Alkali metal halide doped core rod, preparation method thereof and alkali metal halide doped optical fiber

Abstract

The invention discloses an alkali metal halide doped core rod, a preparation method thereof and an alkali metal halide doped optical fiber, and relates to the technical field of optical information. Comprising the following steps: mixing SiO2 powder with an alkali metal halide solution to obtain a mixture; discharging the solution in the mixture to obtain a solid matter; compressing, drying, dehydrating and sintering the solid matter to obtain a doped glass rod; and pickling, extending and polishing the doped glass rod to obtain the alkali metal halide doped core rod. Rapid and uniform doping is realized through physical mixing of SiO2 powder and an alkali metal halide doping solution, the key problems of high difficulty in alkali metal halide gasification, heat preservation and flow control, non-uniform diffusion doping, slow deposition doping rate and the like are solved, after the alkali metal halide is dissolved, alkali metal halide ions are uniformly distributed in the doping solution, and the doping efficiency is improved. Complete and uniform doping can be realized only by simply physically mixing the doping liquid and the SiO2 powder.

Description

TECHNICAL FIELD

[0001] The present application relates to the field of optical information technology, in particular to an alkali metal halide doped core rod and a preparation method thereof, and an alkali metal halide doped optical fiber. BACKGROUND

[0002] G.654 optical fiber has the characteristics of ultra-low attenuation and large effective area, and can be used as the primary choice for future terrestrial super-high-speed backbone transmission network. In the waveguide structure, the G.654 optical fiber at least includes three layers, from inside to outside, a pure SiO2 core layer, a fluorine-doped SiO2 underlay layer and a fluorine-doped SiO2 outer cladding layer. Although the fluorine doping reduces the refractive index of quartz glass, it also synchronously reduces the viscosity; in order to avoid the interface defects and the optical power loss caused thereby due to the mismatch of the core and cladding viscosities, an alkali metal halide element is usually doped in the core layer, so as to satisfy the total reflection condition of the core and cladding and realize the viscosity matching of the core and cladding. At present, PCVD is the mainstream method for manufacturing the G.654 core rod. Under the action of plasma, SiCl4 and O2 are ionized to generate SiO2 and Cl2, and the SiO2 is deposited layer by layer and glassified in situ; after the deposition is completed, the alkali metal halide vapor is introduced into the tube, and heating is performed to make the alkali metal halide vapor diffuse from inside to outside to realize the doping; after the doping is completed, the fluorine-containing gas is introduced to perform repeated etching, and then the G.654 core rod is fused and shrunk.

[0003] However, the method has the following problems: the equipment and process are complex, and the large size of the G.654 core rod or optical rod is difficult to realize due to the limitation of the equipment size; the alkali metal halide ion radius is large and the glass density is high, and the diffusion is difficult, and 90% of the alkali metal halide is wasted due to the escape; the alkali metal halide has high melting and boiling points, and the flow control of the high-temperature gas after gasification is difficult and has low accuracy, and the process repeatability is not high; the alkali metal halide gas is introduced from one side of the glass tube, and the concentration at different horizontal positions is different, resulting in non-uniform axial doping; the alkali metal halide diffuses from the inner wall to the outside, and is easy to be enriched on the inner surface, which not only causes non-uniform radial doping, but also easily causes crystallization. SUMMARY

[0004] The present application provides an alkali metal halide doped core rod and a preparation method thereof, and an alkali metal halide doped optical fiber, so as to solve the problems of the prior art, such as the difficulty in large size of the alkali metal halide doped core rod, high preparation cost, non-uniform doping and unstable product quality.

[0005] In a first aspect, the present application provides a preparation method of an alkali metal halide doped core rod, comprising the following steps: mixing SiO2 powder and an alkali metal halide solution to obtain a mixture; discharging the solution in the mixture to obtain a solid; compressing, drying, dehydrating and sintering the solid to obtain a doped glass rod; The doped glass rod is pickled, stretched and polished to obtain an alkali metal halide doped core rod.

[0006] The present application realizes rapid and uniform doping by adopting physical mixing of SiO2 powder and alkali metal halide doping solution, overcomes key problems such as difficulty in gasification, heat preservation and flow control of alkali metal halide and non-uniformity of diffusion doping and slow deposition doping, after the alkali metal halide is dissolved, alkali metal halide ions are uniformly distributed in the doping solution, only simple physical mixing of the doping solution and SiO2 powder is needed to realize complete and uniform doping, compared with traditional diffusion doping and deposition doping, the present application has obvious advantages, the doping concentration can be accurately controlled by changing the mass fraction of the doping solution and the liquid-solid ratio, and the alkali metal halides are all ionic compounds with high solubility, the doping solution can be prepared in a large concentration range, the doping concentration can be adjusted in a wide range, the excess doping solution can be recycled and used for the next doping, and the utilization rate of the doping substance (alkali metal halide) can theoretically reach 100%, which greatly saves the material cost. The core rod shape can be controlled by compression molding after molding, by controlling parameters such as the mold shape, the weight of SiO2 powder, the pressing load and time, the diameter and length of the core rod can be accurately controlled and different size core rods can be flexibly prepared, which breaks the limitation of the four processes that rely on the deposition process to control the powder rod shape, compared with the traditional in-pipe doping process, the doping of the present application is not constrained by the diameter of the lining pipe, and larger size optical fiber preform rods can be manufactured, which not only improves the utilization rate of the optical rod, but also reduces the overall rod manufacturing cost and the drawing cost. In addition, the raw materials such as SiO2 powder and alkali metal halide doping solution used in the present application have no strict quality requirements and can be recycled, which solves the problems of high material cost and serious waste in the existing doping technology.

[0007] In some embodiments, the alkali metal halide in the alkali metal halide solution includes at least one of KBr, KCl, KI, K2CO3, NaBr, NaCl, NaI and Na2CO3. The above-mentioned alkali metal halides have high solubility, which facilitates the preparation of solutions with different concentration requirements and the control of the doping concentration.

