CN102645699B - Low-attenuation bend-insensitive single-mode fiber - Google Patents

Abstract

The invention relates to a low-attenuation bend-insensitive single-mode optical fiber used in an optical fiber communication system, which includes a core layer and three cladding layers, and is characterized in that the relative refractive index difference Δ1 of the core layer is 0.1% to 0.30%, and the radius R1 3.5μm~4.5μm, there are three cladding layers outside the core layer, the first cladding layer is the inner cladding layer closely surrounding the core layer, its relative refractive index difference Δ2 is 0.1%~-0.1%, the radius R2 is 8μm~10μm, the second The second cladding is a depressed cladding, closely surrounding the inner cladding, its relative refractive index difference Δ3 is -0.4%~-0.1%, and Δ3 is less than Δ2, the radius R3 is 12μm~20μm, and the third cladding is the outer cladding, closely surrounding For all layers in the depressed cladding, the relative refractive index difference Δ4 is -0.20%~0.1%. On the basis of being fully compatible with the existing G.652 standard, the present invention has attenuation performance far superior to conventional G.652.D optical fibers, can meet the macroscopic bending requirements of the G.657.A1 standard, and is beneficial to dense wavelength division multiplexing with system applications.

Description

A low-attenuation bend-insensitive single-mode fiber

technical field

The invention relates to a low-attenuation bend-insensitive single-mode optical fiber used in an optical fiber communication system. The optical fiber has improved bending resistance and lower optical fiber loss, and belongs to the technical field of optical communication. the

Background technique

At present, in the field of optical fiber communication, two types of optical fibers are mainly used, single-mode optical fiber and multi-mode optical fiber. Compared with multimode fiber, single-mode fiber has the advantages of fast transmission rate, large information carrying capacity, and long transmission distance. It is widely used in the construction of optical fiber communication networks. Among them, the optical fiber that meets the ITU-T G. It is also the most widely used fiber in single-mode fiber. With the continuous development of FTTx in recent years, the performance of the original G.652 optical fiber can no longer meet user requirements, and then on the basis of G.652 optical fiber, a new generation of bend-insensitive optical fiber, G.657 optical fiber, has been developed. Among them, the latest G.657 optical fiber standard issued by ITU-T subdivides the G.657 optical fiber into G.657.A class compatible with the G.652 standard and G class not compatible with the G.652 standard. .657. Class B. Among them, the G.657.A fiber is considered to be one of the products most likely to replace the existing G.652 fiber because it is compatible with the G.652 standard and has good bending performance. On the other hand, with the further development of optical amplification technology and wavelength division multiplexing technology, the optical fiber communication system is developing towards higher transmission power and longer transmission distance. As an important transmission medium in optical fiber communication systems, the related performance indicators of single-mode optical fibers need to be further improved to meet the actual development needs of optical fiber communication systems. The attenuation coefficient and mode field diameter of the fiber are two important performance indicators of the single-mode fiber. The smaller the attenuation coefficient of the optical fiber, the longer the transmittable distance of the optical signal it carries. The larger the mode field diameter of the fiber, the larger the effective area, and the weaker the nonlinear effect. The large effective area can effectively suppress nonlinear effects such as self-phase modulation, four-wave mixing, and cross-phase modulation, ensuring the transmission quality of high-power optical signals. Reducing the attenuation coefficient and increasing the effective area can effectively improve the optical signal-to-noise ratio (OSNR: optical-signal-to-noise ratio) in the optical fiber communication system, and further improve the transmission quality and transmission distance of the system. At present, most of the commercialized G.657 optical fibers have excellent bending properties and are compatible with G.652 optical fibers, but they generally have the problem of small mode length and diameter, and the attenuation coefficient of G.657 optical fibers is basically the same as that of G.657 optical fibers. The original G.652 optical fiber is basically the same, there is no major improvement. Inventing a new generation of single-mode fiber that is compatible with the G.652 standard, has bending insensitivity, and has a relatively large mode field diameter with a low attenuation coefficient has become a new challenge in the field of optical communication. the

