JP2001264569A - Dispersion compensating optical fiber and optical transmission system - Google Patents

Abstract

(57) Abstract: Provided is a dispersion-compensating optical fiber that can compensate for chromatic dispersion and dispersion slope of a dispersion-shifted optical fiber, has a small bending loss, and can suppress the occurrence of nonlinear optical phenomena. A dispersion compensating optical fiber according to the present invention has a chromatic dispersion D _DCF of -4 to -4 at a wavelength of 1.55 μm.
0 ps / nm / km and the dispersion slope S _DCF is -0.02-
−0.50 ps / nm ² / km, and the ratio (S _DCF / D _DCF ) between the chromatic dispersion D _DCF and the dispersion slope S _DCF is 0.004 to 0.
A 020 / nm, an effective area is 12～30Myuemu ^2, the transmission loss is at 0.5 dB / miles or less, the polarization mode dispersion is not more than 0.5ps ^/ km ^1/2, the central core region the ratio is the refractive index difference delta ⁺ is 0.8 to 1.7%, the relative refractive index difference delta of the depressed regions ^- a is -1.0 0.5%, the central core region and the depressed regions, respectively Outer diameter ratio (2a
/ 2b) is 0.25 to 0.60.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dispersion compensating optical fiber for compensating chromatic dispersion and dispersion slope of a dispersion-shifted optical fiber, and an optical transmission system using the dispersion compensating optical fiber as a part of an optical transmission line. Things.

[0002]

2. Description of the Related Art Wavelength division multiplexing (WDM)
n Multiplexing) In an optical transmission system that performs optical transmission, in order to further increase the speed and capacity of optical communication, the absolute value of the accumulated chromatic dispersion of the optical transmission line should be minimized in a wide signal light wavelength band. is important. In general, it is difficult to use an optical transmission line using only one type of optical fiber. Therefore, by constructing an optical transmission line by connecting a plurality of types of optical fibers, the accumulated chromatic dispersion of the optical transmission line over a wide band can be reduced. The absolute value is reduced.

For example, US Pat. No. 5,361,319 discloses a standard single-mode optical fiber (SMF: Single Mod Optical Fiber) having a zero-dispersion wavelength around 1.3 μm.
e Fiber) and a dispersion compensating optical fiber (DCF: Dispersion) for compensating chromatic dispersion and dispersion slope at a wavelength of 1.55 μm of this standard single mode optical fiber.
There is disclosed a technique for connecting an optical fiber with a compensating fiber to reduce the absolute value of the accumulated chromatic dispersion in a wavelength band of 1.55 μm of the optical transmission line formed by connecting the optical fibers.

Also, US Pat. No. 5,838,867, Reference 1 “M. Onishi, et al.,“ Third-order disper
sion compensating fibers for non-zero dispersion s
hifted fiber links ", Elec. Lett., Vol.32, No.5, p
p.2344-2345 (1996) ", Reference 2" Kashiwada, et al., "Study of Dispersion Slope Compensating Optical Fiber", 1999 IEICE General Conference, C-3-31 (1999) ", Reference 3" Akasaka " , And others, "DS
Development of dispersion slope compensating fiber for F ", 1997 IEICE Electronics Society Conference, C-3-75
(1997) ", Reference 4" Sugizaki et al., "Development of Dispersion Slope Compensating Fiber (DSCF)", 1998 IEICE Electronics Society Conference, C-3-13 (1998), and Reference 5 "WA Reed, "Fiber Design for Disper
sion Manage Soliton Systems: The Challenge ", ROSC
Symposium, pp.12-14 (1999) ”each has a wavelength of 1.
Non-Zero Dispersion Shift Optical Fiber (NZDSF) having a small positive chromatic dispersion at 55 μm
Fiber) and a wavelength of 1.55 of the dispersion-shifted optical fiber.
A dispersion compensating optical fiber for compensating chromatic dispersion and dispersion slope in μm is connected to reduce the absolute value of the accumulated chromatic dispersion in the 1.55 μm wavelength band of the optical transmission line formed by connecting them. Techniques are disclosed.

[0005] Here, a standard at a wavelength of 1.55 µm is used.
Chromatic dispersion of a single-mode optical fiber (SMF)
_SMFAnd the dispersion slope is S_SMFIt expresses. 1.55μ wavelength
m of a non-zero dispersion shifted optical fiber (NZDSF)
Let chromatic dispersion be D_DSFAnd the dispersion slope is S_DSFIt expresses. Ma
In addition, a dispersion compensating optical fiber (D
The wavelength dispersion of CF) is D_DCFAnd the dispersion slope is S_DCFWhen
Represent. At this time, optical transmission over a wide band including a wavelength of 1.55 μm is performed.
To reduce the absolute value of the accumulated chromatic dispersion of the transmission line, a standard
Chromatic dispersion and dispersion
A dispersion compensating optical fiber for compensating the rope (hereinafter referred to as “SM
It is referred to as "dispersion compensating optical fiber for F". ), The chromatic dispersion D
_DCFAnd dispersion slope S_DCFAnd the ratio (S_DCF/ D_DCF) Is Shin
Chromatic dispersion D of glue mode optical fiber_SMFAnd dispersion slope
S_SMFAnd the ratio (S_SMF/ D_SMF) Is required to be approximately equal to
You. In addition, chromatic dispersion and dispersion of dispersion shifted optical fiber
A dispersion compensating optical fiber for compensating the slope (hereinafter referred to as “D
It is referred to as a dispersion-compensating optical fiber for SF. ), Chromatic dispersion
D_DCFAnd dispersion slope S_DCFAnd the ratio (S_DCF/ D_DCF) Is the minute
Chromatic dispersion D of dispersion-shifted optical fiber_DSFAnd dispersion slope S
_DSFAnd the ratio (S_DSF/ D _DSF) Is required to be approximately equal to
You.

