阅读说明：本技术 一种拉丝光纤扭动控制装置、控制方法及多模光纤 (Drawn optical fiber twisting control device and method and multimode optical fiber ) 是由 张安林 黄荣 肖武丰 王润涵 曹蓓蓓 王海鹰 尹旭峰 于 2020-06-10 设计创作，主要内容包括：本发明公开了一种拉丝光纤扭动控制装置、控制方法及多模光纤,属于光纤制造领域,在拉丝通道中的光纤护层涂覆固化装置下方与牵引轮上方区域增加光纤扭动控制装置,进而通过光纤扭动控制装置在垂直光纤方向上对光纤施加周期性旋转力,以使光纤进行周期性扭动。本发明通过增设光纤扭动控制装置对拉丝涂覆保护层固化后的光纤进行扭动及扭动力的传导,消除光纤预制件拉丝时在石墨炉内熔锥区锥型不规则形变的扰动,降低了光纤芯不圆度,改善了光纤预制件拉丝后折射率偏差,提升了折射率分布精确度。由于光纤扭动旋转,优化了光纤中不稳定残余应力的分布,利于降低残余应力带来的对折射率分布偏差的修正。(The invention discloses a drawn optical fiber twisting control device, a control method and a multimode optical fiber, belonging to the field of optical fiber manufacturing. According to the invention, the optical fiber twist control device is additionally arranged to conduct twist and twist power on the optical fiber after the wire drawing coating protective layer is solidified, so that disturbance of conical irregular deformation of a melting cone area in a graphite furnace during wire drawing of an optical fiber prefabricated part is eliminated, the out-of-roundness of an optical fiber core is reduced, the refractive index deviation of the optical fiber prefabricated part after wire drawing is improved, and the refractive index distribution accuracy is improved. The optical fiber is twisted and rotated, so that the distribution of unstable residual stress in the optical fiber is optimized, and the correction of refractive index distribution deviation caused by the residual stress is favorably reduced.)

1. A drawn optical fiber twist control device, comprising:

the optical fiber torsion control device is positioned in the area below the optical fiber protective layer coating and curing device and above the traction wheel in the wire drawing channel;

the optical fiber twisting control device is used for applying periodic rotating force to the optical fiber in the direction vertical to the optical fiber in the optical fiber drawing stage so as to periodically twist the optical fiber.

2. The apparatus of claim 1, wherein the fiber twist control device is configured to apply a periodic rotational force to the optical fiber through sliding contact with the optical fiber such that the resulting fiber twist is distributed along the optical fiber and conducted to the molten state diameter changing region of the preform to change the molten state diameter changing region taper irregular deformation and the stress distribution in the optical fiber, wherein the periodic rotational force is periodically alternated clockwise and counterclockwise.

3. The apparatus of claim 1 or 2, wherein the fiber twist control means comprises: the optical fiber twisting guide wheel set, the optical fiber twisting limiting wheel, the workbench and the twisting control module;

the optical fiber twisting guide wheel set, the optical fiber twisting limiting wheel and the twisting control module are fixed on the workbench through a connecting bearing, a tension spring and a support frame, so that the optical fiber twisting guide wheel set is arranged in a vertical face opposite mode and is perpendicular to the workbench, and the optical fiber twisting limiting wheel is also perpendicular to the workbench in a vertical face;

the optical fiber twisting guide wheel set is used for twisting the optical fiber in the direction vertical to the optical fiber to form a periodic rotating force;

the optical fiber twisting limiting wheel is used for keeping the optical fiber under the action of the periodic rotating force in a perpendicular stable state in the wire drawing channel;

and the twisting control module is used for controlling the periodic rotating force.

4. The apparatus of claim 3, wherein the fiber twisting guide pulley set is a module consisting of a plurality of guide pulleys on the same working plane, and the fiber is periodically twisted in a direction perpendicular to the fiber by the guide pulleys simultaneously.

5. The device of claim 1, wherein the optical fiber twist control device has a twist frequency of 5-90 m^-1The twisting amplitude is 0.01-6 turns/m.

