Ultra-low differential mode group delay few-mode optical fiber and preparation method thereof

Abstract

The invention belongs to the technical field of few-mode optical fibers, and discloses an ultralow differential mode group delay few-mode optical fiber and a preparation method thereof. The ultralow differential mode group delay few-mode optical fiber provided by the invention comprises a core layer structure, an inner cladding layer structure and an outer cladding layer from inside to outside, the core layer structure comprises a first core layer and a second core layer from inside to outside; the two core layers are provided with gradient sections, the distribution index alpha 1 of the first core layer is 1.5-1.9, and the distribution index alpha 2 of the second core layer is 1.4-1.9; the minimum relative refractive index difference 1 of the first core layer is 0.3% to 0.6%; the maximum relative refractive index difference of the first core layer and the maximum relative refractive index difference of the second core layer are the same and marked as 2, 2 is 0.6%-0.9%, and 2 > 1; the second core layer has a minimum relative refractive index difference 3 of-0.2% to-0.1%. According to the invention, extremely low differential mode group delay can be realized.

Description

Technical Field

[0001] This invention belongs to the field of few-mode fiber technology, and more specifically, relates to an ultra-low differential mode group delay few-mode fiber and its fabrication method. Background Technology

[0002] With the ever-increasing capacity demands of communication and big data services, network bandwidth requirements are escalating, and the capacity of optical transmission networks is gradually approaching the Shannon limit of a single optical fiber. Space division multiplexing (SDM) offers a potential solution to increase data rates by allowing few-mode fibers to transmit light in multiple modes. In other words, mode division multiplexing (MDM) technology based on few-mode fibers can increase transmission capacity several times over. For few-mode fibers, differential mode group delay is a crucial parameter for evaluating their transmission performance; the different effective refractive indices of different modes result in inter-mode delays.

[0003] Current differential mode group delay solutions utilize multiple-input multiple-output equalization (MIMO) for compensation, but this increases equalization complexity. For example, Chinese patent CN112702119A discloses a differential mode group delay compensation method based on optoelectronic fusion. This method calculates the delay difference between different modes and the fundamental mode in a few-mode fiber, adds redundant data of varying amounts at the device end, and performs a first compensation for the differential mode group delay of the few-mode fiber, ensuring that the optical signals corresponding to each mode theoretically arrive at the fiber optic terminal simultaneously. Then, the fundamental mode signals corresponding to different modes are individually fed into different micro-ring resonators, and the speed of light is controlled again by changing the radius of the micro-ring resonators, performing a second compensation for the differential mode group delay of the few-mode fiber. This method effectively reduces the impact of differential mode group delay on the few-mode fiber system, but it suffers from high equipment complexity and manufacturing costs, and cannot optimize differential mode group delay at the fiber level.

[0004] While existing improvements to few-mode fibers can reduce differential mode group delay (DMT) to some extent, they cannot achieve extremely low DMT. For example, Chinese patent CN113189702A discloses a few-mode fiber structure for reducing DMT, employing a special ridge waveguide structure to alter the power distribution of specific modes. This allows the energy of the supported transmission modes to be better confined around the fiber core, increasing the effective refractive index of some modes and thus reducing DMT. This profile design reduces DMT, but cannot achieve extremely low DMT. Another example is Chinese patent CN106772789A, which proposes a low nonlinear coefficient few-mode fiber with a gradually changing core refractive index. This enables three-mode few-mode operation with low nonlinear coefficient and low DMT in the C-band of optical fiber communication, and the nonlinear coefficient and DMT are flatly distributed within the C-band. This gradual distribution method can reduce differential mode group latency, but it cannot achieve extremely low differential mode group latency. Summary of the Invention

[0005] This invention provides an ultra-low differential mode group delay few-mode fiber and its fabrication method, thereby solving the problem that few-mode fibers in the prior art are difficult to achieve extremely low differential mode group delay.

