An optical fiber connection structure and an optical fiber

Abstract

The application discloses a kind of optical fiber connection structure and optical fiber, the optical fiber connection structure is integrated columnar optical fiber, the first end of the optical fiber connection structure is used to connect first optical fiber, the second end of the optical fiber connection structure is used to connect second optical fiber;Wherein, the optical fiber connection structure includes cladding and the wire core area arranged in the cladding inside, the outer diameter of the cladding remains unchanged along the axial direction, the core feature of the optical fiber connection structure gradually changes along the axial direction;The core feature corresponding to the first end is consistent with the core feature of the first optical fiber, the core feature corresponding to the second end is consistent with the core feature of the second optical fiber, and the core feature includes at least one of core radius, refractive index difference and mode field diameter. By adopting the embodiment of the application, low-loss smooth butt joint of different mode field diameter optical fibers can be realized, and multiple types of core coexistence present network cable scenarios can be adapted.

Description

Technical Field

[0001] This invention relates to the field of communications, and more particularly to an optical fiber connection structure and an optical fiber. Background Technology

[0002] Optical fiber is the carrier inside optical cables used to transmit optical signals. With the continuous expansion and upgrading of communication service capacity, a large number of solid optical fiber cables of different specifications have been deployed in the existing network. There are significant differences in the core diameter of optical fibers in various types of optical cables. In engineering construction, line renovation, and fault repair, there are often urgent scenarios where optical fibers with different core diameters need to be interconnected. In actual networking applications, when optical fibers with different core diameters are directly interconnected, problems such as optical mode field mismatch and optical signal leakage are likely to occur, resulting in excessive insertion loss. This leads to the widespread phenomenon of excessive insertion loss in the interconnection of heterogeneous optical fiber cables in the operator's existing network. In severe cases, the excessive loss directly affects the normal opening and stable operation of communication services.

[0003] To address the challenge of splicing optical fibers with different mode field diameters, existing technologies primarily employ mechanical fiber optic connectors. These connectors are typically assembled from multiple independent components. While they enable physical splicing and dual fixation of different fibers, their overall structure is complex and not a fully integrated fiber optic structure. Especially when splicing large-diameter and small-diameter fibers, the mechanical connection is abrupt and rigid, lacking any optical field transition structure. The significant difference in mode field diameter between the large and small-diameter fibers causes a precipitous change in the optical field during splicing. A large amount of optical signal cannot adapt to the rapidly changing transmission channel, exceeding the fiber's total internal reflection condition and leaking out, resulting in significant optical power loss. Therefore, existing connection methods only achieve physical fixation of the fibers and cannot solve the mode field mismatch problem. They fail to fundamentally address the high insertion loss issue caused by splicing fibers with different mode field diameters and are ill-suited for existing communication optical cable networks with multiple fiber core types. Summary of the Invention

[0004] The purpose of this invention is to provide an optical fiber connection structure and optical fiber. The optical fiber connection structure can achieve low-loss smooth connection of optical fibers with different mode field diameters, and is suitable for existing optical cable scenarios where multiple types of fiber cores coexist.

[0005] To achieve the above objectives, embodiments of the present invention provide an optical fiber connection structure, wherein the optical fiber connection structure is an integral cylindrical optical fiber, a first end of the optical fiber connection structure is used to connect a first optical fiber, and a second end of the optical fiber connection structure is used to connect a second optical fiber; wherein... The optical fiber connection structure includes a cladding and a core region disposed inside the cladding. The outer diameter of the cladding remains constant along the axial direction, and the core features of the optical fiber connection structure gradually change along the axial direction. The core characteristics corresponding to the first end are consistent with the core characteristics of the first optical fiber, and the core characteristics corresponding to the second end are consistent with the core characteristics of the second optical fiber. The core characteristics include at least one of core radius, refractive index difference, and mode field diameter.

[0006] As an improvement to the above solution, the core radius of the optical fiber connection structure... Satisfy the following formula: ; in, The axial length of the optical fiber connection structure; The axial position is along the optical fiber connection structure. ; , These are the core radii of the first optical fiber and the second optical fiber, respectively.

