Ytterbium-doped fiber preform, ytterbium-doped active fiber and its preparation method

Abstract

This invention discloses a ytterbium-doped fiber preform, a ytterbium-doped active fiber, and their preparation method. First, a quartz deposition tube with a porous core layer deposited on its inner surface is prepared using the MCVD process. After heating and breaking off one end of the tube, a solution containing ytterbium rare earth salt and a co-doperant is injected into the quartz deposition tube. After thorough soaking and drying / shrinking, a rare earth-doped core rod is obtained. During the liner shrinking stage, vapor containing ytterbium compounds is introduced into the tube to reduce the loss of ytterbium oxide due to diffusion and volatilization during the liner shrinking stage, thereby obtaining a uniformly doped ytterbium-doped fiber preform. The preform prepared by this invention has a uniform ytterbium ion concentration distribution in the core layer, and the ytterbium-doped fiber obtained by drawing exhibits high laser slope efficiency.

Description

Technical Field

[0001] This invention belongs to the field of optical fiber manufacturing and relates to a ytterbium-doped optical fiber preparation technology, specifically to a ytterbium-doped optical fiber preform, a ytterbium-doped active optical fiber, and a preparation method thereof. Background Technology

[0002] Rare-earth-doped fiber preforms are key materials for the production of fiber amplifiers and fiber lasers. Compared with traditional semiconductor laser amplifiers, fiber amplifiers do not require complex processes such as photoelectric conversion, electro-optic conversion, and signal regeneration. They can directly amplify signals optically, exhibiting high gain, large bandwidth, low noise, polarization-insensitive gain, and low lead-in loss within the operating wavelength range. They also possess excellent "transparency," making them particularly suitable for relay amplification in long-distance optical communication. It can be said that fiber amplifiers have laid an important technological foundation for realizing high-capacity, all-optical communication. Rare-earth-doped fiber, as a crucial component of high-power fiber lasers, is a major factor determining the performance of high-power fiber lasers.

[0003] Currently, the main methods for producing rare earth-doped optical fiber preforms include vapor phase methods, such as rare earth chloride vapor deposition and rare earth chelate vapor deposition; solution methods, such as in-tube and out-of-tube rare earth solution immersion; nano-ion direct deposition; and gel methods. Among these, solution methods are the primary methods for preparing doped optical fiber preforms, including the out-of-tube method: using the VAD method to deposit powder rods, immersing the powder rods in a solution containing rare earth elements, and then vitrifying the immersed powder rods in a high-temperature furnace to form the core layer of the rare earth-doped optical fiber preform (CN102108008B); and the in-tube method: sequentially depositing an inner cladding layer and a loose soot core layer inside a deposition tube, injecting a solution containing rare earth chlorides into the deposition tube, and shrinking the deposition tube, inner cladding layer, and loose soot core layer to form a solid preform (CN102515501B, CN1500069, US 5711782A, US5262365A).

[0004] In the in-tube method of rare earth solution doping, the doped rare earth ions and co-dopersants are prone to volatilization in large quantities during the high-temperature melting and shrinkage stage, resulting in uneven distribution of rare earth ions on the cross-section of the core rod. The content of rare earth ions decreases towards the center, exhibiting a V-shaped distribution. Ultimately, the refractive index profile of the fiber obtained by drawing is concave, which affects the matching between the active and passive fibers, leading to a decrease in the thermal stability of the laser, as well as a deterioration in beam quality and a central dark spot. Therefore, ensuring the uniform distribution of rare earth ions is crucial in the liquid phase method for preparing active optical fiber preforms. Summary of the Invention

[0005] One of the objectives of this invention is to address the shortcomings of the existing technology by proposing a method for preparing ytterbium-doped fiber preforms based on the in-tube method. The ytterbium-doped fiber preforms produced by this method have ytterbium ions uniformly distributed in the core layer of the fiber preform, resulting in high fiber laser slope efficiency.

[0006] Another objective of this invention is to provide a method for preparing ytterbium-doped active optical fiber, which uses the aforementioned ytterbium-doped optical fiber preform and is obtained by either drawing the fiber through a spool or by direct drawing. The resulting ytterbium-doped active optical fiber has a stable refractive index in its transverse cross-section and exhibits high gain, large bandwidth, low noise, polarization-insensitive gain, and low lead-in loss within the operating wavelength range.