[0008] In some embodiments, the concentration of the alkali metal halide in the alkali metal halide solution accounts for 0.01% to 1.0%. The concentration of the alkali metal halide in this range can be selected according to the required doping concentration.

[0009] In some embodiments, the mass ratio of SiO2 powder to alkali metal halide solution is (0.5-4):1. The mass ratio of SiO2 powder to alkali metal halide solution in this range can facilitate the mixing of the two, thereby realizing better uniformity of alkali metal doping.

[0010] In some embodiments, the solid is compressed, dried, dehydrated, and sintered to obtain a doped glass rod. The pressure for compressing the solid is 0.5 MPa to 20 MPa. Within this range, the solid can be tightly combined, thereby reducing the bubble density in the core rod after sintering; and / or, The pressure holding time for compressing the solid is 0.5 min to 2 min. Within this range, the desired density and strength of the solid can be obtained, and the solid can be prevented from disintegrating during transfer.

[0011] It should be noted that the solid can be compressed by pressure filtration or suction filtration. The pressure filtration has a pressure of 0.5 MPa to 20 MPa and a pressure holding time of 0.5 min to 2 min. The suction filtration has a negative pressure of -0.1 MPa to -10 MPa and a suction filtration time of 0.5 min to 60 min. After the pressure filtration or suction filtration treatment, the liquid-solid ratio in the solid is 10% to 50%.

[0012] In some embodiments, the solid is compressed, dried, dehydrated, and sintered to obtain a doped glass rod. The drying temperature is 105°C to 600°C. Within this range, the free water in the solid can reach the boiling point and rapidly evaporate; and / or, The drying time is 30 min to 90 min. Within this range, the free water in the solid can be completely removed; and / or, The dehydration temperature is 900°C to 1200°C. Within this range, the hydroxyl groups and bound water in the solid can be efficiently removed without affecting the pore structure; and / or, The dehydration time is 30 min to 150 min. Within this range, the hydroxyl content in the solid can be less than 1 ppm; and / or, The dehydration gas atmosphere is Cl2, O2, and He. The above dehydration gas atmosphere can achieve a high efficiency and degree of hydroxyl removal; and / or, The sintering temperature is 1350°C to 1650°C. Within this range, the possible crystallization temperature range can be avoided, which helps to significantly alleviate the crystallization behavior of the alkali metal doped core rod, greatly improves the quality stability of the product, and the alkali metal doping concentration ≤200 ppm can select the sintering temperature and time as 1350-1500°C, 1-10 h, and the gas atmosphere is He. When the alkali metal doping concentration >200 ppm, the sintering temperature and time can be selected as 1500-1650°C, 10-60 min, and the gas atmosphere is He; and / or, The sintering time is 10 min to 600 min. Within this range, the solid can be completely glassy, non-crystalline, and free of internal macroscopic defects.

[0013] In some embodiments, the SiO2 powder is prepared by a chemical vapor deposition process using SiCl4 as a silicon source, and the chemical vapor deposition process includes any one of flame hydrolysis chemical vapor deposition, plasma enhanced chemical vapor deposition, laser induced chemical vapor deposition, hot wall chemical vapor deposition, ultrasonic spray pyrolysis chemical vapor deposition, and high gravity rotating bed reactor chemical vapor deposition. Using SiCl4 as a silicon source to prepare the SiO2 powder by the chemical vapor deposition process has the advantages of high product purity, fast deposition speed, and low production cost.

[0014] In some embodiments, the purity of SiCl4 is ≥ 99.99%, and the purity of SiCl4 in this range can make the mandrel have a higher purity, avoiding the influence of impurity elements on the quality of the mandrel; and / or, The purity of the alkali metal halide is ≥ 99.99%, and the purity of the alkali metal halide in this range can make the mandrel have a higher purity, avoiding the influence of impurity elements on the quality of the mandrel.

[0015] In a second aspect, the present application provides an alkali metal halide doped mandrel prepared by the preparation method of the alkali metal halide doped mandrel of the first aspect, wherein: The concentration of hydroxyl groups in the alkali metal halide doped mandrel is ≤ 1 ppm, and the concentration of hydroxyl groups in the alkali metal halide doped mandrel in this range can avoid abnormal water peaks and increased attenuation of the optical fiber; and / or, The doping concentration of the alkali metal halide in the alkali metal halide doped mandrel is 20-450 ppm, and the doping concentration of the alkali metal halide in the alkali metal halide doped mandrel in this range can have a lower high-temperature viscosity and a fictive temperature while preventing the mandrel from crystallizing; and / or, The concentration fluctuation of the alkali metal halide doped mandrel in the axial and radial directions is ≤ 5%. The concentration fluctuation of the alkali metal halide doped mandrel in the axial and radial directions in this range can make the mandrel have good viscosity uniformity, avoiding the stress concentration in a local area to produce micro defects during drawing.

[0016] In a third aspect, the present application provides an alkali metal halide doped optical fiber prepared by the alkali metal halide doped mandrel of the second aspect. BRIEF DESCRIPTION OF DRAWINGS

[0017] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the drawings needed in the embodiment description will be briefly introduced below. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0018] Figure 1 A core rod alkali metal doping concentration and crystallization temperature diagram of a preparation method of an alkali metal halide doped core rod according to an embodiment of the present application.

[0019] Figure 2 A process flow chart of a preparation method of an alkali metal halide doped core rod according to an embodiment of the present application.