[0007] As an improvement to the above solution, the refractive index difference of the optical fiber connection structure Satisfy the following formula: ; in, The axial length of the optical fiber connection structure; The axial position is along the optical fiber connection structure. ; , These are the refractive index differences between the first optical fiber and the second optical fiber, respectively.

[0008] As an improvement to the above solution, the mode field diameter of the optical fiber connection structure... Satisfy the following formula: ; in, The axial length of the optical fiber connection structure; The axial position is along the optical fiber connection structure. ; , These are the mode field diameters of the first optical fiber and the second optical fiber, respectively.

[0009] As an improvement to the above solution, the axial length of the optical fiber connection structure satisfy: .

[0010] As an improvement to the above scheme, the mode field diameter of the first optical fiber is larger than that of the second optical fiber.

[0011] As an improvement to the above solution, the two ends of the optical fiber connection structure are respectively connected to the first optical fiber and the second optical fiber by fusion splicing.

[0012] As an improvement to the above scheme, the core region is matched to the mode fields of the first optical fiber and the second optical fiber by means of a refractive index gradient.

[0013] To achieve the above objectives, embodiments of the present invention also provide an optical fiber, including a first optical fiber, a second optical fiber, and the optical fiber connection structure described in any of the above embodiments, wherein the optical fiber connection structure is disposed between the first optical fiber and the second optical fiber.

[0014] Compared with existing technologies, the optical fiber connection structure and optical fiber disclosed in this invention, through the setting of an integrated gradient transition core region, allow the core characteristics of the core region to smoothly transition from the first optical fiber to the second optical fiber along the axial direction. The core characteristics at the first end are consistent with the first optical fiber, and the core characteristics at the second end are consistent with the second optical fiber. This avoids abrupt core changes when directly connecting optical fibers with different mode field diameters, reduces optical signal leakage and energy loss caused by core mismatch, and achieves low-loss connection between optical fibers with different mode field diameters. At the same time, the integrated all-fiber structure requires no additional mechanical connectors, is simple in structure and convenient in operation, and is suitable for communication optical cable construction, renovation and emergency repair scenarios, effectively improving the stability and applicability of interconnection of optical fibers of different specifications. Attached Figure Description

[0015] Figure 1 These are schematic diagrams of optical fiber structures with two different mode field diameters provided in embodiments of the present invention; Figure 2 This is a schematic diagram of the optical fiber connection structure provided in an embodiment of the present invention; Figure 3 This is a schematic diagram of the connection between the optical fiber connection structure provided in this embodiment of the invention and optical fibers with two different mode field diameters; Figure 4 This is another schematic diagram of the connection between the optical fiber connection structure provided in this embodiment of the invention and optical fibers with two different mode field diameters. Detailed Implementation

[0016] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0017] With the continuous improvement of communication capacity, the optical fiber mode field diameter of optical fiber cables with different solid optical fibers is different. This leads to different insertion losses when connecting optical fibers with different core diameters in the operator's optical cable network. In some cases, the insertion loss is too large and affects the opening of the communication system. For example, there are obvious differences in the mode field diameter at 1550nm for optical fibers that comply with the G.652, G.654, G.655, and G.657 standards, as shown in Table 1.

[0018] Table 1 shows the cross-sectional area and mode field diameter of different types of optical fibers.

[0019] Significant differences in mode field diameter result in varying optical power losses when fiber cores of different mode field diameters are spliced. As the transmission rates of actual optical communication systems continuously increase, larger mode field diameter optical fibers are required to ensure stable optical signal transmission and meet long-distance information transmission capabilities. However, at the end point (customer side), where a large number of conventional optical fibers (G.652) already exist, G.652 fiber cores with smaller mode field diameters better match the customer's requirements for transmission rate and optical signal quality. But as transmission rates continue to increase, the demand for low loss and high input optical power in optical fiber networks is growing. G.654E fiber cores, with their superior bending characteristics, lower loss per unit distance, and higher input optical power, are gradually becoming the evolutionary direction for the development and deployment of subsequent transmission network optical fiber networks.

