Method and semi-finished product for manufacturing a multicore fiber

Abstract

A known method for manufacturing a multicore fiber comprises the steps of providing an elongated substrate containing a glass cladding material and having at least two through holes, inserting core rods into the through holes to form a component assembly, and drawing the component assembly to form a multicore fiber or further processing the component assembly to form a preform from which the multicore fiber is drawn, the component assembly being held from above by a glass holder connected to the substrate and forming a welding contact surface. Based on this, in order to identify a method in which the attachment of the core rods to the substrate is not limited by the layout of the holder and in particular allows the installation of all the core rods from above even after the holder has been welded, a holder with an elongated hollow section is used according to the invention, which has a hollow channel with an inner contour larger than the circumference of the hole area in which the through holes are completely present or at least 90% of their hole diameters are present, and has a radial outer dimension larger than the substrate outer diameter.

Description

[Technical Field]

[0001] The present invention provides a method for manufacturing a multicore fiber, comprising the steps of: (a) providing an elongated substrate containing a glass cladding material, the elongated substrate having a first end, a second end, a substrate longitudinal axis, a substrate side region, a radial substrate cross-section, a substrate outer diameter, and at least two through holes extending through the substrate along the substrate longitudinal axis; (b) introducing core rods containing a glass core material into at least two of the through holes, thereby forming a component assembly in which the core rods are distributed within a circumference of the hole area about the substrate longitudinal axis across the radial substrate cross section; (c) drawing the assembly of components to form a multicore fiber or further processing the assembly of components to form a preform from which the multicore fiber is drawn, wherein the assembly of components is held by a glass holder welded in the region of the first end to a substrate to form a welding interface.

[0002] The present invention further provides a semi-finished product for producing a multi-core fiber, comprising: (i) a substrate containing a glass cladding material, the substrate having a first end, a second end, a substrate longitudinal axis, a substrate lateral region, a radial substrate cross-section, and a substrate outer diameter; (ii) at least two through holes distributed across the cross section of the substrate for receiving a core rod, each having a hole diameter and extending through the substrate along the substrate longitudinal axis; (iii) a glass holder connected to the base in the region of the first end to form a welding contact surface.

[0003] In a multicore fiber, multiple optical core regions carrying light waves are integrated into the same fiber. The optical core regions are surrounded by a sheath material and extend along the longitudinal axis of the fiber. This fiber design promises high capacity for signal transmission because multiple signals are combined using spatial multiplexing methods and transmitted simultaneously in each of the core regions. [Background technology]

[0004] To fabricate a multicore fiber, for example, the so-called "stack and draw" method is used. Core rods and quartz glass cylinders of different diameters are bundled together so that they have a relatively high packing density and a certain symmetry. The cylindrical components are inserted into a sheath tube and spatially fixed therein. This assembly is either drawn into a multicore fiber or previously stretched into a preform, from which the multicore fiber is then drawn.

[0005] The stack-and-draw method requires significant calibration effort and can easily lead to dimensional accuracy problems. Due to differences in radial packing density, elongated preforms often have different radii in the azimuthal direction, which must be compensated for by cylindrical grinding.

[0006] These drawbacks are avoided by the methods described in JP 2018-052775(A) and JP 2014-201494(A) for manufacturing a multicore fiber. The substrate is used in the form of a cylinder made from a sheath material and is traversed by a plurality of through-holes extending in the direction of the longitudinal cylindrical axis. One core rod containing the core material is inserted into each of the through-holes, which are made, for example, by longitudinal drilling of the substrate. Due to the manufacturing process, a certain annular gap remains between the core rod and the inner wall of the substrate.

[0007] The assembly of the substrate and the core rod is drawn into a multicore fiber or further processed into a secondary preform, from which a multicore fiber is then drawn. During this drawing or drawing process, the annular gap collapses and the components of the assembly fuse together. To avoid gas entrapment, a negative pressure is applied to the annular gap, and the gap volume is evacuated. To evacuate the gap volume, a substantially cylindrical suction connection piece made of glass is welded to the upper end surface of the substrate, which can simultaneously serve to hold the assembly during the drawing process. This is also referred to below as a "holder." The holder is fixed to a receptacle of a mounting piece of a drawing device, for example, to a chuck of a drawing tower. Summary of the Invention [Problem to be solved by the invention]

[0008] To reduce manufacturing costs, a substrate of as large a volume as possible is fabricated, which is traversed by a large number of through-holes, some of which may extend away from the longitudinal cylindrical axis and some of which may extend near the cylindrical side areas. The larger the volume of the substrate, the greater its weight and the more stable the connection between the substrate and the holder must be.

[0009] Due to the weight of the cylinders, which can be up to 200 kg, the holder must have a sufficiently large contact surface with the substrate to avoid breakage during handling. In addition to the mechanical stresses caused by the weight of the substrate, the contact surface is also subjected to thermally induced tensile stresses that, in combination with the cylinder weight, can slightly exceed 1 MPa.

[0010] The stability of this connection can be increased by using a thicker-walled holder, thereby increasing the size of the connection surface between the base and the holder. On the other hand, the diameter of the holder is often limited by the maximum receptacle width of the mounting piece, and the welded holder must also not be so thick-walled that it blocks the through-hole, since in this case effective evacuation of the annular gap is no longer possible.

[0011] In JP 2018-052775(A), this problem is solved by using an annular intermediate piece with a central opening welded between the base and the holder, which is fluidically connected to all the through-holes via channels.

[0012] JP 2014-201494(A) proposes using a holder consisting of a plurality of hollow cylindrical dummy pieces spanning the length of the holder, the inner and outer diameters of which decrease from the bottom to the top.

[0013] In known solutions, the minimum inner diameter of the holder is smaller than the circumference of the cross-section of the base where the core rod and the opening of the through-hole are located. As a result, the holder completely or partially covers the through-hole (at its protrusion into the cross-section of the base), so that attachment of the core rod to the base from above through the central holder opening is not possible. As a result, attachment of the core rod must be performed from the opposite end of the base or before welding the intermediate piece to the holder.

[0014] Both variants of this method have drawbacks. The first variant makes handling more difficult, and the second variant can damage the core rod inserted into the through-hole due to heat input during subsequent welding of the holder. For example, the core rod can be deformed, especially if it contains a glass with a lower viscosity than the glass of the substrate, as is usually the case. Alternatively, sublimation products can precipitate on the core rod, which can lead to degradation of the optical transmission of the multicore fiber.

