Broadband anti-bending multimode optical fiber and preparation method thereof

Abstract

The invention relates to a broadband bending-resistant multimode optical fiber and a preparation method thereof, the refractive index profile of a core layer is in a gradually-changed parabola shape, the distribution index alpha is 1.95-2.65, the radius R1 of the core layer is 12-35 microns, the delta 1max is 0.9%-1.4%, the relative refractive index difference delta 1min at the R1 position of the edge of the core layer is-0.16%--0.06%, cladding layers comprise an inner cladding layer, a first sunken cladding layer, a second sunken cladding layer and an outer cladding layer from inside to outside in sequence, the inner cladding layer is sequentially provided with a first inner cladding layer and a second inner cladding layer from inside to outside, the single-side width (R4-R3) of the first sunken cladding layer is 1.5-9.0 [mu] m, delta 4 is-1.1%--0.60%, the single-side width (R5-R4) of the second sunken cladding layer is 1.0-3.0 [mu] m, delta 5 is-1.0%--0.55%, the radius R6 of the outer cladding layer is 60-65 [mu] m, and delta 6 is-0.12-0.12%. The core cladding is reasonable in structural design, has the excellent characteristics of high bandwidth, strong bending resistance and low attenuation, and is high in transmission efficiency and excellent in long-term stability and reliability.

Description

Technical Field

[0001] This invention relates to a broadband bend-resistant multimode optical fiber and its fabrication method. The optical fiber has characteristics such as high bandwidth, strong bend resistance, and low attenuation, and belongs to the field of optical communication technology. Background Technology

[0002] In recent years, multimode fiber has become a high-quality solution for short-distance, high-speed transmission networks due to its low system cost advantage. It has been widely used in large data centers, AI computing power network centers, local area office centers, high-performance computing centers, storage area networks, and vehicle optoelectronics. With the widespread commercialization of 400Gb / s and the steady evolution towards 800Gb / s and even 1.6Tb / s, not only are the typical bandwidth values ​​of optical fibers being challenged, but also higher requirements are being placed on the deployment of larger capacity, smaller size, and higher density fiber-to-optical-cable integrated network interconnections.

[0003] Studies have shown that when the refractive index profile of a multimode fiber is constant, it often exhibits high bandwidth performance only for a specific wavelength window. When the application window of the fiber shifts to a larger or smaller wavelength, the bandwidth performance decreases significantly. Therefore, from an application perspective, it is necessary to improve the design of multimode fibers to ensure compatibility with existing OM3 / OM4 (Pro / Ultra) / OM5 multimode fibers, while also possessing low bandwidth-wavelength sensitivity to meet the application requirements of WDM technology within a certain wavelength range. Furthermore, it should achieve excellent bending resistance and high optical transmission efficiency at a smaller diameter to adapt to the new demands of transmission technology advancements on multimode fibers. Based on this, when designing the refractive index profile of a bending-insensitive small-diameter multimode fiber, a method of adding a low-refractive-index region to the fiber cladding is used to limit the leakage of higher-order modes and minimize signal loss. However, the introduction of a depressed cladding causes changes in the propagation constant of higher-order modes near the core edge, resulting in increased modal dispersion of the fiber.

[0004] In addition, small-diameter multimode optical fibers will inevitably bend to varying degrees during use. When the optical fiber is subjected to large bending stress for a long time, it will inevitably reduce the service life of the optical fiber and reduce the transmission performance. Therefore, small-diameter multimode optical fibers should have good bending resistance to meet the needs of different occasions. Summary of the Invention

[0005] To facilitate the explanation of this invention, some terms are defined as follows: Liner: A high-purity glass tube used in the preparation of mandrels; Mandrel: A prefabricated component containing a core layer and a partial cladding layer; Radius: The distance between the outer boundary of this layer and the center point; Core layer: The central part of the optical fiber's cross-section, i.e., the main light-guiding area of ​​the optical fiber; Cladding: includes inner cladding, recessed cladding and outer cladding. Inner cladding refers to the annular region in the cross-section of the optical fiber that is immediately adjacent to the core. Recessed cladding refers to the annular region in the cross-section of the optical fiber that is immediately adjacent to the inner cladding. Outer cladding refers to the annular region in the cross-section of the optical fiber that is immediately adjacent to the recessed cladding. Refractive index profile: The relationship between the refractive index of glass and its radius in an optical fiber or optical fiber preform (including the core rod), i.e., the α profile, which satisfies the following power-law function of refractive index distribution: r Where n1 is the refractive index of the fiber axis; r is the distance from the fiber axis; a is the fiber core radius; α is... Distribution index; 0 represents the refractive index of the fiber core relative to the cladding.

[0006] Relative refractive index i :

[0007] Where, n i n is the refractive index at a distance i from the center of the fiber core; n0 is the refractive index of pure silicon dioxide.

[0008] Numerical aperture: NA = n0 * (Δ1 - Δ2) 1 / 2 = n0*(2Δ) 1 / 2 .

[0009] The contribution of fluorine (F): The difference in refractive index (ΔF) between fluorine-doped (F) quartz glass and pure quartz glass, which represents the amount of fluorine (F) doping.

