Ultralow-loss optical fiber, and drawing preparation method for ultralow-loss optical fiber

Abstract

An ultralow-loss optical fiber, and a drawing preparation method for an ultralow-loss optical fiber. The optical fiber comprises a core layer (110), and a first gradient layer (120), a second gradient layer (130), a first platform layer (140), a second platform layer (150) and an outer cladding layer (160), which sequentially cover the core layer (110), wherein the relative refractive index difference of the first gradient layer (120) and the relative refractive index difference of the second gradient layer (130) both change linearly, the minimum value of the relative refractive index difference of the first gradient layer (120) is greater than the maximum value of the relative refractive index difference of the second gradient layer (130), and the relative refractive index difference of the first platform layer (140) is greater than the maximum value of the relative refractive index difference of the second gradient layer (130). The ultralow-loss optical fiber can improve the transmission performance for optical signals and reduce attenuation, thus improving the usage effect of the optical fiber.

Description

Ultra-low-loss optical fiber and drawing preparation method of ultra-low-loss optical fiber

[0001] The present application claims priority to the Chinese patent application No. 202411251986.X filed on September 6, 2024, and entitled "Ultra-low-loss optical fiber and drawing preparation method of ultra-low-loss optical fiber", the whole content of which is incorporated herein by reference. TECHNICAL FIELD

[0002] The present application relates to the technical field of optical fiber communication, and in particular to an ultra-low-loss optical fiber and a drawing preparation method of the ultra-low-loss optical fiber. BACKGROUND

[0003] Since the advent of optical fiber technology in the 1970s, it has rapidly developed and been widely used around the world. With the explosive growth of Internet and data communication demand, optical fiber communication has become the mainstream technology of backbone network. Optical fiber is not only used for long-distance communication, but also gradually enters the metropolitan area network, access network and home network, promoting the rapid development of the information society.

[0004] At present, the existing doped optical fiber changes the optical properties of the optical fiber by doping specific elements or compounds in the core or cladding to meet the needs of different applications. Different types of doped optical fibers have a wide range of applications in optical fiber amplifiers, optical fiber lasers, dispersion compensation, nonlinear optics and optical fiber sensing. According to the specific application requirements, the appropriate type of doped optical fiber can be selected to optimize the system performance and achieve specific functions.

[0005] However, the existing doped optical fiber has the problem of high attenuation and poor use effect when transmitting optical signals.

[0006] SUMMARY

[0007] The embodiments of the present application provide an ultra-low-loss optical fiber and a drawing preparation method of the ultra-low-loss optical fiber to improve the problem of high attenuation and poor use effect of the existing optical fiber.

[0008] In a first aspect, the embodiments of the present application provide an ultra-low-loss optical fiber, comprising:

[0009] a core layer, and a first gradient layer, a second gradient layer, a first platform layer, a second platform layer and an outer cladding layer successively coated outside the core layer, wherein the relative refractive index difference of the first gradient layer and the relative refractive index difference of the second gradient layer are linearly changed, 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 platform layer is greater than the maximum value of the relative refractive index difference of the second gradient layer.

[0010] In a possible implementation, the relative refractive index difference of the first gradient layer decreases linearly along a direction away from the core layer.

[0011] In a possible implementation, the relative refractive index difference Δn(r) of the first gradient layer satisfies:

[0012] Δn(r)=Δn2+(Δn3-Δn2)(r-r1 / r2-r1) α1 ;

[0013] wherein Δn2 ranges from 0 to 0.05%, Δn3 ranges from -0.2% to 0, Δn2 is greater than Δn3, α1 ranges from 0.5 to 2, r1 is a maximum radius value of the core layer, r1 ranges from 5.5 to 7.5 μm, r2-r1 is a radius value range of the first gradient layer, and r2-r1 ranges from 0.5 to 2 μm.

[0014] In a possible implementation, the mass percentage of silicon dioxide, germanium dioxide, fluorine and phosphorus in the first gradient layer is (1-a-b-c):a:b:c, wherein a ranges from 0% to 1%, b ranges from 0.01% to 0.3%, and c ranges from 0 to 0.2%.

