Radiation-insensitive single-mode optical fiber

Abstract

Disclosed in the present invention is a radiation-insensitive single-mode optical fiber, comprising a core, a first cladding, and a second cladding which are sequentially arranged from inside to outside, or comprising a core, a first buffer layer, a first cladding, a second buffer layer, and a second cladding which are sequentially arranged from inside to outside. The core, the first buffer layer, the first cladding, the second buffer layer, and the second cladding are all made of quartz glass doped with a cerium element, an aluminum element, and a fluorine element. The contents of the cerium element, the aluminum element, and the fluorine element are constant in the radial directions of the core, the first cladding, and the second cladding, respectively, and linearly vary in the first buffer layer and the second buffer layer, respectively. In the present invention, by regulating and controlling the contents of the cerium element, the aluminum element, and the fluorine element in the core, the first cladding, and the second cladding of the optical fiber, the stress distribution of the optical fiber is optimized, the residual stress is reduced, and the generation of fatigue bonds and wire drawing defects in the optical fiber is reduced, thereby improving the radiation resistance of the optical fiber.

Description

A radiation-insensitive single-mode optical fiber Technical Field

[0001] The present invention belongs to the technical field of optical fiber doping structures, and in particular relates to a radiation-insensitive single-mode optical fiber suitable for use in radiation environments. Background Art

[0002] Optical fiber is widely used as an optical transmission medium in special radiation environments, such as marine, aviation, nuclear power plants, and intelligent environmental monitoring, due to its advantages such as low loss, high transmission rate, compact size, light weight, and resistance to electrostatic interference. However, in these irradiated environments, optical fiber communication capabilities often degrade rapidly. The main reason is that ionizing radiation damage causes defects in the quartz fiber material.

[0003] The radiation resistance of optical fibers is closely related to their material structure. Conventional optical fibers typically contain germanium dopants. During the drawing process, due to the effects of drawing tension and the fiber's thermal history, numerous material defects or precursors form in the core layer. These defects or precursors further deteriorate under irradiation, leading to bond breakage or changes in the material's microstructure, resulting in significant additional absorption losses caused by radiation. As these losses rapidly increase, the fiber loses its ability to transmit optical signals. Existing radiation-resistant optical fibers on the market typically use pure silica or fluorine-doped cores, which offer superior radiation resistance compared to germanium-doped fibers. However, to form an optical waveguide, the core and cladding layers of these two single fluorine-doped systems differ significantly in material properties such as viscosity and thermal expansion coefficient. This results in tension being concentrated in the fiber core during the drawing process, increasing residual stress and drawing defects, which in turn degrades the transmission performance of the fiber.

[0004] Furthermore, optical fiber plays a crucial role in long-distance data transmission in the aerospace and nuclear power sectors and is typically laid in cables. Whether in the cabling or laying process, optical fiber inevitably experiences coiling, bending, and twisting. Bends in the fiber significantly increase the additional loss, degrading its transmission performance.

[0005] Researchers at home and abroad have been committed to solving the design and preparation problems of radiation-resistant optical fibers, and have improved the composition, profile design and preparation process of optical fiber materials to adapt to different application requirements. For example, the patent with publication number CN102126825A discloses a method for making radiation-resistant high-performance quartz optical fibers, which regulates the hydroxyl and fluorine content of the core and cladding. The core contains 0-2000ppm of hydroxyl and 0-1000ppm of fluorine, the inner cladding is doped with 10000-20000ppm of fluorine, and the outer cladding is doped with 1000-6000ppm. At the same time, a process combination of VAD+MCVD or PCVD is applied to make the obtained optical fiber have a more stable microstructure and good radiation resistance. However, since this preparation method involves a combination of different deposition processes and involves multiple fusions of the core rod and the fluorine-doped tube, it is very likely to cause the intrinsic water peak to rise, affecting the intrinsic attenuation and radiation additional loss of the optical fiber. At the same time, this method is relatively complicated to operate and is not suitable for industrial mass production. For example, patent publication number CN106646735A discloses a radiation-resistant optical fiber and its preparation process. The fiber is constructed from the outside inwards by an outer coating, outer cladding, inner cladding, and core. The outer coating, outer cladding, and core are doped with varying amounts of variable-valence metal elements: the outer coating contains 200-1000 ppm of a variable-valence metal oxide, the outer cladding contains 200-500 ppm of a variable-valence metal oxide, and the core contains 300-800 ppm of a variable-valence metal oxide. However, the patent does not regulate the material composition of the optical fiber core and cladding. When the optical fiber is rapidly cooled from high temperature to room temperature, the core and cladding cool at different rates and shrink to varying degrees due to the significant disparity in physical properties (such as thermal expansion coefficient and viscosity) between the core and cladding. This induces significant residual stress in the core, leading to an increase in fatigue bonds and defects within the optical fiber, thus affecting the optical fiber's radiation resistance. Summary of the Invention

[0006] In response to one or more of the above-mentioned defects or improvement needs in the prior art, the present invention provides a radiation-insensitive single-mode optical fiber, which optimizes the stress distribution of the optical fiber, reduces the residual stress, and reduces the generation of fatigue bonds and drawing defects in the optical fiber, thereby improving the radiation resistance of the optical fiber.

