Fluoroaluminophosphate glass hetero optical fiber preform and method of making same

Abstract

This invention relates to the field of optical fiber fabrication, and particularly to a fluorinated aluminum-fluorophosphate glass heterostructure optical fiber preform and its fabrication method, comprising: S1: preparing fluorinated aluminum core glass raw materials and fluorophosphate cladding glass raw materials, and melting them separately to obtain fluorinated aluminum core glass melt and fluorophosphate cladding glass melt; S2: preheating the preform forming mold to a preset temperature, and sequentially injecting the fluorophosphate cladding glass melt and the fluorinated aluminum core glass melt into the mold along the side of the mold using a suction injection method to form a core-cladding composite structure preform cylinder; S3: annealing and precision machining the preform cylinder to obtain the fluorinated aluminum-fluorophosphate glass heterostructure optical fiber preform. This invention effectively suppresses surface crystallization of the fluorinated aluminum core during the drawing process, solves the problems of poor core-cladding interface bonding and easy delamination, significantly reduces optical fiber transmission loss, and significantly improves the finished quality and stability of the optical fiber.

Description

Technical Field

[0001] This invention belongs to the field of optical fiber fabrication technology, and particularly relates to a fluorine-aluminum-fluorophosphate glass heterostructure optical fiber preform and its fabrication method. Background Technology

[0002] Fiber optic devices, with their advantages of long transmission distance, strong anti-interference ability, and high stability, are widely used in optical communication, laser transmission, and sensing. For a long time, silica fiber has dominated the market due to its mature manufacturing process and good physicochemical stability. However, the transmission loss of silica fiber increases sharply in the mid-infrared band with wavelengths greater than 2.4 micrometers, severely limiting its application in mid-infrared optical systems such as infrared laser transmission, gas sensing, and thermal imaging.

[0003] To overcome the wavelength limitations of silica optical fibers, researchers have turned to developing novel optical fiber materials suitable for the mid-infrared band. Fluoride glasses and chalcogenide glasses have become important candidate materials due to their wide transmission range and low phonon energy. Among them, chalcogenide glasses, although having a wider transmission range, suffer from stringent preparation conditions, poor thermal stability, and low rare-earth ion doping concentrations, making large-scale applications difficult. In contrast, fluoride glasses (such as fluorinated zirconium-based, fluorinated indium-based, and fluorinated aluminum-based glasses) maintain a wide mid-infrared transmission window while possessing high rare-earth doping capability and good chemical stability, making them an ideal material for mid-infrared optical fibers.

[0004] Among various fluoride glasses, aluminum fluoride (AFL) glass has attracted much attention due to its excellent chemical stability, water resistance, and high rare-earth ion solubility, and is considered an excellent substrate for fabricating mid-infrared fiber optic devices. However, AFL glass also has significant drawbacks: the difference between its glass transition temperature (Tx) and crystallization temperature (Tg) (ΔT=Tx-Tg) is small, resulting in poor thermal stability and a narrow window for fiber drawing processes; at the same time, AFL glass has a high drawing temperature, and during the drawing process, it is prone to reacting with moisture in the air, inducing surface crystallization, agglomeration, and even breakage, which seriously affects the forming quality and optical performance of the fiber.

[0005] Currently, the industry mainly adopts two technical solutions for the preparation of fluorinated aluminum glass optical fibers: one is a single fluorinated aluminum glass system. The optical fiber preform prepared by this method has poor anti-crystallization performance of the glass itself, and there is no effective cladding protection during the drawing process. Problems such as crystallization, agglomeration, and breakage are prominent, resulting in poor fiber quality stability. The other is to use traditional silicate glass as cladding. Since silicate glass and fluorinated aluminum glass have large differences in key parameters such as transition temperature, softening point, and coefficient of thermal expansion, the bonding between the preform core and cladding interface is not tight, which easily produces gaps and bubble defects. Delamination is prone to occur during subsequent drawing, and the crystallization problem of fluorinated aluminum glass cannot be effectively improved, resulting in poor fiber loss control. Summary of the Invention

[0006] In view of this, the present invention aims to provide a fluorine-aluminum glass-fluorophosphate glass heterostructure optical fiber preform and its preparation method. By designing specific fluorine-aluminum glass and fluorophosphate glass compositions, matching the transition temperature, softening point, and coefficient of thermal expansion of the fluorine-aluminum glass and fluorophosphate glass, the fluorophosphate glass can be used as the cladding of the fluorine-aluminum glass, thereby reducing the difficulty of drawing fluorine-aluminum glass optical fibers, improving the quality of the preform, and thus improving the quality of the optical fiber and reducing optical fiber loss.

