Method for manufacturing optical fiber preforms

Abstract

The present invention provides a manufacturing method for optical fiber preforms that satisfies one or more of the following criteria: a method that produces as little manufacturing waste as possible, a method that produces a preform with the most uniform doping possible, a method that is as simple as possible to implement, and a method that is as cost-effective as possible. [Solution] A method for manufacturing an optical fiber matrix includes: a step of synthesizing glass particles using a plasma zone generated by a plasma generator; b step of repeatedly moving the glass matrix forward and backward in the axial direction relative to the plasma generator while the glass matrix is ​​rotating, wherein the forward and backward movement is performed at a relative supply speed between two reversal points; and c step of depositing glass particles on the glass matrix while the glass matrix is ​​moving and rotating relative to the plasma generator.

Description

[Technical Field]

[0001] The present invention relates to a method for manufacturing optical fiber preforms, a. A method and process for synthesizing glass particles using a plasma zone generated by a plasma generator. b. A method step of repeatedly moving a glass matrix material forward and backward in the axial direction relative to a plasma generator while the glass matrix material is in rotational motion, wherein the forward and backward movement is performed at a relative supply speed between two reversal points. c. A method for depositing glass particles onto a glass matrix while the glass matrix is ​​moving and rotating relative to a plasma generator. In a method including, (i) The relative supply rate of the plasma generator to the glass matrix is ​​V at the center of the glass matrix. Mitte Having a right side, (ii) When the plasma generator moves relative to one of the inversion points from the center of the glass matrix, the relative supply rate of the plasma generator to the glass matrix is ​​V Mitte From V hin The value will be reduced to (iii) When the plasma generator moves relative to the center of the glass matrix from one of the reversal points, the relative supply rate of the plasma generator to the glass matrix is ​​V rueck From the value of V Mitte It will be reduced to This invention relates to a method for manufacturing optical fiber preforms characterized by the following. [Background technology]

[0002] The base material for optical fiber manufacturing is often generated by a plasma generator, such as a plasma torch. Such a plasma generator in the form of a plasma torch is sometimes called, for example, a high-frequency induction plasma torch. This is a plasma torch equipped with a high-frequency coil at the edge of a gas flow tube. A high-frequency current is applied to ionize the gas contained therein, and the resulting plasma is emitted from the nozzle. The plasma generator may also be a plasma torch operated by a different technique, for example, microwave radiation. The plasma generator may also be a device that generates plasma by induction. Such a plasma generator preferably includes an induction coil that generates plasma.

[0003] The plasma generated in this manner is used to synthesize glass particles, which are deposited by being deposited onto a glass matrix such as a glass rod or glass tube. For this purpose, a glass precursor such as silicon tetrachloride, an optional dopant such as sulfur hexafluoride, and an optional auxiliary gas such as oxygen and nitrogen or argon are continuously supplied to the plasma, and the glass particles thus synthesized are deposited onto the surface of a glass matrix such as a glass rod or glass tube that moves forward and backward relative to the plasma generator while rotating.

[0004] The deposition of synthesized glass particles is particularly difficult at the edges of the glass matrix because these edges undergo two passes by the plasma generator in a very short time: once in the forward path and immediately afterward again in the backward path, thus imposing particularly high thermal stress on these regions. At the same time, if the plasma generator is located on the opposite edge of the glass matrix, the edges also experience particularly strong cooling. In other words, the edges are cooled particularly strongly during the two passes (when passing the opposite edge) and heated particularly strongly (when passing the corresponding edge twice). In particular, the two direct consecutive passes and the associated particularly strong heating of the corresponding edges result in partial evaporation of the synthesized glass particles deposited on the corresponding edges. This results in a non-uniform material structure at the edges, which experience relatively less thermal stress compared to the central region of the glass matrix. The doping at the edges of synthesized glass particles is also adversely affected by thermal stress, which is why the edges have lower doping than the central region of the glass matrix, as described, for example, in European Patent Application Publication No. 1997783(A2). Lower doping may be the result of thermally induced outward diffusion. Therefore, the high thermal stress at the edges of the glass matrix results in high manufacturing waste because the edges of the glass matrix are unsuitable for further processing for manufacturing optical fibers.

[0005] In principle, there are several methods for depositing synthesized glass particles onto a glass matrix: (1) The particles are initially deposited in the form of a porous layer, and its porosity is subsequently removed by a special heat treatment involving melting. This process leads to densification of the initial porous structure in order to form a homogeneous glass. (2) Alternatively, the deposition is carried out directly as a dense glass layer, thereby eliminating the subsequent densification process.

[0006] The difficulties described above, particularly the thermal stress at the edges of the glass substrate, pose challenges to all of these methods.

[0007] Therefore, the market demands improved methods for manufacturing optical fiber preforms.

[0008] the purpose One objective of the present invention is to overcome at least partially one or more of the drawbacks arising from the prior art.

[0009] In particular, an object of the present invention is to provide a method for manufacturing optical fiber preforms that produce as little manufacturing waste as possible. Furthermore, the method should provide preforms with the most uniform doping possible. The method according to the present invention should be as easy to implement as possible. Furthermore, it should be as cost-effective as possible.

[0010] Preferred Embodiment of the Invention A contribution to at least one of the aforementioned objectives, at least partially, is made by the features of the independent claim. The dependent claim provides a preferred embodiment that contributes to at least one of the objectives, at least partially.

