WO2020181791A1

WO2020181791A1 - Large-size low-attenuation optical fiber preform and preparation method therefor

Info

Publication number: WO2020181791A1
Application number: PCT/CN2019/114407
Authority: WO
Inventors: 莫思铭; 李凡; 眭立洪; 张国栋; 周莉; 李想
Original assignee: 江苏永鼎股份有限公司
Priority date: 2019-03-11
Filing date: 2019-10-30
Publication date: 2020-09-17
Also published as: CN109970335A; CN109970335B

Abstract

Disclosed are a large-size low-attenuation optical fiber preform and a preparation method therefor. The method comprises: preparing a preform core rod comprising an inner core layer, an outer core layer, an inner cladding layer, and a depressed layer by using an MCVD process, then depositing a first outer cladding loose body by means of a VAD process and preparing a primary optical fiber preform by means of primary sintering treatment, and finally depositing a second outer cladding loose body by means of an OVD process and obtaining an optical fiber preform by means of secondary sintering treatment. The diameter of the prepared optical fiber preform may be up to 215 mm, the fiber pulling length of a single preform may be up to 2930 km, the attenuation coefficient of an optical fiber at a wavelength of 1310 nm is as low as 0.298 dB/km, the attenuation coefficient of the optical fiber at a wavelength of 1383 nm is as low as 0.265 dB/km, the attenuation coefficient of the optical fiber at a wavelength of 1550 nm is as low as 0.165 dB/km, and the cutoff wavelength of the optical fiber is from 1265 nm to 1273 nm.

Description

Large-size and low-attenuation optical fiber preform and preparation method thereof

This application claims the priority of the invention patent application with the application number 201910181908.X filed with the State Intellectual Property Office of China on March 11, 2019. The content of the priority text is expressly incorporated into this application by reference.

Technical field

The present application belongs to the technical field of optical fiber preform manufacturing, and in particular relates to a large-size low attenuation optical fiber preform and a preparation method thereof.

Background technique

Optical fiber preform is the upstream product of optical fiber, which determines the performance and type of optical fiber. At the same time, optical fiber preform is also the most profitable part of the entire product chain of optical fiber and cable. For a long time, the manufacturing technology of optical fiber preform has been monopolized by foreign companies. Preforms rely heavily on imports, which hinders the development of my country's optical communication network.

Optical fiber attenuation is an important indicator of optical fiber transmission, which has a decisive impact on the transmission distance of optical fiber communication. The level of optical fiber attenuation directly affects the transmission distance or the distance between relay stations. Therefore, reducing optical fiber attenuation has great practical significance for optical fiber communication. At the same time, the large-size optical fiber preform can be drawn for thousands of kilometers, which greatly improves the production efficiency and becomes an effective method to reduce the cost of optical fiber. At present, major optical fiber manufacturers are conducting research on the manufacturing technology of large-size and low-attenuation optical fiber preforms in order to gain greater initiative in the fierce market competition.

Generally, the technology for manufacturing optical fiber preforms is to first manufacture the preform core rod, and then manufacture the cladding outside the core rod. There are four main core rod manufacturing technologies: improved chemical vapor deposition (MCVD), microwave plasma chemistry Vapor phase deposition (PCVD), external vapor deposition (OVD) and axial vapor deposition (VAD), the outer coating manufacturing technology mainly includes OVD method, sleeve method, plasma spraying method; because the above methods are used in the production of optical fiber preforms Each of the above has advantages and disadvantages. The existing manufacturing of optical fiber preforms is a combination of the above two or more methods in order to obtain large-size and low-attenuation optical fiber preforms. However, the current optical fiber attenuation prepared by large-size optical fiber preforms is difficult to effectively control.

Summary of the invention

The technical problem to be solved by the present invention is to solve the technical problem that the hydroxyl content in the large-sized optical fiber preform is difficult to be effectively controlled in the prior art, thereby providing a large-sized low-attenuation optical fiber preform and a preparation method thereof.

