BEND-RESISTANT MULTIMODAL GLASS FIBER WITH HIGH BANDWIDTH

Description

TECHNICAL FIELD

[0001] The present invention belongs to the technical field of optical communications, and specifically relates to a bending-insensitive high-bandwidth multimode optical fiber.BACKGROUND

[0002] According to TIA / EIA-492AAA standard, multimode optical fibers can be classified into four types, namely OM1, OM2, OM3, and OM4. A high-bandwidth multimode optical fiber (e.g., OM3 / OM4) is widely used in short- and medium-distance fiber optic network systems due to relatively low system costs. The application scenarios of the multimode optical fiber are often a narrow cabinet, a distribution box and other integrated systems. However, when a conventional multimode optical fiber has bending in a small angle, a higher-order mode transmitted near the edge of the optical fiber core can easily be leaked out, resulting in the loss of a signal packet. When the refractive index profile of a bending-resistance multimode optical fiber is designed, a method for increasing a low refractive index region in an optical fiber cladding is generally used to limit the leakage of a higher-order mode and minimize signal loss. In the profile design and process design of a bending-insensitive multimode optical fiber, a main difficulty is how to ensure the macro bending performance, Differential Mode Delay (DMD) performance, and bandwidth performance of the optical fiber through relevant design and obtain an optimal value.

[0003] To obtain a high-bandwidth multimode optical fiber with good stability, the refractive index profile of the optical fiber, especially the refractive index profile of a core layer, is precisely matched with an expected profile. A core layer of a preformed rod of the optical fiber is usually designed to be doped with a certain concentration of one or more of germanium, fluorine, chlorine, phosphorus, and the like, achieving the desired refractive index distribution of the core layer of the optical fiber. The types and contents of dopant elements in the core layer of the optical fiber affect the material dispersion of the optical fiber and thus the sensitivity of the bandwidth of the optical fiber to a wavelength. SiO 2 doped with germanium has a higher material dispersion. Therefore, the existing multimode optical fiber with a higher germanium-doped amount has a very narrow wavelength range corresponding to high bandwidth performance. A small change in the wavelength of a light source can bring about a sharp decrease in the bandwidth performance. However, the multimode optical fiber used in a wavelength division multiplexing (WDM) system needs to maintain high bandwidth performance over a wider range of wavelengths. The transmission distance of a conventional multimode optical fiber with a higher germanium-doped amount in the WDM system is often limited.

[0004] Not only material dispersion affects the bandwidth of the multimode optical fiber, but also intermode dispersion affects the bandwidth performance. To reduce the intermode dispersion of the optical fiber, it is necessary to design the refractive index profile of a core layer of the multimode optical fiber into refractive index distribution with a continuous and gradual decrease from a center to edges, i.e., the refractive index distribution with the following power exponential function: n 2 r = n 1 2 1 − 2 Δ 0 r / a α r < a where n 1 is the refractive index of the axis center of the optical fiber; r is the distance away from the axis center of the optical fiber; a is the radius of the core of the optical fiber; α is a distribution index; and Δ 0 is the refractive index of the core center of the optical fiber relative to a cladding.

[0005] The computational formula of the relative refractive index difference, i.e. Δ i , is as follows: Δ i % = n i 2 − n 0 2 / 2 n i 2 × 100 % where n i is the refractive index at a position i from the core center of the optical fiber; n 0 is the minimum refractive index of the core layer of the optical fiber, which is usually also the refractive index of the cladding of the optical fiber.

[0006] Relevant studies have shown that for the bending-insensitive multimode optical fiber, the amount of doping, the viscosity after doping, and the design of the refractive index of the profile of the core layer affect the DMD and bandwidth of the optical fiber. Therefore, to allow the multimode optical fiber to have good bending-insensitive performance and high-bandwidth performances, it is necessary to optimize a doping system, the viscosity ratio, and the structure of the profile of the multimode optical fiber.

[0007] A Chinese invention patent, Publication No. CN 106383379 A, publishes a bending-insensitive high-bandwidth multimode optical fiber, which produces one fluorine-doped platform layer after a fluorine-doped amount in fluorine germanium co-doping in a core layer gradually increases, and which also carries out fluorine germanium co-doping in an inner cladding. However, the fluorine-doped amount of the inner cladding is not continuous with a platform layer, which is prone to form a stress sudden-change zone between the core layer and a sunken cladding. The viscosity of the optical fiber changes greatly, affecting the bandwidth performance and attenuation performance of the optical fiber.