6. The device according to claim 5, wherein the optical fiber twisting control device has a twisting frequency of 20-60 m^-1The twisting amplitude is 0.1-3 turns/m.

7. The apparatus of claim 5 or 6, wherein the period is 15m to 25m along the length of the optical fiber.

8. A method for controlling the twisting of a drawn optical fiber, comprising:

and an optical fiber twisting control device is added below the optical fiber protective layer coating and curing device and above the traction wheel in the drawing channel, and then the optical fiber is periodically twisted by applying periodic rotating force to the optical fiber in the direction vertical to the optical fiber through the optical fiber twisting control device.

9. The method of claim 8, wherein the fiber twist control device applies a periodic rotational force to the optical fiber through sliding contact with the optical fiber such that the resulting fiber twist is distributed along the optical fiber and conducted to the molten state diameter changing region of the preform to alter the molten state diameter changing region taper irregular deformation and the stress distribution in the optical fiber, wherein the periodic rotational force alternates between clockwise and counterclockwise.

10. A multimode optical fiber prepared according to the method of any one of claims 8 or 9.

Technical Field

The invention belongs to the field of optical fiber manufacturing, and particularly relates to a wiredrawing optical fiber twisting control device, a control method and a multimode optical fiber, which can optimize the residual stress of the optical fiber and the out-of-roundness of a fiber core and realize the improvement of the bandwidth of the multimode optical fiber.

Background

In recent years, multimode optical fiber has become a high-quality solution for short-distance and high-speed transmission networks due to its advantage of low system cost, and has been widely applied in the fields of large-scale data centers, local office centers, high-performance computing centers, storage area networks and the like. With the widespread commercial use of 100Gb/s rates and the steady evolution of the transition to 400Gb/s, the need for high quality, high bandwidth performance multimode optical fibers is increasing.

The optical fiber preform required for producing the multimode optical fiber is prepared by adopting a Plasma Chemical Vapor Deposition (PCVD) process. Introducing high-purity SiCl reactant into a high-purity quartz glass tube in a holding furnace with the temperature of about 1000-1300 ℃ through a certain way₄、O₂And a dopant GeCl₄The high-frequency microwave provided by the microwave source resonant cavity is utilized to activate gas to ionize and form plasma so as to carry out chemical reaction and vapor deposition, and a transparent quartz glass deposition layer is formed. The reaction formula of the multimode optical fiber core rod is as follows:

SiCl₄+O₂＝SiO₂+2Cl₂，GeCl₄+O₂＝GeO₂+2Cl₂。

and carrying out fusion shrinkage through a graphite fusion furnace to prepare the deposited quartz glass tube into a solid multi-mold core rod. Then, the multimode core rod is cleaned, corroded, dried and then combined with the matched sleeve to form a multimode optical fiber preform, and the preform is drawn into an optical fiber through a wire drawing device.

In the process of drawing the prefabricated member into the optical fiber, the multimode optical fiber with high bandwidth performance is obtained by regulating and controlling the stress distribution and the out-of-roundness of the fiber core in the process of drawing the optical fiber. The bandwidth performance refers to the optical fiber full injection bandwidth (OFLBandwidth), and is measured by the FOTP-204 standard test method specified in TIA. The effective mode Bandwidth (effective mode Bandwidth) is measured by adopting an IEC 60793-1-49 method.

The core out-of-roundness is expressed as follows:

N_core＝(d_core-max-d_core-min)/d_core

N_core: indicating core out-of-roundness;

d_core-max: represents the diameter of a circumscribed circle made by the boundary of the fiber core;

d_core-min: diameter of inscribed circle representing core boundary

d_core: the core diameter is indicated.

