CN111676468B

CN111676468B - Optical fiber prefabricated part, multimode optical fiber and preparation method thereof

Info

Publication number: CN111676468B
Application number: CN202010523611.XA
Authority: CN
Inventors: 张安林; 黄荣; 肖武丰; 王润涵; 曹蓓蓓; 王海鹰; 尹旭峰
Original assignee: Yangtze Optical Fibre and Cable Co Ltd
Current assignee: Yangtze Optical Fibre and Cable Co Ltd
Priority date: 2020-06-10
Filing date: 2020-06-10
Publication date: 2022-03-18
Anticipated expiration: 2040-06-10
Also published as: CN111676468A

Abstract

The invention discloses an optical fiber prefabricated part, a multimode optical fiber and a preparation method thereof, belonging to the technical field of optical fiber manufacturing. The sectional control of the multi-flow controller with different opening flow rates of reactants is carried out on the initial stage and the middle stage of depositing the core layer by additionally arranging the reactant gas circuit control, so that the stability of the flow rate control of the dopant at the initial stage of depositing the core rod to the edge of the core layer is ensured, and the refractive index control precision of the initial stage of the core layer is improved. The control stability of the low opening flow is increased, so that the stability of reactants in a core layer deposition stage is facilitated, the disturbance of unstable reactant airflow to the core layer deposition stage is avoided, and the axial uniformity of the core rod is improved.

Description

Optical fiber prefabricated part, multimode optical fiber and preparation method thereof

Technical Field

The invention belongs to the field of optical fiber manufacturing, and particularly relates to an optical fiber prefabricated part, a multimode optical fiber and a preparation method thereof, which can optimize the flow control of a dopant and the out-of-roundness of a fiber core.

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 prefabricated member 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 preparing the multimode optical fiber core rod by the PCVD process, the chemical reaction and the vapor deposition are carried out on the high-purity reactant in the quartz glass tube, and the uniformity of a quartz glass deposition layer in the tube is ensured by rotating the glass tube by a certain rotation angle, so that the deposition layer of the multimode optical fiber core rod has good roundness. Because the deviation of the system control precision is difficult to be completely avoided under the condition of the control parameters (such as feeding pressure, feeding flow, rotation angle and the like) of the existing production process, the multimode optical fiber core rod has certain fiber core out-of-roundness on a deposition layer. 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.

Because the multimode fiber has intermodal dispersion, the performance of bandwidth, transmission distance and the like is limited, and in order to reduce the intermodal dispersion of the multimode fiber, the refractive index profile of the core layer of the multimode fiber needs to be designed into a refractive index distribution which is continuously and gradually reduced from the center to the edge of the core layer, and is generally called as an alpha profile. I.e. a refractive index profile satisfying the following power exponential function:

wherein n is₁: representing the refractive index of the optical fiber axis;

r: represents the distance from the axis of the fiber;

a: represents the fiber core radius;

α: represents a distribution index;

Δ₀: representing the index of refraction of the center of the core relative to the cladding.

Relative refractive index, i.e. Δ_i：

Wherein n is_i: representing the refractive index at a location i from the center of the core;

n₀: which represents the minimum refractive index of the core of the optical fiber and is also typically the refractive index of the cladding of the optical fiber.

When the PCVD process is used for preparing the multimode optical fiber core rod, the SiO is used₂In which a dopant (e.g., GeO) is doped₂、F、P₂O₅、ZrO₂、B₂O₃Etc.) to adjust the graded-down refractive index profile of the multimode optical fiber from the center of the core to the edge. By germanium-fluorine co-doping (GeO)₂/C₂F₆) The refractive index distribution of the core layer and the good out-of-roundness of the fiber core are accurately controlled, so that the intermodal dispersion of the multimode fiber is reduced, and meanwhile, the radial stress distribution of the fiber in the drawing process is finely regulated and controlled, so that the multimode fiber with high bandwidth performance is obtained.

The multimode optical fiber herein comprises a core and a cladding, the core exhibiting a refractive index profile that is parabolic, wherein:

the distribution index alpha is 1.95 to 2.80,

radius of core layer R₁Is 23 to 27 μm in diameter,

maximum relative refractive index difference Δ_1max0.9% -1.3%, the minimum relative refractive index difference delta_1minIs-0.15 to-0.07 percent,

the cladding layer consists of an inner cladding layer, a sunken cladding layer and an outer cladding layer from inside to outside in sequence.

