Method for manufacturing an optical fiber preform

Abstract

The invention relates to a method for manufacturing an optical fiber preform, the method comprising the steps of: a. synthesizing glass particles using a plasma zone generated by a plasma generator; b. repeatedly moving a glass preform axially forward and backward relative to the plasma generator during a rotational movement of the glass preform, wherein the forward and backward movements occur between two reversal points at a relative feed rate; c. depositing the glass particles on the glass preform while the glass preform is moving and rotating relative to the plasma generator.

Description

[0001] This invention relates to a method for manufacturing optical fiber preforms, the method comprising the following steps:

[0002] a. Using a plasma region generated by a plasma generator to synthesize glass particles;

[0003] b. The glass preform is moved axially forward and backward relative to the plasma generator during the rotational movement of the glass preform, wherein the forward and backward movements occur between two reversal points at a relative supply rate;

[0004] c. Depositing glass particles onto the glass preform as it moves and rotates relative to the plasma generator;

[0005] Its features are,

[0006] (i) The relative supply rate of the plasma generator to the glass preform has a value V at the center of the glass preform. Mitte ;

[0007] (ii) If the plasma generator moves relative to one of the reversal points from the center of the glass preform, the relative supply rate of the plasma generator relative to the glass preform decreases from V. Mitte Reduce to value V hin ;

[0008] (iii) If the plasma generator moves relative to the center of the glass preform from one of the reversal points, the relative supply rate of the plasma generator relative to the glass preform decreases from value V. rück Reduce to V Mitte . Background Technology

[0009] Preforms used to manufacture optical fibers are typically generated by plasma generators, such as plasma torches. Such plasma generators, in the form of plasma torches, can be referred to, for example, as high-frequency induction plasma torches: these are plasma torches equipped with high-frequency coils at the edge of a gas flow tube. A high-frequency current is applied to ionize the contained gas, and the resulting plasma is emitted from a nozzle. Plasma generators can also be plasma torches that operate using different techniques, such as microwave radiation. Plasma generators can also be devices that generate plasma by induction. Such plasma generators preferably include induction coils for generating plasma.

[0010] The plasma generated in this manner is used to synthesize glass particles, which are deposited onto glass preforms (such as glass rods or tubes) by deposition. For this purpose, a glass precursor (such as silicon tetrachloride), optional dopant (such as sulfur hexafluoride), and oxygen and any auxiliary gas (such as nitrogen or argon) are continuously supplied to the plasma, and the glass particles synthesized in this manner are deposited onto the surface of the glass preform (such as a glass rod or tube), which moves forward and backward relative to the plasma generator while rotating.

[0011] The deposition of synthetic glass particles at the edges of glass preforms is particularly challenging because these edges are subjected to two passes of the plasma generator within a very short timeframe—once on the forward path and then immediately again on the backward path—thus subjecting these regions to exceptionally high thermal stress. Simultaneously, if the plasma generator is located in the region of the opposite edge of the glass preform, the edge also experiences exceptionally strong cooling. In other words, the edge is cooled exceptionally strongly between the two passes (when passing the opposite edge) and also heated exceptionally strongly (when passing the corresponding edge twice). Specifically, the direct, consecutive two passes and the associated exceptionally strong heating of the corresponding edge cause partial evaporation of the synthetic glass particles deposited on the corresponding edge. This results in an inhomogeneous material structure at the edge compared to the central region of the glass preform, which experiences relatively less thermal stress. Any doping of the synthetic glass particles at the edges is also negatively affected by the thermal stress, which is why the edges have lower doping levels than the central region of the glass preform, for example, as described in European patent application EP 1 997 783 A2. The lower doping may be a result of thermally induced outward diffusion. The high thermal stress at the edges of the glass preforms leads to high manufacturing waste because the edges of the glass preforms are not suitable for further processing to manufacture optical fibers.

[0012] In principle, there are several methods for depositing synthetic glass particles onto glass preforms: (1) the particles are first deposited as a porous layer, and then their porosity is eliminated by melting in a special thermal process. This step results in the densification of the initial porous structure to form a uniform glass. (2) Alternatively, the deposition is carried out directly as a dense glass layer, thereby eliminating the need for a subsequent densification step.

[0013] The aforementioned difficulties (specifically, thermal stress at the edges of the glass preform) pose challenges to all of these methods.

[0014] Therefore, there is a need in the market for an improved manufacturing method for optical fiber preforms.

[0015] Purpose of the invention

[0016] One object of the present invention is to overcome, at least in part, one or more of the disadvantages caused by the prior art.

[0017] Specifically, the object of this invention is to provide a method for manufacturing optical fiber preforms with the lowest possible manufacturing waste. Furthermore, the method should provide preforms with the most uniform doping possible. The method according to the invention should be as simple to implement as possible. Moreover, it should be as cost-effective as possible. Summary of the Invention

[0018] The features of the independent claim contribute to at least partial fulfillment of at least one of the foregoing objectives. The dependent claims provide preferred embodiments that facilitate at least partial fulfillment of at least one of the objectives.

