An ultra-low-loss optical fiber and a drawing method for preparing the same

Abstract

The embodiment of the present application provides a kind of ultra-low loss optical fiber and the drawing preparation method of ultra-low loss optical fiber.The optical fiber includes: core layer, and first gradient layer, second gradient layer, first platform layer, second platform layer and outer cladding successively covered outside the core layer, wherein the relative refractive index difference of first gradient layer and the relative refractive index difference of second gradient layer are linear variation, and the minimum value of the relative refractive index difference of first gradient layer is greater than the maximum value of the relative refractive index difference of second gradient layer, the relative refractive index difference of first platform layer is greater than the maximum value of the relative refractive index difference of second gradient layer.The ultra-low loss optical fiber of the present application can improve the transmission performance of optical signal, reduce attenuation, improve the use effect of optical fiber.

Description

Technical Field

[0001] This application relates to the field of optical fiber communication technology, and in particular to an ultra-low loss optical fiber and a method for drawing and preparing ultra-low loss optical fiber. Background Technology

[0002] Since its invention in the 1970s, fiber optic technology has developed rapidly and been widely used globally. With the explosive growth in demand for the internet and data communication, fiber optic communication has become the mainstream technology for backbone networks. Fiber optics are not only used for long-distance communication but are also gradually being applied to metropolitan area networks, access networks, and home networks, driving the rapid development of the information society.

[0003] Currently, existing doped optical fibers modify their optical properties by incorporating specific elements or compounds into the core or cladding to meet the needs of various applications. Different types of doped fibers have wide applications in fiber amplifiers, fiber lasers, dispersion compensation, nonlinear optics, and fiber optic sensing. Depending on the specific application requirements, an appropriate type of doped fiber can be selected to optimize system performance and achieve specific functions.

[0004] However, existing doped optical fibers suffer from high attenuation and poor performance when transmitting optical signals. Summary of the Invention

[0005] This application provides an ultra-low loss optical fiber and a method for drawing and preparing the ultra-low loss optical fiber, in order to improve the problems of high attenuation and poor performance of existing optical fibers.

[0006] In a first aspect, embodiments of this application provide an ultra-low loss optical fiber, comprising:

[0007] The core layer, and sequentially wrapped around the core layer are a first gradient layer, a second gradient layer, a first plateau layer, a second plateau layer, and an outer cladding layer, wherein the relative refractive index difference of the first gradient layer and the relative refractive index difference of the second gradient layer both exhibit linear changes, and the minimum value of the relative refractive index difference of the first gradient layer is greater than the maximum value of the relative refractive index difference of the second gradient layer, and the relative refractive index difference of the first plateau layer is greater than the maximum value of the relative refractive index difference of the second gradient layer.

[0008] In one possible implementation, the relative refractive index difference of the first gradient layer decreases linearly in the direction away from the core layer.

[0009] In one possible implementation, the relative refractive index difference of the first gradient layer The distribution satisfies:

[0010] ;

[0011] in, The range is 0 to 0.05%. The range is -0.2% to 0, and Greater than , The range is 0.5 to 2. This represents the maximum radius of the core layer. The value range is 5.5–7.5 μm. The radius of the first gradient layer is within a certain range. The value range is 0.5 to 2 μm.

[0012] In one possible implementation, the mass percentages of silicon dioxide, germanium dioxide, fluorine, and phosphorus in the first gradient layer are (1-abc):a:b:c, where a ranges from 0% to 1%, b ranges from 0.01% to 0.3%, and c ranges from 0% to 0.2%.

[0013] In one possible implementation, the relative refractive index difference of the second gradient layer decreases linearly in the direction away from the core layer.

[0014] In one possible implementation, the relative refractive index difference of the second graded layer... The distribution satisfies:

[0015] ;

[0016] in, The range is -0.45% to -0.2%. The range is -0.65% to -0.4%, and Greater than , The range is 0.5 to 3. The radius range for the second gradient layer. The value range is 4 to 12 μm.

