Anti-photonic darkening active optical fiber preform, optical fiber and method of making same

Abstract

The application discloses an anti-photon darkening active optical fiber preform, an optical fiber and a preparation method thereof. First, a quartz lining pipe with a loose core layer deposited on the inner surface is prepared by using an MCVD process, a tail pipe at one end is heated and broken, a mixed solution containing ytterbium-containing rare earth salt and aluminum and cerium-containing co-doping agent is injected into the deposited pipe, and after being soaked sufficiently, drying and melting, a rare earth doped core rod can be obtained, and the anti-photon darkening active ytterbium doped optical fiber can be obtained by directly drawing the core rod or drawing the core rod with an outer sleeve pipe. The ytterbium doped optical fiber prepared by the application has an equilibrium state photon darkening additional loss lower than 10 dB / m at 633 nm, and compared with the existing ytterbium doped active optical fiber, the anti-photon darkening performance is greatly improved without affecting the key performances such as fiber absorption and slope efficiency.

Description

TECHNICAL FIELD

[0001] The application belongs to the field of optical fiber manufacturing, and relates to an optical fiber preparation technology, in particular to a kind of anti-photon darkening active optical fiber preform, optical fiber and preparation method thereof. BACKGROUND

[0002] Rare earth doped optical fiber preform is a key material for producing optical fiber amplifier and optical fiber laser. Compared with the traditional semiconductor laser amplifier, the optical fiber amplifier does not need to go through the complex processes such as photoelectric conversion, electro-optical conversion and signal regeneration, and can directly amplify the signal in all-optical manner. In the working wavelength range, the optical fiber amplifier exhibits high gain, large bandwidth, low noise, polarization-insensitive gain, low introduction loss characteristics, and has good "transparency", and is particularly suitable for long-distance optical communication relay amplification. It can be said that the optical fiber amplifier lays an important technical foundation for realizing high-capacity all-optical communication. As an important component of high-power fiber laser, rare earth doped optical fiber is the main factor determining the performance of high-power fiber laser. However, with the continuous increase of the power of the optical fiber laser, the power attenuation, i.e. the photon darkening phenomenon, occurs, which increases the laser threshold of the laser, reduces the efficiency, reduces the system stability, and shortens the working life, thereby limiting the further development and application of the laser.

[0003] At present, there are many methods to solve the photon darkening, including reducing the number of oxygen defects in the optical fiber; treating the optical fiber with carrier gas; eliminating the color center that has been generated; when the color center has been formed, heat bleaching and light bleaching can be used to eliminate all or part of the loss induced by photon darkening; changing the composition of the optical fiber to slow down the photon darkening, such as doping P in the optical fiber (US2009 / 0011233A1); doping alkali metal ions in the core of the optical fiber (CN107390315A), including one or more of Na ion, K ion, Mg ion, Ca ion, Ba ion and Sr ion, and determining the appropriate concentration and ratio of co-dopant to change the optical basicity of the environment of rare earth ions and reduce the additional loss of photon darkening; adding yttrium and cerium ions in the core (CN102135641A) and the like. However, the process of preparing the optical fiber by these methods reduces the content of ytterbium ions, although it can partially slow down the darkening of the optical fiber, but sacrifices the absorption performance of the optical fiber at 915nm, and the anti-darkening performance of the optical fiber in the red light band is still poor, such as the equilibrium state additional loss at 633nm is usually greater than 100dB / m, and the slope efficiency of the optical fiber laser is reduced. Therefore, the existing technologies for solving the photon darkening are not mature, and there are many problems. It is necessary to develop an optical fiber with high absorption coefficient, high slope efficiency and excellent anti-photon darkening performance. SUMMARY

[0004] One of the purposes of the present application is to provide a preparation method of an anti-photodarkening active optical fiber preform, which is proposed to solve the problems existing in the prior art. By optimizing the content and proportion of rare earth elements and co-doping agents, the anti-photodarkening effect of the optical fiber prepared by drawing the preform of the present application is excellent, and the optical fiber also has the advantages of high absorption coefficient and high skew effect.

[0005] Another purpose of the present application is to obtain an anti-photodarkening active optical fiber by using the anti-photodarkening active optical fiber preform described above through sleeve drawing or direct drawing, which greatly improves the anti-darkening performance of the optical fiber in the red light band. For example, the equilibrium state photodarkening additional loss at 633 nm can reach a level of less than 10 dB / m.

