Preparation method of surface cladding deep fluorine-doped quartz preform based on PCVD (plasma chemical vapor deposition) platform

Abstract

The invention discloses a preparation method of a surface cladding deep fluorine-doped quartz preform based on a PCVD (plasma chemical vapor deposition) platform, which belongs to the technical field of optical fiber manufacturing and comprises the following steps: (1) preparing an initial preform by an in-tube deposition process; (2) corroding the outer lining pipe to obtain a preform to be polished; (3) arranging a polishing liner tube; (4) arranging the polishing liner tube and the to-be-polished preform on a PCVD deposition platform, and arranging an air exhaust system, an air supply system and a resonant cavity; (5) carrying out plasma polishing on the preform to be polished; and (6) carrying out annealing treatment on the polished preform rod to complete the preparation of the preform rod. According to the preparation process, the efficient preparation of the surface cladding deep fluorine-doped quartz preform can be met, the processing quality of the preform can also be considered, the defects existing when the preform is prepared in a traditional polishing mode under an in-pipe deposition process are avoided, the preparation efficiency and the processing quality of the surface cladding deep fluorine-doped quartz preform are improved, and the production cost is reduced. And the processing and application cost of the surface cladding deep fluorine-doped silica fiber is reduced.

Description

Technical Field

[0001] This invention belongs to the field of optical fiber manufacturing technology, specifically relating to a method for preparing a surface-clad deeply fluorine-doped quartz preform based on a PCVD platform. Background Technology

[0002] Deeply fluorine-doped silica preforms with a surface cladding are commonly used to draw large-core, large-cladding power transmission fibers. These fibers are mainly used for high-power energy transmission and have wide applications in industrial lasers, medical fields, and national defense and scientific research. The most significant characteristic of this type of fiber is that the outer cladding is made of deeply fluorine-doped silica, and the numerical aperture formed by the waveguides with adjacent layers is relatively large, generally not less than 0.18.

[0003] To achieve the aforementioned optical fiber drawing, it is necessary to prepare a fluorine-doped quartz preform with a surface cladding layer.

[0004] Currently, the preparation of fluorine-doped quartz preforms with surface cladding is mainly achieved through two process routes: one is the direct preparation using plasma external spray deposition (POD or OPD) technology, which is commonly used abroad; the other is the plasma chemical vapor deposition (PCVD) or modified chemical vapor deposition (MCVD) plus preform etching route, which is commonly used domestically.

[0005] The former's main advantage in preparing fluorine-doped quartz cladding lies in its "depth," meaning the fluorine concentration can reach 7.0 wt% (corresponding to a NA of 0.28), and no additional etching or polishing is required after deposition. However, this external spraying process has a very low deposition rate, especially for the preparation of deeply fluorine-doped preforms, resulting in very low raw material utilization. Furthermore, the deposition rate of fluorine-doped quartz is currently difficult to exceed 0.4 g / min, making it very difficult to control manufacturing costs, and large-scale production cannot significantly reduce time and material costs.

[0006] The latter, in-tube deposition, has advantages in both raw material utilization and deposition rate. Raw material utilization can reach over 90%, and the deposition rate can exceed 1.0 g / min. However, due to the presence of a bushing material, the preform needs to be etched away to achieve the surface coating of the fluorine-doped quartz cladding. Furthermore, etching the preform is time-consuming, and the resulting surface is rough and uneven, with defects in the surface glass structure. Therefore, using this method in the fiber drawing process would significantly negatively impact the red light intensity and strength reliability of the optical fiber. Thus, the etched preform must be polished. Common polishing methods for the etched preform include grinding and flame polishing. Grinding is a cold polishing method, primarily using sandpaper to grind the surface of the preform until it approaches the target diameter. While this process can achieve surface polishing, precise control of concentricity is difficult, leading to grinding deviations and increased processing time and production costs, which is detrimental to mass production and delivery. Flame polishing is a thermal polishing method that uses an oxyhydrogen flame to heat-treat the preform, melting it at high temperatures to make the glass surface dense and smooth, thus achieving the polishing purpose. However, since the byproduct of the oxyhydrogen flame is water, there is a risk of OH contamination of the preform. Furthermore, the choice of preform shape is crucial in flame polishing; it is less effective for larger preforms, while polishing smaller preforms can easily cause bending and deformation.

[0007] The aforementioned situation results in excessively high costs for the preparation of surface-clad deeply fluorine-doped quartz preforms and corresponding optical fibers, which cannot fully meet the mass production needs of surface-clad deeply fluorine-doped optical fibers and present significant limitations. Summary of the Invention

[0008] In response to one or more of the above-mentioned defects or improvement needs of the existing technology, the present invention provides a method for preparing surface-clad deeply fluorine-doped quartz preforms based on a PCVD platform. This method enables the inner tube deposition and surface polishing of surface-clad deeply fluorine-doped quartz preforms based on a PCVD deposition platform, achieving efficient and high-precision preparation of surface-clad deeply fluorine-doped quartz preforms and reducing the preparation and application costs of surface-clad deeply fluorine-doped optical fibers.

