We explore the characteristics of exceptional points of degeneracies (EPDs) in coupled waveguides. Second order EPDs are manifested when two modes coalesce, and we show how this can be associated with PT-symmetry. We also demonstrate fourth order EPDs that are manifested in periodic waveguides when four modes coalesce at the degenerate band edge (DBE). Moreover, we elucidate the impact of imperfect coupling, symmetry breaking or balancing gain and loss on the EPDs. Realization of EPDs in resonators can substantially enhance the slow-light characteristics, such as quality factors and local density of states for various applications including low-threshold lasers and sensors.
Mohamed A. K. Othman and Filippo Capolino, "Coupled waveguides with exceptional points of degeneracies
(Conference Presentation)," Proc. SPIE 9920, Active Photonic Materials VIII, 99201V (Presented at SPIE Nanoscience + Engineering: September 01, 2016; Published: 9 November 2016); https://doi.org/10.1117/12.2238428.5159519958001.
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