JP2000338353A - Dispersion shift optical fiber and its production - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a dispersion shift optical fiber which is large in a mode field diameter and is small in a dispersion slope in a use wavelength band. SOLUTION: This optical fiber is formed by covering the outer peripheral side of a center core 1, covering the outer peripheral side of a first side core 2 with a second side core 3, covering the outer peripheral side of the second side core 3 with an inside clad 4 and covering the outer peripheral side of the inside clad 4 with an outside clad 5. When the specific refractive index difference of the center core 1 with respect to the outside clad 5 is defined as Δ1, the specific refractive index difference of the first side core 2 with respect to the outside clad 5 as Δ2, the specific refractive index difference of the second side core 3 with respect to the outside clad 5 as Δ3 and the specific refractive index difference of the inside clad 4 with respect to the outside clad 5 as Δ4, Δ1>Δ3>Δ4>Δ2 is set and 0.75%<=Δ1<=0.85%, -0.15%<=Δ2<=0, 0.3%<=Δ3<=0.5%, -0.2%<=Δ4<=0 are set.

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 used for, for example, wavelength division multiplexing transmission and a method for manufacturing the same.

[0002]

2. Description of the Related Art As a transmission network for optical communication, a wavelength of 1.3 μm is used.
Single mode optical fibers having zero dispersion in the above wavelength band are laid all over the world. Recently, the amount of communication information tends to increase dramatically due to the development of the information society,
With the increase of such information, wavelength division multiplexing transmission (WDM)
Transmission) has been widely accepted in the communication field, and the era of wavelength division multiplex transmission is now approaching. Wavelength multiplex transmission is a system in which the wavelength of optical communication is not one wavelength but is divided into a plurality of wavelengths to transmit a plurality of optical signals, and is an optical transmission system suitable for large-capacity high-speed communication.

However, when the existing single-mode optical fiber for transmission having zero dispersion in the 1.3 μm wavelength band is used and wavelength-division multiplexing optical communication is performed using the 1.3 μm wavelength band, ordinary light is used. 1.55μ which is the gain band of the amplifier
Since the wavelength band does not match the wavelength band of m (for example, 1.52 to 1.62 μm), there is a problem that an optical amplifier cannot be used, which hinders long-distance optical communication. The wavelength multiplexing optical communication in the 1.55 μm wavelength band is performed using a transmission single mode optical fiber having zero dispersion in the 1.3 μm wavelength band.

However, using a single-mode optical fiber for transmission having zero dispersion in a wavelength band of 1.3 μm,
When optical communication is performed in the wavelength band of 55 μm, the existing single-mode optical fiber for transmission has a positive dispersion of about 16 to 18 ps / nm / km in the wavelength band of 1.55 μm.
Since it has a positive dispersion slope of 0.07 to 0.09 ps / nm ² / km, as the optical signal propagates through the single-mode optical fiber for transmission, the waveform distortion of the signal of each wavelength that is wavelength-multiplexed becomes large, There has been a problem that it becomes difficult to separate signals on the receiving side, the quality of optical communication is reduced, and the reliability of optical communication is lost.

Therefore, recently, in order to solve such a problem, the zero-dispersion wavelength is increased from around 1.31 μm to 1.0.
A method of performing optical transmission using a dispersion-shifted optical fiber shifted to around 55 μm has been proposed. This 1.55
When an optical signal is transmitted at a wavelength of 1.55 μm using a dispersion-shifted optical fiber having zero dispersion at a wavelength of μm, signal transmission without waveform distortion due to dispersion becomes possible.

FIG. 5 shows a refractive index distribution structure of such a dispersion-shifted optical fiber. As shown in FIG. 1, in the conventional dispersion-shifted optical fiber, the center core 1 is covered with a first side core 2 having a smaller refractive index than the center core 1, and the first side core 2 is surrounded around the first side core 2.
It is formed so as to be covered with a clad 5 having a smaller refractive index. The clad 5 is made of, for example, pure quartz. As typical values, the relative refractive index difference Δ1 ′ of the center core 1 with respect to the clad 5 is 0.9%, and the relative refractive index difference of the first side core 2 with respect to the clad 5 is 0.9%. Δ2 ′ is 0.2%.

The relative refractive index differences Δ1 ′ and Δ2 ′ are
When the relative refractive index of the center core 1 when the vacuum refractive index is 1 is n ₁ , the relative refractive index of the first side core 2 is n ₂ , and the relative refractive index of the cladding 5 is n ₀ , the following equation (1) , (2).

