Chiral coupling ytterbium-doped optical fiber and high-power optical fiber laser

Abstract

The invention provides a chiral coupling ytterbium-doped optical fiber and a high-power optical fiber laser, and relates to the technical field of optical fibers. The ytterbium-doped optical fiber sequentially comprises a central fiber core, a plurality of spiral side cores, an inner cladding and an outer cladding from inside to outside, wherein the spiral side cores are spirally wound on the central fiber core along the axial direction of the central fiber core; wherein the basic mode refractive index of at least one spiral side core in the multiple spiral side cores is different from the refractive index of the central fiber core in a preset high-order mode, and the thermo-optical coefficient of the spiral side core with the refractive index different from the refractive index of the central fiber core in the preset high-order mode is larger than that of the central fiber core. The chiral coupling ytterbium-doped optical fiber provided by the invention can effectively remove a high-order mode in the central fiber core.

Description

Technical Field

[0001] This invention relates to the field of optical fiber technology, and in particular to a chiral coupled ytterbium-doped optical fiber and a high-power fiber laser. Background Technology

[0002] Fiber lasers using ytterbium-doped fiber as the gain medium have been widely used in high-end laser processing industries such as laser drilling, laser cutting, laser welding, laser cleaning, and laser quenching, as well as in fields such as laser medicine and laser interception, due to their advantages such as all-electric drive, high electro-optical conversion efficiency, and flexible transmission.

[0003] High-power fiber lasers are limited by the Transverse Mode Instability (TMI) effect, resulting in a large and unstable laser beam spot, which severely affects the processing accuracy and service life of laser processing systems. Just as... Figure 1 As shown, after the laser output power exceeds a certain threshold, the output mode of the ytterbium-doped fiber will change randomly, such as switching between the fundamental mode and higher-order modes, which will lead to spot degradation and a rapid slowdown in the growth of laser output power.

[0004] To achieve high-power output, high-power fiber lasers require a large central core diameter to suppress nonlinear effects and thermal damage caused by high-power lasers. However, ytterbium-doped fiber cores with large central core diameters contain multiple transmission modes, preventing single-mode output and thus failing to meet the transmission requirements of high-power fiber lasers. Furthermore, the inventors discovered that the output power of high-power fiber lasers, reaching kilowatts and tens of thousands of watts, also makes it impossible to remove higher-order modes from the central core. Summary of the Invention

[0005] This invention provides a chiral coupled ytterbium-doped fiber and a high-power fiber laser to solve the problem that current large-core ytterbium-doped fibers cannot effectively suppress the generation of higher-order modes in the central core.

[0006] In a first aspect, embodiments of the present invention provide a chiral coupled ytterbium-doped optical fiber, wherein the ytterbium-doped optical fiber includes, from the inside out, a central core and a plurality of helical side cores, and the plurality of helical side cores are helically wound around the central core along the axial direction of the central core; Among them, at least one of the plurality of spiral edge cores has a fundamental mode refractive index that is different from that of the central fiber core in a preset higher-order mode, and the thermo-optic coefficient of the spiral edge core that is different from that of the central fiber core in the preset higher-order mode is greater than that of the central fiber core.

[0007] In one possible implementation, the fundamental mode refractive index of all helical cores includes at least three different values, and the thermo-optic coefficient of all helical cores is greater than that of the central core.

[0008] In one possible implementation, the preset higher-order mode is the LP11 mode; all the spiral edge cores include three groups, the fundamental mode refractive index of the first group of spiral edge cores is the same as the refractive index of the central fiber core at room temperature in the LP11 mode, the fundamental mode refractive index of the second group of spiral edge cores is the same as the refractive index of the central fiber core at room temperature in the LP21 mode, and the fundamental mode refractive index of the third group of spiral edge cores is the same as the refractive index of the central fiber core at room temperature in the LP02 mode; each of the first group of spiral edge cores, the second group of spiral edge cores, and the third group of spiral edge cores includes at least one spiral edge core.

[0009] In one possible implementation, all spiral cores in the first group of spiral cores have the same thermo-optic coefficient, all spiral cores in the second group of spiral cores have the same thermo-optic coefficient, and all spiral cores in the third group of spiral cores have the same thermo-optic coefficient.

[0010] In one possible implementation, the thermo-optical coefficients of the first set of spiral cores, the second set of spiral cores, and the third set of spiral cores are all different.