[0015] Even if the core rod has not yet been inserted into the through hole, the high temperatures during the welding process can lead to deformation, and in particular narrowing, of the through hole, which makes subsequent installation of the core rod more difficult. This is especially true for through holes that are close to or covered by a weld seam.

[0016] It is therefore an object of the present invention to identify a method for manufacturing a multicore fiber in which the attachment of the core rods to the substrate is not limited by the holder layout, and in particular allows all core rods to be attached from above, even after the holders have been welded.

[0017] Furthermore, it is an object of the present invention to provide a semi-finished product suitable for carrying out this method. DETAILED DESCRIPTION OF THE INVENTION

[0018] With regard to the method, this object is achieved by the invention by virtue of the method mentioned at the beginning, in which a holder is used having an elongated hollow section, the holder having a hollow channel with an inner contour greater than the circumference of the hole area in which the through holes are completely present or in which at least 90% of their hole diameter is present, and the holder has a radial outer dimension greater than the outer diameter of the base body.

[0019] Hereinafter, the first end of the substrate will also be referred to as the "top end" and the opposite second end as the "bottom end." The positional adverbs indicate the position of each end during the fiber drawing process, with the substrate longitudinal axis oriented perpendicular. The first substrate top end surface is associated with the first top end.

[0020] The elongated substrate is substantially cylindrical and has a circular cross section. At the upper and / or lower ends, it may have a thickening or taper. The outer diameter of the substrate is determined by the longitudinal portion of the cylinder between the ends.

[0021] The hollow section is connected to the base body directly or indirectly via an intermediate piece (adapter section). The composite of the hollow section and the base body is designed as a welded composite, forming a welded contact surface. The longitudinal axes of the hollow section and the base body run coaxially. In a longitudinal cross section of the welded composite, if the base body longitudinal axis is oriented vertically, the welded contact surface may run, for example, vertically (parallel to the base body longitudinal axis), horizontally (perpendicular to the base body longitudinal axis), obliquely (inclined relative to the base body longitudinal axis), curved, or a combination of these profiles in different sections.

[0022] The elongated hollow channel of the hollow section has, for example, a polygonal, round, elliptical, or (preferably) circular cross section. In the longitudinal cross section, the hollow channel is cylindrical, or it is not cylindrical but has a longitudinal narrowing or expansion. The internal shape of the hollow channel is designed so that the smallest cross-sectional contour, at the protrusion toward the upper end surface of the base, is outside the circumference of the hole area where the through-holes are completely present or where at least 90% of their hole diameter is present. In the simplest case, i.e., in the case of a hollow channel with a circular cross section and a cylindrical longitudinal cross section, the hollow channel inner diameter is larger than the circumference of the hole area. If the through-hole diameter is covered by up to 10%, a round core rod whose diameter is not more than 90% of the hole diameter can be inserted through the remaining opening.

[0023] Each through hole has a diameter large enough to allow the corresponding core rod to be inserted therein. Conversely, the cross-section of the core rod has an outer contour smaller than the diameter of the through hole. For example, the core rod has an outer diameter smaller than the diameter of the through hole. As the size difference between the core rod outer contour and the through hole diameter increases, it becomes easier to insert the core rod into the through hole. A core rod can also be attached to a through hole whose cross-section is already partially covered by a welded holder, provided that the uncovered cross-section of the through hole surrounds the core rod outer contour in cross section. On the other hand, as the size difference between the through hole diameter and the core rod outer contour increases, the axial mechanical guidance of the core rod within the through hole decreases, which leads to a deterioration in the quality of optical transmission within the multicore fiber. It has been shown that even when a through hole is covered by a welded holder over up to 10% of its diameter, it is still possible to attach a core rod to the first upper end of the substrate, and the cross-sectional dimensions of the core rod are large enough to avoid the above-mentioned drawbacks. However, the overlap of the welded holder with the through hole is preferably less than 10%, so that it is possible to install a core rod with a cross-sectional outer contour that deviates to a lesser extent from the diameter of the through hole. Particularly preferably, there is no overlap of the welded holder with the through hole. To reliably prevent deformation of the through hole during welding of the holder, the hollow portion preferably has an inner diameter larger than the circumference of the hole area, for example, at least 2 mm larger, particularly preferably at least 5 mm larger.

[0024] The outer cross section of the hollow section may be, for example, polygonal, round, elliptical, or in the simplest and preferred case, circular. In longitudinal cross section, the outer contour may be, for example, cylindrical, or it may not be cylindrical and may optionally have a longitudinal narrowing or expansion. The end of the hollow section facing the base body may have a straight, inclined, curved, or structured end face. Its maximum "radial outer dimension" is found as a protrusion toward the upper end face of the base body in the direction of the longitudinal axis of the hollow section. The maximum radial outer dimension of the hollow section limits the outer dimension (transverse) of the welding contact surface, which may be smaller than, but not larger than, the maximum radial outer dimension of the hollow section.

[0025] The fact that the maximum radially outer dimension of the end face of the hollow portion is greater than the outer diameter of the base body allows for a weld contact surface that is greater than just the annular surface defined by the outer diameter of the base body and the circumference of the hole area.

[0026] Drawing the component assembly of substrate and core rod to form a multicore fiber, or further processing to form a preform for a multicore fiber, involves performing one or more of the following hot forming processes one or more times: stretching, crushing, crushing and simultaneously stretching, crushing additional sheath material, crushing additional sheath material and then stretching, crushing additional sheath material and simultaneously stretching.

[0027] To hold the component assembly in a stretching, elongating, or collapsing device, a welded composite of the holder and the base is prefabricated, where the holder allows stable holding of even a relatively large and heavy component assembly and / or a component assembly with a hole area circumference close to the outer diameter of the base.

[0028] It has proven useful to prepare at least part of the weld contact surface, preferably the entire weld contact surface, before the core rod is introduced into the through hole.

[0029] The core rod is introduced into the through hole after the complete or at least partial creation of the welded composite of the holder and the substrate, in this way damage to the core rod due to sublimate deposition and high temperatures during the welding process is reliably prevented or reduced.

