Plasma external deposition equipment and method for manufacturing optical fiber preform

Abstract

The invention discloses plasma external deposition equipment and a plasma external deposition method for manufacturing an optical fiber preform. The equipment comprises a plasma source; the electromagnetic coil is used for generating an induction high-frequency electromagnetic field; the blowtorch is nested in the electromagnetic coil, the blowtorch comprises five layers of structures, and each layer of structure is connected with a gas channel for introducing different raw materials; the lathe is used for fixing the optical fiber preform and controlling rotation of the optical fiber preform and movement of the blowtorch; and the holding furnaces are arranged at two ends of the optical fiber preform. According to the invention, an out-of-tube deposition method is adopted, and gas flow rates of five gas channels are designed and adjusted, so that ionized gas is ionized in a high-frequency electromagnetic field at the minimum flow rate, plasma flame and a high-temperature area are generated, and a silicon raw material and oxygen rapidly pass through the plasma flame and then are rapidly sprayed to the surface of the optical fiber preform; the fluorine raw material is introduced through the edge position of the plasma flame with the lowest relative temperature, volatilization of the fluorine raw material is reduced, the utilization rate of the fluorine raw material can be increased to 60%, and the utilization rate of the silicon raw material can be increased to 70%.

Description

Technical Field

[0001] The present invention belongs to the technical field of optical communication, and in particular relates to a plasma external deposition device and method for manufacturing an optical fiber preform. Background Art

[0002] With the development of the digital economy, emerging industries such as artificial intelligence and optical information processing have developed rapidly, and the demand for the laser industry chain has increased accordingly. Special optical fiber plays an indispensable role as an important transmission medium in laser devices. Since fluorine doping can increase the radiation resistance of optical fiber and there is no obvious additional loss in the range from the communication band to the extreme ultraviolet band, it is often used as the cladding material of special optical fiber. However, the fluorine doping depth required for special optical fiber is relatively large, and the numerical aperture (NA) of the optical fiber needs to be ≥0.22, while the fluorine doping concentration prepared by the common VAD, OVD, and MCVD processes can only reach 2%, and the NA value is <0.17, which cannot meet the demand for fluorine-doped materials required for special optical fibers. Since the plasma source in the PCVD process can activate high-temperature gas into active ions, breaking its thermodynamic equilibrium, and the raw materials are directly vitrified during the deposition process, the diffusion of fluorine raw materials can be reduced, thereby making the fluorine doping depth deeper and more suitable for the production of deep fluorine-doped materials.

[0003] The PCVD process is divided into an in-tube deposition method and an out-tube deposition method. The common in-tube deposition method is affected by the size of the liner tube and cannot prepare large-sized optical fiber preforms. In addition, the in-tube deposition method is affected by the temperature distribution and feed position in the liner tube, which can easily lead to product size fluctuations. The out-of-tube deposition method directly deposits on the surface of the target rod, and can prepare large-sized optical fiber preforms with uniform outer diameters. For example, the Chinese invention patents with publication numbers CN114436521A and CN117185646A both mention the use of this method to prepare large-sized deeply fluorine-doped optical fiber preforms. The product NA values ​​are all >0.17, and the product outer diameters are all >40mm. However, since the temperature of the plasma flame is much higher than the boiling point of the fluorine raw material, and the above method is an out-of-tube deposition method, a large amount of fluorine raw material will volatilize. A three-layer structure blowtorch is used, and the fluorine raw material is introduced through the center layer or the second layer of the blowtorch, which is located just in the high-temperature zone of the flame. The fluorine raw material volatilizes in large quantities, and the fluorine utilization rate is low. Summary of the invention

[0004] In order to solve the technical problems existing in the prior art, the object of the present invention is to provide a plasma external deposition device and method for manufacturing an optical fiber preform.

[0005] In order to achieve the above purpose and the above technical effect, the technical solution adopted by the present invention is:

[0006] A plasma external deposition device for manufacturing an optical fiber preform, comprising:

[0007] a plasma source for generating a high-frequency electromagnetic field;

[0008] An electromagnetic coil, wherein the plasma source is connected to the electromagnetic coil and is used to generate an induced high-frequency electromagnetic field;

[0009] A blowtorch, the blowtorch is nested inside the electromagnetic coil, and the blowtorch comprises a five-layer structure, each layer of the structure is connected to a gas channel, and is used to pass different raw materials;

[0010] A lathe, used to fix the optical fiber preform and control the rotation of the optical fiber preform and the movement of the blowtorch;

[0011] The heat preservation furnace is arranged at both ends of the optical fiber preform rod and is used to improve the axial temperature uniformity of the optical fiber preform rod during the deposition process.

