METHOD FOR PRODUCING A PREFORM OF AN ANTIRESONANT HOLLOW CORE FIBER

Description

Background of the invention

[0001] The invention relates to methods for producing a preform of an antiresonant hollow core fiber. State of the art

[0002] Hollow-core fibers have a core containing an evacuated cavity filled with gas or liquid. In hollow-core fibers, the interaction of light with the glass is less than in solid-core fibers. The refractive index of the core is lower than that of the cladding, so 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 "antiresonance reflection fibers."

[0003] In "photonic bandgap fibers," the hollow core region is surrounded by a cladding in which small hollow channels are periodically arranged. The periodic structure in the cladding causes the effect referred to in semiconductor technology as the "photonic bandgap," whereby light of certain wavelength ranges scattered by the cladding structures experiences constructive interference in the central cavity due to Bragg reflection and cannot propagate transversely in the cladding.

[0004] In the design known as an "antiresonant hollow-core fiber" (ARHCF), the hollow core region is surrounded by an inner cladding region containing so-called antiresonant elements (also known as "antiresonant elements" or "AREs"). The walls of the antiresonant elements, evenly distributed around the hollow core, can act as Fabry-Perot cavities operating in antiresonance, reflecting the incident light and guiding it through the fiber core.

[0005] This fiber technology promises low optical attenuation, a very broad transmission spectrum (including in the UV or IR wavelength range) and low latency in data transmission.

[0006] EP 3 136 143 A1 describes an antiresonant hollow-core fiber (referred to therein as a "hollow-core fiber with no band gap") in which the core can conduct additional modes in addition to the fundamental mode. For this purpose, the core is surrounded by an inner cladding with "non-resonant elements" that provide phase matching of antiresonant modes with the higher modes.

[0007] JP 2018 150184 A discloses a method for producing a preform for antiresonant hollow-core fibers. This method uses welded perforated disks at the cladding tube ends to position the non-resonant elements. A disadvantage has been found in this method is that this type of perforated disk does not achieve the required positioning accuracy of the non-resonant elements (ARE).

[0008] The publication AF: Kosolapov et al. "Hollow-core revolver fiber with a doublecapillary reflective cladding" (in Quantum Electronic, Vol. 46, No. 3, March 29, 2016 (2016-03-29), pages 267-270) describes a positioning template for ARE.

[0009] Further methods for connecting the ARE and the cladding tube are described in the following documents: CN 105807363 B, WO 2015 185761 A1, WO 2017 108061 A1, WO 2018 169487 A1. Technical task

[0010] Antiresonant hollow-core fibers, especially those with nested structural elements, have complex internal geometries, which complicates their precise and reproducible manufacturing. This is especially true because, to maintain the resonance or antiresonance conditions, only dimensional deviations below the order of magnitude of the operating wavelength of the guided light are tolerable. Deviations from the target geometry can be caused by the configuration of the fiber preform, and they can also occur due to unintentional off-scale deformations during the fiber drawing process.

[0011] The aim of the invention is to provide a method for the cost-effective production of a preform for an antiresonant hollow core fiber that avoids limitations of conventional manufacturing methods.

[0012] In particular, it is an object of the invention to provide a method for producing a preform for antiresonant hollow core fibers, with which an exact positioning of the antiresonant elements can be achieved reproducibly in a sufficiently stable manner. Preferred embodiments of the invention

[0013] A contribution to at least partially fulfilling at least one of the aforementioned objects is made by the features of the independent claims. The dependent claims provide preferred embodiments that contribute to at least partially fulfilling at least one of the objects.

[0014] Some of the described features are linked to the term "essentially." The term "essentially" should be understood in such a way that, under real-world conditions and manufacturing techniques, a mathematically precise interpretation of terms such as "superposition," "perpendicular," "diameter," or "parallelism" can never be exact, but only within certain manufacturing error tolerances. For example, "essentially parallel axes" enclose an angle of -5 degrees to 5 degrees to each other, and "essentially equal volumes" encompass a deviation of up to 5% by volume. A "device consisting essentially of quartz glass," for example, comprises a quartz glass content of ≥95 to ≤100% by weight. Furthermore, "essentially perpendicular" encloses an angle of 85 degrees to 95 degrees. Detailed description

[0015] The invention relates to a method for producing a preform of an antiresonant hollow core fiber, comprising the steps: a) Providing a cladding tube having an inner cladding tube bore and a cladding tube longitudinal axis along which a cladding tube wall delimited by an inner side and an outer side extends, b) Preparing a number of anti-resonance element preforms, each comprising an ARE outer tube and an ARE inner tube inserted therein, c) Preparing a positioning template having a number of through-openings penetrating the positioning template, adapted to a longitudinal guide of a respective anti-resonance element preform, wherein the positioning template and the cladding tube are made of the same material, so that the positioning template and the cladding tube have essentially the same chemical substance and the total mass of the different chemical elements in the positioning template and the cladding tube is less than 1 wt.-%, d) attaching the positioning template to a first end of the cladding tube, e) inserting at least parts of the anti-resonance element preforms through the through-openings for arranging the anti-resonance element preforms in the cladding tube inner bore, f) processing an assembly comprising the cladding tube, the anti-resonance element preforms and the positioning template by a hot-forming process selected from at least one of elongation and collapse.

[0016] To overcome the above-mentioned disadvantages of the prior art, the invention provides that the positioning template has at least one centering surface which interacts with the first end of the cladding tube in a self-centering manner such that the anti-resonance element preforms are arranged at desired positions in step e) "insertion".

[0017] The preform manufacturing process uses a positioning template to enable reproducible and precise placement of the antiresonant element preforms in the cladding tube's inner bore. The preform is the component from which the antiresonant hollow core fiber can be drawn. Alternatively, the preform can be further processed into a secondary preform from which the hollow core fiber is drawn. The process comprises the following steps: Step a)

[0018] As part of step a) "Providing," the cladding tube is prepared. This cladding tube has a hollow core extending along the cladding tube's longitudinal axis. In one embodiment, the cladding tube has an outer diameter in the range of 65 to 300 mm, preferably 90 to 250 mm, preferably 120 to 200 mm. In particular, the cladding tube can have a length of at least 1 m. In one embodiment, the cladding tube comprises or consists of a material that is transparent to the working light of the optical fiber, for example, glass, in particular doped or undoped quartz glass (SiO2). Doping enables the adaptation of physical properties, such as the thermal expansion coefficient. Fluorine, chlorine, and / or hydroxyl groups are preferably used as dopants that reduce the viscosity of quartz glass. Step b)

[0019] During step b) "Preparation," a number of anti-resonance element preforms are created. Anti-resonance element preforms are components or parts of the preform that essentially become anti-resonance elements in the hollow core fiber through simple elongation during the fiber drawing process. The individual anti-resonance element preform is constructed from tubular structural elements, some of which can have a wall thickness in the range of 0.1 mm to 2 mm, preferably 0.2 mm to 1.5 mm. The anti-resonance element preforms can be simple or nested components, with each anti-resonance element preform comprising an ARE outer tube and an ARE inner tube inserted therein. The anti-resonance element preforms have at least two walls that, viewed from the direction of the hollow core, have a negative curvature (convex) or no curvature (flat, straight).Further processing of the preform, in particular hot forming steps, can result in intermediate products in which the original anti-resonance element preforms are in a different shape than the original.

[0020] In one embodiment, the antiresonance element preform comprises or consists of a material that is transparent to the working light of the optical fiber, for example, glass, in particular doped or undoped quartz glass (SiO2). Doping enables the adjustment of physical properties, such as the thermal expansion coefficient. Fluorine, chlorine, and / or hydroxyl groups are preferably used as dopants that reduce the viscosity of quartz glass.

[0021] In one embodiment, the anti-resonance element preforms and the cladding tube are made of the same material. In another embodiment, the anti-resonance element preforms and the cladding tube are made of the same material, in particular of undoped or doped quartz glass (SiO2), wherein the amount of doping does not exceed 0.1 wt.%.

[0022] The term "uniform material" describes the material property of two parts. The two parts essentially contain the same chemical substance. The total mass of the different chemical elements in both parts can be less than 1 wt.%, in particular less than 0.5 wt.%, in particular less than 0.1 wt.%. In particular, the chemical composition of the two parts differs by an impurity content of less than 500 wt. ppm, in particular less than 100 wt. ppm, and / or by a dopant content of less than 10,000 wt. ppm, in particular less than 5,000 wt. ppm. Step c)

[0023] During step c) "Preparation," the positioning template is created. The positioning template has a cylindrical, lid-like, or disc-like shape. In one embodiment, the positioning template has a transverse extension of 5 to 200 mm, in particular 15 to 80 mm. In one embodiment, the positioning template and the cladding tube are made of the same material, in particular undoped or doped quartz glass (SiO2), with the amount of doping not exceeding 0.1 wt.%.

