Photonic quasi-crystal fiber with high mode quality and low confinement loss and performance analysis method thereof

Abstract

The invention discloses a photonic quasi-crystal fiber with high mode quality and low confinement loss and a performance analysis method thereof.The optical fiber comprises a central air hole, the central air hole is located in the center of the optical fiber, the radius is optimized to serve as a key structure for mode regulation and control, and an optical fiber ring core tightly wraps the central air hole; all vector modes are limited to be transmitted in the ring; air holes with the diameter d1 of 5.6 microns are formed in the cladding, the air holes are uniformly arranged according to a sextuple symmetric periodic structure array, the distance D1 of each air hole in the cladding is equal to D2 and equal to 9.5 microns, and a perfect matching layer with the thickness of 2.5 microns is arranged outside the cladding; according to the method, a finite element method is adopted for analysis modeling, and mode quality, limiting loss, a nonlinear coefficient, dispersion and walk-off length parameters are obtained through calculation. According to the invention, the long-distance transmission of the optical fiber is realized, the mode of the optical fiber has flat dispersion and low nonlinear coefficient within the band of 1.5-1.6 microns, and the transmission loss can be controlled within a small range.

Description

Technical Field

[0001] The present invention relates to the field of optical fiber technology, and in particular to a photonic quasi-crystal optical fiber with high mode quality and low confinement loss and a performance analysis method thereof. Background Art

[0002] Driven by the continuous innovation of mobile internet, big data, and cloud computing technologies, the global demand for data transmission is increasing day by day. To meet this challenge, many related technologies have been proposed, such as frequency division multiplexing (FDM), time division multiplexing (TDM), polarization division multiplexing (PDM), and wavelength division multiplexing (WDM). However, these solutions are still unable to keep up with the growing demand for communications, and existing communication technologies are also limited by spectrum resource bottlenecks and interference suppression in complex electromagnetic environments. In this context, vortex beams carrying orbital angular momentum (OAM) have become a research hotspot due to their unique advantages. Due to the strict orthogonality between different OAM modes, OAM modes can be used as information carriers, which provides a new technical path for existing communication systems to achieve high-capacity, long-distance and stable transmission.

[0003] Although OAM modes can be transmitted in free space, they are easily affected by external factors such as atmospheric turbulence, which is not conducive to long-distance stable communication needs. Therefore, optical fiber is used as an ideal OAM carrier to suppress external environmental interference. The existing technology includes many types of optical fibers, such as single-mode fiber (SMF), multi-mode fiber (MMF) and photonic crystal fiber (PCF). The existing technology discloses a new type of hollow ring photonic crystal fiber that can support 101 OAM modes and has a mode quality of 78.7% to 90.0% and a power density of less than 10. -8 dB / m low confinement loss and no phase distortion, but due to the excessive dispersion of the high-order modes of this fiber, it is not conducive to long-distance transmission. In long-distance fiber-optic communication systems, the fiber is usually required to meet high mode quality, low nonlinear coefficient, flat dispersion distribution and transmission loss close to the theoretical limit within the communication band. Such characteristics can effectively suppress nonlinear effects such as self-phase modulation (SPM) and four-wave mixing (FWM). However, existing photonic crystal fibers still face multiple technical defects in practical applications. The intensity of their nonlinear effects is usually 100 to 1000 times that of traditional single-mode fibers. The transmission loss characteristics are significantly higher than those of conventional fibers, and the dispersion curve often shows violent oscillations. These defects greatly limit the applicability of photonic crystal fibers in scenarios such as long-distance communications and high-power laser transmission. Summary of the Invention

[0004] Objective of the invention: The objective of the present invention is to provide a photonic quasicrystal fiber with high mode quality and low confinement loss and a method for analyzing its performance.

