Methods for machining preform blanks, preforms, and devices

Abstract

This invention provides a method for manufacturing a preform for multicore fibers that is of particularly high quality, and therefore allows for the production of particularly high-quality multicore fibers with less effort. [Solution] In a method for machining a preform blank 7 for producing a multicore fiber preform, an eccentric hole is created in the preform blank 7 using a drill. The hole extends along the longitudinal range of the preform blank 7. The position of the preform blank 7 and / or the drill is selected such that the drill drift D that occurs during drilling causes a greater change in the position of the hole in the cross section 14 of the preform blank 7 in the azimuthal direction 17 than in the radial direction 18. In this way, harmful radial drift components can be minimized, and a particularly high-quality preform can be produced.

Description

Technical Field

[0001] The present invention relates to a method for machining a preform blank for manufacturing a preform of a multi-core fiber, a method for manufacturing a preform of a multi-core fiber, a preform of a multi-core fiber, and a device for machining a preform blank for manufacturing a preform of a multi-core fiber.

Background Art

[0002] To manufacture an optical fiber, first a preform is manufactured, and then an optical fiber is manufactured from the preform. To manufacture the preform, a preform blank is drilled. Subsequently, a core bar is inserted into the hole. In the case of a multi-core fiber, a plurality of holes for core bars are formed in the preform blank. In order to meet the requirements of the optical properties of the manufactured optical fiber, it is necessary to drill very accurately.

[0003] During drilling, the drill drifts. On the one hand, as the length increases, the drill is pulled downward by gravity, which typically leads to downward drift. Furthermore, other effects also cause drift, which can be directed in any direction. The drift can depend, for example, on the rotational direction of the drill, the rotational speed of the drill, and the direction of gravity. These effects may overlap and thus may result in a drift that varies over the length of the hole. It is desirable to produce holes as long as possible with as high an accuracy as possible.

[0004] German Patent Application Publication No. 102012006410 (B4) discloses a method for manufacturing a hollow quartz glass cylinder, in which an end hole extending coaxially with the central axis is formed in the starting cylinder. The continuously changing drill head position of the drill head is continuously determined by a measuring device, and if there is a deviation, it is returned to the target position. This is achieved by rotating the starting cylinder around the central axis so that the drill head position is again above the central axis.

[0005] European Patent No. 0777544(B1) discloses a method and device for influencing the trajectory of a deep hole drill. In this case, a pressing member, i.e., a separate member, is positioned between the drill rod and the inner wall of an already drilled hole. This causes the drill rod to bend and the drilling tool to deflect in a specific direction.

[0006] Japanese Patent No. 5498086(B2) describes a deep hole drilling method and related machine for horizontal drilling. The downward deflection of the drilling tool due to gravity is measured. A control device corrects the position of the tip of the deep hole drilling tool to compensate for this deflection.

[0007] U.S. Patent No. 9,272,337 (B2) discloses a method for drilling a hole through a workpiece by monitoring the alignment of the drill and the position of the hole and adjusting the drilling path as necessary. Adjusting the drilling path involves selectively applying an axial shock to the drill when the drill is aligned in a particular azimuthal direction. The alignment of the drill and the position of the hole are monitored using an acoustic transmitter and receiver that move at the same speed as the drill moves axially through the workpiece. [Overview of the Initiative] [Problems that the invention aims to solve]

[0008] The objective of the present invention is to improve the fabrication of multicore fiber preforms. [Means for solving the problem]

[0009] This objective is achieved by the method for machining a preform blank as described in claim 1, as well as the method for producing a preform as described in the adjacent claims, a preform for multicore fiber, and a device for machining a preform blank. Advantageous embodiments are defined in the dependent claims.

[0010] To address this challenge, a method for machining a preform blank is provided. The preform blank is used to produce a preform of multicore fibers. Using a drill, eccentric holes extending along the longitudinal range of the preform blank are created within the preform blank. In particular, the position of the preform blank and / or the drill is selected such that drill drift occurring during drilling causes a greater change in the position of the holes in the cross-section of the preform blank in the azimuthal direction than in the radial direction.

[0011] According to the present invention, the objective is not to prevent drift during drilling, but to direct the drift in a direction that is less damaging to the fabricated multicore fiber. It has been shown that drift that is larger in the azimuthal direction than in the radial direction causes significantly less damage than radial drift. In this way, particularly high-quality preforms for multicore fibers, and therefore particularly high-quality multicore fibers, can be manufactured with less effort.

[0012] Holes are made using a drill. The drill is in particular a rotary drill. The drill is in particular equipped with a drill head and / or a drill rod for driving the drill head. The drill rod is usually driven by a motor. Drilling can be done to make blind holes, in particular by cutting off the undrilled end of a particular preform blank, for example by sawing. In this way, through holes can be made. During the making of blind holes, the drill is moved relative to the preform blank from the initial drilling position to the final position. Drilling is done in particular as thrust drilling, that is, by advancing the free end of the drill, in particular the drill head of the drill, into the preform blank. However, drilling is not excluded. The drill enters the preform blank, in particular at the first end face. Drilling is done in particular until the drill reaches a position just before the second end face located on the opposite side. Drilling is done in particular in preform blanks that are solid in at least the area of ​​the hole to be formed. However, it is not excluded that, for example, a pre-formed existing hole may be enlarged during drilling.

