Researchers have created a gear-shaped photonic crystal microring that increases the strength of light-matter interactions without sacrificing optical quality. The result is an on-chip microresonator with an optical quality factor 50 times better than the previous record in slow light devices that could improve microresonators used in a range of photonics applications, including sensing and metrology, nonlinear optics and cavity quantum electrodynamics.
Optical microresonators are structures that enhance light-matter interactions through a combination of long temporal confinement (i.e., high quality factor) and strong spatial confinement of an electromagnetic wave.
The light devices the researchers have developed in many ways integrate the best attributes of two types of optical microresonators — a photonic crystal and a whispering gallery mode resonator — in one device. While combining the two has been attempted in the past, previous microring devices that have succeeded in slowing light to increase interactions (a consequence of the photonic crystal) have had to sacrifice quality factor. In this new “microgear” photonic crystal ring, researchers observed modes with group velocity slowed down by 10 times relative to conventional microring modes without any degradation in quality factor.