CN101446663A - Improved nonzero dispersion-shifted single-mode optical fiber with large mode field distribution - Google Patents

Abstract

The invention is an improved non-zero dispersion-shifted single-mode optical fiber with large mode field distribution, which includes an optical fiber core layer and a cladding layer surrounding the optical fiber core layer, and the optical fiber core layer includes inner core layers with different refractive indices and The outer core layer surrounding the inner core layer, the refractive index of the outer core layer is gradually distributed, and the cladding layer includes an inner cladding layer, a ring core cladding layer and an outer cladding layer with different refractive indices from the inside to the outside, and the outer cladding layer is pure silica glass layer, the refractive index distribution of the optical fiber core layer is n1>n2>nc, and the refractive index distribution of the cladding layer is n4>n3>nc or n4>nc>n3. It has low nonlinear color effect characteristics, that is, large effective area, optimized dispersion and low dispersion slope, which can effectively solve the nonlinear problem and polarization mode dispersion problem affecting high-speed communication, reduce the dispersion management cost of the system, and have low Splice loss, suitable for large-capacity, high-speed, long-distance transmission systems.

Description

An improved non-zero dispersion-shifted single-mode fiber with large mode field distribution

technical field

The invention relates to a non-zero dispersion-shifted single-mode optical fiber designed for a large-capacity, high-speed, long-distance transmission system. The fiber has improved characteristics of low nonlinear effect, that is, large mode field distribution (effective area), optimized chromatic dispersion and low dispersion slope, and has low polarization mode dispersion, low loss and excellent bending resistance, and is compatible with Fiber splicing has the advantages of low splicing loss, suitable for large-capacity, high-speed, long-distance dense wavelength division multiplexing DWDM system transmission, large effective area is conducive to reducing nonlinear effects, and low dispersion slope is conducive to the reduction of dispersion Comprehensive management to meet the long-distance transmission of C+L and S+C+L bands.

Background technique

With the development of optical fiber communication technology, especially the mature application of optical fiber amplifier and wavelength division multiplexing technology, it is no longer the loss of optical fiber that restricts optical fiber communication. The rapid development of global informatization requires large-capacity, high-speed optical fiber communication systems. From the perspective of technology and economy, the development of optical fiber communication technology mainly has two directions. One is to increase the transmission rate of WDM single channel, and the other is to increase the number of WDM channels and increase the working band. Therefore, large capacity, high The speed and long-distance transmission system put forward new requirements for the characteristics and development of optical fibers. At present, for wavelength division multiplexing technology, the main factors restricting the transmission capacity and distance of optical fibers are nonlinear effects, dispersion and optical signal-to-noise ratio (OSNR The English abbreviation of ratio is OSNR).

In the DWDM system, as the capacity increases, the wavelength interval decreases continuously, and the optical nonlinear effects between wavelengths (including four-wave mixing, self-phase modulation, cross-phase modulation, etc.) limit the capacity and capacity of optical transmission. distance. The optical signal-to-noise ratio required by the system increases proportionally with the increase of the single-channel rate, so higher signal optical power is required, which makes the nonlinear effect of the fiber more serious. However, due to the expansion of the wavelength division multiplexing channel band, the dispersion slope causes the dispersion accumulation imbalance of the long and short wavelength edge channels. If the dispersion accumulation imbalance is not well compensated, the regenerative relay distance of the system will be significantly shortened. , which makes dispersion management more complicated and increases the cost of system dispersion compensation. For example, for a 40Gbit/s system, the bandwidth of each channel reaches 80GHz and is nearly 0.8nm, and the influence of the dispersion slope on each frequency component in each channel becomes significant, requiring close to 100% dispersion slope compensation efficiency, which requires the relative The dispersion slope (the relative dispersion slope of the optical fiber is referred to as RDS in English) is as small as possible, and the most effective method is to reduce the dispersion slope and increase the chromatic dispersion appropriately. An effective way to solve these problems is to continuously innovate fiber technology and develop new fibers with low nonlinear effects and dispersion optimization.

