A low-crosstalk multi-core single-mode optical fiber and its fabrication method

Abstract

This invention discloses a low-crosstalk multi-core single-mode optical fiber and its fabrication method. The optical fiber includes several cores and an outer cladding with air-assisted holes covering the cores. Each core comprises a core layer, an inner cladding, and a recessed cladding arranged sequentially from the inside out. The air-assisted holes are arranged in a regular polygonal pattern around the core. By setting the inner cladding, recessed cladding, and air-assisted holes around the core layer, this invention effectively reduces the refractive index of the cladding around the core layer, confining light energy within the core layer and better suppressing crosstalk between cores. The air-assisted hole fabrication and the cladding fabrication are performed simultaneously, making the process more controllable and easier for mass production. When the core layer radius, core spacing, and other parameters are the same, controlling the relative refractive indices of the core layer and the recessed cladding to within 0.500% and -0.500% respectively can achieve the same crosstalk suppression effect and macrobending level. From a process perspective, lower doping levels are easier to control and also more conducive to fiber attenuation control.

Description

Technical Field

[0001] This invention belongs to the field of optical fiber technology, specifically relating to a low crosstalk multi-core single-mode optical fiber and its fabrication method. Background Technology

[0002] With the rapid development of the high-speed information age, the demand for communication network capacity is increasing. Single-mode fiber, limited by factors such as fiber nonlinearity, has a maximum capacity limited to the 100 Tbit / s range. To significantly improve the transmission capacity of fiber optic communication systems, Space-Division Multiplexing (SDM) fiber optic communication technology has become an important choice. Currently, there are two main methods of SDM: one is based on mode multiplexing using few-mode fiber, and the other is spatial multi-core multiplexing. When multi-core fiber is used for SDM communication transmission, each fiber core is an independent physical channel. At both ends of the multi-core fiber, it is connected to the single-mode fiber at the input and output ends respectively using multi-core couplers. The signals received by each single-mode fiber at the receiving end can be directly utilized, making it highly favored.

[0003] Because the inter-core spacing of multi-core optical fibers is generally very small, strong optical coupling occurs between the optical signals in the multiple cores, resulting in crosstalk, which severely affects the transmission performance of the optical fiber. The most direct way to reduce inter-core crosstalk is to increase the inter-core spacing, but this reduces the core density and transmission capacity, and also requires increasing the cladding size. From a process and cost perspective, increasing the inter-core spacing to reduce crosstalk is not the best choice. Summary of the Invention

[0004] To address the technical problems existing in the prior art, the present invention aims to provide a low crosstalk multi-core single-mode optical fiber and its preparation method.

[0005] To achieve the above objectives and technical effects, the technical solution adopted by this invention is as follows:

[0006] A low crosstalk multi-core single-mode optical fiber includes several cores and an outer cladding with air-assisted holes covering the cores. The cores comprise a core layer, an inner cladding, and a recessed cladding arranged sequentially from the inside to the outside. The air-assisted holes are arranged in regular polygons around the cores.

[0007] Furthermore, the core layer is a germanium-doped quartz glass layer with a radius R1 of 3.0–5.5 μm and a relative refractive index difference Δ1 of 0.25%–0.40%.

[0008] Furthermore, the inner cladding is a fluorine-doped quartz glass layer with a radius R2 of 4.5–13.75 μm and a relative refractive index difference Δ2 of -0.03%–0.

[0009] Furthermore, the sunken cladding is a fluorine-doped quartz glass layer with a radius R3 of 10.5–27.5 μm and a relative refractive index difference Δ3 of -0.20%–-0.40%.

[0010] Furthermore, the radius R4 of the air-assisted hole is 2-8 μm, and the relative refractive index difference Δ4 is ​​-31.38%.

[0011] Furthermore, the radius R5 of the outer cladding layer is 62.5–75.0 μm, and the relative refractive index difference Δ5 is 0–0.03%.

[0012] Furthermore, the core spacing between two adjacent cores is 35–50 μm.

[0013] This invention also discloses a method for fabricating low-crosstalk multi-core single-mode optical fiber, comprising the following steps:

[0014] S1. Using silicon tetrachloride as the main raw material, a germanium-doped core layer and a fluorine-doped inner cladding loose body are prepared by axial vapor deposition or external vapor deposition, and then sintered and stretched to obtain stretched core rod I.

[0015] S2. Using silicon tetrachloride as the main raw material, a loose body is prepared by deposition using VAD or OVD method. By controlling the amount of fluorine used in the sintering and fluorination process of the loose body, the purpose of differential fluorine concentration doping is achieved. Then, the fluorine-doped core rod is processed to a suitable size to obtain a sleeve.

[0016] S3. Assemble the extended mandrel I into the sleeve and melt and shrink it to a suitable outer diameter to obtain the required core.