[0009] To achieve the above objectives, this invention provides a method for preparing a surface-clad, deeply fluorine-doped quartz preform based on a PCVD platform, comprising the following steps: (1) An initial preform with a deep fluorine-doped surface cladding and an outer diameter of D1 is prepared in a liner using a deposition process; (2) The outer liner of the initial preform is etched to remove the surface liner and obtain a preform to be polished that meets the design packing ratio or design core packing ratio. (3) Set a polishing liner with an inner diameter D3 that is larger than the outer diameter D2 of the preform to be polished; (4) The polishing liner and the preform to be polished are installed on the PCVD deposition platform. The gas supply system and the gas extraction system are connected to both ends of the polishing liner, and the resonant cavity of the PCVD deposition platform is covered on the outside of the polishing liner, so that the preform to be polished is relatively fixed in the closed cavity formed by the polishing liner. (5) Set the temperature conditions of the PCVD deposition platform, continuously introduce polishing gas into the polishing liner through the gas supply system, and control the gas pressure in the polishing liner through the gas extraction system; after the control conditions reach the expected level, turn on the high-frequency power of the magnetron of the PCVD platform, and ionize the continuously introduced polishing gas through the microwave introduced through the resonant cavity, so that the surface of the preform to be polished can be plasma polished. (6) After polishing, the preform is annealed on the PCVD platform, and finally a fluorine-doped quartz preform with a surface cladding after plasma polishing and annealing is obtained.

[0010] As a further improvement of the present invention, the deeply fluorine-doped surface cladding is a fluorine-doped quartz layer, and the numerical aperture formed by the waveguide formed by the fluorine-doped quartz layer and the adjacent layer is not less than 0.18.

[0011] As a further improvement of the present invention, in process (2), the corrosion treatment of the initial preform is achieved by the following process: immersing the initial preform in hydrofluoric acid or in a mixture of hydrofluoric acid and nitric acid until the target rod diameter is corroded. and / or In the mass production process of preforms, the corrosion of multiple initial preforms is carried out simultaneously in process (2).

[0012] As a further improvement of the present invention, the inner diameter D3 of the polishing liner is 15mm to 40mm larger than the outer diameter D2 of the preform to be polished. and / or The inner diameter of the resonant cavity is larger than the outer diameter of the polishing liner, and the difference between the two does not exceed 0.5 mm.

[0013] As a further improvement of the present invention, in process (5), the gas pressure inside the pipe controlled by the gas extraction system is not greater than 0.05 atm; and / or, the polishing gas is argon, argon-nitrogen mixture or argon-oxygen mixture.

[0014] As a further improvement of the present invention, in process (4), the installation of the polishing liner and the preform to be polished on the PCVD deposition platform is achieved by two locking rotary chuck devices. The locking rotary chuck device includes a locking sleeve, a chuck shaft tube, a chuck flow divider ring, a chuck flange, a chuck pulley, and a housing assembly arranged sequentially along the axial direction. The locking sleeve is used to lock and clamp the outer periphery of the end of the polishing liner; one end of the chuck shaft tube is sealed to the locking sleeve, and the other end is sealed to one end of the chuck diverter ring; and clamping holes are provided axially in the middle of the other end of the chuck diverter ring and the middle of the chuck shaft tube, so that the end of the preform to be polished can be clamped and fixed after passing through the two clamping holes in sequence; the chuck shaft tube is provided with a plurality of connecting holes that connect the polishing liner and the chuck diverter ring; One end of the housing assembly is used to connect to the air supply system or the air extraction system, and the other end can be sealed and assembled to the outer periphery of the chuck distribution ring after the chuck flange and chuck pulley are assembled. Multiple distribution holes communicating with the inner cavity of the housing assembly are opened on the outer periphery of the chuck distribution ring, so that the housing assembly can communicate with the polishing liner through the distribution holes and the communicating holes.

[0015] As a further improvement of the present invention, a liner sealing ring is provided between the locking sleeve and the chuck shaft tube, so that after the locking sleeve is locked and connected with the chuck shaft tube, the liner sealing ring can press against the outer periphery of the end of the polishing liner tube.

[0016] As a further improvement of the present invention, a sealing ring groove is provided circumferentially on the inner wall surface of the clamping hole, and a mandrel sealing ring is embedded in the sealing ring groove, so that the chuck shaft tube and the chuck diverting ring can be respectively sealed and pressed against the outer periphery of the preform to be polished by the mandrel sealing ring.

[0017] As a further improvement of the present invention, a flow divider ring sealing ring is provided between the mating end face of the chuck shaft tube and the chuck flow divider ring; and / or A star-shaped sealing ring is provided between the outer casing and the outer peripheral wall of the chuck diverter ring; and / or The housing assembly is mounted on the outer periphery of the chuck shunt ring via several bearings.

[0018] As a further improvement of the present invention, in process (6), the annealing process of the preform is as follows: Preset the control line for the change of annealing temperature of the preform over time; control the annealing temperature to change in the order of (1000±100)℃, (800±100)℃, and (600±100)℃, and hold each annealing temperature for 15 minutes, with a change time of 30 minutes between two adjacent annealing temperatures.

[0019] The aforementioned improved technical features can be combined with each other as long as they do not conflict with each other.

[0020] In summary, the beneficial effects of the above-described technical solutions conceived by this invention compared with the prior art include: The present invention provides a method for preparing a surface-clad deeply fluorine-doped quartz preform based on a PCVD platform, comprising the following steps: (1) preparing an initial preform with a deeply fluorine-doped surface cladding using an in-tube deposition process; (2) etching the outer liner of the surface of the initial preform to obtain a preform to be polished; (3) setting a polishing liner; (4) mounting the polishing liner and the preform to be polished on a PCVD deposition platform and setting up an extraction system, a gas supply system, and a resonant cavity; (5) performing plasma polishing on the preform to be polished based on the experimental conditions controlled by the PCVD deposition platform; and (6) annealing the polished preform to complete the preparation of the preform. The aforementioned preparation process can both meet the requirements of efficient preparation of surface-clad deeply fluorine-doped quartz preforms and take into account the processing quality of surface-clad deeply fluorine-doped quartz preforms, avoiding the defects of traditional cold polishing and flame polishing methods, improving the preparation efficiency and processing quality of surface-clad deeply fluorine-doped quartz preforms, and reducing the processing and application costs of surface-clad deeply fluorine-doped quartz optical fibers.

