Prof. Zheng Wang
Massachusetts Institute of Technology
Photonic crystals are artificial optical media with periodic subwavelength structures, well known for the photonic bandgap that prohibits the propagation of light. Recent theoretical and experimental studies have shown that magnetized photonic crystals support a unique class of photonic modes selectively prohibiting the backward propagation of light, resulting in the complete suppression of backscattering even in the presence of large disorder. These modes are known as “chiral edge states”, after the optical analogy to electronics edge states in the integer quantum Hall effect, and exist at the surface of certain magnetized photonic crystals at bandgap frequencies. These modes travel only in one direction and allow the formation of one-way waveguides without any backward propagating mode, thereby incapable of backscattering. Their unique transport property is a consequence of nontrivial topological properties of the bulk band structure. We have implemented a waveguide that supports these one-way modes, using a square photonic lattice of magnetized ferrite rods. At microwave operating frequencies, the waveguide exhibits strongly non-reciprocal propagation, with measured forward and backward transmission differing by up to 50 dB, even in the presence of very large obstacles, thus providing experimental evidence for non-zero topological Chern numbers in a photonic system. The application of photonic chiral edge states in slow-light systems and potential implementations at optical frequencies will also be discussed.
Zheng Wang is a Research Scientist at the Research Laboratory of Electronics at MIT. He received a B.S. degree in physics from University of Science and Technology of China in 2000. He earned his Ph.D. degree in applied physics from Stanford University in 2006. His main research interests include novel electromagnetic effects in periodic and subwavelength materials, nanophotonics, and multimaterial microstructured fibers. His work on topological photonic states and piezoelectric fibers has been featured on media outlets including Economist and ABC news. He is a co-author of 24 peer-reviewed journal articles and holds 2 US patents.