PT-symmetry in optics

We review quantum mechanical and optical pseudo-Hermitian systems with an emphasis on PT-symmetric systems important for optics and electrodynamics. One of the most interesting and much discussed consequences of PT symmetry is a phase transition under which the system eigenvalues lose their PT symmetry. We show that although this phase transition is difficult to realize experimentally, a similar transition can be observed in quasi-PT-symmetric systems. Other effects predicted for PT-symmetric systems are not specific for these systems and can be observed in ordinary fully passive systems.