[0020] It's important to note that the Mode Field Diameter (MFD) refers to the effective distribution range of optical signal energy in the core and cladding of an optical fiber, and is a parameter for measuring optical fiber transmission performance. Generally speaking, the larger the physical diameter of the core, the larger the MFD usually is. Unlike the physical diameter of the core, the MFD characterizes the actual distribution range of optical signal energy and is not solely determined by the core size. If there is a difference in the MFD when two fiber segments are spliced, optical energy will leak and experience mode distortion due to mode field mismatch, resulting in additional splicing loss. The larger the difference in MFD, the higher the splicing coupling loss; the smaller the difference, the higher the overlap of optical energy and the lower the coupling loss. For example, G.652B fiber has a mode field diameter of 10μm, while G.654E fiber has a mode field diameter of 12.5μm, a difference of 2.5μm. If end-face splicing is performed directly, the severe mode field mismatch will cause optical energy leakage and significant insertion loss. The present invention sets up an axially gradient transition fiber segment, so that the mode field diameter gradually and linearly transitions from 10μm to 12.5μm along the axial direction, eliminating abrupt changes in the mode field, allowing the optical signal energy distribution to be continuously and adaptively adjusted, reducing the coupling loss of heterogeneous mode field fiber docking, and achieving low-loss seamless fusion splicing.

[0021] See Figure 1 , Figure 1This is a schematic diagram of two optical fiber structures with different mode field diameters provided in an embodiment of the present invention. The first optical fiber is a large mode field diameter fiber, such as a G.654 series ultra-low loss fiber, and the second optical fiber is a small mode field diameter fiber, such as a G.652 series fiber. The mode field diameter of the first optical fiber is larger than that of the second optical fiber. Figure 1 As shown, the core radius of the first optical fiber is The core radius of the second optical fiber is , Because the first fiber has a larger core mode field diameter, it possesses lower unit optical loss and superior nonlinear resistance, meeting the transmission requirements of ultra-high-speed, high-capacity optical fiber communication systems. This effectively reduces the number of electrical repeater stations required and improves the overall signal quality of the system. However, the core radius of this large-mode-field-diameter fiber differs from that of widely deployed conventional fibers (i.e., the second fiber, such as G.652, G.655, and G.657). This mismatch in core radii directly leads to severe light leakage when the optical signal enters the smaller-diameter fiber during fiber splicing, resulting in significant optical power loss. In practical engineering, the insertion loss of such dissimilar fiber splices typically exceeds 0.5 dB, and in some scenarios, it can even reach over 3 dB, affecting the stable operation of the communication system.

[0022] To address this problem, the present invention provides an optical fiber connection structure with different mode field diameters at both ends. By setting a gradient transition core region between the two types of optical fibers, the problem of large optical power loss during the connection of optical fibers with different mode field diameters is solved.

[0023] See Figure 2 , Figure 2 This is a schematic diagram of the optical fiber connection structure provided in an embodiment of the present invention. The optical fiber connection structure is an integral cylindrical optical fiber. The first end of the optical fiber connection structure is used to connect to a first optical fiber, and the second end of the optical fiber connection structure is used to connect to a second optical fiber. The optical fiber connection structure includes a cladding and a core region disposed inside the cladding. The outer diameter of the cladding remains constant along the axial direction, and the core feature of the optical fiber connection structure gradually changes along the axial direction. The core feature corresponding to the first end is consistent with the core feature of the first optical fiber, and the core feature corresponding to the second end is consistent with the core feature of the second optical fiber. The core feature includes at least one of core radius, refractive index difference, and mode field diameter.

