CN116107017A - Ultra-large mode area multi-core optical fiber capable of supporting 10 OAM mode transmissions - Google Patents

Abstract

The invention relates to an ultra-large mode area multi-core optical fiber, which is composed of a plurality of high-refractive index silica-doped round cores. By changing the number of the cores, the refractive index of the cores, the radius of the cores and the distance from the cores to the center of the cladding, the optical characteristics of the optical fiber such as mode field area, dispersion, OAM mode purity, nonlinear coefficient and the like can be adjusted. Under the parameter structure proposed by the invention, the optical fiber can support 10 OAM mode transmissions in the wave band of 1500-1600nm, and the effective refractive index difference of the OAM modes with different orders is 10 ^‑4 The stable transmission condition of the OAM modes is satisfied, and the mode field area of each OAM mode is 3160 mu m ² The above. At 1550nm, the purity of each OAM mode of the fiber capable of supporting transmission is over 99.9%, and the nonlinear coefficient is smaller than 0.032W ^‑1 The dispersion is between 22-24 ps/nm/km. The multi-core optical fiber provided by the invention has the characteristics of ultra-large mode field area, high purity, low dispersion and the like, and has potential in an OAM optical fiber communication system and a high-power OAM optical fiber laserThe application value is high.

Description

Ultra-large mode area multi-core fiber that can support 10 OAM modes of transmission

technical field

The invention belongs to the field of optical fiber technology, in particular to a super-large mode field area multi-core optical fiber that can support orbital angular momentum mode transmission.

Background technique

Orbital Angular Momentum (OAM) mode has become a research hotspot in the field of optical fiber communication in recent years because of its unique optical properties. Different from ordinary eigenvector modes in optical fibers, OAM modes are superimposed by odd-even vector modes with a phase difference of π/2, which are prone to coupling during transmission in ordinary optical fibers and lose the helical phase characteristic. In order to achieve long-distance stable transmission of optical fiber OAM mode, the fiber structure must be specially designed to ensure that the effective refractive index difference between TE, TM mode and HE or EH mode transmitted in the fiber is more than 10 ^-4 , and the parity of EH or HE The mutual degeneracy of the modes can avoid the mutual coupling between the vector modes.

In recent years, the design of special optical fibers that can support the stable transmission of OAM mode has become one of the research focuses in the field of optical fiber OAM communication. However, in order to support the stable transmission of as many OAM modes as possible, most of the OAM transmission fibers reported so far are composed of high-refractive narrow ring core structures. The narrow ring cores provide limited transmission channels, smaller mode field areas and higher Refractive index doped silica will lead to high nonlinear coefficient, which not only affects the performance of space division multiplexing optical fiber communication system, but also limits the research and development of high power OAM fiber laser.

In order to reduce the adverse effects caused by nonlinear effects, researchers have developed some large mode field area fibers that can support OAM mode transmission [Optics Express, 27(20): 27991-28008, 2019]. Increase the core size to increase the effective mode area, so as to achieve the purpose of reducing nonlinear effects. However, simply increasing the fiber core size will lead to vector mode degeneracy, thus affecting the OAM mode transmission stability. Therefore, limited by the transmission characteristics of the OAM mode, the mode field areas of the reported large mode area OAM transmission fibers are all around 500 μm ² , and the corresponding mode nonlinear coefficients have not dropped to ideal values. And the design of OAM transmission fiber needs to consider many optical characteristic parameters, including mode transmission limit loss, communication dispersion, mode field area, nonlinear coefficient, vector model degeneracy (effective refractive index difference between modes, whether OAM stable transmission conditions are met) Therefore, there are many difficulties in the development, design and structural optimization of OAM transmission optical fibers with large mode field area.

Contents of the invention

Aiming at many problems existing in the field of research and development of large mode area OAM transmission optical fibers at present, the present invention designs a super large mode area multi-core optical fiber that can support 10 OAM mode transmissions. The optical fiber is composed of multiple cores arranged in a ring, and the coupling effect between different cores in the multi-core fiber is used to generate a vector supermode with a large mode field area, and finally the OAM mode is formed by using the vector supermode. By changing the number of cores arranged in the multi-core fiber ring, the material refractive index of the core, the core radius and the distance from the core to the center of the cladding, the mode field area, dispersion, OAM mode purity, and Optical properties such as nonlinear coefficients.

