Ultra-large-mode-area multicore optical fiber supporting ten oam mode transmissions

Abstract

The present application relates to a kind of super large mode field area multicore optical fiber, and the fiber core is made of multiple doped silica high refractive index round core.By changing the number of the multicore optical fiber core, core refractive index, core radius and core to cladding center distance, the mode field area of optical fiber, dispersion, OAM mode purity, nonlinear coefficient and other optical properties can be adjusted.Under the parameter structure proposed in the present application, in 1500-1600nm waveband, the optical fiber can support 10 OAM mode transmission, and the effective refractive index difference of different order OAM mode is all in 10 ‑4 Above, meet OAM mode stable transmission condition, and the mode field area of each OAM mode is all in 3160 μm 2 Above.At 1550nm, the purity of each OAM mode that the optical fiber can support transmission is all above 99.9%, and the nonlinear coefficient is less than 0.032 W ‑1 / km, and dispersion is between 22-24ps / nm / km.The multicore optical fiber proposed in the present application has super large mode field area, high purity, low dispersion and other characteristics, and has potential application value in OAM optical fiber communication system and high-power OAM optical fiber laser.

Description

Technical Field

[0001] This invention belongs to the field of optical fiber technology, specifically a multi-core optical fiber with an ultra-large mode area that can support orbital angular momentum mode transmission. Background Technology

[0002] Orbital Angular Momentum (OAM) modes have become a research hotspot in fiber optic communication and other fields in recent years due to their unique optical properties. Unlike ordinary intrinsic vector modes in optical fibers, OAM modes are composed of superimposed odd and even vector modes with a phase difference of π / 2. In ordinary optical fibers, they are prone to coupling and loss of helical phase characteristics during transmission. To achieve stable long-distance transmission of OAM modes in optical fibers, special design of the fiber structure is necessary to ensure that the effective refractive index difference between the TE / TM modes and the HE or EH modes transmitted in the fiber is within 10. -4 In addition, the parity modes of EH or HE must be degenerate to avoid mutual coupling between vector modes.

[0003] In recent years, designing special optical fibers capable of supporting stable transmission in OAM modes has become a key research focus in the field of fiber optic OAM communication. However, in order to support stable transmission of as many OAM modes as possible, most reported OAM transmission fibers are composed of a high-refractive-index narrow-ring core structure. The narrow ring core provides limited transmission channels, and the small mode field area and high-refractive-index doped silicon dioxide result in a very high nonlinear coefficient, which not only affects the performance of space-division multiplexing fiber optic communication systems but also limits the research and development of high-power OAM fiber lasers.

[0004] To mitigate the adverse effects of nonlinearity, researchers have developed large mode area fibers (MAFs) capable of supporting OAM mode transmission [Optics Express, 27(20): 27991-28008, 2019]. These fibers increase the effective mode area by increasing the core size, thereby reducing nonlinearity. However, simply increasing the core size leads to vector mode degeneracy, affecting the stability of OAM mode transmission. Therefore, limited by the transmission characteristics of OAM mode, the mode area of ​​currently reported large MAF OAM transmission fibers is all around 500 μm. 2 Around 100°C, the corresponding mode nonlinearity coefficient did not decrease to the ideal value. Furthermore, the design of OAM transmission fibers requires consideration of numerous optical characteristic parameters, including mode transmission limitation loss, communication dispersion, mode area, nonlinearity coefficient, vector model degeneracy (effective refractive index difference between modes, and whether the OAM stable transmission conditions are met), etc. Therefore, the research, design, and structural optimization of large mode area OAM transmission fibers present many difficulties. Summary of the Invention

[0005] This invention addresses numerous problems existing in the current research and development of large mode area (OAM) transmission fibers by designing an ultra-large mode area multi-core fiber capable of supporting the transmission of 10 OAM modes. This fiber consists of multiple ring-arranged cores. Utilizing the coupling effect between different cores within the multi-core fiber, a vector supermode with an ultra-large mode area is generated, and ultimately, the OAM mode is formed using this vector supermode. By changing the number of ring-arranged cores, the refractive index of the core material, the core radius, and the distance from the core to the cladding center, the optical properties of the fiber, such as mode area, dispersion, OAM mode purity, and nonlinear coefficient, can be adjusted.

