Ultralow-loss optical fiber and wiredrawing preparation method of ultralow-loss optical fiber

Abstract

The embodiment of the invention provides an ultra-low-loss optical fiber and a wiredrawing preparation method of the ultra-low-loss optical fiber. 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 which are sequentially coated outside the core layer, and the relative refractive index difference of the first gradient layer and the relative refractive index difference of the second gradient layer are linearly changed. The minimum value of the relative refractive index difference of the first gradient layer is larger 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 larger than the maximum value of the relative refractive index difference of the second gradient layer. According to the ultra-low loss optical fiber, the transmission performance of optical signals can be improved, attenuation is reduced, and the use effect of the optical fiber is improved.

Description

Technical Field

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

[0002] Since its advent in the 1970s, optical fiber technology has developed rapidly and has 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 networks. Optical fiber is not only used for long-distance communication, but also gradually enters metropolitan area networks, access networks and home networks, promoting the rapid development of the information society.

[0003] At present, existing doped optical fibers change the optical properties of optical fibers by doping specific elements or compounds in the core or cladding to meet the needs of different applications. Different types of doped optical fibers are widely used in the fields of fiber amplifiers, fiber lasers, dispersion compensation, nonlinear optics and fiber sensing. According to specific application requirements, the appropriate type of doped optical fiber can be selected to optimize system performance and achieve specific functions.

[0004] However, the existing doped optical fiber has the problem of high attenuation and poor use effect when transmitting optical signals. Summary of the invention

[0005] The embodiments of the present application provide an ultra-low loss optical fiber and a drawing preparation method for the ultra-low loss optical fiber, so as to improve the problem that the existing optical fiber has high attenuation and poor use effect.

[0006] In a first aspect, an embodiment of the present application provides an ultra-low loss optical fiber, comprising:

[0007] 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 which are sequentially 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 both change linearly, 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.

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

[0009] In a possible implementation, the relative refractive index difference Δn(r) of the first gradient layer satisfies the following distribution:

[0010] Δn(r)=Δn2+(Δn3-Δn2)(r-r1 / r2-r1) α1 ;

[0011] Among them, the range of Δn2 is 0~0.05%, the range of Δn3 is -0.2%~0, and Δn2 is greater than Δn3, the range of α1 is 0.5~2, r1 is the maximum radius value of the core layer, the value range of r1 is 5.5~7.5μm, r2-r1 is the radius value range of the first gradient layer, and the value range of r2-r1 is 0.5~2μm.

[0012] In a possible implementation, the mass percentages of silicon dioxide, germanium dioxide, fluorine, and phosphorus in the first gradient layer are (1-abc): 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%.

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

[0014] In a possible implementation, the relative refractive index difference Δn(r) of the second gradient layer satisfies the following distribution:

[0015] Δn(r)=Δn4+(Δn5-Δn4)(r-r2 / r3-r2) α2 ;

[0016] Among them, the range of Δn4 is -0.45% to -0.2%, the range of Δn5 is -0.65% to -0.4%, and Δn4 is greater than Δn5. The range of α2 is 0.5 to 3, r3-r2 is the radius range of the second gradient layer, and the range of r2-r1 is 4 to 12 μm.

[0017] In a possible implementation manner, 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] In a second aspect, an embodiment of the present application provides a method for preparing an ultra-low loss optical fiber by drawing, which is used to prepare the ultra-low loss optical fiber in the embodiment of the present application, and the method comprises:

[0019] Based on a preset preheating temperature, placing the optical fiber preform in an arc reflective cover for preheating treatment to obtain a preheated optical fiber preform;

[0020] The optical fiber preform rod after preheating treatment is subjected to drawing and coating treatment to obtain an ultra-low loss optical fiber with a coating layer.

[0021] In a possible implementation, the preheating temperature is 1900-2100° C., the distance between the arc reflector and the optical fiber preform is 2-15 cm, and the reflection center of the arc reflector reflecting the diffusely reflected light generated by the heating of the optical fiber preform is the core layer of the optical fiber preform.

[0022] In a possible implementation, the optical fiber preform rod after the preheating treatment is subjected to a drawing and coating process 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 a drawn optical fiber;

[0024] Passing the drawn optical fiber through a plurality of annealing and heat preservation furnaces in sequence for heat preservation and annealing treatment to obtain an optical fiber after the heat preservation and annealing treatment;

[0025] 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 cured to obtain an ultra-low loss optical fiber with a coating layer.

