Method for manufacturing an Anti-resonant hollow-core fiber

Abstract

To provide a method for manufacturing an anti-resonant hollow core fiber with less deformation of an anti-resonant unit.SOLUTION: A method of manufacturing an anti-resonant hollow-core fiber having an outer diameter of less than 500 μ m, comprising the steps of providing a sheath tube 200, preparing a number of anti-resonant units 300 each comprising an ARU outer tube, introducing at least part of the anti-resonant units into the sheath tube inner bore, making a hollow-core assembly 400 comprising the sheath tube and the anti-resonant units by at least partially connecting the anti-resonant units to the sheath tube inner surface, preparing a jacket tube 500, introducing at least part of the hollow-core assembly into the jacket tube inner bore, and drawing the hollow-core fiber from the jacket tube and the hollow-core assembly by a hot-forming process.SELECTED DRAWING: Figure 4

Description

[Technical Field]

[0001] The present invention relates to a method for fabricating an anti-resonant hollow-core fiber. [Background technology]

[0002] Hollow-core fibers have a core with a vacuum cavity filled with a gas or liquid. In hollow-core fibers, the interaction of light with the glass is smaller than in solid-core fibers. Because the refractive index of the core is smaller than that of the surrounding cladding, light transmission by total internal reflection is not possible. Depending on the physical mechanism of light transmission, hollow-core fibers are divided into "photonic bandgap fibers" and "anti-resonant reflecting fibers."

[0003] In an embodiment of a hollow-core fiber called an "anti-resonant hollow-core fiber" (ARHCF), the hollow core region is surrounded by an inner cladding region within which are located what are known as anti-resonant units (also known as "anti-resonant elements" or "ARUs"). The walls of the anti-resonant units, evenly distributed around the hollow core, can act as Fabry-Perot cavities operating at anti-resonance, thereby reflecting incident light and thus enabling waveguiding within the fiber core.

[0004] This technology promises hollow-core fibers with low optical attenuation, a very wide transmission spectrum (even in the UV or IR wavelength range), and low latency during data transmission.

[0005] From WO 2022 157179 A1, an anti-resonant hollow-core fiber is known in which the hollow core is surrounded by an inner cladding with anti-resonant units, which have an outer ARU tube and an inner ARU tube introduced therein.

[0006] WO 2018 / 169487 A1 discloses a method for manufacturing a preform for a hollow-core fiber, in which a first casing region has a plurality of rods and a second casing region has a plurality of tubes surrounded by an outer sheath tube, and the rods, tubes, and sheath tube are joined by a "stack and draw" technique to form the preform.

[0007] The publication "Hollow-Core Fiber Technology: The Rising of Gas Photonics" by Benoit Debord (Fibers, 2019, 7, 16) presents a model that can simulate tubular antiresonant hollow-core fiber drawing and predict the fiber drawing parameters and geometry. (Problem to be solved by the invention)

[0008] For industrial applications, anti-resonant hollow-core fibers with low attenuation are needed. Furthermore, anti-resonant hollow-core fibers that can be easily manufactured on a large scale are needed. This is the only way to keep the cost of anti-resonant hollow-core fibers within reasonable limits. It is important to note that methods for manufacturing anti-resonant hollow-core fibers that give good results on a laboratory scale are not necessarily suitable for large-scale use.

[0009] It is an object of the present invention to provide a method for manufacturing an anti-resonant hollow-core fiber that overcomes the above-mentioned drawbacks.

[0010] In particular, it is an object of the present invention to provide a method for manufacturing an anti-resonant hollow-core fiber that results in less deformation of the anti-resonant unit.

[0011] In particular, it is an object of the present invention to provide a method for manufacturing an anti-resonant hollow-core fiber in which the anti-resonant unit is exposed to the lowest possible temperature during the drawing step. (Means for solving the problem)

[0012] Contributions to the at least partial realization of at least one of the above-mentioned objects are made by the features of the independent claims. The dependent claims provide preferred embodiments that contribute to the at least partial realization of at least one of the objects.

[0013] The following embodiments contribute at least in part to achieving at least one of the aforementioned objects.

[0014] A first embodiment of a method for fabricating an anti-resonant hollow-core fiber having an outer diameter of less than 500 μm comprises: providing a sheath tube comprising a sheath tube inner bore and a sheath tube longitudinal axis along which a sheath tube wall extends, the sheath tube wall being defined by a sheath tube inner surface and a sheath tube outer surface; - providing several anti-resonance units each comprising an ARU outer tube; - introducing at least a portion of the anti-resonance unit into the inner bore of the sheath tube; - creating a hollow core assembly comprising the sheath tube and the anti-resonant unit by at least partially connecting the anti-resonant unit to an inner surface of the sheath tube; providing a jacket tube having a jacket tube inner bore and a jacket tube longitudinal axis along which a jacket tube wall extends, the jacket tube wall being defined by an inner jacket surface and an outer jacket surface; - introducing at least a portion of the hollow core assembly into the jacket tube bore; - Drawing a hollow-core fiber from the jacket tube and hollow-core assembly by a hot-forming process.

[0015] In the step of drawing a hollow-core fiber, The sheath tube has a sheath tube diameter of at least 8 mm; the jacket tube has a jacket tube diameter of at least 25 mm; and It is provided that the ratio of the jacket tube cross-sectional area of ​​the jacket tube wall to the sheath tube cross-sectional area of ​​the sheath tube wall is in the interval [5;40].

[0016] A further embodiment of the method is characterized in that the ratio of the jacket tube cross-sectional area to the sheath tube cross-sectional area is as follows: the ratio is equal to or less than 37, in particular equal to or less than 35, in particular equal to or less than 30; the ratio is 9 or greater, in particular 12 or greater, in particular 15 or greater, in particular 20 or greater; It is characterized by having at least one of the following characteristics.

[0017] This embodiment is a second embodiment of the method, which is particularly dependent on the first embodiment of the method.

[0018] A further embodiment of the method is characterized in that the anti-resonant hollow-core fiber has an outer diameter of less than 450 μm, in particular less than 400 μm, in particular less than 300 μm, in particular less than 270 μm, in particular less than 250 μm.

[0019] This embodiment is a third embodiment of the method that is particularly dependent on the first and second embodiments of the method.

[0020] A further embodiment of the method is characterized in that the core radius R_Faser is: the core radius is less than or equal to 26 μm, in particular less than or equal to 23 μm, in particular less than or equal to 20 μm; and the core radius is 10 μm or more, in particular 12 μm or more, in particular 14 μm or more; It is characterized by having at least one of the following characteristics.

[0021] This embodiment is a fourth embodiment of the method that is particularly dependent on the first to third embodiments of the method.

[0022] A further embodiment of the method is characterized in that the sheath tube comprises: ● The sheath tube diameter is 100mm or less, 90mm or less, 75mm or less, or 50mm or less. ● The sheath tube diameter is 10mm or more, 15mm or more, or 20mm or more. ● The sheath tube wall has a wall thickness of more than 2 mm, more than 3 mm, more than 5 mm, or more than 7.5 mm; The sheath tube wall has a wall thickness of less than 25 mm, less than 20 mm, or less than 15 mm; The sheath tube has a sheath tube length of at least 1 m; the magnitude of the wall thickness of the sheath tube wall varies by less than 10%, particularly less than 5%, particularly less than 3% of the wall thickness over the length of the sheath tube; It is characterized by having at least one of the following characteristics.

[0023] This embodiment is a fifth embodiment of the method that is particularly dependent on the first to fourth embodiments of the method.

[0024] A further embodiment of the method is characterized in that the ARU outer pipe has the ARU inner pipe installed therein.

[0025] This embodiment is a sixth embodiment of the method, which is particularly dependent on the first to fifth embodiments of the method.

[0026] A further embodiment of the method is characterized in that the hollow core assembly comprises three, four, five, six, seven or eight anti-resonant units.

[0027] This embodiment is a seventh embodiment of the method that is particularly dependent on the first to sixth embodiments of the method.

[0028] A further embodiment of the method is characterized in that the at least partial connection of the anti-resonance unit to the inner surface of the sheath tube is performed by: - connecting with a second hot forming process, in particular selected from at least one of stretching and crushing; ● Integral connection of the anti-resonance unit to the inner surface of the sheath tube along the connection seam; ● The anti-resonance unit is integrally connected to a part of the inner surface of the sheath tube at a point. It is characterized by having at least one of the following characteristics.

[0029] This embodiment is an eighth embodiment of the method that is particularly dependent on the first to seventh embodiments of the method.

[0030] A further embodiment of the method is wherein the jacket tube comprises: The jacket tube diameter is 290 mm or less, particularly 220 mm or less, particularly 180 mm or less, particularly 150 mm or less; The jacket tube diameter is 50 mm or more, particularly 60 mm or more, particularly 75 mm or more, particularly 85 mm or more; the jacket tube wall has a wall thickness of more than 20 mm, in particular more than 30 mm, in particular more than 40 mm, in particular more than 50 mm; the jacket tube wall has a wall thickness of less than 90 mm, in particular less than 80 mm, in particular less than 70 mm, in particular less than 60 mm; The jacket tube has a jacket tube length of at least 1 m; The thickness of the jacket tube wall varies by no more than 10%, particularly no more than 5%, particularly no more than 3% of the wall thickness over the length of the jacket tube; It is characterized by having at least one of the following characteristics.