[0020] Figure 3 A process flow chart of a preparation method of an alkali metal halide doped core rod according to an embodiment of the present application. DETAILED DESCRIPTION

[0021] To make the objects, technical solutions and advantages of the present application clearer, the technical solutions of the present application will be described clearly and completely below with reference to the embodiments of the present application. Obviously, the described embodiments are only a part of the embodiments of the present application, rather than all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0022] G.654 optical fiber has the characteristics of ultra-low attenuation and large effective area, and can be the primary choice for future terrestrial super-high-speed backbone transmission network. In the waveguide structure, G.654 optical fiber at least contains three layers, from inside to outside, they are pure SiO2 core layer, fluorine-doped SiO2 underlayer and fluorine-doped SiO2 outer cladding layer. Although fluorine doping reduces the refractive index of quartz glass, it also synchronously reduces the viscosity; in order to avoid the interface defects and the optical power loss caused by the interface defects due to the mismatch of core and cladding viscosities, alkali metal halide elements are usually doped in the core layer, which not only satisfies the total reflection condition of core and cladding, but also realizes the viscosity matching of core and cladding. At present, PCVD is the mainstream method for manufacturing G.654 core rods. Under the action of plasma, SiCl4 and O2 are ionized to generate SiO2 and Cl2, and SiO2 is deposited layer by layer and glassified in situ; after the deposition is completed, alkali metal halide vapor is introduced into the tube, and heating is performed to make it diffuse from inside to outside to realize doping; after the doping is completed, fluorine-containing gas is introduced for repeated etching, and then G.654 core rods are fused and shrunk.

[0023] However, the method has the following problems: the equipment and process complexity are high, and due to the limitation of equipment size, it is difficult to realize large size of G.654 core rods or optical rods; the ion radius of alkali metal halide mainly potassium is large and the glass density is high, so the diffusion is difficult, and 90% of the alkali metal halide is wasted due to escape; the melting and boiling points of alkali metal halide are high, the flow control of high-temperature gas after gasification is difficult and the accuracy is low, and the process repeatability is not high; the alkali metal halide gas is introduced from one side of the glass tube, and the concentration at different horizontal positions is different, resulting in non-uniform axial doping; the alkali metal halide diffuses from the inner wall to the outside, which is easy to enrich on the inner surface, not only resulting in non-uniform radial doping, but also easily causing crystallization phenomenon.

[0024] In view of this, the application provides an alkali metal halide doped core rod and a preparation method thereof, and an alkali metal halide doped optical fiber, so as to improve the problems of the existing alkali metal halide doped core rod, such as difficulty in large-size, high preparation cost, uneven doping, and unstable product quality.

[0025] In a first aspect, the application provides a preparation method of an alkali metal halide doped core rod, comprising the following steps: Mixing SiO2 powder and an alkali metal halide solution to obtain a mixture; Discharging the solution in the mixture to obtain a solid; Tightening, drying, dehydrating, and sintering the solid to obtain a doped glass rod; Acid washing, extending, and polishing the doped glass rod to obtain an alkali metal halide doped core rod.

[0026] The application realizes rapid and uniform doping by using physical mixing of SiO2 powder and an alkali metal halide doping solution, overcomes key problems such as difficulty in gasification, heat preservation, and flow control of alkali metal halide, and uneven diffusion doping and slow deposition doping, after the alkali metal halide is dissolved, alkali metal halide ions are uniformly distributed in the doping solution, only simple physical mixing of the doping solution and SiO2 powder is needed to realize complete and uniform doping, compared with traditional diffusion doping and deposition doping, the application has obvious advantages, the doping concentration can be accurately controlled by changing the mass fraction of the doping solution and the liquid-solid ratio, and the alkali metal halides are all ionic compounds with high solubility, the doping solution can be prepared in a large concentration range, the adjustment range of the doping concentration is wide, the excess doping solution can be recycled and used for the next doping, and the utilization rate of the doping material (alkali metal halide) can theoretically reach 100%, which greatly saves the material cost. The core rod shape can be controlled by compression molding after molding, by controlling parameters such as the shape of the mold, the weight of the SiO2 powder, the pressing load, and the time, the diameter and length of the core rod can be accurately controlled, and different sizes of core rods can be flexibly prepared, which breaks the limitation of the four processes that rely on the deposition process to control the shape of the powder rod, compared with the traditional in-tube doping process, the doping of the application is not constrained by the diameter of the liner tube, and larger size optical fiber preform rods can be manufactured, which not only improves the utilization rate of the optical rod, but also reduces the overall rod preparation cost and the drawing cost. In addition, the raw materials such as SiO2 powder and alkali metal halide doping solution used in the application have no strict quality requirements, and can be recycled, which solves the problems of high material cost and serious waste in the existing doping technology.

[0027] In some embodiments of the first aspect, the alkali metal halide solution comprises at least one of KBr, KCl, KI, K2CO3, NaBr, NaCl, NaI, and Na2CO3. The alkali metal halide has high solubility, which facilitates preparation of solutions with different concentrations and control of the doping concentration.

[0028] In some embodiments of the first aspect, the concentration of the alkali metal halide in the alkali metal halide solution is 0.01% to 1.0%. The concentration of the alkali metal halide in this range can be selected as needed to achieve a desired doping concentration.

[0029] In some embodiments of the first aspect, the mass ratio of the SiO2 powder to the alkali metal halide solution is (0.5-4):1. The mass ratio of the SiO2 powder to the alkali metal halide solution in this range facilitates thorough mixing of the two, thereby achieving good uniformity of the alkali metal doping.

[0030] In some embodiments of the first aspect, the doping glass rod is obtained by compacting, drying, dehydrating, and sintering the solid. In the compacting step, the pressure is 0.5 MPa to 20 MPa, and the holding time is 0.5 min to 2 min. The pressure in this range allows the solid to be tightly bound, thereby reducing the bubble density in the sintered rod. The holding time in this range achieves an ideal density and strength of the solid, preventing the solid from disintegrating during transfer.

[0031] It should be noted that the compacting of the solid can be performed by pressure filtration or suction filtration. In the pressure filtration, the pressure is 0.5 MPa to 20 MPa, and the holding time is 0.5 min to 2 min. In the suction filtration, the negative pressure is -0.1 MPa to -10 MPa, and the filtration time is 0.5 min to 60 min. After the pressure filtration or suction filtration, the liquid-solid ratio in the solid is 10% to 50%.

