JP2003262752A - Optical fiber and optical transmission system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an optical fiber by which Aeff can be expanded in the employed wavelength band selected in the range of 1.53 to 1.61 μm, which has a comparatively simple shape of refractive index distribution, and can be manufactured at a low cost. <P>SOLUTION: The optical fiber is fabricated so that the shape of refractive index distribution has a central core 1; a middle part 2 provided around the outer periphery of the central core and having a lower refractive index than that of the central core; and a cladding 4 provided around the periphery of the middle part 2 and having a higher refractive index than the middle part 2 and a lower refractive index than the central core 1. This optical fiber has an effective core cross section area of 120 μm<SP>2</SP>or more in the employed wavelength band selected in the range of 1.53 to 1.61 μm, and has a cut-off wavelength that is capable of substantially single mode propagation in the employed wavelength band. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an optical fiber and an optical transmission system using the same, and it has a relatively simple structure and has an effective core cross-sectional area in a usable wavelength band selected from 1.53 to 1.61 μm. The present invention relates to an optical fiber which is expanded and capable of suppressing a non-linear effect, and an optical transmission system using the optical fiber.

[0002]

2. Description of the Related Art Due to the practical use of erbium-doped optical fiber amplifiers, systems such as ultra-long-distance non-regenerative repeaters have already been commercialized at wavelengths of 1.53 to 1.61 .mu.m. In addition, with the increase in communication capacity, the development of wavelength division multiplexing transmission has been rapidly advanced, and it has already been commercialized in some transmission lines. It is expected that the number of wavelength division multiplexing will increase rapidly in the future.

In wavelength division multiplex transmission, since one optical fiber transmits several optical signals having different wavelengths,
The optical power propagating through the optical fiber increases rapidly. Therefore, a technique for suppressing non-linear effects and preventing deterioration of transmission characteristics is essential. The magnitude of the nonlinear effect is n ₂ / Aeff
It is represented by. Where n ₂ is the nonlinear refractive index of the optical fiber, A eff is the effective core area of the optical fiber,
In order to suppress the non-linear effect, n ₂ should be reduced or A
It is necessary to increase eff. Since n ₂ is a value peculiar to the material, it is difficult to greatly reduce it in a silica-based optical fiber. Therefore, it is necessary to increase Aeff, and various materials having various complicated refractive index distribution shapes have been developed, but all of them are expensive.

On the other hand, the conventional communication system has 1.3 μm.
Single-mode optical fiber is widely used. However, in the 1.3 μm single mode optical fiber, when the wavelength band used is set to 1.53 to 1.61 μm, the bending loss becomes large, and the transmission loss is deteriorated even by a slight bending that occurs during installation. was there.
Therefore, a cutoff shift optical fiber (CSF) has been proposed in which the bending loss is reduced by improving the 1.3 μm single mode optical fiber. However, since the cutoff shift optical fiber is not intended to reduce the nonlinear effect, its Aeff is not large enough to suppress the nonlinear effect.

[0005]

SUMMARY OF THE INVENTION The present invention has been made in view of the above circumstances, and provides an optical fiber capable of expanding Aeff in a wavelength band used selected from 1.53 to 1.61 μm. The task is to do. Another object is to provide an optical fiber that has a relatively simple refractive index profile and can be manufactured at low cost.

[0006]

