Method and semi-finished product for manufacturing a multicore fiber

Abstract

A known method for manufacturing a multicore fiber with a marker zone close to the edge comprises a method step in which a group of components is reshaped to form a multicore fiber or to form a preform for a multicore fiber, the group of components comprising a cylinder with a cylinder longitudinal axis and an outer surface and with a glass cladding region made from cladding glass, a plurality of core glass regions provided with core glass and extending in the cylinder longitudinal axis direction, surrounded by the cladding glass, and at least one marker element extending in the direction of the cylinder longitudinal axis. On this basis, in order to provide a method for manufacturing a multicore fiber with a marker zone close to the edge with a reduced risk, according to the invention, a marker element is arranged on the outer surface of the glass cladding cylinder, a longitudinal groove is created in the outer surface of the glass cladding region and extends in the direction of the cylinder longitudinal axis, and the marker element is melted in the longitudinal groove before reshaping to form the preform or the multicore fiber.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing a multicore fiber, comprising the method steps of reshaping a group of components to form a multicore fiber or to form a preform for a multicore fiber, the group of components comprising: a cylinder having a cylinder longitudinal axis and an outer surface, the cylinder having a glass cladding region made from cladding glass; a plurality of core glass regions, each of which is provided with a core glass surrounded by a cladding glass and extends in the direction of the longitudinal axis of the cylinder; at least one marker element extending in the direction of the cylinder longitudinal axis; The present invention relates to a method, comprising:

[0002] Additionally, the present invention relates to a preform for manufacturing a multicore fiber, the preform comprising a glass-cladding cylinder having a cylinder longitudinal axis and an outer surface, the glass cladding region made from a cladding glass including a plurality of openings for receiving core rods made from a core glass.

[0003] In a multicore fiber, multiple light-conducting optical core regions (hereinafter also referred to as "signal cores") are integrated into a common fiber. The signal cores extend along the fiber's longitudinal axis. They are surrounded by a cladding material with a lower refractive index, allowing for substantially independent light guidance. This fiber design ensures high signal transmission capacity because different signals coupled to a single optical fiber can be transmitted simultaneously in each of the spatially separated signal cores. This signal transmission method, also known as "spatial multiplexing," can increase data transmission capacity, particularly in optical communications. Multicore fibers are also considered important components for transmitting energy for material processing, as components of optical fiber sensors in measurement and medical technology, and for illumination and imaging purposes in microscopy or endoscopic devices. [Background technology]

[0004] Multicore fibers are manufactured by stretching a solid preform or a group of components. They often consist of synthetically produced quartz glass (SiO2), which may be doped or undoped. The production of synthetic quartz glass includes, for example, plasma or CVD deposition methods known as OVD, VAD, MCVD, PCVD, or FCVD. Liquid or gaseous silicon-containing starting materials are subjected to a chemical reaction (hydrolysis, pyrolysis, or oxidation), and the reaction product, i.e., particulate SiO2, is deposited as a solid from the gas phase on a deposition surface. The starting material is, for example, silicon tetrachloride (SiCl4) or a chlorine-free silicon compound, such as polyalkylsiloxane. The reaction zone is, for example, a burner flame, an electric arc (plasma), or a furnace.

[0005] In the so-called "stack-and-draw" method, core rods and glass cylinders of different diameters are stacked to create a relatively high packing density and a degree of symmetry. The cylindrical components are inserted into a cladding tube and spatially fixed within it. This group is either drawn to form a multicore fiber or further preprocessed to form a preform from which the multicore fiber is drawn.

[0006] The "stack-and-draw" method requires a high level of adjustment effort and easily leads to dimensional instability errors and the introduction of impurities due to the large proportion of free component surfaces. Furthermore, due to differences in radial packing density, elongated preforms often have different radius values ​​in the azimuthal direction, which must be compensated for by cylindrical grinding.

[0007] A semi-finished product and a method for stretching the semi-finished product to produce a multicore fiber are known from US Patent Application Publication No. 2016 / 347645. The semi-finished product forms a multi-part fiber preform consisting of an integral cladding tube made of cladding glass, designed to receive and axially guide a stack of three structurally identical cylindrical stack pieces made of cladding glass, each of which includes a through bore and a longitudinal groove in its cylindrical cladding surface, multiple core rods for insertion into the through bore, and multiple marker rods for insertion into the longitudinal groove. Within the cladding tube bore, the stack pieces are positioned one above the other so that the through bores and longitudinal grooves are aligned. A marker zone of the fiber preform formed by the marker rods extends on the inner cladding surface of the cladding tube.

[0008] US Patent Application Publication No. 2016 / 070058 discloses a preform and a method for producing a multicore fiber by drawing the preform. The preform has a flattened portion on its outer surface that can function as a marker element. In the fiber drawing process, a plastic coating is applied to the multicore fiber.

