Large core diameter optical fiber and forming method thereof

Abstract

The present invention discloses a large-core optical fiber and a forming method thereof, which relates to the field of special optical fiber technology. The large-core optical fiber comprises: a core layer; a sheath made of fluorine-containing silica coated on the outside of the core layer; a protective layer coated on the outside of the sheath; the sheath comprises a first auxiliary buffer layer segment, a depressed layer segment, a second auxiliary buffer layer segment, and an outer cladding segment, wherein the first auxiliary buffer layer segment, the depressed layer segment, the second auxiliary buffer layer segment, and the outer cladding segment are arranged in sequence from the center to the outside of the large-core optical fiber; the outer cladding segment is made of pure silica, the relative refractive index difference of the first auxiliary buffer layer segment is a, the relative refractive index difference of the depressed layer segment is b, the relative refractive index difference of the second auxiliary buffer layer segment is c, and the relative refractive index difference of the outer cladding segment is d, wherein d is greater than c, c is greater than b, b is less than a, and a is less than d. This application can solve the problem that as the diameter of a quartz optical fiber increases, the material becomes more brittle and is more susceptible to internal defects.

Description

Technical Field

[0001] The present invention relates to the technical field of special optical fibers, and in particular to a large-core-diameter optical fiber and a molding method thereof. Background Art

[0002] With the continuous development of industries such as industry, technology, medicine, and scientific research, the requirements for optical fibers are increasing. As one of the specialty optical fibers, large-core optical fibers, unlike the 9μm core diameter single-mode fibers and 50μm or 62.5μm core diameter multimode fibers, have core diameters ranging from 100μm to 1000μm. Their large numerical aperture allows for better optical energy transmission and a wide operating temperature range, capable of withstanding extreme temperatures.

[0003] Like conventional optical fibers, large-core optical fibers are constructed from a quartz core, glass cladding, and organic protective layers. Producing qualified large-core optical fibers requires not only higher standards for the quartz fiber itself, but also crucially, the coating process and curing quality. Quartz fiber is primarily made of silica. Larger diameters increase the brittleness of the material, making it more susceptible to internal defects, resulting in energy loss and ultimately impairing performance. Furthermore, the low-refractive-index coatings currently used are expensive and have a low temperature tolerance, making them susceptible to failure when transmitting high energy. Summary of the Invention

[0004] In order to overcome the above-mentioned defects of the prior art, the technical problem to be solved by the embodiments of the present invention is to provide a large-core-diameter optical fiber and a forming method thereof, which can solve the problem that the larger the diameter of the quartz optical fiber, the more brittle the material, and the easier it is to form internal defects.

[0005] The specific technical solution of the embodiment of the present invention is:

[0006] A large-core optical fiber, comprising:

[0007] A core layer; a wrapping layer made of fluorine-containing silicon dioxide coated on the outside of the core layer; a protective layer coated on the outside of the wrapping layer;

[0008] The wrapping layer includes a first auxiliary buffer layer segment, a depressed layer segment, a second auxiliary buffer layer segment, and an outer cladding layer segment, wherein the first auxiliary buffer layer segment, the depressed layer segment, the second auxiliary buffer layer segment, and the outer cladding layer segment are arranged in sequence from the center of the large-core optical fiber to the outside; the outer cladding layer segment is made of pure silica;

[0009] The relative refractive index difference of the first auxiliary buffer layer segment is a, the relative refractive index difference of the depression layer segment is b, the relative refractive index difference of the second auxiliary buffer layer segment is c, and the relative refractive index difference of the outer cladding segment is d, wherein d is greater than c, c is greater than b, b is less than a, and a is less than d.

[0010] Preferably, the relative refractive index difference of the core layer is parabolic in the diameter direction, the parabolic distribution power index range is between 1.9 and 2.2, the relative refractive index difference at the center of the core layer is the largest, the maximum relative refractive index difference of the core layer is e, e is greater than d, the diameter of the core layer is between 200um and 1000um; the maximum relative refractive index difference e of the core layer is between 1% and 2.2%.

