JP2001051147A - Dispersive shift optical fiber - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a high performance dispersive shift optical fiber suitable for a long-distance system or wavelength multiple transmission according to the recent demand for the larger capacity or longer-distance transmission of optical communication system. SOLUTION: This optical fiber has a dual shape core type refractive index distribution shape and adapts a small diameter solution as core diameter. This optical fiber has an Aeff of 65-95 μm2, in a using wavelength band selected from 1490-1610 nm, a dispersion slope of 0.08-0.14 ps/km/nm2, a bending loss <=100 dB/m, an absolute value of wavelength dispersion value of 0.5-8.0 ps/km/ nm, and a cutoff wavelength propagated in substantially single mode.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dispersion-shifted optical fiber having a large effective core area and a small dispersion slope.

[0002]

2. Description of the Related Art Conventionally, in a long distance system such as an optical amplification repeater transmission system using an optical fiber amplifier, it is important to reduce a nonlinear optical effect. The nonlinear optical effect is almost determined by a nonlinear constant. The nonlinear constant is n2
/ Aeff. Here, n2 is a nonlinear refractive index,
Aeff is the effective core area. Since n2 does not change significantly when the material is determined, increasing Aeff is an effective method for reducing the nonlinear optical effect. On the other hand, in a wavelength division multiplexing transmission system capable of large-capacity transmission, a smaller dispersion slope is preferable. The dispersion slope indicates the wavelength dependence of the chromatic dispersion value, and is a curve obtained by plotting the chromatic dispersion value by taking the wavelength (nm) on the horizontal axis and the chromatic dispersion value (ps / km / nm) on the vertical axis. Is the gradient of In a wavelength division multiplexing transmission system, if the dispersion slope of the transmission line (optical fiber) is large, the difference in the chromatic dispersion value between the wavelengths increases, and the transmission state varies, thus deteriorating the overall transmission characteristics and limiting the transmission distance. Is done. In addition, the transmission line of the optical communication system is required to have a substantially single mode and to maintain a bending loss of 100 dB / m or less as minimum conditions.

Therefore, recently, for example, Japanese Patent Laid-Open No.
2640, JP-A-10-293225, JP-A-8-220362, JP-A-10-24683
In Japanese Patent Application Publication No. 0 (1999), proposals have been made to expand Aeff to some extent by using various refractive index distribution shapes (refractive index profiles).

FIGS. 5 (a) to 5 (c) show examples of the refractive index distribution shape of such a dispersion-shifted optical fiber. FIG. 5A shows a dual shape core type (stepped type).
Reference numeral 11 denotes a central core portion, and a stepped core portion 12 having a lower refractive index than the central core portion 11 is provided on the outer periphery thereof to form a core 14. Have been. A clad 17 having a lower refractive index than the step core portion 12 is provided on the outer periphery of the core 14. The present applicant has disclosed a dispersion-shifted optical fiber using a small-diameter solution in Japanese Patent Application Laid-Open No. H8-220362 with the aim of increasing Aeff in a dual-shape core type refractive index distribution shape. Conventionally, at a wavelength of 1.55 μm, if the core diameter of the dispersion-shifted optical fiber is increased while maintaining the similar shape of the refractive index distribution shape, two or more solutions having a desired wavelength dispersion value are obtained. It is known to exist. At this time, among the solutions whose characteristics such as bending loss and cutoff wavelength are in a relatively practical range,
A solution with a relatively small core diameter is called a small diameter solution, and a solution with a large core diameter is called a large diameter solution.

FIG. 5 (b) shows an example of a segment core type refractive index distribution shape, in which a middle portion 22 having a low refractive index is provided on the outer periphery of a central core portion 21 having a high refractive index. A core 24 is provided on the outer periphery of the intermediate portion 22 by providing a ring core portion 23 having a higher refractive index than the intermediate portion 22 and a lower refractive index than the central core portion 21. Further, a first clad 25 having a lower refractive index than that of the intermediate portion 22 is provided on the outer periphery of the ring core portion 23.
On the outer periphery of the clad 25, a second refractive index higher than that of the first clad 25 and lower than that of the intermediate portion 22 is used.
The clad 26 is provided to form the clad 27.

