Filippo Capolino,
University of California, Irvine, CA, USA

There are various kinds of degeneracies in electromagnetic systems and here we discuss an important
class of them: the case when two or more eigenstates of a system fully coalesce. Such degeneracies can
happen in circuits, resonators (i.e., coupled LC resonators, electromagnetic cavities, etc.), multimode
waveguides and even in quantum systems. This kind of degeneracy that involves the polarization states
can happen in a surprisingly large number of systems. Such degeneracies occur in systems that can be
fully passive or in systems that include gain elements; we discuss the common aspects of these two
classes.