A graded-index non-zero dispersion-shifted optical fiber based on orbital angular momentum mode

Abstract

This invention discloses a graded-index non-zero dispersion-shifted optical fiber based on orbital angular momentum modes, comprising an optical fiber body including a ring core and an optical fiber cladding surrounding the ring core. The optical fiber cladding includes a circular region inside the ring core and an outer optical fiber cladding outside the ring core. This invention aims to provide a feasible optical fiber structure for suppressing four-wave mixing to meet the requirements of low-dispersion transmission of multiple orbital angular momentum modes.

Description

Technical Field

[0001] This invention relates to the field of optical fiber technology, and specifically to a graded-index non-zero dispersion-shifted optical fiber based on orbital angular momentum mode. Background Technology

[0002] When light propagates in optical fiber, the nonlinear effect of the fiber is a major obstacle to its transmission quality. In wavelength division multiplexing systems, the new wavelengths generated by four-wave mixing will affect the signal-to-noise ratio and generate crosstalk between channels.

[0003] To minimize nonlinear effect losses and improve fiber performance, it is necessary to use non-zero dispersion-shifted fibers that retain a certain amount of dispersion at 1550 nm. The appropriate amount of dispersion retained in the 1550 nm window reduces four-wave mixing effects by increasing phase mismatch. For orbital angular momentum modes used in optical fiber communication, multiple orbital angular momentum modes serving as different channels within the fiber should all retain an appropriate amount of dispersion at the 1550 nm window to reduce nonlinear effect losses.

[0004] Currently, there is no non-zero dispersion-shifted fiber design that can simultaneously support multiple orbital angular momentum modes. Previous inventions, such as the fiber design applicable to multiple orbital angular momentum modes (e.g., "A Trench-Assisted Double Step-Indexed Ring Core Fiber" (patent application number: CN202011082327.X), cannot guarantee low dispersion properties for the multiple orbital angular momentum modes within the fiber. Fiber designs meeting the requirements for non-zero dispersion-shifted fibers, such as "Low Dispersion Slope Large Effective Area Non-Zero Dispersion-Shifted Fiber" (patent application number: CN202110979257.6) and "A Vortex Light Non-Zero Dispersion-Shifted Fiber" (patent application number: CN202010977893.0), cannot support orbital angular momentum modes, and the latter cannot support the low dispersion properties of multiple orbital angular momentum modes as described in this invention. Summary of the Invention

[0005] To overcome the problems existing in the prior art, this invention proposes a graded-index non-zero dispersion-shifted optical fiber based on orbital angular momentum modes, aiming to provide a feasible optical fiber structure to suppress four-wave mixing, so as to meet the requirements of low dispersion transmission of multiple orbital angular momentum modes.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] A graded-index non-zero dispersion-shifted optical fiber based on orbital angular momentum mode includes an optical fiber body, the optical fiber body including an annular core 1 and an optical fiber cladding surrounding the annular core 1, the optical fiber cladding including a circular region 2 located inside the annular core 1 and an outer optical fiber cladding 3 located outside the annular core 1.

[0008] The refractive index n1 of the circular region 2, the refractive index n2 of the annular fiber core 1 region, and the refractive index n3 of the outer fiber cladding 3 are described.

[0009] The refractive index n1 of the circular region 2, the refractive index n2 of the annular fiber core 1 region, and the refractive index n3 of the outer fiber cladding 3 satisfy the condition that the values ​​of n1 and n3 are less than the value of n2.

[0010] The refractive index n2 of the annular fiber core 1 region is a gradually changing refractive index; the gradually changing refractive index within the annular fiber core 1 region is greater than that in other regions, and the refractive index distribution satisfies n1 ≤ n3. <n2。

[0011] The material of the optical fiber body, satisfying the above-mentioned refractive index distribution, is a combination of silicon dioxide and germanium-doped silicon dioxide. The graded refractive index n2 of the annular fiber core 1 region satisfies the following equation:

[0012]

[0013] Where r is the distance from the center of the optical fiber, α is the refractive index distribution parameter, and w half R0 is the half-width of region 1 of the annular fiber core, and R0 is the location of the maximum concentration of silicon dioxide germanium doping in region 1 of the annular fiber core. center It is the refractive index at the location of the highest concentration of silicon dioxide germanium doping in region 1 of the annular fiber core.