When the optical fiber prefabricated member is drawn into an optical fiber, the optical fiber prefabricated member is heated to 1500-2000 ℃ in a graphite induction heating furnace, a molten state diameter-changing area is formed at the lower end of the prefabricated member, the optical fiber is drawn under the action of gravity and traction force, and then the optical fiber is annealed in a heat preservation furnace (annealing temperature: 900-1200 ℃), cooled by a cooling pipe He, coated with a protective layer of polyacrylic resin (coating temperature: 20-75 ℃), solidified by a solidification device, provided with a limiting wheel and a traction wheel, and then conveyed to a fiber collecting device by a guide wheel set. In the process of drawing the prefabricated member into the optical fiber, the optical fiber is contacted with gear trains such as a limiting wheel, a traction wheel, a guide wheel set and the like at a high drawing speed (500 m/min-2000 m/min), and the gear trains rotate rapidly along with the optical fiber passing at a high speed. Practice shows that the optical fiber forms continuous unidirectional spin in the contact process with the wheel train, wherein the unidirectional spin refers to that the optical fiber is continuously measured in a unit of 1m from a top view angle, and the optical fiber rotates in a clockwise direction or a counterclockwise direction. The rotating force generated by the continuous unidirectional spinning is transmitted to a lower diameter-changing area of the prefabricated part in a molten state in a graphite induction heating furnace through a non-contact optical fiber drawing channel above a wheel train along the optical fiber drawing direction, the lower part of the diameter-changing area of the prefabricated part can be deformed under the action of the additional rotating force by the diameter-changing area, particularly the deformation of a cone part is intensified, the geometric out-of-roundness of a fiber core is intensified, the residual stress of a formed optical fiber is increased, the distortion of the outer edges of the fiber core and the core layer of the optical fiber is intensified, the deviation between the refractive index distribution of the drawn multimode optical fiber and the designed refractive index of the multimode optical fiber is caused, the refractive index distribution of the multimode optical fiber is.

Disclosure of Invention

Aiming at the defects or improvement requirements of the prior art, the invention provides a wiredrawing optical fiber twisting control device, a control method and a multimode optical fiber, so that the technical problems that the geometric out-of-roundness of a fiber core is aggravated and the residual stress of a formed optical fiber is increased easily in the existing wiredrawing process, the distortion of the outer edge of the fiber core and the outer edge of a core layer of the optical fiber is aggravated, the deviation between the refractive index distribution of the drawn multimode optical fiber and the designed refractive index of the multimode optical fiber is caused, and the refractive index distribution of the multimode optical fiber is seriously influenced are solved.

In order to adjust the unstable residual stress distribution of the multimode optical fiber, the multimode optical fiber needs to be designed in the vertical direction of constant-speed drawing of the optical fiber to apply a periodic external force distribution from the outer cladding layer, the outer edge of the core layer to the center of the core layer, which is generally called as an 'F rotating force'. I.e., an F-rotation force distribution satisfying the following positive (cosine) chord function:

wherein, F: indicating the rotational force to which the optical fiber is subjected;

k: a constant coefficient representing the intrinsic modulus characteristic of the material;

a: representing the amplitude of the wiggling;

w: representing a wiggling angular velocity;

t: representing a wiggling time period;

the angle of twist deviation (i.e., twist initial phase point) is indicated when t is 0.

Relative displacement, speed, angular speed and frequency when the twisting guide wheel is twisted, namely X, V, w and f:

W＝2nf

wherein, X: representing a wiggling displacement;

a: representing the amplitude of the wiggling;

w: representing a wiggling angular velocity;

t: representing a wiggling time period;

represents the angle of twist deviation (i.e., twist initial phase point) when t is 0;

pi: represents a circumferential rate constant;

f: indicating the frequency of the wiggling.

To achieve the above object, according to one aspect of the present invention, there is provided a drawn optical fiber twist control apparatus comprising:

the optical fiber torsion control device is positioned in the area below the optical fiber protective layer coating and curing device and above the traction wheel in the wire drawing channel;

the optical fiber twisting control device is used for applying periodic rotating force to the optical fiber in the direction vertical to the optical fiber in the optical fiber drawing stage so as to periodically twist the optical fiber.

Preferably, the optical fiber twist control device is used for applying periodic rotating force to the optical fiber through sliding contact with the optical fiber, so that the generated optical fiber twist is distributed along the optical fiber and is conducted to the molten state diameter changing area of the prefabricated part, and the irregular deformation of the cone part of the molten state diameter changing area and the stress distribution in the optical fiber are changed, wherein the periodic rotating force is periodically and alternately changed clockwise and anticlockwise.

