A method for preparing deeply fluorine-doped materials for low-loss optical fibers

Abstract

This invention discloses a method for preparing deeply fluorinated materials for low-loss optical fibers, comprising the following steps: preparation of ash rods; purification treatment; fluorine doping 1: lowering the furnace temperature and introducing fluorine gas 1 and He; fluorine doping 2: raising the furnace temperature and introducing fluorine gas 1 and He; fluorine doping 3: raising the furnace temperature and introducing fluorine gas 1 and fluorine gas 2; vitrification treatment: at the vitrification temperature, introducing fluorine gas 1, fluorine gas 2 and He to complete the vitrification of the ash rod; and heat preservation treatment. Based on existing equipment, this invention decomposes the fluorine doping process into three steps at low, medium, and high temperatures, which can minimize fluorine decomposition and facilitate process promotion; the introduction of fluorine gas 2 is used to suppress fluorine decomposition at high temperatures, effectively increasing the fluorine doping amount; the outer diameter of the deeply fluorinated material is 90-120 mm, and the relative refractive index is -0.80% to -0.65%, which has significant advantages in size and refractive index compared to current fluorinated materials.

Description

Technical Field

[0001] This invention belongs to the field of optical fiber fabrication technology, specifically relating to a method for preparing deeply fluorine-doped materials for low-loss optical fibers. Background Technology

[0002] Low-refractive-index fluorine-doped materials have become key materials and core technologies in optical fiber fabrication. Currently, the dominant market-leading products such as bend-resistant fiber, G657.A2, G657.B3 fiber, low-loss fiber (LL), and ultra-low-loss fiber (ULL) are all made using fluorine-doped materials. In the design of bend-resistant and low-loss optical fibers, the low-refractive-index fluorine-doped structure serves as a recessed cladding to suppress transmission energy loss and reduce losses caused by concentration fluctuations, making it a mainstream design scheme for new optical fibers. However, the availability of deeply fluorinated materials for optical fiber preforms has long been a challenge in preform fabrication technology. Large-scale mass production has been mastered by only a few manufacturers such as Heraeus, and China has long relied on imports for deeply fluorinated materials. With the development of optical fiber and preform technology, it is necessary to conduct research and breakthroughs in deeply fluorinated materials.

[0003] Currently, domestic manufacturers have prepared fluorine-doped materials with various fluorine doping depths and sizes using different technical solutions. Chinese invention patent, publication number CN112266162A, discloses a method for preparing fluorine-doped quartz tubes suitable for large-size optical fiber preforms. In terms of product size and refractive index depth, it can basically meet most product requirements, but its minimum relative refractive index is -0.65%, and it does not mention whether a deeper refractive index can be achieved. Chinese invention patent, publication number CN103553320A, discloses a quartz sleeve for large-size optical fiber preform core rods and its manufacturing method, with a minimum relative refractive index of -1.5%, but its relatively small size limits its application range. Chinese invention patent, publication number CN104402213A, discloses a method for vitrifying pure silica loose material with fluorine doping. Through the VAD process, a dense layer and a loose layer with significant differences in core and cladding density are selectively prepared, allowing fluorine to selectively enter the loose layer and form a fluorine-doped cladding with a relative refractive index of -0.362%. The obvious drawback of this process is that due to the large difference in core and cladding density, it is difficult for gas to escape during vitrification, which easily leads to bubble defects.

[0004] With the upgrading of optical fiber performance, higher requirements have been placed on the fluorine doping depth and size of fluorine-doped materials, requiring a relative refractive index of -0.80% to -0.65%. However, there is currently no particularly effective preparation method. Summary of the Invention

[0005] To address the technical problems existing in the prior art, the present invention aims to provide a method for preparing deeply fluorine-doped materials for low-loss optical fibers.

[0006] To achieve the above objectives and technical effects, the technical solution adopted by this invention is as follows:

[0007] A method for preparing a deeply fluorine-doped material for low-loss optical fibers includes the following steps:

[0008] 1) Preparation of ash rods: Porous ash rods were prepared by chemical vapor deposition.

[0009] 2) Purification treatment: Place the ash rods obtained in step 1) into a sintering furnace, introduce Cl2 and He, then raise the furnace temperature and introduce Cl2 and He again;

[0010] 3) Fluorine doping 1: Lower the furnace temperature and introduce fluorine gas 1 and He;

[0011] 4) Fluorine doping 2: Increase furnace temperature and introduce fluorine gas 1 and He;

[0012] 5) Fluorine doping 3: Increase the furnace temperature and introduce fluorine gas 1 and fluorine gas 2;

[0013] 6) Vitrification: Raise the furnace temperature to the glass transition temperature, introduce fluorine gas 1, fluorine gas 2 and He to complete the vitrification of the ash rod and obtain a glass rod;

[0014] 7) Thermal insulation treatment;

[0015] In steps 2) through 6), the ash stick is rotated at a constant speed.