[0006] This invention provides an ultra-low differential mode group delay few-mode fiber, comprising: a core structure, an inner cladding structure, and an outer cladding from the inside out; The core structure includes a first core layer and a second core layer from the inside to the outside; Both the first core layer and the second core layer have a gradient profile. The distribution index α1 of the first core layer ranges from 1.5 to 1.9, and the distribution index α2 of the second core layer ranges from 1.4 to 1.9. The minimum relative refractive index difference Δ1 of the first core layer ranges from 0.3% to 0.6%; the maximum relative refractive index difference of the first core layer is the same as that of the second core layer, denoted as Δ2, and the value of Δ2 ranges from 0.6% to 0.9%, and Δ2 > Δ1; the minimum relative refractive index difference Δ3 of the second core layer ranges from -0.2% to -0.1%.

[0007] Preferably, the inner cladding structure includes a first inner cladding layer, a second inner cladding layer, and a third inner cladding layer from the inside out; The relative refractive index difference of the first inner cladding layer is the same as the minimum relative refractive index difference Δ3 of the second core layer; The relative refractive index difference Δ4 of the second inner cladding layer ranges from 0.1% to 0.3%. The relative refractive index difference Δ5 of the third inner cladding layer ranges from -1.1% to -0.75%.

[0008] Preferably, the core layer structure is a silica glass layer co-doped with germanium, fluorine, and alkali metals, or the core layer structure is a silica glass layer co-doped with germanium and alkali metals; the contribution of the relative refractive index difference of germanium in the core layer structure is 0% to 1.0%, the alkali metal content is 50 ppm to 4000 ppm, and the alkali metal is one or more of lithium, sodium, potassium, and rubidium alkali metal ions.

[0009] Preferably, the radius R1 of the first core layer ranges from 1.5 μm to 3 μm, the radius R2 of the second core layer ranges from 8.5 μm to 10 μm, the radius R3 of the first inner cladding layer ranges from 11.5 μm to 13.5 μm, the radius R4 of the second inner cladding layer ranges from 13 μm to 17 μm, and R4 > R3, the radius R5 of the third inner cladding layer ranges from 20 μm to 25 μm, the outer cladding layer is a pure silica glass layer, and the radius R6 of the outer cladding layer ranges from 62.5 ± 2.5 μm.

[0010] Preferably, the first inner cladding layer is a germanium-fluorine co-doped silica glass layer, or the first inner cladding layer is a fluorine-doped silica glass layer; the contribution of the relative refractive index difference of fluorine in the first inner cladding layer is -0.3% to -0.1%. The second inner cladding layer is a germanium-fluorine co-doped silica glass layer, or the second inner cladding layer is a germanium-doped silica glass layer; the contribution of the relative refractive index difference of germanium in the second inner cladding layer is 0.2% to 0.4%. The third inner cladding is a fluorine-doped silica glass layer, and the contribution of the relative refractive index difference of fluorine in the third inner cladding is -1.1% to -0.75%.

[0011] Preferably, the differential group delay between the LP11 mode and the LP01 mode in the ultra-low differential mode group delay few-mode fiber is less than 1 ps / m.

[0012] Preferably, the effective area of ​​the LP01 mode in the ultra-low differential mode group delay few-mode fiber is 60 μm. 2 Up to 100μm 2 The effective area of ​​the LP11 mode is 110 μm. 2 Up to 150μm 2 .

[0013] Preferably, the LP01 mode in the ultra-low differential mode group delay few-mode fiber has a dispersion of 22 ps / (nm·km) at a wavelength of 1550 nm, and the LP11 mode has a dispersion of 21 ps / (nm·km) at a wavelength of 1550 nm.