[0007] To achieve the above objectives, the technical solution created by this invention is implemented as follows: A fluorine-aluminum-fluorophosphate glass heterostructure optical fiber preform includes a fluorine-aluminum core glass and a fluorophosphate cladding glass wrapped around the fluorine-aluminum core glass. The molar percentage composition of fluoroaluminate fiber core glass is as follows: AlF3: 34mol%≤AlF3≤40mol%; BaF2: 8mol%≤BaF2≤10mol%; CaF2: 15mol%≤CaF2≤20mol%; SrF2: 8mol%≤SrF2≤10mol%; MgF2: 8mol%≤MgF2≤10mol%; PbF2: 0mol%≤MgF2≤10mol%; The molar percentage composition of fluorophosphate clad glass is as follows: Al(PO3)3: 0 mol% <Al(PO3)3≤10mol%; Ba(PO3)2: 0 mol% <Ba(PO3)2≤8mol%; AlF3: 25mol%≤AlF3≤35mol%; BaF2: 0mol%≤BaF2≤6mol%; CaF2: 16mol%≤CaF2≤20mol%; SrF2: 8mol%≤SrF2≤10mol%; MgF2: 8mol%≤MgF2≤10mol%; LiF: 0 mol% ≤ LiF ≤ 14 mol% NaF: 0 mol% ≤ NaF ≤ 5 mol% KF: 0 mol% ≤ KF ≤ 15 mol.

[0008] Furthermore, the rare earth fluoride is any one of YF3, LaF3, GdF3, YbF3, ErF3, TmF3, NdF3, PrF3, and HoF3.

[0009] A method for preparing a fluorine-aluminum-fluorophosphate glass heterostructure optical fiber preform includes the following steps: S1: Prepare raw materials for fluoroaluminate fiber core glass and fluorophosphate cladding glass, and melt them separately to obtain fluoroaluminate fiber core glass melt and fluorophosphate cladding glass melt for later use; S2: Preheat the preform molding mold to the preset temperature, and use the suction injection method to successively inject the fluorophosphate cladding glass melt and the fluoroaluminum fiber core glass melt into the preform molding mold along the side of the preform molding mold to form a fiber core-cladding composite structure preform cylinder; S3: Annealing and precision machining are performed on the core-cladding composite preform cylinder to obtain a fluorine-aluminum-fluorophosphate glass heterostructure optical fiber preform.

[0010] Furthermore, in step S1, the preparation of the fluoroaluminate fiber core glass raw material and the fluorophosphate cladding glass raw material specifically includes: According to the above molar percentage composition of fluoroaluminum fiber core glass, weigh the corresponding weight of glass raw materials to prepare fluoroaluminum fiber core glass raw materials; According to the above molar percentage composition of fluorophosphate clad glass, weigh the corresponding weight of glass raw materials to prepare fluoroaluminum fiber core glass raw materials.

[0011] Furthermore, in step S1, the melting of the fluoroaluminate fiber core glass melt and the fluorophosphate cladding glass melt specifically includes: After the fluoroaluminum fiber core glass raw materials are mixed evenly, they are placed in a crucible and melted and stirred in a furnace at the first melting temperature to obtain fluoroaluminum fiber core glass melt. The fluoroaluminum fiber core glass melt is then cooled to the first holding temperature and kept warm for later use. After the fluorophosphate clad glass raw materials are mixed evenly, they are placed into a crucible and melted and stirred in a furnace at the second melting temperature to obtain a fluorophosphate clad glass melt. The fluorophosphate clad glass melt is then cooled to the second holding temperature and kept warm for later use.

[0012] Furthermore, the first melting temperature is 940°C to 980°C, the melting time is at least 90 minutes, the first holding temperature is 750°C to 800°C, and the holding time is at least 120 minutes.

[0013] Furthermore, the second melting temperature is 850°C to 900°C, and the melting time is at least 40 minutes; the second holding temperature is 730°C to 750°C, and the holding time is at least 60 minutes.