The single-side width of the inner cladding is 1.0-3.0 μm, delta₂Is-0.09% -0.05%,

the single-side width of the sunken cladding is 3.0-7.0 mu m, delta₃Is-1.0 to-0.4 percent,

the outer cladding is pure SiO₂And (4) a glass layer.

The Bandwidth performance refers to the optical fiber full injection Bandwidth (OFL Bandwidth), 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 germanium compensation method is to deposit SiO on the core layer by a certain simulation algorithm by utilizing a software program₂For a single Ge flow controller design 100 piece of GeCl₄And (3) doping Ge for adjusting the refractive index distribution through certain corresponding opening degree control at flow compensation points (namely 100 flow opening degree points corresponding to 1-100 points), thereby realizing ideal core layer refractive index distribution. The existing gas supply pipeline is connected with a single wide-range Ge flow controller and is limited by the influence of unstable flow fluctuation of low opening degree, and the control accuracy of the flow controller refers to the situation that the flow fluctuation is large, the control accuracy is poor or even is not controlled when the actually required flow rate corresponds to the opening degree of the flow controller within the range of 0-10% on the basis of the existing range, so that the large influence is brought to the uniformity of the multimode core rod and the refractive index distribution corresponding to the position of 20-25 um of the edge of the core rod core layer.

Disclosure of Invention

Aiming at the defects or improvement requirements in the prior art, the invention provides an optical fiber preform, a multimode optical fiber and a preparation method thereof, and therefore the technical problem that the uniformity of a multimode core rod and the corresponding refractive index distribution at the edge of a core layer of the core rod are greatly influenced due to the fact that the existing gas supply pipeline is connected with a single wide-range Ge flow controller and is limited by unstable low-opening flow fluctuation is solved.

To achieve the above object, according to one aspect of the present invention, there is provided a method for manufacturing an optical fiber preform, comprising:

and adding a plurality of gas path flow controller control branches of reactants in the PCVD process reaction gas control device, and further controlling the opening degree of each gas path flow controller to ensure that the reactants enter a subsequent deposition process to participate in deposition reaction after flowing through each gas path flow controller for segmented control, thereby obtaining the optical fiber prefabricated member.

Preferably, when there are two reactant gas path flow controllers, the segment control method of the dual gas path flow controller is as follows:

the first stage is that when the deposition of the core layer of the core rod is started at the edge stage, the flow of reactants is controlled independently by a first gas path flow controller;

and in the second stage, when the core layer is deposited to the target stage, automatically starting a second gas path flow controller, meanwhile, keeping the flow opening of the first gas path flow controller constant after reaching the target flow opening, continuously carrying out operation of the second gas path flow controller according to a preset flow opening gradient until the core rod is deposited to the set flow, and keeping the set flow opening to operate until the core rod is deposited completely under the common control of the first gas path flow controller and the second gas path flow controller.

Preferably, the gas path flow controller is GeCl₄A gas path flow controller.

Preferably, the PCVD process reaction gas control device is a closed constant temperature device, and the closed constant temperature device is an electric heating device, and includes a resistance heating device, a constant temperature control device or a temperature control information control device.

Preferably, the heating temperature of the PCVD process reaction gas closed constant temperature device is 40-60 ℃.

Preferably, the heating temperature of the PCVD process reaction gas closed constant temperature device is 45-50 ℃.

According to another aspect of the present invention, there is provided an optical fiber preform prepared based on any one of the above methods

According to another aspect of the present invention, there is provided a method of manufacturing a multimode optical fiber, comprising:

and melting the optical fiber preform prepared by the method by a graphite induction heating furnace, annealing and cooling by stress release under the action of gravity and traction force, coating by two protective layers, and solidifying the coating in a solidifying device to obtain the optical fiber.