[0011] In one possible implementation, the first group of spiral edge cores includes three spiral edge cores, the second group of spiral edge cores includes two spiral edge cores, and the third group of spiral edge cores includes three spiral edge cores. The two spiral edge cores in the second group of spiral edge cores are symmetrically arranged on both sides of the central fiber core, and the first group of spiral edge cores and the third group of spiral edge cores are symmetrically arranged on both sides of the central fiber core.

[0012] In one possible implementation, the first group of spiral edge cores includes two spiral edge cores, the second group of spiral edge cores includes four spiral edge cores, and the third group of spiral edge cores includes two spiral edge cores. The four spiral edge cores in the second group of spiral edge cores are symmetrically arranged on both sides of the central fiber core, and the first group of spiral edge cores and the third group of spiral edge cores are symmetrically arranged on both sides of the central fiber core.

[0013] In one possible implementation, the ytterbium-doped fiber is single-conical, with the central core having a diameter greater than 25 micrometers.

[0014] In one possible implementation, the ytterbium-doped fiber further includes an inner cladding layer, which is circular, D-shaped, or polygonal in shape.

[0015] In a second aspect, the present invention also provides a high-power fiber laser, which includes a chiral coupled ytterbium-doped fiber as described in the first aspect or any of the first aspects above.

[0016] To address the problem that large-core ytterbium-doped fibers cannot effectively suppress the generation of higher-order modes in the central core, this invention provides a chiral-coupled ytterbium-doped fiber. This is achieved by ensuring that the fundamental mode refractive index of at least one helical edge core is different from the refractive index of the central core in a preset higher-order mode, and that the thermo-optical coefficient of the helical edge core with a different refractive index in the preset higher-order mode is greater than that of the central core. Although the temperature rise of the central core is larger and that of the helical edge core is smaller under high-power laser operating conditions, the greater thermo-optical coefficient of the helical edge core in the preset higher-order mode allows the refractive index change of the fundamental mode in the edge core to remain comparable to that of the higher-order modes in the central core, thus maintaining good matching conditions. Attached Figure Description

[0017] Figure 1 This is a schematic diagram illustrating the principle of mode instability in high-power fiber lasers. Figure 2 This is a schematic diagram of the mode field distribution of four typical modes in large-core ytterbium-doped optical fiber; Figure 3 This is a schematic cross-sectional view of the chiral coupled ytterbium-doped optical fiber provided in an embodiment of the present invention. Figure 4 This is a perspective view of the chiral coupled ytterbium-doped optical fiber provided in an embodiment of the present invention; Figure 5 This invention provides a grouping of multiple helical cores within a chiral coupled ytterbium-doped fiber. Figure 6 This is another grouping of multiple helical cores within a chiral coupled ytterbium-doped fiber provided in this embodiment of the invention. Detailed Implementation

[0018] The present application will be described more clearly below with reference to specific embodiments. These embodiments will help those skilled in the art to further understand the function of the present application, but do not limit the present application in any way. It should be noted that those skilled in the art can make several modifications and improvements without departing from the concept of the present application. These all fall within the protection scope of the present application.

[0019] It should be understood that, when used in this application specification and the appended claims, the term "comprising" indicates the presence of the described features, integrals, steps, operations, elements and / or components, but does not exclude the presence or addition of one or more other features, integrals, steps, operations, elements, components and / or a collection thereof.

[0020] It should also be understood that the term “and / or” as used in this application specification and the appended claims means any combination of one or more of the associated listed items and all possible combinations, and includes such combinations.

[0021] In the description of this application and the appended claims, the terms "first," "second," "third," etc., are used only to distinguish descriptions and should not be construed as indicating or implying relative importance.

[0022] References to "one embodiment" or "some embodiments" as described in this specification mean that one or more embodiments of this application include a specific feature, structure, or characteristic described in connection with that embodiment. Therefore, the phrases "in one embodiment," "in some embodiments," "in other embodiments," "in still other embodiments," etc., appearing in different parts of this specification do not necessarily refer to the same embodiment, but rather mean "one or more, but not all, embodiments," unless otherwise specifically emphasized. The terms "comprising," "including," "having," and variations thereof mean "including but not limited to," unless otherwise specifically emphasized.

[0023] Furthermore, the term "multiple" mentioned in the embodiments of this application should be interpreted as two or more.