[0017] S4. Using high-precision drilling equipment, drill holes on the sleeve blank according to the designed distribution diagram of air-assisted holes and core holes to produce the sleeve.

[0018] S5. Assemble the core into the matching core hole of the sleeve post, and then obtain a low crosstalk multi-core single-mode optical fiber preform by melting and stretching.

[0019] S6. The fiber preform is drawn into fibers to obtain a low-crosstalk multi-core single-mode fiber.

[0020] Furthermore, after drawing, the inter-core crosstalk between any two cores in the optical fiber does not exceed -60dB / 100km, the attenuation at the 1550nm band is ≤0.185dB / km, and the macrobending at 1550nm (Ф32×1t) is ≤0.05dB.

[0021] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0022] 1) By setting an inner cladding, a sunken cladding and an air-assisted hole structure around the fiber core layer, the present invention effectively reduces the refractive index of the cladding around the fiber core layer, confines the light energy within the fiber core layer, and better suppresses crosstalk between fiber cores.

[0023] 2) The present invention arranges air auxiliary holes around the core, which avoids the problem of high drilling difficulty (the groove layer is relatively thin and the drilling accuracy requirement is high) caused by the superposition of grooves and air holes as described in some patent literature, or the limited uniformity and cleanliness of pure quartz glass capillary placed in the groove. At the same time, it avoids the adverse effects on the stability of the optical fiber structure, such as too many hollow structures in microstructure optical fiber.

[0024] 3) This invention performs the processing of air-assisted holes and cladding columns simultaneously, making the process more controllable and easier to mass-produce. It also has a significant advantage in terms of doping concentration: when the core layer radius, core spacing and other parameters are the same, the relative refractive index of the core layer and the recessed cladding is controlled within 0.500% and -0.500% respectively in this invention, which can achieve the same crosstalk suppression effect and macrobending level. From a process perspective, less doping is easier to control and also more conducive to fiber attenuation control.

[0025] 4) The overall structure is simple, and the number and arrangement of cores, the diameter and number of air-assisted holes, and the doping concentration can be flexibly adjusted to make the optical fiber performance more ideal. Attached Figure Description

[0026] Figure 1 This is a diagram showing the cross-section and axial refractive index distribution of the optical fiber in Embodiment 1 of the present invention;

[0027] Figure 2 This is a diagram showing the cross-section and axial refractive index distribution of the optical fiber in Embodiment 2 of the present invention. Detailed Implementation

[0028] The present invention will now be described in detail so that its advantages and features can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0029] The following provides a brief overview of one or more aspects to offer a basic understanding of them. This overview is not an exhaustive summary of all conceived aspects, nor is it intended to identify key or decisive elements of all aspects, nor to define the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form to prepare for the more detailed descriptions that follow.

[0030] like Figure 1-2As shown, a low crosstalk multi-core single-mode optical fiber includes several cores and an outer cladding with air-assisted holes covering the cores. The cores include a core layer, an inner cladding, and a recessed cladding arranged sequentially from the inside to the outside. The air-assisted holes are arranged in a regular polygon around the core layer.

[0031] In one specific implementation, the core layer is a germanium-doped quartz glass layer with a radius R1 of 3.0–5.5 μm and a relative refractive index difference Δ1 of 0.25%–0.40%; the inner cladding layer is a fluorine-doped quartz glass layer with a radius R2 of 4.5–13.75 μm and a relative refractive index difference Δ2 of -0.03%–0; and the recessed cladding layer is a fluorine-doped quartz glass layer with a radius R3 of 10.5–27.5 μm and a relative refractive index difference Δ3 of -0.20%–-0.40%.

[0032] The radius R4 of the air-assisted aperture is 2-8 μm, and the relative refractive index difference Δ4 is ​​-31.38%, which is uniformly distributed on the outer side of the cladding of each core.

[0033] The radius R5 of the outer cladding is 62.5–75.0 μm, and the relative refractive index difference Δ5 is 0–0.03%.

[0034] After drawing, the core spacing between two adjacent cores is 35-50μm, and the number and arrangement of cores can be freely designed.

[0035] A method for fabricating a low-crosstalk multi-core single-mode optical fiber includes the following steps:

[0036] S1. Using silicon tetrachloride as the main raw material, a loose bulk material is prepared by axial vapor deposition (VAD) or external vapor deposition (OVD) at a flow rate controlled at 0.3–0.9 L / min. Simultaneously, germanium tetrachloride gas is doped into the core layer at a flow rate controlled at 0.03–0.07 L / min, and carbon tetrafluoride is doped into the inner cladding layer at a flow rate controlled at 0.2–0.8 L / min. The density of the loose bulk material is controlled at 0.25–0.4 g / cm³. 3 Then, it is dehydrated and sintered at a high temperature of 800-1500℃, and finally, it is stretched by equal volume to obtain the stretched core rod I (this step yields the core layer + inner cladding layer);

