WO2020119244A1

WO2020119244A1 - Optical fiber and preparation method therefor

Info

Publication number: WO2020119244A1
Application number: PCT/CN2019/111469
Authority: WO
Inventors: 汤明明; 钱宜刚; 沈一春; 何亮; 秦钰; 吴椿烽
Original assignee: 中天科技精密材料有限公司; 江苏中天科技股份有限公司
Priority date: 2018-12-13
Filing date: 2019-10-16
Publication date: 2020-06-18
Also published as: CN111323871A

Abstract

Disclosed is an optical fiber and a preparation method therefor, relating to the technical field of optical communications. The optical fiber comprises a single germanium-doped silicon dioxide core layer (1), a barrier layer (2), a single fluorine-doped silicon dioxide optical coating layer, and an outer coating layer (6). The barrier layer (2) is used to prevent mutual diffusion between germanium in the single germanium-doped silicon dioxide core layer (1) and fluorine in the single fluorine-doped silicon dioxide optical coating layer. The single fluorine-doped silicon dioxide optical coating layer is divided into three layers, the three layers being a light fluorine-doped layer (3), a main fluorine-doped layer (4), and a secondary fluorine-doped layer (5) sequentially disposed in order from the inside to the outside. The refractive indices of the light fluorine-doped layer (3) and the secondary fluorine-doped layer (5) are each greater than that of the main fluorine-doped layer (4). The single fluorine-doped silicon dioxide optical coating layer employs a layered configuration, such that the amount of fluorine doped in SiO 2 has a gradual concentration variation along a radial direction. The variation enables the cross-sectional viscosity of the optical fiber to demonstrate a trend of gradual variation along the radial direction. The structure can reduce the generation of stress by the optical fiber under the conditions of low macrobend loss of the optical fiber, thereby obtaining a low-loss and low-bend-loss optical fiber.

Description

Optical fiber and its preparation method

Technical field

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

Background technique

This section is intended to provide background or context for the embodiments of the invention recited in the claims. The description here is not admitted to be prior art because it is included in this section.

G.657 optical fiber has been widely used in recent years due to its excellent bending resistance. Its main structure includes a germanium-doped germanium-doped silica core layer and a fluorine-doped silica optical cladding that are arranged from the inside out And the outer cladding, in order to achieve the performance of the optical fiber itself with low bending loss, mainly by reducing the mode field diameter of the optical fiber and increasing the concave cladding; and the concave cladding is achieved by doping in the single fluorine-doped silica optical cladding It is realized by fluorine element with low refractive index.

Due to the incorporation of fluorine element, a part of fluorine element will be mixed with germanium element with high refractive index. In the case of achieving the same refractive index of germanium-doped silica core layer, it will be doped with 10% more than ordinary G.652 fiber. ~15% germanium. The increased doping of germanium will bring about an increase in Rayleigh scattering. In the fiber produced under this condition, the loss in the 1310nm band will generally be 0.010dB/km to 0.015dB/km higher than that of the G.652 fiber. Therefore, an optical fiber is needed to ensure the problem of increased optical fiber attenuation caused by the mutual doping between the germanium-doped silica core layer and the fluorine-doped silica optical cladding.

Summary of the invention

One of the objects of the present invention is to provide an optical fiber which has a low attenuation and a low bending loss.

The technical solutions provided by the present invention are:

An optical fiber including a germanium-doped silica core layer, a barrier layer, a single-fluoride-doped silica optical cladding and an outer cladding in order from inside to outside, the barrier layer is used to prevent the germanium-doped silica core layer The germanium and the fluorine-doped silicon dioxide optical cladding are mutually diffused; wherein the fluorine-doped silicon dioxide optical cladding is divided into three layers, from the inside to the outside, a shallow fluorine-doped layer, a main fluorine-doped layer and an auxiliary For the fluorine-doped layer, the refractive index of the shallow fluorine-doped layer and the auxiliary fluorine-doped layer are larger than the refractive index of the main fluorine-doped layer.

Preferably, the refractive index changes between every two adjacent layers in the barrier layer, the shallow fluorine-doped layer, the main fluorine-doped layer and the auxiliary fluorine-doped layer, and controls the refraction within 1 μm The rate of change is 0.03% to 0.05%.

