Magnetic-optical fiber with core-clad cooperative structure and its preparation method

Abstract

This invention discloses a magneto-optical fiber with a core-cladding co-structure and its fabrication method, belonging to the field of magneto-optical glass and optical fiber fabrication technology. The core of the magneto-optical fiber has a composition of 15Tb4O7−15Al2O3−30SiO2−40B2O3, and the cladding has a composition of 30La2O3−15Al2O3−30SiO2−40B2O3, with completely identical Al2O3, SiO2, and B2O3 contents in both the core and cladding. This achieves a high degree of matching of thermal parameters such as the coefficient of thermal expansion and softening point between the core and cladding, and precisely controls the refractive index difference, fundamentally ensuring the interface stability and light-guiding performance of the drawn fiber. During fabrication, the sol-gel method is used, with nitrates and other materials as raw materials. The process involves sol preparation, aging, drying, two-step pre-firing, and annealing to obtain the core rod and cladding tube, which are then drawn into fibers using the tube-rod method. This method utilizes the molecular-level mixing advantages of sol-gel to effectively suppress high-temperature phase separation and rare-earth ion aggregation, thereby improving optical uniformity; simultaneously, the introduction of B2O3 stabilizes Tb. 3+ The valence state was improved, and its solubility was increased. The process is simple, low-cost, and the resulting optical fiber exhibits excellent magneto-optical properties.

Description

Technical Field

[0001] This invention relates to the field of magneto-optical glass and optical fiber fabrication, and particularly to a magneto-optical optical fiber with a core-cladding cooperative structure and its fabrication method. Background Technology

[0002] Magneto-optical glass is a core component of fiber optic communication, sensing, and laser technologies, containing Tb 3+ Due to its unique magneto-optical effect, Tb magneto-optical glass is widely used in isolators, magneto-optical modulators, and other fields. 3+ Doped glass exhibits no light absorption in the 600nm–1700nm range, making it suitable for C, L, and U band optical modulators. The magneto-optical coefficient (Verdet constant) is a key performance indicator.

[0003] Traditional preparation methods suffer from multiple problems: high-temperature melting easily leads to phase separation of silicate glass, agglomeration of rare earth ions, and a decrease in optical uniformity; Tb in the air... 3+ Easily oxidized to Tb with no magneto-optical response 4+ This reduces the effective ion concentration; quartz glass has a rare earth ion solubility of only 460 ppm, making high-concentration doping difficult; existing technologies (such as improved chemical vapor deposition) are costly and complex. More importantly, mismatches in the thermal parameters (coefficient of thermal expansion, softening point) and refractive index difference between the core and cladding can lead to interface defects and a surge in transmission loss during drawing, disrupting optical signal transmission. Summary of the Invention

[0004] To address the shortcomings of existing technologies, this invention addresses the issue of Tb stabilization through the introduction of B2O3 at low optical alkalinity. 3+ Price state (promoting Tb) 4+ →Tb 3+ (Reduction), depolymerization of the glass network improves ion dispersion, and the regulated glass thermal stability (ΔT=Tx-Tg>200℃) meets the drawing requirements; through the design of core-packaging synergistic design—maintaining consistent Al2O3, SiO2, and B2O3 content, with only La... 3+ Replacement fiber core Tb 3+ This allows for the matching of thermal parameters and reasonable control of refractive index difference, ensuring stable drawing and optical guiding performance. Therefore, a magneto-optical fiber with a core-cladding synergistic structure and its fabrication method are proposed. The molecular-level mixing characteristics of the sol-gel method suppress high-temperature phase separation and ion aggregation, improving optical uniformity; combined with process control, Tb is reduced. 3+ Oxidation increases the effective magneto-optical ion concentration; the network regulation effect of B2O3 enhances Tb. 3+The method achieves high concentration doping by increasing solubility in quartz glass; it uses a tube-rod method combined with a core-packaging synergistic formulation to solve the problem of mismatch between core-packaging thermal parameters and refractive index, ensuring the stability of fiber drawing and light guiding performance; at the same time, this method simplifies the process, reduces equipment costs, and improves production efficiency compared to the traditional chemical vapor deposition method.

