Preparation method of active optical fiber with enhanced anti-photonic darkening performance and optical fiber thereof

Abstract

The application relates to a preparation method of an active optical fiber with enhanced anti-photon darkening performance and the optical fiber. First, an active optical fiber preform is prepared, the active optical fiber preform is clamped to a fiber drawing tower for heating and melting to draw the optical fiber, radiation aging treatment is carried out in the cooling forming stage of the optical fiber drawing, the bare optical fiber passes through a light radiation field to receive a predetermined dose of light radiation, then the optical fiber after the radiation aging treatment is subjected to resin coating and ultraviolet curing treatment, and finally the fiber prepared through the fiber drawing is placed in a deuterium gas environment full of deuterium gas or mixed with inert gas for deuterium gas bleaching treatment. The application can make potential active defects in the optical fiber be largely consumed in advance and be repaired by deuterium gas, so that in subsequent high-power laser work, the optical fiber shows extremely low loss growth rate and extremely high stability, and the anti-photon darkening performance of the active optical fiber is effectively enhanced. The application has simple process, low cost and easy integration.

Description

Technical Field

[0001] This invention relates to a method for fabricating active optical fibers with enhanced resistance to photonic darkening and the optical fiber itself, which is suitable for high-power fiber lasers and amplifiers and belongs to the field of laser transmission technology. Background Technology

[0002] Active optical fibers (such as those doped with rare-earth ions like ytterbium, erbium, and thulium) are the core gain medium in high-power fiber lasers and amplifiers. However, under the long-term influence of high-power lasers, active optical fibers experience a phenomenon called "photon darkening." This phenomenon manifests as a continuous increase in fiber transmission loss and background loss, leading to a decrease in laser output power, reduced slope efficiency, and deterioration in beam quality, severely impacting the long-term reliability and lifespan of the laser.

[0003] To address the aforementioned problems, the most common approach is to load deuterium gas into the optical fiber. Deuterium can bind to pre-existing defect centers (such as oxygen-deficient defects) within the fiber, preventing them from forming absorption centers under laser excitation. However, this method is primarily a preventative measure, and its ability to suppress color centers formed by bond breakage due to high-power lasers during laser operation is limited, with its effectiveness gradually diminishing over time. Alternatively, improving the preform fabrication process to reduce the content of hydroxyl and metallic impurities can purify the fiber material and mitigate photon darkening. However, this method is costly, complex, and cannot eliminate bond breakage and photon darkening effects caused by high-energy lasers. Summary of the Invention

[0004] The technical problem to be solved by the present invention is to overcome the shortcomings of the prior art and provide a method for preparing active optical fibers with enhanced anti-photon darkening performance and the optical fiber thereof. It can not only effectively enhance the anti-darkening performance of active optical fibers, but also has a simple process and low cost.

[0005] The technical solution of the preparation method adopted by the present invention to solve the above-mentioned problems is as follows: First, an active optical fiber preform is prepared. The active optical fiber preform is then clamped in a drawing tower and heated and melted to form an optical fiber. The key feature is that radiation aging treatment is performed during the cooling and forming stage of optical fiber drawing. The bare optical fiber is passed through an illumination radiation field and receives a predetermined dose of light radiation. Then, the optical fiber after radiation aging treatment is coated with resin and cured with ultraviolet light to complete the drawing process. Finally, the drawn optical fiber is placed in an environment filled with deuterium and inert gas, or a mixture of hydrogen and inert gas, for deuterium bleaching treatment, thus completing the entire preparation process.

[0006] According to the above scheme, the light radiation is ultraviolet, gamma ray, or X-ray light radiation.

[0007] According to the above scheme, the ultraviolet wavelength of the ultraviolet light radiation is 200~400 nm, and the irradiation intensity is 0.01~1W / cm².

[0008] According to the above scheme, the irradiation rate of the gamma ray or X-ray radiation is 0.5~30 krad / min.

[0009] According to the above scheme, the wire drawing speed during the wire drawing process is 1~200 m / min, preferably 40~100 m / min, and the wire drawing tension is 10~300g.

[0010] According to the above scheme, the concentration of deuterium or hydrogen gas in the deuterium bleaching treatment is 1~5%, the gas pressure is 1~5 standard atmospheres (0.1Mpa), the treatment temperature is 25~100℃, and the treatment time is 120~240 h (hours).

