Rare earth-doped optical fiber preform, preparation method of rare earth-doped optical fiber preform and optical fiber
By adding a quartz core layer to the rare-earth-doped optical fiber preform and using PCVD vapor phase doping technology to block the loss of F and P elements, the problem of easy volatility of rare-earth-doped optical fibers was solved, the numerical aperture of the fiber core was reduced and the doping elements were evenly distributed, thus improving the high-power laser output and beam quality of the optical fiber.
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- CHINA ELECTRONICS TECH GRP NO 46 RES INST
- Filing Date
- 2025-12-23
- Publication Date
- 2026-04-24
AI Technical Summary
The doping elements in existing rare-earth-doped optical fibers are volatile, resulting in a high numerical aperture in the fiber core, which cannot meet the requirements of high-power laser output and high beam quality.
A quartz core layer is added on the rare earth-doped core layer. Silica is deposited on the pre-volatile rare earth-doped core layer through PCVD vapor phase doping process to form a thin quartz core layer, which prevents the loss of F and P elements and diffuses into the quartz core layer at high temperature, thereby reducing the numerical porosity of the fiber core.
This effectively reduces the numerical aperture of the fiber core, ensures the uniform distribution of doped elements, and improves the high-power laser output and beam quality of the optical fiber.
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Figure CN121913698A_ABST
Abstract
Description
Technical Field
[0001] This invention relates to the field of optical fiber technology, and in particular to a rare-earth-doped optical fiber preform, a method for preparing the rare-earth-doped optical fiber preform, and an optical fiber. Background Technology
[0002] With the rapid development of special optical fibers, the requirements for rare-earth-doped active optical fibers in fiber lasers are becoming increasingly stringent.
[0003] In related technologies, conventionally designed rare-earth-doped fibers typically have a high numerical aperture in the core, resulting in a large number of excited laser modes. Under high-power laser output conditions, mode instability is highly likely to occur, directly affecting laser output power and optical-to-optical conversion efficiency. Conventionally designed rare-earth-doped fibers can no longer meet the requirements of fiber lasers for high-power laser output and high beam quality.
[0004] The inventors discovered that doping the core with fluorine (F) and phosphorus (P) elements can form AlPO4, which can effectively reduce the numerical porosity of the fiber core. However, during the fabrication process, F and P elements are highly volatile when heated, easily forming doping defects, thus preventing a reduction in the numerical porosity of the fiber core. Summary of the Invention
[0005] This invention provides a rare-earth-doped optical fiber preform, a method for preparing the rare-earth-doped optical fiber preform, and an optical fiber, in order to solve the problem that the doping elements in current rare-earth-doped optical fibers are prone to volatilization, resulting in a high numerical aperture in the fiber core.
[0006] In a first aspect, embodiments of the present invention provide a rare-earth-doped optical fiber preform, the optical fiber preform comprising, from the outside to the inside: a quartz layer, a rare-earth-doped core layer and a quartz core layer. The main component of the quartz core layer is silicon dioxide; The quartz layer is formed by thermally melting and shrinking a quartz tube; The rare earth-doped core layer is formed by depositing pre-prepared rare earth dopants and co-dopersants on the inner wall of the quartz tube; wherein the co-dopersants include aluminum, fluorine and phosphorus.
[0007] In one possible implementation, a pre-volatile rare earth-doped core layer is further provided between the rare earth-doped core layer and the quartz core layer, and the concentration of doped rare earth in the pre-volatile rare earth-doped core layer is greater than the concentration of doped rare earth in the rare earth-doped core layer.
[0008] In one possible implementation, the quartz core layer is formed by introducing silicon tetrachloride gas into the quartz tube using a PCVD vapor phase doping process, and depositing silicon dioxide on the pre-volatile rare earth-doped core layer using a microwave heating deposition method. The pre-volatile rare earth-doped core layer is formed by depositing a pre-configured second concentration of doped rare earth and co-doperants onto the rare earth-doped core layer based on the MCVD vapor phase doping process. The rare earth-doped core layer is formed by depositing a pre-prepared first concentration of doped rare earth and co-doperants onto the inner wall of a quartz tube using the MCVD vapor phase doping process.