[0014] Furthermore, in step S2, the preform molding die is placed in an annealing furnace and heated from room temperature to 408°C to 412°C at a heating rate of 10°C / h, and preheated at 408°C to 412°C for 3 hours.

[0015] Furthermore, in step S3, the core-cladding composite preform cylinder is placed in an annealing furnace and held at 408°C to 417°C for 6 hours, and then cooled to room temperature at a rate of 10°C / h.

[0016] Furthermore, in step S3, the outer cylindrical core-cladding composite preform is ground and polished to obtain a fluorine-aluminum-fluorine phosphate glass heterostructure fiber preform.

[0017] Compared with the prior art, the present invention can achieve the following beneficial effects: (1) Through specific component design, the transition temperature, softening point and coefficient of thermal expansion of fluoroaluminate fiber core glass and fluorophosphate clad glass are precisely matched. The coefficient of thermal expansion of fluoroaluminate fiber core glass is slightly greater than that of fluorophosphate clad glass. This design results in a slightly larger shrinkage of fluoroaluminate fiber core glass during the cooling process of injection molding. Under the constraint of fluorophosphate clad glass, a moderate residual compressive stress is formed inside the fluoroaluminate fiber core glass, which promotes tight bonding of the interface, significantly reduces defects such as interface gaps and bubbles, and avoids delamination during the drawing process. (2) Fluorophosphate cladding glass can remain stable at the high drawing temperature required for fluoroaluminate fiber core, effectively isolate the external environment (such as water vapor), significantly suppress the crystallization tendency on the fiber core surface, thereby greatly reducing the risk of fiber agglomeration and breakage during the drawing process, and improving the forming quality and stability of fiber. (3) Fluorophosphate glass itself is easy to process and draw. Combined with optimized melting and forming process parameters, the process window for optical fiber drawing is broadened, the overall difficulty of preform processing and optical fiber drawing is reduced, and production efficiency and product consistency are improved. (4) Thanks to the good core-packet matching and optimized preparation process, the resulting preform has fewer internal defects and higher interface quality. The fiber obtained after drawing exhibits extremely low transmission loss in the mid-infrared band (such as at 1976nm), which can be less than 0.1dB / m, giving full play to the optical advantages of fluoroaluminate glass. (5) Combining the excellent mid-infrared performance of fluoroaluminate glass with the protective effect of fluorophosphate cladding, the prepared optical fiber is suitable for a variety of high-end application fields such as infrared optical transmission, laser transmission, and optical fiber devices, and has high practical value and industrialization potential. Attached Figure Description

[0018] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments and descriptions of the invention are used to explain the invention and do not constitute an undue limitation of the invention. In the drawings: Figure 1 A schematic flowchart illustrating the preparation method of the fluorine-aluminum-fluorophosphate glass heterostructure optical fiber preform according to an embodiment of the present invention. Figure 2 A schematic diagram of the thermal expansion curve of the fluoroaluminate fiber core glass of Embodiment 1 of the present invention; the coefficient of thermal expansion is 16.3083 × 10⁻⁶ at 27℃~300℃. -6 (1 / K); the coefficient of thermal expansion is 15.6500 × 10⁻⁶ at 27℃~300℃. -6 (1 / K); the coefficient of thermal expansion is 14.8128 × 10⁻⁶ at 27℃~100℃. -6 (1 / K); Figure 3 A schematic diagram of the thermal expansion curve of the fluorophosphate clad glass in Example 1 of this invention; the coefficient of thermal expansion is 12.9954 × 10⁻⁶ at 27℃~300℃. -6 (1 / K); the coefficient of thermal expansion is 14.0445 × 10⁻⁶ at 27℃~300℃. -6 (1 / K); the coefficient of thermal expansion is 14.9200 × 10⁻⁶ at 27℃~100℃. -6 (1 / K). Detailed Implementation

[0019] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and specific embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and do not constitute a limitation thereof.

[0020] It should be noted that, unless otherwise specified, the embodiments and features described in the present invention can be combined with each other.

[0021] In the description of this invention, it should be understood that the terms "center," "longitudinal," "lateral," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," and "outer," etc., indicating orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, are used only for the convenience of describing this invention and for 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, and therefore should not be construed as a limitation on this invention. Furthermore, the terms "first," "second," etc., are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, features defined with "first," "second," etc., may explicitly or implicitly include one or more of that feature. In the description of this invention, unless otherwise stated, "a plurality of" means two or more.

