CN104898201B - A kind of single-mode fiber of ultralow attenuation large effective area - Google Patents

Abstract

The present invention relates to a kind of single-mode fiber of ultralow attenuation large effective area, include sandwich layer and covering, it is characterised in that core radius R₁For 4.5~6.5 μm, sandwich layer Δ 1 is 0.05%~0.10%, coats inner cladding outside sandwich layer successively from inside to outside, the first sagging inner cladding, middle inner cladding, the second sagging inner cladding, aids in surrounding layer and surrounding layer, inner cladding diameter R₂For 8.5~14 μm, Δ 2 is 0.35%~0.12%, the first sagging inner cladding diameter R₃For 13~22 μm, Δ 3 is 0.7%~0.30%, middle inner cladding diameter R₄For 14~23 μm, Δ 4 is 0.40%~0.15%；Second sagging inner cladding diameter R₅For 18~30 μm, Δ 5 is 0.6%~0.25%；Aid in surrounding layer radius R₆For 35~50 μm, Δ 6 is 0.55%~0.15%；Surrounding layer is pure silicon dioxide glassy layer.The present invention not only decays low, and effective area is big, and cabled cutoff wavelength is less than 1530nm, and has preferable bending loss, dispersion.

Description

A single-mode optical fiber with ultra-low attenuation and large effective area

technical field

The invention relates to the technical field of optical fiber transmission, in particular to a single-mode optical fiber with ultra-low attenuation and large effective area.

Background technique

With the rapid growth of IP network data services, operators' demand for transmission capacity continues to increase, and the single-fiber capacity in the existing network is gradually approaching the limit value of 100Tbps. The 100G transmission system has entered the first year of commercial use. How to further increase the transmission capacity on the basis of 100G transmission signals is the focus of attention of various system equipment manufacturers and operators.

In 100G and beyond 100G systems, the receiving end adopts coherent reception and digital signal processing technology (DSP), which can digitally compensate the dispersion and polarization mode dispersion (PMD) accumulated in the entire transmission process in the electrical domain; Use various high-order modulation methods to reduce the baud rate of the signal, such as PM-QPSK, PDM-16QAM, PDM-32QAM, and even PDM-64QAM and CO-OFDM. However, high-order modulation methods are very sensitive to nonlinear effects, so higher requirements are placed on the optical signal-to-noise ratio (OSNR). The introduction of low-loss and large-effective-area optical fibers can improve the OSNR and reduce nonlinear effects for the system. When a high-power-density system is used, the nonlinear coefficient is a parameter used to evaluate the performance of the system caused by nonlinear effects. Defined as n2/A _eff . Among them, n2 is the nonlinear refractive index of the transmission fiber, and A _eff is the effective area of the transmission fiber. Increasing the effective area of the transmission fiber can reduce nonlinear effects in the fiber.

At present, the effective area of ordinary single-mode optical fibers used in land transmission system lines is only about 80um ² . In land long-distance transmission systems, the requirements for the effective area of the optical fiber are higher, and the general effective area is above 100um ² . In order to reduce the laying cost and reduce the use of repeaters as much as possible, in a non-repeater transmission system, such as a submarine transmission system, the effective area of the transmission fiber is preferably above 130um ² . However, in the current design of the refractive index profile of an optical fiber with a large effective area, a large effective area is often obtained by increasing the diameter of the optical core layer used to transmit optical signals. There are certain design difficulties in this kind of scheme. On the one hand, the core layer of the optical fiber and the cladding layer close to it mainly determine the basic performance of the optical fiber, and occupy a large proportion in the cost of optical fiber manufacturing. If the radial dimension of the design is too large, it will inevitably increase the manufacturing cost of the optical fiber. Raising the price of optical fiber will become an obstacle to the widespread application of this type of optical fiber. On the other hand, compared with ordinary single-mode fiber, the increase in the effective area of the fiber will lead to the deterioration of some other parameters of the fiber: for example, the cut-off wavelength of the fiber will increase. If the cut-off wavelength is too large, it will be difficult to ensure that the fiber is in the transmission band. The single-mode state of the optical signal; in addition, if the refractive index profile of the fiber is not properly designed, it will also lead to the deterioration of parameters such as bending performance and dispersion.

