Vehicle-mounted multimode optical fiber

Abstract

The application provides a vehicle-mounted multimode optical fiber, which comprises a core layer and a cladding layer covering the core layer; the core layer comprises a first core layer and a second core layer covering the first core layer; the refractive index profile of the first core layer satisfies a graded refractive index distribution, and the minimum relative refractive index difference of the first core layer is greater than 0; the refractive index profile of the second core layer satisfies a linearly decreasing distribution, the maximum relative refractive index difference of the second core layer is equal to the minimum relative refractive index difference of the first core layer, and the minimum relative refractive index difference of the second core layer is less than 0. High-bandwidth transmission in the wavelength range of 850nm to 980nm is realized, and the comprehensive performance requirements of a multimode optical fiber for a vehicle-mounted high-speed data communication system are met.

Description

Technical Field

[0001] This invention relates to the field of optical communication technology, and in particular to a vehicle-mounted multimode optical fiber. Background Technology

[0002] In recent years, the increasing intelligence of automobiles (autonomous driving, in-vehicle entertainment, LiDAR, etc.) has placed extremely high demands on the data bandwidth and reliability of in-vehicle networks. Traditional copper cables can no longer meet the growing demand for high-speed data exchange, and fiber optic Ethernet, with its advantages of large capacity, low loss, and resistance to electromagnetic interference, is gradually becoming the mainstream solution for in-vehicle communication.

[0003] However, the refractive index profile of ordinary OM3 fiber only contains a single graded-index core and a simple cladding. When the operating wavelength shifts from 850nm to 980nm, the mode field distribution of higher-order modes extends towards the edge of the core, resulting in the effective mode bandwidth of traditional OM3 fiber in the 980nm window often being less than 1000MHz·km, far below the 2000MHz·km required by the IEEE 802.3cz standard, which cannot meet the high bandwidth requirements of dual-window systems in vehicles. Summary of the Invention

[0004] This invention provides a vehicle-mounted multimode optical fiber that adjusts the propagation constants of various higher-order modes by using the linearly graded refractive index of the second core layer. Combined with the structural design of continuous refractive indices between the first and second core layers, it solves the problem of asynchronous propagation of higher-order and lower-order modes and the easy occurrence of additional mode coupling in a wide wavelength range, and achieves high-bandwidth transmission in the wavelength range of 850nm to 980nm.

[0005] This invention provides a vehicle-mounted multimode optical fiber, comprising a core layer and a cladding layer covering the core layer; The core layer includes a first core layer and a second core layer covering the first core layer; The refractive index profile of the first core layer satisfies a graded refractive index distribution, and the minimum relative refractive index difference of the first core layer is greater than 0. The refractive index profile of the second core layer satisfies a linear decreasing distribution, the maximum relative refractive index difference of the second core layer is equal to the minimum relative refractive index difference of the first core layer, and the minimum relative refractive index difference of the second core layer is less than 0.

[0006] Optionally, the radius of the first core layer is 16.5 to 20.5 μm, the refractive index distribution index α of the first core layer is 1.95 to 2.15, and the maximum relative refractive index difference Δn1 of the first core layer is 1.25% to 1.85%.

[0007] Optionally, the outer radius of the second core layer is 23.50 to 27.5 μm, and the absolute value of the linear slope k of the second core layer is 0.027 to 0.114% / μm.

[0008] Optionally, the relative refractive index difference Δn2 at the junction of the second core layer and the first core layer is 0.45% to 0.65%.

[0009] Optionally, the first core layer is germanium and fluorine co-doped silicon dioxide; wherein the fluorine doping concentration of the first core layer gradually increases from the inside to the outside; The second core layer is germanium and fluorine co-doped silicon dioxide; wherein, the fluorine doping concentration of the second core layer increases linearly from the inside to the outside, and the germanium doping concentration of the second core layer decreases linearly from the inside to the outside.

[0010] Optionally, the cladding layer includes, from the inside out, a first recessed cladding layer, a second recessed cladding layer, and an outer cladding layer. The first recessed cladding has a constant negative relative refractive index difference that does not change with radius; The second cladding layer has a constant negative relative refractive index difference, and the relative refractive index difference of the first cladding layer is greater than the relative refractive index difference of the second cladding layer.

[0011] Optionally, the cladding layer includes, from the inside out, a first recessed cladding layer, a second recessed cladding layer, and an outer cladding layer. The relative refractive index difference Δn of the first depressed cladding 3.1 The value is -0.30% to -0.60%, and the outer radius R3 is 34.5 to 38.5 μm; The relative refractive index difference Δn of the second depressed cladding 3.2 The value ranges from -0.70% to -1.10%, and the outer radius R4 ranges from 46.5 to 50.5 μm. The outer radius R5 of the outer cladding layer is 62.50 μm.