[0006]

Compared with a standard single mode optical fiber, a dispersion shifted optical fiber has a smaller chromatic dispersion, a larger dispersion slope, and a ratio (S _DSF / D _{DSF) at} a wavelength of 1.55 μm. ) Is large. Therefore, as compared with the dispersion compensating optical fiber for SMF, the dispersion compensating optical fiber for DSF has a small absolute value of chromatic dispersion, a large absolute value of dispersion slope, and a ratio (S _DCF / D _{DCF) at} a wavelength of 1.55 μm. ) Must be large.

However, such a DSF dispersion compensating optical fiber is liable to leak the fundamental mode light even with a slight bending.
Since the bending loss of the fundamental mode light is large, the transmission loss increases when the cable is laid and laid or wound around a coil to form a dispersion compensation module. On the other hand, a dispersion compensating optical fiber for DSF can reduce bending loss by reducing the absolute value of chromatic dispersion, but in this case, four-wave mixing, which is a kind of nonlinear optical phenomenon, is likely to occur. As a result, the waveform of the signal light propagating through the optical transmission line is deteriorated.

Therefore, an optical transmission system that performs signal communication on an optical transmission line constituted by connecting such a dispersion-shifted optical fiber and a dispersion-compensating optical fiber for DSF to perform optical communication is an optical transmission line. Because transmission loss is large or nonlinear optical phenomenon is likely to occur in the optical transmission line,
The length of the relay section cannot be lengthened, and the speed and capacity of optical communication cannot be further increased.

The present invention has been made to solve the above problems, and can compensate for the chromatic dispersion and dispersion slope of a dispersion-shifted optical fiber, has a small bending loss, and suppresses the occurrence of nonlinear optical phenomena. It is an object of the present invention to provide a dispersion compensating optical fiber capable of performing the above. It is another object of the present invention to provide an optical transmission system in which the dispersion compensating optical fiber is used as a part of an optical transmission line, whereby the speed and capacity of optical communication can be further increased.

[0010]

SUMMARY OF THE INVENTION A dispersion compensating light according to the present invention.
The fiber has a wavelength band of 1.50 μm to 1.60 μm.
At a given wavelength, the chromatic dispersion D_DCFIs -4 ps / nm /
km to -40 ps / nm / km, and the dispersion slope S
_DCFIs -0.02 ps / nm^Two/Km~-0.50ps/
nm^Two/ Km and the chromatic dispersion D_DCFAnd dispersion slope S
_DCFAnd the ratio (S_DCF/ D_DCF) Is 0.004 / nm to 0.0
20 / nm and the effective area is 12 μm ^Two~ 30 μm^Two
And the transmission loss is 0.5 dB / km or less,
Modal dispersion is 0.5ps / km^1/2Specially
Sign. Dispersion compensating optical fiber having such features
At the wavelength of 1.55 μm of the dispersion-shifted optical fiber
Can compensate for chromatic dispersion and dispersion slope
In addition, the numerical range of chromatic dispersion is
The four-wave mixing is generated by the sufficient effective cross section.
It is possible to suppress the deterioration of the waveform of the propagating signal light.
it can. Also, this dispersion compensating optical fiber has a chromatic dispersion.
Since the numerical value range is as described above, the bending loss
The increase can be suppressed.

Further, the dispersion compensating optical fiber according to the present invention comprises a central core region including the optical axis center and having a refractive index n ₁ , a depressed region surrounding the central core region and having a refractive index n ₂ , At least a cladding region surrounding the presto region and having a refractive index of n ₄ , wherein the magnitude relation of the respective refractive indices is n ₂ <n ₄ <n ₁ , and the relative refractive index difference of the central core region with respect to the cladding region is 0. 8% ~
1.7%, the relative refractive index difference of the depressed region with respect to the cladding region is -1.0% to -0.5%, and the outer diameter 2a of the central core region and the outer diameter 2b of the depressed region are different. The ratio (2a / 2b) is 0.25 to 0.60. It is also preferable that a ring core region having a refractive index of n ₃ is further provided between the depressed region and the cladding region, and the magnitude relationship between the refractive indices is n ₂ <n ₄ <n ₃ <n _1. . Such a refractive index profile is suitable for realizing a dispersion compensating optical fiber having the above characteristics.

The dispersion compensating optical fiber according to the present invention is based on silica glass and has
O ₂ is added, and F is added to the depressed region. This case is suitable for realizing a dispersion compensating optical fiber having the above-mentioned refractive index profile. The wavelength of the dispersion compensating optical fiber is 1.55 μm.
m can reduce transmission loss.

Further, the dispersion compensating optical fiber according to the present invention is based on silica glass and has P, P in the cladding region.
It is characterized in that one of Cl and F is added. In this case, when the dispersion compensating optical fiber is manufactured by drawing the optical fiber preform, the viscosity of the cladding region can be reduced, and the heating temperature of the optical fiber preform can be lowered. Therefore, G in the central core region
Since the formation of defects such as eO can be suppressed, and the interdiffusion between Ge in the central core region and F in the depressed region can be reduced, an increase in transmission loss can be prevented.

An optical transmission system according to the present invention includes an optical transmission line in which the above-mentioned dispersion compensating optical fiber and another optical fiber are connected, and transmits an optical signal at a predetermined wavelength within a wavelength band of 1.50 μm to 1.60 μm. The average dispersion slope of the entire transmission path is −0.02 ps / nm ² / km to +0.05 ps / n
m ² / km, and the average transmission loss of the entire optical transmission line is 0.25 dB / km or less. In this optical transmission system, the average transmission loss of the optical transmission line is small and the absolute value of the average chromatic dispersion is small in a wide wavelength band, so that the repeater section can be lengthened and the speed and capacity of optical communication can be further increased. Can be planned.

Further, in the optical transmission system according to the present invention, the average chromatic dispersion of the entire optical transmission line is -5 ps / nm / km at all wavelengths within the wavelength band of 1.53 μm to 1.62 μm.
~ + 5 ps / nm / km (more preferably, -1 ps / n
m / km to +1 ps / nm / km). In this case, since the absolute value of the average chromatic dispersion of the entire optical transmission line is small in the optical amplification wavelength band of 1530 nm to 1620 nm of the Er-doped optical fiber amplifier, high-quality optical transmission is possible.