[0009] In the methods known from US Patent Application Publication Nos. 2015 / 284286 and 2015 / 0307387, a soot body based on SiO produced by the OVD method (SiO soot body) is used as a glass cladding cylinder, and a density of 0.8 g / cm 3 ~1.6g / cm 3In the OVD method, the deposition surface is typically the outer surface of a rod-shaped or tubular deposition mandrel that rotates about its longitudinal axis. A substantially cylindrical soot body is deposited by rotating back and forth through a reaction zone. After the deposition process is completed, the deposition mandrel is removed, leaving a central through-opening at the central axis of the cylindrical soot body. The hollow glass cladding cylinder thus produced has a longitudinal bore for receiving a core glass rod. The lower density of SiO2 soot bodies compared to quartz glass makes it easier to fabricate a dimensionally accurate longitudinal bore. The central "OVD through-opening" remaining due to the manufacturing process can result in asymmetric deformation during collapse, potentially destroying the fiber design. Furthermore, the collapse reduces the cross-sectional area of ​​the cladding glass fraction. These drawbacks can be avoided by using a component that closes the OVD through-opening. This can be, for example, a core rod or a filler rod. The filler rod is made of glass with substantially the same refractive index as the hollow glass cladding cylinder. The filler rod can also be manufactured by OVD or press molding, or a combination of press molding and OVD. Furthermore, a channel for receiving the marker element is formed in the hollow glass cladding cylinder. The channel is created by mechanically drilling a bore in the region of the hollow glass cladding cylinder near the edge.

[0010] In multicore fibers, the marker elements serve to form continuous linear marker zones, breaking the symmetry around the signal core and allowing their positions to be clearly identified and assigned to each other relative to each other and to the fiber central axis, which is necessary, for example, so that two multicore fibers can be joined together with low attenuation by their end faces using conventional splicing methods.

[0011] To splice multicore fibers, the fiber ends to be connected are positioned so that their end faces face each other. In a known method, light is simultaneously supplied to all signal cores at the opposite fiber end and collectively detected at the fiber end of the other multicore fiber by a photodetector and a power meter. In particular, when one end of a multicore fiber is unavailable for supplying light, light is irradiated laterally onto the multicore fiber. By relatively displacing the multicore fiber end faces in the horizontal and vertical directions and relatively rotating them in the azimuthal direction, the fusion splicer automatically aligns the fiber ends until the signal cores are correctly assigned and the received collected light power is maximized, and then the fiber ends are fused to each other in this position.

[0012] This splicing method assumes that the multicore fiber is pre-spliced, for example, in a factory. To enable easy splicing of multicore fibers at the installation site, U.S. Patent No. 9,541,707 proposes a multicore fiber design in which multiple signal cores are arranged in a glass cladding region and a marking zone is exposed on the outer surface of the multicore fiber. This particular characteristic of the fiber design is hereinafter also referred to as the "near-edge marker zone."

[0013] To produce a multicore fiber with a marker zone close to the edge, a plurality of through bores extending in the direction of the longitudinal cylinder axis are produced in the glass cladding cylinder. Specifically, a plurality of core rod bores and marker rod bores are produced. The marker rod bores are located as close as possible to the outer surface of the glass cladding cylinder. A core rod is inserted into each core rod bore, and a marker rod is inserted into each marker rod bore. The outer periphery of the glass cladding cylinder is then ground until a portion of the marker rod is exposed. From the components thus produced, a multicore fiber is drawn with the surface on which the marker zone is exposed. Technical Problem

[0014] The glass cladding cylinder is elongated, and therefore the through holes have a large aspect ratio (ratio of length to diameter), which in principle makes dimensionally accurate manufacturing and precise alignment parallel to the longitudinal axis of the glass cladding cylinder more difficult.

[0015] Theoretically, the greater the number of multi-cores, the greater the increase in data transmission capacity compared to an optical fiber with a single fiber core (single-mode fiber or multimode fiber). On the other hand, in principle, each of the multiple cores must have an optical attenuation that roughly corresponds to that of an optical fiber with a single core. This requires that the fiber design does not cause any additional attenuation or impair the independent information transmission of the signal cores as interference signals. However, this can be caused by so-called "crosstalk" between multiple cores, especially if they are too close to each other. This effect therefore requires that a certain minimum distance be maintained between the fiber cores. For these reasons, the available cross-sectional area in the radial cross-section of a multi-core fiber must be fully utilized as much as possible for the occupation of the multiple cores.

[0016] In addition, marker zones are always imperfections in a multicore fiber, which in principle should be as small as possible, but as large as necessary to ensure their detectability. A small size of the marker zone is also advantageous for counteracting other undesirable effects, such as so-called fiber curl or stresses induced in the fiber.

[0017] Therefore, the marker zone, which is additionally introduced into the fiber design, should occupy as small a percentage of the fiber cross section as possible. Therefore, the diameter of the channel for receiving the marker element is small, generally significantly smaller than the diameter of the bore for receiving the core rod. Typically, the channel diameter of the glass cladding cylinder before the fiber drawing process is less than 15 mm, with an aspect ratio of more than 65 (cylinder length is approximately 1 m).

[0018] Even when a high-precision drilling and boring machine is used, dimensionally accurate fabrication and precise alignment of such thin channels in a glass-clad cylinder is difficult. The cost of fabricating a glass-clad cylinder from synthetic quartz glass is high, and losses are particularly painful, especially for small bores to accommodate marker elements that would otherwise result in the finished glass-clad cylinder being rejected.