[0024] The positioning template has a number of through-holes penetrating the positioning template. Each through-hole is configured to establish at least one fluid-conducting connection between the cladding tube's inner bore and an external space through a base body of the positioning template. Furthermore, the inner diameter of the through-hole is designed such that an anti-resonance element preform can be pushed through largely longitudinally. This statement does not limit the use of an expansion of the ARE outer tube, which serves to position the anti-resonance element preforms and will be described in more detail later.

[0025] Furthermore, the through-holes are adapted to a longitudinal guide for each anti-resonance element preform. The through-holes support the anti-resonance element preforms in step f) "Processing," so their design can influence the accuracy of positioning the anti-resonance element preforms in the cladding tube's inner bore. To achieve the desired accuracy in positioning the anti-resonance element preforms at the desired positions, the through-holes can have one or more of the following features: The difference between the inner diameter of the through-hole and the outer diameter of the anti-resonance element preforms can be less than 5% of the outer diameter of the anti-resonance element preforms, in particular less than 3.5%, preferably less than 2%. At least 95%, preferably at least 97%, preferably at least 99.7% of the surface of the through-hole has a roughness Ra of [0.01; 0.4] µm, preferably [0.02; 0.2] µm. The surface of the through-hole has fewer than 1000 microcracks / cm2, preferably fewer than 500 microcracks / cm2.

[0026] In one embodiment, the positioning template and the cladding tube are made of the same material, in particular of undoped or doped quartz glass (SiO2), wherein the amount of doping does not exceed 0.1 wt.%.

[0027] The positioning template and the cladding tube are made of the same material. The term "single material" as defined above describes the material properties of the two parts: the positioning template and the cladding tube. Step d)

[0028] During step d) "Attachment," the positioning template is connected to the first end of the cladding tube. In the method according to the invention, the positioning template serves to position the anti-resonance element preforms in the cladding tube's inner bore. This requires a bond between the positioning template and the cladding tube. Step e)

[0029] During step d) "Insertion," the anti-resonance element preforms are at least partially inserted through the through-holes. The goal is to position the anti-resonance element preforms in the inner bore of the cladding tube. Step f)

[0030] In step d) "Processing", the assembly comprising the cladding tube, the anti-resonance element preforms and the positioning template is further processed by at least one of the hot processes elongation and collapse.

[0031] In the context of the invention, the term "elongation" refers to an increase in the longitudinal dimension of a body. This increase in the longitudinal dimension can be accompanied by a reduction in the transverse dimension of the body. The elongation can be performed to scale, so that, for example, the shape and arrangement of components or parts are reflected in the elongated final product.

[0032] In the context of the invention, the term "collapse" refers to a reduction in the transverse expansion of a body. This reduction in the transverse expansion of the body can occur as a result of an increase in the body's temperature and can, in particular, lead to an increase in the body's longitudinal expansion.

[0033] The term "hot process" refers to a process step in which the temperature of an element is increased by applying heat. Examples of hot processes include: Flame-based hot processes rely on the oxidation of an exothermic gas. One example is the use of hydrogen—also known as "H2"—as a fuel gas (flame hydrolysis). It reacts with the oxygen—also known as "O2"—in the air. Flameless hot processes utilize other heating systems that do not require an open flame. One example is the use of a resistor to convert electrical energy into thermal energy (heat).

[0034] According to the invention, the positioning template has at least one centering surface. This centering surface interacts with the first end of the cladding tube in a self-centering manner such that the anti-resonance element preforms are arranged at the desired positions in step e) "Insertion."

[0035] In the context of the invention, the term self-centering describes an interaction of two bodies which have an external shape designed in such a way that both assume a predefined position relative to each other without external influence.

[0036] Essential for compliance with the resonance or anti-resonance conditions in the future hollow core fiber, or for a further reduction of the attenuation in the future hollow core fiber, is the fulfillment of at least one of the following conditions: The anti-resonance element preforms must be arranged at the pre-calculated target positions in the cladding tube. The anti-resonance element preforms must be arranged at the pre-calculated target positions in the arrangement. The anti-resonance element preforms must be arranged at the pre-calculated target positions in the preform.

[0037] The invention enables a reduction of the deviation of the actual position of the anti-resonance element preforms from the desired position in the cladding tube and / or the arrangement and / or the preform.

[0038] To achieve this reduction, the positioning template has at least the centering surface, which, through self-centering, achieves a reproducible positioning relative to the cladding tube and, derived from this, a reproducible positioning of the through-openings relative to the cladding tube's inner bore. The latter then leads to a reproducible positioning of the anti-resonance element preforms at the desired positions in the cladding tube and / or the assembly and / or the preform.

[0039] After step d) "attachment," a longitudinal axis of the through-opening can be aligned substantially parallel to the longitudinal axis of the cladding tube's longitudinal axis. In one embodiment, the longitudinal axis of the through-opening and the cladding tube's longitudinal axis are configured to be parallel such that, after step d) "attachment" and step e) "insertion," the longitudinal axis of the anti-resonance element preforms and the cladding tube's longitudinal axis form an angle of -1.5 degrees to 1.5 degrees, preferably -0.85 degrees to 0.85 degrees, preferably -0.42 degrees to 0.42 degrees, to each other. This parallelism ensures that the anti-resonance element preforms are arranged at the desired positions in the cladding tube and / or the arrangement and / or the preform, thus ensuring compliance with the resonance or anti-resonance conditions in the subsequent hollow-core fiber.

[0040] The positioning template may in particular comprise a first positioning element, such as a cutout, which cooperates with a first counter-positioning element at the first end of the cladding tube, thus preventing rotation of the positioning template about its longitudinal axis.

[0041] In one embodiment, the positioning template can have at least one cylindrically designed through-opening. The inner diameter of the at least one through-opening has a diameter that is 0.15% to 7%, in particular 0.35% to 6%, in particular 0.55% to 3.5% larger than the outer diameter of the anti-resonance element preforms. With this type of configuration, the anti-resonance element preforms can be pushed directly through the through-opening and can, in particular, lie positively and / or non-positively against the inner wall of the through-openings over the entire length of the positioning template.

[0042] One embodiment is characterized in that the cladding tube is at least partially cut out in the region of the first end to form a counter-centering surface that interacts positively with the centering surface. This type of interaction facilitates the self-centering interaction of the centering surface and the first end of the cladding tube and can occur particularly during step e) "insertion." The operating load can act normally, i.e., at right angles to the surfaces of the two connecting partners.

[0043] One embodiment is characterized by the counter-centering surface and the centering surface interacting in a force-locking manner. This type of interaction can occur during step f) "Machining."

[0044] In one embodiment, an edge of the cladding tube's inner recess is provided with a chamfer at the first end. The resulting surface acts as a counter-centering surface.

[0045] One embodiment is characterized in that the positioning template is at least partially frustoconical in shape, wherein the centering surface is at least partially formed like a lateral surface.

[0046] A truncated cone is a special solid of revolution created by cutting off a smaller cone from a right circular cone parallel to the base. This smaller cone is called the complementary cone of the original truncated cone. The larger of the two parallel circular surfaces is the base, and the smaller is the top surface. The third of the two bounding surfaces is called the lateral surface. The height of a truncated cone is the distance between the base and top surfaces.

[0047] The truncated cone (or conical) shape is created by angling the side surface relative to the longitudinal axis of the positioning template. This type of development increases the geometric area of ​​the lateral surface-like centering surface compared to the peripheral surface of the positioning template. Thus, the positioning template can achieve greater positioning accuracy due to the larger surface area.

[0048] One embodiment is characterized in that the cladding tube is at least partially cut out in a truncated cone shape in the region of the first end. This type of design enables a simple self-centering interaction of the centering surface with the counter-centering surface. During step d) "Attachment," the lateral-surface-like centering surface comes to rest in a force-fitting and / or form-fitting manner in the truncated cone-shaped cutout region of the first end of the cladding tube. By coordinating the design of the centering surface and the counter-centering surface, the positioning template can be inserted into the first end of the tube. When the anti-resonance element preforms are inserted through the through-opening during step e) "Insertion," the positioning template remains in its position and ensures that the anti-resonance element preforms are arranged in the desired positions.

[0049] One embodiment is characterized in that the attachment in step d) "Attachment" is carried out using a flame-based process. In the flame-based process (such as flame hydrolysis), hydrogen – also referred to as "H2" – is preferably used as the fuel gas. It reacts with the oxygen – also referred to as "O2" – in the air. This exothermic reaction generates the energy required in step d). Heat is introduced into the cladding tube, in particular by a burner. In one embodiment, the heat is introduced at an end face of the cladding tube near the positioning template. This heat can be introduced, in particular, by means of a focused flame. The heat flows through the end face of the cladding tube and enters the tube transformation there. The heat escapes – among other places – at the cladding tube's inner bore.There, the heat then acts on the positioning template, which can lead to a material-to-material bond.

