A gas-liquid combined doping device for preparing rare earth doped optical fiber

Abstract

This invention discloses a gas-liquid phase composite doping device for preparing rare-earth-doped optical fibers. The device includes a chelate feed pipe comprising a sleeve and multiple feed pipes. The sleeve has a first end cap and a second end cap installed at its inlet and outlet ends, respectively. The device also includes a process gas container, an oven, a rare-earth solution storage tank, a circulating water cooling device, and a raw material gas evaporator. Multiple first outlet pipes and one second outlet pipe are connected to the process gas container. A second outlet pipe and a liquid delivery pipe extend into the rare-earth solution storage tank. The liquid delivery pipe passes through the circulating water cooling device, which cools the liquid delivery pipe, thus maintaining the temperature of the rare-earth solution flowing into the liner within a set range. This invention allows for classified temperature control of the raw materials entering the liner. Gas-phase doping materials are insulated using an oil bath, while liquid-phase doping materials are insulated using water cooling, preventing mutual interference between gas and liquid. Doping of the raw materials on the inner wall of the liner can be achieved on the same lathe.

Description

Technical Field

[0001] This invention belongs to the field of optical fiber production equipment, and more specifically, relates to a gas-liquid phase composite doping device for preparing rare earth-doped optical fibers. Background Technology

[0002] Rare-earth-doped optical fibers are a crucial component of fiber lasers, and the performance stability of these lasers is primarily determined by the quality of the rare-earth-doped optical fibers. Consequently, numerous scholars have conducted theoretical research on the fabrication processes of rare-earth-doped optical fibers.

[0003] Currently, commonly used rare-earth ion doping techniques include solution immersion, nanodeposition, high-temperature vapor phase doping, and aerosol doping. However, in the fabrication of rare-earth-doped optical fibers, all methods employ single-doping techniques, with high-temperature vapor phase doping and solution immersion being the most widely used.

[0004] High-temperature vapor phase doping technology produces rare-earth-doped optical fibers with high rare-earth ion doping uniformity, but this technology cannot achieve high-concentration doping of rare-earth ions. Solution immersion technology is mature and simple, and can achieve high-concentration doping of rare-earth ions, but the doping uniformity is not as good as that of high-temperature vapor phase doping technology.

[0005] When rare earth elements are doped, some ions require liquid phase doping while others require gas phase doping. Existing technology has enabled liquid phase doping without removing the liner from the lathe.

[0006] However, when a combined liquid-phase doping and gas-phase doping process is required, the working temperatures of the gaseous raw material gas and the liquid rare earth solution are quite different. Gas-phase doping requires a very high temperature for the gaseous raw material gas to be vaporized, while liquid-phase doping is carried out at room temperature. Therefore, it is impossible to complete the process on the same lathe, which makes the gas-liquid phase combined doping process complex and prevents the simultaneous performance of liquid-phase doping and gas-phase doping, thus limiting the design of optical fiber composition. Summary of the Invention

[0007] To address the aforementioned deficiencies or improvement needs of existing technologies, this invention provides a gas-liquid phase composite doping device for preparing rare-earth-doped optical fibers. This device can classify and temperature-control the raw materials input into an external liner. The gaseous raw material for gas-phase doping is kept warm using an oil bath, while the rare-earth solution for liquid-phase doping is kept cold using water cooling, preventing mutual interference between the gas and liquid phases. The device allows for doping of the raw material on the inner wall of the liner on the same lathe, and enables simultaneous gas-liquid phase composite doping with both liquid and gas phase doping.

[0008] To achieve the above objectives, according to the present invention, a gas-liquid phase composite doping device for preparing rare-earth-doped optical fibers is provided, comprising a chelate feeding tube, the chelate feeding tube comprising a sleeve and multiple feeding tubes, wherein a first end cap and a second end cap are respectively installed at the inlet and outlet ends of the sleeve, and each feeding tube passes through the first end cap and the second end cap respectively, so that the circulating oil inside the sleeve provides an oil bath for each feeding tube, characterized in that:

[0009] The gas-liquid phase composite doping equipment also includes a process gas container, an oven, a rare earth solution storage tank, a circulating water cooling device, and a raw material gas evaporator, wherein:

[0010] The process gas container, rare earth solution storage tank, and each raw material gas evaporator are all located outside the oven. The process gas container is connected to multiple first outlet pipes and one second outlet pipe. Each raw material gas evaporator has one first outlet pipe and one conveying pipe extending into it. A portion of each first outlet pipe and a portion of each conveying pipe are located inside the oven. The temperature inside the oven is maintained within a set temperature range to continuously heat the portions of each first outlet pipe and each conveying pipe located inside the oven, thereby maintaining the temperature of the raw material gas flowing into the external liner within the set range. The rare earth solution storage tank has one second outlet pipe and one liquid conveying pipe extending into it. The liquid conveying pipe passes through the circulating water cooling device, allowing the circulating water cooling device to cool the liquid conveying pipe with circulating cooling water, thereby maintaining the temperature of the rare earth solution flowing into the external liner within the set range.

