Multi-mode hollow-core anti-resonance optical fiber

Abstract

The invention discloses a multi-mode hollow-core anti-resonance optical fiber which comprises an outer cladding tube, a cladding region and a fiber core region, the cladding region and the fiber core region are arranged in the outer cladding tube, ten double-nested adjacent tubes are evenly distributed in the cladding region and around the fiber core region in a circumferential mode, and each double-nested adjacent tube is composed of an outer tube, a first embedded tube and two second embedded tubes. The first embedded pipe is located in the outer pipe, and the two second embedded pipes are located in the first embedded pipe. Under the condition that the diameter of a fiber core area is fixed, the number of fiber core guide modes capable of being transmitted is increased by optimizing the gap distance between adjacent tubes of adjacent double nests and the diameters of the outer tube, the first embedded tube and the second embedded tube. According to the invention, the number of transmissible modes can be increased, and the cable has good bending resistance and can show better multi-mode transmission performance.

Description

Technical Field

[0001] The present invention mainly relates to the field of optical fiber technology, in particular to a multimode hollow-core anti-resonant optical fiber. Background Art

[0002] The transmission loss of traditional quartz-based solid-core optical fibers has already approached their theoretical limit, leaving little room for improvement. To push the boundaries of low-loss optical fiber transmission, researchers have begun researching hollow-core optical fibers. Because they guide light through air, hollow-core optical fibers possess optical properties such as low nonlinearity, low loss, near-zero dispersion, and a wide transmission bandwidth. These fibers overcome the limitations of traditional solid-core optical fibers and improve the transmission capacity of optical fiber communications.

[0003] Currently, hollow-core optical fibers are widely used in high-power transmission, high-speed data communications, fiber lasers, and nonlinear optics. Based on their light-guiding mechanisms, hollow-core fibers can be divided into photonic bandgap fibers (PBGFs) and antiresonant fibers (ARFs). Both can achieve low-loss transmission, but compared to photonic bandgap fibers, antiresonant fibers have wider bandwidths and better mode characteristics. Antiresonant fibers achieve light transmission by controlling the coupling between the core mode and the cladding mode through the antiresonance effect, and their potential advantages have attracted widespread attention from researchers. In addition, with the development of the design and preparation technology of antiresonant fibers, the transmission loss has reached an extremely low loss of less than 0.1 dB / km.

[0004] Currently, high-power laser transmission mainly uses single-mode optical fiber. The concentrated energy leads to significant thermal effects, making it difficult to break the power limit. Therefore, multimode antiresonant optical fiber is indispensable in the process of high-power laser transmission. Z. Wang et al. designed a 6-tube conjoined tube ARF. By changing the number of tubes in the conjoined tube and the position of the glass plate, the coupling between the core guided mode and the cladding was controlled to obtain 3 core guided modes with a loss of less than 3.1 dB / km. H. Liu et al. compared and analyzed the multimode performance of a 6-tube non-nested conjoined tube ARF and a 6-tube single-nested conjoined tube ARF, and found that the nested conjoined tube can support 8 core guided modes at a loss threshold of 0.3 dB / km. When the bending radius is 6 cm, these core guided modes can be transmitted at this threshold. C. Goel et al. numerically analyzed a six-tube centrosymmetric single-nested ARF. This fiber utilizes two bifurcated glass plates near the outer cladding, suppressing mode coupling between high-order core guided modes and cladding modes. This results in low-loss propagation of high-order core guided modes. At a loss threshold of 10 dB / km, 16 core guided modes can be transmitted. At a bending radius of 20 cm, eight core guided modes can be transmitted at this threshold. Y. Hao et al. proposed an eight-tube single-nested elliptical conjoined tube ARF, which can transmit 12 core guided modes at a loss threshold of 0.1 dB / km. At a bending radius of 20 cm, eight core guided modes can be transmitted at this threshold. B. Wang et al. reported a six-tube double-nested adjacent tube ARF with solid support rods, which can support 12 core guided modes with losses below 0.172 dB / km. At a bending radius of 20 cm, all these core guided modes can be transmitted at this threshold. However, these multimode antiresonant fibers can only transmit a small amount of core guided modes, and the coupling principle between the core guided modes and the cladding modes needs further study. Summary of the Invention

[0005] In order to further solve the problem that the current antiresonant fiber laser is insufficient to support efficient transmission of higher power or even 10,000 watts of power, the present invention provides a multimode hollow-core antiresonant fiber.