[0005] Technical solution: The photonic quasicrystal fiber with high mode quality and low confinement loss described in the present invention includes a central air hole, a fiber ring core, a cladding, an air hole in the cladding, and an outermost perfect matching layer. The central air hole is located in the center of the fiber and serves as a key structure for mode regulation by optimizing the radius, with the radius set to r1 = 18.4 μm; the fiber ring core width is set to d = 2.8 μm, the fiber ring core tightly wraps the central air hole, and limits the transmission of all vector modes in the ring; air holes with a diameter of d1 = 5.6 μm are set in the cladding, and the air holes are evenly arranged in a six-fold symmetric periodic structure array. The cladding radius is r0 = 62.5 μm, the spacing between each air hole in the cladding is D1 = D2 = 9.5 μm, and a perfect matching layer with a thickness of 2.5 μm is set on the outside of the cladding.

[0006] Furthermore, the optical fiber ring core adopts SSK2 silicate glass material with high refractive index.

[0007] Furthermore, the cladding layer is made of silicon dioxide material.

[0008] Furthermore, the central air hole performs mode control by optimizing the radius, including:

[0009] a. Set the maximum air radius r1 of the optical fiber center to be within the range of 18.0μm to 18.7μm;

[0010] b. By setting the radius of the fiber ring core to a fixed value r2 = 21.2 μm, the value of r1 is continuously optimized and adjusted during the optimization process, so that the ring width is dynamically adjusted between 2.5 μm and 3.2 μm as the central air hole radius r1 changes, and the ring width d = r2 - r1;

[0011] c. Determining that when the ring width is d = 2.8 μm, the mode quantity and quality show the best effect, thereby determining the central air hole radius r1 = 18.4 μm.

[0012] Furthermore, the optical fiber structure evolves on the basis of the sextuplet quasi-crystal structure, introducing air holes at each node of the sextuplet quasi-crystal unit structure to form a quasi-crystal lattice air hole array, removing the central three layers of air holes and introducing a ring core structure to form a photonic crystal fiber structure.

[0013] Furthermore, the six-fold quasi-crystal structure is composed of a equilateral triangle and a square with equal side lengths as basic units, which are combined into a composite unit; the 60° vertex of the equilateral triangle in the composite unit is used as the rotation center, and a 60° rotation is replicated five times to form a six-fold symmetric unit; the symmetric unit is mirror-flipped 180° along one side of the square to obtain a flipped unit; and any one of the flipped units is used as the center, and a 60° rotation is replicated five times again to form a complete six-fold quasi-crystalline unit.

[0014] The performance analysis method for photonic quasicrystal fibers with high mode quality and low confinement loss described in the present invention includes analytical modeling using the finite element method, and calculating the mode quality, confinement loss, nonlinear coefficient, dispersion, and walk-off length parameters. The OAM mode transmitted in the fiber is obtained from the intrinsic mode HE / EH combination with a π / 2 phase, as shown in the following formula:

[0015]

[0016] where l and m represent the topological charge and radial mode of the OAM mode, respectively; the superscripts “even” and “odd” represent the even and odd modes of the corresponding eigenmodes; the superscript “±” represents the direction of circular polarization, “-” is right-hand circular polarization, and “+” is left-hand circular polarization; the subscript “±” represents the rotation direction of the wavefront phase, where “+” and “-” represent counterclockwise and clockwise rotation of the phase, respectively; and i represents the π / 2 phase difference between the odd and even modes of the HE / EH mode.

[0017] Furthermore, the pattern quality is expressed as follows:

[0018]

[0019] in, and It represents the average electric field intensity of the eigenmode of the high refractive index ring in the core and the entire fiber cross section;

[0020] The nonlinear coefficient is inversely proportional to the effective mode area. The larger the effective mode area, the smaller the nonlinear coefficient, the smaller the signal distortion, and the higher the communication efficiency of the optical fiber. The nonlinear coefficient and effective mode area can be expressed by the following formula:

[0021]

[0022] Among them, A eff represents the effective mode area, E(x, y) represents the electric field distribution on the fiber cross section, S is the entire fiber cross section area, and n represents the nonlinear refractive index of the SSK2 material.

