Optical fiber preform, preparation method of optical fiber and high-bandwidth multimode optical fiber

Abstract

The invention relates to an optical fiber preform rod, a preparation method of an optical fiber and a high-bandwidth multimode optical fiber, a diffusion layer is deposited on a core layer in a deposition process to obtain an initial rod body, and then the initial rod body is directly fused and shrunk to obtain a solid preform rod; the viscosity of the rising layer of the diffusion layer is linearly reduced, and the refractive index of the rising layer is linearly increased; the viscosity of the descending layer of the diffusion layer is linearly increased, and the refractive index of the descending layer is linearly decreased; during melting shrinkage, the descending layer with the viscosity design serves as a passivation layer, and volatilization of germanium is reduced; the rising layer migrates high-concentration germanium to the falling layer under the action of thermal diffusion, and the diffusion layer is converted into an extremely narrow glass layer with a constant refractive index, so that the center distortion of a refractive index profile is avoided; a corrosion process is not needed in the melting shrinkage process, so that the cost and working hours are saved, and the production efficiency is improved; in addition, more than 80% of optical fibers manufactured by adopting the solid preform have no obvious refractive index profile center distortion, and the bandwidth performance of multimode optical fibers is improved.

Description

Technical Field

[0001] The present application relates to the field of optical fiber manufacturing technology, and particularly relates to an optical fiber preform, a method for preparing an optical fiber, and a high-bandwidth multimode optical fiber. Background Art

[0002] The optical fiber preform required for producing a graded-index optical fiber can be obtained by introducing high-purity reactants such as SiCl4, O2, GeCl4, etc. into or outside a high-purity quartz glass tube through a certain route, and using a microwave source resonator or a flame torch to excite chemical reactions and chemical vapor deposition to form a transparent quartz glass deposition layer; then, by melting and shrinking in a high-temperature furnace, the deposited quartz glass tube is prepared into a solid optical fiber preform.

[0003] During the melting and shrinking process, the temperature of the preform is between 1600 and 2200 °C, and the substance GeO2 (germanium dioxide) that makes up the preform will volatilize. The volatilization will cause the refractive index to decrease, resulting in a depression in the center of the refractive index profile of the preform. Generally, in order to overcome the depression in the center of the refractive index profile, the "etching process" is generally used to solve it. The etching process means that during the melting and shrinking process, fluorine is introduced into the preform. Under the action of high temperature, fluorine can etch SiO2 and GeO2, thereby realizing the correction of the refractive index profile. However, there are the following problems:

[0004] In actual production, if the etching amount is insufficient, a lower limit will be formed in the rod pattern; if the etching is excessive, a spike will be formed in the rod pattern, and even the refractive index of the central profile of the preform prepared by the etching process still has distortion. Summary of the Invention

[0005] The embodiments of the present application provide an optical fiber preform, a method for preparing an optical fiber, and a high-bandwidth multimode optical fiber to solve the problem in the related art that during the melting and shrinking process, the process of introducing fluorine to control the etching amount to reduce the depression in the center of the refractive index profile requires precise control of the etching amount, resulting in high costs.

[0006] In a first aspect, a method for preparing an optical fiber preform is provided, which includes:

[0007] Depositing a diffusion layer to fill the internal space of the hollow core layer and obtaining an initial rod;

[0008] Melting and shrinking the initial rod to obtain a solid preform;

[0009] Wherein, both the initial rod and the solid preform include a core layer and a diffusion layer; the diffusion layer includes a descending layer and an ascending layer outside it;

[0010] In the initial rod, along the radial direction from outside to inside, the viscosity of the rising layer decreases linearly and the refractive index increases linearly, the viscosity of the falling layer increases linearly and the refractive index decreases linearly, and the refractive index of the core layer increases according to a preset curve;

[0011] In the solid preform rod, along the radial direction from outside to inside, the refractive indices of the core layer and the diffusion layer both increase according to the same preset curve.

[0012] In some embodiments, the deposition area of the rising layer is 0.33% to 3.33% of the area of the core layer;

[0013] The deposition area of the falling layer is 0.15% to 0.90% of the area of the core layer.

[0014] In some embodiments, the maximum refractive index of the core layer is n1, and n1 ranges from 0.85% to 1.1%;

[0015] Along the radial direction from outside to inside, the refractive index of the starting point of the rising layer of the diffusion layer is n1, and the refractive index of the ending point is 1.06 to 1.5 times n1;

[0016] Along the radial direction from outside to inside, the starting point of the falling layer is the ending point of the rising layer, and the refractive index of the ending point of the falling layer is 0.2 to 0.8 times n1.

[0017] In some embodiments, the initial rod sequentially includes a pure glass cladding, a depressed cladding, a transition layer, a core layer, a rising layer, and a falling layer from outside to inside in the radial direction;

[0018] The viscosity of the pure glass cladding is 6.10 Log; the viscosity of the depressed cladding is 5.00 to 5.30 Log; the viscosity of the transition layer is 5.55 to 5.75 Log;

[0019] In the radial direction, and in the direction from outside to inside, the viscosity of the core layer decreases linearly from the depressed cladding to the rising layer, and the viscosity range of the core layer is 5.50 to 5.65 Log; the maximum viscosity of the rising layer is equal to the minimum viscosity of the core layer; the minimum viscosity of the rising layer is equal to the minimum viscosity of the falling layer, and the maximum viscosity of the falling layer is equal to the minimum viscosity of the core layer.