In order to suppress the influence of nonlinearity in the DWDM system, an appropriate dispersion value and reduce the optical power density are required in the transmission band. People have developed non-zero dispersion-shifted fibers and non-zero dispersion-shifted fibers with large effective areas on the basis of dispersion-shifted fibers. A series of design and production patent (application) schemes for this type of optical fiber have been published. The optical fiber suitable for C+L wave band, such as No. 98121639.0 Chinese invention patent application (publication number is CN1220402A) discloses a kind of large effective area non-zero dispersion-shifted optical fiber and its manufacturing method, and its typical dispersion slope is 0.09ps/(nm ² · km), the effective area is more than 80um ² , and the typical value of loss at 1550nm is 0.205dB/km; for example, a positive non-zero dispersion-shifted optical fiber disclosed in the Chinese invention patent No. 03125210.9 and authorized announcement No. CN1219227C. The core is layered, the 1550nm dispersion slope is reduced to 0.085ps/(nm ² km), and the effective area is adjusted to more than 70um ² ; such as the optical fiber with a centrally depressed core structure published in the Chinese invention patent application No. 00806764.3 (publication number CN1348548A) , the effective area of the optical fiber is about 70um ² , and the dispersion slope is 0.09-0.08ps/(nm ² ·km); and so on. No. US2002/0154876A1 US patent application published a parabolic distributed core structure optical fiber, the effective area is greater than 90um ² , but the dispersion at 1550nm is too large, which is 14-20ps/(nm km); the US6459839B1 patent has a trapezoidal A fiber with a large effective area and a depressed core, with an effective area of more than 100um ² and a dispersion slope of 0.08; a kind of optical fiber published in US Patent No. US6396987B1. The slope is less than 0.07ps/(nm ² km), but the effective area is only up to 60um ² ; China Patent Application No. 00802639.4 (publication number is CN1337010A) publishes a step-type refractive index distribution fiber, and the dispersion slope is about 0.09ps/ (nm ² ·km), the dispersion of 1550nm is 7-15ps/(nm·km), and the effective area reaches 60-150um ² ; the central core sunken annular core structure announced by the Chinese patent application No. 03119080.4 (publication number is CN1450369A) Optical fiber, the effective area of the optical fiber is greater than 95um ² , and the dispersion slope is less than 0.065ps/(nm ² ·km); both can be used in the S+C+L band, but the additional loss of the optical fiber fusion is high.

Although there are many types of G..655 optical fibers, most of the large effective area G..655 optical fibers still have a large dispersion slope, or the structure is too complex, which is not conducive to system dispersion management and optical fiber production process control. In the previous process operation, the dispersion slope of the large effective area optical fiber used in the long-distance transmission system was large, which led to the degradation of the performance of the DWDM system and the limitation of the relay distance. For a transmission system with a wide operating wavelength, the direct harm of a large dispersion slope is that the dispersion difference between the long and short wavelength sideband wavelengths is large. The wider the transmission wavelength range, the greater the dispersion difference, and the greater the difficulty and cost of dispersion compensation. Especially for high-speed systems such as 40Gbit/s that require precise dispersion management, its impact becomes a big problem. In practical applications, more complex dispersion management is required, which increases system costs and does not conform to the interests of network operators. Therefore, in order to make full use of the bandwidth resources of the optical fiber and increase the communication capacity, these applications require optimizing the chromatic dispersion, reducing the dispersion slope, and improving the flatness of the working band dispersion while maintaining the characteristics of a large effective area.

The dispersion of an ideal optical fiber should have a constant value in the entire working band, but the refractive index changes with the wavelength, and the dispersion has a dependence on the wavelength. In the design of the optical fiber waveguide structure, the effective area and the dispersion slope are mutually restricted, and the balance of various characteristics needs to be considered in the design of the optical fiber.

In the actual long-distance optical fiber transmission system, it is usually necessary to connect different optical fibers to form a communication link. The refractive index distribution of the non-zero dispersion-shifted fiber is more complicated than that of the standard single-mode fiber. When they are together, due to the mismatch between the mode length and diameter of each other and the geometric parameters of the fiber, it often leads to increased reflection and increased additional loss. The longer the link, the more contacts, the greater the cumulative effect, and serious may cause unacceptable bit errors. Rate. Therefore, the splicing characteristics cannot be ignored in optical fiber manufacturing, and measures need to be taken to reduce the splicing loss of optical fibers and limit the harmful effects of splicing loss on the transmission system.

