General Conditions to Realize Exceptional Points of Degeneracy and Applications

We explore the emergence of exceptional points of degeneracy (EPDs) that denote a coalescence of multiple eigenmodes in coupled-mode structures. We establish the general conditions that lead to observing EPDs of different orders in various coupled systems, either uniform (non-periodic) or periodic. EPDs can be found in lossless systems as well as in systems with gain-loss balance. Also, we provide examples of potential applications of structures with EPDs that help improve the performance of devices, like sensors, oscillators, etc., at microwave and optical frequencies.