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

Patent metadata

Field	Value
Publication number	US-11940648-B2
Application number	US-202017623783-A
Country	US
Kind code	B2
Filing date	Jul 15, 2020
Priority date	Jul 17, 2019
Publication date	Mar 26, 2024
Grant date	Mar 26, 2024

Abstract

Methods are known for producing an anti-resonant hollow-core fiber which has a hollow core extending along a fiber longitudinal axis and an inner jacket region that surrounds the hollow core, said jacket region comprising multiple anti-resonant elements. The known methods have the steps of: providing a cladding tube that has a cladding tube inner bore and a cladding tube longitudinal axis along which a cladding tube wall extends that is delimited by an interior and an exterior; providing a number of tubular anti-resonant element preforms; arranging the anti-resonant element preforms at target positions of the interior of the cladding tube wall, thereby forming a primary preform which has a hollow core region and an inner jacket region; further processing the primary preform in order to form a secondary preform, including an elongation process; and drawing the secondary preform in order to form the hollow-core fiber. The aim of the invention is to achieve a high degree of precision and an exact positioning of the anti-resonant elements in a sufficiently stable and reproducible manner on the basis of the aforementioned methods. This is achieved in that after the primary preform is elongated, at least some of the formerly tubular anti-resonant element preforms of the primary preform have an oval outer cross-sectional shape with a longest cross-sectional axis A L and a shortest cross-sectional axis A K , wherein the ratio A L /A K of the length of the axes ranges from 1.01 to 1.27, and the shortest cross-sectional axis A K runs in a radial direction when viewed from the cladding tube longitudinal axis.

First claim

The invention claimed is:

1. Method for producing 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 of the primary preform to form a secondary preform from which the hollow-core fiber is drawn, 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
(e) drawing the secondary preform to form the hollow-core fiber,
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 A L and a shortest cross-sectional axis A K , wherein the axis length ratio A L /A K is in the range between 1.01 and 1.27, and wherein the shortest cross-sectional axis A K extends in the radial direction when viewed from the longitudinal axis of the cladding tube.

2. Method according to claim 1 , characterized in that at least a portion of the tubular anti-resonance element preforms is composed of several nested structural elements and comprises at least one ARE outer tube and an ARE inner tube running in the ARE outer tube and in parallel to the longitudinal axis of the ARE outer tube, wherein the ARE outer tube has an oval, preferably elliptical, outer cross-sectional shape with the axis length ratio A L /A K in the range between 1.07 and 1.27, and the ARE inner tube has an oval, preferably elliptical, outer cross-sectional shape with the axis length ratio A L /A K in the range between 1.01 and 1.05.

3. Method according to claim 1 , characterized in that the primary preform has an outer diameter in the range of 20 to 70 mm.

4. Method according to claim 1 , characterized in that, during elongation, the primary preform is continuously supplied to a heating zone at a feed rate, softened zone by zone in the heating zone, and removed from the heating zone at a removal rate, wherein the feed rate is set so as to result in a throughput of at least 0.8 g/m in, preferably a throughput in the range from 0.8 g/min to 85 g/min, and particularly preferably a throughput in the range of 3.3 g/min to 85 g/min, and an average dwell time in the heating zone of less than 25 min, preferably an average dwell time in the range of 5 to 25 min.

5. Method according to claim 1 , characterized in that the draw-down ratio during elongation is set to a value in the range of 1.05 to 10, preferably 1.05 to 5.

6. Method according to claim 1 , characterized in that a temperature-controlled heating zone is used for elongating the primary preform, the desired temperature of which is kept with an accuracy of +/−0.1° C.

7. Method according to claim 1 , characterized in that the fixing of the anti-resonance element preforms takes place using a sealing or bonding compound containing amorphous SiO 2 particles.

8. Method according to claim 1 , characterized in that 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 are sealed by means of a sealing or bonding compound when the primary preform is elongated.

9. Method according to claim 1 , characterized in that the inner side of the cladding tube is provided with a longitudinal structure extending in the direction of the longitudinal axis of the cladding tube by machining in the region of the desired positions.

10. Method according to claim 1 , characterized in that the anti-resonance element preforms are positioned at the desired position by means of a positioning template.

11. Method according to claim 10 , characterized in that the positioning template is used in the region of a cladding tube end face, preferably in the region of both cladding tube end faces.

12. Method according to claim 1 , characterized in that, when the primary preform is elongated in accordance with method step (d) and/or when the hollow-core fiber is drawn in accordance with method step (e), several components of the preform made of quartz glass are heated together and softened, wherein the quartz glass of at least some of the preform components contains at least one dopant that lowers the viscosity of quartz glass.

13. Method according to claim 12 , characterized in that additional sheath material is collapsed in accordance with method step (d), and in that the quartz glass of the cladding tube at a measured temperature of 1250° C. has a viscosity at least 0.5 dPa·s higher, preferably a viscosity at least 0.6 dPa·s higher, than the quartz glass of the additionally applied sheath material (if the viscosity is given as a logarithmic value in dPa·).

14. Method according to claim 1 , characterized in that the arrangement of the anti-resonance element preforms at desired positions of the inner side of the cladding tube wall and/or the drawing of the hollow-core fiber in accordance with method step (d) comprises a fixing measure and/or a sealing measure using a sealing or bonding compound containing amorphous SiO 2 particles.

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 A L and a shortest cross-sectional axis A K , wherein the axis l

Assignees

• Heraeus Quarzglas

Inventors

• Rosenberger Manuel
• Hünermann Michael
• Trommer Martin
• Schuster Kay
• Weimann Steffen

Classifications

• G02B6/02328

  Hollow or gas filled core · CPC title

• G02B6/032 Primary

  with non solid core or cladding {(G02B6/02295 takes precedence)} · CPC title

• C03B37/0122

  for making preforms of photonic crystal, microstructured or holey optical fibres · CPC title

• C03B37/01245

  by drawing and collapsing · CPC title

• C03B37/02781 Primary

  Hollow fibres, e.g. holey fibres · CPC title