[0013] The preform blank may be solid or at least partially hollow. When creating holes, one or more central holes and / or eccentric holes may already be present, and one or more holes may extend particularly along the longitudinal range. The central hole may be located along the central longitudinal axis. The preform blank is made of, for example, quartz glass, particularly synthetic quartz glass.

[0014] Eccentric holes are located off-center relative to the cross-section of the preform blank. Therefore, the center of the hole is at a distance from the center of the cross-section. Typically, eccentric holes do not extend along the longitudinal axis of the center of the preform blank. In a circular cross-section, the center of the cross-section is the center of the circle. In a cross-section with a circular base shape, the center of the base shape can function as the center. In the case of a non-circular cross-section, the centroid can function as the center. In particular, when viewed in cross-section, multiple holes are fabricated on a circle called the pitch circle. Specifically, the holes are evenly distributed on the circle.

[0015] The holes extend along the longitudinal range of the preform blank. In particular, the holes extend from a first end face or end face of the preform blank to a second end face or end face. In principle, it is desirable that the holes to be fabricated extend parallel to the central longitudinal axis of the preform blank, at a distance from the central longitudinal axis. However, this is not always possible due to drift.

[0016] A multicore fiber is a core fiber that has multiple cores. The specific number of cores is independent of the method. For example, a multicore fiber can have two, four, or more cores.

[0017] In particular, preform blanks are elongated, for example, cylindrical. Therefore, the cross-section of the preform blank is identical throughout its longitudinal range. In one embodiment, the preform blank is a perfect cylinder.

[0018] In one embodiment, the preform blank has a basic cylindrical shape. The term "basic cylindrical shape" means that some degree of deviation from a perfect cylinder is acceptable. In one example, the preform blank may have a basic cylindrical shape, but may deviate from a perfect cylinder due to flattening. Flattening may extend along the entire length of the preform blank and / or be aligned parallel to the longitudinal axis. For example, flattening may be present for marking purposes. In another example, the preform blank may have a basic cylindrical shape, but may have one or two inclined end faces.

[0019] Drill drift occurs within the preform blank, causing a change in the position of the hole within the cross-section of the preform blank. Therefore, the hole's position changes over the longitudinal range of the preform blank. In other words, the hole "wobbles." Drift results in a deviation of the actual position of the drill or hole from the target position, and from the drill's starting position. This deviation is particularly radial and / or azimuthal. The position of the preform blank and / or drill can be selected such that drill drift during drilling causes a greater change in the hole's position within the cross-section of the preform blank in the azimuthal direction than in the radial direction. For example, the position of the preform blank and / or drill can be selected with respect to gravity.

[0020] For example, if drilling begins at the first end face at a midpoint between the center of the cross-section and the 12 o'clock position on the outer edge of the preform blank, the drill will move from there in a specific direction, for example, towards the upper right, as the length of the hole increases. At the end of the hole on the second end face, the drill will be located further to the right, closer to the outer edge, when viewed from the same direction. In this case, the position of the hole in the cross-section changes in both the azimuthal and radial directions. The radial direction refers to the direction starting from the center of the cross-section and moving outward. The azimuthal or circumferential direction refers to the angular position with respect to rotation about the center or the central longitudinal axis.

[0021] Radial positional variation, also known as the radial component of drift, has drawbacks. To fabricate multicore fibers, multiple eccentric holes are typically created. These are equally spaced on a pitch circle concentric and / or coaxial with the central longitudinal axis in the cross-section of the preform blank. Radial drift causes the diameter of the circle to change over the length of the preform blank. Consequently, the position of the core bars in the resulting fiber is no longer constant, and the core spacing changes, resulting in optical and splice losses in the fiber, impairing its performance. In contrast, positional variation in the azimuthal direction or azimuthal component of drift has been shown not to cause the aforementioned drawbacks. Because the hole positions are larger in the azimuthal direction than in the radial direction, these drawbacks can be minimized with reasonable effort. High-quality multicore fibers can then be fabricated.

[0022] To ensure that the drift extends in a specific direction relative to the cross-section, the appropriate position of the preform blank and / or drill is selected. For example, the position where the drill contacts the preform blank, i.e., the relative position of the drill to the preform blank, can be adjusted. This position can affect how the drift extends within the cross-section. For example, under certain conditions, drift may be shown to extend upward and to the right in the 2 o'clock direction. If the position where the drill contacts the preform blank is selected so that it is upward and to the left in the 10 o'clock direction relative to the center of the cross-section, the resulting drift will substantially extend in the azimuthal direction, or in other words, change in position along the circumferential direction.

[0023] The position at which the drill contacts the preform blank can be selected or adjusted, for example, by spatially aligning the preform blank and the drill. Common spatial alignment refers, in particular, to the spatial positioning of the drill and preform such that the drill is positioned relative to a first end face so that a hole can be formed at a desired position by moving the drill and / or preform blank along the longitudinal axis of the drill and / or preform blank, in particular along a common longitudinal axis. The drill is generally aligned at least substantially parallel, and in particular parallel to the preform blank. For example, the drill may be positioned in front of the first end face.