[0008] To balance the stress and viscosity between the core layer and the sunken cladding, the platform layer is usually designed in the inner cladding between the core layer and the sunken cladding. The relative refractive index difference of the platform layer is one fixed value. However, because a stress between the core layer and the sunken cladding is changed with a change in a radius during the pulling process of the multimode optical fiber, designing the relative refractive index difference of the platform layer as the fixed value can not well balance the stress and viscosity between the core layer and the sunken cladding. In addition, due to different dopants, the platform layer is deformed after the optical fiber is pulled. Therefore, designing the inner cladding as the platform layer with a constant relative refractive index difference in designing the optical fiber can not completely match the stress and viscosity between the core layer and the sunken cladding. The compensation of the stress and viscosity after the optical fiber is pulled is taken into account.

[0009] To solve the above problems of stress difference and viscosity difference, the present application provides a bending-insensitive high-bandwidth multimode optical fiber and a method for preparing the same, and designs a tilted inner cladding structure with a relative refractive index difference, so that the stress and viscosity between the sunken cladding and the core layer can form a continuity, eliminating a sudden-change region, reducing the attenuation of the optical fiber and improving bandwidth performance.SUMMARY

[0010] To solve the technical problems in the prior art, an objective of the present invention is to provide a bending-insensitive high-bandwidth multimode optical fiber and a method for preparing the same.

[0011] To realize the above objective and achieve the above technical effect, the technical solution adopted in the present invention is as follows:

[0012] A bending-insensitive high-bandwidth multimode optical fiber includes a core layer, an extension layer, an inner cladding, a sunken cladding, and an outer cladding disposed sequentially from inside to outside. The core layer has a parabolic refractive index profile, 1.9 to 2.2 of a distribution index α, 0.9% to 1.2% of the maximum relative refractive index difference Δ1 at a center and 24 µm to 25 µm of a radius R1. The extension layer has -0.03% to -0.02% of a relative refractive index difference Δ2. The difference between the radius R2 of the extension layer and the radius R1 of the core layer is 0.5 µm to 3 µm. The inner cladding has 0.005% to 0.03% of the difference between the highest relative refractive index difference and the lowest relative refractive index difference, and 0.5 µm to 4 µm of an unilateral radial width. The sunken cladding has 3 µm to 9 µm of an unilateral radial width and 0.7% to -0.4% of a relative refractive index difference Δ4.

[0013] Further, the extension layer and the inner cladding are silicon dioxide glass layers doped with a dopant, respectively.

[0014] Further, the dopant includes one or a combination of a plurality of fluorine, aluminum, calcium, magnesium, titanium, zirconium, iron, cobalt, nickel, manganese, copper, lithium, sodium, potassium, boron, germanium, and phosphorus.

[0015] Further, the outer cladding is a pure silicon dioxide glass layer and has 62 µm to 63 µm of a radius R5.

[0016] Further, the optical fiber has a bending additional loss of less than 0.2 dB at a wavelength of 850 nm resulting from circling 2 times with a bending radius of 7.5 mm and the bending additional loss of less than 0.5 dB at the wavelength of 1300 nm resulting from circling 2 times with the bending radius of 7.5 mm.

[0017] Compared with the prior art, the beneficial effects of the present invention are as follows: The present invention discloses a bending-insensitive high-bandwidth multimode optical fiber, including a core layer, an extension layer, an inner cladding, a sunken cladding, and an outer cladding disposed sequentially from inside to outside. The core layer has a parabolic refractive index profile, 1.9 to 2.2 of a distribution index α, 0.9% to 1.2% of the maximum relative refractive index difference Δ1 at a center and 24 µm to 25 µm of a radius R1. The extension layer has -0.03% to -0.02% of a relative refractive index difference Δ2. The difference between the radius R2 of the extension layer and the radius R1 of the core layer is 0.5 µm to 3 µm. The inner cladding has 0.005% to 0.03% of the difference between the highest relative refractive index difference and the lowest relative refractive index difference and 0.5 µm to 4 µm of an unilateral radial width. The sunken cladding has 3 µm to 9 µm of an unilateral radial width and -0.7% to -0.4% of a relative refractive index difference Δ4. The present invention allows the optical fiber to have good viscosity performance through reasonable doping, and optimizes the design of the fiber profile at the same time to improve the high bandwidth performance of the multimode optical fiber. The design and optimization of the viscosity of the fluorine / germanium doping of the extension layer and the inner cladding is focused on. Fluorine / germanium or other dopants (e.g., phosphorus) are used to be co-doped in the extension layer (R2-R1). The ratio of fluorine doping increases from the core layer to the extension layer. Fluorine / germanium or other dopants (e.g., phosphorus) are used to be co-doped in the inner cladding (R3-R2). The inner cladding has the same doping amount (excluding fluorine) as that at the outermost end of the extension layer and has the ratio of the fluorine doping that is variable and gradually decreases with an increase in a radius, instead of only using the fluorine doping and keeping unchanged the amount of the fluorine doping. The inner cladding can be variably doped with fluorine, which can be adjusted according to the stress and viscosity tests of the optical fiber. The appropriate variable doping amount and the width of the inner cladding can be selected, thereby achieving an optimal stress difference between the core layer and the extension layer as well as the sunken cladding, reducing the sensitivity of the bandwidth of the optical fiber to a wavelength, and allowing the optical fiber to have a good bending resistance while having a super-high bandwidth performance.BRIEF DESCRIPTION OF THE DRAWINGS