[0016] Furthermore, in step 2), the purification process includes:

[0017] Place the ash rod in a sintering furnace at 1000-1200℃. First, introduce Cl2 at a rate of 0.5-1.5 L / min for 60-100 min. Second, introduce He at a rate of 10-30 L / min for 60-100 min. After that, raise the furnace temperature by 50-100℃ and repeat the first and second steps at least once.

[0018] Furthermore, in step 3), the fluorine doping step 1 includes:

[0019] To complete the purification treatment of the ash rod in step 2), reduce the temperature of the sintering furnace to 1000±50℃, introduce fluorine gas 1 at a rate of 2-5L / min, and introduce He at a rate of 10-20L / min for a treatment time of 100-250min.

[0020] Furthermore, in step 4), the fluorine doping step 2 includes:

[0021] After step 3) is completed, raise the temperature of the sintering furnace to 1200±50℃, introduce fluorine gas 1 at a rate of 3-5L / min, introduce He gas at a rate of 10-20L / min, and process for 100-250min.

[0022] Furthermore, in step 5), the fluorine doping step 3 includes:

[0023] After step 4) is completed, the temperature of the sintering furnace is raised to 1300±50℃, and fluorine gas 1 is introduced at a rate of 3-8L / min, fluorine gas 2 is introduced at a rate of 0.2-2L / min, and He is introduced at a rate of 10-20L / min. The treatment time is 150-250min.

[0024] Furthermore, in step 6), the vitrification process includes:

[0025] After step 5), raise the temperature of the sintering furnace to 1450±20℃, introduce 3-8L / min of fluorine gas 1, 2-5L / min of fluorine gas 2, and 10-30L / min of He, and process for 250-450min to complete the vitrification of the ash rod.

[0026] Furthermore, in step 7), the heat preservation process includes:

[0027] The temperature of the sintering furnace is lowered from the glass transition temperature to the set temperature, and the glass rod that has completed the glass transition is annealed for 6-12 hours.

[0028] Furthermore, the fluorine gas 1 is one or a combination of two or more of CF4, C2F6, C3F8, and SF6, and the fluorine gas 2 is SiF4 gas.

[0029] Furthermore, the relative refractive index of the deeply fluorinated material is -0.80% to -0.65%, and the outer diameter is 90-120 mm.

[0030] The present invention also discloses the application of the deeply fluorinated material prepared by the preparation method of the low-loss optical fiber as described above in the low-loss optical fiber, wherein the 1550 window attenuation of the low-loss optical fiber is ≤0.170dB / km.

[0031] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0032] 1) Based on the existing equipment, the fluorine doping process can be decomposed into three steps at three different temperatures: low temperature, medium temperature, and high temperature. This can minimize fluorine decomposition and facilitate the increase of fluorine doping and the promotion of the process.

[0033] 2) This invention introduces fluorine gas 2 to suppress fluorine decomposition at high temperatures, effectively increasing the fluorine doping amount and reducing the refractive index;

[0034] 3) The fluorine-doped material prepared by this invention has an outer diameter of 90-120 mm and a relative refractive index of -0.80% to -0.65%. Compared with current fluorine-doped materials, it has significant advantages in terms of size and refractive index. The advantage in size is reflected in the fact that when preparing optical fiber preforms, the preforms produced by the large-size fluorine-doped material are larger in size, longer in length, and have a longer corresponding drawing length, resulting in a more obvious cost advantage. The advantage in refractive index is reflected in the fact that the realization of deeper refractive index materials makes it possible to design optical waveguide structures that were previously difficult to achieve. Attached Figure Description

[0035] Figure 1 This is a flowchart of a method for preparing a deeply fluorine-doped material for low-loss optical fibers according to the present invention;

[0036] Figure 2 This is a temperature control curve for a method of preparing a deeply fluorine-doped material for low-loss optical fiber according to Embodiment 1 of the present invention.

[0037] Figure 3 This is a relative refractive index profile of the deeply fluorine-doped material in Example 1 of the present invention;

[0038] Figure 4 This is a relative refractive index profile of the fluorine-doped material in Comparative Example 2. Detailed Implementation

[0039] The present invention will now be described in detail so that its advantages and features can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0040] The following provides a brief overview of one or more aspects to offer a basic understanding of them. This overview is not an exhaustive summary of all conceived aspects, nor is it intended to identify key or decisive elements of all aspects, nor to define the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form to prepare for the more detailed descriptions that follow.