[0009] The rare-earth-doped optical fiber preform provided by this invention adds a quartz core layer on the pre-volatile rare-earth-doped core layer. When heated, the F and P elements in the rare-earth-doped core layer diffuse into the quartz core layer, thereby preventing the loss of F and P elements and further reducing the numerical aperture of the fiber core.
[0010] Secondly, embodiments of the present invention provide a method for preparing rare-earth-doped optical fiber preforms, comprising: Pre-configured rare earth doping and co-doping agents of the first concentration are deposited on the inner wall of the quartz tube to form a rare earth doped core layer; A quartz core layer is deposited on the rare earth-doped core layer; wherein the main component of the quartz core layer is silicon dioxide; The quartz tube with the deposited quartz core layer is thermally shrunk in one step to form an optical fiber preform.
[0011] In one possible implementation, prior to depositing the quartz core layer on the rare-earth-doped core layer, the method further includes: On the surface of the rare earth-doped core layer, a pre-configured second concentration of doped rare earth and co-doped agent is deposited to form a pre-volatile rare earth-doped core layer; wherein the second concentration is greater than the first concentration.
[0012] In one possible implementation, the second concentration is 105%-110% of the first concentration.
[0013] In one possible implementation, the deposition of a pre-configured first concentration of doped rare earth elements and co-dopersant on the inner wall of a quartz tube to form a rare earth-doped core layer includes: Based on the MCVD vapor phase doping process, a pre-configured first concentration of doped rare earth and co-doped agent is deposited on the inner wall of a quartz tube to form a rare earth doped core layer. The deposition of a pre-configured second concentration of doped rare earth elements and co-dopersant on the surface of the rare earth-doped core layer includes: Based on the MCVD vapor phase doping process, a pre-configured second concentration of doped rare earth and co-doped agent is deposited on the surface of the rare earth-doped core layer.
[0014] In one possible implementation, depositing a quartz core layer on the pre-volatile rare-earth-doped core layer includes: Based on the PCVD vapor phase doping process, silicon tetrachloride gas is introduced into the quartz tube, and silicon dioxide is deposited on the pre-volatile rare earth-doped core layer by microwave heating deposition.
[0015] In one possible implementation, the doped rare earth element is one or more of the following elements: ytterbium, erbium, thulium, neodymium, terbium, dysprosium, holmium, samarium, cerium, praseodymium, and promethium; the co-doperants include aluminum, fluorine, and phosphorus.
[0016] In the process of preparing rare-earth-doped optical fiber preforms, the volatile elements in the rare-earth-doped core layer diffuse into the newly deposited quartz core layer upon heating, thus the newly deposited quartz core layer can block the volatilization of the elements. Simultaneously, since the permeability of the quartz tube remains unchanged throughout the preparation process, the uniformity of the doping elements in the optical fiber preform is not affected by pressure changes within the quartz tube, thereby ensuring that the doping elements are uniformly distributed throughout the entire optical fiber preform.
[0017] Thirdly, embodiments of the present invention provide an optical fiber, which is obtained by stretching an optical fiber preform prepared by the rare earth-doped optical fiber preform preparation method described in the second aspect.
[0018] The rare-earth-doped optical fiber preform provided by this invention adds a quartz core layer on top of the rare-earth-doped core layer. When heated, the F and P elements in the rare-earth-doped core layer diffuse into the quartz core layer, which can block the loss of F and P elements, thereby reducing the numerical aperture of the fiber core. Attached Figure Description
[0019] Figure 1 This is a schematic diagram of the structure of the rare earth-doped optical fiber preform before melting and shrinking, provided in an embodiment of the present invention. Figure 2 This is a schematic diagram of the structure of the rare earth-doped optical fiber preform after fusion shrinkage provided in an embodiment of the present invention; Figure 3 This is a flowchart of the method for preparing rare earth-doped optical fiber preforms provided in the embodiments of the present invention. Detailed Implementation
[0020] The present application will be described more clearly below with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the function of the present application, but do not limit the present application in any way. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present application. These all fall within the protection scope of the present application.