[0024] First, the terms used in the embodiments of this application will be explained: Ytterbium-doped fiber: This is an active special optical fiber doped with rare-earth ytterbium ions in a quartz glass matrix. Its absorption band covers the 800-1100nm wavelength range, enabling efficient coupling with semiconductor pump sources. It features long fluorescence lifetime and no excited-state absorption. This fiber improves pump efficiency through a double-clad structure, while the inner cladding employs asymmetric designs such as D-type and rectangular shapes to reduce helical optical loss. Large mode area technology achieves high-power single-mode output by controlling the refractive index difference.

[0025] Chiral-coupled ytterbium-doped fiber: This refers to a fiber core with a chiral, or helical, structure. This structure can affect the way light is transmitted, enabling optical coupling in specific modes.

[0026] The transmission mode of ytterbium-doped fiber is determined by its normalized frequency V. When V < 2.405, ytterbium-doped fiber only supports single-mode transmission, typically the fundamental mode, also known as LP01 mode. However, a larger core diameter will cause V > 2.405, at which point the fiber enters the multimode transmission region, meaning that in addition to the fundamental mode, higher-order modes will also be excited.

[0027] Thermo-optic coefficient: This is a core physical parameter describing the change of a material's refractive index with temperature. It directly determines the impact of temperature fluctuations on optical functions such as light transmission, modulation, and sensing, and is a key indicator for designing high-temperature resistant optical devices, temperature sensors, and thermo-optic modulators. It refers to the change in refractive index of the optical fiber core material for every 1°C increase in temperature; it is usually a positive value. The thermo-optic coefficient of the fiber core can be adjusted by changing its composition.

[0028] Mode refractive index matching refers to the equal refractive indices of different modes at the operating wavelength. In this invention, it means that the refractive index of the modes in the edge core is equal to the refractive index of the higher-order modes in the central core.

[0029] LP mode is a simplified representation of the optical field distribution in optical fiber. Different LP modes correspond to different optical field spatial distributions and transmission characteristics: LP01 mode (fundamental mode): Energy is concentrated in the center of the fiber core, the optical field distribution is Gaussian, the transmission loss is low and the stability is high, and it is the only transmission mode of single-mode fiber.

[0030] LP11, LP21 and LP02 are all high-order modes.

[0031] As described in the background section, optical fibers must have a large core diameter to achieve high power output in order to suppress nonlinear effects and thermal damage caused by high-power lasers. However, optical fibers with larger core diameters will have multiple transmission modes within their cores, such as... Figure 2 The mode field distributions of the four typical modes shown are as follows: LP01 is the fundamental mode, while LP21 and LP02 are all higher-order modes. For fiber lasers, the ideal situation is pure fundamental mode output, but for high-power fiber lasers based on large-core ytterbium-doped fibers, some higher-order modes will inevitably exist in the output modes.

[0032] Using chiral-coupled ytterbium-doped fiber is an effective way to remove higher-order modes in the fiber core. A typical structure of chiral-coupled ytterbium-doped fiber is as follows: Figure 3 and 4As shown, the chiral-coupled ytterbium-doped fiber includes a central core 301, spiral edge cores 302, an inner cladding 303, and an outer cladding 304. The spiral edge core 302 only supports fundamental mode transmission. Currently, in the design of large-core chiral-coupled ytterbium-doped fibers, the refractive index of the LP01 fundamental mode in all spiral edge cores 302 matches the refractive index of the LP11 higher-order modes in the central core 301, meaning they have equal refractive indices at the operating wavelength. Due to this refractive index matching, the higher-order modes in the large central core will first couple to the spiral edge cores. Because the edge cores are distributed in a spiral structure within the ytterbium-doped fiber cladding, the mode transmission loss in the spiral edge cores is relatively high. Therefore, the higher-order modes in the central core, after coupling to the spiral edge cores, will be gradually lost, ultimately achieving the goal of removing the higher-order modes from the central core.

[0033] Furthermore, currently, the refractive indices of all eight helical edge cores 302 in chiral coupled ytterbium-doped fibers are identical. The inventors discovered that for pulsed fiber lasers with an average power not exceeding several hundred watts, the temperature rise in the ytterbium-doped fiber is limited, so the thermo-optic effect—that is, the influence of temperature-dependent refractive index changes on the refractive index matching conditions between the helical edge cores 302 and the central core 301—is not a concern. However, for high-power continuous fiber lasers with output powers reaching several kilowatts or tens of thousands of watts, the temperature rise in and around the ytterbium-doped fiber core can reach tens of degrees Celsius, or even hundreds of degrees Celsius. In this case, the refractive index of the helical edge cores 302 easily becomes mismatched with that of the central core 301, preventing higher-order modes in the central core 301 from coupling to the edge cores, thus making it impossible to remove these higher-order modes.