[Means for Solving the Problems] In order to solve the above problems, the following means for solving the problems are proposed. The first invention is
A central core portion, an intermediate portion having a lower refractive index than the central core portion provided on the outer periphery of the central core portion, and a higher refractive index than the intermediate portion provided around the intermediate portion, and having a higher refractive index than the central core portion. Also has a low refractive index clad, and has a refractive index distribution shape consisting of a central core portion having a radius of r ₁ and an intermediate portion having a radius of r _2.
When the relative refractive index difference between the central core portion and the intermediate portion with respect to the refractive index of the clad is Δ ₁ and Δ ₂ , respectively, the following (1) to (5) are satisfied. It is an optical fiber. (1) 3.0 ≦ r ₂ / r ₁ ≦ 5.0, and (2) Δ ₁
Is 0.30% or less, Δ ₂ is -0.05 to -0.15%
And (3) in an operating wavelength band selected from 1.53 to 1.61 μm, the effective core area is 120 μm ² or more, and (4) in the operating wavelength band, substantially single mode propagation is possible. Has a cutoff wavelength (5)
Bending diameter (2R) is 20 mm in the above wavelength band
Bending loss measured under the condition of 0.7 to 100 dB /
m. A second invention is the optical fiber according to the first invention, characterized in that in (5), the bending loss is 0.7 to 20 dB / m. A third invention is the optical fiber according to the first or second invention, characterized in that in (3), the effective core area is 140 μm ² or more. A fourth invention is the optical fiber according to any one of the first to third inventions, which further satisfies the following (6). (6) Wavelength of 1550 when the optical fiber is an optical fiber strand
The increase in tension winding loss at 10 nm is 10 dB
/ Km or less. A fifth aspect of the invention is the optical fiber according to the fourth aspect of the invention, wherein the increase in the tension winding loss of the sandpaper is 1 dB / km or less in (6). A sixth invention is the optical fiber according to the fifth invention, characterized in that in (6), the increase in sandpaper tension winding loss is 0.3 dB / km or less. 7th
The present invention is a method for manufacturing the optical fiber according to any one of the first to third inventions, wherein the structural parameters are selected so as to satisfy the numerical range described in (1) to (2) above, An optical fiber manufacturing method is characterized in that an optical fiber satisfying the characteristics described in (3) to (5) is manufactured.
An eighth invention is a method for producing the optical fiber according to any one of the fourth to sixth inventions, wherein the structural parameters are selected so as to satisfy the numerical range described in (1) and (2) above. ,
An optical fiber manufacturing method is characterized in that an optical fiber satisfying the characteristics described in (3) to (6) above is manufactured. A ninth invention is a dispersion compensating light for compensating for either one or both of the chromatic dispersion value and the dispersion slope of the optical fiber on the light signal emission side of the optical fiber according to any one of the first to sixth inventions. It is an optical transmission system characterized by arranging fibers. A tenth invention is the optical transmission system of the ninth invention, wherein an average chromatic dispersion value when the optical fiber and the dispersion compensating optical fiber are combined is −6 to
It is an optical transmission system characterized by +6 ps / nm / km.

[0007]

BEST MODE FOR CARRYING OUT THE INVENTION The wavelength band used for the optical fiber of the present invention is selected from the range of 1.53 to 1.61 μm. For example, depending on the amplification wavelength band of the erbium-doped optical fiber amplifier that constructs the communication system, 1.53 to 1.57μ
m, or 1.57 to 1.61 μm is appropriately selected.

Aeff is obtained from the following equation.

[0009]

[Equation 1]

It is desirable that Aeff be as large as possible in order to suppress the non-linear effect. According to the results of studies by the present inventors, when Aeff is less than 120 μm ² , suppression of the nonlinear effect is insufficient. Therefore, in the optical fiber of the present invention, Aeff is 120 μm ² or more, preferably 1
It is set to 40 μm ² or more. On the other hand, if Aeff becomes too large, the deterioration of transmission loss may become large for the following reasons. Therefore, Aeff is substantially 250 μm.
It is m ² or less. That is, when Aeff becomes large, transmission loss may be deteriorated due to, for example, microbend loss, which may cause inconvenience such as difficulty in inspection in the manufacturing process. Further, although the degree of deterioration varies depending on the cable structure, the deterioration of the transmission loss is likely to occur even in a normal use state where the cable is used or the extra length is stored. When the transmission loss increases in the use state as described above, it becomes necessary to increase the input power. As a result, the non-linear effect is more likely to occur as the input power increases, so that the non-linear suppression effect due to the increase of Aeff is reduced.

The bending loss is a value under the condition that the bending diameter (2R) is 20 mm at the wavelength used. Bending loss characteristics should be determined by cabling the optical fiber and the environment in which the optical fiber cable is used. For example, when embedding a tape type optical fiber in a tight structure, a range of 20 dB / m or less is preferably selected, but in the case of a so-called loose tube type optical cable, such a large force is applied. Since it is not performed, 100 dB / m or less is acceptable.

In order to reduce bending loss, it is preferable to shift the cutoff wavelength to the long wavelength side as much as possible.
Further, since the optical fiber of the present invention is a single mode optical fiber, it is necessary to have a cutoff wavelength that substantially guarantees single mode propagation in the used wavelength band. The normal cutoff wavelength is 2 for IEC and CCITT.
It is defined by the value according to the m method (hereinafter referred to as the 2m method). However, in an actual long usage state, single mode propagation is possible even if this value is on the longer wavelength side than the lower limit of the used wavelength band.