Further, the optical transmission system according to the present invention is characterized by including an optical amplifier for optically amplifying signal light propagating through the optical transmission line. In this case, the optical transmission system has a lower loss. The optical amplifier is preferably an Er-doped optical fiber amplifier that amplifies signal light by supplying excitation light to an Er-doped optical fiber in which an Er element is added to an optical waveguide region. Can efficiently amplify signal light. The optical amplifier is preferably a Raman amplifier that optically amplifies the signal light by supplying Raman amplification pump light to the optical transmission line. In this case, it is preferable to optically amplify the signal light in a wide wavelength band. Can be.

Further, the optical transmission system according to the present invention is characterized in that a dispersion compensating optical fiber is fusion-spliced with the other optical fiber and laid in a relay section. In this case, the transmission distance can be extended by the dispersion compensating optical fiber, so that the optical fiber length required for the optical transmission system is shorter than when the dispersion compensating optical fiber is in the form of a module. Short and low overall transmission loss.

Further, in the optical transmission system according to the present invention, the chromatic dispersion of the other optical fiber is +2 ps / nm / k at a predetermined wavelength within a wavelength band of 1.50 μm to 1.60 μm.
m to +10 ps / nm / km (more preferably, +6 ps / nm / km)
/ Nm / km to +10 ps / nm / km). By connecting the dispersion compensating optical fiber and the other optical fiber, the absolute value of the average chromatic dispersion of the entire optical transmission line is reduced. Further, by setting the chromatic dispersion of the other optical fiber to +6 ps / nm / km or more, occurrence of four-wave mixing can be suppressed.

[0019]

Embodiments of the present invention will be described below in detail with reference to the accompanying drawings. In the description of the drawings, the same elements will be denoted by the same reference symbols, without redundant description.

FIG. 1 is a schematic configuration diagram of an optical transmission system 1 according to the present embodiment. In this optical transmission system 1, an optical transmission path 30 is laid between a station (transmitting station or relay station) 10 and a station (receiving station or relay station) 20. The optical transmission line 30 is obtained by fusion-splicing a dispersion-shifted optical fiber 31 and a dispersion-compensating optical fiber 32. In the optical transmission system 1, the multi-wavelength signal light in the 1.55 μm band transmitted from the station 10 propagates through the dispersion-shifted optical fiber 31 and the dispersion-compensating optical fiber 32 to reach the station 20. Or optically amplified at the station 20 and transmitted further downstream.

The dispersion-shifted optical fiber 31 has a wavelength of 1.5
This is a silica-based optical fiber having a small positive chromatic dispersion at 5 μm. This dispersion-shifted optical fiber 31 has a wavelength dispersion D _{DSF of +1.55} μm, for example.
It is about 2 ps / nm / km to +10 ps / nm / km, and the dispersion slope S _DSF is +0.04 ps / nm ² / km
＋+ 0.10 ps / nm ² / km and the transmission loss is about 0.20 dB / km. It should be noted that the dispersion-shifted optical fiber 31 is required to suppress the occurrence of four-wave mixing.
The chromatic dispersion D _DSF is +6 ps / nm / km to +10 ps /
It is preferably about nm / km.

The dispersion compensating optical fiber 32 according to the present embodiment
Is a silica-based optical fiber that compensates for chromatic dispersion and dispersion slope of the dispersion-shifted optical fiber 31 at a wavelength of 1.55 μm. This dispersion compensating optical fiber 32
Is that the chromatic dispersion D _DCF is −4 at a wavelength of 1.55 μm.
ps / nm / km to -40 ps / nm / km, and the dispersion slope S _DCF is -0.02 ps / nm ² / km to-
0.50 ps / nm ² / km, and the ratio (S _DCF / D _DCF ) of the chromatic dispersion D _DCF to the dispersion slope S _DCF is 0.004 /
nm to 0.020 / nm. Also, the dispersion-compensating optical fiber 32, the wavelength band 1.55 .mu.m, the effective cross-sectional area is 12 [mu] m ² 30 .mu.m ^2, transmission loss 0.5d
B / km or less, and the polarization mode dispersion is 0.5 ps / k
m ^1/2 or less.

The dispersion compensating optical fiber 32 having such a characteristic is the same as the wavelength of the dispersion-shifting optical fiber 31 having a wavelength of 1.55 μm.
Not only can the chromatic dispersion and dispersion slope at m be compensated, but the numerical range of chromatic dispersion is as described above and the effective area is sufficient, thereby suppressing the generation of four-wave mixing and propagating signal light. Can be suppressed from deteriorating. The dispersion compensating optical fiber 32
By setting the numerical range of chromatic dispersion as described above, it is possible to suppress an increase in bending loss.

The dispersion compensating optical fiber 32 may be wound around a bobbin to be modularized and provided in the station 20.
It is preferable to be laid between the station 10 and the station 20 as a part of the optical transmission line 30. In the latter case, the required lengths of the dispersion-shifted optical fiber 31 and the dispersion-compensating optical fiber 32 are shorter than in the former case, and the overall transmission loss is smaller.

The optical transmission line 30, in which the dispersion-shifted optical fiber 31 and the dispersion-compensating optical fiber 32 are fusion-spliced, has a total average dispersion slope of-at a wavelength of 1.55 μm.
0.02ps / nm ² /km~+0.05ps/nm ² /
km and the total average transmission loss is 0.25 dB / km
It is as follows. In the optical transmission system 1 that performs optical communication by propagating signal light through the optical transmission line 30, the average transmission loss of the optical transmission line 30 is small and the absolute value of the average chromatic dispersion is small in a wide wavelength band. Therefore, this optical transmission system 1
The length of the relay section can be increased, and the speed and capacity of optical communication can be further increased.