[0011] A first embodiment of the present invention is a method for manufacturing an optical fiber preform. a. A method and process for synthesizing glass particles using a plasma zone generated by a plasma generator. b. A method step of repeatedly moving a glass matrix material forward and backward in the axial direction relative to a plasma generator while the glass matrix material is in rotational motion, wherein the forward and backward movement is performed at a relative supply speed between two reversal points. c. A method for depositing glass particles onto a glass matrix while the glass matrix is ​​moving and rotating relative to a plasma generator. In a method including, (i) The relative supply rate of the plasma generator to the glass matrix is ​​V at the center of the glass matrix. Mitte Having a right side, (ii) When the plasma generator moves relative to one of the inversion points from the center of the glass matrix, the relative supply rate of the plasma generator to the glass matrix is ​​VMitte from V hin is reduced to the value of, (iii) When the plasma generator moves relatively from one of the turning points toward the center of the glass base material, the relative supply rate of the plasma generator to the glass base material is V rueck from the value of V Mitte is reduced to V A method for manufacturing an optical fiber preform, characterized by the above.

[0012] A preferred embodiment of this method is that V rueck > V Mitte > V hin That is, or rather, V rueck has a value greater than V Mitte and V Mitte has a value greater than V hin This embodiment is the second embodiment of this method and preferably depends on the first embodiment of the present invention.

[0013] A preferred embodiment of this method is that the difference in values between V Mitte and V hin substantially corresponds to the difference in values between V rueck and V Mitte This embodiment is the third embodiment of the present invention and preferably depends on the first or second embodiment of the present invention.

[0014] A preferred embodiment of this method is that the reduction in the relative supply rate from V Mitte to V hin and from V rueck to V Mitte has a substantially exponential or parabolic profile. This embodiment is the fourth embodiment of the present invention and preferably depends on one of the previous embodiments of the present invention.

[0015] A preferred embodiment of this method is characterized in that the glass particles synthesized in step a of the method contain a dopant. This embodiment is a fifth embodiment of the present invention and is preferably dependent on one of the prior embodiments of the present invention.

[0016] A preferred embodiment of this method is V Mitte This embodiment is characterized by having a value in the range of 500 mm / min to 3000 mm / min. This embodiment is a sixth embodiment of the present invention and is preferably dependent on one of the prior embodiments of the present invention.

[0017] A preferred embodiment of this method is V hin ga V Mitte It is characterized by having a value in the range of 0.4 to 0.9 times. This embodiment is a seventh embodiment of the present invention and is preferably dependent on one of the prior embodiments of the present invention.

[0018] A preferred embodiment of this method is V rueck ga V Mitte It is characterized by having a value in the range of 1.1 to 1.6 times. This embodiment is an eighth embodiment of the present invention and is preferably dependent on one of the prior embodiments of the present invention.

[0019] A preferred embodiment of this method is characterized in that the average residence time of the plasma generator at each axial position of the glass matrix is ​​substantially the same. This embodiment is a ninth embodiment of the present invention and is preferably dependent on one of the prior embodiments of the present invention.

[0020] A preferred embodiment of this method is one in which the relative supply rate is a value V over the axial range of the glass matrix, corresponding to 0% to 50%, preferably 15% to 45%, of the total axial length of the glass matrix. Mitte This embodiment is characterized by having the following. This embodiment is a tenth embodiment of the present invention and is preferably dependent on one of the prior embodiments of the present invention.

[0021] A preferred embodiment of this method is: (i) Plasma output at the center of the glass matrix is ​​P Mitte Having a right side, (ii) When the plasma generator moves relative to one of the inversion points from the center of the glass matrix, the plasma output is P Mitte From P hin To increase in value, (iii) When the plasma generator moves relative to the center of the glass matrix from one of the inversion points, the plasma output is value P rueck From P Mitte To increase It is characterized by the following.

[0022] This embodiment is an eleventh embodiment of the present invention and is preferably dependent on one of the prior embodiments of the present invention.

[0023] A preferred embodiment of this method is characterized by an increase in plasma output when the relative supply rate is reduced. This embodiment is a twelfth embodiment of the present invention and is preferably dependent on the eleventh embodiment of the present invention.

[0024] A preferred embodiment of this method is that the glass base material in the process of this method reaches a minimum temperature T Min and the highest temperature T Max It has a temperature between T Min and T Max Temperature difference T between Diff This embodiment is characterized by having a maximum temperature of 200K. This embodiment is a thirteenth embodiment of the present invention and is preferably dependent on one of the prior embodiments of the present invention.

[0025] A preferred embodiment of this method is T Max This embodiment is characterized by reaching a maximum value of 2650°C. This embodiment is the 14th embodiment of the present invention and is preferably dependent on the 13th embodiment of the present invention.

[0026] A preferred embodiment of this method is characterized in that the glass base material is a glass rod, the plasma generator is a plasma torch, and the plasma zone is a plasma flame. This embodiment is the 15th embodiment of the present invention and is preferably dependent on one of the prior embodiments of the present invention.

[0027] general If an element of an embodiment described herein "haves" or "comprises" a particular feature (e.g., material), then, in principle, further embodiments are always intended in which the relevant element consists solely of that feature, i.e., without any other components. The words "comprise" or "comprising" are used herein as synonymous with the words "have" or "having".

[0028] In one embodiment, where an element is indicated in the singular form, embodiments in which two or more such elements exist are also intended. The use of terminology with respect to plural elements generally also includes embodiments in which only a single corresponding element is included.

