Low core numerical aperture circularly perturbed mode gain fiber

Abstract

The application relates to the technical field of optical fibers, and provides a low-core numerical aperture circular mode-coupled gain optical fiber which comprises a core layer, an inner cladding layer and a plurality of micro stress units; the inner cladding layer is sleeved outside the core layer, the inner cladding layer is provided with a plurality of filling holes, and the plurality of filling holes are arranged at intervals along the circumference of the core layer; the plurality of micro stress units are filled in the filling holes one by one; and the refractive index of the micro stress unit is smaller than that of the inner cladding layer. The low-core numerical aperture circular mode-coupled gain optical fiber can improve the cladding pumping absorption coefficient, shorten the length of the gain optical fiber, solve the nonlinear problem of the optical fiber laser under high power, form a non-uniform refractive index field and a stress field around the core layer, increase the loss of high-order modes of laser, improve the mode instability threshold of the optical fiber laser under high power, and thus realize high-power single-mode output of the optical fiber laser.

Description

Technical Field

[0001] This invention relates to the field of optical fiber technology, and in particular to a low core numerical aperture circular scrambling mode gain optical fiber. Background Technology

[0002] High-power fiber lasers, with their advantages of high beam quality, compact structure, high photoelectric conversion efficiency, and good heat dissipation, have been widely used in industrial processing, scientific research, laser medicine, and national defense. However, with the continuous increase in output power, nonlinear effects and mode instability have become bottlenecks restricting further breakthroughs in the performance of high-power fiber lasers. Therefore, how to simultaneously improve the nonlinear threshold and mode instability threshold of high-power fiber lasers is a technical problem that needs to be solved in this field. Summary of the Invention

[0003] This invention aims to solve the technical problems existing in related technologies. To this end, this invention proposes a low-core numerical aperture circular mode-scrambling gain fiber, effectively solving the problem of output power limitation and beam quality degradation caused by nonlinear effects and mode instability effects when the output power of fiber lasers is further increased. The low-core numerical aperture circular mode-scrambling gain fiber according to this invention comprises: A fiber core layer, wherein the diameter of the fiber core layer is not less than 25 μm and not more than 60 μm; An inner cladding layer is sleeved on the outside of the fiber core layer. The inner cladding layer has a plurality of filling holes, which are arranged at intervals along the circumference of the fiber core layer. Multiple micro-stress units are provided, each corresponding to a specific micro-stress unit and filling the filling hole; the refractive index of the micro-stress unit is less than that of the inner cladding layer. The core numerical aperture of the low core numerical aperture circular scrambling mode gain fiber is not less than 0.02 and less than 0.06.

[0004] In the low-core numerical aperture circular mode-scratching gain fiber according to the present invention, the diameter of at least one of the micro-stress units is different from the diameter of the other micro-stress units; And / or, the refractive index of at least one of the micro-stress elements is different from the refractive index of the other micro-stress elements.

[0005] The low-core numerical aperture circular mode-scratching gain optical fiber according to the present invention has n micro-stress units; The diameters of each of the micro-stress elements are D 1i The distances r between the edge of each micro-stress unit and the edge of the fiber core layer along the radial direction of the fiber core layer are respectively. 1i (i=1, 2, 3…n); the diameter of the fiber core layer is D0; where D 1i r1i D0 satisfies: 2D0 <D 1i <8D0,D0 <r 1i <3D0.

[0006] In the low core numerical aperture circular scrambling mode gain fiber according to the present invention, each of the micro-stress units has the same diameter, and the distance between the edge of at least one micro-stress unit and the edge of the core layer along the radial direction of the core layer is different from the distance between the edge of the other micro-stress unit and the edge of the core layer along the radial direction of the core layer.

[0007] In the low-core numerical aperture circular scrambling mode gain fiber of the present invention, the ratio of the diameters of any two micro-stress units is greater than 0.9 and less than 1.1.

[0008] The low core numerical aperture circular mode scrambling gain optical fiber of the present invention is wherein the core layer is made of rare earth ion-doped silicon dioxide core; and the micro-stress unit is composed of a matrix silicon dioxide and one or more dopants F, B2O3, Ge2O3, and P2O5.

[0009] In the low core numerical aperture circular scrambling mode gain fiber according to the present invention, the micro-stress unit comprises 1-7 elements.

