Ultralow-attenuation weakening coupling multi-core optical fiber, manufacturing method thereof and multi-core optical cable

Abstract

The invention belongs to the technical field of optical fiber communication, and discloses an ultralow-attenuation weakening coupling multi-core optical fiber, a manufacturing method thereof and a multi-core optical cable. The ultra-low attenuation weakening coupling multi-core optical fiber provided by the invention comprises a common outer cladding and a plurality of fiber cores arranged in the common outer cladding, each fiber core sequentially comprises a core layer, an inner wrapping layer and a sunken layer from inside to outside; the core layer is made of germanium-fluorine co-doped silicon dioxide, and the influence of doping on the viscosity of the core layer is defined as delta eta 1; the inner cladding layer is made of germanium-fluorine co-doped silicon dioxide, and the influence of doping on the viscosity of the inner cladding layer is defined as delta eta 2; the sinking layer is made of single fluorine-doped silicon dioxide or germanium-fluorine co-doped silicon dioxide, and the influence of doping on the viscosity of the sinking layer is defined as delta eta 3; the delta eta 1, the delta eta 2 and the delta eta 3 simultaneously meet the following conditions: 1.1 delta eta 2lt; delta eta 1lt; 0.9 [delta] eta < 2 >, [delta] eta < 3 > gt; 3 [delta] eta < 2 >. The attenuation of the weak coupling multi-core optical fiber can be greatly reduced.

Description

Technical Field

[0001] This invention belongs to the field of optical fiber communication technology, and more specifically, relates to an ultra-low attenuation weakly coupled multi-core optical fiber and its manufacturing method, as well as a multi-core optical cable. Background Technology

[0002] In recent years, with the rise of cloud computing, big data, and mobile internet, data centers, with their efficient inter-server collaboration and data processing capabilities, have become a significant growth hotspot in terms of both total information volume and density, creating an urgent need to improve data center interconnection communication speeds. Due to the large number of devices, complex cabling, and high interface density in data center interconnection communication, simply increasing the modulation bandwidth of devices, adding fiber optic links, or increasing the number of light sources with different stable wavelengths will inevitably increase the cost, power consumption, and complexity of system operation and maintenance. Therefore, adopting new modulation / multiplexing methods to increase the transmission rate of a single fiber / wavelength under limited bandwidth is considered an effective solution to improve data center interconnection speeds. However, in actual fiber optic systems, the expansion capabilities of high-order modulation and polarization multiplexing technologies remain limited due to factors such as system signal-to-noise ratio and fiber nonlinearity, posing a significant challenge to meeting the needs of next-generation data center interconnection communication, such as 800G, 1T, or even 1.6T. Space division multiplexing (SDM) technology based on multi-core or multimode fibers, due to its significant expansion potential in fiber modes and spatial dimensions, and its compatibility with high-order modulation formats and polarization multiplexing technologies, can significantly improve the communication capacity of a single fiber / wavelength. Furthermore, for communication systems with high power consumption requirements, using more spatial channels can relatively reduce the communication capacity of each spatial channel. Therefore, using SDM technology with multiple spatial channels can theoretically achieve higher transmission capacity per unit power consumption without increasing the number of fiber optic links.

[0003] Currently, in the process of optical fiber preform fabrication, the core layer, inner cladding layer, and recessed layer are usually doped to change the refractive index. However, introducing dopants into pure silica material will cause changes in the material viscosity. If not designed properly, the viscosity between the layers of the preform will definitely change drastically. This viscosity difference will cause internal stress in the core, which will lead to residual thermal stress and bond breakage in the optical fiber in subsequent optical fiber manufacturing processes, resulting in increased optical fiber attenuation. Summary of the Invention

[0004] This invention provides an ultra-low attenuation weakly coupled multi-core optical fiber and its manufacturing method, as well as a multi-core optical cable, thereby solving the problem of high attenuation in existing weakly coupled multi-core optical fibers.