[0030] In a preferred variant of the method, at least part of the welding contact surface is generated in the side area of ​​the base body, where the hollow portion engages exclusively or partially with the side area of ​​the base body, and the upper end of the base body is essentially inserted into the hollow channel of the hollow portion, which offers several advantages. For the welded connection between the cavity and the base body, virtually any size of contact surface (i.e. on the base shell) is available. As a result of the large contact surface, even particularly heavy and voluminous component assemblies can be held reliably. Furthermore, since the welded connection is made in the region of the side through-hole, any core rod inserted in the through-hole is less susceptible to thermal influences than if the welded connection were made on the top end surface of the substrate. Therefore, deformation of the through-hole or the core rod inserted therein, as well as impurities as a result of deposition, are prevented or reduced. This applies in particular to through-holes and core rods located near the edges of the substrate. Furthermore, the through-holes in the region of the substrate's top face are not covered by the weld contact surfaces of the substrate's side regions. They are freely accessible, so that the core rod can also be inserted later (after the welded composite has been produced) from the substrate's top face. Evacuation of the annular gap is not hindered or reduced during the fiber drawing process or further processing to form the preform.

[0031] It has also proven advantageous for the welding contact surface to extend in the side region of the substrate along an extension length in the direction of the longitudinal axis of the substrate, the extension length being in the range of 5 mm to 100 mm, preferably at least 10 mm, particularly preferably at least 20 mm.

[0032] The hollow portion thereby surrounds the upper end of the base body, and the welding contact surface is preferably closed to extend around the side area of ​​the base body. For extension lengths along the base body longitudinal axis of 5 mm or more, the welding contact surface not only contributes to weight deflection of the component assembly, but also provides a certain amount of guidance for the component assembly because the hollow portion is gripped, which facilitates coaxial alignment of the longitudinal axes of the base body and the hollow portion and therefore the welding process. Further improvements are achieved when the extension length is at least 10 mm, particularly at least 20 mm. For extension lengths greater than 100 mm, material loss in the holder and base body begins to negate the benefits of increased welding contact surface and improved component guidance and alignment.

[0033] In particular, it has proven advantageous for the weld contact surface to include at least one circumferential step and / or at least one circumferential bevel over its extension length in order to further increase the strength of the weld connection and to simplify assembly and alignment.

[0034] In longitudinal cross section, the welding contact surface optionally has a nonlinear profile with a portion extending parallel to the longitudinal axis of the substrate and at least one step with a portion extending perpendicular to the longitudinal axis of the substrate, and / or at least one bevel with a portion extending at an angle to the longitudinal axis of the substrate. This nonlinear profile in longitudinal cross section results in an increased welding contact surface. The inner contour of the holder and the outer contour of the substrate are adapted to the nonlinear profile of the welding contact surface in a key-and-lock manner.

[0035] In one embodiment, the welding contact surface extends exclusively in the base side region, however, in a preferred method variant, the welding contact surface is produced both in the base side region and on the first base top surface.

[0036] As a result, a larger welding contact surface is available, making it possible to hold a heavy component assembly or preform. The portion of the welding contact surface that extends to the longitudinal axis of the substrate also facilitates coaxial alignment of the hollow and the longitudinal axis of the substrate. Since the weld connection in the region of the substrate side regions removes part of the weight of the component assembly (or of a preform made from the component assembly by fastening a core rod or by stretching), it is not necessary to fully utilize the available contact surface of the substrate top end face. Therefore, some safety margin from the through hole or the core rod inserted therein can be easily maintained.

[0037] In a particularly preferred method variant, an adapter part is used which is connected to the base body in the region of its upper end and has a radially outer dimension greater than the outer diameter of the base body, and which is welded to the hollow cylindrical bore.

[0038] The adapter part is connected, for example by welding, to the side regions and / or the top face of the base body, and is, for example, in the form of an annular profile or in the form of a plate, with a longitudinal or central axis extending coaxially with the longitudinal axis of the base body.

[0039] It has a radially outer dimension greater than the outer diameter of the base, thereby increasing the contact surface available for welding with the hollow section. In this regard, the adapter section connected to the base modifies the first upper end of the base to allow for a larger welding contact surface.

[0040] The direct contact between the hollow section and the adapter part can form the entire weld contact surface. However, a variant of the method is particularly preferred in which part of the weld contact surface is formed by direct contact between the hollow section and the adapter part and a further part of the weld contact surface is formed by direct contact between the hollow section and the base body. In this case, the connection between the hollow section and the base body is formed by a weld contact surface that is made up of a part created by direct contact between the hollow section and the base body and a part created by indirect contact (via the adapter part as an intermediate element).

[0041] The maximum radially outer dimension of the hollow section does not necessarily have to be greater than the maximum radially outer dimension of the adapter section. In the preferred case, the hollow section, which is coaxially welded to the adapter section, ends radially flush with the adapter section, i.e., it does not protrude beyond or into the adapter section.

[0042] In the connection between the adapter portion and the base, the above-mentioned example of direct connection between the hollow portion and the base (by welding to the side region and / or the upper end surface of the base) is suitable and preferable.

[0043] In a preferred variant of the method, an adapter part designed as an annular profile extending around the side area of ​​the basic body is connected to the basic body. The shape and size of the inner side area of ​​the annular profile on the one hand and the shape and size of the side area of ​​the basic body in the region of the upper end face on the other hand correspond to each other according to the lock-and-key principle. In the simplest case, the inner diameter of the profile ring corresponds to the outer diameter of the basic body in this region.

[0044] In cross section, the annular profile preferably has a polygonal shape, for example a rectangular, trapezoidal, triangular or frustoconical shape, where the annular profile has a flat upper side facing the hollow portion, which upper side is welded to the hollow portion.

[0045] In a further preferred method variant, a substantially plate-shaped adapter part is connected to the upper end surface of the base body, wherein the plate-shaped adapter part at least partially covers the circumference of the hole area and at least a portion of the through hole extends through the adapter part.

[0046] The lower side of the adapter part is connected to the upper end surface of the base body, for example by welding. The hollow part is welded to the upper side of the adapter part. The shapes and dimensions of the upper and lower sides may be the same (cylindrical disk) or may differ from each other. The adapter part preferably has the shape of a conical disk, with the radial dimension of the upper side being greater than that of the lower side. It can be designed as a solid plate or a perforated plate, for example with at least one central opening.

[0047] The adapter part, like the hollow part, has a maximum radially outer dimension that is greater than the outer diameter of the base body, thereby increasing the contact surface available for a welded connection with the hollow part. In this procedure, the welded contact surface is generally created only by a direct connection between the hollow part and the adapter part, and optionally, an exclusively indirect connection (via the adapter part as an intermediate element) is created between the hollow part and the base body.

