Preparation method of ultra-low attenuation optical fiber and ultra-low attenuation optical fiber
By fabricating optical fibers using external vapor deposition and in-tube vapor deposition processes, the refractive index and viscosity of the core and cladding were matched, solving the problem of increased fiber attenuation and improving the transmission performance of the optical fiber.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- YANGTZE OPTICAL FIBRE & CABLE CO LTD
- Filing Date
- 2026-01-29
- Publication Date
- 2026-05-01
AI Technical Summary
In the fabrication of optical fibers, existing doping designs cannot effectively balance the refractive index and viscosity matching between the core and cladding, leading to increased fiber attenuation and enhanced Rayleigh scattering.
A fluorine-doped sleeve with non-uniform fluorine distribution was prepared by external vapor deposition process, and alkali metal doping was carried out by internal vapor deposition process to form an optimized doping scheme for the core layer and inner cladding layer. By controlling the distribution of fluorine and alkali metal, the refractive index and viscosity were matched.
The fabricated optical fiber has ultra-low attenuation, large effective area, and good bending resistance, which reduces transmission loss and improves the performance of communication networks.
Smart Images
Figure CN121948828A_ABST
Abstract
Description
A method for fabricating ultra-low attenuation optical fiber and the ultra-low attenuation optical fiber itself. Technical Field
[0001] This application belongs to the field of optical communication equipment, and more specifically, relates to a method for preparing ultra-low attenuation optical fiber and the ultra-low attenuation optical fiber. Background Technology
[0002] With the rapid development of internet technology, the demand for AI computing, data centers, and cross-border financial services is growing rapidly, placing higher demands on high-speed communication optical fibers with low latency, high capacity, and long distances. G654 optical fiber features low transmission loss, reducing the number of repeater stations and offering economic advantages in long-distance transmission. Its large effective area significantly suppresses nonlinear effects, thereby improving overall transmission capacity. Furthermore, G654 optical fiber is compatible with existing systems and suitable for various scenarios such as submarine cables and long-distance terrestrial trunk networks. Therefore, developing G654 optical fiber with ultra-low attenuation characteristics is expected to further break through the performance bottlenecks of traditional optical fibers, becoming an ideal medium to support future higher-speed communication networks.
[0003] Optical fiber signal transmission is based on the principle of total internal reflection, requiring a certain refractive index difference between the core and cladding. Common practices include doping the core with elements such as germanium (Ge) or chlorine (Cl) to increase the refractive index, and doping the cladding with elements such as fluorine (F) or boron (B) to decrease the refractive index. However, although existing doping methods can effectively adjust the refractive index of the corresponding host material SiO2, the introduced elements are mostly present as impurities. Compared to pure SiO2, this causes undesirable density and concentration fluctuations, leading to enhanced Rayleigh scattering and thus increasing fiber attenuation. Furthermore, in addition to attenuation that may be caused by the materials themselves, the stress difference between the core and cladding also introduces additional losses. Therefore, appropriate doping is necessary in optical fiber fabrication to achieve viscosity matching between the core and cladding.
[0004] Currently, a common method is to dope the core layer with alkali metals to reduce fiber attenuation. Alkali metal doping can significantly reduce the viscosity of SiO2, lowering its virtual temperature. Furthermore, due to their high mobility, alkali metals can repair microscopic defects during fiber drawing, further reducing attenuation loss. Therefore, alkali metal doping in the core layer has become a common optimization technique for ultra-low attenuation fibers. However, in existing technologies, to simultaneously satisfy refractive index matching and viscosity matching, it is often necessary to introduce a large number of dopant elements into both the core and cladding layers. This exacerbates Rayleigh scattering, causing additional optical loss and ultimately weakening the expected effect of alkali metal doping. Summary of the Invention
[0005] In response to the deficiencies or improvement needs of existing technologies, this application provides a method for preparing ultra-low attenuation optical fibers. This method aims to solve the technical problem that the doping design scheme in the existing optical fiber preparation process is insufficient, which leads to the inability to effectively balance Rayleigh scattering caused by element doping and interlayer viscosity and refractive index matching, thereby increasing the attenuation of the optical fiber.
