An optical fiber and an optical fiber amplifier

Abstract

The embodiment of the present application provides a kind of optical fiber and optical fiber amplifier, for eliminating the helical light generated under cladding pumping condition, and reduce the loss of pump light, to improve the effective utilization of pump light.The optical fiber includes core, inner cladding, outer cladding and air hole;The core is wrapped in the inner cladding;The outer cladding wraps the core and the inner cladding;The air hole is located at the junction of the inner cladding and the outer cladding;The refractive index of the inner cladding is less than the refractive index of the core;The refractive index of the outer cladding is less than the refractive index of the inner cladding;The refractive index of the air hole is less than the refractive index of the inner cladding.

Description

Technical Field

[0001] This application relates to the field of optical communication, and more particularly to an optical fiber and an optical fiber amplifier. Background Technology

[0002] With the increasing communication capacity year by year, based on technologies such as wavelength division multiplexing (WDM), polarization multiplexing, and multi-level modulation, the transmission capacity of a single optical fiber has reached 100 terabits per second (Tbit / s). The transmission capacity of single-mode fiber is approaching the Shannon limit and is gradually failing to meet the needs of future communication. However, using space division multiplexing technology with multi-core fibers can multiply the number of transmission channels compared to traditional optical fibers, thus effectively solving the problem of transmitting large amounts of information. Single-mode multi-core fiber constructs multiple parallel spatial channels through multiple cores within a single fiber, achieving multiplexing through space division multiplexing. This overcomes the Shannon capacity limitation of optical fiber transmission, expanding the capacity of the transmission system. Multicore fiber (MCF) can provide multiple spatial parallel channels without requiring complex multi-input multi-output decoupling algorithms, making it the most promising new type of transmission fiber for commercialization in recent research, attracting widespread interest from researchers.

[0003] In recent years, research on the application of MCF-based space division multiplexing (SDM) communication systems in backbone networks, access networks, and data centers has gradually increased. For SDM transmission systems to achieve high-capacity, high-speed, and long-distance transmission, fiber amplifiers are indispensable for compensating for transmission loss. Therefore, MCF amplifiers have become crucial for the practical application of SDM technology. MCF can be classified into two types based on its mode: single-mode multi-core and multi-mode multi-core. Single-mode multi-core fibers are further divided into two categories. One type is weakly coupled multi-core fiber, where each core channel is independent, and the distance between cores is typically designed to be 25 to 45 micrometers (μm), with crosstalk between cores generally below -30 dB. The other type is strongly coupled multi-core fiber, where the distance between cores is typically 10 to 20 μm. By reducing the core spacing, increasing the number of cores, and reducing crosstalk between cores, and adopting a transmission mode similar to "supermode," mode-dependent delay is significantly reduced. Therefore, strongly coupled multi-core transmission is also considered a special form of mode division multiplexing. Multi-core erbium-doped fiber amplifiers (MC-EDFAs) that match these two types of single-mode MCFs are generally divided into two types: weakly coupled MC-EDFAs and strongly coupled MC-EDFAs.

[0004] However, the structure based on the MCF causes spiral light to be generated when the cladding of the MCF is pumped, resulting in low effective utilization of pump light by the MCF. This further leads to low energy efficiency of both strongly coupled MC-EDFA and weakly coupled MC-EDFA amplification systems. Summary of the Invention

[0005] This application provides an optical fiber and an optical fiber amplifier to eliminate spiral light generated under cladding pumping conditions and reduce pump light loss, thereby improving the effective utilization rate of pump light.

[0006] In a first aspect, this application provides an optical fiber comprising a core, an inner cladding, an outer cladding, and an air hole; the core is enclosed within the inner cladding; the outer cladding encloses both the core and the inner cladding; the air hole is located at the junction of the inner cladding and the outer cladding; the refractive index of the inner cladding is less than the refractive index of the core; the refractive index of the outer cladding is less than the refractive index of the inner cladding; and the refractive index of the air hole is less than the refractive index of the inner cladding.

[0007] In this embodiment, the junction of the inner cladding layer and the outer cladding layer is the connection point between the inner cladding layer and the outer cladding layer, and the air hole being located at the junction means that the air hole intersects or is tangent to the connection point.

[0008] In this embodiment, an air hole is placed at the junction of the inner cladding and the outer cladding. This allows the pump light from the inner cladding to be scattered by the air hole, thus preventing spiraling and increasing pump light utilization. Simultaneously, the distance between the air hole and the fiber core, designed as described above, effectively reduces pump light loss.

[0009] Optionally, in this embodiment, the shape of the air hole includes a circle, an arc, or a triangle. It is understood that the air holes in the same optical fiber can be the same or different. For example, the same optical fiber can simultaneously include circular and arc-shaped air holes; it can also simultaneously include circular and triangular air holes. Specific details are not limited here. Furthermore, the shape of the air hole is not limited to the shapes mentioned above; it can also include rhombuses, hexagons, etc., which are not specifically limited here. The air hole being located at the junction of the inner cladding and the outer cladding can be understood as the air hole intersecting or being tangent to the connection point between the inner and outer cladding.

