Mode division demultiplexer/multiplexer (MDDM) converts LP01 mode in single mode fibers (SMF) into desired higher order modes in a few mode fiber (FMF), and vice versa. Side-polished SMF and FMF half-couplers are mated for an efficient evanescent mode coupling between two optical fibers (Please also see side-polished fiber and mode selective coupler). The device demonstrates high coupling efficiency and mode extinction ratio over a wide wavelength range. Furthermore, this configuration provides a unique flexibility of starting with a 3-Mode MDDM and adding 3 more modes at a later time when needed. The MDDM is useful for mode division multiplexed communication systems or sensor systems.