In recent years, graphene plasmonics has been one the most promising debated topics among scientists in the THz and nanoelectronic sciences. The conductivity of graphene can be tuned via electrostatic bias, chemical doping, and magnetostatic bias, which can generate dynamic modulation and active control over Surface Plasmon Polaritons (SPPs) to design and fabricate innovative devices in the mid-infrared region, such as polarizers, waveguides, filters, and sensors. This paper briefly reviews of graphene-based nano-couplers, which can be divided into four categories: directional couplers, non-reciprocal couplers, planar couplers, and nano-ribbon couplers. The first category, i.e. directional coupler, is a basis device in a photonic circuit, in which the energy of SPPs is coupled between two adjacent waveguides. A non-reciprocal coupler consists of graphene layers with electric and magnetic biases. The planar coupler is the simplest structure among all these couplers, constituting two graphene layers separated by a dielectric. The fourth category is similar to the dielectric coupler, however, graphene sheets in these structures have a finite width. For all of these mentioned categories, we will introduce the configuration and investigate their potential applications in absorber radar systems.