[0010] The low core numerical aperture circular scrambling mode gain fiber according to the present invention has an inner cladding diameter of 500–1000 μm.

[0011] The above-described one or more technical solutions in the embodiments of the present invention have at least one of the following technical effects: In summary, the low-core numerical aperture circular mode-scratching gain fiber of the present invention, by setting the diameter of the core layer between 25 μm and 60 μm, enables high-power laser output. Simultaneously, by setting the core numerical aperture of the low-core numerical aperture circular mode-scratching gain fiber between 0.02 and 0.06, the fiber normalization frequency can be effectively reduced, thereby suppressing higher-order modes of the laser. Furthermore, by setting multiple micro-stress units with different sizes or refractive indices in the inner cladding around the core layer, these micro-stress units not only perturb the propagation trajectory of the pump light in the inner cladding to improve the cladding pump absorption coefficient, which is beneficial for shortening the length of the gain fiber and improving the nonlinear threshold of the fiber laser at high power, but also create a non-uniform refractive index field and residual stress field around the core layer to increase the loss of higher-order laser modes and improve the mode instability threshold of the fiber laser at high power. This achieves simultaneous improvement of the nonlinear threshold and mode instability threshold of the high-power fiber laser, realizing single-mode high-power laser output.

[0012] Additional aspects and advantages of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description

[0013] To more clearly illustrate the technical solutions in the embodiments of the present invention or related technologies, the drawings used in the description of the embodiments or related technologies will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention and are not considered as limitations on this application. Moreover, those skilled in the art can obtain other drawings based on these drawings without creative effort.

[0014] Figure 1 This is one of the schematic cross-sectional views of the low core numerical aperture circular scrambling mode gain optical fiber provided in the embodiments of the present invention.

[0015] Figure 2 This is the second schematic cross-sectional view of the low core numerical aperture circular scrambling mode gain optical fiber provided in the embodiments of the present invention.

[0016] Figure 3 This is a schematic cross-sectional view of a low-core numerical aperture circular scrambling mode gain optical fiber with different numbers of micro-stress units provided in an embodiment of the present invention.

[0017] Figure label: 1. Low core numerical aperture circular mode scrambling gain fiber; 11. Core layer; 12. Inner cladding; 13. Micro-stress unit; 14. Inner coating; 15. Outer coating. Detailed Implementation

[0018] Embodiments of the present invention are described in detail below. Examples of these embodiments are shown in the accompanying drawings, wherein the same or similar reference numerals denote the same or similar elements or elements having the same or similar functions throughout. The embodiments described below with reference to the accompanying drawings are exemplary and are only used to explain the present invention, and should not be construed as limiting the present invention.

[0019] The specific terms used in this specification are for illustrative purposes only and are not intended to limit the illustrated embodiments. For example, expressions such as "same" and "identical" not only indicate a strictly identical state, but also indicate a state with tolerances or differences in the degree of functionality. For example, expressions indicating relative or absolute arrangement such as "in a certain direction," "along a certain direction," "side by side," "perpendicular," "centered on," "concentric," or "coaxial" not only strictly indicate such an arrangement, but also indicate a state of relative displacement by tolerances or angles or distances with the same degree of functionality.

[0020] The terms “center,” “longitudinal,” “lateral,” “length,” “width,” “thickness,” “upper,” “lower,” “front,” “rear,” “left,” “right,” “vertical,” “horizontal,” “top,” “bottom,” “inner,” “outer,” “clockwise,” “counterclockwise,” “axial,” “radial,” and “circumferential” indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings. They are used only for the convenience of describing the present invention and simplifying the description, and are not intended to indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limiting the present invention.

[0021] Furthermore, features specified as "first" or "second" may explicitly or implicitly include one or more of those features. In the description of this invention, unless otherwise stated, "multiple" means two or more. In the description of the embodiments of this application, "multiple" means two or more, unless otherwise explicitly specified. In the description of the embodiments of this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, B1 and / or B2 can represent: B1 existing alone, B1 and B2 existing simultaneously, and B2 existing alone. Additionally, the character " / " in this document generally indicates that the preceding and following related objects have an "or" relationship.