[0010] Optionally, when the shape of the air hole is circular or arc-shaped, in this embodiment, in order to effectively increase the pump light utilization rate and reduce the pump light loss, the radius of curvature of the air hole satisfies a first relationship, wherein the first relationship is: Where r is the radius of curvature of the air hole, R is the radius of the inner cladding, and d0 is the maximum distance between the air hole and the fiber core.

[0011] Furthermore, the radius of curvature of the air hole and the radius of the inner cladding should satisfy a second relationship, wherein the second relationship is: Where r is the radius of curvature of the air hole, and R is the radius of the inner cladding.

[0012] Optionally, when the shape of the air hole is circular or arc-shaped, the location of the air hole at the junction of the inner cladding and the outer cladding can be defined as a third relation: the third relation is Rr≤d≤R+r, where r is the radius of curvature of the air hole, R is the radius of the inner cladding, and d is the distance between the center of curvature of the air hole and the center of the inner cladding.

[0013] Optionally, in this application, the fiber core is made of a doped material, wherein the refractive index of the fiber core is less than or equal to 1.6, but needs to be greater than the refractive index of the inner cladding.

[0014] Optionally, in this application, the outer cladding layer is a photonic crystal layer with a thickness greater than 10 micrometers and less than 20 micrometers. The difference in refractive index between the alternating crystal layers in the photonic crystal layer is greater than 0.002, and the maximum refractive index of each crystal layer in the photonic crystal layer is less than the refractive index of the inner cladding layer.

[0015] Optionally, in this application, the refractive index of the inner cladding is greater than 1.452, but less than the refractive index of the fiber core.

[0016] In summary, to achieve the best results in this application, the design of the inner cladding, outer cladding, core, and air pores can be as follows: the diameter of the core is greater than 8 micrometers, and the radius of the inner cladding is designed to be...

[0017] Optionally, in this application, the number of fiber cores is at least one. To improve the utilization rate of pump light and reduce pump light loss, the number of air holes can be [n / 2], n, or 2n, where n is the number of fiber cores. It is understood that when the number of fiber cores is 1, the value of [n / 2] is 1, and when the number of fiber cores is greater than 1, the value of [n / 2] can be rounded up or rounded down, and the specific value is not limited here.

[0018] Optionally, to achieve equalized pump light gain for each fiber core, the fiber cores can be arranged as follows:

[0019] When the number of fiber cores is one, it is located in the center of the inner cladding; when the number of fiber cores is greater than one, it can be arranged in a single-layer ring shape. For example, two-core, four-core, and eight-core fibers can be arranged in a single-layer ring shape. That is, when the number of fiber cores is greater than one, the first angular distance between adjacent fiber cores and the center of the inner cladding satisfies the fourth relation; the fourth relation is: Wherein, A is the first angular distance, and n is the number of fiber cores.

[0020] Based on the above scheme, in order to improve the utilization rate of the pump light and reduce the loss of the pump light, the position of the air hole and the position of the fiber core must meet certain conditions, that is, the second angular distance between the air hole and the perpendicular bisector of the adjacent fiber core satisfies the fifth relationship; the fifth relationship is: 0°≤|Theta|≤90°, where Theta is used to indicate the second angular distance.

[0021] Optionally, further, when the air holes are uniformly distributed and the number of air holes is greater than 1, the third angular distance between adjacent air holes and the center of the inner cladding satisfies the sixth relation; the sixth relation is: 0≤alpha≤180°; where alpha is used to indicate the third angular distance.

[0022] In a second aspect, this application provides an optical fiber amplifier that includes the optical fiber described in the first aspect above.

[0023] Thirdly, embodiments of this application provide a communication system that includes the optical fiber amplifier provided in the second aspect above. Attached Figure Description

[0024] Figure 1a This is a schematic diagram of one end face structure of the optical fiber in an embodiment of this application;

[0025] Figure 1b This is a schematic diagram of one end face structure of the optical fiber in an embodiment of this application;

[0026] Figure 1c This is a schematic diagram of one end face structure of the optical fiber in an embodiment of this application;

[0027] Figure 2 This is a schematic diagram illustrating the definition of relevant parameters for each part of the optical fiber in an embodiment of this application;

[0028] Figure 3 This is a schematic diagram showing the location of the air hole at the junction of the inner and outer cladding layers in an embodiment of this application;

[0029] Figure 4a This is a schematic diagram of one end face structure of a single-core optical fiber in an embodiment of this application;

[0030] Figure 4b This is a schematic diagram of one end face structure of a two-core optical fiber in an embodiment of this application;

[0031] Figure 4c This is a schematic diagram of one end face structure of a four-core optical fiber in an embodiment of this application;

[0032] Figure 4d This is a schematic diagram of one end face structure of an eight-core optical fiber in an embodiment of this application;

[0033] Figure 5 This is a schematic diagram of one end face structure of the outer cladding layer in an embodiment of this application;

[0034] Figure 6 For based on Figure 5 The diagram shows the refractive index distribution of the outer cladding, inner cladding, air holes, and core of the optical fiber.