[0006] This application provides a method for fabricating ultra-low attenuation optical fiber, which includes the following steps: S1, preparing a fluorine-doped sleeving with non-uniform fluorine distribution using an external vapor deposition process, wherein the non-uniform fluorine distribution is characterized by a high fluorine content on the outer side and a low fluorine content on the inner side of the fluorine-doped sleeving in the radial direction; S2, stretching and etching the fluorine-doped sleeving to obtain an inner cladding with a predetermined aperture; S3, depositing SiO2 and performing alkali metal doping inside the inner cladding using an in-tube vapor deposition process to form a core layer, and then melting and shrinking the inner cladding with the core layer to obtain a rod-shaped structure; S4, preparing an outer cladding on the outside of the rod-shaped structure using an external vapor deposition process, drying the rod-shaped structure with the outer cladding, and then solidifying it in a fluorine-containing atmosphere to obtain an optical fiber preform; S5, drawing the optical fiber preform to form an optical fiber.
[0007] As a further preferred embodiment, in step S1, the preparation of the fluorine-doped sleeve with uneven fluorine distribution using an external vapor deposition process includes: S11, depositing flame-hydrolyzed SiO2 particles on the outside of a mandrel using an external vapor deposition process to form a soot body; S12, after removing the mandrel, fixing the soot body with a hollow target rod and transferring it to a doping device; S13, after thoroughly drying the soot body, introducing an inert gas containing saturated water vapor into it, so that the soot body achieves a state where the surface hydroxyl groups are more numerous than the internal hydroxyl groups; S14, introducing a fluorine-containing gas into the soot body, utilizing the substitution reaction between fluorine and hydroxyl groups to achieve uneven fluorine distribution in the soot body, and finally sintering to obtain the fluorine-doped sleeve.
[0008] As a further preferred embodiment, in step S13, the thorough drying of the soot body includes: introducing a drying gas from the center of the target rod to remove water and / or hydroxyl groups generated during the deposition process, wherein the drying gas is a chlorine-containing gas; and then removing the residual chlorine during the drying process by purging with oxygen.
[0009] As a further preferred embodiment, in step S14, the fluorine-containing gas is one or a mixture of several of SiF4, SF6, CF4, and C2F6; the fluorine content in the sintered fluorine-doped sleeve near its inner surface is 4000-6000 ppm, and the fluorine content near its outer surface is 8000-10000 ppm.
[0010] As a further preferred embodiment, in step S2, the stretching and etching of the fluorine-doped sleeve to obtain an inner cladding with a predetermined pore size includes: stretching the fluorine-doped sleeve in a stretching furnace and removing impurities from the inner surface of the fluorine-doped sleeve by acid etching, so that the inner diameter is maintained in the range of 10 to 30 mm and the relative refractive index difference is -0.30% to -0.20%.
[0011] As a further preferred embodiment, in step S3, the deposition of SiO2 and alkali metal doping to form a core layer inside the inner cladding using in-tube vapor deposition includes: heating an alkali metal compound, using a carrier gas to carry the source vapor of the alkali metal compound into the tube of the inner cladding, and depositing a chlorine-doped SiO2 layer using O2 and SiCl4 as raw materials to obtain the core layer.
[0012] As a further preferred embodiment, the alkali metal compound is a powdered alkali metal salt, and the average alkali metal content in the core layer after alkali metal doping is 300 to 500 ppm, and the relative refractive index difference of the core layer is 0.01% to 0.05%.
[0013] As a further preferred embodiment, in step S4, the step of drying the rod-shaped structure with the outer cladding and then solidifying it in a fluorine-containing atmosphere to obtain the optical fiber preform includes: drying the rod-shaped structure with the outer cladding in a chlorine-containing gas, and then transferring it to a sintering device for solidification in a SiF4 atmosphere.
[0014] As a further preferred embodiment, in step S5, the process parameters for drawing the optical fiber preform are: drawing speed of 1000 ~ 2000 m / min and drawing tension of 50 ~ 100 g.
[0015] This application also provides an ultra-low attenuation optical fiber prepared by the preparation method described in any of the preceding claims, comprising, from the inside out, a core layer, an inner cladding, and an outer cladding layer coaxially distributed; the core layer has a radius of 5-6 μm and a relative refractive index difference of 0.01%-0.05%, and is co-doped with alkali metal and chlorine, with an average alkali metal content of 300-500 ppm; the inner cladding has an outer ring radius of 19-20 μm, and the fluorine content in the radial direction of the inner cladding is distributed with a high outer ring and a low inner ring, with a fluorine content of 4000-6000 ppm near the inner surface and 8000-10000 ppm near the outer surface; the outer cladding has an outer ring radius of 124-125 μm and a relative refractive index difference of -0.15%--0.10%.
