Refractive Index Dispersion in Ternary Germanate Glasses

The refractive index dispersion in germanate oxyfluoride glasses of GeO 2 -P 2 O 5 -MF 2 (M=Ca, Zn), which are developed for optical fiber application, is investigated in the 0.4-4 µ m wavelength range by the minimum deviation method. The prepared glasses have a GeO 2 content varying from 80 to 30 mol%. The dispersion curves for these glasses tend to shift to shorter wavelengths as the GeO 2 content is decreased. Material dispersions are also derived from the refractive index measurements and the zero-material dispersion wavelengths (λ 0 ) are found in the vicinity of 1.5 µ m. On the basis of the empirical relationship between λ 0 and the minimum loss wavelength (λ 0 ), the λ min values are located at around 1.8 µ m. A minimum loss of as low as 0.08 dB/km is expected for the present germanate glasses.