SE9901541D0 - A fused fiber coupler - Google Patents

Abstract

A fused optical fiber coupler comprises as conventional two or more optical fibers (1) fused to each other and thinned within a short segment. The fibers used have an extra doping of especially selected atoms such as nitrogen in the cores (11). When heating the segments to fusion them to each other, these extra dopant atoms have diffused out of the original core regions and have even been eliminated from the fibers reducing the refractive index of the cores. New cores are formed enclosing the former core regions, making the cores within the heated segments also wider. When pulling the fibers within the heated segments for thinning them these new cores are also being thinned. The redistribution of dopants changes the refractive index profile so that the modefields of light propagating in the segments will be wider than without any diffusion or releasing of dopant. The wider modefields give wider evanescent fields in the fused segments making light interact more easily in the segments, resulting in that the heated segments must not be drawn to such a large extent or to be as thin or narrow as conventional. This gives fused segments considerably thicker than the fused segments of a conventional fused coupler. Such an optical coupler can be more easily handled and is less subjected to breaks or ruptures. In particular, the optical coupler will have a greater fracture load, longer lifetime and a better temperature stability than conventional fused couplers.