[0022] In the description of this invention, it should be noted that, unless otherwise explicitly specified and limited, the terms "installation," "connection," and "linking" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection or an electrical connection; they can refer to a direct connection or an indirect connection through an intermediate medium; and they can refer to the internal connection of two components. Those skilled in the art can understand the specific meaning of the above terms in this invention based on the specific circumstances.

[0023] The following is combined Figures 1 to 3 The present invention describes a low-core numerical aperture circular mode-scratching gain optical fiber.

[0024] like Figure 1 and Figure 2 As shown, this invention provides a low-core numerical aperture circular mode-scrambling gain fiber 1, comprising: a core layer 11, an inner cladding 12, and multiple micro-stress units 13; the diameter of the core layer 11 is not less than 25 μm and not more than 60 μm; the inner cladding 12 is sleeved on the outside of the core layer 11, and the inner cladding 12 has multiple filling holes arranged at intervals along the circumference of the core layer 11; the multiple micro-stress units 13 are correspondingly filled in the filling holes; the refractive index of the micro-stress units 13 is less than the refractive index of the inner cladding 12. The core numerical aperture of the low-core numerical aperture circular mode-scrambling gain fiber 1 is not less than 0.02 and less than 0.06.

[0025] In this embodiment, by setting the diameter of the core layer 11 between 25μm and 60μm, the low core numerical aperture circular mode scrambling gain fiber 1 of this embodiment can achieve high-power laser output; at the same time, by setting the core numerical aperture of the low core numerical aperture circular mode scrambling gain fiber 1 between 0.02 and 0.06, the fiber normalization frequency can be effectively reduced, thereby suppressing higher-order modes of the laser.

[0026] It is understandable that the numerical aperture of the fiber core can be adjusted by changing the materials of the core layer 11 and the inner cladding layer 12, thereby affecting the difference in refractive index between the core layer 11 and the inner cladding layer 12 respectively.

[0027] Meanwhile, in this embodiment, multiple filling holes are opened in the inner cladding 12 and arranged circumferentially along the core layer 11. Micro-stress units 13 are filled in the filling holes, and the refractive index of the micro-stress units 13 is made smaller than that of the inner cladding 12. This allows the micro-stress units 13 to disturb the propagation trajectory of the pump light in the inner cladding 12, destroy the spiral transmission mode of the pump light, increase the overlap efficiency between the pump light transmission trajectory and the rare earth doped core region, and thus improve the cladding pump absorption coefficient.

[0028] Since the micro-stress element 13 is usually made of silicon dioxide doped with other trace elements, due to the difference in the coefficients of thermal expansion between different materials, the micro-stress element 13 can generate residual stress in the surrounding silicon dioxide mass in the area doped with trace elements after undergoing high-temperature drawing and cooling processes during optical fiber fabrication. In the formula, E is the elastic modulus of the material, with the unit being Pa. and Let be the coefficients of thermal expansion of different materials (in 1 / ℃ or 1 / K), and ΔT be the change in temperature (in ℃ or K). This residual stress alters the local refractive index distribution through the photoelastic effect, and its refractive index change satisfies: Δn = -n 3 pσ / 2, where n is the refractive index of the glass material, p is the effective photoelastic coefficient, and σ is the local stress.

[0029] Therefore, the micro-stress unit 13 can not only directly adjust the transverse refractive index distribution of the optical fiber through the material refractive index difference, but also further modulate the effective refractive index distribution near the fiber core layer 11 by utilizing the stress field generated by the difference in thermal expansion coefficients, thereby achieving the control of propagation characteristics of different modes and suppressing higher-order modes of the laser.

[0030] In summary, the low-core numerical aperture circular mode-scratching gain fiber 1 of the present invention, by setting the diameter of the core layer 11 between 25 μm and 60 μm, enables the low-core numerical aperture circular mode-scratching gain fiber 1 to achieve high-power laser output; simultaneously, by setting the core numerical aperture of the low-core numerical aperture circular mode-scratching gain fiber 1 between 0.02 and 0.06, the fiber normalization frequency can be effectively reduced, thereby suppressing higher-order modes of the laser; furthermore, by setting multiple micro-experiments with different sizes or refractive indices in the inner cladding 12 surrounding the core layer 11, The micro-stress unit 13 can not only perturb the propagation trajectory of the pump light in the inner cladding 12 to improve the cladding pump absorption coefficient, which is beneficial to shorten the length of the gain fiber and solve the nonlinear problem of the fiber laser at high power; at the same time, the micro-stress unit 13 can also form a non-uniform refractive index field and residual stress field around the core layer 11 to increase the loss of the higher-order modes of the laser and improve the mode instability threshold of the fiber laser at high power, thereby simultaneously improving the nonlinear threshold and mode instability threshold of the high-power fiber laser and realizing single-mode high-power output of the laser.

