Singular optical characteristics generated by Fibonacci multilayers composed of PT-symmetric elements

In this paper, a class of one-dimensional (1D) Fibonacci quasi-periodic multilayers composed of two parity-time-symmetric (PT-symmetric) elements are designed. Their scattering spectra, transparencies, invisibilities, and other singular optical properties are investigated in detail. It is found that three types of new systematic phases, ten types of new unidirectional transparencies, two types of new bidirectional transparencies and one type of new bidirectional invisibility are created by this class of interesting systems, which possess more types compared with the PT-symmetric periodic multilayers and the Thue–Morse multilayers composed of PT-symmetric elements. It can be seen that although the order degree of the Fibonacci multilayers is lower than that of the other two systems, their types of systematic phases, transparencies, and invisibilities are obtained, their types of systematic phases, transparencies, and invisibilities are more abundant. This proves that, as the order degree of the PT-symmetric system decreases, its types of singular optical properties become more abundant. This work sheds some light on the PT-symmetric optical structures and Fibonacci sequence, offering the possibility to widen their application field. Moreover, it provides a theoretical basis to design new optical devices.