[0012] Furthermore, the plasma source is a radio frequency plasma source with an output power of 30 to 100 kW, which is used to generate a high-frequency electromagnetic field. The electromagnetic coil can generate an induced high-frequency current under the action of the high-frequency electromagnetic field, thereby generating an induced high-frequency electromagnetic field.

[0013] Furthermore, there are five gas channels, namely gas channel T1, gas channel T2, gas channel T3, gas channel T4, and gas channel T5. The height of gas channel T1 is 20 to 30 mm higher than that of gas channel T2. The heights of gas channel T2, gas channel T3, gas channel T4, and gas channel T5 decrease successively. SiCl4 is introduced into the blowtorch head via gas channel T1, oxygen is introduced into the blowtorch head via gas channel T2, and ionized gas is introduced into the blowtorch head via gas channel T3. The ionized gas can be ionized in a high-frequency electromagnetic field. The fluorine raw material is introduced into the blowtorch head from the edge of the plasma flame via gas channel T4, and the cooling gas is introduced into the blowtorch head via gas channel T5.

[0014] Furthermore, the gas flow rate of SiCl4 introduced into the gas channel T1 is the largest, which is 20-25 m / s, the gas flow rate of oxygen introduced into the gas channel T2 is 15-20 m / s, the gas flow rate of ionized gas introduced into the gas channel T3 is 1-3 m / s, the gas flow rate of fluorine raw material introduced into the gas channel T4 is 5-10 m / s, and the gas flow rate of cooling gas introduced into the gas channel T5 is 10-15 m / s.

[0015] Furthermore, the ionized gas is any one or a combination of argon, oxygen, and nitrogen, the fluorine raw material is any one or a combination of CF4, SiF4, C2F6, and SF6, and the cooling gas is any one or a combination of argon, oxygen, and nitrogen.

[0016] Furthermore, the lathe is provided with a radio frequency output cabinet, an upper clamping assembly, a heat preservation furnace, a blowtorch, an optical fiber preform and a lower clamping assembly; the radio frequency output cabinet is connected to a plasma source; the upper clamping assembly is used to clamp the upper portion of the optical fiber preform; the lower clamping assembly is used to clamp the lower portion of the optical fiber preform; optical fiber preforms of different lengths can be matched by adjusting the distance between the upper clamping assembly and the lower clamping assembly; the upper and lower ends of the optical fiber preform are respectively provided with heat preservation furnaces; the blowtorch can reciprocate along the axis of the optical fiber preform.

[0017] The present invention also discloses a plasma external deposition method for manufacturing an optical fiber preform, which uses the plasma external deposition device for manufacturing an optical fiber preform as described above to perform deposition, and comprises the following steps:

[0018] 100: Adjust the height positions of the upper clamping assembly and the lower clamping assembly, adjust the height of the lower clamping assembly to a position convenient for placing the preform, and adjust the height of the upper clamping assembly according to the length of the optical fiber preform;

[0019] 200: vertically mounting the optical fiber preform on a lathe and fixing it with an upper clamping assembly and a lower clamping assembly;

[0020] 300: adjusting the height position of the blowtorch so that the blowtorch is located at the starting deposition point of the optical fiber preform;

[0021] 400: Control the optical fiber preform to rotate at a certain rotation rate R; introduce ionized gas through the gas channel T3; start the plasma source to ionize the ionized gas to generate a plasma flame, and then introduce cooling gas through the gas channel T5;

[0022] 500: Control the torch to move vertically repeatedly at a certain speed V to preheat and polish the surface of the optical fiber preform rod until the surface temperature of the optical fiber preform rod reaches 1500±50°C before entering step 600. In this process, the insulation furnace moves with the torch. When the torch moves to the starting point of the lower part of the optical fiber preform rod, the upper insulation furnace is exactly located at the end position of the upper part of the optical fiber preform rod. On the contrary, when the torch moves to the end position of the upper part of the optical fiber preform rod, the lower insulation furnace is exactly located at the starting position of the lower part of the optical fiber preform rod. At the same time, the temperature T of the insulation furnace gradually decreases with the increase of the diameter of the optical fiber preform rod;

[0023] 600: After polishing, the torch returns to the starting position at the bottom of the optical fiber preform, SiCl4 is introduced through the gas channel T1, oxygen is introduced through the gas channel T2, and SF6 is introduced through the gas channel T4, and then the torch is controlled to move vertically repeatedly for deposition;

[0024] 700: When the outer diameter D of the optical fiber preform reaches the expected requirement, the deposition is completed, and the supply of raw materials in the gas channels T1, T2, and T4 is stopped first, and then the plasma source is turned off, and then the supply of ionized gas and cooling gas in the gas channels T3 and T5 is stopped.