[0005] In a first aspect, the present invention provides an ultra-low attenuation weakly coupled multi-core optical fiber, comprising: a common outer cladding and a plurality of fiber cores disposed in the common outer cladding; each fiber core comprises, from the inside out, a core layer, an inner cladding and a recessed layer; The core layer is made of germanium-fluorine co-doped silicon dioxide, and the effect of doping on the viscosity of the core layer is defined as Δη1. The inner cladding is made of germanium-fluorine co-doped silicon dioxide, and the effect of doping on the viscosity of the inner cladding is defined as Δη2. The material of the sunken layer is either fluorine-doped silicon dioxide or germanium-fluorine co-doped silicon dioxide, and the effect of doping on the viscosity of the sunken layer is defined as Δη3. Δn1, Δn2 and Δn3 simultaneously satisfy: 1.1Δn2<Δn1<0.9Δn2, Δn3>3Δn2.

[0006] Preferably, the effect of doping on the core layer viscosity Δη1 is expressed as: Δη1 = -ΔGe1 + 3ΔF1, where ΔGe1 is the effect of germanium in the core layer on the refractive index, and ΔF1 is the effect of fluorine in the core layer on the refractive index; The effect of doping on the viscosity of the inner cladding, Δη2, is expressed as: Δη2 = -ΔGe2 + 3ΔF2, where ΔGe2 is the effect of germanium in the inner cladding on the refractive index, and ΔF2 is the effect of fluorine in the inner cladding on the refractive index. The effect of doping on the viscosity of the subsided layer, Δη3, is expressed as: Δη3 = -ΔGe3 + 3ΔF3, where ΔGe3 is the effect of germanium on the refractive index in the subsided layer, and ΔF3 is the effect of fluorine on the refractive index in the subsided layer.

[0007] Preferably, the plurality of fiber cores are evenly distributed circumferentially, the number of fiber cores is greater than 2, and the distance between adjacent fiber cores is P, where P>30μm.

[0008] Preferably, the radius r1 of the core layer ranges from 3 μm to 6 μm; the radius r2 of the inner cladding layer ranges from 6 μm to 10 μm, and r2 > r1; the radius r3 of the sunken layer ranges from 10 μm to 13 μm, and r3 > r2.

[0009] Preferably, the optical waveguide is weakly coupled between the cores of the ultra-low attenuation weakly coupled multi-core optical fiber; In the O-band, the attenuation of each core of the ultra-low attenuation weakly coupled multi-core optical fiber is less than 0.27 dB / km; In the C-band, the attenuation of each core of the ultra-low attenuation weakly coupled multi-core optical fiber is less than 0.175 dB / km. In the L-band, the attenuation of each core of the ultra-low attenuation weakly coupled multi-core optical fiber is less than 0.19 dB / km.

[0010] Preferably, in the O-band, C-band, and L-band, when the bending radius R30mm is bent 100 times, the macro bending loss of each core of the ultra-low attenuation weakly coupled multi-core optical fiber is less than or equal to 0.1dB.

[0011] Preferably, in the O-band, C-band and L-band, the fusion loss of each core of the ultra-low attenuation weakly coupled multi-core optical fiber is less than or equal to 0.2dB.

[0012] In a second aspect, the present invention provides a method for manufacturing an ultra-low attenuation weakly coupled multi-core optical fiber as provided in the first aspect of the present invention, comprising the following steps: Multiple homogeneous core rods were prepared using plasma chemical vapor deposition (PCVD). Multiple homogeneous core rods are fitted together with multi-core sleeves to obtain a weakly coupled multi-core optical fiber preform. The weakly coupled multi-core fiber preform is drawn into fibers to obtain an ultra-low attenuation weakly coupled multi-core fiber. The ultra-low attenuation weakly coupled multi-core optical fiber simultaneously satisfies: 1.1Δη2<Δη1<0.9Δη2, Δη3>3Δη2; Δη1 is the effect of doping on the core layer viscosity, Δη2 is the effect of doping on the inner cladding viscosity, and Δη3 is the effect of doping on the subsidence layer viscosity.

[0013] Thirdly, the present invention provides a multi-core optical cable, comprising: a first number n1 loose tubes, each of which contains a second number n2 ultra-low attenuation weakly coupled multi-core optical fibers as provided in the first aspect of the present invention.

[0014] Preferably, when the number of fiber cores in the ultra-low attenuation weakly coupled multi-core optical fiber is n3, the number of channels contained in the multi-core optical cable is n1×n2×n3.