Δ1 ′ = {(n ₁ ² −n ₀ ² ) / 2n ₁ ² } × 100 (1)

Δ2 ′ = {(n ₂ ² −n ₀ ² ) / 2n ₂ ² } × 100 (2)

[0010]

Since wavelength multiplex transmission is a transmission system in which a plurality of light beams having different wavelengths are multiplexed and transmitted, for example, a wavelength of 1.53 μm to 1.53 μm is used.
It is necessary to transmit a wavelength in a band having a certain width such as 8 μm by an optical fiber. Therefore, using a dispersion-shifted optical fiber, a wavelength of 1.55 μm
When performing wavelength division multiplexed optical transmission of band signals, the wavelength 1.55
In order to minimize the dispersion not only for the dispersion of μm but also for signals of other wavelengths in the vicinity, thereby reducing the distortion of the waveform caused by the dispersion, the wavelength 1.
The dispersion slope of the dispersion-shifted optical fiber in the 55 μm band is 0.11 ps / nm ² / km or less (preferably 0.1 μs / nm ² / km).
06 ps / nm ² / km or less).

When a dispersion-shifted optical fiber is used for wavelength division multiplexing transmission, the mode field diameter is set to 8.2 μm or more (preferably 9.5 μm or more) in order to reduce non-linear effects and suppress polarization dispersion. Is required.

However, the characteristics of the conventional dispersion-shifted optical fiber are as shown in Table 1, for example, and the mode field diameter is small, so that the above-mentioned required characteristics cannot be satisfied. In Table 1, the dispersion slope indicates an average value at a wavelength of 1.53 μm to 1.58 μm, and the bending loss indicates a value at a bending radius of 10 mm and a measurement wavelength of 1.55 μm. Table 1 shows typical characteristics of the conventional dispersion-shifted optical fiber. However, in the conventional dispersion-shifted optical fiber, if the mode field diameter is increased, the dispersion slope becomes large. Again, the above required characteristics could not be satisfied.

[0013]

[Table 1]

In the dispersion-shifted optical fiber,
Since a nonlinear effect called four-wave mixing occurs near the zero-dispersion wavelength, a dispersion-shifted optical fiber for wavelength-division multiplexed optical transmission is required to have no zero-dispersion wavelength in the wavelength band used.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to provide a wavelength multiplexing apparatus having a large mode field diameter and a small chromatic dispersion and a small dispersion slope in a used wavelength band. An object of the present invention is to provide a dispersion-shifted optical fiber capable of reducing distortion caused by nonlinear effects, polarization dispersion, and chromatic dispersion when used for transmission, and a method for manufacturing the same.

[0016]

In order to achieve the above-mentioned object, the present invention has the following structure to solve the problem. That is, in the first invention of the dispersion-shifted optical fiber, the outer peripheral side of the center core is covered with the first side core, the outer peripheral side of the first side core is covered with the second side core, and the outer peripheral side of the second side core is covered with the inner clad. A dispersion-shifted optical fiber formed by covering an outer peripheral side of the inner cladding with an outer cladding, wherein a relative refractive index difference of the center core with respect to the outer cladding is Δ1,
The relative refractive index difference of the first side core with respect to the outer cladding is Δ2, the relative refractive index difference of the second side core with respect to the outer cladding is Δ3, and the relative refractive index difference of the inner cladding with respect to the outer cladding is Δ4. Sometimes Δ1>Δ3> Δ2 ≧ Δ4 or Δ1>Δ3> Δ4 ≧ Δ2
And 0.75% ≦ Δ1 ≦ 0.85%,
−0.15% ≦ Δ2 ≦ 0, 0.3% ≦ Δ3 ≦ 0.5%,
−0.2% ≦ Δ4 ≦ 0, and Δ2 ≦ −
As means for solving the problem, a configuration satisfying at least one of 0.05% and Δ4 ≦ −0.05% and satisfying at least one of Δ2 ≧ −0.1% and Δ4 ≧ −0.1% I have.

Further, in the second aspect of the present invention, in addition to the configuration of the first aspect, the diameter of the center core is 3 to 8 μm, and the diameter of the first side core is one of the diameter of the center core. 3 to 2.5 times, the diameter of the second side core is 2.5 to 4 times the center core, and the diameter of the inner cladding is 1
4 to 48 μm, and the diameter of the center core is 4.5 to 4.5 μm.
A configuration that achieves eight times is a means for solving the problem.

Further, the third invention of the dispersion-shifted optical fiber has a structure in which the composition of the inner cladding is substantially the same as the composition of the outer cladding in addition to the structure of the first or second invention. It is a means to solve the problem.

Further, in the fourth invention of the dispersion-shifted optical fiber, the center core, the first side core, the second side core, and the inner cladding are all germanium in addition to the constitution of the first or second invention. And fluorine are doped, and the center core, the first side core, the second side core, and the inner cladding are doped with germanium at different doping amounts per unit volume. I have.

