Polarization-maintaining multi-core optical fiber based on weak coupling mechanism

Abstract

The invention discloses a polarization-maintaining multi-core optical fiber based on a weak coupling mechanism, and belongs to the technical field of multi-core optical fibers. The polarization-maintaining multi-core optical fiber based on the weak coupling mechanism comprises an elliptical fiber core, a stress rod, a circular fiber core, an inner cladding and an outer cladding, the elliptical fiber core is coaxially arranged at the center of the polarization-maintaining multi-core optical fiber, the plurality of circular fiber cores are uniformly distributed on the outer ring of the elliptical fiber core along the circumferential direction, the stress rods are arranged between two adjacent circular fiber cores at equal intervals, and the outer cladding wraps the stress rods and the circular fiber cores. And the inner cladding is filled among the outer cladding, the elliptical fiber core, the stress rods and the circular fiber core.

Description

Technical Field

[0001] The invention relates to a polarization-maintaining multi-core optical fiber based on a weak coupling mechanism. Background Art

[0002] With the rapid development of technologies such as big data, cloud computing and 5G, the demand for bandwidth in modern communication networks continues to rise. As the backbone of current optical communication systems, traditional single-mode optical fiber (SSMF) has limited spatial multiplexing capabilities and its expansion potential has gradually reached its ceiling, making it difficult to meet the rapid growth of data transmission rate and capacity in the future. In this context, multi-core fiber (MCF) has emerged as an innovative spatial multiplexing technology. By integrating multiple cores in a single optical fiber, it significantly improves the transmission capacity and spectrum efficiency of the system.

[0003] However, the development of multi-core optical fiber is not smooth sailing and currently faces a series of challenges:

[0004] a. Cladding size issue: Some designs excessively pursue an increase in the number of fiber cores (e.g., thousand-core fiber), which leads to an increase in the cladding diameter, making these fibers incompatible with existing standard single-mode fiber infrastructure, increasing deployment costs and complexity.

[0005] b. Inadequate core area design: Some existing multi-core optical fiber designs fail to fully consider how to optimize the core layout to maximize space utilization, thus limiting their practical application effectiveness.

[0006] c. Inter-core crosstalk: This is a major technical obstacle faced by multi-core optical fibers. When multiple cores coexist in the same optical fiber, the signals between different cores may interfere with each other. This phenomenon is called inter-core crosstalk. It seriously affects the number and quality of independent communication channels, thereby restricting the overall performance of the system.

[0007] d. Poor bending characteristics: Multi-core optical fiber needs to have good bending characteristics in actual network deployment, but many current designs perform poorly in this regard, affecting its adaptability in various application scenarios.

[0008] In addition, the prior art still has the following deficiencies:

[0009] Core design limitations: The arrangement of the fiber core often lacks optimization considerations for heterogeneous structures, which not only limits the interaction between modes, but may also lead to significant mode interference, reducing transmission quality.

[0010] Lack of polarization-maintaining properties: Traditional multi-core optical fibers have weak processing capabilities for polarization modes and cannot effectively support high-quality parallel communication channels, which is a major defect for applications requiring high stability and low bit error rate.

[0011] Insufficient parameter optimization: In terms of reducing inter-core crosstalk, the existing technology fails to fully utilize the advantages of the low-refractive index auxiliary structure, which directly affects the overall performance and reliability of multi-core optical fiber.

[0012] In order to solve the above problems, the present invention proposes a polarization-maintaining multi-core optical fiber based on a weak coupling mechanism. Summary of the invention

[0013] The purpose of the present invention is to provide a polarization-maintaining multi-core optical fiber based on a weak coupling mechanism to solve the technical problems mentioned in the above background technology.

[0014] The technical solution for achieving the purpose of the present invention is:

[0015] A polarization-maintaining multi-core optical fiber based on a weak coupling mechanism comprises an elliptical core, a stress rod, a circular core, an inner cladding and an outer cladding; the elliptical core is coaxially arranged at the center of the polarization-maintaining multi-core optical fiber, a plurality of circular cores are provided, preferably 4 to 8, the plurality of circular cores are uniformly distributed on the outer ring of the elliptical core along the circumferential direction, the stress rods are arranged between two adjacent circular cores at equal intervals, the outer cladding is wrapped around the stress rods and the outside of the circular core, and the inner cladding is filled between the outer cladding, the elliptical core, the stress rods and the circular core.

[0016] Furthermore, the horizontal radius a1 of the elliptical fiber core is 6-8 μm, and the vertical radius b1 is 4-6 μm.