[0014] Preferably, the attenuation of LP01 and LP11 in the ultra-low differential mode group delay few-mode fiber at a wavelength of 1550 nm is less than or equal to 0.20 dB / km. The ultra-low differential mode group delay few-mode fiber has a macrobending loss of 0.06dB or less when bent 10 times with a bending radius of R15mm at a wavelength of 1550nm, a macrobending loss of 0.18dB or less when bent once with a bending radius of R10mm, and a macrobending loss of 0.6dB or less when bent once with a bending radius of R7.5mm.

[0015] On the other hand, the present invention provides a method for fabricating an ultra-low differential mode group delay few-mode fiber as described above, comprising the following steps: An inner cladding structure and a core structure are sequentially deposited on the inner wall of a quartz liner using plasma chemical vapor deposition (PCVD). After deposition, the core is melted and shrunk to obtain a solid core rod. The solid mandrel is combined with the sleeve to form a preform; The preform is drawn to obtain an ultra-low differential mode group delay few-mode fiber.

[0016] One or more technical solutions provided in this invention have at least the following technical effects or advantages: (1) The core structure of the ultra-low differential mode group delay few-mode fiber provided by the present invention is a double parabolic structure, wherein the minimum relative refractive index difference of the first core layer is Δ1, the maximum relative refractive index difference of the first core layer is Δ2, the maximum relative refractive index difference of the second core layer is Δ2, and the minimum relative refractive index difference of the second core layer is Δ3; the distribution indices of the two core layers correspond to α1 and α2, respectively. Considering that although the traditional graded profile can reduce the differential mode delay, the high refractive index at the center can easily lead to excessive concentration of low-order modes, the first core layer in the present invention adopts a grooved profile structure, which can moderately reduce the refractive index near the axis, making the transmission path length between modes closer, thereby further reducing the delay difference between modes and improving the signal transmission rate and distance; at the same time, the second core layer in the present invention can precisely control the LP11 mode group velocity while increasing the effective area by adjusting the distribution index α2 value, so that the velocities of each mode group are close. Compared to existing few-mode fibers with only one distribution index, this invention sets two distribution indices (α1 and α2), enabling low differential mode group delay through their combined effect. Furthermore, α1 in this invention is set to a graded-ratio type; compared to a conventional step-index profile, the radial gradient of the refractive index achieves group velocity synchronization between different modes, fundamentally offsetting the time delay difference between modes. In summary, this invention employs a graded-ratio core profile and optimizes the distribution indices (including α1 and α2) to adjust the time delay of each mode in the few-mode fiber, achieving extremely low differential mode group delay.

[0017] (2) Based on the special core structure design, the present invention adopts a three-ring inner cladding structure and uses a specific doping method to shift the cladding dispersion curve upward, which can effectively offset the waveguide dispersion difference; the present invention also designs a fiber fluorine doped depression structure (i.e., the third inner cladding), which can significantly reduce the fiber's sensitivity to bending and vibration by reasonably controlling the effective refractive index difference. Attached Figure Description

[0018] Figure 1 This is a schematic diagram of the refractive index profile of a few-mode fiber with ultra-low differential mode group delay provided in an embodiment of the present invention. Detailed Implementation

[0019] To better understand the above technical solutions, the following will provide a detailed explanation of the technical solutions in conjunction with the accompanying drawings and specific implementation methods.

[0020] To facilitate the description of the invention, the following terms are defined: The relative refractive index difference is the difference between the relative refractive index of each layer of the optical fiber (excluding the cladding) and pure silicon dioxide.

[0021] Contribution of relative refractive index difference to germanium (Ge) doping Defined by the following equation: ×100% in, The change in refractive index of silica glass caused by germanium doping in pure silica without other dopants, where... This is the refractive index of the outer cladding layer, i.e., the refractive index of pure silicon dioxide.

[0022] Contribution of relative refractive index difference to fluorine (F) doping Defined by the following equation: ×100% in, The change in refractive index of silica glass caused by fluorine doping in pure silica without other dopants, where... This represents the refractive index of the outer cladding layer, i.e., the refractive index of pure silicon dioxide.