[0019] A first embodiment of the present invention is a method for manufacturing an optical fiber preform, the method comprising the following steps:

[0020] a. Using a plasma region generated by a plasma generator to synthesize glass particles;

[0021] b. The glass preform is moved axially forward and backward relative to the plasma generator during the rotational movement of the glass preform, wherein the forward and backward movements occur between two reversal points at a relative supply rate;

[0022] c. Depositing glass particles onto the glass preform as it moves and rotates relative to the plasma generator;

[0023] Its features are,

[0024] (i) The relative supply rate of the plasma generator to the glass preform has a value V at the center of the glass preform. Mitte ;

[0025] (ii) If the plasma generator moves relative to one of the reversal points from the center of the glass preform, the relative supply rate of the plasma generator relative to the glass preform decreases from V. Mitte Reduce to value V hin ;

[0026] (iii) If the plasma generator moves relative to the center of the glass preform from one of the reversal points, the relative supply rate of the plasma generator relative to the glass preform decreases from value V. rück Reduce to V Mitte .

[0027] The preferred embodiment of this method is characterized in that V rück >VMitte >V hin Or in other words, V rück Having a ratio of V Mitte Larger values, and V Mitte Having a ratio of V hin A larger value. This implementation is a second implementation of the method, which preferably depends on the first implementation of the invention.

[0028] The preferred embodiment of this method is characterized in that V Mitte and V hin The difference between the values ​​basically corresponds to V rück and V Mitte The difference in values ​​between them. This embodiment is a third embodiment of the invention, which preferably depends on the first or second embodiment of the invention.

[0029] The preferred embodiment of this method is characterized by, from V Mitte To V hin And from V rück To V Mitte The decrease in the relative supply rate has a substantially exponential or parabolic distribution. This embodiment is a fourth embodiment of the invention, which preferably depends on one of the foregoing embodiments of the invention.

[0030] A preferred embodiment of the method is characterized in that the glass particles synthesized in step a. contain a dopant. This embodiment is a fifth embodiment of the invention, which preferably depends on one of the foregoing embodiments of the invention.

[0031] The preferred embodiment of this method is characterized in that V Mitte It has values ​​in the range of 500 mm / min and 3000 mm / min. This embodiment is a sixth embodiment of the invention, which preferably depends on an embodiment of the foregoing embodiments of the invention.

[0032] The preferred embodiment of this method is characterized in that V hin With a V of 0.4 times Mitte and 0.9 times V Mitte The values ​​are within the range between [a certain value]. This embodiment is a seventh embodiment of the invention, which preferably depends on one of the foregoing embodiments of the invention.

[0033] The preferred embodiment of this method is characterized in that V rück With a V of 1.1 times Mitte And 1.6 times V MitteThe values ​​are within the range between [a certain value]. This embodiment is the eighth embodiment of the present invention, which preferably depends on one of the foregoing embodiments of the present invention.

[0034] A preferred embodiment of the method is characterized in that the average residence time of the plasma generator at each axial position of the glass preform is substantially the same. This embodiment is a ninth embodiment of the invention, which preferably depends on an embodiment of the foregoing embodiments of the invention.

[0035] A preferred embodiment of the method is characterized in that the relative supply rate has a value V in the axial range corresponding to 0% to 50%, preferably 15% to 45%, of the total axial length of the glass preform. Mitte This embodiment is the tenth embodiment of the present invention, which preferably depends on one of the foregoing embodiments of the present invention.

[0036] The preferred embodiment of this method is characterized in that,

[0037] (i) The plasma power at the center of the glass preform has a value P Mitte ;

[0038] (ii) If the plasma generator moves relative to one of the reversal points from the center of the glass preform, the plasma power increases from P. Mitte Increase to value P hin ;

[0039] (iii) If the plasma generator moves relative to the center of the glass preform from one of the reversal points, the plasma power increases from the value P rück Increase to P Mitte .

[0040] This implementation is the eleventh implementation of the present invention, which preferably depends on one of the foregoing implementations of the present invention.

[0041] A preferred embodiment of the method is characterized in that the plasma power increases when the relative supply rate decreases. This embodiment is the twelfth embodiment of the invention, which preferably depends on the eleventh embodiment of the invention.

[0042] A preferred embodiment of the method is characterized in that, during the process, the glass preform has a temperature between a minimum temperature T and a minimum temperature T. Min and maximum temperature T Max The temperature between, where T Min With T MaxTemperature difference T between Diff The maximum is 200K. This embodiment is the thirteenth embodiment of the present invention, which preferably depends on one of the foregoing embodiments of the present invention.

[0043] The preferred embodiment of this method is characterized in that T Max The maximum temperature is 2650°C. This embodiment is the fourteenth embodiment of the present invention, which preferably depends on the thirteenth embodiment of the present invention.

[0044] A preferred embodiment of the method is characterized in that the glass preform is a glass rod, the plasma generator is a plasma torch, and the plasma zone is a plasma flame. This embodiment is the fifteenth embodiment of the invention, which preferably depends on one of the foregoing embodiments of the invention.

[0045] General

[0046] Regarding the embodiments described herein, where an element "has" or "comprises" a particular feature (e.g., a material), it is always anticipated in principle that another embodiment exists in which the relevant element consists solely of that feature, i.e., excluding any other components. The word "comprises" is used synonymously with the word "has" herein.