[0029] Unless otherwise specified or explicitly excluded from the context, features of different embodiments are, in principle, also possible and expressly intended to be present in other embodiments described herein. Similarly, in principle, all features described herein in relation to methods are also applicable to products and apparatus described herein, and vice versa. For the sake of brevity of explanation, not all such considered combinations are explicitly listed in every case. Technical solutions known to be equivalent to the features described herein are also intended to be, in principle, included within the scope of the present invention.

[0030] In this specification, a range specification includes values ​​that are specified as limits. Therefore, a specification of the type "within the range of X to Y" for a variable A means that A can take values ​​X, Y, and values ​​between X and Y. Thus, a one-sided range of the type "up to Y" for a variable A means values ​​Y and less than Y.

[0031] Some of the characteristics described are associated with the term “substantially”. The term “substantially” should be understood as meaning that, under actual conditions and manufacturing techniques, it is not possible to precisely give mathematically precise interpretations of terms such as “superimposed,” “perpendicular,” “diameter,” or “parallelism,” but rather that they can only be given within a certain tolerance range for manufacturing errors. For example, “substantially perpendicular axes” encompasses an angle between 85 and 95 degrees, and “substantially identical volumes” includes deviations of up to 5 volume percent. For example, “a device made substantially of plastic” includes a plastic content of ≥95% to ≤100% by weight. For example, “substantially complete filling of volume B” includes filling of the total volume of B to ≥95% to ≤100% by volume.

[0032] When referring to a singular noun, if an indefinite or definite article such as "a," "an," or "the" is used, it includes the plural form of that noun unless otherwise specified. When the term "comprising" is used herein and in the claims, it does not exclude any other elements.

[0033] For the purposes of the present invention, the terms “substantially from” and “consisting of” are considered equivalent to the term “comprising.” Where a group is defined below as comprising at least a certain number of embodiments, this should also be understood as disclosing, in one embodiment, a group substantially consisting of only those embodiments, or in one embodiment, a group consisting of only those embodiments.

[0034] The terms “can be obtained” or “can be defined,” and “obtained” or “defined,” are used interchangeably. This means, for example, that the term “obtained” does not imply that the embodiment must be obtained by a series of steps following the term “obtained,” unless the context explicitly indicates otherwise, but such a limited understanding is always included in the terms “obtained” or “defined” as an embodiment. Whenever the terms “including” or “with” are used, these terms are synonymous with “comprising” as defined above. [Modes for carrying out the invention]

[0035] The first subject of the present invention is a method for manufacturing an optical fiber preform, a. A method and process for synthesizing glass particles using a plasma zone generated by a plasma generator. b. A method step of repeatedly moving a glass matrix material forward and backward in the axial direction relative to a plasma generator while the glass matrix material is in rotational motion, wherein the forward and backward movement is performed at a relative supply speed between two reversal points. c. A method for depositing glass particles onto a glass matrix while the glass matrix is ​​moving and rotating relative to a plasma generator. In a method including, (i) The relative supply rate of the plasma generator to the glass matrix has a value of VMitte at the center of the glass matrix. (ii) When the plasma generator moves relative to one of the inversion points from the center of the glass matrix, the relative supply rate of the plasma generator to the glass matrix is ​​reduced from VMitte to Vhin. (iii) When the plasma generator moves relative to the center of the glass matrix from one of the reversal points, the relative supply rate of the plasma generator to the glass matrix is ​​reduced from the Vrueck value to VMitte. This invention relates to a method for manufacturing optical fiber preforms characterized by the following.

[0036] In step a of the method, glass particles are synthesized using a plasma zone generated by a plasma generator. The plasma generator can generate the plasma zone, for example, by an induction coil. In a preferred embodiment, the plasma generator is a plasma torch that generates the plasma zone in the form of a plasma flame.

[0037] To generate glass particles, a glass precursor such as silicon tetrachloride is supplied to the plasma zone, preferably always together with oxygen, argon, and / or nitrogen, and these are converted into glass particles in the plasma zone. Optionally, dopants can be added to adjust the refractive index of the glass particles to suit the application of the matrix material. Preferably, sulfur hexafluoride is added to the plasma zone along with the remaining glass precursor to obtain fluorinated glass particles.

[0038] In step b of the method, a glass base material, such as a glass rod or glass tube, is repeatedly moved forward and backward in the axial direction relative to a plasma generator. Either the glass base material, the plasma generator, or both the glass base material and the plasma generator can be moved. The forward and backward movement of the glass base material relative to the plasma generator takes place between two reversal points where the relative movement changes direction, i.e., for example, a forward movement is reversed into a backward movement. The relative movement takes place in the axial range, i.e., along the longitudinal axis of the glass base material. The relative movement takes place at least along the entire length of the glass base material, preferably beyond the edge region of the glass base material, so that the plasma generator is positioned once at each axial position of the glass base material during each forward and backward movement. In other words, the reversal points are positioned such that the glass base material is located between the two reversal points along its entire axial length.

[0039] Therefore, the synthesized glass particles can be deposited at each axial position of the glass matrix during their relative movement (see step c of the method).

[0040] Simultaneously with relative movement, rotational motion occurs around the longitudinal axis, in other words, the glass matrix rotates, which makes it possible to uniformly deposit the synthesized glass particles around the glass matrix (see method step c).

[0041] The glass base material preferably includes quartz glass. Preferably, the glass base material consists of quartz glass. Depending on the application field of the base material, the quartz glass of the glass base material may contain dopants such as fluorine.

[0042] In step c of the method, glass particles synthesized within the plasma zone of the plasma generator move relative to the plasma generator and are deposited onto a rotating glass matrix.