Contents of the invention

The object of the present invention is to provide a kind of characteristic that has low nonlinear color effect, namely large effective area, optimized dispersion and lower dispersion slope, thereby can effectively solve the nonlinear problem and polarization mode dispersion problem that affect high-speed communication, reduce system Dispersion management cost, and improved non-zero dispersion-shifted single-mode fiber with large mode field distribution and low splicing loss, suitable for large-capacity, high-speed, long-distance transmission systems. For this reason, the present invention adopts following technical scheme:

An improved non-zero dispersion-shifted single-mode optical fiber with a large mode field distribution, which includes an optical fiber core layer and a cladding layer surrounding the optical fiber core layer, and is characterized in that the optical fiber core layer includes inner cores with different refractive indices layer and an outer core layer surrounding the inner core layer, the refractive index of the outer core layer is gradually distributed, and the cladding layer includes an inner cladding layer, a ring core cladding layer and an outer cladding layer with different refractive indices from the inside to the outside, and the outer cladding layer It is a pure silica glass layer, the refractive index distribution of the optical fiber core layer is n1>n2>nc, and the refractive index distribution of the cladding is n4>n3>nc or n4>nc>n3, wherein: n1 is the inner core The refractive index of the layer, n2 is the maximum refractive index of the outer core layer, n3 is the refractive index of the inner cladding layer, n4 is the refractive index of the ring core cladding layer, nc is the refractive index of the outer cladding layer, and the refractive index of the outer core layer is gradually changed from n2 to n3.

As a further improvement and supplement to the above-mentioned technical solution, the present invention also includes the following additional technical features, so that these additional technical features can be applied to the above-mentioned technical solution individually or in any combination when implementing the above-mentioned technical solution:

The waveguide structure parameters of the inner core layer, the outer core layer, the inner cladding layer and the ring core cladding layer are:

0.53%≤Δn1≤0.65%, 3.0um≤R1≤4.0um,

0.15%≤Δn2≤0.40%, 6.4um≤R2≤8.4um,

-0.1%≤Δn3≤0.03%, 11.6um≤R3≤14.6um,

0.15%≤Δn4≤0.25%, 17.6um≤R4≤19.8um,

Among them, Δn1, Δn2, Δn3, and Δn4 are the relative refractive index differences of the inner core layer, outer core layer, inner cladding layer, and ring core cladding layer with nc as the reference refractive index, respectively, and R1, R2, R3, and R4 are the inner core layer, R3, and R4 respectively. The diameter of the outer core, inner cladding, and ring core cladding. The outer cladding layer is a pure silica glass layer, its refractive index is the refractive index nc of pure silica glass, and its relative refractive index difference Δnc=0. From R1 to R2, the refractive index of the outer core layer gradually changes from Δn2 to Δn3.

The gradient distribution of the refractive index of the outer core layer satisfies the formula:

n(r)=nc*[1-2Δ(r/r2) ^α ] ^1/2 , where r1≤r≤r2, r is the radius variable of the outer core layer, r1 is the radius of the inner core layer, r2 is the outer core The radius of the layer, α is the gradient law coefficient.

At least one of germanium, fluorine and phosphorus is doped into the outer core layer, inner cladding layer and ring core cladding layer respectively. It is used to adjust the refractive index distribution of optical fiber parts, match the viscosity and stress, reduce the residual stress in the optical fiber, balance the stress distribution, and stabilize the polarization mode dispersion performance of the optical fiber.

Through the precise adjustment of the refractive index distribution of the optical fiber, especially the gradient coefficient α of the refractive index of the outer core layer, the required mode field distribution (effective area) and dispersion characteristics, that is, dispersion value and dispersion slope, can be obtained, and it has a lower polarization. Mode dispersion, loss, excellent bending performance and fusion splicing performance, so the optical fiber of the present invention has the following characteristics in particular

1550nm dispersion slope≤0.073ps/(nm ² km);

Zero dispersion wavelength≤1500nm;

The effective area is 70～75um ² ;

The dispersion in the range of 1530nm～1565nm is 2.5～6.5ps/(nm·km);

The dispersion within the range of 1565nm～1625nm is 6～12ps/(nm·km);

The loss of 1550 is ≤0.22dB/km, and the loss of 1530nm～1565nm band is ≤0.22dB/km.