[0015] In a possible implementation, the relative refractive index difference of the second gradient layer decreases linearly along a direction away from the core layer.

[0016] In a possible implementation, the relative refractive index difference Δn(r) of the second gradient layer satisfies:

[0017] Δn(r)=Δn4+(Δn5-Δn4)(r-r2 / r3-r2) α2 ;

[0018] wherein Δn4 ranges from -0.45% to -0.2%, Δn5 ranges from -0.65% to -0.4%, Δn4 is greater than Δn5, α2 ranges from 0.5 to 3, r3-r2 is a radius value range of the second gradient layer, and r2-r1 ranges from 4 to 12 μm.

[0019] In a 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%.

[0020] In a second aspect, the embodiments of the present application provide a drawing preparation method of an ultra-low-loss optical fiber, which is used to prepare the ultra-low-loss optical fiber in the embodiments of the present application, and the method comprises:

[0021] The optical fiber preform is placed in the arc reflection cover for preheating treatment based on the preset preheating temperature, and the optical fiber preform after preheating treatment is obtained.

[0022] The optical fiber preform after preheating treatment is subjected to wire drawing coating treatment, and the ultra-low loss optical fiber with a coating layer is obtained.

[0023] In a possible implementation, the preheating temperature is 1900-2100 ℃, the distance between the arc reflection cover and the optical fiber preform is 2-15 cm, and the reflection center of the arc reflection cover for reflecting the diffuse reflection light generated by the heating of the optical fiber preform is the core layer of the optical fiber preform.

[0024] In a possible implementation, the optical fiber preform after preheating treatment is subjected to wire drawing coating treatment, and the ultra-low loss optical fiber with a coating layer is obtained, including:

[0025] The optical fiber preform after preheating treatment is placed in a wire drawing furnace for wire drawing treatment, and the optical fiber after wire drawing treatment is obtained.

[0026] The optical fiber after wire drawing treatment is sequentially passed through a plurality of annealing holding furnaces for annealing and holding treatment, and the optical fiber after annealing and holding treatment is obtained.

[0027] The optical fiber after annealing and holding treatment is subjected to optical fiber coating treatment, and the coating layer on the optical fiber after the optical fiber coating treatment is subjected to solidification treatment, and the ultra-low loss optical fiber with a coating layer is obtained.

[0028] In a possible implementation, the melting temperature in the wire drawing furnace is 1800-2200 ℃, and the wire drawing furnace is filled with a protective gas, wherein the protective gas includes at least one of argon and helium, and the flow rate of the protective gas is 10-50 L / min.

[0029] In a possible implementation, the wire drawing speed V and the internal tension g in the wire drawing treatment satisfy: g = eV + f, wherein the value range of e is 0.08-0.12, and the value range of f is 20-35.

[0030] In a possible implementation, the coating layer includes an inner coating layer and an outer coating layer, wherein the size of the optical fiber after coating of the inner coating layer is 180-205 μm, and the size of the optical fiber after coating of the outer coating layer is 235-252 μm.

[0031] In a possible implementation, the material of the inner coating layer and the material of the outer coating layer are both acrylic resin, wherein,

[0032] The acrylic resin of the inner coating layer satisfies: an elastic modulus is less than or equal to 0.7 MPa, a coating viscosity is (3000-8000) mPa·s at 25 DEG C, a density is (0.95-1.3) g / cm 3 , and an elongation at break is greater than or equal to 125%;

[0033] The acrylic resin of the outer coating layer satisfies: an elastic modulus is greater than or equal to 550 MPa, a coating viscosity is (3000-8000) mPa·s at 25 DEG C, a density is (0.95-1.3) g / cm 3 , and an elongation at break is greater than or equal to 10%.

[0034] The application provides an ultra-low-loss optical fiber and a drawing preparation method of the ultra-low-loss optical fiber. BRIEF DESCRIPTION OF DRAWINGS

[0035] The accompanying drawings, which are incorporated herein and constitute a part of the specification, illustrate embodiments consistent with the application and, together with the description, serve to explain the principles of the application.

