阅读说明：本技术 光纤的制备方法、粉末棒烧结设备 (Preparation method of optical fiber and powder rod sintering equipment ) 是由 周建峰 薛济萍 薛驰 沈一春 钱宜刚 于 2019-08-30 设计创作，主要内容包括：本发明提供一种光纤的制备方法和粉末棒烧结设备。该方法通过在光纤成型过程中将粉末棒的芯层掺入氯来降低芯层在退火时结构的弛豫时间；并且在中包层和内包层掺入适量的氟形成低折射率,有效降低宏弯损耗；粉末棒烧结成玻璃棒之后进行退火处理,降低芯层的虚拟温度,降低因为密度的波动带来的瑞利散射；因为氟和氯的掺杂,使得芯层和中包层的粘度随之降低,也降低了拉丝的衰减值。因此本发明在保证光纤光学参数(截止波长、模场直径、零色散波长)可控范围内有效降低光纤损耗以及弯曲损耗,且制造工艺简单可控,降低了光纤制造成本。(The invention provides a preparation method of an optical fiber and powder rod sintering equipment. The method reduces the relaxation time of the structure of the core layer during annealing by doping chlorine into the core layer of the powder rod in the optical fiber forming process; and proper amount of fluorine is doped into the middle cladding and the inner cladding to form low refractive index, so that macrobending loss is effectively reduced; after the powder rod is sintered into a glass rod, annealing treatment is carried out, so that the virtual temperature of the core layer is reduced, and Rayleigh scattering caused by density fluctuation is reduced; because of the doping of fluorine and chlorine, the viscosity of the core layer and the middle cladding layer is reduced, and the attenuation value of the wire drawing is also reduced. Therefore, the invention effectively reduces the optical fiber loss and the bending loss within the controllable range of the optical parameters (cut-off wavelength, mode field diameter and zero dispersion wavelength) of the optical fiber, has simple and controllable manufacturing process and reduces the manufacturing cost of the optical fiber.)

1. A method of making an optical fiber, comprising the steps of:

sequentially forming a core layer, an inner cladding layer and an intermediate cladding layer on the surface of the target rod, wherein the core layer is mainly composed of silicon dioxide, the core layer is doped with germanium and chlorine, and the inner cladding layer and the intermediate cladding layer are doped with fluorine;

sequentially carrying out dehydroxylation, sintering, vitrification and annealing four stages of treatment on the powder rod to form a glass rod with a preset section refractive index, wherein the annealing stage comprises a plurality of cooling sections and a plurality of constant temperature sections;

forming an outer cladding layer on the surface layer of the glass rod by adopting an axial vapor deposition process or an external vapor deposition process, and then sintering to obtain a transparent optical fiber preform;

and drawing the optical fiber preform into filament, and treating the filament under the annealing and heat preservation conditions to obtain the optical fiber.

2. The method of manufacturing an optical fiber according to claim 1, wherein: the reaction gas for forming the core layer comprises oxygen, hydrogen, silicon tetrachloride, chlorine, germanium tetrachloride and argon, wherein the flow rate of the germanium tetrachloride is controlled to be 50-200cc/min, and the flow rate of the chlorine is controlled to be 300-750 cc/min.

3. The method of manufacturing an optical fiber according to claim 1, wherein: the reaction gas for forming the inner cladding comprises oxygen, hydrogen, silicon tetrachloride, fluoride and argon, wherein the flow rate of the silicon tetrachloride is controlled to be 20-50 g/min, the flow rate of the fluoride is controlled to be 50-400 g/min, and the density of fluorine-doped silicon dioxide powder generated by the reaction is controlled to be 0.5-1.5 g/cm³The thickness of the inner cladding is 1.0-3.0 of the diameter of the core layer.

4. The method of manufacturing an optical fiber according to claim 1, wherein: the reaction gas for forming the middle cladding comprises oxygen, hydrogen, silicon tetrachloride, fluoride and argon, wherein the flow rate of the silicon tetrachloride is controlled to be 20 g/min-50 g/min, the flow rate of the fluoride is controlled to be 50 g/min-900 g/min, and the density of fluorine-doped silicon dioxide powder generated by the reaction is controlled to be 0.5-1.5 g/cm³The thickness of the middle cladding layer is 1.0-3.0 of the diameter of the core layer.

5. The method of manufacturing an optical fiber according to claim 3 or 4, wherein: the fluoride comprises SiF₄、CF₄、SF₆、C₂F₆、SOF₂、C₂F₂Cl₂One or a combination of at least two of (1).

6. The method of manufacturing an optical fiber according to claim 1, wherein: the temperature in the dehydroxylation stage is controlled to be 1000-1200 ℃, and Cl is introduced at the flow rate of 500-1000 cc/min₂Introducing helium at the flow rate of 10-30 l/min to form a reaction atmosphere; bakingA sintering stage, taking the temperature of the dehydroxylation stage as an initial temperature, raising the temperature to 1300-1600 ℃ at a heating rate of 3-6 ℃/min, and keeping introducing helium with a flow rate of 10-30 l/min to form a protective atmosphere; and in the vitrification stage, keeping the temperature for 3-6 h at the end of the sintering stage, and keeping introducing He with the flow rate of 10-30 l/min to form a protective atmosphere.

