Low-loss few-mode optical fiber

Abstract

The application belongs to the technical field of optical fiber, and discloses a low-attenuation few-mode optical fiber, wherein the core layer is three-layered, and the core layer is coated with an inner cladding layer, a sunken cladding layer and an outer cladding layer in sequence; the radius R1 of the first core layer is 2-3.2 μm, and the relative refractive index difference Δ1 is 0.3-0.6%; the radius R2 of the second core layer is 5-8 μm, and the relative refractive index difference Δ2 is 0.6-1.2%; the radius R3 of the third core layer is 7-10 μm, and the relative refractive index difference Δ3 is 0.4-0.8%; the relative refractive index differences of the three core layers are step-type, and the relative refractive index differences satisfy Δ1<Δ3<Δ2; the radius R4 of the inner cladding layer is 12-15 μm, and the relative refractive index difference Δ4 is -0.2%-0.1%; the radius R5 of the sunken cladding layer is 16-19 μm, and the relative refractive index difference Δ5 is -1.0%--0.5%; and the outer cladding layer is a pure silica glass layer. The application has low attenuation and good comprehensive performance.

Description

Technical Field

[0001] This invention belongs to the field of optical fiber technology, and more specifically, relates to a low-attenuation reduced-mode optical fiber. Background Technology

[0002] Single-mode fiber is widely used in fiber optic communication networks due to its advantages such as high transmission speed, large information carrying capacity, and long transmission distance. However, with the increasing demand for capacity from communication and big data services, network bandwidth requirements are intensifying, and the capacity of optical transmission networks is gradually approaching the Shannon limit of a single fiber. Experiments show that using few-mode fiber combined with Multiple Input Multiple Output (MIMO) technology can transmit signals in more than one spatial propagation mode, and MIMO technology can compensate for the mutual coupling between modes, separating each spatial mode at the receiving end. Therefore, few-mode fiber can be used to improve optical transmission capacity.

[0003] Existing research has proposed several parabolic or step-index few-mode fibers, each with its own advantages and disadvantages. Step-index few-mode fibers have a simple manufacturing process and are easy to mass-produce, but their large differential group delay (DGD) remains a problem to be solved. Graded-index few-mode fibers allow for more parameter adjustments to reduce intermodal crosstalk and DGD, but the process is complex, related parameters are difficult to control precisely, and repeatability is poor.

[0004] Furthermore, as a crucial transmission medium in optical fiber communication systems, the performance of optical fibers must be further improved to meet the actual development needs of these systems. Attenuation is one such important performance indicator. The lower the attenuation of the optical fiber, the longer the transmission distance of the optical signal in this medium, and the longer the repeaterless distance of the optical communication system. This significantly reduces the number of repeater stations, improving the reliability of the communication system while substantially reducing construction and maintenance costs.

[0005] How to design few-mode fibers to achieve weak coupling between modes, so that they not only have low attenuation and are easy to manufacture, but also have good overall performance, is a technical problem that needs to be addressed in this field. Summary of the Invention

[0006] The purpose of this invention is to provide a low-attenuation reduced-mode fiber that achieves weak coupling between modes, resulting in low attenuation, ease of manufacturing, and good overall performance.

[0007] This invention provides a low-attenuation reduced-mode fiber, comprising a core layer and a cladding layer. The core layer consists of three layers, arranged from the inside out as a first core layer, a second core layer, and a third core layer. The core layers are surrounded from the inside out by an inner cladding layer, a recessed cladding layer, and an outer cladding layer. The radius R1 of the first core layer is 2–3.2 μm, and the relative refractive index difference Δ1 is 0.3–0.6%. The radius R2 of the second core layer is 5–8 μm, and the relative refractive index difference Δ2 is 0.6–1.2%. The radius R3 of the third core layer is 7–10 μm. m, the relative refractive index difference Δ3 of the third core layer is 0.4 to 0.8%; the relative refractive index difference of the first core layer, the second core layer and the third core layer is step-type, and the relative refractive index difference satisfies Δ1 < Δ3 < Δ2; the radius R4 of the inner cladding is 12 to 15 μm, and the relative refractive index difference Δ4 of the inner cladding is -0.2% to 0.1%; the radius R5 of the recessed cladding is 16 to 19 μm, and the relative refractive index difference Δ5 of the recessed cladding is -1.0% to -0.5%; the outer cladding is a pure silica glass layer.

