A double-clad structure all-solid-state anti-resonant optical fiber with bending resistance

Abstract

A kind of double-clad structure full solid-state anti-resonant optical fiber with bending resistance, its radial section includes in turn from inside to outside fiber core, anti-resonant unit, bending resistance unit and cladding unit;Anti-resonant unit includes multiple anti-resonant rings arranged uniformly along the periphery of fiber core, each anti-resonant ring is tangent to fiber core;Bending resistance unit includes multiple bending resistance round bars, any bending resistance round bar is located outside each adjacent two anti-resonant rings and does not contact with anti-resonant ring.By reasonable setting to component structure, the restriction loss of fundamental mode under bending state is reduced, while maintaining high high-order mode suppression ratio, the utilization efficiency of traditional full solid-state anti-resonant optical fiber to pump light is improved, which helps to further improve the optical-optical conversion efficiency of high-power fiber laser.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical fibers, and particularly relates to a double-cladding structure full-solid-state anti-resonant fiber with bending resistance. BACKGROUND

[0002] With the rapid development of high-end industrial manufacturing and laser medical treatment, higher and higher requirements are put forward for the output power of fiber lasers. In order to suppress the nonlinear effects such as SBS and SRS under high-power output, the nonlinear gain coefficient can be reduced by increasing the mode field area. However, due to the requirement for the quality of the output laser beam, the mode field area of the traditional step-type fiber cannot be increased unlimitedly. In order to increase the mode field area of the single-mode laser fiber, a full-solid-state anti-resonant structure large-mode-area fiber is proposed.

[0003] The transmission principle of the full-solid-state anti-resonant fiber is based on its unique structural characteristics. The fiber cladding of the full-solid-state anti-resonant fiber has several high-refractive-index anti-resonant rings. The thickness of the anti-resonant ring is usually on the order of the transmission wavelength, about several hundred nanometers to several microns. The selection of this size ensures that the anti-resonant ring can effectively interfere with the incident light wave. When the light wave is reflected and propagated in the ring for many times, the reflectivity of a specific wavelength is enhanced due to the interference of the beam phase difference. Since the transmission conditions of the reflected light wave in the ring are similar to those of the Fabry-Perot (F-P) cavity, it also exhibits a wide-spectrum reflection characteristic. Therefore, the interference cancellation condition for the anti-resonant transmission wavelength is: where λm is the anti-resonant transmission wavelength, t is the anti-resonant ring thickness, n1 and n0 represent the refractive indices of the anti-resonant ring and the cladding material respectively, and m is a positive integer.

[0004] Another significant advantage of the full-solid-state anti-resonant fiber is to provide a solution for high-beam-quality large-mode-area transmission. By using the mode coupling principle, the high-order modes transmitted by the fiber core are selectively filtered out, thereby improving the beam quality. According to the modification of the effective refractive index matching condition of the Marcatili-Schmeltzer mode by Patrick.U, when the ratio of the inner diameter of the cladding anti-resonant ring to the diameter of the fiber core is 0.68, the best filtering effect of the high-order modes of the fiber core can be achieved. In the full-solid-state core diameter, rare earth ions can be doped, so that it can be applied to fiber laser systems as a gain medium. This solid anti-resonant fiber suppresses the high-order mode components of the laser on the basis of the large core diameter, and can realize high-power fundamental mode laser output.

[0005] At present, the theoretical simulation can realize single-mode laser output under the condition of mode field diameter of 124 μm, which shows incomparable large-mode-field single-mode characteristics, but actual use still faces some difficulties. When the fiber bending loss is large, small size coiling cannot be carried out, the flexibility and small size integration advantages of the fiber are lost, and the filtering effect of the high-order mode of the anti-resonant structure is greatly reduced under the bending condition, which is not conducive to the improvement of the output beam quality. The sensitivity to bending limits the application of the full solid anti-resonant structure fiber in some narrow space or device, therefore, it is urgent to develop a full solid anti-resonant fiber with bending resistance. SUMMARY

[0006] In view of the above problems, the purpose of the present application is to provide a double-clad full solid anti-resonant fiber with bending resistance, which solves the problems that the fiber cannot be coiled in small size and the filtering effect of the high-order mode of the anti-resonant structure is poor under the bending condition, and the output beam quality is reduced.

[0007] To achieve the above purpose, the technical scheme adopted by the present application comprises:

[0008] A double-clad full solid anti-resonant fiber with bending resistance, the radial cross section of which comprises, from inside to outside, a core, an anti-resonant unit, a bending resistance unit and a cladding unit; the anti-resonant unit comprises a plurality of anti-resonant rings uniformly arranged along the circumference of the outer periphery of the core, and each anti-resonant ring is tangent to the core; the bending resistance unit comprises a plurality of bending resistance rods, and any bending resistance rod is located outside each adjacent two anti-resonant rings and does not contact the anti-resonant ring.