[0011] Preferably, the relative refractive index difference a of the first auxiliary buffer layer segment is between -0.2% and -0.1%; the relative refractive index difference c of the second auxiliary buffer layer segment is between -0.2% and -0.1%; and the relative refractive index difference b of the sunken layer segment is between -1.4% and -0.4%.

[0012] Preferably, the ratio of the diameter of the first auxiliary buffer layer segment to the diameter of the core layer is between 1.01 and 1.06, the ratio of the diameter of the second auxiliary buffer layer segment to the diameter of the core layer is between 1.1 and 1.25, the ratio of the diameter of the sunken layer segment to the diameter of the core layer is between 1.03 and 1.12, and the diameter of the outer cladding segment is between 220um and 1500um.

[0013] Preferably, the core layer is prepared by Ge doping through MCVD.

[0014] Preferably, the protective layer is formed of at least one of the following materials: high temperature resistant acrylate, silicone resin, and polyimide.

[0015] A method for forming a large-core optical fiber as described in any of the above, the forming method comprising the following steps:

[0016] Silicon tetrachloride and oxygen are introduced into a quartz substrate tube to react with each other to generate a product, which is deposited on the inner wall of the substrate tube to form an outer cladding section;

[0017] Then, silicon tetrachloride, oxygen and fluorine-containing gas are introduced into the quartz substrate tube, and the flow rate of the fluorine-containing gas is controlled according to the different relative refractive index differences of the various sections of the wrapping layer to sequentially deposit a fluorine-doped second auxiliary buffer layer section, a depression layer section and a first auxiliary buffer layer section;

[0018] After forming the first auxiliary buffer layer segment, introducing silicon tetrachloride, germanium tetrachloride, and oxygen into the quartz substrate tube to react with each other to generate a product, which is deposited on the inner wall of the first auxiliary buffer layer segment to form a core layer, thereby forming a preform;

[0019] melting the deposited preform rod at high temperature to form a solid optical fiber preform rod;

[0020] The optical fiber preform is drawn into an optical fiber with a preset diameter.

[0021] Preferably, the Ge doping in the core layer is changed by changing the flow rate of germanium tetrachloride.

[0022] Preferably, the step of drawing the optical fiber preform into an optical fiber of a preset diameter specifically includes:

[0023] Melting the optical fiber preform in a heating furnace at a first preset temperature to form an optical fiber with a preset diameter, wherein the first preset temperature is between 1950 degrees and 2100 degrees;

[0024] The heating furnace is uniformly supplied with gas, wherein the gas routes include an upper route, a middle route, and a lower route. The gas output from each gas route is between the inner wall of the heating furnace and the optical fiber preform. When the diameter of the optical fiber preform is between 20 mm and 50 mm, the flow rate of the gas output from the upper route and the middle route is between 15 L / min and 25 L / min. The gas output from the upper route and the middle route is a mixed gas of helium and argon, and the gas output from the lower route is argon.

[0025] The optical fiber emerging from the heating furnace is subjected to thermal annealing gradually decreasing from a second preset temperature, the second preset temperature being between 1200° C. and 950° C.;

[0026] The optical fiber that has undergone thermal annealing enters a cooling tube and is cooled to a temperature at which a protective layer can be applied.

[0027] Preferably, the molding method further comprises the following steps:

[0028] After the cooled optical fiber passes through a pressure coating die and is coated with the coating, the coating is cured into a protective layer by a curing system. Finally, it is pulled by a traction wheel into a continuous filament and collected by an optical fiber collection device. The curing system includes a light curing unit and a heat curing unit, which can be switched between the two. The heat curing unit uses an infrared radiation furnace.

[0029] The coating comprises at least one of high temperature resistant acrylate, silicone resin and polyimide.

[0030] The technical solution of the present invention has the following significant beneficial effects:

[0031] 1. The special design of the relative refractive index difference between the first auxiliary buffer layer segment and the second auxiliary buffer layer segment in the cladding layer can effectively prevent defects such as bubbles and cracks inside and outside the preform rod caused by the volatilization of fluorine during the manufacturing process of the optical fiber with a fluorine-doped cladding layer. This solves the problem that the larger the diameter of the quartz optical fiber, the more brittle the material and the more likely it is to form internal defects. In the case of a large diameter quartz optical fiber, the material strength is improved, making it less likely to form internal defects.

