The stack-and-draw technique has been highly useful for making PCFs for more than 25 years now. The technique involves manually stacking glass capillaries and rods of a few mm diameter to form the desired structure, before drawing the stack down to the desired microstructure. However, the approach is mostly useful for making structures with a hexagonal lattice. Stacking other structures often results in asymmetry imperfections and other undesired outcomes.
Recently, we were successful in securing funding from the highly selective Fraunhofer-Max-Planck cooperation funding program to explore another approach. In collaboration with two Fraunhofer institutes, we plan to use so-called inverse laser drilling to make preforms with structures that would be impossible to make using the traditional stack-and-draw technique, for example hollow-core structures with highly elliptical holes.