[0016] Overall, compared with the prior art, the above-conceptual technical solution proposed in this application has the following main technical advantages: 1. The preparation method of this application first uses external chemical vapor deposition (OVD) to prepare a fluorine-doped sleeving with uneven fluorine distribution; then, it uses in-tube vapor deposition to deposit SiO2 in the tube while achieving alkali metal doping; next, it deposits the outer cladding through OVD; finally, it is made into an optical fiber through a drawing process; this preparation method comprehensively utilizes external chemical vapor deposition and in-tube vapor deposition to achieve an optimized doping scheme, which can achieve better optical fiber profile matching and viscosity matching. The optical fiber prepared by this method has ultra-low attenuation, large effective area and good bending resistance.
[0017] 2. In the preparation of fluorine-doped sleeves, an inert gas containing saturated water vapor is introduced into the flue gas. The bulk temperature difference generated by the slow heat conduction of the flue gas, as well as the characteristics of H2O diffusion and the hydrolysis of silicon-oxygen bonds (Si-O-Si) that require temperature and time, can be used to make the flue gas reach a state with more hydroxyl groups on the surface and fewer hydroxyl groups inside by controlling the preparation conditions such as heating rate, saturated water vapor concentration, reaction temperature and reaction time. Then, fluorine-containing gas is introduced, and the non-uniform distribution of fluorine in the flue gas is achieved by utilizing the substitution reaction between fluorine and hydroxyl groups.
[0018] 3. In the preparation of fluorine-doped sleeves, water and / or hydroxyl groups generated during the deposition process are first removed by chlorine-containing drying gas, and then chlorine is removed by oxygen purging. This achieves thorough drying of the soot body, ensures that the hydroxyl content distribution of the subsequent soot body is not disturbed, and avoids unnecessary impurity doping.
[0019] 4. By heating the alkali metal compound, the alkali metal source vapor is introduced into the tube using a carrier gas. Using O2 and SiCl4 as raw materials, a uniform alkali metal doping and a certain amount of chlorine doping are achieved during the deposition of the core layer using an in-tube vapor phase deposition process. This increases the refractive index while avoiding increased Rayleigh scattering, thus achieving viscosity matching between the core layer and the inner cladding, and also meeting the refractive index requirements.
[0020] 5. By doping the core layer with chlorine and gradually doping the inner cladding with fluorine, refractive index matching and viscosity matching between the core layer and the inner cladding are achieved, reducing stress loss. The uniform doping of alkali metals in the core layer significantly reduces the viscosity and virtual temperature of the core layer, which together promotes the reduction of transmission loss. At the same time, the lower limit region formed between the deep fluorine doping of the inner cladding and the shallow fluorine doping of the outer cladding is beneficial to balancing the large effective area and bending resistance of the optical fiber. Attached Figure Description
[0021] Figure 1 is a schematic diagram of the steps of a method for fabricating an ultra-low attenuation optical fiber according to an embodiment of this application; Figure 2 is a schematic diagram of the structure of the doping device in a method for fabricating an ultra-low attenuation optical fiber according to an embodiment of this application; Figure 3 is a schematic diagram of the cross-sectional structure of an ultra-low attenuation optical fiber according to an embodiment of this application; Figure 4 is a schematic diagram of the relative refractive index difference and radius of each layer of an ultra-low attenuation optical fiber according to an embodiment of this application.
[0022] In all the accompanying drawings, the same reference numerals are used to denote the same elements or structures, wherein: 1, core layer; 2, inner cladding layer; 3, outer cladding layer; 4, doping device; 5, heating device; 6, target rod; 7, upper air inlet; 8, lower air inlet. Detailed Implementation
[0023] To make the objectives, technical solutions, and advantages of this application clearer, the following detailed description is provided in conjunction with the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the scope of this application.