[0005] To address the aforementioned technical problems, this invention provides a magneto-optical fiber with a core-cladding co-structure. The core of the magneto-optical fiber is composed of 15Tb4O7−15Al2O3−30SiO2−40B2O3, and the cladding is composed of 30La2O3−15Al2O3−30SiO2−40B2O3, maintaining consistent Al2O3, SiO2, and B2O3 content in both the core and cladding.

[0006] This invention also provides a method for fabricating a magneto-optical fiber with a core-cladding cooperative structure, the steps of which are as follows:

[0007] S1. Weigh out terbium source, aluminum source, silicon source and boron source as core raw materials according to the proportion of core composition, and weigh out lanthanum source, aluminum source, silicon source and boron source as cladding raw materials according to the proportion of cladding composition.

[0008] S2. Dissolve the core material and the cladding material separately in an alcohol-water mixed solvent, adjust the pH with nitric acid, and stir to obtain the core sol and the cladding sol respectively.

[0009] S3. The core sol and the cladding sol are aged separately;

[0010] S4. Dry the aged fiber core sol and coating sol separately to form fiber core dry gel and coating dry gel.

[0011] S5. Perform a first pre-calcination on the core dry gel and the cladding dry gel to remove organic impurities;

[0012] S6. The core dry gel and the cladding dry gel are subjected to a second pre-firing transformation to obtain core glass and cladding glass.

[0013] S7. Prepare the fiber core glass into a solid fiber core rod, and prepare the cladding glass into a cladding hollow tube that matches the solid fiber core rod.

[0014] S8. The solid fiber core rod is coaxially inserted into the hollow cladding tube using the tube-rod method to form an optical fiber preform.

[0015] S9. Install the optical fiber preform on the drawing tower and draw it in an inert gas atmosphere to obtain a magneto-optical fiber with a core-cladding cooperative structure.

[0016] In some embodiments of the present invention, in step S1, the terbium source is terbium nitrate, the aluminum source is aluminum nitrate, the silicon source is tetraethyl orthosilicate, the boron source is boric acid, and the lanthanum source is lanthanum nitrate.

[0017] As some embodiments of the present invention, in step S2, nitric acid is added to adjust the pH to 2, and the mixture is stirred at 60°C for 1 hour to achieve molecular-level mixing of raw materials using a low-temperature sol system, thereby avoiding ion aggregation caused by high-temperature phase separation.

[0018] As some embodiments of the present invention, in step S2, the volume ratio of ethanol to water in the alcohol-water mixed solvent is 1:3, and the nitric acid concentration is 0.5 mol / L, to ensure accurate pH adjustment.

[0019] As some embodiments of the present invention, in step S3, the core sol and the cladding sol are aged at a constant temperature of 60°C for 24 hours, and stirred once every hour for 5 minutes each time during the aging period to promote uniform polycondensation.

[0020] As some embodiments of the present invention, in step S4, the specific process of drying the aged fiber core sol and the cladding sol is as follows: first, keep warm at a constant temperature of 60°C until the sol system loses its flowing water and is completely transformed into a gel; then raise the temperature to 100°C and keep warm continuously to completely evaporate the liquid water remaining in the gel, and finally form a structurally complete white dry block fiber core dry gel and cladding dry gel, with a total drying time of 72h to 96h.

[0021] As some embodiments of the present invention, the first pre-firing in step S5 adopts a stepped heating mode, raising the temperature from room temperature to 400°C at 10°C / min, and then holding it at that temperature for 6 hours to remove organic impurities.

[0022] As some embodiments of the present invention, the second pre-firing process in step S6 is as follows: based on the first pre-firing, the temperature is first raised to 1000°C at a rate of 5°C / min, and then raised to 1500°C at a rate of 3°C / min, and then held for 2 hours, so that the core dry gel and the cladding dry gel form core glass liquid and cladding glass liquid. Then the core glass liquid and cladding glass liquid are taken out and poured into the preheated mold respectively, and then annealed at 600°C for 6 hours to eliminate internal stress. After cooling in the furnace, the core glass and cladding glass are obtained.

