JPH1073738A - Wavelength multiplex communication link for optical transfer - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a wavelength multiplex communication link for optical transfer capable of wavelength multiplexing communication at super-high speed and with large capacity in a wavelength band of 1550nm by using the existing single mode diver network with 1300nm zero dispersion. SOLUTION: A dispersion compensating fiber DCF having a negative dispersion value ion a 1550nm wavelength band is connected to a single mode fiber SMF of an existing single mode fiber network having 300nm zero dispersion with a length for compensating the dispersion slope of the single mode fiber SMF to zero. A dispersion flat fiber for making the dispersion value zero is connected to the terminal of connection link between the single mode fiber SMF and the dispersion compensating fiber DCF with a length for making a remaining dispersion value zero and the dispersion slope and the dispersion value of the signal mode fiber SMF are adjusted to zero together at the terminal of the dispersion flay fiber DFF.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a wavelength-division multiplex communication link for optical transmission, particularly suitable for ultra-high-speed, large-capacity optical multiplex transmission.

[0002]

2. Description of the Related Art As a fiber network of an optical transmission system, a 1300 nm band zero dispersion single mode fiber network is known. This fiber network has a wavelength of 1300nm
By transmitting this optical signal, a reception signal having almost zero dispersion can be obtained on the reception side.

Recently, using the existing 1300-nm zero-dispersion single-mode fiber network, optical transmission in a wavelength band near the wavelength of 1550 nm, which is an excitation band of an erbium-doped fiber amplifier EDFA provided in an optical transmission line. Attempts have been made to perform wavelength division multiplexing transmission (WDM) in a wide wavelength band around 1550 nm with the aim of further high-speed and large-capacity transmission.

The single mode fiber of the existing 1300 nm zero-dispersion single mode fiber network has a positive dispersion value and a positive dispersion slope characteristic in which the amount of dispersion increases as the wavelength increases. Therefore, when wavelength multiplexing transmission is performed in the 1550 nm wavelength band using the existing 1300 nm band zero-dispersion single mode fiber network, the amount of dispersion increases as the transmission distance of the single mode fiber becomes longer. However, there is a problem that it becomes difficult to separate these signals, and it becomes impossible to perform highly reliable wavelength division multiplexing transmission.
For this reason, it has been generally attempted to perform wavelength multiplex transmission using a communication link (transmission link) in which a single mode fiber is connected to a dispersion compensating fiber having a large negative dispersion value and a negative dispersion slope characteristic. .

[0005]

In the case of performing wavelength division multiplexing transmission using an existing 1300 nm band zero dispersion single mode fiber network, communication is performed in a 1.55 μm wavelength band which is an excitation band of the erbium-doped fiber amplifier. But, for example,
When wavelength multiplex transmission is performed in the wavelength band from 1530 nm to 1560 nm,
A dispersion difference of up to 30 nm × dispersion slope × optical fiber length occurs between the wavelength multiplexed signal lights, and the transmission capacity is limited by the dispersion, which hinders high-speed large-capacity wavelength multiplex transmission.

In order to suppress such chromatic dispersion, when a dispersion compensating fiber is connected to a single mode fiber of an existing 1300 nm band zero dispersion single mode fiber network,
When the dispersion of the center signal wavelength was adjusted to be zero over the entire length, the dispersion value and the dispersion slope value of the dispersion compensating fiber corresponded to the dispersion value and the dispersion slope value of the single-mode fiber on the other end of the connection on a one-to-one basis. It will be just one value. In reality, the dispersion value and dispersion slope of each single-mode fiber used in the existing 1300-nm band zero-dispersion single-mode fiber network vary individually, and in order to compensate for the dispersion of these dispersed single-mode fibers. In this case, it is necessary to produce and connect a dispersion compensating fiber suitable for each single mode fiber, and in practice, it is very difficult to realize this.

In order to completely compensate the dispersion and the dispersion slope of the single mode fiber at the same time, the dispersion of the single mode fiber is D _SMF , the dispersion slope of the single mode fiber is S _SMF , and the dispersion value of the dispersion compensation fiber is D _SMF .
_{When DCF} and dispersion slope are S _DCF , D _SMF / S
It is necessary to satisfy the relationship of _SMF = D _DCF / S _DCF . In general, it is extremely difficult to fabricate a dispersion compensating fiber to satisfy this condition.
It is extremely difficult to completely and simultaneously compensate for the dispersion and dispersion slope of each single-mode fiber used in the nm-band zero-dispersion single-mode fiber network.
This is an obstacle to performing ultra-high-speed and large-capacity WDM transmission using a wavelength band around 1550 nm.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and has as its object to reduce the dispersion and dispersion slope of a single mode fiber used in an existing 1300 nm band zero dispersion single mode fiber network to a wavelength of 1550 nm. It is an object of the present invention to provide a wavelength-division multiplexing communication link for optical transmission that can be easily and completely compensated for in a band and that can perform ultra-high-speed and large-capacity optical multiplex transmission in a 1550 nm wavelength band.