Therefore, in the optical fiber of the present invention, the cutoff wavelength defined by the 2m method is such that single mode propagation is possible depending on the used length and the used wavelength band of the optical fiber, and the bending loss can be reduced as much as possible. Set to the long wavelength side. Specifically, for example, if the cutoff wavelength in the 2 m method is 1.7 μm or less, 5
1.53 to 1.61 in a long state of about 000 m or more
It is possible to realize single mode propagation in the used wavelength band of μm.

In addition, in the optical fiber of the present invention, it is preferable that the increase in loss of tension winding of sandpaper when the optical fiber is an optical fiber strand is 10 dB / km or less. Sandpaper tension winding loss increase is a value measured by the following method. A sandpaper (SiC with an average particle size of 50 μm (for example, model number # 360) is wrapped around the body of a bobbin with a body diameter of 380 mm, and 100 gf around it.
Then, the transmission loss is measured in a state in which one layer of the optical fiber element wire having the structure described later is wound. Then, the optical fiber strand is unwound from the bobbin, and the transmission loss is measured with almost no tension applied (this state is called a tensionless bundle). Then, the difference between these transmission losses is obtained and is set as the increase in sandpaper tension winding loss (Δα).

FIG. 1 is a sectional view showing an example of an optical fiber element wire, which is made of a relatively soft plastic on an optical fiber bare wire 12 composed of a core 12a and a clad 12b provided on the outer periphery thereof. Primary coating layer 13 and secondary coating layer 1 made of a plastic harder than the primary coating layer 13
4 are provided. The bare optical fiber 12 is usually made of a silica glass material, and the primary coating layer 13 is usually made of an ultraviolet curable resin having a Young's modulus of 1 kg / mm ² or less. The secondary coating layer 14 usually has a Young's modulus of 50 k.
An ultraviolet curable resin of g / mm ² or more is used. The ultraviolet curable resin used for the primary coating layer 13 and the secondary coating layer 14 can be selected from urethane acrylate, polybutadiene acrylate, epoxy acrylate, silicon acrylate, polyester acrylate, and the like.

The outer diameter A of the ordinary bare optical fiber 12
Is 100 to 125 μm, and the outer diameter B of the primary coating layer 13 is
Is 130 to 250 μm, and the outer diameter C of the secondary coating layer 14 is 16
It is 0 to 400 μm. More specifically, for example, in a general 250 μm strand, the outer diameter A is 125 μm,
The outer diameter B is about 200 μm, and the outer diameter C is about 250 μm. Further, in a general 400 μm strand, the outer diameter A is 125 μm, the outer diameter B is around 240 μm, and the outer diameter C is 4 μm.
It is set to around 00 μm.

When the cable structure has a so-called tight structure, the range of 1 dB / km or less is preferably selected for the increase in tension winding loss of sandpaper, but in the case of a so-called loose tube type optical cable, the lateral pressure is Since it is small, about 10 dB / km or less is acceptable.
If the increase in the tension winding loss of sandpaper becomes large, the deterioration of the transmission loss becomes large when it is made into a cable, which is inconvenient. This sandpaper tension winding loss increase is due to Aef
Although it depends on the value of f, it also varies depending on the coating outer diameter of the optical fiber and the coating resin. Specifically, Aeff is 120
It is preferable that the sandpaper tension winding loss increase is 10 dB / km or less and the sandpaper tension increase is 10 μm ² or less. Furthermore, Aef
It is preferable that f is 120 μm ² or more and the increase in the tension paper winding loss is 1 dB / km or less. Further, it is preferable that the Aeff is in the range of 120 to 150 μm ² and the increase in sandpaper tension winding loss is 0.3 dB / km or less.

FIG. 2 is a graph showing an example of the relationship between Aeff and the increase in sandpaper tension winding loss. The measurement wavelength at this time is 1550 nm. The optical fiber strands in this example are 250 μm strands and 400 μm strands.
As can be seen from this graph, the increase in sandpaper tension winding loss increases as Aeff increases. And A
When eff is 150 μm ² or less, the increase in 250 μm strand sandpaper tension winding loss is 10 dB / km or less,
Increase in loss caused by tension winding of sandpaper of 400μm wire is 1d
B / km or less, which is sufficiently small.