[0024] The first part of this application provides a method for preparing ultra-low attenuation optical fiber, which includes the following steps: S1, preparing a fluorine-doped sleeve with non-uniform fluorine distribution using an external vapor deposition process, wherein the non-uniform fluorine distribution is characterized by a high fluorine content on the outside and a low fluorine content on the inside of the fluorine-doped sleeve in the radial direction; S2, stretching and etching the fluorine-doped sleeve to obtain an inner cladding 2 with a predetermined aperture; S3, depositing SiO2 and performing alkali metal doping inside the inner cladding 2 using an in-tube vapor deposition process to form a core layer 1, and then melting and shrinking the inner cladding 2 with the core layer 1 to obtain a rod-shaped structure; S4, preparing an outer cladding 3 on its outside using an external vapor deposition process, and then drying the rod-shaped structure with the outer cladding 3 and solidifying it in a fluorine-containing atmosphere to obtain an optical fiber preform; S5, drawing the optical fiber preform into an optical fiber.
[0025] The above five steps are the basic steps of the preparation method of this application. Under the framework constructed by these basic steps, each step of the preparation scheme can be optimized in the following preferred manner: In step S1, the preparation of the fluorine-doped sleeve with uneven fluorine distribution using an external vapor deposition process includes: S11, depositing flame hydrolysis particles of SiO2 on the outside of the mandrel using an external vapor deposition process to form a soot body; S12, after removing the mandrel, fixing the soot body with a hollow target rod 6 and transferring it to the doping device 4; S13, after fully drying the soot body, introducing an inert gas containing saturated water vapor into it, so that the soot body achieves a state in which the surface hydroxyl groups are more numerous than the internal hydroxyl groups; S14, introducing a fluorine-containing gas into the soot body, utilizing the substitution reaction between fluorine and hydroxyl groups to achieve uneven distribution of fluorine in the soot body, and finally sintering to obtain the fluorine-doped sleeve.
[0026] In step S12, thoroughly drying the soot body includes: introducing a drying gas through the center of the target rod 6 to remove water and / or hydroxyl groups generated during the deposition process, wherein the drying gas is a chlorine-containing gas; and then removing the residual chlorine during the drying process by purging with oxygen.
[0027] In step S2, stretching and etching the fluorine-doped sleeve to obtain an inner cladding 2 with a predetermined pore size includes: stretching the fluorine-doped sleeve in a stretching furnace and removing impurities from the inner surface of the fluorine-doped sleeve by acid etching.
[0028] In step S3, depositing SiO2 inside the inner cladding 2 using in-tube vapor deposition and performing alkali metal doping to form the core layer 1 includes: heating the alkali metal compound, using a carrier gas to carry the source vapor of the alkali metal compound into the tube of the inner cladding 2, and depositing a chlorine-doped SiO2 layer using O2 and SiCl4 as raw materials to form the core layer 1.
[0029] In step S4, the step of drying the rod-shaped structure with the outer cladding and then solidifying it in a fluorine-containing atmosphere to obtain the optical fiber preform includes: drying the rod-shaped structure with the outer cladding in a chlorine-containing gas, and then transferring it to a sintering device for solidification in a SiF4 atmosphere.
[0030] To facilitate understanding of the concept of this invention, the entire process, principle, and effects of the preparation method are described in detail below.
[0031] First, step S1 is performed to prepare a fluorine-doped sleeve with uneven fluorine distribution using an external vapor deposition process. The uneven fluorine distribution means that the fluorine content is distributed with higher levels on the outside and lower levels on the inside in the radial direction of the fluorine-doped sleeve.
[0032] The implementation of step S1 can preferably be divided into 4 sub-steps. First, step S11 is implemented. In this embodiment, SiO2 is taken as an example using O2 and SiCl4 as raw materials. It is subjected to flame hydrolysis, and the following reaction occurs: SiCl4 + O2 → SiO2 + 2Cl2 (1), generating SiO2 particles and chlorine gas. The above-mentioned SiO2 particles are deposited on the mandrel through an external vapor deposition process to form a generally hollow tubular soot body.
[0033] Then, step S12 is performed to extract the mandrel from the soot body and then fix the soot body with the hollow target rod 6 and transfer it to the doping device 4.
[0034] In this section, the doping device 4 is exemplified as a hollow container structure with an upper air inlet 7 at the top and a lower air inlet 8 at the bottom. A heating device 5 is installed inside. It is understood that the doping device 4 is for illustrative purposes only and does not imply that the device only has the above-described structure, nor does it imply that the shape and component dimensions of the doping device 4 are consistent with those shown in the figure. In an optional embodiment, the lower end of the target rod 6 is inserted into the upper end of the central hole of the soot body. The target rod 6 and the soot body form a hollow airflow channel. The upper air inlet 7 is used to input airflow into the central hole of the soot body, and the lower air inlet 8 is used to introduce process gas into the doping device 4.