[0035] Figure 7 This is a schematic diagram illustrating the simulation results of optical fibers and traditional optical fibers in terms of spiral light in the embodiments of this application;

[0036] Figure 8 This is a schematic diagram of the simulation results of the photonic crystal layer band diagram of the optical fiber in the embodiment of this application;

[0037] Figure 9 This is a schematic diagram showing the simulation results of optical fiber and traditional optical fiber in terms of optical fiber loss in the embodiments of this application;

[0038] Figure 10 This is a schematic diagram of one end face structure of a four-core optical fiber in an embodiment of this application;

[0039] Figure 11 This is a schematic diagram of the refractive index distribution of the four-core optical fiber in an embodiment of this application;

[0040] Figure 12 For the embodiments of this application Figure 10 The diagram shows the simulation results illustrating the effect of the change in the radius of curvature of the air hole in a four-core optical fiber on the pump light distribution.

[0041] Figure 13 For the embodiments of this application Figure 10 A schematic diagram of the simulation results showing the effect of the distribution variation of the center positions of the four air holes in the four-core optical fiber on the pump light distribution;

[0042] Figure 14 For the embodiments of this application Figure 10 Another simulation result diagram showing the effect of the distribution variation of the center positions of the four air holes in the four-core optical fiber on the pump light distribution;

[0043] Figure 15 For the embodiments of this application Figure 10Another simulation result diagram showing the effect of the distribution variation of the center positions of the four air holes in the four-core optical fiber on the pump light distribution;

[0044] Figure 16 This is a schematic diagram of another end face structure of the four-core optical fiber in this embodiment of the application;

[0045] Figure 17 This is a schematic diagram of another end face structure of the four-core optical fiber in this embodiment of the application;

[0046] Figure 18 This is a schematic diagram of a fiber amplifier including the aforementioned optical fiber in an embodiment of this application.

[0047] Figure 19 This is an application system architecture for optical fiber in the embodiments of this application. Detailed Implementation

[0048] To make the objectives, technical solutions, and advantages of this application clearer, the embodiments of this application are described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of this application, and not all of them. Those skilled in the art will understand that with the emergence of new application scenarios, the technical solutions provided by the embodiments of this application are also applicable to similar technical problems.

[0049] The terms "first," "second," etc., used in the specification, claims, and accompanying drawings of this application are used to distinguish similar objects and are not necessarily used to describe a specific order or sequence. It should be understood that such data can be interchanged where appropriate so that the embodiments described herein can be implemented in a sequence other than that illustrated or described herein. Furthermore, the terms "comprising" and "having," and any variations thereof, are intended to cover non-exclusive inclusion; for example, a process, method, system, product, or device that includes a series of steps or modules is not necessarily limited to those explicitly listed, but may include other steps or modules not explicitly listed or inherent to such processes, methods, products, or devices. The naming or numbering of steps appearing in this application does not imply that the steps in the method flow must be performed in the chronological / logical order indicated by the naming or numbering. The execution order of named or numbered process steps can be changed according to the desired technical purpose, as long as the same or similar technical effect is achieved. The division of units in this application is a logical division. In practical applications, there may be other division methods. For example, multiple units may be combined or integrated into another system, or some features may be ignored or not executed. In addition, the shown or discussed mutual coupling, direct coupling, or communication connection may be through some interface, and the indirect coupling or communication connection between units may be electrical or other similar forms, none of which are limited in this application. Furthermore, the units or sub-units described as separate components may or may not be physically separated, may or may not be physical units, or may be distributed among multiple circuit units. Some or all of the units can be selected to achieve the purpose of the solution in this application according to actual needs.

