▎ 摘　　要

In this study, we investigated the optical bistability (OB) properties of transmitted weak probe light from a defect dielectric medium doped by four-level graphene nanostructure. By using the transform matrix and density matrix methods, we explore the features of transmitted light versus incident light for studying the OB behaviors in a defect slab. Our numerical results show that the threshold of OB in multipoint of incident light can be easily manipulated by some controllable parameters such as Rabi-frequencies of applied fields and optical thickness of the slab. Moreover, we find that the group velocity of transmitted pulse from the defect slab can be adjusted by tuning the optical thickness of the slab. We hope that our study may be suitable for the future all-optical based devices in Nano sizes. (C) 2016 Elsevier GmbH. All rights reserved.