[0023] As a preferred embodiment of the present invention, the second pre-firing process in step S6 is as follows: based on the first pre-firing, the temperature is first increased to 1000°C at a rate of 5°C / min, and then increased to 1500°C at a rate of 3°C / min, and then held for 2 hours, so that the core dry gel and the cladding dry gel form core glass liquid and cladding glass liquid. Then, the core glass liquid and the cladding glass liquid are taken out and poured into the preheated mold respectively. After cooling with the temperature, they are placed in a vacuum furnace and annealed at 600°C for 6 hours. Finally, after cooling with the temperature again, the core glass and the cladding glass are obtained.

[0024] As some embodiments of the present invention, in step S7, the fiber core glass is machined into a solid fiber core rod with a diameter of 2.0±0.1mm, and the cladding glass is machined into a hollow cladding tube with an inner diameter of 2.0±0.05mm and an outer diameter of 25.0±0.1mm, and the concentricity deviation between the solid fiber core rod and the hollow cladding tube is ensured to be ≤0.05mm.

[0025] As some embodiments of the present invention, in step S9, the temperature of the drawing tower is raised to 1100℃~1300℃ in an inert gas atmosphere. After the material head falls off, the magneto-optical fiber with a core-cladding cooperative structure is obtained by controlling the feeding speed and drawing speed of the optical fiber preform.

[0026] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0027] 1. Product Structure Innovation for Precise Core-Clad Performance Matching: By designing specific components for the core (15Tb4O7−15Al2O3−30SiO2−40B2O3) and cladding (30La2O3−15Al2O3−30SiO2−40B2O3), and maintaining complete consistency in the content of the network agglomerates (Al2O3, SiO2, B2O3), only the magneto-optical active components (Tb4O7 / La2O3) are directionally replaced. This synergistic design fundamentally ensures a high degree of matching between the core and cladding in key thermal parameters such as coefficient of thermal expansion and softening point, effectively eliminating core-cladding interface defects and stress caused by thermal mismatch during fiber drawing, and guaranteeing interface stability. Simultaneously, this formulation system can precisely control the refractive index difference between the core and cladding, meeting the basic performance requirements for optical fiber guidance.

[0028] 2. Innovative preparation process to improve material uniformity and performance: The sol-gel method replaces the traditional high-temperature melting method, achieving molecular-level uniform mixing of raw materials in a low-temperature solution state, which greatly suppresses high-temperature phase separation and rare earth ion (Tb) reactions. 3+ The aggregation phenomenon of organic impurities is eliminated, thus producing high-quality glass with high optical uniformity and no scattering defects. Combined with an optimized two-step pre-firing and annealing process, organic impurities are effectively removed and internal stress in the glass is eliminated, further improving the purity and structural stability of the glass.

[0029] 3. Effectively stabilizes the valence state of rare earth ions, achieving high-concentration doping: The formulation introduces a high content of B2O3, utilizing its low optical basicity characteristics to effectively suppress Tb. 3+ During the preparation process, it is oxidized to Tb, which is non-magnetically and optically active. 4+ This ensures a high effective magneto-optical ion concentration. Simultaneously, the network regulation effect of B2O3 significantly improves Tb. 3+ The high solubility of rare earth elements in a quartz glass matrix overcomes the limitations of traditional methods in achieving high-concentration rare earth doping, laying a material foundation for obtaining high magneto-optical coefficients. The measured magneto-optical coefficient of this fiber at a wavelength of 632.8 nm reaches 108.9 rad / (T·m), demonstrating excellent performance.

[0030] 4. Simplified Process and Cost Advantages: Combining the sol-gel method with the mature rod-and-tube method avoids the complex and expensive equipment required by traditional methods such as chemical vapor deposition (MCVD). The entire process is characterized by mild and highly controllable conditions, significantly reducing production costs and equipment barriers, and providing a practical technical path for the large-scale fabrication of high-performance magneto-optical fibers.