[0025] Furthermore, the optical fiber preform is rotated at a rotation rate R of 10 to 60 rpm, and the blowtorch is repeatedly moved vertically at a rate V of 200 to 800 mm / min.

[0026] Compared with the prior art, the present invention has the following beneficial effects:

[0027] 1) According to the temperature distribution characteristics of the plasma flame and the gas usage requirements in the plasma external deposition process, the present invention optimizes the blowtorch into a 5-layer structure, and the height of the gas channel T1 is higher than that of T2. The SiCl4 raw material is introduced through the gas channel T1, and the O2 raw material is introduced through the gas channel T2, which prevents the two raw materials from mixing and depositing on the inner wall of the blowtorch before passing through the ionization high temperature zone. At the same time, the fluorine raw material is introduced through the gas channel T4. The gas in this channel is located at the edge of the plasma flame and has the lowest relative temperature, which can effectively reduce the volatilization of the fluorine raw material;

[0028] 2) The gas in each channel of the blowtorch uses a different flow rate, and the flow rate of each layer differs by 3 to 15 m / s to ensure that the plasma flame is a laminar flame. The raw materials SiCl4 and oxygen pass through the plasma flame at a high speed and are quickly sprayed onto the surface of the optical fiber preform rod, which improves the utilization rate of the raw materials. Specifically, the SiCl4 raw material quickly passes through the high-temperature area of ​​the central layer at a rate of 20 to 25 m / s, and the fluorine raw material is introduced at a slower rate through the edge of the plasma flame with the lowest relative temperature, which reduces the volatilization of the raw materials, and can increase the utilization rate of the fluorine raw material to 60%, and the utilization rate of the silicon raw material to 70%;

[0029] 3) The two ends of the optical fiber preform are insulated by an electric heating insulation furnace. Because it is easy to control and has a fast temperature response, the temperature of the insulation furnace can be adjusted during the deposition process to compensate for the temperature change of the rod body caused by the change of the blowtorch position and the change of the optical fiber preform diameter, avoiding the situation where the temperature at the deposition point is too high and the temperature at the position far away from the deposition point is too low during the deposition process. The axial temperature range of the preform can be controlled within 20°C, which improves the diameter uniformity and doping uniformity of the preform;

[0030] 4) A thermometer is installed near the blowtorch and the holding furnace to monitor the temperature of the deposition point on the surface of the optical fiber preform and the temperature inside the holding furnace, so as to facilitate the adjustment of process parameters such as the blowtorch speed, plasma source power, and holding furnace temperature during the deposition process. By stably controlling the temperature of the deposition point within the range of 1500-1800°C, the volatilization of the raw materials is reduced while ensuring direct vitrification of the raw materials, further improving the utilization rate of the raw materials;

[0031] 5) Add multiple groups of diameter gauges distributed along the axial direction of the optical fiber preform to monitor the real-time diameter change of the optical fiber preform during the deposition process. By correlating the real-time diameter measurement results with the target diameter, gas flow rate, and torch speed, the process parameters can be automatically adjusted when the actual diameter deviates greatly from the target diameter, so as to control the diameter range of the whole rod within 0.5 mm;

[0032] 6) The lathe adopts a vertical structure, which saves equipment floor space. The axis of the optical fiber preform after being fixed is parallel to the lathe, and the axis of the blowtorch is perpendicular to the axis of the optical fiber preform, so that the optical fiber preform is always in a vertical state during the deposition process, and the optical fiber preform product is not easy to bend, which can ensure that the concentricity of the optical fiber preform product is ≤0.3mm. At the same time, the raw materials in the deposition process are not easy to fall back to the blowtorch, which increases the service life of the blowtorch;

[0033] 7) Since the RF power supply is large in size and weight and is not easy to move with the blowtorch, the present invention achieves the fixation of the optical fiber preform rod and the movement of the blowtorch by splitting the RF power supply cabinet and the capacitor cabinet, thereby reducing the height of the equipment and the maximum effective length of the product is >1.5m. BRIEF DESCRIPTION OF THE DRAWINGS

[0034] Figure 1 It is a structural schematic diagram of the lathe of the present invention;

[0035] Figure 2 It is a schematic diagram of the structure of the blowtorch of the present invention;

[0036] Figure 3 It is a flow chart of the present invention. DETAILED DESCRIPTION

[0037] The present invention is described in detail below so that the advantages and features of the present invention can be more easily understood by those skilled in the art, thereby making a clearer and more definite definition of the protection scope of the present invention.