[0024] It can be particularly advantageous to position and / or move the preform blank while keeping the drill stationary. This eliminates the need to move components of the drill, such as the drill bushing, guide bushing, and / or drive unit.

[0025] A specific position of the preform blank and / or drill is selected. In particular, the position of the preform blank and / or drill is also adjusted. In one exemplary embodiment, the preform blank is moved relative to the drill to adjust its position. In one exemplary embodiment, the drill is moved relative to the preform blank to adjust its position. In one exemplary embodiment, both the preform blank and the drill are moved to adjust their positions. Moving the drill refers to a movement different from rotation around the longitudinal axis during drilling, i.e., an additional movement in particular.

[0026] In the first modification, as described above, relative movement can be performed between the preform blank and the drill. However, this is not necessarily required. In the second modification, the preform blank and the drill can be moved in the same manner without changing the relative positions of the preform blank and the drill. For example, the drill can be positioned immediately before the end face of the preform blank above the position where the hole is to be formed. For example, common positioning with respect to the central longitudinal axis of the preform blank can be performed by rotating, for example, about the central longitudinal axis, in order to adjust a common position in space or to adjust a common position with respect to the direction of gravity.

[0027] The specific positions of the preform blank and / or the drill typically depend on the drift that depends on the specific framework conditions, and thus cannot be uniformly defined for all holes. The drift can depend on, for example, the rotational direction of the drill, the rotational speed of the drill, the depth of the hole, and / or the direction of gravity.

[0028] This method is used for machining the preform blank by drill piercing. A machined preform blank is produced. When all the holes are made in the preform blank and further steps such as the insertion of the core bar are optionally performed, there is a preform of the multi-core fiber. Then, a multi-core fiber can be made from this preform.

[0029] In particular, this method is implemented such that, in the case of a preform blank having an outer diameter of 200 mm, the change in the position of the holes in the radial direction is at most ±0.3 mm. In particular, this method is implemented such that the change in the position of the holes in the radial direction is at most ±0.15% of the outer diameter.

[0030] This method can include making a multi-core fiber from the preform. In particular, this method is implemented such that the change in the position of the holes in the radial direction in the produced multi-core fiber is less than 200 nm.

[0031] In one embodiment, the preform blank and the drill are aligned substantially horizontally during drilling, i.e., during hole creation. Horizontal drilling requires significantly less room height and is therefore usually easier to perform. The positional selection according to the present invention makes it possible to achieve maximum accuracy despite the increased drift during horizontal drilling.

[0032] In one embodiment, the method further includes adjusting the desired rotational position of the preform blank and drill around the longitudinal axis of the preform blank, particularly the central longitudinal axis. In particular, the rotational position of the preform blank and / or drill is changed with respect to the longitudinal axis in order to direct the drift in a desired direction. The rotational position refers to the position in which the preform blank or drill is positioned at a specific angle with respect to its respective axis. The change in rotational position can be achieved by rotating around the longitudinal axis or around an axis parallel thereto.

[0033] In one embodiment, the drill and / or preform blank is moved to adjust its rotational position. In one embodiment, the drill and / or preform blank rotates around its longitudinal axis. This allows the position of the drill and preform blank to be adjusted relative to the direction of gravity. Thus, gravity-induced drift can be directed in a desired direction.

[0034] In one embodiment, the positions of the preform blank and the drill are such that the drill is not directly above the central longitudinal axis of the preform blank with respect to gravity. In other words, the drill is not precisely above the central longitudinal axis of the preform blank. Preferably, the angle between the vertical and the position of the drill is at least 10°, and particularly at least 20°, starting from the central longitudinal axis. For example, the relative position of the drill and / or preform blank with respect to gravity is between 9 o'clock and 12 o'clock, for example between 9:30 and 11:30, and in one embodiment, between 10 o'clock and 11 o'clock.

[0035] Drift has often been shown to act not only vertically downwards, but also in other directions, or even primarily in other directions. Therefore, a position off-center from the drill can be particularly effective in directing the resulting drift in the appropriate direction.

[0036] In one embodiment, the position of the preform blank and / or drill to be selected is determined based on at least one previously determined drift direction.

[0037] The pre-determination of drift can be performed, for example, by empirical estimation and / or based on measurements. For example, it is possible to use experience obtained under similar conditions using the same drill, the same material, the same drilling location, the same rotational speed, and / or the same feed rate. In other words, the expected drilling path is predetermined and used as input to select the desired position on the preform blank and / or drill. Drift can also be determined by making test holes.

[0038] In one embodiment, a test hole is created in the test preform blank before the hole is made, and at least one direction of drift in the test hole is determined.

[0039] The determined direction is used to select a specific position. For example, if a drift occurs in the 2 o'clock direction, upward and to the right from the starting center of the borehole, the position of the preform blank and / or drill can be selected so that the preform blank and drill rotate 60° counterclockwise around the central longitudinal axis of the preform blank, starting from the position of the test hole. In this way, the resulting drift results in a change in position along the circumferential direction or on the pitch circle. The change in radial position is minimized. This adjustment can be performed by moving the preform blank and / or drill, for example by shifting and / or rotating it. For example, the preform blank and drill can be rotated together around the central longitudinal axis, an axis parallel to it, and / or a horizontal axis.