[0023] Furthermore, the dispersion is determined by material dispersion CD m and waveguide dispersion CD w The composition is as follows:

[0024]

[0025] Among them, Re(n m ) and Re(n eff ) represent the real part of the material refractive index and the vector mode n effThe real part of λ is the wavelength, and c is the speed of light in a vacuum.

[0026] Furthermore, the limiting loss formula is expressed as:

[0027]

[0028] Among them, Lm(n eff ) represents the imaginary part of the effective refractive index of the vector mode;

[0029] When the transmission distance exceeds the critical walk-off length, the odd and even modes cannot be linearly superimposed to form an OAM mode. In order to verify the stability of long-distance transmission, the walk-off length of the mode is calculated. The walk-off length of 10ps is expressed as:

[0030]

[0031] in, and n eff The effective refractive index of the even and odd modes.

[0032] Beneficial effects: Compared with the existing technology, the present invention has the following significant advantages: the present invention can support 122 OAM modes of stable transmission, which is basically the same as the existing photonic crystal fiber. The mode quality of the supported OAM modes is maintained at more than 97.5%. In the 1.5μm to 1.6μm operating band, the nonlinear coefficient of all modes is less than 0.39W. -1 / km, which can effectively suppress nonlinear effects; the mode limitation loss reaches 10 -15 ~10 -12 The dispersion fluctuation of the supported mode is relatively flat, and the amplitude is controlled within 17.94ps / (nm·km); the 10ps walk-off length of the mode can reach 10 2 ~10 5 m; These excellent properties can make the transmitted signal reach higher accuracy, thus realizing long-distance transmission of optical fiber. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is the cross-sectional structure of the optical fiber;

[0034] Figure 2 This is the formation process of the sextuplet quasicrystal structure;

[0035] Figure 3 is the variation of mode quality (MQ) and mode number with ring width d;

[0036] Figure 4 OAM in optical fiber 2，1OAM 13，1 OAM 27，1 The electric field and phase diagram of

[0037] Figure 5 is the effective refractive index of all eigenmodes HE / EH in the fiber;

[0038] Figure 6 is the effective refractive index of all OAM modes in the fiber;

[0039] Figure 7 is the mode quality of the vector mode in the optical fiber;

[0040] Figure 8 is the nonlinear coefficient of the vector mode in the optical fiber;

[0041] Figure 9 is the dispersion of the vector mode in the fiber;

[0042] Figure 10 is the confinement loss of the vector mode in the optical fiber;

[0043] Figure 11 is the 10ps walk-off length of the vector mode of the optical fiber at a wavelength of 1.55um. DETAILED DESCRIPTION

[0044] The technical solution of the present invention will be further described below with reference to the accompanying drawings.

[0045] The present invention proposes a novel photonic quasi-crystal fiber structure with high-quality mode characteristics and low confinement loss. The fiber adopts a unique composite waveguide design, such as Figure 1It is a cross-sectional schematic diagram, which includes, from the inside to the outside: a central air hole 1, an optical fiber ring core 2, a cladding 3, an air hole 4 in the cladding, and an outermost perfect matching layer 5. The central air hole 1 is located at the center of the fiber and serves as a key structure for mode control by optimizing its radius, set to r1 = 18.4 μm. The fiber ring core 2 has a width of d = 2.8 μm and is made of high-refractive-index SSK2 (Schweres Silikat Kronenglas 2) silicate glass (with an effective refractive index of 1.6023 at an operating wavelength of 1.55 μm). This ring tightly surrounds the central air hole and confines all vector modes within the ring. The cladding 3 is made of silica (with an effective refractive index of 1.444 at an operating wavelength of 1.55 μm). Air holes with a diameter of d1 = 5.6 μm are uniformly arranged in a six-fold symmetric periodic array. This arrangement exhibits excellent rotational symmetry and effectively suppresses mode leakage and loss issues found in traditional photonic crystal fibers. The radius of the cladding 3 is r0 = 62.5 μm. Furthermore, the spacing between each air hole 4 within the cladding 3 is D1 = D2 = 9.5 μm. A perfectly matched layer with a thickness of 2.5 μm is also set outside the cladding 3, which can completely absorb the electromagnetic waves radiated outward and eliminate the non-physical reflection phenomenon at the boundary of the calculation domain.