[0006] To achieve the above object, the technical solution adopted by the present invention is as follows: The present invention provides a multimode hollow-core antiresonant optical fiber, comprising an outer cladding tube, a cladding region within the outer cladding tube, and a core region. Ten double-nested adjacent tubes are evenly distributed in a circle within the cladding region and around the core region. The double-nested adjacent tubes consist of an outer tube, a first inner-embedded tube, and two second inner-embedded tubes, wherein the first inner-embedded tube is located within the outer tube, and the two second inner-embedded tubes are located within the first inner-embedded tubes. When the diameter of the core region is constant, the number of core guided modes that can be transmitted is increased by optimizing the gap spacing between adjacent double-nested adjacent tubes and the diameters of the outer tube, the first inner-embedded tube, and the second inner-embedded tube.

[0007] Furthermore, in each of the double-nested adjacent tubes, the outer tube is inscribed in the outer cladding tube, the first embedded tube is inscribed in the outer tube, the two second embedded tubes are on the same diameter of the first embedded tube and the two second embedded tubes are respectively inscribed in the first embedded tube, the first embedded tubes of each double-nested adjacent tube are on the same circumference of the ring core region, and the spacing between the first embedded tubes of adjacent double-nested adjacent tubes is equal, and the second embedded tubes of each double-nested adjacent tube are on the same circumference of the ring core region.

[0008] Furthermore, the outer tube, the first embedded tube and the two second embedded tubes have the same tube wall thickness.

[0009] Furthermore, the double-nested adjacent tubes are designed as an integral whole, and the outer tube, the first inner tube and the two second inner tubes are an integral structure.

[0010] Furthermore, the outer tubes of the 10 doubly nested adjacent tubes are used to confine the light beam to the fiber core area, preventing light from entering the interior of the doubly nested adjacent tubes or the gaps between the doubly nested adjacent tubes. The first inner tube and the two second inner tubes of the doubly nested adjacent tubes are used to introduce more reflective layers to reduce transmission loss through the multi-layer anti-resonance effect.

[0011] Furthermore, in the core region, the diameter D c Fixed case, set d / D、d n / d The initial value of the outer tube, the first embedded tube, and the second embedded tube are D 、 d 、 d n Through simulation, the influence of the gap spacing between adjacent double-nested adjacent tubes on the number of core guided modes that can be transmitted by the multimode hollow-core anti-resonant fiber at an operating wavelength of 1080 nm is obtained, and the optimal value of the gap spacing between adjacent double-nested adjacent tubes is obtained.

[0012] Furthermore, in the core region, the diameter D c When the gap spacing between adjacent double nested tubes is fixed and the gap spacing between adjacent double nested tubes is the optimal value, the different values of the multimode hollow core antiresonant fiber at the working wavelength of 1080 nm are obtained through simulation. d / D and d n / d Under the condition of the change of the relative effective refractive index of the core guided mode and the cladding mode, the number of core guided modes that can be transmitted by the multimode hollow core antiresonant fiber and the mode field diagram of the corresponding cladding mode, the goal is to maximize the number of core guided modes that can be transmitted, and selectd / D、 d n / d The optimal value of is obtained, and then the optimal diameters of the outer tube, the first embedded tube, and the second embedded tube are determined.

[0013] The specific methods include: D c Fixed, the gap spacing between adjacent double nested adjacent tubes is the optimal value, d n / D When the initial value is set, the simulation results show that the multimode hollow core antiresonant fiber has different d / D Under the condition of the change of the relative effective refractive index of the core guided mode and the cladding mode, the number of core guided modes that can be transmitted by the multimode hollow core antiresonant fiber and the mode field diagram of the corresponding cladding mode, the goal is to maximize the number of core guided modes that can be transmitted, and select d / D Furthermore, in the core region, the diameter D c Fixed, the gap spacing between adjacent double nested adjacent tubes is the optimal value, d / D When the optimal value is obtained, the different d n / d Under the condition of the change of the relative effective refractive index of the core guided mode and the cladding mode, the number of core guided modes that can be transmitted by the multimode hollow core antiresonant fiber and the mode field diagram of the corresponding cladding mode, the goal is to maximize the number of core guided modes that can be transmitted, and select d n / d The optimal value of . d / D、d n / d The optimal value of ultimately determines the optimal diameters of the outer tube, the first embedded tube, and the second embedded tube.