[0024] For example, the outer diameter of the cladding of the optical fiber connection structure remains constant along the axial direction, while the core features of the core region gradually change along the axial direction. Figure 2The solid line outline represents the outer boundary of the optical fiber connection structure, i.e., the physical outer diameter of the cladding, which remains constant along the axial direction; the dashed line outline represents the boundary of the inner core region, whose core characteristics (including at least one of core radius, refractive index difference, and mode field diameter) change with axial position. Continuously changing, for example, the core radius The linear gradient process of the fiber core radius is characterized. It should be noted that the layered illustration in the figure is only for ease of distinguishing the cladding and core regions. The fiber connection structure is a single, integrally formed fiber; the cladding and core regions are formed as a single unit through a process, without any mechanical splicing interface, resulting in a continuous and complete overall structure. The first end of the fiber connection structure is used to connect the first fiber, and the second end is used to connect the second fiber. A schematic diagram of the connection is shown below. Figure 3 and Figure 4 As shown, Figure 3 This is a schematic diagram illustrating the connection between the optical fiber connection structure provided in this embodiment of the invention and optical fibers with two different mode field diameters. Figure 4 This is another schematic diagram of the connection between the optical fiber connection structure provided in this embodiment of the invention and optical fibers with two different mode field diameters.

[0025] For example, the two ends of the optical fiber connection structure are connected to the first optical fiber and the second optical fiber respectively by fusion splicing. Fusion splicing refers to a connection method that uses an optical fiber fusion splicer to heat and melt the end face of the optical fiber through arc discharge, so that the core materials of the two optical fibers fuse together at high temperature. Compared with mechanical connection, fusion splicing has no air gap and reflection interface, and has lower insertion loss and return loss. During fusion splicing, the optical fiber connection structure is fused with the first optical fiber and the second optical fiber using a center point centerline alignment method. For example, the fusion splicer uses a built-in optical imaging system to identify the core axis of the two optical fibers and automatically aligns the center point centerline, so that the core axis of the optical fiber connection structure is coaxial with the core axis of the first optical fiber (or the second optical fiber). After alignment, the fusion splicer first pre-melts the end face of the optical fiber with a low-power arc to eliminate minor defects remaining on the end face, and then increases the arc power to heat and melt the material of the end face of the optical fiber and fuse it together under a slight axial thrust, forming a gapless fusion point. After splicing, a continuous all-fiber link is formed between the first optical fiber, the optical fiber connection structure, and the second optical fiber. The optical signal is transmitted from the first optical fiber to the graded transition fiber segment, where it transitions smoothly along the axis. The optical energy distribution is adaptively adjusted according to the changes in the transmission channel, avoiding optical signal leakage caused by mode field mismatch during direct splicing. Subsequently, the optical signal is smoothly coupled into the second optical fiber with a matching mode field diameter, realizing low-loss splicing between two optical fibers with different mode field diameters.

[0026] Furthermore, the core radius of the optical fiber connection structure Satisfy the following formula: (1); in, The axial length of the optical fiber connection structure; The axial position is along the optical fiber connection structure. ; , These are the core radii of the first optical fiber and the second optical fiber, respectively.

[0027] It should be noted that the core radius is the physical geometric radius of the core region in the cross-section of an optical fiber. It represents a real, measurable physical distance and is an inherent structural dimensional parameter of the optical fiber. The core radius determines the basic structure of the optical fiber, while the mode field diameter determines the coupling loss between the fiber and the interface. Together, they determine the transmission and matching characteristics of a single-mode fiber. The larger the core radius, the more light energy it can hold, and the wider the confined light field, thus increasing the mode field diameter. Conversely, the smaller the core radius, the easier it is for light energy to diffuse into the cladding, and the corresponding mode field diameter will also change accordingly.

[0028] For example, formula (1) is a linear gradient model, which ensures a smooth transition of the core radius from one end to the other in the core region. When the fiber connection structure is closer to the end of the first fiber, the core radius of the core region is [value missing]. The core radius of the fiber is equal to that of the first fiber, achieving a gapless connection with the first fiber and ensuring that the optical signal does not experience reflection or leakage due to abrupt size changes when entering the transition section from the first fiber; when When the fiber connection structure is closer to the end of the second fiber, the core radius of the core region is [value missing]. The core radius of the first fiber is equal to that of the second fiber, achieving smooth coupling and allowing the optical signal to smoothly enter the second fiber with a matched core size. Within the range, the core radius of the core region varies with The linear variation of the fiber core structure allows the mode field distribution of the optical signal to be continuously and smoothly adjusted as the fiber core changes during transmission. This avoids light leakage and energy loss caused by abrupt changes in the fiber core diameter, providing a structural basis for achieving low-loss interconnection between optical fibers with different mode field diameters.