[0017] Furthermore, the circular core radius r is 4-8 μm, and the refractive index difference Δη between the circular core and the inner cladding is 0.5%-0.8%.

[0018] Furthermore, the stress rod is an elliptical boron-doped stress rod, the radius of the major semi-axis a2 of the stress rod is 8-12 μm, and the radius of the minor axis b2 is 5-10 μm; wherein the major axis of the stress rod is perpendicular to the line connecting the centers of two adjacent circular cores.

[0019] Furthermore, the refractive index of the stress rod is 1.415-1.425.

[0020] Furthermore, a first annular groove is provided between the elliptical core and the inner cladding, and the first annular groove is concentrically arranged outside the elliptical core.

[0021] Furthermore, the thickness of the first annular groove is 50-60% of the vertical radius of the elliptical core, and the refractive index of the first annular groove is 1.432-1.437.

[0022] Furthermore, a second annular groove is provided between the circular core and the inner cladding, and the second annular groove is concentrically arranged outside the circular core.

[0023] Furthermore, the thickness of the second annular groove is 50-60% of the radius of the circular core, and the refractive index of the second annular groove is 1.432-1.437.

[0024] Furthermore, the outer cladding has a diameter of 125 μm and a refractive index of 1.444.

[0025] By adopting the above technical solution, the present invention has the following beneficial effects:

[0026] (1) The present invention sets an elliptical core at the center of a polarization-maintaining multi-core optical fiber and introduces a geometric birefringence design, so that the optical fiber can provide multiple independent parallel communication channels in the C+L band, including a combination of spatial modes and polarization modes, effectively breaking the spatial degeneracy and polarization degeneracy of the modes, ensuring the isolation between the three high-efficiency transmission modes (LP01, LP11a and LP11b), and improving the bending performance of the polarization-maintaining multi-core optical fiber by introducing stress rods.

[0027] (2) The horizontal radius a1 of the elliptical core of the polarization-maintaining multi-core optical fiber of the present invention is 6 to 8 μm, and the vertical radius b1 is 4 to 6 μm. The refractive index profile of the elliptical core is different from that of the circular core, forming a heterogeneous structure, thereby improving the mode compatibility and communication quality.

[0028] (3) The stress rod of the present invention is an elliptical boron-doped stress rod, which further enhances the isolation of polarization modes through the stress birefringence mechanism. It is combined with the elliptical fiber core and introduces the design of geometric birefringence and stress birefringence, so that the optical fiber can provide multiple independent parallel communication channels in the C+L band, including a combination of spatial modes and polarization modes.

[0029] (4) The long axis of the stress rod of the present invention is perpendicular to the line connecting the centers of two adjacent circular cores, and the long axis of the elliptical stress rod is perpendicular to the line connecting the centers of two adjacent outer circular cores, thereby ensuring the overall stability and anti-interference ability of the optical fiber; wherein, the long axis of the elliptical stress rod is perpendicular to the line connecting the centers of two adjacent circular cores, so that a more uniform stress distribution can be formed inside the optical fiber; this symmetrical design avoids the deformation of the core caused by non-uniform stress, reduces the shape instability problem of the optical fiber under external mechanical impacts such as stretching and bending, and thus improves the overall structural stability of the optical fiber; the elliptical stress rod has a higher anti-deformation ability due to the mechanical advantage of its long axis direction, and can effectively resist external forces from the vertical direction. When the long axis of the stress rod is perpendicular to the line connecting the circular fiber core, the stress rod can absorb and disperse external forces in two directions at the same time, thereby improving the anti-interference ability of the overall structure; the elliptical stress rod will introduce a stronger stress birefringence effect in the direction perpendicular to the long axis, thereby making the optical fiber more stable to a specific polarization mode; this design complements the geometric birefringence effect of the elliptical fiber core, jointly improving the polarization-maintaining performance of the optical fiber and reducing the crosstalk of the polarization mode; temperature changes and mechanical vibrations in the external environment may introduce stress changes inside the optical fiber, resulting in a decrease in optical performance; the special directional design of the elliptical stress rod can effectively disperse the stress changes caused by such external disturbances, and avoid mode coupling or increased loss caused by local stress concentration.

[0030] (5) The radius r of the circular core of the present invention is 4 to 8 μm, and the refractive index difference Δη with the inner cladding is 0.5% to 0.8%. Boron-doped stress rods are arranged on the periphery of each circular core to further enhance the isolation of the polarization mode through the stress birefringence mechanism, reduce the mode interference between the central elliptical core and the peripheral circular core, and enhance the overall polarization maintaining capability.