[0031] This embodiment is a ninth embodiment of the method that is particularly dependent on the first to eighth embodiments of the method.

[0032] A further embodiment of the method is characterized in that the sheath tube length and the jacket tube length, in particular the sheath tube length, the jacket tube length and the length of the anti-resonance unit differ from the jacket tube length by no more than 15%, in particular by no more than 10%, in particular by no more than 5%.

[0033] This embodiment is a tenth embodiment of the method that is particularly dependent on the first to ninth embodiments of the method.

[0034] A further embodiment of the method is characterized in that the method comprises: The sheath tube cross-sectional area of ​​the sheath tube wall varies by no more than 10%, particularly no more than 5%, particularly no more than 3% over the length of the sheath tube; the cross-sectional area of ​​the jacket tube wall varies by no more than 10%, particularly no more than 5%, particularly no more than 3% over the length of the jacket tube; and the magnitude of the ratio of the jacket tube cross-sectional area to the sheath tube cross-sectional area varies by no more than 10%, particularly no more than 5%, particularly no more than 3% of the jacket tube cross-sectional area over the length of the jacket tube; It is characterized by including at least one of the features.

[0035] This embodiment is an eleventh embodiment of the method, which is particularly dependent on the first to tenth embodiments of the method.

[0036] A further embodiment of the method is characterized in that the method does not have a hot forming process step between the introducing step and the drawing step.

[0037] This embodiment is a twelfth embodiment of the method, which is particularly dependent on the first to eleventh embodiments of the method.

[0038] A further embodiment of the method is characterized in that the method has no intermediate steps between the introducing step and the delineating step.

[0039] This embodiment is a thirteenth embodiment of the method that is particularly dependent on the first to twelfth embodiments of the method.

[0040] A further embodiment of the method is characterized in that the drawing step is performed by a hot forming process selected from at least one of stretching and crushing.

[0041] This embodiment is a fourteenth embodiment of the method that is particularly dependent on the first to thirteenth embodiments of the method.

[0042] A further embodiment of the method is characterized in that the heat introduced into the jacket tube in the hot forming process in the drawing step undergoes at least two heat transfers during transfer between the jacket tube and the sheath tube, and in particular, after the introducing step, a gap exists between the jacket tube and the hollow core assembly, so that the heat introduced into the jacket tube in the hot forming process in the drawing step undergoes at least two heat transfers in the gap.

[0043] This embodiment is a fifteenth embodiment of the method, which is particularly dependent on the first to fourteenth embodiments of the method.

[0044] A further embodiment of the method is to provide a method for forming a hollow core assembly having a clearance of: The radial size of the gap is 4 mm or less, in particular 3 mm or less, in particular 2 mm or less, in particular 1 mm or less; the radial size of the gap is 0.3 mm or more, in particular 0.5 mm or more, in particular 0.75 mm or more, in particular 0.85 mm or more; It is characterized by having at least one of the following characteristics.

[0045] This embodiment is a sixteenth embodiment of the method, which is particularly dependent on the fifteenth embodiment of the method.

[0046] A further embodiment of the method is to provide a first heat transfer coefficient at an outer interface between the gap and the inner surface of the jacket in the range [65;180] W / (m 2 *K), especially in the section [90;150]W / (m 2 *K).

[0047] This embodiment is a 17th embodiment of the method that is particularly dependent on at least one of the 15th and 16th embodiments of the method.

[0048] A further embodiment of the method is to provide a second heat transfer coefficient at the internal interface between the gap and the outside of the sheath tube in the range [65;180] W / (m 2 *K), especially in the section [90;150]W / (m 2 *K).

[0049] This embodiment is an 18th embodiment of the method, which is particularly dependent on the 15th to 17th embodiments of the method.

[0050] A further embodiment of the method is characterized in that the method comprises: - coating the hollow-core fiber with at least one layer, in particular a layer comprising a photocurable polymer; - winding the hollow-core fiber onto a spool; It is characterized by including at least one of the following.

[0051] This embodiment is a 19th embodiment of the method, which is particularly dependent on the first to eighteenth embodiments of the method.

[0052] A further embodiment of the method is characterized in that the hollow-core fiber comprises: the sheath tube, and / or the anti-resonant unit, and / or the ARU outer tube, and / or the ARU inner tube, and / or the jacket tube comprise an amorphous solid, in particular glass, in particular quartz glass; the sheath tube and / or the anti-resonance unit, and / or the ARU outer tube, and / or the ARU inner tube, and / or the jacket tube are made of an amorphous solid, in particular glass, in particular quartz glass; At least two of the sheath tube, the anti-resonant unit, the ARU outer tube, the ARU inner tube, and the jacket tube are made of the same material, and in particular comprise or consist of glass having a refractive index of at least 1.4, in particular 1.4 to 3, in particular 1.4 to 2.8; It is characterized by having at least one of the following characteristics.

[0053] This embodiment is a twentieth embodiment of the method, which is particularly dependent on the first to nineteenth embodiments of the method. DETAILED DESCRIPTION OF THE INVENTION

[0054] In this specification, range specifications include the values ​​specified as limits. Thus, a specification of the type "in the range of X to Y" with respect to a quantity A means that A can take on values ​​X, Y, and values ​​between X and Y.

[0055] Some of the described features are associated with the term "substantially", which should be understood as meaning that under practical conditions and manufacturing techniques, a mathematically precise interpretation of terms such as "perpendicular", "diameter", or "parallelism" can never be given exactly, but only within certain manufacturing tolerances.

[0056] The present invention provides a method for fabricating an anti-resonant hollow-core fiber having an outer diameter of less than 500 μm, comprising the steps of: providing a sheath tube comprising a sheath tube inner bore and a sheath tube longitudinal axis along which a sheath tube wall extends, the sheath tube wall being defined by a sheath tube inner surface and a sheath tube outer surface; - providing several anti-resonance units each comprising an ARU outer tube; - introducing at least a portion of the anti-resonance unit into the inner bore of the sheath tube; - creating a hollow core assembly comprising the sheath tube and the anti-resonant unit by at least partially connecting the anti-resonant unit to an inner surface of the sheath tube; providing a jacket tube having a jacket tube inner bore and a jacket tube longitudinal axis along which a jacket tube wall extends, the jacket tube wall being defined by an inner jacket surface and an outer jacket surface; - introducing at least a portion of the hollow core assembly into the jacket tube bore; - drawing a hollow-core fiber from the jacket tube and hollow-core assembly by a hot-forming process.

[0057] According to the present invention, in the step of drawing a hollow-core fiber, The sheath tube has a sheath tube diameter of at least 8 mm; the jacket tube has a jacket tube diameter of at least 25 mm; and It is provided that the ratio of the jacket tube cross-sectional area of ​​the jacket tube wall to the sheath tube cross-sectional area of ​​the sheath tube wall is in the interval [5;40].

[0058] The end product of the method according to the invention is an anti-resonant hollow-core fiber having an outer diameter of less than 500 μm. Such hollow-core fibers are particularly used as optical fibers in telecommunications, especially in data centers.

[0059] The reduction in temperature on the inner surface of the sheath tube achieved by the above-described method results in an increase in the viscosity of the anti-resonant unit, particularly the ARU inner tube. The greater the stability of the anti-resonant unit during the drawing step, the smaller the fluctuations in the geometric shape of the anti-resonant unit in the hollow-core fiber. Otherwise, these fluctuations would result in deviations of the shape of the drawn hollow-core fiber from the desired fiber profile. However, even small deviations from the desired fiber profile often result in a nonlinear increase in attenuation. Therefore, even the smallest deviations from the desired fiber profile have strong consequences. Therefore, the disclosed type of method significantly reduces the fluctuations in attenuation of drawn anti-resonant hollow-core fibers, particularly.

[0060] In the providing step, a sheath tube is prepared. The sheath tube is an elongated hollow body whose length is significantly greater than its diameter. The sheath tube has a sheath tube inner bore and a sheath tube longitudinal axis along which a sheath tube wall extends, the sheath tube wall being defined by the sheath tube inner surface and the sheath tube outer surface. Due to its tubular structure, the sheath tube has a hollow core extending along the sheath tube longitudinal axis. In particular, the sheath tube can have a length of at least 1 m, particularly 2 m. In one embodiment, the sheath tube includes or consists of a material transparent to the operating light of the optical fiber, such as glass, in particular doped or undoped silica glass (SiO2). Doping allows for adjustment of physical properties such as the thermal expansion coefficient. The dopant used to reduce the viscosity of the silica glass is preferably fluorine, chlorine, and / or hydroxyl.