[0010] The contribution of boron (B): The difference in refractive index (ΔB) between fluorine-doped (F) quartz glass and pure quartz glass, which represents the amount of boron (B) doping.

[0011] Germanium (Ge) contribution: The amount of germanium (Ge) doping is expressed by the difference in refractive index (ΔGe) between germanium-doped quartz glass and pure quartz glass.

[0012] High-density cable: This usually refers to a high-core-count optical cable that can accommodate more cores per unit area or volume.

[0013] The technical problem to be solved by the present invention is to provide a broadband bend-resistant multimode optical fiber and its preparation method, which addresses the shortcomings of the existing technology. The fiber has a reasonable core-cladding structure design and has excellent characteristics of high bandwidth, strong bend resistance, and low attenuation. It also has high transmission efficiency and excellent long-term stability and reliability.

[0014] ​The technical solution adopted by this invention to solve the above-mentioned problems is as follows: It includes a core layer and a cladding layer, the refractive index profile of the core layer is a gradually changing parabolic shape (α power function distribution), characterized in that the core layer distribution index α is 1.95~2.65, the core layer radius R1 is 12~35μm, and the maximum relative refractive index difference Δ at the center of the core layer is... 1max The relative refractive index difference Δ at the core edge R1 is 0.9%~1.4%. 1min The refractive index is -0.16% to -0.06%. The cladding layers, from the inside out, consist of an inner cladding layer, a first depressed cladding layer, a second depressed cladding layer, and an outer cladding layer. The inner cladding layers, from the inside out, are configured as an inner cladding layer I and an inner cladding layer II. The inner cladding layer I increases linearly with increasing radius. The width of one side of the inner cladding layer I (R2-R1) is 0.8~1.4μm, and the relative refractive index difference Δ2 is -0.15% to -0.04%. The width of one side of the inner cladding layer II (R3-R2) is 1.0~3.0μm, and the relative refractive index difference Δ3 is -0.12% to -0.02%. The width of one side of the first depressed cladding layer (R4-R3) is 1.5~9.0μm, and the relative refractive index difference Δ4 is ​​-1.1%. The second cladding layer has a single-sided width (R5-R4) of 1.0~3.0μm and a relative refractive index difference Δ5 of -1.0%~-0.55%. The outer cladding layer has a radius of 60~65μm and a relative refractive index difference Δ6 of -0.12~0.12%.

[0015] According to the above scheme, the relative refractive index difference of the inner two layers is in the shape of a concave curve, and the relative refractive index difference of the second concave layer gradually decreases with the increase of radius in the form of a step curve.

[0016] According to the above scheme, the relative refractive index difference at the starting position of the inner double layer is equal to the relative refractive index difference at the ending position of the inner single layer.

[0017] According to the above scheme, the ratio of the single-side width of the inner two-layer inner packaging to the single-side width of the inner one-layer inner packaging is 1.5~3.

[0018] According to the above scheme, the relative refractive index difference Δ2 of the inner layer is less than or equal to the relative refractive index difference Δ3 of the inner two layers, that is, Δ2≤Δ3.

[0019] According to the above scheme, the relative refractive index difference Δ4 of the first depressed cladding is -0.8% to 0.7%, and the relative refractive index difference Δ5 of the second depressed cladding is -0.68% to -0.58%.

[0020] According to the above scheme, the ratio of the single-side width of the first recessed cladding layer to the single-side width of the second recessed cladding layer is 3 to 5.

[0021] According to the above scheme, the relative refractive index difference Δ4 of the first depressed cladding is less than or equal to the relative refractive index difference Δ5 of the second depressed cladding, that is, Δ4≤Δ5.

[0022] According to the above scheme, the relative refractive index difference Δ between the inner layer one and the inner layer two is... 2（3） The difference in relative refractive index Δ between the first and second depressed cladding layers is greater than the difference in refractive index between the two layers. 4（5） , that is, Δ 2（3） >Δ 4（5） .

[0023] According to the above scheme, the core layer is a silicon dioxide glass layer co-doped with germanium and fluorine (Ge / F), or germanium, phosphorus, and fluorine (Ge / P / F), or germanium, boron, and fluorine (Ge / B / F). Fluorine in the core layer acts as a negative dopant, and the amount of fluorine doping increases from the center of the core layer to its edge. The contribution of fluorine doping at the center of the core layer is Δ. F0 The contribution of fluorine doping at the core edge is -0.12% to -0.04%, Δ. F1 The range is -0.48% to -0.04%.

[0024] According to the above scheme, the inner first layer is a silicon dioxide glass layer co-doped with germanium, fluorine, and phosphorus, with a phosphorus doping contribution ΔP of ≤0.12%, and the inner second layer is a silicon dioxide glass layer co-doped with germanium, fluorine, and boron, with a boron doping contribution ΔB of ≤0.06%.

[0025] According to the above scheme, the first calyx is a fluorine- and boron-doped silica glass layer, with the boron doping contribution ΔB ≤ 0.05%.

[0026] According to the above scheme, the outer cladding layer is a pure silica glass layer, or a silica glass layer doped with one or more of the following dopants: aluminum, calcium, magnesium, titanium, zirconium, iron, cobalt, nickel, manganese, copper, lithium, sodium, potassium, boron, chlorine, etc. The silica (SiO2) glass layer has an aluminum (Al) content of 1~60ppm, a total metal element content of ≤80ppm, and a chlorine (Cl) content of 1300~2300ppm.

