Topological photonics is a rapid developing field, drawing inspirations from the recent successes in electronic systems. Yet, there are two major differences between photons and electrons: (1) photons obey Maxwell’s equations, which permit nonlinearities, whereas the Schrodinger equation is always linear; (2) photons are bosons, which allows one to probe responses at virtually any desired energy (frequency) without the limitation of the Fermi energy as in electrons. Based on these differences, I will present our recent theoretical and experimental results in exploring the role of optical nonlinearity in topological physics. On the theory side, these include defining topological invariants in driven nonlinear photonic crystals [1] and identifying various topological phases, such as the Floquet Chern insulators [1], dipole phases [2], and quadrupole phases [3,4]. On the experiment side, I will present our recent results towards observing Floquet Chern insulators, protecting out-of-plane photon radiation losses using topology [5] and their applications as grating couplers [6]. Finally, I will present an outlook for potential opportunities in science and technology such as night-vision goggles.
[1] Nature Communications 10, 4194 (2019)
[2] Physical Review Letters 126, 113901 (2021)
[3] Nature Communications 11, 3119 (2020)
[4] arXiv:2103.01198
[5] Nature 574, 501 (2019)
[6] Nature 580, 467 (2020)
Bio: Bo Zhen received his B.S. degrees in Mathematics and Physics from Tsinghua University in 2008 and his Ph.D. degree in Physics from MIT in 2014. After a joint postdoc between MIT and Technion, he started his own group in January 2018 at the Department of Physics and Astronomy in the University of Pennsylvania.