[0061] During the preparation step, several anti-resonant units are fabricated. A single anti-resonant unit is configured as a tubular structural element comprising an ARU outer tube. In one embodiment, the anti-resonant unit comprises an ARU outer tube and an ARU inner tube inserted therein. In this embodiment, the anti-resonant unit has at least two walls, which, when viewed from the direction of the hollow core, have a negative curvature (convex) or no curvature (flat, straight).

[0062] In one embodiment, the anti-resonant unit comprises or consists of a material transparent to the operating light of the optical fiber, such as glass, in particular doped or undoped silica glass (SiO2). Doping allows for adjustment of physical properties such as the thermal expansion coefficient. Dopants used to reduce the viscosity of silica glass are preferably fluorine, chlorine, and / or hydroxyl. In one embodiment, the anti-resonant unit and the sheath tube are the same material.

[0063] The term "same material" describes the material properties of the two parts, whereby the two parts consist of substantially the same chemical substance. The total mass of different chemical elements in both parts may be less than 1% by weight, in particular less than 0.5% by weight, in particular less than 0.1% by weight. In particular, the chemical composition of the two parts differs by an impurity content of less than 500 ppm by weight, in particular less than 100 ppm by weight, and / or by a dopant content of less than 10,000 ppm by weight, in particular less than 5,000 ppm by weight.

[0064] During the introducing step, the anti-resonance unit is introduced at least partially into the inner lumen of the sheath tube, with the purpose of locating the anti-resonance unit in the inner lumen of the sheath tube.

[0065] During the fabrication step, a hollow core assembly is produced, also called a cane, which includes a sheath tube and an anti-resonant unit, the anti-resonant unit being at least partially connected to the inner surface of the sheath tube.

[0066] Before the connection, the tubular anti-resonance unit is introduced into the hollow core of the sheath tube, which is also tubular. Then, the anti-resonance unit can be positioned at a predetermined target position within the sheath tube. The at least partial connection of the anti-resonance unit to the inner surface of the sheath tube can be performed as follows: - connecting with a second hot forming process, in particular selected from at least one of stretching and crushing; ● integrally connecting the anti-resonance unit to the inner surface of the sheath tube along a connecting seam; - connecting the anti-resonance unit integrally to a part of the inner surface of the sheath tube at a point; It may include at least one of:

[0067] The term same material refers to the connection of at least two connection partners, which are held together by atomic or molecular forces.

[0068] The anti-resonant units on the inner surface of the sheath tube may be connected at points. In one embodiment, a given anti-resonant unit may be integrally connected to the inner surface of the sheath tube at at least two points only.

[0069] In another embodiment, a given anti-resonant unit may be integrally connected to the inner surface of the sheath tube along a connecting seam, in particular the connecting seam may extend substantially the length of the inner surface of the sheath tube.

[0070] After connection, the longitudinal axis of a given anti-resonant unit can be aligned substantially parallel to the longitudinal axis of the sheath tube. In one embodiment, the longitudinal axes of the anti-resonant unit and the sheath tube can have an angle of −1.5° to 1.5°, preferably −0.85° to 0.85°, preferably −0.42° to 0.42° relative to each other. This parallelism improves the resonance or anti-resonance conditions in the subsequent hollow-core fiber.

[0071] The anti-resonance unit can be connected to the inner surface of the sheath tube, particularly during the second hot forming process.

[0072] In the preparation step, a jacket tube is prepared. The jacket tube is an elongated hollow body whose length is significantly greater than its diameter. The jacket tube comprises a jacket tube inner bore and a jacket tube longitudinal axis along which a jacket tube wall extends, the jacket tube wall being defined by an inner jacket surface and an outer jacket surface. Due to its tubular structure, the jacket tube has a hollow core extending along the jacket tube longitudinal axis. In particular, the jacket tube can have a length of at least 1 m, particularly 2 m. In one embodiment, the jacket tube comprises or consists of a material transparent to the operating light of the optical fiber, such as glass, in particular doped or undoped silica glass (SiO2). Doping allows for adjustment of physical properties such as the thermal expansion coefficient. The dopant used to reduce the viscosity of the silica glass is preferably fluorine, chlorine, and / or hydroxyl. In one embodiment, the antiresonant unit, the jacket tube, and the sheath tube are made of the same material.

[0073] During the introducing step, the hollow core assembly is introduced at least partially into the inner bore of the jacket tube, with the objective of disposing the hollow core assembly in the inner bore of the jacket tube. In one embodiment, the hollow core assembly has three, four, five, six, seven, or eight anti-resonant units.

[0074] During the drawing step, the lateral extent of the jacket tube and hollow core assembly is reduced to obtain a hollow-core fiber. During the drawing step, the longitudinal extent of the fiber assembly consisting of the jacket tube and hollow core assembly can be increased and / or the lateral extent can be decreased. The drawing can be performed to scale, e.g., the shape and arrangement of components or parts are reflected in the final drawn product.

[0075] The drawing step is carried out during a hot forming process. The term "hot forming process" refers to a method step in which the temperature of an element is increased by heating. An example of a hot forming process is as follows: - Flame-based hot forming processes based on the oxidation of exothermic reaction gases. One example is the use of hydrogen (also called "H2") as fuel gas (flame hydrolysis). Hydrogen reacts with oxygen (also known as "O2"), which comes from the air or is added separately. Flameless hot forming processes use other heating systems that do not require an open flame. An example is the use of resistors to convert electrical energy into thermal energy (heat).

[0076] During drawing, the fiber assembly, including the jacket tube and hollow core assembly, may be further processed by at least one of the hot forming processes of stretching and collapsing.

[0077] In the context of the present invention, the term stretching refers to an increase in the longitudinal extent of the body. This increase in longitudinal extent can be accompanied by a decrease in the lateral extent of the fiber assembly. The stretching can be done to a scale, e.g., the shape and arrangement of components or components is reflected in the stretched final product.

[0078] In the context of the present invention, the term collapse is understood to mean a reduction in the lateral extent of the body. Such a reduction in the lateral extent of the fiber assembly may occur as part of an increase in the temperature of the body, which may in particular result in an increase in the longitudinal extent of the body.

[0079] The drawing step includes a hot-forming process for drawing the fiber assembly, including the jacket tube and hollow core assembly, into a hollow-core fiber having an outer diameter of less than 500 μm. To increase the longitudinal extent of the fiber assembly and / or to decrease the lateral extent of the fiber assembly, the fiber assembly can be partially heated in a draw tower to a temperature ranging from 1,800°C to 2,200°C. The draw tower can include an oven in which one end of the fiber assembly is heated until a piece of molten material falls from the fiber assembly and forms a thin strand that is the beginning of the hollow-core fiber.

[0080] The expansion of the cavity can be used in the drawing step to influence the shape and arrangement of the anti-resonant units in the hollow-core fiber. The final size of the anti-resonant units in the hollow-core fiber is difficult to control due to the small wall thickness. If the anti-resonant units in the hollow-core fiber are too small and therefore the distance between the anti-resonant units is too large, the hollow-core fiber may have high attenuation. If the geometric size of the anti-resonant units in the hollow-core fiber is too large, especially if they are expanded too much, contact between adjacent anti-resonant units in the hollow-core fiber may occur, which also leads to increased attenuation. In particular, the final size of the anti-resonant units in the hollow-core fiber can be better controlled when the capillary has a low temperature and therefore an increased viscosity.

[0081] Surprisingly, it has been found that the ratio of the geometric size of the jacket tube to the hollow core assembly during the drawing step has a positive effect on the temperature of the anti-resonance unit. The sheath tube has a sheath tube diameter of at least 8 mm; the jacket tube has a jacket tube diameter of at least 25 mm; and It is intended that the ratio of the jacket tube cross-sectional area of ​​the jacket tube wall to the sheath tube cross-sectional area of ​​the sheath tube wall be in the interval [5;40].

[0082] In the context of the present invention, cross-sectional area refers to an area extending perpendicular to a particular direction or axis and representing a cross section of an object. The sheath tube cross-sectional area is defined in particular as the area resulting from the intersection of the sheath tube with a plane extending perpendicular to the sheath tube longitudinal axis. Due to manufacturing-related variations in the sheath tube diameter and / or the wall thickness of the sheath tube wall, the magnitude of the sheath tube cross-sectional area over the entire length of the sheath tube may be subject to variations of 10%, in particular 5%. The jacket tube cross-sectional area is defined in particular as the area resulting from the intersection of the jacket tube with a plane extending perpendicular to the jacket tube longitudinal axis. Due to manufacturing-related variations in the jacket tube diameter and / or the wall thickness of the jacket tube wall, the magnitude of the jacket tube cross-sectional area over the entire length of the jacket tube may be subject to variations of 10%, in particular 5%.

[0083] The ratio of jacket tube cross-sectional area to sheath tube cross-sectional area must be available during the draw step. This ratio does not have to exist at any point during the process, but must exist during the draw step, i.e., just prior to maximum heat exposure. This may occur particularly when the fiber assembly, including the jacket tube and hollow core assembly, is introduced into the draw tower oven.