[0040] In particular, the test holes are made using the same drill. Specifically, the test preform blanks are made from at least substantially the same material as the preform blanks. Similarly, other parameters such as drilling position, rotational speed, and / or feed rate are selected.

[0041] After determining the direction of drift within the test hole, multiple holes can be created using the determined positions on the preform blank and / or drill.

[0042] In one embodiment, the position of the preform blank and / or drill changes between the creation of the first portion of the hole and the creation of the second portion of the hole. In one embodiment, the relative position between the preform blank and the drill remains the same. The change in position can be achieved, for example, by rotating the preform blank and the drill around an axis parallel to the central longitudinal axis, or, for example, around the central longitudinal axis itself. The movement of the preform blank and the drill can, in principle, be performed simultaneously, for example together, or sequentially, with at least some distance between them. This joint movement has the advantage that the drilling process does not need to be interrupted, or only minimally interrupted. The drill does not need to be removed from the completed portion of the hole.

[0043] The portions of the hole are aligned front to back along the axial direction. The portions of the hole are formed continuously. The change in position occurs between two portions of the hole. The position can be changed while the drill is not operating. The position can be changed while the drill is drilling. In one exemplary embodiment, the hole is formed into three or more portions, for example, four, five, six, eight, or ten portions, with the position changing between them in each case.

[0044] A temporary change in position can compensate for the temporarily altered direction of drift. This allows for particularly effective minimization of the radial drift component. For example, the downward drift component induced by gravity is only effective when the drilling length is longer. This component can be intentionally compensated for, enabling the creation of longer holes with higher precision.

[0045] In further embodiments, the common positions of the preform blank and the drill in space change at least intermittently as the hole is being made. Thus, during drilling, the positions of the preform blank and the drill in space change simultaneously. In particular, the preform blank and the drill rotate around an axis parallel to the longitudinal axis of the preform blank and / or the drill, or around a horizontal axis.

[0046] A continuous process is provided in which the drift is affected at any given time such that harmful radial components are minimized. This allows the above objective to be achieved more effectively.

[0047] In one embodiment, after a hole is made, the preform blank is rotated relative to the drill around its longitudinal axis, particularly its central longitudinal axis. In particular, additional holes are then made. In particular, the preform blank is rotated. In this way, multiple eccentric holes can be made in succession. This enables particularly efficient production of the preform. The position of the preform blank and / or drill to affect the drift may remain the same or change between and during individual drilling operations.

[0048] In one embodiment, the positions of the preform blank and / or drill in space are selected such that the change in the position of the hole in the azimuthal direction is at least twice, and particularly at least four times, greater than the change in the radial direction.

[0049] The coefficient is at least 3, preferably at least 5. In one embodiment, this coefficient is at least 7, at least 10, and in one example at least 15. This makes it possible to adjust for particularly low radial drift. To calculate the coefficient, the same unit, e.g., millimeters, is used for both azimuthal and radial changes.

[0050] In one embodiment, the ratio of the length of the preform blank to the diameter of the hole is greater than 10, and particularly greater than 20. This ratio can be greater than 30, and for example, greater than 35. This ratio may be greater than 40 or 50. As the ratio of the length of the preform to the diameter of the hole increases, drift also increases, which hinders the required precision. The solution according to the present invention enables such a ratio with high precision. Such a ratio ensures short processing time and minimum setup time.

[0051] In one embodiment, multiple holes are created. In one embodiment, the drift of multiple holes in the azimuthal direction is at least substantially the same magnitude. In particular, the drift of multiple holes in the azimuthal direction has the same direction in the same sign, i.e., it does not point in opposite directions. Thus, in multiple holes or all holes, the drift progresses either clockwise or counterclockwise with respect to the center of the cross-section of the preform blank. In this way, the distance between holes remains constant over the length of the preform. This minimizes optical loss and splice loss.

[0052] A further aspect of the present invention is a method for producing a preform for multicore fibers, comprising the method according to the present invention. In particular, a plurality of eccentric holes are produced. The method may include inserting core bars into the holes. All the advantages, features, and embodiments of the method described above can be similarly applied to this method, and vice versa.

[0053] A further aspect of the present invention is a preform for multicore fibers that can be or can be fabricated using the method according to the present invention. The preform includes eccentric holes extending along the longitudinal range of the preform. The positions of the holes in the cross-section of the preform vary over the longitudinal range of the preform. The cross-section of the preform corresponds to the cross-section of a preform blank. The variation in position observed in the cross-section of the preform is greater in the azimuthal direction than in the radial direction. This allows the distance between multiple eccentric holes to be substantially constant. The preform may include core bars inserted into the holes. All the advantages, features, and embodiments of the method described above can be similarly applied to preforms and vice versa.

[0054] In particular, both the start and end points of the hole lie on a pitch circle having the same diameter in the corresponding cross-section. Specifically, each point between the start and end points of the hole lies on a corresponding circle having the same diameter. In this ideal embodiment, drift occurs only in the azimuthal direction, and radial drift is zero. The change in the hole's position is measured in the cross-section, i.e., laterally with respect to the longitudinal range. The change in the hole's position is particularly continuous, i.e., not abrupt.

