WO2015007097A1

WO2015007097A1 - Bending insensitive single mode optical fibre

Info

Publication number: WO2015007097A1
Application number: PCT/CN2014/072843
Authority: WO
Inventors: 龙胜亚; 张磊; 周红燕; 罗杰
Original assignee: 长飞光纤光缆股份有限公司
Priority date: 2013-07-17
Filing date: 2014-03-04
Publication date: 2015-01-22
Also published as: CN103345017A; TW201504701A; TWI522667B; CN103345017B

Abstract

A bending insensitive single mode optical fibre, comprising a core and a cladding. The diameter of the core is 7.6μm - 8.4μm, and the relative refractive index difference Δ1 thereof is 4.66 × 10^—3 ~ 6.12 × 10^—3. The cladding outside the core comprises an inner cladding, a hollow outer cladding and an outer cladding in sequence from inside to outside. The diameter of the inner cladding is 17.4μm - 20μm, and the relative refractive index difference Δ2 thereof is -0.1 × 10^—3 ~ 0.1 × 10^—3. The diameter of the hollow outer cladding is 28μm - 32μm, and the relative refractive index difference Δ3 thereof is -4.37 × 10^—3~-7.25 × 10^—3. By optimizing the depth and width of the hollow outer cladding of the optical fibre, the optical fibre not only has a lower additional bending loss, but also has a stable mechanical property and a uniform material composition. On the basis of keeping effective mode field diameters and bending properties, the process control difficulty is reduced, and the processing efficiency of an optical fibre preform is improved. The optical fibre is far superior to the ITU-TG.657. B3 standard in various performance, so that the requirements of FTTH network laying and device miniaturization can be satisfied.

Description

Bending insensitive single mode fiber

[0001] The present invention relates to a single mode fiber applied to an access network, which has excellent bending resistance and belongs to the field of optical fiber communication transmission.

Background technique

[0002] With the continuous development of optical fiber transmission technology, fiber-to-the-home (FTTH) and fiber-to-the-desktop (FTTd) have become important development directions for communication access network construction. As a fiber that transports coal, it plays a vital role in it. Because in the actual FTTx fiber line laying and configuration process, it is often necessary to perform various operations on the fiber in indoors and in a narrow environment (for example, installing at a corner of a 90° corner, winding the fiber in an increasingly smaller storage box) Processing fiber length, etc.), at this time the fiber needs to withstand high bending stress at a small bending radius, so it is necessary to design and develop an optical fiber with excellent bending resistance to meet the requirements of FTTx network laying and device miniaturization. In November 2009 and June 2010, ITU-T revised the bend-insensitive G.657 fiber standard twice and added a report on the performance of fiber life at small bend radii ("Characteristics of a bending Loss insensitive single mode optical fibre and cable for the access network" and Amendment 1: Revised Appendix 1 -Lifetime expectation in case of small radius bending of single-mode fibre ) ₀ These two modifications basically clarify the environment under different bending radii, G.657A1/A2 fiber and G.657.B3 fiber have different application goals, in which G.657.A1 fiber with minimum bending radius of 10mm is applied to Long-haul networks; G.657.A2 fiber meets minimum Applications under 7.5 mm bend radius are mainly used in metro networks (Metro networks) and B FTTH (fiber to the home); G.657.B3 fibers meet the conditions of use with a minimum bend radius of 5 mm, mainly in FTTd (fiber to The use of desktop and all-optical networks, in the form of indoor fiber/cables, and the problem of fiber life under bending conditions.

[0003] According to the ITU-T regulations and the specific use environment and conditions of G.657.B3 fiber, G.657.B3 fiber is basically used in short-distance communication transmission, which pays more attention to macroscopic bending performance under small bending radius. It is not mandatory to be compatible with the G.652.D standard. In September 2012, in the latest revision of ITU-T G.657, Class B fiber is gradually becoming compatible with G.652 fiber. The introduction of the new standard will be more conducive to the promotion and use of G.657 fiber.

[0004] After years of research, researchers in various countries have found that the mode field diameter and cutoff wavelength of the fiber play a major role in the macroscopic bending loss of the fiber. The MAC value can qualitatively measure the bending performance of the fiber, where: MAC is defined as the mode field diameter and The ratio of the cutoff wavelengths. The smaller the MAC, the better the bending performance of the fiber. Obviously, reducing the mode field diameter and increasing the fiber cut-off wavelength can achieve the purpose of reducing the MAC, thereby obtaining better bending performance. Patents US2007007016A1, CN1971321A and CN1942793A are such methods. However, if the fiber mode field diameter is too small, it is connected to a conventional single mode fiber. When connected, it will bring a large connection loss and limit the fiber input power. At the same time, considering the multi-service characteristics of FTTx, it is hoped that the whole band can be used for transmission. The cut-off wavelength of the cable must be less than 1260 nm, so the space for increasing the cut-off wavelength of the fiber is very limited. If the method of reducing the MAC value of the optical fiber is used alone, the excellent bending performance cannot be effectively obtained, thereby meeting the requirements of the G.657.B3 standard.