[0021] The method for preparing deeply fluorine-doped quartz preforms with surface cladding in this invention utilizes a PCVD deposition platform and employs a combined approach of in-tube deposition of deeply fluorine-doped cladding, batch concentrated acid bath etching, and in-tube low-pressure plasma polishing. This approach achieves high preparation efficiency, low preparation cost, and mass production capability. Simultaneously, the preform annealing process eliminates the brittle fiber breakage problem in large-core-diameter, large-cladding power-transmitting fibers caused by stress differences in traditional preform preparation methods, thereby improving device yield and reliability. Attached Figure Description

[0022] To more clearly illustrate the technical solutions in the embodiments of the present invention, the accompanying drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0023] Figure 1 This is a schematic flowchart of the preparation method of the surface-clad deeply fluorine-doped quartz preform based on the PCVD platform in an embodiment of the present invention. Figure 2 This is an exploded view of the locking rotary chuck device in an embodiment of the present invention; Figure 3 This is a side view of the structure of the locking rotary chuck device in an embodiment of the present invention; Figure 4 This is a sectional view along line AA of the locking rotary chuck device in an embodiment of the present invention; Figure 5This is a partial enlarged view (I) of the locking rotary chuck device in an embodiment of the present invention; Figure 6 This is a BB-direction sectional view of the locking rotary chuck device in an embodiment of the present invention; Figure 7 This is a partial enlarged view (II) of the locking rotary chuck device in an embodiment of the present invention; Figures 8-13 These are refractive index distribution diagrams of the preforms obtained in specific embodiments 1 to 6 of the present invention; In all the accompanying drawings, the same reference numerals denote the same technical features, specifically: 1. Locking sleeve; 2. Chuck shaft tube; 3. Chuck diverter ring; 4. Chuck flange; 5. Chuck pulley; 6. Housing kit; 7. Chuck nut; 8. Liner seal ring; 9. Mandrel seal ring; 10. Diverter ring seal ring; 11. Star seal ring; 12. Butt seal ring; 13. Precast rod to be polished; 14. Polishing liner; 15. Bearing. Detailed Implementation

[0024] 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.

[0025] In the description of this invention, it should be understood that, unless otherwise expressly specified and limited, the terms "center," "longitudinal," "lateral," "length," "width," "thickness," "upper," "lower," "front," "rear," "left," "right," "vertical," "horizontal," "top," "bottom," "inner," "outer," "clockwise," "counterclockwise," "axial," "radial," "circumferential," etc., indicating the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, are only for the convenience of describing this invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation of this invention.

[0026] Furthermore, unless otherwise expressly defined, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one of that feature. In the description of this invention, "a plurality of" means at least two, such as two, three, etc., unless otherwise expressly and specifically defined.

[0027] In this invention, unless otherwise explicitly specified and limited, the terms "installation," "connection," "linking," and "fixing," etc., should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral part; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; they can refer to the internal communication of two components or the interaction between two components, unless otherwise explicitly limited. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0028] In this invention, unless otherwise explicitly specified and limited, "above" or "below" the second feature can mean that the first feature is in direct contact with the second feature, or that the first feature is in indirect contact with the second feature through an intermediate medium. Furthermore, "above," "over," and "on top" of the second feature can mean that the first feature is directly above or diagonally above the second feature, or simply that the first feature is at a higher horizontal level than the second feature. "Below," "below," and "under" the second feature can mean that the first feature is directly below or diagonally below the second feature, or simply that the first feature is at a lower horizontal level than the second feature.

[0029] Below, for reference Figures 1-13 This invention describes a method for preparing a surface-clad, deeply fluorine-doped quartz preform based on a PCVD platform according to a preferred embodiment of the present invention.

[0030] The preform preparation method in the preferred embodiment of this invention aims to utilize the existing mature PCVD platform to prepare deeply fluorine-doped quartz preforms with surface cladding, achieving efficient and high-precision fabrication. Specifically, for the "efficient" fabrication of the preform, the preferred embodiment employs an "in-tube deposition" method to prepare the initial preform, fully leveraging the high deposition rate and raw material utilization of in-tube deposition technology to efficiently and rapidly deposit the deeply fluorine-doped quartz cladding. For the "high-precision" fabrication of the preform, the preferred embodiment specifically designs an efficient and high-precision polishing process based on the PCVD deposition platform to ensure surface polishing of the preform after efficient in-tube deposition, ultimately guaranteeing the precision of the preform fabrication.

[0031] It should be noted that the "preform" in the preferred embodiment of the present invention needs to meet the following characteristics: The outer layer of the preform is a fluorine-doped quartz layer with a high fluorine concentration, generally reaching 4.0 wt% or more, and the numerical aperture formed by the waveguide with the adjacent layer is not less than 0.18.

[0032] Furthermore, the deep fluorine-doped quartz preform with surface cladding is a product whose definition is well-known in the industry. This invention patent does not design the product parameters (such as doping concentration, radial design layer number, etc.) of the product itself, but only focuses on how to efficiently and accurately prepare the forming process of this type of preform.