[0038] A brief summary of one or more aspects is given below to provide a basic understanding of these aspects. This summary is not an exhaustive overview of all conceived aspects, and is neither intended to identify the key or critical elements of all aspects nor to define the scope of any or all aspects. Its only purpose is to give some concepts of one or more aspects in a simplified form as a prelude to a more detailed description that will be given later.

[0039] like Figure 1-3 As shown, a plasma external deposition device for manufacturing an optical fiber preform rod includes a plasma source, an electromagnetic coil, a blowtorch, a lathe, and a holding furnace.

[0040] The plasma source uses a radio frequency plasma source with an output power of 100KW, which converts industrial frequency current into high-frequency current to generate a high-frequency electromagnetic field.

[0041] The electromagnetic coil 7, the plasma source is connected to the electromagnetic coil 7 through a cable and a rectifier circuit, and the electromagnetic coil 7 generates an induced high-frequency current under the action of the high-frequency electromagnetic field, and then generates an induced high-frequency electromagnetic field.

[0042] The blowtorch is nested inside the electromagnetic coil 7 and is made of quartz material to avoid the generation of metal impurities during the ionization process. The blowtorch includes a five-layer structure, and the bottom of each layer of the structure is connected to a gas channel. There are five gas channels in total, which are respectively recorded as gas channel T1, gas channel T2, gas channel T3, gas channel T4, and gas channel T5. Silicon raw material (SiCl4) is introduced into the blowtorch head through gas channel T1, oxygen is introduced into the blowtorch head through gas channel T2, and ionized gas (such as any one or a combination of argon, oxygen, and nitrogen) is introduced into the blowtorch head through gas channel T3. This part of the gas is ionized after passing through a high-frequency electromagnetic field, thereby generating a high-temperature area. Fluorine raw material (such as any one or a combination of CF4, SiF4, C2F6, and SF6) is introduced from the plasma through gas channel T4. The edge of the sub-flame is introduced into the burner head, and the fluorine raw material introduced is located at the edge of the plasma flame, with a relatively low temperature and less volatilization, so that more fluorine raw materials are doped into the optical fiber preform. The cooling gas (such as any one or combination of argon, oxygen, and nitrogen) is introduced into the burner head through the gas channel T5 to isolate the flame from the outer wall of the gas channel T5 to prevent damage to the quartz lamp of this layer, and pinch the plasma flame at the same time. The height of the gas channel T1 is 20 to 30 mm higher than that of the gas channel T2, which can effectively prevent the silicon oxygen raw materials from mixing and depositing on the inner wall of the burner before passing through the ionization high temperature zone. The heights of the gas channels T2, T3, T4, and T5 decrease in sequence. The flow rate of each layer of gas is different, and the flow rate between each layer differs by 3 to 15 m / s to ensure that the flame is a laminar flame.

[0043] In some embodiments, the gas flow rate of SiCl4 introduced into the gas channel T1 is the largest, which is 20-25 m / s, so as to facilitate the rapid spraying of the raw materials on the surface of the preform rod and improve the utilization rate of SiCl4. The gas flow rate of oxygen introduced into the gas channel T2 is 15-20 m / s, and the gas flow rate of ionized gas introduced into the gas channel T3 is 1-3 m / s, which can ensure the effective ionization of the ionized gas. Too high a flow rate will cause arc extinction or the gas cannot be completely ionized. The gas flow rate of fluorine raw materials introduced into the gas channel T4 is 5-10 m / s, and the gas flow rate of cooling gas introduced into the gas channel T5 is 10-15 m / s, which can avoid the cooling gas from being ionized and stabilize the flame shape.

[0044] The lathe is used to fix the optical fiber preform and control the rotation of the optical fiber preform and the movement of the blowtorch. The lathe is a vertical lathe, which can save equipment space and reduce the possibility of deposited particles falling back to the blowtorch, thereby increasing the service life of the blowtorch. At the same time, since the optical fiber preform is always in a vertical state during the deposition process, its concentricity can be guaranteed.