[0005] Compared with the conventional single-mode fiber cross-sectional structure, another effective method for improving the bending performance of the fiber is to adopt the design of the depressed inner cladding. For example, US5032001, US7043125B2 and CN176680 adopt the depressed inner cladding design, and the depressed inner cladding design is adopted. The numerical aperture (NA) of the fiber can be increased without increasing the doping of the core layer, and the increase in attenuation due to doping can be avoided. However, the optimized design of the depressed inner cladding can only improve the macrobend performance of the fiber at a large bending radius to a certain extent. When the bending radius of the optical fiber is less than or equal to 10 mm, it is difficult to prepare a bending insensitive optical fiber conforming to the G.657.A2 standard by using the depressed inner cladding.

[0006] Further research has found that the most effective way to improve the bending resistance of the fiber is to design the fiber profile using the depressed outer cladding structure. The basic waveguide structure is described in the patent US Pat. No. 4,852,968, and the patents US6535679B2 and CN1982928A also adopt the same design. However, all of the above patents only consider how to reduce the bending additional loss, and do not consider the long-term service life of the fiber under a small bending radius in combination with specific applications, nor does it clearly state whether the fiber manufactured according to the description satisfies and is superior to the G.657.B3 standard. The relevant requirements for a minimum 5 mm bend radius. In the study of the submerged outer layer structure fiber, it is found that the depth and width of the submerged outer layer in the fiber profile also have certain requirements: the submerged outer layer is too shallow, too narrow, and can not bring good bending insensitive performance; too deep, Too wide, it may affect the fiber cut-off wavelength and dispersion performance.

[0007] In the bend-insensitive fiber of the depressed outer cladding structure, another factor that affects the macroscopic bending performance of the optical fiber under bending conditions is the diameter ratio of the fiber core cladding. When the optical fiber is in a bent state, since the inner cladding surrounds the core layer, the stress generated by the bending first acts on the inner cladding layer and then passes to the core layer portion, if the core layer, the cladding doping, and the refractive index are not considered, A small core/clad diameter ratio is beneficial to improve fiber bending performance. However, the smaller core/clad diameter ratio tends to affect the MFD and dispersion properties of the fiber, and it is more difficult to match the viscosity and stress during the drawing process, so the suitable core/cladding diameter ratio is also G. An important direction of the 657.B3 fiber profile study. Recent studies have shown that: In fiber-optic links, especially FTTx links, multi-path interference (MPI: Multi-Path Interference) occurs in optical fibers due to multi-point bending and connectors. David.Zhen et al. A method of testing MPI is described in the 2009 OFC/NFOEC ("Test MPI Threshold in Bend Insensitive Fiber Using Coherent Peak-To-Peak Power Method"). Especially in the fiber design of the outer depressed cladding, the following trap layer is too close to the core layer. Once the core layer is offset at the fiber joint, multipath interference is easily generated. The trap layer is too far away from the core layer. There is no need to reduce the additional loss of fiber bending, so precise positioning of the depressed cladding is required. Therefore, reasonable design of the fiber profile, in the core layer, cladding and submerged cladding refractive index profile structure, to achieve a good balance, is a focus of G.657.B3 fiber research and Difficult.