[0027] According to the above scheme, the numerical aperture of the optical fiber is 0.190~0.215.

[0028] According to the above scheme, the outer coating layer is coated with a resin coating layer, and the resin coating layer includes an inner coating layer and an outer coating layer from the inside to the outside. The thickness of the inner coating layer (R7-R6) is 10μm~30μm, and the thickness of the outer coating layer (R8-R7) is 10μm~35μm.

[0029] According to the above scheme, the resin coating layer is a polyurethane acrylate coating layer. The inner coating layer has a Young's modulus ≤ 0.25 MPa and a glass transition temperature (Tg) ≤ -50℃, while the outer coating layer has a Young's modulus ≥ 1050 MPa. The Young's modulus is measured using a D lamp cured in a nitrogen atmosphere at an energy of 1 J / cm² for a 75-micron film, under test conditions of 23℃ and 50% relative humidity. Furthermore, the coating peel strength of the optical fiber is ≤ 0.9 N.

[0030] According to the above scheme, the thickness of the inner coating layer (R7-R6) is 20μm ~ 25μm, and the thickness of the outer coating layer (R8-R7) is 25μm ~ 30μm.

[0031] According to the above scheme, the DMD Inner Mask (5~18μm) and DMD Outer Mask (0~23μm) of the optical fiber are both less than or equal to 0.20 ps / m; the DMD Interval Mask is less than or equal to 0.15 ps / m; under preferred conditions, the DMD Inner Mask (5~18μm) and DMD Outer Mask (0~23μm) of the optical fiber are both less than or equal to 0.10 ps / m, and the DMD Interval Mask is less than or equal to 0.08 ps / m.

[0032] According to the above scheme, the full injection bandwidth (BW) of the optical fiber has 3500MHz at a wavelength of 850nm. km and above, with 2000MHz at a wavelength of 950nm. km and above, with 500MHz at a wavelength of 1300nm. km and above.

[0033] Furthermore, the fiber's full injection bandwidth (BW) has 6500MHz at a wavelength of 850nm. km and above, with 3500MHz at a wavelength of 950nm. km and above, with 700MHz at a wavelength of 1300nm. km and above.

[0034] According to the above scheme, the effective mode bandwidth (EMB) of the optical fiber has 6000MHz at a wavelength of 850nm. km or more; with 6500MHz at a wavelength of 860nm. km or more; with 6000MHz at a wavelength of 870nm. km or more; has 3600MHz at a wavelength of 910nm. km or more; with 2500MHz at a wavelength of 953nm. km or more; with 2400MHz at a wavelength of 980nm. km or more; with 2200MHz at a wavelength of 1060nm. km or more.

[0035] Furthermore, the effective mode bandwidth (EMB) of the optical fiber has 7000MHz at a wavelength of 850nm. km or more; with 7500MHz at a wavelength of 860nm. km or more; with 7000MHz at a wavelength of 870nm. km or more; has 4000MHz at a wavelength of 910nm. km or more; with 2800MHz at a wavelength of 953nm. km or more; with 2500MHz at a wavelength of 980nm. km or more; with 2300MHz at a wavelength of 1060nm. km or more.

[0036] According to the above scheme, the additional bending loss caused by bending the optical fiber twice with a bending radius of 7.5 mm at a wavelength of 850 nm is less than or equal to 0.08 dB; the additional bending loss caused by bending the optical fiber twice with a bending radius of 7.5 mm at a wavelength of 1300 nm is less than or equal to 0.08 dB; the additional bending loss caused by bending the optical fiber twice with a bending radius of 15 mm is less than or equal to 0.02 dB; and the additional bending loss caused by bending the optical fiber twice with a bending radius of 15 mm at a wavelength of 1300 nm is less than or equal to 0.03 dB.

[0037] According to the above scheme, the optical fiber has an attenuation value of less than or equal to 2.1dB at a wavelength of 850nm and an attenuation value of less than or equal to 0.37dB at a wavelength of 1300nm.

[0038] According to the above scheme, the fusion splice loss of the optical fiber at a wavelength of 850nm is less than or equal to 0.01dB, and the fusion splice loss at a wavelength of 1300nm is less than or equal to 0.01dB.

[0039] The technical solution of the optical fiber fabrication method of this invention is as follows: A pure quartz glass liner is clamped and fixed at both ends by rotating chucks on a plasma chemical vapor deposition (PCVD) lathe with a certain rotation angle. The liner is placed in a holding furnace at 1000℃~1300℃ and passes through a high-frequency microwave resonant cavity. The process reactants required for core rod fabrication are formed into stable gaseous substances through a constant temperature and pressure (typically 45±2℃, 0.8±0.1 atm) evaporation system. These gaseous substances are then introduced into the liner from one end of the lathe's rotating chuck through a constant temperature (typically 20℃±2℃) pipe. The gaseous reactants silicon tetrachloride (SiCl4) and... A certain amount of dopants such as germanium (GeCl4), fluorine (C2F6), phosphorus (POCl3), and boron (BCl3) are introduced into O2. Doping is carried out by high-energy plasma excited by a high-frequency microwave resonant cavity in a multi-element doping manner, and finally uniformly deposited in a glassy state on the inner wall of the liner tube. According to the cross-sectional structure design requirements, the cladding and core layers of the optical fiber are deposited sequentially. After deposition, it is fused into a solid core rod by a high-temperature (1800℃~2300℃) fusion lathe. The core rod is cleaned, etched, and dried, and then combined with a matching ferrule to form a multimode optical fiber preform. Finally, the preform is drawn into an optical fiber by a drawing equipment.

