Method for preparing optical fiber preform by means of inside-tube method

Abstract

Disclosed in the present application is a method for preparing an optical fiber preform by means of an inside-tube method. The method for preparing an optical fiber preform by means of an inside-tube method comprises the following preparation steps: providing a preparation device, wherein the preparation device comprises a rotationally mounted quartz tube, an excitation source for exciting chemical deposition of reactants inside the quartz tube, and an air extraction structure located at an air output end of the quartz tube; under a preset deposition condition, determining final mapping relationships between the positions of the excitation source in an axial direction and discharge air-pressure parameters of the quartz tube; acquiring the actual position of the excitation source in the axial direction, and on the basis of the actual position, querying the mapping relationships to determine an actual discharge air-pressure parameter of the quartz tube; and on the basis of the actual discharge air-pressure parameter of the quartz tube, controlling the air extraction structure to operate.

Description

Method for preparing optical fiber preform by in-tube method

[0001] Related applications

[0002] This application claims priority to Chinese Patent Application No. 202410879027.6, filed on July 2, 2024, the entire contents of which are incorporated herein by reference. TECHNICAL FIELD

[0003] The present application relates to the technical field of optical fiber manufacturing, in particular to a method for preparing an optical fiber preform by an in-tube method. BACKGROUND

[0004] The production of optical fiber preform can be prepared by PCVD (Plasma Chemical Vapor Deposition) or MCVD (Modified Chemical Vapor Deposition) of the in-tube method or VAD (Vertical Axial Deposition) and OVD (Outside Vapor Deposition) process of the out-tube method.

[0005] The in-tube method involves passing high-purity reactants such as SiCl4, O2, GeCl4, etc. into a high-purity quartz tube through a certain route, and using a microwave source resonant cavity or a flame torch to excite chemical reactions and vapor deposition to form a quartz glass deposition layer. The reaction formula for preparing the optical fiber preform is as follows: SiCl4+O2=SiO2+2Cl2 GeCl4+O2=GeO2+2Cl2

[0006] In the process of preparing the preform by vapor deposition method, the refractive index distribution of the optical fiber is adjusted by doping dopants (such as Ge, P, F, B, Al, Ti, Zr, etc.) in SiO2. The quartz tube after deposition is prepared into a solid preform by high-temperature furnace shrinking. Then, the preform is combined with a matching sleeve after etching, cleaning, and drying to form an optical fiber preform, which is drawn into an optical fiber by a drawing equipment.

[0007] The axial parameter fluctuation of the optical fiber preform directly affects the performance consistency of the optical fiber, therefore, it is crucial to improve the axial parameter uniformity of the preform. In the process of preparing the preform by the in-tube method, the high-purity reactants perform chemical reactions and vapor deposition in the quartz tube. Since the mixed gas flows from the inlet end to the outlet end in the tube, the composition, temperature, pressure, density, and energy distribution at each point in the tube are uneven, which leads to a certain deviation in the refractive index profile of the preform in the axial direction, and further affects the axial parameter consistency of the preform, increasing the waste fiber rate. The present application proposes a method for preparing an optical fiber preform by an in-tube method to solve the above problems.

[0008] SUMMARY

[0009] The main purpose of the present application is to provide a preparation method of an optical fiber preform by a tube method, aiming to solve the problem that in the traditional mother rod deposition process, the composition, temperature, pressure, density and energy distribution of each point in the tube are uneven, which leads to a certain deviation of the refractive index profile of the mother rod in the axial direction, and further affects the axial parameter consistency of the preform, and increases the waste fiber rate.

[0010] To achieve the above purpose, the preparation method of the optical fiber preform by the tube method provided by the present application comprises the following preparation steps:

[0011] Providing a preparation device, wherein the preparation device comprises a quartz tube installed in rotation, an excitation source for exciting reactants to perform chemical deposition in the quartz tube, and an exhaust structure at the gas outlet end of the quartz tube;

[0012] Under the preset deposition conditions, determining the final mapping relationship between the position of the excitation source in the axial direction and the discharge gas pressure parameter of the quartz tube;

[0013] Obtaining the actual position of the excitation source in the axial direction, and querying the mapping relationship according to the actual position to determine the actual discharge gas pressure parameter of the quartz tube;

[0014] Controlling the action of the exhaust structure according to the actual discharge gas pressure parameter of the quartz tube.

[0015] In an embodiment, determining the final mapping relationship between the position of the excitation source in the axial direction and the discharge gas pressure parameter of the quartz tube comprises:

[0016] Using the preparation device to produce test mother rods multiple times, analyzing the test mother rods to establish the mapping relationship between the position of the excitation source in the axial direction and the discharge gas pressure parameter of the quartz tube, and continuously adjusting the mapping relationship between the position of the excitation source in the axial direction and the discharge gas pressure parameter of the quartz tube;

[0017] When the test mother rod meets the qualified condition, determining that the current mapping relationship corresponding to the test mother rod is the final mapping relationship.

[0018] In an embodiment, the multiple times of using the preparation device to produce test mother rods, analyzing the test mother rods to establish the mapping relationship between the position of the excitation source in the axial direction and the discharge gas pressure parameter of the quartz tube, and continuously adjusting the mapping relationship between the position of the excitation source in the axial direction and the discharge gas pressure parameter of the quartz tube comprise:

[0019] Using the preparation device to produce an initial test mother rod under initial conditions;

[0020] analyzing the initial test preform to establish an initial mapping relationship between the position of the excitation source in the axial direction and the discharge gas pressure parameter of the quartz tube;

[0021] making a process test preform using the preparation device according to the initial mapping relationship;

[0022] analyzing the process test preform to determine a process mapping relationship between the position of the excitation source in the axial direction and the discharge gas pressure parameter of the quartz tube;

[0023] repeating the making of the process test preform using the preparation device according to the process mapping relationship of the previous time until the process test preform meets the qualified condition.

[0024] In an embodiment, after the test preform meets the qualified condition and the current mapping relationship corresponding to the test preform is determined as the final mapping relationship, the method further comprises:

[0025] drawing the test preform that meets the qualified condition to form an optical fiber;

[0026] analyzing the cross-sectional parameter of the optical fiber, and obtaining the position of the cross-sectional parameter of the optical fiber on the preform according to the position of the optical fiber and the total length of the drawing of the test preform;

[0027] correcting the final mapping relationship between the position of the excitation source in the axial direction and the discharge gas pressure parameter of the quartz tube according to the cross-sectional parameter of the optical fiber.

