Low-loss low-crosstalk super-mode fiber

Abstract

The invention provides a low-loss and low-crosstalk super-mode optical fiber. The optical fiber is composed of a pure silicon dioxide elliptical fiber core with step refractive index distribution, a refractive index groove area and a wrapping layer. According to the invention, four-super-mode operation is realized, space super-mode degeneracy is broken, large refractive index difference between super-modes is realized, and the method has the advantages of low loss and low crosstalk, and can be applied to MIMO-FREE scenes.

Description

Technical Field

[0001] The present invention provides a low-loss and low-crosstalk supermode optical fiber, which can be applied to new generation information technology fields such as mode division multiplexing. Background Art

[0002] With the rapid development of various communication services, traditional single-mode optical fiber is limited by the nonlinear Shannon limit and can no longer meet the needs of more communication services [ELLIS AD, ZHAO J, COTTER D. Approaching the Non-Linear Shannon Limit [J]. Journal of Lightwave Technology, 2010, 28 (4): 423-433]. The mode division multiplexing technology based on few-mode optical fiber has doubled the transmission capacity and spectrum efficiency of single-mode optical fiber, becoming a hot topic in the current optical fiber communication field. Few-mode optical fiber is the transmission carrier of information in optical fiber communication system. How to improve the transmission performance of optical fiber and reduce the loss and crosstalk of few-mode optical fiber is an urgent problem to be solved in optical transmission technology.

[0003] In view of the limited capacity of single-mode optical fiber, the traditional round-core few-mode optical fiber currently proposed is constantly breaking through the transmission capacity or spectrum efficiency of optical fiber [BEPPU S, SOMA D, SΜMITA S, et al. 402.7-Tb / s MDM-WDM Transmission over Weakly Coupled 10-Mode Fiber Using Rate-Adaptive PS-16QAM Signals [J]. Journal of Lightwave Technology, 2020, 38: 2835-2841; RADEMACHER G, PUTT NAM BJ, RS, et al. 10.66Peta-Bit / s Transmission over a 38-Core-Three-Mode Fiber. In Optical Fiber Communication Conference (OFC), OSA Technical Digest (Optical Society of America), 2020, Paper Th3H.1; Zhang Q, Han W, Xiong Z, et al. 3×34Gb / sPDM-QPSK signal mode division multiplexing experiment based on fewmode fiber [J]. Optical Communication Technology, 2022, 46 (1): 77-80], but the crosstalk and loss between these circular core few-mode fiber modes still exist. The crosstalk between modes requires the use of multiple-input multiple-output digital signal processing MIMO-DSP. For short-distance communication, the more modes there are, the more serious the complexity, computational complexity, and cost of MIMO-DSP. The loss of optical fiber will affect the transmission distance of the optical communication system. The loss of optical fiber is an important parameter that determines the performance of the optical fiber communication system. In order to solve the crosstalk and loss in optical fiber, elliptical core few-mode fiber, elliptical ring core few-mode fiber and panda-type few-mode fiber are proposed, [PARMIGIANI F, JUNG Y, -NIELSEN L,et al.Elliptical Core Few ModeFibers for Multiple-Input Multiple Output-Free Space Division MultiplexingTransmission[J].IEEE Photonics Technology Letters,2017,29(21):1764-1767;SONGW,CHEN H,WANG J,et al.Panda Type Elliptical Ring Core Few-Mode Fiber[J].Optical Fiber Technology,2020,60:1-5;YANGT,ZHANG H,XI L,et al.Design of aNovel Bow-Tie Polarization Ring-Core Few-ModeFiber for MIMO-Free MDMSystem.In 26th Optoelectronics and Communications Conference,P.Alexander Wai,H.Tam,and C.Yu,eds.,OSA Technical Digest,2021,Paper JS3C.3;WANG L,NEJAD R M,CORSI A,et al.Linearly Polarized Vector Modes:Enabling MIMO-Free Mode-Divisionmultiplexing[J].Optics Express,2017,25(10):11736-11748;;YAN H,LI S,XIE Z,et al.Design of PAND Ring-Core Fiber with 10 Polarization-MaintainingModes[J].Photonics Research,2017,5(1):1-5;CAO Y,ZHAO Y,YU X,et al.Design andCharacterization of 16-Mode PANDA Polarization-Maintaining Few-Mode Ring-CoreFiber for Spatial Division Multiplexing[J].Optical Engineering, 2017, 56:116102] was proposed and demonstrated to have the ability to separate spatial modes and reduce mode coupling.