[0035] Then, step S13 is performed, after the soot body is fully dried, an inert gas such as helium (He) containing saturated water vapor is introduced into it, so that the soot body achieves a state in which the surface hydroxyl groups are more numerous than the internal hydroxyl groups.
[0036] The soot body is thoroughly dried as follows: a drying gas is introduced from the center of the target rod 6. The drying gas is a chlorine-containing gas. In this embodiment, chlorine gas Cl2 is used to remove water and / or hydroxyl groups generated during the deposition process. Then, oxygen is purged until the chlorine remaining during the drying process is completely removed.
[0037] Next, an inert gas containing saturated water vapor is introduced into the soot body through the lower air inlet 8. Taking advantage of the bulk temperature difference generated by the slow heat conduction of the soot body, and the fact that the H2O diffusion and silicon-oxygen bond (Si-O-Si) hydrolysis processes depend on temperature and time, referring to the following formulas (2) and (3), the soot body achieves a state in which the surface hydroxyl groups are more than the internal hydroxyl groups by controlling the preparation conditions such as the heating rate, saturated water vapor concentration, reaction temperature and reaction time.
[0038] The relationship between the time and distance of H2O diffusion is as follows: (2), where, It is the concentration of H2O in the soot. It is time, It is the distance in the direction of diffusion. It is the diffusion coefficient.
[0039] diffusion coefficient The relationship with temperature is as follows: (3), among which, Pre-exponential factors For diffusion activation energy, For ideal gas constant, This refers to absolute temperature.
[0040] It is understandable that, in order to prevent water vapor from being adsorbed and diffused from the inner surface of the soot body during the above step S13, pure inert gas needs to be introduced into the interior of the target rod 6 from the top to create a slightly positive pressure environment inside the soot body.
[0041] Then, step S14 is carried out, in which fluorine-containing gas is introduced into the soot body, and the non-uniform distribution of fluorine in the soot body is achieved by the substitution reaction of fluorine and hydroxyl groups. Finally, the fluorine-doped sleeve is obtained by sintering.
[0042] The fluorine-containing gas is one or a mixture of several of SiF4, SF6, CF4, and C2F6.
[0043] Preferably, the fluorine content in the sintered fluorine-doped sleeve is 4000-6000 ppm near its inner surface and 8000-10000 ppm near its outer surface.
[0044] Thus, the fluorine-doped sleeve with uneven fluorine distribution described in step S1 is obtained.
[0045] Next, in step S2, the fluorine-doped sleeve is stretched and etched to obtain an inner cladding 2 with a predetermined pore size. This step is the process of processing the fluorine-doped sleeve prepared in step S1 into the inner cladding 2. Specifically, the fluorine-doped sleeve is stretched in a stretching furnace, and impurities on the inner surface of the fluorine-doped sleeve are removed by acid etching. During the acid etching process, SiO2 and inclusions in a region of about 1 mm thickness on the inner surface of the fluorine-doped sleeve are etched away. This ensures that the inner pore diameter is within the predetermined range without affecting the fluorine content distribution of the fluorine-doped sleeve.
[0046] The inner diameter is kept between 10 and 30 mm, and the relative refractive index difference is between -0.30% and -0.20%.
[0047] The relative refractive index difference Δn of the corresponding layer after preparation is calculated according to the following formula (5). i : (5) Among them, The refractive index of the corresponding SiO2 layer is... is the refractive index of pure SiO2.
[0048] Then proceed to step S3, where SiO2 is deposited inside the inner cladding 2 using in-tube vapor deposition and alkali metal doping is performed to form a core layer 1. The inner cladding 2 with the core layer 1 is then melted and shrunk to obtain a rod-shaped structure.
[0049] Using the hollow tubular inner cladding 2 described above, SiO2 core layer 1 is deposited and alkali metal doped on the corresponding PCVD (Plasma Chemical Vapor Deposition) or MCVD (Modified Chemical Vapor Deposition) equipment. In this embodiment, the in-tube vapor deposition process is implemented using a PCVD equipment.
[0050] An alkali metal compound is placed at the inlet of the PCVD equipment and heated. The source vapor of the alkali metal compound is carried into the tube of the inner cladding 2 by a carrier gas. At the same time, a chlorine-doped SiO2 layer is deposited using O2 and SiCl4 as raw materials.