[0033] For the preform in the preferred embodiment, the core structure covered by the fluorine-doped cladding can be changed as needed. For example, the fluorine-doped cladding can cover a pure quartz fiber core, or the fluorine-doped cladding can cover a pure quartz cladding and a doped fiber core; or the inner side of the fluorine-doped cladding can have a pure quartz cladding, a fluorine-doped cladding, and a pure quartz fiber core in sequence; or multiple different types of cladding can be provided between the fluorine-doped cladding and the fiber core.

[0034] Obviously, for the preform in the preferred embodiment, the specific inner core layer of the deeply fluorinated cladding is not important, as long as it can be designed and deposited using existing technology, and will not be elaborated here. That is to say, as long as the outermost layer (surface cladding) of the preform is a deeply fluorinated quartz layer, the preform can be prepared using the process method in the preferred embodiment of the present invention.

[0035] Specifically, in the preferred embodiment, the preparation method of the surface-clad deeply fluorine-doped quartz preform based on the PCVD platform preferably follows the process as follows: Figure 1 As shown, and specifically includes the following steps: (1) An initial preform with a deep fluorine-doped surface cladding and an outer diameter of D1 is prepared in a liner using a deposition process; It is understood that the outer diameter of the initial preform is the outer diameter of the liner selected for the deposition process. When selecting the aforementioned liner, it is preferable to determine it based on the size of the fluorine-doped quartz preform with the surface cladding. Specifically, the inner diameter of the liner should be determined, that is, the inner diameter of the liner should not be less than the outer diameter of the preform, so as to provide dimensional redundancy for subsequent surface corrosion and surface polishing.

[0036] In practice, the aforementioned deposition process can be further optimized to be PCVD or MCVD deposition. As for the specific methods of deposition of each layer inside the tube, it can be carried out quickly based on mature technologies in the industry and in conjunction with the parameter design of each layer of the preform. For example, a doped core region or a pure silicon core region can be prepared by deposition processes such as PCVD, MCVD, VAD, and OVD, and then a fluorine-doped quartz cladding can be prepared by POD, OPD, PCVD, and MCVD.

[0037] (2) The outer liner of the initial preform is etched to remove the surface liner and obtain a preform to be polished that meets the design packing ratio or design core packing ratio. Specifically, the cladding ratio of the preform to be polished (as shown in Table 1 below, the CCDR value) refers to the diameter ratio between the deeply fluorine-doped cladding and the adjacent cladding, and it mainly applies to optical fibers / preforms with multiple claddings. For example, for a three-layer optical fiber with a diameter of 34 / 460 / 530, it means that the diameter of the deeply fluorine-doped cladding is 530µm, the diameter of the adjacent inner cladding is 460µm, the core diameter is 34µm, and the cladding ratio is 1.15.

[0038] Accordingly, the core-cladding ratio of the preform to be polished refers to the ratio of the diameter of the deeply fluorinated cladding to the diameter of the adjacent core layer, and it mainly applies to optical fibers / preforms with a single cladding. For example, for a two-layer optical fiber with a diameter of 220 / 242, it means that the diameter of the deeply fluorinated cladding is 242µm, the diameter of the large-diameter core layer is 220µm, and the core-cladding ratio is 1.1.

[0039] More specifically, the corrosion treatment of the initial preform is preferably achieved through the following process: The initial preform is immersed in hydrofluoric acid or a mixture of hydrofluoric acid and nitric acid until the outer liner is corroded and removed and the target rod diameter is achieved.

[0040] In addition, in actual production, the initial corrosion treatment of preforms can be carried out in batches. For example, multiple preforms can be evenly distributed in an acid tank, and the corrosive acid can be circulated in the tank to achieve batch corrosion of multiple preforms, thereby effectively shortening the corrosion treatment time that is spread to a single preform during the batch production of preforms.

[0041] (3) Set a polishing liner with an inner diameter D3 that is larger than the outer diameter D2 of the preform to be polished.

[0042] In actual setup, the inner diameter D3 of the polishing liner is 15mm to 40mm larger than the outer diameter D2 of the preform to be polished. For example, the inner diameter of the polishing liner is 20mm larger than the outer diameter of the preform.

[0043] By utilizing the above-mentioned dimensions, it can be fully ensured that the plasma formed after the subsequent polishing gas (such as argon or mixed gas) is ionized is uniformly distributed under low pressure, and that the high-temperature ion flow formed under a certain spatial flow rate can effectively erode the surface of the preform.

[0044] (4) Install the polishing liner and the preform to be polished onto the PCVD deposition platform. Connect the gas supply system and the gas extraction system to both ends of the polishing liner, and cover the resonant cavity of the PCVD deposition platform on the outside of the polishing liner, so that the preform to be polished is relatively fixed in the closed cavity formed by the polishing liner.

[0045] In the preferred embodiment, the reason for setting a polishing liner and embedding the preform to be polished in the polishing liner before mounting it on the PCVD deposition platform is that the PCVD deposition platform can control the temperature and resonant microwave conditions. Combined with the setting of the gas supply system (gas end) and the gas extraction system (pump end), the preform to be polished can be accurately placed in the plasma polishing environment, thus replacing the conventional cold polishing and flame polishing methods with plasma polishing.

[0046] More specifically, regarding the size design of the resonant cavity and polishing liner in the PCVD deposition platform, it is preferable to select the outer diameter of the polishing liner based on the inner diameter of the existing resonant cavity of the PCVD deposition platform, so as to ensure that the polishing liner meets both the embedding requirements of the preform to be polished and the fitting requirements of the resonant cavity.

[0047] In actual setup, the inner diameter of the resonant cavity is larger than the outer diameter of the polishing liner, and the difference between the two is preferably no more than 0.5 mm. It is understood that when the outer diameter of the polishing liner does not correspond to the existing resonant cavity size of the PCVD deposition platform due to its adaptation to the size of the preform to be polished, the size of the resonant cavity can be changed accordingly. This can be quickly achieved using existing technology and will not be elaborated here.