[0004] Although the above-mentioned elliptical core few-mode fibers, elliptical ring core few-mode fibers and panda-type few-mode fibers have achieved mode separation to a certain extent, the crosstalk between modes is still large and has large intrinsic losses; if the receiving end compensates through digital signal processing, it will still increase the complexity, calculation amount, cost, etc. of the short-distance transmission system. In view of the above problems, and taking into account the advantages of the high mode density of the supermode, the present invention proposes a new type of low-loss, low-crosstalk supermode fiber, which utilizes the strong coupling effect between the four fiber cores and the elliptical core structure, and quadruples the transmission capacity and transmission spectrum efficiency of a single optical fiber, and has lower bending loss and intrinsic loss, which can better separate spatial modes and reduce crosstalk between modes, and is applied to MIMO-FREE operation without multiple-input and multiple-output. Summary of the invention

[0005] With the support of the National Natural Science Foundation of China (No. 61671227 and 61431009), the Natural Science Foundation of Shandong Province (ZR2011FM015), and the special funds for the "Taishan Scholars" construction project, this patent application proposes a low-loss and low-crosstalk supermode optical fiber, which combines the advantages of pure silica elliptical core, step refractive index distribution and groove assistance, breaks the degeneracy of spatial supermodes, eliminates complex MIMO-DSP processing, and realizes MIMO-FREE applications with low loss, low crosstalk and low bending loss, providing important support for in-depth research in the fields of fiber optics, fiber-optic communications, fiber-optic wireless access, optical information processing and new generation information technology.

[0006] The technical solution adopted by the present invention to solve the technical problem is:

[0007] The present invention provides a low-loss and low-crosstalk supermode optical fiber; the optical fiber is composed of four pure silica elliptical cores with a step refractive index distribution, an auxiliary elliptical ring refractive index groove and a cladding; the horizontal radius (semi-major axis) of each elliptical core is a x =2.25μm, vertical radius (semi-minor axis) is a y =1.5μm, ellipticity ρ = a x / a y =1.5; the outer part of the four elliptical cores is the groove area of ​​the elliptical ring structure, and the inner elliptical horizontal radius is R 1x =14.4μm, vertical radius is R 1y =9.6μm; the horizontal radius of the outer ellipse is R 2x =23.4μm, vertical radius is R 2y=15.6μm, the rest is cladding, and the outer cladding radius is R=62.5μm; the center coordinates of the four cores are and The refractive indices of the pure silica core, the refractive index trench region, and the cladding are n 1 =1.4440, n 2 =1.4198, n 3 =1.4220; the effective refractive indices of the four supermodes LP01, LP11a, LP11b and LP21b are 1.436, 1.431, 1.429 and 1.425 respectively, and the large effective refractive index difference between the supermodes realizes low mode crosstalk; the spatial mode degeneracy of the supermodes is broken, and four non-degenerate supermode operations with low intrinsic loss, low crosstalk and low bending loss are realized, thereby eliminating complex MIMO-DSP processing and realizing good transmission of MIMO-FREE applications; the mode field characteristics of the supermode in the optical fiber can be changed by changing the refractive index of the core and cladding or the size, position and refractive index distribution of the cladding.

