Multimode fiber (MMF) has become an ideal medium to realize the short distance communication of “the last kilometer”. But the severe mode dispersion of the MMF limits its transmission ability. Mode group diversity multiplexing (MGDM) is an optical multiple-input multiple-output (MIMO) technique that aims at creating independent communication channels over a MMF and using subsets of propagating modes. This technique enables to carry a number of signals and greatly enhances the transmission capacity of the MMF. A 2-input 2-output direct detection MGDM communication system over 75 m graded-index multimode fiber (GI-MMF) is designed. The excitation of different mode groups is realized by using selective mode excitation. The multiplexing and demultiplexing are realized by offset connectors and mode couplers. The transmission of an analog video signal and a non-return-to-zero (NRZ) digital signal is demonstrated with this system.