[0031] In summary, this invention, through the organic combination of "core-packet co-design" and "low-temperature sol-gel process," has synergistically solved key technical challenges that have long existed in the fabrication of high-performance magneto-optical fibers, such as material uniformity, core-packet matching, ion valence state stability, and high-concentration doping. The resulting optical fibers have broad application prospects in magneto-optical sensing, optical isolators, and other fields. Attached Figure Description

[0032] To more clearly illustrate the specific embodiments of the present invention or the technical solutions in the prior art, the accompanying drawings used in the description of the specific embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only one embodiment of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a DTA diagram of the core of the magneto-optical fiber according to an embodiment of the present invention;

[0034] Figure 2 This is a DTA diagram of the magneto-optical fiber cladding according to an embodiment of the present invention;

[0035] Figure 3 This is a transmittance diagram of the core glass of the magneto-optical fiber in Embodiment 1 of the present invention;

[0036] Figure 4 This is a transmittance diagram of the core glass of the magneto-optical fiber in Embodiment 2 of the present invention. Detailed Implementation

[0037] To make the technical means, creative features, objectives and effects of this invention easier to understand, the technical solutions in the specific embodiments of this invention are described clearly and completely below to further illustrate this invention. Obviously, the specific embodiments described are only a part of the embodiments of this invention, and not all of them.

[0038] Example 1: A method for fabricating a magneto-optical fiber with a core-cladding cooperative structure, comprising the following steps:

[0039] S1. Weigh the core material and cladding material. The core material consists of tetraethyl orthosilicate (silicon source), aluminum nitrate (aluminum source), terbium nitrate (terbium source), and boric acid (boron source). The cladding material uses lanthanum nitrate (lanthanum source) instead of terbium nitrate. The remaining aluminum, silicon, and boron sources are the same as those in the core material. Weigh the materials according to the core composition (15Tb4O7−15Al2O3−30SiO2−40B2O3) and the cladding composition (30La2O3−15Al2O3−30SiO2−40B2O3) to ensure that the content of Al2O3, SiO2, and B2O3 in the core and cladding is consistent.

[0040] S2. Dissolve the core material and cladding material separately in an alcohol-water mixed solvent. The molar ratio of tetraethyl orthosilicate to ethanol and water in the alcohol-water mixed solvent is 1:2:6. Add nitric acid to adjust the pH to 2. The nitric acid concentration is 0.5 mol / L to ensure accurate pH adjustment. Stir at 60°C for 1 hour to form core sol and cladding sol respectively. Use a low-temperature sol system to achieve molecular-level mixing of raw materials and avoid ion aggregation caused by high-temperature phase separation.

[0041] S3, the core sol and the cladding sol were aged at a constant temperature of 60℃ for 24 hours. During the aging period, the mixture was stirred once every hour for 5 minutes each time to promote uniform polycondensation.

[0042] S4. The aged fiber core sol and cladding sol were dried separately: first, they were kept at a constant temperature of 60°C until the sol system lost its flowing water and completely transformed into a gel; then the temperature was raised to 100°C and kept at that temperature to completely evaporate the liquid water remaining in the gel, and finally a structurally complete white dry block fiber core dry gel and cladding dry gel were formed, with a total drying time of 96 hours.

[0043] S5. The core dry gel and the cladding dry gel were pre-fired for the first time using a stepped heating mode, from room temperature to 400℃ at 10℃ / min, and held for 6 hours to remove organic impurities.

[0044] S6. The material after the first pre-firing is pre-firing a second time: the temperature is increased to 1000℃ at a rate of 5℃ / min, and then increased to 1500℃ at a rate of 3℃ / min. The temperature is held for 2 hours. At this time, the core dry gel and the cladding dry gel have formed the core glass liquid and the cladding glass liquid. The core glass liquid and the cladding glass liquid are taken out and poured into the preheated mold respectively. Then, they are annealed at 600℃ for 6 hours to eliminate internal stress. After cooling at the temperature, the core glass and the cladding glass are obtained.

[0045] S7. The fiber core glass and the cladding glass are mechanically processed to obtain a solid fiber core rod with a diameter of 2.0±0.1mm and a hollow cladding tube with an inner diameter of 2.0±0.05mm and an outer diameter of 25.0±0.1mm, respectively. The concentricity deviation between the solid fiber core rod and the hollow cladding tube is ≤0.05mm.

