Method for producing a preform for an optical fiber

Abstract

The invention relates to a method for producing a preform for an optical fiber and a preform for an optical fiber. A method for producing a preform (1) for an optical fiber comprises: creating a first hole (3) in a first preform part (6) starting from a first end face (11) of the first preform part (6); creating a second hole (4) in a second preform part (7) starting from a first end face (11) of the second preform part (7); and joining the first preform part (6) and the second preform part (7) such that the first end face (11) of the first preform part (6) and the first end face (11) of the second preform part (7) are connected to each other. This makes it possible to provide a longer preform for an optical fiber while ensuring high precision of the holes.

Description

[0001] manual

[0002] The present invention relates to a method for producing a preform for optical fiber and a preform for optical fiber.

[0003] To produce optical fiber, a preform is first created, and then the fiber is produced from the preform. Typically, holes are drilled into a cylinder to create the preform. A core rod is then inserted into the hole. Drilling must be very precise to meet the optical property requirements of the fiber to be produced. To increase the length of the preform, multiple preform sections can be connected or joined together.

[0004] To date, the required drilling precision has been achieved up to approximately 1.5 meters in length. Generally, the production of longer preforms is desired. However, drilling longer segments using conventional methods is not feasible because the drilling precision then significantly decreases. On one hand, as length increases, the drill bit is pulled downwards due to gravity, causing drift within the hole. On the other hand, other effects can also contribute to drift. Drift can depend on factors such as the drill bit's rotation direction, rotational speed, and the direction of gravity.

[0005] EP 3 115 344 B1 discloses a method for producing glass fiber preforms, wherein a plurality of core preforms and a plurality of sheath preforms having through holes are produced. The through holes of the sheath preforms are adapted to create connecting holes. At least two core preforms are inserted side-by-side through each connecting hole, such that there is an offset between the connection points of the core preforms and the sheath preforms.

[0006] US Patent 11,370,689 B2 discloses a vacuum method for forming tube-based preforms for optical fibers. The preform arrangement defines a sealed internal chamber to which a vacuum is applied. This arrangement is heated under vacuum until just above the softening point of glass to solidify the preform.

[0007] The purpose of this invention is to enable longer preforms for optical fibers while ensuring high drilling accuracy.

[0008] This objective is achieved by the method according to claim 1 and the preform according to claim 15. Advantageous embodiments are specified in the dependent claims.

[0009] To achieve this objective, a method for producing a preform for optical fiber is used. The method includes creating a first hole in the first preform portion, starting from a first end face of a first preform portion. The method includes creating a second hole in the second preform portion, starting from a first end face of a second preform portion. The method further includes joining the first preform portion and the second preform portion such that the first end faces of the first preform portion and the first end faces of the second preform portion are connected to each other.

[0010] The end faces of the corresponding holes, where they begin, are connected to each other. The holes can be manufactured with exceptional precision at their starting points. There is absolutely no influence from drill drift. Therefore, the position of each hole in the cross-section of the corresponding preform part can be produced with very high accuracy. After joining, the positions of the holes in the contact areas of the two preform parts are then matched with very high precision.

[0011] This method relates to the production of preforms for optical fibers (i.e., optical waveguides), particularly for telecommunications. It can be a core fiber with a single core or a multi-core fiber, i.e., a fiber with multiple cores. In other words, an optical fiber preform is provided. The preform is primarily made of glass (such as quartz glass).

[0012] Holes are created by drilling, particularly using a drill bit. Holes are, in particular, through holes. Drilling can include creating blind holes, and specifically, for example, by sawing to separate the undrilled ends of a particular preform portion. Through holes can be created in this way. Drilling is particularly performed as push drilling, i.e., by advancing the free end of the drill bit into the particular preform portion. Drilling can also, in principle, be performed as pull drilling.

[0013] Specifically, the hole extends along the longitudinal direction of the preform portion. For example, the hole extends along the central longitudinal axis of the preform portion, or extends parallel to the central longitudinal axis at a certain distance from the central longitudinal axis.