[0014] The material of the optical fiber body is selected as follows: the circular region 2 and the outer optical fiber cladding 3 are made of silicon dioxide, and the annular region is made of germanium-doped silicon dioxide with a gradually varying germanium doping concentration. The maximum germanium doping molar concentration is 11 mol%, and the distance between the location of the maximum germanium doping concentration in the annular core 1 region and the center of the optical fiber is 25 μm.

[0015] The overall radius of the optical fiber body is 62.5 μm, the radius of the circular region 2 ranges from 20 μm to 55 μm, the thickness of the annular core 1 region is 2 μm to 4 μm, and the outer optical fiber cladding 3 is the part of the optical fiber excluding the circular region 2 and the annular core 1 region.

[0016] The circular region 2 has a refractive index range of 1-1.444 at 1550 nm, the annular fiber core 1 has a maximum refractive index range of 1.457-1.469 at 1550 nm, and the outer fiber cladding 3 has a refractive index range of 1-1.444 at 1550 nm.

[0017] A trench region 4 can be provided between the annular fiber core 1 region and the outer fiber cladding 3 region. When the fiber body is provided with a trench region 4, the fiber body material is selected as follows:

[0018] Silica is used as the cladding material, germanium-doped silica is used as the high refractive index region material, and fluorine-doped silica is used as the trench material (corresponding to variant structure 1). From the inside to the outside, the material at the circular region 2 is silica, the material at the annular core 1 region is gradually doped germanium-doped silica, the material at the trench region 4 is gradually doped fluorine-doped silica, the material at the outer fiber cladding 3 region is silica, and the trench region 4 is an annular region with a refractive index lower than that of silica. The trench region 4 made of fluorine-doped silica can be doped by the modified chemical vapor deposition method.

[0019] The refractive indices of the circular region 2, annular core 1 region, trench region 4, and outer fiber cladding 3 from the inside to the outside are n1, n2, n3, and n4 respectively.

[0020] The annular core 1 region is a circular ring with a gradually changing refractive index, and its refractive index is greater than that of other regions. The refractive index distribution satisfies n3≤n1≤n4<n2. Under the condition of satisfying the above refractive index distribution, the optical fiber material can be silica, germanium-doped silica, or fluorine-doped silica.

[0021] When there are multiple optical fiber bodies forming a multi-core structure, the multiple optical fiber bodies are arranged in a tight hexagonal structure. The distance and arrangement layers between the multiple optical fiber bodies in the multi-core structure can be appropriately adjusted according to the final radius of the multi-core structure optical fiber.

[0022] The optical fiber is used to suppress the dispersion characteristics of four-wave mixing and to suppress the nonlinear effect.

[0023] The beneficial effects of the present invention:

[0024] In this structure of the present invention, multiple orbital angular momentum modes are restricted to transmit in the annular core 1 region, thereby providing a larger effective mode area to reduce the nonlinear effect. Under certain refractive index contrast and structural parameters, the waveguide dispersion characteristics and material dispersion characteristics of the optical fiber can provide lower dispersion for multiple orbital angular momentum modes.

[0025] The refractive index range of the circular region 2 at 1550 nm is 1 - 1.444, the maximum refractive index range of the annular core 1 region at 1550 nm is: 1.457 - 1.469, the refractive index coefficient α range of the annular core 1 region is 1 - 8, the refractive index range of the outer fiber cladding 3 outside the ring at 1550 nm is 1 - 1.444, the radius range of the circular region 2 is 20 μm - 55 μm, and the thickness of the annular core 1 region is 2 μm to 4 μm. Within the range of the above parameters, the dispersion of multiple orbital angular momentum modes transmitted in the optical fiber design of the present invention can be controlled within a lower range, meeting the standard of non-zero dispersion shifted optical fiber, effectively reducing the dispersion effect continuously accumulated by each mode during transmission, and at the same time suppressing nonlinear effects such as four-wave mixing.