Another optical fiber characteristic that limits long-distance and large-capacity transmission is attenuation. At present, the attenuation of conventional G.652.D optical fibers is generally 0.20dB/km, and the laser energy gradually decreases after long-distance transmission, so relays are required. The form of the signal is amplified again. Compared with the cost of optical fiber and cable, the related equipment and maintenance costs of relay stations account for more than 70% of the entire link system. Therefore, if a low-attenuation or ultra-low attenuation optical fiber is involved, the transmission distance can be effectively extended and construction and maintenance costs can be reduced. . After relevant calculations, if the attenuation of the optical fiber is reduced from 0.20 to 0.16dB/km, the construction cost of the entire link will be reduced by about 30%.

To sum up, the development and design of an ultra-low attenuation and large effective area optical fiber has become an important topic in the field of optical fiber manufacturing. The document US2010022533 proposes a design of a large effective area optical fiber. In order to obtain a lower Rayleigh coefficient, it adopts the design of a pure silicon core without co-doping of germanium and fluorine in the core layer, and its design uses fluorine-doped of silica as the outer coating. For the design of this pure silicon core, it requires complex viscosity matching inside the optical fiber, and requires extremely low speed in the drawing process to avoid the increase in attenuation caused by defects inside the optical fiber caused by high-speed drawing, and the manufacturing process is extremely complicated. .

Document EP2312350 proposes a large effective area optical fiber design with a non-pure silica core design, which adopts a stepped sunken cladding structure design, and there is a design that uses a pure silica outer cladding structure, and the related performance can reach a large effective area optical fiber G .654.B and D requirements. However, in its design, the maximum radius of the fluorine-doped cladding part is 36 μm, although the cut-off wavelength of the fiber can be guaranteed to be less than or equal to 1530 nm, but due to the influence of its small fluorine-doped radius, the microscopic and macroscopic bending properties of the fiber become worse. Therefore, in the process of fiber optic cabling, the attenuation will increase, and the relevant bending performance is not mentioned in the literature.

Document CN10232392A describes an optical fiber with a larger effective area. Although the effective area of the fiber described in this invention has reached more than 150 μm ² , it is achieved by adopting the conventional core layer design in the co-doped mode of germanium and fluorine, and by sacrificing the performance index of the cut-off wavelength. It allows the cut-off wavelength of the optical cable to be above 1450nm, and in the described embodiment, the cut-off wavelength of the cable even reaches above 1800nm. In practical applications, it is difficult to ensure that the optical fiber is cut off in the application band if the cut-off wavelength is too high, and it is impossible to ensure that the optical signal is in a single-mode state during transmission. Therefore, this type of fiber may face a series of practical problems in application. In addition, in the examples cited in the invention, the minimum outer diameter R ₃ of the depressed cladding is 16.3 μm, which is also somewhat large. This invention fails to achieve an optimal combination of fiber parameters (eg, effective area, cut-off wavelength, etc.) and fiber manufacturing costs.

From the above analysis, we can find that it is feasible to use impure silicon core and partially fluorine-doped cladding for ultra-low attenuation optical fiber process design. However, due to the limitation of fiber waveguide design, if pure silica is used as the outer cladding material, how to control the optical parameters of the fiber under such a design is a challenge we face.

Because if pure silicon dioxide without fluorine doping is used as the outer cladding material, three problems will be faced.

First, suppress the fundamental mode cut-off: In the design of optical fiber waveguide, if the difference in refractive index between the outer cladding material and the core material is too small, it will cause the fundamental mode of the optical fiber to leak, thereby affecting the attenuation of the optical fiber. Therefore, the ultra-low attenuation and large effective area optical fiber designed with non-F-doped outer cladding material, because the core layer diameter is larger than the traditional optical fiber, it must be located in the middle of the outer cladding layer and the core layer. mold leakage.

Generally, the traditional large effective area optical fiber adopts a single depressed cladding structure to optimize the waveguide of the glass part of the optical fiber. The main purpose is, first of all, to use the sunken structure to optimize the MFD to obtain a larger effective area, which is the most commonly used method in optical design; secondly, because the core diameter of the fiber with a large effective area is generally relatively large, resulting in the bending of the fiber The performance is poor, so the bent cladding structure is used to optimize the bending performance of the fiber.