[0041] The fluorine doping process is an equilibrium process according to the following equation, using CF4 as a typical fluorine source as an example. CF4 reacts with SiO2 to produce SiO2. 1.5 F, and SiO 1.5 Fluorine (F) decomposes into SiF4 and SiO2 at high temperatures. The final effect of fluorine doping after the chemical reaction can be characterized by refractive index testing; a deeper refractive index indicates a higher amount of fluorine doping. For fluorine doping of various types of ash rods, the deeper the refractive index, the greater the difficulty in preparation.

[0042] Equation 1: CF4 + SiO2 → CO + CO2 + COF2 + SiO 1.5 F

[0043] Equation 2:

[0044] To prepare fluorine-doped materials with high refractive index through the above equilibrium reaction, it is necessary to prevent the reverse reaction as much as possible and increase the fluorine doping amount of SiO2 as much as possible. To this end, this invention creatively divides the fluorine doping process into three steps, corresponding to three different temperatures: low temperature, medium temperature, and high temperature. These are the low temperature fluorine doping process, the medium temperature fluorine doping process, and the high temperature fluorine doping process. By controlling the temperature and density, the fluorine doping amount is increased to the maximum extent, the fluorine decomposition is reduced to the minimum, the forward reaction is increased, and the occurrence of the reverse reaction is suppressed, especially the decomposition of fluorine at high temperature, which also facilitates the promotion of the process.

[0045] like Figure 1-3 As shown, this invention discloses a method for preparing deeply fluorine-doped materials for low-loss optical fibers, comprising the following steps:

[0046] 1) Preparation of ash rods: Porous ash rods are prepared by chemical vapor deposition. The ash rods may contain a core layer and a cladding layer or only a part of them. The main reactants are SiCl4, H2, and O2, with Ar introduced as an auxiliary gas. This step can be done using existing mature technologies.

[0047] 2) Purification treatment: Place the ash rod in a sintering furnace at 1000-1200℃. In the first step, introduce Cl2 at a rate of 0.5-1.5L / min for 60-100min. In the second step, continuously introduce He at a rate of 10-30L / min for 60-100min. After that, raise the furnace temperature by 50-100℃ and repeat the first and second steps at least once. During the ash rod treatment, maintain a rotation speed of 1-2mm / min.

[0048] 3) Fluorine doping 1, i.e. low-temperature fluorine doping: end step 2) purification treatment of the ash rod, reduce the temperature of the sintering furnace to 1000±50℃, introduce 2-5L / min of fluorine gas 1, introduce 10-20L / min of He, process for 100-250min, and keep the ash rod rotating at a speed of 1-2mm / min.

[0049] 4) Fluorine doping 2, i.e. medium-temperature fluorine doping: After step 3), the temperature of the sintering furnace is raised to 1200±50℃, fluorine gas 1 is introduced at 3-5L / min, and He is introduced at 10-20L / min. The treatment time is 100-250min, and the ash rod is always rotated at a speed of 1-2mm / min.

[0050] 5) Fluorine doping 3, i.e. high-temperature fluorine doping: After step 4), the temperature of the sintering furnace is raised to 1300±50℃, fluorine gas 1 is introduced at 3-8L / min, fluorine gas 2 is introduced at 0.2-2L / min, and He is introduced at 10-20L / min. The treatment time is 150-250min, and the ash rod is rotated at a speed of 1-2mm / min throughout.

[0051] 6) Vitrification treatment: After completing the fluorine doping process 3, raise the temperature of the sintering furnace to the glass transition temperature (1450±20℃), introduce fluorine gas 1 at 3-8L / min, fluorine gas 2 at 2-5L / min, and He at 10-30L / min, for a treatment time of 250-450min to complete the vitrification of the ash rod. The ash rod is always rotated at a speed of 1-2mm / min.

[0052] 7) Heat preservation treatment: The temperature of the sintering furnace is reduced from the glass transition temperature to the set temperature of 1100℃, and the glass rod that has completed the glass transition is annealed for 6-12 hours to further remove stress, bubbles, etc., and finally obtain the required low-loss optical fiber deeply fluorine-doped material.

[0053] It should be noted that the porous ash rods of the present invention are prepared by processes such as VAD and OVD. To ensure the final size of the fluorine-doped material, the diameter of the ash rods is controlled at 180-300 mm, and the density is controlled at 0.20-0.50 g / cm³. 3 .

[0054] Fluorine gas 1 is one or a combination of two or more of CF4, C2F6, C3F8, and SF6.

[0055] Fluorine gas 2 is SiF4 gas.

[0056] The purification process employs a high-low temperature cycling method. This ensures that the metals in the ash rod can react fully (especially under conditions of high density) and that the porosity of the ash rod changes by less than 10% before and after purification.