[0008] Preferably, each core layer is a silica glass layer doped with germanium and alkali metals.

[0009] Preferably, each core layer is also doped with fluorine.

[0010] Preferably, the relative refractive index contribution of germanium in each core layer is 0.3% to 1.2%, and the alkali metal content in each core layer is 50 to 4000 ppm.

[0011] Preferably, the alkali metal incorporated is one or more of lithium, sodium, potassium, and rubidium.

[0012] Preferably, 0.3≤△1 / △2≤0.75, 0.45≤△1 / △3≤0.87.

[0013] Preferably, the low-attenuation reduced-mode fiber supports propagation of four LP modes in the C-band: LP01, LP11, LP21 and LP02;

[0014] The parameters of the low-attenuation reduced-mode fiber satisfy the following formula:

[0015]

[0016] Where n1 is the refractive index value of the first core layer and n4 is the refractive index value of the inner cladding layer.

[0017] Preferably, the low-attenuation low-mode fiber has an attenuation of less than or equal to 0.21 dB / km for each mode at a wavelength of 1550 nm.

[0018] Preferably, the macrobending loss of the low-attenuation reduced-mode fiber at a wavelength of 1550nm with a bending radius of R10mm for one turn is equal to or less than 0.25dB.

[0019] Preferably, the low-attenuation low-mode fiber has a differential group delay of 2 to 10 ps / m between each higher-order mode and the fundamental mode at a wavelength of 1550 nm.

[0020] Preferably, the effective area of ​​the fundamental mode and each higher-order mode in the low-attenuation reduced-mode fiber is 100–260 μm. 2 .

[0021] Preferably, the low-attenuation reduced-mode fiber has a dispersion of each mode equal to or less than 27 ps / (nm·km) at a wavelength of 1550 nm; and the mode field diameter of each mode of the low-attenuation reduced-mode fiber at a wavelength of 1550 nm is 11 to 17 μm.

[0022] One or more technical solutions provided in this invention have at least the following technical effects or advantages:

[0023] (1) This invention adopts a three-ring core structure and, through the rational design of the cross-section of each layer of the optical fiber, suppresses the coupling between the LP21 and LP02 modes, achieving weak mode coupling and increasing the transmission capacity of the optical fiber. The comprehensive performance parameters of the few-mode fiber provided by this invention, such as DGD, dispersion of each mode, and bending loss, are good in the application band. Spatial division multiplexing technology can be used to support long-distance signal transmission of four modes, each with a low attenuation coefficient. This invention adopts a step-index core structure and a pure silicon dioxide cladding design, which not only facilitates manufacturing and production but also reduces production costs.

[0024] (2) The present invention adopts a core layer design with germanium and alkali metals, and reasonably designs the viscosity matching inside the optical fiber, which can reduce defects in the optical fiber preparation process and reduce the attenuation coefficient of the optical fiber.

[0025] (3) The present invention designs a reasonable recessed cladding, which can control the effective refractive index difference and greatly reduce the bending loss of the high-order mode of the optical fiber. Attached Figure Description

[0026] Figure 1 A schematic diagram of the refractive index profile of a low-attenuation reduced-mode fiber provided in an embodiment of the present invention;

[0027] Figure 2 This is a schematic cross-sectional view of a low-attenuation reduced-mode optical fiber provided in an embodiment of the present invention. Detailed Implementation

[0028] To facilitate the introduction of this invention, the following terms are first defined:

[0029] Relative refractive index difference Δn i This represents the difference in relative refractive index between each layer of the optical fiber (excluding the cladding) and pure silicon dioxide.

[0030] Starting from the central axis of the optical fiber core, based on the change in refractive index, the layer closest to the central axis is defined as the first core layer, and the outermost layer of the optical fiber, namely the pure silicon dioxide layer, is the cladding layer.

[0031] The relative refractive index difference Δn between the layers of the optical fiber i Defined by the following equation:

[0032]

[0033] Where, n i Let n be the refractive index of each layer of the optical fiber (excluding the cladding). c is the refractive index of the outer cladding layer, i.e., the refractive index of pure silicon dioxide.