[0037] S2. Using silicon tetrachloride as the main raw material, and controlling the flow rate at 0.3–0.9 L / min, a loose material is prepared by axial vapor deposition (VAD) or external vapor deposition (OVD), with the density of the loose material controlled at 0.25–0.35 g / cm³. 3The process involves dehydration, fluorination, and sintering at high temperatures of 800–1500℃, while controlling the amount of fluorine used during the sintering and fluorination of the loose material to achieve the purpose of doping with different fluorine concentrations. The fluorination flow rate is usually between 0.1 and 0.6 L / min. The fluorine-doped sintered mandrel is then processed by drilling and grinding the outer diameter through cold working processes to obtain the appropriate inner / outer diameter, thus producing the sleeve.

[0038] S3. Assemble the extended mandrel I into the sleeve and melt and shrink it to a suitable outer diameter. During the extension process, parameters such as extension power (20-40%), etching power (15-40%), and etching times (2-8 times) need to be controlled to obtain the extended mandrel II, i.e. the core.

[0039] S4. Using high-precision drilling equipment, drill holes in the sleeve blank rod in sequence according to the designed hole distribution diagram (including air-assisted holes and core holes) to produce the sleeve.

[0040] S5. Assemble the extended core rod II into the matching core hole of the sleeve post, and obtain the low crosstalk multi-core single-mode optical fiber preform by melting and stretching.

[0041] S6. The fiber preform is drawn into fibers at a speed of 200-600 m / min to obtain low crosstalk multi-core single-mode fiber.

[0042] According to the above scheme, after the fiber is drawn, the crosstalk between any two cores of the fiber does not exceed -60dB / 100km, the attenuation at 1550nm is ≤0.185dB / km, and the macrobending (Ф32×1t) at 1550nm is ≤0.05dB.

[0043] Example 1

[0044] like Figure 1 As shown, a low-crosstalk multi-core single-mode optical fiber comprises four cores and an outer cladding with air-assisted holes covering the cores. Each core includes a core layer, an inner cladding, and a recessed cladding arranged sequentially from the inside out. Six air-assisted holes are evenly distributed around the periphery of each core, arranged in a regular hexagonal pattern around the core layer. The inter-core spacing at the fiber end face is 45 μm. Each layer satisfies the following:

[0045] The core layer radius R1 = 4.3 μm, and Δ1 is 0.305%;

[0046] The inner cladding radius R2 = 8.2 μm, Δ2 = -0.03%;

[0047] The radius of the sunken cladding is R3 = 16.0 μm, and Δ3 = -0.308%.

[0048] The radius of the air-assisted orifice is R4 = 2.5 μm;

[0049] The outer cladding radius R5 = 62.5 μm, Δ5 = 0;

[0050] Four cores were inserted into four holes in the outer cladding, and then drawn to obtain the desired optical fiber. After drawing, the fiber was tested and found to have an attenuation of 0.180 dB / km at 1550 nm, a macrobend (Ф32×1t) of 0.02 dB, and intercore crosstalk between any two cores of the fiber ranging from -65.712 to -105.337 dB / 100 km.

[0051] A method for fabricating a low-crosstalk multi-core single-mode optical fiber includes the following steps:

[0052] S1. Using silicon tetrachloride as the main raw material, a loose material was prepared by axial vapor deposition (VAD) at a flow rate of 0.3 L / min. Simultaneously, germanium tetrachloride gas was doped into the core layer at a flow rate of 0.04 L / min, and carbon tetrafluoride was doped into the inner cladding layer at a flow rate of 0.2 L / min. The density of the loose material was controlled to be 0.25 g / cm³. 3 Then, it is dehydrated and sintered at 1000℃, and finally, it is stretched by equal volume to obtain the stretched core rod I (this step yields the core layer + inner cladding layer);

[0053] S2. Using silicon tetrachloride as the main raw material, a loose material was prepared by axial vapor deposition (VAD) at a flow rate of 0.3 L / min, with the density of the loose material controlled at 0.25 g / cm³. 3 The process involves dehydration, fluorination, and sintering at 800℃, while controlling the amount of fluorine used during the sintering and fluorination of the loose material to achieve the purpose of doping with different fluorine concentrations. The fluorination flow rate is usually between 0.1 and 0.6 L / min. The fluorine-doped sintered mandrel is then drilled and ground to the appropriate inner / outer diameter through a cold working process to obtain the sleeve.

[0054] S3. Assemble the extended mandrel I into the sleeve and melt and shrink it to a suitable outer diameter. During the extension process, parameters such as extension power (20%), etching power (15%), and etching times (3 times) need to be controlled to obtain the extended mandrel II, i.e. the core.

[0055] S4. Using high-precision drilling equipment, drill holes in the sleeve blank rod in sequence according to the designed hole distribution diagram (including air-assisted holes and core holes) to produce the sleeve.