[0051] The alkali metal source compound is preferably a powdered alkali metal salt, including but not limited to NaCl, NaBr, KNO3, KBr, and KNO3, with a purity of ≥99.999%. In this embodiment, a potassium-containing metal salt is used. By controlling the partial pressure of O2 and SiCl4, a chlorine-doped SiO2 layer is deposited using a PCVD device, allowing K to uniformly enter the SiO2 network. This method not only achieves uniform alkali metal doping but also achieves a certain amount of chlorine doping using O2 and SiCl4 as raw materials. This increases the refractive index while avoiding an increase in Rayleigh scattering, thus achieving viscosity matching between the core layer 1 and the inner cladding layer 2, and also meeting the refractive index requirements.
[0052] The average alkali metal content of the core layer 1 prepared in this embodiment is 300-500 ppm, and the relative refractive index difference of the core layer 1 is 0.01%-0.05%. Since all structures in this application are solid, ppm in this embodiment represents the weight ratio of the substance in the corresponding layer as one part per million.
[0053] Then proceed to step S4, where an outer cladding layer 3 is prepared on the outside of the rod-shaped structure using an external vapor deposition process. After drying the rod-shaped structure with the outer cladding layer 3, it is solidified in a fluorine-containing atmosphere to obtain an optical fiber preform.
[0054] Understandably, the diameter of the rod-shaped structure can be measured before the external vapor deposition process. If the size does not meet the requirements, it can be stretched or etched to meet the predetermined diameter for external vapor deposition.
[0055] Then, the outer cladding layer 3 is prepared by external vapor deposition process. After the rod-shaped structure with the outer cladding layer 3 is dried in chlorine-containing gas, the dried powder rod is transferred to a sintering equipment and solidified in a SiF4 atmosphere to achieve shallow fluorine doping of the outer cladding layer 3.
[0056] The optical fiber preform is prepared by following the above steps. Then, proceed to step S5 to draw the optical fiber preform into an optical fiber. In this embodiment, the process parameters for drawing the optical fiber preform are: drawing speed of 1000 ~ 2000 m / min and drawing tension of 50 ~ 100 g, thereby completing the preparation of the ultra-low attenuation optical fiber.
[0057] Therefore, in the second part of the embodiments of this application, an ultra-low attenuation optical fiber is disclosed, which includes, from the inside to the outside, a core layer 1, an inner cladding layer 2, and an outer cladding layer 3 coaxially distributed; the core layer 1 has a radius R1 of 1 ~ 6 μm, a relative refractive index difference Δn1 of 0.01% ~ 0.05%, and is co-doped with alkali metal and chlorine, with an average alkali metal content of 300 ~ 500 ppm; the inner cladding layer 2 has a radius R2 of 6 ~ 20 μm, and the fluorine content in the radial direction of the inner cladding layer 2 is distributed with a high outer and low inner distribution, the relative refractive index difference Δn2 of the inner cladding layer 2 is graded, with an average value of -0.30% ~ -0.20%, the fluorine content near its inner surface region of the inner cladding layer 2 is 4000 ~ 6000 ppm, and the fluorine content near its outer surface region is 8000 ~ 10000 ppm; the outer cladding layer 3 has a radius R3 of 20 ~ The relative refractive index difference Δn3 of the outer cladding layer 3 is -0.15% to -0.10% at a thickness of 60 μm.
[0058] The ultra-low attenuation optical fiber prepared according to the above method, after actual testing, exhibits a loss of 0.158 dB / km at a wavelength of 1550 nm, preferably 0.153 dB / km, and more preferably 0.148 dB / km; a loss of 0.60 dB / km at a wavelength of 1383 nm, preferably 0.40 dB / km, and more preferably 0.30 dB / km; and an effective area of 120 ~ 150 μm at a wavelength of 1550 nm. 2 The cable cutoff wavelength is equal to or less than 1530nm. When the ultra-low attenuation fiber is bent 100 times with a radius of 30mm, the macro bending loss at a wavelength of 1550nm is equal to or less than 0.01dB, and under preferred conditions it is equal to or less than 0.005dB.