[0055] In one embodiment, the length of the preform is greater than 1.5 m, and in particular at least 2.0 m. The length may be at least 2.5 m. Such lengths can be manufactured with the required precision using the method according to the present invention.

[0056] In one embodiment, the preform includes at least two eccentric holes that extend along the longitudinal range of the preform and whose position within the cross-section varies over the longitudinal range of the preform. In particular, the distance between the holes, as measured in the cross-section, is substantially constant over the longitudinal range. The holes may be slightly twisted relative to each other, which has been proven not to be detrimental to the optical fibers.

[0057] In one embodiment, the distance between the central longitudinal axis of the preform and the center of the hole at the first end face of the preform and the second end face opposite the first end face of the preform is substantially the same. That is, the change in the radial position of the hole is almost zero. A deviation of up to 1%, particularly up to 0.5%, or up to 0.2% in the diameter of the preform blank may be acceptable.

[0058] Preferably, the change in the radial direction is at least twice, and particularly at least four times, smaller than the change in the azimuth direction.

[0059] In further embodiments, the preform includes at least two eccentric holes extending along the longitudinal range of the preform. The positions of the holes vary in the same direction across the longitudinal range of the preform along a curve around the central longitudinal axis of the preform within the cross-section of the preform. Ideally, the curve may be a circular path. In particular, the distance between two adjacent holes is substantially constant over the length of the preform. A deviation of up to 5%, particularly up to 2%, or up to 1% in the diameter of the preform blank may be acceptable.

[0060] A further aspect of the present invention is a device for machining a preform blank. The preform blank is used to produce a preform of multicore fiber. The device comprises a holding device for holding the preform blank, a drill for creating an eccentric hole in the preform blank, and a positioning device, the positioning device being designed to move the holding device and / or drill to adjust the position of the preform blank and / or drill such that drill drift occurring during drilling causes a greater change in the position of the hole in the cross-section of the preform blank in the azimuthal direction than in the radial direction. All the advantages, features, and embodiments of the methods and preforms described above can be similarly applied to the device, and vice versa.

[0061] This device is designed in particular to carry out the method according to the present invention and / or to manufacture a preform according to the present invention. The holding device is designed in particular to hold the preform blank in an alignment state that is at least substantially horizontal. The drill is designed in particular to be aligned at least substantially horizontally.

[0062] The positioning device may be designed to move the drill and / or the holding device together. The movement of the drill and / or the holding device may be rotational. The rotation can be performed around the central longitudinal axis of the preform blank held by the holding device, or around an axis parallel thereto. The positioning device may include a drive device for moving the drill and / or the holding device.

[0063] In one embodiment, the positioning device is designed to rotate the preform blank around the central longitudinal axis of the preform blank. In this way, the relative rotational position of the preform blank and the drill with respect to the central longitudinal axis can be adjusted particularly easily.

[0064] Alternatively or additionally, a positioning device may be designed to move a preform blank or drill in space. This can be achieved, for example, by two translational movements perpendicular to each other in the cross-section of the preform blank. Typically, the drill is stationary except for rotation around its longitudinal axis and the feed required to create the hole, while the preform blank is positioned and / or moved relative to the drill. By appropriately aligning the longitudinal axis of the drill with the longitudinal axis of the preform blank, the direction of drift can be adjusted as desired. The positioning device functions, in particular, to adjust different relative positions of the preform blank with respect to the drill after the hole has been made, so that additional holes can be made in which the drift is directed in the desired manner. This allows all holes in the preform to be made continuously.

[0065] The trajectory of the hole can be determined using ultrasound, CT analysis, and / or optical measurement methods as needed. The holding device may include a V-block for holding the preform blank. The device may further include a cutting fluid supply device. The drill may be a drill for the BTA drilling method. In this case, a coolant and lubricant are supplied from the outside to remove chips generated internally. The device includes a cutting fluid supply device (BOZA) for supplying coolant and lubricant. Preferably, a seal is mounted on the workpiece.

[0066] Exemplary embodiments of the present invention are also described in more detail below with reference to the drawings. Features of the exemplary embodiments may be individually or combined with any of the claimed subject matter unless otherwise specified. The scope of the claimed protection is not limited to the exemplary embodiments. [Brief explanation of the drawing]

[0067] The diagram is shown below. [Figure 1] This is a cross-section of the preform. [Figure 2] This is a cross-section of the preform. [Figure 3] This is a schematic diagram of the drilling process. [Figure 4] This is a schematic diagram of the drilling process before it begins. [Figure 5] This is a schematic diagram of the device. [Figure 6] This is a schematic diagram of the device. [Figure 7] This is a schematic diagram showing the method and process for machining a preform blank. [Figure 8] This is a schematic diagram showing the method and process for machining a preform blank. [Figure 9] This is a schematic diagram showing the method and process for machining a preform blank. [Figure 10] This is a schematic diagram of drift in the drilling process. [Figure 11] This is a schematic diagram of drift in the drilling process. [Figure 12] This is a schematic diagram of the process. [Figure 13] This is a schematic diagram of the process. [Modes for carrying out the invention]

[0068] Figures 1 and 2 show cross-sections 14 of different preforms 1 as examples. Each preform has a circular cross-section 14. Preforms 1 optionally include a central hole 2 extending along the central longitudinal axis of the corresponding preform 1.