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. by adding reactants (e.g. GeCl)₄) The gas path control device performs sectional control on the multiple flow controllers with different opening flow rates of reactants at the initial stage and the intermediate stage of depositing the core rod to the core layer at the deposition stage of the core rod, so that the doping of the core rod to the initial stage of depositing the core rod to the edge of the core layer is ensuredAgents (e.g. GeCl)₄) The flow control stability improves the refractive index control precision of the core layer at the initial stage (namely the edge of the core layer). The control stability of the low opening flow is improved, so that the stability of reactants in the stage of depositing to the core layer is facilitated, the disturbance of unstable reactant airflow to the deposition stage of the core layer is avoided, the axial uniformity of the core rod is improved, the excellent refractive index distribution of the core rod is obtained, the out-of-roundness of the fiber core is reduced, and the uniformity of the fiber core is improved.

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

Drawings

FIG. 1 is a schematic view showing a conventional apparatus for producing a core rod by PCVD according to a comparative example of the present invention and the supply of reactants;

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

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

FIG. 4 is a schematic diagram of a core rod PCVD production apparatus and reactant supply provided by an embodiment of the present invention;

FIG. 5 is a graph showing a deviation of refractive index in a conventional state according to a comparative example of the present invention;

FIG. 6 is a graph of refractive index deviation provided by an embodiment of the present invention;

FIG. 7 is a schematic illustration of an optical fiber according to an embodiment of the present invention;

FIG. 8 is a schematic cross-sectional view of a refractive index profile provided by an embodiment of the present invention;

FIG. 9 is a diagram of differential mode delay in a conventional state of the art according to a comparative example of the present invention;

fig. 10 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.

In the present examples, "first", "second", etc. are used for distinguishing different objects, and are not necessarily used for describing a particular order or sequence.

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 method for preparing an optical fiber preform by optimizing the low-concentration germanium doping precision of the core edge and the fiber core non-circularity, which can not only effectively control the refractive index distribution of a core rod, but also reduce the non-circularity of the fiber core, improve the uniformity of the fiber core, and avoid the core edge distortion 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) Controlling the post-mixed gas reactants to enter a holding furnace 12 and high-purity quartz through a gas end rotary chuck device 7 and an extension pipe 6The glass tube 8 is further heated and then reacts in the high-frequency resonant cavity 9 which runs at a high speed in a reciprocating mode to generate a glass deposition layer on the inner wall of the high-purity quartz glass tube, reaction tail gas is pumped out from the pump end extension tube 11 and the pump end rotary chuck device 10, and the deposited core rod is subjected to fusion shrinkage to prepare the optical fiber preform.

In fig. 7, 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 release, coating of two protective layers is performed in

coating devices

18 and 19, the protective coatings are cured by curing

devices

20 and 21, and then the optical fiber 17 passes through a guide wheel 22 and a limiting wheel 23 and is wound on a fiber collecting barrel 24 through a traction wheel 25.

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. 5 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. Under the existing production state, the deposition of the core layer in the PCVD process adopts a mode of depositing core layer germanium compensation, the deposited germanium of the core layer is compensated by 100 points corresponding to 100 flow openings, the edge of the core layer with refractive index deviation corresponds to the deposition thickness which accounts for about 1.5um of the edge of the core layer, namely the edge of the core layer corresponds to the first 10 points of the initial deposition stage, under the condition of using the existing flow controller, the edge of the core layer is the initial deposition flow control stage, and the reactant GeCl₄The flow opening is poor to be controlled within 0-10%, the stability is poor, furthermore, the flow opening is poor to be controlled within 2-6%, and the sudden change wave occursThe large fluctuation corresponds to the uncontrollable fluctuation of the deposition amount of Ge in the region, which causes the deviation of the refractive index distribution of the core rod, and the deterioration of the roundness of the optical fiber core and the unstable release of the residual stress distribution are caused by the fiber spinning force and the fiber spinning conduction in the process of drawing the optical fiber, which further amplifies the partial refractive index distribution deviation, so that the optical fiber drawn by the drawing has the secondary peak in the interval of 0-3 um and the broadening in the interval of 20-25 um when the Differential Mode Delay (DMD) test is carried out, as shown in fig. 9, thereby seriously affecting the typical value of the effective Mode bandwidth.