[0047] In one implementation, if an element is represented by a singular number, it is also expected that there are implementations containing more than one such element. The use of the terminology for plural elements also, in principle, includes implementations containing only a single corresponding element.

[0048] Unless otherwise indicated or clearly excluded from the context, it is in principle possible, and thus clearly anticipated, for features of different embodiments to also exist in other embodiments described herein. Similarly, it is in principle expected that all features described herein in combination with the method also apply to the products and apparatus described herein, and vice versa. Not all combinations of such considerations are explicitly listed in all cases, merely for the sake of brevity. In principle, the scope of the invention is also intended to cover technical solutions known to be equivalent to the features described herein.

[0049] In this specification, the range specification also includes values ​​designated as limits. Therefore, the specification "within the range from X to Y" relative to the type of variable A means that A can take values ​​X, Y, and values ​​between X and Y. Therefore, the range "up to Y" defined on one side of the type of variable A means values ​​Y and less than Y.

[0050] Some of the characteristics described are associated with the term "substantially". The term "substantially" should be understood in such a way that, under actual conditions and manufacturing techniques, the precise mathematical interpretation of terms such as "overlapping", "perpendicular", "diameter", or "parallel" may not be given precisely, but only within certain manufacturing tolerances. For example, "substantially perpendicular axis" encloses an angle between 85 and 95 degrees, and "substantially equal volumes" includes a deviation of at most 5% by volume. For example, "device composed substantially of plastic" includes a plastic content of ≥95% by weight to ≤100% by weight. For example, "substantially completely filling volume B" includes filling ≥95% by volume to ≤100% by volume of the total volume B.

[0051] When an indefinite or definite article (such as "a," "an," or "the") is used to refer to a singular noun, it includes the plural form of that noun unless otherwise expressly stated. When the term "comprising" is used in this specification and claims, other elements are not excluded.

[0052] For the purposes of this invention, the terms "consistently composed of" and "comprises of" are considered to be embodiments of the term "comprising". When a group is defined below as including at least a specific number of embodiments, this should also be understood to disclose a group that consists substantially only of those embodiments in one embodiment or consists only of those embodiments in one embodiment.

[0053] Terms such as “available” or “definable” and “obtained” or “defined” are used interchangeably. This means, for example, that the term “obtained” does not necessarily mean that the implementation must be obtained, for example, through a sequence of steps following the term “obtained”, unless the context explicitly states otherwise, although this limited understanding is always included as an implementation in the terms “obtained” or “defined.” Whenever the terms “comprising” or “having” are used, these terms are synonymous with “included” as defined above. Detailed Implementation

[0054] The first subject of this invention relates to a method for manufacturing optical fiber preforms, the method comprising the following steps:

[0055] a. Using a plasma region generated by a plasma generator to synthesize glass particles;

[0056] b. The glass preform is moved axially forward and backward relative to the plasma generator during the rotational movement of the glass preform, wherein the forward and backward movements occur between two reversal points at a relative supply rate;

[0057] c. Depositing glass particles onto the glass preform as it moves and rotates relative to the plasma generator;

[0058] Its features are,

[0059] (i) The relative supply rate of the plasma generator relative to the glass preform has a value VMitte at the center of the glass preform;

[0060] (ii) If the plasma generator moves relative to one of the reversal points from the center of the glass preform, the relative supply rate of the plasma generator relative to the glass preform decreases from VMitte to the value Vhin.

[0061] (iii) If the plasma generator moves relative to the center of the glass preform from one of the reversal points, the relative supply rate of the plasma generator relative to the glass preform decreases from the value Vrück to VMitte.

[0062] 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, via an induction coil. In a preferred embodiment, the plasma generator is a plasma torch that generates a plasma zone in the form of a plasma flame.

[0063] To generate glass particles, a glass precursor (such as silicon tetrachloride) is preferably supplied constantly to the plasma region along with oxygen, argon, and / or nitrogen, where it is converted into glass particles. Optionally, dopants may be added to make the refractive index of the glass particles suitable for the application of the preform. Preferably, sulfur hexafluoride is added to the plasma region along with the remaining glass precursor to obtain fluorinated glass particles.

[0064] In step b., a glass preform (such as a glass rod or glass tube) is repeatedly moved axially forward and backward relative to a plasma generator. The glass preform, the plasma generator, or both are movable. The forward and backward movement of the glass preform relative to the plasma generator occurs between two reversal points, at which the relative movement changes direction, i.e., forward movement reverses to backward movement, for example. The relative movement occurs within an axial range, i.e., along the longitudinal axis of the glass preform. The relative movement occurs at least along the entire length of the glass preform, preferably even beyond the edge regions of the glass preform, such that the plasma generator is positioned once at each axial location of the glass preform during each forward and each backward movement. In other words, the reversal points are arranged such that the glass preform is positioned with its axial length between two reversal points.

[0065] Therefore, during each relative movement, synthetic glass particles can be deposited at each axial location of the glass preform (see method step c.).

[0066] Simultaneous rotational movement about the longitudinal axis (or in other words, rotation of the glass preform) with relative movement makes it possible to uniformly deposit synthetic glass particles around the circumference of the glass preform (see method step c.).

[0067] The glass preform preferably comprises quartz glass; more preferably, the glass preform is composed of quartz glass. Depending on the application of the preform, the quartz glass of the glass preform may contain dopants (such as fluorine).