[0036] Fig. 1 is a structural schematic diagram of an ultra-low-loss optical fiber provided by the application;

[0037] Fig. 2 is a diagram of relative refractive index differences of various layers in the ultra-low-loss optical fiber provided by the application;

[0038] Fig. 3 is a flow schematic diagram of a drawing preparation method of the ultra-low-loss optical fiber provided by the application;

[0039] Fig. 4 is a schematic diagram of a scene structure in which a circular arc reflector is used to heat an optical fiber preform;

[0040] Fig. 5 is a structural schematic diagram of an optical fiber drawing device provided by the application.

[0041] Explanation of reference signs:

[0042] 100 - optical fiber preform; 110 - core layer; 120 - first graded layer; 130 - second graded layer; 140 - first platform layer; 150 - second platform layer; 160 - outer cladding layer; 170 - inner coating layer; 180 - outer coating layer; 400 - circular reflector; 510 - preform feeder, 520 - drawing furnace, 530 - 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 DESCRIPTION

[0043] The exemplary embodiments will be described in detail herein with reference to the attached drawings. In the following description, like reference numerals refer to like elements, unless the context clearly dictates otherwise. The following exemplary embodiments described are not meant to represent all embodiments consistent with the present application. Rather, they are merely examples of apparatus and methods consistent with some aspects of the present application as detailed in the appended claims.

[0044] First, the terms involved in this application are explained:

[0045] Core is a key part of the optical fiber structure. It is the central part of the optical fiber, usually made of high-purity glass or plastic. The main function of the core is to conduct optical signals, and its refractive index is higher than that of the cladding, so that light can be transmitted in the core by total internal reflection.

[0046] Graded layer refers to a transition region between the core and the cladding of the optical fiber, whose refractive index gradually changes from the core to the cladding. The purpose of this graded layer is to reduce the reflection loss of light at the interface between the core and the cladding, thereby improving the transmission efficiency and signal quality of the optical fiber.

[0047] Cladding refers to the layer surrounding the core, which has a slightly lower refractive index than the core, and is used to maintain the light signal in the core by total internal reflection, thereby reducing signal loss.

[0048] Coating can be composed of one or more layers of polymer material, and its main function is to protect the optical fiber from physical damage and environmental influences.

[0049] With the advent of the information age of data explosion, the development of both the second industry and the third industry is extremely dependent on high-speed communication networks. Optical fiber communication is currently the most mainstream way of wired communication, because optical fiber is widely used due to its simple material, small size, good privacy, fast transmission speed and other advantages. High-speed optical communication networks have gradually developed from 10G and 40G to the commonly used 100G communication system, and the 400G system is also gradually improving. However, at present, due to the huge amount of information sent, the optical density of the optical signal is too large when it is transmitted in the optical fiber, which is easy to cause the generation of nonlinear effects, so that the bit error rate of the signal is improved. In order to reduce the nonlinear effects of the signal in transmission, reducing the optical density of the optical signal is a relatively effective method, so engineers have designed a fiber with a large effective area that can be applied to high-speed optical communication systems, while also having ultra-low attenuation that can be applied to long-distance non-repeater transmission systems such as submarine cables.

[0050] The effective area of a single-mode optical fiber is related to its mode field diameter. Because during signal transmission, optical signals are not only transmitted in the fiber core layer, but also a part of the signal is transmitted in the fiber cladding, therefore, using the core diameter to express this characteristic does not conform to the actual situation, so the concept of mode field diameter (MFD) is adopted for definition. Generally speaking, the size of the mode field diameter is proportional to the core diameter of the optical fiber, and the relationship between the mode field diameter and the effective area is shown in the following formula:

[0051] A eff = (1 / 4) k π (MFD) 2

[0052] Wherein, Aeff represents the effective area, MFD is the mode field diameter, and K is the correction coefficient. As can be seen from the formula, the larger the mode field diameter, the larger the effective area.