FIG. 2 shows a dispersion compensation optical fiber according to this embodiment.
FIG. 7 is a diagram for explaining a preferred example of a refractive index profile of the iva 32.
is there. As shown in this figure, the dispersion compensating optical fiber 32
Is a central core region including the optical axis center (refractive index n₁, Outer diameter 2
a) and a depressed region surrounding this central core region
(Refractive index n_Two, Outer diameter 2b) and this depressed area
Surrounding cladding region (refractive index n_Four).
The magnitude relation of each refractive index is n _Two<N_Four<N₁ It is. Also,
The dispersion compensating optical fiber 32 has a center with respect to the cladding region.
Core region relative refractive index difference Δ⁺Is between 0.8% and 1.7%
The relative refractive index of the depressed region to the cladding region
Difference Δ^-Is -1.0% to -0.5%, and the central core region
Ratio Ra between the outer diameter 2a of the outer ring and the outer diameter 2b of the depressed region
(= 2a / 2b) is 0.25 to 0.60. This
Dispersion compensation by having such a refractive index profile
The optical fiber 32 has a wavelength component of 1.55 μm.
D_DCF, Dispersion slope S_DCF, Ratio (S_DCF/ D_DCF), Effective
Cross section, transmission loss and polarization mode dispersion are each
Is in the numerical range of

The dispersion compensating optical fiber 32 having such a refractive index profile is preferably made of silica glass, in which GeO ₂ is added to the central core region and F element is added to the depressed region. By doing so, the refractive index profile shown in FIG. 2 can be realized, and the wavelength 1..
Transmission loss at 55 μm can be reduced.

Preferably, any one of P, Cl and F is added to the cladding region. By doing so, the viscosity of the cladding region can be reduced when the dispersion compensating optical fiber 32 is manufactured by drawing the optical fiber preform manufactured by the MCVD method, the VAD method, the OVD method, or the like. In addition, the heating temperature of the optical fiber preform can be reduced. Therefore, the formation of defects such as GeO in the central core region can be suppressed, and the interdiffusion between Ge in the central core region and F in the depressed region can be reduced, thereby preventing an increase in transmission loss. be able to.

FIG. 3 shows a dispersion compensating optical fiber according to this embodiment.
Another preferred example of the refractive index profile of the iva 32 will be described.
FIG. As shown in FIG.
2 is a central core region including the optical axis center (refractive index n₁, Outer diameter
2a) and the depressed area surrounding this central core region
Range (refractive index n_Two, Outer diameter 2b) and this depressed area
Ring core region (index n_Three, Outer diameter 2c)
And the cladding region surrounding this ring core region (refractive
Rate n_Four). The relationship between the refractive indices is n_Two<N
_Four<N_Three<N₁ It is. Such a refractive index profile
The dispersion compensating optical fiber 32 having the
Relative refractive index difference Δ of the central core region⁺0.8% to 1.7%
And the specificity of the depressed region with respect to the cladding region
Fold difference Δ ^-Is -1.0% to -0.5%, and the central core
Ratio R between outer diameter 2a of region and outer diameter 2b of depressed region
a (= 2a / 2b) is 0.25 to 0.60. this
With such a refractive index profile, dispersion compensation
The attenuating optical fiber 32 has a wavelength of 1.55 μm.
Dispersion D_DCF, Dispersion slope S_DCF, Ratio (S_DCF/ D_DCF), Real
Effective area, transmission loss and polarization mode dispersion are each higher
It is in the numerical range described above.

FIG. 4 is a view for explaining another preferred example of the refractive index profile of the dispersion compensating optical fiber 32 according to the present embodiment. Compared to the refractive index profile shown in FIG. 3, the refractive index profile shown in this figure differs in that a low refractive index dip is formed at the center of the central core region. Dispersion-compensating optical fiber 32 having such a refractive index profile also at the wavelength 1.55 .mu.m, the wavelength dispersion D _DCF, dispersion slope S _{D CF,} the ratio (S _DCF / D _DCF), the effective cross-sectional area, transmission loss and polarization Each mode dispersion is in the above numerical range. The dispersion compensating optical fiber 32
When the optical fiber preform is manufactured by drawing an optical fiber preform manufactured by the MCVD method or the OVD method, the refractive index profile has such a dip, but does not adversely affect the transmission characteristics.

FIG. 5 is a graph showing the relationship between the relative refractive index difference Δ ⁻ in the depressed region and the transmission loss at a wavelength of 1.55 μm in the dispersion compensating optical fiber 32 having the refractive index profile shown in FIG. Here, the relative refractive index difference Δ ⁺ of the central core region was set to 1.5%. As can be seen from this graph, as the absolute value of the relative refractive index difference Δ ^{− in} the depressed region increases, the transmission loss at a wavelength of 1.55 μm increases.
In order to reduce the transmission loss at a wavelength of 1.55 μm, it is preferable that the absolute value of the relative refractive index difference Δ ^{− in} the depressed region is 1.0% or less.

Next, specific examples of the dispersion compensating optical fiber 32 and the optical transmission system 1 according to this embodiment will be described with reference to FIGS. FIG.
5 is a table summarizing examples of the dispersion compensating optical fiber 32 and the optical transmission line 30 according to the present embodiment. FIG. 7 is a table summarizing an embodiment of the non-zero dispersion shifted optical fiber 31. FIG. 7 shows various characteristics (wavelength dispersion Disp, dispersion slope Slope, and transmission loss loss) at a wavelength of 1.55 μm for each of NZDSF1 to NZDSF3 as a specific example of the dispersion-shifted optical fiber 31.

FIG. 6 shows various characteristics of the DCF1 to DCF18 at a wavelength of 1.55 μm as a specific embodiment of the dispersion compensating optical fiber 32. FIG. 6 shows various characteristics of the optical transmission line 30 connected to the NZDSF1 to NZDSF3 at a wavelength of 1.55 μm for each of the DCF1 to DCF18. In order from the top column of FIG.
1~DCF18 For each, the relative refractive index difference delta ⁺ of the center core region, the relative index of the depressed region difference delta ^-, the ratio of the outer diameter 2a, the outer diameters central core region and depressed regions of the central core region Ra , Chromatic dispersion Disp, dispersion slope Slope, ratio of chromatic dispersion to dispersion slope (Slope / Disp.
p), cutoff wavelength λ _c , effective area A _eff , mode field diameter MFD, transmission loss loss, polarization mode dispersion PM
D and the bending loss at a bending diameter of 20 mmφ are shown.