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

A method for preparing a large-size and low-attenuation optical fiber preform includes the following steps:

The inner cladding layer, the outer core layer and the inner core layer are sequentially deposited on the inner wall of the quartz tube as the depressed layer using the MCVD process to obtain a deposition tube, and the deposition tube is fused at high temperature to have an inner core layer, an outer core layer, an inner cladding layer and Preformed rod mandrel of the sunken layer;

Use the VAD process to deposit the first cladding loose body on the preform core rod, and pass the first sintering treatment to prepare the primary optical fiber preform;

Use the OVD process to deposit the loose body of the second outer cladding layer on the primary optical fiber preform, and pass the second sintering treatment to prepare the optical fiber preform;

The inner core layer, the outer core layer, the inner cladding layer, the recessed layer, and the first outer cladding layer use silica as the base material and adding dopants, the second outer cladding layer is pure silica, the inner core layer and the outer core layer The relative refractive index of the inner cladding layer, the depressed layer and the first outer cladding layer are Δn ₁ , Δn ₂ , Δn ₃ , Δn ₄ , Δn ₅ , and the relative refractive index is: Δn ₁ >Δn ₂ >0> Δn ₃ >Δn ₅ >Δn ₄ .

Preferably, the first sintering treatment or the second sintering treatment method is: the primary optical fiber preform or the optical fiber preform to be sintered is rotated in the sintering furnace, and the heating coil outside the sintering furnace is moved up and down to the inside of the sintering furnace. Gas heating is used to complete sintering. The moving speed of the heating coil is preferably 5-10 mm/min, and the rotation speed is preferably 3-6 rpm.

Preferably, the first sintering treatment includes three steps of dehydroxylation treatment, fluorine doping treatment and vitrification treatment. Firstly, inert gas and chlorine gas are introduced into the sintering furnace, so that the temperature in the sintering furnace is 25-35 mm/min. The heating rate reaches 900～1100℃, and the temperature is kept for 1-2h to complete the dehydroxylation treatment; secondly, fluorine-containing gas and inert gas are introduced into the sintering furnace to make the temperature in the sintering furnace reach 1100～1300 at a heating rate of 15～25mm/min ℃, keep for 2-3h, complete the fluorine doping treatment; finally, only inert gas is introduced into the sintering furnace, so that the temperature in the sintering furnace reaches 1400～1600℃ at a heating rate of 8～15mm/min, and the heat preservation is 3-4h to complete the glass化处理.

Preferably, the second sintering treatment includes two steps of dehydroxylation treatment and vitrification treatment. Firstly, inert gas and chlorine gas are introduced into the sintering furnace, so that the temperature in the sintering furnace reaches 1000 at a heating rate of 40-60 mm/min. ～1200℃, keep for 2-4 hours to complete the dehydroxylation treatment; then turn off the chlorine gas and pass only inert gas into the sintering furnace to make the temperature in the sintering furnace reach 1300～1500℃ at a heating rate of 10～20mm/min, keep 4 -6h, complete the vitrification process.

Preferably, the inner core layer and the outer core layer are silica glass layers doped with P ₂ O ₅ -F mixture, the relative refractive index Δn ₁ of the inner core layer is 0.35% to 0.45%, and the relative refractive index of the outer core layer The refractive index Δn ₂ is 0.15% to 0.3%, and the ratio b/a of the outer core layer diameter b to the inner core layer diameter a is 1.5-2.

Preferably, the inner cladding layer is a silica glass layer doped with a mixture of Sb ₂ O ₃ -F, the relative refractive index Δn ₃ of the inner cladding layer is -0.2% to -0.05%, and the diameter c of the inner cladding layer and the inner core The ratio c/a of the layer diameter a is 3-4.