[0048] By utilizing the dimensional design between the resonant cavity and the polishing liner, the mutual friction between the resonant cavity and the polishing liner during movement is reduced, and high-frequency microwave leakage caused by excessive gap design is avoided.

[0049] Furthermore, in actual setup, the installation of the polishing liner and the preform to be polished on the PCVD deposition platform is preferably achieved by two locking rotary chuck devices, which clamp both ends of the polishing liner and both ends of the preform to be polished at the working position of the PCVD deposition platform, providing conditions for subsequent plasma polishing operations.

[0050] Specifically, the locking rotary chuck device in the preferred embodiment is as follows: Figures 2-7 As shown, they are installed in pairs during actual use, fixing the two ends of the polishing liner 14 and the mandrel 13 to be polished, respectively.

[0051] like Figure 2 As shown, the locking rotary chuck device in the preferred embodiment preferably includes a locking sleeve 1, a chuck shaft tube 2, a chuck flow divider ring 3, a chuck flange 4, a chuck pulley 5, and a housing kit 6 arranged sequentially along the axial direction.

[0052] The locking sleeve 1 is used to lock and clamp the outer periphery of the end of the polishing liner 14, thus ensuring the relative positional relationship between the locking sleeve 1 and the polishing liner 14. One end of the chuck shaft tube 2 is sealed to the locking sleeve 1, and the other end is sealed to one end of the chuck diverter ring 3; in this way, the relative positional relationship between the chuck shaft tube 2 and the chuck diverter ring 3 relative to the locking sleeve 1 can be established, that is, the relative positional relationship between the polishing liner 14 and the chuck shaft tube 2 and the chuck diverter ring 3 can be established.

[0053] Meanwhile, clamping holes are axially formed at the middle of the other end of the chuck diverter ring 3 and the middle of the chuck shaft tube 2, so that one end of the preform 13 to be polished can be clamped and fixed after passing through the two clamping holes in sequence. That is, both ends of the preform 13 to be polished are supported and fixed by the combination of the chuck shaft tube 2 and the chuck diverter ring 3. At this time, the relative position between the preform 13 to be polished and the polishing liner tube 14 can be defined. Correspondingly, both ends of the preform 13 to be polished protrude from both ends of the polishing liner tube 14 and are assembled with the chuck shaft tube 2 and the chuck diverter ring 3, forming a cavity for polishing gas transmission between the surface of the preform 13 to be polished and the inner circumferential wall of the polishing liner tube 14.

[0054] Furthermore, the chuck shaft tube 2 is provided with several connecting holes that connect the polishing liner tube 14 and the chuck flow divider ring to facilitate the axial delivery of polishing gas. In a preferred embodiment, each connecting hole is preferably opened on the circumferential inner wall surface of the clamping hole, that is, a through hole similar to a plum blossom is formed in the middle of the chuck shaft tube 2.

[0055] Of course, depending on the actual setup requirements, the aforementioned connecting holes can also be placed in other locations, which will not be elaborated here.

[0056] Furthermore, one end of the housing assembly 6 is used to connect to the air supply system or the air extraction system, and the other end can be sealed and assembled to the outer periphery of the chuck distribution ring 3 after the chuck flange 4 and chuck pulley 5 are assembled. Based on the setting of the chuck flange 4, the connection and fixation between the components can be quickly achieved through axial assembly. Utilizing the setting of the chuck pulley 5, the locking rotary chuck device can be quickly installed on the PCVD deposition platform after the assembly with the preform 13 to be polished and the polishing liner 14 is completed. This allows the preform 13 to be rotated during subsequent plasma polishing by matching the chuck pulley 5 with the corresponding mechanism on the PCVD deposition platform.

[0057] Meanwhile, multiple diversion holes are provided on the outer periphery of the chuck diversion ring 3 to connect with the inner cavity of the outer shell assembly 6, so that the outer shell assembly 6 can be connected to the polishing liner 14 through the diversion holes and connecting holes.

[0058] More specifically, in the preferred embodiment of the locking rotary chuck device, a bushing sealing ring 8 is provided between the locking sleeve 1 and the chuck shaft tube 2, such as... Figure 5 , Figure 7 As shown in the figure, the liner sealing ring 8 is sleeved on the outer periphery of the end of the polishing liner 14. The liner sealing ring 8 is clamped axially by the end face assembly between the locking sleeve 1 and the chuck shaft tube 2, so that the liner sealing ring 8 is pressed against the outer periphery of the end of the polishing liner 14.

[0059] Meanwhile, the end clamping of the preform 13 to be polished is preferably achieved by a sealing ring. That is, a sealing ring groove is provided circumferentially on the inner wall of the clamping hole of the chuck shaft tube 2 and the chuck diversion ring 3, and a core rod sealing ring 9 is embedded in the sealing ring groove, so that the end of the preform 13 to be polished passes through the two core rod sealing rings 9 in sequence and is pressed and locked by the two core rod sealing rings 9.

[0060] Furthermore, it is preferable to provide a flow divider ring 10 between the mating end faces of the chuck shaft tube 2 and the chuck flow divider ring 3. This is achieved by opening a receiving groove on the end face of the chuck shaft tube 2 and / or the end face of the chuck flow divider ring 3, and then embedding the flow divider ring 10 into the corresponding receiving groove. This ensures the sealing performance between the chuck shaft tube 2 and the chuck flow divider ring 3 after they are assembled together.