[0026] The optical fiber of the present invention has dispersion characteristics that can meet the requirements for suppressing four-wave mixing. Attached Figure Description

[0027] Figure 1 These are schematic diagrams of the cross-sectional structure and refractive index distribution of the optical fiber under the single-core structure of the present invention, as well as a schematic diagram of the multi-core structure.

[0028] Figure 2 In the optical fiber structure of this invention, when R0 = 25 μm and w half OAM corresponding to fiber structure parameters of 1μm, α=2, mf=11mol%. 1,1 OAM 2,1 OAM 3,1 OAM 4,1 OAM 5,1 OAM 6,1 OAM 7,1 The dispersion of the pattern varies with wavelength.

[0029] Figure 3 In the optical fiber structure of this invention, when R0 = 25 μm and w half OAM under the structural parameters of 1μm and α=2 fiber, with different germanium doping concentrations (mf) in region 1 of the ring core, 1,1 OAM 2,1 OAM 3,1 OAM 4,1 OAM 5,1 OAM 6,1 OAM 7,1 Thermograph of the dispersion value of the mode at 1550nm.

[0030] Figure 4 In the optical fiber structure of this invention, when R0 = 25 μm and w half OAM under different refractive index distribution parameters (α) with fiber structure parameters of 1 μm and mf = 11 mol%. 1,1 OAM 2,1 OAM 3,1 OAM 4,1 OAM 5,1 OAM 6,1 OAM 7,1 Thermograph of the dispersion value of the mode at 1550nm.

[0031] Figure 5 In the optical fiber structure of this invention, in w half OAM at the location (R0) of the maximum germanium doping concentration in region 1 of the ring core under optical fiber structural parameters of 1 μm, α = 2, and mf = 11 mol%. 1,1 OAM 2,1 OAM3,1 OAM 4,1 OAM 5,1 OAM 6,1 OAM 7,1 Thermograph of the dispersion value of the mode at 1550nm.

[0032] Figure 6 In the fiber structure of this invention, under the fiber structure parameters of R0 = 25 μm, α = 2, and mf = 11 mol%, the half-width (w) of different annular cores is... half OAM 1,1 OAM 2,1 OAM 3,1 OAM 4,1 OAM 5,1 OAM 6,1 OAM 7,1 Thermograph of the dispersion value of the mode at 1550nm.

[0033] Figure 7 In the optical fiber structure of this invention, 11 mol% germanium-doped silicon dioxide is used as the fiber core, R0 = 55 μm, w half OAM corresponding to fiber structure parameters of 1μm and α=2 1,1 OAM 2,1 OAM 3,1 OAM 4,1 OAM 5,1 OAM 6,1 OAM 7,1 OAM 8,1 OAM 9,1 OAM 10,1 OAM 11,1 OAM 12,1 OAM 13,1 OAM 14,1 OAM 15,1 The dispersion of the pattern varies with wavelength.

[0034] Figure 8 In the optical fiber structure of this invention, 11 mol% germanium-doped silicon dioxide is used as the fiber core, R0 = 55 μm, w half OAM corresponding to fiber structure parameters of 1μm and α=2 1,1 OAM 2,1 OAM 4,1 OAM 8,1 OAM 15,1 The effective mode field area of ​​the mode varies with wavelength.

[0035] Figure 9In the optical fiber structure of the present invention, germanium-doped silica with a concentration of 11 mol% is used as the core, R0 = 55 μm, w half = 1 μm, α = 2, corresponding to OAM under the optical fiber structure parameters 1,1 、OAM 2,1 、OAM 4,1 、OAM 8,1 、、OAM 15,1 The variation of the nonlinear coefficient of the mode with wavelength.

[0036] Figure 10 It is a schematic diagram of the cross-sectional structure and refractive index distribution of the optical fiber under the single-core variant structure of the present invention, as well as a schematic diagram of the multi-core variant structure. Detailed implementation mode

[0037] The present invention will be further described in detail below with reference to the accompanying drawings.