FIG. 6 further shows DCF1 to DCF1.
8 respectively, the average dispersion slope (Total Slope1) and the average transmission loss (Total Slope1) of the optical transmission line connected to the NZDSF1, and the average dispersion slope (Total Slope) of the optical transmission line connected to the NZDSF2
2) and average transmission loss (Total loss2), and NZ
Average dispersion slope (Total Slope3) and average transmission loss (Total loss) of the optical transmission line connected to DSF3.
3) is shown. These optical transmission lines have a wavelength of 1.55.
The length ratio of each of the dispersion compensating optical fiber and the dispersion shift optical fiber is adjusted so that the entire chromatic dispersion in μm becomes zero, and both optical fibers are fusion-spliced.

As can be seen from these figures, NZDSF
1 to NZDSF3 each have a chromatic dispersion Disp of 4.2 ps / nm / km to 8.0 p at a wavelength of 1.55 μm.
s / nm / km and the dispersion slope is 0.04
7ps / nm ² /km~0.060ps/nm a ² / miles, the transmission loss loss is 0.21 dB / miles. DC
Each of F1 to DCF18 has a relative refractive index difference Δ ⁺ of the central core region of 0.8% to 1.7 at a wavelength of 1.55 μm.
%, And the relative refractive index difference Δ ^{− of the} depressed region is −1.
0% to -0.5%, the outer diameter 2a of the central core region is 3.63 μm to 5.70 μm, and the ratio Ra of the outer diameter of each of the central core region and the depressed region is 0.30.
~ 0.57.

Each of the DCFs 1 to 18 has a wavelength dispersion Disp of -4.
8 ps / nm / km to −38.1 ps / nm / km, and the dispersion slope Slope is −0.051 ps / nm ² / k
m to −0.370 ps / nm ² / km, and the ratio of chromatic dispersion to dispersion slope (Slope / Disp) is 0.004 to 0.
Is 012, the cut-off wavelength λ _c is 760nm~87
0 nm, and the effective area A _eff is 13 μm ^{2 to} 29 μm
² , and the mode field diameter MFD is 4.1 μm or more.
6.2 μm and transmission loss loss is 0.25 dB / km
０．４0.46 dB / km, the polarization mode dispersion PMD is 0.02 ps / km ^1/2 ０．２0.25 ps / km ^1/2 , and the bending loss at a bending diameter of 20 mmφ is 1 dB / m〜74.
dB / m.

Each of DCF1 to DCF18 and NZDS
The optical transmission line formed by connecting the F1 and the F1 has a wavelength of 1.5
At 5 μm, the average dispersion slope (Total Slope1) is −
0.007 ps / nm / km to +0.021 ps / nm
/ Km and the average transmission loss (Total loss1) is 0.22
dB / km to 0.24 dB / km. DCF1-D
The optical transmission line configured by connecting each of the CFs 18 and the NZDSF2 has an average dispersion slope (Total Slope2) of -0.001 ps / nm / k at a wavelength of 1.55 μm.
m to +0.025 ps / nm / km, and the average transmission loss (Total loss2) is 0.22 dB / km to 0.25 dB
/ Km. The optical transmission line formed by connecting each of the DCFs 1 to 18 and the NZDSF 3 has an average dispersion slope (total slope) at a wavelength of 1.55 μm.
pe3) is -0.017 ps / nm / km to +0.020 p
s / nm / km, and the average transmission loss (Total loss 3) is 0.22 dB / km to 0.25 dB / km.

FIG. 8 is a graph showing the chromatic dispersion characteristics of the NZDSF1, DCF5 and optical transmission line (NZDSF1 + DCF5). FIG. 9 shows NZDSF1, DC
It is a graph which shows the wavelength dispersion characteristic of F6 and optical transmission line (NZDSF1 + DCF6). FIG.
DSF1, DCF7 and optical transmission line (NZDSF1 + D
CF7) is a graph showing the wavelength dispersion characteristics of each of them.
FIG. 11 shows NZDSF2, DCF5 and optical transmission line (N
(ZDSF2 + DCF5) is a graph showing the wavelength dispersion characteristics of each. FIG. 12 is a graph showing the chromatic dispersion characteristics of the NZDSF2, the DCF6, and the optical transmission line (NZDSF2 + DCF6). FIG. 13 shows the NZDSF
2, DCF7 and optical transmission line (NZDSF2 + DCF
7) It is a graph which shows each wavelength dispersion characteristic. FIG.
4 is an NZDSF3, a DCF5 and an optical transmission line (NZD
17 is a graph showing wavelength dispersion characteristics of each of SF3 + DCF5). FIG. 15 is a graph showing the chromatic dispersion characteristics of the NZDSF3, DCF6, and the optical transmission line (NZDSF3 + DCF6). FIG. 16 shows the NZDSF
3, DCF7 and optical transmission line (NZDSF3 + DCF
7) It is a graph which shows each wavelength dispersion characteristic. As can be seen from these graphs, any of these optical transmission lines
Optical amplification wavelength band 1530n of Er-doped optical fiber amplifier
In the range of m to 1620 nm, the chromatic dispersion is -5 ps / nm.
/ Km to +5 ps / nm / km. In particular, in each of FIGS. 8 to 10 and FIG. 15, the chromatic dispersion of the optical transmission line is in the range of −1 ps / nm / km to +1 ps / nm / km. Thus, each optical transmission line has a wavelength of 1..
The average chromatic dispersion is small in a wide wavelength band including 55 μm,
High quality optical transmission is possible.