FIG. 5 (c) shows an example of an O-ring type refractive index distribution shape, in which a high refractive index peripheral core portion 32 is provided on the outer periphery of a central low refractive index central core portion 31. Thus, a core 34 having a two-layer structure is formed. By providing a clad 37 having a lower refractive index than the peripheral core portion 32 on the outer periphery of the core 34, the clad 37
, A concave refractive index distribution shape having a three-layer structure is formed.

[0007]

With the recent demand for large capacity and long-distance transmission of optical communication systems, there is a need to provide a high-performance dispersion-shifted optical fiber suitable for long-distance systems and wavelength division multiplexing transmission. Is desired.

[0008]

The inventors of the present invention have made intensive studies in view of the above circumstances, and have found that a dispersion-shifted optical fiber having a dual-shape core type refractive index distribution shape and using a small diameter solution has the following features. In order to obtain something more sophisticated or one that can meet the requirements of individual optical communication systems,
Regarding the expansion of Aeff and the control of the dispersion slope, r is the ratio of the radius r1 of the central core portion to the radius r2 of the step core portion.
It has been found that there is a limit to the value of 2 / r1, and the ratios of Δ2 / Δ1 and Δ1, which are the ratio of the relative refractive index difference Δ1 of the central core portion and the relative refractive index difference Δ2 of the stepped core portion with reference to the cladding. Was. That is, in order to solve the above problems, the present invention proposes the following solutions.

According to a first aspect of the present invention, a central core having a high refractive index;
Provided on the outer periphery, a stepped core portion having a lower refractive index than the central core portion, provided on the outer periphery of the stepped core portion,
In a dispersion-shifted optical fiber having a refractive index distribution shape composed of a cladding having a lower refractive index than that of the stepped core portion and employing a small diameter solution as a core diameter, an Aeff in an operating wavelength band selected from 1490 to 1610 nm. Is 65-9
5 μm ² , dispersion slope is 0.08 to 0.14 ps / k
m / nm ² , the bending loss is 100 dB / m or less, the absolute value of the chromatic dispersion value is 0.5 to 8.0 ps / km / nm,
A dispersion-shifted optical fiber characterized by having a cut-off wavelength that causes substantially single-mode propagation. According to a second aspect, in the dispersion-shifted optical fiber according to the first aspect, the radius of the central core is r1, the radius of the stepped core is r2, and the relative refractive index of the central core based on the refractive index of the cladding. The difference is Δ1, and the relative refractive index difference of the step core is Δ2.
When r2 / r1 is x and Δ2 / Δ1 is y, 5
≦ x ≦ 10, 0.08 ≦ y ≦ 0.22, and 0.6% ≦
A dispersion-shifted optical fiber characterized by Δ1 ≦ 1.2%.

A third aspect of the present invention is the dispersion-shifted optical fiber according to the first or second aspect of the present invention, wherein the dispersion-shifted optical fiber has a zero-dispersion wavelength longer than the wavelength band used. A fourth invention provides the dispersion-shifted optical fiber according to the third invention, wherein 6 ≦ x ≦ 7 and 0.1 ≦ y ≦
0.18, y ≧ (−0.02x + 0.24), 0.6%
≦ Δ1 ≦ 1.2% and Aeff is 65 to 75
μm ² , dispersion slope is 0.125 ps / km / nm ²
A dispersion-shifted optical fiber characterized by the following. A fifth invention is the dispersion-shifted optical fiber according to the third invention, wherein 7 ≦ x ≦ 8, 0.1 ≦ y ≦ 0.16, y ≧
(−0.016x + 0.21), 0.6% ≦ Δ1 ≦ 1.
2%, Aeff is 70 to 80 μm ² , and dispersion slope is 0.130 ps / km / nm ² or less. The sixth invention is the dispersion-shifted optical fiber according to the third invention, wherein
≤x≤8.5, 0.1≤y≤0.16, (-0.02x
+0.26) ≦ y ≦ (−0.02x + 0.32), 0.
6% ≦ Δ1 ≦ 1.2% and Aeff is 75 to
85 μm ² , dispersion slope 0.135 ps / km / n
It is a dispersion-shifted optical fiber characterized by having a diameter of m ² or less.

