Extraordinary optical characteristics in a one-dimensional parity-time symmetric structure of quasiperiodic two-material Octonacci optical waveguide network

We explore Exceptional Points (EPs) within a one-dimensional quasiperiodic Octonacci optical waveguide network. This network consists of segments, each composed of two-material subsegments featuring gain and loss materials, creating a parity-time-symmetric structure. We investigate the trend of EPs across generations 3 to 7 of the Octonacci sequence using the generalized eigenfunction method and transfer matrix method. Our findings reveal that as generations progress, band gaps become more pronounced, and the number of EPs significantly increases within these gaps. In particular, the third generation only supports unidirectional transparency. Bidirectional transparency appears in the fourth generation and becomes more pronounced in later generations. Coherent perfect absorption-lasing points are first seen in the seventh generation. These findings have implications for the design of all-optical devices and wideband and/or narrowband optical filters.