[0007] The technical solution adopted by the present invention to solve the above-mentioned problems is as follows:

[0008] On one hand, the present invention provides a method for preparing ytterbium-doped optical fiber preforms based on the in-tube method, comprising the following steps:

[0009] Quartz deposition tubes with a porous core layer deposited on the inner surface were prepared using the MCVD process.

[0010] After heating and breaking off one end of the tail tube, a solution containing ytterbium rare earth salts is injected into the quartz deposition tube and soaked for a period of time;

[0011] After soaking, the residual solution in the quartz deposition tube is poured out, and nitrogen or inert gas is introduced to purge it. Then, the first process gas is introduced to dry and dehydrate it.

[0012] A second process gas containing ytterbium compound vapor is introduced into the quartz deposition tube to oxidize and shrink the quartz deposition tube. After cooling, a ytterbium-doped optical fiber preform is obtained.

[0013] This invention introduces ytterbium-containing compound vapor into the quartz deposition tube during the melting and shrinking stage. By controlling the partial pressure of the ytterbium-containing compound vapor, the outward diffusion and volatilization of ytterbium oxide in the deposited layer is balanced, thereby obtaining a uniformly doped ytterbium fiber preform. Using this preform, ytterbium-doped active optical fiber with a uniform refractive index on the cross-section can be obtained through fiber drawing, in order to meet the requirements of high-power fiber lasers.

[0014] As a preferred technical solution, the deposition temperature of the loose core layer on the inner surface of the quartz deposition tube is 1200℃ to 1400℃. By controlling the appropriate deposition temperature, a deposition layer with good porosity and uniform density is obtained. When doped with rare earth elements, it has a strong adsorption capacity for ytterbium-containing rare earth salts and co-dopersants, and the rare earth distribution is uniform.

[0015] As a preferred technical solution, the anions in the ytterbium-containing rare earth salt solution are selected from any one or a combination of several of chloride ions, nitrate ions, benzenesulfonic acid groups, tert-pentoxy groups, trifluorosulfonic acid groups, methanesulfonic acid groups, octanoic acid groups, and perfluorooctanoic acid groups.

[0016] As a preferred technical solution, a co-doperic agent is also added to the ytterbium rare earth salt solution during soaking.

[0017] Further preferred, the co-doperb is any one or a combination of compounds containing phosphorus, cerium, and aluminum.

[0018] As a preferred technical solution, the soaking time of the ytterbium rare earth salt solution in the quartz deposition tube is 1-6 hours, with the optimum being 3.5 hours; the soaking temperature is 0℃-70℃, with the optimum being 40℃.

[0019] As a preferred technical solution, the first process gas includes helium, oxygen, and chlorine, and the drying and dehydration temperature is 600°C to 1000°C.

[0020] As a preferred technical solution, the second process gas includes helium and oxygen, and the type of the second process gas can be adapted to the actual process.

[0021] As a preferred technical solution, the ytterbium-containing compounds incorporated into the second process gas include Yb(thd)3 and Yb(NO3)3. It should be noted that it is not limited to these two types; any ytterbium-containing compound that can form vapor at the melting point is acceptable.

[0022] As a preferred technical solution, in the mixed gas composed of the second process gas and ytterbium compound vapor, the volume ratio of ytterbium compound vapor is 5% to 15%. At this volume ratio, the volatilization and adsorption of ytterbium compounds in the loose layer can reach a balance, maintaining the uniformity of ytterbium ion distribution in the mandrel after melting and shrinking.

[0023] As a preferred technical solution, during the melting and shrinking process, the volume ratio fluctuation of ytterbium compound vapor in the mixed gas does not exceed 2%. Maintaining the stability of the volume ratio of ytterbium compound vapor helps to improve the uniformity of ytterbium compound distribution in the loose layer of the preform after melting and shrinking. The fluctuation of no more than 2% means that the difference between the maximum and minimum volume ratio of ytterbium compound vapor does not exceed 2% during the entire melting and shrinking process.

[0024] As a preferred technical solution, the temperature for oxidizing and shrinking the quartz deposition tube is 1600℃ to 2200℃, and the pressure inside the tube is controlled between -1000Pa and 500Pa. Selecting appropriate shrinking temperature and pressure can improve the roundness of the fiber core and the uniformity of the distribution of ytterbium compounds.

