WO2020177352A1

WO2020177352A1 - Optical fiber preform based on continuous fused quartz bushing, and manufacturing method therefor

Info

Publication number: WO2020177352A1
Application number: PCT/CN2019/114350
Authority: WO
Inventors: 莫思铭; 李凡; 眭立洪; 张国栋; 周莉; 李想
Original assignee: 江苏永鼎光纤科技有限公司
Priority date: 2019-03-01
Filing date: 2019-10-30
Publication date: 2020-09-10
Also published as: CN110028235A; CN110028235B

Abstract

Provided are an optical fiber preform based on a continuous fused quartz bushing, and a manufacturing method therefor. The manufacturing method comprises: preparing an optical fiber core rod with a core layer and an inner cladding layer from inside to outside by using a VAD process; depositing a barrier layer loose body containing a Sb2O3-F mixture on the outer portion of the optical fiber core rod by using an OVD process, and then performing a sintering treatment to obtain a synthetic core rod; and combining the synthetic core rod and a continuous fused quartz bushing by using an RIC process to obtain the optical fiber preform. The diameter of the preform can reach 211 mm, the drawing length of a single preform can reach 2920 km, the attenuation of a drawn optical fiber at 1310 nm is as low as 0.271 dB/km, the attenuation coefficient at 1383 nm is as low as 0.245 dB/km, the attenuation coefficient at 1550 nm is as low as 0.145 dB/km, the mode field diameter at 1310 nm is 8.1 μm to 9.2 μm, and the optical cable cut-off wavelength is 1251 nm to 1271 nm.

Description

Optical fiber preform based on continuous fused silica sleeve and manufacturing method thereof

Technical field

The invention relates to an optical fiber preform based on a continuous fused silica sleeve and a manufacturing method thereof, belonging to the field of optical fiber preform manufacturing.

Background technique

At present, the process of producing optical fiber preforms mainly adopts a two-step method, that is, first manufacturing the preform core rod, and then manufacturing the cladding outside the core rod. There are four main core rod manufacturing technologies: improved chemical vapor deposition (MCVD), microwave plasma chemical vapor deposition (PCVD), external vapor deposition (OVD) and axial vapor deposition (VAD), outsourcing Layer manufacturing technology mainly includes OVD method, sleeve method, and plasma spraying method. Among them, the sleeve method is to insert a core rod into a quartz sleeve to form an optical fiber preform, which is currently a better method for manufacturing large-size optical fiber preforms.

Quartz sleeves are made of natural crystalline quartz or synthetic silane by high temperature melting. Quartz sleeves are classified according to process method, use and appearance, including continuous fused quartz sleeves, fused transparent quartz sleeves, and gas refining transparent quartz sleeves , Synthetic quartz sleeves, opaque quartz sleeves, optical quartz sleeves, quartz sleeves for semiconductors, quartz sleeves for electric light sources, etc., among which continuous fused quartz sleeves are prepared by continuous melting method, and the continuous melting method is simple. One-time input of quartz sand to draw the tube directly has a great cost advantage. However, the metal impurity content of the continuous fused silica tube is high, and the hydroxyl content is difficult to control. Using it as the outer covering of the optical fiber preform will increase the loss of the optical fiber and make it It is difficult to apply to the production of optical fiber preforms.

Summary of the invention

The technical problem to be solved by the present invention is: in order to solve the technical problem that using continuous fused silica tube as the outer layer of the optical fiber preform will increase the loss of optical fiber, an optical fiber preform based on continuous fused silica tube and a manufacturing method thereof are provided .

The technical solutions adopted by the present invention to solve its technical problems are:

A manufacturing method of optical fiber preform based on continuous fused silica sleeve, the steps are as follows:

Use the VAD process to prepare fiber core rods with core and inner cladding from the inside to the outside;

The OVD process is used to deposit the loose body of the outer covering containing the Sb ₂ O ₃ -F mixture on the outside of the optical fiber core rod, and then the sintering process is carried out in the sintering furnace to obtain the composite core rod; the sintering treatment method is: passing into the sintering furnace Enter inert gas and chlorine gas, first raise the sintering furnace to 600-800℃ at a heating rate of 50-60℃/min, keep it for 1-2h, and then raise it to 1000-1200℃ at a heating rate of 30-40℃/min. Keep the temperature for 2-4 hours, and finally increase the temperature to 1300-1500°C at a rate of 10-20°C/min, and keep it for 5-7 hours;

Using the RIC process, the synthetic core rod and the continuous fused silica sleeve are combined into an optical fiber preform.