[0026] In a possible implementation, the melting temperature in the wire drawing furnace is 1800-2200° C., 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;

[0027] In a possible implementation, the drawing speed V and the internal tension g in the drawing process satisfy: g=eV+f, wherein the value range of e is 0.08-0.12, and the value range of f is 20-35.

[0028] 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 the inner coating layer is 180-205 μm, and the size of the optical fiber after coating the outer coating layer is 235-252 μm.

[0029] In a possible implementation, the material of the inner coating layer and the material of the outer coating layer are both acrylic resins, wherein:

[0030] The acrylic resin of the inner coating layer meets the following requirements: elastic modulus ≤ 0.7Mpa, and the coating viscosity is (3000~8000)mPa·s at 25℃, and the density is (0.95~1.3)g / cm 3 , elongation at break ≥ 125%;

[0031] The acrylic resin of the outer coating layer meets the following requirements: elastic modulus ≧550Mpa, coating viscosity at 25°C is (3000~8000)mPa·s, density is (0.95~1.3)g / cm 3, elongation at break ≥10%.

[0032] An ultra-low loss optical fiber and a drawing preparation method for the ultra-low loss optical fiber provided in the embodiments of the present application improve the mode distribution of the optical fiber, reduce bending loss, improve material purity and structural design, reduce manufacturing defects, and optimize dispersion characteristics by arranging a first gradient layer and a second gradient layer between the core layer and the platform layer, and adjusting the relative refractive index difference between the first gradient layer and the second gradient layer, so as to make the optical fiber have better consistency and strength, thereby improving the transmission performance of the optical signal, reducing attenuation, and improving the use effect of the optical fiber. BRIEF DESCRIPTION OF THE DRAWINGS

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

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

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

[0036] Figure 3 A schematic diagram of a process for drawing and preparing an ultra-low loss optical fiber provided in an embodiment of the present application;

[0037] Figure 4 A schematic diagram of a scene structure for heating an optical fiber preform using an arc reflector provided in an embodiment of the present application;

[0038] Figure 5 A schematic diagram of the structure of the optical fiber drawing equipment provided in an embodiment of the present application.

[0039] Description of reference numerals:

[0040] 100-optical fiber preform; 110-core layer; 120-first gradient layer; 130-second gradient layer; 140-first platform layer; 150-second platform layer; 160-outer cladding; 170-inner coating layer; 180-outer coating layer; 400-arc reflector; 510-rod feeder, 520-drawing furnace, 530-insulation furnace unit, 540-bare fiber test unit, 550-bare fiber protection tube, 560-coating unit, 570-curing unit, 580-optical fiber size test unit, 590-receiving unit. DETAILED DESCRIPTION

[0041] Exemplary embodiments will be described in detail herein, examples of which are shown in the accompanying drawings. When the following description refers to the drawings, the same numbers in different drawings represent the same or similar elements unless otherwise indicated. The implementations described in the following exemplary embodiments do not represent all implementations consistent with the present application. Instead, they are merely examples of devices and methods consistent with some aspects of the present application as detailed in the appended claims.

[0042] First, the terms involved in this application are explained:

[0043] The 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. Its refractive index is higher than that of the cladding, so that light can be transmitted in the core through 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 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.

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

[0046] The coating can be composed of one or more layers of polymer materials. Its main function is to protect the optical fiber from physical damage and environmental influences.

[0047] With the advent of the information age of data explosion, the development of both the secondary and tertiary industries is extremely dependent on high-speed communication networks. Fiber optic communication is currently the most mainstream way of wired communication, and it is widely used because of its advantages such as simple material, small size, good confidentiality, and fast transmission speed. High-speed optical communication networks have also gradually developed from 10G and 40G to the commonly used 100G communication system, and the 400G system is also gradually being improved. However, due to the huge amount of information sent, the optical signal is easily generated due to excessive light density when it is transmitted in the optical fiber, which increases the bit error rate of the signal. In order to reduce the nonlinear effect of the signal during transmission, reducing the light density of the optical signal is a more effective method. Therefore, engineers have designed an optical fiber with a large effective area that can be used in high-speed optical communication systems, and at the same time make it have ultra-low attenuation, which can be used in long-distance non-relay transmission systems such as submarine cables.