[0015] One or more technical solutions provided in this invention have at least the following technical effects or advantages: The ultra-low attenuation weakly coupled multi-core optical fiber provided by this invention includes a common outer cladding and multiple fiber cores arranged within the common outer cladding. Each fiber core, from the inside out, includes a core layer, an inner cladding, and a recessed layer. The core layer is made of germanium-fluorine co-doped silicon dioxide, and the effect of doping on the core layer viscosity is defined as Δη1. The inner cladding is also made of germanium-fluorine co-doped silicon dioxide, and the effect of doping on the inner cladding viscosity is defined as Δη2. The recessed layer is made of either fluorine-doped silicon dioxide or germanium-fluorine co-doped silicon dioxide, and the effect of doping on the recessed layer viscosity is defined as Δη3. Δη1, Δη2, and Δη3 simultaneously satisfy: 1.1Δη2 < Δη1 < 0.9Δη2, Δη3 > 3Δη2. This invention, without altering the refractive index profile, limits viscosity changes between layers through optimized doping design, reducing viscosity differences between layers (i.e., reducing viscosity fluctuations between fiber layers), thereby significantly reducing fiber attenuation. Compared to ordinary weakly coupled multi-core optical fibers and ordinary multi-core optical cables, the ultra-low attenuation weakly coupled multi-core optical fibers and multi-core optical cables obtained based on multi-core optical fibers provided by this invention have low link attenuation, which can increase the relay distance, reduce the number and cost of optical cable relay stations, and facilitate the realization of space division multiplexing communication systems with high distance capacity product, low implementation cost, and low complexity, thus promoting the application of weakly coupled multi-core optical fibers and optical cables in long-distance trunk lines. Attached Figure Description

[0016] Figure 1 This is a schematic diagram of the end face structure of an ultra-low attenuation weakly coupled multi-core optical fiber provided in Embodiment 1 of the present invention; Figure 2 This is a schematic diagram of the end face structure of an ultra-low attenuation weakly coupled multi-core optical fiber provided in Embodiment 2 of the present invention. Detailed Implementation

[0017] 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.

[0018] In a first aspect, the present invention provides an ultra-low attenuation weakly coupled multi-core optical fiber, comprising: a common cladding and multiple fiber cores disposed in the common cladding; each fiber core comprises, from the inside out, a core layer, an inner cladding layer, and a recessed layer; the core layer is made of germanium-fluorine co-doped silicon dioxide, and the effect of doping on the viscosity of the core layer is defined as Δη1; the inner cladding layer is made of germanium-fluorine co-doped silicon dioxide, and the effect of doping on the viscosity of the inner cladding layer is defined as Δη2; the recessed layer is made of fluorine-doped silicon dioxide or germanium-fluorine co-doped silicon dioxide, and the effect of doping on the viscosity of the recessed layer is defined as Δη3; Δη1, Δη2, and Δη3 simultaneously satisfy: 1.1Δη2 < Δη1 < 0.9Δη2, Δη3 > 3Δη2.

[0019] To reduce viscosity fluctuations between layers in the fiber core and fabricate ultra-low attenuation optical fibers, this invention regulates the viscosity variation of each layer through doping, ensuring that the influence of doping on the viscosity of each layer, Δη1, Δη2, and Δη3, simultaneously satisfies two conditions: (1) 1.1Δη2 < Δη1 < 0.9Δη2; (2) Δη3 > 3Δη2. That is, this invention correlates the viscosity variation relationship (constraint) of each layer with the attenuation of the optical fiber to obtain ultra-low attenuation weakly coupled multi-core optical fibers. Based on this, an ultra-low attenuation weakly coupled multi-core optical fiber is obtained, in which the optical waveguide is weakly coupled between the cores of the ultra-low attenuation weakly coupled multi-core optical fiber; in the O-band (1260nm to 1360nm), the attenuation of each core of the ultra-low attenuation weakly coupled multi-core optical fiber is less than 0.27dB / km; in the C-band (1530nm to 1565nm), the attenuation of each core of the ultra-low attenuation weakly coupled multi-core optical fiber is less than 0.175dB / km; and in the L-band (1565nm to 1625nm), the attenuation of each core of the ultra-low attenuation weakly coupled multi-core optical fiber is less than 0.19dB / km.