[0007] To achieve the above-mentioned object, the present invention provides a radiation-insensitive single-mode optical fiber, comprising a core layer, a first cladding layer, and a second cladding layer arranged in sequence from the inside to the outside; or comprising a core layer, a first buffer layer, a first cladding layer, a second buffer layer, and a second cladding layer arranged in sequence from the inside to the outside;

[0008] The core layer, the first buffer layer, the first cladding layer, the second buffer layer and the second cladding layer are all made of quartz glass doped with cerium, aluminum and fluorine.

[0009] As a further improvement of the present invention,

[0010] The cerium content is constant at A1 in the radial direction of the core layer, constant at A2 in the radial direction of the first cladding, and constant at A3 in the radial direction of the second cladding;

[0011] The aluminum content in the radial direction of the core layer is constant at B1, the aluminum content in the radial direction of the first cladding layer is constant at B2, and the aluminum content in the radial direction of the second cladding layer is constant at B3;

[0012] The content of the fluorine element is constant at C1 in the radial direction of the core layer, constant at C2 in the radial direction of the first cladding layer, and constant at C3 in the radial direction of the second cladding layer.

[0013] As a further improvement of the present invention,

[0014] The cerium content in the first buffer layer changes linearly from A1 to A2 from the inside to the outside in the radial direction, and the cerium content in the second buffer layer changes linearly from A2 to A3 from the inside to the outside in the radial direction;

[0015] The aluminum content in the first buffer layer changes linearly from B1 to B2 from the inside to the outside in the radial direction, and changes linearly from B2 to B3 from the inside to the outside in the radial direction of the second buffer layer;

[0016] The content of the fluorine element changes linearly from C1 to C2 from the inside to the outside in the radial direction of the first buffer layer, and the content changes linearly from C2 to C3 from the inside to the outside in the radial direction of the second buffer layer.

[0017] As a further improvement of the present invention,

[0018] The content of the cerium element in different layer structures is in the order of A1>A3>A2;

[0019] The content of the aluminum element in different layer structures is in the order of B1>B3>B2;

[0020] The relationship between the content of the fluorine element in different layer structures is C2≥C3>C1.

[0021] As a further improvement of the present invention,

[0022] In the core layer, the cerium element content A1 is 1000-2500 ppm, the aluminum element content B1 is 3000-6000 ppm, and the fluorine element content C1 is 3000-15000 ppm;

[0023] In the first cladding, the cerium element content A2 is 50-500 ppm, the aluminum element content B2 is 200-1600 ppm, and the fluorine element content C2 is 10000-20000 ppm;

[0024] In the second cladding, the cerium element content A3 is 500-2000 ppm, the aluminum element content B3 is 1600-5000 ppm, and the fluorine element content C3 is 5000-20000 ppm.

[0025] As a further improvement of the present invention,

[0026] The ratio A1 / A2 of the cerium content in the core layer and the first cladding layer is 5-20; and / or the ratio A1 / A3 of the cerium content in the core layer and the second cladding layer is 1-5.

[0027] As a further improvement of the present invention,

[0028] The relative refractive index difference Δn1 between the core layer and pure silica glass is 0.2% to 0.5%;

[0029] The relative refractive index difference Δn2 between the first cladding and pure silica glass is -0.25% to -0.6%;

[0030] The relative refractive index difference Δn3 between the second cladding and pure silica glass is -0.1% to 0.1%.

[0031] As a further improvement of the present invention, the core layer diameter is 7.5~10μm, the first buffer layer diameter is 10~13μm, the first cladding diameter is 18~24μm, the second buffer layer diameter is 24~30μm, and the second cladding diameter is 124~126μm.

[0032] As a further improvement of the present invention, the maximum stress difference ΔP of the cross section of the radiation-insensitive single-mode optical fiber is less than 10 MPa.

[0033] As a further improvement of the present invention, under an environment where the total radiation dose is 100 kGy, the attenuation of the radiation-insensitive single-mode optical fiber in the 1310 nm and 1550 nm bands is less than 20 dB / km.

[0034] In general, the above technical solutions conceived by the present invention have the following beneficial effects compared with the prior art:

[0035] (1) The radiation-insensitive single-mode optical fiber of the present invention, by regulating the content of cerium, aluminum, and fluorine in the optical fiber core layer, the first cladding layer, and the second cladding layer, avoids the situation in which the deformation degree of each layer is greatly different during the drawing temperature change process and the stress is concentrated in the core layer due to the large differences in material properties such as viscosity and thermal expansion coefficient of different layer structures. The stress distribution ΔP (the difference between the maximum stress and the minimum stress on the optical fiber) of the optical fiber is optimized, the residual stress is reduced, and the generation of fatigue bonds and drawing defects in the optical fiber is reduced, thereby improving the radiation resistance of the optical fiber. In addition, by introducing a linearly varying buffer layer between the core layer / first cladding layer and the first cladding layer / second cladding layer, different dopants are uniformly varied throughout the optical fiber, especially at the interface of different layer structures, so that the microscopic difference in the physical properties of the optical fiber is smaller. Not only is the interface stress smaller, but the stress distribution of the optical fiber as a whole is more uniform, and ΔP is smaller, further improving the radiation resistance of the optical fiber.