[0050] With the increasing communication capacity year by year, based on technologies such as wavelength division multiplexing (WDM), polarization multiplexing (PMO), and multi-level modulation, the transmission capacity of a single optical fiber has reached 100 Tbit / s. The transmission capacity of single-mode fiber is approaching the Shannon limit and is gradually failing to meet future communication needs. However, using space division multiplexing (SDM) technology with multi-core optical fibers can multiply the number of transmission channels compared to traditional optical fibers, thus effectively solving the problem of large-scale information transmission. Single-mode multi-core optical fibers construct multiple parallel spatial channels through multiple cores within a single fiber, achieving multiplexed transmission through space division multiplexing. This overcomes the Shannon capacity limitation of optical fiber transmission, expanding the capacity of the transmission system. MCF can provide multiple parallel spatial channels without requiring complex multi-input multi-output (MIMO) decoupling algorithms, making it the most promising new type of transmission fiber for commercialization in recent research, attracting widespread interest from researchers. In recent years, research on the application of MCF-based SDM communication systems in backbone networks, access networks, and data centers has gradually increased. For SDM transmission systems to achieve high-capacity, high-speed, and long-distance transmission, fiber amplifiers are essential for compensating for transmission loss; therefore, MCF amplifiers are key to the practical application of SDM technology. MCFs can be categorized into single-mode multi-core and multi-mode multi-core based on their mode. Single-mode multi-core fibers are further divided into two types: weakly coupled multi-core fibers, where each core channel is independent, and the distance between cores is typically designed to be 25μm to 45μm, with crosstalk between cores generally below -30dB; and strongly coupled multi-core fibers, where the distance between cores is typically 10μm to 20μm. By reducing the core spacing, increasing the number of cores, and minimizing crosstalk, and employing a "supermode"-like transmission mode, mode-dependent delay is significantly reduced. Therefore, strongly coupled multi-core transmission is considered a special form of mode division multiplexing. MC-EDFAs, which match these two types of single-mode MCFs, are generally also divided into two types: weakly coupled MC-EDFAs and strongly coupled MC-EDFAs. However, the structure of MCFs causes spiral light to be generated under cladding pumping, resulting in low efficiency of pump light utilization and consequently low energy efficiency in amplification systems of both strongly coupled and weakly coupled MC-EDFAs.

[0051] To address this technical problem, embodiments of this application provide an optical fiber 100, such as... Figure 1aThe schematic diagram of the end face structure shown illustrates that the optical fiber 100 includes a core 101, an inner cladding 102, an air hole 103, and an outer cladding 104. The core 101 is enclosed within the inner cladding 102; the outer cladding 104 encloses both the core 101 and the inner cladding 102; the air hole 103 is located at the junction of the inner cladding 102 and the outer cladding 104; the refractive index of the inner cladding 102 is less than that of the core 101; the refractive index of the outer cladding 104 is less than that of the inner cladding 102; and the refractive index of the air hole 103 is less than that of the outer cladding 104.

[0052] Optionally, the shape of the air hole 103 may include circular, arc-shaped, or triangular. It is understood that the air holes 103 may be the same or different within the same optical fiber. For example, a single optical fiber may include both circular and arc-shaped air holes. Figure 1b It can also include both circular and triangular air holes, such as... Figure 1c As shown. Specific details are not limited here. Furthermore, the shape of the air hole 103 is not limited to the shapes mentioned above; it can also include rhombuses, hexagons, etc., without further limitation. The location of the air hole 103 at the junction of the inner cladding layer 102 and the outer cladding layer 104 can be understood as the intersection of the air hole and the connection point between the inner and outer cladding layers. For example... Figure 1a As shown, the air hole 103 is circular, and the connection between the inner cladding layer 102 and the outer cladding layer 104 is the connection between the gray area and the black area. The air hole 103 can intersect or be tangent to the connection.

[0053] The following explanation uses a circular or arc-shaped air hole as an example. For ease of understanding, the following example will be used... Figure 2 The relevant parameter definition diagram shown illustrates the various parts of the optical fiber 100:

[0054] r is the radius of curvature of the air hole 103.

[0055] R is the radius of the inner cladding 102.

[0056] d is the distance between the center of curvature of the air hole 103 and the center of the inner cladding 102.

[0057] dd is used to indicate the distance between the centers of the adjacent fiber cores 101.

[0058] dd0 is used to indicate the diameter of the fiber core 101.

[0059] A is the first angular distance between the adjacent fiber cores 101 and the center of the inner cladding 102.

[0060] alpha is the triangular distance between adjacent air holes 103 and the center of the inner cladding 102.

[0061] Theta is the second angular distance between the air hole 103 and the perpendicular bisector of the adjacent fiber core 101.

[0062] In this embodiment, the specific implementation of the air hole 103 at the junction of the inner cladding layer 102 and the outer cladding layer 104 can satisfy the following condition: the location of the air hole 103 at the junction of the inner cladding layer 102 and the outer cladding layer 104 can be defined by a third relation: the third relation is Rr≤d≤R+r, where r is the radius of curvature of the air hole 103, R is the radius of the inner cladding layer 102, and d is the distance between the center of curvature of the air hole 103 and the center of the inner cladding layer 102. Under this condition, the positional relationship of the air hole 103 at the junction of the inner cladding layer 102 and the outer cladding layer 104 can be as follows: Figure 3 As shown. In Figure 3 In this description, the number of fiber cores 101 is 1, and the number of air holes 103 is 2, 4, or 8. The center of curvature of the air hole 103 can be located at the junction of the inner cladding 102 and the outer cladding 104 (e.g., Figure 3 (as shown in a); it can also be located inside the inner cladding 102 (as shown in a diagram). Figure 3 (as shown in b); it can also be located on the outside of the inner cladding 102 (as shown in b); Figure 3 (As shown in c). It is understandable that... Figure 3 The figures in the middle are schematic diagrams of the end face structure of the optical fiber 100.