[0014] Compared with the prior art, the technical effects of the present invention are: The present invention provides a multimode hollow-core antiresonant optical fiber, comprising an outer cladding tube, a cladding region within the outer cladding tube, and a core region. Ten double-nested adjacent tubes are evenly distributed in a circle around the core region within the cladding region. By optimizing the gap spacing between adjacent double-nested adjacent tubes and the diameters of the outer tube, the first inner-embedded tube, and the second inner-embedded tube, the number of core guided modes that can be transmitted is increased.

[0015] Furthermore, by optimizing the gap spacing between adjacent double nested adjacent tubes, d / D and d n / d , where the diameters of the outer tube, the first embedded tube, and the second embedded tube are D 、 d 、 d n , and the optimal mode coupling parameters can be found. Specifically, under the optimized design parameters given in one embodiment, the multimode hollow-core antiresonant fiber at 1080 nm can support 53 and 58 different core guided modes, respectively, when the propagation loss is less than 2 dB / km and less than 5 dB / km, and can even transmit 50 core guided modes when the propagation loss is less than 1 dB / km. The multimode hollow-core antiresonant fiber proposed and optimized by the present invention couples the cladding mode effective refractive index with higher-order core guided modes to increase the number of modes that can be transmitted. At the same time, the bending characteristics of the fiber are also analyzed. When the bending radius is equal to 20 cm, the number of transmitted core guided modes is almost the same as that of the straight fiber. Even when the bending radius is equal to 5 cm, 42 core guided modes can be transmitted at less than 1 dB / km, showing good anti-bending characteristics and better multimode transmission performance. BRIEF DESCRIPTION OF THE DRAWINGS

[0016] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the following briefly introduces the drawings required for use in the embodiments or the description of the prior art. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained based on the structures shown in these drawings without paying any creative work.

[0017] Figure 1 1 is a schematic cross-sectional view of a multimode hollow-core antiresonant optical fiber according to an embodiment, wherein the numbers in the figure are: 1, core region; 2, double-nested adjacent tubes; 3, outer cladding tube; 11, outer tube; 12, first inner-embedded tube; 13, second inner-embedded tube; Figure 2 The gap spacing between different adjacent double nested adjacent tubes of the multimode hollow core antiresonant optical fiber in one embodiment when the operating wavelength is 1080 nm is: g The relative effective refractive index curve of the core guided mode and cladding mode under ; Figure 3 The gap spacing between different adjacent double nested adjacent tubes of the multimode hollow core antiresonant optical fiber in one embodiment when the operating wavelength is 1080 nm is: gThe curve of the number of modes that can be transmitted under the loss threshold of 1 dB / km, 2 dB / km, and 5 dB / km; Figure 4 The gap spacing between different adjacent double nested adjacent tubes of the multimode hollow core antiresonant optical fiber in one embodiment when the operating wavelength is 1080 nm is: g Mode field diagram of the cladding mode below; Figure 5 The gap spacing between adjacent double nested tubes of the multimode hollow core antiresonant optical fiber in one embodiment when the operating wavelength is 1080 nm is g = Mode field diagram of the first 12 core guided modes at 1.5 μm; Figure 6 The multimode hollow core antiresonant optical fiber in one embodiment is different when the operating wavelength is 1080 nm. d / D The relative effective refractive index curve of the core guided mode and cladding mode under ; Figure 7 The multimode hollow core antiresonant optical fiber in one embodiment is different when the operating wavelength is 1080 nm. d / D The curve of the number of modes that can be transmitted under the loss threshold of 1 dB / km, 2 dB / km, and 5 dB / km; Figure 8 The multimode hollow core antiresonant optical fiber in one embodiment is different when the operating wavelength is 1080 nm. d / D Mode field diagram of the cladding mode below; Figure 9 The multimode hollow core antiresonant optical fiber in one embodiment is different when the operating wavelength is 1080 nm. d n / d The relative effective refractive index curve of the core guided mode and cladding mode under ; Figure 10 The multimode hollow core antiresonant optical fiber in one embodiment is different when the operating wavelength is 1080 nm. d n / d The curve of the number of modes that can be transmitted under the loss threshold of 1 dB / km, 2 dB / km, and 5 dB / km; Figure 11 The multimode hollow core antiresonant optical fiber in one embodiment is different when the operating wavelength is 1080 nm. d n / d Mode field diagram of the cladding mode below; Figure 121. This is a graph showing the number of modes that can be transmitted when a multimode hollow-core antiresonant optical fiber in an embodiment operates at a wavelength of 1080 nm along the x-direction at different bending radii and at loss thresholds of 1 dB / km, 2 dB / km, and 5 dB / km. Figure 13 1 is a bending model of a multimode hollow-core antiresonant optical fiber in an embodiment along the x-direction at an operating wavelength of 1080 nm and a fundamental mode mode field diagram at different bending radii. DETAILED DESCRIPTION

[0018] The following will clearly and completely describe the technical solutions in the embodiments of the present invention in conjunction with the accompanying drawings. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. All other embodiments obtained by ordinary technicians in this field based on the embodiments of the present invention without making any creative efforts shall fall within the scope of protection of the present invention.