[0022] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "assembly," "connection," and "joining" 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 of two components. Those skilled in the art will understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0023] The invention will now be described in detail with reference to the accompanying drawings and embodiments.

[0024] This invention provides a fluorine-aluminum-fluorophosphate glass heterostructure optical fiber preform, comprising a fluorine-aluminum core glass and a fluorophosphate cladding glass, wherein the fluorophosphate cladding glass is wrapped around the fluorine-aluminum core glass.

[0025] Fluorophosphate cladding glass completely covers the fluoroaluminate fiber core glass. During the subsequent fusion drawing process, the surface of the fluoroaluminate fiber core glass never comes into direct contact with the external environment, avoiding surface reactions between external moisture and the fluoroaluminate fiber core glass. The surface of the fluoroaluminate fiber core glass will not crystallize or agglomerate due to environmental factors, thus significantly improving the quality of the finished optical fiber.

[0026] The molar percentage composition of fluoroaluminate fiber core glass is as follows: AlF3: 34mol%≤AlF3≤40mol%; BaF2: 8mol%≤BaF2≤10mol%; CaF2: 15mol%≤CaF2≤20mol%; SrF2: 8mol%≤SrF2≤10mol%; MgF2: 8mol%≤MgF2≤10mol%; PbF2: 0mol%≤MgF2≤10mol%.

[0027] The molar percentage composition of fluorophosphate clad glass is as follows: Al(PO3)3: 0 mol% <Al(PO3)3≤10mol%; Ba(PO3)2: 0 mol% <Ba(PO3)2≤8mol%; AlF3: 25mol%≤AlF3≤35mol%; BaF2: 0mol%≤BaF2≤6mol%; CaF2: 16mol%≤CaF2≤20mol%; SrF2: 8mol%≤SrF2≤10mol%; MgF2: 8mol%≤MgF2≤10mol%; LiF: 0 mol% ≤ LiF ≤ 14 mol% NaF: 0 mol% ≤ NaF ≤ 5 mol% KF: 0 mol% ≤ KF ≤ 15 mol.

[0028] In fluorophosphate clad glass, the proportions of LiF, NaF, and KF can be finely adjusted within their respective molar percentage ranges, and the proportions of Al(PO3)3 and Ba(PO3)2 can be adjusted according to actual matching requirements, as long as they do not deviate from the core requirements of thermodynamic matching and high-temperature protection.

[0029] This invention involves doping rare-earth fluorides into fluoroaluminate fiber core glass. Rare-earth ions, with their high charge, small radius, and strong electric field, strongly attract and anchor surrounding fluoride ions upon introduction into the fluoroaluminate fiber core glass, significantly enhancing the connection strength and rigidity of the glass network (mainly composed of fluoride ions and metal cations). This stronger network makes it more difficult for atoms to rearrange into an ordered crystal structure, effectively widening the temperature range for stable glass existence. This directly provides a wider and safer process window for optical fiber drawing. Rare-earth fluorides can also finely control the physical parameters of the fluoroaluminate fiber core glass, particularly its coefficient of thermal expansion and transition temperature. By doping with rare-earth ions, the coefficient of thermal expansion of the fluoroaluminate fiber core glass is slightly higher than that of the fluorophosphate cladding glass. During cooling, the fluoroaluminate fiber core glass shrinks slightly more. Under the constraint of the fluorophosphate cladding glass, a moderate residual compressive stress is formed inside the fluoroaluminate fiber core glass, resulting in a tight molecular-level bond at the interface, effectively eliminating micro-gap and bubbles. By doping with rare earth ions, the transition temperatures between fluoroaluminate core glass and fluorophosphate clad glass can be matched, ensuring that the fluoroaluminate core glass and fluorophosphate clad glass undergo viscous flow within the same temperature range. This allows them to deform as a whole during injection molding and drawing, avoiding internal defects caused by inconsistent flow behavior.

[0030] The rare earth fluoride can be any one of YF3, LaF3, GdF3, YbF3, ErF3, TmF3, NdF3, PrF3, or HoF3. The choice of rare earth fluoride is only necessary to ensure that the thermodynamic parameters of the fluoroaluminate core glass match those of the fluorophosphate cladding glass, and that it does not affect the infrared optical performance.