7. The method of manufacturing an optical fiber according to claim 1, wherein: the annealing stage sequentially comprises a first cooling section, a first constant temperature section, a second cooling section, a second constant temperature section and a third cooling section, wherein the first cooling section takes the temperature at the end of the vitrification stage as the starting temperature and linearly cools the temperature by 50-75 ℃; taking the temperature at the end of the first cooling section as the temperature of the first constant temperature section, keeping the temperature for 1-3 h, and keeping introducing nitrogen with the flow rate of 5-15 l/min to form a protective atmosphere; the second cooling section takes the temperature of the first constant temperature section as an initial temperature, and the temperature is linearly cooled to 50-75 ℃; taking the temperature at the end of the second cooling section as the temperature of the second constant temperature section, keeping the temperature for 1-3 h, and keeping introducing nitrogen with the flow rate of 5-15 l/min to form protective atmosphere; and the third cooling section takes the temperature of the second constant temperature section as an initial temperature and reduces the temperature to the temperature of the dehydroxylation stage at the speed of 1-3 ℃/min.

8. The method of manufacturing an optical fiber according to claim 1, wherein: the drawing speed is controlled between 2000m/min and 3000m/min, and the drawing tension is controlled between 100g and 200 g.

9. The method of manufacturing an optical fiber according to claim 1, wherein: and the length of the fibril under the annealing and heat preservation conditions in the wire drawing process is 2-4 m.

10. The method of claim 1, wherein the predetermined profile index of refraction characteristic is:

a middle core layer with a radius of 4-6 μm and a refractive index of 0.25-0.35% relative to silicon dioxide;

the inner structure cladding and the middle structure cladding have the radius of 10-25 mu m, and the refractive index of the inner structure cladding relative to silica is-0.03 to-0.06 percent;

an outer cladding having a radius equal to 62.5 μm and a refractive index of 0-0.1%.

11. A powder stick sintering equipment which characterized in that: the powder rod lifting device comprises a heating body, a lifting rod, a lifting mechanism and a middle furnace core pipe for accommodating a powder rod, wherein one end of the lifting rod extends into the middle furnace core pipe through a conversion connector and is connected with a target rod, the other end of the lifting rod is connected with the lifting mechanism, and the powder rod attached to the target rod is suspended below the lifting rod and driven by the lifting mechanism to rotate or lift; the heating body is arranged on the outer side of the middle furnace core pipe, a heating area of the heating body is in radiation coverage with the whole powder rod, an air inlet is formed in the bottom of the middle furnace core pipe, and air valves of the heating body and the air inlet are regulated and controlled by an electrically connected central control device to achieve multi-section sintering.

12. The powder rod sintering apparatus according to claim 11, wherein: the heating body is provided with four groups, and each group is symmetrically arranged on the opposite outer side along the axis of the middle furnace core pipe; the four groups of heating bodies are arranged side by side along the axis of the middle furnace core pipe.

Technical Field

The invention relates to the technical field of optical communication, in particular to a preparation method of an optical fiber and powder rod sintering equipment.

Background

With the development of optical communication technology, especially in the future 400G and above transmission systems, it is one of the important issues in the field of optical fiber manufacturing to reduce the fiber loss and the bending loss within the controllable range of optical parameters (cut-off wavelength, mode field diameter, zero dispersion wavelength) of the optical fiber, and to achieve the simplicity and controllability of the manufacturing process and the reduction of the manufacturing cost of the optical fiber.

It is well known that the attenuation, macrobend, optical parameter properties of optical fibers depend on the performance of the optical fiber preform. For quartz optical fiber, the attenuation at 600nm to 1600nm is mainly from rayleigh scattering, and how to effectively reduce the rayleigh scattering of the optical fiber is the problem to be solved in the present document from the viewpoint of preform production.

Disclosure of Invention

In view of the above, there is a need for a method of making an optical fiber having low loss, bend resistant characteristics.

A method of making an optical fiber comprising the steps of:

sequentially forming a core layer, an inner cladding layer and an intermediate cladding layer on the surface of the target rod, wherein the core layer is mainly composed of silicon dioxide, the core layer is doped with germanium and chlorine, and the inner cladding layer and the intermediate cladding layer are doped with fluorine;

sequentially carrying out dehydroxylation, sintering, vitrification and annealing four stages of treatment on the powder rod to form a glass rod with a preset section refractive index, wherein the annealing stage comprises a plurality of cooling sections and a plurality of constant temperature sections;

forming an outer cladding layer on the surface layer of the glass rod by adopting an axial vapor deposition process or an external vapor deposition process, and then sintering to obtain a transparent optical fiber preform;

and drawing the optical fiber preform into filament, and treating the filament under the annealing and heat preservation conditions to obtain the optical fiber.

Further, the reaction gas for forming the core layer comprises oxygen, hydrogen, silicon tetrachloride, chlorine, germanium tetrachloride and argon gas, wherein the flow rate of the germanium tetrachloride is controlled to be 50-200cc/min, and the flow rate of the chlorine is controlled to be 300-750 cc/min.

Further, the reaction gas for forming the inner cladding comprises oxygen, hydrogen, silicon tetrachloride, fluoride and argon, wherein the flow rate of the silicon tetrachloride is controlled to be 20 g/min-50 g/min, the flow rate of the fluoride is controlled to be 50 g/min-400 g/min, and the density of fluorine-doped silicon dioxide powder generated by the reaction is controlled to be 0.5-1.5 g/cm³The thickness of the inner cladding is 1.5-2.0 of the diameter of the core layer.