For single-mode fiber, the attenuation coefficient of the fiber can be expressed by formula (1):

α = R/λ ⁴ +α _IR + α _IM +α _OH +α _UV +B (1)

Where R is the Rayleigh scattering coefficient, α _IR , α _IM , α _OH , α _UV represent infrared absorption, defect attenuation, OH absorption, and ultraviolet absorption, respectively. In optical fiber materials, the scattering of light due to inhomogeneity constitutes the scattering loss of the optical fiber. Among them, the Rayleigh scattering of optical fiber is one of the three scattering mechanisms, which is linear scattering (that is, it has nothing to do with the frequency of the optical signal). The characteristic of Rayleigh scattering is that its size is inversely proportional to the fourth power of the wavelength, and the loss caused by it is related to the type and concentration of doping materials.

In order to reduce optical fiber attenuation, the following methods can generally be used in the manufacturing process of optical fiber preforms, such as using higher-purity raw materials, improving the production environment and equipment sealing performance to reduce the probability of foreign impurities being introduced, or using larger outer diameters. The preform manufacturing process reduces the overall attenuation of the optical fiber through the dilution effect of the large-size preform. However, from the perspective of cost control and process control, reducing the doping of the fiber and optimizing the profile of the fiber is the simplest and most effective way to reduce the attenuation of the fiber. the

In general, the lower the concentration of dopant material, the smaller the loss due to Rayleigh scattering. Reducing the content of impurities in raw materials, improving the environmental cleanliness in the optical fiber manufacturing process, and reducing the content of impurities introduced from the outside are also a method to reduce the attenuation of optical fibers, such as patent CN201110178833. method to reduce the introduction of external impurities. In the optical fiber manufacturing process, the coating process of the bare optical fiber surface coating is also an important parameter that affects the attenuation performance of the optical fiber. the

However, no matter from the theory or the actual optical fiber manufacturing process, by optimizing the parameters such as core diameter and cladding fluorine concentration, not only the effective area of the single-mode fiber can be increased, but also the Rayleigh scattering in the fiber can be effectively reduced. It is an effective and reliable method to reduce fiber attenuation. However, a larger effective area will cause a significant increase in the bending loss of the fiber (including the macrobending loss and microbending loss of the fiber), especially in the long wavelength region. During the cabling process of the optical fiber or the actual laying and use process, if the bending resistance of the optical fiber cannot meet the requirements, the loss of the signal will increase, and the transmission quality of the signal cannot be guaranteed. Therefore, while the optical fiber has the characteristics of large effective area and low attenuation, it is a difficult problem in the design and manufacture of optical fiber to ensure the macrobending and microbending performance of the optical fiber. the

For ordinary G657 optical fiber, such as a conventional G657 optical fiber profile and manufacturing method described in Chinese patent CN101598834A, the core layer is co-doped with Ge & F. In order to obtain the best macrobending performance, the relative refractive index of the core layer is generally greater than 0.35%, that is, the core layer is doped with more Ge, so it will cause greater Rayleigh scattering, thereby increasing the attenuation of the fiber. the

In order to optimize the attenuation performance of optical fibers, researchers from various countries have done a series of studies. Among them, Chinese patent CN102156323A describes a method of manufacturing a "pure silicon core" large effective area bend-insensitive optical fiber. There is no doping in the core layer (that is, pure silica quartz glass), and the structure of the sunken outer cladding optimizes the macrobending performance of the fiber. However, the "pure silica core" fiber has no doping in the core layer, and the core refractive index is close to that of pure silica, so the glass viscosity of the fiber core layer is relatively high, which brings a lot of problems in the control of fiber drawing tension and the design of fiber profile. A series of problems, and because of its high cut-off wavelength of optical cables, and nonlinear effects, it is difficult to be compatible with existing networks. the

