JP3408713B2 - Dispersion shifted optical fiber - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [0001] BACKGROUND OF THE INVENTION 1. Field of the Invention
Dispersion-shifted optical fiber with almost zero chromatic dispersion in the m band
(Hereinafter abbreviated as DSF), its nonlinear effect
Result, bending loss and dispersion slope are reduced at the same time.
You. [0002] 2. Description of the Related Art DSF has the lowest loss of a silica-based optical fiber.
The chromatic dispersion value in the small wavelength 1.55 μm band is almost zero.
An optical fiber that is
Is well known to have a step-shaped refractive index distribution.
You. DSF having this step-shaped refractive index distribution is
DSF, for example, refractive index of step type, triangular type, etc.
Bending loss is smaller than that with cloth
When the field diameter (hereinafter abbreviated as MFD) is slightly large,
Although it has the above-mentioned features, the normal 1.3 μm band
MFD is smaller than single mode optical fiber
And less than about 8 μm. MFD of optical fiber is small
In this case, it is not only disadvantageous in terms of connection loss.
And the power density of the light propagating in the optical fiber is large.
In the case of optical amplifiers, for example, nonlinear effects are large.
This causes inconvenience such as deterioration of transmission characteristics. [0003] The magnitude of the nonlinear effect is n_Two/ A
It is represented by eff. Where n_TwoIs the nonlinear bending of the optical fiber.
The bending ratio, Aeff, is the effective area of the optical fiber. Non-linear
To reduce the shape effect, n_TwoIs almost constant depending on the material
, It is necessary to increase Aeff.
You. On the other hand, between Aeff and MFD in DSF
Is known to have a relationship represented by the following relational expression:
You. Aeff = k · π / 4 · (MFD)^Two The correction coefficient k in the above equation is a step-type refractive index.
For a DSF with a distribution, a constant value of approximately 0.944
Has been reported. Therefore, Aeff is large.
In order to increase the size, it is necessary to increase the MFD.
However, in a DSF having a step-shaped refractive index distribution,
Since its MFD is almost constant at about 8 μm, Aeff
Cannot be increased, thus reducing nonlinear effects.
It cannot be reduced. In order to solve this problem, the present applicant has
First, Japanese Patent Application No. Hei 7-23191 (published on February 10, 1995)
Wish). This prior invention has a wavelength of 1.55 μm.
Among the core diameters where the chromatic dispersion becomes zero at m, the value is small.
A small core diameter is adopted.
And the correction coefficient increases to about 0.95 to 0.97,
MFD also has a value of about 7.8 to 8.6 μm.
As a result, Aeff becomes large, and the non-linear effect is reduced.
It can be reduced. However, this predecessor
According to the invention, there is an advantage that the Aeff can be increased.
When the bending loss increases by adopting a small core diameter of
The inconvenience to say remained. [0006] Applicants further increase Aeff.
For this reason, Japanese Patent Application No. 8-215707 (August 15, 1996)
Has filed a patent application. This prior invention DSF
As shown in FIG. 3, the central core 11 and the central core
A ring core with a low refractive index provided away from the portion 11
Portion 12 and a ring provided on the outer periphery of the ring core portion 12.
Of the rud 13, the central core 11 and the ring core 12
Having a refractive index profile consisting of the intermediate layer 14 between
Things. And the diameter of the central core portion 11 is 2a.
The outer diameter of the ring core 12 is set to 2b,
Where b / a ≧ 1.5 and w / a
≧ 0.5, relative bending between the central core part 11 and the clad 13
Folding difference △ 1 and the difference between the ring core portion 12 and the clad 13
By appropriately determining the relative refractive index difference △ 2, 1.55 μm
The chromatic dispersion in the band is almost zero, the nonlinear effect is low,
Moreover, it is said that DSF with small bending loss can be obtained.
Is Umono. However, in the DSF of the prior invention,
Can be obtained by increasing Aeff and reducing the nonlinear effect.
The wavelength dispersion multiplex transmission has the disadvantage of increasing the long dispersion slope.
When considering application to roads, improvement is needed. example
If Aeff is 70 μm^TwoIn the degree, the dispersion slope is 0.