[0046] The air hole arrangement structure in cladding 3 is evolved from the six-fold quasi-crystal structure. Figure 2 The figure shows the formation process of a six-fold quasi-crystal structure. Equilateral triangles and squares of equal side length are used as basic units to form a composite unit with a side length equal to the spacing of the air holes in the cladding (9.5 μm). The 60° vertex of the equilateral triangle in the composite unit is rotated 60° and replicated five times to form a six-fold symmetric unit. The symmetric unit is mirrored 180° along one side of the square to form a flipped unit. With any of the upper and lower parts of the flipped unit as the center, the unit is rotated 60° and replicated five more times to form a complete six-fold quasi-crystalline unit. Air holes are introduced at each node of the six-fold quasi-crystalline unit to form a quasi-crystalline lattice air hole array. Finally, the three central air holes are removed and a ring core structure is introduced to form the photonic crystal fiber structure of the present invention.

[0047] In order to obtain higher mode quality and support more modes, the ring width is also optimized. First, the maximum air radius r1 of the optical fiber center is set in the range of 18.0μm to 18.7μm. This parameter will directly affect the mode characteristics and effective refractive index distribution of the optical fiber. Then, by setting the radius of the optical fiber ring core to a fixed value r2 = 21.2μm, the value of r1 is continuously optimized and adjusted during the optimization process, so that the ring width (d = r2-r1) is dynamically adjusted between 2.5μm and 3.2μm as the central air hole radius r1 changes. Figure 3As shown, it is finally determined that when the ring width is d = 2.8 μm, the mode quantity and quality show the best effect, thereby determining the central air hole radius r1 = 18.4 μm.

[0048] This fiber has a central large air hole radius r1 = 18.4 μm (the refractive index of the air inside is 1); a core radius r2 = 21.2 μm; a core width d = 2.8 μm; and a high-refractive-index SSK2 (Schweres Silikat Kronenglas 2) silicate glass material (effective refractive index of 1.6023 at an operating wavelength of 1.55 μm) is used in the core. The diameter of the small air holes in the cladding is d1 = 5.6 μm (the refractive index of the air inside is 1), and the spacing between the small air holes is D1 = D2 = 9.5 μm. To ensure compatibility with other optical fibers, the cladding radius is r0 = 62.5 μm, and the cladding is made of silica (effective refractive index of 1.444 at an operating wavelength of 1.55 μm). A 2.5 μm-thick perfectly matched layer is also placed outside the cladding to absorb outwardly radiated electromagnetic waves and eliminate non-physical reflections at the boundaries of the computational domain.

[0049] According to the structural parameters and refractive index distribution of the optical fiber design, the finite element method was used to analyze parameters such as mode quality, confinement loss, nonlinear coefficient, dispersion and walk-off length in turn to evaluate the optical fiber performance.

[0050] The optical fiber structure of the present invention adopts a unique composite waveguide design. From the inside out, it includes a central air hole 1, an optical fiber ring core 2, a cladding 3, and an air hole 4 within the cladding. Air holes with a diameter of d1 = 5.6 μm are arranged uniformly in a six-fold symmetric periodic structure array. This arrangement has good rotational symmetry and can effectively suppress the mode leakage and loss problems existing in traditional photonic crystal fibers. In addition, the spacing between each air hole 4 is D1 = D2 = 9.5 μm. A perfectly matched layer with a thickness of 2.5 μm is also provided outside the cladding 3 to eliminate non-physical reflection phenomena at the boundary of the computational domain. The radius of the entire optical fiber is set to r0 = 62.5 μm. The operating wavelength of the optical fiber is 1.5 μm to 1.6 μm.