[0063] In this embodiment, in order to achieve gain equalization for each fiber core 101, the arrangement of the fiber core 101 and the air hole 103 needs to meet certain conditions. Specifically, when the number of fiber cores 101 is one, it is located in the center of the inner cladding 102, such as... Figure 4a As shown; when the number of fiber cores 101 is greater than 1, they can be distributed in a single-layer ring shape, that is, when the number of fiber cores 101 is greater than 1, the first angular distance between adjacent fiber cores 101 and the center of the inner cladding 102 satisfies the fourth relation; the fourth relation is: Wherein, A is the first angular distance, and n is the number of fiber cores 101. Their specific arrangement structure can be as follows: Figures 4b to 4d As shown, where Figure 4a This is a schematic diagram of the arrangement of the cores 101 of a two-core optical fiber 100; Figure 4b This is a schematic diagram of the arrangement of the cores 101 of a four-core optical fiber 100; Figure 4c This is a schematic diagram of the arrangement of core 101 in an eight-core optical fiber 100.

[0064] The number of air holes 103 can be designed to be related to the number of fiber cores 101. That is, the number of air holes 103 can be [n / 2], n, or 2n, where... n The number of fiber cores 101. It is understood that when the number of fiber cores 101 is 1, the value of [n / 2] is 1, while when the number of fiber cores 101 is greater than 1, the value of [n / 2] can be either rounded up or rounded down, without specific limitation here. For example, when the number of fiber cores 101 is 1, the number of air holes 103 can be 1 or 2; when the number of fiber cores 101 is 2, the number of air holes 103 can be 1, 2, or 4. The air holes 103 should be evenly distributed, specifically satisfying the following condition: the third angular distance between adjacent air holes 103 and the center of the inner cladding 102 satisfies the sixth relation; the sixth relation is: 0 ≤ alpha ≤ 180°; where alpha is used to indicate the third angular distance. In an exemplary scheme, the positional distribution between the air holes 103 and the fiber cores 101 can be as follows: Figures 4a to 4d As shown.

[0065] In this embodiment, to confine the pump light as much as possible within the inner cladding 102 while minimizing loss, a special structural design is required for the outer cladding 104 to effectively confine the pump light within the inner cladding 102. In this case, the outer cladding 104 can be designed as a photonic crystal layer structure with alternating high and low refractive indices, ensuring that the "bandgap" (i.e., the wavelength band that does not conduct light) of the photonic crystal layer includes the pump light band of the optical fiber 100. Its end-face structure can be specifically designed as follows: Figure 5 As shown. The refractive index distribution of each layer of this optical fiber 100 can be as follows: Figure 6 As shown, the first and third portions are used to indicate the refractive index of the outer cladding 104, the second portion is used to indicate the refractive index of the inner cladding 102 and the fiber core 101, and the space between the first and second portions and between the second and third portions are used to indicate the refractive index of the air hole 103.

[0066] The following uses COMSOL to illustrate the pump light ray simulation results of the optical fiber 100 provided in this invention and the conventional optical fiber 100:

[0067] 1. Considering the contrast of spiral light. Assuming that the local light in the inner cladding 102 is consistent (i.e., the waveguide loss of the inner cladding 102 of the fiber 100 is the same), a comparison is made between the inner cladding 102 of the conventional circular fiber 100 and the circular fiber 100 with air holes 103 in this scheme. The results are as follows: Figure 7 As shown, where Figure 7 (a) in this application is used to indicate the optical fiber 100 provided in this application. Figure 7 (b) in the text is used to indicate the conventional circular inner cladding 102 fiber 100. (By...) Figure 7 It is known that, within the same transmission distance, the pump light in the optical fiber 100 provided in this application can be distributed faster and more uniformly at the end face of the optical fiber 100.

[0068] 2. The wave vector of the reduced Brillouin zone in fiber 100 was obtained by simulating the energy band diagram of the photonic crystal layer. For example... Figure 8 As shown in the energy band diagram of the photonic crystal layer, the light frequency in the region near the normalized frequency of 0.6 cannot exist inside the one-dimensional photonic crystal; that is, it is totally reflected back into the fiber core 101. This region corresponds precisely to the wavelength position of pump light near the 980 nanometer (nm) band. This demonstrates that the photonic crystal layer can effectively confine light within the inner cladding 102 region.

