October 12, 2022
Keio University
Professor Hideyuki Maki of the Department of Applied Physics and Physico-Informatics and Professor Takasumi Tanabe of the Department of Electronics and Electrical Engineering, both at the Faculty of Science and Technology, Keio University, have succeeded in obtaining emission with the narrowest linewidth to date by using a toroid resonator made from silica. As this technology involves a device using a micro-resonator fabricated on a silicon chip and provides narrow-linewidth emission in the 1.55 µm band, a telecommunications wavelength, it is expected to have applications in integrated optical devices such as on-chip integrated optical circuits and optical communication elements.
In addition to emitting light in the telecommunications wavelength band required for optical communications and silicon photonics, carbon nanotubes have recently been expected to have applications in quantum information technology using light, such as quantum cryptography, because they can be realized as a single-photon source at room temperature and in the telecommunications wavelength band. However, the emission linewidth (full width at half maximum) of carbon nanotubes is generally broad, around several tens of nanometers. This has hindered their application in optical communications, as using the emission directly leads to problems such as reduced communication bandwidth and transmission distance due to wavelength dispersion, and makes wavelength multiplexing difficult.
In this study, by using a silica toroid resonator formed on a silicon chip and directly forming carbon nanotubes on it, we succeeded in obtaining ultra-narrow linewidth emission with a full width at half maximum of 74 pm. The Q-factor, which represents the linewidth, reached a value exceeding 20,000. This greatly surpasses the highest previously reported Q-factor for silicon disk resonators (approximately 5,000), and we have successfully observed carbon nanotube emission with the highest Q-factor to date. In the future, this technology is expected to have applications in various on-chip integrated optical devices, including integrated optical devices, optical communication elements, and quantum information elements.
The results of this research were published in the online edition of ACS Applied Nano Materials by the American Chemical Society (ACS) on October 12, 2022 (JST).
For the full press release, please see below.