[0008] The beneficial effects of the invention are as follows:

[0009] 1. The four-elliptical core fiber forms a supermode, breaking the supermode spatial mode degeneracy, eliminating complex MIMO-DSP processing, achieving good transmission of MIMO-FREE applications, and further improving fiber transmission performance.

[0010] 2. The optical fiber combines a pure silica core and a large effective refractive index difference distribution to achieve low loss and low mode crosstalk, providing important support for in-depth research in the fields of fiber optics, fiber optic communications, fiber optic wireless access, optical information processing, and new generation information technology.

[0011] 3. The mode field characteristics of the non-degenerate supermode in the optical fiber can be changed by changing the refractive index of the core, cladding and trench region, the size, position and refractive index distribution of the cladding. BRIEF DESCRIPTION OF THE DRAWINGS

[0012] Figure 1 This is a schematic diagram of the cross-section of a low-loss, low-crosstalk supermode optical fiber of this technology; the optical fiber consists of a pure silica elliptical core with a step refractive index distribution (the horizontal shaded part), a trench region (the oblique shaded circular ring area outside the core) and a cladding (the white part).

[0013] Figure 2 The X-polarized electric field distribution of four supermodes, LP01, LP11a, LP11b and LP21b, at a wavelength of 1.55 μm is given. The equipotential lines in the figure represent the strength of the incident optical electric field. The greater the density, the stronger the electric field.

[0014] Figure 3The effective refractive index of the four supermodes varies with the input wavelength. The solid lines with squares, asterisks, diamonds, and circles are the variations of the LP01, LP11a, LP11b, and LP21b modes, respectively.

[0015] Figure 4 The variation of DMGD of LP21b, LP11b and LP11a supermodes with incident wavelength is shown. The solid lines with circles, asterisks and triangles in the figure represent the variation of DMGD of LP21b, LP11b and LP11a modes respectively.

[0016] Figure 5 The graph shows how the intrinsic loss of the four supermodes varies with the input wavelength. The solid lines with squares, asterisks, circles and triangles are the variations of the intrinsic loss of the LP01, LP11a, LP11b and LP21b modes, respectively.

[0017] Figure 6 The dispersion of LP01, LP11a, LP11b and LP21b supermodes varies with the incident wavelength. The solid lines with circles, asterisks and triangles in the figure represent the variation of material dispersion, waveguide dispersion and total dispersion of each supermode, respectively.

[0018] Figure 7 The bending loss of the LP21b supermode varies with the bending radius. The solid lines with squares, crosses, circles, diamonds, and triangles in the figure represent the variation of the bending loss with the bending radius when the angle θ between the major axis of the ellipse and the X-axis is 0°, 30°, 45°, 60°, and 90°, respectively. DETAILED DESCRIPTION

[0019] The technical solution of the present invention is described in detail below in conjunction with the embodiments and drawings, but the protection scope is not limited thereto.

[0020] Example 1 Figure 1 This is a schematic diagram of a low-loss, low-crosstalk supermode optical fiber in this patent application. The optical fiber consists of a pure silica elliptical core with a step-index refractive index distribution, an auxiliary refractive index groove, and a cladding; the horizontal radius of each elliptical core is and the horizontal radius (semi-major axis) is a x =2.25μm, vertical radius (semi-minor axis) is a y =1.5μm, ellipticity ρ = a x / a y =1.5. The outer part of the four elliptical cores is the groove area of ​​the elliptical ring structure, and the inner ellipse horizontal radius is R 1x =14.4μm, vertical radius is R 1y =9.6μm; the horizontal radius of the outer ellipse is R 2x =23.4μm, vertical radius is R 2y=15.6μm, the rest is the cladding (the white part outside the groove), and the outer cladding radius is R=62.5μm. The center coordinates of the four cores are and The refractive indices of the pure silica core, the refractive index trench region, and the cladding are n 1 =1.4440, n 2 =1.4198, n 3 =1.4220; the effective refractive indices of the four supermodes LP01, LP11a, LP11b and LP21b are 1.436, 1.431, 1.429 and 1.425 respectively, and the large effective refractive index difference between the supermodes realizes low mode crosstalk; the spatial mode degeneracy of the supermodes is broken, and four non-degenerate supermode operations with low intrinsic loss, low crosstalk and low bending loss are realized, thereby eliminating complex MIMO-DSP processing and realizing good transmission of MIMO-FREE applications; the mode field characteristics of the supermode in the optical fiber can be changed by changing the refractive index of the core and cladding or the size, position and refractive index distribution of the cladding.