[0020] In some embodiments, depositing a diffusion layer to fill the internal space of the hollow core layer and obtaining an initial rod specifically includes the following steps:

[0021] According to the partial curve corresponding to the rising layer in the refractive index profile distribution curve corresponding to the deposition formula, controlling the silicon flow rate to be consistent with the flow rate of depositing the core layer, and at the same time controlling the germanium flow rate to increase linearly and the fluorine flow rate to increase linearly to deposit and form the rising layer;

[0022] According to the partial curve corresponding to the descending layer in the refractive index profile distribution curve corresponding to the deposition formula, control the silicon flow rate to be consistent with the flow rate of the deposited core layer, and at the same time control the germanium flow rate to decrease linearly and the fluorine flow rate to decrease linearly to deposit and form the descending layer.

[0023] In some embodiments, the initial rod is necked down to obtain a solid preform, including the following steps:

[0024] Place the initial rod on the rod-forming bed of the high-temperature furnace;

[0025] Adjust the temperature of the high-temperature furnace, and then perform the process of burning and thinning the initial rod on the rod-forming bed 4 to 10 times to form a solid preform; during the burning and thinning process, the running speed of the high-temperature furnace gradually increases with the number of passes, so that the diffusion layer forms a glass layer with a constant refractive index; the speed of the first pass is 6 to 16 mm / min, and the speed of the last pass is 18 to 40 mm / min; the temperature range of the high-temperature furnace is 1500 to 2500 °C.

[0026] In some embodiments, the vapor deposition of the initial rod is the PCVD or MCVD process of the in-tube method, or the OVD process of the out-of-tube method; the in-tube method starts depositing from the edge of the core layer and terminates at the center of the core layer, and the out-of-tube method starts depositing from the center of the core layer and terminates at the edge of the core layer.

[0027] In a second aspect, a method for preparing an optical fiber is provided, which includes the following steps:

[0028] According to the optical fiber preform preparation method, obtain a solid preform;

[0029] Match a sleeve with a suitable area for the solid preform, and then send it to a drawing device to draw it into an optical fiber.

[0030] In a third aspect, a high-bandwidth multimode optical fiber is provided, which is manufactured by the optical fiber preparation method.

[0031] In some embodiments, the center of the refractive index profile of the high-bandwidth multimode optical fiber is smooth without depression; the effective mode bandwidth of the high-bandwidth multimode optical fiber at a working wavelength of 850 nm is above 10000 MHz-km.

[0032] The beneficial effects brought by the technical solutions provided in this application include:

[0033] The embodiments of the present application provide an optical fiber preform, a method for preparing an optical fiber, and a high-bandwidth multimode optical fiber. After the core layer is deposited, a diffusion layer is continuously deposited on the core layer to obtain an initial rod. In the radial direction and from the outside to the inside, the deposited hollow rod sequentially includes a cladding layer, a core layer, a rising layer, and a falling layer. The viscosity of the rising layer decreases linearly, and its refractive index increases linearly. The viscosity of the falling layer increases linearly, and its refractive index decreases linearly. The rising layer and the falling layer form a diffusion layer. The refractive index of the core layer has a graded distribution. Then, the deposited hollow rod is directly drawn down to obtain a solid preform. During the drawing-down process, the falling layer with the above viscosity design can be used as a passivation layer, which can greatly reduce the refractive index profile center distortion caused by the volatilization of GeO2 during the drawing-down process of the preform. Under the action of thermal diffusion, the rising layer migrates high-concentration germanium to the falling layer, so that a very narrow refractive index constant glass layer is formed by transforming the diffusion layer at the center of the core area, avoiding the refractive index profile center distortion. The drawing-down process does not require the use of fluorine to corrode the middle depression of the refractive index profile formed by the volatilization of GeO2. This not only saves the raw material cost of fluorine gas, MFC equipment and its pipeline design, but also greatly saves working hours and improves production efficiency. There is no obvious difference in the attenuation characteristics of the optical fiber prepared by the non-corrosion process compared with the optical fiber prepared by the corrosion process.

[0034] In addition, more than 80% of the optical fibers manufactured from the optical fiber preform prepared by the above process have no obvious refractive index profile center distortion, which is beneficial to improving the bandwidth performance of the multimode optical fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] In order to more clearly illustrate the technical solutions in the embodiments of the present application, the following will briefly introduce the drawings required for the description of the embodiments. Obviously, the drawings in the following description are only some embodiments of the present application. For those of ordinary skill in the art, other drawings can be obtained based on these drawings without creative efforts.

[0036] Figure 1 It is a schematic diagram of the center depression of the refractive index profile of the optical rod provided in the related art;

[0037] Figure 2 It is a schematic diagram of the refractive index profile distribution curve corresponding to the deposition formula provided in the embodiments of the present application;

[0038] Figure 3 It is a schematic diagram of the corresponding relationship between the refractive index profile distribution curve provided in the embodiments of the present application and the hollow rod after deposition in the radial direction from the outside to the inside;

[0039] Figure 4 It is a schematic diagram of the relationship between the viscosity and the radius of the hollow rod after deposition provided in the embodiments of the present application;

[0040] Figure 5 Schematic diagram of the refractive index of the fiber cross-section corresponding to Embodiment 1 provided by the embodiment of the present application;

[0041] Figure 6 Schematic diagram of the refractive index of the fiber cross-section corresponding to Embodiment 2 provided by the embodiment of the present application;

[0042] Figure 7 Schematic diagram of the refractive index of the fiber cross-section corresponding to Embodiment 3 provided by the embodiment of the present application.

[0043] In the figure: 1, cladding; 100, pure glass cladding; 101, depressed cladding; 102, transition layer; 2, core layer; 3, diffusion layer; 300, rising layer; 301, falling layer. Detailed implementation manners

[0044] To make the objectives, technical solutions and advantages of the embodiments of the present application clearer, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings in the embodiments of the present application. Obviously, the described embodiments are some but not all of the embodiments of the present application. All other embodiments obtained by those of ordinary skill in the art based on the embodiments of the present application without creative efforts shall fall within the protection scope of the present application.

