Abstract: A process for fusion joining the ends of optical fibers includes aligning the ends of the two fiber cores to be joined facing each other such that at least one of the ends is free to be displaced laterally and there is no axial force between the two ends. The ends of the fibers are heated by producing a heat field with a predetermined distribution, for a predetermined period until attenuation of light transmitted through the fused joint increases, so as to cause partial fusion of the cores while maintaining sheathing of the fibers intact. A device for fusion splicing the two ends includes two opposed fiber supports for maintaining the end portions of the optical fibers to be fusion spliced in an approximately aligned position, the supports being slidable along the axes of the fibers being mounted on said supports such that their ends are free to move laterally.