[0008] US Patent No. 7,623,747 describes an optical fiber that reduces bending and microbending loss, the depressed outer cladding is co-doped with fluoroquinone, and the doped yttrium can increase the elastic optical coefficient of the depressed outer cladding, and reduce when the optical fiber is subjected to bending or The effect of stress on the refractive index change of the fiber during microbending, but its macrobend characteristics still fail to meet the G.657.B3 standard. Chinese patent CN101680994A, the applicant describes a loss and attenuation performance with a small bending loss, but does not mention a 5 mm bending radius at 1550 nm, and the relative refractive index difference of the depressed outer cladding is -7.28 X 10 ^-3 ~ - 2.62 X 10- ² range, taking into account its deeper sag will cause the fiber cutoff wavelength and high transmission process problems such as MPI, will affect the compatibility of the optical fiber. In Chinese Patent No. 101893732 A, the applicant also proposes a bending-resistant single-mode optical fiber similar to CN101680994A, which has a bending diameter of 20 mm, but its bending performance fails to meet the standard of G.657.B3 optical fiber. The fiber proposed in Chinese patent CN 102590933 A has a narrow undercut and a poor macrobend. The optical fiber involved in CN 102540327 A has a wide sag and good macrobend performance, but the cutoff wavelength is high, which is not compatible with G.652.D fiber. In the design of the optical waveguide, due to the positional change of the fluorine-doped depressed outer cladding, a series of parameters such as the fiber cut-off wavelength and MFD and dispersion will be changed, and the volume of the outer depressed outer layer will be simply increased, although the macrobend of the optical fiber will be improved. Performance, but it will affect the compatibility of the fiber, which is not conducive to the application of bending insensitive fiber in the existing communication network. Compared with CN 102540327 A, this patent optimizes the core diameter and adjusts the relative position and depth of the fluorine-doped depressed inner cladding. The macrobend loss at 10mm bend diameter of 1550nm is less than O.ldB/circle, 1625nm wavelength macrobend The loss is less than or equal to 0.2dB/turn, which is superior to CN 102540327 A and has better macrobend performance, which is more conducive to the configuration of fiber in FTTx.

[0009] The continuous development of FTTH network construction requires that G.657.B3 fiber not only be superior to ITU-T G.657.B3 standard, but also requires full compatibility with G.652.D fiber standard, and a large number of G.657. B3 needs to be able to meet the requirements of low cost, large scale production.

[0010] In addition, in the use of the access network, in addition to the method of welding, the optical fiber connection adopts a mechanical connection method, such as a fiber cold connector, which requires good end face quality after fiber cutting, and thus requires an optical fiber to be very Good material uniformity. Summary of the invention

[0011] To facilitate the introduction of the invention, define some terms:

Core rod: a preform containing a core layer and a partial cladding;

Refractive index profile: the relationship between the refractive index of a fiber and its radius;

Relative refractive index difference: Δ and n _Q are the refractive indices of the respective optical fibers and the pure silica glass, respectively.

[0012] The contribution of fluorine (F): fluorine-doped (F) The absolute value of the refractive index difference of quartz glass relative to pure quartz glass, ie Δ _Ρ = I n _F -n ₀ I , which indicates the fluorine doping (F) quantity;

The contribution of germanium (Ge): the absolute value of the refractive index difference of germanium (Ge)-doped quartz glass relative to pure quartz glass, ie A _Ge = | Noe-no I , which is used to indicate the amount of erbium (Ge) doped;

Casing: thick-walled high-purity quartz glass tube that meets the requirements of a certain cross-sectional area;

OVD Outer Deposition Process: Preparation of Si0 ₂ glass of required thickness on the surface of the mandrel by external vapor deposition and sintering process; VAD outsourcing deposition process: Preparation of Si0 ₂ glass of required thickness on the surface of the mandrel by axial vapor deposition and sintering process; APVD Outsourcing process: melting a natural or synthetic quartz powder on a surface of a mandrel with a high-frequency plasma flame to prepare a SiO ₂ glass of a desired thickness;

O / Si ratio: oxygen introduced into the reaction zone ₍₀₂₎ with silicon tetrachloride (SiCl ₄₎ molar ratio.

[0013] The technical problem to be solved by the present invention is to provide a bending-insensitive single-mode optical fiber for the deficiencies of the above prior art, which not only has a lower bending loss, but also has stable mechanical properties by optimizing the fiber profile. Uniform material composition, and can maintain effective mode field diameter and low attenuation performance, and low cost.

[0014] The technical solution adopted by the present invention to solve the above-mentioned problems is:

The core layer and the cladding layer are characterized in that the core layer diameter 2R1 is 7.6 to 8.4 micrometers, and the core layer relative refractive index difference Δ ₁ is 4.66 Χ 10- ^{3 to} 6.12 Χ 10- ³ , and the outer layer of the core layer is from the inside. to outer cladding to the inner, depressed cladding and an outer cladding, the inner cladding diameter 2R2 of 17.4~20 microns, the inner cladding relative refractive index difference Δ ₂ of ^{^{-0.1 X 10- 3 ~0.1 X 10- 3}} , depressed cladding diameter 2R3 is 28~32 microns, depressed cladding relative refractive index difference Δ ₃ is ^{-4.37 X 10- 3 ~- 7.25 X 10-} 3.

[0015] According to the above scheme, the outer cladding layer is coated on the outer cladding layer, the diameter d of the outer cladding layer is 125 micrometers, and the refractive index of the outer cladding layer is the refractive index of the pure silica glass.