[0036] (2) The radiation-insensitive single-mode optical fiber of the present invention, when wound 10 times at a 30 mm bending diameter, has an additional bending loss of less than 0.1 dB at 1310 nm and an additional bending loss of less than 0.1 dB at 1550 nm. Under a total radiation dose of 100 kGy, the attenuation of the radiation-insensitive single-mode optical fiber of the embodiment of the present invention in the 1310 nm and 1550 nm bands is less than 20 dB / km. Furthermore, the maximum stress difference ΔP of the cross-section of the radiation-insensitive single-mode optical fiber of the embodiment of the present invention is less than 10 MPa. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] FIG1 is a cross-sectional view of the refractive index of a radiation-insensitive single-mode optical fiber and a cross-sectional view of the optical fiber according to an embodiment of the present invention;

[0038] FIG2 is a cross-sectional view of the refractive index of a radiation-insensitive single-mode optical fiber and a cross-sectional view of the optical fiber according to another embodiment of the present invention;

[0039] FIG3 is a cross-sectional view of the optical fiber refractive index and the optical fiber cross-section of Comparative Example 1 of the present invention. Modes for Carrying Out the Invention

[0040] In order to make the objectives, technical solutions and advantages of the present invention more clearly understood, the present invention is further described in detail below with reference to the accompanying drawings and embodiments. It should be understood that the specific embodiments described herein are only intended to illustrate the present invention and are not intended to limit the present invention. In addition, the technical features involved in the various embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

[0041] In the description of the present invention, it should be understood that the terms "center", "longitudinal", "lateral", "length", "width", "thickness", "up", "down", "front", "back", "left", "right", "vertical", "horizontal", "top", "bottom", "inside", "outside", "clockwise", "counterclockwise", "axial", "radial", "circumferential" and the like to indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, and are only for the convenience of describing the present invention and simplifying the description, rather than indicating or implying that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as limiting the present invention.

[0042] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the number of the technical features being referred to. Thus, a feature defined as "first" or "second" may explicitly or implicitly include at least one such feature. In the description of the present invention, "plurality" means at least two, such as two, three, etc., unless otherwise specifically defined.

[0043] In the present invention, unless otherwise specified or limited, the terms "installed," "connected," "connect," "fixed," etc. should be understood in a broad sense. For example, they can refer to fixed connection, detachable connection, or integration; mechanical connection, electrical connection; direct connection, or indirect connection through an intermediate medium; internal communication between two components, or interaction between two components, unless otherwise specified. Those skilled in the art will understand the specific meanings of the above terms in the present invention based on specific circumstances.

[0044] In the present invention, unless otherwise expressly specified or limited, when a first feature is "above" or "below" a second feature, it may mean that the first and second features are in direct contact, or that the first and second features are in indirect contact through an intermediary. Furthermore, when a first feature is "above," "above," or "above" a second feature, it may mean that the first feature is directly above or diagonally above the second feature, or simply means that the first feature is at a higher level than the second feature. When a first feature is "below," "below," or "below" a second feature, it may mean that the first feature is directly below or diagonally below the second feature, or simply means that the first feature is at a lower level than the second feature.

[0045] The present invention provides a radiation-insensitive single-mode optical fiber. By regulating the material composition of different optical fiber structures, the difficulties of improving the radiation resistance, bending performance and residual stress of the existing radiation-resistant optical fiber during the preparation process are overcome.

[0046] The radiation-insensitive single-mode optical fiber of an embodiment of the present invention includes a core layer, a first cladding layer, and a second cladding layer arranged in sequence from the inside to the outside; or includes a core layer, a first buffer layer, a first cladding layer, a second buffer layer, and a second cladding layer arranged in sequence from the inside to the outside; the core layer, the first buffer layer, the first cladding layer, the second buffer layer, and the second cladding layer are all made of silica glass doped with cerium, aluminum, and fluorine.

[0047] The present invention improves the composition and cross-sectional design of optical fiber materials and dopes fluorine and variable valence metal cerium into different structures of the optical fiber (core layer, inner cladding, outer cladding), significantly reducing the radiation-induced loss and sensitivity of the optical fiber to radiation energy. Even when used in extreme areas such as high radiation doses, it can still have good radiation resistance. Cerium is a colorless variable valence element. 3+ It can play a certain protective role on the holes generated by irradiation, thereby reducing the generation of color centers, and Ce 4+ Cerium can capture excess electrons generated by irradiation and suppress the associated color centers created by these captured electrons. Therefore, doping with cerium can effectively reduce the generation of color centers when the optical fiber is irradiated. Furthermore, doping optical fiber with fluorine can achieve radiation hardening. Fluorine atoms bond to color centers or defect centers, and the Si-F bond energy is greater than that of Si-O, thus suppressing defects generated during irradiation and improving the optical fiber's radiation resistance.