[0050] For the purposes of the invention, the term "cohesive bond" refers to the joining of two parts by fusion and by intermolecular or chemical bonding forces, possibly through additives. These connections include, in particular, welded and soldered joints. These are also non-detachable connections that can only be separated by destroying the connecting means.

[0051] One embodiment is characterized in that the anti-resonance element preforms are thermally fixed to the cladding tube wall in step f) "Processing" without flames. The position of the anti-resonance element preforms in the cladding tube, which is determined by the design of the through-openings in the positioning template, can be as follows: The anti-resonance element preforms may touch the inside of the cladding tube inner bore after step e) "Insertion", or a gap may still exist between the anti-resonance element preforms and the inside of the cladding tube inner bore after step e) "Insertion", which gap is closed in particular during step f) "Processing".

[0052] In known processes, the anti-resonance element preforms are thermally fixed to the cladding tube wall using a burner and a flame. Only then does elongation and / or collapse occur. The formation of soot (the term for SiO2 particles) and burn-off have proven to be disadvantageous. These combustion by-products can have various origins: The combustion of the fuel gas in the burner can occur with the formation of a flame with an excess of fuel or with an excess of oxidizer. Known by-products of this type of combustion include soot. Furthermore, the heat input from the burner to the cladding tube can lead to local evaporation of the quartz glass. The resulting soot can then precipitate on the individual parts of the preform, in particular on the anti-resonance element preforms.This then leads to a reduction in the quality of the final preform, which is particularly evident in higher attenuation or fiber breakage.

[0053] The deposit of soot or burn-up material forms particularly on the end face of the cladding tube and on its inner surface. Furthermore, the surfaces of the anti-resonance element preforms are particularly affected. Due to the complexity of the resulting geometry, complete cleaning, for example, with hydrofluoric acid, is hardly possible. By using the positioning template according to the invention, it is now possible to position the anti-resonance element preforms in their desired positions and then, using the flame-free process in step f) "Processing," to bond them firmly to the cladding tube wall without soot or burn-up material being deposited in the assembly.

[0054] Only by using the positioning template according to the invention, which enables precise positioning of the anti-resonance element preforms at the desired positions due to its self-centering design, can flame-based tackling or complete bonding of the anti-resonance element preforms to the cladding tube before step f) "processing" be dispensed with. In previously known manufacturing processes for preforms of an anti-resonance hollow-core fiber, a flame-based hot-forming process is used to weld the anti-resonance element preforms to the cladding tube, ensuring that they retain their position during elongation and / or collapse. The disadvantage of the preforms produced in this way being contaminated with soot or burn-off is overcome by the invention.

[0055] One embodiment of the method is characterized in that the cladding tube has a second end. The first end and the second end are located opposite each other at the outermost end points of the cladding tube.

[0056] An embodiment of the method is characterized in that the method comprises the steps: (i) Creating a second positioning template, comprising a number of second through-openings penetrating the second positioning template, each adapted to a longitudinal guide of an anti-resonance element preform, wherein the second positioning template and the cladding tube are of the same material, so that the second positioning template and the cladding tube have substantially the same chemical substance and the total mass of the different chemical elements in the second positioning template and the cladding tube is less than 1 wt.%, (ii) Combining the second positioning template with the second end of the cladding tube.

[0057] All properties described for the positioning template also apply to the second positioning template and vice versa.

[0058] The second positioning template may in particular comprise a second positioning element, such as a cutout, which cooperates with a second counter-positioning element at the second end of the cladding tube, thus preventing rotation of the second positioning template about its longitudinal axis.

[0059] An embodiment of the method is characterized in that the method comprises the steps: (iii) inserting at least parts of the anti-resonance element preforms through the through-openings of the second positioning template, (iv) wherein the second positioning template has at least one second centering surface which interacts with the second end of the cladding tube in a self-centering manner such that the anti-resonance element preforms are arranged at desired positions in step (iii) "insertion".

[0060] Within the scope of this embodiment, the anti-resonance element preforms are held in the desired position not only by means of the positioning template, but also by a combination of the positioning template and the second positioning template. Both positioning templates have through-openings through which at least some of the anti-resonance element preforms can be passed. Thus, the anti-resonance element preform can be held in the cladding tube at its two opposite ends by the positioning template and the second positioning template. This type of embodiment further increases the inventive precision in positioning the anti-resonance element preforms in the desired positions.

[0061] In one embodiment, the second positioning template can have at least one cylindrically configured second through-opening. The inner diameter of the at least one second through-opening has a diameter that is 0.15% to 7%, in particular 0.35% to 6%, in particular 0.55% to 3.5% larger than the outer diameter of the anti-resonance element preforms. With this type of configuration, the anti-resonance element preforms can be pushed directly through the through-opening and can, in particular, come to rest positively and / or non-positively on the inner wall of the through-openings over the entire length of the second positioning template.

[0062] In a further embodiment, at least one of the second through-openings can have a holding region which serves to support the anti-resonance element preforms at the end. Such a holding region can be achieved by reducing the inner diameter of the second through-opening. A holding region arranged in the second through-opening can serve to limit longitudinal movement of the anti-resonance element preforms in the cladding tube inner bore. As part of the preparation of the arrangement, at least some of the anti-resonance element preforms are inserted through the through-opening of the positioning template into the cladding tube inner bore. The second positioning template, which is attached to the second end of the cladding tube, serves in this embodiment on the one hand to ensure the positioning of the anti-resonance element preforms at the desired positions.Furthermore, longitudinal movement of the anti-resonance element preforms can be prevented during step f) "processing".

[0063] One embodiment of the method is characterized in that the cladding tube is at least partially cut out in the region of the second end in order to form a second counter-centering surface which interacts positively with the second centering surface.

[0064] An embodiment of the method is characterized in that the second positioning template is at least partially frustoconical in shape, wherein the second centering surface is at least partially formed like a lateral surface.

[0065] One embodiment of the method is characterized in that the cladding tube is at least partially cut out in the shape of a truncated cone in the region of the second end.

[0066] An embodiment of the method is characterized in that the method comprises the step: A / Producing a third positioning template, comprising a number of third through-openings penetrating the third positioning template, adapted to a longitudinal guide of a respective anti-resonance element preform, wherein the third positioning template has at least one third centering surface.

[0067] During step A / "Production," a third positioning template is created. The third positioning template can have a cylindrical, lid-like, or disc-like shape. In one embodiment, the third positioning template has a transverse extension of 5 to 200 mm, in particular 15 to 80 mm.

[0068] The third positioning template and the cladding tube can be made of the same material. In one embodiment, the third positioning template and the cladding tube are made of the same material, in particular of undoped or doped quartz glass (SiO2), wherein the amount of doping does not exceed 0.1 wt.%.

[0069] The third positioning template has a number of third through-openings penetrating the third positioning template. Each third through-opening is configured to establish at least one fluid-conducting connection between the cladding tube inner bore and an exterior space through a base body of the third positioning template. Furthermore, the inner diameter of the third through-opening is designed such that an anti-resonance element preform can be pushed through largely longitudinally. This statement does not limit the use of an expansion of the ARE outer tube, which serves to position the anti-resonance element preforms and will be described in more detail later.

[0070] Within the scope of one embodiment, the third positioning template can have at least one cylindrically configured third through-opening. The inner diameter of the at least one third through-opening has a diameter that is 0.15% to 7%, in particular 0.35% to 6%, in particular 0.55% to 3.5% larger than the outer diameter of the anti-resonance element preforms.

[0071] All properties described for the positioning template and / or the second positioning template also apply to the third positioning template and vice versa.

[0072] All properties described for the through openings and / or the second through openings also apply to the third through openings and vice versa.

[0073] An embodiment of the method is characterized in that the method comprises the step: B / Manufacturing a tubular end element, wherein the end element has an active surface in the region of a first end region in order to cooperate with the third centering surface, in particular to cooperate in a form-fitting manner.

[0074] During step B / "Manufacturing," the closure element is created, which is designed to interact with the third positioning template. Furthermore, the tubular closure element is designed to be connected to the cladding tube. The closure element can be tubular, in particular partially funnel-shaped, and generally has a maximum outer diameter that corresponds to that of the cladding tube.

[0075] The third positioning template and the closure element can be made of the same material. In one embodiment, the positioning template and the cladding tube are made of the same material, in particular of undoped or doped quartz glass (SiO2), with the amount of doping not exceeding 0.1 wt.%.

[0076] In one embodiment, the closure element and the cladding tube can be made of the same material. In one embodiment, the closure element and the cladding tube are made of the same material, in particular of undoped or doped quartz glass (SiO2), wherein the amount of doping does not exceed 0.1 wt.%.

[0077] One embodiment of the method is characterized in that the method comprises the steps: C / Linking the third positioning template to the first end region, D / Binding the end element to the second end of the cladding tube, E / Pushing at least parts of the anti-resonance element preforms through the third through-openings to arrange the anti-resonance element preforms in the cladding tube inner bore, wherein the third centering surface interacts in a self-centering manner with the active surface such that the anti-resonance element preforms are arranged at desired positions.