[0018] FIG. 1 is a schematic diagram of a refractive index profile of the present invention; and FIG. 2 is a schematic diagram of a fluorine-doped amount of the present invention. DETAILED DESCRIPTION OF THE EMBODIMENTS

[0019] The present invention is described in detail below so that the advantages and features of the present invention can be more readily understood by a person skilled in the art. Therefore, the scope of protection of the present invention can be more clearly and unambiguously defined.

[0020] A brief overview of one or more aspects is given below to provide a basic understanding of these aspects. This summary is not an exhaustive overview of all aspects contemplated, and is neither intended to identify the critical or decisive elements of all aspects nor to attempt to define the scope of any or all aspects. The sole objective is to give some idea of one or more aspects in a simplified form as a prelude to the more detailed description to be given later.

[0021] As shown in FIGS. 1-2, a bending-insensitive high-bandwidth multimode optical fiber includes a core layer, an extension layer, an inner cladding, a sunken cladding, and an outer cladding disposed sequentially from inside to outside. The core layer has a parabolic refractive index profile, 1.9 to 2.2 of a distribution index α, 24 µm to 25 µm of a radius R1, and 0.9% to 1.2% of the maximum relative refractive index difference Δ1 at a center. The extension layer has a radius R2, 0.5µm to 3µm of an unilateral radial width (R2-R1), and -0.03% to -0.02% of a relative refractive index difference Δ2. The inner cladding has 0.005% to 0.03% of the difference (Δ3-Δ2) between the highest relative refractive index difference and the lowest relative refractive index difference and 0.5µm to 4µm of an unilateral radial width (R3-R2). The sunken cladding has 3 µm to 9 µm of an unilateral radial width (R4-R3) and -0.7% to -0.4% of a relative refractive index difference Δ4. The outer cladding is a pure silicon dioxide glass layer and has 62 µm to 63 µm of a radius R5. A waveguide structure and a doping system are rationally designed, optimizing the viscosity of the optical fiber, and reducing the sensitivity of the bandwidth of the optical fiber to the wavelength. Therefore, the optical fiber has a good bending resistance while having an ultra-high bandwidth performance.

[0022] The extension layer and the inner cladding are silicon dioxide glass layers doped with a dopant, respectively. The dopant includes one or a combination of a plurality of fluorine, aluminum, calcium, magnesium, titanium, zirconium, iron, cobalt, nickel, manganese, copper, lithium, sodium, potassium, boron, germanium, and phosphorus.

[0023] For the present invention, the design and optimization of the viscosity of the fluorine / germanium doping of the extension layer and the inner cladding is focused on. Fluorine / germanium or other dopants (e.g., phosphorus) are used to be co-doped in the extension layer. The ratio of fluorine doping increases from the core layer to the extension layer. Fluorine / germanium or other dopants (e.g., phosphorus) are used to be co-doped in the inner cladding (R3-R2). The inner cladding has the same doping amount (excluding fluorine) as that at the outermost end of the extension layer and has the ratio of the fluorine doping that is variable and gradually decreases with an increase in a radius, instead of only using the fluorine doping and keeping unchanged the amount of the fluorine doping. The inner cladding can be variably doped with fluorine, which can be adjusted according to the stress and viscosity tests of the optical fiber. The appropriate variable doping amount and the width of the inner cladding can be selected, thereby achieving an optimal stress difference between the core layer and the extension layer as well as the sunken cladding, reducing the sensitivity of the bandwidth of the optical fiber to a wavelength, and allowing the optical fiber to have a good bending resistance while having a super-high bandwidth performance.