Fig. 3 is a schematic flow chart of a method for manufacturing an optical fiber preform according to an embodiment of the present invention, including the following steps:

s1: and adding a plurality of gas path flow controller control branches of reactants in the PCVD process reaction gas control device, and further controlling the opening degree of each gas path flow controller to ensure that the reactants enter a subsequent deposition process to participate in deposition reaction after flowing through each gas path flow controller for segmented control, thereby obtaining the optical fiber prefabricated member.

In the embodiment of the invention, a path of reactant (GeCl is used in the invention) is added in the reaction gas control device of the PCVD process₄) The method of the present invention will be described in detail by taking the gas path flow control device as an example.

Wherein, the GeCl₄The gas circuit flow control device includes: GeCl₄The gas circuit flow controller, the gas supply pipeline module, the sensing control module and the PLC control module;

the GeCl4 gas path flow controller is connected with the sensing control module through a gas supply pipeline module and then connected with the PLC control module;

GeCl₄gas path flow controller for GeCl required for core rod deposition₄Automatic control of reactants;

a gas supply pipeline module for providing GeCl required by core rod deposition₄A flow-through channel for reactants;

sensing control module for GeCl₄Signal conversion for accurate control of reactant flow;

PLC control moduleFor accurately controlling GeCl for signal conversion operation₄The flow rate required for the reaction.

In an embodiment of the invention, the reactants (here GeCl) are carried out through a connected Mass Flow Controller (MFC)₄) Flow opening control by controlling two-way GeCl₄The opening degree of the gas path flow controller is used for accurately controlling the doping amount of the core layer dopant.

In particular, bis GeCl₄The flow controller adopts sectional control, the first stage is the edge stage of the core layer deposition of the core rod, and the first GeCl is adopted₄Flow controller for controlling GeCl independently₄Flow, e.g. control of GeCl₄The flow opening is 2-80%, the second stage is the flow opening (such as 15-25%) when the core layer is deposited to the target stage, and the second GeCl is automatically started₄Flow controller and first GeCl₄The flow controller flow opening is maintained constant after reaching the target flow opening (e.g. 80%), and the second GeCl₄The flow controller continues to operate according to the preset flow opening gradient until the core rod is deposited to the set flow, and the flow controller maintains the set flow opening to operate in the first GeCl₄Flow controller and second GeCl₄And the flow controllers are controlled together until the deposition of the core rod is finished.

In an embodiment of the present invention, the first GeCl₄Gas path flow controller and second GeCl₄The gas path flow controller can select the same range or different ranges.

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 the embodiment of the invention, the double-path GeCl is adopted₄The flow controller is connected with a reaction gas circuit flow controller 3 of the reaction gas control device in parallel, and the two paths of GeCl₄The flow controllers are connected in parallel.

In another aspect of the present invention, there is provided a method for preparing a multimode optical fiber, comprising:

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

In the embodiment of the invention, firstly, in the preparation stage of the core rod, GeCl is arranged in a PCVD process reaction gas closed constant temperature device 5 in figure 4₄A flow controller 13(MFC) control branch is additionally arranged on the reaction gas path, and the branch pipeline consists of a high-purity metal pipe and the flow controller 13(MFC) and corresponds to the closed constant temperature device 5. Reactant GeCl₄The gas flow enters a subsequent deposition process to participate in deposition reaction after being controlled by the

flow controllers

4 and 13 in a segmented manner. The double-flow controller (MFC) in this embodiment selects the same range (both: 55 sccm-60 sccm), starts the flow controller 4 (the same or start the flow controller 13) at the initial stage of deposition to the edge of the deposition layer of the core layer, sets the gradient flow value of the compensation flow of germanium (100 flow control points in the interval of 1-100), the opening interval is 4% -20%, and automatically starts the flow controller 13 (the same or start the flow controller 4) when the operation reaches the 11 th point corresponding to the opening, at this time, and (3) keeping the double-flow controller at different opening degrees, simultaneously operating the flow controller 4 (the same or opening the flow controller 13) to 80% of the opening degree, keeping the constant opening degree, operating the flow controller 13 (the same or opening the flow controller 4) to set the gradient opening degree of the germanium compensation value to be 7% -90%, and continuously operating until the end flow opening degree is set for the core rod deposition. In the embodiment of the invention, the flow control of the initial stage of the deposition edge of the core rod layer is stable.