[0009]

As described above, it is difficult to produce a fiber that completely compensates for both the dispersion and the dispersion slope of a single mode fiber at the same time, but it is difficult to make only the dispersion value or the dispersion slope value zero. It can be adjusted very easily by adjusting the length of the fiber for compensating the dispersion value or the dispersion slope. The present inventor pays attention to this point, and attempts to compensate the dispersion value and dispersion slope of a single mode fiber by a two-stage configuration.
That is, first, as a first step, the first-stage dispersion compensating fiber is connected to the single-mode fiber, and the length thereof is adjusted to adjust either the dispersion value or the dispersion slope to zero. Next, a second-stage compensating fiber is connected, and its length is adjusted, so that the dispersion whose dispersion value is adjusted to zero by the first-stage dispersion compensating fiber has a dispersion opposite to the remaining dispersion slope. The dispersion slope is compensated to zero by the dispersion shift fiber having the slope characteristic.
In a link in which the dispersion slope is adjusted to zero by the first-stage dispersion compensating fiber, the dispersion value is adjusted to zero by a dispersion flat fiber having a dispersion slope of zero and a constant dispersion value. Thus, an object of the present invention is to compensate for both the dispersion value and the dispersion slope of a single mode fiber.

The present invention employs the following means to achieve the above object. That is, the first invention relates to a single mode fiber of a 1300 nm band zero dispersion single mode fiber network having zero dispersion in an optical transmission wavelength of 1300 nm band.
In an optical transmission system in which a dispersion compensating fiber having a negative dispersion value in the 50 nm band is connected to compensate for the dispersion in the optical transmission wavelength of 1550 nm, the dispersion slope of the single mode fiber at the wavelength of 1550 nm is represented by S _SMF and the dispersion value. _Is D _SMF , Article length is L
_SMF, S _DCF dispersion slope at a wavelength 1550nm band of the dispersion compensating fiber, a dispersion value D _DCF, when the fiber length was L _DCF, substantially S _SMF × L _SMF / | a = L _DCF relationship | S _DCF A dispersion compensating fiber having a length L _{DCF that} satisfies the condition is connected to the single-mode fiber, and a dispersion flat fiber having a dispersion slope in the 1550 nm wavelength band of almost zero and a dispersion value of D _DFF is substantially D _SMF × L _SMF + D _DCF. × L _DCF +
This is a means for solving the problem with a configuration in which the _strip lengths L _DFF satisfying the relationship of D _DFF × L _DFF = 0 are connected.

The second invention provides a 1300-nm band zero-dispersion single-mode fiber network having a zero-dispersion in the 1300-nm optical transmission wavelength band by connecting a dispersion compensating fiber to a single-mode fiber to reduce the dispersion in the 1550-nm optical transmission wavelength band. In a compensating optical transmission system, the wavelength of the single mode fiber is 1550.
The dispersion slope in the nm band is S _SMF , the dispersion value is D _SMF , the stripe length is L _SMF , the dispersion slope in the 1550 nm wavelength band of the dispersion compensating fiber is S _DCF , the dispersion value is D _DCF , and the stripe length is L _DCF . Then, a dispersion compensating fiber having a length L _DCF substantially satisfying the relationship of D _SMF × L _SMF / | D _DCF | = L _DCF is connected to the single mode fiber, and the dispersion slope in the 1550 nm band is S _DSF , The dispersion-shifted fiber whose dispersion value is almost zero is almost S _SMF × L _SMF + S _DCF × L _DCF +
This is a means for solving the problem with a configuration in which the _strip lengths L _DSF satisfying the relationship of S _DSF × L _DSF = 0 are connected.

In the first aspect of the invention, the dispersion slope is compensated to zero by connecting the dispersion compensating fiber having the length L _{DCF to} the single mode fiber. Next, the dispersion slope is zero (including almost zero) in the link where the single mode fiber and the dispersion compensating fiber are connected, and the dispersion value is D.
Connect the dispersion-flattened fibers to _DFF, that fiber length of the dispersion-flattened fiber is adjusted to L _DFF, residual dispersion value is compensated to zero (including almost zero), the dispersion compensating fiber and dispersion flattened By adjusting the fiber length, both the dispersion value and the dispersion slope of the single mode fiber are compensated, and the above-mentioned conventional problem is solved.