[0032] In some embodiments of the first aspect, the doping glass rod is obtained by compacting, drying, dehydrating, and sintering the solid. In the drying step, the temperature is 105°C to 600°C, which allows the free water in the solid to reach the boiling point and rapidly evaporate. The drying time is 30 min to 90 min, which ensures complete removal of the free water in the solid.

[0033] In conjunction with the first aspect, in some embodiments provided in this application, the process of compressing, drying, dehydrating, and sintering the solid to obtain a doped glass rod involves the following: the dehydration temperature is 900℃~1200℃. Within this temperature range, hydroxyl groups and bound water in the solid can be efficiently removed without affecting the pore structure. The dehydration time is 30min~150min. Within this time range, the hydroxyl content in the solid can be kept below 1ppm. The dehydration gas atmosphere is Cl2, O2, and He. This gas atmosphere allows for high hydroxyl removal efficiency and degree.

[0034] In conjunction with the first aspect, in some embodiments provided in this application, the process of compressing, drying, dehydrating, and sintering the solid to obtain a doped glass rod includes: Figure 1 As shown, the sintering temperature is 1350℃~1650℃. Sintering within this range avoids potential crystallization temperatures, significantly mitigating the crystallization behavior of alkali metal-doped core rods and greatly improving product quality stability. When the alkali metal doping concentration is ≤200ppm, a sintering temperature and time of 1350~1500℃ for 1~10h can be selected, with a He atmosphere. When the alkali metal doping concentration is >200ppm, a sintering temperature and time of 1500~1650℃ for 10~60min can be selected, with a He atmosphere and a sintering time of 10min~600min. Sintering times within this range ensure complete vitrification of the solid, preventing crystallization and eliminating internal macroscopic defects.

[0035] In conjunction with the first aspect, in some embodiments provided in this application, SiO2 powder is prepared using SiCl4 as the silicon source through a chemical vapor deposition (CVD) process. The CVD process includes any one of flame hydrolysis CVD, plasma-enhanced CVD, laser-induced CVD, hot-wall CVD, ultrasonic spray pyrolysis CVD, and high-gravity rotating bed reactor CVD. Using SiCl4 as the silicon source and employing CVD to prepare SiO2 powder offers advantages such as high product purity, fast deposition rate, and low production cost.

[0036] In conjunction with the first aspect, in some embodiments provided in this application, the purity of SiCl4 is ≥99.99%. The purity of SiCl4 within this range can ensure that the core rod has high purity and avoid impurity elements affecting the quality of the core rod.

[0037] In conjunction with the first aspect, in some embodiments provided in this application, the purity of the alkali metal halide is ≥99.99%. The purity of the alkali metal halide within this range can make the core rod have high purity and avoid impurity elements affecting the quality of the core rod.

[0038] The preparation process of the alkali metal doped core rod can adopt a lifting sintering, as shown in Figure 2 , or a hanging sintering, as shown in Figure 3 .

[0039] In a second aspect, the application provides an alkali metal halide doped core rod prepared by the preparation method of the alkali metal halide doped core rod.

[0040] In combination with the second aspect, in some embodiments provided by the application, the hydroxyl concentration in the alkali metal halide doped core rod is ≤1 ppm. When the hydroxyl concentration in the alkali metal halide doped core rod is within this range, the abnormal water peak of the optical fiber and the increase of the attenuation can be avoided.

[0041] In combination with the first aspect, in some embodiments provided by the application, the doping concentration of the alkali metal halide in the alkali metal halide doped core rod is 20-450 ppm. When the doping concentration of the alkali metal halide in the alkali metal halide doped core rod is within this range, the core rod has a lower high-temperature viscosity and a fictive temperature while being free of crystallization. The fictive temperature is a physical parameter of the glass itself, similar to the softening point temperature.

[0042] The doping concentration of the alkali metal in the alkali metal doped core rod can be predicted according to the following formula:

[0043] , wherein, C is the doping concentration of the alkali metal, in ppm; k is the alkali metal retention factor, when the sintering temperature is 1350-1500°C k , the value is 0.85, when the sintering temperature is 1500-1650°C k , the value is 0.7; C m is the content of the alkali metal element in the alkali metal salt; w l is the mass fraction of the dopant in the doping solution; m l is the mass of the doping solution used in the mixing (the mass of the doping solution discharged by pressure filtration or suction filtration is excluded); ms is the mass of the SiO2 powder in the mixing. Through the above formula, the doping concentration of the alkali metal element in the alkali metal doped core rod can be predicted, and a suitable sintering temperature can be selected. For example, the alkali metal salt is KBr (i.e. C m is 39 / (39+80)=32.77%), the mass fraction of the doping solution w l is 0.5%, the mass of the SiO2 powder in the mixture ms and the doping solutionm l 6.0kg and 1.6kg respectively, the sintering temperature is 1540℃ (alkali metal retention factor k 0.7), the above parameters are substituted into the formula to calculate the alkali metal doping concentration C =305.9ppm.

[0044] In combination with the first aspect, in some embodiments provided in the application, the concentration fluctuation of the alkali metal halide doped core rod in the axial and radial directions is ≤5%. The concentration fluctuation of the alkali metal halide doped core rod in the axial and radial directions within this range can make the core rod have good viscosity uniformity, and avoid stress concentration in a local area during fiber drawing to produce micro defects.

[0045] The alkali metal halide doped core rod has all the technical solutions of the preparation method of the alkali metal halide doped core rod, and thus also has all the beneficial effects of the preparation method of the alkali metal halide doped core rod. The application will not be repeated here.

[0046] In a third aspect, the application provides an alkali metal halide doped optical fiber prepared from the alkali metal halide doped core rod of the second aspect. The alkali metal halide doped optical fiber has all the technical solutions of the preparation method of the alkali metal halide doped core rod, and thus also has all the beneficial effects of the preparation method of the alkali metal halide doped core rod. The application will not be repeated here.