Next, as shown in FIG. 8, the refractive index profile of one embodiment of a multimode core rod prepared under dual germanium flow controller conditions is shown, wherein the core refractive index profile is parabolic with a distribution index of α and a core radius of R₁The maximum relative refractive index difference at the center of the core layer is Delta_1maxThe minimum relative refractive index difference at the edge of the core layer is Delta_1min(ii) a The cladding comprises an inner cladding, a sunken cladding and an outer cladding from inside to outside in sequence, and the single-side width of the inner cladding is (R)₂-R₁) Relative refractive index difference of Δ₂(ii) a The single side width of the sunken cladding is (R)₃-R₂) Relative refractive index difference of Δ₃(ii) a The outer cladding layer is a pure silica glass layer. Fig. 7 shows a drawing stage from a preform to an optical fiber, and as shown in fig. 6, refractive index errors of the optical fiber drawn from the preform in a range of 20 to 25um corresponding to the edge of a core layer and in a range of 0 to 3um corresponding to the center of the core layer are substantially reduced, which significantly improves the refractive index deviation of the optical fiber at the corresponding position, and further as shown in fig. 10, when the optical fiber shown in fig. 9 is subjected to Differential Mode Delay (DMD) test, the sub-peak of the optical fiber in the range of 0 to 3um and the broadening of the optical fiber in the range of 20 to 25um are significantly improved, and simultaneously, the fiber core non-circularity is optimized, and the fiber bandwidth is increased (the bandwidth is measured under the full injection condition).

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:

in terms of relevant parameters, the out-of-roundness of the core rod Preform-Cir _ core (%) is reduced from 0.13 of the comparative example to 0.1 and below of the example, the out-of-roundness of the Fiber core Fiber-T-Cir _ core (%) is reduced from 2.65 of the comparative example to 0.5 and below of the example, and the out-of-roundness of the Fiber cladding Fiber-T-Cir _ clad (%) is reduced from 0.35 of the comparative example to 0.13 and below of the example, so that the improvement effect is obvious.

Optical fiber performance aspects: the numerical aperture NA is reduced from more than 0.2 of a comparative example to 0.199 and less of an embodiment, the DMD Inner & Outer Mask @850nm is reduced from about 0.1 of the comparative example to 0.6 and less of the embodiment, the full injection bandwidth @850 is increased from about 6000MHz & km of the comparative example to 9000-11000 MHz & km of the embodiment, the full injection bandwidth @1300 is increased from about 700MHz & km of the comparative example to about 750MHz & km of the embodiment, the effective mode bandwidth @850nm is increased from about 5400MHz & km of the comparative example to 11000-14000 MHz & km of the embodiment, the improvement effect is obvious, and the transmission performance of the multimode optical fiber in the using 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.

Claims

1. A method for manufacturing a core rod for an optical fiber preform, comprising:

in the preparation stage of the core rod, GeCl in a PCVD process reaction gas closed constant temperature device (5)₄A second flow controller (13) control branch is additionally arranged on the reaction gas path, the pipeline of the second flow controller (13) control branch consists of a high-purity metal pipe and a second flow controller (13), and the reactant GeCl₄The airflow enters a subsequent deposition process to participate in deposition reaction after being controlled in a segmented manner by a double-flow controller of a first flow controller (4) and a second flow controller (13), and the double-flow controllers select the same range and are: 55 sccm-60 sccm, and 100 GeCl pieces are designed for each flow controller₄The flow compensation points correspond to 100 flow opening points from 1 point to 100 points, the first flow controller (4) is started at the initial stage of deposition to the edge of a deposition layer of the core layer, the opening interval is between 4% and 20% according to the compensation flow gradient flow value of set germanium, the second flow controller (13) is automatically started when the first flow controller (4) is operated to the 11 th point corresponding to the opening, at the moment, the double flow controllers are kept to be operated to the first flow controller (4) to the opening 80% at different openings, the constant opening of the first flow controller (4) is kept, the second flow controller (13) is operated to set the gradient opening of the compensation value of the germanium to be between 7% and 90%, and the operation is continued until the flow opening is set to be terminated by core rod deposition.

2. An optical fiber preform core rod produced based on the method of claim 1.