The single depressed cladding structure is relatively simple to design and manufacture, so it is very common in ordinary, especially large effective area fiber designs with conventional attenuation coefficients. However, if in the design of ultra-low attenuation and large effective area optical fiber, especially in the ultra-low attenuation and large effective area optical fiber using pure silica material as the outer cladding, because the refractive index of the core layer is the same as that of the pure silica outer cladding The difference is not large, and the core diameter of the large effective area fiber design is generally very large, which is more likely to cause the most troublesome fundamental mode leakage in the fiber waveguide design, causing abnormal long-wavelength attenuation of the fiber. Conventional solutions, such as increasing the volume of a single depressed cladding, will cause the cut-off wavelength of the fiber to exceed the standard. Therefore, finding a better design method for the depressed cladding is also the focus of achieving ultra-low attenuation and large effective area optical fiber design.

Second, consider viscosity matching: If there is no viscosity optimization design in the outer cladding material, its viscosity will not match the viscosity gradient of the inner cladding and core layers, which will also cause defects in the interface position and virtual temperature rise, thereby increasing the optical fiber attenuation. By using a single depressed cladding structure or a double depressed cladding structure, while realizing the optimization of the fiber waveguide, the different doping of different depressed structures is used, which is more conducive to the matching design of the fiber section viscosity. In short, if the design of the sunken cladding is not used, then the viscosity design of the inner cladding part has only one gradient; with a single sunken cladding structure, one gradient can be increased; with a double sunken cladding structure, it is equivalent to an increase of three gradient (the doping of the two sunken cladding positions is different, and the position between the sunken cladding and the sunken cladding can also use special viscosity design).

Third, consider optical profile matching: if pure silica glass is used as the outer cladding material, when considering the viscosity matching design, the doping concentration of each part is limited, and in order to prove that the optical parameters of the fiber meet the requirements of G652 or G654 fiber The parameter requirements not only ensure that the MFD, dispersion and bending performance of the optical fiber meet the standard requirements, but also require us to consider the optical profile design. This requires us to comprehensively consider the optical design of the optical fiber when designing the viscosity, which increases the difficulty of process realization.

Document US8515231B2 proposes a single-mode optical fiber with a double depressed cladding structure, but the design of the high-concentration Ge-doped core rod used in it has a small core diameter, so it cannot achieve ultra-low attenuation performance, and the effective area is significantly smaller than 100 μm ² , can not suppress the nonlinear effect of the fiber.

Contents of the invention

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

Relative refractive index Δn _i :

Counting from the axis of the fiber core, according to the change of the refractive index, the layer closest to the axis is defined as the core layer, and the outermost layer of the fiber, that is, the pure silica layer, is defined as the outer cladding of the fiber.

The relative refractive index Δi of each layer of the fiber is defined by the following equation:

Among them, n _i is the refractive index of the fiber core, and _nc is the refractive index of the outermost cladding layer, that is, the refractive index of pure silicon dioxide without Ge or F doping.

The relative refractive index contribution ΔGe of Ge doping in the fiber core is defined by the following equation,

where n _Ge is the Ge dopant of the hypothetical core, when doped into pure silica without other dopants, it will cause a change in the refractive index of silica glass, where n _c is the refractive index of the outermost cladding, That is, the refractive index of pure silicon dioxide without Ge or F doping.

Effective area A _eff. of optical fiber:

Among them, E is the electric field related to propagation, and R is the distance from the axis to the distribution point of the electric field.

Cable cut-off wavelength λ _cc :

IEC (International Electrotechnical Commission) standard 60793-1-44 defines: the cut-off wavelength λ _cc of the optical cable is the wavelength at which the optical signal no longer propagates as a single-mode signal after propagating 22 meters in the optical fiber. During the test, it is necessary to obtain data by winding a circle with a radius of 14cm and two circles with a radius of 4cm around the optical fiber.

The technical problem to be solved by the present invention is to design a single-mode optical fiber with ultra-low attenuation and large effective area with low optical fiber manufacturing cost, its cabled cut-off wavelength is less than 1530nm, and it has better bending loss and dispersion performance.