[0017] In one possible implementation, the mass percentage of silicon dioxide and fluorine in the second gradient layer is 1 - (0.5% to 1.5%): 0.5% to 1.5%.

[0018] Secondly, embodiments of this application provide a method for drawing and preparing ultra-low loss optical fiber, used to prepare the ultra-low loss optical fiber in the embodiments of this application, the method comprising:

[0019] Based on the preset preheating temperature, the optical fiber preform is placed in the arc reflector for preheating treatment to obtain the preheated optical fiber preform.

[0020] The preheated optical fiber preform is drawn and coated to obtain an ultra-low loss optical fiber with a coating layer.

[0021] In one possible implementation, the preheating temperature is 1900~2100℃, the distance between the arc reflector and the optical fiber preform is 2~15cm, and the reflection center of the arc reflector reflecting the diffuse reflection light generated by the heating of the optical fiber preform is the core layer of the optical fiber preform.

[0022] In one possible implementation, the preheated optical fiber preform is drawn and coated to obtain an ultra-low loss optical fiber with a coating layer, including:

[0023] The preheated optical fiber preform is placed in a drawing furnace for drawing to obtain the drawn optical fiber.

[0024] The drawn optical fiber is sequentially passed through multiple annealing furnaces for heat preservation and annealing treatment to obtain heat preservation and annealing optical fiber.

[0025] The optical fiber after thermal insulation and annealing is coated, and the coating layer on the optical fiber is cured to obtain an ultra-low loss optical fiber with a coating layer.

[0026] In one possible implementation, the melting temperature inside the drawing furnace is 1800~2200℃, and the drawing furnace is filled with a protective gas, wherein the protective gas includes at least one gas selected from argon and helium, and the flow rate of the protective gas is 10~50L / min.

[0027] In one possible implementation, the drawing speed V and the internal tension g in the drawing process satisfy: g = eV + f, where the value of e ranges from 0.08 to 0.12, and the value of f ranges from 20 to 35.

[0028] In one possible implementation, the coating layer includes an inner coating layer and an outer coating layer, wherein the optical fiber after coating with the inner coating layer has a size of 180–205 μm, and the optical fiber after coating with the outer coating layer has a size of 235–252 μm.

[0029] In one possible implementation, both the inner coating layer and the outer coating layer are made of acrylic resin, wherein...

[0030] The acrylic resin for the inner coating layer meets the following requirements: elastic modulus ≤ 0.7 MPa, and at 25°C, the coating viscosity is (3000~8000) mPa•s, and the density is (0.95~1.3) g / cm³. 3 Elongation at break ≥125%;

[0031] The acrylic resin for the outer coating meets the following requirements: elastic modulus ≥ 550 MPa, viscosity at 25°C of (3000~8000) mPa•s, and density of (0.95~1.3) g / cm³. 3 Elongation at break ≥10%.

[0032] This application provides an ultra-low loss optical fiber and a method for drawing and preparing ultra-low loss optical fiber. By setting a first graded layer and a second graded layer between the core layer and the plateau layer, and by adjusting the relative refractive index difference between the first graded layer and the second graded layer, the mode distribution of the optical fiber is improved, bending loss is reduced, material purity and structural design are improved, manufacturing defects are reduced, and dispersion characteristics are optimized. This results in better consistency and strength of the optical fiber, thereby improving the transmission performance of optical signals, reducing attenuation, and improving the overall performance of the optical fiber. Attached Figure Description

[0033] The accompanying drawings, which are incorporated in and form part of this specification, illustrate embodiments consistent with this application and, together with the description, serve to explain the principles of this application.

[0034] Figure 1 A schematic diagram of the structure of the ultra-low loss optical fiber provided in this application;

[0035] Figure 2 A diagram showing the relative refractive index difference of each layer in the ultra-low loss optical fiber provided in the embodiments of this application;

[0036] Figure 3 A schematic flowchart illustrating the method for preparing ultra-low loss optical fiber according to an embodiment of this application;

[0037] Figure 4 A schematic diagram of a scenario structure for heating an optical fiber preform using an arc-shaped reflector, as provided in an embodiment of this application.