[0021] It should be understood that, when used in this application specification and the appended claims, the term "comprising" indicates the presence of the described features, integrals, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or a collection thereof.
[0022] It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.
[0023] In the description of this application and the appended claims, the terms "first," "second," "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.
[0024] References to "one embodiment" or "some embodiments" in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.
[0025] Furthermore, the term "multiple" mentioned in the embodiments of this application should be interpreted as two or more.
[0026] First, the terms used in the embodiments of this application will be explained: MCVD (Metal-Oxygen Vapor Deposition) is a vapor-phase doping process that uses an oxyhydrogen flame as a heat source to perform vapor deposition and high-temperature oxidation reactions within a high-purity quartz glass tube. The chemical reaction mechanism of MCVD involves high-temperature oxidation, and it features high deposition efficiency, simple equipment, low cost, easy control of the refractive index, and the ability to fabricate optical fibers with complex refractive index profiles.
[0027] PCVD (Polycarbonyl Vapor Deposition) is a process that uses microwaves as a heat source to perform vapor deposition and high-temperature oxidation reactions within a high-purity quartz glass tube. The reaction mechanism involves microwave-activated gas generating plasma, which ionizes the reactant gases, resulting in charged ions. The heat released when these charged ions recombine melts the gaseous reactants, forming a transparent thin layer of quartz glass. PCVD deposition utilizes low-pressure plasma to directly deposit gaseous halides and oxygen into the high-purity quartz glass deposition tube at approximately 1000°C, creating the desired rare-earth-doped core layer. The deposited quartz glass tube is then transferred to a glass lathe for forming, where it is melted and condensed into a solid optical fiber preform core using an oxyhydrogen flame. PCVD deposition offers higher raw material deposition efficiency, more precise control over refractive index distribution, and the ability to fabricate optical fibers with complex refractive index profiles.
[0028] Rare-earth-doped fiber: This is an important type of active optical fiber. Rare-earth-doped fiber refers to conventional optical fiber incorporating trace amounts of rare-earth elements (such as ytterbium and erbium) into its core, transforming it from a passive transmission fiber into an active fiber with amplification capabilities. Rare-earth-doped fiber can be used to manufacture fiber amplifiers and fiber lasers.
[0029] Optical fiber preform: This is the core raw material for manufacturing quartz optical fibers; it's a material preform used to draw optical fibers. It is mainly composed of high-purity silicon dioxide, typically requiring a purity of 99.999% or higher. To adjust the refractive index, dispersion, and other characteristics of the fiber, small amounts of doping elements, such as germanium and fluorine, are added. Its structure usually includes an inner high-refractive-index core layer and an outer low-refractive-index cladding layer.
[0030] Co-dopers: refers to the simultaneous addition of two or more different dopants to a matrix material to synergistically optimize the material's properties.
[0031] Core layer: This is the middle part of the optical fiber with a higher refractive index. It is circular and serves as the light guide layer for signal light in the optical fiber.
[0032] Thermal shrinkage: This refers to the property of heat-shrinkable materials to automatically shrink and tightly wrap around a target object after being heated. It is also a process of gradually firing a deposited porous glass tube into a solid glass rod under a specific heat source.
[0033] Numerical aperture: It is an indicator that measures the ability of an optical fiber to receive or transmit optical signals, reflecting the range of incident light angles that the optical fiber can capture.