[0025] As a preferred technical solution, the ytterbium-doped fiber preform obtained after oxidation and shrinkage has a core layer ytterbium ion mass concentration of 500-30000ppm. Within this concentration range, ytterbium doping significantly improves fiber performance and also makes it easier to control the uniformity of the core layer ytterbium ion mass concentration distribution.

[0026] On the other hand, the present invention also provides a ytterbium-doped optical fiber preform, which is prepared using the above-described preparation method.

[0027] On the other hand, the present invention also provides a ytterbium-doped active optical fiber, which is obtained by drawing the ytterbium-doped optical fiber preform as described above through a rod drawing process or by direct drawing.

[0028] This invention enables the preparation of uniformly ytterbium-doped optical fiber preforms and ytterbium-doped optical fibers through a melting and shrinking process without adding existing solution-based production equipment.

[0029] Compared with the prior art, the present invention has the following beneficial effects:

[0030] This invention improves the melting and shrinking process by introducing ytterbium-containing compound vapor during the melting and shrinking stage. This solves the problem of ytterbium ion diffusion and volatilization losses during the melting and shrinking stage of the optical fiber preform. It can utilize existing production equipment and is highly versatile and adaptable. Ytterbium-doped optical fiber preforms produced using this method exhibit uniform ytterbium ion distribution within the preform, resulting in high fiber laser slope efficiency. Attached Figure Description

[0031] Figure 1 The image shows the slope efficiency of the ytterbium-doped fiber laser obtained by drawing the preforms from Example 1 and Comparative Example 1.

[0032] Figure 2 The image shows the slope efficiency of ytterbium-doped fiber laser obtained by drawing the preforms obtained in Example 2 and Comparative Example 2.

[0033] Figure 3 The graph shows the slope efficiency of ytterbium-doped fiber laser obtained by drawing the preforms obtained in Example 3 and Comparative Example 3. Detailed Implementation

[0034] To better understand the present invention, the following embodiments further illustrate the content of the present invention, but the present invention is not limited to the following embodiments.

[0035] Example 1: A quartz deposition tube with a porous core layer deposited on its inner surface was prepared using the MCVD process. 0.3L of an ethanol solution containing ytterbium chloride, cerium chloride, and aluminum chloride was injected into the deposition tube. The ytterbium chloride content was 0.023mol / L, the cerium chloride content was 0.007mol / L, and the aluminum chloride content was 0.16mol / L. The solution was soaked at 40℃ for 3 hours, then the solution was poured out, and nitrogen gas was purged into the quartz liner for 3 hours. Then, He, O2, and Cl2 were introduced between 650℃ and 950℃ to dehydrate the porous core layer. Finally, the quartz tube was melted and shrunk between 1800℃ and 2100℃. During the melting and shrinking stage, Yb(thd)3 vapor was introduced, and the volume percentage of Yb(thd)3 vapor inside the liner was between 10% and 11.5%. This yielded a ytterbium-doped active optical fiber preform.

[0036] Comparative Example 1: A quartz deposition tube with a porous core layer deposited on its inner surface was prepared using the MCVD process. 0.3L of an ethanol solution containing ytterbium chloride, cerium chloride, and aluminum chloride was injected into the deposition tube. The ytterbium chloride content was 0.023mol / L, the cerium chloride content was 0.007mol / L, and the aluminum chloride content was 0.16mol / L. The tube was soaked at 40℃ for 3 hours, the solution was poured out, and nitrogen gas was purged into the quartz liner tube for 3 hours. Then, He, O2, and Cl2 were introduced between 650℃ and 950℃ to dehydrate the porous core layer. Finally, the quartz tube was melted and condensed between 1800℃ and 2100℃ to obtain a ytterbium-doped active optical fiber preform.

[0037] The ytterbium ion concentration distribution of the two types of core rods is shown in Table 1. It can be seen that the ytterbium ion concentration distribution of the preform prepared in Example 1 is more uniform than that of the comparative example.

[0038] Table 1 shows the ytterbium ion concentration distribution in Example 1 and Comparative Example 1.

[0039]

[0040] Example 1: The fiber laser slope efficiency obtained by drawing preforms reached 75.1% (e.g., Figure 1 (As shown). The fiber laser slope efficiency obtained in Comparative Example 1 was only 55.6%, which shows that the ytterbium-doped fiber prepared in this embodiment can significantly improve fiber performance.