[0031] Understandably, similar to conventional optical fibers, the low-core numerical aperture circular mode-scratching gain fiber 1 also includes an inner coating 14 and an outer coating 15. The inner coating 14 is located outside the inner cladding 12 and has a lower refractive index than the inner cladding 12. It can be made of low-refractive-index acrylic resin or other polymeric materials with equivalent refractive index to ensure effective transmission of pump light within the inner cladding 12. The outer coating 15 is located outside the inner coating 14 and is formed of high-refractive-index acrylic resin or other polymeric materials with equivalent refractive index. It is used to improve the mechanical strength, environmental resistance, and reliability of the optical fiber.

[0032] Optionally, the diameter of the core layer 11 can be any value among 25μm, 35μm, 45μm, 55μm and 60μm.

[0033] Optionally, the numerical aperture of the fiber core can be any value among 0.020, 0.025, 0.035, 0.045, and 0.055.

[0034] Optionally, the diameter of the micro-stress element 13 can be any value among 135μm, 150μm, and 165μm.

[0035] Optionally, the distance between the edge of the micro-stress unit 13 and the edge of the core layer 11 along the radial direction of the core layer 11 can be any value among 30μm, 35μm, 40μm, 45μm, and 50μm.

[0036] In some embodiments, the diameter of at least one microstress element 13 is different from the diameter of the other microstress elements 13; and / or, the refractive index of at least one microstress element 13 is different from the refractive index of the other microstress elements 13.

[0037] In this embodiment, some micro-stress units 13 differ from other micro-stress units 13 in diameter or refractive index, thereby forming a non-uniform refractive index distribution and / or a non-uniform stress distribution around the fiber core layer 11.

[0038] Specifically, some micro-stress units 13 can be made to differ in diameter from other micro-stress units 13. Since the refractive index of the micro-stress unit 13 itself is less than that of the inner cladding layer 12, the micro-stress unit 13 can form a low refractive index region of varying size surrounding the fiber core layer 11 within the inner cladding layer 12. This non-uniform refractive index distribution can increase the loss of higher-order modes of the laser, so as to realize the fundamental mode output of the laser.

[0039] Alternatively, the material of some micro-stress units 13 can be different from that of other micro-stress units 13. For example, some micro-stress units 13 can be made of boron-doped silicon dioxide, while other micro-stress units 13 can be made of fluorine-doped silicon dioxide, so that the refractive indices of the two micro-stress units 13 are different, thereby forming a non-uniform refractive index distribution around the core layer 11.

[0040] Alternatively, some micro-stress units 13 may differ from other micro-stress units 13 in both material (refractive index) and diameter, which can also form a non-uniform refractive index distribution around the core layer 11.

[0041] In some embodiments, such as Figure 2 As shown, the diameters of each micro-stress element 13 are D 1i The radial distances between the edges of each micro-stress unit 13 and the edges of the core layer 11 along the core layer 11 are r and r, respectively. 1i (i=1, 2, 3…n); the diameter of the core layer 11 is D0; where D 1i r 1i D0 satisfies: 2D0 <D 1i <8D0,D0 <r 1i <3D0.

[0042] In this embodiment, by adjusting the diameter D of each micro-stress element 13 1i The radial distance r between the edge of the material or each micro-stress unit 13 and the edge of the core layer 11 along the core layer 11. 1iLimitations are imposed to adjust the non-uniform stress field and refractive index field formed by the inner cladding 12 in conjunction with each micro-stress unit 13, thereby further improving the suppression effect of the low-core numerical aperture circular mode-scratching gain fiber 1 on higher-order modes. Preferably, in some embodiments, the diameters of each micro-stress unit 13 are the same, wherein the radial distance between the edge of at least one micro-stress unit 13 and the edge of the core layer 11 is different from the radial distance between the edges of other micro-stress units 13 and the edges of the core layer 11.

