Methods and systems for producing hollow-core preforms, components thereof, and hollow-core optical fibers

A die assembly for making a hollow-core optical fiber preform or a component thereof via extrusion, wherein the hollow-core preform or the component thereof comprises an outer tube and an inner tube, wherein an outer surface of the inner tube contacts an inner surface of the outer tube, the die assembly comprising:

• a first insert comprising a first plate having a plurality of first openings and a mandrel extending from the first plate;
• a second insert comprising a second plate having a plurality of second openings, a column extending from the second plate, and a channel extending through the second plate and the column and configured for receiving therein the mandrel of the first insert while maintaining a first annular gap around the mandrel of the first insert;
• and
• a shell configured for receiving therein the first insert and the second insert and having a first cavity portion and a second cavity portion, wherein the second cavity portion includes a diameter less than a diameter of the first cavity portion, and wherein the second cavity portion is configured to receive therein at least a portion of the column of the second insert whiling maintaining a second annular gap around the column;
• wherein the first insert, the second insert, and the shell are configured such that when the die assembly is in an assembled state and in use, a first material portion extruded from the first annular gap and a second material portion extruded from the second annular gap are coupled upon extrusion from the die assembly.