According to a seventh aspect of the present invention, there is provided the dispersion-shifted optical fiber according to the first or second aspect, wherein the dispersion-shifted optical fiber has a zero-dispersion wavelength on the shorter wavelength side than the wavelength band used. According to an eighth aspect, in the dispersion-shifted optical fiber according to the seventh aspect, 5 ≦ x ≦ 8, 0.12 ≦ y ≦
0.22, (−0.02x + 0.24) ≦ y ≦ (−0.
02x + 0.34), 0.6% ≦ Δ1 ≦ 1.2%, Aeff is 65 to 75 μm ² , and dispersion slope is 0.110 ps / km / nm ² or less. Fiber. According to a ninth aspect, in the dispersion-shifted optical fiber according to the seventh aspect, 5.5 ≦ x
≦ 8, 0.12 ≦ y ≦ 0.20, (−0.02x + 0.
25) ≦ y ≦ (−0.02x + 0.33), 0.6% ≦
Δ1 ≦ 1.2% and Aeff is 70 to 80 μ
m ² and a dispersion slope of 0.115 ps / km / nm ² or less. A tenth invention is directed to the dispersion-shifted optical fiber according to the seventh invention, wherein 6 ≦ x ≦ 8, 0.12 ≦ y ≦ 0.20,
(−0.02x + 0.26) ≦ y ≦ (−0.02x +
0.35), 0.6% ≦ Δ1 ≦ 1.2%, and
Aeff is 75 to 85 μm ² , dispersion slope is 0.12
This is a dispersion-shifted optical fiber characterized by being at most 5 ps / km / nm ² .

[0012]

FIG. 1 shows an example of a refractive index distribution shape of a dispersion-shifted optical fiber according to the present invention.
Are provided, and a clad 7 having a uniform refractive index and a single-layer structure is provided on the outer periphery of the core 4. The central core portion 1 has the highest refractive index, the stepped core portion 2 has a lower refractive index than the central core portion 1, and the clad 7 has a lower refractive index than the stepped core portion 2. In the figure, symbols r1 and r2 indicate the radii of the central core portion 1 and the stepped core portion 2, respectively, and Δ1 and Δ2 are the relative refractive indexes of the central core portion 1 based on the refractive index of the clad 7, respectively. The difference and the relative refractive index difference of the step core portion 2 are shown.

In this example, for example, the center core portion 1 and the stepped core portion 2 are made of germanium-doped quartz glass doped with germanium having a function of increasing the refractive index, and the cladding 7 is made of pure quartz glass. In the refractive index distribution shape of the dispersion-shifted optical fiber, the boundaries between the respective layers (the central core 1, the stepped core 2, and the clad 7) are not clear, and are rounded, that is, in a state in which so-called drooping occurs. There is no particular limitation as long as the characteristics as the dispersion-shifted optical fiber of the present invention can be effectively obtained.

The wavelength band used in the dispersion-shifted optical fiber of the present invention is selected from a wavelength range of 1490 to 1610 nm and an appropriate wavelength band. For example, depending on the amplification wavelength band of an optical fiber amplifier used in an optical communication system, 14
A wavelength band having a predetermined wavelength width (for example, 1500 to 1520 nm) is selected from the range of 90 to 1530 nm.
Alternatively, a wavelength band having a predetermined wavelength width (for example, 1540 to 1565 nm) is selected from the range of 1530 to 1570 nm. Alternatively, a wavelength band having a predetermined wavelength width from a range of 1570 to 1610 nm (for example, 1570 to 1610 nm).
00 nm) is selected. Of these, the range that is often used in recent years is the range of 1530 to 1570 nm.