Preferably, the optical fiber twist control apparatus includes: the optical fiber twisting guide wheel set, the optical fiber twisting limiting wheel, the workbench and the twisting control module;

the optical fiber twisting guide wheel set, the optical fiber twisting limiting wheel and the twisting control module are fixed on the workbench through a connecting bearing, a tension spring and a support frame, so that the optical fiber twisting guide wheel set is arranged in a vertical face opposite mode and is perpendicular to the workbench, and the optical fiber twisting limiting wheel is also perpendicular to the workbench in a vertical face;

the optical fiber twisting guide wheel set is used for twisting the optical fiber in the direction vertical to the optical fiber to form a periodic rotating force;

the optical fiber twisting limiting wheel is used for keeping the optical fiber under the action of the periodic rotating force in a perpendicular stable state in the wire drawing channel;

and the twisting control module is used for controlling the periodic rotating force.

Preferably, the optical fiber twisting guide wheel set is a module, which is composed of a plurality of guide wheels on the same working plane, and further periodically twists the optical fiber in the direction perpendicular to the optical fiber through each guide wheel.

Preferably, the twisting frequency of the optical fiber twisting control device is 5-90 m^-1The twisting amplitude is 0.01-6 turns/m.

Preferably, the twisting frequency of the optical fiber twisting control device is 20-60 m^-1The twisting amplitude is 0.1-3 turns/m.

Preferably, the period is 15m to 25m along the length of the optical fiber.

According to another aspect of the present invention, there is provided a method of controlling twist of a drawn optical fiber, comprising:

and an optical fiber twisting control device is added below the optical fiber protective layer coating and curing device and above the traction wheel in the drawing channel, and then the optical fiber is periodically twisted by applying periodic rotating force to the optical fiber in the direction vertical to the optical fiber through the optical fiber twisting control device.

Preferably, the optical fiber twist control device applies periodic rotating force to the optical fiber through sliding contact with the optical fiber, so that the generated optical fiber twist is distributed along the optical fiber and is transmitted to the molten state diameter changing area of the prefabricated member, and the irregular deformation of the molten state diameter changing area cone part and the stress distribution in the optical fiber are changed, wherein the periodic rotating force is periodically and alternately changed clockwise and anticlockwise.

According to another aspect of the present invention there is provided a multimode optical fibre produced according to any of the above methods.

In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:

1. the optical fiber after the wire drawing coating protective layer is solidified is twisted and the power is twisted by adding the optical fiber twisting control device, so that the disturbance of conical irregular deformation of a melting cone area in a graphite furnace during the wire drawing of an optical fiber prefabricated member is eliminated, the out-of-roundness of an optical fiber core is reduced, the refractive index deviation after the wire drawing of the optical fiber prefabricated member is improved, and the refractive index distribution accuracy is improved. The optical fiber is twisted and rotated, so that the distribution of unstable residual stress in the optical fiber is optimized, and the correction of refractive index distribution deviation caused by the residual stress is favorably reduced.

2. The method is simple, convenient and effective, and has low cost, practicability and strong operability.

Drawings

FIG. 1 is a schematic view of a conventional apparatus for producing a core rod by PCVD according to an embodiment of the present invention;

FIG. 2 is a graph showing the refractive index profiles of a core rod and an optical fiber in a conventional state according to an embodiment of the present invention;

FIG. 3 is a schematic flow chart of a method for controlling the twisting of a drawn optical fiber according to an embodiment of the present invention;

FIG. 4 is a graph of the refractive index deviation in a conventional state according to an embodiment of the present invention;

FIG. 5 is a graph of refractive index deviation provided by an embodiment of the present invention;

FIG. 6 is a schematic diagram of an optical fiber according to an embodiment of the present invention;

FIG. 7 is a top view of a fiber preparation twist provided by an embodiment of the present invention;

