, among other things.

Taking on the challenge of fundamental technologies for 6G

Right after she assumed her post at this university in September 2023, Professor Kitamura published a paper entitled “Deflection of Electromagnetic Waves by Pseudogravity in Distorted Photonic Crystals,” which was the result of collaborative research with a research group from Osaka University’s Graduate School of Engineering Science and others. Based on Einstein’s general theory of relativity, it is known that the propagation trajectory of electromagnetic waves (waves propagated by changes in the electric field and the magnetic field, and electromagnetic waves with a frequency of 3 terahertz or higher are considered light) is also deflected by gravitational fields (fields that exist in space-time when gravity acts) caused by a distortion in space-time, but in this research, the researchers succeeded in deflecting the propagation trajectory of terahertz electromagnetic waves by moderately distorting the arrangement of the lattice constants of photonic crystals with regular periodic structures. She says, “What is particularly noteworthy about this research is that distorted photonic crystals, which are photonic crystals with moderately altered regular periodic structures, retain the properties of photonic crystals but they can also distort space-time. That said, it is technically very difficult to create a moderately distorted structure within the field of light, so for demonstration purposes, we experimented with deflecting the propagation trajectory of terahertz electromagnetic waves which have longer wavelengths than light. As one would expect, terahertz electromagnetic waves are promising in the next-generation mobile communications 6G system (Beyond 5G), and I believe deflecting the trajectory of terahertz electromagnetic waves can be applied as a fundamental technology to control terahertz electromagnetic waves at will.”

In contrast to the distorted photonic crystal research of inserting light from the outside of the crystal, for many years Professor Kitamura has also been researching semiconductor lasers which are active devices that generate light. She explains, “I specialize in generating doughnut-shaped laser beams from semiconductor lasers. I want to explore new possibilities for light by combining a donut beam with a regular high-power laser and by stacking beams of varying wavelengths and shapes. Two or more kinds of large lasers are commonly used in current super-resolution laser microscopes, but with photonic crystal lasers, I have begun new research to see if it may be possible to create a laser microscope with several small one-chip lasers and one switch that can do everything.”

Manipulating light means shaping the future - this is what Professor Kitamura believes as she continues her research every day. What kind of future awaits beyond her photonic crystal research that manipulates light based on the theory of light?

School of Engineering, Tohoku University Driving Force, The Power to Make Tomorrow. INTERVIIEW REPORT

The energy of a female researcher, and dynamic PR activities

Professor Kitamura has lived in the Kansai area since her student days and has acquired the unique vibe and sense of humor that people in Kansai have. “In my lectures, I have tried to include parts intended to elicit laughter, but when I did this at Tohoku University, sometimes no one laughed and my jokes completely fell flat,” she laughs. “However, even I won’t enjoy a lecture without anything lighthearted in it, so I’ll have to work on that,” she says.

When we asked Professor Kitamura what she thinks Tohoku University’s appeal and strengths are, she replied, “Female researchers gather regularly, and they are energetic and full of life. I don’t think there are many universities with such energetic female researchers. Even when I was in Kansai, I’ve had this image of Tohoku University being highly supportive of female researchers, and I think this is because senior female researchers here have always clearly expressed what kind of support they needed.” It helps that the university also has a culture of being receptive to such ideas.

Professor Kitamura also said that the university is “highly conscious of public relations and information dissemination.” She explains, “Honestly, I was surprised at the full support the university offers for press releases. Regarding the press release for the paper on distorted photonic crystals that was published right after I assumed my post, professors from Osaka University who collaborated with the research said that they don’t usually receive this level of support. I feel that Tohoku University is highly conscious of properly disseminating research results outside the university and showing such achievements to society.”

Cherish the dream you had when you were 17 years old

Professor Kitamura says it was her childhood dream to become an official at the United Nations. She says this was her dream because she once saw the removal of land mines in Cambodia in the news. “I thought, to become a UN official, I need to earn a doctorate in some field, and because experiments are interesting, chemistry might be the field. So, I chose to go to The Undergraduate School of Chemical Science and Technology of Kyoto University. When I told my high school teacher about plans, my teacher was very much opposed to it. I was told that medicine or pharmacy were better fields because I could get licensed and I can keep working even if I were to have children. When I look back, I was at my most rebellious stage of adolescent years, and I stuck to my desire to study engineering.”

In June 2024, there was a series of Tohoku University Visiting Lectures held at a high school in Sendai City. One of the lecturers was Professor Kitamura, and her lecture was entitled “Your Dream When You were 17 Years Old.” She says, “I wanted to convey the idea that you get to have the dream you have at 17 only when you are 17, so you should believe in it and give it a go. Cherish the feelings you have during this rebellious phase at 17 years old and it’s better to stick to your honest dreams. Push through without hesitation, and if you do succeed, that’s good, but even if you fail, you can just look back, laugh it off and say you were going through a rebellious phase. This is why I think it’s better to go all out on what you’re thinking about right now.”

Professor Kitamura says it is important to her as a university professor to “turn on the switch that motivates students.” She says, “Each student definitely has their own good qualities, and I want them to find these qualities. I want them to find something they can use as a focal point throughout their school years and after they go out into the world.”

She says students prefacing what they are going to say with “I didn’t study enough but…” or “I don’t know much about this but…” has been bothering her recently. “Maybe it’s because of our culture that values humility, but I think such prefaces are unnecessary. There’s no way you would know about the cutting-edge research from the start. If students can confidently state what they think, they will be highly regarded when they go out into the world. I hope they will have a strong sense of self-affirmation, know who they really are, and contribute to society,” she says.