Method for producing a preform of an anti-resonant hollow-core fiber
A method for producing a preform of an anti-resonant hollow-core fiber, comprising the method steps of a) providing a cladding tube, which has a cladding tube inner bore and a cladding tube longitudinal axis, along which a cladding tube wall extends, which is limited by an inner side and an outer side b) preparing a number of anti-resonance element preforms, which consist of several nested tubular structural elements, comprising an ARE outer tube and an ARE inner tube inserted therein, wherein the structural elements have a structural element longitudinal axis, c) arranging the anti-resonance element preforms on the inner side of the cladding tube wall, and d) thermal fixing of the anti-resonance element preforms to the cladding tube wall by means of heat input.
1. A method for producing a preform of an anti-resonant hollow-core fiber, comprising the method steps of
a) providing a cladding tube, which has a cladding tube inner bore and a cladding tube longitudinal axis, along which a cladding tube wall extends, which is limited by an inner side and an outer side,
b) preparing a number of anti-resonance element preforms formed by nested tubular structural elements including an ARE outer tube and an ARE inner tube inserted therein, wherein the structural elements have a structural element longitudinal axis,
c) arranging the anti-resonance element preforms on the inner side of the cladding tube wall, and
d) thermal fixing of the anti-resonance element preforms to the cladding tube wall by means of heat input,
wherein—the method has the step of
e) introducing a contact element each into at least one anti-resonance element preform in such a way that the contact element increases the heat-absorbing mass of the anti-resonance element preform in step d), in order to slow down a heat flow from the cladding tube into the anti-resonance element preform during the thermal fixing,
wherein the contact element is designed in such a way that what applies is
C_cladding tube>C_contact element>C_anti-resonance element preform, wherein
C_cladding tube is a heat capacity of the solid material of the cladding tube, averaged over a unit volume,
C_contact element is a heat capacity of the contact element and of the ambient air, averaged over the unit volume,
C_anti-resonance element preform is a heat capacity of the anti-resonance element preform and of the ambient air, averaged over the unit volume,
and the unit volume is 25% by volume larger than a volume of the contact element.
2. The method according to claim 1 , wherein step e) comprises the sequential steps of:
/A-1./ connecting the contact element to the anti-resonance element preform,
/A-2./ connecting the anti-resonance element preform to the cladding tube.
3. The method according to claim 1 , wherein step e) comprises the sequential steps of:
/B-1./ heat input to an assembly including the anti-resonance element preform and contact element,
/B-2./ first connecting of the contact element to the anti-resonance element preform by means of a first portion of the heat input,
/B-3./ second connecting of the anti-resonance element preform to the cladding tube by means of a second portion of the heat input.
4. The method according to claim 1 , wherein the thermal fixing in step d) takes place by means of a flame-based process.
5. The method according to claim 1 , wherein the contact element is designed in a rod-like manner so that the contact element has a length of [5; 50] mm and has a diameter of [0.5; 10] mm.
6. The method according to claim 1 , wherein the contact element is introduced into the ARE outer tube of the at least one anti-resonance element preform.
7. The method according to claim 1 , wherein the contact element is introduced into the ARE inner tube of the at least one anti-resonance element preform.
8. The method according to claim 1 , wherein the arranging of the anti-resonance element preforms on the inner side of the cladding tube inner bore comprises an arranging of the anti-resonance element preforms at target positions of the inner side of the cladding tube wall, wherein the arranging of the anti-resonance element preforms takes place by means of a positioning template, which is to be inserted into the cladding tube inner bore, and which has holding elements for positioning the anti-resonance element preforms at the target positions.
9. The method according to claim 1 , wherein the cladding tube inner bore is created by means of machining.
10. The method according to claim 1 , wherein the cladding tube has an outer diameter in the range of 65 to 300 mm.
11. The method according to claim 1 , wherein the method has a step of:
creating a cladding tube closure by means of an at least partial closing of a front-side end of the cladding tube inner bore.
12. A method for producing a secondary preform, from which a hollow-core fiber can be drawn, from a preform, produced according to claim 1 , having the step of
further processing the preform into the secondary preform,
wherein the further processing comprises a one-time or repeated performance of one or more of the following hot-forming processes:
i.) elongating,
ii.) collapsing,
iii.) collapsing and simultaneous elongating,
iv.) adding additional cladding material,
v.) adding additional cladding material and subsequent elongating,
vi.) adding additional cladding material and simultaneous elongating.
13. A method for producing an anti-resonant hollow-core fiber from a preform, produced according to claim 1 , having the step of
further processing the preform into the anti-resonant hollow-core fiber,
wherein the further processing comprises a one-time or repeated performance of one or more of the following hot-forming processes:
i.) elongating,
ii.) collapsing,
iii.) collapsing and simultaneous elongating,
iv.) adding additional cladding material,
v.) adding additional cladding material and subsequent elongating,
vi.) adding additional cladding material and simultaneous elongating.
14. A method for producing a secondary preform, from which a hollow-core fiber can be drawn, from a preform, produced according to claim 1 , having the step of
further processing the preform into the secondary preform,
wherein the further processing comprises a one-time or repeated performance of one or more of the following hot-forming processes:
i.) elongating,
ii.) collapsing and simultaneous elongating,
iii.) adding additional cladding material and subsequent elongating,
iv.) adding additional cladding material and simultaneous elongating.
15. The method according to claim 14 , wherein a relative inner pressure in the range of between 0.05 mbar-20 mbar is set during the elongating in the core region.