[0048] The effective area of ​​a single-mode optical fiber is related to its mode field diameter. During signal transmission, the optical signal is not only transmitted in the optical fiber core layer, but also part of the signal is transmitted in the optical fiber cladding. Therefore, it is not practical to express this characteristic with the core diameter. Therefore, the concept of mode field diameter (MFD) is used to define it. Generally speaking, the size of the mode field diameter is proportional to the core diameter of the optical fiber. The relationship between the mode field diameter and the effective area is shown in the following formula:

[0049]

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

[0051] An ultra-low loss optical fiber and a drawing preparation method for the ultra-low loss optical fiber provided in the embodiments of the present application, the optical fiber using the above design not only has low attenuation but also has a large mode field diameter (typical value 12.5μm), the gradient structure and mass percentage adopted ensure that the optical fiber ensures a good viscosity matching between different layers while ensuring a sufficient refractive index difference, so that the preform has better consistency and strength after melting, the design of the platform layer ensures that the optical fiber has a smaller cable cut-off wavelength, the typical attenuation value is 1550nm≤0.17dB / km, the optical cable cut-off wavelength is ≤1500nm, and the optical fiber strength is increased by 50% to 100% compared with general optical fibers.

[0052] Figure 1 The schematic diagram of the structure of the ultra-low loss optical fiber provided for this application is as follows: Figure 1 As shown, 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 sequentially coated outside 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, 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, 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.

[0053] Among them, by adjusting the relative refractive index difference, various properties of optical fiber can be improved, such as mode control, inter-modal dispersion, bandwidth, bending performance, dispersion management, nonlinear effects, signal quality, transmission distance, manufacturing tolerance and environmental stability. These improvements enable 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.

[0054] At the same time, 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, so that the larger refractive index difference can make the optical signal more tightly confined in the core, thereby reducing the possibility of light escaping when bending, thereby improving and reducing the attenuation of the optical fiber.

[0055] 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 both change linearly, including two situations: the relative refractive index difference of the first gradient layer 120 and the relative refractive index difference of the second gradient layer 130 both decrease linearly in the direction away from the core layer 110 and both increase linearly in the direction away from the core layer 110. Among them, when the relative refractive index difference of the first gradient layer 120 and the relative refractive index difference of the second gradient layer 130 both increase linearly in the direction away from the core layer 110, the inter-modal dispersion can be increased and specific optical properties 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 both decrease linearly in the direction away from the core layer 110, the inter-modal dispersion can be reduced, the bandwidth and transmission distance can be increased, the bending performance can be improved, and the 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 embodiment of the present application, see Figure 1 and Figure 2 The contents shown, ultra-low loss optical fiber includes:

[0057] The core layer 110 has a maximum radius of r1, wherein r1 has a value range of 5.5 to 7.5 μm; the relative refractive index difference of the core layer 110 is Δn1, wherein Δn1 has a value range of 0.05% to 0.15%; in the embodiment of the present application, 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%~

[0059] 2% ):(0.05%~0.5%):(0%~0.35%).

[0060] The first gradient layer 120, the relative refractive index difference Δn(r) of the first gradient layer 120 satisfies the following distribution:

[0061] Δn(r)=Δn2+(Δn3-Δn2)(r-r1 / r2-r1) α1 ;

[0062] Among them, the range of Δn2 is 0~0.05%, the range of Δn3 is -0.2%~0, and Δn2 is greater than Δn3, the range of α1 is 0.5~2, r1 is the maximum radius value of the core layer 110, the value range of r1 is 5.5~7.5μm, r2-r1 is the radius value range of the first gradient layer 120, and the value range of r2-r1 is 0.5~2μm.

[0063] In the embodiment of the present application, the mass percentages of silicon dioxide, germanium dioxide, fluorine, and phosphorus in the first gradient layer 120 are (1-abc): 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%. In the embodiment of the present application, fluorine may refer to the fluorine element, and phosphorus may refer to the phosphorus element.

[0064] The second gradient layer 130, the second gradient layer 130 relative refractive index difference Δn(r) distribution satisfies:

[0065] Δn(r)=Δn4+(Δn5-Δn4)(r-r2 / r3-r2) α2 ;

[0066] Among them, the range of Δn4 is -0.45% to -0.2%, the range of Δn5 is -0.65% to -0.4%, and Δn4 is greater than Δn5. The range of α2 is 0.5 to 3, r3-r2 is the radius range of the second gradient layer 130, and the range of r2-r1 is 4 to 12 μm.