[0045] It should be understood for the present application that:

[0046] The fiber preform required for producing the graded-index fiber can be prepared by the PCVD (Plasma Chemical Vapor Deposition) or MCVD (Modified Chemical Vapor Deposition) of the in-tube method or the OVD (Outside Vapor Deposition) process of the out-tube method. High-purity reactants such as SiCl4, O2, GeCl4, etc. are introduced into or outside the high-purity quartz glass tube through a certain path, and chemical reactions and vapor deposition are carried out by excitation with a microwave source resonator or a flame torch, forming a transparent quartz glass deposition layer. The reaction formula for preparing the graded-index fiber core rod is as follows:

[0047] SiCl4 + O2 = SiO2 + 2Cl2

[0048] GeCl4 + O2 = GeO2 + 2Cl2

[0049] The deposited quartz glass tube is prepared into a solid fiber preform by heat-shrinking in a high-temperature furnace.

[0050] Taking the PCVD technology as an example, multimode optical fibers are generally prepared by the PCVD technology. PCVD is a manufacturing process for depositing preforms by the in-tube method. The preform made by the in-tube method needs to be sintered into a solid preform through the "collapse process". During the collapse process, the temperature of the preform is between 1600 and 2200 °C, and the substance GeO2 (germanium dioxide) that makes up the preform will volatilize. The volatilization will cause the refractive index to decrease, resulting in a depression in the center of the refractive index profile of the preform, as shown in the appendix Figure 1 as shown

[0051] To overcome the depression in the center of the refractive index profile, it is generally solved by using the "etching process". The etching process means that during the collapse process, fluorine is introduced into the preform. Under the action of high temperature, fluorine can etch SiO2 and GeO2, thereby realizing the correction of the refractive index profile. However, it is very difficult to control the amount of etching. The amount of etching is related to factors such as the running speed and stability of the high-temperature furnace, the temperature and stability of the high-temperature furnace, the pore size and uniformity of the preform before etching, the control of the etching pressure, and the flow rate of fluorine gas. In actual production, there are still distortions in the refractive index profile of the center section of the preform prepared by the etching process. If the amount of etching is insufficient, a lower limit will be formed in the preform pattern; if the etching is excessive, a spike will be formed in the preform pattern. The optical fiber prepared with a preform with a distorted refractive index profile will also have a distorted refractive index profile. The bandwidth characteristics of multimode optical fibers with a distorted center of the refractive index profile will be greatly affected and cannot meet the requirements of high-bandwidth application scenarios.

[0052] To eliminate the distortion in the center of the refractive index profile, it is necessary to accurately control the "amount of etching". However, accurately controlling the amount of etching requires a high cost. The amount of etching is related to factors such as the stability of the high-temperature furnace temperature, the uniformity of the pore size, the pressure, and the flow rate of fluorine gas during the etching process.

[0053] First, the temperature stability of the high-temperature furnace. The high-temperature furnace uses graphite components to generate heat, so it requires the protection of rare gas He; He gas cannot be recycled and is expensive. In actual production, cheap Ar gas is used instead, which makes the temperature of the high-temperature furnace affected by the fluctuation of Ar gas, generally fluctuating between 100 and 300 °C. The cheap gas seal generally used in the high-temperature furnace will also leak in oxygen, causing the graphite components to oxidize and become thinner continuously. This will not only affect the temperature stability but also require frequent replacement of graphite components. All these have greatly deteriorated the temperature stability and consistency of the high-temperature furnace and increased the production cost. Second, the temperature of the high-temperature furnace is unstable, and the rod hole diameter during the rod burning process cannot be uniformly controlled, resulting in different sizes in the shape of a "gourd", which greatly affects the corrosion amount at different positions. Due to the instability of the temperature of the high-temperature furnace, the burned thin hole diameters cannot be made consistent for each rod, which brings difficulties to the standardization of the corrosion process control. Third, since the hole diameter is related to the corrosion pressure, if the hole diameter control is inconsistent, the corrosion pressure will also be inconsistent, which will also affect the size of the corrosion amount. Fourth, the stability of the fluorine gas flow control. The flow meters currently used are generally imported MFC (mass flow controllers), which are expensive. Fifth, the stability of the translation speed of the high-temperature furnace. Precise control of the translation speed also requires high-precision machine tools, which also requires high costs.

[0054] Therefore, aiming at the problem that in the above-mentioned necking process, the process of introducing fluorine to control the corrosion amount and reduce the central depression of the refractive index profile requires precise control of the corrosion amount, resulting in high costs, a new method for preparing a preform is proposed. For specific references, please refer to the following description:

[0055] Please refer to Figures 2 - 3 , in the first aspect, a method for preparing an optical fiber preform is proposed, which includes the following steps:

[0056] Step 100, deposit the diffusion layer 3 to fill the internal space of the hollow core layer 2 and obtain the initial rod body, that is, during the deposition of the hollow rod, control the silicon flow rate, germanium flow rate, and fluorine flow rate according to the refractive index profile distribution curve corresponding to the deposition formula to deposit and form the diffusion layer 3 on the inner wall of the core layer 2 to obtain the initial rod body.