[0019] Reference Figure 1 In one embodiment, a multimode hollow-core antiresonant optical fiber is provided, comprising an outer cladding tube 3, a cladding region within the outer cladding tube 3, and a core region 1. Ten double-nested adjacent tubes 2 are evenly distributed in a circle within the cladding region and around the core region. The double-nested adjacent tubes 2 consist of an outer tube 11, a first inner-embedded tube 12, and two second inner-embedded tubes 13. The first inner-embedded tube 12 is located within the outer tube 11, and the two second inner-embedded tubes 13 are located within the first inner-embedded tube 12. When the diameter of the core region 1 is constant, the number of core guided modes that can be transmitted is increased by optimizing the spacing between adjacent double-nested adjacent tubes 2 and the diameters of the outer tube 11, the first inner-embedded tube 12, and the second inner-embedded tube 13.

[0020] from Figure 1 It can be seen that in each of the double-nested adjacent tubes 2 in this embodiment, the outer tube 11 is inscribed in the outer cladding tube 3, the first embedded tube 12 is inscribed in the outer tube 11, the two second embedded tubes 13 are on the same diameter of the first embedded tube 12, and the two second embedded tubes 13 are respectively inscribed in the first embedded tube 12. The first embedded tubes 12 of each double-nested adjacent tube 2 are on the same circumference of the ring core region 1, and the spacing between the first embedded tubes 12 of adjacent double-nested adjacent tubes 2 is equal. The second embedded tubes 13 of each double-nested adjacent tube 2 are on the same circumference of the ring core region 1.

[0021] In this embodiment, the double nested adjacent tubes 2 are designed as an integral structure, and the outer tube 11, the first inner tube 12 and the two second inner tubes 13 are an integral structure. The outer tube 11, the first inner tube 12 and the two second inner tubes 13 have the same wall thickness.

[0022] The outer tubes 11 of the ten doubly nested adjacent tubes 2 are used to confine the light beam to the core area to prevent light from entering the interior of the doubly nested adjacent tubes or the gaps between the doubly nested adjacent tubes. The first inner tube 12 and the two second inner tubes 13 of the doubly nested adjacent tubes 2 are used to introduce more reflective layers to reduce transmission loss through the multi-layer anti-resonance effect.

[0023] Diameter in the core area D c When set, the gap spacing between adjacent double nested tubes g and the diameters of the outer tube, the first inner tube, and the second inner tube D 、 d 、 d n The setting is crucial for introducing a larger number of core guided modes.

[0024] One embodiment proposes to optimize the gap spacing between adjacent double nested adjacent tubes. g and the diameters of the outer tube, the first inner tube, and the second inner tube D 、 d 、 d n The method is as follows: Diameter in the core area D c Fixed case, set d / D、d n / d The initial value of the outer tube, the first embedded tube, and the second embedded tube are D 、 d 、 d n Through simulation, the influence of the gap spacing between adjacent double-nested adjacent tubes on the number of core guided modes that can be transmitted by the multimode hollow-core anti-resonant fiber is obtained when the operating wavelength is 1080nm, and the optimal value of the gap spacing between adjacent double-nested adjacent tubes is obtained.

[0025] Diameter in the core area D c Fixed, the gap spacing between adjacent double nested adjacent tubes is the optimal value, d n / D When the initial value is set, the simulation results show that the multimode hollow core antiresonant fiber has different d / D Under the condition of the change of the relative effective refractive index of the core guided mode and the cladding mode, the number of core guided modes that can be transmitted by the multimode hollow core antiresonant fiber and the mode field diagram of the corresponding cladding mode, the goal is to maximize the number of core guided modes that can be transmitted, and select d / D Furthermore, in the core region, the diameter D c Fixed, the gap spacing between adjacent double nested adjacent tubes is the optimal value, d / D When the optimal value is obtained, the different d n / d Under the condition of the change of the relative effective refractive index of the core guided mode and the cladding mode, the number of core guided modes that can be transmitted by the multimode hollow core antiresonant fiber and the mode field diagram of the corresponding cladding mode, the goal is to maximize the number of core guided modes that can be transmitted, and select d n / d The optimal value of . d / D、d n / d The optimal value of ultimately determines the optimal diameters of the outer tube, the first embedded tube, and the second embedded tube.