[0040] According to the above scheme, the sequential deposition of the cladding and core layer includes the sequential deposition of a second depressed cladding, a first depressed cladding, an inner cladding, and a core layer.

[0041] The beneficial effects of this invention are as follows: 1. By optimizing the cross-sectional structure design and material composition, the bandwidth performance of multimode fiber is improved, the differential mode delay (DMD) performance of multimode fiber is enhanced, and the bandwidth-wavelength sensitivity of the fiber is reduced, thereby improving the optical transmission bandwidth performance. 2. Through the double inner cladding and double recessed cladding design, the refractive index distortion caused by high-order modes, element diffusion, and stress inhomogeneity between the fiber core, inner cladding, and the first and second recessed cladding is effectively avoided, thus significantly improving the fiber's bending insensitivity and attenuation performance. 3. This invention employs a multi-element gradient doping method of germanium, fluorine, phosphorus, and boron in the inner cladding and a step doping method of fluorine and boron in the recessed cladding. This avoids diffusion caused by the concentration difference of doping elements between layers. The reasonable doping combination and concentration ratio between the inner cladding and adjacent recessed cladding, and the optimized material composition and viscosity matching of the inner cladding and recessed cladding, improve the smoothness of fiber stress changes, reduce fiber cross-sectional distortion caused by stress inhomogeneity, and achieve compatibility between high-speed communication and small-diameter fiber performance. 4. The optical fiber of this invention is not only compatible with existing OM3 / OM4 (Pro / ultra) / OM5 multimode fibers, but also supports wavelength division multiplexing (WDM) technology in the 850nm~1060nm wavelength range. 5. Through coating material and thickness design, the outer diameter of the optical fiber of this invention is reduced, meeting the needs of miniaturized high-density cables and effectively saving on the challenges of complex and limited space cabling. Simultaneously, this optical fiber exhibits good stability, maintaining high transmission efficiency and strong stability under long-term operating conditions. 6. The manufacturing method of this invention is simple, low-cost, highly feasible and operable, suitable for large-scale production, and applicable to vehicle-mounted optical communication networks and miniaturized optical devices, adapting to the network demands of rapidly increasing data traffic. Attached Figure Description

[0042] Figure 1 This is a schematic diagram of the radial cross-section structure of an optical fiber according to an embodiment of the present invention.

[0043] Figure 2 This is a schematic diagram of the refractive index profile according to an embodiment of the present invention.

[0044] Figure 3 This is a differential mode delay diagram for a comparative example of the present invention.

[0045] Figure 4 This is a differential mode delay diagram according to an embodiment of the present invention. Detailed Implementation

[0046] Specific embodiments will be given below to further illustrate the present invention.

[0047] The preparation process of this invention is as follows: A pure quartz glass liner is clamped and fixed at both ends by rotating chucks on a plasma chemical vapor deposition (PCVD) lathe with a certain rotation angle. The liner is placed in a holding furnace at 1000℃~1300℃ and passes through a high-frequency microwave resonant cavity. The process reactants required for mandrel preparation are formed into stable gaseous substances through a constant temperature and pressure (typically 45±2℃, 0.8±0.1 atm) evaporation system. These gaseous substances are then introduced into the liner through a constant temperature (typically 20℃±2℃) pipe from one end of the lathe's rotating chuck. A certain amount of germanium (GeCl4), fluorine (C2F6), and phosphorus (PO4) are introduced into the gaseous reactants silicon tetrachloride (SiCl4) and O2. Dopants such as Cl3 and boron (BCl3) are deposited via high-energy plasma excited by a high-frequency microwave resonant cavity in a multi-element doping manner to adjust the corresponding refractive index. The gas flow rate is precisely controlled by a mass flow controller (MFC) throughout the process, and finally, the optical fiber is uniformly deposited in a glassy state on the inner wall of the liner tube. According to the cross-sectional structure design requirements, the optical fiber is deposited sequentially with a second depressed cladding, a first depressed cladding, an inner cladding, and a core layer. After deposition, the core is fused into a solid core rod by a high-temperature (1800℃~2300℃) fusion shrinking lathe. The core rod is then cleaned, etched, and dried, and then prepared into a multimode optical fiber preform by RIT sleeve process and / or OVD process. The preform is then drawn into an optical fiber by a drawing equipment.

[0048] The resulting optical fiber consists of a core and a cladding. The refractive index profile of the core exhibits a parabolic distribution following an α-power exponential function, with a distribution exponent α ranging from 1.95 to 2.65. The core radius R1 ranges from 12 to 35 μm, and the maximum relative refractive index difference Δ at the core center is [not specified]. 1max The relative refractive index difference Δ at the core edge R1 is 0.9%~1.4%. 1min The value ranges from -0.16% to -0.06%. The cladding layers, from the inside out, consist of an inner cladding layer, a first recessed cladding layer, a second recessed cladding layer, and an outer cladding layer.