[0011] Preferably, the temperature inside the oven is maintained at 220℃-240℃.

[0012] Preferably, the temperature of the raw material gas evaporated in the raw material evaporator is maintained at 130℃-200℃.

[0013] Preferably, the temperature of the circulating oil in the casing is maintained at 230°C-240°C.

[0014] Preferably, the circulating water cooling device includes a water cooling pipe and a third end cap. One end of the water cooling pipe is sealed to the second end cap, and the other end is sealed to the third end cap. The infusion pipe passes through the third end cap and the second end cap in sequence and is sealed to the third end cap and the second end cap respectively. The water cooling pipe surrounds the sleeve and there is a gap between the water cooling pipe and the sleeve. The side wall of the water cooling pipe is provided with a first connector and a second connector so that a water chiller can be connected through a pipe to allow circulating cooling water to flow into the water cooling pipe to cool the infusion pipe.

[0015] Preferably, the portion of the infusion tube that protrudes from the second end cap is located below the portion of each feed tube that protrudes from the second end cap.

[0016] Preferably, the circulating water cooling device includes a water cooling pipe, the sleeve and the water cooling pipe both have a D-shaped cross-section, their flat portions are fitted together and they are connected together by welding, and the water cooling pipe is located below the sleeve.

[0017] Preferably, the circulating water cooling device includes a water cooling pipe, the cross-section of the sleeve and the water cooling pipe are both fan-shaped, and they are assembled together to form a complete circle. The arc of the arc portion of the sleeve is greater than the arc of the arc portion of the water cooling pipe, and the water cooling pipe is located below the sleeve.

[0018] Preferably, the oven has a notch, and the feed pipe is mounted on a power mechanism so that the feed end of the sleeve can extend into and out of the oven through the notch under the drive of the power mechanism, and after the feed pipe extends into the oven, the gap between the oven and the feed pipe is sealed by heat insulation cotton.

[0019] Preferably, the second end cap is always outside the oven so that the outlet end of the sleeve is connected to the external liner, thereby allowing the liquid delivery pipe and each feed pipe to extend into the liner, and thus allowing the rare earth solution flowing out of the liquid delivery pipe and the raw material gas flowing out of each feed pipe to be mixed in the liner.

[0020] In summary, compared with the prior art, the above-described technical solutions conceived by this invention can achieve the following beneficial effects:

[0021] 1) The present invention provides a gas-liquid phase composite doping device for preparing rare earth-doped optical fibers. The feeding pipe for conveying gas-phase doping raw materials and the liquid feeding pipe for conveying liquid-phase doping raw materials share the same end cap connected to the liner. However, there is an independent temperature control channel formed by oil bath and water cooling between the feeding pipe and the liquid feeding pipe, so as to maintain the gas-phase doping raw materials and the liquid-phase doping raw materials within their respective suitable temperature ranges, reduce their interaction, and realize the composite doping process of simultaneous gas-phase and liquid phase doping or alternating gas-phase and liquid phase doping on the same lathe.

[0022] 2) In a gas-liquid phase composite doping device for preparing rare-earth-doped optical fibers, the present invention uses a gas-phase method to output the raw material gas in the feed pipe to the external liner for doping. The process gas enters the oven from the outside through the first outlet pipe, is heated in the oven, and then flows downward into the relatively low-temperature raw material evaporation zone outside the oven. After carrying the evaporated raw material gas, the feed pipe enters the oven again from the top. The raw material gas heated in the oven is finally transported into the reaction zone of the external liner through the feed pipe. The present invention uses an oven to heat the raw material gas entering the feed pipe from the raw material gas evaporation tank. The feed pipe can also be kept warm by using oil in the sleeve. Heating and heat preservation can effectively reduce the condensation and solidification of rare earth chelate vapor in the feed pipe, thereby improving the uniformity of rare earth chelate ion doping.

