In recent years, non-Hermitian degeneracies, also known as exceptional points (EPs), have emerged as a new paradigm for engineering the response of optical systems. At such points, an N-dimensional space can be represented by a single eigenvalue and a single eigenvector. As a result, these points are associated with abrupt phase transition in parameter space. Among many different non-conservative photonic configurations, parity-time (PT) symmetric systems are of particular interest since they provide a powerful platform to explore and consequently utilize the physics of exceptional points. In this talk, I will review some of our recent works in the area of non-Hermitian (mainly PT-symmetric) active photonics. For example, in a series of works, we have demonstrated how the generation and judicial utilization of these points in laser systems can result in unexpected dynamics, unusual linewidth behavior, and improved modal response¹. On the other hand, biasing a photonic system at an exceptional point can lead to orders of magnitude enhancement in sensitivity- an effect that may enable a new generation of ultrasensitive optical sensors on chip².

² H. Hodaei, M. A. Miri, M. Heinrich, D. N. Christodoulides, M. Khajavikhan, “Parity-time–symmetric microring lasers,” Science 346, 975 (2014)

² H. Hodaei, A. U. Hassan, S. Wittek, J. H. Garcia-Gracia, R. El-Ganainy, D. N. Christodoulides, M. Khajavikhan, “Enhanced sensitivity in photonic molecule systems using higher order non-Hermitian exceptional points,” Nature 548, 187 (2017)