。According to the measurement method of optical fiber bending performance, in the test of 100 turns around the φ60mm mandrel, the additional loss caused by bending is less than 0.05dB at 1550nm and 1625nm, and in the test of 1 circle around the φ32mm mandrel, the additional loss caused by bending is less than 0.05dB. Both 1550nm and 1625nm are less than 0.5dB. The polarization mode dispersion value of the fiber is ≤0.06ps/

.

The optical fiber core layer of the present invention can be manufactured by but not limited to MCVD, PCVD or OVD to realize the specified optical fiber waveguide structure design.

The beneficial effects of the present invention are:

1. Compared with the previous non-zero dispersion displacement single-mode waveguide structure, the structure of the present invention is relatively simple, not only can be easily obtained, but also the waveguide structure has corresponding dispersion characteristics in the specified numerical range, combined with MCVD, PCVD, 0VD, etc. The process can precisely control the refractive index distribution, easy to carry out production and quality control, and can efficiently obtain the designed optical fiber performance.

2. The optical fiber of the present invention has a large mode field distribution, and the dispersion slope is low. The characteristics of the optical fiber are sufficient to meet the requirements of suppressing nonlinear effects, reduce the cost of system dispersion management, and are suitable for C+L band or S+C+L band DWDM transmission needs.

3. While designing the waveguide, the present invention takes into account the composition design of the optical fiber material, optimizes the matching of viscosity and stress, improves the stress distribution, and improves the PMD performance of the optical fiber. In the present invention, by properly selecting the doping composition of the cladding layer of the prefabricated rod, the internal stress distribution can be optimized, and the PMD performance of the optical fiber can be stabilized.

4. The fusion splicing of the optical fiber of the present invention with other non-zero dispersion-shifted optical fibers NZ-DSF has low splicing loss and excellent splicing performance.

Description of drawings

Fig. 1 is a schematic diagram of the distribution curve of relative refractive index Δ versus diameter in Example 1 of the present invention.

Fig. 2 is a schematic diagram of the distribution curve of relative refractive index Δ versus diameter in Example 2 of the present invention.

Fig. 3 is a schematic diagram of the distribution curve of relative refractive index Δ versus diameter in Example 3 of the present invention.

Fig. 4 is a schematic diagram of the dispersion curves of the optical fiber of the embodiment of the present invention and the existing optical fiber products of the same kind.

Detailed ways

The improved non-zero dispersion-shifted single-mode optical fiber with large mode field distribution of the present invention includes an optical fiber core layer and a cladding layer surrounding the optical fiber core layer, and the optical fiber core layer includes an inner core layer with different refractive indices and a surrounding inner core layer The outer core layer, the refractive index of the outer core layer is gradually distributed, the cladding layer includes an inner cladding layer, a ring core cladding layer and an outer cladding layer with different refractive indices from the inside to the outside, and the outer cladding layer is a pure silica glass layer. It is described in detail through several specific examples below.

Example 1:

As shown in Figure 1 is a kind of optical fiber waveguide refractive index distribution curve of the present invention, following is a group of relative refractive index difference distribution parameters:

The parameters of the inner core layer Core1 are: Δn1 is about 0.60%, R1 is about 3.6um,

The parameters of the outer core layer Core2 are: Δn2 is about 0.25%, R2 is about 7.6um,

The parameters of the inner cladding Clad1 are: Δn3 is about 0.02%, R3 is about 12.8um,

The parameters of the ring core cladding Clad2 are: Δn4 is about 0.21%, R4 is about 17.2um,

The parameters of the outer cladding (that is, the outermost layer) Clad3 are: Δnc is about 0.00%, R5 is 125um,

The outer cladding Clad3 is a pure silica glass layer, and its refractive index is nc (Δnc=0),

The gradient distribution of the refractive index of the outer core layer Core2 satisfies the formula: n(r)=nc*[1-2Δ(r/r2) ^α ] ^1/2 , where r1≤r≤r2, r is the radius variable of the outer core layer, r1 is the radius of the inner core layer, r2 is the radius of the outer core layer, and the gradient law coefficient α is set to 1; the refractive index of the outer core layer Core2 is gradually changed from Δn2 to Δn3 from R1 to R2.

