21.1.16
Candidate Talk: Dr. Yakir Hadad
Department of electrical and computer engineering, The University of Texas at Austin
Yakir Hadad is a candidate to join the Physical Electrionics department in October 2016. He received his B.Sc. and M.Sc. (both summa cum laude) in electrical and computer engineering from Ben-Gurion University in 2006 and 2008, respectively, and a Ph.D. in electrical engineering from Tel-Aviv University in 2014. Since then he is a post-doctoral fellow at the Metamaterials and Plasmonics group led by Prof. Andrea Alu in the University of Texas at Austin working on various applications of complex media, including time variant, and nonlinear. He is currently also a visiting researcher in FOM institute AMOLF, Amsterdam, working on the theory of ordered and disordered plasmonic distributed feedback lasers. His main research interests are wave phenomena in complex media, and analytical modelling in electrodynamics.
Exotic wave phenomena in time-variant and nonlinear media
Abstract: Lorentz reciprocity imposes constraints on radiation and scattering. For instance, a reciprocal antenna in a reciprocal medium will have identical transmission and reception; therefore, in a dense environment a directive antenna will be prone to ‘hear’ its own echoes. In another context, Kirchhoff’s law of thermal radiation dictates that at thermal equilibrium emission and absorption rates are equal, thus imposing intrinsic constraint on efficiency of thermal energy conversion systems. Likewise, a scattering matrix in reciprocal medium will be symmetric, implying particularly that a metasurface that reflects plane wave A to plane wave B will necessarily do the reciprocal process, from B to A, with identical efficiency. Recent works have shown that in very high-Q ring resonators weak spatiotemporal modulation can create drastic non-reciprocity. In the first part of the talk I will show theoretically and experimentally that despite the typically low-Q of radiating and scattering systems, by a proper design that takes advantage of the light-cone natural filtering property, a weak and slow spatiotemporal modulation can exhibit also in these systems significant non-reciprocity, and even completely shut down the transmission or reception channels of an antenna. Possible applications are in radio frequency communication systems, nanophotonics, energy-harvesting and thermal management.
Non-reciprocity and broken time-reversal symmetry were also connected with classical analogs of topological insulators, using ferrites and time-modulation, but yet not nonlinearities. However before studying the physics of 2D or 3D nonlinear topological structures, the fundamental physics of the 1D case should be explored. To that end in the second part of the talk I will discuss the canonical Su-Schrieffer-Heeger (SSH) model, and show that the inclusion of suitable third-order Kerr nonlinearities in the model opens rich physics in topological insulators, including the possibility of supporting self-induced topological transitions based on the applied intensity. A new class of topological solutions will be introduced and discussed, as well as the conditions under which they are achieved, and their dynamics as a function of applied intensity.
Short Bio: Yakir Hadad received his B.Sc. and M.Sc. (both summa cum laude) in electrical and computer engineering from Ben-Gurion University in 2006 and 2008, respectively, and a Ph.D. in electrical engineering from Tel-Aviv University in 2014. Since then he is a post-doctoral fellow at the Metamaterials and Plasmonics group led by Prof. Andrea Alu in the University of Texas at Austin working on various applications of complex media, including time variant, and nonlinear. He is currently also a visiting researcher in FOM institute AMOLF, Amsterdam, working on the theory of ordered and disordered plasmonic distributed feedback lasers. His main research interests are wave phenomena in complex media, and analytical modelling in electrodynamics.
Thursday, January 21st, 2015, at 15:00
Room 011, Kitot building