[0028] In an embodiment, the making of the test preform using the preparation device and the analyzing of the test preform to establish the mapping relationship between the position of the excitation source in the axial direction and the discharge gas pressure parameter of the quartz tube comprises:

[0029] making the test preform using the preparation device;

[0030] cutting the test preform according to a preset interval to obtain different cut sections;

[0031] analyzing the cross-sectional parameter of each cut section;

[0032] dividing the test preform into a plurality of sub-zones along the axial direction according to the plurality of cross-sectional parameters;

[0033] determining the change value of the discharge gas pressure parameter on each sub-zone according to the plurality of cross-sectional parameters on each sub-zone;

[0034] establishing the mapping relationship between the position of the excitation source in the axial direction and the discharge gas pressure parameter of the quartz tube according to the change value of the discharge gas pressure parameter and the position distribution of the plurality of sub-zones in the axial direction.

[0035] In one embodiment, the preset interval is D, and D≦20mm.

[0036] In one embodiment, the number of the plurality of sub-zones is a positive integer, and is greater than or equal to 3; and / or,

[0037] The total length of the quartz tube for depositing the test mother rod is Lt, the plurality of sub-zones include end sub-zones near the feed end and the discharge end of the test mother rod, the length of the end sub-zones is L1, and 0.05Lt≦L1≦0.3Lt; and / or,

[0038] The total length of the quartz tube for depositing the test mother rod is Lt, and Lt≧500mm.

[0039] In one embodiment, the discharge gas pressure parameter of the quartz tube is between 8mbar and 25mbar.

[0040] In one embodiment, the total fluctuation range of the discharge gas pressure parameter of the quartz tube in each of the sub-zones is within 30%.

[0041] In one embodiment, the total length of the quartz tube for depositing the test mother rod is Lt;

[0042] The axial variation parameter of the discharge end pressure of the quartz tube of at least one of the plurality of sub-zones is kept constant, the length of the sub-zone is L2, and L2≧0.2Lt.

[0043] In one embodiment, the discharge gas pressure parameter of the quartz tube is continuously graded in each of the sub-zones along with the axial displacement of the microwave resonant cavity or the flame torch in the preparation device.

[0044] In one embodiment, the profile parameter includes at least one of the relative refractive index difference, the diameter, and the distribution index a of each layer of the test mother rod.

[0045] The technical scheme of the present application can regard the positions corresponding to each profile parameter as the action positions of the excitation source, and then obtain the mapping relationship between the position of the excitation source in the axial direction and the discharge gas pressure parameter of the quartz tube. Through multiple test mother rod tests, the mapping relationship between the excitation source position and the discharge end pressure parameter under the current deposition condition is optimized, and the final mapping relationship is used as the control parameter for actual production. This method can improve the consistency of the axial parameters of the core rod after production, especially in the traditional preparation parameters, the consistency of the axial parameters of the core rod at both ends is poor, and the length of the rod at both ends accounts for a large part of the total length. The production method in the present application can prepare a core rod with an ideal profile in a long axial region, especially with a significantly reduced change slope at both ends, which improves the effective rod length and the output ratio of qualified optical fibers, and has good practical application value. BRIEF DESCRIPTION OF DRAWINGS

[0046] In order to more clearly illustrate the technical scheme in the embodiments or related art, the drawings needed in the embodiment or related art description will be briefly introduced. Obviously, the drawings in the following description are only some embodiments of the present application, and other drawings can be obtained by those skilled in the art without creative labor.

[0047] FIG. 1 is a process flow diagram of the preparation method of the optical fiber preform provided by the present application;

[0048] FIG. 2 is a specific process flow diagram of “determining the final mapping relationship between the position of the excitation source in the axial direction and the discharge gas pressure parameter of the quartz tube” in FIG. 1;

[0049] FIG. 3 is a specific process flow diagram of the part of the process disclosed in FIG. 2;

[0050] FIG. 4 is a part of the process flow diagram after “when the test mother rod meets the qualified condition, determining that the current mapping relationship corresponding to the test mother rod is the final mapping relationship” in FIG. 2;

[0051] FIG. 5 is a specific flowchart of “using the preparation equipment to make a test mother rod, analyzing the test mother rod, and establishing the mapping relationship between the position of the excitation source in the axial direction and the discharge gas pressure parameter of the quartz tube” in FIG. 2;

[0052] FIG. 6 is a structure diagram of the preparation equipment applied to the preparation method of the optical fiber preform in FIG. 1;

[0053] Fig. 7 is a diagram showing the relationship between the cross-sectional parameters of the mother rod and the pressure at the discharge end, corresponding to the second embodiment of the method for preparing the optical fiber preform rod in tube method shown in Fig. 1;

[0054] Fig. 8 is a diagram showing the relationship between the effective rod length of the mother rod and the total length of the mother rod;

[0055] Fig. 9 is a diagram showing the relationship between the cross-sectional parameters of the mother rod and the pressure at the discharge end, corresponding to the first embodiment of the method for preparing the optical fiber preform rod in tube method shown in Fig. 1;

[0056] Fig. 10 is a diagram showing the relationship between the change of the pressure in the sub-zone and the change of Δ0, corresponding to the first embodiment of the method for preparing the optical fiber preform rod in tube method shown in Fig. 1;

[0057] Fig. 11 is a diagram showing the influence of the fluctuation of the pressure at the discharge end on the deposition rate, corresponding to the first embodiment of the method for preparing the optical fiber preform rod in tube method shown in Fig. 1;

[0058] Fig. 12 is a diagram showing the relationship between the cross-sectional parameters of the mother rod and the pressure at the discharge end, corresponding to the third embodiment of the method for preparing the optical fiber preform rod in tube method shown in Fig. 1.