[0012] Optionally, the angle A between the refractive index profile of the second core layer and the horizontal axis is 70º~85º.

[0013] Optionally, the optical fiber has an effective mode bandwidth of ≥5700MHz·km at a wavelength of 850nm and an effective mode bandwidth of ≥2000MHz·km at a wavelength of 980nm.

[0014] Optionally, the optical fiber is wound twice with a bending radius of 7.5 mm, and the additional loss at the 850 nm macrobending is ≤0.1 dB.

[0015] This invention provides a vehicle-mounted multimode optical fiber. It utilizes a parabolic refractive index distribution in the first core layer to provide a basic high bandwidth, a linearly graded refractive index in the second core layer to compensate for the dispersion shift of higher-order modes over a wide wavelength range, and a double-layered recessed cladding to enhance bending resistance. This overall design achieves high bandwidth, low loss, excellent bending resistance, and high transmission efficiency within a wide wavelength range of 850nm to 980nm, meeting the comprehensive performance requirements of high-speed vehicle-mounted data communication systems for multimode optical fibers. Attached Figure Description

[0016] Figure 1 A schematic diagram of the relative refractive index difference of a vehicle-mounted multimode optical fiber provided in an embodiment of the present invention; Figure 2 This is a schematic cross-sectional view of a vehicle-mounted multimode optical fiber provided in an embodiment of the present invention. Detailed Implementation

[0017] To make the objectives, technical solutions, and advantages of this invention clearer, the technical solutions of this invention will be fully described below with reference to the accompanying drawings in the embodiments of this invention, through specific implementation methods. Obviously, the described embodiments are only some, not all, of the embodiments of this invention. All other embodiments obtained by those skilled in the art based on the embodiments of this invention without creative effort fall within the protection scope of this invention.

[0018] Traditional ordinary multimode optical fiber is mainly optimized for 850nm data center applications and has obvious shortcomings in the vehicle environment: on the one hand, its bandwidth is severely attenuated in the 980nm window, which cannot meet the IEEE 802.3cz standard requirement that both windows (850nm and 980nm) be ≥2000MHz·km; on the other hand, ordinary optical fiber has limited bending resistance and high bandwidth-wavelength sensitivity, making it difficult to adapt to the complex working conditions of wide temperature range and small bending radius in vehicle environments.

[0019] Patent CN121679796A proposes an improved scheme: reducing differential mode delay by "filtering" higher-order modes, which improves the bandwidth of the 980nm window to some extent. However, the refractive index step between the edge of the first core layer and the second core layer will induce additional mode dispersion, and the filtering mechanism will cause some higher-order mode energy to be lost, reducing transmission efficiency. Furthermore, under this scheme, the bandwidth-wavelength sensitivity of the optical fiber is still relatively high, and the performance degrades significantly after deviating from the design wavelength, making it difficult to stably support future applications with wider wavelengths.

[0020] To address the shortcomings of the existing technologies, this invention provides a novel automotive multimode fiber based on mode dispersion compensation rather than mode filtering. Through a linearly graded second core layer design, it eliminates abrupt changes in refractive index, retains and compensates for the time delay of all modes, thereby achieving high bandwidth in both 850nm and 980nm dual windows, and realizing low bending loss, low bandwidth-wavelength sensitivity and high transmission efficiency, meeting the stringent requirements of automotive optical communication.

[0021] Figure 1 This is a schematic diagram of the relative refractive index difference profile of a vehicle-mounted multimode optical fiber provided in an embodiment of the present invention. Figure 2 This is a schematic cross-sectional view of a vehicle-mounted multimode optical fiber provided in an embodiment of the present invention. Figure 1 The horizontal axis represents the radius r, in μm; the vertical axis represents the relative refractive index difference Δ, in %. (Reference) Figure 1 and Figure 2 The vehicle-mounted multimode optical fiber provided in this embodiment can be specifically applied to vehicle communication systems such as vehicle Ethernet, sensor data transmission, and infotainment systems. It enables high-bandwidth, low-latency optical signal transmission in the complex electromagnetic environment inside a vehicle, meeting the requirements of high-speed in-vehicle data communication. (Reference) Figure 1 This invention provides a vehicle-mounted multimode optical fiber, including a core layer 10 and a cladding 20 covering the core layer 10; The core layer 10 includes a first core layer 11 and a second core layer 12 covering the first core layer 11; The refractive index profile of the first core layer 11 satisfies a graded refractive index distribution, and the minimum relative refractive index difference of the first core layer 11 is greater than 0. The refractive index profile of the second core layer 12 satisfies a linear decreasing distribution. The maximum relative refractive index difference of the second core layer 12 is equal to the minimum relative refractive index difference of the first core layer 11. The minimum relative refractive index difference of the second core layer 12 is less than 0.