In order to have such characteristics, it is necessary to have a refractive index distribution shape (refractive index profile) as shown in FIG. 3 or 5. The refractive index profile of the first example shown in FIG. 3 has a central core portion 1, an intermediate portion 2 having a lower refractive index than the central core portion 1 provided on the outer periphery thereof, and an intermediate portion 2 provided on the outer periphery thereof. The cladding 4 has a higher refractive index than the intermediate portion 2 and a lower refractive index than the central core portion 1.

In this optical fiber, for example, the central core portion 1 is a quartz glass or pure quartz glass to which germanium is added, which has a function of increasing the refractive index, and an intermediate portion 2
Is made of fluorine-added quartz glass or pure quartz glass having a function of lowering the refractive index, and the clad 4 is made of pure quartz glass, fluorine-containing glass, or chlorine-containing quartz glass having a function of increasing the refractive index. There is. This optical fiber can be manufactured by, for example, the VAD method.

When the radius of the central core portion 1 is r ₁ and the radius of the intermediate portion 2 (core radius) is r ₂ , 3.0 ≦ r
It is preferable that ₂ / r ₁ ≦ 5.0. When r ₂ / r ₁ is less than 3.0, the electromagnetic field of light easily reaches the cladding 4 beyond the intermediate portion 2, and therefore bending loss tends to increase. Further, when r ₂ / r ₁ exceeds 5.0, the effect of providing the intermediate portion 2 is reduced, and the confinement of the electromagnetic field of light to the core becomes too strong, so that the effect of Aeff expansion tends to decrease. is there. The cutoff wavelength is r ₁
It is possible to shift to the long wavelength side by enlarging the value of. As described above, the cutoff wavelength is set by the used length of the optical fiber and the used wavelength band, so it is impossible to unambiguously indicate the numerical range of r ₁ , but normally r
₁ is selected from the range of 5 to 20 μm. The outer diameter of the clad 4 is usually about 125 μm.

Further, the relative refractive index difference between the central core portion and the intermediate portion with reference to the refractive index of the clad is Δ ₁ , respectively.
When the delta _2, delta ₁ 0.30% or less, preferably 0.26% or less, the delta ₂ is a -0.05 -0.15% preferred. When Δ ₁ exceeds 0.30%, Ae
It becomes difficult to expand ff. Also, Δ ₂ is −0.
If it is larger than 05 (the absolute value of Δ ₂ is small), the bending loss is large, and if it is smaller than −0.15% (the absolute value of Δ ₂ is large), Aeff tends to be small.

In FIG. 4, Δ ₂ is -0.05%, r ₂ / r
₁ is fixed at 4.0, and the change in Aeff and bending loss at the working wavelength of 1.55 μm when the cutoff wavelength by the 2 m method is changed by 0.1 μm in the range of 1.3 to 1.7 μm. It is a graph. As the value of r ₁ is smaller and the cutoff wavelength shifts to a shorter wavelength, Ae
ff is small and bending loss tends to be large. On the other hand, the larger the value of r _{1 and} the longer the cutoff wavelength shifts, the larger the Aeff and the smaller the bending loss. The straight lines shown in the graph are grouped by the value of Δ ₁ . Δ ₁ is set at 0.02% intervals in the range of 0.18 to 0.30%. Then, in Aeff, it tends to decrease as Δ ₁ increases. The bending loss tends to decrease as Δ ₁ increases.

In this way, from the graph in which the values of Δ ₂ , r ₂ / r ₁ and the wavelength used are set and the value of r ₁ is changed,
An optical fiber having the refractive index profile shown in FIG. 3 and satisfying the conditions of the present invention is designed by selecting each structural parameter that satisfies the conditions of Aeff, bending loss, and cutoff wavelength in the present invention. can do. At the same time, it is preferable to design in consideration of the conditions for increasing the loss of tension winding of sandpaper. Therefore, it has the refractive index profile shown in FIG. 3 and has the above-mentioned r ₂ / r ₁ and Δ.
_Even when the preferable numerical value ranges of ₁ and Δ ₂ are satisfied, it is not always possible to obtain the ones satisfying the characteristics of Aeff, bending loss, cutoff wavelength, and increase in sandpaper tension winding loss as described above. The properties of the inventive optical fiber are realized by an appropriate combination of these structural parameters. Therefore, in the present invention, it is difficult to specify the invention from the numerical range of these structural parameters, and the invention is specified by the refractive index distribution shape and the characteristic value of the optical fiber. It goes without saying that such a thing could not be realized conventionally.