[0048] This invention ensures fiber manufacturability and optimizes radiation resistance by co-doping cerium, aluminum, and fluorine into the optical fiber. Cerium and fluorine act as radiation hardeners in the optical fiber, exerting opposing effects on the refractive index and varying degrees of influence on the material's physical properties (thermal expansion coefficient and viscosity). Therefore, co-doping is used to form a designed waveguide structure and uniformly distribute stress across the fiber. Aluminum is typically added as a co-dopant with cerium to support the silica skeleton, making cerium more reactive and incorporating into the optical fiber structure, thereby increasing the cerium doping content and its controllable range.

[0049] In the embodiments of the present invention, cerium is present in the form of a variable-valence metal oxide, including CeO2, Ce2O3, etc.; aluminum is present in the form of a metal oxide, including Al2O3; and fluorine is preferably present in the form of [SiO3F], [SiO2F2], [SiOF3], [CeO3F], [CeO2F2], or [CeOF3]. The doping material for cerium is preferably CeCl3; the doping material for aluminum is preferably Al3Cl3; and the doping material for fluorine is preferably one or more of CF4, C2F6, C3F8, SiF4, SF6, C2F2Cl2, and C2F3Cl3.

[0050] As shown in Figure 1, in the first embodiment of the present invention, a radiation-insensitive single-mode optical fiber comprises, from the inside out, a core layer, a first cladding layer, and a second cladding layer. These layers are all made of quartz glass and doped with cerium, aluminum, and fluorine. The core layer has a diameter of D1, the first cladding has a diameter of D2, and the second cladding has a diameter of D3.

[0051] Preferably, the cerium content remains constant in the radial distance of the core layer, the first cladding, and the second cladding, respectively. The content in the core layer is constant at A1 from r=0 to r=(D1 / 2), the content in the first cladding is constant at A2 from r=(D1 / 2) to r=(D2 / 2), and the content in the second cladding is constant at A3 from r=(D2 / 2) to r=(D3 / 2).

[0052] The aluminum content remains constant in the radial distances of the core layer, the first cladding layer, and the second cladding layer. The content in the core layer is constant at B1 from r=0 to r=(D1 / 2), the content in the first cladding layer is constant at B2 from r=(D1 / 2) to r=(D2 / 2), and the content in the second cladding layer is constant at B3 from r=(D2 / 2) to r=(D3 / 2).

[0053] The fluorine content remains constant in the radial distances of the core, first cladding, and second cladding. In the core, the content is constant at C1 from r=0 to r=(D1 / 2), in the first cladding, the content is constant at C2 from r=(D1 / 2) to r=(D2 / 2), and in the second cladding, the content is constant at C3 from r=(D2 / 2) to r=(D3 / 2).

[0054] When the cerium, aluminum, and fluorine content in the core layer, first cladding layer, and second cladding layer are respectively constant in the radial direction, the physical properties of the core layer, first cladding layer, and second cladding layer of optical fibers with different structures are made more similar through the design and regulation of the content of the above-mentioned different elements, thereby eliminating the large residual stress in the optical fiber caused by differences in physical properties (thermal expansion coefficient, viscosity) during the drawing process.

[0055] As shown in Figure 2, in a second embodiment of the present invention, a radiation-insensitive single-mode optical fiber comprises, from the inside out, a core layer, a first buffer layer, a first cladding layer, a second buffer layer, and a second cladding layer. The core layer, first cladding layer, second cladding layer, and buffer layer are all made of a quartz glass matrix and doped with cerium, aluminum, and fluorine. The core layer has a diameter of D1, the first cladding layer has a diameter of D2, the second cladding layer has a diameter of D3, the first buffer layer has a diameter of D4, and the second buffer layer has a diameter of D5.

[0056] Preferably, the cerium content remains constant over the radial distances of the core layer, the first cladding layer, and the second cladding layer, and varies linearly from the inside to the outside of the buffer layer in the radial direction. Specifically, the cerium content in the core layer is constant at A1 from r = 0 to r = (D1 / 2), the cerium content in the first buffer layer varies linearly from A1 to A2 from r = (D1 / 2) to r = (D4 / 2), the cerium content in the first cladding layer is constant at A2 from r = (D4 / 2) to r = (D2 / 2), the cerium content in the second buffer layer varies linearly from A2 to A3 from r = (D2 / 2) to r = (D5 / 2), and the cerium content in the second cladding layer is constant at A3 from r = (D5 / 2) to r = (D3 / 2).

[0057] The aluminum content remains constant in the radial distances of the core, first cladding, and second cladding, and changes linearly from the inside to the outside of the buffer layer in the radial direction. Specifically, the aluminum content in the core is constant at B1 from r = 0 to r = (D1 / 2), changes linearly from B1 to B2 in the first buffer layer from r = (D1 / 2) to r = (D4 / 2), remains constant at B2 in the first cladding from r = (D4 / 2) to r = (D2 / 2), changes linearly from B2 to B3 in the second buffer layer from r = (D2 / 2) to r = (D5 / 2), and remains constant at B3 in the second cladding from r = (D5 / 2) to r = (D3 / 2).