[0034] The relative refractive index contribution of germanium (Ge) doping in the fiber core Δ Ge Defined by the following equation:

[0035]

[0036] Where, n Ge The change in refractive index of silica glass caused by the Ge dopant in the fiber core, when incorporated into pure silica without other dopants, is denoted by n. c is the refractive index of the outer cladding layer, i.e., the refractive index of pure silicon dioxide.

[0037] The relative refractive index contribution Δ of fluorine (F) doping in the fiber core F Defined by the following equation:

[0038]

[0039] Where, n F The change in refractive index of silica glass caused by the F dopant in the fiber core, when incorporated into pure silica without other dopants, is denoted by n. c is the refractive index of the outer cladding layer, i.e., the refractive index of pure silicon dioxide.

[0040] 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.

[0041] This invention provides a low-attenuation reduced-mode optical fiber, see [link to relevant documentation]. Figure 1 and Figure 2The system comprises a core layer and a cladding layer. The core layer consists of three layers, arranged from the inside out as a first core layer, a second core layer, and a third core layer. The core layer is surrounded from the inside out by an inner cladding layer, a recessed cladding layer, and an outer cladding layer. The radius R1 of the first core layer is 2–3.2 μm, and the relative refractive index difference Δ1 is 0.3–0.6%. The radius R2 of the second core layer is 5–8 μm, and the relative refractive index difference Δ2 is 0.6–1.2%. The radius R3 of the third core layer is 7–10 μm. The relative refractive index difference Δ3 of the layers is 0.4 to 0.8%; the relative refractive index difference of the first core layer, the second core layer, and the third core layer is step-type, and the relative refractive index difference satisfies Δ1 < Δ3 < Δ2; the radius R4 of the inner cladding layer is 12 to 15 μm, and the relative refractive index difference Δ4 of the inner cladding layer is -0.2% to 0.1%; the radius R5 of the recessed cladding layer is 16 to 19 μm, and the relative refractive index difference Δ5 of the recessed cladding layer is -1.0% to -0.5%; the outer cladding layer is a pure silica glass layer.

[0042] Specifically, 0.3≤△1 / △2≤0.75, 0.45≤△1 / △3≤0.87; and based on the range of relative refractive index difference, △5<△4.

[0043] The low-attenuation reduced-mode fiber supports propagation of four LP modes in the C-band: LP01, LP11, LP21 and LP02.

[0044] The parameters of the low-attenuation reduced-mode fiber satisfy the following formula:

[0045]

[0046] Where n1 is the refractive index value of the first core layer and n4 is the refractive index value of the inner cladding layer.

[0047] Each core layer is a silica glass layer doped with germanium and alkali metals. Alternatively, each core layer can be a silica glass layer co-doped with germanium, fluorine, and alkali metals, meaning it can also be doped with fluorine. The relative refractive index contribution of germanium in each core layer is 0.3%–1.2%, and the alkali metal content in each core layer is 50–4000 ppm. The doped alkali metals are one or more of lithium, sodium, potassium, and rubidium.

[0048] The inner cladding is doped with at least one element selected from fluorine and germanium, wherein the relative refractive index contribution of germanium is 0% to 0.2% and the relative refractive index contribution of fluorine is -0.3% to 0.8%; the sunken cladding is doped with fluorine, and the radius R6 of the outer cladding is 60 to 100 μm.

[0049] The low-attenuation less-mode fiber has an attenuation of less than or equal to 0.21 dB / km for each mode at a wavelength of 1550 nm; under preferred conditions, it has an attenuation of less than or equal to 0.19 dB / km.

[0050] The macrobending loss of the low-attenuation reduced-mode fiber at a wavelength of 1550nm with a bending radius of R10mm for one full bend is equal to or less than 0.25dB.

[0051] The low-attenuation low-mode fiber has a differential group delay (DGD) of 2–10 ps / m between each higher-order mode and the fundamental mode at a wavelength of 1550 nm.

[0052] The effective area of ​​the fundamental mode and all higher-order modes in the low-attenuation low-mode fiber is 100–260 μm. 2 .

[0053] The low-attenuation less-mode fiber has a dispersion of 27 ps / (nm·km) for each mode at a wavelength of 1550 nm.

[0054] The low-attenuation reduced-mode fiber has a mode field diameter of 11–17 μm at a wavelength of 1550 nm for each mode.