[0020] The effect of doping (i.e., germanium-fluorine co-doping) on ​​the core layer viscosity, Δη1, is expressed as: Δη1 = -ΔGe1 + 3ΔF1, where ΔGe1 is the effect of germanium on the refractive index in the core layer, and ΔF1 is the effect of fluorine on the refractive index in the core layer. Alternatively, Δη1 can be understood as the change in viscosity of the core layer after germanium-fluorine doping relative to pure silicon.

[0021] The effect of doping (i.e. germanium-fluorine co-doping) on ​​the viscosity of the inner cladding, Δη2, is expressed as: Δη2 = -ΔGe2 + 3ΔF2, where ΔGe2 is the effect of germanium in the inner cladding on the refractive index, and ΔF2 is the effect of fluorine in the inner cladding on the refractive index.

[0022] The effect of the doping (i.e. germanium-fluorine co-doping; when the material of the trapped layer is silicon dioxide with single fluorine doping, ΔGe3 is 0) on the viscosity of the trapped layer is expressed as: Δη3 = -ΔGe3 + 3ΔF3, where ΔGe3 is the effect of germanium on the refractive index in the trapped layer, and ΔF3 is the effect of fluorine on the refractive index in the trapped layer.

[0023] That is, the effect of germanium-fluorine co-doping on the viscosity of a certain layer, Δη, is expressed as: Δη = -ΔGe + 3ΔF. Germanium is used to increase the refractive index while simultaneously reducing viscosity; fluorine is used to reduce the refractive index while simultaneously reducing viscosity. The effect of fluorine on viscosity is much stronger than that of germanium. For the same absolute refractive index change, fluorine's viscosity-reducing effect is three times that of germanium.

[0024] Among them, multiple fiber cores are evenly distributed circumferentially, the number of fiber cores is greater than 2, and the distance between adjacent fiber cores is P, where P>30μm.

[0025] The radius of a layer is defined as the distance between the outer boundary of that layer and its center point. The radius r1 of the core layer ranges from 3 μm to 6 μm; the radius r2 of the inner cladding layer ranges from 6 μm to 10 μm, and r2 > r1; the radius r3 of the sunken layer ranges from 10 μm to 13 μm, and r3 > r2.

[0026] In the O-band, C-band, and L-band, after bending 100 times with a bending radius of R30mm, the macro-bending loss of each core of the ultra-low attenuation weakly coupled multi-core optical fiber is less than or equal to 0.1dB. The macro-bending additional loss test method can refer to the method specified in IEC60793-1-47.

[0027] In the O-band, C-band, and L-band, the fusion loss of each core of the ultra-low attenuation weakly coupled multi-core optical fiber is less than or equal to 0.2 dB.

[0028] Secondly, the present invention provides a method for manufacturing an ultra-low attenuation weakly coupled multi-core optical fiber, comprising the following steps: Multiple homogeneous core rods were prepared using plasma chemical vapor deposition (PCVD). Multiple homogeneous core rods are fitted together with multi-core sleeves to obtain a weakly coupled multi-core optical fiber preform. The weakly coupled multi-core fiber preform is drawn into fibers to obtain an ultra-low attenuation weakly coupled multi-core fiber. The ultra-low attenuation weakly coupled multi-core optical fiber simultaneously satisfies: 1.1Δη2<Δη1<0.9Δη2, Δη3>3Δη2; Δη1 is the effect of doping on the core layer viscosity, Δη2 is the effect of doping on the inner cladding viscosity, and Δη3 is the effect of doping on the subsidence layer viscosity.

[0029] The above describes the manufacturing method of the ultra-low attenuation weakly coupled multi-core optical fiber provided in the first aspect of the present invention. The manufacturing process parameters are adjusted with the aim of preparing the ultra-low attenuation weakly coupled multi-core optical fiber provided in the first aspect of the present invention. Therefore, the manufacturing method can be understood by referring to the description of the first aspect of the present invention, and will not be repeated here.

[0030] Thirdly, the present invention provides a multi-core optical cable, comprising: a first number n1 loose tubes, each of which contains a second number n2 ultra-low attenuation weakly coupled multi-core optical fiber.