[0047] The technical solutions provided in the application will be described in detail below in combination with embodiments.

[0048] Embodiment 1 The application embodiment 1 provides a preparation method of an alkali metal halide doped core rod, which comprises the following steps: SiCl4 as silicon source (purity 99.99%), high-purity H2 and O2 as fuel, SiO2 powder is prepared by flame hydrolysis chemical vapor deposition process; ultrapure water (total ion concentration of 12 ppb, TOC of 3 ppb, conductivity of 0.02 mS / m) and KBr (purity 99.99%) are used as raw materials to prepare KBr aqueous solution with mass fraction of 0.5%, which is the doping liquid; SiO2 powder and the doping liquid are poured into a quartz glass container (SiO2 powder mass 6 kg, doping liquid 3 kg, mass ratio of 2:1), and fully mixed by stirring; the excess doping liquid (1.4 kg) is discharged by high-pressure filtration (pressure 5 MPa, pressure holding time 2 min), and the mixture is formed into a compact whole, at this time the liquid-solid ratio in the mixture is 26.7:100; the mixture is moved into a sintering furnace to sequentially perform drying (temperature 105°C, time 60 min), dehydration (temperature 1150°C, time 60 min, gas atmosphere Cl2, O2 and He), sintering (predicted doping concentration 305.9 ppm, temperature 1540°C, time 30 min), to obtain a doped glass rod; the doped glass rod is sequentially subjected to pickling, stretching (equipment is an induction furnace) and polishing (high-temperature polishing, equipment is an induction furnace), to obtain the alkali metal halide doped type core rod.

[0049] Example 2 The application example 2 provides a preparation method of an alkali metal halide doped type core rod, comprising the following steps: SiCl4 as silicon source (purity 99.99%), high-purity CH4 and O2 as fuel, SiO2 powder is prepared by flame hydrolysis chemical vapor deposition process; ultrapure water (total ion concentration of 12 ppb, TOC of 3 ppb, conductivity of 0.02 mS / m) and KCl (purity 99.99%) are used as raw materials to prepare KCl aqueous solution with mass fraction of 0.08%, which is the doping liquid; SiO2 powder and the doping liquid are poured into a quartz glass container (SiO2 powder mass 6 kg, doping liquid 2 kg, mass ratio of 3:1), and fully mixed by stirring; the excess doping liquid (0.6 kg) is discharged by high-pressure filtration (pressure 10 MPa, pressure holding time 30 s), and the mixture is formed into a compact whole, at this time the liquid-solid ratio in the mixture is 23.3:100; the mixture is moved into a sintering furnace to sequentially perform drying (temperature 400°C, time 40 min), dehydration (temperature 1000°C, time 120 min, gas atmosphere Cl2, O2 and He), sintering (predicted doping concentration 83.0 ppm, temperature 1300°C, time 6 h), to obtain a doped glass rod; the doped glass rod is sequentially subjected to pickling, stretching (equipment is an induction furnace) and polishing (mechanical polishing, 1000 mesh), to obtain the alkali metal doped type core rod.

[0050] Example 3 The embodiment 3 of the present application provides a preparation method of an alkali metal halide doped type core rod, comprising the following steps: SiCl4 is used as a silicon source (purity: 99.99%), high-purity O2 is used as a reaction gas, and a SiO2 powder is prepared by using a plasma enhanced chemical vapor deposition process; ultrapure water (total ion concentration: 12 ppb, TOC: 3 ppb, and conductivity: 0.02 mS / m) and NaBr (purity: 99.99%) are used as raw materials to prepare a KCl aqueous solution with a mass fraction of 0.6%, that is, a doping liquid; the SiO2 powder and the doping liquid are poured into a quartz glass container (the mass of the SiO2 powder is 6 kg, the mass of the doping liquid is 2.4 kg, and the mass ratio of the SiO2 powder to the doping liquid is 2.5:1), and the SiO2 powder and the doping liquid are fully mixed by stirring; the excess doping liquid (0.7 kg) is discharged by high-pressure filtration (pressure: 10 MPa, and pressure maintaining time: 30 s), and the mixture is formed into a compact whole, and at this time, the liquid-solid ratio in the mixture is 28.3:100; the mixture is moved into a sintering furnace to sequentially perform drying (temperature: 600 °C, and time: 30 min), dehydration (temperature: 1200 °C, time: 50 min, and gas atmosphere: Cl2, O2 and He), and sintering (provisionally doped concentration: 285.0 ppm, temperature: 1600 °C, and time: 15 min) to obtain a doped glass rod; the doped glass rod is sequentially subjected to pickling, elongation (equipment: an electric resistance furnace) and polishing (mechanical polishing, 800 mesh) to obtain the alkali metal doped type core rod.

[0051] Embodiment 4 The embodiment 4 of the present application provides a preparation method of an alkali metal halide doped type core rod, comprising the following steps: SiCl4(99.99%) as silicon source, high purity O2 as reaction gas, SiO2 powder was prepared by plasma enhanced chemical vapor deposition process; ultrapure water (total ion concentration of 12 ppb, TOC of 3 ppb, conductivity of 0.02 mS / m) and NaBr (purity 99.99%) as raw materials, 1.0% mass fraction of KCl aqueous solution was prepared, which was the doping liquid; SiO2 powder and doping liquid were poured into a quartz glass container (SiO2 powder mass 6 kg, doping liquid 1.5 kg, mass ratio of 4:1), and fully mixed by stirring; the excess doping liquid (0.1 kg) was discharged by high-pressure filtration (pressure 10 MPa, pressure holding time 30 s), and the mixture was formed into a compact whole, at this time the liquid-solid ratio in the mixture was 23.3:100; the mixture was moved into a sintering furnace to dry (temperature 600°C, time 30 min), dehydrate (temperature 1200°C, time 30 min, gas atmosphere Cl2, O2 and He), sinter (predicted doping concentration 442.9 ppm, temperature 1350°C, time 600 min) in turn, and a doped glass rod was obtained; the doped glass rod was acid washed, stretched (equipment is resistance furnace) and polished (mechanical polishing, 800 mesh) in turn, and the alkali metal doped type core rod was obtained.