[0043] In one embodiment, the glass matrix is ​​a glass tube, the plasma zone is generated within the glass tube, and the synthesized glass particles are deposited on the inner surface of the glass tube. In this embodiment, the plasma generator preferably generates the plasma zone by induction, and for this purpose, the plasma generator preferably comprises an induction coil, which is preferably arranged in a sleeve around the glass tube. In this embodiment, the induction coil is moved relative to the glass tube, and the plasma zone generated within the glass tube by the induction coil moves with the induction coil. In this embodiment, the deposition of synthesized glass particles takes place on the inner surface of the glass tube.

[0044] In a further embodiment, the glass base material is a glass rod, and the plasma zone is generated by the plasma flame of a plasma torch. In this embodiment, the plasma torch is moved relative to the glass rod while the plasma flame is spreading over the glass rod, causing the synthesized glass particles to be deposited on the outer surface of the glass rod.

[0045] To achieve the most uniform deposition of glass particles onto the glass matrix, the relative supply rate, i.e., the speed at which the plasma generator and the glass matrix move relative to each other, is matched to the axial position of the plasma generator with respect to the longitudinal axis of the glass matrix. Therefore, the relative supply rate is not constant over the entire length of the glass matrix, but varies depending on the relative position of the plasma generator and the glass matrix.

[0046] At the center of the glass matrix, particularly at the axial center, the relative supply rate is value V. Mitte It has.

[0047] When the plasma generator moves from the center of the glass matrix to one of the inversion points, the relative supply rate is value V. Mitte From value V hin This reduces the relative supply rate. Therefore, when the plasma generator moves from the center of the glass matrix toward one of the reversal points, the relative supply rate is reduced. Mitte From V hin The deceleration can be initiated directly at the center of the glass matrix. In a further embodiment of this method, V Mitte From V hin The deceleration does not begin directly at the center of the glass matrix, but only after the plasma torch has moved relative to the glass matrix from the center to 5% to 40%, preferably 10% to 35%, more preferably 15% to 30%, of the total length of the glass matrix in the direction of the corresponding reversal point.

[0048] Preferably, the relative supply rate is value V hin Until it reaches V Mitte From V hin It decelerates continuously until [a certain point].

[0049] Therefore, V Mitte From V hin If the relative supply rate deceleration to the plasma generator is initiated in the direction of one of the reversal points from the center of the glass matrix, the plasma generator will move above a specific axial position of the glass matrix, relative to the supply rate V Mitte It remains continuously longer than in the case of [another case]. Preferably, the plasma generator has a relative supply rate of value Vhin When this is taken, it remains above a specific axial position of the glass base material for the longest time. Mitte From V hin The reduction in the relative supply rate results in a certain axial position of the glass matrix being passed more slowly the longer the time elapsed since the last pass of the plasma generator at that position. This can at least partially compensate for the increased cooling at the corresponding position of the last pass, resulting in more uniform thermal stress.

[0050] Preferably, at a reversal point located spatially behind the corresponding end of the glass base material, the reversal of relative movement is preferably immediate. Thus, forward movement becomes backward movement, and vice versa.

[0051] When the plasma generator moves relative to the center of the glass matrix from one of the reversal points, the relative supply rate is value V. rueck From value V Mitte This is reduced. Therefore, when the plasma generator moves from one end of the glass matrix toward the center of the glass matrix, the relative supply speed is reduced.

[0052] Preferably, the relative supply rate is value V Mitte Until it reaches V rueck From V Mitte The rate of motion is continuously reduced until a certain value is reached. Therefore, preferably, when moving relative to the center of the glass base material, the relative supply rate reaches the maximum value of the relative supply rate, preferably value V, at the corresponding end of the glass base material. rueck It has, and this value is value V Mitte The value V is preferably continuously reduced until it reaches [value]. Mitte The plasma can only be directly reached at the center of the glass matrix. In a further embodiment, the value V is obtained when the plasma generator remains at 5% to 45%, preferably 10% to 40%, more preferably 15% to 35%, of the total length of the glass matrix, relative to the glass matrix away from the center of the glass matrix. Mitte It reaches.

[0053] Therefore, the plasma generator is directed from the corresponding end of the glass matrix toward the center of the glass matrix, above a specific axial position of the glass matrix, at a relative supply rate V rueck It stays there continuously for a longer period than in the case of [another case]. The plasma generator has a relative supply rate of value V. rueck When this is present, it remains above a specific axial position of the glass base material in the shortest possible time. At the same time, this means that V Mitte and V hin A specific axial position of the glass matrix that has just passed through at a relative supply rate value between V and V is, in a direct, continuous passage, at a higher relative supply rate value, i.e., V rueck and V Mitte The result is that it passes between and . Therefore, V Mitte Immediately after the forward pass, which is slower compared to the previous one, V Mitte The return journey (backward pass) is accelerated in comparison.

[0054] In summary, the relative supply rate profile is as follows:

[0055] The relative supply rate at the center of the glass matrix is ​​value V. Mitte It has the following characteristics: When the plasma generator moves relative to the glass matrix from the center of the glass matrix in one of the inversion points, and reaches the corresponding end of the glass matrix, the slowest relative supply rate, preferably a value V, is used. hin Until it reaches V, the relative supply rate is V Mitte From V hin It is reduced to a certain value. At the reversal point, the direction of relative movement changes. When moving relative to the center of the glass matrix from the corresponding reversal point, the relative supply rate is value V. rueck Take the value V rueck The value V is in the direction of the center of the glass base material. Mitte It is reduced again to V. Mitte Compared to the slower V, immediately after the forward journey to the edge of the glass base material, Mitte Compared to that, the return path from the same edge towards the center of the glass base material is accelerated.