Preferably, the depressed layer is an F-doped silica glass layer, the relative refractive index Δn ₄ of the depressed layer is -0.6% to -0.45%, and the ratio of the diameter d of the depressed layer to the diameter a of the inner core layer is d/ a is 5-6.5.

Preferably, the first outer cladding layer is an F-doped silica glass layer, the relative refractive index Δn ₄ of the first outer cladding layer is -0.35% to -0.25%, and the diameter e of the first outer cladding layer and the inner core layer The ratio e/a of the diameter a is 10-11.5, and the ratio f/a of the diameter f of the optical fiber preform to the diameter a of the inner core layer is 15-17.

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

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

The beneficial effects of the present invention are:

The present invention uses the MCVD process to prepare the preformed rod core rod including the inner core layer, the outer core layer, the inner cladding layer and the depressed layer, and then deposits the first outer cladding layer loose body through the VAD process, and prepares the primary optical fiber through the first sintering process For the preform, the loose body of the second outer cladding layer is finally deposited through the OVD process, and the optical fiber preform is obtained through the second sintering process, in which:

Each layer of the optical fiber preform has an appropriate relative refractive index difference, and further defines the dopant and radius of each layer of the optical fiber preform, which can increase the effective area and reduce the attenuation coefficient of the optical fiber;

Make the primary optical fiber preform or optical fiber preform to be sintered rotate in the sintering furnace, and use the coil to move up and down to heat the gas inside the sintering furnace, so that the primary optical fiber preform or optical fiber preform to be sintered does not need to move up and down. The risk of rod dropping is reduced, and the temperature accuracy and temperature field uniformity in the sintering furnace of the optical fiber preform can be effectively improved. By further limiting the sintering process, the first and second cladding layers have a reasonable structure, which effectively reduces The loss of the optical fiber preform is calculated.

Finally, the diameter of the optical fiber preform prepared by the present invention can reach 215mm, the drawing length of a single preform can reach 2930km, the attenuation of the prepared optical fiber at 1310nm wavelength is as low as 0.298dB/km, and the attenuation coefficient at 1383nm wavelength is as low as 0.265dB/km, the attenuation coefficient at the wavelength of 1550nm is as low as 0.165dB/km, and the cut-off wavelength of the fiber is 1265nm~1273nm.

detailed description

It should be noted that the embodiments in this application and the features in the embodiments can be combined with each other if there is no conflict.

Example 1

This embodiment provides a method for preparing a large-size and low-attenuation optical fiber preform, which includes the following steps:

The inner cladding layer, the outer core layer and the inner core layer are sequentially deposited on the inner wall of the F-doped quartz tube as the depressed layer using the MCVD process to obtain a deposited tube, and the deposited tube is fused at 2300°C to have an inner core layer, an outer core layer, Preformed rod core rods of inner cladding and sinking layer;

The first cladding loose body is deposited on the preform core rod by the VAD process, and the primary optical fiber preform is prepared after the first sintering treatment; the first sintering treatment includes dehydroxylation treatment, fluorine doping treatment and vitrification There are three processing steps. Firstly, He gas and chlorine gas are introduced into the sintering furnace, so that the primary optical fiber preform to be sintered rotates at a speed of 3rpm in the sintering furnace, and the gas inside the sintering furnace is heated by the up and down movement of the heating coil outside the sintering furnace. , The moving speed of the heating coil is 10mm/min, and the temperature in the sintering furnace reaches 900℃ at a heating rate of 25mm/min, and the temperature is kept for 2h to complete the dehydration treatment; secondly, SiF ₄ gas and He gas are introduced into the sintering furnace to maintain The rotation speed of the primary optical fiber preform and the up and down movement of the heating coil make the temperature in the sintering furnace reach 1100°C at a heating rate of 15mm/min, hold for 3 hours, and complete the fluorine doping treatment; finally, only He gas is introduced into the sintering furnace to maintain The rotation speed of the primary optical fiber preform and the up and down movement of the heating coil make the temperature in the sintering furnace reach 1400 ℃ at a heating rate of 8 mm/min, and keep it for 4 hours to complete the vitrification process;