[0032] 2. In the process of forming large-core optical fibers, a low-temperature, slow and steady-speed drawing method is adopted to control the stability of the heating furnace temperature and the gas flow in the furnace, thereby effectively reducing the crystallization phenomenon of the preform rod. In addition, slow and steady-speed drawing can also effectively adjust the fluctuation of the fiber cladding layer diameter.

[0033] 3. By optimizing the relative refractive index difference of the optical fiber profile, the diameter of the optical fiber core layer can be increased and the numerical aperture of the optical fiber can be improved. At the same time, the groove design with d greater than c, c greater than b, b less than a, and a less than d can improve the bending performance of the optical fiber and enhance the focusing ability. Combined with the improvement of internal defects of the optical fiber, the optical fiber light transmission efficiency can be increased to 98%.

[0034] With reference to the following description and drawings, specific embodiments of the present invention are disclosed in detail, indicating how the principles of the present invention can be employed. It should be understood that the embodiments of the present invention are not limited in scope thereby. Features described and / or illustrated for one embodiment may be used in the same or similar manner in one or more other embodiments, combined with features in other embodiments, or substituted for features in other embodiments. BRIEF DESCRIPTION OF THE DRAWINGS

[0035] The drawings described herein are for illustrative purposes only and are not intended to limit the scope of the present invention in any way. In addition, the shapes and proportional dimensions of the various components in the drawings are merely illustrative and are used to help understand the present invention, and are not intended to specifically limit the shapes and proportional dimensions of the various components of the present invention. Those skilled in the art can select various possible shapes and proportional dimensions to implement the present invention according to specific circumstances under the guidance of the present invention.

[0036] Figure 1 2 is a cross-sectional structural diagram of a large-core optical fiber according to an embodiment of the present invention;

[0037] Figure 2 Schematic diagram of the change of relative refractive index difference corresponding to various positions of the cross section of a large-core optical fiber in an embodiment of the present invention;

[0038] Figure 3 Schematic diagram of a drawing device for producing large-core optical fibers according to an embodiment of the present invention;

[0039] Figure 4 Schematic diagram of an optical fiber coating and curing system in an embodiment of the present invention.

[0040] Reference numerals in the above drawings:

[0041] 1. Rod feeding mechanism; 2. Preform rod; 3. Heating furnace; 4. Wire diameter measuring instrument; 5. Bare optical fiber; 501. Core layer; 502. Wrapping layer; 503. Protective layer; 6. Optical fiber coating and curing system; 601. Coater; 602. Light curing unit; 603. Heat curing unit; 604. Sliding track; 7. Traction wheel; 8. Optical fiber collection device; 9. Wire diameter control system. DETAILED DESCRIPTION

[0042] The details of the present invention can be more clearly understood in conjunction with the accompanying drawings and the description of the specific embodiments of the present invention. However, the specific embodiments of the present invention described herein are for illustrative purposes only and are not to be construed as limiting the present invention in any way. Based on the teachings of the present invention, skilled artisans can conceive of any possible variations based on the present invention, all of which should be considered within the scope of the present invention. It should be noted that when an element is referred to as being "disposed on" another element, it can be directly on the other element or there can be an intermediate element. When an element is considered to be "connected to" another element, it can be directly connected to the other element or there can be an intermediate element. The terms "mounted," "connected," and "connected" should be interpreted broadly. For example, they can refer to mechanical or electrical connections, internal communication between two elements, direct connection, or indirect connection through an intermediary. Those skilled in the art will understand the specific meanings of these terms based on the specific circumstances. The terms "vertical," "horizontal," "upper," "lower," "left," "right," and similar expressions used herein are for illustrative purposes only and do not represent the only embodiments.

[0043] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by those skilled in the art to which this application pertains. The terms used herein in the specification of this application are intended only to describe specific embodiments and are not intended to limit this application. The term "and / or" as used herein includes any and all combinations of one or more of the associated listed items.

