Methods for fabricating quartz deposition tubes, rare earth-doped optical fiber preforms, and optical fibers.

Abstract

This invention discloses a quartz deposition tube, a rare-earth-doped optical fiber preform, and an optical fiber fabrication method. The quartz deposition tube includes a liner and a loose layer deposited on the inner wall of the liner using an MCVD process. The density of the loose layer exhibits a radially gradually varying distribution, resulting in a gradually varying adsorption capacity for dopants. After heating and breaking off one end of the quartz deposition tube, a solution of rare-earth salt and co-doperamide is injected into it. After thorough soaking, drying, and melting, a rare-earth-doped core rod is obtained. By designing the gradually varying adsorption capacity of the loose layer for rare earths, the uneven rare-earth distribution caused by volatilization during melting is balanced, resulting in an optical fiber preform with uniform rare-earth doping concentration. The optical fiber is then drawn from this preform to produce an optical fiber with a flat refractive index profile, high laser slope efficiency, and characteristics of high gain, large bandwidth, low noise, polarization-insensitive gain, and low lead-in loss.

Description

Technical Field

[0001] This invention belongs to the field of optical fiber manufacturing and relates to a rare earth doping technology for optical fiber fabrication, specifically to a method for preparing a quartz deposition tube, a rare earth doped optical fiber preform, and an optical fiber. 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 in the core rod, which is V-shaped. The content of rare earth ions decreases towards the center, and the refractive index profile of the fiber obtained by drawing is concave. This affects the matching between 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] To address the shortcomings of the existing technology, one of the objectives of this invention is to provide a quartz deposition tube and its preparation method, which obtains a rare earth-doped quartz deposition tube with gradually varying doping concentration by controlling the radial density of the porous core layer inside the quartz deposition tube.

[0006] Another objective of this invention is to prepare uniformly doped rare earth-doped preforms from the aforementioned quartz deposition tubes through melting and shrinking, thereby solving the problem of uneven radial distribution of rare earth ions caused by the volatilization of rare earth ions during the melting and shrinking process of the quartz deposition tubes.

[0007] Another objective of this invention is to prepare rare-earth-doped optical fibers using the aforementioned rare-earth-doped preforms, thereby solving the problem in the prior art where uneven rare-earth doping leads to uneven refractive index, which further restricts the production and use of high-power optical fibers. The optical fibers prepared using the method of this invention have a flat refractive index distribution on the cross-section and feature high gain, large bandwidth, low noise, polarization-insensitive gain, and low lead-in loss.

[0008] The technical solution adopted by the present invention to solve the above-mentioned problems is as follows:

[0009] On one hand, the present invention provides a quartz deposition tube for preparing optical fiber preforms, comprising a liner and a loose core layer deposited on the inner wall of the liner using an MCVD process, wherein the density of the loose core layer is radially gradually distributed, thereby generating a gradually distributed dopant adsorption capacity.

[0010] As a preferred technical solution, the density of the loose core layer increases closer to the center.

[0011] The density distribution of the porous core layer satisfies the following equation:

[0012] ρ = ρ 0+ A * B 2

[0013] ρ is the density of the loose core layer at any point. ρ 0 represents the density of the loose core layer closest to the inner wall of the liner. B Let A be the radial distance between the corresponding point and the inner wall of the liner, and let A be the gradient coefficient.

[0014] In the above equation, ρ and ρ The unit for 0 is g / cm³ 3 , ρ The value of 0 ranges from 0.275. <A<0.55;

[0015] The distance B is in millimeters (mm), and the value of B is no greater than 2.5.

[0016] A is the gradient coefficient, a dimensionless parameter. Its value is determined by the melting temperature during the preform preparation process and the volatility of rare earth elements at the melting temperature. Generally, it can be set to 0.05-0.21, with the optimal value being 0.1.

[0017] This scheme controls the density distribution of the loose core layer, so that the density of the deposited layer gradually increases from the inner wall of the liner to the center area. This enhances the adsorption capacity of the deposited layer for rare earth doped ions. In other words, after soaking, the rare earth ion content of the deposited layer gradually increases from the inner wall of the liner to the center area of ​​the powder rod. This counteracts the problem of rapid volatilization of rare earth ions in the deposited layer near the center area during the melting and shrinking stage, and improves the problem of V-shaped distribution of rare earth ions in the core rod of the traditional liquid phase method. After melting and shrinking, a uniformly doped optical fiber preform is obtained.

