阅读说明：本技术 一种大模场直径弯曲不敏感单模光纤 (Large-mode-field-diameter bending insensitive single-mode fiber ) 是由 雷汉林 王瑞春 顾立新 朱继红 刘善沛 黄利伟 曹蓓蓓 吴俊� 于 2021-10-11 设计创作，主要内容包括：本发明公开了一种大模场直径弯曲不敏感单模光纤,由内而外依次包括：折射率分布呈抛物线型分布的芯层,折射率依次降低的阶跃型第一下陷包层与第二下陷包层、以及纯二氧化硅外包层；所述第一下陷包层与第二下陷包层的厚度之比在0.6至1.8之间。采用了芯层折射率分布呈抛物线型分布并限定了芯层直径和芯层折射率,以保证弯曲不敏感光纤在单模条件下的大模场直径的实现；对于下陷包层采用双包层的剖面结构,通过内包层掺F来降低内包层的折射率,以达到芯包层折射率差异要求保证光纤波导设计要求,并通过双下陷包层的深度与宽度进行优化配比实现更好的宏弯性能；同时能保持稳定优异的弯曲损耗,避免出现弯曲损耗振荡带来的回音壁模式效应。(The invention discloses a large-mode-field-diameter bending insensitive single-mode optical fiber, which sequentially comprises the following components from inside to outside: the core layer with parabolic distribution of refractive index, the stepped first depressed cladding and the second depressed cladding with successively lowered refractive index, and the pure silica outer cladding; the ratio of the thicknesses of the first depressed cladding layer and the second depressed cladding layer is between 0.6 and 1.8. The refractive index distribution of the core layer is in parabolic distribution, and the diameter and the refractive index of the core layer are limited, so that the realization of the large mode field diameter of the bending insensitive optical fiber under the single mode condition is ensured; the depressed cladding adopts a double-cladding section structure, the refractive index of the inner cladding is reduced by doping F in the inner cladding so as to meet the requirement of core cladding refractive index difference to ensure the design requirement of the optical fiber waveguide, and the optimized matching is carried out on the depth and the width of the double depressed cladding so as to realize better macrobending performance; meanwhile, the bending loss can be kept stable and excellent, and the whispering gallery mode effect caused by bending loss oscillation is avoided.)

1. The utility model provides a crooked insensitive single mode fiber of big mode field diameter which characterized in that from inside to outside includes in proper order: the core layer with parabolic distribution of refractive index, the stepped first depressed cladding and the second depressed cladding with successively lowered refractive index, and the pure silica outer cladding; the ratio of the thicknesses of the first depressed cladding layer and the second depressed cladding layer is between 0.6 and 1.8.

2. The large mode diameter bend insensitive single mode optical fiber of claim 1 wherein the relative refractive index difference Δ n2 of the first depressed cladding is between-0.15% and-0.05% and the first depressed cladding diameter d2 is between 18 μm and 25 μm.

3. The large mode diameter bend insensitive single mode optical fiber of claim 1 wherein the relative refractive index difference Δ n3 of the second depressed cladding is between-0.35% and-0.25% and the second depressed cladding diameter d3 is between 30 μm and 40 μm.

4. The large mode diameter bend insensitive single mode optical fiber of claim 1 wherein the core has a refractive index distributed in an alpha parabolic shape with an index of distribution alpha of 1.5 to 3.5; the maximum relative refractive index difference delta n1 is between 0.30% and 0.38%; the diameter d1 of the core layer is 6.5-7.5 μm.

5. The large mode diameter bend insensitive single mode optical fiber of claim 4 wherein the core refractive index parabolic profile of the fiber is maintained as follows:

whereinThe distance from a certain point of the core layer to the center of the core layer,the refractive index of the spot relative to pure silica,is the refractive index at the center of the core, α is the distribution power index, and Δ is the refractive index difference of the core relative to pure silica.

6. The large mode diameter bend insensitive single mode optical fiber of claim 1 wherein the core of the fiber is a Ge doped silica glass layer and the Ge relative index contribution Δ n1 in the core is between 0.30% and 0.38% and the Ge doping concentration decreases with increasing radius to achieve a parabolic profile of refractive index.