Preferably, the barrier layer is a pure SiO ₂ barrier layer.

Preferably, the refractive index of the germanium-doped silicon dioxide core layer is 0.35% to 0.45%, and the thickness of the germanium-doped silicon dioxide core layer is 4.0 μm to 4.5 μm.

Preferably, the relative refractive index of the barrier layer is -0.01% to 0.01%, and the thickness thereof is 1.5 μm to 2 μm.

Preferably, the shallow fluorine-doped layer has a refractive index of -0.04% to -0.07%, and a thickness of 2.5 μm to 4.2 μm.

Preferably, the refractive index of the main fluorine-doped layer is -0.08% to -0.15%, and the thickness of the main fluorine-doped layer is 5 μm to 8.5 μm.

Preferably, the auxiliary fluorine-doped layer has a refractive index of -0.01% to -0.07% and a thickness of 2.5 to 4.2 μm.

Preferably, the outer cladding is a protective layer of optical fiber, and the outer cladding is a pure SiO ₂ layer; the refractive index of the outer cladding is 0-0.005%, and its thickness is 41.1 μm-49.0 μm.

Another object of the present invention is to provide an optical fiber preparation method, which is used for the preparation of the optical fiber described above, and includes the following steps:

S1: Preparation of germanium-doped fiber core layer;

S2: forming a prefabricated barrier layer in a loose body state on the periphery of the germanium-doped core layer by a vapor deposition method, the prefabricated barrier layer can prevent the diffusion of germanium in the core layer and the fluorine in the prefabricated single-doped silicon dioxide optical cladding diffusion;

S3: forming a prefabricated single-fluorine-doped silica optical cladding on the outer periphery of the prefabricated barrier layer to obtain an optical fiber preform. The pre-fabricated single-fluorine-doped silica optical cladding is divided into three layers to form a stack, which is formed from the inside Outside is the prefabricated shallow fluorine-doped layer, prefabricated main fluorine-doped layer and prefabricated auxiliary fluorine-doped layer, and the refractive index of the resulting shallow fluorine-doped layer and auxiliary fluorine-doped layer are larger than the refractive index of the main fluorine-doped layer. Silica optical cladding structure;

S4: Pass the optical preform through the optical fiber fusion annealing process and the optical fiber coating and curing process to obtain the optical fiber.

Preferably, the density of the loose body of the prefabricated partition is 0.3 g/cm ³ or more.

Compared with the prior art, an optical fiber provided by the present invention includes, from inside to outside, a single-germanium-doped silica core layer, a barrier layer, a single-fluorine-doped silica optical cladding layer, and an outer cladding layer. It is used to prevent the germanium in the germanium-doped silica core layer and the fluorine in the single-doped silicon dioxide optical cladding from interdiffusion; wherein the single-doped silicon dioxide optical cladding is divided into three layers, from inside to outside It is a shallow fluorine-doped layer, a main fluorine-doped layer and an auxiliary fluorine-doped layer, and the refractive indexes of the shallow fluorine-doped layer and the auxiliary fluorine-doped layer are larger than the refractive index of the main fluorine-doped layer. The setting of the barrier layer reduces the offset of the refractive index caused by the migration of the doping element, and the layered setting of the single-doped fluorine-doped silica optical cladding makes the amount of fluorine doped in SiO ₂ have a concentration in the radial direction gradually The process of change, this change process can make the fiber cross-section viscosity change gradually along the radius direction, this structure can reduce the generation of fiber stress under the condition of low macrobending loss of the fiber, and obtain low loss and low bending loss fiber .

The transitional shallow fluorine-doped layer and auxiliary fluorine-doped layer reduce the stress generated by the viscosity mismatch during the preparation of the optical fiber preform and the fiber drawing process, which facilitates the preparation of the optical fiber itself; and through the relatively low refractive index The arrangement of the main fluorine-doped layer uses the main fluorine-doped layer as a depressed cladding to reduce the bending attenuation of the optical fiber; and in the present invention, the fiber refractive index profile structure does not use a single fluorine-doped silica optical package with deep fluorine doping The layer structure reduces the difficulty of the optical fiber preparation process and is beneficial to mass production using VAD and OVD processes.

