▎ 摘　　要

We propose and design an ultra-compact and broadband tunable 1 x 2 multimode interferometer (MMI) in mid-infrared based on a dielectric-loaded graphene plasmonic waveguide. This waveguide has extremely large modal effective indexes and modal effective index contrast, which can shrink the size of MMI greatly. The size of the 1 x 2 MMI is only 0.56 mu m x 1.2 mu m, which corresponds to the device area of only similar to 0.014 lambda(2), where. is the vacuum wavelength. In addition, the central wavelength of the device can be tuned in a broadband from 7 to 9 mu m with the Fermi level of graphene varied from 0.5 to 1eV. Furthermore, the device is easy to be fabricated on a whole graphene layer without the need to etch graphene.