Method of manufacturing a preform of an antiresonant hollow core fibre

A method (700) for producing a preform of an anti-resonant hollow-core fiber, which has a hollow core extending along a fiber longitudinal axis, and a cladding region, which surrounds the hollow core and which comprises at least one anti-resonance element, at least having the method steps of

• (a) providing (710) a cladding tube (200) comprising a cladding tube inner surface and a cladding tube outer surface (210), wherein at least one anti-resonance element preform (400) is arranged at the cladding tube inner surface,
• (b) providing (720) an overlay tube (300) comprising an overlay tube inner surface (310), wherein the overlay tube (300) has an inner diameter, which is larger than an outer diameter of the cladding tube (200),
• (c) arranging (730) the cladding tube (200) inside the overlay tube (300), so that the overlay tube inner surface (310) surrounds the cladding tube outer surface (210),
• (d) adding (740) the overlay tube (300) to the cladding tube (200), so that the overlay tube inner surface (310) connects to the cladding tube outer surface (210),
• wherein a first negative pressure P1 is applied between overlay tube inner surface (310) and cladding tube outer surface (210), and a second negative pressure P2 is applied inside the cladding tube (200) during the adding (740) in method step (d), and
• wherein prior to method step (d), the cladding tube (200) is closed in a gas-impermeable manner at a first cladding tube end (230), and in some regions, the overlay tube inner surface (310) is connected in a gas-impermeable manner to the cladding tube outer surface (210) at a second cladding tube end (235).