[0051] The fiber was analyzed and modeled using the finite element method, and parameters such as mode quality, confinement loss, nonlinear coefficient, dispersion, and walk-off length were calculated. The OAM mode transmitted in the fiber can be obtained from the combination of intrinsic modes (HE / EH) with a π / 2 phase, as shown in the following formula:

[0052]

[0053] Where l and m represent the topological charge and radial mode of the OAM mode, respectively. The superscripts “even” and “odd” represent the even and odd modes of the corresponding eigenmodes. The superscripts “±” represent the circular polarization direction, where “-” is right-hand circular polarization and “+” is left-hand circular polarization. The subscripts “±” represent the rotation direction of the wavefront phase, where “+” and “-” represent the phase rotation in counterclockwise and clockwise directions, respectively. i represents the π / 2 phase difference between the odd and even modes of the HE / EH mode. Figure 4 The figure shows the OAM in the optical fiber. 2，1 OAM 13，1 OAM 27，1 The electric field and phase diagram show that all modes are concentrated in the ring core.

[0054] To ensure stable transmission of OAM modes in optical fibers, it is necessary to ensure that the effective refractive index difference between the HE and EH modes corresponding to the same OAM mode is greater than 10 -4 This can effectively suppress the degradation of OAM mode to linear polarization (LP) mode, thereby significantly reducing inter-mode crosstalk and providing a reliable transmission channel for optical communication. Figure 5 、 6 The figure shows the effective refractive index of all eigenmodes (HE / EH) and the effective refractive index difference of the constituent OAM modes.

[0055] In addition, to evaluate the performance of optical fibers, the mode quality of optical fibers is also studied. Mode quality plays an important role in the stable transmission and multiplexing of OAM modes. Higher mode quality of optical fibers means lower loss and crosstalk, which allows for more efficient transmission of optical signals. It can be expressed as:

[0056]

[0057] in, and It represents the average electric field intensity of the eigenmode of the high refractive index ring in the core and the entire fiber cross section, such as Figure 7 As shown, it can be observed that with the increase of wavelength, the optical signal diffuses from the ring core to the cladding, and the mode quality shows a downward trend, which has been maintained above 97.5%. The proposed optical fiber ensures the robust propagation of the signal, which is beneficial for the high-precision transmission of OAM modes in optical fibers.

[0058] like Figure 8 The figure shows the relationship between the nonlinear coefficient of the vector mode in the optical fiber and the wavelength. The nonlinear coefficient is a crucial parameter in the optical fiber. It is a physical quantity that measures the nonlinear effect and is inversely proportional to the effective mode area. The larger the effective mode area, the smaller the nonlinear coefficient, the smaller the signal distortion, and the higher the communication efficiency of the optical fiber. The nonlinear coefficient and effective mode area can be expressed by the following formula:

[0059]

[0060] Here A eff represents the effective mode area, E(x, y) represents the electric field distribution on the fiber cross section, S is the entire fiber cross section area, and n represents the nonlinear refractive index of SSK2 material, n = 1.7 × 10 -20 m 2 / W. From Figure 8 It can also be seen that the nonlinear coefficient of all modes is less than 0.39W -1 / km, HE in the 1.55μm band 32，1 Reached a minimum value of 0.2406W -1 / km, and the nonlinear coefficient decreases with the increase of wavelength. The lower nonlinear coefficient reduces the distortion of optical signals and is very beneficial for long-distance signal transmission.