Further, in the fifth aspect of the present invention, the center core, the first side core, and the second side core are each doped with germanium and fluorine in addition to the configuration of the third aspect. The center core, the first side core, and the second side core each have a structure in which the doping amounts of the germanium doped per unit volume are different from each other.

Further, a first method for manufacturing a dispersion-shifted optical fiber according to the present invention is the method for manufacturing a dispersion-shifted optical fiber according to the first, second, or fourth invention, wherein the center core, the first side core, This is a means for solving the problem by a configuration in which part or all of the second side core and the inner clad are manufactured by the VAD method.

Further, a second method for manufacturing a dispersion-shifted optical fiber according to the present invention is the method for manufacturing a dispersion-shifted optical fiber according to the third or fifth invention, wherein the center core, the first side core, and the second side core are provided. Part or all of V
This is a means for solving the problem with a configuration manufactured by the AD method.

The present inventor has set out the following in order to solve the above problems.
The profile configuration of the dispersion-shifted optical fiber was variously formed, and the characteristics of the dispersion-shifted optical fiber having each profile configuration, such as the zero dispersion wavelength and the dispersion slope and mode field diameter in the wavelength band of 1.55 μm, were examined. By using the refractive index profile structure of the dispersion-shifted optical fiber described above, a dispersion-shifted optical fiber having characteristics satisfying the above-mentioned problems could be formed.

Specifically, the relative refractive index difference Δ1 of the center core with respect to the outer cladding provided on the outer peripheral side of the optical fiber, the relative refractive index difference Δ2 of the first side core covering the outer peripheral side of the center core with respect to the outer cladding, and The relative refractive index difference Δ3 of the second side core covering the outer peripheral side of the first side core with respect to the outer cladding and the relative refractive index difference Δ4 of the inner cladding covering the outer peripheral side of the second side core with respect to the outer cladding are respectively 0.75% ≦ Δ1. ≤0.85%, -0.15% ≤
Δ2 ≦ -0, 0.3% ≦ Δ3 ≦ 0.5%, −0.2% ≦
Δ4 ≦ 0, and Δ2 ≦ −0.05% and Δ4 ≦ −
At least one of 0.05% and Δ2 ≧ −
When at least one of 0.1% and Δ4 ≧ −0.1% is satisfied, the relationship between the relative refractive index differences of the respective regions of the optical fiber is
If Δ1>Δ3> Δ2 ≧ Δ4, the mode field diameter is 9.5 μm or more and the dispersion slope is 0.11.
ps / ^nm 2 / km can be easily obtained the following optical fiber, Δ1>Δ3> When [Delta] 4 ≧ Delta] 2, the mode field diameter not less than 8.2 .mu.m, the dispersion slope of 0.06 ps / ^nm 2 / An optical fiber of less than km could be easily obtained.

[0025]

Embodiments of the present invention will be described below with reference to the drawings. In the description of the present embodiment, the same reference numerals are given to the same parts as those in the conventional example, and the duplicate description thereof will be omitted. FIG. 1 shows a refractive index profile and a cross-sectional view of a first embodiment of the dispersion-shifted optical fiber according to the present invention.

As shown in the figure, in the dispersion-shifted optical fiber of the embodiment, the outer peripheral side of the center core 1 is covered with the first side core 2, the outer peripheral side of the first side core 2 is covered with the second side core 3, The outer side of the two-side core 3 is covered with an inner clad 4, and the outer side of the inner
, And these components are formed concentrically. In this embodiment, since the outer clad 5 corresponds to the clad 5 of the conventional example, the outer clad is denoted by the same reference numeral 5 as the clad of the conventional example.

The relative refractive index difference between the center core 1 and the outer cladding 5 is Δ1, the relative refractive index difference between the first side core 2 and the outer cladding 5 is Δ2, and the relative refractive index difference between the second side core 3 and the outer cladding 5 is Δ1. Is Δ3,
Assuming that the relative refractive index difference between the inner cladding 4 and the outer cladding 5 is Δ4, Δ1>Δ3> Δ4 ≧ Δ2, and 0.75% ≦ Δ1 ≦ 0.85%, −0.15
% ≦ Δ2 ≦ 0, 0.3% ≦ Δ3 ≦ 0.5%, -0.2%
≦ Δ4 ≦ 0, and Δ2 ≦ −0.05%
And Δ4 ≦ −0.05%, and at least one of Δ2 ≧ −0.1% and Δ4 ≧ −0.1%. Table 2 shows the relative refractive index differences Δ
Representative values of 1, Δ2, Δ3, and Δ4 are shown.

