“…In order to fully utilize the higher order modes (HOM) in FMF, devices are required to control the modes guided in the fiber including excitation, separation and controlled coupling of individual guided modes in a single strand of FMF [12,13]. In addition to some of the early works such as mode selective coupler [13][14][15][16][17] and long period grating [18,19], various techniques have been reported on the basis of holographic filter, phase plate, photonic lantern and integrated circuit [20][21][22][23][24]. We recently reported an all-fiber MDM based on cascaded mode selective couplers (MSC's) for a fiber that supports four spatial modes (LP 01 , LP 11 , LP 21 , and LP 02 ) [25].…”