US Pat. No. 6,917,740 describes a pure silicon core single-mode optical fiber with improved material viscosity mismatch and its manufacturing method. By doping chlorine (Cl) and fluorine (F) in the core layer, the difference between the glass transition temperature Tg of the core layer and the cladding layer is reduced to within 200°C, and the attenuation performance of the optical fiber is optimized. This patent does not involve the research and improvement of the bending performance of the optical fiber, nor does it involve the optical transmission performance of the optical fiber. In U.S. Patent No. 6,449,415, a core layer doped with chlorine (Cl), its relative refractive index is positive, the cladding is doped with fluorine (F), its relative refractive index is negative, and the fiber has an inner cladding It is a structure of depressed cladding. The chlorine-doped core material can effectively reduce the mismatch of the fiber core cladding material and reduce the additional stress generated by the drawing process. At the same time, the inner cladding is a sunken cladding structure, which can improve the bending performance of the optical fiber. However, the sunken cladding structure improves the bending performance. The performance capability is limited, and it will also affect other optical parameters of the fiber, such as the mode field diameter and cut-off wavelength of the fiber. Moreover, in the case of unreasonable design of the outer cladding parameters, the inner depressed cladding structure may cause the leakage problem of the LP01 mode (that is, the attenuation coefficient of the single-mode fiber increases sharply in the long wavelength region). the

In order to optimize the bending performance of single-mode fiber, the following three methods are currently used: one is to adjust the MAC value of the fiber (that is, the ratio of the fiber mode field diameter to the cut-off wavelength). The smaller the MAC value, the better the bending resistance of the fiber. However, the reduction of the mode field diameter will result in a reduction of the effective area, and it is easier to cause more defects and increase the attenuation during wire drawing. At the same time, the cut-off wavelength of the fiber must be smaller than the working wavelength to ensure the single-mode working characteristics, so There is limited space to improve the bending performance of the fiber by changing the MAC value of the fiber. The second is that the bending performance can be improved by using a double-clad structure in which the inner cladding is a depressed cladding, but the depressed cladding may cause the "LP01 mode leakage" phenomenon of the optical fiber. The third is to add a layer of trench-like depressed cladding (trench) outside the inner cladding of the optical fiber to improve the bending performance of the optical fiber while ensuring a large mode field diameter. This method is not sensitive to bending in single-mode optical fibers (ie G.657 optical fiber) has been widely used, such as Chinese patent CN101598834A, US patent US7450807 and European patent EP1978383, etc. No relevant patents or literature reports have been found to further improve the performance of this type of fiber by combining low doping, large core diameter and depressed cladding (trench). Between the attenuation coefficient, effective area and bending performance To achieve effective integration and unity. the

Contents of the invention

To facilitate the introduction of the content of the invention, some terms are defined:

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

Refractive index profile: the relationship between the glass refractive index of an optical fiber or optical fiber preform (including the core rod) and its radius;

Relative refractive index difference: Δn _i =|n _i -n ₀ |, n _i and n ₀ are respectively the refractive index of each part of the corresponding optical fiber and the refractive index of pure silica glass.

Contribution of fluorine (F): the absolute value of the difference in refractive index between fluorine-doped (F) quartz glass and pure quartz glass, that is, ΔF=|n _F -npure _quartz |, which represents fluorine-doped (F) quantity;

Contribution of germanium (Ge): the absolute value of the difference in refractive index between germanium (Ge) doped quartz glass and pure quartz glass, that is, ΔGe=|n _Ge -n _{pure quartz} |, which represents germanium (Ge) doped quantity;

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

RIT process: the core rod is inserted into the sleeve to form an optical fiber preform;

OVD outsourcing deposition process: use external vapor deposition and sintering process to prepare SiO2 glass with required thickness on the surface of core rod;

VAD outsourcing deposition process: use axial vapor deposition and sintering process to prepare SiO2 glass with required thickness on the surface of core rod;

APVD outsourcing process: use high-frequency plasma flame to melt natural or synthetic quartz powder on the surface of core rod to prepare SiO2 glass with required thickness;

O/Si ratio: The molar ratio of oxygen (O2) to silicon tetrachloride (SiCl4) passed into the reaction zone.