[0056] By varying the relative supply speed, it is possible to reduce the thermal stress, particularly at the edges of the glass substrate, and enable more uniform deposition of the synthesized glass particles. This reduces manufacturing waste. In particular, V rueck and V Mitte A relatively fast passage from a specific edge in the direction of the center of the glass substrate, carried out at the relative supply speed between and, reduces the thermal stress. As compensation, the passage in the opposite direction, i.e., from the center of the glass substrate towards the corresponding inversion point, is carried out at the relative supply speed between V Mitte and V hin and is thus carried out in a decelerated manner compared to the value V Mitte in the region of the center of the glass substrate.

[0057] Thus, during the relative movement of the plasma generator from the center of the glass substrate towards the corresponding inversion point, the edges of the glass substrate experience an increase in exposure to the plasma zone compared to the center of the glass substrate, but in the opposite direction, i.e., from the inversion point towards the center of the glass substrate, a relatively reduced exposure to the plasma zone is carried out, particularly in the region of the edges of the glass substrate. Thus, the temperature difference T Diff that a specific axial position of the glass substrate has between two passages can always be reduced compared to the passage at a constant relative supply speed. This ensures more uniform thermal stress over the entire axial length of the glass substrate and results in more uniform deposition of the synthesized glass particles over the axial length of the glass substrate.

[0058] This method is characterized by three different values V Mitte , V hin and V rueck of the relative supply speed, and it can also be seen from the above that the relative supply speed takes values between these three mentioned values.

[0059] From the above, it can be seen that the value of V rueck is greater than the value of V Mitte and that the value of V Mitte is greater than the value of V hin . Thus, the value of V hin is the value of V rueckThe value and V Mitte It lies between the values.

[0060] A preferred embodiment of this method is V Mitte The value and V hin The difference from the value of is substantial, that is, within a certain tolerance, especially within the error tolerance, V rueck The value and V Mitte In this embodiment, V Mitte The value of is exactly V rueck The value and V hin It lies between the values ​​of . In other words, in this embodiment, when the plasma generator moves relative to the glass matrix in the direction from the center of the glass matrix to one of the reversal points, and when the plasma generator moves relative to the glass matrix from one of the reversal points towards the center of the glass matrix, the relative supply rate is reduced by the same value. This is because the temperature difference T at a specific axial position of the glass matrix between passes and passes Diff This can lead to a reduction in [the problem].

[0061] V Mitte From V hin e or V rueck From V Mitte The rate of change of the deceleration of the relative supply rate can be designed in different ways. For example, the rate of change may be linear, resulting in a constant change in the relative supply rate.

[0062] A preferred embodiment of this method is V Mitte From V hin and V rueck From V Mitte The reduction in the relative supply rate to has a substantially exponential or parabolic profile. In this embodiment, the reduction in the relative supply rate is such that the relative supply rate reaches a target value, i.e., V hin or V Mitte The rate of change increases as it approaches the target. In this embodiment, the change in the relative supply rate is not linear but increases gradually.

[0063] This results in a specific axial position of the glass matrix being passed more slowly the longer the time elapsed since the last pass through the plasma generator at that position. This can at least partially compensate for the increased cooling at the corresponding position during the last pass, resulting in more uniform thermal stress. At the same time, the axial position is passed through the plasma generator more quickly the shorter the time elapsed since the last pass through the plasma generator.

[0064] Therefore, a particularly slow outward journey is followed by a particularly fast return journey, which can lead to a more uniform deposition of the synthesized glass particles.

[0065] A preferred embodiment of this method is characterized in that the glass particles synthesized in step a of the method contain a dopant. Preferably, the synthesized glass particles contain a dopant selected from the group consisting of germanium dioxide (GeO2), phosphorus pentoxide (P2O5), fluorine (F2), boron dioxide (B2O3), and aluminum oxide (Al2O3). To introduce the dopant into the synthesized glass particles, a suitable dopant precursor known to those skilled in the art is added to the plasma flame of a plasma torch. Examples of such dopant precursors include germanium tetrachloride (GeCl4), phosphorus oxychloride (POCl3), hydrogen fluoride (HF), silicon tetrafluoride (SiF4), boron trifluoride (BF3), sulfur hexafluoride (SF6), oxygen-containing fluorinating agents such as perfluoroketones, perfluoroethers, or hydrofluoroethers, nitrile-containing fluorinating agents such as perfluoronitriles, boron trichloride (BCl3), and aluminum chloride (AlCl3).

[0066] In particular, the modification of the relative supply rate according to the present invention, which reduces thermal stress at the edges of the glass matrix, also has a positive effect on uniform dopant concentration along the axial length of the glass matrix. In particular, it is possible to achieve more uniform fluorine doping, which is especially sensitive to non-uniform thermal stress during deposition on the glass matrix.

[0067] Relative supply rate V Mitte , V hin, and V rueck This can take on different absolute values. The absolute value can be adjusted, for example, depending on the composition of the glass matrix, the composition of the synthesized glass particles, the length of the glass matrix, its outer diameter, and / or its rotational speed.

[0068] A preferred embodiment of this method is V Mitte However, it is characterized by having a value in the range of 500 mm / min to 3000 mm / min, preferably in the range of 700 mm / min to 2500 mm / min, and more preferably in the range of 800 mm / min to 1500 mm / min.

