Method for manufacturing low-loss optical fiber preform and optical fiber preform

Abstract

The application provides a preparation method of a low-loss optical fiber preform and the optical fiber preform. The preparation method comprises the following steps: providing a core rod, placing the core rod in a deposition cavity of an outer vapor deposition device, forming a first fluorine-doped layer on the surface of the core rod, forming a gradient fluorine-doped layer on the surface of the first fluorine-doped layer, gradually reducing the fluorine-doped depth of the gradient fluorine-doped layer along a direction away from the first fluorine-doped layer, forming a powder body rod, and placing the powder body rod in a sintering furnace for sintering to form the optical fiber preform. The method provided in the application embodiment can reduce the probability of diffusion loss of fluorine ions in the first fluorine-doped layer in the sintering process, improve the uniformity of the fluorine-doped depth of the first fluorine-doped layer, and improve the viscosity matching between the first fluorine-doped layer and the core rod.

Description

Technical Field

[0001] This application relates to the technical field of optical fiber fabrication, and in particular to a method for fabricating a low-loss optical fiber preform and the optical fiber preform itself. Background Technology

[0002] Low-attenuation fiber technology is a core material for high-capacity and long-distance transmission systems. The core of low-attenuation fiber development is reducing scattering loss. Therefore, low-attenuation fibers typically employ a pure silica core design. To achieve total internal reflection (TID) waveguide structure, when a pure silica core is used, the cladding material cannot be a traditional pure silica material. Therefore, a material with a low relative refractive index must be deposited around the pure silica core. This is usually achieved by doping with fluorine, typically using a fluorine-doped sleeving. The lower relative refractive index of the cladding allows for TID compared to a pure silicon core. However, fluorine doping reduces the viscosity of the cladding, and the viscosity of the core and cladding differs at high temperatures. If the viscosity difference between the core and cladding is significant, this viscosity imbalance during fiber manufacturing can cause a mismatch in thermal expansion and contraction at high and low temperatures, resulting in substantial stress between the core and cladding. This stress, acting on the core, significantly increases the light loss passing through it. Therefore, when manufacturing low-attenuation optical fibers, the industry uses alkali metal doping of the core rod to reduce viscosity, thereby achieving viscosity matching between the core rod and the inner cladding.

[0003] In the preparation of optical fiber preforms, a fluorine-doped sleeve is generally fitted onto the outside of the core rod, and the core rod with the fluorine-doped sleeve is placed in a sintering furnace for sintering to form an optical fiber preform with a fluorine-doped outer cladding.

[0004] However, in the aforementioned related technologies, the fluorine doping uniformity of the fluorine-doped layer formed after sintering in a sintering furnace is poor, resulting in uneven fluorine doping depth and making it difficult to match the viscosity between the fluorine-doped layer and the mandrel. Summary of the Invention

[0005] This application provides a method for preparing an optical fiber preform and an optical fiber preform, which solves the technical problem in the above-mentioned related technologies that the fluorine doping uniformity of the fluorine-doped layer formed after sintering in a sintering furnace is poor, resulting in uneven fluorine doping depth of the fluorine-doped layer, which is not conducive to viscosity matching between the fluorine-doped layer and the core rod.

[0006] To achieve the above objectives, the embodiments of this application provide the following technical solutions:

[0007] The first aspect of this application provides a method for preparing an optical fiber preform, the method comprising the following steps;

[0008] Provide core rods;

[0009] The mandrel is placed inside the deposition chamber of an external vapor deposition apparatus;

[0010] A first fluorine-doped layer is formed on the surface of the mandrel;

[0011] A gradient fluorine-doped layer is formed on the surface of the first fluorine-doped layer, and a powder rod is formed therefrom; the fluorine doping depth of the gradient fluorine-doped layer gradually decreases in the direction away from the first fluorine-doped layer.

[0012] The powder rod is placed in a sintering furnace for sintering to form an optical fiber preform.

[0013] Based on the above technical solution, the following improvements can be made to this application.

[0014] In one possible implementation, the step of forming the first fluorine-doped layer on the surface of the mandrel includes:

[0015] The first torch is controlled to move axially on the mandrel and spray the first fluorine-doped silicon material onto the surface of the mandrel;

[0016] When the first fluorinated silicon material on the surface of the mandrel reaches a first preset thickness, the first blowtorch is turned off, and the first fluorinated layer is formed;

[0017] The ratio of the first preset thickness to the outer diameter of the mandrel is greater than or equal to 0.5 and less than or equal to 1.

[0018] In one possible implementation, the step of controlling the axial movement of the first torch on the mandrel and spraying the first fluorine-doped silicon material onto the surface of the mandrel includes:

[0019] Ignite the second and third blowtorches;

[0020] The first blowtorch, the second blowtorch, and the third blowtorch are controlled to move simultaneously in the same direction along the axial direction of the mandrel, so as to control the flame shape of the first blowtorch through the second blowtorch and the third blowtorch;

[0021] The first blowtorch, the second blowtorch, and the third blowtorch are arranged at intervals in a direction perpendicular to the axial direction of the mandrel, and the first blowtorch is located between the second blowtorch and the third blowtorch.

[0022] The second and third torches are spaced apart from the first torch along the axial direction of the mandrel.

[0023] In one possible implementation, the step of forming a graded fluorine-doped layer on the surface of the first fluorine-doped layer includes:

[0024] The first torch is controlled to move along the axial direction of the mandrel and spray the second fluorine-doped silicon material to form several layers of the second fluorine-doped layer;

[0025] The second and third torches are controlled to move along the axial direction of the mandrel and spray the first silicon material to form several layers of the first silicon layer;

[0026] Several layers of the second fluorine-doped layer and several layers of the first silicon layer are alternately stacked radially on the outer surface of the first fluorine-doped layer to form a stacked structure layer;

[0027] The first, second, and third blowtorches are turned off, and the gradient fluorine-doped layer is formed.