[0048] The substantially plate-shaped adapter part is provided with a through-hole extending coaxially with all or at least one of the through-holes of the base body. Preferably, the coaxial through-holes of the adapter part and the base body are produced by drilling in a single work step. Optionally, the adapter part is connected to the top end face of the base body prior to the drilling process, for example by welding.

[0049] With regard to the semi-finished product, the above-mentioned technical object is achieved by the invention from a semi-finished product of the type mentioned at the beginning, in which the holder has an elongated hollow portion, which has an outer radial dimension greater than the outer diameter of the base body and an inner dimension greater than the circumference of the hole area in which the through holes are completely present or in which at least 90% of their hole diameter is present.

[0050] The semi-finished product exists as a welded composite of the holder and the substrate, from which a multicore fiber can be drawn after the core rod has been inserted into the substrate, or which can be further processed into a preform for a multicore fiber.

[0051] In this specification, the first end of the substrate is also referred to as the "upper end" and the opposite second end is also referred to as the "lower end." The first substrate upper end surface is associated with the first upper end. The elongated substrate is substantially cylindrical and has a circular cross section. At the upper and / or lower ends, it may have a thickening or taper. The outer diameter of the substrate is determined in the longitudinal direction of the cylinder between the ends.

[0052] The hollow section is connected to the base body directly or indirectly via an intermediate piece (adapter section). The composite of the hollow section and the base body is designed as a welded composite, forming a welded contact surface. The longitudinal axes of the hollow section and the base body run coaxially. In a longitudinal cross section of the welded composite, if the base body longitudinal axis is oriented vertically, the welded contact surface may run, for example, vertically (parallel to the base body longitudinal axis), horizontally (perpendicular to the base body longitudinal axis), obliquely (inclined relative to the base body longitudinal axis), curved, or a combination of these profiles in different sections.

[0053] The elongated hollow channel of the hollow section has, for example, a polygonal, round, elliptical, or (preferably) circular cross section. In longitudinal cross section, the hollow channel is cylindrical, or it is not cylindrical but has a longitudinal narrowing or expansion. The internal shape of the hollow channel is designed so that its smallest cross-sectional contour, at the protrusion toward the upper end surface of the base, is preferably outside the circumference of the hole area where the through holes are completely present or where at least 90% of their hole diameter is present. The hole diameter is larger than the diameter of the core rod received in the through hole, for example, 10% larger, so that slight coverage of the through hole does not prevent the core rod from filling the through hole. In the preferred case of a hollow channel with a circular cross section and a cylindrical longitudinal cross section, the hollow channel inner diameter is larger than the circumference of the hole area. Preferably, there is no overlap with the through hole due to the welded holder. Optionally, the outer contour of the core rod can be more precisely adapted to the diameter of the through hole, which is preferable, among other things, for more accurate axial guidance of the core rod within the corresponding through hole. In order to reliably prevent deformation of the through hole that may occur during welding of the holder, the hollow portion preferably has an inner diameter that is larger than the circumference of the hole area, for example, it is at least 2 mm larger than the circumference of the hole area, particularly preferably at least 5 mm larger.

[0054] Due to the fact that the protrusion of the inner contour of the hollow channel towards the upper end face of the base is completely or substantially outside the circumference of the hole area, the hollow does not cover the through hole at the protrusion towards the end face of the base, or at most covers only a very small amount (more than 90% of the hole diameter is not covered), so that the through hole remains accessible even after welding of the holder, and as a result, attachment of a core rod to the through hole from the first upper end of the base is possible.

[0055] The outer cross section of the hollow section may be, for example, polygonal, round, elliptical, or in the simplest and preferred case, circular. In longitudinal cross section, the outer contour may be, for example, cylindrical, or it may not be cylindrical and may optionally have a longitudinal narrowing or expansion. The end of the hollow section facing the base body may have a straight, inclined, curved, or structured end face. Its maximum "radial outer dimension" is found as a protrusion toward the upper end face of the base body in the direction of the longitudinal axis of the hollow section. The maximum radial outer dimension of the hollow section limits the outer dimension (transverse) of the welding contact surface, which may be smaller than, but not greater than, the maximum radial outer dimension of the hollow section.

[0056] Due to the fact that the radially outer dimension of the end face of the hollow portion is greater than the outer diameter of the substrate, the weld contact surface can also be greater than the annular surface defined by the outer diameter of the substrate and the circumference of the hole area.

[0057] The core rod is introduced into the through-hole of the semi-finished product after the complete or at least partial production of the welded composite consisting of the holder and the substrate. In this way, damage to the core rod due to the deposition of sublimation products and the high temperatures during the welding process is reliably prevented or reduced. The holder also allows for stable holding of relatively voluminous and heavy component assemblies and preforms.

[0058] In a particularly preferred embodiment, at least a portion of the welding contact surface extends in the side region of the base body. In this case, the hollow portion engages exclusively or partially with the side region of the base body. The upper end of the base body is essentially inserted into the hollow channel of the hollow portion. This provides several advantages. For the welded connection between the hollow section and the substrate, virtually any size of contact surface (i.e. of the substrate shell) is available. As a result of the large contact surface, even particularly heavy and voluminous component assemblies and preforms can be held reliably. Furthermore, since the welded connection is made in the region of the side through-hole, any core rod inserted in the through-hole is less susceptible to thermal influences than if the welded connection were made on the top end surface of the substrate. Therefore, deformation of the through-hole or the core rod inserted therein, as well as impurities as a result of deposition, are prevented or reduced. This applies in particular to through-holes and core rods located near the edges of the substrate. Furthermore, the through-holes in the region of the substrate's top face are not covered by the weld contact surfaces of the substrate's side regions. They are freely accessible, so that the core rod can also be inserted later (after the welded composite has been produced) from the substrate's top face. Evacuation of the annular gap is not hindered or reduced during the fiber drawing process or further processing to form the preform.

[0059] Advantageous embodiments of the semi-finished product according to the invention can be found in the dependent claims. Insofar as the embodiments of the semi-finished product defined in the dependent claims are reproduced in the methods described in the dependent method claims according to the invention, reference is made to the above explanations regarding the corresponding method claims for a supplementary explanation.

[0060] Definition and measurement method Individual terms in the above description are further defined below. The definitions are part of the description of the present invention. For terms and measurement methods not specifically defined herein, the interpretations given by the International Telecommunication Union (ITU) apply. In the event of a discrepancy between one of the definitions below and the rest of the description, the statement made in the description shall prevail.