[0059] BRIEF DESCRIPTION OF THE DRAWINGS

[0060] The objectives, features and advantages of the present application will be further understood from the following detailed description in conjunction with the appended drawings. DETAILED DESCRIPTION

[0061] The technical solutions in the embodiments of the present application will be clearly and completely described with reference to the drawings in the embodiments of the present application. Obviously, the described embodiments are only some of the embodiments of the present application, but not all the embodiments of the present application. Based on the embodiments in the present application, all other embodiments obtained by those skilled in the art without creative work fall within the scope of protection of the present application.

[0062] It should be noted that if the present application involves directional indications (such as up, down, left, right, front, back, etc.), the directional indications are only used to explain the relative position relationship, movement condition, etc. between the components in a certain posture, and if the certain posture changes, the directional indications will also change accordingly.

[0063] In addition, if the description of "first", "second" and the like is involved in the embodiments of the present application, the description of "first", "second" and the like is only for the purpose of description, and cannot be understood as indicating or implying the relative importance of the indicated technical features or implicitly indicating the number of the indicated technical features. Therefore, the features limited by "first", "second" can be explicitly or implicitly included at least one of the features. In addition, if "and / or" or "and / or" appears throughout the text, it means that the three parallel schemes are included, for example, "A and / or B" includes A scheme, or B scheme, or A and B scheme. In addition, the technical solutions of each embodiment can be combined with each other, but it must be based on the realization of the ordinary skilled in the art, when the combination of technical solutions appears contradictory or unachievable, it should be considered that the combination of technical solutions does not exist, nor in the protection scope claimed by the present application.

[0064] The production of optical fiber preform master rod can use PCVD (Plasma Chemical Vapor Deposition) or MCVD (Modified Chemical Vapor Deposition) of in-tube method or VAD (Vertical Axial Deposition) and OVD (Outside Vapor Deposition) process of out-tube method.

[0065] Among them, the in-tube method passes certain ways into high-purity reactants such as SiCl4, O2, GeCl4, etc. in high-purity quartz tube 6, and uses microwave source resonant cavity or flame torch to excite chemical reaction and vapor deposition to form quartz glass deposition layer. The reaction formula of optical fiber master rod preparation is as follows:

[0066] SiCl4+O2=SiO2+2Cl2

[0067] GeCl4+O2=GeO2+2Cl2

[0068] In the process of preparing master rod by vapor deposition method, the refractive index distribution of optical fiber is adjusted by doping dopants (such as Ge, P, F, B, Al, Ti, Zr, etc.) in SiO2. The quartz tube 6 after deposition is prepared into a solid master rod by high temperature furnace melting shrinkage. Then, the master rod is combined with its matching sleeve to form an optical fiber preform rod after etching, cleaning and drying. The preform rod is drawn into an optical fiber by a drawing equipment.

[0069] The axial parameter fluctuation of the optical fiber preform directly affects the performance consistency of the optical fiber, and therefore, it is crucial to improve the axial parameter uniformity of the preform. In the process of preparing the mother rod by the in-tube method, high-purity reactants are subjected to chemical reaction and vapor deposition in the quartz tube 6. Due to the flow of the mixed gas in the tube from the feeding end to the discharging end, the composition, temperature, pressure, density and energy distribution at each point in the tube are uneven, resulting in a certain deviation of the refractive index profile of the mother rod in the axial direction, which further affects the axial parameter consistency of the preform and increases the waste fiber rate. The present application proposes a preparation method of an optical fiber preform by the in-tube method to solve the above problems.

[0070] The present application proposes a preparation method of an optical fiber preform by the in-tube method to solve the above problems.

[0071] For the convenience of introducing the content of the present application, some terms are defined:

[0072] Mass Flow Controller (MFC): a mass flow controller, which is a gas flow stabilizing device for automatically controlling the flow of reactants (such as GeCl4, C2F6, etc.) for mother rod preparation.

[0073] Profile parameters: the profile refractive index of the optical fiber preform can be divided into multiple layers, the radius of each layer is the distance from the outer edge to the center, and the relative refractive index of each layer is the refractive index relative to the cladding, which is usually the refractive index relative to pure silica. The geometric parameters of the profile include the diameter, roundness and concentricity of each layer, and the optical parameters include the relative refractive index and the distribution index.

[0074] The core refractive index profile of the graded-index optical fiber needs to be designed as a refractive index distribution that continuously decreases from the center to the edge of the core, which is usually referred to as "α profile". That is, the refractive index distribution satisfies the following power exponential function:

[0075] Wherein, n1: represents the refractive index of the optical fiber axis;

[0076] r: represents the distance from the optical fiber axis;

[0077] a: represents the radius of the optical fiber core;

[0078] α: represents the distribution index;

[0079] Δ0: represents the refractive index of the core center relative to the cladding.

[0080] Relative refractive index, i.e. Δi:

[0081] Wherein, ni: represents the refractive index at a distance of i positions from the core center;

[0082] n0: represents the minimum refractive index of the optical fiber core, which is usually the refractive index of the cladding of the optical fiber.

[0083] Preform: a preform containing a core and part of a cladding.

[0084] The total length of the preform is the distance between the inflection points at both ends of the reciprocating motion.

[0085] The effective length of the preform is the length in which each cross-sectional parameter meets the production control range requirements.

[0086] Mother rod: a reference preform used to test the axial distribution of cross-sectional parameters.

[0087] As shown in FIG. 1, a schematic diagram of a mother rod PCVD production device and reactant supply is shown. The reaction gas enters the preparation device 100 (which is a constant temperature control device) through a control valve, and a certain gas reactant (such as GeCl4) is smoothly controlled by a mass flow controller, and the remaining reactants are controlled by respective mass flow controllers. The gas reactants are mixed in the pipeline and further heated by the feeding end rotating chuck assembly 4 device and the extension pipe into the heat preservation furnace 3 and the high-purity quartz tube 6, and then reacted in the reciprocating high-speed running excitation source 2 (resonant cavity / flame torch) to generate a glass deposition layer on the inner wall of the high-purity quartz tube 6. The reaction tail gas is extracted from the discharge end extension pipe and the discharge end rotating chuck assembly 4 device, and the mother rod after deposition is prepared into an optical fiber preform after fusion shrinking. The MCVD (modified chemical vapor deposition) production device replaces the high-frequency resonant cavity in the figure with a flame torch, and does not require a heat preservation furnace 3.