[0034] The fabrication process of optical fiber preforms mainly consists of two stages. The first stage is the core deposition stage, where oxygen and helium are used as carrier gases to bring the reactants into the reaction tube from one end. The reaction tube is heated to over 1900°C using an oxyhydrogen flame, causing the reactant gases to undergo a high-temperature oxidation reaction, transforming them into a glassy substance that deposits on the inner wall of the reaction tube, forming a rare-earth-doped core layer. The second stage is the melting and shrinking stage, where the reaction tube is gradually shrunk by controlling the high temperature of the oxyhydrogen flame and the pressure inside the tube, reducing the distance between the intermediate pores until the preform is completely formed. However, because the rare-earth-doped core layer is located on the inner wall of the reaction tube, and it contains fluorine (F) and phosphorus (P) elements used to reduce the numerical aperture of the fiber core, these two elements are highly volatile when heated. Under the combined effects of high temperature and pressure control inside the tube, a large amount of these elements will volatilize and be lost, forming doping defects and affecting the reduction of the numerical aperture.
[0035] Currently, to prevent the volatilization of elements in the core of rare-earth-doped optical fiber preforms, MCVD (Medium-Coefficient of Variation) technology is used to prepare rare-earth-doped optical fiber preforms. After the core layer deposition is completed in the MCVD preform, a 2cm section of the reaction tube is melted and shrunk at a high temperature 1cm from the exhaust gas connection point until it is completely sealed, thus completely closing the channel between the reaction tube and the exhaust gas end. This ensures that during multiple high-temperature shrinkage cycles, the elements in the preform core, after volatilization at high temperatures, will not be expelled with the carried gas but will remain in the reaction tube to continue reacting and depositing. This effectively prevents the problem of uneven doping in the fiber core and low central doping levels caused by element volatilization, thereby ensuring the longitudinal and transverse uniformity of the doped elements in the fiber core.
[0036] It can be seen that the current method for suppressing the volatilization of rare-earth-doped fiber preform core elements involves, after the fiber preform core layer deposition is completed using MCVD, a 2cm section of the reaction tube is fused and sealed at a high temperature at a point 1cm from the exhaust gas connection interface, completely sealing the channel between the reaction tube and the exhaust gas end. This ensures that during multiple high-temperature shrinkage cycles, the elements in the preform core, after volatilizing at high temperatures, will not be expelled with the carried gas but will remain within the reaction tube to continue reacting and depositing.
[0037] The inventors discovered that when preparing optical fiber preforms using the above-mentioned process, because the channel between the reaction tube and the exhaust gas end is completely sealed, during the preform melting and shrinking stage, a significant pressure difference exists between the left end and the sealed right end of the reaction tube due to the pressure control within the tube. This causes the volatilized elements within the tube, although not carried away, to concentrate towards the unsealed end of the reaction tube due to the pressure difference. While this process suppresses element volatilization, it also leads to a decrease in the longitudinal uniformity of the doped elements in the preform.
[0038] To address the issue of rare earth elements, phosphorus, fluorine, and other elements volatilizing due to heat during the melting and shrinkage process in the reaction tube during the deposition of the core layer of rare earth-doped optical fiber preforms, this invention provides a rare earth-doped optical fiber preform, a method for preparing the rare earth-doped optical fiber preform, and an optical fiber.
[0039] Figure 1 and Figure 2 This is a schematic diagram of a rare-earth-doped optical fiber preform provided in an embodiment of the present invention.
[0040] Refer to together Figures 1-2 The rare earth-doped optical fiber preform consists of, from the outside in, a quartz layer 110, a rare earth-doped core layer 120, and a quartz core layer 140.
[0041] The quartz core layer 140 is mainly composed of silicon dioxide. The quartz layer 110 is formed by thermally shrinking the quartz tube 150. The rare earth-doped core layer 120 is formed by depositing pre-prepared rare earth dopants and co-dopersants on the inner wall of the quartz tube 150. The co-dopersants include Al, F, and P elements, which are easily volatile when heated.
[0042] In some embodiments, the quartz core layer 140 is formed by introducing silicon tetrachloride gas into the quartz tube 150 based on the PCVD vapor phase doping process, and depositing silicon dioxide on the pre-volatile rare earth doped core layer 130 by microwave heating deposition.
[0043] In this embodiment, the quartz core layer 140 is made of high-purity silicon dioxide.