FIG. 8 is a diagram of differential mode delay in a conventional state according to an embodiment of the present invention;

fig. 9 is a diagram of differential mode latency provided by an embodiment of the invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is described in further detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

For convenience of introduction to the present disclosure, some terms are defined:

high bandwidth: the typical value of the effective mode bandwidth EMB is 2000 MHz.km or more;

core rod: a preform comprising a core layer and a partial cladding layer;

mass Flow Controller (Mass Flow Controller, MFC): providing precision reactants for core rod preparation (e.g., GeCl)₄) A gas flow stabilizer with automatic flow control;

and (3) germanium compensation: doping with dopants (e.g. GeCl) in the core layer deposition in certain amounts via software calculation₄) Adjusting the refractive index of the core layer to achieve ideal refractive index distribution;

the diameter-variable area is as follows: the lower part of the prefabricated member is transformed into a conical area by a cylindrical shape after being heated in a high-temperature graphite furnace.

The invention provides a wiredrawing optical fiber twisting control device and a wiredrawing optical fiber twisting control method for optimizing the residual stress of an optical fiber and the out-of-roundness of a fiber core, which not only can effectively release and optimize the residual stress, but also can reduce the out-of-roundness of the fiber core, improve the uniformity of the fiber core, and avoid the edge distortion of the core layer caused by the refractive index deviation of the core layer and the unstable residual stress, thereby improving the bandwidth of a multimode optical fiber.

FIG. 1 is a schematic view showing a conventional apparatus for producing a core rod by PCVD and a reactant supply. The conventional reaction gas is introduced into a reaction gas control device 5 (which is a thermostat) through control valves 1 and 2, and a gas reactant (e.g., GeCl)₄) The flow control is smoothly performed by a flow controller 4(MFC), and the rest of the reactants are performed by a flow controller 3 (MFC)¹) And controlling, enabling the later mixed gas reactants to enter a holding furnace 12 and a high-purity quartz glass tube 8 through a gas end rotary chuck device 7 and an extension tube 6, further heating, reacting in a reciprocating high-speed running high-frequency resonance cavity 9 to generate a glass deposition layer on the inner wall of the high-purity quartz glass tube, pumping out reaction tail gas from a pump end extension tube 11 and a pump end rotary chuck device 10, and carrying out melt-shrinkage on the deposited core rod to prepare the optical fiber preform.

In fig. 6, an optical fiber preform 14 is drawn into an optical fiber 17, the optical fiber 17 is annealed and cooled by an annealing furnace 15 and a cooling device 16, and stress relief is performed, then two protective layers are coated in coating devices 18 and 19, the protective coatings are cured by curing devices 20 and 21, and then the optical fiber 17 is wound onto a fiber collecting drum 24 through a guide wheel 23, an optical fiber twisting control device 25 and a traction wheel 22.

In general, in order to ensure a better graded refractive index distribution when a core rod is deposited on a core layer during deposition of a PCVD process, the opening and closing degree of a valve of a flow controller 4(MFC) is controlled by a PLC and a sensor to control the flow rate of a reactant when the core rod is deposited on the core layer, and in order to match the refractive index distribution of the edge of the core layer and the center of the core layer, the range of the flow controller 4(MFC) is 210sccm to meet the requirement of a higher refractive index at the center of the core layer under the conventional condition. In FIG. 2, the reactant (GeCl) conventionally used in the prior art is shown₄) The refractive index distribution of flow setting, A is the plug, and B is optic fibre, sees from the refractive index distribution in figure 2, and obvious deviation has taken place between the optic fibre refractive index and the plug refractive index at sandwich layer edge 20 ~ 25um interval and sandwich layer center 0 ~ 3um interval after the plug is drawn into optic fibre. If the refractive index distribution in fig. 4 is further seen, the refractive index error between the interval of 20-25 um corresponding to the edge of the core layer and the interval of 0-3 um corresponding to the center of the core layer greatly fluctuates, and the refractive index of the optical fiber at the corresponding position obviously deviates. In the existing production stateThe method comprises the following steps that a core layer germanium deposition mode of a PCVD (plasma chemical vapor deposition) process is adopted, the core layer deposited germanium is compensated through 100 points corresponding to 100 flow opening degrees, the edge of the core layer with refractive index deviation corresponds to the deposition thickness which accounts for 1.5um of the edge of the core layer, namely the edge of the core layer corresponds to the first 10 points of the deposition initial stage, the edge of the core layer is the deposition initial flow control stage under the condition of using the existing flow controller, and the reactant GeCl₄The flow opening is poor to be controlled in an interval of 0-10%, the stability is poor, furthermore, the flow opening is poor to be controlled in an interval of 2-6%, the abrupt fluctuation is large, correspondingly, the deposition amount of Ge in the area has non-controllable fluctuation, so that the refractive index distribution of the core rod is deviated, the roundness of the optical fiber core is deteriorated and the residual stress distribution is released unstably due to the spinning force and the conduction of the optical fiber in the process of drawing the optical fiber, the deviation of the partial refractive index distribution is further amplified, and the optical fiber which is drawn is widened in a Differential Mode Delay (DMD) test as shown in figure 8, the secondary peak of the optical fiber in an interval of 0-3 um and the broadening in an interval of 20-25 um, so that the typical value of the bandwidth of an effective Mode is seriously influenced.