[0021] Figure 2 The electric field distribution of four supermode X-polarizations, LP01, LP11a, LP11b and LP21b, at a wavelength of 1.55μm is given. The potential lines in the figure represent the strength of the incident light electric field. The greater the density, the stronger the electric field. In the case of fewer modes, since the mode distribution of the elliptical core few-mode fiber is similar to that of the traditional circular core few-mode fiber (CFMF), the mode symbols LP01, LP11a, LP11b and LP21b of CFMF are still used to represent the four modes corresponding to our supermode fiber.

[0022] Figure 3 The effective refractive index of the four supermodes of the supermode fiber varies with the wavelength of the incident light. The solid lines with squares, asterisks, diamonds and circles in the figure represent the changes in the effective refractive index of the LP01, LP11a, LP11b and LP21b supermodes, respectively. Figure 3 It can be seen that the effective refractive index of the four supermodes decreases with the increase of the wavelength of the incident light, and the change of the effective refractive index is slow; for a given incident wavelength, the effective refractive index of the LP01 supermode is the largest, and the effective refractive index of the LP01, LP11a, LP11b, and LP21b supermodes decreases in turn; the large effective refractive index difference between the supermodes achieves low mode crosstalk.

[0023] Figure 4The variation of DMGD of LP11a, LP11b and LP21b supermodes with input wavelength is shown. The solid lines with circles, asterisks and triangles represent the variation of DMGD of LP21b, LP11b and LP11a supermodes, respectively. In the wavelength range of 1.3μm to 1.59μm, the DMGD value of the LP21b supermode is the largest, and the DMGD value of the LP11a supermode is the smallest; in the wavelength range of 1.59μm to 1.64μm, the DMGD value of the LP11b supermode is the largest, the DMGD value of the LP11a supermode is the smallest, and the DMGD of the three supermodes decreases with the increase of the input wavelength; in the wavelength range of 1.64μm to 1.7μm, the DMGD value of the LP11b supermode is the largest, the DMGD value of the LP21b supermode is the smallest, and the DMGD of the three supermodes decreases with the increase of the input wavelength; when the wavelength is 1.55μm, the DMGD of the LP11a, LP11b and LP21b supermodes are 11.37ps / m, 15ps / m and 16.34ps / m, respectively, with a large differential mode group delay.

[0024] Figure 5 It can be obtained that the intrinsic loss of each supermode in the supermode fiber we proposed in the C-band is small, and the intrinsic losses of LP01, LP11a, LP11b, and LP21b supermodes increase in turn; the intrinsic loss of the proposed optical fiber is significantly smaller than the intrinsic loss of the elliptical four-core germanium-doped equivalent few-mode fiber.