[0044] In order to solve the problem that the larger the diameter of quartz optical fiber, the more brittle the material, and the easier it is to form internal defects, a large core diameter optical fiber is proposed in this application. Figure 1 is a cross-sectional structural diagram of a large core diameter optical fiber according to an embodiment of the present invention, Figure 2 FIG. 1 is a schematic diagram showing the change in relative refractive index difference corresponding to various positions of the large core diameter optical fiber cross section in an embodiment of the present invention. Figure 1 and Figure 2 As shown, a large core optical fiber may include: a core layer 501; a cladding layer 502; and a protective layer 503. The cladding layer 502 is coated on the outside of the core layer 501. The cladding layer 502 is made of silica containing fluorine. The protective layer 503 is coated on the outside of the cladding layer 502.

[0045] The wrapping layer 502 may include a first auxiliary buffer layer segment, a depressed layer segment, a second auxiliary buffer layer segment and an outer cladding layer segment. The first auxiliary buffer layer segment, the depressed layer segment, the second auxiliary buffer layer segment and the outer cladding layer segment are arranged in sequence from the center of the large-core optical fiber to the outside. The outer cladding layer segment is made of pure silica. The relative refractive index difference of the first auxiliary buffer layer segment is a, the relative refractive index difference of the depressed layer segment is b, the relative refractive index difference of the second auxiliary buffer layer segment is c, and the relative refractive index difference of the outer cladding segment is d, wherein d is greater than c, c is greater than b, b is less than a, and a is less than d. The relative refractive index difference design of the first auxiliary buffer layer segment and the second auxiliary buffer layer segment in the wrapping layer 502 can effectively prevent the volatilization of fluorine in the fluorine-doped wrapping layer 502 optical fiber from causing defects such as bubbles and cracks inside and outside the preform 2. The specific calculation formula for the relative refractive index difference of a certain layer segment in this application is as follows: relative refractive index difference of a certain layer segment = (square of the refractive index of the layer segment - square of the refractive index of pure silica) / 2 times the square of the refractive index of the layer segment.

[0046] Furthermore, the relative refractive index difference a of the first auxiliary buffer layer segment is between -0.2% and -0.1%. The relative refractive index difference c of the second auxiliary buffer layer segment is between -0.2% and -0.1%. The relative refractive index difference b of the depressed layer segment is between -1.4% and -0.4%. As feasible, the ratio of the diameter of the first auxiliary buffer layer segment to the diameter of the core layer 501 is between 1.01 and 1.06, the ratio of the diameter of the second auxiliary buffer layer segment to the diameter of the core layer 501 is between 1.1 and 1.25, the ratio of the diameter of the depressed layer segment to the diameter of the core layer 501 is between 1.03 and 1.12, and the diameter of the outer cladding segment is between 220um and 1500um.

[0047] Protective layer 503 is formed from at least one of the following materials: high-temperature resistant acrylate, silicone resin, or polyimide. The high-temperature resistant acrylate can be a photocurable coating comprising a fluorinated acrylate monomer, an acrylate resin oligomer, a photoinitiator, and a silane coupling agent. The fluorinated acrylate monomer can include at least one of the following: hexafluorobutyl acrylate, hexafluoroisopropyl acrylate, octafluoropentyl acrylate, trifluoroethyl methacrylate, or tetrafluoropropyl methacrylate.

[0048] The silicone resin may be a photocurable coating comprising a fluorinated silicone-modified acrylate monomer, an epoxy acrylate oligomer, pentaerythritol triacrylate, and a photoinitiator. The fluorinated silicone-modified acrylate monomer is synthesized from one of hydroxyethyl acrylate, hydroxyethyl methacrylate, hydroxypropyl acrylate, and polyethylene glycol monoacrylate and one of 3,5-bis(trifluoromethyl)phenyldimethylchlorosilane, 1H,1H,2H,2H-perfluorodecyldimethylchlorosilane, and pentafluorophenyldimethylchlorosilane.