[0067] 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% to 1.5%): 0.5% to 1.5%.

[0068] The first platform layer 140 has a radius range of r3 to r4, wherein the value range of r4-r3 is 8 to 20 μm; the relative refractive index difference of the first platform layer 140 is Δn6, and the value range of Δn6 is -0.3% to -0.1%; in the embodiment of the present application, the mass percentage of the first platform layer 140 satisfies:

[0069] SiO2: GeO2: F=[1-(0%~0.15%)-(0.3%~1%)]: (0%~0.15%): (0.3%~

[0070] 1%).

[0071] The second platform layer 150 has a radius range of r4 to r5, wherein the value range of r5-r4 is 6 to 15 μm; the relative refractive index difference of the second platform layer 150 is Δn7, wherein the value range of Δn7 is -0.2% to -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%):

[0073] (0.3%~1%).

[0074] The outer cladding 160 has a radius range of r5 to r6, wherein the value range of r6 is 62 to 63 μm; the relative refractive index difference Δn8 of the outer cladding 160 is 0, and the material of the outer cladding 160 is pure silicon dioxide.

[0075] 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 ≤ 0.7Mpa, and the coating viscosity at 25°C is (3000-8000) mPa·s, and 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 the inner coating layer 170 is 180-205 μm.

[0076] The outer coating layer 180 is made of acrylic resin. The material of the inner coating layer 170 must meet the following requirements: elastic modulus ≧550Mpa, coating viscosity at 25°C is (3000~8000)mPa·s, density is (0.95~1.3)g / cm 3 , the elongation at break is ≥10%, and the size of the optical fiber after coating the outer coating layer 180 is 235-252 μm.

[0077] Based on this, an ultra-low loss optical fiber provided in an embodiment of the present application not only has low attenuation, but also has a large mode field diameter (typical value 12.5μm), and the structure of the first gradient layer 120 and the second gradient layer, as well as the mass percentage, ensure that the optical fiber ensures a good viscosity matching between different layers 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, the typical attenuation value @1550nm≤0.17dB / km, the optical cable cutoff wavelength≤1500nm, and the optical fiber strength is increased by 50% to 100% compared with general optical fibers.

[0078] Figure 3A schematic diagram of the process of drawing and preparing the ultra-low loss optical fiber provided in the embodiment of the present application is shown in FIG. Figure 3 As shown, the wire drawing preparation method comprises:

[0079] S301, placing the optical fiber preform in an arc reflective cover for preheating treatment based on a preset preheating temperature, to obtain the optical fiber preform after the preheating treatment.

[0080] The preheating temperature may be 1900-2100°C.

[0081] The optical fiber preform can be an ultra-low loss optical fiber in the embodiment of the present application, 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 sequentially coated outside the core layer.

[0082] Since the ultra-low loss optical fiber in the embodiment of the present application has a small amount of doping in the core layer, its hardness is much softer than the fluorine-doped depression layer. The hardness adaptation will cause the viscosity adaptation, which will cause the existence of internal stress difference during melting. In order to reduce the viscosity mismatch, the core layer of the optical fiber preform is preheated before melting.

[0083] S302, subjecting the preheated optical fiber preform to drawing and coating treatment to obtain an ultra-low loss optical fiber with a coating layer.

[0084] Among them, in the embodiment of the present application, the method of drawing and coating the optical fiber preform after the preheating treatment to obtain an ultra-low loss optical fiber with a coating layer may include:

[0085] The preheated optical fiber preform is placed in a drawing furnace for drawing to obtain a drawn optical fiber;

[0086] Passing the drawn optical fiber through a plurality of annealing and heat preservation furnaces in sequence for heat preservation and annealing treatment to obtain an optical fiber after the heat preservation and annealing treatment;

[0087] 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 cured to obtain an ultra-low loss optical fiber with a coating layer.

[0088] Among them, the optical fiber drawing furnace is a kind of drawing furnace among the induction drawing furnace and the graphite drawing furnace.

[0089] The fiber drawing process may refer to placing the preform in the fiber drawing furnace to melt after the temperature of the fiber drawing furnace is raised to 1800-2200°C, and then drawing the melted fiber preform.