[0023] 2) In a gas-liquid phase composite doping device for preparing rare earth-doped optical fibers according to the present invention, when the rare earth chelate solution in the delivery pipe is output to the external liner tube for doping using the solution method, the process gas enters the rare earth solution storage tank through the second gas outlet pipe and then forces the rare earth chelate solution out of the rare earth solution storage tank. The solution is then transported through the delivery pipe into the feed pipe and finally reaches the reaction area inside the external glass liner tube. The rare earth chelate solution in the delivery pipe is kept cold by water cooling through a circulating water cooling device to prevent it from being heated and vaporized by the hot rare earth chelate vapor, which would affect the doping.

[0024] 3) The gas delivery and liquid delivery of the present invention are independent of each other and can be relatively independently controlled in temperature. The gas phase doping raw material gas is heated and kept warm in an oven and in an oil bath, while the liquid phase doping is kept cold by cooling water to prevent mutual influence between the gas phase and the liquid phase. The doping of raw materials on the inner wall of the liner can be achieved on the same lathe. Attached Figure Description

[0025] Figure 1 This is a schematic diagram illustrating the principle of the present invention;

[0026] Figure 2 This is a front view of the multi-channel conveying device of the present invention, which connects the infusion pipe and three conveying pipes;

[0027] Figure 3 This is a side view of the multi-channel conveying device of the present invention, which connects the infusion pipe and three conveying pipes. Detailed Implementation

[0028] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention. Furthermore, the technical features involved in the various embodiments of this invention described below can be combined with each other as long as they do not conflict with each other.

[0029] Reference Figures 1-3 A gas-liquid phase composite doping device for preparing rare-earth-doped optical fibers includes a chelate delivery pipe. The chelate delivery pipe comprises a sleeve 1 and multiple delivery pipes 2. A first end cap 3 and a second end cap 4 are respectively installed at the inlet and outlet ends of the sleeve 1. Each delivery pipe 2 passes through the first end cap 3 and the second end cap 4, so that the circulating oil inside the sleeve 1 provides an oil bath to each delivery pipe 2. An inlet pipe and an outlet pipe are connected to the sleeve 1, and the delivery pipes 2 inside the sleeve 1 are uniformly heated by a heated liquid medium. An oil inlet pipe 13 and an oil outlet pipe 14 are connected to a hot oil circulator. For the specific structure of the chelate delivery pipe, please refer to the prior patent with authorization announcement number CN 113431963 B, entitled "A Chelate Delivery Pipe," which will not be elaborated here. The delivery pipes 2 transport the raw material gas.

[0030] The gas-liquid phase composite doping equipment also includes a process gas container, an oven 5, a rare earth solution storage tank 6, a circulating water cooling device, and a raw material gas evaporator 7.

[0031] The process gas container, rare earth solution storage tank 6, and each raw material gas evaporator 7 are all located outside the oven 5. Multiple first gas outlet pipes 8 and one second gas outlet pipe 9 are connected to the process gas container. Each raw material gas evaporator 7 has one first gas outlet pipe 8 and one conveying pipe 2 extending into it. A portion of each first gas outlet pipe 8 and a portion of each conveying pipe 2 are located inside the oven 5. The temperature inside the oven 5 is maintained within a set temperature range to continuously heat the portions of each first gas outlet pipe 8 and each conveying pipe 2 located inside the oven 5, thereby maintaining the temperature of the raw material gas flowing into the external liner of each conveying pipe 2 within the set temperature range. A second gas outlet pipe 9 and a liquid delivery pipe 10 extend into the rare earth solution storage tank 6. The liquid delivery pipe 10 passes through the circulating water cooling device, allowing the circulating water cooling device to cool the liquid delivery pipe 10 with circulating cooling water, thereby maintaining the temperature of the rare earth solution flowing into the external liner of the liquid delivery pipe 10 within the set temperature range. The cooling water can be room temperature water. Since the process gas container stores compressed process gas, if the process gas exits the container and enters the raw material gas evaporator 7, it can pressurize the evaporated raw material gas in the evaporator 7 into the feed pipe 2, allowing the raw material gas to be fed into the external liner for doping. If the process gas enters the rare earth solution storage tank 6, it can pressurize the rare earth solution in the storage tank 6 into the liquid delivery pipe 10, allowing the rare earth solution to be fed into the external liner for doping. The rare earth solution storage tank 6 is equipped with a level gauge to control the amount of rare earth solution used. The process gas can be an inert gas or nitrogen, which will not affect the doping of the raw material gas.