[0056] S5. Assemble the extended core rod II into the matching core hole of the sleeve post, and obtain the low crosstalk multi-core single-mode optical fiber preform by melting and stretching.

[0057] S6. The fiber preform is drawn at a speed of 200m / min to obtain a low crosstalk multi-core single-mode fiber.

[0058] Example 2

[0059] like Figure 2 As shown, a low-crosstalk multi-core single-mode optical fiber comprises seven cores and an outer cladding with air-assisted holes covering the cores. Each core includes a core layer, an inner cladding, and a recessed cladding arranged sequentially from the inside out. Six air-assisted holes are evenly distributed around the periphery of each core, arranged in a regular hexagonal pattern around the core layer. The inter-core spacing at the fiber end face is 48 μm. Each layer satisfies the following:

[0060] The core layer radius R1 = 3.5 μm, and Δ1 is 0.385%;

[0061] The inner cladding radius R2 = 6.8 μm, Δ2 = -0.04%;

[0062] The radius of the sunken cladding is R3 = 14.0 μm, and Δ3 = -0.343%.

[0063] The radius of the air-assisted orifice is R4 = 4.0 μm;

[0064] The outer cladding radius R5 = 75.0 μm, Δ5 = 0;

[0065] Seven cores were inserted into seven holes in the outer cladding, and then drawn to obtain the desired optical fiber. After drawing, the fiber was tested and found to have an attenuation of 0.181 dB / km at 1550 nm, a macrobend (Ф32×1t) of 0.03 dB, and intercore crosstalk between any two cores of the fiber ranging from -80.292 to -112.337 dB / 100 km.

[0066] Same as Example 1.

[0067] Any parts or structures not specifically described in this invention can be made using existing technologies or products, and will not be elaborated upon here.

[0068] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A low-crosstalk multi-core single-mode optical fiber, characterized in that, The device comprises several cores and an outer cladding layer with air-assisted holes covering the cores. Each core consists of a core layer, an inner cladding layer, and a recessed cladding layer arranged sequentially from the inside out. The air-assisted holes are arranged in a regular hexagonal pattern around the core layer. The spacing between two adjacent cores is 35~50μm. The recessed cladding layer is a fluorine-doped quartz glass layer with a radius R3 of 10.5~27.5μm and a relative refractive index difference Δ3 of -0.20%~-0.40%. The radius R4 of the air-assisted holes is 2~8μm and the relative refractive index difference Δ4 is ​​-31.38%.

2. The low crosstalk multi-core single-mode optical fiber according to claim 1, characterized in that, The core layer is a germanium-doped quartz glass layer with a radius R1 of 3.0~5.5μm and a relative refractive index difference Δ1 of 0.25%~0.40%.

3. The low crosstalk multi-core single-mode optical fiber according to claim 1, characterized in that, The inner cladding is a fluorine-doped quartz glass layer with a radius R2 of 4.5~13.75μm and a relative refractive index difference Δ2 of -0.03%~0.

4. The low crosstalk multi-core single-mode optical fiber according to claim 1, characterized in that, The radius R5 of the outer cladding layer is 62.5~75.0μm, and the relative refractive index difference Δ5 is 0~0.03%.

5. A method for fabricating a low-crosstalk multi-core single-mode optical fiber according to any one of claims 1-4, characterized in that, Includes the following steps: S1. Using silicon tetrachloride as the main raw material, a germanium-doped core layer and a fluorine-doped inner cladding loose body are prepared by axial vapor deposition or external vapor deposition, and then sintered and stretched to obtain stretched core rod I. S2. Using silicon tetrachloride as the main raw material, a loose body is prepared by deposition using VAD or OVD method. By controlling the amount of fluorine used in the sintering and fluorination process of the loose body, the purpose of differential fluorine concentration doping is achieved. Then, the fluorine-doped core rod is processed to a suitable size to obtain a sleeve. S3. Assemble the extended mandrel I into the sleeve and melt and shrink it to a suitable outer diameter to obtain the required core. S4. Using high-precision drilling equipment, drill holes on the sleeve blank according to the designed distribution diagram of air-assisted holes and core holes to produce the sleeve. S5. Assemble the core into the matching core hole of the sleeve post, and then obtain a low crosstalk multi-core single-mode optical fiber preform by melting and stretching. S6. The fiber preform is drawn into fibers to obtain a low-crosstalk multi-core single-mode fiber.

6. The method for fabricating a low-crosstalk multi-core single-mode optical fiber according to claim 5, characterized in that, After drawing, the crosstalk between any two cores in the optical fiber does not exceed -60dB / 100km, the attenuation at 1550nm is ≤0.185dB / km, and the macrobending at 1550nm (Ф32×1t) is ≤0.05dB.

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