[0088] The application provides a preparation method of an in-pipe optical fiber preform, and a method for improving the axial consistency of the preform, which can greatly improve the effective length of the mother rod and the output ratio of qualified optical fibers.

[0089] In actual production, the axial distribution of the parameters of the mother rod is affected by high-frequency devices, motion systems, high-temperature distribution, etc., and has certain axial fluctuation. Due to the back-and-forth movement of the resonant cavity or the flame torch, there are acceleration and deceleration processes and movement speed fluctuations at both ends, the axial temperature distribution curve changes in the deposition heat preservation furnace 3, the feeding end reaction gas is heated, the parameters of the region close to the feeding end (IS) of the mother rod deviate from the ideal situation, and the fluctuations are intense. On the other hand, the gas flow fluctuation caused by the exhaust at the discharge end, the gradual accumulation of dust in the pipeline at the discharge end during the deposition process, etc., the parameter fluctuations of the mother rod close to the discharge end (OS) region of the mother rod are more significant.

[0090] The inventor found that when the excitation source 2 (resonant cavity / flame torch) moves along the axial position, the pressure at the discharge end can affect the flow and distribution of the gas, the shape of the plasma, etc., directly affecting the reaction efficiency of the mixed gas, thereby affecting the refractive index profile of the mother rod. By precisely adjusting the pressure at the discharge end, the axial precise control of the diameter, refractive index or distribution index a of each layer of the profile can be realized, and the axial consistency of the mother rod can be improved.

[0091] The influence of the outlet pressure on the profile parameters is affected by the deposition conditions, including the opening of the flame torch, the power of the resonant cavity, the movement speed of the resonant cavity / flame torch, the total flow and component ratio of the mixed gas in the tube, the outlet pressure, the total deposition time, etc. For example, under a certain deposition condition, the distribution index a increases by 0.008 when the outlet pressure increases by 1 mbar. Under another certain deposition condition, the relative refractive index increases by 3% when the outlet pressure increases by 2 mbar, and the diameter relative to the initial condition decreases by 0.7%.

[0092] Therefore, in the present solution, based on the above actual findings, the mapping relationship between the position of the excitation source 2 in the axial direction of the quartz tube 6 and the outlet pressure under a certain production condition is discussed to determine the production parameters of the outlet pressure under this condition. In actual application, if the mapping relationship between the excitation source 2 and the outlet pressure under different conditions is determined, the mapping relationship parameters corresponding to the current production condition can be directly used for control in production to obtain a mother rod with good axial consistency under the current production condition.

[0093] The present application provides a method for preparing an optical fiber preform in a tube, comprising the following steps:

[0094] A preparation device 100 is provided, wherein the preparation device 100 comprises a rotatingly installed quartz tube 6, an excitation source 2 for chemically depositing excitation reactants in the quartz tube 6, and a pumping structure 8 at the gas outlet end of the quartz tube 6. The above structures are the main structures for preparing a core rod, and are not all structures. The auxiliary structures further comprise a rotating chuck assembly 4, which comprises an inlet end rotating chuck assembly 41 and an outlet end chuck assembly 42. The quartz tube 6 is installed between the two chuck assemblies. The bottom of the excitation source 2 is also provided with a corresponding movement structure 7 for moving the excitation source 2 along the axial direction of the quartz tube 6. The pumping structure 8 is used for discharging reaction tail gas and controlling the pressure at the outlet end of the quartz tube. A heat preservation furnace 5 is arranged outside the excitation source 2 and the quartz tube 6 to reduce heat loss and improve reaction effect. The above structures are all conventional structures. The preparation device 100 is a vapor deposition device used in the mother rod production process, which is an existing device. Therefore, the specific structure of the production device will not be explained in detail here. The contents in the following description are also explained and supplemented based on the main reaction structure.

[0095] Under the preset deposition condition, a final mapping relationship between the position of the excitation source 2 in the axial direction and the discharge gas pressure parameter of the quartz tube 6 is determined; the axial variation parameter of the discharge end pressure needs to be iteratively optimized through multiple mother rods, so that the corresponding relationship between the discharge end pressure and the position of the excitation source under a specific deposition condition can be obtained, to obtain stable production data under the current deposition condition. Therefore, under the preset deposition condition, for example, under specific deposition gas, specific gas supply parameters and specific working parameters of the excitation source, the preparation equipment 100 needs to be used multiple times to manufacture test mother rods, the test mother rods are analyzed, the mapping relationship between the position of the excitation source 2 in the axial direction and the discharge gas pressure parameter of the quartz tube 6 is established, and the mapping relationship between the position of the excitation source 2 in the axial direction and the discharge gas pressure parameter of the quartz tube 6 is continuously adjusted. When the test mother rod meets the qualified condition, the current mapping relationship corresponding to the test mother rod is determined as the final mapping relationship.

[0096] In the above process, under certain deposition conditions, in order to ensure the accuracy of the mapping relationship between the position of the excitation source 2 in the axial direction and the discharge gas pressure parameter of the quartz tube 6, we generally need to continuously correct the intermediate mapping relationship obtained by combining the test parameters of multiple mother rods produced under the current deposition condition. Therefore, the "the preparation equipment 100 is used multiple times to manufacture test mother rods, the test mother rods are analyzed, the mapping relationship between the position of the excitation source 2 in the axial direction and the discharge gas pressure parameter of the quartz tube 6 is established, and the mapping relationship between the position of the excitation source 2 in the axial direction and the discharge gas pressure parameter of the quartz tube 6 is continuously adjusted" specifically includes the following steps: using the preparation equipment 100 to manufacture an initial test mother rod under initial conditions; analyzing the initial test mother rod to establish an initial mapping relationship between the position of the excitation source 2 in the axial direction and the discharge gas pressure parameter of the quartz tube 6; using the preparation equipment 100 to manufacture a process test mother rod under the initial mapping relationship; analyzing the process test mother rod to determine a process mapping relationship between the position of the excitation source 2 in the axial direction and the discharge gas pressure parameter of the quartz tube 6.