[0019] Even worse, for marker rod bores close to the edges, only a thin residual wall remains, which can easily break both during the manufacture of the through bore and during further processing, especially when the marker rod is inserted.

[0020] Grinding of the outer periphery of the glass-clad cylinder according to U.S. Patent No. 9,541,707 is carried out when the through-bore is fully equipped with the core rod and marker rod. Apart from the fact that grinding must be carried out with the utmost care and therefore requires a lot of time and money, this method step carries the risk of total loss.

[0021] It is therefore an object of the present invention to provide a method for manufacturing a multicore fiber having a marker zone close to its edge, which reduces the drawbacks of known methods, in particular reducing the risk of rejection.

[0022] 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

[0023] With regard to this method, this object is achieved in accordance with the present invention and based on the method described at the beginning in that marker elements are arranged on the outer surface of a glass cladding cylinder, longitudinal grooves are created on the outer surface of the glass cladding region extending in the direction of the cylinder longitudinal axis, and the marker elements are melted in the longitudinal grooves before reshaping to form a preform or a multicore fiber.

[0024] At least one longitudinal groove is created in the outer surface of the glass cladding region extending in the direction of the longitudinal cylinder axis, and a marker element is placed in this groove and melted in. Placing the marker element on the outer surface of the glass cladding cylinder includes, for example, attaching the marker element in the form of a component in the longitudinal groove on the outer surface, and applying, depositing or pressing the marker element in the form of a layer or mass in the longitudinal groove on the outer surface.

[0025] This procedure has several advantages over the prior art. (1) The effort of creating a bore in the glass cladding cylinder to receive the marker element is eliminated, along with the associated risk of failure. (2) The marker elements melted in the longitudinal grooves are exposed on the outer surface, thus eliminating the effort and risk of failure involved in removing the cladding glass material to expose the marker glass, in contrast to the method known from US Pat. No. 9,541,707. (3) Due to the fact that the marker element is adjacent to the outer surface, axially parallel alignment of the marker element is achieved. Dimensional stability and straightness of the outer surface of the glass cladding cylinder can be relatively easily ensured. For example, by machining or a stretching process, the starting cylinder is stretched to form a cylinder strand from which the glass cladding cylinder is manufactured, or from which multiple glass cladding cylinders are cut to length. To prevent surface damage, the stretching process is preferably performed without the use of a forming tool that engages the stretched cylinder strand. (4) It is possible to omit creating a bore for receiving the marker element. The arrangement on the outer surface allows for particularly small marker elements with an aspect ratio of virtually any size. (5) By melting the marker elements into the longitudinal grooves before reshaping the components to form the multicore fiber or preform, it is possible to ensure that the side edges of the longitudinal grooves filled with the melted marker elements form a continuous transition to the outer surface of the glass cladding region with almost no gradient, thus avoiding structural defects during the fiber drawing process. This has a positive effect on the dimensional stability of the multicore fiber. The marker elements optionally fill the longitudinal grooves completely and ideally have a curvature that matches the outer contour of the outer surface. If the spatial volume of the longitudinal groove and the volume occupied by the marker element after melting are approximately the same size, this contributes to a complete filling of the longitudinal groove. Achieving this is simplified if, before melting, the marker element can protrude to any desired extent relative to the upper edge of the longitudinal groove, and the height of this protrusion is not limited by an outer cladding tube or the like. Such limitations can be omitted in the method according to the invention. (6) During the joining process, the peripheral markers can be detected optically with relative ease. (7) In addition, the azimuthal alignment accuracy of the multicore fiber is high for the splicing process because the peripheral position of the marker is particularly sensitive to angular deviations.

[0026] The edge location of the marker zone in the multicore fiber results from the similar peripheral location of the marker element on the outer cladding of the glass cladding region of the component group or on the outer cylindrical cladding surface of the preform, where "peripheral" means that the marker element is part of the outer surface of the glass cladding region of the component group or the outer surface of the preform.

[0027] The component groups are equipped with marker elements that do not require the creation of separate bores in the glass cladding cylinder, which is associated with the risks and difficulties mentioned above. At the same time, high dimensional stability can be ensured, which manifests itself, for example, in the preform or component group, with deviations of the axial parallelism of the marker elements of less than 0.3 mm / m.

[0028] The longitudinal grooves are filled with marker elements, for example, by inserting cylindrical elements (rods or tubes) made of marker glass that extend parallel to the outer surface of the glass cladding cylinder, or by introducing a bed of marker glass particles, or by coating the interior of the longitudinal grooves with marker glass.

[0029] A marker element in the form of a tube may be open on both sides or at least one side (an opening above the softening zone will suffice). This allows the application of pressure so that hollow channels ("air lines") remain in the finished multicore fiber, thereby preventing complete collapse of the tube's inner bore during re-shaping of the preform or components to form the multicore fiber. Alternatively or additionally, the formation of hollow channels in the multicore fiber may be facilitated by the tube wall comprising a material with a higher viscosity than the cladding glass, so that the bore does not completely collapse during the fiber drawing process.

[0030] The marker elements (components, beds, layers) arranged in the longitudinal grooves are fixed therein by fusion, and for this purpose are melted in the longitudinal grooves over at least a part of their length, preferably locally at several points distributed over their length, and ideally over their entire length.