[0053] The ultra-low loss optical fiber and the drawing preparation method of the ultra-low loss optical fiber provided by the embodiments of the present application adopt the above designed optical fiber which not only has a low attenuation but also has a large mode field diameter (typical value 12.5 μm), and the gradual change structure and the mass percentage ensure that the optical fiber has a sufficient refractive index difference while ensuring good viscosity matching between different levels, so that the preform has better consistency and strength after melting. The design of the platform layer ensures that the optical fiber has a small cable cutoff wavelength, the typical attenuation value is 1550 nm≤0.17 dB / km, the optical cable cutoff wavelength is ≤1500 nm, and the optical fiber strength is improved by 50%~100% compared with the general optical fiber.

[0054] Figure 1 is a structural schematic diagram of an ultra-low-loss optical fiber provided by the present application. As shown in Figure 1, the optical fiber includes a core layer 110, and a first gradient layer 120, a second gradient layer 130, a first platform layer 140, a second platform layer 150, and an outer cladding layer 160 successively wrapped outside the core layer 110. The relative refractive index difference of the first gradient layer 120 and the relative refractive index difference of the second gradient layer 130 are both linearly changed, and the minimum value of the relative refractive index difference of the first gradient layer 120 is greater than the maximum value of the relative refractive index difference of the second gradient layer 130. The relative refractive index difference of the first platform layer 140 is greater than the maximum value of the relative refractive index difference of the second gradient layer 130.

[0055] By adjusting the relative refractive index difference, various properties of the optical fiber 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 the optical fiber to better meet the needs of different application scenarios, from high-speed data communication to long-distance transmission, to high-power laser and amplifier applications.

[0056] Meanwhile, since the minimum value of the relative refractive index difference of the first gradient layer 120 is greater than the maximum value of the relative refractive index difference of the second gradient layer 130, on the one hand, the mode distribution and propagation characteristics in the optical fiber can be more accurately controlled, 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 also be enhanced. A larger refractive index difference can cause the optical signal to be more tightly confined within the core, thereby reducing the likelihood of light escaping when bending, and thus improving the attenuation of the optical fiber.

[0057] In addition, the relative refractive index difference of the first gradient layer 120 and the relative refractive index difference of the second gradient layer 130 are both linearly changed, including the case where the relative refractive index difference of the first gradient layer 120 and the relative refractive index difference of the second gradient layer 130 are both linearly decreasing in the direction away from the core layer 110, and the case where the relative refractive index difference of the first gradient layer 120 and the relative refractive index difference of the second gradient layer 130 are both linearly increasing in the direction away from the core layer 110. When the relative refractive index difference of the first gradient layer 120 and the relative refractive index difference of the second gradient layer 130 are both linearly increasing in the direction away from the core layer 110, the intermodal dispersion can be increased, and specific optical characteristics can be achieved. When the relative refractive index difference of the first gradient layer 120 and the relative refractive index difference of the second gradient layer 130 are both linearly decreasing in the direction away from the core layer 110, the intermodal dispersion can be reduced, the bandwidth and transmission distance can be improved, the bending performance can be improved, and the mode control can be optimized, thereby improving the transmission performance of the optical fiber.

[0058] Figure 2 is a diagram of the relative refractive index difference of each layer in the ultra-low-loss optical fiber provided by the present application. Referring to the contents shown in combination with Figures 1 and 2, the ultra-low-loss optical fiber includes:

[0059] The core layer 110 has a maximum radius r1, where r1 is in a range from 5.5 to 7.5 μm; the core layer 110 has a relative refractive index difference Δn1, where Δn1 is in a range from 0.05% to 0.15%; in the embodiment of the present application, the mass percentage of the core layer 110 satisfies:

[0060] SiO2:GeO2:F:P=[1-(0.2%~2%)-(0.2%~2%)-(0~0.35%)]:(0.2%~2%):(0.05%~0.5%):(0%~0.35%).

[0061] The first gradient layer 120 has a relative refractive index difference Δn(r) distribution satisfying:

[0062] Δn(r)=Δn2+(Δn3-Δn2)(r-r1 / r2-r1) α1 .