As described above, the DCF1 of these embodiments
To DCF 18 at a wavelength of 1.55 μm,
The chromatic dispersion D _DCF is -4 ps / nm / km to -40 ps /
nm / km, and the dispersion slope S _DCF is −
0.02ps / nm ² /km~-0.50ps/nm ² /
km, the chromatic dispersion D _DCF and the dispersion slope S
The ratio of the _{DC F (S DCF / D DCF} ) is 0.004 / nm~0.0
It is in the range of 20 / nm. They also have an effective area of 12 μm ² to 30 in a wavelength band of 1.55 μm.
The transmission loss is within 0.5 μm ² , the transmission loss is 0.5 dB / km or less, and the polarization mode dispersion is 0.5 ps / km ^1/2 or less.

Each of the DCF1 to DCF18 can not only compensate for both the chromatic dispersion and the dispersion slope of the NZDCF1 to NZDCF3 at the wavelength of 1.55 μm, but also has the numerical range of the chromatic dispersion as described above and the effective area. Is sufficient, it is possible to suppress the occurrence of four-wave mixing and to suppress the deterioration of the waveform of the propagating signal light. In addition, each of the DCFs 1 to 18 can suppress an increase in bending loss because the numerical range of the chromatic dispersion is as described above.

An optical transmission line in which any one of the dispersion compensating optical fibers DCF1 to DCF18 and any one of the dispersion-shifting optical fibers NZDCF1 to NZDCF3 are fusion-spliced has an overall average dispersion at a wavelength of 1.55 μm. slope -0.02ps / nm ² /km~+0.05ps/
It is in the range of nm ² / km, and the total average transmission loss is 0.25 dB / km or less. In an optical transmission system that performs optical communication by propagating signal light through such an optical transmission line, the average transmission loss of the optical transmission line is small, and nonlinear optical phenomena are unlikely to occur in a wide wavelength band. Therefore, in this optical transmission system, the relay section can be lengthened, and the speed and capacity of optical communication can be further increased.

FIG. 17 is a configuration diagram of the optical transmission system 1 according to the present embodiment. The station 10 shown in this figure has an Er-doped optical fiber amplifier 11, a Raman amplification pumping light source 12, and an optical coupler 13. Further, the station 20 includes an Er-doped optical fiber amplifier 21, a pump light source 22 for Raman amplification, and an optical coupler 23. Each of the Er-doped optical fiber amplifiers 11 and 21 supplies an excitation light (wavelength 0. 0) to an Er-doped optical fiber in which an Er element is added to the optical waveguide region.
By supplying 98 μm or 1.48 μm), the signal light (wavelength 1.55 μm band) is optically amplified. Raman amplification excitation light source 12 and Raman amplification excitation light source 2
Each of the light sources 2 is a light source that outputs Raman amplification pump light (for example, a wavelength of 1.45 μm) supplied to the optical transmission line 30. The optical coupler 13 supplies the Raman amplification pumping light output from the Raman amplification pumping light source 12 to the optical transmission line 30 and propagates the signal light in the forward direction. The optical coupler 23 supplies the Raman amplification pumping light output from the Raman amplification pumping light source 22 to the optical transmission line 30,
The signal light propagates in the forward direction. That is, the Raman amplification pumping light sources 12 and 22, the optical couplers 13 and 23, and the optical transmission line 30 constitute a Raman amplifier that Raman amplifies the signal light propagating through the optical transmission line 30.

In the optical transmission system 1 shown in FIG.
The signal light in the 1.55 μm band is optically amplified by the Er-doped optical fiber amplifier 11 in the station 10 and the optical coupler 13
And enters the optical transmission line 30. The signal light incident on the optical transmission line 30 is transmitted through the optical transmission line
However, since the optical transmission line 30 is subjected to Raman amplification at the same time, the effective loss is small. The signal light input from the optical transmission line 30 to the station 20 is optically amplified by the Er-doped optical fiber amplifier 21 via the optical coupler 23 in the station 20.

The Er-doped optical fiber amplifier is suitable because it can efficiently amplify signal light.
Further, the Raman amplifier is preferable in that the signal light can be optically amplified in a wide wavelength band. Neither the Er-doped optical fiber amplifier nor the Raman amplifier may be provided, and only one of them may be provided. As described above, the optical transmission system 1 includes the optical amplifier that optically amplifies the signal light propagating through the optical transmission line 30, thereby achieving low loss. Further, since the optical transmission line 30 has low loss as described above, the optical transmission system 1 can increase the length of the relay section and reduce the number of optical amplifiers to be installed. Therefore, the optical transmission system 1 is inexpensive, and can suppress generation of noise due to optical amplification from deteriorating the quality of signal light.

The present invention is not limited to the above embodiment, but can be variously modified. For example, in the above embodiment, the optical transmission line 30 in which the dispersion-shifted optical fiber 31 and the dispersion-compensating optical fiber 32 are fusion-spliced is connected to the stations 10 and
Although described as being laid between 0 and 0, it is not limited to this. The dispersion-shifted optical fiber 31 and the dispersion-compensating optical fiber 32 need not be fusion-spliced, but may be connector-connected. In addition, the dispersion compensating optical fiber 32 may not be laid in the relay section, and may be wound around a coil to be a dispersion compensation module and provided in the station 10 or the station 20.

[0046]

As described above in detail, the dispersion compensating optical fiber according to the present invention has a wavelength band of 1.50 μm or more.
At a predetermined wavelength within 1.60 μm, the chromatic dispersion D _DCF is −4 ps / nm / km to −40 ps / nm / km, and the dispersion slope S _DCF is −0.02 ps / nm ² / km.
−0.50 ps / nm ² / km and the chromatic dispersion D _DCF
And the ratio of dispersion slope S _DCF (S _DCF / D _DCF ) is 0.00
4 / nm to 0.020 / nm, and the effective area is 12
a μm ² ~30μm ^2, transmission loss 0.5 dB / miles
And the polarization mode dispersion is 0.5 ps / km ^1/2 or less. The dispersion compensating optical fiber having such characteristics can not only compensate the chromatic dispersion and the dispersion slope at the wavelength of 1.55 μm of the dispersion-shifted optical fiber, but also has the numerical range of the chromatic dispersion as described above and the effective cross-sectional area. Is sufficient, it is possible to suppress the occurrence of four-wave mixing and to suppress the deterioration of the waveform of the propagating signal light. Further, in the dispersion compensating optical fiber, since the numerical range of the chromatic dispersion is as described above, it is possible to suppress an increase in bending loss.