In the second invention, the dispersion compensating fiber having the length L _DCF is connected to the single mode fiber, and the dispersion value is compensated to zero (including almost zero) by adjusting the length.
Next, a dispersion-shifted fiber having a dispersion value of zero (including almost zero) is connected to the link where the single-mode fiber and the dispersion compensation fiber are connected, and the remaining dispersion slope is reduced to zero (substantially zero) by adjusting the length of the fiber. Including). In this way, the dispersion compensating fiber and the dispersion shift fiber are connected to the single mode fiber, and the length of each is adjusted, so that the dispersion value and the dispersion slope of the single mode fiber are both compensated to zero (including almost zero). As a result, the conventional problem is solved.

[0014]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, embodiments of the present invention will be described. FIG. 1 shows an embodiment of the first invention. In the communication link of this embodiment, a dispersion compensation fiber DCF having a negative dispersion value at a wavelength of 1550 nm is connected to a single mode fiber SMF of an existing 1300 nm zero-dispersion single mode fiber network, and thereafter, a dispersion compensation fiber at a wavelength of 1550 nm is connected. The link is formed by connecting a dispersion flat fiber DFF having a dispersion slope of zero (including almost zero).

The wavelength of the single mode fiber SMF
The dispersion slope at 1550 nm band is S _SMF , the dispersion value is D _SMF ,
The line length is L _SMF and the wavelength of the dispersion compensating fiber DCF is 1550.
When the dispersion slope in the nm band is S _DCF , the dispersion value is D _DCF , and the line length is L _DCF , the line length L _DCF of the dispersion compensating fiber _DCF is adjusted so as to substantially satisfy the following equation (1).

S _SMF × L _SMF / | S _DCF | = L _DCF (1)

By adjusting the length L _DCF , the dispersion slope of the single mode fiber SMF is adjusted to zero (including almost zero), and the dispersion value remains.

Next, the wavelength of the dispersion flat fiber DFF
Assuming that the dispersion slope in the 1550 nm band is zero (including almost zero) and the dispersion value is D _DFF , the length L _DFF of the dispersion flat fiber DFF is adjusted so as to substantially satisfy the following equation (2).

D _SMF × L _SMF + D _DCF × L _DCF + D _DFF × L _DFF = 0 (2)

By connecting the dispersion flat fiber DFF to the connection link between the single mode fiber SMF and the dispersion compensating fiber DCF by adjusting the length L _DFF so as to substantially satisfy the relationship of the equation (2), the residual dispersion value is obtained. Is compensated to zero (including almost zero), and the dispersion flat fiber D
From the end of the FF, a signal in which both the dispersion value and the dispersion slope are compensated to zero is extracted.

In the first invention, the terminal side of the single mode fiber SMF and the dispersion compensating fiber DC
The F and the dispersion flat fiber DFF are each wound on a separate reel, and the respective reels are placed coaxially on top of each other or are placed side by side on the same plane (for example, a floor). The single mode fiber SMF, the dispersion compensating fiber DCF and the dispersion flat fiber DFF are connected by fusion.

FIG. 2 shows an embodiment of the second invention. In this embodiment, the single mode fiber SM of the existing 1300 nm band zero dispersion single mode fiber network is used.
F, a dispersion compensating fiber DCF having a positive or negative dispersion value in the 1550 nm wavelength band is connected to the dispersion compensating fiber D.
A dispersion shift fiber DSF having a dispersion value of zero (including almost zero) in a wavelength band of 1550 nm is connected to the CF.

The dispersion slope of the SMF of the single mode fiber in the 1550 nm wavelength band is S _SMF , the dispersion value is D _SMF , the line length is L _SMF, and the dispersion slope of the dispersion compensation fiber in the 1550 nm wavelength band is S _DCF , When the dispersion value is D _DCF and the length is L _DCF , the length L _DCF of the dispersion compensating fiber _DCF is adjusted so as to substantially satisfy the following equation (3).

D _SMF × L _SMF / | D _DCF | = L _DCF (3)

By adjusting the length L _DCF of the dispersion compensating fiber DCF so as to satisfy the relationship of the equation (3),
The dispersion value of the single mode fiber SMF is compensated to zero (including almost zero), and the dispersion slope remains.