[0049] The inner cladding comprises an inner cladding layer 11 and an inner cladding layer 12 arranged sequentially from the inside out. The refractive indices of the inner cladding layer 11 and the inner cladding layer 12 exhibit a linearly increasing trend followed by a step curve as the fiber radius increases. Specifically, the relative refractive index difference of the inner cladding layer 1 increases linearly with the fiber radius, while the relative refractive index difference of the inner cladding layer 2 exhibits a concave curve, and the relative refractive index difference at the beginning and end positions of the inner cladding layer 2 and inner cladding layer 1 is equal. The double-layer profile material composition and doping design of the inner cladding layer effectively avoids excessive leakage of higher-order modes in the fiber core, improves the transmission performance of higher-order modes in the core, and simultaneously improves refractive index distortion caused by element diffusion between different layers of the core and inner cladding, as well as microcracks inside the fiber caused by stress inhomogeneity. This significantly improves the fiber's bending insensitivity and attenuation performance, reduces bandwidth-wavelength sensitivity, and enhances the long-term stability of the fiber. The width of one side (R2-R1) of the inner cladding layer 11 is 0.8~1.4μm, and the relative refractive index difference Δ2 is -0.15%~-0.04%. The width of one side (R3-R2) of the inner cladding layer 12 is 1.0~3.0μm, and the relative refractive index difference Δ3 is -0.12%~-0.02%. The ratio of the width of the inner cladding layer 12 to the width of the inner cladding layer 12 is 1.5~3. This width ratio range is designed because if the relative refractive index difference Δ2 of the inner cladding layer 12 is too low or the width R2-R1 is too large, it will lead to an excessive number of leaked modes, thereby reducing the bandwidth of the optical fiber. The relative refractive index difference Δ2 of the inner cladding layer 12 is less than or equal to the relative refractive index difference Δ3 of the inner cladding layer 12, i.e., Δ2≤Δ3. The advantage of the concave curve design of the inner cladding with a relative refractive index difference is that it allows for a smooth transition of refractive index between the inner cladding and the concave cladding, reducing microcracks at the interface caused by stress changes, thereby improving the long-term reliability of the optical fiber.

[0050] The refractive indices of the first and second recessed cladding layers 21 and 22 decrease linearly with increasing radius, initially exhibiting a linear, isotropic curve followed by a step-decreasing curve. The double-recessed cladding design optimizes the stress difference between the core, inner cladding, and recessed cladding layers, while reducing the fiber bandwidth's sensitivity to wavelength, resulting in good bend insensitivity and high bandwidth performance. The deeper and wider refractive index of the first recessed cladding layer compared to the second effectively increases bend resistance. The step-decreasing, gently decreasing refractive index difference of the second recessed cladding layer effectively mitigates microcracks and other defects caused by uneven stress between the recessed and outer cladding layers, effectively offsetting damage to small-diameter fibers caused by external pressure and extending service life in confined spaces and harsh environments. The width of the first recessed cladding 21 (R4-R3) is 1.5~9.0 μm, and the relative refractive index difference Δ4 is ​​-1.1%~-0.60%. Preferably, the relative refractive index difference Δ4 of the first recessed cladding is -0.8%~-0.7%. The width of the second recessed cladding (R5-R4) is 1.0~3.0 μm, and the relative refractive index difference Δ5 is -1.0%~-0.55%. Preferably, the relative refractive index difference Δ5 of the second recessed cladding 22 is -0.68%~-0.58%. The ratio of the width of the first recessed cladding to the width of the second recessed cladding is in the range of 3~5, which can effectively improve the bending performance of the optical fiber. The relative refractive index Δ4 of the first recessed cladding 21 is less than or equal to the relative refractive index Δ5 of the second recessed cladding 22, i.e., Δ4≤Δ5. This design effectively reduces the interfacial stress between the outer cladding and the recessed cladding, thereby improving the stability of the optical fiber during long-term use.

[0051] The core layer is a silicon dioxide glass layer co-doped with germanium and fluorine (Ge / F), or germanium, phosphorus, and fluorine (Ge / P / F), or germanium, boron, and fluorine (Ge / B / F). Fluorine acts as a negative dopant in the core layer, and the amount of fluorine doping increases from the center to the edge. The contribution of fluorine doping at the center of the core layer is Δ. F0 The contribution of fluorine doping at the core edge is -0.12% to -0.04%, Δ. F1The concentration is -0.48% to -0.04%. The inner cladding layer is co-doped with germanium, fluorine, phosphorus, and boron. Preferably, when the first layer 11 of the inner cladding layer has a gradually increasing region and is co-doped with germanium, fluorine, and phosphorus, the phosphorus doping contribution ΔP is ≤0.12%, and when the second layer 12 of the inner cladding layer has a gradually decreasing region and is co-doped with germanium, fluorine, and boron, the boron doping contribution ΔB is ≤0.06%. The depressed cladding layer is co-doped with fluorine and boron. Preferably, when the first depressed cladding layer 21 is co-doped with fluorine and boron, the boron doping contribution ΔB is ≤0.05%. The inner cladding employs a multi-element gradient doping design with germanium, fluorine, phosphorus, and boron, while the recessed cladding is designed with fluorine and boron doping. This avoids refractive index distortion caused by diffusion due to differences in dopant concentrations between layers, better matches the reasonable doping combination and concentration ratio between the inner cladding and the adjacent recessed cladding, optimizes the material composition and viscosity matching of the inner and recessed cladding, improves the smoothness of fiber stress changes, reduces fiber profile distortion caused by stress unevenness, and achieves compatibility between high-speed communication and small-diameter fiber performance.