[0061] Furthermore, in actual assembly, the housing assembly 6 is preferably assembled onto the outer periphery of the chuck distribution ring 3 via several bearings 15, for example... Figure 5 , Figure 7 The two bearings 15 are arranged side by side as shown. At the same time, in order to achieve the assembly sealing between the housing kit 6 and the chuck diverter ring 3, it is preferable to have a sealing groove opened in the circumferential direction on the inner peripheral wall surface of the housing kit 6, and to embed a star-shaped sealing ring 11 therein, so as to achieve the assembly sealing between the housing kit 6 and the chuck diverter ring 3 by means of the star-shaped sealing ring 11.

[0062] In actual installation, the housing kit 6 includes an assembly section for fitting and assembling with the chuck diverter ring 3, and an inner cavity section forming a venting cavity. The assembly section is fitted onto the outer periphery of the chuck diverter ring 3, and the end of the chuck diverter ring 3 extends into the inner cavity section. Correspondingly, each diverter hole is circumferentially formed on the outer periphery of the end of the chuck diverter ring 3 and communicates with the inner cavity section.

[0063] More preferably, in order to facilitate the sealed connection between the ends of the two outer casings 6 and the gas supply system and the gas extraction system, a detachable collet nut 7 is preferably provided at the ends of the two outer casings 6, and a mating sealing ring 12 is provided between the collet nut 7 and the ends of the outer casings 6. When the collet nut 7 is locked to the ends of the outer casings 6, the mating sealing ring 12 can be squeezed and deformed, thereby locking the connected gas pipeline.

[0064] By utilizing the paired arrangement of the aforementioned locking rotary chuck device, both ends of the polishing liner 14 and the preform 13 to be polished can be sealed and clamped respectively. In addition, with the connection of the ends of the two outer casing kits 6 to the air supply system and the air extraction system, the preform 13 to be polished can be correspondingly placed in the polishing liner 14 and installed on the PCVD deposition platform, thereby providing conditions for plasma polishing of the preform 13 to be polished by utilizing the existing PCVD deposition platform.

[0065] (5) Set the temperature conditions of the PCVD deposition platform, continuously introduce polishing gas into the polishing liner through the gas supply system, and control the gas pressure in the polishing liner through the gas extraction system; after the control conditions reach the expected level, turn on the high-frequency power of the magnetron of the PCVD platform, and ionize the continuously introduced polishing gas through the microwave introduced through the resonant cavity, so that the surface of the preform to be polished can be plasma polished.

[0066] In actual control, the pressure inside the polishing liner 14 used for plasma polishing is much greater than atmospheric pressure, and its internal pressure is further preferably not greater than 0.05 atm.

[0067] Meanwhile, the preferred polishing gas is argon, an argon-nitrogen mixture, or an argon-oxygen mixture. In actual control, the flow rate Q (in L / min) of the polishing gas is preferably introduced using a mass flow controller (MFC), and the specific flow rate value is designed according to S=Q / P, where S is the pumping speed of the PCVD lathe vacuum pump used for polishing, in L / min; and P is the gas pressure inside the pipe.

[0068] By utilizing the corresponding arrangement of the preform 13 to be polished and the polishing liner 14 on the PCVD deposition platform, the working principle of PCVD can be fully utilized to achieve instantaneous melting and vaporization of the quartz preform surface by low-pressure, high-energy, and high-temperature plasma, thereby achieving atomic-level material removal and achieving an ultra-smooth, defect-free surface polishing effect.

[0069] (6) After polishing, the preform is annealed on the PCVD platform, and finally a fluorine-doped quartz preform with a surface cladding after plasma polishing and annealing is obtained.

[0070] Specifically, through plasma polishing of the preform 13 to be polished in process (5), the outer periphery of the preform 13 to be polished can be fully polished, and surface defects on the outer periphery of the preform can be removed. For the preform to be plasma polished, since the plasma temperature is as high as several thousand degrees Celsius, the high temperature of the plasma will be conducted to the interior of the preform during the plasma polishing process. Thus, even if the surface of the preform can be cooled quickly after the surface polishing is completed, high temperature will still remain inside. Therefore, if the preform is rapidly cooled, a large thermal stress difference will be formed between the inside and outside of the preform, which will affect the subsequent processing of the preform, as well as the cracking of the drawing wire or the unreliability of the optical fiber strength.

[0071] Based on the above reasons, in the preferred embodiment, the preform after plasma polishing undergoes annealing treatment. Furthermore, in the process of the preferred embodiment, the plasma polishing operation is performed on a PCVD deposition platform, which is equipped with a heat-holding furnace capable of temperature regulation and maintenance. Compared to traditional heat source polishing methods such as flame polishing, which cannot achieve immediate annealing and heat preservation, the preform forming process in the preferred embodiment can utilize the PCVD deposition platform to achieve annealing treatment after polishing, effectively avoiding stress differences caused by rapid cooling inside and outside the preform.

[0072] More specifically, in a preferred embodiment, the annealing process for the preform is as follows: Preset the control line for the change of annealing temperature of the preform over time; control the annealing temperature to change in the order of (1000±100)℃, (800±100)℃, and (600±100)℃, and hold each annealing temperature for 15 minutes, with a change time of 30 minutes between two adjacent annealing temperatures.

[0073] Based on the aforementioned process design, the annealing treatment after plasma polishing of the preform can be fully guaranteed, ensuring that the quartz preform cools slowly, is fully annealed, eliminates thermal stress, and improves the preparation quality of the preform.

[0074] To further illustrate the preparation method of the surface-coated fluorine-doped quartz preform of the present invention, the following specific examples 1 to 6 are preferably provided for comparison.

