Optical nano resonators, such as dielectric nano-rods, nano-disks, and plasmonic nano-particles, can concentrate light to ultra-small dimensions. Such nanoscale concentration facilitates optical energy conversion and is frequently used in applications including photovoltaic cells, solar fuel generation, molecular imaging, photodetectors and refractive-index sensors, just to name a few. Here, I would like to explore the limit and unique applications of light concentration based on optical resonance.

Specially, optical cross section limits the amount of light that can be concentrated from the free space to a confined target. It sets the upper bound of the total photon budgets and ultimately limits device performance. I will discuss the universal limit of the cross section from the perspective of a free-space coupled mode theory. We showed that certain novel optical materials present unpreceded opportunities to obtain extremely large optical cross sections. For example, index-near-zero materials can enhance the optical cross section by many orders of magnitude, making nanoscale objects visible to naked eyes. By generalizing this effect, we will also discuss the potential of photonic structures that exhibit Dirac-cone or Weyl points. I will also discuss unique applications enabled by resonant interactions, including an optically-coupled but electrically-isolated photo-detector for light-field sensing. Toward the end, I will provide some outlook on using quantum transitions of electronic structures to construct extremely compact resonant devices.

Zongfu Yu is an assistant professor in the department of electrical and computer engineering at the University of Wisconsin – Madison. His research focuses on novel photonic devices for applications in solar energy conversion, imaging and sensing, and integrated optical communication. His work has been cited over 8000 times with an h-index of 37. He received a Ph.D. degree in Applied Physics in 2009 and a M.S. degree in Management Science and Engineering in 2008, both from Stanford University. He received his B.S. in Physics in 2004 from the University of Science and Technology of China.