[0068] In step c., glass particles synthesized in the plasma region of a plasma generator are deposited onto a glass preform that moves and rotates relative to the plasma generator.

[0069] In one embodiment, the glass preform is a glass tube, and a plasma region is generated within the glass tube, wherein synthetic glass particles are deposited on the inner surface of the glass tube. In this embodiment, the plasma generator preferably generates the plasma region by induction; for this purpose, the plasma generator preferably includes an induction coil, which is preferably arranged in a sleeve-like manner around the glass tube. In this embodiment, the induction coil moves relative to the glass tube, wherein the plasma region generated by the induction coil within the glass tube moves together with the induction coil. In this embodiment, the deposition of synthetic glass particles occurs on the inner surface of the glass tube.

[0070] In another embodiment, the glass preform is a glass rod and the plasma region is generated by the plasma flame of a plasma torch. In this embodiment, the plasma torch moves relative to the glass rod while the plasma flame expands onto the glass rod, causing synthetic glass particles to be deposited on the outer surface of the glass rod.

[0071] To achieve the most uniform deposition of glass particles on the glass preform, the relative feed rate (i.e., the speed at which the plasma generator and the glass preform move relative to each other) is adapted to the axial position of the plasma generator relative to the longitudinal axis of the glass preform. Therefore, the relative feed rate is not constant over the entire length of the glass preform, but depends on the relative arrangement of the plasma generator and the glass preform.

[0072] At the center (specifically, the axial center) of the glass preform, the relative supply rate has a value V. Mitte .

[0073] If the plasma generator moves relative to the glass preform from one of the centers of the glass preform to one of the reversal points, the relative supply rate changes from the value V. Mitte Reduce to value V hin Therefore, if the plasma generator moves from the center of the glass preform toward one of the reversal points, the relative supply rate is slowed down. From V Mitte To V hin The deceleration can be initiated directly at the center of the glass preform. In another embodiment of the method, deceleration from V... Mitte To V hin The deceleration does not begin directly at the center of the glass preform, but only after the plasma torch has moved relative to the glass preform from the center of the glass preform along the direction of the corresponding reversal point at 5% to 40% of the total length of the glass preform, preferably 10% to 35%, more preferably 15% to 30%.

[0074] Preferably, the relative supply rate is from V Mitte Decelerate continuously to V hin until the value V is reached. hin .

[0075] If the relative supply rate is from V Mitte To V hin The deceleration has already begun from the center of the glass preform along the direction of one of the reversal points, and therefore is related to the relative supply rate V. Mitte Compared to the previous case, the plasma generator is held continuously above a specific axial position of the glass preform for a longer period of time. Preferably, this is when the relative supply rate has already taken a value V. hin At that time, the plasma generator is held above the glass preform at a specific axial position for the longest period of time. The relative supply rate is from V Mitte To V hin The reduction in [something] results in a slower passage through a specific axial position of the glass preform, and a longer time elapsed since the plasma generator last passed through that position. This at least partially compensates for the increased cooling at the corresponding position since the last pass, leading to more uniform thermal stress.

[0076] The reversal occurs preferably at a point spatially located behind the corresponding end of the glass preform, and then preferably immediately thereafter, involving relative movement. Thus, forward movement becomes backward movement, and vice versa.

[0077] If the plasma generator moves relative to the center of the glass preform from one of the reversal points, the relative supply rate changes from value V. rück Reduce to value V MitteTherefore, if the plasma generator moves from one end of the glass preform toward the center of the glass preform, the relative supply rate is slowed down.

[0078] Preferably, the relative supply rate is from V rück Decelerate continuously to V Mitte until the value V is reached. Mitte Preferably, during the relative movement along the direction of the center of the glass preform, the relative supply rate thus has its highest value (preferably a value V) at the corresponding ends of the glass preform. rück The value is preferably continuously decreased until it reaches a value V. Mitte Value V can only be achieved directly at the center of the glass preform. Mitte In another embodiment, the value V is reached if the plasma generator is still 5% to 45%, preferably 10% to 40%, more preferably 15% to 35% of the total length of the glass preform relative to its center. Mitte .

[0079] Therefore, from the corresponding end of the glass preform along the center of the glass preform, with respect to the relative supply rate V rück Compared to the previous case, the plasma generator remained above a specific axial position of the glass preform for a longer period of time. This occurred when the relative supply rate had a value V. rück At that time, the plasma generator is held above the glass preform at a specific axial position for the shortest possible duration. Simultaneously, this results in... Mitte and V hin The relative supply rate values ​​between the values ​​of the glass preforms at a specific axial position are higher in direct continuous passage than at a higher relative supply rate value (i.e., at V). rück and V Mitte (between) . Therefore, with V Mitte Compared to decelerating forward, directly following V has Mitte Compared to accelerating backwards.