[0009] Preferably, the anti-resonant unit comprises 6 anti-resonant rings, and the bending resistance unit comprises 6 bending resistance rods.

[0010] Preferably, the ratio of the inner diameter of the anti-resonant ring to the diameter of the core is 0.55-0.75.

[0011] Preferably, the ratio of the inner diameter of the anti-resonant ring to the diameter of the core is 0.68.

[0012] Preferably, the diameter of the core is 40-80 μm, the thickness of the anti-resonant ring is 0.5-4 μm, and the diameter of the bending resistance rod is 10-30 μm.

[0013] Preferably, the diameter of the core is 50 μm, the thickness of the anti-resonant ring is 0.8-3 μm, and the diameter of the bending resistance rod is 10 μm.

[0014] Preferably, the spacing between the adjacent bending resistance rods and the anti-resonant ring is at least 5 μm.

[0015] Preferably, the cladding unit comprises, from inside to outside, an inner cladding layer, an outer cladding layer and a protective layer.

[0016] Preferably, the cross section of the inner cladding is regular octagon.

[0017] Preferably, the refractive index n of the protective layer is 1.45. c > the refractive index n of the anti-resonance ring is 1.45. arf > the refractive index n1 of the inner cladding is greater than the refractive index n0 of the core, and the refractive index n2 of the outer cladding is greater than the refractive index n of the anti-bending round rod. b .

[0018] Compared with the prior art, the advantages of the present application are:

[0019] (1) The double-cladding structure full solid-state anti-resonance optical fiber with anti-bending performance of the present application reduces the confinement loss of the fundamental mode in the bending state while maintaining a high high-order mode suppression ratio through reasonable setting of the component structure, thereby improving the utilization efficiency of pump light of the traditional full solid-state anti-resonance optical fiber and helping to further improve the optical-to-optical conversion efficiency of high-power fiber lasers.

[0020] (2) The double-cladding structure full solid-state anti-resonance optical fiber with anti-bending performance of the present application realizes effective control of the effective refractive index of the cladding mode through reasonable setting of the component structure, and makes the core high-order mode LP11 couple with the fundamental mode in the anti-resonance ring to be filtered out, which is beneficial to the single-mode operation in the core of the optical fiber.

[0021] (3) The double-cladding structure full solid-state anti-resonance optical fiber with anti-bending performance of the present application reduces the bending loss from 0.0083 of the traditional structure full solid-state anti-resonance optical fiber to 0.0043 when the bending radius is 0.3 m through reasonable setting of the component structure.

[0022] (4) The double-cladding structure full solid-state anti-resonance optical fiber with anti-bending performance of the present application significantly improves the high-order mode suppression ratio compared with the traditional anti-bending round rod structure under the bending condition of a bending radius of 0.4-0.7 m, which indicates that the double-cladding full solid-state anti-resonance optical fiber with anti-bending structure has better high-order mode filtering effect under the bending condition, which means that it has better single-mode performance under the bending condition. BRIEF DESCRIPTION OF DRAWINGS

[0023] The accompanying drawings are included to provide a further understanding of the present application, and constitute a part of the specification, and are used together with the following detailed description to explain the present application, but do not constitute a limitation on the present application. In the drawings:

[0024] Figure 1 is a structural schematic diagram of the double-cladding structure full solid-state anti-resonance optical fiber with anti-bending performance of the present application;

[0025] Figure 2The transverse refractive index distribution of the optical fiber of the present application;

[0026] Figure 3 The influence of the bending radius of the optical fiber of the present application on the confinement loss of the fundamental mode;

[0027] Figure 4 The influence of the bending radius of the optical fiber of the present application on the high-order mode suppression ratio;

[0028] Figure 5 The fundamental mode and high-order mode field distribution of the optical fiber of the present application;

[0029] The various reference signs in the drawings represent:

[0030] 1 - inner cladding, 2 - outer cladding, 3 - protective layer, 4 - anti-resonant ring, 5 - anti-bending round rod, 6 - core DETAILED DESCRIPTION

[0031] The present application is not limited to the following specific embodiments, and any equivalent variations made on the basis of the technical solutions of the present application shall fall within the protection scope of the present application.

[0032] It should be noted that the directional terms mentioned herein, such as "inner cavity", "inner periphery", "inner wall" and "outer side", are consistent with the specific directions on the paper of the drawings or the corresponding directions of the space shown in the drawings; all components and devices in the present application, unless otherwise specified, all use the components and devices known in the prior art.