[0028]

[Table 2]

The relative refractive index differences Δ1, Δ2, Δ3, Δ
Reference numeral 4 denotes a relative refractive index of the center core 1 when the refractive index of the vacuum is ₁ , n ₁ , a relative refractive index of the first side core 2 n ₂ , a relative refractive index of the second side core 3 n ₃ , and an inner cladding 4. the relative refractive index n _{4 of,} when the relative refractive index of the outer cladding 5 was set to n _5, are as defined by the following equation (3) to (6), the unit, said as a% .

Δ1 = {(n ₁ ² −n ₅ ² ) / 2n ₁ ² } × 100 (3)

Δ2 = {(n ₂ ² −n ₅ ² ) / 2n ₂ ² } × 100 (4)

Δ3 = {(n ₃ ² −n ₅ ² ) / 2n ₃ ² } × 100 (5)

Δ4 = {(n ₄ ² −n ₅ ² ) / 2n ₄ ² } × 100 (6)

Here, in a dispersion-shifted optical fiber having a refractive index distribution profile as shown in FIG. 1A, if the relative refractive index difference Δ2 of the first side core 2 to the outer cladding 5 is a positive value, the dispersion If the slope becomes large and the relative refractive index difference Δ4 of the inner cladding 4 to the outer cladding 5 becomes a positive value, the mode field diameter becomes insufficiently enlarged, and the cutoff wavelength becomes larger than the wavelength of the signal light. Mode transmission becomes impossible. When both the relative refractive index differences Δ2 and Δ4 are larger than −0.05%, it becomes difficult to increase the mode field diameter and decrease the dispersion slope. Therefore, in this embodiment, as shown in Table 2, Δ2 ≦ 0, Δ4 ≦
0 and at least one of Δ2 and Δ4 is −0.05%
It was made to be as follows.

In the dispersion-shifted optical fiber having a refractive index profile as shown in FIG. 1A, the relative refractive index difference Δ2 of the first side core 2 with respect to the outer cladding 5 is set to less than -0.15%. Alternatively, the relative refractive index difference Δ4 between the inner cladding 4 and the outer cladding 5 is set to −0.
Less than 20%, or their relative refractive index difference Δ
If both Δ2 and Δ4 were simultaneously less than −0.1%, the bending loss at a bending diameter of 20 mm in the wavelength band of 1.55 μm was a large value exceeding 20 dB / m, and it was found that the bending characteristics deteriorated. Therefore, in the present embodiment, as shown in Table 2, both Δ2 and Δ4 are simultaneously set to −0.0.
It was not to be less than 1%.

When the relative refractive index difference Δ2 and the relative refractive index difference Δ4 are determined as described above, the value of the relative refractive index difference Δ1 becomes
0.75% ≦ Δ1 ≦ 0.85 is desirable, and the relative refractive index difference Δ
Since it was found that the value of 3 was desirably 0.3% ≦ Δ3 ≦ 0.5%, in the present embodiment, the values of Δ1 and Δ3 were as shown in Table 2.

Further, in the dispersion-shifted optical fiber of this embodiment, the diameter of the center core 1 is 3 to 8 μm, the diameter of the first side core 2 is 1.3 to 2.5 times the diameter of the center core 1, and
The diameter of the second side core 3 is 2.5 to 4 times that of the center core 1,
The diameter of the inner cladding 4 is 14 to 48 μm, and
The diameter is 4.5 to 8 times the diameter of the center core 1.

In this embodiment, the inner cladding 4
May be substantially the same as the composition of the outer cladding 5. In this case, the relative refractive index difference Δ4 ≒ 0, and the inner cladding 4 does not substantially exist. Also,
The diameter of the inner cladding 4 does not exist. That is, the dispersion-shifted optical fiber according to the present embodiment can be configured in the order of the center core 1, the first side core 2, the second side core 3, and the outer clad 5 from the inside.

Further, in the dispersion-shifted optical fiber of this embodiment, the outer cladding 5 is formed of pure quartz, and the center core 1, the first side core 2, and the second side core 2 are formed in order to realize the above-described refractive index profile configuration. 3 and the inner cladding 4 are made of pure quartz and germanium (G
e) doped with fluorine (F), and
The doping amounts per unit volume of germanium doped in the center core 1, the first side core 2, the second side core 3, and the inner cladding 4 were different from each other.

The present embodiment is configured as described above. When manufacturing the dispersion-shifted optical fiber of the present embodiment, the inventor of the present invention, for example, as shown in FIG. ), The center core 1, the first side core 2, the second side core 3, and the inner cladding 4 are all V
A porous base material was formed by the AD method. In addition, from each of the burners 7, SiCl ₄ , GeC
A mixed gas of l ₄ , H ₂ , and O ₂ is ejected, and the concentration of GeCl ₄ in this gas is made different in each burner 7.