[0080] In summary, the distribution of relative supply rates is as follows:

[0081] The relative supply rate at the center of the glass preform has a value V Mitte During the movement of the plasma generator relative to the glass preform from the center of the glass preform along one of the reversal points, the relative supply rate changes from V... Mitte Reduce to V hin The slowest relative feed rate is reached when the glass preform reaches its corresponding end, preferably a value V. hinAt the reversal point, the direction of relative movement changes. During the relative movement from the corresponding reversal point along the center of the glass preform, the relative supply rate takes a value V. rück It decreases again to the value V along the direction of the center of the glass preform. Mitte The deceleration forward passage to the edge of the glass preform (with V) Mitte Compared to) then directly from the same edge along the center of the glass preform, accelerating backward (with V) Mitte compared to).

[0082] Changing the relative supply rate reduces thermal stress (specifically, thermal stress at the edges of the glass preform), allowing for more uniform deposition of the composite glass particles. This results in less manufacturing waste. Specifically, with V rück and V Mitte The relatively fast passage from a specific edge along the center of the glass preform, at a relative supply rate, reduces thermal stress. In compensation, passage in the opposite direction (i.e., from the center of the glass preform along the corresponding reversal point) at a V... Mitte and V hin The relative supply rates between them are determined, and therefore the value V is related to the center region of the glass preform. Mitte Compared to proceeding by slowing down.

[0083] During the relative movement of the plasma generator from the center of the glass preform along the direction corresponding to the reversal point, the edges of the glass preform thus experience increased exposure to the plasma region compared to the center, while in the opposite direction (i.e., from the reversal point along the center of the glass preform), a relatively reduced exposure to the plasma region occurs, specifically in the edge regions of the glass preform. Therefore, compared to a passage at a always constant relative supply rate, the temperature difference T at a specific axial position of the glass preform between two passes can be reduced. Diff This ensures more uniform thermal stress along the entire axial length of the glass preform, which leads to more uniform deposition of synthetic glass particles along the axial length of the glass preform.

[0084] The method is characterized by three different values ​​V of the relative supply rate. Mitte V hin and V rück The relative supply rate derived from the above also takes a value between the three values ​​mentioned.

[0085] From the above, we can conclude that V rück The value is greater than V Mitte The value of V, and V Mitte The value is greater than V hin The value of V. Therefore, Vhin The value in V rück and V Mitte The values ​​are between.

[0086] The preferred embodiment of this method is characterized in that V Mitte and V hin The difference between the values ​​essentially (i.e., within certain tolerances, specifically within the fault tolerance) corresponds to V. rück and V Mitte The difference between the values. In this implementation, V Mitte The value is exactly in V rück and V hin The values ​​are between. In other words, in this embodiment, if the plasma generator moves relative to the glass preform from the center of the glass preform along one of the reversal points, and if the plasma generator moves relative to the glass preform from one of the reversal points along the center of the glass preform, the relative supply rate decreases by the same value. This can result in a decrease in the temperature difference T between the specific axial position of the glass preform and the passing temperature difference T. Diff .

[0087] The relative supply rate from V Mitte To V hin Or from V rück To V Mitte The rate of change of deceleration can be designed in different ways. For example, the rate of change can be linear, resulting in a constant change in the relative supply rate.

[0088] The preferred embodiment of this method is characterized by, from V Mitte To V hin And from V rück To V Mitte The decrease in the relative supply rate has a generally exponential or parabolic distribution. In this embodiment, the decrease in the relative supply rate has a rate of change that increases as the relative supply rate approaches the target value (i.e., V). hin or V Mitte The greater the rate of change, the more significant the increase. In this implementation, the change in the relative supply rate is not linear, but rather increases gradually.

[0089] The result is that the slower the plasma generator passes through a specific axial position of the glass preform, the longer the time since its last pass at that position. This at least partially compensates for the increased cooling at the corresponding position since its last pass, leading to more uniform thermal stress. Conversely, the faster the plasma generator passes through the axial position, the shorter the time since its last pass.

[0090] Therefore, a particularly slow forward pass is followed by a particularly fast backward pass, which can lead to a more uniform deposition of synthetic glass particles.

[0091] A preferred embodiment of this method is characterized in that the glass particles synthesized in step a. contain a dopant. Preferably, the synthesized glass particles comprise a dopant selected from the group consisting of germanium dioxide (GeO2), phosphorus pentoxide (P2O5), fluorine (F2), boron oxide (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 the 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).

[0092] The variation in the relative supply rate according to the invention (which reduces thermal stress, specifically the thermal stress at the edges of the glass preform) also has a positive effect on the uniform dopant concentration along the axial length of the glass preform. Specifically, more uniform fluorine doping can be achieved, which responds particularly sensitively to non-uniform thermal stress during deposition on the glass preform.

[0093] Relative supply rate V Mitte V hin and V rück Different absolute values ​​can be adopted. The absolute value can be adjusted, for example, depending on the composition of the glass preform, the composition of the synthetic glass particles, the length of the glass preform, its outer diameter and / or its rotational speed.

[0094] The preferred embodiment of this method is characterized in that V Mitte It has values ​​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.

[0095] V hin and V rück The value must specifically be suitable for V Mitte The values ​​of the glass preform, the composition of the synthetic glass particles, the length of the glass preform, its outer diameter and / or its rotational speed are determined in order to achieve the lowest possible thermal stress, specifically the thermal stress at the edges of the glass preform.

[0096] The preferred embodiment of this method is characterized in that V hinWith a V of 0.4 times Mitte and 0.9 times V Mitte Within the range of, preferably within 0.5 times V Mitte and 0.85 times V Mitte Values ​​within the range between.