Next, the wavelength 15 of the dispersion-shifted fiber DSF
The dispersion slope at 50nm band S _DSF, when zero dispersion value (including almost zero), the fiber length was L _DSF, fiber length of dispersion shifted fiber DSF to satisfy substantially the following equation (4) L _DSF
Is adjusted, and this dispersion shift fiber DSF is connected to the end of the dispersion compensation fiber DCF.

S _SMF × L _SMF + S _DCF × L _DCF + S _DSF × L _DSF = 0 (4)

By adjusting the length L _DCF of the dispersion-shifted fiber DSF so as to substantially satisfy the equation (4),
Single mode fiber SMF and dispersion compensation fiber DC
The dispersion slope remaining on the link of F is compensated to zero (including almost zero). As a result, the dispersion-shifted fiber DS
At the end of F, a signal in which both the dispersion value and the dispersion slope of the single mode fiber SMF are compensated to zero (including almost zero) is extracted.

It should be noted that also in the second invention, the end of the single mode fiber SMF and the dispersion compensating fiber DMF
The CF and the dispersion-shifted fiber DSF are wound on separate reels, and the respective reels are coaxially stacked or placed side by side on the same plane (for example, a floor). The single mode fiber SMF, the dispersion compensating fiber DCF, and the dispersion shift fiber DSF are connected by fusion.

[0030]

【Example】

(Embodiment 1) This embodiment corresponds to the first invention. As shown in FIG. 1, a dispersion compensating fiber DCF and a dispersion flat fiber DFF are added to a single mode fiber SMF of an existing 1300 nm band zero dispersion single mode fiber network. Is connected. Single mode fiber S at 1550nm wavelength
The dispersion value D _{SMF of the} MF is 17 ps / nm · km, and the wavelength is 1550 nm.
The dispersion slope D _SMF in the band is 0.058 ps / nm ² · km and the strip length L _SMF is 42 km.

The wavelength 1550 of the dispersion compensating fiber DCF is
The dispersion value _DCF in nm is −102 ps / nm · km, and the wavelength is 1550 nm.
The dispersion slope S _DCF in the band is -0.406 ps / nm ² · km and the strip length L _DCF is 6 km. The dispersion value D _DFF of the dispersion flat fiber DFF at a wavelength of 1550 nm is −6 ps / nm.
Km, the dispersion slope in the 1550 nm band is zero, and the length L _DFF is 17 km.

In the above equation (1), S _SMF = 0.058 ps / nm ² ·
km, L _SMF = 42 km and S _DCF = −0.406 ps / nm ² · km, L _DCF = 6.0 km, and the dispersion compensating fiber D
The CF _strip length L _DCF satisfies the above equation (1).

When wavelength multiplexing communication is performed at a wavelength of 1530 nm to 1560 nm in a wavelength band of 1550 nm, when the dispersion value of the reference wavelength is D ₀ and the dispersion slope in the wavelength band is S ₀ , the wavelength is shifted by ΔF from the reference wavelength F. The dispersion value D ′ of the wavelength F ′ is D ′ = D ₀ +
Since (ΔF = F′−F) represented by S ₀ (F′−F), the dispersion value of the single mode fiber SMF at the wavelength of 1530 nm is 15.84 ps / nm · km, and the dispersion value of the single mode fiber SMF at the wavelength of 1560 nm Is 17.58 ps / nm · km and the single mode fiber S
The dispersion value due to the propagation of the MF strip length of 42 km is 1530 wavelength.
665.28 ps / nm at nm and 714.00 ps / nm at 1550 nm.
nm, and 738.36 ps / nm at a wavelength of 1560 nm.

The dispersion value of the dispersion compensating fiber DCF at a wavelength of 1530 nm is −93.88 ps / nm · km, and at a wavelength of 1560 nm, −.
Since it is 106.06 ps / nm · km, the dispersion value after propagation at a line length of 6 km is −563.28 ps / nm at a wavelength of 1530 nm,
At 50 nm, it becomes -612.00 ps / nm, and at wavelength 1560 nm, -636.
36 ps / nm.

Therefore, the dispersion value at the end of propagation through the single-mode fiber SMF of 42 km and the dispersion compensation fiber DCF of 6 km is constant at 102.15 nm to 1560 nm.
It becomes 00 ps / nm, the dispersion value is flattened to a constant value (102.00 ps / nm), and the dispersion slope is adjusted to zero.