[0014] Drilling always begins from the first end face. This means that drilling starts at the first end face. Specifically, the drill bit first contacts the preform portion at the first end face. Specifically, the drill bit penetrates the first end face and then continues to move parallel to the central longitudinal axis through the specific preform portion. Specifically, drilling continues until the drill bit reaches a position before reaching the second end face of the specific preform portion located on the opposite side. Specifically, the first hole in the first preform portion and the second hole in the second preform portion are arranged in corresponding positions. After engagement, this results in continuous holes or continuous cavities in the preform.

[0015] Specifically, each preform portion is elongated. The end face is specifically the end face of a particular preform portion. In principle, the end face may be partially or completely straight, inclined, and / or curved. Two preform portions may have the same length or different lengths. For example, one preform portion may have a length of 1,000 mm, and another preform portion may have a length of 1,500 mm. Specifically, the two preform portions are identical in terms of their cross-section and / or their diameter. The diameters of the two preform portions may have slight production-related deviations, typically less than 0.5 mm, preferably less than 0.3 mm. This may be due to deviations and / or tolerances during the grinding of the preform blank. If the two preform portions are produced by dividing the preform blank as described below, the diameters are typically identical.

[0016] The order in which the first and second holes are produced is not important. The two holes can be produced sequentially, or at least simultaneously at regular intervals. In particular, they are then joined.

[0017] A preform is assembled or produced from two preform parts by joining. Each first end face is joined to the other. After joining, a second end face lies on the opposite side of the preform. The resulting preform specifically has the same diameter as each individual preform part. The length of the preform can correspond to the sum of the lengths of the individual preform parts. If the production of the preform includes, for example, the creation of blind holes and subsequent separation of one end, the length of the preform can be less than the sum of the lengths of the individual preform parts. One or two un-drilled ends can be separated before and / or after joining. For example, a maximum length of 100 mm can be separated.

[0018] In one embodiment, the first preform portion is cylindrical. In another embodiment, the second preform portion is cylindrical. Therefore, the cross-section of each preform portion is identical throughout its longitudinal direction. In yet another embodiment, the first and / or second preform portion are circular-cylindrical.

[0019] In one embodiment, the first preform portion and / or the second preform portion has a basic cylindrical shape. The term "basic cylindrical shape" means that a certain deviation from a precise cylindrical shape is permissible. In one example, the first preform portion and / or the second preform portion may have a basic cylindrical shape, but deviate from a precise cylindrical shape due to flattening. Flattening may extend along the entire length of a particular preform portion and / or be aligned parallel to the longitudinal axis. Flattening may be present for purposes such as marking.

[0020] In another example, the first preform portion and / or the second preform portion may have a basic cylindrical shape, but with one or two beveled end faces. Beveled end faces can be created, for example, when the preform blank is diced (e.g., during sawing). The pressure acting on the saw blade can cause the saw blade to deflect by several degrees.

[0021] The preform portion may be solid or at least partially hollow. When creating the hole, one or more holes may already exist in the preform portion, wherein one or more holes extend specifically parallel to the central longitudinal axis. In one embodiment, the first preform portion and / or the second preform portion is a hollow cylinder having a central hole along the central longitudinal axis.

[0022] In one embodiment, during drilling, i.e., during the formation of the first and / or second holes, the first and / or second preform portions are oriented substantially horizontally. Horizontal drilling requires significantly lower space height and is therefore generally easier to implement. Although drift increases during horizontal drilling, the joining according to the invention allows for maximum accuracy.

[0023] In one embodiment, the joining is performed by welding. During welding, at least in the joint region, the temperature of the preform portions to be joined is increased, resulting in an adhesive bond. For example, heating can be performed above the glass transition temperature. Welding has been shown to be a particularly advantageous method for achieving this purpose.

[0024] In another embodiment, the method includes dividing a preform blank to produce a first preform portion and a second preform portion. In other words, the preform portions are produced by dividing the preform blank before the holes are manufactured.

[0025] Segmentation refers to mechanical separation. For example, segmentation is performed by a separation method. In particular, the segmentation is carried out generally transversely to the longitudinal direction of the preform blank, preferably at an angle of 90° to the central longitudinal axis.