[0097] The preferred embodiment of this method is characterized in that V rück With a V of 1.1 times Mitte And 1.6 times V Mitte Within the range of, preferably within 1.15 times V Mitte And 1.5 times V Mitte Values ​​within the range between.

[0098] 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 preform is substantially the same (i.e., with a specific tolerance). In this embodiment, V hin and V rück This coordination ensures that the plasma generator as a whole is held at a specific axial position on the glass preform, with V... Mitte and V hin The value of the relative supply rate between or in V rück and V Mitte The two consecutive passages through that specific axial position in opposite directions are achieved by a speed of V. Mitte The situation would be as described if it were passed through twice. In other words, each axial position of the glass preform is thus exposed to the plasma zone generated by the plasma generator for the same duration during two direct, consecutive passes. This results in a more uniform deposition of the synthetic glass particles, specifically at the edges of the glass preform.

[0099] The relative supply rate can have a value V on the axial portion of glass preforms of different lengths. Mitte For example, the relative supply rate takes a value V only precisely at the center of the glass preform. Mitte The relative supply rate has a V-shape in the direction of passage directly in front of the center of the glass preform. rück and V Mitte The values ​​between, and the relative supply rate having V in the passing direction directly behind the glass preform. Mitte and V hin The value between [variable name]. In this embodiment, the relative supply rate has a value V at a point-like axial location (i.e., the center) of the glass preform. Mitte .

[0100] A preferred embodiment of the method is characterized in that the relative supply rate takes the value V within an axial range corresponding to 0% to 50%, preferably 15% to 45%, and more preferably 20% to 40% of the total axial length of the glass preform. Mitte In any case, the axial range includes the center of the glass preform, wherein the center of the glass preform is preferably also the axial center of the axial range.

[0101] In addition to changing the relative supply rate, other process parameters (specifically depending on the axial position of the glass preform) can be changed to make the thermal stress (specifically the thermal stress at the edges of the glass preform) as uniform as possible.

[0102] For example, the rotational movement of the glass preform about its longitudinal axis can be changed (specifically in the form of rotational speed).

[0103] Another possible variation involves a plasma generator in the form of a plasma torch. For example, its distance from the glass preform (preferably in the form of a glass rod) can be varied to allow for the most uniform possible deposition of the synthetic glass particles.

[0104] The preferred embodiment of this method is characterized in that,

[0105] (i) The plasma power at the center of the glass preform has a value P Mitte ;

[0106] (ii) If the plasma generator moves relative to one of the reversal points from the center of the glass preform, the plasma power increases from P. Mitte Increase to value P hin ;

[0107] (iii) If the plasma generator moves relative to the center of the glass preform from one of the reversal points, the plasma power increases from the value P rück Increase to P Mitte .

[0108] In this embodiment, the plasma power therefore varies with the relative supply rate and V Mitte Compared to a decrease, an increase or a rise with the relative supply rate and V Mitte It decreases compared to an increase.

[0109] The temperature of the glass preform at a specific axial position varies during the process of this method, and specifically depends on the time point at which the plasma generator last passes through the corresponding axial position, the dominant plasma power at that time, the dwell time of the plasma generator at the corresponding axial position during that passage, and specifically, in the case of a plasma generator in the form of a plasma torch, on its distance from the glass preform (preferably in the form of a glass rod).

[0110] A preferred embodiment of the method is characterized in that, during the process, the glass preform has a temperature between a minimum temperature T and a minimum temperature T. Min and maximum temperature T Max The temperature between, where T Min With T Max Temperature difference T between Diff The maximum is 200K, preferably up to 190K, and more preferably up to 180K.

[0111] The preferred embodiment of this method is characterized in that T Max The maximum temperature is 2650℃.

[0112] Temperature measurements were performed optically in the spectral range of 4.8 μm to 5.2 μm using a thermal camera (model DIAS PyroView 640G from DIAS Infrared GmbH, Germany). How to perform such measurements and the required parameters are known to those skilled in the art. Attached Figure Description

[0113] The invention is further illustrated by the following examples with the aid of the accompanying drawings. The invention is not limited to the drawings.

[0114] In the attached diagram:

[0115] Figure 1 A schematic exemplary arrangement for performing a method for manufacturing an optical fiber preform is shown.

[0116] Figure 2 An exemplary variation of the relative supply rate is shown in a method for manufacturing optical fiber preforms.

[0117] Figure 3 An exemplary temperature profile of a glass preform in the form of a glass rod during the method according to the invention is shown, compared with the temperature profile of a glass rod during a method having a constant relative feed rate.

[0118] Figure 4 A comparison is shown between the deposition distribution of a preform produced according to the method of the invention and the deposition distribution of a preform produced according to a method having a constant relative supply rate.