[0038] Figure 5 This is a schematic diagram of the structure of the optical fiber drawing equipment provided in the embodiments of this application.

[0039] Explanation of reference numerals in the attached figures:

[0040] 100-Fiber preform; 110-Core layer; 120-First graded layer; 130-Second graded layer; 140-First plateau layer; 150-Second plateau layer; 160-Outer cladding layer; 170-Inner coating layer; 180-Outer coating layer; 400-Arc reflector; 510-Preform feeder; 520-Drawing furnace; 530-Insulation furnace unit; 540-Bare fiber testing unit; 550-Bare fiber protection tube; 560-Coating unit; 570-Curing unit; 580-Fiber size testing unit; 590-Take-up unit. Detailed Implementation

[0041] Exemplary embodiments will now be described in detail, examples of which are illustrated in the accompanying drawings. When the following description relates to the drawings, unless otherwise indicated, the same numbers in different drawings denote the same or similar elements. The embodiments described in the following exemplary embodiments do not represent all embodiments consistent with this application. Rather, they are merely examples of apparatuses and methods consistent with some aspects of this application as detailed in the appended claims.

[0042] First, let me explain the terms used in this application:

[0043] The core is a crucial part of the optical fiber structure. It is the central portion of the fiber and is typically made of high-purity glass or plastic. The main function of the core is to conduct optical signals. Its refractive index is higher than that of the cladding, allowing light to be transmitted within the core via total internal reflection.

[0044] A graded-index layer is a transition region between the core and cladding of an optical fiber, where the refractive index gradually changes from the core to the cladding. The purpose of this graded-index layer is to reduce light reflection loss at the core-cladding interface, thereby improving the fiber's transmission efficiency and signal quality.

[0045] The cladding refers to the outer layer surrounding the fiber core, which has a slightly lower refractive index than the fiber core. It is used to retain the optical signal within the fiber core through total internal reflection, thereby reducing signal loss.

[0046] The coating can consist of one or more polymer materials and its main function is to protect optical fibers from physical damage and environmental influences.

[0047] With the advent of the information age and the explosion of data, the development of both secondary and tertiary industries is heavily reliant on high-speed communication networks. Fiber optic communication is currently the mainstream method of wired communication due to its advantages such as simple material sourcing, small size, good security, and high transmission speed. High-speed optical communication networks have gradually evolved from 10G and 40G to the commonly used 100G communication systems, while 400G systems are under continuous improvement. However, a current issue is that due to the massive amount of information transmitted, the excessive optical density during transmission in optical fibers can easily cause nonlinear effects, increasing the bit error rate. To reduce these nonlinear effects during transmission, reducing the optical density is a relatively effective method. Therefore, engineers have designed an optical fiber with a large effective area suitable for high-speed optical communication systems, while also possessing ultra-low attenuation, making it suitable for long-distance, repeaterless transmission systems such as submarine cables.

[0048] The effective area of ​​a single-mode fiber is related to its mode field diameter (MFD). Since optical signals propagate not only in the fiber core but also in the cladding, using the core diameter to express this characteristic is impractical. Therefore, the concept of mode field diameter (MFD) is used for definition. Generally, the size of the mode field diameter is proportional to the fiber core diameter, and the relationship between the mode field diameter and the effective area is shown in the following formula:

[0049]

[0050] Where Aeff represents the effective area, MFD is the mold field diameter, and K is the correction coefficient. It can be seen from the formula that the larger the mold field diameter, the larger the effective area.

[0051] This application provides an ultra-low loss optical fiber and a method for drawing and preparing ultra-low loss optical fiber. The optical fiber designed above not only has low attenuation but also a large mode field diameter (typical value 12.5 μm). The graded structure and mass percentage ensure that the optical fiber maintains a sufficient refractive index difference while ensuring good viscosity-fluidity matching between different layers. This results in better consistency and strength of the preform after melting. The design of the plateau layer ensures that the optical fiber has a small cable cutoff wavelength, with a typical attenuation value of 1550 nm ≤ 0.17 dB / km and a cable cutoff wavelength of ≤ 1500 nm. The optical fiber strength is 50% to 100% higher than that of ordinary optical fibers.