[0078] During step C / "Connecting," the third positioning template is positively connected to the first end region of the closure element. According to the invention, the third positioning template centers itself through the interaction of the active surface with the third centering surface.

[0079] In a further step, a force-locking and / or material-locking connection can be established between the end element and the third positioning template. The interaction of the third centering surface and the active surface ensures that the relative position of the third positioning template to the end element remains unchanged.

[0080] The third positioning template may in particular have a third positioning element, such as a cutout, which cooperates with a third counter-positioning element on the end element in order to prevent rotation of the third positioning template about its longitudinal axis.

[0081] During step D / "Connecting," the closure element is connected to the second end of the cladding tube. Step D / "Connecting" can, in particular, result in a materially bonded connection between the closure element and the cladding tube. The third positioning template, like the positioning template and / or the second positioning template, serves to ensure that the anti-resonance element preforms are arranged in the desired position in the cladding tube and / or the arrangement and / or the preform. For this purpose, the third positioning template has third through-openings that serve to arrange the anti-resonance element preforms. The third through-openings are designed to hold the anti-resonance element preforms.After at least parts of the anti-resonance element preforms have been pushed through the third through-openings of the third positioning template (step E / ), they are held in the desired positions in the cladding tube's inner bore by two positioning templates—the first positioning template and the third positioning template. Since the closure element is arranged at the second end of the cladding tube and the first positioning template is arranged at the first end of the tube, the anti-resonance element preforms are supported at each end. This arrangement can be processed into a preform using a hot-forming process as part of step f) "Processing."

[0082] One embodiment is characterized in that the closure element (also referred to as a whistle) serves to adjust a negative or positive pressure in the cladding tube. The closure element can be attached using a thermal process. A first end region of the closure element can be positioned at a distance of 0.5 to 20 mm, in particular 1 to 5 mm, from the second end of the cladding tube. The first end region and the second end are heated and then pressed together. This creates a positive connection between the two elements.

[0083] If the applied force is too high, local deformation of the first end region of the closure element and / or the second end of the cladding tube may occur during step D / "Connecting." If this deformation occurs in the region of the positioning template, it may have a negative impact on the anti-resonance element preforms and / or their positioning. To reduce the risk of potential local deformation of the first end region of the closure element and / or the second end of the cladding tube during step D / "Connecting," one embodiment is characterized in that the preform has a first connecting element. The first connecting element can be tubular and have an inner connecting element bore and a longitudinal connecting element axis, along which a connecting element wall bounded by an inner side and an outer side extends.The first connecting element and the cladding tube can be made of identical materials. The first connecting element acts as a buffer between the cladding tube and the closure element. The two are not directly connected, preventing potential deformation in the area of ​​the positioning template. In this respect,... a first end portion of the first connecting element is attached to the second end of the cladding tube and / or a second end portion of the first connecting element is attached to the first end region of the closure element.

[0084] The first connecting element can also be used to hold the cladding tube and / or to adjust a negative or positive pressure in the cladding tube.

[0085] One embodiment is characterized in that the preform has a second connecting element. The second connecting element can be tubular and have an inner connecting element bore and a longitudinal connecting element axis along which a connecting element wall delimited by an inner side and an outer side extends. Like the first connecting element, the second connecting element can serve to hold the cladding tube and / or to adjust a negative or positive pressure in the cladding tube. In this respect, a first end section of the second connecting element can be attached to the first end of the cladding tube. The second connecting element and the cladding tube can be made of identical material.

[0086] One embodiment is characterized in that a diameter of the connecting element inner bore of the first and / or second connecting element is 2-15% larger, in particular 5-10% larger, than a diameter of the cladding tube inner bore. The larger inner diameter of the first and / or second connecting element can allow the respective positioning template to be guided through the connecting element and positioned in the cladding tube. The first and / or second connecting element can have a length of 50 mm to 150 mm in order to effectively prevent potential deformation in the region of at least one of the first, second, or third positioning templates.

[0087] Step f) "Processing" can be flame-free, so that no soot or burn-off is deposited on the anti-resonance element preforms. By using the positioning template, particularly by using the positioning template in combination with the second and / or third positioning template, it is possible to position the anti-resonance element preforms so precisely at the desired positions in the cladding tube and / or the assembly that no flame-based bonding of the anti-resonance element preforms to the cladding tube is required prior to the hot process during step f) "Processing." This option not only increases efficiency compared to previously known manufacturing processes but also reduces attenuation in the finished preform and the finished anti-resonance hollow-core fiber.

[0088] An embodiment of the method is characterized in that at least one of the following steps comprises flame-free thermal bonding or flame-based thermal bonding: Step b) "Prepare", Step d) "Attach", Step (ii) "Combine", Step C / "Link" and Step D / "Tether".

[0089] To achieve a technically rapid process, it may be advantageous to create certain elements of the assembly using flame-based thermal processes. These include, in particular, those elements of the assembly that can be subjected to a cleaning step prior to processing step f) "processing." Thus, in particular, step b) "preparation" and step d) "attachment" can be cost-effectively performed using a flame-based thermal process. However, both the antiresonance element preforms and the combination of cladding tube and positioning template must be cleaned afterwards to remove any deposits from soot or burn-up. This statement also applies to at least one of steps (ii) "combining" and (c) "linking" and (d) "bonding."

[0090] However, if the precision of the arrangement of the anti-resonance element preforms in the preform and / or a reduction of the damping is of primary importance, it may be advantageous to carry out the mentioned steps within the framework of flame-free thermal bonding.

[0091] An embodiment of the method is characterized in that the method comprises at least one of the steps: Thermal fixing, in particular flame-free thermal fixing of at least some of the anti-resonance element preforms to the positioning template, and / or thermal fixing, in particular flame-free thermal fixing of at least some of the anti-resonance element preforms to the second positioning template, and / or thermal fixing, in particular flame-free thermal fixing of at least some of the anti-resonance element preforms to the third positioning template.

[0092] One embodiment of the method is characterized in that the anti-resonance element preforms are only treated by the positioning template, or the positioning template and the second positioning template, or the positioning template and the third positioning template and otherwise held in the cladding tube inner bore without any material bond.

[0093] By using the positioning template, in particular in combination with the second and / or third positioning template, it is possible to position the anti-resonance element preforms in the cladding tube inner bore at the desired positions with such precision that no thermal bonding of the anti-resonance element preforms to the cladding tube inner bore is required before elongation and / or collapse in step f) "Processing".

[0094] The self-centering design of both the positioning template and the second or third positioning template ensures that the anti-resonance element preforms remain in their respective target positions even when the assembly is manipulated. Therefore, no material bond is required between the anti-resonance element preforms and the cladding tube's inner bore.

[0095] An embodiment of the method is characterized in that the ARE outer tube has, in some regions, preferably at a first end of the anti-resonance element preform, an expansion of the outer diameter which is larger than an inner diameter of at least one of the through-openings, the second through-openings and / or the third through-openings.

[0096] The outer diameter widening serves to provide a predetermined holding point on an anti-resonance element preform when it is guided into at least one of the through-holes, the second through-holes, and the third through-holes. The arrangement of the widening on the anti-resonance element preform allows its longitudinal position in the cladding tube to be controlled.

[0097] An embodiment of the method is characterized in that the ARE outer tube has, in some regions, preferably at a second end of the anti-resonance element preform, a taper of the outer diameter which is smaller than an inner diameter of at least one of the through-openings, the second through-openings and / or the third through-openings.

[0098] The tapered portion allows the anti-resonance element preform to be inserted more easily into at least one of the through-holes, the second through-holes, and the third through-holes. A further advantage is that the number of edges is reduced and the risk of splintering of the anti-resonance element preforms during insertion and / or positioning of the anti-resonance element preforms in the through-hole is significantly reduced.

[0099] An embodiment of the method is characterized in that the positioning template and / or the second positioning template and / or the third positioning template has at least one gas flow element which connects the cladding tube inner bore to the environment of the preform in a fluid-conducting manner.

[0100] The gas flow element can be a bore that completely penetrates the positioning template and / or the second and / or third positioning template. The goal is to create a fluid-conducting connection between the cladding tube's inner bore and the surroundings of the preform. This serves to regulate the internal pressure in the cladding tube's inner bore.

[0101] One embodiment is characterized in that the cladding tube's inner bore is created by machining, in particular by drilling, milling, grinding, honing, and / or polishing. Compared to other known forming techniques using heat and pressure, these machining techniques produce more precise and delicate structures and avoid surface contamination by forming tools.