[0069] V hin and V rueck The value of V is chosen to achieve the lowest possible thermal stress, especially at the edges of the glass base material. Mitte The value should be particularly adapted to the composition of the glass matrix, the composition of the synthesized glass particles, the length of the glass matrix, its outer diameter, and / or its rotational speed.

[0070] A preferred embodiment of this method is V hin However, V Mitte It is characterized by having a value in the range of 0.4 to 0.9 times, preferably in the range of 0.5 to 0.85 times.

[0071] A preferred embodiment of this method is V rueck However, V Mitte It is characterized by having a value in the range of 1.1 to 1.6 times, preferably in the range of 1.15 to 1.5 times.

[0072] A preferred embodiment of this method is characterized in that the average residence time of the plasma generator at each axial position of the glass matrix is ​​substantially the same, i.e., has a specific tolerance. In this embodiment, V hin and V rueck teeth, V Mitte and V hin The relative supply rate values ​​between and directly twice consecutively or V Mitte As long as it passes twice at that speed, V rueck and V MitteThe plasma generator is adjusted to remain as a whole at a specific axial position of the glass matrix as it passes in opposite directions. In other words, each axial position of the glass matrix is ​​thus exposed to the plasma zone generated by the plasma generator for the same duration during the two direct, consecutive passes. This results in a more uniform deposition of synthesized glass particles, particularly at the edges of the glass matrix.

[0073] The relative supply rate is a value V across the axial portions of the glass matrix of different lengths. Mitte It can have the following characteristics. For example, the relative supply rate is valued V only at the exact center of the glass matrix. Mitte However, in the direction of passage, just before the center of the glass base material, the relative supply rate is V rueck and V Mitte The value is between V, and immediately after the center of the glass base material in the direction of passage, the relative supply rate is V Mitte and V hin It has a value between V. In this embodiment, the relative supply rate is substantially the value V at the point-like axial position of the glass matrix, i.e., at the center. Mitte It has.

[0074] A preferred embodiment of this method is one in which the relative supply rate is a value V over the axial range of the glass matrix, corresponding to 0% to 50%, preferably 15% to 45%, and more preferably 20% to 40% of the axial length of the glass matrix. Mitte This is characterized by taking the following. In all cases, this axial range includes the center of the glass base material, and the center of the glass base material is preferably also the axis of the axial range.

[0075] In addition to changing the relative supply rate, further processing parameters can also be changed, particularly depending on the axial position of the glass matrix, in order to make the thermal stress as uniform as possible, especially at the edges of the glass matrix.

[0076] For example, the rotational motion of the glass substrate around its longitudinal axis can be changed, particularly in terms of rotational speed.

[0077] Further possible modifications relate to plasma generators in the form of plasma torches. For example, the distance from the glass matrix, preferably in the form of a glass rod, can be varied to allow for the most uniform deposition possible of the synthesized glass particles.

[0078] A preferred embodiment of this method is: (i) Plasma output at the center of the glass matrix is ​​P Mitte Having a right side, (ii) When the plasma generator moves relative to one of the inversion points from the center of the glass matrix, the plasma output is P Mitte From P hin To increase in value, (iii) When the plasma generator moves relative to the center of the glass matrix from one of the inversion points, the plasma output is value P rueck From P Mitte To increase It is characterized by the following.

[0079] Therefore, in this embodiment, the plasma output is when the relative supply rate is V Mitte As it decreases compared to V, it increases, or the relative supply rate is V Mitte It decreases as it increases compared to [the previous value].

[0080] The temperature of the glass matrix at a particular axial position changes during the process of the method and depends in particular on the time of the last pass of the plasma generator at the corresponding axial position, the dominant plasma output at that time, the residence time of the plasma generator at the corresponding axial position during this pass, and, in the case of a plasma generator in the form of a plasma torch, the distance from the glass matrix, preferably in the form of a glass rod.

[0081] A preferred embodiment of this method is that the glass base material in the process of this method reaches a minimum temperature T Min and the highest temperature T Max It has a temperature between T Min and T Max Temperature difference T between DiffHowever, it is characterized by having a maximum temperature of 200K, preferably a maximum of 190K, and more preferably a maximum of 180K.

[0082] A preferred embodiment of this method is T Max It is characterized by reaching a maximum temperature of 2650°C.

[0083] Temperature measurements were performed optically using a thermal camera (DIAS PyroView 640G model, manufactured by DIAS Infrared GmbH, Germany) in the spectral range of 4.8 μm to 5.2 μm. The method for performing such measurements and the necessary parameters are known to those skilled in the art.

[0084] The present invention is further illustrated by the following examples with reference to the drawings. The present invention is not limited to the drawings. [Brief explanation of the drawing]

[0085] [Figure 1] An exemplary schematic configuration for carrying out a method for manufacturing optical fiber preforms is shown. [Figure 2] This illustrates an example of the relative supply rate variation in a method for manufacturing optical fiber preforms. [Figure 3] The following shows an exemplary temperature curve of a glass base material in the form of a glass rod according to the method of the present invention, compared with the temperature curve of a glass rod in a method using a constant relative supply rate. [Figure 4] The deposition profile of a base material produced according to the method according to the present invention is shown, compared with the deposition profile of a base material produced according to a method having a constant relative supply rate.