[0031] Thus, a preferred procedure provides that the marker element has a length and that the marker is completely melted in an area or point along at least 80% of this length, preferably at least 90% of this length.

[0032] Melting the marker element preferably includes a method step in which the glass cladding cylinder is mounted with the cylinder longitudinal axis oriented horizontally so that the longitudinal groove is located on top, and the material of the marker element is heated and softened by a heat source.

[0033] By melting a marker element with a horizontally oriented cylindrical longitudinal axis, the material of the marker element sinks by gravity as soon as it is locally heated and softened, for example by a burner or laser, thereby filling the cavity remaining in the longitudinal groove. Surface tension can result in rounding of the free surface area adjacent to the atmosphere.

[0034] In this way, it is substantially easier to uniformly, preferably completely, fill the longitudinal grooves than if, for example, the marker elements and longitudinal grooves were vertically oriented during the melting process.

[0035] The marker elements fused within the longitudinal grooves are fixed relative to the glass cladding cylinder, which simplifies their handling during later stages of the fiber manufacturing process. During melting, a degree of rounding of the marker material, and therefore conformance to the contours of the outer surface of the glass cladding cylinder, can be achieved as a result of surface tension. After melting the marker elements, the absence of defects and the quality of the melting process can be monitored and improved if necessary.

[0036] Two or more, e.g., four to seven, longitudinal bores (core rod bores) are conventionally fabricated in the glass cladding cylinder, with their longitudinal axes extending parallel to the longitudinal axis of the central bore. The core rod bores may be through or blind, and in each case serve to accommodate at least one core rod made from a core glass. In the radial direction, the composition of the core glass may be uniformly homogeneous or vary gradually or stepwise. This differs from the cladding glass in that light guidance within the core glass region is guaranteed.

[0037] The desired number of core rod bores can be produced in one operation, each occupied by at least one core rod, or only one core rod bore or a first distribution of the desired number of core rod bores can be produced in advance, each occupied by at least one core rod, and the core rod bore occupied by the core rod can be collapsed (this reshaping process is also referred to herein as "consolidation") before the remaining or further distribution of core rod bores is produced in a second or further operation, each occupied by at least one core rod and optionally collapsed. In the simplest case, all core rods have the same dimensions and consist of the same core glass. However, the core rods can also differ with respect to their dimensions and / or the composition of the corresponding core glasses.

[0038] Placing the marker element on the outer surface and fusing it into the longitudinal groove can occur before or after all of the core rod bores have been created and / or filled, or before or after a portion of the core rod bores have been created and / or filled. In a preferred procedure, the marker element is placed on the outer surface and fused into the longitudinal groove, and then the desired core rod bores are created.

[0039] The components thus produced can be reshaped and directly drawn to form a multicore fiber, or consolidated to form a preform for a multicore fiber, the consolidation process being associated with a simultaneous elongation process. The "consolidated preform" thus produced is optionally drawn to form a multicore fiber, or further processed to form a "secondary preform." Further processing to form a "secondary preform" includes, for example, creating additional bores in the glass cladding region and its coating with core glass or other glasses, or performing one or more of the following hot-forming processes once or repeatedly: collapsing, stretching, collapsing, and simultaneous elongation. A multicore fiber is drawn from the secondary preform produced by further processing, in which the peripheral marker elements of the components form a peripheral marker zone.

[0040] Due to the peripheral location of the marker zone, fiber splicing equipment can identify the marker zone more quickly and accurately. Due to the relatively simple detectability of the peripheral marker zone, the marker zone can be made particularly small so that the multicore fiber can be given a relatively low fiber curl during the fiber drawing process. A characteristic of glass fiber is defined as the degree of curvature over a specific length of the fiber and is called "fiber curl." The curvature results from thermal stresses that occur during fiber manufacturing. Large "fiber curl" makes low-attenuation splicing of multicore fibers more difficult.

[0041] Compared to bores, longitudinal grooves are particularly easy to manufacture on the outer surface, for example, by milling with a mechanical milling machine or laser ablation. On the other hand, longitudinal grooves manufactured in this way are as accurate and straight as the glass cladding cylinder itself. Furthermore, the depth or opening width of the longitudinal grooves can be made substantially as small as desired, for example, both less than 15 mm, preferably less than 10 mm, and particularly preferably less than 5 mm. Thus, by filling the longitudinal grooves with marker glass, small-volume, geometrically accurate marker elements can be manufactured in a simple manner, which have an axial deviation of less than 0.3 mm / m in the preform or component group, thus forming a correspondingly small, high-precision marker zone in the multicore fiber.

[0042] The marker glass fills the longitudinal grooves completely or partially. In a particularly preferred method variant, the cladding glass volume V M A cladding glass having a volume V is removed from the glass cladding cylinder to create a longitudinal groove. E A marker element having a V is received in the longitudinal groove. E =V M + / -0.1xV M is.

[0043] The marker glass volume is sized so that the molten marker glass fills the longitudinal groove's open volume as completely as possible, ideally with a curvature that matches the contour of the outer surface. This avoids asymmetries and defects as much as possible during the fiber drawing process. The cross-sectional contours of the longitudinal groove and the marker element do not need to match for this purpose. The longitudinal groove preferably has a circular lower portion.