[0057] It should be understood that the refractive index profile distribution curve refers to Figure 2 In the radial direction shown, from the outside to the inside, a schematic diagram of the sectional refractive index at different positions of the hollow rod after deposition is required; for a clearer understanding of the relationship between different positions and the refractive index, further reference can be made to the content shown in Figure 3 which shows Figure 2Half of the content in [it], that is, the correspondence of half of the deposited hollow rod. That is to say, after completing this step, the diffusion layer 3 has the characteristics of refractive index and viscosity defined as follows. The refractive index profile curve is adjusted as a standard reference for SiCL4, GeCl4, C2F6, and O2. When depositing the core layer, the silicon flow rate decreases linearly with the number of deposition passes; the germanium flow rate increases linearly with the number of deposition passes; the fluorine flow rate decreases linearly with the number of deposition passes.

[0058] Step 200: Neck down the initial rod to obtain a solid preform;

[0059] Among them, in the initial rod, it is configured that: in the radial direction and in the direction from outside to inside, the deposited hollow rod successively includes a cladding 1, a core layer 2, an ascending layer 300, and a descending layer 301; the viscosity of the ascending layer 300 decreases linearly, and its refractive index increases linearly; the viscosity of the descending layer 301 increases linearly, and its refractive index decreases linearly; the ascending layer 300 and the descending layer 301 form a diffusion layer 3; in the solid preform, along the radial direction from outside to inside, the refractive indices of the core layer 2 and the diffusion layer 3 both increase according to the same preset curve, and the refractive index of the core layer 2 has a gradient distribution.

[0060] In step 100, the deposition of the cladding 1 and the core layer 2 is the same as the related processes in the prior art. Reference can be made to the relevant descriptions in Chinese Patent CN102073098B "Broadband Multimode Optical Fiber and Its Manufacturing Method", and the relevant descriptions in Chinese Application CN113292240A "Deposition Method of the Core Layer of a Gradient Refractive Index Profile Optical Fiber Preform".

[0061] During necking down, the special design of viscosity is beneficial to the diffusion of germanium and fluorine at high temperatures. The descending layer 301 under the above viscosity design can be used as a passivation layer, which can greatly reduce the refractive index profile center distortion caused by the volatilization of GeO2 during the necking down process of the preform; under the above viscosity design, the ascending layer 300 migrates high-concentration germanium to the descending layer 301 under the action of thermal diffusion, so as to transform and form an extremely narrow refractive index constant glass layer in the center of the core area, avoiding the refractive index profile center distortion; during the rod necking down process, there is no need to use fluorine to corrode the middle depression of the refractive index profile formed by the volatilization of GeO2. This not only saves the raw material cost of fluorine gas, MFC equipment and its pipeline design, etc., but also greatly saves working hours and improves production efficiency; compared with the optical fiber prepared by the etching process, the attenuation characteristics of the optical fiber prepared by the non-etching process have no obvious difference. The above diffusion layer 3 is only an intermediate product in the process of finally forming the optical fiber and will eventually disappear during the consolidation process. The disappearance here means that the refractive index and viscosity of the descending layer 301 and the ascending layer 300 of the diffusion layer 3 finally change due to the migration of ions, that is, finally the refractive indices of the diffusion layer 3 and the core layer 2 are similar to the preset curve. The above changes are from Figure 2 the part of the diffusion layer 3 marked in [it] changes toFigure 5 The state of curve smoothing shown. Of course, in the most ideal case here, in the actual process, the process of this application allows for errors, but it is required to be within the error range of the ideal curve.

[0062] In addition, for the optical fiber manufactured from the preform prepared by the above process, more than 80% of the optical fibers have no obvious refractive index profile center distortion, which is beneficial to improving the bandwidth performance of multimode optical fibers.

[0063] It should also be understood that during the above collapsing process, mainly germanium ions migrate, and a small amount of fluoride ions migrate; the viscosity is controlled by the doping concentrations of germanium and fluoride; limiting the refractive index itself is to limit the doping concentration, thereby limiting the magnitude of the viscosity and the rate of change with the radius; to a certain extent, the refractive index and the viscosity are in a functional relationship; the combined action of the refractive index and the viscosity can appropriately achieve a solid preform that meets the refractive index requirements during the collapsing process.

[0064] In some preferred embodiments, the refractive index and the viscosity of the diffusion layer 3 are preliminarily limited. In the actual production process, the factors affecting the reduction of the refractive index profile center depression of the diffusion layer 3 during collapsing also include the area sizes of the rising layer 300 and the falling layer 301. Therefore, the following design is also provided:

[0065] The deposition area of the rising layer 300 is 0.33% - 3.33% of the area of the core layer 2;

[0066] The deposition area of the falling layer 301 is 0.15% - 0.90% of the area of the core layer 2.

[0067] By reasonably designing the areas of the rising layer 300 and the falling layer 301, the deposition amount is reduced as much as possible, and the best effect of reducing the refractive index profile center depression is achieved. The area is to limit the thickness of the glass in the refractive index profile center of the rod diagram that participates in the diffusion effect. Excessive thickness will affect the bandwidth.

[0068] Furthermore, this application also gives the specific range of the refractive index of the diffusion layer 3 for better implementation. The maximum refractive index of the core layer 2 is n1, and n1 ranges from 0.85% to 1.1%; along the radius from the outside to the inside, the refractive index at the starting point of the rising layer 300 of the diffusion layer is n1, and the refractive index at the end point is 1.06 - 1.5 times n1; along the radius from the outside to the inside, the starting point of the falling layer 301 is the end point of the rising layer 300, and the refractive index at the end point of the falling layer 301 is 0.2 - 0.8 times n1. This application includes but is not limited to the above range, and only a specific embodiment is given.