Further, the reaction gas for forming the middle cladding comprises oxygen, hydrogen, silicon tetrachloride, fluoride and argon, wherein the flow rate of the silicon tetrachloride is controlled to be 20 g/min-50 g/min, the flow rate of the fluoride is controlled to be 50 g/min-900 g/min, and the density of fluorine-doped silicon dioxide powder generated by the reaction is controlled to be 0.5-1.5 g/cm³The thickness of the middle cladding layer is 1.5-2.0 of the diameter of the core layer.

Further, the fluoride includes SiF₄、CF₄、SF₆、C₂F₆、SOF₂、C₂F₂Cl₂One or a combination of at least two of (1).

Further, the temperature in the dehydroxylation stage is controlled to be 1000-1200 ℃, and chlorine (Cl) is introduced at the flow rate of 500-1000 cc/min₂) Introducing helium (He) at the flow rate of 10-30 l/min to form a reaction atmosphere; in the sintering stage, the temperature of the dehydroxylation stage is taken as the initial temperature, the temperature is increased to 1300-1600 ℃ at the heating rate of 3-6 ℃/min, and helium (He) with the flow rate of 10-30 l/min is kept introduced to form a protective atmosphere; and in the vitrification stage, keeping the temperature for 3-6 h at the end of the sintering stage, and keeping introducing helium (He) with the flow rate of 10-30 l/min to form a protective atmosphere.

Further, the annealing stage sequentially comprises a first cooling section, a first constant temperature section, a second cooling section, a second constant temperature section and a third cooling section, wherein the first cooling section takes the temperature at the end of the vitrification stage as the starting temperature and linearly cools the glass to 50-75 ℃; taking the temperature at the end of the first cooling section as the temperatureThe temperature of the first constant temperature section is kept for 1-3 h, and nitrogen (N) with the flow rate of 5-15 l/min is kept to be introduced during the period₂) Forming a protective atmosphere; the second cooling section takes the temperature of the first constant temperature section as an initial temperature, and the temperature is linearly cooled to 50-75 ℃; taking the temperature at the end of the second cooling section as the temperature of the second constant temperature section, keeping the temperature for 1-3 h, and keeping introducing nitrogen (N) with the flow rate of 5-15 l/min₂) Forming a protective atmosphere; and the third cooling section takes the temperature of the second constant temperature section as an initial temperature and reduces the temperature to the temperature of the dehydroxylation stage at the speed of 1-3 ℃/min.

Furthermore, the drawing speed is controlled between 2000m/min and 3000m/min, and the drawing tension is controlled between 100g and 200 g.

Further, the length of the fibril under the annealing and heat preservation condition in the wire drawing process is 2-4 m.

Further, the preset profile refractive index is characterized by:

a middle core layer with a radius of 4-6 μm and a refractive index of 0.25-0.35% relative to silicon dioxide;

the inner structure cladding and the middle structure cladding have the radius of 10-25 mu m, and the refractive index of the inner structure cladding relative to silica is-0.03 to-0.06 percent;

an outer cladding having a radius equal to 62.5 μm and a refractive index of 0-0.1%.

The invention also provides powder rod sintering equipment, which comprises a heating body, a suspender, a lifting mechanism and a middle furnace core pipe for accommodating the powder rod, wherein one end of the suspender extends into the middle furnace core pipe through a conversion connector and is connected with a target rod, the other end of the suspender is connected with the lifting mechanism, and the suspender suspends the powder rod attached to the target rod below the powder rod and is driven by the lifting mechanism to rotate or lift; the heating body is arranged on the outer side of the middle furnace core pipe, a heating area of the heating body is in radiation coverage with the whole powder rod, an air inlet is formed in the bottom of the middle furnace core pipe, and air valves of the heating body and the air inlet are regulated and controlled by an electrically connected central control device to achieve multi-section sintering.

Furthermore, the central control device adjusts the temperature in the middle furnace core pipe and/or the gas flow introduced from the gas inlet in real time according to the detection parameters.

Further, the central control device can manually adjust and/or automatically adjust the power of the heating body and/or the opening degree of the air valve of the air inlet.

Further, the detection parameter includes one or more of a temperature within the central furnace core tube, a rod diameter of the powder rod, or a transparency of the powder rod.

Furthermore, each heating body is electrically connected with a temperature monitoring device for detecting and feeding back the temperature in the middle furnace core tube in real time.

Furthermore, each heating body is electrically connected with transparency monitoring equipment for detecting transparency and feeding back a vitrification sintering process.

Further, each heating body is electrically connected with rod diameter monitoring equipment for detecting and feeding back the rod diameter of the powder rod in real time.

Further, the rod diameter monitoring equipment adopts a diameter measurement or circumference measurement mode.

Furthermore, the heating body is provided with four groups, and each group is symmetrically arranged on the opposite outer side along the axis of the middle furnace core pipe.

Furthermore, the four groups of heating bodies are arranged side by side along the axis of the middle furnace core pipe.

Compared with the prior art, the core layer of the powder rod is doped with chlorine during the optical fiber molding process to reduce the relaxation time of the structure of the core layer during annealing; and a proper amount of fluorine is doped into the middle coating to form a low refractive index, so that macrobending loss is effectively reduced; after the powder rod is sintered into a glass rod, annealing treatment is carried out, so that the virtual temperature of the core layer is reduced, and Rayleigh scattering caused by density fluctuation is reduced; because of the doping of fluorine and chlorine, the viscosity of the core layer and the middle cladding layer is reduced, and the attenuation value of the wire drawing is also reduced. Therefore, the invention effectively reduces the optical fiber loss and the bending loss within the controllable range of the optical parameters (cut-off wavelength, mode field diameter and zero dispersion wavelength) of the optical fiber, has simple and controllable manufacturing process and reduces the manufacturing cost of the optical fiber.