[0031] (6) A first annular groove and a second annular groove with a low refractive index are respectively provided between the elliptical core and the circular core of the present invention and the inner cladding; and the thickness of the first annular groove is 50 to 60% of the vertical radius of the elliptical core, and the thickness of the second annular groove is 50 to 60% of the radius of the circular core. This design can ensure that the inter-core crosstalk is lower than -0.3dB / km, while maintaining low loss performance when the bending radius is greater than 30cm.

[0032] (7) The optical fiber cladding 1 of the present invention has a diameter of 125 μm and a refractive index of 1.444, which provides the necessary mechanical strength and environmental protection. The size design of the outer cladding takes into account the compatibility with standard single-mode optical fibers, making the optical fiber of the present invention suitable for existing optical fiber network systems.

[0033] (8) The present invention achieves low coupling loss and improves the overall performance of the system by precisely controlling the effective refractive index difference between the spatial mode and the polarization mode between the fiber cores.

[0034] (9) The multi-core optical fiber design proposed in the present invention has polarization-maintaining characteristics, can support high-quality parallel channels, and is suitable for application scenarios with high requirements for polarization mode decomposition capabilities.

[0035] (10) The present invention takes into account the bending loss problem of optical fiber in actual network deployment, and optimizes the design so that the optical fiber can still maintain low loss performance when the bending radius is greater than 30 cm.

[0036] (11) The multi-core optical fiber structure based on the weak coupling polarization maintaining mechanism of the present invention realizes multiple independent parallel communication channels in the 125μm cladding by optimizing the core layout and introducing stress regulation, which significantly improves the communication capacity and spectrum utilization of the optical fiber. At the same time, the design of geometric birefringence and stress birefringence is introduced, so that the optical fiber can provide multiple independent parallel communication channels in the C+L band, including a combination of spatial mode and polarization mode. While realizing high-density communication channels, it significantly reduces the optical fiber bending loss and crosstalk. It is an important technological breakthrough in the fields of long-distance low-loss optical communication, efficient data transmission and optical fiber sensing. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to make the content of the present invention more clearly understood, the present invention is further described in detail below according to specific embodiments and in conjunction with the accompanying drawings, wherein

[0038] Figure 1 It is a schematic structural diagram of a polarization-maintaining multi-core optical fiber based on a weak coupling mechanism according to an embodiment of the present invention.

[0039] Figure 2 It is a schematic structural diagram of the elliptical fiber core and the first annular groove of the present invention.

[0040] Figure 3 It is a schematic structural diagram of the circular fiber core and the second annular groove of the present invention.

[0041] Figure 4 It is a schematic structural diagram of the stress rod of the present invention.

[0042] Figure 5 This is a graph showing the relationship between the vertical radius of the elliptical core and the effective refractive index of the optical fiber.

[0043] Figure 6 This is a graph showing the relationship between the trench thickness and the crosstalk of the middle core.

[0044] The reference numerals in the accompanying drawings are: outer cladding 1, inner cladding 2, second annular groove 3, circular core 4, first annular groove 5, elliptical core 6, stress rod 7; horizontal radius a1 and vertical radius b1 of elliptical core 6; radius r of circular core; major semi-axis a2 and minor axis radius b2 of stress rod; DETAILED DESCRIPTION

[0045] In order to better understand the above technical solution, the above technical solution will be described in detail below in conjunction with the accompanying drawings and specific implementation methods.

[0046] In order to make the purpose, technical solutions and advantages of the embodiments of the present invention clearer, the technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are part of the embodiments of the present invention, not all of the embodiments. Generally, the components of the embodiments of the present invention described and shown in the drawings here can be arranged and designed in various different configurations.

[0047] Therefore, the following detailed description of the embodiments of the present invention provided in the accompanying drawings is not intended to limit the scope of the invention claimed for protection, but merely represents selected embodiments of the present invention. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0048] It should be noted that similar reference numerals and letters denote similar items in the following drawings, and therefore, once an item is defined in one drawing, further definition and explanation thereof is not required in subsequent drawings.

[0049] In the description of the embodiments of the present invention, it should be understood that the terms "center", "up", "down", "left", "right", "vertical", "horizontal", "inside", "outside", etc. indicate orientations or positional relationships based on the orientations or positional relationships shown in the accompanying drawings, or are the orientations or positional relationships in which the inventive product is conventionally placed when used, or are the orientations or positional relationships conventionally understood by those skilled in the art. They are only for the convenience of describing the present invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, be constructed and operated in a specific orientation, and therefore should not be understood as a limitation on the present invention.