Fig. 3 is a schematic flow chart of a method for controlling the twisting of a drawn optical fiber according to an embodiment of the present invention, which includes the following steps:

s1: and an optical fiber twisting control device is added below the optical fiber protective layer coating and curing device and above the traction wheel in the wire drawing channel, and then the optical fiber is periodically twisted by applying periodic rotating force to the optical fiber in the direction vertical to the optical fiber through the optical fiber twisting control device.

In the embodiment of the present invention, as shown in fig. 6, an optical fiber twist control device 25 is added to the region below the optical fiber protective layer coating and curing device and above the traction wheel 22 in the drawing channel, and the optical fiber twist control device 25 includes:

the optical fiber twisting guide wheel set, the optical fiber twisting limiting wheel, the workbench and the twisting control module;

the optical fiber twisting guide wheel set, the optical fiber twisting limiting wheel and the twisting control module are fixed on the workbench through a connecting bearing, a tension spring and a support frame, so that the optical fiber twisting guide wheel set is arranged in a vertical face opposite direction and is vertical to the workbench, and the optical fiber twisting limiting wheel is also vertical to the workbench;

the optical fiber twisting guide wheel set is used for twisting the optical fiber in the direction vertical to the optical fiber to form a periodic rotating force;

in the embodiment of the present invention, the periodic rotational force may be a periodic rotational force that is similar to sine and cosine, that is, a shape or a change rule of sine and cosine, or other forms of periodic rotational forces, which is not limited uniquely in the embodiment of the present invention.

The optical fiber twisting limiting wheel is used for keeping the optical fiber in a perpendicular stable state in the wire drawing channel under the action of periodic rotating force;

and the twisting control module is used for controlling the periodic rotating force.

The optical fiber twisting guide wheel set and the optical fiber twisting limiting wheel are made of alloy materials or non-alloy materials.

The optical fiber twisting guide wheel set is a module consisting of a plurality of (preferably 2 to 4) guide wheels on the same working plane, and periodically twists the optical fiber in the direction perpendicular to the optical fiber, as shown in the optical fiber twisting top view of fig. 7, the arrangement mode is exemplified by 2 twisting guide wheels 26 and an optical fiber twisting limiting wheel 27 in the optical fiber twisting guide wheel set (wherein 28 is the optical fiber in the top view state), but the invention is not limited to the arrangement mode. The optical fiber twisting control device applies periodic rotating force to the optical fiber through sliding contact with the optical fiber, the periodic rotating force is periodically and alternately changed clockwise and anticlockwise, the period is 15-25 m along the length of the optical fiber, the generated optical fiber twisting can be distributed along the optical fiber and is transmitted to a molten state diameter-changing area of the prefabricated part, and the optical fiber twisting is enough to change irregular deformation of a cone part of the molten state diameter-changing area and stress distribution in the optical fiber.