[0069] Furthermore, this application also gives the specific viscosity design of each layer structure of the hollow rod after deposition, as specifically referred to below:

[0070] The initial rod sequentially includes a pure glass cladding 100, a depressed cladding 101, a transition layer 102, a core layer 2, a rising layer 300, and a falling layer 301 from the outside to the inside in the radial direction;

[0071] The viscosity of the pure glass cladding 100 is 6.10 Log; the viscosity of the depressed cladding 101 is 5.00 - 5.30 Log; the viscosity of the transition layer 102 is 5.55 - 5.75 Log;

[0072] In the radial direction and from the outside to the inside, the viscosity of the core layer 2 linearly decreases from the depressed cladding 101 to the rising layer 300. The viscosity range of the core layer 2 is 5.50 - 5.65 Log; the maximum viscosity of the rising layer 300 is equal to the minimum viscosity of the core layer 2; the minimum viscosity of the rising layer 300 is equal to the minimum viscosity of the falling layer 301, and the maximum viscosity of the falling layer 301 is equal to the minimum viscosity of the core layer 2.

[0073] For a more detailed explanation of the above limitations, refer to Figure 4 , Figure 4 The specific meanings of the marks ①②③④⑤⑥ in are as follows: The viscosity Log(η pure glass) of ① is about 6.10; the viscosity Log(η depressed cladding) of ② is 5.00 - 5.30; the viscosity Log(η transition layer) of ③ is 5.55 - 5.75; the viscosity linearly decreases from ③ to ④, and the viscosity Log(η core layer) of ④ is 5.50 - 5.65; the viscosity linearly decreases from ④ to ⑤, and the viscosity Log(η diffusion layer) of ⑤ is 5.10 - 5.30. The viscosity at ⑥ is equal to that at ④. The special design of the above viscosities is conducive to the diffusion of germanium and fluorine at high temperatures, and in the subsequent necking process, the diffusion layer (3) is transformed to form an extremely narrow glass layer with a constant refractive index. The schematic diagram of the relationship between the viscosity and the preform radius is shown in Figure 4 (viscosity at 2200 °C).

[0074] In some preferred embodiments, a deposition diffusion layer 3 is deposited to fill the internal space of the hollow core layer 2 and obtain an initial rod, which specifically includes the following steps:

[0075] According to the partial curve corresponding to the rising layer 300 in the refractive index profile distribution curve corresponding to the deposition formula, control the silicon flow rate to be consistent with the flow rate of depositing the core layer 2, and at the same time control the germanium flow rate to increase linearly and the fluorine flow rate to increase linearly to deposit and form the rising layer 300;

[0076] According to the partial curve corresponding to the falling layer 301 in the refractive index profile distribution curve corresponding to the deposition formula, control the silicon flow rate to be consistent with the flow rate of depositing the core layer 2, and at the same time control the germanium flow rate to decrease linearly and the fluorine flow rate to decrease linearly to deposit and form the falling layer 301. The above gives the specific steps of depositing and forming the diffusion layer 3.

[0077] In some preferred embodiments, the hollow rod after deposition, that is, the initial rod is directly subjected to necking to obtain a solid preform, including the following steps:

[0078] Place the initial rod on the rod-forming bed of the high-temperature furnace;

[0079] Adjust the temperature of the high-temperature furnace, and then perform the necking process on the hollow rod on the rod-forming bed for 4 to 10 passes to form a solid preform; during the necking process, the running speed of the high-temperature furnace gradually increases with the number of passes, so that the diffusion layer 3 forms a glass layer with a constant refractive index; the speed of the first pass is 6 to 16 mm / min, and the speed of the last pass is 18 to 40 mm / min; the temperature range of the high-temperature furnace is 1500 to 2500 °C.

[0080] Through the above settings, during the necking process, under the action of high temperature, the viscosity of the diffusion layer 3 is low, and the germanium inside moves from the rising layer 300 to the falling layer 301; the rate and time of germanium diffusion are controlled by the size of the rod-necking temperature and the number of passes: to achieve a consistent germanium concentration with a narrow width in the core area, thereby reducing the distortion of the refractive index profile in the core area.

[0081] The above-mentioned vapor deposition of the deposited hollow rod is the PCVD or MCVD process of the in-tube method, or the OVD process of the out-of-tube method; the in-tube method starts depositing from the edge of the core layer 2 to the center of the core layer 2, and the out-of-tube method starts depositing from the center of the core layer 2 to the edge of the core layer 2.

[0082] In a second aspect, a method for preparing an optical fiber is proposed, which includes the following steps:

[0083] According to the above-mentioned optical fiber preform preparation method, obtain a solid preform;

[0084] Match a sleeve with a suitable area for the solid preform, and then send it to a drawing device to draw it into an optical fiber.

[0085] In a third aspect, a high-bandwidth multimode optical fiber is proposed, which is manufactured by using the above-mentioned optical fiber preparation method. The center of the refractive index profile of the high-bandwidth multimode optical fiber is smooth and has no depression; the effective mode bandwidth of the high-bandwidth multimode optical fiber at a working wavelength of 850 nm is above 10000 MHz-km.

[0086] Three embodiments are given below for specific illustration.

[0087] Embodiment 1:

[0088] The core refractive index profile of the high-bandwidth multimode fiber with no obvious defects in the core region provided by this embodiment is composed of a diffusion layer 3, a core layer 2, and a cladding 1 coated on the surface of the core layer 2. The refractive index profile of the core layer 2 is a graded distribution, and the maximum refractive index of the core layer 2 is n1, with a value of 0.85%. The diffusion layer 3 is composed of a rising layer 300 with a linearly increasing refractive index and a falling layer 301 with a linearly decreasing refractive index of a certain thickness. The refractive index at the starting point of the rising layer 300 of the diffusion layer is n1, and the refractive index at the end point is 1.06 times n1; the deposition area of the rising layer 300 is 0.33% of the area of the core layer 2. The refractive index at the end point of the falling layer 301 of the diffusion layer is 0.2 times n1; the deposition area of the falling layer 301 is 0.15% of the area of the core layer 2.