[0023] In a first aspect, the present invention provides an ultra-low differential mode group delay few-mode optical fiber, see [link to previous article]. Figure 1The structure comprises, from the inside out, a core layer structure, an inner cladding structure, and an outer cladding layer; the core layer structure includes a first core layer and a second core layer from the inside out; both the first core layer and the second core layer have a gradient profile, the distribution index α1 of the first core layer ranges from 1.5 to 1.9, and the distribution index α2 of the second core layer ranges from 1.4 to 1.9; the minimum relative refractive index difference Δ1 of the first core layer ranges from 0.3% to 0.6%; the maximum relative refractive index difference of the first core layer is the same as that of the second core layer, denoted as Δ2, the value of Δ2 ranges from 0.6% to 0.9%, and Δ2 > Δ1; the minimum relative refractive index difference Δ3 of the second core layer ranges from -0.2% to -0.1%.

[0024] That is, the core structure in this invention is a double parabolic structure, and the relative refractive index difference parameters of the core structure include Δ1, Δ2 and Δ3; specifically, the minimum relative refractive index difference of the first core layer is Δ1, the maximum relative refractive index difference of the first core layer is Δ2, the maximum relative refractive index difference of the second core layer is Δ2, and the minimum relative refractive index difference of the second core layer is Δ3; the distribution indices of the two core layers correspond to α1 and α2, respectively.

[0025] While traditional graded-ratio profiles can reduce differential mode delay, their high central refractive index can lead to excessive concentration of low-order modes. Therefore, the first core layer in this invention employs a recessed profile structure, which appropriately reduces the refractive index near the axis, making the transmission path lengths between modes closer, thereby further reducing the inter-mode delay difference and improving signal transmission rate and distance. Simultaneously, the second core layer in this invention, by adjusting the distribution index α2, can precisely control the LP11 mode group velocity while increasing the effective area, making the velocities of each mode group similar. This invention uses a graded-ratio core layer profile and optimizes the distribution index (including α1 and α2) to adjust the delay of each mode in the few-mode fiber, achieving extremely low differential mode group delay.

[0026] Specifically, in this invention, α1 and α2 jointly determine the LP11 mode and the LP11 group velocity. The essence of the adjustment is to change the rate of decrease of the refractive index, thereby matching the average transmission path length and transmission speed of different modes and achieving group velocity synchronization. Existing few-mode fibers have only one distribution index, while this invention sets two distribution indices (i.e., α1 and α2), which work together to achieve low differential mode group delay. Among them, α1 is set to a graded type. Compared with the conventional step refractive index profile, the radial graded change of the refractive index achieves group velocity synchronization of different modes, fundamentally canceling the delay difference between modes.

[0027] The inner cladding structure includes a first inner cladding layer, a second inner cladding layer, and a third inner cladding layer from the inside out; the relative refractive index difference of the first inner cladding layer is the same as the minimum relative refractive index difference Δ3 of the second core layer; the relative refractive index difference Δ4 of the second inner cladding layer ranges from 0.1% to 0.3%; and the relative refractive index difference Δ5 of the third inner cladding layer ranges from -1.1% to -0.75%.

[0028] That is, the present invention covers the core structure with three inner cladding layers from the inside to the outside.

[0029] The core layer structure (i.e., the first core layer and the second core layer) is a silica glass layer co-doped with germanium, fluorine and alkali metal, or the core layer structure is a silica glass layer co-doped with germanium and alkali metal; the contribution of the relative refractive index difference of germanium in the core layer structure is 0% to 1.0%, the alkali metal content is 50 ppm to 4000 ppm, and the alkali metal is one or more of lithium, sodium, potassium and rubidium alkali metal ions.

