A strongly coupled multicore optical fiber

Abstract

This invention belongs to the field of optical fiber technology and discloses a strongly coupled multi-core optical fiber. The invention includes a common outer cladding and multiple fiber cores; each fiber core includes a core layer, a first inner cladding, and a second inner cladding; the common outer cladding is a fully fluorine-doped silica glass layer with a radius R4 of 62.5–125 μm and a relative refractive index difference Δ4 of -0.35%–-0.2%; the core layer has a radius R1 of 4–7 μm and a relative refractive index difference Δ1 of -0.2%–0.1%; the first inner cladding has a radius R2 of 6–10 μm and a relative refractive index difference Δ2 of -0.38%–-0.3%; the second inner cladding has a radius R3 of 8–12 μm, is concave, and has a maximum relative refractive index difference Δ3. MAX The range is -0.5% to -0.35%, with a minimum relative refractive index difference of Δ4 and |Δ3. MAX The value of / △4︱ ranges from 1.18 to 1.89. This invention optimizes the performance parameters of optical fibers.

Description

Technical Field

[0001] This invention belongs to the field of optical fiber technology, and more specifically, relates to a strongly coupled multi-core optical fiber. Background Technology

[0002] Single-mode fiber offers advantages such as high transmission speed, large information carrying capacity, and long transmission distance, making it widely used in fiber optic communication networks. 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 100Tb / s for a single fiber. Since 2012, space division multiplexing technology based on multi-core and few-mode fibers has become a hot topic in high-capacity fiber optic communication. Multi-core fibers utilize multiple cores for transmission, theoretically allowing for the simultaneous carrying of more data.

[0003] Based on the spacing between the cores, multi-core fibers can be classified into strongly coupled multi-core fibers and weakly coupled multi-core fibers. Weakly coupled multi-core fibers require the addition of a recessed layer between the cores to suppress energy overlap and reduce crosstalk. Strongly coupled fibers are typically used in lasers or amplifiers. Currently, some research and designs of strongly coupled fibers have not sufficiently optimized performance parameters such as spatial mode dispersion and attenuation, resulting in fibers primarily suited for short-distance applications and unsuitable for long-distance use. Furthermore, some existing research and designs of strongly coupled fibers ultimately achieve supermode transmission between modes within the same core, failing to achieve energy coupling between cores. Summary of the Invention

[0004] The purpose of this invention is to provide a strongly coupled multi-core optical fiber to optimize the performance parameters of the strongly coupled multi-core optical fiber.

[0005] This invention provides a strongly coupled multi-core optical fiber, comprising: a common cladding and multiple fiber cores disposed within the common cladding; each fiber core comprises, from the inside out, a core layer, a first inner cladding, and a second inner cladding; the common cladding is a fully fluorine-doped silica glass layer, the radius R4 of the common cladding is 62.5–125 μm, and the relative refractive index difference Δ4 of the common cladding is -0.35%–-0.2%; the radius R1 of the core layer is 4–7 μm, and the relative refractive index difference Δ1 of the core layer is -0.2%–0.1%; the radius R2 of the first inner cladding is 6–10 μm, and the relative refractive index difference Δ2 of the first inner cladding is -0.38%–-0.3%; the radius R3 of the second inner cladding is 8–12 μm, the second inner cladding is concave, and the maximum relative refractive index difference Δ3 of the second inner cladding is... MAX The value is -0.5% to -0.35%, and the minimum relative refractive index difference of the second inner cladding is Δ4, |Δ3. MAX The value of / △4︱ ranges from 1.18 to 1.89.

[0006] Preferably, the core layer is a silicon dioxide glass layer co-doped with germanium, fluorine, and alkali metals.

[0007] Preferably, the relative refractive index contribution of germanium in the core layer is 0.2% to 0.5%, and the alkali metal content is 100 to 3000 ppm.

[0008] Preferably, the alkali metal is one or more of lithium, sodium, potassium, and rubidium.

[0009] Preferably, the number of fiber cores is 4 to 16, the center line of all the fiber cores forms a regular polygon, the distance between the center of all the fiber cores and the center of the common outer cladding is the same, and the core spacing between each fiber core and its nearest neighbor is 16 to 26 μm.

[0010] Preferably, the strongly coupled multi-core optical fiber further includes: a marker core; the marker core is placed inside the common cladding, the distance between the center of the marker core and the center of the fiber core closest to it is 20-30 μm, and the line connecting the center of the marker core and the center of the fiber core passes through the center of the common cladding.

[0011] Preferably, the spatial mode dispersion of the strongly coupled multi-core optical fiber at a wavelength of 1550 nm is equal to or less than 15 ps / km. 1 / 2 .

[0012] Preferably, all cores in the strongly coupled multi-core optical fiber have the same attenuation, and the attenuation of each core in each mode at a wavelength of 1550nm is less than or equal to 0.185dB / km.

[0013] Preferably, the macrobending loss of the strongly coupled multi-core optical fiber at a wavelength of 1550nm with a bending radius of R30mm after 100 turns is equal to or less than 0.04dB.