[0028] Among them, the fluorine doping depth of several second fluorine-doped layers gradually decreases in the direction away from the first fluorine-doped layer.

[0029] In one possible implementation, the step of forming the stacked structure layers is followed by:

[0030] Measure whether the thickness of the stacked structure layer reaches the second preset thickness;

[0031] If the second preset thickness is reached, then the first blowtorch, the second blowtorch, and the third blowtorch are turned off;

[0032] If the second preset thickness is not reached, the first silicon layer and the second fluorine-doped layer are deposited to make the thickness of the stacked structure layer reach the second preset thickness.

[0033] The second preset thickness is 1.5 times the first preset thickness.

[0034] In one possible implementation, after the step of forming a graded fluorine-doped layer on the surface of the first fluorine-doped layer, the method further includes:

[0035] A second silicon layer is formed on the surface of the gradient fluorine-doped layer.

[0036] In one possible implementation, the step of forming a second silicon layer on the surface of the graded fluorine-doped layer includes:

[0037] Control the first, second, and third blowtorches to move simultaneously in the same direction along the axial direction of the mandrel;

[0038] Control the first blowtorch to ignite and stop spraying the first fluorinated silicon material, and control the second and third blowtorches to spray the second silicon material;

[0039] When the weight of the mandrel containing the second silicon material reaches a preset weight, the first blowtorch, the second blowtorch, and the third blowtorch are turned off to form the second silicon layer.

[0040] The preset weight is greater than or equal to 80Kg and less than or equal to 120Kg.

[0041] In one possible implementation, when the first fluorine-doped layer is formed on the surface of the mandrel, the flame temperature of the first torch is greater than or equal to 750°C and less than or equal to 850°C.

[0042] The density of the first fluorine-doped layer on the surface of the mandrel is greater than or equal to 0.2 g / cm³. 3 And less than or equal to 0.3 g / cm 3 ;

[0043] The fluorine doping depth of the first fluorine-doped layer is greater than or equal to -0.3% and less than or equal to -0.2%.

[0044] In one possible implementation, when the gradient fluorine-doped layer is formed on the surface of the first fluorine-doped layer, the flame temperature of the first blowtorch is greater than or equal to 800°C and less than or equal to 1000°C; the flame temperatures of the second blowtorch and the third blowtorch are equal to the flame temperature of the first blowtorch.

[0045] The density of the graded fluorine-doped layer is greater than or equal to 0.3 g / cm³. 3 And less than or equal to 0.5 g / cm 3 ;

[0046] The fluorine doping depth in the gradient fluorine-doped layer is greater than or equal to -0.1% and less than 0.

[0047] In one possible implementation, when the second silicon layer is formed on the surface of the gradient fluorine-doped layer, the flame temperature of the first blowtorch is greater than or equal to 1150°C and less than or equal to 1250°C; the flame temperatures of the second blowtorch and the third blowtorch are equal to the flame temperature of the first blowtorch.

[0048] The density of the second silicon layer is greater than or equal to 0.7 g / cm³. 3 And less than or equal to 0.8 g / cm 3 .

[0049] In one possible implementation, both the first fluorinated silicon material and the second fluorinated silicon material comprise silicon-containing compounds and fluorides;

[0050] And / or, both the silicon-containing compound and the first silicon material are SiCl4 or C8H. 24 O4Si4;

[0051] And / or, the fluoride includes at least one of SiF4, CF4, SF6, C2F6, SOF2 and C2F2Cl2.

[0052] A second aspect of this application provides an optical fiber preform, which is prepared by the preparation method described above.

[0053] This application provides a method for preparing an optical fiber preform and the optical fiber preform itself. The method includes the following steps: providing a core rod; placing the core rod in the deposition chamber of an outside vapor deposition (OVD) device; forming a first fluorine-doped layer on the surface of the core rod; forming a graded fluorine-doped layer on the surface of the first fluorine-doped layer; the fluorine doping depth of the graded fluorine-doped layer gradually decreasing along the direction away from the first fluorine-doped layer to form a powder rod; and sintering the powder rod in a sintering furnace to form an optical fiber preform. By depositing a graded fluorine-doped layer on the outside of the first fluorine-doped layer, the probability of fluorine ions in the first fluorine-doped layer diffusing and escaping during sintering can be reduced, thereby improving the uniformity of the fluorine doping depth of the first fluorine-doped layer and improving the viscosity matching between the first fluorine-doped layer and the core rod. Attached Figure Description

[0054] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0055] Figure 1 A schematic flowchart illustrating the method for preparing an optical fiber preform according to an embodiment of this application;

[0056] Figure 2 This is a schematic diagram of the structure of the OVD external vapor deposition apparatus provided in the embodiments of this application;

[0057] Figure 3 for Figure 2 A structural schematic diagram of the first, second, and third blowtorches from another angle;

[0058] Figure 4 for Figure 2 A structural diagram of the first, second, and third blowtorches at another angle;

[0059] Figure 5 A graph showing the relationship between the distance from the fiber preform to the core rod and the relative refractive index obtained by the preparation method provided in the embodiments of this application;

[0060] Figure 6 A schematic flowchart illustrating the method for preparing an optical fiber preform according to an embodiment of this application;

[0061] Figure 7 A schematic flowchart illustrating the method for preparing an optical fiber preform according to an embodiment of this application;

[0062] Figure 8A schematic flowchart illustrating the method for preparing an optical fiber preform according to an embodiment of this application;

[0063] Figure 9 This is a schematic flowchart illustrating the method for preparing an optical fiber preform according to an embodiment of this application.