[0044] In some embodiments, a second concentration of pre-volatile rare earth-doped core layer 130 is further disposed between the rare earth-doped core layer 120 and the quartz core layer 140.
[0045] The pre-volatile rare earth-doped core layer 130 is formed by depositing a pre-prepared second concentration of doped rare earth and co-doperants onto the rare earth-doped core layer 120 using the MCVD vapor phase doping process.
[0046] The rare earth-doped core layer 120 is formed by depositing a pre-prepared first concentration of doped rare earth and co-doperants on the inner wall of the quartz tube 150 using the MCVD vapor phase doping process.
[0047] In some embodiments, a rare-earth-doped core layer 120 can be formed on the inner wall of a quartz tube 150 using an MCVD deposition process, according to the designed core region refractive index, doping concentration, and core region size. By employing the MCVD doping process, the dopant ions directly mix and undergo oxidation and deposition reactions, resulting in good deposition uniformity and effectively avoiding problems such as bright spots and clusters caused by uneven doping.
[0048] In some embodiments, the first concentration of doped rare earth and co-doped agent can be a preformed target rod prepared based on the first concentration of doped rare earth and co-doped agent, which is installed at the air inlet end of a quartz tube, and then the quartz tube is installed on an MCVD deposition device.
[0049] In this embodiment, the preformed target rod prepared with the first concentration of doped rare earth and co-doped agent has a size smaller than the inner diameter of the quartz tube 150.
[0050] For example, the inner diameter of the quartz tube 150 can be 15mm-51mm.
[0051] In this embodiment, the second concentration is greater than the first concentration.
[0052] For example, the second concentration is 105%-110% of the first concentration.
[0053] By depositing a pre-volatile rare earth-doped core layer 130 with a higher concentration of rare earth doping on the rare earth-doped core layer 120, the concentration of doped F and P elements can be increased, thereby effectively reducing the numerical pore size of the fiber core by forming AlPO4.
[0054] Furthermore, PCVD deposition was used instead of MCVD deposition when preparing the quartz core layer 140. This is because PCVD deposition allows the quartz core layer 140 to be thinner than that obtained by MCVD deposition. This allows the volatile F and P elements to be more evenly distributed in the quartz core layer 140 during diffusion, without large concentration differences due to the thickness of the quartz core layer 140.
[0055] For example, the thickness of the quartz core layer 140 can range from 10um to 500um.
[0056] Because the quartz core layer deposited using PCVD is thinner than the quartz core layer 140 deposited using MCVD, the elements can be distributed more evenly in the quartz core layer 140 during diffusion, and there will be no large concentration differences due to the thickness of the quartz core layer 140.
[0057] In some embodiments, the rare earth dopant is one or more elements selected from ytterbium, erbium, thulium, neodymium, terbium, dysprosium, holmium, samarium, cerium, praseodymium, and promethium. Co-dopers include aluminum, fluorine, and phosphorus.
[0058] In some embodiments, the quartz layer 110 is formed by heating a quartz tube 150 in a graphite furnace to form a quartz layer in one step.
[0059] By using a graphite furnace to heat the reaction tube and shrink it into a rod, further volatilization of the dopant elements is avoided, while ensuring that the dopant elements in the innermost doped core layer can diffuse precisely into the quartz core layer.
[0060] The rare-earth-doped optical fiber preform provided by this invention increases the concentration of doped F and P elements by adding a pre-volatile rare-earth-doped core layer on top of the rare-earth-doped core layer, thereby effectively reducing the numerical aperture of the fiber core. Furthermore, by adding a quartz core layer on top of the pre-volatile rare-earth-doped core layer, the F and P elements in both the pre-volatile and rare-earth-doped core layers diffuse uniformly into the quartz core layer upon heating, thus preventing the loss of F and P elements and further reducing the numerical aperture of the fiber core. Moreover, because the F and P elements in both the pre-volatile and rare-earth-doped core layers diffuse uniformly into the quartz core layer upon heating, the doping elements in the prepared optical fiber preform are also uniformly distributed throughout the entire optical fiber preform.