[0061] base body The substrate is made of glass and includes a through bore for receiving the core rod. The glass adjacent to the through bore has a refractive index lower than that of the glass of the core rod with the highest refractive index. It may be, for example, undoped silica glass or contain at least one dopant that reduces the refractive index of the glass. Fluorine and boron are dopants that can reduce the refractive index of silica glass. The substrate is elongated and has a substantially cylindrical shape with a nominal outer diameter. Deviations from the cylindrical shape and nominal outer diameter may occur in the end region.

[0062] Core Rod The core rod is made of glass and has a radially uniform or non-uniform refractive index profile. The glass with the highest refractive index is generally located at the center axis of the core rod. It can be made of, for example, silica glass with at least one dopant added to increase the refractive index.

[0063] holder The holder serves to hold the component assembly or preform in the apparatus for drawing or elongating. It may be one piece or may be made up of multiple parts.

[0064] A first upper end of the holder is fixed in the apparatus, and the other, opposite lower end is welded to the base of the component assembly or preform either directly or indirectly via an intermediate element, such as an adapter part. The end of the holder facing the base comprises a hollow part with a central hollow channel. In the welded state, the hollow channel and the longitudinal axis of the base extend coaxially.

[0065] At least the end of the holder welded to the substrate is made of glass, preferably the same glass as the substrate, for example, quartz glass.

[0066] Component assembly / (primary) preform / secondary preform / semi-finished product The "component assembly" comprises a substrate with a core rod inserted into a through-hole. By fixing the core rod in the through-hole, e.g., by narrowing the substrate end, a "preform", also referred to herein as a "primary preform", is obtained. The component assembly or (primary) preform is stretched to form a "secondary preform" or directly to form a multicore fiber. The welded composite of the holder and substrate is referred to as a "semi-finished product".

[0067] quartz glass Quartz glass can be, for example, a melt product from naturally occurring SiO2 raw materials (natural quartz glass), or it can be synthetically produced (synthetic quartz glass), or it can consist of a mixture of these quartz glass types. Synthetic transparent quartz glass can be obtained, for example, by flame hydrolysis or oxidation of synthetically produced silicon compounds, by polycondensation of organic silicon compounds by the so-called sol-gel method, or by hydrolysis and precipitation of inorganic silicon compounds in a liquid.

[0068] welding When referring to glass components, welding is understood to mean fusing the components together at their contact surfaces, which is achieved by heating the components to be welded, at least in the region of their contact surfaces, using a heat source such as an oven, burner or laser.

[0069] Welding contact surface The weight of the component assembly or the weight of the preform is supported by the holder via the weld contact surface, the size of which is crucial for the strength of the welded composite consisting of the holder and the substrate or the holder and the preform.

[0070] The weld contact surface is the surface area of ​​the weld connection between the holder on the one hand and the substrate or preform and / or intermediate element connected to the substrate on the other hand. The available contact surface in the holder section determines and limits the size of the weld contact surface.

[0071] The weld interface may be formed directly and / or indirectly between the holder and the substrate. In a direct embodiment, the weld interface connects the holder and the substrate to one another directly. In an indirect embodiment, the holder and the substrate only contact one another indirectly, i.e., through an intermediate element connected to the substrate, and the weld interface connects the holder to the intermediate element.

[0072] Adapter part / intermediate element The adapter part may be a single part or may consist of several parts connected to one another. It is connected to the base body (e.g., by welding) and is thereby arranged laterally on the upper end surface and / or in its side area of ​​the base body. As a result of the connection to the base body, the adapter part is suitable for increasing the available contact surface with the holder, and thus the weld contact surface. At least a portion of the weld contact surface is thereby formed between the holder and the adapter part. The holder is indirectly connected to the base body via this portion of the weld contact surface. In this respect, the adapter part also functions as an intermediate element between the base body and the holder.

[0073] Position display: top / bottom These designations relate to positions during the elongation process and / or fiber drawing process: "Bottom" denotes a position in the direction of the drawing process, and "top" denotes a position opposite to the direction of the drawing process.

[0074] cross section Longitudinal / cross section taken perpendicular to the longitudinal axis.

[0075] Longitudinal cross section Longitudinal / cross section taken parallel to the longitudinal axis. [Brief explanation of the drawings]

[0076] Illustrative Embodiments In the following the invention will be explained in more detail with reference to exemplary embodiments and drawings, in which: [Figure 1]FIG. 1 is a cross-sectional view of a (primary) preform for a multicore fiber in a plan view of a welded holder in a first embodiment. [Figure 2] FIG. 2 is the preform of FIG. 1 in longitudinal cross section. [Figure 3] FIG. 3 is a longitudinal section of a second embodiment of a semi-finished product in the form of a preform for a multicore fiber. [Figure 4] FIG. 4 is a longitudinal section of a third embodiment of a semi-finished product in the form of a preform for a multicore fiber. [Figure 5] FIG. 5 is a longitudinal section of a fourth embodiment of a semi-finished product in the form of a preform for a multicore fiber. [Figure 6] FIG. 6 is a longitudinal section of a fifth embodiment of a semi-finished product in the form of a preform for a multicore fiber. [Figure 7] FIG. 7 is a longitudinal section of a sixth embodiment of a semi-finished product in the form of a preform for a multicore fiber. [Figure 8] FIG. 8 is a longitudinal section of a seventh embodiment of a semi-finished product in the form of a preform for a multicore fiber. [Figure 9] FIG. 9 is a cross-sectional view of a preform for a multicore fiber in a plan view of a welded holder in a further embodiment.

[0077] Fig. 1 shows a schematic cross section of a multicore fiber preform 1 that can be produced using the manufacturing method of the present invention, and Fig. 2 shows the preform 1 in a longitudinal cross section.

[0078] Preform 1 comprises a sheath material cylinder 2 made of synthetically produced undoped quartz glass, having upper and lower end surfaces 2a, 2b, and a cylindrical side region 2c. Sheath material cylinder 2 typically has a length in the range of 500-1500 mm and a nominal outer diameter in the range of 80-230 mm. In this and all following exemplary embodiments, the length is 1000 mm and the nominal outer diameter is 200 mm.