[0022] In this context, the first core layer 11 can be understood as the main light-guiding region of the fiber core; the second core layer 12 can be understood as the annular region immediately surrounding the first core layer 11. The relative refractive index difference Δ can be understood as the relative difference between the refractive index of the core layer and the refractive index of the cladding; the graded refractive index distribution (α-power distribution) can be understood as a radial distribution in which the refractive index of the core layer smoothly decreases from the center to the periphery (parabolic); the linear decreasing distribution can be understood as a radial distribution in which the refractive index of the second core layer 12 linearly and monotonically decreases from the inner boundary to the outer boundary.

[0023] Specifically, the refractive index of the first core layer 11 exhibits a parabolic shape (α-power distribution), smoothly decreasing from its central maximum value Δn1 to Δn2 at the edge. Its cross-section satisfies the following formula: Where α is the power exponent (α≈2), and R1 is the radius of the first core layer 11. The maximum refractive index is at the axis (r=0) of the first core layer 11, where r is the radial coordinate. The refractive index distribution index is... This represents the maximum relative refractive index difference. The first core layer 11 is the region in the optical fiber used to provide the basic bandwidth. The parabolic distribution ensures that the low-order and high-order modes have nearly equal time delays near the 850nm wavelength, which is fundamental to achieving high bandwidth. The minimum relative refractive index difference of the first core layer 11 is greater than 0, meaning that the refractive index at the edge of the first core layer 11 is still higher than the refractive index of the cladding, ensuring that the optical signal is confined within the first core layer 11 for transmission.

[0024] The second core layer 12 is closely attached to the outer side of the first core layer 11, located in an annular region with radii R1 to R2. Its inner boundary is directly connected to the edge of the first core layer 11, and its outer boundary is connected to the inner wall of the cladding. The refractive index of the second core layer 12 decreases linearly and monotonically in the radial direction, smoothly decreasing from the positive value Δn2 at the inner boundary to the negative value at the outer boundary. The entire curve spans the reference refractive index of pure silicon dioxide (i.e., the "0 axis" where Δ=0%), and there are no abrupt changes. Its profile satisfies the formula: Where k is a positive constant (linear slope). for The refractive index difference at the edge of the fiber core. The refractive index difference decreases linearly with radius from the core boundary outwards, representing the radial distance away from the core boundary. The maximum relative refractive index difference of the second core layer 12 is equal to the minimum relative refractive index difference of the first core layer 11 (i.e., refractive index continuity at the inner boundary), while the minimum relative refractive index difference of the second core layer 12 is less than 0 (i.e., the refractive index at the outer boundary is lower than the cladding refractive index). The second core layer 12 compensates for the additional dispersion generated by higher-order modes during wavelength shifts (e.g., from 850 nm to 980 nm) by smoothing the gradient refractive index.

[0025] Those skilled in the art can adjust the α value of the first core layer 11 and the linear slope k of the second core layer 12 to optimize the dispersion compensation effect according to specific transmission wavelength and bandwidth requirements. These variations all fall within the protection scope of this application.

[0026] This application adjusts the propagation constant of higher-order modes by using a linearly graded refractive index of the second core layer, enabling multiple higher-order modes to remain synchronized with lower-order modes over a wide wavelength range. Simultaneously, the refractive indices of the first and second core layers are continuous, avoiding additional mode coupling. This achieves mode dispersion compensation rather than mode filtering, thereby maintaining high bandwidth transmission performance in the 850nm to 980nm wavelength range.

[0027] Optionally, the radius of the first core layer 11 is 16.5 to 20.5 μm, the refractive index distribution index α of the first core layer 11 is 1.95 to 2.15, and the maximum relative refractive index difference Δn1 of the first core layer 11 is 1.25% to 1.85%.