The technical scheme adopted by the present invention to solve the above-mentioned problems is: comprising a core layer and _a cladding layer, characterized in that the core layer radius R1 is 4.5-6.5 μm, and the core layer relative refractive index difference Δ1 is -0.05 % to 0.10%, the core layer is coated with inner cladding from inside to outside, the first sunken inner cladding, the middle inner cladding, the second sunken inner cladding, the auxiliary outer cladding and the outer cladding, and the inner cladding radius R of the optical fiber is R ₂ The relative refractive index difference Δ2 is -0.35%～-0.12%, the radius _R3 of the first depressed inner cladding is 13～22μm, and the relative refractive index difference Δ3 is -0.7%～-0.30%. _The radius R4 of the inner cladding is _14-23 μm, and the relative refractive index difference Δ4 is -0.40% to -0.15%; the radius R5 of the second depressed inner cladding is 18-30 μm, and the relative refractive index difference Δ5 is -0.6% to -0.25% The radius R ₆ of the auxiliary outer cladding is 35-50 μm, and the relative refractive index difference Δ6 is -0.55% to -0.15%; the outer cladding is a pure silica glass layer.

According to the above scheme, the core layer of the optical fiber is a silica glass layer co-doped with germanium and fluorine, or a silica glass layer doped with germanium, wherein the relative refractive index contribution ΔGe of the germanium doping in the core layer is 0.02% to 0.10 %.

According to the above solution, the radius of the middle inner cladding layer is greater than the radius of the first depressed inner cladding layer, and R ₄ -R ₃ ≥ 1 μm.

According to the above solution, the effective area of the optical fiber at a wavelength of 1550 nm is 100-145 μm ² , preferably 120-140 μm ² .

According to the above solution, the cabled cut-off wavelength of the optical fiber is equal to or less than 1530nm.

According to the above scheme, the zero dispersion point of the optical fiber is less than or equal to 1300nm.

According to the above solution, the dispersion of the optical fiber at a wavelength of 1550nm is equal to or less than 23ps/nm*km, and the dispersion of the optical fiber at a wavelength of 1625nm is equal to or less than 27ps/nm*km.

According to the above scheme, the attenuation of the optical fiber at a wavelength of 1550nm is equal to or less than 0.175dB/km; under optimal conditions, it is equal to or less than 0.170dB/km; the attenuation of the optical fiber at a wavelength of 1625nm is equal to or less than 0.204dB/km ; Equal to or less than 0.194dB/km under optimal conditions.

According to the above solution, the microbending loss of the optical fiber at a wavelength of 1700nm is equal to or less than 3dB/km.

According to the above scheme, at the wavelength of 1550nm, the macrobending loss of the optical fiber bent 10 times with a bending radius of R15mm is equal to or less than 0.25dB, and the macrobending loss of the optical fiber bent once at a bending radius of R10mm is equal to or less than 0.75dB.

The beneficial effects of the present invention are as follows: 1. The germanium-doped core layer design is adopted, the viscosity matching inside the optical fiber is reasonably designed, the defects in the optical fiber preparation process are reduced, and the attenuation parameters of the optical fiber are reduced. 2. Design a reasonable optical fiber fluorine-doped sinking structure, and through the reasonable design of the core layer section of the optical fiber, the optical fiber has an effective area equal to or greater than 100μm ² , and in the optimal parameter range, it can reach equal to or greater than 130μm ² , even greater than the effective area of 140μm ² . 3. Using the double-sag cladding structure design, the fundamental mode cut-off problem is effectively suppressed, and the high-order mode coupling method is used to effectively reduce the cut-off wavelength of the fiber. In order to ensure the single-mode state of the optical signal in the C-band transmission application of this type of optical fiber, and have a better effect on improving the bending loss of the optical fiber. 4. The outer cladding structure of the outermost layer adopts the design of pure silica, which reduces the proportion of fluorine-doped glass in the optical fiber, thereby reducing the production cost of the optical fiber.

Description of drawings

FIG. 1 is a distribution diagram of a refractive index profile structure of an embodiment of the present invention.

detailed description

The present invention is described in detail below in conjunction with the examples.