[0018] On the other hand, the present invention also provides a method for preparing a quartz deposition tube, comprising the following steps:

[0019] Prepare the liner to be deposited, and introduce the raw material gas containing silicon tetrachloride and oxygen into the liner for deposition;

[0020] The deposition temperature is controlled to increase layer by layer in order to obtain a loose core layer with gradually increasing density.

[0021] It should be noted that during the deposition of the loose core layer in the liner of this invention, each layer is very thin, so the density distribution is approximately a gradual distribution.

[0022] As a preferred technical solution, the initial deposition temperature is between 1200-1250℃, and the temperature of each subsequent deposition layer increases by 5-15℃, with the highest deposition temperature not exceeding 1350℃. By controlling the deposition temperature, the density of the deposition layer can be changed, so that the density distribution of the loose core layer inside the liner meets the requirements of the above equation.

[0023] As a preferred technical solution, the deposition temperature control method is as follows:

[0024] The temperature of the oxyhydrogen flame is controlled by adjusting the flow rates of hydrogen and oxygen, so that the deposition temperature reaches the set range.

[0025] On the other hand, the present invention also provides a method for preparing rare earth-doped optical fiber preforms based on the in-tube method, using the quartz deposition tube described above, and the preparation method includes the following steps:

[0026] Heat and pull off one end of the tail tube of the quartz deposition tube;

[0027] Prepare a mixed solution containing rare earth salts and co-dopersants, inject the mixed solution into a quartz deposition tube, and soak it thoroughly;

[0028] Slowly pour out the remaining solution, dry, dehydrate, oxidize and fuse the quartz deposition tube to obtain a rare-earth doped preform with uniform doping.

[0029] During the preparation of the quartz deposition tube above, the loose core layer inside the tube is configured to have a high density at the center and a low density near the liner tube, so that the density of the loose core layer is a gradually changing distribution within the cross-section. During the soaking process of the mixed solution, due to the different densities of the loose core layer, the adsorption capacity for rare earths in the mixed solution is also different; the closer to the center, the more rare earths are adsorbed by the loose core layer, resulting in a higher rare earth concentration closer to the middle. During the subsequent fusing process, since the volatilization ability is stronger closer to the center, by designing a reasonable change in the density of the loose core layer to match the volatilization degree during the fusing process, after fusing, the rare earth concentration on the cross-section of the preform is basically uniform, achieving the purpose of complete uniformity in engineering, enabling the subsequent preparation of high-performance optical fibers.

[0030] As a preferred technical solution, the rare earth element of the rare earth salt is selected from any one or more of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu.

[0031] As a preferred technical solution, the co-dopant is any one or a combination of several of the compounds containing phosphorus, cerium, bismuth and aluminum.

[0032] As a preferred technical solution, for the quartz deposition tube injected with the mixed solution, the relationship between the soaking time C and the thickness D of the loose core layer satisfies 2D < C < 4D, where C is in hours and D is in millimeters.

[0033] As a preferred technical solution, the method for drying and dehydrating the quartz deposition tube is as follows:

[0034] Purge with nitrogen or an inert gas, and then introduce the first process gas to dry and dehydrate at a temperature between 600 °C and 1000 °C.

[0035] The first process gas is selected according to the rare earth type and the process type, and can be, for example, a mixed gas composed of helium, oxygen and chlorine.

[0036] As a preferred technical solution, the method for oxidation and fusing is as follows:

[0037] Introduce the second process gas into the quartz deposition tube to oxidize and fuse at a temperature between 1600 °C and 2200 °C. During fusing, the pressure inside the tube is controlled between -1000 Pa and 500 Pa to obtain a rare-earth-containing preform.

[0038] The second process gas is also selected according to the rare earth type and the process type, and can be a process gas composed of helium and oxygen.

[0039] As a preferred technical solution, the core layer of the obtained preform contains one or more rare earth ions, and the mass content of each doped ion is 300-100000ppm.

[0040] On the other hand, the present invention also provides a rare earth-doped optical fiber preform prepared by the above-described preparation method.