[0059] Based on the first and second parts of the above embodiments, this application specifically implements and prepares the following six sets of ultra-low attenuation optical fibers, the specifications and related parameters of which are shown in Table 1 below: Table 1: Parameter Table of Ultra-Low Attenuation Optical Fibers in Six Embodiments of This Application
[0060] In Table 1, R1 is the radius of core layer 1, Δn1 is the relative refractive index difference of core layer 1, R2 is the radius of inner cladding layer 2, Δn2 is the relative refractive index difference of inner cladding layer 2, R3 is the radius of outer cladding layer 3, Δn3 is the relative refractive index difference of outer cladding layer 3, and F... min The F content in the inner cladding layer 2 near the inner surface region, F max The F content is in the region of the inner cladding layer 2 near the outer surface.
[0061] The ultra-low attenuation optical fiber under the above-described implementation scheme was tested, and its optical fiber parameters are shown in Table 2 below: Table 2 Ultra-low attenuation optical fiber parameter table of six embodiments of this application
[0062] In summary, the preparation method provided in this application and the ultra-low attenuation optical fiber prepared therefrom have at least the following beneficial effects: 1. By utilizing the characteristics of H2O diffusion and reaction in SiO2 that depend on temperature and time, hydroxyl groups are generated that are unevenly distributed in the soot body, and then a fluorine-doped sleeving with a low fluorine content distribution inside and high fluorine content outside is generated through the substitution reaction of fluorine and hydroxyl groups, which serves as the inner cladding.
[0063] 2. Uniform alkali metal doping is achieved during core deposition using in-tube deposition technology, and a certain amount of chlorine doping is achieved by controlling the partial pressure of silicon tetrachloride and oxygen, which increases the refractive index while avoiding increased Rayleigh scattering.
[0064] 3. By doping the core layer with chlorine and gradually doping the inner cladding with fluorine, it is beneficial to achieve refractive index matching and viscosity matching between the core layer and the inner cladding, thereby reducing stress loss. At the same time, the lower limit region formed between the deep fluorine doping of the inner cladding and the shallow fluorine doping of the outer cladding is beneficial to balancing the large effective area and bending resistance. The uniform doping of alkali metals in the core layer significantly reduces the viscosity and virtual temperature of the core layer, which together promotes the reduction of transmission loss.
[0065] It should be understood that expressions such as "comprising" and "may include" as used in this application indicate the existence of the disclosed functions, operations, or constituent elements, and do not limit one or more additional functions, operations, and constituent elements. In this application, terms such as "comprising" and / or "having" may be interpreted as indicating a specific characteristic, number, operation, constituent element, component, or combination thereof, but should not be interpreted as excluding the existence or possibility of adding one or more other characteristics, numbers, operations, constituent elements, components, or combinations thereof.
[0066] It should be understood that the terms “center,” “upper,” “lower,” “front,” “rear,” “left,” “right,” “vertical,” “horizontal,” “inner,” “outer,” “clockwise,” “counterclockwise,” “axial,” “radial,” and “circumferential” indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on this application.
[0067] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of technical features indicated. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. In the description of this application, "multiple" means two or more, unless otherwise explicitly specified.
[0068] In this application, unless otherwise expressly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection between two components. Those skilled in the art can understand the specific meaning of the above terms in this application according to the specific circumstances.
[0069] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of this application and is not intended to limit this application. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this application should be included within the protection scope of this application.
Claims
1. A method for fabricating ultra-low attenuation optical fiber, characterized in that, The preparation method includes the following steps: S1, using an external vapor deposition process to prepare a fluorine-doped sleeve with non-uniform fluorine distribution, wherein the non-uniform fluorine distribution is that the fluorine content is distributed with a high outer layer and a low inner layer in the radial direction of the fluorine-doped sleeve; S2, stretching and etching the fluorine-doped sleeve to obtain an inner cladding (2) with a predetermined aperture; S3, depositing SiO2 and performing alkali metal doping inside the inner cladding (2) using an in-tube vapor deposition process to form a core layer (1), and melting and shrinking the inner cladding (2) with the core layer (1) to obtain a rod-shaped structure; S4, preparing an outer cladding (3) outside the rod-shaped structure using an external vapor deposition process, and drying the rod-shaped structure with the outer cladding (3) and then solidifying it in a fluorine-containing atmosphere to obtain an optical fiber preform; S5, drawing the optical fiber preform to form an optical fiber.