[0038] The refractive index-graded non-zero dispersion shifted optical fiber based on the orbital angular momentum mode of the present invention is as Figure 1 shown. In the case of a single-core structure, the optical fiber of the present invention includes a circular region 2, an annular core 1 region, and an outer optical fiber cladding 3 from the inside out, with refractive indices of n1, n2, and n3 respectively. The annular core 1 region is a ring with a gradually changing refractive index, and its refractive index is greater than other regions, and the refractive index distribution satisfies n1 ≤ n3 < n2. The material of the optical fiber body can be materials such as silica and germanium-doped silica under the condition of satisfying the above refractive index distribution.

[0039] The material of the optical fiber body is a combination of silica and germanium-doped silica materials under the condition of satisfying the above refractive index distribution, and the gradually changing refractive index n2 of the annular core 1 region satisfies the following equation:

[0040]

[0041] where r is the distance from the center of the optical fiber, α is the refractive index distribution parameter, w half is the half-width of the annular core 1 region, R0 is the position of the maximum concentration of germanium doping in silica in the annular core 1 region, and n center is the refractive index at the position of the maximum concentration of germanium doping in silica in the annular core 1 region.

[0042] In the present invention, the circles and rings referred to in the circular region 2 and the annular core 1 region both refer to their cross-sectional shapes perpendicular to the axial direction. That is, the annular core 1 region means that the cross-section of the core is annular, and the circular region 2 means that it is filled in the inner ring of the core and has a circular cross-section. In the present invention, the circular region 2 should be in close contact with the inner ring of the core.

[0043] In this invention, the term "gradual refractive index" refers to the fact that the refractive index of the annular core 1 region in the optical fiber body is continuously changing. The refractive index values ​​at different locations are continuously distributed according to the formula for the gradual refractive index n2 of the annular core 1 region, which varies with the distance r from the center of the optical fiber in the location attribute.

[0044] In this invention, non-zero dispersion-shifted fiber refers to the type of fiber defined in the ITU-T G.655 international standard developed by the ITU-T for ITU Telecommunication Standardization Sector, which has non-zero dispersion within the 1530nm to 1565nm operating window and maintains a suitable dispersion system value capable of suppressing four-wave mixing.

[0045] In this example, the circular region 2 and the outer fiber cladding 3 are made of silicon dioxide, and the annular core 1 region is made of germanium-doped silicon dioxide with a gradually varying germanium doping concentration. The maximum germanium doping molar concentration is 11 mol%, and the distance between the location of the maximum germanium doping concentration in the annular core 1 region and the center of the fiber is 25 μm. The above cross-sectional structure remains unchanged along the length of the fiber. In the case of a multi-core structure, the fiber of the present invention can contain multiple identical single-core structures. Figure 2 For R0 = 25 μm, w half OAM under fiber structure parameters of 1μm, α=2, mf=11mol% 1,1 OAM 2,1 OAM 3,1 OAM 4,1 OAM 5,1 OAM 6,1 OAM 7,1 The dispersion of the modes varies with wavelength. As shown in the figure, the dispersion of the seven orbital angular momentum modes in the optical fiber of this invention remains between 0 ps / nm / km and 10 ps / nm / km in the C-band (1530nm-1565nm), which is significant for OAM. 1,1 To OAM 7,1 This dispersion characteristic meets the ITU-T G.655.C standard for non-zero dispersion shifted optical fibers.

[0046] The orbital angular momentum (OAM) mode is a unique distribution of light propagating in an optical fiber. It features a phase singularity at its center, where the light intensity is zero, and the phase of the light wave exhibits a helical distribution perpendicular to the propagation direction. Also known as phase vortex light, the orbital angular momentum mode can be represented as OAM. l,mWhere l (l=±1,±2,±3…) is the topological charge number, which also corresponds to the number of phase jumps of the light wave perpendicular to the propagation direction, and m is the radial order of the intensity distribution of the orbital angular momentum modes in the radial direction. The orbital angular momentum modes propagating in an optical fiber can be composed of the fiber's vector eigenmodes through the following relationship:

[0047]

[0048]

[0049] For example, when the topological charge number is 1, the orbital angular momentum mode is... and The two modes are linearly combined. Orbital angular momentum modes can serve as a carrier of optical information, distinct from phase and polarization modes. This means that orbital angular momentum modes offer a new dimension for information transmission and expand new channels. Orbital angular momentum modes with different topological charge numbers can be used as different communication channels and can be applied to mode-division multiplexing (MDF) technology.