Further, the dispersion compensating optical fiber according to the present invention comprises a central core region including the optical axis center and having a refractive index n ₁ , a depressed region surrounding the central core region and having a refractive index n ₂ , At least a cladding region surrounding the presto region and having a refractive index of n ₄ , wherein the magnitude relation of the respective refractive indices is n ₂ <n ₄ <n ₁ , and the relative refractive index difference of the central core region with respect to the cladding region is 0. 8% ~
1.7%, the relative refractive index difference of the depressed region with respect to the cladding region is -1.0% to -0.5%, and the outer diameter 2a of the central core region and the outer diameter 2b of the depressed region are different. Preferably, the ratio (2a / 2b) is between 0.25 and 0.60. It is also preferable that a ring core region having a refractive index of n ₃ is further provided between the depressed region and the cladding region, and the magnitude relationship between the refractive indices is n ₂ <n ₄ <n ₃ <n _1. . Such a refractive index profile can realize a dispersion compensating optical fiber having the above characteristics.

The dispersion compensating optical fiber according to the present invention is based on silica glass and has a central core region of Ge.
The case where O ₂ is added and F is added to the depressed region is suitable for realizing a dispersion compensating optical fiber having the above-described refractive index profile. Further, the transmission loss of the dispersion compensating optical fiber at a wavelength of 1.55 μm can be reduced.

Further, the dispersion compensating optical fiber according to the present invention is based on silica glass and has P, P in the cladding region.
When any one of Cl and F is added, the viscosity of the cladding region can be reduced when the dispersion compensating optical fiber is manufactured by drawing the optical fiber preform. The heating temperature can be lowered. Therefore, the formation of defects such as GeO in the central core region can be suppressed, and the interdiffusion between Ge in the central core region and F in the depressed region can be reduced, thereby preventing an increase in transmission loss. be able to.

The optical transmission system according to the present invention comprises an optical transmission line in which the above-mentioned dispersion compensating optical fiber and another optical fiber are connected. The optical transmission system transmits light at a predetermined wavelength within a wavelength band of 1.50 μm to 1.60 μm. The average dispersion slope of the entire transmission path is −0.02 ps / nm ² / km to +0.05 ps / n
m ² / km, and the average transmission loss of the entire optical transmission line is 0.25 dB / km or less. In this optical transmission system, the average transmission loss of the optical transmission line is small and the absolute value of the average chromatic dispersion is small in a wide wavelength band, so that the repeater section can be lengthened and the speed and capacity of optical communication can be further increased. Can be planned.

The wavelength band is 1.53 μm to 1.62 μm.
The average chromatic dispersion of the entire optical transmission line at all wavelengths within m is from −5 ps / nm / km to +5 ps / nm / km (more preferably, from −1 ps / nm / km to +1 ps / nm / k).
In the case of m), the absolute value of the average chromatic dispersion of the entire optical transmission line is small in the optical amplification wavelength band of 1530 nm to 1620 nm of the Er-doped optical fiber amplifier, so that high-quality optical transmission is possible.

When an optical amplifier for amplifying the signal light propagating through the optical transmission line is provided, the optical transmission system has a lower loss. Further, the optical amplifier is preferably an Er-doped optical fiber amplifier, and in this case, the signal light can be optically amplified with high efficiency. The optical amplifier is also preferably a Raman amplifier, in which case the signal light can be optically amplified in a wide wavelength band.

It is preferable that the dispersion compensating optical fiber is laid in the repeater section. In this case, the required length of the dispersion compensating optical fiber is short, and the overall transmission loss is small.

The wavelength band is 1.50 μm to 1.60 μm.
The wavelength dispersion of the other optical fiber is +2 ps / nm / km to +10 ps / nm / km (more preferably, +6 ps / nm / km to +10 ps / nm) at a predetermined wavelength within m.
/ Km). By connecting the dispersion compensating optical fiber and the other optical fiber, the absolute value of the average chromatic dispersion of the entire optical transmission line is reduced. Further, by setting the chromatic dispersion of the other optical fiber to +6 ps / nm / km or more, occurrence of four-wave mixing can be suppressed.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram of an optical transmission system according to an embodiment.

FIG. 2 is a diagram illustrating a preferred example of a refractive index profile of the dispersion compensating optical fiber according to the embodiment.

FIG. 3 is a diagram illustrating another preferred example of the refractive index profile of the dispersion compensating optical fiber according to the embodiment.

FIG. 4 is a diagram illustrating another preferred example of the refractive index profile of the dispersion compensating optical fiber according to the embodiment.

5 is a relative refractive index difference Δ of a depressed region in the dispersion compensating optical fiber having the refractive index profile shown in FIG.
⁶ is a graph showing a relationship between-and transmission loss at a wavelength of 1.55 μm.

FIG. 6 is a table summarizing examples of a dispersion compensating optical fiber and an optical transmission line according to the present embodiment.

FIG. 7 is a table summarizing an embodiment of a non-zero dispersion shifted optical fiber.

FIG. 8 shows NZDSF1, DCF5 and an optical transmission line (NZ
(DSF1 + DCF5) is a graph showing the wavelength dispersion characteristics of each.

FIG. 9 shows NZDSF1, DCF6 and an optical transmission line (NZ
(DSF1 + DCF6) is a graph showing the wavelength dispersion characteristics of each of them.

FIG. 10 shows NZDSF1, DCF7 and an optical transmission line (N
(ZDSF1 + DCF7) is a graph showing the wavelength dispersion characteristics of each.

FIG. 11 shows NZDSF2, DCF5 and an optical transmission line (N
(ZDSF2 + DCF5) is a graph showing the wavelength dispersion characteristics of each.