[0049] Among them, the polyimide can be a thermosetting coating with a solid mass content of 10% to 30%, including polyamic acid, nanopowder and solvent. The polyamic acid is synthesized by one or two of fluorine-substituted bisphenol A diether dianhydride, 4,4'-(hexafluoroisopropylene) diphthalic anhydride (abbreviated as: hexafluorodianhydride), 3,3',4,4'-benzophenone tetracarboxylic dianhydride, 1,3-bis(3,4-dicarboxybenzoyl)phthalic anhydride, 3,3',4,4'-dimethyldiphenylsilane tetracarboxylic dianhydride and m-phenylenediamine, dihydroxybenzidine, 2,2'-bis(trifluoromethyl)-4,4'-diaminobiphenyl, 4,4'-silylated diamine diphenyl ether, bis(4-aminophenyl)tetraphenyldisiloxane, 2,4-diamino-1-[(4'-trifluoromethyl)phenoxyphenyl]aniline. The nanopowder can be one of silicon dioxide, titanium dioxide and zirconium dioxide. The solvent used can be one of N,N-dimethylformamide, N,N-diethylacetamide and N-methylpyrrolidone.

[0050] As feasible, Figure 2 As shown, the relative refractive index difference of core layer 501 is parabolic in the diameter direction, with the parabolic distribution power exponent ranging from 1.9 to 2.2. The relative refractive index difference is greatest at the center of core layer 501. The maximum relative refractive index difference of core layer 501 is e, where e is greater than d. The diameter of core layer 501 is between 200 μm and 1000 μm. The maximum relative refractive index difference e of core layer 501 is between 1% and 2.2%. Core layer 501 can be Ge-doped by MCVD.

[0051] The large core diameter optical fiber in the present application can be made by the following molding method, which at least includes the following steps:

[0052] Silicon tetrachloride and oxygen are introduced into a quartz substrate tube, where they react to produce a product that is deposited on the inner wall of the tube to form the outer cladding segment. Using the MCVD method, silicon tetrachloride (SiCl4) and high-purity oxygen are introduced into the inner wall of the quartz substrate tube. At high temperatures, the reaction produces a product that is deposited on the inner wall of the tube to form the outer cladding segment.

[0053] After the outer cladding layer is formed, silicon tetrachloride, oxygen, and a fluorine-containing gas are introduced into the quartz substrate tube. By controlling the flow rate of the fluorine-containing gas according to the relative refractive index differences between the various sections of the cladding layer 502, a fluorine-doped second auxiliary buffer layer section, a depressed layer section, and a first auxiliary buffer layer section are sequentially deposited. The relative refractive index differences between the various sections of the cladding layer 502 are described above as d greater than c, c greater than b, b less than a, and a less than d. The smaller the relative refractive index differences, the greater the flow rate of the fluorine-containing gas in the silicon tetrachloride, oxygen, and fluorine-containing gas introduced into the quartz substrate tube.

[0054] After forming the first auxiliary buffer layer segment, silicon tetrachloride, germanium tetrachloride, and oxygen are introduced into the quartz substrate tube to react and produce a product, which is deposited on the inner wall of the first auxiliary buffer layer segment to form the core layer 501, thereby forming the preform 2. Alternatively, the Ge doping level in the core layer 501 can be varied by changing the flow rate of the germanium tetrachloride, thereby enabling the formation of a large-core optical fiber in subsequent steps. This large-core optical fiber meets the following requirements: the relative refractive index difference of the core layer 501 is parabolic in the diameter direction, with the parabolic distribution power index ranging from 1.9 to 2.2, the relative refractive index difference is greatest at the center of the core layer 501, and the maximum relative refractive index difference of the core layer 501 is e, where e is greater than d. Furthermore, the maximum relative refractive index difference e of the core layer 501 is between 1% and 2.2%.

[0055] The deposited preform rod 2 is melted and shrunk at high temperature to form a solid optical fiber preform rod 2.

[0056] The optical fiber preform rod 2 is drawn into an optical fiber of a preset diameter, which can meet the relative refractive index difference requirements of each layer of the large core diameter optical fiber and each layer segment in the cladding layer 502.