Drawings

The present invention will be described in further detail with reference to the accompanying drawings and specific embodiments.

FIG. 1 is a flow chart of the preparation of an optical fiber according to the present invention.

FIG. 2 is a schematic view of VAD vapor deposition processing equipment according to an embodiment of the present invention.

FIG. 3 is a schematic view of a powder rod sintering apparatus according to an embodiment of the present invention.

Fig. 4 is a schematic diagram of the furnace temperature curve of the sintering device shown in fig. 3.

FIG. 5 is a schematic diagram of the cross-sectional refractive index structure of an optical fiber.

FIG. 6 is a schematic diagram of a stress profile of an optical fiber.

Description of reference numerals:

core layer blowtorch 1

Inner cladding blowtorch 2

Middle cladding blast lamp 3

Powder stick 7

Target bar 6

Boom 5

Deposition apparatus 10

Lifting mechanism 25

Boom 24

Middle furnace core tube 21

Heating body 22

Air inlet 23

Sintering apparatus 20

The following detailed description further illustrates embodiments of the invention in conjunction with the above-described figures.

Detailed Description

So that the manner in which the above recited objects, features and advantages of embodiments of the present invention can be understood in detail, a more particular description of the invention, briefly summarized above, may be had by reference to the embodiments thereof which are illustrated in the appended drawings. In addition, the features of the embodiments of the present application may be combined with each other without conflict.

In the following description, numerous specific details are set forth to provide a thorough understanding of embodiments of the invention, and the described embodiments are merely a subset of embodiments of the invention, rather than a complete embodiment. All other embodiments obtained by a person of ordinary skill in the art based on the embodiments of the present invention without any creative effort belong to the protection scope of the embodiments of the present invention.

"VAD" herein refers to axial vapor deposition, and is used throughout to refer to: VApor Axial position, VAD for short.

Herein, "OVD" refers to the outside vapor deposition method, which is generally known as: outside vapor Deposition, OVD for short.

Unless defined otherwise, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which embodiments of the present invention belong. The terminology used herein in the description of the invention is for the purpose of describing particular embodiments only and is not intended to be limiting of the embodiments of the invention.

The invention relates to a preparation method of an optical fiber, which is used for forming a low-loss and bending-resistant quartz optical fiber. It is known that the attenuation of a silica fiber at 600nm to 1600nm is mainly due to rayleigh scattering, and the attenuation α caused by rayleigh scattering can be calculated by the following formula:

wherein λ is the wavelength, R_EXPIs Rayleigh scattering coefficient (dB/km/mum)⁴)，α_IMAttenuation of absorption due to material defects, alpha_IRAttenuation for infrared absorption, alpha_OHHydroxyl absorption decay; when the Rayleigh scattering coefficient is confirmed, the material and structure are determined, alpha_IM+α_IR+α_OHAre the corresponding constants. Thus, only the Rayleigh scattering coefficient (R) is determined_EXP) Attenuation (α) due to rayleigh scattering can be obtained.

Emphasis on improving Rayleigh scattering coefficient (R) at preform production angle_EXP) The size of (2). For a fiber profile, the magnitude of this coefficient is related to the scattering coefficient of the core and the optical cladding.

In the above formula (2), Rcore is the rayleigh scattering coefficient of the core layer, Rclad is the rayleigh scattering coefficient of the cladding layer, and x (λ) is the percentage of the rayleigh scattering coefficient of the sum of the cladding layer and the core layer, since light is mainly transmitted in the core layer, the rayleigh scattering coefficient (R) is the rayleigh scattering coefficient_EXP) The contribution of (a) is mainly determined by the core layer (the ratio of Rcore may be larger). Rayleigh scattering is caused by density fluctuations on the one hand and concentration fluctuations on the other hand. From the density (R) of the glass itself_d) And concentration fluctuation (R) of doping_c) From the angle of view of (A), thus the Rayleigh scattering coefficient (R)_EXP) This can be expressed by the following formula.

R_EXP＝R_d+R_c……………………(3)

Wherein R is_dAnd R_cRespectively, the rayleigh scattering coefficient changes due to density fluctuations and concentration fluctuations. Wherein R is_cThe concentration fluctuation factor, which is mainly influenced by the doping concentration of the glass portion of the fiber, is theoretically the less germanium (Ge) and fluorine (F) or other doping, the smaller Rc, which is also the reason for achieving ultra-low attenuation performance with pure silicon core design.

R_Pure＝4.1×10^-4T_f……………………(4)

Rayleigh scattering coefficient (R) from pure silicon glass_pure) It can be seen that this coefficient is related only to the virtual temperature (T)_f) Is related to the size of the cell. Virtual temperature (T) of glass_f) Is a physical parameter characterizing the structure of the glass, defined as the temperature at which the structure of the glass is no longer adjusted to reach a certain equilibrium state after the glass is rapidly cooled from a certain temperature T to room temperature.

For lightly doped glasses, the rayleigh scattering coefficient (R) has been practically demonstrated_EXP) Also mainly by the density fluctuation factor (R)_d) And (6) determining.