12ps / km / nm^TwoAeff is 80
μm^TwoTo the extent, the dispersion slope is 0.15 ps / km /
nm^TwoAeff is about 110 μm^TwoIn the degree, 0.1
7ps / km / nm^TwoTo the extent that the wavelength
The difference in transmission speed between the different signal lights becomes large. [0008] SUMMARY OF THE INVENTION Therefore, in the present invention,
Challenges include nonlinear effects, bending losses and dispersion slopes.
Both are to obtain a reduced DSF. [0009] [Means for Solving the Problems]To solve such problems
Therefore, the invention according to claim 1 includes a central core portion and
A first ring portion provided on an outer periphery of the core portion;
A second ring portion provided on the outer periphery of the ring portion, and the second ring portion;
A third ring portion provided on the outer periphery of the ring portion;
And a clad provided on the outer periphery of the
The outer diameter of the first ring part is 2a, the outer diameter of the first ring part is 2b,
The outer diameter of the ring portion was 2c, and the outer diameter of the third ring portion was 2d.
Then b / a ≧ 1.5 and (c−b) /a≦5.0
And (dc) /a≦5.0, with the central core part
The relative refractive index difference from the cladding is
The relative refractive index difference between the second ring portion and the clad is Δ2.
The relative refractive index difference is Δ3, and the relative refractive index between the third ring portion and the clad is
When the rate difference is Δ4, Δ1 = 0.5 to 2.0%,
Δ2 / Δ1 = −0.5 to 0.5 and Δ3 / Δ1 =
0 to 1.0, and Δ4 / Δ1 = 0 to −0.5,
The refractive index of the central core portion is n0, and the refractive index of the first ring portion is n.
1. Refractive index of the second ring portion is n2, refraction of the third ring portion
When the index is n3 and the refractive index of the cladding is n4, n0>
n2 and n2> n1 and n3 <n4, the wave
In the 1.55 μm band, chromatic dispersion is almost zero.
Is not zero and the effective area is 65-120 μm ²
And the bending loss is 0.1 to 100 dB / m.
And the dispersion slope is 0.07 to 0.14 ps / km
/ Nm ^{2, and the cutoff wavelength is 1.55} μm band
Must always take values that result in single-mode propagation in
This is a dispersion-shifted optical fiber that is a feature. [0010] BEST MODE FOR CARRYING OUT THE INVENTION The DSF of the present invention
Almost zero chromatic dispersion in 1.55 μm band
Is not zero and the effective area Aeff is 65
~ 120 μm ^TwoAnd a bending loss of 0.1 to 100
dB / m and a dispersion slope of 0.07 to 0.1
4ps / km / nm^TwoAnd the cutoff wavelength is
Has a value that always causes single mode propagation in the wavelength band
Things. Here, the wavelength used is 1.55 μm band.
Indicates a wavelength range of 1520 nm to 1580 nm.
It is something. Also, chromatic dispersion is almost zero,
The wavelength dispersion value is -5 to +5 ps / nm.
km, but the chromatic dispersion value is 0 ps /
It is necessary not to take a value of nm · km. this is,
If the chromatic dispersion value is 0 ps / nm · km, four-photon mixing
The effect of nonlinear optical effects such as
That's why. The effective area Aeff is expressed by the following relational expression:
Is defined by Bending loss is wavelength 1.55μ
m means the value under the condition that the bending diameter (2R) is 20 mm.
I do. Cutoff wavelength is 2m of JIS or CCITT
Values measured by the
And the measured value. Also the dispersion throw
Is the wavelength dependence of the chromatic dispersion value.
The wavelength (nm) is represented by the chromatic dispersion value (ps / km · n) on the vertical axis.
m) and take the slope of the curve when plotting the variance
That's what it says. [0012] (Equation 1) An optical fiber satisfying such characteristic values is
D with small nonlinear effect, bending loss and dispersion slope
SF. Aeff is 65 μm^TwoLess than nonlinear effect
Is not enough, 120μm^TwoIs more than
Sometimes it is impossible to manufacture. In addition, bending loss is 1
When it exceeds 00dB / m, the DSF has a slight curvature
Loss also increases, which is inconvenient. Also the dispersion throw
Uses a small diameter solution as the core diameter as described later.