7. The large mode field diameter bend insensitive single mode optical fiber of claim 1 which meets the g.657.a2 standard.

8. The large mode diameter bend insensitive single mode optical fiber of claim 1 having a mode field diameter at 1310nm of 8.8-9.4 μm, a cable cut-off wavelength of 1260nm or less, and a zero dispersion wavelength of 1300-1324 nm.

9. The large mode diameter bend insensitive single mode optical fiber of claim 1 having an attenuation at a wavelength of 1310nm equal to or less than 0.324 dB/km; attenuation of the optical fiber at a wavelength of 1383nm is equal to or less than 0.284 dB/km; attenuation at a wavelength of 1550nm is equal to or less than 0.184 dB/km; attenuation at a wavelength of 1625nm is equal to or less than 0.204 dB/km;

the macro-bending loss of the 1550nm window at the R15mm-10 circles is less than or equal to 0.03dB, and the macro-bending loss of the 1625nm window is less than or equal to 0.08 dB; the macrobending loss of a 1550nm window at R10mm-1 turn is less than or equal to 0.06dB, and the macrobending loss of a 1625nm window is less than or equal to 0.1 dB; the macrobending loss of a 1550nm window at R7.5mm-1 circle is less than or equal to 0.2dB, and the macrobending loss of a 1625nm window is less than or equal to 0.5 dB;

the microbending loss of the optical fiber at the wavelength of 1700nm is less than or equal to 2 dB/km.

10. The large mode field diameter bend insensitive single mode optical fiber of claim 1, wherein the large mode field diameter bend insensitive single mode optical fiber has R15mm-10 turns with 1550nm window macrobend loss less than or equal to 0.01dB, 1625nm window macrobend loss less than or equal to 0.04 d; the R10mm-1 turn 1550nm window macrobending loss is less than or equal to 0.03dB, and the 1625nm window macrobending loss is less than or equal to 0.06 dB; and the macrobending loss of a 1550nm window at an R7.5mm-1 turn is less than or equal to 0.1dB, and the macrobending loss of a 1625nm window is less than or equal to 0.2 dB.

Technical Field

The invention belongs to the technical field of optical fiber communication, and particularly relates to a large-mode-field-diameter bending insensitive single-mode optical fiber.

Background

With the large-area popularization of Fiber To The Home (FTTH), how to realize good operation of optical fibers in a small space and at a bend angle and ensure the transmission performance of the optical fibers under a bending condition under the demand of a high-density wiring network; by reducing the mode field diameter of the fiber, the optical field can be more tightly bound in the core, resulting in lower bending losses. However, the small mode field diameter fiber has serious nonlinear effect, which affects the further improvement of the power. And the practical engineering application is limited by considering the problems of fusion loss and the like caused by the difference between the typical mode field diameter of the G.652 optical fiber and the G.657 optical fiber. In order to better meet the requirements of FTTx network laying and device miniaturization, G.657.A2 bending insensitive optical fiber with large mode field diameter needs to be developed to optimize the problem that the fusion loss of G.652 optical fiber and G.657.A2 optical fiber is larger due to the difference of mode field diameters, so that G.657.A2 bending insensitive single-mode optical fiber with large mode field diameter and bending performance needs to be developed to ensure that an optical fiber network with smaller bending radius is smooth in a small space.

Some methods have been proposed to increase the mode field diameter of single mode fiber by using core layer parabolic refractive index distribution, for example, patent CN105334570 describes a large mode field single mode fiber which uses core layer refractive index distribution with the distribution index α in the range of 1.5 to 9.0 parabolic distribution, and patent CN110488411 also describes a large mode field single mode fiber which uses core layer refractive index distribution with the distribution index α in the range of 2.2 to 2.5 parabolic distribution. However, the parabolic core refractive index design greatly affects the bending performance of the optical fiber. In order to balance the bending performance of the single mode fiber with large mode field diameter, on one hand, the mode field diameter requirement is compromised to a certain extent, and the mode field diameter of the G.657.A2 fiber at the wavelength of 1310nm is generally difficult to reach more than 8.8 um; and the other adopts a low-refractive-index depressed cladding layer which is doped with fluorine deeply to reduce the bending loss. This is true of patent CN105334570 and patent CN 110488411.