[0026] Therefore, preform parts are produced by dividing the preform blank, these preform parts are drilled and then reassembled to form a preform.

[0027] In one implementation, the division is carried out using a saw, particularly a circular saw. It has been found that sawing, especially sawing using a circular saw, is a particularly suitable method for dividing preform blanks.

[0028] In another embodiment, the end faces generated during the segmentation are the first end face of the first preform portion and the first end face of the second preform portion.

[0029] During the splitting process, two new end faces are created. In this embodiment, these new end faces correspond to the end faces to be subsequently joined. In other words, after drilling, the two preform parts are joined again at the surfaces where they were initially connected to each other. In this way, the material structure of the preform parts or the produced preform largely corresponds to the material structure of the preform blank. Furthermore, the resulting end faces fit together particularly well. This has proven to be particularly advantageous for achieving this objective. Especially in the case of hollow cylinders, misalignment of the central hole is avoided.

[0030] In another embodiment, the joining is performed such that the relative angular positions of the first preform portion and the second preform portion with respect to the longitudinal axis correspond to the relative angular positions of the first preform portion and the second preform portion in the preform blank. In other words, the joining is performed such that the angular positions relative to the central longitudinal axis are the same after joining as before splitting. Typically, the first preform portion and / or the second preform portion are rotated along their respective longitudinal axes until the desired angular positions are achieved. The longitudinal axis is in particular the common longitudinal axis of the two preform portions before joining, which therefore corresponds to the longitudinal axis of the preform after joining.

[0031] In this way, any deviation from 90° during segmentation can be compensated for. This is particularly advantageous in ensuring high precision. This implementation prevents any gaps or kinks from forming in the preform.

[0032] In one embodiment, markings are applied prior to splitting. The markings are applied to the preform blank. This is done so that the relative angular positions of the first and second preform portions can be set based on the markings prior to joining. The markings are specifically applied to the side surfaces of the preform blank.

[0033] Markings can be applied to the outside of the preform blank. For example, in areas intended for slitting points, lines, preferably parallel to the longitudinal axis, particularly thin lines, can be applied. During slitting, in this case, the lines are also slit. Before joining, the two portions of the lines can then be aligned with each other. This makes it particularly easy to restore the initial angular position of the preform portions. This ensures exceptionally high precision.

[0034] Alternatively or additionally, markings can be applied inside the preform blank. For example, marking holes, parallel to the longitudinal axis of the preform blank, can be created at a distance from the longitudinal axis. The marking holes are thus applied at locations that disrupt rotational symmetry. In this way, the angular positions of the two preform portions can be set based on these marking holes before joining. A marking rod having a refractive index different from that of the preform blank can be inserted into the marking holes. Markings inside the preform blank can be produced with minimal technical effort because the required accuracy of the position of marking holes along the axis of a particular preform blank is significantly lower than the requirements for master holes in preform portions. Markings inside the preform blank can also be used to mark the core in the produced fibers.

[0035] Specifically, prior to joining, the relative angular positions of the first and second preform portions are set based on markings. These markings can also be used to set the angular positions during drilling.

[0036] Specifically, before creating the first and / or second hole, the drill bit and the preform portion are aligned relative to the central longitudinal axis, such that holes are created in the cross-section of a particular preform portion at defined angular positions relative to the longitudinal axis. This ensures that one or more eccentric holes are created at corresponding locations.

[0037] In one embodiment, the preform is used for multi-core fibers. Specifically, a plurality of first holes are formed starting from a first end face of a first preform portion. Specifically, a plurality of second holes are formed starting from a first end face of a second preform portion. Specifically, the first holes are parallel to each other and / or parallel to the longitudinal axis of the first preform portion. Specifically, the second holes are parallel to each other and / or parallel to the longitudinal axis of the first preform portion.

[0038] Multicore fibers are fibers with multiple cores. The specific number of cores is independent of the method. For example, multicore fibers can have two, four, or more cores.

[0039] Specifically, the number of first holes corresponds to the number of second holes. Specifically, the first holes in the first preform portion and the second holes in the second preform portion are arranged at corresponding positions. This means that, after joining, there are continuous holes extending along the entire length of the preform.