Aeff is obtained from the following equation.

[0016]

(Equation 1)

In the present invention, A
Since eff is 65 to 95 μm ² , the nonlinear effect can be suppressed. Those exceeding 95 μm ² are difficult to manufacture. The dispersion slope in the used wavelength band is 0.1.
08 to 0.14 ps / km / nm ² . Within this range, it is possible to prevent significant transmission deterioration due to the dispersion slope in the wavelength division multiplexing transmission.

The bending loss refers to a value under the condition that the bending diameter (2R) is 20 mm in the used wavelength band. The smaller the bending loss, the better. In the present invention, the bending loss is 100 dB / m or less, preferably 50 dB / m or less. If it exceeds 100 dB / m, the transmission loss is likely to be deteriorated due to slight bending applied to the dispersion-shifted optical fiber, and an extra loss is likely to occur during installation and handling, which is inconvenient.

The absolute value of the chromatic dispersion value is 0.5 to 8.0 ps.
/ Km / nm. Absolute value is 0.5ps / km / n
If it is smaller than m, the chromatic dispersion value is close to zero, and four-photon mixing, which is one of the nonlinear effects, is likely to occur, which is inconvenient. On the other hand, if it is larger than 8.0 ps / km / nm, waveform distortion may occur and the deterioration of transmission characteristics may increase. Further, as will be described in detail later, since the chromatic dispersion value can be controlled to a positive value or a negative value, it is possible to respond to the demands of various optical communication systems, for example, using soliton transmission. A design applicable to a system or the like can be designed.

Since the dispersion-shifted optical fiber of the present invention is a single-mode optical fiber, it is necessary to have a cut-off wavelength that substantially guarantees single-mode propagation in the wavelength band used. The usual cutoff wavelength is C
It is defined by the value of the CITT 2m method (hereinafter referred to as the 2m method). However, in an actual long use state, even if this value is longer than the lower limit of the use wavelength band, single mode propagation is possible.

Therefore, in the dispersion-shifted optical fiber of the present invention, the cut-off wavelength defined by the 2m method is set so that single-mode propagation is possible depending on the used length and used wavelength band of the dispersion-shifted optical fiber. Specifically, for example, the cutoff wavelength in the 2m method is 1.8 μm
Then, in a long state of about 5000 m or more, single mode propagation in the above-mentioned used wavelength band can be realized.

In the present invention, a small diameter solution is used as the core diameter as described above. Specifically, in setting four structural parameters, r2, r1, Δ2, and Δ1, which will be described later, by simulation, A is set so that the core diameter becomes a small-diameter solution and in the above-mentioned desired use wavelength band.
Design conditions that satisfy characteristic values such as eff and dispersion slope are determined. In addition, as an actual manufacturing method of the dispersion-shifted optical fiber of the present invention, a conventional method such as a CVD method and a VAD method can be applied.

FIG. 2 is a graph showing an analysis result regarding the structural parameters of the dispersion-shifted optical fiber.
In the cases where r1 is 5.0, 7.0, and 9.0, the trajectory of the small diameter solution when △ 2 / △ 1 and △ 1 are changed is shown. The curve of Δ2 / Δ1 shows the characteristics when Δ2 / Δ1 is fixed to the value shown on each curve and Δ1 is changed. Further, the curve of Δ1 shows the characteristics when Δ1 is fixed to the value shown on each curve and Δ2 / Δ1 is changed. For example, when r2 / r1 is 9.0,
When moving from right to left in the graph on the curve of Δ2 / Δ1 = 0.14, Δ1 changes from 0.9 to 2.0. Then, for example, a curve of Δ2 / Δ1 = 0.14 and Δ
The point where the curves of 1 = 1.4 intersect is that Δ2 / Δ1 is 0.1
4 shows the characteristics of the dispersion-shifted optical fiber when Δ1 is 1.4. The analysis condition is that the wavelength used is 15
50 nm, and the chromatic dispersion value of the used wavelength is -2.0 ps
/ Km / nm. The zero dispersion wavelength is not constant because the dispersion slope is different, but is approximately 1565 nm or more, and is on the longer wavelength side than the used wavelength (band).