[0026] In one embodiment, based on Figure 1 The structure of the embodiment shown first sets the initial structural parameters of the multimode hollow-core antiresonant optical fiber: D c = 55 μm, g = 1.5 μm, d / D = 0.6 and d n / D = 0.4. 1080 nm is selected as the operating wavelength, which corresponds to the transmission wavelength of the common 1 μm high-power fiber laser. First, the gap spacing between adjacent double nested adjacent tubes is optimized. After finding the optimal value of the gap spacing between adjacent double nested adjacent tubes, its parameters are fixed and then optimized. d / D and d n / D , specifically including: Diameter in the core area D c = 55 μm, set d / D、d n / d The initial value of d / D = 0.6 and d n / D= 0.4, and the effect of the gap spacing between adjacent double-nested adjacent tubes on the number of core guided modes that can be transmitted by the multimode hollow-core anti-resonant fiber at an operating wavelength of 1080 nm is obtained through simulation, and the optimal value of the gap spacing between adjacent double-nested adjacent tubes is obtained. g = 1.5 μm.

[0027] Further, in D c = 55 μm, g = 1.5 μm and d n / D = 0.4, the simulation results show that the working wavelength of the multimode hollow core antiresonant fiber is 1080 nm. d / D The impact on the number of core guided modes that can be transmitted by multimode hollow core antiresonant optical fiber is to maximize the number of core guided modes that can be transmitted, and obtain d / D The optimal value of is 0.75. D c = 55μm, g = 1.5 μm and d / D = 0.75, the simulation results show that the multimode hollow core antiresonant fiber has different d n / D The impact on the number of core guided modes that can be transmitted by multimode hollow core antiresonant optical fiber is to maximize the number of core guided modes that can be transmitted, and obtain d n / D The optimal value of is 0.4. d / D、d n / d The optimal value of the outer tube, the first embedded tube, and the second embedded tube are finally determined. D 、 d 、 d n They are 22.4 μm, 16.8 μm and 6.7 μm respectively.

[0028] In another embodiment, based on Figure 1 The structure of the embodiment shown in the figure optimizes the specific parameters of the multimode hollow core anti-resonant optical fiber. The specific structure is as follows: Figure 1 As shown, it has been described in detail in the above embodiments and will not be repeated here. D c is 55 μm, the diameters of the outer tube, the first embedded tube, and the second embedded tube areD 、 d 、 d n 22.4 μm, 16.8 μm and 6.7 μm respectively; the gap spacing between adjacent double nested adjacent tubes g The outer tube, the first embedded tube and the two second embedded tube wall thickness is 1.5 μm; t The base material of the multimode hollow-core antiresonant fiber is SiO2.

[0029] like Figures 2 to 5 As shown, the gap spacing between adjacent double nested adjacent tubes was analyzed. g The impact on the number of transmission modes of multimode hollow core antiresonant optical fiber. First, a relative effective refractive index is defined, which is the difference between the refractive index of air and the effective refractive index of the mode, that is, 1- n eff . Figure 2 The gap spacing between different adjacent double nested tubes of multimode hollow core antiresonant fiber at the operating wavelength of 1080 nm is given. g The relative effective refractive index curve of the core guided mode and cladding mode under g As the core diameter is fixed, the relative effective refractive index of the core guided mode remains almost unchanged, and the relative effective refractive index of the fundamental mode is the smallest. At the same time, the relative effective refractive index of the cladding mode, which has the greatest impact on the transmitted core guided mode, is shown by the dotted line of the five-pointed star, and the corresponding mode field diagram is shown in Figure 4 As shown, Figure 4 It is the gap distance between different adjacent double nested adjacent tubes of multimode hollow core antiresonant fiber at the working wavelength of 1080nm g The mode field diagram of the cladding mode under the gap spacing g As the cladding mode increases, the relative effective refractive index increases gradually. Figure 3 The gap spacing between different adjacent double nested tubes of multimode hollow core antiresonant fiber at the working wavelength of 1080nm is given. g The curve of the number of modes that can be transmitted under the loss threshold of 1 dB / km, 2 dB / km, and 5 dB / km. g = 1.0 μm, the multimode hollow-core antiresonant fiber can transmit 15, 18, and 23 core guided modes at three loss thresholds. g When the wavelength is increased to 1.5 μm, the multimode hollow core antiresonant fiber can transmit 20 modes at a loss threshold of 1 dB / km. At the same time, the first 12 core guided modes (not considering polarization and mode degeneracy) under this parameter are as follows Figure 5 As shown, from LP 01 -like core guided mode to LP 41 -like core guided mode. With the gap spacingg continues to increase, Figure 5 The gap distance between adjacent double nested tubes of multimode hollow core antiresonant fiber at the operating wavelength of 1080 nm g = Mode field diagram of the first 12 core guided modes at 1.5μm. The number of transmitted modes decreases at the three loss thresholds. This is because the larger the g, the farther the adjacent cladding tubes are from each other, and the easier it is for light to leak through the gap. The overall loss of the core guided mode is large, resulting in a decrease in the number of modes. Therefore, choose g = 1.5 μm was taken as the optimal parameter.