[0052] Figure 1 A schematic diagram of the structure of the ultra-low loss optical fiber provided in this application is shown below. Figure 1 As shown, the optical fiber includes a core layer 110, and a first graded layer 120, a second graded layer 130, a first plateau layer 140, a second plateau layer 150, and an outer cladding layer 160 sequentially clad around the core layer 110. The relative refractive index difference of the first graded layer 120 and the relative refractive index difference of the second graded layer 130 both exhibit linear changes, and the minimum value of the relative refractive index difference of the first graded layer 120 is greater than the maximum value of the relative refractive index difference of the second graded layer 130, and the relative refractive index difference of the first plateau layer 140 is greater than the maximum value of the relative refractive index difference of the second graded layer 130.

[0053] By adjusting the relative refractive index difference, various properties of optical fibers can be improved, such as mode control, intermodal dispersion, bandwidth, bending performance, dispersion management, nonlinear effects, signal quality, transmission distance, manufacturing tolerance, and environmental stability. These improvements enable optical fibers to better meet the needs of different application scenarios, from high-speed data communication to long-distance transmission, and even high-power laser and amplifier applications.

[0054] Meanwhile, since the minimum relative refractive index difference of the first graded layer 120 is greater than the maximum relative refractive index difference of the second graded layer 130, on the one hand, the mode distribution and propagation characteristics in the optical fiber can be controlled more precisely, the transmission performance of the optical fiber can be optimized, the interference between different modes can be reduced, and the signal quality can be improved. On the other hand, the bending resistance of the optical fiber can be enhanced, so that the larger refractive index difference can confine the optical signal more tightly within the fiber core, thereby reducing the possibility of light escaping when bending, which can improve and reduce the attenuation of the optical fiber.

[0055] Furthermore, the linear variation of the relative refractive index difference of the first graded layer 120 and the relative refractive index difference of the second graded layer 130 includes two cases: both the relative refractive index difference of the first graded layer 120 and the relative refractive index difference of the second graded layer 130 decrease linearly in the direction away from the core layer 110, and both increase linearly in the direction away from the core layer 110. When the relative refractive index difference of the first graded layer 120 and the relative refractive index difference of the second graded layer 130 increase linearly in the direction away from the core layer 110, intermodal dispersion can be increased and specific optical characteristics can be achieved. When the relative refractive index difference of the first graded layer 120 and the relative refractive index difference of the second graded layer 130 decrease linearly in the direction away from the core layer 110, intermodal dispersion can be reduced, bandwidth and transmission distance can be increased, bending performance can be improved, and mode control can be optimized, thereby improving the transmission performance of the optical fiber.

[0056] Figure 2 For the relative refractive index difference diagram of each layer in the ultra-low loss optical fiber provided in the embodiments of this application, please refer to the combined diagram. Figure 1 and Figure 2 The contents shown include ultra-low loss optical fibers:

[0057] The core layer 110 has a maximum radius of r1, where r1 ranges from 5.5 to 7.5 μm; the relative refractive index difference of the core layer 110 is Δn1, where Δn1 ranges from 0.05% to 0.15%; in this embodiment, the mass percentage of the core layer 110 satisfies:

[0058] SiO2: GeO2: F: P = [1-(0.2%~2%)-(0.2%~2%)-(0~0.35%)]: (0.2%~2%): (0.05%~0.5%): (0%~0.35%).

[0059] The first gradient layer 120, the relative refractive index difference of the first gradient layer 120 The distribution satisfies:

[0060] ;

[0061] in, The range is 0 to 0.05%. The range is -0.2% to 0, and Greater than , The range is 0.5 to 2. This represents the maximum radius value of the core layer 110. The value range is 5.5–7.5 μm. The radius range for the first gradient layer 120 is given. The value range is 0.5 to 2 μm.