BRIEF DESCRIPTION

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

FIG. 1 is a schematic cross-sectional view of an optical fiber according to an embodiment of the present invention.

2 is a schematic diagram of the refractive index profile of the optical fiber of FIG. 1 in the present invention.

Fig. 3 shows the attenuation parameter characteristics of the optical fiber prepared by the VAD process under different densities of the partition layer in the present invention in a loose body state.

Reference sign description:

单掺锗二氧化硅Germanium-doped silicon dioxide	11
隔断层 Partition	22
浅掺氟层Shallow fluorine doped layer	33
主掺氟层Main fluorine-doped layer	44
辅掺氟层Auxiliary fluorine doped layer	55
外包层Outer cladding	66

The following specific embodiments will further describe embodiments of the present invention with reference to the above drawings.

detailed description

In order to be able to more clearly understand the above objects, features and advantages of the embodiments of the present invention, the present invention will be described in detail below with reference to the accompanying drawings and specific embodiments. It should be noted that, in the case of no conflict, the features in the embodiments of the present application may be combined with each other.

In the following description, many specific details are set forth in order to fully understand the embodiments of the present invention. The described embodiments are only a part of the embodiments of the present invention, but not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative efforts fall within the protection scope of the embodiments of the present invention.

In this paper, "Rayleigh scattering" is a kind of scattering, also known as "molecular scattering", which refers to the scattering of light waves by particles with a linearity of scattering particles much smaller than the wavelength.

Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the technical field that belong to the embodiments of the present invention. The terminology used in the description of the present invention herein is for the purpose of describing specific embodiments, and is not intended to limit the embodiments of the present invention.

The optical fiber, as shown in FIGS. 1 and 2, includes a single-doped germanium-doped silica core layer 1, a single-doped fluorine-doped silica optical cladding, and an outer cladding 6, and the single-doped germanium-doped silica core layer 1 and the single-doped fluorine A barrier layer 2 is provided between the silica optical cladding to prevent the diffusion of germanium and fluorine. The arrangement of the barrier layer 2 makes it possible to reduce the mixing of germanium in the germanium-doped silica core layer 1 and the fluorine in the single-doped silicon dioxide optical cladding during the preparation of the optical fiber preform and the fiber drawing process. The barrier layer 2 blocks the fluorine in the single-doped silicon dioxide optical cladding from entering the single-germanium-doped silicon dioxide core layer 1, which can effectively reduce the Rayleigh scattering in the optical fiber, thereby achieving low attenuation of the optical fiber itself; At the same time, through the setting of the barrier layer 2, the fluorine in the single-doped silicon dioxide optical cladding is blocked to ensure that the fluorine content in the single-doped silicon dioxide optical cladding is always kept constant to avoid the reduction of the fluorine content Phenomenon leading to increased bending loss.

In some embodiments, the barrier layer 2, the shallow fluorine-doped layer 3, the main fluorine-doped layer 4, and the auxiliary fluorine-doped layer 5 change in refractive index gradually between adjacent two layers, And control the refractive index change within each 1μm from 0.03% to 0.05%.

In some embodiments, the refractive index of the single-doped germanium silica core layer 1 is

0.35% to 0.45%, the radius of the single-doped germanium silica core layer 1 is 4.0 μm to 4.5 μm. By limiting the refractive index and radius of the single-doped germanium-doped silicon dioxide core layer 1, the single-doped germanium-doped silicon dioxide core layer 1 can have a relatively good refractive index, which ensures that there is less transmission attenuation during use.

In some embodiments, in order to separate the germanium-doped silicon dioxide core layer 1 and the fluorine-doped silicon dioxide optical cladding of the barrier layer 2, the relative refractive index of the barrier layer 2 is -0.01% to 0.01% The thickness is 1.5 μm to 2 μm, and in some embodiments, the bulk density of the barrier layer is 0.32 g/cm ³ to 0.35 g/cm ³ . In the present invention, the partition layer 2 functions as a partition, on the one hand, the physical partition is realized by the partition layer 2, and on the other hand, it is achieved by controlling the density of the layer in the loose body state.