[0030] The radius R1 of the first core layer ranges from 1.5 μm to 3 μm, and the radius R2 of the second core layer ranges from 8.5 μm to 10 μm; the radius R3 of the first inner cladding layer ranges from 11.5 μm to 13.5 μm, the radius R4 of the second inner cladding layer ranges from 13 μm to 17 μm, and R4 > R3; the radius R5 of the third inner cladding layer ranges from 20 μm to 25 μm; the outer cladding layer is a pure silica glass layer, and the radius R6 of the outer cladding layer ranges from 62.5 ± 2.5 μm.

[0031] The first inner cladding layer is a germanium-fluorine co-doped silica glass layer, or the first inner cladding layer is a fluorine-doped silica glass layer; the contribution of the relative refractive index difference of fluorine in the first inner cladding layer is -0.3% to -0.1%; the second inner cladding layer is a germanium-fluorine co-doped silica glass layer, or the second inner cladding layer is a germanium-doped silica glass layer; the contribution of the relative refractive index difference of germanium in the second inner cladding layer is 0.2% to 0.4%; the third inner cladding layer is a fluorine-doped silica glass layer, and the contribution of the relative refractive index difference of fluorine in the third inner cladding layer is -1.1% to -0.75%.

[0032] The differential group delay (DGD) between the LP11 mode and the LP01 mode in the ultra-low differential mode group delay few-mode fiber is less than 1 ps / m.

[0033] The effective area of ​​the LP01 mode in the ultra-low differential mode group delay few-mode fiber is 60 μm. 2 Up to 100μm 2 The effective area of ​​the LP11 mode is 110 μm. 2Up to 150μm 2 .

[0034] The LP01 mode in the ultra-low differential mode group delay few-mode fiber has a dispersion of 22 ps / (nm·km) at a wavelength of 1550 nm, and the LP11 mode has a dispersion of 21 ps / (nm·km) at a wavelength of 1550 nm.

[0035] The ultra-low differential mode group delay few-mode fiber has attenuation of LP01 and LP11 less than or equal to 0.20 dB / km at a wavelength of 1550 nm. The ultra-low differential mode group delay few-mode fiber has a macrobending loss of 0.06dB or less when bent 10 times with a bending radius of R15mm at a wavelength of 1550nm, a macrobending loss of 0.18dB or less when bent once with a bending radius of R10mm, and a macrobending loss of 0.6dB or less when bent once with a bending radius of R7.5mm.

[0036] Based on the special core structure design, this invention adopts a three-ring inner cladding structure and uses a specific doping method to shift the cladding dispersion curve upward, which can effectively offset the waveguide dispersion difference. This invention also designs a fluorine-doped dimpled structure for optical fibers, which can significantly reduce the sensitivity to bending and vibration by reasonably controlling the effective refractive index difference.

[0037] In summary, this invention, through the design of a special core layer structure, the construction of a multi-element doping system for the core layer, and the adoption of a three-layer inner cladding structure and a groove auxiliary structure, not only achieves lower dispersion and bending losses, but also achieves low transmission losses and extremely low differential group delay.

[0038] Secondly, the present invention provides a method for fabricating the above-mentioned ultra-low differential mode group delay few-mode fiber, comprising the following steps: S1. The inner cladding structure and the core structure are sequentially deposited on the inner wall of the quartz liner using plasma chemical vapor deposition (PCVD) process (i.e., the third inner cladding, the second inner cladding, the first inner cladding, the second core layer and the first core layer are deposited sequentially). After deposition, the core is melted and shrunk to obtain a solid core rod. The quartz liner is a high-purity quartz liner. After deposition, high-purity Freon gas can be introduced to clean the inner wall, and then the liner is melted and shrunk into the solid core rod using a melting and shrinking technology. S2. Combine the solid mandrel with the sleeve to form a preformed rod; The sleeve is a low-hydroxyl sleeve, and the solid core rod and the low-hydroxyl sleeve can be combined using a fishing device to form the preform rod; S3. The preform is drawn to obtain an ultra-low differential mode group delay few-mode fiber.