[0058] The fluorine content remains constant over the radial distances of the core, first cladding, and second cladding, and varies linearly from the inside to the outside of the buffer layer. Specifically, the fluorine content in the core is constant at C1 from r = 0 to r = (D1 / 2), varies linearly from C1 to C2 in the first buffer layer from r = (D1 / 2) to r = (D4 / 2), remains constant at C2 in the first cladding from r = (D4 / 2) to r = (D2 / 2), varies linearly from C2 to C3 in the second buffer layer from r = (D2 / 2) to r = (D5 / 2), and remains constant at C3 in the second cladding from r = (D5 / 2) to r = (D3 / 2).

[0059] It should be noted that, in this embodiment, the cerium, aluminum, and fluorine elements vary linearly from the inside to the outside of the buffer layer in the radial direction, wherein the linear variation refers to a gradual increase or decrease in the content from the inside to the outside in the radial direction.

[0060] When the cerium, aluminum, and fluorine content are kept constant in the radial direction of the core layer, the first cladding layer, and the second cladding layer, respectively, and change linearly in the buffer layer, not only do the physical properties of the core layer, the first cladding layer, and the second cladding layer become more similar, but the addition of the buffer layer also allows different dopants to change evenly throughout the entire optical fiber, especially at the interfaces of the core layer / first cladding layer and the first cladding layer / second cladding layer. This results in smaller microscopic differences in the optical fiber's physical properties, such as the thermal expansion coefficient and viscosity, which not only reduces interfacial stress but also makes the overall stress distribution of the optical fiber more uniform and reduces residual stress.

[0061] It can be understood that the difference between the above two embodiments is that the second embodiment adds a first buffer layer and a second buffer layer on the basis of the first embodiment.

[0062] On the basis of the technical solutions of the above two embodiments, taking into account the process doping limit, the requirements of the optical fiber waveguide, and the material composition of the core layer, the first cladding layer, the second cladding layer, and the buffer layer having similar physical properties, the content relationship of the above doping elements is as follows: the content relationship of the cerium element in different layer structures is A1>A3>A2; the content relationship of the aluminum element in different layer structures is B1>B3>B2; the content relationship of the fluorine element in different layer structures is C2≥C3>C1.

[0063] Furthermore, in order to design the physical properties of the core layer, the first cladding layer, the second cladding layer, and the buffer layer to be more similar and to achieve a more uniform stress distribution over the entire cross-section of the optical fiber, the contents of the doping elements are as follows: in the core layer, the cerium content A1 is 1000-2500 ppm, the corresponding aluminum content B1 is 3000-6000 ppm, and the fluorine content C1 is 3000-15000 ppm; in the first cladding layer, the cerium content A2 is 50-500 ppm, the corresponding aluminum content B2 is 200-1600 ppm, and the fluorine content C2 is 10000-20000 ppm; in the second cladding layer, the cerium content A3 is 500-2000 ppm, the corresponding aluminum content B3 is 1600-5000 ppm, and the fluorine content C3 is 5000-20000 ppm.

[0064] In order to design the physical properties of the core layer, the first cladding, the second cladding, and the buffer layer to be more similar and the stress distribution on the entire cross-section of the optical fiber to be more uniform, it is further preferred that, in the core layer, the cerium element content A1 is 1500-2500 ppm, the corresponding aluminum element content B1 is 3000-5000 ppm, and the fluorine element content C1 is 5000-12000 ppm; in the first cladding, the cerium element content A2 is 100-400 ppm, the corresponding aluminum element content B2 is 200-1200 ppm, and the fluorine element content C2 is 10000-18000 ppm; in the second cladding, the cerium element content A3 is 500-1500 ppm, the corresponding aluminum element content B3 is 1600-4000 ppm, and the fluorine element content C3 is 8000-18000 ppm.

[0065] Furthermore, the ratio of cerium content in the core layer to the first cladding, A1 / A2, is preferably between 5 and 20. By introducing the first cladding and regulating the ratio of cerium content in the core layer to the first cladding, while also meeting the other parameter ranges set by the present invention, the refractive index difference (Δn1-Δn2) between the optical fiber core layer and the first cladding can be effectively increased, thereby improving the fiber's bend insensitivity. If the ratio of cerium content in the core layer to the first cladding is too small, the required fluorine content in the inner cladding increases, which can easily lead to multiple bubbles during the preform production process and make the process unmanufacturable. If the ratio of cerium content in the core layer to the inner cladding is too large, the controllable range of fluorine content in the core layer is extremely narrow, resulting in a decrease in (Δn1-Δn2), a decrease in bend resistance, and an increase in residual stress in the optical fiber.

[0066] Furthermore, the ratio of the cerium content in the core layer to the second cladding, A1 / A3, is preferably between 1 and 5. By regulating the cerium content ratio in the core layer and the second cladding while meeting the other parameter ranges specified in the present invention, the residual stress of the optical fiber can be optimized. If the cerium content ratio in the core layer and the second cladding is too small, while meeting the requirements of the optical fiber waveguide, the required fluorine content in the second cladding increases, making the process unmanufacturable. If the cerium content ratio in the core layer and the second cladding is too large, the controllable range of the core layer fluorine content is extremely narrow, and the residual stress of the optical fiber increases.