[0050] Figures 3 to 6 The parameters to be adjusted are: maximum germanium doping concentration (mf) in the annular core 1 region of the optical fiber of the present invention; refractive index distribution parameter (α); location of maximum germanium doping concentration (R0) in the annular core 1 region; and half-width (w) of the annular core 1 region. half When ), it corresponds to OAM 1,1 To OAM 7,1 The dispersion heatmap of the modes at 1550 nm. The figure shows that various parameter combinations of the fiber of this invention can provide low dispersion characteristics at 1550 nm for multiple orbital angular momentum modes, meeting the requirements for suppressing four-wave mixing.

[0051] Figure 7 R0 = 55 μm, w half OAM under fiber structure parameters of 1μm, α=2, mf=11mol% 1,1 OAM 2,1 OAM 3,1 OAM 4,1 OAM 5,1 OAM 6,1 OAM 7,1 OAM 8,1 OAM 9,1 OAM 10,1 OAM 11,1 OAM 12,1 OAM 13,1 OAM 14,1 OAM 15,1The dispersion of the modes varies with wavelength. As shown in the figure, the dispersion of the fifteen orbital angular momentum modes in the optical fiber of this invention remains between 0 ps / nm / km and 10 ps / nm / km in the C-band (1530nm-1565nm), which is significant for OAM. 1,1 To OAM 15,1 This dispersion characteristic meets the ITU-T G.655.C standard for non-zero dispersion shifted fibers, providing the smallest possible positive dispersion while avoiding zero dispersion, thereby avoiding nonlinear effects such as four-wave mixing.

[0052] Figure 8 R0 = 55 μm, w half OAM under fiber structure parameters of 1μm, α=2, mf=11mol% 1,1 OAM 2,1 OAM 4,1 OAM 8,1 OAM 15,1 The effective mode field area of ​​the mode varies with wavelength. The figure shows the orbital angular momentum mode (OAM) in the optical fiber of this invention. 1,1 To OAM 15,1 The effective mode area in the C-band (1530nm-1565nm) is all around 1350mm². 2 above.

[0053] Figure 9 R0 = 55 μm, w half OAM under fiber structure parameters of 1μm, α=2, mf=11mol% 1,1 OAM 2,1 OAM 4,1 OAM 8,1 OAM 15,1 The nonlinear coefficients of the mode vary with wavelength. The figure shows the orbital angular momentum mode (OAM) in the optical fiber of this invention. 1,1 To OAM 15,1 The nonlinear coefficients in the C-band (1530nm-1565nm) are all within 9×10⁻⁶. -2 The following demonstrates that the fiber optic design of this invention effectively suppresses nonlinear effects.

[0054] Figure 10This is a variant of the refractive index-graded non-zero dispersion shifted fiber based on orbital angular momentum modes. In the case of a single-core structure, the fiber of the present invention includes a circular region 2, an annular core 1 region, a trench region 4, and an outer fiber cladding 3 from the inside out, with refractive indices of n1, n2, n3, and n4 respectively. The annular core 1 region is a ring with a gradually changing refractive index, and its refractive index is greater than other regions. The refractive index distribution satisfies n3 ≤ n1 ≤ n4 < n2. The fiber material can be silica, germanium-doped silica, fluorine-doped silica, etc. under the condition of the above refractive index distribution. The above cross-sectional structure remains unchanged along the length direction of the fiber; in the case of a multi-core structure, the variant of the fiber of the present invention can include multiple identical single-core variant structures.