[0063] where Δn2 is in a range from 0 to 0.05%, Δn3 is in a range from -0.2% to 0, Δn2 is greater than Δn3, α1 is in a range from 0.5 to 2, r1 is the maximum radius value of the core layer 110, r1 is in a range from 5.5 to 7.5 μm, and r2-r1 is the radius value range of the first gradient layer 120, r2-r1 is in a range from 0.5 to 2 μm.

[0064] In the embodiment of the present application, the mass percentage of silicon dioxide, germanium dioxide, fluorine and phosphorus in the first gradient layer 120 is (1-a-b-c):a:b:c, where a is in a range from 0% to 1%, b is in a range from 0.01% to 0.3%, and c is in a range from 0 to 0.2%; in the embodiment of the present application, fluorine can refer to fluorine element, and phosphorus can refer to phosphorus element.

[0065] The second gradient layer 130 has a relative refractive index difference Δn(r) distribution satisfying:

[0066] Δn(r)=Δn4+(Δn5-Δn4)(r-r2 / r3-r2) α2 .

[0067] where Δn4 is in a range from -0.45% to -0.2%, Δn5 is in a range from -0.65% to -0.4%, Δn4 is greater than Δn5, α2 is in a range from 0.5 to 3, and r3-r2 is the radius value range of the second gradient layer 130, r2-r1 is in a range from 4 to 12 μm.

[0068] In the embodiment of the present 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%.

[0069] The first platform layer 140 has a radius range of r3-r4, wherein the value range of r4-r3 is 8-20 μm; the relative refractive index difference of the first platform layer 140 is Δn6, and the value range of Δn6 is -0.3%- -0.1%; in the embodiment of the present application, the mass percentage of the first platform layer 140 satisfies:

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

[0071] The second platform layer 150 has a radius range of r4-r5, wherein the value range of r5-r4 is 6-15 μm; the relative refractive index difference of the second platform layer 150 is Δn7, wherein the value range of Δn7 is -0.2%- -0.05%, and Δn7>Δn6; in the embodiment of the present application, the mass percentage of the second platform layer 150 satisfies:

[0072] SiO2:GeO2:F=[1-(0.1%-0.3%)-(0.15%-0.5%)]:(0%-0.15%):(0.3%-1%).

[0073] The outer cladding layer 160 has a radius range of r5-r6, wherein the value range of r6 is 62-63 μm; the relative refractive index difference of the outer cladding layer 160 is Δn8=0, and the material of the outer cladding layer 160 is pure silica.

[0074] The inner coating layer 170 is made of acrylic resin material, and the material of the inner coating layer 170 needs to satisfy: the elastic modulus is ≦0.7 Mpa, the coating viscosity at 25°C is (3000-8000) mPa·s, the density is (0.95-1.3) g / cm 3 , the elongation at break is ≧125%, and the size of the optical fiber after coating of the inner coating layer 170 is 180-205 μm.

[0075] The outer coating layer 180 is made of acrylic resin material, and the material of the inner coating layer 170 needs to satisfy: the elastic modulus is ≧550 Mpa, the coating viscosity at 25°C is (3000-8000) mPa·s, the density is (0.95-1.3) g / cm 3 , the elongation at break is ≧10%, and the size of the optical fiber after coating of the outer coating layer 180 is 235-252 μm.

[0076] Based on this, the super low loss optical fiber provided by the embodiment of the application not only has a lower attenuation, but also has a larger mode field diameter (typical value 12.5 μm), and the structure and mass percentage of the first gradient layer 120 and the second gradient layer ensure that the optical fiber has a good viscosity matching between different levels while ensuring a sufficient refractive index difference, so that the preform has better consistency and strength after melting, and the design of the platform layer ensures that the optical fiber has a smaller cable cutoff wavelength, a typical attenuation value @ 1550 nm ≤ 0.17 dB / km, and a cable cutoff wavelength ≤ 1500 nm. The optical fiber strength is improved by 50% to 100% compared to a general optical fiber.

