Multi-core fiber couplers (MCFC) provide access to individual cores with negligible optical loss and without an additional Fan-in/Fan-out (FIFO). Side-polished SMF and MCF are mated for an efficient evanescent mode coupling between two optical cores (Please also see the side-polished fiber). The side-polishing method allows the geometric dimensions of the multi-cores unperturbed. This unique approach makes it possible to realize various functions that ordinary directional couplers provide such as WDM, tap and variable-ratio couplers.