[0064] Explanation of reference numerals in the attached figures:

[0065] 10-core rod;

[0066] 100 - Deposition chamber; 200 - Chuck; 300 - Track; 400 - First torch; 500 - Second torch;

[0067] 600 - Third blowtorch; 700 - Diameter gauge; 800 - Weighing instrument; 900 - Exhaust device. Detailed Implementation

[0068] As described in the background section, the fluorine doping uniformity of the fluorine-doped layer formed after sintering in the prior art is poor, resulting in uneven fluorine doping depth and hindering viscosity matching between the fluorine-doped layer and the core rod. This problem arises because, in the prior art, a fluorine-doped sleeve is used as the fluorine doping layer during the fabrication of the optical fiber preform. The sleeve is placed over the core rod, and then the core rod with the sleeve is placed in a sintering furnace for densification. During sintering, because no protective layer is provided on the outside of the sleeve, fluorine ions in the sleeve are lost, resulting in uneven fluorine doping depth on the core rod surface and consequently poor viscosity matching between the fluorine-doped layer and the core rod.

[0069] To address the aforementioned technical problems, this application provides a method for preparing an optical fiber preform and the optical fiber preform itself. The method includes the following steps: providing a core rod; placing the core rod in the deposition chamber of an Outside Vapor Deposition (OVD) apparatus; forming a first fluorine-doped layer on the surface of the core rod; forming a gradient fluorine-doped layer on the surface of the first fluorine-doped layer, wherein the fluorine doping depth of the gradient fluorine-doped layer gradually decreases along the direction away from the first fluorine-doped layer to form a powder rod; and sintering the powder rod in a sintering furnace to form an optical fiber preform. By depositing a gradient fluorine-doped layer on the outside of the first fluorine-doped layer, the probability of fluorine ions in the first fluorine-doped layer diffusing and escaping during sintering can be reduced, thereby improving the uniformity of the fluorine doping depth of the first fluorine-doped layer and improving the viscosity matching between the first fluorine-doped layer and the core rod.

[0070] To make the above-mentioned objectives, features, and advantages of the embodiments of this application more apparent and understandable, the technical solutions of the embodiments of this application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. All other embodiments obtained by those skilled in the art based on the embodiments of this application without creative effort are within the scope of protection of this application.

[0071] refer to Figure 1 This application provides a method for preparing an optical fiber preform, which may include the following steps;

[0072] Step S101: A core rod 10 is provided, which can be prepared by vapor phase axial deposition (VAD). In some embodiments, alkali metal doping is performed during the deposition process. The raw material and an atomized alkali metal solution are mixed together and reacted at high temperature. The generated SiO2 and the oxide of the metal salt are deposited on the target rod. The hoist rotates and rises, and axial deposition forms a powder rod. The powder rod after deposition is dehydroxylated and vitrified in a sintering furnace to obtain a transparent core rod 10. In some embodiments, the alkali metal can be one or two of sodium, potassium, rubidium, and cesium.

[0073] Step S102: Place the mandrel 10 into the deposition chamber 100 of the outside vapor deposition (OVD) apparatus.

[0074] refer to Figure 2 , Figure 3 and Figure 4 In some embodiments, the OVD apparatus includes a chuck 200 and a control unit (not shown). The chuck 200 is disposed within the deposition chamber 100 and is used to mount the mandrel 10. The chuck 200 can rotate the mandrel 10 relative to the deposition chamber 100. The control unit can be connected to the chuck 200 and can control the rotational speed of the chuck 200, thereby controlling the rotational speed of the mandrel 10 via the chuck 200.

[0075] Step S103: A first fluorine-doped layer is formed on the surface of the core rod 10. By directly depositing the first fluorine-doped layer on the surface of the core rod 10 using the OVD process, the influence of interfacial stress generated by the melting and shrinkage of the fluorine-doped sleeve during heating in the sintering furnace on the scattering loss in the finished optical fiber can be avoided, thereby reducing the scattering loss in the finished optical fiber and improving its performance.

[0076] In step S104, a gradient fluorine-doped layer is formed on the surface of the first fluorine-doped layer to form a powder rod. The fluorine doping depth of the gradient fluorine-doped layer gradually decreases in the direction away from the first fluorine-doped layer. In some embodiments, after the first fluorine-doped layer is deposited, a gradient fluorine-doped layer can be deposited on the surface of the first fluorine-doped layer to form a powder rod having a core rod 10, a first fluorine-doped layer, and a gradient fluorine-doped layer. By depositing a gradient fluorine-doped layer on the surface of the first fluorine-doped layer, so that the fluorine doping depth of the gradient fluorine-doped layer gradually decreases in the direction away from the first fluorine-doped layer, and the fluorine doping depth of the first fluorine-doped layer is greater than the fluorine doping depth of the gradient fluorine-doped layer, the diffusion and loss of fluorine ions in the first fluorine-doped layer during sintering can be reduced, thereby improving the uniformity of the first fluorine-doped layer.

[0077] By setting a graded fluorine-doped layer, the attenuation level at 1550nm can reach 0.165dB / Km, and the temperature of the optical fiber preform during drawing can be increased, which helps to reduce the viscosity of the core rod 10 and the interfacial stress between the core rod 10 and the first fluorine-doped layer.

[0078] It is understandable that the fluorine doping depth is negatively correlated with the relative refractive index; that is, the greater the fluorine doping depth, the smaller the relative refractive index. Since the fluorine doping depth of the first fluorine-doped layer is greater than that of the graded fluorine-doped layer, the relative refractive index of the first fluorine-doped layer is less than that of the graded fluorine-doped layer.