However, the depth and width of the cladding layer are limited by the size standards of single mode fibers, the fluorine doping process, and the rod making process. Therefore, no bending insensitive fiber with large mode field diameter which can meet the G.657.A2 standard exists at present.

Disclosure of Invention

Aiming at the defects or improvement requirements of the prior art, the invention provides a bending insensitive single-mode fiber with a large mode field diameter, and aims to realize the bending insensitive fiber with the mode field diameter of more than 8.8 mu m by optimizing the sizes of a refractive index section of a core layer and a double sunken cladding layer, and meet the requirement of the G.657.A2 standard, thereby solving the technical problems that the parabolic fiber core section adopted by the prior art has large bending loss and cannot meet the requirement of the G.657.A2 standard.

To achieve the above object, according to one aspect of the present invention, there is provided a large mode field diameter bend insensitive single mode optical fiber, comprising in order from inside to outside: the core layer with parabolic distribution of refractive index, the stepped first depressed cladding and the second depressed cladding with successively lowered refractive index, and the pure silica outer cladding; the ratio of the thicknesses of the first depressed cladding layer and the second depressed cladding layer is between 0.6 and 1.8.

Preferably, the relative refractive index difference delta n2 of the first depressed cladding of the large mode field diameter bending insensitive single mode fiber is between-0.15% and-0.05%, and the diameter d2 of the first depressed cladding is between 18 μm and 25 μm.

Preferably, the relative refractive index difference delta n3 of the second depressed cladding of the large mode field diameter bending insensitive single mode fiber is between-0.35% and-0.25%, and the diameter d3 of the second depressed cladding is between 30 μm and 40 μm.

Preferably, the refractive index of the core layer of the large mode field diameter bending insensitive single-mode fiber is distributed according to an alpha-order parabola shape, and the distribution index alpha is 1.5-3.5; the maximum relative refractive index difference delta n1 is between 0.30% and 0.38%; the diameter d1 of the core layer is 6.5-7.5 μm.

Preferably, the large mode field diameter bend insensitive single mode fiber has a core refractive index parabolic profile relationship as follows:

whereinThe distance from a certain point of the core layer to the center of the core layer,the refractive index of the spot relative to pure silica,the refractive index at the center of the core, α is the distribution power index, and Δ is the refractive index difference of the core relative to the pure silica cladding.

Preferably, the core layer of the large-mode-field-diameter bending-insensitive single-mode optical fiber is a silica glass layer doped with Ge, the relative refractive index contribution quantity delta n1 of the germanium in the core layer is 0.30% -0.38%, and the germanium doping concentration is gradually decreased with the increase of the radius to obtain the refractive index of a parabolic distribution.

Preferably, the large mode field diameter bend insensitive single mode optical fiber meets the g.657.a2 standard.

Preferably, the mode field diameter of the large-mode-field-diameter bending-insensitive single-mode optical fiber at 1310nm is 8.8-9.4 μm, the cut-off wavelength of the optical cable is less than or equal to 1260nm, and the zero-dispersion wavelength is 1300-1324 nm.

Preferably, the large mode field diameter bend insensitive single mode optical fiber has an attenuation equal to or less than 0.324dB/km at a wavelength of 1310 nm; attenuation of the optical fiber at a wavelength of 1383nm is equal to or less than 0.284 dB/km; attenuation at a wavelength of 1550nm is equal to or less than 0.184 dB/km; attenuation at a wavelength of 1625nm is equal to or less than 0.204 dB/km;

the macro-bending loss of the 1550nm window at the R15mm-10 circles is less than or equal to 0.03dB, and the macro-bending loss of the 1625nm window is less than or equal to 0.08 dB; the macrobending loss of a 1550nm window at R10mm-1 turn is less than or equal to 0.06dB, and the macrobending loss of a 1625nm window is less than or equal to 0.1 dB; and the macrobending loss of a 1550nm window at an R7.5mm-1 turn is less than or equal to 0.2dB, and the macrobending loss of a 1625nm window is less than or equal to 0.5 dB.

The microbending loss of the optical fiber at the wavelength of 1700nm is less than or equal to 2 dB/km.