FIG. 5 shows a second example of the refractive index distribution shape of the optical fiber of the present invention. The difference between this refractive index distribution shape and the refractive index distribution shape of the first example shown in FIG. 3 is that the ring core portion 3 is provided between the intermediate portion 2 and the cladding 4.
Is provided. Such a refractive index distribution shape may be generally called a profile with a ring. The refractive index of the ring core portion 3 is higher than that of the intermediate portion 2 and the cladding 4, and lower than that of the central core portion 1.

In this optical fiber, for example, the central core portion 1 and the ring core portion 3 are made of germanium-doped quartz glass,
The intermediate portion 2 is made of fluorine-added quartz glass or pure quartz glass, and the clad 4 is made of pure quartz glass or chlorine-added quartz glass. This optical fiber can also be manufactured by the VAD method or the like, as in the first example.

In this example, when the radius of the ring core portion 3 (core radius) is r ₃ , 3.0 ≦ r ₂ / r ₁
It is preferable that ≦ 4.0 and 4.0 ≦ r ₃ / r ₁ ≦ 5.0. When r ₂ / r ₁ is less than 3.0, the electromagnetic field distribution of light easily reaches the ring core portion 3 beyond the intermediate portion 2, so that the bending loss tends to increase. Also, r ₂
If / r ₁ exceeds 4.0, the light confinement in the core becomes too strong, and the effect of providing the intermediate portion 2 decreases, and A
The effect of expanding eff tends to decrease. Also, r ₃ /
If r ₁ is less than 4.0, the effect of providing the ring core portion 3 tends to decrease, and the effect of increasing Aeff tends to decrease. Further, when r ₃ / r ₁ exceeds 5.0, bending loss tends to increase. Also, as described above, the cutoff wavelength can be shifted to the long wavelength side by increasing the value of r ₁ , and in this example, the normal r ₁
Is selected from the range of 5 to 20 μm. The outer diameter of the clad 4 is usually about 125 μm.

Further, in this example, when the relative refractive index difference of the ring core portion with reference to the refractive index of the clad is Δ ₃ , Δ ₁ is 0.35% or less and Δ ₂ is 0 to −0.
2% and Δ ₃ are preferably +0.05 to + 0.2%. When Δ ₁ exceeds 0.35%, it becomes difficult to increase Aeff. Further, when Δ ₂ is smaller than −0.2% (when the absolute value of Δ ₂ is large), Aeff tends to be small. If Δ ₃ is less than +0.05, the effect of providing the ring core portion 3 is reduced, and the effect of increasing Aeff tends to be reduced. If Δ ₃ exceeds + 0.2%, bending loss tends to increase.

However, similar to the first example, it has the refractive index profile shown in FIG. 5 and has the above-mentioned r ₂ /
Even if the preferable numerical value ranges of r ₁ , r ₃ / r ₁ , Δ ₁ , Δ ₂ , and Δ ₃ are satisfied, the above Aeff, bending loss, cutoff wavelength, and increase in sandpaper tension winding loss are not always satisfied. However, the characteristics of the optical fiber of the present invention are realized by an appropriate combination of these structural parameters.

In the present invention, in an optical fiber having a refractive index profile having a relatively simple structure as shown in FIGS. 3 and 5, Aeff can be expanded by appropriately adjusting the structural parameters. Further, it is possible to provide an optical fiber having a cutoff wavelength that reduces bending loss and enables single mode propagation in a used wavelength band selected from 1.53 to 1.61 μm at low cost. Furthermore, it is possible to reduce the increase in the tension paper winding loss. As a result, 1.53 to 1.61μ
In the used wavelength band selected from m, the nonlinear effect can be suppressed to prevent the deterioration of the transmission loss, and the transmission loss is less likely to be deteriorated even by the microbend applied to the optical fiber at the time of installation, and the single An optical fiber that can ensure mode propagation can be provided.

The optical fiber of the present invention can be combined with a so-called dispersion compensating optical fiber to construct an optical transmission system. The wavelength band used by this optical transmission system is the same as the wavelength band used by the optical fiber of the present invention described above. The dispersion compensating optical fiber has a chromatic dispersion value having a different sign and a larger absolute value than the chromatic dispersion value of the optical fibers forming most of the transmission line. Similarly, the dispersion slope may have a different sign and a larger absolute value than the dispersion slope of the optical fiber forming most of the transmission line.
The dispersion slope is a slope of a curve obtained by plotting the wavelength dispersion value with the wavelength on the horizontal axis and the wavelength dispersion value on the vertical axis, and is an index showing the wavelength dependence of the wavelength dispersion value. When the dispersion slope is large, when transmitting optical signals of a plurality of different wavelengths such as wavelength division multiplexing transmission, the transmission state varies between wavelengths, which causes transmission deterioration. Therefore, when it is applied to wavelength division multiplex transmission, it is preferable to use one that can simultaneously compensate for the chromatic dispersion value and the dispersion slope. Further, depending on the application, it is possible to use one that compensates only the dispersion slope.