[0077] FIG. 3 is a flowchart of a drawing preparation method of the super low loss optical fiber provided by the embodiment of the application, as shown in FIG. 3, the drawing preparation method comprises:

[0078] S301, based on a preset preheating temperature, the optical fiber preform is placed in a circular arc reflection cover for preheating treatment, and an optical fiber preform after preheating treatment is obtained.

[0079] The preheating temperature can be 1900-2100 ℃.

[0080] The optical fiber preform can be a super low loss optical fiber comprising a core layer, and a first gradient layer, a second gradient layer, a first platform layer, a second platform layer and an outer cladding layer successively coated outside the core layer in the embodiment of the application.

[0081] Since the doping amount of the super low loss optical fiber in the core layer in the embodiment of the application is very small, the hardness thereof is much softer than that of the fluorine-doped down layer, and the adaptation of the hardness will cause the adaptation of the viscosity, which will cause the existence of internal stress difference when melting. In order to reduce the viscosity mismatch, the core layer of the optical fiber preform is preheated before melting.

[0082] S302, the optical fiber preform after preheating treatment is subjected to drawing coating treatment, and a super low loss optical fiber with a coating layer is obtained.

[0083] In the embodiment of the application, the method of drawing coating treatment on the optical fiber preform after preheating treatment to obtain a super low loss optical fiber with a coating layer can comprise:

[0084] placing the optical fiber preform after preheating treatment in a drawing furnace for drawing treatment to obtain an optical fiber after drawing treatment;

[0085] passing the optical fiber after drawing treatment through a plurality of annealing holding furnaces in sequence for annealing and holding treatment to obtain an optical fiber after annealing and holding treatment;

[0086] The optical fiber after the heat preservation annealing treatment is subjected to optical fiber coating treatment, and the coating layer on the optical fiber after the optical fiber coating treatment is subjected to curing treatment, so that the ultra-low-loss optical fiber with the coating layer is obtained.

[0087] The optical fiber drawing furnace is one of an induction drawing furnace and a graphite drawing furnace.

[0088] The drawing treatment can refer to placing the preform rod in the optical fiber drawing furnace for melting after the temperature of the optical fiber drawing furnace is increased to 1800-2200 ℃, and then drawing the melted optical fiber preform rod.

[0089] The melting environment in the optical fiber drawing furnace is filled with a protective gas, and the protective gas is preferably an inert gas. In some embodiments, the protective gas includes at least one of argon and helium, and the flow rate of the protective gas is 10-50 L / min. In the protective gas environment, the oxygen content is ≤100 ppm.

[0090] The optical fiber drawing speed is ≥50 m / min. Assuming that the drawing speed is V and the internal tension is g, the relationship between the V value and the G value is g=aV+b, wherein the value range of a is 0.08-0.12, and the value range of b is 20-35.

[0091] The heat preservation annealing treatment can refer to passing through n temperature zones (2≦n≦6) with different temperatures on the optical fiber path, and the optical fiber stays in the entire temperature zone for (0.1-1) s. The temperature of different heat preservation furnaces is set in a gradient from top to bottom. The temperature of the optical fiber entering the annealing zone is between 1100 ℃ and 1600 ℃. After the annealing is completed, the temperature of the optical fiber is 750 ℃-900 ℃. The entire annealing process is completed in a nitrogen environment. The oxygen content in the nitrogen environment is less than 200 ppm, and the nitrogen flow rate is (5-25) L / min. The circulation mode of the upper inlet and the lower outlet is adopted. Through the circulation of nitrogen, the oxygen content and the water molecule content in the annealing environment can be reduced.

[0092] The optical fiber coating treatment can refer to coating the optical fiber with an acrylic resin material. The coating material of the optical fiber is divided into two layers, namely, an inner layer and an outer layer. The inner layer material needs to meet the following requirements: the elastic modulus is ≦0.7 Mpa, the coating viscosity at 25 ℃ is (3000-8000) mPa·s, the density is (0.95-1.3) g / cm 3 , and the elongation at break is ≧125%; the outer coating material needs to meet the following requirements: the elastic modulus is ≧550 Mpa, the coating viscosity at 25 ℃ is (3000-8000) mPa·s, the density is (0.95-1.3) g / cm 3, elongation at break is greater than or equal to 10%. The fiber size is 180-205 μm after the first coating material coating, and the fiber size is 235-252 μm after the second coating.