[0034] Furthermore, current chiral-coupled ytterbium-doped fibers do not require specific thermo-optic coefficients for all spiral edge cores 302. The inventors also discovered that for high-power continuous fiber lasers with output powers reaching kilowatts and tens of thousands of watts, the temperature rise in the core and surrounding areas of the ytterbium-doped fiber can reach tens of degrees Celsius, or even hundreds of degrees Celsius. The thermo-optic effect significantly impacts the refractive index matching condition between the edge core and the central core. Since the laser in the ytterbium-doped fiber is mainly concentrated in the central core 301, the temperature rise in the central core 301 is the largest, while the temperature rise in the spiral edge core 302 is smaller. Therefore, if the thermo-optic coefficient of the central core 301 is close to that of the spiral edge core 302, the refractive index change of the fundamental mode of the spiral edge core 302 will be significantly smaller than the refractive index change of the higher-order modes in the central core 301. This will lead to the failure of the refractive index matching condition between the spiral edge core 302 and the central core 301, ultimately making it impossible to remove the higher-order modes in the central core.

[0035] To ensure the stability of the laser beam spot output by a high-power laser and improve the performance of the high-power laser, this invention provides a chiral coupled ytterbium-doped fiber, which can guarantee the stability of the laser beam spot under high power and effectively remove higher-order modes in the fiber core.

[0036] This invention provides a chiral coupled ytterbium-doped fiber, which is still as Figure 3 and 4 As shown, the ytterbium-doped fiber includes a central core 301 and multiple spiral side cores 302 from the inside out. The multiple spiral side cores 302 are spirally wound around the central core 301 along the axial direction of the central core 301.

[0037] Under high-power laser operating conditions, as the laser power continuously increases, the refractive index of the central core 301 will continuously increase, and the proportion of higher-order modes LP21 and LP02 in the central core 301 will continuously increase. The inventors found that the greater the difference between the refractive index of the central core 301 and the cladding, the higher the proportion of higher-order modes in the central core 301 will be. In order to filter out the higher-order modes in the central core, it is necessary to adjust the refractive index and thermo-optic coefficient of multiple spiral cores 302 at room temperature in order to eliminate the influence of high power.

[0038] As previously mentioned, in current chiral-coupled ytterbium-doped fibers, the refractive index of the LP01 fundamental mode in all helical edge cores 302 matches the refractive index of the LP11 higher-order modes in the central core 301; that is, the refractive index of the fundamental mode in all helical edge cores 302 is the same. The inventors discovered that for pulsed fiber lasers with an average power not exceeding several hundred watts, the temperature rise in the ytterbium-doped fiber is limited, so the thermo-optic effect—that is, the influence of temperature-dependent refractive index changes on the refractive index matching condition between the helical edge cores 302 and the central core 301—does not need to be considered. However, for high-power continuous fiber lasers with output powers reaching several kilowatts or tens of thousands of watts, the temperature rise in and around the ytterbium-doped fiber core can reach tens of degrees Celsius, or even hundreds of degrees Celsius. In this case, the refractive index of the helical edge cores 302 easily becomes mismatched with that of the central core 301, preventing the higher-order modes in the central core 301 from coupling to the edge cores, thus making it impossible to remove the higher-order modes from the central core 301.

[0039] In the chiral coupled ytterbium-doped fiber of the present invention, among a plurality of helical cores, at least one helical core has a fundamental mode refractive index that is different from that of the central core in a preset higher-order mode, and the thermo-optic coefficient of the helical core with a refractive index different from that of the central core in the preset higher-order mode is greater than that of the central core.

[0040] An example preset advanced mode could be LP11 mode.

[0041] In some embodiments, the ytterbium-doped optical fiber may further include an inner cladding 303 and an outer cladding 304.