[0031] This invention also provides a method for preparing a fluorine-aluminum-fluorophosphate glass heterostructure optical fiber preform, such as... Figure 1 As shown, the preparation method includes the following steps: S1: Prepare raw materials for fluoroaluminate fiber core glass and fluorophosphate cladding glass, and melt them separately to obtain fluoroaluminate fiber core glass melt and fluorophosphate cladding glass melt for later use.

[0032] Using AlF3, BaF2, CaF2, SrF2, MgF2, PbF2, and rare earth fluorides as raw materials, a certain weight of glass raw materials is weighed according to the above molar percentage composition of fluoroaluminum fiber core glass. The raw materials are thoroughly stirred to form a glass batch. The glass batch is placed in a crucible and melted in a furnace at 940℃~980℃ for at least 90 minutes, with continuous stirring to ensure glass homogeneity. The temperature is then uniformly reduced to 750℃~800℃ and held for at least 120 minutes to obtain fluoroaluminum fiber core glass melt for later use.

[0033] Using Al(PO3)3, Ba(PO3)2, AlF3, BaF2, CaF2, SrF2, MgF2, LiF, NaF, and KF as raw materials, according to the above molar percentage composition of fluorophosphate clad glass, a certain weight of glass raw materials is weighed and thoroughly stirred to form a glass batch. The glass batch is placed in a crucible and melted in a furnace at 850°C to 900°C for at least 40 minutes, with continuous stirring to ensure glass homogeneity. Then, the temperature is uniformly lowered to 730°C to 750°C and held for at least 60 minutes to obtain fluorophosphate clad glass melt for later use.

[0034] The present invention uses crucibles that are resistant to high temperatures and do not react with glass raw materials, such as platinum crucibles or glassy carbon crucibles.

[0035] S2: Preheat the preform molding mold to the preset temperature, and use the suction injection method to successively inject the fluorophosphate cladding glass melt and the fluoroaluminum fiber core glass melt into the preform molding mold along the side of the preform molding mold to form a fiber core-cladding composite structure preform cylinder.

[0036] The preform molding die is placed in an annealing furnace and heated from room temperature to 408-412℃ at a rate of 10℃ / h. It is then preheated at 408-412℃ for 3 hours to complete the preheating of the preform molding die. Subsequently, the prepared fluorophosphate clad glass melt is slowly poured into the preform molding die along its side. Then, fluoroaluminum fiber core glass melt is slowly poured into the preform molding die containing the fluorophosphate clad glass melt along its side, forming a fiber core-clad composite preform cylinder.

[0037] S3: Annealing and precision machining are performed on the core-cladding composite preform cylinder to obtain a fluorine-aluminum-fluorophosphate glass heterostructure optical fiber preform.

[0038] The core-cladding composite preform cylinder was placed in an annealing furnace and held at 408℃ to 417℃ for 6 hours, then slowly cooled to room temperature at a rate of 10℃ / h. After annealing, the outer diameter of the annealed core-cladding composite preform cylinder was ground and polished to obtain aluminoferrite-fluorophosphate glass heterostructure optical fiber preform.

[0039] This invention provides a fluorine-aluminum-fluorophosphate glass heterostructure optical fiber preform and its preparation method. The key lies in the specific proportions of the fluorine-aluminum core glass and the fluorophosphate cladding glass, as well as the matching preparation process. Table 1 lists the specific molar percentage composition and some performance parameters of three fluorine-aluminum core glass examples (1-core, 2-core, and 3-core). Table 2 lists the specific molar percentage composition and some performance parameters of three fluorophosphate cladding glass examples (1-packet, 2-packet, and 3-packet) that match the fluorine-aluminum core glass in Table 1.

[0040] Table 1. Mole percentage composition of the fluoroaluminum fiber core glass examples

[0041] Table 2. Mole percentage composition of fluorophosphate cladding glass examples

[0042] Example 1: Melting fluoroaluminate glass molten material: Select the first group of formulas (i.e., 1 core) according to Table 1, weigh 15g of glass raw materials and mix them thoroughly to form a glass batch; add the glass batch to a platinum crucible and place it in a furnace at 980℃ to melt for 90min, stirring constantly to ensure the glass is homogeneous. Then, cool it down to 800℃ at a uniform rate and hold it for 120min to obtain a fluoroaluminum fiber core glass melt, which is kept at 800℃ for later use.