[0057] During the fluorine doping process, fluorine gas at a rate of 2-5 L / min is introduced at 1000±50℃. Through thermal diffusion, fluorine ions can completely diffuse to the center. After diffusion is complete, the diameter and density of the ash rod remain basically unchanged.

[0058] During the fluorine doping process, the sintering furnace temperature is raised to 1200±50℃, and fluorine gas is introduced at a rate of 3-5 L / min. This increases the temperature, raises the thermal diffusion activation energy, accelerates the chemical reaction, and further enhances the diffusion capacity. Simultaneously, the ash rod shrinks, reducing its porosity. After diffusion is complete, the diameter of the ash rod shrinks by 80±5% relative to its initial size, and its density increases to 0.60-0.85 g / cm³. 3 ;

[0059] During the fluorine doping process 3, the sintering furnace temperature is raised to 1300±50℃, and fluorine gas 1 (such as CF4) is introduced at a rate of 3-8 L / min, followed by fluorine gas 2 (such as SiF4) at a rate of 0.2-2 L / min. The soot rod further shrinks. After diffusion is complete, the diameter of the soot rod shrinks by 60±5% relative to the fluorine doping process 2, and the density increases to 1.0-1.4 g / cm³. 3 ;

[0060] During the vitrification process, the temperature of the sintering furnace is raised to the glass transition temperature, and 3-8 L / min of fluorine gas 1 is introduced to further increase the fluorine doping amount. Introducing 2-5 L / min of fluorine gas 2 (such as SiF4) can weaken the decomposition of fluorine at high temperature and promote the chemical reaction to proceed in the forward direction.

[0061] Relative refractive index: Through this method, the fluorine doping depth of the obtained fluorine-doped material is further reduced to -0.80% to -0.65%, and the outer diameter of the fluorine-doped material is 90-120 mm.

[0062] Example 1

[0063] like Figure 1-3 As shown, a method for preparing a deeply fluorine-doped material for low-loss optical fibers includes the following steps:

[0064] 1) Ash rod preparation: Porous ash rods are prepared by OVD process. The ash rod may contain a core layer and a cladding layer or only a part of them. The main reaction raw materials are SiCl4, H2 and O2 raw materials, and Ar is introduced as an auxiliary gas. Existing processes can be used.

[0065] 2) Purification treatment: The ash rods are placed in a U-shaped sintering furnace for dehydration and purification treatment. The temperature is set to T1 = 1050℃. In the first step, Cl2 is introduced at a rate of 1.0 L / min for 60 min. In the second step, He is continuously introduced at a rate of 15 L / min for 60 min. After that, the furnace temperature is increased by 100℃ to T2 = 1150℃. The first and second steps are repeated twice. The treatment time can be adjusted according to the density of the ash rods. This process is mainly to ensure the dehydration and purification effect of the ash rods. During the treatment stage, the ash rods are rotated at a speed of 2 mm / min.

[0066] 3) Fluorine doping 1, i.e., low-temperature fluorine doping: After the purification treatment of the flue gas rod is completed, the sintering furnace temperature is reduced to T3 = 1000℃, and fluorine gas 1 (CF4) is introduced at a rate of 4.5 L / min, followed by He at a rate of 20 L / min, for a treatment time of 250 min; the flue gas rod is kept rotating at a speed of 2 mm / min throughout this process. After this stage is completed, the diameter and density of the flue gas rod remain basically unchanged.

[0067] 4) Fluorine doping 2, i.e., medium-temperature fluorine doping: After step 3), the sintering furnace temperature is raised to T4 = 1200℃, and fluorine gas 1 (CF4) is introduced at a rate of 4.5 L / min, followed by He at a rate of 20 L / min, for a processing time of 250 min. Throughout this process, the ash rod is rotated at a speed of 2 mm / min. After this process, the diameter of the ash rod shrinks by 80 ± 5% relative to its initial size, and the density increases to 0.60-0.85 g / cm³. 3 ;

[0068] 5) Fluorine doping 3, i.e., high-temperature fluorine doping: After step 4), the sintering furnace temperature is raised to T5 = 1300℃, and fluorine gas 1 (CF4) is introduced at a rate of 5 L / min, fluorine gas 2 (SiF4) at a rate of 1.0 L / min, and He at a rate of 20 L / min for 250 min. Throughout this process, the ash rod is rotated at a speed of 2 mm / min. The ash rod further shrinks; after diffusion is complete, the diameter of the ash rod shrinks by 60 ± 5% relative to that of the medium-temperature fluorine doping, and the density increases to 1.0-1.4 g / cm³. 3 ;

[0069] 6) Vitrification treatment: After completing the fluorine doping process 3, the temperature of the sintering furnace is raised to the glass transition temperature T6 = 1450℃, fluorine gas 1 (CF4) is introduced at a rate of 5L / min, fluorine gas 2 (SiF4) is introduced at a rate of 3.5L / min, and He is introduced at a rate of 30L / min. The treatment time is 410min to complete the vitrification of the ash rod, and the rod is rotated at a speed of 2mm / min throughout.