The technical problem to be solved by the present invention is to provide a low-attenuation bend-insensitive single-mode optical fiber with reasonable refractive index profile design, low attenuation and good bending resistance in view of the above-mentioned deficiencies in the prior art. the

The technical scheme of the single-mode optical fiber of the present invention is:

It includes a core layer and three cladding layers. The difference is that the relative refractive index difference Δ1 of the core layer is 0.1%~0.30%, the radius R1 is 3.5μm~4.5μm, and there are three cladding layers outside the core layer. The first cladding layer The layer is the inner cladding closely surrounding the core layer, its relative refractive index difference Δ2 is 0.1%~-0.1%, the radius R2 is 8μm~10μm, the second cladding is a sunken cladding, closely surrounding the inner cladding, its relative refractive index difference Δ3 is -0.4%~-0.1%, and Δ3 is less than Δ2, the radius R3 is 12μm~20μm, the third cladding is the outer cladding, which closely surrounds all the layers of the sunken cladding, which is compared with the refractive index of pure quartz, The relative refractive index difference Δ4 is -0.20%~0.1%.

According to the above scheme, the core layer is composed of quartz glass doped with fluorine (F) and germanium (Ge) or quartz glass doped with other dopants, and the contribution of fluorine (F) in the core layer ΔF is -0.08 %~-0.02%. the

According to the above scheme, the first cladding layer is composed of quartz glass or pure quartz glass doped with fluorine (F) and germanium (Ge) at the same time, the ratio R2/R1 of the radius R2 of the first cladding layer to the radius R1 of the core layer is 1.7~2.9, and the difference Δ1-Δ2 of the relative refractive index difference between the first cladding layer and the core layer is 0.2%~0.40%. the

According to the above scheme, the second cladding layer is composed of fluorine (F) doped quartz glass, and its relative refractive index difference Δ3 is smaller than that of other cladding layers. the

According to the above solution, the third cladding layer may be a pure quartz glass layer, or a quartz glass layer doped with fluorine or other dopants. the

The optical fiber of the present invention has the following characteristics:

The mode field diameter of the optical fiber at the wavelength of 1310nm is 8.6~9.8 microns, the zero dispersion wavelength is 1300~1324nm, and the dispersion slope of the optical fiber at the zero dispersion wavelength is not more than 0.092ps/nm2*km.

The attenuation coefficient of optical fiber at 1310nm wavelength is less than or equal to 0.325dB/km, the attenuation coefficient at 1383nm wavelength is less than or equal to 0.325dB/km, and the attenuation coefficient at 1550nm wavelength is less than or equal to 0.185dB/km. the

The optical fiber has a cable cutoff wavelength less than or equal to 1260nm. the

At a wavelength of 1625 nanometers, the additional loss is less than or equal to 1dB or even 0.1dB for 10 turns around the bending radius of 15mm; the additional loss is less than or equal to 1.5dB or even 0.2dB for 1 turn around the bending radius of 10mm . 