[0006] The technical scheme adopted by the present application to solve the above-mentioned problems is as follows:

[0007] On the one hand, the present application provides a preparation method of an anti-photodarkening active optical fiber preform, comprising the following steps:

[0008] A quartz deposition tube with a loose core layer deposited on the inner surface is prepared by using the MCVD process;

[0009] After heating the quartz deposition tube and breaking off the tail pipe at one end, a mixed solution containing ytterbium rare earth salt and co-doping agent is injected into the deposition tube and soaked sufficiently, and the co-doping agent contains at least cerium;

[0010] After soaking, the quartz deposition tube is dried and dehydrated, and then shrunk to obtain a cerium-containing anti-photodarkening active optical fiber preform.

[0011] The present application obtains an anti-photodarkening active optical fiber preform by co-doping ytterbium and cerium. After drawing the optical fiber, the redox couple Ce 3+ / Ce 4+ exists in the optical fiber, which can capture electrons and holes related to color center formation, thereby inhibiting photodarkening and achieving an anti-photodarkening effect.

[0012] As a preferred technical scheme, the deposition temperature of the loose core layer is 1200-1400℃, and the rare earth doping amount is controlled by controlling the density of the loose layer through the deposition temperature.

[0013] Further preferably, the deposition temperature of the loose core layer is 1300-1350℃.

[0014] Further preferably, in order to adjust the NA value, F is doped in the loose core layer, and the concentration of F element is 1000-5000ppm.

[0015] As a preferred technical scheme, the solvent in the mixed solution is water, a volatile organic solvent, or a mixed solvent composed of water and a volatile organic solvent.

[0016] Further preferably, the volatile organic solvent comprises ethanol, propanol.

[0017] As a preferred technical solution, the co-doping agent further comprises an aluminum-containing compound.

[0018] Further preferably, the co-doping agent is an aluminum-containing, cerium-containing halide salt, specifically cerium chloride, aluminum chloride, or other halide salt that can be dissolved in a solvent.

[0019] As a preferred technical solution, the ytterbium-containing rare earth salt is ytterbium chloride.

[0020] As a preferred technical solution, the quartz deposition tube into which the ytterbium-containing rare earth salt solution is injected is soaked for 1-6 hours, and most preferably for 3.5 hours; the soaking temperature is between 0°C and 50°C, and most preferably is 40°C.

[0021] As a preferred technical solution, after sufficient soaking, the drying and dehydration method is as follows:

[0022] Nitrogen or inert gas is introduced into the quartz deposition tube to perform purging, and then a first process gas is introduced to perform drying, oxidation, and dehydration at a temperature between 600°C and 1000°C.

[0023] The first process gas comprises helium, oxygen, and chlorine.

[0024] As a preferred technical solution, the melting and shrinking method is as follows:

[0025] After the drying and dehydration of the quartz deposition tube are completed, a second process gas is introduced to perform melting and shrinking at a temperature between 1600°C and 2200°C, and the pressure in the tube is controlled to be between -1000 Pa and 500 Pa, thereby obtaining a rare earth-doped optical fiber preform, wherein the ytterbium ion concentration in the core layer of the preform is 16000-30000 ppm, the aluminum ion concentration is 12000-20000 ppm, the cerium ion concentration is 2000-10000 ppm, the fluorine ion concentration is 8000-15000 ppm, and the NA value of the fiber core is 0.06-0.1.

[0026] The second process gas comprises helium and oxygen.

[0027] In another aspect, the present application also provides an anti-photodarkening active optical fiber, which is obtained by performing sleeve-drawing or direct-drawing on the anti-photodarkening active optical fiber preform prepared by the above preparation method.

[0028] As a preferred technical scheme, in the obtained anti-photonic darkening active optical fiber, by selecting the concentration of the rare earth salt and the co-doping agent in the mixed solution in the process of preparing the preform, the ytterbium ion concentration in the fiber core layer is 16000-30000ppm, the aluminum ion concentration is 12000-20000ppm, the cerium ion concentration is 2000-10000ppm, the fluorine ion concentration is 8000-15000ppm, and the NA value of the fiber core is 0.06-0.1.

[0029] The ytterbium-doped optical fiber preform prepared according to the above scheme has excellent anti-photonic darkening performance, and in particular, the equilibrium photonic darkening additional loss at the red light band, such as 633nm, can reach a level of less than 10dB / m.

[0030] Compared with the prior art, the anti-photonic darkening active optical fiber has the following beneficial effects:

[0031] Without increasing the existing solution method production equipment and process, by changing the doping components of the optical fiber, optimizing the content of cerium ions, the ytterbium ion concentration in the fiber core layer is 16000-30000ppm, and the cerium ion concentration is 2000-10000ppm, so that the anti-photonic darkening performance of the ytterbium-doped optical fiber can be prepared, and by further adjusting the aluminum ion concentration to 12000-20000ppm and the fluorine ion concentration to 8000-15000ppm, the ytterbium-doped optical fiber with excellent comprehensive performance and excellent anti-photonic darkening performance can be obtained. BRIEF DESCRIPTION OF DRAWINGS

[0032] Figure 1 The flow chart for preparing the anti-photonic darkening active optical fiber in the embodiments of the present application is shown. DETAILED DESCRIPTION

[0033] In order to better understand the present application, the content of the present application will be further illustrated below in combination with the embodiments, but the present application is not limited to the following embodiments.