[0119] Figure 1 A schematic exemplary arrangement 100 for a method of manufacturing an optical fiber preform is shown. The arrangement includes a glass preform 110 in the form of a glass rod made of quartz glass, wherein the glass preform 110 is clamped between two glass sleeves 120 at its axial edge 115 for fixation. Arrangement 100 also includes a plasma generator 130 in the form of a plasma torch. During the method, the plasma generator 130 is used to synthesize optionally doped glass particles in a plasma region 140 in the form of a plasma flame from the plasma torch. For this purpose, during the method, glass precursors and optional dopants, along with oxygen and any auxiliary gases, are constantly supplied to the plasma generator 130, specifically to the plasma region 140 in the form of a plasma flame. These glass particles synthesized in this way are deposited onto the glass preform 110 by the expansion of the plasma flame as the glass preform 110 undergoes rotational movement about its longitudinal axis and the plasma generator 130 and the glass preform 110 move relative to each other in a manner that moves axially forward and backward. During this relative movement, the glass preform 110, plasma generator 130, or both the glass preform 110 and plasma generator 130 are movable. In the illustrated embodiment, the plasma generator 130 moves (indicated by two opposing arrows on the plasma generator 130). The relative movement between the plasma generator 130 and the glass preform 110 occurs between two reversal points 150, 150'. In the illustrated embodiment of the method, this means that the plasma generator 130 repeatedly moves from one reversal point 150, 150' to the opposite reversal point 150, 150' while the glass preform 110 rotates about its own longitudinal axis. This allows the glass particles synthesized in the plasma zone 140 to be deposited on the entire surface of the glass preform 110. In the illustrated embodiment, the reversal points 150, 150' are located at the axial height of the sleeve 120 and therefore outside the axial range of the glass preform 110. Because the relative movement changes direction at the reversal points 150, 150' (i.e., forward movement becomes backward movement, or vice versa), the reversal points 150, 150' may be exposed to the plasma region 140 for a relatively long period of time. If the reversal points 150, 150' are arranged at the axial height of the glass preform 110, this could result in high thermal stress at the corresponding location on the glass preform 110. This is why it is preferable not to arrange the reversal points 150, 150' at the axial height of the glass preform 110. Furthermore, the reversal points 150, 150' are equidistant from the center 160 (specifically the axial center 160) of the glass preform 110, which promotes uniform deposition of the synthetic glass particles along the entire length of the glass preform 110.

[0120] To describe the relative movement of the glass preform 110 and the plasma generator 140, specifically the change in the relative supply rate, refer to... Figure 2 .

[0121] Figure 2 It shows the use of Figure 1 The relative supply rate varies with the relative movement of the plasma generator 130 and the glass preform 110 in the arrangement 100. The relative supply rate is adapted to be controlled by the plasma generator 130 (see [reference]). Figure 1 The axial position relative to the glass preform 110. Example 2A shows the axial position of the glass preform 110 as passed by the plasma generator 130 at a given point in time in the method. It can be seen that during the passage, the plasma generator 130 is at least relatively from the reversal point 150, 150' (see... Figure 1 One of them passes through the center 160 of the glass preform 110 (see Figure 1 Move to the axially opposite reversal points 150, 150', where when the reversal points 150, 150' are reached, the movement is reversed in the direction of the other reversal point 150, 150'.

[0122] Example 2B shows the dependence on Figure 2 The value of the relative supply rate of the plasma generator 130 to the glass preform 110 at the axial position of A. If the plasma generator 130 is located at the center 160 of the glass preform 110 (marked by the dashed line 200), the relative supply rate takes the value V. Mitte 170. If the plasma generator 130 moves from the center 160 of the glass preform 110 in the direction of the reversal point 150' (following the illustration from the dashed line 200 to the right), the relative supply rate changes from the value V. Mitte 170 decreased to value V hin 180, which is taken when the reversal point 150' is reached. In the illustrated embodiment, V hin Corresponding to 0.8 times V Mitte At reversal point 150', a reversal of movement occurs. This reversal guides the plasma generator 130 from reversal point 150' via the center 160 of the glass preform 110 to the axially opposite reversal point 150 (following a further rightward illustration). This reversal of relative movement begins with a relative supply rate that takes the value V. rück 190, which is shown as a negative value at this time point in the method to illustrate the direction of movement. During the relative movement of the plasma generator 130 from the reversal point 150' along the direction of the center 160 of the glass preform 110, the relative supply rate again changes from V rück Reduce to V MitteIn the illustrated implementation, V rück Corresponding to 1.2 times V Mitte This sequence of relative movements is repeated, each time with an alternating direction of relative movement, until the desired deposition of synthetic glass particles on the glass preform 110 is achieved.

[0123] Example 2B shows that the decrease in the relative supply rate in the illustrated implementation has an exponential distribution.

[0124] Figure 3 It shows that due to Figure 2 The temperature difference T in Kelvin resulting from the aforementioned change in the relative supply rate Diff (Graph 220). Temperature difference T Diff The maximum temperature T of the glass preform 110 in the form of a glass rod during the process sequence. Max and minimum temperature T Min The temperature difference of the comparison glass rods is shown in Figure 230 for comparison, where the comparison glass rods pass through at a constant relative supply rate instead of a varying relative supply rate, in which case the constant value has a value V. Mitte Apart from this, the materials and methods are identical. The temperature difference (plotted on the y-axis) is shown relative to the corresponding axial position measured (plotted on the x-axis). For clarity, the end of the glass rod 110 is marked with a dashed line 210.