[0006] Under the fiber parameter structure proposed in this invention, the fiber can support 10 OAM modes in the 1500-1600nm band, and the effective refractive index difference between different orders of OAM modes is within 10. -4 The above conditions satisfy the stable transmission requirements of OAM mode, and the mode field area of ​​each OAM mode is within 3160μm. 2 That's all. Furthermore, at 1550nm, the purity of all OAM modes supported by this fiber is above 99.9%, and the nonlinear coefficient is less than 0.032W. -1 The dispersion is between 22-24 ps / nm / km. The multi-core fiber proposed in this invention has characteristics such as ultra-large mode area, high purity, and low dispersion, and has potential application value in OAM fiber communication systems and high-power OAM fiber lasers.

[0007] The ultra-large mode field area multi-core optical fiber supporting 10 OAM modes described in this invention comprises two parts: a core and a cladding. The core consists of multiple doped silica cores with radius r and refractive index n1, while the cladding is made of pure silica. Each core is distance L from the center of the cladding. The relationship between the refractive index n1 of the core material and the refractive index of the cladding material is set as n = (n1 - n2) / n2 (where the refractive index of pure silica is n2). By changing the multi-core structure parameters (e.g., the number of cores, refractive index n1, core radius r, and core distance L), coupled supermodes can be generated between the cores. The mode field energy of these supermodes covers all core regions, forming an ultra-large mode field area.

[0008] Advantages of this invention:

[0009] This invention proposes an ultra-large mode area multi-core optical fiber capable of supporting 10 OAM modes. Compared with ordinary high-refractive-index ring-core OAM transmission optical fibers, this fiber can support different OAM modes (including... Stable transmission of ) with an effective mode refractive index difference of 1×10 eigenmodes.-4 The purity of each OAM mode exceeds 99.9%. Through reasonable structural design and optimized physical parameters, this optical fiber can support a mode field area of ​​3160μm for all OAM modes transmitted in the 1500nm-1600nm communication band. 2 This fiber exhibits the above properties, along with low dispersion and extremely small nonlinear coefficients. It holds potential application value in OAM fiber communication systems and high-power OAM fiber lasers.

[0010] The present invention will be further described below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0011] Figure 1 A schematic diagram of the cross-section of a multi-core fiber with an ultra-large mode field area that can support OAM mode transmission;

[0012] Figure 2 The diagram shows the energy and phase distribution of each OAM mode supported by this ultra-large mode area multi-core fiber. The text labeled in the diagram indicates the vector mode type and purity of each OAM mode.

[0013] Figure 3 The relationship between the mode area and wavelength for different vector modes of this ultra-large mode area multi-core fiber is shown.

[0014] Figure 4 The relationship between the intermodal refractive index difference of different vector modes in this ultra-large mode field area multi-core fiber and wavelength.

[0015] Figure 5 The relationship between dispersion and wavelength for different vector modes in this ultra-large mode area multi-core fiber is shown.

[0016] Figure 6 The relationship between the nonlinear coefficients of different vector modes of this ultra-large mode area multi-core fiber and wavelength; Detailed Implementation

[0017] The present invention and technical solution will be further described in detail below with reference to the accompanying drawings.

[0018] A multi-core optical fiber with an ultra-large mode field area that can support 10 OAM mode transmissions, with a cross-sectional structure as follows: Figure 1 As shown, the fiber core is composed of multiple high-refractive-index cores with radius r and refractive index n1. The distance from each core to the cladding center is L. The relationship between the refractive index n1 of the core material and the refractive index of the cladding material is set as n = (n1 - n2) / n2 (the refractive index of pure silicon dioxide is n2).