[0089] First, PCVD deposition. When designing the PCVD deposition formula, the raw materials are SiCL4, GeCl4, C2F6, and O2. When depositing the core layer 2, the silicon flow rate decreases linearly with the number of deposition passes; the germanium flow rate increases linearly with the number of deposition passes; the fluorine flow rate decreases linearly with the number of deposition passes. When depositing the diffusion layer, the viscosity of the rising layer 300 is relatively low, the silicon flow rate remains unchanged, the germanium flow rate increases linearly, and the fluorine flow rate increases linearly; the viscosity of the falling layer 301 is relatively high, the silicon flow rate remains unchanged, the germanium flow rate decreases linearly, and the fluorine flow rate decreases linearly. The special design of the viscosity is beneficial to the diffusion of germanium and fluorine at high temperatures. The schematic diagram of the relationship between the viscosity and the preform radius is shown in Figure 4 (viscosity at 2200°C).

[0090] Second step, drawing into a rod. The deposited hollow rod undergoes 4 passes of thinning process on the rod-forming bed, and the temperature of the high-temperature furnace is 1500°C. During the thinning process, the walking speed of the high-temperature furnace gradually increases with the number of passes. The speed in the first pass is 6 mm / min, and the speed in the last pass is 18 mm / min. The last pass is for solidifying, that is, the thinned hollow preform is drawn into a solid preform, and the walking speed in the last pass is 1.2 times the walking speed in the last pass of thinning. During the drawing process, under the action of high temperature, the viscosity of the diffusion layer is relatively low, and the germanium inside moves from the rising layer 300 to the falling layer 301; the rate and time of germanium diffusion are controlled by the size and number of passes of the drawing temperature: to achieve a uniform germanium concentration in a relatively narrow width in the core region, so as to reduce the distortion of the refractive index profile in the core region. The deposited hollow preform can obtain a solid preform with less distortion of the refractive index profile in the core region through the drawing process.

[0091] Third step, sleeving and drawing. A suitable area of sleeve is matched to the solid preform, and then it is sent to the drawing tower for high-speed drawing, and the diameter of the bare fiber is controlled at ~125 μm, and the coated diameter is ~245 μm.

[0092] Fourth step, use a PK instrument to measure the effective mode bandwidth at a wavelength of 850 nm. The test lengths are 10 km and 0.2 km respectively.

[0093] The refractive index profile of the optical fiber prepared in this embodiment is shown in the appendix Figure 5 as follows.

[0094] Example 2:

[0095] The core refractive index profile of the high-bandwidth multimode optical fiber with no obvious defects in the core region provided in this embodiment is composed of a diffusion layer, a core layer 2, and a cladding layer coated on the surface of the core layer 2. The refractive index profile of the cross-section of the core layer 2 is a graded distribution, and the maximum refractive index of the core layer 2 is n1, and its value is 0.97%. The diffusion layer is composed of a rising layer 300 with a linearly increasing refractive index of a certain thickness and a falling layer 301 with a linearly decreasing refractive index of a certain thickness. The refractive index at the starting point of the rising layer 300 of the diffusion layer is n1, and the refractive index at the end point is 1.28 times n1; the deposited area of the rising layer 300 is 2.04% of the area of the core layer 2. The refractive index at the end point of the falling layer 301 of the diffusion layer is 0.6 times n1; the deposited area of the falling layer 301 is 0.55% of the area of the core layer 2.

[0096] First, PCVD deposition. When designing the PCVD deposition formula, the raw materials are SiCL4, GeCl4, C2F6, and O2. When depositing the core layer 2, the silicon flow rate decreases linearly with the number of deposition passes; the germanium flow rate increases linearly with the number of deposition passes; the fluorine flow rate decreases linearly with the number of deposition passes. When depositing the diffusion layer, the viscosity of the rising layer 300 is relatively low, the silicon flow rate remains unchanged, the germanium flow rate rises linearly, and the fluorine flow rate rises linearly; the viscosity of the falling layer 301 is relatively high, the silicon flow rate remains unchanged, the germanium flow rate decreases linearly, and the fluorine flow rate decreases linearly. The special design of the viscosity is beneficial to the diffusion of germanium and fluorine at high temperatures. The schematic diagram of the relationship between the viscosity and the radius of the preform is shown in Appendix 4 (viscosity at 2200 °C).

[0097] Second step, collapsing into a rod. The deposited hollow rod is subjected to 7 passes of the thinning process on the rod-forming bed, and the temperature of the high-temperature furnace is 2000 °C. During the thinning process, the running speed of the high-temperature furnace gradually increases with the number of passes. The speed of the first pass is 11 mm / min, and the speed of the last pass is 29 mm / min. The last pass is for solidification, that is, the thinned hollow preform is burned into a solid preform, and the running speed of the last pass is 1.9 times the running speed of the last pass of thinning. During the collapsing process, under the action of high temperature, the viscosity of the diffusion layer 3 is relatively low, and the germanium inside moves from the rising layer 300 to the falling layer 301; the rate and time of germanium diffusion are controlled by the size and number of passes of the collapsing temperature: to achieve a uniform germanium concentration in the core region with a relatively narrow width, so as to reduce the distortion of the refractive index profile in the core region. The deposited hollow preform can obtain a solid preform with less distortion of the refractive index profile in the core region through the collapsing process.

[0098] Third step, sleeving and drawing. The solid preform is matched with a sleeve of a suitable area, and then sent to the drawing tower for high-speed drawing, and the diameter of the bare fiber is controlled at ~125 μm, and the diameter of the coating is ~245 μm.