[0062] In this embodiment of the application, the mass percentages of silicon dioxide, germanium dioxide, fluorine, and phosphorus in the first gradient layer 120 are (1-abc): a:b:c, where a ranges from 0% to 1%, b ranges from 0.01% to 0.3%, and c ranges from 0 to 0.2%. In this embodiment of the application, fluorine can refer to the element fluorine, and phosphorus can refer to the element phosphorus.

[0063] The second gradient layer 130 has a relative refractive index difference. The distribution satisfies:

[0064] ;

[0065] in, The range is -0.45% to -0.2%. The range is -0.65% to -0.4%, and Greater than , The range is 0.5 to 3. The radius range for the second gradient layer 130 is given. The value range is 4 to 12 μm.

[0066] In the embodiments of this application, the mass percentage of silicon dioxide and fluorine in the second gradient layer 130 is 1-(0.5%~1.5%):0.5%~1.5%.

[0067] The first plateau layer 140 has a radius ranging from r3 to r4, where the value of r4-r3 ranges from 8 to 20 μm; the relative refractive index difference of the first plateau layer 140 is Δn6, where the value of Δn6 ranges from -0.3% to -0.1%; in this embodiment, the mass percentage of the first plateau layer 140 satisfies:

[0068] SiO2: GeO2: F=[1-(0%~0.15%)-(0.3%~1%)]: (0%~0.15%): (0.3%~1%).

[0069] The second plateau layer 150 has a radius ranging from r4 to r5, where the value of r5-r4 ranges from 6 to 15 μm; the relative refractive index difference of the second plateau layer 150 is Δn7, where the value of Δn7 ranges from -0.2% to -0.05%, and Δn7 > Δn6; in this embodiment, the mass percentage of the second plateau layer 150 satisfies:

[0070] SiO2: GeO2: F=[1-(0.1%~0.3%)-(0.15%~0.5%)]: (0%~0.15%): (0.3%~1%).

[0071] The outer cladding layer 160 has a radius ranging from r5 to r6, where r6 ranges from 62 to 63 μm. The relative refractive index difference Δn8 of the outer cladding layer 160 is 0, and the material of the outer cladding layer 160 is pure silicon dioxide.

[0072] The inner coating layer 170 is made of acrylic resin. The material of the inner coating layer 170 must meet the following requirements: elastic modulus ≤ 0.7 MPa, viscosity at 25°C of (3000~8000) mPa•s, and density of (0.95~1.3) g / cm³. 3 The fiber has a breaking elongation ≥125%, and the size of the fiber after coating layer 170 is 180~205μm.

[0073] The outer coating layer 180 is made of acrylic resin. The inner coating layer 170 must meet the following material requirements: elastic modulus ≥ 550 MPa, viscosity at 25°C of (3000~8000) mPa•s, and density of (0.95~1.3) g / cm³. 3 The fiber has a breaking elongation ≥10%, and the size of the fiber after coating with an outer coating layer of 180 is 235~252μm.

[0074] Based on this, the ultra-low loss optical fiber provided in this application embodiment not only has low attenuation, but also has a large mode field diameter (typical value 12.5μm). The structure of the first graded layer 120 and the second graded layer, as well as the mass percentage, ensure that the optical fiber maintains a sufficient refractive index difference while ensuring good viscosity-fluidity matching between different layers. This results in better consistency and strength of the preform after melting. The design of the plateau layer ensures that the optical fiber has a small cable cutoff wavelength, with a typical attenuation value of ≤0.17dB / km at 1550nm and a cable cutoff wavelength of ≤1500nm. The optical fiber strength is 50% to 100% higher than that of ordinary optical fibers.

