CHARACTERIZATION OF FLUORIDE GLASSES FOR SINGLE-MODE OPTICAL FIBERS WITH LARGE REFRACTIVE-INDEX DIFFERENCE

In order to obtain fluoride glass optical fibers with large refractive index difference between the core and the cladding, refractive indices and viscosities of PbF2-doped core glasses and HfF4-incorporated cladding glasses were systematically investigated. From the point of view of viscosity matching, it was found that the 9 mol% PbF2-doped core glass containing 14 mol% NaF was the most adequate choice in combination with the 43 mol% HfF4-incorporated cladding glass containing 22 mol% NaF. Using a casting method, single-mode fluoride glass fibers with relative refractive index difference of 2.9% were successfully fabricated.