Under the optical fiber parameter structure proposed by the present invention, in the 1500-1600nm band, the optical fiber can support 10 OAM mode transmissions, and the effective refractive index differences between different order OAM modes are all above 10 ^-4 , which meets the OAM mode stable transmission conditions, and the mode field area of each OAM mode is above 3160 μm ² . In addition, at 1550nm, the purity of each OAM mode supported by the optical fiber is above 99.9%, the nonlinear coefficient is less than 0.032W ^-1 /km, and the dispersion is between 22-24ps/nm/km. The multi-core optical fiber proposed by the invention has the characteristics of super large mode field area, high purity, low dispersion and the like, and has potential application value in OAM optical fiber communication systems and high-power OAM optical fiber lasers.

The ultra-large mode field area multi-core optical fiber capable of supporting 10 OAM mode transmissions of the present invention includes two parts: a core and a cladding. The core part is composed of a number of doped silica cores with radius r and material refractive index n ₁ , the cladding part is composed of pure silica, and the distance from each core to the center of the cladding is L. The relationship between the refractive index n ₁ of the core material and the refractive index of the cladding material is set as n=(n ₁ −n ₂ )/n ₂ (the material refractive index of pure silica is n ₂ ). By changing the parameters of the multi-core structure (such as the number of cores, the refractive index n ₁ of the material, the radius r of the core, and the distance L between the cores), a coupling supermode can be generated between each core, and the mode field energy of the supermode covers all fibers. The core area forms a super large mode field area.

Advantages of the present invention:

)的稳定传输，不同本征模式之间的有效模式折射率差值达到了1×10^-4以上，且各个OAM模式纯净度均超过99.9％，通过设计合理的结构，优化物理参数，该光纤在1500nm-1600nm通信波段可支持传输的各个OAM模式的模场面积均达到了3160μm²以上，且具有较小的色散特性和极小的非线性系数。该光纤在OAM光纤通信系统及高功率OAM光纤激光器中有潜在的应用价值。The present invention proposes an ultra-large mode field area multi-core optical fiber that can support 10 OAM mode transmissions. Compared with ordinary high-refractive index ring-core OAM transmission optical fibers, the optical fiber can not only support different OAM modes (including

) stable transmission, the effective mode refractive index difference between different eigenmodes has reached more than 1×10 ^-4 , and the purity of each OAM mode exceeds 99.9%. By designing a reasonable structure and optimizing physical parameters, the optical fiber The mode field area of each OAM mode that can support transmission in the 1500nm-1600nm communication band has reached more than 3160μm ² , and has small dispersion characteristics and extremely small nonlinear coefficients. The optical fiber has potential application value in OAM optical fiber communication system and high power OAM optical fiber laser.

The present invention will be further described below in conjunction with the accompanying drawings and implementation.

Description of drawings

Figure 1 is a schematic cross-sectional view of a multi-core optical fiber with an ultra-large mode field area that can support OAM mode transmission;

Figure 2 is a diagram of the mode field energy and phase distribution of each OAM mode supported by the ultra-large mode field area multi-core fiber. The text marked in the figure is the type of vector mode corresponding to each OAM mode and the purity of the OAM mode;

Fig. 3 is the variation relation of the mode field area of the different vector modes of the ultra-large mode field area multi-core fiber with the wavelength;

Fig. 4 is the relationship between the refractive index difference between the modes of different vector modes of the ultra-large mode field area multi-core fiber as a function of wavelength;

Fig. 5 is the variation relation of dispersion with wavelength in different vector modes of the ultra-large mode field area multi-core fiber;

Fig. 6 is the variation relation of the nonlinear coefficient of the different vector modes of the ultra-large mode field area multi-core fiber with the wavelength;

Detailed ways

The present invention and technical solutions will be further described in detail below in conjunction with the accompanying drawings.

A super-large mode area multi-core fiber that can support 10 OAM mode transmission, the cross-sectional structure is shown in Figure 1. The core part of the optical fiber is composed of multiple high-refractive-index cores with a radius r and a material refractive index n _1. The distance between each core and the center of the cladding is L. The relationship between the refractive index n ₁ of the core material and the refractive index of the cladding material is set as n=(n ₁ −n ₂ )/n ₂ (the material refractive index of pure silica is n ₂ ).