The dispersion flat fiber DFF connected to the connection link between the single mode fiber SMF and the dispersion compensation fiber DCF has a dispersion slope of zero at a wavelength of 1550 nm and a dispersion value of -6 ps / nm · km at a wavelength of 1550 nm. Therefore, the dispersion value of each wavelength (1530 nm to 1560 nm) propagating through the strip length of 17 km is -102.00 ps / nm. As a result, the dispersion value of 102.00 ps / nm of each wavelength in the 1550 nm band remaining at the terminal end of the dispersion compensating fiber DCF is completely compensated for by the dispersion value −102.00 ps / nm generated during a total length of 17 km of the dispersion flat fiber DFF. At the end of the dispersion flat fiber DFF, a signal in which both the dispersion slope and the dispersion value become zero in the 1550 nm band is extracted. Table 1 shows the calculation results of the dispersion values when these fibers propagate.

[0037]

[Table 1]

It should be _noted that D _SMF , L _SMF , D
The values of _DCF , L _DCF , D _DFF , and L _DFF are set to 1530 nm, 15
Substituting each value for each 50nm and 1560nm and calculating
At any wavelength, the calculation results on the left side are all zero, and it can be confirmed that the above expression (2) is satisfied.

(Embodiment 2) This embodiment also corresponds to the first invention, and has the same wavelength of 1550 nm and 17 ps as in the first embodiment.
/ Nm · km dispersion D _SMF and 0.058
The line length L _SMF with the dispersion slope S _SMF of ps / nm ² · km is
A dispersion compensation fiber DCF having a dispersion value D _DCF of −102 ps / nm · km at a wavelength of 1550 nm and a dispersion slope S _DCF of −0.290 ps / nm ² · km at a wavelength of 1550 nm is applied to a single mode fiber SMF of 42 km. fiber SMF dispersion slope are connected by 8.4 km of fiber length L _DCF to be zero, furthermore, to its end, with the dispersion slope S _DFF is zero at a wavelength 1550nm band, the dispersion value D _DFF at a wavelength of 1550nm 10ps /
A dispersion flat fiber DFF of nm · km is connected. Also in this embodiment, S _SMF = 0.
058ps / nm ² · km, L _SMF = 42km, S _DCF = −0.290ps
By substituting a value of / nm ² · km, L _DCF = 8.4 km
Thus, the expression (1) is sufficiently satisfied. Also,
(2) the wavelength 1530nm as a value of D _SMF on the left side of Formula 15.8
4 ps / nm • km, 17ps / nm • km, wavelength 1560 at 1550nm
For nm, substitute a value of 17.58 ps / nm · km, respectively.
L _SMF = 42 km, _DCF value of -96.2 at a wavelength of 1530 nm
ps / nm · km, -12.0 ps / nm · km at 1550 nm, wavelength 1
At 560 nm, substitute the value of -104.9 ps / nm · km,
Further, L _DCF = 8.4 km, D _DFF = 10 ps / nm · km, L _DFF
By substituting = 14.28 km, the calculated value on the left side becomes zero at each wavelength, and the expression (2) is sufficiently satisfied. Table 2 shows the calculation results of dispersion at the time of propagation of each fiber in the second embodiment.

[0040]

[Table 2]

Also in this embodiment, the dispersion and the dispersion slope are 1550 nm at the end of the dispersion flat fiber DFF.
It is confirmed that a signal which becomes zero in the wavelength band is extracted.

(Embodiment 3) This embodiment corresponds to the second invention, and has a dispersion value D _SMF = 17 ps / nm · km at a wavelength of 1550 nm of an existing 1300 nm band zero dispersion single mode fiber network.
Dispersion slope S _SMF at wavelength 1550 nm band = 0.058 ps / nm ²
・ Distance D _DCF = −102 ps / nm · k at a wavelength of 1550 nm in a single mode fiber SMF having a length of L _SMF = 42 km with km.
m, dispersion slope S _DCF in the wavelength 1550 nm band = -0.406 ps
/ Dispersion compensation fiber DCF which nm with ² · miles is connected with a fiber length L _DCF = 7km to the zero dispersion value, dispersion slope D _DSF = 0 in addition wavelength 1550nm band to the end.
08ps / nm ² · km, dispersion value D _DSF at 1550nm wavelength = 0ps /
nm · km dispersion-shifted fiber DSF has a length of L _DSF = 5.07
They are connected to be 5 km.