In some embodiments, as shown in FIG. 1, the single fluorine-doped silica optical cladding is divided into three layers, and here, the single fluorine-doped silica optical cladding is a shallow fluorine-doped layer 3 from the inside to the outside , The main fluorine-doped layer 4 and the auxiliary fluorine-doped layer 5; and the refractive index of the shallow fluorine-doped layer 3 and the auxiliary fluorine-doped layer 5 are greater than the refractive index of the main fluorine-doped layer 4; here, the refractive index and thickness of each layer are as follows Shown: The refractive index of the main fluorine-doped layer 4 is -0.08%～-0.15%, the thickness of the main fluorine-doped layer 4 is 5μm～8.5μm; the refractive index of the shallow fluorine-doped layer 3 is -0.04%～-0.07%, the thickness is 2.5 μm to 4.2 μm; the refractive index of the auxiliary fluorine-doped layer 5 is -0.01% to -0.07%, and the thickness is 2.5 to 4.2 μm. By adopting the method of interlayer transition, the gradual change of the amount of fluorine doped in the single-fluorine-doped silica optical cladding makes the viscosity of the fiber cross-section gradually change in the radial direction, thereby making the long-wavelength attenuation in the fiber There is a significant reduction effect. The G.657 fiber with this structure has lower attenuation in the 1550nm band than the G.657 fiber without this structure.

0.008dB/km～0.013dB/km, the general attenuation value can reach below 0.178dB/km; and in this embodiment, by defining the main fluorine-doped layer 4 as the lowest refractive index part of the fiber cross section direction, the single-doped germanium dioxide The light of the silicon core layer 1 plays a major binding role, while the shallow fluorine-doped layer 3 and the auxiliary fluorine-doped layer 5 located on the inner and outer sides of the main fluorine-doped layer 4 mainly play a role of auxiliary binding.

In some embodiments, as shown in FIG. 1, it further includes an outer cladding 6 located on the outermost side. During use, the outer cladding 6 serves as a mechanical protective layer of the optical fiber. The outer cladding 6 is a pure SiO ₂ layer and the outer cladding 6 The refractive index is 0 to 0.005%, and its thickness is 41.1 μm to 49.0 μm. In this way, the inner single germanium-doped silica core layer 1 and the single fluorine-doped silica optical cladding are protected by the arrangement of the outer cladding layer 6.

The structure of a low-attenuation and low-bending-loss optical fiber provided by Example 1 to Example 10 is basically the same as the above specific embodiment, the difference is that the refractive index and specific thickness between the layers are different, and the specific performance is as follows:

The optical fiber with low attenuation and low bending loss provided in the above embodiments can be realized by processes such as VAD, OVD, MCVD, and PCVD, and the specific performance is as follows:

The optical fiber provided by the present invention can reduce the germanium in the single germanium-doped silica core layer 1 and the single-fluorine-doped silica optical cladding in the preparation of the optical fiber preform and the fiber drawing process through the setting of the barrier layer 2 The fluorine-doped compound is used to block the fluorine in the single-doped silicon dioxide optical cladding from entering the single-doped germanium silica core layer 1 through the barrier layer 2, which can effectively reduce the Rayleigh scattering in the optical fiber, thereby achieving Low attenuation of the fiber itself; through the setting of the barrier layer 2, the fluorine in the single-fluorine-doped silica optical cladding is blocked to ensure that the content of fluorine in the single-fluorine-doped silica optical cladding is always kept certain to avoid fluorine The decrease in the content leads to an increase in bending loss.

It can be drawn from the table that the G.657 fiber with the refractive index profile structure in the present invention has a typical attenuation value of 0.318dB/km at 1310nm and a typical attenuation of 1550nm when the mode field diameter (MFD) at 1310nm is 8.58μm The value is 0.177dB/km, the typical value of the bending loss of 1550nm/R7.5 is 0.048dB, and the typical value of the bending loss of 1625nm/R7.5 is 0.128dB, which ensures low bending loss while ensuring low attenuation.