[0034] Embodiment 1:

[0035] A quartz deposition tube with a F-doped loose core layer deposited on the inner surface is prepared by using the MCVD process, 0.3L of an ethanol solution containing ytterbium chloride, cerium chloride and aluminum chloride is injected into the deposition tube, and the solution is soaked at 40℃ for 3.2 hours, then the solution is poured out, nitrogen is introduced into the quartz liner tube for 3h, then He, O2 and Cl2 are introduced between 650℃-950℃ to dehydrate the loose core layer, and finally the quartz tube is fused and shrunk at 1800℃-2100℃, to obtain a ytterbium-cerium co-doped optical fiber preform. The above preform is sleeved with an octagonal pure silicon sleeve to draw a fiber with a core diameter of 14.3um and an octagonal parallel edge spacing of the cladding of 249.6um.

[0036] Comparative Examples 1A, 1B, 1C, 1D (without cerium doping):

[0037] A quartz deposition tube with F-doped loose core layer deposited on the inner surface was prepared by MCVD process. 0.3 L of ethanol solution containing ytterbium chloride, aluminum chloride was injected into the deposition tube, and soaked at 40°C for 3.2 hours. The solution was poured out, and nitrogen was blown into the quartz liner for 3 hours. Then, He, O2, Cl2 were introduced at 650-950°C to dehydrate the loose core layer. Finally, the quartz tube was fused and shrunk at 1800-2100°C, and a ytterbium-doped fiber preform was obtained. The above preform was sleeved with an octagonal pure silica sleeve, and a fiber with a core diameter of 14.3 um and an octagonal cladding with a parallel edge distance of 249.6 um was obtained.

[0038]

[0039] Table 1 is a table of ion concentration and performance characterization of the fiber of Example 1 and Comparative Example 1

[0040] The main characteristics of the fiber in the above Example 1 and Comparative Example 1 are shown in Table 1. It can be seen that the active fiber of the present embodiment 1 has excellent anti-photonic darkening performance without reducing the absorption coefficient and the slope efficiency compared with Comparative Example 1.

[0041] Example 2:

[0042] A quartz deposition tube with F-doped loose core layer deposited on the inner surface was prepared by MCVD process. 0.3 L of ethanol solution containing ytterbium chloride, cerium chloride, aluminum chloride was injected into the deposition tube, and soaked at 43°C for 3 hours. The solution was poured out, and nitrogen was blown into the quartz liner for 3 hours. Then, He, O2, Cl2 were introduced at 650-950°C to dehydrate the loose core layer. Finally, the quartz tube was fused and shrunk at 1800-2100°C, and a ytterbium-cerium co-doped fiber preform was obtained. The above preform was sleeved with an octagonal pure silica sleeve, and a fiber with a core diameter of 14.1 um and an octagonal cladding with a parallel edge distance of 250.2 um was obtained.

[0043] Comparative Examples 2A, 2B, 2C, 2D (low ytterbium content):

[0044] A quartz deposition tube with F-doped loose core layer deposited on the inner surface was prepared by MCVD process. 0.3 L of ethanol solution containing ytterbium chloride, aluminum chloride and cerium chloride was injected into the deposition tube. Different proportions of ytterbium chloride were used in different comparative examples. The solution was soaked at 43°C for 3 hours, and then poured out. Nitrogen was introduced into the quartz liner for 3 hours, and then He, O2 and Cl2 were introduced at 650-950°C to dehydrate the loose core layer. Finally, the quartz tube was fused and shrunk at 1800-2100°C to obtain a ytterbium-doped fiber preform. The preform was sleeved with an octagonal pure silica sleeve to draw a fiber with a core diameter of 14.1 um and a cladding octagonal parallel edge distance of 250.2 um.

[0045]

[0046] Table 2 is a table of ion concentration and performance characterization of the fiber in Example 2 and Comparative Example 2.

[0047] The main characteristics of the fiber in Example 2 and Comparative Example 2 are shown in Table 2. It can be seen that the absorption coefficient and the slope efficiency of the ytterbium-doped active fiber prepared by the present example are significantly improved compared with the comparative example, and the fiber also has excellent anti-photonic darkening performance.