Thereafter, the porous base material formed as described above is made transparent vitrified under the vitrification conditions shown in Table 3, and at the time of this vitrification, the center core 1 and the first side core 2
, The second side core 3 and the inner cladding 4 are doped with fluorine, and the outer cladding 5
Was formed by an external method to produce a dispersion-shifted optical fiber.

[0042]

[Table 3]

When the characteristics of the dispersion-shifted optical fiber of this embodiment manufactured as described above were evaluated, for example, as shown in Table 4, the mode field diameter was 8.4 μm.
Which satisfies the required characteristic that the mode field diameter is 8.2 μm or more, and uses the wavelength band (wavelength 1.55 μm).
m band; for example, the dispersion slope at a wavelength of 1.53 μm to 1.58 μm) is 0.04 ps / nm ² / km;
Dispersion slope satisfy the required properties such is 0.11ps / ^nm 2 / km or less, further, the dispersion slope was said that it is 0.06ps / ^nm 2 / km or less, which satisfies the more desirable characteristics required. A dispersion-shifted optical fiber which has a small chromatic dispersion in the wavelength band used and can reduce the waveform distortion of signal light caused by nonlinear effects, polarization dispersion and chromatic dispersion when used for wavelength division multiplexing transmission. It was confirmed that.

[0044]

[Table 4]

In Table 4, the bending loss is a value at a bending radius of 10 mm and a measurement wavelength of 1.55 μm. Table 4 shows typical values of the characteristics of the dispersion-shifted optical fiber according to the present embodiment. All of the dispersion-shifted optical fibers according to the present embodiment having the above configuration can satisfy the required characteristics. Was something.

In this embodiment, the center core 1, the first side core 2, the second side core 3, and the inner clad 4
Are all manufactured by the VAD method, the porous preform manufactured by the VAD method is vitrified, and an outer cladding 5 is provided therearound to manufacture a dispersion-shifted optical fiber. A dispersion-shifted optical fiber can be easily manufactured.

Further, in the present embodiment, since the center core 1, the first side core 2, the second side core 3, and the inner cladding 4 are doped with germanium at the time of forming the porous base material by the VAD method, the center core 1 It is easy to adjust the doping amounts of germanium to be doped into the first side core 2, the second side core 3, and the inner cladding 4 so as to be different from each other. The center core 1, the first side core 2, the second side core 3, and the inner cladding 4 are doped with germanium and fluorine by doping fluorine during the vitrification of the porous base material. The structure is easily formed, and the dispersion-shifted optical fiber exhibiting the above excellent effects can be easily formed, and
It can be formed reliably.

In this embodiment, when the composition of the inner cladding 4 is substantially the same as the composition of the outer cladding 5, doping of the inner cladding 4 with germanium or fluorine can be omitted. The manufacturing process can be further simplified.

FIG. 3 shows a refractive index profile of a second embodiment of the dispersion-shifted optical fiber according to the present invention. In the figure, the same reference numerals are given to the same parts as those in the first embodiment, and the duplicated description is omitted.

The dispersion-shifted optical fiber of the second embodiment is substantially the same as the dispersion-shifted optical fiber of the first embodiment, and the dispersion-shifted optical fiber of the second embodiment is the same as the first embodiment. The difference from the dispersion-shifted optical fiber of the embodiment is that the relative refractive index difference of the center core 1 with respect to the outer cladding 5 is Δ1, the relative refractive index difference of the first side core 2 with respect to the outer cladding 5 is Δ2, The relative refractive index difference of the side core 3 with respect to the outer cladding 5 is Δ3,
Relative refractive index difference Δ of inner cladding 4 to outer cladding 5
4 is such that Δ1>Δ3> Δ2 ≧ Δ4.

Table 5 shows typical values of the refractive index profile structure of the dispersion shifted optical fiber according to the second embodiment. In this embodiment, for the same reason as in the first embodiment, Δ2 ≦ 0, Δ4 ≦ 0, and at least one of Δ2 and Δ4 is set to −0.05% or less, and Both Δ2 and Δ4 were not allowed to be simultaneously less than -0.1%.

[0052]

[Table 5]

The present embodiment is configured as described above. When manufacturing the dispersion-shifted optical fiber of this embodiment, as in the first embodiment, as shown in FIG. The center core 1, the first side core 2, the second side core 3, and the inner clad 4 are all formed by a VAD method to form a porous base material, and the porous base material is formed into a transparent glass, and an outer clad 5 is provided. did.