[0025] Figure 6The figure shows how the dispersion of LP01, LP11a, LP11b and LP21b supermodes changes with the incident wavelength. The solid lines with circles, asterisks and triangles in the figure represent the changes in the material dispersion, waveguide dispersion and total dispersion of each spatial supermode. It can be seen from the figure that in the wavelength range of 1.3um to 1.7um, the waveguide dispersion of the LP01 supermode changes relatively smoothly, and the material dispersion and total dispersion of the LP01 supermode increase with the increase of the incident wavelength. In the C-band (1.53um to 1.565um) wavelength range, the total dispersion of the LP01 supermode gradually increases from 17.40ps / (nm·km) to 19.66ps / (nm·km). In the wavelength range of 1.3um to 1.7um, the waveguide dispersion of the LP11a supermode gradually decreases, and the material dispersion and total dispersion of the LP11a supermode increase with the increase of the incident wavelength. In the C-band wavelength range, the total dispersion of the LP11a supermode gradually increases from 14.57ps / (nm·km) to 15.42ps / (nm·km). In the wavelength range of 1.3um to 1.7um, the waveguide dispersion of the LP11b gradually decreases, the material dispersion gradually increases, and the total dispersion changes relatively smoothly; in the C-band wavelength range, the total dispersion of the LP11b supermode gradually decreases from 5.08ps / (nm·km) to 4.36ps / (nm·km). In the wavelength range of 1.3um to 1.7um, the waveguide dispersion and total color of the LP21b supermode gradually decrease, and the material dispersion gradually increases; in the C-band wavelength range, the total dispersion of the LP21b supermode gradually decreases from -20.79ps / (nm·km) to -28.15ps / (nm·km).

[0026] Figure 7 The figure shows how the bending loss of the LP21b supermode changes with the bending radius. The solid lines with squares, crosses, circles, diamonds and triangles in the figure respectively represent how the bending loss changes with the bending radius when the angle θ between the major axis of the ellipse and the X-axis is 0°, 30°, 45°, 60° and 90°. It can be seen from the figure that the bending loss of the LP21b supermode gradually decreases with the increase of the bending radius at 0°, 30°, 45°, 60° and 90°; as the angle θ increases, the bending loss of the LP21b supermode gradually decreases. The bending losses of other supermodes are smaller.

[0027] In summary, the proposed optical fiber realizes the operation of four non-degenerate supermodes with low intrinsic loss, low crosstalk and low bending loss. It should be pointed out that the specific implementation is only a more representative example of the present invention. Obviously, the technical solution of the present invention is not limited to the above-mentioned embodiment, and there are many variations. Those skilled in the art who can obtain the information clearly disclosed by the present invention or obtained without objection based on the written description of the document should be considered as the scope of protection of this patent.

Claims

1. A low-loss, low-crosstalk supermode optical fiber; Features: The optical fiber consists of four pure silica elliptical cores with step refractive index distribution, auxiliary elliptical ring refractive index grooves and cladding; the horizontal radius (major semi-axis) of each elliptical core is a x =2.25μm, vertical radius (semi-minor axis) is a y =1.5μm, ellipticity ρ = a x / a y =1.5; the outer part of the four elliptical cores is the groove area of ​​the elliptical ring structure, and the inner elliptical horizontal radius is R 1x =14.4μm, vertical radius is R 1y =9.6μm; the horizontal radius of the outer ellipse is R 2x =23.4μm, vertical radius is R 2y =15.6μm, the rest is cladding, and the outer cladding radius is R=62.5μm; the center coordinates of the four cores are and The refractive indices of the pure silica core, the refractive index trench region, and the cladding are n 1 =1.4440, n 2 =1.4198, n 3 =1.4220; the effective refractive indices of the four supermodes LP01, LP11a, LP11b and LP21b are 1.436, 1.431, 1.429 and 1.425 respectively; In the C-band range, the DMGD value of the LP21b supermode is the largest, and the DMGD value of the LP11a supermode is the smallest; at a wavelength of 1.55μm, the DMGDs of the LP11a, LP11b and LP21b supermodes are 11.37ps / m, 15ps / m and 16.34ps / m, respectively; in the C-band range, the total dispersion of the LP01 supermode gradually increases from 17.40ps / (nm·km) to 19.66ps / (nm·km), the total dispersion of the LP11b supermode gradually decreases from 5.08ps / (nm·km) to 4.36ps / (nm·km), and the total dispersion of the LP21b supermode gradually decreases from -20.79ps / (nm·km) to -28.15ps / (nm·km).

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