[0014] Preferably, the fiber core closest to the marked core is marked as fiber core number 1, and the other fiber cores are numbered sequentially in a clockwise or counterclockwise direction; the welding loss between fiber cores with the same number is equal to or less than 0.5dB, and the welding loss between fiber cores with different numbers is equal to or less than 0.7dB.

[0015] One or more technical solutions provided in this invention have at least the following technical effects or advantages:

[0016] (1) The present invention optimizes the spatial mode dispersion of the optical fiber by rationally designing the cross-sectional structure of the optical fiber; the second inner cladding is concave and has the lowest refractive index, which can reduce the influence of stress on the core layer under bending conditions, thereby effectively increasing the bending resistance of the optical fiber. The spatial mode dispersion and macro bending loss performance parameters of the strongly coupled multi-core optical fiber provided by the present invention are good in the application band, which is beneficial to the transmission of optical fiber in the field of communication; the common outer cladding adopts the design of a fully fluorine-doped silica glass layer, which can reduce the attenuation coefficient of the optical fiber.

[0017] (2) The core layer of this invention is designed with germanium, fluorine and alkali metal co-doped silica glass layer, and the viscosity matching inside the optical fiber is reasonably designed, which can reduce defects in the optical fiber preparation process and further reduce the attenuation coefficient of the optical fiber.

[0018] (3) The present invention rationally designs the core spacing between the fiber core and its nearest neighboring fiber core. The smaller core spacing can realize strong coupling supermode between the fiber cores. The electric field distribution of the supermode can be regarded as the overlap and strong reconstruction of independent modes, which can achieve higher mode density, thereby effectively reducing nonlinear effects and achieving better optical fiber transmission.

[0019] (4) The present invention rationally designs the position of the marker core, which helps to reduce splicing loss and overall link loss. Attached Figure Description

[0020] Figure 1 A schematic diagram of the refractive index profile of a strongly coupled multi-core optical fiber provided in an embodiment of the present invention;

[0021] Figure 2 A schematic diagram of the end face structure of a strongly coupled multi-core optical fiber provided in an embodiment of the present invention;

[0022] Figure 3 This is a schematic diagram of the core structure in a strongly coupled multi-core optical fiber provided in an embodiment of the present invention. Detailed Implementation

[0023] To facilitate the introduction of the invention, the following terms are first defined:

[0024] Relative refractive index Δn i This represents the relative refractive index difference between each layer of the optical fiber and pure silicon dioxide.

[0025] Starting from the central axis of the optical fiber core, the layer closest to the central axis is defined as the core layer based on the change in refractive index, and the outermost layer of the optical fiber is a fully fluorine-doped silica glass layer.

[0026] The relative refractive index difference Δn between the layers of the optical fiber i Defined by the following equation:

[0027]

[0028] Where, n i Let n be the refractive index of each layer of the optical fiber. c is the refractive index of pure silicon dioxide.

[0029] The contribution of the relative refractive index difference of Ge doping in the fiber core to Δ Ge Defined by the following equation:

[0030]

[0031] 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, where n c is the refractive index of pure silicon dioxide.

[0032] 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.

[0033] This invention provides a strongly coupled multi-core optical fiber, see [link to relevant documentation]. Figures 1 to 3 The system comprises: a common outer cladding layer and multiple fiber cores disposed within the common outer cladding layer; each fiber core comprises, from the inside out, a core layer, a first inner cladding layer, and a second inner cladding layer; the common outer cladding layer is a fully fluorine-doped silica glass layer, the radius R4 of the common outer cladding layer is 62.5–125 μm, and the relative refractive index difference Δ4 of the common outer cladding layer is -0.35%–-0.2%; the radius R1 of the core layer is 4–7 μm, and the relative refractive index difference Δ1 of the core layer is -0.2%–0.1%; the radius R2 of the first inner cladding layer is 6–10 μm, and the relative refractive index difference Δ2 of the first inner cladding layer is -0.38%–-0.3%; the radius R3 of the second inner cladding layer is 8–12 μm, the second inner cladding layer is concave, and the maximum relative refractive index difference Δ3 of the second inner cladding layer is... MAX The value is -0.5% to -0.35%, and the minimum relative refractive index difference of the second inner cladding is Δ4, |Δ3. MAX The value of / △4︱ ranges from 1.18 to 1.89.

[0034] The core layer is a silica glass layer co-doped with germanium, fluorine, and alkali metals. The relative refractive index contribution of germanium in the core layer is 0.2%–0.5%, and the alkali metal content is 100–3000 ppm. The alkali metal is one or more of lithium, sodium, potassium, and rubidium.

[0035] All fiber cores are homogeneous, and the number of fiber cores is 4 to 16. The center line of all fiber cores forms a regular polygon. The distance between the center of all fiber cores and the center of the common outer cladding is the same. The core spacing P between each fiber core and its nearest neighbor is 16 to 26 μm.

[0036] To facilitate identification of the positions of each core, the strongly coupled multi-core optical fiber also includes a marker core. The marker core is placed within the common cladding, and the distance between the center of the marker core and the center of the core closest to it is 20–30 μm. Furthermore, the line connecting the center of the marker core and the center of the core passes through the center of the common cladding. That is, the marker core is located 20–30 μm directly above one of the cores. The core closest to the marker core is labeled as core number 1, and the other cores are numbered sequentially in a clockwise or counterclockwise direction; for example, the other cores are numbered 2–8 in a clockwise direction.

