Small-size bend-insensitive low-group-delay multimode optical fiber and method of manufacture

Abstract

The application discloses a small-size bending-insensitive low-group-time-delay multimode optical fiber and a preparation method thereof. The multimode optical fiber comprises, from inside to outside, a core layer, a transition layer, a platform layer, an isolation layer, a third sunken cladding layer, a second sunken cladding layer, a first sunken cladding layer and an outer cladding layer. The relative refractive index difference of the transition layer is -0.04% to -0.03%, the relative refractive index difference of the platform layer is -0.04% to -0.03%, the relative refractive index difference of the isolation layer is -0.035% to -0.03%, the relative refractive index difference of the third sunken cladding layer is -0.3% to -0.2%, the relative refractive index difference of the second sunken cladding layer is -0.8% to -0.4%, and the relative refractive index difference of the first sunken cladding layer is -0.3% to -0.2%. Through reasonable design of the fiber structure and a doping system, the application realizes transmission within ten modes, reduces fiber attenuation and group time delay, and enhances the bending loss resistance of the fiber to long and short wavelengths.

Description

TECHNICAL FIELD

[0001] The application belongs to the technical field of optical communication, and particularly relates to a small-size bend-insensitive low group delay multimode optical fiber and a preparation method thereof. BACKGROUND

[0002] With the rapid development of various communication services, the traditional single-mode optical fiber has been difficult to meet the demand of more communication services due to the limitation of the nonlinear Shannon limit, and therefore, it is very urgent to develop a new information transmission dimension to meet the increasing demand of communication capacity. As a promising method to improve the capacity of optical fiber communication system, space division multiplexing has attracted widespread attention. Space division multiplexing includes mode division multiplexing (MDM) and core division multiplexing. Among them, mode division multiplexing technology is a commonly used method to expand the channel capacity of a single optical fiber. This technology usually couples multiple transmission modes in a single optical fiber to increase the number of channels and complete the expansion of communication capacity. The medium of this signal transmission mode is a multimode optical fiber that allows multiple fiber modes to transmit simultaneously, and this information transmission mode generally needs large-scale multiple input multiple output digital signal processing (MIMO DSP) to complete the entire process. In order to meet the need of the receiving end to receive these signals simultaneously, different mode optical signals transmitted by the Multiple in Multiple out method should have minimal DMD (Differential Mode Delay). Greater group delay will increase the complexity of the system receiving link. Therefore, reducing the group delay is a must in the design of multimode optical fiber. For mode division multiplexing, in the case of minimizing DMD, the number of modes increases the mutual crosstalk ability of high-order modes, thereby improving the group delay of the optical fiber. Therefore, in the design of mode division multiplexing optical fiber, a smaller number of optical fiber modes is usually used, thereby the low crosstalk ability of the optical fiber needs to be ensured.

[0003] In order to meet the requirement of minimizing group delay and low crosstalk between different modes of optical signals, the refractive index structure in accordance with Gaussian curve distribution is adopted in the design of the refractive index of the fiber core, and the dispersion of the high-order mode transmitted in the core is further constrained, so as to improve the information transmission efficiency in the mode division multiplexing system. However, due to the multiple modes of the multimode optical fiber, only a small part of the modes are used for transmitting optical signals, and the utilization rate of the modes and the inter-mode interference are serious. Therefore, in the design of the refractive index profile of the multimode optical fiber, a small-size core rod is generally adopted to reduce the number of modes of the optical fiber, so that the optical fiber has low crosstalk performance, and the group delay and transmission length of the optical fiber can be improved. At present, when the conventional multimode optical fiber is subjected to small-angle bending, the high-order mode transmitted near the edge of the core is easy to leak out, thereby causing signal packet loss. Generally, a method of designing a low refractive index region in the cladding of the optical fiber is adopted to limit the leakage of the high-order mode, so as to reduce the signal loss. In the profile design and process design of the small-size bending-insensitive multimode optical fiber, the main difficulty is how to ensure the low loss, low crosstalk, DMD performance and C-band transmission capacity of the optical fiber through relevant design.