[0043] Melting of fluorophosphate-clad glass melt: According to Table 2, select the first group of formulas (1 pack), weigh 35g of glass raw materials, mix them thoroughly to form a glass batch; add the glass batch to a platinum crucible, place it in a 900℃ furnace and melt for 40 minutes, stirring constantly to ensure the glass is homogeneous. Then, cool it down to 750℃ at a uniform rate and hold it for 60 minutes to obtain fluorophosphate-clad glass melt, and keep it at 750℃ for later use.

[0044] Injection molding: Using the injection method, the preform molding mold is first placed in an annealing furnace and heated from room temperature to 412℃ at a heating rate of 10℃ / h. The preform molding mold is preheated at this temperature for 3 hours. After preheating, the prepared fluorophosphate clad glass melt is slowly injected into the preform molding mold along the side of the mold. Then, the fluoroaluminum fiber core glass melt is slowly injected into the preform molding mold containing the fluorophosphate clad glass melt along the side of the mold, forming a fiber core-clad composite structure preform cylinder. Annealing treatment: The core-cladding composite preform cylinder is placed in an annealing furnace and held at 412℃ for 6 hours. Then, it is slowly cooled to room temperature at a cooling rate of 10℃ / h to complete the annealing treatment. Finishing process: The cylindrical core-cladding composite preform after annealing is subjected to external cylindrical grinding and polishing to remove surface impurities and defects, thereby obtaining a fluorine-aluminum-fluorophosphate heterostructure optical fiber preform that meets the dimensional accuracy requirements.

[0045] Figure 2 The thermal expansion curve of the fluoroaluminate fiber core glass in Embodiment 1 of the present invention is shown. Figure 3 It shows the relationship with Figure 2Thermal expansion curves of fluorophosphate clad glass paired with fluoroaluminum fiber core glass. (Comparison) Figure 2 and Figure 3 It is evident that the coefficient of thermal expansion of fluorophosphate cladding glass is slightly lower than that of fluoroaluminate fiber core glass, and the two values ​​are close and their curve trends are similar. This carefully designed coefficient of thermal expansion ensures that the shrinkage of fluoroaluminate fiber core glass is slightly larger during preform cooling and fiber drawing. Under the constraint of fluorophosphate cladding glass, a moderate residual compressive stress is formed inside the fluoroaluminate fiber core glass, thereby achieving a tight bond at the core-cladding interface and effectively avoiding delamination and interface defects.

[0046] Example 2 Melting fluoroaluminate glass molten material: According to Table 1, select the second group of formulas (i.e., 2 cores), weigh 15g of glass raw materials, mix them thoroughly to form a glass batch; add the glass batch to a platinum crucible, place it in a furnace at 950℃ and melt for 90min, stirring constantly to ensure the glass is homogeneous. Then, cool it uniformly to 780℃ and hold it for 120min to obtain fluoroaluminum fiber core glass melt, and maintain the temperature at 780℃ for later use.

[0047] Melting of fluorophosphate-clad glass melt: According to Table 2, select the second group of formulas (2 packs), weigh 35g of glass raw materials, mix them thoroughly to form a glass batch; add the glass batch to a platinum crucible, place it in an 870℃ furnace and melt for 60 minutes, stirring constantly to ensure the glass is homogeneous. Then, cool it down at a constant rate to 740℃ and hold it for 120 minutes to obtain a fluorophosphate-clad glass melt, which is kept at 740℃ for later use.

[0048] Injection molding: Using the injection method, the preform molding mold is first placed in an annealing furnace and heated from room temperature to 408℃ at a heating rate of 10℃ / h. The preform molding mold is preheated at this temperature for 3 hours. After preheating, the prepared fluorophosphate clad glass melt is slowly injected into the preform molding mold along the side of the mold. Then, the fluoroaluminum fiber core glass melt is slowly injected into the preform molding mold containing the fluorophosphate clad glass melt along the side of the mold, forming a fiber core-clad composite structure preform cylinder. Annealing treatment: The core-cladding composite preform cylinder is placed in an annealing furnace and held at 408℃ for 6 hours. Then, it is slowly cooled to room temperature at a cooling rate of 10℃ / h to complete the annealing treatment. Finishing process: The cylindrical core-cladding composite preform after annealing is subjected to external cylindrical grinding and polishing to remove surface impurities and defects, thereby obtaining a fluorine-aluminum-fluorophosphate heterostructure optical fiber preform that meets the dimensional accuracy requirements.