[0125] Figure 3 The variable relative supply rate according to the invention (which depends on the axial position of the plasma generator 140 and the glass preform 110 in the value V) is shown. Mitte V hin and V rück The variation between these temperature variations results in more uniform thermal stress (smaller temperature differences, specifically in the region of the edge 115 of the glass preform 110). This leads to a more uniform deposition of synthetic glass particles on the glass preform 110, resulting in less manufacturing waste (see also...). Figure 4 ).

[0126] Figure 4 It shows Figure 2 The deposition distribution 240 of the preform manufactured by the method according to the invention and Figure 3 The dominant temperature difference T Diff (See graph 220) and Figure 3A comparison of the deposition distribution 250 (see graph 230) of comparative preforms manufactured using a method employing a comparative glass rod at a constant relative feed rate and corresponding temperature difference is presented. In each case, the ratio of the outer diameter of the starting glass rod to the outer diameter of the final preform is plotted relative to the axial position (x-axis) over the entire length of the preform (y-axis). In each case, a value V is used. Mitte The relative supply rate passing through the center 160 of the preform results in considerable deposits in each case. However, a significant difference is observed at the two edges of the preform: although the comparative preform shows significantly less deposits at the edges, the edges of the preform manufactured according to the invention are significantly raised, resulting in less manufacturing waste.

[0127] Figure Labels

[0128] 100 layout

[0129] 110 glass preform

[0130] 120 glass sleeve

[0131] 130 plasma generator

[0132] 140 plasma region

[0133] 150, 150' Reversal Point

[0134] 160 glass preform center

[0135] 170V Mitte

[0136] 180V hin

[0137] 190V rück

[0138] 200 dashed line

[0139] 210 End of glass preform

[0140] 220 with a temperature difference of variable relative supply rate

[0141] 230 temperature difference at a constant relative supply rate

[0142] 240 Depositional distribution with variable relative supply rate

[0143] 250 Depositional distribution at a constant relative supply rate

Claims

1. A method for manufacturing an optical fiber preform, the method comprising the following steps: a. Glass particles are synthesized using a plasma region (140) generated by a plasma generator (130); b. The glass preform (110) is moved axially forward and backward relative to the plasma generator (130) during the rotational movement of the glass preform (110), wherein the forward and backward movement occurs at a relative supply rate between two reversal points (150, 150'). c. Depositing the glass particles onto the glass preform (110) as the glass preform (110) moves and rotates relative to the plasma generator (130); Its features are, (i) The relative supply rate of the plasma generator (130) relative to the glass preform (110) has a value V at the center (160) of the glass preform (110). Mitte ; (ii) If the plasma generator (130) moves relative to one of the reversal points (150, 150') from the center (160) of the glass preform (110), then the relative supply rate of the plasma generator (130) relative to the glass preform (110) increases from V Mitte Reduce to value V hin ; (iii) If the plasma generator (130) moves relative to the center (160) of the glass preform (110) from one of the reversal points (150, 150'), the relative supply rate of the plasma generator (130) relative to the glass preform (110) decreases from the value V. rück Reduce to V Mitte .

2. The method according to claim 1, wherein V rück >V Mitte >V hin .

3. The method according to claim 1 or 2, wherein V Mitte and V hin The difference between the values ​​basically corresponds to V rück and V Mitte The difference in values ​​between them.

4. The method according to any one of the preceding claims, wherein from V Mitte To V hin And from V rück To V Mitte The reduction in the relative supply rate is generally exponential or parabolic.

5. The method according to any one of the preceding claims, wherein the glass particles synthesized in step a. contain a dopant.

6. The method according to any one of the preceding claims, wherein V Mitte It has values ​​in the range between 500 mm / min and 3000 mm / min.

7. The method according to any one of the preceding claims, wherein V hin With a V of 0.4 times Mitte and 0.9 times V Mitte Values ​​within the range between.

8. The method according to any one of the preceding claims, wherein V rück With a V of 1.1 times Mitte And 1.6 times V Mitte Values ​​within the range between.

9. The method according to any one of the preceding claims, wherein the average residence time of the plasma generator (130) at each axial position of the glass preform (110) is substantially the same.

10. The method according to any one of the preceding claims, wherein the relative supply rate takes the value V within an axial range corresponding to 0-50% of the total axial length of the glass preform (110). Mitte .

11. The method according to any one of the preceding claims, wherein (i) The plasma power in the center (160) of the glass preform (110) has a value P. Mitte ; (ii) If the plasma generator (130) moves relative to one of the reversal points (150, 150') from the center (160) of the glass preform (110), the plasma power increases from P Mitte Increase to value P hin ; (iii) If the plasma generator (130) moves relative to one of the reversal points (150, 150') toward the center (160) of the glass preform (110), the plasma power increases from the value P rück Increase to P Mitte .

12. The method of claim 11, wherein if the relative supply rate decreases, the plasma power increases.

13. The method according to any one of the preceding claims, wherein during the process of the method, the glass preform (110) has a temperature between a minimum temperature T and a minimum temperature T. Min and maximum temperature T Max The temperature between, where T Min With T Max Temperature difference T between Diff Maximum 200K.

14. The method of claim 13, wherein T Max The maximum value of 2650℃ is adopted.

15. The method according to any one of the preceding claims, wherein the glass preform (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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