[0057] As feasible, the steps may specifically include: Figure 3 As shown, an optical fiber preform 2 is fed into a heating furnace 3 using a feeding mechanism 1. The preform is melted in the heating furnace 3 at a first preset temperature, between 1950°C and 2100°C, to form an optical fiber of a preset diameter. Compared to the 1900°C to 2200°C temperature commonly used in the prior art, the drawing speed is slower. To reduce losses in the preform 2, the preform 2 is cooled and raised during the drawing process. This can easily lead to crystallization in the preform 2. An effective approach to this problem is to strictly control the temperature of the heating furnace 3 to a stable level between 1950°C and 2100°C, while also stabilizing the gas flow rate within the furnace. The low-temperature, slow, steady-speed drawing method employed in this application can reduce the formation of internal defects during fiber formation, resulting in high-performance, large-core-diameter optical fibers. Specifically, the drawing speed can be controlled between 5m / min and 500m / min.

[0058] Gas is uniformly introduced into the heating furnace 3. The gas routes include an upper route, a middle route, and a lower route. The gas output from each gas route is between the inner wall of the heating furnace 3 and the optical fiber preform 2. The temperature of the output gas is basically consistent with that in the heating furnace 3. If the gas flow in the furnace is unstable or too small or too large, it will cause air flow turbulence, thereby causing temperature fluctuations and causing crystallization of the preform 2. After a large number of experiments, it was found that when the diameter of the optical fiber preform 2 is between 20mm and 50mm, the flow rate of the gas output from the upper route and the middle route is between 15L / min and 25L / min, the type of gas output from the upper route and the middle route is a mixed gas of helium and argon, and the type of gas output from the lower route is argon.

[0059] The optical fiber coming out of the heating furnace 3 undergoes thermal annealing at a temperature gradually decreasing from a second preset temperature, which can be selected between 1200° C. and 950° C., so as to fully release the internal stress of the optical fiber.

[0060] The thermally annealed optical fiber enters the cooling tube and is cooled to a temperature at which the protective layer 503 can be applied. The thermally annealed optical fiber can first be measured for diameter by the wire diameter measuring instrument 4 and then enter the cooling tube and be cooled to a temperature at which the protective layer 503 can be applied.

[0061] After the cooled optical fiber passes through a pressure coating die and is coated with the coating, the coating is cured into a protective layer 503 by a curing system, and finally is pulled into continuous filaments by a traction wheel 7 and collected by an optical fiber collection device 8; the curing system includes a thermal curing unit 603, and the thermal curing unit 603 uses an infrared radiation furnace.

[0062] In the above steps, the optical fiber after cooling is a bare optical fiber 5, such as Figure 4 As shown, the bare optical fiber 5 then passes through the optical fiber coating and curing system 6 for processing. That is, after being coated with the coating by the pressure coater 601, the coating is cured into a protective coating by the curing system, which is then drawn into a continuous filament by the traction wheel 7 and then collected by the optical fiber collection device 8. The stability of the optical fiber drawing can be achieved through the combined action of the filament diameter control system 9 and the traction wheel 7. The curing system can include a light curing unit 602 and a heat curing unit 603, both of which are mounted on a sliding track 604. The sliding track 604 can be switched to control the coated optical fiber to pass through the light curing unit 602 or the heat curing unit 603. The light curing unit 602 refers to the use of light to achieve curing. The heat curing unit 603 refers to the use of temperature to achieve curing. An infrared radiation furnace can be used. The infrared radiation furnace adopts a segmented heating method. Due to the strong penetrability of infrared rays, uniform thermal curing of the coating can be achieved. At the same time, the segmented temperature control can ensure uniform volatilization of the solvent, resulting in a high-quality coating.

[0063] Alternatively, the coating applied to the bare optical fiber 5 can be a single layer, using one of heat-resistant acrylate, silicone resin, and polyimide. Such coatings offer the advantages of high temperature resistance and low cost. The coating applied to the bare optical fiber 5 can be two layers, comprising an inner coating and an outer coating. The inner coating can be one of heat-resistant acrylate, silicone resin, and polyimide. The outer coating can be one of heat-resistant acrylate, silicone resin, and polyimide. The inner and outer coatings can be different.

