Optical fiber loss reduction

With the introduction of optical fiber amplifiers, numerous experiments on long-haul and large-capacity transmissions at 1.55-μm band have been done. To realize high-grade transmission systems, further reduction of optical fiber losses is necessary. In reduction of optical fiber losses, Rayleigh scattering loss, infrared absorption loss, and losses due to imperfections should be further reduced. Among these, Rayleigh scattering and infrared absorption losses are fixed by the used dopants. On the other hand, losses due to imperfections depend not only on the fabrication process but also on the viscosity properties of the core and cladding materials. To reduce loss due to imperfections, the viscosity matching of core and cladding materials is quite effective. This type of viscosity-matching technique, unexplored until now, will be clarified by the authors. The method of viscosity matching over the fiber cross section is first presented; then the viscosity characteristics of silica glasses doped with GeO2, F, or codoped with GeO2 and F together with their Rayleigh scattering behavior are experimentally clarified. Finally, the loss behavior of fabricated viscosity-matched fibers is described and the effectiveness of the matching technique is demonstrated.