[0039] According to the optical fiber technical solution given in the first aspect, the present invention designs the parameters of the optical fiber within the specified range, manufactures the core rod according to the design requirements of the optical fiber through PCVD process, and completes the manufacturing of the entire preform through external processes such as sleeve process.

[0040] Currently, optical fiber fabrication primarily utilizes preform drawing, with mainstream processes including: chemical vapor deposition (MCVD), off-rod chemical vapor deposition (OVD), axial vapor deposition (VAD), and plasma-activated chemical vapor deposition (PCVD). Each of these four methods has its advantages and disadvantages. Considering that PCVD, through microwave plasma layer-by-layer deposition, offers the finest control over the refractive index profile and the clearest interlayer interfaces, it can fabricate high-performance optical fibers with complex structures such as dispersion compensation, polarization maintenance, and multi-clad structures, exhibiting extremely low loss, in a single process. Therefore, this invention prioritizes PCVD as the preferred fabrication process. Specifically, this invention, based on mature PCVD technology, precisely controls the profile structure to fabricate few-mode fibers, achieving extremely low differential mode group delay while ensuring excellent optical performance.

[0041] The following five embodiments further illustrate the present invention. The structure, material parameters, and main performance parameters of the few-mode optical fibers corresponding to the five embodiments (corresponding to serial numbers 1 to 5 in Tables 1 and 2) are shown in Tables 1 and 2.

[0042] Table 1: Structural and material parameters of the few-mode optical fibers corresponding to the five embodiments

[0043] Table 2: Main performance parameters of few-mode fibers corresponding to the 5 examples

[0044] Based on the above data, it can be seen that the few-mode fiber provided by this invention can achieve extremely low differential group delay across the entire link. For example, the differential group delay (DGD) between the LP11 and LP01 modes in the few-mode fiber of Example 3 is only -0.26 ps / m. The negative sign only reflects the phase correlation characteristics between modes; that is, the absolute value of DGD is 0.26 ps / m, which falls within the range of ultra-low differential group delay recognized in the industry. Overall, the few-mode fiber provided by this invention not only has low attenuation and is easy to manufacture, but also exhibits good comprehensive performance in terms of dispersion and bending loss of each mode.

[0045] Finally, it should be noted that the above specific embodiments are only used to illustrate the technical solutions of the present invention and not to limit it. Although the present invention has been described in detail with reference to examples, those skilled in the art should understand that modifications or equivalent substitutions can be made to the technical solutions of the present invention without departing from the spirit and scope of the technical solutions of the present invention, and all such modifications or substitutions should be covered within the scope of the claims of the present invention.

Claims

1. A few-mode fiber with ultra-low differential mode group delay, characterized in that, include: From the inside out, the core structure, inner cladding structure, and outer cladding; The core structure includes a first core layer and a second core layer from the inside to the outside; Both the first core layer and the second core layer have a gradient profile. The distribution index α1 of the first core layer ranges from 1.5 to 1.9, and the distribution index α2 of the second core layer ranges from 1.4 to 1.

9. The minimum relative refractive index difference Δ1 of the first core layer ranges from 0.3% to 0.6%; the maximum relative refractive index difference of the first core layer is the same as that of the second core layer, denoted as Δ2, and the value of Δ2 ranges from 0.6% to 0.9%, and Δ2 > Δ1; the minimum relative refractive index difference Δ3 of the second core layer ranges from -0.2% to -0.1%.

2. The ultra-low differential mode group delay few-mode fiber according to claim 1, characterized in that, The inner cladding structure includes a first inner cladding, a second inner cladding, and a third inner cladding from the inside out; The relative refractive index difference of the first inner cladding layer is the same as the minimum relative refractive index difference Δ3 of the second core layer; The relative refractive index difference Δ4 of the second inner cladding layer ranges from 0.1% to 0.3%. The relative refractive index difference Δ5 of the third inner cladding layer ranges from -1.1% to -0.75%.