[0075] The experimental parameters in Examples 1 to 6 are shown in Table 1. The experiments mainly focused on different numerical apertures (NA) and different target CCDRs (core-to-pack ratio / pack-to-pack ratio).

[0076] Specifically, the CCDR / NA of Example 1 is 1.1 / 0.20; the CCDR / NA of Example 2 is 1.1 / 0.22; the CCDR / NA of Example 3 is 1.2 / 0.22; the CCDR / NA of Example 4 is 1.33 / 0.22; the CCDR / NA of Example 5 is 1.1 / 0.24; and the CCDR / NA of Example 6 is 1.18 / 0.26.

[0077] For deeply fluorine-doped surface claddings with different numerical pore sizes (NA) and different target CCDRs, the time required to prepare the fluorine-doped cladding using the in-tube deposition process varies, corresponding to differences in the preform diameter D1 and the target preform diameter D2 after batch etching. Accordingly, to achieve in-tube low-pressure plasma polishing to match the different diameters of the preforms after etching, resonant cavities of different sizes are modified, corresponding to different tube inner diameters D3 used in each embodiment.

[0078] To ensure polishing quality and considering the surface roughness of the preform after corrosion, the wall thickness of the polishing tube needs to be reduced to increase the plasma movement space. In the preferred embodiment, the two resonant cavity dimensions involved in Embodiments 1, 3, 5 and Embodiments 2, 4, 6 are ø60 and ø50, respectively. Compared to the resonant cavity specifications, the wall thickness of the polishing liner 14 is preferably designed to be 1.5mm. This setting ensures that the difference between the inner diameter of the resonant cavity and the outer diameter of the polishing liner 14 is less than 0.5mm, effectively avoiding the risk of high-frequency microwave leakage that may be caused by excessive gap between the two, and ensuring the reliability of the resonant cavity application.

[0079] Table 1 Test parameters and test results in Examples 1-6

[0080] In addition, to compare the preparation efficiency with conventional molding methods, Table 1 further shows the time required to prepare the same number of six preforms with the same design parameters (corresponding to Examples 1 to 6) using the POD process.

[0081] Furthermore, in actual operation, the preparation process can be selected accordingly for the preparation of preforms of different specifications. Taking the experimental conditions in Example 1 as an example, the vacuum pump speed S of the PCVD deposition platform used is 2600 L / min, and the polishing pressure P is 0.01 atm. According to Q=S / P, the argon flow rate Q=26 L / min at 1 atm pressure. Of course, the actual given values ​​can also be fine-tuned according to the working conditions. For example, it is necessary to maintain plasma stability and pressure balance to fine-tune the working conditions to ensure that the argon or mixed gas is uniformly covered on the surface of the preform.

[0082] In addition, two parameters corresponding to gas ionization in each embodiment need to be designed: high-frequency power and gas pressure inside the polishing tube. The high-frequency power is related to the size of the resonant cavity and the size of the preform 13 to be polished. Based on PCVD deposition process experience, ø60 is matched with 6000W, and the polishing rod diameter is greater than 30mm. ø50 is matched with 4500W, and the polishing rod diameter does not exceed 30mm. Correspondingly, the pressure inside the tube is given according to the optimal vacuum pressure value for argon or mixed gas ionization, generally between 0.01 and 0.05 atm. The specific design value can be adjusted based on the plasma deformation at the gas detachment end and the polishing start position at the pump end.

[0083] After the preform is polished, the initial temperature of the holding furnace needs to be set during the polishing stage. Based on the conditions for full annealing of quartz glass at high temperature, it is usually designed to be around 1000℃. According to the annealing temperature of the preform and the stress distribution of the pulled optical fiber, the holding time should not be less than 15 minutes, and the cooling rate should not be faster than 20℃ / min.

[0084] Based on the aforementioned design, six sets of preforms can be fabricated, yielding six sets of test results as shown in Table 1. The refractive index distributions of the six sets of preforms are as follows: Figures 8-13 As shown in the figure. The experimental results demonstrate that, for surface-clad deeply fluorine-doped quartz preforms of the same specifications, under the premise of ensuring preform preparation accuracy (i.e., not using the forming method of inner tube deposition + physical polishing / flame polishing), the preparation method in the preferred embodiment of this invention can shorten the preparation time by 48% to 60% compared to existing plasma deposition preparation methods. This significantly improves the preparation efficiency of surface-clad deeply fluorine-doped quartz preforms, reduces the processing cost of surface-clad deeply fluorine-doped optical fibers, and enables mass production of such optical fibers. In terms of manufacturing cost, production efficiency, and processing quality, it better meets the requirements of industrial mass production.

[0085] The method for preparing deeply fluorine-doped quartz preforms with surface cladding in this invention utilizes a PCVD deposition platform and employs a combined approach of in-tube deposition of deeply fluorine-doped cladding, batch concentrated acid bath etching, and in-tube low-pressure plasma polishing. This approach achieves high preparation efficiency, low preparation cost, and mass production capability. Simultaneously, the preform annealing process eliminates the brittle fiber breakage problem in large-core-diameter, large-cladding power-transmitting fibers caused by stress differences in traditional preform preparation methods, thereby improving device yield and reliability.