The properties of the resulting fiber are as follows:

1550nm effective area: 74um ² ,

Zero dispersion wavelength: 1487nm,

Dispersion at 1550nm: 4.45ps/(nm km),

Dispersion slope at 1550nm: 0.0714ps/(nm ² ·km),

Dispersion at 1530nm: 3.03ps/(nm km),

Dispersion at 1625nm: 9.866ps/(nm km),

Optical cable cut-off wavelength: 1330nm,

Loss at 1550: 0.20dB/km,

The maximum value of additional loss at 1550nm and 1625nm is 0.04dB when the macrobend φ60mm is wound 100 times.

The maximum value of the additional loss at 1550nm and 1625nm is 0.05dB when the macrobending φ32mm is wound once.

The dispersion slope of the optical fiber characteristics described in this embodiment is less than 0.073ps/(nm ² ·km) at 1550nm, the effective area is 74um ² , and the attenuation and bending performance are excellent. The splicing loss of NZ-DSF fiber is less than 0.06dB. The optical fiber characteristics can be applied to the transmission needs of the DWDM system in the C+L band.

Example 2:

According to the optical fiber waveguide refractive index distribution curve shown in Figure 2, the following is a set of relative refractive index difference distribution parameters:

The parameters of the inner core layer Core1 are: Δn1 is about 0.58%, R1 is about 3.8um,

The parameters of the outer core layer Core2 are: Δn2 is about 0.24%, R2 is about 7.8um,

The parameters of the inner cladding Clad1 are: Δn3 is about -0.05%, R3 is about 13.0um,

The parameters of the ring core cladding Clad2 are: Δn4 is about 0.23%, R4 is about 18.2um,

The parameters of the outer cladding Clad3 are: Δnc is about 0.00%, R5 is about 125um,

The outer cladding Clad3 is a pure silica glass layer, and its refractive index is nc,

The gradient distribution of the refractive index of the outer core layer Core2 satisfies the formula: n(r)=nc*[1-2Δ(r/r2) ^α ] ^1/2 , where

In r1≤r≤r2, r is the radius variable of the outer core layer, r1 is the radius of the inner core layer, r2 is half of the outer core layer

The gradient law coefficient α takes 1; the refractive index of the outer core layer Core2 gradually changes from Δn2 to Δn3 from R1 to R2.

The properties of the resulting fiber are as follows:

1550nm effective area: 72um ² ,

Zero dispersion wavelength: 1470nm,

Dispersion at 1550nm: 5.29ps/(nm km),

Dispersion slope at 1550nm: 0.068ps/(nm ² ·km),

Dispersion at 1530nm: 3.94ps/(nm km),

Dispersion at 1565nm: 6.29ps/(nm km),

Dispersion at 1625nm: 10.48ps/(nm km),

Optical cable cut-off wavelength: 1330nm,

Loss at 1550: 0.20dB/km,

The maximum value of additional loss at 1550nm and 1625nm is 0.035dB when the macrobending φ60mm is wound 100 times.

The maximum value of the additional loss at 1550nm and 1625nm is 0.045dB when the macrobending φ32mm is wound once.

The dispersion slope of the optical fiber characteristics described in this embodiment is less than 0.07ps/(nm ² ·km) at 1550nm, the effective area is 72um ² , and the attenuation and bending performance are excellent. -The splicing loss of DSF fiber is less than 0.06dB. The optical fiber characteristics can be applied to the transmission needs of the DWDM system in the C+L band.