[0084] It is further provided that the sheath tube has a sheath tube diameter of at least 8 mm and the jacket tube has a jacket tube diameter of at least 25 mm, and therefore both the sheath tube and the jacket tube require a minimum wall thickness to achieve the described effect.

[0085] It is further provided that the ratio of the jacket tube cross-sectional area of ​​the jacket tube wall to the sheath tube cross-sectional area of ​​the sheath tube wall is in the interval [5;40].

[0086] Surprisingly, when the ratio of the jacket tube cross-sectional area to the sheath tube cross-sectional area is within the interval [5;40], two opposing effects occurring in the drawing step of an antiresonant hollow-core fiber with an outer diameter less than 500 μm are optimally reconciled when: ● On the other hand, the temperature of the inner surface of the jacket also decreases, i.e., the temperature of the anti-resonance unit also decreases. • On the other hand, the wall thickness of the jacket tube wall is large enough to absorb most of the stresses that occur during drawing.

[0087] The ratio also appears to affect the temperature on the inner surface of the sheath tube, i.e., the anti-resonant unit.

[0088] On the one hand, the temperature of the jacket material must be high to ensure a suitable viscosity for the drawing step, and on the other hand, the temperature on the inner surface of the sheath tube, and therefore also the temperature of the anti-resonant unit, should be low so that drawing preferably does not adversely affect the shape of the anti-resonant unit.

[0089] A thin-walled jacket tube combined with a very thick-walled sheath tube results in a greater reduction in the temperature on the sheath tube's inner surface. However, the drawing step is associated with shear in the material, especially quartz glass, which introduces stress. If the hollow-core assembly has too large a sheath tube dimension, i.e., a very thick wall, the difference in flow velocity from the outside of the sheath tube to the area of ​​the antiresonant unit becomes too large, causing excessive stress to be frozen into the hollow-core fiber. This can have a negative impact on the strength of the hollow-core fiber.

[0090] A thick-walled jacket tube combined with a very thin-walled sheath tube can dominate the drawing temperature during the drawing step, resulting in the jacket tube having to be heated very strongly. While the jacket tube absorbs most of the stress, the anti-resonant unit is exposed to higher temperatures and may collapse more severely, contrary to the desired structural integrity.

[0091] A further embodiment is a jacket tube having a cross-sectional area to sheath tube cross-sectional area ratio of: the ratio is equal to or less than 37, in particular equal to or less than 35, in particular equal to or less than 30; ● The ratio is 9 or more, especially 12 or more, especially 15 or more, especially 20 or more. It is characterized by having at least one of the following characteristics.

[0092] These further limitations on the ratio of the jacket tube cross-sectional area to the sheath tube cross-sectional area surprisingly result in reduced deformation of the anti-resonant unit during fabrication of the hollow-core fiber.

[0093] Another embodiment is characterized in that the antiresonant hollow-core fiber has an outer diameter of less than 450 μm, in particular less than 400 μm, in particular less than 300 μm, in particular less than 270 μm, in particular less than 250 μm. To produce antiresonant hollow-core fibers with smaller outer diameters, the fiber assembly needs to be heated more and more. The use of cross-sectional area ratios according to the invention ensures that deformation of the antiresonant unit due to heat input during production of the hollow-core fiber is minimized.

[0094] A further embodiment is one in which the core radius R_Faser is: the core radius is less than or equal to 26 μm, in particular less than or equal to 23 μm, in particular less than or equal to 20 μm; and the core radius is 10 μm or more, in particular 12 μm or more, in particular 14 μm or more; It is characterized by having at least one of the following characteristics.

[0095] The hollow-core fiber has a core radius, which results from the shortest distance between the longitudinal axis of the anti-resonant hollow-core fiber and the anti-resonant unit. To produce an anti-resonant hollow-core fiber with a smaller core radius, the fiber assembly needs to be heated more and more. The use of the cross-sectional area ratio according to the present invention ensures that deformation of the anti-resonant unit due to heat input during fabrication of the hollow-core fiber is minimized.

[0096] In a further embodiment, the sheath tube comprises: ● The sheath tube diameter is 100mm or less, 90mm or less, 75mm or less, or 50mm or less. ● The sheath tube diameter is 10mm or more, 15mm or more, or 20mm or more. ● The sheath tube wall has a wall thickness of more than 2 mm, more than 3 mm, more than 5 mm, or more than 7.5 mm; The sheath tube wall has a wall thickness of less than 25 mm, less than 20 mm, or less than 15 mm; The sheath tube has a sheath tube length of at least 1 m; the magnitude of the wall thickness of the sheath tube wall varies by less than 10%, particularly less than 5%, particularly less than 3% of the wall thickness over the length of the sheath tube; It is characterized by having at least one of the following characteristics.

[0097] The listed parameters have a positive influence on the temperature reduction effect of the anti-resonance unit.

[0098] In a further embodiment, the sheath tube comprises: The jacket tube diameter is 290 mm or less, particularly 220 mm or less, particularly 180 mm or less, particularly 150 mm or less; The jacket tube diameter is 50 mm or more, particularly 60 mm or more, particularly 75 mm or more, particularly 85 mm or more; the jacket tube wall has a wall thickness of more than 15 mm, in particular more than 20 mm, in particular more than 30 mm, in particular more than 40 mm; the jacket tube wall has a wall thickness of less than 90 mm, in particular less than 80 mm, in particular less than 70 mm, in particular less than 60 mm; The jacket tube has a jacket tube length of at least 1 m; The thickness of the jacket tube wall varies by no more than 10%, particularly no more than 5%, particularly no more than 3% of the wall thickness over the length of the jacket tube; It is characterized by having at least one of the following characteristics.

[0099] The listed parameters have a positive influence on the temperature reduction effect of the anti-resonance unit.

[0100] A further embodiment is characterized in that the sheath tube length and the jacket tube length, in particular the sheath tube length, the jacket tube length, and the length of the anti-resonance unit, differ from the jacket tube length by 15% or less, in particular 10% or less, in particular 5% or less. In this embodiment, the sheath tube length and the jacket tube length are identical within the specified difference range. This particularly facilitates connection in the step of producing the hollow core assembly.

[0101] A further embodiment is a method comprising: The sheath tube cross-sectional area of ​​the sheath tube wall varies by no more than 10%, particularly no more than 5%, particularly no more than 3% over the length of the sheath tube; the cross-sectional area of ​​the jacket tube wall varies by no more than 10%, particularly no more than 5%, particularly no more than 3% over the length of the jacket tube; and the magnitude of the ratio of the jacket tube cross-sectional area to the sheath tube cross-sectional area varies by no more than 10%, particularly no more than 5%, particularly no more than 3% of the jacket tube cross-sectional area over the length of the jacket tube; It is characterized by having at least one of the following characteristics.

[0102] For manufacturing reasons, there are variations in the geometric dimensions of the jacket tube and / or sheath tube, which may be within the given intervals to further explain the ratios according to the invention.

[0103] A further embodiment is characterized in that the method is free of any hot-forming process step between the introducing and drawing steps. By "free of any hot-forming process step" it is meant that no heating takes place between the two steps, i.e. the introducing and drawing steps, which would significantly change the viscosity of the two elements, i.e. the hollow core assembly and the jacket tube, in particular to temperatures above 500°C. This has the advantage that there is no heating of the anti-resonant elements which could lead to deformations in the geometric design which could result in an increase in the attenuation of the hollow-core fiber.

[0104] A further embodiment is characterized in that the method has no intermediate steps between the introducing step and the drawing step. In this case, "no intermediate steps" means that there are no further intermediate steps between the introducing and drawing steps that result in significant structural and / or chemical changes in the two elements, i.e., the hollow core assembly and the jacket tube. "No intermediate steps" does not include method steps such as cleaning, polishing, and / or inspection of the hollow core assembly and / or the jacket tube. The embodiment without intermediate steps has the advantage that the ratio of the jacket tube cross-sectional area to the sheath tube cross-sectional area is maintained between the introducing and drawing steps. This facilitates precise adjustment of the ratio, thereby ensuring a reduced temperature in the anti-resonance unit.

[0105] A further embodiment is characterized in that the heat introduced into the jacket tube in the hot forming process in the drawing step undergoes at least two heat transfers during transfer between the jacket tube and the sheath tube, and in particular, after the introducing step, a gap exists between the jacket tube and the hollow core assembly, so that the heat introduced into the jacket tube in the hot forming process in the drawing step undergoes at least two heat transfers in the gap.

[0106] As described above, the introducing step involves at least partial introduction of the hollow core assembly into the inner bore of the jacket tube. To ensure this mechanical introduction, the maximum diameter of the hollow core assembly must be smaller than the minimum diameter of the inner bore of the jacket tube. As a result, a gap is formed between the jacket tube and the hollow core assembly. Surprisingly, it has been found that the design of this gap has a significant impact on the maximum temperature of the anti-resonance unit during the drawing step.