[0028] Specifically, the radius R1 of the first core layer 11 is set to 16.5–20.5 μm (e.g., 18.5 μm). This radius range ensures that the optical fiber has a sufficiently large core diameter near the 850 nm wavelength to support multimode transmission, while also taking into account the bending performance of the optical fiber. The refractive index distribution index α is set to 1.95–2.15. This α value is close to the ideal parabolic distribution (α=2), thereby enabling the low-order mode and the high-order mode to achieve optimal equal-delay transmission near the 850 nm wavelength, thus achieving high bandwidth performance. The maximum relative refractive index difference Δn1 is set to 1.25%–1.85%, providing sufficient light guiding capability to confine the optical signal within the first core layer 11 for transmission, while also providing a suitable refractive index margin for dispersion compensation of the second core layer 12. Through the optimized combination of the above parameters, the vehicle-mounted multimode fiber can support a high effective bandwidth at a wavelength of 850nm, and in conjunction with the linear graded refractive index profile of the second core layer 12, it can also maintain good bandwidth performance in the extended band of 980nm wavelength.

[0029] Those skilled in the art can adjust the values ​​of R1, α, and Δn1 within the above range to optimize the transmission performance of the optical fiber according to the specific vehicle communication rate and transmission distance requirements. These variations all fall within the protection scope of this application.

[0030] Optionally, the outer radius of the second core layer 12 is 23.50 to 27.5 μm, and the absolute value of the linear slope k of the second core layer 12 is 0.027 to 0.114% / μm.

[0031] Among them, the outer radius R2 of the second core layer 12 can be understood as the outer boundary radius of the second core layer 12 (i.e., the distance from the fiber core center to the interface between the second core layer 12 and the cladding); the absolute value of the linear slope k can be understood as the rate at which the refractive index of the second core layer 12 decreases linearly in the radial direction (in % / μm).

[0032] Specifically, the outer radius R2 of the second core layer 12 is set to 23.5–27.5 μm. R2–R1, i.e., the thickness of the second core layer 12, is approximately 3–11 μm. The second core layer 12 is used to accommodate the field distribution of higher-order modes and provide sufficient dispersion compensation space. The absolute value of the linear slope k of the second core layer 12 is set to 0.027–0.114% / μm. The absolute value of the linear slope k can be understood as the rate at which the refractive index of the second core layer 12 decreases from a positive value at the inner boundary to a negative value at the outer boundary: when the value of k is small, the refractive index decreases gently, and the compensation effect is mild, suitable for applications with small wavelength shifts; when the value of k is large, the refractive index decreases steeply, and the compensation effect is significant, suitable for applications with large wavelength shifts.

[0033] Those skilled in the art can adjust the values ​​of R2 and k within the above range to optimize the transmission performance of the optical fiber according to the specific operating wavelength range and dispersion compensation requirements. These variations all fall within the protection scope of this application.

[0034] Optionally, the relative refractive index difference Δn2 at the junction of the second core layer 12 and the first core layer 11 is 0.45% to 0.65%.

[0035] The junction between the second core layer 12 and the first core layer 11 can be understood as the interface where the edge of the first core layer 11 (r=R1) coincides with the inner boundary of the second core layer 12; the relative refractive index difference Δn2 can be understood as the difference between the refractive index of the edge of the first core layer 11 (which is also the inner boundary of the second core layer 12) and the refractive index of the cladding at this junction.

[0036] Specifically, the relative refractive index difference Δn2 at the junction of the second core layer 12 and the first core layer 11 is set to 0.45%–0.65%. The value of Δn2 is equal to the minimum relative refractive index difference at the edge of the first core layer 11, and also the maximum relative refractive index difference at the inner boundary of the second core layer 12. This ensures that the refractive index of the first core layer 11 and the second core layer 12 is continuous at the junction (without abrupt changes), avoiding additional mode coupling and signal loss caused by refractive index discontinuities. The range of Δn2 ensures that there is still a sufficient refractive index difference (positive value) at the edge of the first core layer 11 to constrain the transmission of higher-order modes within the first core layer 11, while also providing an appropriate starting value for the linearly decreasing distribution of the second core layer 12. This allows the second core layer 12 to smoothly transition its refractive index from this positive value to a negative value at the outer boundary, thereby achieving dispersion compensation for higher-order modes over a wide wavelength range. If Δn2 is too low (<0.45%), the light guiding capability at the edge of the first core layer 11 will be weakened, and higher-order modes may leak prematurely; if Δn2 is too high (>0.65%), the second core layer 12 will need a larger linear slope to transition to a negative value within a limited thickness, which may introduce additional mode coupling or manufacturing difficulties.

[0037] Those skilled in the art can adjust the value of Δn2 within the above range to optimize the transmission performance of the optical fiber according to specific bandwidth and dispersion compensation requirements, and these variations all fall within the protection scope of this application.