[0050] In the description of the embodiments of the present invention, it is also necessary to explain that, unless otherwise clearly specified and limited, the terms "set", "installed", "connected" and "connected" should be understood in a broad sense. For example, it can be a fixed connection, a detachable connection, or an integral connection; it can be directly connected, or indirectly connected through an intermediate medium, or it can be the internal connection of two components. For ordinary technicians in this field, the specific meanings of the above terms in the present invention can be understood according to specific circumstances. The present invention is further described below in conjunction with the accompanying drawings. The following embodiments are only used to more clearly illustrate the technical solution of the present invention, and cannot be used to limit the scope of protection of the present invention.

[0051] (Example 1)

[0052] See Figures 1 to 3A polarization-maintaining multi-core optical fiber based on a weak coupling mechanism comprises an elliptical core 6, a stress rod 7, a circular core 4, an inner cladding 2 and an outer cladding 1; the elliptical core 6 is coaxially arranged at the center of the polarization-maintaining multi-core optical fiber, five circular cores 4 are provided, and multiple circular cores 4 are uniformly distributed on the outer ring of the elliptical core 6 along the circumferential direction, the stress rods 7 are arranged at equal intervals between two adjacent circular cores 4, the outer cladding 1 is wrapped around the stress rods 7 and the outside of the circular core 4, and the inner cladding 2 is filled between the outer cladding 1, the elliptical core 6, the stress rods 7 and the circular core 4.

[0053] The horizontal radius a1 of the elliptical core 6 is 7 μm, and the vertical radius b1 is 5.3 μm; the elliptical core 6 is doped with a specific GeO2 quartz material, and its refractive index profile is different from that of the circular core 4, forming a heterogeneous structure to improve the mode compatibility and communication quality.

[0054] Depend on Figure 5 It can be seen that the LP01 mode has the highest effective refractive index and is excited first, which is the basis for low-loss single-mode transmission of optical fiber; high-order modes such as LP11 and LP21 series may be excited under specific conditions due to the small difference in effective refractive index; when b1 is 5.3μm, multiple modes exist at the same time, indicating that the optical fiber may enter a multi-mode working state at this time; this design needs to be optimized to avoid interference of high-order modes on the main mode; boron-doped stress rod 7 can significantly enhance the polarization mode isolation of the elliptical core by introducing stress birefringence; the difference in effective refractive index of different modes, such as the LP01 and LP11 series combined with the structural design of stress rods, helps to improve the anti-interference ability of optical fiber and adapt to communication needs in complex environments.

[0055] When the vertical radius b1 of the elliptical core 6 of this embodiment is 5.3 μm, the effective refractive index of the elliptical core 6 is 1.4489, the radius r of the circular core 4 is 5.5 μm, the refractive index difference Δη between the specific GeO2 doped quartz material and the inner cladding 2 is 0.6%, and the refractive index is 1.453.

[0056] The stress rod 7 is an elliptical boron-doped stress rod, which further enhances the isolation of polarization modes through the stress birefringence mechanism; the radius of the major semi-axis a2 of the stress rod is 10 μm, and the radius of the minor axis b2 is 5.5 μm, wherein the major axis of the stress rod is perpendicular to the line connecting the centers of two adjacent circular fiber cores 4, ensuring the overall stability and anti-interference ability of the optical fiber.

[0057] The refractive index of the stress rod 7 is 1.42.

[0058] A first annular groove 5 is provided between the elliptical core 6 and the inner cladding 2, and the first annular groove 5 is concentrically arranged outside the elliptical core 6; the thickness of the first annular groove 5 is 50% of the vertical radius of the elliptical core 6, and the refractive index of the first annular groove 5 is 1.435;

[0059] A second annular groove 3 is provided between the circular core 4 and the inner cladding 2, and the second annular groove 3 is concentrically arranged on the outside of the circular core 4; the thickness of the second annular groove 3 is 50% of the radius of the circular core 4, and the refractive index of the second annular groove 3 is 1.435; such a design can ensure that the inter-core crosstalk is lower than -0.3dB / km, while maintaining low loss performance when the bending radius is greater than 30cm.

[0060] The outer cladding 1 has a diameter of 125 μm and is made of pure SiO2 material with a refractive index of 1.444; it provides necessary mechanical strength and environmental protection; the outer size of the cladding is designed to take into account the compatibility with standard single-mode optical fibers, making the optical fiber of this embodiment suitable for existing optical fiber network systems.