[0069] Figure 2 shows, as an example, five eccentric holes 2 in addition to an arbitrary central hole 2. These eccentric holes are regularly distributed, for example, on a pitch circle (not individually marked), which can be concentric with the outer contour of the preform 1 and / or coaxial with the central longitudinal axis of the preform 1.

[0070] Figure 3 schematically illustrates the drilling process for creating a hole 2 in a preform blank 7. The drill 20 is moved along a direction 23 parallel to the longitudinal axis 15 of the preform blank 7, and in this process, rotates in particular about its longitudinal axis. The drill 20 typically comprises a drill head 21 driven by a drill rod 22. These components are shown here purely schematically. Typically, the drill rod 22 has a smaller diameter than the drill head 21. The drill rod 22 is driven, for example, by a drive unit not shown.

[0071] It is clear that the drill 20 penetrates the preform blank 7 at the first end face 11, thereby creating a hole 2. The hole 2 is eccentric, i.e., off-center. The longitudinal axis of the drill 20 is aligned parallel to the central longitudinal axis 15 of the preform blank 7. The position where the drill 20 contacts the first end face 11 or enters the cross section of the preform blank 7 is shown here, purely as an example, at the 6 o'clock position in the line of sight along direction 23.

[0072] Figure 4 shows the state before the start of eccentric drilling. The preform blank 7 may optionally already have a central hole. The drill 20 is positioned in front of the first end face 11 so that drilling can be performed by translational movement along its longitudinal axis or the central longitudinal axis 15. The drilling position 3 of the borehole to be created is marked on the first end face 11 with a dashed line.

[0073] Figures 5 and 6 show schematic diagrams of some components of the device 30. The preform blank 8 is held by elements of the holding device 32. The holding device 32 can be used to rotate the preform blank 7 around its central longitudinal axis. For example, the position of the preform blank 7 can be adjusted according to the invention, possibly together with the position of the drill 20. Thus, the holding device may be part of the positioning device 34.

[0074] The holding device 32 can also be used to adjust the position of the preform blank 7 relative to the drill 20 so that a second eccentric hole can be fabricated after a first eccentric hole has been fabricated, as shown in Figures 7 to 9. Alternatively or additionally, the holding device 32 may be designed to move the preform blank 7 in a plane perpendicular to its longitudinal range. For example, the holding device 32 comprises two translation devices 38 perpendicular to each other, as schematically shown in Figure 6. The holding device 32 can interact with a positioning device 34 to move the holding device 32. Alternatively or additionally, the holding device 32 holds the preform blank 7 in a fixed position.

[0075] The drill 20 is held by an optional drill holder 39, which can be used to move the drill 20 in a plane perpendicular to its longitudinal range. For example, the drill holder 39 comprises two translation devices 38 perpendicular to each other, as schematically shown in Figure 6. Thus, there may be a translation device 38 for the preform blank 7 and / or a translation device 38 for the drill 20. The drill holder 39 can be used to move the drill 20 relative to the preform blank 7 to adjust the position according to the present invention. The drill holder 39 may be part of a positioning device 34 for moving the holding device 32 and / or the drill 20. The positioning device 34 may comprise or consist of the drill holder 39. The drill holder 39 can be used to advance the drill 20 along its longitudinal axis during drilling.

[0076] Figures 7-9 illustrate the process for fabricating a preform using the cross-section 14 of the preform blank 7. For example, based on pre-formed test holes or experience with comparable systems, it is known that a drill drift toward the upper right in the 1 o'clock direction is expected. This can be determined at any drill position. To direct the drift relative to the cross-section 14 of the preform blank 7 in the desired direction (see Figures 10 and 11 below for this), the drill position 4 marked with a cross on the preform blank 7 was selected such that drilling in the cross-section 14 was not performed vertically above the center of the cross-section corresponding to the central longitudinal axis of the preform blank 7. Instead, the drill position was slightly shifted downward to the left to approximately the 11 o'clock position to minimize the radial component of the shift. In particular, all holes 2 are formed at this position.

[0077] Before creating the first hole, the required positions can be adjusted by positioning or moving the preform blank 7 and / or the drill. The preform blank 7 can be translated, i.e., shifted, for example, within the plane of its cross-section 14, and / or rotated, for example, around a rotation axis aligned parallel to the central longitudinal axis. Alternatively or additionally, the drill can be translated, i.e., shifted, for example, within the plane of its cross-section 14, and / or rotated, for example, around a rotation axis aligned parallel to the central longitudinal axis.

[0078] Figure 7 shows the situation before or during the first eccentric drilling. Optionally, the central hole may be pre-formed. The drill is positioned at drill position 4, marked with a cross, and as a result, the hole can be created by translation along the central longitudinal axis. Furthermore, drilling position 3, where the hole is also formed, is marked with a dashed line.