The beneficial effects of the present invention are: 1. On the basis of being fully compatible with the existing G.652 standard, it has an attenuation performance far superior to that of conventional G.652.D optical fibers, thereby reducing the need for construction of related base stations and The cost of other system equipment. 2. Compared with the ordinary G.652 optical fiber, the second cladding with the smallest relative refractive index in this optical fiber structure can effectively confine the optical signal to propagate in the fiber core, and at the same time, in the bent state, it can effectively prevent the optical signal from going to the The external leakage ensures the bending resistance of the optical fiber, including the macrobending resistance and microbending performance of the optical fiber, which can meet the macrobending requirements of the G.657.A1 standard and ensure the attenuation performance of the optical fiber after being cabled. 3. Compared with the conventional G.657 optical fiber, the mode field diameter of the optical fiber of the present invention is larger, and its effective area is also increased accordingly, so that greater power into the fiber can be obtained, which is beneficial to Dense Wavelength Division Multiplexing (DWDM) system application. 4. Due to the relative increase in mode length and diameter, when the optical fiber of the present invention is fused with a conventional G.652 optical fiber, the splicing loss is smaller and the compatibility is higher. 5. The core layer is doped with fluorine and germanium at the same time, so that the viscosity of the core layer material is reduced, which can match the viscosity of the core layer and the cladding layer, and avoid the viscosity mismatch of the "pure silicon core" optical fiber, so that the inside of the optical fiber after drawing The residual stress of the fiber will be further reduced, which is beneficial to improve the attenuation performance of the fiber, and the fluorine-doped (F) contribution of the fluorine-doped layer of the second cladding layer is less than -0.20%, forming a "sag cladding layer" on the fiber section. " structure to ensure avoiding the phenomenon of "LP01 mold leakage", and because its viscosity is greater than that of the second cladding, the third cladding material with higher viscosity will carry a larger proportion of the drawing tension during drawing, so that it can be effectively It prevents the stress caused by the drawing tension from concentrating on the fiber core to increase the attenuation of the fiber, and improves the reliability of the fiber in use.

Description of drawings

Fig. 1 is a radial cross-sectional schematic view of an embodiment of the present invention. In the figure, 00 corresponds to the core layer of the optical fiber, 10 corresponds to the first cladding layer of the optical fiber, 20 corresponds to the second cladding layer of the optical fiber, and 30 corresponds to the third cladding layer of the optical fiber. the

Fig. 2 is a schematic diagram of the refractive index profile of an embodiment of the present invention. the

Detailed ways

Detailed examples will be given below to further illustrate the present invention. the

The bare optical fiber in this embodiment includes a core layer and a cladding layer. The core layer 00 is composed of quartz glass doped with fluorine (F) and germanium (Ge) or quartz glass doped with fluorine and other dopants; surrounding the core layer There are three cladding. The first cladding layer 10 closely surrounds the core layer and is composed of quartz glass doped with fluorine (F) and germanium (Ge) prepared by PCVD process; the second cladding layer 20 closely surrounds the first cladding layer, and the second cladding layer is made of fluorine-doped (F) A silica glass composition whose relative refractive index Δ3 is smaller than that of the other cladding layers. The third cladding 30 is all layers that immediately surround the second cladding. The third cladding layer can be a quartz glass layer doped with fluorine or other dopants, or the third cladding layer can be a pure silicon layer, that is, the relative refractive index difference is 0%. The coating layer of the optical fiber in this embodiment adopts the "wet on wet (wet on wet)" coating process, and the drawing speed is 1000-1500m/min. the

According to the technical scheme of the above-mentioned single-mode optical fiber, the parameters of the optical fiber are designed within the specified range, and the mandrel manufacturing process such as the known PCVD process, MCVD process, OVD process or VAD process is manufactured according to the design requirements of the optical fiber Mandrel, the entire preform is manufactured through outsourcing processes such as casing process, OVD process or VAD process. The PCVD process has certain advantages when performing high-concentration fluorine (F) doping. the

The refractive index profile of the pulled optical fiber was tested using NR-9200 equipment (EXFO). The refractive index profile of the optical fiber and the main parameters of the dopant material are shown in Table 1. the

The macrobending additional loss test method refers to the method specified in IEC 60793-1-47. Since the longer the wavelength is, the more sensitive it is to bending, so the bending additional loss of the optical fiber at 1550nm and 1625nm wavelength is mainly tested to accurately evaluate the optical fiber in the whole band range. Bend sensitivity within (especially L-band). Wind the optical fiber into 1 circle or 10 circles according to a certain diameter, and then release the circle, and test the change of optical power before and after the circle, which is used as the macrobending additional loss of the fiber. the