[0061] Figure 3 This is a flowchart illustrating the implementation of a rare-earth-doped optical fiber preform preparation method provided in an embodiment of the present invention.
[0062] Refer to together Figures 1-3 The method for preparing the rare-earth-doped optical fiber preform includes: S110. Deposit the pre-configured first concentration of doped rare earth and co-doped agent on the inner wall of the quartz tube to form a rare earth doped core layer.
[0063] The quartz tube is made of silicon dioxide.
[0064] In some embodiments, the doping rare earth element is one or more of the elements selected from ytterbium, erbium, thulium, neodymium, terbium, dysprosium, holmium, samarium, cerium, praseodymium, and promethium; the co-doping agent includes aluminum, fluorine, and phosphorus.
[0065] In this embodiment, a rare earth-doped core layer 120 can be formed on the inner wall of a quartz tube 150 by using an MCVD deposition process according to the designed core region refractive index, doping concentration, and core region size.
[0066] In the preparation method provided in this embodiment, the MCVD doping process is used, in which the dopant ions are directly mixed and undergo oxidation and deposition reactions, resulting in good deposition uniformity and effectively avoiding problems such as bright spots and clusters caused by uneven doping.
[0067] In some embodiments, the first concentration of doped rare earth and co-doped agent can be a preformed target rod prepared based on the first concentration of doped rare earth and co-doped agent, which is installed at the air inlet end of a quartz tube, and then the quartz tube is installed on an MCVD deposition device.
[0068] In this embodiment, the preformed target rod prepared with the first concentration of doped rare earth and co-doped agent has a size smaller than the inner diameter of the quartz tube 150.
[0069] For example, the inner diameter of the quartz tube 150 can be 15mm-51mm.
[0070] In some embodiments, a pre-configured second concentration of doped rare earth and co-doped agent is deposited on the surface of the rare earth-doped core layer to form a pre-volatile rare earth-doped core layer.
[0071] After the rare earth-doped core layer 120 is prepared, a pre-volatile rare earth-doped core layer 130 needs to be prepared on the rare earth-doped core layer 120.
[0072] In order to increase the concentration of doped F and P elements, thereby effectively reducing the numerical pore size of the fiber core by forming AlPO4, a pre-volatile rare earth doped core layer 130 needs to be deposited on the surface of the rare earth doped core layer.
[0073] In some embodiments, the second concentration is greater than the first concentration.
[0074] For example, the second concentration is 105%-110% of the first concentration.
[0075] In this embodiment, based on the MCVD vapor phase doping process, a pre-configured second concentration of doped rare earth and co-doped agent can be deposited on the surface of the rare earth-doped core layer 120 to form a pre-volatile rare earth-doped core layer 130.
[0076] S120, Deposit a quartz core layer on a rare earth-doped core layer.
[0077] Considering that the quartz core layer 140 deposited using PCVD is thinner than that deposited using MCVD, the F and P elements can be more uniformly distributed in the quartz core layer 140 during diffusion, without significant concentration differences due to the excessive thickness of the quartz core layer 140. Therefore, PCVD is used to deposit the quartz core layer 140 in this invention. The main component of the quartz core layer is silicon dioxide.
[0078] During the preparation process, the quartz tube 150 is removed from the three-jaw chuck of the MCVD deposition lathe and mounted on the three-jaw chuck of the PCVD lathe for alignment and fixation.
[0079] After fixing the quartz tube 150 to the PCVD equipment, the microwave heat source can be turned on to introduce SiCl4 gas into the reaction tube. The quartz core layer 140 is deposited on the inner wall of the reaction tube by microwave heating deposition.
[0080] In some embodiments, the thickness of the quartz core layer 140 deposited by PCVD ranges from 10µm to 500µm.
[0081] S130. The quartz tube with the deposited quartz core layer is thermally shrunk in one step to form an optical fiber preform.