[0038] Optionally, the first core layer 11 is germanium and fluorine co-doped silicon dioxide; wherein the fluorine doping concentration of the first core layer 11 gradually increases from the inside to the outside; the second core layer 12 is germanium and fluorine co-doped silicon dioxide; wherein the fluorine doping concentration of the second core layer 12 increases linearly from the inside to the outside, and the germanium doping concentration of the second core layer 12 decreases linearly from the inside to the outside.

[0039] In this context, germanium (Ge) doping can be understood as adding germanium oxide (GeO2) to a silicon dioxide (SiO2) matrix to increase the refractive index of the quartz glass (positive doping effect), making the core layer refractive index higher than that of the pure silicon dioxide cladding, thus guiding optical signals. Fluorine (F) doping can be understood as adding fluorine to a silicon dioxide matrix to reduce the refractive index of the quartz glass (negative doping effect), thus achieving a parabolic or linearly graded refractive index profile. Those skilled in the art can control the concentration distribution of germanium and fluorine doping by adjusting the flow rates of GeCl4 and SiF4 (or CF4) gases in the chemical vapor deposition or plasma chemical vapor deposition process according to the target refractive index profile; these variations all fall within the scope of protection of this application.

[0040] Specifically, in the automotive multimode optical fiber provided in this embodiment of the invention, the first core layer 11 is made of germanium- and fluorine-doped silicon dioxide material. The fluorine doping concentration gradually increases from the center to the edge of the first core layer 11, causing the refractive index to smoothly decrease from its maximum value at the center to Δn2 at the edge, achieving a parabolic (α-power exponent) refractive index distribution. Simultaneously, the germanium doping concentration is adjusted synergistically from the center outwards, with the germanium and fluorine doping concentrations at the edge of the first core layer 11 jointly determining the value of Δn2. The second core layer 12 also uses germanium- and fluorine-doped silicon dioxide material. The fluorine doping concentration linearly increases from the inner boundary to the outer boundary of the second core layer 12, causing the refractive index to linearly decrease radially. The germanium and fluorine doping together achieve a linearly gradual distribution of the refractive index of the second core layer 12, smoothly decreasing from a positive value Δn2 at the inner boundary to a negative value at the outer boundary. At the inner boundary, the germanium and fluorine doping concentrations of the first core layer 11 and the second core layer 12 are continuous (without abrupt changes), ensuring the continuity of the refractive index; at the outer boundary, the fluorine doping concentration of the second core layer 12 reaches its maximum, making the refractive index lower than the cladding refractive index (Δ<0), thus achieving dispersion compensation for higher-order modes.

[0041] Optionally, the cladding 20 comprises, from the inside out, a first recessed cladding 21, a second recessed cladding 22, and an outer cladding 23. The first recessed cladding 21 has a constant negative relative refractive index difference that does not change with the radius. The second recessed cladding 22 has a constant negative relative refractive index difference, and the relative refractive index difference of the first recessed cladding 21 is greater than that of the second recessed cladding 22. The first recessed cladding 21 can be understood as the inner cladding region immediately adjacent to the outer boundary of the second core layer 12, possessing a constant negative relative refractive index difference (refractive index lower than that of pure silicon dioxide). The second recessed cladding 22 can be understood as the intermediate cladding region located between the first recessed cladding 21 and the outer cladding 23, also possessing a constant negative relative refractive index difference, but with a further reduction in refractive index to form a deeper refractive index depression structure. The outer cladding 23 can be understood as the outermost cladding of the optical fiber, typically pure silicon dioxide (refractive index reference layer).

[0042] Specifically, in the vehicle-mounted multimode optical fiber provided in this embodiment of the invention, the cladding, from the inside out, includes a first recessed cladding 21, a second recessed cladding 22, and an outer cladding 23. The first recessed cladding 21 has a constant negative relative refractive index difference (e.g., Δn). 3.1 The negative refractive index (NRI) ranges from -0.30% to -0.60%, and this value does not change with the radius (i.e., a step-type depression). Its inner boundary is directly connected to the outer boundary of the second core layer 12, causing the negative refractive index value (minimum relative refractive index difference) at the outer boundary of the second core layer 12 to further decrease to an even more negative value, enhancing the binding ability of higher-order modes. The second depressed cladding layer 22 also has a constant negative relative refractive index difference (e.g., Δn). 3.2 The refractive index difference of the first depressed cladding 21 is greater than that of the second depressed cladding 22, meaning the refractive index of the second depressed cladding 22 is lower than that of the first depressed cladding 21, forming a double-depressed structure. The first depressed cladding 21 provides the main bending resistance. When the fiber bends, the optical field diffuses outward from the bend; the negative refractive index region causes the diffused higher-order modes to be "barriered" by the refractive index, thus guiding them back to the core layer and significantly reducing macro-bending loss. The second depressed cladding 22 further enhances the bending resistance while filtering out a very small number of residual higher-order modes. The stepped structure of the double-depressed cladding can more effectively suppress bending loss while avoiding mode distortion caused by an excessively deep single depressed layer. The outer cladding 23 is pure silicon dioxide, with its refractive index as a reference (Δ=0%), providing mechanical protection and structural support for the fiber.