[0044] In a preferred procedure, the production of the component group comprises the following method steps: (a) providing a glass cladding cylinder containing cladding glass; (b) providing a core rod comprising a core glass; (c) providing a marker element; (d) creating at least one longitudinal groove on the outer surface of the glass cladding cylinder; (e) creating a core rod bore extending along the cylinder longitudinal axis; (f) disposing and fusing a marker element within the longitudinal groove; (g) introducing a core rod into the core rod bore, thereby forming a core glass region;

[0045] The component group thus produced includes a glass cladding cylinder, a marker element, and at least two core rods. The list designations (a)-(g) merely designate a preferred, but not required, order of the method steps.

[0046] By attaching the marker element to the glass cladding cylinder, the marker element benefits from its straightness and alignment, these properties being virtually transferred to the marker element, which extends along the longitudinal axis of the glass cladding cylinder, preferably over its entire length.

[0047] The marker glass preferably differs from the cladding glass and any glass filler material in at least one physical and / or chemical property selected from refractive index, color, fluorescence and / or specific glass density.

[0048] The characteristic (or characteristics) that distinguish the marker element from the glass of the component group particularly influences the visual appearance of the marker element and is preferably detectable by an optical sensor. The glass composition of the marker glass can be based on quartz glass. The refractive index of the quartz glass can be changed by doping. For example, doping the marker quartz glass with fluorine reduces the refractive index compared to undoped quartz glass. Incorporating carbon into the marker quartz glass can result in a black coloration. Depending on the oxidation state, doping the marker quartz glass with titanium results in a gray-blue coloration. Doping the marker quartz glass with rare earth metals or germanium oxide results in fluorescence at dopant-specific wavelengths. The specific glass density of the marker element can be changed by pores, which is manifested in a reduced optical transparency compared to bubble-free glass.

[0049] The glass cladding cylinder is preferably a hollow cylinder having a central bore.

[0050] Such hollow cylinders can be obtained, for example, by the OVD (Outside Vapor Deposition) method after the deposition mandrel is removed. The production of hollow glass-clad cylinders based on the OVD process is cost-effective compared to other manufacturing methods, especially the VAD (Vapor Axial Deposition) process. However, it has the disadvantage that the aforementioned central bore may remain. This can be completely or partially closed by a core rod or glass rod containing another glass filler material.

[0051] With regard to the semi-finished product, the above technical object is achieved by a semi-finished product having the features of claim 8.

[0052] The semi-finished product according to the invention comprises a glass cladding cylinder having an opening for receiving a core rod, the outer surface of which has at least one recess extending in the direction of the longitudinal axis of the cylinder and designed as a longitudinal groove in which the marker element is melted.

[0053] The recesses form longitudinal grooves (longitudinal slots) on the outer surface of the glass-cladding cylinder. Longitudinal grooves on the outer surface are particularly easy to manufacture, for example, by milling with a mechanical milling machine or by laser ablation, compared to bores. On the other hand, the longitudinal grooves manufactured in this manner are as precise and linear as the glass-cladding cylinder itself. Furthermore, the depth or opening width of the longitudinal grooves can be made substantially as small as desired, for example, both less than 15 mm, preferably less than 10 mm, and particularly preferably less than 5 mm.

[0054] The marker element fused in the longitudinal groove is fixed relative to the glass cladding cylinder, which simplifies its handling during later stages of the fiber manufacturing process, for example, it is easy to check the freedom from faults and the quality of the fusion process before the opening of the glass cladding cylinder is filled with the core rod.

[0055] In a longitudinal groove, the marker element (component, bed, layer) is melted within the longitudinal groove locally over at least part of its length, preferably at multiple points distributed over its length, and ideally over its entire length.

[0056] Taking this into consideration, a preferred embodiment of the semi-finished product provides that the marker element has a length and that the marker element is melted partially or in spots completely into the longitudinal groove along at least 80% of this length, preferably along at least 90% of this length.

[0057] In a preferred embodiment of the preform, the marker element comprises a hollow channel filled with gas.

[0058] Gases such as air or nitrogen exhibit a particularly high refractive index increase relative to the surrounding cladding glass and are therefore easy to detect even at small radial dimensions.

[0059] The longitudinal grooves are preferably designed to receive marker elements that have a deviation in their axial alignment of less than 0.3 mm / m, thus forming a high-precision marker zone in the multicore fiber obtained from the semi-finished product.

[0060] The glass cladding cylinder is preferably a hollow cylinder having a central bore.

[0061] The semi-finished product is provided for carrying out the method according to the invention and is suitable and designed for this purpose. The comments made regarding the glass cladding cylinder in relation to the method according to the invention also apply to the semi-finished product and are incorporated herein.

[0062] 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 remainder of the description, the statements made elsewhere in the description shall prevail.

[0063] Glass cladding cylinder / glass cladding area The glass cladding cylinder has an elongated, substantially cylindrical shape. Deviations from the cylindrical shape may occur in the region of the end faces. The glass cladding cylinder is designed as a solid cylinder or a hollow cylinder. The glass cladding cylinder includes a cladding glass that forms the glass cladding region. The cladding glass may consist of, for example, undoped silica glass or may include at least one dopant that reduces the refractive index of the silica glass. Fluorine and boron are dopants that can reduce the refractive index of the silica glass.