[0079] refer to Figure 5 , Figure 5 The diagram schematically illustrates the change in relative refractive index between the first fluorine-doped layer and the graded fluorine-doped layer. Figure 5 In the diagram, the horizontal axis represents the distance to the core rod 10. The closer the distance to the core rod 10, the closer it is to the intersection of the horizontal and vertical axes. Region A shows the curve of the relative refractive index of the first fluorine-doped layer changing with the distance from the first fluorine-doped layer to the core rod 10, and Region B shows the curve of the relative refractive index of the graded fluorine-doped layer changing with the distance from the graded fluorine-doped layer to the core rod 10. Figure 5 It can be seen that the relative refractive index of the first fluorine-doped layer does not change from the side closer to the core rod 10 to the side farther away from the core rod 10. However, since the fluorine doping depth of the graded fluorine-doped layer gradually decreases along the direction away from the first fluorine-doped layer, the relative refractive index of the graded fluorine-doped layer gradually increases from the side closer to the core rod 10 to the side farther away from the core rod 10.

[0080] Step S105: The powder rod is placed in a sintering furnace for sintering to form an optical fiber preform. By sintering the first fluorine-doped layer and the graded fluorine-doped layer deposited on the core rod 10 in the sintering furnace at the same time, the existing technology using multi-layer fluorine-doped sleeves, which requires each sleeve layer to be sintered in the sintering furnace, is avoided. This reduces the number of times the sintering furnace is used during the optical fiber preform preparation process and improves the service life of the sintering furnace.

[0081] refer to Figure 6 In some embodiments, the step of forming a first fluorine-doped layer on the surface of the mandrel 10 may include;

[0082] Step S201: Control the first blowtorch 400 to move axially along the mandrel 10 and spray the first fluorine-doped silicon material onto the surface of the mandrel 10.

[0083] refer to Figure 2 In some embodiments, the OVD apparatus may further include a first torch 400, a track 300, and a control unit. The track 300 is disposed within the deposition chamber 100 and located below the chuck 200. The track 300 extends axially along the mandrel 10, and its length is greater than the axial length of the mandrel 10. The first torch 400 is disposed on the track 300. The control unit is connected to the track 300 and can control the track 300 to move the first torch 400 axially along the mandrel 10. The first torch 400 is connected to a raw material tube containing raw material. The raw material undergoes a chemical reaction in the oxyhydrogen flame emitted by the first torch 400 to form a doped loose powder, which is a first fluorinated silicon material.

[0084] In some embodiments, the first fluorinated silicon material may include a silicon-containing compound and a fluoride. Specifically, the silicon-containing compound may be SiCl4 or C8H4. 24 O4Si4, the fluoride may include at least one of SiF4, CF4, SF6, C2F6, SOF2 and C2F2Cl2.

[0085] refer to Figure 2 The mandrel 10 has two axial ends, which can be a first end and a second end. The first blowtorch 400 can move from the first end to the second end to spray the first fluorinated silicon material onto the entire outer surface of the mandrel 10. In specific implementation, the first blowtorch 400 can reciprocate between the first end and the second end. It can be understood that the first blowtorch 400 moving from the first end to the second end and then back to the first end constitutes one round, and the first blowtorch 400 can perform multiple rounds of spraying when spraying the first fluorinated silicon material onto the surface of the mandrel 10.

[0086] In some embodiments, the OVD device may have a plurality of first torches 400, all of which are disposed on the track 300 and are spaced apart along the extension direction of the track 300. By providing a plurality of first torches 400, the efficiency of depositing the first fluorine-doped silicon material on the surface of the mandrel 10 can be improved.

[0087] In step S202, when the first fluorinated silicon material on the surface of the mandrel 10 reaches the first preset thickness, the first torch 400 is turned off and the first fluorinated layer is formed. The ratio of the first preset thickness to the outer diameter of the mandrel 10 is greater than or equal to 0.5 and less than or equal to 1. For example, the ratio of the first preset thickness to the outer diameter of the mandrel 10 can be 0.6, 0.7, 0.8 or 0.9.

[0088] refer to Figure 2 In some embodiments, the OVD device may further include a diameter gauge 700 disposed on a track 300. The diameter gauge 700 is movable from a first end to a second end of the mandrel 10 along the extension direction of the track 300, thereby enabling the detection of the outer diameter of the mandrel 10 on which the first fluorinated silicon material is deposited. The OVD device may have multiple diameter gauges 700, which are spaced apart on the track 300 along the extension direction of the track 300.

[0089] The diameter gauge 700 can move simultaneously with the first blowtorch 400 along the extension direction of the track 300. The diameter gauge 700 is connected to the control unit. The control unit calculates the outer diameter of the mandrel 10 with the first fluorinated silicon material deposited on it at this time based on the data fed back by the diameter gauge 700, and calculates the thickness of the first fluorinated silicon material deposited on the surface of the mandrel 10 at this time. If the ratio of the thickness of the first fluorinated silicon material to the outer diameter of the mandrel 10 is greater than or equal to 0.5 and less than or equal to 1, the control unit controls the first blowtorch 400 to stop spraying the first fluorinated silicon material onto the surface of the mandrel 10 and forms the first fluorinated silicon layer.

[0090] Continue to refer to Figure 2 In some embodiments, the OVD device may further include an exhaust device 900, which is connected to the deposition chamber 100 and can be disposed on the side of the mandrel 10 facing away from the first torch 400. The exhaust device 900 can discharge the exhaust gas generated when the first torch 400 is burning out of the deposition chamber 100.

[0091] In an exemplary embodiment, when the first fluorinated silicon material is sprayed onto the surface of the mandrel 10 until the first fluorinated layer is formed, the flame temperature of the first blowtorch 400 can be greater than or equal to 750°C and less than or equal to 850°C. For example, the flame temperature of the first blowtorch 400 can be 780°C, 790°C, 800°C, 810°C or 830°C.