[0041] Example 2: A quartz deposition tube with a porous core layer deposited on its inner surface was prepared using the MCVD process. 0.3L of an ethanol solution containing ytterbium chloride, aluminum chloride, and erbium chloride was injected into the deposition tube. The ytterbium chloride content was 0.021mol / L, the aluminum chloride content was 0.15mol / L, and the erbium chloride content was 0.005mol / L. The solution was soaked at 45℃ for 3.5 hours, the solution was poured out, and nitrogen gas was purged into the quartz liner for 3 hours. Then, He, O2, and Cl2 were introduced between 650℃ and 950℃ to dehydrate the porous core layer. Finally, the quartz tube was melted and shrunk between 1800℃ and 2100℃. During the melting and shrinking stage, Yb(NO3)3 vapor was introduced, and the volume percentage of Yb(NO3)3 vapor inside the liner was between 13.5% and 14.7%. This yielded a ytterbium-doped optical fiber preform.

[0042] Comparative Example 2: A quartz deposition tube with a porous core layer deposited on its inner surface was prepared by MCVD process. 0.3L of an ethanol solution containing ytterbium chloride, aluminum chloride, and erbium chloride was injected into the deposition tube. The ytterbium chloride content was 0.021mol / L, the aluminum chloride content was 0.15mol / L, and the erbium chloride content was 0.005mol / L. The tube was soaked at 45℃ for 3.5 hours, the solution was poured out, and nitrogen gas was purged into the quartz liner tube for 3 hours. Then, He, O2, and Cl2 were introduced between 650℃ and 950℃ to dehydrate the porous core layer. Finally, the quartz tube was melted and shrunk between 1800℃ and 2100℃ to obtain a ytterbium-doped optical fiber preform.

[0043] The ytterbium ion concentration distribution of the two types of core rods is shown in Table 2. It can be seen that the ytterbium ion concentration distribution of the preform prepared by Example 2 is more uniform than that of the comparative example.

[0044] Table 2 shows the ytterbium ion concentration distribution in Example 2 and Comparative Example 2.

[0045]

[0046] Example 2: The fiber laser slope efficiency obtained by drawing preforms reached 73.8% (e.g., Figure 2 (As shown). The fiber laser slope efficiency obtained in Comparative Example 2 was only 54.9%, which shows that the ytterbium-doped fiber prepared in this embodiment can significantly improve fiber performance.

[0047] Example 3: A quartz deposition tube with a porous core layer deposited on its inner surface was prepared using the MCVD process. 0.31 L of an ethanol solution containing ytterbium chloride, aluminum chloride, and phosphoric acid was injected into the deposition tube. The ytterbium chloride content was 0.025 mol / L, the aluminum chloride content was 0.17 mol / L, and the phosphoric acid content was 0.15 mol / L. The solution was soaked at 43 °C for 4 hours, then the solution was poured out, and nitrogen gas was purged into the quartz liner for 3.5 hours. Then, He, O2, and Cl2 were introduced between 650 °C and 950 °C to dehydrate the porous core layer. Finally, the quartz tube was melted and shrunk between 1800 °C and 2100 °C. During the melting and shrinking stage, Yb(NO3)3 vapor was introduced, and the volume percentage of Yb(NO3)3 vapor inside the liner was between 5.2% and 6.9%. This yielded a ytterbium-doped optical fiber preform.

[0048] Comparative Example 3: A quartz deposition tube with a porous core layer deposited on its inner surface was prepared by MCVD process. 0.31L of an ethanol solution containing ytterbium chloride, aluminum chloride, and phosphoric acid was injected into the deposition tube. The ytterbium chloride content was 0.025mol / L, the aluminum chloride content was 0.17mol / L, and the phosphoric acid content was 0.15mol / L. The tube was soaked at 43℃ for 4 hours, the solution was poured out, and nitrogen gas was purged into the quartz liner tube for 3.5h. Then, He, O2, and Cl2 were introduced between 650℃ and 950℃ to dehydrate the porous core layer. Finally, the quartz tube was melted and condensed between 1800℃ and 2100℃ to obtain a ytterbium-doped optical fiber preform.

[0049] The ytterbium ion concentration distribution of the two types of core rods is shown in Table 3. It can be seen that the ytterbium ion concentration distribution of the preform prepared by Example 3 is more uniform than that of the comparative example.