[0067] In a preferred embodiment, the relative refractive index difference Δn1 between the core and pure silica glass is 0.2% to 0.5%; the relative refractive index difference Δn2 between the first cladding and pure silica glass is -0.25% to -0.6%; and the relative refractive index difference Δn3 between the second cladding and pure silica glass is -0.1% to 0.1%. The values ​​of Δn1 and Δn3 are determined based on the numerical aperture requirements of standard communication bands. If Δn2 is too small, the fiber's bending performance will not be significantly improved. If Δn2 is too large, the process limit will be exceeded, making the process unfeasible.

[0068] In a preferred embodiment, the core layer diameter D1 is 7.5~10μm; the first buffer layer diameter D4 is 10~13μm; the first cladding diameter D2 is 18~24μm; the second buffer layer diameter D5 is 24~30μm; and the second cladding diameter D3 is 124~126μm. The values ​​of D1 and D3 are formulated in accordance with the numerical aperture requirements of the standard communication band. If the first cladding diameter D2 is too small, the optimization of the optical fiber's bending resistance is not obvious. If D2 is too large, the optical fiber's numerical aperture is too large and the mode field diameter is too small, which does not meet the application requirements of the standard communication band. If the buffer layer D4 and D5 are too small, there is no buffering effect, and different elements will still mutate at the interface, resulting in uneven stress distribution that is not optimized. If D4 and D5 are too large, the optical fiber's mode field diameter is too large and does not meet the application requirements of the standard communication band.

[0069] The radiation-insensitive single-mode optical fiber of the present invention controls the contents of cerium, aluminum, and fluorine in the optical fiber core layer, the first cladding layer, and the second cladding layer to avoid the situation in which the deformation of each layer during the drawing temperature change process is greatly different and the stress is concentrated in the core layer due to the large differences in material properties such as viscosity and thermal expansion coefficient among different layer structures. As a result, the stress distribution ΔP (the difference between the maximum stress and the minimum stress on the optical fiber) of the optical fiber is optimized, the residual stress is reduced, and the generation of fatigue bonds and drawing defects in the optical fiber is reduced, thereby improving the radiation resistance of the optical fiber.

[0070] Furthermore, by introducing a linearly varying buffer layer between the core layer / first cladding and the first cladding / second cladding, different dopants vary evenly throughout the entire optical fiber, especially at the interfaces of different layer structures, thereby minimizing the microscopic differences in the physical properties of the optical fiber. Not only is the interfacial stress small, but the overall stress distribution of the optical fiber is more uniform, and ΔP is smaller, further improving the optical fiber's radiation resistance.

[0071] Furthermore, the radiation-insensitive single-mode optical fiber of the embodiment of the present invention exhibits a bending loss of less than 0.1 dB at 1310 nm and less than 0.1 dB at 1550 nm when wound 10 times at a 30 mm bending diameter. Under a total radiation dose of 100 kGy, the attenuation of the radiation-insensitive single-mode optical fiber of the embodiment of the present invention in the 1310 nm and 1550 nm wavelength bands is less than 20 dB / km. Furthermore, the maximum stress difference ΔP across the cross section of the radiation-insensitive single-mode optical fiber of the embodiment of the present invention is less than 10 MPa.

[0072] The following are specific embodiments:

[0073] According to the technical solution of the radiation-insensitive single-mode optical fiber, the parameters of the optical fiber are designed, and the preparation method is as follows:

[0074] A pure silicon liner is prepared via outside vapor deposition (OVD). After cleaning the liner, plasma chemical vapor deposition (PCVD) or modified chemical vapor deposition (MCVD) is used to deposit cerium, aluminum, and fluorine co-doped silicon dioxide inside the liner. This is then melted and condensed into the first preform using a high-temperature furnace or an oxyhydrogen flame. The deposition raw materials include SiCl₄, O₂, C₂F₆, vaporized cerium salt (CeCl₃), and vaporized aluminum salt (AlCl₃), the co-dopant. The content and distribution of the various elements in the optical fiber are controlled by maintaining a constant or linearly varying set point on the flowmeters for each raw material gas. The elements react and deposit on the liner wall at the high temperature generated by the oxyhydrogen flame or the high energy generated by the resonant cavity.

[0075] The first preform is corroded with acid and alkali and cleaned with pure water to obtain a second preform, and the second preform is drawn on a drawing tower to obtain a radiation-insensitive single-mode optical fiber.

[0076] The cross-sectional parameters of the radiation-insensitive single-mode optical fibers prepared in various embodiments and comparative examples of the present invention are shown in Table 1.