Then, by arranging the optical fiber of the present invention on the incident side of the optical signal and arranging the dispersion compensating optical fiber on the emitting side of the optical signal, the optical fiber on the incident side is transmitted and accumulated. The chromatic dispersion value or the dispersion slope is canceled and compensated by the dispersion-compensating optical fiber having a relatively short length on the exit side. As a result, one or both of the average chromatic dispersion value and dispersion slope in the state where these optical fibers are combined (the state in which the optical fiber and the dispersion compensating optical fiber are combined) becomes small, and the transmission degradation due to chromatic dispersion is reduced. Can be suppressed. Further, the optical fiber of the present invention has a large Aeff and can suppress the transmission deterioration due to the non-linear effect, and as a result, an optical transmission system having very good transmission characteristics can be constructed.

The dispersion compensating optical fiber is not particularly limited as long as it can compensate either or both of the chromatic dispersion value and the dispersion slope of the optical fiber of the present invention. For example, those proposed in No. 147301 can be exemplified. This dispersion-compensating optical fiber has the same refractive index distribution shape as that shown in FIG. 3, and its structural parameters are adjusted to impart characteristics as a dispersion-compensating optical fiber. The structural parameter is appropriately adjusted by the chromatic dispersion value of the optical fiber to be compensated or the dispersion slope. This dispersion compensating optical fiber can also be manufactured by the VAD method or the like, like the optical fiber of the present invention. The constituent material of each layer may be the same as that of the optical fiber of the present invention.

Further, when the chromatic dispersion of the optical fibers forming most of the transmission line is compensated, the dispersion compensation for the dispersion slope required for completely compensating the dispersion slope of the optical fiber on the compensating side is performed. The ratio of the dispersion slope values of the optical fiber is called the dispersion slope compensation rate. In addition,
The dispersion slope per unit length can be calculated by multiplying the dispersion slope per unit length by the used length. In this optical transmission system, it is preferable to set the used length of the optical fiber and the characteristics and used length of the dispersion compensating optical fiber so that the compensation rate of the dispersion slope is 80% or more. As described above, the average chromatic dispersion value of the optical transmission system for compensating the chromatic dispersion in the dispersion compensating optical fiber is preferably as small as possible. By selecting and combining the used length, -6 to
A range of +6 ps / km / nm is obtained.

[0035]

EXAMPLES The present invention will be described in detail below with reference to examples. (Example 1) An optical fiber having the refractive index profile shown in FIG. 3 was manufactured by the VAD method. The central core was made of germanium-doped quartz glass, the middle part was made of fluorine-doped quartz glass, and the clad was made of pure quartz glass.
In this optical fiber, Δ ₁ and Δ ₂ are 0.2
It was 4% and -0.05%. Further, r ₁ and r ₂ are 6.6 μm and 26.5 μm, respectively, and the cladding outer diameter is 125.
was μm. Table 1 shows the characteristics of this optical fiber.
Each characteristic value is a measured value at 1.55 μm. Also,
The cutoff wavelength is a value measured by the 2m method.

[0036]

[Table 1]

(Example 2) Pure quartz glass was used as the central core,
Other than forming the clad from fluorine-doped quartz glass,
An optical fiber was manufactured in the same manner as in Example 1. Regarding the optical characteristics of this optical fiber, the transmission loss is lower than that of the optical fiber of Example 1 by about 0.01 dB / km, that is, 0.178 dB / k.
The optical fiber was the same as the optical fiber of Example 1 shown in Table 1 except that it was m.

Example 3 An optical fiber having the refractive index profile shown in FIG. 5 was manufactured by the VAD method. The central core portion and the ring core portion were made of germanium-doped quartz glass, the middle portion was made of fluorine-doped quartz glass, and the clad was made of pure quartz glass. In this optical fiber,
Δ ₁ , Δ ₂ , and Δ ₃ are 0.28% and −0.0, respectively.
It was 5% and + 0.13%. Further, r ₁ , r ₂ , r
₃ is 7.75 μm, 26.35 μm, 31
μm, and the outer diameter of the clad was about 125 μm. Table 2 shows the characteristics of this optical fiber. Each characteristic value is 1.
It is the measured value at 55 μm. Further, the cutoff wavelength is a value measured by the 2m method.