[0055] Working principle of the present invention:

[0056] By adjusting the geometric parameters of the gradually changing high refractive index region and selecting the doping materials used in the present invention, the waveguide structure dispersion and material dispersion of multiple orbital angular momentum modes transmitted within the fiber design of the present invention are both controlled within a relatively low range, meeting the standards of non-zero dispersion shifted fibers, and can effectively reduce the dispersion effect accumulated by each mode with the increase of transmission distance in a multi-mode fiber communication system.

Claims

1. A graded-index non-zero dispersion-shifted optical fiber based on orbital angular momentum mode, characterized in that it includes an optical fiber body, the optical fiber body including an annular core (1) and an optical fiber cladding surrounding the annular core (1), the optical fiber cladding including a circular region (2) located inside the annular core (1) and an outer optical fiber cladding (3) located outside the annular core (1). The refractive index n1 of the circular region (2), the refractive index n2 of the annular fiber core (1) region, and the refractive index n3 of the outer fiber cladding (3) are described. The refractive index n1 of the circular region (2), the refractive index n2 of the annular fiber core (1) region, and the refractive index n3 of the outer fiber cladding (3) satisfy the condition that the values ​​of n1 and n3 are less than the value of n2. The material of the optical fiber body is selected as follows: the circular region (2) and the outer optical fiber cladding (3) are made of silicon dioxide, and the annular core (1) region is made of germanium-doped silicon dioxide with a gradually varying germanium doping concentration, with a maximum germanium doping molar concentration of 11 mol%. The overall radius of the optical fiber body is 62.5 μm, the radius of the circular region (2) ranges from 20 μm to 55 μm, the thickness of the annular core (1) region is 2 μm to 4 μm, and the outer optical fiber cladding (3) is the part of the optical fiber body excluding the circular region (2) and the annular core (1) region. The circular region (2) has a refractive index range of 1-1.444 at 1550 nm, and the annular core (1) region has a maximum refractive index range of: 1.457-1.469, the refractive index of the outer fiber cladding (3) is 1-1.444 in the range of 1550nm; The refractive index n2 of the annular fiber core (1) region is a gradually changing refractive index; the gradually changing refractive index within the annular fiber core (1) region is greater than that in other regions, and the refractive index distribution satisfies n1≤n3. <n2; The material of the optical fiber body is a combination of silicon dioxide and germanium-doped silicon dioxide, satisfying the above refractive index distribution. The graded refractive index n2 of the annular fiber core (1) region satisfies the following equation: in, r It is the distance from the center of the optical fiber. α It is the refractive index distribution parameter. w half It is half the width of the annular core (1) region. R 0 This is the location of the highest concentration of silicon dioxide germanium doping within the region of the annular fiber core (1). n center It is the refractive index at the location of the highest concentration of silicon dioxide germanium doping in the annular fiber core (1); when R 0=55μm w half =1μm、 α =2. Maximum concentration of germanium doping in the annular fiber core (1) region mf =11mol% OAM under fiber structure parameters 1,1 OAM 2,1 OAM 3,1 OAM 4,1 OAM 5,1 OAM 6,1 OAM 7,1 OAM 8,1 OAM 9,1 OAM 10,1 OAM 11,1 OAM 12,1 OAM 13,1 OAM 14,1 OAM 15,1 The dispersion of the modes varies with wavelength; the dispersion of the fifteen orbital angular momentum modes in the optical fiber in the C-band 1530nm-1565nm ranges from 0ps / nm / km to 10ps / nm / km.

2. A graded-index non-zero dispersion-shifted optical fiber based on orbital angular momentum mode as described in claim 1, characterized in that, When multiple optical fiber bodies are combined to form a multi-core structure, the multiple optical fiber bodies are arranged in a close hexagonal structure. The distance between the multiple optical fiber bodies and the number of arrangement layers within the multi-core structure can be appropriately adjusted according to the final radius of the multi-core structure optical fiber.

3. A graded-index non-zero dispersion-shifted optical fiber based on orbital angular momentum mode as described in claim 1, characterized in that, The optical fiber is used to suppress the dispersion characteristics of four-wave mixing and to suppress nonlinear effects.

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