The second cladding loose body is deposited on the primary optical fiber preform by the OVD process, and the optical fiber preform is prepared by the second sintering treatment; the second sintering treatment includes two steps of dehydroxylation treatment and vitrification treatment, First, pass He gas and chlorine gas into the sintering furnace, so that the optical fiber preform to be sintered rotates at a rotation speed of 3 rpm in the sintering furnace. The gas inside the sintering furnace is heated by the up and down movement of the heating coil outside the sintering furnace, and the heating coil moves The speed is 10mm/min, and the temperature in the sintering furnace reaches 1000℃ at a heating rate of 40mm/min, and the temperature is kept for 4 hours to complete the dehydroxylation treatment; then the chlorine gas is turned off, and only inert gas is introduced into the sintering furnace to make the temperature in the sintering furnace Reach 1300℃ at a heating rate of 10mm/min, keep it for 6 hours, and complete the vitrification process;

The inner core layer and the outer core layer are silica glass layers doped with P ₂ O ₅ -F mixture, the relative refractive index Δn ₁ of the inner core layer is 0.35%, and the relative refractive index Δn ₂ of the outer core layer is 0.15 %, the ratio b/a of the outer core layer diameter b to the inner core layer diameter a is 1.5; the inner cladding layer is a silica glass layer doped with Sb ₂ O ₃ -F mixture, and the relative refractive index of the inner cladding layer Δn ₃ is -0.2%, the ratio c/a of the inner cladding diameter c to the inner core layer diameter a is 3; the relative refractive index Δn ₄ of the sinking layer is -0.6%, and the sinking layer diameter d is The ratio d/a of the core layer diameter a is 5; the first cladding layer is an F-doped silica glass layer, the relative refractive index Δn ₄ of the first cladding layer is -0.35%, and the first cladding layer diameter e is equal to The ratio e/a of the inner core diameter a is 10, and the ratio f/a of the diameter f of the optical fiber preform to the inner core diameter a is 15.

After testing, the diameter of the optical fiber preform reaches 205mm, and the prepared optical fiber preform is drawn into the fiber online. The length of a single rod can reach 2880km. After the drawing, the attenuation of the fiber at 1310nm is 0.301dB/km, and the attenuation at 1383nm It is 0.265dB/km, the attenuation at 1550nm is 0.165dB/km, and the cut-off wavelength is 1273nm.

Example 2

The inner cladding layer, the outer core layer and the inner core layer are sequentially deposited on the inner wall of the F-doped quartz tube as the depressed layer by the MCVD process to obtain a deposition tube, and the deposition tube is fused at 2400°C to have an inner core layer, an outer core layer, Preformed rod core rods of inner cladding and sinking layer;

The first cladding loose body is deposited on the preform core rod by the VAD process, and the primary optical fiber preform is prepared after the first sintering treatment; the first sintering treatment includes dehydroxylation treatment, fluorine doping treatment and vitrification There are three processing steps. Firstly, He gas and chlorine gas are introduced into the sintering furnace, so that the primary optical fiber preform to be sintered rotates at a rotation speed of 6 rpm in the sintering furnace. The up and down movement of the heating coil outside the sintering furnace can affect the gas inside the sintering furnace. Heating, the moving speed of the heating coil is 5mm/min, and the temperature in the sintering furnace reaches 1100℃ at a heating rate of 35mm/min, and the temperature is kept for 1h to complete the dehydration treatment; secondly, CF ₄ gas and He gas are passed into the sintering furnace. Maintain the rotation speed of the primary optical fiber preform and the up and down movement of the heating coil to make the temperature in the sintering furnace reach 1300°C at a heating rate of 25mm/min, hold for 2 hours, and complete the fluorine doping treatment; finally, only He gas is introduced into the sintering furnace. Maintain the rotation speed of the primary optical fiber preform and the up and down movement of the heating coil, so that the temperature in the sintering furnace reaches 1600°C at a heating rate of 15 mm/min, and the temperature is kept for 3 hours to complete the vitrification process;