Preferably, the sintered synthetic mandrel is heat-treated. The heat treatment method is: cooling the synthetic mandrel held at 1300-1500°C for 5-7h to a temperature of <100°C within 2 minutes, and then heat the cooled synthetic mandrel The mandrel is heated to 700-1000°C for 2 to 3 hours, and finally the synthetic mandrel is cooled to 300-500°C for 3 to 5 hours.

Preferably, the steps of using the VAD process to prepare the optical fiber core rod are: first deposit the powder core rod by the axial vapor deposition method; then perform the dehydroxylation treatment, fluorine doping treatment and vitrification treatment on the powder core rod in the sintering furnace: During the hydroxyl treatment, pass Cl ₂ gas and inert gas into the sintering furnace, and the dehydroxylation temperature is 800～1000℃; during the fluorine doping treatment, pass fluorine-containing gas and inert gas into the sintering furnace, and the temperature of the sintering furnace is 1000 ～1300℃; During the vitrification process, only inert gas is introduced into the sintering furnace, and the glass transition temperature is 1400～1600℃.

Preferably, the RIC process steps are: corroding the surface of the synthetic mandrel with a mixed acid of hydrofluoric acid and nitric acid with a molar ratio of 1:0.5-1.5, the corrosion depth is not less than 0.6mm, and then cleaning the corroded synthetic mandrel After drying, insert the synthetic mandrel into the continuous fused silica sleeve to form an optical fiber preform.

Preferably, the core layer is a silica glass layer doped with P ₂ O ₅ or B ₂ O ₃ , and the relative refractive index Δn ₁ of the core layer is 0.3% to 0.4%; the inner cladding layer is doped with GeO ₂ For the silica glass layer of the -F mixture, the relative refractive index Δn ₂ of the inner cladding layer is -0.05% to -0.01%, and the ratio b/a of the fiber core rod diameter b to the core layer diameter a is 3 to 5.

Preferably, the relative refractive index Δn ₃ of the outer cladding layer is -0.25% to -0.1%, and the ratio c/a of the diameter c of the synthetic core rod to the diameter a of the core layer is 7-9.

Preferably, the synthetic mandrel is fixed in the center of the continuous fused silica sleeve in the RIC process, and the gap between the synthetic mandrel and the continuous fused silica sleeve is controlled to be less than 3 mm, and the effective diameter d of the optical fiber preform is equal to the diameter of the synthetic mandrel. The ratio d/c of c is 2～3.

Preferably, the metal impurity content in the continuous fused quartz sleeve is less than 20 ppm, and the hydroxyl content is less than 6 ppm.

The present invention also provides an optical fiber preform manufactured by the above method.

The present invention also provides a single-mode optical fiber, which is formed by directly drawing the above-mentioned optical fiber preform, or formed by drawing after drawing.

In addition, in order to clearly illustrate the technical solutions of the present invention, the definitions and descriptions of the terms involved in the present invention are as follows:

OVD process: Use external vapor deposition and sintering process to prepare the required thickness of quartz glass.

VAD process: Use axial vapor deposition and sintering process to prepare quartz glass of required thickness.

RIC process: The synthetic mandrel and sleeve are processed, including tapering, extension, corrosion, cleaning, and drying, and then the synthetic mandrel is inserted into the sleeve to form a large-size optical fiber preform.

Continuous fused quartz casing: a casing made of natural quartz sand using continuous melting process.

The relative refractive index Δn _{1 of the} core layer is defined by the following equation:

Among them, n ₁ is the absolute refractive index of the core layer, and n _c is the absolute refractive index of pure silica glass.

The relative refractive index of the inner cladding Δn ₂ is defined by the following equation:

Among them, n ₂ is the absolute refractive index of the inner cladding, and n _c is the absolute refractive index of pure silica glass.

The relative refractive index Δn _{3 of the} outer cladding is defined by the following equation:

Among them, n ₃ is the absolute refractive index of the cladding, and n _c is the absolute refractive index of pure silica glass.

The effective diameter of the optical fiber preform is the outer diameter of the solid preform, and for the RIC preform,

The CSA is the cross-sectional area;

The gap between the synthetic mandrel and the sleeve: the unilateral distance between the synthetic mandrel and the sleeve, that is, Gap=[inner diameter of the sleeve (ID)-outer diameter of the synthetic mandrel (c)]/2.