[0102] One embodiment is characterized in that the cladding tube has an outer diameter in the range of 65 to 300 mm, in particular from 90 to 250 mm, and in particular a length of at least 1 m. The accuracy of the positioning of the anti-resonance element preforms in the cladding tube is improved by providing tubular structural elements, at least some of which have a wall thickness in the range of 0.2 to 2 mm, preferably a wall thickness in the range of 0.25 to 1 mm, and wherein a cladding tube is provided with an outer diameter in the range of 65 to 300 mm, preferably with an outer diameter in the range of 90 to 250 mm, preferably with an outer diameter in the range of 120 to 200 mm. In addition, these components can each have a length of at least 1 m.

[0103] Such large-volume structural elements (anti-resonance element preforms, ARE inner tube, or ARE outer tube) simplify handling. Furthermore, with a vertical arrangement of the cladding tube and structural elements, the gravitational force supports the parallelism and vertical alignment of the longitudinal axes of the anti-resonance element preforms when the anti-resonance element preforms are positioned at their upper end at the desired position.

[0104] The above-mentioned objects are also achieved by a method for producing a secondary preform, comprising the method according to one of the preceding embodiments, comprising the step Further processing of the preform into the secondary preform, wherein the further processing comprises a single or repeated execution of one or more of the following hot forming processes: i.) Elongation, ii.) Collapse, iii.) Collapse and simultaneous elongation, iv.) Collapse of additional mantle material, v.) Collapse of additional mantle material and subsequent elongation, vi.) Collapse of additional mantle material and simultaneous elongation.

[0105] The starting point for the production of the antiresonant hollow-core fiber is a preform. In the method according to the invention, the preform is further processed into a secondary preform by performing one or more hot-forming processes.

[0106] During elongation, the preform is lengthened. This elongation can occur without simultaneous collapse. Elongation can be carried out to scale, so that, for example, the shape and arrangement of components or parts of the primary preform are reflected in the elongated final product. During elongation, the primary preform can also be drawn out of scale and its geometry can be changed. During collapse, an internal bore is narrowed or annular gaps between tubular components are closed or narrowed. Collapse is usually accompanied by elongation. The secondary preform produced in this way can already be designed and suitable for drawing a hollow core fiber. Optionally, the secondary preform can be further processed, for example by elongating it or adding additional cladding material.

[0107] The above-mentioned objects are also achieved by a method for producing an antiresonant hollow core fiber from a preform, comprising the method according to one of the preceding embodiments, comprising the step Further processing of the preform into the antiresonant hollow core fiber, wherein the further processing comprises a single or repeated execution of one or more of the following hot forming processes: i.) Elongation, ii.) Collapse, iii.) Collapse and simultaneous elongation, iv.) Collapse of additional mantle material, v.) Collapse of additional mantle material and subsequent elongation, vi.) Collapse of additional mantle material and simultaneous elongation.

[0108] The starting point for the production of the antiresonant hollow-core fiber is a preform. The antiresonant hollow-core fiber is created through a hot-process, particularly by elongating the preform.

[0109] During elongation, the preform is lengthened. Elongation can be performed to scale, so that, for example, the shape and arrangement of components or parts of the primary preform are reflected in the elongated final product. However, during elongation, the primary preform can also be drawn out of scale, and its geometry can be changed. Collapse narrows an internal bore or closes or narrows annular gaps between tubular components.

[0110] To elongate and produce the antiresonant hollow-core fiber from the preform, the preform can be passed vertically through a furnace. A lower end of the preform, from which the antiresonant hollow-core fiber is drawn in the form of a bulb, is heated to drawing temperature. The drawn fiber is then cooled from the drawing temperature by a gas flow directed counter to the drawing direction.

[0111] In one embodiment, the antiresonant hollow-core fiber is coated with an adhesion promoter, with this step being performed during the drawing process during glass fiber production. Subsequently, in a second, subsequent step, the antiresonant hollow-core fiber is coated with a plastic. This second step can be performed at a time independent of the drawing process during glass fiber production.

[0112] The plastic used for the coating can be one or more of the following materials: polyurethane acrylates, acrylates, polyolefins, polyamides (nylon), polyethers, polyurethane monoacrylates, fluoroalkyl methylacrylates or polyimide.

[0113] One embodiment is characterized in that, in at least one of steps f) "machining" and "further processing" of the assembly, a relative internal pressure (a negative pressure compared to the ambient atmospheric pressure) in the range between -10 and -300 mbar, in particular -50 and -250 mbar, is set in the cladding tube's inner bore during the elongation and / or collapse process. This pressure window ensures that the OD / ID ratio (ratio of outer diameter to inner diameter of the cladding tube) does not become too small during the elongation and / or collapse process.

[0114] One embodiment is characterized in that, in the "further processing" step, during the elongation of the preform into an antiresonant hollow core fiber, a relative internal pressure (an overpressure compared to the ambient atmospheric pressure) in the range between 0.05 mbar and 20 mbar is set in the core region. A relative internal pressure of less than 0.05 mbar can cause the antiresonant element preforms to expand excessively. Conversely, a relative internal pressure of more than 20 mbar in the core region can result in the gas pressure within the hollow channels of the antiresonant element preforms being insufficient for them to expand sufficiently during the hot forming process.

[0115] The temperature of a heating zone during the hot forming process should be as constant as possible. Therefore, it is advantageous to use a temperature-controlled heating element during the hot forming process, whose target temperature is maintained to within + / - 0.1°C. This allows temperature fluctuations during the hot forming process to be limited to less than + / - 0.5°C.

[0116] All properties and characteristics described for the through openings also apply to the second through openings and / or the third through openings and vice versa.

[0117] All properties and characteristics described for the positioning template also apply to the second positioning template and / or the third positioning template and vice versa.

[0118] The properties and features disclosed in the description may be essential for various embodiments of the claimed invention, both separately and in any combination. The properties and features disclosed for the preform or the antiresonant hollow-core fiber are also disclosed for the process, and vice versa.

[0119] The invention is further illustrated below by means of exemplary figures. The invention is not limited to the figures. Figures

[0120] It shows Fig. 1 shows a partial longitudinal section through an antiresonant hollow core fiber, Fig. 2 shows a partial cross section through an antiresonant hollow core fiber, Fig. 3 shows a partial longitudinal section through elements of a first embodiment of an arrangement, Fig. 4 shows an arrangement according to Figure 3 , Fig. 5 the preform according to Figure 3 and 4, Fig. 6 a partial longitudinal section through elements of a further embodiment of an arrangement, Fig. 7 an arrangement according to Figure 6 , Fig. 8the preform according to Figure 7 and 8 , Fig. 9 another embodiment of an arrangement, Fig. 10 the assembled preform according to Figure 9 , Fig. 11which in Figure 9 illustrated embodiment supplemented by a connecting element, Fig. 12 the assembled preform according to Figure 11 , Fig. 13 a first embodiment of a positioning template, Fig. 14 a further embodiment of a positioning template, Fig. 15 a further embodiment of a positioning template, Fig. 16 a partially assembled preform with a positioning template according to Figure 13 , Fig. 17 a preform in step f) "processing", Fig. 18 a flow chart of a method for producing a preform, and Fig. 19 a flow chart of a method for producing an antiresonant hollow core fiber. Description of the characters

[0121] Figure 1 shows a longitudinal section through an antiresonant hollow core fiber 2400. Shown is a section of the antiresonant hollow core fiber 2400 between two section lines AA and BB. The antiresonant hollow core fiber 2400 has a cladding 2450. In the illustrated embodiment of the antiresonant hollow core fiber 2400, the cladding 2450 is constructed from an elongated cladding tube 200 and an elongated cladding material 2452. Since in the illustrated embodiment the cladding material 2452 and the cladding tube material 200 are made of identical materials, the transition between the two materials in Figure 2marked with a dashed line. The antiresonant hollow-core fiber 2400 has a hollow core 2470. An electromagnetic wave can propagate through the hollow core 2470. In the illustrated embodiment, two antiresonant elements 2410 are arranged within the hollow core 2470. They are integrally connected to an inner surface 2480 of the cladding 2450. The antiresonant elements 2410 have an ARE fiber outer tube 2420 and an ARE fiber inner tube 2430. The ARE fiber inner tube 2430 is arranged in the ARE fiber outer tube 2420. The antiresonant elements 2410 are arranged parallel to a longitudinal axis 2460 of the antiresonant hollow-core fiber 2400.

[0122] The Figure 2 shows a cross section that Figure 1 shown antiresonant hollow core fiber 2400. This Figure 2illustrates the arrangement of an anti-resonance element 2410 on an inner surface 2480 delimiting the hollow core 2470. The anti-resonance elements 2410 are tubular, with the ARE fiber inner tube 2430 being integrally connected to the ARE fiber outer tube 2420. The illustrated ARE fiber inner tube 2430 and / or ARE fiber outer tube 2420 can partially have a wall thickness in the range of 0.2-2 µm. The illustrated jacket tube 2450 can have an outer diameter in the range of 90-250 mm with a length of at least 1 m. The inner diameter of the hollow core 2470 is preferably 10-50 millimeters.