Example 3:

According to the optical fiber waveguide refractive index distribution curve shown in Figure 3, the following is a set of relative refractive index difference distribution parameters:

The parameters of the inner core layer Core1 are: Δn1 is about 0.56%, R1 is about 4.0um,

The parameters of the outer core layer Core2 are: Δn2 is about 0.22%, R2 is about 8.0um,

The parameters of the inner cladding Clad1 are: Δn3 is about -0.07%, R3 is about 13.6um,

The parameters of the first ring core cladding Clad2 are: Δn4 is about 0.22%, R4 is about 19.2um,

The parameters of the second ring core cladding Clad3 are: Δn5 is about 0.-08%, R5 is about 20.8um,

The parameters of the outermost layer, that is, the outer cladding layer Clad4 are: Δnc is about 0.00%, R6 is 125um,

The cladding layer Clad4 is a pure silica glass layer with a refractive index nc (Δnc=0),

The gradient distribution of the refractive index of the outer core layer satisfies the formula: n(r)=nc*[1-2Δ(r/r2) ^α ] ^1/2 , where r1≤r≤r2, r is the radius variable of the outer core layer , r1 is the radius of the inner core layer, r2 is the radius of the outer core layer, and the gradient law coefficient α is taken as 1; the refractive index of the outer core layer Core2 is gradually changed from Δn2 to Δn3 from R1 to R2.

The properties of the resulting fiber are as follows:

1550nm effective area: 73um ² ,

Zero dispersion wavelength: 1450nm,

Dispersion at 1550nm: 6.6ps/(nm km),

Dispersion slope at 1550nm: 0.068ps/(nm ² ·km),

Dispersion at 1530nm: 5.3ps/(nm km),

Dispersion at 1625nm: 11.5ps/(nm km),

Cable cut-off wavelength: 1320nm,

Loss at 1550: 0.20dB/km,

The maximum value of additional loss at 1550nm and 1625nm is 0.04dB when the macrobend φ60mm is wound 100 times.

The maximum value of the additional loss at 1550nm and 1625nm is 0.045dB when the macrobending φ32mm is wound once.

The dispersion slope of the fiber characteristics described in Example 3 at 1550nm is less than 0.07ps/(nm ² ·km), the effective area is 73um ² , and the attenuation and bending performance are excellent. The splicing loss of NZ-DSF fiber is less than 0.06dB. The optical fiber characteristics are suitable for the transmission needs of the DWDM system in the S+C+L band.

Definitions of some terms in the present invention:

The refractive index difference Δ is defined by the following equation:

Relative refractive index difference Δni%=[(ni ² —nc ² )/2ni ² ](1)

Where ni is the refractive index of the fiber in the i-th layer, nc is the refractive index of the pure silica glass part of the outer cladding, which is used as a reference refractive index in this application.

The refractive index profile is defined as the relationship between the refractive index ni or Δni and its position ri (radius) relative to the center of the fiber at a selected portion of the fiber.

Gradient distribution of refractive index, satisfying the formula: n(r)=nc*[1-2Δ(r/a) ^α ] ^1/2 , 0≤r≤a

Among them: r is the radius variable; α is the gradient law coefficient, which determines the shape of the change curve, and can take the value (0, ∞); a is a constant, which can be determined as a different constant when designing various refractive indices.

Total dispersion is defined as the algebraic sum of optical fiber material dispersion and waveguide dispersion. In the field of optical fiber communication technology, the dispersion of optical fiber refers to the total dispersion, and its unit is ps/(nm·km).

The dispersion slope indicates the dependence of the dispersion on the wavelength. Since the refractive index changes with the wavelength, the fiber dispersion value also changes with the wavelength. The dispersion slope indicates this variability. It takes the wavelength as the abscissa, and the dispersion value is the slope of the curve drawn on the ordinate, and its unit is ps/(nm ² ·km).

Ds=dD/dλ

In a wavelength division multiplexing system, if the dispersion slope of the transmission link is large, the difference in dispersion values between wavelengths becomes large, which will reduce the transmission characteristics of the system or increase the cost of dispersion compensation.

Effective area Aeff＝2π(∫E ² rdr) ² /(∫E ⁴ rdr)(2)

where the integral limit is from 0 to ∞, and E is the electric field related to propagation.

DWDM is an acronym for Dense Wavelength Division Multiplexing.