[0033] EMBODIMENT

[0034] The embodiment discloses a double-clad structure full-solid anti-resonant optical fiber with anti-bending performance, which comprises a core 6, an anti-resonant unit, an anti-bending unit and a cladding unit from inside to outside in the radial cross section; the anti-resonant unit comprises a plurality of anti-resonant rings 4 arranged uniformly along the outer periphery of the core 6, and each anti-resonant ring 4 is tangent to the core 6; the anti-bending unit comprises a plurality of anti-bending round rods 5, and any anti-bending round rod 5 is located outside each adjacent two anti-resonant rings 4 and does not contact the anti-resonant ring 4.

[0035] The function is to reduce the confinement loss of the fundamental mode in the bending state while maintaining a high high-order mode suppression ratio, thereby improving the utilization efficiency of the traditional full-solid anti-resonant optical fiber on the pump light and helping to further improve the light-light conversion efficiency of the high-power fiber laser. Figure 2 The refractive index profile distribution of the transverse and longitudinal cross-sections of the optical fiber is shown in the drawings.

[0036] The cladding unit of the embodiment comprises an inner cladding 1, an outer cladding 2 and a protective layer 3 from inside to outside, the surface of the inner cladding 1 is a regular octagon, and the coating materials of the outer cladding 2 and the protective layer 3 are formed by high-temperature coating and ultraviolet curing in sequence.

[0037] In this embodiment, the anti-resonance unit includes six anti-resonance rings 4, and the anti-bending unit includes six anti-bending round rods 5. The ratio of the inner diameter of the anti-resonance ring 4 to the diameter of the fiber core 6 is 0.55–0.75, preferably 0.68.

[0038] The diameter of the fiber core 6 disclosed in this embodiment is 40-80 μm, preferably 50 μm; the thickness of the anti-resonance ring 4 is 0.5-4 μm, preferably 0.8-3 μm; the diameter of the anti-bending round rod 5 is 10-30 μm, preferably 10 μm; the distance between adjacent anti-bending round rods 5 and the anti-resonance ring 4 is at least 5 μm, which is 5 μm in this embodiment.

[0039] In this embodiment, the refractive index n of the protective layer 3 is... c > Anti-resonant ring 4 refractive index n arf >Inner cladding 1 refractive index n1 = Core 6 refractive index n0 >Outer cladding 2 refractive index n2 >Bending-resistant round bar 5 refractive index n b .

[0040] In this embodiment, the fiber core 6 is composed of SiO2, Al2O3, P2O5, SiF4, and RE2O3, wherein RE is a lanthanide trivalent rare earth ion, which can be selected as Yb. 3+ Er 3+ Ho 3+ Pr 3+ Dy 3+ One or more of the following: the inner cladding layer 1 is made of SiO2, the anti-resonance ring 4 is made of SiO2 and GeO2, the anti-bending round rod 5 is made of SiO2 and B2O3 or SiO2 and SiF4, the outer cladding layer 2 is made of a low refractive index polymer, and the protective layer 3 is made of a high refractive index polymer.

[0041] Considering the refractive index n of pure quartz glass 石英 The C-value is 1.4572, and considering a wide-bandwidth first-order anti-resonant waveguide, the C-value of Ge-doped quartz glass prepared by the MCVD method is... Ge Content <15 mol.%, n arf The value can vary between 1.4572 and 1.4850. arf The difference Δn between the refractive index n0 and the core arf =n arf The range of -n0 is 0-0.0278. The t-value comparison table for this invention is shown below:

[0042] Table 1. t-value comparison table

[0043]

[0044]

[0045] Figure 3 The simulation results of the transmission mode of the embodiment are shown by using the finite element simulation software COMSOL Multiphysics. In the simulation process, mode analysis is performed on the cross section of the optical fiber. In the simulation, the structure of the embodiment optical fiber is modeled first. Triangles with a maximum grid unit of λ / 5 are used to divide the anti-resonant ring, the anti-bending circular rod structure and the narrow area around it. Triangles with a maximum grid unit of λ / 4 are used to divide the inner cladding, the core and the outer cladding. In addition, a perfect matched layer (PML) is added outside the outer cladding to leak the simulated outer cladding light and eliminate the influence of scattering. The fundamental mode (LP01) field distribution and the first high-order mode (LP11) field distribution of the simulation results are shown in Figure 3 It can be seen that, through the design of the structure, the effective refractive index of the cladding mode is effectively controlled, and the core high-order mode LP11 is coupled with the fundamental mode in the anti-resonant ring to be filtered out, which is beneficial to the single-mode operation in the core of the optical fiber.