[0011] According to the above scheme, the optical fiber includes a core layer and a cladding layer, with two resin coating layers coated on the outside of the cladding layer. The diameter of the core layer is 20~400μm, and the outer diameter of the cladding layer is 80~800μm. According to the above scheme, the radial cross-section of the outer periphery of the cladding is a regular octagon. When the pump light is reflected at the non-circular boundary, it is easier to change the propagation angle. This design is like a "light mode stirrer," forcing the light to change its path, thereby greatly increasing the probability of the pump light crossing with the centrally doped fiber core, allowing more pump light to be absorbed and converted into laser light.

[0012] According to the above scheme, the core layer is a rare earth-doped silica glass layer. The doping components and concentrations are as follows: Yb2O3 0.01~1% mol, Al2O3 0.1~5% mol, P2O5 0~10% mol, Ce2O3 0~0.1 mol, GeO2 0~3% mol, and F 0~2% mol. The core rod prepared according to the above composition is more prone to defects during irradiation compared to pure quartz glass.

[0013] The optical fiber of the present invention is an active optical fiber prepared by the above method.

[0014] The beneficial effects of this invention are as follows: 1. When the optical fiber is drawn but before the coating is cured, irradiation treatment is performed to ensure that the energy acts directly on the glass matrix and receives a predetermined dose of high-energy radiation. This induces a large number of color centers and unstable defects in the optical fiber, actively generating a large number of defect targets that can be reacted by deuterium gas, simulating the "aging" process under long-term laser operation. The irradiated pre-aged optical fiber is placed in an environment filled with deuterium gas or a mixture of deuterium gas and inert gas, and kept at a certain temperature and pressure for a period of time. Deuterium gas will penetrate into the optical fiber and react with the irradiated and inherent defects of the optical fiber to achieve "bleaching," that is, neutralize the activity of these defects. This synergistic effect allows a large number of potential active defects inside the optical fiber to be "consumed" in advance and "repaired" by deuterium gas. Therefore, in subsequent high-power laser operation, it exhibits extremely low loss growth rate and extremely high stability, effectively enhancing the anti-photon darkening performance of active optical fibers. 2. The process is simple and easy to integrate. It can be directly integrated into existing optical fiber drawing production lines, adding only one processing step between drawing and coating. No large-scale modifications to existing equipment are required, resulting in low processing costs and significant performance improvements. 3. By proactively addressing intrinsic defects in the optical fiber, the impact of minor differences between different batches of preforms on the final product's anti-darkening performance is reduced, improving product consistency and reliability. Attached Figure Description

[0015] Figure 1 This is a schematic diagram of the radial cross-sectional structure of an optical fiber in one embodiment of the present invention.

[0016] Figure 2 This is a process flow diagram of the wire drawing process in one embodiment of the present invention.

[0017] Figure 3 This is a comparison chart of the loss spectrum curves of the optical fiber of the present invention and that of the comparative example in one embodiment of the present invention.

[0018] Figure 4 This is a comparison chart of the aging performance test curves of the optical fiber of the present invention and the comparative example in one embodiment of the present invention. Detailed Implementation

[0019] The present invention will be further described below with reference to the embodiments and accompanying drawings.

[0020] Example 1: A ytterbium-doped silica active optical fiber preform was prepared and clamped in a drawing tower for drawing. The preform was heated to approximately 2000°C and melted to form an optical fiber with a core diameter of 60 μm and a cladding outer diameter (longest diagonal) of 125 μm. The radial cross-section of the cladding outer periphery was a regular octagon, and the drawing tension was 50 g. After passing through a cooling tube, the drawn optical fiber was immediately guided through an ultraviolet radiation tube with an ultraviolet light source wavelength of 254 nm, an irradiation intensity of 50 mW / cm², and an optical fiber throughput speed of 60 m / min. The optical fiber entered a coating system and was sequentially coated with a low-refractive-index inner coating 2 and a high-refractive-index outer coating 1, and then cured in an ultraviolet curing oven. After curing, the optical fiber was wound onto a reel. The radiation-aged optical fiber was then placed in an environment filled with a mixture of deuterium and inert gas, and kept at a certain temperature and pressure for a period of time, with a deuterium concentration of 3%, a temperature of 40°C, a pressure of 2 atmospheres, and a duration of 168 hours. The deuterium gas penetrates into the optical fiber and reacts chemically with the inherent defect centers of the fiber, achieving "bleaching," that is, neutralizing the activity of these defects.

[0021] Comparative example: The same preform and drawing parameters were used, but coating and curing were performed directly after drawing, and then the fibers were subjected to conventional deuterium loading for 7 days in a high-pressure deuterium chamber.