[0093] The curing treatment can refer to one of UV curing or LED curing, a 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, argon, a single curing furnace gas flow is 10-15 L, the oxygen content in the curing environment is less than 50 ppm, in the curing process, the fiber is exposed to the air environment for not more than 0.04 S when passing through different curing furnaces, after curing in the curing furnace, the inner coating curing degree of the fiber is 87-94%, and the outer layer curing degree is 92-100%, wherein the outer layer curing degree is not less than the inner layer curing degree.

[0094] FIG. 4 is a schematic diagram of a scene structure for heating the optical fiber preform using a circular arc reflector according to an embodiment of the present application. As shown in FIG. 4, the optical fiber preform 100 is located in the circular arc reflector 400 during the preheating process. The shortest distance L between the circular arc reflector 400 and the surface of the optical fiber preform 100 is 2-15 cm. When the preheating temperature is 1900-2100 °C, the optical fiber preform 100 will radiate strong diffuse reflection light. In the present embodiment, the diffuse reflection light is reflected by the circular arc reflector 400 and concentrated at the arc center, i.e., the core layer position of the optical fiber preform 100, thereby completing the preheating process of the core layer position of the optical fiber preform 100.

[0095] FIG. 5 is a structural schematic diagram of an optical fiber drawing device according to an embodiment of the present application. As shown in FIG. 5, the optical fiber drawing device 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 deliver the optical fiber preform 100 after the preheating process to the drawing furnace 520 for drawing processing in the drawing furnace 520. The heat preservation furnace unit 530 is used to perform heat preservation annealing processing on the optical fiber preform 100 after the drawing processing. The bare fiber testing unit 540 and the bare fiber protection tube 550 are used to test the bare optical fiber after the heat preservation annealing processing. The coating unit 560 is used to perform coating operation on the bare optical fiber. The curing unit 570 is used to perform curing operation on 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 the optical fiber.

[0096] The intensity contrast of the parameters of the optical fiber of the present application is shown in the following table:

[0097] From the above description, it can be seen that the above-mentioned embodiments of the present application achieve the following technical effects: by adopting the first and second gradient layers between the core layer and the platform layer, and by adjusting the relative refractive index difference of the first and second gradient layers, the mode distribution of the optical fiber is improved, the bending loss is reduced, the material purity and structural design are improved, the manufacturing defects are reduced, and the dispersion characteristics are optimized, so that the optical fiber has better consistency, and the intensity is maintained above 150 KPSI.

[0098] The preferred embodiments of the present application and experimental verification are described in detail above. It should be understood that those skilled in the art can make many modifications and changes without creative labor according to the concept of the present application. Therefore, any technical solution obtained by logical analysis, reasoning or limited experiment on the basis of the prior art according to the concept of the present application shall be within the protection scope determined by the claims.

Claims

1. An ultra-low-loss optical fiber, characterized in that, The optical fiber comprises a core layer and a first gradient layer, a second gradient layer, a first platform layer, a second platform layer and an outer cladding layer successively coated outside the core layer, wherein the relative refractive index difference of the first gradient layer and the relative refractive index difference of the second gradient layer are linearly changed, 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 platform layer is greater than the maximum value of the relative refractive index difference of the second gradient layer. The relative refractive index difference of the first gradient layer decreases linearly in a direction away from the core layer.

2. The optical fiber of claim 1, wherein, The Δn2 is in a range of 0-0.05%, the Δn3 is in a range of -0.2%-0, the Δn2 is greater than the Δn3, the α1 is in a range of 0.5-2, the r1 is a maximum radius value of the core layer, the r1 is in a range of 5.5-7.5 μm, the r2-r1 is a radius value range of the first gradient layer, and the r2-r1 is in a range of 0.5-2 μm.