FIGS. 3 and 4 show distributions of characteristic values with changes in Δ2 / Δ1 and Δ1 when r2 / r1 is 7.0 and 9.0, respectively, as in the graph shown in FIG. FIG. These graphs further show the distribution of the cutoff wavelength (λc) and the dispersion slope. That is, Δ2 / Δ1 is 0.10, 0.12,
The distribution of the cutoff wavelength is also shown on each of the curves 0.14 and 0.16. For example, Δ2 / Δ1 is 0.1
In the case of 0, the cutoff wavelength is distributed in the range of 1.0 to 1.1. On the other hand, when Δ2 / Δ1 is 0.12, the cutoff wavelength is in the range of 1.1 to 1.2 and 1.2 to 1.3.
Distributed in the range. When Δ2 / Δ1 is constant, it can be seen that increasing Δ1 reduces the cutoff wavelength.

The curve of the dispersion slope has an inverted U-shape and is distributed in a contour line. The dispersion slope is smaller on the outer side of the contour distribution, and is larger on the inner side. Therefore, for example, in the graph shown in FIG. 3, Δ2 / Δ1 is 0.14 and Δ1 is 1.4 (Δ2 / Δ1
(The point where the curve of 0.14 and the curve of Δ1 = 1.4 intersect)
In the case of, a cutoff wavelength of 1.3 to 1.4 μm and a dispersion slope of 0.122 to 0.124 ps / km / nm ² are obtained.

From the graph shown in FIG. 3, r2 / r1 is 5
Aeff is 65 μ
A practical bending loss can be obtained in the region of m ² or more. On the other hand, when r2 / r1 is large, a larger Aeff is obtained. However, as can be seen by comparing the graphs shown in FIGS. 3 and 4, when r2 / r1 is large, the dispersion slope tends to be large. To obtain one suitable for a wavelength division multiplexing system, the dispersion slope in the used wavelength band is 0.14p.
s / km / nm ² or less.
2 / r1 is set to 10 or less. Therefore, r2 / r1
When x = 5, the range of 5 ≦ x ≦ 10 is desirable.

On the other hand, if す ぎ る 2 / △ 1 is too small, the bending loss becomes large, making it impractical. Therefore, Δ2 / Δ1 is set to 0.08 or more. On the other hand, if △ 2 / △ 1 is too large, the cutoff wavelength becomes long, and it becomes impossible to secure single mode propagation in the used wavelength band. Therefore, Δ2 / Δ1 is set to 0.22 or less. Therefore, when Δ2 / Δ1 = y, the range of 0.08 ≦ y ≦ 0.22 is desirable.
Δ2 / Δ1 (y) can be further adjusted by the bending loss allowed in each optical communication system and the required cutoff wavelength.

Δ1 is set to 0.6 to 1.2%. 0.6
%, The bending loss becomes too large, and the chromatic dispersion value may not be controlled to a desired value. 1.2%
If the ratio exceeds, Aeff cannot be sufficiently enlarged, and the Rayleigh loss may increase. These r
The preferred ranges of 2 / r1 (x), Δ2 / Δ1 (y), and Δ1 are the same when the zero dispersion wavelength is on the shorter wavelength side than the used wavelength band.

Then, a combination of the structural parameters from these numerical ranges is selected and designed to satisfy the characteristics of the dispersion-shifted optical fiber of the present invention. In the dispersion-shifted optical fiber of the present invention, r2, that is, the radius of the core is not particularly limited.
１２12 μm. The outer diameter of the cladding 7 (dispersion shifted optical fiber) is usually about 125 μm.