[0079] A plurality of through bores 4a and 4b extend through the sheath material cylinder 2 in the direction of the cylinder longitudinal axis 3. Each of the through bores 4a and 4b serves to receive a core rod 55 having a substantially circular cross section. In all embodiments, the core rod 55 is made of synthetically produced quartz glass that is conventionally doped with germanium. The through bores 4a and 4b are arranged in a symmetrical pattern, with the through bore 4a furthest from the perpendicularly oriented sheath material cylinder longitudinal axis 3 and adjacent to a hole region circumference 4c that extends coaxially relative to the longitudinal axis 3, and the remaining through bores 4b further away from the hole region circumference 4c.

[0080] A hollow cylinder 6 made of naturally occurring fused undoped quartz glass is welded to the upper end surface 2a of the sheath material cylinder 2. The hollow cylinder 6 has a center axis and a central axis 6a extending coaxially with the longitudinal axis 3 of the sheath material cylinder.

[0081] 2 shows that the weld end 7 of the hollow cylinder 6 facing the upper end surface 2a of the sheath material cylinder 2 has an inner diameter expansion over a vertically oriented longitudinal portion 7b. The expanded inner diameter corresponds to the outer diameter of the sheath material cylinder 2. The vertically oriented longitudinal portion 7b has a length L2 and abuts against a side region of the sheath material cylinder 2 and is welded thereto.

[0082] The inner circumferential step surface 7a is horizontally oriented and has a step depth L1. It rests on the upper end surface 2a of the sheath material cylinder 2 and is welded thereto. The size of the weld contact surface, which determines the strength of the welded connection, is composed of the welded longitudinal portions L1 and L2 and the corresponding radial dimensions. These dimensions are summarized in Table 1 for Embodiment 1 below and for Embodiments 2-7 below. The weld contact surface is highlighted by a thick black line S in the longitudinal cross sections shown in Figures 2-9.

[0083] The inner circumferential step surface 7a terminates in an inner diameter of 180 mm. This diameter is larger than the diameter of the hole area circumference 4c (170 mm). This means that the inner circumferential step surface 7a does not cover any of the core rod 55. Nor does it cover any of the through bores 4a and 4b. The diameter of the through bores is typically in the range of 5 mm to 50 mm, and is 30 mm in this embodiment and in all exemplary embodiments described below.

[0084] The production of the preform 1 according to FIGS. 1 and 2 is explained in more detail below. A cylinder of synthetically produced undoped quartz glass with a length of 1000 mm is fabricated and set to a nominal outer diameter of 200 mm by cylindrical grinding. Through-bores 4a, 4b with a diameter of 30 mm are created by mechanical drilling along the longitudinal axis 3. The through-bores 4a, which are further from the longitudinal axis 3, lie within a circle 4c with a diameter of 170 mm.

[0085] The internally stepped welding end 7 of the synthetically produced hollow cylinder 6 of undoped quartz glass is then brought into contact with and welded to the top end surface and side region of the sheath material cylinder 2. The welding is performed by heating the welding end 7 with a burner flame, thereby creating a vertically oriented welding surface having width L2 extending around the cylinder side region 2 and an annular welding surface having width L1 extending to the end surface.

[0086] A core rod 55 made of Ge-doped quartz glass is fabricated with a length of approximately 1000 mm and an outer diameter of approximately 28 mm. Known techniques such as VAD (Vapor Phase Axial Deposition), OVD (Outside Vapor Deposition) or MCVD (Modified Chemical Vapor Deposition) are suitable for this purpose.

[0087] The core rod 55 is inserted into the through bores 4a and 4b from either below or above, since the welded hollow cylinder 6 does not cover the through bores 4a and 4b and the through bores 4a and 4b are not deformed by welding the hollow cylinder 6. The core rod 55 is preferably inserted into the through bores 4a and 4b from above.

[0088] The lower end of the sheath material cylinder 2, to which the core rod 5 is attached, is then heated to collapse the annular gap around the core rod 5. The component assembly of the sheath material cylinder 2 and the core rod 5 thus fixed forms the primary preform 1, which is then stretched to form a secondary preform. In this case, the preform 1 is held in a stretching apparatus by a hollow cylinder 6 having a vertical orientation of its longitudinal axis 3, while a negative pressure is applied to the hollow cylinder 6. The secondary preform thus produced is finally drawn into a multicore fiber in a conventional manner in a drawing apparatus, in which the secondary preform is also held by the hollow cylinder 6.

[0089] In the preferred approach described above, the core rod 5 is inserted after welding the sheath material cylinder 2 to the hollow cylinder 6. In another, less preferred approach, the core rod 5 is inserted into the through bores 4a and 4b, and only afterwards are the sheath material cylinder 2 and the hollow cylinder 6 welded together.

[0090] 1 and 2 are used in Figures 3 to 8, the same or equivalent components and elements are thus designated as described above with reference to the description of the first embodiment of the preform 1 and its manufacture. In all embodiments of the preform, the outer diameter of the hollow cylinder is greater than the outer diameter of the sheath material cylinder 2 and its inner diameter is greater than the circumference 4c of the hole area.

[0091] [Table 1]

[0092] [Table 2] explanation: MM cylinder: Sheath material cylinder ID: Inner diameter AD:Outer diameter "Cylindrical" shape: continuously cylindrical "Predominantly cylindrical" shape: there is a deviation from a cylindrical shape in the region of the first end Circumference of hole area: diameter of a circle in which through-bores lie at 100% or at least 90% of their diameter Length L1: The total length of the (horizontal) longitudinal part of the weld contact surface extending perpendicular to the longitudinal axis (on one side of a longitudinal cross section through the cavity wall). Length L2: The total length of the (vertical) longitudinal portion of the weld contact surface extending horizontally to the longitudinal axis (on one side of a longitudinal cross section through the cavity wall). Length L3: The total length of the non-horizontal and non-vertical longitudinal portion of the weld contact surface (on one side of a longitudinal cross section through the cavity wall). Percentage: Percentage of the surface area of ​​the relevant longitudinal portion to the total area of ​​the weld contact surface L1+L2+L3: Total length of the weld contact surface (on either side of a longitudinal section through the cavity wall) Δ Reference (%): Difference in total surface area to the surface area of ​​the reference welding contact surface (annular surface between the nominal sheath material cylinder outer diameter and the circumference of the hole area) In the last row of Table 1, the difference in total surface area of ​​the weld interface is given as a percentage based on the surface area of ​​the reference weld interface, defined as the annular surface between the outer diameter of the sheath material cylinder and the circumference of the hole area (not overlapping the through bore). This means that in all embodiments, the weld interface is larger than the corresponding reference weld interface.

