▎ 摘　　要

In this paper, the figure of merit (FOM) of a surface plasmon resonance (SPR) biosensor based on gold-graphene structure is studied in the visible and near infrared region. As the wavelength of incident light increases, the FOM of the proposed SPR biosensor with different number of graphene layers increases firstly and then decreases, indicating an optimal wavelength for realizing the largest FOM (called peak FOM). For the proposed SPR biosensor with monolayer graphene, the peak FOM that shows at 890 nm is up to 33.05 RIU-1, which is 133% higher than the FOM (14.17 RIU-1) at 630 nm (near a common-used wavelength 633 nm). In addition, the effect of dispersion of graphene on the performance of the proposed biosensor is also analyzed. With the increase of the number of graphene layers, the peak FOM of the proposed biosensor decreases, but the optimal wavelength remains unchanged. Furthermore, the origin of FOM enhancement at optimal wavelength is determined by analyzing the electric field intensity inside the proposed SPR biosensor. Besides, the performances of SPR biosensors with different prism and metal are compared. It is believed that the FOM of a graphene based SPR biosensor can be enhanced by optimizing the wavelength of incident light and the number of graphene layers.