[0045] In some embodiments, a lathe is provided with a radio frequency output cabinet 1 (belonging to the radio frequency power supply part, and its function is to transmit the high-frequency current after voltage regulation and rectification to the electromagnetic coil, thereby generating a high-frequency electromagnetic field), an upper clamping assembly 2, a heat preservation furnace 3, a blowtorch 4, an optical fiber preform 5 and a lower clamping assembly 6. The radio frequency output cabinet 1 is connected to a plasma source. The upper clamping assembly 2 is used to clamp the upper part of the optical fiber preform 5, and the lower clamping assembly 6 is used to clamp the lower part of the optical fiber preform 5. Optical fiber preforms 5 of different lengths can be matched by adjusting the distance between the upper clamping assembly 2 and the lower clamping assembly 6. The upper and lower ends of the optical fiber preform 5 are respectively provided with a heat preservation furnace 3. The upper and lower ends of the optical fiber preform 5 are heated and insulated by electric heating, so as to improve the axial temperature uniformity of the optical fiber preform rod body during the deposition process, and avoid cracking of the rod body and uneven fluorine doping concentration caused by excessively high temperature at one end of the rod body and excessively low temperature at the other end during the deposition process. The blowtorch 4 can reciprocate along the axis of the optical fiber preform 5.

[0046] The radio frequency power supply is composed of a voltage regulating circuit, a rectifier circuit, a capacitor circuit and other parts. The conventional design is to integrate the voltage regulating circuit, the rectifier circuit, the capacitor circuit and the like together and make a radio frequency power supply cabinet, which is large in size and heavy. Therefore, the present invention separates the capacitor circuit part and forms a capacitor cabinet, which can move with the blowtorch 4, thereby reducing the moving load.

[0047] In some embodiments, the RF output cabinet 1, the insulation furnace 3, and the blowtorch 4 are all installed on a mobile base, which drives the RF output cabinet 1, the insulation furnace 3, and the blowtorch 4 to move up and down. When the length of the deposited product is the same, this movement method can shorten the moving stroke of the equipment by half relative to the movement of the rod body, thereby reducing the overall height of the equipment.

[0048] In some embodiments, a plurality of groups of diameter gauges are arranged along the axial direction of the optical fiber preform 5, and the diameter gauges, the upper clamping assembly 2, the holding furnace 3, the blowtorch 4 and the lower clamping assembly 6 are respectively connected to the controller. The diameter change of the optical fiber preform during the deposition process is monitored by the diameter gauge and the real-time diameter measurement result is uploaded to the controller. The controller compares and analyzes the real-time diameter measurement result with the target diameter, and adjusts the gas flow rate, the rotation rate R, the blowtorch movement speed V, and the holding furnace temperature T according to the analysis result to control the diameter range of the entire optical fiber preform within 0.5 mm.

[0049] In some embodiments, thermometers are respectively provided near the insulation furnace 3 and the blowtorch 4, and the thermometers are connected to the controller. The thermometers near the insulation furnace 3 and the blowtorch 4 respectively monitor the internal temperature of the insulation furnace and the temperature of the deposition point on the surface of the optical fiber preform 5 and upload them to the controller. During the deposition process, the controller adjusts the process parameters such as the blowtorch speed, plasma source power, and insulation furnace temperature. By stably controlling the temperature of the deposition point within the range of 1500 to 1800°C, the volatilization of the raw materials is reduced while ensuring direct vitrification of the raw materials, thereby further improving the utilization rate of the raw materials.

[0050] A plasma external deposition method for manufacturing an optical fiber preform comprises the following steps:

[0051] 100: Adjust the height positions of the upper clamping assembly 2 and the lower clamping assembly 6, adjust the height of the lower clamping assembly 6 to a position convenient for loading the rod, adjust the height of the upper clamping assembly 2 according to the length of the optical fiber preform rod 5 to be deposited, and the maximum clamping length between the upper clamping assembly 2 and the lower clamping assembly 6 is 2.5 m;

[0052] 200: Install the optical fiber preform 5 on a lathe and fix it with an upper clamping assembly 2 and a lower clamping assembly 6;

[0053] 300: adjusting the height of the blowtorch 4 so that the blowtorch 4 is located at the starting deposition point of the optical fiber preform 5;

[0054] 400: The optical fiber preform 5 is rotated at a rotation rate R of 10 to 60 rpm. Ionized gas (argon, oxygen) is introduced through the gas channel T3, with the argon flow rate being 20 to 50 SLM and the oxygen flow rate being 30 to 50 SLM. The plasma source is started to ionize the gas to generate a plasma flame, and then cooling gas oxygen is introduced through the gas channel T5, with the flow rate being 100 to 200 SLM;