[0123] The illustrated antiresonant hollow-core fiber 2400 is manufactured from a preform 100, which will be described in more detail below. The antiresonant hollow-core fiber 2400 is manufactured from the preform 100, in particular, by performing one or more of the following hot-forming processes once or repeatedly: elongation 2300, collapse 2100, and collapse 2200 of additional cladding material.

[0124] The Figure 3shows individual parts of a first embodiment of an arrangement 110 of a preform 100 according to the invention of an antiresonant hollow-core fiber 2400. The arrangement 110 has a cladding tube 200. The cladding tube 200 is tubular in design and comprises a cladding tube wall 210, which has a thickness 211 in the range of 20 mm to 90 mm. Within the scope of the method, an antiresonant element preform 300 is to be arranged on an inner side 215 of the cladding tube 200. The antiresonant elements 2410 are created from this antiresonant element preform 300 by appropriate processes.

[0125] In known methods, the anti-resonance element preforms 300 are individually inserted into a cladding tube 200. A graphite element can be used to position the anti-resonance element preforms 300. Due to the tube geometries and tolerances, these graphite elements are manufactured with a gap, which, however, leads to play for both the graphite element and the anti-resonance element preforms 300. If, for example, six anti-resonance element preforms 300 are inserted, it cannot be guaranteed that an exact angular spacing of 60° is always maintained. Furthermore, with the described technology, it is possible for the anti-resonance element preforms to rotate radially along the length of the tube.

[0126] Subsequently, in known processes, the anti-resonance element preforms 300 are fixed to the two end faces of the cladding tube 200. This is done by selectively fusing them with a hand-held torch. This creates soot, or burn-off, which deposits on the glass surfaces. This generally particularly affects the end face of the cladding tube, its inner surface, and the surfaces of the anti-resonance element preforms. Due to the complexity of the resulting geometry, a complete cleanup of the assembly is virtually impossible.

[0127] To overcome these disadvantages, the following method 2000 for producing a preform 100 of an antiresonant hollow core fiber 2400 is disclosed, comprising the method steps a) Providing 1000 a cladding tube 200 having a cladding tube inner bore 220 and a cladding tube longitudinal axis 230, along which a cladding tube wall 210 bounded by an inner side 215 and an outer side 216 extends, b) Preparing 1100 a number of anti-resonance element preforms 300, each comprising an ARE outer tube 310 and an ARE inner tube 320 inserted therein, c) Preparing 1200 a positioning template 400, having a number of through-openings 410 penetrating the positioning template 400, adapted to a longitudinal guide of a respective anti-resonance element preform 300, wherein the positioning template 400 and the cladding tube 200 are made of the same material, so that the positioning template 400 and the cladding tube 200 have essentially the same chemical substance and the total mass of the different chemical elements in the positioning template 400 and the cladding tube 200 is less than 1 wt.-%, d) attaching 1300 the positioning template 400 to a first end 250 of the cladding tube 200, e) inserting 1400 at least parts of the anti-resonance element preforms 300 through the through-openings 410 to arrange the anti-resonance element preforms in the cladding tube inner bore 220, f) processing 1500 an assembly 100 comprising the cladding tube 200, the anti-resonance element preforms 300 and the positioning template 400 by a hot-forming process selected from at least one of elongation and collapse.

[0128] It is provided that the method is designed such that the positioning template 400 has at least one centering surface 420 which interacts with the first end 250 of the cladding tube 200 in a self-centering manner such that the anti-resonance element preforms 300 are arranged at desired positions in step e) "Insertion" 1400.

[0129] In step c) "Preparation" 1200, the positioning template 400 is created, comprising a number of through-openings 410 penetrating the positioning template 400, adapted to a longitudinal guide of an anti-resonance element preform 300, wherein the positioning template 400 and the cladding tube 200 are made of the same material.

[0130] In Figure 4Parts of the anti-resonance element preforms are guided through the through-openings 410 and protrude into the cladding tube inner bore 220 (step e) "Insertion" 1400). The positioning template 400 is lowered toward the cladding tube 200 during step d) "Attachment" 1300. After the force-fitting and / or form-fitting attachment of the positioning template 400 to the cladding tube 200, the assembly 110, comprising the cladding tube 200, the anti-resonance element preforms 300, and the positioning template 400, is further processed into the preform 100 by the hot-forming process selected from at least one of elongation and collapse.

[0131] The positioning template 400 to be used is designed so that the through-holes 410 for the anti-resonance element preforms 300 are always at the same angular distance from one another, thus automatically ensuring symmetry. Furthermore, a gas flow element is provided in the center of the disk for the gas flow. This allows, for example, purging or cleaning with gas as well as the application of negative pressure throughout the entire tube structure during the subsequent process. The size of the hole can influence the gas flow through the core area and the anti-resonance element preforms.

[0132] The Figure 5 shows the preform 100. Due to the self-centering interaction of the centering surface 420 of the positioning template 400 with the first end 250 of the cladding tube 200, the anti-resonance element preforms remain at predefined target positions in step e) "Introduction" 1400 and in particular also in step f) "Processing" 1500.

[0133] One aspect of the process is that the precise joining of the cladding tube 200 and the anti-resonance element preforms 300 can take place directly in a processing system (usually a vertical glass lathe) and thus only one process step is necessary for assembling and pulling out the entire preform.

[0134] One embodiment of the method 2000 is characterized in that the anti-resonance element preforms 300 are thermally fixed to the cladding tube wall 210 in step f) "Processing" 1500 without the use of flames. A prior, selective melting of the anti-resonance element preforms 300 and the cladding tube 200, in particular the cladding tube wall 210, in particular with a hand torch, is omitted.

[0135] The Figures 6 , 7 and 8 show another embodiment of the assembly 110' and the preform 100' manufactured using the disclosed method. The embodiment according to Figures 6 , 7 and 8 largely agrees with the above-described and Figures 3 , 4 , 5 and 6 illustrated embodiment, so that to avoid repetition, reference is made to the above description. A structure which is evident from the description of the Figures 3 , 4 , 5 and 6 is repeated has the same reference numeral.

[0136] Variations of a different version of the Figures 3 , 4 , 5 and 6 structure shown have the same reference numeral with an apostrophe (').

[0137] Deviating from the Figures 3 and 4 The cladding tube 200' shown not only has a counter-centering surface 251 at the first end 250. In addition, the cladding tube 200' has a second counter-centering surface 261 at a second end 260. The method includes the following steps: (i) Creating a second positioning template 500, comprising a number of second through-openings 510 penetrating the second positioning template 500, each adapted to a longitudinal guide of an anti-resonance element preform 300, wherein the second positioning template 500 and the cladding tube 200' are made of the same material, so that the second positioning template 500 and the cladding tube 200 have essentially the same chemical substance and the total mass of the different chemical elements in the second positioning template 500 and the cladding tube 200 is less than 1 wt.%, (ii) Combining the second positioning template 500 with the second end 260 of the cladding tube 200'.

[0138] In the illustrated embodiment, the positioning template 500 is at least partially frustoconical in shape. The second centering surface 520 is partially lateral in shape.

[0139] The cladding tube 200' is at least partially cut out in the region of the second end 260 in order to form a second counter-centering surface 261, which can cooperate positively with the second centering surface 520. In Figure 6 the cladding tube 200' is at least partially cut out in the shape of a truncated cone in the region of the second end 260.

[0140] The Figure 7shows step (iii) "inserting" at least parts of the anti-resonance element preforms 300 through the second through-openings 510 of the second positioning template 500. This is followed by step f) "processing" 1500 of the assembly, comprising the cladding tube 200', the anti-resonance element preforms 300, the positioning template 400, and the second positioning template 500, by a hot-forming process selected from at least one of elongation and collapse. Combined, the second centering surface 520 interacts with the second end 260 of the cladding tube 200' in a self-centering manner such that the anti-resonance element preforms are arranged at desired positions in step (iii) "inserting" and in particular in step f) "processing" 1500, which Figure 8 clarified.

[0141] The Figures 9 and 10show an embodiment of an assembly 110" and a preform 100" manufactured using the disclosed method. The embodiment according to Figures 9 and 10 largely agrees with the above-described and Figures 3 , 4 , 5 and 6 illustrated embodiment, so that to avoid repetition, reference is made to the above description. A structure which is evident from the description of the Figures 3 , 4 , 5 and 6 is repeated, has the same reference numeral. Modifications of a variant of the Figures 3 , 4 , 5 and 6 The structure shown has the same reference numeral with two apostrophes (").

[0142] The Figure 9shows the arrangement 110" which can be formed into a preform 100" by elongation and / or collapse during step f) "Processing". The necessary process includes the step: A / Producing a third positioning template 600, having a number of third through-openings 610 penetrating the third positioning template 600, adapted to a longitudinal guide of each anti-resonance element preform 300, wherein the third positioning template 600 has at least one third centering surface 620.