When the characteristics of the dispersion-shifted optical fiber of the second embodiment manufactured as described above were evaluated,
For example, as shown in Table 6, the mode field diameter is 10 μm.
m, which satisfies the required characteristics of a mode field diameter of 8.2 μm or more.
It satisfies the more desirable required characteristics such as being larger than 5 μm, and uses the wavelength band to be used (wavelength 1.55 μm).
In the μm band; for example, in a wavelength of 1.53 μm to 1.58 μm), the required characteristics such as a dispersion slope of 0.106 ps / nm ² / km and a dispersion slope of 0.11 ps / nm ² / km or less are satisfied. . A dispersion-shifted optical fiber which has a small chromatic dispersion in the wavelength band used and can reduce the waveform distortion of signal light caused by nonlinear effects, polarization dispersion and chromatic dispersion when used for wavelength division multiplexing transmission. It was confirmed that.

[0055]

[Table 6]

In Table 6, the bending loss indicates a value at a bending radius of 10 mm and a measurement wavelength of 1.55 μm. Table 5 shows typical values of the characteristics of the dispersion-shifted optical fiber of the present embodiment. However, the dispersion-shifted optical fiber of the present embodiment having the above configuration can satisfy the required characteristics. Was something.

As described above, in the second embodiment, as in the first embodiment, an excellent dispersion-shifted optical fiber satisfying the required characteristics of the dispersion-shifted optical fiber can be obtained. As in the case of the first embodiment, the same effect that a dispersion-shifted optical fiber capable of achieving the above-described excellent effects can be easily and reliably manufactured with a small number of manufacturing steps can be obtained.

The present invention is not limited to the above-described embodiment, but can take various embodiments. For example, in each of the above embodiments, the center core 1 and the first side core 2
Although the whole and the second side core 3 and the inner cladding 4 are formed by the VAD method, they are not necessarily formed by the VAD method, and a part of them may be formed by the VAD method. However, if some or all of them are formed by the VAD method, the number of steps of the dispersion-shifted optical fiber can be reduced, and the dispersion-shifted optical fiber of the present invention can be easily manufactured. In particular, the center core 1 and the first side core 1 2 and 2
When the side core 3 and the inner cladding 4 are all formed by the VAD method, the dispersion-shifted optical fiber of the present invention can be manufactured more easily.

In each of the above embodiments, the outer clad 5 is formed of pure quartz, and the center core 1, the first side core 2, the second side core 3, and the inner clad 4 are formed.
Are formed by doping germanium and fluorine into pure quartz, and the doping amounts per unit volume of germanium doped in the center core 1, the first side core 2, the second side core 3, and the inner cladding 4 are different from each other. As described above, the composition of each component forming the dispersion-shifted optical fiber is not particularly limited, and is appropriately set.

For example, the center core 1 and the second side core 3
When germanium is doped into germanium, germanium also diffuses into the first side core 2, so that the refractive index profile structure of the center core 1, the first side core 2, the second side core 3, and the inner cladding 4 is Δ1>Δ3> Δ4 ≧ Δ2 In some cases, the first side core 2 may not be doped with germanium. When the refractive index profile structure satisfies Δ1>Δ3> Δ2 ≧ Δ4, the dispersion-shifted optical fiber of the present invention can be formed without doping the inner cladding 4 with germanium.

However, rather than forming the dispersion-shifted optical fiber of the present invention by utilizing the diffusion of germanium from an adjacent region, it is more likely that each region is doped with a different amount of germanium than that of the present invention. In order to easily form a characteristic refractive index profile structure of the optical fiber, it is preferable that each region is doped with a different amount of germanium.

Further, in the dispersion-shifted optical fiber of the present invention, the relative refractive index differences Δ1, Δ2, Δ3, and Δ4 satisfy the relationship Δ1>Δ3> Δ4 ≧ Δ2 or Δ1>Δ3> Δ2 ≧ Δ
4 and 0.75% ≦ Δ1 ≦ 0.85
%, -0.15% ≦ Δ2 ≦ 0, 0.3% ≦ Δ3 ≦ 0.5
%, -0.2% ≦ Δ4 ≦ 0, and Δ2
≦ −0.05% and Δ4 ≦ −0.05%, and Δ2 ≧ −0.1% and Δ4 ≧ −0.1%
It is sufficient that at least one of the above is satisfied, and the diameter of each component is not particularly limited. Can be formed.

However, as in the above embodiment, the diameter of the center core 1 is 3 to 8 μm, the diameter of the first side core 2 is 1.3 to 2.5 times the diameter of the center core 1, and the diameter of the second side core 3 is 2.5 to 4 times the diameter of center core 1, inner cladding 4
Is 14 to 48 μm and the diameter of the center core 1 is 4.5 to 8 times as large as the diameter of the center core 1, so that the dispersion-shifted optical fiber satisfying the above-mentioned required characteristics can be used as the dispersion fiber currently used. It can be formed into an optical fiber of the same size as a shift optical fiber or a single mode optical fiber, and therefore, easily and reliably satisfy the above-mentioned required characteristics using currently used optical fiber manufacturing technology. A dispersion shifted optical fiber can be formed.