[0055] 500: Start the moving base, and make the blowtorch 4 move up and down repeatedly at a speed V of 200 to 800 mm / min, and preheat and polish the surface of the optical fiber preform 5 until the surface temperature of the optical fiber preform 5 reaches 1500°C before entering the next step, so that the raw materials during deposition are more easily attached to the surface of the optical fiber preform 5, and the axial diameter and doping uniformity of the optical fiber preform 5 are improved. In this process, the insulation furnace 3 moves with the blowtorch 4. When the blowtorch 4 moves to the starting point at the lower part of the optical fiber preform 5, the insulation furnace 3 at the upper end of the optical fiber preform 5 is exactly located at the end position at the upper part of the optical fiber preform 5. On the contrary, when the blowtorch 4 moves to the end position at the upper part of the optical fiber preform 5, the insulation furnace 3 at the lower end of the optical fiber preform 5 is exactly located at the starting position at the lower part of the optical fiber preform 5. At the same time, the temperature T of the insulation furnace gradually decreases with the increase of the diameter of the optical fiber preform 5;

[0056] 600: After polishing, the blowtorch 4 returns to the starting position at the bottom of the optical fiber preform 5, and SiCl4 is introduced through the gas channel T1 with a flow rate of 4 to 15 SLM, oxygen is introduced through the gas channel T2 with a flow rate of 10 to 30 SLM, and SF6 is introduced through the gas channel T4 with a flow rate of 2 to 20 SLM. Then the blowtorch 4 starts to move up and down repeatedly for deposition. In this process, the rotation rate R of the optical fiber preform 5 is changed from small to large in the range of 10 to 60 rpm, and the moving speed V of the blowtorch 4 is changed from large to small in the range of 200 to 800 mm / min, so as to compensate for the temperature fluctuation caused by the change of the diameter of the preform, thereby ensuring the uniformity of the outer diameter of the preform; in the deposition process, the diameter of the optical fiber preform 5 is obtained by testing multiple groups of diameter gauges distributed along its axial direction, and the diameter gauge is used to monitor the real-time diameter change of the optical fiber preform during the deposition process and upload the real-time diameter measurement result to the controller, and the controller compares and analyzes the real-time diameter measurement result with the target diameter, and adjusts the gas flow rate, the rotation rate R, the blowtorch moving speed V, and the holding furnace temperature T according to the analysis result, so as to control the diameter range of the entire optical fiber preform within 0.5 mm;

[0057] 700: When the outer diameter D of the optical fiber preform 5 reaches the expected requirement, the deposition is completed. The outer diameter D can be adjusted according to the specific product requirements and can be within the range of 25 to 70 mm. When it is completed, the supply of raw materials in the gas channels T1, T2, and T4 is stopped first, and then the power of the plasma source is reduced to perform arc extinguishing operation. After the plasma flame is turned off, the plasma source is completely turned off. After 5 to 10 minutes, the supply of raw materials in the gas channels T3 and T5 is stopped.

[0058] Example 1

[0059] The initial diameter of the optical fiber preform 5 to be deposited is 25 mm, and the initial length is 1 m. After F-doping, the diameter becomes 37 mm, and the total length becomes 2 m.

[0060] First, the optical fiber preform 5 to be deposited with an initial length of 1m and an initial diameter of 25mm is mounted on a lathe, and the upper and lower ends of the optical fiber preform 5 are fixed with the upper clamping assembly 2 and the lower clamping assembly 6, and then the blowtorch 4 is lowered to the starting point of the lower end of the optical fiber preform 5 to be deposited. At this time, the insulation furnace 3 at the lower end is located below the starting point of the lower end of the optical fiber preform 5, and the insulation furnace at the upper end is just located at the starting point of the upper end of the optical fiber preform 5. Subsequently, the rotation function of the upper clamping assembly 2 and the lower clamping assembly 6 is turned on, so that the optical fiber preform 5 rotates at a rotation rate R of 10rpm, 40SLM of argon gas is introduced into the blowtorch through the gas channel T3, and the plasma source is started to start the arc. After about 10s, the plasma arc reaches a stable state, and at this time, 150SLM of oxygen is introduced into the blowtorch through the gas channel T5, and the argon gas in the gas channel T3 is replaced with oxygen. Start the mobile base, and move the blowtorch 4 up and down repeatedly at a speed V of 200mm / min. During this process, the temperature of the insulation furnace is maintained at 1200℃ until the overall surface temperature of the optical fiber preform 5 reaches 1500℃ (temperature monitoring is performed by a thermometer fixed on the mobile base), and then the blowtorch 4 returns to the lower starting point. 8SLM of SiCl4 is introduced into the gas channel T1, 15SLM of O2 is introduced into the gas channel T2, and 3SLM of SF6 is introduced into the gas channel T4. The temperature of the insulation furnace is maintained at 1150℃, and the rotation rate R is still 10rpm. The blowtorch 4 moves up and down repeatedly at a speed of 780mm / min to evenly spray the raw materials on the surface of the optical fiber preform 5. During the deposition process, the diameter of the optical fiber preform 5 is obtained by testing multiple groups of diameter gauges distributed along its axial direction. The diameter gauge is used to monitor the real-time diameter change of the optical fiber preform during the deposition process and upload the real-time diameter measurement results to the controller. The controller compares and analyzes the real-time diameter measurement results with the target diameter. , and according to the analysis results, the gas flow rate, rotation rate R, torch speed V, and holding furnace temperature T are adjusted to make the rotation rate R, speed V, and holding furnace temperature T change with the increase of the diameter of the optical fiber preform 5, as shown in Table 1, until the diameter of the optical fiber preform 5 reaches the set diameter of 37 mm, then the torch 4 returns to the lower starting point, the holding furnace 3 stops heating, the T1, T2, and T4 gas channels stop supplying raw materials, and the gas flow rate drops to zero, then the plasma source power is reduced, and the plasma source is turned off after the plasma flame is completely extinguished. After 5 minutes, the gas supply of gas channels T3 and T5 is turned off, and the final product NA value can reach 0.24, and the fluorine raw material utilization rate is 60%.