[0030] like Figures 6 to 11 , further analyzed the structural parameters of the double nested adjacent tubes ( d / D and d n / d ) on the transmission mode number of multimode hollow core antiresonant optical fiber, where the core area diameter D c 55 μm, g = 1.5 μm. Figure 6 The multimode hollow core antiresonant fiber is different when the operating wavelength is 1080 nm. d / D The relative effective refractive index curve of the core guided mode and cladding mode under Figure 7 The multimode hollow core antiresonant fiber is different when the operating wavelength is 1080 nm. d / D The curve of the number of modes that can be transmitted at loss thresholds of 1 dB / km, 2 dB / km, and 5 dB / km is shown in the figure. Figure 8 Yes = Multimode hollow core antiresonant fiber is different at the operating wavelength of 1080 nm d / D The mode field diagram of the cladding mode under . It can be seen that when d / D When smaller, Figure 6 The number of low-order core guided modes that can be supported at the mode coupling point between the medium and high-order core guided modes and the cladding modes is relatively small, and the corresponding mode number is as follows: Figure 7 As shown. d / D With the increase of d / D = 0.75, the relative effective refractive index of the core guided mode supported at the mode coupling point is the highest. Therefore, a large number of modes can be transmitted, and the loss is lower than 1 dB / km. The number of core guided modes that can be transmitted is as high as 50, 53, and 58, respectively. Figure 7 This is becaused / D As the distance between the first and second tube layers increases, the distance between them gradually decreases. The cladding mode that has the greatest impact on the transmitted core guided mode changes from the space between the first and second layers to the space between the second and third layers. Therefore, the relative effective refractive index is further away from the core fundamental mode. Figure 8 shown.

[0031] like Figures 9 to 11 As shown, Figure 9 The multimode hollow core antiresonant fiber is different when the operating wavelength is 1080 nm. d n / d The relative effective refractive index curve of the core guided mode and cladding mode under Figure 10 The multimode hollow core antiresonant fiber is different when the operating wavelength is 1080 nm. d n / d The curve of the number of modes that can be transmitted at loss thresholds of 1 dB / km, 2 dB / km, and 5 dB / km is shown in the figure. Figure 11 The multimode hollow core antiresonant fiber is different when the operating wavelength is 1080 nm. d n / d Mode field diagram of the cladding mode below. d n / d In the range of 0.25-0.45, the relative effective refractive index of the cladding mode gradually increases, so theoretically Figure 9 The number of core guided modes that can be supported at the mode coupling point will gradually increase, but the larger d n / d This reduces the spacing between the two adjacent nested tubes in the third layer, generating additional resonances and increasing the overall loss of the core guided mode. As a result, the number of modes transmitted under the three loss thresholds decreases, such as Figure 10 In order to transmit more core guided modes, select d / D = 0.75 and d n / d = 0.4 as the optimal value for the embedded tube.