[0092] The OVD device may include an infrared temperature measuring device (not shown in the figure), which is connected to a control unit. This infrared temperature measuring device can detect the flame temperature of the first blowtorch 400 in real time and send the detected flame temperature to the control unit. The control unit can then control the flame combustion state of the first blowtorch 400, thereby enabling precise control of the flame temperature. Furthermore, if the OVD device also has a second blowtorch 500 and a third blowtorch 600, the infrared temperature measuring device can also detect the temperatures of the second blowtorch 500 and the third blowtorch 600, thereby controlling the flame combustion state of the second blowtorch 500 and the third blowtorch 600 through the control unit.

[0093] The density of the first fluorine-doped layer formed on the surface of the mandrel 10 is greater than or equal to 0.2 g / cm³. 3 And less than or equal to 0.3 g / cm 3 For example, the density of the first fluorine-doped layer can be 0.23 g / cm³. 3 0.24g / cm 3 0.26g / cm 3 or 0.27g / cm 3 .

[0094] The fluorine doping depth of the first fluorine-doped layer is greater than or equal to -0.3% and less than or equal to -0.2%. For example, the fluorine doping depth of the first fluorine-doped layer can be -0.27%, -0.25%, or -0.22%.

[0095] refer to Figure 7 In some embodiments, the step of controlling the first torch 400 to move axially along the mandrel 10 and to spray the first fluorine-doped silicon material onto the surface of the mandrel 10 may include:

[0096] Step S301: Ignite the second torch 500 and the third torch 600. After igniting the second torch 500 and the third torch 600, the second torch 500 and the third torch 600 can only burn the flame without spraying the deposit material.

[0097] refer to Figure 2 , Figure 3 and Figure 4 In some embodiments, the OVD device may further include a second torch 500 and a third torch 600, both of which are mounted on the track 300. The first torch 400, the second torch 500, and the third torch 600 are arranged at intervals in a direction perpendicular to the axial direction of the mandrel 10, with the first torch 400 located between the second torch 500 and the third torch 600. The second torch 500 and the third torch 600 are both spaced apart from the first torch 400 in the axial direction of the mandrel 10, and the second torch 500 and the third torch 600 are located on the same straight line.

[0098] Step S302: Control the first blowtorch 400, the second blowtorch 500 and the third blowtorch 600 to move in the same direction along the axis of the mandrel 10, so as to control the flame shape of the first blowtorch 400 through the second blowtorch 500 and the third blowtorch 600.

[0099] refer to Figure 2 In practical implementation, because the exhaust device 900 discharges the waste gas from the deposition chamber 100 to the outside of the deposition chamber 100, the flame of the first blowtorch 400 will vibrate during the exhaust process, affecting the spray stability of the first blowtorch 400, thereby affecting the uniformity of the distribution of the first fluorinated silicon material on the surface of the mandrel 10. Furthermore, when the second blowtorch 500 and the third blowtorch 600 shape the flame of the first blowtorch 400, the flame temperature of the second blowtorch 500 and the third blowtorch 600 is equal to the flame temperature of the first blowtorch 400.

[0100] refer to Figure 3 and Figure 4 In some examples, if there are multiple first torches 400, there can also be multiple second torches 500 and multiple third torches 600. The number of second torches 500 and multiple third torches 600 is equal to the number of first torches 400, and the multiple second torches 500 and multiple third torches 600 are arranged at intervals along the axial direction of the mandrel 10.

[0101] refer to Figure 8 In some embodiments, the step of forming a graded fluorine-doped layer on the surface of the first fluorine-doped layer may include:

[0102] In step S401, the first torch 400 is controlled to move along the axial direction of the mandrel 10 and spray the second fluorinated silicon material to form several layers of the second fluorinated layer. The fluorine concentration of the second fluorinated silicon material is lower than that of the first fluorinated silicon material. The second fluorinated silicon material may also include silicon-containing compounds and fluorides. In specific implementations, the silicon-containing compound may be SiCl4 or C8H. 24 O4Si4, the fluoride may include at least one of SiF4, CF4, SF6, C2F6, SOF2 and C2F2Cl2.

[0103] refer to Figure 2 The first torch 400 can move in multiple turns along the axial direction of the mandrel 10 to deposit the second fluorinated silicon material multiple times on the surface of the first fluorinated layer. When there is one torch, the first torch 400 can form two second fluorinated layers when it moves in one turn along the axial direction of the mandrel 10. When there are multiple first torches 400, 2n second fluorinated layers can be deposited when it moves in one turn, where n is the number of first torches 400.

[0104] In step S402, while controlling the first torch 400 to spray the second fluorinated silicon material onto the mandrel 10, the second torch 500 and the third torch 600 are simultaneously controlled to move along the axial direction of the mandrel 10 and spray the first silicon material to form several layers of the first silicon layer.

[0105] refer to Figure 2 The first torch 400, the second torch 500, and the third torch 600 move simultaneously, with the second torch 500 and the third torch 600 spaced apart from the first torch 400 along the axial direction of the mandrel 10. If all torches are located at the first end of the mandrel 10, and the first torch 400 is closer to the first end than the second torch 500 and the third torch 600, during the movement of all torches, the first torch 400 first deposits a second fluorine-doped layer on the surface of the first fluorine-doped layer, and then the second torch 500 and the third torch 600 jointly deposit a first silicon layer on the second fluorine-doped layer.