[0046] S8. Using the tube-rod method, a solid fiber core rod is coaxially inserted into a hollow cladding tube to form an optical fiber preform, which is then transferred to the fiber drawing equipment.

[0047] S9. Install the optical fiber preform on the drawing tower, raise the temperature of the drawing tower to 1200℃ in an inert gas atmosphere, and after the preform falls off, draw the magneto-optical fiber with a core-cladding cooperative structure by controlling the feeding speed and drawing speed of the optical fiber preform.

[0048] The core of this magneto-optical fiber with a core-cladding co-structure is composed of 15Tb4O7−15Al2O3−30SiO2−40B2O3, and the cladding is composed of 30La2O3−15Al2O3−30SiO2−40B2O3. The contents of Al2O3, SiO2, and B2O3 in the core and cladding are consistent.

[0049] To verify the performance of the magneto-optical fiber with a core-cladding co-structure obtained in this embodiment, the matching of the core and cladding thermal parameters, the compliance with fiber drawing process requirements and refractive index difference, and the guarantee of light guiding performance and basic indicators, tests were conducted. The magneto-optical fiber with a core-cladding co-structure has a magneto-optical coefficient of 108.9 rad / (Tm) at a wavelength of 632 nm, which is significantly improved compared to other glass magneto-optical fibers. The magneto-optical performance can be further enhanced by optimizing the process. Table 1 shows the refractive index of the cladding and core of the magneto-optical fiber with a core-cladding co-structure, and the refractive index matching between the cladding and core is excellent. Figure 1 DTA diagram of the core of a magneto-optical fiber with a core-cladding cooperative structure; Figure 2 The DTA diagram of the cladding of a magneto-optical fiber with a core-cladding cooperative structure clearly reflects the matching of the core and cladding in terms of thermal properties. Figure 3 The transmittance diagram of the core glass of the magneto-optical fiber with a core-packet cooperative structure demonstrates its excellent optical performance.

[0050] Example 2: A method for fabricating a magneto-optical fiber with a core-cladding cooperative structure, comprising the following steps:

[0051] S1. Weigh the core material and cladding material. The core material consists of tetraethyl orthosilicate (silicon source), aluminum nitrate (aluminum source), terbium nitrate (terbium source), and boric acid (boron source). The cladding material uses lanthanum nitrate (lanthanum source) instead of terbium nitrate. The remaining aluminum, silicon, and boron sources are the same as those in the core material. Weigh the materials according to the core composition (15Tb4O7−15Al2O3−30SiO2−40B2O3) and the cladding composition (30La2O3−15Al2O3−30SiO2−40B2O3) to ensure that the content of Al2O3, SiO2, and B2O3 in the core and cladding is consistent.

[0052] S2. Dissolve the core material and cladding material separately in an alcohol-water mixed solvent. The molar ratio of tetraethyl orthosilicate to ethanol and water in the alcohol-water mixed solvent is 1:2:6. Add nitric acid to adjust the pH to 2. The nitric acid concentration is 0.5 mol / L to ensure accurate pH adjustment. Stir at 60°C for 1 hour to form core sol and cladding sol respectively. Use a low-temperature sol system to achieve molecular-level mixing of raw materials and avoid ion aggregation caused by high-temperature phase separation.

[0053] S3, the core sol and the cladding sol were aged at a constant temperature of 60℃ for 24 hours. During the aging period, the mixture was stirred once every hour for 5 minutes each time to promote uniform polycondensation.

[0054] S4. The aged fiber core sol and cladding sol were dried separately: first, they were kept at a constant temperature of 60°C until the sol system lost its flowing water and completely transformed into a gel; then the temperature was raised to 100°C and kept at that temperature to completely evaporate the liquid water remaining in the gel, and finally a structurally complete white dry block fiber core dry gel and cladding dry gel were formed, with a total drying time of 72 hours.