Preferably, the R15mm-10 circles of 1550nm window macrobending loss of the large-mode-field-diameter bending insensitive single-mode optical fiber is less than or equal to 0.01dB, and the 1625nm window macrobending loss is less than or equal to 0.04dB, and the R10mm-1 circles of 1550nm window macrobending loss is less than or equal to 0.03dB, and the 1625nm window macrobending loss is less than or equal to 0.06 dB; and the macrobending loss of a 1550nm window at an R7.5mm-1 turn is less than or equal to 0.1dB, and the macrobending loss of a 1625nm window is less than or equal to 0.2 dB.

In general, compared with the prior art, the above technical solution contemplated by the present invention can achieve the following beneficial effects:

1. the refractive index distribution of the core layer is in parabolic distribution, and the diameter and the refractive index of the core layer are limited, so that the realization of the large mode field diameter of the bending insensitive optical fiber under the single mode condition is ensured;

2. the depressed cladding adopts a double-cladding section structure, the refractive index of the inner cladding is reduced by doping F in the inner cladding so as to meet the requirement of core cladding refractive index difference to ensure the design requirement of the optical fiber waveguide, and the optimized matching is carried out on the depth and the width of the double depressed cladding so as to realize better macrobending performance; meanwhile, the bending loss can be kept stable and excellent, and the whispering gallery mode effect caused by bending loss oscillation is avoided.

3. The optical fiber conforms to the standard of G.657.A2 bending insensitive optical fiber, keeps good macrobending loss and lower attenuation level under the bending radius of 7.5mm, 10mm and 15mm, realizes large mode field diameter, meets the requirement of complex layout environment of an access network, and is compatible with G.652 optical fiber.

Drawings

FIG. 1 is a schematic view of a radial cross-section structure of an optical fiber provided by the present invention;

FIG. 2 is a cross-sectional view of the refractive index of an optical fiber provided by the present invention.

Detailed Description

In order to make the objects, technical solutions and advantages of the present invention more apparent, the present invention is further described in detail with reference to the following embodiments. It should be understood that the specific embodiments described herein are merely illustrative of the invention and are not intended to limit the invention. In addition, the technical features involved in the embodiments of the present invention described below may be combined with each other as long as they do not conflict with each other.

The following are definitions and descriptions of some terms involved in the present invention:

starting from the axis of the optical fiber core, according to the corresponding refractive index variation trend, the layer which is defined as the layer closest to the axis at the center is the optical fiber core layer, the part close to the optical fiber core layer is defined as a first depressed inner cladding, the part close to the first depressed inner cladding is defined as a second depressed inner cladding, and the outermost layer of the optical fiber, namely a pure silica layer, is defined as an optical fiber outer cladding.

The OVD process comprises the following steps: the quartz glass with the required thickness and the required refractive index profile is prepared by an external vapor deposition and sintering process.

The PCVD process comprises the following steps: and preparing the quartz glass with the required thickness and the required refractive index profile by using a plasma chemical vapor deposition process.

VAD process: the quartz glass with the required thickness and the required refractive index profile is prepared by axial vapor deposition and sintering processes.

And (3) a melting and shrinking process: and carrying out high-temperature fusion shrinkage by using a doped quartz glass rod and a doped quartz liner tube to obtain quartz glass with the required thickness and the required refractive index profile.

Performing: the optical fiber is a material prefabricated member which is distributed by a core layer and a cladding layer and can be drawn according to the design requirement of the optical fiber.

Relative refractive index deltan of each layer of the optical fiber_iDefined by the following equation, Δ n_i=Which isIn n_iIs the refractive index of the glass at each location of the fiber, and nc is the refractive index of the outer cladding, i.e., pure silica.

The test method of the cut-off wavelength lambda cc of the optical cable refers to the method specified in IEC 60793-1-44.

The macrobend additional loss test method refers to the method specified in IEC 60793-1-47.

The microbending loss test method is referred to as method B in IEC-62221.

The invention provides a large-mode-field-diameter bending insensitive single-mode optical fiber, which sequentially comprises the following components from inside to outside: the core layer with parabolic distribution of refractive index, the stepped first depressed cladding and the second depressed cladding with successively lowered refractive index, and the pure silica outer cladding; the ratio of the thicknesses of the first depressed cladding layer and the second depressed cladding layer is between 0.6 and 1.8.