[0052] Example 5 The application embodiment 5 provides a preparation method of an alkali metal halide doped type core rod, SiCl4(99.99%) as silicon source, high purity CH4 and O2 as fuel, SiO2 powder was prepared by flame hydrolysis chemical vapor deposition process; ultrapure water (total ion concentration of 12 ppb, TOC of 3 ppb, conductivity of 0.02 mS / m) and KCl (purity 99.99%) as raw materials, 0.01% mass fraction of KCl aqueous solution was prepared, which was the doping liquid; SiO2 powder and doping liquid were poured into a quartz glass container (SiO2 powder mass 1 kg, doping liquid 2 kg, mass ratio of 0.5:1), and fully mixed by stirring; the excess doping liquid (1.5 kg) was discharged by high-pressure filtration (pressure 10 MPa, pressure holding time 30 s), and the mixture was formed into a compact whole, at this time the liquid-solid ratio in the mixture was 50:100; the mixture was moved into a sintering furnace to dry (temperature 400°C, time 40 min), dehydrate (temperature 900°C, time 150 min, gas atmosphere Cl2, O2 and He), sinter (predicted doping concentration 18.3 ppm, temperature 1650°C, time 10 min) in turn, and a doped glass rod was obtained; the doped glass rod was acid washed, stretched (equipment is induction furnace) and polished (mechanical polishing, 1000 mesh) in turn, and the alkali metal doped type core rod was obtained.

[0053] Comparative example 1 The present application provides a preparation method of an alkali metal halide doped core rod, comprising the following steps: A pure silicon reaction liner tube with an outer diameter of 40 mm and an inner diameter of 32 mm is placed in a PCVD (plasma chemical vapor deposition) device, and SiCl4 (purity 99.99%) required for depositing a core layer is introduced into the liner tube from left to right, and glassification is performed while depositing SiO2; after the deposition is completed, the hollow glass tube is placed on a fusion shrinking lathe, a certain amount of KBr powder (purity 99.99%) is placed in the left side of the glass tube, a resistance furnace is placed below to heat it (temperature 960°C), the KBr is evaporated into a gaseous form, and the KBr gas is sent into the glass tube by relying on O2 as a carrier gas; the glass tube is heated left and right reciprocally by using a high-temperature graphite furnace, so that the KBr gas diffuses outward from the inner wall of the glass tube at high temperature; after the doping is completed, the potassium element enriched on the inner wall is etched away by using C2F6; under negative pressure and high temperature (temperature 2000°C), the glass tube is fused and shrunk into a solid glass rod; finally, the original reaction liner tube is removed by physical polishing and mechanical polishing (1200 mesh) on the outer surface, and an alkali metal doped core rod is obtained.

[0054] Comparative Example 2 The present application provides a preparation method of an alkali metal halide doped core rod, comprising the following steps: At 5°C, 0.8 kg of hydrochloric acid (0.02η) is added to 6.0 kg of rectified ethyl silicate (purity 99.99%) for partial hydrolysis, and then the obtained solution is treated with 3 g of potassium ethoxide and stirred vigorously, followed by sequentially adding 1.4 kg of hydrochloric acid (0.02η) and 2.2 kg of water to completely hydrolyze it, to obtain a hydrolysis solution; at 20°C, a mixed solution of 0.5 L of ammonia water (29%), 8.4 L of ethanol and 2.7 kg of water is added to a mixture of 8.0 kg of ethyl silicate and 8.5 L of ethanol, the mixture is placed under negative pressure for 12 h, the alcohol in the mixture is replaced with water, and finally hydrochloric acid (2η) is added to adjust the pH value of the mixture to 4.5, and the obtained solution is stirred to obtain a SiO2 dispersion; the SiO2 dispersion and the hydrolysis solution are mixed into a sol solution, ammonia water (0.2η) and water are added, the pH value and volume of the sol solution are adjusted to 4.20 and 20 L respectively, the sol solution is transferred to a cylindrical container, and is gelled at 20°C and dried at 600°C to obtain a dry gel; the dry gel is transferred to a sintering furnace for dehydration (1100°C, 6 h) and sintering (1500°C, 6 h) in sequence, and is extended through an induction furnace, to obtain an alkali metal doped core rod.

[0055] Comparative Example 3 The present application provides a preparation method of an alkali metal halide doped core rod, comprising the following steps: SiO2 powder loose bodies with a density of 0.5 g / cm 3 The alkali metal doped loose bodies were transferred into a sintering furnace for dehydration (1100℃, 6h) and sintering (1500℃, 6h), and then were extended in an induction furnace to obtain the alkali metal doped core rods.

[0056] Performance test The alkali metal halide doped core rods prepared in Examples 1 to 5 and Comparative Examples 1 to 3 were sliced and sampled (sampling at equal intervals, 20 samples for each core rod) and polished. The same positions of the 20 samples were tested for alkali metal doping concentration by laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS), and the concentration fluctuation was calculated and used to represent the doping uniformity in the axial direction of the core rod; different positions on the same sample were tested for alkali metal doping concentration by laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS), and the concentration fluctuation was calculated and used to represent the doping uniformity in the radial direction of the core rod.

[0057] In order to represent the product performance of the alkali metal doped core rods, the alkali metal halide doped core rods prepared in Examples 1 to 5 and Comparative Examples 1 to 3 were extended to a specific diameter (18mm), and then a fluorine-doped depression layer and a fluorine-doped outer cladding layer were covered on the surface thereof by a sleeve melting and shrinking process, the relative refractive indexes of the fluorine-doped depression layer and the fluorine-doped outer cladding layer were -0.33% and -0.26% respectively, to obtain a complete alkali metal doped optical fiber preform (G.654.E optical fiber preform), and an alkali metal doped optical fiber (G.654.E optical fiber) was drawn therefrom, and the performance thereof was determined, and the specific test methods were as follows: Hydroxyl content (ppm): Fourier infrared spectroscopy (FTIR).