[0049] Example 3 Melting fluoroaluminate glass molten material: According to Table 1, select the third group of formulas (i.e., 3 cores), weigh 15g of glass raw materials, mix them thoroughly to form a glass batch; add the glass batch to a platinum crucible, place it in a furnace at 940℃ and melt for 90min, stirring constantly to ensure the glass is homogeneous. Then, cool it uniformly to 750℃ and hold it for 120min to obtain fluoroaluminum fiber core glass melt, and keep it at 750℃ for later use.

[0050] Melting of fluorophosphate-clad glass melt: According to Table 2, select the third group of formulas (3 packs), weigh 35g of glass raw materials, mix them thoroughly to form a glass batch; add the glass batch to a platinum crucible, place it in an 850℃ furnace and melt for 40 minutes, stirring constantly to ensure the glass is homogeneous. Then, cool it uniformly to 730℃ and hold it for 60 minutes to obtain fluorophosphate-clad glass melt, and keep it at 730℃ for later use.

[0051] Injection molding: Using the injection method, the preform molding mold is first placed in an annealing furnace and heated from room temperature to 417℃ at a heating rate of 10℃ / h. The preform molding mold is preheated at this temperature for 3 hours. After preheating, the prepared fluorophosphate clad glass melt is slowly injected into the preform molding mold along the side of the mold. Then, the fluoroaluminum fiber core glass melt is slowly injected into the preform molding mold containing the fluorophosphate clad glass melt along the side of the mold, forming a fiber core-clad composite structure preform cylinder. Annealing treatment: The core-cladding composite preform cylinder is placed in an annealing furnace and held at 417℃ for 6 hours. Then, it is slowly cooled to room temperature at a cooling rate of 10℃ / h to complete the annealing treatment. Finishing process: The cylindrical core-cladding composite preform after annealing is subjected to external cylindrical grinding and polishing to remove surface impurities and defects, thereby obtaining a fluorine-aluminum-fluorophosphate heterostructure optical fiber preform that meets the dimensional accuracy requirements.

[0052] The fluorine-aluminum-fluorophosphate heterostructure fiber preforms prepared in the above three embodiments were drawn into optical fibers at suitable temperatures. Test results showed that the fiber core-cladding interface was clear and defect-free, and the transmission loss at a wavelength of 1976 nm was less than 0.1 dB / m, far lower than the loss level of traditional fluorine-aluminum homostructure fibers. The fluorine-aluminum-fluorophosphate heterostructure fiber preforms did not exhibit cracking or crystallization during subsequent processing and storage, demonstrating good environmental stability and process adaptability.

[0053] It should be understood that the various forms of processes shown above can be used to reorder, add, or delete steps. For example, the steps described in this invention disclosure can be executed in parallel, sequentially, or in different orders, as long as the desired result of the technical solution disclosed in this invention can be achieved, and this is not limited herein.

[0054] The specific embodiments described above do not constitute a limitation on the scope of protection of this invention. Those skilled in the art should understand that various modifications, combinations, sub-combinations, and substitutions can be made according to design requirements and other factors. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of this invention should be included within the scope of protection of this invention.

Claims

1. A fluorialum-fluorphosphate glass hetero optical fiber preform, characterized by, This includes fluoroaluminate fiber core glass and fluorophosphate cladding glass that wraps around the fluoroaluminate fiber core glass; The molar percentage composition of fluoroaluminate fiber core glass is as follows: AlF3: 34mol%≤AlF3≤40mol%; BaF2: 8mol%≤BaF2≤10mol%; CaF2: 15mol%≤CaF2≤20mol%; SrF2: 8mol%≤SrF2≤10mol%; MgF2: 8mol%≤MgF2≤10mol%; PbF2: 0mol%≤MgF2≤10mol%; Rare earth fluorides: 15 mol% ≤ Rare earth fluorides ≤ 20 mol% The molar percentage composition of fluorophosphate clad glass is as follows: Al(PO3)3: 0 mol% <Al(PO3)3≤10mol%; Ba(PO3)2: 0 mol% <Ba(PO3)2≤8mol%; AlF3: 25mol%≤AlF3≤35mol%; BaF2: 0mol%≤BaF2≤6mol%; CaF2: 16mol%≤CaF2≤20mol%; SrF2: 8mol%≤SrF2≤10mol%; MgF2: 8mol%≤MgF2≤10mol%; LiF: 0 mol% ≤ LiF ≤ 14 mol% NaF: 0 mol% ≤ NaF ≤ 5 mol% KF: 0 mol% ≤ KF ≤ 15 mol.