[0031] When the number of fiber cores in the ultra-low attenuation weakly coupled multi-core optical fiber is n3, the number of channels contained in the multi-core optical cable is n1×n2×n3.

[0032] The ultra-low attenuation weakly coupled multi-core optical fiber included in the multi-core optical cable is the ultra-low attenuation weakly coupled multi-core optical fiber provided in the first aspect of the present invention.

[0033] The following examples, 1 and 2, are given in conjunction with the parameters to further illustrate the present invention.

[0034] Example 1: Example 1 provides an ultra-low attenuation weakly coupled multi-core optical fiber, see [link to example]. Figure 1 The number of fiber cores is 4, meaning the common outer cladding contains four homogeneous fiber cores. The main parameters of the corresponding refractive index profile structure are shown in Table 1, and the main performance parameters are shown in Table 2. Wherein, D is the diameter of the common outer cladding.

[0035] Table 1. Main structural parameters of the four-core optical fiber provided in Example 1

[0036] Table 2 Main performance parameters of the four-core optical fiber provided in Example 1

[0037] As shown in Table 2, the four cores of the ultra-low attenuation weakly coupled multi-core optical fiber provided in Example 1 have very low attenuation in the C+L band, and the macrobending and splicing losses of each core are also very small, making it suitable for long-distance communication transmission.

[0038] The corresponding method for fabricating ultra-low attenuation weakly coupled multi-core optical fiber includes: using a four-core fluorine-doped sleeve with an outer diameter (OD) of 80 mm, the sleeve containing four holes with an OD of 15 mm, and the distance between the center of the four holes and the center of the sleeve is 25.6 mm. Four core rods with an OD of 14 mm were fabricated using PCVD technology. The four core rods had identical cross-sections. Both the core layer and the inner cladding were germanium- and fluorine-doped silica glass. The radius of the core layer in the core rod was 2.11 mm, and the effect of germanium- and fluorine-doping on the viscosity of the core layer was Δη1 -1.19. The radius of the inner cladding in the core rod was 4.16 mm, and the effect of germanium- and fluorine-doping on the viscosity of the inner cladding was Δη2 -1.26. The material of the recessed layer in the core rod was fluorine-doped silica, and the radius of the recessed layer was 7.68 mm. The effect of fluorine on the viscosity of the recessed layer was Δη3 -2.4. The above four core rods were then combined with a sleeve and drawn to obtain an ultra-low attenuation weakly coupled four-core optical fiber in the C+L band.

[0039] To better understand the present invention and its advantages and to verify them, a comparative example (denoted as Comparative Example 1) is given below.

[0040] Comparative Example 1 shows a conventional attenuated weakly coupled multi-core fiber with 4 cores, meaning that the common outer cladding contains four homogeneous cores. The main parameters of the corresponding refractive index profile structure are shown in Table 3, and the main performance parameters are shown in Table 4.

[0041] Table 3 shows the main structural parameters of the four-core optical fiber provided in Comparative Example 1.

[0042] Table 4 shows the main performance parameters of the four-core optical fiber provided in Comparative Example 1.

[0043] Comparing Tables 1 and 3, it can be seen that the optical fibers of Example 1 and Comparative Example 1 have the same structure, the same width of each layer, and the same refractive index (ΔGe+ΔF) of each layer (that is, ΔGe1+ΔF1, ΔGe2+ΔF2, and ΔGe3+ΔF3 are all the same for both optical fibers). However, the Δη of each layer is different (that is, Δη1, Δη2, and Δη3 are different for the two optical fibers), and the Δη of each layer in Comparative Example 1 has a larger difference.

[0044] Comparing Tables 2 and 4, it can be seen that the optical fiber corresponding to Comparative Example 1 has significantly higher attenuation.

[0045] The above data also confirms that, without changing the refractive index profile, the present invention, through optimized doping design, limits the viscosity changes between layers, reduces the viscosity differences between layers, and lowers fiber attenuation.

[0046] Example 2: Example 2 provides an ultra-low attenuation weakly coupled multi-core optical fiber, see [link / reference] Figure 2 The number of fiber cores is 7, that is, the common outer cladding contains seven homogeneous fiber cores, and the main parameters of the corresponding refractive index profile structure are shown in Table 5.