[0069] 3. Consider fiber optic loss of 100%. For example... Figure 9 The image shows the fiber 100 loss results provided in this application compared to conventional D-type fiber 100 and octagonal fiber 100 with inner cladding 102. From... Figure 9 As shown, under the same specifications, the waveguide confinement loss using a solid photonic crystal layer is lower, by eight orders of magnitude, compared to the loss of fiber 100 with a cladding 102 in traditional D-type fiber 100 and octagonal fiber 100.

[0070] The following description uses an example where the fiber optic cable 100 has 4 fiber cores 101, 4 air holes 103, and the air holes 103 are arc-shaped. For details, please refer to [link to relevant documentation]. Figure 10The diagram shows the end face structure of the optical fiber 100. The diameter of the fiber core 101 is dd0 ≥ 8 μm. The distance between the centers of adjacent fiber cores 101 is greater than the diameter of the fiber core 101, i.e., dd ≥ dd0, where dd indicates the distance between the centers of adjacent fiber cores 101. The radius R of the inner cladding 102 satisfies 50 μm ≤ R ≤ 60 μm. For better performance, the preferred radius of the inner cladding 102 is 55 μm. The distance between the curvature center of the air hole 103 and the center of the inner cladding 102 is d, and its size satisfies Rr≤d≤R+r, where r is the curvature radius of the air hole 103, and the value of the curvature radius of the air hole 103 is: r≥2μm; the angle between the straight line defined by the center of the adjacent fiber core 101 and the straight line defined by the center of the air hole 103 and the center of the inner cladding 102 is set as φ, and φ satisfies 0≤φ≤90°; the angular distance between the adjacent air holes 103 and the center of the inner cladding 102 is 90°, and the thickness of the photonic crystal layer (i.e., the outer cladding 104) is greater than 10μm and less than 20μm. In order to achieve better results, the preferred value of the thickness of the photonic crystal layer is 14μm, and its position is close to the inner cladding 102 and the air hole 103, and the number of alternating dielectric layers of the photonic crystal layer is greater than 10, and the preferred value is 14 layers. The fiber core 101 is made of a doped material with a refractive index less than or equal to 1.6, preferably 1.51. The inner cladding 102 has a refractive index less than that of the fiber core 101 but greater than 1.452, preferably 1.5. The refractive index difference between the high and low refractive index layers of the photonic crystal is greater than 0.002, and the preferred refractive index values ​​for the corresponding high and low refractive index layers are 1.452 and 1.45, respectively. The air hole 103 has a refractive index lower than that of the low refractive index layer of the photonic crystal, preferably 1.0. Figure 11 This is a schematic diagram showing the refractive index distribution of the optical fiber 100 when the above-mentioned preferred values ​​are used.

[0071] based on Figure 10 The fiber 100 shown below is illustrated using COMSOL simulation results for the pump light of various parts of the fiber 100 provided by this invention:

[0072] 1. The radius of curvature r of air hole 103 is analyzed, and the simulation results are as follows: Figure 12 As shown. In this embodiment, the simulation is performed with the center of the air hole 103 located at the junction of the inner cladding 102 and the outer cladding 104. For each value of r, there is a corresponding COMSOL simulation end-face diagram (i.e., the left side of the group diagram for each r value), a pump light initial radiation diagram (the upper right side of the group diagram for each r value), and an end-face distribution diagram of the fiber 100 after pump light transmission of 0.42 (the lower right side of the group diagram for each r value). According to... Figure 12As can be seen from the simulation results shown, as the curvature radius r of the air holes 103 increases, the pump light gradually changes from an uneven sparse distribution to a uniform dense distribution. As r further increases, the pump light becomes sparse again. In this simulation result, for the optical fiber 100 with four air holes 103, when the radius of the air holes 103 is between 4 μm and 8 μm, the distribution of the pump light in the optical fiber 100 is better.

[0073] 2. Analyze the influence of the distribution change of the center position of the four air holes 103 on the pump light distribution. The simulation results are as Figure 13 shown. In this embodiment, the simulation is carried out with the center of the air hole 103 located at the junction of the inner cladding 102 and the outer cladding 104. Here, d is the distance between the center position of the air hole 103 and the center of the inner cladding 102, R is the radius of the inner cladding 102, and r is the curvature radius of the air hole 103. There is an end-face distribution diagram of the optical fiber 100 after the pump light is transmitted for 0.45 at each value of d. From Figure 13 the shown simulation result diagram, it can be seen that when d < R, as d decreases, the effect of suppressing the spiral light gradually becomes worse.

