PROPERTIES OF A MATCHED HALIDE GLASS PAIR FOR THE FABRICATION OF LARGE NUMERICAL APERTURE CORE-CLADDING PREFORM STRUCTURES

A large numerical aperture core-cladding structure is required for drawing single-mode fibers for the fabrication of Pr-doped 1.3 mu m optical fibre amplifiers. Geometrical restrictions on fibres and hence on preforms are important for confining the optical pump power into a small core volume (3-5 mu m diameter) in order to promote efficient amplification at 1.3 mu m Cadmium mixed halide glasses exhibiting lower phonon energies than the standard fluorozirconate compositions have been designed, and their optical and thermal properties are reported. The refractive indices of core and cladding glasses have been measured as a function of wavelength in the visible region and their values have been extrapolated to the signal and pump wavelengths. The mismatch stresses in the core-cladding structure at room temperature have been estimated from the measured expansion coefficient data.