Optical structures with local { PT} -symmetry

We propose a new class of optical synthetic materials that are described by non-Hermitian Hamiltonians. The building blocks of such systems are coupled -symmetric elements (dimers), with coupling t . Despite the lack of global -symmetry, these systems have a robust parameter region of real spectra (exact phase) even in cases where the complex refractive index n = β + iγ of each dimer is random. The validity of our proposition is confirmed for representative cases where we calculate the borders of the exact phase in terms of β, γ and t .