[0024] The optical fiber of the present invention has a bending additional loss of less than 0.2 dB at a wavelength of 850 nm resulting from circling 2 times with a bending radius of 7.5 mm and the bending additional loss of less than 0.5 dB at the wavelength of 1300 nm resulting from circling 2 times with the bending radius of 7.5 mm.Embodiment 1

[0025] As shown in FIGS. 1-2, a bending-insensitive high-bandwidth multimode optical fiber comprising a core layer, an extension layer, an inner cladding, a sunken cladding, and an outer cladding disposed sequentially from inside to outside. The core layer has a refractive index profile in the form of a parabolic shape. Fluorine / germanium is co-doped in the core layer so that the core layer has 1.0% of the maximum relative refractive index difference Δ1 at a center, 2.08 of a distribution index α, and 24.5 µm of a radius. The extension layer has a radius R2. Fluorine / germanium is co-doped in the extension layer, so that the extension layer has 2 µm of an unilateral radial width (R2-R1), and -0.03% of a relative refractive index difference Δ2. Fluorine is doped in the inner cladding. The inner cladding has -0.03% of the minimum relative refractive index difference Δ2, -0.02% of the maximum relative refractive index difference Δ3, 0.01% of the difference (Δ3-Δ2) between the maximum relative refractive index difference and the minimum relative refractive index difference, and 1.5 µm of an unilateral radial width (R3-R2). Fluorine is doped in the sunken cladding. The sunken cladding has -0.6% of a relative refractive index difference Δ4, and 6 µm of an unilateral radial width (R4-R3).

[0026] Performance tests are performed on Embodiment 1 and results are shown in Table 1. Table 1The bandwidth (MHz·km) of the optical fiberEmbodiment 1@850 nm full injection bandwidth4260@1300 nm full injection bandwidth684@850 nm effective mode bandwidth7134R=7.5 mm, 2 turns @850 nm (dB)0.046R=7.5mm, 2 turns @1300nm (dB)0.153

[0027] The optical fiber of the present invention has a bending additional loss of less than 0.2 dB at a wavelength of 850 nm resulting from circling 2 times with a bending radius of 7.5 mm and the bending additional loss of less than 0.5 dB at the wavelength of 1300 nm resulting from circling 2 times with the bending radius of 7.5 mm.

[0028] A part or a structure that the present invention is not specifically described adopts the prior art or existing products, which is not repeated here.

[0029] The forgoing is only an embodiment of the present invention and does not therefore limit the patent scope of the present invention. The patent scope of the present invention is defined by the appended claims.

Claims

1. A bending-insensitive high-bandwidth multimode optical fiber, comprising a core layer, an extension layer, an inner cladding, a sunken cladding, and an outer cladding disposed sequentially from inside to outside, wherein the core layer has a parabolic refractive index profile, 1.9 to 2.2 of a distribution index α, 0.9% to 1.2% of a maximum relative refractive index difference Δ1 at a center, 0.5 µm to 4 µm of an unilateral radial width, and the sunken cladding has 3 µm to 9 µm of an unilateral radial width and -0.7% to -0.4% of a relative refractive index difference Δ4, characterized in that the core layer has a radius R1 of 24 µm to 25 µm, the extension layer has -0.03% to -0.02% of a relative refractive index difference Δ2, a difference between the radius R2 of the extension layer and the radius R1 of the core layer is 0.5 µm to 3 µm and the inner cladding has 0.005% to 0.03% of a difference between a highest relative refractive index difference and a lowest relative refractive index difference.

2. The bending-insensitive high-bandwidth multimode optical fiber according to claim 1, characterized in that the extension layer and the inner cladding are silicon dioxide glass layers doped with a dopant, respectively.

3. The bending-insensitive high-bandwidth multimode optical fiber according to claim 2, characterized in that the dopant comprises one or a combination of a plurality of fluorine, aluminum, calcium, magnesium, titanium, zirconium, iron, cobalt, nickel, manganese, copper, lithium, sodium, potassium, boron, germanium, and phosphorus.

4. The bending-insensitive high-bandwidth multimode optical fiber according to claim 1, characterized in that the outer cladding is a pure silicon dioxide glass layer and has 62 µm to 63 µm of a radius R5.

5. The bending-insensitive high-bandwidth multimode optical fiber according to claim 1, characterized in that the optical fiber has a bending additional loss of less than 0.2 dB at a wavelength of 850 nm resulting from circling 2 times with a bending radius of 7.5 mm and the bending additional loss of less than 0.5 dB at the wavelength of 1300 nm resulting from circling 2 times with the bending radius of 7.5 mm.