[0070] 7) Heat preservation treatment: After the glass rod has completed the glass transition, the temperature of the sintering furnace is reduced from 1450℃ to the set temperature T7=1100℃ for annealing treatment for 8 hours to further remove stress, bubbles, etc.

[0071] Characterization tests: The glass rod obtained in step 7 was characterized in terms of appearance, dimensions, and doping amount. Its relative refractive index was -0.772%, ranging from -0.80% to -0.65%. The relative refractive index profile is shown below. Figure 3 As shown, the outer diameter of the glass rod is 106 mm, which is within the range of 90-120 mm.

[0072] Example 2

[0073] like Figure 1-2 As shown, a method for preparing a deeply fluorine-doped material for low-loss optical fibers includes the following steps:

[0074] 1) Ash rod preparation: Porous ash rods are prepared by OVD process. The ash rods include a core layer and a cladding layer. The main reaction raw materials are SiCl4, H2 and O2, and Ar is introduced as an auxiliary gas.

[0075] 2) Purification treatment: The ash rods are placed in a U-shaped sintering furnace for dehydration and purification treatment. The temperature is set at 1050℃. In the first step, Cl2 is introduced at a rate of 1.0L / min for 60min. In the second step, He is continuously introduced at a rate of 15L / min for 60min. After that, the furnace temperature is increased by 100℃ to 1150℃. The first and second steps are repeated at least once. The treatment time can be adjusted appropriately according to the density of the ash rods. This process is mainly to ensure the dehydration and purification effect of the ash rods. During the treatment of the ash rods, they are rotated at a speed of 2mm / min.

[0076] 3) Fluorine doping 1, i.e., low-temperature fluorine doping: After the purification treatment of the flue gas rod is completed, the sintering furnace temperature is reduced to 950℃, and fluorine gas 1 (CF4) is introduced at a rate of 4.5L / min, followed by He at a rate of 20L / min, for a treatment time of 250min; the flue gas rod is kept rotating at a speed of 2mm / min throughout the process. After this stage is completed, the diameter and density of the flue gas rod remain basically unchanged.

[0077] 4) Fluorine doping 2, i.e., medium-temperature fluorine doping: After step 3), the sintering furnace temperature is raised to 1200℃, fluorine gas 1 (CF4) is introduced at a rate of 4.5 L / min, and He is introduced at a rate of 20 L / min for 250 min. Throughout this process, the ash rod is kept rotating at a speed of 2 mm / min.

[0078] 5) Fluorine doping 3, i.e., high-temperature fluorine doping: After step 4), the sintering furnace temperature is raised to 1300℃, and fluorine gas 1 (CF4) is introduced at a rate of 5 L / min, fluorine gas 2 (SiF4) at a rate of 1.0 L / min, and He at a rate of 20 L / min, for a processing time of 250 min. Throughout this process, the ash rod is kept rotating at a speed of 2 mm / min.

[0079] 6) Vitrification treatment: After completing the fluorine doping process 3, the temperature of the sintering furnace is raised to the glass transition temperature of 1450℃, 5.0L / min fluorine gas 1 (CF4) is introduced, 3.5L / min fluorine gas 2 (SiF4) is introduced, and 30L / min He is introduced. The treatment time is 410min to complete the vitrification of the ash rod, and the rotation speed is maintained at 2mm / min throughout.

[0080] 7) Heat preservation treatment: After the glass rod has completed the glass transition, the temperature of the sintering furnace is reduced from 1450℃ to the set temperature of 1100℃ for annealing treatment for 8 hours to further remove stress, bubbles, etc.

[0081] The glass rod obtained in step 7) was characterized in terms of appearance, size and doping amount. Its relative refractive index was -0.766%, between -0.80% and -0.65%, and the outer diameter of the glass rod was 109 mm, within the range of 90-120 mm.

[0082] The rest is the same as in Example 1.

[0083] Example 3

[0084] like Figure 1-2 As shown, a method for preparing a deeply fluorine-doped material for low-loss optical fibers includes the following steps:

[0085] 1) Ash rod preparation: Porous ash rods are prepared by OVD process. The ash rods include a core layer and a cladding layer. The main reaction raw materials are SiCl4, H2 and O2, and Ar is introduced as an auxiliary gas.