Based on the wavelength of 1550 nm, D
_SMF = 17ps / nm · km, L _SMF = 42km, _DCF = -102ps
By substituting / nm · km, the calculated value on the left side of Expression (3) is L _DCF = 7.0 km, which satisfies the condition of Expression (3). Note that the dispersion value of the single mode fiber SMF at a wavelength of 1530 nm is D _SMF = 15.84 ps / nm · km,
The dispersion at a wavelength of 1530 nm of the dispersion compensating fiber DCF is −93.8.
8 ps / nm · km, and when this is substituted into the equation (3), the length L _DCF of the dispersion compensating fiber is 7.086 km. Also,
The dispersion value D _SMF of the single mode fiber SMF at a wavelength of 1560 nm is 17.58 ps / nm · km,
The dispersion value _DCF of the dispersion compensating fiber in nm is -106.06
ps / nm · km, and substituting these values into equation (3) gives the dispersion compensating fiber DCF at a wavelength of 1560 nm.
Length L _DCF = 6.962 km, wavelengths of 1530 nm and 1560
Also in nm, the dispersion compensating fiber D obtained by equation (3)
The CF strip length L _DCF is about 7 km, and the wavelength is 1530 nm to 1560 nm.
At each of the wavelengths, the above expression (3) is satisfied.

In addition, S _SMF = 0.058 ps / nm ^{2 in} equation (4)
Km, L _SMF = 42 km, S _DCF = -0.406 ps / nm ² km,
L _DCF = 7 km, S _DSF = 0.08 ps / nm ² · km, L _DSF = 5.
By substituting 075 km, the calculated value becomes zero, and the expression (4) is satisfied.

The dispersion values at the time of propagation of each fiber in the third embodiment are as shown in Table 3. At the end of the dispersion shift fiber DSF, both the dispersion value and the dispersion slope become zero, and the single mode fiber SMF
It is demonstrated that the dispersion value and the dispersion slope are both compensated.

[0046]

[Table 3]

Embodiment 4 This embodiment also corresponds to the second invention. The single mode fiber SMF of the existing 1300 nm band zero dispersion single mode fiber network has a wavelength of 1550 nm.
And the dispersion value D _SMF = 17 ps / nm · km, the dispersion slope S _SMF at the wavelength of 1550 nm = 0.058 ps / nm ² · km, and the line length L _SMF = 42
km, and this single mode fiber SMF
The length L is set such that the dispersion value at 1550 nm is D _DCF = −102 ps / nm · km, and the dispersion compensating fiber DCF having the dispersion slope S _DCF = −0.290 ps / nm ² · km is at the end and the dispersion value is zero. _DCF
= 7 km, and the dispersion slope S _DSF at the 1550 nm wavelength band is connected to the end of the dispersion compensating fiber DCF =
−0.1 ps / nm ² · km, dispersion value D _DSF at a wavelength of 1550 nm =
0ps / nm ・ km dispersion shift fiber _DSF
= 4.06 km to obtain a connected transmission link.

In the fourth embodiment, the following equation (3) is used.
D _SMF = 17 ps / nm · km, L _SMF = 42 km, D _DCF = -102
By substituting ps / nm · km, the length L _DCF of the dispersion compensating fiber DCF at which the dispersion value at the wavelength of 1550 nm becomes zero is 7 km, which satisfies the equation (3). At a wavelength of 1530 nm, D _SMF = 15.84 ps / nm · k
By substituting m, D _DCF = -96.2 ps / nm · km,
The line length L _DCF obtained by the equation (3) is 6.916 km, and at a wavelength of 1560 nm, D _SMF = 17.58 ps / nm · km,
D _DCF = −104.9 ps / nm · km.
By substituting into the equation, the line length L _DCF = 7.039 km, and at any of the wavelengths of 1530 nm and 1560 nm,
The length L _DCF obtained by the equation (3) is 15
7km which is almost the same as the strip length at 50nm, wavelength 1550nm
The strip length L _DCF required for each wavelength in the band almost satisfies the expression (3).

Also, S _SMF = 0.058 ps / nm ² · km, L
_SMF = 42 km, S _DCF = -0.290 ps / nm ² · km, L _DCF =
By substituting 7 km, S _DSF = -0.1 ps / nm ² · km, and L _DSF = 4.06 km, the calculation result on the left side of equation (4) becomes zero, satisfying equation (4). The calculated values of dispersion at the time of fiber propagation in this embodiment are as shown in Table 4. At the end of the dispersion-shifted fiber DSF, the dispersion slope and the dispersion value are both zero, and the dispersion value and single-mode fiber SMF It can be confirmed that both the dispersion slopes are compensated for zero.

