In photonic integrated circuits,information is usually encoded in the optical path.In this work,based on the multi-mode dielectric-loaded surface plasmon polariton waveguide,we numerically design a directional coupler,which can divide the different waveguide eigenmodes into different optical paths.The results show a possibility to encode information onto different waveguide modes.We also experimentally demonstrate that the splitting ratio of this directional coupler structure can be tuned without changing its size.