[0043] In some embodiments, the ratio of the diameters of any two micro-stress elements 13 is not less than 0.9 and not greater than 1.1.

[0044] Preferably, in some embodiments, the inner cladding 12 is provided with four micro-stress units 13 arranged equidistantly from each other. The micro-stress units 13 include units A, B, C and D arranged equidistantly from each other in a clockwise direction. Units A, B, C and D are all made of fluorine-doped silicon dioxide. The diameters of units A, B and C and the radial distances of the edges of the core layer 11 along the core layer 11 are the same. The diameter of unit D is larger than the diameters of the other units. The radial distance between unit D and the edges of the core layer 11 along the core layer 11 is smaller than the radial distances of the diameters of units A, B and C and the radial distances of the edges of the core layer 11 along the core layer 11.

[0045] Preferably, in some embodiments, the inner cladding 12 is provided with four micro-stress units 13 arranged equidistantly from each other. The micro-stress units 13 include units A, B, C, D and E arranged equidistantly from each other along the clockwise center. Units A, B, C, D and E are all made of fluorine-doped silicon dioxide. The diameters of units A, B, C, D and E are the same as the radial distance of the edge of the core layer 11 along the core layer 11.

[0046] The following provides comparative example 1 and several specific embodiments, along with corresponding simulation results (as shown in Table 1), to illustrate the technical effects of the above-mentioned arrangement of micro-stress elements 13: Table 1 Specific Example Data

[0047] Note: In Table 1, B represents boron-doped silicon dioxide and F represents fluorine-doped silicon dioxide.

[0048] Comparative Example 1: The core layer 11 has a diameter of 25 μm, the inner cladding layer 12 has a diameter of 600 μm, the numerical aperture (NA) of the core is 0.045, and no micro-stress elements are set in the inner cladding layer.

[0049] Simulations were performed at a working wavelength of 1080 nm, and the simulation results are as follows: fundamental mode loss is 0.02 dB / m, LP11 higher-order mode loss is 44.56 dB / m, and higher-order mode suppression ratio is 2.24 × 10⁻⁶. 3 .

[0050] Example 1: The difference compared to Comparative Example 1 is that: the inner cladding 12 contains four micro-stress elements 13 arranged equidistantly from each other. Each micro-stress element 13 includes elements A, B, C, and D arranged equidistantly from each other in a clockwise direction. The diameters of elements A, B, C, and D are respectively D... 11 D 12 D 13 D 14 All are 150 μm, and the r values ​​corresponding to elements A, B, C, and D are... 11 r 12 r 13 r 14 All are 45 μm. Units A and C of micro-stress element 13 are made of fluorine-doped silicon dioxide, and units B and D are made of boron-doped silicon dioxide; the refractive index difference between boron-doped silicon dioxide and the cladding is -0.008, the refractive index difference between fluorine-doped silicon dioxide and the cladding is -0.004, and the core numerical aperture (NA) is 0.045.

[0051] Simulations were performed at a working wavelength of 1080 nm, and the simulation results show that the fundamental mode loss is 5.24 × 10⁻⁶. -4 The loss of the higher-order mode of LP11 is 3.7 × 10 dB / m. 2 dB / m, higher-order mode suppression ratio is 7.7×10 5 , Compared to a double-clad active fiber with a core diameter of 25μm and a cladding diameter of 600μm (Comparative Example 1), the higher-order mode suppression ratio is improved by about 315 times under the same conditions.

[0052] Example 2: The difference from Example 1 is that Unit A, Unit B and Unit C are made of fluorine-doped silicon dioxide, while Unit D is made of boron-doped silicon dioxide.

[0053] Simulations were performed at a working wavelength of 1080 nm, and the simulation results show that the fundamental mode loss is 2.06 × 10⁻⁶. -4 The loss of the higher-order mode of LP11 is 3.14 × 10 dB / m. 2 dB / m, higher-order mode suppression ratio is 1.52×10 6Compared to a double-clad active fiber with a core diameter of 25μm and a cladding diameter of 600μm (Comparative Example 1), under the same conditions, the higher-order mode suppression ratio is improved by about 680 times.

[0054] Example 3: The difference from Example 1 is that units A, B, C, and D are all fluorine-doped silicon dioxide, and the r values ​​corresponding to units A, B, C, and D are... 11 r 12 r 13 r 14 It is 30μm.