[0050]

[Table 4]

The optical transmission line including only the single mode fiber SMF has a dispersion of 17 ps / nm · km at a wavelength of 1550 nm,
Since it has a dispersion slope of 0.058 p / nm ² · km in the wavelength 1550 nm band, it has a dispersion value of 15.84 ps / nm · km at a wavelength of 1530 nm and a dispersion value of 17.58 ps / nm · km at a wavelength of 1560 nm. Have. Therefore, the difference in dispersion between the two wavelengths of 1530 nm and 1560 nm is a large value of 1.74 ps / nm · km, and the wavelength has a large dispersion value. Therefore, the signal capacity is greatly limited by this dispersion. Will be.

The dispersion value at a wavelength of 1550 nm is, for example, −85 ps / nm · km in the single mode fiber SMF having the above characteristics.
And the dispersion slope at the wavelength of 1550 nm is 0.11 ps /
With a dispersion compensation fiber DCF of nm ² · km connected, the total dispersion value is 0 ps / nm · km and the dispersion slope is 0.08 ps / nm ²
In a km optical transmission link, a difference in dispersion value of 2.4 ps / nm · km occurs between signals at wavelengths of 1530 nm and 1560 nm per 1 km of line length, and transmission capacity is similarly limited.

On the other hand, in each of the embodiments of the present invention, a dispersion compensating fiber is connected to a single mode fiber to compensate one of the dispersion slope and the dispersion value to zero (including substantially zero). Since the dispersion-shifted fiber is connected and the dispersion value or dispersion slope remaining at zero while the dispersion slope or dispersion value compensated to zero is maintained at zero, the dispersion value and dispersion slope at the end of the dispersion-shifted fiber are compensated. Is zero at each wavelength in the 1550 nm wavelength band, and therefore, the difference in dispersion between the wavelengths is zero, which enables ultra-high-speed and large-capacity WDM optical communication without being limited by the transmission capacity due to dispersion. Become.

To increase the signal light noise ratio (SNR), for example, the signal power P _S may be increased. However, if the signal power P _S is increased, the self-phase modulation SPM, which is a nonlinear effect of the optical fiber, is increased. (Self-Phase Modulat
The problem is that the spectral broadening due to ion) causes waveform degradation associated with fiber dispersion. The dispersion limit when the self-phase modulation becomes a problem is given by the following equation (5).

B ³ L ³ D ≦ 1.5 × 10 ¹⁰ × Z ² exp (−αZ) / {1-exp (−αZ)} (5)

In this equation, B is the optical transmission speed, L is the length of the optical fiber (transmission line length), D is the dispersion value of the fiber, Z is the relay interval, and α is the transmission line loss.

When the calculation is performed using the equation (5), the wavelength division multiplexing communication capacity is limited at a medium distance when the chromatic dispersion is 3 ps / nm · km. As shown in the above, since both the chromatic dispersion and the dispersion slope are compensated to zero (including almost zero), D ≒ 0 in the above equation (5), and regardless of the transmission path length L, the equation (5) And the effect of avoiding the influence of the dispersion limit due to self-phase modulation can be obtained.

The present invention is not limited to the above-described embodiments and examples, but may employ various embodiments. For example, in the embodiments and examples of the first invention, the dispersion compensating fiber DCF is connected to the single mode fiber SMF, and the dispersion flat fiber DFF is connected to this connection link. May be reversed.

In the embodiment of the second invention and the embodiment thereof, the dispersion compensating fiber DCF is connected to the single mode fiber SMF, and the dispersion shift fiber DSF is further connected to this connection link. The connection order of the dispersion shift fiber DSF and the dispersion shift fiber DSF may be reversed.

[0060]

According to a first aspect of the present invention, a dispersion compensating fiber is connected to a single mode fiber of an existing 1300 nm band zero dispersion single mode fiber network with a strip length such that the dispersion slope becomes zero (including almost zero). Further, the dispersion slope of the connection link between the single mode fiber and the dispersion compensating fiber is zero (including substantially zero), and the dispersion remaining at the connection end of the dispersion compensating fiber is zero (including substantially zero). The dispersion flat fiber is connected with the strip length to compensate the dispersion to zero (including almost zero), and the dispersion slope and dispersion value of the single mode fiber are totally compensated to zero (including almost zero). , The transmission capacity is not limited, thereby enabling ultra-high-speed and large-capacity wavelength-division multiplexed optical communication.

As described above, the dispersion slope and the dispersion value of the single mode fiber are compensated by adjusting the lengths of the dispersion compensating fiber and the dispersion flat fiber as described above. Even if the dispersion slope and dispersion value of the single-mode fiber used in the existing 1300-nm zero-dispersion single-mode fiber network vary individually, the dispersion slope and dispersion of each single-mode fiber with these dispersions will vary. Both values can be easily compensated for to zero, and a practically useful communication link that can solve the conventional problems at once can be provided.