[0055] S5. The core dry gel and the cladding dry gel were pre-fired for the first time using a stepped heating mode, from room temperature to 400℃ at 10℃ / min, and held for 6 hours to remove organic impurities.

[0056] S6. The material after the first pre-firing is pre-firing a second time: the temperature is increased to 1000℃ at a rate of 5℃ / min, and then increased to 1500℃ at a rate of 3℃ / min. The temperature is held for 2 hours. At this time, the core dry gel and the cladding dry gel have formed the core glass liquid and the cladding glass liquid. The core glass liquid and the cladding glass liquid are taken out and poured into the mold respectively. After cooling at the temperature, they are placed in a vacuum furnace at 600℃ for 6 hours for annealing. After annealing, the core glass and the cladding glass are obtained.

[0057] S7. The fiber core glass and the cladding glass are mechanically processed to obtain a solid fiber core rod with a diameter of 2.0±0.1mm and a hollow cladding tube with an inner diameter of 2.0±0.05mm and an outer diameter of 25.0±0.1mm, respectively. The concentricity deviation between the solid fiber core rod and the hollow cladding tube is ≤0.05mm.

[0058] S8. Using the tube-rod method, a solid fiber core rod is coaxially inserted into a hollow cladding tube to form an optical fiber preform, which is then transferred to the fiber drawing equipment.

[0059] S9. Install the optical fiber preform on the drawing tower, raise the temperature of the drawing tower to 1100℃ in an inert gas atmosphere, and after the preform head falls off, draw the magneto-optical fiber with a core-cladding cooperative structure by controlling the feeding speed and drawing speed of the optical fiber preform.

[0060] In this embodiment, a different annealing method was used than that in Embodiment 1.

[0061] To verify the performance of the magneto-optical fiber with a core-cladding co-structure obtained in this embodiment, the matching of the core and cladding thermal parameters, the compliance with fiber drawing process requirements and refractive index difference, and the guarantee of light guiding performance and basic indicators, tests were conducted. The magneto-optical fiber with the core-cladding co-structure has a magneto-optical coefficient of 108.9 rad / (Tm) at a wavelength of 632 nm. This shows that the annealing method in this embodiment reduces Tb. 4+ Oxidized to Tb 3+ The magneto-optical fiber produced has superior magneto-optical performance; Table 1 shows the refractive index of the cladding and core of the magneto-optical fiber with a core-cladding cooperative structure. Figure 4 The transmittance diagram of the core glass of the magneto-optical fiber with a core-packet cooperative structure demonstrates its excellent optical performance.

[0062] Table 1. Refractive index of cladding and core of magneto-optical fiber

[0063]

[0064] As can be seen from Table 1, the magneto-optical fiber prepared by the method of the present invention exhibits excellent refractive index matching between the cladding and core.

[0065] The main technical features, basic principles, and related advantages of the present invention have been described above. It will be apparent to those skilled in the art that the present invention is not limited to the details of the exemplary embodiments described above, and that the present invention can be implemented in other specific forms without departing from the concept or basic characteristics of the invention. Therefore, the above-described embodiments should be considered exemplary and non-limiting in all respects. The scope of the present invention is defined by the appended claims rather than the foregoing description, and thus all variations falling within the meaning and scope of the equivalents of the claims are intended to be included within the present invention.

[0066] Furthermore, it should be understood that although this specification describes various embodiments, not every embodiment contains only one independent technical solution. This way of describing the specification is only for clarity. Those skilled in the art should regard the specification as a whole, and the technical solutions in each embodiment can also be appropriately combined to form other embodiments that can be understood by those skilled in the art.

