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

Method for producing an anti-resonant hollow-core fiber comprising a hollow core, extending along a longitudinal axis of the fiber, and a sheath region surrounding the hollow core and comprising a number of anti-resonance elements, having the method steps of:

• (a) providing a primary preform for the hollow-core fiber, which preform has at least one cladding tube having a cladding tube wall, an inner cladding tube bore and a longitudinal cladding tube axis, along which the cladding tube wall delimited by an inner side and an outer side extends,
• (b) forming a number of precursors for anti-resonance elements at setpoint positions of the cladding tube wall, and
• (c) elongating the primary preform to form the hollow-core fiber or further processing the primary preform to form a secondary preform from which the hollow-core fiber is drawn, wherein the further processing comprises carrying out one or more of the following hot-forming processes once or repeatedly:
• (i) elongation,
• (ii) collapse,
• (iii) collapse and simultaneous elongation,
• (iv) collapse of additional sheath material,
• (v) collapse of additional sheath material and subsequent elongation,
• (vi) collapse of additional sheath material and simultaneous elongation,
• wherein the formation of the anti-resonance element precursors comprises the formation of elongated pressure chambers, which respectively adjoin, in the region of the setpoint positions of the anti-resonance elements, a deformable wall that can be deformed under pressure and heat, and which, when a process according to method step (c) is carried out, cause a bulge in a section of the deformable wall in the direction of the inner cladding tube bore as a result of pressure and heat, thereby forming an anti-resonance element or a precursor thereof.