[0086] 2) Purification treatment: The ash rods are placed in a U-shaped sintering furnace for dehydration and purification treatment. The temperature is set at 1050℃. In the first step, Cl2 is introduced at a rate of 1.0L / min for 60min. In the second step, He is continuously introduced at a rate of 15L / min for 60min. After that, the furnace temperature is increased by 100℃ to 1150℃. The first and second steps are repeated at least once. The treatment time can be adjusted appropriately according to the density of the ash rods. This process is mainly to ensure the dehydration and purification effect of the ash rods. During the treatment of the ash rods, they are rotated at a speed of 2mm / min.

[0087] 3) Fluorine doping 1, i.e., low-temperature fluorine doping: After the purification treatment of the flue gas rod is completed, the sintering furnace temperature is reduced to 1000℃, and fluorine gas 1 (CF4) is introduced at a rate of 4.5L / min, followed by He at a rate of 20L / min, for a treatment time of 250min; the flue gas rod is kept rotating at a speed of 2mm / min throughout the process. After this stage is completed, the diameter and density of the flue gas rod remain basically unchanged.

[0088] 4) Fluorine doping 2, i.e., medium-temperature fluorine doping: After step 3), the sintering furnace temperature is raised to 1250℃, fluorine gas 1 (CF4) is introduced at a rate of 4.5 L / min, and He is introduced at a rate of 20 L / min for 250 min. Throughout this process, the ash rod is kept rotating at a speed of 2 mm / min.

[0089] 5) Fluorine doping 3, i.e., high-temperature fluorine doping: After step 4), the sintering furnace temperature is raised to 1300℃, and fluorine gas 1 (CF4) is introduced at a rate of 5 L / min, fluorine gas 2 (SiF4) at a rate of 1.0 L / min, and He at a rate of 20 L / min, for a processing time of 250 min. Throughout this process, the ash rod is kept rotating at a speed of 2 mm / min.

[0090] 6) Vitrification treatment: After completing the fluorine doping process 3, the temperature of the sintering furnace is raised to the glass transition temperature of 1450℃, 5.0L / min fluorine gas 1 (CF4) is introduced, 3.5L / min fluorine gas 2 (SiF4) is introduced, and 30L / min He is introduced. The treatment time is 410min to complete the vitrification of the ash rod, and the rotation speed is maintained at 2mm / min throughout.

[0091] 7) Heat preservation treatment: After the glass rod has completed the glass transition, the temperature of the sintering furnace is reduced from 1450℃ to the set temperature of 1100℃ for annealing treatment for 8 hours to further remove stress, bubbles, etc.

[0092] The glass rod obtained in step 7) was characterized in terms of appearance, size and doping amount. Its relative refractive index was -0.788%, between -0.80% and -0.65%, and the outer diameter of the glass rod was 115 mm, within the range of 90-120 mm.

[0093] The rest is the same as in Example 1.

[0094] Example 4

[0095] like Figure 1-2 As shown, a method for preparing a deeply fluorine-doped material for low-loss optical fibers includes the following steps:

[0096] 1) Ash rod preparation: Porous ash rods are prepared by OVD process. The ash rods include a core layer and a cladding layer. The main reaction raw materials are SiCl4, H2 and O2, and Ar is introduced as an auxiliary gas.

[0097] 2) Purification treatment: The ash rods are placed in a U-shaped sintering furnace for dehydration and purification treatment. The temperature is set at 1050℃. In the first step, Cl2 is introduced at a rate of 1.0L / min for 60min. In the second step, He is continuously introduced at a rate of 15L / min for 60min. After that, the furnace temperature is increased by 100℃ to 1150℃. The first and second steps are repeated at least once. The treatment time can be adjusted appropriately according to the density of the ash rods. This process is mainly to ensure the dehydration and purification effect of the ash rods. During the treatment of the ash rods, they are rotated at a speed of 2mm / min.

[0098] 3) Fluorine doping 1, i.e., low-temperature fluorine doping: After the purification treatment of the flue gas rod is completed, the sintering furnace temperature is reduced to 1000℃, and fluorine gas 1 (CF4) is introduced at a rate of 4.5L / min, followed by He at a rate of 20L / min, for a treatment time of 250min; the flue gas rod is kept rotating at a speed of 2mm / min throughout the process. After this stage is completed, the diameter and density of the flue gas rod remain basically unchanged.

[0099] 4) Fluorine doping 2, i.e., medium-temperature fluorine doping: After step 3), the sintering furnace temperature is raised to 1200℃, fluorine gas 1 (CF4) is introduced at a rate of 4.5 L / min, and He is introduced at a rate of 20 L / min for 250 min. Throughout this process, the ash rod is kept rotating at a speed of 2 mm / min.