[0041] On the other hand, the present invention provides a rare earth-doped optical fiber, wherein the rare earth-doped preform prepared by the above-mentioned preparation method is drawn into a fiber by drawing the preform or by drawing the fiber directly.

[0042] Because the rare earth doped preform used in this invention is doped with highly uniform rare earth elements to prepare optical fibers, the rare earth elements on the optical fiber are also highly uniform after drawing. This results in a flat distribution of the refractive index on the cross-section of the optical fiber, which has the characteristics of high gain, large bandwidth, low noise, polarization-insensitive gain, and low lead-in loss.

[0043] Compared with the prior art, the present invention has the following beneficial effects:

[0044] This invention solves the problem of uneven rare-earth ion distribution in rare-earth doped optical fiber preforms by optimizing the powder rod deposition and melting process. This invention can utilize existing in-tube solution-based equipment, offering strong versatility and adaptability. Rare-earth doped optical fiber preforms produced using this method exhibit uniform rare-earth ion distribution, resulting in optical fibers with a smooth refractive index profile and high laser slope efficiency. Attached Figure Description

[0045] Figure 1 This is a schematic diagram of the quartz deposition tube structure obtained in a specific implementation method.

[0046] Figure 2 The image shows the laser slope efficiency of the erbium-ytterbium co-doped optical fiber obtained by drawing the preforms obtained in Example 1 and Comparative Example 1.

[0047] Figure 3 The image shows the laser slope efficiency of the ytterbium-doped fiber obtained by drawing the preforms obtained in Example 2 and Comparative Example 2.

[0048] 100 - Quartz deposition tube, 110 - Liner, 120 - Loose core layer, 130 - Center. Detailed Implementation

[0049] 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.

[0050] like Figure 1As shown, the present invention provides a quartz deposition tube for preparing optical fiber preforms, comprising a liner and a loose core layer deposited on the inner wall of the liner using an MCVD process, wherein the density of the loose core layer is radially gradually distributed, thereby producing a gradually distributed doping capability for dopants.

[0051] Example 1:

[0052] MCVD process was used to prepare a quartz deposition tube with a porous core layer deposited on its inner surface. A pure silicon liner tube with an outer diameter of 28 mm and an inner diameter of 22 mm was prepared. Silicon tetrachloride, oxygen, and other raw material gases were introduced. The hydrogen-oxygen flame deposition temperature was controlled by adjusting the flow rates of hydrogen and oxygen, thereby adjusting the deposition temperature to the set value. The initial deposition temperature was 1225℃, and the deposition temperature gradually increased with each subsequent layer by 7.5℃, for a total of 11 layers. The highest deposition temperature reached 1300℃. As the deposition temperature changed, the density of the deposited porous core layer gradually increased. The final parameters of the quartz deposition tube were: the density of the porous core layer closest to the inner wall of the liner tube was 0.3 g / cm³. 3 The loose core layer has a deposition thickness of 2.2 mm, and the density of the loose core layer at any point B from the inner wall of the liner is ρ = 0.3 + 0.11 * B. 2 (g / cm 3 ).

[0053] A 0.3L ethanol solution containing ytterbium chloride, erbium chloride, and aluminum chloride was injected into the deposition tube. The ytterbium chloride content was 0.023mol / L, the erbium chloride content was 0.015mol / L, and the aluminum chloride content was 0.16mol / L. The solution was soaked for 6 hours, and then the solution was poured out. The quartz liner was purged with nitrogen for 3 hours. Then, He, O2, and Cl2 were introduced between 650℃ and 950℃ to dehydrate the loose core layer. Finally, the quartz tube was melted and shrunk between 1800℃ and 2100℃ to obtain an erbium-ytterbium co-doped preform. After drawing, an erbium-ytterbium co-doped optical fiber with a specification of 25 / 300 was obtained.

[0054] Comparative Example 1 of Example 1:

[0055] Quartz deposition tubes with a porous core layer deposited on the inner surface were prepared using the MCVD process. The porous core layer had a deposition thickness of 2.2 mm and a density of 0.31 g / cm³. 3 .