[0064] Core rod / core glass area The core rods contain core glass with a radially uniform or non-uniform refractive index profile. The core glass of each core rod forms a core glass region. The core rod may include a region made of a core glass with a relatively high refractive index and at least one additional region made of another glass with a relatively low refractive index, such as silica glass doped with fluorine and / or chlorine. The glass with the highest refractive index is generally located at the central axis of the core rod. It may be made of silica glass doped with at least one dopant to increase the refractive index. In a multicore fiber, the core rod forms at least one signal core through which the transmitted signal is primarily transported. The signal core may be adjacent to other glass regions with lower refractive indices, also provided by the core rod.

[0065] Marker element / marker material / marker glass The marker elements comprise a marker material or consist partially of air or another gas. In particular, the marker elements comprise at least one marker glass having a composition different from that of the cladding glass and / or a density different from that of the cladding glass. The marker elements are present in the preform and in the component as components or as layers or masses on the components, and form optically detectable marker zones in the multicore fiber.

[0066] Component Group / Consolidated Preform / Secondary Preform A "component group" includes a glass cladding cylinder into which a core rod is inserted and at least one marker element. By fixing the core rod in the core rod bore, for example by narrowing the end of the glass cladding cylinder or by collapsing and fusing, a "preform," also referred to herein as a "consolidated preform," is obtained. The component group or the (consolidated) preform is elongated to form a "secondary preform" or to directly form a multicore fiber. The term "semi-finished product" here encompasses component group, consolidated preform, and secondary preform. Reshaping the component group includes elongating or forming a consolidated preform to form a multicore fiber.

[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] Fusion When referring to components made from glass, fusion is understood to mean that the components are fused together at their contact surfaces, which is achieved by heating the components at least in the region of the contact surfaces by means of a heat source such as a furnace, burner, or laser.

[0069] Position display:Top / Bottom These designations relate to positions during the elongation process and / or fiber drawing process: "bottom" indicates a position in the direction of the drawing process, and "top" indicates a position opposite to the direction of the drawing process.

[0070] cross section Longitudinal / cross section taken perpendicular to the longitudinal axis.

[0071] Longitudinal cross section Longitudinal / cross section taken parallel to the longitudinal axis.

[0072] Boa The terms "bore," "center bore," "inner bore," or "longitudinal bore" refer to a hole having any internal shape, such as produced by a drilling process or by depositing a layer of material onto the outer surface of a mandrel by a deposition or pressing process, followed by removal of the mandrel. [Brief explanation of the drawings]

[0073] Illustrative Embodiments In the following, the invention will be explained in more detail with reference to exemplary embodiments and drawings. [Figure 1] FIG. 1 in particular shows, in a schematic view, a cross-section of a solid glass cladding cylinder having a longitudinal groove and a through bore in its outer surface. [Figure 2] FIG. 2 specifically shows, in a schematic view, a group of components including the solid glass cladding cylinder of FIG. 1, a core rod inserted in the core rod bore, and a marker element inserted in the longitudinal groove. [Figure 3] FIG. 3 in particular shows, in a schematic view, a cross-sectional view of a consolidated preform including a solid glass cladding cylinder, a marker element, and a core rod. [Figure 4] FIG. 4 in particular shows, in a schematic view, a cross-sectional view of a consolidated preform including a hollow glass cladding cylinder, a marker element, and a core rod. [Figure 5] FIG. 5 in particular shows, in a schematic view, a cross-sectional view of a hollow glass cladding cylinder having a central bore and a through bore for receiving a core rod.

[0074] Example 1 FIG. 1 shows a schematic cross section of a cylinder 1 made of cladding glass, which serves as a substrate for manufacturing a multicore fiber. The glass-cladding cylinder 1 consists of undoped, synthetically produced quartz glass. The quartz glass forms the glass cladding region 1a. The glass-cladding cylinder 1 has a length of 1500 mm and is adjusted to a nominal outer diameter of 200 mm by cylindrical grinding. A longitudinal groove 5 is created in the cylinder outer cladding 4. Four bores 3 are manufactured in a predetermined (here, secondary) configuration by mechanical drilling in the direction of the cylinder longitudinal axis 2, which in the illustration of FIG. 1 extends perpendicular to the sheet plane. The bores 3 serve to receive the core rods (FIG. 2) and have a diameter of 24 mm. The bores 3 pass entirely through the cylinder 1 (through bores). In another embodiment, the bores are designed as blind bores.

[0075] A longitudinal groove 5 milled into the cylinder outer cladding 4 extends the entire length of the glass cladding cylinder 1. It is semicircular in cross section with an opening width of 10 mm and a depth of 5 mm.