[0004] In order to obtain a low group delay multimode optical fiber with good stability, a certain concentration of one or more of germanium, fluorine, chlorine and phosphorus is generally added in the core layer of the optical fiber preform rod to realize the desired refractive index distribution of the optical fiber core layer. The type and content of the doping elements in the core layer of the optical fiber will affect the material dispersion of the optical fiber, thereby affecting the wavelength sensitivity of the group delay of the optical fiber. SiO2 doped with germanium elements has high material dispersion. Therefore, the wavelength range corresponding to the low group delay performance of the existing multimode optical fiber with high germanium doping amount is very narrow, and a small change in the wavelength of the light source will cause a sharp decline in the group delay performance.

[0005] In the application in the wavelength dimension, the current mainstream optical fiber communication band is divided into five parts, namely O, E, S, C and L five bands, according to the transmission loss of quartz, and the wavelength range is 1260-1625nm. At present, the main research is concentrated in the C band.

[0006] The related research shows that for the multimode optical fiber, the diameter of the core layer and the maximum refractive index of the core layer will affect the number of modes transmitted by the optical fiber, and the amount of doping, the viscosity after doping and the core profile refractive index design will affect the DMD and C-band group delay of the optical fiber. Therefore, in order to make the multimode optical fiber have good bending insensitivity and low group delay performance, the doping system, viscosity ratio and profile structure of the multimode optical fiber need to be optimized. SUMMARY

[0007] In order to solve the technical problems existing in the prior art, the purpose of the present application is to provide a small-size bending-insensitive low group delay multimode optical fiber and a preparation method thereof.

[0008] To achieve the above object and achieve the above technical effect, the technical scheme adopted by the present application is as follows:

[0009] A small-size bending-insensitive low-group-time-delay multimode optical fiber, comprising a core layer, a transition layer, a platform layer, an isolation layer, a third sunken cladding layer, a second sunken cladding layer, a first sunken cladding layer and an outer cladding layer arranged in sequence from inside to outside, the refractive index profile of the core layer is parabolic, the distribution index alpha is 1.8-2.1, the maximum relative refractive index difference Delta1max of the core layer center is 0.35-0.45%, the relative refractive index difference Delta2 of the transition layer is -0.04%- -0.03%, the relative refractive index difference of the platform layer is -0.04%- -0.03%, the relative refractive index difference Delta3 of the isolation layer is -0.035%- -0.03%, the relative refractive index difference Delta4 of the third sunken cladding layer is -0.3%- -0.2%, the relative refractive index difference Delta5 of the second sunken cladding layer is -0.8%- -0.4%, and the relative refractive index difference of the first sunken cladding layer is -0.3%- -0.2%.

[0010] Further, the radius R2 of the transition layer is different from the radius R1 of the core layer by 0.2-0.5 microns.

[0011] Further, the radius R3 of the platform layer is different from the radius R2 of the transition layer by 1-2 microns.

[0012] Further, the radius R4 of the isolation layer is different from the radius R3 of the platform layer by 1-2 microns.

[0013] Further, the radius R5 of the third sunken cladding layer is different from the radius R4 of the isolation layer by 1-2 microns.

[0014] Further, the radius R6 of the second sunken cladding layer is different from the radius R5 of the third sunken cladding layer by 3-6 microns.

[0015] Further, the single-side radial width R7 of the first sunken cladding layer is different from the radius R6 of the second sunken cladding layer by 1-3 microns.

[0016] Further, the radius R1 of the core layer is 14-16 microns, the highest relative refractive index of the core layer is 0.35%-0.45%, the lowest relative refractive index is 0%, and the relative refractive index of the core layer gradually decreases from 0.35%-0.45% to 0%.

[0017] Further, the small-size bending-insensitive low-group-time-delay multimode optical fiber can transmit within ten modes, and the ten modes of transmission modes are respectively: LP01, LP11a, LP12a, LP11b, LP12b, LP02, LP31a, LP21a, LP31b and LP21b.

[0018] This invention also discloses a method for fabricating a small-size, bend-insensitive, low-group-delay multimode fiber, comprising the following steps:

[0019] S1, the core layer was prepared using depressurized plasma chemical vapor deposition:

[0020] S2, a transition layer, a plateau layer, an isolation layer, a third depressed cladding layer, a second depressed cladding layer, and a first depressed cladding layer were prepared by plasma chemical vapor deposition.