[0029] Furthermore, the refractive index difference of the optical fiber connection structure Satisfy the following formula: (2); in, , These are the refractive index differences between the first optical fiber and the second optical fiber, respectively.

[0030] It should be noted that the refractive index difference refers to the relative difference between the refractive index of the fiber core and the refractive index of the cladding. It is an optical parameter that determines the transmission mode and the ability to confine optical signals in an optical fiber. In an optical fiber, the optical signal is confined to the vicinity of the core through total internal reflection, relying on the refractive index difference between the core and cladding. The magnitude of the refractive index difference directly affects the numerical aperture, mode field diameter, and bending loss of the optical fiber. In this invention, the refractive index difference of the optical fiber connection structure... The continuous gradual change along the axial direction, combined with the linear change of the fiber core radius, allows the energy distribution and transmission mode of the optical signal to be adjusted synchronously with the channel change, avoiding mode distortion and energy leakage caused by refractive index step, and providing a reliable optical basis for low-loss interconnection between different optical fibers.

[0031] For example, the fiber core region matches the mode fields of the first and second optical fibers through a refractive index gradient. To ensure a continuous and distortion-free transition of the optical signal's mode field distribution with changes in the fiber core size, the relative refractive index difference of the fiber connection structure... It also changes linearly and gradually along the axial direction, in line with the core radius. The changing trend remains consistent. Formula (2) is also a linear gradient model, ensuring a smooth transition of the refractive index difference from one end to the other. When At this time, the refractive index difference of the optical fiber connection structure The refractive index difference is equal to that of the first optical fiber, achieving a stepless connection with the first optical fiber and ensuring that the transmission mode is not distorted due to a sudden change in refractive index when the optical signal enters the transition section from the first optical fiber; when At this time, the refractive index difference of the optical fiber connection structure The refractive index difference is equal to that of the second optical fiber, achieving smooth coupling and allowing the optical signal to enter the second optical fiber efficiently in a compatible mode; Within the range, the refractive index difference varies with The linear variation, combined with the gradual change in fiber core radius, allows the mode field distribution of the optical signal to be adjusted synchronously with the changes in the transmission channel, avoiding energy leakage and mode mismatch loss caused by abrupt changes in refractive index, and further ensuring low-loss docking performance.

[0032] Furthermore, the mode field diameter of the optical fiber connection structure Satisfy the following formula: (3); in, , These are the mode field diameters of the first optical fiber and the second optical fiber, respectively.

[0033] For example, formula (3) is also a linear gradient model, ensuring a smooth transition of the modulus diameter from one end to the other. When At this time, the mode field diameter of the fiber optic connection structure is... The mode field diameter is equal to that of the first optical fiber, achieving a stepless connection with the first optical fiber and ensuring that the optical signal does not experience reflection or leakage due to abrupt changes in energy distribution when entering the transition section from the first optical fiber; when At this time, the mode field diameter of the fiber optic connection structure is... The mode field diameter is equal to that of the second optical fiber, achieving smooth coupling and allowing the optical signal to smoothly enter the second optical fiber with a matched energy distribution; Within the range, the diameter of the mode field increases with... The linear variation of the mode field structure allows the energy distribution of the optical signal to be continuously and smoothly adjusted as the transmission channel changes during transmission. This avoids optical power leakage and additional losses caused by abrupt changes in the mode field diameter, providing optical assurance for low-loss interfacing between optical fibers with different mode field diameters.