[0043] Optionally, the cladding 20 includes, from the inside out, a first recessed cladding 21, a second recessed cladding 22, and an outer cladding 23; the relative refractive index difference Δn of the first recessed cladding 21 3.1 The relative refractive index difference Δn of the second depressed cladding 22 is -0.30% to -0.60%, and the outer radius R3 is 34.5 to 38.5 μm. 3.2 The outer radius is -0.70% to -1.10%, and the outer radius R4 is 46.5 to 50.5 μm; the outer radius R5 of the outer cladding 23 is 62.50 μm.

[0044] Among them, the relative refractive index difference Δn of the first depressed cladding 21 3.1 The refractive index difference between the first recessed cladding 21 and pure silicon dioxide can be understood as the difference in refractive index; the outer radius R3 of the first recessed cladding 21 can be understood as the radial thickness boundary of the first recessed cladding 21; the relative refractive index difference Δn of the second recessed cladding 22 can be understood as the difference in refractive index between the two cladding layers. 3.2 The refractive index difference between the second cladding 22 and pure silicon dioxide can be understood as the difference in refractive index. The outer radius R4 of the second cladding 22 can be understood as the radial thickness boundary of the second cladding 22. The outer radius R5 of the outer cladding 23 can be understood as the outermost radius of the optical fiber.

[0045] Specifically, in the vehicle-mounted multimode optical fiber provided in this embodiment of the invention, the cladding, from the inside out, includes a first recessed cladding 21, a second recessed cladding 22, and an outer cladding 23. The relative refractive index difference Δn of the first recessed cladding 21... 3.1 The relative refractive index difference Δn of the second depressed cladding 22 is -0.30% to -0.60%, with an outer radius R3 of 34.5 to 38.5 μm and a thickness of approximately R3-R2≈9-15 μm. 3.2 The variability is -0.70% to -1.10%, the outer radius R4 is 46.5 to 50.5 μm, and its thickness is approximately R4-R3≈10-14 μm. The outer radius R5 of the outer cladding 23 is 62.50 μm (that is, the cladding radius of a standard 50 μm core diameter multimode fiber is 62.5 μm, corresponding to an outer diameter of 125 μm).

[0046] Optionally, the angle A between the refractive index profile of the second core layer 12 and the horizontal axis is 70º~85º.

[0047] The angle A between the refractive index profile of the second core layer 12 and the horizontal axis can be understood as the angle between the line on which the refractive index of the second core layer 12 decreases linearly with the radius and the radius axis. This angle is determined by the linear slope k (tanA=k).

[0048] Specifically, in the vehicle-mounted multimode fiber provided in this embodiment of the invention, the angle A between the refractive index profile of the second core layer 12 and the horizontal axis is set to 70°~85°. This angle range corresponds to the linear slope k. As can be seen from the previous embodiments, in a specific embodiment, k is 0.027~0.114% / μm, that is, tan70°≈2.75% / μm to tan85°≈11.43% / μm. When A is in the range of 70°~85°, the refractive index decrease rate of the second core layer 12 is moderate, which can provide sufficient dispersion compensation effect, so that the higher-order modes maintain close equal time delay with the lower-order modes in the wide wavelength range of 850nm to 980nm, and can avoid refractive index profile distortion or increased mode coupling caused by too fast a decrease rate (A>85°), while avoiding insufficient dispersion compensation or excessive thickness of the second core layer 12 caused by too slow a decrease rate (A<70°).

[0049] Optionally, the optical fiber has an effective mode bandwidth of ≥5700MHz·km at a wavelength of 850nm and an effective mode bandwidth of ≥2000MHz·km at a wavelength of 980nm.

[0050] The effective mode bandwidth can be understood as the product of the effective bandwidth that a multimode fiber can actually support at a specific wavelength and the transmission distance (unit: MHz·km), after considering factors such as light source wavelength shift, mode dispersion, and differential mode delay.