[0021] S3, Prepare the outer coating layer;

[0022] S4, the core layer, transition layer, platform layer, isolation layer, third recessed cladding, second recessed cladding, first recessed cladding and outer cladding are combined to form an optical fiber preform;

[0023] S5, the fiber preform is drawn into small-sized, bend-insensitive, low-group-delay multimode fiber.

[0024] Compared with the prior art, the beneficial effects of the present invention are as follows:

[0025] This invention discloses a small-size, bend-insensitive, low-group-delay multimode optical fiber and its fabrication method. By rationally designing the fiber structure and doping system, the number of available modes is optimized, enabling transmission within ten modes and reducing modal dispersion, thereby lowering the group delay of the fiber. Simultaneously, the fiber viscosity is optimized. Through the design of a plateau layer and an isolation layer, the stress and viscosity between the depressed cladding and core layers are made continuous, eliminating abrupt change regions and thus reducing fiber attenuation and group delay. This also reduces the sensitivity of the fiber's group delay to wavelength, enabling the fiber to possess both excellent bend resistance and low delay performance. By designing a three-layered depressed cladding—a third, a second, and a first—the fiber's resistance to bending loss at both long and short wavelengths is enhanced. The additional bending loss caused by two turns with a 7.5 mm bending radius at 850 nm is less than 0.2 dB, and at 1550 nm, the additional bending loss caused by two turns with a 7.5 mm bending radius is less than 0.5 dB. The maximum differential-mode delay is less than 37.76 ps / km, and at 1550 nm, based on MFMP (mirror-flipped mode arrangement), the transmission distance can reach 3000 km. Attached Figure Description

[0026] Fig. 1 This is a schematic diagram of the refractive index profile of the present invention;

[0027] Fig. 2 This is a schematic diagram showing the fluorine doping amount of the present invention. Detailed Implementation

[0028] The present invention will now be described in detail so that its advantages and features can be more easily understood by those skilled in the art, thereby providing a clearer and more explicit definition of the scope of protection of the present invention.

[0029] The following provides a brief overview of one or more aspects to offer a basic understanding of them. This overview is not an exhaustive summary of all conceived aspects, nor is it intended to identify key or decisive elements of all aspects, nor to define the scope of any or all aspects. Its sole purpose is to present some concepts of one or more aspects in a simplified form to prepare for the more detailed descriptions that follow.

[0030] like Figs. 1-2 As shown, a small-sized, bend-insensitive, low-group-delay multimode fiber includes, from the inside out, a core layer, a transition layer, a plateau layer, an isolation layer, a third depressed cladding, a second depressed cladding, a first depressed cladding, and an outer cladding. The core layer has a parabolic refractive index profile with a distribution index α of 1.8–2.1, a maximum relative refractive index difference Δ1max at the core center of 0.35–0.45%, and a core radius R1 of 14–16 μm. The transition layer has a relative refractive index difference Δ2 of -0.04%–-0.03%, and its radius R2 differs from the core radius R1 by 0.2–0.5 μm. The plateau layer has a relative refractive index difference of -0.04%–-0.03%, and its radius R3 differs from the transition layer radius R2 by 1–2 μm. The isolation layer has a relative refractive index difference Δ3 of -0.035%–-0.03%. The radius R4 differs from the radius R3 of the plateau layer by 1–2 μm; the relative refractive index difference Δ4 of the third cladding layer is -0.3% to -0.2%, and the radius R5 of the third cladding layer differs from the radius R4 of the isolation layer by 1–2 μm; the relative refractive index difference Δ5 of the second cladding layer is -0.8% to -0.4%, and the radius R6 of the second cladding layer differs from the radius R5 of the third cladding layer by 3–6 μm; the radial width R7 of the first cladding layer differs from the radius R6 of the second cladding layer by 1–3 μm, the relative refractive index difference of the first cladding layer is -0.3% to -0.2%, and the radius R8 of the outer cladding layer is 62 μm to 63 μm.

[0031] The highest relative refractive index of the core layer is 0.35% to 0.45%, and the lowest relative refractive index is 0%. The relative refractive index of the core layer gradually decreases from 0.35% to 0.45% to 0%.