[0061] Table 1

[0062] Outer diameter D(mm) Speed ​​R(rpm) Blowtorch speed V(mm / min) Holding furnace temperature T(℃) 25 10 780 1150 29 15 710 1100 32 17 660 1080 35 19 630 1050 37 22 600 1030

[0063] Example 2

[0064] Compared with Example 1, the size of the optical fiber preform produced in this example is improved. Its initial diameter is 30 mm, and the diameter of the product after doping with F is 50 mm. The total length of the product is still 2 m, and the deposition steps are the same as in Example 1.

[0065] Due to the increase in the product size of the optical fiber preform 5, in order to ensure the deposition efficiency, the gas consumption of each layer of the blowtorch is increased accordingly. The gas flow rate of gas channel T1 is 15SLM, the gas flow rate of gas channel T2 is 30SLM, the gas flow rate of gas channel T3 is 50SLM, the gas flow rate of gas channel T4 is 10SLM, and the gas flow rate of gas channel T5 is 200SLM. The process parameters such as the rotation rate R and the blowtorch movement speed V in the process are shown in Table 2. The NA value of the final product can reach 0.24, and the utilization rate of fluorine raw materials is 60%.

[0066] Table 2

[0067] Outer diameter D(mm) Speed ​​R(rpm) Blowtorch speed V(mm / min) Holding furnace temperature T(℃) 30 18 700 1100 35 25 620 1070 40 30 550 1040 44 33 480 1010 47 35 430 980 50 37 400 950

[0068] Parts or structures not specifically described in the present invention may adopt existing technologies or existing products and will not be described in detail here.

[0069] The above descriptions are merely embodiments of the present invention and are not intended to limit the patent scope of the present invention. Any equivalent structure or equivalent process transformation made using the contents of the present invention specification, or directly or indirectly applied in other related technical fields, are also included in the patent protection scope of the present invention.

Claims

1. A plasma external deposition device for manufacturing optical fiber preform, characterized in that: include: a plasma source for generating a high-frequency electromagnetic field; An electromagnetic coil, wherein the plasma source is connected to the electromagnetic coil and is used to generate an induced high-frequency electromagnetic field; A blowtorch, the blowtorch is nested inside the electromagnetic coil, and the blowtorch comprises a five-layer structure, each layer of the structure is connected to a gas channel, and is used to pass different raw materials; A lathe, used to fix the optical fiber preform and control the rotation of the optical fiber preform and the movement of the blowtorch; The heat preservation furnace is arranged at both ends of the optical fiber preform rod and is used to improve the axial temperature uniformity of the optical fiber preform rod during the deposition process.

2. The plasma external deposition device for manufacturing optical fiber preform according to claim 1, characterized in that: The plasma source is a radio frequency plasma source with an output power of 30 to 100 kW, which is used to generate a high-frequency electromagnetic field. The electromagnetic coil can generate an induced high-frequency current under the action of the high-frequency electromagnetic field, thereby generating an induced high-frequency electromagnetic field.