The above formula (5) shows the density fluctuation factor (R)_d) Where n is the refractive index of the core layer relative to the quartz glass, ρ is the photoelastic coefficient, k is the material constant, β_TFor isothermal compressibility, the virtual temperature (T) is seen_f) The larger the density fluctuation factor (R)_d) And the smaller the attenuation (alpha). The refractive index (n) is generally several percent, and it is necessary to increase the refractive index (n) of the core layer by 1/n⁸Can become small, the density fluctuation factor (R)_d) And attenuation (alpha) are correspondingly reduced, but although germanium doping can effectively improve the refractive index of the core layer, the germanium doping can greatly contribute to concentration factors and cause negative influence on virtual temperature to offset beneficial effects. Therefore, in order to reduce the loss of the optical fiber, the most important process is to reduce the germanium doping amount of the core layer and reduce the virtual temperature of the glass on the premise of not reducing the refractive index of the core layer or even improving the refractive index of the core layer, thereby achieving the purpose of effectively reducing the Rayleigh scattering of the optical fiber.

Therefore, referring to fig. 1, the method for manufacturing an optical fiber according to the present invention includes the following steps:

step S1: and sequentially forming a core layer, an inner cladding layer and an intermediate cladding layer on the surface of the target rod, wherein the core layer is mainly composed of silicon dioxide, the core layer is doped with germanium and chlorine, and the inner cladding layer and the intermediate cladding layer are doped with fluorine.

In one embodiment, the reaction gas for forming the core layer includes oxygen, hydrogen, silicon tetrachloride, chlorine, germanium tetrachloride, and argon (Ar) gas, and these gases are respectively introduced at the same time, or each gas is provided with a separate pipeline and simultaneously leads to the same outlet. Wherein the flow rate of the germanium tetrachloride is controlled to be 50-200cc/min, and the flow rate of the chlorine gas is controlled to be 300-750 cc/min. This step SiCl₄At with O₂During the reaction, the proper reaction temperature is controlled to generate SiO₂In the reaction process, a macrocyclic Si-O-Cl structure is formed, and chlorine (Cl) is solidified in the powder, so that the chlorine (Cl) doping is realized. In order to ensure the total reflection of the optical fiber, the refractive index of the core layer is larger than that of the cladding layer; one is the core layer is doped with germanium to increase the relative refractive index of the core layer, and the other is the cladding layer is doped with fluorine to decrease the relative refractive index of the cladding layer; doping of germaniumThe impurity brings the improvement of the refractive index and simultaneously has obvious contribution to the concentration factor (Rc); the pure silicon is designed to ensure that the core layer and the inner cladding layer keep enough refractive index difference, a large amount of fluorine is needed to be doped, the viscosity is low, the viscosity of the pure silicon is not balanced with the viscosity of the high-viscosity core layer, and therefore the virtual temperature (T) is obtained_f) The rapid increase causes the density fluctuation factor (Rd) of the fiber to increase, which not only negates the benefits of the reduced concentration factor (Rc), but is more likely to cause reverse fiber attenuation anomalies. The doping of chlorine can realize the modification of glass materials similar to alkali metal ions, and can improve the refractive index of optical fibers, reduce the viscosity of the optical fibers and accelerate the structural relaxation of glass. It should be further noted that the concentration of the chloride ions does not contribute significantly to the concentration factor of the optical fiber, so that doping different from fluorine will cause a decrease in the refractive index of the core layer, and doping of chlorine can reduce the doping amount of germanium without affecting the refractive index, thereby effectively reducing the attenuation coefficient of the optical fiber.

In a specific embodiment, the reaction gas for forming the inner cladding comprises oxygen, hydrogen, silicon tetrachloride, fluoride and argon (Ar) gas, wherein the flow rate of the silicon tetrachloride is controlled to be 20g/min to 50g/min, the flow rate of the fluoride is controlled to be 50g/min to 400g/min, and the density of the fluorine-doped silicon dioxide powder generated by the reaction is controlled to be 0.5 g/cm to 1.5g/cm³The thickness of the inner cladding is 1.5-2.0 of the diameter of the core layer. Wherein the fluoride comprises SiF₄、CF₄、SF₆、 C₂F₆、SOF₂、C₂F₂Cl₂One or a combination of at least two of (1). In the step, the doping of fluorine (F) generates Si-F to replace high-tension Si-O bonds, so that the viscosity and the virtual temperature of the glass can be reduced. A certain amount of fluorine (F) is doped to form an inner cladding, which is beneficial to matching the viscosity of the germanium-doped core layer and the fluorine-doped middle cladding layer, and better realizes transition to form an integral structure.

In a specific embodiment, the reaction gas for forming the middle cladding layer comprises oxygen, hydrogen, silicon tetrachloride, fluoride and argon (Ar) gas, wherein the flow rate of the silicon tetrachloride is controlled to be 20g/min to 50g/min, the flow rate of the fluoride is controlled to be 50g/min to 900g/min, and the fluorine-doped dioxide generated by the reaction isThe density of the silicon powder is controlled to be 0.5-1.5 g/cm³The thickness of the middle cladding layer is 1.5-2.0 of the diameter of the core layer. Wherein the fluoride comprises SiF₄、CF₄、SF₆、C₂F₆、SOF₂、C₂F₂Cl₂One or a combination of at least two of (1). In the step, the fluorine (F) doping generates Si-F to replace a high-tension Si-O bond, so that the viscosity and the virtual temperature of the glass can be reduced, and the fluorine (F) doping can effectively reduce the refractive index of the middle cladding, thereby inhibiting the transmission energy loss of the optical fiber during bending, effectively reducing the macrobend loss, and improving the bending resistance of the final optical fiber.

