A tapered core structure is written on the end of an optical fiber using a 3D-printing process. The tapered core may expand the mode diameter for improved coupling between fibers or may reduce the mode diameter to enhance coupling to a waveguide smaller than the fiber core. The written core is surrounded by a cladding. The diameter of the core is varied while it is being written, allowing a wide range of taper profiles to be implemented. The 3D-printing process is readily adapted to permit multiple fibers to have tapered cores written on their ends during the same process cycle.