[0051] Specifically, in the vehicle-mounted multimode optical fiber provided in this embodiment of the invention, the effective mode bandwidth is ≥5700MHz·km at a wavelength of 850nm, indicating that the optical fiber has excellent high-bandwidth transmission capability at a wavelength of 850nm, which can meet the high bandwidth requirements of high-speed vehicle data communication (such as 10Gbps, 25Gbps Ethernet); at a wavelength of 980nm, the effective mode bandwidth is ≥2000MHz·km, indicating that the optical fiber still maintains high bandwidth performance at the 980nm wide-band extended wavelength, supporting the flexible operation of optical transceiver modules in a wide band range. The vehicle-mounted multimode optical fiber provided in this application can simultaneously support the transmission of multiple high-speed communication protocols (such as vehicle Ethernet, sensor data, and infotainment systems) on a single optical fiber link, meeting the requirements of vehicle communication systems for high bandwidth and multi-wavelength transmission.

[0052] Optionally, the fiber is wound twice with a bending radius of 7.5 mm, and the additional loss at the 850 nm macrobend is ≤0.1 dB.

[0053] Among them, macrobending additional loss can be understood as the extra transmission loss caused by the leakage of some optical signal from the core to the cladding when the optical fiber is bent; bending radius can be understood as a standardized bending test condition that simulates the bending of optical fiber in a narrow space in a vehicle environment.

[0054] Specifically, when wound twice with a bending radius of 7.5 mm, the macro-bending additional loss at 850 nm wavelength is ≤0.1 dB. This indicates that the automotive multimode fiber provided in this embodiment of the invention has difficulty leaking higher-order modes to the cladding 23 even with a small bending radius (7.5 mm), thereby controlling the bending additional loss to an extremely low level. This bending resistance enables the automotive multimode fiber to adapt to the complex wiring requirements within the limited space inside the vehicle, including small-radius bends in narrow spaces such as door hinges, behind the dashboard, and under the seats without significantly increasing transmission loss, ensuring the stable operation of the vehicle communication system under complex environments such as vibration and temperature changes.

[0055] Table 1 shows the structural parameters and performance test parameters of the embodiments of the present invention.

[0056] Table 1 To further illustrate the structural design and performance advantages of the automotive multimode fiber of this application, this application also provides a comparison table of structural parameters and performance test parameters for several embodiments. As shown in Table 1, Embodiments 1 to 5 respectively give the fiber structure parameters and corresponding performance test results under different combinations of refractive index profile parameters. All embodiments fall within the parameter range protected by the claims of this application.

[0057] Regarding structural parameters, the radius R1 of the first core layer 11 is in the range of 16.5–20.5 μm, the refractive index distribution index α is in the range of 1.95–2.15, and the maximum relative refractive index difference Δn1 is in the range of 1.25%–1.85%; the outer radius R2 of the second core layer 12 is in the range of 23.5–27.5 μm, the included angle A is in the range of 70°–85°, and the relative refractive index difference Δn2 at the junction of the first core layer 11 and the second core layer 12 is... Within the range of 0.45% to 0.65%; the outer radius R3 of the first depressed cladding 21 is within the range of 34.5 to 38.5 μm, and the relative refractive index difference Δn3.1 is within the range of -0.30% to -0.60%; the outer radius R4 of the second depressed cladding 22 is within the range of 46.5 to 50.5 μm, and the relative refractive index difference Δn3.2 is within the range of -0.70% to -1.10%; the outer radius R5 of the outer cladding 23 is 62.50 μm.

[0058] Regarding performance test results, the attenuation at 850nm was ≤2.20dB / km for all embodiments, and the attenuation at 980nm was ≤1.45dB / km, indicating that the optical fiber has low transmission loss across the entire wavelength range; the effective mode bandwidth (EMB) at 850nm was ≥5700MHz·km for all embodiments, and the effective mode bandwidth at 980nm was ≥2500MHz·km for all embodiments, indicating that the optical fiber has excellent bandwidth performance over a wide wavelength range; the additional loss of the 850nm macrobend with a bending radius of 7.5mm with two turns was ≤0.10dB for all embodiments, indicating that the optical fiber has excellent bending resistance.

[0059] Taking Example 4 as an example, the first core layer 11 has a radius R1 of 16.50 μm, a refractive index distribution index α of 2.01, and a maximum relative refractive index difference Δn1 of 1.38%. The second core layer 12 has an outer radius R2 of 27.00 μm, an included angle A of 85.00°, and Δn2 of 0.48%. The first depressed cladding 21 has a radius R3 of 35.50 μm and a Δn3.1 of -0.45%. The second depressed cladding 22 has a radius R4 of 47.00 μm and a Δn3.2 of -1.00%. This example achieves an effective mode bandwidth of 6890 MHz·km at 850 nm and an effective mode bandwidth of 3180 MHz·km at 980 nm, with a macro-bending loss of only 0.05 dB at 7.5 mm, demonstrating excellent overall performance.