[0107] The term heat transport (also called heat transfer) is understood to be the transport of energy in the form of heat across at least one thermodynamic system boundary. There are three types of heat transport mechanisms: • In thermal conduction or conduction, kinetic energy is transferred between adjacent atoms or molecules without the transport of matter; • In heat flow or convection, thermal energy is carried along a flowing medium; • In thermal radiation, heat energy is transferred as electromagnetic waves.

[0108] The various types of heat transport mechanisms are often referred to as heat transfer and are described by heat transfer coefficients. The physical quantity of heat transfer is heat flow, which describes the amount of thermal energy transferred from a hotter location to a colder location over a period of time.

[0109] A further embodiment is a first heat transfer coefficient at the outer interface between the gap and the inner surface of the jacket in the range [65;180] W / (m 2*K), especially in the section [90;150]W / (m 2 *K). These structural characteristics of the hollow-core fiber, together with the ratio of the jacket tube cross-sectional area to the sheath tube cross-sectional area, result in a further reduction in the temperature of the inner surface of the sheath tube.

[0110] A further embodiment is a second heat transfer coefficient at the inner interface between the gap and the outer surface of the sheath tube in the range [65;180] W / (m 2 *K), especially in the section [90;150]W / (m 2 *K). These structural characteristics of the hollow-core fiber, along with the ratio of the jacket tube cross-sectional area to the sheath tube cross-sectional area, also result in a further reduction in the temperature of the inner surface of the sheath tube.

[0111] A further embodiment is one in which, when the hollow core assembly is centered in the jacket tube bore, the gap is: The radial size of the gap is less than or equal to 4 mm, in particular less than or equal to 3 mm, in particular less than or equal to 2 mm, in particular less than or equal to 1 mm. the radial size of the gap is 0.05 mm or more, in particular 0.1 mm or more, 0.3 mm or more, in particular 0.5 mm or more, in particular 0.75 mm or more, in particular 0.85 mm or more; It is characterized by having at least one of the following characteristics.

[0112] The geometric size of the gap can affect the temperature of the anti-resonant unit during the drawing step, and it has surprisingly been found that the gap is particularly effective in attenuating the transport of heat from the jacket to the anti-resonant unit, especially within one of the parameters described above.

[0113] A further embodiment is a method comprising: - coating the hollow-core fiber with at least one layer, in particular a layer comprising a photocurable polymer; - winding the hollow-core fiber onto a spool; It is characterized by including at least one of the following.

[0114] When hollow-core fibers are drawn from an oven, they undergo thermal deformation, resulting in the appearance of microcracks on the surface of the bare hollow-core fiber. These microcracks can be expanded by atmospheric H2O once exposed to the atmosphere. To increase the strength of hollow-core fibers, thin layers, especially polymer layers, are applied to the hollow-core fiber after the drawing step.

[0115] Further embodiments are directed to hollow-core fibers comprising: the sheath tube, and / or the anti-resonant unit, and / or the ARU outer tube, and / or the ARU inner tube, and / or the jacket tube comprise an amorphous solid, in particular glass, in particular quartz glass; the sheath tube and / or the anti-resonance unit, and / or the ARU outer tube, and / or the ARU inner tube, and / or the jacket tube are made of an amorphous solid, in particular glass, in particular quartz glass; At least two of the sheath tube, the anti-resonant unit, the ARU outer tube, the ARU inner tube, and the jacket tube are made of the same material, and in particular comprise or consist of glass having a refractive index of at least 1.4, in particular 1.4 to 3, in particular 1.4 to 2.8; It is characterized by having at least one of the following characteristics.

[0116] The above-mentioned features result in a further temperature reduction, especially in the region of the anti-resonant unit during the drawing step. These structural properties of the hollow-core fiber, together with the ratio of the jacket tube cross-sectional area to the sheath tube cross-sectional area, result in a further reduction in the temperature of the inner surface of the sheath tube.

[0117] The term interval [a;b] describes a connected subset of the set of real numbers R.

[0118]

number

[0119] The term "in the interval [a; b]" should be understood as including both endpoints of the range, i.e., a and b.

[0120] Furthermore, disclosures of ranges should preferably be understood to include both endpoints of the range. Furthermore, any disclosures of ranges in this document should preferably be understood to also disclose preferred subranges in which one endpoint or both endpoints are excluded. For example, specifying a range from X1 to X2 should be understood to specify a range inclusive of the two endpoints X1 and X2.

[0121] The features and characteristics disclosed in this specification may be essential to various embodiments of the claimed invention both separately and in combination with one another.

[0122] The invention is further explained by the following examples with the aid of the drawings, to which the invention is not limited. [Brief explanation of the drawings]

[0123] The following is shown: [Figure 1] FIG. 10 is a cross-sectional view of the anti-resonance unit with an enlarged detail of the seam line. [Figure 2] A cross-sectional view of the sheath tube and three anti-resonance units. [Figure 3] FIG. 2 is a cross-sectional view of a jacket tube. [Figure 4] a hollow core assembly and a jacket tube. [Figure 5] FIG. 5 is a cross-sectional view of the hollow core assembly and jacket tube of FIG. 4. [Figure 6] FIG. 1 is a cross-sectional view of a hollow core assembly, a jacket tube, an oven, and an anti-resonant hollow-core fiber. [Figure 7] FIG. 1 is a cross-sectional view of an anti-resonant hollow-core fiber. [Figure 8] 1 illustrates method steps for fabrication of an anti-resonant hollow-core fiber. [Figure 9] FIG. 10 is a further cross-sectional view of the sheath tube and jacket tube. [Figure 10] FIG. 10 is a further cross-sectional view of the sheath tube and jacket tube. [Figure 11] FIG. 10 is a further cross-sectional view of the oven, sheath tube, and jacket tube. [Figure 12] FIG. 10 is a diagram of the temperature along the inside surface of the sheath tube plotted against the distance to the underside of the oven.

[0124] The starting point for the method of fabricating an anti-resonant hollow-core fiber having an outer diameter of less than 500 μm is the preparation 3100 of several anti-resonant units 300. FIG. 1 shows the anti-resonant unit 300. In the illustrated version, the anti-resonant unit 300 includes an ARU outer tube 310 and an ARU inner tube 340 introduced therein. The ARU outer tube 310 is a tubular structure, which, in the illustrated embodiment, has an arc-shaped cross section. The ARU outer tube 310 is a tubular structure. In FIG. 1, the ARU outer tube 310 and the ARU inner tube 340 introduced therein extend within the plane of the drawing.

[0125] The ARU outer tube 310 has an ARU outer wall 315 made of or made of a material that is transparent to the operating light of the optical fiber, such as glass, particularly doped or undoped silica glass (SiO2).

[0126] The cross section shown in Figure 1 shows that the ARU outer pipe 310 has an arc-shaped cross section. In the context of the present invention, the term arc refers to a portion of a circular line. Two points on a circle divide the circular line into two arcs. The term arc describes when the outline of an element follows one of two arcs.

[0127] 1 also shows a cross section of ARU inner tube 340. ARU inner tube 340 is a tubular structure with an arc-shaped cross section. ARU inner tube 340 has a wall 345 made of or made of a material that is transparent to the operating light of the optical fiber, such as glass, particularly doped or undoped silica glass (SiO2).

[0128] Arc-shaped ARU outer tube 310 and arc-shaped ARU inner tube 340 are connected to each other along two connecting lines 370, 370′ disposed substantially parallel to longitudinal axis 311. Notably, this joining can be achieved by a hot forming process. For clarity, a portion of anti-resonant unit 300 is shown enlarged in FIG. 1 around connecting line 370.

[0129] A further step in the method of manufacturing an anti-resonant hollow-core fiber includes step 3000 of providing a sheath tube 200. Figure 2 shows a cross section of the sheath tube 200, which comprises a sheath tube inner bore 220 and a sheath tube longitudinal axis 230 along which a sheath tube wall 210 extends, the sheath tube wall being defined by a sheath tube inner surface 215 and a sheath tube outer surface 216. The sheath tube 200 has a sheath tube diameter 212 and a sheath tube inner diameter 213. The sheath tube wall 210 has a wall thickness 211. The sheath tube 200 has the following: ● The sheath tube diameter 212 is 100 mm or less, 90 mm or less, 75 mm or less, or 50 mm or less; ● The sheath tube diameter 212 is 10 mm or more, 15 mm or more, or 20 mm or more; the sheath tube wall 210 has a wall thickness 211 of greater than 2 mm, greater than 3 mm, greater than 5 mm, greater than 7.5 mm; the sheath tube wall 210 has a wall thickness 211 of less than 25 mm, less than 20 mm, less than 15 mm; The sheath tube 200 has a sheath tube length of at least 1 m; the magnitude of the wall thickness 211 of the sheath tube wall 210 varies by less than 10%, in particular less than 5%, in particular less than 3% of the wall thickness over the sheath tube length; It may have at least one of the following characteristics:

[0130] During the introducing step 3200, at least a portion of the anti-resonant unit 300 is introduced into the sheath tube lumen 220. Further, the anti-resonant unit 300 can be positioned within the sheath tube lumen 220 at a desired location.