In addition, in the VAD deposition process of the step S1, a proper amount of germanium (Ge) and chlorine (Cl) is introduced into the core layer, and fluoride is introduced into the intermediate coating layer, so that the doping process is formed in one step in the deposition process, the production cost is reduced, and large-scale batch production can be performed.

Step S2: and sequentially carrying out dehydroxylation, sintering, vitrification and annealing on the powder rod to form the glass rod with a preset section refractive index, wherein the annealing stage comprises a plurality of cooling sections and a plurality of constant temperature sections. The arrangement of atoms can be more uniform through multi-step annealing treatment, because the relaxation of the glass structure needs time, the multi-step annealing can enable the structure arrangement to be more sufficient and perfect, and finally the purpose of reducing Rayleigh scattering is achieved.

In one embodiment, the predetermined profile index of refraction is characterized as shown in FIG. 5:

a middle core layer with a radius of 4-6 μm and a refractive index of 0.25-0.35% relative to silicon dioxide;

the inner structure cladding and the middle structure cladding have the radius of 10-25 mu m, and the refractive index of the inner structure cladding and the middle structure cladding relative to silicon dioxide is-0.03 to-0.06 percent;

an outer cladding layer having a radius of 62.5 μm and a refractive index of 0 to 0.1%.

Referring to fig. 4, to obtain the glass rod with the predetermined profile refractive index characteristic, the specific parameters of step S2 are controlled as follows:

the temperature in the dehydroxylation stage is controlled to be 1000-1200 ℃ to 50 DEG CIntroducing Cl at the flow rate of 0 cc/min-1000 cc/min₂And introducing He at the flow rate of 10-30 l/min to form a reaction atmosphere. The chlorine gas is used for removing the hydroxyl and the water in the stage.

And in the sintering stage, the temperature of the dehydroxylation stage is taken as the initial temperature, the temperature is increased to 1300-1600 ℃ at the heating rate of 3-6 ℃/min, and He with the flow rate of 10-30 l/min is kept introduced to form a protective atmosphere.

And in the vitrification stage, keeping the temperature for 3-6 h at the end of the sintering stage, and keeping introducing He with the flow rate of 10-30 l/min to form a protective atmosphere.

An annealing stage comprising in order:

1) a first cooling section, wherein the temperature at the end of the vitrification stage is taken as the initial temperature, and the linear cooling is carried out to 50-75 ℃;

2) the first constant temperature section takes the temperature at the end of the first cooling section as the temperature of the first constant temperature section, the heat preservation time is 1-3 h, and N with the flow of 5-15 l/min is kept introduced during the heat preservation time₂Forming a protective atmosphere;

3) a second cooling section, wherein the temperature of the first constant temperature section is used as an initial temperature, and the linear cooling is carried out for 50-75 ℃;

4) a second constant temperature section, wherein the temperature at the end of the second cooling section is taken as the temperature of the second constant temperature section, the heat preservation time is 1-3 h, and N with the flow of 5-15 l/min is kept introduced during the heat preservation time₂Forming a protective atmosphere;

5) and in the third cooling section, the temperature of the second constant temperature section is taken as the initial temperature, and the temperature is reduced to the temperature of the dehydroxylation stage according to the speed of 1-3 ℃/min.

According to the invention, the powder rod is subjected to annealing treatment after sintering and vitrification, and due to the doping of fluorine (F) and chlorine (Cl), the relaxation time of rearrangement of the optical fiber glass structure can be reduced, the rearrangement of the structure is accelerated during the conventional subsequent annealing treatment, the virtual temperatures of the core layer, the inner cladding layer and the middle cladding layer are reduced, and the Rayleigh scattering caused by the fluctuation of density can be reduced, so that the attenuation of the optical fiber is further reduced.

Step S3: and forming an outer cladding layer on the surface layer of the glass rod by adopting an axial vapor deposition process or an external vapor deposition process, and then sintering to obtain the transparent optical fiber preform. The outer cladding is prepared by vapor deposition (VAD, OVD). And the vapor deposition process is to place the finished glass rod on an OVD machine for deposition, to finish the deposition after the target weight or rod diameter is reached, to sinter the glass rod, to prepare the powder rod into a transparent glass rod, to finish the low-loss bending-resistant optical fiber prefabricated rod. The production of the outer cladding may also be performed using a high purity quartz sleeve for the fusion.

Step S4: and drawing the optical fiber preform into filament, and treating the filament under the annealing and heat preservation conditions to obtain the optical fiber.

In one embodiment, the drawing speed is controlled between 2000m/min and 3000m/min, and the drawing tension is controlled between 100g and 200 g. And the length of the fibril under the annealing and heat preservation conditions in the wire drawing process is 2-4 m. Referring to fig. 6, in the steps S1-S2, fluorine (F) and chlorine (Cl) are doped to reduce viscosity during the core rod manufacturing process, while the outer cladding formed in the step S3 is not doped or is doped a small amount, so that the viscosity of the formed core rod is less than that of the outer cladding, and during the high-speed drawing process, residual compressive stress (negative value) is formed at the core rod portion corresponding to the optical fiber, and tensile stress (positive value) is formed at the outer cladding, thereby achieving the purpose of reducing attenuation. A section of 2m to 4m annealing heat preservation treatment is added at the bottom of the optical fiber drawing furnace, so that the optical fiber is ensured to have a section of annealing and cooling process, the core layer of the optical fiber can be ensured to form residual compressive stress after drawing, and meanwhile, the optical fiber is internally provided with lower virtual temperature, so that lower Rayleigh scattering is realized.