[0034] It should be noted that, , , , , , For known parameters, these can be directly obtained by consulting the product specifications or industry standard documents provided by the fiber optic manufacturers, based on the specific models of the first and second optical fibers. For example, when the first fiber is a G.654 series fiber and the second fiber is a G.652 series fiber, the above parameters can be directly obtained from the corresponding standard documents or publicly available information from the manufacturers, without the need for additional measurement.

[0035] To verify the matching accuracy between the two ends of the optical fiber connection structure of this invention and the first and second optical fibers, and to ensure unbiased coupling of the core radius, refractive index difference, and mode field diameter, this invention uses the classical formula for mode field diameter to deduce the core radii of the input and output ends, and establishes matching constraints. The specific process is as follows: Combining the classical theoretical formula of single-mode fiber MFD, the correspondence between the core radius at the input end and the MFD can be derived to ensure unbiased matching with the first fiber. The classical theoretical formula of MFD satisfies: (4); in, This is the core radius of the optical fiber. The operating wavelength of the optical signal. The refractive index of the optical fiber core. This represents the relative refractive index difference of the optical fiber; when At this time, the input end must ensure that the MFD and core parameters of the fiber connection structure are completely consistent with those of the first fiber. Substituting into the above formulas (1) to (3), the constraint conditions can be obtained: , , Because the core radius in formula (4) and Since the relationship is implicit, it is difficult to solve directly. Therefore, this invention obtains the formula for calculating the core radius of the input end (i.e., the first optical fiber) by reverse derivation of formula (4): (5); in, The refractive index of the first optical fiber core; Since formula (5) is an implicit function, it can be solved by iteration in engineering. Iteration theory is a mature applied physics and mathematics method. The solution process of iteration can refer to existing technology and will not be elaborated here. In this invention, formula (5) mainly achieves the following functions: 1. Physical origin: The implicit function is derived from the Petermann mode field radius formula of single-mode fiber; 2. Mathematical essence: The univariate nonlinear equation has no analytical solution, and fixed-point iteration is adopted; 3. Convergence guarantee: The single-mode fiber is in the compression mapping interval and converges monotonically and quickly; 4. Engineering practice: Only 1 to 3 iterations are needed to achieve a design accuracy of 0.01μm, which can be directly used for the core diameter design of tapered mode field transition fiber; Therefore, the iteration accuracy is controlled at 0.01μm during iteration until the calculated value matches the theoretical value. The deviation is ≤0.05μm, thus ensuring the matching of the core radius, refractive index difference and mode field diameter at the input end; Similarly, when In order to achieve parameter adaptation with the second optical fiber, the optical fiber connection structure must meet the following requirements: At this time, the input end must ensure that the MFD and core parameters of the fiber connection structure are completely consistent with those of the second fiber. Substituting into the above formulas (1) to (3), the constraint conditions can be obtained: , , After reversing the classical MFD theoretical formula, the formula for calculating the core radius of the output end (i.e., the second fiber) can be obtained as follows: (6); in, denoted as , where is the refractive index of the second optical fiber core.

[0036] It should be noted that formulas (5) and (6) describe the relationship between the mode field diameters of the first and last fibers with different core radii and the intermediate graded-mode-field fiber, proving that there is a clear optical correlation between the core radius, refractive index difference, and mode field diameter. Based on this optical correlation characteristic, this invention designs the fiber connection structure, using the core radii of the first and last fibers as the basis for the optical fiber connection. , Based on this, formulas (5) and (6) were used to verify that the mode field diameters at both ends were perfectly matched with the mode field diameters of the first and second optical fibers, ensuring that there were no abrupt changes in the mode field at both ends of the transition section; in addition, the core radius was used to verify that the mode field diameters at both ends were perfectly matched with the mode field diameters of the first and second optical fibers, ensuring that there were no abrupt changes in the mode field diameter at both ends of the transition section; With relative refractive index difference The synchronous linear gradual change makes the mode field diameter This also allows for a smooth transition, from the mode field diameter of the first fiber... The mode field diameter gradually changes to that of the second fiber. Therefore, the practical significance of formulas (5) and (6) lies in the fact that by designing the graduated mode field of the cylindrical fiber in the fiber connection structure, the mode fields at both ends of the fiber connection structure are matched with the mode fields of the first and second fibers, thereby solving the problems of difficult fabrication process and weak fusion splicing of existing tapered optical fibers. In addition, during the matching process at both ends, the cladding refractive index must be kept uniform (usually taken as 1.45), and MFD matching is achieved only by adjusting the core radius and refractive index difference, avoiding fusion alignment errors caused by differences in cladding parameters. Through the above back-calculation and iterative solution, the present invention can ensure that the parameters at both ends of the fiber connection structure are completely consistent with the optical characteristics of the first and second fibers, providing theoretical and technological guarantees for achieving low-loss splicing between fibers with different mode field diameters.