[0060] The above embodiments demonstrate that the present application provides a basic high bandwidth through the parabolic refractive index distribution of the first core layer 11, compensates for the dispersion shift of higher-order modes in a wide band through the linearly graded refractive index of the second core layer 12, and enhances the bending resistance through the double-layered recessed cladding. The overall design can achieve high bandwidth, low loss, excellent bending resistance and high transmission efficiency in a wide band from 850nm to 980nm, meeting the comprehensive performance requirements of multimode optical fiber for vehicle high-speed data communication systems.

[0061] Note that the above description is merely a preferred embodiment of the present invention and the technical principles employed. Those skilled in the art will understand that the present invention is not limited to the specific embodiments described herein, and various obvious changes, readjustments, combinations, and substitutions can be made without departing from the scope of protection of the present invention. Therefore, although the present invention has been described in detail through the above embodiments, the present invention is not limited to the above embodiments, and may include many other equivalent embodiments without departing from the concept of the present invention, the scope of which is determined by the scope of the appended claims.

Claims

1. A vehicle-mounted multimode optical fiber, characterized in that, Includes a core layer and a cladding layer covering the core layer; The core layer includes a first core layer and a second core layer covering the first core layer; The refractive index profile of the first core layer satisfies a graded refractive index distribution, and the minimum relative refractive index difference of the first core layer is greater than 0. The refractive index profile of the second core layer satisfies a linear decreasing distribution, the maximum relative refractive index difference of the second core layer is equal to the minimum relative refractive index difference of the first core layer, and the minimum relative refractive index difference of the second core layer is less than 0.

2. The vehicle-mounted multimode optical fiber according to claim 1, characterized in that, The radius of the first core layer is 16.5 to 20.5 μm, the refractive index distribution index α of the first core layer is 1.95 to 2.15, and the maximum relative refractive index difference Δn1 of the first core layer is 1.25% to 1.85%.

3. The vehicle-mounted multimode optical fiber according to claim 1, characterized in that, The outer radius of the second core layer is 23.50 to 27.5 μm, and the absolute value of the linear slope k of the second core layer is 0.027 to 0.114% / μm.

4. The vehicle-mounted multimode optical fiber according to claim 1, characterized in that, The relative refractive index difference Δn2 at the junction of the second core layer and the first core layer is 0.45% to 0.65%.

5. The vehicle-mounted multimode optical fiber according to claim 1, characterized in that, The first core layer is germanium and fluorine co-doped silicon dioxide; wherein, the fluorine doping concentration of the first core layer gradually increases from the inside to the outside; The second core layer is germanium and fluorine co-doped silicon dioxide; wherein, the fluorine doping concentration of the second core layer increases linearly from the inside to the outside, and the germanium doping concentration of the second core layer decreases linearly from the inside to the outside.

6. The vehicle-mounted multimode optical fiber according to claim 1, characterized in that, The cladding layer, from the inside out, includes a first recessed cladding layer, a second recessed cladding layer, and an outer cladding layer. The first recessed cladding has a constant negative relative refractive index difference that does not change with radius; The second cladding layer has a constant negative relative refractive index difference, and the relative refractive index difference of the first cladding layer is greater than the relative refractive index difference of the second cladding layer.

7. The vehicle-mounted multimode optical fiber according to claim 6, characterized in that, The cladding layer, from the inside out, includes a first recessed cladding layer, a second recessed cladding layer, and an outer cladding layer. The relative refractive index difference Δn of the first depressed cladding 3.1 -0.30% to -0.60%, and the outer radius R3 is 34.5 to 38.5 μm; The relative refractive index difference Δn of the second depressed cladding 3.2 The value ranges from -0.70% to -1.10%, and the outer radius R4 ranges from 46.5 to 50.5 μm. The outer radius R5 of the outer cladding layer is 62.50 μm.

8. The vehicle-mounted multimode optical fiber according to claim 1, characterized in that, The angle A between the refractive index profile of the second core layer and the horizontal axis is 70º~85º.

9. The vehicle-mounted multimode optical fiber according to claim 1, characterized in that, The optical fiber has an effective mode bandwidth of ≥5700MHz·km at a wavelength of 850nm and an effective mode bandwidth of ≥2000MHz·km at a wavelength of 980nm.

10. The vehicle-mounted multimode optical fiber according to claim 1, characterized in that, The optical fiber is wound twice with a bending radius of 7.5 mm, and the additional loss at the 850 nm macrobending is ≤0.1 dB.

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