[0032] The process gas container may consist of only one process gas storage tank, storing compressed process gas used to expel raw material gas and rare earth solution from the raw material gas evaporator 7 and rare earth solution storage tank 6, respectively. Each first outlet pipe 8 and each second outlet pipe 9 are connected to the tank body. Alternatively, the process gas container may contain multiple process gas storage tanks, with each first outlet pipe 8 connected to one of the storage tanks, or multiple first outlet pipes 8 connected to one storage tank, while the second outlet pipe 9 is connected to one of the storage tanks. This allows for convenient placement of the process gas storage tanks.

[0033] The heating temperature inside the oven 5 and the oil bath temperature are both to ensure that the raw material gas in each conveying pipe 2 does not condense inside the conveying pipe 2, maintaining the gas phase to enter the external liner for doping. The circulating water cooling device ensures that the rare earth solution conveyed in the liquid conveying pipe 10 maintains a low temperature, preventing vaporization and maintaining the liquid phase to enter the external liner for doping.

[0034] If both gaseous raw material gas and liquid rare earth solution are simultaneously transported into the liner for doping via a pipeline, the temperature difference between the gas and liquid phases can cause some of the gaseous phase to condense and solidify on the pipeline before entering the liner, while some of the liquid phase will vaporize on the pipeline. This reduces the amount of rare earth elements entering the liner, resulting in material waste and optical fiber composition deviation, making it impossible to guarantee that the actual manufactured optical fiber meets the designed optical fiber composition requirements. This invention uses oil baths and water cooling to maintain the operating temperatures of the gaseous and liquid doping raw materials, making simultaneous gaseous and liquid doping possible. This eliminates the optical fiber composition design limitations caused by the inability to perform gaseous and liquid doping simultaneously, ensuring that the manufactured optical fiber composition is consistent with the designed optical fiber composition.

[0035] Furthermore, the temperature inside the oven 5 is maintained at 220℃-240℃ to fully heat each of the first exhaust pipes 8 and each conveying pipe 2, ensuring that their portions inside the oven 5 are kept at a high temperature. Heating the first exhaust pipes 8 allows the process gas to enter the raw material gas evaporator 7 and preheat the evaporated raw material gas. Then, the oven 5 and oil bath can insulate the raw material gas inside the conveying pipes 2, preventing condensation due to excessively low temperatures and carbonization due to excessively high temperatures on the inner walls of the conveying pipes 2.

[0036] Furthermore, the temperature of the raw material gas evaporated in the raw material evaporator is maintained at 130℃-200℃, so that the evaporated raw material gas can be kept at a relatively high temperature. After being heated by the oven 5, the process gas entering the raw material evaporator undergoes heat transfer with the raw material gas, and the temperature of the raw material gas entering the feed pipe 2 can also be further increased under the heating of the oven 5.

[0037] Furthermore, the temperature of the circulating oil in the sleeve 1 is maintained at 230℃-240℃, which can heat and insulate the conveying pipe 2, so that the raw material gas in the conveying pipe 2 is kept at a relatively high temperature and will not condense in the conveying pipe 2.

[0038] As a preferred embodiment, the circulating water cooling device includes a water-cooling pipe 11 and a third end cap 12. One end of the water-cooling pipe 11 is sealed to the second end cap 4, and the other end is sealed to the third end cap 12. The infusion pipe 10 passes sequentially through the third end cap 12 and the second end cap 4 and is sealed to both end caps 12 and 4 respectively. The water-cooling pipe 11 surrounds the sleeve 1 and has a gap between it and the sleeve 1. A first connector 17 and a second connector 17 are provided on the side wall of the water-cooling pipe 11 so that circulating cooling water can be introduced into the water-cooling pipe 11 to cool the infusion pipe 10 through a pipe connected to a water chiller. This structure, where the water-cooling pipe 11 is fixed by the third end cap 12 and the second end cap 4, and the water-cooling pipe 11 surrounds the sleeve 1, makes the circulating water cooling device easy to assemble. Preferably, the water-cooling pipe 11 is welded to the second end cap 4 and the third end cap 12.

[0039] Furthermore, the portion of the infusion tube 10 that extends from the second end cap 4 is located below the portion of each feed tube 2 that extends from the second end cap 4. This is because the hot gaseous raw material gas will flow upward. Therefore, the solution output by the infusion tube 10 is less affected by the temperature of the raw material gas and is less likely to be heated and vaporized, thus affecting the doping effect.