[0047] Table 5 Main structural parameters of seven-core optical fiber

[0048] The corresponding method for fabricating ultra-low attenuation weakly coupled multi-core optical fiber includes: using a seven-core sleeve with an OD of 80mm, the sleeve containing seven holes with an OD of 15mm, wherein the outer six holes are arranged in a regular hexagon with a side length of 22.4mm, and the center hole is 22.4mm away from the center hole of the sleeve. Seven core rods with an OD of 14 mm were fabricated using PCVD technology. The seven core rods had identical cross-sections, and both the core layer and inner cladding were germanium- and fluorine-doped silica glass. The radius of the core layer was 1.65 mm, and the effect of germanium- and fluorine-doping on the viscosity of the core layer was Δη1 -0.67. The radius of the inner cladding was 3.25 mm, and the effect of germanium- and fluorine-doping on the viscosity of the inner cladding was Δη2 -0.71. The material of the recessed layer in the core rod was fluorine-doped silica, and the radius of the recessed layer was 6.51 mm. The effect of fluorine on the viscosity of the recessed layer was Δη3 -1.2. The seven core rods were then drawn with a sleeve to obtain an ultra-low attenuation weakly coupled seven-core optical fiber with a glass portion diameter of 150.2 μm.

[0049] A multi-core optical cable was fabricated using the aforementioned ultra-low attenuation weakly coupled seven-core optical fiber. The cable type was GYTA-12, containing six loose tubes. Each loose tube contained 12 ultra-low attenuation weakly coupled seven-core optical fibers. The diameter of the loose tubes was 2.4 mm, resulting in a final outer diameter of 11 mm for the optical cable. This optical cable contained 504 channels.

[0050] If a single-core optical cable of the same specifications is manufactured, the number of channels is only 72. It can be seen that the transmission capacity of the ultra-low attenuation weakly coupled seven-core optical fiber provided by this invention is 7 times that of the traditional single-core optical fiber, which greatly improves the channel density of the optical cable, that is, the optical cable of the same diameter has a greater transmission capacity.

[0051] The present invention also tested the main parameters of the optical cable (i.e., the multi-core optical cable made of ultra-low attenuation weakly coupled seven-core optical fiber). The maximum values ​​of the main performance parameters of the 504 channels at 1310nm are shown in Table 6.

[0052] Table 6 Main performance parameters of multi-core optical cables

[0053] Based on the above data, it can be seen that the ultra-low attenuation weakly coupled multi-core optical fiber provided by this invention has a homogeneous core, and its core density is 7 times that of traditional single-core optical fiber. The fiber attenuation in the 1310nm band is less than 0.27 dB / km, and the macrobending and splicing losses after fiber and cabling are also very low. Therefore, the ultra-low attenuation weakly coupled multi-core optical fiber provided by this invention meets the requirements of long-distance communication applications. This invention not only facilitates manufacturing and production of optical fibers but also reduces production costs. The multi-core optical cable provided by this invention can increase channel density while maintaining the same cable size, or reduce the cable size while keeping the number of channels consistent, which is beneficial for realizing a space-division multiplexing communication system with high distance-capacity product, low implementation cost, and low complexity.

[0054] In summary, the weakly coupled multi-core optical fiber provided by this invention has very low attenuation. In addition, the fiber has low macrobending and splice loss, which can increase the optical cable channel density or reduce the optical cable size.

[0055] 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. An ultra-low attenuation weakly coupled multi-core optical fiber, characterized in that, include: A common outer cladding and multiple fiber cores disposed in the common outer cladding; each fiber core includes, from the inside out, a core layer, an inner cladding layer and a recessed layer; The core layer is made of germanium-fluorine co-doped silicon dioxide, and the effect of doping on the viscosity of the core layer is defined as Δη1. The inner cladding is made of germanium-fluorine co-doped silicon dioxide, and the effect of doping on the viscosity of the inner cladding is defined as Δη2. The material of the sunken layer is either fluorine-doped silicon dioxide or germanium-fluorine co-doped silicon dioxide, and the effect of doping on the viscosity of the sunken layer is defined as Δη3. Δn1, Δn2, and Δn3 simultaneously satisfy: 1.1Δn2<Δn1<0.9Δn2, Δn3>3Δn2.