Also in the second invention, the dispersion compensating fiber is added to the existing single-mode fiber of the 1300-band nm zero-dispersion single-mode fiber network by setting the dispersion value of the single-mode fiber to zero (including substantially zero). A dispersion-shifted fiber having zero dispersion (including substantially zero dispersion) around 1550 nm in wavelength is connected to the connection link, and the dispersion slope remaining at the end of the dispersion compensating fiber is compensated to zero (including substantially zero). At the end of a communication link (transmission link) formed by connecting a single mode fiber, a dispersion compensating fiber, and a dispersion shift fiber, both the dispersion slope and the dispersion value become zero (including almost zero). As a result, the wavelength division multiplexing communication can be performed at a very high speed and with a large capacity without being limited by the dispersion as in the first aspect.

Moreover, since the compensation of the dispersion value and the dispersion slope can be achieved by adjusting the lengths of the dispersion compensating fiber and the dispersion shift fiber, the compensation adjustment of the dispersion slope and the dispersion value becomes extremely easy, and Even if the dispersion slopes and dispersion values of individual single-mode fibers used in the existing 1300-nm zero-dispersion single-mode fiber network vary as in the invention, the dispersion slopes of these individual single-mode fibers can be easily adjusted. Both the dispersion values can be adjusted to zero (including almost zero), and a practically usable communication link suitable for ultra-high-speed and large-capacity wavelength-division multiplexing communication can be provided.

Furthermore, in both the first and second aspects of the present invention, both the dispersion slope and the dispersion value can be compensated to zero at the end of the communication link, so that the influence of the dispersion limit due to self-phase modulation can be avoided. This makes it possible to perform ultra-high-speed, large-capacity, long-distance wavelength multiplex communication with high reliability.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of an embodiment of the first invention.

FIG. 2 is an explanatory diagram of an embodiment of the second invention.

[Explanation of symbols]

 SMF single mode fiber DCF dispersion compensating fiber DFF dispersion flat fiber DSF shift fiber

Continued on the front page (51) Int.Cl. ⁶ Identification number Reference number in the agency FI Technical display location H04J 14/02 H04B 10/14 10/135 10/13 10/12

Claims (2)

[Claims] 1. An optical transmission wavelength of 1300 having zero dispersion in a 1300 nm band.
In a light transmission system for compensating dispersion in an optical transmission wavelength of 1550 nm by connecting a dispersion compensation fiber having a negative dispersion value in a wavelength of 1550 nm to a single mode fiber of a zero-dispersion single mode fiber network in an nm band, the single mode fiber In the 1550 nm wavelength band, the dispersion slope is S _SMF , the dispersion value is D _SMF , the strip length is L _SMF , and the dispersion compensating fiber has a wavelength of 15 nm.
When the dispersion slope in the 50 nm band is S _DCF , the dispersion value is D _DCF , and the strip length is L _DCF , almost S _SMF × L _SMF / | S _DCF
A dispersion compensating fiber having a length L _DCF satisfying the relationship of | = L _DCF is connected to the single mode fiber,
The dispersion slope at the wavelength of 1550 nm is almost zero, and the dispersion value is D.
_The dispersion flat fiber to be _DFF is almost D _SMF × L _SMF
A wavelength-division multiplexing communication link for optical transmission, characterized in that the link is connected with a _strip length L _DFF that satisfies the relationship of + D _DCF × L _DCF + D _DFF × L _DFF = 0. 2. The 1300 having zero dispersion in an optical transmission wavelength of 1300 nm band.
Optical transmission wavelength 1550 by connecting dispersion compensating fiber to single mode fiber of nm-band zero dispersion single mode fiber network.
In an optical transmission system for compensating dispersion in the nm band, the dispersion slope of the single mode fiber in the 1550 nm band is S _SMF , the dispersion value is D _SMF , the line length is L _SMF , and the wavelength of the dispersion compensating fiber is 1550 nm. S _DCF dispersion slope, when a dispersion value D _DCF, the fiber length was L _DCF, substantially _{D SMF × L SMF / | D} DCF | = L dispersion compensating fiber fiber length L _DCF satisfying the relation of _DCF is the A dispersion mode fiber connected to a single mode fiber and having a dispersion slope in the 1550 nm band of S _DSF and a dispersion value of almost zero is substantially S _SMF × L _SMF + S _DCF × L _DCF + S _DSF × L
1. A wavelength division multiplexing communication link for optical transmission, characterized in that the link is connected with a line length L _DSF satisfying the relationship _DSF = 0.