Extrusion for micron-scale optical structures

The fabrication of photonic crystal fibres using the "stack-and-draw" method has become routine, most technical difficulties having been resolved, both for fused silica and soft glasses. The technique does, however, have its limits, being unsuitable for producing structures beyond simple symmetrical lattices (hexagonal, square, graphene-like, etc.) or membranes. Extrusion, widely used in industry, is much more suitable for producing structures with non-standard or asymmetrical geometries. In, the die material clearly must be able to withstand the temperatures needed to achieve the correct  glass viscosity, without contaminating the glass. The Glass Studio has an extrusion system with loading force up to 100 kN, temperature up to ~1100oC, and position control to ~1 μm stepping accuracy, with comprehensive data logging facilities (temperature, force, extrusion rate etc.). We have successfully developed techniques for extruding structures with many different geometries from tellurite, germanate and lead-silicate glasses. 

(a) Schematic of the extrusion system. (b) The extrusion unit is placed inside the furnace (the region within the green cylinder in (a)). Inset: photograph of an extrusion die manufactured by 3D printing. (c-e) Extrusion dies for X-shaped triple nanoweb fibre, multicore triple beam fibre, and single-ring fibre. (f-h) Scanning electron micrographs of fibres fabricated using extrusion dies depicted in (c-e).