[0106] If there is only one first blowtorch 400, one second blowtorch 500, and one third blowtorch 600, after all the blowtorches move once, a stacked layer of one first silicon layer and one second fluorine-doped layer will be formed. If there are multiple first blowtorches 400, 500, and 600 of the same quantity, after all the blowtorches move once, the same number of first silicon layers and second fluorine-doped layers will be formed, and at this time, the multiple first silicon layers and multiple second fluorine-doped layers will be stacked on top of each other. After all the blowtorches move multiple times, a stacked structure layer of multiple first silicon layers and multiple second fluorine-doped layers will be formed.

[0107] In some embodiments, when multiple rounds of deposition of the second fluorinated silicon material and the first silicon material are required on the first fluorinated layer, the amount of fluoride in the second fluorinated silicon material sprayed from the first torch 400 can be reduced after each one or more rounds of deposition of the second fluorinated silicon material. This allows the fluorination depth of the second fluorinated layer to be gradually reduced during the deposition process, thereby causing the fluorination depth of the stacked structure layer to gradually decrease in the direction away from the first fluorinated layer. That is, the fluorination depth of the second fluorinated layer on the side closer to the first fluorinated layer is greater than the fluorination depth of the second fluorinated layer on the side farther from the first fluorinated layer.

[0108] In step S403, when the stacked structure layer reaches a certain thickness, the first blowtorch 400, the second blowtorch 500 and the third blowtorch 600 are turned off, and a gradient fluorine-doped layer is formed. This stacked structure layer is the gradient fluorine-doped layer.

[0109] In some embodiments, during the deposition of the second fluorine-doped layer, the flame temperatures of the first blowtorch 400, the second blowtorch 500, and the third blowtorch 600 are the same, and the flame temperatures of the first blowtorch 400, the second blowtorch 500, and the third blowtorch 600 are all greater than or equal to 800°C and less than or equal to 1000°C. For example, the flame temperatures of the first blowtorch 400, the second blowtorch 500, and the third blowtorch 600 can be 850°C, 900°C, and 950°C, respectively.

[0110] In some embodiments, the density of the gradient fluorine-doped layer is greater than or equal to 0.3 g / cm³. 3 And less than or equal to 0.5 g / cm 3 For example, the density of the graded fluorine-doped layer can be 0.34 g / cm³. 3 0.37g / cm 3 0.41 g / cm 3 0.46 g / cm 3 Or 0.49g / cm 3 .

[0111] In some examples, the fluorine doping depth of the graded fluorine-doped layer is greater than or equal to -0.1% and less than 0. For example, the fluorine doping depth of the graded fluorine-doped layer can be -0.09%, -0.07%, -0.06%, -0.04%, or -0.03%. In specific implementations, the fluorine doping depth of the second fluorine-doped layer closest to the first fluorine-doped layer can be -0.1%, and the fluorine doping depth of the second fluorine-doped layer on the side opposite to the first fluorine-doped layer can be -0.01%.

[0112] refer to Figure 9 In one possible implementation, the step of forming the stacked structure layers may further include:

[0113] Step S501: Measure whether the thickness of the stacked structure layer reaches the second preset thickness.

[0114] In some embodiments, the second preset thickness can be 1.5 times the first preset thickness. By making the second preset thickness greater than the first preset thickness, the probability of the first fluorine-doped layer being diffused and lost during sintering can be further reduced.

[0115] In step S502, if the second preset thickness is reached, the first blowtorch 400, the second blowtorch 500 and the third blowtorch 600 are turned off, and the stacked structure layer at this time is used as the gradient fluorine-doped layer.

[0116] In step S503, if the second preset thickness is not reached, the first silicon layer and the second fluorine-doped layer are formed to make the thickness of the stacked structure layer reach the second preset thickness until the thickness of the stacked structure layer reaches the second preset thickness.

[0117] In practical implementation, the OVD device can obtain the data fed back by the diameter measuring instrument 700 through the control unit, calculate the outer diameter of the mandrel 10 with the stacked structure layer deposited at this time, and calculate the thickness of the stacked structure layer deposited on the surface of the mandrel 10 at this time. If the thickness of the stacked structure layer at this time is 1.5 times the thickness of the first fluorinated silicon layer, the control unit controls all the torches to stop working and takes the stacked structure layer at this time as the first fluorinated silicon layer.

[0118] In some embodiments, after forming a gradient fluorine-doped layer on the surface of the first fluorine-doped layer, a second silicon layer may be formed on the surface of the gradient fluorine-doped layer. The second silicon layer protects both the gradient fluorine-doped layer and the first fluorine-doped layer.

[0119] In one possible implementation, the step of forming a second silicon layer on the surface of the gradient fluorine-doped layer may include: controlling a first blowtorch 400, a second blowtorch 500, and a third blowtorch 600 to move simultaneously in the same direction along the axial direction of the mandrel 10; controlling the first blowtorch 400 to ignite and stop spraying the first fluorine-doped silicon material; controlling the second blowtorch 500 and the third blowtorch 600 to spray the second silicon material; and when the weight of the mandrel 10 containing the second silicon material reaches a preset weight, turning off the first blowtorch 400, the second blowtorch 500, and the third blowtorch 600 to form the second silicon layer. In some embodiments, the preset weight is greater than or equal to 80 kg and less than or equal to 120 kg, for example, the first preset weight may be 85 kg, 90 kg, 100 kg, or 150 kg.

[0120] refer to Figure 2 In some embodiments, the OVD device may further include a weighing instrument 800, which is disposed at the end of the chuck 200. The weighing instrument 800 can be used to detect the mass of the mandrel 10 deposited with a first fluorine-doped layer, a gradient fluorine-doped layer, and a second silicon material in real time. The weighing instrument 800 is connected to a control unit, which can determine the difference between the weight data obtained by the weighing instrument 800 and a preset weight. When the difference between the weight data and the preset weight is 0, the control unit turns off the first blowtorch 400, the second blowtorch 500, and the third blowtorch 600, so that the second silicon material deposited on the mandrel 10 at this time is used as the second silicon layer.