[0090] The molten environment in the optical fiber drawing furnace is filled with a protective gas, which 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 to 50 L / min, wherein the oxygen content in the protective gas environment is ≤100 ppm.

[0091] The optical fiber drawing speed is ≥50m / min. Assuming 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, where the value range of a is 0.08-0.12, and the value range of b is 20-35.

[0092] The heat preservation annealing treatment can refer to the fiber path passing through n temperature zones with different temperatures (2≦n≦6). The fiber stays in the entire temperature zone for (0.1~1)S. The temperature settings of different heat preservation furnaces are set in a gradient decreasing order from top to bottom. The temperature of the fiber entering the annealing interval is between 1100℃ and 1600℃. After annealing, the fiber temperature is 750℃~900℃. The entire annealing process is completed in a nitrogen environment. The oxygen content in the nitrogen environment is less than 200ppm, and the nitrogen flow rate is (5~25)L / min. The circulation method of upper air intake and lower air extraction is adopted. By circulating nitrogen, in addition to reducing the oxygen content, the content of water molecules in the annealing environment can also be reduced.

[0093] Optical fiber coating refers to the use of acrylic resin materials to coat optical fibers. The optical fiber coating material is divided into two layers, the inner layer and the outer layer. The inner layer material is required to meet the following requirements: elastic modulus ≦ 0.7Mpa, coating viscosity at 25°C is (3000~8000) mPa·s, density is (0.95~1.3) g / cm 3 , elongation at break ≧125%; the outer coating material needs to meet the following requirements: elastic modulus ≧550Mpa, coating viscosity at 25°C is (3000~8000)mPa·s, density is (0.95~1.3)g / cm 3 , elongation at break ≧10%. The size of the optical fiber after the primary coating material is 180-205 μm, and the size of the optical fiber after the secondary coating is 235-252 μm.

[0094] Curing treatment may refer to one of UV curing (Ultraviolet Curing) or LED curing (LED Curing), and the curing environment is isolated by non-oxygen gas. In some embodiments, the non-oxygen gas used may be at least one of nitrogen, helium, and argon. The gas flow rate of a single curing furnace is 10L to 15L, and the oxygen content in the curing environment is less than 50ppm. During the curing process, when the optical fiber passes through different curing furnaces, it shall not be exposed to the air environment for more than 0.04S. After curing in the curing furnace, 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 shall not be less than the curing degree of the inner layer.

[0095] Figure 4 A schematic diagram of a scene structure for heating an optical fiber preform rod using an arc reflector provided in an embodiment of the present application is shown in FIG. Figure 4 As shown, the optical fiber preform 100 is located in the arc reflective cover 400 during the preheating treatment, and the shortest distance L between the arc reflective cover 400 and the surface of the optical fiber preform 100 is 2 to 15 cm. When the optical fiber preform 100 is preheated using the arc reflective cover 400, when the preheating temperature is 1900 to 2100° C., the optical fiber preform 100 itself will radiate strong diffuse reflected light. In the embodiment of the present application, the diffuse reflected light is reflected and concentrated to the arc center, i.e., the core layer position of the optical fiber preform 100, thereby completing the preheating treatment of the core layer position of the optical fiber preform 100.

[0096] Figure 5 A schematic diagram of the structure of the optical fiber drawing device provided in the embodiment of the present application is shown in FIG. 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 test unit 540, a bare fiber protection tube 550, a coating unit 560, a curing unit 570, an optical fiber size test unit 580, and a take-up unit 590; wherein, the rod feeder 510 is used to transport the optical fiber preform 100 after preheating treatment to the drawing furnace 520 for drawing treatment in the drawing furnace 520, the heat preservation furnace unit 530 is used to perform heat preservation annealing treatment on the optical fiber preform 100 after drawing treatment, the bare fiber test unit 540 and the bare fiber protection tube 550 are used to test the bare optical fiber after heat preservation annealing treatment, 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 test unit is used to test the cured optical fiber; and the take-up unit 590 is used to sort and collect the optical fiber.

[0097] The intensity comparison of the optical fiber of the present invention under various parameters is shown in the following table:

[0098]

[0099]

[0100] From the above description, it can be seen that the above-mentioned embodiments of the present invention achieve the following technical effects: by arranging the first gradient layer and the second gradient layer between the core layer and the platform layer, and by adjusting the relative refractive index difference between the first gradient layer and the second gradient layer, 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 strength is maintained above 150KPSI.