Bow degree: When the bar rotates one circle around the central axis, the maximum value of the position of the bar center deviated from the rotation axis per unit length.

Core/clad concentricity error: the distance between the center of the core layer of the fiber and the center of the fiber.

The beneficial effects of the present invention are:

The present invention uses the VAD process to prepare an optical fiber core rod including a core layer and an inner cladding layer, and then prepares an outer cladding layer containing Sb ₂ O ₃ -F through the OVD process, and finally prepares a large-size and low-loss optical fiber preform through the RIC process, wherein: After the sintering process, the reasonable outer cover layer deposited by the OVD process is further subjected to a heat treatment process, so that the barrier layer has a reasonable material composition and structure, which can effectively prevent the metal impurities and hydroxyl groups in the fused quartz sleeve from diffusing to the core layer, effectively reducing The loss of the drawn fiber is reduced, and the diameter of the synthetic mandrel prepared by the OVD process is uniform, which can accurately control the gap between the sleeve and the synthetic mandrel in the RIC process and reduce the concentricity error of the fiber core/cladding; the powder mandrel is prepared by the VAD method, Then through reasonable dehydroxylation, fluorine doping and vitrification process, not only can effectively remove the hydroxyl group, the fluorine doping process can also optimize the viscosity matching of the core and cladding, thereby reducing the Rayleigh scattering and loss of the drawn fiber; The fused silica tube is used as the outer coating material of the optical fiber preform, and large-size optical fiber preform can be obtained. Finally, the diameter of the optical fiber preform prepared by the present invention can reach 211mm, the drawing length of a single preform can reach 2920km, the attenuation of the prepared optical fiber at 1310nm wavelength is as low as 0.271dB/km, and the attenuation coefficient at 1383nm wavelength is as low as 0.245dB/km, the attenuation coefficient at 1550nm wavelength is as low as 0.145dB/km, the optical fiber prepared from the optical fiber preform has a mode field diameter of 8.1～9.2μm at 1310nm wavelength, and the cut-off wavelength of the optical fiber is 1251nm～1271nm .

detailed description

The present invention will now be described in further detail.

Example 1

The powder core rod is prepared by the axial vapor deposition method (VAD method), and then the powder core rod is subjected to dehydroxylation treatment, fluorine doping treatment and vitrification treatment in the sintering furnace: during the dehydroxylation treatment, pass Cl into the sintering furnace ₂ gas and He gas, Cl ₂ gas flow rate is 1000mL/min, He gas flow rate is 20L/min, and dehydroxylation temperature is 800°C; during fluorine doping treatment, SiF ₄ gas and He gas, SiF ₄ gas and The flow ratio of He gas is 4:1, in which the He gas flow rate is 30L/min, and the sintering furnace temperature is 1000°C; during vitrification, only He gas is introduced into the sintering furnace, and the He gas flow rate is 40L/min, vitrification The temperature is 1400℃;

After testing, the fiber core rod has a core-cladding ratio b/a of 3, the core layer is a silica glass layer doped with P ₂ O ₅ , and the relative refractive index difference Δn ₁ of the core layer is 0.3%; The layer is a silica glass layer doped with GeO ₂ -F mixture, and the relative refractive index Δn ₂ of the inner cladding layer is -0.05%.

The OVD process is used to deposit the outer covering containing the Sb ₂ O ₃ -F mixture on the outside of the optical fiber core rod, and then perform sintering treatment to obtain a synthetic core rod; the sintering treatment method is: inert gas and chlorine gas are passed into the sintering furnace, Cl _{2 The} gas flow rate is 800mL/min and the He gas flow rate is 40L/min. First, the sintering furnace is raised to 600°C at a heating rate of 50°C/min, kept for 2 hours, and then raised to 1000°C at a heating rate of 30°C/min. Keep the temperature for 4 hours, and finally increase it to 1300°C at a heating rate of 10°C/min, and keep it for 7 hours;

After testing, the ratio c/a of the diameter c of the synthetic core rod to the diameter a of the core layer is 7 and the relative refractive index Δn ₃ of the outer cladding layer is -0.25%;