[0040] As another preferred embodiment, the circulating water cooling device includes a water-cooling pipe 11. Both the sleeve 1 and the water-cooling pipe 11 have D-shaped cross-sections, their flat portions are fitted together and connected by welding, with the water-cooling pipe 11 located below the sleeve 1. Alternatively, the circulating water cooling device includes a water-cooling pipe 11, both the sleeve 1 and the water-cooling pipe 11 have fan-shaped cross-sections, and they are assembled together to form a complete circle. The arc of the arc portion of the sleeve 1 is greater than the arc of the arc portion of the water-cooling pipe 11, with the water-cooling pipe 11 located below the sleeve 1. Both embodiments allow for the separation of the sleeve 1 and the water-cooling pipe 11. The sleeve 1 contains an oil bath, while the water-cooling pipe 11 contains cooling water for water cooling, creating independent temperature zones. This minimizes heat transfer between the sleeve 1 and the water-cooling pipe 11, reducing mutual interference.

[0041] The chelate conveying pipe and the water-cooling pipe 11 of the circulating water cooling device together form a multi-channel conveying device 16.

[0042] Furthermore, the oven 5 has a notch, and the feed pipe 2 is mounted on a power mechanism so that the feed end of the sleeve 1 can extend into and exit the oven 5 through the notch under the drive of the power mechanism. After the feed pipe 2 extends into the oven 5, the gap between the oven 5 and the feed pipe 2 is sealed with heat insulation cotton. The equipment adjusts the feed pipe 2 through the power device at the bottom to reach the appropriate position in different working states. The working states are divided into: preparation state, gas phase state, and liquid phase state. In the preparation state, the feed pipe 2 does not enter the oven 5, so the oven 5 does not need to work, thus saving energy.

[0043] Furthermore, the second end cap 4 is always outside the oven 5 so that the outlet end of the sleeve 1 is connected to the external liner, thereby allowing the liquid delivery pipe 10 and each feed pipe 2 to extend into the liner, and thus allowing the rare earth solution flowing out of the liquid delivery pipe 10 and the raw material gas flowing out of each feed pipe 2 to be mixed inside the liner. The liner can be mounted on a lathe, and the lathe drives the rotation to perform doping on the inner wall of the liner.

[0044] The gas-liquid phase composite doping device for preparing rare-earth-doped optical fibers of the present invention involves evaporating rare-earth chelate elements at low evaporation temperatures into raw material gas in a raw material evaporator, which is then transported to an external liner via a feed pipe 2. Meanwhile, rare-earth chelate ions, which cannot become gaseous at low temperatures, are transported to the external liner via a liquid feed pipe 10. The raw material gas transported in the gas phase improves the uniformity of rare-earth ion doping, while the rare-earth chelate ions transported in the liquid phase ensure the doping concentration of rare-earth ions.

[0045] Each region of the present invention is relatively independent and can be controlled at a relatively independent temperature. The outer shell of the oven 5 is made of heat-insulating material. A receiving box 15 connected to the oven 5 can be made of heat-insulating material outside the oven 5. The temperature inside the receiving box 15 is room temperature. Pipe channels and valves are retained in the heat-insulating material. Electrical control components can be placed inside the receiving box 15 to ensure that process gas and raw material gas can flow directly in each region.

[0046] When using the gas-phase doping method, the process gas enters the oven 5 from the process gas container outside the oven 5 through the first outlet pipe 8. After being heated, it flows downward into the raw material evaporation zone where the ambient temperature is relatively low. After carrying the raw material vapor, it flows upward again into the oven 5, and finally enters the reaction zone of the glass liner through the feed pipe 2. This structure can effectively reduce the condensation of rare earth vapor in the feed pipe 2, thereby improving the uniformity of rare earth ion doping.

[0047] When using solution doping, the process gas enters the oven 5 from the process gas container outside the oven 5 through the second outlet pipe 9, and then enters the rare earth solution storage tank 6, where the solution is forced out. It then enters the low-temperature zone for water cooling via the delivery pipe 10. The delivery pipe 10 is immersed in circulating cooling water to ensure its ambient temperature is normal, allowing the rare earth solution to ultimately reach the liner in liquid phase.

[0048] This invention can ensure that gas-phase doping and solution doping can be carried out simultaneously, by introducing the raw material gas and rare earth solution into the liner at the same time, without affecting the rotation of the liner driven by the lathe.

[0049] Those skilled in the art will readily understand that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included within the scope of protection of the present invention.