[0040] In one embodiment, the preform has a length greater than 1.5m, particularly at least 2.0m. The length can be at least 2.5m, particularly about 3.0m. Using current methods, it is impossible to produce preforms of this length with the required precision.

[0041] In one embodiment, the first preform portion and / or the second preform portion has a maximum length of 1.5 m. The length can be at most 1.25 m or 1.0 m. The length can be at least 0.5 m or 0.75 m. For example, the two preform portions have the same length. This length has proven particularly advantageous for achieving maximum accuracy.

[0042] In another embodiment, the ratio of the preform's length to the diameter of the first and / or second hole is greater than 35, particularly greater than 50. As the ratio of the preform's length to the hole's diameter increases, drift also increases, which offsets the required accuracy. The solution according to the invention allows such a ratio to have high precision.

[0043] Another aspect of the invention is a preform for optical fibers, particularly for multi-core fibers. This preform can be produced using the method according to the invention, or produced using the method according to the invention. The ratio of the length of the preform to the diameter of the first and / or second aperture is greater than 35, particularly greater than 50. Alternatively or additionally, the length of the preform is greater than 1.5 m, particularly at least 2.0 m. Such a preform cannot be produced using conventional methods. All the advantages, features, and embodiments of the above methods can be similarly applied to the preform, and vice versa.

[0044] Exemplary embodiments of the invention are explained in more detail below with reference to the accompanying drawings. Unless otherwise indicated, features of the exemplary embodiments may be combined with the claimed subject matter, individually or in combination. The scope of protection claimed is not limited to the exemplary embodiments.

[0045] The attached diagram shows:

[0046] Figure 1 and Figure 2 Cross-sectional view of the preform.

[0047] Figure 3 A schematic diagram of the drilling process.

[0048] Figure 4 : Schematic diagram of the preform part

[0049] Figure 5 and Figure 6 A schematic diagram of the process steps for producing preforms.

[0050] Figures 7 to 9 : A schematic diagram of other methods and steps used to produce preforms.

[0051] Figures 10 to 12 A schematic diagram of the process steps during the production of the preform, and

[0052] Figure 13 Cross-sectional view of a preform blank with markings.

[0053] Figure 1 and Figure 2 Cross-sections of various preforms 1 that can be produced according to the present invention are shown by way of example. Each preform has a circular cross-section. The preform 1 typically has a central hole 2 extending along the central longitudinal axis of a particular preform 1. Each hole 2 may be formed by a first hole or a second hole corresponding to a portion of the preform.

[0054] Figure 2 Five eccentric holes 2, in addition to the optional central hole 2, are shown by way of example. These eccentric holes are, for example, regularly distributed on a circle that can be arranged concentrically with the outer contour of the preform 1.

[0055] Figure 3 A drilling method for creating a hole 3 in the first preform portion 6 is schematically illustrated. A drill bit 20 moves along a direction 23 parallel to the longitudinal axis 17 of the preform portion 6 and, in particular, rotates about its longitudinal axis. The drill bit 20 typically includes a drill head 21 driven by a drill rod 22. These components are shown purely schematically here; typically, the diameter of the drill rod 22 is smaller than the diameter of the drill head 21. The drill rod 22 is driven, for example, by a drive unit not shown.

[0056] Clearly, drill bit 20 has penetrated the first preform portion 6 at the first end face 11, thereby creating the first hole 3. The first hole 3 is shown here purely by way of example as a center hole.

[0057] Figure 4 The first preform portion 6 with the first hole 3, prepared in this manner, is shown. Figure 3 and Figure 4 The contents shown and described above similarly apply to the hole 4 in the second preform part 7.

[0058] Figure 5 The diagram schematically illustrates the formation of a first hole in a first preform portion 6, starting from a first end face 11, and a second hole in a second preform portion 7, also starting from a first end face 11. Arrow 23 indicates the direction of movement of a particular drill bit. The corresponding second end face 12 is arranged on opposite end faces of the particular preform portions 7 and 8.