[0042] In the chiral coupled ytterbium-doped fiber designed in this invention, although the temperature rise of the central core 301 is larger and the temperature rise of the helical edge core 302 is smaller as the laser power increases, the fundamental mode refractive index of at least one helical edge core 302 is different from that of the central core in LP11 mode. Furthermore, the thermo-optical coefficient of this helical edge core, which has a different refractive index from that of the central core in a preset higher-order mode, is greater than that of the central core. Therefore, the refractive index change of the fundamental mode of the helical edge core, which has a different refractive index from that of the central core in a preset higher-order mode, can still be comparable to the refractive index change of the higher-order modes in the central core. Thus, good matching conditions can still be maintained.

[0043] In some embodiments, in order to further filter out higher-order modes in the central core 301, the fundamental mode refractive index of all spiral edge cores can be set to at least three different values, and the thermo-optic coefficient of all spiral edge cores is greater than that of the central core.

[0044] In this embodiment, all helical cores can be divided into three groups. The fundamental mode refractive index of the first group of helical cores is the same as that of the central core in LP11 mode at room temperature. The fundamental mode refractive index of the second group of helical cores is the same as that of the central core in LP21 mode at room temperature. The fundamental mode refractive index of the third group of helical cores is the same as that of the central core in LP02 mode at room temperature. Furthermore, each of the first, second, and third groups of helical cores includes at least one helical core.

[0045] In some embodiments, the thermo-optic coefficients of all spiral cores in the first group of spiral cores are the same, the thermo-optic coefficients of all spiral cores in the second group of spiral cores are the same, and the thermo-optic coefficients of all spiral cores in the third group of spiral cores are the same.

[0046] For example, the thermo-optic coefficients of the first group of spiral cores, the second group of spiral cores, and the third group of spiral cores may all be different.

[0047] In some embodiments, such as Figure 5 As shown, the first group of spiral edge cores 501 may include 3 spiral edge cores, the second group of spiral edge cores may include 2 spiral edge cores, and the third group of spiral edge cores 502 may include 3 spiral edge cores. The 2 spiral edge cores in the second group of spiral edge cores are symmetrically arranged on both sides of the central fiber core, and the first group of spiral edge cores 501 and the third group of spiral edge cores 502 are symmetrically arranged on both sides of the central fiber core.

[0048] In some embodiments, such as Figure 6As shown, the first group of spiral edge cores 501 includes 2 spiral edge cores, the second group of spiral edge cores includes 4 spiral edge cores, and the third group of spiral edge cores 502 includes 2 spiral edge cores. The 4 spiral edge cores in the second group of spiral edge cores are symmetrically arranged on both sides of the central fiber core. The first group of spiral edge cores 501 and the third group of spiral edge cores 502 are symmetrically arranged on both sides of the central fiber core.

[0049] In some embodiments, the ytterbium-doped fiber can be a single cone shape with a central core diameter greater than 25 micrometers.

[0050] In this embodiment, the unique tapered structure of the single-tapered ytterbium-doped fiber plays a crucial role in improving beam quality. Within the tapered region of the fiber, the core-cladding diameter gradually changes, and this gradient structure allows for effective modulation of the transmitted optical modes. It can suppress the transmission of higher-order modes, concentrating more optical energy on the fundamental mode, thereby improving beam quality.

[0051] In some embodiments, ytterbium-doped fiber serves as the core gain medium for high-power fiber lasers and amplifiers. Its performance depends not only on the doping concentration and structure of the fiber core, but also significantly on the shape design of the cladding. This directly affects the coupling efficiency, absorption uniformity, heat dissipation, and ultimately, the laser output power and beam quality. Different cladding shapes alter the propagation path and mode distribution of the pump light within the fiber, resulting in differentiated application adaptability. The pump light is the energy source that excites ytterbium ions in the fiber core to achieve population inversion; the shape of the cladding directly determines whether the pump light can efficiently enter the fiber and be fully absorbed by the core.

[0052] In this embodiment, the inner cladding layer is circular, D-shaped, or polygonal in shape.

[0053] The circular inner cladding is simple to prepare, but it has low coupling efficiency and uneven absorption.

[0054] Polygonal cladding, such as square, hexagonal, and octagonal cladding, can be used. The planar sidewalls of polygons break the symmetrical transmission of circular beams, causing the pump light to reflect multiple times between different sidewalls. Each reflection has a chance to penetrate the central core, significantly increasing the interaction frequency with the core. Furthermore, polygonal claddings exhibit high absorption efficiency. For square claddings, the pump light absorption efficiency can reach over 80%, while for hexagonal claddings it can even reach 90%. This reduces the impact of fiber loss on laser output. Additionally, polygonal claddings have extremely high tolerance for the incident angle of the pump source, allowing compatibility with multiple side-pump modules, thus enabling high-power laser output.