PMD is an acronym for Fiber Polarization Mode Dispersion.

The bending resistance of an optical fiber refers to the additional loss under specified test conditions. The test process is to test the loss of the optical fiber under normal conditions, then wind the optical fiber around the mandrel according to the standard requirements, and measure the loss value. The difference between the two measurements is the additional bending loss caused by bending. The specified standard test conditions include 100 turns on a mandrel with a diameter of 75mm and 1 turn on a mandrel with a diameter of 32mm. Generally, the maximum permissible loss caused by bending is based on the accessory bending loss at 1310nm and 1550nm, and the unit is dB. In this application, the additional losses at wavelengths of 1550nm and 1625nm are measured under the condition that the mandrels of 60mm and 32mm are wound 100 times and 1 time respectively, and the maximum value is taken as the measurement result.

Splice loss is measured by OTDR at 1550nm and averaged.

Claims (5)

1, a kind of improved non-zero dispersion displacement single mode optical fibre with big mould field distribution, it comprises fiber core layer and the covering that is enclosed on the fiber core layer, it is characterized in that described fiber core layer comprises inner sandwich layer with different refractivity and the outer sandwich layer that surrounds described inner sandwich layer, the refractive index of described outer sandwich layer is a graded profile, covering comprises the inner cladding from inside to outside with different refractivity, ring core covering and surrounding layer, surrounding layer is the pure silicon dioxide glassy layer, the index distribution of described fiber core layer is n1〉n2〉nc, described cladding index is distributed as n4〉n3〉nc or n4〉nc〉n3, wherein: n1 is the refractive index of inner sandwich layer, n2 is the largest refractive index of outer sandwich layer, n3 is the refractive index of inner cladding, n4 is the refractive index of ring core covering, and nc is the refractive index of surrounding layer.

2, a kind of improved non-zero dispersion displacement single mode optical fibre with big mould field distribution according to claim 1 is characterized in that the waveguiding structure parameter of described inner sandwich layer, outer sandwich layer, inner cladding, ring core covering is:

53％≤Δn1≤0.65％， 3.0um≤R1≤4.0um，

15％≤Δn2≤0.40％， 6.4um≤R2≤8.4um，

-0.1％≤Δn3≤0.03％， 11.6um≤R3≤14.6um，

15％≤Δn4≤0.25％， 17.6um≤R4≤1.8um，

Wherein Δ n1, Δ n2, Δ n3, Δ n4 are respectively inner sandwich layer, outer sandwich layer, inner cladding, ring core covering with the refractive index contrast of nc as the reference refractive index, R1, R2, R3, R4 are respectively the diameter of inner sandwich layer, outer sandwich layer, inner cladding, ring core covering, from R1 to R2, the refractive index of outer sandwich layer by Δ n2 gradual change to Δ n3.

3, a kind of improved non-zero dispersion displacement single mode optical fibre according to claim 1 with big mould field distribution, it is characterized in that described outer sandwich layer gradually changed refractive index distributes satisfies formula:

N (r)=nc*[1-2 Δ (r/r2) ^α] ^1/2, r1≤r≤r2 wherein, r is the radius variable of outer sandwich layer, and r1 is the radius of inner sandwich layer, and r2 is the radius of outer sandwich layer, and α is a gradual change rule coefficient.

4, a kind of improved non-zero dispersion displacement single mode optical fibre with big mould field distribution according to claim 1 is characterized in that mixing respectively at least a of germanium, fluorine, three kinds of elements of phosphorus in described inner cladding, ring core covering.

5, a kind of improved non-zero dispersion displacement single mode optical fibre with big mould field distribution according to claim 1 is characterized in that:

1550nm chromatic dispersion gradient≤0.073ps/ (nm ²Km);

Zero-dispersion wavelength≤1500nm;

Useful area is 70～75um ²

Chromatic dispersion in 1530nm～1565nm scope is 2.5～6.5ps/ (nmkm);

Chromatic dispersion in 1565nm～1625nm scope is 6～12ps/ (nmkm);

Loss≤0.22dB/km of 1550 is at the loss≤0.22dB/km of 1530nm～1565nm wave band.

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