0.07 ps / km / nm^TwoThat is, 0.
14ps / km / nm^TwoExceeds the wavelength multiplexing communication system.
It is difficult to apply to systems. In addition, DSFs are usually
This is a single-mode optical fiber,
Need to perform single mode propagation,
The cutoff wavelength guarantees single-mode propagation
There must be. The DSF of the present invention has such characteristic values.
In order for this to work, for example,
First need to have a rate distribution shape (profile)
Condition. In FIG. 1, reference numeral 1 denotes a central core portion.
A first ring portion 2 is provided on the outer periphery of the central core portion 1.
On the outer periphery of the first ring portion 2, a second ring portion 3 is provided.
A third ring portion is provided on the outer periphery of the second ring portion 4.
4 is provided on the outer periphery of the third ring portion 4.
5 are provided, which are the same around the central core portion 1.
They are arranged in a heart shape. Here, the refraction of the central core 1
Rate n₀, The refractive index of the first ring portion 2 is n₁, Second ring part
The refractive index of 3 is n_Two, The refractive index of the third ring portion 4 is n_Three,
The refractive index of the head 5 is n_FourThen n₀> N_TwoWhere n_Two> N₁
Where n_Three<N_FourIt has become. Further, in the profile of FIG.
The relative refractive index difference between the core part 1 and the clad 5 is Δ1, the first phosphorus
The relative refractive index difference between the ring portion 2 and the clad 5 is △ 2, the second ring
The relative refractive index difference between the part 3 and the clad 5 is △ 3, the third ring part
Assuming that the relative refractive index difference between No. 4 and clad 5 is △ 4, △ 1
Is 0.5 to 2.0%, and △ 2 / △ 1 is -0.5 to 0.
5, $ 3 / $ 1 is 0-1.0, $ 4 / $ 1 is 0--0.
5 range. Further, the second requirement is that the profile shown in FIG.
In the file, the outer diameter of the central core portion 1 is 2a,
The outer diameter of the ring portion 2 is 2b, the outer diameter of the second ring portion 3 is 2c,
Assuming that the outer diameter of the 3 ring portion 4 is 2d, b / a is1.5 or less
Above, preferably1.5 to 6, and (c−b) / a is
5.0Hereinafter, it is preferably 0.5 to 5.0, and (d−
c) / a is5.0Hereinafter, preferably 0.1 to 5.0.
It is. When b / a is less than 1.5, Aeff is sufficiently large.
If more than 6 are not available,
The inconvenience that controllability deteriorates occurs. (C−b) / a is 0.
If it is less than 5, the effect of Aeff enlargement becomes weak, and exceeds 5.0.
Characteristics deteriorate controllability and increase dispersion slope.
Disadvantages occur. If (dc) / a is less than 0.1,
The effect of shifting the cutoff wavelength to the shorter wavelength side is fully obtained.
If it exceeds 5.0, the controllability of the characteristics deteriorates, which is inconvenient.
Become. In the DSF of the present invention, the third ring portion 4
Is newly provided, and the refractive index of this portion is changed to the refractive index of the cladding 5.
By setting the Aeff value lower than
With a low slope.
is there. Then, the above-mentioned parameters, # 1, # 2 /
Δ1, Δ3 / Δ1, Δ4 / Δ1, b / a, (c−b) /
By setting a, (dc) / a in the above range,
The DSF of the present invention satisfying the above characteristics can be obtained.
You. Table 1 meets the above first and second requirements,
Specific parameters for obtaining DSF having the above characteristics
Data combination and the DSF power
Cut-off wavelength (λc), Aeff, bending loss, dispersion slot
It shows the value of the loop. [0018] [Table 1] As can be seen from Table 1, each parameter
Target characteristics by combining from a wide range of
It becomes clear that the obtained DSF can be obtained. like this
From the viewpoint of the present invention, in the present invention, the value of the DSF structural parameter
Therefore, it is difficult to specify the invention, and
In this case, the identification is performed. And heels
Characteristic value cannot be obtained with the conventionally known DSF.
Needless to say, In the DSF of the present invention, the DSF of the prior invention
Similarly to the above, the chromatic dispersion in the wavelength band of 1.55 μm is almost the same.