[0061] The dispersion of optical fiber is caused by the pulse broadening caused by the different propagation speeds of light of different frequencies or modes during the transmission process of optical signals, which directly affects the transmission performance of optical fibers. The dispersion of optical fiber is mainly composed of material dispersion (CDm) and waveguide dispersion (CDw). The specific formula is as follows:

[0062]

[0063] In the formula Re(n m ) and Re(n eff ) represent the real part of the material refractive index and the vector mode n eff The real part of , λ is the wavelength, and c represents the speed of light in vacuum. Figure 9 As shown, it can be seen that the dispersion fluctuation remains flat, with a maximum amplitude of 17.94 ps / (nm km). Flat dispersion helps signals transmit over longer distances without the need for additional dispersion compensation.

[0064] Confinement loss describes the energy attenuation during light transmission in an optical fiber. The lower the confinement loss, the less energy leaks from the core to the cladding, ensuring efficient long-distance signal transmission. In addition, the cladding pore distribution also affects confinement loss. The denser the cladding pore distribution, the better the circular symmetry, and the corresponding lower the CL. The six-fold quasicrystal structure pore array greatly improves the pore density and circular symmetry, thereby achieving low confinement loss. Confinement loss can be expressed by the following formula:

[0065]

[0066] Among them, Lm(n eff ) represents the imaginary part of the effective refractive index of the vector mode. Figure 10The figure shows the relationship between the limiting loss of different eigenmodes and wavelength. It can be seen that the limiting loss fluctuates greatly with wavelength, mainly concentrated in 10 -15 ~10 -12 The low limiting loss also indicates a good prospect for long-distance information transmission.

[0067] Due to the difference in transmission rates between the odd and even HE / EH modes that make up the OAM mode, a mode walk-off effect occurs. When the transmission distance exceeds the critical walk-off length, the odd and even modes cannot linearly superimpose to form an OAM mode. To verify the stability of long-distance transmission, the mode walk-off length was calculated. A walk-off length of 10 ps can be expressed as:

[0068]

[0069] In the formula and n eff The effective refractive index of the even and odd modes is as follows: Figure 11 All modes can be observed as shown in L 10ps The walk-away length can reach 10 2 ~10 5 m, within this range, odd and even modes can be linearly superimposed to form OAM modes, which contributes to stable long-distance transmission of optical fibers.

Claims

1. A photonic quasi-crystal fiber with high mode quality and low confinement loss, characterized in that The invention comprises a central air hole (1), an optical fiber ring core (2), a cladding (3), an air hole (4) in the cladding, and an outermost perfect matching layer (5), wherein the central air hole (1) is located at the center of the optical fiber and is used as a key structure for mode control by optimizing the radius, and the radius is set to r1=18.4μm; the width of the optical fiber ring core is set to d=2.8μm, the optical fiber ring core (2) tightly wraps the central air hole (1), and limits all vector modes from being transmitted in the ring; an air hole (4) with a diameter of d1=5.6μm is set in the cladding (3), and the air holes (4) are uniformly arranged in a six-fold symmetric periodic structure array, the radius of the cladding (3) is r0=62.5μm, the spacing between each air hole in the cladding (3) is D1=D2=9.5μm, and a perfect matching layer (5) with a thickness of 2.5μm is set outside the cladding.

2. The photonic quasi-crystal fiber with high mode quality and low confinement loss according to claim 1, characterized in that The optical fiber ring core (2) is made of SSK2 silicate glass material with a high refractive index.

3. The photonic quasicrystal fiber with high mode quality and low confinement loss according to claim 1, characterized in that The cladding (3) is made of silicon dioxide material.