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

Experiments show that the mode field diameter of the optical fiber manufactured according to the technical scheme of the present invention can reach more than 8.7 μm at the wavelength of 1310 nm, the cut-off wavelength of the optical cable is guaranteed to be below 126 nm, and the attenuation coefficient at the wavelength of 1550 nm is guaranteed to be 0.185 dB/km Below, and the optical fiber has good bending resistance, including good macrobending resistance and microbending performance. At the wavelength of 1550nm, the additional loss of the fiber is less than or equal to 0.5dB for one turn around the bending radius of 10mm; for around 15mm The additional loss of bending radius around 10 turns is less than or equal to 0.2dB; at the wavelength of 1625nm, the additional loss of bending around a bending radius of 10mm is less than or equal to 1.0dB; the additional loss of bending around a bending radius of 15mm is less than or equal to 10 turns 0.8dB. At the same time, the microbending loss of the optical fiber at 1700nm is less than 1.5dB/km. the

Table 1: Structure and material composition of optical fibers

Table 2: Main performance parameters of optical fibers

Claims (8)

1. A low-attenuation bend-insensitive single-mode optical fiber, comprising a core layer and three cladding layers, characterized in that the relative refractive index difference Δ1 of the core layer is 0.1% ~ 0.30%, and the radius R1 is 3.5 μm ~ 4.5 μm, There are three cladding layers outside the core layer, the first cladding layer is the inner cladding layer closely surrounding the core layer, its relative refractive index difference Δ2 is 0.1%~-0.1%, the radius R2 is 8μm~10μm, and the second cladding layer is the sunken cladding layer , closely surrounds the inner cladding, its relative refractive index difference Δ3 is -0.4%~-0.1%, and Δ3 is less than Δ2, the radius R3 is 12μm~20μm, the third cladding is the outer cladding, and closely surrounds all the layers of the sunken cladding , the relative refractive index difference Δ4 is -0.20%~0.1%. 2. The low-attenuation bend-insensitive single-mode optical fiber according to claim 1, characterized in that the first cladding is composed of quartz glass or pure silica glass doped with fluorine (F) and germanium (Ge) at the same time, the second The difference Δ1-Δ2 of the relative refractive index difference between a cladding layer and the core layer is 0.2%~0.40%. 3. The low-attenuation bend-insensitive single-mode optical fiber according to claim 1 or 2, characterized in that the second cladding is composed of fluorine-doped silica glass, and its relative refractive index difference Δ3 is smaller than that of other claddings. 4. The low-attenuation bend-insensitive single-mode optical fiber according to claim 1 or 2, characterized in that said third cladding layer is a pure silica glass layer, or a silica glass layer doped with fluorine or other dopants. 5. The low-attenuation bend-insensitive single-mode optical fiber according to claim 1 or 2, characterized in that the mode field diameter of the optical fiber at a wavelength of 1310 nm is 8.6 to 9.8 microns. 6. The low-attenuation bend-insensitive single-mode optical fiber according to claim 1 or 2, characterized in that the attenuation coefficient of the optical fiber at 1310nm wavelength is less than or equal to 0.325dB/km, and the attenuation coefficient at 1550nm wavelength is less than or equal to 0.185dB /km. 7. The low-attenuation bend-insensitive single-mode optical fiber according to claim 1 or 2, characterized in that the optical fiber has a cable cut-off wavelength less than or equal to 1260nm. 8. The low-attenuation bend-insensitive single-mode optical fiber according to claim 1 or 2, characterized in that the optical fiber is at a wavelength of 1625 nm, and the additional loss is less than or equal to 1dB for bending 10 turns around a bending radius of 15 mm; The additional loss of the bending radius of mm is less than or equal to 1.5dB around one turn.