Use the RIC process to combine the synthetic core rod and the continuous fused silica sleeve into an optical fiber preform, specifically: the surface of the synthetic core rod is corroded with a mixed acid of hydrofluoric acid and nitric acid with a molar ratio of 1:0.5, and the corrosion depth is not less than 0.6mm, then clean and dry the corroded synthetic mandrel, insert the synthetic mandrel into the continuous fused quartz sleeve, and fix the synthetic mandrel in the center of the continuous fused quartz sleeve to control the synthetic mandrel and continuous fused quartz sleeve The gap between them is less than 3mm, and the fiber preform is combined into an optical fiber preform. The diameter of the optical fiber preform reaches 201mm. The ratio d/c of the effective diameter d of the optical fiber preform to the composite core rod diameter c is 2, and the prepared optical fiber preform is drawn online To make low-loss optical fiber, the length of a single rod can reach 2850km. Among them, the metal impurity content of the fused silica sleeve is shown in Table 1, and the performance parameters of the optical fiber are shown in Table 2.

Table 1 Impurity content distribution of continuous fused silica casing

Table 2 Optical fiber parameters after drawing the preform

Example 2

The powder core rod is prepared by the axial vapor deposition method (VAD method), and then the powder core rod is subjected to dehydroxylation treatment, fluorine doping treatment and vitrification treatment in the sintering furnace: during the dehydroxylation treatment, pass Cl into the sintering furnace ₂ gas and He gas, Cl ₂ gas flow rate is 1000mL/min, He gas flow rate is 20L/min, and dehydroxylation temperature is 1000°C; during fluorine doping treatment, SiF ₄ gas and He gas, SiF ₄ gas and The flow ratio of He gas is 3:1, among which the He gas flow is 30L/min, and the sintering furnace temperature is 1300℃; during vitrification, only He gas is introduced into the sintering furnace, and the He gas flow is 40L/min, vitrification The temperature is 1600℃;

After testing, the fiber core rod has a core-wrap ratio b/a of 5, the core layer is a silica glass layer doped with B ₂ O ₃ , and the relative refractive index difference Δn ₁ of the core layer is 0.4%; The layer is a silica glass layer doped with GeO ₂ -F mixture, and the relative refractive index Δn ₂ of the inner cladding layer is -0.01%.

The OVD process is used to deposit the outer covering containing the Sb ₂ O ₃ -F mixture on the outside of the optical fiber core rod, and then perform sintering treatment to obtain a synthetic core rod; the sintering treatment method is: inert gas and chlorine gas are passed into the sintering furnace, Cl _{2 The} gas flow rate is 800mL/min and the He gas flow rate is 40L/min. First, the sintering furnace is raised to 800°C at a heating rate of 60°C/min, kept for 1 hour, and then raised to 1200°C at a heating rate of 40°C/min. Insulate for 2h, and finally rise to 1500℃ at a heating rate of 20℃/min for 5h;

After testing, the ratio c/a of the diameter c of the synthetic core rod to the diameter a of the core layer is 9 and the relative refractive index Δn ₃ of the outer cladding layer is -0.1%;

Use the RIC process to combine the synthetic mandrel and the continuous fused silica sleeve into an optical fiber preform, specifically: the surface of the synthetic mandrel is corroded with a mixed acid of hydrofluoric acid and nitric acid with a molar ratio of 1:1.5, and the corrosion depth is not less than 0.6mm, then clean and dry the corroded synthetic mandrel, insert the synthetic mandrel into the continuous fused quartz sleeve, and fix the synthetic mandrel in the center of the continuous fused quartz sleeve to control the synthetic mandrel and continuous fused quartz sleeve The gap between them is less than 3mm, and the fiber preform is combined into an optical fiber preform. The diameter of the optical fiber preform reaches 211mm. The ratio d/c of the effective diameter d of the optical fiber preform to the composite core rod diameter c is 3, and the prepared optical fiber preform is drawn online For low-loss optical fiber, the length of a single rod can reach 2920km; among them, the metal impurity content of the fused silica sleeve is shown in Table 3, and the performance parameters of the optical fiber are shown in Table 4.