[0076] Figure 2 shows a group of components 10, including the glass cladding cylinder 1, the core rod 7, and the marker rod 6 inserted into the longitudinal groove 5. The marker rod 6 is also 1500 mm long and 3.5 mm in diameter. It is made of synthetically produced fluorine-doped quartz glass, commercially available under the name F320. Both the viscosity and refractive index of the fluorine-doped quartz glass of the marker rod 6 are lower than those of the undoped quartz glass of the cylinder 1. The marker rod 6 is obtained by tool-free elongation of a starting cylinder made of F320 quartz glass. It has a smooth, damage-free surface produced by the molten mass and is characterized by high dimensional stability and straightness, allowing it to be inserted easily into the longitudinal groove 5. The marker rod 6 inserted into the longitudinal groove 5 is melted and fixed within the longitudinal groove 5 by spot heating using a burner. The glass volume of the former marker rod 6 corresponds to the spatial volume of the longitudinal groove 5 so that the marker glass 11 fills the longitudinal groove 6 exactly and completely. In this case, the glass cladding cylinder 1 is mounted with its longitudinal axis oriented horizontally, with the longitudinal groove 5 located on its upper side. The glass material of the marker element 6 is heated and softened by the burner, thereby sinking into the longitudinal groove 5 and completely filling it. Due to surface tension, the surface of the softened glass mass adjacent to the free atmosphere shows a slight bulge.

[0077] In an alternative method variant, the marker rod 6 is melted over its entire length in the longitudinal groove 5. This allows, as can be seen in Figure 3, to achieve a certain degree of rounding of the marker material 11 as a result of surface tension, and therefore a conformance to the circular contour of the outer surface of the glass cladding cylinder 1. After melting the marker rod 6, the absence of defects and melt quality can be monitored and improved if necessary.

[0078] In a further alternative method variant, a tube is used as the marker element made of silica glass doped with a dopant that increases the viscosity of the silica glass, such as aluminum oxide (Al2O3). The tube has an inner diameter of 8 mm (or at least 10 mm) and a length of 1500 mm. During the melting of the Al2O3-doped silica glass tube, which is open on both sides, into the longitudinal groove 5, excess pressure is generated and maintained within the pipe bore, thus preventing collapse of the pipe bore. This pipe bore is also maintained during later stages of the manufacturing process so that air-filled hollow channels ("airlines") remain in the finished multicore fiber.

[0079] Further, in this embodiment, four core rods 7 made of Ge-doped quartz glass are fabricated, each having a length of approximately 1500 mm and an outer diameter of approximately 22 mm. Known techniques, such as MCVD (modified chemical vapor deposition), are also suitable for this purpose. Figure 2 shows a schematic of the core rods 7 inserted into the bore 3. The core glass of the core rods 7 forms the core glass region 7a. The lower end of the glass cladding cylinder 1, to which the core rods 7 are attached, is then heated, causing the annular gap 8 around the core rods 7 to collapse.

[0080] 3 shows a schematic representation of a thus consolidated preform 20 containing the former group of components, namely, the glass cladding cylinder 1, the core rod 7, and the marker rod 6, which form a marker glass mass 11 within the preform. The latter is exposed on the cylindrical outer cladding 4 and on a line 12 extending radially outward from the center point, which does not belong to the axis of symmetry of the fiber design.

[0081] The consolidated preform 20 is then elongated to form a secondary preform. In this case, the preform 20 is held in an elongation apparatus by a holder with its cylindrical longitudinal axis 2 aligned vertically. The secondary preform thus produced is finally drawn in a drawing apparatus in a conventional manner to form a multicore fiber. Except for the smaller radial dimension, its cross section substantially corresponds to the cross section of the consolidated preform 20 shown in FIG. 3. The former core rod 7 forms the signal core extending along the longitudinal axis of the fiber, and the former marker glass mass 11 forms a marker zone on the cylindrical cladding surface of the multicore fiber. The multicore fiber is characterized by particularly low fiber curl and particularly good splicing behavior.

[0082] Example 2 Therefore, to the extent that the same reference numbers are used in Figures 4 and 5 as in Figures 1-3, the same or equivalent components or components of the semi-finished product are referenced as described in more detail above with reference to Example 1.

[0083] FIG. 5 shows a schematic cross-section of a hollow glass-cladding cylinder 41 manufactured in a known manner using the OVD method. In this method, SiO2 soot particles are formed by passing a high-purity SiO2 starting material, such as silicon tetrachloride, through a deposition burner and feeding it into the burner flame, from which solid SiO2 is formed. This is deposited from the gas phase in the form of fine SiO2 soot particles onto the outer surface of a cylindrical deposition mandrel rotating around its longitudinal axis, with the deposition burner performing a reversible movement back and forth along the longitudinal axis of the deposition mandrel. A SiO2 soot body is formed on the outer surface of the deposition mandrel. After the deposition process is completed, the deposition mandrel is removed, leaving a central inner bore 42. The SiO2 soot body is then vitrified in a furnace under vacuum, while the central inner bore 42 remains intact, i.e., is maintained.

[0084] The hollow cylinder 41 thus obtained is made of undoped synthetically produced quartz glass, has a length of 1500 mm, is adjusted by cylindrical grinding to an outer diameter of 200 mm and is adjusted by boring and honing to an inner diameter of 42 mm.

[0085] A longitudinal groove 5 extending the entire length of the glass cladding cylinder 41, having a semicircular cross section, an opening width of 10 mm and a depth of 5 mm, is milled into the cylinder outer cladding 4.