[0055] Simulations were performed at a working wavelength of 1080 nm, and the simulation results show that the fundamental mode loss is 6.43 × 10⁻⁶. -9 The loss of the higher-order mode of LP11 is 4.72 × 10 dB / m. 2 dB / m, higher-order mode suppression ratio is 7.33×10 10 Compared to a double-clad active fiber with a core diameter of 25 μm and a cladding diameter of 600 μm (Comparative Example 1), under the same conditions, the higher-order mode suppression ratio is improved by approximately 3.27 × 10⁻⁶. 7 times.

[0056] When r11, r12, r13, and r14 corresponding to units A, B, C, and D are 35 μm, the higher-order mode suppression ratio is improved by approximately 9.91 × 10⁻⁶. 4 times.

[0057] Example 4: The difference from Example 1 is that units A, B, C, and D are all fluorine-doped silicon dioxide, and the diameters of units A, B, and C are D, respectively. 11 D 12 D 13 All are 150 μm, and the r values ​​corresponding to unit A, unit B, and unit C are... 11 r 12 r 13 It is 50μm.

[0058] When the diameter of unit D is D 14 The value is 135 μm, and the r value corresponding to unit D is... 14 When the wavelength is 65 μm, simulations were performed at a working wavelength of 1080 nm. The simulation results show that the fundamental mode loss is 9.44 × 10⁻⁶. -5 The loss of the higher-order mode of LP11 is 3.39 × 10 dB / m. 2 dB / m, higher-order mode suppression ratio is 3.59×10 6Compared to a double-clad active fiber with a core diameter of 25μm and a cladding diameter of 600μm (Comparative Example 1), under the same conditions, the higher-order mode suppression ratio is improved by about 1603 times.

[0059] When the diameter of unit D is D 14 For 150 μm, the r corresponding to unit D 14 At a resolution of 50 μm, the higher-order mode suppression ratio was improved by approximately 9.91 × 10⁻⁶. 4 times.

[0060] When the diameter of unit D is D 14 The value is 165 μm, and the r value corresponding to element D is... 14 At a size of 35 μm, the higher-order mode suppression ratio is improved by approximately 1.7 × 10⁻⁶. 8 times.

[0061] Example 5: The difference compared to Comparative Example 1 is that: the inner cladding 12 contains 5 micro-stress elements 13 arranged equidistantly from the center. The micro-stress elements 13 include elements A, B, C, D, and E arranged equidistantly from the center in a clockwise direction. The diameters of elements A, B, C, D, and E are D, D, and D, respectively. 11 D 12 D 13 D 14 and D 15 All are 150 μm, and the r values ​​corresponding to units A, B, C, D, and E are... 11 r 12 r 13 r 14 and r 15 All are 50 μm. Units A, B, C, and D of micro-stress element 13 are made of fluorine-doped silicon dioxide, and unit E is made of boron-doped silicon dioxide; the refractive index difference between boron-doped silicon dioxide and the cladding is -0.008, the refractive index difference between fluorine-doped silicon dioxide and the cladding is -0.004, and the numerical aperture (NA) of the core is 0.045.

[0062] Simulations were performed at a working wavelength of 1080 nm, and the simulation results show that the fundamental mode loss is 8.21 × 10⁻⁶. -5 The loss of the higher-order mode of LP11 is 9.62 × 10 dB / m. 1 dB / m, higher-order mode suppression ratio is 1.17×10 6 Compared with Comparative Example 1, under the same conditions, the higher-order mode suppression ratio was improved by approximately 522 times.

[0063] When the diameter D of unit E 15 At a size of 135 μm, the higher-order mode suppression ratio is improved by approximately 199 times.

[0064] Example 6: The difference from Example 5 is that Unit A, Unit B, Unit C, Unit D and Unit E are all made of fluorine-doped silicon dioxide.

[0065] When r 11 r 12 r 13 r 14 and r 15 When both are 50 μm, the simulation results show that the fundamental mode loss is 1.28 × 10⁻⁶. -5 The loss of the higher-order mode of LP11 is 1.29 × 10 dB / m. 2 dB / m, higher-order mode suppression ratio is 1.00×10 7 Compared to a double-clad active fiber with a core diameter of 25μm and a cladding diameter of 600μm, the higher-order mode suppression ratio is improved by approximately 4485 times under the same conditions.