Example 11:

The invention also provides a method for preparing an optical fiber, which is used to prepare the optical fiber in the above technical solution, and the specific steps are as follows:

S1: preparing a germanium-doped core layer: the germanium-doped core layer is formed by initially depositing 3-10 g/min SiCl ₄ and 200-400 mg/min GeCl ₄ on the target rod.

S2: forming a prefabricated barrier layer in a loose body state on the periphery of the germanium-doped core layer by a vapor deposition method, and forming a prefabricated single-fluorine-doped silica optical cladding on the periphery of the prefabricated barrier layer to obtain an optical fiber preform, in this embodiment In this case, the viscosity of the prefabricated barrier layer is close to the viscosity of the germanium-doped core, and the prefabricated barrier layer can effectively prevent the diffusion of germanium in the core layer and the diffusion of fluorine in the prefabricated single-doped silica optical cladding.

By using the vapor deposition method to form the barrier layer 2, during the preparation process, as a layer of physical barrier, it can effectively prevent the optical fiber and its raw material at high temperature, the germanium in the germanium-doped silica core layer 1 and the single fluorine-doped The refractive index offset caused by the mutual doping of fluorine in the silica optical cladding occurs, thereby reducing the concentration of dopants in the germanium-doped silicon dioxide core layer 1 or the fluorine-doped silica optical cladding . This reduction in concentration can, on the one hand, reduce material scattering and, on the other hand, reduce material stress, which can help reduce the attenuation coefficient of fiber transmission.

In some embodiments, the density of the prefabricated partition loose body is

From 0.32g/cm ³ to 0.35g/cm ³ , as shown in Figure 3, Figure 3 shows the characteristics of the attenuation parameters of the optical fiber prepared by the VAD process under different densities of the barrier layer 2 in the loose body state. Here, it can be drawn from Figure 3 that when the density of the loose body is above 0.3g/cm ³ , the attenuation of 1310nm and 1550nm has reached a lower value, and the density in the loose body state is between 0.32g/cm ^³ ~ 0.35g / cm ^3, the attenuation reaches a minimum value.

In this embodiment, the prefabricated single-fluorine-doped silica optical cladding is divided into three layers to form a stack, which is a prefabricated shallow fluorine-doped layer, a prefabricated main fluorine-doped layer and a prefabricated auxiliary fluorine-doped layer in order from inside to outside, and finally obtains The single fluorine-doped silica optical cladding structure in which the refractive indexes of the shallow fluorine-doped layer 3 and the auxiliary fluorine-doped layer 5 are both greater than the refractive index of the main fluorine-doped layer 4. In this way, through the setting of the concentration change of the single fluorine-doped silica optical cladding, the deep fluorine-doped single fluorine-doped silica optical cladding structure is not adopted, which reduces the difficulty of the optical fiber manufacturing process and is beneficial to the use of VAD, OVD Process mass production.

S3: The optical fiber preform is obtained through optical fiber fusion annealing process and optical fiber coating and curing process to obtain optical fiber:

In this process, the optical fiber melting annealing process: the preform enters the drawing furnace from the top of the drawing furnace, the temperature inside the drawing furnace body is set to 2000 ~ 2200 ℃, the preform melts and draws in the drawing furnace furnace body, the traction speed is greater than 2000m/ min; After the traction is completed, the optical fiber enters the thermal insulation annealing furnace, the temperature of the heating element in the thermal insulation annealing furnace is controlled at 900～1300℃, and a gradient temperature field of 800～1200℃ is formed in the annealing thermal insulation furnace, and the optical fiber is in the thermal insulation annealing furnace Gradually lower the temperature and basically release the internal stress.

Optical fiber coating and curing process: the optical fiber enters the coating machine for coating, and then enters the ultraviolet curing furnace, the ambient temperature is 20 to 28 ℃, the environmental humidity is 40 to 60%, the power of the ultraviolet curing furnace is controlled at 70 to 95%, ultraviolet An exhaust system is used in the light curing furnace to extract the cured volatiles from the surface coating of the optical fiber and remove harmful gases to form the final optical fiber.