[0086] By mechanical boring in the direction of the longitudinal axis 2, four evenly distributed further bores 3 with a diameter of 42 mm are produced around the central inner bore 42.

[0087] A marker rod made of synthetically produced fluorine-doped quartz glass, commercially available under the name F520, is inserted into the longitudinal groove 5. Its length is 1500 mm and its diameter is 7 mm. It is obtained by tool-free elongation of a starting cylinder made of F520 quartz glass, resulting in a smooth, damage-free surface that is generated in the molten mass. The marker rod features high dimensional stability, allowing it to be inserted into the longitudinal groove 5 without difficulty. The marker rod is first fixed in the longitudinal groove 5 at three fixing points by point heating using a burner, distributed over 95% of its length at the ends and in the center. It is then melted in the longitudinal groove 5 along its entire length. In this process, the fluorine-doped quartz glass of the marker rod melts and distributes throughout the longitudinal groove 5, completely filling it. Surface tension results in a certain rounding of the marker glass gob 11 and therefore a conformance to the circular contour of the outer surface 4 of the hollow glass cladding cylinder 41. The absence of errors and the quality of the molten marker glass gob 11 are monitored.

[0088] The modified hollow glass cladding cylinder 41 serves as a preform for fabricating a multicore fiber. In a later stage of this fabrication process, the bores 3 are filled with identical core rods 7, each having a diameter of 40 mm, and the central inner bore 42 of the hollow glass cladding cylinder 41 is filled with a filler rod made of cladding glass or another glass material. In this embodiment, the central bore 42 is similarly filled with the core rod 7, also having a diameter of 40 mm. The lower end of the glass cladding cylinder 41 with the core rod 7 is then heated to collapse the annular gap around the core rod 7. Figure 4 schematically illustrates a preform 40 consolidated using the modified hollow glass cladding cylinder 41 of Figure 5.

[0089] It consists of the components of the former group, namely the hollow glass cladding cylinder 41 forming the glass cladding region 1a, the core rod forming the core glass region 7a, and the marker rod forming the marker glass gob 11 in the preform 40, which is then elongated to form a secondary preform and finally drawn in a drawing apparatus to form the multicore fiber in the conventional manner. The marker zone close to the edge is particularly precise and has a small volume, so that the multicore fiber is characterized by particularly low fiber curl and particularly good splicing behavior.

Claims

1. A method for manufacturing a multicore fiber, comprising the method steps of reshaping a group of components (10) to form said multicore fiber or to form a preform (20, 40) for said multicore fiber, said group of components (10) comprising: a glass cladding cylinder (1, 41) having a cylinder longitudinal axis (2) and an outer surface (4), and having a glass cladding region (1a) made from cladding glass; a plurality of core glass regions (7a) provided with a core glass and extending in the direction of the cylinder longitudinal axis (2), surrounded by the cladding glass; at least one marker element (6) extending in the direction of said cylinder longitudinal axis (2); Including, the marker element (6) is arranged on the outer surface (4) of the glass cladding cylinder (1, 41), and a longitudinal groove (5) is created in the outer surface (4) of the glass cladding region (1 a) and extends in the direction of the cylinder longitudinal axis (2), and before the re-shaping process to form the preform (20, 40) or the multi-core fiber, the marker element (6) is melted in the longitudinal groove (5), 10. The method of claim 1, wherein the melting of the marker element (6) comprises the method step of: mounting the glass cladding cylinder (1, 41) with the cylinder longitudinal axis oriented horizontally so that the longitudinal groove (5) is located on the upper side of the glass cladding cylinder (1, 41), and the material of the marker element (6) is heated and softened by a heat source.

2. 2. A method according to claim 1, characterized in that the marker element (6) has a length and that the melting is carried out partially or completely in points along at least 80% of this length.

3. Cladding glass volume V Ｍ is removed from the glass cladding cylinder (1, 41) to create the longitudinal groove (5), and a cladding glass having a volume V Ｅ A marker element (6) having a V is received in the longitudinal groove (5). Ｅ =V Ｍ + / -0.1xV Ｍ The method of claim 1, wherein

4. The reshaping of said component group (10) comprises the following method steps: (a) providing the glass cladding cylinder (1, 41) containing the cladding glass; (b) providing a core rod (7) comprising said core glass; (c) providing a marker element (6); (d) creating at least one longitudinal groove (5) on the outer surface (4) of the glass cladding cylinder (1, 41); (e) creating a core rod bore (3) extending along the cylinder longitudinal axis (2); (f) placing and melting said marker element (6) in said longitudinal groove (5); (g) introducing the core rod (7) into the core rod bore (3) while forming the core glass region (7a); 2. The method of claim 1, comprising:

5. 2. A method according to claim 1, characterized in that the marker element (6) is provided in the form of a cylindrical component.

6. 2. The method according to claim 1, wherein a hollow cylinder (41) having a central bore (102) is used as the glass cladding cylinder (1, 41), and comprises the glass cladding region made of cladding glass and a plurality of core glass regions provided with core glass.

7. The marker element (6) includes at least one marker glass, 2. The method of claim 1, wherein the marker glass differs from the cladding glass in at least one physical and / or chemical property, the property being selected from refractive index, color, fluorescence and / or a specific glass density.

Images