Of the two core diameters that are almost zero,
Diameter, which reduces bending losses.
Control and increase the Aeff and dispersion throw
0.14 ps / km / nm^TwoCan be
Things. The DSF of the present invention can be used in a normal VAD method or the like.
Therefore, the central core portion 1 and the second ring portion 3 can be manufactured.
By germanium doped silica or pure silica,
The first ring part 2, the third ring part 4, and the clad 5 are pure
By using pure silica or fluorine-doped silica
Created. In the profile shown in FIG. 1, the second ring
Due to the presence of the part 3, the electric field intensity distribution of the optical power of the transmission light is
Optical fiber because it has a long tail on the cladding 5 side
A significant part of the soot that becomes the cladding during the production of the base metal
How to combine the minutes with the soot that is the core
It is desirable to take. FIG. 2 shows a prototype fiber of the DSF of the present invention.
This shows an example of an actual measurement profile, which is measured by the RNFP method.
It is specified. Table 2 shows the characteristic values of this prototype fiber.
As shown, having the characteristics required by the present invention
You can see that it is. [0023] [Table 2][0024] As described above, the DSF of the present invention is
The chromatic dispersion is almost zero in the 1.55 μm wavelength band.
Low nonlinear effect, bending loss and dispersion slope
It will be small. Therefore, the DSF of the present invention has a low loss
Wavelength division multiplexing by optical amplification relay in 1.55μm band
It is suitable for ultra-long distance optical communication systems using
You.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a diagram showing an example of a profile in a DSF of the present invention. FIG. 2 is a view showing an actually measured profile of a prototype fiber of a DSF of the present invention. FIG. 3 is a diagram showing a profile of a DSF shown in the prior invention. [Description of References] 1 ... Center core part 2 ... First ring part 3 ... Second ring part 4 ... Third ring part 5 ... Clad

Continuation of front page (72) Inventor Koichi Takahashi 1440 Mutsuzaki, Sakura City, Chiba Prefecture Fujikura Co., Ltd. Sakura Plant (56) References JP-A-6-11620 (JP, A) JP-A-10-239550 (JP, A) GAOY et al. , Attenuation-Optimized Dispersion-Flattened Quadruple-Clad Fibers with Moderate F-Dopping in the First, IEEE PHOTON ICE TECHNOLOGY, USA. 4 (6), p. 638−641 (58) Field surveyed (Int.Cl. ⁷ , DB name) G02B 6/00-6/02 G02B 6/10 G02B 6/16-6/22 G02B 6/44

Claims (1)

(57) [Claims] [Claim 1] A center core portion and an outer periphery of the center core portion are provided.
And a first ring portion provided on the outer periphery of the first ring portion.
And a second ring portion provided on the outer periphery of the second ring portion.
And a third ring portion provided on the outer periphery of the third ring portion.
Consists of a vignetting cladding, 2a the outer diameter of the central core portion, the outer diameter of the first ring part 2b,
The outer diameter of the second ring portion is 2c, and the outer diameter of the third ring portion is 2d.
Where b / a ≧ 1.5 and (c−b) / a ≦
5.0 and (dc) /a≦5.0, the relative refractive index difference between the central core and the clad is Δ1, the first phosphorus
The relative refractive index difference between the ring portion and the cladding is Δ2,
The relative refractive index difference from the clad is Δ3, and the third ring
Δ1 = 0.5-
2.0% and Δ2 / Δ1 = −0.5 to 0.5
Δ3 / Δ1 = 0-1.0 and Δ4 / Δ1 = 0-−
0.5, the refractive index of the central core portion is n0, and the refractive index of the first ring portion is n
1. Refractive index of the second ring portion is n2, refraction of the third ring portion
When the index is n3 and the refractive index of the cladding is n4, n0>
n2, n2> n1, and n3 <n4, and in the 1.55 μm band, the chromatic dispersion is almost zero and not zero, and the effective area is 65 to 120 μm
² , the bending loss is 0.1 to 100 dB / m, and the dispersion slope is 0.07 to 0.14 ps / km.
A dispersion-shifted optical fiber having a value of / nm ² and a value in which a single mode propagation is always performed in a ^{cutoff wavelength} band of ^1.55 μm.