The refractive index of the core layer is distributed according to an alpha-order parabolic shape, and the distribution index alpha is 1.5-3.5; the maximum relative refractive index difference delta n1 is between 0.30% and 0.38%; the diameter d1 of the core layer is 6.5-7.5 μm;

the core refractive index parabolic profile of the fiber is maintained as follows:

whereinThe distance from a certain point of the core layer to the center of the core layer,the refractive index of the spot relative to pure silica,the refractive index at the center of the core, α is the distribution power index, and Δ is the refractive index difference of the core relative to the pure silica cladding.

The core layer of the optical fiber is a silica glass layer doped with Ge, the relative refractive index contribution quantity delta n1 of the germanium in the core layer is 0.30% -0.38%, and the germanium doping concentration is gradually decreased along with the increase of the radius to obtain the refractive index of parabolic distribution.

The relative refractive index difference delta n2 of the first depressed cladding is between-0.15% and-0.05%, and the diameter d2 of the first depressed cladding is between 18 and 25 mu m;

the relative refractive index difference delta n3 of the second depressed cladding is between-0.35% and-0.25%, and the diameter d3 of the second depressed cladding is between 30 and 40 mu m;

the pure silicon dioxide outer cladding layer has the diameter d4 of 120-140 mu m.

The large mode field diameter bending insensitive single mode fiber meets the G.657.A2 standard;

the diameter of a mode field at 1310nm is 8.8-9.4 mu m, the cut-off wavelength of the optical cable is less than or equal to 1260nm, and the zero dispersion wavelength is 1300-1324 nm;

attenuation at a wavelength of 1310nm is equal to or less than 0.324 dB/km; attenuation of the optical fiber at a wavelength of 1383nm is equal to or less than 0.284 dB/km; attenuation at a wavelength of 1550nm is equal to or less than 0.184 dB/km; attenuation at a wavelength of 1625nm is equal to or less than 0.204 dB/km;

the macro-bending loss of the 1550nm window at the R15mm-10 circles is less than or equal to 0.03dB, and the macro-bending loss of the 1625nm window is less than or equal to 0.08 dB; the macrobending loss of a 1550nm window at R10mm-1 turn is less than or equal to 0.06dB, and the macrobending loss of a 1625nm window is less than or equal to 0.1 dB; and the macrobending loss of a 1550nm window at an R7.5mm-1 turn is less than or equal to 0.2dB, and the macrobending loss of a 1625nm window is less than or equal to 0.5 dB.

The microbending loss of the optical fiber at the wavelength of 1700nm is less than or equal to 2 dB/km. Preferably, the R15mm-10 circles of the bending insensitive single-mode fiber with large mode field diameter have 1550nm window macrobending loss less than or equal to 0.01dB and 1625nm window macrobending loss less than or equal to 0.04dB; the macrobending loss of a 1550nm window at R10mm-1 turn is less than or equal to 0.03dB, and the macrobending loss of a 1625nm window is less than or equal to 0.06 dB; and the macrobending loss of a 1550nm window at an R7.5mm-1 turn is less than or equal to 0.1dB, and the macrobending loss of a 1625nm window is less than or equal to 0.2 dB.

In order to reduce the bending loss, a commonly used method is a step-type depressed cladding structure profile, and this method needs to dope F to implement depressed cladding, so that the core cladding achieves a relatively large refractive index difference, and ensures a certain width of the depressed cladding. In such a method, the influence of the width of the dip layer and the refractive index difference between the dip layer and the cladding layer on the bending loss, the mode field diameter, and the cutoff wavelength is monotonously changed, that is, the bending loss is gradually reduced as the absolute value of the width of the dip layer and the refractive index difference increases; the mode field diameter decreases with increasing absolute value of the refractive index difference and decreases with increasing width of the dip layer within a certain range. It is often difficult to achieve a good balance of large mode field diameter and excellent macrobend performance.