[0016] According to the above scheme, the core layer is a quartz glass layer doped with germanium (Ge) and fluorine (F), and the material composition is

Si0 _₂ -Ge0 ₂ -F-Cl, wherein fluorine (F) is a contribution Δ F ^{1 X 10- 3 ~1 · 6 Χ} 10- 3.

[0017] According to the above aspect, the inner cladding layer is a quartz glass layer doped with germanium (Ge) and fluorine (F).

[0018] According to the above scheme, the depressed outer cladding layer is a fluorine-doped (F)-doped quartz glass layer.

[0019] According to the above scheme, the optical fiber has a mode field diameter of 8.2 to 9.2 μm at a wavelength of 1310 nm (nm).

[0020] According to the above scheme, the attenuation coefficient of the optical fiber at a wavelength of 1310 nm is less than or equal to 0.354 dB/km,

The attenuation coefficient at 1383nm wavelength is less than or equal to 0.354dB/km, and the attenuation coefficient at 1550nm wavelength is less than or equal to

0.214dB/km, the attenuation coefficient at 1625nm wavelength is less than or equal to 0.234dB/km.

[0021] According to the above aspect, the optical fiber has a cable cut-off wavelength of less than or equal to 1260 nm.

[0022] According to the above scheme, the optical fiber has an additional loss of less than or equal to 0.03 dB around a radius of 10 mm around a bend of 10 mm at a wavelength of 1550 nm; and an additional loss less than or equal to one turn around a bend radius of 7.5 mm.

0.08 dB _; for a bend around a 5 mm bend radius, the additional loss is less than or equal to 0.15 dB. At a wavelength of 1625 nm, the additional loss is less than or equal to O.ldB for one turn around a bend radius of 10 mm; for a bend around 7.5 mm The additional radius of the curved radius is less than or equal to 0.25 dB around one turn; the additional loss is less than or equal to 0.45 dB for one turn around a 5 mm bend radius.

[0023] According to the above solution, the dynamic fatigue parameter of the optical fiber is 29~33.

[0024] The beneficial effects of the present invention are as follows: 1. By optimizing the fiber profile, especially optimizing the depth and width of the fiber sag outer cladding to form a specific fiber profile structure, the fiber not only has lower bending additional loss, but also It has stable mechanical properties and uniform material composition. 2. Optimization of fiber cross-section structure. On the basis of maintaining effective mode field diameter and bending performance, the proportion of the submerged outer layer in the fiber cross-section is reduced, and the fiber is directly reduced. The deposition processing amount of the core, precision and complex parts in the preform manufacturing, thereby reducing the difficulty of process control, improving the processing efficiency of the optical fiber preform, thereby reducing the manufacturing cost of the optical fiber; 3. The optical fiber of the present invention is in various The performance is far superior to the ITU-T G.657.B3 standard, especially its excellent macrobend performance, which can meet the requirements of FTTH network laying and device miniaturization. 4. The preferred fiber of the present invention is fully compatible with G.652.D fiber and has a lower splice loss when soldered to conventional G.652.D. DRAWINGS

1 is a schematic cross-sectional view of a refractive index of a fiber of the present invention.

detailed description

Detailed embodiments will be given below in conjunction with the drawings.

[0027] Embodiment 1:

The optical fiber includes a core layer and a cladding layer, and the outer layer of the core layer is an inner cladding layer, a depressed outer cladding layer and an outer cladding layer from the inside to the outside. Diameter of core layer 2R1, relative refractive index difference A i, depressed inner cladding and outer cladding diameters are 2R2, 2R3, and the inner cladding relative index difference of the depressed cladding are successively eight, and eight ₂ _3. The outer cladding is coated on the outer cladding layer, the diameter d of the outer cladding is 125 micrometers, and the refractive index of the outer cladding is the refractive index of pure silica glass.

[0028] The core and the inner cladding is doped with germanium and fluorine vitreous silica layer, the material component Si0 _₂ -Ge0 ₂ -F-Cl, in the present embodiment, by optimizing the fiber sectional rational structure, the optical fiber satisfying the performance parameters Based on the G.657.B3 standard, it is compatible with the G.652.D standard and thus has better upward compatibility.

[0029] The macrobend additional loss test method refers to the method specified in IEC 60793-1-47. The longer the wavelength is, the more sensitive it is to bending. Therefore, the main fiber is subjected to bending additional loss at 1625 nm to accurately evaluate the fiber in the full band range. The bending sensitivity of (especially the L-band). The optical fiber is wound into a circle or a circle at a certain diameter, and then the circle is released, and the change of the optical power before and after the loop is tested, thereby taking the macrobend additional loss of the optical fiber. In order to accurately evaluate the mechanical properties of the fiber, a reliable method must be used to test the intensity distribution of the fiber. The screening test screens the fibers with larger cracks, and the fiber tested through the screening test must be further analyzed to find and evaluate the reliability of the fiber. The main performance parameters of the fiber are shown in Table 2.