[0075] Figure 3 A schematic flowchart of the ultra-low loss optical fiber drawing method provided in this application embodiment is shown below. Figure 3As shown, the fiber preparation method includes:

[0076] S301. Based on the preset preheating temperature, the optical fiber preform is placed in an arc reflector for preheating treatment to obtain a preheated optical fiber preform.

[0077] The preheating temperature can be 1900~2100℃.

[0078] The optical fiber preform can be an ultra-low loss optical fiber consisting of a core layer and a first graded layer, a second graded layer, a first plateau layer, a second plateau layer and an outer cladding layer sequentially wrapped around the core layer in the embodiments of this application.

[0079] Because the ultra-low loss optical fiber in this embodiment has a very low doping concentration in the core layer, its hardness is much softer than that of the fluorine-doped recessed layer. This hardness mismatch leads to a viscosity-flow mismatch, resulting in a difference in internal stress during melting. To reduce viscosity mismatch, the core layer of the optical fiber preform is preheated before melting.

[0080] S302. The preheated optical fiber preform is drawn and coated to obtain an ultra-low loss optical fiber with a coating layer.

[0081] In this embodiment of the application, the method for drawing and coating a preheated optical fiber preform to obtain an ultra-low loss optical fiber with a coating layer may include:

[0082] The preheated optical fiber preform is placed in a drawing furnace for drawing to obtain the drawn optical fiber.

[0083] The drawn optical fiber is sequentially passed through multiple annealing furnaces for heat preservation and annealing treatment to obtain heat preservation and annealing optical fiber.

[0084] The optical fiber after thermal insulation and annealing is coated, and the coating layer on the optical fiber is cured to obtain an ultra-low loss optical fiber with a coating layer.

[0085] Among them, the optical fiber drawing furnace is one type of drawing furnace, namely, the induction drawing furnace and the graphite drawing furnace.

[0086] Fiber drawing refers to the process of heating the fiber drawing furnace to 1800-2200℃, placing the preform in the furnace for melting, and then drawing the molten fiber preform into fibers.

[0087] The molten environment inside the optical fiber drawing furnace is filled with a protective gas, preferably an inert gas. In some embodiments, the protective gas includes at least one gas selected from argon and helium. The flow rate of the protective gas is 10~50 L / min, and the oxygen content in the protective gas environment is ≤100 ppm.

[0088] If the fiber drawing speed is ≥50m / min, and the drawing speed is V, and the internal tension is g, then the relationship between the V and G values ​​is g=aV+b, where the value of a ranges from 0.08 to 0.12, and the value of b ranges from 20 to 35.

[0089] The heat preservation annealing process involves passing the optical fiber through n temperature zones (2≦n≦6) with varying temperatures. The optical fiber resides in each temperature zone for (0.1~1) seconds. The temperatures of the different heat preservation furnaces decrease sequentially from top to bottom. The optical fiber enters the annealing zone at temperatures between 1100°C and 1600°C, and after annealing, the fiber temperature is between 750°C and 900°C. The entire annealing process is carried out in a nitrogen atmosphere with an oxygen content of less than 200 ppm and a nitrogen flow rate of (5~25) L / min. A circulating method with top-inlet and bottom-outlet air extraction is used. By circulating nitrogen, the oxygen content is reduced, as is the water content in the annealing environment.

[0090] Fiber optic coating refers to coating optical fibers with acrylic resin. The coating material consists of two layers: an inner layer and an outer layer. The inner layer material must meet the following requirements: elastic modulus ≤ 0.7 MPa, viscosity at 25°C of (3000~8000) mPa•s, and density of (0.95~1.3) g / cm³. 3 The elongation at break should be ≥125%; the outer coating material should meet the following requirements: elastic modulus ≥550 MPa, coating viscosity at 25°C (3000~8000) mPa•s, and density (0.95~1.3) g / cm³. 3 The elongation at break is ≥10%. The fiber size is 180-205 μm after the first coating and 235-252 μm after the second coating.

