ABSTRACT
There is significant interest in optical fibers whose cross sections contain more than one single-mode core. Optical fibers are normally spliced together by removing the coating, cleaving the fiber ends so that their end faces are flat and perpendicular to the fiber axis and butting them together in a V-groove. The near field refers to the field of a fiber or waveguide on the far end face in air. The far field of a fiber or waveguide is the field emerging from its far end into air as measured at a sufficiently large distance from the end face. For single-mode fibers and waveguides with relatively small core sizes of the order of a few wavelengths of the source light, the far field is diffracted at the end face. Waveguides and fibers are illuminated by a variety of sources, including lasers, LEDs, or light propagating out of another fiber or waveguide.