[0143] In order to produce the illustrated preform 100", the following step is required: B / Manufacturing a tubular end element 700, wherein the end element 700 has an active surface 710 in the region of a first end region 730 in order to cooperate with the third centering surface 620, in particular to cooperate in a form-fitting manner.

[0144] The illustrated arrangement 110" has a funnel-like closure element 700. The outer diameter of the closure element 700 in the first end region 730 substantially corresponds to the outer diameter of the cladding tube 200. At the opposite second end region 740, the diameter of the closure element 700 is reduced to form an outlet 790. This outlet 790 can serve, among other things, to regulate the pressure conditions in the at least one anti-resonance element preform 300 or within the cladding tube inner bore 220.

[0145] The Figure 10 shows the finished preform 100", which - starting from Figure 9 - after going through the following steps, C / Linking the third positioning template 600 to the first end region 730, D / Binding the end element 700 to the second end 260 of the cladding tube 200, E / Pushing at least parts of the anti-resonance element preforms 300 through the third through-openings 610 to arrange the anti-resonance element preforms 300 in the cladding tube inner bore 220, wherein the third centering surface 620 interacts in a self-centering manner with the active surface 710 such that the anti-resonance element preforms 300 are arranged at desired positions.

[0146] In the illustrated embodiment, the anti-resonance element preforms 300 are held at two positions at the ends. First, the anti-resonance element preforms 300 are held by the positioning template 400 at the first end 250 of the cladding tube 200. In addition, the third positioning template 600 provides further end-side support for the anti-resonance element preforms 300. Together, the positioning template 400 and the third positioning template 600 ensure that the anti-resonance element preforms 300 are held at the desired positions within the cladding tube inner bore 220.

[0147] The antiresonance element preforms 300 can be thermally fixed to the cladding tube inner bore in step f) "Processing" without flames. This step is particularly illustrated by the Figure 17, which illustrates the passage of the assembly through an electric furnace 800 as part of step f) "Processing." Reference is made to the explanations given therein.

[0148] The Figures 11 and 12 show an embodiment of an assembly 110" and a preform 100", which is analogous in its external shape to that shown in Figure 9 and 10 illustrated. In this respect, reference is made to the above description to avoid repetition. Deviating from this, the arrangement 110" has a first connecting element 900 and a second connecting element 910. The first connecting element 900 is arranged at the first end 250 of the cladding tube 200 and the second connecting element 910 is arranged at the second end 260 of the cladding tube.

[0149] The Figures 13 to 15 show different designs of the positioning template 400, 400', 400".

[0150] In Figure 13A disc-like positioning template 400 is shown. This positioning template is shaped like a truncated cone, so that the side surfaces completely form the centering surfaces 420. The through openings 410 are tubular and have a constant inner diameter 411 along their longitudinal extent.

[0151] The difference between the inner diameter of the through-openings 410 and an outer diameter of the anti-resonance element preform 300 should be between 0.15% and 7%, in particular 0.35% and 6%, in particular 0.55% and 3.5%.

[0152] The positioning template 400' in Figure 14 has more inclined side surfaces, which form the centering surfaces 420. Collar region 422 is arranged above the centering surfaces 420. The first end 250 of the cladding tube 200 can be designed such that only the counter-centering surface 251 interacts with the centering surface 420, or, on the one hand, the counter-centering surface 251 interacts with the centering surface 420 and, on the other hand, the collar region 422 interacts with a counter-collar region on the cladding tube 200, in particular in a form-fitting and / or force-fitting manner. Such interaction reinforces the self-centering effect.

[0153] The through openings 410 are tubular in design.

[0154] The Figure 15 shows an embodiment of the positioning template 400", which in its external form is analogous to that shown in Figure 14 Deviating from the above, the positioning template 400" does not have tubular through-openings 410 which have a constant inner diameter. Rather, the through-openings 410' are designed tubularly in sections, with two sections having a different inner diameter. The through-openings 410' have a tubular receiving area 430, the inner diameter of which is adapted to the outer diameter of the anti-resonance element preforms 300 in order to be able to guide them at least partially, a tubular holding area 434, the inner diameter of which is smaller than the outer diameter of the anti-resonance element preforms 300 and which is designed to hold the anti-resonance element preforms 300, and a funnel-like transition area 432, which connects the receiving area 430 and the holding area 434.

[0155] This type of design of the feedthroughs 410 can fulfill two functions. The receiving area 430 serves, in particular, to position the anti-resonance element preforms 300 in the cladding tube inner bore 220. The primary function of the receiving area 430 is therefore to prevent transverse movements of the anti-resonance element preforms 300. The holding area 434, on the other hand, primarily serves to prevent longitudinal movement of the respective anti-resonance element preform 300.

[0156] All for the positioning template 400,400',400" in the Figures 13 to 15 The features shown and properties described also apply to the second positioning template 500 and / or the third positioning template 600.

[0157] The Figure 16 The arrangement 110‴ shown for a preform corresponds to that in Figure 9shown arrangement 100" for a preform 100". The two embodiments differ only in that the Figure 16 shown arrangement 110‴ has a third positioning template 600' which is structurally corresponding to the Figure 15 The positioning template 400" prevents longitudinal movement of the anti-resonance element preforms 300. These are positioned transversely by the tubular receiving areas 430 and longitudinally by the holding areas 434. This prevents the anti-resonance element preforms 300 from deviating from the desired position.

[0158] As explained, in known methods, the anti-resonance element preforms 300 are fixed to the two end faces of the cladding tube 200. This is done by selectively fusing them with a hand-held torch. This creates soot, or burn-off, which deposits on the glass surfaces and thus leads to a reduction in the quality of the preform. To overcome this disadvantage, one embodiment of the method described here is characterized in that the anti-resonance element preforms 300 are thermally fixed to the cladding tube wall 210 in step f) "Processing" 1500 without the use of flames.

[0159] The Figure 17 shows the creation of the Figure 8 shown preform 100' as part of step f) "Processing" 1500. The movement arrow 810 illustrates the direction from which the assembly 110' is moved into an electric furnace 800 - a flameless heat source - so that the preform 100' is created.

[0160] The illustrated arrangement 110' comprises the cladding tube 200'. The positioning template 400 and the second positioning template 500 are shaped like a truncated cone. The centering surface 420 and the second centering surface 520 are partially designed like a lateral surface. In this respect, the cladding tube 200 and the positioning template 400, as well as the second positioning template 500, can be configured such that they can each interact in a form-fitting manner. The elements are combined to form the arrangement 110' in the following steps: Attaching the positioning template 400 to a first end 250 of the cladding tube 200', combining the second positioning template 500 with the second end 160 of the cladding tube 200', inserting at least portions of the anti-resonance element preforms 300 through the through-openings 410 to arrange the anti-resonance element preforms in the cladding tube inner bore, and pushing at least portions of the anti-resonance element preforms 300 through the second through-openings 510 of the second positioning template 500.

[0161] In Figure 17An electric furnace 800 is listed as the flameless heat source. The assembly is heated in the hot zone of the furnace to a temperature at which the quartz glass becomes significantly less viscous and allows deformation. At the same time, one of the two working heads in which the assembly is clamped is moved, causing the cladding tube 200 to taper to a thinner cross-section and collapse. The connection between the anti-resonance element preforms 300 and the cladding tube 200 is created precisely at this point, where the tube is heated and tapered, gradually over its entire length as the process progresses.

[0162] The use of an 800-gauge electric furnace eliminates the need for a manual torch process to fix the 300-gauge antiresonance element preforms. Manual torch processes are subject to burn-off and soot formation problems associated with torch use. The contamination cannot be completely removed afterward, so the preform is already contaminated during further processing. This can lead to, among other things, blistering, inclusions, and subsequent fiber breakage during drawing. Using the furnace eliminates these problems, allowing the production of a clean preform.

[0163] In the context of step f) "Processing" 1500, the anti-resonance element preform 300 can only be the positioning template 400,400',400", or the positioning template 400,400',400" and the second positioning template 500, or the positioning template 400,400',400" and the third positioning template 600,600' and otherwise held in the cladding tube inner bore 220 without any material bond.

[0164] One aspect of the process is that the precise joining of cladding tube 200 can take place directly in a processing system (such as a vertical glass lathe) and thus only one process step is necessary for assembling and pulling out the entire preform.

[0165] In Figure 17 the anti-resonance element preform 300 shown is held in the cladding tube inner bore 220 only by the positioning template 400, 400', 400" and the second positioning template 500 and otherwise without material bond.