[0097] For the convenience of testing process and more intuitive reflection of the mapping relationship between the axial direction of the parent rod and the discharge end pressure, the test parent rod is usually divided into sub-zones along the axial direction of the test parent rod during the testing of the test parent rod, and the mapping relationship between each sub-zone and the discharge end pressure is established. Specifically, the following steps are included: a test parent rod is prepared by using a preparation device 100; the test parent rod is cut according to a preset interval to obtain different cut sections, wherein the preset interval is generally less than or equal to 20 mm, and less than or equal to 10 mm is preferred; the section parameters of each cut section are analyzed and obtained; the test parent rod is divided into a plurality of sub-zones along the axial direction according to a plurality of section parameters; the discharge gas pressure parameter change value of each sub-zone is determined according to a plurality of section parameters on each sub-zone; and the mapping relationship between the axial position of the excitation source 2 and the discharge gas pressure parameter of the quartz tube 6 is established according to the discharge gas pressure parameter change value and the axial position distribution of the plurality of sub-zones.

[0098] The above testing method for a single parent rod is applied to a plurality of test parent rods, so that the mapping relationship between the axial position of the excitation source 2 and the discharge gas pressure parameter of the quartz tube 6 is corrected. In short, after the single test parent rod is divided into sub-zones, the mapping relationship between the axial position of the excitation source 2 and the discharge gas pressure parameter of the quartz tube 6 corresponding to the current test parent rod is obtained by the above method, and then the next test parent rod is produced by using the current mapping relationship parameter, and the mapping relationship data corresponding to the current test parent rod is obtained again by the above analysis method. The mapping relationship data of the previous parent rod is corrected by using the current mapping relationship data. In this way, the previous production data is continuously corrected, and when the relative refractive index difference, diameter and distribution index α of each layer of the produced test parent rod meet the production requirements, the mapping relationship between the axial position of the excitation source 2 and the discharge gas pressure parameter of the quartz tube 6 produced by the current test parent rod is used as the standard production data under the current deposition condition.

[0099] In actual production process, the discharge end pressure has a greater impact on the distribution index α, followed by the relative refractive index, and then the diameter. For graded-index optical fibers, especially multimode optical fibers, the axial zoning of the discharge end pressure is mainly based on the distribution index α. For step-index profile, the axial zoning of the discharge end pressure is mainly based on the relative refractive index.

[0100] The pressure at the outlet end is between 5mbar and 30mbar. The pressure at the outlet end is high at present, but too high will result in too low deposition efficiency and dust accumulation leading to pipe blockage. By setting the corresponding outlet end pressure when the excitation source 2 moves to each end point, the pressure in the sub-zone changes continuously. The greater the axial variation slope of the profile parameter in the sub-zone, the greater the axial variation slope of the outlet end pressure. When the profile parameter in the sub-zone changes little, only a small perturbation of <0.5%, the outlet end pressure can be kept stable, and the total fluctuation amplitude of the outlet gas pressure parameter of the quartz tube 6 in each sub-zone is generally controlled within 30% during production.

[0101] The parameters of the two end sub-zones fluctuate greatly, and the corresponding outlet end pressure adjustment range is also larger, so enough length is needed to avoid sharp changes in the outlet end pressure, and the length of the mother rod is generally 500mm to 2500mm. Therefore, the length of the two end sub-zones is 0.05 to 0.3 times the length of the mother rod.

[0102] Generally speaking, due to reasons such as movement turn-back and feeding and discharging, the parameters of the two ends fluctuate greatly, and the parameter change trend of the middle region differs from that of the actual equipment and process parameters. Therefore, the mother rod can be divided into three regions in the axial direction for doping compensation. In the case of significant axial fluctuation of some intermediate parameters, further subdivision can be made.

[0103] After determining the mapping relationship between the final position of the excitation source 2 in the axial direction and the outlet gas pressure parameter of the quartz tube 6, in the actual production process, the actual position of the excitation source 2 in the axial direction can be obtained according to the corresponding mapping relationship, and the actual outlet gas pressure parameter of the quartz tube 6 can be determined by querying the mapping relationship according to the actual position.

[0104] Thus, during production, the action of the pumping structure 8 can be controlled according to the actual outlet gas pressure parameter of the quartz tube 6. The position of the excitation source 2 during production is corresponded to the actual pressure at the outlet end, thereby improving the consistency of the axial parameters of the mother rod after production.

[0105] It is additionally needed to be supplemented that the mapping relationship between the axial position of the excitation source 2 and the discharge gas pressure parameter of the quartz tube 6 is mainly adjusted and referred to the test parameters of the test mother rod, and after the test parameters of the test mother rod are qualified, the fiber parameters after drawing are used as auxiliary adjustment reference, which specifically includes the following steps: drawing the test mother rod meeting the qualified condition to form an optical fiber; analyzing the cross-sectional parameters of the optical fiber, and obtaining the position of the cross-sectional parameters of the optical fiber on the test mother rod according to the position of the optical fiber and the total length of the test mother rod, for example, the cross-sectional parameters of the optical fiber after drawing, the position of the optical fiber and the total length of the test mother rod can be converted into the axial position of the cross-sectional parameters on the test mother rod. For example, if the total length of the test mother rod is 200 km, the test optical fiber is at the 100th km, that is, the measured cross-sectional parameters are at the 50% of the axial length of the test mother rod; and the final mapping relationship between the axial position of the excitation source 2 and the discharge gas pressure parameter of the quartz tube 6 is corrected through the cross-sectional parameters of the optical fiber.

[0106] In the above process, the axial variation parameter of the discharge end pressure needs to be iteratively optimized through multiple test mother rods, and the response relationship of the discharge end pressure to the cross-sectional parameters under specific deposition conditions can be obtained. Under this condition, the axial variation of the cross-sectional parameters of the test mother rod can be fitted into a smooth curve, and the corresponding axial variation curve of the discharge end pressure can be directly calculated according to the above response relationship. Although it is good to continuously change the discharge end pressure along the axial direction to continuously compensate, there are inevitable errors in parameter control in actual production, and the control mode of keeping the discharge end pressure unchanged in a certain region is simpler and more stable. Therefore, at least one sub-region of the discharge end pressure keeps unchanged in the partition, and the length of the sub-region is L2, and L2≧0.2Lt, where Lt is the total length of the test mother rod.