[0037] Furthermore, to verify the optical matching characteristics of the fiber optic connection structure of the present invention at any axial position, and to ensure that the mode field diameter can also smoothly transition synchronously and without abrupt distortion after the core radius and relative refractive index difference are linearly gradient along the axial direction, the linearly gradient... , Substituting into the classical MFD formula, we obtain the expression for the diameter of the mode field at any axial position. This process satisfies the following formula: (7); in, The refractive index of the fiber core in the optical fiber connection structure; because and They are positively correlated, and the change in refractive index difference Δ in single-mode fibers is extremely small (typically only 0.1%~0.3%), which can be approximated in engineering. .when hour, , , Substituting these parameters into formula (7), we get .when hour, , , Substituting these parameters into formula (7), we get This proves that formula (7) does not result in a step abrupt change when the MFD of the first and second fibers is matched at both ends. Furthermore, formula (7) applies throughout the entire process. Within the interval, and linear change, The change curve is almost linear, so the linear formula (3) can be used to approximate the complex formula (7). The error can be ignored. Moreover, its value at both ends is consistent with the formula (7), which not only ensures the matching of both ends with the first and second optical fibers, but also enables the rapid calculation of the MFD at any position of the gradient segment, taking into account both accuracy and engineering practicality.

[0038] Furthermore, the axial length of the optical fiber connection structure satisfy: .

[0039] For example, by substituting the mode field diameter data of G.652B and G.654E optical fibers in Table 1 into formula (3) for simulation calculation and engineering verification, the following conclusions can be drawn: ① The mode field diameter of G.652B fiber is 10μm, while that of G.654E fiber is 12.5μm. The difference in mode field diameter between the two is significant. When |=2.5μm, the optimal solution is a transition linear graded fiber length L=15mm, because when L=15mm, the mode field change rate is... satisfy: After substituting the parameters, the modulus change rate is obtained. The value is 0.167 μm / mm, which indicates that the gradient change is sufficiently gentle. During the transmission of the optical signal, the mode field distribution can be continuously adjusted with the fiber structure, avoiding energy leakage and mode distortion caused by abrupt changes in the mode field, and minimizing coupling loss. ② If the designed transition linear fiber length L < 10 mm, then the mode field change rate If the length is too large, the optical signal cannot smoothly adjust its mode field distribution within the transition section, which will cause the coupling loss between the transition fiber and the fibers with different mode fields on both sides to increase sharply, and the engineering yield will not meet the usage requirements. Therefore, the present invention sets the lower limit of the length to 10mm, that is, L≥10mm, to ensure that the mode field change process is smooth enough. ③ If the length L of the transition linear graded fiber is greater than 20mm, the overall rigidity of the transition fiber segment is enhanced and the flexibility is reduced. During the optical cable laying process, it is easily damaged by bending stress, which affects long-term reliability. Therefore, the present invention sets the upper limit of the length to 20mm, that is, L≤20mm, which takes into account both the mechanical performance of the transition segment and the ease of laying.

[0040] Based on the differences in mode field diameters of different types of optical fibers in Table 1 and the three conclusions drawn from the above simulation verification results, the axial length of the optical fiber connection structure of the present invention can be obtained. satisfy: The preferred value is L=15mm. This range ensures that the linear gradient process of the mode field diameter, core radius and refractive index difference is sufficiently smooth, realizing low-loss coupling between optical fibers with different mode field diameters. It also takes into account the mechanical flexibility and ease of deployment of the transition section, effectively reducing the bending risk in engineering applications. This allows the optical fiber connection structure of the present invention to achieve a better balance between transmission performance and engineering practicality.