[0121] In some embodiments, the second silicon material can be the same as the first silicon material, and the second silicon material can be SiCl4 or C8H. 24 O4Si4.

[0122] In one possible implementation, when depositing the second silicon material on the surface of the gradient fluorine-doped layer to form the second silicon layer, the flame temperatures of the first torch 400, the second torch 500, and the third torch 600 are all greater than or equal to 1150°C and less than or equal to 1250°C. For example, the flame temperatures of the first torch 400, the second torch 500, and the third torch 600 can all be 1190°C, 1200°C, or 1230°C.

[0123] In some embodiments, the density of the second silicon layer is greater than or equal to 0.7 g / cm³. 3 And less than or equal to 0.8 g / cm 3 For example, the density of the second silicon layer can be 0.71 g / cm³. 3 0.73g / cm 3 0.75g / cm 3 Or 0.77g / cm 3 .

[0124] refer to Figure 2 In one specific embodiment, an alkali metal doped core rod 10 is prepared by the VAD process, with a diameter of 40 mm, a length of 2000 mm, a deposition target weight of 50 kg, and a target outer diameter of 250 mm.

[0125] The deposition chamber 100 contains four torches: the first torch 400, the second torch 500, and the third torch 600. Each first torch 400 initially contains 1000cc of fluorine doping, and the amount of fluorine doping in each torch 400 is adjusted according to the target number of passes. 20g of SiCl4 is required when depositing the first fluorine-doped layer, 30g of SiCl4 is required when depositing the graded fluorine-doped layer, and 35g of SiCl4 is required when depositing the second silicon layer.

[0126] Based on the first preset thickness, the number of deposition cycles for the first fluorine-doped layer is calculated to be 120, the number of deposition cycles for the gradient fluorine-doped layer is 180, the number of deposition cycles for the second silicon layer is 300, and the total number of cycles is 600.

[0127] During the deposition of the first fluorine-doped layer, the flame temperature of the first torch 400 was controlled at 820℃, and the density of the first fluorine-doped layer was 0.28 g / cm³. 3 The flame temperature of the first torch 400, the second torch 500, and the third torch 600 during the deposition of the graded fluorine-doped layer was 950℃, and the density of the graded fluorine-doped layer was 0.4 g / cm³. 3 During the deposition of the second silicon layer, the flame temperature of the first torch 400, the second torch 500, and the third torch 600 was 1250℃, and the density of the second silicon layer was 0.88 g / cm³. 3 .

[0128] Among them, the fluorine doping depth of the first fluorine-doped layer of the final optical fiber preform is -0.22%, and the fluorine doping depth of the graded fluorine-doped layer is reduced from -0.09% to 0.

[0129] Tests using relevant equipment show that the light produced using the optical fiber preform prepared by the method provided in this application has an attenuation value of 0.162 dB / Km at a wavelength of 1550 nm, which is 0.013 dB / Km lower than that of conventional optical fiber.

[0130] This application also provides an optical fiber preform, which is prepared by the preparation method described above. The optical fiber preform prepared by the above method can improve the uniformity of optical fluorine doping, increase the temperature of the optical fiber preform during fiber drawing, which is beneficial for reducing the viscosity of the core rod 10 and the interfacial stress between the core rod 10 and the first fluorine-doped layer, and can improve the preparation efficiency of the optical fiber preform.

[0131] The various embodiments or implementation methods described in this specification are presented in a progressive manner. Each embodiment focuses on the differences from other embodiments, and the same or similar parts between the embodiments can be referred to each other.

[0132] It should be noted that phrases such as "in specific implementations," "in some embodiments," "in this embodiment," and "exemplarily" in the specification indicate that the described embodiments may include specific features, structures, or characteristics, but not every embodiment necessarily includes that specific feature, structure, or characteristic. Furthermore, such phrases do not necessarily refer to the same embodiment. Moreover, when a specific feature, structure, or characteristic is described in connection with an embodiment, implementing such a feature, structure, or characteristic in conjunction with other embodiments, whether explicitly described or not, is within the knowledge scope of those skilled in the art.

[0133] Generally speaking, terms should be understood at least in part by their use in context. For example, at least in part by context, the term "one or more" as used in the text can be used to describe any feature, structure, or characteristic of the singular meaning, or a combination of features, structures, or characteristics of the plural meaning. Similarly, at least in part by context, terms such as "a" or "the" can also be understood to convey either singular or plural usage.

[0134] It should be readily understood that “on,” “above,” and “on top of” in this disclosure should be interpreted in the broadest manner, such that “on” means not only “directly on something” but also “on something” with an intermediate feature or layer therebetween, and that “above” or “on top of” means not only “on something” but also “on something” without an intermediate feature or layer therebetween (i.e., directly on something).

[0135] Furthermore, for ease of explanation, spatially relative terms such as "below," "below," "under," "above," and "above" may be used to describe the relationship of one element or feature relative to other elements or features as shown in the figures. Spatially relative terms are intended to encompass different orientations of the device in use or operation other than those shown in the figures. The device may have other orientations (rotated 90 degrees or in other orientations), and the spatially relative descriptive terms used herein may be interpreted accordingly.

[0136] Finally, it should be noted that the above embodiments are only used to illustrate the technical solutions of this application, and are not intended to limit them. Although this application has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some or all of the technical features therein. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the scope of the technical solutions of the embodiments of this application.