In the embodiment of the invention, the reaction gas control device is a closed constant temperature device which is an electric heating device and comprises a resistance heating device, a constant temperature control device or a temperature control information control device.

In the embodiment of the invention, the heating temperature of the reaction gas control device is 40-60 ℃, and preferably 45-50 ℃.

In an embodiment of the present invention, the flow controller is connected in parallel with a reaction gas path flow controller of a reaction gas control device.

In the embodiment of the present invention, when the optical fiber twisting guide wheel and the optical fiber twisting limit guide wheel are made of an alloy material, a ceramic-coated wheel surface is preferred.

In the embodiment of the invention, the twisting frequency of the optical fiber rotary twisting device is preferably 5-90 m^-1More preferably 20 to 60m^-1The twisting amplitude is preferably 0.01 to 6 turns/m, more preferably 0.1 to 3 turns/m.

The following describes the implementation of the present invention in detail with a specific embodiment.

In the embodiment of the present invention, as shown in fig. 6, in the fiber drawing stage, a twisting control device 25 is additionally arranged between the lower part of the fiber drawing channel curing device 21 and the traction wheel 22, the twisting control device 25 is composed of a fiber twisting guide wheel set 26, a fiber twisting limiting wheel 27, a workbench and a twisting control module in fig. 7, and the contact wheel surface of the twisting guide wheel and the fiber is preferably ceramic coated, but the present invention is not limited to this material coating. The twisting frequency of the twisting control device 25 in the embodiment of the invention is 30-60 m at a certain wire drawing speed^-1The twisting amplitude is 0.3-3 turns/m, the optical fiber rotation amplitude is 0-5 turns/m, the optical fiber rotation period is 10-30 m, approximate sine and cosine twisting and twisting force generated to the optical fiber in the process of drawing the optical fiber improve the molten state cone shape, the non-roundness of the optical fiber core and the instability of residual stress distribution release, further reduce the refractive index deviation in the drawing stage, as shown in figure 5, the refractive index error between the range of 20-25 um corresponding to the edge of the core layer and the range of 0-3 um corresponding to the center of the core layer is greatly reduced and obviously improved, and further as shown in fig. 9, when the optical fiber is subjected to Differential Mode Delay (DMD) test, as shown in fig. 8, the sub-peak of the optical fiber in the interval of 0 to 3um and the broadening of the optical fiber in the interval of 20 to 25um are obviously improved, and simultaneously, the non-circularity of the fiber core is optimized, and the bandwidth of the optical fiber is improved (the bandwidth is measured under the condition of full injection).

The full injection bandwidth is measured according to the FOTP-204 method, and the test adopts the full injection condition. The Effective Mode Bandwidth (Effective Mode Bandwidth) is measured by adopting an IEC 60793-1-49 method.

Table 1: optical fiber related and performance parameters

As can be seen from table 1 above:

related parameters:

the out-of-roundness Preform-Cir _ core (%) of the core rod is reduced from 0.13 of the comparative example to 0.1 and below of the examples;

the Fiber-T-Cir _ core (%) of the out-of-roundness of the Fiber core dropped from 2.65 of the comparative example to below 0.5 of the example;

the Fiber-T-Cir _ clad (%) of the out-of-roundness of the Fiber cladding is reduced from 0.35 of the comparative example to 0.13 of the example and below, and the improvement effect is obvious.

Optical fiber performance aspects:

the numerical aperture NA is reduced from more than 0.2 of the comparative example to 0.199 and less of the example;

the DMD Inner & Outer Mask @850nm both dropped to about 0.1 for the comparative example to 0.6 and below for the examples;

the full implantation bandwidth @850 is increased from about 6000MHz & km of the comparative example to 9000-11000 MHz & km of the example;

the full implant bandwidth @1300 increases from about 700MHz · km for the comparative example to about 750MHz · km for the example;

the effective mode bandwidth @850nm is increased from about 5400MHz & km of a comparative example to 11000-14000 MHz & km of an embodiment, the improvement effect is obvious, and the transmission performance of the multimode optical fiber in the use process is greatly improved.

It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.