[0058] Average doping concentration (ppm): Laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS).

[0059] Radial concentration fluctuation (%): Laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS).

[0060] Axial concentration fluctuation (%): Laser ablation-inductively coupled plasma mass spectrometry (LA-ICP-MS).

[0061] 1550nm attenuation (dB / km): Optical time domain reflectometer (OTDR) test method.

[0062] 1625nm attenuation (dB / km): Optical time domain reflectometer (OTDR) test method.

[0063] 1550nm mode field diameter (μm): Variable aperture method.

[0064] Cutoff wavelength (nm): Transmittance power method.

[0065] Effective area (pm2): Variable aperture method. 2 ): Variable aperture method.

[0066] The test results are shown in Tables 1 and 2.

[0067] Table 1 Performance of alkali metal halide-doped core rods of Examples 1-5 and alkali metal halide-doped core rods of Comparative Examples 1-3

[0068] As can be seen from Table 1, in terms of hydroxyl content, the hydroxyl content in Examples 1-5 is 0.02-0.38 ppm, which is smaller than that of Comparative Examples 1-3; in terms of alkali metal concentration uniformity, when the doping concentration range is 20-450 ppm, the alkali metal doping concentration fluctuation of Examples 1-5 in the axial and radial directions is less than 5%, which is much better than that of Comparative Examples 1-3; in terms of comprehensive manufacturing cost, the manufacturing cost of Examples 1-5 is 468-491 yuan / kg, which is 49.3% or less of that of Comparative Examples 1-2.

[0069] Table 2 Performance of alkali metal halide-doped optical fibers of Examples 1-5 and alkali metal halide-doped optical fibers of Comparative Examples 1-3

[0070] As can be seen from Table 2, compared with the G.654.E optical fibers prepared from the core rods of Comparative Examples 1-3, the G.654.E optical fibers prepared from the core rods of Examples 1-5 have lower signal attenuation at 1550 nm and 1625 nm. Therefore, compared with the methods of Comparative Examples 1-3, the alkali metal-doped core rods manufactured by the present application have obvious performance and cost advantages and have the potential for large-scale popularization and application.

[0071] Comparative Example 1 has high equipment and process complexity due to the PCVD process mechanism, and it is difficult to scale up the G.654 core rod or optical rod due to the limitation of equipment size; the potassium-based alkali metal halide ion has large radius and high glass density, making it difficult to diffuse, and 90% of the alkali metal halide is wasted due to escape; the alkali metal halide has high melting and boiling points, and it is difficult to control the flow of high-temperature gas after gasification and has low accuracy, resulting in low process repeatability; the alkali metal halide gas is introduced from one side of the glass tube, and the concentration at different horizontal positions is different, resulting in uneven axial doping; the alkali metal halide diffuses from the inner wall to the outside, which is easy to enrich on the inner surface, not only resulting in uneven radial doping, but also easily causing crystallization.

[0072] Comparative Example 2 uses a sol-gel method to prepare SiO2, and Comparative Example 2 is an alkyl silicate and low-temperature conditions, and the doping reaction occurs when the dopant is mixed with the SiO2gel. The metal alcoholate of potassium (potassium ethoxide) is used as the dopant, which will hydrolyze to form KOH and alcohol. Since the melting point of KOH is only 361°C, it means that under the high temperature conditions of dehydration and sintering, KOH will quickly vaporize and escape from the SiO2loose body, and cannot chemically react with SiO2at high temperatures and achieve effective doping; at the same time, the low-melting-point KOH is easy to form droplets in the SiO2loose body and accumulate locally, resulting in the appearance of local potassium-rich areas, which not only significantly increases the crystallization probability, but also causes refractive index distortion, affecting the quality of the optical fiber and the uniformity of the attenuation. In addition, since KOH is a strong base, it is a catalyst for depolymerizing the SiO2network. Under high temperature conditions, it not only easily corrodes the SiO2network and causes structural defects, further increasing the attenuation of the optical fiber, but also severely shortens the service life of the furnace core tube for dehydration and sintering, indirectly increasing the manufacturing cost of the optical rod. In addition, KOH contains hydroxyl groups, which will cause additional infrared absorption loss, and its impact on the attenuation of the optical fiber at 1383 nm cannot be ignored.

[0073] Comparative Example 3 directly soaks the SiO2loose body in the dopant solution for doping. Due to the loose and porous and low-density characteristics (0.3-0.8 g / cm3) of the loose body, it will absorb a large amount of dopant solution, making it difficult to maintain a stable shape and even causing disintegration. Even if the remaining part after soaking can be sintered, after sintering, there will be problems such as many bubbles, opacity, high hydroxyl content, surface defects, etc. Therefore, this method cannot properly solve the problem of optical rod forming. However, by controlling the water content in the mixture after doping through pressure filtration or suction filtration, the present application can reduce the problems of many bubbles, opacity, and high hydroxyl content after sintering; by using a mold and high-pressure load, the shape of the SiO2powder body is controlled, and the surface defect problem is solved.