Claims

1. A method for fabricating magneto-optical optical fibers with a core-cladding cooperative structure, characterized in that, The steps are as follows: S1. Weigh out terbium source, aluminum source, silicon source and boron source as core raw materials according to the proportion of core composition, and weigh out lanthanum source, aluminum source, silicon source and boron source as cladding raw materials according to the proportion of cladding composition. S2. Dissolve the core material and the cladding material separately in an alcohol-water mixed solvent, adjust the pH with nitric acid, and stir to obtain the core sol and the cladding sol respectively. S3. The core sol and the cladding sol are aged separately; S4. Dry the aged fiber core sol and coating sol separately to form fiber core dry gel and coating dry gel. S5. Perform a first pre-calcination on the core dry gel and the cladding dry gel to remove organic impurities; S6. The core dry gel and the cladding dry gel are subjected to a second pre-firing transformation to obtain core glass and cladding glass. S7. Prepare the fiber core glass into a solid fiber core rod, and prepare the cladding glass into a cladding hollow tube that matches the solid fiber core rod. S8. The solid fiber core rod is coaxially inserted into the hollow cladding tube using the tube-rod method to form an optical fiber preform. S9. Install the optical fiber preform on the drawing tower and draw it in an inert gas atmosphere to obtain a magneto-optical fiber with a core-cladding cooperative structure. In step S4, the specific process of drying the aged fiber core sol and cladding sol is as follows: First, keep it at a constant temperature of 60°C until the sol system loses its flowing water and is completely transformed into a gel; then raise the temperature to 100°C and keep it at that temperature to completely evaporate the liquid water remaining in the gel, and finally form a structurally complete white dry block fiber core dry gel and cladding dry gel, with a total drying time of 72h to 96h. Step S5, the first pre-fired, adopts a stepped heating mode, raising the temperature from room temperature to 400℃ at 10℃ / min, and then holding it at that temperature for 6 hours to remove organic impurities. Step S6, the second pre-firing process, is as follows: Based on the first pre-firing, the temperature is first increased to 1000℃ at a rate of 5℃ / min, and then increased to 1500℃ at a rate of 3℃ / min. The temperature is then maintained for 2 hours, so that the core dry gel and the cladding dry gel form core glass liquid and cladding glass liquid. Then the core glass liquid and cladding glass liquid are taken out and poured into the preheated mold respectively. Then it is annealed in a vacuum furnace at 600℃ for 6 hours, and cooled at room temperature to obtain fiber-core glass and cladding glass; or, After being cooled at room temperature, the glass is annealed in a vacuum furnace at 600°C for 6 hours, and then cooled at room temperature again to obtain fiber core glass and cladding glass.

2. The method according to claim 1, characterized in that, In step S1, the terbium source is terbium nitrate, the aluminum source is aluminum nitrate, the silicon source is tetraethyl orthosilicate, the boron source is boric acid, and the lanthanum source is lanthanum nitrate.

3. The method according to claim 1, characterized in that, In step S2, nitric acid is added to adjust the pH to 2, and the mixture is stirred at 60°C for 1 hour. The volume ratio of ethanol to water in the alcohol-water mixed solvent is 1:3, and the concentration of nitric acid is 0.5 mol / L.

4. The method according to claim 1, characterized in that, In step S3, the core sol and the cladding sol are aged at a constant temperature of 60°C for 24 hours. During the aging period, the mixture is stirred once every hour for 5 minutes each time to promote uniform polycondensation.

5. The method according to claim 1, characterized in that, In step S7, the fiber core glass is machined into a solid fiber core rod with a diameter of 2.0±0.1mm, and the cladding glass is machined into a hollow cladding tube with an inner diameter of 2.0±0.05mm and an outer diameter of 25.0±0.1mm, ensuring that the concentricity deviation between the solid fiber core rod and the hollow cladding tube is ≤0.05mm.

6. The method according to claim 1, characterized in that, In step S9, the temperature of the drawing tower is raised to 1100℃~1300℃ in an inert gas atmosphere. After the material head falls off, the magneto-optical fiber with a core-cladding cooperative structure is obtained by controlling the feeding speed and drawing speed of the optical fiber preform.

7. A magneto-optical fiber with a core-cladding cooperative structure, characterized in that, The magneto-optical fiber is prepared by the method described in any one of claims 1 to 6. The core composition of the magneto-optical fiber is 15Tb4O7−15Al2O3−30SiO2−40B2O3, and the cladding composition is 30La2O3−15Al2O3−30SiO2−40B2O3, maintaining the same content of Al2O3, SiO2, and B2O3 in the core and cladding.

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