[0064] The large core diameter optical fiber and its forming method in this application can have the following advantages:

[0065] 1. The special design of the relative refractive index difference between the first auxiliary buffer layer segment and the second auxiliary buffer layer segment in the cladding layer 502 can effectively prevent defects such as bubbles and cracks inside and outside the preform rod 2 caused by the volatilization of fluorine during the manufacturing process of the optical fiber having the fluorine-doped cladding layer 502. This solves the problem that the larger the diameter of the quartz optical fiber, the more brittle the material and the more likely it is to form internal defects. When the diameter of the quartz optical fiber is large, the material strength is improved, making it less likely to form internal defects.

[0066] 2. In the process of forming large-core optical fibers, a low-temperature, slow and steady-speed drawing method is adopted to control the temperature of the heating furnace 3 and the stability of the gas flow in the furnace, thereby effectively reducing the crystallization phenomenon of the preform rod 2. In addition, the slow and steady-speed drawing can also effectively adjust the fluctuation of the diameter of the optical fiber sheath 502.

[0067] 3. The infrared radiation furnace is heated in sections. Infrared rays have strong penetrability, which can achieve uniform thermal curing of the coating. At the same time, the section temperature control can make the solvent evaporate evenly to obtain high-quality coating.

[0068] 4. By optimizing the relative refractive index difference of the optical fiber profile, the diameter of the optical fiber core layer 501 can be increased, and the numerical aperture of the optical fiber can be improved. At the same time, the groove design with d greater than c, c greater than b, b less than a, and a less than d can improve the bending performance of the optical fiber and enhance the focusing ability. Combined with the improvement of internal defects of the optical fiber, the optical fiber light transmission efficiency can be increased to 98%.

[0069] All articles and references disclosed, including patent applications and publications, are incorporated herein by reference for all purposes. The term "essentially consisting of..." describing a combination should include the identified elements, ingredients, parts or steps and other elements, ingredients, parts or steps that do not substantially affect the basic novel features of the combination. The use of the terms "comprising" or "including" to describe the combination of elements, ingredients, parts or steps herein also contemplates an embodiment that is essentially composed of these elements, ingredients, parts or steps. By using the term "may", it is intended to illustrate that any attribute described that "may" include is optional. Multiple elements, ingredients, parts or steps can be provided by a single integrated element, ingredient, part or step. Alternatively, a single integrated element, ingredient, part or step can be divided into separate multiple elements, ingredients, parts or steps. The disclosure "one" or "an" used to describe an element, ingredient, part or step is not intended to exclude other elements, ingredients, parts or steps.

[0070] Each embodiment in this specification is described in a progressive manner, and each embodiment focuses on the differences from other embodiments. The same or similar parts between the embodiments can be referred to each other. The above embodiments are only for illustrating the technical concept and features of the present invention. Their purpose is to enable people familiar with this technology to understand the content of the present invention and implement it accordingly, and they cannot be used to limit the scope of protection of the present invention. Any equivalent changes or modifications made according to the spirit of the present invention should be included in the scope of protection of the present invention.

Claims

1. A method for forming a large core diameter optical fiber, characterized in that: The large-core optical fiber comprises: A core layer; a wrapping layer made of fluorine-containing silicon dioxide coated on the outside of the core layer; a protective layer coated on the outside of the wrapping layer; The wrapping layer includes a first auxiliary buffer layer segment, a depressed layer segment, a second auxiliary buffer layer segment, and an outer cladding layer segment, wherein the first auxiliary buffer layer segment, the depressed layer segment, the second auxiliary buffer layer segment, and the outer cladding layer segment are arranged in sequence from the center of the large-core optical fiber to the outside; the outer cladding layer segment is made of pure silica; The relative refractive index difference of the first auxiliary buffer layer segment is a, the relative refractive index difference of the depressed layer segment is b, the relative refractive index difference of the second auxiliary buffer layer segment is c, and the relative refractive index difference of the outer cladding segment is d, wherein d is greater than c, c is greater than b, b is less than a, and a is less than d; The molding method comprises the following steps: Silicon tetrachloride and oxygen are introduced into a quartz substrate tube to react with each other to generate a product, which is deposited on the inner wall of the substrate tube to form an outer cladding section; Then, silicon tetrachloride, oxygen and fluorine-containing gas are introduced into the quartz substrate tube, and the flow rate of the fluorine-containing gas is controlled according to the different relative refractive index differences of the various sections of the wrapping layer to sequentially deposit a fluorine-doped second auxiliary buffer layer section, a depression layer section and a first auxiliary buffer layer section; After forming the first auxiliary buffer layer segment, introducing silicon tetrachloride, germanium tetrachloride, and oxygen into the quartz substrate tube to react with each other to generate a product, which is deposited on the inner wall of the first auxiliary buffer layer segment to form a core layer, thereby forming a preform; melting the deposited preform rod at high temperature to form a solid optical fiber preform rod; The optical fiber preform is drawn into an optical fiber with a preset diameter.