[0037] The structure and main performance parameters of the optical fibers in the three embodiments provided by the present invention are shown in Tables 1 and 2. Since the attenuation of the eight fiber cores is consistent, the fusion splicing loss test only tests the attenuation of one fiber core before and after fusion splicing.

[0038] Table 1. Structure and material composition of the eight-core optical fiber in the example.

[0039]

[0040] Table 2 Main performance parameters of the eight-core optical fiber in Example 2

[0041]

[0042]

[0043] According to Tables 1 and 2, the spatial mode dispersion of the strongly coupled multi-core optical fiber at a wavelength of 1550 nm is equal to or less than 15 ps / km. 1 / 2 All cores in the strongly coupled multi-core optical fiber have the same attenuation. The attenuation of each core in each mode at a wavelength of 1550 nm is less than or equal to 0.185 dB / km, and under preferred conditions (e.g., Example 1), it is equal to or less than 0.175 dB / km. The macrobending loss of each mode in the strongly coupled multi-core optical fiber at a wavelength of 1550 nm with a bending radius of R30 mm for 100 turns is equal to or less than 0.04 dB. The fusion splice loss between cores with the same designation (i.e., cores in the same position) is equal to or less than 0.5 dB, and the fusion splice loss between cores with different designations (i.e., cores in different positions) is equal to or less than 0.7 dB.

[0044] In summary, the strongly coupled multi-core optical fiber provided by this invention not only has low attenuation, but also good overall performance in terms of macrobending, spatial mode dispersion and fusion splice loss.

[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 strongly coupled multi-core optical fiber, characterized in that, include: The system comprises a common outer cladding and multiple fiber cores disposed within the common outer cladding; each fiber core, from the inside out, includes a core layer, a first inner cladding, and a second inner cladding; the common outer cladding is a fully fluorine-doped silica glass layer, with a radius R4 of 62.5–125 μm and a relative refractive index difference Δ4 of -0.35%–-0.2%; the core layer has a radius R1 of 4–7 μm and a relative refractive index difference Δ1 of -0.2%–0.1%; the first inner cladding has a radius R2 of 6–10 μm and a relative refractive index difference Δ2 of -0.38%–-0.3%; the second inner cladding has a radius R3 of 8–12 μm, and the refractive index distribution curve of the second inner cladding is concave, with a maximum relative refractive index difference Δ3. MAX The value is -0.5% to -0.35%, and the minimum relative refractive index difference of the second inner cladding is Δ4, |Δ3. MAX The value of / △4︱ ranges from 1.18 to 1.

89.

2. The strongly coupled multi-core optical fiber according to claim 1, characterized in that, The core layer is a silica glass layer co-doped with germanium, fluorine, and alkali metals.

3. The strongly coupled multi-core optical fiber according to claim 2, characterized in that, The relative refractive index contribution of germanium in the core layer is 0.2% to 0.5%, and the content of alkali metals is 100 to 3000 ppm.

4. The strongly coupled multi-core optical fiber according to claim 2, characterized in that, The alkali metal is one or more of lithium, sodium, potassium, and rubidium.

5. The strongly coupled multi-core optical fiber according to claim 1, characterized in that, The number of fiber cores is 4 to 16, the center line of all the fiber cores forms a regular polygon, the distance between the center of all the fiber cores and the center of the common outer cladding is the same, and the core spacing between each fiber core and its nearest neighbor is 16 to 26 μm.

6. The strongly coupled multi-core optical fiber according to claim 1, characterized in that, Also includes: The marking core is placed within the common outer cladding layer. The distance between the center of the marking core and the center of the nearest fiber core is 20-30 μm, and the line connecting the center of the marking core and the center of the fiber core passes through the center of the common outer cladding layer.

7. The strongly coupled multi-core optical fiber according to claim 1, characterized in that, The spatial mode dispersion of the strongly coupled multi-core optical fiber at a wavelength of 1550 nm is equal to or less than 15 ps / km. 1 / 2 .

8. The strongly coupled multi-core optical fiber according to claim 1, characterized in that, All cores in the strongly coupled multi-core optical fiber have the same attenuation, and the attenuation of each core in each mode at a wavelength of 1550nm is less than or equal to 0.185dB / km.

9. The strongly coupled multi-core optical fiber according to claim 1, characterized in that, The macrobending loss of the strongly coupled multi-core optical fiber at a wavelength of 1550nm with a bending radius of R30mm after 100 turns is equal to or less than 0.04dB in each mode.

10. The strongly coupled multi-core optical fiber according to claim 6, characterized in that, The fiber core closest to the marked core is marked as fiber core number 1, and the other fiber cores are numbered sequentially in a clockwise or counterclockwise direction; the welding loss between fiber cores with the same number is equal to or less than 0.5dB, and the welding loss between fiber cores with different numbers is equal to or less than 0.7dB.

Images