[0019] The cladding material of this ultra-large mode area multi-core fiber is selected as pure silicon dioxide, and the core material is doped silicon dioxide. There are 10 cores with a core radius r = 17.24 μm and a core-to-cladding center distance L = 22.73 μm. The refractive index n1 of the core material is related to the refractive index n2 of the cladding material by n = 0.0243. Under these structural parameters, the mode characteristics of the photonic crystal fiber are as follows: Figures 2 to 6 As shown.

[0020] Figure 2 This diagram shows the mode field energy and phase distribution of each OAM mode supported by the ultra-large mode field area multi-core fiber of this invention. The text labeled in the diagram indicates the vector mode type and purity of each OAM mode. As can be seen from the diagram, all OAM modes exhibit a spiral phase distribution, and the mode purity is greater than 99.9%.

[0021] Figure 3 The figure shows the relationship between the mode area and wavelength for different vector modes in this ultra-large mode area multi-core fiber. As can be seen from the figure, within the wavelength range of 1500nm-1600nm, the mode area for all vector modes supported by this fiber can reach 3160μm. 2 above.

[0022] Figure 4 This figure shows the relationship between the intermodal refractive index difference of different vector modes in this ultra-large mode area multi-core fiber and wavelength. As can be seen from the figure, the effective refractive index difference of different vector eigenmodes is greater than 1 × 10⁻⁶. -4 This ensures stable transmission in OAM mode. Figure 2 and Figure 4 This indicates that the aforementioned ultra-large mode area multi-core optical fiber can support stable transmission in 10 OAM modes, including... There are a total of 10 OAM modes.

[0023] Figure 5 The figure shows the relationship between dispersion and wavelength for different vector modes of this ultra-large mode area multi-core fiber. As can be seen from the figure, at a wavelength of 1500 nm, the dispersion values ​​of all vector intrinsic modes that this multi-core fiber can support transmission are between 22-24 ps / nm / km, indicating relatively low dispersion. Furthermore, in the 1500 nm-1600 nm band, the dispersion variation range is within 8 ps / nm / km, showing relatively flat dispersion.

[0024] Figure 6 The figure shows the relationship between the nonlinear coefficients of different vector modes in this ultra-large mode area multi-core fiber and wavelength. As can be seen from the figure, at a wavelength of 1500 nm, the nonlinear coefficients of all vector eigenmodes that this multi-core fiber can support transmission are less than 0.032 W. -1 / km, proving that the optical fiber has the characteristics of ultra-large mode field area and extremely small nonlinear coefficient.

[0025] The parts of this invention not described in detail are common knowledge to those skilled in the art.

Claims

1. A multi-core optical fiber with an ultra-large mode area capable of supporting 10 OAM modes, wherein the mode area of ​​each OAM mode is 3160μm in the 1500-1600nm band. 2 The multi-core optical fiber comprises a core and a cladding. The core consists of multiple circular cores with radius r and refractive index n1. Each circular core is distanced L from the center of the cladding. The core radius ranges from 15μm to r to 18μm, and the number of cores is between 8 and 12. The distance from each circular core to the center of the cladding ranges from 20μm to L to 30μm. The relationship between the refractive index n1 of the core material and the refractive index n2 of the cladding material is n = (n1 - n2) / n2. The refractive index n2 of the cladding material is the refractive index of pure silicon dioxide, so the value of n ranges from 0.02 to n to 0.

05. By changing the number of cores, the refractive index relationship n, the core radius r, and the core distance L, a coupled supermode can be generated between the cores. The mode field energy of the supermode covers all core regions, forming a very large mode field area. This optical fiber can support the stable transmission of multiple OAM modes with very large mode field areas.

2. The ultra-large mode area multi-core optical fiber supporting 10 OAM mode transmission as described in claim 1, characterized in that: The fiber cores are all made of doped silicon dioxide.

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