[0093] 3 shows an embodiment of a preform 31 having an upper end surface 2a of the sheath material cylinder 2 cut at a step, in contrast to FIG. 2. The rectangular step 2d of the stepped profile thus produced has a depth L1a.

[0094] The weld end 7 of the hollow cylinder 6 has an inner diameter expansion over a vertically oriented longitudinal portion 7b. The expanded inner diameter corresponds to the outer diameter of the sheath material cylinder 2 in the region of the rectangular step 2d. The vertically oriented longitudinal portion 7b has a length L2 and abuts and is welded to a side region of the sheath material cylinder 2 in the region of the rectangular step 2d.

[0095] The weld end 7 of the hollow cylinder 6 is welded over a length L1a to the rectangular step 2d and over a length L1b, which corresponds to the inner diameter expansion of the hollow cylinder 2, to the upper end surface of the sheath material cylinder. In this way, a particularly stable welded connection is achieved and additional guidance of the hollow cylinder 6 is obtained. The sum of the lengths L1a and L1b corresponds to the total proportion L1 of the horizontal orientation of the weld contact surface S.

[0096] In contrast to FIG. 3, in the embodiment of preform 41 in FIG. 4, the upper end surface 2a of sheath material cylinder 2 is cut into two steps. The cut includes a cylindrical surface 2e extending vertically from top to bottom with a length L2, which opens into a downwardly widening truncated cone (shown in cross section as conical section 2f) with a shell line length L3. Conical section 2f forms a 30-degree cone angle with longitudinal axis 3a and extends to cylindrical side region 2c. Thus, sheath material cylinder 2 and hollow cylinder 6 are welded to each other along the inclined shell line length L3 and along the vertically oriented length L2. The sum of lengths L2 and L3 represents the weld contact surface S.

[0097] In the embodiment of the preform 51 of Figure 5, an adapter part is provided in addition to the hollow cylinder 6. The latter consists of a circumferential quartz glass ring 8 of rectangular cross section, the inner diameter of which corresponds to the outer diameter of the sheath material cylinder 2. The adapter part (quartz glass ring 8) serves as a flange-like extension of the outer diameter of the sheath material cylinder 6. It is first welded with its inner side area 8c to the cylindrical side area 2c of the sheath material cylinder 2, so that the central axis of the quartz glass ring and the longitudinal axis 6 of the sheath material cylinder 2 extend coaxially.

[0098] The hollow cylinder 6 has an outer diameter corresponding to the outer diameter of the quartz glass ring 8 and an inner diameter smaller than the quartz glass ring 8 by a length L1b. It is installed on the joining material (sheath material cylinder 2 and quartz glass ring 8) and welded to the upper end surfaces of the quartz glass ring 8 and the sheath material cylinder 2 so that the longitudinal axes 3 and 6a extend coaxially. The resulting weld contact surface S consists of an outer ring with width L1a and an inner ring with width L1b. Here, L1a denotes the ring width of the weld connection between the hollow cylinder 6 and the quartz glass ring 8, and L1b denotes the ring width of the weld connection between the hollow cylinder 6 and the sheath material cylinder 2. By adding up the lengths L1a and L1b, a total percentage L1 of the horizontal orientation of the weld contact surface S is obtained, totaling 100%, where the weld contact surface S extends across the entire wall width of the hollow cylinder 6.

[0099] This embodiment has the advantage that no mechanical processing steps are required to produce shoulders, bevels, etc., either on the hollow cylinder 6 or on the sheath material cylinder 2 .

[0100] Alternatively, and equally preferably, the quartz glass ring 8 may also be first welded to the lower end surface of the hollow cylinder 6, and then these joined materials may be welded to the cylinder side region 2c and the upper end surface of the sheath material cylinder 6.

[0101] In contrast to Figure 5, the circumferential quartz glass ring 9 has a cross section that substantially corresponds to a right-angled isosceles triangle in the embodiment of the preform 61 of Figure 6. It is first welded at its inner side area 9c to the cylindrical side area 2c of the sheath material cylinder 2 so that the central axis of the quartz glass ring 9 and the longitudinal axis 6 of the sheath material cylinder 2 extend coaxially.

[0102] The hollow cylinder 6 has an outer diameter corresponding to the outer diameter of the quartz glass ring 9 and an inner diameter smaller than the quartz glass ring 9 by a length L1b. It is placed on the joined material made of the sheath material cylinder 2 and the quartz glass ring 9 and welded to the upper end surfaces of the quartz glass ring 9 and the sheath material cylinder 2 so that the corresponding longitudinal axes 3 and 6a extend coaxially. The resulting weld contact surface S is composed of an outer ring with a width L1a and an inner ring with a width L1b. Here, L1a denotes the ring width of the weld connection between the hollow cylinder 6 and the quartz glass ring 9, and L1b denotes the ring width of the weld connection between the hollow cylinder 6 and the sheath material cylinder 2. The sum of the lengths L1a and L1b results in a total percentage L1 of the horizontal orientation of the weld contact surface S, which is 100%. Again, the weld contact surface S extends across the entire wall width of the hollow cylinder 6.

[0103] This embodiment also has the advantage that no mechanical processing steps are required to produce shoulders, bevels, etc., either on the hollow cylinder 6 or on the sheath material cylinder 2 .

[0104] In the embodiment of preform 71 shown in FIG. 7, the sheath material cylinder 2 has an upper end 10 that flares upward in a conical manner. It is otherwise cylindrical. The flared upper end 10 is created, for example, by removing no or a small amount of glass material there during cylindrical grinding of the cylinder side region 2 to adjust the nominal outer diameter. A hollow cylinder 6 is welded to the upper thickened end of the sheath material cylinder so that the corresponding longitudinal axes 3 and 6a extend coaxially. Here too, the weld contact surface S extends exclusively horizontally across the entire wall width of the hollow cylinder 6.

[0105] In the embodiment of the preform 81 according to the invention shown in FIG. 8, the adapter part serves to extend the upper end 2a of the sheath material cylinder 2. The adapter part is in the form of a conical disk 11 (more precisely, a truncated cone) made of undoped quartz glass and having a thickness of 15 mm. Its smallest diameter corresponds to the outer diameter of the sheath material cylinder 2, and its largest diameter corresponds to the outer diameter of the hollow cylinder 6. The conical disk 11 is welded over its entire surface to the upper end face of the sheath material cylinder 2, thus covering the entire circumference 4c of the bore area. The through holes 4a and 4b for receiving the core rod 5 are therefore only made subsequently, i.e., after welding the sheath material cylinder 2 to the conical disk 11, which, together with the sheath material cylinder 2, is provided with a drilled passage.