[0059] Figure 6The diagram illustrates the subsequent joining of preform portions 6 and 7, thus prepared, to produce preform 1. Preform portions 6 and 7 are positioned relative to each other such that their first end faces 11 face each other and are in contact. Typically, at least one preform portion has been rotated about an axis extending, for example, perpendicular to its longitudinal axis. This can occur, for example, after holes have been formed in the relevant preform portion. Now, the two preform portions 6 and 7 are joined in this alignment. The longitudinal axes of the two preform portions 6 and 7 coincide and correspond to the longitudinal axis of the preform thus produced.

[0060] The second end face 12 is therefore located on the opposite outer end face. The engagement of the first end face 11 ensures very high precision, wherein the positions of the corresponding holes 3 and 4 are precisely defined relative to the cross-section and are unaffected by any drift. In this way, a preform 1 with a length of, for example, 3 m can be produced. In particular, the preform portions 6 and 7 are welded together.

[0061] Figures 7 to 9 Additional method steps for producing preforms are shown. For example... Figure 7 As shown, the preform blank 10 is divided at the dividing position 18—for example, by sawing. This produces a first preform portion 6 and a second preform portion 7. Subsequently, for example, according to Figure 5 and / or Figure 3 Drilling is performed. Figure 8 The following scenario is illustrated, where preformed portions 6 and 7 have corresponding holes 3 and 4 and can be joined. After joining, as... Figure 9 As shown, there is a preform with continuous holes 2.

[0062] Figures 10 to 12 Further method steps for dividing the preform blank 10 are shown. First, as indicated by reference numeral 15, a mark 15 is applied to the outer side of the preform blank 10. The mark 15 is shown here by way of example as an axially aligned line. The mark 15 extends on both sides of the preform blank 10, as... Figure 12 The division position is indicated by the mark 18. Mark 15 allows the restoration of the original relative angular positions of preform portions 6 and 7 in the preform blank after division and drilling and before joining.

[0063] Figure 13 A cross-section of the preform blank 10 is shown. The blank has an eccentric marking hole inside, designated as a mark 15. The marking hole extends at a distance from the central longitudinal axis of the preform blank 10. Figure 11 and Figure 12 As shown and described above, the marking holes can be generated before splitting and can be used for relative alignment of preformed parts 6 and 7 before joining.

[0064] In one embodiment, the preform is assembled or constituted from exactly two preform portions. In the case of more than two preform portions, the end faces where the connection hole does not begin must always be connected. Therefore, the advantage according to the invention, namely, precise matching of holes in the end faces to be joined, cannot be fully realized. Conversely, if the preform comprises exactly two preform portions, precise matching can be fully ensured.

[0065] Experiments were conducted to evaluate the quality of the preform based on the deviation between the hole positions on the joint end faces of the two preform portions. For this purpose, preforms were produced considering all different possibilities when joining the two preform portions. The first end face from which a specific hole begins, i.e., the drill entry side, is denoted by a. The second end face from which the specific hole ends, i.e., the drill exit side, is denoted by b. The position of the hole on this side is affected by drill drift. The first preform portion is denoted by 1, and the second preform portion by 2. The results are summarized in the table below:

[0066]

[0067] Table: Preform Quality Based on Hole Position Deviation. Legend: ++ Acceptable Deviation, - Unacceptable Deviation, -- Maximum and Unacceptable Deviation

[0068] Clearly, the method according to the invention provides an acceptable hole location and therefore a preferred result, in which the first end face (1a) of the first preform portion and the first end face (2a) of the second preform portion engage with each other (1a-2a). Conversely, in cases 1a-2b and 1b-2a where the first end face (inlet side) is connected to the second end face (outlet side), larger unacceptable deviations are found. The largest and also unacceptable deviation is found in cases 1b-2b where the two second end faces or outlet sides are connected to each other. Clearly, only one of the four possibilities leads to the desired result.

[0069] In one embodiment, a mark is formed on the first preform portion. The mark may be formed before or after (preferably before) the first hole is formed. In one embodiment, a mark is formed on the second preform portion. The mark may be formed in the second preform portion before or after (preferably before) the second hole is formed. The mark may be used to identify the side where a particular first end face is located. In this way, it can be ensured that the first or second end face is joined during joining. The mark may include an orientation indicating the angular position of the preform portion. This prevents misalignment after the preform blank is optionally segmented if the end faces are not aligned perfectly perpendicular to the longitudinal extent of the preform blank.

