Double-sided unidirectional reflectivity

We study the effect of unidirectional reflectivity in the bilayer optical model with the balanced loss/gain terms. It was found that if the impedances characterizing the scattering part are different from those describing the leads, a new effect of double-sided unidirectional reflectivity emerges. In this case the vanishing of reflectivity occurs either for the left or right reflectivity, depending on the frequency of scattering wave. It is shown that the alternation of the unidirectional reflectivity from the left to the right can occur even if the corresponding Hamiltonian is non-PT-symmetric. Our analytical results are demonstrated by numerical data.