[0048] Example 3:

[0049] A quartz deposition tube with F-doped loose core layer deposited on the inner surface was prepared by MCVD process. 0.31 L of ethanol solution containing ytterbium chloride, cerium chloride and aluminum chloride was injected into the deposition tube. The solution was soaked at 45°C for 3 hours, and then poured out. Nitrogen was introduced into the quartz liner for 3 hours, and then He, O2 and Cl2 were introduced at 650-950°C to dehydrate the loose core layer. Finally, the quartz tube was fused and shrunk at 1800-2100°C to obtain a ytterbium-cerium co-doped fiber preform. The preform was sleeved with an octagonal pure silica sleeve to draw a fiber with a core diameter of 10 um and a cladding octagonal parallel edge distance of 124.8 um.

[0050] Comparative Example 3 (high cerium content):

[0051] A quartz deposition tube with F-doped loose core layer deposited on the inner surface was prepared by MCVD process. 0.31 L of ethanol solution containing ytterbium chloride and aluminum chloride was injected into the deposition tube. The solution was soaked at 45°C for 3 hours, and then poured out. Nitrogen was introduced into the quartz liner for 3 hours, and then He, O2 and Cl2 were introduced at 650-950°C to dehydrate the loose core layer. Finally, the quartz tube was fused and shrunk at 1800-2100°C to obtain a ytterbium-doped fiber preform. The preform was sleeved with an octagonal pure silica sleeve to draw a fiber with a core diameter of 10 um and a cladding octagonal parallel edge distance of 124.8 um.

[0052]

[0053]

[0054] Table 3 is a table of ion concentration and performance characterization of the optical fiber in Example 3 and Comparative Example 3

[0055] The main characteristics of the optical fiber in Example 3 and Comparative Example 3 are shown in Table 3. It can be seen that although cerium can improve the aging resistance of the optical fiber, too high concentration of cerium will reduce the absorption and slope efficiency of the optical fiber.

[0056] The above only describes the preferred embodiments of the present application, and it should be noted that for those skilled in the art, without departing from the inventive concept, several improvements and changes can be made, which are within the protection scope of the present application.

Claims

1. A method of making an anti-photodarkening active optical fiber preform, characterized by, The method comprises the following steps: A quartz deposition tube with a loose core layer deposited on its inner surface is prepared by using MCVD process; After the quartz deposition tube is heated and the tail pipe at one end is pulled off, a mixed solution containing ytterbium rare earth salt and co-doping agent is injected into the deposition tube, and the co-doping agent is a compound containing cerium, aluminum and fluorine, and the quartz deposition tube is soaked sufficiently; After the soaking is completed, the quartz deposition tube is dried, oxidized, dehydrated and collapsed to obtain a cerium-containing anti-photonic darkening active optical fiber preform, wherein the ytterbium ion concentration in the core layer of the preform is 16000-30000 ppm, the aluminum ion concentration is 12000-20000 ppm, the cerium ion concentration is 2000-10000 ppm, the fluorine ion concentration is 8000-15000 ppm, and the NA value of the fiber core is 0.06-0.

1.

2. The method of claim 1, wherein the anti-photodarkening active fiber preform is prepared by the steps of: The deposition temperature of the loose core layer is 1200-1400℃. ​ 3. The method of claim 1, wherein the anti-photodarkening active fiber preform is prepared by the steps of: The solvent in the mixed solution is water, a volatile organic solvent or a mixed solvent composed of water and a volatile organic solvent. ​ 4. The method of claim 3, wherein the anti-photodarkening active fiber preform is prepared by the steps of: The volatile organic solvent includes ethanol and propanol. ​ 5. The method for preparing the anti-photonic darkening active optical fiber preform according to claim 1, characterized in that, The quartz deposition tube containing the ytterbium rare earth salt solution is soaked for 1-6 hours at a temperature of 0-50℃.

6. The method of claim 1, wherein the anti-photodarkening active fiber preform is prepared by the steps of: After the soaking is completed, the quartz deposition tube is dried, oxidized and dehydrated by the following method: ​ Nitrogen or inert gas is introduced into the quartz deposition tube to blow, and then a first process gas is introduced to dry, oxidize and dehydrate the quartz deposition tube at a temperature of 600-1000℃.

7. The method for preparing the anti-photonic darkening active optical fiber preform according to claim 1, characterized in that, The collapsing method is as follows: After the drying and dehydration of the quartz deposition tube are completed, a second process gas is introduced into the quartz deposition tube at a temperature of 1600-2200℃ to collapse the quartz deposition tube, and the pressure in the tube is controlled at -1000 Pa to 500 Pa to obtain a rare earth doped optical fiber preform.

8. An anti-photodarkening active optical fiber preform, characterized in that, The anti-photonic darkening active optical fiber preform is obtained by using the preparation method of any one of claims 1-7.

9. An anti-photodarkening active optical fiber, characterized by The anti-photonic darkening active optical fiber preform is obtained by using the preparation method of any one of claims 1-7.

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