[0082] After the quartz core layer 140 is prepared, the deposited quartz tube 150 can be loaded onto a PCVD-specific melting and shrinking lathe, and the reaction tube can be thermally shrunk into an optical fiber preform in one go by heating with a graphite furnace.
[0083] The reaction tube is melted and condensed into a rod by heating with a graphite furnace, which avoids further volatilization of the doped elements and ensures that the doped elements in the innermost rare earth doped core layer 120 can diffuse into the quartz core layer 140.
[0084] Furthermore, during the preparation process of this invention, volatile elements in the pre-volatile rare-earth-doped core layer 130 and rare-earth-doped core layer 120 diffuse into the newly deposited quartz core layer 140 upon heating, thus the newly deposited quartz core layer 140 can block the volatilization of elements. Simultaneously, since the quartz core layer deposited using PCVD is thinner than that deposited using MCVD, the elements can be more uniformly distributed in the quartz core layer 140 during diffusion, avoiding significant concentration differences due to the excessive thickness of the quartz core layer 140. Furthermore, since the permeability of the quartz tube remains unchanged throughout the preparation process, the uniformity of the doped elements in the optical fiber preform is not affected by pressure changes within the quartz tube, thus ensuring uniform distribution throughout the entire optical fiber preform.
[0085] Thirdly, the present invention also provides an optical fiber, which is obtained by stretching an optical fiber preform prepared by any rare earth-doped optical fiber preform preparation method according to any one of the second aspects.
[0086] After obtaining the optical fiber preform, the optical fiber can be obtained through a stretching process, also known as fiber drawing. The specific process is as follows: First, the prepared optical fiber preform is fixed on the chuck of the feed mechanism at the top of the drawing tower. To prevent microcracks from forming due to oxidation during heating of the preform, and to prevent impurities such as hydroxyl groups from penetrating and affecting transmission performance, a protective atmosphere is created by filling the heating furnace with inert gases such as high-purity argon or nitrogen. Then, the feed mechanism slowly feeds the preform into the heating furnace.
[0087] Next, the furnace temperature is precisely raised to approximately 2000℃. This temperature allows the quartz preform to soften sufficiently, transforming it into a molten state with good ductility. During the heating process, the temperature gradient is controlled through multiple temperature zones to prevent localized overheating that could cause lattice distortion or bubbles in the preform, ensuring the stability of the material foundation for subsequent stretching.
[0088] Then, the softened preform tip droops due to its own gravity, and the traction device below provides stable tension via a servo motor, continuously drawing the drooping molten glass thinner. During stretching, the traction speed is precisely controlled, and a laser diameter gauge monitors the bare fiber diameter in real time. This monitoring system is linked to the traction device; if the diameter deviates from the set standard value, the traction speed is immediately adjusted to ensure that the bare fiber diameter tolerance is controlled within a very small range.
[0089] Secondly, the surface of freshly drawn bare optical fibers contains microcracks, making them susceptible to corrosion from moisture and other substances when exposed to air, potentially leading to breakage. Therefore, they must be immediately placed in a coating and curing system after stretching. Currently, a dual-coating process using UV curing is commonly employed: the first layer is a modified silicone resin coating, 20-30 μm thick, which improves the fiber's resistance to microbending; the second layer is a modified epoxy acrylic coating, providing high-strength protection for the fiber. After coating, rapid curing is achieved through UV irradiation, forming a coated optical fiber with a diameter of approximately 250 μm.
[0090] Finally, the coated and cured optical fiber is guided by a traction roller to a take-up drum for winding. After winding, the optical fiber undergoes multiple performance tests, such as testing tensile strength, transmission attenuation, and dispersion, to ensure that the finished optical fiber meets the standards for use in communication and other scenarios.
[0091] It should be understood that the sequence number of each step in the above embodiments does not imply the order of execution. The execution order of each process should be determined by its function and internal logic, and should not constitute any limitation on the implementation process of the embodiments of this application.
[0092] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.