Table 3 Impurity content distribution of continuous fused silica casing

Table 4 Optical fiber parameters after preform drawing

Example 3

The powder core rod is prepared by the axial vapor deposition method (VAD method), and then the powder core rod is subjected to dehydroxylation treatment, fluorine doping treatment and vitrification treatment in the sintering furnace: during the dehydroxylation treatment, pass Cl into the sintering furnace ₂ gas and He gas, Cl ₂ gas flow rate is 1000mL/min, He gas flow rate is 20L/min, and dehydroxylation temperature is 900°C; during fluorine doping treatment, SiF ₄ gas and He gas, SiF ₄ gas and The flow ratio of He gas is 4:1, in which the He gas flow rate is 30L/min, and the sintering furnace temperature is 1200°C; during vitrification, only He gas is introduced into the sintering furnace, and the He gas flow rate is 40L/min. The temperature is 1500℃;

After testing, the core-packing ratio b/a of the fiber core rod is 4.5, the core layer is a silica glass layer doped with B ₂ O ₃ , and the relative refractive index difference Δn ₁ of the core layer is 0.35%; The layer is a silica glass layer doped with GeO ₂ -F mixture, and the relative refractive index Δn ₂ of the inner cladding layer is -0.03%.

The OVD process is used to deposit the outer covering containing the Sb ₂ O ₃ -F mixture on the outside of the optical fiber core rod, and then perform sintering treatment to obtain a synthetic core rod; the sintering treatment method is: inert gas and chlorine gas are passed into the sintering furnace, Cl _{2 The} gas flow rate is 800mL/min, and the He gas flow rate is 40L/min. First, the sintering furnace is raised to 700°C at a heating rate of 55°C/min, kept for 1.5h, and then raised to 1100°C at a heating rate of 35°C/min ，Hold for 3h, finally raise to 1400℃ at a heating rate of 15℃/min, keep for 6h;

After testing, the ratio c/a of the diameter c of the synthetic core rod to the diameter a of the core layer is 8, and the relative refractive index Δn ₃ of the outer cladding layer is -0.15%;

Use the RIC process to combine the synthetic mandrel and the continuous fused silica sleeve into an optical fiber preform. Specifically, the surface of the synthetic mandrel is corroded with a mixed acid of hydrofluoric acid and nitric acid at a molar ratio of 1:1, and the corrosion depth is not less than 0.6mm, then clean and dry the corroded synthetic mandrel, insert the synthetic mandrel into the continuous fused quartz sleeve, and fix the synthetic mandrel in the center of the continuous fused quartz sleeve to control the synthetic mandrel and continuous fused quartz sleeve The gap between them is less than 3mm, and the optical fiber preform is combined into an optical fiber preform. The diameter of the optical fiber preform reaches 205mm, and the ratio d/c of the effective diameter d of the optical fiber preform to the composite core rod diameter c is 2.5. The prepared optical fiber preform is drawn online For low-loss optical fiber, the length of a single rod can reach 2895km; among them, the metal impurity content of the fused silica sleeve is shown in Table 5, and the performance parameters of the optical fiber are shown in Table 6.

Table 5 Impurity content distribution of continuous fused silica casing

Table 6 Optical fiber parameters after drawing the preform

Example 4

The only difference between Example 4 and Example 3 is that the sintered synthetic mandrel is heat-treated. The heat treatment method is: the synthetic mandrel that has been kept at 1400°C for 6 hours is cooled to a temperature of <100°C within 2 minutes, and then The cooled synthetic mandrel was heated to 700°C for 3 hours, and finally the synthetic mandrel was cooled to 300°C and held for 5 hours. Finally, the diameter of the obtained optical fiber preform reached 208mm. The prepared optical fiber preform was drawn into low-loss optical fiber online. The length of the rod can reach 2905km. The performance parameters of the optical fiber are shown in Table 7.

Table 7 Performance parameters of the optical fiber after drawing the preform

Example 5

The difference between Example 5 and Example 3 is that the sintered synthetic mandrel is heat-treated. The heat treatment method is: the synthetic mandrel that has been kept at 1400°C for 6 hours is cooled to a temperature of <100°C within 2 minutes, and then The cooled synthetic mandrel was heated to 1000°C for 2h, and finally the synthetic mandrel was cooled to 500°C and held for 3h. Finally, the diameter of the obtained optical fiber preform reached 210mm. The prepared optical fiber preform was drawn into low-loss optical fiber online. The length of the rod can reach 2913km, and the performance parameters of the optical fiber are shown in Table 8.

Table 8 Performance parameters of optical fiber after preform drawing

Taking the above-mentioned ideal embodiment according to the present invention as enlightenment, through the above-mentioned description content, relevant workers can make various changes and modifications without departing from the scope of the technical idea of the present invention. The technical scope of the present invention is not limited to the content of the description, and its technical scope must be determined according to the scope of the claims.