[0099] Step 4: Use a PK instrument to measure the effective mode bandwidth at a wavelength of 850 nm. The test lengths are 10 km and 0.2 km respectively.

[0100] The refractive index profile of the optical fiber prepared in this embodiment is as shown in the appendix Figure 6 as follows.

[0101] Example 3:

[0102] The core refractive index profile of the high-bandwidth multimode optical fiber with no obvious defects in the core region provided in this embodiment is composed of a diffusion layer, a core layer 2, and a cladding layer coated on the surface of the core layer 2. The refractive index profile of the core layer 2 is a graded distribution, and the maximum refractive index of the core layer 2 is n1, and its value is 1.1%. The diffusion layer is composed of a rising layer 300 with a linearly increasing refractive index and a falling layer 301 with a linearly decreasing refractive index. The refractive index at the starting point of the rising layer 300 of the diffusion layer is n1, and the refractive index at the end point is 1.5 times n1; the deposition area of the rising layer 300 is 3.33% of the area of the core layer 2. The refractive index at the end point of the falling layer 301 of the diffusion layer is 0.8 times n1; the deposition area of the falling layer 301 is 0.90% of the area of the core layer 2.

[0103] First, PCVD deposition. When designing the PCVD deposition formula, the raw materials are SiCL4, GeCl4, C2F6, and O2. When depositing the core layer 2, the silicon flow rate decreases linearly with the number of deposition passes; the germanium flow rate increases linearly with the number of deposition passes; the fluorine flow rate decreases linearly with the number of deposition passes. When depositing the diffusion layer, the viscosity of the rising layer 300 is relatively low, the silicon flow rate remains unchanged, the germanium flow rate rises linearly, and the fluorine flow rate rises linearly; the viscosity of the falling layer 301 is relatively high, the silicon flow rate remains unchanged, the germanium flow rate decreases linearly, and the fluorine flow rate decreases linearly. The special design of the viscosity is beneficial to the diffusion of germanium and fluorine at high temperatures. The schematic diagram of the relationship between the viscosity and the preform radius is shown in Appendix 4 (viscosity at 2200 °C).

[0104] Second step, draw down into a rod. The deposited hollow rod is subjected to 10 passes of the draw-down process on a rod-making bed, and the temperature of the high-temperature furnace is 2500 °C. During the draw-down process, the traveling speed of the high-temperature furnace gradually increases with the number of passes. The speed of the first pass is 16 mm / min, and the speed of the last pass is 40 mm / min. The last pass is for solidification, that is, the drawn hollow preform is drawn into a solid preform, and the traveling speed of the last pass is 2.5 times the traveling speed of the last draw-down pass. During the draw-down process, under the action of high temperature, the viscosity of the diffusion layer 3 is relatively low, and the germanium inside moves from the rising layer 300 to the falling layer 301; the rate and time of germanium diffusion are controlled by the draw-down temperature and the number of passes: to achieve a uniform germanium concentration in a relatively narrow width of the core region, so as to reduce the distortion of the refractive index profile in the core region. The deposited hollow preform can obtain a solid preform with less distortion of the refractive index profile in the core region after the draw-down process.

[0105] Step 3: Sleeve and draw wire. Match a sleeve of a suitable area to the solid preform, and then send it to the drawing tower for high-speed wire drawing, controlling the diameter of the bare fiber at ~125 μm and the coated diameter at ~245 μm.

[0106] Step 4: Use a PK instrument to measure the effective mode bandwidth at a wavelength of 850 nm. The test lengths are 10 km and 0.2 km respectively.

[0107] The refractive index profile of the optical fiber prepared in this embodiment is as shown in the appendix Figure 7 as follows.

[0108] Comparative Example 1: Compared with Example 1, except that no diffusion layer is designed in the first-step PCVD deposition and the etching process is used in the second step, the other process procedures and parameters are exactly the same.

[0109] Comparative Example 2: Compared with Example 2, except that no diffusion layer is designed in the first-step PCVD deposition and the etching process is used in the second step, the other process procedures and parameters are exactly the same.

[0110] Comparative Example 3: Compared with Example 3, except that no diffusion layer is designed in the first-step PCVD deposition and the etching process is used in the second step, the other process procedures and parameters are exactly the same.

[0111] Refer to the following table

[0112]

[0113] It can be seen from the data analysis in the table that the high-bandwidth multimode optical fiber manufactured by using the optical fiber preform preparation method and the optical fiber preparation method of this application has obvious advantages over the high-bandwidth multimode optical fiber obtained by the general process, and can greatly improve the effective bandwidth at 850 nm.

[0114] In the description of this application, it should be noted that the orientation or positional relationship indicated by terms such as "upper" and "lower" is based on the orientation or positional relationship shown in the drawings. It is only for the convenience of describing this application and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, so it cannot be understood as a limitation to this application. Unless otherwise clearly specified and limited, the terms "installation", "connection" and "connection" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be a mechanical connection or an electrical connection; it can be directly connected, or indirectly connected through an intermediate medium, and it can be the communication inside two elements. For those of ordinary skill in the art, the specific meanings of the above terms in this application can be understood according to specific circumstances.

[0115] It should be noted that in this application, relational terms such as "first" and "second" are only used to distinguish one entity or operation from another entity or operation, and do not necessarily require or imply any actual relationship or order between these entities or operations. Moreover, the term "comprising", "including" or any other variation thereof is intended to cover non-exclusive inclusion, so that a process, method, article or device comprising a series of elements not only includes those elements but also includes other elements not expressly listed, or further includes elements inherent to such process, method, article or device. Without further limitation, an element defined by the statement "comprising an..." does not exclude the presence of additional identical elements in the process, method, article or device comprising the said element.