[0077] The optical fiber cross-sectional structures of Examples 1 and 2, as shown in Figure 2, each comprise a core layer, a first buffer layer, a first cladding layer, a second buffer layer, and a second cladding layer, arranged in order from the inside out. The first buffer layer surrounds the core layer, the first cladding layer closely surrounds the first buffer layer, the second buffer layer closely surrounds the first cladding layer, and the second cladding layer closely surrounds the second buffer layer. The core layer, first buffer layer, first cladding layer, second buffer layer, and second cladding layer are all made of silica glass doped with cerium, aluminum, and fluorine. The doping elements in the first and second buffer layers vary linearly from the inside out in the radial direction.

[0078] 1 , the optical fiber cross-sectional structures of Examples 3 and 4 include a core layer, a first cladding layer, and a second cladding layer. The first cladding layer surrounds the core layer, and the second cladding layer surrounds the first cladding layer. The core layer, the first cladding layer, and the second cladding layer are all made of quartz glass doped with cerium, aluminum, and fluorine.

[0079] The cross-sectional structure of the optical fiber of Comparative Example 1 is shown in FIG3 , and includes a core layer and a cladding layer, wherein the cladding layer only comprises one layer, and the cladding layer tightly surrounds the core layer; the core layer and the cladding layer are both quartz glass doped with cerium, aluminum, and fluorine elements.

[0080] The optical fiber cross-sectional structure of Comparative Example 2, referring to Figure 1, includes a core layer, a first cladding layer, and a second cladding layer. The first cladding layer surrounds the core layer, and the second cladding layer surrounds the first cladding layer. The core layer is made of pure silica quartz glass, and the first and second cladding layers are both made of quartz glass doped with a single fluorine element.

[0081] Referring to Figure 2 , the cross-sectional structure of the optical fiber of Comparative Example 3 comprises, from the inside out, a core layer, a first buffer layer, a first cladding layer, a second buffer layer, and a second cladding layer, arranged in that order. Surrounding the core layer is the first buffer layer, which is tightly surrounded by the first cladding layer, which is tightly surrounded by the second buffer layer, which is tightly surrounded by the first cladding layer, and which is tightly surrounded by the second cladding layer. The core layer, first buffer layer, first cladding layer, second buffer layer, and second cladding layer are all made of quartz glass doped with cerium, aluminum, and fluorine.

[0082] The method for detecting optical fiber performance in the embodiments and comparative examples of the present invention is as follows:

[0083] The optical fiber was irradiated with a cobalt-60 radiation source at a temperature of 25±3°C, with a total dose of 100 kGy. During the irradiation period, light sources with wavelengths of 1310 nm and 1550 nm were used to measure the radiation-induced attenuation of the optical fiber.

[0084] The additional bending loss of the optical fiber was tested using an optical analyzer (PK Company). The fiber was wound 10 times with a bending diameter of 30 mm to measure the attenuation difference before and after bending.

[0085] The stress distribution curve of the optical fiber was tested using a fiber optic three-dimensional refractive index analyzer (EXFO) to calculate the difference between the maximum and minimum stress values ​​across the entire optical fiber cross section.

[0086] The optical fiber performance test results in the embodiments of the present invention and the comparative examples are shown in Table 2.

[0087] Table 1 Fiber profile parameters

[0088]

[0089] Table 2 Fiber performance test results

[0090] Performance Example 1 Example 2 Example 3 Example 4 Comparative Example 1 Comparative Example 2 Comparative Example 3 Radiation additional attenuation (dB / km@1310nm) 5.96.112.917.625.835.429.7 Radiation additional attenuation (dB / km@1550nm) 6.57.114.019.727.134.230.1 Bending additional attenuation@1310nm (dB) 0.0040.0060.0080.010.080.050.006 Bending additional attenuation@1550nm (dB) 0.0700.0250.0940.0860.3510.1630.093 Maximum stress difference ΔP (MPa) 2.94.77.39.815.759.530.3

[0091] The difference between Examples 1 and 2 and Examples 3 and 4 lies in the presence or absence of a buffer layer. The results show that in Examples 1 and 2 with a buffer layer, the optical fiber ΔP is smaller and the stress uniformity is better, resulting in smaller radiation loss and better radiation resistance.

[0092] The difference between Example 3 and Example 4 is that the present invention sets the cerium content A1 in the core layer to 1000-2500 ppm, preferably 1500-2500 ppm; the cerium content A2 in the first cladding is 50-500 ppm, preferably 100-400 ppm. The values ​​of Example 3 are within the preferred range, while the values ​​of Example 4 are not within the preferred range. Therefore, the optical fiber of Example 3 has a smaller ΔP and better stress uniformity, resulting in smaller radiation loss and better radiation resistance.

[0093] The difference between comparative example 1 and embodiments 1, 2, 3, and 4 lies in the presence or absence of the first cladding, which plays a role in bending resistance. From the additional bending attenuation, it can be seen that the introduction of the sunken first cladding in embodiments 1, 2, 3, and 4 greatly improves the bending resistance.

[0094] The difference between Comparative Example 2 and Examples 1, 2, 3, and 4 lies in whether the values ​​of each element are within the set range of the present invention. The parameters of Comparative Example 2 exceed the value range, and the material composition and physical properties of each layer structure are quite different, which makes the ΔP of the optical fiber larger and the residual stress increased after drawing, resulting in greater radiation loss and poor radiation resistance.