2. The fluorine-aluminum-fluorophosphate glass heterostructure optical fiber preform as described in claim 1, characterized in that, The rare earth fluoride is any one of YF3, LaF3, GdF3, YbF3, ErF3, TmF3, NdF3, PrF3, and HoF3.

3. A method for preparing a fluorine-aluminum-fluorophosphate glass heterostructure optical fiber preform as described in claim 1 or 2, comprising the following steps: S1: Prepare raw materials for fluoroaluminate fiber core glass and fluorophosphate cladding glass, and melt them separately to obtain fluoroaluminate fiber core glass melt and fluorophosphate cladding glass melt for later use; S2: Preheat the preform molding mold to the preset temperature, and use the suction injection method to successively inject the fluorophosphate cladding glass melt and the fluoroaluminum fiber core glass melt into the preform molding mold along the side of the preform molding mold to form a fiber core-cladding composite structure preform cylinder; S3: Annealing and precision machining are performed on the core-cladding composite preform cylinder to obtain a fluorine-aluminum-fluorophosphate glass heterostructure optical fiber preform.

4. The method for preparing the fluorine-aluminum-fluorophosphate glass heterostructure optical fiber preform according to claim 3, characterized in that, In step S1, the preparation of the fluoroaluminate fiber core glass raw material and the fluorophosphate cladding glass raw material specifically includes: According to the molar percentage composition of the fluoroaluminate fiber core glass as described in claim 1, the corresponding weight of glass raw materials is weighed and prepared into fluoroaluminate fiber core glass raw materials; According to the molar percentage composition of the fluorophosphate clad glass as described in claim 1, the corresponding weight of glass raw materials is weighed and prepared into fluoroaluminum fiber core glass raw materials.

5. The method for preparing the fluorine-aluminum-fluorophosphate glass heterostructure optical fiber preform according to claim 3, characterized in that, In step S1, the melting of the fluoroaluminate fiber core glass melt and the fluorophosphate cladding glass melt specifically includes: After the fluoroaluminum fiber core glass raw materials are mixed evenly, they are placed in a crucible and melted and stirred in a furnace at the first melting temperature to obtain fluoroaluminum fiber core glass melt. The fluoroaluminum fiber core glass melt is then cooled to the first holding temperature and kept warm for later use. After the fluorophosphate clad glass raw materials are mixed evenly, they are placed into a crucible and melted and stirred in a furnace at the second melting temperature to obtain a fluorophosphate clad glass melt. The fluorophosphate clad glass melt is then cooled to the second holding temperature and kept warm for later use.

6. The method for preparing the fluorine-aluminum-fluorophosphate glass heterostructure optical fiber preform according to claim 5, characterized in that, The first melting temperature is 940°C to 980°C, the melting time is at least 90 minutes, the first holding temperature is 750°C to 800°C, and the holding time is at least 120 minutes.

7. The method for preparing the fluorine-aluminum-fluorophosphate glass heterostructure optical fiber preform according to claim 5, characterized in that, The second melting temperature is 850°C to 900°C, and the melting time is at least 40 minutes; the second holding temperature is 730°C to 750°C, and the holding time is at least 60 minutes.

8. The method for preparing the fluorine-aluminum-fluorophosphate glass heterostructure optical fiber preform according to claim 3, characterized in that, In step S2, the preform molding die is placed in an annealing furnace and heated from room temperature to 408°C to 412°C at a heating rate of 10°C / h, and preheated at 408°C to 412°C for 3 hours.

9. The method for preparing the fluorine-aluminum-fluorophosphate glass heterostructure optical fiber preform according to claim 3, characterized in that, In step S3, the core-cladding composite preform cylinder is placed in an annealing furnace and held at 408°C to 417°C for 6 hours, and then cooled to room temperature at a rate of 10°C / h.

10. The method for preparing the fluorine-aluminum-fluorophosphate glass heterostructure optical fiber preform according to claim 3, characterized in that, In step S3, the outer cylindrical core-cladding composite preform is ground and polished to obtain a fluorine-aluminum-fluorophosphate glass heterostructure fiber preform.

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