It includes a core layer and a cladding layer. The core layer is a silicon dioxide glass layer co-doped with germanium and fluorine, or a silicon dioxide glass layer doped with germanium. The core layer is covered with an inner cladding layer from inside to outside in sequence. A sunken inner cladding, an intermediate inner cladding, a second sunken inner cladding, an auxiliary outer cladding and an outer cladding. The standard diameter of the outer cladding is 125 μm.

Table 1 lists the refractive index profile parameters of the preferred embodiment of the present invention, wherein ΔGe is the relative refractive index contribution of germanium doping in the core layer. Table 2 shows the optical transmission characteristics corresponding to the optical fibers described in Table 1.

Table 1. Optical fiber profile parameters of the embodiment of the present invention

Table 2. Fiber Optics and Bending Performance Parameters of Embodiments of the Invention

Claims (10)

1. A single-mode optical fiber with large effective area at ultra-low attenuation, comprising a core layer and a cladding layer, characterized in that the radius R _of the core layer is 4.5～6.5 μm, and the relative refractive index difference Δ1 of the core layer is-0.05 %～0.10%, the core layer is covered with the inner cladding layer from the inside to the outside, the first sunken inner cladding layer, the middle inner cladding layer, the _second sunken inner cladding layer, the auxiliary outer cladding layer and the outer cladding layer, and the radius R of the inner cladding layer is 8.5 ~14μm, the relative refractive index difference Δ2 is -0.35%～-0.12%, the radius _R3 of the first depressed inner cladding is 13～22μm, the relative refractive index difference Δ3 is -0.7%～-0.30%, the middle inner cladding The radius R ₄ is 14-23 μm, and the relative refractive index difference Δ4 is -0.40% to -0.15%; the radius R ₅ of the second depressed inner cladding is 18-30 μm, and the relative refractive index difference Δ5 is -0.6% to -0.25%; The radius R ₆ of the auxiliary outer cladding layer is 35-50 μm, and the relative refractive index difference Δ6 is -0.55%--0.15%; the outer cladding layer is a pure silica glass layer. 2. The single-mode optical fiber with ultra-low attenuation and large effective area according to claim 1, characterized in that the core layer of the optical fiber is a silicon dioxide glass layer co-doped with germanium and fluorine, or is silicon dioxide doped with germanium The glass layer, wherein the relative refractive index contribution ΔGe of germanium doping in the core layer is 0.02% to 0.10%. 3. The single-mode optical fiber with ultra-low attenuation and large effective area according to claim 1 or 2, characterized in that the radius of the intermediate inner cladding is greater than the radius of the first depressed inner cladding, and R ₄ -R ₃ ≥ 1 μm. 4. The single-mode optical fiber with ultra-low attenuation and large effective area according to claim 1 or 2, characterized in that the effective area of the optical fiber at a wavelength of 1550 nm is 100-145 μm ² . 5. The single-mode optical fiber with ultra-low attenuation and large effective area according to claim 1 or 2, characterized in that the cabled cut-off wavelength of the optical fiber is equal to or less than 1530nm. 6. The single-mode optical fiber with ultra-low attenuation and large effective area according to claim 1 or 2, characterized in that the zero dispersion point of the optical fiber is less than or equal to 1300 nm. 7. The single-mode optical fiber with ultra-low attenuation and large effective area according to claim 1 or 2, characterized in that the dispersion of the optical fiber at the wavelength of 1550nm is equal to or less than 23ps/nm*km, and the optical fiber at the wavelength of 1625nm The dispersion is equal to or less than 27ps/nm*km. 8. The single-mode optical fiber with ultra-low attenuation and large effective area according to claim 1 or 2, characterized in that the attenuation of the optical fiber at the wavelength of 1550nm is equal to or less than 0.175dB/km, and the attenuation of the optical fiber at the wavelength of 1625nm The attenuation is equal to or less than 0.204dB/km. 9. The single-mode optical fiber with ultra-low attenuation and large effective area according to claim 1 or 2, characterized in that the microbending loss of the optical fiber at a wavelength of 1700 nm is equal to or less than 3 dB/km. 10. The single-mode optical fiber with ultra-low attenuation and large effective area according to claim 1 or 2, characterized in that the optical fiber is at a wavelength of 1550nm, and the macrobending loss of bending radius R15mm for 10 turns is equal to or less than 0.25dB, R10mm The macro-bending loss of one turn of bending radius is equal to or less than 0.75dB.