[0066] When the diameter D of unit E 15 At a size of 165 μm, the higher-order mode suppression ratio is improved by approximately 1.7 × 10⁻⁶. 4 times.

[0067] When r 11 r 12 r 13 r 14 and r 15 When both are 45 μm, the higher-order mode suppression ratio is improved by approximately 4.98 × 10⁻⁶. 4 Optionally, the core layer 11 is made of rare-earth ion-doped silicon dioxide core, wherein the rare-earth ions include Yb. 3+ Er 3+ Tm 3+ Ho 3+ One or more co-doped with it.

[0068] Optionally, the micro-stress unit 13 is composed of a matrix silicon dioxide and one or more materials selected from dopants F, B2O3, Ge2O3, and P2O5.

[0069] Alternatively, in some embodiments, such as Figure 3 As shown in (I)-(VIII), there are 1-7 micro-stress elements 13.

[0070] Optionally, in some embodiments, the diameter of the inner cladding 12 is 500–1000 μm. Specifically, the diameter of the inner cladding 12 can be any value selected from 500 μm, 600 μm, 700 μm, 800 μm, or 1000 μm.

[0071] Finally, it should be noted that the above embodiments are only for illustrating the present invention and not for limiting the present invention. Although the present invention has been described in detail with reference to the embodiments, those skilled in the art should understand that various combinations, modifications, or equivalent substitutions of the technical solutions of the present invention do not depart from the spirit and scope of the technical solutions of the present invention and should be covered within the protection scope of the present invention.

Claims

1. A low-core numerical aperture circular mode-scratching gain optical fiber, characterized in that, include: A fiber core layer, wherein the diameter of the fiber core layer is not less than 25 μm and not more than 60 μm; An inner cladding layer is sleeved on the outside of the fiber core layer. The inner cladding layer has a plurality of filling holes, which are arranged at intervals along the circumference of the fiber core layer. Multiple micro-stress units are provided, each corresponding to a specific micro-stress unit and filling the filling hole; the refractive index of the micro-stress unit is less than that of the inner cladding layer. The core numerical aperture of the low core numerical aperture circular scrambling mode gain fiber is not less than 0.02 and less than 0.

06.

2. The low-core numerical aperture circular mode-scratching gain optical fiber according to claim 1, characterized in that, At least one of the micro-stress elements has a different diameter than the other micro-stress elements; And / or, the refractive index of at least one of the micro-stress elements is different from the refractive index of the other micro-stress elements.

3. The low-core numerical aperture circular mode-scratching gain optical fiber according to claim 1, characterized in that, There are n micro-stress units; The diameters of each of the micro-stress elements are D 1i The distances r between the edge of each micro-stress unit and the edge of the fiber core layer along the radial direction of the fiber core layer are respectively. 1i (i=1, 2, 3…n); the diameter of the fiber core layer is D0; Among them, D 1i r 1i D0 satisfies: 2D0 <D 1i <8D0,D0 <r 1i <3D0.

4. The low-core numerical aperture circular mode-scratching gain optical fiber according to any one of claims 1-3, characterized in that, Each of the micro-stress units has the same diameter, wherein the distance between the edge of at least one micro-stress unit and the edge of the core layer along the radial direction of the core layer is different from the distance between the edges of the other micro-stress units and the edges of the core layer along the radial direction of the core layer.

5. The low-core numerical aperture circular mode-scratching gain optical fiber according to any one of claims 1-3, characterized in that, The ratio of the diameters of any two micro-stress elements is not less than 0.9 and not greater than 1.

1.

6. The low-core numerical aperture circular scrambling mode gain optical fiber according to any one of claims 1 or 2, characterized in that, The core layer is made of rare earth ion-doped silicon dioxide core; the micro-stress unit is composed of a silicon dioxide matrix and one or more dopants, such as F, B2O3, Ge2O3, and P2O5.

7. The low-core numerical aperture circular scrambling mode gain optical fiber according to any one of claims 1 or 2, characterized in that, The number of micro-stress units is 1 to 7.

8. The low-core numerical aperture circular scrambling mode gain optical fiber according to any one of claims 1 or 2, characterized in that, The inner cladding diameter is 500–1000 μm.

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