[0056] A 0.3L ethanol solution containing ytterbium chloride, erbium chloride, and aluminum chloride was injected into a quartz deposition tube. The ytterbium chloride content was 0.023mol / L, the erbium chloride content was 0.015mol / L, and the aluminum chloride content was 0.16mol / L. The tube was soaked for 6 hours, the solution was poured out, and the quartz liner was purged with nitrogen for 3 hours. Then, He, O2, and Cl2 were introduced between 650℃ and 950℃ to dehydrate the loose core layer. Finally, the quartz tube was melted and shrunk between 1800℃ and 2100℃ to obtain an erbium-ytterbium co-doped preform. After drawing, an erbium-ytterbium co-doped optical fiber with a specification of 25 / 300 was obtained.

[0057] The erbium-ytterbium ion concentration distribution in the core layer of the two erbium-ytterbium co-doped optical fibers mentioned above is shown in Table 1. It can be seen that the erbium-ytterbium ion concentration distribution in the erbium-ytterbium co-doped optical fiber prepared by Example 1 is uniform.

[0058] Table 1 shows a comparison of the ytterbium ion concentration and erbium ion concentration distribution between Example 1 and Comparative Example 1.

[0059]

[0060] Example 1 shows that the erbium-ytterbium co-doped fiber laser obtained by fiber drawing achieved a slope efficiency of 72.8% (e.g., Figure 1 (As shown). The fiber laser slope efficiency obtained in Comparative Example 1 is only 53.1%, which shows that the erbium-ytterbium co-doped fiber prepared in this embodiment can significantly improve the fiber performance.

[0061] Example 2

[0062] A quartz deposition tube with a porous core layer deposited on its inner surface was prepared using the same MCVD process as in Example 1. The parameters for the quartz deposition tube were as follows: the initial deposition temperature was 1215°C, and the deposition temperature gradually increased thereafter, with an increase of 8°C for each layer, for a total of 13 layers. The highest deposition temperature was 1311°C, and the density of the porous core layer closest to the inner wall of the liner was 0.28 g / cm³. 3 The loose core layer has a deposition thickness of 2.3 mm, and the density of the loose core layer at any point B from the inner wall of the liner is ρ = 0.28 + 0.13 * B. 2 (g / cm 3 ).

[0063] A 0.3L ethanol solution containing ytterbium chloride and aluminum chloride was injected into a quartz deposition tube. The ytterbium chloride content was 0.025mol / L and the aluminum chloride content was 0.18mol / L. The tube was soaked for 6 hours, the solution was poured out, and the quartz liner was purged with nitrogen for 3.5 hours. Then, He, O2, and Cl2 were introduced between 650℃ and 950℃ to dehydrate the loose core layer. Finally, the quartz tube was melted and shrunk between 1800℃ and 2100℃ to obtain a ytterbium-doped preform. After drawing, a ytterbium-doped optical fiber with a specification of 14 / 250 was obtained.

[0064] Comparative Example 2 of Example 2

[0065] Quartz deposition tubes with a porous core layer deposited on the inner surface were prepared using the MCVD process. The porous core layer had a deposition thickness of 2.3 mm and a density of 0.30 g / cm³. 3 .

[0066] A 0.3L ethanol solution containing ytterbium chloride and aluminum chloride was injected into a quartz deposition tube. The ytterbium chloride content was 0.025mol / L and the aluminum chloride content was 0.18mol / L. The tube was soaked for 6 hours, the solution was poured out, and the quartz liner was purged with nitrogen for 3.5 hours. Then, He, O2, and Cl2 were introduced between 650℃ and 950℃ to dehydrate the loose core layer. Finally, the quartz tube was melted and shrunk between 1800℃ and 2100℃ to obtain a ytterbium-doped preform. After drawing, a ytterbium-doped optical fiber with a specification of 14 / 250 was obtained.

[0067] The ytterbium ion concentration distribution of the two types of ytterbium-doped optical fibers is shown in Table 2. It can be seen that the ytterbium ion concentration distribution of the ytterbium-doped optical fiber prepared by Example 2 is more uniform than that of Comparative Example 2.

[0068] Table 2 shows a comparison of the ytterbium ion concentration and erbium ion concentration distribution between Example 2 and Comparative Example 2.

[0069]

[0070] Example 2: The fiber laser slope efficiency obtained by drawing the fiber reached 75.2% (e.g., Figure 2 (As shown). The fiber laser slope efficiency obtained in Comparative Example 2 was only 56.6%, which shows that the ytterbium-doped fiber preform prepared in this embodiment can significantly improve fiber performance.