[0074] On Figure 13 this basis, further reduce d, and then gradually move away from the boundary of the inner and outer claddings 104 (at this time d < 49 < R) to obtain Figure 14 the result shown. As can be seen from Figure 14 the shown, when d = 49 μm, within the same time, the pump light can be quickly and effectively distributed more evenly on the end face of the optical fiber 100. As d continues to decrease to 45 μm (i.e., relatively close to the core 101), at this time the distribution of the pump light begins to appear sparse again. In addition to the above situation, the distribution of the corresponding pump light is also analyzed when d > R, as Figure 15 . At this time, the air holes 103 move away from the boundary of the inner and outer claddings 104 and approach the outer cladding 104. As can be seen from Figure 15 the shown, as the value of d increases, the angular dependence of the scattering of the pump light becomes more and more serious, and the pump light is distributed more and more sparsely and unevenly on the entire end face of the inner cladding 102, and it is very easy to generate spiral light. As can be seen from Figures 13 to 15 the shown simulation results, as the center of the air hole 103 moves away from the cladding and shifts outward, the effect gradually becomes worse.

[0075] 3. Analyze the distribution of the pump light on the end face of the optical fiber 100 in the inner cladding 102 under the conditions of symmetric distribution and asymmetric distribution of the four air holes 103 at the interface of the inner and outer claddings 104. Figure 16 What is shown is the end-face distribution of the pump light in the corresponding situation after the same time. As can be seen from Figure 16As can be seen, compared to the symmetrical distribution of air holes 103, in the case of an asymmetrical distribution of air holes 103, the corresponding pump light intensity concentration area will deviate from the center and move towards one side of the asymmetrical air hole 103, that is, the pump light distribution at the end face also becomes asymmetrical. In this state, different fiber cores 101 receive pump light differently, resulting in an imbalance in pump gain between fiber cores 101. Therefore, in order to achieve balanced pump gain of fiber cores 101, it is better to design the air holes 103 to be located on the axis of symmetry of the corresponding fiber core 101.

[0076] In the above description, in order to improve the utilization rate of the pump light and reduce its loss, the position of the air hole and the position of the fiber core satisfy a certain condition, namely, the second angular distance between the air hole and the perpendicular bisector of the adjacent fiber core satisfies the fifth relation; the fifth relation is: 0°≤|Theta|≤90°. When the number of air holes 103 is 4, it is always described as Theta = 90°. In fact, as long as the air holes 103 are evenly distributed, the value of Theta is not limited, for example, Theta = 45° or Theta = 30°, etc.

[0077] According to the above Figure 16 The simulation results show that the position of the air hole 103 affects the uniformity of the pump light distribution. The positional distribution of the air hole 103 can achieve either non-uniform or uniform distribution of the pump light across the fiber cores 101, thus resulting in slightly different gains or identical gains for different fiber cores 101. Based on this, for special applications requiring uneven pump gain, a method can be adopted... Figure 17 The optical fiber 100 shown. Figure 17 The parameters shown are Figure 10 The only difference is that the air holes 103 are asymmetrically distributed about the center of the inner cladding 102 at the boundary of the inner and outer cladding 104, that is, the four air holes 103 are arranged arbitrarily in an asymmetrical manner.

[0078] The optical fiber 100 in the above embodiments of this application can be applied to, for example... Figure 18 The optical amplifier shown is an end-packed pump type. Signal light is injected into the fiber core 101 of the optical fiber 100 through a spatial optical path, while pump light enters the fiber core 101 of the optical fiber 100 through the spatial optical path.

[0079] This optical amplifier can be applied to, for example... Figure 19 The communication system shown in (a) of this application uses a fiber core 101 of the optical fiber 100 to be excited by a laser, which amplifies the transmitted optical signal. The final optical amplifier structure can be as follows: Figure 19 As shown in (b) of the diagram.

[0080] Figure 19 The communication system shown in (a) can be applied to various communication systems, such as: Global System of Mobile Communication (GSM), Code Division Multiple Access (CDMA), Wideband Code Division Multiple Access (WCDMA), Long Term Evolution (LTE), LTE Frequency Division Duplex (FDD), LTE Time Division Duplex (TDD), Universal Mobile Telecommunication System (UMTS), 5G communication system, and future wireless communication systems.

[0081] In this application, the first communication device can be a user equipment (UE), and various embodiments are described in conjunction with UE. User equipment (UE) can also refer to terminal equipment, access terminal, user unit, user station, mobile station, mobile station, remote station, remote terminal, mobile device, user terminal, terminal, wireless communication equipment, user agent, or user device. Access terminal can be a cellular phone, cordless phone, Session Initiation Protocol (SIP) phone, Wireless Local Loop (WLL) station, Personal Digital Assistant (PDA), handheld device with wireless communication capabilities, computing device, or other processing device connected to a wireless modem, in-vehicle device, wearable device, terminal equipment in a 5G network, or terminal equipment in a future PLMN network, etc.

[0082] Those skilled in the art will clearly understand that, for the sake of convenience and brevity, the specific working processes of the systems, devices, and units described above can be referred to the corresponding processes in the foregoing method embodiments, and will not be repeated here.