2. The method for fabricating ultra-low attenuation optical fiber according to claim 1, characterized in that, In step S1, the preparation of the fluorine-doped sleeve with uneven fluorine distribution using an external vapor deposition process includes: S11, depositing flame-hydrolyzed SiO2 particles on the outside of the mandrel using an external vapor deposition process to form a soot body; S12, after removing the mandrel, fixing the soot body with a hollow target rod (6) and transferring it to the doping device (4); S13, after fully drying the soot body, introducing an inert gas containing saturated water vapor into it, so that the soot body achieves a state where the surface hydroxyl groups are more numerous than the internal hydroxyl groups; S14, introducing a fluorine-containing gas into the soot body, utilizing the substitution reaction between fluorine and hydroxyl groups to achieve uneven fluorine distribution in the soot body, and finally sintering to obtain the fluorine-doped sleeve.
3. The method for fabricating ultra-low attenuation optical fiber according to claim 2, characterized in that, In step S13, the process of thoroughly drying the soot includes: introducing a drying gas through the center of the target rod (6) to remove water and / or hydroxyl groups generated during the deposition process, wherein the drying gas is a chlorine-containing gas; and then removing the residual chlorine during the drying process by purging with oxygen.
4. The method for fabricating ultra-low attenuation optical fiber according to claim 2, characterized in that, In step S14, the fluorine-containing gas is one or a mixture of several of SiF4, SF6, CF4, and C2F6; the fluorine content in the sintered fluorine-doped sleeve is 4000-6000 ppm near its inner surface and 8000-10000 ppm near its outer surface.
5. The method for fabricating ultra-low attenuation optical fiber according to claim 1, characterized in that, In step S2, stretching and etching the fluorine-doped sleeve to obtain an inner cladding layer (2) with a predetermined pore size includes: stretching the fluorine-doped sleeve in a stretching furnace and removing impurities from the inner surface of the fluorine-doped sleeve by acid etching, so that the inner diameter is maintained in the range of 10 to 30 mm and the relative refractive index difference is -0.30% to -0.20%.
6. The method for fabricating ultra-low attenuation optical fiber according to claim 1, characterized in that, In step S3, the process of depositing SiO2 and performing alkali metal doping to form a core layer (1) inside the inner cladding (2) using in-tube vapor deposition includes: heating the alkali metal compound, using a carrier gas to carry the source vapor of the alkali metal compound into the tube of the inner cladding (2), and simultaneously depositing a chlorine-doped SiO2 layer inside the tube using O2 and SiCl4 as raw materials to obtain the core layer (1).
7. The method for fabricating ultra-low attenuation optical fiber according to claim 6, characterized in that, The alkali metal compound is a powdered alkali metal salt, and the average alkali metal content in the core layer (1) after alkali metal doping is 300 ~ 500 ppm, and the relative refractive index difference of the core layer (1) is 0.01% ~ 0.05%.
8. The method for fabricating ultra-low attenuation optical fiber according to claim 1, characterized in that, In step S4, the step of drying the rod-shaped structure with the outer cladding (3) and then solidifying it in a fluorine-containing atmosphere to obtain an optical fiber preform includes: drying the rod-shaped structure with the outer cladding (3) in a chlorine-containing gas and then transferring it to a sintering device to solidify it in a SiF4 atmosphere.
9. The method for fabricating ultra-low attenuation optical fiber according to claim 1, characterized in that, In step S5, the process parameters for drawing the optical fiber preform are: drawing speed of 1000 ~ 2000 m / min and drawing tension of 50 ~ 100 g.
10. An ultra-low attenuation optical fiber prepared by the preparation method according to any one of claims 1 to 9, characterized in that, The ultra-low attenuation optical fiber comprises, from the inside out, a core layer (1), an inner cladding layer (2), and an outer cladding layer (3) arranged coaxially. The core layer (1) has a radius of 5-6 μm and a relative refractive index difference of 0.01%-0.05%. The core layer (1) is co-doped with alkali metal and chlorine, with an average alkali metal content of 300-500 ppm. The outer ring radius of the inner cladding layer (2) is 19-20 μm. The fluorine content in the inner cladding layer (2) is distributed radially with a higher content on the outside and a lower content on the inside. The fluorine content near the inner surface of the inner cladding layer (2) is 4000-6000 ppm, and the fluorine content near the outer surface is 8000-10000 ppm. The outer ring radius of the outer cladding layer (3) is 124-125 μm, and the relative refractive index difference is -0.15%--0.10%.