[0131] In a fabricating step 3300, the hollow core assembly 400 is fabricated from the sheath tube 200 and the anti-resonant unit 300. To this end, the anti-resonant unit 300 is at least partially connected to the sheath tube inner surface 215. The connection can be made during a hot forming process.

[0132] A further step in the method of manufacturing an anti-resonant hollow-core fiber includes step 3100 of providing a jacket tube 500. Figure 3 shows a cross section of the jacket tube 500. The jacket tube 500 comprises a jacket tube inner bore 520 and a jacket tube longitudinal axis 530 along which extends a jacket tube wall 510, the jacket tube wall being defined by an inner jacket surface 515 and an outer jacket surface 516. The jacket tube 500 has a jacket tube diameter 512 and a jacket tube inner diameter 513. The jacket tube wall 510 has a wall thickness 511. The jacket tube 500 has the following: The jacket tube diameter 512 is 290 mm or less, in particular 220 mm or less, in particular 180 mm or less, in particular 150 mm or less; The jacket tube diameter 512 is 50 mm or more, particularly 60 mm or more, particularly 75 mm or more, particularly 85 mm or more; the jacket tube wall 510 has a wall thickness 511 of more than 20 mm, in particular more than 30 mm, in particular more than 40 mm, in particular more than 50 mm, the jacket tube wall 510 has a wall thickness 511 of less than 90 mm, in particular less than 80 mm, in particular less than 70 mm, in particular less than 60 mm; The jacket tube has a jacket tube length of at least 1 m; the magnitude of the wall thickness 511 of the jacket tube wall 510 varies by no more than 10%, in particular no more than 5%, in particular no more than 3% of the wall thickness 511 over the jacket tube length; It may have at least one of the following characteristics:

[0133] 4 shows a three-dimensional representation of the hollow core assembly 400 and jacket tube 500. In this embodiment, the hollow core assembly 400 has two anti-resonant units 300 connected to the sheath tube inner surface 215 of the sheath tube 200. Depending on the intended application of the anti-resonant hollow core fiber 1000, the hollow core assembly 400 can have three, four, five, six, seven, or eight anti-resonant units 300. The at least partial connection of the anti-resonant units 300 to the sheath tube inner surface 215 can be as follows: - connecting with a second hot forming process, in particular selected from at least one of stretching and crushing; - integrally connecting the anti-resonance unit 300 to the sheath tube inner surface 215 along a connecting seam; The anti-resonance unit 300 is integrally connected at a point to a part of the sheath tube inner surface 215 of the sheath tube wall 210; The present invention can include at least one of the following features:

[0134] Depending on the embodiment, the sheath tube length and the jacket tube length, in particular the sheath tube length, the jacket tube length, and the length of the anti-resonance unit, may differ by no more than 15%, in particular no more than 10%, in particular no more than 5% based on the jacket tube length.

[0135] 5 shows a cross section of a fiber assembly 100 comprising a jacket tube 500 and a hollow core assembly 400 between two intersection lines AA and BB. The illustrated portion of the hollow core assembly 400 comprises a sheath tube 200 and an anti-resonance unit 300, which are connected to an inner sheath tube surface 215 of the sheath tube 200. The anti-resonance unit 300 has an outer ARU tube 310 and an inner ARU tube 340. The hollow core assembly 400 is surrounded by the jacket tube 500.

[0136] To ensure reliable introduction 3500 of the hollow core assembly 400 into the jacket tube 500, the maximum diameter of the hollow core assembly must be smaller than the minimum diameter of the jacket tube bore. As a result, a gap 600 is formed between the jacket tube 500 and the hollow core assembly 400. This gap 600 has a radial size 610. Surprisingly, it has been found that the design of this gap has a significant impact on the maximum temperature of the anti-resonance unit during the drawing step.

[0137] In one embodiment, the gap 600 that exists between the jacket tube 500 and the hollow core assembly is such that heat introduced into the jacket tube 500 during the hot forming process, particularly in the drawing step, undergoes at least two thermal transitions within the gap 600. In particular, considering the central location of the hollow core assembly 400 within the jacket tube bore 520, the gap 600 is such that: the radial size 610 of the gap 600 is equal to or less than 4 mm, in particular equal to or less than 3 mm, in particular equal to or less than 2 mm, in particular equal to or less than 1 mm; the radial size 610 of the gap 600 is 0.3 mm or more, in particular 0.5 mm or more, in particular 0.75 mm or more, in particular 0.85 mm or more; It may have at least one of the following characteristics:

[0138] During the drawing step 3600, the longitudinal extent of the fiber assembly consisting of the jacket tube and the hollow core assembly is increased and / or the lateral extent is decreased. This is done during a hot-forming process. The term "hot-forming process" refers to a method step in which the temperature of an element is increased by heating. The drawing step 3600 is particularly illustrated by FIG. 6 , which shows the fiber assembly 100 passing through an electric oven 800. The oven 800 is a device for controlled heat generation for transfer of heat to a spatial zone 805. The movement arrow 810 indicates the direction in which the fiber assembly 100 moves into the spatial zone 805 at a predetermined feed rate. The oven 800 has an oven height 820 and an inner diameter 830.

[0139] The action of heat on the fiber assembly 100 softens its material, resulting in active and / or passive actions that increase its longitudinal extent and / or decrease its lateral extent. At the end of the oven run, an anti-resonant hollow-core fiber 1000 is produced.

[0140] The following exemplary diagram illustrates the effect that drawing step 3600 can have on the geometric size of fiber assembly 100. Thus, jacket tube 500 can have a jacket tube diameter of 290 mm or less, particularly 220 mm or less. After passing through oven 800, the anti-resonant hollow-core fiber can have an outer diameter of less than 500 μm, particularly less than 300 μm; thus, the reduction in lateral extent that drawing step 3600 can cause is nearly three orders of magnitude.

[0141] Furthermore, the draw 3600 can be performed to scale, such that, for example, the shape and arrangement of the components or parts of the primary preform are reflected in the elongated final product. In particular, the draw 3600 can be performed to scale so that the geometric ratios of the anti-resonant unit 300, particularly the ARU outer tube 310 and the ARU inner tube 340, can be maintained before and after the draw. In this case, the geometry, extent, and arrangement of the components or parts of the fiber assembly 100 are reflected in the drawn final product.

[0142] Additionally, draw 3600 can be performed such that different regions within the fiber assembly undergo different geometric changes. For example, a given geometric change in draw 3600 can be varied by applying overpressure to ARU outer tube 310 and / or ARU inner tube 340. Furthermore, applying different pressures to given components of fiber assembly 100 during draw 3600 can vary the following: ● Jacket tube diameter 512 vs. jacket tube inner diameter 513, ● Sheath tube diameter 212 vs. sheath tube inner diameter 213, • The outer diameter versus the inner diameter of the ARU outer pipe 310; and / or ● Outside diameter vs. inside diameter of ARU inner pipe 340; Additionally, the size ratios of the jacket tube 500, the sheath tube 200, the ARU outer tube 310, and / or the ARU inner tube 340 relative to one another can be changed for different pressures.

[0143] A further embodiment is characterized in that the method does not have a hot forming process step between the introducing step 3500 and the drawing step 3600. "No hot forming process step" means that no heating takes place between the two steps of introducing 3500 and drawing 3600, which would significantly change the viscosity of the two elements, namely the hollow core assembly and the jacket tube, in particular to temperatures above 500°C.

[0144] In particular, after the delineating step 3600, the following - coating the hollow-core fiber with at least one layer, in particular a layer comprising a photocurable polymer; - winding the hollow-core fiber onto a spool; At least one of the following can be performed.

[0145] Figure 7 also illustrates the result of the drawing step 3600, showing a cross section of an anti-resonant hollow-core fiber 1000 produced from the fiber assembly 100. The anti-resonant hollow-core fiber 1000 has a hollow core 2320. Electromagnetic waves can propagate through the hollow core 2320. The hollow-core fiber 1000 has a core radius 2310, which results from the shortest distance between the longitudinal axis 2300 of the anti-resonant hollow-core fiber 1000 and the ARU outer tube 1310. Figure 7 illustrates that the drawing step 3600 causes the following transitions to occur: ● The sheath tube 200 becomes the fiber sheath tube 1200; ● Jacket tube 500 becomes fiber jacket tube 1500, The anti-resonance unit 300 becomes a fiber anti-resonance unit 1300; ARU outer tube 310 becomes fiber ARU outer tube 1310; The ARU inner pipe 340 becomes the fiber ARU inner pipe 1320.

[0146] The fiber sheath tube 1200 and the fiber jacket tube 1500 are integrally connected such that it is impossible, or only possible with great effort, to distinguish one from the other. Figure 7 further illustrates the arrangement of multiple anti-resonant units 1300 on the inner surface 1215 that defines the hollow core. In one embodiment, the anti-resonant hollow-core fiber 1000 can have three, four, five, six, seven, or eight anti-resonant units 1300.