[0100] 5) Fluorine doping 3, i.e., high-temperature fluorine doping: After step 4), the sintering furnace temperature is raised to 1350℃, and fluorine gas 1 (CF4) is introduced at a rate of 5 L / min, fluorine gas 2 (SiF4) at a rate of 1.0 L / min, and He at a rate of 20 L / min, for a processing time of 250 min. Throughout this process, the ash rod is rotated at a speed of 2 mm / min.

[0101] 6) Vitrification treatment: After completing the fluorine doping process 3, the temperature of the sintering furnace is raised to the glass transition temperature of 1450℃, 5.0L / min fluorine gas 1 (CF4) is introduced, 3.5L / min fluorine gas 2 (SiF4) is introduced, and 30L / min He is introduced. The treatment time is 410min to complete the vitrification of the ash rod, and the rotation speed is maintained at 2mm / min throughout.

[0102] 7) Heat preservation treatment: After the glass rod has completed the glass transition, the temperature of the sintering furnace is reduced from 1450℃ to the set temperature of 1100℃ for annealing treatment for 8 hours to further remove stress, bubbles, etc.

[0103] The glass rod obtained in step 7) was characterized in terms of appearance, size and doping amount. Its relative refractive index was -0.796%, between -0.80% and -0.65%, and the outer diameter of the glass rod was 116 mm, within the range of 90-120 mm.

[0104] The rest is the same as in Example 1.

[0105] Comparative Example 1

[0106] A method for preparing a deeply fluorine-doped material for low-loss optical fibers includes the following steps:

[0107] 1) Ash rod preparation: Porous ash rods are prepared by OVD process. The ash rods include a core layer and a cladding layer. The main reaction raw materials are SiCl4, H2 and O2, and Ar is introduced as an auxiliary gas.

[0108] 2) Purification treatment: The ash rod is placed in a U-shaped sintering furnace for dehydration and purification treatment. The temperature is set at 1050℃. In the first step, Cl2 is introduced at a rate of 1.0 L / min for 60 min. In the second step, He is continuously introduced at a rate of 15 L / min for 60 min. After that, the furnace temperature is increased by 100℃ to 1150℃. The first and second steps are repeated at least once. During the treatment of the ash rod, it is rotated at a speed of 2 mm / min.

[0109] 3) Fluorine doping 1, i.e. low-temperature fluorine doping: After the purification treatment of the flue gas rod is completed, the temperature of the sintering furnace is reduced to 1000℃, fluorine gas 1 (CF4) is introduced at a rate of 4.5L / min, and He is introduced at a rate of 20L / min for a treatment time of 250min; the flue gas rod is kept rotating at a speed of 2mm / min throughout the process.

[0110] 4) Fluorine doping 2, i.e., medium-temperature fluorine doping: After step 3), the sintering furnace temperature is raised to 1200℃, fluorine gas 1 (CF4) is introduced at a rate of 4.5 L / min, and He is introduced at a rate of 20 L / min for 250 min. Throughout this process, the ash rod is kept rotating at a speed of 2 mm / min.

[0111] 5) Fluorine doping 3, i.e., high-temperature fluorine doping: After step 4), the sintering furnace temperature is raised to 1380℃, and fluorine gas 1 (CF4) is introduced at a rate of 5 L / min, fluorine gas 2 (SiF4) at a rate of 1.0 L / min, and He at a rate of 20 L / min, for a processing time of 250 min. Throughout this process, the ash rod is rotated at a speed of 2 mm / min.

[0112] 6) Vitrification treatment: After completing the fluorine doping process 3, the temperature of the sintering furnace is raised to the glass transition temperature of 1450℃, 5.0L / min fluorine gas 1 (CF4) is introduced, 3.5L / min fluorine gas 2 (SiF4) is introduced, and 30L / min He is introduced. The treatment time is 410min to complete the vitrification of the ash rod, and the rotation speed is maintained at 2mm / min throughout.

[0113] 7) Heat preservation treatment: After the glass rod has completed the glass transition, the temperature of the sintering furnace is reduced from 1450℃ to the set temperature of 1100℃ for annealing treatment, which takes 8 hours.

[0114] Same as Example 1.

[0115] Comparative Example 2

[0116] The difference between this comparative example and Example 1 is that this comparative example only performed steps 1), 2), 5), 6), and 7), omitting steps 3) and 4). The remaining steps are the same as in Example 1. The final relative refractive index profile of the glass rod is shown in the figure. Figure 4As shown.

[0117] Characterization results analysis:

[0118] Compared with Example 1, the temperature of the high-temperature fluorine doping process in Comparative Example 1 is higher. After characterizing the appearance of the glass rod obtained in Comparative Example 1, bubbles were found throughout the rod, which did not meet the requirements for appearance and relative refractive index. This indicates that vitrification is difficult at this time, and it is difficult to obtain the deeply fluorinated material required by the present invention.