[0055] The D-shaped inner cladding can optimize pump coupling in a specific direction. By adjusting the ratio of the plane to the arc, the reflection path of the pump light can be controlled, avoiding "local overheating" of the fiber core caused by excessive local pump light. It is especially suitable for medium-power laser systems that are sensitive to heat dissipation.

[0056] In order to cope with the temperature changes caused by high-power lasers, the refractive index of the spiral core can easily become mismatched with that of the central core. Figure 5 Taking this as an example, the present invention designs a heterogeneous gradient spiral core.

[0057] The invention comprises a total of eight helical edge cores. The refractive index of the fundamental mode in each of the first group of helical edge cores 501 is the same as that in the LP11 mode of the central fiber core, and the thermo-optical coefficient of each helical edge core in the first group of helical edge cores 501 is greater than that of the central fiber core. Therefore, although the temperature rise of the central fiber core is larger than that of the helical edge cores under high-power laser operating conditions, the larger thermo-optical coefficient of the helical edge cores allows the refractive index change of the fundamental mode in the helical edge cores to remain comparable to that in the LP11 mode of the central fiber core, thus maintaining good matching conditions.

[0058] As laser power increases, the refractive index of the central fiber core also increases, leading to a greater proportion of higher-order modes such as LP21 and LP02 within the central fiber core. Therefore, special design is required to filter out these higher-order modes in the central fiber core.

[0059] The two helical cores in the second set are symmetrically arranged on both sides of the central core. The fundamental mode refractive index of the second set of helical cores is the same as that of the central core in LP21 mode at room temperature, and their thermo-optical coefficients are also greater than those of the central core. Therefore, although the temperature rise of the central core is larger and that of the helical cores is smaller under high-power laser operating conditions, the larger thermo-optical coefficients of the two helical cores in the second set mean that the refractive index change of the fundamental mode in the two helical cores in the second set can still be comparable to that in the central core in LP21 mode, thus maintaining good matching conditions.

[0060] Furthermore, the fundamental mode refractive index of the three spiral edge cores within the third group of spiral edge cores 502 is the same as that of the central fiber core in LP02 mode at room temperature, and the thermo-optical coefficient of each spiral edge core within the third group of spiral edge cores 502 is greater than that of the central fiber core. Therefore, although the temperature rise of the central fiber core is larger and that of the edge cores is smaller under high-power laser operating conditions, the larger thermo-optical coefficient of each spiral edge core within the third group of spiral edge cores 502 means that the refractive index change of the fundamental mode of each spiral edge core within the third group of spiral edge cores 502 can still be comparable to the refractive index change in LP02 mode of the central fiber core, thus maintaining good matching conditions.

[0061] The chiral coupled ytterbium-doped fiber provided by this invention features three sets of helical cores, each with a different fundamental refractive index. These refractive indices are identical to those of the LP11, LP21, and LP02 modes in the central core at room temperature, respectively. Furthermore, each of the three helical cores has a different thermo-optical coefficient, ensuring that even with increasing laser power and varying temperatures between the central and variable cores, the fundamental mode refractive index in the helical cores matches the refractive indices of the three main higher-order modes in the central core.

[0062] The chiral coupled ytterbium-doped fiber provided by this invention not only ensures that the refractive index of the fundamental mode in the helical core is the same as that in the LP11 mode in the central core under high-power laser operating conditions, but also solves the problem of excessive proportion of LP21 and LP02 modes in the central core due to excessive laser power.

[0063] The chiral coupled ytterbium-doped fiber provided by this invention features a fundamental mode refractive index that differs from that of the central core in a predetermined higher-order mode. Furthermore, the thermo-optical coefficient of the helical edge core, which has a different refractive index from the central core in the predetermined higher-order mode, is greater than that of the central core. Although the temperature rise of the central core is larger and that of the helical edge core is smaller under high-power laser operating conditions, the greater thermo-optical coefficient of the helical edge core in the predetermined higher-order mode allows the refractive index change of the fundamental mode in the edge core to remain comparable to that of the higher-order mode in the central core, thus maintaining good matching conditions.