In the case where the inner cladding 4 does not substantially exist, the diameter of the center core 1 is 3 to 8 μm.
The diameter of the first side core 2 is 1.3 times or more the diameter of the center core 1
The diameter of the second side core 3 is 2.5 times that of the center core 1.
By making it 5 to 4 times, the dispersion-shifted optical fiber satisfying the above-mentioned required characteristics can be formed into an optical fiber having the same size as the currently used dispersion-shifted optical fiber or single-mode optical fiber. And therefore, using currently used fiber optic manufacturing techniques,
A dispersion-shifted optical fiber that satisfies the above required characteristics can be easily and reliably formed.

Further, the refractive index profile structure of the dispersion-shifted optical fiber of the present invention is not always limited to the structure shown in FIG. 1 or FIG. 3, and the relative refractive index differences Δ1, Δ2,.
The relationship of Δ3 and Δ4 is Δ1>Δ3> Δ4 ≧ Δ2 or Δ
1>Δ3> Δ2 ≧ Δ4, and 0.75% ≦
Δ1 ≦ 0.85%, −0.15% ≦ Δ2 ≦ 0, 0.3%
≦ Δ3 ≦ 0.5%, −0.2% ≦ Δ4 ≦ 0, and Δ2 ≦ −0.05% and Δ4 ≦ −0.05%
And at least one of Δ2 ≧ −0.1% and Δ4 ≧ −0.1% may be satisfied. For example, a structure as shown in FIGS. And
The refractive index distribution of at least one of the center core 1 and the second side core 3 may have a parabolic shape that is convex upward.

[0066]

According to the present invention, by adopting a characteristic configuration obtained by variously examining the refractive index profile structure of the dispersion-shifted optical fiber, the mode field diameter is large and the wavelength in the operating wavelength band is large. A dispersion-shifted optical fiber having a small dispersion slope can be obtained. Therefore, when the dispersion-shifted optical fiber of the present invention is used for wavelength division multiplexing transmission, it can be an excellent dispersion-shifted optical fiber that can reduce distortion caused by nonlinear effects, polarization dispersion, and chromatic dispersion. .

Specifically, the relative refractive index difference Δ1 of the center core with respect to the outer cladding provided on the outer peripheral side of the optical fiber, the relative refractive index difference Δ2 of the first side core covering the outer peripheral side of the center core with respect to the outer cladding, and The relative refractive index difference Δ3 of the second side core covering the outer peripheral side of the first side core with respect to the outer cladding and the relative refractive index difference Δ4 of the inner cladding covering the outer peripheral side of the second side core with respect to the outer cladding are respectively 0.75% ≦ Δ1. ≤0.85%, -0.15% ≤
Δ2 ≦ 0, 0.3% ≦ Δ3 ≦ 0.5%, −0.2% ≦ Δ
4 ≦ 0, and Δ2 ≦ −0.05% and Δ4 ≦ −
At least one of 0.05% and Δ2 ≧ −
In a state where at least one of 0.1% and Δ4 ≧ −0.1% is satisfied, if the relation of the relative refractive index difference Δ in each region of the optical fiber is Δ1>Δ3> Δ2 ≧ Δ4, the mode field diameter is And the dispersion slope is 0.1 μm or more.
1 ps / nm ² / km or less, Δ1> Δ
3> Δ4 ≧ Δ2, the mode field diameter is set to 8.2 μm or more, and the dispersion slope is set to 0.06 ps.
/ Nm ² / km or less.

In particular, the diameter of the center core is 3 to 8 μm, and the diameter of the first side core is 1.3 times or more the diameter of the center core.
2.5 times, the diameter of the second side core is 2.
According to the dispersion-shifted optical fiber of the present invention, which has a diameter of 5 to 4 times, an inner cladding diameter of 14 to 48 μm, and a diameter of the center core of 4.5 to 8 times, currently used light By using the fiber manufacturing technique, it is possible to very easily and surely form a dispersion-shifted optical fiber exhibiting the above-described excellent effects.

In the dispersion-shifted optical fiber of the present invention, when the composition of the inner cladding is substantially the same as the composition of the outer cladding, the diameter of the center core is 3 to
8 μm, the diameter of the first side core is set to 1.3 to 2.5 times the diameter of the center core, and the diameter of the second side core is set to 2.5 to 4 times the center core. By using the currently used optical fiber manufacturing technology, a dispersion-shifted optical fiber exhibiting the above-described excellent effects can be formed very easily and reliably.

The center core, the first side core, the second side core, and the inner cladding are all doped with germanium and fluorine, and the center core, the first side core, the second side core, and the inner cladding are doped respectively. According to the dispersion-shifted optical fiber of the present invention, in which the doping amounts per unit volume of the germanium are different from each other, the refractive index profile structure can be formed very easily, and the dispersion shift having the excellent effect can be achieved. The optical fiber can be formed more easily.

