Systems that become PT symmetric through interaction

In this article, we consider an interesting class of optical and other systems in which the interaction or coupling makes the systems PT symmetric. We aim to compare their dynamical behaviors with that of the usual PT-symmetric systems with intrinsic loss-gain terms. In particular, we focus on the interesting nonreciprocal nature of the PT-symmetric systems which has a promising application in optical diodes and optical isolators. We check whether the nonreciprocal nature is common to all PT-symmetric systems and, if not, what are the situations under which it can be observed. Due to the recent interest in studying spontaneous symmetry breaking in coupled waveguide systems, we here present such symmetry-breaking bifurcations in certain reciprocal and nonreciprocal PT-symmetric systems.