The invention uses the core layer with a smaller diameter, and is matched with the parabolic refractive index distribution with the distribution index alpha of 1.5-3.5, so that the super-large mode field diameter of more than 8.8 mu m is realized in the extremely limited core layer diameter, the nonlinear effect is inhibited, the welding loss is reduced, and more optimized space is reserved for the low-refractive-index depressed cladding layer as far as possible. In order to prevent the bending performance from being obviously deteriorated due to the design of a large mode field diameter, the step type first sunken cladding layer and the second sunken cladding layer with sequentially reduced refractive indexes are adopted to realize bending loss, so that the bending performance is improved, and particularly, the thickness and the refractive index difference of the first cladding layer and the second cladding layer are optimized, so that any one of the first sunken cladding layer and the second cladding layer is not too narrow or too low, the macro-bending performance is good, and the G.657.A2 standard can be met.

Particularly, the macro-bending loss of the double-depressed-cladding-layer structure is reduced by more than 50% and kept stable under the bending radii of 7.5mm, 10mm and 15mm by matching with the double-depressed-cladding design with optimized size and refractive index.

The manufacturing method adopted by the optical fiber is that PCVD/VAD + sleeve liner tube fusion shrinkage + OVD technology is used for preparing the needed optical fiber preform, VAD technology or PCVD technology is used for preparing a core rod corresponding to an optical fiber core layer and an F-doped sinking cladding layer, a doped quartz liner tube is used for preparing the corresponding needed F-doped sinking cladding layer, and the core rod and the F-doped liner tube are fused into a solid rod at high temperature for OVD technology outer cladding treatment; the preform prepared by the OVD can be drawn to obtain the large mode field diameter bending insensitive single mode fiber meeting the G.657.A2 fiber standard.

The following are examples:

the optical fiber comprises a core layer, a first depressed cladding, a second depressed cladding, an outer cladding and a coating layer from inside to outside in sequence, wherein the refractive index and the geometric distribution are shown in figure 2: a core layer Ge-doped silica glass layer with a diameter d1 and a relative refractive index difference delta n 1; the inner diameter of the first sunken cladding layer is d2, and the relative refractive index difference is delta n 2; the diameter of the second depressed inner cladding is d3, and the relative refractive index difference is delta n 3; the ratio of the thicknesses of the first depressed cladding layer and the second depressed cladding layer is the depressed cladding thickness ratio, and the outer cladding diameter is d 4.

According to the technical scheme of the large mode field diameter bend insensitive single mode fiber of the G657A2 optical fiber standard, the main parameters of the implemented fiber refractive index profile structure are shown in the table 1:

TABLE 1 optical fiber profile and geometry parameters for the examples

The main performance parameters of the fiber are shown in table 2.

TABLE 2 optical fiber Main Performance parameters of the examples

Comparative example

The results of measuring the bending loss performance parameters by comparing low attenuation bend insensitive single mode optical fibers described in publication No. CN105334570A are shown in table 3:

TABLE 3 comparative example bend loss Performance parameters

The experiment shows that: the bending loss of the fluorine-doped depressed clad optical fiber with different depths and widths at a specific bending radius is obviously different, when the bending diameter of the fiber is increased, the macroscopic bending loss at the specific diameter fluctuates, and the oscillation phenomenon at a long wavelength is more obvious than that at a short wavelength at certain diameters.

By comparing the thickness ratio of the sunken cladding layer and the fluorine-doped depth, the bending loss at each bending radius is obviously improved and can be kept stable after the sunken cladding layer is optimized in the patent example on the fluorine-doped depth and width. The macrobending loss energy under the bending radius of 7.5mm, 10mm and 15mm is reduced by more than 50 percent and kept stable.

With the macro-bending data of the comparative examples and experiments on the fluorine-doped depth and the depressed cladding thickness ratio, when the fluorine-doped depth is too shallow and too narrow, the bending loss at a small bending radius is increased, but when the fluorine-doped depressed cladding is too deep and too wide, the bending loss at a large bending radius is oscillated. By optimizing the proportion of the fluorine-doped depth and the thickness of the double-sunken cladding layer, macrobending loss under different bending radii can be stably reduced, so that the G.657.A2 standard can be well met.

It will be understood by those skilled in the art that the foregoing is only a preferred embodiment of the present invention, and is not intended to limit the invention, and that any modification, equivalent replacement, or improvement made within the spirit and principle of the present invention should be included in the scope of the present invention.