3. The plasma external deposition device for manufacturing optical fiber preform according to claim 1, characterized in that: There are five gas channels, namely gas channel T1, gas channel T2, gas channel T3, gas channel T4, and gas channel T5. The height of gas channel T1 is 20 to 30 mm higher than that of gas channel T2. The heights of gas channel T2, gas channel T3, gas channel T4, and gas channel T5 decrease successively. SiCl4 is introduced into the blowtorch head via gas channel T1, oxygen is introduced into the blowtorch head via gas channel T2, and ionized gas is introduced into the blowtorch head via gas channel T3. The ionized gas can be ionized in a high-frequency electromagnetic field. The fluorine raw material is introduced into the blowtorch head from the edge of the plasma flame via gas channel T4, and the cooling gas is introduced into the blowtorch head via gas channel T5.

4. The plasma external deposition device for manufacturing optical fiber preform according to claim 3, characterized in that: The gas flow rate of SiCl4 introduced into the gas channel T1 is the largest, which is 20-25 m / s; the gas flow rate of oxygen introduced into the gas channel T2 is 15-20 m / s; the gas flow rate of ionized gas introduced into the gas channel T3 is 1-3 m / s; the gas flow rate of fluorine raw material introduced into the gas channel T4 is 5-10 m / s; and the gas flow rate of cooling gas introduced into the gas channel T5 is 10-15 m / s.

5. The plasma external deposition device for manufacturing optical fiber preform according to claim 3, characterized in that: The ionized gas is any one or a combination of argon, oxygen, and nitrogen; the fluorine raw material is any one or a combination of CF4, SiF4, C2F6, and SF6; and the cooling gas is any one or a combination of argon, oxygen, and nitrogen.

6. The plasma external deposition device for manufacturing optical fiber preform according to claim 1, characterized in that: The lathe is provided with a radio frequency output cabinet, an upper clamping assembly, a heat preservation furnace, a blowtorch, an optical fiber preform and a lower clamping assembly. The radio frequency output cabinet is connected to a plasma source. The upper clamping assembly is used to clamp the upper part of the optical fiber preform. The lower clamping assembly is used to clamp the lower part of the optical fiber preform. Optical fiber preforms of different lengths can be matched by adjusting the distance between the upper clamping assembly and the lower clamping assembly. The upper and lower ends of the optical fiber preform are respectively provided with heat preservation furnaces. The blowtorch can reciprocate along the axis of the optical fiber preform.

7. A plasma external deposition method for manufacturing an optical fiber preform, characterized in that: Deposition is performed using a plasma external deposition device for manufacturing an optical fiber preform as claimed in any one of claims 1 to 6, comprising the following steps: 100: Adjust the height positions of the upper clamping assembly and the lower clamping assembly, adjust the height of the lower clamping assembly to a position convenient for placing the preform, and adjust the height of the upper clamping assembly according to the length of the optical fiber preform; 200: vertically mounting the optical fiber preform on a lathe and fixing it with an upper clamping assembly and a lower clamping assembly; 300: adjusting the height position of the blowtorch so that the blowtorch is located at the starting deposition point of the optical fiber preform; 400: Control the optical fiber preform to rotate at a certain rotation rate R; introduce ionized gas through the gas channel T3; start the plasma source to ionize the ionized gas to generate a plasma flame, and then introduce cooling gas through the gas channel T5; 500: Control the torch to move vertically repeatedly at a certain speed V to preheat and polish the surface of the optical fiber preform rod until the surface temperature of the optical fiber preform rod reaches 1500±50°C before entering step 600. In this process, the insulation furnace moves with the torch. When the torch moves to the starting point of the lower part of the optical fiber preform rod, the upper insulation furnace is exactly located at the end position of the upper part of the optical fiber preform rod. On the contrary, when the torch moves to the end position of the upper part of the optical fiber preform rod, the lower insulation furnace is exactly located at the starting position of the lower part of the optical fiber preform rod. At the same time, the temperature T of the insulation furnace gradually decreases with the increase of the diameter of the optical fiber preform rod; 600: After polishing, the torch returns to the starting position at the bottom of the optical fiber preform, SiCl4 is introduced through the gas channel T1, oxygen is introduced through the gas channel T2, and SF6 is introduced through the gas channel T4, and then the torch is controlled to move vertically repeatedly for deposition; 700: When the outer diameter D of the optical fiber preform reaches the expected requirement, the deposition is completed, and the supply of raw materials in the gas channels T1, T2, and T4 is stopped first, and then the plasma source is turned off, and then the supply of ionized gas and cooling gas in the gas channels T3 and T5 is stopped.

8. The plasma external deposition method for manufacturing an optical fiber preform according to claim 7, characterized in that: The optical fiber preform rod rotates at a rotation rate R of 10 to 60 rpm, and the blowtorch moves vertically repeatedly at a rate V of 200 to 800 mm / min.

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