Patent ID: 11940648
Assignee: HERAEUS QUARZGLAS GMBH & CO. KG
Field: Other special machines (Mechanical engineering)
Classification: CPC C  G | IPC C  G

Claim 14:
15. Method for producing a preform for an anti-resonant hollow-core fiber comprising a hollow core extending along a longitudinal axis of the fiber and an inner sheath region surrounding the hollow core, which sheath region comprises several anti-resonance elements, comprising the method steps of:
(a) providing a cladding tube comprising an inner bore of the cladding tube and a longitudinal axis of the cladding tube, along which a cladding tube wall delimited by an inner side and an outer side extends,
(b) providing a number 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, which comprises a hollow core region and an inner sheath region,
(d) further processing the primary preform to form a secondary preform for the hollow-core fiber, wherein the further processing comprises an elongation and optionally a single or repeated performance of one or more of the following hot-forming processes:
(i) collapse,
(ii) collapse and simultaneous elongation,
(iii) collapse of additional sheath material,
(iv) collapse of additional sheath material and subsequent elongation,
(v) collapse of additional sheath material and simultaneous elongation, and
characterized in that, after elongation in accordance with method step (d), at least a portion of the former tubular anti-resonance element preforms of the primary preform has an oval outer cross-sectional shape, with a longest cross-sectional axis AL and a shortest cross-sectional axis AK, wherein the axis length ratio AL/AK is in the range between 1.01 and 1.27, and wherein the shortest cross-sectional axis AK extends in the radial direction when viewed from the longitudinal axis of the cladding tube.