[0032] The highest relative refractive index of the transition layer is 0%, and the lowest relative refractive index is -0.04% to -0.03%. The relative refractive index of the transition layer gradually decreases from 0% to -0.04% to -0.03%.

[0033] Both the core layer and the transition layer are silicon dioxide glass layers doped with fluorine, chlorine and germanium.

[0034] The platform layer, isolation layer, third recessed cladding layer, second recessed cladding layer, and first recessed cladding layer are all silicon dioxide glass layers doped with fluorine and chlorine.

[0035] The outer cladding layer is a pure silica glass layer.

[0036] The multimode optical fiber disclosed in this invention can transmit in more than ten modes with a transmission wavelength of 1535nm-1570nm in the C-band. The ten transmission modes are: LP01, LP11a, LP12a, LP11b, LP12b, LP02, LP31a, LP21a, LP31b and LP21b.

[0037] The multimode optical fiber disclosed in this invention exhibits a bending-induced loss of less than 0.2 dB at 850 nm wavelength due to two turns with a bending radius of 7.5 mm; and a bending-induced loss of less than 0.5 dB at 1550 nm wavelength due to two turns with a bending radius of 7.5 mm. The maximum differential-mode delay is less than 37.76 ps / km. Based on MFMP (mirror-flipped mode) arrangement, the multimode optical fiber of this invention can achieve a transmission distance of up to 3000 km at 1550 nm wavelength.

[0038] This invention targets wavelengths λ∈[λC-Δλ; λC+Δλ], where Max|DMD link|<37.76ps / km, where λC is the center transmission wavelength of the fiber's desired operating band, 2Δλ (the fluctuation range of wavelength λ∈[λC-Δλ; λC+Δλ]) is the width of the operating band, and Max|DMD link| is the absolute maximum value of the differential mode group delay between any combination of guided modes. λC=1550nm and Δλ=15nm. In the 1530~1565nm band, this invention achieves Max|DMD link|<37.76ps / km.

[0039] To obtain low group delay multimode fiber with good stability, the core refractive index profile of the multimode fiber needs to be designed with a refractive index distribution that gradually decreases from the center to the edge, i.e., a refractive index distribution of a power function as follows:

[0040]

[0041] Where n(0) is the refractive index of the fiber axis, r is the distance from the fiber axis, a is the fiber core radius, r < a, α is the distribution index, and Δ is the refractive index of the fiber core center relative to the cladding.

[0042] To balance the stress and viscosity of the core and the cladding, a plateau layer is designed between them. Since the stress between the core and the cladding changes with the radius during the multimode fiber drawing process, and considering the different dopants in the fiber, the plateau layer will deform after drawing. Therefore, the deformation of the plateau layer is preset when designing the fiber. The change in the relative refractive index of the fiber cannot be constant. A plateau layer with a constant relative refractive index and an isolation layer with a relative refractive index tilted upward are designed.

[0043] To improve the fiber's resistance to macro-bending loss, three recessed cladding layers—a third recessed cladding layer, a second recessed cladding layer, and a first recessed cladding layer—are designed between the isolation layer and the outer cladding layer. The third and first recessed cladding layers can improve the fiber's resistance to bending loss at short wavelengths, while the second recessed cladding layer, by doping with dopants such as fluorine to reduce the refractive index, can improve the fiber's resistance to bending loss at long wavelengths.

[0044] This invention also discloses a method for fabricating a small-size, bend-insensitive, low-group-delay multimode fiber, comprising the following steps:

[0045] S1, a core layer doped with fluorine, chlorine, and germanium was prepared using depressurized plasma chemical vapor deposition:

[0046] S2, a transition layer, a plateau layer, an isolation layer, a third depressed cladding layer, a second depressed cladding layer, and a first depressed cladding layer were prepared by plasma chemical vapor deposition.

[0047] S3, Prepare the outer coating layer;

[0048] S4, the core layer, transition layer, platform layer, isolation layer, third recessed cladding, second recessed cladding, first recessed cladding and outer cladding are combined to form an optical fiber preform;

[0049] S5, the fiber preform is drawn into small-sized, bend-insensitive, low-group-delay multimode fiber.