[0055] The structure and main performance parameters of the optical fibers in the four embodiments provided by the present invention are shown in Tables 1 and 2.

[0056] Table 1. Structure and material composition of the few-mode fiber in the embodiments.

[0057]

[0058] Table 2. Main performance parameters of the few-mode fiber in the examples.

[0059]

[0060] In summary, the low-attenuation reduced-mode fiber provided by this invention can achieve weak coupling between modes, and not only has low attenuation and is easy to manufacture, but also has good overall performance in terms of DGD, dispersion and bending loss of each mode.

[0061] 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 low-attenuation reduced-mode optical fiber, comprising a core layer and a cladding layer, characterized in that, The core layer consists of three layers, from the inside out: a first core layer, a second core layer, and a third core layer. Each core layer is surrounded by an inner cladding layer, a recessed cladding layer, and an outer cladding layer, from the inside out. The radius R1 of the first core layer is 2–3.2 μm, and the relative refractive index difference Δ1 of the first core layer is 0.3–0.6%. The radius R2 of the second core layer is 5–8 μm, and the relative refractive index difference Δ2 of the second core layer is 0.6–1.2%. The radius R3 of the third core layer is 7–10 μm, and the relative refractive index difference Δ3 of the third core layer is 0.4–0.8%. The relative refractive index difference between the first core layer, the second core layer, and the third core layer is step-type, and the relative refractive index difference satisfies Δ1 < Δ3 < Δ2, 0.3 ≤ Δ1 / Δ2 ≤ 0.75, and 0.45 ≤ Δ1 / Δ3 ≤ 0.87; the radius R4 of the inner cladding is 12 to 15 μm, and the relative refractive index difference Δ4 of the inner cladding is -0.2% to 0.1%; the radius R5 of the recessed cladding is 16 to 19 μm, and the relative refractive index difference Δ5 of the recessed cladding is -1.0% to -0.5%; the outer cladding is a pure silica glass layer.

2. The low-attenuation low-mode optical fiber according to claim 1, characterized in that, Each core layer is a silica glass layer doped with germanium and alkali metals.

3. The low-attenuation low-mode optical fiber according to claim 2, characterized in that, Each core layer also contains fluorine.

4. The low-attenuation low-mode optical fiber according to claim 2, characterized in that, The relative refractive index contribution of germanium in each core layer is 0.3% to 1.2%, and the alkali metal content in each core layer is 50 to 4000 ppm.

5. The low-attenuation low-mode optical fiber according to claim 2, characterized in that, The alkali metals incorporated are one or more of lithium, sodium, potassium, and rubidium.

6. The low-attenuation low-mode optical fiber according to claim 1, characterized in that, The low-attenuation reduced-mode fiber supports propagation of four LP modes in the C-band: LP01, LP11, LP21 and LP02. The parameters of the low-attenuation reduced-mode fiber satisfy the following formula: in, This represents the refractive index value of the first core layer. This represents the refractive index value of the inner cladding.

7. The low-attenuation low-mode optical fiber according to claim 1, characterized in that, The low-attenuation less-mode fiber has an attenuation of less than or equal to 0.21 dB / km for each mode at a wavelength of 1550 nm.

8. The low-attenuation low-mode optical fiber according to claim 1, characterized in that, The macrobending loss of the low-attenuation reduced-mode fiber at a wavelength of 1550nm with a bending radius of R10mm for one full bend is equal to or less than 0.25dB.

9. The low-attenuation low-mode optical fiber according to claim 1, characterized in that, The low-attenuation low-mode fiber has a differential group delay of 2–10 ps / m between each higher-order mode and the fundamental mode at a wavelength of 1550 nm.

10. The low-attenuation low-mode optical fiber according to claim 1, characterized in that, The effective area of ​​the fundamental mode and all higher-order modes in the low-attenuation low-mode fiber is 100–260 μm. 2 .

11. The low-attenuation low-mode optical fiber according to claim 1, characterized in that, The low-attenuation reduced-mode fiber has a dispersion of 27 ps / (nm·km) for each mode at a wavelength of 1550 nm; the mode field diameter of each mode in the low-attenuation reduced-mode fiber at a wavelength of 1550 nm is 11 to 17 μm.

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