[0074] In summary, by using physical mixing of SiO2 powder and alkali metal halide doping liquid to achieve rapid and uniform doping, the key problems such as difficulty in gasification, heat preservation and flow control of alkali metal halide, non-uniformity of diffusion doping and slow deposition doping rate are overcome. After the dissolution of alkali metal halide, alkali metal halide ions are uniformly distributed in the doping liquid. Only simple physical mixing of the doping liquid and SiO2 powder can achieve complete uniform doping. Compared with traditional diffusion doping and deposition doping, it has obvious advantages. The doping concentration can be accurately controlled by changing the mass fraction of the doping liquid and the liquid-solid ratio. Moreover, alkali metal halides are all ionic compounds with high solubility, and the concentration range of the prepared doping liquid is large, so the adjustment range of the doping concentration is wide. The excess doping liquid can be recycled and used for the next doping. The utilization rate of the doping material (alkali metal halide) can theoretically reach 100%, which greatly saves the material cost. The core rod shape can be controlled by compression molding after molding. By controlling the mold shape, SiO2 powder weight, pressing load and time, etc., the diameter and length of the core rod can be accurately controlled and different size core rods can be flexibly prepared. The application breaks the limitation of the four processes relying on the deposition process to control the powder rod shape. Compared with the traditional in-pipe doping process, the doping of the application is not constrained by the diameter of the liner pipe, and the manufacturing of larger size optical fiber preform rods can be realized. Not only the utilization rate of the optical rod can be improved, but also the overall rod manufacturing cost and drawing cost can be reduced. In addition, the SiO2 powder and alkali metal halide doping liquid used in the application have no strict quality requirements and can be recycled, solving the problems of high material cost and serious waste in the existing doping technology.

[0075] In the description of the present specification, the description of the terms "one embodiment / way", "some embodiments / ways", "example", "specific example" or "some examples" means that the specific features, structures, materials or characteristics described in connection with the embodiment / way or example are included in at least one embodiment / way or example of the present application. In the present specification, the illustrative description of the above terms does not necessarily refer to the same embodiment / way or example. Moreover, the specific features, structures, materials or characteristics described can be combined in any appropriate manner in any one or more embodiments / ways or examples. In addition, the skilled person in the art can combine and combine the different embodiments / ways or examples described in the present specification and the features of the different embodiments / ways or examples without contradiction.

[0076] It has to be noted that, in the present application, terms like "first", "second", and the like in the description and in the claims are used to distinguish between similar elements and not necessarily to describe a sequential or chronological order. Furthermore, the terms "comprises", "comprising", or any other variation thereof, are intended to cover a non-exclusive inclusion, such that a process, method, article, or apparatus that comprises a list of elements does not include only those elements but can also include other elements not expressly listed or inherent to such process, method, article, or apparatus. An element proceeded by "comprises... a" does not, without more constraints, exclude the presence of additional identical elements in the process, method, article, or apparatus that comprises the element. The term "plurality" denotes two or more, for example two, three or four unless expressly specified otherwise.

[0077] The foregoing is considered as illustrative only of the principles of the application. Numerous modifications and changes will readily occur to those skilled in the art, and the generic principles defined herein can be applied to other embodiments without departing from the spirit or scope of the application. Accordingly, the scope of the application is indicated by the appended claims rather than by the foregoing description, and all changes that come within the meaning and range of equivalents are intended to be embraced therein.

Claims

1. A method for producing an alkali metal halide-doped core rod, characterized by, The method comprises the following steps: mixing SiO2 powder and an alkali metal halide solution to obtain a mixture; removing the solution in the mixture to obtain a solid; compressing, drying, dehydrating and sintering the solid to obtain a doped glass rod; acid washing, elongating and polishing the doped glass rod to obtain an alkali metal halide doped core rod.

2. The method of producing an alkali metal halide-doped core rod according to claim 1, wherein In the alkali metal halide solution, the alkali metal halide comprises at least one of KBr, KCl, KI, K2CO3, NaBr, NaCl, NaI and Na2CO3.

3. The method of producing an alkali metal halide-doped core rod according to claim 1, wherein In the alkali metal halide solution, the concentration of the alkali metal halide accounts for 0.01% to 1.0%.

4. The method of producing an alkali metal halide-doped core rod according to claim 1, wherein The mass ratio of the SiO2 powder to the alkali metal halide solution is (0.5-4):

1.

5. The method of producing an alkali metal halide-doped core rod according to claim 1, wherein In the step of compressing, drying, dehydrating and sintering the solid to obtain a doped glass rod: the pressure for compressing the solid is 0.5 MPa to 20 MPa; and / or, the pressure holding time for compressing the solid is 0.5 min to 2 min.

6. The method of producing an alkali metal halide-doped core rod according to claim 1, wherein In the step of compressing, drying, dehydrating and sintering the solid to obtain a doped glass rod: the temperature for drying is 105°C to 600°C; and / or, the time for drying is 30 min to 90 min; and / or, the temperature for dehydrating is 900°C to 1200°C; and / or, the time for dehydrating is 30 min to 150 min; and / or, the gas atmosphere for dehydrating is Cl2, O2 and He; and / or, the temperature for sintering is 1350°C to 1650°C; and / or, the time for sintering is 10 min to 600 min.

7. The method of producing an alkali metal halide-doped core rod according to claim 1, wherein The SiO2 powder is prepared by chemical vapor deposition process using SiCl4 as a silicon source, and the chemical vapor deposition process comprises any one of flame hydrolysis chemical vapor deposition, plasma enhanced chemical vapor deposition, laser-induced chemical vapor deposition, hot-wall chemical vapor deposition, ultrasonic spray pyrolysis chemical vapor deposition and supergravity rotating bed reactor chemical vapor deposition.

8. The method for preparing the alkali metal halide doped core rod according to claim 7, wherein: the purity of SiCl4 is ≥99.99%; and / or, the purity of the alkali metal halide is ≥99.99%.

9. An alkali metal halide doped type rod characterized in that, The alkali metal halide doped core rod is prepared by the method according to any one of claims 1 to 8, wherein: the hydroxyl concentration in the alkali metal halide doped core rod is ≤1 ppm; and / or, the doping concentration of the alkali metal halide in the alkali metal halide doped core rod is 20-450 ppm; and / or, the concentration fluctuation of the alkali metal halide doped core rod in the axial and radial directions is ≤5%.

10. An alkali metal halide-doped optical fiber, characterized by, The alkali metal halide doped core rod is prepared by the method according to claim 9.

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