[0061] Figure 6 is the relationship between the trench thickness and the crosstalk of the middle core; Figure 6 It can be seen that the crosstalk of all modes shows a downward trend with the increase of the groove thickness; the decrease amplitude of the crosstalk curves of different modes is different, and the initial value of the crosstalk, that is, when the groove thickness is 1μm, the difference is relatively large.

[0062] This is because the annular groove improves the localization of the mode and limits the expansion of the mode field by adjusting the refractive index distribution around the fiber core; when the groove thickness is small, the expansion range of the mode field is larger, and the mode field overlap between the central elliptical core 6 and the outer circular core 4 is large, resulting in higher crosstalk; as the groove thickness increases, the mode field is gradually confined to the inside of the fiber core, the mode field overlap between different fiber cores is significantly reduced, and the crosstalk is reduced.

[0063] The specific embodiments described above further illustrate the objectives, technical solutions and beneficial effects of the present invention in detail. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the present invention. Any modifications, equivalent substitutions, improvements, etc. made within the spirit and principles of the present invention should be included in the protection scope of the present invention.

Claims

1. A polarization-maintaining multi-core optical fiber based on a weak coupling mechanism, characterized in that: The optical fiber comprises an elliptical fiber core (6), a stress rod (7), a circular fiber core (4), an inner cladding (2), and an outer cladding (1); the elliptical fiber core (6) is coaxially arranged at the center of the polarization-maintaining multi-core optical fiber, a plurality of circular fiber cores (4) are provided, and the plurality of circular fiber cores (4) are evenly distributed in the circumferential direction on the outer ring of the elliptical fiber core (6), the stress rod (7) is evenly spaced between two adjacent circular fiber cores (4), the outer cladding (1) is wrapped around the stress rod (7) and the outer side of the circular fiber core (4), and the inner cladding (2) is filled between the outer cladding (1), the elliptical fiber core (6), the stress rod (7), and the circular fiber core (4).

2. The polarization-maintaining multi-core optical fiber based on weak coupling mechanism according to claim 1, characterized in that: The horizontal radius a1 of the elliptical fiber core (6) is 6 to 8 μm, and the vertical radius b1 is 4 to 6 μm.

3. The polarization-maintaining multi-core optical fiber based on weak coupling mechanism according to claim 1, characterized in that: The radius r of the circular fiber core (4) is 4 to 8 μm, and the refractive index difference Δη between the circular fiber core (4) and the inner cladding (2) is 0.5% to 0.8%.

4. The polarization-maintaining multi-core optical fiber based on weak coupling mechanism according to claim 1, characterized in that: The stress rod (7) is an elliptical boron-doped stress rod, the radius of the major semi-axis a2 of the stress rod is 8-12 μm, and the radius of the minor axis b2 is 5-10 μm, wherein the major axis of the stress rod is perpendicular to the line connecting the centers of two adjacent circular fiber cores (4).

5. The polarization-maintaining multi-core optical fiber based on weak coupling mechanism according to claim 4, characterized in that: The refractive index of the stress rod (7) is 1.415-1.

425.

6. The polarization-maintaining multi-core optical fiber based on weak coupling mechanism according to claim 1 or 2, characterized in that: A first annular groove (5) is provided between the elliptical core (6) and the inner cladding (2), and the first annular groove (5) is concentrically arranged outside the elliptical core (6).

7. The polarization-maintaining multi-core optical fiber based on weak coupling mechanism according to claim 6, characterized in that: The thickness of the first annular groove (5) is 50-60% of the vertical radius of the elliptical core (6), and the refractive index of the first annular groove (5) is 1.432-1.

437.

8. The polarization-maintaining multi-core optical fiber based on weak coupling mechanism according to claim 1 or 3, characterized in that: A second annular groove (3) is provided between the circular fiber core (4) and the inner cladding (2), and the second annular groove (3) is concentrically arranged outside the circular fiber core (4).

9. The polarization-maintaining multi-core optical fiber based on weak coupling mechanism according to claim 1, characterized in that: The thickness of the second annular groove (3) is 50-60% of the radius of the circular core (4), and the refractive index of the second annular groove (3) is 1.432-1.

437.

10. The polarization-maintaining multi-core optical fiber based on weak coupling mechanism according to claim 1, characterized in that: The outer cladding (1) has a diameter of 125 μm and a refractive index of 1.444.

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