Claims

A method for manufacturing an optical fiber preform based on a continuous fused silica sleeve is characterized in that the steps are as follows:

Use the VAD process to prepare fiber core rods with core and inner cladding from the inside to the outside;

The OVD process is used to deposit the loose body of the outer covering containing the Sb 2 O 3 -F mixture on the outside of the optical fiber core rod, and then the sintering process is carried out in the sintering furnace to obtain the composite core rod; the sintering treatment method is: passing into the sintering furnace Enter inert gas and chlorine gas, first raise the sintering furnace to 600-800℃ at a heating rate of 50-60℃/min, keep it for 1-2h, and then raise it to 1000-1200℃ at a heating rate of 30-40℃/min. Keep the temperature for 2-4 hours, and finally increase the temperature to 1300-1500°C at a rate of 10-20°C/min, and keep it for 5-7 hours;

Using the RIC process, the synthetic core rod and the continuous fused silica sleeve are combined into an optical fiber preform.
The method for manufacturing an optical fiber preform based on a continuous fused silica sleeve according to claim 1, wherein the sintered synthetic core rod is heat treated, and the heat treatment method is: heat preservation at 1300-1500°C. The synthetic mandrel after 7h is cooled to a temperature of <100℃ within 2min, then the cooled synthetic mandrel is heated to 700～1000℃ for 2～3h, and finally the synthetic mandrel is cooled to 300～500℃ and kept for 3～5h .
The method for manufacturing an optical fiber preform based on a continuous fused silica sleeve according to claim 1 or 2, wherein the step of preparing the optical fiber core rod by the VAD process is: first depositing the powder core rod by the axial vapor deposition method; Then in the sintering furnace, the powder core rod is subjected to dehydroxylation treatment, fluorine doping treatment and vitrification treatment: during the dehydroxylation treatment, Cl 2 gas and inert gas are introduced into the sintering furnace, and the dehydroxylation temperature is 800-1000℃; During fluorine doping treatment, fluorine-containing gas and inert gas are introduced into the sintering furnace, and the temperature of the sintering furnace is 1000～1300℃; during vitrification, only inert gas is introduced into the sintering furnace, and the glass transition temperature is 1400～1600 ℃.
The method for manufacturing an optical fiber preform based on a continuous fused silica sleeve according to any one of claims 1 to 3, wherein the RIC process step is: using the surface of the synthetic core rod with a molar ratio of 1:0.5-1.5 The mixed acid of hydrofluoric acid and nitric acid is corroded, the corrosion depth is not less than 0.6mm, then the corroded synthetic mandrel is cleaned and dried, and the synthetic mandrel is inserted into the continuous fused silica sleeve to form an optical fiber preform.
The method for manufacturing an optical fiber preform based on a continuous fused silica sleeve according to any one of claims 1 to 4, wherein the core layer is silica doped with P 2 O 5 or B 2 O 3 For the glass layer, the relative refractive index Δn 1 of the core layer is 0.3% to 0.4%; the inner cladding layer is a silica glass layer doped with GeO 2 -F mixture, and the relative refractive index Δn 2 of the inner cladding layer is -0.05% to -0.01%, the ratio b/a of the fiber core rod diameter b to the core layer diameter a is 3 to 5.
The method for manufacturing an optical fiber preform based on a continuous fused silica tube according to any one of claims 1-5, wherein the relative refractive index Δn 3 of the outer cladding layer is -0.25% to -0.1%, and the composite The ratio c/a of the core rod diameter c to the core layer diameter a is 7-9.
The method for manufacturing an optical fiber preform based on a continuous fused silica tube according to any one of claims 1-6, wherein the synthetic core rod is fixed at the center of the continuous fused silica tube in the RIC process, and the composite core rod is controlled The gap between the fused silica sleeve and the continuous fused silica sleeve is less than 3 mm, and the ratio d/c of the effective diameter d of the optical fiber preform to the diameter c of the composite core rod is 2 to 3.
The method for manufacturing an optical fiber preform based on a continuous fused silica sleeve according to any one of claims 1 to 5, wherein the metal impurity content in the continuous fused silica sleeve is less than 20 ppm, and the hydroxyl content is less than 6 ppm.
An optical fiber preform manufactured by the method of any one of claims 1-8.
A single-mode optical fiber, characterized in that the optical fiber is formed by directly drawing the optical fiber preform according to claim 9, or drawing after drawing.