[0101] The preferred specific embodiments and experimental verification of the present invention are described in detail above. It should be understood that ordinary technicians in this field can make many modifications and changes based on the concept of the present invention without creative work. Therefore, all technical solutions that can be obtained by technicians in this technical field based on the concept of the present invention through logical analysis, reasoning or limited experiments on the basis of the prior art should be within the scope of protection determined by the claims.

Claims

1. An ultra-low loss optical fiber, characterized in that: include: 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 sequentially 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 both change linearly, 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.

2. The optical fiber according to claim 1, characterized in that The relative refractive index difference of the first graded layer decreases linearly in a direction away from the core layer.

3. The optical fiber according to claim 2, characterized in that The relative refractive index difference Δn(r) of the first gradient layer satisfies the following distribution: Δn(r)=Δn2+(Δn3-Δn2)(r-r1 / r2-r1) α1 ; Among them, the range of Δn2 is 0~0.05%, the range of Δn3 is -0.2%~0, and the Δn2 is greater than the Δn3, the range of α1 is 0.5~2, the r1 is the maximum radius value of the core layer, the value range of r1 is 5.5~7.5μm, the r2-r1 is the radius value range of the first gradient layer, and the value range of r2-r1 is 0.5~2μm.

4. 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, wherein the value range of a is 0% to 1%, the value range of b is 0.01% to 0.3%, and the value range of c is 0 to 0.2%.

5. The ultra-low loss optical fiber according to claim 1, characterized in that: The relative refractive index difference of the second graded layer decreases linearly in a direction away from the core layer.

6. The optical fiber according to claim 5, characterized in that The relative refractive index difference Δn(r) of the second gradient layer satisfies the following distribution: Δn(r)=Δn4+(Δn5-Δn4)(r-r2 / r3-r2) α2 ; Among them, the range of Δn4 is -0.45% to -0.2%, the range of Δn5 is -0.65% to -0.4%, and Δn4 is greater than Δn5, the range of α2 is 0.5 to 3, r3-r2 is the radius range of the second gradient layer, and the range of r2-r1 is 4 to 12 μm.

7. 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% to 1.5%): 0.5% to 1.5%.

8. A method for drawing and preparing ultra-low loss optical fiber, characterized in that: For preparing the ultra-low loss optical fiber according to any one of claims 1 to 8, the method comprises: Based on a preset preheating temperature, placing the optical fiber preform in an arc reflective cover for preheating treatment to obtain a preheated optical fiber preform; The optical fiber preform rod after preheating treatment is subjected to drawing and coating treatment to obtain an ultra-low loss optical fiber with a coating layer.

9. The method according to claim 8, characterized in that The preheating temperature is 1900-2100° C., the distance between the arc reflector and the optical fiber preform is 2-15 cm, and the reflection center of the arc reflector reflecting the diffusely reflected light generated by the heating of the optical fiber preform is the core layer of the optical fiber preform.

10. The method according to claim 8, characterized in that The method of subjecting the preheated optical fiber preform to drawing and coating to obtain an ultra-low loss optical fiber with a coating layer comprises: The preheated optical fiber preform is placed in a drawing furnace for drawing to obtain a drawn optical fiber; Passing the drawn optical fiber through a plurality of annealing and heat preservation furnaces in sequence for heat preservation and annealing treatment to obtain an optical fiber after the heat preservation and annealing treatment; 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 cured to obtain an ultra-low loss optical fiber with a coating layer.

11. The method according to claim 10, characterized in that The melting temperature in the wire drawing furnace is 1800-2200° C., 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.

12. The method according to claim 10, characterized in that 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 according to claim 10, characterized in that 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 μm, and the size of the optical fiber after coating the outer coating layer is 235-252 μm.

14. The method according to claim 13, characterized in that 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 ≤ 0.7Mpa, and the coating viscosity is (3000-8000) mPa·s at 25°C, and the density is (0.95-1.3) g / cm 3 , elongation at break ≥ 125%; The acrylic resin of the outer coating layer meets the following requirements: elastic modulus ≧550Mpa, coating viscosity at 25°C is (3000-8000) mPa·s, density is (0.95-1.3) g / cm 3 , elongation at break ≥10%.

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