Table 1 Structure and material composition of the optical fiber Core layer cladding submerged outer layer

Refractive index difference refractive index difference \ refractive index difference

Diameter (l^) Ai diameter (MJ) Δ ₂ diameter (μιη) i Α ₃

(X10- (Χ10" ^! ) il(xio" ³ )

1 7.64 4.75 17.9 0.9 31.1 6.9

2 7.7 5.16 18.2 1.4 30.7 7.15

3 8.09 5.09 19.8 0.6 Ξ9.9 6.86

7.92 5.76 17.9 - 0.9 28.5 6.95

5 8.34 i.98 1 .8 -0.8 28.7 6.89

6 8.16 5.53 17. e 0.5 30.1 7.24

7 7.91 5.62 18.3 1.2 29.2 7.16

8 7.87 5.57 17.8 0.6 30.2 7.25

9 7.88 6.05 19.6 0.4 31.3 7

10 8.25 4.9 18.6 -0.1 28.4 6.8 2 main performance parameters of the fiber

Claims

Claim

The magnetic core layer has a diameter of 2R1 of 7. 6~8. 4 micrometers, and the relative refractive index difference of the core layer is A ^ 4. 66 X 10 - ^{³ ~6.} 12 X 10- ^3, the outer cladding layer from the core layer inside to outside of the inner cladding, the outer cladding and a depressed outer cladding, the inner cladding 17. the diameter 2R2 of 4~20 micrometers, the inner cladding relative refractive index difference Δ ₂ is -0.1 X 10 - ³ 〜0. 1 X 10 - ³ , the diameter of the depressed outer cladding is 2 to ^{3 3} , and the relative refractive index difference Δ ₃ of the depressed outer cladding is -4. 37 X 10 - ³ 〜 - 7. 25 X 10- ^3.

2. The bend insensitive single mode fiber according to claim 1, wherein the depressed outer cladding is covered with an outer cladding, the outer diameter d is 125 micrometers, and the outer cladding has a refractive index of pure silica glass.

3. Press according to claim 12 or bend-insensitive single-mode optical fiber wherein the core is doped with germanium and fluorine vitreous silica layer, the material component Si0 _₂ -Ge0 ₂ -F-Cl, The contribution amount of fluorine is IX 10 - ^{3 to 1.} 6 X 10 - ³ .

4. A bend insensitive single mode fiber according to claim 3, wherein said inner cladding is a quartz glass layer doped with bismuth and fluorine.

5. A bend insensitive single mode fiber according to claim 1 or 2, wherein said depressed outer cladding is a fluorine-doped quartz glass layer.

6微米。 The bending-insensitive single-mode fiber according to claim 1 or 2, characterized in that the mode diameter of the fiber at a wavelength of 1310 nm is 8. 2 ~ 9. 2 microns.

The bend-insensitive single-mode optical fiber according to claim 1 or 2, wherein the optical fiber has an attenuation coefficient at a wavelength of 1310 nm of less than or equal to 0. 354 dB/km, and an attenuation coefficient at a wavelength of 1383 nm is less than or 。 234dB/km, the attenuation coefficient at a wavelength of 1550nm is less than or equal to 0. 214dB / km, the attenuation coefficient at a wavelength of 1625nm is less than or equal to 0. 234dB / km.

8. A bend insensitive single mode fiber according to claim 1 or 2, wherein said fiber has a cable cut-off wavelength of less than or equal to 1260 nm.

And the additional loss is less than or equal to 0. 03dB; for the bending of the optical fiber at a wavelength of 1550 nm, for a bending radius around a radius of 10 mm; The additional loss is less than or equal to 0.08 dB around a 7.5 mm bend radius around one turn. For a bend around a 5 mm bend radius, the additional loss is less than or equal to 0.15 dB; at a wavelength of 1625 nm, for a bend radius around 10 mm The additional loss is less than or equal to 0. ldB; for a bending radius around 7.5 mm, the additional loss is less than or equal to 0.25 dB around 1 mm of the bending radius. The additional loss is less than or equal to 0 around 1 radius around the 5 mm bending radius. 45dB.

10. The bend insensitive single mode fiber according to claim 1 or 2, wherein the fiber has a dynamic fatigue parameter of 29 to 33.