FIGS. 2, 2A and 2B are a front view, an end view and a schematic view showing a structure according to the present invention for coupling fiber element cores end-to-end with accuracy and with a tuning capability by providing a series of sleeves (claddings) for each coupled element, some of which sleeves (claddings) and the cores of which are eccentrically placed for rotation to a position of accur