[0116] The above are only specific embodiments of the present application, enabling those skilled in the art to understand or implement the present application. Various modifications to these embodiments will be obvious to those skilled in the art, and the general principles defined herein can be implemented in other embodiments without departing from the spirit or scope of the present application. Therefore, the present application will not be limited to these embodiments shown herein, but rather to the broadest scope consistent with the principles and novel features claimed herein.

Claims

1. A method for preparing an optical fiber preform, characterized in that: It includes: Depositing a diffusion layer (3) to fill the inner space of the hollow core layer (2) and obtain an initial rod; Melting and shrinking the initial rod body to obtain a solid preform rod; Wherein, the initial rod body and the solid preform rod both comprise a core layer (2) and a diffusion layer (3); the diffusion layer (3) comprises a descending layer (301) and an ascending layer (300) outside the descending layer (301); In the initial rod body, radially from the outside to the inside, the viscosity of the rising layer (300) decreases linearly and the refractive index increases linearly, the viscosity of the descending layer (301) increases linearly and the refractive index decreases linearly, and the refractive index of the core layer (2) increases according to a preset curve; In the solid preform rod, radially from the outside to the inside, the refractive indices of the core layer (2) and the diffusion layer (3) both increase according to the same preset curve.

2. The method for preparing an optical fiber preform according to claim 1, characterized in that: The deposition area of ​​the rising layer (300) is 0.33% to 3.33% of the area of ​​the core layer (2); The deposition area of ​​the descending layer (301) is 0.15% to 0.90% of the area of ​​the core layer (2).

3. The method for preparing an optical fiber preform according to claim 1 or 2, characterized in that: The maximum refractive index of the core layer (2) is n1, and the value of n1 is 0.85% to 1.1%; From the outside to the inside in the radial direction, the refractive index of the starting point of the rising layer (300) of the diffusion layer is n1, and the refractive index of the end point is 1.06 to 1.5 times of n1; From the outside to the inside in the radial direction, the starting point of the descending layer (301) is the end point of the ascending layer (300), and the refractive index of the end point of the descending layer (301) is 0.2 to 0.8 times of n1.

4. The method for preparing an optical fiber preform according to claim 1, wherein: The initial rod body includes, from the outside to the inside in radial direction, a pure glass cladding layer (100), a sunken cladding layer (101), a transition layer (102), a core layer (2), a rising layer (300) and a descending layer (301); The viscosity of the pure glass cladding (100) is 6.10 Log; the viscosity of the sunken cladding (101) is 5.00-5.30 Log; the viscosity of the transition layer (102) is 5.55-5.75 Log; In the radial direction and in the direction from outside to inside, the viscosity of the core layer (2) decreases linearly from the sunken cladding (101) to the rising layer (300), and the viscosity range of the core layer (2) is 5.50 to 5.65 Log; the maximum viscosity of the rising layer (300) is equal to the minimum viscosity of the core layer (2); the minimum viscosity of the rising layer (300) is equal to the minimum viscosity of the descending layer (301), and the maximum viscosity of the descending layer (301) is equal to the minimum viscosity of the core layer (2).

5. The method for preparing an optical fiber preform according to claim 1, wherein: Depositing a diffusion layer (3) to fill the inner space of the hollow core layer (2) and obtain an initial rod body specifically comprises the following steps: According to the portion of the curve corresponding to the rising layer (300) in the refractive index profile distribution curve corresponding to the deposition formula, the silicon flow rate is controlled to be consistent with the flow rate of the deposited core layer (2), and the germanium flow rate and the fluorine flow rate are controlled to increase linearly, so as to deposit and form the rising layer (300); According to the partial curve corresponding to the descending layer (301) in the refractive index profile distribution curve corresponding to the deposition formula, the silicon flow is controlled to be consistent with the flow of the deposited core layer (2), and the germanium flow and the fluorine flow are controlled to decrease linearly, so as to deposit and form the descending layer (301).

6. The method for preparing an optical fiber preform according to claim 1, characterized in that: The initial rod body is melted and shrunk to obtain a solid preform rod, comprising the following steps: The initial rod body is placed on the rod bed of the high temperature furnace; The temperature of the high-temperature furnace is adjusted, and then the initial rod body on the rod forming bed is subjected to 4 to 10 sintering processes to form a solid preform rod; during the sintering process, the speed of the high-temperature furnace is gradually increased with the number of passes, so that the diffusion layer (3) forms a glass layer with a constant refractive index; wherein the speed of the first pass is 6 to 16 mm / min, and the speed of the last pass is 18 to 40 mm / min; the temperature range of the high-temperature furnace is 1500 to 2500°C.

7. The method for preparing an optical fiber preform according to claim 1, wherein: The vapor deposition of the initial rod body is a PCVD or MCVD process in the tube method, or an OVD process in the tube method; the tube method starts deposition from the edge of the core layer (2) and ends at the center of the core layer (2), and the tube method starts deposition from the center of the core layer (2) and ends at the edge of the core layer (2).

8. A method for preparing an optical fiber, characterized in that: It includes the following steps: Obtaining a solid preform according to the method for preparing an optical fiber preform as claimed in any one of claims 1 to 7; The solid preform rod is matched with a sleeve of suitable area and then sent to a drawing device to be drawn into an optical fiber.

9. A high-bandwidth multimode optical fiber, characterized in that: It is manufactured using the optical fiber preparation method as claimed in claim 8.

10. The high-bandwidth multimode optical fiber according to claim 9, characterized in that: The refractive index profile of high-bandwidth multimode optical fiber is smooth at the center without depression; the effective mode bandwidth of high-bandwidth multimode optical fiber at the working wavelength of 850nm is above 10000MHz-km.

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