[0052] The outer cladding layer is a pure silica glass layer, or a silica glass layer doped with one or more of the following dopants: aluminum, calcium, magnesium, titanium, zirconium, iron, cobalt, nickel, manganese, copper, lithium, sodium, potassium, boron, chlorine, etc. The silica (SiO2) glass layer has an aluminum (Al) content of 1~60ppm, a total metal element content of ≤80ppm, and a chlorine (Cl) content of 1300~2300ppm.

[0053] The optical fiber has an outer cladding coated with a cured polymer resin coating. This coating consists of an inner coating and an outer coating. In a typical structure, the inner coating is in direct contact with the glass fiber. The inner coating is designed as a softer coating to buffer and dissipate stress distortion in the fiber caused by the forces exerted on the outer coating and its surface, thereby minimizing stress in the glass fiber. The outer coating is designed as a harder coating to buffer against damage caused by external forces during cabling, handling, and installation. Preferably, the refractive index of the inner coating is greater than that of the glass fiber cladding region, thus stripping erroneous optical signals from the fiber core. The inner coating is designed to maintain sufficient adhesion to the glass fiber while also providing good peelability and leaving no residue during thermal aging. Furthermore, the coating peel force of the optical fiber is ≤0.9N. Preferably, the polymer material of the resin coating is polyurethane acrylate. Furthermore, the inner coating layer has a Young's modulus ≤ 0.25 MPa and a glass transition temperature (Tg) ≤ -50℃, while the outer coating layer has a Young's modulus ≥ 1050 MPa. The Young's modulus was measured using a D lamp cured in a nitrogen atmosphere at an energy of 1 J / cm² for a 75-micron film, under conditions of 23℃ and 50% relative humidity. The coating layer curing was performed using a UV lamp and / or LED light source. The thickness of the inner coating layer (R7-R6) is 10 μm to 30 μm, preferably 20 μm to 25 μm. The thickness of the outer coating layer (R8-R7) is 10 μm to 35 μm, preferably 25 μm to 30 μm. This double-layer coating design ensures that the optical fiber exhibits good mechanical properties while maintaining excellent high and low temperature performance during the fabrication of small-volume, high-density cables.

[0054] According to the present invention, an array of optical fiber preforms was prepared and drawn into optical fibers. The structural parameters and performance parameters of the optical fibers are shown in Table 1. In the table, Δ2 and Δ5 are values ​​that are approximately in the middle or slightly below the center. Table 1: Core structure parameters and main performance parameters of optical fibers

[0055] The numerical aperture NA was measured according to the IEC 60793-1-43-2001 (NA) method.

[0056] The full injection bandwidth was measured according to the IEC60793-1-41 method, and the test was conducted under full injection conditions.

[0057] Differential mode delay (DMD) is measured according to IEC 60793-1-49. The length of the fiber under test is 1000m ± 20%. A probe single-mode fiber is connected between the fiber under test and the light source to limit the incident light mode of the fiber under test to single-mode. The incident light pulse width is less than or equal to 100ps. The light source is incident perpendicularly to the end face of the fiber under test, and the light is scanned radially along the end face. The time difference between the fastest and slowest light pulses arriving at the output end of the fiber under test is measured, which is the differential mode delay. At the same time, using these DMD data, calculations are performed to simulate a series of specified input modes to obtain the effective mode bandwidth (EMBc).

[0058] Macrobending loss is measured according to the FOTP-62 (IEC-60793-1-47) method. The fiber under test is wound with a certain diameter (e.g., 10mm, 15mm, 20mm, 30mm, etc.) once, and then the loop is released. The change in optical power before and after the loop is measured, and this is used as the macrobending loss of the fiber. During the test, an encircled flux injection condition is used. The encircled flux injection condition can be obtained by the following method: a 2-meter-long section of ordinary 50-micron core diameter multimode fiber is fused to the front end of the fiber under test, and a 25mm diameter loop is wound in the middle of this fiber. When full injection light is injected into this fiber, the fiber under test is in the encircled flux injection condition.

[0059] Attenuation and / or fusion loss are measured according to the IEC 60793-1-40-2001 method, which is the attenuation A(λ) and attenuation coefficient α(λ) between two cross sections 1 and 2 separated by a distance L on a fiber segment at wavelength λ.

[0060] Experiments show that the high-speed communication and narrow-diameter optical fiber manufactured according to the technical solution of the present invention has good compatibility with ordinary multimode optical fiber, and has high bandwidth and strong bending resistance. It has good high-speed communication and transmission performance in wavelengths of 850nm~980nm and 1060nm. In particular, due to its miniaturized design and performance advantages, it is widely used in vehicle systems and various complex and narrow spaces under long-term working conditions. The optical fiber has good stability.