[0041] Furthermore, embodiments of the present invention also provide an optical fiber, including a first optical fiber, a second optical fiber, and the optical fiber connection structure described in any of the above embodiments, wherein the optical fiber connection structure is disposed between the first optical fiber and the second optical fiber.

[0042] Compared with existing technologies, the optical fiber connection structure and optical fiber disclosed in this invention, through the setting of an integrated gradient transition core region, allow the core characteristics of the core region to smoothly transition from the first optical fiber to the second optical fiber along the axial direction. The core characteristics at the first end are consistent with the first optical fiber, and the core characteristics at the second end are consistent with the second optical fiber. This avoids abrupt core changes when directly connecting optical fibers with different mode field diameters, reduces optical signal leakage and energy loss caused by core mismatch, and achieves low-loss connection between optical fibers with different core diameters. Simultaneously, the integrated all-fiber structure requires no additional mechanical connectors, is simple in structure and convenient in operation, and is suitable for communication optical cable construction, renovation, and emergency repair scenarios, effectively improving the stability and applicability of interconnecting optical fibers of different specifications.

[0043] The above description represents the preferred embodiments of the present invention. It should be noted that those skilled in the art can make various improvements and modifications without departing from the principles of the present invention, and these improvements and modifications are also considered to be within the scope of protection of the present invention.

Claims

1. An optical fiber connection structure, characterized in that, The optical fiber connection structure is an integrated cylindrical optical fiber. The first end of the optical fiber connection structure is used to connect to the first optical fiber, and the second end is used to connect to the second optical fiber. The optical fiber connection structure includes a cladding and a core region disposed inside the cladding. The outer diameter of the cladding remains constant along the axial direction, and the core features of the optical fiber connection structure gradually change along the axial direction. The core characteristics corresponding to the first end are consistent with the core characteristics of the first optical fiber, and the core characteristics corresponding to the second end are consistent with the core characteristics of the second optical fiber. The core characteristics include at least one of core radius, refractive index difference, and mode field diameter.

2. The optical fiber connection structure as described in claim 1, characterized in that, The fiber core radius of the optical fiber connection structure Satisfy the following formula: ； in, The axial length of the optical fiber connection structure; The axial position is along the optical fiber connection structure. ; , These are the core radii of the first optical fiber and the second optical fiber, respectively.

3. The optical fiber connection structure as described in claim 1, characterized in that, The refractive index difference of the optical fiber connection structure Satisfy the following formula: ； in, The axial length of the optical fiber connection structure; The axial position is along the optical fiber connection structure. ; , These are the refractive index differences between the first optical fiber and the second optical fiber, respectively.

4. The optical fiber connection structure as described in claim 1, characterized in that, The mode field diameter of the optical fiber connection structure Satisfy the following formula: ； in, The axial length of the optical fiber connection structure; The axial position is along the optical fiber connection structure. ; , These are the mode field diameters of the first optical fiber and the second optical fiber, respectively.

5. The optical fiber connection structure as described in claim 1, characterized in that, The axial length of the optical fiber connection structure satisfy: .

6. The optical fiber connection structure as described in claim 1, characterized in that, The mode field diameter of the first optical fiber is larger than that of the second optical fiber.

7. The optical fiber connection structure as described in claim 1, characterized in that, The two ends of the optical fiber connection structure are respectively connected to the first optical fiber and the second optical fiber by fusion splicing.

8. The optical fiber connection structure according to claim 4, characterized in that, The core region is matched to the mode fields of the first and second optical fibers by means of a refractive index gradient.

9. An optical fiber, characterized in that, It includes a first optical fiber, a second optical fiber, and an optical fiber connection structure as described in any one of claims 1 to 8, wherein the optical fiber connection structure is disposed between the first optical fiber and the second optical fiber.

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