[0095] The difference between Comparative Example 3 and Examples 1, 2, 3, and 4 is that the ratio A1 / A2 of the cerium content in the core layer and the first cladding set in the present invention is preferably 5 to 20, while A1 / A2 in Comparative Example 3 is 25, which exceeds the range. The material composition and physical properties of the core layer and the first cladding are quite different, resulting in a larger ΔP of the optical fiber after drawing and increased residual stress, resulting in greater radiation loss and poor radiation resistance.

[0096] It will be easily understood by those skilled in the art that the above description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, and improvements made within the spirit and principles of the present invention should be included in the scope of protection of the present invention.

Claims

1. A radiation-insensitive single-mode optical fiber, characterized in that, It includes a core layer, a first cladding layer, and a second cladding layer arranged in sequence from the inside to the outside; or, it includes a core layer, a first buffer layer, a first cladding layer, a second buffer layer, and a second cladding layer arranged in sequence from the inside to the outside; The core layer, the first buffer layer, the first cladding layer, the second buffer layer, and the second cladding layer are all quartz glass doped with cerium element, aluminum element, and fluorine element.

2. The radiation-insensitive single-mode optical fiber according to claim 1, wherein The content of the cerium element is constant at A1 in the radial direction of the core layer, constant at A2 in the radial direction of the first cladding layer, and constant at A3 in the radial direction of the second cladding layer; The content of the aluminum element is constant at B1 in the radial direction of the core layer, constant at B2 in the radial direction of the first cladding layer, and constant at B3 in the radial direction of the second cladding layer; The content of the fluorine element is constant at C1 in the radial direction of the core layer, constant at C2 in the radial direction of the first cladding layer, and constant at C3 in the radial direction of the second cladding layer.

3. The radiation-insensitive single-mode optical fiber according to claim 1 or 2, wherein The content of the cerium element linearly changes from A1 to A2 from the inside to the outside in the radial direction of the first buffer layer, and linearly changes from A2 to A3 from the inside to the outside in the radial direction of the second buffer layer; The content of the aluminum element linearly changes from B1 to B2 from the inside to the outside in the radial direction of the first buffer layer, and linearly changes from B2 to B3 from the inside to the outside in the radial direction of the second buffer layer; The content of the fluorine element linearly changes from C1 to C2 from the inside to the outside in the radial direction of the first buffer layer, and linearly changes from C2 to C3 from the inside to the outside in the radial direction of the second buffer layer.

4. The radiation-insensitive single-mode optical fiber according to claim 2 or 3, wherein The magnitude relationship of the content of the cerium element in different layer structures is A1 > A3 > A2; The magnitude relationship of the content of the aluminum element in different layer structures is B1 > B3 > B2; The magnitude relationship of the content of the fluorine element in different layer structures is C2 ≥ C3 > C1.

5. The radiation-insensitive single-mode optical fiber according to any one of claims 2-4, wherein In the core layer, the content of the cerium element A1 is 1000-2500 ppm, the content of the aluminum element B1 is 3000-6000 ppm, and the content of the fluorine element C1 is 3000-15000 ppm; In the first cladding layer, the content of the cerium element A2 is 50-500 ppm, the content of the aluminum element B2 is 200-1600 ppm, and the content of the fluorine element C2 is 10000-20000 ppm; In the second cladding layer, the content of the cerium element A3 is 500-2000 ppm, the content of the aluminum element B3 is 1600-5000 ppm, and the content of the fluorine element C3 is 5000-20000 ppm.

6. The radiation-insensitive single-mode optical fiber according to claim 5, characterized in that, The ratio of the content of the cerium element in the core layer to that in the first cladding layer A1 / A2 is 5-20; and / or, The ratio of the content of the cerium element in the core layer to that in the second cladding layer A1 / A3 is 1-5.

7. The radiation-insensitive single-mode optical fiber according to any one of claims 1-6, wherein The relative refractive index difference Δn1 between the core layer and pure silica glass is 0.2% - 0.5%; The relative refractive index difference Δn2 between the first cladding and pure silica glass is -0.25% to -0.6%; The relative refractive index difference Δn3 between the second cladding and pure silica glass is -0.1% to 0.1%.

8. The radiation-insensitive single-mode optical fiber according to any one of claims 1-6, characterized in that The core diameter is 7.5 to 10 μm, the first buffer layer diameter is 10 to 13 μm, the first cladding diameter is 18 to 24 μm, the second buffer layer diameter is 24 to 30 μm, and the second cladding diameter is 124 to 126 μm.

9. The radiation-insensitive single-mode optical fiber according to any one of claims 1-6, characterized in that The maximum stress difference ΔP of the cross-section of the radiation-insensitive single-mode optical fiber is less than 10 MPa.

10. The radiation-insensitive single-mode optical fiber according to any one of claims 1-6, characterized in that, Under the environment of a total radiation dose of 100 kGy, the attenuation of the radiation-insensitive single-mode optical fiber in the 1310 nm and 1550 nm bands is less than 20 dB / km.

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