[0050] Table 3 shows the ytterbium ion concentration distribution in Example 3 and Comparative Example 3.

[0051]

[0052] Example 3: The fiber laser slope efficiency obtained by drawing preforms reached 78.6% (e.g., Figure 3 (As shown). The fiber laser slope efficiency obtained in Comparative Example 3 was only 56.1%, which shows that the ytterbium-doped fiber prepared in this embodiment can significantly improve fiber performance.

[0053] The above description is only a preferred embodiment of the present invention. It should be noted that those skilled in the art can make several improvements and modifications without departing from the inventive concept of the present invention, and these all fall within the protection scope of the present invention.

Claims

1. A method for preparing ytterbium-doped optical fiber preforms based on the in-tube method, characterized in that, Includes the following steps: Quartz deposition tubes with a porous core layer deposited on the inner surface were prepared using the MCVD process. After heating and breaking off one end of the tail tube, a solution containing ytterbium rare earth salts is injected into the quartz deposition tube and soaked for a period of time; After soaking, the residual solution in the quartz deposition tube is poured out, and nitrogen or inert gas is introduced to purge it. Then, the first process gas is introduced to dry and dehydrate it. A second process gas containing ytterbium compound vapor is introduced into the quartz deposition tube to oxidize and shrink the quartz deposition tube. After cooling, a ytterbium-doped optical fiber preform is obtained. The second process gases include helium and oxygen; Ytterbium compounds in vapor include Yb(thd)3 and Yb(NO3)3.

2. The method for preparing ytterbium-doped optical fiber preforms based on the in-tube method according to claim 1, characterized in that: The deposition temperature of the loose core layer on the inner surface of the quartz deposition tube is 1200℃ to 1400℃.

3. The method for preparing ytterbium-doped optical fiber preform based on the in-tube method according to claim 1, characterized in that: The anions in the ytterbium-containing rare earth salt solution are selected from any one or a combination of several of chloride ions, nitrate ions, benzenesulfonic acid groups, tert-pentoxy groups, trifluorosulfonic acid groups, methanesulfonic acid groups, octanoic acid groups, and perfluorooctanoic acid groups.

4. The method for preparing ytterbium-doped optical fiber preform based on the in-tube method according to claim 3, characterized in that: During soaking, the ytterbium rare earth salt solution is also mixed with a co-doping agent.

5. The method for preparing ytterbium-doped optical fiber preforms based on the in-tube method according to claim 4, characterized in that: The co-doperb is any one or a combination of compounds containing phosphorus, cerium, aluminum, and erbium.

6. The method for preparing ytterbium-doped optical fiber preform based on the in-tube method according to claim 1, characterized in that: The soaking time of the ytterbium rare earth salt solution in the quartz deposition tube is 1-6 hours, and the soaking temperature is 0℃-70℃.

7. The method for preparing ytterbium-doped optical fiber preform based on the in-tube method according to claim 1, characterized in that: The first process gas includes helium, oxygen, and chlorine, and the drying and dehydration temperature is 600°C to 1000°C.

8. The method for preparing ytterbium-doped optical fiber preforms based on the in-tube method according to claim 1, characterized in that: In the mixture of the second process gas and ytterbium compound vapor, the volume ratio of ytterbium compound vapor is 5% to 15%.

9. The method for preparing ytterbium-doped optical fiber preform based on the in-tube method according to claim 8, characterized in that: During the melting and shrinking process, the volume ratio fluctuation of ytterbium compound vapor in the mixed gas does not exceed 2%.

10. The method for preparing ytterbium-doped optical fiber preform based on the in-tube method according to claim 1, characterized in that: The temperature for oxidizing and shrinking the quartz deposition tube is 1600℃ to 2200℃, and the pressure inside the tube is controlled between -1000Pa and 500Pa.

11. The method for preparing ytterbium-doped optical fiber preform based on the in-tube method according to claim 1, characterized in that: The mass concentration of ytterbium ions in the core layer of the ytterbium-doped optical fiber preform obtained after oxidation and shrinkage is 500-30000 ppm.

12. A ytterbium-doped optical fiber preform, characterized in that: The preparation is carried out using the preparation method described in any one of claims 1-11.

13. A ytterbium-doped active optical fiber, characterized in that, The ytterbium-doped optical fiber preform as described in any one of claims 1 to 11 is obtained by drawing the fiber through a rod or by direct drawing.

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