[0046] Figure 4 The mode field limitation loss of the anti-bending double-cladding ytterbium-doped all-solid anti-resonant optical fiber in the embodiment is shown in the case of a bending radius of 0.3-0.7 m. It can be seen that, compared with the traditional anti-bending circular rod structure, the fundamental mode bending loss of the anti-bending all-solid anti-resonant optical fiber is significantly reduced. The bending loss of the optical fiber is defined as the difference between the fundamental mode limitation loss under the bending condition and the fundamental mode limitation loss under the flat condition. When the bending radius is 0.3 m, the bending loss is reduced from 0.0083 of the traditional structure all-solid anti-resonant optical fiber to 0.0043.

[0047] Figure 5 The high-order mode suppression ratio of the anti-bending double-cladding ytterbium-doped all-solid anti-resonant optical fiber in the embodiment is shown in the case of a bending radius of 0.3-0.7 m. It can be seen that, under the bending condition of a bending radius of 0.4-0.7 m, compared with the traditional anti-bending circular rod structure, the high-order mode suppression ratio of the anti-bending all-solid anti-resonant optical fiber is significantly improved, indicating that the double-cladding all-solid anti-resonant optical fiber with the anti-bending structure has better high-order mode filtering effect under the bending condition, which means that it has better single-mode performance under the bending condition.

[0048] The preferred embodiments of the present disclosure are described in detail above in combination with the drawings, but the present disclosure is not limited to the specific details in the above-described embodiments. Within the technical concept range of the present disclosure, various simple modifications can be made to the technical solutions of the present disclosure, and these simple modifications all belong to the protection range of the present disclosure.

[0049] It should be further noted that various specific technical features described in the above detailed description are not to be interpreted as essential to the present disclosure, and that any of these features can be combined in any suitable manner, and that the present disclosure is not limited to any specific combination of features.

[0050] Furthermore, various different embodiments disclosed herein can be combined to form additional embodiments, and that such additional embodiments should also be considered as falling within the scope of the present disclosure.

Claims

1. A double-clad structure all-solid-state anti-resonant optical fiber having a bending resistance, characterized by, Its radial cross section, from the inside out, includes a fiber core (6), an anti-resonance unit, a bending-resistant unit, and a cladding unit; The anti-resonance unit includes a plurality of anti-resonance rings (4) uniformly arranged along the outer periphery of the fiber core (6), and each of the anti-resonance rings (4) is tangent to the fiber core (6). The anti-bending unit includes multiple anti-bending round bars (5), each of which is located outside of two adjacent anti-resonant rings (4) and does not contact the anti-resonant rings (4); The anti-resonance unit includes six anti-resonance rings (4), and the anti-bending unit includes six anti-bending round bars (5); The covering unit includes an inner covering layer (1), an outer covering layer (2), and a protective layer (3) from the inside out; The inner cladding (1) has a regular octagonal surface.

2. The double-clad structure all-solid-state anti-resonant optical fiber having a bending resistance according to claim 1, wherein, The ratio of the inner diameter of the anti-resonant ring (4) to the diameter of the fiber core (6) is 0.55-0.

75.

3. The double-clad structure all-solid-state anti-resonant optical fiber having a bending resistance according to claim 2, wherein, The ratio of the inner diameter of the anti-resonant ring (4) to the diameter of the fiber core (6) is 0.

68.

4. The double-clad structure all-solid-state anti-resonance fiber having a bending resistance according to claim 3, wherein The diameter of the fiber core (6) is 40~80μm, the thickness of the anti-resonance ring (4) is 0.5~4μm, and the diameter of the anti-bending round rod (5) is 10~30μm.

5. The double-clad structure all-solid-state anti-resonant optical fiber having a bending resistance according to claim 4, wherein, The diameter of the fiber core (6) is 50 μm, the thickness of the anti-resonance ring (4) is 0.8-3 μm, and the diameter of the anti-bending round rod (5) is 10 μm.

6. The double-clad structure all-solid-state anti-resonant optical fiber having a bending resistance according to claim 5, wherein, The distance between adjacent anti-bending round bars (5) and anti-resonance rings (4) is at least 5 μm.

7. The double-clad structure all-solid-state anti-resonant optical fiber having a bending resistance according to claim 6, wherein, The protective layer (3) refractive index n c The anti-resonant ring (4) refractive index n arf The inner cladding (1) refractive index n1= The core (6) refractive index n0> The outer cladding (2) refractive index n2> The anti-bending round bar (5) refractive index n b .

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