The second cladding loose body is deposited on the primary optical fiber preform by the OVD process, and the optical fiber preform is prepared by the second sintering treatment; the second sintering treatment includes two steps of dehydroxylation treatment and vitrification treatment, First, pass He gas and chlorine gas into the sintering furnace, so that the optical fiber preform to be sintered rotates at a speed of 6 rpm in the sintering furnace. The gas inside the sintering furnace is heated by the up and down movement of the heating coil outside the sintering furnace, and the moving speed of the heating coil The temperature in the sintering furnace is set to 5mm/min, and the temperature in the sintering furnace is increased to 1200℃ at a heating rate of 60mm/min, and the temperature is kept for 2 hours to complete the dehydroxylation treatment. The heating rate of 20mm/min reaches 1500℃, and the heat preservation is 4h to complete the vitrification treatment;

The inner core layer and the outer core layer are silica glass layers doped with P ₂ O ₅ -F mixture, the relative refractive index Δn ₁ of the inner core layer is 0.45%, and the relative refractive index Δn ₂ of the outer core layer is 0.3 %, the ratio b/a of the outer core layer diameter b to the inner core layer diameter a is 2; the inner cladding layer is a silica glass layer doped with Sb ₂ O ₃ -F mixture, and the relative refractive index of the inner cladding layer Δn ₃ is -0.05%, the ratio c/a of the inner cladding diameter c to the inner core layer diameter a is 4; the relative refractive index Δn ₄ of the depressed layer is -0.45%, and the depressed layer diameter d is The ratio d/a of the core layer diameter a is 6.5; the first outer cladding layer is an F-doped silica glass layer, and the relative refractive index Δn ₄ of the first outer cladding layer is -0.25%. The ratio e/a of e to the inner core diameter a is 11.5, and the ratio f/a of the fiber preform diameter f to the inner core diameter a is 17.

After testing, the diameter of the optical fiber preform reaches 215mm. The prepared optical fiber preform is drawn on-line to draw the fiber. The length of a single rod can reach 2930km. After drawing, the fiber attenuation at 1310nm is 0.302dB/km and the attenuation at 1383nm. It is 0.271dB/km, the attenuation at 1550nm is 0.171dB/km, and the cut-off wavelength is 1265nm.

Example 3

The inner cladding layer, the outer core layer and the inner core layer are sequentially deposited on the inner wall of the F-doped quartz tube as the depressed layer using the MCVD process to obtain a deposited tube, and the deposited tube is fused at 2500°C to have an inner core layer, an outer core layer, Preformed rod core rods of inner cladding and sinking layer;

The first cladding loose body is deposited on the preform core rod by the VAD process, and the primary optical fiber preform is prepared after the first sintering treatment; the first sintering treatment includes dehydroxylation treatment, fluorine doping treatment and vitrification There are three processing steps. Firstly, He gas and chlorine gas are introduced into the sintering furnace to make the primary optical fiber preform to be sintered rotate at a speed of 5 rpm in the sintering furnace, and the gas inside the sintering furnace is heated by the up and down movement of the heating coil outside the sintering furnace. , The moving speed of the heating coil is 8mm/min, and the temperature in the sintering furnace is reached to 1000℃ at a heating rate of 30mm/min, and the temperature is kept for 1.5h to complete the dehydration treatment; secondly, SF ₆ gas and He gas are introduced into the sintering furnace. Maintain the rotation speed of the primary optical fiber preform and the up and down movement of the heating coil, make the temperature in the sintering furnace reach 1200℃ at a heating rate of 20mm/min, hold for 2.5 hours, and complete the fluorine doping treatment; finally, only He gas is introduced into the sintering furnace , Maintain the rotation speed of the primary optical fiber preform and the up and down movement of the heating coil, so that the temperature in the sintering furnace reaches 1500°C at a heating rate of 12 mm/min, and keep it for 3.5 hours to complete the vitrification process;