[0022] Performance Testing: The optical fibers prepared in Example 1 of this invention and the optical fibers prepared in the comparative example were wound into optical fiber spirals and placed in the same all-fiber laser structure for accelerated photon darkening experiments. They were operated continuously for 500 hours at the same pump power (to achieve a cavity photon density 5 times that of conventional operating conditions).

[0023] Results: The output power of the comparative fiber decreased by approximately 15% after 500 hours. The output power of the fiber in Example 1 of this invention decreased by less than 3% after 500 hours.

[0024] Conclusion: Experimental results show that the "radiation pre-aging-deuterium bleaching" process provided by this invention can significantly improve the anti-photon darkening performance of active optical fibers.

[0025] Example 2: A ytterbium-doped silica active optical fiber preform was prepared and clamped in a drawing tower for drawing. The preform was heated to approximately 2000°C to melt and drawn into an optical fiber with a core diameter of 20 μm and a cladding outer diameter of 400 μm. The radial cross-section of the cladding outer periphery was a regular octagon, and the drawing tension was 70 g. After passing through a cooling tube, the drawn fiber was immediately guided through an ultraviolet radiation tube with an ultraviolet light source wavelength of 254 nm, an irradiation intensity of 50 mW / cm², and a fiber throughput speed of 30 m / min. The fiber entered a coating system, where a low-refractive-index inner coating and a high-refractive-index outer coating were applied sequentially, followed by curing in an ultraviolet curing oven. After curing, the fiber was wound onto a reel. The radiation-aged optical fiber was then placed in an environment filled with deuterium or a mixture of deuterium and inert gases, and kept at a certain temperature and pressure for a period of time (3% deuterium concentration, 40°C, 3 atmospheres, 168 hours). The deuterium penetrated into the optical fiber and reacted chemically with the inherent defect centers of the fiber, achieving "bleaching," that is, neutralizing the activity of these defects.

[0026] Comparative example: The same preform and drawing parameters were used, but coating and curing were performed directly after drawing, and then the fibers were subjected to conventional deuterium loading for 7 days in a high-pressure deuterium chamber.

[0027] Performance testing: The optical fibers prepared in Example 2 of this invention and the optical fibers prepared in the comparative example were wound into optical fiber spirals and placed in the same all-fiber laser structure for aging tests. They were then continuously operated for 500 hours at the same pump power.

[0028] Results: The output power of the comparative fiber decreased by approximately 10% after 500 hours. The output power of the fiber in Example 2 of this invention decreased by less than 2% after 500 hours.

[0029] Conclusion: Experimental results show that the "radiation pre-aging-deuterium bleaching" process provided by this invention can significantly improve the anti-photon darkening performance of active optical fibers.

[0030] Example 3: A ytterbium-doped silica active optical fiber preform was prepared and clamped in a drawing tower for drawing. The preform was heated to approximately 2000°C and melted, and drawn into an optical fiber with a core diameter of 30 μm and a cladding outer diameter of 250 μm. The radial cross-section of the cladding outer periphery was a regular octagon, and the drawing tension was 40 g. After passing through a cooling tube, the drawn optical fiber was immediately guided through an X-ray radiation tube with an irradiation rate of 5 rad / min and a fiber throughput speed of 1 m / min. The optical fiber entered a coating system and was sequentially coated with a low-refractive-index inner coating and a high-refractive-index outer coating, and then cured in an ultraviolet curing oven. After curing, the optical fiber was wound onto a reel. The radiation-aged optical fiber was then placed in an environment filled with deuterium gas or a mixture of deuterium gas and inert gas, and maintained at a certain temperature and pressure for a period of time. The deuterium gas concentration was 4%, the temperature was 40°C, the pressure was 4 atmospheres, and the time was 216 h. Deuterium gas can penetrate into optical fibers and react chemically with the inherent defect centers of the fibers, achieving "bleaching," that is, neutralizing the activity of these defects.

[0031] Appendix Figure 3 The blue line in the figure represents the fiber loss spectrum after irradiation. As can be seen from the figure, the loss in the 500-750 nm band is relatively large (≥50 dB / km) after irradiation. This loss value is mainly caused by non-bridging oxygen hole defects. The red line represents the loss curve after deuterium treatment. As can be seen from the figure, the loss curve decreases significantly in the 500~750 nm range, indicating that the non-bridging oxygen hole defects caused by radiation were repaired by deuterium after deuterium treatment.