[0079] After the holes are created, a movement corresponding to a clockwise rotation 25 of the preform blank 7 around the central longitudinal axis of the preform blank 7 at a predetermined angle is performed. This is shown in Figure 8. Here, using equally spaced boreholes, the angle is calculated as 360° / n, where n is the number of boreholes to be created. Here, five boreholes are created purely as an example. Therefore, the angle is 72°. After the rotation, the completed hole 2 is located at approximately the 2 o'clock position in the upper right, and the drill position 4 is located at approximately the 11 o'clock position in front of the next hole to be created.

[0080] To change the angle, it is simple and practical to rotate the preform blank 7 around its central longitudinal axis, as shown in the figure. The drill can then be left stationary. However, instead of or in addition to this, moving the preform blank, rotating the preform around a different axis, and / or moving and / or rotating the drill are not excluded. The spatial positions of the drill and the preform blank may remain the same or change. The important thing is that the same relative position of the preform blank 7 with respect to the drill with respect to gravity, i.e., the position at approximately 11 o'clock here, is adjusted so that the drift can be directed again in the desired direction.

[0081] To form the next hole 2, the above process is repeated as shown in Figure 9. After two further repetitions (not shown), all holes 2 are completed.

[0082] Figures 10 and 11 show cutouts of a cross-section 14 of a preform to illustrate drift in a conventional method (Figure 10) and a method according to the present invention (Figure 11). For example, four holes are formed at equal intervals on a pitch circle of the cross-section 14. This pitch circle is shown as an inner target pitch circle 43 by a dotted line. The drill position 3, marked with a solid line, is positioned such that the center of each drill hole lies on the target pitch circle 43. This figure shows a top view of the first end face from which drilling begins. In this case, the drill position is located at the center above the center of the cross-section. Ideally, the holes should terminate at the same point on the same pitch circle on the opposite second end face.

[0083] However, drift occurs, which results in a displacement of the hole at the point where the drill is located at the end, or after the hole has been made. These positions are shown using the final position of the drill 5, marked with a dashed line. It is clear that the drill moves upward and to the right during the drilling process, i.e., according to an angle α with respect to the horizontal line H perpendicular to the direction of gravity. The resulting drift D, radial component Dr, and azimuthal component Da are shown. The radial component Dr extends radially 18, and the azimuthal component Da extends azimuthal 17. Furthermore, a coordinate system 40 is shown, with its origin at the center of the cross section. Starting from there, the target radius 45 and the actual radius 46 of a particular pitch circle are shown. The target radius 45 of the target pitch circle 42 is the radius present at the first end face 11. The actual radius 46 of the actual pitch circle 43 is the radius present at the second end face and shifted by the drift. The radial component Dr corresponds to the effective change in radius.

[0084] Figure 11 shows the same situation when the position of the preform blank 7 and / or drill is adjusted such that the drift causes a greater change in the position of the hole in the cross section 14 in the azimuthal direction 17 than in the radial direction 18. The symbols are the same as in Figure 11, and therefore only the differences are explained.

[0085] The angle α is the same. However, due to the selected relative position of the drill and the preform blank 7 with respect to the direction of gravity, here, as an example, it corresponds to the drilling position 3 between 10 o'clock and 11 o'clock. It is clear that the drift D has the same magnitude and direction as in the situation shown in Figure 10. However, due to the change in position, the radial component Dr becomes significantly smaller and the azimuthal component Da becomes significantly larger. The ratio of Da to Dr is approximately 3.8. The actual pitch circle 43 deviates significantly less from the target pitch circle 42. In this way, the quality of the preform, and therefore the quality of the optical fiber produced from the preform, can be greatly improved. It is also clear that the radial component Dr can be further reduced by further rotating the relative position of the drill and the preform blank counterclockwise, i.e., by changing the azimuthal position of the drill position with respect to the direction of gravity. In this case, the drift extends tangentially with respect to the target pitch circle 42 and has only a minimal radial component.

[0086] Figures 12 and 13 similarly show cutouts of section 14. The arrows indicate the drift from the drilling position to the final position 5 in each case. Note that the figures are rotated around the center of section 14 as the axis for illustrative purposes and deviate from the actual state. Figure 12 substantially corresponds to the situation in Figure 11, or a further optimized relative position where the desired position has been adjusted once before drilling, tangential drift exists, and as a result, a specific radial component of the drift still exists.

[0087] However, in Figure 13, continuous or semi-continuous changes in position occur. For example, after creating the first portion of the hole, the drill and the preform blank are rotated together and / or simultaneously, and then further portions of the hole are created. This corresponds to a semi-continuous process and can be repeated any number of times. Alternatively or additionally, the drill and the preform blank may be rotated together and simultaneously in space and / or with respect to gravity during drilling. This corresponds to a continuous process. This results in a continuously adapted drift, which ultimately progresses only in the azimuthal direction, as indicated by the simplified straight arrows.

[0088] In principle, a distinction can be made between predictable and unpredictable drift. The overall drift can be understood as a superposition of predictable and unpredictable drift. Information regarding predictable drift, such as the direction of the drift, can be determined, for example, before drilling. This can be done, for example, by creating a test hole under the same or similar conditions. Furthermore, unpredictable drift may occur.

[0089] In one embodiment, the position of the drill and / or the resulting drift is determined. This can be performed during and / or continuously during drilling. Measurements that can be called online measurements can be performed during drilling. For example, information regarding the position of a portion of the drill can be determined. A measuring device can be used to determine such a position. For example, the position of at least a portion of the drill can be measured preferably with respect to or within the cross-section of the preform blank. This determination can be made as described in German Patent Application No. 102012006410.