[0083] In the several embodiments provided in this application, it should be understood that the disclosed systems, apparatuses, and methods can be implemented in other ways. For example, the apparatus embodiments described above are merely illustrative; for instance, the division of units is only a logical functional division, and in actual implementation, there may be other division methods. For example, multiple units or components may be combined or integrated into another system, or some features may be ignored or not executed. Furthermore, the coupling or direct coupling or communication connection shown or discussed may be an indirect coupling or communication connection between apparatuses or units through some interfaces, and may be electrical, mechanical, or other forms.

[0084] The units described as separate components may or may not be physically separate. The components shown as units may or may not be physical units; that is, they may be located in one place or distributed across multiple network units. Some or all of the units can be selected to achieve the purpose of this embodiment according to actual needs.

[0085] Furthermore, the functional units in the various embodiments of this application can be integrated into one processing unit, or each unit can exist physically separately, or two or more units can be integrated into one unit. The integrated unit can be implemented in hardware or as a software functional unit.

[0086] If the integrated unit is implemented as a software functional unit and sold or used as an independent product, it can be stored in a computer-readable storage medium. Based on this understanding, the technical solution of this application, in essence, or the part that contributes to the prior art, or all or part of the technical solution, can be embodied in the form of a software product. This computer software product is stored in a storage medium and includes several instructions to cause a computer device (which may be a personal computer, server, or network device, etc.) to execute all or part of the steps of the methods described in the various embodiments of this application. The aforementioned storage medium includes various media capable of storing program code, such as USB flash drives, portable hard drives, read-only memory (ROM), random access memory (RAM), magnetic disks, or optical disks.

Claims

1. An optical fiber, characterized in that, include: Core, inner cladding, outer cladding, and air pores; The fiber core is encased within the inner cladding layer; The outer cladding layer encloses the fiber core and the inner cladding layer; The air hole is located at the junction of the inner cladding and the outer cladding, and the air hole intersects or is tangent to the junction; The refractive index of the inner cladding is less than that of the fiber core; The refractive index of the outer cladding layer is less than the refractive index of the inner cladding layer; The refractive index of the air hole is less than that of the inner cladding.

2. The optical fiber according to claim 1, characterized in that, The shape of the air hole can be circular, arc-shaped, or triangular.

3. The optical fiber according to claim 2, characterized in that, When the shape of the air hole is circular or arc-shaped, the radius of curvature of the air hole satisfies the first relationship; The first relation is: , wherein The radius of curvature of the air hole is... The radius of the inner cladding is [missing information]. This refers to the maximum distance between the air hole and the fiber core.

4. The optical fiber according to claim 3, characterized in that, The radius of curvature of the air hole and the radius of the inner cladding satisfy the second relationship; The second relation is: , wherein The radius of curvature of the air hole is... The radius of the inner cladding is given.

5. The optical fiber according to any one of claims 3 to 4, characterized in that, The distance between the center of curvature of the air hole and the center of the inner cladding satisfies the third relation; The third relation is: , wherein The radius of curvature of the air hole is... The radius of the inner cladding is [missing information]. The distance between the center of curvature of the air hole and the center of the inner cladding is given.

6. The optical fiber according to claim 1, characterized in that, The fiber core is made of a doped material and the refractive index of the fiber core is less than or equal to 1.

6.

7. The optical fiber according to claim 1, characterized in that, The outer cladding layer is a photonic crystal layer, and the thickness of the photonic crystal layer is greater than 10 micrometers and less than 20 micrometers.

8. The optical fiber according to claim 7, characterized in that, The refractive index of the inner cladding is greater than 1.

452.

9. The optical fiber according to claim 7, characterized in that, The difference in refractive index between the alternating crystal layers in the photonic crystal layer is greater than 0.

002.

10. The optical fiber according to claim 1, characterized in that, The number of fiber cores is The number of air holes is , ,or , wherein The integer is greater than 1. The value can be either rounded up or rounded down.

11. The optical fiber according to claim 10, characterized in that, When the number of fiber cores is greater than 1, the first angular distance between adjacent fiber cores and the center of the inner cladding satisfies the fourth relation; The fourth relation is: , wherein The first angular distance, the The number of fiber cores.

12. The optical fiber according to claim 10, characterized in that, The second angular distance between the air hole and the perpendicular bisector of the adjacent fiber core satisfies the fifth relation; The fifth relation is: , wherein Used to indicate the second angular distance.

13. The optical fiber according to claim 1, characterized in that, When the number of fiber cores is 1, the number of air holes is 1 or 2.

14. The optical fiber according to claim 10, characterized in that, When the number of air holes is greater than 1, the triangular distance between adjacent air holes and the center of the inner cladding satisfies the sixth relation. The sixth relation is: ; Among them, the Used to indicate the third angle distance.

15. An optical fiber amplifier, characterized in that, The fiber amplifier comprises the fiber optic cable according to any one of claims 1 to 14.

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