[0039]

[Table 2]

(Comparative Example 1) An optical fiber having a step type refractive index distribution shape in which a clad having a low refractive index was provided around a core having a high refractive index was manufactured. The core was made of germanium-doped quartz glass, and the clad was made of pure quartz glass. In this optical fiber, the relative refractive index difference of the core based on the refractive index of the cladding is 0.34%,
The core radius is 4.8 μm, and the clad outer diameter is approximately 125 μm.
Met. Ae of this optical fiber at 1.55 μm
The measured value of ff is about 88 μm ² , and the bending loss is 5 dB /
The cutoff wavelength in the m, 2m method was 1.37 μm.

From the above results, Examples 1 to 1 according to the present invention
In the optical fiber of No. 3, Aeff can be sufficiently expanded, the bending loss and the increase in sandpaper tension winding loss are small, and the optical fiber has a cutoff wavelength capable of single mode propagation at 1.55 μm. It could be confirmed. And it became clear that Aeff can be expanded more than the optical fiber of the comparative example 1, and a nonlinear effect can be suppressed.

(Example 4) An optical fiber of Example 2 and a dispersion compensating optical fiber for compensating the chromatic dispersion value and the dispersion slope of this optical fiber were produced, and the dispersion compensating light was emitted to the optical signal output side of the optical fiber. An optical transmission system was constructed by connecting fibers. At this time, the optical fiber of the second embodiment is 30.
9 km, the dispersion compensating optical fiber was 5.0 km, and the total number of transmission lines was 35.9 km. The dispersion compensating optical fiber has a refractive index profile similar to that shown in FIG.
Example 2 by adjusting its structural parameters
An optical fiber having a chromatic dispersion value and a dispersion slope with different signs from those of the optical fiber of was used. The constituent materials and the manufacturing method are the same as those in Example 2.
Same as. Table 3 also shows the structural parameters and characteristics of the dispersion compensating optical fiber, and the compensation factor of the dispersion slope.

[0043]

[Table 3]

The average chromatic dispersion value of the transmission line in the state where the optical fiber of Example 2 and the dispersion compensating optical fiber are combined is 1.5.
At 5 μm, it is almost zero, and the remaining dispersion slope is +0.147 ps / nm ² in the total length of the transmission line, which is +0.004 ps / km when converted per length.
/ Nm ² and a very small dispersion slope was obtained. Therefore, the optical fiber of Example 2 according to the present invention is used on the incident side of the optical signal, and this optical fiber is Aef.
Since f is large, there is almost no transmission deterioration due to non-linear effects, and since the chromatic dispersion value and the dispersion slope are compensated on the output side, there is no deterioration in transmission characteristics due to dispersion characteristics, and very good transmission characteristics are obtained. An optical transmission system having

[0045]

As described above, in the present invention,
In an optical fiber having a refractive index profile with a relatively simple structure, Aeff can be expanded by adjusting the structural parameters, and single mode propagation can be performed in the used wavelength band selected from 1.53 to 1.61 μm. An optical fiber having a cut-off wavelength can be provided at low cost. Also, the bending loss can be reduced to a value according to the application. As a result, 1.53 ~
In the used wavelength band selected from 1.61 μm, the nonlinear effect can be suppressed to prevent the deterioration of the transmission loss, and the transmission loss is less likely to be deteriorated by the microbend provided to the optical fiber at the time of installation, Further, it is possible to provide an optical fiber that can guarantee single mode propagation. Furthermore, by combining the optical fiber of the present invention and the dispersion compensating optical fiber, it is possible to suppress the transmission deterioration due to the non-linear effect and the dispersion characteristic, and to construct an optical transmission system having a good transmission characteristic.

[Brief description of drawings]

FIG. 1 is a cross-sectional view showing an example of an optical fiber strand.

FIG. 2 is a graph showing an example of a relationship between Aeff and increase in tension winding loss of sandpaper.

FIG. 3 shows a first refractive index distribution shape of the optical fiber of the present invention.
It is a graph showing an example of.