[0090] When selecting the position of the preform blank and / or drill, the measured position and / or drift can be taken into consideration. Based on the measured position and / or drift, the position of the preform blank and / or drill can be changed. This can be done during drilling and / or between the fabrication of the two parts of the hole. In this way, the trajectory of the hole can be affected, thus allowing for the management of unpredictable drift.

[0091] In particular, during drilling, it is possible to determine when a change in position is necessary to reach a specific target. If a change is necessary, the position can be changed. For example, a change can be made when a threshold is exceeded. The target may be, for example, a drift that is larger in the azimuthal direction than in the radial direction, and in some cases by a specific coefficient as described above, or the maximum absolute drift in the radial direction.

[0092] "Substantially horizontal" means that a certain degree of deviation from horizontal alignment is acceptable. This deviation is typically 15° or less, preferably 10° or less. [Explanation of Symbols]

[0093] 1 Preform 2 holes 3. Drilling location 4. Drill position 5 Final position 7 Preformed Blanks 11 First end face 12 Second end face 14 Cross-section 15. Central longitudinal axis 17 Azimuth direction 18 Radial 20 Drills 21 Drill head 22 Drill Rods 23 directions 25 rotations 30 devices 32 Retaining devices 34 Positioning devices 38 Translational Devices 39 Drill holder 40 Coordinate Systems 42 Target Pitch Circle 43 Actual Pitch Circle 45 Target radius 46 Actual radius D Dorito Dr radial component Da Azimuth component H horizontal α angle

Claims

1. A method for machining a preform blank (7) to produce a preform blank (1) of multicore fiber, wherein an eccentric hole (2) extending along the longitudinal range of the preform blank (7) is created in the preform blank (7) using a drill (20), and the position of the preform blank (7) and / or the drill (20) is selected such that the drift (D) of the drill (20) occurring during drilling causes a greater change in the position of the hole (2) in the cross section (14) of the preform blank (7) in the azimuthal direction (17) than in the radial direction (18).

2. The method according to claim 1, wherein the preform blank (7) and the drill (20) are aligned substantially horizontally.

3. The method according to claim 1, further comprising adjusting the desired rotational positions of the preform blank (7) and the drill (20) around the central longitudinal axis (15) of the preform blank (7).

4. The method according to claim 1, wherein the positions of the preform blank (7) and the drill (20) are such that the drill (20) is located at a position other than directly above the central longitudinal axis (15) of the preform blank (7) with respect to the direction of gravity.

5. The method according to claim 1, wherein the selected position of the preform blank (7) and / or the drill (20) is determined based on at least one predetermined direction of the drift (D).

6. The method according to claim 5, wherein, before the hole (2) is made, a test hole is made in a test preform blank and at least one direction of the drift (D) in the test hole is determined.

7. The method according to claim 1, wherein the position of the preform blank (7) and / or the drill (20) changes between the fabrication of the first portion of the hole (2) and the fabrication of the second portion of the hole (2).

8. The method according to claim 1, wherein, at the same time as the hole (2) is formed, the common position in the space between the preform blank (7) and the drill (20) changes by at least a gap.

9. The method according to claim 1, wherein, after the hole (2) is made, the preform blank (7) is rotated with respect to the drill (20) about the central longitudinal axis (15) of the preform blank (7), and thereafter an additional hole (2) is made.

10. The method according to claim 1, wherein the position of the preform blank (7) and / or the drill (20) is selected such that the change in the position of the hole (2) is at least twice, and particularly at least four times, greater in the azimuthal direction (17) than in the radial direction (18).

11. A method for producing a preform (1) for multicore fiber, comprising the method according to claim 1.

12. A preform (1) for a multicore fiber that can be manufactured by the method of claim 1, comprising eccentric holes (2) extending along a longitudinal range of the preform (1), wherein the position of the holes (2) in a cross section (14) of the preform (1) changes over the longitudinal range of the preform (1), and the change in position observed in the cross section (14) of the preform (1) is greater in the azimuthal direction (17) than in the radial direction (18).

13. The preform (1) according to claim 12, wherein the preform (1) includes at least two eccentric holes (2) extending along the longitudinal range of the preform (1), the position of the eccentric holes (2) varies in the same direction along a curve around the central longitudinal axis (15) of the preform (1) within the cross section (14) of the preform (1) and over the longitudinal range of the preform (1).

14. A device (30) for machining a preform blank (7) to produce a preform (1) of multicore fiber, comprising: a holding device (32) for holding the preform blank (7); a drill (20) for creating an eccentric hole (2) in the preform blank (7); and a positioning device (34) designed to move the holding device (32) and / or the drill (20) to adjust the position of the preform blank (7) and / or the drill (20) such that the drift (D) of the drill (20) occurring during drilling causes a greater change in the position of the hole (2) in the cross section (14) of the preform blank (7) in the azimuthal direction (17) than in the radial direction (18).

15. The device according to claim 14, wherein the positioning device (34) is configured to rotate the preform blank (7) about the central longitudinal axis (15) of the preform blank (7).

Images