[0091] The curing process can refer to either UV curing or LED curing. The curing environment is isolated using a non-oxygen gas. In some embodiments, the non-oxygen gas used can be at least one of nitrogen, helium, and argon. The gas flow rate of a single curing oven is 10L to 15L. The oxygen content in the curing environment is less than 50ppm. During the curing process, when the optical fiber passes through different curing ovens, its exposure to air should not exceed 0.04s. After curing in the curing oven, the curing degree of the inner coating of the optical fiber is 87% to 94%, and the curing degree of the outer layer is 92% to 100%, wherein the curing degree of the outer layer should not be less than that of the inner layer.

[0092] Figure 4 This is a schematic diagram of a scenario structure for heating an optical fiber preform using an arc-shaped reflector, as provided in an embodiment of this application. Figure 4 As shown, the optical fiber preform 100 is located inside the arc reflector 400 during preheating. The shortest distance L between the arc reflector 400 and the surface of the optical fiber preform 100 is 2 to 15 cm. When the arc reflector 400 is used to preheat the optical fiber preform 100, the optical fiber preform 100 will radiate strong diffuse reflection light when the preheating temperature is 1900 to 2100°C. In this embodiment, the arc reflector 400 is used to reflect the diffuse reflection light and concentrate it at the arc center, i.e., the core layer of the optical fiber preform 100, thereby completing the preheating treatment of the core layer of the optical fiber preform 100.

[0093] Figure 5 This is a schematic diagram of the structure of the optical fiber drawing equipment provided in the embodiments of this application, as shown below. Figure 5 As shown, the optical fiber drawing equipment includes: a rod feeder 510, an optical fiber preform 100, a drawing furnace 520, a heat preservation furnace unit 530, a bare fiber testing unit 540, a bare fiber protection tube 550, a coating unit 560, a curing unit 570, an optical fiber size testing unit 580, and a take-up unit 590. The rod feeder 510 is used to transport the preheated optical fiber preform 100 to the drawing furnace 520 for drawing. The heat preservation furnace unit 530 is used to perform heat preservation annealing on the drawn optical fiber preform 100. The bare fiber testing unit 540 and the bare fiber protection tube 550 are used to test the annealed bare optical fiber. The coating unit 560 is used to coat the bare optical fiber. The curing unit 570 is used to cure the coated bare optical fiber. The optical fiber testing unit is used to test the cured optical fiber. The take-up unit 590 is used to collect and organize the optical fiber.

[0094] The intensity comparison of the optical fiber under various parameters of this invention is shown in the table below:

[0095]

[0096]

[0097] As can be seen from the above description, the above embodiments of the present invention achieve the following technical effects: by setting a first graded layer and a second graded layer between the core layer and the plateau layer, and by adjusting the relative refractive index difference between the first graded layer and the second graded layer, the mode distribution of the optical fiber is improved, bending loss is reduced, material purity and structural design are improved, manufacturing defects are reduced, and dispersion characteristics are optimized, so that the optical fiber has better consistency and the intensity is maintained above 150 KPSI.

[0098] The preferred embodiments and experimental verifications of the present invention have been described in detail above. It should be understood that those skilled in the art can make numerous modifications and variations based on the concept of the present invention without creative effort. Therefore, all technical solutions that can be obtained by those skilled in the art based on the concept of the present invention through logical analysis, reasoning, or limited experimentation on the basis of existing technology should be within the scope of protection defined by the claims.