The dispersion-shifted optical fiber of the present invention depends on whether it has a zero-dispersion wavelength on the long wavelength side or a zero-dispersion wavelength on the short wavelength side of the used wavelength band.
Different structure parameter restrictions.

In the case where the wavelength has a zero-dispersion wavelength on the longer wavelength side than the used wavelength band, the following restrictions are imposed.

That is, in order to obtain a dispersion-shifted optical fiber having an Aeff of 65 to 75 μm ² and a dispersion slope of 0.125 ps / km / nm ² or less, it is preferable to satisfy the following conditions.

When r2 / r1 is x and Δ2 / Δ1 is y, 6 ≦ x ≦ 7, 0.1 ≦ y ≦ 0.18, y ≧ (−0.02x + 0.24), 0.6% ≦ Δ1 ≦ 1.2%.

In order to obtain a dispersion-shifted optical fiber having an Aeff of 70 to 80 μm ² and a dispersion slope of 0.130 ps / km / nm ² or less, it is preferable to satisfy the following conditions. 7 ≦ x ≦ 8, 0.1 ≦ y ≦ 0.16, y ≧ (−0.016x + 0.21), 0.6% ≦ Δ1 ≦ 1.2%.

In order to obtain a dispersion-shifted optical fiber having an Aeff of 75 to 85 μm ² and a dispersion slope of 0.135 ps / km / nm ² or less, it is preferable to satisfy the following conditions. 7 ≦ x ≦ 8.5, 0.1 ≦ y ≦ 0.16, (−0.02x + 0.26) ≦ y ≦ (−0.02x +
0.32), 0.6% ≦ Δ1 ≦ 1.2%.

On the other hand, when the wavelength has a zero dispersion wavelength on the shorter wavelength side than the used wavelength band, the following restrictions are imposed.

That is, in order to obtain characteristics of Aeff 65 to 75 μm ² and a dispersion slope of 0.110 ps / km / nm ² or less, it is preferable to satisfy the following conditions. 5 ≦ x ≦ 8, 0.12 ≦ y ≦ 0.22, (−0.02x + 0.24) ≦ y ≦ (−0.02x +
0.34), 0.6% ≦ Δ1 ≦ 1.2%. Here, even if x (r2 / r1) and y (△ 2 / △ 1) satisfy these ranges, if x is large and y is small, it is necessary to set △ 1 large. As a result, there is a possibility that the transmission loss becomes worse due to an increase in the Rayleigh loss. To prevent this, Δ1 is limited. That is, if △ 1 is set in the above range, a transmission loss that does not cause any practical problem can be obtained. The limitation of Δ1 in the following case is based on the same reason.

In order to obtain a dispersion-shifted optical fiber having an Aeff of 70 to 80 μm ² and a dispersion slope of 0.115 ps / km / nm ² or less, it is preferable to satisfy the following conditions. 5.5 ≦ x ≦ 8, 0.12 ≦ y ≦ 0.20, (−0.02x + 0.25) ≦ y ≦ (−0.02x +
0.33), 0.6% ≦ Δ1 ≦ 1.2%.

In order to obtain a dispersion-shifted optical fiber having an Aeff of 75 to 85 μm ² and a dispersion slope of 0.125 ps / km / nm ² or less, it is preferable to satisfy the following conditions. 6 ≦ x ≦ 8, 0.12 ≦ y ≦ 0.20, (−0.02x + 0.26) ≦ y ≦ (−0.02x +
0.35), 0.6% ≦ Δ1 ≦ 1.2%. Note that, depending on the used wavelength band and the setting conditions of the zero-dispersion wavelength, r1, r2, Δ1, and
Needless to say, it is necessary to adjust the specific value of Δ2.