[0086] 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 method for preparing a surface-clad, deeply fluorine-doped quartz preform based on a PCVD platform, characterized in that, Includes the following steps: (1) An initial preform with a deep fluorine-doped surface cladding and an outer diameter of D1 was prepared by in-tube deposition process; (2) Etch away the surface liner of the initial preform and obtain a preform to be polished that meets the design packing ratio or design core packing ratio; (3) Set a polishing liner with an inner diameter D3 that is larger than the outer diameter D2 of the preform to be polished; (4) The polishing liner and the preform to be polished are installed on the PCVD deposition platform. The gas supply system and the gas extraction system are connected to both ends of the polishing liner, and the resonant cavity of the PCVD deposition platform is covered on the outside of the polishing liner, so that the preform to be polished is relatively fixed in the closed cavity formed by the polishing liner. (5) Set the temperature conditions of the PCVD deposition platform, continuously introduce polishing gas into the polishing liner through the gas supply system, and control the gas pressure in the polishing liner through the gas extraction system; after the control conditions reach the expected level, turn on the high-frequency power of the magnetron of the PCVD platform, and ionize the continuously introduced polishing gas through the microwave introduced through the resonant cavity, so that the surface of the preform to be polished can be plasma polished. (6) After polishing, the preform is annealed on the PCVD platform, and finally a fluorine-doped quartz preform with a surface cladding after plasma polishing and annealing is obtained.

2. The method for preparing a surface-clad deeply fluorine-doped quartz preform based on a PCVD platform according to claim 1, characterized in that, The deeply fluorine-doped surface cladding is a fluorine-doped quartz layer, and the numerical aperture formed by the waveguide formed by it and the adjacent layer is not less than 0.

18.

3. The method for preparing a surface-clad deeply fluorine-doped quartz preform based on a PCVD platform according to claim 1, characterized in that, In process (2), the initial preform is corroded by the following process: the initial preform is immersed in hydrofluoric acid or in a mixture of hydrofluoric acid and nitric acid until it is corroded to the target rod diameter. and / or In the mass production process of preforms, the corrosion of multiple initial preforms is carried out simultaneously in process (2).

4. The method for preparing a surface-clad deeply fluorine-doped quartz preform based on a PCVD platform according to any one of claims 1 to 3, characterized in that, The inner diameter D3 of the polishing liner is 15mm to 40mm larger than the outer diameter D2 of the preform to be polished. and / or The inner diameter of the resonant cavity is larger than the outer diameter of the polishing liner, and the difference between the two does not exceed 0.5 mm.

5. The method for preparing a surface-clad deeply fluorine-doped quartz preform based on a PCVD platform according to any one of claims 1 to 3, characterized in that, In process (5), the gas pressure inside the pipe controlled by the pumping system is not greater than 0.05 atm; and / or, the polishing gas is argon, argon-nitrogen mixture or argon-oxygen mixture.

6. The method for preparing a surface-clad deeply fluorine-doped quartz preform based on a PCVD platform according to any one of claims 1 to 3, characterized in that, In process (4), the installation of the polishing liner and the preform to be polished on the PCVD deposition platform is achieved by two locking rotary chuck devices. The locking rotary chuck device includes a locking sleeve, a chuck shaft tube, a chuck flow divider ring, a chuck flange, a chuck pulley, and a housing assembly arranged sequentially along the axial direction. The locking sleeve is used to lock and clamp the outer periphery of the end of the polishing liner; one end of the chuck shaft tube is sealed to the locking sleeve, and the other end is sealed to one end of the chuck diverter ring; and clamping holes are provided axially in the middle of the other end of the chuck diverter ring and the middle of the chuck shaft tube, so that the end of the preform to be polished can be clamped and fixed after passing through the two clamping holes in sequence; the chuck shaft tube is provided with a plurality of connecting holes that connect the polishing liner and the chuck diverter ring; One end of the housing assembly is used to connect to the air supply system or the air extraction system, and the other end can be sealed and assembled to the outer periphery of the chuck distribution ring after the chuck flange and chuck pulley are assembled. Multiple distribution holes communicating with the inner cavity of the housing assembly are opened on the outer periphery of the chuck distribution ring, so that the housing assembly can communicate with the polishing liner through the distribution holes and the communicating holes.

7. The method for preparing a surface-clad deeply fluorine-doped quartz preform based on a PCVD platform according to claim 6, characterized in that, A liner sealing ring is provided between the locking sleeve and the chuck shaft tube, so that after the locking sleeve is locked and connected to the chuck shaft tube, the liner sealing ring can press the outer periphery of the end of the polishing liner tube.

8. The method for preparing a surface-clad deeply fluorine-doped quartz preform based on a PCVD platform according to claim 6, characterized in that, A sealing ring groove is provided circumferentially on the inner wall surface of the clamping hole, and a mandrel sealing ring is embedded in the sealing ring groove, so that the chuck shaft tube and the chuck diverting ring can be sealed and pressed against the outer periphery of the preform to be polished by the mandrel sealing ring.

9. The method for preparing a surface-clad deeply fluorine-doped quartz preform based on a PCVD platform according to claim 6, characterized in that, A flow divider ring sealing ring is provided between the mating end face of the chuck shaft tube and the chuck flow divider ring; and / or A star-shaped sealing ring is provided between the outer casing and the outer peripheral wall of the chuck diverter ring; and / or The housing assembly is mounted on the outer periphery of the chuck shunt ring via several bearings.

10. The method for preparing a surface-clad fluorine-doped quartz preform based on a PCVD platform according to any one of claims 1-3 and 7-9, characterized in that, In process (6), the annealing process of the preform is as follows: Preset the control line for the change of annealing temperature of the preform over time; control the annealing temperature to change in the order of (1000±100)℃, (800±100)℃, and (600±100)℃, and hold each annealing temperature for 15 minutes, with a change time of 30 minutes between two adjacent annealing temperatures.

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