▎ 摘　　要

Optical bistability effect is investigated in a complex system composed of graphene and Thue-Morse photonic crystals (PCs). The Thue-Morse PCs submitted to parity-time-symmetry (PT-symmetry) are stacked alternatively with two dielectric slabs according to Thue-Morse sequence. Optical fractal states and the exceptional points (EPs) induced by the Thue-Morse PCs could greatly localize the electric fields. The optical third-order nonlinear effect of graphene has been enhanced by the strong local electric fields and subsequently, low-threshold optical bistability is achieved. The EPs splitting and the thresholds of optical bistability can be further decreased by modulating the gain-loss factor of dielectrics in the PT-symmetry. Otherwise, the optical bistable performance could be improved by the chemical potential of graphene as well. The study may have potential applications in all-optical switches.