[0107] Example One:

[0108] For graded-index multimode optical fiber, bandwidth is the most important, so the core layer of a is the main partition basis. Delta affects NA (numerical aperture of the fiber), the requirement range of NA is large, and then delta is considered as a partition index. Finally, the core diameter is considered as a partition basis. Referring to FIGS. 8 to 11, a 1580mm core rod is selected as a mother rod for testing. Specifically, a test point is taken on the test mother rod at an interval of 20mm, and then the cross section at the test point is tested by a cross section testing device to measure the cross section parameters (including the relative refractive index of each layer, the diameter, and if it is a graded refractive index, the distribution index a) of each cross section. According to the cross section parameter changes of the test mother rod, the axial position of the test mother rod in the device is divided into four sub-zones. Specifically, the lengths of the two sub-zones corresponding to the feeding end and the discharging end are respectively set to 240mm and 440mm, and the lengths of the two middle sub-zones are 260mm, 640mm from the feeding end to the discharging end. According to the test parameters at the corresponding positions, the pressure values corresponding to the pumping structure 8 at the excitation source 2 are adjusted between 10mbar and 25mbar in the plurality of sub-zones, so as to form a mapping relationship between the position of the excitation source 2 in the axial direction and the discharge gas pressure parameter of the quartz tube 6. Then, the above mapping relationship is used as the production control parameter under the current deposition condition. Then, the above control parameter is used for production. Specifically, the quartz tube 6 is fixed on the rotating clamp assembly 4 of the preparation device 100, the reaction gas is introduced into the quartz tube 6 through the flow control device 5, and the excitation source 2 (resonant cavity / flame torch) is started to work and reciprocate along the axial direction of the quartz tube 6 (during this process, the working parameters of the excitation source 2 are constant), so as to promote the reaction of the reaction gas and the deposition on the inner wall of the quartz tube 6, and the pressure value of the pumping structure 8 corresponding to the discharge end of the quartz tube 6 is recorded when the excitation source 2 is at different positions in the axial direction of the quartz tube 6. Through the above process, another middle mother rod is produced. The current mother rod is tested again, and the test parameters are referred to the above content. The related cross section test parameters corresponding to the current mother rod can be obtained. Specifically, as shown in FIG. 9, the axial position of the mother rod in the device can be divided into four regions according to the parameter change. The sub-zone 1 close to the feeding port and the sub-zone close to the discharging end are affected by factors such as temperature change, pressure fluctuation, mechanical vibration, speed fluctuation, etc., and show a large change slope and parameter fluctuation. The middle state of the mother rod is stable, and the fluctuation amplitude can be controlled within ±1%, and more preferably within ±0.5%. Under the condition that part of the process conditions are appropriate, as shown in FIG. 7, the parameter change slope and fluctuation of the sub-zone 2 are small, and at this time, the sub-zone 2 can be combined with the middle sub-zone, and sometimes only three sub-zones are needed.The constant discharge end pressure is used in the comparative example, and the discharge end pressure is adjusted according to the axial position in the embodiment, so that the compensation and control of the refractive index deviation can be realized, the deviation of the cross-sectional parameters at both ends is significantly reduced, the core rod close to the ideal cross section in a longer axial region is prepared, and the change slope at both ends is significantly reduced, the effective rod length is increased, and the output ratio of qualified optical fibers is increased.

[0109] Then, the pressure change of the discharge end in the corresponding subzone is adjusted according to the obtained corresponding test parameters, the above test process is repeated, the test parameter change and the pressure change relationship curve between the discharge end in the corresponding subzone are established, and the optimal final mapping relationship between the excitation source 2 position and the discharge end pressure of the current deposition condition is continuously optimized. The test mother rod qualified in the final test is drawn to form an optical fiber, and the cross-sectional parameters of the optical fiber after drawing of the test mother rod, the position of the optical fiber and the total length of the mother rod after drawing can be converted into the axial position of the cross-sectional parameters of the core rod. According to the output ratio of qualified optical fibers, the test results of the optical fiber and the position thereof, the axial change trend of the discharge end pressure is further adjusted.

[0110] The final mapping relationship parameters between the excitation source 2 position and the discharge end pressure under the current deposition condition are obtained, and the relationship between the test parameters of the core rod produced and the discharge end pressure is shown in FIG. 9, wherein the α of the subzones 1, 2 and 4 is significantly increased, and the change slope is obviously reduced. This is beneficial to increase the output ratio of high-end multimode optical fibers.

[0111] In the embodiment, the △0 deviation amount of the two intermediate subzones can be controlled to be less than 0.7. In the specific production process, the final mapping relationship is used as a control parameter, and the corresponding current deposition condition is used for production to improve the axial parameter quality of the mother rod. In addition, according to different requirements, the deposition condition can be changed, and the corresponding mapping relationship parameters are obtained in the above manner, so that another corresponding mapping relationship can be directly used for production control under one production condition to obtain a core rod finally meeting the production requirements.

[0112] In the specific cross-sectional test parameters, the change of the α parameter is the main influence parameter of the actual partition, and the specific reasons can be explained with reference to 8. It can be seen that the total length of the mother rod is the distance between the inflection points of the reciprocating motion, the effective rod length is the length of each cross-sectional parameter meeting the production control range requirement, and the total length is definitely greater than the effective rod length.

[0113] In addition, since the excitation source itself has a certain length, and the deposition is not uniform, the deposition amount on both sides is less, so after repeated deposition, the two ends will form a horn, so that the length of the rod at both ends of the core rod cannot meet the geometric index. Therefore, although the total length of the deposition is longer, the actual length of the qualified core rod obtained is actually not long. The horn at the discharge end of the quartz tube 6 after deposition is long. The part of the horn will be cut or fused after melting.

[0114] For the graded-index multimode optical fiber, bandwidth is the most important, so the core layer α is the main partition basis. Δ affects NA (numerical aperture of the optical fiber), and the required range of NA is large, and then Δ is considered as the partition index. Finally, the core diameter is considered as the partition basis.

[0115] On the other hand, as shown in Figure 10, the discharge end pressure of sub-zone 1 and sub-zone 2 is reduced, and Δ0 is also reduced synchronously, and the Δ0 distribution of sub-zone 2 and sub-zone 3 is more stable. The pressure of sub-zone 4 is increased, and Δ0 is increased.