[0119] Compared to Example 1, Comparative Example 2 lacks the low- and medium-temperature two-step fluorine doping process, which is... Figure 4 It can be seen that the glass rod obtained in Comparative Example 2 has a serious problem of warping on both sides in the cross-sectional structure, forming a V-shaped cross-section. Although the lowest point is close to the refractive index of -0.80%, the relatively shallow refractive index of the warped edge is manifested as uneven refractive index of the radial cross section of the fluorine-doped material, which does not meet the requirements for use and makes it difficult to obtain the deeply fluorine-doped material required by the present invention.

[0120] As can be seen from the above, the three-step fluorine doping process of low, medium and high temperature and the fluorine doping temperature used for each step play a decisive role in obtaining deeply fluorinated materials with a relative refractive index of -0.80% to -0.65% and an outer diameter of 90-120 mm. The three-step fluorine doping process of low, medium and high temperature is indispensable. Only by simultaneously using the three-step fluorine doping process of low, medium and high temperature and the corresponding low, medium and high temperature as disclosed in this invention can the desired deeply fluorinated materials be obtained.

[0121] Any parts or structures not specifically described in this invention can be made using existing technologies or products, and will not be elaborated upon here.

[0122] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A method for preparing a deeply fluorine-doped material for low-loss optical fibers, characterized in that, Includes the following steps: 1) Preparation of ash rods: Porous ash rods were prepared by chemical vapor deposition. 2) Purification treatment: Place the ash rods obtained in step 1) into a sintering furnace, introduce Cl2 and He, then raise the furnace temperature and introduce Cl2 and He again; 3) First step: Fluorine doping: Lower the furnace temperature and introduce fluorine gas and He; 4) Second step: Fluorine doping: Increase furnace temperature and introduce fluorine gas and He; 5) Third step: Fluorine doping: Increase the furnace temperature and introduce fluorine gas one and fluorine gas two; 6) Vitrification: Raise the furnace temperature to the glass transition temperature, introduce fluorine gas I, fluorine gas II and He to complete the vitrification of the ash rod and obtain a glass rod; 7) Thermal insulation treatment; In steps 2) through 6), the ashtray rotates at a constant speed throughout. In step 3), the first step of fluorine doping includes: After completing the purification treatment of the ash rod in step 2), reduce the temperature of the sintering furnace to 1000±50℃, introduce 2-5L / min of fluorine gas, introduce 10-20L / min of He, and process for 100-250min. In step 4), the second step of fluorine doping includes: After step 3) is completed, raise the temperature of the sintering furnace to 1200±50℃, introduce 3-5L / min of fluorine gas, introduce 10-20L / min of He, and process for 100-250min. In step 5), the third step of fluorine doping includes: After step 4) is completed, raise the temperature of the sintering furnace to 1300±50℃, introduce fluorine gas one at a rate of 3-8L / min, fluorine gas two at a rate of 0.2-2L / min, and He at a rate of 10-20L / min, for a processing time of 150-250min.

2. The method for preparing a deeply fluorine-doped material for low-loss optical fiber according to claim 1, characterized in that, Step 2) includes the purification process as follows: Place the ash rod in a sintering furnace at 1000-1200℃. First, introduce Cl2 at a rate of 0.5-1.5 L / min for 60-100 min. Second, introduce He at a rate of 10-30 L / min for 60-100 min. After that, raise the furnace temperature by 50-100℃ and repeat the first and second steps at least once.

3. The method for preparing a deeply fluorine-doped material for low-loss optical fibers according to claim 1, characterized in that, Step 6) includes the vitrification process: After step 5), raise the temperature of the sintering furnace to 1450±20℃, introduce 3-8L / min of fluorine gas one, 2-5L / min of fluorine gas two, and 10-30L / min of He, and process for 250-450min to complete the vitrification of the ash rod.

4. The method for preparing a deeply fluorine-doped material for low-loss optical fiber according to claim 1, characterized in that, In step 7), the insulation process includes: The temperature of the sintering furnace is lowered from the glass transition temperature to the set temperature, and the glass rod that has completed the glass transition is annealed for 6-12 hours.

5. The method for preparing a deeply fluorine-doped material for low-loss optical fibers according to claim 1, characterized in that, The first fluorine gas is one or a combination of two or more of CF4, C2F6, C3F8, and SF6, and the second fluorine gas is SiF4 gas.

6. The method for preparing a deeply fluorine-doped material for low-loss optical fibers according to claim 1, characterized in that, The relative refractive index of the deeply fluorinated material is -0.80% to -0.65%, and the outer diameter is 90-120 mm.

7. The application of a deeply fluorinated material prepared by the method for preparing a low-loss optical fiber according to any one of claims 1-6 in a low-loss optical fiber.

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