Two-die assembly for the extrusion of glasses with dissimilar thermal properties for fibre optic preforms

Extrusion of a preform based on core and cladding glasses with different thermal properties is demonstrated. The core glass (50BaO–8B2O3–42P2O5) exhibits refractive index of 1.604 and softening temperature of 607 °C, while the cladding glass (70Ba(PO3)2–30B2O3) exhibits refractive index of 1.594 and softening temperature of 650 °C. Due to the softer nature of the core glass compared to the cladding glass, a novel two-die assembly method is employed for extrusion. The results show that the core glass flows through the cladding glass and be extruded first before stabilising to enable the extrusion of a cane of core and cladding glasses.