[0032] In summary, the optimal embodiment parameter design is finally obtained, namely: the core area diameter D c When the diameter of the outer tube, the first inner tube and the second inner tube is 55 μm, D 、 d 、 d nThe gap spacing between adjacent double nested tubes is 22.4 μm, 16.8 μm and 6.7 μm respectively. g 1.5 μm. In addition, the gap spacing between adjacent double nested tubes is set to g 1.5μm; the wall thickness of the outer tube, the first embedded tube and the two second embedded tubes t The substrate material of the multimode hollow core antiresonant fiber is SiO2. Next, the anti-bending properties of the optimized multimode hollow core antiresonant fiber are further discussed. Figure 12 and Figure 13 As shown, Figure 12 This is a curve of the number of modes that can be transmitted when the optimized multimode hollow-core antiresonant fiber operates at a wavelength of 1080 nm along the x-direction at different bending radii and at loss thresholds of 1 dB / km, 2 dB / km, and 5 dB / km. Figure 13 This is the bending model of the optimized multimode hollow-core antiresonant fiber along the x-direction at an operating wavelength of 1080 nm and the fundamental mode field diagram at different bending radii.

[0033] from Figure 12 As can be seen in the simulation, the multimode hollow core antiresonant fiber is obtained D c = 55 μm, g = 1.5 μm, d / D =0.75 and d n / D = 0.4 When the working wavelength is 1080 nm, the bending radius along the x direction (x direction is the axial length direction of the optical fiber) is R b The number of core guided modes that can be transmitted when the loss is lower than 1 dB / km, 2 dB / km, and 5 dB / km at 5 cm, 10 cm, 15 cm, 20 cm, and ∞, where ∞ represents straight fiber. As the bending radius increases, the number of core guided modes that can be transmitted increases until it reaches the number of core guided modes that can be transmitted by straight fiber. Figure 12 In, when R b = 20 cm, the number of core guided modes that can be transmitted by multimode hollow core antiresonant fiber is almost the same as that of straight fiber when the loss is less than 1 dB / km, 2 dB / km, and 5 dB / km. As the bending radius decreases, the number of core guided modes that can be transmitted decreases. R b= 5 cm, the loss threshold is 1 dB / km, 2 dB / km, 5 dB / km, and the supported core guided modes are still as high as 42, 46, and 51, showing excellent anti-bending properties. Figure 13 The bending model along the x-direction and the fundamental mode field diagrams under different bending radii are given. It can be seen that as the bending radius increases, the mode field in the fiber core moves along the x-direction and gradually approaches the mode field distribution of the straight fiber.

[0034] In summary, by optimizing the design of physical parameters, the present invention optimizes the gap spacing between adjacent double nested adjacent tubes, d / D and d n / d , finding the optimal mode coupling parameters. At 1080 nm, with propagation losses below 2 dB / km and below 5 dB / km, 53 and 58 different core guided modes can be supported, respectively. Even 50 core guided modes can be transmitted at propagation losses below 1 dB / km. The multimode hollow-core antiresonant fiber (DNA-ARF) proposed in this invention couples the effective refractive index of the cladding mode with higher-order core guided modes, increasing the number of modes that can be transmitted. The bending characteristics of the proposed multimode hollow-core antiresonant fiber were also analyzed. With a bending radius of 20 cm, the number of transmitted core guided modes is almost the same as that of straight fiber. Even with a bending radius of 5 cm, 42 core guided modes can be transmitted at a temperature below 1 dB / km, demonstrating excellent bending resistance and superior multimode transmission performance compared to similar fibers.

[0035] Matters not covered by the present invention are known technologies.

[0036] The technical features of the above embodiments can be combined arbitrarily. To make the description concise, not all possible combinations of the technical features in the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0037] The above-described embodiments merely represent several implementation methods of the present application. While the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the invention. It should be noted that a person of ordinary skill in the art may make various modifications and improvements without departing from the spirit of the present application, and such modifications and improvements are intended to fall within the scope of protection of the present application. Therefore, the scope of protection of the present application shall be determined by the appended claims.

[0038] The foregoing description is merely a preferred embodiment of the present invention and is not intended to limit the present invention. Those skilled in the art will readily appreciate that the present invention is susceptible to various modifications and variations. Any modifications, equivalent substitutions, or improvements made within the spirit and principles of the present invention shall be included within the scope of protection of the present invention.

Claims

1. A multimode hollow-core antiresonant optical fiber, characterized in that: The invention comprises an outer cladding tube, a cladding region within the outer cladding tube, and a core region. Ten double-nested adjacent tubes are evenly distributed in a circle within the cladding region and around the core region. The double-nested adjacent tubes consist of an outer tube, a first inner-embedded tube, and two second inner-embedded tubes. The first inner-embedded tube is located within the outer tube, and the two second inner-embedded tubes are located within the first inner-embedded tubes. When the diameter of the core region is constant, the number of core guided modes that can be transmitted is increased by optimizing the gap spacing between adjacent double-nested adjacent tubes and the diameters of the outer tube, the first inner-embedded tube, and the second inner-embedded tube.