The preparation method of the optical fiber provided by the present invention blocks the germanium in the core layer and the fluorine in the single-fluorine-doped silica optical cladding through the blocking layer in the loose body state, thereby effectively avoiding the two elements Mixing with each other results in an increase in the attenuation coefficient of the fiber or an increase in bending loss.

The above embodiments are only used to illustrate the technical solutions of the embodiments of the present invention and not to limit them. Although the embodiments of the present invention are described in detail with reference to the above preferred embodiments, those of ordinary skill in the art should understand that the technology of the embodiments of the present invention can be Modifications or equivalent replacements of the solutions shall not depart from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

An optical fiber, characterized in that it includes a single-doped germanium-doped silica core layer, a barrier layer, a single-doped fluoro-doped silica optical cladding and an outer cladding in order from the inside to the outside, the barrier layer is used to prevent single-doped germanium Germanium in the silicon oxide core layer and fluorine in the single fluorine-doped silica optical cladding interdiffuse; wherein the single fluorine-doped silica optical cladding is divided into three layers, from the inside to the outside, the shallow fluorine-doped layer, the main The fluorine-doped layer and the auxiliary fluorine-doped layer, the refractive index of the shallow fluorine-doped layer and the auxiliary fluorine-doped layer are larger than the refractive index of the main fluorine-doped layer.
The optical fiber according to claim 1, characterized in that: the refractive index between every two adjacent layers of the blocking layer, the shallow fluorine-doped layer, the main fluorine-doped layer and the auxiliary fluorine-doped layer Gradual change, and control the refractive index change within each 1μm from 0.03% to 0.05%.
The optical fiber according to claim 1, wherein the barrier layer is a pure SiO 2 barrier layer.
The optical fiber according to claim 1, wherein the refractive index of the single-doped germanium-doped silica core layer is 0.35% to 0.45%, and the radius of the single-doped germanium-doped silica core layer is 4.0 μm to 4.5 μm.
The optical fiber according to claim 1, wherein the relative refractive index of the barrier layer is -0.01% to 0.01%, and the thickness thereof is 1.5 μm to 2 μm.
The optical fiber according to claim 1, wherein the shallow fluorine-doped layer has a refractive index of -0.04% to -0.07% and a thickness of 2.5 μm to 4.2 μm.
The optical fiber according to claim 1, wherein the refractive index of the main fluorine-doped layer is -0.08% to -0.15%, and the thickness of the main fluorine-doped layer is 5 μm to 8.5 μm.
The optical fiber according to claim 1, wherein the auxiliary fluorine-doped layer has a refractive index of -0.01% to -0.07% and a thickness of 2.5 to 4.2 μm.
The optical fiber according to claim 1, wherein the outer cladding is a protective layer of the optical fiber, and the outer cladding is a pure SiO 2 layer; the refractive index of the outer cladding is 0 to 0.005%, and the thickness is 41.1μm～49.0μm.
A method for preparing an optical fiber, which is used for preparing the optical fiber according to any one of claims 1-8, characterized in that it includes the following steps:

S1: Preparation of germanium-doped fiber core layer;

S2: forming a prefabricated barrier layer in a loose body state on the periphery of the germanium-doped core layer by a vapor deposition method, the prefabricated barrier layer can prevent the diffusion of germanium in the core layer and the fluorine in the prefabricated single-doped silicon dioxide optical cladding diffusion;

S3: forming a prefabricated single-fluorine-doped silica optical cladding on the outer periphery of the prefabricated barrier layer to obtain an optical fiber preform. The pre-fabricated single-fluorine-doped silica optical cladding is divided into three layers to form a stack, which is formed from the inside Outside is the prefabricated shallow fluorine-doped layer, prefabricated main fluorine-doped layer and prefabricated auxiliary fluorine-doped layer, and the refractive index of the resulting shallow fluorine-doped layer and auxiliary fluorine-doped layer are larger than the refractive index of the main fluorine-doped layer. Silica optical cladding structure;

S4: Pass the optical preform through the optical fiber fusion annealing process and the optical fiber coating and curing process to obtain the optical fiber.
The method for preparing an optical fiber according to claim 10, wherein the density of the loose body of the prefabricated partition is 0.3 g/cm 3 or more.