[0070] The marking can be any marking that is specifically visible on the outer side of a particular preform portion. The marking can be temporary or permanent. In principle, the marking can be applied at any point on a particular preform portion and / or have any shape or design, provided that its shape and / or position makes it suitable for directly or indirectly identifying one side of the first end face. In particular, the marking should not be mirror-symmetrical about a plane that is centered relative to the longitudinal extension of the particular preform portion and extends perpendicular to the longitudinal extension direction. The above statements regarding markings applied prior to segmentation also apply to the markings described herein, and vice versa.

[0071] List of reference numerals in the attached figures

[0072] Preform 1

[0073] Hole 2

[0074] First hole 3

[0075] Second hole 4

[0076] First preform part 6

[0077] Second preform part 7

[0078] 10 preform blanks

[0079] First end face 11

[0080] Second end face 12

[0081] Mark 15

[0082] Longitudinal axis 17

[0083] Segmentation position 18

[0084] Drill bit 20

[0085] Drill head 21

[0086] Drill pipe 22

[0087] Direction 23

Claims

1. A method for producing a preform (1) for optical fiber, comprising: - A first hole (3) is generated in the first preform part (6) starting from the first end face (11) of the first preform part (6). - A second hole (4) is generated in the second preform part (7) starting from the first end face (11) of the second preform part (7). - Join the first preform portion (6) and the second preform portion (7) such that the first end face (11) of the first preform portion (6) and the first end face (11) of the second preform portion (7) are connected to each other.

2. The method according to claim 1, wherein the first preform portion (6) and / or the second preform portion (7) are cylindrical.

3. The method according to any one of the preceding claims, wherein the first preform portion (6) and / or the second preform portion (7) have a basic cylindrical shape.

4. The method according to the preceding claim, wherein the first preform portion (6) and / or the second preform portion (7) are oriented substantially horizontally during drilling.

5. The method according to any one of the preceding claims, wherein the joining is performed by welding.

6. The method according to any one of the preceding claims, wherein the method further comprises: - Divide the preform blank (10) to produce the first preform portion (6) and the second preform portion (7).

7. The method according to the preceding claim, wherein the division is performed using a saw, particularly a circular saw.

8. The method according to any one of the preceding two claims, wherein the end face generated during the segmentation is the first end face (11) of the first preform portion (6) and the first end face (11) of the second preform portion (7).

9. The method according to the preceding claim, wherein the engagement is performed such that the relative angular positions of the first preform portion (6) and the second preform portion (7) with respect to the longitudinal axis (17) correspond to the relative angular positions of the first preform portion (6) and the second preform portion (7) in the preform blank (10).

10. The method according to the preceding claim, wherein a mark (15) is applied prior to the division, such that the relative angular positions of the first preform portion (6) and the second preform portion (7) can be adjusted based on the mark (15) prior to the joining.

11. The method according to any one of the preceding claims, wherein the preform (1) is used for multi-core fibers, wherein a plurality of first holes (3) are made starting from the first end face (11) of the first preform portion (6), and wherein a plurality of second holes (4) are made starting from the first end face (11) of the second preform portion (7).

12. The method according to any one of the preceding claims, wherein the preform (1) has a length greater than 1.5 m, particularly at least 2.0 m.

13. The method according to any one of the preceding claims, wherein the first preform portion (6) and / or the second preform portion (7) has a maximum length of 1.5 m.

14. The method according to any one of the preceding claims, wherein the ratio of the length of the preform (1) to the diameter of the first hole (3) and / or the second hole (4) is greater than 35, particularly greater than 50.

15. A preform (1) for optical fibers, particularly for multi-core fibers, said preform being capable of being produced by the method according to any one of the preceding claims, wherein - The ratio of the length of the preform (1) to the diameter of the first hole (3) and / or the second hole (4) is greater than 35, particularly greater than 50, and / or - The length of the preform (1) is greater than 1.5m, and in particular at least 2.0m.

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