Interview with Fellows

“This research was ranked top of the list of highly cited articles on frequency combs in 2019 and one of the top-downloaded papers in the flied of frequency combs over the last two years in Optica”. Interview with MULTIPLY Fellow Shuangyou Zhang

Dr.Shuangyou Zhang received his Bachelors in Electronics from Jilin University, and PhD in Electronics from Peking University. His research interests include optical frequency combs and their applications, chip-scale atomic clock, two-photon-transition for optical frequency standards and integrated photonics.

Shuangyou works at the Max Planck Institute for the Science of Light in Germany and the title of his MULTIPLY Fellowship was “Microcomb-based Compact Optical Clock”. This project was successful and Shuangyou told us more about this in the interview.

You have already finished your MULTIPLY Fellowship. What was the main benefit for you in this programme?
This programme enabled me to move into the rapidly developing cutting-edge research, namely microresonators-based frequency combs (microcombs). During the fellowship, I acquired diverse knowledge, not only scientific research skills, but also complementary skills, like project management, supervision, and proposal writing.

Did you achieve the main goal of your proposal?
Yes, the main goal of my proposal has been achieved.

We demonstrated a new scheme to generate stable soliton freqeunecy combs in microresonators using an auxiliary laser to passively stabilize the temperature of a microresonator. This scheme increases the soliton access range by a factor of 100 and enables us to demonstrate a new world record for the threshold power (780 microwatt) of soliton frequency combs, which would enable these combs to operate for more than a year on a mobile-phone battery. This significantly reduces the power requirements and increases the stability of soliton frequency combs and is a crucial discovery for future optical clocks, where low power consumption frequency combs will be a critical component in allowing them to run for much longer in portable devices than currently available. This research was ranked top of the list of highly cited articles on frequency combs in 2019 and one of the top-downloaded papers in the flied of frequency combs over the last two years in Optica.

We managed to generate an ultrastable THz wave using a soliton microcomb, which could provide a route towards highly stable continuous terahertz wave generation in chip-scale packages for out-of-the-lab applications. In particular, such systems would be useful as compact tools for high-capacity wireless communication, spectroscopy, imaging, remote sensing, and astrophysical applications.

We demonstrated that the spectrum of a soliton microcomb can be extended by bi-chromatic pumping resulting in two combs that synchronize their repetition rate via cross-phase modulation. This technique could be useful for the generation of super broadband frequency combs, which are a key enabling technology for frequency metrology and spectroscopy.

This sounds really fantastic, congratulations, great job! How different is what you did from what was written in the proposal?
My research was essentially carried out as proposed. Only the part of the proposal related to the two-photon transition was not carried out because our group moved from National Physical Laboratory to Max Planck Institute for the Science of Light, which has no background in atomic physics.

Is what you are doing now closely related to what you did during the fellowship?
Yes, I’m still continuing the same research topic on microcombs.

You work with Pascal Del’Haye. Could you please tell us more about your research group? What are you working on?
Our group leader Pascal Del’Haye joined the UK National Physical Laboratory in 2105 and started the Microphotonics Research Group. At the end of 2019, the group was relocated to Max Planck Institute for the Science of Light in Germany. Our research group mainly focuses on the study of nonlinear photonics in ultra-high-Q microresonators. Currently, our main research is on interaction of counterpropagating light and optical frequency comb generation in whispering gallery resonators. I’m mainly working on optical frequency comb generation in microresoantors, including the fabrication of microresonators and comb generations in these resonators.

What research skills have you acquired during your work in this scientific group?
Nonlinear photonics in ultra-high-Q microresonators and frequency comb generations in microresonators. After moving to Germany, I gained a lot of nanofabrication skills for on-chip photonic devices.

Do you have any dreams about future scientific collaborations?
In the past years, due to the global pandemic, travel and in-person collaboration have been limited. We have some collaborations with some research groups in British Universities. I’m looking forward to more efficient collaborations in the near future.

What is the best thing about your work?
The best thing about microcomb research is that you can learn cutting-edge technology. It is a rapidly growing field. Lots of technology and knowledge are emerging rapidly.