[0116] In fact, as shown in Figure 11, under the above deposition conditions, the fluctuation of the pressure has little effect on the deposition rate, so there is no obvious change in the core diameter before and after the improvement.

[0117] Example two:

[0118] For the step refractive index rod, such as single mode fiber, the control of refractive index is more important, and then the core diameter is considered as the partition basis. Referring to the content of FIG. 7, a 1200mm mother rod is selected for testing. Specifically, a test point is taken on the test mother rod at an interval of 10mm, and then the cross section at the test point is tested by a cross section testing device to measure the cross section parameters (including the relative refractive index of each layer, the diameter, and if it is a graded refractive index, the distribution index a) of each cross section. According to the cross section parameter change of the test mother rod, the axial position of the test mother rod in the device is divided into four sub-zones. Specifically, the lengths of the two sub-zones corresponding to the feeding end and the discharging end are respectively set to 210mm and 230mm, the length of one of the intermediate sub-zones close to the feeding end is set to 430mm, and the length of the other intermediate sub-zone is 330mm. According to the test parameters at the corresponding positions, the pressure values corresponding to the pumping structure 8 at the excitation source 2 in the plurality of sub-zones are adjusted between 8mbar and 23mbar to form a mapping relationship between the position of the excitation source 2 in the axial direction and the discharge gas pressure parameter of the quartz tube 6, and then the above mapping relationship is used as the production control parameter under the current deposition condition. Then the above control parameter is used for production. Specifically, the quartz tube 6 is fixed on the rotating chuck assembly 4 of the preparation device 100, the reaction gas is introduced into the quartz tube 6 through the flow control device 5, and the excitation source 2 (resonant cavity / flame torch) is started to work and reciprocates along the axial direction of the quartz tube 6 (during this process, the working parameters of the excitation source 2 are constant), so as to promote the reaction of the reaction gas and the deposition on the inner wall of the quartz tube 6, and the pressure value of the pumping structure 8 corresponding to the discharge end of the quartz tube 6 is recorded when the excitation source 2 is at different positions in the axial direction of the quartz tube 6. Through the above process, another intermediate mother rod is produced. The current mother rod is tested again, the test parameters are referred to the above content, the pressure change of the discharge end in the corresponding sub-zone is adjusted according to the corresponding test parameters obtained, the above test process is repeated, and the relationship curve between the test parameter change of each sub-zone and the pressure change of the discharge end is established. The curve is analyzed to obtain the corresponding Δ0 deviation. The test mother rod that finally passes the test is drawn to form an optical fiber, and the cross section parameters of the optical fiber after the test mother rod is drawn, the position of the optical fiber and the total length of the mother rod after drawing can be converted into the axial position of the cross section parameters on the rod. According to the output proportion of the qualified optical fiber, the test result of the optical fiber and the position thereof, the axial variation trend of the discharge end pressure is further adjusted. The final mapping relationship between the best position of the excitation source 2 and the discharge end pressure corresponding to the current deposition condition is determined. In this embodiment, the Δ0 deviation of the two intermediate sub-zones can be controlled to be 0.6 to 0.8.In a specific production process, the final mapping relationship is used as a control parameter to produce under the corresponding current deposition condition, so as to improve the axial parameter quality of the mother rod. In addition, the deposition condition can be changed according to different requirements, and the corresponding mapping relationship parameter is obtained in the above manner. Therefore, under one production condition, another corresponding mapping relationship can be directly used for production control to obtain a core rod that finally meets the production requirements.

[0119] Example Three

[0120] As shown in FIG. 12, a 900mm mother rod is selected for testing. Specifically, a test point is taken at an interval of 10mm on the test mother rod, and then the profile at the test point is tested by a profile testing device to measure the profile parameters (including the relative refractive index and diameter of each layer, and the distribution index a if it is a graded refractive index) of each profile. According to the profile parameter changes of the test mother rod, the axial position of the test mother rod in the device is divided into five sub-zones. Specifically, the lengths of the two sub-zones corresponding to the feeding end and the discharging end are respectively set to 180mm and 160mm, the length of one of the intermediate sub-zones close to the feeding end is set to 120mm, and the lengths of the other two intermediate sub-zones are 360mm and 80mm. According to the test parameters at the corresponding positions, the pressure values corresponding to the pumping structure 8 at the excitation source 2 in the plurality of sub-zones are adjusted between 9mbar and 20mbar to form a mapping relationship between the position of the excitation source 2 in the axial direction and the discharge pressure parameter of the quartz tube 6, and then the above mapping relationship is used as the production control parameter under the current deposition condition. Then, the production is carried out with the above control parameter. Specifically, the quartz tube 6 is fixed on the rotating chuck 4 of the preparation device 100, the reaction gas is introduced into the quartz tube 6 through the flow control device 5, and the excitation source 2 (resonant cavity / flame torch) is started to work and reciprocate along the axial direction of the quartz tube 6 (in this process, the working parameters of the excitation source 2 are constant), so as to promote the reaction of the reaction gas and the deposition on the inner wall of the quartz tube 6, and the pressure values of the pumping structure 8 corresponding to the discharge end of the quartz tube 6 are recorded when the excitation source 2 is at different positions in the axial direction of the quartz tube 6. Through the above process, another intermediate mother rod is produced. Then, the current mother rod is tested, and the test parameters are referred to the above content. According to the corresponding test parameters obtained, the pressure change of the discharge end in the corresponding sub-zone is adjusted, the above test process is repeated, and the relationship curve between the test parameter change of each sub-zone and the pressure change of the discharge end is established. The curve is analyzed to determine the △0 deviation amount in each sub-zone. The test mother rod that passes the final test is drawn to form an optical fiber, and the profile parameters of the optical fiber after the test mother rod is drawn, the position of the optical fiber and the total length of the mother rod drawn are converted into the profile parameter corresponding to the axial position of the core rod. According to the output proportion of the qualified optical fiber, the test result of the optical fiber and the position thereof, the axial variation trend of the discharge end pressure is further adjusted to determine the final mapping relationship between the optimal position of the excitation source 2 and the discharge end pressure corresponding to the current deposition condition. In this embodiment, the △0 deviation amount of the two intermediate sub-zones can be controlled to be 0.7 to 1.In a specific production process, the final mapping relationship is used as a control parameter to produce under the corresponding current deposition condition, so as to improve the axial parameter quality of the mother bar. In addition, the deposition condition can be changed according to different requirements, and the corresponding mapping relationship parameter is obtained in the above manner, so that under one production condition, another corresponding mapping relationship can be directly used for production control to obtain a final core rod that meets the production requirements.