The center core, the first side core, and the second
Each of the side cores is doped with germanium and fluorine, and the center core, the first side core, and the second side core have different doping amounts per unit volume of the germanium different from each other according to the present invention. Similarly, the optical fiber can very easily form the refractive index profile structure,
A dispersion-shifted optical fiber exhibiting the above-described excellent effects can be formed more easily.

Further, according to the method of manufacturing the dispersion shifted optical fiber of the present invention, the center core, the first side core, and the second
By manufacturing a part or all of the side core and the inner cladding by the VAD method, it is possible to easily manufacture a dispersion-shifted optical fiber exhibiting the above-mentioned excellent effects very easily by using the VAD method.

[Brief description of the drawings]

FIG. 1 is a configuration diagram showing a refractive index profile (a) and a cross-sectional view (b) of a first embodiment of a dispersion-shifted optical fiber according to the present invention.

FIG. 2 is an explanatory view showing an example in which a porous preform is formed by a VAD method by the method of manufacturing a dispersion-shifted optical fiber according to the present invention.

FIG. 3 is a configuration diagram showing a refractive index profile of a second embodiment of the dispersion shifted optical fiber according to the present invention.

FIG. 4 is a configuration diagram showing a refractive index profile of another embodiment of the dispersion-shifted optical fiber according to the present invention.

FIG. 5 is an explanatory diagram showing an example of a refractive index profile of a conventional dispersion-shifted optical fiber.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Center core 2 1st side core 3 2nd side core 4 Inner clad 5 Outer clad (cladding) 7 Burner

Continued on the front page F term (reference) 2H050 AA01 AB05X AB05Y AB10X AB20X AC14 AC15 AC28 AC36 AC73 AC76 AD00 4G021 EA01 EB05

Claims (7)

[Claims] 1. An outer peripheral side of a center core is covered with a first side core, an outer peripheral side of the first side core is covered with a second side core, and an outer peripheral side of the second side core is covered with an inner clad,
A dispersion-shifted optical fiber formed by covering an outer peripheral side of the inner cladding with an outer cladding, wherein a relative refractive index difference of the center core with respect to the outer cladding is Δ1, and a relative refractive index of the first side core with respect to the outer cladding. When the difference is Δ2, the relative refractive index difference of the second side core with respect to the outer cladding is Δ3, and the relative refractive index difference of the inner cladding with respect to the outer cladding is Δ4,
Δ1>Δ3> Δ2 ≧ Δ4 or Δ1>Δ3> Δ4 ≧ Δ2, and 0.75% ≦ Δ1 ≦ 0.85%, −
0.15% ≦ Δ2 ≦ 0, 0.3% ≦ Δ3 ≦ 0.5%, −
0.2% ≦ Δ4 ≦ 0, and Δ2 ≦ −0.
A dispersion-shifted optical fiber that satisfies at least one of 05% and Δ4 ≦ −0.05%, and satisfies at least one of Δ2 ≧ −0.1% and Δ4 ≧ −0.1%. 2. The diameter of the center core is 3 to 8 μm, and the diameter of the first side core is 1.3 to 2.5 times the diameter of the center core.
The diameter of the second side core is 2.5 to 4 times that of the center core.
2. The dispersion-shifted optical fiber according to claim 1, wherein the diameter of the inner cladding is 14 to 48 [mu] m and the diameter of the center core is 4.5 to 8 times. 3. The dispersion-shifted optical fiber according to claim 1, wherein the composition of the inner cladding is substantially the same as the composition of the outer cladding. 4. The center core, the first side core, the second side core, and the inner cladding are all doped with germanium and fluorine, and the center core, the first side core, the second side core, and the inner cladding are respectively doped. 3. The dispersion-shifted optical fiber according to claim 1, wherein the doping amounts of the germanium per unit volume are different from each other. 5. The center core, the first side core, and the second side core are all doped with germanium and fluorine, and the germanium unit doped in the center core, the first side core, and the second side core, respectively. 4. The dispersion-shifted optical fiber according to claim 3, wherein the doping amounts per volume are different from each other. 6. The method according to claim 1, wherein said first or second means is selected.
A method for manufacturing a dispersion-shifted optical fiber according to any one of claims 1 to 3, wherein a part or all of the center core, the first side core, the second side core, and the inner clad are manufactured by a VAD method. 7. The method of manufacturing a dispersion-shifted optical fiber according to claim 3, wherein a part or all of the center core, the first side core, and the second side core are VAD.
A method for producing a dispersion-shifted optical fiber, characterized by being produced by a method.