[0086] Figure 1 shows an exemplary schematic configuration 100 in a method for manufacturing optical fiber preforms. This configuration comprises a glass preform 110 in the form of a glass rod made of quartz glass, which is clamped at its axial edge 115 between two glass sleeves 120 to fix it in place. Configuration 100 further comprises a plasma generator 130 in the form of a plasma torch. In the course of this method, the plasma generator 130 plays a role in synthesizing optionally doped glass particles in a plasma zone 140 in the form of a plasma flame of the plasma torch. For this purpose, a glass precursor and optionally a dopant, as well as oxygen and optional auxiliary gases, are continuously supplied to the plasma generator 130, in particular to the plasma zone 140 in the form of a plasma flame, during the method. These glass particles synthesized in this manner are deposited on the glass matrix 110 by the spreading of a plasma flame as the plasma generator 130 and the glass matrix 110 move relative to each other in axial forward and backward movements, while the glass matrix 110 undergoes rotational motion about its longitudinal axis. During this relative movement, the glass matrix 110, the plasma generator 130, or the glass matrix 110 and the plasma generator 130 can be moved. In the shown embodiment, the plasma generator 130 moves (indicated by two opposite arrows on the plasma generator 130). The relative movement between the plasma generator 130 and the glass matrix 110 takes place between two inversion points 150, 150'. In the embodiment of the shown method, this means that while the glass matrix 110 rotates about its longitudinal axis, the plasma generator 130 repeatedly moves from one inversion point 150, 150' to the opposite inversion point 150, 150'. This allows the glass particles synthesized in the plasma zone 140 to be deposited across the entire surface of the glass matrix 110. In the shown embodiment, the inversion points 150, 150' are located at the axial height of the sleeve 120 and are therefore outside the axial range of the glass matrix 110. Relative movement changes direction at the inversion points 150, 150', i.e., forward movement becomes backward movement or vice versa, so it is possible that the inversion points 150, 150' are exposed to the plasma zone 140 for a relatively long period of time.If the inversion points 150 and 150' are located at the axial height of the glass matrix 110, this can result in high thermal stress at the corresponding locations in the glass matrix 110, which is why it is preferable not to place the inversion points 150 and 150' at the axial height of the glass matrix 110. Furthermore, the inversion points 150 and 150' are equidistant from the center 160 of the glass matrix 110, particularly from the axis 160, which facilitates the uniform deposition of synthesized glass particles along the entire length of the glass matrix 110.

[0087] To illustrate the relative movement between the glass base material 110 and the plasma generator 140, particularly the change in relative supply rate, please refer to Figure 2.

[0088] Figure 2 shows the relative supply rate change of the relative movement between the plasma generator 130 and the glass matrix 110 using the configuration 100 of Figure 1. The relative supply rate is adapted to the axial position that the plasma generator 130 (see Figure 1) takes relative to the glass matrix 110. Figure 2A shows the axial position of the glass matrix 110 as the plasma generator 130 passes through at a given point in the method. During passage, it can be seen that the plasma generator 130 moves axially from one of the reversal points 150, 150' (see Figure 1) through the center 160 (see Figure 1) of the glass matrix 110 to the opposite reversal point 150, 150', at least relatively speaking, and upon reaching the reversal point 150, 150', the movement reverses in the direction of the other reversal point 150, 150'.

[0089] Figure 2B shows the relative supply rate of the plasma generator 130 to the glass base material 110, depending on the axial position in Figure 2A. When the plasma generator 130 is located at the center 160 of the glass base material 110 (indicated by the dashed line 200), the relative supply rate is value V. Mitte Take 170. When the plasma generator 130 moves from the center 160 of the glass base material 110 towards the reversal point 150' (see the diagram to the right of the dashed line 200), the relative supply rate is the value V. Mitte The value V taken when the value reaches the reversal point of 150' from 170. hinIt is reduced to 180. In the shown embodiment, V hin is V Mitte This corresponds to 0.8 times. At the reversal point 150', the movement is reversed. The reversal of movement guides the plasma generator 130 axially from the reversal point 150' through the center 160 of the glass base material 110 to the opposite reversal point 150 (see the diagram further to the right). This reverse relative movement corresponds to the value V rueck Starting with a relative feed rate of 190, which is shown as a negative value at this point in this method to illustrate the direction of movement. The relative feed rate is V while the plasma generator 130 moves relative to the center 160 of the glass matrix 110 from the reversal point 150'. rueck From V Mitte It is reduced again. In the shown embodiment, V rueck is V Mitte This corresponds to 1.2 times the original value. This sequence of relative movement is repeated each time, alternating the direction of relative movement, until the desired deposition of the synthesized glass particles onto the glass matrix 110 is achieved.

[0090] Figure 2B shows that the reduction in relative supply rate in the shown embodiment has an exponential profile.

[0091] Figure 3 shows the temperature difference T resulting from the above change in the relative supply rate in Figure 2. Diff (Graph 220) is shown in Kelvin. Temperature difference T Diff The maximum temperature T that the glass base material 110 in the form of a glass rod has during the process of the method sequence is Max and minimum temperature T Min This results from the following. For comparison, the temperature difference of the comparative glass rod (Graph 230) is shown, and the comparative glass rod has a constant value, not a changing relative supply rate, in this case the value V Mitte The material was passed through at a constant relative feed rate. In other respects, the material and method conditions were identical. The temperature difference (plotted on the y-axis) was plotted against the corresponding axial position of the measurement (plotted on the x-axis). For clarity, the end of the glass rod 110 was marked with a dashed line 210.

[0092] Figure 3 shows the values ​​V depending on the axial position of the plasma generator 140 and the glass base material 110. Mitte , V hin and V rueck The varying relative supply rate of the present invention, which changes between these two points, results in more uniform thermal stress (particularly a smaller temperature difference in the region of the edge 115 of the glass matrix 110). This leads to more uniform deposition of the glass particles synthesized on the glass matrix 110, resulting in less production waste (see also Figure 4).