[0050] Example 1

[0051] like Figs. 1-2As shown, a small-sized, bend-insensitive, low-group-delay multimode fiber includes, from the inside out, a core layer, a transition layer, a plateau layer, an isolation layer, a third depressed cladding, a second depressed cladding, a first depressed cladding, and an outer cladding. The core layer has a parabolic refractive index profile with a distribution index α of 2. The maximum relative refractive index difference Δ1max at the core center is 0.4%, and the core radius R1 is 14 μm. Fluorine and germanium are co-doped in the transition layer. The radius R2 of the transition layer differs from the core radius R1 by 0.4 μm (R2 - R1 = 0.4 μm). The lowest relative refractive index difference Δ2 in the transition layer is -0.035%, and the highest is 0%. The radius R3 of the plateau layer differs from the transition layer radius R2 by 1.5 μm (R3 - R2 = 1.5 μm), and the relative refractive index difference in the plateau layer is -0.035%. Fluorine doping is performed in the isolation layer, with a lowest relative refractive index difference of -0.035% and a highest of -0.03%. The radius of the isolation layer R4 differs from the radius of the plateau layer R3 by 1.2 μm, i.e., R4-R3=1.2 μm. The relative refractive index difference Δ4 of the third cambered layer is -0.25%. The radius of the third cambered layer R5 differs from the radius of the isolation layer R4 by 1.2 μm, i.e., R5-R4=1.2 μm. The relative refractive index difference Δ5 of the second cambered layer is -0.6%. The radius of the second cambered layer R6 differs from the radius of the third cambered layer R5 by 6 μm, i.e., R6-R5=6 μm. The radial width of the first cambered layer R7 on one side differs from the radius of the second cambered layer R6 by 1.2 μm, i.e., R7-R6=1.2 μm. The relative refractive index difference of the first cambered layer is -0.25%. The radius of the outer camber R8 is 62 μm.

[0052] Performance tests were conducted on Example 1, and the results are shown in Table 1.

[0053] Table 1

[0054]

[0055]

[0056] As shown in Table 1, the multimode optical fiber disclosed in Example 1 can transmit in more than ten modes with a transmission wavelength of 1535nm-1570nm in the C-band. The ten transmission modes are: LP01, LP11a, LP12a, LP11b, LP12b, LP02, LP31a, LP21a, LP31b and LP21b.

[0057] The multimode fiber disclosed in Example 1 exhibits a bending-induced loss of less than 0.2 dB at 850 nm wavelength due to two bends with a bending radius of 7.5 mm; and a bending-induced loss of less than 0.5 dB at 1550 nm wavelength due to two bends with a bending radius of 7.5 mm. The maximum differential-mode delay is less than 37.76 ps / km. Furthermore, based on MFMP (mirror-flipped mode) arrangement, the multimode fiber can achieve a transmission distance of up to 3000 km at 1550 nm wavelength.

[0058] A method for fabricating a small-size, bend-insensitive, low-group-delay multimode fiber includes the following steps:

[0059] S1, a core layer doped with fluorine, chlorine, and germanium was prepared using depressurized plasma chemical vapor deposition:

[0060] Specifically, using SiCl4, GeCl4, CF4, and O2 as raw materials, a core rod (i.e., core layer) with a maximum relative refractive index difference Δ1max of 0.4% and a distribution index α of 2 is prepared by deposition and melting.

[0061] S2, a transition layer, a plateau layer, an isolation layer, a third depressed cladding layer, a second depressed cladding layer, and a first depressed cladding layer were prepared by plasma chemical vapor deposition.

[0062] S3 uses liner and sleeve purchased from the market to prepare the outer cladding;

[0063] S4, the core layer, transition layer, platform layer, isolation layer, third recessed cladding, second recessed cladding, first recessed cladding and outer cladding are combined to form an optical fiber preform;

[0064] S5, the fiber preform is drawn into small-sized, bend-insensitive, low-group-delay multimode fiber.

[0065] Any parts or structures not specifically described in this invention can be made using existing technologies or products, and will not be elaborated upon here.

[0066] The above description is merely an embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural or procedural transformations made based on the content of the present invention specification, or direct or indirect applications in other related technical fields, are similarly included within the patent protection scope of the present invention.