FIG. 2 is a schematic diagram of a powder rod deposition apparatus according to the present invention.

The powder rod deposition equipment 10 is VAD equipment and comprises a target rod 6, a deposition chamber 4, a middle cladding blast lamp 3, an inner cladding blast lamp 2, a core layer blast lamp 1, a suspender 5 and an upper deposition cavity; wherein the content of the first and second substances,

an upper deposition cavity is arranged at the upper part of the deposition chamber 4, a suspender 5 is arranged in the upper deposition cavity, the suspender 5 is provided with a hook, the suspender 5 is connected with a lifting mechanism, and a target rod 6 is hung on the hook of the suspender 5 connected with the lifting mechanism;

and a middle cladding blast lamp 3, an inner cladding blast lamp 2 and a core layer blast lamp 1 are sequentially arranged on one side of the lower part of the deposition chamber. The thickness and density of the inner cladding are controlled by controlling the flow of the silicon tetrachloride, the flow ratio of hydrogen and oxygen and the like of the inner cladding and the middle cladding blowtorch.

The procedure for depositing the powder rods using the apparatus shown in FIG. 2 is as follows:

firstly, introducing oxygen, hydrogen, silicon tetrachloride, germanium tetrachloride, chlorine and argon (Ar) gas into a core layer blast lamp 1, forming silicon dioxide and germanium dioxide through high-temperature reaction to be attached to the end face of a target rod to form a loose core layer with a certain density, and monitoring the temperature of deposition flame in the deposition process to improve the weight percentage of chlorine (Cl) in the core layer to be 5-45%; GeCl is introduced into the core layer blast lamp₄The flow rate is controlled to be 50-200cc/min, and Cl is introduced into the core layer₂The flow rate of (2) is controlled to be 300-750 cc/min;

then, a silicon dioxide layer with a certain thickness surrounding the surface of the core layer is used as an inner cladding, and oxygen, hydrogen, silicon tetrachloride, fluoride and argon (Ar) gas are introduced into the inner cladding blowtorch 2; the inner cladding is filled with SlCl₄The flow rate is controlled to be 20g/min to 50g/min, the flow rate of the fluoride is controlled to be 50cc/min to 400cc/min, and the powder density is controlled to be 0.5 g/cm to 1.5g/cm³The thickness of the powder is 1.5-2.0 of the rod diameter of the core layer;

and finally, a silicon dioxide layer with a certain thickness surrounding the surface of the inner cladding layer is used as a middle cladding layer, and oxygen, hydrogen, silicon tetrachloride, fluoride and argon (Ar) gas are introduced into the middle cladding layer blast lamp 3. Stopping deposition after the powder body is deposited to a set length; the middle cladding layer is introduced into SlCl₄The flow rate is controlled to be 20g/min to 50g/min, the flow rate of the fluoride is controlled to be 50cc/min to 900cc/min, and the powder density is controlled to be 0.5 g/cm to 1.5g/cm³The thickness of the powder is 1.5-2.0 of the rod diameter of the core layer.

FIG. 3 is a schematic view of a sintering apparatus for powder rods according to the present invention.

The sintering equipment 20 comprises a heating body 22, a suspender 24, a lifting mechanism 25 and a middle furnace core pipe 21 for accommodating the powder rod 7, wherein one end of the suspender 24 extends into the middle furnace core pipe through a conversion connector and is connected with the target rod 6, the other end of the suspender 24 is connected with the lifting mechanism 25, the suspender 24 suspends the powder rod 7 attached on the target rod 6 below the suspender, and is driven by the lifting mechanism 25 to rotate or lift; the heating body 22 is arranged outside the middle furnace core tube 21, and the heating area of the heating body radiatively covers the whole powder rod 7.

In a specific embodiment, the sintering apparatus 20 includes a central control device, and the central control device adjusts the temperature inside the middle furnace core tube and/or the gas flow introduced from the gas inlet in real time according to the detected parameters, so as to realize multi-stage sintering. The central control device can be used for manually adjusting and/or automatically adjusting the power of the heating body and/or the opening degree of the air valve of the air inlet.

In one embodiment, the heating body 22 is provided with four groups, and each group is symmetrically arranged at the opposite outer sides along the axis of the middle furnace core pipe 21; the four groups of heating bodies 22 are arranged side by side along the axis of the middle furnace core pipe. Specifically, the four groups of heating bodies can be respectively provided with temperature monitoring equipment, rod diameter monitoring equipment and transparency monitoring equipment, and the powder rods in the dehydroxylation and sintering processes are monitored so as to adjust the temperature and the gas flow in real time. The temperature monitoring equipment is used for detecting and feeding back the temperature in the middle furnace core pipe in real time; the transparency monitoring equipment is used for detecting transparency and feeding back a vitrification sintering process; the rod diameter monitoring equipment is used for detecting and feeding back the rod diameter of the powder rod in real time, and the rod diameter is measured by adopting a diameter measurement or circumference measurement mode; in other embodiments, each heating body may be connected to only one or any two monitoring devices, and not all configurations are required. Each group of heating bodies can also be a plurality of circumferentially and uniformly distributed or circumferential structures, and the heating bodies can be set according to actual needs.