The second cladding loose body is deposited on the primary optical fiber preform by the OVD process, and the optical fiber preform is prepared by the second sintering treatment; the second sintering treatment includes two steps of dehydroxylation treatment and vitrification treatment, First, pass He gas and chlorine gas into the sintering furnace, so that the optical fiber preform to be sintered rotates at a speed of 5 rpm in the sintering furnace. The gas inside the sintering furnace is heated by the up and down movement of the heating coil outside the sintering furnace, and the moving speed of the heating coil The temperature in the sintering furnace is 8mm/min, and the temperature in the sintering furnace reaches 1100°C at a heating rate of 50mm/min, and the temperature is kept for 3 hours to complete the dehydroxylation treatment; The heating rate of 15mm/min reaches 1400℃, and the temperature is kept for 6 hours to complete the vitrification process;

The inner core layer and the outer core layer are silica glass layers doped with P ₂ O ₅ -F mixture, the relative refractive index Δn ₁ of the inner core layer is 0.4%, and the relative refractive index Δn ₂ of the outer core layer is 0.2 %, the ratio b/a of the outer core layer diameter b to the inner core layer diameter a is 1.7; the inner cladding layer is a silica glass layer doped with Sb ₂ O ₃ -F mixture, and the relative refractive index of the inner cladding layer Δn ₃ is -0.1%, the ratio c/a of the inner cladding diameter c to the inner core layer diameter a is 3.5; the relative refractive index Δn ₄ of the sinking layer is -0.5%, and the sinking layer diameter d is The ratio d/a of the core layer diameter a is 6; the first cladding layer is an F-doped silica glass layer, the relative refractive index Δn ₄ of the first cladding layer is -0.3%, and the diameter of the first cladding layer is The ratio e/a of e to the inner core diameter a is 11, and the ratio f/a of the diameter f of the optical fiber preform to the inner core diameter a is 16.

After testing, the diameter of the optical fiber preform reaches 210mm. The prepared optical fiber preform is drawn online to draw a low-loss optical fiber. The length of a single rod can reach 2915km. After the drawing, the attenuation of the fiber at 1310nm is 0.298dB/km. The attenuation is 0.272dB/km, the attenuation at 1550nm is 0.168dB/km, and the cut-off wavelength is 1268nm.

Taking the above-mentioned ideal embodiment based on this application as enlightenment, through the above description content, relevant staff can make various changes and modifications without departing from the technical idea of this application. The technical scope of this application is not limited to the content in the specification, and its technical scope must be determined according to the scope of the claims.

Claims

A method for preparing a large-size low-attenuation optical fiber preform is characterized in that it comprises the following steps:

The inner cladding layer, the outer core layer and the inner core layer are sequentially deposited on the inner wall of the quartz tube as the depressed layer using the MCVD process to obtain a deposition tube, and the deposition tube is fused at high temperature to have an inner core layer, an outer core layer, an inner cladding layer and Preformed rod mandrel of the sunken layer;

Use the VAD process to deposit the first cladding loose body on the preform core rod, and pass the first sintering treatment to prepare the primary optical fiber preform;

Use the OVD process to deposit the loose body of the second outer cladding layer on the primary optical fiber preform, and pass the second sintering treatment to prepare the optical fiber preform;