Claims

1. A small size bend-insensitive low-group-velocity multimode optical fiber, characterized by, The application relates to a small-size bending-insensitive low-group-time-delay multimode optical fiber, which comprises, from inside to outside, a core layer, a transition layer, a platform layer, an isolation layer, a third sunken cladding layer, a second sunken cladding layer, a first sunken cladding layer and an outer cladding layer, the refractive index profile of the core layer is parabolic, the distribution index alpha is 1.8-2.1, the maximum relative refractive index difference Delta1max of the core layer center is 0.35-0.45%, the relative refractive index difference Delta2 of the transition layer is -0.04% to -0.03%, the relative refractive index difference of the platform layer is -0.04% to -0.03%, the relative refractive index difference Delta3 of the isolation layer is -0.035% to -0.03%, the relative refractive index difference Delta4 of the third sunken cladding layer is -0.3% to -0.2%, the relative refractive index difference Delta5 of the second sunken cladding layer is -0.8% to -0.4%, and the relative refractive index difference of the first sunken cladding layer is -0.3% to -0.2%. The outer cladding layer is a pure silica glass layer, and the above relative refractive index differences are compared with the refractive index of the outer cladding layer.

2. The small-size bend-insensitive low-group-velocity multimode optical fiber according to claim 1, characterized in that, The radius R2 of the transition layer is 0.2-0.5 mu m different from the radius R1 of the core layer.

3. The small-size, bend-insensitive, low-group-velocity, multimode optical fiber according to claim 1, characterized in that, The radius R3 of the platform layer is 1-2 mu m different from the radius R2 of the transition layer.

4. The small-size, bend-insensitive, low-group-velocity, multimode optical fiber according to claim 1, characterized in that, The radius R4 of the isolation layer is 1-2 mu m different from the radius R3 of the platform layer.

5. The small-size, bend-insensitive, low-group-velocity, multimode optical fiber according to claim 1, characterized in that, The radius R5 of the third sunken cladding layer is 1-2 mu m different from the radius R4 of the isolation layer.

6. The small-size, bend-insensitive, low-group-velocity, multimode optical fiber according to claim 1, characterized in that, The radius R6 of the second sunken cladding layer is 3-6 mu m different from the radius R5 of the third sunken cladding layer.

7. The small-size, bend-insensitive, low-group-velocity, multimode optical fiber according to claim 1, characterized in that, The radius R7 of the first sunken cladding layer is 1-3 mu m different from the radius R6 of the second sunken cladding layer.

8. The small-size, bend-insensitive, low-group-velocity, multimode optical fiber according to claim 1, characterized in that, The radius R1 of the core layer is 14-16 mu m, the highest relative refractive index difference of the core layer is 0.35%-0.45%, the lowest relative refractive index difference is 0%, and the relative refractive index difference of the core layer gradually reduces from 0.35%-0.45% to 0%.

9. The small-size, bend-insensitive, low-group-velocity, multimode optical fiber according to claim 1, characterized in that, The small-size bending-insensitive low-group-time-delay multimode optical fiber can transmit in ten modes, and the ten transmission modes are respectively LP01, LP11a, LP12a, LP11b, LP12b, LP02, LP31a, LP21a, LP31b and LP21b.

10. A method of manufacturing a small-size, bend-insensitive, low-group- delay, few-mode optical fiber according to any one of claims 1 to 9, characterized in that, The application further discloses a preparation method of the small-size bending-insensitive low-group-time-delay multimode optical fiber. S1, a core layer is prepared by adopting a reduced-pressure plasma chemical vapor deposition method; S2, a transition layer, a platform layer, an isolation layer, a third sunken cladding layer, a second sunken cladding layer and a first sunken cladding layer are respectively prepared by adopting a plasma chemical vapor deposition method; S3, an outer cladding layer is prepared; S4, the core layer, the transition layer, the platform layer, the isolation layer, the third sunken cladding layer, the second sunken cladding layer, the first sunken cladding layer and the outer cladding layer are combined to form an optical fiber preform; S5, the optical fiber preform is drawn to obtain the small-size bending-insensitive low-group-time-delay multimode optical fiber.

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