FIG. 4 is a cutoff wavelength by the 2m method and a used wavelength of 1.5 when the structural parameters shown in FIG. 3 are changed.
6 is a graph showing an example of the relationship between Aeff and bending loss at 5 μm.

FIG. 5 shows a second refractive index distribution shape of the optical fiber according to the present invention.
It is a graph showing an example of.

[Explanation of symbols]

1 ... Central core part, 2 ... Intermediate part, 3 ... Ring core part, 4 ...
Cladding r ₁ ... Radius of central core portion, r ₂ ... Radius of intermediate portion, r ₃ ... Radius of ring core portion, Δ ₁ ... Refractive index of central core portion, Δ ₂ ... Refractive index of intermediate portion, Δ ₃ ... Ring core portion Index of refraction.

   ─────────────────────────────────────────────────── ─── Continued front page    (72) Inventor Akira Wada             Fuji Co., Ltd. 1440 Rokuzaki, Sakura City, Chiba Prefecture             Kura Sakura Office (72) Inventor Ryozo Yamauchi             Fuji Co., Ltd. 1440 Rokuzaki, Sakura City, Chiba Prefecture             Kura Sakura Office (72) Inventor Takaaki Suzuki             Fuji Co., Ltd. 1440 Rokuzaki, Sakura City, Chiba Prefecture             Kura Sakura Office (72) Inventor Shoichiro Matsuo             Fuji Co., Ltd. 1440 Rokuzaki, Sakura City, Chiba Prefecture             Kura Sakura Office (72) Inventor Manabu Saito             Fuji Co., Ltd. 1440 Rokuzaki, Sakura City, Chiba Prefecture             Kura Sakura Office F-term (reference) 2H050 AC09 AC14 AC71 AC73 AC75                       AC76 AD01

Claims (10)

[Claims] 1. A central core part, an intermediate part provided on the outer periphery of the central core part and having a lower refractive index than the central core part, and a higher refractive index than the intermediate part provided around the intermediate part, A cladding having a refractive index lower than that of the central core portion is formed, and a radius of the central core portion is r ₁ , and a radius of the intermediate portion is r _2.
When the relative refractive index difference between the central core portion and the intermediate portion with reference to the refractive index of the clad is Δ ₁ and Δ ₂ , respectively, the following (1) to (5) are satisfied. And optical fiber. (1) 3.0 ≦ r ₂ / r ₁ ≦ 5.0, and (2) Δ ₁
Is 0.30% or less, Δ ₂ is -0.05 to -0.15%
And (3) in an operating wavelength band selected from 1.53 to 1.61 μm, the effective core area is 120 μm ² or more, and (4) in the operating wavelength band, substantially single mode propagation is possible. Has a cutoff wavelength (5)
Bending diameter (2R) is 20 mm in the above wavelength band
Bending loss measured under the condition of 0.7 to 100 dB /
m. 2. In (5) above, the bending loss is 0.7.
The optical fiber according to claim 1, wherein the optical fiber has a value of -20 dB / m. 3. The optical fiber according to claim 1, wherein in (3), the effective core area is 140 μm ² or more. 4. The optical fiber according to claim 1, further satisfying the following (6). (6) When the optical fiber is an optical fiber, the increase in sandpaper tension winding loss at a wavelength of 1550 nm is 10 dB / km or less. 5. The optical fiber according to claim 4, wherein in (6), the increase in sandpaper tension winding loss is 1 dB / km or less. 6. The optical fiber according to claim 5, wherein in (6), the increase in sandpaper tension winding loss is 0.3 dB / km or less. 7. A method for manufacturing the optical fiber according to claim 1, wherein the structural parameters are selected so as to satisfy the numerical range described in (1) and (2) above. Then, an optical fiber satisfying the characteristics described in (3) to (5) above is manufactured. 8. A method for manufacturing the optical fiber according to claim 4, wherein the structural parameters are selected so as to satisfy the numerical range described in (1) and (2) above. Then, an optical fiber that satisfies the characteristics described in (3) to (6) above is manufactured. 9. A dispersion compensator for compensating either or both of a chromatic dispersion value and a dispersion slope of the optical fiber on the optical signal emission side of the optical fiber according to claim 1. Description: An optical transmission system in which an optical fiber is arranged. 10. The optical transmission system according to claim 9, wherein the average chromatic dispersion value when the optical fiber and the dispersion compensating optical fiber are combined is −6 to +6 ps / nm / km. Optical transmission system.