Claims

1. A gas-liquid phase composite doping device for preparing rare-earth-doped optical fibers, comprising a chelate feeding tube, the chelate feeding tube comprising a sleeve and multiple feeding tubes, wherein a first end cap and a second end cap are respectively installed at the inlet and outlet ends of the sleeve, and each feeding tube passes through the first end cap and the second end cap respectively, so that the circulating oil inside the sleeve provides an oil bath to each feeding tube, characterized in that: The gas-liquid phase composite doping equipment also includes a process gas container, an oven, a rare earth solution storage tank, a circulating water cooling device, and a raw material gas evaporator, wherein: The process gas container, rare earth solution storage tank, and each raw material gas evaporator are all located outside the oven. The process gas container is connected to multiple first outlet pipes and one second outlet pipe. Each raw material gas evaporator has one first outlet pipe and one conveying pipe extending into it. A portion of each first outlet pipe and a portion of each conveying pipe are located inside the oven. The temperature inside the oven is maintained within a set temperature range to continuously heat the portions of each first outlet pipe and each conveying pipe located inside the oven, thereby maintaining the temperature of the raw material gas flowing into the external liner within the set range. The rare earth solution storage tank has one second outlet pipe and one liquid conveying pipe extending into it. The liquid conveying pipe passes through the circulating water cooling device, allowing the circulating water cooling device to cool the liquid conveying pipe with circulating cooling water, thereby maintaining the temperature of the rare earth solution flowing into the external liner within the set range.

2. The gas-liquid phase composite doping device for preparing rare-earth-doped optical fibers according to claim 1, characterized in that, The temperature inside the oven is maintained at 220℃-240℃.

3. The gas-liquid phase composite doping device for preparing rare-earth-doped optical fibers according to claim 1, characterized in that, The temperature of the raw material gas evaporated in the raw material evaporator is maintained at 130℃-200℃.

4. The gas-liquid phase composite doping device for preparing rare-earth-doped optical fibers according to claim 1, characterized in that, The temperature of the circulating oil inside the casing is maintained at 230℃-240℃.

5. The gas-liquid phase composite doping device for preparing rare-earth-doped optical fibers according to claim 1, characterized in that, The circulating water cooling device includes a water cooling pipe and a third end cap. One end of the water cooling pipe is sealed to the second end cap, and the other end is sealed to the third end cap. The infusion pipe passes through the third end cap and the second end cap in sequence and is sealed to the third end cap and the second end cap respectively. The water cooling pipe surrounds the sleeve and there is a gap between the water cooling pipe and the sleeve. The side wall of the water cooling pipe is provided with a first connector and a second connector so that a water chiller can be connected through a pipe to allow circulating cooling water to flow into the water cooling pipe to cool the infusion pipe.

6. The gas-liquid phase composite doping device for preparing rare-earth-doped optical fibers according to claim 1, characterized in that, The portion of the infusion tube that protrudes from the second end cap is located below the portion of each feed tube that protrudes from the second end cap.

7. The gas-liquid phase composite doping device for preparing rare-earth-doped optical fibers according to claim 1, characterized in that, The circulating water cooling device includes a water cooling pipe. Both the sleeve and the water cooling pipe have a D-shaped cross-section. Their flat portions are fitted together and they are connected by welding. The water cooling pipe is located below the sleeve.

8. The gas-liquid phase composite doping device for preparing rare-earth-doped optical fibers according to claim 1, characterized in that, The circulating water cooling device includes a water cooling pipe. Both the sleeve and the water cooling pipe have a fan-shaped cross-section and are assembled together to form a complete circle. The arc of the arc portion of the sleeve is greater than the arc of the arc portion of the water cooling pipe, and the water cooling pipe is located below the sleeve.

9. The gas-liquid phase composite doping device for preparing rare-earth-doped optical fibers according to claim 1, characterized in that, The oven has a notch, and the feed pipe is mounted on a power mechanism so that the feed end of the sleeve can extend into and out of the oven through the notch under the drive of the power mechanism. After the feed pipe extends into the oven, the gap between the oven and the feed pipe is sealed with heat insulation cotton.

10. The gas-liquid phase composite doping device for preparing rare-earth-doped optical fibers according to claim 1, characterized in that, The second end cap is always outside the oven so that the outlet end of the sleeve can be connected to the external liner, thereby allowing the liquid delivery pipe and each feed pipe to extend into the liner, and thus allowing the rare earth solution flowing out of the liquid delivery pipe and the raw material gas flowing out of each feed pipe to be mixed in the liner.

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