4. The photonic quasicrystal fiber with high mode quality and low confinement loss according to claim 1, characterized in that The central air hole (1) performs mode control by optimizing the radius, including: a. Setting the maximum air radius r1 of the optical fiber center (2) in the range of 18.0 μm to 18.7 μm; b. By setting the radius of the optical fiber ring core (2) to a fixed value r2 = 21.2 μm, the value of r1 is continuously optimized and adjusted during the optimization process, so that the ring width is dynamically adjusted between 2.5 μm and 3.2 μm as the radius r1 of the central air hole (1) changes, and the ring width d = r2-r1; c. It was determined that when the ring width is d = 2.8 μm, the mode quantity and quality show the best effect, thereby determining the radius of the central air hole (1) r1 = 18.4 μm.

5. The photonic quasicrystal fiber with high mode quality and low confinement loss according to claim 1, characterized in that The optical fiber structure evolves on the basis of the sextuplet quasi-crystal structure, introducing air holes at each node of the sextuplet quasi-crystal unit structure to form a quasi-crystal lattice air hole array, removing the central three layers of air holes and introducing a ring core structure to form a photonic crystal optical fiber structure.

6. The photonic quasi-crystal fiber with high mode quality and low confinement loss according to claim 5, characterized in that The six-fold quasi-crystal structure uses equilateral triangles and squares with equal side lengths as basic units to form a composite unit; with the 60° vertex of the equilateral triangle in the composite unit as the rotation center, it is rotated 60° and replicated five times to form a six-fold symmetric unit; the symmetric unit is mirror-flipped 180° along one side of the square to obtain a flipped unit; with any one of the flipped units as the center, it is rotated 60° and replicated five times again to form a complete six-fold quasi-crystalline unit.

7. A method for analyzing the performance of photonic quasi-crystal fibers with high mode quality and low confinement loss, characterized in that: This involves analytical modeling using the finite element method, and the calculation of mode quality, confinement loss, nonlinear coefficient, dispersion, and walk-off length parameters. The OAM mode transmitted in the optical fiber is obtained from the intrinsic mode HE / EH combination with a π / 2 phase, as shown in the following formula: Where l and m represent the topological charge and radial mode of the OAM mode, respectively; the superscripts "even" and "odd" represent the even and odd modes of the corresponding eigenmodes; the superscript "±" represents the circular polarization direction, where "-" is right-hand circular polarization and "+" is left-hand circular polarization; the subscript "±" represents the rotation direction of the wavefront phase, where "+" and "-" represent counterclockwise and clockwise rotation, respectively; and i represents the π / 2 phase difference between the odd and even modes of the HE / EH mode.

8. The photonic quasi-crystal fiber with high mode quality and low confinement loss according to claim 7, characterized in that The mode quality is expressed by the formula: in, and It represents the average electric field intensity of the eigenmode of the high refractive index ring in the core and the entire fiber cross section; The nonlinear coefficient is inversely proportional to the effective mode area. The larger the effective mode area, the smaller the nonlinear coefficient, the smaller the signal distortion, and the higher the communication efficiency of the optical fiber. The nonlinear coefficient and effective mode area can be expressed by the following formula: Among them, A eff represents the effective mode area, E(x, y) represents the electric field distribution on the fiber cross section, S is the entire fiber cross section area, and n represents the nonlinear refractive index of the SSK2 material.

9. The photonic quasi-crystal fiber with high mode quality and low confinement loss according to claim 7, characterized in that The dispersion is determined by the material dispersion CD m and waveguide dispersion CD w The composition is as follows: Among them, Re(n m ) and Re(n eff ) represent the real part of the material refractive index and the vector mode n eff The real part of λ is the wavelength, and c is the speed of light in a vacuum.

10. The photonic quasi-crystal fiber with high mode quality and low confinement loss according to claim 7, characterized in that The limiting loss formula is expressed as: Among them, Lm(n eff ) represents the imaginary part of the effective refractive index of the vector mode; When the transmission distance exceeds the critical walk-off length, the odd and even modes cannot be linearly superimposed to form an OAM mode. In order to verify the stability of long-distance transmission, the walk-off length of the mode is calculated. The walk-off length of 10ps is expressed as: in, and n eff The effective refractive index of the even and odd modes.

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