[0071] 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 quartz deposition tube for preparing optical fiber preforms, characterized in that, It includes a liner tube and a loose core layer deposited on the inner wall of the liner tube by the MCVD process, and the density of the loose core layer is gradually changed in the radial direction, so as to produce a gradually changed adsorption capacity for doping substances. The closer to the center, the greater the density of the loose core layer; The density distribution of the loose core layer satisfies the following equation: ρ = ρ 0+ A B 2 ρ is the density of the loose core layer at any point. ρ 0 represents the density of the loose core layer closest to the inner wall of the liner. B Where A is the radial distance between the corresponding point and the inner wall of the liner, and A is the gradient coefficient. The ρ and ρ The unit for 0 is g / cm³ 3 , ρ The value of 0 is in the range of 0.275 < ρ 0 < 0.55; the radial distance B is in millimeters, and the value of B is no greater than 2.5; A is a dimensionless parameter with a value range of 0.05-0.

21.

2. A method for preparing a quartz deposition tube for preparing an optical fiber preform as described in claim 1, characterized in that, It includes the following steps: Prepare the liner tube to be deposited, and introduce the raw material gas containing silicon tetrachloride and oxygen into the liner tube for deposition; control the deposition temperature to increase layer by layer to obtain a loose core layer with gradually increasing density.

3. The method for preparing the quartz deposition tube according to claim 2, characterized in that, The initial deposition temperature is between 1200 - 1250 °C, the subsequent deposition temperature increment for each layer is 5 - 15 °C, and the highest deposition temperature does not exceed 1350 °C.

4. A method for preparing rare-earth-doped optical fiber preforms based on an in-tube method, comprising using the quartz deposition tube described in claim 1 for preparing optical fiber preforms, characterized in that, The preparation method includes the following steps: Prepare a mixed solution containing rare earth salt and co - dopant, inject the mixed solution into the quartz deposition tube, and soak it fully; Slowly pour out the remaining solution, dry, dehydrate, oxidize and collapse the quartz deposition tube to obtain a rare earth - doped fiber preform with uniform doping.

5. The method for preparing rare-earth-doped optical fiber preforms based on the in-tube method according to claim 4, characterized in that: The rare earth element of the rare earth salt is selected from any one or more of Sc, Y, La, Ce, Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu.

6. The method for preparing rare-earth-doped optical fiber preforms based on the in-tube method according to claim 4, characterized in that: The co - dopant is any one or several combinations of compounds containing phosphorus, cerium, bismuth and aluminum.

7. The method for preparing rare-earth-doped optical fiber preforms based on the in-tube method according to claim 4, characterized in that: For the quartz deposition tube injected with the mixed solution, the relationship between the soaking time C and the thickness D of the loose core layer satisfies 2D < C < 4D, where the unit of C is hour and the unit of D is millimeter.

8. The method for preparing rare-earth-doped optical fiber preforms based on the in-tube method according to claim 4, characterized in that: The method for drying and dehydrating the quartz deposition tube is as follows: Purge with nitrogen or inert gas, and then introduce the first process gas to dry and dehydrate at 600 °C to 1000 °C.

9. The method for preparing rare-earth-doped optical fiber preforms based on the in-tube method according to claim 4, characterized in that: The method for oxidation and collapse is as follows: Introduce the second process gas into the quartz deposition tube at 1600 °C to 2200 °C for oxidation and collapse. When collapsing, the pressure in the tube is controlled at - 1000 Pa to 500 Pa to obtain a rare earth - doped fiber preform.

10. The method for preparing rare-earth-doped optical fiber preforms based on the in-tube method according to claim 4, characterized in that: The types of rare earth ions in the core layer of the obtained preform are one or more, and the mass content of each doping ion is 300 - 100000 ppm.

11. A rare-earth-doped optical fiber preform, characterized in that: It is prepared by using the preparation method of the rare earth - doped fiber preform based on the in - tube method according to any one of claims 4 to 10.

12. A rare-earth-doped optical fiber, characterized in that, The rare earth - doped preform prepared by using the preparation method of the rare earth - doped fiber preform based on the in - tube method according to any one of claims 4 to 10 is drawn into a rare earth - doped fiber through sleeve drawing or direct drawing.

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