The inner core layer, the outer core layer, the inner cladding layer, the recessed layer, and the first outer cladding layer use silica as the base material and adding dopants, the second outer cladding layer is pure silica, the inner core layer and the outer core layer The relative refractive index of the inner cladding layer, the depressed layer, and the first outer cladding layer are Δn 1 , Δn 2 , Δn 3 , Δn 4 , Δn 5 , and the relative refractive index is: Δn 1 >Δn 2 >0>Δn 3 >Δn 5 >Δn 4 .
The method for preparing a large-format low-attenuation optical fiber preform according to claim 1, wherein the first sintering treatment or the second sintering treatment method is: making the primary optical fiber preform to be sintered or the optical fiber preform Rotate in the sintering furnace, and heat the gas inside the sintering furnace by moving up and down the heating coil outside the sintering furnace to complete sintering. The moving speed of the heating coil is preferably 5-10 mm/min, and the rotation speed is preferably 3-6 rpm.
The method for preparing a large-format low-attenuation optical fiber preform according to claim 1 or 2, wherein the first sintering treatment includes three steps of dehydroxylation treatment, fluorine doping treatment and vitrification treatment. Inert gas and chlorine gas are introduced into the furnace to make the temperature in the sintering furnace reach 900-1100°C at a heating rate of 25-35mm/min, and hold for 1-2h to complete the dehydroxylation treatment; secondly, fluorine-containing gas and gas are introduced into the sintering furnace Inert gas, make the temperature in the sintering furnace reach 1100-1300℃ at a heating rate of 15-25mm/min, keep the temperature for 2-3h, and complete the fluorine doping treatment; finally, only inert gas is introduced into the sintering furnace to make the temperature in the sintering furnace below The heating rate of 8～15mm/min reaches 1400～1600℃, and the temperature is kept for 3-4h to complete the vitrification process.
The method for preparing a large-format low-attenuation optical fiber preform according to any one of claims 1 to 3, wherein the second sintering treatment includes two steps of dehydroxylation treatment and vitrification treatment. Inert gas and chlorine gas are introduced to make the temperature in the sintering furnace reach 1000-1200°C at a heating rate of 40-60 mm/min, and hold for 2-4 hours to complete the dehydroxylation treatment; then turn off the chlorine gas and pass only inert gas into the sintering furnace Use gas to make the temperature in the sintering furnace reach 1300-1500°C at a heating rate of 10-20mm/min, keep it for 4-6h, and complete the vitrification process.
The method for preparing a large-size low-attenuation optical fiber preform according to any one of claims 1 to 4, wherein the inner core layer and the outer core layer are silica doped with P 2 O 5 -F mixture Glass layer, the relative refractive index Δn 1 of the inner core layer is 0.35% to 0.45%, the relative refractive index Δn 2 of the outer core layer is 0.15% to 0.3%, and the ratio of the diameter b of the outer core layer to the diameter a of the inner core layer b/a is 1.5-2.
The method for preparing a large-format low-attenuation optical fiber preform according to any one of claims 1-5, wherein the inner cladding is a silica glass layer doped with Sb 2 O 3 -F mixture, and the inner cladding The relative refractive index Δn 3 is -0.2% to -0.05%, and the ratio c/a of the inner cladding diameter c to the inner core diameter a is 3-4.
The method for preparing a large-format low-attenuation optical fiber preform according to any one of claims 1-6, wherein the depressed layer is an F-doped silica glass layer, and the relative refractive index Δn 4 of the depressed layer is -0.6% to -0.45%, the ratio d/a of the diameter d of the sinking layer to the diameter a of the inner core layer is 5-6.5.
The method for preparing a large-format low-attenuation optical fiber preform according to any one of claims 1-7, wherein the first cladding layer is an F-doped silica glass layer, and the relative refractive index of the first cladding layer is The ratio Δn 4 is -0.35% to -0.25%, the ratio e/a of the diameter e of the first outer cladding layer to the diameter a of the inner core layer is 10-11.5, and the diameter f of the optical fiber preform and the inner core layer diameter a The ratio f/a is 15-17.
An optical fiber preform manufactured by the method of any one of claims 1-8.
An optical fiber, characterized in that the optical fiber is formed by directly drawing the optical fiber preform according to any one of claims 1-8, or formed by drawing after drawing.