Broadband nanophotonics and nonreciprocal nanophotonics

Abstract:  Two topics will be discussed: broadband nanophotonics and nonreciprocal nanophotonics.

Broadband nanophotonics concerns managing sunlight and thermal radiation for energy applications. It is strongly motivated by the demands for renewable energy and energy efficiency. More importantly, it presents new challenges for the field of photonics due to its extremely broadband nature. This part of talk will focus on the fundamental limit of broadband light absorption. A classical theory based on geometrical optics was developed two decades ago. I will discuss its limitation and then present a new theory based on wave optics. The wave-domain theory reveals that broadband absorption is directly related to density of states. This new understanding has helped researchers in this field to design extremely efficient absorbers that perform much better than the fundament limit predicted by the classical ray optics theory.

My second topics is nonreciprocal nanophotonics. Reciprocity is guaranteed when light propagates in a linear media that has time reversal symmetry and/or spatial inversion symmetry. Typically, magneto-optical effects are used to break these symmetries and create nonreciprocal optical devices, e.g. isolators and circulators. Are there any other physical mechanisms that allow us to do so? It is well known that a time dependent system breaks time-reversal symmetry. How can we use dynamics in time-dependent system to create a broadband isolator? What are the connections between dynamically modulated photonic systems and magnetically created nonreciprocity? These questions will be discussed in the second half of the talk.

Bio: Zongfu Yu is a postdoctoral scholar at Stanford University. He has numerous publications in the area of nanophotonics, many of which are in high-profile journals and are frequently cited. He has co-authored a number of review articles and book chapters and has given many invited talks. Zongfu is a recipient of the Stanford University Postdoc Research Award (2010). He has a Ph.D. degree (2009) in Applied Physics, a M.S. degree (2008) in Management Science and Engineering, both from Stanford University, as well as a B.S. degree (2004) in Physics from the University of Science and Technology of China.