FIG. 12 shows NZDSF2, DCF6 and an optical transmission line (N
(ZDSF2 + DCF6) is a graph showing the wavelength dispersion characteristics of each.

FIG. 13 shows NZDSF2, DCF7 and an optical transmission line (N
(ZDSF2 + DCF7) is a graph showing the wavelength dispersion characteristics of each.

FIG. 14 shows NZDSF3, DCF5 and an optical transmission line (N
(ZDSF3 + DCF5) is a graph showing the wavelength dispersion characteristics of each.

FIG. 15 shows NZDSF3, DCF6 and an optical transmission line (N
(ZDSF3 + DCF6) is a graph showing the wavelength dispersion characteristics of each.

FIG. 16 shows NZDSF3, DCF7 and an optical transmission line (N
(ZDSF3 + DCF7) is a graph showing the wavelength dispersion characteristics of each.

FIG. 17 is a configuration diagram of an optical transmission system according to the present embodiment.

[Explanation of symbols]

DESCRIPTION OF SYMBOLS 1 ... Optical transmission system, 10 ... Station, 11 ... Er doped optical fiber amplifier, 12 ... Raman amplification pumping light source, 13 ... Optical coupler, 20 ... Station, 21 ... Er doped optical fiber amplifier, 2
2 ... Raman amplification pumping light source, 23 ... Optical coupler, 30 ... Optical transmission line, 31 ... Dispersion shift optical fiber, 32 ... Dispersion compensating optical fiber.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme coat ゛ (Reference) H04B 10/28 H04B 9/00 W 10/02 M 10/18 (72) Inventor Kato Shiori Yokohama, Kanagawa 1F, Tayacho, Ichisakae-ku Sumitomo Electric Industries, Ltd. Yokohama Works F-term (reference) 2H050 AB05X AB08Y AB10Y AB18Y AC14 AC28 AC38 AC71 AC73 AC76 4G062 AA06 BB02 LA03 LB06 LB08 LB10 MM04 NN01 5F072 AB09 AK06 QJJ07K02 FA02

Claims (14)

[Claims] 1. At a predetermined wavelength within a wavelength band of 1.50 μm to 1.60 μm, the chromatic dispersion D _DCF is −4 ps / nm / km to −40 ps /.
nm / km and the dispersion slope S _DCF is −0.02 ps / nm ² / km to −
0.50 ps / nm ² / km, and the ratio of the chromatic dispersion D _DCF to the dispersion slope S _DCF (S _DCF / D
_DCF) is 0.004 / nm~0.020 / nm, an effective area is 12 [mu] m ² 30 .mu.m ^2, the transmission loss is at 0.5 dB / miles or less, the polarization mode dispersion 0.5 ps / A dispersion compensating optical fiber having a length of km ^1/2 or less. Has a central core region having a wherein a refractive index n ₁ including an optical axis center, and the depressed region having a refractive index n ₂ surrounds the central core region, the refractive index n ₄ surrounding the depressed region And at least a cladding region, wherein the magnitude relationship between the refractive indices is n ₂ <n ₄ <n ₁ , and the relative refractive index difference between the cladding region and the central core region is 0.8% to 1.7%. A relative refractive index difference of the depressed region with respect to the cladding region is -1.0% to -0.5%, and a ratio of an outer diameter 2a of the central core region to an outer diameter 2b of the depressed region. 2. The dispersion compensating optical fiber according to claim 1, wherein (2a / 2b) is 0.25 to 0.60. 3. The depressed region and the cladding region.
Refractive index n between _ThreeFurther has a ring core region with
And the relationship between the refractive indices is n_Two<N_Four<N_Three<N₁ Is
3. The dispersion compensating optical fiber according to claim 2, wherein: 4. The dispersion compensating optical fiber according to claim 2, wherein GeO ₂ is added to said central core region and F is added to said depressed region based on silica glass. 5. The dispersion compensating optical fiber according to claim 2, wherein one of P, Cl and F is added to said cladding region based on silica glass. 6. An optical transmission line to which the dispersion compensating optical fiber according to claim 1 and another optical fiber are connected, wherein said optical transmission line has a predetermined wavelength within a wavelength band of 1.50 μm to 1.60 μm. The overall average dispersion slope is -0.
02ps / nm ² /km~+0.05ps/nm ² / km
And the overall average transmission loss of the optical transmission line is 0.25
An optical transmission system characterized by being at most dB / km. 7. An optical transmission line having an average chromatic dispersion of -5 ps / nm / km to +5 ps / nm / km in all wavelengths within a wavelength band of 1.53 μm to 1.62 μm. Item 7. The optical transmission system according to Item 6. 8. An optical transmission line having an average chromatic dispersion of −1 ps / nm / km to +1 ps / nm / km in all wavelengths within a wavelength band of 1.53 μm to 1.62 μm. Item 7. The optical transmission system according to Item 6. 9. The optical transmission system according to claim 6, further comprising an optical amplifier for optically amplifying the signal light propagating through the optical transmission line. 10. The optical amplifier according to claim 1, wherein the optical amplifier is an Er-doped optical fiber amplifier that amplifies the signal light by supplying the pumping light to an Er-doped optical fiber in which an Er element is added to an optical waveguide region. The optical transmission system according to claim 9, wherein 11. The optical transmission system according to claim 9, wherein the optical amplifier is a Raman amplifier that optically amplifies the signal light by supplying Raman amplification pump light to the optical transmission line. 12. The optical transmission system according to claim 6, wherein said dispersion compensating optical fiber is laid in a repeater section together with said another optical fiber. 13. A wavelength band of 1.50 μm to 1.60 μm.
7. The optical transmission system according to claim 6, wherein the chromatic dispersion of the other optical fiber is +2 ps / nm / km to +10 ps / nm / km at a predetermined wavelength. 14. A wavelength band of 1.50 μm to 1.60 μm.
7. The optical transmission system according to claim 6, wherein the chromatic dispersion of the another optical fiber is +6 ps / nm / km to +10 ps / nm / km at a predetermined wavelength.