The working principle is as follows: the suspension rod 24 suspends the powder rod 7 and can be driven to rotate; the central core tube 21 accommodates the powder rod 7 and provides a processing atmosphere from the gas inlet 23; the lifting mechanism 25 lowers the powder rod 7 to a preset position, the heating body 22 is electrified to work outside the middle furnace core pipe 21, and heating and heat preservation treatment are carried out according to a set process to finish the processes of dehydroxylation, sintering, vitrification and annealing.

The following examples illustrate the results of performance tests using the optical fiber preparation method of the present invention and the products obtained.

Powder rod deposition

1) Controlling the temperature of the flame of the core layer to be 850-950 ℃;

2) the core layer is filled with Cl₂The amount of (b) is set between 400 cc/min;

3) GeCl introduced into core layer₄The flow rate of (2) is controlled at 100 cc/min;

4) the inner cladding is introduced into CF₄The flow rate of (2) was set at 200cc/min, and SlCl was introduced₄The flow rate is controlled to be 25 g/min;

5) the middle cladding layer is introduced into CF₄The flow rate of (2) was set at 800cc/min, and SlCl was introduced₄The flow rate is controlled at 45 g/min;

6) according to the flow setting, the section refractive index (Delta 1) of the formed intermediate core layer is between 0.332 and 0.337 percent, and the relative refractive index (Delta 2) of the formed inner structure cladding layer and the intermediate structure cladding layer is between-0.03 and-0.04 percent; the inner and middle cladding layers may achieve a consistent relative refractive index by diffusion of fluorine (F) (see fig. 5). In other embodiments, the relative refractive indices of the inner and middle structural cladding layers may not be equal.

Secondly, sintering the core rod

Dehydroxylating the four sections of heating bodies according to a preset temperature curve, setting the dehydroxylation temperature T11080 ℃ in the first stage, and introducing 700cc/min Cl from the bottom of a middle furnace core pipe₂Introducing 15L/min He;

in the second stage, after the dehydroxylation is finished, the temperature is increased to T21450 ℃ according to the heating rate of 4 ℃/min, and 15L/min He is kept introduced;

the third stage, keeping the temperature at T21450 ℃ for 3.5h, sintering the powder rod into a transparent glass rod, and keeping introducing 15L/min He;

the fourth stage, the temperature is reduced by 50 ℃ on the basis of the temperature T2 to reach the temperature T3, the temperature is kept for 3 hours, and N of 10L/min is introduced₂；

The fifth stage, cooling to 70 deg.C to T4 deg.C based on T3 temperature, maintaining the temperature for 2h, introducing 10L/min N₂；

The sixth stage, the temperature is reduced to T1 according to the speed of 2 ℃/min on the basis of the temperature of T4, and N of 10L/min is introduced₂；

Thirdly, outer cladding:

adopting OVD deposition process, extending the sintered core rod to 50mm diameter and 1800mm length, performing OVD deposition, and introducing chlorine (Cl) after the deposition is finished₂) And (4) dehydroxylating and sintering to finally form the low-loss bending-resistant optical fiber preform. The relative refractive index (Delta 3) of the obtained outer cladding is 0-0.1%.

Fourthly, drawing wires:

1) the speed of wire drawing is controlled between 2000m/min and 2100 m/min;

2) controlling the tension of the drawn wire to be 140-160 g;

3) controlling the length of the fibril to be 3.5m in the heat-preservation annealing treatment;

the preset fiber profile parameters are shown in table 1 below.

TABLE 1

Where r2 includes a core layer, an inner cladding layer, and an intermediate cladding layer, where the inner cladding layer and the intermediate cladding layer have the same refractive index. In other examples, the inner cladding and the middle cladding may not have the same refractive index, and the outer cladding may be pure quartz, as shown in FIG. 5, with a refractive index of 0.

Optical fiber test performance parameters:

TABLE 2

TABLE 3

TABLE 4

TABLE 5

TABLE 6

TABLE 7

The zero dispersion value is: 1302 nm-1324 nm

TABLE 8

Optical cable cut-off wavelength: less than or equal to 1260nm

TABLE 9

As can be seen from the table above, the 1550nm attenuation of the optical fiber is lower than 0.180dB/km, the cable wavelength is lower than 1260nm, the 20mm macrobending loss at 1550nm is less than 0.5 dB/turn, and the performances of the attenuation, macrobending loss and the like are obviously superior to those of the conventional product.

In conclusion, the preparation method of the optical fiber is simple to operate, the manufacturing cost is reduced, and the prepared optical fiber has the characteristics of low loss and bending resistance and meets the requirements of optical communication development. Compared with the prior art, the method has the following beneficial effects:

1. the profile structure is established in the VAD deposition process, repeated fluorine doping through multiple steps is not needed, the production cost is reduced, and the large-scale production is facilitated;

2. the refractive index is increased by introducing a proper amount of germanium into the core layer instead of only increasing the content of chlorine (Cl), so that the difficulty in designing the section is reduced;

3. the virtual temperature and the viscosity of the core layer are well adjusted when the prefabricated rod is manufactured, the adjustment of a wire drawing furnace and a wire drawing process is not needed when the wire drawing is carried out, the adaptability of the prefabricated rod to wire drawing conditions is improved, and the requirement on the wire drawing conditions is reduced.

Although the embodiments of the present invention have been described in detail with reference to the preferred embodiments, it should be understood by those skilled in the art that various changes may be made and equivalents may be substituted without departing from the spirit and scope of the embodiments of the present invention.