[0032] Comparative example: The same preform and drawing parameters were used, but coating and curing were performed directly after drawing, and then the fibers were subjected to conventional deuterium loading for 9 days in a high-pressure deuterium chamber.

[0033] Performance testing: The optical fibers prepared in Example 3 of this invention and the optical fibers prepared in the comparative example were wound into optical fiber spirals and placed in the same all-fiber laser structure for aging tests. They were operated continuously for 24 hours at the same pump power.

[0034] Results: The output power of the comparative fiber decreased by approximately 2% after 24 hours. The output power of the fiber in Example 3 of this invention decreased by less than 0.5% after 24 hours.

[0035] Conclusion: Experimental results show that the "radiation pre-aging-deuterium bleaching" process provided by this invention can significantly improve the anti-photon darkening performance of active optical fibers.

Claims

1. A method for fabricating active optical fibers with enhanced anti-photon darkening performance, comprising first preparing an active optical fiber preform, then clamping the active optical fiber preform into a drawing tower, heating and melting it to draw it into an optical fiber, characterized in that... Radiation aging treatment is performed during the cooling and forming stage of optical fiber drawing. The bare optical fiber is passed through an illumination radiation field and receives a predetermined dose of light radiation. Then, the optical fiber after radiation aging treatment is coated with resin and cured with ultraviolet light to complete the fiber drawing process. Finally, the fiber is placed in an environment filled with deuterium and inert gas, or a mixture of hydrogen and inert gas, for deuterium bleaching treatment, thus completing the entire preparation process.

2. The method for fabricating active optical fiber with enhanced anti-photon darkening performance according to claim 1, characterized in that... The light radiation mentioned is ultraviolet, gamma ray, or X-ray light radiation.

3. The method for fabricating active optical fiber with enhanced anti-photon darkening performance according to claim 2, characterized in that... The ultraviolet light radiation has an ultraviolet wavelength of 200~400 nm and an irradiation intensity of 0.01~1 W / cm².

4. The method for fabricating active optical fiber with enhanced anti-photon darkening performance according to claim 2, characterized in that... The irradiation rate of the gamma-ray or X-ray radiation is 0.5~30 krad / min.

5. The method for fabricating active optical fiber with enhanced anti-photon darkening performance according to claim 1 or 2, characterized in that... The drawing speed during the drawing process is 1~200 m / min, and the drawing tension is 10~300g.

6. The method for fabricating active optical fiber with enhanced anti-photon darkening performance according to claim 1 or 2, characterized in that... During the deuterium bleaching treatment, the concentration of deuterium or hydrogen is 1-5%, the pressure is 1-4 standard atmospheres, the treatment temperature is 25-100℃, and the treatment time is 120-240 h.

7. The method for fabricating active optical fiber with enhanced anti-photon darkening performance according to claim 1 or 2, characterized in that... The optical fiber includes a core layer and a cladding layer, with two resin coating layers on the outside of the cladding layer. The diameter of the core layer is 20~400μm, and the outer diameter of the cladding layer is 80~800μm.

8. The method for fabricating active optical fiber with enhanced anti-photon darkening performance according to claim 7, characterized in that... The radial cross section of the outer periphery of the cladding is a regular octagon.

9. The method for fabricating active optical fiber with enhanced anti-photon darkening performance according to claim 7, characterized in that... The core layer is a rare-earth-doped silica glass layer, and the doping components and concentrations are as follows: Yb2O3 0.01~1% mol, Al2O3 0.1~5 mol%, P2O5 0~10 mol%, Ce2O3 0~0.1 mol%, GeO2 0~3 mol%, and F 0~2 mol.

10. An active optical fiber with enhanced resistance to photonic darkening, characterized in that... The active optical fiber is prepared according to any of the active optical fiber preparation methods for enhancing anti-photon darkening performance as described in claims 1-9.

11. The active optical fiber with enhanced anti-photonic darkening performance according to claim 10, characterized in that... The optical fiber includes a core layer and a cladding layer, with two resin coating layers on the outside of the cladding layer. The diameter of the core layer is 20~400μm, and the outer diameter of the cladding layer is 80~800μm.

12. The active optical fiber with enhanced anti-photonic darkening performance according to claim 10, characterized in that... The core layer is a rare earth-doped silica glass layer, and the doping components and concentrations are as follows: Yb2O3 0.01~1 mol%, Al2O3 0.1~5 mol%, P2O5 0~10 mol%, Ce2O3 0~0.1 mol%, GeO2 0~3 mol%, and F 0~2 mol.

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