Claims

1. A method for preparing a low-loss optical fiber preform, characterized in that, The preparation method includes the following steps; Provide core rods; The mandrel is placed inside the deposition chamber of an external vapor deposition apparatus; A first fluorine-doped layer is formed on the surface of the mandrel; A gradient fluorine-doped layer is formed on the surface of the first fluorine-doped layer, and a powder rod is formed thereon; the fluorine doping depth of the gradient fluorine-doped layer gradually decreases in the direction away from the first fluorine-doped layer, and the fluorine doping depth of the first fluorine-doped layer is greater than the fluorine doping depth of the gradient fluorine-doped layer. The powder rod is placed in a sintering furnace for sintering to form an optical fiber preform; The step of forming a first fluorine-doped layer on the surface of the mandrel includes: The first torch is controlled to move axially on the mandrel and spray the first fluorine-doped silicon material onto the surface of the mandrel; When the first fluorinated silicon material on the surface of the mandrel reaches a first preset thickness, the first blowtorch is turned off, and the first fluorinated layer is formed; The ratio of the first preset thickness to the outer diameter of the mandrel is greater than or equal to 0.5 and less than or equal to 1; The step of forming a gradient fluorine-doped layer on the surface of the first fluorine-doped layer includes: The first torch is controlled to move along the axial direction of the mandrel and spray the second fluorine-doped silicon material to form several layers of the second fluorine-doped layer; The second and third torches are controlled to move along the axial direction of the mandrel and spray the first silicon material to form several layers of the first silicon layer; Several layers of the second fluorine-doped layer and several layers of the first silicon layer are alternately stacked radially on the outer surface of the first fluorine-doped layer to form a stacked structure layer; Measure whether the thickness of the stacked structure layer reaches the second preset thickness; If the second preset thickness is reached, the first blowtorch, the second blowtorch, and the third blowtorch are turned off, and the gradient fluorine-doped layer is formed. If the second preset thickness is not reached, the first silicon layer and the second fluorine-doped layer are deposited to make the thickness of the stacked structure layer reach the second preset thickness. The fluorine doping depth of several second fluorine-doped layers gradually decreases in the direction away from the first fluorine-doped layer, and the second preset thickness is 1.5 times the first preset thickness. The step of controlling the first torch to move axially on the mandrel and spraying the first fluorine-doped silicon material onto the surface of the mandrel includes: Ignite the second and third blowtorches; The first blowtorch, the second blowtorch, and the third blowtorch are controlled to move simultaneously in the same direction along the axial direction of the mandrel, so as to control the flame shape of the first blowtorch through the second blowtorch and the third blowtorch; In this process, after the second and third torches are ignited, the second and third torches do not spray the deposit material, but only burn the flame; The first blowtorch, the second blowtorch, and the third blowtorch are arranged at intervals in a direction perpendicular to the axis of the mandrel, with the first blowtorch located between the second blowtorch and the third blowtorch; The second and third torches are spaced apart from the first torch along the axial direction of the mandrel.

2. The preparation method according to claim 1, characterized in that, The step of forming a graded fluorine-doped layer on the surface of the first fluorine-doped layer further includes: A second silicon layer is formed on the surface of the gradient fluorine-doped layer.

3. The preparation method according to claim 2, characterized in that, The step of forming a second silicon layer on the surface of the graded fluorine-doped layer includes: Control the first, second, and third blowtorches to move simultaneously in the same direction along the axial direction of the mandrel; Control the first blowtorch to ignite and stop spraying the first fluorinated silicon material, and control the second and third blowtorches to spray the second silicon material; When the weight of the mandrel containing the second silicon material reaches a preset weight, the first blowtorch, the second blowtorch, and the third blowtorch are turned off to form the second silicon layer. The preset weight is greater than or equal to 80Kg and less than or equal to 120Kg.

4. The preparation method according to claim 3, characterized in that, When the first fluorine-doped layer is formed on the surface of the mandrel, the flame temperature of the first blowtorch is greater than or equal to 750°C and less than or equal to 850°C. The density of the first fluorine-doped layer on the surface of the mandrel is greater than or equal to 0.2 g / cm³. 3 And less than or equal to 0.3 g / cm 3 ; The fluorine doping depth of the first fluorine-doped layer is greater than or equal to -0.3% and less than or equal to -0.2%.

5. The preparation method according to claim 4, characterized in that, When a gradient fluorine-doped layer is formed on the surface of the first fluorine-doped layer, the flame temperature of the first blowtorch is greater than or equal to 800°C and less than or equal to 1000°C; the flame temperatures of the second blowtorch and the third blowtorch are equal to the flame temperature of the first blowtorch. The density of the graded fluorine-doped layer is greater than or equal to 0.3 g / cm³. 3 And less than or equal to 0.5 g / cm 3 ; The fluorine doping depth in the gradient fluorine-doped layer is greater than or equal to -0.1% and less than 0.

6. The preparation method according to claim 2, characterized in that, When the second silicon layer is formed on the surface of the gradient fluorine-doped layer, the flame temperature of the first blowtorch is greater than or equal to 1150°C and less than or equal to 1250°C; the flame temperatures of the second blowtorch and the third blowtorch are equal to the flame temperature of the first blowtorch. The density of the second silicon layer is greater than or equal to 0.7 g / cm³. 3 And less than or equal to 0.8 g / cm 3 .

7. The preparation method according to claim 1, characterized in that, Both the first fluorinated silicon material and the second fluorinated silicon material include silicon-containing compounds and fluorides; And / or, both the silicon-containing compound and the first silicon material are SiCl4 or C8H. 24 O4Si4; And / or, the fluoride includes at least one of SiF4, CF4, SF6, C2F6, SOF2 and C2F2Cl2.

8. An optical fiber preform, characterized in that, The optical fiber preform is prepared by the preparation method as described in any one of claims 1 to 7 above.

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