[0147] As shown in FIG. 8, a method for fabricating an anti-resonant hollow-core fiber 1000 having an outer diameter of less than 500 μm includes: providing 3000 a sheath tube 200 comprising a sheath tube inner bore 220 and a sheath tube longitudinal axis 230 along which a sheath tube wall 210 extends, the sheath tube wall being defined by a sheath tube inner surface 215 and a sheath tube outer surface 216; a step 3100 of preparing several anti-resonance units 300, each comprising an ARU outer tube 310; Step 3200 of introducing at least a portion of the anti-resonance unit 300 into the sheath tube inner bore 220; a step 3300 of fabricating a hollow core assembly 400 comprising the sheath tube 200 and the anti-resonant unit 300 by at least partially connecting the anti-resonant unit 300 to the sheath tube inner surface 215; providing 3400 a jacket tube 500 having a jacket tube inner bore 520 and a jacket tube longitudinal axis 530 along which a jacket tube wall 510 extends, the jacket tube wall being defined by an inner jacket surface 515 and an outer jacket surface 516; Step 3500 of introducing at least a portion of the hollow core assembly 400 into the jacket tube bore 520; • Step 3600 of drawing the hollow-core fiber 1000 from the jacket tube 500 and hollow-core assembly 400 by a hot-forming process.

[0148] In the step 3600 of drawing the hollow-core fiber 1000, the sheath tube 200 has a sheath tube diameter 212 of at least 8 mm; the jacket tube 500 has a jacket tube diameter 512 of at least 25 mm; and It is provided that the ratio of the jacket tube cross-sectional area 550 of the jacket tube wall 510 to the sheath tube cross-sectional area 450 of the sheath tube wall 410 is in the interval [5;40].

[0149] 9 shows a cross section of a fiber assembly 100 having a jacket tube 500 and a hollow core assembly 400. The sheath tube 200 has a sheath tube wall 210 with a sheath tube cross-sectional area 450. The jacket tube 500 has a jacket tube wall 510 with a jacket tube cross-sectional area 550.

[0150] The sheath tube cross-sectional area 450 refers to the area resulting from the intersection of the sheath tube 200 with a plane extending perpendicular to the sheath tube longitudinal axis 230. The jacket tube cross-sectional area 550 is defined as the area resulting from the intersection of the jacket tube 500 with a plane extending perpendicular to the sheath tube longitudinal axis 530. In Figure 9, the sheath tube 200 and the jacket tube 500 are aligned with each other so that the jacket tube longitudinal axis 530 and the sheath tube longitudinal axis 230 are coincident.

[0151] The method is characterized in that the ratio of the jacket tube cross-sectional area 550 to the sheath tube cross-sectional area 450 is in the interval [5;40]. Surprisingly, only in the disclosed interval: On the other hand, a decrease in the temperature of the jacket inner surface 515 and the anti-resonance unit 300 occurs; and On the other hand, it has been proven that the wall thickness 511 of the jacket tube wall 510 is large enough to absorb most of the stresses occurring during the drawing 3600, in particular more than 80%.

[0152] A further embodiment of the method is where the ratio of the jacket tube cross-sectional area 550 to the sheath tube cross-sectional area 450 is as follows: the ratio is equal to or less than 37, in particular equal to or less than 35, in particular equal to or less than 30; the ratio is 9 or greater, in particular 12 or greater, in particular 15 or greater, in particular 20 or greater; It is characterized by having at least one of the following characteristics.

[0153] 10 shows a cross-sectional view of one embodiment of a fiber assembly 100' comprising a jacket tube 500 and a hollow core assembly 400. The fiber assembly 100' differs from the fiber assembly 100 only in that a gap 600 exists between the jacket tube 500 and the sheath tube 200 after the introduction step 3500. All other elements of the fiber assembly 100' are consistent with the fiber assembly 100.

[0154] In particular, gap 600 can be designed so that heat introduced into jacket tube 500 during the drawing step in the hot forming process undergoes at least two thermal transitions within gap 600 .

[0155] The first heat transfer coefficient at the outer interface between the gap and the inner surface of the jacket is in the interval [65;180] W / (m 2 *K), especially in the section [90;150]W / (m 2 Alternatively or additionally, the second heat transfer coefficient at the inner interface between the gap and the outer surface of the sheath tube may be in the interval [65;180] W / (m *K) for temperatures between 500 and 900°C. 2 *K), especially in the section [90;150]W / (m 2 *K).

[0156] Therefore, considering the central location of the hollow core assembly 400 within the jacket tube bore 520, the size 610 of the gap 600 is determined as follows: The gap is 4 mm or less, particularly 3 mm or less, particularly 2 mm or less, particularly 1 mm or less; The gap is 0.3 mm or more, particularly 0.5 mm or more, particularly 0.75 mm or more, particularly 0.85 mm or more. It may have at least one of the following characteristics:

[0157] 12 shows the results of a simulation of the temperature distribution in the anti-resonance unit 300 of the fiber assembly 100. For the numerical calculations, the P1 radiation model was used for radiative heat transfer in semitransparent media and the ray-shot method for radiation on semitransparent surfaces.

[0158] The starting point for the simulation was a fiber assembly 100 comprising a jacket tube 500 and a hollow core assembly 400. Figure 11 shows the arrangement of the elements: oven 800, jacket tube 500, and sheath tube 200. In the simulation, the fiber assembly 100 had a jacket tube length of 210 mm and a sheath tube length of exactly the same length.

[0159] The sheath tube 200, jacket tube 500, and oven 800 are aligned with one another so that the jacket tube longitudinal axis 530, the sheath tube longitudinal axis 230, and the oven longitudinal axis 840 are coincident. The oven 800 has an oven height 820 of 120 mm and an inner diameter 830 of 35 mm. The oven is connected at its ends to upper and lower contact areas 850 and 860, which are passively designed and do not generate heat.

[0160] During the simulation, the fiber assembly 100 was positioned so that the lower ends of the sheath tube 400 and jacket tube 500 terminated at the lower end 815 of the oven 800, also shown in Figure 11. The fiber assembly 100 was fed into the electric oven 800 at a feed rate of 8 mm / min during the drawing step 3600. The initial temperature of the fiber assembly 100 was 20°C.

[0161] A Gaussian-like temperature profile was assumed along the oven height 820, with the maximum temperature at the center of the oven 800. The temperature distribution along the sheath tube inner surface 215 was calculated.

[0162] [Table 1]

[0163] 12, the temperature along the sheath tube inner surface 215 is plotted against the distance to the oven lower surface 815. The following is plotted: ● The results marked with dots for fiber assemblies where the ratio of the jacket tube cross-sectional area 550 to the sheath tube cross-sectional area 450 is outside the interval [5;40] and ● The results are marked by dashed lines for fiber assembly 100, where the ratio of the jacket tube cross-sectional area 550 to the sheath tube cross-sectional area 450 is within the interval [5;40].

[0164] It can be seen that a reduction in temperature at the sheath tube inner surface 215 is achieved when the ratio of the jacket tube cross-sectional area 550 to the sheath tube cross-sectional area 450 is within the interval [5;40].

[0165] As shown in FIG. 11, the calculated temperature of a fiber assembly 100 in which the ratio of the jacket tube cross-sectional area 550 to the sheath tube cross-sectional area 450 is within the interval [5;40] is approximately 5° C. lower than the temperature achieved at the sheath tube inner surface 215 when the ratio of the jacket tube cross-sectional area 550 to the sheath tube cross-sectional area 450 is outside the interval [5;40].

[0166] This seemingly small temperature difference has a significant impact on the actual fabrication of antiresonant hollow-core fiber. Slight changes in the viscosity of the antiresonant unit, especially the ARU inner tube, often result in changes in the geometry. These variations, which can occur during drawing, result in deviations of the antiresonant hollow-core fiber shape from the desired fiber profile. However, even small deviations from the desired fiber profile often result in a nonlinear increase in attenuation. Thus, even the smallest deviations from the desired fiber profile can have strong consequences. Therefore, the disclosed method of reducing the temperature on the sheath tube inner surface 215 significantly increases the attenuation of the drawn antiresonant hollow-core fiber. [Explanation of symbols]

[0167] 100, 100' Anti-resonant Hollow Core Fiber Fiber Assembly 200 Sheath Tube 210 Sheath tube wall 211 Wall thickness of sheath tube 200 212 sheath tube diameter 213 Sheath tube inner diameter 215 Sheath tube inner surface 216 Sheath tube outer surface 220 Sheath tube inner hole 230 Sheath tube longitudinal axis 300 Anti-resonance unit (ARE) 310 ARU outer tube 311 Longitudinal axis 315 ARU outer unit wall 317 Inside the ARU outer unit 340 ARU inner tube 345 ARU inner unit wall 370, 370' connecting seam 400 Hollow Core Assembly 450 Sheath tube cross section 500 jacketed tube 510 Jacketed Tube Wall 511 Jacket Tube 500 Wall Thickness 512 jacket tube diameter 513 Jacket tube inner diameter 515 Jacket inside 516 Jacket outer surface 520 Jacket tube inner hole 530 Jacket tube longitudinal axis 550 Jacket tube cross section area 600 gap 610 Radial size of gap 800 oven 805 Spatial Zone 810 Movement Arrow 815 Bottom of Oven 800 820 oven height 830 Oven inner diameter 840 Oven longitudinal axis 850 Upper contact area 860 Lower contact area 1000 Anti-resonant hollow core fiber 1200 Fiber sheath tube 1215 Inside 1300 Fiber Anti-Resonance Unit 1310 Fiber ARU outer tube 1340 Fiber ARU Inner Tube 1500 Fiber Jacketed Tube 2310 Core Radius 2300 Longitudinal axis 2320 Hollow Core Provide 3000 sheath tubes 3100 Prepare some anti-resonance units 3200 Install 3300 Create a hollow core assembly 3400 Prepare the jacketed tube 3500 Install 3600 Drawing hollow-core fiber