2. The ultra-low attenuation weakly coupled multi-core optical fiber according to claim 1, characterized in that, The effect of doping on the core layer viscosity Δη1 is expressed as: Δη1 = -ΔGe1 + 3ΔF1, where ΔGe1 is the effect of germanium in the core layer on the refractive index, and ΔF1 is the effect of fluorine in the core layer on the refractive index; The effect of doping on the viscosity of the inner cladding, Δη2, is expressed as: Δη2 = -ΔGe2 + 3ΔF2, where ΔGe2 is the effect of germanium in the inner cladding on the refractive index, and ΔF2 is the effect of fluorine in the inner cladding on the refractive index. The effect of doping on the viscosity of the subsided layer, Δη3, is expressed as: Δη3 = -ΔGe3 + 3ΔF3, where ΔGe3 is the effect of germanium on the refractive index in the subsided layer, and ΔF3 is the effect of fluorine on the refractive index in the subsided layer.

3. The ultra-low attenuation weakly coupled multi-core optical fiber according to claim 1, characterized in that, Multiple fiber cores are evenly distributed circumferentially, the number of fiber cores is greater than 2, and the distance between adjacent fiber cores is P, where P>30μm.

4. The ultra-low attenuation weakly coupled multi-core optical fiber according to claim 1, characterized in that, The radius r1 of the core layer ranges from 3 μm to 6 μm; the radius r2 of the inner cladding layer ranges from 6 μm to 10 μm, and r2 > r1; the radius r3 of the sunken layer ranges from 10 μm to 13 μm, and r3 > r2.

5. The ultra-low attenuation weakly coupled multi-core optical fiber according to claim 1, characterized in that, The optical waveguide is weakly coupled between the cores of the ultra-low attenuation weakly coupled multi-core optical fiber. In the O-band, the attenuation of each core of the ultra-low attenuation weakly coupled multi-core optical fiber is less than 0.27 dB / km. In the C-band, the attenuation of each core of the ultra-low attenuation weakly coupled multi-core optical fiber is less than 0.175 dB / km. In the L-band, the attenuation of each core of the ultra-low attenuation weakly coupled multi-core optical fiber is less than 0.19 dB / km.

6. The ultra-low attenuation weakly coupled multi-core optical fiber according to claim 1, characterized in that, In the O-band, C-band, and L-band, when the bending radius is R30mm and the fiber is bent 100 times, the macro bending loss of each core of the ultra-low attenuation weakly coupled multi-core optical fiber is less than or equal to 0.1dB.

7. The ultra-low attenuation weakly coupled multi-core optical fiber according to claim 1, characterized in that, In the O-band, C-band, and L-band, the fusion loss of each core of the ultra-low attenuation weakly coupled multi-core optical fiber is less than or equal to 0.2 dB.

8. A method for manufacturing an ultra-low attenuation weakly coupled multi-core optical fiber as described in any one of claims 1 to 7, characterized in that, Includes the following steps: Multiple homogeneous core rods were prepared using plasma chemical vapor deposition (PCVD). Multiple homogeneous core rods are fitted together with multi-core sleeves to obtain a weakly coupled multi-core optical fiber preform. The weakly coupled multi-core fiber preform is drawn into fibers to obtain an ultra-low attenuation weakly coupled multi-core fiber. The ultra-low attenuation weakly coupled multi-core optical fiber simultaneously satisfies: 1.1Δη2<Δη1<0.9Δη2, Δη3>3Δη2; Δη1 is the effect of doping on the core layer viscosity, Δη2 is the effect of doping on the inner cladding viscosity, and Δη3 is the effect of doping on the subsidence layer viscosity.

9. A multi-core optical cable, characterized in that, include: A first number n1 of loose tubes, each of which contains a second number n2 of ultra-low attenuation weakly coupled multi-core optical fibers as described in any one of claims 1 to 7.

10. The multi-core optical cable according to claim 9, characterized in that, When the number of fiber cores in the ultra-low attenuation weakly coupled multi-core optical fiber is n3, the number of channels contained in the multi-core optical cable is n1×n2×n3.

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