A method of manufacturing a preform, the method including positioning at least one glass tube in a glass outer cladding to form a preform precursor, the glass tube comprising a first open end and a second open end, forming a preform from the preform precursor, and thermally treating at least one of the preform precursor and the preform. The thermally treating including sealing the first open end and the second open end of the glass tube to form a closed tube and heating and/or cooling the glass tube to manipulate gas pressure within the closed glass tube.

A method for producing a preform for an anti-resonant hollow-core fiber which comprises a hollow core extending along a longitudinal axis of the fiber and a sheath that surrounds the hollow core and through which hollow channels pass.

In a known method for fabricating a preform for an antiresonant hollow-core fiber with an ALIF design, tubular antiresonance element preforms (ARE preforms for short), that each comprise a primary tube and at least two secondary tubes, are evenly distributed around the inside of a cladding tube to form a primary preform. The primary preform is either drawn into a hollow-core fiber or further processed into a secondary preform.

A method of manufacturing a preform for a hollow core optical fiber including: a redraw step including: (1) heating a workpiece including: (a) a cladding tube including (i) a cladding interior, (ii) a cladding outer surface at a cladding outer radius, and (iii) a cladding thickness; and (b) a capillary disposed within the cladding interior, the capillary including (i) a capillary interior, (ii) a capillary outer radius, (iii) a capillary inner radius, (iv) a capillary thickness, and (v) a capillary aspect ratio corresponding to the ratio of the capillary inner radius to the capillary outer radius, and (2) manipulating a gas pressure within the capillary interior or the cladding interior, via a source of gas or a vacuum, to vary the aspect ratio of the capillary. Both the cladding outer radius and the cladding thickness change during the redraw step by less than 20%.