[0121] The above merely describes exemplary embodiments of the present application, and does not limit the patent scope of the present application. Any equivalent structural transformation made by using the content of the present application specification and drawings, or direct / indirect application in other related technical fields is included in the patent protection scope of the present application.

Claims

1. A method for producing an optical fiber preform by an inside-the-pipe method, wherein, The preparation method of the tube-in-process optical fiber preform includes the following steps: Providing a preparation device, wherein the preparation device includes a rotatingly installed quartz tube, an excitation source for exciting a reactant to perform chemical deposition in the quartz tube, and a pumping structure at an air outlet end of the quartz tube; Determining a final mapping relationship between an axial position of the excitation source and an air outlet pressure parameter of the quartz tube under preset deposition conditions; Obtaining an actual axial position of the excitation source, and querying the mapping relationship according to the actual axial position to determine an actual air outlet pressure parameter of the quartz tube; Controlling the pumping structure to act according to the actual air outlet pressure parameter of the quartz tube.

2. The method of making an optical-fiber preform in a tube according to claim 1, wherein, The final mapping relationship between the axial position of the excitation source and the air outlet pressure parameter of the quartz tube includes: Using the preparation device to produce a test preform multiple times, analyzing the test preform to establish the mapping relationship between the axial position of the excitation source and the air outlet pressure parameter of the quartz tube, and continuously adjusting the mapping relationship between the axial position of the excitation source and the air outlet pressure parameter of the quartz tube; When the test preform meets a qualified condition, determining that a current mapping relationship corresponding to the test preform is a final mapping relationship.

3. The method of making an optical-fiber preform in a tube according to claim 2, wherein, The multiple times of using the preparation device to produce a test preform, analyzing the test preform to establish the mapping relationship between the axial position of the excitation source and the air outlet pressure parameter of the quartz tube, and continuously adjusting the mapping relationship between the axial position of the excitation source and the air outlet pressure parameter of the quartz tube include: Using the preparation device to produce an initial test preform under initial conditions; Analyzing the initial test preform to establish an initial mapping relationship between the axial position of the excitation source and the air outlet pressure parameter of the quartz tube; Using the preparation device to produce a process test preform according to the initial mapping relationship; Analyzing the process test preform to determine a process mapping relationship between the axial position of the excitation source and the air outlet pressure parameter of the quartz tube; Repeating the use of the preparation device to produce a process test preform again according to the process mapping relationship of the previous time until the process test preform meets a qualified condition.

4. The method of making an optical-fiber preform in a tube according to claim 2, wherein, After the determination that the current mapping relationship corresponding to the test preform is the final mapping relationship when the test preform meets the qualified condition, the method further includes: Drawing a fiber from the test preform that meets the qualified condition to form an optical fiber; Analyzing a cross-sectional parameter of the optical fiber, obtaining a position of the cross-sectional parameter of the optical fiber on the preform according to a total length of the drawn optical fiber and a position of the optical fiber on the preform; and Correcting the final mapping relationship between the axial position of the excitation source and the air outlet pressure parameter of the quartz tube according to the cross-sectional parameter of the optical fiber.

5. The method of making an in-fiber optical preform as claimed in claim 2, wherein, The use of the preparation device to produce a test preform, analyzing the test preform to establish the mapping relationship between the axial position of the excitation source and the air outlet pressure parameter of the quartz tube includes: Using the preparation device to produce a test preform; Cross-sectioning the test preform according to a preset interval to obtain different cross-sections; Analyzing cross-sectional parameters of the cross-sections; and According to the profile parameters, the test boule is divided into a plurality of sub-zones along its axis; According to the profile parameters on each of the sub-zones, a change value of the outlet gas pressure parameter on each of the sub-zones is determined; According to the change value of the outlet gas pressure parameter and the position distribution of the sub-zones in the axial direction, a mapping relationship between the position of the excitation source in the axial direction and the outlet gas pressure parameter of the quartz tube is established.

6. The method of making an in-fiber optical preform as claimed in claim 5, wherein, The preset interval is D, and D≦20mm.

7. The method of making an in-fiber optical preform as claimed in claim 5, wherein, The number of the plurality of sub-zones is a positive integer and is greater than or equal to 3; and / or, The total length of the quartz tube for depositing the test boule is Lt, the plurality of sub-zones include end sub-zones close to the inlet end and the outlet end of the test boule, the length of the end sub-zones is L1, and 0.05Lt≦L1≦0.3Lt; and / or, The total length of the quartz tube for depositing the test boule is Lt, and Lt≧500mm.

8. The method of making an in-fiber optical preform as claimed in claim 5, wherein, The outlet gas pressure parameter of the quartz tube is between 8mbar and 25mbar.

9. The method of making an in-fiber optical preform as claimed in claim 5, wherein, The total fluctuation amplitude of the outlet gas pressure parameter of the quartz tube in each of the sub-zones is within 30%.

10. The method of making an optical-fiber preform in a tube according to Claim 5, wherein, The total length of the quartz tube for depositing the test boule is Lt; The axial variation parameter of the outlet end pressure of the quartz tube of at least one of the plurality of sub-zones is kept constant, and the length of the sub-zone is L2, L2≧0.2Lt.

11. The method of making an in-fiber optical preform as claimed in claim 5, wherein, The outlet gas pressure parameter of the quartz tube is continuously and gradually changed in each of the sub-zones with the axial displacement of the microwave resonant cavity or the flame torch in the preparation device.

12. The method of making an intra-fiber optical preform as claimed in claim 1, wherein, The profile parameters include at least one of the relative refractive index difference, the diameter and the distribution index a of each layer of the test boule.

Images