The cladding material of the ultra-large mode area multi-core optical fiber is selected as pure silica, the core material is doped silica, the number of cores is 10, the core radius r=17.24 μm, and the core to cladding The center distance L=22.73 μm, the relationship value n=0.0243 between the refractive index n ₁ of the core material and the refractive index n ₂ of the cladding material. Under this structural parameter, the mode characteristics of the photonic crystal fiber are shown in Fig. 2 to Fig. 6 .

Fig. 2 is the mode field energy and phase distribution diagram of each OAM mode supported by the ultra-large mode field area multi-core fiber of the present invention. The text marked in the figure is the type of vector mode corresponding to each OAM mode and the purity of the OAM mode. It can be seen from the figure that all OAM mode phases are spirally distributed, and the mode purity is greater than 99.9%.

Fig. 3 is the relationship between the mode field area of different vector modes of the ultra-large mode field area multi-core fiber and the wavelength. It can be seen from the figure that within the wavelength range of 1500nm-1600nm, the mode field area of different vector modes that the optical fiber can support can reach more than 3160μm ² .

共计10个OAM模式。Fig. 4 shows the variation relationship of inter-mode refractive index difference with wavelength in different vector modes of the ultra-large mode field area multi-core fiber. It can be seen from the figure that the effective refractive index difference of different vector eigenmodes is greater than 1×10 ^-4 , which ensures the stable transmission of the OAM mode. Fig. 2 and Fig. 4 show that the described multi-core fiber with ultra-large mode field area can support the stable transmission of 10 OAM modes, including

There are 10 OAM modes in total.

Fig. 5 shows the variation relationship of dispersion with wavelength in different vector modes of the ultra-large mode field area multi-core fiber. It can be seen from the figure that at the wavelength of 1500nm, the dispersion value of each vector eigenmode that the multi-core fiber can support transmission is between 22-24ps/nm/km, and the dispersion is small, and in the 1500nm-1600nm band At , the variation range of the dispersion is within 8ps/nm/km, and the dispersion is relatively flat.

Fig. 6 shows the relationship between the nonlinear coefficient of different vector modes of the ultra-large mode field area multi-core fiber and the wavelength. It can be seen from the figure that at a wavelength of 1500nm, the nonlinear coefficients of the vector eigenmodes supported by the multi-core fiber are all less than 0.032W ^-1 /km, which proves that the fiber has a super large mode field area and a very small Properties of nonlinear coefficients.

Parts not described in detail in the present invention belong to the common knowledge of those skilled in the art.

Claims (4)

1. An ultra-large mode field area multi-core fiber that can support 10 OAM mode transmissions, including two parts, the core and the cladding. The core part is composed of multiple circular cores with a radius r and a material refractive index n ₁ . The distance from each circular core to the cladding center is L. By changing the structural parameters of the multi-core fiber (such as the number of cores, the refractive index of the material, the radius of the core, and the distance L between the cores), a coupling supermode can be generated between each core, and the mode field energy of the supermode covers all the cores. area, forming a super large mode field area, the fiber can support the stable transmission of multiple OAM modes with super large mode field area. 2. A kind of ultra-large mode area multi-core optical fiber capable of supporting 10 OAM mode transmissions according to claim 1, characterized in that: a plurality of core materials of the optical fiber are all doped silica, cladding The material is composed of pure silica. 3. A super-large mode area multi-core optical fiber capable of supporting 10 OAM mode transmissions according to claim 1, characterized in that: the value range of the core radius is 15 μm < r < 18 μm, and the number of cores is between 8- Among the 12, the range of the distance from each core to the cladding center is 20 μm<L<30 μm. 4. A kind of ultra-large mode field area multi-core optical fiber that can support 10 OAM mode transmissions according to claim 1, characterized in that: the relationship between the refractive index _n of the core material and the refractive index of the cladding material is set n=(n ₁ −n ₂ )/n ₂ (refractive index of pure silicon dioxide is n ₂ ), then the range of n is 0.02<n<0.05.

Images