[0093] Figure 4 compares the comparative deposition profile 250 of the present invention in Figure 2 and the dominant temperature difference T in Figure 3 with the comparative deposition profile 250 of the comparative base material produced by the method using a comparative glass rod with a constant relative supply rate and the corresponding temperature difference in Figure 3 (see Graph 230). Diff The deposition profile 240 of the matrix material generated by the method (see Graph 220) is shown. In each case, the ratio of the outer diameter of the starting glass rod to the outer diameter of the final matrix material (y-axis) is plotted against the axial position (x-axis) along the entire length of the matrix material. The value V in each case is shown. Mitte In the central 160 of the base material passing through at a relative feed rate, comparable deposits can be found in each case. However, significant differences can be found at the two edges of the base material. The comparative base material shows significantly less deposit at the edges, while the edges of the base material manufactured according to the present invention are significantly more raised in comparison, which reduces manufacturing waste. [Explanation of Symbols]

[0094] 100 configurations 110 Glass base material 120 Glass Sleeve 130 Plasma Generator 140 Plasma Zones 150, 150' turning point 160 Center of the glass base material 170 V Mitte 180 V hin 190 Vrueck 200 dashed line 210 Edge of glass base material 220 Temperature difference using changing relative supply rate 230 Temperature difference using a constant relative supply rate 240 Sedimentation profiles using changing relative supply rates 250 Sedimentation profiles using a constant relative supply rate

Claims

1. A method for manufacturing optical fiber preforms, a. A method and step for synthesizing glass particles using a plasma zone (140) generated by a plasma generator (130), b. A method step of repeatedly moving the glass base material (110) forward and backward in the axial direction relative to the plasma generator (130) while the glass base material (110) is rotating, wherein the forward and backward movement is performed at a relative supply speed between two reversal points (150, 150'), c. A method step of depositing glass particles on the glass base material (110) while the glass base material (110) is moving and rotating relative to the plasma generator (130), In a method including, (i) The relative supply rate of the plasma generator (130) to the glass base material (110) is V at the center (160) of the glass base material (110) Ｍｉｔｔｅ Having a right side, (ii) When the plasma generator (130) moves relative to the glass base material (110) from the center (160) toward one of the reversal points (150, 150'), the relative supply rate of the plasma generator (130) to the glass base material (110) is V Ｍｉｔｔｅ From V ｈｉｎ The value will be reduced to (iii) When the plasma generator (130) moves relative to the center (160) of the glass base material (110) from one of the reversal points (150, 150'), the relative supply rate of the plasma generator (130) to the glass base material (110) is V ｒｕｅｃｋ From the value of V Ｍｉｔｔｅ It will be reduced to A method for manufacturing optical fiber preforms, characterized by the following.

2. V ｒｕｅｋ >V Ｍｉｔｔｅ >V ｈｉｎ The method according to claim 1.

3. V Ｍｉｔｔｅ and V ｈｉｎ where the difference in value between and is substantially corresponding to the difference in value between V ｒｕｅｃｋ and V Ｍｉｔｔｅ The method according to claim 1

4. V Ｍｉｔｔｅ From V ｈｉｎ and V ｒｕｅｃｋ From V Ｍｉｔｔｅ The method according to claim 1, wherein the reduction in the relative supply rate to includes a substantially exponential or parabolic profile.

5. The method according to claim 1, wherein the glass particles synthesized in step a contain a dopant.

6. V Ｍｉｔｔｅ The method according to claim 1, wherein the value is in the range of 500 mm / min to 3000 mm / min.

7. V ｈｉｎ However, V Ｍｉｔｔｅ The method according to claim 1, wherein the value is in the range of 0.4 to 0.9 times.

8. V ｒｕｅｋ However, V Ｍｉｔｔｅ The method according to claim 1, wherein the value is in the range of 1.1 to 1.6 times.

9. The method according to claim 1, wherein the average residence time of the plasma generator (130) at each axial position of the glass base material (110) is substantially the same.

10. The relative supply rate is a value V over the axial range of the glass base material (110) corresponding to 0-50% of the axial length of the glass base material (110). Ｍｉｔｔｅ The method according to claim 1, wherein the method is used to obtain the desired result.

11. (i) The plasma output at the center (160) of the glass base material (110) is P Ｍｉｔｔｅ Having a stake, (ii) When the plasma generator (130) moves relative to the center (160) of the glass base material (110) toward one of the inversion points (150, 150'), the plasma output is P Ｍｉｔｔｅ From P ｈｉｎ The value increases (iii) When the plasma generator (130) moves relative to the center (160) of the glass base material (110) from one of the reversal points (150, 150'), the plasma output is value P ｒｕｅｃｋ From P Ｍｉｔｔｅ It increases The method according to claim 1.

12. The method according to claim 11, wherein the plasma output increases when the relative supply rate is reduced.

13. In the process of the above method, the glass base material (110) reaches the lowest temperature T Ｍｉｎ and the highest temperature T Ｍａｘ It has a temperature between T Ｍｉｎ and T Ｍａｘ Temperature difference T between the two Ｄｉｆｆ The method according to claim 1, wherein the maximum temperature is 200K.

14. T Ｍａｘ The method according to claim 13, wherein the maximum value is 2650°C.

15. The method according to claim 1, wherein the glass base material (110) is a glass rod, the plasma generator (130) is a plasma torch, and the plasma zone (140) is a plasma flame.

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