Claims
1. A rare-earth-doped optical fiber preform, characterized in that, The optical fiber preform consists of, from the outside in, a quartz layer, a rare earth-doped core layer, and a quartz core layer. The quartz layer is formed by thermally melting and shrinking a quartz tube; The rare earth-doped core layer is formed by depositing pre-prepared rare earth doping and co-doping agents on the inner wall of the quartz tube; wherein the co-doping agents include aluminum, fluorine and phosphorus. The main component of the quartz core layer is silicon dioxide.
2. The rare-earth-doped optical fiber preform as described in claim 1, characterized in that, A pre-volatile rare earth-doped core layer is also provided between the rare earth-doped core layer and the quartz core layer, and the concentration of rare earth doped in the pre-volatile rare earth-doped core layer is greater than the concentration of rare earth doped in the rare earth-doped core layer.
3. The rare-earth-doped optical fiber preform as described in claim 2, characterized in that, The quartz core layer is formed by introducing silicon tetrachloride gas into the quartz tube using the PCVD vapor phase doping process, and depositing silicon dioxide on the pre-volatile rare earth-doped core layer using microwave heating deposition. The pre-volatile rare earth-doped core layer is formed by depositing a pre-configured second concentration of doped rare earth and co-doperants into the rare earth-doped core layer based on the MCVD vapor phase doping process. The rare earth-doped core layer is formed by depositing a pre-prepared first concentration of doped rare earth and co-doperants onto the inner wall of the quartz tube using the MCVD vapor phase doping process.
4. A method for preparing rare-earth-doped optical fiber preforms, characterized in that, include: Pre-configured rare earth doping and co-doping agents of the first concentration are deposited on the inner wall of the quartz tube to form a rare earth doped core layer; A quartz core layer is deposited on the rare earth-doped core layer; wherein the main component of the quartz core layer is silicon dioxide; The quartz tube with the deposited quartz core layer is thermally shrunk in one step to form an optical fiber preform.
5. The method for preparing rare-earth-doped optical fiber preforms as described in claim 4, characterized in that, Before depositing the quartz core layer on the rare earth-doped core layer, the method further includes: On the surface of the rare earth-doped core layer, a pre-configured second concentration of doped rare earth and co-doped agent is deposited to form a pre-volatile rare earth-doped core layer; wherein the second concentration is greater than the first concentration.
6. The method for preparing rare-earth-doped optical fiber preforms as described in claim 5, characterized in that, The second concentration is 105%-110% of the first concentration.
7. The method for preparing rare-earth-doped optical fiber preforms as described in claim 5, characterized in that, The process of depositing a pre-configured first concentration of doped rare earth elements and co-dopersant onto the inner wall of a quartz tube to form a rare earth-doped core layer includes: Based on the MCVD vapor phase doping process, a pre-configured first concentration of doped rare earth and co-doped agent is deposited on the inner wall of a quartz tube to form a rare earth doped core layer. The deposition of a pre-configured second concentration of doped rare earth elements and co-dopersant on the surface of the rare earth-doped core layer includes: Based on the MCVD vapor phase doping process, a pre-configured second concentration of doped rare earth and co-doped agent is deposited on the surface of the rare earth-doped core layer.
8. The method for preparing rare-earth-doped optical fiber preforms as described in claim 4, characterized in that, The deposition of a quartz core layer on the rare earth-doped core layer includes: Based on the PCVD vapor phase doping process, silicon tetrachloride gas is introduced into the quartz tube, and silicon dioxide is deposited on the rare earth-doped core layer by microwave heating deposition.
9. The method for preparing rare-earth-doped optical fiber preforms according to any one of claims 4-8, characterized in that, The doped rare earth element is one or more of the following elements: ytterbium, erbium, thulium, neodymium, terbium, dysprosium, holmium, samarium, cerium, praseodymium, and promethium; the co-doperants include aluminum, fluorine, and phosphorus.
10. An optical fiber, characterized in that, The optical fiber is obtained by stretching an optical fiber preform prepared by the rare earth-doped optical fiber preform preparation method according to any one of claims 4-9.