[0166] The Figure 18 shows an embodiment of a method 2000 for producing a preform 100 of an antiresonant hollow core fiber 2400, with the method steps a) Providing 1000 a cladding tube 200 having a cladding tube inner bore 220 and a cladding tube longitudinal axis 230, along which a cladding tube wall 210 bounded by an inner side 215 and an outer side 216 extends, b) Preparing 1100 a number of anti-resonance element preforms 300, each comprising an ARE outer tube 310 and an ARE inner tube 320 inserted therein, c) Preparing 1200 a positioning template 400, 400', 400", having a number of through-openings 410, 410' penetrating the positioning template 400, 400', 400", adapted to a longitudinal guide of a respective anti-resonance element preform 300, wherein the positioning template 400,400',400" and the cladding tube 200 are made of the same material, so that the positioning template 400,400',400" and the cladding tube 200 have essentially the same chemical substance and the total mass of the different chemical elements in the positioning template 400,400',400" and the cladding tube 200 is less than 1 wt.%, d) attaching 1300 the positioning template 400, 400', 400" to a first end 250 of the cladding tube 200, e) inserting 1400 at least parts of the anti-resonance element preforms 300 through the through-openings 410, 410' to arrange the anti-resonance element preforms in the cladding tube inner bore 220, f) processing 1500 an assembly 110 comprising the cladding tube 200, the anti-resonance element preforms 300 and the positioning template 400, 400', 400" by a hot-forming process selected from at least one of elongation and collapse.

[0167] It is provided that the method is designed such that the positioning template 400, 400', 400" has at least one centering surface 420, which interacts with the first end 250 of the cladding tube 200 in a self-centering manner such that the anti-resonance element preforms 300 are arranged at desired positions in step e) "Insertion" 1400.

[0168] The Figure 19 shows an embodiment of a method for producing an antiresonant hollow core fiber 2400 from a preform 100, in particular produced according to one of the preceding method steps 1000 to 1500, comprising the step Further processing of the preform 100 to the antiresonant hollow core fiber 2400, wherein the further processing comprises a single or repeated execution of one or more of the following hot forming processes: Collapse 2100, collapse 2200 of additional mantle material, and elongation 2300.

[0169] All properties and characteristics described for the through openings also apply to the second through openings and / or the third through openings and vice versa.

[0170] All properties and characteristics described for the positioning template also apply to the second positioning template and / or the third positioning template and vice versa.

[0171] All properties and characteristics described for the process also apply to the preform and / or the antiresonant hollow core fiber and vice versa.

[0172] Unless otherwise stated, all physical quantities specified in the claims, the description, and the figures are determined under standard conditions according to DIN 1343. The statement "under standard conditions" refers to measurements under conditions according to DIN 1343. The features disclosed for the devices, in particular preform, secondary preform, or antiresonant hollow-core fiber, are also disclosed for the method, and vice versa.

Claims

1. A method for producing a preform (100, 100', 100") of an anti-resonant hollow-core fiber, comprising the steps of: a) providing (1000) a cladding tube (200), which comprises a cladding-tube inner bore and a cladding-tube longitudinal axis, along which a cladding-tube wall extends that is delimited by an inner face and an outer face; b) preparing (1100) a number of anti-resonance-element preforms (300), each comprising an ARE outer tube and an ARE inner tube inserted therein; c) preparing (1200) a positioning template (400, 400', 400"), comprising a number of through-openings passing through the positioning template (400, 400', 400"), each through-opening being adapted for longitudinal guidance of an anti-resonance-element preform (300), the positioning template (400, 400', 400") and the cladding tube (200) being made of the same material, so that the positioning template (400, 400', 400") and the cladding tube (200) comprise substantially the same chemical substance and the total mass of the different chemical elements in the positioning template (400, 400', 400") and the cladding tube (200) is less than 1 wt.%; d) attaching (1300) the positioning template (400, 400', 400") to a first end of the cladding tube (200); e) introducing (1400) at least parts of the anti-resonance-element preforms (300) through the through-openings in order to arrange the anti-resonance-element preforms (300) in the cladding-tube inner bore; and f) processing (1500) an assembly (110, 110', 110", 110‴) comprising the cladding tube (200), the anti-resonance-element preforms (300) and the positioning template (400, 400', 400") by means of a hot-forming process selected from at least one of elongation and collapse, characterized in that the positioning template (400, 400', 400") comprises at least one centering surface which interacts with the first end of the cladding tube (200) in a self-centering manner such that the anti-resonance-element preforms (300) are arranged at desired positions in step e) "introducing."2. The method according to claim 1, characterized in that the cladding tube (200) is at least partially cut out in the region of the first end (250) in order to form a mating centering surface (251) which interacts interlockingly with the centering surface.

3. The method according to one of the preceding claims, characterized in that the anti-resonance-element preforms (300) in step f) "processing" are thermally fixed in a flame-free manner to the cladding-tube wall (210).

4. The method according to one of the preceding claims, characterized in that the cladding tube (200) comprises a second end (260).

5. The method according to claim 4, characterized in that the method comprises the steps of: (i) creating a second positioning template (500), comprising a number of second through-openings (510) passing through the second positioning template (500), each second through-opening being adapted for longitudinal guidance of an anti-resonance-element preform (300), the second positioning template (500) and the cladding tube (200) being made of the same material, so that the second positioning template (500) and the cladding tube (200) comprise substantially the same chemical substance and the total mass of the different chemical elements in the second positioning template (500) and the cladding tube (200) is less than 1 wt.%; and (ii) combining the second positioning template (500) with the second end of the cladding tube (200).

6. The method according to claim 5, characterized in that the method comprises the steps of: (iii) sliding at least parts of the anti-resonance-element preforms (300) through the second through-openings (510) of the second positioning template (500); and (iv) the second positioning template (500) comprising at least one second centering surface (520) which interacts with the second end of the cladding tube (200) in a self-centering manner such that the anti-resonance-element preforms (300) are arranged at desired positions in step (iii) "sliding."7. The method according to claim 6, characterized in that the cladding tube (200) is at least partially cut out in the region of the second end (260) in order to form a second mating centering surface (261) which interacts interlockingly with the second centering surface.

8. The method according to one of the preceding claims, characterized in that the method comprises the step of: A / making a third positioning template (600, 600') comprising a number of third through-openings (610, 610') passing through the third positioning template (600, 600'), each third through-opening being adapted for longitudinal guidance of an anti-resonance-element preform (300), the third positioning template (600, 600') comprising at least one third centering surface (620).

9. The method according to claim 8, characterized in that the method comprises the step of: B / manufacturing a tubular closure element (700), the closure element (700) comprising an active surface (710) in the region of a first end region (730) in order to interact with the third centering surface (620), in particular interlockingly.

10. The method according to claim 9, characterized in that the method comprises the steps of: C / linking the third positioning template (600, 600') to the first end region (730); D / connecting the closure element (700) to the second end of the cladding tube (200); and E / sliding at least parts of the anti-resonance-element preforms (300) through the third through-openings (610, 610') in order to arrange the anti-resonance-element preforms (300) in the cladding-tube inner bore (220), the third centering surface (620) interacting with the active surface (710) in a self-centering manner such that the anti-resonance-element preforms (300) are arranged at desired positions.

11. The method according to one of the preceding claims, characterized in that at least one of the following steps comprises flame-free thermal bonding or flame-based thermal bonding: • step b) "preparing"; • step d) "attaching"; • step (ii) "combining"; • step C / "linking"; and • step D / "binding."12. The method according to one of the preceding claims, characterized in that the anti-resonance-element preforms (300), before step f) "processing," are held in the cladding-tube inner bore only by • the positioning template (400, 400', 400"); or • the positioning template (400, 400', 400") and the second positioning template (500); or • the positioning template (400, 400', 400") and the third positioning template (600, 600'), and otherwise without an integral bond.

13. The method according to one of the preceding claims, characterized in that the positioning template (400, 400', 400") and / or the second positioning template (500) and / or the third positioning template (600, 600') comprises at least one gas flow element which connects the cladding-tube inner bore to the surrounding area of the preform in a fluid-conducting manner.

14. A method for producing a secondary preform, comprising the method according to one of the preceding claims 1 to 13, comprising the step of • further processing the preform (100, 100', 100") to form the secondary preform, wherein the further processing comprises carrying out one or more of the following hot-forming processes once or repeatedly: i.) elongation; ii.) collapse; iii.) collapse and simultaneous elongation; iv.) collapse on of additional casing material; v.) collapse on of additional casing material and subsequent elongation; and vi.) collapse on of additional casing material and simultaneous elongation.

15. A method for producing an anti-resonant hollow-core fiber from a preform (100, 100', 100"), comprising the method according to one of the preceding claims 1 to 13, comprising the step of • further processing the preform (100, 100', 100") to form the anti-resonant hollow-core fiber, wherein the further processing comprises carrying out one or more of the following hot-forming processes once or repeatedly: i.) elongation; ii.) collapse; iii.) collapse and simultaneous elongation; iv.) collapse on of additional casing material; v.) collapse on of additional casing material and subsequent elongation; and vi.) collapse on of additional casing material and simultaneous elongation.