Claims

1. A broadband bend-resistant multimode optical fiber, comprising a core layer and a cladding layer, wherein the refractive index profile of the core layer is a graded parabolic shape, characterized in that... The core layer distribution index α is 1.95~2.65, the core layer radius R1 is 12~35μm, and the maximum relative refractive index difference Δ at the core layer center is... 1max The relative refractive index difference Δ at the core edge R1 is 0.9%~1.4%. 1min The refractive index is -0.16% to -0.06%. The cladding layers, from the inside out, consist of an inner cladding layer, a first depressed cladding layer, a second depressed cladding layer, and an outer cladding layer. The inner cladding layers, from the inside out, are configured as an inner cladding layer I and an inner cladding layer II. The inner cladding layer I increases linearly with increasing radius. The width of one side of the inner cladding layer I (R2-R1) is 0.8~1.4μm, and the relative refractive index difference Δ2 is -0.15% to -0.04%. The width of one side of the inner cladding layer II (R3-R2) is 1.0~3.0μm, and the relative refractive index difference Δ3 is -0.12% to -0.02%. The width of one side of the first depressed cladding layer (R4-R3) is 1.5~9.0μm, and the relative refractive index difference Δ4 is ​​-1.1%. The second cladding layer has a single-sided width (R5-R4) of 1.0~3.0μm and a relative refractive index difference Δ5 of -1.0%~-0.55%. The outer cladding layer has a radius of 60~65μm and a relative refractive index difference Δ6 of -0.12~0.12%.

2. The broadband bend-resistant multimode optical fiber according to claim 1, characterized in that... The relative refractive index difference of the inner two layers is in the shape of a concave curve, and the relative refractive index difference of the second concave layer gradually decreases with the increase of radius in the form of a step curve.

3. The broadband bend-resistant multimode optical fiber according to claim 2, characterized in that... The relative refractive index difference at the starting position of the inner double layer is equal to the relative refractive index difference at the ending position of the inner single layer.

4. The broadband bend-resistant multimode optical fiber according to claim 1 or 2, characterized in that... The ratio of the single-side width of the inner two-layer inner packaging to the single-side width of the inner one-layer inner packaging is 1.5 to 3.

5. The broadband bend-resistant multimode optical fiber according to claim 1 or 2, characterized in that... The relative refractive index difference Δ2 of the inner first layer is less than or equal to the relative refractive index difference Δ3 of the inner second layer, that is, Δ2≤Δ3.

6. The broadband bend-resistant multimode optical fiber according to claim 1 or 2, characterized in that... The relative refractive index difference Δ4 of the first depressed cladding is -0.8% to 0.7%, and the relative refractive index difference Δ5 of the second depressed cladding is -0.68% to -0.58%.

7. The broadband bend-resistant multimode optical fiber according to claim 1 or 2, characterized in that... The ratio of the single-side width of the first recessed cladding layer to the single-side width of the second recessed cladding layer is 3 to 5.

8. The broadband bend-resistant multimode optical fiber according to claim 7, characterized in that... The relative refractive index difference Δ4 of the first depressed cladding is less than or equal to the relative refractive index difference Δ5 of the second depressed cladding, i.e., Δ4≤Δ5.

9. The broadband bend-resistant multimode optical fiber according to claim 1 or 2, characterized in that... The relative refractive index difference Δ between the inner single-layer and double-layer encapsulation 2（3） The difference in relative refractive index Δ between the first and second depressed cladding layers is greater than the difference in refractive index between the two layers. 4（5） , that is, Δ 2（3） >Δ 4（5） .

10. The broadband bend-resistant multimode optical fiber according to claim 1 or 2, characterized in that... The core layer is a silicon dioxide glass layer co-doped with germanium and fluorine, or germanium, phosphorus and fluorine, or germanium, boron and fluorine. Fluorine acts as a negative dopant in the core layer, and the amount of fluorine doping increases from the center to the edge. The contribution of fluorine doping at the center of the core layer is Δ. F0 The contribution of fluorine doping at the core edge is -0.12% to -0.04%, Δ. F1 The range is -0.48% to -0.04%.

11. The broadband bend-resistant multimode optical fiber according to claim 1 or 2, characterized in that... The inner encapsulation layer is a silicon dioxide glass layer co-doped with germanium, fluorine, and phosphorus, with a phosphorus doping contribution ΔP of ≤0.12%. The inner encapsulation layer is a silicon dioxide glass layer co-doped with germanium, fluorine, and boron, with a boron doping contribution ΔB of ≤0.06%.

12. The broadband bend-resistant multimode optical fiber according to claim 1 or 2, characterized in that... The first calyx is a fluorine- and boron-doped silica glass layer, with a boron doping contribution ΔB ≤ 0.05%.

13. The broadband bend-resistant multimode optical fiber according to claim 1 or 2, characterized in that... The outer cladding layer is a pure silica glass layer, or a silica glass layer doped with one or more of the following dopants: aluminum, calcium, magnesium, titanium, zirconium, iron, cobalt, nickel, manganese, copper, lithium, sodium, potassium, boron, chlorine, etc. The aluminum content of the doped silica glass layer is 1~60ppm, the total metal content is ≤80ppm, and the chlorine content is 1300~2300ppm.

