The Scattering Problem in PT-Symmetric Periodic Structures of 1D Two-Material Waveguide Networks

A PT-symmetric periodic structure with two-material waveguide networks is constructed. In this study, how changing the number of cells affects the transmission properties is investigated. The results show that the PT-unbroken (broken) region of the system is only determined by the cell structure, regardless of the number of unit cells. This means that any system has the same exceptional points (EPs), regardless of the number of cells and as long as the cell structure is consistent. In addition, it is confirmed that the coherent perfect absorbers and lasers (CPA lasers) occur in our model. The transfer matrix method is used to derive a sufficient condition for achieving the CPA laser point. A simple, effective formula for predicting the CPA laser state in an N unit cell system is derived.