2. The method for forming a large core optical fiber according to claim 1, wherein: The relative refractive index difference of the core layer is parabolic in the diameter direction, and the parabolic distribution power exponent ranges from 1.9 to 2.

2. The relative refractive index difference at the center of the core layer is the largest. The maximum relative refractive index difference of the core layer is e, e is greater than d, and the diameter of the core layer is between 200um and 1000um; the maximum relative refractive index difference e of the core layer is between 1% and 2.2%.

3. The method for forming a large core optical fiber according to claim 1, wherein: The relative refractive index difference a of the first auxiliary buffer layer segment is between -0.2% and -0.1%; the relative refractive index difference c of the second auxiliary buffer layer segment is between -0.2% and -0.1%; and the relative refractive index difference b of the sunken layer segment is between -1.4% and -0.4%.

4. The method for forming a large core optical fiber according to claim 3, wherein: The ratio of the diameter of the first auxiliary buffer layer segment to the diameter of the core layer is between 1.01 and 1.06, the ratio of the diameter of the second auxiliary buffer layer segment to the diameter of the core layer is between 1.1 and 1.25, the ratio of the diameter of the sunken layer segment to the diameter of the core layer is between 1.03 and 1.12, and the diameter of the outer cladding segment is between 220um and 1500um.

5. The method for forming a large core optical fiber according to claim 1, wherein: The core layer is prepared by Ge doping through MCVD.

6. The method for forming a large-core optical fiber according to claim 1, wherein: The protective layer is formed of at least one of the following materials: high temperature resistant acrylate, silicone resin, and polyimide.

7. The method for forming a large-core optical fiber according to claim 1, wherein: The change of Ge doping in the core layer is achieved by changing the flow rate of germanium tetrachloride.

8. The method for forming a large core optical fiber according to claim 1, wherein: The step of drawing the optical fiber preform into an optical fiber of a preset diameter specifically includes: Melting the optical fiber preform in a heating furnace at a first preset temperature to form an optical fiber with a preset diameter, wherein the first preset temperature is between 1950 degrees and 2100 degrees; The heating furnace is uniformly supplied with gas, wherein the gas routes include an upper route, a middle route, and a lower route. The gas output from each gas route is between the inner wall of the heating furnace and the optical fiber preform. When the diameter of the optical fiber preform is between 20 mm and 50 mm, the flow rate of the gas output from the upper route and the middle route is between 15 L / min and 25 L / min. The gas output from the upper route and the middle route is a mixed gas of helium and argon, and the gas output from the lower route is argon. The optical fiber emerging from the heating furnace is subjected to thermal annealing gradually decreasing from a second preset temperature, the second preset temperature being between 1200° C. and 950° C.; The optical fiber that has undergone thermal annealing enters a cooling tube and is cooled to a temperature at which a protective layer can be applied.

9. The method for forming a large core optical fiber according to claim 8, wherein: The molding method further comprises the following steps: After the cooled optical fiber passes through a pressure coating die and is coated with the coating, the coating is cured into a protective layer by a curing system. Finally, it is pulled by a traction wheel into a continuous filament and collected by an optical fiber collection device. The curing system includes a light curing unit and a heat curing unit, which can be switched between the two. The heat curing unit uses an infrared radiation furnace. The coating comprises at least one of high temperature resistant acrylate, silicone resin and polyimide.

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