Claims

1. An ultra-low loss optical fiber, characterized in that, include: The core layer comprises a first gradient layer, a second gradient layer, a first plateau layer, a second plateau layer, and an outer cladding layer sequentially surrounding the core layer. The relative refractive index difference of the first gradient layer and the relative refractive index difference of the second gradient layer both exhibit linear changes. Furthermore, the minimum relative refractive index difference of the first gradient layer is greater than the maximum relative refractive index difference of the second gradient layer, and the relative refractive index difference of the first plateau layer is greater than the maximum relative refractive index difference of the second gradient layer. The relative refractive index difference of the first gradient layer decreases linearly away from the core layer. The distribution satisfies: ； Among them, the The range is 0 to 0.05%, the stated The range is -0.2% to 0, and the stated Greater than the The The range is 0.5 to 2, the aforementioned The maximum radius value of the core layer, the The value range is 5.5–7.5 μm, the The outer boundary radius of the first gradient layer, the The radius of the first gradient layer is within a certain range. The value range is 0.5–2 μm; The relative refractive index difference of the second gradient layer decreases linearly away from the core layer; The relative refractive index difference of the second graded layer The distribution satisfies: ； Among them, the The range is -0.45% to -0.2%, the aforementioned The range is -0.65% to -0.4%, and the stated Greater than the The The range is 0.5 to 3, the aforementioned The outer boundary radius of the second gradient layer, The radius of the second gradient layer is within a certain range. The value range is 4 to 12 μm.

2. The optical fiber according to claim 1, characterized in that, The mass percentages of silicon dioxide, germanium dioxide, fluorine, and phosphorus in the first gradient layer are (1-abc): a:b:c, where the value of a ranges from 0% to 1%, the value of b ranges from 0.01% to 0.3%, and the value of c ranges from 0% to 0.2%.

3. The optical fiber according to claim 1, characterized in that, The mass percentage of silicon dioxide and fluorine in the second gradient layer is 1 - (0.5%~1.5%): 0.5%~1.5%.

4. A method for preparing ultra-low loss optical fiber by drawing, characterized in that, The method for preparing the ultra-low loss optical fiber according to any one of claims 1 to 3 includes: Based on the preset preheating temperature, the optical fiber preform is placed in the arc reflector for preheating treatment to obtain the preheated optical fiber preform. The preheated optical fiber preform is drawn and coated to obtain an ultra-low loss optical fiber with a coating layer.

5. The method according to claim 4, characterized in that, The preheating temperature is 1900~2100℃, the distance between the arc reflector and the optical fiber preform is 2~15cm, and the reflection center of the arc reflector reflecting the diffuse reflection light generated by the heating of the optical fiber preform is the core layer of the optical fiber preform.

6. The method according to claim 4, characterized in that, The process of drawing and coating the preheated optical fiber preform to obtain an ultra-low loss optical fiber with a coating layer includes: The preheated optical fiber preform is placed in a drawing furnace for drawing to obtain the drawn optical fiber. The drawn optical fiber is sequentially passed through multiple annealing furnaces for heat preservation and annealing treatment to obtain heat preservation and annealing optical fiber. The optical fiber after thermal insulation and annealing is coated, and the coating layer on the optical fiber is cured to obtain an ultra-low loss optical fiber with a coating layer.

7. The method according to claim 6, characterized in that, The melting temperature inside the drawing furnace is 1800~2200℃, and the drawing furnace is filled with a protective gas, wherein the protective gas includes at least one gas selected from argon and helium, and the flow rate of the protective gas is 10~50L / min.

8. The method according to claim 6, characterized in that, In the wire drawing process, the wire drawing speed V and the internal tension g satisfy the following condition: g = eV + f, where the value of e ranges from 0.08 to 0.12, and the value of f ranges from 20 to 35.

9. The method according to claim 6, characterized in that, The coating layer includes an inner coating layer and an outer coating layer, wherein the optical fiber after coating with the inner coating layer has a size of 180–205 μm, and the optical fiber after coating with the outer coating layer has a size of 235–252 μm.

10. The method according to claim 9, characterized in that, Both the inner coating layer and the outer coating layer are made of acrylic resin, wherein, The acrylic resin of the inner coating layer meets the following requirements: elastic modulus ≤ 0.7 MPa, and the coating viscosity at 25°C is (3000~8000) mPa•s, and the density is (0.95~1.3) g / cm³. 3 Elongation at break ≥125%; The acrylic resin used in the outer coating layer meets the following requirements: elastic modulus ≥ 550 MPa, viscosity at 25°C of (3000~8000) mPa•s, and density of (0.95~1.3) g / cm³. 3 Elongation at break ≥10%.

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