Methods for producing a hollow-core fiber and for producing a preform for a hollow-core fiber

A method for producing an anti-resonant hollow-core fiber having a hollow core extending along a longitudinal axis of the hollow-core fiber and an inner sheath surrounding the hollow core, which inner sheath includes a plurality of anti-resonance elements, the method comprising the steps of:

• (a) providing a cladding tube having an inner bore and a longitudinal axis, along which a cladding tube wall delimited by an inner side and an outer side extends;
• (b) providing a plurality of tubular anti-resonance element preforms;
• (c) arranging the anti-resonance element preforms at desired positions of the inner side of the cladding tube wall to form a primary preform having an outer diameter in the range of 20 to 70 mm;
• (d) further processing of the primary preform into a secondary preform from which the hollow-core fiber is drawn, wherein the further processing includes elongating the primary preform and a single or repeated performance of one or more of the following hot-forming processes:
• (i) collapsing additional sheath material,
• (ii) collapsing additional sheath material and simultaneously elongating the primary preform, and
• (e) drawing the secondary preform to form the hollow-core fiber, wherein the secondary preform resulting from further processing of the primary preform according to step (d) has an outside diameter in the range of 20 to 70 mm,
• further comprising fixing and/or sealing using a sealing or bonding compound containing amorphous SiO2 particles to arrange the anti-resonance element preforms and/or elongate the primary preform and/or draw the hollow-core fiber, and
• wherein open ends of the anti-resonance element preforms and/or individual structural elements of the anti-resonance element preforms and/or any annular gap between tube elements of the anti-resonance element preforms are sealed by the sealing or bonding compound when the primary preform is elongated and/or when the hollow-core fibers are drawn.