Hereinafter, a specific example will be described with reference to a design example.
Tables 1 and 2 show the structural parameters and characteristic values of the dispersion-shifted optical fiber produced by the CVD method using the small diameter solution. In the table, λc is the cutoff wavelength, MFD
Is the mode field diameter.

[0041]

[Table 1]

No. 1 in Table 1 The dispersion-shifted optical fibers 1 to 9 have a negative chromatic dispersion value at 1550 nm, about -2 ps / km / nm, a zero-dispersion wavelength of about 1565 nm or more, and a zero-dispersion wavelength smaller than the wavelength band used. It is designed on the long wavelength side.

No. 1 to 3 are design examples of dispersion-shifted optical fibers having an Aeff of about 70 μm ² . Any of the dispersion-shifted optical fibers satisfies the above-mentioned preferable structural parameter conditions. And the dispersion slope is 0.12
A value of 5 ps / km / nm ² or less is obtained. No.
4 to 6 are design examples of dispersion-shifted optical fibers having an Aeff of about 75 μm ² . At this time, the dispersion slope is 0.1
A value of 30 ps / km / nm ² or less is obtained. N
o. 7 to 9 are design examples of dispersion-shifted optical fibers having an Aeff of about 80 μm ² . At this time, the dispersion slope has a value of 0.135 ps / km / nm ² or less.

No. 2 in Table 2 The dispersion-shifted optical fibers 10 to 18 have a positive chromatic dispersion value at 1550 nm, around 2 ps / km / nm, a zero dispersion wavelength of about 1540 nm or less, and use the zero dispersion wavelength (band).
It is designed on the shorter wavelength side.

[0045]

[Table 2]

No. 10 to 12 have an Aeff of 70 μm
² is a design example of a dispersion-shifted optical fiber of around ² . At this time, the dispersion slope has a value of 0.110 ps / km / nm ² or less. No. 13 to 15 are design examples of dispersion-shifted optical fibers having an Aeff of about 75 μm ² . At this time, the dispersion slope is 0.115 ps / km / n
A value of m ² or less is obtained. No. 16-18 are A
This is a design example of a dispersion-shifted optical fiber having an eff of about 80 μm ² . At this time, the dispersion slope is 0.125 ps / k
A value of m / nm ² or less is obtained.

[0047]

As described above, in the present invention,
Since the chromatic dispersion value of the used wavelength band is controlled to be within a certain range without being zero, and Aeff is expanded,
It is possible to provide a dispersion-shifted optical fiber that is less likely to cause a nonlinear effect and is suitable for a long-distance system such as an optical amplification repeater transmission system using an optical fiber amplifier. Also,
The dispersion slope is controlled to be small and is applicable to wavelength division multiplex transmission. Also, since the chromatic dispersion value can be adjusted to either a positive or negative value, the sign of the chromatic dispersion value can be set according to the optical communication system.

[Brief description of the drawings]

FIG. 1 is a diagram showing an example of a refractive index distribution shape of a dispersion shifted optical fiber of the present invention.

FIG. 2 is an analysis result showing a locus of a small diameter solution when △ 2 / △ 1 and △ 1 are changed when r2 / r1 is 5.0, 7.0, and 9.0, respectively. It is a graph of.

FIG. 3 shows Δ2 / Δ1 and Δ when r2 / r1 is 7.0.
6 is a graph showing a distribution of characteristic values according to a change of 1.

FIG. 4 shows Δ2 / Δ1 and Δ when r2 / r1 is 9.0.
6 is a graph showing a distribution of characteristic values according to a change of 1.

5 (a) to 5 (c) are diagrams showing examples of refractive index distribution shapes of a conventional dispersion shifted optical fiber.

[Description of Signs] 1 ... Center core, 2 ... Step core, 4 ... Core, 7 ... Clad.