[0106] The hollow cylinder is then welded to the planar upper side of the conical disk 11 so that the longitudinal axes 3 and 6a extend coaxially. The conical disk 11 and the hollow cylinder 6 have a maximum diameter greater than the outer diameter of the sheath material cylinder 2, thereby increasing the contact surface available for the weld connection with the hollow cylinder 6. The weld contact surface S is generated only by the direct connection between the hollow cylinder 6 and the conical disk 11, i.e., without any direct contact between the hollow cylinder 6 and the sheath material cylinder 2. It extends exclusively horizontally across the entire wall width of the hollow cylinder 6.

[0107] In contrast to the embodiment shown in FIGS. 1 and 2, in the embodiment of the preform 12 in FIG. 9, the minimum inner diameter of the hollow cylinder 6 is 164 mm (instead of 180 mm), which is therefore smaller than the circumference 4c of the hole area, which has a diameter of 170 mm. Therefore, the hollow cylinder 6 partially covers the through-bore 4a, away from the longitudinal axis 6a, at its protrusion into the cross-section of the substrate. Nevertheless, since the core rod 5 has a smaller outer diameter than the cross-section of the area not covered by the hollow cylinder 2, it is possible to fit the core rod 5 from above through the inner bore of the pre-welded hollow cylinder 2 into the sheath material cylinder 2. In this embodiment, the core rod diameter is 28 mm, and the diameter of the partially covered through-bore is 33 mm. Since 3 mm of this is covered by the hollow cylinder 2, the uncovered exposed cross-section has a minimum dimension of 30 mm.

[0108] 1 to 9 show a preform with a core rod (or a component assembly consisting of a sheath material cylinder and a core rod) attached. The figures also show a schematic representation of the semi-finished product (shell material cylinder and holder) used to produce the corresponding preform before the core rod 5 is inserted into the through-holes 4a and 4b. The above description of the exemplary embodiments of the (primary) preforms and their connection to the holder, including the tabular data, also applies to the corresponding semi-finished product for producing the component assembly or the primary preform. The component assembly and / or the preform, respectively, can be obtained from the semi-finished product by inserting the core rod 5, preferably from above, into the through-bores 4a and 4b, from which a secondary preform or directly a multicore fiber can be drawn.

Claims

1. 1. A method for manufacturing a multicore fiber, comprising: (a) providing an elongated substrate containing a glass cladding material, the elongated substrate having a first end, a second end, a substrate longitudinal axis, a substrate lateral area, a radial substrate cross-section, a substrate outer diameter, and at least two through holes extending through the substrate along the substrate longitudinal axis; (b) inserting a core rod containing a glass core material into the at least two through holes, thereby forming a component assembly; (c) drawing the assembly of components to form the multicore fiber or further processing the assembly of components to form a preform from which the multicore fiber is drawn, the assembly of components being held by a glass holder connected to the substrate in the region of the first end to form a welding interface; A holder is used having an elongated hollow portion, the hollow channel having an inner contour greater than the circumference of the hole area in which the through holes are entirely present or in which at least 90% of their hole diameter is present, and having a radially outer dimension greater than the outer diameter of the substrate, wherein: an adapter part is used, which is connected to the base body in the region of the first end and has a radially outer dimension greater than the outer diameter of the base body, and which is welded to the hollow part; Alternatively, a method is used in which a substrate is used that has an enlarged first end that is produced by removing no or a small amount of glass material therein during cylindrical grinding of the substrate side area, and a hollow cylinder is welded to the enlarged first end so that corresponding longitudinal axes extend coaxially.

2. 2. The method of claim 1, wherein at least a portion of the weld contact surface, preferably the entire weld contact surface, is prepared before the core rod is inserted.

3. 3. The method according to claim 1 or 2, characterized in that the welding contact surface extends in the base side region along an extension length in the direction of the base longitudinal axis, the extension length being in the range from 5 mm to 100 mm, preferably at least 10 mm, particularly preferably at least 20 mm.

4. 3. The method according to claim 1 or 2, characterized in that the welding contact surface comprises at least one circumferential step and / or at least one circumferential bevel over the extension length.

5. 3. The method of claim 1 or 2, wherein a substantially plate-like adapter part is connected to the top end surface of the base body, the plate-like adapter part at least partially covering the circumference of the hole area, and at least some of the through holes extending through the adapter part.

6. A semi-finished product for manufacturing a multi-core fiber, (i) a substrate containing a glass cladding material, the substrate having a first end, a second end, a substrate longitudinal axis, a substrate lateral region, a radial substrate cross-section, and a substrate outer diameter; (ii) at least two through holes distributed across the substrate cross section for receiving core rods, each having a hole diameter and extending through the substrate along the substrate longitudinal axis; (iii) a glass holder connected to the substrate in the region of the first end to form a welding contact surface; the holder comprises an elongated hollow portion having an outer radial dimension greater than the outer diameter of the substrate and an inner dimension greater than the circumference of a hole area in which the through holes are entirely present or at least 90% of their hole diameters are present, wherein: an adapter part connected to the base in the region of the first end of the base and having a radially outer dimension greater than the outer diameter of the base, welded to the hollow part; or a semi-finished product, wherein the substrate has a flared first end and a hollow cylinder is welded to the flared first end of the substrate such that their respective longitudinal axes are coaxial.

7. 7. The semi-finished product according to claim 6, wherein at least a portion of the welding contact surface is formed on the base side region.

8. 8. The semi-finished product according to claim 6 or 7, characterized in that the welding contact surface extends around the base body side area along an extension length in the direction of the base body longitudinal axis, the extension length being in the range from 5 mm to 100 mm, preferably at least 10 mm, particularly preferably at least 20 mm.

9. 9. The semi-finished product according to claim 8, characterized in that the welding contact surface comprises at least one circumferential step and / or at least one circumferential bevel over the extension length.

10. 8. A semi-finished product according to claim 6 or 7, characterized in that a substantially plate-like adapter part is connected to the top end surface of the base body, the plate-like adapter part at least partially covering the circumference of the hole area, and at least a part of the through-hole extending through the adapter part.

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