3. The ultra-low differential mode group delay few-mode fiber according to claim 1, characterized in that, The core layer structure is a silica glass layer co-doped with germanium, fluorine, and alkali metals, or the core layer structure is a silica glass layer co-doped with germanium and alkali metals; the contribution of the relative refractive index difference of germanium in the core layer structure is 0% to 1.0%, the alkali metal content is 50 ppm to 4000 ppm, and the alkali metal is one or more of lithium, sodium, potassium, and rubidium alkali metal ions.

4. The ultra-low differential mode group delay few-mode fiber according to claim 2, characterized in that, The radius R1 of the first core layer ranges from 1.5 μm to 3 μm, and the radius R2 of the second core layer ranges from 8.5 μm to 10 μm; the radius R3 of the first inner cladding layer ranges from 11.5 μm to 13.5 μm, the radius R4 of the second inner cladding layer ranges from 13 μm to 17 μm, and R4 > R3; the radius R5 of the third inner cladding layer ranges from 20 μm to 25 μm; the outer cladding layer is a pure silica glass layer, and the radius R6 of the outer cladding layer ranges from 62.5 ± 2.5 μm.

5. The ultra-low differential mode group delay few-mode fiber according to claim 2, characterized in that, The first inner cladding layer is a germanium-fluorine co-doped silica glass layer, or the first inner cladding layer is a fluorine-doped silica glass layer; the contribution of the relative refractive index difference of fluorine in the first inner cladding layer is -0.3% to -0.1%. The second inner cladding layer is a germanium-fluorine co-doped silica glass layer, or the second inner cladding layer is a germanium-doped silica glass layer; the contribution of the relative refractive index difference of germanium in the second inner cladding layer is 0.2% to 0.4%. The third inner cladding is a fluorine-doped silica glass layer, and the contribution of the relative refractive index difference of fluorine in the third inner cladding is -1.1% to -0.75%.

6. The ultra-low differential mode group delay few-mode fiber according to claim 1, characterized in that, The differential group delay between the LP11 mode and the LP01 mode in the ultra-low differential mode group delay few-mode fiber is less than 1 ps / m.

7. The ultra-low differential mode group delay few-mode fiber according to claim 1, characterized in that, The effective area of ​​the LP01 mode in the ultra-low differential mode group delay few-mode fiber is 60 μm. 2 Up to 100μm 2 The effective area of ​​the LP11 mode is 110 μm. 2 Up to 150μm 2 .

8. The ultra-low differential mode group delay few-mode fiber according to claim 1, characterized in that, The LP01 mode in the ultra-low differential mode group delay few-mode fiber has a dispersion of 22 ps / (nm·km) at a wavelength of 1550 nm, and the LP11 mode has a dispersion of 21 ps / (nm·km) at a wavelength of 1550 nm.

9. The ultra-low differential mode group delay few-mode fiber according to claim 1, characterized in that, The ultra-low differential mode group delay few-mode fiber has an attenuation of LP01 and LP11 of less than or equal to 0.20 dB / km at a wavelength of 1550 nm. The ultra-low differential mode group delay few-mode fiber has a macrobending loss of 0.06dB or less when bent 10 times with a bending radius of R15mm at a wavelength of 1550nm, a macrobending loss of 0.18dB or less when bent once with a bending radius of R10mm, and a macrobending loss of 0.6dB or less when bent once with a bending radius of R7.5mm.

10. A method for fabricating an ultra-low differential mode group delay few-mode fiber as described in any one of claims 1 to 9, characterized in that, Includes the following steps: An inner cladding structure and a core structure are sequentially deposited on the inner wall of a quartz liner using plasma chemical vapor deposition (PCVD). After deposition, the core is melted and shrunk to obtain a solid core rod. The solid mandrel is combined with the sleeve to form a preform; The preform is drawn to obtain an ultra-low differential mode group delay few-mode fiber.

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