[0064] Corresponding to any of the chiral coupled ytterbium-doped fibers described above, this embodiment of the invention also provides a high-power fiber laser, which includes any of the chiral coupled ytterbium-doped fibers described above and has the advantages of the chiral coupled ytterbium-doped fibers described above, which will not be repeated here.

[0065] The above embodiments are only used to illustrate the technical solutions of the present invention, and are not intended to limit it. Although the present invention has been described in detail with reference to the foregoing embodiments, those skilled in the art should understand that modifications can still be made to the technical solutions described in the foregoing embodiments, or equivalent substitutions can be made to some of the technical features. Such modifications or substitutions do not cause the essence of the corresponding technical solutions to deviate from the spirit and scope of the technical solutions of the embodiments of the present invention.

Claims

1. A chiral coupled ytterbium-doped optical fiber, characterized in that, Ytterbium-doped optical fiber consists of a central core and multiple spiral side cores from the inside out. The multiple spiral side cores are spirally wound around the central core along the axial direction of the central core. Among the plurality of helical edge cores, at least one helical edge core has a fundamental mode refractive index that is different from that of the central fiber core in a preset higher-order mode, and the thermo-optic coefficient of the helical edge core that has a different refractive index from that of the central fiber core in the preset higher-order mode is greater than that of the central fiber core.

2. The chiral coupled ytterbium-doped optical fiber as described in claim 1, characterized in that, The fundamental mode refractive index of all helical cores includes at least three different values, and the thermo-optical coefficient of all helical cores is greater than that of the central core.

3. The chiral coupled ytterbium-doped optical fiber as described in claim 2, characterized in that, The preset higher-order mode is LP11 mode; all the spiral edge cores include 3 groups, the fundamental mode refractive index of the first group of spiral edge cores is the same as the refractive index of the central fiber core at room temperature in LP11 mode, the fundamental mode refractive index of the second group of spiral edge cores is the same as the refractive index of the central fiber core at room temperature in LP21 mode, and the fundamental mode refractive index of the third group of spiral edge cores is the same as the refractive index of the central fiber core at room temperature in LP02 mode; each of the first group of spiral edge cores, the second group of spiral edge cores, and the third group of spiral edge cores includes at least one spiral edge core.

4. The chiral coupled ytterbium-doped optical fiber as described in claim 3, characterized in that, The thermo-optic coefficients of all spiral cores in the first group of spiral cores are the same, the thermo-optic coefficients of all spiral cores in the second group of spiral cores are the same, and the thermo-optic coefficients of all spiral cores in the third group of spiral cores are the same.

5. The chiral coupled ytterbium-doped optical fiber as described in claim 4, characterized in that, The thermo-optic coefficients of the first group of spiral cores, the second group of spiral cores, and the third group of spiral cores are all different.

6. The chiral coupled ytterbium-doped optical fiber as described in claim 3, characterized in that, The first group of spiral edge cores includes 3 spiral edge cores, the second group of spiral edge cores includes 2 spiral edge cores, and the third group of spiral edge cores includes 3 spiral edge cores. The 2 spiral edge cores in the second group of spiral edge cores are symmetrically arranged on both sides of the central fiber core, and the first group of spiral edge cores and the third group of spiral edge cores are symmetrically arranged on both sides of the central fiber core.

7. The chiral coupled ytterbium-doped optical fiber as described in claim 3, characterized in that, The first group of spiral edge cores includes 2 spiral edge cores, the second group of spiral edge cores includes 4 spiral edge cores, and the third group of spiral edge cores includes 2 spiral edge cores. The 4 spiral edge cores in the second group of spiral edge cores are symmetrically arranged on both sides of the central fiber core, and the first group of spiral edge cores and the third group of spiral edge cores are symmetrically arranged on both sides of the central fiber core.

8. The chiral coupled ytterbium-doped optical fiber according to any one of claims 1-7, characterized in that, The ytterbium-doped fiber is single-conical, and the diameter of the central core is greater than 25 micrometers.

9. The chiral coupled ytterbium-doped optical fiber according to any one of claims 1-7, characterized in that, The ytterbium-doped optical fiber also includes an inner cladding layer, which is circular, D-shaped, or polygonal in shape.

10. A high-power fiber laser, characterized in that, The high-power fiber laser includes the chiral coupled ytterbium-doped fiber as described in any one of claims 1-9.

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