3. The optical fiber of claim 2, wherein, The relative refractive index difference Δn(r) distribution of the first graded layer satisfies: Δn(r) = Δn2 + (Δn3 - Δn2)(r - r1 / r2 - r1) α1 ; The mass percentage of silicon dioxide, germanium dioxide, fluorine and phosphorus in the first gradient layer is (1-a-b-c):a:b:c, the a is in a range of 0%-1%, the b is in a range of 0.01%-0.3%, and the c is in a range of 0-0.2%.

4. The optical fiber of claim 1, wherein, The relative refractive index difference of the second gradient layer decreases linearly in a direction away from the core layer.

5. The ultra-low loss optical fiber of claim 1, wherein, The Δn4 is in a range of -0.45%- -0.2%, the Δn5 is in a range of -0.65%- -0.4%, the Δn4 is greater than the Δn5, the α2 is in a range of 0.5-3, the r3-r2 is a radius value range of the second gradient layer, and the r2-r1 is in a range of 4-12 μm.

6. The optical fiber of claim 5, wherein, The relative refractive index difference Δn(r) distribution of the second graded layer satisfies: Δn(r) = Δn4+ (Δn5- Δn4)(r-r2 / r3-r2) α2 ; The mass percentage of silicon dioxide and fluorine in the second gradient layer is 1-(0.5%-1.5%):0.5%-1.5%.

7. The optical fiber of claim 1, wherein, The method for preparing the ultra-low-loss optical fiber in any one of claims 1-8 comprises:

8. A method of drawing an ultra-low-loss optical fiber, characterized in that, placing the optical fiber preform in a circular arc reflection cover for preheating treatment based on a preset preheating temperature to obtain an optical fiber preform after preheating treatment; performing wire drawing coating treatment on the optical fiber preform after preheating treatment to obtain an ultra-low-loss optical fiber with a coating layer. The preheating temperature is 1900-2100 ℃, the distance between the circular arc reflection cover and the optical fiber preform is 2-15 cm, and the reflection center of the circular arc reflection cover for reflecting the diffuse reflection light generated by the heating of the optical fiber preform is the core layer of the optical fiber preform.

9. The method of claim 8, wherein, The method for preparing the ultra-low-loss optical fiber with a coating layer by performing wire drawing coating treatment on the optical fiber preform after preheating treatment comprises:

10. The method of claim 8, wherein, placing the optical fiber preform after preheating treatment in a wire drawing furnace for wire drawing treatment to obtain an optical fiber after wire drawing treatment; performing heat preservation annealing treatment on the optical fiber after wire drawing treatment successively through a plurality of heat preservation annealing furnaces to obtain an optical fiber after heat preservation annealing treatment; and ​ The optical fiber after the heat preservation annealing treatment is subjected to optical fiber coating treatment, and the coating layer on the optical fiber after the optical fiber coating treatment is subjected to curing treatment, so that the super low loss optical fiber with the coating layer is obtained.

11. The method of claim 10, wherein, The melting temperature in the wire drawing furnace is 1800-2200 DEG C, the wire drawing furnace is filled with protective gas, the protective gas comprises at least one of argon and helium, and the flow of the protective gas is 10-50 L / min.

12. The method of claim 10, wherein, In the wire drawing process, the wire drawing speed V and the internal tension g satisfy g=eV+f, wherein the value range of e is 0.08-0.12, and the value range of f is 20-35.

13. The method of claim 10, wherein, The coating layer comprises an inner coating layer and an outer coating layer, wherein the size of the optical fiber after coating the inner coating layer is 180-205 mu m, and the size of the optical fiber after coating the outer coating layer is 235-252 mu m.

14. The method of claim 13, wherein, The material of the inner coating layer and the material of the outer coating layer are both acrylic resin, wherein, The acrylic resin of the inner coating layer satisfies: elastic modulus ≦ 0.7 MPa, and paint viscosity at 25 DEG C is (3000-8000) mPa-s, density is (0.95-1.3) g / cm 3 , elongation at break is ≧ 125%. The acrylic resin of the outer coating layer satisfies: elastic modulus >= 550 Mpa, paint viscosity at 25℃ is (3000-8000) mPa-s, density is (0.95-1.3) g / cm 3 , elongation at break >= 10%.

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