2. The multimode hollow-core antiresonant optical fiber according to claim 1, wherein: In each of the double-nested adjacent tubes, the outer tube is inscribed in the outer cladding tube, the first inner tube is inscribed in the outer tube, the two second inner tubes are on the same diameter of the first inner tube and the two second inner tubes are respectively inscribed in the first inner tube, the first inner tubes of each of the double-nested adjacent tubes are on the same circumference of the ring fiber core region, and the spacing between the first inner tubes of adjacent double-nested adjacent tubes is equal, and the second inner tubes of each of the double-nested adjacent tubes are on the same circumference of the ring fiber core region.

3. The multimode hollow-core antiresonant optical fiber according to claim 2, wherein: The outer tube, the first embedded tube and the two second embedded tubes have the same tube wall thickness.

4. The multimode hollow-core antiresonant optical fiber according to claim 1, 2 or 3, wherein: The double-nested adjacent tubes are designed as an integral whole, and the outer tube, the first inner tube and the two second inner tubes are an integral structure.

5. The multimode hollow-core antiresonant optical fiber according to claim 4, wherein: The outer tubes of the 10 double-nested adjacent tubes are used to confine the light beam to the fiber core area, preventing light from entering the interior of the double-nested adjacent tubes or the gaps between the double-nested adjacent tubes. The first inner tube and two second inner tubes of the double-nested adjacent tubes are used to introduce multiple reflection layers to reduce transmission loss through the multi-layer anti-resonance effect.

6. The multimode hollow-core antiresonant optical fiber according to claim 3, wherein: Diameter in the core area D c Fixed case, set d / D、d n / d The initial value of the outer tube, the first embedded tube, and the second embedded tube are D 、 d 、 d n Through simulation, the influence of the gap spacing between adjacent double-nested adjacent tubes on the number of core guided modes that can be transmitted by the multimode hollow-core anti-resonant fiber at an operating wavelength of 1080 nm is obtained, and the optimal value of the gap spacing between adjacent double-nested adjacent tubes is obtained.

7. The multimode hollow-core antiresonant optical fiber according to claim 6, wherein: Diameter in the core area D c When the gap spacing between adjacent double nested tubes is fixed and the gap spacing between adjacent double nested tubes is the optimal value, the different values of the multimode hollow core antiresonant fiber at the working wavelength of 1080 nm are obtained through simulation. d / D and d n / d Under the condition of the change of the relative effective refractive index of the core guided mode and the cladding mode, the number of core guided modes that can be transmitted by the multimode hollow core antiresonant fiber and the mode field diagram of the corresponding cladding mode, the goal is to maximize the number of core guided modes that can be transmitted, and select d / D、d n / d The optimal value of is obtained, and then the optimal diameters of the outer tube, the first embedded tube, and the second embedded tube are determined.

8. The multimode hollow-core antiresonant optical fiber according to claim 1, 2, 3, 5, 6, or 7, wherein: Core area diameter D c is 55 μm, the diameters of the outer tube, the first embedded tube, and the second embedded tube are D 、 d 、 d n 22.4 μm, 16.8 μm and 6.7 μm respectively; the gap spacing between adjacent double nested adjacent tubes g The outer tube, the first embedded tube and the two second embedded tube wall thickness is 1.5 μm; t 0.8 μm.

9. The multimode hollow-core antiresonant optical fiber according to claim 8, wherein: The base material of multimode hollow core antiresonant optical fiber is SiO2.

10. The multimode hollow-core antiresonant optical fiber according to claim 8, characterized in that: The simulation obtains the bending radius of the multimode hollow core antiresonant fiber along the axial length of the fiber at an operating wavelength of 1080 nm. R b The number of core guided modes that can be transmitted when the loss is lower than 1 dB / km, 2 dB / km, and 5 dB / km at 5 cm, 10 cm, 15 cm, 20 cm, and ∞, where ∞ represents a straight fiber. As the bending radius increases, the number of core guided modes that can be transmitted increases continuously until it reaches the number of core guided modes that can be transmitted by a straight fiber. As the bending radius decreases, the number of core guided modes that can be transmitted decreases. R b = 5 cm, the loss threshold is 1 dB / km, 2 dB / km, and 5 dB / km, and the supported core guided modes are still as high as 42, 46, and 51.

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