14. The broadband bend-resistant multimode optical fiber according to claim 1 or 2, characterized in that... The numerical aperture of the optical fiber is 0.190~0.

215.

15. The broadband bend-resistant multimode optical fiber according to claim 1 or 2, characterized in that... The outer coating is coated with a resin coating layer, which includes an inner coating layer and an outer coating layer from the inside to the outside. The thickness of the inner coating layer (R7-R6) is 10μm~30μm, and the thickness of the outer coating layer (R8-R7) is 10μm~35μm.

16. The broadband bend-resistant multimode optical fiber according to claim 15, characterized in that... The resin coating is a polyurethane acrylate coating. The inner coating has a Young's modulus ≤ 0.25 MPa and a glass transition temperature (Tg) ≤ -50℃. The outer coating has a Young's modulus ≥ 1050 MPa. The coating peel force of the optical fiber is ≤ 0.9 N.

17. The broadband bend-resistant multimode optical fiber according to claim 15, characterized in that... The thickness of the inner coating layer (R7-R6) is 20μm to 25μm, and the thickness of the outer coating layer (R8-R7) is 25μm to 30μm.

18. The broadband bend-resistant multimode optical fiber according to claim 1 or 2, characterized in that... The DMD InnerMask (5~18μm) and DMD Outer Mask (0~23μm) of the optical fiber are both less than or equal to 0.20 ps / m; the DMD Interval Mask is less than or equal to 0.15 ps / m.

19. The broadband bend-resistant multimode optical fiber according to claim 1 or 2, characterized in that... The optical fiber has a full injection bandwidth of 3500MHz at a wavelength of 850nm. km and above, with 2000MHz at a wavelength of 950nm. km and above, with 500MHz at a wavelength of 1300nm. km and above.

20. The broadband bend-resistant multimode optical fiber according to claim 1 or 2, characterized in that... The effective mode bandwidth 2 of the optical fiber has 6000MHz at a wavelength of 850nm. km or more; with 6500MHz at a wavelength of 860nm. km or more; with 6000MHz at a wavelength of 870nm. km or more; has 3600MHz at a wavelength of 910nm. km or more; with 2500MHz at a wavelength of 953nm. km or more; with 2400MHz at a wavelength of 980nm. km or more; with 2200MHz at a wavelength of 1060nm. km or more.

21. The broadband bend-resistant multimode optical fiber according to claim 1 or 2, characterized in that... The optical fiber has an additional bending loss of less than or equal to 0.08 dB at a wavelength of 850 nm with a bending radius of 7.5 mm for two turns, less than or equal to 0.08 dB at a wavelength of 1300 nm with a bending radius of 7.5 mm for two turns, less than or equal to 0.02 dB at a bending radius of 15 mm for two turns, and less than or equal to 0.03 dB at a wavelength of 1300 nm with a bending radius of 15 mm for two turns.

22. The broadband bend-resistant multimode optical fiber according to claim 1 or 2, characterized in that... The optical fiber has an attenuation of less than or equal to 2.1 dB at a wavelength of 850 nm and an attenuation of less than or equal to 0.37 dB at a wavelength of 1300 nm.

23. The broadband bend-resistant multimode optical fiber according to claim 1 or 2, characterized in that... The optical fiber has a fusion loss of less than or equal to 0.01 dB at a wavelength of 850 nm and a fusion loss of less than or equal to 0.01 dB at a wavelength of 1300 nm.

24. A method for fabricating a broadband multimode optical fiber according to any one of claims 1-23, characterized in that... A pure quartz glass liner is clamped and fixed at both ends by rotating chucks on a plasma chemical vapor deposition (PCVD) lathe with a certain rotation angle. The liner is placed in a holding furnace at 1000℃~1300℃ and passes through a high-frequency microwave resonant cavity. The process reactants required for mandrel preparation are formed into a stable gaseous state through a constant temperature and pressure evaporation system. This gaseous state is then introduced into the liner through a constant temperature pipe from one end of the lathe's rotating chuck. Dopants GeCl4, C2F6, and PO are introduced into the gaseous reactants silicon tetrachloride and O2. One or more of Cl3 and BCl3 are doped and deposited via high-energy plasma excited by a high-frequency microwave resonant cavity in a multi-element doping manner, and finally uniformly deposited in a glassy state on the inner wall of the liner tube. The optical fiber is deposited with cladding and core layer in sequence according to the cross-sectional structure design requirements. After deposition, it is fused into a solid core rod by a high-temperature fusion shrinking lathe at 1800℃~2300℃. The core rod is cleaned, etched and dried, and then combined with a matching ferrule to form a multimode optical fiber preform. Finally, the preform is drawn into an optical fiber by a drawing equipment.

25. The method for fabricating broadband bend-resistant multimode optical fiber according to claim 24, characterized in that... The sequential deposition of the coating and core layer includes the sequential deposition of a second depressed coating, a first depressed coating, an inner coating, and a core layer; the temperature and pressure of the process reactants in the constant temperature and pressure evaporation system are 45±2℃ and 0.8±0.1atm, respectively.

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