Claims

1. A method for manufacturing an anti-resonant hollow-core fiber (1000) having an outer diameter of less than 500 μm, comprising: providing (3000) a sheath tube (200) comprising a sheath tube inner bore (220) and a sheath tube longitudinal axis (230) along which a sheath tube wall (210) extends, the sheath tube wall being defined by a sheath tube inner surface (215) and a sheath tube outer surface (216); - providing (3100) several anti-resonance units (300) each comprising an ARU outer tube (310); - introducing (3200) at least a portion of the anti-resonance unit (300) into the sheath tube lumen; - creating (3300) a hollow core assembly (400) comprising said sheath tube (200) and said anti-resonant unit (300) by at least partially connecting said anti-resonant unit (300) to said sheath tube inner surface (215); - providing (3400) a jacket tube (500) comprising a jacket tube inner bore (520) and a jacket tube longitudinal axis (530) along which a jacket tube wall (510) extends, said jacket tube wall being defined by an inner jacket surface (515) and an outer jacket surface (516); - introducing (3500) at least a portion of said hollow core assembly (400) into said jacket tube bore (520); - drawing (3600) said hollow-core fiber from said jacket tube (500) and said hollow-core assembly (400) by a hot-forming process; In the step (3600) of drawing the hollow-core fiber (1000), the sheath tube (200) has a sheath tube diameter (212) of at least 8 mm; - said jacket tube (500) has a jacket tube diameter (512) of at least 25 mm; and - A method characterized in that the ratio of the jacket tube cross-sectional area (550) of the jacket tube wall (510) to the sheath tube cross-sectional area (450) of the sheath tube wall (210) is in the interval [5;40].

2. The ratio of the jacket tube cross-sectional area (550) to the sheath tube cross-sectional area (450) is as follows: said ratio is equal to or less than 37, in particular equal to or less than 35, in particular equal to or less than 30; said ratio is greater than or equal to 9, in particular greater than or equal to 12, in particular greater than or equal to 15, in particular greater than or equal to 20; 10. A method for manufacturing an anti-resonant hollow-core fiber (1000) according to claim 1, characterized in that it has at least one of the following characteristics:

3. The sheath tube (200) has the following: the sheath tube diameter (212) is 100 mm or less, 90 mm or less, 75 mm or less, or 50 mm or less; the sheath tube diameter (212) is 10 mm or more, 15 mm or more, or 20 mm or more; said sheath tube wall (210) has a wall thickness (211) of more than 2 mm, more than 3 mm, more than 5 mm, more than 7.5 mm; the sheath tube wall (210) has a wall thickness (211) of less than 25 mm, less than 20 mm, less than 15 mm; the sheath tube (200) has a sheath tube length of at least 1 m; the size of the wall thickness (211) of the sheath tube wall (210) varies by less than 10%, in particular less than 5%, in particular less than 3% of the wall thickness (211) over the sheath tube length; 10. A method for manufacturing an anti-resonant hollow-core fiber (1000) according to claim 1, characterized in that it has at least one of the following characteristics:

4. The at least partial connection of the anti-resonance unit (300) to the sheath tube inner surface (215) may include the following steps: - connecting in a second hot forming process, in particular selected from at least one of stretching and crushing; - integrally connecting said anti-resonance unit (300) to said sheath tube inner surface (215) along a connecting seam; - integrally connecting the anti-resonance unit (300) to a portion of the sheath tube inner surface (215) at a point; 2. A method for manufacturing an anti-resonant hollow-core fiber (1000) according to claim 1, characterized in that it has at least one of the following characteristics:

5. The jacket tube (500) has the following: the jacket tube diameter (512) is equal to or less than 290 mm, in particular equal to or less than 220 mm, in particular equal to or less than 180 mm, in particular equal to or less than 150 mm; the jacket tube diameter (512) is 50 mm or more, in particular 60 mm or more, in particular 75 mm or more, in particular 85 mm or more; said jacket tube wall (510) has a wall thickness (511) of more than 15 mm, in particular more than 20 mm, in particular more than 30 mm, in particular more than 40 mm; said jacket tube wall (510) has a wall thickness (511) of less than 90 mm, in particular less than 80 mm, in particular less than 70 mm, in particular less than 60 mm; said jacket tube (500) having a jacket tube length of at least 1 m; the size of the wall thickness (511) of the jacket tube wall (510) varies by no more than 10%, in particular no more than 5%, in particular no more than 3% of the wall thickness (511) over the jacket tube length; 10. A method for manufacturing an anti-resonant hollow-core fiber (1000) according to claim 1, characterized in that it has at least one of the following characteristics:

6. 2. A method for manufacturing an anti-resonant hollow-core fiber (1000) according to claim 1, characterized in that the sheath tube length and the jacket tube length, in particular the sheath tube length, the jacket tube length and the length of the anti-resonant unit (300) differ from the jacket tube length by no more than 15%, in particular no more than 10%, in particular no more than 5%.

7. The method comprises the steps of: the sheath tube cross-sectional area (450) of the sheath tube wall (210) varies in size by no more than 10%, in particular no more than 5%, in particular no more than 3% over the sheath tube length; the jacket tube cross-sectional area (550) of the jacket tube wall (510) varies in size by no more than 10%, in particular no more than 5%, in particular no more than 3% over the jacket tube length; and the magnitude of the ratio of the jacket tube cross-sectional area (550) to the sheath tube cross-sectional area (450) varies over the jacket tube length by no more than 10%, in particular no more than 5%, in particular no more than 3% of the jacket tube cross-sectional area (550); 10. A method for manufacturing an anti-resonant hollow-core fiber (1000) according to claim 1, characterized in that it has at least one of the following characteristics:

8. 2. The method for manufacturing an antiresonant hollow-core fiber (1000) according to claim 1, characterized in that the method does not include any hot-forming process step between the introducing step (3500) and the drawing step (3600).

9. 2. The method for manufacturing an anti-resonant hollow-core fiber (1000) according to claim 1, characterized in that the method does not include any intermediate steps between the introducing step (3500) and the drawing step (3600).

10. 10. The method of manufacturing an anti-resonant hollow-core fiber (1000) according to claim 1, wherein the drawing step (3600) is performed by a hot-forming process selected from at least one of stretching and crushing.

11. 2. The method for manufacturing an anti-resonant hollow-core fiber (1000) according to claim 1, characterized in that the heat introduced into the jacket tube (500) during the hot-forming process in the drawing step (3600) undergoes at least two heat transfers during transfer between the jacket tube (500) and the sheath tube (200), and in particular, after the introducing step (3500), a gap (600) exists between the jacket tube (500) and the hollow core assembly (400), so that the heat introduced into the jacket tube (500) during the hot-forming process in the drawing step (3600) undergoes at least two heat transfers in the gap (600).

12. When the hollow core assembly (400) is positioned at the center of the jacket tube bore (520), the gap (600) is as follows: the radial size (610) of said gap (600) is equal to or less than 4 mm, in particular equal to or less than 3 mm, in particular equal to or less than 2 mm, in particular equal to or less than 1 mm; the radial size (610) of the gap (600) is 0.3 mm or greater, in particular 0.5 mm or greater, in particular 0.75 mm or greater, in particular 0.85 mm or greater; 12. A method for manufacturing an anti-resonant hollow-core fiber (1000) according to claim 11, characterized in that it has at least one of the following characteristics:

13. The first heat transfer coefficient at the outer interface between the gap (600) and the jacket inner surface (515) is [65; 180] W / (m ２ *K), especially [90; 150] W / (m ２ 12. A method for manufacturing an anti-resonant hollow-core fiber (1000) according to claim 11, characterized in that:

14. A second heat transfer coefficient at the inner interface between the gap (600) and the sheath tube outer surface (216) is [65; 180] W / (m ２ *K), especially [90; 150] W / (m ２ 12. A method for manufacturing an anti-resonant hollow-core fiber (1000) according to claim 11, characterized in that:

15. The method comprises the steps of: coating said hollow-core fiber with at least one layer, in particular a layer comprising a photocurable polymer; winding the hollow-core fiber onto a spool; 10. The method of manufacturing an anti-resonant hollow-core fiber (1000) according to claim 1, characterized in that it comprises at least one of:

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