Claims (10)

[Claims] And a stepped core provided on the outer periphery of the stepped core, the stepped core having a lower refractive index than the center core, and a stepped core provided on the outer periphery of the stepped core. In a dispersion-shifted optical fiber having a refractive index distribution shape composed of a cladding having a lower refractive index than the stepped core portion and employing a small diameter solution as a core diameter, Aeff is in a used wavelength band selected from 1490 to 1610 nm. 65-95 μm ² , dispersion slope 0.08-0.14 ps / km / nm ² , bending loss of 1
00 dB / m or less, and the absolute value of the chromatic dispersion value is 0.5 to 8.
A dispersion-shifted optical fiber having a cutoff wavelength of 0 ps / km / nm and substantially single-mode propagation. 2. The dispersion-shifted optical fiber according to claim 1, wherein the radius of the central core is r1, the radius of the stepped core is r2, and the relative refractive index of the central core based on the refractive index of the cladding. The difference is Δ1, and the relative refractive index difference of the step core is Δ2.
Where r2 / r1 is x and Δ2 / Δ1 is y, 5 ≦ x ≦ 10, 0.08 ≦ y ≦ 0.22, and 0.6%
≤ Δ1 ≤ 1.2%, a dispersion-shifted optical fiber. 3. The dispersion-shifted optical fiber according to claim 1, wherein the dispersion-shifted optical fiber has a zero-dispersion wavelength on a longer wavelength side than a used wavelength band. 4. The dispersion-shifted optical fiber according to claim 3, wherein 6 ≦ x ≦ 7, 0.1 ≦ y ≦ 0.18, y ≧ (−0.02
x + 0.24), 0.6% ≦ Δ1 ≦ 1.2%, Aeff is 65 to 75 μm ² , and dispersion slope is 0.125 ps / km / nm ² or less. fiber. 5. The dispersion-shifted optical fiber according to claim 3, wherein 7 ≦ x ≦ 8, 0.1 ≦ y ≦ 0.16, y ≧ (−0.01
6x + 0.21), 0.6% ≦ Δ1 ≦ 1.2%, Aeff is 70 to 80 μm ² , and dispersion slope is 0.130 ps / km / nm ² or less. fiber. 6. The dispersion-shifted optical fiber according to claim 3, wherein 7 ≦ x ≦ 8.5, 0.1 ≦ y ≦ 0.16, (−0.02x + 0.26) ≦ y ≦ (−0. 02x +
0.32), 0.6% ≦ Δ1 ≦ 1.2%, Aeff is 75 to 85 μm ² , and dispersion slope is 0.135 ps / km / nm ² or less. fiber. 7. The dispersion-shifted optical fiber according to claim 1, wherein the dispersion-shifted optical fiber has a zero-dispersion wavelength on a shorter wavelength side than a used wavelength band. 8. The dispersion-shifted optical fiber according to claim 7, wherein 5 ≦ x ≦ 8, 0.12 ≦ y ≦ 0.22, (−0.02x + 0.24) ≦ y ≦ (−0.02x +
0.34), 0.6% ≦ Δ1 ≦ 1.2%, Aeff is 65 to 75 μm ² , and dispersion slope is 0.110 ps / km / nm ² or less. fiber. 9. The dispersion-shifted optical fiber according to claim 7, wherein 5.5 ≦ x ≦ 8, 0.12 ≦ y ≦ 0.20, (−0.02x + 0.25) ≦ y ≦ (−0. 02x +
0.33), 0.6% ≦ Δ1 ≦ 1.2%, Aeff is 70 to 80 μm ² , and dispersion slope is 0.115 ps / km / nm ² or less. fiber. 10. The dispersion-shifted optical fiber according to claim 7, wherein 6 ≦ x ≦ 8, 0.12 ≦ y ≦ 0.20, (−0.02x + 0.26) ≦ y ≦ (−0.02x +
0.35), 0.6% ≦ Δ1 ≦ 1.2%, Aeff is 75 to 85 μm ² , and dispersion slope is 0.125 ps / km / nm ² or less. fiber.